Transcriptional Regulation in Hypoplastic Left Heart Syndrome

About This Grant

PROJECT SUMMARY Hypoplastic left heart syndrome (HLHS) is a congenital heart disease (CHD) characterized by a small left ventricular (LV) chamber, thick LV wall, and negligible LV function. HLHS has the highest morbidity and mortality rates among CHDs. There is an urgent need for novel therapies, ideally through correcting LV growth defects before birth. However, these efforts have been impeded by limited understanding of molecular underpinnings of HLHS. To study the underlying mechanisms of HLHS, we focused on MYRF, a transcription factor (TF) recently linked to HLHS but the disease mechanisms remain unknown. Moreover, it is still unclear which cardiac cell type(s) contributes to the MYRF-mediated HLHS. To address these major gaps in knowledge, we examined the expression pattern of MYRF in mammalian heart and found it was expressed in epicardial cells (EPCs), endothelial cells (ECs), and cardiomyocytes (CMs). More importantly, specifically ablating MYRF in EPCs and ECs, but not in CMs, recapitulates many critical disease features of HLHS. Based on our preliminary data, we hypothesize that epicardial and endothelial MYRF regulate the expression of genes essential for left ventricle morphogenesis. We propose to test this hypothesis with two specific aims. In Aim 1, we will determine the role of MYRF in EPCs and ECs. we will fully characterize the cardiac phenotypes of Myrf EPC- and EC-KO mice, including determining the roles of epicardial degeneration and the defective endocardium on LV morphogenesis, respectively. We will investigate potential EPC and EC impairments in proliferation, survival, migration, and the capacity of EPCs to differentiate into other cardiac cell types via epithelial-to-mesenchymal transition (EMT). scMultiome (scRNA-seq + scATAC-seq) in conjunction with spatial transcriptomics will be used to untangle the multi-cell-lineage contribution to the phenotypes of EPC-KO and EC-KO mice. Aim 2 will elucidate the respective roles and mechanisms of MYRF nuclear-translocating N-terminus and ER-resident C-terminus. We will utilize state-of-the-art techniques routinely employed by our group to study MYRF N-terminal TF function: MYRF ChIP- seq, histone modification profiling, and IP-MS will be performed and integrated with scMultiome data to elucidate MYRF-driven transcriptional networks across diverse cardiac cell types. Mouse models specifically abolishing the function of MYRF N-terminal domains or C-terminus will be analyzed to determine the contributions of MYRF N- and C-terminus to its transcriptional regulatory activities and the pathogenesis of HLHS. The completion of these studies will substantially advance our understanding of the essential role of MYRF in the etiology of HLHS, paving the way for novel therapeutics to combat the devastating disease. Additionally, the multi-omics datasets generated by our study will greatly facilitate the research on CHD.