Skin aging in humans is complex and is induced by internal and external factors. Studies have pointed towards biological processes including alterations in DNA repair and stability, mitochondrial function, cell cycle and apoptosis, ubiquitin-induced proteolysis, and cellular metabolism dysfunction. Untargeted metabolomics is key to better characterize and understand biological processes involved in (accelerated) aging at the level of multiple organ and tissues. Characterize metabolic changes in relation to human skin aging and explore if/how an extract from dessication tolerant medicinal herb, Myrothamnus flabellifolia, could affect skin aging and related metabolites. We evaluated clinical characteristics and untargeted metabolomic profiles of the skin of 32 individuals both before (D0) and after (D56) the application of a specific formulation containing extract from M. flabellifolia. Using conditional independence networks we explored how the formulation affected the correlation structure amongst skin metabolic features. Using an MWAS approach, we explored which molecular features were (i) dysregulated at the end of the experiment, and (ii) associated with changes in clinical characteristics during that period. Our analyses indicated clear metabolic changes and clinical improvement of skin radiance and texture after 56 days of treatment. Of the 419 assayed metabolites, 109 were either dysregulated at D56 or associated with at least one clinical sign. Of these, 12 compounds were detected in the green gel or red powder, the two active components of the extract, in particular trehalose, which was detected in both the green gel and the red powder. Collectively, this study demonstrates biochemical changes after application of the active formula, suggestive of its embodiment. Changes in the skin metabolome associated with the clinical signs we assayed helps hypothesizing molecular pathways involved in improvement of skin quality and aging signs.

Apparent skin age can be determined by several clinical measurements and may differ from chronological age, hence defining age acceleration/deceleration (Age A/D). Using data from 360 women with dermatological scoring of 21 clinical signs, we defined 3 well-separated co-occurring classes capturing the dryness, the elasticity and the oily nature of the skin. We related the risk of each clinical signs to the stratum corneum levels of 5 pre-selected proteins, we identified specific chronological age-adjusted signatures of each clinical sign. Using variable selection approaches, we identified 6 (of the 21) clinical signs which were jointly predictive of chronological age and used to define the clinical skin age, and subsequently age A/D. Applying univariate and multivariate approaches we found that stratum corneum levels of insulin degrading enzyme (IDE) was protective against (beta = - 1.74, p = 3.3 x 10(-6); selection proportion > 90%) accelerated skin ageing. In conclusion, our results support the fact that molecular markers found in the stratum corneum could predict skin ageing acceleration/deceleration.

Topically applied all-trans-retinoic acid (RA) is a gold-standard anti-aging molecule used in dermatology. As its cosmetic counterpart used in anti-aging, Retinol (ROL) is also a known metabolic precursor of RA. Despite this metabolic link, they haven’t been compared exhaustively in vivo at a mechanistic level. Therefore, to highlight the effect of a topical application of both molecules on in vivo skin, we undertook a longitudinal 1-year study and performed an untargeted proteomic analysis to get a more holistic view on the underlying biological mechanisms of action. The generation of the temporal proteomics signatures of retinol and all-trans-retinoic acid reveals the impact of these molecules on biological functions related to the aging of skin. New biological functions impacted by retinoids were discovered: glycan metabolism and protein biosynthesis. In addition, the temporal analysis reveals highest modulations at early time points while the physical measures, such as epidermal thickening, was mostly observed at the latest time point, demonstrating a strong time lapse between molecular and morphological impacts. Finally, these global temporal signatures could be used to identify new cosmetic compounds of interest.

