Involvement of the NLRC4-Inflammasome in Diabetic Nephropathy

Renoprotective effect of rosmarinic acid by inhibition of indoxyl sulfate-induced renal interstitial fibrosis via the NLRP3 inflammasome signaling

We previously reported that rosmarinic acid (RA) ameliorated renal fibrosis in a unilateral ureteral obstruction (UUO) murine model of chronic kidney disease. This study aimed to determine whether RA attenuates indoxyl sulfate (IS)-induced renal fibrosis by regulating the activation of the NLRP3 inflammasome/IL-1β/Smad circuit. We discovered the NLRP3 inflammasome was activated in the IS treatment group and downregulated in the RA-treated group in a dose-dependent manner. Additionally, the downstream effectors of the NLRP3 inflammasome, cleaved-caspase-1 and cleaved-IL-1β showed similar trends in different groups. Moreover, RA administration significantly decreased the ROS levels of reactive oxygen species in IS-treated cells. Our data showed that RA treatment significantly inhibited Smad-2/3 phosphorylation. Notably, the effects of RA on NLRP3 inflammasome/IL-1β/Smad and fibrosis signaling were reversed by the siRNA-mediated knockdown of NLRP3 or caspase-1 in NRK-52E cells. In vivo, we demonstrated that expression levels of NLRP3, c-caspase-1, c-IL-1β, collagen I, fibronectin and α-SMA, and TGF- β 1 were downregulated after treatment of UUO mice with RA or RA + MCC950. Our findings suggested RA and MCC950 synergistically inhibited UUO-induced NLRP3 signaling activation, revealing their renoprotective properties and the potential for combinatory treatment of renal fibrosis and chronic kidney inflammation.

To Explore the Putative Molecular Targets of Diabetic Nephropathy and their Inhibition Utilizing Potential Phytocompounds

BACKGROUND

This review critically addresses the putative molecular targets of Diabetic Nephropathy (DN) and screens effective phytocompounds that can be therapeutically beneficial, and highlights their mechanistic modalities of action.

INTRODUCTION

DN has become one of the most prevalent complications of clinical hyperglycemia, with individual-specific variations in the disease spectrum that leads to fatal consequences. Diverse etiologies involving oxidative and nitrosative stress, activation of polyol pathway, inflammasome formation, Extracellular Matrix (ECM) modifications, fibrosis, and change in dynamics of podocyte functional and mesangial cell proliferation adds up to the clinical complexity of DN. Current synthetic therapeutics lacks target-specific approach, and is associated with the development of inevitable residual toxicity and drug resistance. Phytocompounds provides a vast diversity of novel compounds that can become an alternative therapeutic approach to combat the DN.

METHODS

Relevant publications were searched and screened from research databases like GOOGLE SCHOLAR, PUBMED and SCISEARCH. Out of 4895 publications, the most relevant publications were selected and included in this article.

RESULT

This study critically reviews over 60 most promising phytochemical and provides with their molecular targets, that can be of pharmacological significance in context to current treatment and concomitant research in DN.

CONCLUSION

This review highlights those most promising phytocompounds that have the potential of becoming new safer naturally-sourced therapeutic candidates and demands further attention at clinical level.

NAIP/NLRC4 inflammasome participates in macrophage responses to Trypanosoma cruzi by a mechanism that relies on cathepsin-dependent caspase-1 cleavage

Inflammasomes are large protein complexes that, once activated, initiate inflammatory responses by activating the caspase-1 protease. They play pivotal roles in host defense against pathogens. The well-established role of NAIP/NLRC4 inflammasome in bacterial infections involves NAIP proteins functioning as sensors for their ligands. However, recent reports have indicated the involvement of NLRC4 in non-bacterial infections and sterile inflammation, even though the role of NAIP proteins and the exact molecular mechanisms underlying inflammasome activation in these contexts remain to be elucidated. In this study, we investigated the activation of the NAIP/NLRC4 inflammasome in response to Trypanosoma cruzi, the protozoan parasite responsible for causing Chagas disease. This parasite has been previously demonstrated to activate NLRP3 inflammasomes. Here we found that NAIP and NLRC4 proteins are also required for IL-1β and Nitric Oxide (NO) release in response to T. cruzi infection, with their absence rendering macrophages permissive to parasite replication. Moreover, Nlrc4 -/- and Nlrp3 -/- macrophages presented similar impaired responses to T. cruzi, underscoring the non-redundant roles played by these inflammasomes during infection. Notably, it was the live trypomastigotes rather than soluble antigens or extracellular vesicles (EVs) secreted by them, that activated inflammasomes in a cathepsins-dependent manner. The inhibition of cathepsins effectively abrogated caspase-1 cleavage, IL-1β and NO release, mirroring the phenotype observed in Nlrc4 -/-/Nlrp3 -/- double knockout macrophages. Collectively, our findings shed light on the pivotal role of the NAIP/NLRC4 inflammasome in macrophage responses to T. cruzi infection, providing new insights into its broader functions that extend beyond bacterial infections.

SGLT-2 Inhibitors and the Inflammasome: What's Next in the 21st Century?

The nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome in the kidney and the heart is increasingly being suggested to play a key role in mediating inflammation. In the kidney, NLRP3 activation was associated with the progression of diabetic kidney disease. In the heart, activation of the NLRP3 inflammasome was related to the enhanced release of interleukin-1β (IL-1β) and the subsequent induction of atherosclerosis and heart failure. Apart from their glucose-lowering effects, SGLT-2 inhibitors were documented to attenuate activation of the NLRP3, thus resulting in the constellation of an anti-inflammatory milieu. In this review, we focus on the interplay between SGLT-2 inhibitors and the inflammasome in the kidney, the heart and the neurons in the context of diabetes mellitus and its complications.

Mitophagy, Inflammasomes and Their Interaction in Kidney Diseases: A Comprehensive Review of Experimental Studies

Mitophagy is an important mechanism for mitochondrial quality control by regulating autophagosome-specific phagocytosis, degradation and clearance of damaged mitochondria, and involved in cell damage and diseases. Inflammasomes are important inflammation-related factors newly discovered in recent years, which are involved in cell innate immunity and inflammatory response, and play an important role in kidney diseases. Based on the current studies, we reviewed the progress of mitophagy, inflammasomes and their interaction in kidney diseases.

