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433Keratinocytes are gatekeepers of mast cell access to the skin Z Wang, N Mascarenhas, X Sun and A Di Nardo Dermatology, UC San Diego, La Jolla, CA Stem cell factor (SCF) is crucial for the development, proliferation, and final maturation of mast cells (MCs). Here we show that despite the production of SCF by epidermal keratinocytes, fibroblasts, and endothelial cells, mice with conditional deletion of Scf (K14-cre Scf fl/fl ) in keratinocytes do not have MCs in the skin, confirming that SCF produced by keratinocytes is essential for recruiting MCs to the dermis. Anti-SCF and anti-chymase immunofluorescent staining reveals normal levels of SCF and MCs in the gut mucosa of K14-cre and K14-cre Scf fl/fl mice. MCs in the skin of K14-cre Scf fl/fl mice can be rescued by subcutaneous injection of SCF (50 mg/kg/day in 100 ml PBS) for 4 weeks. These same mice are also deprived of skin

Recent studies have focused on the negative effects of visible light (VL) on the skin, which lead to activation of metalloproteinases and oxidative stress induction, worsening clinical signs such as, melasma or post-inflammatory hyperpigmentation. The objective was to complete the existing scientific evidence of FernblockÒ about its photoprotection potential against VL. We developed two in vitro studies, regarding physicochemical level protection and biological activity. Sunscreen formulations containing FernblockÒ were selected and their transmittance of solar simulated VL was calculated by spectroradiometric measurement.In the second study, we examined FernblockÒ's action mechanism against blue light from digital devices on skin cells. All samples showed VL absorbance capacity above the levels established in the references consulted as proposals for VL-SPF. Regarding biological studies, treatment with FernblockÒ prior to VL radiation prevents alteration of mitochondrial morphology and function in fibroblasts and significantly reduces the activation of opsin 3 in melanocytes and the photo-oxidation of melanin. We elucidate a scoring system to evaluate the photoprotection potential against VL consisting of different study levels from in vitro to clinical scientific evidence. Thus, FernblockÒ added to different combinations of organic and mineral sunscreens can significantly increase visible light protection as demonstrated by both physiochemical and biological studies.

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