The molecular signature of in vitro senescence in human mesenchymal stem cells

We investigated the molecular characteristics of in vitro senescence in human bone marrow-derived mesenchymal stem cells. After prolonged in vitro expansion, MSCs underwent cellular senescence characterized by growth arrest and distinctive morphological alterations, such as an enlarged and flattened morphology, and SA β-gal activity. Slight reduction in telomere length was observed during 16 population doublings, however, telomere length was maintained much longer length than 4.5 kb, the critical size of the telomere. The expression of p16INK4a was increased during in vitro culture of MSCs and other cell cycle inhibitory proteins, such as p53, p21 and p14 were not increased in Western blot analysis. In whole-transcriptome oligonucleotide microarray analysis between highly proliferative MSCs at early passage and senescent MSCs at late passage, we identified 583 differentially expressed genes by more than two-fold change and paired T-test (P-value <0.05). Gene ontology analysis revealed that genes involved in vacuole, cell death and chromatin assembly were up-regulated in senescent MSCs, and genes involved in cell cycle, DNA repair, cytoskeletal part and DNA metabolism were down-regulated. This study will be valuable in understanding the in vitro senescence of mesenchymal stem cells.