Understanding the critical role of microRNAs in HIV-1 pathogenesis

Abstract

MicroRNAs (miRNAs) are ~22 nucleotide small RNAs which are critical regulators of mRNA translation and have key roles in HIV-1 infection. We characterized miRNA changes in CD4+ T cells from 7 patients with chronic HIV-1 infection (CHI), 7 long term non progressors (LTNPs) and 8 healthy controls (HC). There were 111 up- and 52 down-regulated miRNAs in CHI relative to HC, and 70 up- and 27 down-regulated miRNAs in LTNPs relative to HC. Let-7 miRNAs were found to be highly expressed in CD4+ T cells from HC whilst significantly and differentially decreased in CHI and LTNPs. We modulated let-7 levels in an in-vitro model and found no direct effect on HIV-1 replication kinetics. We therefore investigated whether miRNAs played a role in the altered cytokine milieu associated with chronic infection. As several in silico algorithms consistently suggested that let-7 miRNAs target the 3’ untranslated (3’UTR) region of IL10, we focused on this as a target. IL-10 was significantly increased in plasma from CHI compared to HC and also in the supernatant of HIV-1infected HUT78 cells compared to uninfected cultures. Using HUT78 cells infected with HIV-1, we noted let-7b was down-regulated within 72 hours and let-7c within 24 hours. We over-expressed let-7 miRNAs and showed decreases in IL-10 for let-7b, let-7f and let-7c. Using anti-miRNAs we showed increased IL-10 levels for let-7c, let-7f and let-7b. We confirmed that let-7 was binding to the IL10 3’UTR using a reporter construct. We performed a microarray in CD4+ T cell subsets revealing that Blimp-1 was preferentially expressed in activated regulatory T cells. Blimp-1 is a zinc finger transcriptional repressor known to play a role in IL-2 expression. We found that miR-9 played a pivotal role in regulating Blimp-1, that Blimp-1 levels were markedly elevated in CHI compared to LTNPs and HC and its expression in CHI may explain the dysfunctional endogenous IL-2 secretion noted in CHI. We investigated the expression of miRNAs in monocytes and found only two miRNAs which were differentially expressed between patient groups. By understanding the interaction between miRNAs and HIV-1, this work has resulted in unique insights into HIV-1 pathogenesis