Phenotyping of Nod1/2 double deficient mice and characterization of Nod1/2 in systemic inflammation and associated renal disease

Ileocolonic Healing After Extended Small Bowel Resection in Mice: NOD2 Deficiency Impairs Anastomotic Healing and Postoperative Outcome

BACKGROUND

Nucleotide-binding oligomerization domain-containing protein 2 (NOD2) mutations are a genetic risk factor for Crohn disease. Ileocecal resection is the most often performed surgery in Crohn disease. We investigated the effect of Nod2 knockout (KO) status on anastomotic healing after extended ileocecal resection (ICR) in mice.

METHODS

Male C57BL6/J wild-type and Nod2 KO mice underwent an 11 cm resection of the terminal ileum including the cecum. An end-to-end jejuno-colostomy was performed. Animals were killed after 5 days investigating bursting pressure, hydroxyproline content, and expression of matrix metabolism genes, key cytokines, and histology of the anastomosis.

RESULTS

Mortality was higher in the Nod2 KO group but not because of local or septic complications. Bursting pressure was significantly reduced in the Nod2 KO mice (32.5 vs 78.0 mmHg, P < 0.0024), whereas hydroxyprolin content was equal. The amount of granulation tissue at the anastomosis was similar but more unstructured in the Nod2 KO mice. Gene expression measured by real-time polymerase chain reaction showed significantly increased expression for Collagen 1alpha and for collagen degradation as measured by matrix metalloproteinase-2, -9, and -13 in the Nod2 KO mice. Gelatinase activity from anastomotic tissue was enhanced by Nod2 status. Gene expression of arginase I, tumor necrosis factor-α, and transforming growth factor-ß but not inducible nitric oxide synthase were also increased at the anastomosis in the Nod2 KO mice compared with the control mice.

CONCLUSIONS

We found that Nod2 deficiency results in significantly reduced bursting pressure after ileocecal resection. This effect is mediated via an increased matrix turnover. Patients with genetic NOD2 variations may be prone to anastomotic failure after bowel resection.

Beyond classic concepts in thyroid homeostasis: Immune system and microbiota

It has long been known that thyroid hormones have implications for multiple physiological processes and can lead to serious illness when there is an imbalance in its metabolism. The connections between thyroid hormone metabolism and the immune system have been extensively described, as they can participate in inflammation, autoimmunity, or cancer progression. In addition, changes in the normal intestinal microbiota involve the activation of the immune system while triggering different pathophysiological disorders. Recent studies have linked the microbiota and certain bacterial fragments or metabolites to the regulation of thyroid hormones and the general response in the endocrine system. Even if the biology and function of the thyroid gland has attracted more attention due to its pathophysiological importance, there are essential mechanisms and issues related to it that are related to the interplay between the intestinal microbiota and the immune system and must be further investigated. Here we summarize additional information to uncover these relationships, the knowledge of which would help establish new personalized medical strategies.

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.

Genetic Deletion of NOD1 Prevents Cardiac Ca2+ Mishandling Induced by Experimental Chronic Kidney Disease

Risk of cardiovascular disease (CVD) increases considerably as renal function declines in chronic kidney disease (CKD). Nucleotide-binding oligomerization domain-containing protein 1 (NOD1) has emerged as a novel innate immune receptor involved in both CVD and CKD. Following activation, NOD1 undergoes a conformational change that allows the activation of the receptor-interacting serine/threonine protein kinase 2 (RIP2), promoting an inflammatory response. We evaluated whether the genetic deficiency of Nod1 or Rip2 in mice could prevent cardiac Ca²⁺ mishandling induced by sixth nephrectomy (Nx), a model of CKD. We examined intracellular Ca²⁺ dynamics in cardiomyocytes from Wild-type (Wt), Nod1^-/- and Rip2^-/- sham-operated or nephrectomized mice. Compared with Wt cardiomyocytes, Wt-Nx cells showed an impairment in the properties and kinetics of the intracellular Ca²⁺ transients, a reduction in both cell shortening and sarcoplasmic reticulum Ca²⁺ load, together with an increase in diastolic Ca²⁺ leak. Cardiomyocytes from Nod1^-/--Nx and Rip2^-/--Nx mice showed a significant amelioration in Ca²⁺ mishandling without modifying the kidney impairment induced by Nx. In conclusion, Nod1 and Rip2 deficiency prevents the intracellular Ca²⁺ mishandling induced by experimental CKD, unveiling new innate immune targets for the development of innovative therapeutic strategies to reduce cardiac complications in patients with CKD.

