Nod1 and nod2 are expressed in human and murine renal tubular epithelial cells and participate in renal ischemia reperfusion injury

Human pulmonary microvascular endothelial cells respond to DAMPs from injured renal tubular cells

Acute kidney injury (AKI) causes distant organ dysfunction through yet unknown mechanisms, leading to multiorgan failure and death. The lungs are one of the most common extrarenal organs affected by AKI, and combined lung and kidney injury has a mortality as high as 60%-80%. One mechanism that has been implicated in lung injury after AKI involves molecules released from injured kidney cells (DAMPs, or damage-associated molecular patterns) that promote a noninfectious inflammatory response by binding to pattern recognition receptors (PRRs) constitutively expressed on the pulmonary endothelium. To date there are limited data investigating the role of PRRs and DAMPs in the pulmonary endothelial response to AKI. Understanding these mechanisms holds great promise for therapeutics aimed at ameliorating the devastating effects of AKI. In this study, we stimulate primary human microvascular endothelial cells with DAMPs derived from injured primary renal tubular epithelial cells (RTECs) as an ex-vivo model of lung injury following AKI. We show that DAMPs derived from injured RTECs cause activation of Toll-Like Receptor and NOD-Like Receptor signaling pathways as well as increase human primary pulmonary microvascular endothelial cell (HMVEC) cytokine production, cell signaling activation, and permeability. We further show that cytokine production in HMVECs in response to DAMPs derived from RTECs is reduced by the inhibition of NOD1 and NOD2, which may have implications for future therapeutics. This paper adds to our understanding of PRR expression and function in pulmonary HMVECs and provides a foundation for future work aimed at developing therapeutic strategies to prevent lung injury following AKI.

Lipotoxicity and immunometabolism in ischemic acute kidney injury: current perspectives and future directions

Dysregulated lipid metabolism is implicated in the pathophysiology of a range of kidney diseases. The specific mechanisms through which lipotoxicity contributes to acute kidney injury (AKI) remain poorly understood. Herein we review the cardinal features of lipotoxic injury in ischemic kidney injury; lipid accumulation and mitochondrial lipotoxicity. We then explore a new mechanism of lipotoxicity, what we define as "immunometabolic" lipotoxicity, and discuss the potential therapeutic implications of targeting this lipotoxicity using lipid lowering medications.

Recombinant antithrombin attenuates acute kidney injury associated with rhabdomyolysis: an in vivo animal study

BACKGROUND

Rhabdomyolysis is characterized by the destruction and necrosis of skeletal muscle tissue, resulting in acute kidney injury (AKI). Recombinant antithrombin (rAT) has DNA repair and vascular endothelial-protection properties. Herein, we investigated whether rAT therapy has beneficial effects against rhabdomyolysis-induced AKI. Ten-week-old male B6 mice were injected with 5 mL/kg of 50% glycerol intramuscularly in the left thigh after 24 h of fasting to create a rhabdomyolysis mouse model. Further, 750 IU/kg rAT was injected intraperitoneally at 24 and 72 h after the rhabdomyolysis model was established. The mice were euthanized after 96 h for histological analysis. Saline was administered to mice in the control group.

RESULTS

Blood tests show elevated serum creatinine, urea nitrogen, and neutrophil gelatinase-associated lipocalin levels in rhabdomyolysis. Loss of tubular epithelial cell nuclei and destruction of the tubular luminal surface structure was observed in the untreated group, which improved with rAT treatment. Immunostaining for Ki-67 showed increased Ki-67-positive nuclei in the tubular epithelial cells in the rAT group, suggesting that rAT may promote tubular epithelial cell regeneration. The microvilli of the brush border of the renal tubules were shed during rhabdomyolysis, and rAT treatment reduced this injury. The vascular endothelial glycocalyx, which is usually impaired by rhabdomyolysis, became functional following rAT treatment.

CONCLUSIONS

Treatment with rAT suppressed rhabdomyolysis-induced AKI, suggesting that rAT therapy may be a novel therapeutic approach.

The role of innate immunity in diabetic nephropathy and their therapeutic consequences

Diabetic nephropathy (DN) is an enduring condition that leads to inflammation and affects a substantial number of individuals with diabetes worldwide. A gradual reduction in glomerular filtration and emergence of proteins in the urine are typical aspects of DN, ultimately resulting in renal failure. Mounting evidence suggests that immunological and inflammatory factors are crucial for the development of DN. Therefore, the activation of innate immunity by resident renal and immune cells is critical for initiating and perpetuating inflammation. Toll-like receptors (TLRs) are an important group of receptors that identify patterns and activate immune responses and inflammation. Meanwhile, inflammatory responses in the liver, pancreatic islets, and kidneys involve inflammasomes and chemokines that generate pro-inflammatory cytokines. Moreover, the activation of the complement cascade can be triggered by glycated proteins. This review highlights recent findings elucidating how the innate immune system contributes to tissue fibrosis and organ dysfunction, ultimately leading to renal failure. This review also discusses innovative approaches that can be utilized to modulate the innate immune responses in DN for therapeutic purposes.

Ootheca mantidis mitigates renal fibrosis in mice by the suppression of apoptosis via increasing the gut microbe Akkermansia muciniphila and modulating glutamine metabolism

Renal interstitial fibrosis (RIF), a progressive process affecting the kidneys in chronic kidney disease (CKD), currently lacks an effective therapeutic intervention. Traditional Chinese medicine (TCM) has shown promise in reducing RIF and slowing CKD progression. In this study, we demonstrated the dose-dependent attenuation of RIF by Ootheca mantidis (SPX), a commonly prescribed TCM for CKD, in a mouse model of unilateral ureteral obstruction (UUO). RNA-sequencing analysis suggested that SPX treatment prominently downregulated apoptosis and inflammation-associated pathways, thereby inhibiting the fibrogenic signaling in the kidney. We further found that transplantation of fecal microbiota from SPX-treated mice conferred protection against renal injury and fibrosis through suppressing apoptosis in UUO mice, indicating that SPX ameliorated RIF via remodeling the gut microbiota and reducing apoptosis in the kidneys. Further functional exploration of the gut microbiota combined with fecal metabolomics revealed increased levels of some probiotics, including Akkermansia muciniphila (A. muciniphila), and modulations in glutamine-related amino acid metabolism in UUO mice treated with SPX. Subsequent colonization of A. muciniphila and supplementation with glutamine effectively mitigated cell apoptosis and RIF in UUO mice. Collectively, these findings unveil a functionally A. muciniphila- and glutamine-involved gut-renal axis that contributes to the action of SPX, and provide important clue for the therapeutic potential of SPX, A. muciniphila, and glutamine in combatting RIF.

