Evidences for age-related modulation of human hematopoietic progenitor cell proliferation

In order to identify hints of ageing in circulating hematopoietic stem cells (HSCs), putative senescence markers like the cellular level of carbonyl-modified proteins and senescence associated beta-galactosidase activity were measured. Furthermore, the number of HSCs in the periphery and their proliferative capacity in vitro were analyzed in buffy coats of fifty five individuals: 27 young [age, 19-43 years; mean age 31] and 28 middle-aged individuals [age, 45-66 years; mean age 56]. The effect of humoral factors on cell proliferation in culture was studied by expansion of the cells in the presence of plasma pools from children and elderly donors. Using a multiplex flow cytometry method, the plasma pools used in the proliferation experiments were assayed for the presence or absence of 25 chemokines. Within the age range analyzed, no age-dependent differences in the number of isolated CD34(+) cells were found. Both sources of progenitor cells were able to reach comparable cell density in culture, but cells from the middle-aged subjects proliferated only sufficiently in the presence of plasma obtained from older donors. Cells from middle-aged donors exhibited elevated levels of carbonyl-modified proteins and showed increased beta-galactosidase activity in comparison to the cells from young donors. Our study shows that although two markers of ageing i.e. carbonylated proteins and senescent associated beta-galactosidase activity are increased in HSCs from middle-aged donors, the number and proliferative capacity of HSCs are still maintained.