(Project 1. Mechanistic studies) Despite continued advances in combination antiretroviral therapy (cART) to treat infection by the Human Immunodeficiency Virus (HIV), a considerable number of people infected with HIV develop neurocognitive impairments that are collectively known as HIV-Associated Neurocognitive Disorders (HAND). Although the severity of cognitive impairment in the post-cART era is generally milder than was observed pre-cART, neurocognitive impairment eventually occurs in approximately 30-50% of people infected with HIV, suggesting that there is ongoing cerebral injury despite reasonable control of viral replication. This treatment-gap highlights the importance of discovering an adjunctive therapy that could protect the CNS. Although the precise mechanisms for these residual cognitive impairments are not understood, they are thought to involve a loss of central bioenergetic homeostasis, and persistent low-level inflammation that contributes to dendritic and synaptic damage. In this complex environment, an ideal therapeutic agent for HAND would have multiple effects that regulate neuroprotection, neurotrophic and anti-inflammatory responses. Insulin has numerous actions in brain that regulate many of the same neural pathways perturbed by HIV infection including energy metabolism, lipid metabolism, neurotransmitter channel activity, neurite outgrowth, synaptic strength, and inflammatory signaling, suggesting that insulin might protect the CNS in the setting of HIV-infection. Our preliminary data supports this hypothesis showing that insulin protects cultured neurons from inflammatory, excitotoxic, and HIV- protein induced toxicity as well as prevents cognitive deficits in a murine Eco HIV infection model of HAND. The mechanistic studies proposed in Project 1 will focus on elucidating the mechanism of this therapeutic effect including evaluating the interactions of insulin signaling with ceramide and cellular bioenergetics, and the effects of these interactions on dendritic structure, synaptic functions and microglial activation using in vitro model systems that recapitulate key aspects of CNS HIV infection. The findings from these studies will provide new mechanistic insights into the therapeutic effects of insulin and may help to provide information on biomarkers to be utilized in translational studies.
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