Molecular mechanisms: Dysregulation of monoamine transporters by HIV-1 Tat and cocaine

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Perturbation of dopaminergic transmission is implicated as a risk factor of HIV-1 associated neurocognitive disorders (HAND). Dopaminergic system plays a causal role in drug rewarding and modulation of the brain function including cognition. Prefrontal cortex is an important brain region for higher cognitive function, where norepinephrine transporter (NET) is the primary mechanism of homeostatic regulation of stable synaptic dopaminergic tone. HIV-1 Tat protein and cocaine synergistically increase synaptic dopamine levels, thereby producing neurocognitive impairment. Our initial findings show that in vitro exposure to recombinant Tat1-86 inhibits dopamine and norepinephrine reuptake by dopamine transporter (DAT) and NET and Tat binds to DAT and NET through a direct protein-protein interaction. We have demonstrated that Tat-induced inhibition of DAT function is mediated by binding to allosteric binding site(s) on DAT, not by interacting with the DA uptake site. Accordingly, attenuating Tat binding to DAT would be expected to have minimal influence on physiological DA transport. Indeed, our recent findings show that a novel quinazoline series of allosteric modulators decrease cocaine potency for inhibition of DA uptake and attenuate Tat-induced inhibition of DA reuptake and cocaine binding by DAT. We hypothesize that Tat, via the unique allosteric modulatory sites, perturbs the DAT and NET regulatory network that normally sustains concentrative DA or NE transport and potentiates cocaine’s effect on DAT and NET, resulting in DA/NE-linked neuropsychiatric dysfunction prominently featured in HAND. We will (Aim 1) Identify the binding sites for Tat in human NET, and explore allosteric modulation of this transporter by Tat and cocaine; (Aim 2) determine the pathogenic role of DAT/NET-mediated dopaminergic transmission in inducible Tat transgenic mice by assessment of Fast-scan cyclic voltammetry and whole cell patch clamp recording; and (Aim 3) perform proof of concept studies using novel allosteric modulators to establish their potential for therapeutic application in HAND using integrated computational modeling, pharmacological, and behavioral approaches. Our long-term goal is to explore new ways to target DAT/NET for therapeutic interventions to improve neurocognitive dysfunction of HAND in concurrent cocaine abusers.