Role of NF-κB–p53 crosstalk in ultraviolet A-induced cell death and G1 arrest in human dermal fibroblasts

Sunscreens and Photoaging: A Review of Current Literature

Sunscreens have been on the market for many decades as a means of protection against ultraviolet-induced erythema. Over the years, evidence has also shown their efficacy in the prevention of photoaging, dyspigmentation, DNA damage, and photocarcinogenesis. In the USA, most broad-spectrum sunscreens provide protection against ultraviolet B (UVB) radiation and short-wavelength ultraviolet A (UVA) radiation. Evidence suggests that visible light and infrared light may play a role in photoaging and should be considered when choosing a sunscreen. Currently, there is a paucity of US FDA-approved filters that provide protection against long UVA (> 370 nm) and none against visible light. Additionally, various sunscreen additives such as antioxidants and photolyases have also been reported to protect against and possibly reverse signs of photoaging. This literature review evaluates the utility of sunscreen in protecting against photoaging and further explores the requirements for an ideal sunscreen.

Opsin 3 is a key regulator of ultraviolet A-induced photoageing in human dermal fibroblast cells

Background

Chronic exposure to ultraviolet (UV) radiation (mainly UVA) induces a sustained increase of matrix metalloproteinases (MMPs), especially MMP1, MMP2, MMP3 and MMP9 in human skin fibroblasts. MMPs can lead to the degradation of fibrous connective tissue, which is the main cause of skin photoageing. The molecular mechanisms through which fibroblasts sense UVA and trigger the cell signalling pathways involved in the upregulation of MMPs have not been well elucidated.

Objectives

Here, we investigated the function and potential mechanisms of photoageing of opsin (OPN)3 in normal human dermal fibroblasts (NHDFs).

Methods

Real‐time polymerase chain reaction and Western blot analysis were used to analyse the expression levels of OPN3 in NHDFs and photoageing models. Subsequently, NHDFs transfected with OPN3 inhibitors and indicators related to photoageing before and after UVA irradiation included expression levels of MMP1, MMP2, MMP3 and MMP9, and signalling pathway protein molecules were examined.

Results

We provide evidence that OPN3 initiates UVA phototransduction in NHDFs. OPN3 triggers phosphorylation of activator protein 1 and ultimately upregulates MMP1, MMP2, MMP3 and MMP9 in NHDFs through activating Ca²⁺/calmodulin‐dependent protein kinase II, cyclic adenosine monophosphate response element‐binding protein, extracellular signal‐regulated kinase, c‐JUN N‐terminal kinase and p38. Here, we demonstrate for the first time that OPN3 is the key sensor responsible for upregulating MMP1, MMP2, MMP3 and MMP9 in NHDFs following UVA exposure via the calcium‐dependent G protein‐coupled signalling pathway.

Conclusions

Our studies provide insights into the understanding of the molecular mechanisms through which human skin cells respond to UVA radiation and may reveal molecular targets for skin photoageing prevention or clinical management.

What's already known about this topic?

Photoaged fibroblasts accumulate with long‐term ultraviolet (UV) exposure.

Matrix metalloproteinases (MMPs) play an important role in the pathogenesis of photoageing.

MMP1, MMP2, MMP3 and MMP9 are responsible for the destruction of fibroblast collagen in severely photodamaged skin.

Opsins (OPNs) are light‐sensitive members of the superfamily of heptahelical G protein‐coupled receptors, a family of cell surface receptors that are activated by a variety of stimuli and mediate signalling across membranes.

What does this study add?

OPN3 is highly expressed in fibroblasts and responds to UVA irradiation.

OPN3 regulates the expression of MMP1, MMP2, MMP3 and MMP9 via the calcium‐dependent G protein‐coupled signalling pathway.

OPN3 is a light‐sensitive sensor that plays an important role in photoageing of the skin.

Linked Comment: Julie Thornton. Br J Dermatol 2020; 182:1086–1087.

