Cyclic AMP signaling enhances lipopolysaccharide sensitivity and interleukin-33 production in RAW264.7 macrophages

Strategies targeting IL-33/ST2 axis in the treatment of allergic diseases

Interleukin-33 (IL-33) and its receptor Serum Stimulation-2 (ST2, also called Il1rl1) are members of the IL-1 superfamily that plays a crucial role in allergic diseases. The interaction of IL-33 and ST2 mainly activates NF-κB signaling and MAPK signaling via the MyD88/IRAK/TRAF6 module, resulting in the production and secretion of pro-inflammatory cytokines. The IL-33/ST2 axis participates in the pathogenesis of allergic diseases, and therefore serves as a promising strategy for allergy treatment. In recent years, strategies blocking IL-33/ST2 through targeting regulation of IL-33 and ST2 or targeting the molecules involved in the signal transduction have been extensively studied mostly in animal models. These studies provide various potential therapeutic agents other than antibodies, such as small molecules, nucleic acids and traditional Chinese medicines. Herein, we reviewed potential targets and agents targeting IL-33/ST2 axis in the treatment of allergic diseases, providing directions for further investigations on treatments for IL-33 induced allergic diseases.

Heat-Labile Enterotoxin Decreases Macrophage Phagocytosis of Enterotoxigenic Escherichia coli

Enterotoxigenic E. coli (ETEC) are endemic in low-resource settings and cause robust secretory diarrheal disease in children less than five years of age. ETEC cause secretory diarrhea by producing the heat-stable (ST) and/or heat-labile (LT) enterotoxins. Recent studies have shown that ETEC can be carried asymptomatically in children and adults, but how ETEC subvert mucosal immunity to establish intestinal residency remains unclear. Macrophages are innate immune cells that can be exploited by enteric pathogens to evade mucosal immunity, so we interrogated the ability of ETEC and other E. coli pathovars to survive within macrophages. Using gentamicin protection assays, we show that ETEC H10407 is phagocytosed more readily than other ETEC and non-ETEC isolates. Furthermore, we demonstrate that ETEC H10407, at high bacterial burdens, causes nitrite accumulation in macrophages, which is indicative of a proinflammatory macrophage nitric oxide killing response. However, at low bacterial burdens, ETEC H10407 remains viable within macrophages for an extended period without nitrite accumulation. We demonstrate that LT, but not ST, intoxication decreases the number of ETEC phagocytosed by macrophages. Furthermore, we now show that macrophages exposed simultaneously to LPS and LT produce IL-33, which is a cytokine implicated in promoting macrophage alternative activation, iron recycling, and intestinal repair. Lastly, iron restriction using deferoxamine induces IL-33 receptor (IL-33R) expression and allows ETEC to escape macrophages. Altogether, these data demonstrate that LT provides ETEC with the ability to decrease the perceived ETEC burden and suppresses the initiation of inflammation. Furthermore, these data suggest that host IL-33/IL-33R signaling may augment pathways that promote iron restriction to facilitate ETEC escape from macrophages. These data could help explain novel mechanisms of immune subversion that may contribute to asymptomatic ETEC carriage.

The Paradigm Change of IL-33 in Vascular Biology

In this review, we focus on the actual understanding of the role of IL-33 in vascular biology in the context of the historical development since the description of IL-33 as a member of IL-1 superfamily and the ligand for ST2 receptor in 2005. We summarize recent data on the biology, structure and signaling of this dual-function factor with both nuclear and extracellular cytokine properties. We describe cellular sources of IL-33, particularly within vascular wall, changes in its expression in different cardio-vascular conditions and mechanisms of IL-33 release. Additionally, we summarize the regulators of IL-33 expression as well as the effects of IL-33 itself in cells of the vasculature and in monocytes/macrophages in vitro combined with the consequences of IL-33 modulation in models of vascular diseases in vivo. Described in murine atherosclerosis models as well as in macrophages as an atheroprotective cytokine, extracellular IL-33 induces proinflammatory, prothrombotic and proangiogenic activation of human endothelial cells, which are processes known to be involved in the development and progression of atherosclerosis. We, therefore, discuss that IL-33 can possess both protective and harmful effects in experimental models of vascular pathologies depending on experimental conditions, type and dose of administration or method of modulation.

