Cathelicidin Antimicrobial Peptide LL37 Induces Toll-Like Receptor 8 and Amplifies IL-36γ and IL-17C in Human Keratinocytes

Cathepsin S: A key drug target and signalling hub in immune system diseases

The lysosomal cysteine protease cathepsin S supports host defence by promoting the maturation of MHC class-II proteins. In contrast, increased cathepsin S activity mediates tissue destructive immune responses in autoimmune and inflammatory diseases. Therefore, cathepsin S is a key target in drug discovery programs. Here, we critically reviewed the specific mechanisms by which cathepsin S mediates autoimmune and hyperinflammatory responses to identify new targets for therapeutic immunomodulation. To this end, we performed literature review utilizing PubMed, drug database of US FDA, European Medicines Agency and the Drug-Gene Interaction Database. Cathepsin S destroys T cell epitopes and reduces endogenous antigen diversity, impairing negative selection of autoreactive T cells that could recognize these epitopes. Moreover, cathepsin S critically regulates inflammatory disease severity by generating proinflammatory molecules (PAR-1, PAR-2, IL-36γ, Fractalkine, Endostatin, Ephrin-B2), inactivating anti-inflammatory mediators (SLPI) and degrading molecules involved in antimicrobial and immunomodulatory responses (surfactant protein-A, LL-37, beta-defensins), inter-endothelial/-epithelial barrier function, gene repair and energy homeostasis. These pathways could be targeted by repositioning of existing drugs. These findings suggest that inhibiting cathepsin S or a specific downstream target of cathepsin S by repositioning of existing drugs could be a promising strategy for treating autoimmune and inflammatory diseases. Current cathepsin S inhibitors in clinical trials face challenges, highlighting the need for innovative inhibitors that function effectively in various cellular compartments with differing pH levels, without targeting the shared catalytic site of cysteine cathepsins.

Targeting the STAT3/IL-36G signaling pathway can be a promising approach to treat rosacea

BACKGROUND

Rosacea is an inflammatory skin disorder characterized by the release of inflammatory mediators from keratinocytes, which are thought to play a crucial role in its pathogenesis. Despite an incidence of approximately 5.5%, rosacea is associated with a poor quality of life. However, as the pathogenesis of rosacea remains enigmatic, treatment options are limited.

OBJECTIVES

To investigate the pathogenesis of rosacea and explore new therapeutic strategies.

METHODS

Transcriptome data from rosacea patients combined with immunohistochemical staining were used to investigate the activation of STAT3 in rosacea. The role of STAT3 activation in rosacea was subsequently explored by inhibiting STAT3 activation both in vivo and in vitro. The key molecules downstream of STAT3 activation were identified through data analysis and experiments. Dual-luciferase assay and ChIP-qPCR analysis were used to validate the direct binding of STAT3 to the IL-36G promoter. DARTS, in combination with experimental screening, was employed to identify effective drugs targeting STAT3 for rosacea treatment.

RESULTS

STAT3 signaling was hyperactivated in rosacea and served as a promoter of the keratinocyte-driven inflammatory response. Mechanistically, activated STAT3 directly bind to the IL-36G promoter region to amplify downstream inflammatory signals by promoting IL-36G transcription, and treatment with a neutralizing antibody (α-IL36γ) could mitigate rosacea-like inflammation. Notably, a natural plant extract (pogostone), which can interact with STAT3 directly to inhibit its activation and affect the STAT3/IL36G signaling pathway, was screened as a promising topical medication for rosacea treatment.

CONCLUSIONS

Our study revealed a pivotal role for STAT3/IL36G signaling in the development of rosacea, suggesting that targeting this pathway might be a potential strategy for rosacea treatment.

The Contribution of Human Antimicrobial Peptides to Fungi

Various species of fungi can be detected in the environment and within the human body, many of which may become pathogenic under specific conditions, leading to various forms of fungal infections. Antimicrobial peptides (AMPs) are evolutionarily ancient components of the immune response that are quickly induced in response to infections with many pathogens in almost all tissues. There is a wide range of AMP classes in humans, many of which exhibit broad-spectrum antimicrobial function. This review provides a comprehensive overview of the mechanisms of action of AMPs, their distribution in the human body, and their antifungal activity against a range of both common and rare clinical fungal pathogens. It also discusses the current research status of promising novel antifungal strategies, highlighting the challenges that must be overcome in the development of these therapies. The hope is that antimicrobial peptides, as a class of antimicrobial agents, will soon progress through large-scale clinical trials and be implemented in clinical practice, offering new treatment options for patients suffering from infections.

