An inflammasome-independent role for epithelial-expressed Nlrp3 in renal ischemia-reperfusion injury

Intracerebroventricular infusion of secretoneurin inhibits neuronal NLRP3-Apoptosis pathway and preserves learning and memory after cerebral ischemia

Transient global cerebral ischemia (GCI) results in delayed neuronal death, primarily apoptosis, in the hippocampal CA1 subregion, which leads to severe cognitive deficits. While therapeutic hypothermia is an approved treatment for patients following cardiac arrest, it is associated with various adverse effects. Secretoneurin (SN) is an evolutionarily conserved neuropeptide generated in the brain, adrenal medulla and other endocrine tissues. In this study, SN was infused into the rat brain by intracerebroventricular injection 1 day after GCI, and we demonstrated that SN could significantly preserve spatial learning and memory in the Barnes maze tasks examined on days 14-17 after GCI. To further investigate underlying pathways involved, we demonstrated that, on day 5 after GCI, SN could significantly inhibit GCI-induced expression levels of Apoptosis Inducing Factor (AIF) and cleaved-PARP1, as well as neuronal apoptosis and synaptic loss in the hippocampal CA1 region. Additionally, SN could attenuate GCI-induced activation of both caspase-1 and caspase-3, and the levels of pro-inflammatory cytokines IL-1β and IL-18 in the CA1 region. Mechanically, we observed that treatment with SN effectively inhibited NLRP3 protein elevation and the bindings of NLRP3-ASC and ASC-caspase-1 in hippocampal neurons after GCI. In summary, our data indicate that SN could effectively attenuate NLRP3 inflammasome formation, as well as the activation of caspase-1 and -3, the production of pro-inflammatory cytokines, and ultimately the neuronal apoptotic loss induced by GCI. Potential neuronal pyroptosis, or caspase-1-dependent cell death, could also be involved in ischemic neuronal death, which needs further investigation.

Cell death induced by acute renal injury: a perspective on the contributions of accidental and programmed cell death

The involvement of cell death in acute kidney injury (AKI) is linked to multiple factors including energy depletion, electrolyte imbalance, reactive oxygen species, inflammation, mitochondrial dysfunction, and activation of several cell death pathway components. Since our review in 2003, discussing the relative contributions of apoptosis and necrosis, several other forms of cell death have been identified and are shown to contribute to AKI. Currently, these various forms of cell death can be fundamentally divided into accidental cell death and regulated or programmed cell death based on functional aspects. Several death initiator and effector molecules switch molecules that may act as signaling components triggering either death or protective mechanisms or alternate cell death pathways have been identified as part of the machinery. Intriguingly, several of these cell death pathways share components and signaling pathways suggesting complementary or compensatory functions. Thus, defining the cross talk between distinct cell death pathways and identifying the unique molecular effectors for each type of cell death may be required to develop novel strategies to prevent cell death. Furthermore, depending on the multiple forms of cell death simultaneously induced in different AKI settings, strategies for combination therapies that block multiple cell death pathways need to be developed to completely prevent injury, cell death, and renal function. This review highlights the various cell death pathways, cross talk, and interactions between different cell death modalities in AKI.

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

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

Renal macrophages and NLRP3 inflammasomes in kidney diseases and therapeutics

Macrophages are exceptionally diversified cell types and perform unique features and functions when exposed to different stimuli within the specific microenvironment of various kidney diseases. In instances of kidney tissue necrosis or infection, specific patterns associated with damage or pathogens prompt the development of pro-inflammatory macrophages (M1). These M1 macrophages contribute to exacerbating tissue damage, inflammation, and eventual fibrosis. Conversely, anti-inflammatory macrophages (M2) arise in the same circumstances, contributing to kidney repair and regeneration processes. Impaired tissue repair causes fibrosis, and hence macrophages play a protective and pathogenic role. In response to harmful stimuli within the body, inflammasomes, complex assemblies of multiple proteins, assume a pivotal function in innate immunity. The initiation of inflammasomes triggers the activation of caspase 1, which in turn facilitates the maturation of cytokines, inflammation, and cell death. Macrophages in the kidneys possess the complete elements of the NLRP3 inflammasome, including NLRP3, ASC, and pro-caspase-1. When the NLRP3 inflammasomes are activated, it triggers the activation of caspase-1, resulting in the release of mature proinflammatory cytokines (IL)-1β and IL-18 and cleavage of Gasdermin D (GSDMD). This activation process therefore then induces pyroptosis, leading to renal inflammation, cell death, and renal dysfunction. The NLRP3-ASC-caspase-1-IL-1β-IL-18 pathway has been identified as a factor in the development of the pathophysiology of numerous kidney diseases. In this review, we explore current progress in understanding macrophage behavior concerning inflammation, injury, and fibrosis in kidneys. Emphasizing the pivotal role of activated macrophages in both the advancement and recovery phases of renal diseases, the article delves into potential strategies to modify macrophage functionality and it also discusses emerging approaches to selectively target NLRP3 inflammasomes and their signaling components within the kidney, aiming to facilitate the healing process in kidney diseases.

Connexin32 gap junction channels deliver miR155-3p to mediate pyroptosis in renal ischemia-reperfusion injury

OBJECTIVES

To explore whether the gap junction (GJ) composed by connexin32(Cx32) mediated pyroptosis in renal ischemia-reperfusion(I/R) injury via transmitting miR155-3p, with aim to provide new strategies for the prevention and treatment of acute kidney injury (AKI) after renal I/R.

METHODS

8-10 weeks of male C57BL/ 6 wild-type mice and Cx32 knockdown mice were divided into two groups respectively: control group and renal I/R group. MCC950 (50 mg/kg. ip.) was used to inhibit NLRP3 in vivo. Human kidney tubular epithelial cells (HK - 2) and rat kidney tubular epithelial cells (NRK-52E) were divided into high-density group and low-density group, and treated with hypoxia reoxygenation (H/R) to mimic I/R. The siRNA and plasmid of Cx32, mimic and inhibitor of miR155-3p were transfected into HK - 2 cells respectively. Kidney pathological and functional injuries were measured. Western Blot and immunofluorescent staining were used to observe the expression of NLRP3, GSDMD, GSDMD-N, IL - 18, and mature IL-18. The secretion of IL-18 and IL-1β in serum, kidney tissue and cells supernatant were detected by enzyme-linked immuno sorbent assay (ELISA) kit, and the expression of NLPR3 and miR155-3p were detected by RT-qPCR and fluorescence in situ hybridization (FISH).

RESULTS

Tubular pyroptosis were found to promote AKI after I/R in vivo and Cx32-GJ regulated pyroptosis by affecting the expression of miR155-3p after renal I/R injury. In vitro, H/R could lead to pyroptosis in HK-2 and NRK-52E cells. When the GJ channels were not formed, and Cx32 was inhibited or knockdown, the expression of miR155-3p was significantly reduced and the pyroptosis was obviously inhibited, leading to the reduction of injury and the increase of survival rate. Moreover, regulating the level of miR155-3p could affect survival rate and pyroptosis in vitro after H/R.

