The stem cell niches in bone
Tong Yin1 and Linheng Li1,2
1Stowers Institute for Medical Research, Kansas City, Missouri, USA.
2Department of Pathology and Laboratory Medicine, Kansas University Medical Center, Kansas City, Kansas, USA.
Address correspondence to: Linheng Li, Stowers Institute for Medical Research, 1000 East 50th Street, Kansas City, Missouri 64110, USA. Phone: (816) 926-4081; Fax: (816) 926-2023
The stem cell niche is composed of a specialized populationof cells that plays an essential role in regulating adult stemcell self-renewal and differentiation. In adults, osteoblasts,responsible for osteogenesis, and hematopoietic cells, responsiblefor hematopoiesis, are closely associated in the bone marrow,suggesting a reciprocal relationship between the two. It wasrecently discovered that a subset of osteoblasts functions asa key component of the HSC niche (namely, the osteoblastic niche),controlling HSC numbers. HSCs interact not only with osteoblastsbut also with other stromal cells, including endothelial cells.Sinusoidal endothelial cells in bone marrow have been revealedas an alternative HSC niche called the vascular niche. In thisReview we compare the architecture of these 2 HSC niches inbone marrow. We also highlight the function of osteoblasts inmaintaining a quiescent HSC microenvironment and the likelyrole of the vascular niche in regulating stem cell proliferation,differentiation, and mobilization. In addition, we focus onstudies of animal models and in vitro assays that have provideddirect insights into the actions of these osteoblastic and vascularniches, revealing central roles for numerous signaling and adhesionmolecules. Many of the discoveries described herein may contributeto future clinical treatments for hematopoietic and bone-relateddisorders, including cancer.
Source: J. Clin. Invest. 116:1195-1201 (2006)