The aging effect of chemotherapy on cultured human mesenchymal stem cells

Various agents, including chemotherapeutic drugs, can induce cell senescence. However, the mechanisms involved in the aging pathway, particularly the stress that chemotherapy imposes on telomeres, are still undefined. To address these issues, human mesenchymal stem cells (MSCs) were assessed as target cells to investigate the initiation of the aging process by chemotherapy. The MSCs were obtained from bone marrow (BM) cells from normal adults and grown in the presence of platelet lysates. Cultured MSCs were identified for immunophenotype, and for growth and differentiation properties. The MSCs were exposed to 10 nM doxorubicin and 500 ng/mL etoposide, sublethal doses that induce DNA double-stranded breaks. Telomere length (TL) was assessed by flow-fluorescence in situ hybridization and Southern blotting. Initial TL shortening was detectable in MSCs at 5 days after drug exposure, with progressive reduction compared with untreated cells at 7, 14, 21, and 28 days in culture. After a single exposure, MSCs were unable to regain the lost telomere sequences for up to 28 days in culture. The ATM phosphorylation was documented early after drug exposure, while no telomerase activation was observed. Chemotherapy-induced TL shortening was associated with reduced clonogenic activity in vitro and accelerated adipose differentiation. Analogous behavior in the differentiation pattern was observed in naturally aged MSCs. These results indicate that cultured MSCs represent a useful cellular model to investigate novel drugs that may favor or, conversely, might prevent TL loss in human stem cells. The TL shortening is a permanent signature of previous chemotherapy-mediated DNA damage, and predicts impaired proliferative and differentiation potential.