CONCLUSIONS

The GJ channels composed of Cx32 regulated tubular pyroptosis in renal I/R injury by transmitting miR155-3p. Inhibition of Cx32 could reduce the level of miR155-3p further to inhibit pyroptosis, leading to alleviation of renal I/R injury which provided a new strategy for preventing the occurrence of AKI. Video Abstract.

Insights into the Therapeutic uses of Plant Derive Phytocompounds onDiabetic Nephropathy

Diabetic nephropathy (DN) is one of the primary consequences of diabetes mellitus, affecting many people worldwide and is the main cause of death under the age of sixty. Reactive oxygen species (ROS) production rises during hyperglycemia and is crucial to the development of diabetic complications. Advanced glycation end products (AGEs) are produced excessively in a diabetic state and are accumulated in the kidney, where they change renal architecture and impair renal function. Another important targeted pathway for the formation of DN includes nuclear factor kappa-B (NF-kB), Nuclear factor E2-related factor 2 (Nrf2), NLR family pyrin domain containing 3 (NLRP3), protein kinase B/mammalian target of rapamycin (Akt/mTOR), and autophagy. About 40% of individuals with diabetes eventually acquire diabetic kidney disease and end-stage renal disease that needs hemodialysis, peritoneal dialysis, or kidney transplantation to survive. The current state of acceptable therapy for this kidney ailment is limited. The studies revealed that some naturally occurring bioactive substances might shield the kidney by controlling oxidative stress, renal fibrosis, inflammation, and autophagy. In order to provide new potential therapeutic lead bioactive compounds for contemporary drug discovery and clinical management of DN, this review was designed to examine the various mechanistic pathways by which conventional plants derive phytocompounds that are effective for the control and treatment of DN.

Inflammasome pathway in kidney transplantation

Kidney transplantation is the best available renal replacement therapy for patients with end-stage kidney disease and is associated with better quality of life and patient survival compared with dialysis. However, despite the significant technical and pharmaceutical advances in this field, kidney transplant recipients are still characterized by reduced long-term graft survival. In fact, almost half of the patients lose their allograft after 15-20 years. Most of the conditions leading to graft loss are triggered by the activation of a large immune-inflammatory machinery. In this context, several inflammatory markers have been identified, and the deregulation of the inflammasome (NLRP3, NLRP1, NLRC4, AIM2), a multiprotein complex activated by either whole pathogens (including fungi, bacteria, and viruses) or host-derived molecules, seems to play a pivotal pathogenetic role. However, the biological mechanisms leading to inflammasome activation in patients developing post-transplant complications (including, ischemia-reperfusion injury, rejections, infections) are still largely unrecognized, and only a few research reports, reviewed in this manuscript, have addressed the association between abnormal activation of this pathway and the onset/development of major clinical effects. Finally, the regulation of the inflammasome machinery could represent in future a valuable therapeutic target in kidney transplantation.

Canonical and non-canonical functions of NLRP3

BACKGROUND

Since its discovery, NLRP3 is almost never separated from its major role in the protein complex it forms with ASC, NEK7 and Caspase-1, the inflammasome. This key component of the innate immune response mediates the secretion of proinflammatory cytokines IL-1β and IL-18 involved in immune response to microbial infection and cellular damage. However, NLRP3 has also other functions that do not involve the inflammasome assembly nor the innate immune response. These non-canonical functions have been poorly studied. Nevertheless, NLRP3 is associated with different kind of diseases probably through its inflammasome dependent function as through its inflammasome independent functions.

AIM OF THE REVIEW

The study and understanding of the canonical and non-canonical functions of NLRP3 can help to better understand its involvement in various pathologies. In parallel, the description of the mechanisms of action and regulation of its various functions, can allow the identification of new therapeutic strategies.

KEY SCIENTIFIC CONCEPTS OF THE REVIEW

NLRP3 functions have mainly been studied in the context of the inflammasome, in myeloid cells and in totally deficient transgenic mice. However, for several year, the work of different teams has proven that NLRP3 is also expressed in other cell types where it has functions that are independent of the inflammasome. If these studies suggest that NLRP3 could play different roles in the cytoplasm or the nucleus of the cells, the mechanisms underlying NLRP3 non-canonical functions remain unclear. This is why we propose in this review an inventory of the canonical and non-canonical functions of NLRP3 and their impact in different pathologies.

Mitochondrial antiviral signaling protein: a potential therapeutic target in renal disease

Mitochondrial antiviral signaling protein (MAVS) is a key innate immune adaptor on the outer mitochondrial membrane that acts as a switch in the immune signal transduction response to viral infections. Some studies have reported that MAVS mediates NF-κB and type I interferon signaling during viral infection and is also required for optimal NLRP3 inflammasome activity. Recent studies have reported that MAVS is involved in various cancers, systemic lupus erythematosus, kidney diseases, and cardiovascular diseases. Herein, we summarize the structure, activation, pathophysiological roles, and MAVS-based therapies for renal diseases. This review provides novel insights into MAVS's role and therapeutic potential in the pathogenesis of renal diseases.

Psoralen Alleviates Renal Fibrosis by Attenuating Inflammasome-Dependent NLRP3 Activation and Epithelial-Mesenchymal Transition in a Mouse Unilateral Ureteral Obstruction Model

The role of psoralen (PS), a major active component extracted from Psoralea corylifolia L. seed, in renal fibrosis is still unclear. Thus, the objective of this study was to evaluate the effects of PS on the development and progression of renal fibrosis induced by unilateral ureteral obstruction (UUO) in a mouse model. Mice were divided into four groups: PS (20 mg/kg, i.g., n = 5), PS + sham (n = 5), UUO (n = 10), and PS + UUO (n = 10). PS was intragastrically administered 24 h before UUO and continued afterwards for 7 days. All mice were killed 7 days post UUO. Severe tubular atrophy, tubular injury, and tubulointerstitial fibrosis (TIF) were significantly developed in UUO mice. A higher expression of transforming growth factor-β1 (TGF-β1) was accompanied by elevated levels of α-smooth muscle actin (α-SMA) and phosphorylated Smad2/3 (pSmad2/3) at 7 days post UUO. However, PS treatment reduced tubular injury, interstitial fibrosis, and the expression levels of TGF-β1, α-SMA, and pSmad2/3. Furthermore, the levels of macrophages (represented by F4/80 positive cells) and the inflammasome, reflected by inflammasome markers such as nucleotide-binding and oligomerization domain-like receptors protein 3 (NLRP3) and cleaved caspase1 (cCASP-1), were significantly decreased by PS treatment. These results suggest that PS merits further exploration as a therapeutic agent in the management of chronic kidney disease (CKD).

