Cobalt chloride pre-treatment enhances the calcium handling of human embryonic stem cells-derived cardiomyocytes

Abstract

Hypoxia is an important factor governing the proliferation, differentiation and maintenance of the cardiovascular system during embryonic development. At a molecular level, hypoxia inducible factor-1 (HIF-1) plays a pivotal role in handling the hypoxia signal. Our previous study has demonstrated the direct involvement of HIF-1α subunit in promoting the cardiac differentiation of murine embryonic stem cells (ESCs). Here, we report an alternative experimental approach of using cobalt chloride to induce HIF-1α stabilization in the human ESCs for promoting cardiac differentiation. In brief, treatment of undifferentiated hES2 human ESCs with 50 μM cobalt chloride remarkably increased the protein levels of the HIF-1α subunit, which was associated with increased expressions of early cardiac specific transcription factors and cardiotrophic factors including NK2 transcription factor related locus 5, vascular endothelial growth factor and cardiotrophin-1. When the pre-treated cells were subjected to cardiac differentiation, notable increase in the occurrence of beating embryoid bodies, along with increased expressions of the cardiac specific markers, such as myosin heavy (MHC-A and MHC-B) and light (MLC2V) chains were observed. Confocal calcium imaging analysis further indicated that the maximum upstroke and decay velocities were significantly increased in both non-caffeine and caffeine-induced calcium transient in cardiomyocytes derived from the cobalt chloride pre-treated cells, suggesting these cells were functionally more mature. In conclusion, the findings from the present study suggested that cobalt chloride pretreatment can enhance the maturation of calcium handling of cardiomyocytes derived from ESC for therapeutic applications.