Effects of HIV-1 Tat protein and methamphetamine on VMAT2-mediated dopamine transmission in the context of neuroHIV and drug abuse

PROJECT SUMMARY More than 38 million people are living with Human Immunodeficiency Virus (HIV) infection worldwide which continues to be a global public health problem. Despite the widespread use of efficacious combination of antiretroviral therapy (cART), up to 70% of HIV-positive individuals suffer from cognitive and behavioral deficits collectively known as HIV associated neurocognitive disorders (HAND). Although acute viral replication has been well controlled with cART in the early stage of HIV infection, long-term HIV-1 viral protein exposure within the CNS causes dopaminergic deficits and neurocognitive impairments despite the advent of cART. Substance abuse such as methamphetamine (METH) have been shown to increase the incidence of HAND and exacerbate its severity. Among the viral proteins, HIV-1 transactivator of transcription (Tat) protein plays a significant role in viral replication in the early stage of HIV infection and the pathophysiological effects on development of HAND. Dopamine (DA) transporter (DAT) transports the extracellular dopamine (DA) into cytosolic space of the synaptic terminals, whereas the vesicular monoamine transporter2 (VMAT2) transports the cytosolic DA into synaptic vesicles, whereby both DA transporter and VMAT2 are critical for normal DA homeostasis. Our published studies have demonstrated that Tat protein increases extracellular DA concentration by directly inhibiting DAT, however, the cellular mechanisms underlying Tat-induced inhibition of VMAT2-mediated DA release/uptake remains unexplored. We hypothesize that HIV-1 Tat, acting via the unique binding sites, perturbs the VMAT2 regulatory network that normally sustains concentrative DA transport and potentiates METH’s effect on VMAT2 function, resulting in DA-linked neuropsychiatric dysfunction prominently featured in HAND. Studying single Tat protein allow us to identify targets for Tat binding and develop therapeutic approaches to prevent Tat-mediated neurological damages. The purpose of the proposed investigation is to understand the molecular mechanisms of dysregulation of VMAT2-mediated DA transmission induced by HIV-1 Tat and METH and explore the potential of novel compounds for the prevention of HAND. The specific aims to be pursued in the proposed investigation are: (1) through computational modeling and experimental validation, identify the recognition binding pockets on human VMAT2 for Tat, METH, or novel VMAT2 inhibitors and explore the potential interactions of the inhibitors with Tat and METH, (2) accelerate the pathophysiological roles of VMAT2 in Tat- and METH-dysregulated DA system, and (3) perform proof-of-concept studies using pharmacological and genetic approaches as biological probes to establish their potential for therapeutic application in HAND in concurrent METH users.