Ly6C+ Macrophages Mediate AKT-dependent Lgr5+ Stem Cell Activation And Hair Follicle Regeneration

The relationship inflammation, stem cells and cancer has long been recognized. It has been investigated that inflammatory processesduring wound healing linked to the pathological state of many tumors.During skin injury, replenishment of epithelial cell loss is supplied by the proliferation of epidermal stem cells in response to pro-inflammatory cytokines, and besides the cytokines, numerous growth factors released by lymphocytes and macrophages during wound healing that could promote stem cell proliferation and plasticity. While the detailed mechanism that interpreting how the inflammatory microenvironment stimulate stem cells during the wound healing, and how these stem cells react to these stimulates and undergo proliferation process, is poorly understood.In this study we showed that stem cells in the epidermis and hair follicles were activated after wounding with Akt phosphorylation(Akt-P), resulting in a dramatic transition of telogen to anagen phase of the hair follicle around the wound in mice. We also found that the Lgr5-expressing cells in the hair follicle germ response earlier to tissue injury and begin to proliferation than the stem cells in bulge, in addition, the Lgr5-expressing cellalso contribute to the re-epithelizaiton during the wound healing, but not to homeostasis of the epidermis. Inhibition of Akt or PI3 K led to the loss of the injury-induced telogen-anagen follicle transition, whereas suppression of PTEN caused injury-independent telogen-anagen follicle transition. Impressively, inducible knockout of Pten in Lgr-5+ stem cells in Lgr5tm1(cre/ERT2)Cle/Ptenflox/flox mice led to increased AKT phosphorylation and proliferation ofLgr-5+ stem cellsand accelerated telogen-anagen follicle transition. We further improved Lgr-5+ stem cells is dispensable for hair follicle recycling, even ablation of Lgr-5+ stem cells do delayed the hair follicle recycling process, while the CD34+ stem cells in the bulge give rise to Lgr-5+cells after it loses. Suppression of inflammation by dexamethsone or NF-κB inhibitor abolished wounding induced stem cell Akt phosphorylation and telogen-anagen follicle transition. Moreover, local injection of LPS activated macrophages mediated stem cell Akt-P and anagen follicles, whereas depletion of macrophages in mice led to the loss of injury-induced stem cell Akt-P and anagen follicles. Further analysis using Cx3cr1CreER/R26 iDTRmice which depleted tissue macrophages identified that Ly6ChighCX3CR1 low inflammatory macrophages, but not Ly6 C lowCX3CR1highMHCIIhigh resident macrophages were largely responsible for injury-induced stem cell activation and anagen follicles.In conclusion, ourstudyindicated that blood borne macrophages recruited into acute skin injury activated PI3K/AKT in Lgr-5+ hair follicle stem cells, largely through the release of inflammatory cytokine, and led to hair follicle regeneration, suggesting that macrophages recruited into the damaged skin contribute to the stem cell niche for hair follicle regeneration, and the inflammatory cytokineserve as a crucial mediator between myeloid cells and epidermal stem cells activation during wound healing.