Role of the inflammasome in insulin resistance and type 2 diabetes mellitus

The inflammasome is a protein complex composed of a variety of proteins in cells and which participates in the innate immune response of the body. It can be activated by upstream signal regulation and plays an important role in pyroptosis, apoptosis, inflammation, tumor regulation, etc. In recent years, the number of metabolic syndrome patients with insulin resistance (IR) has increased year by year, and the inflammasome is closely related to the occurrence and development of metabolic diseases. The inflammasome can directly or indirectly affect conduction of the insulin signaling pathway, involvement the occurrence of IR and type 2 diabetes mellitus (T2DM). Moreover, various therapeutic agents also work through the inflammasome to treat with diabetes. This review focuses on the role of inflammasome on IR and T2DM, pointing out the association and utility value. Briefly, we have discussed the main inflammasomes, including NLRP1, NLRP3, NLRC4, NLRP6 and AIM2, as well as their structure, activation and regulation in IR were described in detail. Finally, we discussed the current therapeutic options-associated with inflammasome for the treatment of T2DM. Specially, the NLRP3-related therapeutic agents and options are widely developed. In summary, this article reviews the role of and research progress on the inflammasome in IR and T2DM.

Study on the mechanism of Phellinus igniarius total flavonoids in reducing uric acid and protecting uric acid renal injury in vitro

Background

Uric acid nephropathy (UN) is a complication of hyperuricemia (HUA), which has a great impact on people's lives. Here, we evaluated the therapeutic potential of total flavonoids of Phellinus igniarius (TFPI) in vivo and studied the anti UN effect of TFPI in vitro.

Methods

Hyperuricemia was induced by intraperitoneal injection of potassium oxonate in ICR mice. After intervention with TFPI, we evaluated the levels of serum uric acid (UA) and creatinine (CR), and the contents of xanthine oxidase (XOD) and adenosine deaminase (ADA) in liver. To explore the effect and molecular mechanism of TFPI on UN, we treated HK-2 cells with monosodium urate (MSU) to study the effect of TFPI on apoptosis and inflammation. In addition, to explore the mechanism of TFPI on uric acid transport we evaluated the relationship between uric acid transporter ABCG2 and inflammatory signaling pathway TLR4-NLRP3.

Results

In the model mice, TFPI significantly decreased the levels of UA and Cr, which may be related to the inhibition of XOD enzyme activity. In HK-2 cells, the response of TFPI to MSU can effectively inhibit apoptosis and activation of TLR4-NLRP3 signaling pathway and promote the expression of ABCG2.

Conclusions

TFPI can significantly inhibit the release of inflammatory factors and promote the expression of ABCG2 by targeting TLR4 receptor and NLRP3 inflammasome. And targeted inhibition of XOD enzyme activity to reduce uric acid level and inhibit the development of UN.

Review of potential biomarkers of inflammation and kidney injury in diabetic kidney disease

Diabetic kidney disease is expected to increase rapidly over the coming decades with rising prevalence of diabetes worldwide. Current measures of kidney function based on albuminuria and estimated glomerular filtration rate do not accurately stratify and predict individuals at risk of declining kidney function in diabetes. As a result, recent attention has turned towards identifying and assessing the utility of biomarkers in diabetic kidney disease. This review explores the current literature on biomarkers of inflammation and kidney injury focussing on studies of single or multiple biomarkers between January 2014 and February 2020. Multiple serum and urine biomarkers of inflammation and kidney injury have demonstrated significant association with the development and progression of diabetic kidney disease. Of the inflammatory biomarkers, tumour necrosis factor receptor-1 and -2 were frequently studied and appear to hold most promise as markers of diabetic kidney disease. With regards to kidney injury biomarkers, studies have largely targeted markers of tubular injury of which kidney injury molecule-1, beta-2-microglobulin and neutrophil gelatinase-associated lipocalin emerged as potential candidates. Finally, the use of a small panel of selective biomarkers appears to perform just as well as a panel of multiple biomarkers for predicting kidney function decline.

A Glimpse of Inflammation and Anti-Inflammation Therapy in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a common complication of diabetes mellitus and a major cause of end-stage kidney disease (ESKD). The pathogenesis of DKD is very complex and not completely understood. Recently, accumulated evidence from in vitro and in vivo studies has demonstrated that inflammation plays an important role in the pathogenesis and the development of DKD. It has been well known that a variety of pro-inflammatory cytokines and related signaling pathways are involved in the procession of DKD. Additionally, some anti-hyperglycemic agents and mineralocorticoid receptor antagonists (MRAs) that are effective in alleviating the progression of DKD have anti-inflammatory properties, which might have beneficial effects on delaying the progression of DKD. However, there is currently a lack of systematic overviews. In this review, we focus on the novel pro-inflammatory signaling pathways in the development of DKD, including the nuclear factor kappa B (NF-κB) signaling pathway, toll-like receptors (TLRs) and myeloid differentiation primary response 88 (TLRs/MyD88) signaling pathway, adenosine 5′-monophosphate-activated protein kinase (AMPK) signaling pathways, inflammasome activation, mitochondrial DNA (mtDNA) release as well as hypoxia-inducible factor-1(HIF-1) signaling pathway. We also discuss the related anti-inflammation mechanisms of metformin, finerenone, sodium-dependent glucose transporters 2 (SGLT2) inhibitors, Dipeptidyl peptidase-4 (DPP-4) inhibitors, Glucagon-like peptide-1 (GLP-1) receptor agonist and traditional Chinese medicines (TCM).

