Project Summary The often debilitating side-effect of standard pharmacotherapy for Parkinson disease (PD), levodopa-induced dyskinesia (LID) continues to be a serious complication of medical treatment for individuals with PD. Despite eventually occurring in greater than 90% of individuals, there is the only one FDA-approved drug for LID. However, it is only partially effective, works best in cases of mild LID, and can itself produce significant adverse events. Maintaining the motor benefits of PD therapies while avoiding LID remains a significant unmet clinical need. Our research program has been validating striatal voltage gated CaV1.3 calcium channels as a therapeutic target for LID amelioration. Our initial proof-of-principle data demonstrated that reducing striatal CaV1.3 expression with adeno-associated virus (rAAV) CaV1.3 short-hairpin (sh)RNA expression in YOUNG (2mo) MALE parkinsonian rats provided near complete, uniform protection against LID induction, and provided significant (60%) reversal of already established severe LID. Importantly this approach did NOT interfere with, and in fact appeared to enhance, motor activation of levodopa. As age is the greatest risk factor for PD and that there are sex-related differences in both PD and LID, in the first iteration of this R01 we expanded our target validation studies into older male and female parkinsonian rats and nonhuman primates (NHPs). For these studies, we principally employed the proactive approach of preventing LID induction, reasoning that if aging precluded, or significantly diminished the ability of this molecular therapy to ameliorate LID severity, a proactive paradigm was the most reasonable initial approach. Using a mix of proactive (rat & NHP) and reversibility paradigms (rat only), our studies performed during the first iteration of this award continue to robustly support the concept that striatal CaV1.3 silencing is a potent therapeutic for preventing LID induction (rats & NHPs) and escalation of pre-existing mild LID (rats) in aging parkinsonian subjects of both sexes. However, these studies provide crucial scientific insight that advancing age, female sex, and introducing CaV1.3 silencing after LID induction in older parkinsonian rats (15-18 mos) increased variability and decreased overall benefit of therapeutic response. In contrast, in aged parkinsonian NHPs (24-29 yo) proactive intervention with AAV-CaV1.3-shRNA provided profound antidyskinetic benefit and significant diminution of long-standing severe parkinsonian disability, ‘ON’ and ‘OFF’ levodopa, in both male and female aged macaques. We posit the next logical steps for this research program, aimed at understanding the potential clinical application of this gene therapy in PD, is to define the therapeutic benefit (i.e., reversal of LID and parkinsonian disability) once LID have been induced using the gold standard preclinical parkinsonian NHP model. We propose here a series of studies directed at determining the...