Effects of dietary restriction on hematopoietic stem-cell aging are genetically regulated

Abstract

Diminished stem-cell functions with age may be a major cause of anemias and other defects. Unfortunately, treatments that increase stem-cell function can also increase the incidence of cancers. Lifelong dietary restriction (DR) is known to decrease spontaneous cancers and lengthen lifespan. This study examines the effect of DR on the ability of bone marrow cells to repopulate irradiated recipients and produce erythrocytes and lymphocytes. In BALB/cByJ (BALB) mice, repopulating abilities decline with age; DR ameliorates this trend. In C57BL/6J (B6) and (BALB x B6) F1 hybrid (F1) mice, repopulating abilities increase with age; DR maintains this increase. Hematopoietic stem cell (HSC) numbers are highly variable in aged BALB mice; however, the observed loss of marrow function results from a major loss in repopulating ability per HSC. DR greatly ameliorates this loss of function with age. In contrast, function per HSC in B6 mice is affected neither by age nor by DR. Thus, DR increases or maintains increased marrow repopulating ability with age in the 3 different genotypes tested, but effects on function per HSC depend on genotype. That DR increases or maintains stem-cell function with age, while decreasing cancer, has far-reaching health implications.

Figure 1

Determining the frequencies of hematopoietic precursors in BALB and B6. The BMCs from old and young, DR- and AL-fed BALB mice were analyzed by 2 different flow criteria. (A) The gates used in the SP + Kit criterion, first gating for the Hoechst double low fluorescence side population,^,,, and then for c-kit⁺. (B) The series of gates (lin⁻, c-Kit⁺, Sca-1⁻, CD34^±, CD135^±) used in the mKSL criterion to determine LT-HSC, ST-HSC, and MPP subpopulations. (C) How the same mKSL criterion was used on B6 mice to determine the numbers of precursors.

Figure 2

BALB: Effects of DR and age on in vivo functional abilities of BMCs and numbers of HSCs. BMCs from young AL, young DR, old AL, and old DR, female BALB (Gpi1^a) mice were each mixed 1:1 with BMCs from a standard competitor pool of young female congenic BALB (Gpi1^b) mice. This mixture was injected intravenously into lethally irradiated young female BALB recipients. Donor (Gpi1^a) contributions to erythrocytes and lymphocytes in the peripheral blood of replicates were averaged 6 months after transplantation. A total of 3-9 young AL, old AL, or old DR donors were used over the course of 3 experiments. (A) Total marrow functional ability based on the average composition of erythrocytes and lymphocytes (E & L). (B) Total marrow functional ability expressed in repopulating units. (C) Numbers of LT-HSCs present in the original donor marrow using the mKSL flow criterion. Counts from young DR were not available (**P < .01; ***P < .001). (D) Functional ability per LT-HSC in the subset of animals using mKSL flow criterion (*P < .05; **P < .01). (E) Numbers of HSCs present in the original donor marrow using the SP + Kit flow criterion. Counts from young DR were not available. (F) Functional ability per HSC in the subset of animals using the SP + Kit flow criterion (**P < .01). Functional ability of old AL versus others in panel A is significant (P < .001). Error bars represent SE.

Figure 3

B6: Effects of DR and age on in vivo functional abilities of BMCs and numbers of LT-HSCs. (A) Total marrow functional ability based on the average composition of erythrocytes and lymphocytes. (B) Total marrow functional ability expressed in repopulating units. (C) Numbers of LT-HSCs present in the original donor marrow using the mKSL criterion (*P < .05; ***P < .001). (D) Functional ability per LT-HSC in animals using the mKSL criterion (**P < .01). Assays were conducted as described in the legend to Figure 1, except that donors and recipients were B6 Gpi1^b and competitors were B6 Gpi1^a. A total of 5-7 donors of each type was used over the course of 2 experiments. Old versus young functional ability in Figure 3A was significant at P < .001. Error bars represent SE.

Figure 4

(BALB × B6) F1: Effects of DR and age on in vivo functional abilities of BMCs. (A) Total marrow functional ability based on the average composition of erythrocytes and lymphocytes. (B) Total marrow functional ability expressed in repopulating units. Assays were performed as described in the legend to Figure 1, except that recipients and donors were (BALB × B6) F1 hybrids with Gpi1^a/b and Gpi1^a competitors. A total of 3 to 5 donors was used for each type. Old versus young were significantly different (P < .01). Error bars represent SE.

Figure 5

Multilineage repopulation 6 months after transplantation. Data are analyses of the ratios of percentage donor erythroid cells/percentage donor lymphoid cells (E/L) in CRA recipients of BMCs from the same donors examined in Figures 1–3 (*P < .05; **P < .01). Error bars represent SE.