Prognostic value of inflammation and immune-related gene NOD2 in clear cell renal cell carcinoma

Inflammation and immune responses play important roles in cancer development and prognosis. We identified 59 upregulated inflammation- and immune-related genes (IIRGs) in clear cell renal cell carcinoma (ccRCC) from The Cancer Genome Atlas database. Among the upregulated IIRGs, nucleotide binding oligomerization domain 2 (NOD2), PYD and CARD domain (PYCARD) were also confirmed to be upregulated in the Oncomine database and in three independent GEO data sets. Tumor immune infiltration resource database analysis revealed that NOD2 and PYCARD levels were significantly positively correlated with infiltration levels of B cells, CD4+ T cells, CD8+ T cells, neutrophils, macrophages and dendritic cells. Multivariate Cox hazards regression analysis indicated that based on clinical variables (age, gender, tumor grade, pathological TNM stage), NOD2, but not PYCARD, was an independent, unfavorable ccRCC prognostic biomarker. Functional enrichment analyses (GSEA) showed that NOD2 was involved in innate immune responses, inflammatory responses, and regulation of cytokine secretion. Meanwhile, mRNA and protein levels of NOD2 were elevated in four ccRCC cell lines (786-O, ACHN, A498 and Caki-1), and its knockdown significantly inhibited IL-8 secretion, thereby inhibiting ccRCC cell proliferation and invasion. Furthermore, results showed that miR-20b-5p targeted NOD2 to alleviate NOD2-mediated IL-8 secretion. In conclusion, NOD2 is a potential prognostic biomarker for ccRCC and the miR-20b-5p/NOD2/IL-8 axis may regulate inflammation- and immune-mediated tumorigenesis in ccRCC.

Peptidoglycan fragment release and NOD activation by commensal Neisseria species from humans and other animals

Neisseria gonorrhoeae, a human restricted pathogen, releases inflammatory peptidoglycan (PG) fragments that contribute to the pathophysiology of pelvic inflammatory disease. The genus Neisseria is also home to multiple species of human- or animal-associated Neisseria that form part of the normal microbiota. Here we characterized PG release from the human-associated nonpathogenic species Neisseria lactamica and Neisseria mucosa and animal-associated Neisseria from macaques and wild mice. An N. mucosa strain and an N. lactamica strain were found to release limited amounts of the proinflammatory monomeric PG fragments. However, a single amino acid difference in the PG fragment permease AmpG resulted in increased PG fragment release in a second N. lactamica strain examined. Neisseria isolated from macaques also showed substantial release of PG monomers. The mouse colonizer Neisseria musculi exhibited PG fragment release similar to that seen in N. gonorrhoeae with PG monomers being the predominant fragments released. All the human-associated species were able to stimulate NOD1 and NOD2 responses. N. musculi was a poor inducer of mouse NOD1, but ldcA mutation increased this response. The ability to genetically manipulate N. musculi and examine effects of different PG fragments or differing amounts of PG fragments during mouse colonization will lead to a better understanding of the roles of PG in Neisseria infections. Overall, we found that only some nonpathogenic Neisseria have diminished release of proinflammatory PG fragments, and there are differences even within a species as to types and amounts of PG fragments released.

The Immunometabolic Gene N-Acetylglucosamine Kinase Is Uniquely Involved in the Heritability of Multiple Sclerosis Severity

The clinical severity of multiple sclerosis (MS), an autoimmune disorder of the central nervous system, is thought to be determined by environmental and genetic factors that have not yet been identified. In a recent genome-wide association study (GWAS), a single nucleotide polymorphism (SNP), rs10191329, has been associated with MS severity in two large independent cohorts of patients. Different approaches were followed by the authors to prioritize the genes that are transcriptionally regulated by such an SNP. It was concluded that the identified SNP regulates a group of proximal genes involved in brain resilience and cognitive abilities rather than immunity. Here, by conducting an alternative strategy for gene prioritization, we reached the opposite conclusion. According to our re-analysis, the main target of rs10191329 is N-Acetylglucosamine Kinase (NAGK), a metabolic gene recently shown to exert major immune functions via the regulation of the nucleotide-binding oligomerization domain-containing protein 2 (NOD2) pathway. To gain more insights into the immunometabolic functions of NAGK, we analyzed the currently known list of NAGK protein partners. We observed that NAGK integrates a dense network of human proteins that are involved in glucose metabolism and are highly expressed by classical monocytes. Our findings hold potentially major implications for the understanding of MS pathophysiology.

Inhibiting Peptidoglycan Hydrolase Alleviates MRSA Pneumonia Through Autolysin-Mediated MDP-NOD2 Pathway

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is a cause of staph infection that is difficult to treat because of resistance to some antibiotics. A recent study indicated that diarylurea ZJ-2 is a novel antibacterial agent against multi-drug resistant Enterococcus faecium. In this work, we refined the bactericidal mechanism of ZJ-2 as a peptidoglycan (PG) hydrolase by affecting AtlA-mediated PG homeostasis.

Methods

A wild-type strain (WT) and a mutant strain (ΔatlA) were used to investigate the effects of ZJ-2 on the cell wall, PG, and autolysin regulatory system by antimicrobial susceptibility testing, hemolytic toxin assay, microanalysis, autolysis assay, qRT-PCR, ELISA and mouse model of pneumonia.

Results

The results revealed that ZJ-2 down-regulated the expression of genes related to peptidoglycan hydrolase (PGH) (sprX, walR, atlA, and lytM), and reduced the levels of PG, muramyl dipeptide (MDP), cytokines, and hemolytic toxin, while ΔatlA interfered with the genes regulation and PG homeostasis. In the mouse MRSA pneumonia model, the same trend was observed in the nucleotide oligomerization domain protein 2 (NOD2) and relative proinflammatory factors.

Conclusion

ZJ-2 may act as a novel inhibitor of PG hydrolyse, disrupting autolysin-mediated PG homeostasis, and reducing inflammation by down-regulating the MDP-NOD2 pathway.

Clinical outcomes and perioperative morbidity and mortality following segmental resections of the colon for Crohn's colitis

INTRODUCTION

Crohn's disease (CD) is a chronic inflammatory bowel disease of a multifactorial pathogenesis. Recently numerous genetic variants linked to an aggressive phenotype were identified, leading to a progress in therapeutic options, resulting in a decreased necessity for surgery. Nevertheless, surgery is often inevitable. The aim of the study was to evaluate possible risk factors for postoperative complications and disease recurrence specifically after colonic resections for CD.

PATIENTS AND METHODS

A total of 241 patients who underwent colonic and ileocaecal resections for CD at our instiution between 2008 and 2018 were included. All data was extracted from clinical charts.

RESULTS

Major complications occurred in 23.8% of all patients. Patients after colonic resections showed a significantly higher rate of major postoperative complications compared to patients after ICR (p =  < 0.0001). The most common complications after colonic resections were postoperative bleeding (22.2%), the need for revision surgery (27.4%) and ICU (17.2%) or hospital readmission (15%). As risk factors for the latter, we identified time interval between admission and surgery (p = 0.015) and the duration of the surgery (p = 0.001). Isolated distal resections had a higher risk for revision surgery and a secondary stoma (p = 0.019). Within the total study population, previous bowel resections (p = 0.037) were identified as independent risk factors for major perioperative complications.

CONCLUSION

The results indicate that both a complex surgical site and a complex surgical procedure lead to a higher perioperative morbidity in colonic resections for Crohn's colitis.

Identification, characterization and the inflammatory regulating effect of NOD1/2 in sturgeon

As an ancient species with both conservation and commercial value, Sturgeon's inflammatory regulation mechanism is a research point. Nucleotide-binding and oligomerization domain-containing proteins 1 and 2 (NOD1/2) are classical intracellular pattern recognition receptors (PRRs) in immunity of anti-bacterial infection. However, the characterization and function of NOD1/2 in Sturgeon are still unclear. In this study, we analyzed the synteny relationship of NOD1/2 genes between Acipenser ruthenus and representative fishes at the genome-level. Results showed that the ArNOD2 collinear genes pair was present in all representative fishes. The duplicated ArNOD1/2 genes were under purifying selection during evolution as indicated by their Ka/Ks values. To explore the function of NOD1/2, we further investigated their expression patterns and the effects of pathogenic infection, PAMPs treatment, and siRNA interference in Acipenser baerii, the sibling species of A. ruthenus. Results showed that both AbNOD1/2 were expressed at early developmental stages and in different tissues. Pathogenic infection in vivo and PAMPs treatment in vitro demonstrated that AbNOD1/2 could respond to pathogen stimulation. siRNA interference with AbNOD1/2 inhibited expression levels of RIPK2 and inflammatory cytokines compared to the control group after iE-DAP or MDP treatment. This study hinted that the AbNOD1/2 could stimulate the inflammatory cytokines response during evolutionary processes.

