tretinoin and Fatty-Liver

Quiescent hepatic stellate cells (HSCs) in healthy liver store 80% of total liver retinols and release them depending on the extracellular retinol status. However, HSCs activated by liver injury lose their retinols and produce a considerable amount of extracellular matrix, subsequently leading to liver fibrosis. Emerging evidence suggests that retinols and their metabolites such as retinoic acids (RAs) contribute to liver regeneration, fibrosis and tumor. However, it is not clear yet why HSCs lose retinol, which enzymes are involved in the retinol metabolism of HSCs and what function of retinol metabolites on HSCs upon liver injury. Recently, our group and collaborators have demonstrated that during activation, HSCs not only lose retinols but also metabolize them into RAs by alcohol dehydrogenases and retinaldehyde dehydrogenases. As transcriptional factors, metabolized RAs induce retinoic acid early inducible-1 and suppressor of cytokine signaling 1 in HSCs, which plays an important role in the interaction between HSCs and natural killer cells. In addition, RAs released from HSCs may induce hepatic cannabinoid receptor 1 expression in alcoholic liver steatosis or regulate immune responses upon liver inflammation. The present review summarizes the role of endogenous metabolized RAs on HSCs themselves and on other liver cells including hepatocytes and immune cells. Moreover, the effects of exogenous retinol and RA treatments on HSCs and liver disease are discussed.

Topics: Animals; Carcinoma, Hepatocellular; Extracellular Matrix; Fatty Liver; Hepatic Stellate Cells; Hepatitis; Humans; Liver Cirrhosis; Liver Diseases; Liver Neoplasms; Liver Regeneration; Tretinoin; Vitamin A

To explore the role of retinoic acid (RA) in the liver, we developed transgenic mice expressing RA receptor a-dominant negative form (RARE) in hepatocytes using albumin promoter and enhancer. The RARE m ice developed microvesicular steatosis andspotty focal necrosis. Mitochondrial beta-oxidation activity of fatty acids and related enzymes were down-regulated, while peroxisomal beta-oxidation and related enzymes were up-regulated. Expression of cytochrome p4504a10, cytochrome p4504a12, and cytochrome p4504a14 was increased. Formation of H2O2 and 8-OHdG was increased. With age, these mice developed liver tumor. Feeding on a high-RA diet reversed histological and biochemical abnormalities and inhibited the occurrence of liver tumors. These results suggest that hepatic loss of RA function leads to the development of steatohepatitis and liver tumors.

Topics: Animals; Cytochrome P-450 Enzyme System; Disease Models, Animal; Fatty Acids; Fatty Liver; Hepatocytes; Lipid Metabolism; Liver Neoplasms; Mice; Mice, Transgenic; Oxidative Stress; Receptors, Retinoic Acid; Retinoic Acid Receptor alpha; Tretinoin

In this study, treatment of C57BL/6J (wild type, WT) mice fed a high-fat diet (HFD) with retinoic acid (RA) decreased body weight and subcutaneous and visceral fat content, reversed the apparent hepatosteatosis, and reduced hepatic intracellular triglyceride and serum alanine transaminase (ALT) and aspartate aminotransferase (AST) concentrations. Moreover, RA treatment improved glucose tolerance and insulin sensitivity in WT mice fed a HFD. However, these RA-induced effects in WT mice fed a HFD were alleviated in liver specific Sirtuin 1 (Sirt1) deficient (LKO) mice fed a HFD. Furthermore, RA also could not improve glucose tolerance and insulin sensitivity in LKO mice fed a HFD. The mechanism studies indicated that RA indeed increased the expression of hepatic Sirt1 and superoxide dismutase 2 (Sod2), and inhibited the expression of sterol regulatory element binding protein 1c (Srebp-1c) in WT mice in vivo and in vitro. RA decreased mitochondrial reactive oxygen species (ROS) production in WT primary hepatocytes and increased mitochondrial DNA (mtDNA) copy number in WT mice liver. However, these RA-mediated molecular effects were also abolished in the liver and primary hepatocytes from LKO mice. In summary, RA protected against HFD-induced hepatosteatosis by decreasing Srebp-1c expression and improving antioxidant capacity through a Sirt1-mediated mechanism.

