5E). As is the case in Bambi mRNA expression, a deficiency in TLR4 signaling canceled EGFR signaling pathway all these LDL-induced changes in collagen 1α1 and 1α2 mRNA expression (Fig. 5E). In addition, treatment with Bambi-siRNA reversed the LDL-induced increase in the mRNA expression of collagen 1α1 and 1α2 in HSCs treated with LPS and TGFβ (Fig. 5F). Furthermore, in the same way as in
the in vitro study, treatment with antagomirs against miR33a significantly alleviated the activation of HSCs in the mouse model of liver fibrosis induced by carbon tetrachloride (CCl4). This occurred through the suppression of FC accumulation and the subsequent inhibition of TLR4-mediated down-regulation of Bambi in HSCs (Supporting Fig. 8). We used TLR4-deficient mice to assess whether the exacerbation of liver fibrosis in NASH by increased cholesterol intake was dependent on TLR4 signal transduction. Significant differences were selleckchem not observed in the extent of liver fibrosis or in the hepatic mRNA levels of collagen 1α1, collagen 1α2, and αSMA, between MCD diet-fed and MCD+HC
diet-fed TLR4-deficient mice (Fig. 6A-C). Similarly, the increased cholesterol intake did not enhance liver fibrosis in the HF diet-induced NASH in TLR4-deficient mice (Fig. 6D-F). Nuclear accumulation of hepatic SREBP2 decreased in the two mouse models of NASH and further declined following supplementation with cholesterol (Supporting Fig. 9A). Cholesterol supplementation significantly decreased the hepatic mRNA levels of LDLR and HMGCR, which are downstream molecules of SREBP2, in both the animal models (Supporting Fig. 9B,C). We next detailed the SREBP2-mediated feedback system of cholesterol homeostasis in hepatocytes and HSCs in vitro. The nuclear form of SREBP2 in hepatocytes was dramatically decreased by treatments with LDL (Fig. 7A) and
25-hydroxycholesterol, which promotes Scap-Insig complex formation. These treatments also significantly decreased the nuclear form of SREBP2 in quiescent HSCs but did not affect that in activated HSCs (Fig. 7A). Quantitative analysis P-type ATPase showed that the decrease was significantly enhanced in hepatocytes, compared with HSCs, and quiescent HSCs, compared with activated HSCs (Fig. 7A). MβCD reportedly delivers cholesterol to cells without passing through lysosomes. Treatment with a cholesterol-MβCD complex also dramatically decreased the nuclear form of SREBP2 in hepatocytes (Fig. 7A). This treatment significantly decreased the nuclear form of SREBP2 in quiescent HSCs but did not affect that in activated HSCs (Fig. 7A). Quantitative analysis showed that the decrease was significantly enhanced in hepatocytes, compared with HSCs, and in quiescent HSCs, compared with activated HSCs (Fig. 7A). Scap expression levels were much higher in quiescent and activated HSCs than in hepatocytes (Fig. 7B).