Second heart field (SHF) cells are an essential source of cardiac progenitors that migrate into the arterial and venous poles of the growing heart tube during early cardiac development, eventually representing the majority of cells present in the right ventricle (RV) and outflow tract (OFT). Notably, a significant portion of congenital heart defects in humans is linked to OFT malformation, often as a result of transcriptional mis-regulation affecting SHF progenitors and cardiac neural crest cells.
In research projects funded by the Swiss National Science Foundation and the Swiss Heart Foundation we combine genome engineering, fluorescent reporter tagging and single cell methods to identify and functionally characterize cardiac enhancers regulating transcription factors (TFs) with key roles in SHF development and RV/OFT formation (e.g. Gata4, Hand2 and Tbx5). Hereby, we leverage CRISPR/Cas9 genome editing for efficient generation of tailored enhancer knockout (KO) mouse models to investigate the impact of cardiac enhancer loss on target gene expression, chromatin topology and cardiac morphogenesis. Using fluorescent reporter transgenes in combination with transcriptomic and epigenomic profiling it is our goal to determine cell-type specific and overlapping functions of cardiac enhancers, eventually at single-cell resolution. Taken together, these studies are expected to shed light on the cis-regulatory complexity, chromatin architecture and transcriptional robustness underlying mammalian heart development, and will help to pinpoint the functional relevance of human heart disease-associated genomic variants.
The abundant pool of non-myocytes in the adult mammalian heart, of which about 50% are cardiac fibroblasts, has significant potential for conversion into induced cardiomyocyte-like cells (iCMs). Recent studies have demonstrated that reactivation of a cocktail of developmental TFs in resident fibroblasts led to the emergence of iCMs coupled with improved cardiac function in a mouse model of myocardial infarction.
In another project in the framework of the SNSF Eccellenza grant it is our goal to establish a system based on CRISPR epigenome editing (CRISPRa) to enable efficient and more flexible control of cardiac reprogramming factors in target cell types, such as cardiac fibroblasts. Using this system, it is our aim to define novel cis-regulatory mechanisms driving cell fate transitions during cardiac differentiation and the fibroblast-to-cardiomyocyte conversion. Re-activation of developmental enhancers, in association with locus-specific epigenomic remodeling, is expected to play a major role in cardiac reprogramming. Understanding these mechanisms will be important to improve future therapeutic applications with the goal to promote cardiac muscle regeneration, e.g. following ischemic heart disease.