The impact of airborne ultrafine particulate matter on human keratinocyte stem cells.

OBJECTIVE: Air pollution is today fully acknowledged to be a significant public health problem. Rapid urbanization exposed us to a variety of unhealthy ambient air pollutants at high concentrations. The emergence of airborne ultrafine particles has added an additional dimension to this already complex problem of air pollution. The skin has different functions, one of them being the protection against the deleterious effect of external agents. The aim of this study is to evaluate the impact of airborne ultrafine particles (UFP) pollution on skin aging and on keratinocyte differentiation. METHODS: Ex vivo human skin biopsies and cultured keratinocytes stem cells (KSC) were submitted to diesel exhaust-derived UFP. Reactive oxygen species (ROS) production was assessed with the MitoSOX™ probe. Keratinocyte stemness potential was evaluated by the immunodetection of keratin 15 (K15) and p63 (∆N isoforms). Effect of UFP on the epithelial niche maintenance was evaluated by immunodetection of Sox9. Reconstructed epidermis model was used to assess the impact of UFP on keratinocyte differentiation and aging. RESULTS: UFP exposure induced ROS production and disturbed K15, ∆Np63 and Sox9 expression in KSC or ex vivo skin. Finally, investigations on reconstructed epidermis revealed a phenotype marked by impaired keratinocyte differentiation. CONCLUSION: These results indicate that UFP pollution is a potent extrinsic factor of skin aging, affecting the keratinocyte stem cell potential and the skin renewal process.

OBJECTIF: La pollution de l'air est désormais pleinement reconnue comme un problème de santé publique important. L'urbanisation rapide nous a exposés à une variété de polluants atmosphériques ambiants malsains à des concentrations élevées. L'émergence de particules ultrafines en suspension dans l'air a ajouté une dimension supplémentaire à ce problème déjà complexe de la pollution de l'air. La peau exerce différentes fonctions, l'une d'elles étant la protection contre l'effet délétère d'agents extérieurs. L'objectif de cette étude est d'évaluer l'impact de la pollution par les particules ultrafines (UFP) aéroportées sur le vieillissement cutané et sur la différenciation des kératinocytes. MÉTHODES: Des biopsies de peau humaine ex vivo et des kératinocytes souches (KSC) en culture ont été mis en présence d'UFP provenant d'échappement de véhicule diesel. La production d'espèces réactives de l'oxygène (ROS) a été évaluée avec la sonde MitoSOX™. Le potentiel de souche des kératinocytes a été évalué par immunodétection de la kératine 15 (K15) et p63 (isoformes ∆N). L'effet des UFP sur la niche épithéliale a été évalué par immunodétection de Sox9. Un modèle d'épiderme reconstruit a été utilisé pour évaluer l'impact des UFP sur la différenciation et le vieillissement des kératinocytes. RÉSULTATS: L'exposition aux UFP a induit la production de ROS, a perturbé l'expression de K15, ∆Np63 et de Sox9 dans les KSC et dans la peau ex vivo. Enfin, des investigations sur des épidermes reconstruits ont révélé un phénotype marqué par une différenciation altérée des kératinocytes. CONCLUSION: Ces résultats indiquent que la pollution par les UFP est un facteur extrinsèque puissant du vieillissement cutané, affectant le potentiel des cellules souches de kératinocytes et le processus de renouvellement cutané.

Modulation of Piezo1 influences human skin architecture and oxytocin expression.