Abstract Background The effects of air pollutants, particularly polycyclic aromatic hydrocarbons (PAHs), on the skin microbiome remain poorly understood. Thus, to better understand the interplay between air pollutants, microbiomes, and skin conditions, we applied metagenomics and metabolomics to analyze the effects of PAHs in air pollution on the skin microbiomes of over 120 subjects residing in two cities in China with different levels of air pollution. Results The skin microbiomes differentiated into two cutotypes (termed 1 and 2) with distinct taxonomic, functional, resistome, and metabolite compositions as well as skin phenotypes that transcended geography and host factors. High PAH exposure was linked to dry skin and cutotype 2, which was enriched with species with potential biodegradation functions and had reduced correlation network structure integrity. The positive correlations identified between dominant taxa, key functional genes, and metabolites in the arginine biosynthesis pathway in cutotype 1 suggest that arginine from bacteria contributes to the synthesis of filaggrin-derived natural moisturizing factors (NMFs), which provide hydration for the skin, and could explain the normal skin phenotype observed. In contrast, no correlation with the arginine biosynthesis pathway was observed in cutotype 2, which indicates the limited hydration functions of NMFs and explains the observed dry skin phenotype. In addition to dryness, skin associated with cutotype 2 appeared prone to other adverse conditions such as inflammation. Conclusions This study revealed the roles of PAHs in driving skin microbiome differentiation into cutotypes that vary extensively in taxonomy and metabolic functions and may subsequently lead to variations in skin–microbe interactions that affect host skin health. An improved understanding of the roles of microbiomes on skin exposed to air pollutants can aid the development of strategies that harness microbes to prevent undesirable skin conditions.

N-linked glycosylation is a major post-translational modification of proteins that conditions their biological functions (Varki et al., 2009). Glycomic studies identified precise N-glycans as biomarkers for cancer, rheumatoid arthritis, neurological diseases (Arnold et al., 2008), and aging (Kristic et al., 2014).

Metabolomics is emerging as a strong approach to understand the state of cellular and biological processes at different stages of the growth and disease. Metabolite profile can be viewed as the closest representation of a given phenotype including the skin. Skin retains numerous metabolites that either fulfill specific physiological function or are by-products of metabolism. The skin surface can be sampled in a non-invasive way to detect and quantify metabolites related to a disease or skin condition. Here, we performed untargeted metabolomics using mass-spectrometry, on skin samples from 134 women, aged 25-45 years, living in China. We detected 350 metabolites on skin surface of the study population. These women also underwent dermatological assessment for 16 different skin conditions that included pigmentary disorders, wrinkles, dry skin and acne etc. Each skin condition evaluation included an assessment of different sub-conditions or modalities, in total 35 modalities were recorded by dermatological examination. Taking different statistical approaches, we established metabolite profiles that correlated with each skin condition. To achieve this and for each skin condition, we divided the study subjects into 2 groups, with or without a condition. We proceeded to perform univariate and multivariate statistical analysis. Thus, we obtained a set of metabolites or molecular signature associated with each skin condition based on significant correlation. In order to understand the biological connection for each signature, we considered two approaches: metabolite pathway analysis and network inference, based on graphical models (graphical lasso). In conclusion, these molecular maps indicate towards involvement of skin biological processes such as barrier function, oxidative stress and DNA damage that could be linked/ associated to a skin clinical manifestation such as dry skin, wrinkles and pigmentary disorders.

