Astroglia are indispensable component of the tripartite synapse ensheathing innumerous soma and synapses. Its proximity to neurons aids the regulation of neuronal functions, health and survival through dynamic neuroglia crosstalk. Susceptibility of astrocyte to HIV-1 infection and subsequent latency culminates in compromised neuronal health. The viral protein HIV-1 transactivator of transcription (Tat) is neurotoxic. HIV-1 Tat is detected in brain of AIDS patients even in cases where viral load is non-detectable due to successful HAART therapy. Recently, we demonstrated that HIV-1 Tat triggers excess ATP release from astrocytes that causes neuronal death by activating purinergic receptor system. Using well-characterized model system of human primary astrocytes and neurons, we probed into the molecular mechanism for enhanced ATP release in HIV-1 Tat affected astrocytes. HIV-1 Tat modulated the miRNA machinery in astrocytes and perturbed the levels of voltage dependent anion channel 1 (VDAC1), a channel present in the outer mitochondrial membrane and plasma membrane that regulates extracellular ATP release. Our studies with autopsy tissue sections also showed concordantly dysregulated VDAC1 and miR-320a levels in HIV-1 patients suffering from mild cognitive impairment (MCI). We report a novel molecular cascade of miRNA-mediated ATP release through regulation of VDAC1. Downregulation of VDAC1 either with miR-320a mimic or VDAC1 siRNA in HIV-1 Tat-affected astroglia could rescue the neurons from glia-mediated indirect death. Our findings reveal a novel upstream therapeutic target that could be employed to thwart the astroglia-mediated neurotoxicity in HIV-1 neuropathogenesis. GLIA 2017;65:250-263.

In addition to glial cells, HIV-1 infection occurs in multipotent human neural precursor cells (hNPCs) and induces quiescence in NPCs. HIV-1 infection of the brain alters hNPC stemness, leading to perturbed endogenous neurorestoration of the CNS following brain damage by HIV-1, compounding the severity of dementia in adult neuroAIDS cases. In pediatric neuroAIDS cases, HIV-1 infection of neural stem cell can lead to delayed developmental milestones and impaired cognition. Using primary cultures of human fetal brain-derived hNPCs, we gained novel insights into the role of a neural stem cell determinant, tripartite containing motif 32 (TRIM32), in HIV-1 Tat-induced quiescence of NPCs. Acute HIV-1 Tat treatment of hNPCs resulted in proliferation arrest but did not induce differentiation. Cellular localization and levels of TRIM32 are critical regulators of stemness of NPCs. HIV-1 Tat exposure increased nuclear localization and levels of TRIM32 in hNPCs. The in vitro findings were validated by studying TRIM32 localization and levels in frontal cortex of HIV-1-seropositive adult patients collected at post mortem as well as by infection of hNPCs by HIV-1. We observed increased percentage of cells with nuclear localization of TRIM32 in the subventricular zone (SVZ) as compared with age-matched controls. Our quest for probing into the mechanisms revealed that TRIM32 is targeted by miR-155 as downregulation of miR-155 by HIV-1 Tat resulted in upregulation of TRIM32 levels. Furthermore, miR-155 or siRNA against TRIM32 rescued HIV-1 Tat-induced quiescence in NPCs. Our findings suggest a novel molecular cascade involving miR-155 and TRIM32 leading to HIV-1 Tat-induced attenuated proliferation of hNPCs. The study also uncovered an unidentified role for miR-155 in modulating human neural stem cell proliferation, helping in better understanding of hNPCs and diseased brain.