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Ultraviolet-B (UV-B) radiation overexposure causes function impairment of epidermal stem cells (ESCs). We explored the mechanism of Annexin A1 (ANXA1) ameliorating UV-B-induced ESC mitochondrial dysfunction/cell injury. ESCs were cultured in vitro and irradiated with different doses of UV-B. Cell viability/ANXA1 protein level were assessed. After oe-ANXA1 transfection, ESCs were treated with oe-ANXA1/UV-B irradiation/CCCP/CCG-1423/3-methyladenine for 12 h. Cell viability/death, and adenosine triphosphate (ATP)/reactive oxygen species (ROS) levels were determined. Mitochondrial membrane potential (MMP) changes/DNA (mtDNA) content/oxygen consumption and RhoA activation were assessed. ROCK1/p-MYPT1/MYPT1/(LC3BII/I)/Beclin-1/p62 protein levels were determined. Mitochondrial morphology was observed. Mito-Tracker Green (MTG) and LC3B levels were determined. UV-B irradiation decreased cell viability/ANXA1 expression in a dose-dependent manner. UV-B-treated ESCs exhibited reduced cell viability/ATP content/MMP level/mitochondrial respiratory control ratio/mtDNA number/RhoA activity/MYPT1 phosphorylation/MTG + LC3B + cells/(LC3BII/I) and Beclin-1 proteins, increased cell death/ROS/p62/IL-1β/IL-6/TNF-α expression, contracted mitochondrial, disappeared mitochondrial cristae, and increased vacuolar mitochondria, which were averted by ANXA1 overexpression, suggesting that UV-B induced ESC mitochondrial dysfunction/cell injury/inflammation by repressing mitophagy, but ANXA1 promoted mitophagy by activating the RhoA/ROCK1 pathway, thus repressing UV-B's effects. Mitophagy activation ameliorated UV-B-caused ESC mitochondrial dysfunction/cell injury/inflammation. Mitophagy inhibition partly diminished ANXA1-ameliorated UV-B's effects. Conjointly, ANXA1 promoted mitophagy by activating the RhoA/ROCK1 pathway, thereby improving UV-B-induced ESC mitochondrial dysfunction/cell injury., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Introduction: Healthcare-acquired infections and overuse of antibiotics are a common problem. Rising emergence of antibiotic and antiseptic resistances requires new methods of microbial decontamination or decolonization as the use of far-UV-C radiation., Methods: The microbicidal efficacy of UV-C radiation (222 nm, 233 nm, 254 nm) was determined in a quantitative carrier test and on 3D-epidermis models against Staphylococcus (S.) aureus, S.epidermidis, S.haemolyticus, S.lugdunensis, Klebsiella pneumoniae, and Pseudomonas aeruginosa. To mimic realistic conditions, sodium chloride solution, mucin, albumin, artificial saliva, artificial wound exudate and artificial sweat were used., Results: In sodium chloride solution, irradiation with a dose of 40 mJ/cm 2 (233 nm) was sufficient to achieve 5 lg reduction independent of bacteria genus or species. In artificial sweat, albumin and artificial wound exudate, a reduction >3 lg was reached for most of the bacteria. Mucin and artificial saliva decreased the reduction to <2 lg. On 3D epidermis models, reduction was lower than in the carrier test., Conclusion: UV-C radiation at 233 nm was proven to be efficient in bacteria inactivation independent of genus or species thus being a promising candidate for clinical use in the presence of humans and on skin/mucosa., Competing Interests: Declaration of competing interest None., (Copyright © 2024 The Author(s). Published by Elsevier Masson SAS.. All rights reserved.)