Renoprotective Effects of a Novel Receptor-Interacting Protein Kinase 2 Inhibitor, AS3334034, in Uninephrectomized Adriamycin-Induced Chronic Kidney Disease Rats

Renal inflammation is a final common pathway of chronic kidney disease (CKD), and its progression can be used to effectively gauge the degree of renal dysfunction. Inflammatory mechanisms contribute to glomerulosclerosis and tubulointerstitial fibrosis, which are hallmarks of CKD leading to end-stage renal disease. Receptor-interacting protein kinase 2 (RIP2) is largely committed to nucleotide-binding oligomerization domain signaling as a direct effector and transmits nuclear factor-κB (NF-κB)-mediated proinflammatory cytokine production. In the present study, we hypothesized that if inflammation via RIP2 and NF-κB signaling plays an important role in renal failure, then the anti-inflammatory effect of RIP2 inhibitors should be effective in improving CKD. To determine its pharmacologic potency, we investigated the renoprotective properties of the novel RIP2 inhibitor AS3334034 [7-methoxy-6-(2-methylpropane-2-sulfonyl)-N-(4-methyl-1H-pyrazol-3-yl)quinolin-4-amine] in uninephrectomized adriamycin-induced CKD rats. Six weeks' repeated administration of AS3334034 (10 mg/kg, once daily) significantly reduced urinary protein excretion and prevented the development of glomerulosclerosis and tubulointerstitial fibrosis. In addition, AS3334034 showed beneficial effects on renal function, as demonstrated by a decrease in levels of plasma creatinine and blood urea nitrogen and attenuation of a decline in creatinine clearance. Furthermore, AS3334034 significantly attenuated inflammation, renal apoptosis, and glomerular podocyte loss. These results suggest that the RIP2 inhibitor AS3334034 suppresses the progression of chronic renal failure via an anti-inflammatory effect and is therefore potentially useful in treating patients with CKD. SIGNIFICANCE STATEMENT: The receptor-interacting protein kinase 2 (RIP2) inhibitor AS3334034 suppresses the progression of chronic renal failure via an anti-inflammatory effect, suggesting that the nucleotide-binding oligomerization domain-RIP2 axis might play a crucial role in the pathogenesis of inflammatory kidney diseases. AS3334034 is expected to be potentially useful in the treatment of patients with chronic kidney disease.

The expression of NOD2, NLRP3 and NLRC5 and renal injury in anti-neutrophil cytoplasmic antibody-associated vasculitis

Background

Nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) are intracellular sensors of pathogens and molecules from damaged cells to regulate the inflammatory response in the innate immune system. Emerging evidences suggested a potential role of NLRs in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). This study aimed to investigate the expression of nucleotide-binding oligomerization domain containing protein 2 (NOD2), NOD-like receptor family pyrin domain containing 3 (NLRP3) and NOD-like receptor family CARD domain containing 5 (NLRC5) in kidneys of AAV patients, and further explored their associations with clinical and pathological parameters.

Methods

Thirty-four AAV patients in active stage were recruited. Their renal specimens were processed with immunohistochemistry to assess the expression of three NLRs, and with double immunofluorescence to detect NLRs on intrinsic and infiltrating cells. Analysis of gene expression was also adopted in cultured human podocytes. The associations between expression of NLRs and clinicopathological parameters were analyzed.

