Pulmonary hypertension (PH) is a devastating disease of the blood vessels in the lung in which excessive proliferation and impaired apoptosis contribute to vascular obstruction, right ventricular hypertrophy (RVH), RV failure and eventually death. We discovered that the hyperproliferative phenotype in the pulmonary artery smooth muscle layer is associated with a metabolic reprogramming that induces a Warburg phenotype. Further, we demonstrated that the loss of mitochondrial bioenergetics in pulmonary arterial smooth muscle cells (PASMC) isolated from pulmonary hypertensive rats (PH-PASMC) was due to a loss of electron transport chain (ETC) Complex I assembly and activity. However, the mechanism by which the loss of Complex I assembly occurs is unresolved and is the focus of our application. Our published studies have shown that cGMP-dependent protein kinase G Iα (PKG-Iα) activity is attenuated in various models of PH through a mechanism that involves its nitration. However, cGMP-independent PKG-Iα activity is increased in PH rats and is localized to mitochondria. Interestingly, mitochondrial bioenergetics are also restored when PH-PASMC are incubated with a PKG inhibitor. Overall hypothesis: Impaired mitochondrial function and the metabolic reprogramming in PH-PASMC occurs, at least in part, through a previously unidentified signaling cascade mediated by the mitochondrial localized PKG- Iα and is a viable therapeutic target in PH. Approach: We will test our hypothesis using a variety of state-of-the-art methodologies that include structural, biophysical, biochemical, functional assays as well as preclinical rodent models of PH. In specific Aim (SA) #1 we will elucidate the mechanism by which mitochondrial cGMP-independent PKG-Iα activity is enhanced during the development of PH. SA#2 will then elucidate the role played by cGMP-independent PKG-Iα activity in the loss of Complex I assembly in PASMC during the development of PH. SA#3 will validate cGMP-independent mito