Exposure to cardiomyogenic stimuli fails to transdifferentiate human umbilical cord blood-derived mesenchymal stem cells

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Abstract
The ability of human umbilical cord blood-derived mesenchymal stem cells (UCBMSCs) to transdifferentiate towards cardiomyocytes remains unclear. The aim of this study was to direct UCBMSCs to the cardiac lineage by exposure to: (1) 5-azacytidine (AZ) or dimethyl sulfoxide (DMSO); (2) a combination of growth factors involved in early cardiomyogenesis (BMP-2 + bFGF + IGF-1); (3) the Wnt signaling activators lithium chloride (LiCl) and phorbol-12-myristate-13-acetate (PMA); and (4) direct contact with neonatal rat cardiomyocytes. Expression of cardiomyocyte-specific proteins and β-catenin were assessed by quantitative RT-PCR, immunofluorescence and Western blot. Cocultures of human UCBMSCs with neonatal rat cardiomyocytes were also analyzed for the presence of calcium oscillations and changes in electrical potential using Fura Red and di-4-ANEPPS confocal imaging, respectively. Induction of cardiac-specific proteins was not detected in 5-AZ- or DMSO-treated cells. Following DMSO addition, β-catenin cytoplasmic expression increased, but did not translocate into cell nuclei to promote cardiac gene activation. Likewise, neither co-stimulation with BMP-2 + bFGF + IGF-1, nor exposure to LiCl and PMA resulted in the acquisition of a cardiac phenotype by UCBMSCs. Direct contact with neonatal rat cardiomyocytes promoted neither the expression of cardiomyocyte-specific proteins, nor the presence of calcium rhythmic oscillations and potential-dependent fluorescence emission in UCBMSCs. The cardiomyogenic stimuli investigated in this study failed to transdifferentiate human UCBMSCs. Alternative strategies or regulatory factors and signaling pathways may be better suited to recruit UCBMSCs into cardiac cell lineage.

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