Metabolic control of human cardiomyocyte function and maturation
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Cardiovascular diseases remain a leading cause of morbidity and mortality in the world, despite advances in drug and therapeutic developments. The complex nature of cardiac diseases such as myocardial infarction and heart failure require innovative approaches to elucidate disease mechanisms, identify molecular targets and develop novel therapies. The advent of human pluripotent stem cell (hPSC) technologies allowed for robust and reliable generations of contracting human cardiomyocytes (CMs) in vitro. hPSC-CMs hold great promise for a broad range of research and clinical applications including studying myocardial physiology, modeling cardiac diseases, and transplanting healthy cells to repair the damaged heart. However, one major limitation of hPSC-CMs differentiated in vitro is that they are relatively immature and resemble embryonic CMs. These cells lack well defined cellular edges and mature sarcomeres, which makes it difficult to quantitatively assess contractile functions using traditional edge detection technologies. In addition, hPSC-CMs cultured in traditional glucose rich media lack metabolic and functional maturity, utilizing mainly glycolysis for energy production, similar to the embryonic heart. To address these limitations, we first devised a novel technology to simultaneously quantify hPSC-CMs’ contractile kinetics, force generation and electrical activities at the single cell resolution. This methodology allowed us to examine the impact of energy substrates and metabolic pathway utilization on CM physiology and function. We identified that Hypoxia Inducible Factor 1 alpha (HIF1α) and its transcriptional target Lactate Dehydrogenase A (LDHA) are aberrantly upregulated in hPSC-CMs cultured in traditional glucose rich media. By using small molecules and siRNA, we demonstrated that inhibition of HIF1α/LDHA shifts hPSC-CMs’ metabolism from glycolysis to oxidative phosphorylation, which resulted in improved CM structural and functional maturation. Furthermore, we investigated the energy substrate dependency of hPSC-CMs in response to in vitro hypoxic and ischemia-reperfusion injuries. We observed that hPSC-CMs cultured in glucose rich media lack physiological responses to hypoxic insults. On the other hand, in vitro coverslip ischemia-reperfusion resulted in CM death and apoptosis, independent of glucose cultures. These findings highlighted the importance of bioenergetics in modeling cardiac diseases in vitro and provided us with the basis for a potential drug screening platform using hPSC-CMs.