Bcl-3 acts as an innate immune modulator by controlling antimicrobial responses in keratinocytes

Innate Antiviral Immunity in the Skin

Barrier sites such as the skin play a critical role in immune defense. They must maintain homeostasis with commensals and rapidly detect and limit pathogen invasion. This is accomplished in part through the production of endogenous antimicrobial peptides and proteins, which can be either constitutive or inducible. Here, we focus particularly on the control of innate antiviral proteins and present the basic aspects of their regulation in the skin by interferons (IFNs), IFN-independent immunity, and environmental factors. We also discuss the activity and (dys-)function of antiviral proteins in the context of skin-tropic viruses and highlight the relevance of the innate antiviral pathway as a potential therapeutic avenue for vulnerable patient populations and skin diseases with high risk for virus infections.

Vitamin D shows in vivo efficacy in a placebo-controlled, double-blinded, randomised clinical trial on canine atopic dermatitis

Atopic dermatitis (AD) in dogs is among the most common skin diseases in small animal practice. It is an inflammatory disease based on a genetic predisposition to develop hypersensitivity against environmental and food allergens and typical clinical signs up exposure. Treatment sometimes can be difficult and associated with adverse effects. Previous studies evaluating cholecalciferol as treatment for human AD have shown promising results. With canine AD being a good animal model for its human counterpart, it was hypothesised that cholecalciferol might have beneficial clinical effects in dogs, too. In this randomised, placebo-controlled, double-blinded eight-week cross-over study, 23 client-owned dogs received either systemic cholecalciferol (n=16), a vitamin D receptor analogue (n=8) or placebo (n=13). Blood samples for ionised calcium were obtained regularly during the study, and Canine Atopic Dermatitis Extent and Severity Index and pruritus scores, blood levels of vitamin D metabolites, measurements of skin pH and transepidermal water loss were determined before and after. Pruritus and lesion scores decreased significantly in the cholecalciferol group versus placebo. No differences in water loss or skin pH were observed. An increase in serum 25-hydroxycholecalciferol strongly correlated with a reduction in pruritus. Systemic cholecalciferol may be a viable treatment option for canine AD.

Improved clinical outcome and biomarkers in adults with papulopustular rosacea treated with doxycycline modified-release capsules in a randomized trial

BACKGROUND

Patients with rosacea have increased amounts of cathelicidin and protease activity but their usefulness as disease biomarkers is unclear.

OBJECTIVE

We sought to evaluate the effect of doxycycline treatment on cathelicidin expression, protease activity, and clinical response in rosacea.

METHODS

In all, 170 adults with papulopustular rosacea were treated for 12 weeks with doxycycline 40-mg modified-release capsules or placebo in a multicenter, randomized, double-blind, placebo-controlled study. Clinical response was compared with cathelicidin and protease activity in stratum corneum samples obtained by tape strip and in skin biopsy specimens obtained from a random subset of patients.

RESULTS

Treatment with doxycycline significantly reduced inflammatory lesions and improved investigator global assessment scores compared with placebo. Cathelicidin expression and protein levels decreased over the course of 12 weeks in patients treated with doxycycline. Low levels of protease activity and cathelicidin expression at 12 weeks correlated with treatment success. Low protease activity at baseline was a predictor of clinical response in the doxycycline treatment group.

LIMITATIONS

Healthy control subjects were not studied.

CONCLUSIONS

Improved clinical outcome correlated with reduced cathelicidin and protease activity, supporting both the mechanism of doxycycline and the potential of these molecules as biomarkers for rosacea.

