Interleukin-1 receptor-associated kinase-2 genetic variant rs708035 increases NF-κB activity through promoting TRAF6 ubiquitination

Pathways for macrophage uptake of cell-free circular RNAs

Circular RNAs (circRNAs) are stable RNAs present in cell-free RNA, which may comprise cellular debris and pathogen genomes. Here, we investigate the phenomenon and mechanism of cellular uptake and intracellular fate of exogenous circRNAs. Human myeloid cells and B cells selectively internalize extracellular circRNAs. Macrophage uptake of circRNA is rapid, energy dependent, and saturable. CircRNA uptake can lead to translation of encoded sequences and antigen presentation. The route of internalization influences immune activation after circRNA uptake, with distinct gene expression programs depending on the route of RNA delivery. Genome-scale CRISPR screens and chemical inhibitor studies nominate macrophage scavenger receptor MSR1, Toll-like receptors, and mTOR signaling as key regulators of receptor-mediated phagocytosis of circRNAs, a dominant pathway to internalize circRNAs in parallel to macropinocytosis. These results suggest that cell-free circRNA serves as an "eat me" signal and danger-associated molecular pattern, indicating orderly pathways of recognition and disposal.

Modulation of IRAK enzymes as a therapeutic strategy against SARS-CoV-2 induced cytokine storm

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the current pandemic coronavirus disease 2019 (COVID-19). Dysregulated and excessive production of cytokines and chemokines, known as cytokine storm, is frequently seen in patients with severe COVID-19 disease and it can provoke a severe systematic inflammation in the patients. The IL-1R/TLRs/IRAKs signaling network is a key pathway in immune cells that plays a central role in regulating innate immunity and inflammatory responses via stimulating the expression and production of various proinflammatory molecules including cytokines. Modulation of IRAKs activity has been proposed to be a promising strategy in the treatment of inflammatory disorders. In this review, we highlight the biochemical properties of IRAKs and their role in regulating inflammatory molecular signaling pathways and discuss the potential targeting of IRAKs to suppress the SARS-CoV-2-induced cytokine storm in COVID-19 patients.

Hyperfunction variant rs708035 of interleukin 1 receptor-associated kinases 2 gene involved in the predisposition of leprosy infection

BACKGROUND

Mycobacterium leprae (slow-growing bacteria) is the etiological agent for leprosy infection, which is a chronic granulomatous disease. Symptoms initiate with the loss of sensation in the affected areas, which can lead to severe injuries, cuts and burns. IRAK2 (interleukin-1 receptor-associated kinases 2) is reported to function in the regulation of the NFκB pathway. The frequency of the IRAK2 polymorphism (rs708035) was unknown in the Pakistani population. Therefore, the study was designed to identify the role of the rs708035 SNP (single nucleotide polymorphism) in susceptibility to leprosy.

METHODOLOGY

The case-control study was designed, and participants were selected by Ridley-Jopling Classification. Blood samples from healthy individuals and patients were collected after ethical approval. Genomic DNA was extracted for the amplification of selected polymorphisms by tetra-primer amplification refractory mutation system polymerase chain reaction. The desired products were observed via agarose gel (2.5%) electrophoresis followed by data analysis using bioinformatics tools (SNP Stats and SHEsis) and statistical tests (odds ratio, OR, and chi square).

RESULTS

The study revealed that the mutant genotype (TT) was found to be frequent among cases (22.80%) in comparison with the controls (1.66%). The SNP rs708035 was significantly associated with the progression of leprosy (χ²  = 17.62, p < 0.0001). The targeted SNP significantly increases the risk of leprosy 2.3 times (OR = 2.3119, 95% CI 1.2729-4.1989, p < 0.01). The genetic model also confirms the significant association of the A/T genotype with leprosy in the over-dominant model (OR = 2.83, 95% CI 1.16-6.89, p < 0.001).

CONCLUSIONS

The study revealed a significant association of the targeted SNP with leprosy and provided baseline data regarding the association of rs708035. The current research could be utilized for the preparation of biomarkers by considering a larger sample size.