1,4NQ-BC enhances the lung inflammation by mediating the secretion of IL-33 which derived from macrophages

Black carbon (BC) is a product of incomplete combustion of fossil fuels and vegetation. The compelling evidence has demonstrated that it has a close relationship with several respiratory and cardiovascular diseases. BC provides the reactive sites and surfaces to absorb various chemicals, such as polycyclic aromatic hydrocarbons (PAH). Naphthoquinone is a typical PAHs which was found in particulate matter (PM) and 1,4NQ-BC owned high oxidative potential and cytotoxicity. IL-33 is an alarmin which increases innate immunity through Th2 responses. It was reported that IL-33 was a potent inducer of pro-inflammatory cytokines, like IL-6. In our previous study, it was revealed that 1,4NQ-BC instilled intratracheally to mice could trigger the lung inflammation and stimulate the secretion of IL-33 in lung tissue. We found that IL-33 could induce inflammation in lung itself. When the macrophages were eliminated, the secretion of IL-33 was reduced and the pathological damage in the lung was relieved after exposure to 1,4NQ-BC. Both MAPK and PI3K/AKT signal pathways were involved in the process of IL-33 secretion and the lung inflammation induced by 1,4NQ-BC. The findings herein support the notion that after exposure to 1,4NQ-BC, the increased secretion of IL-33 was mainly derived from macrophages through both MAPK and PI3K/AKT signal pathways.

A Phytocomplex Consisting of Tropaeolum majus L. and Salvia officinalis L. Extracts Alleviates the Inflammatory Response of Dermal Fibroblasts to Bacterial Lipopolysaccharides

Background

The antimicrobial activity and effects of a phytocomplex consisting of Tropaeolum flos (T) and Salviae folium (S) extracts on the cytokine levels and transcription factors on dermal fibroblast BJ exposed to bacterial lipopolysaccharides were examined.

Methods

In order to select the most optimal combination ratio of the two extracts for using in vitro, the physicochemical characterization of vegetal extract mixtures was performed and the antioxidant and antibacterial activities were evaluated on five different formulations of T : S, namely, 1 : 1, 1 : 2, 2 : 1, 3 : 1, and 1 : 3. The best combination of bioactive compounds with regard to antioxidant and antibacterial activities (T : S 1 : 2) was selected for in vitro evaluation of the anti-inflammatory effect. Human dermal fibroblast BJ cells were treated with two doses of the extract mixture and then exposed to bacterial lipopolysaccharides (LPS). The levels of the cytokines involved in inflammatory response, namely, interleukin- (IL-) 6, tumor necrosis factor- (TNF-) α, IL-31, and IL-33, were quantified by ELISA, and the expression of transcription factors, namely, signal transducer and activator of transcription (STAT) 3, nuclear factor kappa B (NFκB), and phosphorylated NFκB (pNFκB), were evaluated by western blot analysis.

Results

The results have shown that the mixture of T : S 1 : 2 exhibited significant antibacterial effects on Staphylococcus aureus ATCC 25923. LPS exposure increased the cytokine levels in BJ cells and enhanced the NFκB expression. The pretreatment of BF cells exposed to LPS with the two doses of the extract mixture markedly inhibited the increase of IL-33 and TNF-α levels and amplified the NFκB expression and its activation, especially with the high dose. The low doses of the extract reduced NFκB expression but increased its activation.

Conclusions

These experimental findings suggest that the mixture of T : S 1 : 2 can exert some protection against bacterial infections and inflammation induced by LPS in BJ cells being a good therapeutic option in related conditions associated with inflammation.

