sirolimus and Hypertrophy

The skeletal muscle is a tissue with adaptive properties which are essential to the survival of many species. When mechanically stimulated it is liable to undergo remodeling, namely, changes in its mass/volume resulting mainly from myofibrillar protein accumulation. The mTOR pathway (mammalian target of rapamycin) via its effector p70s6k (ribosomal protein kinase S6) has been reported to be of importance to the control of skeletal muscle mass, particularly under mechanical stimulation. However, not all mechanical stimuli are capable of activating this pathway, and among those who are, there are differences in the activation magnitude. Likewise, not all skeletal muscle fibers respond to the same extent to mechanical stimulation. Such evidences suggest specific mechanical stimuli through appropriate cellular signaling to be responsible for the final physiological response, namely, the accumulation of myofibrillar protein. Lately, after the mTOR signaling pathway has been acknowledged as of importance for remodeling, the interest for the mechanical/chemical mediators capable of activating it has increased. Apart from the already known MGF (mechano growth factor), some other mediators such as phosphatidic acid (PA) have been identified. This review article comprises and discusses relevant information on the mechano-chemical transduction of the pathway mTOR, with special emphasis on the muscle protein synthesis.

Topics: Adaptation, Biological; Animals; Humans; Hypertrophy; Mechanotransduction, Cellular; Muscle Fibers, Skeletal; Muscle Proteins; Muscle, Skeletal; Phenotype; Physical Stimulation; Ribosomal Protein S6 Kinases, 70-kDa; Sirolimus

Recent work has shown that the mTOR (mammalian target of rapamycin) pathway is an integral cell growth regulator. The mTOR pathway involves two functional complexes, TORC1 and TORC2, which have been defined by both their association with raptor or rictor, respectively, and their sensitivity to short-term rapamycin inhibition. Loss of tumor suppressors TSC1 or TSC2 leads to aberrant activation of TORC1, which has been implicated in the control of cell size. As a result, both physiologic and pathologic tissue hypertrophy are associated with TORC1 activation. Some clinical examples include skeletal and cardiac muscle hypertrophy, vascular restenosis, and compensatory nephrotic hypertrophy. Clarification of the mTOR pathway may lead to increased understanding of both the etiology and consequences of aberrant cell size regulation. This review covers some of the biochemical regulation of the mTOR pathway that may be important to the regulation of cell size, and it will present several potential clinical applications where the control of cell size may be biologically significant.

Topics: Antibiotics, Antineoplastic; Cell Size; Humans; Hypertrophy; Muscles; Neoplasms; Protein Kinases; Sirolimus; TOR Serine-Threonine Kinases

The present study aimed to explore the contribution of mammalian target of rapamycin (mTOR) in deoxycorticosterone acetate (DOCA) salt-induced hypertension and related pathophysiological changes in cardiovascular and renal tissues. DOCA salt loading resulted in an increase in systolic blood pressure, diastolic blood pressure, and mean blood pressure along with the activity of ribosomal protein S6, the effector protein of mTOR. Treatment with rapamycin, the selective inhibitor of mTOR, initiated at the fourth week of DOCA- salt administration normalized the systolic blood pressure and attenuated ribosomal protein S6 activity in the heart, aorta, and kidney. Cardiac and vascular hypertrophy, oxidative stress, and infiltration of macrophages (CD68+), the marker of inflammation, were also reduced in rapamycin-treated, DOCA-salt, hypertensive rats. In addition, renal hypertrophy and dysfunction were also reduced with rapamycin-treated hypertensive rats. Moreover, these pathophysiological changes in DOCA-salt hypertensive rats were associated with increased NADPH oxidase (NOX) activity, gp91phox (formerly NOX2) expression, ERK1/2, and p38 MAPK activities in the heart, aorta, and kidney were minimized by rapamycin. These data indicate that mTOR plays an important role in regulating blood pressure and the development of cardiovascular and renal pathophysiological changes, most likely due to increased NOX expression/activity, ERK1/2, and p38 MAPK activity with macrophages infiltration in the heart, kidney, and aorta. Pharmacological inhibition of mTOR and related signaling pathways could serve as a novel target for the treatment of hypertension.

Topics: Acetates; Animals; Blood Pressure; Desoxycorticosterone Acetate; Hypertension; Hypertrophy; Inflammation; Male; Mammals; Oxidative Stress; p38 Mitogen-Activated Protein Kinases; Rats; Ribosomal Protein S6; Sirolimus; TOR Serine-Threonine Kinases

The iron (Fe) metabolism plays important role in regulating systemic metabolism and obesity development. The Fe inside cells can form iron-sulfur (Fe-S) clusters, which are usually assembled into target proteins with the help of a conserved cluster assembly machinery. Family with sequence similarity 96A (FAM96A; also designated CIAO2A) is a cytosolic Fe-S assembly protein involved in the regulation of cellular Fe homeostasis. However, the biological function of FAM96A in vivo is still incompletely defined. Here, we tested the role of FAM96A in regulating organismal Fe metabolism, which is relevant to obesity and adipose tissue homeostasis. We found that in mice genetically lacking FAM96A globally, intracellular Fe homeostasis was interrupted in both white and brown adipocytes, but the systemic Fe level was normal. FAM96A deficiency led to adipocyte hypertrophy and organismal energy expenditure reduction even under nonobesogenic normal chow diet-fed conditions. Mechanistically, FAM96A deficiency promoted mechanistic target of rapamycin (mTOR) signaling in adipocytes, leading to an elevation of de novo lipogenesis and, therefore, fat mass accumulation. Furthermore, it also caused mitochondrial defects, including defects in mitochondrial number, ultrastructure, redox activity, and metabolic function in brown adipocytes, which are known to be critical for the control of energy balance. Moreover, adipocyte-selective FAM96A knockout partially phenocopied global FAM96A deficiency with adipocyte hypertrophy and organismal energy expenditure defects but the mice were resistant to high-fat diet-induced weight gain. Thus, FAM96A in adipocytes may autonomously act as a critical gatekeeper of organismal energy balance by coupling Fe metabolism to adipose tissue homeostasis.

Topics: Adipose Tissue; Adipose Tissue, Brown; Animals; Carrier Proteins; Diet, High-Fat; Energy Metabolism; Homeostasis; Hypertrophy; Iron; Mice; Mice, Inbred C57BL; Mice, Knockout; Obesity; Sirolimus; Sulfur; TOR Serine-Threonine Kinases

Mechanical signals, such as those evoked by maximal-intensity contractions (MICs), can induce an increase in muscle mass. Rapamycin-sensitive signaling events are widely implicated in the regulation of this process; however, recent studies indicate that rapamycin-insensitive signaling events are also involved. Thus, to identify these events, we generate a map of the MIC-regulated and rapamycin-sensitive phosphoproteome. In total, we quantify more than 10,000 unique phosphorylation sites and find that more than 2,000 of these sites are significantly affected by MICs, but remarkably, only 38 of the MIC-regulated events are mediated through a rapamycin-sensitive mechanism. Further interrogation of the rapamycin-insensitive phosphorylation events identifies the S473 residue on Tripartite Motif-Containing 28 (TRIM28) as one of the most robust MIC-regulated phosphorylation sites, and extensive follow-up studies suggest that TRIM28 significantly contributes to the homeostatic regulation of muscle size and function as well as the hypertrophy that occurs in response to increased mechanical loading.

Topics: Animals; Glycolysis; Hypertrophy; Male; Mechanotransduction, Cellular; Mice, Inbred C57BL; Mice, Knockout; MTOR Inhibitors; Muscle Contraction; Muscle, Skeletal; Phosphorylation; Proteome; Proteomics; Sirolimus; Skeletal Muscle Enlargement; TOR Serine-Threonine Kinases; Tripartite Motif-Containing Protein 28

The regenerative effect of Epimedium and its major bioactive flavonoid icariin (ICA) have been documented in traditional medicine, but their effect on sarcopenia has not been evaluated. The aim of this study was to investigate the effects of Epimedium extract (EE) on skeletal muscle as represented by differentiated C2C12 cells. Here we demonstrated that EE and ICA stimulated C2C12 myotube hypertrophy by activating several, including IGF-1 signal pathways. C2C12 myotube hypertrophy was demonstrated by enlarged myotube and increased myosin heavy chains (MyHCs). In similar to IGF-1, EE/ICA activated key components of the IGF-1 signal pathway, including IGF-1 receptor. Pre-treatment with IGF-1 signal pathway specific inhibitors such as picropodophyllin, LY294002, and rapamycin attenuated EE induced myotube hypertrophy and MyHC isoform overexpression. In a different way, EE induced MHyC-S overexpression can be blocked by AMPK, but not by mTOR inhibitor. On the level of transcription, EE suppressed myostatin and MRF4 expression, but did not suppress atrogenes MAFbx and MuRF1 like IGF-1 did. Differential regulation of MyHC isoform and atrogenes is probably due to inequivalent AKT and AMPK phosphorylation induced by EE and IGF-1. These findings suggest that EE/ICA stimulates pathways partially overlapping with IGF-1 signaling pathway to promote myotube hypertrophy.

