Tyrosine kinase inhibitors of Ripk2 attenuate bacterial cell wall-mediated lipolysis, inflammation and dysglycemia

Bruton's tyrosine kinase (BTK) inhibitors alter blood glucose and insulin in obese mice but reduce inflammation independent of BTK

Obesity is associated with metabolic inflammation, which can contribute to insulin resistance, higher blood glucose, and higher insulin indicative of prediabetes progression. The nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome is a metabolic danger sensor implicated in metabolic inflammation. Many features of metabolic disease can activate the NLRP3 inflammasome; however, it is not yet clear which upstream triggers to target, and there are no clinically approved NLRP3 inflammasome inhibitors for metabolic disease. Bruton's tyrosine kinase (BTK) mediates activation of the NLRP3 inflammasome. Ibrutinib is the most-studied pharmacological inhibitor of BTK, and it can improve blood glucose control in obese mice. However, inhibitors of tyrosine kinases are permissive, and it is unknown if BTK inhibitors require BTK to alter endocrine control of metabolism or metabolic inflammation. We tested whether ibrutinib and acalabrutinib, a new generation BTK inhibitor with higher selectivity, require BTK to inhibit the NLRP3 inflammasome, metabolic inflammation, and blood glucose in obese mice. Chronic ibrutinib administration lowered fasting blood glucose and improved glycemia, whereas acalabrutinib increased fasting insulin levels and increased markers of insulin resistance in high-fat diet-fed CBA/J mice with intact Btk. These metabolic effects of BTK inhibitors were absent in CBA/CaHN-Btkxid/J mice with mutant Btk. However, ibrutinib and acalabrutinib reduced NF-κB activity, proinflammatory gene expression, and NLRP3 inflammasome activation in macrophages with and without functional BTK. These data highlight that the BTK inhibitors can have divergent effects on metabolism and separate effects on metabolic inflammation that can occur independently of actions on BTK.NEW & NOTEWORTHY Bruton's tyrosine kinase (BTK) is involved in immune function. It was thought that BTK inhibitors improve characteristics of obesity-related metabolic disease by lowering metabolic inflammation. However, tyrosine kinase inhibitors are permissive, and it was not known if different BTK inhibitors alter host metabolism or immunity through actions on BTK. We found that two BTK inhibitors had divergent effects on blood glucose and insulin via BTK, but inhibition of metabolic inflammation occurred independently of BTK in obese mice.

Receptor Interacting Ser/Thr-Protein Kinase 2 as a New Therapeutic Target

Receptor interacting serine/threonine protein kinase 2 (RIPK2) is a downstream signaling molecule essential for the activation of several innate immune receptors, including the NOD-like receptors (NOD1 and NOD2). Recognition of pathogen-associated molecular pattern proteins by NOD1/2 leads to their interaction with RIPK2, which induces release of pro-inflammatory cytokines through the activation of NF-κB and MAPK pathways, among others. Thus, RIPK2 has emerged as a key mediator of intracellular signal transduction and represents a new potential therapeutic target for the treatment of various conditions, including inflammatory diseases and cancer. In this Perspective, first, an overview of the mechanisms that underlie RIPK2 function will be presented along with its role in several diseases. Then, the existing inhibitors that target RIPK2 and different therapeutic strategies will be reviewed, followed by a discussion on current challenges and outlook.

Microbiota and Nod-like receptors balance inflammation and metabolism during obesity and diabetes

Gut microbiota influence host immunity and metabolism during obesity. Bacterial sensors of the innate immune system relay signals from specific bacterial components (i.e., postbiotics) that can have opposing outcomes on host metabolic inflammation. NOD-like receptors (NLRs) such as Nod1 and Nod2 both recruit receptor-interacting protein kinase 2 (RIPK2) but have opposite effects on blood glucose control. Nod1 connects bacterial cell wall-derived signals to metabolic inflammation and insulin resistance, whereas Nod2 can promote immune tolerance, insulin sensitivity, and better blood glucose control during obesity. NLR family pyrin domain containing (NLRP) inflammasomes can also generate divergent metabolic outcomes. NLRP1 protects against obesity and metabolic inflammation potentially because of a bias toward IL-18 regulation, whereas NLRP3 appears to have a bias toward IL-1β-mediated metabolic inflammation and insulin resistance. Targeting specific postbiotics that improve immunometabolism is a key goal. The Nod2 ligand, muramyl dipeptide (MDP) is a short-acting insulin sensitizer during obesity or during inflammatory lipopolysaccharide (LPS) stress. LPS with underacylated lipid-A antagonizes TLR4 and counteracts the metabolic effects of inflammatory LPS. Providing underacylated LPS derived from Rhodobacter sphaeroides improved insulin sensitivity in obese mice. Therefore, certain types of LPS can generate metabolically beneficial metabolic endotoxemia. Engaging protective adaptive immunoglobulin immune responses can also improve blood glucose during obesity. A bacterial vaccine approach using an extract of the entire bacterial community in the upper gut promotes protective adaptive immune response and long-lasting improvements in blood glucose control. A key future goal is to identify and combine postbiotics that cooperate to improve blood glucose control.

