Mutation analysis of IL36RN gene in Japanese patients with palmoplantar pustulosis

Paediatric pustulotic arthro-osteitis patient with an IL36RN variant, heterozygous c.115+6T>C, who was successfully treated with tonsillectomy: A case report and literature review

Pustulotic arthro-osteitis (PAO) is an infrequent condition, with its manifestation in children being even rare. Some reports propose an association between genetic variants and the onset of PAO. Currently, no definitive treatment protocol exists for paediatric patients with PAO. In this study, we present the paediatric case of PAO with an IL36RN variant who was successfully treated with tonsillectomy.

Genetic underpinnings of the psoriatic spectrum

The psoriatic field includes both rare and common subtypes. Common complex forms include psoriasis vulgaris and psoriatic arthritis. In these subtypes, certain HLA alleles remain the most relevant genetic factors, although genome-wide association studies lead to the detection of more than 80 susceptibility loci. They mainly affect innate and adaptive immunity and explain over 28 % of the heritability. Pustular psoriasis comprises a group of rarer subtypes. Using exome sequencing, several disease genes were identified for mainly generalized pustular psoriasis, and an oligogenic inheritance is likely. Treatment studies based on the affected IL-36 pathway indicate a high response rate in this subtype further supporting the pathophysiological relevance of the affected gene products.

A Rare Case of New-Onset Crohn's Disease in a Patient With Chronic Palmoplantar Pustulosis

A 44-year-old woman who had been diagnosed with palmoplantar pustulosis (PPP) at 34 years old was diagnosed with moderate Crohn's disease (CD) based on endoscopic, radiological, and pathological findings. As treatment with corticosteroids, ultraviolet, and cyclosporin had achieved partial response, PPP had been refractory in a chronic continuous state. Oral prednisolone was initially started to treat CD, but clinical remission was not achieved. Intravenous ustekinumab was subsequently started at 260 mg for clinical remission of CD. Eight weeks after starting ustekinumab, clinical remission and mucosal healing were achieved and PPP manifestations on the palms and soles were markedly improved. Ustekinumab appears to offer an effective therapeutic option for patients with PPP but has yet to be approved for this induction in Japan. CD is a rare gastrointestinal involvement in PPP patients that requires attention.

Differential cell composition and split epidermal differentiation in human palm, sole, and hip skin

Palmoplantar skin is structurally and functionally unique, but the transcriptional programs driving this specialization are unclear. Here, we use bulk and single-cell RNA sequencing of human palm, sole, and hip skin to describe the distinguishing characteristics of palmoplantar and non-palmoplantar skin while also uncovering differences between palmar and plantar sites. Our approach reveals an altered immune environment in palmoplantar skin, with downregulation of diverse immunological processes and decreased immune cell populations. Further, we identify specific fibroblast populations that appear to orchestrate key differences in cell-cell communication in palm, sole, and hip. Dedicated keratinocyte analysis highlights major differences in basal cell fraction among the three sites and demonstrates the existence of two spinous keratinocyte populations constituting parallel, site-selective epidermal differentiation trajectories. In summary, this deep characterization of highly adapted palmoplantar skin contributes key insights into the fundamental biology of human skin and provides a valuable data resource for further investigation.

Involvement of Molecular Mechanisms between T/B Cells and IL-23: From Palmoplantar Pustulosis to Autoimmune Diseases

Palmoplantar pustulosis (PPP) is a disease that causes recurrent blisters and aseptic pustules on the palms and soles. It has been suggested that both innate and acquired immunity are involved. In particular, based on the tonsils and basic experiments, it has been assumed that T and B cells are involved in its pathogenesis. In addition, the results of clinical trials have suggested that IL-23 is closely related to the pathogenesis. This review describes PPP and the genetic background, the factors involved in the onset and exacerbation of disease and its relation to the molecular mechanism. In addition, we describe the usefulness of biological therapy and its implications in relation to the importance in pathology, the pathogenesis of PPP, the importance of the role of the IL-23-Th17 axis and IL-36 in PPP. Furthermore, we describe an animal experimental model of PPP, the efficacy and mechanism of action of guselkumab, an anti-IL-23 antibody, the latest research, and finally the possibility for it to be effective for other autoimmune diseases.

