TLR3 mediates release of IL-1β and cell death in keratinocytes in a caspase-4 dependent manner

NETs contribute to psoriasiform skin inflammation: A novel therapeutic approach targeting IL-36 cytokines by a small molecule tetrahydroxystilbene glucoside

BACKGROUND

Psoriasis, a chronic immune-mediated skin disease with pathological features such as aberrant differentiation of keratinocytes, dermal-epidermal inflammation, and angiogenesis. 2,3,5,4'-Tetrahydroxy stilbene 2-Ο-β-d-glucoside (2354Glu) is a natural small molecule polyhydrostilbenes isolated from Polygonum multiglorum Thunb. The regulation of IL-36 subfamily has led to new pharmacologic strategies to reverse psoriasiform dermatitis.

PURPOSE

Here we investigated the therapeutic potential of 2354Glu and elucidated the underlying mechanism in psoriasis.

METHODS

The effects of 2354Glu on IL-36 signaling were assessed by psoriasiform in vivo, in vitro and ex vivo model. The in vivo mice model of psoriasis-like skin inflammation was established by applying imiquimod (IMQ), and the in vitro and ex vitro models were established by stimulating mouse primary keratinocyte, human keratinocytes cells (HaCaT) and ex vivo skin tissue isolated from the mice back with Polyinosine-polycytidylic acid (Poly(I:C)), IMQ, IL-36γ and Lipopolysaccharide (LPS) respectively. Moreover, NETs formation was inhibited by Cl-amidine to evaluate the effect of NETs in psoriatic mouse model. The effects of 2354Glu on skin inflammation were assessed by western blot, H&E, immunohistochemistry, immunofluorescence, enzyme-linked immunosorbent assay and real-time quantitative PCR.

RESULTS

In Poly(I:C)-stimulated keratinocytes, the secretion of IL-36 was inhibited after treatment with 2354Glu, similar to the effects of TLR3, P2X7R and caspase-1 inhibitors. In aldara (imiquimod)-induced mice, 2354Glu (100 and 25 mg/kg) improved immune cell infiltration and hyperkeratosis in psoriasis by directly targeting IL-36 in keratinocytes through P2X7R-caspase-1. When treatment with 2354Glu (25 mg/kg) was insufficient to inhibit IL-36γ, NETs reduced pathological features and IL-36 signaling by interacting with keratinocytes to combat psoriasis like inflammation.

CONCLUSION

These results indicated that NETs had a beneficial effect on psoriasiform dermatitis. 2354Glu alleviates psoriasis by directly targeting IL-36/P2X7R axis and NET formation, providing a potential candidate for the treatment of psoriasis.

Mechanistic Investigation of WWOX Function in NF-kB-Induced Skin Inflammation in Psoriasis

Psoriasis is a chronic inflammatory skin disease characterized by epidermal hyperproliferation, aberrant differentiation of keratinocytes, and dysregulated immune responses. WW domain-containing oxidoreductase (WWOX) is a non-classical tumor suppressor gene that regulates multiple cellular processes, including proliferation, apoptosis, and migration. This study aimed to explore the possible role of WWOX in the pathogenesis of psoriasis. Immunohistochemical analysis showed that the expression of WWOX was increased in epidermal keratinocytes of both human psoriatic lesions and imiquimod-induced mice psoriatic model. Immortalized human epidermal keratinocytes were transduced with a recombinant adenovirus expressing microRNA specific for WWOX to downregulate its expression. Inflammatory responses were detected using Western blotting, real-time quantitative reverse transcription polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay. In human epidermal keratinocytes, WWOX knockdown reduced nuclear factor-kappa B signaling and levels of proinflammatory cytokines induced by polyinosinic: polycytidylic acid [(poly(I:C)] in vitro. Furthermore, calcium chelator and protein kinase C (PKC) inhibitors significantly reduced poly(I:C)-induced inflammatory reactions. WWOX plays a role in the inflammatory reaction of epidermal keratinocytes by regulating calcium and PKC signaling. Targeting WWOX could be a novel therapeutic approach for psoriasis in the future.