Inflammation in kidney repair: Mechanism and therapeutic potential

The kidney has a remarkable ability of repair after acute kidney injury (AKI). However, when injury is severe or persistent, the repair is incomplete or maladaptive and may lead to chronic kidney disease (CKD). Maladaptive kidney repair involves multiple cell types and multifactorial processes, of which inflammation is a key component. In the process of inflammation, there is a bidirectional interplay between kidney parenchymal cells and the immune system. The extensive and complex crosstalk between renal tubular epithelial cells and interstitial cells, including immune cells, fibroblasts, and endothelial cells, governs the repair and recovery of the injured kidney. Further research in this field is imperative for the discovery of biomarkers and promising therapeutic targets for kidney repair. In this review, we summarize the latest progress in the immune response and inflammation during maladaptive kidney repair, analyzing the interaction between immune cells and intrinsic kidney cells, pointing out the potentialities of inflammation-related pathways as therapeutic targets, and discussing the challenges and future research prospects in this field.

DAMPs Released From Injured Renal Tubular Epithelial Cells Activate Innate Immune Signals in Healthy Renal Tubular Epithelial Cells

BACKGROUND

Renal ischemia-reperfusion injury (IRI) predictably causes acute kidney injury after shock and major cardiovascular procedures in all kidneys procured for transplantation. The earliest events of IRI are triggered by molecules released from injured cells, damage-associated molecular patterns (DAMPs), that bind pattern recognition receptors (PRRs) constitutively expressed on many cells within the kidney. Activation of PRR signaling leads to production of proinflammatory molecules, which incite a cascade of inflammatory events leading to acute kidney injury. Renal tubular epithelial cells (RTECs) are particularly susceptible to ischemic injury, and proximal RTEC injury is pathognomonic of renal IRI. To better understand how injured RTECs contribute to the cycle of deleterious inflammation in the setting of renal IRI, this study asked whether DAMPs released from injured RTECs induced PRR signals in healthy RTECs.

METHODS

Human RTECs were necrosed ex vivo to release intracellular DAMPs and resulting necrotic supernatant used to stimulate healthy RTECs, T lymphocytes, and monocytes.

RESULTS

DAMPs released from necrosed RTECs upregulated PRRs known to be associated with renal IRI and activated mitogen-activated protein kinase signaling pathways. Proinflammatory cytokines were upregulated in response to necrotic supernatant, and this upregulation was abrogated by MEK-1 inhibition. The RTEC-derived DAMPs were also potent inducers of T-cell activation/proliferation and monocyte migration.

CONCLUSIONS

This is the first study to our knowledge to show that endogenous DAMPs released from injured RTECs directly activate PRR signaling in healthy RTECs. These findings provide new insights directed to therapeutics for renal IRI.

Intestinal microbiota-derived membrane vesicles and their role in chronic kidney disease

Intestinal microbiota-derived membrane vesicles (MVs) play essential roles in immunomodulation and maintenance of the intestinal micro-ecosystem. The relationship between MVs and chronic kidney disease (CKD) has remained undefined. This review provides a survey of the structure and biological function of different vesicle types and summarizes the possible pathogenic mechanisms mediated by MVs, which may be of great clinical significance in the diagnosis and treatment of chronic kidney disease.

The IL-18/IL-18R1 signalling axis: Diagnostic and therapeutic potential in hypertension and chronic kidney disease

Chronic kidney disease (CKD) is inherently an inflammatory condition, which ultimately results in the development of end stage renal disease or cardiovascular events. Low-grade inflammatory diseases such as hypertension and diabetes are leading causes of CKD. Declines in renal function correlate with elevated circulating pro-inflammatory cytokines in patients with these conditions. The inflammasome is an important inflammatory signalling platform that has been associated with low-grade chronic inflammatory diseases. Notably, activation and assembly of the inflammasome causes the auto cleavage of pro-caspase-1 into its active form, which then processes the pro-inflammatory cytokines pro-interleukin (IL)-1β and pro-IL-18 into their active forms. Currently, the nod-like receptor protein 3 (NLRP3) inflammasome has been implicated in the development of CKD in pre-clinical and clinical settings, and the ablation or inhibition of inflammasome components have been shown to be reno-protective in models of CKD. While clinical trials have demonstrated that neutralisation of IL-1β signalling by the drug anakinra lowers inflammation markers in haemodialysis patients, ongoing preclinical studies are showing that this ability to attenuate disease is limited in progressive models of kidney disease. These results suggest a potential predominant role for IL-18 in the development of CKD. This review will discuss the role of the inflammasome and its pro-inflammatory product IL-18 in the development of renal fibrosis and inflammation that contribute to the pathophysiology of CKD. Furthermore, we will examine the potential of the IL-18 signalling axis as an anti-inflammatory target in CKD and its usefulness as diagnostic biomarker to predict acute kidney injury.

Novel insights into NOD-like receptors in renal diseases

Nucleotide-binding oligomerization domain-like receptors (NLRs), including NLRAs, NLRBs (also known as NAIPs), NLRCs, and NLRPs, are a major subfamily of pattern recognition receptors (PRRs). Owing to a recent surge in research, NLRs have gained considerable attention due to their involvement in mediating the innate immune response and perpetuating inflammatory pathways, which is a central phenomenon in the pathogenesis of multiple diseases, including renal diseases. NLRs are expressed in different renal tissues during pathological conditions, which suggest that these receptors play roles in acute kidney injury, obstructive nephropathy, diabetic nephropathy, IgA nephropathy, lupus nephritis, crystal nephropathy, uric acid nephropathy, and renal cell carcinoma, among others. This review summarises recent progress on the functions of NLRs and their mechanisms in the pathophysiological processes of different types of renal diseases to help us better understand the role of NLRs in the kidney and provide a theoretical basis for NLR-targeted therapy for renal diseases.

Nucleotide-Oligomerizing Domain-1 Activation Exaggerates Cigarette Smoke-Induced Chronic Obstructive Pulmonary-Like Disease in Mice

Introduction

Chronic obstructive pulmonary disease (COPD) is a progressive condition related to abnormal inflammatory responses. As an inflammatory driver, nucleotide-binding oligomerizing domain-1 (NOD1) is highly expressed in pulmonary inflammatory cells; however, the roles of NOD1 in COPD are unknown.

Methods

A COPD mouse model was established by lipopolysaccharides tracheal instillation plus cigarette smoke (CS) exposure. NOD1 activation was induced by C12-iE-DAP (iE) treatment in both control and COPD mice. Inflammatory infiltration, pulmonary histological damage and gene expression were measured to evaluate the lung function of treated mice.

Results

The results showed that NOD1 was up-regulated in COPD mice, which significantly exaggerated CS-induced impairment of lung function, demonstrated by increased airway resistance, functional residual capacity and pulmonary damages. Mechanistically, NOD1 activation strongly activated the TLR4/NF-κB signaling pathway and then increased inflammatory responses and promoted the secretion of inflammatory cytokines.