Therapeutic potential of targeting IL-1 family cytokines in chronic inflammatory skin diseases

The interleukin-1 (IL-1) family of cytokines is a central regulator of a myriad of immunological responses. It comprises several cytokines, including those belonging to the IL-1, IL-36 and IL-18 subfamilies, as well as IL-33. The IL-1 family primarily plays a role in orchestrating innate immune responses but also in adaptive immunity. Increased interest in the IL-1 family occurred following the discovery that dysregulation of IL-1 signalling underlies the pathogenesis of several monogenic auto-inflammatory diseases, characterized by sterile inflammation involving the skin and other organs. This also provided increased understanding of the role of innate immunity and the IL-1 family in polygenic auto-inflammatory skin conditions, such as neutrophilic dermatoses, as well as in some of the most common chronic inflammatory skin diseases, such as psoriasis or hidradenitis suppurativa. Several therapeutic agents have been developed to inhibit the IL-1 family members and their signalling pathways. These have shown therapeutic efficacy in several chronic inflammatory skin disorders. The aim of this review is to thoroughly describe the consequences of pathological dysregulation of IL-1, IL-33, IL-36, IL-18 pathways in dermatological conditions and to provide a forward-looking update on therapeutic strategies targeting signalling by IL-1 family cytokines.

Clinical background of patients with psoriasiform skin lesions due to tumor necrosis factor antagonist administration at a single center

Paradoxical reaction (PR) occurs when a drug elicits a reaction contrary to what was expected. To clarify the clinical features and genetic background of individuals susceptible to PR, we analyzed the clinical course of patients in whom psoriatic eruptions worsened or newly developed during tumor necrosis factor (TNF) antagonist administration and the role of focal infections and genetic variations. Of 125 patients who received TNF antagonist therapy for psoriasis, acrodermatitis continua of Hallopeau (ACH), generalized pustular psoriasis (GPP), or palmoplantar pustular psoriasis (PPP), eight patients with PR were surveyed at our hospital Dermatology Department between 2010 and 2021. A survey was also done on six patients who received TNF antagonist therapy for Crohn's disease, rheumatoid arthritis, ankylosing spondylitis, and hidradenitis suppurativa and were referred to our department due to PR. Additionally, Sanger sequencing analysis was performed for all exons and flanking introns of IL36RN (interleukin 36 receptor antagonist), CARD14 (caspase recruitment domain-containing protein 14), and AP1S3 (adaptor-related protein complex 1 subunit sigma 3). The clinical assessment of the 14 patients demonstrated an average age at PR onset of 48.4 years, a male : female ratio of 5:9, and a mean administration period until onset of 9.2 months. The clinical types of PR were plaque psoriasis, PPP, GPP, pustulosis, acne, ACH, hair loss, and exacerbation of arthralgia. Histopathology revealed psoriasiform dermatitis in three patients. One patient continued TNF antagonist therapy. All of the patients with psoriasis and GPP had dental infections, suggesting that focal infection may be a risk factor of the development of PR following TNF antagonist therapy. Gene analysis demonstrated CARD14 gene variants associated with RA, CD, AS, or PPP in four patients. In addition, all of the patients with ACH and PPP experienced PR, suggesting that these diseases may predispose patients to PR to TNF antagonist therapy.

Role of IL-36γ/IL-36R Signaling in Corneal Innate Defense Against Candida albicans Keratitis

Purpose

Interleukin (IL)-36 cytokines have been shown to play either beneficial or detrimental roles in the infection of mucosal tissues in a pathogen-dependent manner, but their involvement in fungal keratitis remains elusive. We herein investigated their expression and function in mediating corneal innate immunity against Candida albicans infection.

Methods

Gene expression in mouse corneas with or without C. albicans infection was determined by regular RT- and real-time (q)-PCR, Western blot analysis, ELISA or proteome profile assay. The severity of C. albicans keratitis was assessed using clinical scoring, bacterial counting, and myeloperoxidase (MPO) activity as an indicator of neutrophil infiltration. IL36R knockout mice and IL-33-specific siRNA were used to assess the involvement IL-33 signaling in C. albicans-infected corneas. B6 CD11c-DTR mice and clodronate liposomes were used to define the involvement of dendritic cells (DCs) and macrophages in IL-36R signaling and C. albicans keratitis, respectively.

Results

IL-36γ were up-regulated in C57BL6 mouse corneas in response to C. albicans infection. IL-36 receptor-deficient mice display increased severity of keratitis, with a higher fungal load, MPO, and IL-1β levels, and lower soluble sIL-1Ra and calprotectin levels. Exogenous IL-36γ prevented fungal keratitis pathogenesis with lower fungal load and MPO activity, higher expression of sIL-1Ra and calprotectin, and lower expression of IL-1β, at mRNA or protein levels. Protein array analysis revealed that the expression of IL-33 and REG3G were related to IL-36/IL36R signaling, and siRNA downregulation of IL-33 increased the severity of C. albicans keratitis. Depletion of dendritic cells or macrophages resulted in severe C. albicans keratitis and yet exhibited minimal effects on exogenous IL-36γ-induced protection against C. albicans infection in B6 mouse corneas.

Conclusions

IL-36/IL36R signaling plays a protective role in fungal keratitis by promoting AMP expression and by suppressing fungal infection-induced expression of proinflammatory cytokines in a dendritic cell- and macrophage-independent manner.