The tyrosine kinase inhibitor Dasatinib reduces cardiac steatosis and fibrosis in obese, type 2 diabetic mice

BACKGROUND

Cardiac steatosis is an early yet overlooked feature of diabetic cardiomyopathy. There is no available therapy to treat this condition. Tyrosine kinase inhibitors (TKIs) are used as first or second-line therapy in different types of cancer. In cancer patients with diabetes mellitus, TKIs reportedly improved glycemic control, allowing insulin discontinuation. They also reduced liver steatosis in a murine model of non-alcoholic fatty liver disease. The present study aimed to determine the therapeutic effect of the second-generation TKI Dasatinib on lipid accumulation and cardiac function in obese, type 2 diabetic mice. We also assessed if the drug impacts extra-cardiac fat tissue depots.

METHODS

Two studies on 21-week-old male obese leptin receptor mutant BKS.Cg-+Leprdb/+Leprdb/OlaHsd (db/db) mice compared the effect of Dasatinib (5 mg/kg) and vehicle (10% DMSO + 90% PEG-300) given via gavage once every three days for a week or once every week for four weeks. Functional and volumetric indices were studied using echocardiography. Post-mortem analyses included the assessment of fat deposits and fibrosis using histology, and senescence using immunohistochemistry and flow cytometry. The anti-adipogenic action of Dasatinib was investigated on human bone marrow (BM)-derived mesenchymal stem cells (MSCs). Unpaired parametric or non-parametric tests were used to compare two and multiple groups as appropriate.

RESULTS

Dasatinib reduced steatosis and fibrosis in the heart of diabetic mice. The drug also reduced BM adiposity but did not affect other fat depots. These structural changes were associated with improved diastolic indexes, specifically the E/A ratio and non-flow time. Moreover, Dasatinib-treated mice had lower levels of p16 in the heart compared with vehicle-treated controls, suggesting an inhibitory impact of the drug on the senescence signalling pathway. In vitro, Dasatinib inhibited human BM-MSC viability and adipogenesis commitment.

CONCLUSIONS

Our findings suggest that Dasatinib opposes heart and BM adiposity and cardiac fibrosis. In the heart, this was associated with favourable functional consequences, namely improvement in an index of diastolic function. Repurposing TKI for cardiac benefit could address the unmet need of diabetic cardiac steatosis.

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.

Blocking RIPK2 Function Alleviates Myocardial Ischemia/Reperfusion Injury by Regulating the AKT and NF-κB Pathways

OBJECTIVE

Inflammation and oxidation brought on by myocardial ischemia-reperfusion (MI/R) injury lead to cardiomyocyte apoptosis and necrosis. The receptor interacting serine/threonine kinase 2 (RIPK2) plays significant roles in oxidative stress and excessive inflammation. The purpose of this research is to examine the roles of RIPK2 in MI/R injury.

METHODS

The in vivo animal model was constructed by acute coronary I/R, and the in vitro cell model was established by oxygen and glucose deprivation/reperfusion (OGD/R)-stimulated cardiomyocyte injury. RIPK2 expression was examined using qRT-PCR and Western blot. CCK-8 was proposed as a method for detecting cell proliferation. ELISA was utilized to measure inflammatory cytokines (TNF-α, IL-6, and IL-1β) and myocardial injury indicators (CK-MB, Mb, cTnI, and LDH). The levels of MDA and ROS were determined by the kit and fluorescent probe. H&E was conducted to assess MI/R injury after silencing of RIPK2.

RESULTS

In MI/R rats and OGD/R-treated H9C2 cardiomyocytes, RIPK2 was overexpressed at both the mRNA and protein levels. RIPK2 inhibition promoted cell proliferation while inhibiting apoptosis, as evidenced by decreased TUNEL-positive cells and cleaved caspase-3. RIPK2 inhibition reduced MDA and ROS levels, as well as the contents of inflammatory factors. RIPK2 silencing reduced CK-MB, Mb, cTnI, and LDH levels in rat serum and alleviated MI/R injury. Furthermore, RIPK2 inhibition increased p-AKT while decreasing NF-B p-p65 expression.

CONCLUSION

Silencing of RIPK2 reduced apoptosis, proinflammatory factors, and oxidative stress in MI/R by activating AKT and suppressing NF-κB signals, suggesting a potential therapeutic strategy for MI/R injury.

Activation of NOD1 and NOD2 in the development of liver injury and cancer

Hepatocytes and liver-resident antigen-presenting cells are exposed to microbe-associated molecular patterns (MAMPs) and microbial metabolites, which reach the liver from the gut via the portal vein. MAMPs induce innate immune responses via the activation of pattern recognition receptors (PRRs), such as toll-like receptors (TLRs), nucleotide-binding oligomerization domain 1 (NOD1), and NOD2. Such proinflammatory cytokine responses mediated by PRRs likely contribute to the development of chronic liver diseases and hepatocellular carcinoma (HCC), as shown by the fact that activation of TLRs and subsequent production of IL-6 and TNF-α is required for the generation of chronic fibroinflammatory responses and hepatocarcinogenesis. Similar to TLRs, NOD1 and NOD2 recognize MAMPs derived from the intestinal bacteria. The association between the activation of NOD1/NOD2 and chronic liver diseases is poorly understood. Given that NOD1 and NOD2 can regulate proinflammatory cytokine responses mediated by TLRs both positively and negatively, it is likely that sensing of MAMPs by NOD1 and NOD2 affects the development of chronic liver diseases, including HCC. Indeed, recent studies have highlighted the importance of NOD1 and NOD2 activation in chronic liver disorders. Here, we summarize the roles of NOD1 and NOD2 in hepatocarcinogenesis and liver injury.