Crosstalk between NOD2 and TLR2 suppresses the development of TLR2-mediated experimental colitis

Nucleotide-binding oligomerization domain 2 (NOD2) is an intracellular sensor for muramyl dipeptide (MDP), a degradation product of bacterial cell wall peptidoglycan (PGN). PGN stimulates cell-surface Toll-like receptor 2 (TLR2) independently of NOD2, indicating the presence of crosstalk between extracellular TLR2 and intracellular NOD2 upon exposure to PGN. NOD2-deficient mice were sensitive, while TLR2-deficient mice were resistant to experimental colitis induced by intrarectal administration of PGN. Severe colitis in NOD2-deficient mice was accompanied by increased expression of nuclear factor-kappa B-dependent cytokines and decreased expression of autophagy-related 16-like 1 (ATG16L1). MDP activation of NOD2 enhanced autophagy mediated by TLR2 in human dendritic cells. mRNA expression of TLR2 tended to be higher in the colonic mucosa of patients with active ulcerative colitis compared to that of those in remission. Induction of remission was associated with increased mRNA expression of ATG16L1 in both ulcerative colitis and Crohn's disease patients. Conversely, mRNA expression of receptor-interacting serine/threonine-protein kinase 2 was higher in the inflammatory colonic mucosa of patients with active disease than in the non-inflamed mucosa of patients in remission, in both ulcerative colitis and Crohn's disease. These findings highlight the role of NOD2-TLR2 crosstalk in the immunopathogenesis of colitis.

The expanding clinical spectrum of autoinflammatory diseases with NOD2 variants: a case series and literature review

Objective

To assess the impact conferred by NOD2 variants on the clinical spectrum of patients with systemic autoinflammatory diseases (SAIDs) in Greece.

Methods

Consecutive patients (n=167) with confirmed SAIDs who underwent screening by next generation sequencing (NGS) targeting 26 SAID-associated genes, and carried at least one NOD2 gene variant, were retrospectively studied. The demographic, clinical and laboratory parameters were recorded.

Results

In total, 24 rare NOD2 variants in 23/167 patients (14%) were detected. Notably, 18 patients had at least one co-existing variant in 13 genes other than NOD2. Nine patients had juvenile- and 14 adult-onset disease. All patients presented with symptoms potentially induced by the NOD2 variants. In particular, the candidate clinical diagnosis was Yao syndrome (YAOS) in 12 patients (7% of the whole SAID cohort). The clinical spectrum of patients with YAOS (mean episode duration 8 days) was fever (n=12/12), articular symptoms (n=8), gastrointestinal symptoms (n=7; abdominal pain/bloating in 7; diarrhea in 4; oral ulcers in 3), serositis (n=7), and rash (n=5), while the inflammatory markers were elevated in all but one patient. Most of these patients showed a poor response to nonsteroidal anti-inflammatory drugs (n=7/9), colchicine (n=6/8) and/or anti-TNF treatment (n=3/4), while a complete response was observed in 6/10 patients receiving steroids and 3/5 on anti-IL1 treatment. Another 8 patients were diagnosed with either FMF (n=6) or PFAPA syndrome (n=2) presenting with prominent diarrhea (n=7), oral ulcers (n=2), periorbital swelling and sicca-like symptoms (n=1), or maculopapular rash (n=1). One patient had a clinically undefined SAID, albeit characterized by oral ulcers and diarrhea. Finally, one patient presented with chronic relapsing urticaria with periorbital edema and inflammatory markers, and another one had a Crohn-like syndrome with good response to anti-IL-1 but refractory to anti-TNF treatment.

Conclusion

NOD2 variants were detected in 1 out of 7 SAID patients and seem to have an impact on disease phenotype and treatment response. Further studies should validate combined molecular and clinical data to better understand these distinct nosological entities.

Heterozygous variants of NOD2, IL10RA, PLA2G6 and COL7A1 correlate with Crohn's disease

To identify candidate pathogenic genes of early-stage Crohn's disease (CD) and predict potential roles of genetic factors in CD, we performed whole exome sequencing on a child with early-stage Crohn's disease (CD) and her parents (core family), found that the patient carried heterozygous variants of 4 genes: NOD2 c. 2257 C > T, IL10RA c. 301 C > T, PLA2G6 c. 2029 C > T, COL7A1 c. 3190 G > A. Heterozygous variants of NOD2, IL10RA, PLA2G6 and COL7A1, intestinal inflammatory response is triggered, normal intestinal wall tissue damage, leading to CD phenotype.

Vaccines and Dementia: Part I. Non-Specific Immune Boosting with BCG: History, Ligands, and Receptors

Vaccines such as Bacille Calmette-Guérin (BCG) can apparently defer dementia onset with an efficacy better than all drugs known to date, as initially reported by Gofrit et al. (PLoS One14, e0224433), now confirmed by other studies. Understanding how and why is of immense importance because it could represent a sea-change in how we manage patients with mild cognitive impairment through to dementia. Given that infection and/or inflammation are likely to contribute to the development of dementias such as Alzheimer's disease (Part II of this work), we provide a historical and molecular background to how vaccines, adjuvants, and their component molecules can elicit broad-spectrum protective effects against diverse agents. We review early studies in which poxvirus, herpes virus, and tuberculosis (TB) infections afford cross-protection against unrelated pathogens, a concept known as 'trained immunity'. We then focus on the attenuated TB vaccine, BCG, that was introduced to protect against the causative agent of TB, Mycobacterium tuberculosis. We trace the development of BCG in the 1920 s through to the discovery, by Freund and McDermott in the 1940 s, that extracts of mycobacteria can themselves exert potent immunostimulating (adjuvant) activity; Freund's complete adjuvant based on mycobacteria remains the most potent immunopotentiator reported to date. We then discuss whether the beneficial effects of BCG require long-term persistence of live bacteria, before focusing on the specific mycobacterial molecules, notably muramyl dipeptides, that mediate immunopotentiation, as well as the receptors involved. Part II addresses evidence that immunopotentiation by BCG and other vaccines can protect against dementia development.

NOD2 attenuates osteoarthritis via reprogramming the activation of synovial macrophages

OBJECTIVE

Synovial inflammation, which precedes other pathological changes in osteoarthritis (OA), is primarily initiated by activation and M1 polarization of macrophages. While macrophages play a pivotal role in the inflammatory process of OA, the mechanisms underlying their activation and polarization remain incompletely elucidated. This study aims to investigate the role of NOD2 as a reciprocal modulator of HMGB1/TLR4 signaling in macrophage activation and polarization during OA pathogenesis.

DESIGN

We examined NOD2 expression in the synovium and determined the impact of NOD2 on macrophage activation and polarization by knockdown and overexpression models in vitro. Paracrine effect of macrophages on fibroblast-like synoviocytes (FLS) and chondrocytes was evaluated under conditions of NOD2 overexpression. Additionally, the in vivo effect of NOD2 was assessed using collagenase VII induced OA model in mice.

RESULTS

Expression of NOD2 was elevated in osteoarthritic synovium. In vitro experiments demonstrated that NOD2 serves as a negative regulator of HMGB1/TLR4 signaling pathway. Furthermore, NOD2 overexpression hampered the inflammatory paracrine effect of macrophages on FLS and chondrocytes. In vivo experiments revealed that NOD2 overexpression mitigated OA in mice.

CONCLUSIONS

Supported by convincing evidence on the inhibitory role of NOD2 in modulating the activation and M1 polarization of synovial macrophages, this study provided novel insights into the involvement of innate immunity in OA pathogenesis and highlighted NOD2 as a potential target for the prevention and treatment of OA.

The crosstalk between microbial sensors ELMO1 and NOD2 shape intestinal immune responses

Microbial sensors play an essential role in maintaining cellular homoeostasis. Our knowledge is limited on how microbial sensing helps in differential immune response and its link to inflammatory diseases. Recently we have confirmed that ELMO1 (Engulfment and Cell Motility Protein-1) present in cytosol is involved in pathogen sensing, engulfment, and intestinal inflammation. Here, we show that ELMO1 interacts with another sensor, NOD2 (Nucleotide-binding oligomerization domain-containing protein 2), that recognizes bacterial cell wall component muramyl dipeptide (MDP). The polymorphism of NOD2 is linked to Crohn's disease (CD) pathogenesis. Interestingly, we found that overexpression of ELMO1 and mutant NOD2 (L1007fs) were not able to clear the CD-associated adherent invasive E. coli (AIEC-LF82). The functional implications of ELMO1-NOD2 interaction in epithelial cells were evaluated by using enteroid-derived monolayers (EDMs) from ELMO1 and NOD2 KO mice. Subsequently we also assessed the immune response in J774 macrophages depleted of either ELMO1 or NOD2 or both. The infection of murine EDMs with AIEC-LF82 showed higher bacterial load in ELMO1-KO, NOD2 KO EDMs, and ELMO1 KO EDMs treated with NOD2 inhibitors. The murine macrophage cells showed that the downregulation of ELMO1 and NOD2 is associated with impaired bacterial clearance that is linked to reduce pro-inflammatory cytokines and reactive oxygen species. Our results indicated that the crosstalk between microbial sensors in enteric infection and inflammatory diseases impacts the fate of the bacterial load and disease pathogenesis.