HIGHLIGHTS

The patients suffering from leprosy faced various comorbidities, including hypertension and diabetes. The study reports for the first time a significant association of interleukin 1 receptor associated kinases 2 (IRAK2) single nucleotide polymorphism (SNP) rs708035 among the Pakistani population (Karachi). The current study provides baseline data to develop diagnostic biomarkers for early detection of leprosy.

Multi-locus SNP analyses of interleukin 1 receptor associated kinases 2 gene polymorphisms with the susceptibility to rheumatoid arthritis

Background

The genetic polymorphisms (rs708035, rs3844283) of Interleukin-1 receptor associated kinases 2 (IRAK2) is involved in the NFκB regulatory pathway. The frequencies of IRAK2 gene are unknown in Pakistani population. Therefore, the study was designed to examine the association of targeted single nucleotide polymorphism(s) in IRAK2 gene of RA patients.

Methodology

The study participants were selected by ACR/EULAR 2010 standards. After ethical approval, the blood samples of patients and healthy controls were collected for the extraction of DNA followed by the amplification of targeted polymorphism(s) via Tetra-primer Amplification Refractory Mutation System (T-ARMS PCR). Desired products were observed via agarose gel electrophoresis.

Results

The allele frequency of wild type A and C is frequent among patients and mutant T and G is frequent among controls. The rs708035 showed significant protective association while rs3844283 was found to be associated with risk of RA. Genetic model associations were applied to determine the role of genotypes. In combination analyses of alleles revealed AC haplotype was found to be associated with risk and TG provide protection against RA. Moreover, targeted SNPs were found to be in 61% Linkage Disequilibrium among the targeted population.

Conclusions

Current study revealed the protective and risk association of targeted SNPs (rs708035, rs3844283). Study might be beneficial as it provides baseline data regarding targeted SNPs and their role in the disease progression. This could be served as potential biomarker for diagnostic purpose and effectively utilized in precision medicine approach.

The extreme C-terminus of IRAK2 assures full TRAF6 ubiquitination and optimal TLR signaling

Macrophages are fundamental for initiation, maintenance, and resolution of inflammation. They can be activated by 'Toll-like receptor' (TLR) engagement, which initiates critical pathways to fight infections. 'Interleukin receptor-associated kinase 2' (IRAK2) is part of the membrane-proximal Myddosome formed at IL-1R/TLRs, but utility and regulation of IRAK2 within is not completely understood. In this study, we addressed the importance of the evolutionary conserved extreme C-terminus of IRAK2 in TLR signaling. The last 55 amino acids lack any known functional domain. The C-terminus deletion mutant IRAK2Δ55 was hypofunctional and disabled to conduct TLR4-inducible NF-κB and ERK2 activation. Accordingly, it could neither fully support subsequent CD40 cell surface expression nor IL-6 and nitric oxide release. Interestingly, IRAK2Δ55 was still capable to bind to 'tumor necrosis factor receptor-associated factor 6' (TRAF6), which is requisite to activate TRAF6 as an E3-ubiquitin ligase for further downstream signaling. However, IRAK-dependent auto-ubiquitination of TRAF6 was impaired, when IRAK2Δ55 was bound. Thus, the conserved last 55 amino acids enable IRAK2 to sustain an optimal TLR response. This knowledge might spark ideas how overshooting inflammatory responses could be modified without blocking the entire immune response.

Role of the Host Genetic Susceptibility to 2009 Pandemic Influenza A H1N1

Influenza A virus (IAV) is the most common infectious agent in humans, and infects approximately 10-20% of the world's population, resulting in 3-5 million hospitalizations per year. A scientific literature search was performed using the PubMed database and the Medical Subject Headings (MeSH) "Influenza A H1N1" and "Genetic susceptibility". Due to the amount of information and evidence about genetic susceptibility generated from the studies carried out in the last influenza A H1N1 pandemic, studies published between January 2009 to May 2020 were considered; 119 papers were found. Several pathways are involved in the host defense against IAV infection (innate immune response, pro-inflammatory cytokines, chemokines, complement activation, and HLA molecules participating in viral antigen presentation). On the other hand, single nucleotide polymorphisms (SNPs) are a type of variation involving the change of a single base pair that can mean that encoded proteins do not carry out their functions properly, allowing higher viral replication and abnormal host response to infection, such as a cytokine storm. Some of the most studied SNPs associated with IAV infection genetic susceptibility are located in the FCGR2A, C1QBP, CD55, and RPAIN genes, affecting host immune responses through abnormal complement activation. Also, SNPs in IFITM3 (which participates in endosomes and lysosomes fusion) represent some of the most critical polymorphisms associated with IAV infection, suggesting an ineffective virus clearance. Regarding inflammatory response genes, single nucleotide variants in IL1B, TNF, LTA IL17A, IL8, IL6, IRAK2, PIK3CG, and HLA complex are associated with altered phenotype in pro-inflammatory molecules, participating in IAV infection and the severest form of the disease.

