Lifespan extension and growth kinetics in response to continuous mTOR inhibition varies among different BM-MSC samples.

(A) Cumulative population doubling (PD) curves of BM-MSC samples derived from 5 healthy young donors (BM09, BM12, BM13, BM16 and BM18) until replicative arrest in control conditions (DMSO) or in the continuous presence of rapamycin (RAPA). Each symbol represents a passage of rapamycin-treated (triangle) and untreated (dot) cells. The passage when untreated BM09, BM13, BM16 and BM18 samples entered replicative senescence while the corresponding rapamycin-treated cells continue to proliferate is referred to as the “deviation passage” and is indicated by an arrow. Since rapamycin had no impact on lifespan extension of BM12, no “deviation passage” was assigned for this sample. (B) PD time (PDT) of BM-MSC samples at each passage in control conditions (dot) or in the continuous presence of rapamycin (triangle). (C) Cumulative PD curves of BM09 in which rapamycin was removed (RAPA removal) until cells ceased growth and then replaced in culture medium (RAPA replacement). Each dot represents a passage of cells. Data shown in panels A to C are representative of results from at least two independent experiments.