OBJECTIVE: Throughout our existence, the skin senses and analyses the mechanical forces imposed by the environment. In response to these environmental forces, skin can deform itself and achieve a biological response. The subsequent cutaneous plasticity emerges from mechanical properties arising from the collective action of the skin cells, particularly keratinocytes, that govern the tensile strength via cell-to-cell adhesions and via cell-matrix adhesion structures. In addition to serving as force-bearing entities, keratinocytes respond to forces by activating signalling pathways to control their own fate and function. To detect and adapt to mechanical signals, keratinocytes possess a panel of sensory receptors and junctional intercellular structures. Mechanically activated ion channel Piezo1 has been described as a force sensor and as being involved in pleasant touch perception. In this study, relationships between Piezo1 modulation and oxytocin synthesis were investigated. METHODS: The expression of Piezo1 in the skin was studied and compared with the expression of TRPV1. Dooku1 antagonist and Jedi1 agonist were used to modulate Piezo1. The level of E-cadherin and oxytocin was monitored in ex vivo skin biopsies by immunodetection. RESULTS: Taken together, our results illustrate the major role of mechanosensitive ion channel Piezo1 in skin barrier integrity, and in peripheral oxytocin synthesis in the skin. CONCLUSION: In conclusion, this study highlights the relationships between pleasant touch, soft touch and local oxytocin synthesis.

OBJECTIF: Tout au long de notre existence, la peau détecte et analyse les forces mécaniques imposées par l'environnement. En réponse à ces forces environnementales, la peau peut se déformer et obtenir une réponse biologique. La plasticité cutanée qui s'ensuit émerge des propriétés mécaniques découlant de l'action collective des cellules cutanées, en particulier les kératinocytes, qui déterminent la résistance à la traction via les adhérences intercellulaires et les structures d'adhésion cellule-matrice. En plus de servir d'entités porteuses de force, les kératinocytes répondent aux forces en activant les voies de signalisation pour contrôler leur propre destin et leur propre fonction. Pour détecter et s'adapter aux signaux mécaniques, les kératinocytes possèdent un panel de récepteurs sensoriels et de structures intercellulaires jonctionnelles. Le canal ionique activé mécaniquement Piezo1 a été décrit comme un capteur de force et comme étant impliqué dans la perception d'un toucher agréable. Dans cette étude, les relations entre la modulation Piezo1 et la synthèse de l'ocytocine ont été étudiées. MÉTHODES: L'expression de Piezo1 dans la peau a été étudiée et comparée à l'expression de TRPV1. L'antagoniste Dooku1 et l'agoniste Jedi1 ont été utilisés pour moduler Piezo1. Le taux de cadhérine-E et d'ocytocine a été contrôlé dans des biopsies cutanées ex vivo par immunodétection. RÉSULTATS: Dans l'ensemble, nos résultats illustrent le rôle majeur du canal ionique mécanosensible Piezo1 dans l'intégrité de la barrière cutanée et dans la synthèse de l'ocytocine périphérique dans la peau. CONCLUSION: En conclusion, cette étude met en évidence les relations entre le toucher agréable, le toucher doux et la synthèse d'ocytocine locale.

Co-culture of iNeurons with primary human skin cells provides a reliable model to examine intercellular communication.

OBJECTIVE: The skin is a sensory organ, densely innervated with various types of sensory nerve endings, capable of discriminating touch, environmental sensations, proprioception, and physical affection. Neurons communication with skin cells confer to the tissue the ability to undergo adaptive modifications during response to environmental changes or wound healing after injury. Thought for a long time to be dedicated to the central nervous system, the glutamatergic neuromodulation is increasingly described in peripheral tissues. Glutamate receptors and transporters have been identified in the skin. There is a strong interest in understanding the communication between keratinocytes and neurons, as the close contacts with intra-epidermal nerve fibers is a favorable site for efficient communication. To date, various coculture models have been described. However, these models were based on non-human or immortalized cell line. Even the use of induced pluripotent stem cells (iPSCs) is posing limitations because of epigenetic variations during the reprogramming process. METHODS: In this study, we performed small molecule-driven direct conversion of human skin primary fibroblasts into induced neurons (iNeurons). RESULTS: The resulting iNeurons were mature, showed pan-neuronal markers, and exhibited a glutamatergic subtype and C-type fibers characteristics. Autologous coculture of iNeurons with human primary keratinocytes, fibroblasts, and melanocytes was performed and remained healthy for many days, making possible to study the establishment of intercellular interactions. CONCLUSION: Here, we report that iNeurons and primary skin cells established contacts, with neurite ensheathment by keratinocytes, and demonstrated that iNeurons cocultured with primary skin cells provide a reliable model to examine intercellular communication.

miR-203 represses keratinocyte stemness by targeting survivin.

