Myocardial TGFβ2 Is Required for Atrioventricular Cushion Remodeling and Myocardial Development.

Among the three transforming growth factor beta (TGFβ) ligands, TGFβ2 is essential for heart development and is produced by multiple cell types, including myocardium. Heterozygous mutations in in patients of connective tissue disorders result in congenital heart defects and adult valve malformations, including mitral valve prolapse (MVP) with or without regurgitation. germline knockout fetuses exhibit multiple cardiac defects but the role of myocardial-TGFβ2 in heart development is yet to be elucidated. Here, myocardial conditional knockout (CKO) embryos were generated by crossing mice with ; Cre mice. embryos were normal, viable. Cell fate mapping was done using dual-fluorescent mice. Cre-mediated deletion was assessed by genomic PCR. RNAscope in situ hybridization was used to detect the loss of myocardial expression. Histological, morphometric, immunohistochemical, and in situ hybridization analyses of CKOs and littermate controls at different stages of heart development (E12.5-E18.5) were used to determine the role of myocardium-derived TGFβ2 in atrioventricular (AV) cushion remodeling and myocardial development. CKOs exhibit a thin ventricular myocardium, AV cushion remodeling defects and developed incomplete AV septation defects. The loss of myocardial resulted in impaired cushion maturation and dysregulated cell death. Phosphorylated SMAD2, a surrogate for TGFβ signaling, was "paradoxically" increased in both AV cushion mesenchyme and ventricular myocardium in the CKOs. Our results indicate that TGFβ2 produced by cardiomyocytes acting as cells autonomously on myocardium and via paracrine signaling on AV cushions are required for heart development.