Identification of Cholesterol 25-Hydroxylase as a Novel Host Restriction Factor and a Part of the Primary Innate Immune Responses against Hepatitis C Virus Infection

Abstract

Hepatitis C virus (HCV), a single-stranded positive-sense RNA virus of the Flaviviridae family, causes chronic liver diseases, including hepatitis, cirrhosis, and cancer. HCV infection is critically dependent on host lipid metabolism, which contributes to all stages of the viral life cycle, including virus entry, replication, assembly, and release. 25-Hydroxycholesterol (25HC) plays a critical role in regulating lipid metabolism, modulating immune responses, and suppressing viral pathogens. In this study, we showed that 25HC and its synthesizing enzyme cholesterol 25-hydroxylase (CH25H) efficiently inhibit HCV infection at a postentry stage. CH25H inhibits HCV infection by suppressing the maturation of SREBPs, critical transcription factors for host lipid biosynthesis. Interestingly, CH25H is upregulated upon poly(I·C) treatment or HCV infection in hepatocytes, which triggers type I and III interferon responses, suggesting that the CH25H induction constitutes a part of host innate immune response. To our surprise, in contrast to studies in mice, CH25H is not induced by interferons in human cells and knockdown of STAT-1 has no effect on the induction of CH25H, suggesting CH25H is not an interferon-stimulated gene in humans but rather represents a primary and direct host response to viral infection. Finally, knockdown of CH25H in human hepatocytes significantly increases HCV infection. In summary, our results demonstrate that CH25H constitutes a primary innate response against HCV infection through regulating host lipid metabolism. Manipulation of CH25H expression and function should provide a new strategy for anti-HCV therapeutics. IMPORTANCERecent studies have expanded the critical roles of oxysterols in regulating immune response and antagonizing viral pathogens. Here, we showed that one of the oxysterols, 25HC and its synthesizing enzyme CH25H efficiently inhibit HCV infection at a postentry stage via suppressing the maturation of transcription factor SREBPs that regulate lipid biosynthesis. Furthermore, we found that CH25H expression is upregulated upon poly(I·C) stimulation or HCV infection, suggesting CH25H induction constitutes a part of host innate immune response. Interestingly, in contrast to studies in mice showing that ch25h is an interferon-stimulated gene, CH25H cannot be induced by interferons in human cells but rather represents a primary and direct host response to viral infection. Our studies demonstrate that the induction of CH25H represents an important host innate response against virus infection and highlight the role of lipid effectors in host antiviral strategy. H epatitis C virus (HCV), a causative agent of acute and chronic liver diseases, is an enveloped positive-sense single-stranded RNA virus belonging to the family of Flaviviridae. Approximately 170 million people worldwide are infected with HCV. The tremendous progress has been achieved in the therapeutics of chronic hepatitis C thanks to the development of direct antiviral agents (DAAs), but the worldwide application of the...

25-Hydroxycholesterol Inhibition of Lassa Virus Infection through Aberrant GP1 Glycosylation

“…CH25H is an interferon-stimulated gene, and its expression is upregulated during infection with hepatitis C and influenza viruses (16, 29). How LASV infection upregulates CH25H is unknown, especially since LASV-infected human cells produce undetectable or very low levels of type-I IFN (30, 31).…”

“…The antiviral function of 25HC involves multiple mechanisms, including blocking fusion of the viral envelope with host membranes (14), inhibiting viral replication (14, 15), and inhibiting the formation of viral replication complexes on intracellular membranes (17). 25HC was also reported to inhibit a postentry step of viral infection by repressing the activation of SREBP (16), a transcription factor required for lipid and cholesterol biosynthesis. More recently, 25HC has also been shown to block the replication of nonenveloped viruses (18).…”

Interferon Control of the Sterol Metabolic Network: Bidirectional Molecular Circuitry-Mediating Host Protection

“…Recent studies have also revealed more detail regarding the regulation of CH25H. Mboko et al (93) showed that CH25H expression in mice is, at least partly, dependent on IRF1 and Xiang et al (94) demonstrated an IFN-independent induction of CH25H in hepatocytes in response to viral infection (93, 94). In this regard, evidence to-date suggests that CH25H gene expression is regulated in a cell-specific manner and it cannot be considered a prototypic ISG.…”

Immunometabolic Signaling Pathways Contribute to Macrophage and Dendritic Cell Function

“…42,81 Notably, a number of studies have identified anti-viral activity of CH25H/25-HC against HCV potentially involving multiple mechanisms. 43,69,78,79,85–87 Finally, an exciting study has been published recently examining the non-coding transcriptome in HCV-infected cells in the presence and absence of 25-HC treatment, demonstrating that 25-HC alters the miR environment of these cells. miR-185 and miR-130b were shown to be induced by 25-HC treatment in infected cells and to inhibit HCV through a mechanism involving regulation of hepatic lipid metabolism and virus-induced lipid microenvironments (miR-185 and miR-130b) and an effect on IFNs (miR-130b).…”

“…31 Similarly, regulation of inflammasome components by SREBPs has been suggested to be an artefact of back-crossing deficits in in-bred mouse strains. 95 At least one report has challenged IFN sensitivity of CH25H in humans 87 and, in particular, many aspects of CH25H and 25-HC expression and regulation are not understood in humans, where protein expression of CH25H is reported to be low. 85 With these concerns in mind, acknowledgment must be made of studies that include a focused effort to realize applicability of findings across experimental models and consider translational impact.…”