Interleukin-1 receptor antagonist modulates the progression of a spontaneously occurring IgA nephropathy in mice

Inhibition of excessive autophagy alleviates renal injury and inflammation in a rat model of immunoglobulin A nephropathy

The pathogenesis of immunoglobulin A nephropathy (IgAN) is closely related to immunity and inflammation. The clinical process of IgAN varies greatly, making the assessment of prognosis challenging and limiting progress on effective treatment measures. Autophagy is an important pathway for the development of IgAN. However, the role of autophagy in IgAN is complex, and the consequences of autophagy may change during disease progression. In the present study, we evaluated the dynamic changes in autophagy during IgAN. Specifically, we examined autophagy in the kidney of a rat model of IgAN at different time points. We found that autophagy was markedly and persistently induced in IgAN rats, and the expression level of inflammation was also persistently elevated. The autophagy enhancer rapamycin and autophagy inhibitor 3-methyladenine were used in this study, and the results showed that 3-methyladenine can alleviate renal injury and inflammation in IgAN rats. Our study provides further evidence for autophagy as a therapeutic target for IgAN.

The Role of Inflammasomes in Glomerulonephritis

The inflammasome is an immune multiprotein complex that activates pro-caspase 1 in response to inflammation-inducing stimuli and it leads to IL-1β and IL-18 proinflammatory cytokine production. NLRP1 and NLRP3 inflammasomes are the best characterized and they have been related to several autoimmune diseases. It is well known that the kidney expresses inflammasome genes, which can influence the development of some glomerulonephritis, such as lupus nephritis, ANCA glomerulonephritis, IgA nephropathy and anti-GBM nephropathy. Polymorphisms of these genes have also been described to play a role in autoimmune and kidney diseases. In this review, we describe the main characteristics, activation mechanisms, regulation and functions of the different inflammasomes. Moreover, we discuss the latest findings about the role of the inflammasome in several glomerulonephritis from three different points of view: in vitro, animal and human studies.

Involvement of Inflammasome Components in Kidney Disease

Inflammasomes are multiprotein complexes with an important role in the innate immune response. Canonical activation of inflammasomes results in caspase-1 activation and maturation of cytokines interleukin-1β and -18. These cytokines can elicit their effects through receptor activation, both locally within a certain tissue and systemically. Animal models of kidney diseases have shown inflammasome involvement in inflammation, pyroptosis and fibrosis. In particular, the inflammasome component nucleotide-binding domain-like receptor family pyrin domain containing 3 (NLRP3) and related canonical mechanisms have been investigated. However, it has become increasingly clear that other inflammasome components are also of importance in kidney disease. Moreover, it is becoming obvious that the range of molecular interaction partners of inflammasome components in kidney diseases is wide. This review provides insights into these current areas of research, with special emphasis on the interaction of inflammasome components and redox signalling, endoplasmic reticulum stress, and mitochondrial function. We present our findings separately for acute kidney injury and chronic kidney disease. As we strictly divided the results into preclinical and clinical data, this review enables comparison of results from those complementary research specialities. However, it also reveals that knowledge gaps exist, especially in clinical acute kidney injury inflammasome research. Furthermore, patient comorbidities and treatments seem important drivers of inflammasome component alterations in human kidney disease.

Role of Macrophages and Related Cytokines in Kidney Disease

Inflammation is a key characteristic of kidney disease, but this immune response is two-faced. In the acute phase of kidney injury, there is an activation of the immune cells to fight against the insult, contributing to kidney repair and regeneration. However, in chronic kidney diseases (CKD), immune cells that infiltrate the kidney play a deleterious role, actively participating in disease progression, and contributing to nephron loss and fibrosis. Importantly, CKD is a chronic inflammatory disease. In early CKD stages, patients present sub-clinical inflammation, activation of immune circulating cells and therefore, anti-inflammatory strategies have been proposed as a common therapeutic target for renal diseases. Recent studies have highlighted the plasticity of immune cells and the complexity of their functions. Among immune cells, monocytes/macrophages play an important role in all steps of kidney injury. However, the phenotype characterization between human and mice immune cells showed different markers; therefore the extrapolation of experimental studies in mice could not reflect human renal diseases. Here we will review the current information about the characteristics of different macrophage phenotypes, mainly focused on macrophage-related cytokines, with special attention to the chemokine CCL18, and its murine functional homolog CCL8, and the macrophage marker CD163, and their role in kidney pathology.

Interleukin-6 Signaling and Anti-Interleukin-6 Therapeutics in Cardiovascular Disease

IL (interleukin)-6 is a pivotal cytokine of innate immunity, which enacts a broad set of physiological functions traditionally associated with host defense, immune cell regulation, proliferation, and differentiation. Following recognition of innate immune pathways leading from the NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3) inflammasome to IL-1 to IL-6 and on to the hepatically derived clinical biomarker CRP (C-reactive protein), an expanding literature has led to understanding of the proatherogenic role for IL-6 in cardiovascular disease and thus the potential for IL-6 inhibition as a novel method for vascular protection. In this review, we provide an overview of the mechanisms by which IL-6 signaling occurs and how that impacts upon pharmacological inhibition; describe murine models of IL-6 and atherogenesis; summarize human epidemiological data outlining the utility of IL-6 as a biomarker of vascular risk; outline genetic data suggesting a causal role for IL-6 in systemic atherothrombosis and aneurysm formation; and then detail the potential role of IL-6 inhibition in stable coronary disease, acute coronary syndromes, heart failure, and the atherothrombotic complications associated with chronic kidney disease and end-stage renal failure. Finally, we review anti-inflammatory and antithrombotic findings for ziltivekimab, a novel IL-6 ligand inhibitor being developed specifically for use in atherosclerotic disease and poised to be tested formally in a large-scale cardiovascular outcomes trial focused on individuals with chronic kidney disease and elevated levels of CRP, a population at high residual atherothrombotic risk, high residual inflammatory risk, and considerable unmet clinical need.

