Acyl-CoA:cholesterol acyltransferase 1 mediates liver fibrosis by regulating free cholesterol accumulation in hepatic stellate cells.

Acyl-coenzyme A: cholesterol acyltransferase (ACAT) catalyzes the conversion of free cholesterol (FC) to cholesterol ester, which prevents excess accumulation of FC. We recently found that FC accumulation in hepatic stellate cells (HSCs) plays a role in progression of liver fibrosis, but the effect of ACAT1 on liver fibrosis has not been clarified. In this study, we aimed to define the role of ACAT1 in the pathogenesis of liver fibrosis. ACAT1-deficient and wild-type mice, or Toll-like receptor 4 (TLR4)(-/-)ACAT1(+/+) and TLR4(-/-)ACAT1(-/-) mice were subjected to bile duct ligation (BDL) for 3 weeks or were given carbon tetrachloride (CCl4) for 4 weeks to induce liver fibrosis. ACAT1 was the major isozyme in mice and human primary HSCs, and ACAT2 was the major isozyme in mouse primary hepatocytes and Kupffer cells. ACAT1 deficiency significantly exaggerated liver fibrosis in the mouse models of liver fibrosis, without affecting the degree of hepatocellular injury or liver inflammation, including hepatocyte apoptosis or Kupffer cell activation. ACAT1 deficiency significantly increased FC levels in HSCs, augmenting TLR4 protein and downregulating expression of transforming growth factor-β (TGFβ) pseudoreceptor Bambi (bone morphogenetic protein and activin membrane-bound inhibitor), leading to sensitization of HSCs to TGFβ activation. Exacerbation of liver fibrosis by ACAT1 deficiency was dependent on FC accumulation-induced enhancement of TLR4 signaling. ACAT1 deficiency exaggerates liver fibrosis mainly through enhanced FC accumulation in HSCs. Regulation of ACAT1 activities in HSCs could be a target for treatment of liver fibrosis.

Tomita K ，Teratani T ，Suzuki T ，Shimizu M ，Sato H ，Narimatsu K ，Usui S ，Furuhashi H ，Kimura A ，Nishiyama K ，Maejima T ，Okada Y ，Kurihara C ，Shimamura K ，Ebinuma H ，Saito H ，Yokoyama H ，Watanabe C ，Komoto S ，Nagao S ，Sugiyama K ，Aosasa S ，Hatsuse K ，Yamamoto J ，Hibi T ，Miura S ，Hokari R ，Kanai T ... -  《-》

A high-cholesterol diet exacerbates liver fibrosis in mice via accumulation of free cholesterol in hepatic stellate cells.

Some studies have indicated that dietary cholesterol has a role in the progression of liver fibrosis. We investigated the mechanisms by which dietary cholesterol might contribute to hepatic fibrogenesis. C57BL/6 mice were fed a high-cholesterol diet or a control diet for 4 weeks; liver fibrosis then was induced by bile-duct ligation or carbon tetrachloride administration. Hepatic stellate cells (HSCs) were isolated from mice fed high-cholesterol diets or from Niemann-Pick type C1-deficient mice, which accumulate intracellular free cholesterol. After bile-duct ligation or carbon tetrachloride administration, mice fed high-cholesterol diets had significant increases in liver fibrosis and activation of HSCs compared with mice fed control diets. There were no significant differences in the degree of hepatocellular injury or liver inflammation, including hepatocyte apoptosis or Kupffer cell activation, between mice fed high-cholesterol or control diets. Levels of free cholesterol were much higher in HSCs from mice fed high-cholesterol diets than those fed control diets. In cultured HSCs, accumulation of free cholesterol in HSCs increased levels of Toll-like receptor 4 (TLR4), leading to down-regulation of bone morphogenetic protein and activin membrane-bound inhibitor (a pseudoreceptor for transforming growth factor [TGF]β); the HSCs became sensitized to TGFβ-induced activation. Liver fibrosis was not aggravated by the high-cholesterol diet in C3H/HeJ mice, which express a mutant form of TLR4; HSCs that express mutant TLR4 were not activated by accumulation of free cholesterol. Dietary cholesterol aggravates liver fibrosis because free cholesterol accumulates in HSCs, leading to increased TLR4 signaling, down-regulation of bone morphogenetic protein and activin membrane-bound inhibitor, and sensitization of HSC to TGFβ. This pathway might be targeted by antifibrotic therapies.

Teratani T ，Tomita K ，Suzuki T ，Oshikawa T ，Yokoyama H ，Shimamura K ，Tominaga S ，Hiroi S ，Irie R ，Okada Y ，Kurihara C ，Ebinuma H ，Saito H ，Hokari R ，Sugiyama K ，Kanai T ，Miura S ，Hibi T ... -  《-》

Free cholesterol accumulation in hepatic stellate cells: mechanism of liver fibrosis aggravation in nonalcoholic steatohepatitis in mice.

