Photosensitivity and type I IFN responses in cutaneous lupus are driven by epidermal-derived interferon kappa

Rethinking the Pathogenesis of Cutaneous Lupus

Knowledge of the etiology of cutaneous lupus is rapidly evolving. Dissection of the pathologic events in lesional skin has led to knowledge of important cell populations and transcriptional changes contributing to disease. Recently, the study of nonlesional skin in patients with systemic lupus has also identified key abnormalities that likely contribute to a propensity for inflammation. These include an elevated type I IFN signature, overproduction of IFNs, and an absence of Langerhans cells. These changes promote aberrant inflammation in response to known triggers of disease, such as UV light. Further research will undoubtedly accelerate our understanding of this disfiguring disease.

Role of type I interferons and innate immunity in systemic sclerosis: unbalanced activities on distinct cell types?

PURPOSE OF REVIEW

The role of type I IFNs (IFN-I) in the promotion of autoimmunity has been well established. However, its role in the skin fibrosis of systemic sclerosis (SSc) is less clear. IFN-I can participate to tissue repair, and, here, we will consider the extent to which IFN-I's role in SSc skin fibrosis may reflect in part IFN-I functions during wound healing.

RECENT FINDINGS

Studies are beginning to delineate whether IFN-I has a protective or pathogenic role and how IFN-I affects tissue biology. Recent support for a pathogenic role came from a study depleting plasmacytoid dendritic cells during bleomycin-induced skin fibrosis. The depletion reduced the bleomycin-induced IFN-I-stimulated transcripts and both prevented and reversed fibrosis. Additionally, two recent articles, one identifying SSc endothelial cell injury markers and one showing repressed IFN signaling in SSc keratinocytes, suggest the possibility of unbalanced IFN-I activities on distinct cells types.

SUMMARY

Recent results support a pathogenic role for IFN-I in skin fibrosis, and recent studies along with others suggest a scenario whereby SSc skin damage results from too much IFN-I-activity driving vasculopathy in combination with too little IFN-I-mediated epidermal integrity and antifibrotic fibroblast phenotype.

The early local and systemic Type I interferon responses to ultraviolet B light exposure are cGAS dependent

Most systemic lupus erythematosus (SLE) patients are photosensitive and ultraviolet B light (UVB) exposure worsens cutaneous disease and precipitates systemic flares of disease. The pathogenic link between skin disease and systemic exacerbations in SLE remains elusive. In an acute model of UVB-triggered inflammation, we observed that a single UV exposure triggered a striking IFN-I signature not only in the skin, but also in the blood and kidneys. The early IFN-I signature was significantly higher in female compared to male mice. The early IFN-I response in the skin was almost entirely, and in the blood partly, dependent on the presence of cGAS, as was skin inflammatory cell infiltration. Inhibition of cGAMP hydrolysis augmented the UVB-triggered IFN-I response. UVB skin exposure leads to cGAS-activation and both local and systemic IFN-I signature and could contribute to acute flares of disease in susceptible subjects such as patients with SLE.

Treatment of cutaneous lupus erythematosus: current approaches and future strategies

PURPOSE OF REVIEW

Cutaneous lupus erythematosus (CLE) is a highly heterogeneous autoimmune disease. No specific Federal Drug Administration-approved therapies for CLE-alone are available, and resistance to conventional treatments is common. This review will summarize current treatment approaches and pending treatment strategies.

RECENT FINDINGS

Research into the pathogenesis of CLE is accelerating. A skewed type I interferon production and response contribute to CLE lesions. The pathophysiology of lesions may be similar among the lesional subtypes, and patients with a more TLR9-driven disease mechanism may have more benefit from hydroxychloroquine. Case reports continue to support the use of dapsone for CLE, especially bullous lupus erythematosus. Rituximab and Belimumab have efficacy in patients with systemic lupus erythematosus and severe active CLE. The significant role for type I interferons in CLE and encouraging clinical data suggest anifrolumab as a very promising agent for CLE. Dapirolizumab, BIIB059, Ustekinumab and Janus kinase inhibitors also have supportive early data as promising new strategies for CLE treatment.

SUMMARY

Continued research to understand the mechanisms driving CLE will facilitate the development and approval of new targets. The pipeline for new treatments is rich.