A negative feedback loop involving NF-κB/TIR8 regulates IL-1β-induced epithelial- myofibroblast transdifferentiation in human tubular cells

Renal tubular epithelial-myofibroblast transdifferentiation (EMT) plays a central role in the development of renal interstitial fibrosis (RIF). The profibrotic cytokine interleukin (IL)-1 and the IL-1 receptor (IL-1R) also participate in RIF development, and Toll/IL-1R 8 (TIR8), a member of the Toll-like receptor superfamily, has been identified as a negative regulator of IL-1R signaling. However, the functions of TIR8 in IL-1-induced RIF remain unknown. Here, human embryonic kidney epithelial cells (HKC) and unilateral ureteric obstruction (UUO)-induced RIF models on SD rats were used to investigate the functions of TIR8 involving IL-1β-induced EMT. We showed that IL-1β primarily triggers TIR8 expression by activating nuclear factor-κB (NF-κB) in HKC cells. Conversely, high levels of TIR8 in HKC cells repress IL-1β-induced NF-κB activation and inhibit IL-1β-induced EMT. Moreover, in vitro and in vivo findings revealed that TIR8 downregulation facilitated IL-1β-induced NF-κB activation and contributed to TGF-β1-mediated EMT in renal tubular epithelial cells. These results suggested that TIR8 exerts a protective role in IL-1β-mediated EMT and potentially represents a new target for RIF treatment.

Pyroptosis: A New Frontier in Kidney Diseases

Pyroptosis is a pattern of programmed cell death that significantly differs from apoptosis and autophagy in terms of cell morphology and function. The process of pyroptosis is characterized predominantly by the formation of gasdermin protein family-mediated membrane perforation, cell collapse, and the release of inflammatory factors, including IL-1β and IL-18. In recent years, with the rise of pyroptosis research, scholars have devoted time to study the mechanism of pyroptosis in kidney-related diseases. Pyroptosis is probably involved in kidney diseases through two pathways: the caspase-1-mediated canonical pathway and the caspase-4/5/11-mediated noncanonical pathway. In addition, some scholars have identified targets for the treatment of kidney-related diseases from the viewpoint of pyroptosis and developed corresponding medicines, which may become a recommendation for prognosis, targeted treatment, and clinical diagnosis of kidney diseases. This paper focuses on the up-to-date advances in the field of pyroptosis, especially on the key pathogenic role of pyroptosis in the development and progression of kidney diseases. It presents a more in-depth understanding of the pathogenesis of kidney diseases and introduces novel therapeutic targets for the prevention and clinical treatment of kidney diseases.

Vascular pathologies in chronic kidney disease: pathophysiological mechanisms and novel therapeutic approaches

Cardiovascular disease (CVD) is a major cause of death in patients with chronic kidney disease (CKD). Both conditions are rising in incidence as well as prevalence, creating poor outcomes for patients and high healthcare costs. Recent data suggests CKD to be an independent risk factor for CVD. Accumulation of uremic toxins, chronic inflammation, and oxidative stress have been identified to act as CKD-specific alterations that increase cardiovascular risk. The association between CKD and cardiovascular mortality is markedly influenced through vascular alterations, in particular atherosclerosis and vascular calcification (VC). While numerous risk factors promote atherosclerosis by inducing endothelial dysfunction and its progress to vascular structural damage, CKD affects the medial layer of blood vessels primarily through VC. Ongoing research has identified VC to be a multifactorial, cell-mediated process in which numerous abnormalities like mineral dysregulation and especially hyperphosphatemia induce a phenotype switch of vascular smooth muscle cells to osteoblast-like cells. A combination of pro-calcifying stimuli and an impairment of inhibiting mechanisms like fetuin A and vitamin K-dependent proteins like matrix Gla protein and Gla-rich protein leads to mineralization of the extracellular matrix. In view of recent studies, intercellular communication pathways via extracellular vesicles and microRNAs represent key mechanisms in VC and thereby a promising field to a deeper understanding of the involved pathomechanisms. In this review, we provide an overview about pathophysiological mechanisms connecting CKD and CVD. Special emphasis is laid on vascular alterations and more recently discovered molecular pathways which present possible new therapeutic targets.

LCC18, a benzamide-linked small molecule, ameliorates IgA nephropathy in mice

IgA nephropathy (IgAN), an immune complex-mediated process and the most common primary glomerulonephritis, can progress to end-stage renal disease in up to 40% of patients. Accordingly, a therapeutic strategy targeting a specific molecular pathway is urgently warranted. Aided by structure characterisation and target identification, we predicted that a novel ring-fused 6-(2,4-difluorophenyl)-3-(3-(trifluoromethyl)phenyl)-2H-benzo[e][1,3]oxazine-2,4(3H)-dione (LCC18) targets the NLRP3 inflammasome, which participates in IgAN pathogenesis. We further developed biomarkers for the disease. We used two complementary IgAN models in C57BL/6 mice, involving TEPC-15 hybridoma-derived IgA, and in gddY mice. Moreover, we created specific cell models to validate therapeutic effects of LCC18 on IgAN and to explain its underlying mechanisms. IgAN mice benefited significantly from treatment with LCC18, showing dramatically improved renal function, including greatly reduced proteinuria and renal pathology. Mechanistic studies showed that the mode of action specifically involved: (1) blocking of the MAPKs/COX-2 axis-mediated priming of the NLRP3 inflammasome; (2) inhibition of ASC oligomerisation and NLRP3 inflammasome assembly by inhibiting NLRP3 binding to PKR, NEK7 and ASC; and (3) activation of autophagy. LCC18 exerts therapeutic effects on murine IgAN by differentially regulating NLRP3 inflammasome activation and autophagy induction, suggesting this new compound as a promising drug candidate to treat IgAN. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Accelerated, severe lupus nephritis benefits from treatment with honokiol by immunoregulation and differentially regulating NF-κB/NLRP3 inflammasome and sirtuin 1/autophagy axis

Using honokiol (HNK), a major anti-inflammatory bioactive compound in Magnolia officinalis, we show a potent therapeutic outcome against an accelerated, severe form of lupus nephritis (ASLN). The latter may follow infectious insults that act as environmental triggers in the patients. In the current study, an ASLN model in NZB/W F1 mice was treated with HNK by daily gavage after onset of the disease. We show that HNK ameliorated the ASLN by improving renal function, albuminuria, and renal pathology, especially reducing cellular crescents, neutrophil influx, fibrinoid necrosis in glomeruli, and glomerulonephritis activity scores. Meanwhile, HNK differentially regulated T cell functions, reduced serum anti-dsDNA autoantibodies, and inhibited NLRP3 inflammasome activation in the mice. The latter involved: (a) suppressed production of reactive oxygen species and NF-κB activation-mediated priming signal of the inflammasome, (b) reduced mitochondrial damage, and (c) enhanced sirtuin 1 (SIRT1)/autophagy axis activation. In conclusion, HNK represents a new drug candidate for acute, severe episodes of LN capable of alleviating renal lesions in ASLN mice by negatively regulating T cell functions and by enhancing SIRT1/autophagy axis-lessened NLRP3 inflammasome activation.