Psoriasis: Immunological and genetic blueprints driving pathogenesis and potential for personalized therapies

Psoriasis is a long-lasting inflammatory skin condition that impacts millions globally. The occurrence of this disorder differs significantly across various areas, resulting from a complex interplay of genetic and environmental influences. In psoriasis, the pathogenesis represents a complex interaction of innate and adaptive immunity that plays a significant role in the disease manifestation process. Many genetic factors predispose to psoriasis, which is considered a polygenic disease. Several genes concerning pathways like NF-κB and PI3K/Akt that modulate the amplification of inflammatory response and keratinocyte dysregulation have been elaborated in the light of their differential expression, susceptibility loci, and polymorphisms. Such genetic insights could open a whole new avenue for precision medicine in which biomarkers and gene-targeting therapies are promising options for personalized treatment. This review emphasizes the need for complex investigations into psoriasis, from molecular mechanisms to clinical manifestations, to bridge the gap between basic research and therapeutic development by furthering the understanding of psoriasis and paving the way for innovative treatments addressing skin lesions and systemic effects.

Disease heterogeneity and molecular classification of inflammatory palmoplantar diseases

BACKGROUND

Palmoplantar pustulosis (PPP) is an inflammatory disease characterized by relapsing eruptions of neutrophil-filled, sterile pustules on the palms and soles that can be clinically difficult to differentiate from non-pustular palmoplantar psoriasis (palmPP) and dyshidrotic palmoplantar eczema (DPE).

OBJECTIVE

We sought to identify overlapping and unique PPP, palmPP, and DPE drivers to provide molecular insight into their pathogenesis.

METHODS

We performed bulk RNA sequencing of lesional PPP (n = 33), palmPP (n = 5), and DPE (n = 28) samples, as well as 5 healthy nonacral and 10 healthy acral skin samples.

RESULTS

Acral skin showed a unique immune environment, likely contributing to a unique niche for palmoplantar inflammatory diseases. Compared to healthy acral skin, PPP, palmPP, and DPE displayed a broad overlapping transcriptomic signature characterized by shared upregulation of proinflammatory cytokines (TNF, IL-36), chemokines, and T-cell-associated genes, along with unique disease features of each disease state, including enriched neutrophil processes in PPP and to a lesser extent in palmPP, and lipid antigen processing in DPE. Strikingly, unsupervised clustering and trajectory analyses demonstrated divergent inflammatory profiles within the 3 disease states. These identified putative key upstream immunologic switches, including eicosanoids, interferon responses, and neutrophil degranulation, contributing to disease heterogeneity.

CONCLUSION

A molecular overlap exists between different inflammatory palmoplantar diseases that supersedes clinical and histologic assessment. This highlights the heterogeneity within each condition, suggesting limitations of current disease classification and the need to move toward a molecular classification of inflammatory acral diseases.

Glioblastoma Multiforme: Sensitivity to Antimicrobial Peptides LL-37 and PG-1, and Their Combination with Chemotherapy for Predicting the Overall Survival of Patients

Background/Objectives: Glioblastomas (GBMs) are the most malignant and intractable of all cancers, with an unfavorable clinical prognosis for affected patients. The objective was to analyze the sensitivity of GBM cells to the antimicrobial peptides (AMPs) cathelicidin (LL-37) and protegrin-1 (PG-1), both alone and in combination with chemotherapy, to predict overall survival (OS) in the patients. Methods: The study was conducted on 27 GBM patients treated in the neurosurgical department of the Almazov Medical Research Centre (Saint Petersburg, Russia) from 2021 to 2024. The cytotoxic effects of chemotherapy, AMPs, and their combinations on brain tumor cells were assessed by an MTT assay using a 50% inhibitory concentration (IC50). Results: In GBM cells from the patients, LL-37 and PG-1 exhibited strong anticancer effects, surpassing those of chemotherapy drugs. These LL-37 and PG-1 anticancer effects were associated with a statistically significant increase in life expectancy and OS in GBM patients. These findings were confirmed by experiments on rats with C6 glioma, where the intranasal administration of LL-37 (300 μM) and PG-1 (600 μM) increased the life expectancy of the animals to 69 and 55 days, respectively, compared to 24 days in the control group (HR = 4.139, p = 0.0005; HR = 2.542, p = 0.0759). Conclusions: Additionally, the combination of LL-37 and PG-1 with chemotherapy drugs showed that a high IC50 of LL-37 with cisplatin (cutoff > 800 μM) in GBM cells was associated with increased life expectancy (19 vs. 5 months, HR = 4.708, p = 0.0101) and OS in GBM patients. These combinations could be used in future GBM treatments.