Discussion

This study demonstrates that NOD1 is an important risk factor in the progression of COPD; therefore, targeting NOD1 in lung tissues is a potential strategy for COPD treatment.

Defining therapeutic targets for renal fibrosis: Exploiting the biology of pathogenesis

Renal fibrosis is a failed wound-healing process of the kidney tissue after chronic, sustained injury, which is a common pathway and pathological marker of virtually every type of chronic kidney disease (CKD), regardless of cause. However, there is a lack of effective treatment specifically targeting against renal fibrosis per se to date. The main pathological feature of renal fibrosis is the massive activation and proliferation of renal fibroblasts and the excessive synthesis and secretion of extracellular matrix (ECM) deposited in the renal interstitium, leading to structural damage, impairment of renal function, and eventually end-stage renal disease. In this review, we summarize recent advancements regarding the participation and interaction of many types of kidney residents and infiltrated cells during renal fibrosis, attempt to comprehensively discuss the mechanism of renal fibrosis from the cellular level and conclude by highlighting novel therapeutic targets and approaches for development of new treatments for patients with renal fibrosis.

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.

NOD1/RIP2 signalling enhances the microglia-driven inflammatory response and undergoes crosstalk with inflammatory cytokines to exacerbate brain damage following intracerebral haemorrhage in mice

BACKGROUND

Secondary brain damage caused by the innate immune response and subsequent proinflammatory factor production is a major factor contributing to the high mortality of intracerebral haemorrhage (ICH). Nucleotide-binding oligomerization domain 1 (NOD1)/receptor-interacting protein 2 (RIP2) signalling has been reported to participate in the innate immune response and inflammatory response. Therefore, we investigated the role of NOD1/RIP2 signalling in mice with collagenase-induced ICH and in cultured primary microglia challenged with hemin.

METHODS

Adult male C57BL/6 mice were subjected to collagenase for induction of ICH model in vivo. Cultured primary microglia and BV2 microglial cells (microglial cell line) challenged with hemin aimed to simulate the ICH model in vitro. We first defined the expression of NOD1 and RIP2 in vivo and in vitro using an ICH model by western blotting. The effect of NOD1/RIP2 signalling on ICH-induced brain injury volume, neurological deficits, brain oedema, and microglial activation were assessed following intraventricular injection of either ML130 (a NOD1 inhibitor) or GSK583 (a RIP2 inhibitor). In addition, levels of JNK/P38 MAPK, IκBα, and inflammatory factors, including tumour necrosis factor-α (TNF-α), interleukin (IL)-1β, and inducible nitric oxide synthase (iNOS) expression, were analysed in ICH-challenged brain and hemin-exposed cultured primary microglia by western blotting. Finally, we investigated whether the inflammatory factors could undergo crosstalk with NOD1 and RIP2.

RESULTS

The levels of NOD1 and its adaptor RIP2 were significantly elevated in the brains of mice in response to ICH and in cultured primary microglia, BV2 cells challenged with hemin. Administration of either a NOD1 or RIP2 inhibitor in mice with ICH prevented microglial activation and neuroinflammation, followed by alleviation of ICH-induced brain damage. Interestingly, the inflammatory factors interleukin (IL)-1β and tumour necrosis factor-α (TNF-α), which were enhanced by NOD1/RIP2 signalling, were found to contribute to the NOD1 and RIP2 upregulation in our study.

CONCLUSION

NOD1/RIP2 signalling played an important role in the regulation of the inflammatory response during ICH. In addition, a vicious feedback cycle was observed between NOD1/RIP2 and IL-1β/TNF-α, which could to some extent result in sustained brain damage during ICH. Hence, our study highlights NOD1/RIP2 signalling as a potential therapeutic target to protect the brain against secondary brain damage during ICH.

The pathogenesis of renal injury in obstructive jaundice: A review of underlying mechanisms, inducible agents and therapeutic strategies

Kidney injury is one of the main complications of obstructive jaundice (OJ) and its pathogenesis has not been clarified. As an independent risk factor for OJ associated with significant morbidity and mortality, it can be mainly divided into two types of morphological injury and functional injury. We called these dysfunctions caused by OJ-induced kidney injury as OJKI. However, the etiology of OJKI is still not fully clear, and research studies on how OJKI becomes a facilitated factor of OJ are limited. This article reviews the underlying pathological mechanism from five aspects, including metabolisms of bile acids, hemodynamic disturbances, oxidative stress, inflammation and the organic transporter system. Some nephrotoxic drugs and measures that can enhance or reduce the renal function with potential intervention in perioperative periods to alleviate the incidence of OJKI were also described. Furthermore, a more in-depth study on the pathogenesis of OJKI from multiple aspects for exploring more targeted treatment measures were further put forward, which may provide new methods for the prevention and treatment of clinical OJKI and improve the prognosis.

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.

Metabolic Flexibility and Innate Immunity in Renal Ischemia Reperfusion Injury: The Fine Balance Between Adaptive Repair and Tissue Degeneration

Renal ischemia reperfusion injury (IRI), a common event after renal transplantation, causes acute kidney injury (AKI), increases the risk of delayed graft function (DGF), primes the donor kidney for rejection, and contributes to the long-term risk of graft loss. In the last decade, epidemiological studies have linked even mild episodes of AKI to chronic kidney disease (CKD) progression, and innate immunity seems to play a crucial role. The ischemic insult triggers an acute inflammatory reaction that is elicited by Pattern Recognition Receptors (PRRs), expressed on both infiltrating immune cells as well as tubular epithelial cells (TECs). Among the PRRs, Toll-like receptors (TLRs), their synergistic receptors, Nod-like receptors (NLRs), and the inflammasomes, play a pivotal role in shaping inflammation and TEC repair, in response to renal IRI. These receptors represent promising targets to modulate the extent of inflammation, but also function as gatekeepers of tissue repair, protecting against AKI-to-CKD progression. Despite the important considerations on timely use of therapeutics, in the context of IRI, treatment options are limited by a lack of understanding of the intra- and intercellular mechanisms associated with the activation of innate immune receptors and their impact on adaptive tubular repair. Accumulating evidence suggests that TEC-associated innate immunity shapes the tubular response to stress through the regulation of immunometabolism. Engagement of innate immune receptors provides TECs with the metabolic flexibility necessary for their plasticity during injury and repair. This could significantly affect pathogenic processes within TECs, such as cell death, mitochondrial damage, senescence, and pro-fibrotic cytokine secretion, well-known to exacerbate inflammation and fibrosis. This article provides an overview of the past 5 years of research on the role of innate immunity in experimental and human IRI, with a focus on the cascade of events activated by hypoxic damage in TECs: from programmed cell death (PCD) and mitochondrial dysfunction-mediated metabolic rewiring of TECs to maladaptive repair and progression to fibrosis. Finally, we will discuss the important crosstalk between metabolism and innate immunity observed in TECs and their therapeutic potential in both experimental and clinical research.