A Spectrum of Skin Disease: How Staphylococcus aureus Colonization, Barrier Dysfunction, and Cytokines Shape the Skin

Cytokines are key mediators of skin homeostasis and disease through their effects on keratinocytes, skin barrier integrity, immune activation, and microbial ecology. Sirobhushanam et al. (2020) suggest that the IFN signature in lupus erythematosus (LE) alters expression of epithelial barrier and adhesin genes, which, in turn, promotes Staphylococcus aureus colonization. This work highlights the need to better understand both barrier function and S. aureus colonization in LE, two new potential therapeutic targets for the treatment of LE.

Selective Janus Kinase 1 Inhibition Is a Promising Therapeutic Approach for Lupus Erythematosus Skin Lesions

Background

Cutaneous lupus erythematosus (CLE) is an interferon (IFN) -driven autoimmune skin disease characterized by an extensive cytotoxic lesional inflammation with activation of different innate immune pathways. Aim of our study was to investigate the specific role of Janus kinase 1 (JAK1) activation in this disease and the potential benefit of selective JAK1 inhibitors as targeted therapy in a preclinical CLE model.

Methods

Lesional skin of patients with different CLE subtypes and healthy controls (N = 31) were investigated on JAK1 activation and expression of IFN-associated mediators via immunohistochemistry and gene expression analyses. The functional role of JAK1 and efficacy of inhibition was evaluated in vitro using cultured keratinocytes stimulated with endogenous nucleic acids. Results were confirmed in vivo using an established lupus-prone mouse model.

Results

Proinflammatory immune pathways, including JAK/STAT signaling, are significantly upregulated within inflamed CLE skin. Here, lesional keratinocytes and dermal immune cells strongly express activated phospho-JAK1. Selective pharmacological JAK1 inhibition significantly reduces the expression of typical proinflammatory mediators such as CXCL chemokines, BLyS, TRAIL, and AIM2 in CLE in vitro models and also improves skin lesions in lupus-prone TREX1^–/– -mice markedly.

Conclusion

IFN-associated JAK/STAT activation plays a crucial role in the pathophysiology of CLE. Selective inhibition of JAK1 leads to a decrease of cytokine expression, reduced immune activation, and decline of keratinocyte cell death. Topical treatment with a JAK1-specific inhibitor significantly improves CLE-like skin lesions in a lupus-prone TREX1^–/– -mouse model and appears to be a promising therapeutic approach for CLE patients.

Cutaneous Lupus Erythematosus: Current and Future Pathogenesis-Directed Therapies

Cutaneous lupus erythematosus (CLE) is an autoimmune disease of the skin with significant morbidity. Current treatments are often inadequate to control disease and there are no Food and Drug Administration (FDA)-approved therapies for this potentially debilitating disease, underscoring an unmet medical need. Recent insights into disease pathogenesis have implicated innate and adaptive immune components, including type I and type III interferons in the development of CLE. Promising clinical trials based on these insights are now underway. However, the full spectrum of immune cells, cytokines, and environmental triggers contributing to disease remain to be elucidated. In this review, we will highlight the current understanding of CLE immunopathogenesis, the ongoing clinical trial landscape, and provide a framework for designing future therapeutic strategies for CLE based on new insights into disease pathogenesis.

Staphylococcus aureus Colonization Is Increased on Lupus Skin Lesions and Is Promoted by IFN-Mediated Barrier Disruption

Cutaneous inflammation is recurrent in systemic lupus erythematosus (SLE), yet mechanisms that drive cutaneous inflammation in SLE are not well defined. Type I IFNs are elevated in nonlesional SLE skin and promote inflammatory responses. Staphylococcus aureus, known to induce IFN production, could play a role in cutaneous inflammation in SLE. We show here that active cutaneous lupus erythematosus lesions are highly colonized (∼50%) by S. aureus. To define the impact of IFNs on S. aureus colonization, we examined the effects of type I and type II IFNs on S. aureus adherence and invasion. An increase in adherent S. aureus was observed after exposure to both IFN-α and -γ, whereas IFN-γ appeared to inhibit invasion of S. aureus. Cutaneous lupus erythematosus lesional skin microarray data and RNA sequencing data from SLE keratinocytes identified repression of barrier gene expression, such as filaggrin and loricrin, and SLE keratinocytes exhibited increased S. aureus-binding integrins. These SLE-associated changes could be replicated by IFN treatment of keratinocytes. Further, SLE keratinocytes exhibited increased binding to S. aureus. Together, these data suggest that chronic exposure to IFNs induces barrier disruption that allows for higher S. aureus colonization in SLE skin.