Ablative fractional laser treatment is considered the gold standard for skin rejuvenation. In order to understand how fractional laser works to rejuvenate skin, we performed microarray profiling on skin biopsies to identify temporal and dose-response changes in gene expression following fractional laser treatment. The backs of 14 women were treated with ablative fractional laser (Fraxel®) and 4 mm punch biopsies were collected from an untreated site and at the treated sites 1, 3, 7, 14, 21 and 28 days after the single treatment. In addition, in order to understand the effect that multiple fractional laser treatments have on skin rejuvenation, several sites were treated sequentially with either 1, 2, 3, or 4 treatments (with 28 days between treatments) followed by the collection of 4 mm punch biopsies. RNA was extracted from the biopsies, analyzed using Affymetrix U219 chips and gene expression was compared between untreated and treated sites. We observed dramatic changes in gene expression as early as 1 day after fractional laser treatment with changes remaining elevated even after 1 month. Analysis of individual genes demonstrated significant and time related changes in inflammatory, epidermal, and dermal genes, with dermal genes linked to extracellular matrix formation changing at later time points following fractional laser treatment. When comparing the age-related changes in skin gene expression to those induced by fractional laser, it was observed that fractional laser treatment reverses many of the changes in the aging gene expression. Finally, multiple fractional laser treatments, which cover different regions of a treatment area, resulted in a sustained or increased dermal remodeling response, with many genes either differentially regulated or continuously upregulated, supporting previous observations that maximal skin rejuvenation requires multiple fractional laser treatments. In conclusion, fractional laser treatment of human skin activates a number of biological processes involved in wound healing and tissue regeneration., Competing Interests: The authors have declared that no competing interests exist.

Ultraviolet B (UVB) induces morphological and functional changes of the skin. This study investigated the effect of UVB on keratinocyte senescence and the development of reconstructed human epidermis (RHE). Primary normal human keratinocytes (NHK) from juvenile foreskin were irradiated with UVB (30 mJ cm-2) and these effects were compared to NHK that underwent senescence in the late passage. UVB enhanced the accumulation of reactive oxygen species (ROS) and halted cell replication as detected by BrdU cell proliferation assay. The senescence phenotype was evaluated by beta-galactosidase (β-gal) staining and qPCR of genes related to senescent regulation, i.e. p16INK4a, cyclin D2, and IFI27. Senescence induced by high dose UVB resulted in morphological changes, enhanced β-gal activity, elevated cellular ROS levels and reduced DNA synthesis. qPCR revealed differential expression of the genes regulated senescence. p16INK4a expression was significantly increased in NHK exposed to UVB whereas enhanced IFI27 expression was observed only in cultural senescence. The levels of cyclin D2 expression were not significantly altered either by UVB or long culturing conditions. UVB significantly induced the aging phenotype in keratinocytes and impaired epidermal development. RHE generated from UVB-irradiated keratinocytes showed a thinner cross-sectional structure and the majority of keratinocytes in the lower epidermis were degenerated. The 3D epidermis model is useful in studying the skin aging process.

The study of long-lived and regenerative animal models has revealed diverse protective responses to stressors such as aging and tissue injury. Spiny mice (Acomys) are a unique mammalian model of skin wound regeneration, but their response to other types of physiological skin damage has not been investigated. In this study, we examine how spiny mouse skin responds to acute UVB damage or chronological aging compared to non-regenerative C57Bl/6 mice (M. musculus). We find that, compared to M. musculus, the skin epidermis in A. cahirinus experiences a similar UVB-induced increase in basal cell proliferation but exhibits increased epidermal turnover. Notably, A. cahirinus uniquely form a suprabasal layer co-expressing Keratin 14 and Keratin 10 after UVB exposure concomitant with reduced epidermal inflammatory signaling and reduced markers of DNA damage. In the context of aging, old M. musculus animals exhibit typical hallmarks including epidermal thinning, increased inflammatory signaling and senescence. However, these age-related changes are absent in old A. cahirinus skin. Overall, we find that A. cahirinus have evolved novel responses to skin damage that reveals new aspects of its regenerative phenotype., Competing Interests: The authors have declared that no competing interests exist.

