Employing the influence of endodermal cells on proliferation and differentiation of cardiomyocytes for cell therapy of the myocardium

Heart attacks and a variety of aquired and congenital cardiomyopathies are immense medical threats and a considerable socio-economic burden. These diseases lead to partial loss of myocardium which can not regenerate due to blocked reentry into the cardiomyocyte cell cycle. Heart repair by cell therapy seems to be an feasible alternative to heart transplantations. Embryonic stem cell derived cardiomyocytes are fully differrentiated and remain in the cell cycle for quite some time, thus showing perhaps the way how to keep differentiated human cardiomyocytes replicating in culture and in infarcted zones of the heart. Replication of cardiomyocytes is positively influenced by a factor secreted from parietal endoderm in a leukemia inhibitory factor (LIF) independent pathway. This project focuses on the influence of factors secreted by endodermal cells on maintenance of the proliferating and differentiated state of cardiomyocytes. Here we propose to identify this endodermal factor and a LIF/LIFR independent signaling pathway sustaining cell division in differentiated cardiomyocytes and to establish conditions for the therapeutical culture of differentiated and proliferating cardiomyocytes.

This project focused on the paracrine influence of extra-embryonic endoderm secreted factors on early in vitro cardiomyogenesis to understand the molecular cues inducing and guiding the early development of cardiomyocytes and to provide concepts for generation and maintenance of cardiomyocytes for future cell therapy of the heart. We identified Secreted-Protein-Acidic-Rich-in-Cysteine, SPARC, and S100A4 as new factors expressed in parietal endoderm cells which significantly influence signal transduction, transcription of cardiac specific genes, and the development of early cardiomyocytes. Further we demonstrated that isogenic embryonic stem cells differentially express the leukaemia inhibitory factor receptor gene, due to epigenetic variations already evident in the inner cell mass. These variations predispose the cardiomyogenic potential of embryonic stem cell lines in a janus-activated- kinase dependent manner. These results provide new insights in the complex regulatory network guiding cardiomyogenesis, demonstrate that in vitro differentiation of embryonic stem cells partially recapitulates early embryogenesis, and foster efficient in vitro differentiation of cardiomyocytes for myocardial cell therapy.