miR-205/IRAK2 signaling pathway is associated with urban airborne PM2.5-induced myocardial toxicity

Exposure to fine particulate matter (PM_2.5) is closely linked with cardiovascular diseases. However, the underlying mechanism of PM_2.5 on cardiac function remains unknown. This study was aimed to investigate the role of microRNA-205 (miR-205) on PM_2.5-induced myocardial inflammation and cardiac dysfunction. PM_2.5 increased the levels of reactive oxygen species (ROS) and malondialdehyde (MDA), following by decreased cell viability and antioxidant enzymes, resulting in apoptosis of cardiomyocytes (AC16). The histopathological and ultrastructural analysis demonstrated that PM_2.5 caused myocardial damage via interstitial edema, inflammatory cell infiltration, and myocardial fiber destruction. PM_2.5 enhanced the release of inflammatory factors in AC16 cells and heart tissue. Microarray analysis and dual-luciferase reporter gene assays demonstrated that PM_2.5-induced down-regulation of miR-205 regulated interleukin 1 receptor-associated kinase 2 (IRAK2), which further activated the TNF receptor-associated factor 6 (TRAF6)/nuclear transcription factor-κB (NF-κB) signaling pathway in vivo. Moreover, the chemical mimics of miR-205 markedly inhibited the IRAK2/TRAF6/NF-κB signaling pathway, whereas the chemical inhibitors of miR-205 amplified PM_2.5-induced activation of the IRAK2 signaling pathway in vitro. In summary, our results found that PM_2.5 could trigger myocardial toxicity via miR-205 negative regulating the IRAK2/TRAF6/NF-κB signaling pathway. Our study suggests that miR-205 could be a promising target molecule for mitigating the hazardous effects of PM_2.5 on the cardiovascular system.

LncRNA TLR8-AS1 promotes metastasis and chemoresistance of ovarian cancer through enhancing TLR8 mRNA stability

Ovarian cancer is diagnosed as the most deadly gynecological tumor. Ovarian cancer metastasis affects chemoresistance and confers poor patient prognosis. In present work, we intended to elucidate whether long non-coding RNAs (lncRNAs) TLR8-AS1 regulated cell metastasis and chemoresistance of ovarian cancer, and uncover the molecular mechanism of TLR8-AS1 in the modulation of ovarian cancer progression. Firstly, bioinformatics analyses identified TLR8-AS1 as a cancer-associated fibroblasts regulated lncRNA in ovarian cancer. Further experiments revealed that TLR8-AS1 augmented cell metastasis and chemoresistance of ovarian cancer in vitro and in vivo. Moreover, TLR8-AS1 upregulates TLR8 by stabilizing TLR8 mRNA, thus activating NF-κB signaling and promoting ovarian cancer metastasis and chemoresistance. Besides, TCGA data analysis suggested that TLR8-AS1 is elevated in ovarian cancer in comparison to adjacent non-cancerous tissues. High TLR8-AS1 expression levels were measured in metastatic ovarian cancer and correlated with poor patient prognosis. The clinical data supported the mechanism and biological significance of TLR8-AS1 dysregulation in ovarian cancer development. Our work demonstrates that TLR8-AS1 can be applied as a diagnostic and prognostic indicator for ovarian cancer, and maybe an alternative target for the treatment of ovarian cancer.