Over time and with the evolution of discoveries, it appears that there are many physiological ways that lead to the development of hair loss in an individual. The direct deleterious role of inflammatory cytokines and chemokines and the contribution of effector morphogenetic pathways (mostly the Wnt/β-catenin pathway) together with systemic inflammatory pathways and lipid mediator synthesis entities have been highlighted (Garza et al., 2012Garza L.A. Liu Y. Yang Z. Alagesan B. Lawson J.A. Norberg S.M. et al.Prostaglandin D2 inhibits hair growth and is elevated in bald scalp of men with androgenetic alopecia.Sci Transl Med. 2012; 4: 126ra34Crossref PubMed Scopus (163) Google Scholar; Jaworsky et al., 1992Jaworsky C. Kligman A.M. Murphy G.F. Characterization of inflammatory infiltrates in male pattern alopecia: implications for pathogenesis.Br J Dermatol. 1992; 127: 239-246Crossref PubMed Scopus (166) Google Scholar; Mahé et al., 2000Mahé Y.F. Michelet J.F. Billoni N. Jarrousse F. Buan B. Commo S. et al.Androgenetic alopecia and microinflammation.Int J Dermatol. 2000; 39: 576-584Crossref PubMed Scopus (121) Google Scholar; Millar et al., 1999Millar S.E. Willert K. Salinas P.C. Roelink H. Nusse R. Sussman D.J. et al.WNT signaling in the control of hair growth and structure.Dev Biol. 1999; 207: 133-149Crossref PubMed Scopus (232) Google Scholar; Whiting, 1993Whiting D.A. Diagnostic and predictive value of horizontal sections of scalp biopsy specimens in male pattern androgenetic alopecia [published correction appears in J Am Acad Dermatol 1993;29:554].J Am Acad Dermatol. 1993; 28: 755-763Abstract Full Text PDF PubMed Scopus (283) Google Scholar). These identified effectors and targets are activated sequentially and to different proportions according to one’s genetic background, way of life, sex, and age. Thus, there is a need to better understand and diagnose an individual’s specific dysregulated processes responsible for hair loss to better define the best solution for that individual. We performed a full transcriptome sequencing on anagen pilosebaceous units (PUs) isolated from occipital and vertex scalp regions of 10 volunteers with Hamilton grade IV male androgenetic alopecia (Figure 1a and b). Tissue samples from hair transplant surgeries were collected with written informed patient consent after approval from the Centre Médico-Chirurgical du Cuir chevelu center, Paris, France. The noninvolved scalp regions were considered as a positive control to highlight which pathways are actually involved in the active mechanistic transduction and/or transmission of alopecia. Transcriptome-based principal component analysis perfectly helped in separating balding samples and control samples, with some samples being from different but close regions (Figure 1c). Comparative analysis of gene expression led to the identification of 1,336 differentially expressed genes (PBH < 0.05), of which 366 displayed at least a two-fold change between the balding and control samples (Supplementary Table S1). A heatmap construction of normalized expression values for the top modulated genes further illustrated these differences (Figure 1d). An overview of the 50 top-ranking pathways significantly enriched among the differentially expressed genes is provided in Supplementary Table S2. It revealed enrichment in previously described gene ontology terms associated with hair follicle (HF) development, Wnt/β-catenin and TGF-β/BMP signaling pathways deregulation, and cytokinic and PG imbalances (Andl et al., 2002Andl T. Reddy S.T. Gaddapara T. Millar S.E. WNT signals are required for the initiation of hair follicle development.Dev Cell. 2002; 2: 643-653Abstract Full Text Full Text PDF PubMed Scopus (758) Google Scholar; Garza et al., 2012Garza L.A. Liu Y. Yang Z. Alagesan B. Lawson J.A. Norberg S.M. et al.Prostaglandin D2 inhibits hair growth and is elevated in bald scalp of men with androgenetic alopecia.Sci Transl Med. 2012; 4: 126ra34Crossref PubMed Scopus (163) Google Scholar; Jaworsky et al., 1992Jaworsky C. Kligman A.M. Murphy G.F. Characterization of inflammatory infiltrates in male pattern alopecia: implications for pathogenesis.Br J Dermatol. 1992; 127: 239-246Crossref PubMed Scopus (166) Google Scholar; Mahé et al., 2000Mahé Y.F. Michelet J.F. Billoni N. Jarrousse F. Buan B. Commo S. et al.Androgenetic alopecia and microinflammation.Int J Dermatol. 