Activation of RIPK2-mediated NOD1 signaling promotes proliferation and invasion of ovarian cancer cells via NF-κB pathway

The goal of this study was to investigate the role and mechanism of action of nucleotide oligomerization domain receptor 1 (NOD1) in ovarian cancer. Results showed that the expressions of NOD1 and receptor interacting serine/threonine kinase 2 (RIPK2) were notably upregulated in non-metastatic and metastatic ovarian tumors compared with matched non-tumor tissues, and their expression in metastatic tumor tissues was higher than that in non-metastatic tumors. Overexpression of NOD1 facilitated the expression of proliferation-related proteins (PCNA and Ki67) and proliferation and invasion of ovarian cancer cells. Overexpression of NOD1 promoted NF-κB expression and phosphorylation. Importantly, NOD1 bound with RIPK2, and silencing of RIPK2 partly rescued the promotion of NOD1 to NF-κB expression and its phosphorylation. The promotion of NOD1 to ovarian cancer cell proliferation and invasion was partly reversed by RIPK2 silencing. Results from our in vivo study indicate that overexpression of NOD1 accelerated the growth of ovarian cancer tumors, expression of proliferation-related proteins, and activation of NF-κB. However, silencing of NOD1 suppressed tumor growth. In summary, NOD1 facilitates ovarian cancer progression by activating NF-κB signaling by binding to RIPK2. We suggest a new strategy for the treatment of ovarian cancer.

Gut microbiota-based vaccination engages innate immunity to improve blood glucose control in obese mice

Objective

Obesity and diabetes increase circulating levels of microbial components derived from the gut microbiota. Individual bacterial factors (i.e., postbiotics) can have opposing effects on blood glucose.

Methods

We tested the net effect of gut bacterial extracts on blood glucose in mice using a microbiota-based vaccination strategy.

Results

Male and female mice had improved glucose and insulin tolerance five weeks after a single subcutaneous injection of a specific dose of a bacterial extract obtained from the luminal contents of the upper small intestine (SI), lower SI, or cecum. Injection of mice with intestinal extracts from germ-free mice revealed that bacteria were required for a microbiota-based vaccination to improve blood glucose control. Vaccination of Nod1^−/−, Nod2^−/−, and Ripk2^−/− mice showed that each of these innate immune proteins was required for bacterial extract injection to improve blood glucose control. A microbiota-based vaccination promoted an immunoglobulin-G (IgG) response directed against bacterial extract antigens, where subcutaneous injection of mice with the luminal contents of the lower SI elicited a bacterial extract-specific IgG response that is compartmentalized to the lower SI of vaccinated mice. A microbiota-based vaccination was associated with an altered microbiota composition in the lower SI and colon of mice. Lean mice only required a single injection of small intestinal-derived bacterial extract, but high fat diet (HFD)-fed, obese mice required prime-boost bacterial extract injections for improvements in blood glucose control.

Conclusions

Subversion of the gut barrier by vaccination with a microbiota-based extract engages innate immunity to promote long-lasting improvements in blood glucose control in a dose-dependent manner.

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Subcutaneous injection of gut bacterial extracts improved blood glucose control in mice.

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Microbiota-based vaccination engaged NOD1-NOD2-RIPK2 to alter blood glucose.

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Microbiota-based vaccination promoted a proximal gut IgG response.

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Microbiota-based vaccination altered the composition of the gut microbiome.

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Obese mice required prime-boost injections to improve blood glucose control.

Metabolic endotoxemia is dictated by the type of lipopolysaccharide

Lipopolysaccharides (LPSs) can promote metabolic endotoxemia, which is considered inflammatory and metabolically detrimental based on Toll-like receptor (TLR)4 agonists, such as Escherichia coli-derived LPS. LPSs from certain bacteria antagonize TLR4 yet contribute to endotoxemia measured by endotoxin units (EUs). We found that E. coli LPS impairs gut barrier function and worsens glycemic control in mice, but equal doses of LPSs from other bacteria do not. Matching the LPS dose from R. sphaeroides and E. coli by EUs reveals that only E. coli LPS promotes dysglycemia and adipose inflammation, delays intestinal glucose absorption, and augments insulin and glucagon-like peptide (GLP)-1 secretion. Metabolically beneficial endotoxemia promoted by R. sphaeroides LPS counteracts dysglycemia caused by an equal dose of E. coli LPS and improves glucose control in obese mice. The concept of metabolic endotoxemia should be expanded beyond LPS load to include LPS characteristics, such as lipid A acylation, which dictates the effect of metabolic endotoxemia.