Topics: Animals; Cell Differentiation; Cell Line; Chromones; Flavonoids; Gene Expression Regulation; Hypertrophy; Insulin-Like Growth Factor I; Mice; Morpholines; Myoblasts; Myosin Heavy Chains; Podophyllotoxin; Signal Transduction; Sirolimus

Topics: Animals; Antihypertensive Agents; Cell Proliferation; Cyclic AMP-Dependent Protein Kinases; Down-Regulation; Epoprostenol; Humans; Hypertrophy; Hypoxia; Immunosuppressive Agents; Mechanistic Target of Rapamycin Complex 1; Mice; Mice, Knockout; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Pulmonary Arterial Hypertension; Pulmonary Artery; Rats; Receptors, Immunologic; Receptors, Prostaglandin; RNA, Messenger; Sirolimus; Vascular Remodeling

Primary valvular heart disease is a prevalent cause of morbidity and mortality in both industrialized and developing countries. Although the primary consequence of valvular heart disease is myocardial dysfunction, treatment of valvular heart diseases centers around valve repair or replacement rather than prevention or reversal of myocardial dysfunction. This is particularly evident in primary mitral regurgitation (MR), which invariably results in eccentric hypertrophy and left ventricular (LV) failure in the absence of timely valve repair or replacement. The mechanism of LV dysfunction in primary severe MR is entirely unknown.. Here, we developed the first mouse model of severe MR. Valvular damage was achieved by severing the mitral valve leaflets and chords with iridectomy scissors, and MR was confirmed by echocardiography. Serial echocardiography was performed to follow up LV morphology and systolic function. Analysis of cardiac tissues was subsequently performed to evaluate valve deformation, cardiomyocyte morphology, LV fibrosis, and cell death. Finally, dysregulated pathways were assessed by RNA-sequencing analysis and immunofluorescence.. In the ensuing 15 weeks after the induction of MR, gradual LV dilatation and dysfunction occurred, resulting in severe systolic dysfunction. Further analysis revealed that severe MR resulted in a marked increase in cardiac mass and increased cardiomyocyte length but not width, with electron microscopic evidence of sarcomere disarray and the development of sarcomere disruption. From a mechanistic standpoint, severe MR resulted in activation of multiple components of both the mammalian target of rapamycin and calcineurin pathways. Inhibition of mammalian target of rapamycin signaling preserved sarcomeric structure and prevented LV remodeling and systolic dysfunction. Immunohistochemical analysis uncovered a differential pattern of expression of the cell polarity regulator Crb2 (crumbs homolog 2) along the longitudinal axis of cardiomyocytes and close to the intercalated disks in the MR hearts. Electron microscopy images demonstrated a significant increase in polysome localization in close proximity to the intercalated disks and some areas along the longitudinal axis in the MR hearts.. These results indicate that LV dysfunction in response to severe MR is a form of maladaptive eccentric cardiomyocyte hypertrophy and outline the link between cell polarity regulation and spatial localization protein synthesis as a pathway for directional cardiomyocyte growth.

Topics: Animals; Cell Adhesion Molecules; Cell Shape; Cell Size; Disease Models, Animal; Echocardiography; Fibrosis; Gene Expression Profiling; Hypertrophy; Infusion Pumps, Implantable; Magnetic Resonance Imaging; Male; Mice; Mitral Valve; Mitral Valve Insufficiency; Myocytes, Cardiac; Polyribosomes; RNA, Messenger; Sirolimus; Systole; TOR Serine-Threonine Kinases; Ventricular Dysfunction, Left

Cartilage is a kind of special connective tissue which does not contain neither blood vessels nor lymphatics and nerves. Therefore, the damage in cartilage is difficult to be repaired spontaneously. Constructing tissue engineered cartilage provides a new technique for cartilage repairing. Mesenchymal stem cells (MSCs) possess a unique capability of self-renew and can differentiate into pre-chondrocytes which are frequently applied as seed cells in tissue engineering. However, in regenerated cartilage the chondrocytes derived from MSCs can hardly maintain homeostasis and preferentially present hypertrophic like phenotype. We investigated the effects of cyanidin, a natural organic compound, on chondrogenic and subsequent hypertrophic differentiation of MSCs in order to seek approaches to inhibit chondrocyte hypertrophy. We evaluated the effects of cyanidin on expression of chondrogenic and hypertrophic marker genes through RT-PCR, Western blot, alcian blue staining, and immunocytochemistry. The results showed that both chondrogenic related genes Sox9, Col2a1, and hypertrophic marker genes Runx2, Col10a1 were inhibited by cyanidin. In addition, we found that cyanidin promoted Nrf2 and p62 expression and suppressed LC3B expression during chondrogenic stage of MSCs. Meanwhile phosphorylation of IκBα and autophagosome related protein LC3B were inactivated by cyanidin during chondrocyte hypertrophic stage. Furthermore, rapamycin, an autophagy activator, abrogated the inhibitory effect of cyanidin on chondrogenic, and hypertrophic differentiation of MSCs. In conclusion, one potential mechanism of cyanidin, by which the chondrogenic and hypertrophic differentiation of MSCs were inhibited, was due to decreased autophagy activity. Our results indicated that cyanidin was a potential therapeutic agent for keeping mature chondrocyte functions.

Topics: Animals; Anthocyanins; Autophagosomes; Autophagy; Cell Differentiation; Cell Line; Chondrocytes; Chondrogenesis; Collagen Type II; Collagen Type X; Core Binding Factor Alpha 1 Subunit; Dose-Response Relationship, Drug; Gene Expression Regulation; Glycosaminoglycans; Hypertrophy; Mesenchymal Stem Cells; Mice, Inbred C3H; Microtubule-Associated Proteins; NF-E2-Related Factor 2; NF-KappaB Inhibitor alpha; Phosphorylation; Sequestosome-1 Protein; Signal Transduction; Sirolimus; SOX9 Transcription Factor; Time Factors

Cardiac trabeculae are mesh-like muscular structures within ventricular walls. Subtle perturbations in trabeculation are associated with many congenital heart diseases (CHDs), and complete failure to form trabeculae leads to embryonic lethality. Despite the severe consequence of an absence of trabecular formation, the exact function of trabeculae remains unclear. Since ErbB2 signaling plays a direct and essential role in trabecular initiation, in this study, we utilized the erbb2 zebrafish mutant as a model to address the function of trabeculae in the heart. Intriguingly, we found that the trabeculae-deficient erbb2 mutant develops a hypertrophic-like (HL) phenotype that can be suppressed by inhibition of Target of Rapamycin (TOR) signaling in a similar fashion to adult mammalian hearts subjected to mechanical overload. Further, cell transplantation experiments demonstrated that erbb2 mutant cells in an otherwise wildtype heart did not undergo hypertrophy, indicating that erbb2 mutant HL phenotypes are due to a loss of trabeculae. Together, we propose that trabeculae serve to enhance contractility and that defects in this process lead to wall-stress induced hypertrophic remodeling.

Topics: Animals; Animals, Genetically Modified; Hypertrophy; Immunosuppressive Agents; Morphogenesis; Mutation; Myocardium; Receptor, ErbB-2; Signal Transduction; Sirolimus; Zebrafish; Zebrafish Proteins

Narrowing of the lumbar spinal canal is a condition called lumbar spinal stenosis (LSS) and is a high-morbidity problem in the elderly. LSS is commonly caused by hypertrophy of the ligamentum flavum (HLF). Previous studies showed that fibrosis of the ligamentum flavum (LF) largely contributed to HLF. However, the underlying pathomechanism remains unclear. Insulin-like growth factor-1 (IGF-1) is known to have an intimate relationship with fibrosis in various tissues. Nevertheless, currently, there are few studies regarding IGF-1 in HLF. In this study, we investigated the role of IGF-1 in HLF and its potential molecular mechanism of action.. First, the IGF-1, phosphorylation of IGF-1 receptor (pIGF-1R), phosphorylation of AKT (pAKT), phosphorylation of S6(pS6), collagen I and collagen III expression levels were examined via immunohistochemistry and Western blotting in LF tissues from patients with LSS or Non-LSS. Second, primary LF cells were isolated from adults with a normal LF thickness and were cultured with different concentrations of IGF-1 with or without NVP-AEW541/rapamycin.. The results showed that IGF-1, pIGF-1R, pAKT, pS6, collagen I and collagen III protein expression in the LSS group was significantly higher than that in the Non-LSS group. Meanwhile, pIGF-1R, pAKT, pS6, collagen I and collagen III protein expression was significantly enhanced in LF cells after IGF-1 exposure, which can be notably blocked by NVP-AEW541. In addition, pS6, collagen I and collagen III protein expression was blocked by rapamycin.. Enhanced IGF-1 promotes the synthesis of collagen I and collagen III via the mTORC1 signaling pathway, which eventually contributes to hypertrophy of the ligamentum flavum.

Topics: Aged; Case-Control Studies; Cell Survival; Collagen Type I; Collagen Type III; Female; Gene Expression; Humans; Hypertrophy; Insulin-Like Growth Factor I; Ligamentum Flavum; Male; Mechanistic Target of Rapamycin Complex 1; Middle Aged; Phosphorylation; Proto-Oncogene Proteins c-akt; Receptor, IGF Type 1; Ribosomal Protein S6 Kinases; Signal Transduction; Sirolimus

Articular chondrocyte activation, involving aberrant proliferation and prehypertrophic differentiation, is essential for osteoarthritis (OA) initiation and progression. Disruption of mechanistic target of rapamycin complex 1 (mTORC1) promotes chondrocyte autophagy and survival, and decreases the severity of experimental OA. However, the role of cartilage mTORC1 activation in OA initiation is unknown. In this study, we elucidated the specific role of mTORC1 activation in OA initiation, and identify the underlying mechanisms.. Expression of mTORC1 in articular cartilage of OA patients and OA mice was assessed by immunostaining. Cartilage-specific tuberous sclerosis complex 1 (Tsc1, mTORC1 upstream inhibitor) knockout (TSC1CKO) and inducible Tsc1 KO (TSC1CKO. mTORC1 activation stimulates articular chondrocyte proliferation and differentiation to initiate OA, in part by downregulating FGFR3 and PPR.

Topics: Adult; Aged; Animals; Butylamines; Cartilage, Articular; Cell Proliferation; Chondrocytes; Down-Regulation; Female; Humans; Hypertrophy; Immunosuppressive Agents; Knee Joint; Male; Mechanistic Target of Rapamycin Complex 1; Menisci, Tibial; Mice; Mice, Knockout; Middle Aged; Osteoarthritis; Osteoarthritis, Knee; Receptor, Fibroblast Growth Factor, Type 3; Receptor, Parathyroid Hormone, Type 1; Reverse Transcriptase Polymerase Chain Reaction; Sirolimus; TOR Serine-Threonine Kinases; Tuberous Sclerosis Complex 1 Protein; Tumor Suppressor Proteins; Young Adult

Skeletal muscle remodels metabolic capacity, contractile and exercise phenotype in response to physiological demands. This adaptive remodeling response to physical activity can ameliorate/prevent diseases associated with poor diet and lifestyle. Our previous work demonstrated that skeletal muscle-specific transgenic expression of the neuron-derived orphan nuclear receptor, Nor-1 drives muscle reprogramming, improves exercise endurance, and oxidative metabolism. The current manuscript investigates the association between exercise, Nor-1 expression and the role of Nor-1 in adaptive remodeling. We demonstrate that Nor-1 expression is induced by exercise and is dependent on calcium/calcineurin signaling (in vitro and in vivo). Analysis of fatigue-resistant transgenic mice that express Nor-1 in skeletal muscle revealed increased hypertrophy and vascularization of muscle tissue. Moreover, we demonstrate that transgenic Nor-1 expression is associated with increased intracellular recycling, ie, autophagy, involving 1) increased expression of light chain 3A or LC3A-II, autophagy protein 5, and autophagy protein 12 in quadriceps femoris muscle extracts from Tg-Nor-1 (relative to Wild-type (WT) littermates); 2) decreased p62 expression indicative of increased autophagolysosome assembly; and 3) decreased mammalian target of rapamycin complex 1 activity. Transfection of LC3A-GFP-RFP chimeric plasmid demonstrated that autophagolysosome formation was significantly increased by Nor-1 expression. Furthermore, we demonstrated a single bout of exercise induced LC3A-II expression in skeletal muscle from C57BL/6 WT mice. This study, when combined with our previous studies, demonstrates that Nor-1 expression drives multiple physiological changes/pathways that are critical to the beneficial responses of muscle to exercise and provides insights into potential pharmacological manipulation of muscle reprogramming for the treatment of lifestyle induced chronic diseases.

