UVB Exposure Prevents Atherosclerosis by Regulating Immunoinflammatory Responses

Associations and mediators between vitiligo and cardiovascular diseases: a Mendelian randomization study

Previous studies yielded conflicting results on the associations between vitiligo and cardiovascular diseases (CVD), and its underlying mechanisms remain unclear. This MR study aims to elucidate the underlying causal association between vitiligo and the risk of CVD, as well as the potential mediator. Using summary statistics from genome-wide association study (GWAS), we conducted a bidirectional two-sample Mendelian randomization (MR) analysis and mediation analysis to investigate the causal association between vitiligo and 13 CVD outcomes and potential mediators. The IVW method was the main MR analysis method, supplemented by MR-Egger, weighted median, and weighted mode methods. Multiple sensitivity analyses were applied to enhance the robustness of the results. Bioinformatics analysis involved Protein-Protein Interaction (PPI) network, Gene Ontology (GO) and GeneMANIA functional analysis analysis. MR analysis indicated that genetically predicted vitiligo was significantly associated with higher risk of coronary heart disease (CHD) (OR = 1.0199, 95% CI = 1.0024-1.0377, p = 0.026). There was no significant causal association between vitiligo and 12 other cardiovascular diseases. And reverse MR analysis found no causal effect of CVD on vitiligo. CCL11 was identified to partially mediate the association between vitiligo and CHD. GO and GeneMANIA suggested that CCL11 may mediate the association between vitiligo and CHD through chemokine-related functions and pathways. Our study revealed the potential causal association between vitiligo and CHD, with CCL11 as a potential mediator. Further studies are necessitated to elucidate the exact association and the mechanisms.

Overview of multifunctional Tregs in cardiovascular disease: From insights into cellular functions to clinical implications

Regulatory T cells (Tregs) are crucial in regulating T-cell-mediated immune responses. Numerous studies have shown that dysfunction or decreased numbers of Tregs may be involved in inflammatory cardiovascular diseases (CVDs) such as atherosclerosis, hypertension, myocardial infarction, myocarditis, cardiomyopathy, valvular heart diseases, heart failure, and abdominal aortic aneurysm. Tregs can help to ameliorate CVDs by suppressing excessive inflammation through various mechanisms, including inhibition of T cells and B cells, inhibition of macrophage-induced inflammation, inhibition of dendritic cells and foam cell formation, and induction of anti-inflammatory macrophages. Enhancing or restoring the immunosuppressive activity of Tregs may thus serve as a fundamental immunotherapy to treat hypertension and CVDs. However, the precise molecular mechanisms underlying the Tregs-induced protection against hypertension and CVDs remain to be investigated. This review focuses on recent advances in our understanding of Tregs subsets and function in CVDs. In addition, we discuss promising strategies for using Tregs through various pharmacological approaches to treat hypertension and CVDs.

Novel UV-B Phototherapy With a Light-Emitting Diode Device Prevents Atherosclerosis by Augmenting Regulatory T-Cell Responses in Mice

BACKGROUND

Ultraviolet B (UV-B) irradiation is an effective treatment for human cutaneous disorders and was shown to reduce experimental atherosclerosis by attenuating immunoinflammatory responses. The aim of this study was to clarify the effect of specific wavelengths of UV-B on atherosclerosis and the underlying mechanisms focusing on immunoinflammatory responses.

METHODS AND RESULTS

Based on light-emitting diode technology, we developed novel devices that can emit 282 nm UV-B, which we do not receive from natural sunlight, 301 nm UV-B, and clinically available 312 nm UV-B. We irradiated 6-week-old male atherosclerosis-prone Apoe-/- (apolipoprotein E-deficient) mice with specific wavelengths of UV-B and evaluated atherosclerosis and immunoinflammatory responses by performing histological analysis, flow cytometry, biochemical assays, and liquid chromatography/mass spectrometry-based lipidomics. Irradiation of 282 nm UV-B but not 301 or 312 nm UV-B significantly reduced the development of aortic root atherosclerotic plaques and plaque inflammation. This atheroprotection was associated with specifically augmented immune responses of anti-inflammatory CD4+ Foxp3 (forkhead box P3)+ regulatory T cells in lymphoid tissues, whereas responses of other immune cells were not substantially affected. Analysis of various lipid mediators revealed that 282 nm UV-B markedly increased the ratio of proresolving to proinflammatory lipid mediators in the skin.