Type-2 epithelial-mesenchymal transition in oral mucosal nonneoplastic diseases

The oral mucosa is a membranous structure comprising epithelial and connective tissue that covers the oral cavity. The oral mucosa is the first immune barrier to protect the body against pathogens for systemic protection. It is frequently exposed to mechanical abrasion, chemical erosion, and pathogenic invasion, resulting in oral mucosal lesions, particularly inflammatory diseases. Epithelial-mesenchymal transition (EMT) is a crucial biological process in the pathogenesis of oral mucosal disorders, which are classified into three types (types 1, 2, and 3) based on their physiological consequences. Among these, type-2 EMT is crucial in wound repair, organ fibrosis, and tissue regeneration. It causes infectious and dis-infectious immunological diseases, such as oral lichen planus (OLP), oral leukoplakia, oral submucosal fibrosis, and other precancerous lesions. However, the mechanism and cognition between type-2 EMT and oral mucosal inflammatory disorders remain unknown. This review first provides a comprehensive evaluation of type-2 EMT in chronically inflammatory oral mucosal disorders. The aim is to lay a foundation for future research and suggest potential treatments.

Skin models for cutaneous melioidosis reveal Burkholderia infection dynamics at wound's edge with inflammasome activation, keratinocyte extrusion and epidermal detachment

Melioidosis is a serious infectious disease endemic in Southeast Asia, Northern Australia and has been increasingly reported in other tropical and subtropical regions in the world. Percutaneous inoculation through cuts and wounds on the skin is one of the major modes of natural transmission. Despite cuts in skin being a major route of entry, very little is known about how the causative bacterium Burkholderia pseudomallei initiates an infection at the skin and the disease manifestation at the skin known as cutaneous melioidosis. One key issue is the lack of suitable and relevant infection models. Employing an in vitro 2D keratinocyte cell culture, a 3D skin equivalent fibroblast-keratinocyte co-culture and ex vivo organ culture from human skin, we developed infection models utilizing surrogate model organism Burkholderia thailandensis to investigate Burkholderia-skin interactions. Collectively, these models show that the bacterial infection was largely limited at the wound’s edge. Infection impedes wound closure, triggers inflammasome activation and cellular extrusion in the keratinocytes as a potential way to control bacterial infectious load at the skin. However, extensive infection over time could result in the epidermal layer being sloughed off, potentially contributing to formation of skin lesions.

Ellagitannins from Rosa roxburghii suppress poly(I:C)-induced IL-8 production in human keratinocytes

The anti-inflammatory effects of a 50% aqueous extract of Rosa roxburghii fruit (RRFE) and two ellagitannins (strictinin and casuarictin) isolated from the RRFE were evaluated in a cell model of skin inflammation induced by self-RNA released from epidermal cells damaged by UV ray (UVR) irradiation. The RRFE inhibited interleukin-8 (IL-8) mRNA expression in normal human epidermal keratinocytes (NHEKs) stimulated with polyinosinic:polycytidylic acid (poly(I:C)), a ligand of toll-like receptor-3 (TLR-3). The plant-derived anti-inflammatory agents, dipotassium glycyrrhizinate (GK2) and allantoin, had no influence on the IL-8 expression. The purified compounds, strictinin and casuarictin, inhibited the IL-8 mRNA expression and IL-8 release induced in NHEKs by poly(I:C). These ellagitannins were thus found to be responsible for the biological activity exhibited by the RRFE. This study demonstrates that RRFE and isolated RRFE compounds show promise as ingredients for products formulated to improve skin disorders induced by UVR irradiation.

