FIGURE 3.

Endothelial interactions with HSCs in the BM vascular niche. Quiescent HSCs preferentially locate in arteriolar niches surrounded by NG2⁺ pericytes. Arteriolar ECs and NG2⁺ pericytes release quiescence-inducing factors including SCF, CXCL12, and PDGF-B. Proliferative HSCs move away from arterioles toward sinusoidal niches. Sinusoidal ECs to release proliferative factors such as Osteopontin, FGF-2, E-selectin, and Notch ligands. HSC differentiation is induced by the endothelial release of G-CSF, GM-CSF or interleukins. Reciprocally, HSCs can induce endothelial proliferation by releasing proangiogenic factors such as VEGFA. HSC, hematopoietic stem cell, EC, endothelial cell; FGF, fibroblast-derived growth factor; TGF, transforming growth factor; CXCL12, C-X-C motif chemokine 12; VEGF, vascular endothelial growth factor; BMP, bone morphogenetic protein; PDGF, platelet-derived growth factor; SCF, stem cell factor; G-CSF, granulocyte colony-stimulating factor; GM-CSF, granulocyte-macrophage colony-stimulating factor.