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Because they limit, even reverse, age-induced skin alterations, retinoids became a staple in cosmetology. However, their use can result in undesired secondary effects and there is a demand for natural sources of compounds with retinoid-like effects. A preliminary screening identified a Harungana madagascariensis plant extract (HME) as possibly inducing genes stimulated by retinol. We analysed its effect on gene and protein expression, comparing it to retinoids.Gene expression was analysed by real-time qPCR on RNA from isolated fibroblasts subjected to retinol or the plant extract for 6, 48 or 96 h. Skin markers were quantified in fibroblasts cultured with retinol or extract containing medium, and UV-aged skin explants subjected to topical applications of creams containing retinol, retinaldehyde or HME.Real-time qPCR shows that the extract induced all RARs and RXRs, even RXRγ that was not induced by retinol. Eighty-eight per cent of the 25 early retinoid reaction genes induced by a concentration of retinol are induced by the extract. In fibroblasts, only the extract increased collagen III labelling, while collagen I and fibronectin labelling are increased by retinol and the extract, with higher levels for the extract. When topically applied to UV-aged skin explants, only the cream containing the HME led to increased labelling of CRABP1 in the epidermis. CRABP2 and Ki67 are induced by all three creams and no effect was detected on RXRs. In the dermisthe extract containing cream increased CRABP2, total collagen, procollagen I and collagen I while creams with retinol or retinaldehyde only affected some of these proteins.The HME induces an overall retinol-like gene induction profile in isolated fibroblasts and retinoid-like stimulation of protein synthesis in both isolated fibroblasts and photoaged skin explants.Limitant, voire inversant les altérations cutanées induites par l'âge, les rétinoïdes sont devenus incontournables en cosmétologie. Cependant, leur application topique peut entraîner des effets secondaires indésirables et il existe une demande pour des composés naturels ayant des effets similaires à ceux des rétinoïdes. Un screening préliminaire nous avait permis d'identifier un extrait de la plante Harungana madagascariensis (HME) comme pouvant induire des gènes stimulés par le rétinol. Nous avons donc analysé son effet sur l'expression de gènes et de protéines induits par les rétinoïdes et comparé les résultats à ceux obtenus en présence de rétinoïdes. MÉTHODES: L'expression de gènes a été analysée par qPCR en temps réel réalisée sur l'ARN de fibroblastes isolés soumis au rétinol ou à l'extrait végétal pendant 6, 48 ou 96 heures. Différentes protéines cutanées ont été quantifiés dans des fibroblastes cultivés en présence de rétinol ou d'un milieu contenant l'extrait. Des quantifications ont également été faites sur des explants de peau vieillie par les UV et soumis à des applications topiques de crèmes contenant du rétinol, du rétinaldéhyde ou le HME.La qPCR en temps réel montre que l'extrait induit tous les gènes RARs et RXRs, même RXRγ qui n'était pas induit par le rétinol. Quatre-vingt-huit pour cent des 25 gènes impliqués dans la réaction précoce aux rétinoïdes induits par une concentration de rétinol ont été induits par l'extrait. Dans les fibroblastes, seul l'extrait a augmenté le marquage du collagène III, tandis que le marquage du collagène I et de la fibronectine a été augmenté par le rétinol et l'extrait, avec des niveaux plus élevés pour l'extrait. En application topique sur des explants de peau vieillie par les UV, seule la crème contenant le HME a entraîné une augmentation du marquage de CRABP1 dans l'épiderme. CRABP2 et Ki67 ont été induits par les trois crèmes et aucun effet n'a été détecté sur les RXRs. Dans le derme, la crème contenant l'extrait a augmenté CRABP2, le collagène total, le procollagène I et le collagène I, tandis que les crèmes contenant du rétinol ou du rétinaldéhyde n'ont affecté que certaines de ces protéines.Chez les fibroblastes isolés, le HME induit un profil d'induction génique globalement similaire à celui du rétinol. Chez les fibroblastes isolés et des explants de peau photo-vieillie, il entraine une stimulation de la synthèse protéique similaire à celle des rétinoïdes.

Whatever the exposure route, chemical, physical and biological pollutants modify the whole organism response, leading to nerve, cardiac, respiratory, reproductive, and skin system pathologies. Skin acts as a barrier for preventing pollutant modifications. This review aims to present the available scientific models, which help investigate the impact of pollution on the skin. The research question was "Which experimental models illustrate the impact of pollution on the skin in humans?" The review covered a period of 10 years following a PECO statement on in vitro, ex vivo, in vivo and in silico models. Of 582 retrieved articles, 118 articles were eligible. In oral and inhalation routes, dermal exposure had an important impact at both local and systemic levels. Healthy skin models included primary cells, cell lines, co-cultures, reconstructed human epidermis, and skin explants. In silico models estimated skin exposure and permeability. All pollutants affected the skin by altering elasticity, thickness, the structure of epidermal barrier strength, and dermal extracellular integrity. Some specific models concerned wound healing or the skin aging process. Underlying mechanisms were an exacerbated inflammatory skin reaction with the modulation of several cytokines and oxidative stress responses, ending with apoptosis. Pathological skin models revealed the consequences of environmental pollutants on psoriasis, atopic dermatitis, and tumour development. Finally, scientific models were used for evaluating the safety and efficacy of potential skin formulations in preventing the skin aging process or skin irritation after repeated contact. The review gives an overview of scientific skin models used to assess the effects of pollutants. Chemical and physical pollutants were mainly represented while biological contaminants were little studied. In future developments, cell hypoxia and microbiota models may be considered as more representative of clinical situations. Models considering humidity and temperature variations may reflect the impact of these changes.