The Interplay of Autophagy and Oxidative Stress in the Kidney: What Do We Know?

BACKGROUND

Autophagy, as an indispensable metabolism, plays pivotal roles in maintaining intracellular homeostasis. Nutritional stress, amino acid deficiency, oxidative stress, and hypoxia can trigger its initiation. Oxidative stress in the kidney activates essential signal molecules, like mammalian target of rapamycin (mTOR), adenosine monophosphate-activated protein kinase (AMPK), and silent mating-type information regulation 2 homolog-1 (SIRT1), to stimulate autophagy, ultimately leading to degradation of intracellular oxidative substances and damaged organelles. Growing evidence suggests that autophagy protects the kidney from oxidative stress during acute ischemic kidney injury, chronic kidney disease, and even aging.

SUMMARY

This review emphasizes the cross talk between reactive oxygen species (ROS) signaling pathways and autophagy during renal homeostasis and chronic kidney disease according to the current latest research and provides therapeutic targets during kidney disorders by adjusting autophagy and suppressing oxidative stress.

KEY MESSAGES

ROS arise through an imbalance of oxidation and antioxidant defense mechanisms, leading to impaired cellular and organ function. Targeting the overproduction of ROS and reactive nitrogen species, reducing the antioxidant enzyme activity and the recovery of the prooxidative-antioxidative balance provide novel therapeutic regimens to contribute to recovery in acute and chronic renal failure. Although, in recent years, great progress has been made in understanding the molecular mechanisms of oxidative stress and autophagy in acute and chronic renal failure, the focus on clinical therapies is still in its infancy. The growing number of studies on the interactive mechanisms of oxidative stress-mediated autophagy will be of great importance for the future treatment and prevention of kidney diseases.

Acid-sensing ion channel 1a exacerbates renal ischemia-reperfusion injury through the NF-κB/NLRP3 inflammasome pathway

Ischemia-reperfusion injury (IRI) is the main cause of acute kidney injury (AKI), and there is no effective therapy. Microenvironmental acidification is generally observed in ischemic tissues. Acid-sensing ion channel 1a (ASIC1a) can be activated by a decrease in extracellular pH which mediates neuronal IRI. Our previous study demonstrated that, ASIC1a inhibition alleviates renal IRI. However, the underlying mechanisms have not been fully elucidated. In this study, we determined that renal tubule-specific deletion of ASIC1a in mice (ASIC1afl/fl/CDH16cre) attenuated renal IRI, and reduced the expression of NLRP3, ASC, cleaved-caspase-1, GSDMD-N, and IL-1β. Consistent with these in vivo results, inhibition of ASIC1a by the specific inhibitor PcTx-1 protected HK-2 cells from hypoxia/reoxygenation (H/R) injury, and suppressed H/R-induced NLRP3 inflammasome activation. Mechanistically, the activation of ASIC1a by either IRI or H/R induced the phosphorylation of NF-κB p65, which translocates to the nucleus and promotes the transcription of NLRP3 and pro-IL-1β. Blocking NF-κB by treatment with BAY 11-7082 validated the roles of H/R and acidosis in NLRP3 inflammasome activation. This further confirmed that ASIC1a promotes NLRP3 inflammasome activation, which requires the NF-κB pathway. In conclusion, our study suggests that ASIC1a contributes to renal IRI by affecting the NF-κB/NLRP3 inflammasome pathway. Therefore, ASIC1a may be a potential therapeutic target for AKI. KEY MESSAGES: Knockout of ASIC1a attenuated renal ischemia-reperfusion injury. ASIC1a promoted the NF-κB pathway and NLRP3 inflammasome activation. Inhibition of the NF-κB mitigated the NLRP3 inflammasome activation induced by ASIC1a.

Decipher the Immunopathological Mechanisms and Set Up Potential Therapeutic Strategies for Patients with Lupus Nephritis

Lupus nephritis (LN) is one of the most severe complications in patients with systemic lupus erythematosus (SLE). Traditionally, LN is regarded as an immune complex (IC) deposition disease led by dsDNA-anti-dsDNA-complement interactions in the subendothelial and/or subepithelial basement membrane of glomeruli to cause inflammation. The activated complements in the IC act as chemoattractants to chemically attract both innate and adaptive immune cells to the kidney tissues, causing inflammatory reactions. However, recent investigations have unveiled that not only the infiltrating immune-related cells, but resident kidney cells, including glomerular mesangial cells, podocytes, macrophage-like cells, tubular epithelial cells and endothelial cells, may also actively participate in the inflammatory and immunological reactions in the kidney. Furthermore, the adaptive immune cells that are infiltrated are genetically restricted to autoimmune predilection. The autoantibodies commonly found in SLE, including anti-dsDNA, are cross-reacting with not only a broad spectrum of chromatin substances, but also extracellular matrix components, including α-actinin, annexin II, laminin, collagen III and IV, and heparan sulfate proteoglycan. Besides, the glycosylation on the Fab portion of IgG anti-dsDNA antibodies can also affect the pathogenic properties of the autoantibodies in that α-2,6-sialylation alleviates, whereas fucosylation aggravates their nephritogenic activity. Some of the coexisting autoantibodies, including anti-cardiolipin, anti-C1q, anti-ribosomal P autoantibodies, may also enhance the pathogenic role of anti-dsDNA antibodies. In clinical practice, the identification of useful biomarkers for diagnosing, monitoring, and following up on LN is quite important for its treatments. The development of a more specific therapeutic strategy to target the pathogenic factors of LN is also critical. We will discuss these issues in detail in the present article.

Risk of Major Cardiovascular Disease after Exposure to Contrast Media: A Nationwide Population-Based Cohort Study on Dialysis Patients

Contrast associated kidney injury is caused by side effects of iodinated contrast media (ICM), including inflammation. Chronic inflammation among dialysis patient contributes to atherosclerosis, which leads to simultaneous conditions of the kidney, brain, and vasculature. Data to investigate the pathologic effects of ICM on cardiovascular complications in dialysis patients are lacking. Dialysis patients who had been exposed to ICM from computed tomography (ICM-CT) were allocated as the ICM-CT cohort (N = 3751), whereas dialysis patients without ICM exposure were randomly allocated as the non-ICM cohort (N = 17,196). Furthermore, 540 pairs were selected for analyses through propensity score-matching in terms of age, sex, comorbidities, dialysis vintage, and index date. During a median follow-up of 10.3 years, ICM-CT cohort had significantly higher risks in the following, compared with non-ICM cohort: all-cause mortality (adjusted hazard ratio [aHR], 1.36; 95% confidence interval [CI], 1.26-1.47), cardiovascular events (aHR,1.67; 95% CI, 1.39-2.01), acute coronary syndrome (adjusted HR: 2.92; 95% CI, 1.72-4.94), sudden cardiac arrest (aHR, 1.69; 95% CI, 0.90-3.18), heart failure (aHR, 1.71; 95% CI,1.28-2.27), and stroke (aHR, 1.84; 95% CI,1.45-2.35). The proinflammatory ICM is significantly associated with an increased risk of major cardiovascular events in patients on dialysis.