Research progress of keratinocyte-programmed cell death in UV-induced Skin photodamage

Programmed cell death (PCD) is a basic component of life and an important terminal path for cells. A variety of biological events are associated with PCD, including the conservation of tissue homeostasis and removal of harmful cells. Overexposure of the skin to UV radiation causes skin photodamage. Keratinocytes are the first line of defence against ultraviolet radiation. During UV radiation, the keratinocyte can undergo four modes of PCD: apoptosis, pyroptosis, necroptosis and autophagy. The molecular mechanisms of these four modes of PCD have been widely studied as potential therapeutic targets for the prevention of UV-induced skin inflammation, ageing and skin cancer. In this review, we summarize the role of keratinocyte PCD in the pathogenesis of UV-induced skin photodamage. This article will provide new research directions for the design of intervention strategies for the treatment and prevention of skin photodamage.

miR-19a/b and miR-20a Promote Wound Healing by Regulating the Inflammatory Response of Keratinocytes

Persistent and impaired inflammation impedes tissue healing and is a characteristic of chronic wounds. A better understanding of the mechanisms controlling wound inflammation is needed. In this study, we show that in human wound-edge keratinocytes, the expressions of microRNA (miR)-17, miR-18a, miR-19a, miR-19b, and miR-20a, which all belong to the miR-17∼92 cluster, are upregulated during wound repair. However, their levels are lower in chronic ulcers than in acute wounds at the proliferative phase. Conditional knockout of miR-17∼92 in keratinocytes as well as injection of miR-19a/b and miR-20a antisense inhibitors into wound edges enhanced inflammation and delayed wound closure in mice. In contrast, conditional overexpression of the miR-17∼92 cluster or miR-19b alone in mice keratinocytes accelerated wound closure in vivo. Mechanistically, miR-19a/b and miR-20a decreased TLR3-mediated NF-κB activation by targeting SHCBP1 and SEMA7A, respectively, reducing the production of inflammatory chemokines and cytokines by keratinocytes. Thus, miR-19a/b and miR-20a being crucial regulators of wound inflammation, the lack thereof may contribute to sustained inflammation and impaired healing in chronic wounds. In line with this, we show that a combinatory treatment with miR-19b and miR-20a improved wound healing in a mouse model of type 2 diabetes.

Autophagy Suppresses Toll-Like Receptor 3-Mediated Inflammatory Reaction in Human Epidermal Keratinocytes

Autophagy, one mechanism of programmed cell death, is fundamental to cellular homeostasis. Previous studies have identified autophagy as a novel mechanism by which cytokines control the immune response. However, its precise role in immune-related inflammatory skin diseases such as psoriasis remains unclear. Thus, this study explored the functional role of autophagy in psoriatic inflammation of epidermal keratinocytes. Strong light chain 3 immunoreactivity was observed in epidermal keratinocytes of both human psoriatic lesions and imiquimod-induced mice psoriatic model, and it was readily induced by polycytidylic acid (poly (I:C)), which stimulates Toll-like receptor 3 (TLR3), in human epidermal keratinocytes in vitro. Rapamycin-induced activation of autophagy significantly reduced poly (I:C)-induced inflammatory reaction, whereas, inhibition of autophagy by 3-methyladeine increased that. Our results indicate that the induction of autophagy may attenuate TLR3-mediated immune responses in human epidermal keratinocytes, thus providing novel insights into the mechanisms underlying the development of inflammatory skin diseases including psoriasis.

Pyroptosis: The missing puzzle among innate and adaptive immunity crosstalk

Pyroptosis is a newly discovered programmed cell death with inflammasome formation. Pattern recognition receptors that identify repetitive motifs of prospective pathogens such as LPS of gram-negative bacteria are crucial to pyroptosis. Upon stimulation by pathogen-associated molecular patterns or damage-associated molecular patterns, proinflammatory cytokines, mainly IL-1 family members IL-1β and IL-18, are released through pyroptosis specific pore-forming protein, gasdermin D. Even though IL-1 family members are mainly involved in innate immunity, they can be factors in adaptive immunity. Given the importance of IL-1 family members in health and diseases, deciphering the role of pyroptosis in the regulation of innate and adaptive immunity is of great importance, especially with the recent progress in identifying the exact mechanism of such a pathway. In this review, we will focus on how the innate inflammatory mediators can regulate the adaptive immune system and vice versa via pyroptosis.