Although nonalcoholic steatohepatitis (NASH) is associated with hypercholesterolemia, the underlying mechanisms of this association have not been clarified. We aimed to elucidate the precise role of cholesterol in the pathophysiology of NASH. C57BL/6 mice were fed a control, high-cholesterol (HC), methionine-choline-deficient (MCD), or MCD+HC diet for 12 weeks or a control, HC, high-fat (HF), or HF+HC diet for 24 weeks. Increased cholesterol intake accelerated liver fibrosis in both the mouse models without affecting the degree of hepatocellular injury or Kupffer cell activation. The major causes of the accelerated liver fibrosis involved free cholesterol (FC) accumulation in hepatic stellate cells (HSCs), which increased Toll-like receptor 4 protein (TLR4) levels through suppression of the endosomal-lysosomal degradation pathway of TLR4, and thereby sensitized the cells to transforming growth factor (TGF)β-induced activation by down-regulating the expression of bone morphogenetic protein and activin membrane-bound inhibitor. Mammalian-cell cholesterol levels are regulated by way of a feedback mechanism mediated by sterol regulatory element-binding protein 2 (SREBP2), maintaining cellular cholesterol homeostasis. Nevertheless, HSCs were sensitive to FC accumulation because the high intracellular expression ratio of SREBP cleavage-activating protein (Scap) to insulin-induced gene (Insig) disrupted the SREBP2-mediated feedback regulation of cholesterol homeostasis in these cells. HSC activation subsequently enhanced the disruption of the feedback system by Insig-1 down-regulation. In addition, the suppression of peroxisome proliferator-activated receptor γ signaling accompanying HSC activation enhanced both SREBP2 and microRNA-33a signaling. Consequently, FC accumulation in HSCs increased and further sensitized these cells to TGFβ-induced activation in a vicious cycle, leading to exaggerated liver fibrosis in NASH. These characteristic mechanisms of FC accumulation in HSCs are potential targets to treat liver fibrosis in liver diseases including NASH.

Tomita K ，Teratani T ，Suzuki T ，Shimizu M ，Sato H ，Narimatsu K ，Okada Y ，Kurihara C ，Irie R ，Yokoyama H ，Shimamura K ，Usui S ，Ebinuma H ，Saito H ，Watanabe C ，Komoto S ，Kawaguchi A ，Nagao S ，Sugiyama K ，Hokari R ，Kanai T ，Miura S ，Hibi T ... -  《-》

Niemann-Pick Type C2 Protein Mediates Hepatic Stellate Cells Activation by Regulating Free Cholesterol Accumulation.

Twu YC ，Lee TS ，Lin YL ，Hsu SM ，Wang YH ，Liao CY ，Wang CK ，Liang YC ，Liao YJ ... -  《INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES》

Interleukin-17A plays a pivotal role in cholestatic liver fibrosis in mice.

It was recently reported that serum interleukin (IL)-17 levels increased in liver fibrosis associated with human alcoholic liver disease. However, the role of IL-17 in liver fibrosis has not yet been elucidated. Therefore, the aim of this study was to evaluate the role of IL-17 on cholestatic liver fibrosis. IL-17A knockout (KO) and wild-type (WT) mice were subjected to bile duct ligation. Animals were sacrificed at designated times, and serum and liver tissues were collected. The mRNA expression of hepatic fibrotic markers was assessed, and distribution of activated hepatic stellate cells (HSCs) was determined by immunohistochemical staining. In an in vitro study, Kupffer cells (KCs) and HSCs were isolated from WT mice. KCs were cultured with IL-17A or IL-17F, and production of tumor necrosis factor α (TNF-α) and transforming growth factor β1 (TGF-β1) was measured. HSCs were cultured with IL-17A or IL-17F, and morphologic changes were assessed by immunohistochemical staining. Liver damage observed in the WT mice was significantly improved in the KO mice. Serum TNF-α and TGF-β1 levels were significantly decreased in the KO compared with the WT mice. The hepatic mRNA expression of TNF-α, TGF-β1, and collagen 1α1, which increased in the WT mice, also significantly decreased in the KO mice. Increased hepatic fibrosis in the WT mice was significantly improved in the KO mice. Cytokine production was increased in IL-17A-treated KCs. The most remarkable myofibroblast-like changes were observed in isolated HSCs in the presence of IL-17A. IL-17A was involved in the pathogenesis of cholestatic liver fibrosis by activation of both the KCs and HSCs.

Hara M ，Kono H ，Furuya S ，Hirayama K ，Tsuchiya M ，Fujii H ... -  《-》