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Gary Van Zant

Publications and source records attributed to Gary Van Zant.

At least 19 recordsLinked to original sources
PubMed2007

The quantitative trait gene latexin influences the size of the hematopoietic stem cell population in mice.

We mapped quantitative trait loci that accounted for the variation in hematopoietic stem cell (HSC) numbers between young adult C57BL/6 (B6) and DBA/2 (D2) mice. In reciprocal chromosome 3 congenic mice, introgressed D2 alleles increased HSC numbers owing to enhanced proliferation and self-renewal and reduced apoptosis, whereas B6 alleles had the opposite effects. Using oligonucleotide arrays, real-time PCR and protein blots, we identified latexin (Lxn), a gene whose differential transcription and expression was associated with the allelic differences. Expression was inversely correlated with the number of HSCs; therefore, ectopic expression of Lxn using a retroviral vector decreased stem cell population size. We identified clusters of SNPs upstream of the Lxn transcriptional start site, at least two of which are associated with potential binding sites for transcription factors regulating stem cells. Thus, promoter polymorphisms between the B6 and D2 alleles may affect Lxn gene expression and consequently influence the population size of hematopoietic stem cells.

Animals↗
PubMed2006

The impact of altered p53 dosage on hematopoietic stem cell dynamics during aging.

A temporal decline in tissue stem cell functionality may be a key component of mammalian aging. The tumor suppressor p53 has recently been implicated as a potential regulator of aging. We examined age-associated hematopoietic stem cell (HSC) dynamics in mice with varying p53 activities. Reduced p53 activity in p53+/- mice was associated with higher numbers of proliferating hematopoietic stem and progenitor cells in old age compared with aged wild-type (p53+/+) mice. We also assessed HSC dynamics in a p53 mutant mouse model (p53+/m) with higher apparent p53 activity than wild-type mice. The p53 hypermorphic (p53+/m) mice display phenotypes of premature aging. Many aged p53+/m organs exhibit reduced cellularity and atrophy, suggesting defects in stem-cell regenerative capacity. HSC numbers from old p53+/m mice fail to increase with age, unlike those of their p53+/+ and p53+/- counterparts. Moreover, transplantation of 500 HSCs from old p53+/m mice into lethally irradiated recipients resulted in reduced engraftment compared with old wild-type p53+/+ and p53+/- HSCs. Thus, alteration of p53 activity affects stem-cell numbers, proliferation potential, and hematopoiesis in older organisms, supporting a model in which aging is caused in part by a decline in tissue stem cell regenerative function.

Aging↗
PubMed2006

Increased hematopoietic stem cell mobilization in aged mice.

Hematopoietic stem and progenitor cells (HSPCs) are located in the bone marrow in close association with a highly organized 3-dimensional structure formed by stroma cells, referred to as the niche. Mobilization of HSPCs from bone marrow to peripheral blood in response to granulocyte colony-stimulating factor (G-CSF) requires de-adhesion of HSPCs from the niche. The influence of aging of HSPCs on cell-stroma interactions has not been determined in detail. Using a mouse model of G-CSF-induced mobilization, we demonstrated that the ability to mobilize hematopoietic stem cells is approximately 5-fold greater in aged mice. Competitive mobilization experiments confirmed that enhanced mobilization ability was intrinsic to the stem cell. Enhanced mobilization efficiency of primitive hematopoietic cells from aged mice correlated with reduced adhesion of hematopoietic progenitor cells to stroma and with elevated levels of GTP-bound Cdc42. These results might indicate that stroma-stem cell interactions are dynamic over a lifetime and result in physiologically relevant changes in the biology of primitive hematopoietic cells with age.

Aging↗
PubMed2006

Advances in hematopoietic stem cell research through mouse genetics.

PURPOSE OF REVIEW: Successful bone marrow transplantation involves migration of hematopoietic stem cells through the blood, entering the extravascular hematopoietic cords, lodging in the proper niche, and expanding and differentiating to produce large numbers of mature cells -- all without depletion of the stem cell pool. An additional variable in these processes is the age of both the donor bone marrow and the recipient. Basic stem cell biology and transplant biology aim to uncover the molecular mechanisms controlling these processes. RECENT FINDINGS: Mouse genetics is a frequently used tool that allows dissection of individual pathways that influence properties of hematopoietic stem cells. Recently, the conception of a niche has been expanded to include evidence for a vascular and an endosteal niche. Additionally, hematopoietic stem cell interactions within the niche have been further defined, documenting the importance of cell cycle, cell adhesion, response to cytokine stimulation and age-dependent functional changes. A new model for hematopoietic stem cell aging was proposed that supports the hypothesis that stem cell aging is at least partially due to an accumulation of DNA damage leading to exhaustion. SUMMARY: This review focuses on the last year's progress using mouse genetics as a tool to study intrinsic mechanisms of hematopoietic stem cell biology.