[Establishment of a congenital chloride diarrhea-associated SLC26A3 c.392C>G (p.P131R) polymorphism-expressing cell model and a preliminary analysis of its mechanism of action]

OBJECTIVE

To establish a congenital chloride diarrhea (CCD)-associated SLC26A3 c.392C>G (p.P131R) polymorphism-expressing cell model, and to investigate its biological function.

METHODS

The sequence of the SLC26A3 gene in GenBank was used to design the upstream and downstream single-guide RNA (sgRNA) that could specifically recognize the 392 locus of the SLC26A3 gene, and the sgRNA was mixed with the pSpCas9-puro vector after enzyme digestion to construct an eukaryotic recombinant expression plasmid (pSpCas9-SLC26A3). Caco-2 cells were transfected with the recombinant plasmid and synthesized single-stranded DNA oligonucleotides (ssODNs), and Taqman genotyping assay and Sanger sequencing were used to identify the expression of SLC26A3 c.392C>G (p.P131R) in Caco-2 cells. Wild-type Caco-2 cells were selected as normal control group and the Caco-2 cells with successful expression of SLC26A3 c.392C>G (p.P131R) was selected as P131R group. Both groups were treated with 100 ng/mL tumor necrosis factor-α (TNF-α), and then the normal control group was named as TNF-α group, and the P131R group was named as TNF-α+P131R group. Electric cell-substrate impedance sensing (ECIS) assay was used to evaluate the change in the monolayer barrier function of intestinal epithelial cells in the above four groups, and Western blot was used to measure the change in the expression of SLC26A3 protein in the normal control group and the P131R group.

RESULTS

The eukaryotic recombinant expression plasmid (pSpCas9-SLC26A3) was successfully constructed. Both Taqman genotyping assay and Sanger sequencing confirmed the successful establishment of the Caco-2 cell model of SLC26A3 c.392C>G (p.P131R) expression. ECIS assay showed that compared with the normal control group, the P131R group had a significant increase in the monolayer permeability of intestinal epithelial cells (P<0.05), and at the same time, the P131R group had a significantly greater increase in cell membrane permeability after the induction with 100 ng/mL TNF-α (P<0.05). Western blot showed that compared with the normal control group, the P131R group had a significant reduction in the expression of SLC26A3 protein (P=0.001).

CONCLUSIONS

SLC26A3 c.392C>G (p.P131R) can reduce the expression of SLC26A3 protein, increase the monolayer permeability of intestinal epithelial cells, and thus lead to diarrhea.

IRAK2 is associated with systemic lupus erythematosus risk

INTRODUCTION

Interleukin-1 receptor-associated kinases (IRAKs) are serine-threonine kinases involved in toll-like receptor and interleukin-1 signaling pathways. They play a key role in inflammation and innate immunity. IRAKs have been previously incriminated in autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis and inhibition of IRAKs has been recently regarded as a potential therapeutic strategy for SLE.

OBJECTIVES

The aim of the present study was to test the association between IRAK2 rs708035 and rs3844283 with SLE.

MATERIAL AND METHODS

IRAK2 rs708035 and rs3844283 were genotyped by mutagenically separated polymerase chain reaction (MS-PCR) in 142 SLE patients and 149 age- and gender-matched controls.

RESULTS

The hyperfunctional IRAK2 rs708035 A allele was more frequent among SLE patients than controls (62.9% versus 54.7%, p = 0.046). IRAK2 rs3844283 C allele was present in 66.5% of patients and 75.5% of controls. The CC genotype was the most frequently exhibited genotype. It was carried by 45.1% of patients with SLE and 57.7% of controls. The G allele was associated with an increased risk of SLE (OR = 1.54, 95%, CI = 1.07-2.22, p = 0.017). IRAK2 rs708035 and IRAK2 rs3844283 were in linkage disequilibrium (D' = 0.64). The AG haplotype was more frequently observed in SLE patients than in controls (0.292 versus 0.194, p = 0.008).