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Persistent IKKα phosphorylation induced apoptosis in UVB and Poly I:C co-treated HaCaT cells plausibly through pro-apoptotic p73 and abrogation of IκBα

Toll-like receptor 3 (TLR3), a member of pattern recognition receptors, is reported to initiate skin inflammation by recognizing double-strand RNA (dsRNA) released from UVB-irradiated cells. Recently, we have discovered the NF-κB pathway activated by TLR3 is involved in apoptosis of UVB-Poly I:C-treated HaCaT cells. The real culprit for apoptosis has not been precisely identified since the system of NF-κB pathway is complex. In this study, we silenced main transcriptional factors in NF-κB family, RelA, RelB and c-Rel, but to our surprise the results show that none of them participate in apoptosis induction in UVB-Poly I:C-treated HaCaT cells. Therefore, we moved to investigate the apoptosis-associated molecules in the upstream of NF-κB pathway. We firstly checked the expression of IκBα, an NF-κB inhibitor. UVB (4.8 mJ/cm²) and Poly I:C (0.3 μg/mL) co-treatment decreased IκBα expression level in a time-dependent manner. Silencing IκBα with siRNA further enhanced UVB-Poly I:C-induced cell death. We then investigated IκB kinase (IKK) complex that contributes to the degradation of IκBα. IKK is composed of IKKα, IKKβ and NEMO. Treatment with IKK-16, an IKKα/β inhibitor, significantly diminished UVB-Poly I:C-induced IκBα degradation and thus apoptosis. Silencing either IKKα or NEMO but not IKKβ with corresponding siRNA inhibited apoptosis. Tumor repressor p73, a homologue of p53, is reported to mediate IKKα-induced apoptosis in DNA damage response. Silencing p73 reduced cell apoptosis in UVB-Poly I:C-treated HaCaT cells. In summary, UVB and Poly I:C co-treatment activates IKKα and NEMO, which diminishes anti-apoptotic IκBα, resulting in enhancement of apoptosis through p73. The findings partially clarify the possible molecular mechanism of pro-apoptotic NF-κB pathway activated by TLR3 in the fate of UVB-irradiated epidermis.

Sub-lethal ultraviolet B irradiation and Poly I:C treatment synergistically induced apoptosis of HaCaT cells through NF-κB pathway

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/cm²) 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.

Apigenin inhibits UVA-induced cytotoxicity in vitro and prevents signs of skin aging in vivo

Apigenin (4',5,7-trihydroxyflavone) is a flavone that has been reported to have anti-inflammatory, antioxidant and anti-carcinogenic properties. In this study, we investigated the protective effects of apigenin on skin and found that, in experiments using cells, apigenin restored the viability of normal human dermal fibroblasts (nHDFs), which had been decreased by exposure to ultraviolet (UV) radiation in the UVA range. Using a senescence-associated (SA)-β-gal assay, we also demonstrate that apigenin protects against the UVA-induced senescence of nHDFs. Furthermore, we found that apigenin decreased the expression of the collagenase, matrix metalloproteinase (MMP)-1, in UVA-irradiated nHDFs. UVA, which has been previously identified as a photoaging-inducing factor, has been shown to induce MMP-1 expression. The elevated expression of MMP-1 impairs the collagen matrix, leading to the loss of elasticity and skin dryness. Therefore, we examined the clinical efficacy of apigenin on aged skin, using an apigenin‑containing cream for clinical application. Specifically, we measured dermal density, skin elasticity and the length of fine wrinkles in subjects treated with apigenin cream or the control cream without apigenin. Additionally, we investigated the effects of the apigenin-containing cream on skin texture, moisture and transepidermal water loss (TEWL). From these experiments, we found that the apigenin‑containing cream increased dermal density and elasticity, and reduced fine wrinkle length. It also improved skin evenness, moisture content and TEWL. These results clearly demonstrate the biological effects of apigenin, demonstrating both its cellular and clinical efficacy, and suggest that this compound holds promise as an anti-aging cosmetic ingredient.

Identification of ultraviolet B radiation‑induced microRNAs in normal human dermal papilla cells