The role of admixture in the rare variant contribution to inflammatory bowel disease

BACKGROUND

Identification of rare variants involved in complex, polygenic diseases like Crohn's disease (CD) has accelerated with the introduction of whole exome/genome sequencing association studies. Rare variants can be used in both diagnostic and therapeutic assessments; however, since they are likely to be restricted to specific ancestry groups, their contributions to risk assessment need to be evaluated outside the discovery population. Prior studies implied that the three known rare variants in NOD2 are absent in West African and Asian populations and only contribute in African Americans via admixture.

METHODS

Whole genome sequencing (WGS) data from 3418 African American individuals, 1774 inflammatory bowel disease (IBD) cases, and 1644 controls were used to assess odds ratios and allele frequencies (AF), as well as haplotype-specific ancestral origins of European-derived CD variants discovered in a large exome-wide association study. Local and global ancestry was performed to assess the contribution of admixture to IBD contrasting European and African American cohorts.

RESULTS

Twenty-five rare variants associated with CD in European discovery cohorts are typically five-fold lower frequency in African Americans. Correspondingly, where comparisons could be made, the rare variants were found to have a predicted four-fold reduced burden for IBD in African Americans, when compared to European individuals. Almost all of the rare CD European variants were found on European haplotypes in the African American cohort, implying that they contribute to disease risk in African Americans primarily due to recent admixture. In addition, proportion of European ancestry correlates the number of rare CD European variants each African American individual carry, as well as their polygenic risk of disease. Similar findings were observed for 23 mutations affecting 10 other common complex diseases for which the rare variants were discovered in European cohorts.

CONCLUSIONS

European-derived Crohn's disease rare variants are even more rare in African Americans and contribute to disease risk mainly due to admixture, which needs to be accounted for when performing cross-ancestry genetic assessments.

Molecular diagnostic yield for Blau syndrome in previously diagnosed juvenile idiopathic arthritis with uveitis or cutaneous lesions

OBJECTIVE

Diagnostic pitfalls often arise in the community because of potentially misleading similarities between juvenile idiopathic arthritis (JIA) and Blau syndrome, an immune-related disorder caused by NOD2 gene mutations. It remains unclear in which population and to which extent next-generation sequencing techniques can aid in diagnosis.

METHODS

We evaluated clinical usefulness of targeted next-generation sequencing in previously diagnosed JIA. Participants were required to have symptoms and signs suspected of Blau syndrome, including at least uveitis or cutaneous lesions in addition to arthritis. Targeted sequencing was conducted on NOD2 gene to detect diagnostic variants classified as pathogenic or likely pathogenic for Blau syndrome. We assessed the molecular diagnostic yield and clinical implications on patient care.

RESULTS

Between May 1, 2008, and June 1, 2021, sequencing data were accrued from 123 previously diagnosed JIA (median age: 5 years; female: 62.6%). Targeted NOD2 sequencing yielded a positive molecular diagnosis of Blau syndrome in 21.1% (95% CI, 14.9%-29.2%), encompassing six heterozygous missense mutations classified as pathogenic variants. Among those receiving a molecular diagnosis, changes in clinical management and treatment were considered as having occurred in 38.5%. Nine predictors were identified to be associated with a higher diagnostic yield, providing clinical clues to suspect the possibility of Blau syndrome.

CONCLUSION

Among some patients with pediatric-onset arthritis complicated with uveitis or cutaneous lesions, reassessing their diagnosis of JIA may be warranted. Targeted NOD2 sequencing established the molecular diagnosis of Blau syndrome in nearly one fifth of these cases and provided clinically relevant information for patient-care decisions.

E3 ligase SOCS3 regulates NOD2 expression by ubiquitin proteasome system in lung cancer progression

PURPOSE

Despite lung cancer is one of the leading causes of cancer-related deaths, it remains hard to discover effective diagnostic and therapeutic approaches. Moreover, the five-year survival rate is relatively lower than other tumors. So urgent needs for finding a new theranostic target to treat lung cancer effectively. This study aims to present SOCS3 and NOD2 proteins as novel targets for diagnosis and therapy.

METHODS

We first confirmed SOCS3 expression level in patients' tissues. Then, we applied knockdown and overexpression of SOCS3 on lung cancer cell lines and performed proliferation, migration, and invasion assay. After that, we found NOD2 is a target of SOCS3 and introduced overexpression of NOD2 to A549 for verifying reduced tumorigenicity of lung cancer cells.

RESULTS

We identified protein expression level of SOCS3 was frequently higher in tumor tissues than adjacent normal tissues. Truly, overexpression of SOCS3 promoted proliferation, migration, and invasion capacity of lung cancer cells. We found that SOCS3 interacts with NOD2 and SOCS3 ubiquitinates NOD2 directly. Furthermore, lung cancer tissues with higher SOCS3 expression showed lower NOD2 expression. We confirmed overexpression of NOD2 leads to suppressed tumorigenicity of lung cancer cells, and these effects occurred through MAPK pathway.

CONCLUSION

Collectively, our work reveals novel roles of SOCS3 in lung tumorigenesis and proposes SOCS3 as a promising biomarker candidate for therapeutic and diagnostic target for lung cancer.

Cell membrane-camouflaged bufalin targets NOD2 and overcomes multidrug resistance in pancreatic cancer

AIMS

Multidrug resistance in pancreatic cancer poses a significant challenge in clinical treatment. Bufalin (BA), a compound found in secretions from the glands of toads, may help overcome this problem. However, severe cardiotoxicity thus far has hindered its clinical application. Hence, the present study aimed to develop a cell membrane-camouflaged and BA-loaded polylactic-co-glycolic acid nanoparticle (CBAP) and assess its potential to counter chemoresistance in pancreatic cancer.

METHODS

The toxicity of CBAP was evaluated by electrocardiogram, body weight, distress score, and nesting behavior of mice. In addition, the anticarcinoma activity and underlying mechanism were investigated both in vitro and in vivo.

RESULTS

CBAP significantly mitigated BA-mediated acute cardiotoxicity and enhanced the sensitivity of pancreatic cancer to several clinical drugs, such as gemcitabine, 5-fluorouracil, and FOLFIRINOX. Mechanistically, CBAP directly bound to nucleotide-binding and oligomerization domain containing protein 2 (NOD2) and inhibited the expression of nuclear factor kappa-light-chain-enhancer of activated B cells. This inhibits the expression of ATP-binding cassette transporters, which are responsible for chemoresistance in cancer cells.

CONCLUSIONS

Our findings indicate that CBAP directly inhibits NOD2. Combining CBAP with standard-of-care chemotherapeutics represents a safe and efficient strategy for the treatment of pancreatic cancer.

Loss of NOD2 in macrophages improves colitis and tumorigenesis in a lysozyme-dependent manner

Background

Crohn's disease (CD) is a complex and poorly understood myeloid-mediated disorder. Genetic variants with loss of function in the NOD2 gene confer an increased susceptibility to ileal CD. While Nod2 in myeloid cells may confer protection against T-cell mediated ileopathy, it remains unclear whether it may promote resolution of the inflamed colon. In this study, we evaluated the function of Nod2 in myeloid cells in a model of acute colitis and colitis-associated colon cancer (CAC).

Methods

To ablate Nod2 specifically within the myeloid compartment, we generated LysMCre/+;Nod2fl/fl mice. The role of NOD2 was studied in a setting of Dextran Sodium Sulfate (DSS)-induced colitis and in azoxymethane (AOM)/DSS model. Clinical parameters were quantified by colonoscopy, histological, flow cytometry, and qRT-PCR analysis.

Results

Upon DSS colitis model, LysMCre/+;Nod2fl/fl mice lost less weight than control littermates and had less severe damage to the colonic epithelium. In the AOM/DSS model, endoscopic monitoring of tumor progression revealed a lowered number of adenomas within the colon of LysMCre/+;Nod2fl/fl mice, associated with less expression of Tgfb. Mechanistically, lysozyme M was required for the improved disease severity in mice with a defect of NOD2 in myeloid cells.

Conclusion

Our results indicate that loss of Nod2 signaling in myeloid cells aids in the tissue repair of the inflamed large intestine through lysozyme secretion by myeloid cells. These results may pave the way to design new therapeutics to limit the inflammatory and tumorigenic functions of NOD2.

Multifaceted roles and regulation of nucleotide-binding oligomerization domain containing proteins

Nucleotide-binding oligomerization domain-containing proteins, NOD1 and NOD2, are cytosolic receptors that recognize dipeptides and tripeptides derived from the bacterial cell wall component peptidoglycan (PGN). During the past two decades, studies have revealed several roles for NODs beyond detecting PGN fragments, including activation of an innate immune anti-viral response, NOD-mediated autophagy, and ER stress induced inflammation. Recent studies have also clarified the dynamic regulation of NODs at cellular membranes to generate specific and balanced immune responses. This review will describe how NOD1 and NOD2 detect microbes and cellular stress and detail the molecular mechanisms that regulate activation and signaling while highlighting new evidence and the impact on inflammatory disease pathogenesis.