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.

HSP70-Mediated NLRP3 Inflammasome Suppression Underlies Reversal of Acute Kidney Injury Following Extracellular Vesicle and Focused Ultrasound Combination Therapy

Acute kidney injury (AKI) is the abrupt loss of renal function, for which only supportive therapies exist. Mesenchymal stromal cell (MSC)-derived extracellular vesicles (EVs) have been shown to be therapeutically effective in treating AKI by spurring endogenous cell proliferation and survival while suppressing inflammation. Pre-treating kidneys with pulsed focused ultrasound (pFUS) has also been shown to enhance MSC therapy for AKI, but its role in MSC-derived EV therapy remains unexplored. Using a mouse model of cisplatin-induced AKI, we show that combination therapy with pFUS and EVs restores physiological and molecular markers of kidney function, more so than either alone. Both pFUS and EVs downregulate heat shock protein 70 (HSP70), the NLRP3 inflammasome, and its downstream pro-inflammatory cytokines IL-1β and IL-18, all of which are highly upregulated in AKI. In vitro knockdown studies suggest that HSP70 is a positive regulator of the NLRP3 inflammasome. Our study therefore demonstrates the ability of pFUS to enhance EV therapy for AKI and provides further mechanistic understanding of their anti-inflammatory and regenerative effects.

Erythropoietin Ameliorates Ischemia/Reperfusion-Induced Acute Kidney Injury via Inflammasome Suppression in Mice

Acute kidney injury (AKI) is the most common condition in hospitalized patients. As ischemia/reperfusion-induced AKI (IR-AKI) is as a major contributor to end-stage disease, an effective therapeutic intervention for IR-AKI is imperative. Erythropoietin (EPO) is a potent stimulator of erythroid progenitor cells and is significantly upregulated during hypoxia. Here, we investigated the renoprotective effects of EPO in an IR-AKI mouse model. Mice were assigned to sham, EPO only, and IR only groups, and the IR group was treated with EPO prior to injury. EPO was administered twice at 30 min prior to bilateral renal artery occlusion, and 5 min before reperfusion, with all mice sacrificed 24 h after IR-AKI. The serum was harvested for renal functional measurements. The kidneys were subjected to histological evaluation, and the biochemical changes associated with renal injury were assessed. EPO significantly attenuated the renal dysfunction associated with IR-AKI, as well as tissue injury. Apoptotic cell death and oxidative stress were significantly reduced in EPO-treated mice. Macrophage infiltration and expression of ICAM-1 and MCP-1 were also significantly reduced in EPO-treated mice. Furthermore, the expression of inflammasome-related factors (NLRP1, NLRP3, and caspase-1 cleavage), via the activation of the COX-2 and NF-B signaling pathways were significantly reduced following EPO treatment. To our knowledge, this is the first study to demonstrate that inflammasome-mediated inflammation might be a potential target of EPO as a treatment for ischemic AKI.

TLR2 and NODs1 and 2 cooperate in inflammatory responses associated with renal ischemia reperfusion injury

Pattern recognition receptors (PRRs) are potent triggers of tissue injury following renal ischemia/reperfusion injury (IRI). Specific PRRs, such as the toll-like receptor 2 (TLR2) and the nucleotide-binding oligomerization domain-like receptors (NLRs) NOD1 and NOD2 are promising targets to abrogate inflammatory injury associated with renal IRI. Several recent reports have shown there is crosstalk between TLRs and NODs, which might boost inflammatory responses to tissue injury. This study examined the relative roles of TLR2 and NODs 1 and 2 in activation of myeloid cells that contribute to inflammation after renal IRI. We found that TLR2 and NOD1 and 2 signaling induces neutrophil, macrophage and dendritic cell migration in vitro, however their blockade only decreases neutrophil infiltration into ischemic kidneys. The results of this study suggest that future therapies targeted to innate immune blockade should consider that either TLR2 or NOD1/2 blockade could decrease neutrophil inflammation following an ischemic insult to the kidney, however blockade of these PRRs would not likely impact infiltration of dendritic cells or macrophages. Developing rational approaches that target innate immunity in IRI-induced acute kidney injury requires an understanding of the relative role of PRRs in directing inflammation in the kidney.

Ligustrazine ameliorates acute kidney injury through downregulation of NOD2‑mediated inflammation

Ligustrazine has been used to alleviate clinical acute kidney injury (AKI); however, the underlying molecular mechanisms are poorly understood. In order to further elucidate the molecular mechanism underlying its occurrence, the role of nucleotide-binding oligomerization domain-containing 2 (NOD2) in AKI was investigated in the present study, and the results indicated that ligustrazine exerts an important protective effect against AKI in vivo by inhibiting the upregulation of NOD2 expression and reducing apoptosis of kidney cells following ischemia/reperfusion injury in rat models. Furthermore, the inhibitory role of ligustrazine on the upregulation of NOD2 and apoptosis of kidney cells induced by CoCl₂ and oxygen and glucose deprivation followed by reoxygenation was investigated in in vitro experiments. The effect of ligustrazine on NOD2 downregulation was partially blocked by inhibiting autophagy. To the best of our knowledge, the results of the present study are the first to provide evidence that ligustrazine can inhibit NOD2-mediated inflammation to protect against renal injury, which may be in part attributed to the induction of autophagy. These findings may help design and develop new approaches and therapeutic strategies for AKI to prevent the deterioration of renal function.

Inflammation in Renal Diseases: New and Old Players

Inflammation, a process intimately linked to renal disease, can be defined as a complex network of interactions between renal parenchymal cells and resident immune cells, such as macrophages and dendritic cells, coupled with recruitment of circulating monocytes, lymphocytes, and neutrophils. Once stimulated, these cells activate specialized structures such as Toll-like receptor and Nod-like receptor (NLR). By detecting danger-associated molecules, these receptors can set in motion major innate immunity pathways such as nuclear factor ĸB (NF-ĸB) and NLRP3 inflammasome, causing metabolic reprogramming and phenotype changes of immune and parenchymal cells and triggering the secretion of a number of inflammatory mediators that can cause irreversible tissue damage and functional loss. Growing evidence suggests that this response can be deeply impacted by the crosstalk between the kidneys and other organs, such as the gut. Changes in the composition and/or metabolite production of the gut microbiota can influence inflammation, oxidative stress, and fibrosis, thus offering opportunities to positively manipulate the composition and/or functionality of gut microbiota and, consequentially, ameliorate deleterious consequences of renal diseases. In this review, we summarize the most recent evidence that renal inflammation can be ameliorated by interfering with the gut microbiota through the administration of probiotics, prebiotics, and postbiotics. In addition to these innovative approaches, we address the recent discovery of new targets for drugs long in use in clinical practice. Angiotensin II receptor antagonists, NF-ĸB inhibitors, thiazide diuretics, and antimetabolic drugs can reduce renal macrophage infiltration and slow down the progression of renal disease by mechanisms independent of those usually attributed to these compounds. Allopurinol, an inhibitor of uric acid production, has been shown to decrease renal inflammation by limiting activation of the NLRP3 inflammasome. So far, these protective effects have been shown in experimental studies only. Clinical studies will establish whether these novel strategies can be incorporated into the arsenal of treatments intended to prevent the progression of human 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.

