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

Authors

  • Kengo Tomita,

    Corresponding author
    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
    2. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan
    • Address reprint requests to: Kengo Tomita, M.D., Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, 3-2 Namiki, Tokorozawa-shi, Saitama 359-8513, Japan. E-mail: kengo@ndmc.ac.jp; fax: +81 4-2996-5201.

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    • These authors contributed equally to this work.

  • Toshiaki Teratani,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan
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    • These authors contributed equally to this work.

  • Takahiro Suzuki,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan
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  • Motonori Shimizu,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Hirokazu Sato,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Kazuyuki Narimatsu,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Yoshikiyo Okada,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Chie Kurihara,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Rie Irie,

    1. Department of Pathology, Kawasaki Municipal Hospital, Kanagawa, Japan
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  • Hirokazu Yokoyama,

    1. Health Center, Keio University School of Medicine, Tokyo, Japan
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  • Katsuyoshi Shimamura,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan
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  • Shingo Usui,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
    2. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan
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  • Hirotoshi Ebinuma,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan
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  • Hidetsugu Saito,

    1. Graduate School of Pharmaceutical Sciences, Keio University Faculty of Pharmacy, Tokyo, Japan
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  • Chikako Watanabe,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Shunsuke Komoto,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Atsushi Kawaguchi,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Shigeaki Nagao,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Kazuo Sugiyama,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan
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  • Ryota Hokari,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Takanori Kanai,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan
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  • Soichiro Miura,

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan
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  • Toshifumi Hibi

    1. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan
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  • Potential conflict of interest: Nothing to report.

Abstract

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. Conclusion: These characteristic mechanisms of FC accumulation in HSCs are potential targets to treat liver fibrosis in liver diseases including NASH. (Hepatology 2014;58:154–169)

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