Caspase-1 and the inflammasome promote polycystic kidney disease progression

We and others have previously shown that the presence of renal innate immune cells can promote polycystic kidney disease (PKD) progression. In this study, we examined the influence of the inflammasome, a key part of the innate immune system, on PKD. The inflammasome is a system of molecular sensors, receptors, and scaffolds that responds to stimuli like cellular damage or microbes by activating Caspase-1, and generating critical mediators of the inflammatory milieu, including IL-1β and IL-18. We provide evidence that the inflammasome is primed in PKD, as multiple inflammasome sensors were upregulated in cystic kidneys from human ADPKD patients, as well as in kidneys from both orthologous (PKD1 RC/RC or RC/RC) and non-orthologous (jck) mouse models of PKD. Further, we demonstrate that the inflammasome is activated in female RC/RC mice kidneys, and this activation occurs in renal leukocytes, primarily in CD11c+ cells. Knock-out of Casp1, the gene encoding Caspase-1, in the RC/RC mice significantly restrained cystic disease progression in female mice, implying sex-specific differences in the renal immune environment. RNAseq analysis implicated the promotion of MYC/YAP pathways as a mechanism underlying the pro-cystic effects of the Caspase-1/inflammasome in females. Finally, treatment of RC/RC mice with hydroxychloroquine, a widely used immunomodulatory drug that has been shown to inhibit the inflammasome, protected renal function specifically in females and restrained cyst enlargement in both male and female RC/RC mice. Collectively, these results provide evidence for the first time that the activated Caspase-1/inflammasome promotes cyst expansion and disease progression in PKD, particularly in females. Moreover, the data suggest that this innate immune pathway may be a relevant target for therapy in PKD.

NLRP3 inflammasome: A potential therapeutic target to minimize renal ischemia/reperfusion injury during transplantation

Renal transplantation is currently the best treatment option for patients with end-stage kidney disease. Ischemia/reperfusion injury (IRI), which is an inevitable event during renal transplantation, has a profound impact on the function of transplanted kidneys. It has been well demonstrated that innate immune system plays an important role in the process of renal IRI. As a critical component of innate immune system, Nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome has received great attention from scientific community over the past decade. The main function of NLRP3 inflammasome is mediating activation of caspase-1 and maturation of interleukin (IL)-1β and IL-18. In this review, we summarize the associated molecular signaling events about NLRP3 inflammasome in renal IRI, and highlight the possibility of targeting NLRP3 inflammasome to minimize renal IRI during transplantation.

Anti-inflammatory potential of stevia residue extract against uric acid-associated renal injury in mice

Abnormal uric acid level result in the development of hyperuricemia and hallmark of various diseases, including renal injury, gout, cardiovascular disorders, and non-alcoholic fatty liver. This study was designed to explore the anti-inflammatory potential of stevia residue extract (STR) against hyperuricemia-associated renal injury in mice. The results revealed that STR at dosages of 150 and 300 mg/kg bw and allopurinol markedly modulated serum uric acid, blood urea nitrogen, and creatinine in hyperuricemic mice. Serum and renal cytokine levels (IL-18, IL-6, IL-1Β, and TNF-α) were also restored by STR treatments. Furthermore, mRNA and immunohistochemistry (IHC) analysis revealed that STR ameliorates UA (uric acid)-associated renal inflammation, fibrosis, and EMT (epithelial-mesenchymal transition) via MMPS (matrix metalloproteinases), inhibiting NF-κB/NLRP3 activation by the AMPK/SIRT1 pathway and modulating the JAK2-STAT3 and Nrf2 signaling pathways. In summary, the present study provided experimental evidence that STR is an ideal candidate for the treatment of hyperuricemia-mediated renal inflammation. PRACTICAL APPLICATIONS: The higher uric acid results in hyperuricemia and gout. The available options for the treatment of hyperuricemia and gout are the use of allopurinol, and colchicine drugs, etc. These drugs possess several undesirable side effect. The polyphenolic compounds are abundantly present in plants, for example, stevia residue extract (STR) exert a positive effect on human health. From this study results, we can recommend that polyphenolic compounds enrich STR could be applied to develop treatment options for the treatment of hyperuricemia and gout.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Novel insights into NOD-like receptors in renal diseases

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

Fimasartan ameliorates renal ischemia reperfusion injury via modulation of oxidative stress, inflammatory and apoptotic cascades in a rat model

Ischemia-reperfusion injury (IRI) can be defined as changes in the functions and structures of the tissues resulting from the restoration of blood after a period of ischemia. This study aimed to assess the potential protective effect of Fimasartan (angiotensin receptor antagonist) in the bilateral renal IRI in male rats through its potential effect on renal functions, modulation of the inflammatory cascade, oxidative stress, and apoptotic effect. The animals were equally assigned into four groups. The sham (negative control) group was exposed to surgical conditions without induction of IRI. The control group was exposed to ischemia by occluding the renal pedicles by clamps for 30 min, followed by restoration of blood for 2h. The vehicle-treated group received dimethyl sulfoxide (DMSO) by intraperitoneal injection (IP) 30 minutes before clamping. Fimasartan-treated group: rats pretreated with Fimasartan a dose of 3 mg/kg IP; this was half hour before occluding the renal pedicles. Animals were then exposed to 30 min ischemia (clamping the renal pedicles) followed by 2h reperfusion by releasing the clamps. Blood samples were collected to examine the levels of serum urea and creatinine. Renal tissue was used to measure the levels of cytokines (TNFα, IL-6) and total antioxidant capacity (TAC). Immunohistochemistry was used to assess the levels of Bax, caspase 3, and Bcl-2. Histopathological analyses were performed to detect the parenchymal injury. The present study shows that pretreatment with Fimasartan improves kidney function through its effects on oxidative stress, cytokines, and apoptotic markers.

Human Endothelial Progenitor Cells Protect the Kidney against Ischemia-Reperfusion Injury via the NLRP3 Inflammasome in Mice

Ischemia-reperfusion injury (IRI) is a major cause of acute kidney injury (AKI) and progression to chronic kidney disease (CKD). However, no effective therapeutic intervention has been established for ischemic AKI. Endothelial progenitor cells (EPCs) have major roles in the maintenance of vascular integrity and the repair of endothelial damage; they also serve as therapeutic agents in various kidney diseases. Thus, we examined whether EPCs have a renoprotective effect in an IRI mouse model. Mice were assigned to sham, EPC, IRI-only, and EPC-treated IRI groups. EPCs originating from human peripheral blood were cultured. The EPCs were administered 5 min before reperfusion, and all mice were killed 72 h after IRI. Blood urea nitrogen, serum creatinine, and tissue injury were significantly increased in IRI mice; EPCs significantly improved the manifestations of IRI. Apoptotic cell death and oxidative stress were significantly reduced in EPC-treated IRI mice. Administration of EPCs decreased the expression levels of NLRP3, cleaved caspase-1, p-NF-κB, and p-p38. Furthermore, the expression levels of F4/80, ICAM-1, RORγt, and IL-17RA were significantly reduced in EPC-treated IRI mice. Finally, the levels of EMT-associated factors (TGF-β, α-SMA, Snail, and Twist) were significantly reduced in EPC-treated IRI mice. This study shows that inflammasome-mediated inflammation accompanied by immune modulation and fibrosis is a potential target of EPCs as a treatment for IRI-induced AKI and the prevention of progression to CKD.