GeGen QinLian decoction alleviate influenza virus infectious pneumonia through intestinal flora

Influenza in humans is often accompanied by gastroenteritis-like symptoms. GeGen QinLian decoction (GQD), a Chinese herb formula, has been widely used to treat infectious diarrhea for centuries and has the effect of restoring intestinal flora. Studies have also reported that GQD were used to treat patients with influenza. However, whether regulating the intestinal flora is one of the ways GQD treats influenza has not been confirmed. In present research, we conducted a systemic pharmacological study, and the results showed that GQD may acts through multiple targets and pathways. In influenza-infected mice, GQD treatment reduced mortality and lung inflammation. Most importantly, the mortality and lung inflammation were also reduced in influenza-infected mice that have undergone fecal microbiota transplantation (FMT) from GQD (FMT-GQD) treated mice. GQD treatment or FMT-GQD treatment restores the intestinal flora, resulting in an increase in Akkermansia_muciniphila, Desulfovibrio_C21_c20 and Lactobacillus_salivarius, and a decrease in Escherichia_coli. FMT-GQD treatment inhibited the NOD/RIP2/NF-κB signaling pathway in the intestine and affected the expression of downstream related inflammatory cytokines in mesenteric lymph nodes (mLNs) and serum. In addition, FMT-GQD treatment showed systemic protection by restraining the inflammatory differentiation of CD4⁺ T cells. In conclusion, our study shows that GQD can affect systemic immunity, at least in part, through the intestinal flora, thereby protect the mice against influenza virus infectious pneumonia.

NOD1-Targeted Immunonutrition Approaches: On the Way from Disease to Health

Immunonutrition appears as a field with great potential in modern medicine. Since the immune system can trigger serious pathophysiological disorders, it is essential to study and implement a type of nutrition aimed at improving immune system functioning and reinforcing it individually for each patient. In this sense, the nucleotide-binding oligomerization domain-1 (NOD1), one of the members of the pattern recognition receptors (PRRs) family of innate immunity, has been related to numerous pathologies, such as cancer, diabetes, or cardiovascular diseases. NOD1, which is activated by bacterial-derived peptidoglycans, is known to be present in immune cells and to contribute to inflammation and other important pathways, such as fibrosis, upon recognition of its ligands. Since immunonutrition is a significant developing research area with much to discover, we propose NOD1 as a possible target to consider in this field. It is relevant to understand the cellular and molecular mechanisms that modulate the immune system and involve the activation of NOD1 in the context of immunonutrition and associated pathological conditions. Surgical or pharmacological treatments could clearly benefit from the synergy with specific and personalized nutrition that even considers the health status of each subject.

RIPK2 is an unfavorable prognosis marker and a potential therapeutic target in human kidney renal clear cell carcinoma

Receptor Interacting Serine/Threonine Kinase 2 (RIPK2) is located on chromosome 8q21 and encodes a protein containing a C-terminal caspase activation and recruitment domain (CARD), which is a component of signaling complexes in both the innate and adaptive immune pathways. To estimate the value of RIPK2 in evaluating the prognosis and guiding the targeted therapy for patients with kidney renal clear cell carcinoma (KIRC), we analyzed total 526 KIRC samples from The Cancer Genome Atlas (TCGA) database. Our result showed that RIPK2 was upregulated in KIRC tumor samples compared with normal samples. Cox regression was performed to calculate the hazard ratio of RIPK2 expression as an unfavorable prognosis feature for overall survival. Moreover, RIPK2 expression was positively correlated to the high-risk clinical stage, and metastasis features. The upregulation of RIPK2 was strongly correlated with various immune signaling pathway dysregulations as well as immune phenotypes changes in KIRC patient’s cohort. In addition, inhibition of RIPK2 activity by either shRNA-mediated knockdown or inhibitor significantly reduced kidney cancer cell viability, trans-migration in vitro, and impaired tumor growth in vivo. In conclusion, elevated RIPK2 expression indicates a worse prognosis for KIRC patients and could serve as a potential prognostic biomarker and therapeutic target in kidney cancer.

Transcriptome-Wide High-Throughput m6A Sequencing of Differential m6A Methylation Patterns in the Human Rheumatoid Arthritis Fibroblast-Like Synoviocytes Cell Line MH7A

Introduction

N6-methyladenosine (m6A) is the most frequent internal modification in eukaryotic mRNAs and is closely related to the occurrence and development of many diseases, especially tumors. However, the relationship between m6A methylation and rheumatoid arthritis (RA) is still a mystery.

Methods

Two high-throughput sequencing methods, namely, m6A modified RNA immunoprecipitation sequence (m6A-seq) and RNA sequence (RNA-seq) were performed to identify the differentially expressed m6A methylation in human rheumatoid arthritis fibroblast-like synoviocytes cell line MH7A after stimulation with TNF-α. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were used to obtain enriched GO terms and significant KEGG pathways. Then, four candidate genes, Wilms tumor 1-associating protein (WTAP), receptor-interacting serine/threonine protein kinase 2 (RIPK2), Janus kinase 3 (JAK3) and tumor necrosis factor receptor SF10A (TNFRSF10A) were selected to further validate the m6A methylation, mRNA and protein expression levels in MH7A cells and synovial tissues of adjuvant arthritis (AA) rats by RT-qPCR and Western blot.

