Heterogeneity in skin surface and barrier function have been reported among skin color types. Since, epidermal morphogenesis is the result of a balance between keratinocyte proliferation and differentiation processes, we aimed to characterize the epidermis biology between African descent skin type and European descent skin type on ex-vivo and in vitro tissues. Firstly, ex vivo skin samples from dark/brown skin type and light/intermediary/tan skin type of young donors (n=10 per skin type) were used to compare the expression of epidermal markers keratins 14 and 15 (K14/K15) and filaggrin, as well as proliferation marker (Ki67) between skin color types. Secondly, epidermal morphogenesis is influenced by the cross-talk between keratinocytes and dermal fibroblasts; thus, we investigated the behavior of keratinocytes isolated of each skin type using a full-thickness in vitro skin model with a dermal equivalent containing papillary fibroblasts from each skin types (n=3/4 per skin type). We observed that darker skin types have increased proliferation and lower level of K14, K15 and filaggrin when compared to lighter skin types. In vitro skin reconstruction with keratinocytes of dark skins have shown lower granular layers, lower filaggrin 1 and 2 accumulation in stratum corneum. Expression of mRNA for terminal differentiation processes were regulated differently between keratinocytes of darker skins and lighter skins in in vitro model. Additionally, reconstructed skins created with fibroblasts from dark skins have increased KGF secretion levels and increased epidermal proliferation when compared with the skin model with fibroblasts from lighter skin types. Overall, this study brought evidences that both keratinocytes and fibroblasts contribute to the different behavior of different skin color types upon some skin disorders and aging.

N-linked glycosylation is an important post translational modification of proteins that highly conditions their structure and biological function. Human blood plasma glycomics have shown that significant decreases of complex N-glycans are observed with aging. In skin, glycomic studies have shown that the epidermis is characterized by an abundance of high mannose N-glycosylated proteins, that play a role in SC lipid remodeling, desquamation and barrier function. In this study, the N-glycome of the stratum corneum (SC) was characterized and over 30 different types of N-glycans were identified including oligomannose, hybrid and complex N glycans. In small clinical cohorts (n=10) where the SC was sampled from aged and dry skin no qualitative differences in the N glycome were identified. However, significant quantitative decreases were observed for some N-glycans. Thus, changes in N-glycosylation, during aging and in dry skin conditions, may alter SC desquamation, barrier function, hydration and microbiome diversity. These novel glycan biomarkers should help in both the development and selection of glycan-mimics as potential cosmetic ingredients to treat the condition of aged and/or dry skin.

Topical skin cleansers are commonly used products to clean the skin. To investigate the time needed for skin and its microbiota to recover, a group of 30 healthy volunteers from 30 to 50 years old were selected according to both photo ageing and chronological age score. We evaluated the skin before, immediately after, 3h and 6h after cleansing using a harsh soap. Especially, total bacterial load by QPCR (V1-V3 16S rRNA KAPA Biosystems kit with SYBER Green), bacterial community using Next generation sequencing (Amplification V1-V3 on Illumina MiSeq platform) in addition to skin clinical evaluation, self-assessment and instrumental methods were followed during this clinical trial. Instrumental evaluation including skin hydration, barrier function and pH are altered just after cleansing and recover within 6 hours. Clinical expert evaluation and self-assessment revealed that a harsh wash increases dryness, roughness and discomfort and these skin alterations do not recover even after 6 hours. The harsh wash decreased the quantity, diversity and changes the community structure of the skin bacterial communities. Importantly compared to before washing the alterations on skin bacteria after 3 hours are higher (load and beta diversity) than just after washing meaning that the skin bacteria has difficulty to recover. In addition, skin bacteria are not at all recovered after 6h. All this important findings show that it is important to propose a skin routine that will firstly clean by respecting the diversity of skin microbiota secondly will feed the skin microbiota and facilitate their recovery.

In atopic dermatitis (AD), the skin barrier is disturbed, and the expression of calcium-dependent S100 proteins and the calcium gradient is also altered in the epidermis. The calmodulin-like skin protein (CLSP), which is expressed in the differentiated epidermis, is believed to modulate the function of calcium-dependent proteins involved in barrier formation and is significantly increased in the epidermis of psoriatic patients. We, therefore, investigated the CLSP level in skin biopsies taken from patients with acute exacerbated and non-exacerbated AD as well as from healthy control subjects. Immunohistochemical, Western blot and ELISA analyses showed significant increases (P < 0.03) in CLSP level in the epidermis from patients with acute exacerbated AD as compared to that from patients with non-exacerbated AD and from control subjects. Such increased expression of CLSP may help re-establish a functional epidermal barrier in acute AD.

Using fluorescein isothiocyanate (FITC)-labeled lectins we were able to demonstrate the presence of specific carbohydratemoieties in normal human and reconstructed epidermis. Evidence is provided that in both cases the strongly reduced lectin staining at the level of the stratum corneum is the result of a hindered accessibility of the lectins in this lipid-rich hydrophobic environment. Isolated corneocytes and purified cornified envelopes (CEs) exhibited clearly glycosylated structures reacting with distinct lectins. The presence of glycosidase activity, particularly in the upper layers of the epidermis characterized by an acidic environment (pH 5.5), indicates that modifications of the sugar residues might be important in epidermal homeostasis, barrier behavior and desquamation. Absent or strongly reduced glycosidase activity in the stratum corneum of reconstructed epidermis with an impaired pH gradient could be in part responsible for the reduced barrier function and the lack of desquamation in this model.