Niemann-Pick Type C2 Protein Regulates Free Cholesterol Accumulation and Influences Hepatic Stellate Cell Proliferation and Mitochondrial Respiration Function

Abstract

Liver fibrosis is the first step toward the progression to cirrhosis, portal hypertension, and hepatocellular carcinoma. A high-cholesterol diet is associated with liver fibrosis via the accumulation of free cholesterol in hepatic stellate cells (HSCs). Niemann-Pick type C2 (NPC2) plays an important role in the regulation of intracellular free cholesterol homeostasis via direct binding with free cholesterol. Previously, we reported that NPC2 was downregulated in liver cirrhosis tissues. Loss of NPC2 enhanced the accumulation of free cholesterol in HSCs and made them more susceptible to transforming growth factor (TGF)-β1. In this study, we showed that knockdown of NPC2 resulted in marked increases in platelet-derived growth factor BB (PDGF-BB)-induced HSC proliferation through enhanced extracellular signal-regulated kinases (ERK), p38, c-Jun N-terminal kinases (JNK), and protein kinase B (AKT) phosphorylation. In contrast, NPC2 overexpression decreased PDGF-BB-induced cell proliferation by inhibiting p38, JNK, and AKT phosphorylation. Although NPC2 expression did not affect caspase-related apoptosis, the autophagy marker light chain 3β (LC3B) was decreased in NPC2 knockdown, and free cholesterol accumulated in the HSCs. The mitochondrial respiration functions (such as oxygen consumption rate, ATP production, and maximal respiratory capacity) were decreased in NPC2 knockdown, and free cholesterol accumulated in the HSCs, while NPC2-overexpressed cells remained normal. In addition, NPC2 expression did not affect the susceptibility of HSCs to lipopolysaccharides (LPS), and U18666A treatment induced free cholesterol accumulation, which enhanced LPS-induced Toll-like receptor 4 (TLR4), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 phosphorylation, interleukin (IL)-1 and IL-6 expression. Our study demonstrated that NPC2-mediated free cholesterol homeostasis controls HSC proliferation and mitochondrial function.

Methyl helicterate inhibits hepatic stellate cell activation through downregulating the ERK1/2 signaling pathway

“…PDGF‐BB is a strong HSC mitogen which can promote HSC proliferation and activation . As shown in Figure B, treatment with PDGF‐BB significantly promoted the proliferation of HSC‐T6 cells.…”

“…PDGF-BB is a strong HSC mitogen which can promote HSC proliferation and activation. 15 As shown in Figure 1B HSC-T6 cell proliferation in a concentration-dependent manner.…”

“…The IC50, that is, 50% inhibitory concentration, was 22.12 μM. Therefore, the concentrations of 3.75, 7.5 or 15 μM were chosen for further experiments.3.2 | MH inhibited HSC-T6 cell proliferation PDGF-BB is a strong HSC mitogen which can promote HSC proliferation and activation 15. As shown in Figure1B, treatment with PDGF-BB significantly promoted the proliferation of HSC-T6 cells.…”

Role of Metabolism in Hepatic Stellate Cell Activation and Fibrogenesis

“…Further support for the role of FC in liver fibrosis was demonstrated by studies on the Niemann–Pick type C2 protein (NPC2) ( Twu et al, 2016 ; Wang Y. H. et al, 2018 ; Figure 4 ). NPC2 regulates intracellular cholesterol trafficking and homeostasis by directly binding with FC and expression of NPC2 is down-regulated in CCl4- and thioacetamide (TAA)-induced liver fibrosis tissues.…”

RNASeq Analysis of Aedes albopictus Mosquito Midguts after Chikungunya Virus Infection

“…One of the genes that was identified to be upregulated, and later validated by qRT-PCR, was a homolog of the Neimann Pick 2 ( NPC2 ) gene, which in humans encodes for an intracellular cholesterol transporter. Loss of function mutations in the NPC2 gene lead to a lysosomal disorder known as Niemann–Pick disease type C, which causes an increased accumulation of lipids in cellular compartments and leads to cell death [44,45]. In many viral infections, replication and assembly of the viral particles occur at the lysosomal and other intracellular membrane-bound organelles, including DENV infection in its vector Aedes aegypti [46].…”