Results

Using m6A-seq, we identified a total of 206 genes with differentially expressed m6A methylation, of which 118 were significantly upregulated and 88 genes were significantly downregulated. Likewise, 1207 differentially mRNA expressed mRNAs were obtained by RNA-seq, of which 793 were upregulated and 414 downregulated. Further joint analysis showed that the m6A methylation and mRNA expression levels of 88 genes changed significantly, of which 30 genes displayed increased m6A methylation and decreased mRNA expression, 57 genes displayed decreased m6A methylation and increased mRNA expression increased, and 1 gene displayed increased m6A methylation and increased mRNA expression. GO and KEGG analyses indicated that these unique genes were mainly enriched in inflammation-related pathways, cell proliferation and apoptosis. In addition, the validations of WTAP, RIPK2, JAK3 and TNFRSF10A were in accordance with the m6A and RNA sequencing results.

Conclusion

This study established the transcriptional map of m6A in MH7A cells and revealed the potential relationship between RNA methylation modification and RA related genes. The results suggested that m6A modification was associated with the occurrence and course of RA to some extent.

Inflammation promotes adipocyte lipolysis via IRE1 kinase

Obesity associates with inflammation, insulin resistance, and higher blood lipids. It is unclear if immune responses facilitate lipid breakdown and release from adipocytes via lipolysis in a separate way from hormones or adrenergic signals. We found that an ancient component of ER stress, inositol-requiring protein 1 (IRE1), discriminates inflammation-induced adipocyte lipolysis versus lipolysis from adrenergic or hormonal stimuli. Our data show that inhibiting IRE1 kinase activity was sufficient to block adipocyte-autonomous lipolysis from multiple inflammatory ligands, including bacterial components, certain cytokines, and thapsigargin-induced ER stress. IRE1-mediated lipolysis was specific for inflammatory triggers since IRE1 kinase activity was dispensable for isoproterenol and cAMP-induced lipolysis in adipocytes and mouse adipose tissue. IRE1 RNase activity was not associated with inflammation-induced adipocyte lipolysis. Inhibiting IRE1 kinase activity blocked NF-κB activation, interleukin-6 secretion, and adipocyte-autonomous lipolysis from inflammatory ligands. Inflammation-induced lipolysis mediated by IRE1 occurred independently from changes in insulin signaling in adipocytes, suggesting that inflammation can promote IRE1-mediated lipolysis independent of adipocyte insulin resistance. We found no role for canonical unfolded protein responses or ABL kinases in linking ER stress to IRE1-mediated lipolysis. Adiponectin-Cre-mediated IRE1 knockout in mice showed that adipocyte IRE1 was required for inflammatory ligand-induced lipolysis in adipose tissue explants and that adipocyte IRE1 was required for approximately half of the increase in blood triglycerides after a bacterial endotoxin-mediated inflammatory stimulus in vivo. Together, our results show that IRE1 propagates an inflammation-specific lipolytic program independent from hormonal or adrenergic regulation. Targeting IRE1 kinase activity may benefit metabolic syndrome and inflammatory lipid disorders.

Knockdown of RIPK2 Inhibits Proliferation and Migration, and Induces Apoptosis via the NF-κB Signaling Pathway in Gastric Cancer

RIPK2 is a 62 kDa protein and a member of the receptor interacting protein kinases (RIPK) family. It was previously demonstrated that RIPK2 might play a role in promoting malignant tumor progression; however, the precise function of RIPK2 in the onset and progression of gastric cancer (GC) remains unclear. In the current study, we investigated the role of RIPK2 in GC. First, we explored the expression levels of RIPK2 in multiple cancers, including GC, using a bioinformatics approach. We constructed the RIPK2-associated protein-protein interaction network using the search tool for the retrieval of interacting genes/proteins for gene ontology and Kyoto encyclopedia of genes and genomes analysis. Next, we compared the RIPK2 expression levels between GC cells and normal gastric mucosal epithelial cell (GES-1) using reverse transcription quantitative PCR analysis. We downregulated the expression of RIPK2 in GC cells to determine the effects of RIPK2 on cell growth, migration, and apoptosis. Finally, we used western blotting to investigate the RIPK2 downstream signaling pathway involved in the regulation of GC progression. Our results showed that RIPK2 was overexpressed in various tumor tissues, including GC, compared to non-cancer tissues. Moreover, RIPK2 expression was significantly upregulated in all four GC cell lines (MGC-803,SGC-7901, HGC-27 and AGS) comparing the GES-1 cells. Silencing of RIPK2 suppressed GC cell growth by inhibiting migration, and inducing apoptosis through the nuclear factor-κB (NF-κB) signaling pathway. In summary, we demonstrate that RIPK2 plays an important role in modulating GC cell proliferation, migration, and apoptosis through the NF-κB signaling pathway. Therefore, RIPK2 functions as a potential oncogene. We believe that RIPK2 can be used as a candidate biomarker, as well as a diagnostic tool, and the therapeutic target for GC.

