A precise analysis of the relative contribution of UVA1 and visible light colour domains in solar light-induced skin pigmentation.

BACKGROUND: Solar light induces or aggravates hyperpigmentation issues. The contribution of UVA1, as well as visible light (VL), especially high-energy blue-violet visible (HEV) light, is now clearly established. OBJECTIVES: This work aimed at determining the relative contribution of UVA1, HEV and VL wavelength bands and their sub-domains in pigmentation induction. METHODS: Two clinical studies using solar simulators equipped with specific bandpass physical filters were carried out. Volunteers (FSPT III-IV) were exposed on the back to UVA1 + HEV (350-450 nm), UVA1 (350-400 nm), HEV (400-450 nm) or part of UVA1 + HEV (370-450 nm) in Study 1 (n = 27) and to VL (400-700 nm), HEV (400-450 nm), Blue (400-500 nm), Green (500-600 nm) and Green+Red (500-700 nm) domains in Study 2 (n = 25). Pigmentation level was assessed by visual scoring and colorimetry at different time points postexposure, up to Day 43. RESULTS: Induced pigmentation was detected in all exposed conditions, peaking at 2 h and thereafter progressively decreasing but remaining persistent up to Day 43. In Study 1, UVA1 showed an additive effect with HEV, with a significant contribution coming from the Longest UVA1 rays (370-400 nm). Study 2 demonstrated that 24 h postexposure, the Blue domain accounted for 71% of VL-induced pigmentation, the HEV one for 47%, the Green one for 37% and the Green+Red one for 36%, confirming no significant effect for Red light. CONCLUSIONS: Altogether, these results underline the need for UVA1 photoprotection up to 400 nm and highlight the importance of protecting the skin from solar VL wavelengths and especially from HEV, Blue and Green light, to limit induced pigmentation.

The Damaging Effects of Long UVA (UVA1) Rays: A Major Challenge to Preserve Skin Health and Integrity.

Within solar ultraviolet (UV) light, the longest UVA1 wavelengths, with significant and relatively constant levels all year round and large penetration properties, produce effects in all cutaneous layers. Their effects, mediated by numerous endogenous chromophores, primarily involve the generation of reactive oxygen species (ROS). The resulting oxidative stress is the major mode of action of UVA1, responsible for lipid peroxidation, protein carbonylation, DNA lesions and subsequent intracellular signaling cascades. These molecular changes lead to mutations, apoptosis, dermis remodeling, inflammatory reactions and abnormal immune responses. The altered biological functions contribute to clinical consequences such as hyperpigmentation, inflammation, photoimmunosuppression, sun allergies, photoaging and photocancers. Such harmful impacts have also been reported after the use of UVA1 phototherapy or tanning beds. Furthermore, other external aggressors, such as pollutants and visible light (Vis), were shown to induce independent, cumulative and synergistic effects with UVA1 rays. In this review, we synthetize the biological and clinical effects of UVA1 and the complementary effects of UVA1 with pollutants or Vis. The identified deleterious biological impact of UVA1 contributing to clinical consequences, combined with the predominance of UVA1 rays in solar UV radiation, constitute a solid rational for the need for a broad photoprotection, including UVA1 up to 400 nm.

Clinical and Biological Characterization of Skin Pigmentation Diversity and Its Consequences on UV Impact.

Skin color diversity is the most variable and noticeable phenotypic trait in humans resulting from constitutive pigmentation variability. This paper will review the characterization of skin pigmentation diversity with a focus on the most recent data on the genetic basis of skin pigmentation, and the various methodologies for skin color assessment. Then, melanocyte activity and amount, type and distribution of melanins, which are the main drivers for skin pigmentation, are described. Paracrine regulators of melanocyte microenvironment are also discussed. Skin response to sun exposure is also highly dependent on color diversity. Thus, sensitivity to solar wavelengths is examined in terms of acute effects such as sunburn/erythema or induced-pigmentation but also long-term consequences such as skin cancers, photoageing and pigmentary disorders. More pronounced sun-sensitivity in lighter or darker skin types depending on the detrimental effects and involved wavelengths is reviewed.