Aging↗
PubMed2005

Effects of aging on the homing and engraftment of murine hematopoietic stem and progenitor cells.

To test the hypothesis that aging has negative effects on stem-cell homing and engraftment, young or old C57BL/6 bone marrow (BM) cells were injected, using a limiting-dilution, competitive transplantation method, into old or young Ly5 congenic mice. Numbers of hematopoietic stem cells (HSCs) and progenitor cells (HPCs) recovered from BM or spleen were measured and compared with the numbers initially transplanted. Although the frequency of marrow competitive repopulation units (CRUs) increased approximately 2-fold from 2 months to 2 years of age, the BM homing efficiency of old CRUs was approximately 3-fold lower than that of young CRUs. Surprisingly, the overall size of individual stem-cell clones generated in recipients receiving a single CRU was not affected by donor age. However, the increased ages of HSC donors and HSC transplant recipients caused marked skewing of the pattern of engraftment toward the myeloid lineage, indicating that HSC-intrinsic and HSC-extrinsic (microenvironmental) age-related changes favor myelopoiesis. This correlated with changes after transplantation in the rate of recovery of circulating leukocytes, erythrocytes, and platelets. Recovery of the latter was especially blunted in aged recipients. Collectively, these findings may have implications for clinical HSC transplantation in which older persons increasingly serve as donors for elderly patients.

Age Factors↗
PubMed2005

Regulation of hematopoietic stem cell aging in vivo by a distinct genetic element.

Until recently, stem cells were thought to be endowed with unlimited self-renewal capacity and, thus, assumed exempt from aging. But accumulating evidence over the past decade compellingly argues that a measurable and progressive replicative impairment in the hematopoietic, intestinal, and muscle stem cell activity exists from adulthood to old age, resulting in a decline in stem cell function and rendering stem cell aging as the possible link between cellular aging and organismal aging. By using a previously uncharacterized congenic animal model to study genetic regulation of hematopoietic stem cell aging, we have demonstrated definitively that a locus on murine chromosome 2 regulates hematopoietic stem cell aging. In addition to demonstrating that hematopoietic stem cell aging is regulated by a distinct genetic element, experimental evidence links the response of hematopoietic stem cells to DNA double-strand breaks to cellular aging, suggesting DNA integrity influences stem cell aging.

Aging↗
PubMed2004

Stem cells, aging, and cancer: inevitabilities and outcomes.

Given the unique abilities of a stem cell to self-renew, differentiate, and proliferate, it is no wonder that they are critically important to an organism during development and to maintain homeostasis. Likewise, when something goes awry within a stem cell, it is likely to have far-reaching effects, since stem cells persist throughout the lifetime of the individual. Two significant biological phenomena that involve stem cells are the inevitable process of aging and a major health issue whose incidence increases with aging: cancer. In this review, we summarize evidence and theories concerning these two stem cell processes. The inability of stem cells to be passaged indefinitely in mice and the data supporting regular replication of the quiescent stem cell pool are discussed. Further, the current evidence indicating a stem cell origin of acute myeloid leukemia, including examples from both experimental mouse models and human clinical samples, is evaluated. Finally, we propose a model in which aging of the stem cell population of the hematopoietic system in particular can create conditions that are permissive to leukemia development; in fact, we suggest that aging is a secondary event in leukemogenesis.

Acute Disease↗
PubMed2004

Genetic analysis of progenitor cell mobilization by granulocyte colony-stimulating factor: verification and mechanisms for loci on murine chromosomes 2 and 11.