Topics: Animals; Antioxidants; Cells, Cultured; Diet, High-Fat; Fatty Liver; Gene Expression Regulation; Lipogenesis; Mice; Mice, Inbred C57BL; Oxidative Stress; Polymerase Chain Reaction; Sirtuin 1; Sterol Regulatory Element Binding Protein 1; Tretinoin

Mice deficient in small heterodimer partner (SHP) are protected from diet-induced hepatic steatosis resulting from increased fatty acid oxidation and decreased lipogenesis. The decreased lipogenesis appears to be a direct consequence of very low expression of peroxisome proliferator-activated receptor gamma 2 (PPAR-γ2), a potent lipogenic transcription factor, in the SHP(-/-) liver. The current study focused on the identification of a SHP-dependent regulatory cascade that controls PPAR-γ2 gene expression, thereby regulating hepatic fat accumulation. Illumina BeadChip array (Illumina, Inc., San Diego, CA) and real-time polymerase chain reaction were used to identify genes responsible for the linkage between SHP and PPAR-γ2 using hepatic RNAs isolated from SHP(-/-) and SHP-overexpressing mice. The initial efforts identify that hairy and enhancer of split 6 (Hes6), a novel transcriptional repressor, is an important mediator of the regulation of PPAR-γ2 transcription by SHP. The Hes6 promoter is specifically activated by the retinoic acid receptor (RAR) in response to its natural agonist ligand, all-trans retinoic acid (atRA), and is repressed by SHP. Hes6 subsequently represses hepatocyte nuclear factor 4 alpha (HNF-4α)-activated PPAR-γ2 gene expression by direct inhibition of HNF-4α transcriptional activity. Furthermore, we provide evidences that atRA treatment or adenovirus-mediated RAR-α overexpression significantly reduced hepatic fat accumulation in obese mouse models, as observed in earlier studies, and the beneficial effect is achieved by the proposed transcriptional cascade.. Our study describes a novel transcriptional regulatory cascade controlling hepatic lipid metabolism that identifies retinoic acid signaling as a new therapeutic approach to nonalcoholic fatty liver diseases.

Topics: Animals; Basic Helix-Loop-Helix Transcription Factors; Blood Glucose; Fatty Liver; Gene Expression Regulation; Lipid Metabolism; Liver; Male; Mice; Mice, Inbred C57BL; Non-alcoholic Fatty Liver Disease; PPAR gamma; Receptors, Cytoplasmic and Nuclear; Receptors, Retinoic Acid; Repressor Proteins; Retinoic Acid Receptor alpha; Transcription, Genetic; Tretinoin

Topics: Animals; Fatty Liver; Male; Non-alcoholic Fatty Liver Disease; PPAR gamma; Receptors, Cytoplasmic and Nuclear; Tretinoin

Topics: Animals; Fatty Liver; Insulin Resistance; Leptin; Male; Receptors, Leptin; Tretinoin

Topics: Animals; Fatty Liver; Insulin Resistance; Leptin; Male; Receptors, Leptin; Tretinoin