New insights in photoaging, UVA induced damage and skin types.

UVA radiation is the most prevalent component of solar UV radiation; it deeply penetrates into the skin and induces profound alterations of the dermal connective tissue. In recent years, the detrimental effects of UVA radiation were more precisely demonstrated at cellular and molecular levels, using adequate methods to identify biological targets of UVA radiation and the resulting cascade impairment of cell functions and tissue degradation. In particular gene expression studies recently revealed that UVA radiation induces modulation of several genes confirming the high sensitivity of dermal fibroblasts to UVA radiation. The major visible damaging effects of UVA radiation only appear after years of exposure: it has been clearly evidenced that they are responsible for more or less early signs of photoageing and photocarcinogenesis. UVA radiation appears to play a key role in pigmented changes occurring with age, the major sign of skin photoaging in Asians. Skin susceptibility to photoaging alterations also depends on constitutive pigmentation. The skin sensitivity to UV light has been demonstrated to be linked to skin color type.

Exposure to non-extreme solar UV daylight: spectral characterization, effects on skin and photoprotection.

The link between chronic sun exposure of human skin and harmful clinical consequences such as photo-aging and skin cancers is now indisputable. These effects are mostly due to ultraviolet (UV) rays (UVA, 320-400 nm and UVB, 280-320 nm). The UVA/UVB ratio can vary with latitude, season, hour, meteorology and ozone layer, leading to different exposure conditions. Zenithal sun exposure (for example on a beach around noon under a clear sky) can rapidly induce visible and well-characterized clinical consequences such as sunburn, predominantly induced by UVB. However, a limited part of the global population is exposed daily to such intense irradiance and until recently little attention has been paid to solar exposure that does not induce any short term clinical impact. This paper will review different studies on non-extreme daily UV exposures with: (1) the characterization and the definition of the standard UV daylight and its simulation in the laboratory; (2) description of the biological and clinical effects of such UV exposure in an in vitro reconstructed human skin model and in human skin in vivo, emphasizing the contribution of UVA rays and (3) analysis of photoprotection approaches dedicated to prevent the harmful impact of such UV exposure.

A chronic pro-inflammatory environment contributes to the physiopathology of actinic lentigines.

Actinic lentigines (AL) or age spots, are skin hyperpigmented lesions associated with age and chronic sun exposure. To better understand the physiopathology of AL, we have characterized the inflammation response in AL of European and Japanese volunteers. Gene expression profile showed that in both populations, 10% of the modulated genes in AL versus adjacent non lesional skin (NL), i.e. 31 genes, are associated with inflammation/immune process. A pro-inflammatory environment in AL is strongly suggested by the activation of the arachidonic acid cascade and the plasmin pathway leading to prostaglandin production, along with the decrease of anti-inflammatory cytokines and the identification of inflammatory upstream regulators. Furthermore, in line with the over-expression of genes associated with the recruitment and activation of immune cells, immunostaining on skin sections revealed a significant infiltration of CD68+ macrophages and CD4+ T-cells in the dermis of AL. Strikingly, investigation of infiltrated macrophage subsets evidenced a significant increase of pro-inflammatory CD80+/CD68+ M1 macrophages in AL compared to NL. In conclusion, a chronic inflammation, sustained by pro-inflammatory mediators and infiltration of immune cells, particularly pro-inflammatory M1 macrophages, takes place in AL. This pro-inflammatory loop should be thus broken to normalize skin and improve the efficacy of age spot treatment.

Preclinical corrective gene transfer in xeroderma pigmentosum human skin stem cells.

