- Open Access
Nrf2 null enhances UVB-induced skin inflammation and extracellular matrix damages
- Constance Lay Lay Saw1, 2,
- Anne Yuqing Yang1, 2,
- Mou-Tuan Huang1, 3,
- Yue Liu1, 3,
- Jong Hun Lee1, 2,
- Tin Oo Khor1, 2,
- Zheng-Yuan Su1, 2,
- Limin Shu1, 2,
- Yaoping Lu1, 3,
- Allan H Conney^1, 3 and
- Ah-Ng Tony Kong1, 2, 3Email author
© Saw et al.; licensee BioMed Central Ltd. 2014
- Received: 13 March 2014
- Accepted: 17 June 2014
- Published: 5 August 2014
Nrf2 plays a critical role in defending against oxidative stress and inflammation. We previously reported that Nrf2 confers protection against ultraviolet-B (UVB)-induced inflammation, sunburn reaction, and is involved in sulforaphane-mediated photo-protective effects in the skin. In this study, we aimed to demonstrate the protective role of Nrf2 against inflammation-mediated extracellular matrix (ECM) damage induced by UVB irradiation. Ear biopsy weights were significantly increased in both Nrf2 wild-type (Nrf2 WT) and knockout (Nrf2 KO) mice one week after UVB irradiation. However, these weights increased more significantly in KO mice compared to WT mice, suggesting a greater inflammatory response in KO mice. In addition, we analyzed the protein expression of numerous markers, including macrophage inflammatory protein-2 (MIP-2), pro-matrix metalloproteinase-9 (MMP-9), and p53. p53, a regulator of DNA repair, was overexpressed in Nrf2 KO mice, indicating that the absence of Nrf2 led to more sustained DNA damage. There was also more substantial ECM degradation and increased inflammation in UVB-irradiated Nrf2 KO mice compared to UVB-irradiated WT mice. Furthermore, the protective effects of Nrf2 in response to UVB irradiation were mediated by increased HO-1 protein expression. Collectively, our results show that Nrf2 plays a key role in protecting against UVB irradiation and that the photo-protective effect of Nrf2 is closely related to the inhibition of ECM degradation and inflammation.
- Nuclear factor (erythroid-derived 2)-like 2 (NFE2L2 or Nrf2)
The incidence of non-melanoma skin cancer has steadily increased, and ultraviolet (UV) light is one of the major causes of non-melanoma skin cancer. In fact, UV-induced non-melanoma skin cancer is the most common type of cancer in the US and worldwide [1, 2]. UVB is the most potent form of UV radiation; exposure to UVB radiation both burns the skin and drives the initiation, promotion, and progression of skin carcinogenesis . UV irradiation induces the delayed expression of UV-responsive genes such as matrix metalloproteinases (MMPs), which degrade macromolecular components of the extracellular matrix (ECM), and these changes represent a hallmark of carcinogenesis and aging . Moreover, altered ECM metabolism has been implicated in various diseases . Oxidative stress, such as that caused by excessive reactive oxygen species (ROS), is caused by UVB damage to DNA, protein, and lipids and can lead to inflammation, gene mutation, and immunosuppression [6, 7]. Due to the critical role of ROS in UVB-induced photo-carcinogenesis, ROS detoxification mechanisms have emerged as effective approaches for cancer prevention . Nuclear factor erythroid-2 (NF-E2)-related factor 2 (Nrf2), a member of the cap ‘n’ collar family of redox-sensitive bZIP (basic leucine zipper) proteins, is the major transcriptional regulator of the expression of genes encoding phase II detoxifying/antioxidant enzymes, including heme oxygenase-1 (HO-1) . HO-1 exhibits broad cytoprotective effects in various inflammatory diseases  and was shown to play a critical protective role in limiting oxidative damage in a UVB-induced model . MMP-9 was reported to be upregulated in angiogenic dysplasias and invasive cancers of the epidermis in a mouse model of multistage tumorigenesis. Notably, MMP-9 is predominantly expressed in neutrophils, macrophages, and mast cells rather than oncogene-positive neoplastic cells . It has also been reported that the disruption of Nrf2 enhanced the up-regulation of key inflammatory transcription factors, such as nuclear factor kappa B (NF-κB) and MMP-9 , and increased expression of macrophage inflammatory protein-2 (MIP-2), a neutrophil chemotactic factor, was observed in response to 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced epidermal hyperplasia in mice . The p53 tumor suppressor gene plays an important role in protecting cells against DNA damage and strand breaks , and the impact of UVB on p53 has been experimentally verified . Moreover, p53 is known to be activated by DNA damage , oxidative stress , and inflammation [17, 18].