IgA Nephropathy Benefits from Compound K Treatment by Inhibiting NF-κB/NLRP3 Inflammasome and Enhancing Autophagy and SIRT1

IgA nephropathy (IgAN), the most common primary glomerular disorder, has a relatively poor prognosis yet lacks a pathogenesis-based treatment. Compound K (CK) is a major absorbable intestinal bacterial metabolite of ginsenosides, which are bioactive components of ginseng. The present study revealed promising therapeutic effects of CK in two complementary IgAN models: a passively induced one developed by repeated injections of IgA immune complexes and a spontaneously occurring model of spontaneous grouped ddY mice. The potential mechanism for CK includes 1) inhibiting the activation of NLRP3 inflammasome in renal tissues, macrophages and bone marrow-derived dendritic cells, 2) enhancing the induction of autophagy through increased SIRT1 expression, and 3) eliciting autophagy-mediated NLRP3 inflammasome inhibition. The results support CK as a drug candidate for IgAN.

Xenon blunts NF-κB/NLRP3 inflammasome activation and improves acute onset of accelerated and severe lupus nephritis in mice

Xenon, an inert anesthetic gas, is increasingly recognized to possess desirable properties including cytoprotective and anti-inflammatory effects. Here we evaluated the effects of xenon on the progression of lupus nephritis (LN) in a mouse model. A two hour exposure of either 70% xenon or 70% nitrogen balanced with oxygen was administered daily for five weeks to female NZB/W F1 mice that had been induced to develop accelerated and severe LN. Xenon treatment improved kidney function and renal histology, and decreased the renal expression of neutrophil chemoattractants, thereby attenuating glomerular neutrophil infiltration. The effects of xenon were mediated primarily by deceasing serum levels of anti-double stranded DNA autoantibody, inhibiting reactive oxygen species production, NF-κB/NLRP3 inflammasome activation, ICAM-1 expression, glomerular deposition of IgG and C3 and apoptosis, in the kidney; and enhancing renal hypoxia inducible factor 1-α expression. Proteomic analysis revealed that the treatment with xenon downregulated renal NLRP3 inflammasome-mediated cellular signaling. Similarly, xenon was effective in improving renal pathology and function in a spontaneous LN model in female NZB/W F1 mice. Thus, xenon may have a therapeutic role in treating LN but further studies are warranted to determine applicability to patients.

Tris DBA Ameliorates Accelerated and Severe Lupus Nephritis in Mice by Activating Regulatory T Cells and Autophagy and Inhibiting the NLRP3 Inflammasome

Tris (dibenzylideneacetone) dipalladium (Tris DBA), a small-molecule palladium complex, has been shown to inhibit cell growth and proliferation in pancreatic cancer, lymphocytic leukemia, and multiple myeloma. In the current study, we examined the therapeutic effects of Tris DBA on glomerular cell proliferation, renal inflammation, and immune cells. Treatment of accelerated and severe lupus nephritis (ASLN) mice with Tris DBA resulted in improved renal function, albuminuria, and pathology, including measurements of glomerular cell proliferation, cellular crescents, neutrophils, fibrinoid necrosis, and tubulointerstitial inflammation in the kidneys as well as scoring for glomerulonephritis activity. The treated ASLN mice also showed significantly decreased glomerular IgG, IgM, and C3 deposits. Furthermore, the compound was able to 1) inhibit bone marrow-derived dendritic cell-mediated T cell functions and reduce serum anti-dsDNA autoantibody levels; 2) differentially regulate autophagy and both the priming and activation signals of the NLRP3 inflammasome; and 3) suppress the phosphorylation of JNK, ERK, and p38 MAPK signaling pathways. Tris DBA improved ASLN in mice through immunoregulation by blunting the MAPK (ERK, JNK)-mediated priming signal of the NLRP3 inflammasome and by regulating the autophagy/NLRP3 inflammasome axis. These results suggest that the pure compound may be a drug candidate for treating the accelerated and deteriorated type of lupus nephritis.

The Role of Inflammasome-Dependent and Inflammasome-Independent NLRP3 in the Kidney

Cytoplasmic nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) forms an inflammasome with apoptosis-associated speck-like protein containing a CARD (ASC) and pro-caspase-1, which is followed by the cleavage of pro-caspase-1 to active caspase-1 and ultimately the activation of IL-1β and IL-18 and induction of pyroptosis in immune cells. NLRP3 activation in kidney diseases aggravates inflammation and subsequent fibrosis, and this effect is abrogated by genetic or pharmacologic deletion of NLRP3. Inflammasome-dependent NLRP3 mediates the progression of kidney diseases by escalating the inflammatory response in immune cells and the cross-talk between immune cells and renal nonimmune cells. However, recent studies have suggested that NLRP3 has several inflammasome-independent functions in the kidney. Inflammasome-independent NLRP3 regulates apoptosis in tubular epithelial cells by interacting with mitochondria and mediating mitochondrial reactive oxygen species production and mitophagy. This review will summarize the mechanisms by which NLRP3 functions in the kidney in both inflammasome-dependent and inflammasome-independent ways and the role of NLRP3 and NLRP3 inhibitors in kidney diseases.

High-sensitivity C-reactive protein and the risk of chronic kidney disease progression or acute kidney injury in post-myocardial infarction patients

BACKGROUND

Persistent, low-grade inflammation likely participates in the pathophysiology of both atherosclerosis and kidney disease. Although high-sensitivity C-reactive protein (hsCRP) predicts future cardiovascular risk in patients with chronic kidney disease (CKD), it is unknown whether hsCRP levels predict adverse renal outcomes in patients with cardiovascular disease.

