Vasculature cross-talking with adult skin epithelial stem cells (SC) is not understood.  Skin vasculature undergoes dramatic remodeling during adult hair cycle. A transient dermal horizontal plexus under the hair germ (HPuHG) neighbors the hair follicle SC  activation zone during the quiescence phase of hair homeostasis (cycle). Increased density of HPuHG can be induced by reciprocal mutations in the epithelium (Runx1) and endothelium (Alk1), accompanied by prolonged quiescence of hair follicle SCs and delayed hair growth. Suggestively, skin vasculature produces BMP4, a well-established hair follicle SC quiescence-inducing factor, known to halt hair cycle. Thus, coordinated remodeling of the adult epithelial and endothelial skin compartments may modulate hair follicle SC activation for proper tissue homeostasis of adult skin. Importantly, increased vasculature near the hair germ during the quiescent phase appears to enforce SC quiescence and to delay entry into anagen.

Skin Vasculature And Hair Follicle Stem Cells Cross-talking Associated With Stem Cell Activation And Tissue Homeostasis