CONCLUSIONS

We demonstrated that 282 nm UV-B irradiation effectively reduces aortic inflammation and the development of atherosclerosis by systemically augmenting regulatory T-cell responses and modulating the balance between proresolving and proinflammatory lipid mediators in the skin. Our findings indicate that a novel 282 nm UV-B phototherapy could be an attractive approach to treat atherosclerosis.

All-Cause and Cause-Specific Mortality among Patients with Vitiligo: A Nationwide Population-Based Study in Korea

Vitiligo is a common autoimmune skin disorder; however, there is limited information about risks of mortality among patients with vitiligo. Therefore, we aimed to investigate the mortality in patients with vitiligo. A population-based cohort study was conducted using the data linkage of the National Health Insurance Service database and the National Death Registry. Patients with incident vitiligo were matched with sociodemographic factors-matched controls without vitiligo in a 1:5 ratio. All-cause and cause-specific mortalities were compared between patients with vitiligo and controls. In total, 107,424 patients with incident vitiligo and 537,120 matched controls were included. The mortality rates were 34.8 and 45.3 per 10,000 person-years in patients and controls, respectively. Patients with vitiligo showed a significantly lower risk of mortality (adjusted hazard ratio = 0.75, 95% confidence interval = 0.72-0.78). The cause-specific mortality from infectious diseases, oncologic diseases, hematologic diseases, endocrine diseases, neurologic diseases, cardiovascular diseases, respiratory diseases, and renal/urogenital disease was significantly lower in patients with vitiligo. Patients with vitiligo were associated with a lower risk of mortality, suggesting that vitiligo-associated autoimmunity might contribute to reduced morbidity and mortality.

Impact of ultraviolet radiation on cardiovascular and metabolic disorders: The role of nitric oxide and vitamin D

BACKGROUND/PURPOSE

Ultraviolet (UV) radiation has both harmful and beneficial effects on human skin and health. It causes skin damage, aging, and cancer; however, it is also a primary source of vitamin D. Additionally, UV radiation can impact energy metabolism and has protective effects on several cardiovascular and metabolic disorders in mice and humans. However, the mechanisms of UV protection against these diseases have not been clearly identified.

METHODS

This review summarizes the systemic effects of UV radiation on hypertension and several metabolic diseases such as obesity, diabetes, and nonalcoholic fatty liver disease (NAFLD) in mice, and we also consider the mechanisms of action of the related regulators nitric oxide (NO) and vitamin D.

RESULTS

UV exposure can lower blood pressure and prevent the development of cardiovascular diseases and metabolic disorders, such as metabolic syndrome, obesity, and type 2 diabetes, primarily through mechanisms that depend on UV-induced NO. UV radiation may also effectively delay the onset of type 1 diabetes through mechanisms that rely on UV-induced vitamin D. UV-induced NO and vitamin D play roles in preventing and slowing the progression of NAFLD.

CONCLUSION

UV exposure is a promising nonpharmacological intervention for cardiovascular and metabolic disorders. NO and vitamin D may play a crucial role in mediating these effects. However, further investigations are required to elucidate the exact mechanisms and determine the optimal dosage and exposure duration of UV radiation.

Weak UVB Irradiation Promotes Macrophage M2 Polarization and Stabilizes Atherosclerosis

Atherosclerosis (AS) is a chronic cardiovascular disease endangering human health and is one of the most common causes of myocardial infarction and stroke. Macrophage polarization plays a vital role in regulating plaque stability. As an important component of sunlight, ultraviolet B (UVB) has been proven to promote vitamin D and nitric oxide synthesis. This research used an AS model in ApoE-/- mice to study the effects of UVB on macrophage polarization and atherosclerotic plaque stability. In vitro, UVB irradiation increased arginase-I (Arg-I, M2 macrophage) and macrophage mannose receptor (CD206) expression, while the expression of inducible nitric oxide synthase (iNOS) (M1 macrophage) and CD86 was decreased. UVB promoted Akt phosphorylation in vitro. In vivo, UVB irradiation promoted the stabilization of atherosclerotic lesion plaques, while the phenotype of M2 macrophages increased. Our research provides new evidence for UVB in preventing and treating atherosclerosis.