Results

The expression of NOD2, NLRP3 and NLRC5 was significantly higher in kidneys from AAV patients than those from normal controls, minimal change disease or class IV lupus nephritis. These NLRs co-localized with podocytes and infiltrating inflammatory cells. The mean optical density of NOD2 in glomeruli was significantly higher in crescentic class than non-crescentic class, and correlated with levels of proteinuria and serum creatinine at renal biopsy. The mean optical density of NLRC5 in glomeruli was significantly higher in crescentic class than non-crescentic class, and correlated with proteinuria level, Birmingham Vasculitis Activity Score and the proportion of crescents in the renal specimen.

Conclusions

The expression of three NLRs was upregulated in kidneys of AAV patients. The expression of NOD2 and NLRC5 was associated with the severity of renal lesions in AAV.

NOD1 and NOD2 of the innate immune system is differently expressed in human clear cell renal cell carcinoma, corresponding healthy renal tissue, its vasculature and primary isolated renal tubular epithelial cells

PURPOSE

NOD1 and NOD2 (nucleotide-binding oligomerization domain)-receptors are intracellular receptors and belong to the family of pattern recognition receptors being present in both human and murine renal tubular cells. Besides, NOD1 has been proved to promote apoptosis, upon its overexpression. Hence, we aimed to investigate NOD1 and NOD2 expression in human clear cell renal cell carcinoma (ccRCC).

METHODS

Tumor and corresponding adjacent healthy tissues from 41 patients with histopathological diagnosis of ccRCC as well as primary isolated renal tubular epithelial cells (TECs) and tumor tissue from a murine xenograft model using CAKI-1 ccRCC cells were analyzed.

RESULTS

NOD1 and NOD2 mRNA was constitutively expressed in both tumor and adjacent healthy renal tissue, with NOD1 being significantly lower and in contrast NOD2 significantly higher expressed in tumor tissue compared to healthy tissues. Immunohistochemically, NOD1 was located not only in the cytoplasm, but also in the nucleus in ccRCC tissue whereas NOD2 was solely localized in the cytoplasm in both human ccRCC as well as in the healthy tubular system. Focusing on the vasculature, NOD2 displayed broader expression than NOD1. In primary TECs as well as CAKI-1 cells NOD1 and NOD2 was constitutively expressed and increasable upon LPS stimulation. In the mouse xenograft model, human NOD1 mRNA was significantly higher expressed compared to NOD2. In contrast hereto, we observed a shift towards lower mouse NOD1 compared to NOD2 mRNA expression.

CONCLUSION

In view of reduced apoptosis-associated NOD1 expression in ccRCC tissue opposed to higher expression of NOD2 in tumor vasculature, inducibility of NOD expression in TECs as well as the detected shift of NOD1 and NOD2 expression in the mouse xenograft model, modulation of NOD receptors might, therefore, provide a molecular therapeutic approach in ccRCC.

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.

No difference in renal injury and fibrosis between wild-type and NOD1/NOD2 double knockout mice with chronic kidney disease induced by ureteral obstruction

Background

Chronic kidney disease (CKD) is characterized by sustained tissue damage and ongoing tubulo-interstitial inflammation and fibrosis. Pattern recognition receptors (PRRs) including Toll-like receptors (TLRs) and NOD-like receptors (NLRs) can sense endogenous ligands released upon tissue damage, leading to sterile inflammation and eventually irreversible kidney disease. It is known that NOD1 and NOD2 contribute to the pathogenesis of various inflammatory diseases, including acute kidney injury. However their role in chronic kidney disease is largely unknown. The aim of this study was therefore to investigate the contribution of NOD1 and NOD2 in renal interstitial fibrosis and obstructive nephropathy.

