Origin of congenital coronary arterio-ventricular fistulae from anomalous epicardial and myocardial development

Abstract

Coronary Artery Fistulae (CAFs) are cardiac congenital anomalies consisting of an abnormal communication of a coronary artery with either a cardiac chamber or another cardiac vessel. In humans, these congenital anomalies can lead to complications such as myocardial hypertrophy, endocarditis, heart dilatation and failure. Unfortunately, despite their clinical relevance, the aetiology of CAFs remains unknown. In this work, we have used two different species (mouse and avian embryos) to experimentally model CAFs morphogenesis. Both conditional Itga4 (alpha 4 integrin) epicardial deletion in mice and cryocauterisation of chick embryonic hearts disrupted epicardial development and ventricular wall growth, two essential events in coronary embryogenesis. Additional transcriptomics and in vitro analyses were performed to better understand how arterio-ventricular connections are originated in the embryonic heart. Our results suggest myocardial discontinuities in the developing heart promote the formation of endocardial pouch-like structures resembling human CAF. The structure of these CAF-like anomalies was compared with histopathological data from a paediatric heart CAF, showing histomorphological and immunochemical similarities, including an accumulation of smooth muscle positive cells in the pouch-like structure wall. In vitro experiments showed the abnormal contact between the epicardium and the endocardium may promote the precocious differentiation of epicardial cells to smooth muscle. Our results suggest that myocardial discontinuities in the embryonic ventricular wall promote the early contact of the endocardium with epicardial-derived coronary progenitors at the cardiac surface, leading to ventricular endocardial extrusion, precocious differentiation of coronary smooth muscle cells, and the formation of pouch-like aberrant coronary-like structures in direct connection with the ventricular lumen. Our results may provide relevant information for the early diagnosis of these congenital anomalies and the molecular mechanisms that regulate their embryogenesis.