Stem cell laboratory

Availability of pluripotent human cells may open new strategies for the treatment of a range of diseases and disorders. Human embryonic stem cells are pluripotent and therefore, can serve as promising cell sources in cell transplantation therapies. However, human embryonic stem cells are critical to be used due to the relevant legal and ethical considerations regarding the usage of human embryos and the problem of tissue rejection after transplantation. These concerns may be overcome if pluripotent stem cells can be directly derived from somatic cells of patients. The aims of our research group are the generation of pluripotent stem cells and cardiomyocytes from human somatic cells in order to investigate the molecular mechanisms of heart development and cardiovascular diseases, lastly discovering new drugs and establishing cell-based therapies for heart regeneration.

Research focus
Reprogramming of human fibroblasts, keratinocytes, mesenchymal stem cells and blood cells into pluripotent stem cells
Induced pluripotent stem cells (iPSCs) have been generated from mouse and human somatic cells by overexpression of the four ‘Yamanaka’ factors (Oct4, Sox2, c-Myc, and Klf4) or another set of factors (Oct4, Sox2, Nanog and Lin28) using a lentiviral system. In our lab, we generated iPSCs from different human somatic cells (fibroblasts, keratinocytes, mesenchymal stem cells and blood cells) and compared their reprogramming efficiency and differentiation potentials. Although the reprogramming efficiency through the lentiviral system is very high, their application in cell-based therapy is hurdled due to their potential risk of activating proto-oncogenes. Currently we are working on the generation of transgene-free iPSCs.

Induction of pluripotency in spermatogonial stem cells
In 2006, we reported that unipotent male germline stem cells derived from the adult mouse testis, so called spermatogonial stem cells (SSCs), could be induced into pluripotent stem cells under in vitro culture conditions. We are using this mouse SSC system to obtain a better understanding of the molecular mechanisms controlling the induction of unipotent germline stem cells into pluripotent stem cells. This will help us to converse human SSCs into pluripotent stem cells.

Differentiation of pluripotent stem cells into functional cardiomyocytes
The generation of a large number of functional cardiomyocytes would be one of the prerequisites for cell-based heart regeneration therapy, e.g. after myocardial infarction. Recently, different protocols for differentiation of human pluripotent stem cells into functional cardiomyocytes have been reported. However, many of them are cell line-specific. Currently, we are working on the establishment of optimized protocols for the generation of a large amount of cardiomyocytes from patient-specific iPSCs. The development of strategies involved in the selection and purification of cardiomyocytes is one of our focuses. In addition, we are working on induction of maturation of cardiomyocytes in vitro.

Cardiovascular disease modeling using iPSCs
Genome wide association studies indicate that cardiovascular diseases can be caused by monogenic defects in genes encoding for cytoskeletal, contractile, nuclear membrane, calcium-regulating, and ion channel proteins. Over the past years, many different animal models have been generated for studying cardiovascular diseases, which have shed light on our understanding of the onset, development and progression of the diseases. However, animal models alone are often inadequate representations of human diseases due to genetic and physiological differences. The human iPSC technology allows us modeling a disease in a culture dish, which is based on the their unique capacity, similar to human embryonic stem cells, to continuously self-renew and to give rise to all cell types in the human body. Generation of patient-specific cardiomyocytes from iPSCs allows us gaining deeper insights into the actual genetic and signaling mechanisms, which play important roles in the development of the heart, in heart failure and in arrhythmias. With the establishment of a platform based on patient-specific cardiomyocytes, we furthermore facilitate the identification of therapeutic targets as well as preclinical drug screenings for an individualized treatment of cardiovascular diseases.

Direct Reprogramming of somatic cells to cardiac cells
The above mentioned studies on generation of iPSCs point out the possibility of regenerating tissues by first reverting adult somatic cells to pluripotent stem cells and then by differentiating these cells into various cell types. Alternatively, it should be possible to convert one cell type into another directly, without the need to first revert the cell to a pluripotent state. Previous studies have shown that primary dermal fibroblasts can be converted into skeletal muscle-like cells by forced expression of MyoD, a master regulatory factor of myogenesis. Recent studies have shown that a specific combination of three transcription factors (Ngn3, Pdx1 and MafA) can reprogram differentiated pancreatic exocrine cells in adult mice into cells that closely resemble beta cells. These data suggest a general paradigm for directing cell reprogramming without reversion to a pluripotent stem cell state. We are interested in direct reprogramming of human somatic cells into cardiac cells by the combination of several cardiac-specific factors, for example in order to obtain new insights regarding the cell-based heart regeneration therapy.

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