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.

Caspase-11 promotes NLRP3 inflammasome activation via the cleavage of pannexin1 in acute kidney disease

Ischemia/reperfusion (I/R) injury is a major cause of acute kidney injury (AKI) in clinic. The activation of NLRP3 inflammasome is associated with inflammation and renal injury in I/R-induced AKI. In the current study we explored the molecular and cellular mechanisms for NLRP3 inflammasome activation following renal I/R. Mice were subjected to I/R renal injury by clamping bilateral renal pedicles. We showed that I/R injury markedly increased caspase-11 expression and the cleavage of pannexin 1 (panx1) in the kidneys accompanied by NLRP3 inflammasome activation evidenced by the activation of caspase-1 and interlukin-1β (IL-1β) maturation. In Casp-11^-/- mice, I/R-induced panx1 cleavage, NLRP3 inflammasome activation as well as renal functional deterioration and tubular morphological changes were significantly attenuated. In cultured primary tubular cells (PTCs) and NRK-52E cells, hypoxia/reoxygenation (H/R) markedly increased caspase-11 expression, NLRP3 inflammasome activation, IL-1β maturation and panx1 cleavage. Knockdown of caspase-11 attenuated all those changes; similar effects were observed in PTCs isolated from Casp-11^-/- mice. In NRK-52E cells, overexpression of caspase-11 promoted panx1 cleavage; pretreatment with panx1 inhibitor carbenoxolone or knockdown of panx1 significantly attenuated H/R-induced intracellular ATP reduction, extracellular ATP elevation and NLRP3 inflammasome activation without apparent influence on H/R-induced caspase-11 increase; pretreatment with P2X7 receptor inhibitor AZD9056 also attenuated NLRP3 inflammasome activation. The above results demonstrate that the cleavage of panx1 by upregulated caspase-11 is involved in facilitating ATP release and then NLRP3 inflammasome activation in I/R-induced AKI. This study provides new insight into the molecular mechanism of NLRP3 inflammasome activation in AKI.

The Role of NLRP3 Inflammasome in Lupus Nephritis

Lupus nephritis (LN) is the most frequent and severe of systemic lupus erythematosus (SLE) clinical manifestations and contributes to the increase of morbidity and mortality of patients due to chronic kidney disease. The NLRP3 (NLR pyrin domain containing 3) is a member of the NLR (NOD-like receptors), and its activation results in the production of pro-inflammatory cytokines, which can contribute to the pathogenesis of LN. In this review manuscript, we approach the relation between the NLRP3 inflammasome, SLE, and LN, highlighting the influence of genetic susceptibility of NLRP3 polymorphisms in the disease; the main functional studies using cellular and animal models of NLRP3 activation; and finally, some mechanisms of NLRP3 inhibition for the development of possible therapeutic drugs for LN.

NLRP3 associated with chronic kidney disease progression after ischemia/reperfusion-induced acute kidney injury

Nod-like receptor protein 3 (NLRP3), as an inflammatory regulator, has been implicated in acute kidney injury (AKI). Failed recovery after AKI can lead to chronic kidney disease (CKD). However, the role of NLRP3 in the AKI-CKD transition is still unknown. A mild or severe AKI mouse model was performed by using ischemia-reperfusion injury (IRI). We evaluated the renal NLRP3 expression in acute and chronic phases of ischemic AKI, respectively. Although serum creatinine (Cr) and blood urea nitrogen (BUN) levels in AKI chronic phase were equivalent to normal baseline, histological analysis and fibrotic markers revealed that severe AKI-induced maladaptive tubular repair with immune cell infiltration and fibrosis. Tubular damage was restored completely in mild AKI rather than in severe AKI. Of note, persistent overexpression of NLRP3 was also found in severe AKI but not in mild AKI. In the severe AKI-induced chronic phase, there was a long-term high level of NLRP3 in serum or urine. Overt NLRP3 was mainly distributed in the abnormal tubules surrounded by inflammatory infiltrates and fibrosis, which indicated the maladaptive repair. Renal Nlrp3 overexpression was correlated with infiltrating macrophages and fibrosis. Renal NLRP3 signaling-associated genes were upregulated after severe AKI by RNA-sequencing. Furthermore, NLRP3 was found increased in renal tubular epitheliums from CKD biopsies. Together, persistent NLRP3 overexpression was associated with chronic pathological changes following AKI, which might be a new biomarker for evaluating the possibility of AKI-CKD transition.

Resveratrol affects the expression of uric acid transporter by improving inflammation

Resveratrol (RSV), a polyphenol, non‑flavonoid plant‑derived antitoxin, ameliorates hyperuricemia and kidney inflammation. The present study aimed to establish a model of high‑fat diet (HFD)‑induced insulin resistance (IR) and to determine the specific mechanism of RSV to improve kidney inflammation and reduce uric acid (UA). C57BL/6J mice were fed a HFD for 12 weeks and their glucose tolerance was evaluated by intraperitoneal glucose tolerance testing. The mice were then administered RSV for 6 weeks, and blood and kidney samples were collected. Serum UA and insulin concentrations were determined using ELISA kits. Hematoxylin and eosin, periodic acid‑Schiff and Masson staining were performed to observe the pathological changes of the kidney, and electron microscopy was used to observe changes in the kidney ultrastructure. The renal concentrations of interleukin (IL)‑6, IL‑18, IL‑1β and tumor necrosis factor‑α (TNF‑α) were measured using ELISA kits, and western blotting evaluated changes in the protein expression levels of various indicators. RSV significantly ameliorated HFD‑induced IR and reduced blood UA levels. Long‑term IR can lead to lipid deposition, glycogen accumulation, inflammatory damage and fibrotic changes in the kidney of mice. This leads to a significant increase in the expression of UA transport‑related proteins, an increase in UA reabsorption and an increase in blood UA levels. Notably, RSV intervention was able to reverse this process. The effect of RSV may be achieved by inhibiting the NOD‑like receptor family, pyrin domain‑containing 3 (NLRP3) inflammasome and Toll‑like receptor 4 (TLR4)/myeloid differentiation factor 88/nuclear factor‑κB signaling pathway. In conclusion, RSV may improve kidney inflammation through TLR4 and NLRP3 signaling pathways, and reduce the expression of UA transporter proteins in the kidney of insulin‑resistant mice, thereby reducing blood UA levels.