The pathogenesis of systemic lupus erythematosus: Harnessing big data to understand the molecular basis of lupus

Systemic lupus erythematosus (SLE) is a chronic, systemic autoimmune disease that causes damage to multiple organ systems. Despite decades of research and available murine models that capture some aspects of the human disease, new treatments for SLE lag behind other autoimmune diseases such as Rheumatoid Arthritis and Crohn's disease. Big data genomic assays have transformed our understanding of SLE by providing important insights into the molecular heterogeneity of this multigenic disease. Gene wide association studies have demonstrated more than 100 risk loci, supporting a model of multiple genetic hits increasing SLE risk in a non-linear fashion, and providing evidence of ancestral diversity in susceptibility loci. Epigenetic studies to determine the role of methylation, acetylation and non-coding RNAs have provided new understanding of the modulation of gene expression in SLE patients and identified new drug targets and biomarkers for SLE. Gene expression profiling has led to a greater understanding of the role of myeloid cells in the pathogenesis of SLE, confirmed roles for T and B cells in SLE, promoted clinical trials based on the prominent interferon signature found in SLE patients, and identified candidate biomarkers and cellular signatures to further drug development and drug repurposing. Gene expression studies are advancing our understanding of the underlying molecular heterogeneity in SLE and providing hope that patient stratification will expedite new therapies based on personal molecular signatures. Although big data analyses present unique interpretation challenges, both computationally and biologically, advances in machine learning applications may facilitate the ability to predict changes in SLE disease activity and optimize therapeutic strategies.

Interferon target-gene expression and epigenomic signatures in health and disease

Multiple type I interferons and interferon-γ (IFN-γ) are expressed under physiological conditions and are increased by stress and infections, and in autoinflammatory and autoimmune diseases. Interferons activate the Jak-STAT signaling pathway and induce overlapping patterns of expression, called 'interferon signatures', of canonical interferon-stimulated genes (ISGs) encoding molecules important for antiviral responses, antigen presentation, autoimmunity and inflammation. It has now become clear that interferons also induce an 'interferon epigenomic signature' by activating latent enhancers and 'bookmarking' chromatin, thus reprogramming cell responses to environmental cues. The interferon epigenomic signature affects ISGs and other gene sets, including canonical targets of the transcription factor NF-κB that encode inflammatory molecules, and is involved in the priming of immune cells, tolerance and the training of innate immune memory. Here we review the mechanisms through which interferon signatures and interferon epigenomic signatures are generated, as well as the expression and functional consequences of these signatures in homeostasis and autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis and systemic sclerosis.

Interferon Kappa Is Up-Regulated in Psoriasis and It Up-Regulates Psoriasis-Associated Cytokines in vivo

Purpose

There is increased type I interferon signature in psoriasis patients. Interferon-kappa (IFN-κ) is a member of type I interferon family that is constitutively expressed by keratinocytes. In this study, we investigate whether IFN-κ is involved in psoriasis etiology.

Patients and methods

Twenty healthy individuals, 20 psoriasis vulgaris patients and 10 atopic dermatitis (AD) were included for this study. Immunohistochemistry staining, normal human epidermal keratinocytes (NHEK) culture, Ca₂Cl-induced differentiation, quantitative reverse transcription (qRT-PCR), ELISA and murine experiments were performed.

Results

We found IFN-κ protein expression was extremely low in the epidermis of normal skin, but it was significantly increased in the suprabasal layers of epidermal keratinocytes in psoriatic skin lesions. However, its expression in the skin lesions of AD was similar to normal skin. Additionally, IFN-κ protein was detected in sera from psoriasis patients, but not in sera from normal subjects and AD. We further investigated the regulation of IFNk gene expression in NHEK. We found that IFNk was significantly induced by types of nucleic acid pathogen recognition receptor (PRR) agonists in NHEK. While its expression was significantly induced by itself and IFN-γ, it was inhibited by type 2 immunity cytokines IL4 and IL13; other inflammatory cytokines including IL1 super-family members and IL17A did not alter its expression. Addition of recombinant IFN-κ did not affect keratinocytes differentiation. Using the murine experimental model, we demonstrated that subcutaneous administration of recombinant IFN-κ did not increase skin thickness, but significantly increased the transcription of TNFA and IL17A in mice skin.

Conclusion

Increased IFN-κ in psoriasis may be caused by injured cells-released nucleic acids, increased IFN-γ and self-activation. Its enhancement may contribute to the etiology of the disease by enhancing TNFA and IL17A gene expression.

