nephrin and Nephrosis

Studies of Mendelian forms of focal segmental glomerulosclerosis (FSGS) and nephrotic syndrome have provided new insights into the mechanism of these diseases. Congenital nephrotic syndrome and familial forms of FSGS form a spectrum of podocyte diseases of varying severity and age of onset. Mutations in both nephrin gene (NPHS1) alleles lead to congenital nephrosis, podocyte foot process efacement, and loss of slit-diaphragm structure. Mutations in both podocin gene (NPHS2) alleles lead to a wide range of human disease, from childhood-onset steroid-resistant FSGS and minimal change disease to adult-onset FSGS. Dominantly inherited mutations in ACTN4, the alpha-actinin-4 gene, can lead to a slowly progressive adult-onset form of FSGS. In addition, FSGS is observed as part of several rare multisystem inherited syndromes. Here we review recent progress in understanding the genetic basis of FSGS in humans.

Topics: Animals; Drug Resistance; Epithelial Cells; Genetic Predisposition to Disease; Glomerulosclerosis, Focal Segmental; Humans; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Membrane Proteins; Nephrosis; Nephrotic Syndrome; Point Mutation; Proteins; Steroids

Nephrin is a key structural component of the podocyte slit diaphragm, and proper expression of nephrin on the cell surface is critical to ensure integrity of the blood filtration barrier. Maintenance of nephrin within this unique cell junction has been proposed to require dynamic phosphorylation events and endocytic recycling, although the molecular mechanisms that control this interplay are poorly understood. Here, we investigated the possibility that the phosphotyrosine adaptor protein ShcA regulates nephrin turnover. Western blotting and immunostaining analysis confirmed that ShcA is expressed in podocytes. In immunoprecipitation and pulldown assays, ShcA,

Topics: Animals; Biotinylation; Cell Membrane; Cytosol; Endocytosis; HEK293 Cells; Humans; Kidney Diseases; Male; Membrane Proteins; Nephrosis; Phosphorylation; Podocytes; Proteinuria; Rats; Rats, Sprague-Dawley; Signal Transduction; Src Homology 2 Domain-Containing, Transforming Protein 1; Tyrosine; Up-Regulation

Topics: Animals; Antibodies; Cell Movement; Ephrin-B1; HEK293 Cells; Humans; JNK Mitogen-Activated Protein Kinases; Membrane Proteins; Mice; Mice, Knockout; Nephrosis; Phosphorylation; Podocytes; Rats

Podocyte injury is a key event in proteinuric kidney disease and eventually glomerular scarring. While adrenomedullin (AM), a potent vasodilatory peptide, has been reported to confer renoprotection in several experimental models of kidney diseases, its effect on injured podocytes and the related mechanism is still largely unknown.. Employing Western blotting analysis, immunoprecipitation and immunofluorescence, we investigated the effects of AM on the expressions of podocyte cytoskeletal proteins and Rho-family small GTPases (Rho GTPases) in puromycin aminonucleoside (PAN)-induced podocyte injury, both in cultured podocytes and in PAN nephrosis rats. Urinary protein excretion and the morphologic changes of kidney in PAN nephrosis rats were evaluated. Glutathione-S-transferase pull-down assay was applied for Rho GTPases activity.. PAN induced massive albuminuria and morphologic injury, which were significantly mitigated by AM administration. AM significantly antagonized not only the PAN-decreased expressions of synaptopodin, nephrin, CD2AP and podocin, but also the PAN-disrupted interactions between synaptopodin-RhoA, nephrin-CD2AP, and CD2AP-Rac1-cortactin. These effects of AM in cultured podocytes were mostly significantly blocked by H89, a PKA inhibitor. AM dramatically upregulated the PAN-induced Rho GTPases protein expressions and their activities. PAN increased the expressions of endogenous AM and its receptor RAMP2 which was furthermore upregulated by AM administration.. AM alleviated podocyte injury induced by PAN both in cell culture and in PAN nephrosis. The beneficial effects of AM on podocytes can be attributable to direct modulation of podocyte cytoskeletal proteins and Rho GTPases, mainly via a PKA-dependent pathway.

Topics: Adaptor Proteins, Signal Transducing; Adrenomedullin; Albuminuria; Animals; cdc42 GTP-Binding Protein; Cell Line; Cortactin; Cytoskeletal Proteins; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Male; Membrane Proteins; Mice; Microfilament Proteins; Nephrosis; Neuropeptides; Podocytes; Puromycin Aminonucleoside; rac1 GTP-Binding Protein; Rats; Rats, Sprague-Dawley; Receptor Activity-Modifying Protein 2; rho GTP-Binding Proteins; rhoA GTP-Binding Protein; Vasodilator Agents

Podocytes are critically involved in the maintenance of the glomerular filtration barrier and are key targets of injury in many glomerular diseases. Chronic injury leads to progressive loss of podocytes, glomerulosclerosis, and renal failure. Thus, it is essential to maintain podocyte survival and avoid apoptosis after acute glomerular injury. In normal glomeruli, podocyte survival is mediated via nephrin-dependent Akt signaling. In several glomerular diseases, nephrin expression decreases and podocyte survival correlates with increased vascular endothelial growth factor (VEGF) signaling. How VEGF signaling contributes to podocyte survival and prevents apoptosis remains unknown. We show here that Gα-interacting, vesicle-associated protein (GIV)/girdin mediates VEGF receptor 2 (VEGFR2) signaling and compensates for nephrin loss. In puromycin aminonucleoside nephrosis (PAN), GIV expression increased, GIV was phosphorylated by VEGFR2, and p-GIV bound and activated Gαi3 and enhanced downstream Akt2, mammalian target of rapamycin complex 1 (mTORC1), and mammalian target of rapamycin complex-2 (mTORC2) signaling. In GIV-depleted podocytes, VEGF-induced Akt activation was abolished, apoptosis was triggered, and cell migration was impaired. These effects were reversed by introducing GIV but not a GIV mutant that cannot activate Gαi3. Our data indicate that after PAN injury, VEGF promotes podocyte survival by triggering assembly of an activated VEGFR2/GIV/Gαi3 signaling complex and enhancing downstream PI3K/Akt survival signaling. Because of its important role in promoting podocyte survival, GIV may represent a novel target for therapeutic intervention in the nephrotic syndrome and other proteinuric diseases.