METHODS

We studied all myocardial infarction (MI) survivors undergoing hsCRP testing >30 days after their MI during routine health care in Stockholm, Sweden (2006-2011), with available information on estimated glomerular filtration rate (eGFR). HsCRP tests measured during hospitalization/emergency room visits, followed by antibiotics or indicative of acute illness, were excluded, together with patients with ongoing/recent cancer, chronic infections, or immunosuppression. Inflammation was defined over a 3-month baseline window. Study outcomes were CKD progression (composite of doubling plasma creatinine, renal replacement therapy, or renal death) and acute kidney injury (AKI, acute creatinine peaks according to Kidney Disease: Improving Global Outcomes criteria). Multivariable Cox regression was used to adjust for age, sex, eGFR, hemoglobin, time since MI, comorbidities, undertaken procedures, and medications.

RESULTS

A total of 12,905 patients (62% men, mean age 73 years and 3 years since MI) were included, of whom 35% had an eGFR<60 mL/min/1.73 m². The mean (SD) hsCRP was 3.0 (4.4) mg/L. Baseline hsCRP levels were increasingly higher across lower eGFR categories. During a median follow-up of 3.2 years, 1,019 CKD progressions and 1,481 AKI events were recorded. Patients with hsCRP ≥2 mg/L were at higher risk of both CKD progression (adjusted hazard ratio 1.42; 95% CI 1.21-1.66) and AKI (1.29; 1.13-1.47) compared to those with hsCRP <2 mg/L. This association persisted across single CKD severity stages and after further hsCRP categorization into 4 groups (≤1, 1-3, 3-10, >10 mg/L). Results were robust across subgroups of patients and after exclusion of events occurring during the first 6-12 months.

CONCLUSIONS

In post-MI patients undergoing routine health care, elevated hsCRP was associated with subsequent risk of AKI and progression of CKD, irrespective of baseline kidney function.

Melatonin prevents sepsis-induced renal injury via the PINK1/Parkin1 signaling pathway

Melatonin (N-acetyl-5-methoxytryptamine; MT) has been shown to have a protective effect against sepsis-induced renal injury, however, the mechanisms underlying the function of MT remain to be elucidated. Therefore, in the present study, the potential mechanisms underlying the preventive role of MT in sepsis-induced renal injury were investigated. Hematoxylin and eosin staining was used to detect the effect of MT on the reduction of renal tissue damage, and immunohistochemistry (IHC), ELISA and western blot analysis were performed to determine the influence of MT on the protein expression of PTEN-induced putative kinase 1 (PINK1), nucleotide-oligomerization binding domain and leucine-rich repeat pyrin domain-containing 3 (NLRP3), apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC1), interleukin (IL)-18, IL-1β, IL-6 and cleaved caspase-1. Finally, a TUNEL assay was used to compare the rate of apoptosis of renal tissues among the sham, cecal ligation and puncture (CLP), and CLP + MT groups. The extent of tissue damage in the CLP group was the highest and the extent of tissue damage in the sham group was the lowest. The IHC and western blot analysis showed that the sham group had the highest protein level of PINK1, whereas the CLP group had the lowest protein level of PINK1. By contrast, the sham group had the lowest protein level of NLRP, whereas the CLP group had the highest level of NLRP3. Furthermore, CLP treatment enhanced the protein expression of ASC1 and cleaved caspase-1, whereas the administration of MT reduced the protein expression of ASC1 and cleaved caspase-1 to a certain degree. Finally, the apoptotic rate was found to be the highest in the CLP group and the lowest in the sham group. Taken together, in evaluating the therapeutic effect of MT on sepsis-induced renal injury, the results of the present study showed that MT alleviated sepsis-induced renal injury by regulating the expression of PINK1, Parkin1, NLRP3, ASC and cleaved caspase-1 in rats.

Inhibition of Interleukin-1β by Canakinumab and Cardiovascular Outcomes in Patients With Chronic Kidney Disease

BACKGROUND

Inflammation contributes to chronic kidney disease (CKD), in part mediated through activation of interleukin (IL)-1β by the NLRP3 inflammasome within the kidney. This process also likely contributes to the accelerated atherosclerosis associated with nephropathy.

OBJECTIVES

The authors hypothesized that canakinumab, a human monoclonal antibody targeting IL-1β, might reduce cardiovascular event rates and improve renal function among post-myocardial infarction patients with CKD.

METHODS

Stable post-myocardial infarction patients with high-sensitivity C-reactive protein (hsCRP) ≥ 2mg/l were randomly allocated to placebo or to 1 of 3 doses of canakinumab (50, 150, or 300 mg) given subcutaneously once every 3 months. Participants were followed for incident myocardial infarction, stroke, hospitalization for unstable angina requiring urgent revascularization, cardiovascular death, or death from any cause over a median follow-up period of 3.7 years (maximum 5 years). All patients additionally had serial monitoring of estimated glomerular filtration rate (eGFR), creatinine, the urine albumin to creatinine ratio (uACR), and were monitored for adverse renal and urinary events.

RESULTS

Of 10,061 participants, 1,875 (18.6%) had baseline eGFR <60 ml/min/1.73 m². These moderate CKD patients had higher incidence rates for major adverse vascular events compared with those with eGFR ≥60 ml/min/1.73 m² (6.92 vs. 4.13 per 100 person-years; p < 0.0001). Random allocation to canakinumab reduced the risk of major adverse cardiovascular events among those with CKD (hazard ratio: 0.82; 95% confidence interval: 0.68 to 1.00; p = 0.05) with the largest cardiovascular benefits accruing among those who achieved on-treatment hsCRP levels below 2 mg/l measured after taking the first dose (hazard ratio: 0.68; 95% confidence interval: 0.53 to 0.86; p = 0.0015). Comparable effects were observed among those with baseline albuminuria or diabetes. Canakinumab had neither clinically meaningful benefits nor substantive harms with respect to serial measures of eGFR, creatinine, the uACR, or reported adverse renal events during trial follow-up.

CONCLUSIONS

IL-1β inhibition with canakinumab reduces major adverse cardiovascular event rates among high-risk atherosclerosis patients with CKD, particularly among those with a robust anti-inflammatory response to initial treatment. These cardiovascular benefits accrued with no adverse clinical renal events. (Canakinumab Anti-inflammatory Thrombosis Outcomes Study [CANTOS]; NCT01327846).

