Influence of in vitro biomimicked stem cell 'niche' for regulation of proliferation and differentiation of human bone marrow-derived mesenchymal stem cells to myocardial phenotypes: serum starvation without aid of chemical agents and prevention of spontaneous stem cell transformation enhanced by the matrix environment.

Niche appears important for preventing the spontaneous differentiation or senescence that cells undergo during in vitro expansion. In the present study, it was revealed that human bone marrow-derived mesenchymal stem cells (hBM-MSCs) undergo senescence-related differentiation into the myocardial lineage in vitro without any induction treatment. This phenomenon occurred over the whole population of MCSs, much different from conventional differentiation with limited frequency of occurrence, and was accompanied by a change of morphology into large, flat cells with impeded proliferation, which are the representative indications of MSC senescence. By culturing MSCs under several culture conditions, it was determined that induction treatment with 5-azacytidine was not associated with the phenomenon, but the serum-starvation condition, under which proliferation is severely hampered, caused senescence progression and upregulation of cardiac markers. Nevertheless, MSCs gradually developed a myocardial phenotype under normal culture conditions over a prolonged culture period and heterogeneous populations were formed. In perspectives of clinical applications, this must be prevented for fair and consistent outcomes. Hence, the biomimetic 'niche' was constituted for hBM-MSCs by cultivating on a conventionally available extracellular matrix (ECM). Consequently, cells on ECM regained a spindle-shape morphology, increased in proliferation rate by two-fold and showed decreased expression of cardiac markers at both the mRNA and protein levels. In conclusion, the outcome indicates that progression of MSC senescence may occur via myocardial differentiation during in vitro polystyrene culture, and this can be overcome by employing appropriate ECM culture techniques.