Topics: Animals; Apoptosis; Cell Line; Cell Survival; Cells, Cultured; Disease Models, Animal; GTP-Binding Protein alpha Subunits, Gi-Go; Intracellular Signaling Peptides and Proteins; Male; Membrane Proteins; Mice; Microfilament Proteins; Nephrosis; Phosphatidylinositol 3-Kinases; Podocytes; Proto-Oncogene Proteins c-akt; Puromycin Aminonucleoside; Rats; Rats, Sprague-Dawley; Signal Transduction; TOR Serine-Threonine Kinases; Vascular Endothelial Growth Factor A

Increasing data has shown that the cytoskeletal reorganization of podocytes is involved in the onset of proteinuria and the progression of glomerular disease. Nephrin behaves as a signal sensor of the slit diaphragm to transmit cytoskeletal signals to maintain the unique structure of podocytes. However, the nephrin signaling cascade deserves further study. IQGAP1 is a scaffolding protein with the ability to regulate cytoskeletal organization. It is hypothesized that IQGAP1 contributes to actin reorganization in podocytes through interaction with nephrin. IQGAP1 expression and IQGAP1-nephrin colocalization in glomeruli were progressively decreased and then gradually recovered in line with the development of foot process fusion and proteinuria in puromycin aminonucleoside-injected rats. In cultured human podocytes, puromycin aminonucleoside-induced disruption of F-actin and disorders of migration and spreading were aggravated by IQGAP1 siRNA, and these effects were partially restored by a wild-type IQGAP1 plasmid. Furthermore, the cytoskeletal disorganization stimulated by cytochalasin D in COS7 cells was recovered by cotransfection with wild-type IQGAP1 and nephrin plasmids but was not recovered either by single transfection of the wild-type IQGAP1 plasmid or by cotransfection of mutant IQGAP1 [△1443(S→A)] and wild-type nephrin plasmids. Co-immunoprecipitation analysis using lysates of COS7 cells overexpressing nephrin and each derivative-domain molecule of IQGAP1 demonstrated that the poly-proline binding domain and RasGAP domain in the carboxyl terminus of IQGAP1 are the target modules that interact with nephrin. Collectively, these findings showed that activated IQGAP1, as an intracellular partner of nephrin, is involved in actin cytoskeleton organization and functional regulation of podocytes.

Topics: Actin Cytoskeleton; Animals; Binding Sites; Cell Line; Chlorocebus aethiops; COS Cells; Humans; Male; Membrane Proteins; Nephrosis; Podocytes; Puromycin Aminonucleoside; ras GTPase-Activating Proteins; Rats, Wistar; RNA Interference

Defects in sialylation are known to have serious consequences on podocyte function leading to collapse of the glomerular filtration barrier and the development of proteinuria. However, the cellular processes underlying aberrant sialylation in renal disease are inadequately defined. We have shown in cultured human podocytes that puromycin aminonucleoside (PAN) downregulates enzymes involved in sialic acid metabolism and redox homeostasis and these can be rescued by co-treatment with free sialic acid. The aim of the current study was to ascertain whether sialic acid supplementation could improve renal function and attenuate desialylation in an in vivo model of proteinuria (PAN nephrosis) and to delineate the possible mechanisms involved. PAN nephrotic rats were supplemented with free sialic acid, its precursor N-acetyl mannosamine or the NADPH oxidase inhibitor apocynin. Glomeruli, urine, and sera were examined for evidence of kidney injury and therapeutic efficacy. Of the three treatment regimens, sialic acid had the broadest efficacy in attenuating PAN-induced injury. Proteinuria and urinary nephrin loss were reduced. Transmission electron microscopy revealed that podocyte ultrastructure, exhibited less severe foot process effacement. PAN-induced oxidative stress was ameliorated as evidenced by a reduction in glomerular NOX4 expression and a downregulation of urine xanthine oxidase levels. Sialylation dysfunction was improved as indicated by reduced urinary concentrations of free sialic acid, restored electrophoretic mobility of podocalyxin, and improved expression of a sialyltransferase. These data indicate that PAN induces alterations in the expression of enzymes involved in redox control and sialoglycoprotein metabolism, which can be ameliorated by sialic acid supplementation possibly via its properties as both an antioxidant and a substrate for sialylation.

Topics: Acetophenones; Animals; Dietary Supplements; Hexosamines; Kidney Glomerulus; Membrane Proteins; Microscopy, Electron, Transmission; N-Acetylneuraminic Acid; NADPH Oxidase 4; NADPH Oxidases; Nephrosis; Oxidative Stress; Podocytes; Proteinuria; Puromycin Aminonucleoside; Rats

Minimal-change nephrotic syndrome (MCNS) is a kidney disease defined by selective proteinuria and hypoalbuminemia occurring in the absence of cellular glomerular infiltrates or immunoglobulin deposits. Recent observations suggest that nuclear factor κB (NF-κB) of podocyte is strongly associated with the development of proteinuria in MCNS. Dehydroxymethylepoxyquinomicin (DHMEQ) is a novel NF-κB inhibitor that potently inhibits DNA-binding activity of NF-κB, resulting in several therapeutic effects in various pathological conditions. We conducted this study to ask whether DHMEQ may ameliorate the nephrosis in mice induced by puromycin aminonucleoside (PAN), which is considered to be an animal model for MCNS.. Pretreatment with DHMEQ alleviated the proteinuria and reversed the serum abnormalities in mice nephrosis induced by 450 mg/kg of PAN. Increased serum interleukin-6 level in PAN-induced nephrosis was also completely suppressed by DHMEQ. Electron microscopic analyses of glo-meruli indicated that DHMEQ can inhibit the podocyte foot process effacement via blocking the translocation of podocyte NF-κB from cytoplasm to nucleus.. These results suggest that DHMEQ can be a potential therapeutic agent for MCNS.

Topics: Adenosine Deaminase; Albuminuria; Animals; Benzamides; Blood Proteins; Cholesterol; Cyclohexanones; Glycerolphosphate Dehydrogenase; Interleukin-6; Intracellular Signaling Peptides and Proteins; Kidney; Male; Membrane Proteins; Mice; Mice, Inbred BALB C; Mice, Inbred C3H; Mice, Inbred C57BL; Nephrosis; NF-kappa B; Proteinuria; Puromycin Aminonucleoside; Rats; Serum Albumin

Nephrin, a structural molecule, is also a signaling molecule after phosphorylation. Inhibition of nephrin phosphorylation is correlated with podocyte injury. The PINCH-1-ILK-α-parvin (PIP) complex plays a crucial role in cell adhesion and cytoskeleton formation. We hypothesized that nephrin phosphorylation influenced cytoskeleton and cell adhesion in podocytes by regulating the PIP complex. The nephrin phosphorylation, PIP complex formation, and F-actin in Wistar rats intraperitoneally injected with puromycin aminonucleoside were gradually decreased but increased with time, coinciding with the recovery from glomerular/podocyte injury and proteinuria. In cultured podocytes, PIP complex knockdown resulted in cytoskeleton reorganization and decreased cell adhesion and spreading. Nephrin and its phosphorylation were unaffected after PIP complex knockdown. Furthermore, inhibition of nephrin phosphorylation suppressed PIP complex expression, disorganized podocyte cytoskeleton, and decreased cell adhesion and spreading. These findings indicate that alterations in nephrin phosphorylation disorganize podocyte cytoskeleton and decrease cell adhesion through a PIP complex-dependent mechanism.

