Inter-species differences in response to hypoxia in iPSC-derived cardiomyocytes from humans and chimpanzees

Despite anatomical similarities, there appear to be differences in susceptibility to cardiovascular disease between primates. For example, humans are prone to ischemia-induced myocardial infarction unlike chimpanzees, which tend to suffer from fibrotic disease. However, it is challenging to determine the relative contributions of genetic and environmental effects to complex disease phenotypes within and between primates. The ability to differentiate cardiomyocytes from induced pluripotent stem cells (iPSCs), now allows for direct inter-species comparisons of the gene regulatory response to disease-relevant perturbations. A consequence of ischemia is oxygen deprivation. Therefore, in order to understand human-specific regulatory adaptations in the heart, and to potentially gain insight into the evolution of disease susceptibility and resistance, we developed a model of hypoxia in human and chimpanzee cardiomyocytes. We differentiated eight human and seven chimpanzee iPSC lines into cardiomyocytes under normoxic conditions, and subjected these cells to 6 hours of hypoxia, followed by 6 or 24 hours of re-oxygenation. We collected genome-wide gene expression data as well as measurements of cellular stress at each time-point. The overall cellular and transcriptional response to hypoxic stress is generally conserved across species. Supporting the functional importance of precise regulatory response to hypoxia, we found that genes that respond to hypoxic stress in both species are depleted for association with expression quantitative trait loci (eQTLs) in the heart, and cardiovascular-related genes. We also identified hundereds of inter-species regulatory differences in our study. In particular, RASD1, which is associated with coronary artery disease, is up-regulated specifically in humans following hypoxia.