[37] PPAR-α
antagonism leads to hepatic lipid accumulation.[22] miR-27′s induction selleck of lipid accumulation was also reversed by the PPAR-α agonist bezafibrate (Fig. 3). Therefore, HCV-induced expression of miR-27 represents a novel mechanism by which the virus inhibits PPAR-α signaling and promotes steatosis (Fig. 6). Overexpression of individual viral proteins revealed that both core and NS4B independently activate miR-27a and miR-27b expression (Fig. 1F; Supporting Fig. S2). Both of these viral proteins have previously been reported to promote lipogenesis.[38] In the case of HCV core, its expression has previously been shown to down-regulate PPAR-α expression.[39] Separate studies demonstrated that HCV core[27] and NS4B[28] promote SREBP activity through the PI3K pathway. Our results suggest that the viral Sotrastaurin chemical structure proteins also use the PI3K pathway for activation of miR-27 expression to induce steatosis (Supporting Fig. S3). Furthermore, these results are consistent with a
model of steatosis where HCV core modulates PPAR-α expression through up-regulation of miR-27 expression. The observed repression of ANGPTL3 (Supporting Fig. S4A) may be another mechanism by which HCV-induced miR-27 expression promotes triglyceride accumulation in vivo. A previous study suggested that miR-27b inhibits ANGPTL3 expression in response to dyslipidemia to prevent lipid accumulation in circulation.[14] This is due to its role as an inhibitor of lipoprotein lipase (LPL), a key enzyme in free fatty acid uptake.[40] Decreased ANGPTL3 levels would lead to increased LPL activity and fatty acid uptake into hepatocytes, highlighting an additional mechanism contributing to miR-27′s role in HCV-induced steatosis in patients. Our results also suggest that miR-27 levels can influence the HCV viral lifecycle. At the level of replication, miR-27b appears to play an antiviral role against HCV genotype 1b replication (Fig. 4). As miR-27 is not predicted to have conserved binding sites in the HCV genome,[41] inhibition of HCV replication is most likely dependent on miR-27′s regulation of host gene expression. HCV genotype 2a appears less susceptible to miR-27-mediated
上海皓元医药股份有限公司 inhibition (Supporting Fig. 10), consistent with previous observations of sequence-dependent variation in HCV resistance against metabolic inhibitors.[42] Our previous work demonstrated that PPAR-α antagonism is capable of inhibiting genotype 1b HCV replication by inducing hepatic lipid accumulation and blocking the biosynthesis of new lipids required for protein lipidation.[22] This disrupts the HCV-induced cellular lipid environment required for efficient HCV replication.[22] Here we propose an analogous model where miR-27 acts like an endogenous PPAR-α antagonist, resulting in disruption of HCV replication complexes (Fig. 6). An additional antiviral mechanism in vivo for miR-27 may lie in its regulation of ANGPTL3.