2000; 39: 576-584Crossref PubMed Scopus (121) Google Scholar; Millar et al., 1999Millar S.E. Willert K. Salinas P.C. Roelink H. Nusse R. Sussman D.J. et al.WNT signaling in the control of hair growth and structure.Dev Biol. 1999; 207: 133-149Crossref PubMed Scopus (232) Google Scholar; Whiting, 1993Whiting D.A. Diagnostic and predictive value of horizontal sections of scalp biopsy specimens in male pattern androgenetic alopecia [published correction appears in J Am Acad Dermatol 1993;29:554].J Am Acad Dermatol. 1993; 28: 755-763Abstract Full Text PDF PubMed Scopus (283) Google Scholar) (Supplementary Tables S2 and S3). In addition to these findings that agree with previous research, we could highlight a profound alteration in the expression of HF junctional proteins in alopecia regions (Figure 2a and Supplementary Table S2), especially cadherin-based junctional complexes consisting of adherens junctions and desmosomes. For example, the major component of adherens junctions, E-cadherin (CDH1), was decreased by at least 25% in 70% of progression areas of alopecia (Figure 2b). E-cadherin is a calcium-dependent glycoprotein that links neighboring cells through homotypic interactions. Its cytoplasmic domains can associate with various partners, including β- and δ-catenins (CTNNB1 and CTNND1, respectively). Cadherin-catenin complexes thus mediate the coupling of the intracellular actin cytoskeleton of neighboring cells (Aberle et al., 1996Aberle H. Schwartz H. Kemler R. Cadherin-catenin complex: protein interactions and their implications for cadherin function.J Cell Biochem. 1996; 61: 514-523Crossref PubMed Scopus (709) Google Scholar). The expression of β-catenin (CTNNB1), β-actin (ACTB), and actin-binding proteins such as tubulins (TUBB and TUBB2A), gelsolin (GSN), and myosins (MYO3B, MYO5B, and MYO6) also decreased in alopecic PUs (Figure 2a). These results coincide with findings showing that loss of E-cadherins alters the proliferation and differentiation of the HFs, thus compromising adherens junctions and loosening intercellular tightness in the inner root sheath and the hair cuticle (Tinkle et al., 2004Tinkle C.L. Lechler T. Pasolli H.A. Fuchs E. Conditional targeting of E-cadherin in skin: insights into hyperproliferative and degenerative responses.Proc Natl Acad Sci USA. 2004; 101: 552-557Crossref PubMed Scopus (150) Google Scholar; Young et al., 2003Young P. Boussadia O. Halfter H. Grose R. Berger P. Leone D.P. et al.E-cadherin controls adherens junctions in the epidermis and the renewal of hair follicles.EMBO J. 2003; 22: 5723-5733Crossref PubMed Scopus (112) Google Scholar). Similarly, other various genes encoding desmosomal cadherins were found to be underexpressed in balding PUs (Figure 2a). Desmosomes are known to orchestrate proliferation to differentiation transition events during HF induction and cycling. For instance, desmoglein 4 gene, which is highly abundant in HFs, was shown to be mutated in families with inherited hypotrichosis, and this was associated with compromised desmosomal adhesion and perturbed keratinocyte behavior (Kljuic et al., 2003Kljuic A. Bazzi H. Sundberg J.P. Martinez-Mir A. O'Shaughnessy R. Mahoney M.G. et al.Desmoglein 4 in hair follicle differentiation and epidermal adhesion: evidence from inherited hypotrichosis and acquired pemphigus vulgaris.Cell. 2003; 113: 249-260Abstract Full Text Full Text PDF PubMed Scopus (270) Google Scholar). Indeed, we found decreased expression of desmoglein 4 gene in all balding samples (Figure 2c). In addition to cadherin-based junctions, intercellular communications can be mediated through gap junctions. In our transcriptomes, GJA1, GJA3, GJB2, and GJB6 were also found to be significantly downregulated in alopecia regions (Figure 2a, 2d–g). These genes are expressed in dermal papilla and connective tissue sheath cells and are believed to have a critical role in hair tissue homeostasis (Iguchi et al., 2003Iguchi M. Hara M. Manome H. Kobayasi H. Tagami H. Aiba S. Communication network in the follicular papilla and connective tissue sheath through gap junctions in human hair follicles.Exp Dermatol. 2003; 12: 283-288Crossref PubMed Scopus (16) Google Scholar; Salomon et al., 1994Salomon D. Masgrau E. Vischer S. Ullrich S. Dupont E. Sappino P. et al.Topography of mammalian connexins in human skin.J Invest Dermatol. 