Methods

To do so, we performed unilateral ureteral obstruction (UUO) in wild type (WT) and NOD1/NOD2 double deficient (DKO) mice and analysed renal damage, fibrosis and inflammation. Data were analysed using the non-parametric Mann-Whitney U-test.

Results

Minor changes in inflammatory response were observed in NOD1/2 DKO mice, while no effects were observed on renal injury and the development of fibrosis.

Conclusion

No difference in renal injury and fibrosis between WT and NOD1/NOD2 DKO mice following obstructive nephropathy induced by ureteral obstruction.

Electronic supplementary material

The online version of this article (10.1186/s12882-018-0867-8) contains supplementary material, which is available to authorized users.

An endogenous nanomineral chaperones luminal antigen and peptidoglycan to intestinal immune cells

In humans and other mammals it is known that calcium and phosphate ions are secreted from the distal small intestine into the lumen. However, why this secretion occurs is unclear. Here, we show that the process leads to the formation of amorphous magnesium-substituted calcium phosphate nanoparticles that trap soluble macromolecules, such as bacterial peptidoglycan and orally fed protein antigens, in the lumen and transport them to immune cells of the intestinal tissue. The macromolecule-containing nanoparticles utilize epithelial M cells to enter Peyer's patches, small areas of the intestine concentrated with particle-scavenging immune cells. In wild-type mice, intestinal immune cells containing these naturally formed nanoparticles expressed the immune tolerance-associated molecule 'programmed death-ligand 1', whereas in NOD1/2 double knockout mice, which cannot recognize peptidoglycan, programmed death-ligand 1 was undetected. Our results explain a role for constitutively formed calcium phosphate nanoparticles in the gut lumen and show how this helps to shape intestinal immune homeostasis.

Pattern recognition receptors and the inflammasome in kidney disease

Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain receptors (NLRs) are families of pattern recognition receptors that, together with inflammasomes, sense and respond to highly conserved pathogen motifs and endogenous molecules released upon cell damage or stress. Evidence suggests that TLRs, NLRs and the NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome have important roles in kidney diseases through regulation of inflammatory and tissue-repair responses to infection and injury. In this Review, we discuss the pathological mechanisms that are related to TLRs, NLRs and NLRP3 in various kidney diseases. In general, these receptors are protective in the host defence against urinary tract infection, but can sustain and self-perpetuate tissue damage in sterile inflammatory and immune-mediated kidney diseases. TLRs, NLRs and NLRP3, therefore, have become promising drug targets to enable specific modulation of kidney inflammation and suppression of immunopathology in kidney disease.

Therapeutic targeting of NOD1 receptors

The nucleotide-binding oligomerization domain 1 (NOD1) protein is an intracellular receptor for breakdown products of peptidoglycan (PGN), an essential bacterial cell wall component. NOD1 responds to γ-D-glutamyl-meso-diaminopimelic acid, which is an epitope unique to PGN structures from all Gram-negative bacteria and certain Gram-positive bacteria. Upon ligand recognition, NOD1 undergoes conformational changes and self-oligomerization mediated by the nucleotide-binding NACHT domains, followed by the recruitment and activation of the serine threonine kinase receptor-interacting protein 2 leading to the activation of NF-κB and MAPK pathways and induction of inflammatory genes. Much of our knowledge is derived from seminal studies using mice deficient in NOD1 and confirming an essential role for NOD1 in the host immune response against gastrointestinal and respiratory pathogens. In addition, recent studies have revealed a role for intracellular NOD1 receptors in the regulation of vascular inflammation and metabolism. This review will discuss our current understanding of intracellular NOD1 receptors in host immunity and chronic inflammatory disorders with a focus on cardiovascular diseases. Although therapeutic advances may have to wait until the complex interplay with pathogens, danger signals, other pattern recognition receptors and overlapping metabolic pathways is further unravelled, the steadily growing body of knowledge suggest that NOD1 antagonism might represent attractive candidate to reduce excessive inflammation associated to intestinal, cardiovascular and metabolic diseases.