Honey bee (Apis mellifera) venom induces AIM2 inflammasome activation in human keratinocytes

m6A-methylated Lonp1 drives mitochondrial proteostasis stress to induce testicular pyroptosis upon environmental cadmium exposure

Cadmium (Cd) is a widely distributed typical environmental pollutant and one of the most toxic heavy metals. It is well-known that environmental Cd causes testicular damage by inducing classic types of cell death such as cell apoptosis and necrosis. However, as a new type of cell death, the role and mechanism of pyroptosis in Cd-induced testicular injury remain unclear. In the current study, we used environmental Cd to generate a murine model with testicular injury and AIM2-dependent pyroptosis. Based on the model, we found that increased cytoplasmic mitochondrial DNA (mtDNA), activated mitochondrial proteostasis stress occurred in Cd-exposed testes. We used ethidium bromide to generate mtDNA-deficient testicular germ cells and further confirmed that increased cytoplasmic mtDNA promoted AIM2-dependent pyroptosis in Cd-exposed cells. Uracil-DNA glycosylase UNG1 overexpression indicated that environmental Cd blocked UNG-dependent repairment of damaged mtDNA to drive the process in which mtDNA releases to cytoplasm in the cells. Interestingly, we found that environmental Cd activated mitochondrial proteostasis stress by up-regulating protein expression of LONP1 in testes. Testicular specific LONP1-knockdown significantly reversed Cd-induced UNG1 protein degradation and AIM2-dependent pyroptosis in mouse testes. In addition, environmental Cd significantly enhanced the m6A modification of Lonp1 mRNA and its stability in testicular germ cells. Knockdown of IGF2BP1, a reader of m6A modification, reversed Cd-induced upregulation of LONP1 protein expression and pyroptosis activation in testicular germ cells. Collectively, environmental Cd induces m6A modification of Lonp1 mRNA to activate mitochondrial proteostasis stress, increase cytoplasmic mtDNA content, and trigger AIM2-dependent pyroptosis in mouse testes. These findings suggest that mitochondrial proteostasis stress is a potential target for the prevention of testicular injury.

The role of hepatocyte mitochondrial DNA in liver injury

Hepatocytes, the predominant cellular constituents of the liver, exhibit the highest mitochondrial density within the human body. Remarkably, experimental insights from the latter part of the previous century involving extracellular injection of mitochondrial DNA (mtDNA) elucidated its potential to incite autoimmune disorders. Consequently, in instances of liver injury, the substantial release of mtDNA has the potential to trigger the activation of the innate immune response, thereby inducing sustained pathogenic consequences within the organism. This article provides a comprehensive retrospective analysis of recent literature pertaining to the impact of mtDNA release on various hepatic cell populations, elucidating its role and potential mechanisms in liver injury. The findings underscore the central role of mtDNA in modulating the immune system, primarily through the orchestration of a cytokine storm, further exacerbating the occurrence of liver injury.

Mitochondrial DNA-triggered innate immune response: mechanisms and diseases

Various cellular stress conditions trigger mitochondrial DNA (mtDNA) release from mitochondria into the cytosol. The released mtDNA is sensed by the cGAS-MITA/STING pathway, resulting in the induced expression of type I interferon and other effector genes. These processes contribute to the innate immune response to viral infection and other stress factors. The deregulation of these processes causes autoimmune diseases, inflammatory metabolic disorders and cancer. Therefore, the cGAS-MITA/STING pathway is a potential target for intervention in infectious, inflammatory and autoimmune diseases as well as cancer. In this review, we focus on the mechanisms underlying the mtDNA-triggered activation of the cGAS-MITA/STING pathway, the effects of the pathway under various physiological and pathological conditions, and advances in the development of drugs that target cGAS and MITA/STING.

Role of NLRP3 in the exacerbation of ozone-induced allergic rhinitis

OBJECTIVE

Allergic rhinitis (AR) is an immunoglobulin E (IgE)-mediated inflammatory disorder of the nasal mucosa, and the impact of ozone on AR is gaining increasing attention. Although NOD-like receptor thermal protein domain associated protein 3 (NLRP3) plays a crucial role in the pathogenesis of AR, its regulatory mechanisms in ozone-induced exacerbation remain unclear. Therefore, we explored the impact of ozone inhalation on inflammation in AR and investigated the regulatory mechanisms involving NLRP3.

METHODS

Fifty female Sprague-Dawley rats were selected and divided into five groups: normal control (NC), normal with ozone exposure (NE), AR model, AR with ozone exposure (ARE), and ARE treated with the NLRP3 inhibitor MCC950 (ARE+MCC950). Behavioral changes were observed in the rats, and the expression of NLRP3, active-caspase 1, and GSDMD-N was detected by western blotting. The expression levels of interleukin (IL)- 4, IL-5, IL-13, IL-1β, and ovalbumin-specific IgE (OVA-sIgE) in nasal lavage fluid as well as IL-6 in the serum were measured by ELISA. The expression and distribution of NLRP3 and IL-1β in nasal mucosal tissue were detected by immunohistochemistry, and pathological changes and eosinophilic infiltration in nasal mucosal tissue were observed by hematoxylin and eosin (HE) staining. The effects of ozone exposure on inflammation in the nasal mucosal tissue of rats with AR and the relationship between NLRP3 and inflammation were analyzed.