Nucleotide-binding oligomerization domain 1 (NOD1) modulates liver ischemia reperfusion through the expression adhesion molecules

BACKGROUND & AIMS

In liver transplantation, organ shortage leads to the use of marginal grafts that are more susceptible to ischemia-reperfusion (IR) injury. We identified nucleotide-binding oligomerization domain 1 (NOD1) as an important modulator of polymorphonuclear neutrophil (PMN)-induced liver injury, which occurs in IR. Herein, we aimed to elucidate the role of NOD1 in IR injury, particularly focusing on its effects on the endothelium and hepatocytes.

METHOD

Nod1 WT and KO mice were treated with NOD1 agonists and subjected to liver IR. Expression of adhesion molecules was analyzed in total liver, isolated hepatocytes and endothelial cells. Interactions between PMNs and hepatocytes were studied in an ex vivo co-culture model using electron microscopy and lactate dehydrogenase levels. We generated NOD1 antagonist-loaded nanoparticles (np ALINO).

RESULTS

NOD1 agonist treatment increased liver injury, PMN tissue infiltration and upregulated ICAM-1 and VCAM-1 expression 20 hours after reperfusion. NOD1 agonist treatment without IR increased expression of adhesion molecules (ICAM-1, VCAM-1) in total liver and more particularly in WT hepatocytes, but not in Nod1 KO hepatocytes. This induction is dependent of p38 and ERK signaling pathways. Compared to untreated hepatocytes, a NOD1 agonist markedly increased hepatocyte lysis in co-culture with PMNs as shown by the increase of lactate dehydrogenase in supernatants. Interaction between hepatocytes and PMNs was confirmed by electron microscopy. In a mouse model of liver IR, treatment with np ALINO significantly reduced the area of necrosis, aminotransferase levels and ICAM-1 expression.

CONCLUSION

NOD1 regulates liver IR injury through induction of adhesion molecules and modulation of hepatocyte-PMN interactions. NOD1 antagonist-loaded nanoparticles reduced liver IR injury and provide a potential approach to prevent IR, especially in the context of liver transplantation.

LAY SUMMARY

Nucleotide-binding oligomerization domain 1 (NOD1) is as an important modulator of polymorphonuclear neutrophil (PMN)-induced liver injury, which occurs in ischemia-reperfusion. Here, we show that the NOD1 pathway targets liver adhesion molecule expression on the endothelium and on hepatocytes through p38 and ERK signaling pathways. The early increase of adhesion molecule expression after reperfusion emphasizes the importance of adhesion molecules in liver injury. In this study we generated nanoparticles loaded with NOD1 antagonist. These nanoparticles reduced liver necrosis by reducing PMN liver infiltration and adhesion molecule expression.

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.

How Tubular Epithelial Cell Injury Contributes to Renal Fibrosis

The renal tubules are the major component of the kidney and are vulnerable to a variety of injuries including ischemia, proteinuria, toxins, and metabolic disorders. It has long been believed that tubules are the victim of injury. In this review, we shift this concept to renal tubules as a driving force in the progression of kidney disease. In response to injury, tubular epithelial cells (TECs) can synthesize and secrete varieties of bioactive molecules that drive interstitial inflammation and fibrosis. Innate immune-sensing receptors on the TECs also aggravate immune responses. Necroinflammation, an auto-amplification loop between tubular cell death and interstitial inflammation, leads to the exacerbation of renal injury. Furthermore, TECs also play an active role in progressive renal injury via mechanisms associated with the conversion into collagen-producing fibroblast phenotype, cell cycle arrest at both G1/S and G2/M checkpoints, and metabolic disorder. Thus, a better understanding the mechanisms by which tubular injury drives AKI and CKD is necessary for the development of therapeutics to halt the progression of CKD.

NOD2 promotes dopaminergic degeneration regulated by NADPH oxidase 2 in 6-hydroxydopamine model of Parkinson's disease

Background

In Parkinson’s disease (PD), loss of striatal dopaminergic (DA) terminals and degeneration of DA neurons in the substantia nigra (SN) are associated with inflammation. Nucleotide-binding oligomerization domain-containing protein (NOD)2, one of the first discovered NOD-like receptors, plays an important role in inflammation. However, the role of NOD2 has not been elucidated in PD.

Methods

NOD2 mRNA and protein expression in the SN and the striatum of C57BL/6 mice treated with 6-hydroxydopamine (6-OHDA) was measured. We next investigated the potential contribution of the NOD2-dependent pathway to 6-OHDA-induced DA degeneration using NOD2-deficient (NOD2^−/−) mice. Assays examining DA degeneration and inflammation include HPLC, Western blot, immunohistochemistry, TUNEL staining, and cytometric bead array. To further explore a possible link between NADPH oxidase 2 (NOX2) and NOD2 signaling in PD, microglia were transfected with shRNA specific to NOX2 in vitro and apocynin were given to mice subjected to 6-OHDA and muramyl dipeptide (MDP) striatal injection.

Results

The expression of NOD2 was upregulated in an experimental PD model induced by the neurotoxin 6-OHDA. NOD2 deficiency resulted in a protective effect against 6-OHDA-induced DA degeneration and neuronal death, which was associated with the attenuated inflammatory response. Moreover, silencing of NOX2 in microglia suppressed the expression of NOD2 and the inflammatory response induced by 6-OHDA and attenuated the toxicity of conditioned medium from 6-OHDA or MDP-stimulated microglia to neuronal cells. Furthermore, apocynin treatment inhibited NOD2 upregulation and DA degeneration in the SN of WT mice induced by 6-OHDA and MDP.

Conclusion

This study provides the direct evidence that NOD2 is related to 6-OHDA-induced DA degeneration through NOX2-mediated oxidative stress, indicating NOD2 is a novel innate immune signaling molecule participating in PD inflammatory response.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1289-z) contains supplementary material, which is available to authorized users.

Apocynin inhibited NLRP3/XIAP signalling to alleviate renal fibrotic injury in rat diabetic nephropathy

AIMS

In this animal study, we tried to test the hypothesis that apocynin could play an anti-inflammation role by inhibiting NLRP3/X-linked inhibitor of apoptosis protein (XIAP) signalling and have an effect on antifibrosis in rats with diabetic nephropathy.

