Role of glial CCR5 in mediating HIV-1 Tat and opiate neurotoxicity and behavioral phenotype

• Main Author: Kim, Sarah
• Format: Others
• Published: VCU Scholars Compass 2019
• Subjects: HIV; HAND; CCR5; maraviroc; opiate; BDNF; Neuroscience and Neurobiology
• Online Access: https://scholarscompass.vcu.edu/etd/6006; https://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=7086&context=etd

Human immunodeficiency virus type 1 (HIV-1) persists in certain CNS cell populations, despite peripheral control of the infection with modern antiretroviral therapy. Infected and/or activated cells release viral proteins, such as trans-activator of transcription (Tat) and various pro-inflammatory factors such as CCL5, creating a positive loop of neuro-inflammation. This serves as the basis for the resulting sublethal and lethal neuropathology that manifests as a spectrum of HIV-mediated CNS impairments, known as HIV-associated neurocognitive disorders (HAND). Opiates, which exist as an interlinked epidemic with HIV-1 infections, exacerbate these neurological effects through direct and indirect mechanisms that disrupt both glial and neuronal function. We hypothesize this is due to converging actions on the CCL5-CCR5 signaling axis by HIV-1 Tat and morphine co-exposure, primarily mediated at the level of the glia, whose consequent activation leads to neuronal damage. We performed repeated measure studies on mixed glia and neuron co-cultures obtained from C57Bl/6J and/or CCR5 knockout mice, treated with Tat and/or morphine for 72 hours. As established in prior studies, morphine worsened Tat-induced neurotoxicity in wild-type co-cultures; substitution of CCR5-null glia eliminated the interactive effects of Tat and morphine, but substitution of CCR5-null neurons did not. Overall, these results suggest that glial CCR5, but not neuronal CCR5, is a convergence point for the interactive effects of Tat and morphine that result in neuron loss. Additional experiments involving treatments with naloxone, a MOR antagonist, or the CCR5 antagonist maraviroc, confirmed each receptor’s role in mediating Tat + morphine toxicity. Quite surprisingly, in co-cultures of wild-type neurons and CCR5-null glia, morphine entirely protected neurons from the neurotoxic effects of Tat. We hypothesize that this effect may reflect an imbalance of neurotrophic factors, particularly BDNF and its neurotoxic precursor proBDNF, whose levels are altered in HIV+ and illicit drug-using patients and may contribute to changes in neuronal signaling and survival exhibited in HAND. Related behavioral tests of anxiety, motor and cognitive function – three areas of neurologic decline seen in HAND – were performed in inducible Tat-transgenic mice that were treated with maraviroc via oral gavage. Tat-mediated impairment was observed in the Barnes Maze, a measure of spatial memory, and was ameliorated by maraviroc. Finally, we assessed the role of CCR5 in mediating Tat and/or morphine effects on psychomotor sensitization and dendritic morphology. With both in vitro and in vivo studies, our findings support the hypothesis that CCR5 plays a central role in driving HIV-1 Tat and/or morphine-mediated neuronal damage.