Biomedical subjects

S H Cheshier

Publications and source records attributed to S H Cheshier.

5 recordsLinked to original sources

PubMed2005

Hematopoietic stem cells give rise to perivascular endothelial-like cells during brain tumor angiogenesis.

Bone marrow (BM) cells have recently been shown to give rise to skeletal, hepatic, cardiac, neural, and vascular endothelial tissues. However, it has been shown that this is the result of cell fusion rather than transdifferentiation of hematopoietic stem cells (HSC). For this study, we established a mouse model of brain tumor growth to investigate the differentiation potential of HSC into endothelial cells during brain tumor-induced angiogenesis. Nontransgenic (GFP(neg)) recipient mice were lethally irradiated, and their hematopoietic cells were subsequently repopulated by transplantation of a single green fluorescent protein (GFP)-expressing HSC. Rat glioma (RT-2/RAG) cells were then injected into the striatum of the chimeric mice 6-8 weeks post-transplantation. The animals were sacrificed 3-9 days after tumor implantation, and the mobilization, temporal-spatial distribution, and lineage-specific marker expression profile of the GFP(+) cells within the growing tumor were analyzed. We saw that GFP(+) cells gave rise to elongated, CD34(+)/Flk-1(+) cells that incorporated into the endothelium of tumor blood vessels. However, all GFP(+) cells were also CD45(+), and the presence of CD45 on the HSC-derived endothelial-like cells supports the hypothesis that the hematopoietic cells were recruited into the tumor milieu. The fact that we failed to demonstrate the expression of von Willebrand factor in these cells argues against a true endothelial identity. Nevertheless, the recruitment of HSC-derived endothelial-like cells was an extremely rare event in normal brain parenchyma, and, thus, the permissive influence afforded by the growing tumor appeared to enhance the perivascular tropism and acquisition of an endothelial phenotypes by a population of HSC-derived cells.

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PubMed2001

Cyclophosphamide/granulocyte colony-stimulating factor causes selective mobilization of bone marrow hematopoietic stem cells into the blood after M phase of the cell cycle.

Cytokine-mobilized peripheral blood hematopoietic stem cells (MPB HSC) are widely used for transplantation in the treatment of malignancies, but the mechanism of HSC mobilization is unclear. Although many HSC in bone marrow (BM) cycle rapidly and expand their numbers in response to cytoreductive agents, such as cyclophosphamide (CY), and cytokines, such as granulocyte colony-stimulating factor (G-CSF), MPB HSC are almost all in the G(0) or G(1) phase of the cell cycle. This has raised the question of whether a subset of noncycling BM HSC is selectively released, or whether cycling BM HSC are mobilized after M phase, but before the next S phase of the cell cycle. To distinguish between these possibilities, mice were treated with one dose of CY followed by daily doses of G-CSF, and dividing cells were marked by administration of bromodeoxyuridine (BrdU) during the interval that BM HSC are expanding. After CY and 4 days of G-CSF, 98.5% of the 2n DNA content long-term repopulating MPB (LT)-HSC stained positively for BrdU, and therefore derived from cells that divided during the treatment interval. Next, LT-HSC from mice previously treated with a single dose of CY, which kills cycling cells, and 3 daily doses of G-CSF, were nearly all killed by a second dose of CY, suggesting that CY/G-CSF causes virtually all LT-HSC to cycle. Analysis of cyclin D2 messenger RNA (mRNA) expression and total RNA content of MPB HSC suggests that these cells are mostly in G(1) phase. After CY/G-CSF treatment, virtually all BM LT-HSC enter the cell cycle; some of these HSC then migrate into the blood, specifically after M phase, and are rapidly recruited to particular hematopoietic organs.

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PubMed2000

The role of apoptosis in the regulation of hematopoietic stem cells: Overexpression of Bcl-2 increases both their number and repopulation potential.

Hematopoietic stem cells (HSC) give rise to cells of all hematopoietic lineages, many of which are short lived. HSC face developmental choices: self-renewal (remain an HSC with long-term multilineage repopulating potential) or differentiation (become an HSC with short-term multilineage repopulating potential and, eventually, a mature cell). There is a large overcapacity of differentiating hematopoietic cells and apoptosis plays a role in regulating their numbers. It is not clear whether apoptosis plays a direct role in regulating HSC numbers. To address this, we have employed a transgenic mouse model that overexpresses BCL-2 in all hematopoietic cells, including HSC: H2K-BCL-2. Cells from H2K-BCL-2 mice have been shown to be protected against a wide variety of apoptosis-inducing challenges. This block in apoptosis affects their HSC compartment. H2K-BCL-2-transgenic mice have increased numbers of HSC in bone marrow (2.4x wild type), but fewer of these cells are in the S/G(2)/M phases of the cell cycle (0.6x wild type). Their HSC have an increased plating efficiency in vitro, engraft at least as well as wild-type HSC in vivo, and have an advantage following competitive reconstitution with wild-type HSC.

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PubMed1999

In vivo proliferation and cell cycle kinetics of long-term self-renewing hematopoietic stem cells.

A rare set of hematopoietic stem cells (HSC) must undergo a massive expansion to produce mature blood cells. The phenotypic isolation of HSC from mice offers the opportunity to determine directly their proliferation kinetics. We analyzed the proliferation and cell cycle kinetics of long-term self-renewing HSC (LT-HSC) in normal adult mice. At any one time, approximately 5% of LT-HSC were in S/G2/M phases of the cell cycle and another 20% were in G1 phase. BrdUrd incorporation was used to determine the rate at which different cohorts of HSC entered the cell cycle over time. About 50% of LT-HSC incorporated BrdUrd by 6 days and >90% incorporated BrdUrd by 30 days. By 6 months, 99% of LT-HSC had incorporated BrdUrd. We calculated that approximately 8% of LT-HSC asynchronously entered the cell cycle per day. Nested reverse transcription-PCR analysis revealed cyclin D2 expression in a high proportion of LT-HSC. Although approximately 75% of LT-HSC are quiescent in G0 at any one time, all HSC are recruited into cycle regularly such that 99% of LT-HSC divide on average every 57 days.

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PubMed1997

Hematopoietic stem cells: challenges to expectations.

The past year provided a number of challenges to our expectations regarding hematopoietic stem cell (HSC) biology. Evidence has emerged that HSCs arise intraembryonically before they can be detected in the yolk sac. A number of genes that may regulate the formation, self-renewal, or differentiation of HSC have been identified. New markers for purifying HSCs have also been described. Although different groups have attributed different properties to HSCs, it now appears that the differences may be explained by variations in assay conditions rather than by differences in the HSCs themselves. Finally, insights have emerged into the complexity of the regulation of HSC proliferation and adhesion properties.

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