Biomedical subjects

D D Cooper

Publications and source records attributed to D D Cooper.

5 recordsLinked to original sources

PubMed2000

Paradigm shifts in stem-cell biology.

Hematopoiesis is a physiologic process that can be transplanted by intravenous infusion of stem and progenitor cells. Because these cells contribute to blood production over a lifespan, they are attractive targets for cell-based therapies of hematologic malignancies and genetic defects. A more complete understanding of the basic biology of hematopoiesis will accelerate our progress toward the clinical goal of improved stem-cell-based therapies. Many advances in recent years have brought us closer to that goal and have, in addition, challenged a number of dogmatic notions about hematopoiesis. Three of these advances are briefly addressed here: (1) an emerging appreciation of the complex relationship between cell-cycle status, engraftment potential, and self-renewal in the hematopoietic system; (2) the demonstration of new progenitor populations and lineage relationships in early hematopoietic development; and (3) a reanalysis of the embryonic origins of hematopoiesis. These and other advances are allowing the mysteries of hematopoiesis to be unlocked at a pace that was unimaginable just a few years ago.

Animals↗

PubMed2000

Modulation of hematopoietic stem/progenitor cell engraftment by transforming growth factor beta.

OBJECTIVE: To investigate if cell cycle progression plays a role in modulating the engraftment potential of mouse hematopoietic stem and progenitor cells (HSPC). MATERIALS AND METHODS: HSPC were isolated from adult mouse bone marrow, cultured in vitro under conditions promoting cell cycle arrest, and subsequently were evaluated for cell cycle status, clonogenic activity, and transplant potential. RESULTS In the presence of steel factor (STL) as a survival cytokine, transforming growth factor beta (TGF-beta) increased the G0/G1 fraction of cycling progenitor cells (Rh(high)) after a 20-hour culture. Clonogenic activity of quiescent long-term repopulating (Rh(low)) HSPC was unaffected by this culture, whereas clonogenic potential of Rh(high) cells decreased by about 30%. In competitive repopulation assays, Rh(low) cells cultured in STL + TGF-beta engrafted better than cells cultured in STL alone. However, culture in STL + TGF-beta did not overcome the failure of Rh(high) cells to engraft after transplant. We also utilized a two-stage culture system to first induce proliferation of Rh(low) HSPC by a 48-hour culture in STL + interleukin 6 + Flt-3 ligand, followed by shifting the culture to STL + TGF-beta for 24 hours to induce cycle arrest. A competitive repopulation assay demonstrated a relative decrease in repopulating potential in cultures that were cycle arrested compared to those that were not. CONCLUSION: Cell cycle progression by itself cannot account for the decrease in repopulating potential that is observed after ex vivo expansion. Other determinants of engraftment must be identified to facilitate the transplantation of cultured HSPC.

Animals↗

PubMed1999

(R)evolutionary considerations in hematopoietic development.

Evolutionary aspects of three characteristics of the mammalian hematopoietic system are considered in the context of both established and recent data. First, the lineage relationships among early members of the hematopoietic hierarchy are reconsidered in a tripartite model proposing lineage segregation based on vascular function, innate immunity, and acquired immunity on an evolutionary time scale. Second, the observation of two stem cell populations that differ in cell cycle status is considered as an evolved mechanism to enhance survival of the species in response to exposure to environmental toxins. Finally, the mobilization of hematopoietic stem cells into the peripheral circulation is proposed to be a mechanism for rapid dissemination of myeloid function during acute bacterial infections. These revolutionary hypotheses challenge some conventional concepts of stem cell biology, and provide an evolutionary context for considering mammalian hematopoiesis.

Animals↗

PubMed1998

Rhodamine-123 staining in hematopoietic stem cells of young mice indicates mitochondrial activation rather than dye efflux.

Low-intensity fluorescence of rhodamine-123 (Rh-123) discriminates a quiescent hematopoietic stem cell (HSC) population in mouse bone marrow, which provides stable, long-term hematopoiesis after transplantation. Rh-123 labels mitochondria with increasing intensity proportional to cellular activation, however the intensity of staining also correlates with the multidrug resistance (MDR) phenotype, as Rh-123 is a substrate for P-glycoprotein (P-gp). To address the mechanisms of long-term repopulating HSC discrimination by Rh-123, mouse bone marrow stem and progenitor cells were isolated based on surface antigen expression and subsequently separated into subsets using various fluorescent probes sensitive to mitochondrial characteristics and/or MDR function. We determined the cell cycle status of the separated populations and tested for HSC function using transplantation assays. Based on blocking studies using MDR modulators, we observed little efflux of Rh-123 from HSC obtained from young (3- to 4-week-old) mice, but significant efflux from HSC derived from older animals. A fluorescent MDR substrate (Bodipy-verapamil, BodVer) and Rh-123 both segregated quiescent cells into a dim-staining population, however Rh-123-based separations resulted in better enrichment of HSC function. Similar experiments using two other fluorescent probes with specificity for either mitochondrial mass or membrane potential indicated that mitochondrial activation is more important than either mitochondrial mass or MDR function in defining HSC in young mice. This conclusion was supported by morphologic studies of cell subsets separated by Rh-123 staining.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1981

The effect of a thirty per cent reduction in physician fees on Medicaid surgery rates in Massachusetts.

In this paper, we use an interrupted time series analysis to assess the effect of a 30 per cent reduction in the Medicaid reimbursement fee for physician services on the rate at which eight elective surgical procedures were performed in the Massachusetts Medicaid population. Tonsillectomy/adenoidectomy is the only procedure in which there was a statistically significant decline in the rate of surgery in most areas of the state following the fee cut. There is some evidence of an increase in the rate of disc surgeries/spinal fusions. The rate of other procedures increased in some areas of the state and decreased in other areas in the period after the fee cut.

Adenoidectomy↗