The β-blocker carvedilol prevents ultraviolet (UV)-induced skin cancer, but the mechanism is unknown. Since carvedilol possesses antioxidant activity, this study investigated whether carvedilol prevents oxidative photodamage of skin, a precursor event in skin carcinogenesis. The effects of carvedilol, metoprolol (a β-blocker without antioxidant property), and 4-hydroxycarbazole (4-OHC, a carvedilol synthesis intermediate and a free radical scavenger) were compared on UV- or H 2 O 2 -induced cell death and reactive oxygen species (ROS) production in murine epidermal JB6 P+ cells. Although carvedilol attenuated cell death, metoprolol and 4-OHC failed to show protective effects. As expected, increased cellular ROS induced by H 2 O 2 or UV was abolished by carvedilol and 4-OHC, but not by metoprolol. Consistently, carvedilol attenuated the formation of UV-induced cyclobutane pyrimidine dimers (CPDs) and release of prostaglandin E 2 in JB6 P+ cells. Carvedilol's activity was further confirmed in full thickness 3D human reconstituted skin, where carvedilol attenuated UV-mediated epidermal thickening, the number of Ki-67 and p53 positive cells as well as CPD formation. Based on pathway-specific Polymerase Chain Reaction (PCR) Array analysis, carvedilol treatment in many cases normalized UV-induced expression changes in DNA repair genes. Thus, carvedilol's photoprotective activity is not attributed to β-blockade or direct ROS-scavenging capacity, but likely via DNA repair regulation., Competing Interests: The authors declare no conflicts of interest.

Allomelanin is a type of nitrogen-free melanin most commonly found in fungi. Its existence enhances resistance of the organisms to environmental damage and helps fungi survive harsh radiation conditions such as those found on spacecraft and inside contaminated nuclear power plants. We report the preparation and characterization of artificial allomelanin nanoparticles (AMNPs) via oxidative oligomerization of 1,8-dihydroxynaphthalene (1,8-DHN). We describe the resulting morphological and size control of AMNPs and demonstrate that they are radical scavengers. Finally, we show that AMNPs are taken up by neonatal human epidermal keratinocytes and packaged into perinuclear caps where they quench reactive oxygen species generated following UV exposure.

Repetitive exposure to ultraviolet radiation (UVR) results in continuous insults to the skin, including continuous loss of the capacities of epidermal stem cells (ESCs). Takeda G-protein-coupled receptor-5 (TGR5) participates in a variety of physiological activities, but its biological function in skin has not been reported. In this study, we report that TGR5 could be detected in ESCs and its expression was reduced after ultraviolet B (UV-B) irradiation. Treatment with the specific TGR5 agonist 3-(2-chlorophenyl)-N-(4-chlorophenyl)-N,5-dimethylisoxazole-4-carboxamide (GPBARA) prevented UV-B-induced oxidative stress by reducing 4-hydroxy-2-nonenal and increasing the level of glutathione. We also found that the presence of GPBARA improved UV-B irradiation-induced mitochondrial dysfunction by elevating mitochondrial membrane potential. Interestingly, our results indicate that GPBARA pretreatment suppressed UV-B irradiation-induced reduced cell viability, release of lactic dehydrogenase, and secretion of high mobility group box 1. Notably, GPBARA pretreatment inhibited UV-B irradiation-induced decrease in integrin β1 and Krt19, dependent on TGR5. Mechanistically, we found that the activation of TGR5 by GPBARA increased Wnt1, Wnt3a, Myc, and cyclin D1 in ESCs. Our data suggest a new function of TGR5 in regulating ESCs., (© 2019 Wiley Periodicals, Inc.)

