LAUSR

AIMS Congenital heart disease (CHD) is the most common genetic birth defect, which has considerable morbidity and mortality. We focused on deciphering key regulators that govern cardiac progenitors and cardiogenesis. FOXK1 is a forkhead/winged helix transcription factor known to regulate cell cycle kinetics and is restricted to mesodermal progenitors, somites and the heart. In the present study, we define an essential role for FOXK1 during cardiovascular development. METHODS & RESULTS We used the mouse embryoid body system to differentiate control and Foxk1 KO ESCs into mesodermal, cardiac progenitor cells and mature cardiac cells. Using flow cytometry, immunohistochemistry, cardiac beating, transcriptional and ChIP qPCR assays, bulk RNAseq and ATACseq analyses, FOXK1 was observed to be an important regulator of cardiogenesis. Flow cytometry analyses revealed perturbed cardiogenesis in Foxk1 KO EBs. Bulk RNAseq analysis at two developmental stages showed a significant reduction of the cardiac molecular program in Foxk1 KO EBs compared to the control EBs. ATACseq analysis during EB differentiation demonstrated that the chromatin landscape nearby known important regulators of cardiogenesis was significantly relaxed in control EBs compared to Foxk1 KO EBs. Furthermore, we demonstrated that in the absence of FOXK1, cardiac differentiation was markedly impaired by assaying for cTnT expression and cardiac contractility. We demonstrate that FOXK1 is an important regulator of cardiogenesis by repressing the Wnt/β-catenin signaling pathway and thereby promoting differentiation. CONCLUSIONS These results identify FOXK1 as an essential transcriptional and epigenetic regulator of cardiovascular development. Mechanistically, FOXK1 represses Wnt signaling to promote the development of cardiac progenitor cells. TRANSLATIONAL PERSPECTIVE Congenital heart disease is the most common birth defect. Deciphering the networks that govern cardiomyocyte specification, proliferation and differentiation will provide insights regarding therapeutic interventions for cardiovascular disease. The winged helix/forkhead family of transcription factors have been shown to have critical roles in epigenetics, organogenesis, cellular proliferation and differentiation. FOXK1 is an important transcription factor that regulates cardiovascular development through the Wnt signaling pathway. This FOXK1-Wnt pathway defines a network that may be therapeutically targeted to promote cardiogenesis.