Topics: Animals; Autophagosomes; Autophagy; Calcineurin; Calcium; Cell Line; DNA-Binding Proteins; Hypertrophy; Lysosomes; Mechanistic Target of Rapamycin Complex 1; Mice, Inbred C57BL; Mice, Transgenic; Microtubule-Associated Proteins; Models, Biological; Muscle, Skeletal; Neovascularization, Physiologic; Nerve Tissue Proteins; Phenotype; Physical Conditioning, Animal; Receptors, Steroid; Receptors, Thyroid Hormone; RNA, Messenger; Signal Transduction; Sirolimus

Loss of skeletal muscle mass and force aggravates age-related sarcopenia and numerous pathologies, such as cancer and diabetes. The AKT-mTORC1 pathway plays a major role in stimulating adult muscle growth; however, the functional role of its downstream mediators in vivo is unknown. Here, we show that simultaneous inhibition of mTOR signaling to both S6K1 and 4E-BP1 is sufficient to reduce AKT-induced muscle growth and render it insensitive to the mTORC1-inhibitor rapamycin. Surprisingly, lack of mTOR signaling to 4E-BP1 only, or deletion of S6K1 alone, is not sufficient to reduce muscle hypertrophy or alter its sensitivity to rapamycin. However, we report that, while not required for muscle growth, S6K1 is essential for maintaining muscle structure and force production. Hypertrophy in the absence of S6K1 is characterized by compromised ribosome biogenesis and the formation of p62-positive protein aggregates. These findings identify S6K1 as a crucial player for maintaining muscle function during hypertrophy.

Topics: Adaptor Proteins, Signal Transducing; Animals; Carrier Proteins; Cell Cycle Proteins; Eukaryotic Initiation Factors; Humans; Hypertrophy; Mice; Mice, Knockout; Muscle, Skeletal; Oncogene Protein v-akt; Peptides; Phosphoproteins; Phosphorylation; Protein Aggregates; Ribosomal Protein S6 Kinases, 70-kDa; Ribosomes; Sarcopenia; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

The molecular mechanism underlying renal hypertrophy and progressive nephron damage remains poorly understood. Here we generated congenic ribosomal protein S6 (rpS6) knock-in mice expressing nonphosphorylatable rpS6 and found that uninephrectomy-induced renal hypertrophy was significantly blunted in these knock-in mice. Uninephrectomy-induced increases in cyclin D1 and decreases in cyclin E in the remaining kidney were attenuated in the knock-in mice compared with their wild-type littermates. Uninephrectomy induced rpS6 phosphorylation in the wild-type mice; however, no rpS6 phosphorylation was detected in uninephrectomized or sham-operated knock-in mice. Nonetheless, uninephrectomy stimulated comparable 4E-BP1 phosphorylation in both knock-in and wild-type mice, indicating that mTORC1 was still activated in the knock-in mice. Moreover, the mTORC1 inhibitor rapamycin prevented both rpS6 and 4E-BP1 phosphorylation, significantly blunted uninephrectomy-induced renal hypertrophy in wild-type mice, but did not prevent residual renal hypertrophy despite inhibiting 4E-BP1 phosphorylation in uninephrectomized knock-in mice. Thus, both genetic and pharmacological approaches unequivocally demonstrate that phosphorylated rpS6 is a downstream effector of the mTORC1-S6K1 signaling pathway mediating renal hypertrophy. Hence, rpS6 phosphorylation facilitates the increase in cyclin D1 and decrease in cyclin E1 that underlie the hypertrophic nature of uninephrectomy-induced kidney growth.

Topics: Adaptor Proteins, Signal Transducing; Animals; Carrier Proteins; Cell Cycle Proteins; Cyclin D1; Cyclin E; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinase 4; Eukaryotic Initiation Factors; Female; Gene Knock-In Techniques; Hypertrophy; Kidney; Male; Mechanistic Target of Rapamycin Complex 1; Mice; Multiprotein Complexes; Nephrectomy; Oncogene Proteins; Phosphoproteins; Phosphorylation; Ribosomal Protein S6; Ribosomal Protein S6 Kinases, 90-kDa; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Rapamycin (RAPA) has been successfully used for myoblast allotransplantation in X chromosome-linked muscular dystrophy mice. However, the mechanism of skeletal myogenesis, particularly in starved condition by RAPA, remains elusive. For this reason, we investigated the effect of RAPA on C2C12 myogenesis in serum-starved condition.. Serum-free treated C2C12 cells were mimicked as skeletal myogenesis in nutrition shortage microenvironment. A methylthiazoletetrazolium (MTT) assay was used to investigate different RAPA concentrations on serum-free treated C2C12 cells and the following assays were used to detect the characteristic of C2C12 myogenesis by RAPA in vitro.. We found that 150 ng/mL of RAPA did not significantly suppress the viability of C2C12 differentiated cells by MTT assay. The RAPA concentration could protect myoblast serum-starved cells effectively from apoptosis through flow cytometry and retain myogenic regulatory factors through quantitative polymerase chain reaction analysis. However, RAPA significantly suppressed cell migration in wound healing assay (P<0.05). Morphological analyses indicated that RAPA also significantly suppressed myotube hypertrophy in serum-starved C2C12 cells. Western blot analysis revealed that the ratio of phosphate extracellular signal-regulated kinase/extracellular signal-regulated kinase and the protein level of p-Akt decreased in the proliferation medium and in the differentiation medium, respectively.. These findings suggest that myoblast cells are sensitive to RAPA under a serum-starved microenvironment. As an immunosuppressive agent, RAPA shall be used as a considering dosage and as a safe strategy for future myoblast allotransplantation.

Topics: Animals; Cell Fusion; Cell Line; Cell Movement; Cell Proliferation; Cell Survival; Culture Media, Serum-Free; Dose-Response Relationship, Drug; Extracellular Signal-Regulated MAP Kinases; Gene Expression Regulation; Hypertrophy; Immunosuppressive Agents; Mice; Muscle Development; Myoblasts; Phosphorylation; Proto-Oncogene Proteins c-akt; Sirolimus; Time Factors; Wound Healing

To examine the effects of the Akt/mammalian target of rapamycin (mTOR) pathway on masseter muscle hypertrophy and myosin heavy chain (MHC) transition in response to mechanical overload, we analyzed the effects of bite-opening (BO) on the hypertrophy and MHC composition of masseter muscle of BO-rats treated or not treated with rapamycin (RAPA), a selective mTOR inhibitor. The masseter muscle weight in BO-rats was significantly greater than that in controls, and this increase was attenuated by RAPA treatment. Expression of slow-twitch MHC isoforms was significantly increased in BO-rats with/without RAPA treatment, compared with controls, but the magnitude of the increase was much smaller in RAPA-treated BO-rats. Phosphorylation of p44/42 MAPK (ERK1/2), which preserves fast-twitch MHC isoforms in skeletal muscle, was significantly decreased in BO-rats, but the decrease was abrogated by RAPA treatment. Calcineurin signaling is known to be important for masseter muscle hypertrophy and fast-to-slow MHC isoform transition, but expression of known calcineurin activity modulators was unaffected by RAPA treatment. Taken together, these results indicate that the Akt/mTOR pathway is involved in both development of masseter muscle hypertrophy and fast-to-slow MHC isoform transition in response to mechanical overload with inhibition of the ERK1/2 pathway and operates independently of the calcineurin pathway.

Topics: Animals; Biomechanical Phenomena; Bite Force; Calcineurin; Hypertrophy; MAP Kinase Signaling System; Masseter Muscle; Myosin Heavy Chains; Oncogene Protein v-akt; Organ Size; Phosphorylation; Protein Isoforms; Rats; Rats, Wistar; Signal Transduction; Sirolimus; Stress, Mechanical; TOR Serine-Threonine Kinases

The mammalian target of rapamycin (mTOR), a regulator of cellular protein synthesis and cell growth, plays an important role in the progression of renal hypertrophy and renal dysfunction in experimental chronic kidney disease models. Because the mTOR activity is regulated by nutrients including amino acids, we tested the hypothesis that the renoprotective effect of a low-protein diet (LPD) might be associated with the attenuation of the renal mTOR pathway. In this study, 5/6 nephrectomized rats were fed an LPD or a normal protein diet (NPD), and a number of rats that were fed an NPD received rapamycin (1.0 mg kg⁻¹ d⁻¹), a specific inhibitor of mTOR. After 6 weeks, renal tissue was collected to evaluate the activity of the mTOR pathway and histologic changes. The phosphorylation of p70S6k, a kinase in the downstream of mTOR, was significantly higher in the NPD-fed rats that showed progressive renal dysfunction than in the sham-operated rats (NPD). The LPD attenuated the excessive phosphorylation of p70S6k concomitant with reduced proteinuria and improved renal histologic changes in the 5/6 nephrectomized rats. The effects of the LPD were similar to the effects of rapamycin. The expression of phosphorylated p70S6k was significantly correlated with proteinuria (r² = 0.63, P < .001), the glomerular area (r² = 0.60, P < .001), and the number of phosphorylated Smad2-positive cells in the glomerulus (r² = 0.26, P < .05) of these rats. These results suggest that the preventive effect of an LPD on the progression of renal failure is associated with attenuation of the activated mTOR/p70S6k pathway in the rat remnant kidney model.