NOD1 activation induces oxidative stress via NOX1/4 in adipocytes

Activation of innate immune components promotes cell autonomous inflammation in adipocytes. Oxidative stress links pattern recognition receptor-mediated detection of inflammatory ligands and the immune response. Reactive oxygen species (ROS) may mediate the effect of nucleotide-binding oligomerization domain protein-1 (NOD1) activation on inflammation in adipocytes. Here, we define the potential role of NADPH oxidase (NOX)-derived ROS in NOD1-mediated inflammatory response in adipocytes. Differentiated 3T3-L1 adipocytes were treated with NOD1 activating ligand D-gamma-Glu-meso-diaminopimelic acid (iE-DAP) to evaluate the oxidative stress and contribution of NOX as source of intracellular ROS. NOD1 activation potently induced ROS generation in 3T3-L1 adipocytes. Of the NOX family members, expression of NOX1 and NOX4 was increased upon NOD1 activation, in a PKCδ-dependent manner. siRNA-mediated down-regulation of NOX1 or NOX4 inhibited NOD1-mediated ROS production and increased the expression of antioxidant defense enzyme catalase and superoxide dismutase (SOD). siRNA-mediated lowering of NOX1 or NOX4 also suppressed NOD1-mediated activation of JNK1/2 and NF-κB, and consequent activation of inflammatory response in 3T3-L1 adipocytes. In summary, our findings demonstrate that NOD1 activation provokes oxidative stress in adipocytes via NOX1/4 and that oxidative stress, at least in part, contributes to induction of inflammatory response. Defining the source of ROS after immune response engagement may lead to new therapeutic strategies for adipose tissue inflammation.

The NLRP3 inflammasome regulates adipose tissue metabolism

Adipose tissue regulates metabolic homeostasis by participating in endocrine and immune responses in addition to storing and releasing lipids from adipocytes. Obesity skews adipose tissue adipokine responses and degrades the coordination of adipocyte lipogenesis and lipolysis. These defects in adipose tissue metabolism can promote ectopic lipid deposition and inflammation in insulin-sensitive tissues such as skeletal muscle and liver. Sustained caloric excess can expand white adipose tissue to a point of maladaptation exacerbating both local and systemic inflammation. Multiple sources, instigators and propagators of adipose tissue inflammation occur during obesity. Cross-talk between professional immune cells (i.e. macrophages) and metabolic cells (i.e. adipocytes) promote adipose tissue inflammation during metabolic stress (i.e. metaflammation). Metabolic stress and endogenous danger signals can engage pathogen recognition receptors (PRRs) of the innate immune system thereby activating pro-inflammatory and stress pathways in adipose tissue. The Nod-like receptor protein 3 (NLRP3) inflammasome can act as a metabolic danger sensor to a wide range of pathogen- and damage-associated molecular patterns (PAMPs and DAMPs). Activation of the NLRP3 inflammasome facilitates caspase-1 dependent production of the pro-inflammatory cytokines IL-1β and IL-18. Activation of the NLRP3 inflammasome can promote inflammation and pyroptotic cell death, but caspase-1 is also involved in adipogenesis. This review discusses the role of the NLRP3 inflammasome in adipose tissue immunometabolism responses relevant to metabolic disease. Understanding the potential sources of NLRP3 activation and consequences of NLRP3 effectors may reveal therapeutic opportunities to break or fine-tune the connection between metabolism and inflammation in adipose tissue during obesity.

Lysozyme is a component of the innate immune system linked to obesity associated-chronic low-grade inflammation and altered glucose tolerance

BACKGROUND & AIMS

Several proteins of the innate immune system are known to be deregulated with insulin resistance. We here aimed to investigate the relationship among circulating lysozyme (both plasma concentration and activity) and obesity-associated metabolic disturbances.

METHODS

Plasma lysozyme concentration was determined cross-sectionally in a discovery (Cohort 1, n = 137) and in a replication cohort (Cohort 2, n = 181), in which plasma lysozyme activity was also analyzed. Plasma lysozyme was also evaluated longitudinally in participants from the replication cohort (n = 93). Leukocyte lysozyme expression (LYZ mRNA) were also investigated in an independent cohort (Cohort 3, n = 76), and adipose tissue (AT) LYZ mRNA (n = 25) and plasma peptidoglycan levels (n = 61) in subcohorts from discovery cohort.

RESULTS

Translocation of peptidoglycan (as inferred from its increased circulating levels) was linked to plasma lysozyme, hyperinsulinemia and dyslipidemia in obese subjects. In both discovery and replication cohorts, plasma lysozyme levels and activity were significantly increased in obesity in direct association with obesity-associated metabolic disturbances and inflammatory parameters, being circulating lysozyme negatively correlated with fasting glucose, HbA1c and insulin resistance (HOMA-IR) in obese subjects. Of note, total cholesterol (p < 0.0001) and LDL cholesterol (p = 0.003) contributed independently to age-, gender- and BMI adjusted plasma lysozyme activity. Longitudinally, changes in HbA1c levels and serum LDL cholesterol were negatively associated with circulating lysozyme antimicrobial activity. On the contrary, the change in glucose infusion rate during the clamp (insulin sensitivity) was positively associated with lysozyme concentration.