Juxtaposition of IL-1β and IFN-γ expression and apoptosis of keratinocytes in adult-onset Still's disease

Backgroud: Recently, atypical persistent skin eruptions (APSEs) have been documented as a new manifestation of adult-onset Still's disease (AOSD), with a unique pathological feature of necrotic keratinocytes in the upper third of the epidermis, but the mechanism has not been elucidated. The aim of this study was to explore the potential mechanism of the unique pathological phenomenon of APSEs.Methods: Clinical and pathological data from 26 AOSD patients with APSEs and 6 with evanescent skin eruptions (ESEs) were reviewed. Fourteen APSE biopsies and 6 ESE biopsies were selected for multi-spectrum immunohistochemistry with 5 disease controls and 5 healthy controls.Results: The unique pathological manifestation was present in all APSE patients but was hardly found in ESE patients. There were more CD4 + T-cells infiltrated in the dermis of APSEs than in the dermis of ESEs. IL-1β and IFN-γ were specifically expressed in the upper third of the epidermis and were juxtaposed to the loci of the necrotic keratinocytes.Conclusion: Our findings showed important cellular and molecular derangements related to the APSE-specific pathological phenomena and helped to understand the pathogenesis of dyskeratosis in the epidermis. The findings could also pave a way to explore an effective intervention to this potentially life-threatening disorder.

Inhibition of Poly(I:C)-Induced Inflammation by Salvianolic Acid A in Skin Keratinocytes

Background

Skin keratinocytes participate actively in inducing immune responses when external pathogens are introduced, thereby contributing to elimination of pathogens. However, in condition where the excessive inflammation is occurred, chronic skin disease such as psoriasis can be provoked.

Objective

We tried to screen the putative therapeutics for inflammatory skin disease, and found that salvianolic acid A (SAA) has an inhibitory effect on keratinocyte inflammatory reaction. The aim of this study is to demonstrate the effects of SAA in poly(I:C)-induced inflammatory reaction in skin keratinocytes.

Methods

We pre-treated keratinocytes with SAA then stimulated with poly(I:C). Inflammatory reaction of keratinocytes was verified using real-time polymerase chain reaction, enzyme-linked immunosorbent assay and Western blot.

Results

When skin keratinocytes were pre-treated with SAA, it significantly inhibited poly (I:C)-induced expression of inflammatory cytokines including interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor-α, and CCL20. SAA inhibited poly(I:C)-induced activation of nuclear factor-κB signaling. And SAA also inhibited inflammasome activation, evidenced by decrease of IL-1β secretion. Finally, SAA markedly inhibited poly(I:C)-induced NLRP3 expression.

Conclusion

These results demonstrate that SAA has an inhibitory effect on poly(I:C)-induced inflammatory reaction of keratinocytes, suggesting that SAA can be developed for the treatment of inflammatory skin diseases such as psoriasis.

IL-1 Receptor Antagonist Reduced Chemical-Induced Keratinocyte Apoptosis through Antagonism to IL-1α/IL-1β