Background: Ultraviolet (UV)B radiation has long been considered a carcinogen in both epidemiological surveys and experimental studies. However, recent work has suggested that different dosages of UVB exert different influences on cells. There are also co-carcinogenesis factors such as arsenic that affect the role of UVB., Aim: To explore the co-carcinogenesis effect of UVB and arsenic on the mouse epidermal cell line JB6 and the mechanism underlying it., Methods: Growth of JB6 cells was measured by MTT assay. We carried out a comet assay to determine the DNA damage caused by UVB and arsenic, and tested the expression of DNA repair protein by western blotting. Reactive oxygen species (ROS) were measured using DCF and DHE staining, and changes in antioxidant enzymes were assessed using western blotting., Results: Viability assays showed that arsenic increased the UVB-induced death rate. Arsenic enhanced DNA damage caused by UVB both directly by injury to double-stranded DNA and indirectly by reducing the capability of DNA repair in JB6 cells. All of these effects are the results of increased ROS generation and reduced expression of the antioxidant enzyme superoxide dismutase (SOD)1., Conclusion: Arsenic was found to enhance UVB-induced production of ROS and to downregulate SOD1 expression, leading to DNA damage and apoptosis in mouse skin cells. The combination of arsenic and UVB exposure was found to differentially regulate the expression of SOD1 and SOD2., (© 2018 British Association of Dermatologists.)

Impact Statement: In this study, our experiments confirmed that 50 Hz EMF affected hair follicle regrowth, and 50 Hz EMF enhanced K15 + stem cells proliferation in the hair bulb and follicular outer root sheath of hair follicles. Those results indicated that 50 Hz EMF may be beneficial for functional healing of hair loss.

Photobiomodulation (PBM) therapy is based on the exposure of biological tissues to low-level laser light (coherent light) or light-emitting diodes (LEDs; noncoherent light), leading to the modulation of cellular functions, such as proliferation and migration, which result in tissue regeneration. PBM therapy has important clinical applications in regenerative medicine. Vitiligo is an acquired depigmentary disorder resulting from disappearance of functional melanocytes in the involved skin. Vitiligo repigmentation depends on available melanocytes derived from (a) melanocyte stem cells located in the bulge area of hair follicles and (b) the epidermis at the lesional borders, which contains a pool of functional melanocytes. Since follicular melanoblasts (MBs) are derived from the melanocyte stem cells residing at the bulge area of hair follicle, the process of vitiligo repigmentation presents a research model for studying the regenerative effect of PBM therapy. Previous reports have shown favourable response for treatment of vitiligo with a low-energy helium-neon (He-Ne) laser. This review focuses on the molecular events that took place during the repigmentation process of vitiligo triggered by He-Ne laser (632.8 nm, red light). Monochromatic radiation in the visible and infrared A (IRA) range sustains matrix metalloproteinase (MMP), improves mitochondrial function, and increases adenosine triphosphate (ATP) synthesis and O 2 consumption, which lead to cellular regenerative pathways. Cytochrome c oxidase in the mitochondria was reported to be the photoacceptor upon which He-Ne laser exerts its effects. Mitochondrial retrograde signalling is responsible for the cellular events by red light. This review shows that He-Ne laser initiated mitochondrial retrograde signalling via a Ca 2+ -dependent cascade. The impact on cytochrome c oxidase within the mitochondria, an event that results in activation of CREB (cyclic-AMP response element binding protein)-related cascade, is responsible for the He-Ne laser promoting functional development at different stages of MBs and boosting functional melanocytes. He-Ne laser irradiation induced (a) melanocyte stem cell differentiation; (b) immature outer root sheath MB migration; (c) differentiated outer root sheath MB melanogenesis and migration; and (d) perilesional melanocyte migration and proliferation. These photobiomodulation effects result in perifollocular and marginal repigmentation in vitiligo., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Skin provides the protective barrier for our body and undergoes the continuous regeneration in order to overcome damage from exposure to harmful environments and wounds. Epidermal stem cells (ESCs) play critical roles in skin regeneration. Humanin analogue, S14G-humanin (HNG), a prominent member of a newly discovered family of mitochondrial-derived peptides, has been shown to be a cytoprotective derivative in multiple cell types. In this study, we isolated mouse epidermal stem cells and investigated the cytoprotective effects of HNG on ESCs upon ultraviolet (UV)-B treatment. We show that HNG suppresses UV-B-induced ROS production and increases antioxidant glutathione expression. HNG-pretreated cells exhibit very mild production of cytokines, including TNF-α, IL-1β, and IL-6, upon exposure to UV-B. HNG pretreatment is protective against UV-B-mediated cytotoxicity and promotes ESC survival. Moreover, HNG treatment attenuates the UV-B-induced reduction in mitochondrial membrane potential (MMP) and preserves their identity and stem cell capacity. Mechanistically, HNG treatment ameliorates the UV-B-induced reduction in Wnt/β-catenin pathway proteins, including Wtn3a, Myc, and cyclin D1. Collectively, our data suggest that HNG acts as a pro-survival and anti-oxidative stress agent in ESCs and has the potential to be used in ESC-mediated therapies., (Copyright © 2018. Published by Elsevier Masson SAS.)