1994; 103: 240-247Crossref PubMed Scopus (122) Google Scholar). To rule out the possibility that decreased expression of these markers is due to a smaller dermal papilla in alopecia PUs, a set of defined human dermal papilla signature genes (Ohyama et al., 2012Ohyama M. Kobayashi T. Sasaki T. Shimizu A. Amagai M. Restoration of the intrinsic properties of human dermal papilla in vitro.J Cell Sci. 2012; 125: 4114-4125Crossref PubMed Scopus (99) Google Scholar) was compared. Interestingly, we observed similar expression levels of the dermal genes in balding and nonbalding conditions (Supplementary Figure S1), suggesting that the downregulation of gap junction and other junctional genes is independent of the size of dermal papilla. Finally, a last set of genes encoding tight junction components were found in lower amounts in individuals with balding PUs than in controls (Figure 2a). Widespread in HFs, tight junction proteins form an effective seal between the hair and the surrounding dermis. Their expression and distribution change during HF cycles and play important functions in hair growth and regression (Brandner et al., 2003Brandner J.M. McIntyre M. Kief S. Wladykowski E. Moll I. Expression and localization of tight junction-associated proteins in human hair follicles.Arch Dermatol Res. 2003; 295: 211-221Crossref PubMed Scopus (52) Google Scholar). We next undertook a deep analysis of transcriptomic datasets available in public repositories (GSE90594 and GSE36169) comparing balding versus nonbalding full scalp biopsies (Garza et al., 2012Garza L.A. Liu Y. Yang Z. Alagesan B. Lawson J.A. Norberg S.M. et al.Prostaglandin D2 inhibits hair growth and is elevated in bald scalp of men with androgenetic alopecia.Sci Transl Med. 2012; 4: 126ra34Crossref PubMed Scopus (163) Google Scholar; Michel et al., 2017Michel L. Reygagne P. Benech P. Jean-Louis F. Scalvino S. Ly Ka So S. et al.Study of gene expression alteration in male androgenetic alopecia: evidence of predominant molecular signalling pathways.Br J Dermatol. 2017; 177: 1322-1336Crossref PubMed Scopus (18) Google Scholar). We compared obtained lists of differentially expressed genes (P < 0.05) with our predefined 23 junctional gene set. Interestingly, we confirmed a high overlap of downregulated junctional genes (16 of 23; ∼70% in GSE90594, and 10 of 23; ∼43% in GSE36169) with their gene lists, with additional eight junctional genes that were specifically downregulated in either studies (Figure 2h and Supplementary Table S4). These data likely suggest a global mechanism of junctional alterations that may have an impact not only on the HF itself but also on its surrounding scalp environment. Altogether, our findings provide us with additional insights into androgenetic alopecia pathogenesis. We propose that by analogy with atopic dermatitis and to lesser extent seasonal skin dryness, the alterations of the scalp barrier function and HFs junctional networks could constitute a previously unreported hallmark of alopecia. This to date neglected target may allow to develop pharmacologically and physically strategies to protect the follicular units from chronic perifollicular assaults by pollutants, chemical, physical, or microbial aggressors to limit the oxyinflammatory cascade into the HF unit. Datasets related to this article have been submitted to the ArrayExpress database under the accession number E-MTAB-9557. Elias Bou Samra: http://orcid.org/0000-0002-3728-3804 Yann Franck Mahé: http://orcid.org/0000-0001-7403-4471 Mickael Le Balch: http://orcid.org/0000-0002-4435-3452 Nükhet Cavusoglu: http://orcid.org/0000-0001-9350-5312 Pierre Bouhanna: http://orcid.org/0000-0003-1158-8965 Khalid Bakkar: http://orcid.org/0000-0002-0088-9431 Conceptualization: KB, YFM, EBS; Data Curation: YFM, EBS; Formal Analysis: EBS; Investigation: KB, MLB; Methodology: NC, EBS; Resources: PB; Supervision: NC, EBS; Validation: EBS; Writing – Original Draft Preparation: YM, EBS The authors state no conflict of interest. Download .xlsx (.12 MB) Help with xlsx files Table S1 Download .xlsx (5.36 MB) Help with xlsx files Table S2 Download .xlsx (.02 MB) Help with xlsx files Table S3 Download .xlsx (.02 MB) Help with xlsx files Table S4 This study was approved by the Medical and Surgical Scalp Center of Wagram (CMCC Wagram, Paris, France) Ethics Committee. Written informed consent was obtained from all participants. The study included 10 male individuals diagnosed with androgenetic alopecia (Hamilton–Norwood classification grade IV, age range = 23–66, median age = 42.9), who were undergoing elective hair transplantation surgery. For each donor, 10 pilosebaceous