Topics: Actins; Adaptor Proteins, Signal Transducing; Animals; Antibiotics, Antineoplastic; Cell Adhesion; Cell Line; Cytoskeleton; Kidney Glomerulus; LIM Domain Proteins; Male; Membrane Proteins; Mice; Microfilament Proteins; Nephrosis; Phosphorylation; Podocytes; Protein Serine-Threonine Kinases; Puromycin Aminonucleoside; Rats; Rats, Wistar; RNA Interference; RNA, Small Interfering

The slit diaphragm (SD) is a complex of podocyte-specific proteins and plays a significant role in glomerular filtration. To understand podocyte biology, it is important to determine the expression amount of the SD complex proteins. This study aimed to quantify the absolute amount of nephrin, which is believed to be a major component of SD, in podocytes and to apply that method to normal and puromycin aminonucleoside (PAN) nephrosis rats.. The counting method for podocyte number in a glomerulus was developed by three-dimensional reconstruction imaging of Wilms tumor (WT-1) immunofluorescence on isolated glomeruli. Absolute amount of nephrin was quantified by mass spectrometry using the selected reaction monitoring (SRM) mode with a stable isotope-labeled peptide.. The number of podocytes per glomerulus was 95.5±17.6 in the control rats, 90.7±19.2 on Day 4 and 90.7±26.2 on Day 7 in PAN nephrosis rats. The amount of nephrin per glomerulus in control rats was 1.02±0.11 fmol and those in PAN nephrosis rats were reduced to 0.46±0.06 fmol and 0.35±0.04 fmol on Day 4 and Day 7. The nephrin amount per podocyte was significantly decreased association with the development of proteinuria in PAN nephrosis rats.. This study established the absolute quantification of nephrin and determined the amount of nephrin in a podocyte of normal and PAN nephrosis rat kidneys. This highly sensitive and selective quantification method for protein is a useful tool for the analysis of SD protein in a podocyte.

Topics: Animals; Antibiotics, Antineoplastic; Kidney Glomerulus; Male; Membrane Proteins; Nephrosis; Peptide Fragments; Podocytes; Proteomics; Puromycin Aminonucleoside; Rats; Rats, Inbred F344; Tandem Mass Spectrometry; WT1 Proteins

Sinomenine (SN, 1) is a pure compound extracted from the Sinomenium acutum plant. We investigated the protective effects and mechanism of action of SN in a rat model of doxorubicin (DOX)-induced nephrosis. Nephrosis was induced by a single dose of 5 mg/kg DOX, and DOX-treated rats received a daily i.p. injection of 10 or 30 mg/kg SN, or saline (n = 6). Urine and serum biochemical parameters, serum TNF-α and IL-1β levels, nephrin, podocin, α-actinin-4, and peroxisome proliferator-activated receptor-α (PPAR-α) protein expression, and renal ultrastructure were examined at day 28. Compound 1 significantly attenuated the effect of DOX on urine and serum biochemical parameters. Electron microscopy demonstrated that 1 suppressed DOX-induced increases in foot process width. Compared with those in control rats, nephrin, podocin, and PPAR-α protein expressions decreased in the glomeruli of DOX-treated rats, and this effect was significantly attenuated by 1. However, no appreciable alterations were observed in the expression level of α-actinin-4. DOX significantly increased serum TNF-α and IL-1β compared with those in control rats, and 1 significantly reduced the serum levels of TNF-α and IL-1β. SN ameliorates DOX-induced nephrotic syndrome in rats, resulting in a modulation of renal nephrin, podocin expression, and thereby protecting podocytes from injury.

Topics: Animals; Doxorubicin; Interleukin-1beta; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Male; Membrane Proteins; Models, Biological; Molecular Structure; Morphinans; Nephrosis; PPAR alpha; Rats; Tumor Necrosis Factor-alpha

To investigate the effects of Huaiqihuang Granule, a compound Chinese herbal medicine, on expressions of nephrin and podocin of slit diaphragm of glomerular podocytes in rats with adriamycin-induced nephrosis and to explore the mechanism in reducing the proteinuria.. Twenty SD rats were randomly divided into five groups: control group, model group, glucocorticoid group, Huaiqihuang Granule group and Huaiqihuang Granule plus glucocorticoid group. The 24-hour urine was collected 7, 14, 21 and 28 days after adriamycin injection respectively to measure 24-hour urinary protein, and all rats were sacrificed after 28-day treatment. Pathological changes in renal tissues were observed under a light microscope and an electron microscope. Expressions of nephrin and podocin mRNAs in renal cortex were determined by real-time polymerase chain reaction, and protein levels of nephrin and podocin were detected by Western blotting.. (1) In the model group and the treatment groups, the level of urinary protein increased significantly from the 14th day. (2) Under the light microscope, inflammatory cells and slight fibroplasia were found in renal interstitium of the model group, but there were less inflammatory cells in renal interstitium in the intervention groups than in the model group. Under the electron microscope, 29 days after adriamycin injection, extensive fusion of foot processes was observed. (3) The expressions of nephrin and podocin were higher in treatment groups than in the model group. (4) Proteinuria level was negatively correlated with the expressions of nephrin mRNA and nephrin and podocin proteins.. The above results indicate that Huaiqihuang Granule can maintain the integrity of the slid diaphragram in podocyte, alleviate the lesion of glomerular filtration membrane, and decrease the proteinuria by up-regulating the expressions of nephrin and podocin. Huaiqihuang Granule plus glucocorticoid maybe has better effects than glucocorticoid alone.

Topics: Animals; Doxorubicin; Drugs, Chinese Herbal; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Male; Membrane Proteins; Nephrosis; Rats; Rats, Sprague-Dawley

The function of glomerular podocytes is closely associated with the actin cytoskeleton. In this study, we studied the role of the small Rho-GTPase, Rac1, in actin organization in podocytes.. Conditionally immortalized mouse podocytes (MP) stably expressing nephrin or control plasmid were used.. In MP, Rac1 activity increased significantly at 1 week of differentiation. MP stably expressing nephrin showed Rac1 activity significantly higher and more sustained than vector-expressing control cells. Antibody-mediated cross-linking of nephrin also activated Rac1. Differentiated MP showed more distinct lamellipodia/cellular processes, as compared with undifferentiated cells, which was further augmented by nephrin expression. Transient transfection of constitutively active Rac1 markedly increased the number of lamellipodia/cellular processes in undifferentiated MP, while the Rac1 inhibitor caused actin cytoskeleton derangement in differentiating MP. In the rat model of puromycin aminonucleoside nephrosis, RhoA activity was increased at Day 7 (at the peak of proteinuria), while Rac1 activity increased significantly only at Day 14, when the recovery process had started.. Rac1 is activated in differentiating MP and nephrin potentiates Rac1 activation. Rac1 likely contributes to lamellipodia formation in differentiating MP and may contribute to process formation in podocytes recovering from injuries.

Topics: Actins; Animals; Cell Differentiation; Cells, Cultured; Cytoskeleton; Enzyme Activation; Kidney Glomerulus; Male; Membrane Proteins; Mice; Nephrosis; Podocytes; Puromycin Aminonucleoside; rac1 GTP-Binding Protein; ras GTPase-Activating Proteins; Rats; Rats, Sprague-Dawley; rhoA GTP-Binding Protein

The tyrosine phosphorylation of nephrin is reported to regulate podocyte morphology via the Nck adaptor proteins. The Pak family of kinases are regulators of the actin cytoskeleton and are recruited to the plasma membrane via Nck. Here, we investigated the role of Pak in podocyte morphology. Pak1/2 were expressed in cultured podocytes. In mouse podocytes, Pak2 was predominantly phosphorylated, concentrated at the tips of the cellular processes, and its expression and/or phosphorylation were further increased when differentiated. Overexpression of rat nephrin in podocytes increased Pak1/2 phosphorylation, which was abolished when the Nck binding sites were mutated. Furthermore, dominant-negative Nck constructs blocked the Pak1 phosphorylation induced by antibody-mediated cross linking of nephrin. Transient transfection of constitutively kinase-active Pak1 into differentiated mouse podocytes decreased stress fibers, increased cortical F-actin, and extended the cellular processes, whereas kinase-dead mutant, kinase inhibitory construct, and Pak2 knockdown by shRNA had the opposite effect. In a rat model of puromycin aminonucleoside nephrosis, Pak1/2 phosphorylation was decreased in glomeruli, concomitantly with a decrease of nephrin tyrosine phosphorylation. These results suggest that Pak contributes to remodeling of the actin cytoskeleton in podocytes. Disturbed nephrin-Nck-Pak interaction may contribute to abnormal morphology of podocytes and proteinuria.