OBJECTIVE: It is notable that there is significant inter-individual variability in humans and inter-strain variability in mice in the ability to mobilize hematopoietic stem and progenitor cells, suggesting that there is genetic regulation of mobilization. In the murine system, loci on chromosomes 2 and 11 have been linked to an inter-strain variation in granulocyte colonystimulating factor (G-CSF)-induced stem cell mobilization proficiency. The aim of this study was to verify this linkage and to gain insight into the function of these loci. METHODS: Animals congenic for the loci on chromosomes 2 and 11 were generated by a speed-congenic approach and the function of the loci were further analyzed in doubly congenic animals and with a competitive transplantation/mobilization protocol. RESULTS: The analysis of congenic animals verified that both loci are linked to mobilization proficiency. Analysis of mobilization in doubly congenic animals suggested that both loci act in the same regulatory pathway. Mobilization experiments conducted with mice that had previously been competitively repopulated with congenic and parental-strain BM revealed that the locus on chromosome 11 operates via a progenitor cell-intrinsic mechanism. CONCLUSION: We confirmed linkage of loci on chromosomes 2 and 11 to G-CSF-induced mobilization and thus validated their role as regulators of hematopoietic progenitor cell mobilization in mice. These findings will be useful for further studies directed at identifying genes that regulate mobilization proficiency.

Animals↗
PubMed2003

Ionizing radiation and busulfan induce premature senescence in murine bone marrow hematopoietic cells.

Exposure of murine bone marrow (BM) cells to ionizing radiation (IR; 4 Gy) resulted in >95% inhibition of the frequency of various day types of cobblestone area-forming cells in association with the induction of apoptosis in hematopoietic stem cell alike cells (Lin(-) ScaI(+) c-kit(+) cells; IR: 64.8 +/- 0.4% versus control: 20.4 +/- 0.5%; P < 0.001) and progenitors (Lin(-) ScaI(-) c-kit(+) cells; IR: 46.2 +/- 1.4% versus control: 7.8 +/- 0.5%; P < 0.001). Incubation of murine BM cells with busulfan (BU; 30 micro M) for 6 h also inhibited the cobblestone area-forming cell frequency but failed to cause a significant increase in apoptosis in these two types of hematopoietic cells. After 5 weeks of long-term BM cell culture, 33% and 72% of hematopoietic cells survived IR- and BU-induced damage, respectively, as compared with control cells, but they could not form colony forming units-granulocyte macrophages. Moreover, these surviving cells expressed an increased level of senescence-associated beta-galactosidase, p16(Ink4a), and p19(Arf). These findings suggest that IR inhibits the function of hematopoietic stem cell alike cells and progenitors primarily by inducing apoptosis, whereas BU does so mainly by inducing premature senescence. In addition, induction of premature senescence in BM hematopoietic cells also contributes to IR-induced inhibition of their hematopoietic function. Interestingly, the induction of hematopoietic cell senescence by IR, but not by BU, was associated with an elevation in p53 and p21(Cip1/Waf1) expression. This suggests that IR induces hematopoietic cell senescence in a p53-p21(Cip1/Waf1)-dependent manner, whereas the induction of senescence by BU bypasses the p53-p21(Cip1/Waf1) pathway.

Animals↗
PubMed2003

Genetic control of stem cells: implications for aging.

Stem cells are currently at the center of both controversy and notoriety. The harvest of human embryonic or fetal stem cells, at least with methods available now, necessarily involves the sacrifice of the embryo or fetus. This critical step in the procurement of stem cells has stimulated intense discussion at all levels of academia, government, and society in general. What societal benefits, if any, justify such a strategy for obtaining these stem cells? In other species it has been possible to generate virtually all cell types found in adult organs from embryonic stem cells. This ability has opened endless clinical possibilities for tissue and organ replacement through the transplantation of cells derived from embryonic stem cells. Luckily, there may be an alternative to this ethical dilemma. It is becoming increasingly clear that stem cells exist in many, if not all, adult tissues. Adult stem cells normally replenish tissue cells lost through the wear and tear of aging or damage from injury or disease. With the proper coaxing in tissue culture and when transplanted, these stem cells may regenerate the full repertoire of organotypic cells and thus may therapeutically regenerate tissues in vivo in much the same way as embryonic stem cells do. For several reasons, the best-studied stem cells are those of the blood-forming system. Mature blood cells generally have short functional life spans, usually measured in days, and therefore require replenishment at a steady pace throughout one's lifetime. Stem cells are intimately involved in this renewal and, because of the relative ease of access to the bone marrow, stem cells have been well studied. Second, bone marrow transplantation following radiation or high-dose chemotherapy in the treatment of cancer has fostered research on the basic biology and therapeutic uses of hematopoietic stem cells over the more than 30 years stem cell transplantation has been used clinically. It is my aim to review what is known about the genes controlling hematopoietic stem cell function. Identifying, and ultimately manipulating, the genes that regulate stem cell number, replication rate, and self-renewal capacity may have important clinical benefits. I discuss evidence suggesting that the characterization of least some of these stem cell genes will shed light on mechanisms important in the aging process. I advance the hypothesis that stem cells accumulate cellular damage during aging that diminishes their developmental potency and ability to replenish blood cells, particularly after hematopoietic stress. In this view, the impaired function of stem cells in hematopoietic and in other self-renewing tissues limits the longevity of animals, and perhaps of humans.

