Major Age‐Related Changes Of Mouse Hematopoietic Stem/Progenitor Cells

Abstract

To study age-related changes of mouse bone marrow (BM) cells and hematopoietic stem cells (HSCs), we isolated rhodamine-123(low) (Rh(low)) Thy1.1(low) Lin(-)Sca-1(+) (TLS) HSCs from the BM of old mice and compared their functional characteristics to cells of the same phenotype isolated from young mice. We observed impaired recovery of B lymphocytes and decreased self-renewal in recipients of old Rh(low) cells compared to young Rh(low) cells. Blockade of Rh efflux using verapamil improved lymphoid reconstitution by enriched HSCs, and isolation of aged HSCs based on efflux of a fluorescent multi-drug resistance (MDR) substrate (Bodipy-verapamil) resulted in enrichment of HSC activity equivalent to that obtained with Rh. These observations suggest a complex relationship between MDR activity and HSC function during aging. To address whether the difference between young and aged donors was intrinsic to the HSC compartment or was due to a shift in HSC phenotype, we co-transplanted normal BM derived from young or old donors and followed repopulation simultaneously in the same recipient animals. In a parallel experiment, we co-transplanted HSCs purified from old donors with BM derived from young donors. In both experiments, transplants were given to both young and old recipients. The results show a clear defect in B-cell engraftment from either BM or HSCs of old donors, irrespective of the age of the recipient. In contrast, myeloid engraftment was predominantly derived from BM or HSCs derived from aged donors, again irrespective of recipient age. These data suggest a stem cell basis for B-cell immuno-senescence and the increased incidence of myelocytic leukemia in elderly people.

Epigenetic regulation of aging stem cells

“…Early studies comparing HSC number in short-and long-lived mouse strains using in vitro cobblestone-forming assays reported an age-dependent decrease in HSC number in short-lived mouse strains (CH3/He, CBA/J and DBA/2), but an increase in HSC number in the longlived C57BL/6 mouse strain (de Haan et al, 1997;de Haan and Van Zant, 1999). Likewise, quantification of HSCs by fluorescence-activated cell sorting (FACS) using cell surface markers indicate that the frequency of cells expressing stem and progenitor markers (KLS; c-Kit þ , Lin À , Sca1 þ ) increases with age in C57BL/6 mice (Sudo et al, 2000;Kim et al, 2003;Rossi et al, 2005;Pearce et al, 2007). The observed increase in HSCs with age is due to specific expansion of the HSC compartment capable of long-term reconstitution of the hematopoietic system in a recipient mouse, termed LT-HSCs (Rossi et al, 2005;Chambers et al, 2007;Pearce et al, 2007).…”

“…HSCs isolated from older mice show defects in mobilization and homing to bone marrow (Morrison et al, 1996;Kim et al, 2003;Liang et al, 2005;Xing et al, 2006). In competitive transplantation assays, a rigorous test for both self-renewal and multipotency during which donor HSCs are co-injected with wild-type bone marrow and assessed for their ability to regenerate all blood lineages, aged HSCs shows defect in long-term reconstitution of the immune system (Sudo et al, 2000;Kamminga et al, 2005;Rossi et al, 2005;Chambers et al, 2007).…”

“…In competitive transplantation assays, a rigorous test for both self-renewal and multipotency during which donor HSCs are co-injected with wild-type bone marrow and assessed for their ability to regenerate all blood lineages, aged HSCs shows defect in long-term reconstitution of the immune system (Sudo et al, 2000;Kamminga et al, 2005;Rossi et al, 2005;Chambers et al, 2007). Aged HSCs also give rise to more cells of myeloid lineage at the expense of lymphoid fates (Sudo et al, 2000;Kim et al, 2003;Rossi et al, 2005;Cho et al, 2008;Guerrettaz et al, 2008). This myeloid bias in aging HSC populations has been explained by alterations in the subcomposition of the HSC pool, which is thought to contain clones with pre-determined differentiation bias (Dykstra et al, 2007;Cho et al, 2008;Beerman et al, 2010a;Morita et al, 2010).…”

Cell intrinsic and extrinsic mechanisms of stem cell aging depend on telomere status

“…One hallmarks of HSC aging is the skewing of hemato-/lymphopoiesis (decreased lymphopoiesis and increased myelopoiesis) occurring during human and mouse aging (Kim et al, 2003;Morrison et al, 1996;Rossi et al, 2005;Sudo et al, 2000). The skewing of hemato-/lymphopoiesis occurs in aging wild type mice and in Terc-/-mice with dysfunctional telomeres (Rossi et al, 2005;Rudolph et al, 1999;.…”

Unraveling the complex regulation of stem cells: implications for aging and cancer

“…In the hematopoietic system, we and others have shown that both quantitative and qualitative changes do occur in the stem cell population with age. [20][21][22][23][24] Further, in mice, the extent of the aging of HSCs is strain dependent, highlighting the importance of genetic influences on the aging process. [25][26][27][28] In addition to the genetic factors regulating stem cell aging, it is likely that epigenetic changes in chromatin structure play important roles in regulating gene transcription and thus influence the aging process.…”