Studies have established that autophagy constitutes an efficient process to recycle cellular components and certain proteins. The phenomenon was demonstrated primarily in response to nutrient starvation, and there are increasing evidences that it is implied in differentiation. Keratinocyte differentiation was going along an activation of lysosomal enzymes and organelle clearance, and terminal steps are sometimes described as a specialized form of cell death leading to corneocytes. We examined whether initiation of the process in human keratinocyte HaCaT involves autophagy. The KSFM™ culture medium was substituted by M199, which contains a low glucose concentration but a high calcium level (known to induce differentiation). Metabolic stress reduced enhanced cell number in G(1) phase, without apoptotic features (ΔΨmt and membrane integrity are unchanged). Morphological changes were associated with a lower integrin ß1 expression and modifications of protein levels involved in keratinocyte differentiation (involucrin, keratin K10 and ΔNp63α). Whereas autophagic signalling was supported by SIRT1 and pAMPK (T172) increase according to time kinetic, which led to the disappearance of mTOR phosphorylated on S2448 residue. The significant Bcl-X(L) level reduction with stress promoted autophagy, by the release of Beclin-1, whereas ATG5-ATG12 and LC3-II that are involved in autophagosome formation were enhanced significantly. Then, the level of lysosomal protein cathepsin B rose to execute autophagy. Kinetic studies established that autophagy would constitute an early signalling process required for keratinocyte commitment in differentiation pathway.

Short title: Transcriptome analysis of dermal fibroblasts Abbreviations: ECM, extracellular matrix; Fp, papillary fibroblast; Fr, reticular fibroblast; Pn, number of cell passage. COL, collagen; MMP, matrix metalloproteinase Word count: 995 words

UV irradiation is a major environmental factor causing skin dryness, aging and cancer. UVB in particular triggers cumulative DNA damage, oxidative stress and mitochondrial dysfunction. The objective of our study was to provide both qualitative and quantitative analysis of how mitochondria respond to UVB irradiation in normal human epidermal keratinocytes (NHEK) of healthy donors, with the rationale that monitoring mitochondrial shape will give an indication of cell population fitness and enable the screening of bioactive agents with UVB-protective properties. Our results show that NHEK undergo dose-dependent mitochondrial fragmentation after exposure to UVB. In order to obtain a quantitative measure of this phenomenon, we implemented a novel tool for automated quantification of mitochondrial morphology in live cells based on confocal microscopy and computational calculations of mitochondrial shape descriptors. This method was used to substantiate the effects on mitochondrial morphology of UVB irradiation and of knocking-down the mitochondrial fission-mediating GTPase Dynamin-related protein 1 (DRP1). Our data further indicate that all the major mitochondrial dynamic proteins are expressed in NHEK but that their level changes were stronger after mitochondrial uncoupler treatment than following UVB irradiation or DRP1 knock-down. Our system and procedures might be of interest for the identification of cosmetic or dermatologic UVB-protective agents.

Atopic dermatitis (AD) is the most common skin inflammatory disease, affecting up to 3% of adults and 20% of children. Skin barrier impairment is thought to be the primary factor in this disease. Currently, there is no method proposed to monitor non-invasively the different molecular disorders involved in the upper layer of AD skin. Raman microspectroscopy has proved to be a powerful tool to characterize some AD molecular descriptors such as lipid content, global hydration level, filaggrin and its derivatives. Our investigations aimed to extend the use of in vivo Raman microspectroscopy as a rapid and non-invasive diagnostic technique for lipid conformation and organization, protein secondary structure and bound water content analysis in atopic skin. Our approach was based on the analysis of Raman data collected on the stratum corneum (SC) of 11 healthy and 10 mild-to-moderate atopic patients. Atopic skin revealed a modification of lipid organization and conformation in addition to the decrease of the lipid-to-protein ratio. This study also highlighted a reduction of the bound water and an increase in protein organized secondary structure in atopic skin. All these descriptors worsen the barrier function, state and appearance of the skin in AD. This precise and relevant information will allow an in vivo follow-up of the pathology and a better evaluation of the pharmacological activity of therapeutic molecules for the treatment of AD.

