Project Summary/Abstract Parkinson’s disease (PD) is classically characterized by the progressive loss of dopaminergic neurons leading to the emergence of debilitating motor, and non-motor symptoms. As the CNS does not replace neurons lost to injury or disease, a primary focus in developing therapeutic strategies for PD has centered around the idea of grafting replacement dopaminergic neurons. Early neurosurgical approaches using fetal ventral midbrain allografts produced some mixed, but encouraging results. As fetal donor tissue presents challenges in regard to sourcing and ethics, variability, immunogenicity, and cost, recent efforts have focused on the prospect of using induced pluripotent cells driven to a dopaminergic neuronal fate. The advantages of this precision medicine approach, where the patient’s own cells are engineered into the replacement neurons, is offset by the effort and cost to produce and differentiate cells under cGMP conditions, with the ultimate delivery requiring invasive neurosurgery. We propose to bypass the need to generate dopaminergic neurons exogenously, by using an alternative approach where glial progenitor cells already present in the Parkinson’s patient’s brain could be directly reprogrammed to become dopaminergic neurons. In exploring this approach, access to adult human glial progenitor cells from non-affected or PD-patients is a limitation and reprogramming of adult human glial progenitor cells into dopaminergic neurons has not yet been reported. We have successfully targeted rat oligodendrocyte progenitor cells (OPCs) in vivo to reprogram them into a neuronal lineage. With this Exploratory/Developmental R21 mechanism award, we propose to lineage reprogram human OPCs into dopaminergic neurons to ultimately replace neurons lost in PD. In Aim 1, we will test the hypothesis that PD- derived fibroblasts directly reprogrammed into human OPCs without passing through a pluripotent state retain their epigenetic signature and can model the human OPCs we eventually intend to target for neuronal replacement in the PD brain. Aim 2 will test the hypothesis that temporal sequential reprogramming can direct adult-derived human OPCs from non-affected and PD-patients to become dopamine neurons. These in vitro studies, determining the timing and sequence of lineage specification instructions to generate dopaminergic neurons, will lay the necessary foundation for the future step using direct in vivo delivery to model a reprogramming neuronal replacement therapy for PD. This project also has implications for testing the capacity to drive the generated human OPCs to complete differentiation as oligodendrocytes and to then address myelination deficiencies in Parkinson’s disease.