We previously reported the critical role of nuclear Nrf2 in the classical 2-stage model of skin carcinogenesis induced by the chemical carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) and the tumor promoter TPA in Nrf2 knockout (Nrf2 KO) and wild-type (WT) mice . We also recently reported that Nrf2 plays an important role in the SFN-mediated protective effects against UVB-induced inflammation . To explore the potential impact of Nrf2 on UVB-induced inflammatory ECM damage in the skin, we studied the potential biomarkers involved in ECM degradation and inflammation in Nrf2 KO and WT mice, as these markers may be relevant to human skin carcinogenesis and photoaging [8, 21–24]. Based on this context, our current study aimed to ascertain the role of Nrf2 in UVB-induced ECM damage by focusing on inflammation and DNA repair in Nrf2 KO and Nrf2 WT mice.
Male and female Nrf2 KO and WT C57BL/6 mice were obtained as previously described . The offspring of the eighth generation of Nrf2 KO mice on the C57BL/6 background were used in this study. The genotype of each animal was confirmed using DNA extracted from the tail and analyzed by PCR. Nrf2 WT mice were purchased from The Jackson Laboratory (Bar Harbor, ME, USA). Mice were housed at the Rutgers Animal Facility, maintained under 12-h light/dark cycles, and provided ad libitum access to food and water. Animal experiments were performed in accordance with the Guide for the Care and Use of Laboratory Animals. All animal experimental procedures were approved by the Animal Care and Use Committee of Rutgers, The State University of New Jersey (Protocol Number: 04-003).
To induce skin inflammation, animals received a single dose of UVB light (300 mJ/cm2) as previously described [20, 25]. These UV lamps (FS72T12-UVB-HO; National Biological Corp., Twinsburg, OH, USA) emit little or no radiation < 280 nm and > 375 nm. The lamps emit UVB (280-320 nm; 75-80% of total energy) and UVA (320-375 nm; 20-25% of total energy), as described in our previous studies [20, 25]. The dose of UVB was quantified using a UVB Spectra 305 dosimeter (Daavlin Co., Bryan, OH, USA). The radiation was calibrated with an IL-1700 research radiometer/photometer (International Light Inc., Newburyport, MA, USA).
Experiments were performed in Nrf2 WT and KO mice to determine whether a single dose of 300 mJ/cm2 UVB irradiation would be sufficient to induce inflammatory reactions in the skin. Seven days after UVB irradiation, ear punches (6 mm in diameter) were obtained and weighed. Two sets of experiments were conducted in Nrf2 WT and KO mice after UVB exposure (at 8 h and 8 days). For each experiment, 4 groups of mice were evaluated: (1) no UVB in Nrf2 WT mice; (2) UVB in Nrf2 WT mice; (3) no UVB in Nrf2 KO mice; and (4) UVB in Nrf2 KO mice. A minimum of three animals was included in each group. The hair on the dorsal region of each mouse was removed 2 days before UVB irradiation, as previously described . At the end of the experiment, the mice were sacrificed by cervical dislocation, and the skin samples were frozen in liquid nitrogen and stored at -80°C.
Preparation of skin specimens and histological examination
Skin samples were obtained from the dorsal area of the mouse and were placed in 10% phosphate-buffered formalin at room temperature overnight. The samples were then dehydrated in increasing concentrations (80, 95, and 100%) of ethanol, cleared in xylene, and embedded in Paraplast Plus (Fisher Scientific, Pittsburgh, PA, USA). Four-micrometer serial sections were cut from the skin block, deparaffinized, rehydrated, and stained with hematoxylin and eosin (H&E). The H&E sections were examined under a light microscope (Nikon Eclipse E600, Japan).
ELISA for pro-inflammatory proteins and p53
The protein levels of pro-inflammatory cytokines and p53 were determined using two-site sandwich enzyme-linked immunosorbent assays (ELISAs). Dorsal skin tissues were homogenized in phosphate-buffered saline (PBS) containing 0.4 M NaCl, 0.05% Tween-20, 0.5% bovine serum albumin, 0.1 mM phenylmethylsulphonyl fluoride, 0.1 mM benzethonium chloride, 10 mM EDTA, and 200 KIU aprotinin per mL. The homogenates were centrifuged at 12,000 × g for 15 min at 4°C. The supernatant was used for the determination of cytokines levels. Pro-matrix metalloproteinase-9 (pro-MMP-9; DY909), macrophage inflammatory protein-2 (MIP-2; DY452), and p53 (DYC1746-2) kits were purchased from R&D Systems, Inc. (Minneapolis, MN, USA).