CONCLUSION

This study for the first time ever reveals the association of IRAK2 rs708035 and IRAK2 rs3844283 and the corresponding haplotypes with SLE. Our findings give additional rationale to target IRAKs in the treatment of SLE.Key Points• IRAK2 rs708035 A allele is more frequent in SLE patients than in controls and IRAK2 rs3844283 G allele is associated with SLE susceptibility.• These two alleles are in linkage disequilibrium.• The AG haplotype is associated with SLE.

miR-497a-5p attenuates lipopolysaccharide-induced inflammatory injury by targeting IRAK2

Acute lung injury (ALI) is a severe acute inflammatory reaction of the lungs caused by a variety of factors, which can lead to a high mortality rate. MicroRNAs are a novel therapeutic molecule that play a vital role in many diseases. However, its mechanism of action in lipopolysaccharide (LPS)-induced mouse ALI is not clear. The study aimed to investigate the mechanism of action of miR-497 in LPS-induced ALI. As a result, it was found that the expression of miR-497 in the inflammatory reaction showed a decrease in time and dose trends. Importantly, miR-497 reduced LPS-induced expression levels of related inflammatory factors. In addition, we also demonstrated that IRAK2 is a direct target molecule of miR-497. Interestingly, we further found that miR-497 inhibits the expression of IRAK2 by targeting IRAK2-3'UTR. Therefore, miR-497 can partially negatively regulate the activation of IRAK2-NF-κB pathway in LPS-induced inflammatory responses.

Functional characterization of SLC26A3 c.392C>G (p.P131R) mutation in intestinal barrier function using CRISPR/CAS9-created cell models

Background

Congenital chloride diarrhea (CCD) in a newborn is a rare autosomal recessive disorder with life-threatening complications, requiring early diagnostics and treatment to prevent severe dehydration and infant mortality. SLC26A3 rs386833481 (c.392C>G; p.P131R) gene polymorphism is an important genetic determinant of CCD. Here, we report the influence of the non-synonymous SLC26A3 variant rs386833481 gene polymorphism on the function of the epithelial barrier and the potential mechanisms of these effects.

Results

We found that P131R-SLC26A3 increased dysfunction of the epithelial barrier compared with wild type SLC26A3 in human colonic Caco-2 and mouse colonic CMT-93 cells. When P131R-SLC26A3 was subsequently reverted to wild type, the epithelial barrier function was restored similar to wild type cells. Further study demonstrated that variant P131R-SLC26A3 disrupts function of epithelial barrier through two distinct molecular mechanisms: (a) decreasing SLC26A3 expression through a ubiquitination pathway and (b) disrupting a key interaction with its partner ZO-1/CFTR, thereby increasing the epithelial permeability.

Conclusion

Our study provides an important insight of SLC26A3 SNPs in the regulation of the epithelial permeability and indicates that SLC26A3 rs386833481 is likely a causative mutation in the dysfunction of epithelial barrier of CCD, and correction of this SNP or increasing SLC26A3 function could be therapeutically beneficial for chronic diarrhea diseases.

A miRNA Host Response Signature Accurately Discriminates Acute Respiratory Infection Etiologies

Background: Acute respiratory infections (ARIs) are the leading indication for antibacterial prescriptions despite a viral etiology in the majority of cases. The lack of available diagnostics to discriminate viral and bacterial etiologies contributes to this discordance. Recent efforts have focused on the host response as a source for novel diagnostic targets although none have explored the ability of host-derived microRNAs (miRNA) to discriminate between these etiologies. Methods: In this study, we compared host-derived miRNAs and mRNAs from human H3N2 influenza challenge subjects to those from patients with Streptococcus pneumoniae pneumonia. Sparse logistic regression models were used to generate miRNA signatures diagnostic of ARI etiologies. Generalized linear modeling of mRNAs to identify differentially expressed (DE) genes allowed analysis of potential miRNA:mRNA relationships. High likelihood miRNA:mRNA interactions were examined using binding target prediction and negative correlation to further explore potential changes in pathway regulation in response to infection. Results: The resultant miRNA signatures were highly accurate in discriminating ARI etiologies. Mean accuracy was 100% [88.8-100; 95% Confidence Interval (CI)] in discriminating the healthy state from S. pneumoniae pneumonia and 91.3% (72.0-98.9; 95% CI) in discriminating S. pneumoniae pneumonia from influenza infection. Subsequent differential mRNA gene expression analysis revealed alterations in regulatory networks consistent with known biology including immune cell activation and host response to viral infection. Negative correlation network analysis of miRNA:mRNA interactions revealed connections to pathways with known immunobiology such as interferon regulation and MAP kinase signaling. Conclusion: We have developed novel human host-response miRNA signatures for bacterial and viral ARI etiologies. miRNA host response signatures reveal accurate discrimination between S. pneumoniae pneumonia and influenza etiologies for ARI and integrated analyses of the host-pathogen interface are consistent with expected biology. These results highlight the differential miRNA host response to bacterial and viral etiologies of ARI, offering new opportunities to distinguish these entities.

