Regulation of The Methylation and Expression Levels of the BMPR2 Gene by SIN3a As A Novel Therapeutic Mechanism in Pulmonary Arterial Hypertension

Background: Epigenetic mechanisms are critical in the pathogenesis of pulmonary arterial hypertension (PAH). Previous studies have suggested that hypermethylation of the Bone Morphogenetic Protein Receptor Type 2 (BMPR2) promoter is associated with BMPR2 downregulation and progression of PAH. Here, we investigated for the first time the role of Switch-Independent 3a (SIN3a), a transcriptional regulator, in the epigenetic mechanisms underlying hypermethylation of BMPR2 in the pathogenesis of PAH. Methods: We used lung samples from PAH patients and non-PAH controls, preclinical mouse and rat PAH models, and human pulmonary arterial smooth muscle cells (hPASMC). Expression of SIN3a was modulated using a lentiviral vector or a siRNA in vitro and a specific Adeno-Associated Virus serotype 1 (AAV1) or a lentivirus encoding for human SIN3a in vivo . Results: SIN3a is a known transcriptional regulator; however, its role in cardiovascular diseases, especially PAH, is unknown. Interestingly, we detected a dysregulation of SIN3 expression in patients and in rodent models, which is strongly associated with decreased BMPR2 expression. SIN3a is known to regulate epigenetic changes. Therefore, we tested its role in the regulation of BMPR2 and found that BMPR2 is regulated by SIN3a. Interestingly, SIN3a overexpression inhibited hPASMC proliferation and upregulated BMPR2 expression by preventing the methylation of the BMPR2 promoter region. RNA sequencing analysis suggested that SIN3a downregulated the expression of DNA and histone methyltransferases such as DNMT1 and EZH2 while promoting the expression of the DNA demethylase TET1. Mechanistically, SIN3a promoted BMPR2 expression by decreasing CTCF binding to the BMPR2 promoter. Finally, we identified intratracheal delivery of AAV1.hSIN3a to be a beneficial therapeutic approach in PAH- by attenuating pulmonary vascular and RV remodeling, decreasing RVSP and mPAP pressure, and restoring BMPR2 expression in rodent models of PAH. Conclusions: Altogether, our study unveiled the protective/beneficial role of SIN3a in pulmonary hypertension. We also identified a novel and distinct molecular mechanism by which SIN3a regulates BMPR2 in hPASMC. Our study also identified lung-targeted SIN3a gene therapy using AAV1 as a new promising therapeutic strategy for treating patients with PAH.