Role of SIN3a in the epigenetic regulation of the Bone Morphogenetic Protein Receptor Type 2 in pulmonary arterial hypertension

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Project Summary PAH is a fatal disease characterized by the progressive remodeling of the distal pulmonary vascular arteries, resulting in elevated pulmonary vascular resistance and pulmonary artery pressure, which may lead to serious complications, such as right heart failure, and ultimately death. Accumulating evidence indicates that endothelial dysfunction is one of the first triggers in PAH that leads to uncontrolled proliferation of vascular cells, vascular remodeling, and occlusion of the pulmonary blood vessels. One of the most common pathomechanisms in PAH is the alteration of the Bone Morphogenetic Protein Type 2 Receptor (BMPR2) signaling in vascular cells. The loss of BMPR2 function, induced by mutation or a loss of expression, is associated with a severe hemodynamic profile and poor outcomes in PAH patients. Multiple studies point to the pulmonary endothelium as the cell type that is most critically impacted by BMPR2 loss in PAH. However, the molecular mechanisms underlying the regulation of BMPR2 expression and its associated PAH-like phenotype remain largely unknown. Our group has recently shown that SIN3a plays a central role in the DNA and histone methylation of the BMPR2 promoter in pulmonary artery smooth muscle cells and the pathogenesis of PAH. However, the epigenetic and transcriptional mechanisms by which SIN3a regulates the BMPR2 gene in PAEC remain to be elucidated. proposal are to uncover the role of SIN3a in the pulmonary endothelial dysfunction Our objectives in this in PAH, identify the downstream mechanisms underlying the regulation of BMPR2 expression in PAEC, and evaluate the therapeutic effects of modified mRNA encoding SIN3a in animal models of PAH. Our preliminary data showed that SIN3a is significantly downregulated in hPAEC isolated from PAH patients. In vitro, we observed that SIN3a silencing downregulates BMPR2 expression and signaling while potentiating PAEC proliferation and migration. Mechanistically, we discovered a novel molecular pathway by which SIN3a modulates BMPR2 levels in hPAECs. Our data showed that SIN3a overexpression upregulates FOXK2 by repressing Enhancer of Zeste Homolog 2 (EZH2)-mediated histone methylation in the FOXK2 promoter. Ultimately, SIN3a overexpression increases FOXK2 binding to the BMPR2 promoter and upregulates BMPR2 levels in hPAECs. Based upon these findings, we hypothesize that the loss of SIN3a impairs BMPR2 expression in PAEC, triggers endothelial dysfunction and vascular remodeling in PAH. In this proposal, our hypothesis will be tested by pursuing the following three specific aims: Aim 1) To investigate the role of SIN3a in endothelial cell dysfunction and decipher the molecular mechanism underlying the regulation of BMPR2 in PAH-hPAEC. Aim 2) To elucidate the effects of SIN3a deficiency in the onset of PAH in smooth muscle cells and endothelial cells using a dual approach. Aim 3) To evaluate the therapeutic efficacy of SIN3a modRNA in preclinical models of PAH. Defining the regulatory mechanisms underlying the loss of BMPR2 expression in PAH will be of great relevance. Finally, restoring the expression of SIN3a in the lungs using SIN3a modified RNA might be a new promising strategy for treating PAH.