The structure function of the death domain of human IRAK-M

Replenishing IRAK-M expression in retinal pigment epithelium attenuates outer retinal degeneration

Chronic inflammation is a constitutive component of many age-related diseases, including age-related macular degeneration (AMD). Here, we identified interleukin-1 receptor-associated kinase M (IRAK-M) as a key immunoregulator in retinal pigment epithelium (RPE) that declines during the aging process. Rare genetic variants of IRAK3, which encodes IRAK-M, were associated with an increased likelihood of developing AMD. In human samples and mouse models, IRAK-M abundance in the RPE declined with advancing age or exposure to oxidative stress and was further reduced in AMD. Irak3-knockout mice exhibited an increased incidence of outer retinal degeneration at earlier ages, which was further exacerbated by oxidative stressors. The absence of IRAK-M led to a disruption in RPE cell homeostasis, characterized by compromised mitochondrial function, cellular senescence, and aberrant cytokine production. IRAK-M overexpression protected RPE cells against oxidative or immune stressors. Subretinal delivery of adeno-associated virus (AAV)-expressing human IRAK3 rescued light-induced outer retinal degeneration in wild-type mice and attenuated age-related spontaneous retinal degeneration in Irak3-knockout mice. Our data show that replenishment of IRAK-M in the RPE may redress dysregulated pro-inflammatory processes in AMD, suggesting a potential treatment for retinal degeneration.

Importance of serum IRAK3 as a biochemical marker in relation to severity and neurological outcome of human severe traumatic brain injury: A prospective longitudinal cohort study

BACKGROUND

Interleukin-1 receptor-associated kinase 3 (IRAK3) may modulate inflammation in brain immunity. We determined the prognostic role of serum IRAK3 in severe traumatic brain injury (sTBI).

METHODS

In this prospective longitudinal cohort study, serum IRAK3 concentrations of 131 sTBI patients and 131 controls were quantified. Extended Glasgow outcome scale (GOSE) scores of 1-4 at 180 days after trauma signified a poor prognosis. Univariate and multivariate analyses were sequentially adopted to appraise severity correlations and prognosis associations.

RESULTS

There were significantly higher serum IRAK3 concentrations in patients than in controls. Serum IRAK3 concentrations of patients were independently correlated with Glasgow coma scale (GCS) scores, Rotterdam computed tomography (CT) scores and posttraumatic180-day GOSE scores. Also, IRAK3 concentrations were independently associated with 180-day poor prognosis, but not with death. Prognosis prediction model, in which GCS scores, Rotterdam scores and serum IRAK3 concentrations were merged, was portrayed using the nomogram. The model was rather stable, clinically usable and efficiently discriminative of poor prognosis under calibration curve, decision curve and receiver operating characteristic curve.

CONCLUSIONS

A substantial enhancement of serum IRAK3 concentrations after head trauma is independently related to severity and neurological outcome, substantializing serum IRAK3 as a promising prognostic biomarker of sTBI.

The IRAK-M death domain: a tale of three surfaces

The anti-inflammatory interleukin-1 receptor associated kinase-M (IRAK-M) is a negative regulator of MyD88/IRAK-4/IRAK-1 signaling. However, IRAK-M has also been reported to activate NF-κB through the MyD88/IRAK-4/IRAK-M myddosome in a MEKK-3 dependent manner. Here we provide support that IRAK-M uses three surfaces of its Death Domain (DD) to activate NF-κB downstream of MyD88/IRAK-4/IRAK-M. Surface 1, with central residue Trp74, binds to MyD88/IRAK-4. Surface 2, with central Lys60, associates with other IRAK-M DDs to form an IRAK-M homotetramer under the MyD88/IRAK-4 scaffold. Surface 3; with central residue Arg97 is located on the opposite side of Trp74 in the IRAK-M DD tetramer, lacks any interaction points with the MyD88/IRAK-4 complex. Although the IRAK-M DD residue Arg97 is not directly involved in the association with MyD88/IRAK-4, Arg97 was responsible for 50% of the NF-κB activation though the MyD88/IRAK-4/IRAK-M myddosome. Arg97 was also found to be pivotal for IRAK-M's interaction with IRAK-1, and important for IRAK-M's interaction with TRAF6. Residue Arg97 was responsible for 50% of the NF-κB generated by MyD88/IRAK-4/IRAK-M myddosome in IRAK-1/MEKK3 double knockout cells. By structural modeling we found that the IRAK-M tetramer surface around Arg97 has excellent properties that allow formation of an IRAK-M homo-octamer. This model explains why mutation of Arg97 results in an IRAK-M molecule with increased inhibitory properties: it still binds to myddosome, competing with myddosome IRAK-1 binding, while resulting in less NF-κB formation. The findings further identify the structure-function properties of IRAK-M, which is a potential therapeutic target in inflammatory disease.

