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

Abstract

Chronic neuroinflammation is observed in HIV+ individuals on suppressive combination antiretroviral therapy (cART) and is thought to cause HIV-associated neurocognitive disorders. We have recently reported that expression of HIV intron-containing RNA (icRNA) in productively infected monocyte-derived macrophages induces pro-inflammatory 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 pro-inflammatory cytokine production. Blocking of HIV-1 icRNA expression, but not multiply spliced viral RNA, either via infection with virus expressing a Rev-mutant deficient for HIV icRNA nuclear export or infection in the presence of small molecule inhibitor of 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 pro-inflammatory responses in productively infected microglia. Novel strategies targeting HIV icRNA expression specifically are needed to suppress HIV-induced neuroinflammation.

N6-methyladenosine modification of HIV-1 RNA suppresses type-I interferon induction in differentiated monocytic cells and primary macrophages

“…It remains to be established whether m 6 A modifications of HIV-1 RNA regulate innate immune responses in primary CD4 + T-cells. Moreover, recent studies suggest that HIV-1 intron-containing RNA activates innate immune signaling and IFN-I induction in primary dendritic cells, macrophages, microglia, and CD4 + T cells [48][49][50]. It is conceivable that, during chronic HIV-1 infection, multiple cellular and viral mechanisms can regulate IFN-I induction and innate immune activation in infected cells and individuals.…”

The Splice of Life: Does RNA Processing Have a Role in HIV-1 Persistence?

“…Such cells could exert pressure on the host immune system, causing persistent immune activation and thus contributing to rapid disease progression. Interestingly, it was recently shown that viral protein expression is not even necessary for US RNA to cause immune activation because intron-containing HIV-1 RNA can induce innate immune signaling in diverse cell types, such as dendritic cells, macrophages, and CD4+ T cells [ 38 , 39 , 40 ].…”

Intragenic proviral elements support transcription of defective HIV-1 proviruses

“…In addition, it has been demonstrated that partially spliced and unspliced HIV-1 RNAs are recognized by MAVS-dependent nucleic acid sensing pathways and mediate IFN-I responses (11,12,57). The defective mRNA sequences generated from the intragenic elements that we have characterized initiate transcription within Env and span the intron leading us to speculate that these mRNAs could be proinflammatory.…”