MicroRNA Regulation of Cellular Senescence in Human Adult Stem Cells

In most clinical applications, human mesenchymal stem cells (hMSCs) are expanded on a large scale before administration. However, prolonged in vitro culture of hMSCs results in cellular senescence with loss of capabilities and therapeutic potential. MicroRNAs (miRNAs) are small non-coding RNAs that regulate diverse biological processes by repressing gene expression at post-transcriptional levels. To determine the functions of miRNAs regulating cellular senescence in hMSCs, we deleted DGCR8 encoding a RNA binding protein essential for miRNA processing. Interestingly, DGCR8 knockdown in early-passage hMSCs resulted in severe proliferation defects with senescence-associated changes, namely increased levels of p21 expression and senescence-associated b-galactosidase activity. Furthermore, reactive oxygen species levels greatly increased in DGCR8-depleted hMSCs. In addition, a subset of miRNAs predicted to target p21 was significantly downregulated in both DGCR8-knockdown hMSCs. Taken together, our results indicate that miRNA depletion in hMSCs leads to an early onset of cellular senescence. Therefore, miRNAs are essential for preventing cellular senescence in hMSCs.