Shh and p50/Bcl3 signaling crosstalk drives pathogenesis of BCCs in Gorlin syndrome

Nevoid basal cell carcinoma syndrome (NBCCS) is a rare autosomal dominant disorder that is due, in large measure, to aberrant Shh signaling driven by mutations in the tumor suppressor gene Ptch1. Here, we describe the development of Ptch1+/-/ SKH-1 mice as a novel model of this disease. These animals manifest many features of NBCCS, including developmental anomalies and are remarkably sensitive to both ultraviolet (UVB) and ionizing radiation that drive the development of multiple BCCs. Just as in patients with NBCCS, Ptch1+/-/SKH-1 also spontaneously develops BCCs and other neoplasms such as rhabdomyomas/rhabdomyosarcomas. Administration of smoothened inhibitors (vismodegib/itraconazole/cyclopamine) or non-steroidal anti-inflammatory drug (sulindac/sulfasalazine) each result in partial resolution of BCCs in these animals. However, combined administration of these agents inhibits the growth of UVB-induced BCCs by >90%. Employing small molecule- and decoy-peptide-based approaches we further affirm that complete remission of BCCs could only be achieved by combined inhibition of p50-NFκB/Bcl3 and Shh signaling. We posit that Ptch1+/-/SKH-1 mice are a novel and relevant animal model for NBCCS. Understanding mechanisms that govern genetic predisposition to BCCs should facilitate our ability to identify and treat NBCCS gene carriers, including those at risk for sporadic BCCs while accelerating development of novel therapeutic modalities for these patients.

Bcl-3 puts the brakes on contact hypersensitivity

B-cell lymphoma (Bcl)-3 is a nonclassical member of the IκB protein family known to interact with transcriptionally inactive NF-κB1 and NF-κB2 homodimers to modulate gene expression. Besides its action as an oncoprotein, Bcl-3 has been shown to have both proinflammatory and anti-inflammatory functions depending on the cell-type affected. In this issue of the European Journal of Immunology, Tassi et al. [Eur. J. Immunol. 2015. 45: 1059-1068] report that Bcl-3 inhibits the production of the proinflammatory chemokines CXCL9 and CXCL10 in keratinocytes, thereby restricting the influx of CD8(+) effector T cells in a mouse model of allergic contact dermatitis. In addition, mice with a global deficiency of Bcl-3 show enhanced ear swelling responses in the late phase of contact hypersensitivity responses. Besides keratinocytes, other radioresistant cell types appear to also utilize Bcl-3 to dampen the inflammatory response. This Commentary will discuss the evidence supporting Bcl-3 as a critical player in limiting inflammation during the later stages of contact hypersensitivity.

The NF-κB regulator Bcl-3 modulates inflammation during contact hypersensitivity reactions in radioresistant cells

Bcl-3 is an atypical member of the IκB family. Bcl-3 functions as a cofactor of p50/NF-κB1 or p52/NF-κB2 homodimers in nuclei, where it modulates NF-κB-regulated transcription in a context-dependent way. Bcl-3 has tumorigenic potential, is critical in host defense of pathogens, and has been reported to ameliorate or exacerbate inflammation, depending on disease model. However, cell-specific functions of Bcl-3 remain largely unknown. Here, we explored the role of Bcl-3 in a contact hypersensitivity (CHS) mouse model, which depends on the interplay between keratinocytes and immune cells. Bcl-3-deficient mice exhibited an exacerbated and prolonged CHS response to oxazolone. Increased inflammation correlated with higher production of chemokines CXCL2, CXCL9, and CXCL10, and consequently increased recruitment of neutrophils and CD8(+) T cells. BM chimera experiments indicated that the ability of Bcl-3 to reduce the CHS response depended on Bcl-3 activity in radioresistant cells. Specific ablation of Bcl-3 in keratinocytes resulted in increased production of CXCL9 and CXCL10 and sustained recruitment of specifically CD8(+) T cells. These findings identify Bcl-3 as a critical player during the later stage of the CHS reaction to limit inflammation via actions in radioresistant cells, including keratinocytes.

Atopic dermatitis and vitamin D: facts and controversies

Patients with atopic dermatitis have genetically determined risk factors that affect the barrier function of the skin and immune responses that interact with environmental factors. Clinically, this results in an intensely pruriginous and inflamed skin that allows the penetration of irritants and allergens and predisposes patients to colonization and infection by microorganisms. Among the various etiological factors responsible for the increased prevalence of atopic diseases over the past few decades, the role of vitamin D has been emphasized. As the pathogenesis of AD involves a complex interplay of epidermal barrier dysfunction and dysregulated immune response, and vitamin D is involved in both processes, it is reasonable to expect that vitamin D's status could be associated with atopic dermatitis' risk or severity. Such association is suggested by epidemiological and experimental data. In this review, we will discuss the evidence for and against this controversial relationship, emphasizing the possible etiopathogenic mechanisms involved.