Ultraviolet (UV) radiation impairs intracellular functions by directly damaging DNA and by indirectly generating reactive oxygen species (ROS), which induce cell cycle arrest and apoptosis. UV radiation can also alter gene expression profiles, including those of mRNA and microRNA (miRNA). The effects of UV radiation on cellular functions and gene expression have been widely documented in human skin cells such as keratinocytes, melanocytes and dermal fibroblasts, but the effect it has on other types of skin cell such as dermal papilla cells, which are crucial in the induction of hair follicle growth, remains unknown. In the current study, the effect of UV radiation on physiological changes and miRNA-based expression profiles in normal human dermal papilla cells (nHDPs) was investigated. UVB radiation of ≥50 mJ/cm² displayed high cytotoxicity and apoptosis in a dose-dependent manner. In addition, ROS generation was exhibited in UVB-irradiated nHDPs. Furthermore, using miRNA microarray analysis, it was demonstrated that the expression profiles of 42 miRNAs in UVB-irradiated nHDPs were significantly altered compared with those in the controls (35 upregulated and 7 downregulated). The biological functions of the differentially expressed miRNAs were studied with gene ontology analysis to identify their putative target mRNAs, and were demonstrated to be involved in cell survival- and death-related functions. Overall, the results of the present study provide evidence that miRNA-based cellular mechanisms may be involved in the UVB-induced cellular response in nHDPs.

Ultraviolet A-induced cathepsin K expression is mediated via MAPK/AP-1 pathway in human dermal fibroblasts

Background

Cathepsin K (CatK), a cysteine protease with the potent elastolytic activity, plays a predominant role in intracellular elastin degradation in human dermal fibroblasts (HDFs), and contributes to solar elastosis. In previous studies, CatK expression was downregulated in photoaged skin and fibroblasts, but upregulated in acute UVA-irradiated skin and fibroblasts. The underlying mechanisms regulating UVA-induced CatK expression remain elusive.

Objective

This study investigates mechanisms involved in the regulation of UVA-induced CatK expression in HDFs.

Methods

Primary HDFs were exposed to UVA. Cell proliferation was analyzed using a colorimetric assay of relative cell number. Quantitative real-time RT-PCR and Western blot were performed to detect CatK expression in HDFs on three consecutive days after 10 J/cm² UVA irradiation, or cells treated with increasing UVA doses. UVA-activated MAPK/AP-1 pathway was examined by Western blot. Effects of inhibition of MAPK pathway and knockdown of Jun and Fos on UVA-induced CatK expression were also measured by real-time RT-PCR and Western blot.

Results

UVA significantly increased CatK mRNA and protein expression in a dose-dependent manner. UVA-induced CatK expression occurred along with UVA-activated phosphorylation of JNK, p38 and Jun, UVA-increased expression of Fos. Inactivation of JNK and p38MAPK pathways both remarkably decreased UVA-induced CatK expression, which was suppressed more by inhibition of JNK pathway. Furthermore, knockdown of Jun and Fos significantly attenuated basal and UVA-induced CatK expression.

Conclusion

UVA is capable of increasing CatK expression in HDFs, most likely by activation of MAPK pathway and of AP-1, which has been shown to be the case for matrix metalloproteinases. As current strategies for selecting anti-photoaging agents focus on their ability to decrease MMPs' expression through inhibiting UV- activated MAPK pathway, future strategies should also consider their effect on CatK expression.

Chronic exposure to Rhodobacter sphaeroides extract Lycogen™ prevents UVA-induced malondialdehyde accumulation and procollagen I down-regulation in human dermal fibroblasts

UVA contributes to the pathogenesis of skin aging by downregulation of procollagen I content and induction of matrix metalloproteinase (MMP)-associated responses. Application of antioxidants such as lycopene has been demonstrated as a convenient way to achieve protection against skin aging. Lycogen™, derived from the extracts of Rhodobacter sphaeroides, exerts several biological effects similar to that of lycopene whereas most of its anti-aging efficacy remains uncertain. In this study, we attempted to examine whether Lycogen™ could suppress malondialdehyde (MDA) accumulation and restore downregulated procollagen I expression induced by UVA exposure. In human dermal fibroblasts Hs68 cells, UVA repressed cell viability and decreased procollagen I protein content accompanied with the induction of MMP-1 and MDA accumulation. Remarkably, incubation with 50 μM Lycogen™ for 24 h ameliorated UVA-induced cell death and restored UVA-induced downregulation of procollagen in a dose-related manner. Lycogen™ treatment also prevented the UVA-induced MMP-1 upregulation and intracellular MDA generation in Hs68 cells. Activation of NFκB levels, one of the downstream events induced by UVA irradiation and MMP-1 induction, were also prevented by Lycogen™ administration. Taken together, our findings demonstrate that Lycogen™ may be an alternative agent that prevents UVA-induced skin aging and could be used in cosmetic and pharmaceutical applications.

