Stem Cell Research and Jonsson Comprehensive Cancer Center in California have discovered an important distinction in how blood-forming stem cells are supported by their micro-environments during rest and after injury. The body appears to switch the type of cell that produces a single growth factor during healthy times and during stress or injury — for instance, radiation treatment for cancer. The results could have implications for treating cancer, when people’s blood-forming stem cells may be substantially depleted, and for people undergoing certain types of transplants. The study, led by Dr. John Chute, a member of the center and a Professor of Hematology/Oncology at the David Geffen School of Medicine at UCLA, was published in Cell Stem Cell. The article is titled “Distinct Bone Marrow Sources of Pleiotrophin Control Hematopoietic Stem Cell Maintenance and Regeneration.” Blood-forming, or hematopoietic, stem cells can differentiate into various types of mature blood elements — white blood cells, red blood cells, and platelets. They live in “vascular niches” in the bone marrow, where different types of surrounding cells support them, partly by secreting compounds called growth factors. The UCLA study focused on a growth factor called pleiotrophin (PTN). Dr. Chute and his team had previously discovered pleiotrophin, but had yet to determine which type of cells secrete it. “In stem cell research, two important questions are, ‘What are the microenvironment cells that regulate stem cells,’ and ‘How do they do it?’” Dr. Chute said. To find out, the team bred mice that lacked pleiotrophin expression in various types of bone marrow cells — including endothelial cells, which line the blood vessels, and stromal cells, which make up connective tissue.
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