Circ_0000181 regulates miR-667-5p/NLRC4 axis to promote pyroptosis progression in diabetic nephropathy

Our previous research demonstrated that NOD-like receptor family CARD domain-containing protein 4 (NLRC4) inflammasome was overexpressed in renal tissues of patients with diabetic nephropathy (DN). This study further investigated the effect of circRNAs-miRNAs interaction on NLRC4 and their potential mechanisms. DN mice models were first established using STZ. Then, pyroptosis related marker expression was detected using qPCR, western blot (WB), and immunohistochemistry analysis. After that, differentially expressed circRNAs, miRNAs, and mRNAs were investigated using next-generation sequencing. Additionally, the function and potential mechanism of circ_0000181 and miR-667-5p on pyroptosis were measured in vitro DN cell model using MTS, WB, and Enzyme-linked immunosorbent assay. There was an apparent elevation of NLRC4, Caspase1, IL-1β, and IL-18 levels in DN mice. The next-generation sequencing results revealed that there were 947 circRNAs and 390 miRNAs significantly different between the DN and sham kidney tissue, of which circ_0000181 and miR-667-5p had potential targeting effects with NLRC4. Dual-luciferase and functional rescue experiments demonstrated that circ_0000181 promoted NLRC4 inflammasome activation via competitive sponge of miR-667-5p, promoted the release of IL-1β and IL-18, and caused pyroptosis. Altogether, circ_0000181 regulates miR-667-5p/NLRC4 axis to promote pyroptosis progression in DN.

The role of CDH2 and MCP-1 mRNAs of blood extracellular vesicles in predicting early-stage diabetic nephropathy

Background

Extracellular vesicles (EVs), including exosomes and microvesicles, are involved in intercellular communication by transferring biomolecules such as mRNA, which has been shown to be as essential biomarkers for many physiological and pathological conditions such as diabetic nephropathy (DN). This study aimed to investigate the expression of CDH1, CDH2, MCP-1, and PAI-1 mRNAs in blood EVs of DN patients and to determine their accuracy in predicting early-stage DN.

Methods

We recruited 196 participants, including 35 overt DN patients, 53 incipient DN patients, 62 diabetic patients (DM), and 46 healthy individuals. Quantification of the mRNA profile of blood EVs was performed using the qRT-PCR method. The diagnostic performance of mRNA was evaluated using receiver operating characteristic analysis.

Results

The mRNA expression of CDH2 and MCP-1 was downregulated in overt DN group (0.22-fold change and 0.15-fold change, respectively) and incipient DN group (0.60-fold change and 0.43-fold change, respectively) compared to DM group (1.72-fold change and 2.77-fold change, respectively), while PAI-1 mRNA expression decreased in incipient DN group (0.70-fold change) and DM group (0.58-fold change) compared to control. However, the expression level of CDH1 mRNA was not significantly different among the four groups (p = 0.408). Moreover, CDH2 and MCP-1 mRNAs inversely correlated with creatinine (r = -0.370 and r = -0.361, p<0.001) and Alb/Cr ratio (r = -0.355 and r = -0.297, p<0.001). 1/CDH2 mRNA also predicted overt DN with an accuracy of 0.75 (95%CI: 0.65–0.85) and incipient DN with an accuracy of 0.61 (95%CI: 0.50–0.71) while 1/MCP-1 mRNA had an accuracy of 0.66 (95%CI: 0.55–0.77) for overt DN prediction and an accuracy of 0.61 (95%CI: 0.51–0.71) for incipient DN prediction.

Conclusion

CDH2 and MCP-1 mRNAs expression in blood EVs was decreased with the development of DN, suggesting the renoprotective effect of these mRNAs in diabetic individuals. Moreover, their quantifications could serve as diagnostic biomarkers for early-stage DN.

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.

Sphingomyelin synthase 1 mediates hepatocyte pyroptosis to trigger non-alcoholic steatohepatitis

OBJECTIVE

Lipotoxic hepatocyte injury is a primary event in non-alcoholic steatohepatitis (NASH), but the mechanisms of lipotoxicity are not fully defined. Sphingolipids and free cholesterol (FC) mediate hepatocyte injury, but their link in NASH has not been explored. We examined the role of free cholesterol and sphingomyelin synthases (SMSs) that generate sphingomyelin (SM) and diacylglycerol (DAG) in hepatocyte pyroptosis, a specific form of programmed cell death associated with inflammasome activation, and NASH.

DESIGN

Wild-type C57BL/6J mice were fed a high fat and high cholesterol diet (HFHCD) to induce NASH. Hepatic SMS1 and SMS2 expressions were examined in various mouse models including HFHCD-fed mice and patients with NASH. Pyroptosis was estimated by the generation of the gasdermin-D N-terminal fragment. NASH susceptibility and pyroptosis were examined following knockdown of SMS1, protein kinase Cδ (PKCδ), or the NLR family CARD domain-containing protein 4 (NLRC4).

RESULTS

HFHCD increased the hepatic levels of SM and DAG while decreasing the level of phosphatidylcholine. Hepatic expression of Sms1 but not Sms2 was higher in mouse models and patients with NASH. FC in hepatocytes induced Sms1 expression, and Sms1 knockdown prevented HFHCD-induced NASH. DAG produced by SMS1 activated PKCδ and NLRC4 inflammasome to induce hepatocyte pyroptosis. Depletion of Nlrc4 prevented hepatocyte pyroptosis and the development of NASH. Conditioned media from pyroptotic hepatocytes activated the NOD-like receptor family pyrin domain containing 3 inflammasome (NLRP3) in Kupffer cells, but Nlrp3 knockout mice were not protected against HFHCD-induced hepatocyte pyroptosis.

CONCLUSION

SMS1 mediates hepatocyte pyroptosis through a novel DAG-PKCδ-NLRC4 axis and holds promise as a therapeutic target for NASH.

Hyperglycaemia-associated macrophage pyroptosis accelerates periodontal inflamm-aging

AIM

Pyroptosis and inflamm-aging have been newly identified to be involved in diabetic periodontitis. This study aimed to elucidate whether macrophage pyroptosis plays a role in periodontal inflamm-aging by impacting the senescence of fibroblasts, as well as the potential mechanism via NLR family CARD domain-containing protein 4 (NLRC4) phosphorylation.

