PROJECT SUMMARY/ABSTRACT Oligodendroglia are responsible for producing the myelin sheaths that protect, electrically insulate and metabolically support axons in the central nervous system (CNS) and are vulnerable to injury in multiple sclerosis (MS) and other neuropathologies leading to conduction block, axonopathy and permanent neurologic impairment. While many currently available therapies target inflammatory aspects of MS, ongoing protection of axons and long-term recovery of function will depend on new strategies to protect and regenerate myelin sheaths. Considerable evidence supports tremendous potential for innate myelin repair since axon remyelination is observed in many albeit not all MS lesions. Even in MS lesions where remyelination is absent or incomplete, oligodendrocyte progenitor cells (OPCs) are present, but fail to differentiate for reasons not well understood. Among the factors deregulated in demyelinating conditions, including MS, are serine proteases. Several years ago the discovery of a set of enzyme-activated G protein-coupled receptors, the Protease Activated Receptors (PARs), led to a new conceptual framework for understanding how serine proteases may impact disease, with these receptors permitting activating enzymes to signal in a hormone like fashion. Recent findings in the PIs laboratory demonstrate that mice with PAR1 gene knockout exhibit an accelerated pattern of myelin development and an enhancement in myelin regeneration in the adult CNS, yet the cellular mechanisms that mediate these effects are unknown. We hypothesize that PAR1 is an extracellular switch that can be therapeutically turned off after demyelination to enhance the capacity for myelin production. We further hypothesize that the pro-myelinating effects of PAR1 gene knockout depend in part on OPC intrinsic cellular mechanisms. We will test these hypothesis using newly generated PAR1-floxed mice to determine when after demyelination PAR1 inhibition will result in therapeutic enhancements in myelin regeneration and if PAR1-targeting in OPCs is sufficient to mediate these effects. In Aim 1, we will use conditional gene targeting approaches to determine if knockout of PAR1 after Cuprizone-mediated demyelination promotes myelin repair. In Aim 2, we will use conditional gene targeting approaches to determine the regulatory role of OPC PAR1 in myelin regeneration in the Cuprizone model and in myelin production developmentally. The proposed developmental studies will serve to define the cellular mechanisms by which an understudied, but highly druggable receptor regulates myelin biology in health and disease.