Vascular Niche in HSC Development, Maintenance and Regulation

Abstract

Hematopoietic stem cells (HSC) are multi-potent cells that have ability to self-renew and differentiate to all blood cell lineages. To function properly, HSC are regulated within unique microenvironments, or so called HSC niches , which are composed of specialized supporting cells and extracellular matrix. During mammalian embryogenesis, sites of hematopoiesis change over the course of gestation, as does the HSC niche composition: from extraembryonic yolk sac and placenta, to embryonic aorta-gonad-mesonephros region, fetal liver, and finally fetal bone marrow where HSC predominantly reside postnatally. From their first emergence to their final destination in bone marrow, HSC reside in close proximity to, and interact with vascular cells. There are three main vascular niche types; sinusoidal, arteriolar and perivascular. The interactions between HSC and vascular niche cells have been of great research interest; however, our understanding of the cellular phenotypes within vascular niches, and the molecular basis of vascular niche-HSC interactions, is still rudimentary. In this chapter, we will discuss the developmental relationships between HSC and vascular endothelial cells during HSC ontogeny, and the role of postnatal vascular niches in the regulation of HSC maintenance and function.