BackgroundLine‐field confocal optical coherence tomography (LC‐OCT) is an imaging technique providing “optical biopsies” of the skin in real time and non‐invasively. At a center optical wavelength of 1.3 µm, this innovative technology can be applied to dermo‐cosmetic product development due to both high image resolution (~2 µm) and sufficient penetration (~0.5 mm). Nevertheless, the precise dermal area analyzed with LC‐OCT has never been identified. In this study, the objective was to compare LC‐OCT images with histological sections of the same area, in order to validate a new method for in vivo and non‐invasive quantification of superficial dermis thickness. Once validated, this standardized and quantitative method was used to assess age‐related changes of the superficial dermis.Materials and MethodsEx vivo LC‐OCT acquisitions and hematoxylin‐eosin‐safran staining were performed on a panel of four healthy Caucasian female volunteers. In vivo LC‐OCT study of skin aging was performed on a panel of 37 healthy Caucasian female divided into five different age‐groups.ResultsComparison with histological sections revealed that LC‐OCT images allow the visualization and the quantification of the superficial portion of papillary dermis. Applied to different age‐group of volunteers, LC‐OCT images show a constant decrease in this superficial dermis thickness with age.ConclusionsIn conclusion, we have introduced LC‐OCT as a novel technique for in vivo and non‐invasive evaluation of superficial dermis thickness. This approach could be used in the future to demonstrate visually and quantitatively the capacity of a dermo‐cosmetic active ingredient to renormalize the structural properties of the dermis.

Dermal papilla cells (DPCs) play a pivotal role in the regulation of hair follicle (HF) growth, formation, and cycling, mainly through paracrine mechanisms. In the last decade, extracellular vesicles (EVs) have been recognized as a new paracrine mechanism that can modify the physiological state of recipient cells by transferring biological material. Herein, we investigated the effect of EVs isolated from stimulated human dermal fibroblasts (DFs) on DPC activation and HF growth. We found that these EVs (st-EVs) enhanced HF growth ex vivo. Comparative transcriptomic analysis on DPCs identified specific activation of the NDP gene, encoding the non-Wnt ligand Norrin. We found that Norrin was secreted by st-EVs-stimulated DPCs activating in a noncell autonomous manner β-catenin pathway in follicular keratinocytes (human HF keratinocyte [HHFK]) and hair growth ex vivo. Although Norrin-specific receptor Frizzled4 was barely detected in HHFK, we found its presence in DF-EVs. Accordingly, DF-EVs provided Frizzled4 to potentiate Norrin effects ex vivo. Our study identifies DF-EVs as efficient activators of DPCs and Norrin as a novel modulatory player in HF physiopathology. STEM CELLS 2019;37:1166-1175 SIGNIFICANCE STATEMENTDermal papilla cells (DPCs) control the growth and regeneration of hair follicles (HFs) via cellcell interactions and extracellular molecules. These data demonstrate that activated dermal fibroblasts (DFs) secrete specific extracellular vesicles (st-EVs) that enhance HF growth ex vivo. DPCs treated with st-EVs secrete Norrin, a non-Wnt ligand that activates the β-catenin pathway of recipient human hair follicular keratinocytes. DF-EVs contain Norrin-specific Frizzled4 receptor that is barely detected in human HF keratinocytes. Combinatory treatment of Norrin and DF-EVs is sufficient to recapitulate the stimulating effect ex vivo of st-EVs on HF growth. The study identifies Norrin as a novel modulatory player in HF physiopathology.

The inflammatory context contributes to the morphological, functional and transcriptomic changes observed in AD skin. As a result, this compromised RE model shares some characteristics with those found in AD skin and thus can be used as a relevant tool for screening formulations and drugs for the treatment of AD.

OBJECTIVE: Although xerosis is a common skin disorder among the population, there is no in vivo global study focusing on xerotic skin. Hence, the objective of this study was to characterize xerotic skin from the surface to the molecular scale with in vivo and noninvasive approaches. METHODS: For this purpose, 15 healthy volunteers with normal skin and 19 healthy volunteers with xerotic skin were selected by a dermatologist, thanks to a visual scorage. Firstly, the skin surface was characterized with biometric measurements. Then, the state of skin dryness was assessed by in vivo confocal microscopy. The molecular signature of xerotic skin was then determined by in vivo confocal Raman microspectroscopy. Finally, an identification of stratum corneum (SC) lipids was performed using Normal phase liquid chromatography (NP-LC) coupled to two detectors: Corona and High Resolution/Mass Spectroscopy (HR/MS). RESULTS: Results obtained at the skin surface displayed an increase in the transepidermal water loss (TEWL) and a decrease in the hydration rate in xerotic skin. Confocal microscopy revealed an alteration of the cell shape in xerotic skin. Moreover, confocal Raman microspectroscopy demonstrated directly in vivo and noninvasively the lack of organization and conformation of lipids in this skin. Finally, HPLC analyses revealed that the three ceramide sub-classes (NdS, NS and EOP) significantly decrease in xerosis. Altogether, these results identify parameters for the characterization of xerotic skin compared to normal. CONCLUSION: This study highlighted discriminative parameters from the surface to the molecular level in vivo and non-invasively between xerotic and normal skins. These results will be useful for the development of new cosmetic active ingredients dedicated to xerotic skin.