Topics: Animals; Cell Proliferation; Cells, Cultured; Diet, Protein-Restricted; Dietary Proteins; Disease Models, Animal; Hypertrophy; Kidney; Male; Phosphorylation; Proteinuria; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Rats, Wistar; Ribosomal Protein S6 Kinases, 70-kDa; Signal Transduction; Sirolimus; Smad2 Protein; TOR Serine-Threonine Kinases

Chronic renal failure (CRF) is associated with increased cardiovascular mortality, and medial vascular smooth muscle cell (VSMC) hypertrophy, proliferation, and calcification play a pivotal role in uremic vasculopathy. Glucose transporter-1 (GLUT1) facilitates the transport of glucose into VSMCs, and GLUT1 overexpression associated with high glucose influx leads to a stimulation of VSMC proliferation. However, the role of GLUT1 in uremic vasculopathy remains unclear. This study aimed to identify changes in the expression of GLUT1 in VSMCs in the setting of experimental uremia and investigate whether Akt/tuberous sclerosis complex subunit 2 (TSC2)/mammalian target of rapamycin (mTOR)/ribosomal S6 protein kinase (S6K) signaling, which plays a crucial role in VSMC proliferation and glucose metabolism, is involved in the regulation of GLUT1 expression.. In vivo experimental CRF was induced in Wistar rats by 5/6 nephrectomy, and the GLUT1 expression in aortic tissue was determined by the reverse transcriptase-polymerase chain reaction, immunoblotting, and immunohistochemical staining. Indoxyl sulfate (IS) is a uremic retention solute proven with pro-proliferative effect on rat VSMCs, and we further studied the expression of GLUT1 in rat A7r5 rat embryonic aortic cells stimulated by IS in the presence or absence of phloretin, a GLUT1 inhibitor, to explore the pathogenic role of GLUT1 in uremic vasculopathy. The contribution of Akt/TSC2/mTOR/S6K signaling in modifying the GLUT1 expression was also assessed.. Eight weeks after 5/6 nephrectomy, aortic tissue obtained from CRF rats exhibited increased wall thickness and VSMC hypertrophy, hyperplasia, and degeneration. Compared with the sham-operated control group, the messenger (m)RNA and protein abundance of GLUT1 were both markedly increased in CRF rats. In vitro, IS induced a significant increase in expression of GLUT1 protein as well as pro-proliferative cyclin D1 and p21 mRNA and a modest increase in expression of antiapoptotic p53 mRNA in A7r5 cells, whereas inhibition of GLUT1 mediated glucose influx reduced the pro-proliferative and antiapoptotic effects of IS. In addition to increased GLUT1 expression, IS significantly suppressed Akt and TSC2 phosphorylation after 6-hour and 12-hour treatment, but increased S6K phosphorylation after 3-hour treatment. Inactivation of mTOR downstream signaling by rapamycin treatment inhibited S6K phosphorylation and abolished the stimulatory effect of IS on GLUT1 expression.. In vivo and in vitro experimental CRF displayed prominent GLUT1 upregulation in VSMCs. The uremic toxin IS stimulated proliferation of VSMCs possibly through induction of GLUT1 expression. The Akt/TSC/mTOR/S6K signaling pathway may be one of the mechanisms underlying the upregulation of GLUT1 expression in uremic VSMCs.

Topics: Animals; Aorta; Apoptosis; Blotting, Western; Cell Line; Cell Proliferation; Cyclin D1; Cyclin-Dependent Kinase Inhibitor p21; Disease Models, Animal; Glucose; Glucose Transporter Type 1; Hyperplasia; Hypertrophy; Immunohistochemistry; Indican; Male; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Nephrectomy; Phloretin; Phosphorylation; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; Renal Insufficiency; Reverse Transcriptase Polymerase Chain Reaction; Ribosomal Protein S6 Kinases; RNA, Messenger; Signal Transduction; Sirolimus; Time Factors; TOR Serine-Threonine Kinases; Tuberous Sclerosis Complex 2 Protein; Tumor Suppressor Protein p53; Tumor Suppressor Proteins; Up-Regulation; Uremia

Previous molecular studies showed that the mTOR inhibitor rapamycin prevents bladder smooth muscle hypertrophy in vitro. We investigated the effect of rapamycin treatment in vivo on bladder smooth muscle hypertrophy in a rat model of partial bladder outlet obstruction.. A total of 48 female Sprague-Dawley® rats underwent partial bladder outlet obstruction and received daily subcutaneous injections of rapamycin (1 mg/kg) or vehicle commencing 2 weeks postoperatively. A total of 36 rats underwent sham surgery and received rapamycin or vehicle. Rats were sacrificed 3, 6 and 12 weeks after surgery. Before sacrifice, voiding was observed in a metabolic cage for 24 hours. Bladder-to-body weight in gm bladder weight per kg body weight and post-void residual urine were assessed. We evaluated Col1a1, Col3a1, Eln and Mmp7 mRNA expression and histology. Two-factor ANOVA and the post hoc t test were applied.. Bladder outlet obstruction caused a significant increase in bladder weight in all obstructed groups. Three weeks postoperatively (1 week of treatment) there was no difference in the bladder-to-body weight ratio in the obstructed group. However, at 6 and 12 weeks (4 and 10 weeks of treatment, respectively) the bladder-to-body weight ratio of rats with obstruction plus rapamycin was significantly lower than that of rats with obstruction plus vehicle. Post-void residual urine volume after 6 and 12 weeks of obstruction was lower in obstructed rats with rapamycin compared to that in obstructed rats with vehicle. Rapamycin decreased the obstruction induced expression of Col1a1, Col3a1, Eln and Mmp7.. Rapamycin prevents mechanically induced hypertrophy in cardiovascular smooth muscle. In vivo mTOR inhibition may attenuate obstruction induced detrusor hypertrophy and help preserve bladder function.

Topics: Analysis of Variance; Animals; Biopsy, Needle; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Schedule; Female; Hypertrophy; Immunohistochemistry; Injections, Subcutaneous; Muscle Hypertonia; Muscle, Smooth; Random Allocation; Rats; Rats, Sprague-Dawley; Reference Values; Sirolimus; TOR Serine-Threonine Kinases; Treatment Outcome; Urinary Bladder; Urinary Bladder Neck Obstruction

Mammalian target of rapamycin (mTOR) hyperactivity in perinatal neural progenitor cells (NPCs) of tuberous sclerosis complex 1 (Tsc1) heterozygote mice leads to heterotopia and abnormal neuronal morphogenesis as seen in patients with tuberous sclerosis. Considering that pathological hyperactive mTOR also occurs in individuals carrying no genetic mutations, we examined whether increasing mTOR activity in neonatal NPCs of wild-type mice would recapitulate the above phenotypes. Electroporation of a plasmid encoding constitutively active Ras-homolog enriched in brain (Rheb(CA)) into subventricular zone NPCs increased mTOR activity in newborn cells. At 19 d post-electroporation (dpe), heterotopia and ectopic cells with a neuronal morphology were observed along the migratory path [rostral migratory stream (RMS)] and in the olfactory bulb (OB). These ectopic cells displayed action potentials and received synaptic inputs identifying them as synaptically integrated neurons. RMS heterotopias contained astrocytes, neurons, and entrapped neuroblasts. Immunostaining at 3 dpe revealed the presence of Mash1(+) Olig2(-) cells in the migratory route accompanied by ectopic neuronal differentiation and altered direction and speed of neuroblast migration at 7 dpe, suggesting a non-cell-autonomous disruption of migration. At >19 dpe, newborn Rheb(CA)-expressing neurons displayed altered distribution and formed micronodules in the OB. In addition, they displayed increased dendritic complexity along with altered membrane biophysics and increased frequency of GABAergic synaptic inputs. OB heterotopia, micronodules, and dendrite hypertrophy were notably prevented by rapamycin treatment, suggesting their mTOR dependence. Collectively, these data show that increasing mTOR activity in neonatal NPCs of wild-type mice recapitulate the pathologies observed in Tsc1 mutant mice. In addition, increased mTOR activity in individuals without known mutations could significantly impact neurogenesis and circuit formation.

Topics: Animals; Animals, Newborn; Cell Differentiation; Cell Enlargement; Cell Line, Tumor; Cell Movement; Cerebral Ventricles; Dendrites; Electroporation; Female; Hypertrophy; Male; Mice; Monomeric GTP-Binding Proteins; Neural Stem Cells; Neurogenesis; Neurons; Neuropeptides; Olfactory Bulb; Ras Homolog Enriched in Brain Protein; Sirolimus; Stem Cells; TOR Serine-Threonine Kinases

Myostatin inhibition by follistatin (FS) offers a new approach for muscle mass enhancement. The aim of the present study was to characterize the mediators responsible for the FS hypertrophic action on skeletal muscle in male mice. Because IGF-I and IGF-II, two crucial skeletal muscle growth factors, are induced by myostatin inhibition, we assessed their role in FS action. First, we tested whether type 1 IGF receptor (IGF-IR) is required for FS-induced hypertrophy. By using mice expressing a dominant-negative IGF-IR in skeletal muscle, we showed that IGF-IR inhibition blunted by 63% fiber hypertrophy caused by FS. Second, we showed that FS caused the same degree of fiber hypertrophy in wild-type and IGF-II knockout mice. We then tested the role of the signaling molecules stimulated by IGF-IR, in particular the Akt/mammalian target of rapamycin (mTOR)/70-kDa ribosomal protein S6 kinase (S6K) pathway. We investigated whether Akt phosphorylation is required for the FS action. By cotransfecting a dominant-negative form of Akt together with FS, we showed that Akt inhibition reduced by 65% fiber hypertrophy caused by FS. Second, we evaluated the role of mTOR in FS action. Fiber hypertrophy induced by FS was reduced by 36% in rapamycin-treated mice. Finally, because the activity of S6K is increased by FS, we tested its role in FS action. FS caused the same degree of fiber hypertrophy in wild-type and S6K1/2 knockout mice. In conclusion, the IGF-IR/Akt/mTOR pathway plays a critical role in FS-induced muscle hypertrophy. In contrast, induction of IGF-II expression and S6K activity by FS are not required for the hypertrophic action of FS.

Topics: Animals; Base Sequence; DNA Primers; Follistatin; Humans; Hypertrophy; Insulin-Like Growth Factor II; Male; Mice; Mice, 129 Strain; Mice, Knockout; Mice, Transgenic; Muscle, Skeletal; Proto-Oncogene Proteins c-akt; Receptor, IGF Type 1; Recombinant Proteins; Ribosomal Protein S6 Kinases; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Transfection

Cell cycle arrest is not yet senescence. When the cell cycle is arrested, an inappropriate growth-promotion converts an arrest into senescence (geroconversion). By inhibiting the growth-promoting mTOR pathway, rapamycin decelerates geroconversion of the arrested cells. And as a striking example, while causing arrest, p53 may decelerate or suppress geroconversion (in some conditions). Here I discuss the meaning of geroconversion and also the terms gerogenes, gerossuppressors, gerosuppressants, gerogenic pathways, gero-promoters, hyperfunction and feedback resistance, regenerative potential, hypertrophy and secondary atrophy, pro-gerogenic and gerogenic cells.

