Fig. 1. Senescent features of BMMSCs from patients with MM.

a HC-MSCs were characterized by spindle-like morphology, while MM-MSCs were larger and irregular (40× magnification). b Typical colonies at the third passage in six-well plates are exhibited. c MM-MSCs showed degressive cumulative CFU-F numbers at passages 1, 3, and 5 in comparison with HC-MSCs. d Doubling times of MSCs at passages 1, 3, and 5 were obviously higher in MM patients (n = 15) than of control group(n = 10). e Cell proliferation ability was determined by CCK-8 assay. After the culture period of 7 days, the count of living cells in accordance with the optical density from MM groups were growing more slowly than that from the control group (n = 4). f, g Cell cycle distribution of MSC was determined by flow cytometric analysis. We observed a reduction in S phase and an increase in G₀/G₁ phase for MM-MSC (n = 10) compared to HC-MSCs(n = 5). h, i SA-β-gal was performed to identify the senescent MSCs. The amount of SA-β-gal-positive cells was significantly elevated in MM-MSCs (n = 15) at each time point detection. j–l Expression of senescence-related gene p21 increased in MM-MSC (n = 46), as determined by RT-PCR and western blot. The results are expressed as means ± SD. Compared with HC-MSC, the significance was set as *p ≤ 0.05; **p ≤ 0.01