Cell-free adipose tissue extracts as a novel treatment for rosacea by downregulating TRPV1

Rosacea is a chronic inflammatory skin disease that typically affects the central facial area. Its main clinical symptoms include paroxysmal flushing, telangiectasia, and non-temporary erythema. Cell-free adipose tissue extracts (ATEs) are liquid components extracted from human adipose tissue that contain large amounts of growth factors. Despite the scar-reducing, anti-aging, and wound-healing effects of ATEs, the efficacy of ATEs in rosacea remains unknown. Therefore, the anti-rosacea effects of ATEs were investigated in human cathelicidin peptide (LL-37) induced rosacea mice and capsaicin (CAP)-stimulated HaCaT keratinocytes. In vitro, ATEs significantly reduced TRPV1 expression, intracellular calcium ions influx and the release of inflammatory factors (such as KLK5, IL-6, IL-8 and TNF-α) after intervening in CAP-stimulated cells. The in vivo results revealed that ATEs alleviated rosacea symptoms, such as erythema score, erythema area, transepidermal water loss, abnormal epidermal thickness, mast cell infiltration and telangiectasia upon downregulating TRPV1 and CD31 expression. Moreover, the up-regulated TRPV1 protein expression was also recovered by ATEs administration in vivo and in vitro. Meanwhile, ATEs demonstrated good biocompatibility. In summary, ATEs could be a potential therapeutic agent for rosacea by regulating inflammation and alleviating telangiectasia.

Molecular aspects of Interleukin-36 cytokine activation and regulation

Interleukin-36 (IL-36) cytokines are structurally similar to other Interleukin-1 superfamily members and are essential to convey inflammatory responses at epithelial barriers including the skin, lung, and gut. Due to their potent effects on immune cells, IL-36 cytokine activation is regulated on multiple levels, from expression and activation to receptor binding. Different IL-36 isoforms convey specific responses as a consequence of particular danger- or pathogen-associated molecular patterns. IL-36 expression and activation are regulated by exogenous pathogens, including fungi, viruses and bacteria but also by endogenous factors such as antimicrobial peptides or cytokines. Processing of IL-36 into potent bioactive forms is necessary for host protection but can elevate tissue damage. Indeed, exacerbated IL-36 signalling and hyperactivation are linked to the pathogenesis of diseases such as plaque and pustular psoriasis, emphasising the importance of understanding the molecular aspects regulating IL-36 activation. Here, we summarise facets of the electrochemical properties, regulation of extracellular cleavage by various proteases and receptor signalling of the pro-inflammatory and anti-inflammatory IL-36 family members. Additionally, this intriguing cytokine subfamily displays many characteristics that are unique from prototypical members of the IL-1 family and these key distinctions are outlined here.

The immunological understanding on germinal center B cells in psoriasis

The development of psoriasis is mainly driven by the dysregulation of T cells within the skin, marking a primary involvement of these cells in the pathogenesis. Although B cells are integral components of the immune system, their role in the initiation and progression of psoriasis is not as pivotal as that of T cells. The paradox of B cell suggests that, while it is crucial for adaptive immunity, B cells may contribute to the exacerbation of psoriasis. Numerous ideas proposed that there are potential relationships between psoriasis and B cells especially within germinal centers (GCs). Recent research projected that B cells might be triggered by autoantigens which then induced molecular mimicry to alter B cells activity within GC and generate autoantibodies and pro-inflammatory cytokines, form ectopic GC, and dysregulate the proliferation of keratinocytes. Hence, in this review, we gathered potential evidence indicating the participation of B cells in psoriasis within the context of GC, aiming to enhance our comprehension and advance treatment strategies for psoriasis thus inviting many new researchers to investigate this issue.

