Expression of HIV-1 Intron-Containing RNA in Microglia Induces Inflammatory Responses

Chronic neuroinflammation is observed in HIV+ individuals on suppressive combination antiretroviral therapy (cART) and is thought to cause HIV-associated neurocognitive disorders. We recently reported that expression of HIV intron-containing RNA (icRNA) in productively infected monocyte-derived macrophages induces proinflammatory responses. Microglia, yolk sac-derived brain-resident tissue macrophages, are the primary HIV-1-infected cell type in the central nervous system (CNS). In this study, we tested the hypothesis that persistent expression of HIV icRNA in primary human microglia induces innate immune activation. We established multiple orthogonal primary human microglia-like cell cultures, including peripheral blood monocyte-derived microglia (MDMG) and induced pluripotent stem cell (iPSC)-derived microglia. Unlike MDMG, human iPSC-derived microglia (hiMG), which phenotypically mimic primary CNS microglia, were robustly infected with replication-competent HIV-1, and establishment of productive HIV-1 infection and de novo viral gene expression led to proinflammatory cytokine production. Blocking of HIV-1 icRNA expression, but not multiply spliced viral RNA, via either infection with virus expressing a Rev-mutant deficient for HIV icRNA nuclear export or infection in the presence of a small molecule inhibitor of the chromosome region maintenance 1 (CRM1)-mediated viral icRNA nuclear export pathway attenuated induction of innate immune responses. These studies suggest that Rev-CRM1-dependent nuclear export and cytosolic sensing of HIV-1 icRNA induces proinflammatory responses in productively infected microglia. Novel strategies targeting HIV icRNA expression specifically are needed to suppress HIV-induced neuroinflammation. IMPORTANCE Although peripheral viremia can be effectively suppressed with the advent of highly active antiretroviral therapy, a significant portion of HIV+ individuals still suffer from neurocognitive disorders. Despite suppressive therapy, HIV persists in various tissues, including the central nervous system (CNS), leading to chronic inflammation, the chief driver of neurocognitive disorders. While persistent infection has been described in CNS-resident macrophages and microglia, molecular mechanisms of how HIV infection in microglia contributes to neuronal inflammation have remained unclear. In this study, we used multiple primary human microglia-like cellular platforms and demonstrate that HIV-1 intron-containing RNA induces microglial activation and damage. Since current antiretroviral therapy does not suppress HIV-1 transcription, new therapeutics targeting HIV RNA expression may help to treat HIV-associated neurocognitive disorders.