RESULTS

Upregulation of NLRP3 was observed in the AR rat model, and ozone further aggravated the expression of NLRP3 in the nasal mucosal tissue. Compared to the AR, NC, and NE groups, NLRP3 inflammasomes were activated in the ARE group, and the expression levels of related indexes active-caspase 1 and GSDMD-N were significantly increased; the expression levels of Th2 inflammatory factors IL-4, IL-5, IL-13, and OVA-sIgE were increased, and inflammatory factors such as IL-1β and IL-6 expression was also significantly increased. HE staining revealed that ozone aggravated damage to the nasal mucosal tissue in AR. Compared with the ARE group, the expression of NLRP3 inflammasomes was downregulated, sneezing and scratching symptoms were reduced, inflammatory indicators in nasal lavage fluid were decreased, and nasal mucosal tissue damage was alleviated in rats in the ARE+MCC950 group.

CONCLUSION

Ozone exposure significantly increased the inflammatory response in an animal model of AR. MCC950 can selectively inhibit the expression of NLRP3, inhibit the activity of inflammasomes, and reduce nasal mucosal inflammation by regulating the NLRP3-caspase-1-IL-1β pathway.

Understanding the role of NLRP3-mediated pyroptosis in allergic rhinitis: A review

Allergic rhinitis (AR) is a chronic, inflammatory disease of the nasal mucosa, caused by the immunoglobulin E-mediated immune response. The annual incidence rate of AR is on the rise, exerting a significant impact on individuals' physical and mental wellbeing. The treatment effect in some patients is still not ideal, as the pathogenesis of AR is complex and diverse. Recent studies have shown that NLRP3 inflammasome-mediated pyroptosis is widely involved in the occurrence and development of AR through various pathways. This article reviews the mechanism of pyroptosis and its research progress in the field of AR, and puts forward possible therapeutic targets to offer innovative approaches for its management.

Potential roles of inflammasomes in the pathophysiology of Psoriasis: A comprehensive review

Psoriasis is an inflammatory skin disease whose pathophysiology is attributed to both innate and adaptive immune cells and molecules. Despite the crucial roles of the immune system in psoriasis, it cannot be categorized as an autoimmune disease because of the lack of main signs of autoimmunity, such as specific antibodies, well-defined antigens, and autoimmune genetic risk factors. The presence of some cellular and molecular properties, such as the presence of neutrophils in skin lesions and the activation of the innate immune system, attributes psoriasis to a group of diseases called autoinflammatory disorders. Autoinflammatory diseases refer to a group of inherited disorders whose main manifestations are recurrent fever, a high level of acute-phase reactant, and a tendency for inflammation of the skin, joints, and other organs like the nervous system. In most autoinflammatory disorders, it has been seen that complexes of the high-molecular-weight protein named inflammasomes have significant roles. The inflammasome complex usually is formed and activated in the stimulated immune cell cytoplasm, and its activation consequently leads to inflammatory events such as producing of active caspase-1, mature interleukin-1β (IL-1β), and IL-18 and can cause an inflammatory programmed cell death called pyroptosis. Since the identification of inflammasomes, it has been shown that there are close links between them and hereditary and acquired autoinflammatory diseases like psoriasis. In this review, we aim to focus on well-defined inflammasome and their role in the pathophysiology of psoriasis.

Mitochondrial DNA Release in Innate Immune Signaling

According to the endosymbiotic theory, most of the DNA of the original bacterial endosymbiont has been lost or transferred to the nucleus, leaving a much smaller (∼16 kb in mammals), circular molecule that is the present-day mitochondrial DNA (mtDNA). The ability of mtDNA to escape mitochondria and integrate into the nuclear genome was discovered in budding yeast, along with genes that regulate this process. Mitochondria have emerged as key regulators of innate immunity, and it is now recognized that mtDNA released into the cytoplasm, outside of the cell, or into circulation activates multiple innate immune signaling pathways. Here, we first review the mechanisms through which mtDNA is released into the cytoplasm, including several inducible mitochondrial pores and defective mitophagy or autophagy. Next, we cover how the different forms of released mtDNA activate specific innate immune nucleic acid sensors and inflammasomes. Finally, we discuss how intracellular and extracellular mtDNA release, including circulating cell-free mtDNA that promotes systemic inflammation, are implicated in human diseases, bacterial and viral infections, senescence and aging.

Pyroptosis and Its Role in Cervical Cancer

Pyroptosis, an inflammatory programmed cell death, is characterized by the caspase-mediated pore formation of plasma membranes and the release of large quantities of inflammatory mediators. In recent years, the morphological characteristics, induction mechanism and action process of pyroptosis have been gradually unraveled. As a malignant tumor with high morbidity and mortality, cervical cancer is seriously harmful to women's health. It has been found that pyroptosis is closely related to the initiation and development of cervical cancer. In this review the mechanisms of pyroptosis and its role in the initiation, progression and treatment application of cervical cancer are summarized and discussed.

The central role of a two-way positive feedback pathway in molecular targeted therapies-mediated pyroptosis in anaplastic thyroid cancer

BACKGROUND

Anaplastic thyroid carcinoma (ATC) is one of the most aggressive tumours. We previously confirmed that apatinib has potential therapeutic effects on ATC via regulated cell death (RCD). As a newly identified RCD, pyroptosis demonstrates direct antitumour activity different from apoptosis or autophagy. Therefore, the clinical significance, regulatory role and underlying mechanisms of pyroptosis in ATC were focused on in this study.