Multifactorial functions of the inflammasome component NLRP3 in pathogenesis of chronic kidney diseases

The NLRP3 inflammasome is a cytosolic multiprotein caspase-activating complex platform involved in innate immunity required for the maturation and release of interleukin (IL)-1β and IL-18. Both cytokines activate their respective receptors present on cells inside and outside kidneys, resulting in the release of other proinflammatory cytokines to set up an inflammatory milieu both within the kidney and systemically. The canonical NLRP3-ASC-caspase-1-IL-1β-IL-18 axis has been shown to contribute to the pathophysiology of several kidney diseases by regulating renal necroinflammation. However, many recent studies have emphasized the inflammasome-independent functions of NLRP3 in chronic kidney disease (CKD) pathogenesis. This review highlights the contribution of the inflammasome-independent functions of NLPR3, for example, in fibrotic tissue remodeling, in tubular epithelial cell apoptosis, and in metabolic pathways, during the development and progression of CKD in various experimental models and humans. Interestingly, therapies targeting the inflammasome effectors (e.g., IL-1 receptor antagonists and IL-1β) have been approved for therapeutic use for NLRP3-dependent diseases; however, no NLRP3 antagonists have been approved for therapeutic use until now. This review highlights the double-edged sword-like functions of NLRP3 in the regulation of renal necroinflammation and fibrosis and therefore emphasizes the urgent need for specific NLRP3 inhibitors because of the broad therapeutic potential they offer for the treatment of CKD.

In vitro effects of interleukin (IL)-1 beta inhibition on the epithelial-to-mesenchymal transition (EMT) of renal tubular and hepatic stellate cells

Background

The epithelial to mesenchymal transition (EMT) is a multi-factorial biological mechanism involved in renal and hepatic fibrosis and the IL-1 beta has been assumed as a mediator of this process although data are not exhaustive. Therefore, the aim of our study was to evaluate the role of this cytokine in the EMT of renal proximal tubular epithelial cells (HK-2) and stellate cells (LX-2) and the protective/anti-fibrotic effect of its inhibition by Canakinumab (a specific human monoclonal antibody targeted against IL-1beta).

Methods

Both cell types were treated with IL-1 beta (10 ng/ml) for 6 and 24 h with and without Canakinumab (5 μg/ml). As control we used TGF-beta (10 ng/ml). Expression of EMT markers (vimentin, alpha-SMA, fibronectin) were evaluated through western blotting and immunofluorescence. Genes expression for matrix metalloproteinases (MMP)-2 was measured by Real-Time PCR and enzymatic activity by zymography. Cellular motility was assessed by scratch assay.

Results

IL-1 beta induced a significant up-regulation of EMT markers in both cell types and increased the MMP-2 protein expression and enzymatic activity, similarly to TGF-beta. Moreover, IL-1 beta induced a higher rate of motility in HK-2. Canakinumab prevented all these modifications in both cell types.

Conclusions

Our results clearly demonstrate the role of IL-1 beta in the EMT of renal/stellate cells and it underlines, for the first time, the therapeutic potential of its specific inhibition on the prevention/minimization of organ fibrosis.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1770-1) contains supplementary material, which is available to authorized users.

Inflammasomes in the Kidney

Inflammasomes influence a diverse range of kidney disease, including acute and chronic kidney diseases, and those mediated by innate and adaptive immunity. Both IL-18 and in particular IL-1β are validated therapeutic targets in several kidney diseases. In addition to leukocyte-derived inflammasomes, renal tissue cells express functional inflammasome components. Furthermore, a range of endogenous substances that directly activate inflammasomes also mediate kidney injury. Many of the functional studies have focussed on the NLRP3 inflammasome, and there is also evidence for the involvement of other inflammasomes in some conditions. While, at least in some disease, the mechanistic details of the involvement of the inflammasome remain to be elucidated, therapies focussed on inflammasomes and their products have potential in treating kidney disease in the future.

The NLRP3 inflammasome in kidney disease and autoimmunity

The NLRP3 inflammasome is an intracellular platform that converts the pro-inflammatory cytokines interleukin (IL)-1β and IL-18 to their active forms in response to 'danger' signals, which can be either host or pathogen derived, and mediates a form of inflammatory cell death called pyroptosis. This component of the innate immune system was initially discovered because of its role in rare autoinflammatory syndromes called cryopyrinopathies, but it has since been shown to mediate injurious inflammation in a broad range of diseases. Inflammasome activation occurs in both immune cells, primarily macrophages and dendritic cells, and in some intrinsic kidney cells such as the renal tubular epithelium. The NLRP3 inflammasome has been implicated in the pathogenesis of a number of renal conditions, including acute kidney injury, chronic kidney disease, diabetic nephropathy and crystal-related nephropathy. The inflammasome also plays a role in autoimmune kidney disease, as IL-1β and IL-18 influence adaptive immunity through modulation of T helper cell subsets, skewing development in favour of Th17 and Th1 cells that are important in the development of autoimmunity. Both IL-1 blockade and two recently identified specific NLRP3 inflammasome blockers, MCC950 and β-hydroxybutyrate, have shown promise in the treatment of inflammasome-mediated conditions. These targeted therapies have the potential to be of benefit in the growing number of kidney diseases in which the NLRP3 inflammasome has been implicated.

NLRP3 inflammasome: Pathogenic role and potential therapeutic target for IgA nephropathy

We have previously showed that IL-1β is involved in the pathogenesis of both spontaneously occurring and passively induced IgA nephropathy (IgAN) models. However, the exact causal-relationship between NLRP3 inflammasome and the pathogenesis of IgAN remains unknown. In the present study, we showed that [1] IgA immune complexes (ICs) activated NLRP3 inflammasome in macrophages involving disruption of mitochondrial integrity and induction of mitochondrial ROS, bone marrow-derived dendritic cells (BMDCs) and renal intrinsic cells; [2] knockout of NLRP3 inhibited IgA ICs-mediated activation of BMDCs and T cells; and [3] knockout of NLRP3 or a kidney-targeting delivery of shRNA of NLRP3 improved renal function and renal injury in a mouse IgAN model. These results strongly suggest that NLRP3 inflammasome serves as a key player in the pathogenesis of IgAN partly through activation of T cells and mitochondrial ROS production and that a local, kidney-targeting suppression of NLRP3 be a therapeutic strategy for IgAN.

