Stem cell niche

The stem cell niche is the spatially defined microenvironment — composed of neighbouring stromal cells, vascular elements, extracellular matrix, soluble factors, and biophysical cues such as stiffness and oxygen tension — that locally regulates stem cell quiescence, self-renewal, and differentiation. Landmark niches include the bone marrow endosteal and perivascular niches for haematopoietic stem cells, the intestinal crypt base for Lgr5-positive intestinal stem cells, and the bulge region of hair follicles for epidermal stem cells. With ageing, niche integrity deteriorates through ECM stiffening, loss of supporting stromal cells, inflammatory cytokine accumulation, and SASP from local senescent cells, impairing stem cell function even when the stem cells themselves retain intrinsic self-renewal potential — a distinction with therapeutic implications, since restoring niche signals can partially rejuvenate aged stem cell activity.