Xeroderma pigmentosum (XP) is a devastating disease associated with dramatic skin cancer proneness. XP cells are deficient in nucleotide excision repair (NER) of bulky DNA adducts including ultraviolet (UV)-induced mutagenic lesions. Approaches of corrective gene transfer in NER-deficient keratinocyte stem cells hold great hope for the long-term treatment of XP patients. To face this challenge, we developed a retrovirus-based strategy to safely transduce the wild-type XPC gene into clonogenic human primary XP-C keratinocytes. De novo expression of XPC was maintained in both mass population and derived independent candidate stem cells (holoclones) after more than 130 population doublings (PD) in culture upon serial propagation (>10(40) cells). Analyses of retrovirus integration sequences in isolated keratinocyte stem cells suggested the absence of adverse effects such as oncogenic activation or clonal expansion. Furthermore, corrected XP-C keratinocytes exhibited full NER capacity as well as normal features of epidermal differentiation in both organotypic skin cultures and in a preclinical murine model of human skin regeneration in vivo. The achievement of a long-term genetic correction of XP-C epidermal stem cells constitutes the first preclinical model of ex vivo gene therapy for XP-C patients.

Genetic correction of stem cells in the treatment of inherited diseases and focus on xeroderma pigmentosum.

Somatic stem cells ensure tissue renewal along life and healing of injuries. Their safe isolation, genetic manipulation ex vivo and reinfusion in patients suffering from life threatening immune deficiencies (for example, severe combined immunodeficiency (SCID)) have demonstrated the efficacy of ex vivo gene therapy. Similarly, adult epidermal stem cells have the capacity to renew epidermis, the fully differentiated, protective envelope of our body. Stable skin replacement of severely burned patients have proven life saving. Xeroderma pigmentosum (XP) is a devastating disease due to severe defects in the repair of mutagenic DNA lesions introduced upon exposure to solar radiations. Most patients die from the consequences of budding hundreds of skin cancers in the absence of photoprotection. We have developed a safe procedure of genetic correction of epidermal stem cells isolated from XP patients. Preclinical and safety assessments indicate successful correction of XP epidermal stem cells in the long term and their capacity to regenerate a normal skin with full capacities of DNA repair.

Induced pluripotent stem cells reprogramming overcomes technical limitations for highly pigmented adult melanocyte amplification and integration in 3D skin model.

Understanding pigmentation regulations taking into account the original skin color type is important to address pigmentary disorders. Biological models including adult melanocytes from different phenotypes allow to perform fine-tuned explorative studies and support discovery of treatments adapted to populations' skin color. However, technical challenges arise when trying to not only isolate but also amplify melanocytes from highly pigmented adult skin. To bypass the initial isolation and growth of cutaneous melanocytes, we harvested and expanded fibroblasts from light and dark skin donors and reprogrammed them into iPSC, which were then differentiated into melanocytes. The resulting melanocyte populations displayed high purity, genomic stability, and strong proliferative capacity, the latter being a critical parameter for dark skin cells. The iPSC-derived melanocyte strains expressed lineage-specific markers and could be successfully integrated into reconstructed skin equivalent models, revealing pigmentation status according to the native phenotype. In both monolayer cultures and 3D skin models, the induced melanocytes demonstrated responsiveness to promelanogenic stimuli. The data demonstrate that the iPSC-derived melanocytes with high proliferative capacity maintain their pigmentation genotype and phenotypic properties up to a proper integration into 3D skin equivalents, even for highly pigmented cells.

Identification and functional validation of SRC and RAPGEF1 as new direct targets of miR-203, involved in regulation of epidermal homeostasis.