METHODS

In a phase II trial, patients with anaplastic or poorly differentiated thyroid carcinoma received apatinib 500 mg once daily. Multiple assays were implemented to evaluate the antitumour efficacy of apatinib and/or melittin in vitro and in vivo. High-throughput sequencing was applied to analyse differential mRNAs expression in ATC cells treated by apatinib with or without melittin. In situ Hoechst 33342/PI double-staining, LDH release assay and enzyme-linked immunosorbent assay (ELISA) were employed to determine pyroptosis. In mechanism exploration, quantitative RT-PCR, Western blotting and si-RNA knocking down were executed.

RESULTS

Seventeen patients were evaluable. Apatinib showed a promising therapeutic effect by a disease control rate (DCR) of 88.2%; however, treatment was terminated in 23.5% of patients due to intolerable toxicity. To reduce adverse events, a pyroptosis-mediated synergistic antitumour effect of apatinib and melittin was identified in treatment of ATC in vitro and in vivo. The caspase-1-gasdermin D (GSDMD) axis-mediated pyroptosis was the key to extra antitumour effect of the combination of apatinib and melittin. Moreover, caspase-3-gasdermin E (GSDME) pyroptosis pathway also functioned importantly in addition to caspase-1-GSDMD pathway. Evidenced by in vitro and in vivo study, a two-way positive feedback interaction was innovatively confirmed between caspase-1-GSDMD and caspase-3-GSDME axes.

CONCLUSIONS

Through pyroptosis mediated by caspase-1-GSDMD and caspase-3-GSDME axes synchronically, low-dosage apatinib and melittin could synergistically achieve a comparable therapeutic potential with reduced AEs. More importantly, a two-way positive feedback interaction is innovatively proposed between these two axes, which provide a new prospect of targeted therapy.

mtDNA in the Pathogenesis of Cardiovascular Diseases

The incidence rate of cardiovascular disease (CVD) has been increasing year by year and has become the main cause for the increase of mortality. Mitochondrial DNA (mtDNA) plays a crucial role in the pathogenesis of CVD, especially in heart failure and ischemic heart diseases. With the deepening of research, more and more evidence showed that mtDNA is related to the occurrence and development of CVD. Current studies mainly focus on how mtDNA copy number, an indirect biomarker of mitochondrial function, contributes to CVD and its underlying mechanisms including mtDNA autophagy, the effect of mtDNA on cardiac inflammation, and related metabolic functions. However, no relevant studies have been conducted yet. In this paper, we combed the current research status of the mechanism related to the influence of mtDNA on the occurrence, development, and prognosis of CVD, so as to find whether these mechanisms have something in common, or is there a correlation between each mechanism for the development of CVD?

Non-Coding RNAs: Master Regulators of Inflammasomes in Inflammatory Diseases

Emerging data indicates that non-coding RNAs (ncRNAs) represent more than just “junk sequences” of the genome and have been found to be involved in multiple diseases by regulating various biological process, including the activation of inflammasomes. As an important aspect of innate immunity, inflammasomes are large immune multiprotein complexes that tightly regulate the production of pro-inflammatory cytokines and mediate pyroptosis; the activation of the inflammasomes is a vital biological process in inflammatory diseases. Recent studies have emphasized the function of ncRNAs in the fine control of inflammasomes activation either by directly targeting components of the inflammasomes or by controlling the activity of various factors that control the activation of inflammasomes; consequently, ncRNAs may represent potential therapeutic targets for inflammatory diseases. Understanding the precise role of ncRNAs in controlling the activation of inflammasomes will help us to design targeted therapies for multiple inflammatory diseases. In this review, we summarize the regulatory role and therapeutic potential of ncRNAs in the activation of inflammasomes by focusing on a range of inflammatory diseases, including microbial infection, sterile inflammatory diseases, and fibrosis-related diseases. Our goal is to provide new ideas and perspectives for future research.

Antimycin A-induced mitochondrial dysfunction regulates inflammasome signaling in human retinal pigment epithelial cells

Age-related macular degeneration (AMD) is a severe retinal eye disease where dysfunctional mitochondria and damaged mitochondrial DNA in retinal pigment epithelium (RPE) have been demonstrated to underlie the pathogenesis of this devastating disease. In the present study, we aimed to examine whether damaged mitochondria induce inflammasome activation in human RPE cells. Therefore, ARPE-19 cells were primed with IL-1α and exposed to the mitochondrial electron transport chain complex III inhibitor, antimycin A. We found that antimycin A-induced mitochondrial dysfunction caused caspase-1-dependent inflammasome activation and subsequent production of mature IL-1β and IL-18 in human RPE cells. AIM2 and NLRP3 appeared to be the responsible inflammasome receptors upon antimycin A-induced mitochondrial damage. We aimed at verifying our findings using hESC-RPE cells but antimycin A was absorbed by melanin. Therefore, results were repeated on D407 RPE cell cultures. Antimycin A-induced mitochondrial and NADPH oxidase-dependent ROS production occurred upstream of inflammasome activation, whereas K⁺ efflux was not required for inflammasome activation in antimycin A-treated human RPE cells. Collectively, our data emphasize that dysfunctional mitochondria regulate the assembly of inflammasome multiprotein complexes in the human RPE cells. The present study associates AIM2 with the pathogenesis of AMD.