Animals↗
PubMed2003

Ionizing radiation and busulfan inhibit murine bone marrow cell hematopoietic function via apoptosis-dependent and -independent mechanisms.

OBJECTIVE: Ionizing radiation (IR) and busulfan (BU) are commonly used as preconditioning regimens for bone marrow transplantation (BMT). We examined whether induction of apoptosis in murine bone marrow (BM) hematopoietic cells contributes to IR- and BU-induced suppression of their hematopoietic function. METHODS: The hematopoietic functions of hematopoietic stem cells (HSCs) and progenitors were analyzed by the cobblestone area-forming cell (CAFC) assay. Apoptosis was determined by measuring 3,3'-dihexyloxacarbocyanine iodide (DiCO6) uptake, annexin V staining, and/or sub-G(0/1) cells. Four cell types were studied: murine BM mononuclear cells (BM-MNCs), linage-negative hematopoietic cells (Lin-) cells), Lin- Scal+ c-kit+ cells, and Lin- Scal- c-kit+ cells by flow cytometry. RESULTS: Exposure of BM-MNCs to IR (4 Gy) or incubation of the cells with BU (30 microM) resulted in a significant reduction in CAFC frequency (p<0.001). The survival fractions of various day-types of CAFC for the irradiated cells were less than 10%, while that for BU-treated cells was 71.3% on day 7 and progressively declined to 5.3% on day 35. Interestingly, IR significantly induced apoptosis in BM-MNCs, Lin- cells, HSCs, and progenitors, whereas BU failed to increase apoptosis in these cells. In addition, preincubation of BM-MNCs with z-Val-Ala-Asp (OCH3)-fluoromethylketone, methyl ester (z-VAD) attenuated IR-induced reduction in CAFC but not that induced by BU. CONCLUSION: IR and BU differentially suppress the hematopoietic function of HSCs and progenitors by fundamentally different mechanisms. IR inhibits the function primarily by the induction of HSC and progenitor apoptosis. In contrast, BU suppresses HSC and progenitor function via an apoptosis-independent mechanism.

Animals↗
PubMed2003

The role of stem cells in aging.

The objectives of this review were first to critically review what is known about the effects of aging on stem cells in general, and hematopoietic stem cells in particular. Secondly, evidence is marshalled in support of the hypothesis that aging stem cells play a critical role in determining the effects of aging on organ function, and ultimately on the lifespan of a mammal. Aging has both quantitative and qualitative effects on stem cells. On balance, the qualitative changes are the more important since they affect the self-renewal potential, developmental potential, and interactions with extrinsic signals, including those from stroma. Although hematopoiesis is generally maintained at normal and life-supporting levels during normal aging, diminished function is acutely apparent when old stem cells are subjected to stress. There is ample evidence of diminished self-renewal capacity, restriction of the breadth of developmental potency, and decreased numbers of progeny of old stem cells subjected to hematopoietic demands. The prediction is made that whatever plasticity in developmental potential possessed by a young stem cell is lost during aging. Those parts of the world enjoying an ever-increasing standard of living are also inhabited by an increasingly elderly population. The effects of age on many physiological functions are not well studied or appreciated. A public health challenge to provide increased quality of life for this growing segment of the population requires more attention to the variable of age in experimental studies. Stem cell populations are likely to be a fruitful subject for studies of this type.

Aging↗
PubMed2003

The nature and identification of quantitative trait loci: a community's view.

This white paper by eighty members of the Complex Trait Consortium presents a community's view on the approaches and statistical analyses that are needed for the identification of genetic loci that determine quantitative traits. Quantitative trait loci (QTLs) can be identified in several ways, but is there a definitive test of whether a candidate locus actually corresponds to a specific QTL?

Animals↗
PubMed2003

Genetic control of stem-cell properties and stem cells in aging.