Potential role of microorganisms in the pathogenesis of rosacea

Rosacea is a skin condition of abnormal inflammation and vascular dysfunction. The active contribution of a microbial agent in the development or progression of rosacea continues to be debated. Research supports the presence of commensal Demodex folliculorum mites at increased density in the skin and associates Helicobacter pylori infection of the gut with rosacea. Fewer studies implicate Staphylococcus epidermidis, Chlamydophila pneumoniae, and the Demodex-associated bacteria Bacillus oleronius. No research, however, provides a mechanism by which colonization by a microorganism translates to manifestation of the condition. Prevailing and emerging principles in the biology of the microbiome and the pathophysiology of rosacea may help to reconcile these lingering questions. Here the microorganisms implicated in rosacea are reviewed and the reaction of the microbiome to inflammation and to changes in microenvironments and macroenvironments are discussed to explain potential roles for microorganisms in rosacea pathophysiology.

Update on the role of systemic vitamin D in atopic dermatitis

Atopic dermatitis (AD) is a common chronic inflammatory type of eczema. The underlying cause of AD has not been established. Several studies have shown initial epidermal barrier dysfunction with subsequent immune activation as the underlying mechanism. Recently, in addition to its classical role in calcium homeostasis, vitamin D has been recognized for its effect on immunomodulation. Animal studies, case reports, and randomized clinical trials have suggested that vitamin D, through various mechanisms, may alleviate the symptoms of AD. The majority of these studies indicate an inverse relationship between the severity of atopic dermatitis and vitamin D levels. Furthermore, studies have shown that, in individuals with AD who are deficient in vitamin D, repletion of vitamin D results in decreased severity of disease. We present a review of the present literature that suggests a potentially significant role for vitamin D in the treatment of AD.

Epidermal inactivation of the glucocorticoid receptor triggers skin barrier defects and cutaneous inflammation

The glucocorticoid (GC) receptor (GR) mediates the effects of physiological and pharmacological GC ligands and has a major role in cutaneous pathophysiology. To dissect the epithelial versus mesenchymal contribution of GR in developing and adult skin, we generated mice with keratinocyte-restricted GR inactivation (GR epidermal knockout or GR(EKO) mice). Developing and early postnatal GR(EKO) mice exhibited impaired epidermal barrier formation, abnormal keratinocyte differentiation, hyperproliferation, and stratum corneum (SC) fragility. At birth, GR(EKO) epidermis showed altered levels of epidermal differentiation complex genes, proteases and protease inhibitors which participate in SC maintenance, and innate immunity genes. Many upregulated genes, including S100a8/a9 and Tslp, also have increased expression in inflammatory skin diseases. Infiltration of macrophages and degranulating mast cells were observed in newborn GR(EKO) skin, hallmarks of atopic dermatitis. In addition to increased extracellular signal-regulated kinase activation, GR(EKO) newborn and adult epidermis had increased levels of phosphorylated signal transducer and activator of transcription 3, a feature of psoriasis. Although adult GR(EKO) epidermis had a mild phenotype of increased proliferation, perturbation of skin homeostasis with detergent or phorbol ester triggered an exaggerated proliferative and hyperkeratotic response relative to wild type. Together, our results show that epidermal loss of GR provokes skin barrier defects and cutaneous inflammation.

Cathelicidin antimicrobial peptide LL-37 in psoriasis enables keratinocyte reactivity against TLR9 ligands

Here we show that keratinocytes in psoriatic lesional skin express increased Toll-like receptor (TLR) 9 that similarly localizes with elevated expression of the cathelicidin antimicrobial peptide LL-37. In culture, normal human keratinocytes exposed to LL-37 increased TLR9 expression. Furthermore, when keratinocytes were exposed to LL-37 and subsequently treated with TLR9 ligands such as CpG or genomic DNA, keratinocytes greatly increased production of type I interferons. This response mimicked observations in the epidermis of psoriatic lesional skin as keratinocytes in psoriatic lesions produce greater amounts of interferon-β than normal skin lacking LL-37. The mechanism for induction of type I interferons in keratinocytes was dependent on TLR9 expression but not on a DNA-LL-37 complex. These findings suggest that keratinocytes recognize and respond to DNA and can actively participate in contributing to the immunological environment that characterizes psoriasis.

