Selective activation of Toll-like receptor 7 in activated hepatic stellate cells may modulate their profibrogenic phenotype.

Cholestatic liver injury may activate HSCs (hepatic stellate cells) to a profibrogenic phenotype, contributing to liver fibrogenesis. We have previously demonstrated the involvement of TLR (Toll-like receptor) 7 in the pathogenesis of biliary atresia. In the present study we investigated the ability of TLR7 to modulate the profibrogenic phenotype in HSCs. Obstructive jaundice was associated with significant down-regulation of TLR7. Primary HSCs isolated from BDL (bile duct ligation) rats with obstructive jaundice exhibited reduced expression of TLR7 and increased expression of α-SMA (α-smooth muscle actin) and collagen-α1 compared with sham rats, reflecting HSC-mediated changes. Treatment of primary activated rat HSCs and rat T6 cells with CL075, a TLR7 and TLR8 ligand, significantly decreased expression of MCP-1 (monocyte chemotactic protein-1), TGF-β1 (transforming growth factor-β1), collagen-α1 and MMP-2 (matrix metalloproteinase-2), and inhibited cell proliferation and migration. In contrast, silencing TLR7 expression with shRNA (short hairpin RNA) in T6 cells effectively blocked the effects of CL075 stimulation, reversing the changes in MCP-1, TGF-β1 and collagen-α1 expression and accelerating cell migration. Our results indicate that obstructive jaundice is associated with down-regulation of TLR7 and up-regulation of profibrogenic gene expression in HSCs. Selective activation of TLR7 may modulate the profibrogenic phenotype in activated HSCs associated with cholestatic liver injury. Abbreviations: BDL, bile duct ligation; DAPI, 4′,6-diamidino-2-phenylindole; ECM, extracellular matrix; F-actin, filamentous actin; FBS, fetal bovine serum; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GFAP, glial fibrillary acidic protein; GFP, green fluorescent protein; HCV, hepatitis C virus; HSC, hepatic stellate cell; IFN, interferon; MCP-1, monocyte chemotactic protein-1; MMP-2, matrix metalloproteinase-2; qRT-PCR, quantitative real-time PCR; shRNA, short hairpin RNA; α-SMA, α-smooth muscle actin; TGF-β1, transforming growth factor-β1; TLR, Toll-like receptor; WST-1, water-soluble tetrazolium salt 1