Topics: Actins; Animals; Antibiotics, Antineoplastic; Cell Line; Gene Expression Regulation; Gene Expression Regulation, Enzymologic; Humans; Isoenzymes; Kidney Glomerulus; Membrane Proteins; Mice; Nephrosis; p21-Activated Kinases; Phosphorylation; Plakins; Podocytes; Puromycin Aminonucleoside; Rats

Mizoribine (MZR) is an imidazole nucleoside used as a therapeutic immunosuppressive agent. Though a previous report showed that MZR ameliorates proteinuria in puromycin aminonucleoside (PAN) nephropathy, the effect of MZR on podocytes has not been clarified. In this study, we determined whether MZR directly prevents PAN-induced podocyte injury.. Rats were intravenously injected once on day 0 with 100 mg/kg of PAN and received daily subcutaneous injections of MZR at a dose of 10 mg/kg from days 0 to 14. Cultured podocytes were pretreated with 50 microg/ml of MZR and then treated with 30 microg/ml of PAN.. In rat PAN nephrosis, treatment with MZR from days 0 to 14 almost completely inhibited proteinuria. Immunofluorescence staining of nephrin was diminished, showing a discontinuous pattern in saline-treated PAN rats. In contrast, MZR treatment resulted in maintenance of a normal linear pattern. In cultured podocytes exposed to PAN, the percentages of viable cells were significantly increased with MZR treatment. The protective effect of MZR on PAN-induced podocyte injury was independent of inosine 5'-monophosphate dehydrogenase that is a known target enzyme of MZR as an immunosuppressant. MZR reduced PAN-induced integrin-linked kinase activation (ILK) and phosphorylation of glycogen synthase kinase-3beta (GSK3beta) in vivo and in vitro.. MZR directly prevents PAN-induced podocyte injury, possibly by affecting signaling cascades involving ILK and GSK3beta.

Topics: Animals; Immunosuppressive Agents; IMP Dehydrogenase; Male; Membrane Proteins; Nephrosis; Podocytes; Protein Serine-Threonine Kinases; Puromycin Aminonucleoside; Rats; Rats, Wistar; Ribonucleosides

It is still unclear what happens in the glomerulus when proteinuria starts. Using puromycin aminonucleoside nephrosis (PAN) rats, we studied early ultrastructural and permeability changes in relation to the expression of the podocyte-associated molecules nephrin, α-actinin, dendrin, and plekhh2, the last two of which were only recently discovered in podocytes.. Using immune stainings, semiquantitative measurement was performed under the electron microscope. Permeability was assessed using isolated kidney perfusion with tracers. Possible effects of ACE inhibition were tested.. By day 2, some patchy foot process effacement, but no proteinuria, appeared. The amount of nephrin was reduced in both diseased and normal areas. The other proteins showed few changes, which were limited to diseased areas. By day 4, foot process effacement was complete and proteinuria appeared in parallel with signs of size barrier damage. Nephrin decreased further, while dendrin and plekhh2 also decreased but α-actinin remained unchanged. ACE inhibition had no significant protective effect.. PAN glomeruli already showed significant pathology by day 4, despite relatively mild proteinuria. This was preceded by altered nephrin expression, supporting its pivotal role in podocyte morphology. The novel proteins dendrin and plekhh2 were both reduced, suggesting roles in PAN, whereas α-actinin was unchanged.

Topics: Actinin; Animals; Kidney Diseases; Kidney Glomerulus; Male; Membrane Proteins; Nephrosis; Nerve Tissue Proteins; Permeability; Proteins; Proteinuria; Puromycin Aminonucleoside; Rats; Rats, Sprague-Dawley

To investigate podocyte injury and the expression of nephrin and VEGF in rat nephrosis model induced by adriamycin.. The rat adriamycin induced nephrosis model was established, while the biochemical indicators in blood and urine were measured and the pathological changes of the renal tissue were evaluated by light microscope and electron microscope. The podocyte number was counted, and the expression levels of nephrin, VEGF were examined at different time by means of immunohistochemistry.. After second injected with adriamycin,the model group nephrin presented a weak signal in the end of the first week (P < 0.05), and the expression of VEGF started to increase at the end of the eighth week (P < 0.05). The podocyte number decreased at the end of the eighth week (P < 0.05). The expression of nephrin and the number of podocyte were negatively correlated with the 24-hour urine protein, blood urea nitrogen and serum creatinine; while the expression of VEGF was positively correlated with the 24-hour urine protein, blood urea nitrogen and serum creatinine.. The decrease of nephrin expression and the change of its distribution might be the significant factors resulting in considerable proteinuria. VEGF participated in the process of proteinuria and glomerular sclerosis in the development of rat adriamycin nephrosis.

Topics: Animals; Doxorubicin; Male; Membrane Proteins; Nephrosis; Podocytes; Random Allocation; Rats; Rats, Sprague-Dawley; Vascular Endothelial Growth Factor A

It has been proposed that nephrotic syndrome is a consequence of an imbalance between oxidant and anti-oxidant activity. Nephrin plays an important role in maintaining glomerular filtration barrier. This study aimed to explore the relationship between the expression of glomerular nephrin and oxidative stress reaction in rats with adriamycin (ADR)-induced nephrosis, and the protection of prednisone and vitamin E against renal injuries.. Nephrosis was induced by single intravenous injection of ADR (5 mg/kg). The prednisone intervention group was administered with prednisone (10 mg/kg daily) between 1 and 4 weeks after ADR injection. The vitamin E intervention group received vitamin E of 20 mg/kg daily from 1 week before ADR injection till to 4 weeks after ADR injection. Control rats were intravenously injected with normal saline. After 7, 14, 21 and 28 days of ADR injection, the indexes of oxidative stress reaction of the renal cortex, malondialdehyde (MDA), superoxide dismutase (SOD) and total antioxidative capacity (T-AOC), were measured using the chemical chromatometry. The protein expression of glomerular nephrin was measured by immunohistochemistry.. Prednisone or vitamin E treatment reduced urinary protein from 14 days to 28 days after ADR injection. MDA levels of renal cortex increased, while renal activities of SOD and T-AOC as well as nephrin protein contents decreased in untreated nephrosis group from 7 days after ADR injection compared with those in the control rats. Compared with the untreated nephrosis group, prednisone treatment resulted in an increase in nephrin protein contents 28 days after ADR injection; Vitamin E treatment decreased renal MDA levels and increased renal activities of SOD and T-AOC and nephrin protein contents 28 days after ADR injection. Nephrin staining showed a sable linear-like pattern along the capillary loops of glomerulus in the control rats. Nephrin staining presented a light tan discontinuous short linear-like or punctiform pattern along the capillary loops of glomerulus in the untreated ADR group. Prednisone or vitamin E treatment ameliorated abnormal expression of nephrin induced by nephrosis. Glomerular nephrin expression level was negatively correlated with renal MDA level and positively correlated with renal activities of SOD and T-AOC.. A reduction of glomerular nephrin expression is closely related to oxidative stress reaction. Prednisone and vitamin E have protective effects against renal injuries induced by ADR in rats.