Background: Ultraviolet radiation (UVR) is known to be harmful to normal human epidermal keratinocytes (NHEKs) of the epidermal skin layer, as well as to hair-follicle-associated keratinocytes. An oral formulation containing l-cystine, thiamin, calcium d-pantothenate, medicinal yeast, keratin and p-aminobenzoic acid (Panto[vi]gar®) has demonstrated clinical efficacy for the treatment of diffuse telogen effluvium; however, its mode of action at the cellular level, and in particular whether protective mechanisms are involved, has yet to be elucidated., Objectives: To assess the capacity of ingredients of this oral formulation, both separately and in combination, to modulate the effects of UVR in growth-limited NHEKs in vitro., Methods: NHEKs were incubated in keratinocyte basal medium, keratinocyte basal medium lacking cystine, thiamin, calcium d-pantothenate, folic acid and biotine (minimal growth medium [MGM]) or MGM plus test compound. Test compounds comprised the following four ingredients related to the oral formulation: l-cystine, thiamin, calcium d-pantothenate and folic acid (a proposed metabolite of p-aminobenzoic acid), and a combination of these (Panto[vi]gar®-in vitro correlate; P-IC). The effect of different doses of these compounds on the metabolic activity and proliferation of NHEKs was tested, as well as their influence on the impact of UV light on NHEKs assessed by monitoring metabolic activity, cell number and apoptosis induction., Results: Compared with basal medium, MGM reduced the proliferation of NHEKs in a time-dependent manner. Reduced proliferation is a characteristic of the multifactorial and complex phenotype associated with diffuse hair loss. l-cystine (50 μM) increased metabolic activity and proliferation 3-fold versus MGM (p < 0.05). Thiamin also had a significant effect (p < 0.05) on proliferation and metabolic activity of NHEKs, but calcium d-pantothenate and folic acid did not when tested individually in this in vitro model. In the presence of P-IC, metabolic activity increased 4-fold and proliferation 3-fold compared with MGM alone (p < 0.05 for both). Following UV irradiation, cells in MGM showed a 72% reduction in metabolic activity, while P-IC-treated cells showed only a 12-18% reduction. The observed prevention of the UV-induced reduction in metabolic activity was not simply due to filtering UVR by the P-IC components, as P-IC-mediated reduction of this effect persisted even when P-IC was washed out during UV irradiation., Conclusion: This study demonstrated that l-cystine and thiamin are essential for proliferation of epidermal keratinocytes and suggests a novel, UV-protective potential of formulations combining l-cystine and thiamin in growth-limited inter-follicular NHEKs in vitro., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

Ultraviolet A (UVA) irradiation is a potential environmental stressor, which contributes to inflammation, photoaging, and carcinogenesis. UVA causes endoplasmic reticulum stress, hence phosphorylates the α subunit of eIF2. Meanwhile, UVA also induces expression of haem oxygenase-1 (HO-1) and nuclear factor erythroid-derived two related factor 2 (Nrf2) in human skin cells. In mouse JB6 cell, we found high dose UVA could change cell morphology, cause cell viability loss. UVA irradiation activated phosphorylation of eIF2α and Nrf2-HO-1 pathway in a dose-dependent manner. Besides, modulation of eIF2α phosphorylation status could alter expression pattern of Nrf2-HO-1 signalling. Salubrinal, a selective inhibitor of eIF2α dephosphorylation, increased the S phase in cell cycle of JB6 cells after UVA irradiation, suggesting phosphorylation status of eIF2α may affect cellular homeostasis under UVA irradiation. The study directed to further acknowledge about the relationship of UVA-induced eIF2α phosphorylation and Nrf2-HO-1 pathway, which may play a role in phototherapy and photo protection.

