A direct and indirect mechanism for CCR5 in morphine and HIV-1 mediated neurodegeneration

A DIRECT AND INDIRECT MECHANISM FOR CCR5 IN OPIOID AND HIV-1 MEDIATED NEURODEGENERATION By Elizabeth M. Podhaizer, Ph.D. A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University. Virginia Commonwealth University, 2014 Major Director: Kurt F. Hauser, Ph.D., Professor of Pharmacology & Toxicology Human immunodeficiency virus (HIV)-1 infection currently affects over 34 million people worldwide, and despite the use of cART, the prevalence of HIV-1 associated neurocognitive impairments (HAND) has not declined. Additionally, other co-morbid factors such as the abuse of injection drugs (i.e. heroin, morphine) increase both the frequency and the speed by which patients progress to AIDS. To begin to understand the mechanisms, we chose to examine a pathway, through CCR5, which may act as a convergence point for opioids and HIV-1 proteins. C-C chemokine receptor 5 (CCR5) is an immune receptor involved in physiological processes in the brain in addition to mediating neuroinflammatory signaling events, and it is a co-receptor for HIV-1. CCR5 interacts directly with gp120 to facilitate HIV-1 infection, and may interact indirectly with HIV-1 Tat through convergent signaling mechanisms. Additionally, CCR5 is modified by opioid responses, and so may be central to opioid-HIV-1 interactions that are seen in our model. We hypothesized that CCR5 would mediate the opioid-HIV-1 interaction. We examined both HIV-1 gp120 and HIV-1 Tat, both for interactions with opioids and modification by the CCR5 antagonist, maraviroc. HIV-1 gp120ADA was neurotoxic on its own, but showed no interactions with morphine. However, further probing revealed that morphine can in fact modify the neurotoxic effects of gp120, but that the response is dependent on gp120 strain. We did, however, find that morphine did enhance the neurotoxicity of Tat, which we’ve shown previously, as well as that inhibition of CCR5 can prevent this interactive effect. Additionally, use of CCR5 knockout glia or neurons modified the response and suggests that neurons and glia play different roles in the integration of opioid and HIV-1 signals. Sublethal effects of morphine and Tat were also dampened by maraviroc pretreatment or use of knockout cells, as was the secretion of chemokine ligands. Manipulation of CCR5 showed utility in preventing neurodegenerative effects both to HIV-1 proteins alone as well as to the interactive opioid-HIV-1 signaling responses and suggests that maraviroc, a cART therapeutic used to prevent viral entry, may also aid in reducing the chronic inflammatory state of the CNS that leads to the persistent neurocognitive complications