Distinct NOD2 mutations reported in three families with Blau syndrome (BS) from a single center in India - Case series and review of literature

OBJECTIVE

Blau syndrome (BS), considered a rare pediatric autoinflammatory disease, is characterised by a triad of granulomatous arthritis, dermatitis and uveitis. Here we present a tale of three families visited in our outpatient department in the last two years (2020-2022) where more than one member was affected with either skin, ophthalmological and joint involvement with either biopsy-proven granuloma or genetic mutation at NOD2 gene suggesting the diagnosis of BS.

CASE SERIES

The first family had three affected members where the mother and her two children had skin changes, polyarthritis and a pathogenic mutation in NOD2 gene (exon 4, c.1000C > T, p.Arg334Trp) suggesting BS. The second family had two affected members where both mother and her son had uveitis, skin changes with NOD2 mutation at exon 4 with c.1147G > A (p Glu 383 Lys) variant. The son also had polyarthritis and his skin biopsy was suggestive of granulomatous inflammation. In the third family with two affected members, we found a mutation in NOD2 on exon 4 (c 1324C > T, p.Lys 442 Phe) which was described as pathogenic with only one report published till date.

CONCLUSION

These three cases presented to us within the last two years and led to a diagnosis of BS in three other family members with discrete mutations (commonest to rarest) on the NOD2 gene in the three families.

Antimicrobial overproduction sustains intestinal inflammation by inhibiting Enterococcus colonization

Loss of antimicrobial proteins such as REG3 family members compromises the integrity of the intestinal barrier. Here, we demonstrate that overproduction of REG3 proteins can also be detrimental by reducing a protective species in the microbiota. Patients with inflammatory bowel disease (IBD) experiencing flares displayed heightened levels of secreted REG3 proteins that mediated depletion of Enterococcus faecium (Efm) from the gut microbiota. Efm inoculation of mice ameliorated intestinal inflammation through activation of the innate immune receptor NOD2, which was associated with the bacterial DL-endopeptidase SagA that generates NOD2-stimulating muropeptides. NOD2 activation in myeloid cells induced interleukin-1β (IL-1β) secretion to increase the proportion of IL-22-producing CD4+ T helper cells and innate lymphoid cells that promote tissue repair. Finally, Efm was unable to protect mice carrying a NOD2 gene variant commonly found in IBD patients. Our findings demonstrate that inflammation self-perpetuates by causing aberrant antimicrobial activity that disrupts symbiotic relationships with gut microbes.

Topical N-phosphonacetyl-l-aspartate is a dual action candidate for treating non-melanoma skin cancer

Each year, 3.3 million Americans are diagnosed with non-melanoma skin cancers (NMSC) and an additional 40 million individuals undergo treatment of precancerous actinic keratosis lesions. The most effective treatments of NMSC (surgical excision and Mohs surgery) are invasive, expensive and require specialised training. More readily accessible topical therapies currently are 5-fluorouracil (a chemotherapeutic agent) and imiquimod (an immune modulator), but these can have significant side effects which limit their efficacy. Therefore, more effective and accessible treatments are needed for non-melanoma cancers and precancers. Our previous work demonstrated that the small molecule N-phosphonacetyl-L-aspartate (PALA) both inhibits pyrimidine nucleotide synthesis and activates pattern recognition receptor nucleotide-binding oligomerization domain 2. We propose that topical application of PALA would be an effective NMSC therapy, by combining the chemotherapeutic and immune modulatory features of 5-fluorouracil and imiquimod. Daily topical application of PALA to mouse skin was well tolerated and resulted in less irritation, fewer histopathological changes, and less inflammation than caused by either 5-fluorouracil or imiquimod. In an ultraviolet light-induced NMSC mouse model, topical PALA treatment substantially reduced the numbers, areas and grades of tumours, compared to vehicle controls. This anti-neoplastic activity was associated with increased expression of the antimicrobial peptide cathelicidin and increased recruitment of CD8+ T cells and F4/80+ macrophages to the tumours, demonstrating both immunomodulatory and anti-proliferative effects. These findings indicate that topical PALA is an excellent candidate as an effective alternative to current standard-of-care NMSC therapies.

Regulation of type I IFN responses by deubiquitinating enzyme A in inflammatory bowel diseases

The development of Inflammatory bowel disease (IBD) is driven by excessive production of pro-inflammatory cytokines including TNF-α, IL-12, and IL-23. This notion is supported by the remarkable clinical success of biologics targeting these cytokines. Recognition of cell wall components derived from intestinal bacteria by Toll-like receptors (TLRs) induces the production of these pro-inflammatory cytokines by macrophages and dendritic cells in human IBD and experimental colitis model. Although sensing of bacterial nucleic acids by endosomal TLRs, specifically TLR3, TLR7, and TLR9 leads to robust production of type I IFNs, it remains debatable whether TLR-mediated type I IFN responses are pathogenic or protective in IBD patients. Additionally, recent studies identified deubiquitinating enzyme A (DUBA) as a novel negative regulator of TLR-mediated type I IFN responses. In light of these observations and their potential applications, in this review, we summarize recent findings on the roles of type I IFN responses and DUBA-mediated negative regulation of these responses in human IBD and experimental colitis model.

Unfolded protein response is involved in resistance to Neospora caninum infection via IRE1α-XBP1s-NOD2 Axis

Neospora caninum, an intracellular protozoan parasite, causes neosporosis resulting in major losses in the livestock industry worldwide. However, no effective drugs or vaccines have been developed to control neosporosis. An in-depth study on the immune response against N. caninum could help to search for effective approaches to prevent and treat neosporosis. The host unfolded protein response (UPR) functions as a double-edged sword in several protozoan parasite infections, either to initiate immune responses or to help parasite survival. In this study, the roles of the UPR in N. caninum infection in vitro and in vivo were explored, and the mechanism of the UPR in resistance to N. caninum infection was analyzed. The results revealed that N. caninum triggered the UPR in mouse macrophages, such as the activation of the IRE1 and PERK branches, but not the ATF6 branch. Inhibition of the IRE1α-XBP1s branch increased the N. caninum number both in vitro and in vivo, while inhibition of the PERK branch did not affect the parasite number. Furthermore, inhibition of the IRE1α-XBP1s branch reduced the production of cytokines by inhibiting NOD2 signalling and its downstream NF-κB and MAPK pathways. Taken together, the results of this study suggest that the UPR is involved in the resistance of N. caninum infection via the IRE1α-XBP1s branch by regulating NOD2 and its downstream NF-κB and MAPK pathways to induce the production of inflammatory cytokines, which provides a new perspective for the research and development of anti-N. caninum drugs.

Dietary fat differentially modulates the response of bone marrow-derived macrophages to TLR4 and NOD2 agonists

Consumption of diets high in fat has been linked to the development of obesity and related metabolic complications. Such associations originate from the enhanced, chronic, low-grade inflammation mediated by macrophages in response to translocated bacteria, bacterial products, or dietary constituents such as fatty acids (FAs). Nucleotide-binding Oligomerization Domain 2 (NOD2) senses muramyl dipeptide (MDP), a component of bacterial peptidoglycan. The inability to sense peptidoglycan through NOD2 has been demonstrated to lead to dysbiosis, increased bacterial translocation, inflammation and metabolic dysfunction. Currently, it is unknown how consumption of HFDs with different FA compositions might influence NOD2-dependent responses. In this study, we subjected WT mice to a control diet or to HFDs comprised of various ratios of unsaturated to saturated fats and determined the macrophage response to TLR4 and NOD2 agonists. A HFD with equal ratios of saturated and unsaturated fats enhanced subsequent responsiveness of macrophages to LPS but not to MDP. However, a high-unsaturated fat diet (HUFD) or a high-saturated fat diet (HSFD) both decreased the responsiveness to NOD2 agonists compared to that observed in control diet (CD) fed mice. These data suggest that dietary fatty acid composition can influence the subsequent macrophage responsiveness to bacterial products.

Autophagy in Crohn's Disease: Converging on Dysfunctional Innate Immunity

Crohn's disease (CD) is a chronic inflammatory bowel disease marked by relapsing, transmural intestinal inflammation driven by innate and adaptive immune responses. Autophagy is a multi-step process that plays a critical role in maintaining cellular homeostasis by degrading intracellular components, such as damaged organelles and invading bacteria. Dysregulation of autophagy in CD is revealed by the identification of several susceptibility genes, including ATG16L1, IRGM, NOD2, LRRK2, ULK1, ATG4, and TCF4, that are involved in autophagy. In this review, the role of altered autophagy in the mucosal innate immune response in the context of CD is discussed, with a specific focus on dendritic cells, macrophages, Paneth cells, and goblet cells. Selective autophagy, such as xenophagy, ERphagy, and mitophagy, that play crucial roles in maintaining intestinal homeostasis in these innate immune cells, are discussed. As our understanding of autophagy in CD pathogenesis evolves, the development of autophagy-targeted therapeutics may benefit subsets of patients harboring impaired autophagy.

