CXCL8-mediated glial cross-talk and neuroprotection in HIV-1 Dementia

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Currently, almost 35 million people live with HIV-1 infection worldwide. HIV-1-associated dementia (HAD) along with mild neurocognitive disorder and asymptomatic neurocognitive impairment comprises the HIV- associated neurocognitive disorder (HAND). Inflammation associated with milder forms of HIV encephalitis shows presence of activated microglia, reactive astrogliosis and neuronal injury in areas of inflammation. A few years ago, we began novel investigations into the potential mechanisms associated with glial activation & their contribution in neuro-AIDS. Primary human glial cells were used in preliminary experiments and CXCL8 was among the key molecules upregulated in activated astrocytes and other neural cells. Importantly, CXCL8 was neuroprotective in cultured human neurons exposed to HIV-1-related neurotoxins. Biological relevance of this observation was further confirmed as HIV-1-infected brain tissues demonstrated greater CXCL8 levels as compared to age-matched controls. We propose that CXCL8 plays a key regulatory role in the intercellular interactions in HIV-1 CNS infection. Microglial infection and activation leads to upregulation of IL-1¿. IL-1¿, a prototypical inflammatory stimulus for astrocytes, enhances CXCL8 production by astrocytes in CNS. CXCL8 further recruits microglia and regulates microglial activation and HIV-1 infection. Taken together, ultimately these events may lead to CXCL8-mediated direct or indirect neuroprotection. To these ends, we will address the following specific questions: How is CXCL8 regulated in activated astrocytes in HAD and what mechanisms are involved? (Aim 1) How does glial CXCL8 regulate microglial recruitment, activation and infection? (Aim 2) How does CXCL8 regulate neuronal survival and/or function during the process of HAD? (Aim 3) In Aim 1, human brain tissue specimens and primary human neural cells will be utilized to delineate CXCL8 profiles and to identify the cellular sources for CXCL8 in HAD. Primary human neural cells will be exposed to HAD-specific stimuli and CXCL8 regulation will be evaluated. The intracellular signaling pathways involved in IL-8 regulation, specifically, NF-¿B, p38MAPK and/or SHP2 will be studied in astrocytes. The role of intercellular interactions between activated astrocytes and microglia via CXCL8-mediated in regulation of microglial activation, recruitment and HIV-1 infection will be evaluated in Aim 2. The mechanisms of CXCL8 neuroprotection and the ensuing signal transduction specifically through Akt/PKB, ERK1/2, Bcl-2 and Bax and the role of TNF receptors in these neuroprotective events will be investigated using primary human neurons in Aim 3. Taken together, the studies proposed in this application will provide novel data about CXCL8-mediated glial cross-talk and neuropathogenesis and lead to novel insights into regulation of glial inflammatory responses that have both basic and clinical significance.