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.

NLRP3 inflammasome in cardiovascular diseases: Pathophysiological and pharmacological implications

Growing evidence points out the importance of nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) inflammasome in the pathogenesis of cardiovascular diseases (CVDs), including hypertension, myocardial infarct (MI), ischemia, cardiomyopathies (CMs), heart failure (HF), and atherosclerosis. In this regard, intensive research efforts both in humans and in animal models of CVDs are being focused on the characterization of the pathophysiological role of NLRP3 inflammasome signaling in CVDs. In addition, clinical and preclinical evidence is coming to light that the pharmacological blockade of NLRP3 pathways with drugs, including novel chemical entities as well as drugs currently employed in the clinical practice, biologics and phytochemicals, could represent a suitable therapeutic approach for prevention and management of CVDs. On these bases, the present review article provides a comprehensive overview of clinical and preclinical studies about the role of NLRP3 inflammasome in the pathophysiology of CVDs, including hypertension, MI, ischemic injury, CMs, HF and atherosclerosis. In addition, particular attention has been focused on current evidence on the effects of drugs, biologics, and phytochemicals, targeting different steps of inflammasome signaling, in CVDs.

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.

SIRT1 alleviates hepatic ischemia-reperfusion injury via the miR-182-mediated XBP1/NLRP3 pathway

The hepatoprotection of histone deacetylase sirtuin 1 (SIRT1) has been identified to attenuate ischemia-reperfusion (IR)-triggered inflammation and liver damage. This study was performed to characterize the function of SIRT1 in hepatic IR injury. In in vivo assays on liver-specific knockout mice of SIRT1, we first validated the effect of SIRT1 knockout on liver damage and XBP1/NLRP3 inflammasome activation. Next, we examined whether knockdown of XBP1/NLRP3 or miR-182 agomir could reverse the effect of SIRT1 knockout. In in vitro assays, NCTC1469 cells subjected to hypoxia/reoxygenation (H/R) were transduced with small interfering RNA (siRNA)/activator of SIRT1 or miR-182 agomir to confirm the effect of SIRT1 on NCTC1469 cell behaviors as well as the regulation of miR-182 and the XBP1/NLRP3 signaling pathway. Hepatic IR injury was appreciably aggravated in SIRT1 knockout mice, and SIRT1 knockdown abolished the inhibition of XBP1/NLRP3 inflammasome activation, which was reversed by NLRP3 knockdown, XBP1 knockdown, or miR-182 agomir. Mechanistically, miR-182 expression was positively regulated by SIRT1 in hepatic IR injury in mice, and miR-182 inhibited the expression of XBP1 by binding to the 3' untranslated region (UTR) of XBP1. The histone deacetylase SIRT1 inhibits the downstream XBP1/NLRP3 inflammatory pathway by activating miR-182, thus alleviating hepatic IR injury in mice.

Rhabdomyolysis-Induced AKI Was Ameliorated in NLRP3 KO Mice via Alleviation of Mitochondrial Lipid Peroxidation in Renal Tubular Cells

Introduction: A recent study showed that early renal tubular injury is ameliorated in Nod-like receptor pyrin domain-containing protein 3 (NLRP3) KO mice with rhabdomyolysis-induced acute kidney injury (RIAKI). However, the precise mechanism has not been determined. Therefore, we investigated the role of NLRP3 in renal tubular cells in RIAKI. Methods: Glycerol-mediated RIAKI was induced in NLRP3 KO and wild-type (WT) mice. The mice were euthanized 24 h after glycerol injection, and both kidneys and plasma were collected. HKC-8 cells were treated with ferrous myoglobin to mimic a rhabdomyolytic environment. Results: Glycerol injection led to increase serum creatinine, aspartate aminotransferase (AST), and renal kidney injury molecule-1 (KIM-1) level; renal tubular necrosis; and apoptosis. Renal injury was attenuated in NLRP3 KO mice, while muscle damage and renal neutrophil recruitment did not differ between NLRP3 KO mice and WT mice. Following glycerin injection, increases in cleaved caspase-3, poly (ADP-ribose) polymerase (PARP), and a decrease in the glutathione peroxidase 4 (GPX-4) level were observed in the kidneys of mice with RIAKI, and these changes were alleviated in the kidneys of NLRP3 KO mice. NLRP3 was upregulated, and cell viability was suppressed in HKC-8 cells treated with ferrous myoglobin. Myoglobin-induced apoptosis and lipid peroxidation were significantly decreased in siNLRP3-treated HKC-8 cells compared to ferrous myoglobin-treated HKC-8 cells. Myoglobin reduced the mitochondrial membrane potential and increased mitochondrial fission and reactive oxygen species (ROS) and lipid peroxidation levels, which were restored to normal levels in NLRP3-depleted HKC-8 cells. Conclusions: NLRP3 depletion ameliorated renal tubular injury in a murine glycerol-induced acute kidney injury (AKI) model. A lack of NLRP3 improved tubular cell viability via attenuation of myoglobin-induced mitochondrial injury and lipid peroxidation, which might be the critical factor in protecting the kidney.

Sex-dependent mechanisms involved in renal tolerance to ischemia-reperfusion: Role of inflammation and histone H3 citrullination

Ischemia-reperfusion (I/R) injury, an inevitable result of kidney transplantation, triggers early inflammatory events that affect graft viability. Evidence from human transplantation and preclinical models of I/R suggests that a female hormonal environment positively influences the ability to recover from ischemic injury. However, the mechanisms behind these effects remain mostly unexplored. Here, we studied the influence of sex on pro-inflammatory mediators involved in the pathophysiology of acute I/R injury in male, female, and female ovariectomized (OVX) Wistar rats that underwent unilateral renal ischemia for 45 min, followed by 24 h of reperfusion. We found improved renal function, reduced cytokine expression, and decreased infiltration of myeloperoxidase-positive cells in females after I/R, when compared to their male and female OVX counterparts. Remarkably, citrullination of histone H3 was exacerbated in serum and renal tubules of females after I/R. In contrast, we observed lower levels of citrullinated histone H3 in male and female OVX rats in response to I/R, mostly in neutrophil extracellular traps. Our results demonstrate that female sex promotes renal I/R tolerance by attenuating pro-inflammatory mediators involved in I/R-induced damage.

