Epithelial Shh Leads to HF Neogenesis in Wounds.
To determine if Shh activation could induce HFN in scar-forming wounds, Shh was overexpressed in epithelial cells in K14-CreER; LSL-Shh or K14-CreER; LSL-Shh; Gli1-LacZ mice and HFN was examined in small wounds. To induce Shh overexpression, TAM was injected into control and K14-CreER; LSL-Shh or K14-CreER; LSL-Shh; Gli1-LacZ mice from PW1d to indicated time points in FIG. 24. This treatment resulted in extensive HFN in wounds compared to control wounds (FIG. 24a, b). Epidermal Shh overexpression resulted in Gli1 activation in both the epidermis and dermis, corresponding to the areas of HFN. Shh-driven hair germs expressed Lef1 and K17 and exhibited normal hair follicle morphogenesis. AP+ DPs were associated with overlying K17+ epithelial buds as typically observed in HFN. Eventually, many of these hair follicles (52±16%, mean±s.d.) grew downward to form mature hair follicles with hair shafts, an event rarely observed in control small wounds. New DP expressed Lef1 and Noggin as well as AP, further demonstrating their DP identity. Aberrant basaloid growths resembling superficial basal-cell carcinomas (BCCs) were rarely in these wounds.
Previous studies noted that HFN in large wounds in WT mice was limited to the central area of the wounds. Given the ability of Shh to induce ectopic HFN in small wounds, exogenous Shh might overcome the inability of new hair follicles to form outside this central region in large wounds. In large wounds from TAM-treated K14-CreER; LSL-Shh mice, extensive DP formation was observed covering the entire wound area compared with TAM-treated controls. (FIG. 24c-e). These results verify the potency of Shh activation to overcome regional inhibition of HFN.