Effects on peripheral and central nervous system of key inflammatory intercellular signalling peptides and proteins in psoriasis

Psoriasis is a chronic systemic inflammatory cutaneous disease. Where the immune system plays an important role in its pathogenesis, with key inflammatory intercellular signalling peptides and proteins including IL-17 and IL-23. The psychoneurological system also figures prominently in development of psoriasis. There is a high prevalence of comorbidity between psoriasis and mental health disorders such as depression, anxiety and mania. Patients with psoriasis often suffer from pathological pain in the lesions, and their neurological accidents could improve the lesions in innervated areas. The immune system and the psychoneurological system interact closely in the pathogenesis of psoriasis. Patients with psoriasis exhibit abnormal levels of neuropeptides both in circulating and localized lesion, acting as immunomodulators involved in the inflammatory response. Moreover, receptors for inflammatory factors are expressed in both peripheral and central nervous systems (CNSs), suggesting that nervous system can receive and be influenced by signals from immune system. Key inflammatory intercellular signalling peptides and proteins in psoriasis, such as IL-17 and IL-23, can be involved in sensory signalling and may affect synaptic plasticity and the blood-brain barrier of CNS through the circulation. This review provides an overview of the multiple effects on the peripheral and CNS under conditions of systemic inflammation in psoriasis, providing a framework and inspiration for in-depth studies of neuroimmunomodulation in psoriasis.

Skin barrier-inflammatory pathway is a driver of the psoriasis-atopic dermatitis transition

As chronic inflammatory conditions driven by immune dysregulation are influenced by genetics and environment factors, psoriasis and atopic dermatitis (AD) have traditionally been considered to be distinct diseases characterized by different T cell responses. Psoriasis, associated with type 17 helper T (Th17)-mediated inflammation, presents as well-defined scaly plaques with minimal pruritus. AD, primarily linked to Th2-mediated inflammation, presents with poorly defined erythema, dry skin, and intense itching. However, psoriasis and AD may overlap or transition into one another spontaneously, independent of biological agent usage. Emerging evidence suggests that defects in skin barrier-related molecules interact with the polarization of T cells, which forms a skin barrier-inflammatory loop with them. This loop contributes to the chronicity of the primary disease or the transition between psoriasis and AD. This review aimed to elucidate the mechanisms underlying skin barrier defects in driving the overlap between psoriasis and AD. In this review, the importance of repairing the skin barrier was underscored, and the significance of tailoring biologic treatments based on individual immune status instead of solely adhering to the treatment guidelines for AD or psoriasis was emphasized.

Increased LL37 in psoriasis and other inflammatory disorders promotes LDL uptake and atherosclerosis

Patients with chronic inflammatory disorders such as psoriasis have an increased risk of cardiovascular disease and elevated levels of LL37, a cathelicidin host defense peptide that has both antimicrobial and proinflammatory properties. To explore whether LL37 could contribute to the risk of heart disease, we examined its effects on lipoprotein metabolism and show that LL37 enhanced LDL uptake in macrophages through the LDL receptor (LDLR), scavenger receptor class B member 1 (SR-B1), and CD36. This interaction led to increased cytosolic cholesterol in macrophages and changes in expression of lipid metabolism genes consistent with increased cholesterol uptake. Structure-function analysis and synchrotron small-angle x-ray scattering showed structural determinants of the LL37-LDL complex that underlie its ability to bind its receptors and promote uptake. This function of LDL uptake is unique to cathelicidins from humans and some primates and was not observed with cathelicidins from mice or rabbits. Notably, Apoe-/- mice expressing LL37 developed larger atheroma plaques than did control mice, and a positive correlation between plasma LL37 and oxidized phospholipid on apolipoprotein B (OxPL-apoB) levels was observed in individuals with cardiovascular disease. These findings provide evidence that LDL uptake can be increased via interaction with LL37 and may explain the increased risk of cardiovascular disease associated with chronic inflammatory disorders.

