Right ventricular pressure overload disturbs T-tubule maturation via MEF2D's transcriptional regulation of BIN1

Right ventricular pressure overload (RVPO) is a critical pathophysiological feature of numerous pediatric cardiovascular diseases. Transverse tubules (T-tubules) form the foundation for efficient excitation-contraction coupling in mature cardiomyocytes. We hypothesized that RVPO impairs T-tubule maturation through the regulatory protein bridging integrator 1 (BIN1). In right ventricular samples from children with tetralogy of Fallot, characterized by RVPO, and in a neonatal rat RVPO model induced by pulmonary artery banding (PAB), T-tubule maturation was disrupted. RNA-seq revealed significant downregulation of T-tubule-associated genes, with Bin1 among the most suppressed. Bin1 overexpression restored T-tubule maturation in PAB rats. ATAC-seq showed reduced chromatin accessibility at Bin1 loci; motif analysis identified Mef2d (myocyte enhancer factor 2D) as the top enriched transcription factor. Mef2d knockdown rescued Bin1 expression and T-tubule maturation, and mutation of the Mef2d binding sites within the Bin1 promoter abolished the inhibitory effect of Mef2d on Bin1 promoter activity. This study delineates a phenomenon and a mechanism of cardiomyocyte maturation under pathological stress. The findings not only advance our understanding of this most pivotal event in postnatal cardiac development but also unveil a potential therapeutic direction for pediatric cardiovascular diseases associated with RVPO.