Abstract 4366250: Targeting SIN3a-Mediated FOXK2 Regulation to Restore BMPR2 Expression and Reverse Endothelial Dysfunction in Pulmonary Arterial Hypertension

Background: Pulmonary Arterial Hypertension (PAH) is a rare, progressive lung disease with limited treatment options. Loss of BMPR2 expression is a well-established contributor to PAH pathogenesis. While SIN3a is known to regulate BMPR2 epigenetically in smooth muscle cells, its role in pulmonary arterial endothelial cells (PAECs) remains unclear. Hypothesis: SIN3a functions as a transcriptional modulator in PAECs, promoting BMPR2 expression by activating FOXK2 and suppressing histone methyltransferase EZH2. Its downregulation in PAH leads to altered chromatin states and upregulation of pro-proliferative genes contributing to pulmonary endothelial dysfunction and vascular remodeling. Furthermore, intercellular crosstalk between PAECs and pulmonary smooth muscle cells exacerbates these pathological changes; however, SIN3a overexpression counteracts these effects by restoring FOXK2/BMPR2 signaling axis. Methods: SIN3a expression was assessed in hPAECs from PAH patients and non-PAH controls. Functional studies included cell proliferation, migration assays, and FOXK2/BMPR2 expression by qPCR and western blotting. SIN3a-FOXK2 interaction was assessed using Co-IP and immunostaining. FOXK2 binding to the BMPR2 promoter was examined by ChIP-qPCR. In vivo , SIN3a gene therapy was delivered using EC-specific AAV vectors in SuHx-treated mice, with hemodynamic and histological evaluation. Results: SIN3a was downregulated in human PAH lungs and PAH-PAECs, affecting FOXK2 and BMPR2 signaling. SIN3a overexpression reduced PAEC proliferation and migration, upregulated FOXK2 and BMPR2, and repressed EZH2. FOXK2 knockdown lowered BMPR2, but SIN3a restored it in FOXK2-depleted PAEC-cells. Co-IP and immunostaining showed that SIN3a physically interacts with FOXK2 and enhances its nuclear localization. ChIP-qPCR confirmed FOXK2 enrichment at the BMPR2 promoter. Conditioned media from SIN3a-overexpressing PAH-PAECs significantly halted smooth muscle cells proliferation and migration, highlighting intercellular crosstalk and regulation. SIN3a gene therapy significantly reduced RV systolic pressure, Fulton index, and vascular remodeling in SuHx mice. Conclusions: SIN3a significantly enhances BMPR2 expression via FOXK2-mediated pathway, effectively reducing endothelial dysfunction and mitigating vascular remodeling at the interface of endothelial and smooth muscle cells. Therefore, SIN3a gene therapy stands out as a compelling strategy to address and slow the progression of PAH.