Depletion of Foxp3+ regulatory T cells augments CD4+ T cell immune responses in atherosclerosis-prone hypercholesterolemic mice

Compelling evidence suggests a crucial role for Foxp3⁺ regulatory T cells (Tregs) in the control of atherosclerosis. Although suppression of pro-inflammatory CD4⁺ T cell immune responses is supposed to be important for athero-protective action of Foxp3⁺ Tregs, few studies have provided direct evidence for this protective mechanism. We investigated the impact of Foxp3⁺ Treg depletion on CD4⁺ T cell immune responses and the development of atherosclerosis under hypercholesterolemia. We employed DEREG (depletion of regulatory T cells) mice on an atherosclerosis-prone low-density lipoprotein receptor-deficient (Ldlr ^-/-) background, which carry a diphtheria toxin (DT) receptor under the control of the foxp3 gene locus. In these mice, DT injection led to efficient depletion of Foxp3⁺ Tregs in spleen, lymph nodes and aorta. Depletion of Foxp3⁺ Tregs augmented CD4⁺ effector T cell immune responses and aggravated atherosclerosis without affecting plasma lipid profile. Notably, the proportion of pro-inflammatory IFN-γ-producing T cells were increased in spleen and aorta following Foxp3⁺ Treg depletion, implying that Foxp3⁺ Tregs efficiently regulate systemic and aortic T cell-mediated inflammatory responses under hypercholesterolemia. Unexpectedly, Foxp3⁺ Treg depletion resulted in an increase in anti-inflammatory IL-10-producing T cells, which was not sufficient to suppress the augmented proinflammatory T cell immune responses caused by reduced numbers of Foxp3⁺ Tregs. Our data indicate that Foxp3⁺ Tregs suppress pro-inflammatory CD4⁺ T cell immune responses to control atherosclerosis under hypercholesterolemia.

Recent Advances on the Role and Therapeutic Potential of Regulatory T Cells in Atherosclerosis

Atherosclerotic diseases, including ischemic heart disease and stroke, are a main cause of mortality worldwide. Chronic vascular inflammation via immune dysregulation is critically involved in the pathogenesis of atherosclerosis. Accumulating evidence suggests that regulatory T cells (Tregs), responsible for maintaining immunological tolerance and suppressing excessive immune responses, play an important role in preventing the development and progression of atherosclerosis through the regulation of pathogenic immunoinflammatory responses. Several strategies to prevent and treat atherosclerosis through the promotion of regulatory immune responses have been developed, and could be clinically applied for the treatment of atherosclerotic cardiovascular disease. In this review, we summarize recent advances in our understanding of the protective role of Tregs in atherosclerosis and discuss attractive approaches to treat atherosclerotic disease by augmenting regulatory immune responses.

Multi-responsive deep-ultraviolet emission in praseodymium-doped phosphors for microbial sterilization

Perusing multimode luminescent materials capable of being activated by diverse excitation sources and realizing multi-responsive emission in a single system remains a challenge. Herein, we utilize a heterovalent substituting strategy to realize multimode deep-ultraviolet (UV) emission in the defect-rich host Li2CaGeO4 (LCGO). Specifically, the Pr3+ substitution in LCGO is beneficial to activating defect site reconstruction including the generation of cation defects and the decrease of oxygen vacancies. Regulation of different traps in LCGO:Pr3+ presents persistent luminescence and photo-stimulated luminescence in a synergetic fashion. Moreover, the up-conversion luminescence appears with the aid of the 4f discrete energy levels of Pr3+ ions, wherein incident visible light is partially converted into germicidal deep-UV radiation. The multi-responsive character enables LCGO:Pr3+ to response to convenient light sources including X-ray tube, standard UV lamps, blue and near-infrared lasers. Thus, a dual-mode optical conversion strategy for inactivating bacteria is fabricated, and this multi-responsive deep-UV emitter offers new insights into developing UV light sources for sterilization applications. Heterovalent substituting in trap-mediated host lattice also provides a methodological basis for the construction of multi-mode luminescent materials.