The epidermis is mostly composed of keratinocytes and forms a protecting barrier against external aggressions and dehydration. Epidermal homeostasis is maintained by a fine-tuned balance between keratinocyte proliferation and differentiation. In the regulation of this process, the keratinocyte-specific miR-203 microRNA is of the outmost importance as it promotes differentiation, notably by directly targeting and down-regulating mRNA expression of genes involved in keratinocyte proliferation, such as ΔNp63, Skp2 and Msi2. We aimed at identifying new miR-203 targets involved in the regulation of keratinocyte proliferation/differentiation balance. To this end, a transcriptome analysis of human primary keratinocytes overexpressing miR-203 was performed and revealed that miR-203 overexpression inhibited functions like proliferation, mitosis and cell cycling, and activated differentiation, apoptosis and cell death. Among the down-regulated genes, 24 putative target mRNAs were identified and 8 of them were related to proliferation. We demonstrated that SRC and RAPGEF1 were direct targets of miR-203. Moreover, both were down-regulated during epidermal morphogenesis in a 3D reconstructed skin model, while miR-203 was up-regulated. Finally silencing experiments showed that SRC or RAPGEF1 contributed to keratinocyte proliferation and regulated their differentiation. Preliminary results suggest their involvement in skin carcinoma hyperproliferation. Altogether this data indicates that RAPGEF1 and SRC could be new mediators of miR-203 in epidermal homeostasis regulation.

Photo-aging evaluation - In vitro biological endpoints combined with collagen density assessment with multi-photon microscopy.

BACKGROUND: Ultraviolet exposure has profound effect on the dermal connective tissue of human skin. OBJECTIVE: We aimed to develop and validate an evaluation method/methodology using a full-thickness reconstructed skin model, to assess the anti-photoaging efficacy of cosmetic ingredients and sunscreen formulas by blending multi relevant biological endpoints including the newly developed dermal collagen quantification method with Multi-photon microscopy. METHODS: The response of ex vivo human skin to UVA exposure was first characterized with multiphoton microscopy. Reconstructed full-thickness skin models was then used to reproduce the data and to create a proof-of-concept study by treating the models with sunscreen prototypes A or B, which differ on their UVA absorption properties, and systemic Vitamin C (Vit C). After exposure to UVA, the collagen density was quantified via multiphoton microscopy with automatic imaging processing. Histology, fibroblasts number, metalloprotease 1 (MMP1) secretion were also assessed. RESULTS: UVA exposure induced pronounced reduction in collagen density and increased MMP1 secretion within both ex vivo human skin and reconstructed skin. Histological damage and fibroblast disappearance was observed with reconstructed skin. Within the proof-of-concept study prototype B, possessing higher UVA filtration, gave better protection than prototype A on the UV associated biological markers, and association with Vit C boosted sunscreen formula efficacy. CONCLUSIONS: The photoaging evaluation method, consists of multi biological markers as well as dermal collagen quantification, is a relevant mean to assess the pre-clinical efficacy of anti-photoaging ingredients and sunscreen products. This approach is also beneficial for evaluating the efficacy of sunscreens and photoprotective ingredients.

Sunscreens with the New MCE Filter Cover the Whole UV Spectrum: Improved UVA1 Photoprotection In Vitro and in a Randomized Controlled Trial.

BACKGROUND: UVA1 rays (340-400 nm) contribute to carcinogenesis, immunosuppression, hyperpigmentation, and aging. Current sunscreen formulas lack sufficient absorption in the 370-400 nm wavelengths range. Recently, a new UVA1 filter, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate (MCE) exhibiting a peak of absorption at 385 nm, was approved by the Scientific Committee on Consumer Safety for use in sunscreen products. These studies evaluated, in a three-dimensional skin model and in vivo, the protection afforded by state-of-the-art sunscreen formulations enriched with MCE. TRIAL DESIGN: This study is a monocentric, double-blinded, randomized, and comparative trial. This study is registered at ClinicalTrials.gov with the identification number NCT04865094. METHODS: The efficacy of sunscreens with MCE was compared with that of reference formulas. In a three-dimensional skin model, histology, protein, and gene expression were analyzed. In the clinical trial, pigmentation was analyzed in 19 volunteers using colorimetric measurements and visual scoring. RESULTS: MCE addition in reference formulas enlarged the profile of absorption up to 400 nm; reduced UVA1-induced dermal and epidermal alterations at cellular, biochemical, and molecular levels; and decreased UVA1-induced pigmentation. CONCLUSIONS: Addition of MCE absorber in sunscreen formulations leads to full coverage of UV spectrum and improved UVA1 photoprotection. The data support benefits in the long term on sun-induced consequences, especially those related to public health care issues.

