Biomedical subjects
Publications and source records attributed to Robert C Fisher.
One of the most active areas of research in medicine today is stem cell biology. This review introduces the reader to the field of stem cell biology and its therapeutic potential. More importantly, the potential application of stem cell therapy in acute lung injury will be explored.
Historically, physicians have attributed delayed platelet engraftment following umbilical cord blood transplant to decreased numbers of stem cells in cord blood compared with adult bone marrow. However, recent studies suggest that delayed platelet engraftment may be caused by an intrinsic inability of neonatal stem cells to produce mature, polyploid megakaryocytes. We tested this hypothesis by transplanting adult bone marrow and newborn liver hematopoietic stem and progenitor cells from transgenic mice expressing green fluorescent protein into myeloablated wild-type recipients and comparing the size and ploidy levels of megakaryocytes that developed in adult transplant recipients. Transplanted stem and progenitor cells, regardless of their source, gave rise to megakaryocytes that were larger than normal adult megakaryocytes as early as 7 days post-transplant. However, megakaryocytes that developed after transplant of neonatal stem and progenitor cells were significantly smaller than those derived from adult stem and progenitor cells. Furthermore, megakaryocytes derived from neonatal cells had lower ploidy values than megakaryocytes derived from adult cells at 18 days post-transplant, when ploidy could first be reliably measured in the bone marrow. These differences in size and ploidy disappeared by 1 month post-transplant. The largest megakaryocytes developed in the spleen. These results suggest that, in the mouse, the microenvironment is responsible for some of the maturational differences in size and ploidy between neonatal and adult megakaryocytes. Furthermore, neonatal and adult megakaryocyte progenitors also have cell-intrinsic differences in the way they engraft and respond to thrombocytopenic stress. These differences may contribute to the delay in platelet engraftment that frequently complicates cord blood transplants.
Despite normal levels of erythropoiesis in PU.1(-/-) embryos, PU.1(-/-) fetal hematopoietic progenitors are unable to establish sustained erythropoiesis in the adult bone marrow. This study demonstrates that PU.1(-/-) fetal erythroid progenitors are synergistically expanded by TPO plus SCF, but not combinations of EPO plus SCF, IL-3 or GM-CSF. The EPO defect is not corrected by a constitutively active variant of EPOR. Microarray analysis identified several candidate PU.1 target genes known to affect cytokine signaling and gene regulation in the erythroid lineage. These data suggest that PU.1 plays an important role in regulating the proliferation of immature erythroid progenitors.