1. To delineate the molecular mechanisms underlying congenital heart defects and cardiomyopathies in rare genetic disorders

a. To study congenital heart defects and cardiomyopathies in RASopathies

We currently focus on deciphering the impact of Noonan syndrome (NS)-associated RAF1 mutations on cardiogenesis and cardiac function. NS constitutes one of the most common causes of congenital heart defects (CHDs) and belongs to a group of genetic disorders called RASopathies that are caused by germ-line mutations affecting genes residing along the canonical RAS-MAPKinase signaling pathway. Unlike the non-RAF1 associated NS patients, more than 95% of infants with NS RAF1 mutations present at birth with cardiomyopathies and a variety of severe CHDs. Our previous work used hiPSC-derived cardiomyocytes to model hypertrophic cardiomyopathy in Noonan syndrome (Jaffré et al. Circulation. 2019). Nevertheless, the molecular mechanisms underlying cardiogenesis defects in NS remain poorly understood and an important need lingers to uncover therapeutic strategies through the in-depth investigation of the molecular mechanisms responsible for CHDs and cardiomyopathies in NS. To tackle this issue, we have generated a unique toolkit of genetic models of cardiogenesis using NS and CRISPR/Cas9-generated hiPSCs. By taking advantage of our unique hiPSCs platform, we aim to overcome the gap in understanding the impact of NS mutations on human cardiogenesis.

b. To define the molecular mechanisms underlying MED12-associated cardiac defects

Hardikar syndrome (HS) is a very rare disorder characterized by facial clefting, pigmentary retinopathy, biliary anomalies, intestinal malrotation and severe cardiac defects. Until 2020, the molecular etiology of the disorder was unknown. Recently, a landmark study identified de novo pathogenic nonsense and frameshift variants in the MED12 X-chromosome gene in seven female children. MED12 is part of the PIC Mediator complex, which conveys information from gene-specific regulatory proteins to RNA polymerase II to regulate transcriptional initiation and transcriptional termination.

Through our collaborations with clinicians in New York City (Dr. Bruce Lerman) and Cincinnati (Dr. Nicole Weaver), we recently identified HS individuals exhibiting cardiac defects and carrying missense or frameshift mutations in MED12, and recently generated patient-derived MED12 mutant hiPSCs. Using this disease modelling platform, we will interrogate the cellular and molecular impact of the HS MED12 mutations on cardiogenesis, and delineate how HS-associated MED12 mutations perturb cardiomyocyte function. 

2. To uncover new causative genes for cardiac disorders and study their functional and molecular impact using patient-specific hiPSCs as a disease model

To date, only 20% of human protein-coding disease genes have been associated with one or more human phenotypes, highlighting the tremendous amount of research that remains to be done. More than ever, the progresses in sequencing have revolutionized medicine by allowing us to quickly sequence patient genomes, giving us a unique opportunity to uncover new disease causative genes. Hence, through collaborations with cardiologists and pediatric cardiologists in Australia and the U.S.A., our main goal will be to identify new gene mutations that could underlie cardiac disorders (CHDs, cardiomyopathies, arrythmias) and characterize these mutations using our hiPSC-based disease modeling platform. Importantly, these studies will also further elaborate the biology of the heart by interrogating the contributions of novel genes to cardiogenesis and cardiac function.

3. To discover novel therapeutic strategies for patients with genetic cardiomyopathies using hiPSC-based high-throughput precision medicine screening platforms 

For many children with genetic cardiomyopathies, there are currently no specific treatments. To tackle this issue, I propose to leverage the differentiation of human iPSCs into 2D and 3D platforms to model cardiomyopathies in a dish and implement a high-throughput screening platform to rapidly identify and characterize new therapeutic approaches. Contrary to the current animal-based models, implementation of a high-throughput platform with patient-derived cardiac cells will drastically accelerate the discovery of novel therapies for cardiomyopathies (precision medicine). Importantly, similar screening strategies could be applied to other types of genetic cardiomyopathies or could be rapidly implemented by differentiating hiPSCs in other cell types of interest (cardiac fibroblasts, skeletal muscle cells, neurons, endothelial cells, etc…).