units (PUs) at the anagen phase were isolated from each involved (balding; vertex) and noninvolved (control; occipital) scalp region using the follicular unit extraction technique. Less invasive than other grafting techniques, the follicular unit extraction procedure does not use a scalpel and removes PUs one by one using circular micropunches whose diameter does not exceed 0.9 mm. Isolated PUs were immediately placed into a vial for RNA extraction. Each PU consisted of epithelial components, which include the inner root sheath and outer root sheath and the matrix; mesenchymal components, which include the dermal papilla and connective tissue sheath; and the sebaceous glands surrounded by arrector pili muscles. To obtain sufficient mRNA material for sequencing procedures, 10 PUs were dissected and pooled for occipital and vertex areas from each donor. Total RNA was isolated from the 20 samples with the RNeasy micro kit (Qiagen, Germantown, MD). Purity and integrity of the RNA was assessed on the Agilent 2100 Bioanalyzer with the RNA 6000 NanoLabChip reagent set (Agilent Technologies, Palo Alto, CA) and the Nanodrop spectrophotometer (ThermoScientific, Wilmington, DE). All samples had RNA integrity number values > 7. Library preparation and RNA sequencing were carried out as described in the NuGEN Ovation Universal RNA-Seq System User Guide (NuGEN Technologies, San Carlos, CA), the Illumina NextSeq 500 System Guide (Illumina, San Diego, CA), and the KAPA Library Quantification Kit - Illumina/ABI Prism User Guide (Kapa Biosystems, Woburn, MA). In brief, 75 ng of total RNA were reverse transcribed into first strand cDNA using a mixture of random and poly-dT primers, omitting the integrated DNase treatment step. Second strand synthesis, using a nucleotide analog enabling strand retention, generated double stranded cDNA. The double stranded cDNA was fragmented to an average size of 200–500 bases. Next, an end repair was performed to generate blunt-ended double stranded cDNA, followed by the ligation of the indexing adapters, a strand selection via nucleotide analog-targeted degradation and a reduction of the rRNA content. Finally, cDNA libraries were created by 18 cycles PCR enrichment. Equimolar amounts of each library were sequenced on a NextSeq 500, for a 75-nucleotides paired-end sequencing. The effective library sizes were computed using function calcNormFactors from the edgeR package (Robinson et al., 2010Robinson M.D. McCarthy D.J. Smyth G.K. edgeR: a Bioconductor package for differential expression analysis of digital gene expression data.Bioinformatics. 2010; 26: 139-140Crossref PubMed Scopus (18080) Google Scholar). Mean-variance relationship was estimated using the voom function from the limma package (Ritchie et al., 2015Ritchie M.E. Phipson B. Wu D. Hu Y. Law C.W. Shi W. et al.limma powers differential expression analyses for RNA-sequencing and microarray studies.Nucleic Acids Res. 2015; 43: e47Crossref PubMed Scopus (12284) Google Scholar) and injected into the statistical model as observational-level weights. Linear regression models were applied using function lm from the stats package. Comparisons of interest were computed through statistical contrasts, using the emmeans package (Lenth, 2016Lenth R.V. Least-squares Means: the R package lsmeans.J Stat Softw. 2016; 69: 33Crossref Scopus (3396) Google Scholar). The empirical Bayes method (function eBayes from the limma package) was used to compute moderated P-values. The P-values were then corrected for multiple comparisons using the Benjamini and Hochberg’s false discovery rate controlling procedure (function p.adjust from package stats with parameter method=BH). Principal component analyses of sample expression levels are performed with gene signals centered but not scaled (using function prcomp from package stats). Hierarchical clustering of genes is performed using the complete agglomerative method, passing the Euclidean distances between centered and scaled gene signals to function hclust from package stats. Datasets related to this article can be found at https://www.ebi.ac.uk/arrayexpress/experiments/E-MTAB-9557/, hosted at ArrayExpress database (Athar et al., 2019Athar A. Füllgrabe A. George N. Iqbal H. Huerta L. Ali A. et al.ArrayExpress update - from bulk to single-cell expression data.Nucleic Acids Res. 2019; 47: D711-D715Crossref PubMed Scopus (221) Google Scholar).