Neuropeptides and neurohormones in immune, inflammatory and cellular responses to ultraviolet radiation

Humans are exposed to varying amounts of ultraviolet radiation (UVR) through sunlight. UVR penetrates into human skin leading to release of neuropeptides, neurotransmitters and neuroendocrine hormones. These messengers released from local sensory nerves, keratinocytes, Langerhans cells (LCs), mast cells, melanocytes and endothelial cells (ECs) modulate local and systemic immune responses, mediate inflammation and promote differing cell biologic effects. In this review, we will focus on both animal and human studies that elucidate the roles of calcitonin gene-related peptide (CGRP), substance P (SP), nerve growth factor (NGF), nitric oxide and proopiomelanocortin (POMC) derivatives in mediating immune and inflammatory effects of exposure to UVR as well as other cell biologic effects of UVR exposure.

Exploring the effect of UV-C radiation on earthworm and understanding its genomic integrity in the context of H2AX expression

Maintaining genomic stability is inevitable for organism survival and it is challenged by mutagenic agents, which include ultraviolet (UV) radiation. Whenever DNA damage occurs, it is sensed by DNA-repairing proteins and thereby performing the DNA-repair mechanism. Specifically, in response to DNA damage, H2AX is a key protein involved in initiating the DNA-repair processes. In this present study, we investigate the effect of UV-C on earthworm, Perionyx excavatus and analyzed the DNA-damage response. Briefly, we expose the worms to different doses of UV-C and find that worms are highly sensitive to UV-C. As a primary response, earthworms produce coelomic fluid followed by autotomy. However, tissue inflammation followed by death is observed when we expose worm to increased doses of UV-C. In particular, UV-C promotes damages in skin layers and on the contrary, it mediates the chloragogen and epithelial outgrowth in intestinal tissues. Furthermore, UV-C promotes DNA damages followed by upregulation of H2AX on dose-dependent manner. Our finding confirms DNA damage caused by UV-C is directly proportional to the expression of H2AX. In short, we conclude that H2AX is present in the invertebrate earthworm, which plays an evolutionarily conserved role in DNA damage event as like that in higher animals.

Both cardiovascular and cerebrovascular events are decreased following long-term narrowband ultraviolet B phototherapy in patients with vitiligo: a propensity score matching analysis

BACKGROUND

Systemic effects of long-term narrowband ultraviolet B (NB-UVB) phototherapy have not been well studied in vitiligo patients. An 11-year nationwide population-based retrospective cohort study was conducted using the Korean National Health Insurance claims database (2007-2017).

OBJECTIVES

To investigate the effects of long-term NB-UVB phototherapy on the risk of cardiovascular and cerebrovascular events in vitiligo patients.

METHODS

This study included vitiligo patients with ≥100 phototherapy sessions (phototherapy group, n = 3229) and <3 phototherapy sessions (no phototherapy group, n = 9687), in which covariables with age, sex, insurance type and comorbidities such as diabetes, hypertension and hyperlipidemia were matched by 1 : 3 propensity score matching. The outcomes of interest were cardiovascular (ischaemic heart disease and myocardial infarction) and cerebrovascular events (cerebrovascular infraction and haemorrhage). Cox proportional hazards models were used to assess the associations between NB-UVB phototherapy and each event.

RESULTS

The risk of cardiovascular or cerebrovascular events was significantly decreased in the phototherapy group compared with the no phototherapy group [hazard ratio (HR) 0.637, 95% confidence interval (CI) 0.523-0.776]. Subgroup analysis revealed that the risk of cardiovascular (HR: 0.682, 95% CI: 0.495-0.940) and cerebrovascular events (HR: 0.601, 95% CI: 0.470-0.769) were significantly lower in the phototherapy group than the no phototherapy group, respectively.

CONCLUSIONS

Our findings suggest that long-term NB-UVB phototherapy could decrease the risk of cardiovascular and cerebrovascular events in patients with vitiligo.