MATERIALS AND METHODS

Diabetes was induced in mice using streptozotocin. Periodontal pyroptosis and senescence were detected using immunohistochemical analysis. Prior to evaluating senescence in human gingival fibroblasts cultured with conditioned medium derived from macrophages, RAW 264.7 macrophages were confirmed to undergo pyroptosis by scanning electron microscopy and gasdermin D (GSDMD) detection. The NLRC4-related pathway was examined under hyperglycaemic conditions.

RESULTS

Our data showed that macrophage pyroptosis induced the expression of senescent markers in vivo and in vitro. Importantly, clearance of pyroptotic macrophages rescued senescence in fibroblasts. Furthermore, GSDMD activation and pyroptosis in hyperglycaemia were found to be mediated by NLRC4 phosphorylation.

CONCLUSIONS

Hyperglycaemia could initially induce macrophage pyroptosis and lead to cellular senescence, thereby critically contributing to periodontal pathogenesis in diabetes. In particular, NLRC4 phosphorylation could be a potential therapeutic target for the inhibition of this process.

Advances in understanding the innate immune-associated diabetic kidney disease

Millions of human deaths occur annually due to chronic kidney disease, caused by diabetic kidney disease (DKD). Despite having effective drugs controlling the hyperglycemia and high blood pressure, the incidence of DKD is increasing, which indicates the need for the development of novel therapies to control DKD. In this article, we discussed the recent advancements in the basic innate immune mechanisms in renal tissues triggered under the diabetes environment, leading to the pathogenesis and progression of DKD. We also summarized the currently available innate immune molecules-targeting therapies tested against DKD in clinical and preclinical settings, and highlighted additional drug targets that could potentially be employed for the treatment of DKD. The improved understanding of the disease pathogenesis may open avenues for the development of novel therapies to rein in DKD, which consequently, can reduce morbidity and mortality in humans in the future.

Activation of the NLRC4 inflammasome in renal tubular epithelial cell injury in diabetic nephropathy

Renal tubular interstitial injury plays a key role in the progression of diabetic nephropathy (DN) and, thus, the study of renal tubular injury in DN is important. The aim of the present study was to elucidate the role of the NLR family CARD domain containing 4 (NLRC4) inflammasome in renal tubular epithelial cell (RTEC) injury in DN. Human kidney biopsy tissues were obtained from patients with DN, and normal kidney tissues were obtained from nephrectomies performed for renal hamartoma. Human RTECs (HK2 cells) were divided into normal glucose (D-glucose 5.6 mmol/l), high glucose (HG; 30 mmol/l), high osmotic (D-glucose 5.6 mmol/l + D-mannitol 24.4 mmol/l), HG + NLRC4 small interfering (si)RNA or HG + siRNA control groups. Then, the expression levels of NLRC4, PTEN-induced kinase 1 (PINK1) and parkin, as well as the levels of mitochondrial reactive oxygen species, which are associated with mitophagy, were observed. The expression levels of NLRC4, PINK1, parkin and phosphorylated parkin in the RTECs of patients with DN were higher compared with those in normal controls. In HK2 cells, HG stimulated the expression of NLRC4, the secretion of IL-1β and IL-18 and cell death. Moreover, knockdown of NLRC4 expression in HK2 cells treated with HG reduced the secretion of the inflammatory cytokines, IL-1β and IL-18. The findings of the present study may provide a rationale for the development of treatments for patients with DN by preventing inflammasome activation.

Metabolic regulators of enigmatic inflammasomes in autoimmune diseases and crosstalk with innate immune receptors

Nucleotide‐binding domain and leucine‐rich repeat receptor (NLR)‐mediated inflammasome activation is important in host response to microbes, danger‐associated molecular patterns (DAMPs) and metabolic disease. Some NLRs have been shown to interact with distinct cell metabolic pathways and cause negative regulation, tumorigenesis and autoimmune disorders, interacting with multiple innate immune receptors to modulate disease. NLR activation is therefore crucial in host response and in the regulation of metabolic pathways that can trigger a wide range of immunometabolic diseases or syndromes. However, the exact mode by which some of the less well‐studied NLR inflammasomes are activated, interact with other metabolites and immune receptors, and the role they play in the progression of metabolic diseases is still not fully elucidated. In this study, we review up‐to‐date evidence regarding NLR function in metabolic pathways and the interplay with other immune receptors involved in GPCR signalling, gut microbiota and the complement system, in order to gain a better understanding of its link to disease processes.

Cannabinoids as Key Regulators of Inflammasome Signaling: A Current Perspective

Inflammasomes are cytoplasmic inflammatory signaling protein complexes that detect microbial materials, sterile inflammatory insults, and certain host-derived elements. Inflammasomes, once activated, promote caspase-1–mediated maturation and secretion of pro-inflammatory cytokines, interleukin (IL)-1β and IL-18, leading to pyroptosis. Current advances in inflammasome research support their involvement in the development of chronic inflammatory disorders in contrast to their role in regulating innate immunity. Cannabis (marijuana) is a natural product obtained from the Cannabis sativa plant, and pharmacologically active ingredients of the plant are referred to as cannabinoids. Cannabinoids and cannabis extracts have recently emerged as promising novel drugs for chronic medical conditions. Growing evidence indicates the potent anti-inflammatory potential of cannabinoids, especially Δ⁹-tetrahydrocannabinol (Δ⁹-THC), cannabidiol (CBD), and synthetic cannabinoids; however, the mechanisms remain unclear. Several attempts have been made to decipher the role of cannabinoids in modulating inflammasome signaling in the etiology of chronic inflammatory diseases. In this review, we discuss recently published evidence on the effect of cannabinoids on inflammasome signaling. We also discuss the contribution of various cannabinoids in human diseases concerning inflammasome regulation. Lastly, in the milieu of coronavirus disease-2019 (COVID-19) pandemic, we confer available evidence linking inflammasome activation to the pathophysiology of COVID-19 suggesting overall, the importance of cannabinoids as possible drugs to target inflammasome activation in or to support the treatment of a variety of human disorders including COVID-19.