Environmental pollution is composed of several factors, namely particulate matter (PM 2.5 , PM 10 ), ozone and Ultra Violet (UV) rays among others and first and the most exposed tissue to these substances is the skin epidermis. It has been established that several skin disorders such as eczema, acne, lentigines and wrinkles are aggravated by exposure to atmospheric pollution. While pollutants can interact with skin surface, contamination of deep skin by ultrafine particles or Polycyclic aromatic hydrocarbons (PAH) might be explained by their presence in blood and hair cortex. Molecular mechanisms leading to skin dysfunction due to pollution exposure have been poorly explored in humans. In addition to various host skin components, cutaneous microbiome is another target of these environment aggressors and can actively contribute to visible clinical manifestation such as wrinkles and aging. The present study aimed to investigate the association between pollution exposure, skin microbiota, metabolites and skin clinical signs in women from two cities with different pollution levels. Untargeted metabolomics and targeted proteins were analyzed from D-Squame samples from healthy women (n = 67 per city), aged 25–45 years and living for at least 15 years in the Chinese cities of Baoding (used as a model of polluted area) and Dalian (control area with lower level of pollution). Additional samples by swabs were collected from the cheeks from the same population and microbiome was analysed using bacterial 16S rRNA as well as fungal ITS1 amplicon sequencing and metagenomics analysis. The level of exposure to pollution was assessed individually by the analysis of polycyclic aromatic hydrocarbons (PAH) and their metabolites in hair samples collected from each participant. All the participants of the study were assessed for the skin clinical parameters (acne, wrinkles, pigmented spots etc.). Women from the two cities (polluted and less polluted) showed distinct metabolic profiles and alterations in skin microbiome. Profiling data from 350 identified metabolites, 143 microbes and 39 PAH served to characterize biochemical events that correlate with pollution exposure. Finally, using multiblock data analysis methods, we obtained a potential molecular map consisting of multi-omics signatures that correlated with the presence of skin pigmentation dysfunction in individuals living in a polluted environment. Overall, these signatures point towards macromolecular alterations by pollution that could manifest as clinical sign of early skin pigmentation and/or other imperfections.

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.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Skin is particularly exposed to oxidative stress, either from environmental insults such as sunlight or pollution or as a consequence of specific impairments in antioxidant status resulting from pathologies or aging. Traditionally, antioxidant products are exogenously provided to neutralize pro-oxidant species. However, another approach based on stimulation of endogenous antioxidant defense pathways is more original. Resveratrol (RSV) was reported to activate the Nrf2 pathway at nontoxic doses, from 20 μM up to 100μM, in primary culture of NHKs or in full-thickness reconstructed human skin. In parallel, a significant increase in glutathione (GSH) content, assessed by LC/MS analysis, was observed in both models. Following the development of a dedicated protocol for the reconstructed skin sectioning, a perfect visualization of the Stratum corneum, Epidermis was obtained on 10μm sections of some frozen samples. Thus MALDI-FTICR imaging at 20μm of spatial resolution was used to investigate the GSH distribution and relative quantification in both Stratum corneum and Epidermis of RSV treated reconstructed human skins at 20 and 100μM compared to a non-treated condition. GSH amount was confirmed to be significatively increased in the reconstructed tissues following a Resveratrol treatment at 20 μM and 100μM.

BackgroundSkin acts as a protective barrier against direct contact with pollutants but inhalation and systemic exposure have indirect effect on keratinocytes. Exposure to diesel exhaust has been linked to increased oxidative stress.ObjectiveTo investigate global proteomic alterations in diesel particulate extract (DPE)/ its vapor exposed skin keratinocytes.MethodsWe employed Tandem Mass Tag (TMT)-based proteomics to study effect of DPE/ DPE vapor on primary skin keratinocytes.ResultsWe observed an increased expression of oxidative stress response protein NRF2, upon chronic exposure of primary keratinocytes to DPE/ its vapor which includes volatile components such as polycyclic aromatic hydrocarbons (PAHs). Mass spectrometry-based quantitative proteomics led to identification 4490 proteins of which 201 and 374 proteins were significantly dysregulated (≥1.5 fold, p ≤ 0.05) in each condition, respectively.Proteins involved in cellular processes such as cornification (cornifin A), wound healing (antileukoproteinase) and differentiation (suprabasin) were significantly downregulated in primary keratinocytes exposed to DPE/ DPE vapor. These results were corroborated in 3D skin models chronically exposed to DPE/ DPE vapor. Bioinformatics analyses indicate that DPE and its vapor affect distinct molecular processes in skin keratinocytes. Components of mitochondrial oxidative phosphorylation machinery were seen to be exclusively overexpressed upon chronic DPE vapor exposure. In addition, treatment with an antioxidant like vitamin E partially restores expression of proteins altered upon exposure to DPE/ DPE vapor.ConclusionsOur study highlights distinct adverse effects of chronic exposure to DPE/ DPE vapor on skin keratinocytes and the potential role of vitamin E in alleviating adverse effects of environmental pollution.