Immunobiology of Atherosclerosis: A Complex Net of Interactions

Cardiovascular disease is the leading cause of mortality worldwide, and atherosclerosis the principal factor underlying cardiovascular events. Atherosclerosis is a chronic inflammatory disease characterized by endothelial dysfunction, intimal lipid deposition, smooth muscle cell proliferation, cell apoptosis and necrosis, and local and systemic inflammation, involving key contributions to from innate and adaptive immunity. The balance between proatherogenic inflammatory and atheroprotective anti-inflammatory responses is modulated by a complex network of interactions among vascular components and immune cells, including monocytes, macrophages, dendritic cells, and T, B, and foam cells; these interactions modulate the further progression and stability of the atherosclerotic lesion. In this review, we take a global perspective on existing knowledge about the pathogenesis of immune responses in the atherosclerotic microenvironment and the interplay between the major innate and adaptive immune factors in atherosclerosis. Studies such as this are the basis for the development of new therapies against atherosclerosis.

Exposure to solar ultraviolet radiation limits diet-induced weight gain, increases liver triglycerides and prevents the early signs of cardiovascular disease in mice

BACKGROUND AND AIMS

Sunlight exposure is associated with a number of health benefits including protecting us from autoimmunity, cardiovascular disease, obesity and diabetes. Animal studies have confirmed that ultraviolet (UV)-B radiation, independently of vitamin D, can limit diet-induced obesity, metabolic syndrome and atherosclerosis. The aim of this study is to investigate whether exposure to the UV radiation contained in sunlight impacts on these disease parameters.

METHODS AND RESULTS

We have trialled an intervention with solar UV in obese and atherosclerosis-prone mice. We have discovered that solar-simulated UV can significantly limit diet-induced obesity and reduce atheroma development in mice fed a diet high in sugar and fat. The optimal regime for this benefit was exposure once a week to solar UV equivalent to approximately 30 min of summer sun. Exposure to this optimal dose of solar UV also led to a significant increase in liver triglycerides which may protect the liver from damage.

CONCLUSION

Our results show that the UV contained in sunlight has the potential to prevent and treat chronic disease at sites distant from irradiated skin. A major health challenge going forward will be to harness the power of the sun safely, without risking an increase in skin cancers.

CTLA-4 Protects against Angiotensin II-Induced Abdominal Aortic Aneurysm Formation in Mice

Vascular inflammation via T-cell-mediated immune responses has been shown to be critically involved in the pathogenesis of abdominal aortic aneurysm (AAA). T-cell coinhibitory molecule cytotoxic T-lymphocyte–associated antigen-4 (CTLA-4) is known to act as a potent negative regulator of immune responses. However, the role of this molecule in the development of AAA remains completely unknown. We determined the effects of CTLA-4 overexpression on experimental AAA. We continuously infused CTLA-4 transgenic (CTLA-4-Tg)/apolipoprotein E–deficient (Apoe^−/−) mice or control Apoe^−/− mice fed a high-cholesterol diet with angiotensin II by implanting osmotic mini-pumps and evaluated the development of AAA. Ninety percent of angiotensin II-infused mice developed AAA, with 50% mortality because of aneurysm rupture. Overexpression of CTLA-4 significantly reduced the incidence (66%), mortality (26%), and diameter of AAA. These protective effects were associated with a decreased number of effector CD4⁺ T cells and the downregulated expression of costimulatory molecules CD80 and CD86, ligands for CTLA-4, on CD11c⁺ dendritic cells in lymphoid tissues. CTLA-4-Tg/Apoe^−/− mice had reduced accumulation of macrophages and CD4⁺ T cells, leading to attenuated aortic inflammation, preserved vessel integrity, and decreased susceptibility to AAA and aortic rupture. Our findings suggest T-cell coinhibitory molecule CTLA-4 as a novel therapeutic target for AAA.

Human health in relation to exposure to solar ultraviolet radiation under changing stratospheric ozone and climate