The Synergistic Potential of Combining PD-1/PD-L1 Immune Checkpoint Inhibitors with NOD2 Agonists in Alzheimer's Disease Treatment

Our research over the past decade has compellingly demonstrated the potential of Nucleotide-binding oligomerization domain-containing protein 2 (NOD2) receptor agonists in Alzheimer's disease (AD) treatment. These agonists facilitate the conversation of pro-inflammatory monocytes into patrolling monocytes, leading to the efficient clearance of amyloid-β (Aβ) in the AD-affected cerebrovascular system. This approach surpasses the efficacy of targeting Aβ formation, marking a significant shift in therapeutic strategies. Simultaneously, inhibitors of PD-1/PD-L1 immune check point or glycogen synthase kinase 3 beta (GSK3β), which modulates PD-1, have emerged as potent AD treatment modalities. PD-1 inhibitor exhibits a profound potential in monocytes' recruitment to the AD-afflicted brain. Recent evidence suggests that an integrated approach, combining the modulation of NOD2 and PD-1, could yield superior outcomes. This innovative combinatorial therapeutic approach leverages the potential of MDP to act as a catalyst for the conversion of inflammatory monocytes into patrolling monocytes, with the subsequent recruitment of these patrolling monocytes into the brain being stimulated by the PD-1 inhibitor. These therapeutic interventions are currently under preclinical investigation by pharmaceutical entities, underscoring the promise they hold. This research advocates for the modulation, rather than suppression, of the innate immune system as a promising pharmacological strategy in AD.

Effect of curcumin on the expression of NOD2 receptor and pro-inflammatory cytokines in fibroblast-like synoviocytes (FLSs) of rheumatoid arthritis (RA) patients

BACKGROUND

Previous studies has shown that nucleotide-binding and oligomerization domain-containing protein 2 (NOD2) is expressed in Fibroblast-like synoviocytes (FLSs) of rheumatoid arthritis (RA) patients which is stimulated by muramyl dipeptide (MDP) present in the joint environment and induces inflammation via the NF-κB pathway. Also, other studies have shown that curcumin inhibits proliferation, migration, invasion, and Inflammation and on the other hand increases the apoptosis of RA FLSs. In this study, we aim to evaluate the effect of curcumin, a natural anti-inflammatory micronutrient, on the expression of NOD2 and inflammatory cytokines.

METHODS

Synovial membranes were collected from ten patients diagnosed with RA and ten individuals with traumatic injuries scheduled for knee surgery. The FLSs were isolated and treated with 40 μM curcumin alone or in combination with 20.3 μM MDP for 24 h. mRNA was extracted, and real-time PCR was performed to quantitatively measure gene expression levels of NOD2, p65, IL-6, TNF-α, and IL-1β.

RESULTS

The study findings indicate that administering MDP alone can significantly increase the mRNA expression levels of IL-6 and IL-1β in the trauma group and TNF-α in the RA group. Conversely, administering curcumin alone or in combination whit MDP can significantly reduce mRNA expression levels of P65 and IL-6 in FLSs of both groups. Moreover, in FLSs of RA patients, a single curcumin treatment leads to a significant reduction in NOD2 gene expression.

CONCLUSION

This study provides preliminary in vitro evidence of the potential benefits of curcumin as a nutritional supplement for RA patients. Despite the limitations of the study being an investigation of the FLSs of RA patients, the results demonstrate that curcumin has an anti-inflammatory effect on NOD2 and NF-κB genes. These findings suggest that curcumin could be a promising approach to relieve symptoms of RA.

NOD2 in monocytes negatively regulates macrophage development through TNFalpha

Objective

It is believed that intestinal recruitment of monocytes from Crohn's Disease (CD) patients who carry NOD2 risk alleles may repeatedly give rise to recruitment of pathogenic macrophages. We investigated an alternative possibility that NOD2 may rather inhibit their differentiation from intravasating monocytes.

Design

The monocyte fate decision was examined by using germ-free mice, mixed bone marrow chimeras and a culture system yielding macrophages and monocyte-derived dendritic cells (mo-DCs).

Results

We observed a decrease in the frequency of mo-DCs in the colon of Nod2-deficient mice, despite a similar abundance of monocytes. This decrease was independent of the changes in the gut microbiota and dysbiosis caused by Nod2 deficiency. Similarly, the pool of mo-DCs was poorly reconstituted in a Nod2-deficient mixed bone marrow (BM) chimera. The use of pharmacological inhibitors revealed that activation of NOD2 during monocyte-derived cell development, dominantly inhibits mTOR-mediated macrophage differentiation in a TNFα-dependent manner. These observations were supported by the identification of a TNFα-dependent response to muramyl dipeptide (MDP) that is specifically lost when CD14-expressing blood cells bear a frameshift mutation in NOD2.

Conclusion

NOD2 negatively regulates a macrophage developmental program through a feed-forward loop that could be exploited for overcoming resistance to anti-TNF therapy in CD.

Tofacitinib, a suppressor of NOD2 expression, is a potential treatment for Blau syndrome

Introduction

Blau syndrome is a rare autosomal dominant autoinflammatory granulomatous disease caused by a mutation in the NOD2 gene. It is characterized by a clinical trial of granulomatous dermatitis, arthritis, and uveitis. Tofacitinib is a pan Janus kinase (JAK) inhibitor used for treatment of Blau syndrome and idiopathic sarcoidosis. Here, we evaluated its effect on inflammatory pathways associated with Blau syndrome. The effect of tofacitinib on downstream pathways regulated by mutant NOD2 was analyzed using luciferase assays with overexpression of NOD2 mutants.

Methods

The effect of tofacitinib on the upstream pathway for the induction of NOD2 expression and proinflammatory cytokine production was assessed using monocytic cell lines differentiated from Blau syndrome patient-derived induced pluripotent stem cells.

Results

Tofacitinib did not suppress the increased spontaneous transcriptional activity of NF-κB by mutant NOD2. In addition, mutant NOD2 was not involved in the transcription of ISRE and GAS, which are activated by type 1 and type 2 interferons (IFN), respectively. On the other hand, IFNγ induced the expression of NOD2, which led to the production of inflammatory cytokines by an autoinflammatory mechanism only in cells with mutant NOD2.

Discussion

Tofacitinib suppressed the induction of NOD2 by IFNγ, thereby inhibiting the production of pro-inflammatory cytokines. Thus, tofacitinib showed anti-inflammatory effects through suppression of NOD2 expression. The JAK inhibitor tofacitinib is a potential therapeutic agent for Blau syndrome because it suppresses the autoinflammation seen in Blau syndrome by inhibiting the expression of NOD2.

IL-10 Modulates the Expression and Activation of Pattern Recognition Receptors in Mast Cells

Mast cells (MCs) are involved in several immune-related responses, including those in bacterial infections, autoimmune diseases, inflammatory bowel diseases, and cancer, among others. MCs identify microorganisms by pattern recognition receptors (PRRs), activating a secretory response. Interleukin (IL)-10 has been described as an important modulator of MC responses; however, its role in PRR-mediated activation of MC is not fully understood. We analyzed the activation of TLR2, TLR4, TLR7 and Nucleotide-binding oligomerization domain-containing protein 2 (NOD2) in mucosal-like MCs (MLMCs) and peritoneum-derived cultured MCs (PCMCs) from IL-10^-/- and wild-type (WT) mice. IL-10^-/- mice showed a reduced expression of TLR4 and NOD2 at week 6 and TLR7 at week 20 in MLMC. In MLMC and PCMC, TLR2 activation induced a reduced secretion of IL-6 and TNFα in IL-10^-/- MCs. TLR4- and TLR7-mediated secretion of IL-6 and TNFα was not detected in PCMCs. Finally, no cytokine release was induced by NOD2 ligand, and responses to TLR2 and TLR4 were lower in MCs at 20 weeks. These findings indicate that PRR activation in MCs depends on the phenotype, ligand, age, and IL-10.

Lactobacillus acidophilus supernatant alleviates osteoporosis by upregulating colonic SERT expression

Aims: To investigate the involvement of serotonin transporter (SERT) in colonic epithelial cells in the anti-osteoporosis role of Lactobacillus acidophilus (LA) supernatant (LAS). Methods: The abundance of fecal LA and bone mineral density (BMD) in patients with osteoporosis (OP) or severe osteoporosis were assessed. The protective role of LA in osteoporosis and the expression of SERT and relative signaling were evaluated. Results: Abundance of fecal LA was decreased in patients with severe OP and was positively correlated with BMD. Supplementing LAS to mice alleviated senile osteoporosis. In vitro, NOD2/RIP2/NF-κB signaling was inhibited by LAS due to increased SERT expression. Conclusion: LAS alleviates OP in mice by producing protective metabolites and upregulating SERT expression and represents a promising therapeutic agent.

The Role of Genetic and Epigenetic Regulation in Intestinal Fibrosis in Inflammatory Bowel Disease: A Descending Process or a Programmed Consequence?

