Novel roles of toll-like receptor-3 and microRNA-155 in HIV-1 infection of human macrophages

Gokul Swaminathan

doi:10.17918/00009747

HIV-1 infection of macrophages plays a key role in viral pathogenesis and progression to AIDS. Toll-like receptors (TLR) are innate immune receptors present in macrophages that detect various components of microbes and trigger host defenses. Mechanisms by which TLR activation modulates HIV-1 infectivity and the specific role of TLRs in sensing HIV-1 infection are not well characterized. By using primary monocyte-derived macrophages (MDMs) from healthy human donors, we found that activation of TLR3 and TLR4 abrogates HIV-1 infection through the upregulation of microRNA-155 (miR-155). In addition, ectopic miR-155 expression remarkably diminished HIV-1 infection in primary MDMs. TLR3 activation and ectopic miR-155 expression resulted in accumulation of HIV-1 late reverse transcription (RT) products and significant reduction in integrated pro-viruses. Furthermore, miR-155 downregulated several HIV-1 dependency factors involved in nuclear import of pre-integration complexes (ADAM10, Nup153, LEDGF/p75) and thereby inhibited HIV-1 at a pre-integration stage. Time-course experiments revealed that miR-155 expression was upregulated only until 24 hrs post TLR3 stimulation. This limited existence of miR-155 had a direct impact on HIV-1 inhibition, wherein the accumulated late RT products decreased as miR-155 levels waned. Interestingly, we observed that the anti-inflammatory cytokine, IL-10 was responsible for the stringent negative regulation of miR-155. TLR3 primarily senses dsRNA, a common viral replication intermediate that is absent during retroviral replication. Although viral particles of HIV-1 contain two copies of ssRNA genuine, each ssRNA contains multiple hairpin-like secondary structures that could potentially mimic a dsRNA entity. Therefore, we hypothesized that TLR3 could sense and respond to HIV-1 infection. By performing TLR3 inhibition studies in human macrophages as well as using bone marrow derived macrophages from TLR3-/- mice, we identified that TLR3 is required for production of HIV-1-induced IFN[beta], miR-155 and various inflammatory cytokines. Overall, our data suggests that TLR3 plays complementary roles in HIV-1 infection: pre-stimulation of TLR3 prior to HIV-1 infection induces miR-155 to impair viral nuclear import, and secondly, activation of TLR3 by HIV-1 controls viral replication through the generation of miR-155 and IFN[beta]. These studies highlight the therapeutic potential for manipulating TLR3 & miR-155 expression to control HIV-1 infection and replication.

Novel roles of toll-like receptor-3 and microRNA-155 in HIV-1 infection of human macrophages

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Novel roles of toll-like receptor-3 and microRNA-155 in HIV-1 infection of human macrophages

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