Question:

The development of the embryonic heart occurs under hypoxic conditions which regulate cardiac differentiation programs. In the present study the effects of hypoxia on cardiac differentiation of mouse embryonic stem (ES) cells and the underlying signaling pathways were investigated.

Results:

Cultivation of ES cell-derived embryoid bodies under different periods of hypoxia (1% oxygen) resulted in increased numbers of contracting cardiac cell foci, expression of cardiac genes and activation of JAK2, STAT3, PI3K and AKT. Furthermore upregulation of vascular endothelial growth factor (VEGF), fibroblast growth factor-2 (FGF-2), platelet-derived growth factor BB (PDGF-BB) and cardiotrophin-1 (CT-1) protein expression was observed. Switching from hypoxia to normoxia raised reactive oxygen species (ROS) as well as nitric oxide (NO) generation, resulted in a second burst of JAK2, STAT3, PI3K and AKT phosphorylation and enhanced the expression of VEGF, FGF-2, PDGF-BB and CT-1 as well as cardiac genes. Treatment of differentiating embryoid bodies with CT-1 increased VEGF and PDGF-BB expression. Gene-silencing of CT-1 by siRNA significantly inhibited cardiomyogenesis of ES cells as well as VEGF and PDGF-BB expression.

Conclusions:

Our results suggest that cardiac cell differentiation under hypoxic conditions is critically regulated by CT-1 which regulates VEGF and PDGF-BB expression.