Extracellular interleukin 1 alpha (IL-1α) released from keratinocytes is one of the endpoints for in vitro assessments of skin irritancy. Although cells dying via primary skin irritation undergo apoptosis as well as necrosis, IL-1α is not released in apoptotic cells. On the other hand, active secretion has been identified in interleukin-1 receptor antagonist (IL-1ra), which was discovered to be a common, upregulated, differentially-expressed gene in a microarray analysis performed with keratinocytes treated using cytotoxic doses of chemicals. This study examined whether and how IL-1ra, particularly extracellularly released IL-1ra, was involved in chemically-induced keratinocyte cytotoxicity and skin irritation. Primary cultured normal adult skin keratinocytes were treated with cytotoxic doses of chemicals (hydroquinone, retinoic acid, sodium lauryl sulfate, or urshiol) with or without recombinant IL-1ra treatment. Mouse skin was administered irritant concentrations of hydroquinone or retinoic acid. IL-1ra (mRNA and/or intracellular/extracellularly released protein) levels increased in the chemically treated cultured keratinocytes with IL-1α and IL-1β mRNAs and in the chemically exposed epidermis of the mouse skin. Recombinant IL-1ra treatment significantly reduced the chemically-induced apoptotic death and intracellular/extracellularly released IL-1α and IL-1β in keratinocytes. Collectively, extracellular IL-1ra released from keratinocytes could be a compensatory mechanism to reduce the chemically-induced keratinocyte apoptosis by antagonism to IL-1α and IL-1β, suggesting potential applications to predict skin irritation.

Caspase-4 activation by a bacterial surface protein is mediated by cathepsin G in human gingival fibroblasts

Caspase-4 is an inflammatory caspase; however, its mechanism of activation is poorly understood. In this study, we demonstrate that Td92, a surface protein of the periodontal pathogen Treponema denticola and a homolog of the Treponema pallidum surface protein Tp92, activates caspase-4 and induces pyroptosis in primary cultured human gingival fibroblasts (HGFs) via cathepsin G activation. Cathepsin G inhibition or siRNA knockdown of cathepsin G inhibited Td92-induced caspase-4 activation and cell death. Td92-induced cell death was significantly inhibited by siRNA knockdown of gasdermin D. Td92 treatment resulted in the binding of cathepsin G to caspase-4 and the coaggregation of these two molecules. In addition, Td92 induced IL-1α expression and secretion, and this was inhibited by caspase-4 knockdown. Cytochalasin D did not block Td92-induced caspase-4 activation, suggesting that Td92 internalization is not required for caspase-4 activation. Our results demonstrate that cathepsin G is directly engaged in caspase-4 activation by a bacterial ligand, which is responsible for cell death and IL-1α secretion in HGFs.

Apoptosis and Necroptosis as Host Defense Strategies to Prevent Viral Infection

Antiviral transcriptional responses and regulated cell death are crucial components of the host response to virus infection. However, in contrast to the signaling pathways that promote antiviral transcription, those that initiate cell death following virus infection are less understood. Several recent studies have identified pattern recognition receptors (PRRs) of the mammalian innate immune system that activate cell death pathways. These same receptors also have established roles in the induction of antiviral gene expression. In this review we discuss the mechanisms by which PRRs can serve dual roles as initiators of inflammatory gene expression and as inducers of apoptosis and necroptosis following virus infection.

Poly I:C induces collective migration of HaCaT keratinocytes via IL-8

Background

Delayed wound healing reduces the quality of life (QOL) of patients. Thus, understanding the mechanism of wound healing is indispensable for better management. However, the role of innate immunity in wound healing is thus far unknown. Recently the involvement of TLR3 in wound healing has been evaluated. The systemic administration of polyriboinosinic-polyribocytidylic acid (poly I:C ; a substitute for viral dsRNA and a ligand of toll-like receptor 3), enhances wound healing in vivo. The aim of this study is to improve our understanding of the link between innate immunity and human wound healing, particularly in re-epithelialization.

Results

The present study showed that poly I:C significantly accelerated collective HaCaT cell migration in a scratch assay. Poly I:C also increased IL-8 and bFGF production, and anti-IL-8 antibodies significantly inhibited the migration caused by poly I:C. Human recombinant IL-8 also accelerated collective HaCaT cell migration. An immunofluorescence assay and enzyme-linked immunosorbent assay (ELISA) also revealed that poly I:C decreased E-cadherin protein levels and increased vimentin protein levels, and anti-IL-8 antibody reversed this effect. In contrast, nucleic/cytosolic protein ratios of Snail 1 were unchanged in all tested conditions.

