The Vascular Niche

The vascular niche is composed of at least two cell types: HSCs and endothelial cells. During embryogenesis both cell types follow similar, but distinct, patterns of development (Ueno and Weissman 2006). In the adult, vascular endothelial cells contribute to the maintenance of HSCs in vitro (Li et al. 2004) and are required for in vivo hematopoiesis (Avecilla et al. 2004). Recently, HSCs identified by the cell surface marker phenotype CD150+ CD244- CD48- were shown to localize in close proximity to sinusoidal endothelium or osteoblasts in the spleen and bone marrow. The spleen contained HSCs associated with the sinusoidal endothelium, with 62% located in the parafollicular regions. In the bone marrow, HSCs localized to the sinusoidal endothelium accounted for 0.0067 ± 0.0016% of total marrow cells. It was estimated that 60% of the HSCs were in contact with the endothelium, and because only 10% of the bone marrow contacts this area, HSCs are sixfold more likely to contact sinusoids (Kiel et al. 2005).

0 0

Post a comment