CONCLUSIONS

Increased plasma lysozyme levels and activity are found in obese subjects. The longitudinal findings suggest that plasma lysozyme might be protective on the development of obesity-associated metabolic disturbances.

RIPK2 Dictates Insulin Responses to Tyrosine Kinase Inhibitors in Obese Male Mice

Tyrosine kinase inhibitors (TKIs) used in cancer are also being investigated in diabetes. TKIs can improve blood glucose control in diabetic cancer patients, but the specific kinases that alter blood glucose or insulin are not clear. We sought to define the role of Receptor Interacting Serine/Threonine Kinase 2 (RIPK2) in mouse models of insulin resistance. We tested the TKI gefitinib, which inhibits RIPK2 activity, in wild-type (WT), Nod1-/-, Nod2-/-, and Ripk2-/- mice fed an obesogenic high-fat diet. Gefitinib lowered blood glucose during a glucose tolerance test (GTT) in a nucleotide-binding oligomerization domain (NOD)-RIPK2-independent manner in all obese mice. However, gefitinib lowered glucose-stimulated insulin secretion only in obese Ripk2-/- mice. Gefitinib had no effect on insulin secretion in obese WT, Nod1-/-, or Nod2-/- mice. Hence, genetic deletion of Ripk2 promoted the insulin-sensitizing potential of gefitinib, since this TKI lowered both blood glucose and insulin only in Ripk2-/- mice. Gefitinib did not alter the inflammatory profile of pancreas, adipose, liver, or muscle tissues in obese Ripk2-/- mice compared with obese WT mice. We also tested imatinib, a TKI that does not inhibit RIPK2 activity, in obese WT mice. Imatinib lowered blood glucose during a GTT, consistent with TKIs lowering blood glucose independently of RIPK2. However, imatinib increased glucose-stimulated insulin secretion during the glucose challenge. These data show that multiple TKIs lower blood glucose, where actions of TKIs on RIPK2 dictate divergent insulin responses, independent of tissue inflammation. Our data show that RIPK2 limits the insulin sensitizing effect of gefitinib, whereas imatinib increased insulin secretion.

Statins activate the NLRP3 inflammasome and impair insulin signaling via p38 and mTOR

Statins lower cholesterol and risk of cardiovascular disease. Statins can increase blood glucose and risk of new-onset diabetes. It is unclear why statins can have opposing effects on lipids versus glucose. Statins have cholesterol-independent pleiotropic effects that influence both insulin and glucose control. Statin lowering of isoprenoids required for protein prenylation promotes pancreatic β-cell dysfunction and adipose tissue insulin resistance. Protein prenylation influences immune function and statin-mediated adipose tissue insulin resistance involves the NLR family pyrin domain-containing 3 (NLRP3) inflammasome and IL-1β. However, the intracellular cues that statins engage to activate the NLRP3 inflammasome and those responsible for IL-1β-mediated insulin resistance in adipose tissue have not been identified. We hypothesized that stress kinases or components of the insulin signaling pathway mediated statin-induced insulin resistance. We tested the associations of p38, ERK, JNK, phosphatase, and tensin homolog (PTEN), and mTOR in statin-exposed adipose tissue from WT and IL-1β^-/- mice. We found that statins increased phosphorylation of p38 in WT and IL-1β^-/- mice. Statin activation of p38 upstream of IL-1β led to priming of this NLRP3 inflammasome effector in macrophages. We found that mTORC1 inhibition with low doses of rapamycin (2 or 20 nM) lowered macrophage priming of IL-1β mRNA and secretion of IL-1β caused by multiple statins. Rapamycin (20 nM) or the rapalog everolimus (20 nM) prevented atorvastatin-induced lowering of insulin-mediated phosphorylation of Akt in mouse adipose tissue. These results position p38 and mTOR as mediators of statin-induced insulin resistance in adipose tissue and highlight rapalogs as candidates to mitigate the insulin resistance and glycemic side effects of statins.

Postbiotics for NOD2 require nonhematopoietic RIPK2 to improve blood glucose and metabolic inflammation in mice

Defining the host receptors and metabolic consequences of bacterial components can help explain how the microbiome influences metabolic diseases. Bacterial peptidoglycans that activate nucleotide-binding oligomerization domain-containing (NOD)1 worsen glucose control, whereas NOD2 activation improves glycemia. Receptor-interacting serine/threonine-protein kinase 2 (RIPK2) is required for innate immunity instigated by NOD1 and NOD2. The role of RIPK2 in the divergent effects of NOD1 versus NOD2 on blood glucose was unknown. We found that whole body deletion of RIPK2 negated all effects of NOD1 or NOD2 activation on blood glucose during an acute, low level endotoxin challenge in mice. It was known that NOD1 in hematopoietic cells participates in insulin resistance and metabolic inflammation in obese mice. It was unknown if RIPK2 in hematopoietic cells is required for the glucose-lowering and anti-inflammatory effects of NOD2 activation. We hypothesized that RIPK2 in nonhematopoietic cells dictated the glycemic effects of NOD2 activation. We found that whole body deletion of RIPK2 prevented the glucose-lowering effects of repeated NOD2 activation that were evident during a glucose tolerance test (GTT) in high-fat diet (HFD)-fed wild-type (WT) mice. NOD2 activation lowered glucose during a GTT and lowered adipose tissue inflammation in mice with RIPK2 deleted in hematopoietic cells. We conclude that RIPK2 in nonhematopoietic cells mediates the glucose lowering and anti-inflammatory effects of NOD2-activating postbiotics. We propose a model where lipopolysaccharides and NOD1 ligands synergize in hematopoietic cells to promote insulin resistance but NOD2 activation in nonhematopoietic cells promotes RIPK2-dependent immune tolerance and lowering of inflammation and insulin resistance.

