GDF10 in Neonatal Heart Development - Project Summary/Abstract Critical maturation steps of mammalian heart development take place during the first few weeks after birth. During this time, cardiomyocytes undergo critical changes in cell structure, metabolism and gene expression, all which are essential for the proper function of the heart. CM are in contact with different cell types including fibroblasts, which have been identified as key central regulators of ventricular maturation and remodeling during both development and injury. However, the pathways utilized by fibroblasts and cardiomyocytes cells to communicate during postnatal heart development remain unknown. Recently RNA sequencing identified Growth differentiation factor 10 (GDF10), also known as Bmp3b, as an upregulated ligand in postnatal cardiac fibroblasts compared to mature quiescent fibroblasts which suggest, GDF10 plays a role in the crosstalk between cardiomyocyte and fibroblasts during neonatal development. Interestingly, in skeletal muscle, GDF10 is essential for maintaining myofiber mass maintenance and adult Gdf10 null mice develop left ventricle hypertrophy. Further, single-cell sequencing of fat cells found GDF10 to directly modulate PPAR-gamma nuclear abundance and transcriptional activity, which is known to be important for cardiac energy shift in cardiomyocyte, suggesting that GDF10 might be important for mitochondrial maturation during heart development. However, the exact role of GDF10 in the proper maturation of the heart remains to be defined. Our preliminary studies indicate that in vitro treatment with GDF10 induces size increase and a switch towards mature myosin isoform expression in neonatal cardiomyocyte which suggests that GDF10 action during cardiac development might be important for proper maturation. Further, gene expression profiling of neonatal cardiomyocyte and fibroblasts revealed fibroblast expressed GDF10 to strongly correlate with Activin receptor expression on cardiomyocytes, which have been implicated in GDF family signaling in cardiomyocytes. Finally, our preliminary studies show that gdf10 null hearts at postnatal day 7 have myocardial growth defects similar to hypoplastic left heart syndrome. The central hypothesis of this proposal is that cardiac fibroblast secreted GDF10, signaling through activin receptors, is essential for cardiomyocyte hypertrophy and mitochondrial maturation during development. Aim 1 will determine if GDF10, through Smad 1/5/8 signaling induces cardiomyocytes hypertrophy and mitochondrial maturation. In parallel, bulk RNA-sequencing of GDF10, activin receptor inhibitor ACE031 and GDF10+ACE031 treated cardiomyocyte cells will give us an in-depth understanding of direct GDF10 targets that induce CM maturation. In Aim 2, we will determine whether GDF10 signaling is required for CM hypertrophy and metabolic maturation in vivo by extensively examining gdf10 null hearts and measuring changes in cardiomyocyte cell size and sarcomeric assembly. Additionally, we will evaluate fetal and adult metabolic and contractile protein gene expression of Gdf10 null mice compared to controls. Our long-term goal is to determine GDF10 as a key crosstalk ligand between fibroblasts and cardiomyocytes in the mammalian postnatal cardiac development and if the loss of this communication impairs maturation of cardiomyocytes by decreasing cardiomyocyte hypertrophy.