Expression and Cell Type-specific Localization of Inflammasome Sensors in the Spinal Cord of SOD1(G93A) Mice and Sporadic Amyotrophic lateral sclerosis Patients

Inflammasomes are key components of the innate immune system and activation of these multiprotein platforms is a crucial event in the etiopathology of amyotrophic lateral sclerosis (ALS). Inflammasomes consist of a pattern recognition receptor (PRR), the adaptor protein apoptosis-associated speck-like protein containing a CARD (ASC) and caspase 1. Exogenous or endogenous "danger signals" can trigger inflammasome assembly and promote maturation and release of pro-inflammatory cytokines, including interleukin 1β. Previous studies have demonstrated presence and activation of NLRP3 in spinal cord tissue from SOD1^(G93A) mice and human sporadic ALS (sALS) patients. However, regulation and cell type-specific localization of other well-known PRRs has not yet been analysed in ALS. Here, we explored gene expression, protein concentration and cell type-specific localization of the NLRP1, NLRC4 and AIM2 inflammasomes in spinal cord samples from SOD1^(G93A) mice and sALS patients. Transcription levels of NLRP1 and NLRC4, but not AIM2, were elevated in symptomatic SOD1^(G93A) animals. Immunoblotting revealed elevated protein levels of NLRC4, which were significantly increased in sALS vs. control patients. Immunofluorescence studies revealed neuronal labelling of all investigated PRRs. Staining of AIM2 was detected in all types of glia, whereas glial type-specific labelling was observed for NLRP1 and NLRC4. Our findings revealed pathology-related and cell type-specific differences in the expression of subsets of PRRs. Besides NLRP3, NLRC4 appears to be linked more closely to ALS pathogenesis.

Mitochondrial DNA: A Key Regulator of Anti-Microbial Innate Immunity

During the last few years, mitochondrial DNA has attained much attention as a modulator of immune responses. Due to common evolutionary origin, mitochondrial DNA shares various characteristic features with DNA of bacteria, as it consists of a remarkable number of unmethylated DNA as 2′-deoxyribose cytidine-phosphate-guanosine (CpG) islands. Due to this particular feature, mitochondrial DNA seems to be recognized as a pathogen-associated molecular pattern by the innate immune system. Under the normal physiological situation, mitochondrial DNA is enclosed in the double membrane structure of mitochondria. However, upon pathological conditions, it is usually released into the cytoplasm. Growing evidence suggests that this cytosolic mitochondrial DNA induces various innate immune signaling pathways involving NLRP3, toll-like receptor 9, and stimulator of interferon genes (STING) signaling, which participate in triggering downstream cascade and stimulating to produce effector molecules. Mitochondrial DNA is responsible for inflammatory diseases after stress and cellular damage. In addition, it is also involved in the anti-viral and anti-bacterial innate immunity. Thus, instead of entire mitochondrial importance in cellular metabolism and energy production, mitochondrial DNA seems to be essential in triggering innate anti-microbial immunity. Here, we describe existing knowledge on the involvement of mitochondrial DNA in the anti-microbial immunity by modulating the various immune signaling pathways.

Bee venom attenuates Porphyromonas gingivalis and RANKL-induced bone resorption with osteoclastogenic differentiation

Porphyromonas gingivalis (P. gingivalis) is one of the major periodontal pathogens leading to inflammation and alveolar bone resorption. Bone resorption is induced by osteoclasts, which are multinucleated giant cells. Osteoclastic bone resorption is mediated by enhanced receptor activator of nuclear factor-kappa B ligand (RANKL) signaling. Therefore, the down-regulation of RANKL downstream signals is regarded as an effective therapeutic target in the treatment of bone loss-associated disorders. The aim of this study was to evaluate whether purified bee venom (BV) could attenuate P. gingivalis-induced inflammatory periodontitis and RANKL-induced osteoclast differentiation. Inflammatory periodontitis induced by P. gingivalis increased alveolar bone resorption and increased expression of TNF-α and IL-1β, while BV treatment resulted in decreased bone loss and pro-inflammatory cytokines. Similarly, RANKL-induced multinucleated osteoclast differentiation and osteoclast-specific gene expression, such as nuclear factor of activated T cells 1 (NFATc1), cathepsin K, tartrate-resistant acid phosphatase (TRAP), and integrin αvβ3 were significantly suppressed by treatment with BV. We show that BV reduces P. gingivalis-induced inflammatory bone loss-related periodontitis in vivo and RANKL-induced osteoclast differentiation, activation, and function in vitro. These results suggest that BV exerts positive effects on inflammatory periodontitis associated osteoclastogenesis.

Immune modulation of liver sinusoidal endothelial cells by melittin nanoparticles suppresses liver metastasis

Liver sinusoidal endothelial cells (LSECs) are responsible for the immunologic tolerance of liver which is a common site for visceral metastases, suggesting its potential role as an target for cancer immunotherapy. However, targeted modulation of LSECs is still not achieved thus far. Here, we report LSECs are specifically targeted and modulated by melittin nanoparticles (α-melittin-NPs). Intravital imaging shows that LSECs fluoresce within 20 s after intravenous injection of α-melittin-NPs. α-melittin-NPs trigger the activation of LSECs and lead to dramatic changes of cytokine/chemokine milieu in the liver, which switches the hepatic immunologic environment to the activated state. As a result, α-melittin-NPs resist the formation of metastatic lesions with high efficiency. More strikingly, the survival rate reaches 80% in the spontaneous liver metastatic tumor model. Our research provides support for the use of α-melittin-NPs to break LSEC-mediated immunologic tolerance, which opens an avenue to control liver metastasis through the immunomodulation of LSECs.

