Stem Cell-Based Cardiac Ischemia Model

Ischemic heart disease is the most common cardiovascular disease and causes more deaths and morbidity than any other disease. A lot of effort has been put into research of drugs and treatments for alleviating the ischemia-reperfusion injury and for minimizing the infarct size after reperfusion. However, most of the research has been conducted in different animal models and reproducing the results in human has proven difficult. Difference in physiology and disease mechanism stemming from the species difference has been suggested as one reason for the failure. Thus, human based models are needed.

The main aim of this dissertation was to establish a human based model of cardiac ischemia-reperfusion. Human adult cardiomyocytes are difficult to acquire due to invasive harvesting, but human induced pluripotent stem cells (hiPSC) can be endlessly differentiated into cardiomyocytes (CM), providing an unlimited source of human cardiomyocytes. Nevertheless, hiPSC-derived CMs (hiPSC-CMs) are developmentally immature resembling more foetal than adult CMs hindering their utilization in several applications. Especially the metabolic immaturity has been suggested to make hiPSC-CMs resistant to hypoxia induced injury limiting their use in modelling cardiac ischemia- reperfusion. Despite the immature phenotype, hiPSC-CMs have recently been utilized in modelling myocardial ischemia-reperfusion. However, these studies have focused on cell viability and molecular markers of hypoxia and cell injury, but the functional responses have been significantly less characterized.

The first study of this dissertation focused on inducing maturation of the hiPSC-CMs by culturing them on polyethylene terephthalate textiles, which was observed to improve structural maturation of the CMs. In addition to topographical cues, coculture with other cell types is known to improve hiPSC-CM maturation. Furthermore, cardiac function is tightly regulated by cardiac autonomic nervous system (cANS), which is also known to contribute to ischemia-reperfusion injury and related arrhythmias. Thus, the second study of this thesis focused on establishing a cardiac innervation model, which in the future could be used in studying the effect of cANS to the ischemia- reperfusion injury and its treatments. In the third and fourth study of this dissertation, cardiac ischemia and reperfusion were modelled by inducing hypoxia and reoxygenation to hiPSC-CMs. As electrophysiology is an important aspect of CM function and contraction, microelectrode array technology was used to capture the electrophysiological responses of the hiPSC-CMs to different oxygen conditions and the observed changes were compared to the electrophysiological changes known to occur in adult CMs during ischemia and reperfusion.

The results presented in this dissertation show that hiPSC-CMs have potential as a cell model of cardiac ischemia-reperfusion. The platform utilized for inducing hypoxia and reoxygenation to the hiPSC-CMs allows the use of extensive set of methods for thorough characterization of the hiPSC- CM response to the ischemic insult. Furthermore, the incorporated continuous measurement of oxygen partial pressure further improves the understanding of the cellular responses to hypoxia and reoxygenation and allows the validation of specific oxygen conditions experienced by the cells. The platform for the ischemia modelling could be utilized with the presented cardiac innervation model, which would allow the modelling of the cANS in ischemia-reperfusion and be the next step for in vitro ischemia modelling.