IRAK3 Knockout and Wildtype THP-1 Monocytes as Models for Endotoxin Detection Assays and Fusobacterium nucleatum Bacteriophage FNU1 Cytokine Induction

Microbial resistance to antibiotics poses a tremendous challenge. Bacteriophages may provide a useful alternative or adjunct to traditional antibiotics. To be used in therapy, bacteriophages need to be purified from endotoxins and tested for their effects on human immune cells. Interleukin-1 Receptor Associated Kinase-3 (IRAK3) is a negative regulator of inflammation and may play a role in the modulation of immune signalling upon bacteriophage exposure to immune cells. This study aimed to investigate the immune effects of crude and purified bacteriophage FNU1, a bacteriophage that targets the oral pathobiont Fusobacterium nucleatum, on wildtype and IRAK3 knockout THP-1 monocytic cell lines. The IRAK3 knockout cell line was also used to develop a novel endotoxin detection assay. Exposure to crude FNU1 increased the production of pro-inflammatory cytokines (Tumour necrosis factor - alpha (TNF-α) and Interleukin 6 (IL-6)) compared to purified FNU1 in wildtype and IRAK3 knockout THP-1 monocytes. In the IRAK3 knockout THP-1 cells, exposure to crude FNU1 induced a higher immune response than the wildtype monocytes, supporting the suggestion that the inhibitory protein IRAK3 regulates reactions to endotoxins and impurities in bacteriophage preparations. Finally, the novel endotoxin detection assay generated here provides a robust and accurate method for determining endotoxin concentrations.

Replenishing Age-Related Decline of IRAK-M Expression in Retinal Pigment Epithelium Attenuates Outer Retinal Degeneration

Unchecked, chronic inflammation is a constitutive component of age-related diseases, including age-related macular degeneration (AMD). Here we identified interleukin-1 receptor-associated kinase (IRAK)-M as a key immunoregulator in retinal pigment epithelium (RPE) that declines with age. Rare genetic variants of IRAK-M increased the likelihood of AMD. IRAK-M expression in RPE declined with age or oxidative stress and was further reduced in AMD. IRAK-M-deficient mice exhibited increased incidence of outer retinal degeneration at earlier ages, which was further exacerbated by oxidative stressors. The absence of IRAK-M disrupted RPE cell homeostasis, including compromised mitochondrial function, cellular senescence, and aberrant cytokine production. IRAK-M overexpression protected RPE cells against oxidative or immune stressors. Subretinal delivery of AAV-expressing IRAK-M rescued light-induced outer retinal degeneration in wild-type mice and attenuated age-related spontaneous retinal degeneration in IRAK-M-deficient mice. Our data support that replenishment of IRAK-M expression may redress dysregulated pro-inflammatory processes in AMD, thereby treating degeneration.

IRAK-M Ablation Promotes Status Epilepticus-Induced Neuroinflammation via Activating M1 Microglia and Impairing Excitatory Synaptic Function

Epilepsy is one of the most common neurological disorders. The pro-epileptic and antiepileptic roles of microglia have recently garnered significant attention. Interleukin-1 receptor-associated kinase (IRAK)-M, an important kinase in the innate immune response, is mainly expressed in microglia and acts as a negative regulator of the TLR4 signaling pathway that mediates the anti-inflammatory effect. However, whether IRAK-M exerts a protective role in epileptogenesis as well as the molecular and cellular mechanisms underlying these processes are yet to be elucidated. An epilepsy mouse model induced by pilocarpine was used in this study. Real-time quantitative polymerase chain reaction and western blot analysis were used to analyze mRNA and protein expression levels, respectively. Whole-cell voltage-clamp recordings were employed to evaluate the glutamatergic synaptic transmission in hippocampal neurons. Immunofluorescence was utilized to show the glial cell activation and neuronal loss. Furthermore, the proportion of microglia was analyzed using flow cytometry. Seizure dynamics influenced the expression of IRAK-M. Its knockout dramatically exacerbated the seizures and the pathology in epilepsy and increased the N-methyl-d-aspartate receptor (NMDAR) expression, thereby enhancing glutamatergic synaptic transmission in hippocampal CA1 pyramidal neurons in mice. Furthermore, IRAK-M deficiency augmented hippocampal neuronal loss via a possible mechanism of NMDAR-mediated excitotoxicity. IRAK-M deletion promotes microglia toward the M1 phenotype, which resulted in high levels of proinflammatory cytokines and was accompanied by a visible increase in the expressions of key microglial polarization-related proteins, including p-STAT1, TRAF6, and SOCS1. The findings demonstrate that IRAK-M dysfunction contributes to the progression of epilepsy by increasing M1 microglial polarization and glutamatergic synaptic transmission. This is possibly related to NMDARs, particularly Grin2A and Grin2B, which suggests that IRAK-M could serve as a novel therapeutic target for the direct alleviation of epilepsy.