Paeoniflorin suppresses IL-33 production by macrophages

Objective: Interleukin (IL)-33 has been attracting more and more attention as a new member of theIL-1 cytokine family in recent years. However, the underlying mechanisms referred to the regulation of endogenous IL-33 production are not fully illustrated. Paeoniflorin (PF) has been reported to possess multiple pharmacological activities, including anti-inflammation and anti-allergy. In this study, we aimed to investigate the effect of PF on IL-33 production by macrophages and explore the underlying mechanisms.Methods: In vivo, IL-33 production in mice after lipopolysaccharide (LPS) injection together with PF application was detected by enzyme-linked immunosorbent assay (ELISA). In vitro, MTT, Real-time PCR, ELISA, Calcium (Ca²⁺) imaging and Western blot were used to assess the cytotoxicity of PF, IL-33 expression at mRNA and protein levels, Ca²⁺ influx, protein kinase C (PKC) activity, nuclear factor-kappa B (NF-κB), and mitogen-activated protein kinase (MAPK) activation in LPS-stimulated RAW264.7 macrophages with PF administration.Results: Our results indicated that PF (5 and 25 mg/kg) significantly reduced the production of TNF-a, IL-1β, and IL-33 in the peritoneal exudate of LPS-treated mice. In vitro assay, upregulation of PF concentration (≥ 20 μM) showed an increased cytotoxicity in RAW264.7 cells during the 24-h cell culture. PF (10 μM) inhibited IL-33 production, Ca²⁺ influx, PKC activity, NF-κB (p65) activation, and P38MAPK phosphorylation in LPS-treated macrophages. Notably, NF-κB inhibitor (BAY 11-7085), P38MAPK inhibitor (SB203580), and Ca²⁺ blocker (NiCl₂) also curbed LPS-induced IL-33 production, respectively.Conclusions: PF suppresses IL-33 production by macrophages via inhibiting NF-κB and P38MAPK activation associated with the regulation of Ca²⁺ mobilization.

Could interleukin-33 and its suppressor of tumorigenicity 2 (ST2) receptor have a role in cervical human papillomavirus (HPV) infections?

Why most women can clear human papillomavirus (HPV) infections while others can develop permanent infections. The stimulation of immunotolerance of the immune system of the host by the persistent HPV infection may be the answer to this question. Interleukin-33 (IL-33) may play a role in the pathogenesis of HPV infection, this hypothesis was thought to be due to the rapid release of IL-33 from damaged cells following tissue damage, necrosis, and activation of the inflammasome. Thus, in this study, the role of IL-33/suppressor of tumorigenicity 2 (ST2) was emphasized in HPV positive and HPV negative cervical tissues. A total of 80 were assessed. The reduced levels of IL-33 and ST2 are associated with cervical HPV infections. There was a statistically significant 42% positive correlation between IL-33 and ST2 in the HPV-positive group. Surprisingly, our data showed no significant difference between the expression levels of IL-33 or ST2 and working status, type of delivery, pre- and post-operative pathology, cigarette, educational status, locality, birth control method, gynecological, and colposcopic findings. We found that as a result of our study; low IL-33 and ST2 levels were associated with HPV infections.

Alnus Sibirica Extracts Suppress the Expression of Inflammatory Cytokines Induced by Lipopolysaccharides, Tumor Necrosis Factor-α, and Interferon-γ in Human Dermal Fibroblasts

