CELL-KINETICS OF HEMATOPOIETIC COLONY-FORMING-UNITS IN SPLEEN (CFU-S)IN YOUNG AND OLD MICE

The growth potential of the hemopoietic progenitor cells from young an d old mice is similar. Previous studies of their cell-kinetics showed no significant differences between them when measured by the incorpora tion of tritiated thymidine ([H-3]TdR). A different approach for explo ring stem-cell kinetics in aged animals is provided by another method; the incorporation of bromodeoxyuridine (BrdUrd) during DNA synthesis followed by exposure to near-ultraviolet light (near-UV) kills BrdUrd labelled cells in DNA-synthesis (S-phase). This BrdUfd-near UV cytocid e (BUUV) reveals the size of cycling fractions at the level of hemopoi etic progenitor cells; it also demonstrates the velocity of the cells entering S-phase when cells are labeled by a continuous infusion of Br dUrd by an osmotic pump, followed by an appropriate colony-assay for e ach progenitor cell. We compared the cell kinetics of young and old he mopoietic progenitor cells (CFU-S) by this approach. Osmotic pumps wer e implanted subcutaneously in the backs of young (2 months) and old (2 2 months) male C57BL/6CrSlc mice for 2, 4, 8, 12, and 16 days to conti nuously infuse BrdUrd at a flow-rate of 1 mg/h per kg. Cells were harv ested from femoral marrow of the infused mice, plated in non-coated ba cterial plates, and exposed to a single dose of near-UV at 4000 J/m(2) . After BUUV cytocide, bone-marrow cells were assayed for 8- and 13-da y CFU-S colonies. In the 8-day colonies, the cytocide fraction of CFU- S from young mice increased rapidly, whereas the fraction from old mic e showed flatter curves. Both curves reached a plateau at 52.6% for yo ung, and 43.9% for old mice, and then converged 4 days after labeling. In the 13-day colonies, the curve for the aged was much flatter than that for the young; however, the plateaus in both young and old are si milar, but at much lower values than earlier, i.e. 24.5% and 16.0%, re spectively. The size of the cycling fraction of progenitor cells was c lose in the two groups during the steady-state cell-cycle. However, th e velocity of the cell cycle at a progenitor level was very different, old mice being much slower. Further, within the progenitors, the cell cycle was much slower in the primitive ones and became faster when th e stem cells differentiated into mature progenitor cells. (C) 1998 Els evier Science Ireland Ltd. All rights reserved.