The Molecular Basis and Clinical Consequences of Chronic Inflammation in Prostatic Diseases: Prostatitis, Benign Prostatic Hyperplasia, and Prostate Cancer

Chronic inflammation is now recognized as one of the major risk factors and molecular hallmarks of chronic prostatitis, benign prostatic hyperplasia (BPH), and prostate tumorigenesis. However, the molecular mechanisms by which chronic inflammation signaling contributes to the pathogenesis of these prostate diseases are poorly understood. Previous efforts to therapeutically target the upstream (e.g., TLRs and IL1-Rs) and downstream (e.g., NF-κB subunits and cytokines) inflammatory signaling molecules in people with these conditions have been clinically ambiguous and unsatisfactory, hence fostering the recent paradigm shift towards unraveling and understanding the functional roles and clinical significance of the novel and relatively underexplored inflammatory molecules and pathways that could become potential therapeutic targets in managing prostatic diseases. In this review article, we exclusively discuss the causal and molecular drivers of prostatitis, BPH, and prostate tumorigenesis, as well as the potential impacts of microbiome dysbiosis and chronic inflammation in promoting prostate pathologies. We specifically focus on the importance of some of the underexplored druggable inflammatory molecules, by discussing how their aberrant signaling could promote prostate cancer (PCa) stemness, neuroendocrine differentiation, castration resistance, metabolic reprogramming, and immunosuppression. The potential contribution of the IL1R-TLR-IRAK-NF-κBs signaling molecules and NLR/inflammasomes in prostate pathologies, as well as the prospective benefits of selectively targeting the midstream molecules in the various inflammatory cascades, are also discussed. Though this review concentrates more on PCa, we envision that the information could be applied to other prostate diseases. In conclusion, we have underlined the molecular mechanisms and signaling pathways that may need to be targeted and/or further investigated to better understand the association between chronic inflammation and prostate diseases.

Mutations in the Vicinity of the IRAK3 Guanylate Cyclase Center Impact Its Subcellular Localization and Ability to Modulate Inflammatory Signaling in Immortalized Cell Lines

Interleukin-1 receptor-associated kinase 3 (IRAK3) modulates the magnitude of cellular responses to ligands perceived by interleukin-1 receptors (IL-1Rs) and Toll-like receptors (TLRs), leading to decreases in pro-inflammatory cytokines and suppressed inflammation. The molecular mechanism of IRAK3's action remains unknown. IRAK3 functions as a guanylate cyclase, and its cGMP product suppresses lipopolysaccharide (LPS)-induced nuclear factor kappa-light-chain-enhancer of activated B cell (NFκB) activity. To understand the implications of this phenomenon, we expanded the structure-function analyses of IRAK3 through site-directed mutagenesis of amino acids known or predicted to impact different activities of IRAK3. We verified the capacity of the mutated IRAK3 variants to generate cGMP in vitro and revealed residues in and in the vicinity of its GC catalytic center that impact the LPS-induced NFκB activity in immortalized cell lines in the absence or presence of an exogenous membrane-permeable cGMP analog. Mutant IRAK3 variants with reduced cGMP generating capacity and differential regulation of NFκB activity influence subcellular localization of IRAK3 in HEK293T cells and fail to rescue IRAK3 function in IRAK3 knock-out THP-1 monocytes stimulated with LPS unless the cGMP analog is present. Together, our results shed new light on the mechanism by which IRAK3 and its enzymatic product control the downstream signaling, affecting inflammatory responses in immortalized cell lines.

Geniposide protected against cerebral ischemic injury through the anti-inflammatory effect via the NF-κB signaling pathway

Context

Accumulated evidence indicates that geniposide exhibits neuroprotective effects in ischemic stroke. However, the potential targets of geniposide remain unclear.

Objective

We explore the potential targets of geniposide in ischemic stroke.

Materials and methods

Adult male C57BL/6 mice were subjected to the middle cerebral artery occlusion (MCAO) model. Mice were randomly divided into five groups: Sham, MCAO, and geniposide-treated (i.p. twice daily for 3 days before MCAO) at doses of 25, 75, or 150 mg/kg. We first examined the neuroprotective effects of geniposide. Then, we further explored via biological information analysis and verified the underlying mechanism in vivo and in vitro.

Results

In the current study, geniposide had no toxicity at concentrations of up to 150 mg/kg. Compared with the MCAO group, the 150 mg/kg group of geniposide significantly (P < 0.05) improved neurological deficits, brain edema (79.00 ± 0.57% vs 82.28 ± 0.53%), and infarct volume (45.10 ± 0.24% vs 54.73 ± 2.87%) at 24 h after MCAO. Biological information analysis showed that the protective effect was closely related to the inflammatory response. Geniposide suppressed interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS) expression in the brain homogenate, as measured by enzyme-linked immunosorbent assay (ELISA). Geniposide upregulated A20 and downregulated TNF receptor-associated factor-6 and nuclear factor kappa-B phosphorylation in the MCAO model and lipopolysaccharide-treated BV2 cells at 100 μM.

Conclusions

Geniposide exhibited a neuroprotective effect via attenuating inflammatory response, as indicated by biological information analysis, in vivo and in vitro experiments, which may provide a potential direction for the application of geniposide in the treatment of ischemic stroke.