The epidermis undergoes constant renewal during its lifetime. This is possible due to a special population of keratinocyte stem cells (KSCs) located at the basal layer. These cells are surrounded by their direct progeny, keratinocyte progenitors or transient amplifying cells (TAs), which arise from cell division. Skin is exposed every day to sun radiation; in particular, UVA radiation penetrates through the epidermis and induces damage to KSCs and TAs. Although keratinocytes in the basal layer are the most likely skin carcinomas and/or photoaging cells of origin, surprisingly few studies have addressed the specific responses of these cells to UV radiation. In this study, we showed for the first time that keratinocyte stem cells were more resistant to UVA irradiation than their direct progeny, transient amplifying cells. Using both the MTT assay and clonogenic assay, we found that KSCs were more photo-resistant compared to TAs after exposure to different doses of UVA (from 0 to 50 J/cm2). Moreover, KSCs had a greater ability to reconstruct human epidermis (RHE) after UVA exposure compared with TAs. Finally, investigations of DNA repair using the comet assay showed that DNA single-strand breaks and thymine dimers were repaired quicker and more efficiently in KSCs compared with TAs. In a previous work, we showed that the same stem cell population was more resistant to ionizing radiation, another carcinogenic agent. Collectively, our results combined with other observations demonstrate that keratinocyte stem cells, which are responsible for epidermal renewal throughout life, are equipped with an efficient arsenal against several genotoxic agents. Our future work will try to identify the factors or signaling pathways that are responsible for this differential photo-sensitivity and DNA repair capacity between KSCs and TAs., Competing Interests: E.M, N.B and F.D. are employees of Gattefosse. O.D. is hospital practitioner at Civil Hospitals of Lyon. W.R. is Prof. at University Grenoble Alpes. The financial support from Gattefosse does not alter the authors’ adherence to all PLOS ONE policies on sharing data and materials and there are no restrictions on sharing of data and/or materials.

Ultraviolet B (UVB) irradiation exerts multiple effects on skin cells, inducing apoptosis, senescence and carcinogenesis. Toll-like receptor 3, a member of pattern recognition receptors, is reported to initiate inflammation by recognizing double-strand RNA (dsRNA) released from UVB-irradiated cells. It has not been studied, however, whether apoptosis induction in UVB irradiation is attributed to TLR3 activation. Here, we report on the pro-apoptotic role of TLR3 in UVB-irradiated epidermal cells. Poly I:C, an analogue of dsRNA that activates TLR3, was used in combination with sub-lethal UVB (4.8 mJ/cm 2 ) irradiation for investigating the effects of TLR3 activation on human immortalized keratinocyte HaCaT cells. Although sub-lethal dose of either Poly I:C or UVB alone did not induce cell death, UVB-Poly I:C co-treatment synergistically induced cell death by activation of caspase-3 and cleavages of ICAD and PARP, with apoptotic features when stained with Annexin V/PI or Hoechst 33342. Treatment with pan-caspase inhibitor, Z-VAD, attenuated UVB-Poly I:C-induced cell death. Silencing TLR3 by siRNA rescued HaCaT cells from UVB-Poly I:C-induced apoptosis. NF-κB, a major downstream component of TLR3 pathway, that usually negatively regulates the classical TLR3 apoptotic pathway, was analyzed by western blotting and immunofluorescence confocal microscopy. The results indicate to our surprise that NF-κB is translocated to nucleus in the cells co-treated with UVB-Poly I:C. The nuclear translocation of NF-κB is attenuated by TLR3 silencing. Treatment with BAY, an inhibitor of NF-κB pathway, blocked UVB-Poly I:C-induced apoptosis. Therefore, we conclude that NF-κB pathway plays a cytotoxic role in UVB-Poly I:C-treated HaCaT cells, mediating TLR3-related apoptosis., (Copyright © 2018. Published by Elsevier Ltd.)