The protein samples were prepared as described above for the ELISAs. The protein concentration was measured using Bio-Rad protein assay reagent (Hercules, CA, USA). Equal amounts of protein (50 μg) from each sample were loaded onto a homemade 10% Tris/glycine SDS-polyacrylamide gel containing 0.1% SDS and run at 200 V for 1 h. The proteins were transferred to a nitrocellulose membrane by electroblotting using a Bio-Rad semidry transfer blotting apparatus over 1.5 h at 90 V (Bio-Rad, Hercules, CA, USA). The membrane was blocked with blocking buffer (Odyssey system, LI-COR Biosciences, Lincoln, NE, USA) for 1 h at room temperature. The primary antibodies were diluted in the same blocking buffer and were added to detect the target proteins. After an overnight incubation at 4°C, the membrane was washed with TBST (Tris-buffered saline and 0.05% Tween-20) and then incubated with the secondary antibody. Finally, the target protein bands were visualized with an Odyssey infrared imager. Antibodies against β-actin and HO-1 were purchased from Santa Cruz Biotechnology, Inc. (CA, USA). Densitometry was performed using the Image J software (version 1.44, National Institute of Health, USA). The relative protein expression was obtained by first calculating the relative intensity compared to the control (no UVB treatment) sample on the same blot and then normalizing this value to the intensity of β-actin from the same sample.
Data presentation and statistical analysis
The data are presented as the mean ± standard error of the mean (SEM), except as otherwise stated. Student’s t-test was used to determine statistically significant differences between groups. A p value < 0.05 was considered statistically significant.
A single dose of 300 mJ/cm2 UVB significantly increased the ear biopsy weight, and Nrf2 KO mice were more susceptible to UVB-induced skin edema
The absence of Nrf2 gene expression increased the UVB-induced skin thickness
Nrf2 KO mice were significantly more susceptible to UVB-induced inflammation and ECM degradation
Nrf2 KO mice were more susceptible to UVB-induced upregulation of p53
UVB increased expression of the Nrf2 target HO-1, an antioxidant biomarker, in Nrf2 WT mice compared to Nrf2 KO mice
In the present study, we investigated the photo-protective role of Nrf2 in inflammation-mediated ECM damage induced by UV, and our results indicated that Nrf2 KO mice were more susceptible to UVB radiation. Erythema has long been used as an indicator of UV-induced inflammation  and has been characterized as a reliable, reproducible and quantitative measurement of the degree of UV-induced inflammation . Thus, measuring the weight or thickness of irritated skin is a reliable indicator of inflammation [20, 28]. The results presented here demonstrated that UVB exposure significantly increased the ear biopsy weight in Nrf2 KO mice by almost 100%, whereas the ear biopsy weight only increased by 16% in Nrf2 WT mice. Moreover, the ratio of ear biopsy weights suggested that Nrf2 KO mice were more susceptible to UVB-induced skin edema (Figure 1). In addition, Nrf2 KO mice exhibited a greater increase in skin thickness after UVB exposure (Figure 2), which suggested that the loss of Nrf2 resulted in increased sensitivity to UVB radiation, thereby implying that there was more active inflammation in Nrf2-deficient mice. Therefore, we performed various biological assays to demonstrate that the observed UVB-induced responses were related to inflammation, ECM stability, and DNA damage. It has been reported in in vivo studies of human skin that UV irradiation significantly affects the coordinated regulation of various MMPs; after a single exposure to UV, MMP-9 activity increased 4-fold compared to non-UV irradiated human skin in a time-dependent manner . MIP-2, a key mediator of neutrophil recruitment, is involved in the early infiltration of neutrophils into UVB-exposed skin . In our study, UVB irradiation significantly enhanced the expression