Topics: Animals; Doxorubicin; Kidney Glomerulus; Male; Malondialdehyde; Membrane Proteins; Nephrosis; Oxidative Stress; Prednisone; Rats; Rats, Wistar; Superoxide Dismutase; Vitamin E

The renoprotective effect of cilnidipine ((+/-)-2-methoxyethyl 3-phenyl-2(E)-propenyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate, CAS 132203-70-4), a L/N-type calcium channel antagonist, on puromycin aminonucleoside (PAN)-induced nephrosis was investigated in rats. In the Experiment I, rats were given an intravenous injection of PAN (70 mg/kg). Cilnidipine (3 mg/kg/day) and enalapril (CAS 75847-73-3, 5 mg/kg/day) were administered orally from 6 days after treatment with PAN (day 6) to day 26, and urinary analysis was performed on days 9, 15, 20 and 27. In the Experiment II, nephrosis was also induced by intravenous injection of PAN (70 or 100 mg/kg) in rats which were treated with cilnidipine and enalapril from days 6 to 10. Systolic blood pressure was measured on day 7 and urinary analysis was performed on day 10. On day 11, serum was collected and the kidneys were removed for immunofluorescence staining for nephrin and podocin proteins. In PAN-treated rats, the daily urinary protein excretion was dramatically elevated on day 5, reached a peak on day 9 and gradually returned to a normal level from days 15 to 27. Cilnidipine (3 mg/kg/ day) significantly suppressed the increase in proteinuria on day 9 and also improved the decrease in creatinine clearance without evident effect on the blood pressure. Furthermore, the elevations in serum total cholesterol and triglyceride tended to be suppressed by cilnidipine. The expression of nephrin and podocin proteins in PAN-treated rats showed the granular pattern in the glomeruli, while the intensity of staining seemed to be dependent on the urinary protein excretion level in the cilnidipine-treated rats. The results obtained in this study suggest a renoprotective effect of cilnidipine in PAN-induced nephrosis in rats.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Antimetabolites, Antineoplastic; Blood Pressure; Calcium Channel Blockers; Calcium Channels, L-Type; Calcium Channels, N-Type; Creatinine; Dihydropyridines; Enalapril; Fluorescent Antibody Technique; Male; Membrane Proteins; Nephrosis; Protective Agents; Proteinuria; Puromycin Aminonucleoside; Rats; Rats, Sprague-Dawley

Proteinuria caused by glomerular disease is characterized by podocyte injury. Vasopressin V2 receptor antagonists are effective in reducing albuminuria, although their actions on glomerular podocytes have not been explored. The objective of this study was to evaluate the effects of tolvaptan, a selective oral V2 receptor antagonist, on podocytes in a puromycin aminonucleoside (PAN)-induced nephrosis rat model.. Rats were allocated to a control, PAN nephrosis, or tolvaptan-treated PAN nephrosis group (n = 9 per group). Urinary protein excretion and serum levels of total protein, albumin, creatinine, and total cholesterol were measured on day 10. The influence of tolvaptan on podocytes was examined in renal tissues by immunofluorescence and electron microscopy.. PAN induced massive proteinuria and serum creatinine elevation on day 10, both of which were significantly ameliorated by tolvaptan. Immunofluorescence studies of the podocyte-associated proteins nephrin and podocin revealed granular staining patterns in PAN nephrosis rats. In tolvaptan-treated rats, nephrin and podocin expressions retained their normal linear pattern. Electron microscopy showed foot process effacement was ameliorated in tolvaptan-treated rats.. Tolvaptan is protective against podocyte damage and proteinuria in PAN nephrosis. This study indicates that tolvaptan exerts a renoprotective effect by affecting podocyte morphology and probably function in PAN nephrosis. Tolvaptan is a promising pharmacological tool in the treatment of renal edema.

Topics: Animals; Antibiotics, Antineoplastic; Antidiuretic Hormone Receptor Antagonists; Benzazepines; Desmin; Humans; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Male; Membrane Proteins; Nephrosis; Organ Size; Podocytes; Puromycin Aminonucleoside; Rats; Rats, Sprague-Dawley; Tolvaptan; WT1 Proteins

Extracts of Tripterygium wilfordii Hook F have been used to treat glomerulonephritis for more than 30 years in China with dramatic antiproteinuric effects. Triptolide, a diterpene triepoxide, is one of the major active components of these extracts. To clarify its antiproteinuric effects we induced podocyte injury by puromycin aminonucleoside. Triptolide effectively reduced the proteinuria induced by puromycin in nephrotic rats without reducing the glomerular filtration rate. The antiproteinuric effect was associated with improvement in the foot process effacement, a decrease in the podocyte injury marker desmin as well as the restoration of nephrin and podocin expression and distribution. In cultured mouse podocytes triptolide pretreatment prevented the puromycin-induced disruption of the actin cytoskeleton and microfilament-associated synaptopodin while protecting nephrin and podocin expression. Triptolide suppressed reactive oxygen species generation and p38 mitogen-activated protein kinase activation while restoring RhoA signaling activity. These results show that triptolide ameliorates puromycin aminonucleoside-mediated podocyte injury in vivo and in vitro.

Topics: Animals; Cells, Cultured; Cholesterol; Cytoskeleton; Desmin; Diterpenes; Epoxy Compounds; Glomerular Filtration Rate; Intracellular Signaling Peptides and Proteins; MAP Kinase Signaling System; Membrane Proteins; Mice; Nephrosis; Phenanthrenes; Podocytes; Proteinuria; Puromycin Aminonucleoside; Rats; Reactive Oxygen Species; Serum Albumin; Triglycerides

Phosphorylation of tyrosine residue (Y1204) of rat nephrin by Fyn kinase allows Nck adaptor protein binding to nephrin motifs, which include the phosphorylated tyrosine. This phosphorylation-dependent switch induces actin polymerization in a cell culture system. Here, we generated an antibody recognizing phosphorylated nephrin at the Nck binding sites pY1204 and pY1228 to determine the phosphorylation status of nephrin using a rat model of puromycin aminonucleoside-induced nephrosis. Changes in globular actin (G-actin) and filamentous actin (F-actin) contents in isolated glomeruli were measured by western blot. Before experimental nephrosis, both Y1204 and Y1228 were phosphorylated, and most of the actin was filamentous. Before the onset of overt proteinuria, however, phosphorylation of both Y1204 and Y1228 rapidly decreased and became almost undetectable. During this period, the amount of F-actin in glomeruli began to decrease, whereas G-actin increased. Phosphorylation of nephrin at Y1228 in glomeruli of patients with minimal change nephrosis was significantly decreased compared with that in normal glomeruli. Our study suggests that tyrosine phosphorylation of nephrin by regulating F-actin formation may be important for the maintenance of normal podocyte morphology and function.