IL-36 promotes anti-viral immunity by boosting sensitivity to IFN-α/β in IRF1 dependent and independent manners

The functions of the IL-36 cytokines remain poorly understood. We report a previously unrecognized mechanism whereby IL-36 promotes innate antiviral immunity in mouse and human models of herpes simplex virus-1 (HSV-1) infections. HSV-1 actively suppresses production of type I interferon (IFN); our data reveal that IL-36 overcomes this immune evasion strategy by increasing cellular sensitivity to IFN. IL-36β deficient mice display impaired IFN responses and poorly restrict viral replication in skin keratinocytes. In mouse and human keratinocytes IL-36 elicits an antiviral state driven by STAT1 and STAT2 via enhanced expression of IFNAR1 and IFNAR2 subunits of the type I IFN receptor. The degree of IFN regulatory factor 1 (IRF1) involvement is species dependent, with IRF1 playing a more prominent role in human cells. Similar mechanisms are activated by IL-1. Overall, IL-36 acts as an antiviral cytokine by potentiating type I IFN signaling and thereby upholds immune responses to viruses that limit the production of IFNs.

JAK inhibitors for the treatment of autoimmune and inflammatory diseases

Cytokines play a central role in the pathophysiology of autoimmune and inflammatory diseases. Several cytokines signal through the JAK-STAT pathway, which is now recognized as a major target to inhibit the effect of a wide array of cytokines. JAK inhibitors are increasingly used in the setting of inflammatory and autoimmune diseases. While the currently approved drugs are panJAK inhibitors, more selective small molecules are being developed and tested in various rheumatic disorders. In this extensive review, we present evidence- or hypothesis-based perspectives for these drugs in various rheumatologic conditions, such as rheumatoid arthritis, systemic lupus erythematosus, giant cell arteritis, and autoinflammatory diseases.

Molecular Profiling of Cutaneous Lupus Lesions Identifies Subgroups Distinct from Clinical Phenotypes

Cutaneous lupus erythematosus (CLE) is a common manifestation of systemic lupus erythematosus (SLE), and CLE can also develop without systemic involvement. CLE can be difficult to treat and negatively contributes to quality of life. Despite the importance of CLE, our knowledge of what differentiates cutaneous lupus subtypes is limited. Here, we utilized a large cohort of 90 CLE lesional biopsies to compare discoid lupus erythematosus (DLE) and subacute cutaneous lupus (SCLE) in patients with and without associated SLE in order to discern the drivers of disease activity and possibly uncover better treatment targets. Overall, we found that DLE and SCLE share many differentially expressed genes (DEG) reflecting type I interferon (IFN) signaling and repression of EGFR pathways. No differences between CLE only and SLE-associated CLE lesions were found. Of note, DLE uniquely expresses an IFN-γ node. Unbiased cluster analysis of the DEGs identified two groups separated by neutrophilic vs. monocytic signatures that did not sort the patients based on clinical phenotype or disease activity. This suggests that unbiased analysis of the pathobiology of CLE lesions may be important for personalized medicine and targeted therapeutic decision making.

Interferon pathway in SLE: one key to unlocking the mystery of the disease

SLE is characterised by an activation of the interferon (IFN) system, which leads to an increased expression of IFN-regulated genes. The reasons behind the IFN signature in SLE are (1) the existence of endogenous IFN inducers, (2) activation of several IFN-producing cell types, (3) production of many different IFNs, (4) a genetic setup promoting IFN production and (5) deficient negative feedback mechanisms. The consequences for the immune system is a continuous stimulation to an immune response, and for the patient a number of different organ manifestations leading to typical symptoms for SLE. In the current review, we will present the existing knowledge of the IFN system and pathway activation in SLE. We will also discuss how this information can contribute to our understanding of both the aetiopathogenesis and some organ manifestations of the disease. We will put forward some issues that are unresolved and should be clarified in order to make a proper stratification of patients with SLE, which seems important when selecting a therapy aiming to downregulate the IFN system.

Cutaneous lupus erythematosus: new insights into pathogenesis and therapeutic strategies

Cutaneous lupus erythematosus (CLE) is an autoimmune disease that can present as an isolated skin disease or as a manifestation within the spectrum of systemic lupus erythematosus. The clinical spectrum of CLE is broad, ranging from isolated discoid plaques to widespread skin lesions. Histologically, skin lesions present as interface dermatitis (inflammation of the skin mediated by anti-epidermal responses), which is orchestrated by type I and type III interferon-regulated cytokines and chemokines. Both innate and adaptive immune pathways are strongly activated in the formation of skin lesions owing to continuous re-activation of innate pathways via pattern recognition receptors (PRRs). These insights into the molecular pathogenesis of skin lesions in CLE have improved our understanding of the mechanisms underlying established therapies and have triggered the development of targeted treatment strategies that focus on immune cells (for example, B cells, T cells or plasmacytoid dendritic cells), as well as immune response pathways (for example, PRR signalling, Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signalling and nuclear factor-κB signalling) and their cytokines and chemokines (for example, type I interferons, CXC-chemokine ligand 10 (CXCL10), IL-6 and IL-12).