Anakinra reduces blood pressure and renal fibrosis in one kidney/DOCA/salt-induced hypertension

OBJECTIVE

To determine whether a clinically-utilised IL-1 receptor antagonist, anakinra, reduces renal inflammation, structural damage and blood pressure (BP) in mice with established hypertension.

METHODS

Hypertension was induced in male mice by uninephrectomy, deoxycorticosterone acetate (2.4mg/d,s.c.) and replacement of drinking water with saline (1K/DOCA/salt). Control mice received uninephrectomy, a placebo pellet and normal drinking water. 10days post-surgery, mice commenced treatment with anakinra (75mg/kg/d, i.p.) or vehicle (0.9% saline, i.p.) for 11days. Systolic BP was measured by tail cuff while qPCR, immunohistochemistry and flow cytometry were used to measure inflammatory markers, collagen and immune cell infiltration in the kidneys.

RESULTS

By 10days post-surgery, 1K/DOCA/salt-treated mice displayed elevated systolic BP (148.3±2.4mmHg) compared to control mice (121.7±2.7mmHg; n=18, P<0.0001). The intervention with anakinra reduced BP in 1K/DOCA/salt-treated mice by ∼20mmHg (n=16, P<0.05), but had no effect in controls. In 1K/DOCA/salt-treated mice, anakinra modestly reduced (∼30%) renal expression of some (CCL5, CCL2; n=7-8; P<0.05) but not all (ICAM-1, IL-6) inflammatory markers, and had no effect on immune cell infiltration (n=7-8, P>0.05). Anakinra reduced renal collagen content (n=6, P<0.01) but paradoxically appeared to exacerbate the renal and glomerular hypertrophy (n=8-9, P<0.001) that accompanied 1K/DOCA/salt-induced hypertension.

CONCLUSION

Despite its anti-hypertensive and renal anti-fibrotic actions, anakinra had minimal effects on inflammation and leukocyte infiltration in mice with 1K/DOCA/salt-induced hypertension. Future studies will assess whether the anti-hypertensive actions of anakinra are mediated by protective actions in other BP-regulating or salt-handling organs such as the arteries, skin and brain.

Is the inflammasome a potential therapeutic target in renal disease?

The inflammasome is a large, multiprotein complex that drives proinflammatory cytokine production in response to infection and tissue injury. Pattern recognition receptors that are either membrane bound or cytoplasmic trigger inflammasome assembly. These receptors sense danger signals including damage-associated molecular patterns and pathogen-associated molecular patterns (DAMPS and PAMPS respectively). The best-characterized inflammasome is the NLRP3 inflammasome. On assembly of the NLRP3 inflammasome, post-translational processing and secretion of pro-inflammatory cytokines IL-1β and IL-18 occurs; in addition, cell death may be mediated via caspase-1. Intrinsic renal cells express components of the inflammasome pathway. This is most prominent in tubular epithelial cells and, to a lesser degree, in glomeruli. Several primary renal diseases and systemic diseases affecting the kidney are associated with NLRP3 inflammasome/IL-1β/IL-18 axis activation. Most of the disorders studied have been acute inflammatory diseases. The disease spectrum includes ureteric obstruction, ischaemia reperfusion injury, glomerulonephritis, sepsis, hypoxia, glycerol-induced renal failure, and crystal nephropathy. In addition to mediating renal disease, the IL-1/ IL-18 axis may also be responsible for development of CKD itself and its related complications, including vascular calcification and sepsis. Experimental models using genetic deletions and/or receptor antagonists/antiserum against the NLRP3 inflammasome pathway have shown decreased severity of disease. As such, the inflammasome is an attractive potential therapeutic target in a variety of renal diseases.

Osthole mitigates progressive IgA nephropathy by inhibiting reactive oxygen species generation and NF-κB/NLRP3 pathway

Renal reactive oxygen species (ROS) and mononuclear leukocyte infiltration are involved in the progressive stage (exacerbation) of IgA nephropathy (IgAN), which is characterized by glomerular proliferation and renal inflammation. The identification of the mechanism responsible for this critical stage of IgAN and the development of a therapeutic strategy remain a challenge. Osthole is a pure compound isolated from Cnidiummonnieri (L.) Cusson seeds, which are used as a traditional Chinese medicine, and is anti-inflammatory, anti-apoptotic, and anti-fibrotic both in vitro and in vivo. Recently, we showed that osthole acts as an anti-inflammatory agent by reducing nuclear factor-kappa B (NF-κB) activation in and ROS release by activated macrophages. In this study, we examined whether osthole could prevent the progression of IgAN using a progressive IgAN (Prg-IgAN) model in mice. Our results showed that osthole administration resulted in prevention of albuminuria, improved renal function, and blocking of renal progressive lesions, including glomerular proliferation, glomerular sclerosis, and periglomerular mononuclear leukocyte infiltration. These findings were associated with (1) reduced renal superoxide anion levels and increased Nrf2 nuclear translocation, (2) inhibited renal activation of NF-κB and the NLRP3 inflammasome, (3) decreased renal MCP-1 expression and mononuclear leukocyte infiltration, (4) inhibited ROS production and NLRP3 inflammasome activation in cultured, activated macrophages, and (5) inhibited ROS production and MCP-1 protein levels in cultured, activated mesangial cells. The results suggest that osthole exerts its reno-protective effects on the progression of IgAN by inhibiting ROS production and activation of NF-κB and the NLRP3 inflammasome in the kidney. Our data also confirm that ROS generation and activation of NF-κB and the NLRP3 inflammasome are crucial mechanistic events involved in the progression of the renal disorder.