OBJECTIVE: The epidermis possesses the capacity to replace dying cells and to heal wounds, thanks to resident stem cells, which have self-renewal properties. In skin physiology, miRNAs have been shown to be involved in many processes, including skin and hair morphogenesis. Recently, differentiation of epidermal stem cells was shown to be promoted by the miR-203. The miR-203 is upregulated during epidermal differentiation and is of interest because of significant targets. METHODS: By utilizing a bioinformatic tool, we identified a target site for miR-203 in the survivin mRNA. Silencing miR-203 was managed with the use of antagomir; the silencing of survivin was performed with a siRNA. Survivin expression was determined by qPCR or immunofluorescence in cultured cells, and by immunohistochemistry in skin sections. Involucrin expression was used as marker of keratinocyte differentiation. A rice extract with previously demonstrated anti-aging properties was evaluated on miR-203 modulation. RESULTS: In this study, we identified a miR-203/survivin axis, important for epidermal homeostasis. We report that differentiation of keratinocyte is dependent on the level of miR-203 expression and that inhibition of miR-203 can increase the expression of survivin, an epidermal marker of stemness. CONCLUSION: In summary, our findings suggest that miR-203 target 3'UTR region of survivin mRNA and directly represses survivin expression in the epidermis. The rice extract was identified as modulator of miR-203 and pointed out as a promising microRNA-based strategy in treating skin changes occurring with aging.

Reconstruction of functional human epidermis equivalent containing 5%IPS-derived keratinocytes treated with mitochondrial stimulating plant extracts.

Reconstructed human epidermis equivalents (RHE) have been developed as a clinical skin substitute and as the replacement for animal testing in both research and industry. KiPS, or keratinocytes derived from induced pluripotent stem cells (iPSCs) are frequently used to generate RHE. In this study, we focus on the mitochondrial performance of the KiPS derived from iPSCs obtained from two donors. We found that the KiPS derived from the older donor have more defective mitochondria. Treatment of these KiPS with a plant extract enriched in compounds known to protect mitochondria improved mitochondrial respiration and rendered them fully competent to derive high-quality RHE. Overall, our results suggest that improving mitochondrial function in KiPS is one of the key aspects to obtain a functional RHE and that our plant extracts can improve in this process.

Steroidogenic Factor-1 Lineage Origin of Skin Lesions in Carney Complex Syndrome.

Carney complex is a rare familial multineoplastic syndrome predisposing to endocrine and nonendocrine tumors due to inactivating mutations of PRKAR1A, leading to perturbations of the cAMP‒protein kinase A signaling pathway. Skin lesions are the most common manifestation of Carney complex, including lentigines, blue nevi, and cutaneous myxomas in unusual locations such as oral and genital mucosa. Unlike endocrine disorders, the pathogenesis of skin lesions remains unexplained. In this study, we show that embryonic invalidation of the Prkar1a gene in steroidogenic factor-1‒expressing cells leads to the development of familial skin pigmentation alterations, reminiscent of those in patients with Carney complex. Immunohistological and molecular analyses, coupled with genetic monitoring of recombinant cell lineages in mouse skin, suggest that familial lentiginosis and myxomas occur in skin areas specifically enriched in dermal melanocytes. In lentigines- and blue nevi‒prone areas from mutant mice and patients, Prkar1a/PRKAR1A invalidation occurs in a subset of dermal fibroblasts capable of inducing, under the influence of protein kinase A signaling, the production of promelanogenic EDN3 and hepatocyte GF signals. Our model strongly suggests that the origin of the typical Carney complex cutaneous lesions is the result of noncell-autonomous promelanogenic activity of a dermal fibroblast population sharing a community of origin with steroidogenic factor-1 lineage.

