Anaplerotic reprogramming of endothelial cells in pulmonary hypertension

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Pulmonary arterial hypertension (PAH) is a life-threatening disease with unmet medical needs. Currently, available therapies fail to substantially reduce PAH progression and mortality, which remains near 50% five years after diagnosis. The cancer-like proliferation of the distal pulmonary arteries is the primary cause of increased pulmonary vascular resistance, leading to right heart failure. Recent studies highlighted a critical role of metabolic reprogramming in triggering pulmonary vascular remodeling. However, the particular mechanistic link that connects the metabolic reprogramming with the uncontrolled proliferation of pulmonary vascular cells has not been established. Nevertheless, the lack of this knowledge generates a critical barrier that prevents effective therapeutics that target vascular remodeling. During the previous grant cycle, we showed that increased oxidative stress in the PAH lungs in patients and animal models results in the nitration mediated Akt activation. The activation of Akt via nitration of tyrosine Y350 induces overexpression of Pyruvate Carboxylase (PC), leading to anaplerotic stimulation of remodeling. We reported that inhibition of both Akt nitration or PC-mediated anaplerosis resulted in marked attenuation of PAH in preclinical models. In cell culture experiments, we observed that Akt nitration changes the pulmonary artery endothelial cells (PAEC) morphology, proliferation rate, and gene expressions. The microarray profiling showed upregulation of multiple markers of Endothelial to Mesenchymal Transition (EndMT) in response to Akt nitration (PDGFRa, TGFbR, SMAD3, RUNX2). To identify the possible mechanisms of EndMT, we performed a mass spectrometry analysis of PC interactome. We found a direct binding of PC to the Cyclin-Dependent Kinase 5 (CDK5) attenuated by Akt nitration inhibition. Our data indicate that PC could activate CDK5 in the cytosol. CDK5, in turn, phosphorylates RUNX2 – a well-established mediator of mesenchymal transition. Indeed, two recent publications showed activation of CDKs and RUNX2 signaling in PAH patients. However, these reports did not provide mechanistic insights. In the current proposal, we hypothesize that Akt nitration triggers PC expression and accumulation in the cytosol leading to activation of the CDK5/RUNX2 axis-mediated EndMT and vascular remodeling in PAH. We will test this hypothesis with the following aims: 1) To elucidate the role of nitration (Y350) mediated Akt activation in EndMT events; 2) To determine whether cytosolic PC plays a key role in CDK5/RUNX2 axis activation; 3) To examine the effect of targeted protein degraders (PROTACs) on EndMT in vivo.