Hypoxia is beneficial for the differentiation of stem cells transplanted for myocardial injury,but mechanisms underlying this benefit remain unsolved. Here, we report the impact of hypoxia-induced Jagged1 expression in cardiomyocytes(CMs) for driving the differentiation of cardiac stem cells(CSCs).Forced hypoxia-inducible factor 1α(HIF-1α) expression and physical hypoxia(5% O_2) treatment could induce Jagged1 expression in neonatal rat CMs. Pharmacological inhibition of HIF-1α by YC-1 attenuated hypoxia-promoted Jagged1 expression in CMs. An ERK inhibitor(PD98059), but not inhibitors of JNK(SP600125), Notch(DAPT), NF-κB(PTDC), JAK(AG490), or STAT3(Stattic) suppressed hypoxiainduced Jagged1 protein expression in CMs. c-Kit^+ CSCs isolated from neonatal rat hearts using a magnetic-activated cell sorting method expressed GATA4, SM22α or vWF, but not Nkx2.5 and cTnI.Moreover, 87.3% of freshly isolated CSCs displayed Notch1 receptor expression. Direct co-culture of CMs with BrdU-labeled CSCs enhanced CSCs differentiation, as evidenced by an increased number of BrdU^+/Nkx2.5^+ cells, while intermittent hypoxia for 21 days promoted co-culture-triggered differentiation of CSCs into CM-like cells. Notably, YC-1 and DAPT attenuated hypoxia-induced differentiation.Our results suggest that hypoxia induces Jagged1 expression in CMs primarily through ERK signaling,and facilitates early cardiac lineage differentiation of CSCs in CM/CSC co-cultures via HIF-1α/Jagged1/Notch signaling.