Modulation of Inflammatory Cytokine Production in Human Monocytes by cGMP and IRAK3

Interleukin-1 receptor-associated kinase-3 (IRAK3) is a critical checkpoint molecule of inflammatory responses in the innate immune system. The pseudokinase domain of IRAK3 contains a guanylate cyclase (GC) centre that generates small amounts of cyclic guanosine monophosphate (cGMP) associated with IRAK3 functions in inflammation. However, the mechanisms of IRAK3 actions are poorly understood. The effects of low cGMP levels on inflammation are unknown, therefore a dose–response effect of cGMP on inflammatory markers was assessed in THP-1 monocytes challenged with lipopolysaccharide (LPS). Sub-nanomolar concentrations of membrane permeable 8-Br-cGMP reduced LPS-induced NFκB activity, IL-6 and TNF-α cytokine levels. Pharmacologically upregulating cellular cGMP levels using a nitric oxide donor reduced cytokine secretion. Downregulating cellular cGMP using a soluble GC inhibitor increased cytokine levels. Knocking down IRAK3 in THP-1 cells revealed that unlike the wild type cells, 8-Br-cGMP did not suppress inflammatory responses. Complementation of IRAK3 knockdown cells with wild type IRAK3 suppressed cytokine production while complementation with an IRAK3 mutant at GC centre only partially restored this function. Together these findings indicate low levels of cGMP form a critical component in suppressing cytokine production and in mediating IRAK3 action, and this may be via a cGMP enriched nanodomain formed by IRAK3 itself.

A systematic review and meta-analyses of interleukin-1 receptor associated kinase 3 (IRAK3) action on inflammation in in vivo models for the study of sepsis

Background

Interleukin-1 receptor associated kinase 3 (IRAK3) is a critical modulator of inflammation and is associated with endotoxin tolerance and sepsis. Although IRAK3 is known as a negative regulator of inflammation, several studies have reported opposing functions, and the temporal actions of IRAK3 on inflammation remain unclear. A systematic review and meta-analyses were performed to investigate IRAK3 expression and its effects on inflammatory markers (TNF-α and IL-6) after one- or two-challenge interventions, which mimic the hyperinflammatory and immunosuppression phases of sepsis, respectively, using human or animal in vivo models.

Methods

This systematic review and meta-analyses has been registered in the Open Science Framework (OSF) (Registration DOI: 10.17605/OSF.IO/V39UR). A systematic search was performed to identify in vivo studies reporting outcome measures of expression of IRAK3 and inflammatory markers. Meta-analyses were performed where sufficient data was available.

Results

The search identified 7778 studies for screening. After screening titles, abstracts and full texts, a total of 49 studies were included in the systematic review. The review identified significant increase of IRAK3 mRNA and protein expression at different times in humans compared to rodents following one-challenge, whereas the increases of IL-6 and TNF-α protein expression in humans were similar to rodent in vivo models. Meta-analyses confirmed the inhibitory effect of IRAK3 on TNF-α mRNA and protein expression after two challenges.

Conclusions

A negative correlation between IRAK3 and TNF-α expression in rodents following two challenges demonstrates the association of IRAK3 in the immunosuppression phase of sepsis. Species differences in underlying biology affect the translatability of immune responses of animal models to human, as shown by the dissimilarity in patterns of IRAK3 mRNA and protein expression between humans and rodents following one challenge that are further influenced by variations in experimental procedures.

IRAK1 and IRAK4 as emerging therapeutic targets in hematologic malignancies

PURPOSE OF REVIEW

Cell intrinsic and extrinsic perturbations to inflammatory signaling pathways are a hallmark of development and progression of hematologic malignancies. The interleukin 1 receptor-associated kinases (IRAKs) are a family of related signaling intermediates (IRAK1, IRAK2, IRAK3, IRAK4) that operate at the nexus of multiple inflammatory pathways implicated in the hematologic malignancies. In this review, we explicate the oncogenic role of these kinases and review recent therapeutic advances in the dawning era of IRAK-targeted therapy.

RECENT FINDINGS

Emerging evidence places IRAK signaling at the confluence of adaptive resistance and oncogenesis in the hematologic malignancies and solid tissue tumors. Preclinical investigations nominate the IRAK kinases as targetable molecular dependencies in diverse cancers.

SUMMARY

IRAK-targeted therapies that have matriculated to early phase trials are yielding promising preliminary results. However, studies of IRAK kinase signaling continue to defy conventional signaling models and raise questions as to the design of optimal treatment strategies. Efforts to refine IRAK signaling mechanisms in the malignant context will inspire deliberate IRAK-targeted drug development and informed combination therapy.

