Abstract MP174: Cardiomyocyte-specific Deletion of Parathyroid Hormone Receptor 1 During Development Leads to Left Ventricular Hypoplasia

Abstract

Congenital heart defects occur in approximately 1% of all births and signify the most common human birth defects. Our lab previously demonstrated that cardiomyocyte specific deletion of Sphingosine 1-Phosphate Receptor 1 (S1P 1 ), a G protein-coupled receptor (GPCR) that couples exclusively to Gαi, leads to ventricular noncompaction in mice. Gαs- and Gαi-coupled GPCRs activate and inhibit adenylate cyclase, respectively, thereby regulating cAMP production. These GPCRs play important roles in adult cardiac health and disease, but their contributions to heart development are not well understood. We hypothesized that tight regulation of cAMP via Gαs- and Gαi-coupled GPCRs is a critical determinant of cardiomyocyte maturation and cardiac development. Here, we report that Parathyroid Hormone Receptor 1 (Pth1r) which couples to Gαs, is a mediator of cardiomyocyte maturation. Using mice with a Cre allele in the myosin light chain 2a locus ( Myl7 Cre/+, also known as Mlc2a Cre/+ ), we found that cardiomyocyte-specific deletion of Pth1r during development led to reduced postnatal survival. Hearts collected from surviving Pth1r cardiomyocyte mutant mice displayed left ventricular (LV) hypoplasia, and fetal cardiac genes Nppa (natriuretic peptide A) and β myosin heavy chain (Myh7) were upregulated in the hearts of surviving mutants. At 14.5 days post coitus (dpc) and 18.5 dpc, Pth1r cardiomyocyte mutant mice also showed LV hypoplasia. Furthermore, we observed decreased cardiomyocyte proliferation in Pth1r cardiomyocyte mutant hearts during development. Isolated cardiomyocytes from C57BL/6 wild-type embryos showed increased cAMP production after stimulation of Pth1r; Pth1r-dependent cAMP increases were inhibited by activation of S1P 1 . Overall, our results indicate a critical role for Pth1r signaling during heart development and suggest that cAMP levels must be tightly controlled in cardiomyocytes for normal cardiac development. LV hypoplasia is one of the key features of hypoplastic left heart syndrome (HLHS), one of the most severe forms of congenital heart disease; these studies may provide new approaches for the study and treatment of LV hypoplasia and HLHS.