To be able to conduct our functional and applied science projects, we have been developing additional tools. For instance, we have established a chemically defined culture system termed FTDA, for growing and expanding hPSCs in an undifferentiated state (see figure). Moreover, we have set up methodology for either disrupting or overexpressing genes in hPSCs in a controlled manner. Furthermore, we have devised a directed differentiation protocol for converting the undifferentiated hPSCs into cardiomyocytes at a high efficiency. This procedure is a key platform for our work in the lab. Currently, we are focusing on ways to improve the handling and maturation of the hPSC-derived cardiomyocytes for downstream applications.
Our previous and ongoing research shows that the human pluripotent stem cell state is metastable meaning that in the absence of self-renewal promoting factors, the cells would differentiate into default fates.
Key roles in sustaining self-renewal are played by the FGF and Activin pathways, as they actively sustain the undifferentiated state and/or specifically inhibit neuroectodermal differentiation (see figure). By contrast, the induction of a cardiac fate requires additional input by the WNT and BMP pathways, as well as further manipulations downstream. Interestingly, the extrinsic factors that need to be applied here tend to mimic signals operating during early mammalian development, and the genes that become activated in response to this are key players orchestrating gastrulation in vivo. Hence, this system presents an excellent model for studying early human development - in the culture dish. In the lab, we have started to functionally analyze the intriguing process of undifferentiated hPSCs giving rise to spontaneously contracting cardiomyocytes.
Our approach shows that molecular investigation of hPSCs may result in improved differentiation protocols and so, we also seek to employ our procedure for applied purposes. For example, heart muscle cells may be derived from wild-type hPSCs to then serve as a test system for detecting cardiotoxic side-effects of drugs (see figure). Alternatively, hPSCs may be generated from patient cells such as fibroblasts derived from a skin punch biopsy. We have generated such patient-specific hiPSCs from individuals suffering from rare genetic heart diseases. Because a given disease-causing mutation will still be present in the hiPSCs generated as well as in their differentiated progeny, hiPSC-cardiomyocytes may be utilized to recapitulate the disease at the cellular level. Through electrophysiological as well as molecular analysis, we could indeed show that the cellular disease phenotypes match to those seen in the patient. Hence, patient-specific hiPSC-cardiomyocytes may be used to identify and evaluate drugs that may balance the disease phenotype such as, for instance, stress-induced arrhythmia.