Conclusion

Our findings demonstrated that poly I:C accelerated collective HaCaT cell migration via autocrine/paracrine secretions of IL-8 and the subsequent incomplete epithelial-mesenchymal transition (EMT). Our findings provide a new strategy for wound healing by regulating innate immune systems in re-epithelialization.

Saturated fatty acids activate caspase-4/5 in human monocytes, triggering IL-1β and IL-18 release

Obesity is associated with metabolic tissue infiltration by monocyte-derived macrophages. Saturated fatty acids contribute to proinflammatory gene induction in tissue-embedded immune cells. However, it is unknown how circulating monocytes, the macrophage precursors, react to high-fat environments. In macrophages, saturated fatty acids activate inflammatory pathways and, notably, prime caspase-associated inflammasomes. Inflammasome-activated IL-1β contributes to type 2 diabetes. We hypothesized that 1) human monocytes from obese patients show caspase activation, and 2) fatty acids trigger this response and consequent release of IL-1β/IL-18. Human peripheral blood monocytes were sorted by flow cytometry, and caspase activity was measured with a FLICA dye-based assay. Blood monocytes from obese individuals exhibited elevated caspase activity. To explore the nature and consequence of this activity, human THP1 monocytes were exposed to saturated or unsaturated fatty acids. Caspase activity was revealed by isoform-specific cleavage and enzymatic activity; cytokine expression/release was measured by qPCR and ELISA. Palmitate, but not palmitoleate, increased caspase activity in parallel to the release of IL-1β and IL-18. Palmitate induced eventual monocyte cell death with features of pyroptosis (an inflammation-linked cell death program involving caspase-4/5), scored through LDH release, vital dye influx, cell volume changes, and nuclear morphology. Notably, selective gene silencing or inhibition of caspase-4/5 reduced palmitate-induced release of IL-1β and IL-18. In summary, monocytes from obese individuals present elevated caspase activity. Mechanistically, palmitate activates a pyroptotic program in monocytes through caspase-4/5, causing inflammatory cytokine release, additional to inflammasomes. These caspases represent potential, novel, therapeutic targets to taper obesity-associated inflammation.

Rosmarinic acid inhibits poly(I:C)-induced inflammatory reaction of epidermal keratinocytes

AIMS

Keratinocytes are the predominant cells in the epidermis, exerting their primary role of physical barrier through sophisticated differentiation process. In addition, keratinocytes contribute to the activation of innate immunity, providing the surveillant role against external pathogens. It has been known that chronic skin inflammatory disease such as psoriasis can be provoked by viral pathogens including double-stranded RNA. In this study, we demonstrated that rosmarinic acid (RA) has an inhibitory potential on inflammatory reaction induced by double-stranded RNA mimic poly(I:C) in epidermal keratinocytes.

MAIN METHODS

We cultured human epidermal keratinocytes and induced inflammatory reaction by poly(I:C) treatment. The effect of RA on inflammatory reaction of keratinocytes was determined by RT-PCR and Western blot.

KEY FINDINGS

RA significantly inhibited poly(I:C)-induced expression of inflammatory cytokines including IL-1β, IL-6, IL-8, CCL20, and TNF-α, and downregulated NF-κB signaling pathway in human keratinocytes. In addition, RA significantly inhibited poly(I:C)-induced inflammasome activation, in terms of secretion of active form of IL-1β and caspase-1. Furthermore, RA markedly inhibited poly(I:C)-induced NLRP3 and ASC expression.

SIGNIFICANCE

These results indicate that RA can inhibit poly(I:C)-induced inflammatory reaction of keratinocytes, and suggest that it may be a potential candidate for the treatment of psoriasis.