CD8+ T cells with high TGF‑β1 expression cause lymph node fibrosis following HIV infection

Lymph node (LN) fibrosis resulting in cluster of differentiation (CD) 4+ T cell reduction following human immunodeficiency virus (HIV) infection is an important step in the pathogenesis of acquired immunodeficiency syndrome. The mechanisms mediating LN fibrosis following HIV infection have not been completely elucidated. In order to investigate the mechanism of LN fibrosis, the expression of transforming growth factor (TGF)‑β1 was determined in the LNs of HIV‑infected individuals by immunohistochemistry and fluorescence‑based flow cytometry. The effect of stimulated CD8+ T cells on collagen secretion by fibroblasts was detected using immunofluorescence staining and western blot analysis. The results demonstrated that the LNs of HIV‑infected individuals exhibited a significantly increased proportion of CD8+ T cells with high TGF‑β1 expression. These CD8+ T cells demonstrated increased CD38 and programmed cell death protein 1 expression and decreased CD127 expression compared with the controls. CD8+ T cells from the LNs of non‑HIV infected individuals expressed a high TGF‑β1 level following stimulation with phorbol‑12‑myristate 13‑acetate. These CD8+T cells subsequently induced the secretion of a large amount of type I collagen in human lymphatic fibroblasts. The results of the present study indicated that CD8+ T cells with high TGF‑β1 expression served an important role in LN fibrosis following HIV infection.

The secret life of kinases: insights into non-catalytic signalling functions from pseudokinases

Over the past decade, our understanding of the mechanisms by which pseudokinases, which comprise ∼10% of the human and mouse kinomes, mediate signal transduction has advanced rapidly with increasing structural, biochemical, cellular and genetic studies. Pseudokinases are the catalytically defective counterparts of conventional, active protein kinases and have been attributed functions as protein interaction domains acting variously as allosteric modulators of conventional protein kinases and other enzymes, as regulators of protein trafficking or localisation, as hubs to nucleate assembly of signalling complexes, and as transmembrane effectors of such functions. Here, by categorising mammalian pseudokinases based on their known functions, we illustrate the mechanistic diversity among these proteins, which can be viewed as a window into understanding the non-catalytic functions that can be exerted by conventional protein kinases.

Loss of TAB3 expression by shRNA exhibits suppressive bioactivity and increased chemical sensitivity of ovarian cancer cell lines via the NF-κB pathway

Ovarian cancer is a leading cause of death among gynaecologic malignancies. Despite many years of research, it still remains sparing in reliable diagnostic markers and methods for early detection and screening. Transforming growth factor β-activated protein kinase 1 (TAK1)-binding protein 3 (TAB3) was initially characterized as an adapter protein essential for TAK1 activation in response to IL-1β or TNFα, however, the physiological role of TAB3 in ovarian cancer tumorigenesis is still not fully understood. In this study, we evaluated the effects of TAB3 on ovarian cancer cell lines. Expressions of TAB3 and PCNA (proliferating cell nuclear antigen) were found to be gradually increased in EOC tissues and cell lines, by western blot analysis and qRT-PCR. Distribution of TAB3 was further analysed by immunohistochemistry. In vitro, knockdown of TAB3 expression in HO8910 or SKOV3 ovarian cancer cells significantly inhibited bioactivity of ovarian cancer cells, including proliferation and cell-cycle distribution, and promoted chemical sensitivity to cisplatin and paclitaxel treatment via inhibiting NF-κB pathways. In conclusion, our study strongly suggests a novel function of TAB3 as an oncogene that could be used as a biomarker for ovarian cancer. It provides a new insight into the potential mechanism for therapeutic targeting, in chemotherapy resistance, common in ovarian cancer.