The Montreal Protocol has limited increases in the UV-B (280-315 nm) radiation reaching the Earth's surface as a result of depletion of stratospheric ozone. Nevertheless, the incidence of skin cancers continues to increase in most light-skinned populations, probably due mainly to risky sun exposure behaviour. In locations with strong sun protection programs of long duration, incidence is now reducing in younger age groups. Changes in the epidemiology of UV-induced eye diseases are less clear, due to a lack of data. Exposure to UV radiation plays a role in the development of cataracts, pterygium and possibly age-related macular degeneration; these are major causes of visual impairment world-wide. Photodermatoses and phototoxic reactions to drugs are not uncommon; management of the latter includes recognition of the risks by the prescribing physician. Exposure to UV radiation has benefits for health through the production of vitamin D in the skin and modulation of immune function. The latter has benefits for skin diseases such as psoriasis and possibly for systemic autoimmune diseases such as multiple sclerosis. The health risks of sun exposure can be mitigated through appropriate sun protection, such as clothing with both good UV-blocking characteristics and adequate skin coverage, sunglasses, shade, and sunscreen. New sunscreen preparations provide protection against a broader spectrum of solar radiation, but it is not clear that this has benefits for health. Gaps in knowledge make it difficult to derive evidence-based sun protection advice that balances the risks and benefits of sun exposure.

Exposure to Ultraviolet Radiation in the Modulation of Human Diseases

This review focuses primarily on the beneficial effects for human health of exposure to ultraviolet radiation (UVR). UVR stimulates anti-inflammatory and immunosuppressive pathways in skin that modulate psoriasis, atopic dermatitis, and vitiligo; suppresses cutaneous lesions of graft-versus-host disease; and regulates some infection and vaccination outcomes. While polymorphic light eruption and the cutaneous photosensitivity of systemic lupus erythematosus are triggered by UVR, polymorphic light eruption also frequently benefits from UVR-induced immunomodulation. For systemic diseases such as multiple sclerosis, type 1 diabetes, asthma, schizophrenia, autism, and cardiovascular disease, any positive consequences of UVR exposure are more speculative, but could occur through the actions of UVR-induced regulatory cells and mediators, including 1,25-dihydroxy vitamin D₃, interleukin-10, and nitric oxide. Reduced UVR exposure is a risk factor for the development of several inflammatory, allergic, and autoimmune conditions, including diseases initiated in early life. This suggests that UVR-induced molecules can regulate cell maturation in developing organs.

Regulatory T cells as a new therapeutic target for atherosclerosis

Atherosclerosis is an autoimmune disease caused by self- and non-self-antigens contributing to excessive activation of T and B cell immune responses. These responses further aggravate vascular infiammation and promote progression of atherosclerosis and vulnerability to plaques via releasing pro-infiammatory cytokines. Regulatory T cells (Tregs) as the major immunoregulatory cells, in particular, induce and maintain immune homeostasis and tolerance by suppressing the immune responses of various cells such as T and B cells, natural killer (NK) cells, monocytes, and dendritic cells (DCs), as well as by secreting inhibitory cytokines interleukin (IL)-10, IL-35 and transcription growth factor β (TGF-β) in both physiological and pathological states. Numerous evidence demonstrates that reduced numbers and dysfunction of Treg may be involveved in atherosclerosis pathogenesis. Increasing or restoring the numbers and improving the immunosuppressive capacity of Tregs may serve as a fundamental immunotherapy to treat atherosclerotic cardiovascular diseases. In this article, we briefiy present current knowledge of Treg subsets, summarize the relationship between Tregs and atherosclerosis development, and discuss the possibilities of regulating Tregs for prevention of atherosclerosis pathogenesis and enhancement of plaque stability. Although the exact molecular mechanisms of Treg-mediated protection against atherosclerosis remain to be elucidated, the strategies for targeting the regulation of Tregs may provide specific and significant approaches for the prevention and treatment of atherosclerotic cardiovascular diseases.

Environmental effects of ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2017

The Environmental Effects Assessment Panel (EEAP) is one of three Panels of experts that inform the Parties to the Montreal Protocol. The EEAP focuses on the effects of UV radiation on human health, terrestrial and aquatic ecosystems, air quality, and materials, as well as on the interactive effects of UV radiation and global climate change. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than previously held. Because of the Montreal Protocol, there are now indications of the beginnings of a recovery of stratospheric ozone, although the time required to reach levels like those before the 1960s is still uncertain, particularly as the effects of stratospheric ozone on climate change and vice versa, are not yet fully understood. Some regions will likely receive enhanced levels of UV radiation, while other areas will likely experience a reduction in UV radiation as ozone- and climate-driven changes affect the amounts of UV radiation reaching the Earth's surface. Like the other Panels, the EEAP produces detailed Quadrennial Reports every four years; the most recent was published as a series of seven papers in 2015 (Photochem. Photobiol. Sci., 2015, 14, 1-184). In the years in between, the EEAP produces less detailed and shorter Update Reports of recent and relevant scientific findings. The most recent of these was for 2016 (Photochem. Photobiol. Sci., 2017, 16, 107-145). The present 2017 Update Report assesses some of the highlights and new insights about the interactive nature of the direct and indirect effects of UV radiation, atmospheric processes, and climate change. A full 2018 Quadrennial Assessment, will be made available in 2018/2019.

