Thyroid hormone receptor alpha modulates fibrogenesis in hepatic stellate cells.

OBJECTIVE: Progressive hepatic fibrosis can be considered the final stage of chronic liver disease. Hepatic stellate cells (HSC) play a central role in liver fibrogenesis. Thyroid hormones (TH, e.g. thyroxine; T4 and triiodothyronine; T3) significantly affect development, growth, cell differentiation and metabolism through activation of TH receptor α and/or ß (TRα/ß). Here, we evaluated the influence of TH in hepatic fibrogenesis. DESIGN: Human liver tissue was obtained from explanted livers following transplantation. TRα-deficient (TRα-KO) and wild-type (WT) mice were fed a control or a profibrogenic methionine-choline deficient (MCD) diet. Liver tissue was assessed by qRT-PCR for fibrogenic gene expression. In vitro, HSC were treated with TGFß in the presence or absence of T3. HSC with stable TRα knockdown and TRα deficient mouse embryonic fibroblasts (MEF) were used to determine receptor-specific function. Activation of HSC and MEF was assessed using the wound healing assay, Western blotting, and qRT-PCR. RESULTS: TRα and TRß expression is downregulated in the liver during hepatic fibrogenesis in humans and mice. TRα represents the dominant isoform in HSC. In vitro, T3 blunted TGFß-induced expression of fibrogenic genes in HSC and abrogated wound healing by modulating TGFß signalling, which depended on TRα presence. In vivo, TRα-KO enhanced MCD diet-induced liver fibrogenesis. CONCLUSION: These observations indicate that TH action in non-parenchymal cells is highly relevant. The interaction of TRα with TH regulates the phenotype of HSC via the TGFß signalling pathway. Thus, the TH-TR axis may be a valuable target for future therapy of liver fibrosis.

Targeting myosin 1c inhibits murine hepatic fibrogenesis.

Myosin 1c (Myo1c) is an unconventional myosin that modulates signaling pathways involved in tissue injury and repair. In this study, we observed that Myo1c expression is significantly upregulated in human chronic liver disease such as nonalcoholic steatohepatitis (NASH) and in animal models of liver fibrosis. High throughput data from the GEO-database identified similar Myo1c upregulation in mice and human liver fibrosis. Notably, transforming growth factor-ß1 (TGF-ß1) stimulation to hepatic stellate cells (HSCs), the liver pericyte and key cell type responsible for the deposition of extracellular matrix, upregulates Myo1c expression, whereas genetic depletion or pharmacological inhibition of Myo1c blunted TGF-ß-induced fibrogenic responses, resulting in repression of α-smooth muscle actin (α-SMA) and collagen type I α 1 chain (Col1α1) mRNA. Myo1c deletion also decreased fibrogenic processes such as cell proliferation, wound healing response, and contractility when compared with vehicle-treated HSCs. Importantly, phosphorylation of mothers against decapentaplegic homolog 2 (SMAD2) and mothers against decapentaplegic homolog 3 (SMAD3) were significantly blunted upon Myo1c inhibition in GRX cells as well as Myo1c knockout (Myo1c-KO) mouse embryonic fibroblasts (MEFs) upon TGF-ß stimulation. Using the genetic Myo1c-KO mice, we confirmed that Myo1c is critical for fibrogenesis, as Myo1c-KO mice were resistant to carbon tetrachloride (CCl4)-induced liver fibrosis. Histological and immunostaining analysis of liver sections showed that deposition of collagen fibers and α-SMA expression were significantly reduced in Myo1c-KO mice upon liver injury. Collectively, these results demonstrate that Myo1c mediates hepatic fibrogenesis by modulating TGF-ß signaling and suggest that inhibiting this process may have clinical application in treating liver fibrosis.NEW & NOTEWORTHY The incidences of liver fibrosis are growing at a rapid pace and have become one of the leading causes of end-stage liver disease. Although TGF-ß1 is known to play a prominent role in transforming cells to produce excessive extracellular matrix that lead to hepatic fibrosis, the therapies targeting TGF-ß1 have achieved very limited clinical impact. This study highlights motor protein myosin-1c-mediated mechanisms that serve as novel regulators of TGF-ß1 signaling and fibrosis.