Targeting NLRP3 inflammasome as a promising approach for treatment of diabetic nephropathy: Preclinical evidences with therapeutic approaches

Diabetes mellitus is an increasingly prevalent disease around the globe. The epidemic of diabetes mellitus and its complications pretenses the foremost health threat globally. Diabetic nephropathy is the notable complication in diabetes, leading to end-stage renal disease (ESRD) and premature death. Abundant experimental evidence indicates that oxidative stress and inflammation are the important mediators in diabetic kidney diseases and interlinked with various signal transduction molecular mechanisms. Inflammasomes are the critical components of innate immunity and are recognized as a critical mediator of inflammation and autoimmune disorders. NOD-like receptor protein 3 (NLRP3) inflammasome is the well-characterized protein and it exhibits the sterile inflammation through the regulation of pro-inflammatory cytokines interleukin (IL)-1β and IL-18 production in tissues. In recent years, the role of NLRP3 inflammasome in the pathophysiology of diabetic kidney diseases in both clinical and experimental studies has generated great interest. In the current review, we focused on and discussed the role of NLRP3 inflammasome in diabetic nephropathy. A literature review was performed using online databases namely, PubMed, Scopus, Google Scholar and Web of science to explore the possible pharmacological interventions that blunt the NLRP3 inflammasome-caspase-1-IL-1β/IL-18 axis and shown to have a beneficial effect in diabetic kidney diseases. This review describes the inhibition of NLRP3 inflammasome activation as a promising therapeutic target for drug discovery in future.

The Inflammasome in Chronic Complications of Diabetes and Related Metabolic Disorders

Diabetes mellitus (DM) ranks seventh as a cause of death worldwide. Chronic complications, including cardiovascular, renal, and eye disease, as well as DM-associated non-alcoholic fatty liver disease (NAFLD) account for most of the morbidity and premature mortality in DM. Despite continuous improvements in the management of late complications of DM, significant gaps remain. Therefore, searching for additional strategies to prevent these serious DM-related conditions is of the utmost importance. DM is characterized by a state of low-grade chronic inflammation, which is critical in the progression of complications. Recent clinical trials indicate that targeting the prototypic pro-inflammatory cytokine interleukin-1β (IL-1 β) improves the outcomes of cardiovascular disease, which is the first cause of death in DM patients. Together with IL-18, IL-1β is processed and secreted by the inflammasomes, a class of multiprotein complexes that coordinate inflammatory responses. Several DM-related metabolic factors, including reactive oxygen species, glyco/lipoxidation end products, and cholesterol crystals, have been involved in the pathogenesis of diabetic kidney disease, and diabetic retinopathy, and in the promoting effect of DM on the onset and progression of atherosclerosis and NAFLD. These metabolic factors are also well-established danger signals capable of regulating inflammasome activity. In addition to presenting the current state of knowledge, this review discusses how the mechanistic understanding of inflammasome regulation by metabolic danger signals may hopefully lead to novel therapeutic strategies targeting inflammation for a more effective treatment of diabetic complications.

NLRP3 Inflammasome in Cardioprotective Signaling

The NLRP3 inflammasome may contribute to infarct development during acute cardiac ischemia-reperfusion (IR). Because infarct size strongly correlates with the degree of heart failure in the long term, therapies that reduce reperfusion injury are still needed as first primary care against heart failure development. Inhibition of the NLRP3 inflammasome is currently viewed as such a potential therapy. However, previous research studies directed at inhibition of various inflammatory pathways in acute cardiac IR injury were often disappointing. This is because inflammation is a double-edged sword, detrimental when hyperactive, but beneficial at lower activity, with activity critically dependent on time of reperfusion and cellular location. Moreover, several inflammatory mediators can also mediate cardioprotective signaling. It is reasonable that this also applies to the NLRP3 inflammasome, although current literature has mainly focused on its detrimental effects in the context of acute cardiac IR. Therefore, in this review, we focus on beneficial, cardioprotective properties of the NLRP3 inflammasome and its components NLRP3, ASC, and caspase-1. The results show that (1) NLRP3 deficiency prevents cardioprotection in isolated heart by ischemic preconditioning and in vivo heart by TLR2 activation, associated with impaired STAT3 or Akt signaling, respectively; (2) ASC deficiency also prevents in vivo TLR2-mediated protection; and (3) caspase-1 inhibition results in decreased infarction but impaired protection through the Akt pathway during mild ischemic insults. In conclusion, the NLRP3 inflammasome is not only detrimental, it can also be involved in cardioprotective signaling, thus fueling the future challenge to acquire a full understanding of NLRP3 inflammasome role in cardiac IR before embarking on clinical trials using NLRP3 inhibitors.

Carthamin Yellow Protects the Heart Against Ischemia/Reperfusion Injury With Reduced Reactive Oxygen Species Release and Inflammatory Response

Carthamin yellow (CY) is a flavonoid compound isolated from safflower, which is widely used clinically in China. It has various pharmacological effects including promoting blood circulation to remove blood stasis and alleviating pain. Ischemic heart disease is one of the main culprits of illness and death. Here, in this study, ex vivo and in vivo models were used to investigate whether CY reduces ischemia/reperfusion injury. In vitro experiments further verify and explain the potential mechanisms of CY cardioprotective function. Isolated hearts from male rats with or without CY pretreatment before ischemia which underwent 30-minute ischemia followed by 60-minute reperfusion showed that CY pretreatment significantly reduced the infarct size and lactate dehydrogenase release. The in vivo experiments also indicated CY preadministration (i.v.) reduced infarct size and improved the heart function, which was impaired by myocardial ischemia/reperfusion injury. The in vitro model on myocardial cell also showed that CY reduced ischemia/reperfusion injury by reducing the lactate dehydrogenase and reactive oxygen species (ROS) releasing. Eliminating ROS with N-acetylcysteine or preinject CY into rat jugular vein reduces the expression of IL-6, TNF-a, and, especially, IL-1b in an in vivo I/R model. Also, CY pretreatment strongly reduces ischemia/reperfusion-induced NLRP3 up-expression and caspase-1 activation. Our results indicated CY reduced ischemia-reperfusion injury when administered before reperfusion. The reduction in injury is accompanied by a reduced ROS release and decreased inflammatory response.

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

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

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

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

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.

P2X4 receptor exacerbates ischemic AKI and induces renal proximal tubular NLRP3 inflammasome signaling

We tested the hypothesis that the P2X4 purinergic receptor (P2X4) exacerbates ischemic acute kidney injury (AKI) by promoting renal tubular inflammation after ischemia and reperfusion (IR). Supporting this, P2X4-deficient (KO) mice were protected against ischemic AKI with significantly attenuated renal tubular necrosis, inflammation, and apoptosis when compared to P2X4 wild-type (WT) mice subjected to renal IR. Furthermore, WT mice treated with P2X4 allosteric agonist ivermectin had exacerbated renal IR injury whereas P2X4 WT mice treated with a selective P2X4 antagonist (5-BDBD) were protected against ischemic AKI. Mechanistically, induction of kidney NLRP3 inflammasome signaling after renal IR was significantly attenuated in P2X4 KO mice. A P2 agonist ATPγS increased NLRP3 inflammasome signaling (NLRP3 and caspase 1 induction and IL-1β processing) in isolated renal proximal tubule cells from WT mice whereas these increases were absent in renal proximal tubules isolated from P2X4 KO mice. Moreover, 5-BDBD attenuated ATPγS induced NLRP3 inflammasome induction in renal proximal tubules from WT mice. Finally, P2X4 agonist ivermectin induced NLRP3 inflammasome and pro-inflammatory cytokines in cultured human proximal tubule cells. Taken together, our studies suggest that renal proximal tubular P2X4 activation exacerbates ischemic AKI and promotes NLRP3 inflammasome signaling.