Transgenic mice expressing dominant-negative retinoic acid receptor (RAR) α specifically in the liver exhibit steatohepatitis, which leads to the development of liver tumors. Although the cause of steatohepatitis in these mice is unknown, diminished hepatic expression of insulin-like growth factor-1 suggests that insulin resistance may be involved. In the present study, we examined the effects of retinoids on insulin resistance in mice to gain further insight into the mechanisms responsible for this condition. Dietary administration of all-trans-retinoic acid (ATRA) significantly improved insulin sensitivity in C57BL/6J mice, which served as a model for high-fat, high-fructose diet-induced nonalcoholic fatty liver disease (NAFLD). The same effect was observed in genetically insulin-resistant KK-A(y) mice, occurring in concert with activation of leptin-signaling pathway proteins, including signal transducer and activator of transcription 3 (STAT3) and Janus kinase 2. However, such an effect was not observed in leptin-deficient ob/ob mice. ATRA treatment significantly up-regulated leptin receptor (LEPR) expression in the livers of NAFLD mice. In agreement with these observations, in vitro experiments showed that in the presence of leptin, ATRA directly induced LEPR gene expression through RARα, resulting in enhancement of STAT3 and insulin-induced insulin receptor substrate 1 phosphorylation. A selective RARα/β agonist, Am80, also enhanced hepatic LEPR expression and STAT3 phosphorylation and ameliorated insulin resistance in KK-A(y) mice.. We discovered an unrecognized mechanism of retinoid action for the activation of hepatic leptin signaling, which resulted in enhanced insulin sensitivity in two mouse models of insulin resistance. Our data suggest that retinoids might have potential for treating NAFLD associated with insulin resistance.

Topics: Animals; Cells, Cultured; Disease Models, Animal; Fatty Liver; Hepatocytes; Immunohistochemistry; Insulin Resistance; Leptin; Male; Mice; Mice, Inbred C57BL; Mice, Obese; Non-alcoholic Fatty Liver Disease; Random Allocation; Receptors, Leptin; Reference Values; Sensitivity and Specificity; Signal Transduction; Tretinoin; Up-Regulation

Excess dietary fat can cause hepatic steatosis, which can progress into severe liver disorders including steatohepatitis and cirrhosis. Steroid receptor coactivator-3 (SRC-3), a member of the p160 coactivator family, is reported as a key regulator of adipogenesis and energy homeostasis. We sought to determine the influence of SRC-3 on hepatic steatosis and the mechanism beneath.. The influence of siRNA-mediated SRC-3 silencing on hepatic lipid accumulation was assessed in HepG2 cells. The molecular mechanism of SRC-3 regulation of hepatic lipid metabolism was also studied. Moreover, the effect of SRC-3 ablation on hepatic steatosis was examined in SRC-3 deficient mice.. In this study, we report that SRC-3 ablation reduces palmitic acid-induced lipid accumulation in HepG2 cells. Moreover, deletion of SRC-3 ameliorates hepatic steatosis and inflammation response in mice fed a high fat diet (HFD). These metabolic improvements can presumably be explained by the reduction in chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) expression and the subsequent elevation in peroxisome proliferator-activated receptor α (PPARα) level. At the molecular level, SRC-3 interacts with retinoic receptor α (RARα) to activate COUP-TFII expression under all-trans retinoic acid (ARTA) treatment.. These findings indicate a crucial role for SRC-3 in regulating hepatic lipid metabolism and provide the possible novel inner mechanisms.

Topics: Animals; COUP Transcription Factor II; Dietary Fats; Disease Models, Animal; Fatty Liver; Gene Knockdown Techniques; Hep G2 Cells; Humans; Immunohistochemistry; Lipid Metabolism; Liver Cirrhosis, Experimental; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Non-alcoholic Fatty Liver Disease; Nuclear Receptor Coactivator 3; PPAR alpha; Promoter Regions, Genetic; Receptors, Retinoic Acid; Retinoic Acid Receptor alpha; RNA Interference; RNA, Small Interfering; Tretinoin