of MIP-2 in both Nrf2 WT and KO mice (Figure 3A). However, the increase in MIP-2 expression was much greater in Nrf2 KO mice compared to WT mice (Figure 3B). These MIP-2 findings correlate with those of a previous study in which MIP-2 expression was increased in mice after UVB irradiation . Photoaged skin displays prominent alterations in the collagenous ECM of connective tissue , and the detrimental effects of ECM degradation include diminished structural integrity, impaired wound healing, loss of cell viability, and cancer metastasis . There is growing interest in understanding the role of aberrant ECM modifications, especially regarding the “cancer stem cell niche” and the “metastatic niche” during key stages of cancer progression [7, 32]. Pro-MMP-9 expression was increased significantly in Nrf2 KO mice compared to WT mice (Figures 3C and 3D), and these results indicated that the absence of Nrf2 augmented the expression of matrix-degrading proteinases, including pro-MMP-9, in response to UVB irradiation. Furthermore, many ECM fragments that are created via degradation by various MMPs act as chemotactic factors that cause endothelial and inflammatory cells to migrate into areas of active tumor cell proliferation and growth . Thus, the photo-protective effect of Nrf2 was mediated by a reduction in MMP-9 expression. The p53 tumor suppressor gene is typically activated by DNA damage , oxidative stress , and/or inflammation [17, 18], and we observed that both of Nrf2 WT and KO mice exhibited increased p53 expression in response to UVB exposure, although the p53 expression was higher in KO mice. Regarding the role of p53 in DNA repair, increased p53 expression correlates with increased DNA damage, suggesting that the loss of Nrf2 may fail to protect DNA but could enable abundant p53 to repair the DNA damage. Indeed, a previous study showed that the extent of DNA damage correlates with the amount of UV exposure in various skin cells and models . In our study, the higher p53 expression observed in Nrf2 KO mice after UVB exposure could be an indicator of more sustained DNA damage in need of repair. HO-1 is a downstream antioxidant enzyme that is regulated by Nrf2 and has a broad cytoprotective effect in various inflammatory diseases and UVB irradiation [9, 10]. In our study, UVB exposure enhanced HO-1 expression by 43% in Nrf2 WT mice and by 24% in Nrf2 KO mice (Figure 5), which indicated that the photo-protective effect of Nrf2 was mediated by HO-1.
UVB irradiation induces aberrant biological responses, such as increased skin erythema and thickness, up-regulated expression of inflammatory and ECM-degrading enzymes, and augmented DNA damage. According to our results, these biological responses were milder in WT mice compared to Nrf2 KO mice. In addition, our UVB-induced mechanistic study revealed that the protective effect of Nrf2 was mediated by HO-1, and these findings suggest that Nrf2 plays a key role in protecting against UVB irradiation. Moreover, our study is the first to demonstrate that the photo-protective effect of Nrf2 is closely related to the inhibition of ECM degradation and inflammation through the overexpression of HO-1.
The authors would like to thank the members of Tony Kong’s laboratory for helpful discussions. This work was supported in part by institutional funds.
- Stern RS: Prevalence of a history of skin cancer in 2007: results of an incidence-based model. Arch Dermatol. 2010, 146 (3): 279-282.View ArticlePubMedGoogle Scholar
- Diepgen TL, Mahler V: The epidemiology of skin cancer. Br J Dermatol. 2002, 146 (Suppl 61): 1-6.View ArticlePubMedGoogle Scholar
- Brash DE, Ziegler A, Jonason AS, Simon JA, Kunala S, Leffell DJ: Sunlight and sunburn in human skin cancer: p53, apoptosis, and tumor promotion. J Investig Dermatol Symp Proc. 1996, 1 (2): 136-142.PubMedGoogle Scholar
