Serial depletion and regeneration of the murine hematopoietic system. Implications for hematopoietic organization and the study of cellular aging

Abstract

The mouse hematopoietic system was subjected to repeated depletion and regeneration either by serial transfer of bone marrow cells through lethally irradiated recipients or by repeated treatment with the cycle-active drug hydroxyurea (HU). The capacity of surviving stem cells to proliferate and self-renew was assayed at intervals by two methods: (a) the spleen colony method; and (b) competitive repopulation of irradiated recipients using chromosome markers, with normal bone marrow cells as an internal control. The progressive decline in stem cell function that occurred during serial transfer of bone marrow and that had already begun after a single transfer was not seen during HU treatment; up to 25 pairs of HU injections given over more than 1 yr had no discernible effect on the number of stem cells present 3 wk after the final injection or on their capacity to self-renew. Within 2 d after exposure to HU, the average self-renewal capacity of surviving stem cells was enhanced. This implies that the drug selectively eliminates poorly self-renewing stem cells and hence that these enter cycle more readily than stem cells with a high self-replicative potential. However, the fact of being in cycle at the time of injection did not of itself affect self-renewal. The results show that serial transfer of bone marrow is not a valid method for studying clonal aging phenomena because it does not fulfill the assumptions on which such studies are based. No evidence was obtained for any intrinsic limitation in the capacity of bone marrow populations for repeated regeneration after HU-induced depletion. However, this does not necessarily imply that individual hematopoietic clones are capable of indefinite expansion because hematopoiesis may (as suggested by the relative resistance of highly self-replicative stem cells to mitogenic signals) proceed on the basis of clonal succession.

Studies of hematopoietic stem cells spared by 5-fluorouracil.

“…Both this population and that remaining after the selective killing of cells synthesizing DNA had an AI close to 1. This is consistent with the findings of Ross et al (8) showing that the proportion of cycling CFU-S does not necessarily reflect the proportion of the CFU-S subset with elevated proliferative capacity.…”

“…Recent studies have shown that the capacity of the stem cell compartment to restore hematopoiesis in irradiated mice is not compromised either during aging of the animal (21) or after 'aging' simulated by repetitive rounds of proliferation caused by repeated hydroxyurea injections (8). In fact, in both studies, old stem cells were more effective than young stem cells in restoring hematopoiesis.…”

Effect of chemotherapy for acute myelogenous leukemia on hematopoietic and fibroblast marrow progenitors

“…3,40 Ectopic transplantation of individual fibroblastic clones grown in vitro from mouse marrow beneath the renal system to recover to a normal level. 28 In our study population, we could demonstrate CFU-GM, but not LTC-IC capsule of syngeneic hosts demonstrated that approximately 15% produced a marrow organ containing the full spectrum regeneration. The persistent derangement of the LTC-IC compartment associated with a normal CFU-GM incidence of stromal cell types of the hematopoietic microenvironment.…”

Extensive in vivo self-renewal, long-term reconstitution capacity, and hematopoietic multipotency of Pax5-deficient precursor B-cell clones

“…The one, short-term HSC (ST-HSC), possesses limited self-renewal potential, pluripotency, and only short-term reconstitution capacity, while the other, long-term HSC (LT-HSC) has long-term selfrenewal and hematopoietic reconstitution capacity. 6 While HSCs have been found to persist throughout life in almost constant numbers, 7,8 and while 3 to 5 consecutive transplantations of HSCs into lethally irradiated hosts have suggested that they might undergo 80 to 200 divisions, [9][10][11][12][13] their in vitro capacity for selfrenewal appears limited to about 20 cell divisions. 14 Therefore, the self-renewal capacity of LT-HSCs appears to be strongly dependent on conditions, which can be provided by the host in vivo, but are insufficient with current in vitro culture conditions.…”