Studies to uncover genes regulating stem cells usually adopt one of two distinct lines of investigation: forward genetics and reverse genetics approaches. The forward genetics approach proceeds from measurable phenotypic differences to genetic polymorphism and, as the name implies, the path of investigation is reversed using reverse genetics. The number of newly discovered loci responsible for stem cell-specific phenotypes and functioning is increasing at a rapid rate owing to the success of both approaches. These loci regulate stem cells by intrinsic (cell autonomous) and/or extrinsic mechanisms and dictate stem-cell fate decisions. During the aging process, stem cells undergo both quantitative and qualitative changes, which are hypothesized to affect both the rate of aging and the longevity of an organism.

Aging↗
PubMed2002

A genetic and genomic analysis identifies a cluster of genes associated with hematopoietic cell turnover.

Hematopoietic stem cells from different strains of mice vary widely with respect to their cell cycle activity. In the present study we used complementary genetic and genomic approaches to identify molecular pathways affecting this complex trait. We identified a major quantitative trait locus (QTL) associated with variation in cell proliferation in C57BL/6 and DBA/2 mice to a 10 centimorgan (cM) region on chromosome 11. A congenic mouse model confirmed that a genomic interval on chromosome 11 in isolation confers the proliferation phenotype. To detect candidate genes we performed subtractive hybridizations and gene arrays using cDNA from highly enriched stem cells from parental strains. Intriguingly, a disproportionate number of differentially expressed genes mapped to chromosome 11 and, more specifically, these transcripts occurred in 3 distinct clusters. The largest cluster colocalized exactly with the cell cycling QTL. Such clustering suggested the involvement of genetic variation that affects higher-order chromosomal organization. This hypothesis was reinforced by the fact that differentially expressed genes mapped to recombination "coldspots," as a consequence of which clustered genes are collectively inherited. These findings suggest the functional interdependence of these closely linked genes. Our data are consistent with the hypothesis that this isolated cell cycle QTL does not result from a mutation in a single gene but rather is a consequence of variable expression of a collection of highly linked genes.

Animals↗
PubMed2002

Analysis of the hematopoietic potential of muscle-derived cells in mice.

Cells in murine muscle have been reported to differentiate into hematopoietic stem and progenitor cells and thus repopulate the hematopoietic system of an irradiated animal. This activity was attributed to muscle stem cells. We used an in vitro and in vivo approach to identify the hematopoietic repopulating activity found in muscle tissue of mice by antibody staining and cell sorting. We confirmed existence of a hematopoietic repopulating cell in muscle tissue, but the data strongly suggest that repopulation is due not to muscle stem cells but to hematopoietic cells present in muscle tissue. Unexpectedly, the blood-forming cells were enriched in muscle relative to their frequency in peripheral blood.

Animals↗
PubMed2002

Genetically determined variation in the number of phenotypically defined hematopoietic progenitor and stem cells and in their response to early-acting cytokines.

Quantitative trait analysis may shed light on mechanisms regulating hematopoiesis in vivo. Strain-dependent variation existed among C57BL/6 (B6), DBA/2, and BXD recombinant inbred mice in the responsiveness of primitive progenitor cells to the early-acting cytokines kit ligand, flt3 ligand, and thrombopoietin. A significant quantitative trait locus was found on chromosome 2 that could not be confirmed in congenic mice, however, probably because of epistasis. Because it has been shown that alleles of unknown X-linked genes confer a selective advantage to hematopoietic stem cells in vivo in humans and in cats, we also analyzed reciprocal male D2B6F1 and B6D2F1 mice, revealing an X-linked locus regulating the responsiveness of progenitor and stem cells to early-acting factors. Among DBA/2, B6, and BXD recombinant inbred mice, correlating genetic variation was found in the absolute number and frequency of Lin(-)Sca1(++)kit(+) cells, which are highly enriched in hematopoietic progenitor and stem cells, and in the number of Lin(-)Sca1(++)kit(-) cells, a population whose biologic significance is unknown, suggesting that both populations are functionally related. Suggestive quantitative trait loci (QTLs) for the number of Lin(-)Sca1(++) cells on chromosomes 2, 4, and 7 were confirmed in successive rounds of mapping. The locus on chromosome 2 was confirmed in congenic mice. We thus demonstrated genetic variation in the response to cytokines critical for hematopoiesis in vivo and in the pool size of cells belonging to a phenotype used to isolate essentially pure primitive progenitor and stem cells, and we identified loci that may be relevant to the regulation of hematopoiesis in steady state.

Animals↗