Ampelopsis japonica Makino Extract Inhibits the Inflammatory Reaction Induced by Pathogen-Associated Molecular Patterns in Epidermal Keratinocytes

Background

Keratinocytes are the major cells in epidermis, providing barrier components such as cornified cells through the sophisticated differentiation process. In addition, keratinocytes exerts their role as the defense cells via activation of innate immunity. It has been known that pathogen-associated molecular patterns (PAMPs) including double-strand RNA and nucleotides can provoke inflammatory reaction in keratinocytes.

Objective

The aim of this study is to evaluate the effect of Ampelopsis japonica Makino extract (AE) on PAMPs-induced inflammatory reaction of keratinocytes.

Methods

The effects of AE were determined using poly (I:C)-induced inflammation and imiquimod-induced psoriasiform dermatitis models.

Results

In cultured keratinocytes, AE significantly inhibited poly(I:C)-induced expression of inflammatory cytokines, such as interleukin (IL)-1β, IL-6, IL-8 and tumor necrosis factor-α. AE significantly inhibited poly(I:C)-induced release of caspase-1 active form (p20), and down-regulated nuclear factor-κB signaling pathway. In imiquimod-induced psoriasiform dermatitis model, topical application of AE resulted in significant reduction of epidermal hyperplasia.

Conclusion

These results suggest that AE may be a potential candidate for the treatment of skin inflammation.

The Inflammasome and the Epidermal Growth Factor Receptor (EGFR) Are Involved in the Staphylococcus aureus-Mediated Induction of IL-1alpha and IL-1beta in Human Keratinocytes

Staphylococcus (S.) aureus is an important pathogen causing various infections including those of the skin. Keratinocytes are able to sense invading S. aureus and to initiate a fast defense reaction by the rapid release of innate defense mediators such as antimicrobial peptides and cytokines. There is increasing evidence that the cytokines IL-1alpha and IL-1beta, which both signal through the IL-1 receptor, play an important role in cutaneous defense against S. aureus. The aim of this study was to gain more insight into the underlying mechanisms leading to the S. aureus-induced IL-1alpha and IL-1beta expression in keratinocytes. Infection of human primary keratinocytes with S. aureus led to the induction of gene expression and protein secretion of IL-1alpha and IL-1beta. Full S. aureus-induced IL-1 protein release required the inflammasome components caspase-1 and ASC (apoptosis-associated speck-like protein containing a CARD) whereas gene induction of IL-1alpha and IL-beta by S. aureus was not dependent on caspase-1 and ASC. Since patients receiving anti-cancer therapy by inhibition of the epidermal growth factor receptor (EGFR) often suffer from skin infections caused by S. aureus we additionally evaluated whether the EGFR pathway may be involved in the IL-1alpha and IL-1beta induction by S. aureus. Inactivation of the EGFR with a blocking antibody decreased the S. aureus-mediated IL-1alpha and IL-1beta induction in primary keratinocytes. Moreover, the use of siRNA experiments revealed that ADAM17 (A Disintegrin and A Metalloprotease 17), a metalloproteinase known to mediate the shedding and release of EGFR ligands, was required for full induction of IL-1alpha and IL-1beta in keratinocytes infected with S. aureus. A failure of keratinocytes to adequately upregulate IL-1alpha and IL-1beta may promote S. aureus skin infections.