Inflammatory bowel diseases (IBDs) are a group of chronic diseases characterized by recurring periods of exacerbation and remission. Fibrosis of the intestine is one of the most common complications of IBD. Based on current analyses, it is evident that genetic factors and mechanisms, as well as epigenetic factors, play a role in the induction and progression of intestinal fibrosis in IBD. Key genetic factors and mechanisms that appear to be significant include NOD2, TGF-β, TLRs, Il23R, and ATG16L1. Deoxyribonucleic acid (DNA) methylation, histone modification, and ribonucleic acid (RNA) interference are the primary epigenetic mechanisms. Genetic and epigenetic mechanisms, which seem to be important in the pathophysiology and progression of IBD, may potentially be used in targeted therapy in the future. Therefore, the aim of this study was to gather and discuss selected mechanisms and genetic factors, as well as epigenetic factors.

Ileocolonic Healing after Small Ileocecal Resection in Mice: NOD2 Deficiency Impairs Anastomotic Healing by Local Mechanisms

Ileocecal resection (ICR) is frequently performed in Crohn's disease (CD). NOD2 mutations are risk factors for CD. Nod2 knockout (ko) mice show impaired anastomotic healing after extended ICR. We further investigated the role of NOD2 after limited ICR. C57B16/J (wt) and Nod2 ko littermates underwent limited ICR including 1-2 cm terminal ileum and were randomly assigned to vehicle or MDP treatment. Bursting pressure was measured on POD 5, and the anastomosis was analyzed for matrix turn-over and granulation tissue. Wound fibroblasts from subcutaneously implanted sponges were used for comparison. The M1/M2 macrophage plasma cytokines were analyzed. Mortality was not different between groups. Bursting pressure was significantly decreased in ko mice. This was associated with less granulation tissue but was not affected by MDP. However, anastomotic leak (AL) rate tended to be lower in MDP-treated ko mice (29% vs. 11%, p = 0.07). mRNA expression of collagen-1α (col1 α), collagen-3α (col3 α), matrix metalloproteinase (mmp)2 and mmp9 was increased in ko mice, indicating increased matrix turn-over, specifically in the anastomosis. Systemic TNF-α expression was significantly lower in ko mice. Ileocolonic healing is impaired in Nod2 ko mice after limited ICR by local mechanisms maybe including local dysbiosis.

NOD-like Receptors-Emerging Links to Obesity and Associated Morbidities

Obesity and its associated metabolic morbidities have been and still are on the rise, posing a major challenge to health care systems worldwide. It has become evident over the last decades that a low-grade inflammatory response, primarily proceeding from the adipose tissue (AT), essentially contributes to adiposity-associated comorbidities, most prominently insulin resistance (IR), atherosclerosis and liver diseases. In mouse models, the release of pro-inflammatory cytokines such as TNF-alpha (TNF-α) and interleukin (IL)-1β and the imprinting of immune cells to a pro-inflammatory phenotype in AT play an important role. However, the underlying genetic and molecular determinants are not yet understood in detail. Recent evidence demonstrates that nucleotide-binding and oligomerization domain (NOD)-like receptor (NLR) family proteins, a group of cytosolic pattern recognition receptors (PRR), contribute to the development and control of obesity and obesity-associated inflammatory responses. In this article, we review the current state of research on the role of NLR proteins in obesity and discuss the possible mechanisms leading to and the outcomes of NLR activation in the obesity-associated morbidities IR, type 2 diabetes mellitus (T2DM), atherosclerosis and non-alcoholic fatty liver disease (NAFLD) and discuss emerging ideas about possibilities for NLR-based therapeutic interventions of metabolic diseases.

Circular RNA circ_0008896 contributes to oxidized low-density lipoprotein-induced aortic endothelial cell injury via targeting miR-188-3p/NOD2 axis

We aimed to investigate the role and mechanism of circ_0008896 in Atherosclerosis (AS) by using oxidized low-density lipoprotein (ox-LDL)-induced human aortic endothelial cell (HAECs). Levels of genes and proteins were measured by quantitative real-time PCR and Western blot. Functional experiments, including enzyme-linked immunosorbent assay analysis, cell counting kit-8, 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, tube formation assays and the detection of reactive oxygen species (ROS), malondialdehyde (MDA) and superoxide dismutase (SOD) generation, were performed to investigate the role of circ_0008896 on ox-LDL-induced HAEC damage. Circ_0008896 was increased in AS patients and ox-LDL-stimulated HAECs. Functionally, circ_0008896 knockdown reversed ox-LDL-induced inflammatory response, oxidative stress, apoptosis as well as arrest of proliferation and angiogenesis in HAECs in vitro. Mechanistically, circ_0008896 functioned as a sponge for miR-188-3p to relieve the repression of miR-188-3p on its target NOD2. A series of rescue experiments showed that miR-188-3p inhibition attenuated the protective effects of circ_0008896 knockdown on ox-LDL-stimulated HAECs, and NOD2 overexpression abolished the beneficial action of miR-188-3p in the suppression of inflammatory response and oxidative stress, and the promotion of cell growth and angiogenesis in HAECs under ox-LDL treatment. Circ_0008896 silencing attenuates ox-LDL-induced inflammatory response, oxidative stress, and growth arrest in HAECs in vitro, adding further understanding for the pathogenesis of AS.

Peptidoglycan-induced modulation of metabolic and inflammatory responses

Bacterial cell wall peptidoglycan is composed of innate immune ligands and, due to its important structural role, also regulates access to many other innate immune ligands contained within the bacteria. There is a growing body of literature demonstrating how innate immune recognition impacts the metabolic functions of immune cells and how metabolic changes are not only important to inflammatory responses but are often essential. Peptidoglycan is primarily sensed in the context of the whole bacteria during lysosomal degradation; consequently, the innate immune receptors for peptidoglycan are primarily intracellular cytosolic innate immune sensors. However, during bacterial growth, peptidoglycan fragments are shed and can be found in the bloodstream of humans and mice, not only during infection but also derived from the abundant bacterial component of the gut microbiota. These peptidoglycan fragments influence cells throughout the body and are important for regulating inflammation and whole-body metabolic function. Therefore, it is important to understand how peptidoglycan-induced signals in innate immune cells and cells throughout the body interact to regulate how the body responds to both pathogenic and nonpathogenic bacteria. This mini-review will highlight key research regarding how cellular metabolism shifts in response to peptidoglycan and how systemic peptidoglycan sensing impacts whole-body metabolic function.

RIPosomes are targets of IRGM-SQSTM1-dependent autophagy

The NOD1-NOD2-RIPK2-NFKB/NF-κB pro-inflammatory axis plays a significant role in regulating the immune response to bacterial infection. However, an excess of NFKB-dependent cytokine response can be detrimental and, thus, should be kept under control to maintain the innate immune balance. In our recent study, first, we showed that bacterial infection induces the biogenesis of RIPK2 oligomers (RIPosomes) that are recruited around the bacteria to enhance an NFKB-dependent pro-inflammatory response. Next, we showed that SQSTM1- and IRGM-dependent selective macroautophagy/autophagy degrades RIPosomes and their components to limit NOD1-NOD2-RIPK2-NFKB pro-inflammatory signaling. Consistently, depletion of IRGM results in an augmented RIPK2-dependent pro-inflammatory cytokine response induced by Shigella flexneri and Salmonella typhimurium. Further, bacterial infection- and DSS-induced gut inflammation in irgm1^KO mice is dampened upon therapeutic inhibition of RIPK2. Taken together, we showed that autophagy selectively degrades RIPosomes to suppress inflammation and maintain innate immune homeostasis.

Activation of nucleotide-binding oligomerization domain 2 by muramyl dipeptide negatively regulates Toll-like receptor 9-mediated colonic inflammation through the induction of deubiquitinating enzyme A expression

Mutations in nucleotide-binding oligomerization domain 2 (NOD2) are associated with Crohn's disease (CD). Although NOD2 activation contributes to the maintenance of intestinal homeostasis through the negative regulation of pro-inflammatory cytokine responses mediated by Toll-like receptors (TLRs), the effects of NOD2 activation on interferon (IFN)-α responses induced by TLR9 have been poorly defined. To explore the cross-talk between NOD2 and TLR9, human monocytes or dendritic cells (DCs) were stimulated with NOD2 and/or TLR9 ligands to measure IFN-α production. The severity of dextran sodium sulfate (DSS)-induced colitis was compared in mice treated with NOD2 and/or TLR9 ligands. Expression of IFN-α and IFN-stimulated genes (ISGs) was examined in the colonic mucosa of patients with inflammatory bowel disease (IBD). NOD2 activation reduced TLR9-induced IFN-α production by monocytes and DCs in a deubiquitinating enzyme A (DUBA)-dependent manner. Activation of DUBA induced by the co-stimulation of TLR9 and NOD2 inhibited Lys63-linked polyubiquitination of TRAF3 and suppressed TLR9-mediated IFN-α production. NOD2 activation in hematopoietic cells protected mice from TLR9-induced exacerbation of DSS-induced colitis by down-regulating IFN-α responses and up-regulating DUBA expression. Colonic mucosa of patients with active and remitted IBD phases was characterized by the enhanced and reduced expression of ISGs, respectively. Expression levels of IFN-α and IL-6 positively correlated in the active colonic mucosa of patients with ulcerative colitis and CD, whereas DUBA expression inversely correlated with that of IFN-α in patients with CD. Collectively, these data suggest that DUBA-dependent negative effect of NOD2 on TLR9-mediated IFN-α responses contributes to the maintenance of intestinal homeostasis.