Evaluation of Inflammasome Activation in Peripheral Blood Mononuclear Cells of Hemodialysis Treated Patients with Glomerulonephritis

Recently, it has been found that abnormal activation of inflammasomes, the intracellular multiprotein complexes, plays an important role in the pathogenesis and the development of inflammatory diseases. To determine whether the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is involved in chronic inflammatory condition reported in glomerulonephritic- hemodialysis (HD) patients, we investigated the mRNA levels of NLRP3, CASP-1, ASC, IL-1β, IL-18, NLRC4, and P2X7 in human peripheral blood mononuclear cells (PBMCs) collected from 28 glomerulonephritic-HD patients. To confirm the mRNA quantification results, we investigated the IL-1ß content and Caspase 1 activity in serum and PBMC lysates, respectively. Compared with PBMCs derived from healthy subjects, genes encoding proinflammatory cytokines such as IL-1β and IL-18 as well as NLRP3, ASC, CASP-1 were markedly overexpressed in those derived from patients. Moreover, there was no significant difference between the expression level of P2X 7 mRNA in PBMCs isolated from glomerulonephritis-HD patients and controls. The serum level of active IL1-β and cell lysate CASP-1 activity were up-regulated in patients compared to controls. We also revealed that PBMCs isolated from glomerulonephritis-HD patients had elevated mRNA levels of NLRC4 compared to controls, suggesting the priming of NLRC4 inflammasome. These results revealed that the NLRP3-ASC-caspase-1 axis might have a role in increased inflammation severity reported in glomerulonephritic patients undergoing hemodialysis. These findings provide new insights into molecular mechanisms underlying chronic inflammation in HD- glomerulonephritic patients. Additionally, the NLRP3 inflammasome pathway can be attractive as a potential therapeutic target for complication avoidance in HD- glomerulonephritic patients.

Loss of NLRP6 expression increases the severity of acute kidney injury

BACKGROUND

Nlrp6 is a nucleotide-binding oligomerization domain-like receptor (NLR) that forms atypical inflammasomes. Nlrp6 modulates the gut epithelium interaction with the microbiota. However, the expression and function of Nlrp6 in the kidney, a sterile environment, have not been characterized. We explored the role of Nlrp6 in acute kidney injury (AKI).

METHODS

In a transcriptomics array of murine nephrotoxic AKI, Nlrp6 and Naip3 were the only significantly downregulated NLR genes. The functional implications of Nlrp6 downregulation were explored in mice and in cultured murine tubular cells.

RESULTS

Nlrp6 was expressed by healthy murine and human kidney tubular epithelium, and expression was reduced during human kidney injury or murine nephrotoxic AKI induced by cisplatin or a folic acid overdose. Genetic Nlrp6 deficiency resulted in upregulation of kidney extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK) phosphorylation and more severe AKI and kidney inflammation. In cultured tubular cells, Nlrp6 downregulation induced by specific small interfering RNA resulted in upregulation of ERK1/2 and p38 phosphorylation and chemokine messenger RNA expression and downregulation of the nephroprotective gene Klotho. MAPK inhibition prevented the inflammatory response in Nlrp6-deficient cells.

CONCLUSION

Nlrp6 dampens sterile inflammation and has a nephroprotective role during nephrotoxic kidney injury through suppression of MAP kinase activation.

Blockade of anti-dsDNA ameliorates systemic lupus erythematosus in MRL/Faslpr mice through ameliorating inflammation via the PKCδ-NLRC4 axis

Anti-double-stranded DNA (anti-dsDNA) is closely associated with the inflammatory burden in the brain after ischemic stroke. Here, we studied the inflammatory cascade and investigated the mechanisms behind the pro-inflammatory role of dsDNA in systemic lupus erythematosus (SLE). The serum levels of interleukin-1beta (IL-1β) and IL-6 in SLE patients and the corresponding controls were evaluated using ELISA, and the expression level of caspase-1 was evaluated using quantitative real-time polymerase chain reaction (qRT-PCR). We found that the serum levels of IL-1β and IL-6 were increased in the SLE patients. The expression of caspase-1 was upregulated and positively correlated with the levels of pro-inflammatory factors. The level of anti-dsDNA was also elevated and positively correlated with the results for the mean fluorescence intensity (MFI) of caspase-1. Additionally, we evaluated the functions of PRKCD encoding protein kinase c delta (PKCδ) and NLRC4, in vivo, in MRL/Faslpr mice. We found that renal injury was aggravated, and the levels of pro-inflammatory factors were increased in the MRL/Faslpr mice. We also found that increased levels of NLRC4 in the mice exacerbated renal injury and increased the levels of pro-inflammatory factors, whereas inhibition of PKCδ had the opposite results. These findings provide unique perspectives on pathogenesis of SLE and indicate that inhibition of anti-dsDNA could attenuate renal inflammatory burden, representing a promising therapeutic opportunity for SLE.

New Insights into the Mechanisms of Pyroptosis and Implications for Diabetic Kidney Disease

Pyroptosis is one special type of lytic programmed cell death, featured in cell swelling, rupture, secretion of cell contents and remarkable proinflammation effect. In the process of pyroptosis, danger signalling and cellular events are detected by inflammasome, activating caspases and cleaving Gasdermin D (GSDMD), along with the secretion of IL-18 and IL-1β. Pyroptosis can be divided into canonical pathway and non-canonical pathway, and NLRP3 inflammasome is the most important initiator. Diabetic kidney disease (DKD) is one of the most serious microvascular complications in diabetes. Current evidence reported the stimulatory role of hyperglycaemia-induced cellular stress in renal cell pyroptosis, and different signalling pathways have been shown to regulate pyroptosis initiation. Additionally, the inflammation and cellular injury caused by pyroptosis are tightly implicated in DKD progression, aggravating renal fibrosis, glomerular sclerosis and tubular injury. Some registered hypoglycaemia agents exert suppressive activity in pyroptosis regulation pathway. Latest studies also reported some potential approaches to target the pyroptosis pathway, which effectively inhibits renal cell pyroptosis and alleviates DKD in in vivo or in vitro models. Therefore, comprehensively compiling the information associated with pyroptosis regulation in DKD is the main aim of this review, and we try to provide new insights for researchers to dig out more potential therapies of DKD.