Liver sinusoidal endothelial cells are known to promote immune tolerance in liver. Here, the authors target these cells using melittin nanoparticles and show alterations in the liver immune environment and suppression of liver metastases.

Interleukin 1-β, interleukin-1 receptor antagonist and vitamin D levels in children with atopic dermatitis

Introduction

Among the broad spectrum of cytokines, interleukin 1-β (IL-1β) has been implicated in induction and subsequent aggravation of skin lesions in atopic dermatitis (AD). A considerable body of evidence suggests that vitamin D status also influences the risk and/or severity of AD.

Material and methods

Fifty-seven children suffering from mild to severe AD were enrolled in the study. The control group consisted of 33 matched healthy children. In all the children serum concentrations of IL-1β/IL-1F2 and the interleukin-1 receptor antagonist IL-Ra/1F3 were measured. Serum 25(OH)D concentration was obtained for 49 patients with AD and all healthy children.

Results

In children with AD 59.2% of children had insufficiency, 24.5% had deficiency and 16.3% had a sufficient serum 25(OH)D level. In the control group 26.5%, 52.9% and 20% of participants had insufficiency/deficiency/sufficiency of 25(OH)D, respectively. The severity of AD was positively correlated with total IgE level, percentage and absolute count of eosinophils and IL-1Ra. IL-1β correlated with IL-1Ra.

Conclusions

In children with AD the serum vitamin D level was lower than in healthy children. The correlation between severity of AD and IL-1Ra may prove that inflammasome-dependent IL-1β is involved in immunopathogenesis of the disease. Further studies are needed on a larger population of children to confirm the role of this cytokine in development of AD.

Therapeutic effects of bee venom on experimental atopic dermatitis

Atopic dermatitis (AD) is a chronic skin inflammatory disease characterized by recurrent eczema and itching. It is caused by a poorly controlled immune response and damage to the skin barrier. Purified bee venom (BV) is a natural toxin produced by honeybees (Apis mellifera L.), and is well known for its anti-inflammatory, analgesic and anti-cancer effects against various types of disease. However, treatment strategies based on anti-inflammatory properties have not been adequately studied in AD. Thus, the present study examined the progression of AD-like skin lesions induced by ovalbumin (OVA) and the mechanism of action of BV. BV, administered by intraperitoneal inoculation, was observed to reduce the symptoms of AD, in addition to the serum immunoglobulin E levels, according to dorsal skin thickness and histopathologic analysis. The treatment also inhibited the infiltration of eosinophils and mast cells. These results suggested that it is possible to develop novel AD alternative therapy using BV by effectively suppressing allergic skin inflammation in AD.

Antimicrobial Peptides and Their Therapeutic Potential for Bacterial Skin Infections and Wounds

Alarming data about increasing resistance to conventional antibiotics are reported, while at the same time the development of new antibiotics is stagnating. Skin and soft tissue infections (SSTIs) are mainly caused by the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) which belong to the most recalcitrant bacteria and are resistant to almost all common antibiotics. S. aureus and P. aeruginosa are the most frequent pathogens isolated from chronic wounds and increasing resistance to topical antibiotics has become a major issue. Therefore, new treatment options are urgently needed. In recent years, research focused on the development of synthetic antimicrobial peptides (AMPs) with lower toxicity and improved activity compared to their endogenous counterparts. AMPs appear to be promising therapeutic options for the treatment of SSTIs and wounds as they show a broad spectrum of antimicrobial activity, low resistance rates and display pivotal immunomodulatory as well as wound healing promoting activities such as induction of cell migration and proliferation and angiogenesis. In this review, we evaluate the potential of AMPs for the treatment of bacterial SSTIs and wounds and provide an overview of the mechanisms of actions of AMPs that contribute to combat skin infections and to improve wound healing. Bacteria growing in biofilms are more resistant to conventional antibiotics than their planktonic counterparts due to limited biofilm penetration and distinct metabolic and physiological functions, and often result in chronification of infections and wounds. Thus, we further discuss the feasibility of AMPs as anti-biofilm agents. Finally, we highlight perspectives for future therapies and which issues remain to bring AMPs successfully to the market.

Mitochondrial DNA as an inflammatory mediator in cardiovascular diseases

Mitochondria play a central role in multiple cellular functions, including energy production, calcium homeostasis, and cell death. Currently, growing evidence indicates the vital roles of mitochondria in triggering and maintaining inflammation. Chronic inflammation without microbial infection — termed sterile inflammation — is strongly involved in the development of heart failure. Sterile inflammation is triggered by the activation of pattern recognition receptors (PRRs) that sense endogenous ligands called damage-associated molecular patterns (DAMPs). Mitochondria release multiple DAMPs including mitochondrial DNA, peptides, and lipids, which induce inflammation via the stimulation of multiple PRRs. Among the mitochondrial DAMPs, mitochondrial DNA (mtDNA) is currently highlighted as the DAMP that mediates the activation of multiple PRRs, including Toll-like receptor 9, Nod-like receptors, and cyclic GMP–AMP synthetase/stimulator of interferon gene pathways. These PRR signalling pathways, in turn, lead to the activation of nuclear factor-κB and interferon regulatory factor, which enhances the transcriptional activity of inflammatory cytokines and interferons, and induces the recruitment of inflammatory cells. As the heart is an organ comprising abundant mitochondria for its ATP consumption (needed to maintain constant cyclic contraction and relaxation), the generation of massive amounts of mitochondrial radical oxygen species and mitochondrial DAMPs are predicted to occur and promote cardiac inflammation. Here, we will focus on the role of mtDNA in cardiac inflammation and review the mechanism and pathological significance of mtDNA-induced inflammatory responses in cardiac diseases.

