SUMMARY This application will study a novel role of the enzyme phosphatidylinositol-glycan-specific phospholipase D (GPLD1) in relation to physical activity (PA), cognitive outcomes, and relevant mediating pathways, including inflammation, coagulation, mitochondrial indices and vascular remodeling in aging people with HIV (PWH). Although PA promotes better cognitive function and quality of life in HIV, PA is problematic for many aging PWH due to physical limitations from neuropathy, cardiopulmonary disease, and other conditions. Systemic GPLD1 was recently shown to recapitulate the neurogenic and cognitive benefits of exercise and may represent an alternative approach to gain neural benefits of exercise for those with physical limitations. In an existing cohort of 100 PWH (50 participating in a PA intervention and 50 controls), we will quantify how GPLD1 levels change before and after the PA intervention and how these levels associate with plasma markers of inflammation, clotting, vascular remodeling, mitochondrial indices and neurocognitive (NC) performance. We propose PWH with higher levels of PA documented by Fitbit and accelerometer monitoring will show greater increases in GPLD1 than those with lower PA. We hypothesize that higher GPLD1 at baseline will associate with improved markers of inflammation, abnormal clotting, mitochondrial indices and vascular remodeling and that greater increases in GPLD1 during the PA intervention will correlate with larger improvements in these indices. Additionally, we expect that higher baseline GPLD1 will associate with better NC performance and that GPLD1 increases during the 6-month PA intervention will associate with improving NC performance. In addition to human studies, we will perform translational work to evaluate mechanisms by which GPLD1 exerts salutary effects. These will include studies in an animal model of virally suppressed PWH on antiretroviral therapy (ART), the EcoHIV mouse model. In these animals, we will measure the effects of GPLD1 administration on cognition and markers of inflammation and clotting, including evaluating if the beneficial effects of GPLD1 are blocked by an inhibitor (phosphatidic acid). In addition, we will characterize inflammation, mitochondrial indices and synaptodendritic integrity in brain tissue from GPLD1-treated mice. We expect GPLD1 treatment in EcoHIV mice will improve behavioral performance, reduce brain tissue inflammation and improve synaptodendritic integrity and mitochondrial indices. In service of future Phase 1 clinical trials, we will examine GPLD1 effects on liver toxicity in mice. We will also evaluate neuronal cultures for GPLD1 effects on mitochondrial biogenesis and neurogenesis by exposing cultures to plasma from humans in the PA intervention. We expect PWH plasma with higher PA will stimulate hippocampal mitochondrial biogenesis and neurogenesis compared to lower PA, and will determine if serum GPLD1 associates with these outcomes. Examining GPLD...