Topics: Animals; Atrophy; Cell Cycle Checkpoints; Cellular Senescence; Feedback, Physiological; Humans; Hypertrophy; Protein Kinase Inhibitors; Signal Transduction; Sirolimus; Terminology as Topic; TOR Serine-Threonine Kinases; Tumor Suppressor Protein p53

Exposure of proximal tubular epithelial cells to high glucose contributes to the accumulation of tubulointerstitial and matrix proteins in diabetic nephropathy, but how this occurs is not well understood. We investigated the effect of the signaling molecule tuberin, which modulates the mammalian target of rapamycin pathway, on renal hypertrophy and fibronectin expression. We found that the kidney mass was significantly greater in partially tuberin-deficient (TSC2(+/-) ) diabetic rats than wild-type diabetic rats. Furthermore, TSC2(+/-) rats exhibited significant increases in the basal levels of phospho-tuberin and fibronectin expression in the kidney cortex. Increased levels of phosphorylated tuberin associated with an increase in fibronectin expression in both wild-type and TSC2(+/-) diabetic rats. Treatment with insulin abrogated the diabetes-induced increase in fibronectin expression. In vitro, high glucose enhanced fibronectin expression in TSC2(+/-) primary proximal tubular epithelial cells; both inhibition of Akt and inhibition of the mammalian target of rapamycin could prevent this effect of glucose. In addition, forced expression of tuberin in tuberin-null cells abolished the expression of fibronectin protein. Taken together, these data suggest that tuberin plays a central role in the development of renal hypertrophy and in modulating the production of the matrix protein fibronectin in diabetes.

Topics: Animals; Base Sequence; Cells, Cultured; Diabetes Mellitus, Type 1; Diabetic Nephropathies; Fibronectins; Gene Expression; Gene Targeting; Glucose; Hypertrophy; Kidney; Male; Models, Biological; Phosphorylation; Promoter Regions, Genetic; Proto-Oncogene Proteins c-akt; Rats; Ribosomal Protein S6 Kinases, 70-kDa; RNA, Messenger; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Tuberous Sclerosis Complex 2 Protein; Tumor Suppressor Proteins

Retinal pigment epithelial (RPE) cell dysfunction plays a central role in various retinal degenerative diseases, but knowledge is limited regarding the pathways responsible for adult RPE stress responses in vivo. RPE mitochondrial dysfunction has been implicated in the pathogenesis of several forms of retinal degeneration. Here we have shown that postnatal ablation of RPE mitochondrial oxidative phosphorylation in mice triggers gradual epithelium dedifferentiation, typified by reduction of RPE-characteristic proteins and cellular hypertrophy. The electrical response of the retina to light decreased and photoreceptors eventually degenerated. Abnormal RPE cell behavior was associated with increased glycolysis and activation of, and dependence upon, the hepatocyte growth factor/met proto-oncogene pathway. RPE dedifferentiation and hypertrophy arose through stimulation of the AKT/mammalian target of rapamycin (AKT/mTOR) pathway. Administration of an oxidant to wild-type mice also caused RPE dedifferentiation and mTOR activation. Importantly, treatment with the mTOR inhibitor rapamycin blunted key aspects of dedifferentiation and preserved photoreceptor function for both insults. These results reveal an in vivo response of the mature RPE to diverse stressors that prolongs RPE cell survival at the expense of epithelial attributes and photoreceptor function. Our findings provide a rationale for mTOR pathway inhibition as a therapeutic strategy for retinal degenerative diseases involving RPE stress.

Topics: Animals; Autophagy; Cell Death; Cell Dedifferentiation; Cell Movement; Cell Survival; Female; Glycolysis; Hepatocyte Growth Factor; Hypertrophy; Male; Mice; Mice, Transgenic; Oxidative Phosphorylation; Photoreceptor Cells, Vertebrate; Proto-Oncogene Proteins c-akt; Proto-Oncogene Proteins c-met; Retinal Degeneration; Retinal Pigment Epithelium; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Ubiquitin-mediated protein degradation is necessary for both increased ventricular mass and survival signaling for compensated hypertrophy in pressure-overloaded (PO) myocardium. Another molecular keystone involved in the hypertrophic growth process is the mammalian target of rapamycin (mTOR), which forms two distinct functional complexes: mTORC1 that activates p70S6 kinase-1 to enhance protein synthesis and mTORC2 that activates Akt to promote cell survival. Independent studies in animal models show that rapamycin treatment that alters mTOR complexes also reduces hypertrophic growth and increases lifespan by an unknown mechanism. We tested whether the ubiquitin-mediated regulation of growth and survival in hypertrophic myocardium is linked to the mTOR pathway. For in vivo studies, right ventricle PO in rats was conducted by pulmonary artery banding; the normally loaded left ventricle served as an internal control. Rapamycin (0.75 mg/kg per day) or vehicle alone was administered intraperitoneally for 3 days or 2 wk. Immunoblot and immunofluorescence imaging showed that the level of ubiquitylated proteins in cardiomyocytes that increased following 48 h of PO was enhanced by rapamycin. Rapamycin pretreatment also significantly increased PO-induced Akt phosphorylation at S473, a finding confirmed in cardiomyocytes in vitro to be downstream of mTORC2. Analysis of prosurvival signaling in vivo showed that rapamycin increased PO-induced degradation of phosphorylated inhibitor of κB, enhanced expression of cellular inhibitor of apoptosis protein 1, and decreased active caspase-3. Long-term rapamycin treatment in 2-wk PO myocardium blunted hypertrophy, improved contractile function, and reduced caspase-3 and calpain activation. These data indicate potential cardioprotective benefits of rapamycin in PO hypertrophy.

Topics: Animals; Calpain; Caspase 3; Hypertrophy; Immunosuppressive Agents; Inhibitor of Apoptosis Proteins; Male; Models, Animal; Myocardium; Proteins; Proto-Oncogene Proteins c-akt; Rats; Rats, Inbred F344; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Ubiquitination

Topics: Androstadienes; Animals; Hypertrophy; Insulin-Like Growth Factor I; MAP Kinase Signaling System; Mechanistic Target of Rapamycin Complex 1; Mice; Multiprotein Complexes; Muscle Proteins; Muscle, Skeletal; Organ Size; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Proteins; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Tuberous Sclerosis Complex 2 Protein; Tumor Suppressor Proteins; Weight-Bearing; Wortmannin

Nutrition and physical activity have profound effects on skeletal muscle metabolism and growth. Regulation of muscle mass depends on a thin balance between growth-promoting and growth-suppressing factors. Over the past decade, the mammalian target of rapamycin (mTOR) kinase has emerged as an essential factor for muscle growth by mediating the anabolic response to nutrients, insulin, insulin-like growth factors and resistance exercise. As opposed to the mTOR signaling pathway, the AMP-activated protein kinase (AMPK) is switched on during starvation and endurance exercise to upregulate energy-conserving processes. Recent evidence indicates that mTORC1 (mTOR Complex 1) and AMPK represent two antagonistic forces governing muscle adaption to nutrition, starvation and growth stimulation. Animal knockout models with impaired mTORC1 signaling showed decreased muscle mass correlated with increased AMPK activation. Interestingly, AMPK inhibition in p70S6K-deficient muscle cells restores cell growth and sensitivity to nutrients. Conversely, muscle cells lacking AMPK have increased mTORC1 activation with increased cell size and protein synthesis rate. We also demonstrated that the hypertrophic action of MyrAkt is enhanced in AMPK-deficient muscle, indicating that AMPK acts as a negative feedback control to restrain muscle hypertrophy. Our recent results extend this notion by showing that AMPKα1, but not AMPKα2, regulates muscle cell size through the control of mTORC1 signaling. These results reveal the diverse functions of the two catalytic isoforms of AMPK, with AMPKα1 playing a predominant role in the control of muscle cell size and AMPKα2 mediating muscle metabolic adaptation. Thus, the crosstalk between AMPK and mTORC1 signaling is a highly regulated way to control changes in muscle growth and metabolic rate imposed by external cues.

Topics: Aminoimidazole Carboxamide; AMP-Activated Protein Kinases; Animals; Cell Size; Food; Gene Knockout Techniques; Humans; Hypertrophy; Mechanistic Target of Rapamycin Complex 1; Mice; Motor Activity; Multiprotein Complexes; Muscle Development; Muscles; Protein Subunits; Proteins; Ribonucleotides; Signal Transduction; Sirolimus; Starvation; TOR Serine-Threonine Kinases

Chronic mechanical loading (CML) of skeletal muscle induces compensatory growth and the drug rapamycin has been reported to block this effect. Since rapamycin is considered to be a highly specific inhibitor of the mammalian target of rapamycin (mTOR), many have concluded that mTOR plays a key role in CML-induced growth regulatory events. However, rapamycin can exert mTOR-independent actions and systemic administration of rapamycin will inhibit mTOR signalling in all cells throughout the body. Thus, it is not clear if the growth inhibitory effects of rapamycin are actually due to the inhibition of mTOR signalling, and more specifically, the inhibition of mTOR signalling in skeletal muscle cells. To address this issue, transgenic mice with muscle specific expression of various rapamycin-resistant mutants of mTOR were employed. These mice enabled us to demonstrate that mTOR, within skeletal muscle cells, is the rapamycin-sensitive element that confers CML-induced hypertrophy, and mTOR kinase activity is necessary for this event. Surprisingly, CML also induced hyperplasia, but this occurred through a rapamycin-insensitive mechanism. Furthermore, CML was found to induce an increase in FoxO1 expression and PKB phosphorylation through a mechanism that was at least partially regulated by an mTOR kinase-dependent mechanism. Finally, CML stimulated ribosomal RNA accumulation and rapamycin partially inhibited this effect; however, the effect of rapamycin was exerted through a mechanism that was independent of mTOR in skeletal muscle cells. Overall, these results demonstrate that CML activates several growth regulatory events, but only a few (e.g. hypertrophy) are fully dependent on mTOR signalling within the skeletal muscle cells.

