Disrupting <scp>BMP</scp> / <scp>TGF</scp> ‐β Signaling: Modulation of <i>AQP1</i> and <i>TGFB1</i> in Human Pulmonary Microvascular Endothelial Cells

Pulmonary arterial hypertension (PAH) is a chronic disorder with high fatality rates, and its progression is highly associated with the genetic background. Alongside pathogenic variants in genes central to the BMP/TGF-β signaling pathway, recent evidence has linked aquaporin 1 (AQP1) gene variants to PAH. While BMP9 shows promise as a PAH therapy, emerging conflicting evidence challenges this prospect. Herein, we modulated the gene expression of AQP1 and TGFB1 and examined their effect, before and after BMP9 administration, on BMP9, BMP10, BMPR2, AQP1, TGFBR1, and TGFB1 in human pulmonary microvascular endothelial cells (HPMECs) in vitro. Our results demonstrated that silencing of the AQP1 gene resulted in decreased BMPR2 mRNA and protein, downregulated TGFB1 and TGFBR1 mRNA, while tending to reduce TGFBR1 protein levels. BMP9 exogenous administration affected only TGFB1 mRNA, restoring control levels. Silencing of the TGFB1 gene downregulated BMPR2 mRNA and protein levels and affected the expression of its ligands; BMP9 mRNA and protein increased, while BMP10 mRNA levels decreased. Exogenous BMP9 treatment of TGFB1-silenced cells decreased AQP1 mRNA and protein levels. Our results indicate that modulation of AQP1 and TGFB1 genes could possibly disrupt the complex signaling pathway, and that the effects of BMP9 may be cell- and context-dependent. Together, these findings could provide a novel perspective on the interactions of the BMP/TGF-β signaling pathway.