Actinic lentigines from Japanese and European volunteers share similar impaired biological functions.

BACKGROUND: Hyperpigmented spots develop earlier and with a higher incidence in Asian individuals compared with Europeans. Although actinic lentigines (AL) are very common, the biological events underlying their formation remain ill-defined. OBJECTIVE: AL from Japanese volunteers were characterized through morphological and gene expression analyses. Data were then compared with published data on European volunteers. METHODS: AL on hands were selected through dermoscopic imaging and pattern scoring in Japanese women. Skin biopsies of AL and adjacent non-lesional (NL) skin were processed for histology and gene expression profiling. Japanese and European studies were compared after harmonizing the data using the same mathematical and statistical methods. RESULTS: Histologically, AL from Japanese individuals revealed deep epidermal invaginations with melanin accumulation in the depth of epidermal rete ridges. Transcriptomic data identified 245 genes differentially expressed in AL versus NL skin samples, associated with the different skin compartments and multiple functional families and biological processes, such as epidermal homeostasis, extracellular matrix organization and ion binding/transmembrane transport. Strikingly, melanogenesis-related genes were not significantly modulated in AL compared with NL skin. Comparison of the molecular profiles of Japanese and European AL showed that a huge majority of genes were modulated in the same way, recapitulating the overall biological alterations. CONCLUSION: AL from Japanese volunteers exhibited morphological and molecular alterations of the whole skin structure with impairment of multiple biological functions similar to that found in European women. These findings will contribute to the development of efficient treatments of AL lesions.

A broad-spectrum sunscreen prevents UVA radiation-induced gene expression in reconstructed skin in vitro and in human skin in vivo.

The efficacy of sunscreens to protect against ultraviolet (UV) A radiation is usually assessed by measuring erythema formation and pigmentation. The biological relevance of these endpoints for UVA-induced skin damage, however, is not known. We therefore carried out two complementary studies to determine UVA protection provided by a broad-spectrum sunscreen product at a molecular level by studying UVA radiation-induced gene expression. One study was performed on human reconstructed skin in vitro with a semi-global gene expression analysis of 227 genes in fibroblasts and 244 in keratinocytes. The second one was conducted in vivo in human volunteers and focused on genes involved in oxidative stress response and photo-ageing (haeme oxygenase-1, superoxide dismutase-2, glutathione peroxidase, catalase, matrix metalloproteinase-1). In-vitro UVA radiation induced modulation of genes involved in extracellular matrix homeostasis, oxidative stress, heat shock responses, cell growth, inflammation and epidermal differentiation. Sunscreen pre-application abrogated or significantly reduced these effects, as underlined by unsupervised clustering analysis. The in vivo study confirmed that the sunscreen prevented UVA radiation-induced transcriptional expression of the five studied genes. These findings indicate the high efficacy of a broad-spectrum sunscreen in protecting human skin against UVA-induced gene responses and suggest that this approach is a biologically relevant complement to existing methods.

Effect of C-xyloside on morphogenesis of the dermal epidermal junction in aged female skin. An ultrastuctural pilot study.

