Replenishment of Damaged Bone Marrow Niches By Circulating Hematopoietic Stem Cells

Hematopoietic Stem and Progenitor Cells (HSPC) support life-long production of blood cells through multipotent differentiation and self-renewal. Adult HSPC reside predominantly in the bone marrow (BM) but low levels of HSPC can be found in the bloodstream (Wright et al, Science 2001). The spontaneous egress of HSPC from the BM into the circulation follow circadian cycles which are in anti-phase with the chemokine Cxcl12produced by the niche microenvironment (Mendez-Ferrer et al, Nature 2008). This phenomenon is regulated exogenously by the molecular clock, which orchestrates the circadian release of noradrenaline by the sympathetic nervous system. Medullary HSPC are crucial for haematopoiesis under normal and stress conditions; in contrast, the physiological function of circulating HSPC remains largely unknown. Here we aimed at exploring the role of circulating HSPC.