MAIN METHODS

Diabetic nephropathy rats were induced by tail-vein injection of streptozotocin at 60 mg/kg body weight in sodium citrate buffer (0.01 M, pH 4.5) with unrestricted access to food/water for 12 weeks, and rats with blood glucose levels above 18.0 mM were considered diabetic; the damage index for glomerular mesangial cells damage index was calculated by morphological examinations; protein and mRNA changes were analysed by western blotting immunohistochemistry and real-time quantitative polymerase chain reaction; interstitial fibrosis was assessed and scored using Masson's staining.

KEY FINDINGS

In rats with diabetic nephropathy, apocynin (1) reduced renal injury and improved renal function; (2) downregulated the expression of NLRP3 in renal cortex; (3) downregulated the expression of XIAP in renal cortex; and (4) attenuated renal fibrosis.

SIGNIFICANCE

As an inhibitor of reactive oxygen species (ROS), apocynin could downregulate the expression of NLRP3 and XIAP, and alleviate renal fibrosis, which meant not only that ROS was one type of ligands of NLRP3, but also that ROS mechanism and NLRP3 activation might be therapeutic targets in the treatment of diabetic nephropathy in the future.

NLRC5 deficiency protects against acute kidney injury in mice by mediating carcinoembryonic antigen-related cell adhesion molecule 1 signaling

There is significant progress in understanding the structure and function of NLRC5, a member of the nucleotide oligomerization domain-like receptor family. However, in the context of MHC class I gene expression, the functions of NLRC5 in innate and adaptive immune responses beyond the regulation of MHC class I genes remain controversial and unresolved. In particular, the role of NLRC5 in the kidney is unknown. NLRC5 was significantly upregulated in the kidney from mice with renal ischemia/reperfusion injury. NLRC5 deficient mice significantly ameliorated renal injury as evidenced by decreased serum creatinine levels, improved morphological injuries, and reduced inflammatory responses versus wild type mice. Similar protective effects were also observed in cisplatin-induced acute kidney injury. Mechanistically, NLRC5 contributed to renal injury by promoting tubular epithelial cell apoptosis and reducing inflammatory responses were, at least in part, associated with the negative regulation of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1). To determine the relative contribution of NLRC5 expression by parenchymal cells or leukocytes to renal damage during ischemia/reperfusion injury, we generated bone marrow chimeric mice. NLRC5 deficient mice engrafted with wild type hematopoietic cells had significantly lower serum creatinine and less tubular damage than wild type mice reconstituted with NLRC5 deficient bone marrow. This suggests that NLRC5 signaling in renal parenchymal cells plays the dominant role in mediating renal damage. Thus, modulation of the NLRC5-mediated pathway may have important therapeutic implications for patients with acute kidney injury.

Expression and in vitro assessment of tumorigenicity for NOD1 and NOD2 receptors in breast cancer cell lines

OBJECTIVE

Immune-related pathways have been frequently associated to tumorigenesis. NOD1 and NOD2 are innate immune receptors responsible for sensing a subset of bacterial-derived components, and to further translate these pathogenic signals through pro-inflammatory and survival pathways. NOD1 and NOD2 have been further associated with tumorigenesis, particularly in gastrointestinal cancers. NOD1 has also been suggested to be a tumor suppressor gene in a model of estrogen receptor-dependent breast cancer. Contrarily, NOD2 polymorphisms are associated with higher risk of breast cancer, with no tumor suppressor role being reported. To better delineate this issue, we investigated NOD1 and NOD2 expression in a panel of breast cancer cell lines, as well as their potential impact in breast tumorigenesis based on in vitro assays.

RESULTS

The highly invasive Hs578T breast cell line presented the second highest NOD1 expression and the lowest NOD2 expression in our panel. Therefore, we investigated whether NOD1 and/or NOD2 might act as a tumor suppressor in this cell model. Our studies indicate that overexpression of either NOD1 or NOD2 reduces cell proliferation and increases clonogenic potential in vitro. Elucidation of NOD1 and NOD2 effects on tumor cell viability and proliferation may unveil potential targets for future therapeutic intervention.

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.

Novel identified aluminum hydroxide-induced pathways prove monocyte activation and pro-inflammatory preparedness

Aluminum-based adjuvants are the most widely used adjuvants in human vaccines. A comprehensive understanding of the mechanism of action of aluminum adjuvants at the molecular level, however, is still elusive. Here, we unravel the effects of aluminum hydroxide Al(OH)₃ by a systems-wide analysis of the Al(OH)₃-induced monocyte response. Cell response analysis by cytokine release was combined with (targeted) transcriptome and full proteome analysis. Results from this comprehensive study revealed two novel pathways to become activated upon monocyte stimulation with Al(OH)₃: the first pathway was IFNβ signaling possibly induced by DAMP sensing pathways like TLR or NOD1 activation, and second the HLA class I antigen processing and presentation pathway. Furthermore, known mechanisms of the adjuvant activity of Al(OH)₃ were elucidated in more detail such as inflammasome and complement activation, homeostasis and HLA-class II upregulation, possibly related to increased IFNγ gene expression. Altogether, our study revealed which immunological pathways are activated upon stimulation of monocytes with Al(OH)₃, refining our knowledge on the adjuvant effect of Al(OH)₃ in primary monocytes.

SIGNIFICANCE

Aluminum salts are the most used adjuvants in human vaccines but a comprehensive understanding of the working mechanism of alum adjuvants at the molecular level is still elusive. Our Systems Vaccinology approach, combining complementary molecular biological, immunological and mass spectrometry-based techniques gave a detailed insight in the molecular mechanisms and pathways induced by Al(OH)₃ in primary monocytes. Several novel immunological relevant cellular pathways were identified: type I interferon secretion potentially induced by TLR and/or NOD like signaling, the activation of the inflammasome and the HLA Class-I and Class-II antigen presenting pathways induced by IFNγ. This study highlights the mechanisms of the most commonly used adjuvant in human vaccines by combing proteomics, transcriptomics and cytokine analysis revealing new potential mechanisms of action for Al(OH)₃.

NOD1 and NOD2: Molecular targets in prevention and treatment of infectious diseases

Nucleotide-binding oligomerization domain (NOD) 1 and NOD2 are pattern-recognition receptors responsible for sensing fragments of bacterial peptidoglycan known as muropeptides. Stimulation of innate immunity by systemic or local administration of NOD1 and NOD2 agonists is an attractive means to prevent and treat infectious diseases. In this review, we discuss novel data concerning structural features of selective and non-selective (dual) NOD1 and NOD2 agonists, main signaling pathways and biological effects induced by NOD1 and NOD2 stimulation, including induction of pro-inflammatory cytokines, type I interferons and antimicrobial peptides, induction of autophagy, alterations of metabolism. We also discuss interactions between NOD1/NOD2 and Toll-like receptor agonists in terms of synergy and cross-tolerance. Finally, we review available animal data on the role of NOD1 and NOD2 in protection against infections, and discuss how these data could be applied in human infectious diseases.

