Structural-functional organisation of the bone marrow hematopoietic stem cells niches

Abstract

This article focuses on (1) the analysis of the structural-functional organization of bone marrow niches of the hematopoietic stem cells, (2) the role of the intercellular contact interactions and humoral regulation factors in these niches, in particular CXCL12, SCF and TGFβ, and (3) the intracellular signal pathways: Notch, Wnt and Shh. The two types of niches, switching from one into another: endosteal niches located on the endost surface at the borderline with bone marrow cavity and the vascular niches included into bone marrow parenchyma. It is emphasized that the main role in the formation of the niches of both types is ascribed to the multipotent stromal cells, which serve as a base for differentiation of the osteoblasts, spindle-shaped N-cadherin+CD45– osteoblasts (SNO-cells), nestin-expressing cells (Nes+ cells), cells with leptin receptor (Lepr+ cells), abundant producing CXCL12 reticular cells (CAR-cells) and NG2-pericytes. The endothelial cells are no less important. Also, the adipocytes, osteoclasts, macrophages and megakaryocytes, regulatory T-cells and neuronal cells are involved in the niche functioning. It is postulated that osteoblasts and CAR-cells play a crucial role in the genesis of immune system cells: common lymphoid precursors, B-lymphocytes, natural killer and dendritic cells.