Structural anomalies in a published NMR-derived structure of IRAK-M

Signaling by Toll-Like Receptors and the Interleukin-1 Receptor (IL1-R) involves intracellular binding of MyD88, followed by assembly of IL1-R Associated Kinases (IRAKs) into the so-called Myddosome. Using NMR, Nechama et al. determined the structure of the IRAK-M death domain monomer (PDBid: 5UKE). With this structure, they performed a docking study to model the location of IRAK-M in the Myddosome. Based on this, they present a molecular basis for selectivity of IRAK-M towards IRAK1 over IRAK2 binding. When we attempted to use 5UKE as a homology modeling template, we noticed that our 5UKE-based models had structural issues, such as disallowed torsion angles and solvent exposed tryptophans. We therefore analyzed the NMR ensemble of 5UKE using structure validation tools and we compared 5UKE with homologous high-resolution X-ray structures. We identified several structural anomalies in 5UKE, including packing issues, frayed helices and improbable side chain conformations. We used Yasara to build a homology model, based on two high resolution death domain crystal structures, as an alternative model for the IRAK-M death domain (atomic coordinates, modeling details and validation are available at https://swift.cmbi.umcn.nl/gv/service/5uke/). Our model agrees better with known death domain structure information than 5UKE and also with the chemical shift data that was deposited for 5UKE.

Downregulation of IRAK3 by miR-33b-3p relieves chondrocyte inflammation and apoptosis in an in vitro osteoarthritis model

Interleukin-1 receptor-associated kinase-3 (IRAK3) has a distinctive role in regulating inflammation. However, the functional role of IRAK3 and regulatory mechanism underlying the pathogenesis of osteoarthritis (OA) remain unclear. Here, we first found that IRAK3 was upregulated, while miR-33b-3p was downregulated in the cartilage of OA patients and IL-1β-induced CHON-001 cells. IRAK3 was confirmed as the direct target of miR-33b-3p and negatively regulated by miR-33b-3p. There was an inverse correlation between IRAK3 mRNA expression and miR-33b-3p expression in OA cartilage tissues. The in vitro functional experiments showed that miR-33b-3p overexpression caused a remarkable increase in viability, a significant decrease in inflammatory mediators (IL-1β and TNF-α), and apoptosis in IL-1β-induced CHON-001 cells. Importantly, IRAK3 knockdown imitated, while overexpression reversed the effects of miR-33b-3p on IL-1β-induced inflammation and apoptosis in CHON-001 cells. Collectively, miR-33b-3p significantly alleviated IL-1β-induced inflammation and apoptosis by downregulating IRAK3, which may serve as a promising target for OA.

Analysis of interleukin-1 receptor associated kinase-3 (IRAK3) function in modulating expression of inflammatory markers in cell culture models: A systematic review and meta-analysis

BACKGROUND

IRAK3 is a critical modulator of inflammation in innate immunity. IRAK3 is associated with many inflammatory diseases, including sepsis, and is required in endotoxin tolerance to maintain homeostasis of inflammation. The impact of IRAK3 on inflammatory markers such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in cell culture models remains controversial.

OBJECTIVE

To analyse temporal effects of IRAK3 on inflammatory markers after one- or two-challenge interventions in cell culture models.

METHODS

A systematic search was performed to identify in vitro cell studies reporting outcome measures of expression of IRAK3 and inflammatory markers. Meta-analyses were performed where sufficient data were available. Comparisons of outcome measures were performed between different cell lines and human and mouse primary cells.

RESULTS

The literature search identified 7766 studies for screening. After screening titles, abstracts and full-texts, a total of 89 studies were included in the systematic review.

CONCLUSIONS

The review identifies significant effects of IRAK3 on decreasing NF-κB DNA binding activity in cell lines, TNF-α protein level at intermediate time intervals (4h-15h) in cell lines or at long term intervals (16h-48h) in mouse primary cells following one-challenge. The patterns of TNF-α protein expression in human cell lines and human primary cells in response to one-challenge are more similar than in mouse primary cells. Meta-analyses confirm a negative correlation between IRAK3 and inflammatory cytokine (IL-6 and TNF-α) expression after two-challenges.

IRAK3 modulates downstream innate immune signalling through its guanylate cyclase activity

Interleukin-1 receptor associated kinase 3 (IRAK3) is a cytoplasmic homeostatic mediator of inflammatory responses and is potentially useful as a prognostic marker in inflammation. IRAK3 inhibits signalling cascades downstream of myddosome complexes associated with toll like receptors. IRAK3 contains a death domain that interacts with other IRAK family members, a pseudokinase domain and a C-terminus domain involved with tumour necrosis factor receptor associated factor 6 (TRAF6). Previous bioinformatic studies revealed that IRAK3 contained a guanylate cyclase centre in its pseudokinase domain but its role in IRAK3 action is unresolved. We demonstrate that wildtype IRAK3 is capable of producing cGMP. Furthermore, we show that a specific point mutation in the guanylate cyclase centre reduced cGMP production. Cells containing toll like receptor 4 and a nuclear factor kappa-light-chain-enhancer of activated B cells (NFĸB) reporter system were transfected with IRAK3 or mutant IRAK3 proteins. Cell-permeable cGMP treatment of untransfected control cells suppresses downstream signalling through modulation of the NFĸB in the presence of lipopolysaccharides. Cells transfected with wildtype IRAK3 also suppress lipopolysaccharide induced NFĸB activity in the absence of exogenous cGMP. Lipopolysaccharide induced NFĸB activity was not suppressed in cells transfected with the IRAK3 mutant with reduced cGMP-generating capacity. Whereas in the presence of exogenously applied cell-permeable cGMP the IRAK3 mutant was able to retain its function by suppressing lipopolysaccharide induced NFĸB activity. Furthermore, increasing the amount of membrane permeable cGMP did not affect IRAK3's ability to reduce NFĸB activity. These results suggest that cGMP generated by IRAK3 may be involved in regulatory function of the protein where the presence of cGMP may selectively affect downstream signalling pathway(s) by modulating binding and/or activity of nearby proteins that interact in the inflammatory signalling cascade.

