title: Free cholesterol accumulation in hepatic stellate cells: mechanism of liver fibrosis aggravation in nonalcoholic steatohepatitis in mice.
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.
  
  
  CONCLUSIONS
  These characteristic mechanisms of FC accumulation in HSCs are potential targets to treat liver fibrosis in liver diseases including NASH.
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Defense Medical College, Saitama, Japan; Division of Gastroenterology and Hepatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Kengo
authors.initials: K
authors.lastname: Tomita
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Teratani
authors.forename: Takahiro
authors.initials: T
authors.lastname: Suzuki
authors.forename: Motonori
authors.initials: M
authors.lastname: Shimizu
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Sato
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Narimatsu
authors.forename: Yoshikiyo
authors.initials: Y
authors.lastname: Okada
authors.forename: Chie
authors.initials: C
authors.lastname: Kurihara
authors.forename: Rie
authors.initials: R
authors.lastname: Irie
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Yokoyama
authors.forename: Katsuyoshi
authors.initials: K
authors.lastname: Shimamura
authors.forename: Shingo
authors.initials: S
authors.lastname: Usui
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Ebinuma
authors.forename: Hidetsugu
authors.initials: H
authors.lastname: Saito
authors.forename: Chikako
authors.initials: C
authors.lastname: Watanabe
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Komoto
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kawaguchi
authors.forename: Shigeaki
authors.initials: S
authors.lastname: Nagao
authors.forename: Kazuo
authors.initials: K
authors.lastname: Sugiyama
authors.forename: Ryota
authors.initials: R
authors.lastname: Hokari
authors.forename: Takanori
authors.initials: T
authors.lastname: Kanai
authors.forename: Soichiro
authors.initials: S
authors.lastname: Miura
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Hibi
mesh_terms: D000818:Animals; D002784:Cholesterol / Q000008:administration & dosage / Q000378:metabolism*; D004195:Disease Models, Animal; D015536:Down-Regulation; D005234:Fatty Liver / Q000150:complications* / Q000378:metabolism; D055166:Hepatic Stellate Cells / Q000378:metabolism*; D008103:Liver Cirrhosis / Q000209:etiology* / Q000378:metabolism; D008262:Macrophage Activation; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D035683:MicroRNAs / Q000378:metabolism; D047495:PPAR gamma / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011973:Receptors, LDL / Q000378:metabolism; D015398:Signal Transduction; D051782:Sterol Regulatory Element Binding Protein 2 / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism; D015854:Up-Regulation
chemical_list: C485672:Bambi protein, mouse; C506119:Insig1 protein, mouse; D008565:Membrane Proteins; D035683:MicroRNAs; C550417:Mirn33 microRNA, mouse; D047495:PPAR gamma; D012333:RNA, Messenger; D011973:Receptors, LDL; C497391:Srebf2 protein, mouse; D051782:Sterol Regulatory Element Binding Protein 2; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D016212:Transforming Growth Factor beta; D002784:Cholesterol