PROJECT SUMMARY/ ABSTRACT: Pulmonary arterial hypertension (PAH), a progressive and deadly condition characterized by pre-capillary disease with vaso-occlusive lesions and severe elevations in pulmonary arterial pressure, is attributed to both loss of vascular relaxation and severe vascular remodeling. Significant dysregulation of apoptosis, or programmed cell death, in pulmonary arterial smooth muscle cells (PASMCs) prevents turnover of abnormal PASMCs and contributes significantly to vascular remodeling. Currently approved treatments target vasodilation and slow progression of PAH, but drugs targeting reversal of vascular remodeling, and particularly cell death, that can serve as effective therapies to reverse disease have yet to be identified. We recently discovered the presence photoreceptors, or opsins, in rodent systemic and pulmonary blood vessels and elucidated the pathway by which they mediate vasorelaxation in response to blue light. In pulmonary arterial smooth muscle cells (PASMCs), we recently found that blue light exposure also selectively induces cell death in PASMCs from a model of PAH. In contrast, in normal PASMCs, apoptosis can be induced by blue light only when G protein-coupled receptor kinase-2 (GRK2), a negative regulator of opsin activity, is inhibited. Thus, the focus of my proposal is to explore this intriguing finding and elucidate the mechanism by which blue light induces apoptosis. We will employ the Sugen-hypoxia rat model of severe PAH to isolate PASMCs used in in vitro experiments. In Specific Aim 1, we will determine whether expression of opsin receptors is increased or expression of GRK2 is decreased, in PAH PASMCs. In Specific Aim 2, we will measure intracellular K+ ([K+]i) to determine if blue light exposure increases the susceptibility to apoptosis, in of PAH PASMC through efflux of K+ via cyclic nucleotide-gated K+ channels, and in Specific Aim 3, we will measure cleaved (active) caspase-3 levels and activity to determine whether blue light exposure increases caspase-3 activity in PAH PASMCs. With the completion of the research proposed in this application, we will characterize a completely novel, wavelength-specific, light-activated molecular switch, which could be harnessed for treatment of PAH to prevent and potentially reverse remodeling by selectively restoring apoptosis in abnormal PASMCs. The funds from this award will not only allow for the training necessary for the applicant to realize this goal, but also provide the opportunity to begin developing methods for in vivo application of the results.