Expression of TLR2, NOD1, and NOD2 and the NLRP3 Inflammasome in Renal Tubular Epithelial Cells of Male versus Female Mice

BACKGROUND

Gender-biased outcomes are associated with acute kidney injury (AKI) and human and animal studies have shown that females are preferentially protected from renal ischemia. However, the reason for this is not known. One clue might lie with pattern recognition receptors (PRRs), which are triggers of ischemic injury when ligated by molecules in the ischemic milieu. Several PRR families are expressed by renal tubular epithelial cells (RTEs) and incite cell death signaling and production of pro-inflammatory molecules. Blockade of specific PRRs (e.g., TLR2, NOD1, NOD2, and NLRP3) provides highly significant protection from ischemic RTE injury. As a first step to understand gender-biased outcomes of AKI, we tested whether constitutive gender-based differences exist in expression of these PRRS in RTEs.

METHODS

To determine whether PRR expression differences exist, primary RTEs isolated from male and female WT kidneys were examined by FACS, qPCR, and Western Blot for expression of TLR2, NOD1, NOD2, and NLRP3 inflammasome components.

RESULTS

No RTE gender-based differences in TLR2, NOD1, NOD2, NLRP3, or ASC were found. RTEs from female kidneys had approximately half the mRNA, but the same protein concentration of pro-caspase-1 compared to RTEs isolated from male kidneys.

CONCLUSIONS

Our findings indicate that intrinsic gender differences in RTE expression of TLR2, NOD1, NOD2, NLRP3, and ASC are not responsible for the gender-biased outcomes observed in ischemia/reperfusion injury. The lower caspase-1 mRNA expression in RTEs from females warrants further exploration of additional upstream signals that might differentially regulate caspase-1 in male vs. female RTEs.

Ischemia as a factor affecting innate immune responses in kidney transplantation

PURPOSE OF REVIEW

Ischemic injury inevitably occurs during the procurement of organs for transplantation, and the injury is worsened by inflammation following reperfusion. The purpose of this review is to describe the role of the innate immune system in ischemia-induced renal injury in kidneys procured for transplantation. The key role of pattern recognition receptors in immune responses to ischemia is described. Innate immune receptors are emerging novel targets for the amelioration of ischemic injury of donor kidneys.

RECENT FINDINGS

Several families of pattern recognition receptors are direct mediators of early injurious events during kidney procurement, and also innate and adaptive immune responses after transplantation. The deleterious events associated with the activation of the innate immune system in donor kidneys significantly contribute to short and long-term allograft outcomes.

SUMMARY

Although a number of therapies have been proposed to decrease ischemic donor kidney injury, targeting the innate immune system is an exciting new area that is gaining significant interest in transplantation. As we learn more about how these important receptors are regulated by ischemia, strategies will likely evolve to allow their modulation in ischemic renal injury.

The Nucleotide Oligomerization Domain-Like Receptors in Kidney Injury

BACKGROUND

Inflammation is a hallmark of almost all forms of renal injury and the activation of the innate immune system is of importance in the development of many kidney diseases. Pattern recognition receptors (PRRs) act as sensors of the innate immune system to detect pathogen- or damage-associated molecular patterns, which initiate immune responses to resolve infections and repair damaged tissues. Abnormalities in PRR activation will lead to excessive inflammation.

SUMMARY

Nucleotide oligomerization domain (NOD)-like receptors (NLRs) are recently identified intracellular PRRs that are essential to innate immune responses and tissue homeostasis. A better understanding of the function of NLRs will provide unexpected opportunities to develop new therapies for kidney diseases by modulation of the innate immune system.

KEY MESSAGES

NLRs are constitutively expressed in the kidney and emerging evidence has shown that activation of NLRs plays an important role in the pathogenesis of renal injury. Among NLRs, NOD2 and NLRP3 inflammasome are the best characterized members in the kidney. In this review, we summarize current knowledge about the pathological mechanisms that are related to NOD2 and NLRP3 inflammasome in various kidney diseases by their canonical and non-canonical effects and discuss the opportunities of pharmacological targeting of NLR-mediated signaling pathways at multiple levels for the treatment of renal disease.

The Critical Role of Innate Immunity in Kidney Transplantation

For a long time now, kidney transplant rejection has been considered the consequence of either cellular or antibody-mediated reaction as a part of adaptive immunity response. The role of innate immunity, on the other hand, had been unclear for many years and was thought to be only ancillary. There is now consistent evidence that innate immune response is a condition necessary to activate the machinery of rejection. In this setting, the communication between antigen-presenting cells and T lymphocytes is of major importance. Indeed, T cells are unable to cause rejection if innate immunity is not activated. This field is currently being explored and several experiments in animal models have proved that blocking innate immunity activation can promote tolerance of the graft instead of rejection. The aim of this review is to systematically describe all the steps of innate immunity response in kidney transplant rejection, from antigen recognition to T-cells activation, with a focus on clinical consequences and possible future perspectives.

NODding off in acute kidney injury with progranulin?

Inflammation is a common feature of murine models of AKI. The endogenous mechanisms which serve to limit inflammation and reduce the severity of AKI are poorly understood. Zhou et al identify progranulin as one such protective mediator. Deficiency of progranulin was associated with increased inflammation and increased injury in both ischemic and nephrotoxic models of AKI. Moreover, administration of exogenous progranulin reduced AKI even when delivered after AKI was established. Interference in NOD2 pathways is suggested as a possible mechanism for protection. PRGN-based therapeutics are under development and might have application in the treatment or prevention of AKI.

Role of the NOD1/NF-κB pathway on bovine neutrophil responses to crude lipopolysaccharide

Cytosolic nucleotide oligomerisation domain (NOD)-like receptors play an important role in host defence against infection. Reduced NOD1 expression has been observed in dysfunctional neutrophils derived from periparturient cattle known to be most susceptible to coliform mastitis. However, whether impairment of NOD1 suppresses the immune responses of bovine neutrophils during bacterial infections remains unknown. Crude (phenol extracted) lipopolysaccharide (cLPS), which often contains other immunostimulatory molecules, including NOD1 agonist, is known to induce almost the whole bacterial response. This study was conducted to explore the role of NOD1/nuclear factor (NF)-κB pathway in the cytokine and functional responses of bovine neutrophils challenged with Escherichia coli-derived cLPS. Freshly isolated blood neutrophils from healthy heifers were pre-incubated for 2 h with ML130, a selective inhibitor of NOD1/NF-κB pathway. Cells were then exposed to cLPS for additional 4 h. Inhibition of the NOD1/NF-κB pathway resulted in a decrease in cLPS-induced phosphorylation of the inhibitor of NF-κBα (IκBα) in neutrophils. Impairment of the NOD1/NF-κB pathway tended to down-regulate mRNA levels of pro-inflammatory cytokines interleukin (IL)-1β and tumour necrosis factor (TNF)-α, chemokines IL-8 and C-X-C motif ligand 2 (CXCL2), and adhesion molecules CD11b and CD62L, in cLPS-challenged cells. Functional analyses showed that blocking the NOD1/NF-κB pathway inhibited neutrophil migration and phagocytic killing capacity, and promoted neutrophil death upon cLPS stimulation. The data presented here demonstrate that activation of NOD1/NF-κB pathway contributes to the functional responses of neutrophils to cLPS.

