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

Abstract

In chronic liver diseases, regardless of their etiology, the development of fibrosis is the first step toward the progression to cirrhosis, portal hypertension, and hepatocellular carcinoma. Hepatic stellate cells (HSCs) are the main profibrogenic cells that promote the pathogenesis of liver fibrosis, and so it is important to identify the molecules that regulate HSCs activation and liver fibrosis. Niemann-Pick type C2 (NPC2) protein plays an important role in the regulation of intracellular cholesterol homeostasis by directly binding with free cholesterol. However, the roles of NPC2 in HSCs activation and liver fibrosis have not been explored in detail. Since a high-cholesterol diet exacerbates liver fibrosis progression in both rodents and humans, we propose that the expression of NPC2 affects free cholesterol metabolism and regulates HSCs activation. In this study, we found that NPC2 is decreased in both thioacetamide- and carbon tetrachloride-induced liver fibrosis tissues. In addition, NPC2 is expressed in quiescent HSCs, but its activation status is down-regulated. Knockdown of NPC2 in HSC-T6 cells resulted in marked increases in transforming growth factor-β1 (TGF-β1)-induced collagen type 1 α1 (Col1a1), α-smooth muscle actin (α-SMA) expression, and Smad2 phosphorylation. In contrast, NPC2 overexpression decreased TGF-β1-induced HSCs activation. We further demonstrated that NPC2 deficiency significantly increased the accumulation of free cholesterol in HSCs, increasing Col1a1 and α-SMA expression and activating Smad2, and leading to sensitization of HSCs to TGF-β1 activation. In contrast, overexpression of NPC2 decreased U18666A-induced free cholesterol accumulation and inhibited the subsequent HSCs activation. In conclusion, our study has demonstrated that NPC2 plays an important role in HSCs activation by regulating the accumulation of free cholesterol. NPC2 overexpression may thus represent a new treatment strategy for liver fibrosis.

Vitamin A‐coupled liposome system targeting free cholesterol accumulation in hepatic stellate cells offers a beneficial therapeutic strategy for liver fibrosis

“…7,8 Another group reported that regulation of FC accumulation by the Niemann-Pick type C2 protein plays a key role in TGFβ-induced HSC activation. 9 We further showed that HSC activation downregulated peroxisome proliferator-activated receptor-γ (PPARγ) signaling, which led to enhanced signaling by sterol regulatory element-binding protein 2 (SREBP2) and microRNA-33a (miR-33a); this resulted in increased FC accumulation through upregulation of low-density lipoprotein receptor (LDLR) expression and diminished expression of ATP-binding cassette transporter A1 (ABCA1). 10 These findings suggest that FC accumulation in HSCs contributes to a "vicious cycle" of HSC activation, which occurs even under non-high-cholesterol conditions, and could function as a mediator in promoting HSC activation.…”

“…Recently, we showed that the accumulation of free cholesterol (FC) in HSCs sensitized the cells to activation by transforming growth factor‐β (TGFβ) by augmenting Toll‐like receptor 4 (TLR4) signaling and the subsequent inhibition of the expression of TGFβ‐pseudoreceptor Bambi (bone morphogenetic protein and activin membrane‐bound inhibitor) . Another group reported that regulation of FC accumulation by the Niemann‐Pick type C2 protein plays a key role in TGFβ‐induced HSC activation . We further showed that HSC activation downregulated peroxisome proliferator‐activated receptor‐γ (PPARγ) signaling, which led to enhanced signaling by sterol regulatory element‐binding protein 2 (SREBP2) and microRNA‐33a (miR‐33a); this resulted in increased FC accumulation through upregulation of low‐density lipoprotein receptor (LDLR) expression and diminished expression of ATP‐binding cassette transporter A1 (ABCA1) .…”

Niemann-Pick type C2 protein supplementation in experimental non-alcoholic fatty liver disease

“…Recently, Twu et al[ 38 ] demonstrated that NPC2 overexpression attenuates TGF-β sensitization by mobilizing cholesterol. The authors concluded that NPC2 might prove an effective agent against liver fibrosis progression.…”

Antifibrotic Effects of a Barbituric Acid Derivative on Liver Fibrosis by Blocking the NF-κB Signaling Pathway in Hepatic Stellate Cells

“…LX2 cells and HSC-T6 cells (an immortalized strain of rat HSCs) (Twu et al, 2016) were cultured in Dulbecco's modified Eagle's medium (DMEM; Gibco BRL, Grand Island, NY, USA) with 1% heat-inactivated fetal bovine serum (FBS; HyClone, Logan, UT, USA), penicillin and streptomycin (100 U/ml), nonessential amino acids (0.1 mM), and L-glutamine (2 mM) at 37°C in a 5% CO 2 incubator. Murine RAW264.7 macrophages (Bioresource Collection and Research Center, BCRC 60001, Taiwan) were cultured in DMEM supplemented with 10% FBS, penicillin and SCHEME 1 | Synthesis of compound 4a, 4b, 4c, and 5.…”