The effects of Alnus sibirica (AS) extracts on cytokine expression induced by inflammatory stimulants were examined in human dermal fibroblasts (HDFs) and RAW264.7 cells. The anti-oxidative effect and effect on cell viability of AS extracts were evaluated, and four extracts with the highest anti-oxidative effects were selected. HDFs and RAW264.7 cells were treated with inflammatory stimulants, and the expression of cytokines involved in acute (IL-6 and IL-10) and chronic (IL-18) inflammation, the initiation of the immune response (IL-33), and non-specific immune responses (IL-1β, IL-8, and TNF-α) were determined using a reverse-transcription polymerase chain reaction. LPS increased the expression of all the cytokines, except for IL-18; however, AS extracts, particularly AS2 and AS4, reduced this increase, and TNF-α treatment markedly increased the expression of cytokines related to non-specific immune responses. IFN-γ treatment induced no significant changes, except for increased IL-33 expression in HDFs. AS extracts inhibited the increase in the expression of IL-33 and other cytokines in HDFs. Thus, the exposure of HDFs and RAW264.7 cells to inflammatory stimulants increased the expression of cytokines related to all the inflammatory processes. HDFs are involved not only in simple tissue regeneration but also in inflammatory reactions in the skin. AS2 and AS4 may offer effective therapy for related conditions.

Endogenous Neurosteroid (3α,5α)3-Hydroxypregnan-20-one Inhibits Toll-like-4 Receptor Activation and Pro-inflammatory Signaling in Macrophages and Brain

The endogenous neurosteroid (3α,5α)3-hydroxypregnan-20-one (3α,5α-THP, allopregnanolone) has protective activity in animal models of alcoholism, depression, traumatic brain injury, schizophrenia, multiple sclerosis, and Alzheimer’s disease that is poorly understood. Because these conditions involve proinflammatory signaling through toll-like receptors (TLRs), we examined the effects of 3α,5α-THP, and pregnenolone on TLR4 activation in both the periphery and the central nervous system (CNS). We used monocytes/macrophages (RAW264.7) as a model of peripheral immune signaling and studied innately activated TLR4 in the ventral tegmental area (VTA) of selectively bred alcohol-preferring (P) rats. LPS activated the TLR4 pathway in RAW264.7 cells as evidenced by increased levels of p-TAK1, TRAF6, NF-κB p50, phospho-NF-κB- p65, pCREB, HMGB1, and inflammatory mediators, including MCP-1 and TNFα. Both 3α,5α-THP and pregnenolone (0.5–1.0μM) substantially (~80%) inhibited these effects, indicating pronounced inhibition of TLR4 signaling. The mechanism of inhibition appears to involve blockade of TLR4/MD-2 protein interactions in RAW246.7 cells. In VTA, 3α,5α-THP (15 mg/kg, IP) administration reduced TRAF6 (~20%), CRF (~30%), and MCP-1 (~20%) levels, as well as TLR4 binding to GABA_A receptor α2 subunits (~60%) and MyD88 (~40%). The data suggest that inhibition of proinflammatory neuroimmune signaling underlies protective effects of 3α,5α-THP in immune cells and brain, apparently involving blocking of protein-protein interactions that initiate TLR4-dependent signaling. Inhibition of pro-inflammatory TLR4 activation represents a new mechanism of 3α,5α-THP action in the periphery and the brain.

Tranilast inhibits interleukin-33 production by macrophages

Tranilast is an anti-allergy medication that inhibits the release of chemical mediators such as histamine. However, the mechanisms underlying its anti-allergy effects are not fully understood. Interleukin (IL)-33, a novel member of the IL-1 cytokine family, promotes T helper type 2 immune responses and plays a pathogenic role in allergic disorders. In the present study, we examined the effects of tranilast on IL-33 production by RAW264.7 macrophages. Lipopolysaccharide (LPS) increased both IL-33 mRNA expression and IL-33 protein synthesis. Tranilast significantly inhibited LPS-induced IL-33 protein production by RAW264.7 macrophages in a dose-dependent manner; these same effects were observed on IL-33 mRNA levels in RAW264.7 macrophages and a primary culture of macrophages. LPS markedly activated Akt in RAW264.7 macrophages, whereas tranilast suppressed LPS-induced Akt activation. The effects of tranilast on Akt activation appeared to be responsible for the decrease in IL-33 production. Our present findings suggest that the inhibition of IL-33 production by tranilast might contribute to the anti-allergy effects of this medication.