Topics: Ablation Techniques; Animals; Hypertrophy; Male; Mice; Mice, Transgenic; Muscle, Skeletal; Mutation; Ribosomes; Sirolimus; TOR Serine-Threonine Kinases; Weight-Bearing

Regenerative capacity is progressively lost with age. Here we show that pregnancy markedly improved liver regeneration in aged mice concomitantly with inducing a switch from proliferation-based liver regeneration to a regenerative process mediated by cell growth. We found that the key mediator of this switch was the Akt/mTORC1 pathway; its inhibition blocked hypertrophy, while increasing proliferation. Moreover, pharmacological activation of this pathway sufficed to induce the hypertrophy module, mimicking pregnancy. This treatment dramatically improved hepatic regenerative capacity and survival of old mice. Thus, cell growth-mediated mass reconstitution, which is relatively resistant to the detrimental effects of aging, is employed in a physiological situation and holds potential as a therapeutic strategy for ameliorating age-related functional deterioration.

Topics: Aging; Animals; Antibiotics, Antineoplastic; Cell Proliferation; Female; Hepatectomy; Hepatocytes; Hyperplasia; Hypertrophy; Liver; Liver Regeneration; Male; Mechanistic Target of Rapamycin Complex 1; Mice; Mice, Inbred C57BL; Multiprotein Complexes; Pregnancy; Proteins; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Transcription Factors

Myostatin deficiency leads to both an increased rate of protein synthesis and skeletal muscle hypertrophy. However, the mechanisms involved in mediating these effects are not yet fully understood. Here, we demonstrate that genetic loss of myostatin leads to enhanced muscle expression of both protein kinase B and mammalian target of rapamycin/S6K signalling components, consistent with their elevated activity. This is associated with a reduction in the expression of PGC1alpha and COX IV, proteins which play important roles in maintaining mitochondrial function. Furthermore, we show that these changes in signalling and protein expression are largely independent of alterations in intramuscular amino acid content. Our findings, therefore, reveal potential new mechanisms and further contribute to our understanding of myostatin-regulated skeletal muscle growth and function.

Topics: Animals; Hypertrophy; Mammals; Mice; Muscle Development; Muscle, Skeletal; Myostatin; Protein Biosynthesis; Proteins; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus

Topics: Administration, Oral; Exercise; Humans; Hypertrophy; Muscle Contraction; Muscle Proteins; Muscle, Skeletal; Phosphorylation; Protein Biosynthesis; Protein Kinase Inhibitors; Protein Kinases; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Elevated testosterone concentrations induce cardiac hypertrophy but the molecular mechanisms are poorly understood. Anabolic properties of testosterone involve an increase in protein synthesis. The mammalian target of rapamycin complex 1 (mTORC1) pathway is a major regulator of cell growth, but the relationship between testosterone action and mTORC1 in cardiac cells remains unknown. Here, we investigated whether the hypertrophic effects of testosterone are mediated by mTORC1 signaling in cultured cardiomyocytes. Testosterone increases the phosphorylation of mTOR and its downstream targets 40S ribosomal protein S6 kinase 1 (S6K1; also known as RPS6KB1) and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1). The S6K1 phosphorylation induced by testosterone was blocked by rapamycin and small interfering RNA to mTOR. Moreover, the hormone increased both extracellular-regulated kinase (ERK1/2) and protein kinase B (Akt) phosphorylation. ERK1/2 inhibitor PD98059 blocked the testosterone-induced S6K1 phosphorylation, whereas Akt inhibition (Akt-inhibitor-X) had no effect. Testosterone-induced ERK1/2 and S6K1 phosphorylation increases were blocked by either 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid-acetoxymethylester or by inhibitors of inositol 1,4,5-trisphosphate (IP(3)) pathway: U-73122 and 2-aminoethyl diphenylborate. Finally, cardiomyocyte hypertrophy was evaluated by, the expression of beta-myosin heavy chain, alpha-skeletal actin, cell size, and amino acid incorporation. Testosterone increased all four parameters and the increase being blocked by mTOR inhibition. Our findings suggest that testosterone activates the mTORC1/S6K1 axis through IP(3)/Ca(2+) and MEK/ERK1/2 to induce cardiomyocyte hypertrophy.

Topics: Androgens; Animals; Calcium; Calcium Signaling; Carrier Proteins; Cells, Cultured; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Flavonoids; Hypertrophy; Intracellular Membranes; Intracellular Signaling Peptides and Proteins; Myocytes, Cardiac; Phosphoproteins; Phosphorylation; Protein Kinases; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Ribosomal Protein S6 Kinases; RNA, Small Interfering; Signal Transduction; Sirolimus; Testosterone; TOR Serine-Threonine Kinases; Transcription Factors

Removal of one kidney stimulates synthesis of RNA and protein, with minimal DNA replication, in all nephron segments of the remaining kidney, resulting in cell growth (increase in cell size) with minimal cell proliferation (increase in cell number). In addition to the compensatory renal hypertrophy caused by nephron loss, pathophysiological renal hypertrophy can occur as a consequence of early uncontrolled diabetes. However, the molecular mechanism underlying renal hypertrophy in these conditions remains unclear. In the present study, we report that deletion of S6 kinase 1 (S6K1) inhibited renal hypertrophy seen following either contralateral nephrectomy or induction of diabetes. In wild-type mice, hypertrophic stimuli increased phosphorylation of 40S ribosomal protein S6 (rpS6), a known target of S6K1. Immunoblotting analysis revealed that S6K1(-/-) mice exhibited moderately elevated basal levels of rpS6, which did not increase further in response to the hypertrophic stimuli. Northern blotting indicated a moderate upregulation of S6K2 expression in the kidneys of S6K1(-/-) mice. Phosphorylation of the eukaryotic translation initiation factor 4E-binding protein 1, another downstream target of the mammalian target of rapamycin (mTOR), was stimulated to equivalent levels in S6K1(-/-) and S6K1(+/+) littermates during renal hypertrophy, indicating that mTOR was still activated in the S6K1(-/-) mice. The highly selective mTOR inhibitor, rapamycin, inhibited increased phosphorylation of rpS6 and blocked 60-70% of the hypertrophy seen in wild-type mice but failed to prevent the approximately 10% hypertrophy seen in S6K1(-/-) mice in response to uninephrectomy (UNX) although it did inhibit the basal rpS6 phosphorylation. Thus the present study provides the first genetic evidence that S6K1 plays a major role in the development of compensatory renal hypertrophy as well as diabetic renal hypertrophy and indicates that UNX- and diabetes-mediated mTOR activation can selectively activate S6K1 without activating S6K2.

Topics: Adaptor Proteins, Signal Transducing; Animals; Blood Glucose; Carrier Proteins; Cell Cycle Proteins; Cell Proliferation; Diabetes Mellitus, Experimental; Diabetic Nephropathies; Disease Models, Animal; Enzyme Inhibitors; Eukaryotic Initiation Factors; Gene Expression Regulation, Enzymologic; Hypertrophy; Kidney; Male; Mice; Mice, Knockout; Nephrectomy; Phosphoproteins; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor); Ribosomal Protein S6; Ribosomal Protein S6 Kinases, 70-kDa; Signal Transduction; Sirolimus; Time Factors; TOR Serine-Threonine Kinases

Topics: Animals; Cell Proliferation; Diabetes Mellitus, Experimental; Diabetic Nephropathies; Enzyme Inhibitors; Eukaryotic Initiation Factors; Gene Expression Regulation, Enzymologic; Humans; Hypertrophy; Kidney; Mice; Mice, Knockout; Phosphorylation; Protein Kinases; Ribosomal Protein S6; Ribosomal Protein S6 Kinases, 70-kDa; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Sirolimus (SRL) is a potent and specific immunosuppressive drug used in organ transplantation, as basic therapy or in combination with calcineurin inhibitors. Although SRL is a nonnephrotoxic drug, many reports have related its use with the development of proteinuria, especially after conversion. Therefore, the aim of this study was to elucidate the interrelation between early and late SRL administration on the development of glomerular hypertrophy and proteinuria in a model of renal mass reduction (RMR).. Rats underwent 2/3 cryoablation of the left kidney and subsequent right nephrectomy (n=42) or sham operations (n=29). Two weeks before (early study) or 12 weeks after (late study) surgery, SRL or vehicle was administered three times weekly. Creatinine clearance and proteinuria were determined throughout the study, and a complete histologic analysis was performed at the end of the study.. Treatment with SRL had no effect on creatinine clearance, independently of the administration time. Four weeks after RMR, a significant increase in proteinuria was observed. Proteinuria was stabilized after early and late SRL administration, whereas vehicle-treated animals showed a further increase in proteinuria. Glomerular hypertrophy was strongly associated with proteinuria, and early SRL introduction prevented glomerular enlargement. The histologic analysis showed less structural damage in the two groups of animals treated with SRL than in the control group.. Although early SRL introduction blocked glomerular hypertrophy, SRL treatment revealed the potential to halt progression of proteinuria and histologic damage at any time of administration in a model of RMR.

Topics: Animals; Creatinine; Disease Models, Animal; Disease Progression; Hypertrophy; Immunosuppressive Agents; Kidney; Kidney Diseases; Kidney Glomerulus; Male; Protein Kinases; Proteinuria; Rats; Rats, Wistar; Sirolimus; TOR Serine-Threonine Kinases

The efficacy of mammalian target of rapamycin (mTOR) inhibitors is currently tested in patients affected by autosomal dominant polycystic kidney disease. Treatment with mTOR inhibitors has been associated with numerous side effects. However, the renal-specific effect of mTOR inhibitor treatment cessation in polycystic kidney disease is currently unknown. Therefore, we compared pulse and continuous everolimus treatment in Han:SPRD rats. Four-week-old male heterozygous polycystic and wild-type rats were administered everolimus or vehicle by gavage feeding for 5 wk, followed by 7 wk without treatment, or continuously for 12 wk. Cessation of everolimus did not result in the appearance of renal cysts up to 7 wk postwithdrawal despite the reemergence of S6 kinase activity coupled with an overall increase in cell proliferation. Pulse everolimus treatment resulted in striking noncystic renal parenchymal enlargement and glomerular hypertrophy that was not associated with compromised kidney function. Both treatment regimens ameliorated kidney function, preserved the glomerular-tubular connection, and reduced proteinuria. Pulse treatment at an early age delays cyst development but leads to striking glomerular and parenchymal hypertrophy. Our data might have an impact when long-term treatment using mTOR inhibitors in patients with autosomal dominant polycystic kidney disease is being considered.