- Brenneisen P, Sies H, Scharffetter-Kochanek K: Ultraviolet-B irradiation and matrix metalloproteinases - From induction via signaling to initial events, in Cell Signaling, Transcription, and Translation as Therapeutic Targets. Edited by: Diederich M. 2002, 31-43. New York: Acad Sciences.Google Scholar
- Hansson J, Vasan RS, Ärnlöv J, Ingelsson E, Lind L, Larsson A, Michaëlsson K, Sundstrom J: Biomarkers of extracellular matrix metabolism (MMP-9 and TIMP-1) and risk of stroke, myocardial infarction, and cause-specific mortality: cohort study. PLoS One. 2011, 6 (1): e16185. 10.1371/journal.pone.0016185PubMed CentralView ArticlePubMedGoogle Scholar
- Afaq F, Adhami VM, Mukhtar H: Photochemoprevention of ultraviolet B signaling and photocarcinogenesis. Mutat Res Fund Mol Mech Mutagen. 2005, 571 (1–2): 153-173.View ArticleGoogle Scholar
- Lee JH, Khor TO, Shu L, Su ZY, Fuentes F, Kong AN: Dietary phytochemicals and cancer prevention: Nrf2 signaling, epigenetics, and cell death mechanisms in blocking cancer initiation and progression. Pharmacol Ther. 2012, 137 (2): 153-171.PubMed CentralView ArticlePubMedGoogle Scholar
- Schafer M, Dutsch S, auf dem Keller U, Navid F, Schwarz A, Johnson DA, Johnson JA, Werner S: Nrf2 establishes a glutathione-mediated gradient of UVB cytoprotection in the epidermis. Genes Dev. 2010, 24 (10): 1045-1058. 10.1101/gad.568810PubMed CentralView ArticlePubMedGoogle Scholar
- Gozzelino R, Jeney V, Soares MP: Mechanisms of Cell Protection by Heme Oxygenase-1, Annual Review of Pharmacology and Toxicology. 2010, 323-354. Palo Alto: Annual Reviews.Google Scholar
- Black AT, Gordon MK, Heck DE, Gallo MA, Laskin DL, Laskin JD: UVB light regulates expression of antioxidants and inflammatory mediators in human corneal epithelial cells. Biochem Pharmacol. 2011, 81 (7): 873-880. 10.1016/j.bcp.2011.01.014PubMed CentralView ArticlePubMedGoogle Scholar
- Coussens LM, Tinkle CL, Hanahan D, Werb Z: MMP-9 supplied by bone marrow-derived cells contributes to skin carcinogenesis. Cell. 2000, 103 (3): 481-490. 10.1016/S0092-8674(00)00139-2PubMed CentralView ArticlePubMedGoogle Scholar
- Mao L, Wang H, Qiao L, Wang X: Disruption of Nrf2 enhances the upregulation of nuclear factor-kappaB activity, tumor necrosis factor-alpha, and matrix metalloproteinase-9 after spinal cord injury in mice. Mediat Inflamm. 2010, 2010: 238321.Google Scholar
- Wang HQ, Smart RC: Overexpression of protein kinase C-alpha in the epidermis of transgenic mice results in striking alterations in phorbol ester-induced inflammation and COX-2, MIP-2 and TNF-alpha expression but not tumor promotion. J Cell Sci. 1999, 112 (20): 3497-3506.PubMedGoogle Scholar
- Nelson WG, Kastan MB: DNA strand breaks: the DNA template alterations that trigger p53-dependent DNA damage response pathways. Mol Cell Biol. 1994, 14 (3): 1815-1823.PubMed CentralView ArticlePubMedGoogle Scholar
- van Kranen HJ, de Laat A, van de Ven J, Wester PW, de Vries A, Berg RJ, van Kreijl CF, de Gruijl FR: Low incidence of p53 mutations in UVA (365-nm)-induced skin tumors in hairless mice. Canc Res. 1997, 57 (7): 1238-1240.Google Scholar
- Han ES, Muller FL, Perez VI, Qi W, Liang H, Xi L, Fu C, Doyle E, Hickey M, Cornell J, Epstein CJ, Roberts LJ, Van Remmen H, Richardson A: The in vivo gene expression signature of oxidative stress. Physiol Genomics. 2008, 34 (1): 112-126. 10.1152/physiolgenomics.00239.2007PubMed CentralView ArticlePubMedGoogle Scholar
- Ak P, Levine AJ: p53 and NF-kappaB: different strategies for responding to stress lead to a functional antagonism. Faseb J. 2010, 24 (10): 3643-3652. 10.1096/fj.10-160549View ArticlePubMedGoogle Scholar
- Reuter S, Gupta SC, Chaturvedi MM, Aggarwal BB: Oxidative stress, inflammation, and cancer: how are they linked?. Free Radic Biol Med. 2010, 49 (11): 1603-1616. 10.1016/j.freeradbiomed.2010.09.006PubMed CentralView ArticlePubMedGoogle Scholar
- Xu C, Huang MT, Shen G, Yuan X, Lin W, Khor TO, Conney AH, Kong AN: Inhibition of 7, 12-dimethylbenz(a)anthracene-induced skin tumorigenesis in C57BL/6 mice by sulforaphane is mediated by nuclear factor E2-related factor 2. Canc Res. 2006, 66 (16): 8293-8296. 10.1158/0008-5472.CAN-06-0300. 10.1158/0008-5472.CAN-06-0300View ArticleGoogle Scholar