Analyses of Transcriptomics upon IL-1β-Stimulated Mouse Chondrocytes and the Protective Effect of Catalpol through the NOD2/NF-κB/MAPK Signaling Pathway

The overall objective of this study was to investigate the mechanism of inflammation on chondrocyte injury and the protective effect of catalpol on chondrocytes in an inflammatory environment. Chondrocytes were isolated and cultured from the knee joints of three-day-old newborn mice. Alcian Blue staining and the immunocytochemistry staining of type II collagen were used to identify the purity of chondrocytes. Primary chondrocytes were stimulated by IL-1β (10 ng/mL) and subjected to transcriptome analysis. Differentially expressed genes (DEGs) were further analyzed based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. In this experimental study, we performed the viability assay to determine the effects of different concentrations of catalpol on the cell viability of chondrocytes. Chondrocytes were seeded in six-well plates and exposed to 10 μM catalpol 2 h prior to treatment with IL-1β (10 ng/mL). Quantitative real-time (qPCR) and Western blotting were performed to evaluate the RNA and protein expression, respectively. Based on the results of transcriptomics analysis, we found the NOD2 signaling pathway, the NF-kappa B signaling pathway, and the MAPK signaling pathway showed significant changes in chondrocyte damage caused by inflammation. Catalpol (10 μM and 100 μM) could significantly reduce NO, IL-6, IL-1β, and TNF-α in supernatant of chondrocytes. Catalpol significantly inhibited the mRNA expression of IL-1, IL-6, and IL-12 in chondrocytes induced by IL-1β. Catalpol markedly inhibited MMP3, MMP13 mRNA, and protein levels. Catalpol could significantly reduce TNF-α mRNA levels in inflammatory chondrocytes. Inflammation causes significant increases in mRNA levels and protein levels of NOD2, mRNA levels, and protein levels were markedly suppressed by catalpol. In addition, catalpol could significantly increase IKBα protein levels and significantly lower intranuclear P65 levels. Catalpol significantly lowered the phosphorylation protein levels of ERK, p38, and JNK. Our transcriptomic analysis demonstrated that the activation of NOD2 and its downstream pathways, NF-κB and MAPK, is an important cause of the inflammatory injury to chondrocytes induced by IL-1β. Catalpol inhibited the activation of the NOD2 signaling pathway, which reduced the phosphorylation of ERK, p38, and JNK, inhibited the degradation of IκBα, inhibited p65 translocation into the nucleus, reduced the release of inflammatory cytokines, and attenuated the inflammatory damage to chondrocytes.

Lentiviral Gene Transfer Corrects Immune Abnormalities in XIAP Deficiency

BACKGROUND

X-linked inhibitor of apoptosis protein (XIAP) deficiency is a severe immunodeficiency with clinical features including hemophagocytic lymphohistiocytosis (HLH) and inflammatory bowel disease (IBD) due to defective NOD2 responses. Management includes immunomodulatory therapies and hematopoietic stem cell transplant (HSCT). However, this cohort is particularly susceptible to the chemotherapeutic regimens and acutely affected by graft-vs-host disease (GvHD), driving poor long-term survival in transplanted patients. Autologous HSC gene therapy could offer an alternative treatment option and would abrogate the risks of alloreactivity.

METHODS

Hematopoietic progenitor (Lin-ve) cells from XIAPy/- mice were transduced with a lentiviral vector encoding human XIAP cDNA before transplantation into irradiated XIAP y/- recipients. After 12 weeks animals were challenged with the dectin-1 ligand curdlan and recovery of innate immune function was evaluated though analysis of inflammatory cytokines, body weight, and splenomegaly. XIAP patient-derived CD14+ monocytes were transduced with the same vector and functional recovery was demonstrated using in vitro L18-MDP/NOD2 assays.

RESULTS

In treated XIAPy/- mice, ~40% engraftment of gene-corrected Lin-ve cells led to significant recovery of weight loss, splenomegaly, and inflammatory cytokine responses to curdlan, comparable to wild-type mice. Serum IL-6, IL-10, MCP-1, and TNF were significantly reduced 2-h post-curdlan administration in non-corrected XIAPy/- mice compared to wild-type and gene-corrected animals. Appropriate reduction of inflammatory responses was observed in gene-corrected mice, whereas non-corrected mice developed an inflammatory profile 9 days post-curdlan challenge. In gene-corrected patient CD14+ monocytes, TNF responses were restored following NOD2 activation with L18-MDP.

CONCLUSION

Gene correction of HSCs recovers XIAP-dependent immune defects and could offer a treatment option for patients with XIAP deficiency.

A Protective Role of NOD2 on Oxazolone-induced Intestinal Inflammation Through IL-1β-mediated Signalling Pathway

BACKGROUND AND AIMS

NOD2 has emerged as a critical player in the induction of both Th1 and Th2 responses for potentiation and polarisation of antigen-dependent immunity. Loss-of-function mutations in the NOD2-encoding gene and deregulation of its downstream signalling pathway have been linked to Crohn's disease. Although it is well documented that NOD2 is capable of sensing bacterial muramyl dipeptide, it remains counter-intuitive to link development of overt intestinal inflammation to a loss of bacterial-induced inflammatory response. We hypothesised that a T helper bias could also contribute to an autoimmune-like colitis different from inflammation that is fully fledged by Th1 type cells.

METHODS

An oedematous bowel wall with a mixed Th1/Th2 response was induced in mice by intrarectal instillation of the haptenating agent oxazolone. Survival and clinical scoring were evaluated. At several time points after instillation, colonic damage was assessed by macroscopic and microscopic observations. To evaluate the involvement of NOD2 in immunochemical phenomena, quantitative polymerase chain reaction [PCR] and flow cytometry analysis were performed. Bone marrow chimera experimentation allowed us to evaluate the role of haematopoietic/non-hematopoietic NOD2-expressing cells.

RESULTS

Herein, we identified a key regulatory circuit whereby NOD2-mediated sensing of a muramyl dipeptide [MDP] by radio-resistant cells improves colitis with a mixed Th1/Th2 response that is induced by oxazolone. Genetic ablation of either Nod2 or Ripk2 precipitated oxazolone colitis that is predominantly linked to a lack of interferon-gamma. Bone marrow chimera experiments revealed that inactivation of Nod2 signalling in non-haematopoietic cells is causing a biased M1-M2 polarisation of macrophages and a decreased frequency of splenic regulatory T cells that correlates with an impaired activation of CD4 + T cells within mesenteric lymph nodes. Mechanistically, mice were protected from oxazolone-induced colitis upon administration of MDP in an interleukin-1- and interleukin-23-dependent manner.

CONCLUSIONS

These findings indicate that Nod2 signalling may prevent pathological conversion of T helper cells for maintenance of tissue homeostasis.

Inflammation Regulation by Bacterial Molecular Patterns

Stimulation of innate immunity by bacterial molecular patterns can induce an enhanced cellular immune response to pathogens that are associated with innate immune memory shaped by epigenetic changes. Immunological memory can be expressed in the acceleration/intensification of inflammation, as well as in the exact opposite-to maintain tolerance and non-response to a repeated stimulus. Tolerance is one of the central concepts of immunity and is ensured by the consistency of all parts of the immune response. The severe consequences of inflammation force researchers to study in detail all stages of the downstream pathways that are activated after exposure to a stimulus, while the formation of non-response to a pro-inflammatory stimulus has not yet received a detailed description. Elucidation of the mechanism of tolerance is an urgent task for the prevention and treatment of inflammatory diseases. The aim of this investigation was to study the dynamic changes in the gene expression of A20 and ATF3, the inflammation suppressors, against the background of the expression of the genes of the innate immunity receptors TLR4 and NOD2 and the pro-inflammatory cytokine TNF-α under the influence of TLR4 and NOD2 agonists, lipopolysaccharide (LPS) and glucosaminylmuramyl dipeptide (GMDP). The mechanism of inflammation regulation by bioregulators of bacterial origin-LPS and GMDP-was evaluated in vitro in human peripheral blood mononuclear cells and in vivo after i.p. administration of LPS and GMDP to mice. Gene expression was assessed by RT-PCR. Innate immune receptors and the pro-inflammatory cytokine TNF-α were found to develop early in response to LPS and GMDP, both in vitro and in vivo. Genes of cytosolic proteins controlling inflammation (A20 and ATF3) were expressed later. Prior exposure of the innate immune system to LPS and muramyl peptides may modulate host defense against acute inflammation. As a result of the study, new data were obtained on dynamic changes in deubiquitinase A20 and the transcription factor ATF3, which are involved in the limitation and suppression of inflammatory reactions caused by fragments of bacterial cell walls-LPS and GMDP. Thus, bioregulators of bacterial origin LPS and GMDP, along with pro-inflammatory factors, activate the expression of genes that suppress inflammation, which should be considered when analyzing data from studies of the pro-inflammatory properties of LPS and GMDP and when developing drugs based on them.

