Hair-Follicle Mesenchymal Stem Cell Activity during Homeostasis and Wound Healing

The mesenchymal components of the hair follicle-the dermal papilla (DP) and dermal sheath (DS)-are maintained by hair follicle dermal stem cells, but the position of this stem cell population throughout the hair cycle, its contribution to the maintenance of the dermis, and the existence of a migratory axis from the DP to the dermis remain unclear. In this study, we show that during homeostasis DP and DS cells are confined to their compartments, and during the regression phase of the hair cycle, some DP/DS cells undergo apoptosis and subsequently are internalized by nearby adipocytes. In contrast, during wound healing, DP/DS cells move toward the wound but do not directly participate in follicle neogenesis. Furthermore, hair follicle dermal stem cells, driving the cyclic renewal of the DS during the hair cycle, are heterogeneous and are housed during the growth phase within the most proximal part of the DS. Our analysis provides insight into the mechanisms of tissue maintenance and reveals a potential function of adipocytes in phagocytosis.