Adult mesenchymal stem cells (MSCs) hold great promise for the repair of heart defects. Both bone marrow-derived mesenchymal stem cells (BMSCs) and adipose tissue-derived stem cells (ASCs) are multipotent and may be induced by 5-azacytidine to differentiate into cardiomyocytes. However, the differentiation potential of human MSCs into sinus node-like cells has not been studied extensively. The aim of this study was to analyze the differences in proliferation and phenotype of ASCs and BMSCs from the same donors and to evaluate their capacity to differentiate into sinus node-like cells in vitro. Five passaged cells from bone marrow and adipose tissue were treated with 10 µM 5-azacytidine for 48 h and further cultured in complete medium for 4 weeks. A comparative study of cultured ASCs and BMSCs was carried out, and the morphological parameters, proliferative capacity, expression of surface markers and differentiation potential to sinus node-like cells were characterized. No morphologic differences were observed between ASCs and BMSCs. Flow cytometric analysis revealed that ASCs and BMSCs both expressed CD29, CD44, CD90 and CD105 and did not express CD34 and CD14, while CD49d, CD106 and CD34 were differentially expressed. Growth curves and doubling time determined with the Cell Counting Kit-8 (CCK-8) demonstrated that ASCs had a stronger proliferative ability than BMSCs. Histological immuofluorescence staining suggested that ASCs and BMSCs were capable of differentiating into sinus node-like cells and that the positive expression ratios of cTNI were higher in ASCs compared to BMSCs at 4 weeks. Expression of the HCN2 and HCN4 genes was detected by reverse transcriptase polymerase chain reaction, and the results revealed that the expression of the HCN genes appeared earlier in ASC-derived sinus node-like cells. ASCs expressed HCN2 and HCN4 shortly after induction with 5-azacytidine for 2 weeks, although BMSCs expressed these genes after 4 weeks. The expression levels of HCN2 and HCN4 mRNA in ASC-derived cells were higher compared to those of BMSCs at 4 weeks. In conclusion, ASCs may be a better candidate as a novel source of cell therapy in sinus bradycardia disorders than BMSCs.

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