HSC Niche: Regulation of Mobilization and Homing

The bone marrow (BM) contains hematopoietic progenitor cells (HPCs) and hematopoietic stem cells (HSCs) that are confined by their biochemical and cellular microenvironments, known as stem cell niches. Biochemical factors secreted by cellular components in niches regulate stem cell survival, proliferation, and migration in an extrinsic manner. HSC migration is an essential biological process during embryonic development and for steady hematopoiesis in adult life. A proper HSC trafficking that involves migration, homing, and engraftment is critical to efficient BM and HSC transplantation, as well. The functional importance of many biochemical factors and mobilization agents in HSC trafficking has been studied and reported, but still, a lot remains unknown. A defect in the biochemical microenvironment not only affects HSC properties, but it also causes deregulation of the niche functionality that leads to the development of various malignant and nonmalignant hematological diseases. BM transplantation is performed to treat various hematological disorders. An improved understanding of molecular and biochemical signals regulating HSC mobilization is critical in the efficient and safer use of these factors as therapeutic tools. Here in this chapter, we summarize the current knowledge on the functional properties of primary regulators of HSC trafficking and their clinical applications.