Characterization of a New Full-Thickness In Vitro Skin Model.

Since 30 years, bioengineering allowed to reconstruct human tissues using normal human cells. Skin is one of the first organ to be reconstructed thanks to the development of specific cell culture media and supports favoring the culture of human skin cells, such as fibroblasts, keratinocytes, or melanocytes. Skin models have evolved from epidermis to complex models including a dermis. The purpose of the present study was to design a reconstructed full-thickness (FT) skin suitable to perform in vitro testing of both molecules and plant extracts. First, we reconstructed epidermis with normal human keratinocytes displaying the expected multilayered morphology and expressing specific epidermal proteins (e-cadherin, claudin-1, p63, Ki67, Keratin 10, filaggrin, and loricrin). Then, a dermal equivalent was developed using a collagen matrix allowing the growth of fibroblasts. The functionality of the dermis was demonstrated by the measurement of skin parameters such as rigidity or elasticity with Ballistometer® and other parameters such as the contraction over time and the expression of dermal proteins. The combination of these two compartments (dermis and epidermis) allowed to reconstruct an FT model. This study model allowed to study the communication between compartments and with the establishment of a dermoepidermal junction showing the expression of specific proteins (collagen XVII, laminin, and collagen IV). Impact statement The objective of our research project was to design a three-dimensional human full-thickness (FT) skin suitable to perform in vitro testing of molecules and plant ingredients. The combination of these two reconstructed compartments (dermis and epidermis) allowed to reconstruct an FT model. This study model allowed to study the communication between compartments and with the establishment of a dermoepidermal junction showing the expression of specific proteins (collagen XVII, laminin, and collagen IV). This in vitro model can be use by cosmetic and pharmaceutical industries to study the effect of chemical or natural compounds on the skin.

Establishment and performance assessment of an in-house 3D Reconstructed Human Cornea-Like Epithelium (RhCE) as a screening tool for the identification of liquid chemicals with potential eye hazard.

The objective of this project was to develop an in-house 3D Reconstructed Human Cornea-Like Epithelium (RhCE) to be used as a screening tool in early stages of product development. This study reports the establishment of the experimental procedure and the performance assessment of the model to discriminate liquid chemicals classified as causing serious eye damage/irritation (UN-GHS Category 1/2) from liquid chemicals not requiring such hazard classification (UN-GHS No Category). Histological examination of this ocular equivalent model, based on Normal Human Keratinocytes (NHK) cultured in a chemically defined medium, revealed a stratified and well-organized tissue construct. Moreover, barrier robustness and functionality were demonstrated by the effective time-50 (ET50) of Triton X-100 measurement. The prediction model is based on cytotoxicity assessment following a test chemical exposure. When the mean tissue viability was over 60%, the chemical was defined as No Category; otherwise, it was classified as Category 1/2. In accordance with the applicable OECD guidance document (ENV/JM/MONO (2015)23), the performance of the model for eye hazard identification was evaluated with the minimum list of reference chemicals. As a result, the method scored 84.4% Accuracy, 70.8% Specificity, 100% Sensitivity and 93.3% for Concordance, demonstrating prediction performances close to those of Validated Reference Methods that are commonly used for regulatory purposes. Finally, these results suggest that this in-house RhCE based test method is a qualitative and accurate screening tool for eye hazard identification of liquid chemicals.

Property characterization of reconstructed human epidermis equivalents, and performance as a skin irritation model.