Predictive value of conjointly examined IL-1ra, TNF-R I, TNF-R II, and RANTES in patients with primary glomerulonephritis

Interleukin-1 receptor antagonist (IL-1ra), tumor necrosis factor soluble receptors (sTNF-R) type I and II, and regulated upon activation, normal T-cell expressed and secreted (RANTES) play an important role in the modulation of primary glomerulonephritis (GN) course. The aim of the study was to assess whether pre-treatment measurements of IL-1ra, sTNF-R, and RANTES assessed conjointly may be useful as predicting factors in patients with GN. In 84 patients (45 males and 39 female) serum concentration (pg/mL) and urinary excretion (pg/mgCr) of cytokines were measured. After 12 months of therapy with steroids and cyclophosphamide the patients were divided into two subgroups: Responders (R) and Non-Responders (NR) according to the treatment results. The urinary IL-1ra, TNF-RI and RII were significantly higher in R than NR (1,732 vs 646 with P < 0.001, 13.1 vs 6.3 with P = 0.005, and 33.6 vs 14.4 with P = 0.012). The urinary RANTES excretion was increased in NR (79.6 vs 28.5; P < 0.001). The multivariable analysis showed that if conjointly assessed, only urinary IL-1ra, TNF-R I and R II, RANTES with 85% probability pointed the feature remission (R). In conclusion, the urinary excretion of IL-1ra, TNF-R I and R II, and RANTES examined conjointly are effective in predicting favorable response to immunosuppressive treatment in patients with GN.

WT1 and Pax2 re-expression is required for epithelial-mesenchymal transition in 5/6 nephrectomized rats and cultured kidney tubular epithelial cells

Mature tubular epithelial cells in the adult kidney can undergo epithelial-mesenchymal transition (EMT), a phenotypic change that is linked to the pathogenesis of renal interstitial fibrosis. EMT may be considered the reverse of mesenchymal-epithelial transition, which occurs during normal kidney development. The Wilms' tumor suppressor gene WT1 and the paired box 2 gene Pax2 are needed to induce mesenchymal-epithelial transition and play key roles in the progression of nephrogenesis. However, until now, WT1 and Pax2 have not been tested for their direct involvement in the process of renal tubular EMT. In this study, we explored the potential roles of WT1 and Pax2 in EMT that is induced in the remnant kidney of rats following 5/6 nephrectomy. We also examined WT1 and Pax2 in cultured renal tubular epithelial (NRK52E) cells treated with interleukin-1α and investigated the effects of blocking EMT using RNA interference. We showed that WT1 and Pax2 were re-expressed in the EMT models, and these were accompanied by decreased expression of E-cadherin and increased expression of vimentin, Snail and α-smooth muscle actin. Silencing WT1 and Pax2 by RNA interference blocked the interleukin-1α-induced EMT in the NRK52E cells, as reflected in the suppression of α-SMA and Snail expression, the restoration of E-cadherin expression and normal cell morphology. Our experiments suggested that the re-expression of WT1 and Pax2 in the tubular epithelial cells plays important roles in the promotion of EMT, and there may be therapeutic value in silencing Pax2 and WT1 to prevent or reverse renal fibrosis.

The inflammasomes in kidney disease

Renal inflammation is a universal response to infectious and noninfectious triggers. Sensors of the innate immune system, such as Toll-like receptors or RIG-like receptors, provide danger recognition platforms on renal cells that integrate and translate the diverse triggers of renal inflammation by inducing cell activation and the secretion of proinflammatory cytokines and chemokines. As a new entry, the inflammasome-forming NLR genes integrate various danger signals into caspase-1-activating platforms that regulate the processing and secretion of pro-IL-1β and pro-IL-18 into the mature and active cytokines. Accumulating data now document a role for the NLRP3 inflammasome and IL-1β/IL-18 in many diseases, including atherosclerosis, diabetes, amyloidosis, malaria, crystal-related diseases, and other autoinflammatory disorders, identifying this innate immune pathway as an attractive therapeutic target. Here we review the current knowledge regarding inflammasome signaling and outline existing evidence on the expression and functional role of the inflammasome-caspase-1-IL-1β/IL-18 axis in kidney disease. We further provide a perspective on the potential roles of the inflammasomes in the pathogenesis of acute and chronic kidney diseases.

Identificação da Leptospira interrogans sorovar pomona em camundongos geneticamente selecionados, para a alta e baixa produção de anticorpos, através da técnica de imunoperoxidase em tecido renal e isolamento bacteriano em meio de Fletcher

O presente trabalho teve por objetivo identificar a presença da Leptospira interrogans sorovar pomona em camundongos geneticamente selecionados para a alta e baixa resposta a anticorpos. Todos os animais foram submetidos ao isolamento bacteriano, imunohistoquímica (imunoperoxidase) em cortes de tecido renal e coloração através da hematoxilina-eosina. A técnica de imunoperoxidase apresentou-se pouco mais sensível em relação ao cultivo, entretanto, ambas foram bons parâmetros de identificação do agente. Presença de lesões renais mais intensas ocorreram em períodos em que houve maior número de bactérias isoladas em meio de cultivo. Camundongos da linhagem HIV-A conseguiram eliminar as leptospiras com maior eficiência e rapidez em relação as linhagem LIV-A, entretanto o estudo demonstrou que ambas linhagens da seleção IV-A foram eficientes em controlar o processo infeccioso.

Interleukin-1 induces tubular epithelial-myofibroblast transdifferentiation through a transforming growth factor-beta1-dependent mechanism in vitro

Interleukin-1 (IL-1) has been shown to exert profibrotic activity in a number of disease models, including crescentic glomerulonephritis and pulmonary fibrosis, but the mechanisms by which this operates are poorly understood. Recent studies have identified a novel mechanism promoting renal fibrosis: tubular epithelial-myofibroblast transdifferentiation (TEMT). The present study examined whether IL-1 can stimulate TEMT in vitro. Cells of the normal rat kidney tubular epithelial cell line (NRK52E) were grown to confluence on collagen-coated plates and cultured for 5 days in the presence 1 to 20 ng/mL of IL-1alpha. Doses of 10 to 20 ng/mL of IL-1 caused transdifferentiation of NRK52E cells into myofibroblast-like cells. Scanning electron microscopy identified IL-1-induced morphological changes as a loss of apical-basal polarity and microvilli, cell hypertrophy, and the development of an elongated and invasive appearance. Phenotypically, IL-1-induced TEMT was characterized by de novo messenger RNA and protein expression of the mesenchymal marker alpha-smooth muscle actin, shown by Northern blotting, immunohistochemistry, and Western blotting. This was accompanied by loss of the epithelial marker E-cadherin. The addition of an excess of IL-1-receptor antagonist completely inhibited IL-1-induced TEMT. IL-1 was shown to stimulate the secretion of active transforming growth factor-beta1 (TGF-beta1) by NRK52E cells. Furthermore, the addition of a neutralizing anti-TGF-beta1 antibody inhibited IL-1-induced TEMT. In conclusion, IL-1 is a profibrogenic cytokine capable of inducing TEMT through a TGF-beta1-dependent mechanism. This may represent a novel mechanism by which IL-1 induces renal fibrosis in vivo.

