Abstract
Hepatic fibrogenesis is characterized by activation of hepatic stellate cells (HSCs) and accumulation of extracellular matrix (ECM). The impact of ECM on TGF-β-mediated fibrogenic signaling pathway in HSCs has remained obscure. We studied the role of non-receptor tyrosine kinase focal adhesion kinase (FAK) family members in TGF-β-signaling in HSCs. We used a CCl4-induced liver fibrosis mice model to evaluate the effect of FAK family kinase inhibitors on liver fibrosis. RT-PCR and Western blot were used to measure the expression of its target genes; α-SMA, collagen, Nox4, TGF-β1, Smad7, and CTGF. Pharmacological inhibitors, siRNA-mediated knock-down, and plasmid-based overexpression were adopted to modulate the function and the expression level of proteins. Association of PYK2 activation with liver fibrosis was confirmed in liver samples from CCl4-treated mice and patients with significant fibrosis or cirrhosis. TGF-β treatment up-regulated expression of α-SMA, type I collagen, NOX4, CTGF, TGF-β1, and Smad7 in LX-2 cells. Inhibition of FAK family members suppressed TGF-β-mediated fibrogenic signaling. SiRNA experiments demonstrated that TGF-β1 and Smad7 were upregulated via Smad-dependent pathway through FAK activation. In addition, CTGF induction was Smad-independent and PYK2-dependent. Furthermore, RhoA activation was essential for TGF-β-mediated CTGF induction, evidenced by using ROCK inhibitor and dominant negative RhoA expression. We identified that TGF-β1-induced activation of PYK2-Src-RhoA triad leads to YAP/TAZ activation for CTGF induction in liver fibrosis. These findings provide new insights into the role of focal adhesion molecules in liver fibrogenesis, and targeting PYK2 may be an attractive target for developing novel therapeutic strategies for the treatment of liver fibrosis.
Highlights
Hepatic fibrogenesis is characterized by activation of hepatic stellate cells (HSCs) and accumulation of extracellular matrix (ECM)
The characteric findings of liver fibrosis was mitigated in PF-431396-treated mice (Fig. 1B), suggesting collagen accumulation induced by CCl4 was suppressed by inhibition of focal adhesion kinase (FAK)/proline-rich tyrosine kinases 2 (PYK2)
The interaction between HSCs and ECM through focal adhesion mediated by FAK family kinases is one of the important steps during the process of liver fibrogenesis[24,27]
Summary
Hepatic fibrogenesis is characterized by activation of hepatic stellate cells (HSCs) and accumulation of extracellular matrix (ECM). We identified that TGF-β1-induced activation of PYK2-Src-RhoA triad leads to YAP/TAZ activation for CTGF induction in liver fibrosis. These findings provide new insights into the role of focal adhesion molecules in liver fibrogenesis, and targeting PYK2 may be an attractive target for developing novel therapeutic strategies for the treatment of liver fibrosis. Abbreviations HSC Hepatic stellate cells TGF Transforming growth factor CTGF Connective tissue growth factor FAK Focal adhesion kinase CCl4 Carbon tetrachloride YAP Yes-associated protein ALT Alanine aminotransferase AST Aspartate aminotransferase α-SMA Alpha-smooth muscle actin ROCK Rho-associated protein kinase skku.edu. Liver fibrosis is characterized by dysregulated production of extracellular matrix (ECM) by activated hepatic stellate cells (HSCs)[1,2]. The precise mechanisms of crossing mechanical signals to intracellular signaling pathway to modulate YAP are still unclear
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