Pancreatic Acinar Cells Employ miRNAs as Mediators of Intercellular Communication to Participate in the Regulation of Pancreatitis-Associated Macrophage Activation

Macrophage activation plays an important role in the inflammatory response in acute pancreatitis. In the present study, the activation of AR42J pancreatic acinar cells was induced by taurolithocholate treatment. The results showed that the culture medium from the activated AR42J cells significantly enhanced NFκB activation in the macrophages compared to that without taurolithocholate treatment. Additionally, the precipitates obtained from ultracentrifugation of the culture media that were rich in exosomes were markedly more potent in activating macrophages compared with the supernatant fraction lacking exosomes. The results indicated that the mediators carried by the exosomes played important roles in macrophage activation. Exosomal miRNAs were extracted and examined using microarrays. A total of 115 differentially expressed miRNAs were identified, and 30 showed upregulated expression, while 85 displayed downregulated expression. Target genes of the differentially expressed miRNAs were predicted using TargetScan, MiRanda, and PicTar software programs. The putative target genes were subjected to KEGG functional analysis. The functions of the target genes were primarily enriched in MAPK pathways. Specifically, the target genes regulated macrophage activation through the TRAF6-TAB2-TAK1-NIK/IKK-NFκB pathway. As the mediators of signal transduction, miRNAs and their predicted target mRNAs regulate every step in the MAPK pathway.

A frequent hypofunctional IRAK2 variant is associated with reduced spontaneous hepatitis C virus clearance

Patients carrying very rare loss-of-function mutations in interleukin-1 receptor-associated kinase 4 (IRAK4), a critical signaling mediator in Toll-like receptor signaling, are severely immunodeficient, highlighting the paramount role of IRAK kinases in innate immunity. We discovered a comparatively frequent coding variant of the enigmatic human IRAK2, L392V (rs3844283), which is found homozygously in ∼15% of Caucasians, to be associated with a reduced ability to induce interferon-alpha in primary human plasmacytoid dendritic cells in response to hepatitis C virus (HCV). Cytokine production in response to purified Toll-like receptor agonists was also impaired. Additionally, rs3844283 was epidemiologically associated with a chronic course of HCV infection in two independent HCV cohorts and emerged as an independent predictor of chronic HCV disease. Mechanistically, IRAK2 L392V showed intact binding to, but impaired ubiquitination of, tumor necrosis factor receptor-associated factor 6, a vital step in signal transduction.

CONCLUSION

Our study highlights IRAK2 and its genetic variants as critical factors and potentially novel biomarkers for human antiviral innate immunity.

CHOP links endoplasmic reticulum stress to NF-κB activation in the pathogenesis of nonalcoholic steatohepatitis

During metabolic stress, the UPR transcription factor CHOP activates NF-κB through a pathway involving IRAK2 expression, resulting in hepatocyte secretion of cytokines IL-8 and TNFα, which trigger inflammation and hepatocellular death.

Free fatty acid induction of inflammation and cell death is an important feature of nonalcoholic steatohepatitis (NASH) and has been associated with disruption of the endoplasmic reticulum and activation of the unfolded protein response (UPR). After chronic UPR activation, the transcription factor CHOP (GADD153/DDIT3) triggers cell death; however, the mechanisms linking the UPR or CHOP to hepatoceullular injury and inflammation in the pathogenesis of NASH are not well understood. Using HepG2 and primary human hepatocytes, we found that CHOP induces cell death and inflammatory responses after saturated free fatty acid exposure by activating NF-κB through a pathway involving IRAK2 expression, resulting in secretion of cytokines IL-8 and TNFα directly from hepatocytes. TNFα facilitates hepatocyte death upon exposure to saturated free fatty acids, and secretion of both IL-8 and TNFα contribute to inflammation. Of interest, CHOP/NF-κB signaling is not conserved in primary rodent hepatocytes. Our studies suggest that CHOP plays a vital role in the pathophysiology of NASH by induction of secreted factors that trigger inflammation and hepatocellular death via a signaling pathway specific to human hepatocytes.