Impact of interleukin-1 receptor antagonist and tumor necrosis factor-alpha gene polymorphism on IgA nephropathy

BACKGROUND

It is evident that cytokines play an important role in the pathogenesis as well as disease progression in IgA nephropathy (IgAN). The level of cytokine production is influenced by different genotypes that reflect gene polymorphism of the pertinent cytokine. Interleukin-1 receptor antagonist (IL-1ra) and tumor necrosis factor-alpha (TNF-alpha) gene polymorphism have been found to affect disease susceptibility and activity in several inflammatory diseases. However, the impact of these polymorphisms in IgAN patients has not previously been thoroughly studied.

METHODS

We investigated 111 cases of biopsy-proven IgAN and 100 healthy, normal controls for their IL-1ra and TNF-alpha gene polymorphism. IL-1ra gene polymorphism was characterized as a variable number of tandem repeats of a 86 bp sequence within intron 2. Five alleles were identified and were designated as IL1RN*1, IL1RN*2, IL1RN*3, IL1RN*4, and IL1RN*5, corresponding to 4, 2, 5, 3, 6 repeats, respectively. A polymorphism in the promoter region of the TNF-alpha gene was also studied. This polymorphism involved a guanidine to adenosine transition at position -308 and was designated as TNF1 (-308G) and TNF2 (-308A).

RESULTS

There were 54 male and 57 female patients with a mean age of 30.3 +/- 12.5 years and a disease duration of 66. 8 +/- 47.2 months. The mean duration of the follow-up period was 47. 3 +/- 32.6 months. In the patient group, the allele frequencies of IL1RN*1, IL1RN*2, IL1RN*3, IL1RN*4, and IL1RN*5 were 89.6%, 9.9%, 0%, 0.5%, and 0%, respectively, whereas the corresponding carriage rates were 100%, 19.8%, 0%, 0.9%, and 0%, respectively. An excessive carriage of IL2RN*2 was found in the patients when compared with normal controls (allele frequency, 9.9 vs. 2.5%, P < 0.0001). The allele frequencies of TNF1 and TNF2 were 94.1 and 5.9%, respectively, and the carriage rates were 99.1 and 10.8%, respectively, in the patients, which was not significantly different from those of normal controls. When the patients were stratified into mild and severe groups according to their initial presentation, none of the studied alleles correlated with the severity. However, patients with gross hematuria were associated with a higher carriage rate of TNF2 when compared with patients without gross hematuria (allele frequency, 15. 4 vs. 4.6%, P = 0.0552; carriage rate, 30.8% vs. 8.2%, P = 0.0272). Renal survival analysis revealed that the TNF2 carrier had a renal survival comparable with TNF2 (-) patients. However, the carriage of the IL1RN*2 allele was associated with a significantly poorer long-term outcome with a median survival time of 72 months, as compared with those without IL1RN*2 (134 months, P < 0.01).

CONCLUSION

IL-1ra and TNF-alpha gene polymorphism may affect disease susceptibility as well as disease activity and long-term outcome in human IgAN. Treatment with an IL-1ra or IL-1 blocking agent may be relevant in those carrying the IL1RN*2 allele.

Evidence for genetic factors in the development and progression of IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is the most common glomerulonephritis in the world among patients undergoing renal biopsy. Once considered a relatively benign condition, longitudinal follow-up studies have revealed that in fact 9 to 50% of patients progress to end-stage renal disease within 20 years of disease onset. In the three decades since its first description by Jean Berger and Nicole Hinglais, clinical, epidemiologic, and immunologic studies of the pathogenesis of primary (idiopathic) mesangial glomerulonephritis with predominant IgA deposits have characterized the features of IgAN as a distinct glomerular disease entity. However, the basic molecular mechanism(s) underlying abnormal IgA deposition in the mesangium with ensuing extracellular matrix expansion and mesangial cell proliferation remains poorly understood. The task of elucidating the molecular basis of IgAN is made especially challenging by the fact that both environmental and genetic components likely contribute to the development and progression of IgAN.

METHODS AND RESULTS

We review here the evidence for genetic factors in the development and progression of IgAN, including a reappraisal of earlier conflicting results from small immunogenetic case-control studies, the evidence for racial differences in the prevalence of IgAN, a detailed summary of all reported occurrences of familial IgAN worldwide, and an exhaustive review of new insights gained through the study of two murine models of hereditary IgAN: the ddY and the uteroglobin-deficient mouse.

CONCLUSIONS

With the development of powerful molecular genetic approaches to the study of both Mendelian and complex human genetic diseases, and the successful efforts of investigators to identify and clinically characterize large IgAN multiplex families, we propose that genetic analysis of familial IgAN is the most promising approach to the identification of IgAN disease/susceptibility genes. Alternatively, if the case-control study design is employed to identify associations between particular candidate genes or markers and the development of IgAN, spurious associations caused by the effects of population stratification should be ruled out by confirming the findings using powerful and sensitive family-based methodologies such as the transmission/dysequilibrium test (TDT).

Rationales for treating IgA nephropathies

An outline is given of the pathophysiology of IgA nephropathy (IgA) in order to emphasize the role of eicosanoids, angiotensin II, and reactive oxygen species. ACE inhibitors and early corticosteroid usage are prime therapies. Tonsillectomy is to be considered, certainly for individual cases. It is logical that other components of a cocktail could be (i) thromboxane antagonists, (ii) leukotriene antagonists, or (iii) PAF antagonist. In theory there should be benefit from antioxidants. Fish oils have not come up to expectation. PDGF aptamers look promising for the prevention of mesangial cell proliferation. Heparins are not used in the way that they could be. Various other agents could help reduce decline.