Introduction: Generation of induced pluripotent stem cells (iPSCs) and their differentiation into cardiomyocytes (CMCs) have created exciting possibilities in cardiac medicine. However, the long-term impact of iPSC-derived CMC implantation on cardiac function remains elusive. After the first month following injection, only less than 10% of the implanted cells remain alive. In contrast, during development mesodermal precursors differentiate into a functional myocardium without substantial cell loss.
Hypothesis: The poor survival of iPSC-derived CMCs is mainly attributable to the lack of evolutionarily determined microenvironment in which the normal differentiation process takes place. Thus, we hypothesize that the embryonic or adult heart-derived extracellular matrix (ECM) provides a better culture environment for CMC differentiation.
Methods: We utilized a highly efficient, viral-free combination of DNA and mRNA transcription factor approach to generate iPSCs and functional CMCs from adult human cells. To analyze CMC contractility, we recorded cultures using both time-lapse and high frame-rate video microscopy. ECM from adult and embryonic chicken hearts was extracted using a high salt/urea protocol, and lyofilized. iPSCs were grown on a variety of substrates, including rehydrated cardiac ECM or electrospinned films. The quality of differentiation was characterized by molecular markers, electron microscopy and tracking beat frequencies.
Results: Heart ECM extracts provide a supportive environment for CMC differentiation. When grown on ECM extracted from adult chicken hearts, the maturation of iPSCs-derived cardiomyocytes exceeds those that were cultured using matrigel environments. For example, in vitro beat rates are higher on heart ECM (Figure, red symbols) than on matrigel (black).
Conclusions: Culture environments containing heart-derived matrix is a promising avenue to improve the quality of iPSC-derived cardiomyocytes.