Abstract 2172: The Transcription Factor CHF1/Hey2 Regulates Coronary Vascular Development
Background: The coronary vasculature originates from epicardial cells through epicardial to mesenchymal transformation followed by migration into the myocardial layers and differentiation into vascular components. We and others have identified CHF1/Hey2 as a transcription factor that is exclusively expressed in the compact myocardium layer during mouse development, and have reported that CHF1/Hey2 homozygotes (KO) show a variety of cardiovascular developmental abnormalities including ventricular septal defect, deformed valves and cardiomyopathy. However, its role in coronary vascular development remains unknown. We hypothesized that CHF1/Hey2 also regulates coronary vascular development through signaling pathways originating from non-epicardial cells.
Methods and Results: KO mice developed a thin compact myocardial layer of the left ventricle with grossly normal epicardial and subepicardial layers, however, there were fewer large vessels in the myocardial layers at E15.5. CD31 staining and isolectin B4 labeling detected abnormal vascular structures in the myocardial layers of E15.5 KO embryos. Reduced recruitment of vascular smooth muscle cells into the coronary arteries was seen in E18.5 KO embryos as demonstrated by αSMA staining. Both arterial and vein identity are lowered in coronary arteries and veins of E18.5 KO demonstrated by EphrinB2 and EphB4 staining, respectively. Whole mount CD31 staining and VEGFR2 staining of sections from the hearts of E18.5 KOs indicated that EphB4 negative vein networks were increased in the surface layers of the myocardium compared to those of the controls. CHF1/Hey2 is not expressed in the epicardium in vivo, and in the same manner, cultured epicardium-derived cells (EPDCs) isolated from E12.5 wild type mice showed no CHF1 expression. However, there were some αSMA positive cells from EPDCs of E12.5 KO after several passages without any treatment.
Conclusion: CHF1 deficiency in the compact myocardium caused impaired vascular formation, the reduced recruitment of vascular smooth muscle cells into coronary arteries and abnormally remodeled vein networks. These findings suggest that CHF1 may regulate the later steps of coronary vascular development in a non-cell autonomous fashion.