Bone Morphogenetic Protein Antagonist "Protein Related To Dan And Cerberus" Promotes Differentiation Of Embryonic Stem Cells To Atrial Cardiomyocytes

The molecular factors that regulate cardiac differentiation have been extensively studied, yet, relatively little is known about how cardiomyocytes acquire atrial versus ventricular characteristics. Embryonic stem (ES) cells, which have the potential to differentiate to a wide array of distinct cell types, including most types of cardiovascular cells, offer a pertinent in vitro model to work out the molecular mechanisms of atrial specification and differentiation. We discovered that the secreted antagonist of BMP signaling, Protein Related to Dan and Cerberus (PRDC, also called Gremlin2) leads to a surge in cardiomyocytic differentiation when applied to mouse ES-derived cardiac progenitor cells. This property is unique to PRDC among tested BMP antagonists. Lineage expansion is restricted to cardiomyocytes, with the differentiation of endodermal, blood, endothelial and neuronal cells being unaffected. Using molecular and electrophysiological analyses, we show that PRDC-induced cardiomyocytes acquire atrial characteristics. Consistent with the in vitro results, we found that injection of PRDC mRNA into the developing zebrafish embryo leads to supernumerary contracting areas. The ectopic cardiomyocytes express atrial-, but not ventricular- specific cardiac genes. We determined that PRDC treatment induces the expression of COUP-TFII, a known transcriptional regulator of atrial differentiation, but suppresses Notch signaling. Inhibition of Notch is sufficient to induce atrial-specific genes; however, blocking Notch does not expand the cardiogenic fields. Taken together, our data suggest that antagonism of BMP and Notch signaling by PRDC is a critical early step in the specification, expansion and differentiation of atrial progenitor cells. This information might be relevant for treating atrial degeneration, as well as for understanding the etiology of atrial fibrillation.