Association of NOD1 and NOD2 polymorphisms with Guillain-Barré syndrome in Northern Indian population

BACKGROUND

Nucleotide oligomerization domain (NOD) proteins are cytosolic pattern recognition receptors that respond to bacterial substrate and induce NF-κB activation in host. Association of NOD polymorphisms have been studied in many autoimmune disorders, however its role in Guillain-Barré syndrome (GBS) remains unknown. We have investigated NOD1 Glu266Lys and NOD2 (Arg702Trp and Gly908Arg) gene polymorphisms among patients with GBS.

MATERIALS AND METHOD

Polymorphisms in NOD-1 (Glu266Lys) and NOD-2 (Arg702Trp and Gly908Arg) genes were studied using polymerase chain reaction-restriction fragment length polymorphism in 105 patients with GBS and 100 healthy controls.

RESULTS

Homozygous genotype (Lys/Lys) of NOD1 was significantly associated with GBS (p=0.013); and its subtypes viz. acute motor axonal neuropathy (AMAN) and acute inflammatory demyelinating polyneuropathy (AIDP) (p=0.008 and p=0.024 respectively) than controls. In NOD2 (Arg702Trp and Gly908Arg) polymorphisms, only heterozygous genotype (Arg/Trp and Gly/Arg) showed significant association with GBS (p=0.001 and p=0.01 respectively); subtypes AMAN, acute motor-sensory axonal neuropathy (AMSAN) and AIDP showed association with heterozygote Arg702Trp (p=0.001; p=0.029 and p=0.001 respectively) whereas only AIDP was associated with heterozygote genotype Gly908Arg (p=0.003).

CONCLUSION

NOD1 (Glu266Lys) and NOD2 (Arg702Trp and Gly908Arg) polymorphisms were associated with an increased susceptibility to GBS. These polymorphisms could be genetic marker to GBS susceptibility.

Inflammation in AKI: Current Understanding, Key Questions, and Knowledge Gaps

Inflammation is a complex biologic response that is essential for eliminating microbial pathogens and repairing tissue after injury. AKI associates with intrarenal and systemic inflammation; thus, improved understanding of the cellular and molecular mechanisms underlying the inflammatory response has high potential for identifying effective therapies to prevent or ameliorate AKI. In the past decade, much knowledge has been generated about the fundamental mechanisms of inflammation. Experimental work in small animal models has revealed many details of the inflammatory response that occurs within the kidney after typical causes of AKI, including insights into the molecular signals released by dying cells, the role of pattern recognition receptors, the diverse subtypes of resident and recruited immune cells, and the phased transition from destructive to reparative inflammation. Although this expansion of the basic knowledge base has increased the number of mechanistically relevant targets of intervention, progress in developing therapies that improve AKI outcomes by modulation of inflammation remains slow. In this article, we summarize the most important recent developments in understanding the inflammatory mechanisms of AKI, highlight key limitations of the commonly used animal models and clinical trial designs that may prevent successful clinical application, and suggest priority approaches for research toward clinical translation in this area.

NLRP3 Inflammasome Involvement in the Organ Damage and Impaired Spermatogenesis Induced by Testicular Ischemia and Reperfusion in Mice

We investigated the role of the nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) inflammasome during testis ischemia and reperfusion injury (TI/R) in wild-type (WT) and NLRP3 knock-out (KO) mice. WT and KO mice underwent 1 hour testicular ischemia followed by 4 hours and 1 and 7 days of reperfusion or a sham TI/R. Furthermore, two groups of WT mice were treated at the beginning of reperfusion and up to 7 days with two inflammasome inhibitors, BAY 11-7082 (20 mg/kg i.p.) or Brilliant Blue G (45.5 mg/kg i.p.), or vehicle. Animals were killed with a pentobarbital sodium overdose at 4 hours and 1 and 7 days, and bilateral orchidectomies were performed. Biochemical and morphologic studies were carried out in all groups. TI/R in WT mice significantly increased caspase-1 and interleukin (IL)-1β mRNA after 4 hours and IL-18 mRNA at 1 day of reperfusion (P ≤ 0.05). There was also a significant increase in caspase-3 and terminal deoxynucleotidyl transferase-mediated digoxigenin-deoxyuridine nick-end labeling-positive cells, marked histologic damage, and altered spermatogenesis in WT mice in both testes after 1 and 7 days of reperfusion. KO TI/R mice, WT TI/R BAY 11-7082, and Brilliant Blue G treated mice showed a significant reduced IL-1β and IL-18 mRNA expression, blunted caspase-1 and -3 expression, minor histologic damages, low terminal deoxynucleotidyl transferase-mediated digoxigenin-deoxyuridine nick-end labeling activity, and preserved spermatogenesis. These data suggest that the activation of NLRP3 plays a key role in TI/R, and its inhibition might represent a therapeutic target for the management of patients with unilateral testicular torsion.

Simultaneous deletion of NOD1 and NOD2 inhibits in vitro alloresponses but does not prevent allograft rejection

Pattern recognition receptors (PRRs) play an important role in host anti-donor responses to transplanted tissue. A key trigger of the host alloresponse involves recognition of foreign antigen presented on activated antigen presenting cells by the host T cells. Emerging data suggest that PRR blockade can abrogate host anti-donor responses by interfering with activation of antigen presenting cells, particularly activation of dendritic cells. Our study asked whether blockade of a well-characterized family of intracellular PRRs, the NOD family, interfered with alloantigen recognition and allograft rejection. We found that deletion of either NOD1 or NOD2 in antigen presenting cells (APCs) had no effect on induction of T cell proliferation to alloantigen, but that simultaneous deletion of NOD1 and NOD2 significantly inhibited T cell responses. There was however no effect of the NOD deletion on skin graft rejection when NOD1×NOD2 skin was transplanted onto allogeneic hosts or when WT skin was transplanted onto NOD1×NOD2 deficient recipients. The conclusion of this study is that in vitro alloresponses are negatively impacted by the simultaneous deletion of NOD1 and NOD2, but that allograft rejection across a stringent allo barrier is not affected. Our results suggest that the NOD family members, NOD1 and NOD2, play a collaborative role in T cell activation by alloantigen and that their blockade in vitro can inhibit T cell responses.