Role of Inflammasomes in Kidney Diseases via Both Canonical and Non-canonical Pathways

Inflammasomes, multiprotein complex induced by harmful factors in the body, play a crucial role in innate immunity. Activation of inflammasomes lead to the activation of casepase-1 and then the secretion of inflammatory cytokines, including IL-1β and IL-18, subsequently leading to a type of cell death called pyroptosis. There are two types of signaling pathways involved in the process of inflammasome activation: the canonical and the non-canonical signaling pathway. The canonical signaling pathway is mainly dependent on casepase-1; the non-canonical signal pathway, which was recently discovered, is mainly dependent on caspase-11, but is also meditated by caspase-4, caspase-5, and caspase-8. Kidney inflammation is basically associated with inflammatory factor exudation and inflammatory cell infiltration. Several studies have showed that inflammasomes are closely related to kidney diseases, especially the NOD-, LRR- and pyrin domain-containing 3 (NLRP3) inflammasome, which play a role in regulating kidney inflammation and fibrosis. In this review, we focus on the relationship between inflammasomes and kidney diseases, especially the role of the NLRP3 inflammasome in different kinds of kidney disease via both canonical and non-canonical signal pathways.

The role of inflammasomes in kidney disease

Inflammasomes are multiprotein innate immune complexes that regulate caspase-dependent inflammation and cell death. Pattern recognition receptors, such as nucleotide-binding oligomerization domain (NOD)-like receptors and absent in melanoma 2 (AIM2)-like receptors, sense danger signals or cellular events to activate canonical inflammasomes, resulting in caspase 1 activation, pyroptosis and the secretion of IL-1β and IL-18. Non-canonical inflammasomes can be activated by intracellular lipopolysaccharides, toxins and some cell signalling pathways. These inflammasomes regulate the activation of alternative caspases (caspase 4, caspase 5, caspase 11 and caspase 8) that lead to pyroptosis, apoptosis and the regulation of other cellular pathways. Many inflammasome-related genes and proteins have been implicated in animal models of kidney disease. In particular, the NLRP3 (NOD-, LRR- and pyrin domain-containing 3) inflammasome has been shown to contribute to a wide range of acute and chronic microbial and non-microbial kidney diseases via canonical and non-canonical mechanisms that regulate inflammation, pyroptosis, apoptosis and fibrosis. In patients with chronic kidney disease, immunomodulation therapies targeting IL-1β such as canakinumab have been shown to prevent cardiovascular events. Moreover, findings in experimental models of kidney disease suggest that small-molecule inhibitors targeting NLRP3 and other inflammasome components are promising therapeutic agents.

Cathelicidin-related antimicrobial peptide protects against ischaemia reperfusion-induced acute kidney injury in mice

BACKGROUND AND PURPOSE

Despite recent advances in understanding its pathophysiology, treatment of acute kidney injury (AKI) remains a major unmet medical need, and novel therapeutic strategies are needed. Cathelicidin-related antimicrobial peptide (CRAMP) with immunomodulatory properties has an emerging role in various disease contexts. Here, we aimed to investigate the role of CRAMP and its underlying mechanisms in AKI.

EXPERIMENTAL APPROACH

The human homologue LL-37 and CRAMP were measured in blood samples of AKI patients and in experimental AKI mice respectively. Experimental AKI was induced in wild-type and CRAMP-deficient (Cnlp^-/- ) mice by ischaemia/reperfusion (I/R). Therapeutic evaluation of CRAMP was performed with exogenous CRAMP (5 mg·kg^-1 , i.p.) treatment.

KEY RESULTS

Cathelicidin expression was inversely related to clinical signs in patients and down-regulated in renal I/R-induced injury in mice. Cnlp^-/- mice exhibited exacerbated I/R-induced renal dysfunction, aggravated inflammatory responses and apoptosis. Moreover, over-activation of the NLRP3 inflammasome in Cnlp^-/- mice was associated with I/R-induced renal injury. Exogenous CRAMP treatment markedly attenuated I/R-induced renal dysfunction, inflammatory response and apoptosis, correlated with modulation of immune cell infiltration and phenotype. Consistent with Cnlp^-/- mouse data, CRAMP administration suppressed renal I/R-induced NLRP3 inflammasome activation, and its renal protective effects were mimicked by a specific NLRP3 inhibitor CY-09. The reno-protective and NLRP3 inhibitory effects of CRAMP required the EGF receptor.

CONCLUSION AND IMPLICATIONS

Our results suggest that CRAMP acts as a novel immunomodulatory mediator of AKI and modulation of CRAMP may represent a potential therapeutic strategy.

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

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

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.

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

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

IgA1 deposition may induce NLRP3 expression and macrophage transdifferentiation of podocyte in IgA nephropathy

BACKGROUND

The NLRP3 inflammasome plays an important role in mediating podocyte injury in various kidney diseases. The aim of this study was to investigate whether NLRP3 expression associated with podocyte injury was involved in the pathogenesis of IgA nephropathy (IgAN).

METHODS

NLRP3 inflammasomes and macrophage marker (F4/80) were detected in the renal tissues of IgAN patients. Association between kidney NLRP3 levels and the clinical feature of IgAN patients was analyzed. Podocytes were incubated with serum containing dys-glycosylated IgA1 protein isolated from IgAN patients. Expression of NLRP3 inflammasomes, F4/80, inflammatory cytokine and renal fibrosis marker were measured using RT-PCR and Western blotting.

RESULTS

Renal NLRP3 inflammasome expression was significantly increased in IgAN patients compared to normal control tissues. Moreover, co-expression of NLRP3 and F4/80 could be observed in the podocytes of IgAN patients. Patients with eGFR < 60 ml/min/1.73 m² had remarkably higher tubular NLRP3 expression (P < 0.05), while patients with gross proteinuria (≥ 3.5 g/day) had a significantly higher glomerular NLRP3 expression (P < 0.05). Further analysis indicated that dys-glycosylated IgA1 isolated from IgAN patient serum could induce podocyte expression of NLRP3 and the macrophage marker F4/80, which could lead to induction of an inflammatory reaction (increased expression of ICAM-1) and fibrosis (increased expression of α-SMA).

CONCLUSION

Dys-glycosylated IgA1 isolated from IgAN patient serum could induce NLRP3 expression in podocytes and initiate podocyte macrophage transdifferentiation (PMT). After PMT, podocytes secrete proinflammatory cytokines that can contribute to the inflammation cascade and renal fibrosis changes associated with IgAN.