At Least Two Genes Encode Many Variants of Irak3 in Rainbow Trout, but Neither the Full-Length Factor Nor Its Variants Interfere Directly With the TLR-Mediated Stimulation of Inflammation

The interleukin-1-receptor-associated kinase 3 (IRAK3) is known in mammals as a negative feedback regulator of NF-κB-mediated innate-immune mechanisms. Our RNA-seq experiments revealed a prototypic 1920-nt sequence encoding irak3 from rainbow trout (Oncorhynchus mykiss), as well as 20 variants that vary in length and nucleotide composition. Based on the DNA-sequence information from two closely related irak3 genes from rainbow trout and an irak3-sequence fragment from Atlantic salmon retrieved from public databases, we elucidated the underlying genetic causes for this striking irak3 diversity. Infecting rainbow trout with a lethal dose of Aeromonas salmonicida enhanced the expression of all variants in the liver, head kidney, and peripheral blood leucocytes. We analyzed the functional impact of the full-length factor and selected structural variants by overexpressing them in mammalian HEK-293 cells. The full-length factor enhanced the basal activity of NF-κB, but did not dampen the TLR2-signaling-induced levels of NF-κB activation. Increasing the basal NF-κB-activity through Irak3 apparently does not involve its C-terminal domain. However, more severely truncated factors had only a minor impact on the activity of NF-κB. The TLR2-mediated stimulation did not alter the spatial distribution of Irak3 inside the cells. In salmonid CHSE-214 cells, we observed that the Irak3-splice variant that prominently expresses the C-terminal domain significantly quenched the stimulation-dependent production of interleukin-1β and interleukin-8, but not the production of other immune regulators. We conclude that the different gene and splice variants of Irak3 from trout play distinct roles in the activation of immune-regulatory mechanisms.

Interleukin-1 receptor associated kinase (IRAK)-M -mediated type 2 microglia polarization ameliorates the severity of experimental autoimmune encephalomyelitis (EAE)

Toll-like receptor 4 (TLR4) play a key role in activating the innate immune system during pathogen recognition. In the pathogenesis of multiple sclerosis (MS), activated TLR4 together with myeloid differentiation primary response gene 88 (MyD88) produce an inflammatory microenvironment that promotes the differentiation of microglia into the M1 phenotype, who plays a key role in the pathogenesis of MS. Interleukin-1 receptor-associated kinase (IRAK)-M is specifically expressed in microglia in central nervous system (CNS) and act as a negative regulator of TLR4-MyD88 signaling pathway. Moreover, previous studies have shown that IRAK-M promotes the differentiation of type 2 microglia; however, its role in MS has not been explored. In the present study, we demonstrated that IRAK-M expression is elevated during EAE, and IRAK-M^-/- mice significantly accelerated course and increased severity of disease, accompanied by a visible increase of the M1 microglia infiltrated. In conclusion, these data indicates that IRAK-M significantly improves EAE onset through down-regulation of the TLR4-MyD88 signaling pathway, which finally leads to differentiation of M2 phenotype in the microglia. Our study suggests that IRAK-M may be a potential therapeutic target for the treatment of MS.

Elevated pre-activation basal level of nuclear NF-κB in native macrophages accelerates LPS-induced translocation of cytosolic NF-κB into the cell nucleus

Signaling via Toll-like receptor 4 (TLR4) in macrophages constitutes an essential part of the innate immune response to bacterial infections. Detailed and quantified descriptions of TLR4 signal transduction would help to understand and exploit the first-line response of innate immune defense. To date, most mathematical modelling studies were performed on transformed cell lines. However, properties of primary macrophages differ significantly. We therefore studied TLR4-dependent activation of NF-κB transcription factor in bone marrow-derived and peritoneal primary macrophages. We demonstrate that the kinetics of NF-κB phosphorylation and nuclear translocation induced by a wide range of bacterial lipopolysaccharide (LPS) concentrations in primary macrophages is much faster than previously reported for macrophage cell lines. We used a comprehensive combination of experiments and mathematical modeling to understand the mechanisms of this rapid response. We found that elevated basal NF-κB in the nuclei of primary macrophages is a mechanism increasing native macrophage sensitivity and response speed to the infection. Such pre-activated state of macrophages accelerates the NF-κB translocation kinetics in response to low agonist concentrations. These findings enabled us to refine and construct a new model combining both NF-κB phosphorylation and translocation processes and predict the existence of a negative feedback loop inactivating phosphorylated NF-κB.