In recent years, in vitro skin models combining cell biology and tissue engineering have been developed in order to replace animal models for toxicological studies and to serve as research support to better understand skin biology. This study reports the development and characterization of a epidermal tissue equivalent meant to be used to develop and to evaluate the effect of applied cosmetic ingredients, and for alternative toxicological testing. This epidermis equivalent model was characterized relative to the morphological characteristics of short- and long-term maintained tissues by performing histological studies. We also studied the integrity of the epidermal barrier. Finally, with the goal of validating its use as a skin irritation test, we studied the irritation potential of 20 chemical references listed in OECD Test Guideline N°439 (In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method). In 2015, OECD officially published the updated version of the Validated Reference Method (VRM) that uses reconstructed human epidermis models for irritation testing, thus offering the possibility for proposed putative similar test methods to obtain a validation agreement through Performance Standards-based validation. In this study, we observed that the epidermal equivalent we developed showed similarities to human in vivo skin, based on the analyzed parameters. Moreover, its performances as a skin irritation test were similar to the ones described in the OECD Test Guideline N°439.

Modulating the expression of survivin and other basal epidermal proteins protects human skin from UVB damage and oxidative stress.

BACKGROUND: The chromosomal passenger complex (CPC) is an assembly made of four interacting proteins: survivin, borealin, INCENP, and aurora kinase B. CPC is the key regulatory complex responsible for the correct development of cellular mitosis, accompanying each step of the chromosomal segregation. This control of mitosis is particularly important in undifferentiated cells that must renew themselves and also further differentiate and specialize. The epidermis is a self-renewing tissue that needs to continuously generate new cells through proliferation and differentiation of progenitor cells. Both the mitosis supervision by the CPC and a correct extracellular environment are physiologically required for the homeostasis of the adult keratinocyte stem cells (KSCs) of the epidermis. KSCs are mainly found in the basal layer of the epidermis and are responsible for the replenishment and maintenance of the tissue, by compensating for the loss of terminally differentiated cells called corneocytes, especially during aging. AIM: The aim of our study was to investigate the implication of survivin in epidermal renewal and the relationships between survivin expression and UVB-induced DNA damage levels in cultured human keratinocytes and in skin biopsies. In parallel, the effects of a treatment by compound IV08.009 were studied. MATERIAL AND METHODS: Cultured human keratinocytes and skin biopsies were used in this study. KSCs-enriched fractions of keratinocytes were isolated from total keratinocytes by differential attachment to a type IV collagen matrix. Survivin expression levels were assessed by immunoblotting in cultured keratinocytes, and α6-integrin, ß1-integrin, keratin 15, and survivin were observed after immunodetection in skin biopsies cross sections. Comet assay, immunodetection of CPDs and of cleaved-caspase 3, and electron microscopy were used to characterize UVB-induced DNA damage. RESULTS: We demonstrated the ability of compound IV08.009 to efficiently protect ex vivo skin against basal UVB-induced damage. Moreover, comet assay studies demonstrated the efficacy of IV08.009 in protecting DNA damage from UVB stress. We found that IV08.009 protects skin from apoptosis induced by oxidative stress, ex vivo. Electron microscopy confirmed the protective efficiency of IV08.009 on cell ultrastructural damage induced by UVB exposure. CONCLUSION: Compound IV08.009 demonstrated to be effective in regulating survivin expression and in preserving the basal epidermis from stresses such as UVB and H2 O2 . These results suggest a protective activity of IV08.009 on the essential renewing potential of KSCs.

Modulation of telomere binding proteins: a future area of research for skin protection and anti-aging target.

Telomere shortening is considered as one of the main characteristics of cellular aging by limiting cellular division. Besides the fundamental advances through the discoveries of telomere and telomerase, which were recognized by a Nobel Prize, telomere protection remains an essential area of research. Recently, it was evidenced that studying the cross-talks between the proteins associated with telomere should provide a better understanding of the mechanistic basis for telomere-associated aging phenotypes. In this review, we discuss the current knowledge on telomere shortening, telomerase activity, and the essential role of telomere binding proteins in telomere stabilization and telomere-end protection. This review highlights the capacity of telomere binding proteins to limit cellular senescence and to maintain skin tissue homeostasis, which is of key importance to reduce accelerated tissue aging. Future studies addressing telomere protection and limitation of DNA damage response in human skin should include investigations on telomere binding proteins. As little is known about the expression of telomere binding proteins in human skin and modulation of their expression with aging, it remains an interesting field of skin research and a key area for future skin protection and anti-aging developments.