UVB exposure can contribute to the development of skin cancer by modulating protein tyrosine kinase (PTK) signaling. It has been suggested that UVB radiation increases the ligand-dependent activation of PTKs and induces PTP inactivation. Our recent studies have shown that T-cell protein tyrosine phosphatase (TC-PTP) attenuates skin carcinogenesis induced by chemical regimens, which indicates its critical role in the prevention of skin cancer. In the current work, we report that TC-PTP increases keratinocyte susceptibility to UVB-induced apoptosis via the downregulation of Flk-1/JNK signaling. We showed that loss of TC-PTP led to resistance to UVB-induced apoptosis in vivo epidermis. We established immortalized primary keratinocytes (IPKs) from epidermal-specific TC-PTP-deficient (K14Cre.Ptpn2 fl/fl ) mice. Immortalized TC-PTP-deficient keratinocytes (TC-PTP/KO IPKs) showed increased cell survival against UVB-induced apoptosis which was concomitant with a UVB-mediated increase in Flk-1 phosphorylation, especially on tyrosine residue 1173. Inhibition of Flk-1 by either its specific inhibitors or siRNA in TC-PTP/KO IPKs reversed this effect and significantly increased cell death after UVB irradiation in comparison with untreated TC-PTP/KO IPKs. Immunoprecipitation analysis using the TC-PTP substrate-trapping mutant TCPTP-D182A indicated that TC-PTP directly interacts with Flk-1 to dephosphorylate it and their interaction was stimulated by UVB. Following UVB-mediated Flk-1 activation, the level of JNK phosphorylation was also significantly increased in TC-PTP/KO IPKs compared to control IPKs. Similar to our results with Flk-1, treatment of TC-PTP/KO IPKs with the JNK inhibitor SP600125 significantly increased apoptosis after UVB irradiation, confirming that the effect of TC-PTP on UVB-mediated apoptosis is regulated by Flk-1/JNK signaling. Western blot analysis showed that both phosphorylated Flk-1 and phosphorylated JNK were significantly increased in the epidermis of TC-PTP-deficient mice compared to control mice following UVB. Our results suggest that TC-PTP plays a protective role against UVB-induced keratinocyte cell damage by promoting apoptosis via negative regulation of Flk-1/JNK survival signaling.

We developed human dermo-epidermal skin substitutes that are presently applied in phase I and II clinical trials. Here, we used these very same skin equivalents containing melanocytes, named MelSkin, as an experimental skin model. We investigated the effects of ultraviolet B (UVB) irradiation on the skin grafts transplanted on immune-compromised rats. The irradiation induces a strong wound healing response going along with massive proliferation of basal keratinocytes, basically quiescent under nonirradiated, homeostatic conditions. As a consequence of UVB irradiation, the initially clearly defined basal keratinocyte (mono)layer expands into about 3 layers of keratinocytes, all of which still express the basal keratinocyte marker keratin 15. In contrast, epidermal melanocytes remain quiescent under these circumstances. Moreover, the Wnt inhibitors Dickkopf 3 and Wif1 are downregulated upon UVB irradiation in basal keratinocytes, whereas melanocytes continue to express Wnt inhibitors. These findings suggest that there is (a) a suprabasal population, proliferating in the homeostatic state, hence maintaining the integrity of the epidermis, and (b) a basal, usually quiescent keratinocyte population that is induced to massively proliferate upon irradiation. Importantly, the finding that MelSkin responds in a physiological fashion to UVB is of paramount importance in light of the planned clinical application., (Copyright © 2017 John Wiley & Sons, Ltd.)