Background Mesenchymal stem cells(MSC) were reported to differentiate into cardiomyocytes(CMC) in vivo when injected to rat myocardium. However, the mechanism of differentiation of MSC is obscure. A few in vitro data suggested MSC-CMC cell-cell interaction be of the essence in differentiation. We hypothesized that infarcted myocardial protein and oscillating pressure may induce differentiation of human MSC without cell-cell interaction.
Methods and Results We cultured MSC from human cord blood(Medipost Inc) in oscillating pressure chamber(150 to 10 mmHg, 150 cycles/min) under the condition of mixture of rat serum with protein purified from myocardium with or without infarction. Both immunostaining for Cx43, and troponin-T(T-T) and RT-PCR for α-MHC, β-MHC, Cx43, GATA4, T-T, MEF_2c, ANP, and GAPDH were done at 7th and 14th day. We changed the culture conditions of MSC with cross-combination of the following environments:1)normal myocardial protein or serum 2)infarcted myocardial protein or serum, and 3)in pressure chamber or not. MSC cultured with normal serum did not express the cardiac markers, and those with normal myocardial protein showed T-T, GATA4, and ANP very weakly. With addition of pressure chamber to previous milieu, there was additional expression of β-MHC and Cx43. With infarcted myocardial protein, MSC expressed all cardiac markers except α-MHC, to which condition the addition of pressure chamber induced all cardiac markers strongly. MSC expressed Cx43 and T-T in immunocytochemical staining also. To reveal the underlying intracellular signaling pathway of CMC differentiation, several candidate signaling pathways such as GSK-βcatenin, PKC, p38MAPK, JNK, ERK and PI3K were investigated. When SB for p38MARK and DMAP for JNK added to the culture media, the expression of cardiac markers was suppressed, whereas GSK, PKC, ERK and PI3K inhibition did not altered the differentiation of MSC.
Conclusions Infarcted myocardium and oscillating pressure can induce the differentiation of MSC into CMC in the absence of cell-cell interaction, which suggests that biochemical and mechanical factors through p38MAPK and JNK pathway are essential for stem cell differentiation.
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