Exploring the Role of IL-36 Cytokines as a New Target in Psoriatic Disease

Unmet needs in the treatment of psoriasis call for novel therapeutic strategies. Pustular psoriasis and psoriatic arthritis often represent a therapeutic challenge. Focus on IL-36 cytokines offers an interesting approach, as the IL-36 axis has been appointed a critical driver of the autoinflammatory responses involved in pustular psoriasis. Two IL-36R blocking antibodies, imsidolimab and spesolimab, are currently undergoing phase II and III clinical trials, with promising results.

IL-1 Family Antagonists in Mouse and Human Skin Inflammation

Interleukin (IL)-1 family cytokines initiate inflammatory responses, and shape innate and adaptive immunity. They play important roles in host defense, but excessive immune activation can also lead to the development of chronic inflammatory diseases. Dysregulated IL-1 family signaling is observed in a variety of skin disorders. In particular, IL-1 family cytokines have been linked to the pathogenesis of psoriasis and atopic dermatitis. The biological activity of pro-inflammatory IL-1 family agonists is controlled by the natural receptor antagonists IL-1Ra and IL-36Ra, as well as by the regulatory cytokines IL-37 and IL-38. These four anti-inflammatory IL-1 family members are constitutively and highly expressed at steady state in the epidermis, where keratinocytes are a major producing cell type. In this review, we provide an overview of the current knowledge concerning their regulatory roles in skin biology and inflammation and their therapeutic potential in human inflammatory skin diseases. We further highlight some common misunderstandings and less well-known observations, which persist in the field despite recent extensive interest for these cytokines.

Similarity and difference between palmoplantar pustulosis and pustular psoriasis

Palmoplantar pustulosis is a chronic inflammatory disorder characterized by sterile pustules predominantly involving the palms and soles. Palmoplantar pustulosis has many similar aspects to psoriasis, either plaque and pustular type, namely familial occurrence between palmoplantar pustulosis and psoriasis, the appearance of the Köbner phenomenon, joint involvement, and nail involvement. Pustular psoriasis is classified into generalized and localized types, and there are a number of papers regarding palmoplantar pustulosis as an acral variant of localized pustular psoriasis. Many Japanese dermatologists consider palmoplantar pustulosis to be a distinct entity from pustular psoriasis, and the coexistence of palmoplantar pustulosis and psoriasis is rare. However, outside Japan, palmoplantar pustulosis is often considered to be palmoplantar psoriasis or palmoplantar pustular psoriasis, and extra-palmoplantar lesions are also considered to be psoriasis. The purpose of the current review is to compare the similarities and differences between palmoplantar pustulosis and generalized/localized pustular psoriasis. Japanese patients with palmoplantar pustulosis have a close relationship with focal infection, and the associated bone-joint manifestation exclusively involves the anterior chest wall. Furthermore, pediatric occurrence of palmoplantar pustulosis is extremely rare, and difference of genetic background between palmoplantar pustulosis and psoriasis has also been reported. Treatment of focal infection often results in dramatic effects on both cutaneous lesions and joint pain of palmoplantar pustulosis. Those findings suggest that palmoplantar pustulosis should be separately considered from either palmoplantar psoriasis or palmoplantar pustular psoriasis. The clinicopathological features and therapeutic approach of both diseases are discussed.

"Autoinflammatory psoriasis"-genetics and biology of pustular psoriasis

Psoriasis is a chronic inflammatory skin condition that has a fairly wide range of clinical presentations. Plaque psoriasis, which is the most common manifestation of psoriasis, is located on one end of the spectrum, dominated by adaptive immune responses, whereas the rarer pustular psoriasis lies on the opposite end, dominated by innate and autoinflammatory immune responses. In recent years, genetic studies have identified six genetic variants that predispose to pustular psoriasis, and these have highlighted the role of IL-36 cytokines as central to pustular psoriasis pathogenesis. In this review, we discuss the presentation and clinical subtypes of pustular psoriasis, contribution of genetic predisposing variants, critical role of the IL-36 family of cytokines in disease pathophysiology, and treatment perspectives for pustular psoriasis. We further outline the application of appropriate mouse models for the study of pustular psoriasis and address the outstanding questions and issues related to our understanding of the mechanisms involved in pustular psoriasis.