Topics: Administration, Oral; Animals; Drug Administration Schedule; Emulsions; Everolimus; Hypertrophy; Immunosuppressive Agents; Kidney; Kidney Glomerulus; Male; Polycystic Kidney Diseases; Protein Kinases; Proteinuria; Pulse Therapy, Drug; Rats; Sirolimus; TOR Serine-Threonine Kinases

We examined the effect of 28 days of overload on mammalian target of rapamycin (mTOR) and extracellular signal-regulated kinase (ERK) signaling in young adult (Y; 6-month old) and aged (O; 30-month old) Fischer 344 x Brown Norway rats subjected to bilateral synergist ablation (SA) of two thirds of the gastrocnemius muscle or sham surgery (CON). Although plantaris (PLA) muscle hypertrophy was attenuated by aging, mTOR phosphorylation was 44% and 35% greater in Y SA and O SA compared with CON (p = .038). Ribosomal protein S6 phosphorylation was 114% and 24% higher in Y SA and O SA compared with CON (p = .009). Eukaryotic initiation factor 2Bepsilon phosphorylation was 33% and 9% higher in Y SA and O SA compared with CON (p = .04). Translational signaling in young adult and aged plantaris muscle is equally responsive to chronic overload.

Topics: Age Factors; Aging; Analysis of Variance; Animals; Chronic Disease; Disease Models, Animal; Extracellular Signal-Regulated MAP Kinases; Hypertrophy; Immunoblotting; Linear Models; Male; Mitogen-Activated Protein Kinases; Muscle, Skeletal; Organ Size; Phosphorylation; Probability; Protein Kinases; Random Allocation; Rats; Rats, Inbred BN; Rats, Inbred F344; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Cardiomyocyte hypertrophy differs according to the stress exerted on the myocardium. While pressure overload-induced cardiomyocyte hypertrophy is associated with depressed contractile function, physiological hypertrophy after exercise training associates with preserved or increased inotropy. We determined the activation state of myocardial Akt signaling with downstream substrates and fetal gene reactivation in exercise-induced physiological and pressure overload-induced pathological hypertrophies. C57BL/6J mice were either treadmill trained for 6 weeks, 5 days/week, at 85-90% of maximal oxygen uptake (VO(2max)), or underwent transverse aortic constriction (TAC) for 1 or 8 weeks. Total and phosphorylated protein levels were determined with SDS-PAGE, and fetal genes by real-time RT-PCR. In the physiologically hypertrophied heart after exercise training, total Akt protein level was unchanged, but Akt was chronically hyperphosphorylated at serine 473. This was accompanied by activation of the mammalian target of rapamycin (mTOR), measured as phosphorylation of its two substrates: the ribosomal protein S6 kinase-1 (S6K1) and the eukaryotic translation initiation factor-4E binding protein-1 (4E-BP1). Exercise training did not reactivate the fetal gene program (beta-myosin heavy chain, atrial natriuretic factor, skeletal muscle actin). In contrast, pressure overload after TAC reactivated fetal genes already after 1 week, and partially inactivated the Akt/mTOR pathway and downstream substrates after 8 weeks. In conclusion, changes in opposite directions of the myocardial Akt/mTOR signal pathway appears to distinguish between physiological and pathological hypertrophies; exercise training associating with activation and pressure overload associating with inactivation of the Akt/mTOR pathway.

Topics: Adaptor Proteins, Signal Transducing; Animals; Aorta, Thoracic; Cardiomegaly; Carrier Proteins; Cell Cycle Proteins; Cell Size; Constriction, Pathologic; Echocardiography; Enzyme Activation; Eukaryotic Initiation Factors; Exercise Test; Female; Heart Ventricles; Hypertrophy; Mice; Mice, Inbred C57BL; Models, Biological; Myocardium; Myocytes, Cardiac; Phosphoproteins; Phosphorylation; Physical Conditioning, Animal; Protein Kinases; Proto-Oncogene Proteins c-akt; Random Allocation; Ribosomal Protein S6 Kinases; Serine; Signal Transduction; Sirolimus; Time Factors; TOR Serine-Threonine Kinases

Recent studies suggested the involvement of the Akt/mammalian target of rapamycin (mTOR) pathway in the pathogenesis of diabetic nephropathy. The effect of mTOR blockade by rapamycin in diabetic nephropathy was investigated, but in vivo study of rapamycin treatment in the course of early diabetes is still insufficient. This study was designed to determine the therapeutic effects of rapamycin on diabetic nephropathy at an early stage.. Diabetes was induced in Sprague-Dawley rats with streptozotocin, and rapamycin (1 mg/kg) was administered by daily gavage for 4 weeks. Renal structural changes and some factors involved in the early pathogenesis of diabetic nephropathy were tested. The activation level of the Akt/mTOR pathway was also determined.. Rapamycin treatment reduced albuminuria, glomerular enlargement, glomerular basement membrane thickening, renal macrophage recruitment, and levels of renal mRNA expression of proliferating cell nuclear antigen, transforming growth factor-beta1, vascular endothelial growth factor, and monocyte chemoattractant protein-1 without change in blood glucose level and blood pressure in experimental diabetic rats. In addition, treatment with rapamycin also down-regulated the enhanced levels of renal p-Akt, phospho-p70S6 kinase, and phospho-ribosomal S6 protein in diabetic rats.. Rapamycin treatment can prevent the early renal structural changes of diabetes in experimental rats, and thus halt the early steps of the development of diabetic nephropathy. mTOR blockade might be beneficial for the treatment of diabetic nephropathy.

Topics: Albuminuria; Animals; Anti-Inflammatory Agents; Cell Proliferation; Diabetes Mellitus, Experimental; Diabetic Nephropathies; Glomerular Basement Membrane; Hypertrophy; Kidney; Kidney Glomerulus; Male; Protein Kinases; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Early diabetic nephropathy is characterized by renal hypertrophy that is mainly due to proximal tubular hypertrophy. Mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase, and its signaling has been reported to regulate protein synthesis and cellular growth, specifically, hypertrophy. Therefore, we examined the effect of mTOR signaling on diabetic renal hypertrophy by using the specific inhibitor for mTOR, rapamycin. Ten days after streptozotocin-induced diabetes, mice showed kidney hypertrophy with increases in the phosphorylation of p70S6kinase and the expression of cyclin kinase inhibitors, p21(Cip1) and p27(Kip1), in the kidneys. The intraperitoneal injection of rapamycin (2 mg/kg/day) markedly attenuated the enhanced phosphorylation of p70S6kinase, the increment of cyclin-dependent kinase inhibitors, and renal enlargement without any changes of clinical parameters, including blood glucose, blood pressure, and food intake. Overexpression of a constitutive active form of p70S6kinase resulted in increased cell size of cultured mouse proximal tubule cells; thus, activation of p70S6kinase causes hypertrophy of proximal tubular cells. Our findings suggest that activation of mTOR signaling causes renal hypertrophy at the early stage of diabetes.

Topics: Animals; Diabetes Mellitus, Experimental; Diabetic Nephropathies; Disease Progression; Hypertrophy; Immunosuppressive Agents; Injections, Intraperitoneal; Kidney; Male; Mice; Mice, Inbred C57BL; Organ Size; Protein Kinases; Severity of Illness Index; Signal Transduction; Sirolimus; Streptozocin; TOR Serine-Threonine Kinases; Treatment Outcome

Loss of functioning nephrons stimulates the growth of residual kidney tissue to augment work capacity and maintain normal renal function. This growth largely occurs by hypertrophy rather than from hyperplasia of the remaining nephrons. The signaling mechanisms that increase RNA and protein synthesis during compensatory renal hypertrophy are unknown. This study found that the remaining kidney hypertrophied 42% by 16 d after unilateral nephrectomy (UNX) in DBA/2 mice. Immunoblotting analysis revealed increased phosphorylation of the 40S ribosomal protein S6 (rpS6) and the eukaryotic translation initiation factor (eIF) 4E-binding protein 1 (4E-BP1), the two downstream effectors of the mammalian target of rapamycin (mTOR). The highly specific mTOR inhibitor rapamycin blocked UNX-increased phosphorylation of both rpS6 and 4E-BP1. UNX increased the content of not only 40S and 60S ribosomal subunits but also 80S monosomes and polysomes in the remaining kidney. Administration of rapamycin decreased UNX-induced polysome formation and shifted the polysome profile in the direction of monosomes and ribosomal subunits. Pretreatment of the mice with rapamycin inhibited UNX-induced hypertrophy. These studies demonstrate that activation of the mTOR signaling pathway in the remaining kidney after UNX plays an essential role in modulating RNA and protein synthesis during development of compensatory renal hypertrophy.

Topics: Adaptation, Physiological; Adaptor Proteins, Signal Transducing; Animals; Carrier Proteins; Cell Cycle Proteins; Eukaryotic Initiation Factors; Hypertrophy; Immunosuppressive Agents; Kidney; Male; Mice; Mice, Inbred DBA; Nephrectomy; Phosphoproteins; Phosphorylation; Polyribosomes; Protein Kinases; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

The molecular mechanisms of airway smooth muscle hypertrophy, a feature of severe asthma, are poorly understood. We previously established a conditionally immortalized human bronchial smooth muscle cell line with a temperature-sensitive SV40 large T antigen. Temperature shift and loss of large T cause G1-phase cell cycle arrest that is accompanied by increased airway smooth muscle cell size. In the present study, we hypothesized that phosphorylation of eukaryotic initiation factor-4E (eIF4E)-binding protein (4E-BP), which subsequently releases eIF4E and initiates cap-dependent mRNA translation, was required for airway smooth muscle hypertrophy. Treatment of cells with chemical inhibitors of PI 3-kinase and mammalian target of rapamycin blocked protein synthesis and cell growth while decreasing the phosphorylation of 4E-BP and increasing the binding of 4E-BP to eIF4E, consistent with the notion that 4E-BP1 phosphorylation and eIF4E function are required for hypertrophy. To test this directly, we infected cells with a retrovirus encoding a phosphorylation site mutant of 4E-BP1 (AA-4E-BP-1) that dominantly inhibits eIF4E. Upon temperature shift, cells infected with AA-4E-BP-1, but not empty vector, failed to undergo hypertrophic growth. We conclude that phosphorylation of 4E-BP, eIF4E release, and cap-dependent protein synthesis are required for hypertrophy of human airway smooth muscle cells.

