| Summary: | 碩士 === 國立陽明大學 === 臨床牙醫學研究所 === 99 === Mesenchymal stem cell is one specific type of adult stem cells, which can be isolated from bone marrow or dental pulp, cultured expansion in vitro, and have the ability to differentiate into multiple lineage of cells and tissues. Owing to being easily obtained and isolated, expanded in culture to a very high number, and lack of adverse effects in clinical applications, MSCs are now applied in a variety of cell therapies. However, entering the senescence state decreases the proliferation rate and restricts the culture expansion of MSCs. In order to improve the efficiency of MSCs in clinical applications, we therefore went further to explore the mechanism of MSCs senescence. We compared several gene and protein expressions in early and late passage bone marrow stem cells (BMSCs), and found that Rb and DNMT1 both expressed high in early passage BMSCs and then reduced after expansion. Some previous studies revealed that Rb could stimulate the activity of DNMT1 promoter, and the others showed that the methylation of p21 and p16 (the MSCs senescence gene) would silence the gene and prevent MSCs from entering the senescence stage. To figure out the relationship between Rb, DNMT1 and MSCs senescence, we used siRNA to knockdown Rb in early passage BMSCs, and found that the expression of DNMT1 also declined accordingly. After few passages of expansion, BMSCs with Rb knockdown quickly got into premature senescence stage. On the contrary, transient expression of Rb in late passage MSCs upregulated the expression of DNMT1. Taken together, these studies suggest Rb expressed in early passage MSCs upregulates DNMT1 expression and inhibits senescence in MSCs. In the future, overexpression of Rb in MSCs might be applied to inhibit the expression of senescence genes, and then improve the efficiency of MSCs in clinical use.
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