When developing new cosmetics, it is extremely important to consider the safety of consumers. Absence of potential irritancy is generally assessed using an OECD TG439 compliant Reconstructed Human Epidermis (RHE) systems and MTT assays, resulting in an irritant/not irritant classification. To gain insight into the irritancy of molecules/finished cosmetic products and to predict the outcome of irritation tests performed on subjects whatever their nature, we developed a test that uses skin explants and histological analysis. Results showed that this irritation test is sensitive enough to accurately and repeatably detect known irritants. If the diverse origin of the skin explants used led to variability in the histological alterations scored, the overall grading of irritancy is highly reproducible. Finally, when testing 120 non-alcoholic cosmetics of various galenic forms, comparison of data between the ex vivo irritation tests and of a 24-/48-h human patch test revealed a single false negative, very close to the limit, and a 10% false positive rate. It was not possible to calculate the sensitivity of the ex vivo irritation test; however, its specificity was 89.9% and its accuracy was 89.1%. Similar results, with a slightly higher false positive rate, were found when testing 49 alcoholic cosmetics. These values exceed the minimum requirements of OECD TG439.

The aging process, especially of the skin, is governed by changes in the epidermal, dermo-epidermal, and dermal compartments. Type I collagen, which is the major component of dermis extracellular matrix (ECM), constitutes a prime target for intrinsic and extrinsic aging-related alterations. In addition, under the aging process, pro-inflammatory signals are involved and collagens are fragmented owing to enhanced matrix metalloproteinase activities, and fibroblasts are no longer able to properly synthesize collagen fibrils. Here, we demonstrated that low levels of type I collagen detected in aged skin fibroblasts are attributable to an inhibition of COL1A1 transcription. Indeed, on one hand, we observed decreased binding activities of specific proteins 1 and 3, CCAAT-binding factor, and human collagen-Krüppel box, which are well-known COL1A1 transactivators acting through the -112/-61-bp promoter sequence. On the other hand, the aging process was accompanied by elevated amounts and binding activities of NF-κB (p65 and p50 subunits), together with an increased number of senescent cells. The forced expression of NF-κB performed in young fibroblasts was able to establish an old-like phenotype by repressing COL1A1 expression through the short -112/-61-bp COL1A1 promoter and by elevating the senescent cell distribution. The concomitant decrease of transactivator functions and increase of transinhibitor activity is responsible for ECM dysfunction, leading to aging/senescence in dermal fibroblasts.

Despite several investigations, the transcriptional mechanisms that regulate the expression of both type I collagen genes (COL1A1 and COL1A2) in either physiological or pathological situations, such as scleroderma, are not completely known. We have investigated the role of hc-Krox transcription factor on type I collagen expression by human dermal fibroblasts. hc-Krox exerted a stimulating effect on type I collagen protein synthesis and enhanced the corresponding mRNA steady-state levels of COL1A1 and COL1A2 in foreskin fibroblasts (FF), adult normal fibroblasts (ANF), and scleroderma fibroblasts (SF). Forced hc-Krox expression was found to up-regulate COL1A1 transcription through a -112/-61-bp sequence in FF, ANF, and SF. Knockdown of hc-Krox by short interfering RNA and decoy strategies confirmed the transactivating effect of hc-Krox and decreased substantially COL1A1 transcription levels in all fibro-blast types. The -112/-61-bp sequence bound specifically hc-Krox but also Sp1 and CBF. Attempts to elucidate the potential interactions between hc-Krox, Sp1, and Sp3 revealed that all of them co-immunoprecipitate from FF cellular extracts when a c-Krox antibody was used and bind to the COL1A1 promoter in chromatin immunoprecipitation assays. Moreover, hc-Krox DNA binding activity to its COL1A1-responsive element is increased in SF, cells producing higher amounts of type I collagen compared with ANF and FF. These data suggest that the regulation of COL1A1 gene transcription in human dermal fibroblasts involves a complex machinery that implicates at least three transcription proteins, hc-Krox, Sp1, and Sp3, which could act in concert to up-regulate COL1A1 transcriptional activity and provide evidence for a pro-fibrotic role of hc-Krox.