Anti-Inflammatory Role of Langerhans Cells and Apoptotic Keratinocytes in Ultraviolet-B-Induced Cutaneous Inflammation

UV radiation, particularly UVB, is the major risk factor for the induction of skin cancer, and it induces skin inflammation and immunosuppression. Although reports documented that Langerhans cells (LCs) play various roles in photobiology, little is known about whether they contribute to UVB-induced cutaneous inflammation. Recently, the anti-inflammatory effect of apoptotic cells was noted. This study focuses on the roles of LCs and apoptotic cells in UVB-induced cutaneous inflammation. We show that LCs are essential for resolution of UVB-induced cutaneous inflammation. Administration of quinolyl-valyl-O-methylaspartyl-[2,6-difluophenoxy]-methyl ketone, a broad-spectrum caspase inhibitor with potent antiapoptotic properties, inhibited the formation of UVB-induced apoptotic cells and aggravated UVB-induced cutaneous inflammation in wild-type mice. In contrast, exacerbation of UVB-induced cutaneous inflammation following quinolyl-valyl-O-methylaspartyl-[2,6-difluophenoxy]-methyl ketone administration was not observed in LC-depleted mice. These results suggest that the interaction between LCs and apoptotic cells is critical for resolution of UVB-induced cutaneous inflammation. Interestingly, UVB-induced apoptotic keratinocytes were increased in LC-depleted mice. In addition, we revealed that UVB-induced apoptotic keratinocytes were phagocytosed by LCs ex vivo and that prolongation of UVB-induced cutaneous inflammation following treatment with Cytochalasin D, an inhibitor of phagocytosis, was partially attenuated in LC-depleted mice. Collectively, our findings demonstrate that the interaction between LCs and apoptotic cells, possibly via LC-mediated phagocytosis of apoptotic keratinocytes, has an essential anti-inflammatory role in the resolution of UVB-induced cutaneous inflammation.

Ultraviolet B Exposure Inhibits Angiotensin II-Induced Abdominal Aortic Aneurysm Formation in Mice by Expanding CD4+Foxp3+ Regulatory T Cells

Background

Pathogenic immune responses are known to play an important role in abdominal aortic aneurysm (AAA) development. Ultraviolet B (UVB) irradiation has been demonstrated to have therapeutic potential not only for cutaneous diseases but also for systemic inflammatory diseases in mice by suppressing immunoinflammatory responses. We investigated the effect of UVB irradiation on experimental AAA.

Methods and Results

We used an angiotensin II–induced AAA model in apolipoprotein E–deficient mice fed a high‐cholesterol diet. Mice aged 10 weeks were irradiated with 5 kJ/m²UVB once weekly for 6 weeks (UVB‐irradiated, n=38; nonirradiated, n=42) and were euthanized for evaluation of AAA formation at 16 weeks. Overall, 93% of angiotensin II–infused mice developed AAA, with 60% mortality possibly because of aneurysm rupture. UVB irradiation significantly decreased the incidence (66%) and mortality (29%) of AAA (P=0.004 and P=0.006, respectively). UVB‐irradiated mice had significantly smaller diameter AAA (P=0.008) and fewer inflammatory cells in the aortic aneurysm tissue than nonirradiated mice, along with systemic expansion of CD4⁺Foxp3⁺ regulatory T cells and decreased effector CD4⁺CD44^highCD62L^low T cells in para‐aortic lymph nodes. Genetic depletion of regulatory T cells abrogated these beneficial effects of UVB treatment, demonstrating a critical role of regulatory T cells.

Conclusions

Our data suggest that UVB‐dependent expansion of regulatory T cells has beneficial effects on experimental AAA and may provide a novel strategy for the treatment of AAA.