A placebo-controlled randomized pilot study was performed on five postmenopausal women aged from 60 to 75 years. The women applied 320 mg (2 mg/cm(2)) of either placebo or 10% C-ß-D-xylopyranoside-2-hydroxy-propane (C-xyloside) cream to each outer forearm twice daily for 3 months. At the end of the treatment, skin biopsies were collected from application areas on both forearms. Transmission electron microscope examinations revealed skin ultrastructural changes at the dermal epidermal junction (DEJ) after 10% C-xyloside application for 3 months. The morphological appearance of the DEJ showed strong improvements, with more homogeneous and regular lamina densa in the C-xyloside-treated compared to the placebo treated skin areas. The number of zones showing basement membrane re-duplication was indeed strikingly reduced on C-xyloside-treated skin. These ultrastructural results were further confirmed by a statistically significant increase in the expression levels of α6-integrin the and laminin-332, as estimated by immunohistochemistry. Altogether, these data suggest that topical C-xyloside application in vivo may be efficient in inducing a better dermal-epidermal cohesion when such a junction is deficient, as is the case in photo-aged or chronologically aged skin. Moreover, a statistically significant increase in CD44 expression was noted in the epidermis of C-xyloside-treated compared to the placebo treated skin areas.

Simultaneous NAD(P)H and FAD fluorescence lifetime microscopy of long UVA-induced metabolic stress in reconstructed human skin.

Solar ultraviolet longwave UVA1 exposure of human skin has short-term consequences at cellular and molecular level, leading at long-term to photoaging. Following exposure, reactive oxygen species (ROS) are generated, inducing oxidative stress that might impair cellular metabolic activity. However, the dynamic of UVA1 impact on cellular metabolism remains unknown because of lacking adequate live imaging techniques. Here we assess the UVA1-induced metabolic stress response in reconstructed human skin with multicolor two-photon fluorescence lifetime microscopy (FLIM). Simultaneous imaging of nicotinamide adenine dinucleotide (NAD(P)H) and flavin adenine dinucleotide (FAD) by wavelength mixing allows quantifying cellular metabolism in function of NAD(P)+/NAD(P)H and FAD/FADH2 redox ratios. After UVA1 exposure, we observe an increase of fraction of bound NAD(P)H and decrease of fraction of bound FAD indicating a metabolic switch from glycolysis to oxidative phosphorylation or oxidative stress possibly correlated to ROS generation. NAD(P)H and FAD biomarkers have unique temporal dynamic and sensitivity to skin cell types and UVA1 dose. While the FAD biomarker is UVA1 dose-dependent in keratinocytes, the NAD(P)H biomarker shows no dose dependence in keratinocytes, but is directly affected after exposure in fibroblasts, thus reflecting different skin cells sensitivities to oxidative stress. Finally, we show that a sunscreen including a UVA1 filter prevents UVA1 metabolic stress response from occurring.

Ultraviolet A within sunlight induces mutations in the epidermal basal layer of engineered human skin.

The ultraviolet B (UVB) waveband within sunlight is an important carcinogen; however, UVA is also likely to be involved. By ascribing mutations to being either UVB or UVA induced, we have previously shown that human skin cancers contain similar numbers of UVB- and UVA-induced mutations, and, importantly, the UVA mutations were at the base of the epidermis of the tumors. To determine whether these mutations occurred in response to UV, we exposed engineered human skin (EHS) to UVA, UVB, or a mixture that resembled sunlight, and then detected mutations by both denaturing high-performance liquid chromatography and DNA sequencing. EHS resembles human skin, modeling differential waveband penetration to the basal, dividing keratinocytes. We administered only four low doses of UV exposure. Both UVA and UVB induced p53 mutations in irradiated EHS, suggesting that sunlight doses that are achievable during normal daily activities are mutagenic. UVA- but not UVB-induced mutations predominated in the basal epidermis that contains dividing keratinocytes and are thought to give rise to skin tumors. These studies indicate that both UVA and UVB at physiological doses are mutagenic to keratinocytes in EHS.

Functional consequences of mitochondrial DNA deletions in human skin fibroblasts: increased contractile strength in collagen lattices is due to oxidative stress-induced lysyl oxidase activity.