Emerging Role of the IL-36/IL-36R Axis in Multiple Inflammatory Skin Diseases

IL-36 is a most recent member of the IL-1 cytokine family, primarily expressed at barrier sites of the body such as the skin, lungs, and intestine. It plays a vital role in inflammation and is implicated in the development of various cutaneous; intestinal; and pulmonary disorders, including psoriasis, inflammatory bowel disease, and chronic obstructive pulmonary disease. IL-36 comprises 4 isoforms: the proinflammatory IL-36α, IL-36β, and IL-36γ and the anti-inflammatory IL-36R antagonist. An imbalance between proinflammatory and anti-inflammatory IL-36 isoforms can contribute to the inflammatory fate of cells and tissues. IL-36 cytokines signal through an IL-36R heterodimer mediating their function through canonical signaling cacade, including the NF-B pathway. Prominent for its role in psoriasis, IL-36 has recently been associated with disease mechanisms in atopic dermatitis, hidradenitis suppurativa, neutrophilic dermatoses, autoimmune blistering disease, and Netherton syndrome. The major cutaneous source of IL-36 cytokines is keratinocytes, pointing to its role in the communication between the epidermis, innate (neutrophils, dendritic cells) immune system, and adaptive (T helper [Th]1 cells, Th17) immune system. Thus, cutaneous IL-36 signaling is crucial for the immunopathological outcome of various skin diseases. Consequently, the IL-36/IL-36R axis has recently been recognized as a promising drug target for the treatment of inflammatory disorders beyond psoriasis. This review summarizes the current update on IL-36 cytokines in inflammatory skin diseases.

IL-17A-driven psoriasis is critically dependent on IL-36 signaling

Plaque psoriasis is an autoinflammatory and autoimmune skin disease, affecting 1-3% of the population worldwide. Previously, high levels of IL-36 family cytokines were found in psoriatic skin lesions, thereby contributing to keratinocyte hyperproliferation and infiltration of immune cells such as neutrophils. While treatment with anti-IL36 receptor (IL36R) antibodies was recently approved for generalized pustular psoriasis (GPP), it remains unclear, if targeting the IL36R might also inhibit plaque psoriasis. Here we show that antibody-mediated inhibition of IL36R is sufficient to suppress imiquimod-induced psoriasis-like skin inflammation and represses the disease's development in a model that depends on IL-17A overexpression in the skin. Importantly, treatment with anti-IL36R antibodies inhibited skin inflammation and attenuated psoriasis-associated, systemic inflammation. This is possibly due to a widespread effect of IL36R inhibition, which not only suppresses pro-inflammatory gene expression in keratinocytes, but also the activation of other immune cells such as T-cells or dendritic cells. In conclusion, we propose that inhibition of the IL-36 signaling pathway might constitute an attractive, alternative approach for treating IL-17A-driven psoriasis and psoriasis-linked comorbidities.

Crosstalk: keratinocytes and immune cells in psoriasis

In the past, psoriasis was considered a skin disease caused only by keratinocyte disorders. However, the efficacy of immunosuppressive drugs and biologics used to treat psoriasis proves that psoriasis is an immune-mediated disease. Indeed, a variety of immune cells are involved in the pathogenesis of psoriasis, including dendritic cells, Th17 cells, and resident memory T cells. Furthermore, keratinocytes play a role in the development of psoriasis as immune cells by secreting antibacterial peptides, chemokines, tumor necrosis factor-α, interleukin (IL)-36, and IL-23. These immune cells and skin cells interact and drive the aberrant differentiation and proliferation of keratinocytes. This crosstalk between keratinocytes and immune cells critical in the pathogenesis of psoriasis forms an inflammatory loop, resulting in the persistence or exacerbation of psoriasis plaques.

Risk of candidiasis associated with interleukin-17 inhibitors: Implications and management

The application of interleukin-17 (IL-17) inhibitors, including secukinumab, ixekizumab, brodalumab, and bimekizumab, are associated with elevated risk of candidiasis. These medications interfere with the IL-17 pathway, which is essential for maintaining mucosal barriers and coordinating the immune response against Candida species. The observational data and clinical trials demonstrate the increased incidence of candidiasis in individuals treated with IL-17 inhibitors. Brodalumab and bimekizumab pose a greater risk than secukinumab in eliciting candidiasis, whereas the data regarding ixekizumab are equivocal. Higher doses and prolonged treatment duration of IL-17 inhibitors increase the risk of candidiasis by compromising the immune response against Candida species. Prior to prescribing IL-17 inhibitors, healthcare professionals should comprehensively evaluate patients' medical histories and assess their risk factors. Patients should be educated on the signs and symptoms of candidiasis to facilitate early detection and intervention. Future research should focus on identifying the risk factors associated with candidiasis in patients receiving IL-17 inhibitors. Prospective studies and long-term surveillance are required to explore the impact of specific inhibitors on the incidence and severity of candidiasis and to evaluate the effectiveness of combination therapies, such as concurrent use of IL-17 inhibitors and prophylactic antifungal agents.