Topics: Actins; Animals; Antibodies; Antimetabolites, Antineoplastic; Chlorocebus aethiops; COS Cells; Cytoskeleton; Humans; Kidney Glomerulus; Membrane Proteins; Nephrosis; Phosphorylation; Podocytes; Protein-Tyrosine Kinases; Puromycin Aminonucleoside; Rats; Rats, Sprague-Dawley; Signal Transduction

Rho kinase (ROCK) inhibition reduces systemic blood pressure (BP) and decreases renal damage in animal models of kidney disease. The aim of this study was to determine if ROCK inhibition might have beneficial effects in glomerular disease processes that are independent of systemic BP.. We investigated the effects of the ROCK inhibitor Y27632 and hydralazine in murine puromycin aminonucleoside (PAN) nephrosis.. Treatment with either Y27632 or hydralazine similarly reduced systolic BP compared to vehicle-treated controls. Seven days after treatment with PAN, albuminuria, proteinuria and effacement of podocyte foot processes were significantly reduced in Y27632- and hydralazine-treated mice compared to vehicle-treated animals. Treatment with PAN significantly reduced expression of the podocyte proteins nephrin and Neph1, and the loss of glomerular nephrin was attenuated by treatment with Y27632 but not by treatment with hydralazine. In cultured podocytes, PAN potently activated both Rho and ROCK, and PAN-induced ROCK activation was prevented by Y27632.. The ROCK inhibitor Y27632 attenuated glomerular nephrin loss in murine PAN nephrosis independent of its effects on systemic BP.

Topics: Amides; Animals; Antihypertensive Agents; Cells, Cultured; Disease Models, Animal; Epithelial Cells; Kidney Glomerulus; Membrane Proteins; Mice; Nephrosis; Podocytes; Puromycin Aminonucleoside; Pyridines; rho-Associated Kinases

Uchida et al. show in this issue that in rat and human nephrosis, tyrosine phosphorylation of nephrin is reduced, and this is accompanied by a decrease in F-actin in glomeruli. This, together with previous studies, suggests that the nephrin protein complex is a signaling nexus that regulates actin dynamics in podocytes.

Topics: Actins; Animals; Humans; Kidney Glomerulus; Membrane Proteins; Nephrosis; Phosphorylation; Podocytes; Protein-Tyrosine Kinases; Signal Transduction

Snail is a DNA-binding molecule that plays a pivotal role in regulating cell adhesion and epithelial to mesenchymal transition. Visceral epithelial cells (podocytes) in kidney glomeruli form a sophisticated cell-cell junction called a slit diaphragm that prevents the loss of plasma protein during ultrafiltration. Nephrin, located in the slit diaphragm and critical for maintaining the integrity of this structure, belongs to the class of cell adhesion molecules of the immunoglobulin super-family. As previously reported, the transcriptional activity of nephrin is a determinant of the integrity of the slit diaphragm in puromycin aminonucleoside (PAN) nephrosis rats. Here, we examined the role of Snail in nephrin expression. In accordance with the downregulation of nephrin in PAN nephrosis rats, Snail was upregulated in vivo and its DNA-binding activity was stimulated in injured podocytes while normal podocytes did not express Snail. An in vitro study demonstrated that Snail bound to E-box motifs in a specific segment of the rat nephrin gene repressed the transcription of nephrin and downregulated nephrin protein. We also found that the expression level of Snail in injured podocytes was regulated by GSK3, which is known to phosphorylate Snail and induce its proteolysis. Pharmacological in vitro and in vivo inhibition studies of GSK3 suggested that GSK3 activity decreased in injured podocytes and this change partially contributed to the decrease in nephrin and increase in Snail and proteinuria. Concordantly, we found that Wnt-2 was upregulated in injured podocytes and activated the Wnt canonical pathway. As the Wnt canonical pathway inactivates GSK3, it is likely that Wnt-2 accounts for the accumulation of Snail in injured podocytes. In conclusion, Snail is a key molecule, which perturbs the integrity of the slit diaphragm through transcriptional repression of nephrin under pathological conditions. Wnt-GSK3 pathway participates in this mechanism.

Topics: Amino Acid Sequence; Animals; Base Sequence; Cell Line; DNA Primers; Epithelial Cells; Gene Expression Regulation; Immunohistochemistry; In Situ Hybridization; Kidney Glomerulus; Male; Membrane Proteins; Molecular Sequence Data; Nephrosis; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; Snail Family Transcription Factors; Transcription Factors; Transcription, Genetic

Topics: Adaptor Proteins, Signal Transducing; Angiotensin-Converting Enzyme Inhibitors; Cytoskeletal Proteins; Diaphragm; Humans; Kidney Glomerulus; Membrane Proteins; Nephrosis; Nephrotic Syndrome; Podocytes; Proteinuria

Nephrin, podocin, CD2AP, and alpha-actinin-4 are important podocyte proteins that help maintain the integrity of the slit diaphragm and prevent proteinuria. Studies have shown that angiotensin-converting enzyme inhibitors, glucocorticoids, and all-trans retinoic acid (ATRA) have antiproteinuric effects. However, it is still unclear whether these drugs, with different pharmacological mechanisms, lead to a reduction in proteinuria by changing the expression and distribution of these important podocyte proteins. In this study, changes in the expression and distribution of nephrin, podocin, CD2AP, and alpha-actinin-4 were dynamically detected in Adriamycin-induced nephrotic (ADR) rats treated with three different drugs: lisinopril, prednisone, and ATRA. Nephropathy was induced by an intravenous injection of Adriamycin. After Adriamycin injection, rats received lisinopril, prednisone, and ATRA treatment, respectively. Renal tissues were collected at Days 3, 7, 14, and 28. The distribution and the expression of messenger RNA and protein of nephrin, podocin, CD2AP, and alpha-actinin-4 were detected by indirect immunofluorescence, real-time polymerase chain reaction, and Western blotting, respectively. With the intervention of lisinopril, prednisone, and ATRA, changes in the expression of nephrin, podocin, and CD2AP were diverse, which was different from that detected in ADR rats. After lisinopril and prednisone intervention, podocin exhibited prominent earlier changes compared with those of nephrin and CD2AP, whereas CD2AP showed more prominent changes after ATRA intervention. There was no change in the expression of alpha-actinin-4 molecule. In summary, we conclude that the antiproteinuric effects of lisinopril, prednisone, and ATRA were achieved by changes in the expression and distribution of the important podocyte molecules nephrin, podocin, CD2AP, and alpha-actinin-4. The pattern in the change of podocyte molecules after lisinopril and prednisone intervention was similar, but the pattern in the change of podocyte molecules after ATRA intervention was different from that of lisinopril or prednisone intervention.