Deletions within the mitochondrial DNA (mtDNA) are thought to contribute to extrinsic skin aging. To study the translation of mtDNA deletions into functional and structural changes in the skin, we seeded human skin fibroblasts into collagen gels to generate dermal equivalents. These cells were either derived from Kearns-Sayre syndrome (KSS) patients, who constitutively carry large amounts of the UV-inducible mitochondrial common deletion, or normal human volunteers. We found that KSS fibroblasts, in comparison with normal human fibroblasts, contracted the gels faster and more strongly, an effect that was dependent on reactive oxygen species. Gene expression and Western blot analysis revealed significant upregulation of lysyl oxidase (LOX) in KSS fibroblasts. Treatment with the specific LOX inhibitor beta-aminopropionitrile decreased the contraction difference between KSS and normal human fibroblast equivalents. Also, addition of the antioxidant N-tert-butyl-alpha-phenylnitrone reduced the contraction difference by inhibiting collagen gel contraction in KSS fibroblasts, and both beta-aminopropionitrile and N-tert-butyl-alpha-phenylnitrone diminished LOX activity. These data suggest a causal relationship between mtDNA deletions, reactive oxygen species production, and increased LOX activity that leads to increased contraction of collagen gels. Accordingly, increased LOX expression was also observed in vivo in photoaged human and mouse skin. Therefore, mtDNA deletions in human fibroblasts may lead to functional and structural alterations of the skin.

Large scale study of epidermal recovery after stratum corneum removal: dynamics of genomic response.

The stratum corneum (SC) is a superficial skin compartment that protects the body from the outside environment. Any disturbance of this function induces cascading steps of molecular and cellular repair in the whole epidermis. The aim of this study was to investigate epidermal gene expression following SC removal by tape stripping. Twenty-nine healthy male volunteers were included (27 +/- 4 years old). Tape stripping was processed on one inner forearm, the other unstripped forearm served as a control. Epidermis samples were collected at 2, 6, 19, 30 and 72 h after tape stripping. Trans-epidermal water loss measurements were performed at each step to monitor barrier restoration. Total RNA was extracted from collected epidermis samples and analysed by using DermArray cDNA microarrays. Among 4000 genes under investigation, we found that the expression of 370 genes varied significantly at least once during the time following stripping. Using an original clustering method, the modulated genes were gathered into eight groups. A functional characterization of the clusters enabled us to get a dynamic and global view of the main molecular processes taking place during epidermal recovery.

NK Cell and Fibroblast-Mediated Regulation of Skin Squamous Cell Carcinoma Invasion by CLEC2A Is Compromised in Xeroderma Pigmentosum.

The ability of cancer cells to invade and disseminate can be affected by components of the surrounding microenvironment. To identify dermal components that regulate the growth of epidermal carcinomas, we studied the genetic disease called xeroderma pigmentosum that bears mutations in genes involved in the nucleotide excision repair of DNA. Patients with xeroderma pigmentosum are more prone to develop cutaneous tumors than the general population and their dermal fibroblasts display the features of dermal cancer-associated fibroblasts, which promote the invasion of keratinocytes. Here, we report that 3-dimensional dermal cultures of fibroblasts from healthy donors but not from patients with xeroderma pigmentosum complementation group C express CLEC2A, which is the ligand of the activating NK cell receptor NKp65. A similar loss of CLEC2A was observed in sporadic dermal cancer-associated fibroblasts and upon the culture of fibroblasts with cutaneous squamous cell carcinoma-conditioned medium. Using an innovative 3-dimensional organotypic skin culture model that contain NK cells in addition to fibroblasts and squamous cell carcinoma cells, we unveiled a key role of CLEC2A that orchestrates a crosstalk between fibroblasts and NK cells, thereby leading to the control of squamous cell carcinoma invasion. These findings indicate that CLEC2A-expressing dermal fibroblasts play a major role in immune surveillance of the skin.