Mitochondria-Associated Endoplasmic Reticulum Membranes (MAMs) and Their Prospective Roles in Kidney Disease

Mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) serve as essential hubs for interorganelle communication in eukaryotic cells and play multifunctional roles in various biological pathways. A defect in ER-mitochondria signaling or MAMs dysfunction has pleiotropic effects on a variety of intracellular events, which results in disturbances of the mitochondrial quality control system, Ca2+ dyshomeostasis, apoptosis, ER stress, and inflammasome activation, which all contribute to the onset and progression of kidney disease. Here, we review the structure and molecular compositions of MAMs as well as the experimental methods used to study these interorganellar contact sites. We will specifically summarize the downstream signaling pathways regulated by MAMs, mainly focusing on mitochondrial quality control, oxidative stress, ER-mitochondria Ca2+ crosstalk, apoptosis, inflammasome activation, and ER stress. Finally, we will discuss how alterations in MAMs integrity contribute to the pathogenesis of kidney disease and offer directions for future research.

Tacrolimus ameliorates tubulointerstitial inflammation in diabetic nephropathy via inhibiting the NFATc1/TRPC6 pathway

Tubulointerstitial inflammation is crucial for the progression of diabetic nephropathy (DN), and tubular cells act as a driving force in the inflammatory cascade. Emerging data suggested that tacrolimus (TAC) ameliorates podocyte injury and macrophage infiltration in streptozotocin (STZ) mice. However, the effect of TAC on tubulointerstitial inflammation remains unknown. We found that albuminuria and tubulointerstitial damage improved in db/db mice treated with TAC. Macrophage infiltration and expression of IL‐6, TNF‐α, fibronectin, collagen 1 and cleaved caspase 3 were inhibited as well. In addition, the expression of nuclear factor of activated T cell 1 (NFATc1) and transient receptor potential channel 6 (TRPC6) was up‐regulated in the kidneys of DN patients and correlated with tubular injury and inflammation. The expression of NFATc1 and TRPC6 also increased in the kidneys of db/db mice and HK‐2 cells with high glucose (HG), while TAC inhibited these effects. HG‐induced inflammatory markers and apoptosis were reversed by TAC and NFATc1 siRNA in HK‐2 cells, which was abolished by TRPC6 plasmid. Furthermore, HG‐induced TRPC6 expression was inhibited by NFATc1 siRNA, while NFATc1 nuclear translocation was inhibited by TAC, but was restored by TRPC6 plasmid in HK‐2 cells under HG conditions. These findings suggest that TAC ameliorates tubulointerstitial inflammation in DN through NFATc1/TRPC6 feedback loop.

Inflammasome activation in podocytes: a new mechanism of glomerular diseases

INTRODUCTION

Inflammasome is a multi-protein complex which is an important constituent of innate immunity. It mainly consists of three parts, apoptosis-associated speck-like protein containing caspase recruitment domain (ASC), caspase protease, and a NOD-like receptor (NLR) family protein (such as NLRP1) or an HIN200 family protein (such as AIM2). Inflammasome is widely studied in many autoimmune diseases and chronic inflammatory reactions, such as familial periodic autoinflammatory response, type 2 diabetes, Alzheimer's disease, and atherosclerosis. Activation of inflammasome in the kidney has been widely reported in glomerular and tubular-interstitial diseases. Podocytes play a critical role in maintaining the normal structure and function of glomerular filtration barrier. Recently, it has been demonstrated that podocytes, as a group of renal residential cells, can express all necessary components of NLRP3 inflammasome, which is activated and contribute to inflammatory response in the local kidney.

METHODS

Literature review was conducted to further summarize current evidence of podocyte NLRP3 inflammasome activation and related molecular mechanisms under different disease conditions.

RESULTS

Podocytes are a key component of the glomerular filtration barrier, and the loss of podocyte regeneration is a major limiting factor in the recovery of proteinuria. Through a more comprehensive study of inflammasome in podocytes, it will provide new targets and possibilities for the treatment of kidney diseases.

Roles of pattern recognition receptors in diabetic nephropathy

Diabetic nephropathy (DN) is currently the most common complication of diabetes. It is considered to be one of the leading causes of end-stage renal disease (ESRD) and affects many diabetic patients. The pathogenesis of DN is extremely complex and has not yet been clarified; however, in recent years, increasing evidence has shown the important role of innate immunity in DN pathogenesis. Pattern recognition receptors (PRRs) are important components of the innate immune system and have a significant impact on the occurrence and development of DN. In this review, we classify PRRs into secretory, endocytic, and signal transduction PRRs according to the relationship between the PRRs and subcellular compartments. PRRs can recognize related pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs), thus triggering a series of inflammatory responses, promoting renal fibrosis, and finally causing renal impairment. In this review, we describe the proposed role of each type of PRRs in the development and progression of DN.

Research Progress on the Role of Inflammasomes in Kidney Disease

Inflammasomes are multimeric complexes composed of cytoplasmic sensors, apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC or PYCARD), and procaspase-1 and play roles in regulating caspase-dependent inflammation and cell death. Inflammasomes are assembled by sensing pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) and initiate inflammatory responses by activating caspase-1. Activated caspase-1 promotes the release of the inflammatory cytokines interleukin-1β (IL-1β) and IL-18 and eventually induces pyroptosis. Inflammasomes are closely related to kidney diseases. In particular, the NLRP3 (NACHT, LRR, and PYD domain-containing protein 3) inflammasome has been shown to cause acute and chronic kidney diseases by regulating canonical and noncanonical mechanisms of inflammation. Small-molecule inhibitors that target NLRP3 and other components of the inflammasome are potential options for the treatment of kidney-related diseases such as diabetic nephropathy. This article will focus on the research progress on inflammasomes and the key pathogenic roles of inflammasomes in the development and progression of kidney diseases and explore the potential of this intracellular inflammation to further prevent or block the development of the kidney disease.