Absent in melanoma 2 (AIM2) expressed in human dental pulp mediates IL-1β secretion in response to cytoplasmic DNA

The inflammasome has been determined to play an important role in inflammatory diseases in recent years. Absent in melanoma 2 (AIM2), an inflammasome that recognizes cytoplasmic DNA, has recently been identified as a critical regulator of immune responses. In this study, we explored whether AIM2 was expressed in human dental pulp and defined the role of AIM2 in regulating interleukin (IL)-1β secretion. We demonstrated that AIM2 was only detected in the odontoblast layer of healthy dental pulp, whereas strong expression was observed in inflamed dental pulp. Stimulation with interferon gamma (IFN-γ) and cytoplasmic DNA significantly activated the AIM2 inflammasome and increased IL-1β secretion in human dental pulp cells (HDPCs) in a time- and dose-dependent manner. Moreover, the knockdown of AIM2 downregulated both cleaved-caspase-1 expression and IL-1β release in HDPCs. These results suggest that AIM2 expressed in human dental pulp plays an important role in the immune defense by activating the inflammasome signaling pathway.

PCNA-interacting peptides reduce Akt phosphorylation and TLR-mediated cytokine secretion suggesting a role of PCNA in cellular signaling

Proliferating cell nuclear antigen (PCNA), commonly known as a nuclear protein essential for regulation of DNA replication, DNA repair, and epigenetics, has recently been associated with multiple cytosolic functions. Many proteins containing one of the two known PCNA-interacting motifs, the AlkB homologue 2 PCNA interacting motif (APIM) and the PCNA-interacting peptide (PIP)-box, are considered to be mainly cytosolic. APIM is found in more than 20 kinases and/or associated proteins including several direct or indirect members of the mitogen-activated protein kinase (MAPK) and PI3K/Akt pathways. Mass spectrometry analysis of PCNA-pull downs verified that many cytosolic proteins involved in the MAPK and PI3K/Akt pathways are in complex with PCNA. Furthermore, treatment of cells with a PCNA-interacting APIM-containing peptide (APIM-peptide) reduced Akt phosphorylation in human peripheral blood monocytes and a human keratinocyte cell line (HaCaT). Additionally, the APIM-peptide strongly reduced the cytokine secretion from monocytes stimulated with toll like receptor (TLR) ligands and potentiated the effects of MAPK and PI3K/Akt inhibitors. Interestingly, the protein level of the APIM-containing PKR/RIG-1 activator protein (PACT) was initially strongly reduced in HaCaT cells stimulated with APIM-peptide in combination with the TLR ligand polyinosinic-polycytidylic acid (polyIC). Our results suggest that PCNA has a platform role in cytosol affecting cellular signaling.

Interleukin-1α released from HSV-1-infected keratinocytes acts as a functional alarmin in the skin

Herpes simplex virus-1 (HSV-1) is a human pathogen that utilizes several strategies to circumvent the host immune response. An immune evasion mechanism employed by HSV-1 is retention of interleukin-1β (IL-1β) in the intracellular space, which blocks the pro-inflammatory activity of IL-1β. Here, we report that HSV-1 infected keratinocytes actively release the also pro-inflammatory IL-1α, preserving the ability of infected cells to signal danger to the surrounding tissue. The extracellular release of IL-1α is independent of inflammatory caspases. In vivo recruitment of leukocytes to early HSV-1 micro-infection sites within the epidermis is dependent upon IL-1 signalling. Following cutaneous HSV-1 infection, mice unable to signal via extracellular IL-1α exhibit an increased mortality rate associated with viral dissemination. We conclude that IL-1α acts as an alarmin essential for leukocyte recruitment and protective immunity against HSV-1. This function may have evolved to counteract an immune evasion mechanism deployed by HSV-1.

Candida Immunity

The human pathogenic fungus Candida albicans is the predominant cause of both superficial and invasive forms of candidiasis. C. albicans primarily infects immunocompromised individuals as a result of either immunodeficiency or intervention therapy, which highlights the importance of host immune defences in preventing fungal infections. The host defence system utilises a vast communication network of cells, proteins, and chemical signals distributed in blood and tissues, which constitute innate and adaptive immunity. Over the last decade the identity of many key molecules mediating host defence against C. albicans has been identified. This review will discuss how the host recognises this fungus, the events induced by fungal cells, and the host innate and adaptive immune defences that ultimately resolve C. albicans infections during health.