Topics: Actinin; Adaptor Proteins, Vesicular Transport; Angiotensin-Converting Enzyme Inhibitors; Animals; Antibiotics, Antineoplastic; Doxorubicin; Glucocorticoids; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Lisinopril; Male; Membrane Proteins; Microfilament Proteins; Nephrosis; Podocytes; Prednisone; Proteinuria; Random Allocation; Rats; Rats, Sprague-Dawley; Tretinoin

Nephrin is a transmembrane molecule essential for morphology and function of kidney podocytes. We and others reported previously that the cytoplasmic domain of human and mouse nephrin interacts with the adaptor protein, Nck, in a tyrosine phosphorylation-dependent manner. In the current study, we characterized the interaction of rat nephrin with Nck and further addressed its impact on cell morphology. Rat nephrin expressed in Cos-1 cells co-immunoprecipitated with Nck in a manner dependent on the phosphorylation of Y1204 and Y1228. Nephrin from normal rat glomeruli was also tyrosine phosphorylated and associated with Nck. Overexpression of rat nephrin in HEK293T cells induced morphological changes resembling process formation, which became more distinct when the extracellular domain of nephrin was cross-linked by antibodies. The morphological changes were attenuated by expression of dominant negative constructs of Nck. In the rat model of podocyte injury and proteinuria, nephrin tyrosine phosphorylation and nephrin-Nck interaction were both reduced significantly. Taken together, we propose that Nck couples nephrin to the actin cytoskeleton in glomerular podocytes and contributes to the maintenance of normal morphology and function of podocytes.

Topics: Adaptor Proteins, Signal Transducing; Animals; Chlorocebus aethiops; COS Cells; Humans; Kidney; Kidney Glomerulus; Membrane Proteins; Mice; Nephrosis; Oncogene Proteins; Phosphorylation; Podocytes; Protein Binding; Rats

Podocytes are critical in maintaining the filtration barrier of the glomerulus and are dependent on the slit diaphragm (SD) proteins nephrin, podocin, and CD2-associated protein (CD2AP) to function optimally. The effects of normal human plasma and nephrotic plasma on podocytes were tested, focusing particularly on the SD complex. With the use of a conditionally immortalized human podocyte cell line, it first was shown that exposure to normal and non-nephrotic human plasma leads to a concentration of nephrin, podocin, CD2AP, and actin at the cell surface. Next, the effects of plasma from patients with nephrotic conditions to non-nephrotic conditions were compared. When exposed to all nephrotic plasma samples (and a non-human serum control), nephrin podocin and CD2AP assumed a cytoplasmic distribution; nephrin and synaptopodin were selectively downregulated, and the relocation of nephrin induced by nephrotic plasma could be rescued back to the plasma membrane by co-incubation with non-nephrotic plasma. Furthermore, intracellular calcium signaling was altered by nephrotic plasma, which was mediated by tyrosine kinase phosphorylation. With the use of nephrin mutant human cell lines, it was shown that this signaling and translocation response to normal plasma is nephrin dependent. This work demonstrates that nephrotic plasma seems to be deficient in factors that act via the podocyte SD complex, which are essential in maintaining its physiologic function.

Topics: Actins; Adaptor Proteins, Signal Transducing; Adolescent; Blood Proteins; Calcium; Calcium Signaling; Cell Line, Transformed; Child; Cytoskeletal Proteins; Female; Humans; Infant; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Male; Membrane Proteins; Middle Aged; Mutation; Nephrosis; Proteins

Decreased expression levels of the glomerular slit membrane proteins, nephrin and podocin, have been reported after the onset of puromycin aminonucleoside (PA) nephrosis. We examined nephrin and podocin expressions prior to the onset of proteinuria of PA nephrosis to elucidate the proteinuria induction mechanism of PA. PA nephrosis was induced by a subcutaneous single injection of 120 mg kg(-1) PA. The mRNA levels of nephrin and podocin in whole kidney total RNA were quantified by the TaqMan real time PCR quantification system. The localization and levels of nephrin and podocin molecules were analyzed by immunofluorescence and Western blotting, respectively. Albuminuria and proteinuria were significant on days 3 and 4 in PA nephrosis rats. The protein levels of nephrin and podocin decreased significantly at day 3. The protein localization of nephrin and podocin changed at day 2 and day 1, respectively. The mRNA level of nephrin increased at day 2 and subsequently decreased at day 4. The podocin mRNA level did not change significantly. In conclusions, the protein level of nephrin and podocin decreased at the onset of albuminuria in the PA nephrosis. However, the first change induced by PA was the change of podocin localization from a linear pattern to a dot-like one prior to the onset of albuminuria.

Topics: Animals; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Male; Membrane Proteins; Nephrosis; Puromycin Aminonucleoside; Rats; Rats, Sprague-Dawley; RNA, Messenger

MAGUK with inverted domain structure-1 (MAGI-1) is a membrane-associated protein with one guanylate kinase, six PSD-95/Dlg-A/ZO-1 (PDZ), and two WW domains and is localized at tight junctions in epithelial cells. MAGI-1 interacts with various proteins and is proposed to function as a scaffold protein. In the previous study, we discovered a MAGI-1-interacting cell adhesion molecule junctional adhesion molecule 4 (JAM4). Both proteins are highly expressed in glomerular podocytes in the kidney and partially colocalized. In this study, we have further searched for a binding partner of MAGI-1 in the kidney through yeast two-hybrid screening and obtained nephrin. Nephrin is a cell adhesion molecule specifically localized at the slit diaphragm between neighboring foot processes of podocytes. Biochemical studies reveal that nephrin directly binds to the middle PDZ domains of MAGI-1 through its carboxyl terminus but does not bind to ZO-1. MAGI-1 forms a tripartite complex with nephrin and JAM4 in vitro. Immunoelectron microscopy shows that the localization of MAGI-1 is restricted to the slit diaphragm, whereas JAM4 is also distributed on apical membranes of podocytes. In puromycin aminonucleoside-induced nephrotic podocytes, MAGI-1 is localized with nephrin at the displaced slit diaphragm. These data indicate that MAGI-1 is a component of the slit diaphragm and tightly interacts with nephrin and JAM4 in vivo. MAGI-1 may play a role in determining the boundary between the apical and the bosolateral domain at the level of slit diaphragm.

Topics: Adaptor Proteins, Signal Transducing; Animals; Cell Adhesion Molecules; Chlorocebus aethiops; COS Cells; Fluorescent Antibody Technique, Indirect; Glomerular Mesangium; Guanylate Kinases; Humans; Membrane Proteins; Microscopy, Immunoelectron; Nephrosis; Phosphoproteins; Podocytes; Protein Binding; Rats; Tight Junctions; Two-Hybrid System Techniques; Zonula Occludens-1 Protein

Nephrin, podocin and alpha-actinin are all involved in proteinuria, but it is unclear which molecular event plays a crucial role during the development of proteinuria. Immunofluorescence staining and real-time quantitative polymerase chain reaction were used to study the glomerular expression of these molecules in puromycin aminonucleoside (PAN) nephrosis. Morphometric methods were applied to evaluate the podocyte foot process (FP) morphology. Two days after PAN injection, nephrin and podocin staining became discontinuous, podocin intensity decreased and FP swelled. Nephrin protein and mRNA decreased at day 5. Both podocin and nephrin intensity decreased dramatically when heavy proteinuria occurred, but nephrin mRNA was regained. When proteinuria disappeared, podocin recovered whereas nephrin did not (P = 0.02); alpha-actinin intensity increased (P = 0.009) and the distribution changed. The podocyte FP volume density correlated negatively with nephrin (r = -0.78, P = 0.0001) and podocin immunofluorescence intensity (r = -0.76, P = 0.0001). We conclude that, before the onset of proteinuria, the first response was the nephrin and podocin distribution change, podocin protein decrease and swollen FP; the podocin quantitative change was earlier than nephrin. Podocin and nephrin distribution and the protein level was associated with proteinuria more closely than their mRNA level. The delayed alpha-actinin induction might be a reparative response.