NOD2 inhibits the proliferation of esophageal adenocarcinoma cells through autophagy

AIM

To study the regulatory mechanism of NOD2 in the inhibition of esophageal adenocarcinoma cell proliferation.

METHODS

Cell experiments: after confirming the decrease in NOD2 expression in esophageal adenocarcinoma, we overexpressed NOD2 in esophageal adenocarcinoma cells via lentivirus, compared and verified the changes in esophageal adenocarcinoma cell proliferation before and after NOD2 overexpression, and compared the overexpression group with the control group by mRNA sequencing to identify pathways that may affect cell proliferation. Then, the autophagy level of multiple groups were assessed, and the results were verified by rescue experiments. In vivo experiments: we administered esophageal adenocarcinoma cells to nude mice to form tumors under their skin and then injected the tumors with NOD2 overexpression lentivirus and negative control lentivirus. After a period of time, the growth curve of the tumor was generated, and the tumor was removed to generate sections. Ki67 was labeled with immunohistochemistry to verify cell proliferation, and the protein was extracted from the tissue to detect the molecular indices of the corresponding pathway.

RESULTS

Upregulation of NOD2 expression inhibited the proliferation of esophageal adenocarcinoma cells. Upregulation of NOD2 expression increased the autophagy level of esophageal adenocarcinoma cells via ATG16L1. After ATG16L1 was inhibited, NOD2 had no significant effect on autophagy and proliferation of esophageal adenocarcinoma cells. Enhanced autophagy in esophageal adenocarcinoma cell lines inhibited cell proliferation. In vivo, the upregulation of NOD2 expression improved the autophagy level of tumor tissue and inhibited cells proliferation.

CONCLUSION

NOD2 can activate autophagy in esophageal adenocarcinoma cells through the ATG16L1 pathway and inhibit cell proliferation.

Corneal Ulcers with NOD2 Mutations Presenting with Mixed Syndromic Phenotype

PURPOSE

To report a case of corneal ulcers in a patient with NOD2 mutations unique to but phenotypically resembling well-characterized syndromic phenotypes like Blau syndrome.

OBSERVATION

A 25-year-old female with a medical history of type I diabetes mellitus, Asperger syndrome, and neuropathy presented with bilateral corneal ulcers. Her visual acuity was 20/200 OU. Macular edema was identified OS, and posterior synechiae OS suggested a history of anterior uveitis.Genetic testing confirmed NOD2 mutations, and her tear film was positive for matrix metallopeptidase 9. Recent intravenous immunoglobulin therapy improved her neuropathy, and an aggressive regimen of erythromycin ointment and lubrication has improved her ophthalmic symptoms.

CONCLUSION AND IMPORTANCE

This case advances our understanding of NOD2's role in regulating inflammatory processes of the eye. In addition to precipitating uveitis, patients with these mutations may also be at increased risk of developing corneal pathology related to their reduced capacity to moderate inflammatory processes.

Postbiotic muramyl dipeptide alleviates colitis via activating autophagy in intestinal epithelial cells

The pathogenesis of IBD is complicated and still unclear. Nucleotide-binding oligomerization domain 2 (NOD2) plays a significant role in regulating gut inflammation under the activation of muramyl dipeptide (MDP), which is used as a postbiotic. The study aimed to investigate the effect of MDP on the intestinal barrier in colitis and the mechanism involved. In this study, C57BL/6 mice were challenged with dextran sodium sulfate (DSS) for establishing a colitis model with the pre-treatment of MDP in vivo. Intestinal permeability was reflected by detecting the serum concentration of 4 kDa Fluorescein Isothiocyanate-Dextran. The expression of inflammation, barrier-related proteins, and autophagy was tested by Western Blotting. Proliferation and apoptosis in intestinal epithelial cells were detected by immunohistochemistry. Caco-2 cells were exposed to lipopolysaccharide for imitating inflammation in vitro. The findings showed that administration of MDP ameliorated losses of body weight loss, gross injury, and histology score of the colon in the DSS-induced colitis mice. MDP significantly ameliorated the condition of gut permeability, and promoted intestinal barrier repair by increasing the expression of Zonula occludens-1 and E-cadherin. Meanwhile, MDP promoted proliferation and reduced apoptosis of intestinal epithelial cells. In the experiment group treated with MDP, LC3 was upregulated, and p62 was downregulated, respectively. These results suggested that MDP stimulation attenuates intestinal inflammation both in vivo and in vitro. Potentially, MDP reduced the intestinal barrier damage by regulating autophagy in intestinal epithelial cells. Future trials investigating the effects of MDP-based postbiotics on IBD may be promising.

Impact of antibiotic perturbation on fecal viral communities in mice

Viruses and bacteriophages have a strong impact on intestinal barrier function and the composition and functional properties of commensal bacterial communities. Shifts of the fecal virome might be involved in human diseases, including inflammatory bowel disease (IBD). Loss-of-function variants in the nucleotide-binding oligomerization domain-containing protein 2 (NOD2) gene are associated with an increased risk of developing Crohn's disease, a subtype of human chronic IBD, where specific changes in fecal viral communities have also been described. To improve our understanding of the dynamics of the enteric virome, we longitudinally characterized the virome in fecal samples from wild-type C57BL/6J and NOD2 knock-out mice in response to an antibiotic perturbation. Sequencing of virus-like particles demonstrated both a high diversity and high interindividual variation of the murine fecal virome composed of eukaryotic viruses and bacteriophages. Antibiotics had a significant impact on the fecal murine virome. Viral community composition only partially recovered in the observation period (10 weeks after cessation of antibiotics) irrespective of genotype. However, compositional shifts in the virome and bacteriome were highly correlated, suggesting that the loss of specific phages may contribute to prolonged dysregulation of the bacterial community composition. We suggest that therapeutic interference with the fecal virome may represent a novel approach in microbiota-targeted therapies.

Gut microbial DL-endopeptidase alleviates Crohn's disease via the NOD2 pathway

The pattern-recognition receptor NOD2 senses bacterial muropeptides to regulate host immunity and maintain homeostasis. Loss-of-function mutations in NOD2 are associated with Crohn's disease (CD), but how the variations in microbial factors influence NOD2 signaling and host pathology is elusive. We demonstrate that the Firmicutes peptidoglycan remodeling enzyme, DL-endopeptidase, increased the NOD2 ligand level in the gut and impacted colitis outcomes. Metagenomic analyses of global cohorts (n = 857) revealed that DL-endopeptidase gene abundance decreased globally in CD patients and negatively correlated with colitis. Fecal microbiota from CD patients with low DL-endopeptidase activity predisposed mice to colitis. Administering DL-endopeptidase, but not an active site mutant, alleviated colitis via the NOD2 pathway. Therapeutically restoring NOD2 ligands with a DL-endopeptidase-producing Lactobacillus salivarius strain or mifamurtide, a clinical analog of muramyl dipeptide, exerted potent anti-colitis effects. Our study suggests that the depletion of DL-endopeptidase contributes to CD pathogenesis through NOD2 signaling, providing a therapeutically modifiable target.

NOD2-mediated HDAC6/NF-κb signalling pathway regulates ferroptosis induced by extracellular histone H3 in acute liver failure

Acute liver failure (ALF) is life-threatening and often associated with high mortality rates. The aim of the present study was to investigate whether extracellular histone H3 could induce ferroptosis in hepatic macrophages in ALF and explore its potential mechanism. RAW264.7 macrophages and C57BL/6 mice were used in this study. LPS, D-galactosamine (D-Gal), histone H3, histone H3 antibody, NOD2 agonist Muramyl Dipeptide (MDP) and HDAC6-siRNA were administered in this study. The key molecules of ferroptosis, NOD2, HDAC6 and the NF-κb pathway, were detected. In vitro, histone H3 was released into the extracellular environment from cell nucleus after LPS exposure. In addition, histone H3 could induce ferroptosis in RAW264.7 macrophages with increased level of Fe²⁺ and ROS and decreased levels of GPX4 and GSH. MDP further aggravated ferroptosis in RAW264.7 macrophages stimulated by histone H3, which was accompanied by elevated NOD2, HDAC6, p-P65 and IκBα. HDAC6-siRNA ameliorated ferroptosis in RAW264.7 macrophages induced by histone H3, which was accompanied by decreased levels of HDAC6, p-P65 and IκBα. However, HDAC6-siRNA did not alter NOD2 levels in RAW264.7 macrophages administered histone H3. In vivo, the levels of NOD2, HDAC6 the NF-κb pathway and ferroptosis were increased in ALF mice, which were downregulated by histone H3 antibody and upregulated by histone H3. Extracellular histone H3 could induce ferroptosis in hepatic macrophages in ALF by regulating theNOD2-mediated HDAC6/NF-κb signalling pathway.