Regulation of cathelicidin antimicrobial peptide expression by an endoplasmic reticulum (ER) stress signaling, vitamin D receptor-independent pathway

Vitamin D receptor (VDR)-dependent mechanisms regulate human cathelicidin antimicrobial peptide (CAMP)/LL-37 in various cell types, but CAMP expression also increases after external perturbations (such as infection, injuries, UV irradiation, and permeability barrier disruption) in parallel with induction of endoplasmic reticulum (ER) stress. We demonstrate that CAMP mRNA and protein expression increase in epithelial cells (human primary keratinocytes, HaCaT keratinocytes, and HeLa cells), but not in myeloid (U937 and HL-60) cells, following ER stress generated by two mechanistically different, pharmacological stressors, thapsigargin or tunicamycin. The mechanism for increased CAMP following exposure to ER stress involves NF-κB activation leading to CCAAT/enhancer-binding protein α (C/EBPα) activation via MAP kinase-mediated phosphorylation. Furthermore, both increased CAMP secretion and its proteolytic processing to LL-37 are required for antimicrobial activities occur following ER stress. In addition, topical thapsigargin also increases production of the murine homologue of CAMP in mouse epidermis. Finally and paradoxically, ER stress instead suppresses the 1,25(OH)(2) vitamin D(3)-induced activation of VDR, but blockade of VDR activity does not alter ER stress-induced CAMP up-regulation. Hence, ER stress increases CAMP expression via NF-κB-C/EBPα activation, independent of VDR, illuminating a novel VDR-independent role for ER stress in stimulating innate immunity.

Atopic dermatitis - from new pathophysiologic insights to individualized therapy

Recently, important novel insights into the complex pathophysiology of atopic dermatitis (AD) have been gained. However, in most cases the therapy of AD is limited to base line therapy with emollients combined with symptomatic, rather general immunosuppressive treatment approaches of the flare-ups. Latest research findings together with experiences from daily clinical practice, which support the concept that a combination of general disease features together with specific trigger factors in the individual patients drive the disease, might be helpful for a subclassification of patients with AD based on the most relevant pathophysiologic modifications. Subclassification of patients with AD seems indispensable to introduce rationale-based, individualized treatment approaches of AD, which target specific modified pathways. In this review, we provide an overview about a selection of pathophysiologic pathways, which hold promise to represent targets of such therapeutic approaches in the near future.

Modifications of the innate immune system in atopic dermatitis

Atopic dermatitis (AD) is a frequent chronic inflammatory skin disease which is often complicated by recurrent microbial superinfections. Genetically based modifications which might have an impact on the innate immune system, such as impairment of the skin barrier, modifications of pattern recognition receptors, deficiency of antimicrobial peptides, antiviral natural killer cells and plasmacytoid dendritic cells, facilitate the entry of allergens and infectious microbes into the skin, where they encounter immunocompetent cells. The micromilieu in the skin of AD patients further potentiates dysfunctions of the innate immune system, leading to a vicious circle promoting the disease. This article provides an overview of modifications of the innate immune system in AD.

The IκB family member Bcl-3 coordinates the pulmonary defense against Klebsiella pneumoniae infection

