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

HIV-1 associated neurocognitive disorders (HAND) remain highly prevalent in the era of effective antiretroviral therapy. Cocaine abuse increases the incidence of HAND and exacerbates the severity of HAND by enhancing viral replication. Abnormal dopaminergic transmission is implicated as a risk determinant of HAND. Therefore, there is a pressing need to define the molecular mechanism(s) by which the impaired dopamine (DA) system by HIV-1 infection affects the progression of HAND in concurrent cocaine abusers. The presynaptic dopamine transporter (DAT) is essential for DA homeostasis and maintaining stable synaptic dopaminergic tone involved in attention, learning, memory, and motivation. HIV-1 Tat protein and cocaine synergistically increase synaptic DA levels by directly inhibiting DAT activity, ultimately leading to dopaminergic neuron damage. Within the current grant cycle, our published work has demonstrated that Tat-induced inhibition of DAT is mediated by binding to allosteric binding site(s) on DAT, not interacting with the DA uptake site. Further, we propose that Tat via the unique allosteric modulatory sites perturbs the DAT and NET regulatory network that normally sustains concentrative DA or NE transport, resulting in DA/NE-linked neuropsychiatric dysfunction prominently featured in HAND. Moreover, we hypothesize that attenuating Tat and cocaine binding to DAT/NET through novel allosteric modulators without changing physiological DA/NE reuptake would be beneficial to the preservation of neurocognitive function in HIV-infected individuals. Through the proposed studies in this competitive renewal, which expands our current study of the Tat and cocaine interaction with DAT, we intend to identify the unique binding sites in human DAT/NET for Tat-induced dysfunction of DA system. Furthermore, we will use computational modeling and medicinal chemistry approaches to refine the existing candidate molecules with allosteric modulatory effects on DAT and further verify allosteric modulators as a novel therapeutic agent for HAND. The specific aims include: (1) Identify the recognition binding sites in human NET for Tat, and explore allosteric modulation of this transporter by Tat and cocaine interaction; (2) To determine the pathogenic role of DAT/NET-mediated dopaminergic transmission in the prefrontal cortex in iTat-Tg mice. (3) To perform proof of concept studies using novel allosteric modulators to establish their potential for therapeutic application in HAND.