Endotoxin Tolerant Dendritic Cells Suppress Inflammatory Responses in Splenocytes via Interleukin-1 Receptor Associated Kinase (IRAK)-M and Programmed Death-Ligand 1 (PDL-1)

BACKGROUND Sepsis causes the highest mortality in non-cardiovascular intensive care units worldwide. Recent research has demonstrated that the late phase of sepsis, characterized as septic immunosuppression, is the central pathophysiological mechanism of immune dysfunction. Investigating the suppressive mechanism of immune cells may identify possible targets for therapy. MATERIAL AND METHODS We used LPS 2-hit model for dendritic cells (DCs) to establish endotoxin tolerance, and co-cultured with splenocytes. Co-culture responses and gene expressions were evaluated. RESULTS Endotoxin tolerant DCs showed irresponsiveness in pro-inflammatory cytokine production and expressed negative regulator genes of inflammation. When co-cultured with splenocytes, suppression of inflammatory responses and T cells apoptosis were observed with elevated expression of IRAK-M and PDL-1, and interference and neutralization of these 2 molecules led to partly reversed suppression of inflammation. CONCLUSIONS Our research found direct regulation of endotoxin tolerant DCs to other immune cells and suggested a possible mechanism via IRAK-M and PDL-1. This may inform research on septic immunosuppression and suggests possible therapeutic targets for sepsis.

The IL-33-PIN1-IRAK-M axis is critical for type 2 immunity in IL-33-induced allergic airway inflammation

Interleukin 33 (IL-33) is among the earliest-released cytokines in response to allergens that orchestrate type 2 immunity. The prolyl cis-trans isomerase PIN1 is known to induce cytokines for eosinophil survival and activation by stabilizing cytokines mRNAs, but the function of PIN1 in upstream signaling pathways in asthma is unknown. Here we show that interleukin receptor associated kinase M (IRAK-M) is a PIN1 target critical for IL-33 signaling in allergic asthma. NMR analysis and docking simulations suggest that PIN1 might regulate IRAK-M conformation and function in IL-33 signaling. Upon IL-33-induced airway inflammation, PIN1 is activated for binding with and isomerization of IRAK-M, resulting in IRAK-M nuclear translocation and induction of selected proinflammatory genes in dendritic cells. Thus, the IL-33-PIN1-IRAK-M is an axis critical for dendritic cell activation, type 2 immunity and IL-33 induced airway inflammation.

IL-33 orchestrates type 2 immunity in allergic asthma. Here the authors show, using biochemical, structural and patient data, that upon IL-33 or allergic challenge, the isomerase Pin1 modifies IRAK-M to control the production of pro-inflammatory cytokines in the setting of airway inflammation.

Effect of IRAK-M on Airway Inflammation Induced by Cigarette Smoking

Background

IRAK-M, negatively regulating Toll-like receptor, is shown the dual properties in the varied disease contexts. We studied the effect of IRAK-M deficiency on cigarette smoking- (CS-) induced airway inflammation under acute or subacute conditions in a mouse model.

Methods

A number of cellular and molecular techniques were used to detect the differences between IRAK-M knockout (KO) and wild type (WT) mice exposed to 3-day or 7-week CS.

Results

Airway inflammation was comparable between IRAK-M KO and WT mice under 3-day CS exposure. Upon short-term CS exposure and lipopolysaccharide (LPS) inhalation, IRAK-M KO mice demonstrated worse airway inflammation, significantly higher percentage of Th17 cells and concentrations of proinflammatory cytokines in the lungs, and significantly elevated expression of costimulatory molecules CD40 and CD86 by lung dendritic cells (DCs) or macrophages. Conversely, 7-week CS exposed IRAK-M KO mice demonstrated significantly attenuated airway inflammation, significantly lower concentrations of proinflammatory cytokines in the lungs, significantly increased percentage of Tregs, and lower expression of CD11b and CD86 by lung DCs or macrophages.

Conclusions

IRAK-M plays distinctive effect on CS-induced airway inflammation, and influences Treg/Th17 balance and expression of costimulatory molecules by DCs and macrophages, depending on duration and intensity of stimulus.

IRAK-M alters the polarity of macrophages to facilitate the survival of Mycobacterium tuberculosis

Background

Intracellular bacterium, Mycobacterium tuberculosis (M. tb), infects specifically macrophages as host cells. IRAK-M, a member of IRAK family, is a negative regulator in TLR signaling and specifically expresses in monocytes and macrophages. The role of IRAK-M in intracellular growth of M. tb and macrophage polarization was explored, for deeply understanding the pathogenesis of M. tb, the significance of IRAK-M to innate immunity and pathogen-host interaction.