- Saw CL, Huang MT, Liu Y, Khor TO, Conney AH, Kong AN: Impact of Nrf2 on UVB-induced skin inflammation/photoprotection and photoprotective effect of sulforaphane. Mol Carcinog. 2011, 50 (6): 479-486. 10.1002/mc.20725View ArticlePubMedGoogle Scholar
- Marrot L, Jones C, Perez P, Meunier JR: The significance of Nrf2 pathway in (photo)-oxidative stress response in melanocytes and keratinocytes of the human epidermis. Pigment Cell Melanoma Res. 2008, 21 (1): 79-88.View ArticlePubMedGoogle Scholar
- auf dem Keller U, Huber M, Beyer TA, Kumin A, Siemes C, Braun S, Bugnon P, Mitropoulos V, Johnson DA, Johnson JA, Hohl D, Werner S: Nrf transcription factors in keratinocytes are essential for skin tumor prevention but not for wound healing. Mol Cell Biol. 2006, 26 (10): 3773-3784. 10.1128/MCB.26.10.3773-3784.2006PubMed CentralView ArticlePubMedGoogle Scholar
- Wondrak GT, Cabello CM, Villeneuve NF, Zhang S, Ley S, Li Y, Sun Z, Zhang DD: Cinnamoyl-based Nrf2-activators targeting human skin cell photo-oxidative stress. Free Radic Biol Med. 2008, 45 (4): 385-395. 10.1016/j.freeradbiomed.2008.04.023PubMed CentralView ArticlePubMedGoogle Scholar
- MacLeod AK, McMahon M, Plummer SM, Higgins LG, Penning TM, Igarashi K, Hayes JD: Characterization of the cancer chemopreventive NRF2-dependent gene battery in human keratinocytes: demonstration that the KEAP1-NRF2 pathway, and not the BACH1-NRF2 pathway, controls cytoprotection against electrophiles as well as redox-cycling compounds. Carcinogenesis. 2009, 30 (9): 1571-1580. 10.1093/carcin/bgp176PubMed CentralView ArticlePubMedGoogle Scholar
- Lu YP, Lou YR, Yen P, Mitchell D, Huang MT, Conney AH: Time course for early adaptive responses to ultraviolet B light in the epidermis of SKH-1 mice. Canc Res. 1999, 59 (18): 4591-4602.Google Scholar
- Eaglstein WH, Sakai M, Mizuno N: Ultraviolet radiation-induced inflammation and leukocytes. J Invest Dermatol. 1979, 72 (2): 59-63. 10.1111/1523-1747.ep12530248View ArticlePubMedGoogle Scholar
- Cole C, Sambuco C, Forbes P, Davies R: Response to ultraviolet radiation: ear swelling in hairless mice. Photodermatol. 1984, 1 (3): 114-118.PubMedGoogle Scholar
- Huang MT: Inhibitory effects of black tea theaflavin derivatives on 12-O-tetradecanoylphorbol-13-acetate-induced inflammation and arachidonic acid metabolism in mouse ears. Mol Nutr Food Res. 2006, 50 (2): 115-122. 10.1002/mnfr.200500101View ArticlePubMedGoogle Scholar
- Fisher GJ, Wang ZQ, Datta SC, Varani J, Kang S, Voorhees JJ: Pathophysiology of premature skin aging induced by ultraviolet light. N Engl J Med. 1997, 337 (20): 1419-1428. 10.1056/NEJM199711133372003View ArticlePubMedGoogle Scholar
- Komatsu J, Koyama H, Maeda N, Aratani Y: Earlier onset of neutrophil-mediated inflammation in the ultraviolet-exposed skin of mice deficient in myeloperoxidase and NADPH oxidase. Inflamm Res. 2006, 55 (5): 200-206. 10.1007/s00011-006-0071-3View ArticlePubMedGoogle Scholar
- Gonzalez S, Moran M, Kochevar IE: Chronic photodamage in skin of mast cell-deficient mice. Photochem Photobiol. 1999, 70 (2): 248-253. 10.1111/j.1751-1097.1999.tb07996.xView ArticlePubMedGoogle Scholar
- Lu P, Takai K, Weaver VM, Werb Z: Extracellular matrix degradation and remodeling in development and disease. Cold Spring Harb Perspect Biol. 2011, 3 (12):Google Scholar
- Mott JD, Werb Z: Regulation of matrix biology by matrix metalloproteinases. Curr Opin Cell Biol. 2004, 16 (5): 558-564. 10.1016/j.ceb.2004.07.010PubMed CentralView ArticlePubMedGoogle Scholar
- Marrot L, Planel E, Ginestet AC, Belaidi JP, Jones C, Meunier JR: In vitro tools for photobiological testing: molecular responses to simulated solar UV of keratinocytes growing as monolayers or as part of reconstructed skin. Photochem Photobiol Sci. 2010, 9 (4): 448-458. 10.1039/b9pp00145jView ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.