Effect and Regulation of the NLRP3 Inflammasome During Renal Fibrosis

Renal fibrosis is a common pathological process where certain primary or secondary kidney diseases can continue to progress to the end-stage of the kidney disease; however, the molecular mechanisms underlying renal fibrosis remain unclear. Recently, research focusing on examining the function of inflammasomes has attracted a great deal of attention, and data derived from these research projects have increased our understanding of the effects and regulation of inflammasomes during renal fibrosis. Based on this, the present review summarizes recent findings in regard to NLRP3 inflammasome functions during various kidney diseases, and these findings indicate that the NLRP3 inflammasome not only mediates the inflammatory response but is also associated with pyroptosis, mitochondrial regulation, and myofibroblast differentiation during renal fibrosis. These novel findings provide us with a more in-depth understanding of the pathogenesis of renal fibrosis and will aid in the identification of new targets that can be used for the prevention and treatment of this disease.

Hyperglycemia-induced inflamm-aging accelerates gingival senescence via NLRC4 phosphorylation

Inflamm-aging was recently affiliated with the progression of diabetic complications. Local cellular senescence together with senescence-associated secretory phenotype (SASP) are the main contributors to inflamm-aging. However, little is known about their involvement in diabetic periodontitis. Gingiva is the first line of host defense in the periodontium, and macrophages are key SASP-carrying cells. Here, we explored the molecular mechanism by which hyperglycemia drives the inflamm-aging in the gingival tissue of diabetic mice and macrophages. We demonstrated that hyperglycemia increased the infiltrated macrophage senescence in gingival tissue of diabetic mice. Simultaneously, hyperglycemia elevated the local burden of senescent cells in gingival tissue and induced the serum secretion of SASP factors in vivo Moreover, in vitro, high glucose induced macrophage senescence and SASP factors secretion through phosphorylation of NLRC4, which further stimulated the NF-κB/Caspase-1 cascade via an IRF8-dependent pathway. Deletion of NLRC4 or IRF8 abolished hyperglycemia-induced cellular senescence and SASP in macrophages. In addition, we found that treatment with metformin inhibited NLRC4 phosphorylation and remarkably decreased cellular senescence and SASP in the context of hyperglycemia. Our data demonstrated that hyperglycemia induces the development of inflamm-aging in gingival tissue and suggested that NLRC4 is a potential target for treatment of diabetes-associated complications.

Roles of Inflammasomes in Inflammatory Kidney Diseases

The immune system has a central role in eliminating detrimental factors, by frequently launching inflammatory responses towards pathogen infection and inner danger signal outbreak. Acute and chronic inflammatory responses are critical determinants for consequences of kidney diseases, in which inflammasomes were inevitably involved. Inflammasomes are closely linked to many kidney diseases such as acute kidney injury and chronic kidney diseases. Inflammasomes are macromolecules consisting of multiple proteins, and their formation initiates the cleavage of procaspase-1, resulting in the activation of gasdermin D as well as the maturation and release of interleukin-1β and IL-18, leading to pyroptosis. Here, we discuss the mechanism in which inflammasomes occur, as well as their roles in inflammatory kidney diseases, in order to shed light for discovering new therapeutical targets for the prevention and treatment of inflammatory kidney diseases and consequent end-stage renal disease.

Inflammasome inhibitors: promising therapeutic approaches against cancer

Inflammation has long been accepted as a key component of carcinogenesis. During inflammation, inflammasomes are potent contributors to the activation of inflammatory cytokines that lead to an inflammatory cascade. Considering the contributing role of inflammasomes in cancer progression, inflammasome inhibitors seem to have a promising future in cancer treatment and prevention. Here, we summarize the structures and signaling pathways of inflammasomes and detail some inflammasome inhibitors used to treat various forms of cancer, which we expect to be used in novel anticancer approaches. However, the practical application of inflammasome inhibitors is limited in regard to specific types of cancer, and the associated clinical trials have not yet been completed. Therefore, additional studies are required to explore more innovative and effective medicines for future clinical treatment of cancer.

Metabolic regulation of inflammasomes in inflammation

Inflammasome activation and subsequent inflammatory cytokine secretion are essential for innate immune defence against multiple stimuli and are regarded as a link to adaptive immune responses. Dysfunction of inflammasome activation has been discovered at the onset or progression of infectious diseases, autoimmune diseases and cancer, all of which are also associated with metabolic factors. Furthermore, many studies concerning the metabolic regulation of inflammasome activation have emerged in recent years, especially regarding the activity of the NLRP3 inflammasome under metabolic reprogramming. In this review, we discuss the molecular mechanisms of the interactions between metabolic pathways and inflammasome activation, which exerts further important effects on various diseases.

Disulfide-bond A oxidoreductase-like protein protects against ectopic fat deposition and lipid-related kidney damage in diabetic nephropathy

Ectopic fat deposition (EFD) in the kidney has been shown to play a causal role in diabetic nephropathy; however, the mechanism underlying EFD remains elusive. By transcriptome analysis, we found decreased expression levels of disulfide-bond A oxidoreductase-like protein (DsbA-L) in the kidneys of diabetic mice (induced by high-fat diet plus Streptozotocin) compared with control mice. Increased expression of adipocyte differentiation-related protein and abnormal levels of collagen I, fibronectin, and phosphorylated 5'AMP-activated kinase (p-AMPK), adipose triglyceride lipase (p-ATGL), and HMG-CoA reductase (p-HMGCR) were also observed in diabetic mice. These alterations were accompanied by deposition of lipid droplets in the kidney, and were more pronounced in diabetic DsbA-L knockout mice. In vitro, overexpression of DsbA-L ameliorated high glucose-induced intracellular lipid droplet deposition in a human proximal tubular cell line, and DsbA-L siRNA aggravated lipid droplet deposition and reduced the levels of p-AMPK, p-ATGL, and p-HMGCR. High glucose and palmitic acid treatment enhanced the expression of interleukin-1β and interleukin-18; these enhancements were further increased after treatment with DsbA-L siRNA but alleviated by co-treatment with an AMPK activator. In kidney biopsy tissue from patients with diabetic nephropathy, DsbA-L expression was negatively correlated with EFD and tubular damage. Collectively, these results suggest that DsbA-L has a protective role against EFD and lipid-related kidney damage in diabetic nephropathy. Activation of the AMPK pathway is a potential mechanism underlying DsbA-L action in the kidney.

