MicroRNAs regulate the expression of many genes and subsequently control various cellular processes, such as the immune response to viral infections mediated by type I interferon (IFN). In this study, the expression pattern of two interferon-related microRNAs, miR-146a and miR-155, was examined in healthy and HCV-genotype-4-infected peripheral blood mononuclear cells (PBMCs) using qRT-PCR. In contrast to other viral infections, the expression pattern was similar in both healthy and infected PBMCs. This could be attributed to attenuation of IFN pathway by HCV, which was assessed by investigating the expression of MxA, an interferon-stimulated gene, that showed lower expression in HCV-infected PBMCs. To determine the site of interference of HCV in the IFN pathway, expression of both microRNAs was examined following stimulation of PBMCs with IFN-α2a, an activator of the JAK/STAT pathway as well as with imiquimod, a toll-like receptor-7 (TLR-7) agonist that promotes interferon release. IFN stimulation induced the expression of miR-146a and miR-155 in HCV-infected and healthy PBMCs. Stimulation with imiquimod led to a down-regulation of both microRNAs in infected PBMCs, while it increased their expression in healthy PBMCs, indicating that HCV might interfere with miR-146a and miR-155 expression at sites upstream of interferon release, specifically in the TLR-7 pathway. The pattern of expression of both miR-146a and miR-155 was very similar with a strong positive correlation, but showed no correlation to the patients' clinical or histopathological parameters or response to treatment. In conclusion, HCV infection might repress the induction of miR-146a and miR-155 by interfering with TLR-7 signaling.
Keywords: HCV; IFN, interferon; Interferon; PBMCs; PBMCs, peripheral blood mononuclear cells; TLR, toll-like receptor; TLR-7; miR, microRNA; miR-146a; miR-155.