Topics: Adaptor Proteins, Signal Transducing; Bronchi; Carrier Proteins; Cell Cycle Proteins; Cell Enlargement; Cell Line; Chromones; Enzyme Inhibitors; Eukaryotic Initiation Factor-4E; Humans; Hypertrophy; Imidazoles; Morpholines; Muscle, Smooth; Mutation; p38 Mitogen-Activated Protein Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphoproteins; Phosphorylation; Protein Kinases; Pyridines; Sirolimus; Temperature; TOR Serine-Threonine Kinases; Transfection

We have already reported Gas6 is involved in glomerular hypertrophy observed in diabetic nephropathy. However, the molecular mechanisms involved in glomerular hypertrophy are still unknown, especially in vivo.. In vivo, diabetes was induced in rats and mice by streptozotocin (STZ) and the activation of the Akt/mTOR pathway in glomeruli was examined. In vitro, mesangial hypertrophy was assessed by [(3)H]leucine incorporation and measuring cell areas.. Akt, p70 S6 kinase, and 4E-BP-1 were induced and phosphorylated in rat glomerular lysates after 12 weeks of STZ injection when mesangial and glomerular hypertrophy was observed. We then examined the role of Gas6 by treating STZ-rats with warfarin, and found that warfarin treatment inhibited the phosphorylation of these molecules as well as the hypertrophy. We next examined whether high glucose stimulation can induce the expression of Gas6/Axl in mesangial cells. Stimulation of the cells with 25 mmol/L of glucose increased the expression of Gas6/Axl and mesangial cell size compared with that with 5.6 mmol/L of glucose. This hypertrophic effect was abolished in mesangial cells derived from Gas6 knockout mice. We also found that LY294002 and rapamycin blocked Gas6-induced activation of the Akt/mTOR pathway and mesangial hypertrophy. Furthermore, less phosphorylated Akt-positive or 4E-BP-1-positive areas were found in STZ-treated Gas6 knockout mice than in STZ-treated wild-type mice.. Our study indicates that the Akt/mTOR pathway is a key signaling cascade in Gas6-mediated mesangial and glomerular hypertrophy and revealed a crucial role of Gas6/Axl and the Akt/mTOR pathway in the development of diabetic nephropathy.

Topics: Adaptor Proteins, Signal Transducing; Animals; Antibiotics, Antineoplastic; Butadienes; Carrier Proteins; Cell Cycle Proteins; Cells, Cultured; Chromones; Cyclin-Dependent Kinase Inhibitor p27; Diabetes Mellitus, Experimental; Diabetic Nephropathies; Enzyme Inhibitors; Eukaryotic Initiation Factors; Female; Glomerular Mesangium; Glucose; Hypertrophy; Intercellular Signaling Peptides and Proteins; Intracellular Signaling Peptides and Proteins; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Morpholines; Nitriles; Phosphoproteins; Protein Kinases; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Ribosomal Protein S6 Kinases, 70-kDa; Sirolimus; TOR Serine-Threonine Kinases; Tumor Suppressor Proteins

The purpose of this study was to identify the potential downstream functions associated with mammalian target of rapamycin (mTOR) signaling during myotube hypertrophy. Terminally differentiated myotubes were serum stimulated for 3, 6, 12, 24, and 48 h. This treatment resulted in significant myotube hypertrophy (protein/DNA) and increased RNA content (RNA/DNA) with no changes in DNA content or indices of cell proliferation. During myotube hypertrophy, the increase in RNA content was accompanied by an increase in tumor suppressor protein retinoblastoma (Rb) phosphorylation and a corresponding increase in the availability of the ribosomal DNA transcription factor upstream binding factor (UBF). Serum stimulation also induced an increase in cyclin D1 protein expression in the differentiated myotubes with a concomitant increase in cyclin D1-dependent cyclin-dependent kinase (CDK)-4 activity toward Rb. The increases in myotube hypertrophy and RNA content were blocked by rapamycin treatment, which also prevented the increase in cyclin D1 protein expression, CDK-4 activity, Rb phosphorylation, and the increase in UBF availability. Our findings demonstrate that activation of mTOR is necessary for myotube hypertrophy and suggest that the role of mTOR is in part to modulate cyclin D1-dependent CDK-4 activity in the regulation of Rb and ribosomal RNA synthesis. On the basis of these results, we propose that common molecular mechanisms contribute to the regulation of myotube hypertrophy and growth during the G1 phase of the cell cycle.

Topics: Animals; Cell Cycle; Cell Enlargement; Cells, Cultured; Culture Media; Cyclin D1; Cyclin-Dependent Kinase 4; Hypertrophy; Muscle Fibers, Skeletal; Muscle, Skeletal; Myoblasts; Phosphorylation; Pol1 Transcription Initiation Complex Proteins; Protein Kinases; Rats; Retinoblastoma Protein; RNA, Ribosomal; Serum; Sirolimus; TOR Serine-Threonine Kinases

A necessary mediator of cardiac myocyte enlargement is protein synthesis, which is controlled at the levels of both translation initiation and elongation. Eukaryotic elongation factor-2 (eEF2) mediates the translocation step of peptide-chain elongation and is inhibited through phosphorylation by eEF2 kinase. In addition, p70S6 kinase can regulate protein synthesis by phosphorylating eEF2 kinase or via phosphorylation of ribosomal protein S6. We have recently shown that eEF2 kinase is also controlled by phosphorylation by AMP-activated protein kinase (AMPK), a key regulator of cellular energy homeostasis. Moreover, the mammalian target of rapamycin has also been shown to be inhibited, indirectly, by AMPK, thus leading to the inhibition of p70S6 kinase. Although AMPK activation has been shown to modulate protein synthesis, it is unknown whether AMPK could also be a regulator of cardiac hypertrophic growth. Therefore, we investigated the role of AMPK activation in regulating protein synthesis during both phenylephrine- and Akt-induced cardiac hypertrophy. Metformin and 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside were used to activate AMPK in neonatal rat cardiac myocytes. Activation of AMPK significantly decreased protein synthesis induced by phenylephrine treatment or by expression of constitutively active Akt. Activation of AMPK also resulted in decreased p70S6 kinase phosphorylation and increased phosphorylation of eEF2, suggesting that inhibition of protein synthesis involves the eEF2 kinase/eEF2 axis and/or the p70S6 kinase pathway. Together, our data suggest that the inhibition of protein synthesis by pharmacological activation of AMPK may be a key regulatory mechanism by which hypertrophic growth can be controlled.

Topics: Aminoimidazole Carboxamide; AMP-Activated Protein Kinases; Animals; Animals, Newborn; Antibiotics, Antineoplastic; Calcium-Calmodulin-Dependent Protein Kinases; Cells, Cultured; Elongation Factor 2 Kinase; Enzyme Activation; Green Fluorescent Proteins; Hypertrophy; Hypoglycemic Agents; Immunoblotting; Luminescent Proteins; Metformin; Microscopy, Fluorescence; Multienzyme Complexes; Myocytes, Cardiac; Phenylephrine; Phosphorylation; Protein Serine-Threonine Kinases; Rats; Ribonucleotides; Ribose; Ribosomal Protein S6; Ribosomal Protein S6 Kinases, 70-kDa; Sirolimus; Time Factors

The mechanisms that regulate mammalian cell size during development and homeostatic maintenance are poorly understood. The tumor suppressor Pten is required for correct maintenance of mammalian neuronal soma size. Selective inactivation of Pten in postnatal granule neurons of the cerebellum and dentate gyrus in mouse causes cell-autonomous hypertrophy as well as more complex phenotypes, including progressive macrocephaly, seizures, and premature death. To determine the contribution of mTor signaling to Pten-mediated growth regulation in the mammalian nervous system, we treated Pten conditional knockout mice with CCI-779, a specific mTor inhibitor. mTor inhibition decreased the seizure frequency and death rate in Pten mutant mice, prevented the increase in Pten-deficient neuronal soma size in young mice, and reversed neuronal soma enlargement in adult mice. mTor inhibition did not decrease the size of wild-type adult neurons. Thus, mTor is required for neuronal hypertrophy downstream of Pten deficiency, but is not required for maintenance of normal neuronal soma size. mTOR inhibitors may be useful therapeutic agents for diseases in brain resulting from PTEN deficiency such as Lhermitte-Duclos disease or glioblastoma multiforme.

Topics: Animals; Brain; Cell Division; Cerebellum; Dentate Gyrus; Genes, Tumor Suppressor; Hypertrophy; Mice; Mice, Knockout; Mice, Transgenic; Neurons; Phosphoric Monoester Hydrolases; Protein Kinase Inhibitors; Protein Kinases; PTEN Phosphohydrolase; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Tumor Suppressor Proteins

Nerve activity controls fiber size and fiber type in skeletal muscle, but the underlying molecular mechanisms remain largely unknown. We have previously shown that Ras-mitogen-activated protein kinase and calcineurin control fiber type but not fiber size in regenerating rat skeletal muscle. Here we report that constitutively active protein kinase B (PKB), also known as Akt, increases fiber size and prevents denervation atrophy in regenerating and adult rat muscles but does not affect fiber type profile. The coexistence of hypertrophic muscle fibers overexpressing activated PKB with normal-size untransfected fibers within the same muscle points to a cell-autonomous control of muscle growth by PKB. The physiological role of this pathway is confirmed by the finding that PKB kinase activity and phosphorylation status are significantly increased in innervated compared with denervated regenerating muscles in parallel with muscle growth. Muscle fiber hypertrophy induced by activated PKB and by a Ras double mutant (RasV12C40) that activates selectively the phosphoinositide 3-kinase-PKB pathway is completely blocked by rapamycin, showing that the mammalian target of rapamycin kinase is the major downstream effector of this pathway in the control of muscle fiber size. On the other hand, nerve activity-dependent growth of regenerating muscle is only partially inhibited by dominant negative PKB and rapamycin, suggesting that other nerve-dependent signaling pathways are involved in muscle growth. The present results support the notion that fiber size and fiber type are regulated by nerve activity through different mechanisms.

Topics: Animals; Electric Stimulation; Hypertrophy; Male; Muscle Denervation; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Atrophy; Mutation; Phosphatidylinositol 3-Kinases; Phosphorylation; Protein Kinases; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; Regeneration; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Topics: Animals; Body Weight; Cyclosporine; Disease Models, Animal; Everolimus; Glomerulosclerosis, Focal Segmental; Graft Rejection; Hypertrophy; Immunosuppressive Agents; Kidney Transplantation; Organ Size; Proteinuria; Rats; Rats, Inbred F344; Rats, Inbred Lew; Sirolimus

Topics: Animals; Digestive System; Dogs; Female; Heart; Hypertrophy; Immunosuppressive Agents; Kidney Transplantation; Mycophenolic Acid; Myocardium; Necrosis; Polyenes; Sirolimus; Tacrolimus; Transplantation, Homologous