Statins Promote Interleukin-1β-Dependent Adipocyte Insulin Resistance Through Lower Prenylation, Not Cholesterol

Statins lower cholesterol and adverse cardiovascular outcomes, but this drug class increases diabetes risk. Statins are generally anti-inflammatory. However, statins can promote inflammasome-mediated adipose tissue inflammation and insulin resistance through an unidentified immune effector. Statins lower mevalonate pathway intermediates beyond cholesterol, but it is unknown whether lower cholesterol underpins statin-mediated insulin resistance. We sought to define the mevalonate pathway metabolites and immune effectors that propagate statin-induced adipose insulin resistance. We found that LDL cholesterol lowering was dispensable, but statin-induced lowering of isoprenoids required for protein prenylation triggered NLRP3/caspase-1 inflammasome activation and interleukin-1β (IL-1β)-dependent insulin resistance in adipose tissue. Multiple statins impaired insulin action at the level of Akt/protein kinase B signaling in mouse adipose tissue. Providing geranylgeranyl isoprenoids or inhibiting caspase-1 prevented statin-induced defects in insulin signaling. Atorvastatin (Lipitor) impaired insulin signaling in adipose tissue from wild-type and IL-18^-/- mice, but not IL-1β^-/- mice. Atorvastatin decreased cell-autonomous insulin-stimulated lipogenesis but did not alter lipolysis or glucose uptake in 3T3-L1 adipocytes. Our results show that statin lowering of prenylation isoprenoids activates caspase-1/IL-1β inflammasome responses that impair endocrine control of adipocyte lipogenesis. This may allow the targeting of cholesterol-independent statin side effects on adipose lipid handling without compromising the blood lipid/cholesterol-lowering effects of statins.

NOD1: An Interface Between Innate Immunity and Insulin Resistance

Insulin resistance is driven, in part, by activation of the innate immune system. We have discussed the evidence linking nucleotide-binding oligomerization domain (NOD)1, an intracellular pattern recognition receptor, to the onset and progression of obesity-induced insulin resistance. On a molecular level, crosstalk between downstream NOD1 effectors and the insulin receptor pathway inhibits insulin signaling, potentially through reduced insulin receptor substrate action. In vivo studies have demonstrated that NOD1 activation induces peripheral, hepatic, and whole-body insulin resistance. Also, NOD1-deficient models are protected from high-fat diet (HFD)-induced insulin resistance. Moreover, hematopoietic NOD1 deficiency prevented HFD-induced changes in proinflammatory macrophage polarization status, thus protecting against the development of metabolic inflammation and insulin resistance. Serum from HFD-fed mice activated NOD1 signaling ex vivo; however, the molecular identity of the activating factors remains unclear. Many have proposed that an HFD changes the gut permeability, resulting in increased translocation of bacterial fragments and increased circulating NOD1 ligands. In contrast, others have suggested that NOD1 ligands are endogenous and potentially lipid-derived metabolites produced during states of nutrient overload. Nevertheless, that NOD1 contributes to the development of insulin resistance, and that NOD1-based therapy might provide benefit, is an exciting advancement in metabolic research.

RIPK2: New Elements in Modulating Inflammatory Breast Cancer Pathogenesis

Inflammatory breast cancer (IBC) is a rare and aggressive form of breast cancer that is associated with significantly high mortality. In spite of advances in IBC diagnoses, the prognosis is still poor compared to non-IBC. Due to the aggressive nature of the disease, we hypothesize that elevated levels of inflammatory mediators may drive tumorigenesis and metastasis in IBC patients. Utilizing IBC cell models and patient tumor samples, we can detect elevated NF-κB activity and hyperactivation of non-canonical drivers of NF-κB (nuclear factor kappaB)-directed inflammation such as tyrosine phosphorylated receptor-interacting protein kinase 2 (pY RIPK2), when compared to non-IBC cells or patients. Interestingly, elevated RIPK2 activity levels were present in a majority of pre-chemotherapy samples from IBC patients at the time of diagnosis to suggest that patients at diagnosis had molecular activation of NF-κB via RIPK2, a phenomenon we define as “molecular inflammation”. Surprisingly, chemotherapy did cause a significant increase in RIPK2 activity and thus molecular inflammation suggesting that chemotherapy does not resolve the molecular activation of NF-κB via RIPK2. This would impact on the metastatic potential of IBC cells. Indeed, we can demonstrate that RIPK2 activity correlated with advanced tumor, metastasis, and group stage as well as body mass index (BMI) to indicate that RIPK2 might be a useful prognostic marker for IBC and advanced stage breast cancer.