The p38 Mitogen-Activated Protein Kinase Critically Regulates Human Keratinocyte Inflammasome Activation

Inflammasomes are key intracellular signaling platforms involved in innate immune responses to micro-organisms and danger signals. Extracellular signal-regulated kinase, Jun N-terminal kinase, and p38 mitogen-activated protein kinase family members are activated by numerous environmental stresses. Recently, it has been reported that Jun N-terminal kinase is involved in inflammasome activation in myeloid immune cells. To date, the role of mitogen-activated protein kinase in inflammasome activity in keratinocytes has not been investigated. Here, we show that, in primary human keratinocytes, p38 mitogen-activated protein kinase is required for inflammasome activation and IL-1β secretion. Using selective small molecule inhibitors, small interfering RNA gene silencing, and CRISPR/Cas9-based deletion, we demonstrate the above and identify p38α and p38δ as critical regulators of ASC oligomerization, inflammasome activation, and IL-1β secretion in keratinocytes. Furthermore, our data suggest that the nature of the mitogen-activated protein kinase regulating inflammasome activity exhibits a certain cell specificity, with p38 playing a predominant role in keratinocytes and Jun N-terminal kinase 1 in cells of myeloid origin.

Advances in the understanding of mitochondrial DNA as a pathogenic factor in inflammatory diseases

Mitochondrial DNA (mtDNA) has many similarities with bacterial DNA because of their shared common ancestry. Increasing evidence demonstrates mtDNA to be a potent danger signal that is recognised by the innate immune system and can directly modulate the inflammatory response. In humans, elevated circulating mtDNA is found in conditions with significant tissue injury such as trauma and sepsis and increasingly in chronic organ-specific and systemic illnesses such as steatohepatitis and systemic lupus erythematosus. In this review, we examine our current understanding of mtDNA-mediated inflammation and how the mechanisms regulating mitochondrial homeostasis and mtDNA release represent exciting and previously under-recognised important factors in many human inflammatory diseases, offering many new translational opportunities.

Bee Venom Inhibits Porphyromonas gingivalis Lipopolysaccharides-Induced Pro-Inflammatory Cytokines through Suppression of NF-κB and AP-1 Signaling Pathways

Periodontitis is a chronic inflammatory disease that leads to destruction of tooth supporting tissues. Porphyromonas gingivalis (P. gingivalis), especially its lipopolysaccharides (LPS), is one of major pathogens that cause periodontitis. Bee venom (BV) has been widely used as a traditional medicine for various diseases. Previous studies have demonstrated the anti-inflammatory, anti-bacterial effects of BV. However, a direct role and cellular mechanism of BV on periodontitis-like human keratinocytes have not been explored. Therefore, we investigated the anti-inflammatory mechanism of BV against P. gingivalis LPS (PgLPS)-induced HaCaT human keratinocyte cell line. The anti-inflammatory effect of BV was demonstrated by various molecular biological methods. The results showed that PgLPS increased the expression of Toll-like receptor (TLR)-4 and pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-8, and interferon (IFN)-γ. In addition, PgLPS induced activation of the signaling pathways of inflammatory cytokines-related transcription factors, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and activator protein 1 (AP-1). BV effectively inhibited those pro-inflammatory cytokines through suppression of NF-κB and AP-1 signaling pathways. These results suggest that administration of BV attenuates PgLPS-induced inflammatory responses. Furthermore, BV may be a useful treatment to anti-inflammatory therapy for periodontitis.

Immune Activation in the Liver by Nucleic Acids

Viral infection in the liver, including hepatitis B virus (HBV) and hepatitis C virus (HCV) infection, is a major health problem worldwide, especially in developing countries. The infection triggers a pro-inflammatory response in patients that is crucial for host defense. Recent studies have identified multiple transmembrane and cytosolic receptors that recognize pathogen-derived nucleic acids, and these receptors are essential for driving immune activation in the liver. In addition to sensing DNA/RNA from pathogens, these intracellular receptors can be activated by nucleic acids of host origin in response to sterile injuries. In this review, we discuss the expanding roles of these receptors in both immune and nonimmune cells in the liver.

Opposing roles of LTB4 and PGE2 in regulating the inflammasome-dependent scorpion venom-induced mortality

Tityus serrulatus sting causes thousands of deaths annually worldwide. T. serrulatus-envenomed victims exhibit local or systemic reaction that culminates in pulmonary oedema, potentially leading to death. However, the molecular mechanisms underlying T. serrulatus venom (TsV) activity remain unknown. Here we show that TsV triggers NLRP3 inflammasome activation via K(+) efflux. Mechanistically, TsV triggers lung-resident cells to release PGE2, which induces IL-1β production via E prostanoid receptor 2/4-cAMP-PKA-NFκB-dependent mechanisms. IL-1β/IL-1R actions account for oedema and neutrophil recruitment to the lungs, leading to TsV-induced mortality. Inflammasome activation triggers LTB4 production and further PGE2 via IL-1β/IL-1R signalling. Activation of LTB4-BLT1/2 pathway decreases cAMP generation, controlling TsV-induced inflammation. Exogenous administration confirms LTB4 anti-inflammatory activity and abrogates TsV-induced mortality. These results suggest that the balance between LTB4 and PGE2 determines the amount of IL-1β inflammasome-dependent release and the outcome of envenomation. We suggest COX1/2 inhibition as an effective therapeutic intervention for scorpion envenomation.