Methods

IRAK-M expression was detected in M. tb infected macrophages and in human lung tissue of pulmonary tuberculosis with immunofluorescence staining, Western blot and immunohistochemistry. IRAK-M knock-down and over-expressing cell strains were constructed and intracellular survival of M. tb was investigated by acid-fast staining and colony forming units. Molecular markers of M1-type (pSTAT1 and iNOS) and M2-type (pSTAT6 and Arg-1) macrophages were detected using Western blot in IRAK-M knockdown U937 cells infected with M. tb H37Rv. U937 cells were stimulated with immunostimulant CpG7909 into M1 status and then infected with M. tb H37Rv. Expression of IRAK-M, IRAK-4 and iNOS was detected with immunofluorescence staining and Western blot, to evaluate the effect of IRAK-M to CpG directed M1-type polarization of macrophages during M. tb infection. Molecules related with macrophage’s bactericidal ability such as Hif-1 and phosphorylated ERK1/2 were detected with immunohistochemistry and Western blot.

Results

IRAK-M increased in M. tb infected macrophage cells and also in human lung tissue of pulmonary tuberculosis. IRAK-M over-expression resulted in higher bacterial load, while IRAK-M interference resulted in lower bacterial load in M. tb infected cells. During M. tb infection, IRAK-M knockdown induced M1-type, while inhibited M2-type polarization of macrophage. M1-type polarization of U937 cells induced by CpG7909 was inhibited by M. tb infection, which was reversed by IRAK-M knockdown in U937 cells. IRAK-M affected Hif-1 and MAPK signaling cascade during M. tb infection.

Conclusions

Conclusively, IRAK-M might alter the polarity of macrophages, to facilitate intracellular survival of M. tb and affect Th1-type immunity of the host, which is helpful to understanding the pathogenesis of M. tb.

A novel mouse model of conditional IRAK-M deficiency in myeloid cells: application in lung Pseudomonas aeruginosa infection

Myeloid cells such as macrophages are critical to innate defense against infection. IL-1 receptor-associated kinase M (IRAK-M) is a negative regulator of TLR signaling during bacterial infection, but the role of myeloid cell IRAK-M in bacterial infection is unclear. Our goal was to generate a novel conditional knockout mouse model to define the role of myeloid cell IRAK-M during bacterial infection. Myeloid cell-specific IRAK-M knockout mice were generated by crossing IRAK-M floxed mice with LysM-Cre knock-in mice. The resulting LysM-Cre⁺/IRAK-M^fl/wt and control (LysM-Cre^-/IRAK-M^fl/wt) mice were intranasally infected with Pseudomonas aeruginosa (PA). IRAK-M deletion, inflammation, myeloperoxidase (MPO) activity and PA load were measured in leukocytes, bronchoalveolar lavage (BAL) fluid and lungs. PA killing assay with BAL fluid was performed to determine mechanisms of IRAK-M-mediated host defense. IRAK-M mRNA and protein levels in alveolar and lung macrophages were significantly reduced in LysM-Cre⁺/IRAK-M^fl/wt mice compared with control mice. Following PA infection, LysM-Cre⁺/IRAK-M^fl/wt mice have enhanced lung neutrophilic inflammation, including MPO activity, but reduced PA load. The increased lung MPO activity in LysM-Cre⁺/IRAK-M^fl/wt mouse BAL fluid reduced PA load. Generation of IRAK-M conditional knockout mice will enable investigators to determine precisely the function of IRAK-M in myeloid cells and other types of cells during infection and inflammation.

Activator protein 1 promotes the transcriptional activation of IRAK-M

Interleukin-1 receptor-associated kinase M (IRAK-M) is a well-known negative regulator for Toll-like receptor signaling, which can regulate immune homeostasis and tolerance in a number of pathological settings. However, the mechanism for IRAK-M regulation at transcriptional level remains largely unknown. In this study, a 1.4kb upstream sequence starting from the major IRAK-M transcriptional start site was cloned into luciferase reporter vector pGL3-basic to construct the full-length IRAK-M promoter. Luciferase reporter plasmids harboring the full-length and the deletion mutants of IRAK-M were transfected into 293T and A549 cells, and their relative luciferase activity was measured. The results demonstrated that activator protein 1(AP-1) cis-element plays a crucial role in IRAK-M constitutive gene transcription. Silencing of c-Fos and/or c-Jun expression suppressed the IRAK-M promoter activity as well as its mRNA and protein expressions. As a specific inhibitor for AP-1 activation, SP600125 also significantly suppressed the basal transcriptional activity of IRAK-M, the binding activity of c-Fos/c-Jun with IRAK-M promoter, and IRAK-M protein expression. Taken together, the result of this study highlights the importance of AP-1 in IRAK-M transcription, which offers more information on the role of IRAK-M in infectious and non-infectious diseases.