Alcoholism can result in fatty liver that can progress to steatohepatitis, cirrhosis, and liver cancer. Mice fed alcohol develop fatty liver through endocannabinoid activation of hepatic CB(1) cannabinoid receptors (CB(1)R), which increases lipogenesis and decreases fatty acid oxidation. Chronic alcohol feeding also up-regulates CB(1)R in hepatocytes in vivo, which could be replicated in vitro by co-culturing control hepatocytes with hepatic stellate cells (HSC) isolated from ethanol-fed mice, implicating HSC-derived mediator(s) in the regulation of hepatic CB(1)R (Jeong, W. I., Osei-Hyiaman, D., Park, O., Liu, J., Bátkai, S., Mukhopadhyay, P., Horiguchi, N., Harvey-White, J., Marsicano, G., Lutz, B., Gao, B., and Kunos, G. (2008) Cell Metab. 7, 227-235). HSC being a rich source of retinoic acid (RA), we tested whether RA and its receptors may regulate CB(1)R expression in cultured mouse hepatocytes. Incubation of hepatocytes with RA or RA receptor (RAR) agonists increased CB(1)R mRNA and protein, the most efficacious being the RARgamma agonist CD437 and the pan-RAR agonist TTNPB. The endocannabinoid 2-arachidonoylglycerol (2-AG) also increased hepatic CB(1)R expression, which was mediated indirectly via RA, because it was absent in hepatocytes from mice lacking retinaldehyde dehydrogenase 1, the enzyme catalyzing the generation of RA from retinaldehyde. The binding of RARgamma to the CB(1)R gene 5' upstream domain in hepatocytes treated with RAR agonists or 2-AG was confirmed by chromatin immunoprecipitation and electrophoretic mobility shift and antibody supershift assays. Finally, TTNPB-induced CB(1)R expression was attenuated by small interfering RNA knockdown of RARgamma in hepatocytes. We conclude that RARgamma regulates CB(1)R expression and is thus involved in the control of hepatic fat metabolism by endocannabinoids.

Topics: Animals; Arachidonic Acids; Catalysis; Chromatin Immunoprecipitation; Endocannabinoids; Fatty Liver; Glycerides; Hepatocytes; Liver; Male; Mice; Mice, Inbred C57BL; Protein Structure, Tertiary; Receptor, Cannabinoid, CB1; Receptors, Retinoic Acid; Retinoic Acid Receptor gamma; Retinoids; Transcription, Genetic; Tretinoin

Although attention has focused on the chemopreventive action of retinoic acid (RA) in hepatocarcinogenesis, the functional role of RA in the liver has yet to be clarified. To explore the role of RA in the liver, we developed transgenic mice expressing RA receptor (RAR) alpha- dominant negative form in hepatocytes using albumin promoter and enhancer. At 4 months of age, the RAR alpha- dominant negative form transgenic mice developed microvesicular steatosis and spotty focal necrosis. Mitochondrial beta-oxidation activity of fatty acids and expression of its related enzymes, including VLCAD, LCAD, and HCD, were down-regulated; on the other hand, peroxisomal beta-oxidation and its related enzymes, including AOX and BFE, were up-regulated. Expression of cytochrome p4504a10, cytochrome p4504a12, and cytochrome p4504a14 was increased, suggesting that omega-oxidation of fatty acids in microsomes was accelerated. In addition, formation of H2O2 and 8-hydroxy-2'-deoxyguanosine was increased. After 12 months of age, these mice developed hepatocellular carcinoma and adenoma of the liver. The incidence of tumor formation increased with age. Expression of beta-catenin and cyclin D1 was enhanced and the TCF-4/beta-catenin complex was increased, whereas the RAR alpha/ beta-catenin complex was decreased. Feeding on a high-RA diet reversed histological and biochemical abnormalities and inhibited the occurrence of liver tumors. These results suggest that hepatic loss of RA function leads to the development of steatohepatitis and liver tumors. In conclusion, RA plays an important role in preventing hepatocarcinogenesis in association with fatty acid metabolism and Wnt signaling.

Topics: 8-Hydroxy-2'-Deoxyguanosine; Animals; beta Catenin; Cytoskeletal Proteins; Deoxyguanosine; Diet; Dose-Response Relationship, Drug; Enzymes; Fatty Acids; Fatty Liver; Genes, Dominant; Hydrogen Peroxide; Liver; Liver Neoplasms; Male; Mice; Mice, Transgenic; Mitochondria, Liver; Oxidation-Reduction; Receptors, Retinoic Acid; Retinoic Acid Receptor alpha; RNA, Messenger; Trans-Activators; Tretinoin