Erythropoiesis, anemia and the bone marrow microenvironment.

The in vivo regulation of erythropoiesis involves the integration of a range of intrinsic and cell extrinsic cues. The macrophage contained within the erythroblastic island is central to the normal differentiation and support of erythroid development. The contributions of other cell types found within the local bone marrow microenvironment are also likely to play important roles depending on the context. Such cell types include osteoblasts, osteoclasts, adipocytes, endothelial cells in addition to developing hematopoietic cells. There are data correlating changes in erythroid homeostasis, particularly in anemic states such as hemoglobinopathies, with alterations in the skeleton. The interaction and coordination of erythroid development and skeletal homeostasis, particularly in setting of erythroid demand, may represent a centrally regulated axis that is important physiologically, pharmacologically and in the pathology of anemia states.