Elevated caspase‑1 activity and IL‑1β expression are associated with the IPAF inflammasome in an experimental model of allergy

Previous studies have indicated that interleukin (IL)‑1β has an important role in the development of allergic diseases. Therefore, the present study aimed to investigate the upstream pathway underlying IL‑1β production in an experimental model of allergy. BALB/c mice (female, 6‑8 weeks old) were sensitized to recombinant (r)Che a 2 by intraperitoneal injection of rChe a 2 adsorbed onto an alum gel suspension on days 0, 7, 14 and 21. In the control group, mice received an injection of 20 mM phosphate‑buffered saline absorbed onto alum via the same route. The allergic status of the mice was confirmed serologically by measuring allergen‑specific immunoglobulin (Ig)E levels. The protein expression levels of IL‑1β and the mRNA expression levels of inflammasome compartments were measured by enzyme‑linked immunosorbent assay and semi‑quantitative reverse transcription polymerase chain reaction, respectively. In addition, caspase‑1 activity was determined by fluorometric assay. Sensitized mice exhibited significantly increased levels of specific IgE (P<0.05). IL‑1β production and caspase‑1 activity were significantly higher in the sensitized mice compared with the control group. In addition, no significant differences were observed between the control and sensitized mice in the expression of genes associated with the inflammasome, including NLR family, pyrin domain containing 3; apoptosis‑associated speck‑like protein; and NLR family, apoptosis inhibitory protein 5. However, IL‑1β converting enzyme protease‑activating factor (IPAF) expression was significantly increased in sensitized mice compared with in the control group (P<0.05). These data indicate that caspase‑1 activation and IL‑1β expression are associated with the IPAF inflammasome. Therefore, based on this association, the IPAF inflammasome may be considered for IL‑1β production in the experimental model of allergy.

Is the inflammasome relevant for epithelial cell function?

Inflammasomes are intracellular protein complexes that sense microbial components and damage of infected cells. Following activation by molecules released by pathogens or injured cells, inflammasomes activate caspase-1, allowing secretion of the pro-inflammatory cytokines IL-1β and IL-18 from innate immune cells. Inflammasomes are also expressed in epithelial cells, where their function has attracted less attention. Nonetheless, depending on the tissue, epithelial inflammasomes can mediate inflammation, wound healing, and pain sensitivity. We review here recent findings on inflammasomes found in epithelial tissues, highlighting the importance of these protein complexes in the response of epithelial tissues to microbial infections.

Cationic membrane-active peptides - anticancer and antifungal activity as well as penetration into human skin

Cationic antimicrobial peptides are ancient natural broad-spectrum antibiotics, and several compounds also exhibit anticancer activity. However, most applications pertain to bacterial infections, and treatment for skin cancer is less frequently considered. The cytotoxicity of melittin, cecropin A, protegrin-1 and histatin 5 against squamous skin cancer cell lines and normal human keratinocytes was evaluated and compared to established drugs. The results show that melittin clearly outperforms 5-fluorouracil regarding antitumor activity. Importantly, combined melittin and 5-fluorouracil enhanced cytotoxic effects on cancer cells and reduced toxicity on normal keratinocytes. Additionally, minimum inhibitory concentrations indicate that melittin also shows superior activity against clinical and laboratory strains of Candida albicans compared to amphotericin B. To evaluate its potential for topical applications, human skin penetration of melittin was investigated ex vivo and compared to two non-toxic cell-penetrating peptides (CPPs), low molecular weight protamine (LMWP) and penetratin. The stratum corneum prevents penetration into viable epidermis over 6 h; however, the peptides gain access to the viable skin after 24 h. Inhibition of digestive enzymes during skin penetration significantly enhances the availability of intact peptide. In conclusion, melittin may represent an innovative agent for non-melanoma skin cancer and infectious skin diseases. In order to develop a drug candidate, skin absorption and proteolytic digestion by skin enzymes need to be addressed.

Update on skin allergy

Skin diseases with an allergic background such as atopic dermatitis, allergic contact dermatitis, and urticaria are very common. Moreover, diseases arising from a dysfunction of immune cells and/or their products often manifest with skin symptoms. This review aims to summarize recently published articles in order to highlight novel research findings, clinical trial results, and current guidelines on disease management. In recent years, an immense progress has been made in understanding the link between skin barrier dysfunction and allergic sensitization initiating the atopic march. In consequence, new strategies for treatment and prevention have been developed. Novel pathogenic insights, for example, into urticaria, angioedema, mastocytosis, led to the development of new therapeutic approaches and their implementation in daily patient care. By understanding distinct pathomechanisms, for example, the role of IL-1, novel entities such as autoinflammatory diseases have been described. Considerable effort has been made to improve and harmonize patient management as documented in several guidelines and position papers.