Friend or foe: emerging role of nuclear factor kappa-light-chain-enhancer of activated B cells in cell senescence

The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) proteins are a family of ubiquitously expressed transcription factors that regulate the response to cellular stress. They mediate innate and adaptive immunity through the initiation of an inflammatory response to pro-inflammatory signals. The role of persistent inflammation in aiding tumor development has led to the NF-κB family of transcription factors being strongly implicated in promoting cancer. However, recent studies have now revealed that NF-κB can also function as a tumor suppressor through the induction of cellular senescence. Cellular senescence is a stable cell cycle arrest that normal cells undergo in response to a variety of intrinsic and extrinsic stimuli including: progressive telomere shortening, changes in telomeric structure, or other forms of genotoxic stress. Senescence can compromise tissue repair and regeneration, contributing to tissue and organismal aging via the accumulation of senescent cells, depletion of stem/progenitor cells and secretion of an array of inflammatory cytokines, chemokines, and matrix metalloproteinases. Senescence can also lead to the removal of potentially cancerous cells, thereby acting as a potent tumor suppressor mechanism. Herein, we review the evidence indicating a role for NF-κB in tumor suppression via cellular senescence and suggest that depending upon the subunit expressed, the biological context, and the type and intensity of the signal, NF-κB can indeed promote senescence growth arrest.

Hyperbaric oxygen preconditioning protects skin from UV-A damage

Hyperbaric oxygen therapy (HBOT) is used for a number of applications, including the treatment of diabetic foot ulcers and CO poisoning. However, we and others have shown that HBOT can mobilize cellular antioxidant defenses, suggesting that it may also be useful under circumstances in which tissue protection from oxidative damage is desired. To test the protective properties of hyperbaric oxygen (HBO) on a tissue level, we evaluated the ability of a preconditioning treatment regimen to protect cutaneous tissue from UV-A-induced oxidative damage. Three groups of hairless SKH1-E mice were exposed to UV-A 3 days per week for 22 weeks, with two of these groups receiving an HBO pretreatment either two or four times per week. UV-A exposure increased apoptosis and proliferation of the skin tissue, indicating elevated levels of epithelial damage and repair. Pretreatment with HBO significantly reduced UV-A-induced apoptosis and proliferation. A morphometric analysis of microscopic tissue folds also showed a significant increase in skin creasing following UV-A exposure, which was prevented by HBO pretreatment. Likewise, skin elasticity was found to be greatest in the group treated with HBO four times per week. The effects of HBO were also apparent systemically as reductions in caspase-3 activity and expression were observed in the liver. Our findings support a protective function of HBO pretreatment from a direct oxidative challenge of UV-A to skin tissue. Similar protection of other tissues may likewise be achievable.

Dexamethasone reduces sensitivity to cisplatin by blunting p53-dependent cellular senescence in non-small cell lung cancer

Introduction

Dexamethasone (DEX) co-treatment has proved beneficial in NSCLC patients, improving clinical symptoms by the reduction of side effects after chemotherapy. However, recent studies have shown that DEX could render cancer cells more insensitive to cytotoxic drug therapy, but it is not known whether DEX co-treatment could influence therapy-induced senescence (TIS), and unknown whether it is in a p53-dependent or p53-independent manner.

Methods

We examined in different human NSCLC cell lines and detected cellular senescence after cisplatin (DDP) treatment in the presence or absence of DEX. The in vivo effect of the combination of DEX and DDP was assessed by tumor growth experiments using human lung cancer cell lines growing as xenograft tumors in nude mice.

Results

Co-treatment with DEX during chemotherapy in NSCLC resulted in increased tumor cell viability and inhibition of TIS compared with DDP treated group. DEX co-treatment cells exhibited the decrease of DNA damage signaling pathway proteins, the lower expression of p53 and p21^CIP1, the lower cellular secretory program and down-regulation of NF-κB and its signaling cascade. DEX also significantly reduced DDP sensitivity in vivo.

Conclusions

Our results underscore that DEX reduces chemotherapy sensitivity by blunting therapy induced cellular senescence after chemotherapy in NSCLC, which may, at least in part, in a p53-dependent manner. These data therefore raise concerns about the widespread combined use of gluocorticoids (GCs) with antineoplastic drugs in the clinical management of cancer patients.