Bcl-3 is an atypical member of the IκB family that has the potential to positively or negatively modulate nuclear NF-κB activity in a context-dependent manner. Bcl-3's biologic impact is complex and includes roles in tumorigenesis and diverse immune responses, including innate immunity. Bcl-3 may mediate LPS tolerance, suppressing cytokine production, but it also seems to contribute to defense against select systemic bacterial challenges. However, the potential role of Bcl-3 in organ-specific host defense against bacteria has not been addressed. In this study, we investigated the relevance of Bcl-3 in a lung challenge with the Gram-negative pathogen Klebsiella pneumoniae. In contrast to wild-type mice, Bcl-3-deficient mice exhibited significantly increased susceptibility toward K. pneumoniae pneumonia. The mutant mice showed increased lung damage marked by neutrophilic alveolar consolidation, and they failed to clear bacteria in lungs, which correlated with increased bacteremic dissemination. Loss of Bcl-3 incurred a dramatic cytokine imbalance in the lungs, which was characterized by higher levels of IL-10 and a near total absence of IFN-γ. Moreover, Bcl-3-deficient mice displayed increased lung production of the neutrophil-attracting chemokines CXCL-1 and CXCL-2. Alveolar macrophages and neutrophils are important to antibacterial lung defense. In vitro stimulation of Bcl-3-deficient alveolar macrophages with LPS or heat-killed K. pneumoniae recapitulated the increase in IL-10 production, and Bcl-3-deficient neutrophils were impaired in intracellular bacterial killing. These findings suggest that Bcl-3 is critically involved in lung defense against Gram-negative bacteria, modulating functions of several cells to facilitate efficient clearance of bacteria.

[What's new in dermatological research?]

Fundamental research in Dermatology has been once more very active during the past year and more specifically focused on immunological grounds of inflammatory diseases, the identification of risk loci associated with psoriasis and tumors, cutaneous lymphomas and on the genodermatosis where large international collaborative studies provided with a molecular understanding of an increasing amount of conditions especially affecting pigmentation and differentiation. In silico investigations become increasingly prominent especially with the rising power of new actor, China, the demographical and resulting epidemiological weight of which can hardly be challenged. Some of these fundamental breakthroughs might result in practical interventions although in an undefined future.

The vitamin D-antimicrobial peptide pathway and its role in protection against infection

Vitamin D deficiency has been correlated with increased rates of infection. Since the early 19th century, both environmental (i.e., sunlight) and dietary sources (cod liver) of vitamin D have been identified as treatments for TB. The recent discovery that vitamin D induces antimicrobial peptide gene expression explains, in part, the 'antibiotic' effect of vitamin D and has greatly renewed interest in the ability of vitamin D to improve immune function. Subsequent work indicates that this regulation is biologically important for the response of the innate immune system to wounds and infection and that deficiency may lead to suboptimal responses toward bacterial and viral infections. The regulation of the cathelicidin antimicrobial peptide gene is a human/primate-specific adaptation and is not conserved in other mammals. The capacity of the vitamin D receptor to act as a high-affinity receptor for vitamin D and a low-affinity receptor for secondary bile acids and potentially other novel nutritional compounds suggests that the evolutionary selection to place the cathelicidin gene under control of the vitamin D receptor allows for its regulation under both endocrine and xenobiotic response systems. Future studies in both humans and humanized mouse models will elucidate the importance of this regulation and lead to the development of potential therapeutic applications.

The central role of Bcl-3 in atopic dermatitis

Cytokines and hormones are essential mediators in the regulation of antimicrobial peptide and protein (AMP) levels during host defense responses. In this issue, Büchau et al. identify and characterize B-cell leukemia-3 as an important modulator of AMP expression during the innate immune response in keratinocytes as well as in the chronic inflammatory skin disorder atopic dermatitis.

Multifunctional host defense peptides: antimicrobial peptides, the small yet big players in innate and adaptive immunity

The term 'antimicrobial peptides' refers to a large number of peptides first characterized on the basis of their antibiotic and antifungal activities. In addition to their role as endogenous antibiotics, antimicrobial peptides, also called host defense peptides, participate in multiple aspects of immunity (inflammation, wound repair, and regulation of the adaptive immune system) as well as in maintaining homeostasis. The possibility of utilizing these multifunctional molecules to effectively combat the ever-growing group of antibiotic-resistant pathogens has intensified research aimed at improving their antibiotic activity and therapeutic potential, without the burden of an exacerbated inflammatory response, but conserving their immunomodulatory potential. In this minireview, we focus on the contribution of small cationic antimicrobial peptides - particularly human cathelicidins and defensins - to the immune response and disease, highlighting recent advances in our understanding of the roles of these multifunctional molecules.