Inflammasomes

Inflammasomes are large cytosolic multiprotein complexes that assemble in response to detection of infection- or stress-associated stimuli and lead to the activation of caspase-1-mediated inflammatory responses, including cleavage and unconventional secretion of the leaderless proinflammatory cytokines IL-1β and IL-18, and initiation of an inflammatory form of cell death referred to as pyroptosis. Inflammasome activation can be induced by a wide variety of microbial pathogens and generally mediates host defense through activation of rapid inflammatory responses and restriction of pathogen replication. In addition to its role in defense against pathogens, recent studies have suggested that the inflammasome is also a critical regulator of the commensal microbiota in the intestine. Finally, inflammasomes have been widely implicated in the development and progression of various chronic diseases, such as gout, atherosclerosis, and metabolic syndrome. In this perspective, we discuss the role of inflammasomes in infectious and noninfectious inflammation and highlight areas of interest for future studies of inflammasomes in host defense and chronic disease.

Protective effect of melittin against inflammation and apoptosis on Propionibacterium acnes-induced human THP-1 monocytic cell

Melittin is a cationic, hemolytic peptide that is the main toxic component in the venom of the honey bee (Apis mellifera). It has been used in treatment of various chronic inflammatory diseases. However, the cellular mechanism and the anti-apoptotic effect of melittin in Propionibactierium acnes (P. acnes)-induced THP-1 cells have not been explored. In the present study, we investigated the anti-inflammatory and anti-apoptotic mechanism by examining the effect of melittin on P. acnes-induced THP-1 monocytic cells. THP-1 monocytic cells were stimulated by heat-killed P. acnes in the presence of melittin. The expression levels of pro-inflammatory cytokines, NF-κB signaling, caspase family, and PARP signaling were measured by ELISA or Western blot analysis. The number of apoptotic cells and changes of cell morphology were examined using fluorescence microscopy and flow cytometry. Heat-killed P. acnes increased the secretion of pro-inflammatory cytokines and cleavage of caspase-3 and -8 in heat-killed P. acnes-induced THP-1 cells. However, treatment with melittin inhibited the pro-inflammatory cytokines and cleavage of the caspase-3 and -8. Moreover, the cleaved PARP appeared after 8h of heat-killed P. acnes treatment and its cleavage was reduced by melittin treatment. These results demonstrate that 1.0×10(7) CFU/ml of heat-killed P. acnes induces THP-1 cell apoptosis and secretion of inflammatory cytokines. Also, administration of melittin significantly decreases the expression of various inflammatory cytokines in heat-killed P. acnes-treated THP-1 monocytic cells. In particular, melittin exerts anti-apoptotic effects against 1.0×10(7) CFU/ml of heat-killed P. acnes injury to THP-1 cells.

The inflammasomes in autoinflammatory diseases with skin involvement

During the past years, significant progress in the understanding of the complexity, regulation, and relevance of innate immune responses underlying several inflammatory conditions with neutrophilic skin involvement has been made. These diseases belong to the novel class of autoinflammatory diseases, and several are caused by mutations in genes regulating the function of innate immune complexes, termed inflammasomes, leading to enhanced secretion of the proinflammatory cytokine IL-1β. Consequently, targeting of IL-1β has proven successful in the treatment of these diseases, and the identification of related pathogenic mechanisms in other more common skin diseases characterized by autoinflammation and neutrophilic tissue damage also provides extended opportunities for therapy by interfering with IL-1 signaling.

Role of the inflammasome in defense against venoms

Venoms consist of a complex mixture of toxic components that are used by a variety of animal species for defense and predation. Envenomation of mammalian species leads to an acute inflammatory response and can lead to the development of IgE-dependent venom allergy. However, the mechanisms by which the innate immune system detects envenomation and initiates inflammatory and allergic responses to venoms remain largely unknown. Here we show that bee venom is detected by the NOD-like receptor family, pyrin domain-containing 3 inflammasome and can trigger activation of caspase-1 and the subsequent processing and unconventional secretion of the leaderless proinflammatory cytokine IL-1β in macrophages. Whereas activation of the inflammasome by bee venom induces a caspase-1-dependent inflammatory response, characterized by recruitment of neutrophils to the site or envenomation, the inflammasome is dispensable for the allergic response to bee venom. Finally, we find that caspase-1-deficient mice are more susceptible to the noxious effects of bee and snake venoms, suggesting that a caspase-1-dependent immune response can protect against the damaging effects of envenomation.

Specific inflammasomes in complex diseases

Blocking the cytokines Interleukin-1beta (IL-1β) and Interleukin-18 (IL-18) benefits a diverse range of inflammatory pathologies. In each of these diseases, different cytoplasmic innate immune receptors nucleate individual protein complexes known as inflammasomes, to regulate the production of active IL-1β or IL-18. This review will outline the complex diseases where these cytokines are pathogenic, and explain which inflammasome(s) may be responsible. For example, inflammasomes nucleated by NLRP3 and NLRP6 integrate signals from metabolic and commensal systems contributing to metabolic dysfunction and type 2 diabetes. On the other hand, NLRP1 and AIM2 are more broadly implicated in autoimmunity and allergy. Furthermore, each inflammasome has unique roles in pathogen recognition, which may determine the outcome of polymicrobial infection and link different infectious co-morbidities to chronic inflammatory disease. We can now imagine a time when targeted inflammasome inhibitors will be employed in the clinic, tailoring treatments to particular diseases, and perhaps individual patients.