NLRC4 suppresses IL-17A-mediated neutrophil-dependent host defense through upregulation of IL-18 and induction of necroptosis during Gram-positive pneumonia

Gram-positive pathogens, including Staphylococcus aureus, cause necrotizing pneumonia. The central feature of S. aureus pneumonia is toxin-induced necroptosis of immune and resident cells, which impedes host defense. However, the role of the NLRC4 in the lung following S. aureus infection remains elusive. Here, we demonstrate that S. aureus activates the NLRC4 to drive necroptosis and IL-18 production, which impaired IL-17A-dependent neutrophil-mediated host susceptibility. In particular, Nlrc4^-/- mice exhibit reduced necroptosis, enhanced neutrophil influx into the lungs, decreased bacterial burden, and improved host survival. Loss of NLRC4 signaling in both hematopoietic and non-hematopoietic cells contributes to the host protection against S. aureus pneumonia. Secretion of IL-17A by γδ T cells is essential for neutrophil recruitment into the lungs of Nlrc4^-/- mice following infection. Moreover, treatment of wild-type mice with necroptosis inhibitors or genetic ablation of MLKL and IL-18 improves host defense against S. aureus infection, which is associated with increased IL-17A+γδ T cells and neutrophils. Taken together, these novel findings reveal that S. aureus activates the NLRC4 to dampen IL-17A-dependent neutrophil accumulation through induction of necroptosis and IL-18. Thus, modulating the function of the NLRC4 may be an attractive therapeutic approach for treating S. aureus infections.

Piperine ameliorated lupus nephritis by targeting AMPK-mediated activation of NLRP3 inflammasome

BACKGROUND

Lupus nephritis (LN) is a leading cause of mortality. The activation of NLRP3 inflammasome contributed to LN development and thus became a therapeutic target. Here we assessed the therapeutic potential of piperine, a bioactive compound known to target NLRP3 inflammasome, on LN development both in vivo and in vitro.

METHODS

LN was induced in BALB/c mice via intraperitoneal injection of pristane. Upon treatment with increasing doses of piperine, we assessed renal lesions, measured serum levels of pro-inflammatory cytokines, and examined expressions of key components of NLRP3 inflammasome in kidney. To explore the molecular mechanisms, we treated the proximal tubular epithelial HK-2 cells with lipopolysaccharide (LPS) and ATP, and examined the effects of piperine on pyroptosis and the activation of NLRP3 inflammasome. Furthermore, we assessed the significance of AMPK signaling in piperine functions in HK-2 cells.

RESULTS

In pristane-injected mice, piperine significantly ameliorated LN development in a dose-dependent manner, which was associated with the inhibition of NLRP3 inflammasome and the reduction of serum IL-1β, but not of IL-18 level. In HK-2 cells, piperine potently inhibited pyroptosis and the activation of NLRP3 inflammasome in response to LPS + ATP. The effects of piperine were mediated by blocking AMPK activation, and the AMPK agonist metformin bypassed the activities of piperine, and resumed pyroptosis as well as the activation on NLRP3 inflammasome.

CONCLUSIONS

By targeting AMPK, piperine significantly suppressed the activation of NLRP3 inflammasome, inhibited the release of pro-inflammatory cytokines, blocked the pyroptosis of tubular epithelial cells, and thus suppressed the development of LN.

A brain in flame; do inflammasomes and pyroptosis influence stroke pathology?

Stroke is one of the leading causes of death and disability worldwide. Inflammation plays a key role across the time course of stroke, from onset to the post-injury reparative phase days to months later. Several regulatory molecules are implicated in inflammation, but the most established inflammatory mediator of acute brain injury is the cytokine interleukin-1. Interleukin-1 is regulated by large, macromolecular complexes called inflammasomes, which play a central role in cytokine release and cell death. In this review we highlight recent advances in inflammasome research and propose key roles for inflammasome components in the progression of stroke damage.

Function of NLRP3 in the Pathogenesis and Development of Diabetic Nephropathy

Background

The aim of this research was to study the function of NLRP3 in the pathogenesis and development of diabetic nephropathy (DN).

Material/Methods

We compared the expression of NLRP3-related protein in human glomerular mesangial cells under high glucose conditions at different times and in rats with DN of different ages. We also compared changes in IL-18 and IL-1β expression levels at different stages of DN.

Results

After six hours, 12 hours, and 24 hours of high glucose stimulation, the secretion of IL-1β in human glomerular mesangial cells, compared to unstimulated cells, was 1.85-fold, 3.04-fold, and 4.14-fold; the expression of NLRP3 increased by 2.20-fold, 4.62-fold, and 8.32-fold; and the expression of caspase-1 was increased by 1.60-fold, 2.72-fold, and 3.67-fold. The expression levels of nephrin in eight-week-old and 12-week-old DN rats compared to 4-week rats were 49.60% and 21.20%, respectively. The IL-1β levels compared to four-week DN rats were 2.57-fold and 4.17-fold, respectively; NLRP3 levels were 1.29-fold and 2.17-fold respectively, and caspase-1 levels were 3.37-fold and 4.16-fold, respectively. The serum levels of IL-18 and IL-1β in the DN group were the highest at 218.53±30.69 pg/mL and 62.47±9.36 pg/mL, respectively; followed by the mild DN group at 177.07±32.88 pg/mL and 28.13±5.37 pg/mL, respectively, with the diabetic mellitus (DM) group having the lowest levels at 141.47±9.49 pg/mL and 15.53±3.26 pg/mL, respectively. The healthy control group levels were 99.40±22.72 pg/mL and 12.40±5.08 pg/mL, respectively.

Conclusions

NLRP3 and high glucose activation may participate in the occurrence and development of DN by mediating the inflammatory response.