Hepatitis C virus nonstructural protein 5A perturbs lipid metabolism by modulating AMPK/SREBP-1c signaling

Abstract

BackgroundSteatosis is an important clinical manifestation associated with chronic hepatitis C virus (HCV) infection. AMP-activated protein kinase (AMPK), a major mediator of lipid metabolism, regulates HCV-associated hepatic steatosis, but the underlying mechanisms remain obscure. Here we investigated the mechanism of HCV nonstructural protein 5A (NS5A)-induced lipid accumulation by the AMPK/SREBP-1c pathway.MethodsWe generated model mice by injecting recombinant lentiviral particles expressing the NS5A protein (genotype 3a) via the tail vein. The serum levels of alanine aminotransferase (ALT), free fatty acids (FFAs) and triglycerides (TG) were examined. H&E and Oil Red O staining were used to examine lipid droplets. Immunohistochemistry staining, quantitative real-time PCR and Western blotting were used to determine the expression of lipogenic genes.ResultsOur results showed that the serum levels of ALT, FFAs and TG, as well as the accumulation of hepatic lipid droplets, were increased significantly in mice infected with NS5A-expressing lentiviral particles. NS5A inhibited AMPK phosphorylation and increased the expression levels of sterol regulatory element binding protein-1c (SREBP-1c), acetyl-coenzyme A carboxylase 1 (ACC1) and fatty acid synthase (FASN) in vivo and in vitro. Further investigation revealed that pharmacological activation or ectopic expression of AMPK neutralized the upregulation of SREBP-1c, ACC1 and FASN, and ameliorated hepatic lipid accumulation induced by NS5A. Ectopic expression of SREBP-1c enhanced NS5A-induced hepatic lipid accumulation, which was dramatically reversed by pharmacological activation of AMPK.ConclusionsCollectively, we demonstrate that NS5A induces hepatic lipid accumulation via the AMPK/SREBP-1c pathway.

Hijacking of Lipid Droplets by Hepatitis C, Dengue and Zika Viruses—From Viral Protein Moonlighting to Extracellular Release

“…Transient increases in the level of expression and the proteolytic activation of both SREBP-1 and SREBP-2 have been found during HCV infection, followed by increased lipogenesis of cholesterol and membrane lipids [8,19,44]. Specifically, the HCV core, NS4B, NS5A and the 3 -untranslated region (UTR) have been found to activate SREBP signaling pathways, thereby enhancing the activity of a variety of enzymes involved in lipid biosynthesis (Table 2) [44][45][46][47][48][49][50][51].…”

“…Recently, HCV NS5A was found to trigger accumulation of hepatic LDs in a mouse model through a 5 adenosine monophosphate-activated protein kinase (AMPK)-SREBP-1c-dependent pathway [45]. AMPK is a master sensor of cellular energy levels and plays an important role in regulating lipid metabolism, including fatty acid synthesis and oxidation.…”

“…AMPK is a master sensor of cellular energy levels and plays an important role in regulating lipid metabolism, including fatty acid synthesis and oxidation. NS5A was shown to inhibit AMPK activation, which subsequently resulted in increased expression of SREBP-1c and other lipid metabolism genes along with increased LD levels [45]. Here, we propose that the cytoplasmic LD (cLD)associated HCV proteins core and non-structural protein 5A (NS5A) may also use nuclear LDs (nLDs) as a sequestration platform for interfering with host LD-associated proteins (pink circle).…”

“…Alternatively, it has been suggested that HCV may hijack autophagy proteins to promote translation of incoming HCV RNA and initiate viral replication [82]. The role of autophagy in regulating host lipid homeostasis and innate immune responses, including the interferon response, may also be targeted by HCV [45,80].…”

Multifaceted Role of AMPK in Viral Infections

“…Furthermore, it was shown in vivo and in vitro that HCV nonstructural protein 5A (NS5A) inhibits AMPK phosphorylation. This resulted in increased expression of sterol regulatory element-binding protein-1c (SREBP-1c), acetyl-coenzyme A carboxylase 1 (ACC1) and fatty acid synthase (FASN) and contributed to HCV-associated hepatic steatosis [ 127 , 128 ].…”