Skin is particularly exposed to oxidative stress, either from environmental insults such as sunlight or pollution or as a consequence of specific impairments in antioxidant status resulting from pathologies or aging. Traditionally, antioxidant products are exogenously provided to neutralize pro-oxidant species. However, another approach based on stimulation of endogenous antioxidant defense pathways is more original. Resveratrol (RSV) was reported to activate the Nrf2 pathway at nontoxic doses, from 20 μM up to 100μM, in primary culture of NHKs or in full-thickness reconstructed human skin. In parallel, a significant increase in glutathione (GSH) content, assessed by LC/MS analysis, was observed in both models. Following the development of a dedicated protocol for the reconstructed skin sectioning, a perfect visualization of the Stratum corneum, Epidermis was obtained on 10μm sections of some frozen samples. Thus MALDI-FTICR imaging at 20μm of spatial resolution was used to investigate the GSH distribution and relative quantification in both Stratum corneum and Epidermis of RSV treated reconstructed human skins at 20 and 100μM compared to a non-treated condition. GSH amount was confirmed to be significatively increased in the reconstructed tissues following a Resveratrol treatment at 20 μM and 100μM.

Cigarette smoking has been associated with multiple negative effects on human skin. Long-term physiological effects of cigarette smoke are through chronic and not acute exposure. Molecular alterations due to chronic exposure to cigarette smoke remain unclear. Primary human skin keratinocytes chronically exposed to cigarette smoke condensate (CSC) showed a decreased wound-healing capacity with an increased expression of NRF2 and MMP9. Using quantitative proteomics, we identified 4728 proteins, of which 105 proteins were overexpressed (≥2-fold) and 41 proteins were downregulated (≤2-fold) in primary skin keratinocytes chronically exposed to CSC. We observed an alteration in the expression of several proteins involved in maintenance of epithelial barrier integrity, including keratin 80 (5.3 fold, p value 2.5 × 10-7), cystatin A (3.6-fold, p value 3.2 × 10-3), and periplakin (2.4-fold, p value 1.2 × 10-8). Increased expression of proteins associated with skin hydration, including caspase 14 (2.2-fold, p value 4.7 × 10-2) and filaggrin (3.6-fold, p value 5.4 × 10-7), was also observed. In addition, we report differential expression of several proteins, including adipogenesis regulatory factor (2.5-fold, p value 1.3 × 10-3) and histone H1.0 (2.5-fold, p value 6.3 × 10-3) that have not been reported earlier. Bioinformatics analyses demonstrated that proteins differentially expressed in response to CSC are largely related to oxidative stress, maintenance of skin integrity, and anti-inflammatory responses. Importantly, treatment with vitamin E, a widely used antioxidant, could partially rescue adverse effects of CSC exposure in primary skin keratinocytes. The utility of antioxidant-based new dermatological formulations in delaying or preventing skin aging and oxidative damages caused by chronic cigarette smoke exposure warrants further clinical investigations and multi-omics research.

The study aimed at detecting differentially expressed proteins in the stratum corneum of dandruff versus non-dandruff scalps to better understand dandruff aetiology. iTRAQ-based quantitative proteomic analysis revealed a total of 68 differentially expressed biomarkers. A detailed analysis of their known physiological functions provided new insights into the affected metabolic pathways of a dandruff scalp. Dandruff scalp showed (1) profound changes in the expression and maturation of structural and epidermal differentiation related proteins, that are responsible for the integrity of the skin, (2) altered relevant factors that regulate skin hydration, and (3) an imbalanced physiological protease–protease inhibitor ratio. Stratum corneum proteins with antimicrobial activity, mainly those derived from sweat and sebaceous glands were also found modified. Comparing our data with those reported for atopic dermatitis revealed that about 50 % of the differentially expressed proteins in the superficial layers of the stratum corneum from dandruff and atopic dermatitis are identical.