Topics: Actinin; Animals; Antibiotics, Antineoplastic; Disease Models, Animal; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Male; Membrane Proteins; Nephrosis; Proteins; Proteinuria; Puromycin Aminonucleoside; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

Nephrin is a recently identified protein that is a key component of the slit diaphragm. This protein may play a crucial role in maintaining the glomerular filtration barrier, and mutations in the gene for nephrin reportedly lead to congenital nephrosis. However, the expression of nephrin in acquired glomerular disease has not yet been fully clarified. To address this issue, we analysed the expression and localization of nephrin by morphological analysis based on immunoelectron microscopy in normal glomeruli and in glomeruli from proteinuric experimental models.. Twenty rats were divided into three experimental groups (n = 16 total) and a control group (n = 4). Rats in the experimental groups received a single intravenous injection of puromycin aminonucleoside (PAN), and were sacrificed at 1 (n = 4), 2 (n = 6) and 3 weeks (n = 6) post-injection. Nephrin expression was assessed by immunoelectron microscopy using a polyclonal antibody against nephrin and gold particles. It was quantified by counting the gold particles and the slit diaphragms and by measuring the average foot process width in microphotographs.. The average foot process width in the 1 week group (5924.5 +/- 1523.9 nm) was far greater than that of controls (1112.9 +/- 79.8 nm), but decreased thereafter. The average number of total gold particles per unit length (10 000 nm) of the glomerular basement membrane (GBM) underlying the foot processes was reduced at 1 week (26.0 +/- 9.5), compared with controls (335.3 +/- 125.5), but increased thereafter. Also, the average number of junctional gold particles per unit length of the GBM was lower than controls (208.4 +/- 1.7) at 1 week (10.1 +/- 3.5), but increased thereafter. There were no significant differences between the numbers of junctional gold particles per slit diaphragm among the groups, but significant differences were observed in the distributions of gold particles among the groups. Gold particles were more frequently seen in cytoplasm at 1 week.. The present ultrastructural studies showed that nephrin expression and its distribution were altered in PAN-treated rats, and this occurred in parallel with foot process effacement. Nephrin expression returned to normal with improved resolution of the effacement. Nephrin expression was found to be rather preserved in areas without foot process effacement, even in PAN-treated rats. The significance of the above findings in terms of proteinuria and foot process effacement needs further clarification.

Topics: Animals; Disease Models, Animal; Kidney; Kidney Glomerulus; Male; Membrane Proteins; Microscopy, Immunoelectron; Nephrosis; Proteins; Puromycin Aminonucleoside; Rats; Rats, Sprague-Dawley

The mouse, as opposed to the rat, is relatively resistant to the experimental nephrosis induced by puromycin aminonucleoside. The reason for this species specificity is not known. Apolipoprotein E (apoE)-deficient mice were used to determine whether hypercholesterolemia plays a role in inducing proteinuria.. Thirty-two mice were divided into normal and high cholesterol diet groups and then divided further into four subgroups: puromycin, puromycin+probucol, probucol and control. Urinary albumin of these mice was analyzed by nephelometry. The lipid peroxidation (LPO) end products malonyldialdehyde (MDA) and 4-hydroxynonenal (4-HNE) were detected by immunohistochemistry, and the expression level of the glomerular slit diaphragm protein, nephrin, was studied by immunohistochemistry and real time RT-PCR.. Overt proteinuria was induced by puromycin only in the apoE knockout mice ingesting the high cholesterol diet. The staining intensities of MDA and 4-HNE were stronger in the glomeruli of proteinuric mice compared to glomeruli of non-proteinuric mice. When serum cholesterol levels were reduced by probucol, proteinuria decreased and fewer LPO end products were seen immunohistochemically. Three and eight days after puromycin injection the level of nephrin mRNA in the kidneys of proteinuric mice decreased in comparison to the controls. Puromycin-treated mice kidneys demonstrated a clearly reduced reactivity to the nephrin antibodies.. Hypercholesterolemia, possibly via LPO, is a prerequisite for puromycin-inducible glomerular damage in the mouse. Furthermore, nephrin protein and mRNA levels appear to be candidate markers of glomerular damage in the mouse.

Topics: Animals; Apolipoproteins E; Cholesterol, Dietary; Hypercholesterolemia; Immunohistochemistry; Lipid Peroxidation; Membrane Proteins; Mice; Mice, Knockout; Nephrosis; Protein Synthesis Inhibitors; Proteins; Proteinuria; Puromycin; RNA, Messenger

High concentrations of alpha-fetoprotein (AFP) are used for prenatal diagnosis of the Finnish type of congenital nephrotic syndrome (NPHS1). We investigated the validity of this test. We retrospectively established fetal NPHS1 genotype and assessed renal pathology in 21 pregnancies that had been terminated because of raised concentrations of AFP in amniotic fluid. 12 fetuses were homozygous and nine were heterozygous (carriers) for NPHS1 mutations. Raised concentrations of AFP and similar proteinuric features in fetal kidneys were seen in both groups, indicating that these signs are unreliable for prenatal diagnosis of congenital nephrosis. We strongly recommend the use of mutation analysis of the NPHS1 gene to confirm the AFP results in prenatal diagnosis of NPHS1.

Topics: Alleles; alpha-Fetoproteins; Amniotic Fluid; Female; Finland; Genotype; Humans; Membrane Proteins; Mutation; Nephrosis; Pregnancy; Prenatal Diagnosis; Proteins; Proteinuria; Retrospective Studies; Statistics, Nonparametric

Despite of the increased availability of genetically modified mouse strains, the experimental models in the rat have provided the most widely employed and versatile models for the study of renal pathophysiology and functional genetics. The identification of the human gene mutated in the congenital nephrotic syndrome of the Finnish type (NPHS1) has recently been reported, and its protein product has been termed nephrin. Here we report the molecular cloning and characterization of rat nephrin cDNA. Rat nephrin cDNA has an open reading frame of 3705 bp, shows 82% sequence identity with human nephrin cDNA, and shows characteristic rat-specific splicing variants. The translated nucleotide sequence has 89% sequence identity at the amino acid level. The signal sequence, glycosylation, and cysteine localization patterns are nearly identical to those of human nephrin. As in the human, the rat nephrin transcript is expressed in a tissue-restricted pattern. Antipeptide antibodies raised to the intracellular nephrin-specific domain identified immunoreactivity exclusively within the rat kidney glomerulus by indirect immunofluorescence. Initial results with semiquantitative reverse transcriptase-polymerase chain reaction analysis showed a remarkable down-regulation of nephrin-specific mRNA in the puromycin nephrosis of the rat.

Topics: Alternative Splicing; Amino Acid Sequence; Animals; Blotting, Northern; Cloning, Molecular; DNA, Complementary; Down-Regulation; Fluorescent Antibody Technique, Indirect; Humans; Kidney Cortex; Male; Membrane Proteins; Mice; Molecular Sequence Data; Nephrosis; Polymerase Chain Reaction; Protein Biosynthesis; Proteins; Puromycin Aminonucleoside; Rats; Rats, Sprague-Dawley; RNA, Messenger; Sequence Homology, Amino Acid; Tissue Distribution