Neuropeptide FF increases M2 activation and self-renewal of adipose tissue macrophages

The quantity and activation state of adipose tissue macrophages (ATMs) impact the development of obesity-induced metabolic diseases. Appetite-controlling hormones play key roles in obesity; however, our understanding of their effects on ATMs is limited. Here, we have shown that human and mouse ATMs express NPFFR2, a receptor for the appetite-reducing neuropeptide FF (NPFF), and that NPFFR2 expression is upregulated by IL-4, an M2-polarizing cytokine. Plasma levels of NPFF decreased in obese patients and high-fat diet-fed mice and increased following caloric restriction. NPFF promoted M2 activation and increased the proliferation of murine and human ATMs. Both M2 activation and increased ATM proliferation were abolished in NPFFR2-deficient ATMs. Mechanistically, the effects of NPFF involved the suppression of E3 ubiquitin ligase RNF128 expression, resulting in enhanced stability of phosphorylated STAT6 and increased transcription of the M2 macrophage-associated genes IL-4 receptor α (Il4ra), arginase 1 (Arg1), IL-10 (Il10), and alkylglycerol monooxygenase (Agmo). NPFF induced ATM proliferation concomitantly with the increase in N-Myc downstream-regulated gene 2 (Ndrg2) expression and suppressed the transcription of Ifi200 cell-cycle inhibitor family members and MAF bZIP transcription factor B (Mafb), a negative regulator of macrophage proliferation. NPFF thus plays an important role in supporting healthy adipose tissue via the maintenance of metabolically beneficial ATMs.

Endogenous prostaglandin E2 amplifies IL-33 production by macrophages through an E prostanoid (EP)2/EP4-cAMP-EPAC-dependent pathway

When activated through toll-like receptors (TLRs), macrophages generate IL-33, an IL-1 family member that induces innate immune responses through ST2 signaling. LPS, a TLR4 ligand, induces macrophages to generate prostaglandin E₂ (PGE₂) through inducible COX-2 and microsomal PGE₂ synthase 1 (mPGES-1) (1). We demonstrate that IL-33 production by bone marrow-derived murine macrophages (bmMFs) requires the generation of endogenous PGE₂ and the intrinsic expression of EP₂ receptors to amplify NF-κB-dependent, LPS-induced IL-33 expression via exchange protein activated by cAMP (EPAC). Compared with WT cells, bmMFs lacking either mPGES-1 or EP₂ receptors displayed reduced LPS-induced IL-33 levels. A selective EP₂ agonist and, to a lesser extent, EP₄ receptor agonist potentiated LPS-induced IL-33 generation from both mPGES-1-null and WT bmMFs, whereas EP₁ and EP₃ receptor agonists were inactive. The effects of PGE₂ depended on cAMP, were mimicked by an EPAC-selective agonist, and were attenuated by EPAC-selective antagonism and knockdown. LPS-induced p38 MAPK and NF-κB activations were necessary for both IL-33 production and PGE₂ generation, and exogenous PGE₂ partly reversed the suppression of IL-33 production caused by p38 MAPK and NF-κB inhibition. Mice lacking mPGES-1 showed lower IL-33 levels and attenuated lung inflammation in response to repetitive Alternaria inhalation challenges. Cumulatively, our data demonstrate that endogenous PGE₂, EP₂ receptors, and EPAC are prerequisites for maximal LPS-induced IL-33 expression and that exogenous PGE₂ can amplify IL-33 production via EP₂ and EP₄ receptors. The ubiquitous induction of mPGES-1-dependent PGE₂ may be crucial for innate immune system activation during various IL-33 driven pathologic disorders.

Regulation of muscle growth and regeneration by the immune system

Diseases of muscle that are caused by pathological interactions between muscle and the immune system are devastating, but rare. However, muscle injuries that involve trauma and regeneration are fairly common, and inflammation is a clear feature of the regenerative process. Investigations of the inflammatory response to muscle injury have now revealed that the apparently nonspecific inflammatory response to trauma is actually a complex and coordinated interaction between muscle and the immune system that determines the success or failure of tissue regeneration.