Skin presenting a higher level of caspase-14 is better protected from UVB irradiation according to in vitro and in vivo studies.

Caspase-14, a cysteine endoproteinase belonging to the conserved family of aspartate-specific proteinases, was shown to play an important role in the terminal differentiation of keratinocytes and barrier function of the skin. In the present study, we developed a biofunctional compound that we described as a modulator of caspase-14 expression. Using normal human keratinocytes (NHK) in culture and human skin biopsies, this compound was shown to increase caspase-14 expression and partially reverse the effect of caspase-14-specific siRNA on NHK. Moreover, the increase in filaggrin expression visualized on skin biopsies and the recovery of the barrier structure after tape-stripping indicated that this compound could exhibit a beneficial effect on the skin barrier function. Considering the possible link between caspase-14 and the barrier function, a UVB irradiation on NHK and skin biopsies previously treated with the caspase-14 inducer, was performed. Results indicated that pretreated skin biopsies exhibited less signs of UV damage such as active caspase-3 and cyclobutane pyrimidine dimers (CPDs). Likewise, pretreated NHK were protected from UV-induced genomic DNA damage, as revealed by the Comet Assay. Finally, a clinical test showed a reduction of transepidermal water loss (TEWL) on the treated skin compared with placebo, under UV stress condition, confirming a protecting effect. Taken together, these results strongly suggest that, by increasing caspase-14 expression, the biofunctional compound could exhibit a protective effect on the skin barrier function, especially in case of barrier damage and UV irradiation.

Mitochondria: a new focus as an anti-aging target in skin care.

Mitochondria, long considered to have the primary role in cellular energetic, have been the center of much research interest in the recent past. Technological advances in microscopy and development of new and specific fluorescent dyes for visualization of mitochondrial dynamics in living cells have facilitated the newfound interest in these fascinating organelles, which are now implicated in diverse cellular functions crucial in health and disease. Mitochondria play crucial roles in several age-related diseases, and in the physiology of normal aging. In this review, we discuss the structural and functional aspects of mitochondria and their implications to the aging process, as well as its significance to skin aging. Available information on active molecules that can impact the mitochondrial functions, and their potential use in skin care products is also discussed, highlighting these organelles as a new focus for anti-aging strategies in personal care.

Porcine odorant-binding protein selectively binds to a human olfactory receptor.

Odorant-binding proteins (OBPs) represent a highly abundant class of proteins secreted in the nasal mucus by the olfactory neuroepithelium. These proteins display binding affinity for a variety of odorant molecules, thereby assuming the role of carrier during olfactory perception. However, no specific interaction between OBP and olfactory receptors (ORs) has yet been shown and early events in olfaction remain so far poorly understood at a molecular level. Two human ORs, OR 17-209 and OR 17-210, were fused to a Green Fluorescent Protein and stably expressed in COS-7 cell lines. Interaction with OBP was investigated using a highly purified radioiodinated porcine OBP (pOBP) preparation, devoid of any ligand in its binding cavity. No specific binding of the pOBP tracer could be detected with OR 17-209. In contrast, OR 17-210 exhibited specific saturable binding (K(d) = 9.48 nM) corresponding to the presence of a single class of high-affinity binding sites (B(max) = 65.8 fmol/mg prot). Association and dissociation kinetics further confirmed high-affinity interaction between pOBP and OR 17-210. Autoradiographic studies of labeled pOBP to newborn mouse slices revealed the presence of multiple specific binding sites located mainly in olfactory tissue but also in several other peripheral tissues. Our data thus demonstrate a high-affinity interaction between OBP and OR, indicating that under physiological conditions, ORs may be specifically associated with an OBP partner in the absence of odorant. This provides further evidence of a novel role for OBP in the mechanism of olfactory perception.