Protective Effects of Cannabinoids in HIV Neuropathogenesis

DESCRIPTION (provided by applicant): The neuropathogenesis of HIV-1 involves a complex interaction between viral proteins, glial and neuronal mediators, and environmental factors, such as drugs of abuse. However, surprisingly little is known about the effects of cannabinoids on HIV-1 neuropathogenesis, despite the facts that cannabinoid receptors are abundantly expressed in the striatum and that the nigrostriatal dopaminergic area is highly susceptible to HIV-1-related neuropathology. In addition, marked depletion of dopaminergic neurons, activated microglia, reactive astrocytes, and oxidative damage within this brain region are salient features of HAD. Microglia are an important source of inflammatory mediators, including cytokines, chemokines, and reactive oxygen species, all of which contribute to brain damage. When stimulated by interleukin (IL)-12, astrocytes produce neurotoxic reactive nitrogen species and chemokines, such as CCL2 and CX3CL1, which may recruit macrophages/microglia to the striatum. Among the viral-related factors, the virotoxin HIV-1 gp120 protein triggers several neuropathogenic responses in microglia and astrocytes. Based upon previous work in our laboratory demonstrating that synthetic cannabinoids inhibit expression of HIV-1 in human microglia and suppress production of inflammatory mediators by human astrocytes, and a substantial body of literature from non-human systems demonstrating neuroprotective properties of cannabinoids, the central hypothesis underlying this research project is that synthetic cannabinoids will protect dopaminergic neurons against the toxic effects of gp120 through a mechanism involving inhibition of activated microglia and astrocytes. While acknowledging the direct toxic effect gp120 can have on neurons, we intend to fill important gaps in knowledge regarding the effects of cannabinoids on the interaction of gp120 with the glial cells involved in HIV-1 neuropathogenesis. For this project, we will use two newly developed human cell culture models: a midbrain cell culture model and a neural precursor cell (NPC)-derived dopaminergic neuron model. We will use these models, as well as highly purified human microglial cells and astrocytes in experiments that investigate the protective effects of synthetic cannabinoids against gp120-induced damage to dopaminergic neurons through characterization of functional impairment, apoptosis, and oxidative damage of dopaminergic neurons and chemokine production by glial cells, assess the ability of cannabinoids to ameliorate gp120-mediated damage to dopaminergic neurons and to inhibit chemokine production in both cell culture models, and investigate the specific mechanisms by which cannabinoids inhibit microglia-mediated damage to dopaminergic neurons and inhibit gp120- and IL-12-mediated functional effects on astrocytes. Through the innovative use of primary human brain cell culture models, we hope to advance the understanding of how synthetic cannabinoids alter the toxic effects of gp120 on the brain cells involved in the neuropathogenesis of HIV-1, with the long term objective of translating discoveries arising from these studies into a new treatment method for HAD. Project Narrative Despite the therapeutic impact of anti-retroviral therapy (ART), HIV-1-associated dementia (HAD) remains a serious threat to AIDS patients, and there currently remains no specific therapy for the neurological manifestations of HIV-1. Based upon recent work that the nigrostriatal dopaminergic area is a critical brain region for the neuronal dysfunction and death seen in HAD, that synthetic cannabinoids inhibit HIV-1 expression in human microglia and suppress production of inflammatory mediators in human astrocytes, as well as a substantial literature demonstrating neuroprotective properties of cannabinoids in other systems, experiments have been designed to test the central hypothesis that synthetic cannabinoids will protect dopaminergic neurons against the toxic effects of the HIV protein gp120 through a mechanism involving inhibition of activated microglia and astrocytes. Through the innovative use of primary human brain cell culture models, we hope to advance the understanding of how synthetic cannabinoids alter the toxic effects of gp120 on the brain cells involved in the neuropathogenesis of HIV-1, with the long term objective of translating discoveries arising from these studies into a new treatment method for HAD.