Susceptibility of murine induced pluripotent stem cell-derived cardiomyocytes to hypoxia and nutrient deprivation

INTRODUCTION: Induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) may be suitable for myocardial repair. While their functional and structural properties have been extensively investigated, their response to ischemia-like conditions has not yet been clearly defined. METHODS: iPS-CMs were differentiated and enriched from murine iPS cells expressing eGFP and puromycin resistance genes under the control of an alpha-MHC promoter. iPS-CMs maturity and function were characterized by microscopy, rt-PCR, calcium transient recordings, electrophysiology, and mitochondrial function assays, and compared to those from neonatal murine cardiomyocytes (N-CMs). iPS-CMs as well as N-CMs were exposed for 3 h to hypoxia (1% O2) and glucose/serum deprivation (GSD), and viability, apoptosis markers, reactive oxygen species (ROS), mitochondrial membrane potential (Deltapsim) and intracellular stress signaling cascades were investigated. Then, the iPS-CMs response to mesenchymal stromal cell-conditioned medium (MSC-CoM) was determined. RESULTS: iPS-CMs displayed key morphological and functional properties that were comparable to those of N-CMs, but several parameters indicated an earlier iPS-CMs maturation stage. During hypoxia/GSD, iPS-CMs exhibited a significantly higher proportion of poly-caspase-active, 7-AAD- and TUNEL-positive cells than N-CMs. The average mitochondrial membrane potential (Deltapsim) was reduced in "ischemic" iPS-CMs but remained unchanged in N-CMs, ROS production was only increased in "ischemic" iPS-CMs, and oxidoreductase activity in iPS-CMs dropped more rapidly than in N-CMs. In iPS-CMs, hypoxia/GSD led to upregulation of Hsp70 transcripts and decreased STAT3 phosphorylation and total PKCepsilon protein expression. Treatment with MSC-CoM preserved oxidoreductase activity and restored pSTAT3 and PKCepsilon levels. CONCLUSION: iPS-CMs appear to be particularly sensitive to hypoxia and nutrient deprivation. Counteracting the ischemic susceptibility of iPS-CMs with MSC-conditioned medium may help enhance their survival and efficacy in cell-based approaches for myocardial repair