Palmoplantar Pustulosis: Recent Advances in Etiopathogenesis and Emerging Treatments

Palmoplantar pustulosis (PPP) is a chronic, recurrent skin disease belonging to the spectrum of psoriasis. It is characterized by an eruption of sterile pustules on the palms and soles. Recent studies in PPP have focused on genetic differences between pustular phenotypes and the role of the innate immunological system and the microbiome in the etiopathogenesis of the disease. Mutations in IL36RN (a major predisposing factor for generalized pustular psoriasis) were found in selected patients with PPP and were associated with earlier disease onset. Studies have shown that the interleukin (IL)-17 and IL-36 pathways might be involved in the pathogenesis of PPP. A microbiome has been demonstrated in the vesicopustules of PPP, and an abundance of Staphylococcus appears to be increased by smoking. Improved understanding of the underlying etiopathogenesis of PPP has led to advances in treatment options, and targeted therapies for PPP have been evaluated or are under evaluation against more than 12 molecules in ongoing clinical trials. These targets include CXCR2 (IL-8 receptor type B), granulocyte colony-stimulating factor receptor, IL-1 receptor, IL-8, IL-12, IL-23, IL-17A, IL-17 receptor, IL-36 receptor, phosphodiesterase-4, and tumor necrosis factor-α.

Guselkumab for the treatment of palmoplantar pustulosis

INTRODUCTION

Palmoplantar pustulosis, or pustulosis palmaris et plantaris (PPP), is a chronic, recurrent inflammatory skin disease that is sometimes unresponsive to conventional therapy. The anti-interleukin 23 antibody guselkumab is effective for treating PPP.

AREAS COVERED

This review details the current understanding of PPP and discusses why guselkumab may be effective. Guselkumab is only approved for the treatment of PPP in Japan. In the United States, Canada, the European Union, and several other countries, it is approved for the treatment of moderate-to-severe plaque psoriasis, but not for PPP. Furthermore, guselkumab was approved only 1 year ago; its efficacy will be proven only by phase 2 and 3 clinical trials.

EXPERT OPINION

The first double-blinded randomized placebo-controlled trial (RCT) of guselkumab for PPP has been completed. The drug was effective, and guselkumab could be used as a new agent for PPP treatment, in addition to several conventional therapeutics. However, several issues remain. For example, there is no mouse model of PPP, so careful observation of human PPP patients and establishment of a good experimental PPP model are essential.

Palmoplantar pustulosis: Current understanding of disease definition and pathomechanism

Pustulosis palmaris et plantaris, or palmoplantar pustulosis (PPP), is a chronic pustular dermatitis involving the palms and soles and is characterized by vesicles, pustules, erythema, lichenification, and abnormal desquamation. It is one of the most common skin diseases in Japan but its pathomechanism is unclear and the disease remains poorly defined. Consequently, adequate treatment for PPP is lacking. As a localized type of pustular psoriasis, PPP has long been treated with the conventional therapies used for plaque-type psoriasis, especially in Western countries. However, PPP may be a distinct entity, with a much lower prevalence in Western countries than in Japan. Furthermore, while treatment has yielded insights into the underlying pathology in plaque-type psoriasis, the pathogenesis of PPP has yet to be elucidated. In 2018, Gulselkumab, a monoclonal antibody against interleukin (IL)-23, was certified for use in Japan and is the first biologic effective in PPP both in Japanese and other patients. In this review, we summarize the current understanding of PPP, including the revised definition and possible pathomechanism. The information presented herein provides a more complete picture of PPP and may facilitate the development of improved treatment options.

Lack of association between mutation in IL36RN and palmoplantar pustular psoriasis in Chinese patients

Background

Palmoplantar pustulosis is considered to be a localized pustular psoriasis confined to the palms and soles. Mutation of the IL36RN gene, encoding interleukin-36 receptor antagonist (IL-36Ra), is associated with generalized pustular psoriasis, but IL36RN mutations in Chinese palmoplantar pustulosis patients have not previously been investigated.

Objective

The aim of this study was to evaluate the mutation of IL36RN in Chinese patients with palmoplantar pustulosis.

Methods

Fifty-one Han Chinese patients with palmoplantar pustulosis were recruited. All exons and exon-intron boundary sequences of IL36RN were amplified in polymerase chain reactions, and Sanger sequencing of the amplicons was performed.

Results

Among the 51 palmoplantar pustulosis patients, four different single-base substitutions were identified in nine patients. The mutations were c.140A>G/p.Asn47Ser in five patients, c.258G>A/p.Met86IIe in two patients, and c.115+6T>C and c.169G>A/p.Val57IIe in one patient each. All mutations were heterozygous. Comparison with the human genome database and reported literature suggested that these variants may not be pathogenic mutations causing palmoplantar pustulosis. Furthermore, there was no difference in disease severity, onset age, or disease duration between patients with these heterozygous IL36RN variants and those without (p > 0.1).

Study limitation

Lack of the further evaluation of IL36Ra protein in palmoplantar pustulosis lesions.

Conclusions

The four variants of IL36RN identified did not appear to be associated with the specific phenotypes of palmoplantar pustulosis.