Various receptor tyrosine kinases (RTKs)-mediated

signaling, such as HGF/c-Met, has been shown to be involved in this process. Grb2-associated binder 1 (Gab1) is a scaffolding adaptor protein that acts downstream of RTKs and has been shown to be required for hepatocyte proliferation during liver regeneration. However, the role of Gab1 in liver fibrosis progression during chronic cholestatsis has remained unclear. The aim of this study was to elucidate this issue using cholestasis-induced mouse liver fibrosis model. Methods: Hepatocyte-specific Gab1 knockout (KO) mice were generated using Cre-loxP system. KO and wild type (WT) mice were subjected to bile duct ligation (BDL) to induce cholestasis-induced ALK signaling pathway liver

fibrosis. Results KO mice had an increased number of apoptotic hepatocytes Temsirolimus mw (p<0.05) and a decreased number of proliferating hepatocytes (p<0.05) compared with WT mice at 5 days after BDL. KO mice also showed an increase in the number of infiltrating neutrophils and macrophages. These data indicates that hepatic loss of Gab1 enhanced liver injury and inflammation. We next examined liver fibrosis of these mice at 10 days after BDL. KO mice developed more severe liver fibrosis with a 2-fold increase in the fibrosis area assessed by picrosirius red staining (p<0.05) and a 1.5-fold increase in hepatic hydroxyproline content (p<0.05). αSMA staining also showed enhanced activation of hepatic stallate cells in KO mouse liver. Consistent with this, KO mice demonstrated an increased expression of fibrosis related genes, such as Col 1α, ACTA2 orTGFβ1 (p<0.05). This abnormal liver fibrosis in KO mice was associated with increased tyrosine phosphorylation of c-Met, which might be a result of negative

feedback due to hepatic loss of Gab1, a key signal transducer of HGF/c-Met signaling. Finally, cDNA microarray analysis identified chemokine CCL5, which HSP90 has been shown to have a fibrosis-promoting activity in recent reports, as an up-regulated gene in the liver of KO mice at 1 0 days after BDL. Further validation by qRT-PCR demonstrated that KO mouse livers displayed a 5-fold increase in gene expression of CCL5 (p<0.05). Moreover, administration of CCL5 antagonist significantly improved liver fibrosis in KO mice, indicating that the induction of CCL5 in KO mice was functional. Conclusion: Loss of Gab1 in the hepatocytes exacerbates liver fibrosis after BDL in mice. Gab1 might protect from liver fibrosis via suppression of CCL5 in the liver. Disclosures: Tetsuo Takehara – Grant/Research Support: Chugai Pharmaceutical Co., MSD K.K.