PACIFIC

Heart failure (HF) is a major life-threatening disease affecting more than 1 million people in France and is associated with a high mortality rate. While the etiology of HF is diverse (coronary artery disease, myocardial infarction, hypertension, aging, etc.), they are all associated with aberrant myocardial tissue remodeling and cardiac fibrosis. The principal feature of cardiac fibrosis is an excessive accumulation of extracellular matrix (ECM) which reduces tissue compliance, increases myocardial stiffness, leads to mechanical and electrical dysfunction and eventually to heart failure. However, there is currently no effective anti-fibrotic therapeutic strategy that could complement the current therapies for HF. To achieve an anti-fibrotic therapy, a better understanding of the mechanisms contributing to cardiac fibrosis is needed. Activated cardiac fibroblasts are essential for the production of ECM proteins however, recent studies have established that cardiac fibroblasts represent a very heterogeneous cell population. The exact nature of activated fibroblasts and consequently the sources of cardiac fibrosis remains poorly understood. In this research project, we propose to evaluate the role in cardiac fibrosis of a novel population of cardiac cells that reside in the myocardium and that we have demonstrated recently to be fibrogenic in response to an ischemic injury. This population has been identified based upon the expression of the pan-stem cell marker, Pw1/Peg3 (referred hereafter as PW1). In normal hearts, PW1 is expressed in the interstitial cells of the heart and is not expressed in cardiac myocytes. Cardiac PW1+ cells were isolated and displayed both colony forming capacity and cell fate plasticity in vitro to form mesenchymal-lineage cells (adipocytes, osteoblasts, chondrocytes), as well as fibroblasts and smooth muscle cells but not cardiomyocytes. In ischemic hearts, the number of PW1+ cells markedly increased and we demonstrated that a significant proportion (~22%) of fibroblasts were derived from PW1 expressing cells. Based on this first study and on additional preliminary results, we propose that cardiac PW1+ cells contribute to cardiac fibrosis (i) by directly giving rise to fibroblasts thus representing a source of additional ECM and (ii) by orchestrating a microenvironment that further favors resident fibroblasts activation. We therefore propose to further elucidate the role of cardiac PW1+ cells in myocardial fibrogenesis in two different models of cardiac diseases (cardiac ischemia and pharmacologically-induced pressure overload) in genetically-modified mice. We will use high field MRI to non-invasively detect and quantify diffuse interstitial fibrosis processes. The project will be organized in 4 specific tasks with the following aims: (1) to study whether genetic ablation of cardiac PW1+ cells limits fibrotic scar tissue and improves cardiac function, (2) to develop an innovative anti-fibrotic strategy targeting ?V-containing integrins expressed at the surface of cardiac PW1+ cells (3) to define the molecular pathways underlying the fibrogenic cell fate potential of cardiac PW1+ cells and (4) to characterize the cardiac PW1+ cells microenvironment and cellular interactions with fibroblasts. The consortium includes two different partners with complementary skills and expertise: one partner has extensive expertise in cardiac diseases, biology and pharmacology of heart failure, and stem cell biology and has primarily described PW1/Peg3 cells and developed unique tools to investigate the biological function of these cells; one partner has expertise in cardiac imaging with high-field MRI and has developed innovative computing tools to image and quantify myocardial dense vs. interstitial fibrosis. This project has a great potential for fundamental and translational discovery and brings promising and innovative perspectives for the treatment of cardiac fibrosis.