Nucleic Acid Immunity in the Pathogenesis of Cutaneous Lupus Erythematosus

Cutaneous lupus erythematosus can be a devastating painful and mutilating disease that is associated with an inflammatory response in the skin driven by type I interferon activation. Clearance defects in the extra- and intracellular space lead to an enhanced prevalence of nucleic acids that represent danger signals for the innate immune system. Self nucleic acids can stimulate DNA and RNA sensors that have originally evolved to ensure viral defense. Their activation can induce a type I interferon dominated response in resident skin cells, macrophages and dendritic cells that subsequently progresses to adaptive immune stimulation. The genetic exploration of rare monogenic type I interferon driven diseases helped to identify these pathogenic concepts. Based on a genetic susceptibility lupus patients are more vulnerable to environmental trigger factors such as UV-irradiation that can provoke inflammation with local tissue destruction and eventually systemic disease. Understanding of these pathogenic concepts is a prerequisite for development of targeted therapies.

Plucked hair follicles from patients with chronic discoid lupus erythematosus show a disease-specific molecular signature

OBJECTIVE

When faced with clinical symptoms of scarring alopecia-the standard diagnostic pathway involves a scalp biopsy which is an invasive and expensive procedure. This project aimed to assess if plucked hair follicles (HFs) containing living epithelial cells can offer a non-invasive approach to diagnosing inflammatory scalp lesions.

METHODS

Lesional and non-lesional HFs were extracted from the scalp of patients with chronic discoid lupus erythematosus (CDLE), psoriasis and healthy controls. RNA was isolated from plucked anagen HFs and microarray, as well as quantitative real-time PCR was performed.

RESULTS

Here, we report that gene expression analysis of only a small number of HF plucked from lesional areas of the scalp is sufficient to differentiate CDLE from psoriasis lesions or healthy HF. The expression profile from CDLE HFs coincides with published profiles of CDLE from skin biopsy. Genes that were highly expressed in lesional CDLE corresponded to well-known histopathological diagnostic features of CDLE and included those related to apoptotic cell death, the interferon signature, complement components and CD8+ T-cell immune responses.

CONCLUSIONS

We therefore propose that information obtained from this non-invasive approach are sufficient to diagnose scalp lupus erythematosus. Once validated in routine clinical settings and compared with other scarring alopecias, this rapid and non-invasive approach will have great potential for paving the way for future diagnosis of inflammatory scalp lesions.

Ultraviolet light induces increased T cell activation in lupus-prone mice via type I IFN-dependent inhibition of T regulatory cells

Ultraviolet (UV) light is a known trigger of skin and possibly systemic inflammation in systemic lupus erythematosus (SLE) patients. Although type I interferons (IFN) are upregulated in SLE skin after UV exposure, the mechanisms to explain increased UVB-induced inflammation remain unclear. This paper compares the role of type I IFNs in regulating immune cell activation between wild-type and lupus-prone mice following UVB exposure. 10-week old female lupus-prone (NZM2328), wild-type (BALB/c) and iNZM mice (lack a functional type I IFN receptor on NZM2328 background) were treated on their dorsal skin with 100 mJ/cm² of UVB for 5 consecutive days. Following UVB treatment, draining lymph node cell populations were characterized via flow cytometry and suppression assays; treated skin was examined for changes in expression of type I IFN genes. Only NZM2328 mice showed an increase in T cell numbers and activation 2 weeks post UVB exposure. This was preceded by a significant increase in UVB-induced type I IFN expression in NZM2328 mice compared to BALB/c mice. Following UVB exposure, both BALB/c and iNZM mice demonstrated an increase in functional T regulatory (T_Reg) cells; however, this was not seen in NZM2328 mice. These data suggest a skewed UVB-mediated T cell response in lupus-prone mice where activation of T cells is enhanced secondary to a type I IFN-dependent suppression of T_Reg cells. Thus, we propose type I IFNs are important for UVB-induced inflammation in lupus-prone mice and may be an effective target for prevention of UVB-mediated flares.

The female-biased factor VGLL3 drives cutaneous and systemic autoimmunity

Autoimmune disease is 4 times more common in women than men. This bias is largely unexplained. Female skin is "autoimmunity prone," showing upregulation of many proinflammatory genes, even in healthy women. We previously identified VGLL3 as a putative transcription cofactor enriched in female skin. Here, we demonstrate that skin-directed overexpression of murine VGLL3 causes a severe lupus-like rash and systemic autoimmune disease that involves B cell expansion, autoantibody production, immune complex deposition, and end-organ damage. Excess epidermal VGLL3 drives a proinflammatory gene expression program that overlaps with both female skin and cutaneous lupus. This includes increased B cell-activating factor (BAFF), the only current biologic target in systemic lupus erythematosus (SLE); IFN-κ, a key inflammatory mediator in cutaneous lupus; and CXCL13, a biomarker of early-onset SLE and renal involvement. Our results demonstrate that skin-targeted overexpression of the female-biased factor VGLL3 is sufficient to drive cutaneous and systemic autoimmune disease that is strikingly similar to SLE. This work strongly implicates VGLL3 as a pivotal orchestrator of sex-biased autoimmunity.

Advancing understanding, diagnosis, and therapies for cutaneous lupus erythematosus within the broader context of systemic lupus erythematosus

Cutaneous lupus erythematosus (CLE) is an autoimmune disease that can be associated with systemic lupus erythematosus (SLE) symptoms. The pathogenesis of both CLE and SLE is multifactorial, involving genetic susceptibility, environmental factors, and innate and adaptive immune responses. Despite the efficacy of current medications, many patients remain refractory, highlighting the necessity for new treatment options. Unfortunately, owing to challenges related in part to trial design and disease heterogeneity, only one new biologic in the last 50 years has been approved by the US Food and Drug Administration for the treatment of SLE. Thus, although SLE and CLE have a similar pathogenesis, patients with CLE who do not meet criteria for SLE cannot benefit from this advancement. This article discusses the recent trials and emphasizes the need to include patients with single-organ lupus, such as CLE, in SLE trials.

Hypersensitive IFN Responses in Lupus Keratinocytes Reveal Key Mechanistic Determinants in Cutaneous Lupus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease in which 70% of patients experience disfiguring skin inflammation (grouped under the rubric of cutaneous lupus erythematosus [CLE]). There are limited treatment options for SLE and no Food and Drug Administration-approved therapies for CLE. Studies have revealed that IFNs are important mediators for SLE and CLE, but the mechanisms by which IFNs lead to disease are still poorly understood. We aimed to investigate how IFN responses in SLE keratinocytes contribute to development of CLE. A cohort of 72 RNA sequencing samples from 14 individuals (seven SLE and seven healthy controls) were analyzed to study the transcriptomic effects of type I and type II IFNs on SLE versus control keratinocytes. In-depth analysis of the IFN responses was conducted. Bioinformatics and functional assays were conducted to provide implications for the change of IFN response. A significant hypersensitive response to IFNs was identified in lupus keratinocytes, including genes (IFIH1, STAT1, and IRF7) encompassed in SLE susceptibility loci. Binding sites for the transcription factor PITX1 were enriched in genes that exhibit IFN-sensitive responses. PITX1 expression was increased in CLE lesions based on immunohistochemistry, and by using small interfering RNA knockdown, we illustrated that PITX1 was required for upregulation of IFN-regulated genes in vitro. SLE patients exhibit increased IFN signatures in their skin secondary to increased production and a robust, skewed IFN response that is regulated by PITX1. Targeting these exaggerated pathways may prove to be beneficial to prevent and treat hyperinflammatory responses in SLE skin.

Human and Murine Evidence for Mechanisms Driving Autoimmune Photosensitivity

Ultraviolet (UV) light is an important environmental trigger for systemic lupus erythematosus (SLE) patients, yet the mechanisms by which UV light impacts disease are not fully known. This review covers evidence in both human and murine systems for the impacts of UV light on DNA damage, apoptosis, autoantigen exposure, cytokine production, inflammatory cell recruitment, and systemic flare induction. In addition, the role of the circadian clock is discussed. Evidence is compared in healthy individuals and SLE patients as well as in wild-type and lupus-prone mice. Further research is needed into the effects of UV light on cutaneous and systemic immune responses to understand how to prevent UV-light mediated lupus flares.