The role of Toll-like receptors in renal diseases

Regulation of renal aquaporin water channels in acute pyelonephritis

Acute pyelonephritis (APN) is most frequently caused by uropathogenic Escherichia coli (UPEC), which ascends from the bladder to the kidneys during a urinary tract infection. Patients with APN have been reported to have reduced renal concentration capacity under challenged conditions, polyuria, and increased aquaporin-2 (AQP2) excretion in the urine. We have recently shown increased AQP2 accumulation in the plasma membrane in cell cultures exposed to E. coli lysates and in the apical plasma membrane of inner medullary collecting ducts in a 5-day APN mouse model. This study aimed to investigate if AQP2 expression in host cells increases UPEC infection efficiency and to identify specific bacterial components that mediate AQP2 plasma membrane insertion. As the transepithelial water permeability in the collecting duct is codetermined by AQP3 and AQP4, we also investigated whether AQP3 and AQP4 localization is altered in the APN mouse model. We show that AQP2 expression does not increase UPEC infection efficiency and that AQP2 was targeted to the plasma membrane in AQP2-expressing cells in response to the two pathogen-associated molecular patterns (PAMPs), lipopolysaccharide and peptidoglycan. In contrast to AQP2, the subcellular localizations of AQP1, AQP3, and AQP4 were unaffected both in lysate-incubated cell cultures and in the APN mouse model. Our finding demonstrated that cellular exposure to lipopolysaccharide and peptidoglycan can trigger the insertion of AQP2 in the plasma membrane revealing a new regulatory pathway for AQP2 plasma membrane translocation, which may potentially be exploited in intervention strategies.NEW & NOTEWORTHY Acute pyelonephritis (APN) is associated with reduced renal concentration capacity and increased aquaporin-2 (AQP2) excretion. Uropathogenic Escherichia coli (UPEC) mediates changes in the subcellular localization of AQP2 and we show that in vitro, these changes could be elicited by two pathogen-associated molecular patterns (PAMPs), namely, lipopolysaccharide and peptidoglycan. UPEC infection was unaltered by AQP2 expression and the other renal AQPs (AQP1, AQP3, and AQP4) were unaltered in APN.

The Terminalia chebula Retz extract treats hyperuricemic nephropathy by inhibiting TLR4/MyD88/NF-κB axis

ETHNOPHARMACOLOGICAL RELEVANCE

Hyperuricemic nephropathy (HN) is a renal injury caused by hyperuricemia and is the main cause of chronic kidney disease and end-stage renal disease. ShiWeiHeZiSan, which is composed mainly of components of Terminalia chebula Retz. And is recorded in the Four Medical Tantras, is a typical traditional Tibetan medicinal formula for renal diseases. Although T. chebula has been reported to improve renal dysfunction and reduce renal cell apoptosis, the specific mechanism of the nephroprotective effects of T. chebula on HN is still unclear.

AIM OF THE STUDY

This study was conducted to evaluate the effects and specific mechanism of T. chebula extract on HN through network pharmacology and in vivo and in vitro experiments.

MATERIALS AND METHODS

Potassium oxalate (1.5 g/kg) and adenine (50 mg/kg) were combined for oral administration to establish the HN rat model, and the effects of T. chebula extract on rats in the HN model were evaluated by renal function indices and histopathological examinations. UPLC-Q-Exactive Orbitrap/MS analysis was also conducted to investigate the chemical components of T. chebula extract, and the potential therapeutic targets of T. chebula in HN were predicted by network pharmacology analysis. Moreover, the activation of potential pathways and the expression of related mRNAs and proteins were further observed in HN model rats and uric acid-treated HK-2 cells.

RESULTS

T. chebula treatment significantly decreased the serum uric acid (SUA), blood urea nitrogen (BUN) and serum creatinine (SCr) levels in HN rats and ameliorated renal pathological injury and fibrosis. A total of 25 chemical components in T. chebula extract were identified by UPLC-Q-Exactive Orbitrap/MS analysis, and network pharmacology analysis indicated that the NF-κB pathway was the potential pathway associated with the therapeutic effects of T. chebula extract on HN. RT‒PCR analysis, immunofluorescence staining and ELISA demonstrated that the mRNA and protein levels of TLR4 and MyD88 were significantly decreased in the renal tissue of HN rats after treatment with T. chebula extract at different concentrations, while the phosphorylation of P65 and the secretion of TNF-α and IL-6 were significantly inhibited. The results of in vitro experiments showed that T. chebula extract significantly decreased the protein levels of TLR4, MyD88, p-IκBα and p-P65 in uric acid-treated HK-2 cells and inhibited the nuclear translocation of p65 in these cells. In addition, the expression of inflammatory factors (IL-1β, IL-6 and TNF-α) and fibrotic genes (α-SMA and fibronectin) was significantly downregulated by T. chebula extract treatment, while E-cadherin expression was significantly upregulated.

CONCLUSION

T. chebula extract exerts nephroprotective effects on HN, such as anti-inflammatory effects and fibrosis improvement, by regulating the TLR4/MyD88/NF-κB axis, which supports the general use of T. chebula in the management of HN and other chronic kidney diseases.

Comprehensive analysis of the relationship between xanthine oxidoreductase activity and chronic kidney disease

Chronic kidney disease (CKD) is a common disease that seriously endangers human health. However, the potential relationship between xanthine oxidoreductase (XOR) activity and CKD remains unclear. In this study, we used clinical data, CKD datasets from the Gene Expression Omnibus database, and untargeted metabolomics to explain the relationship between XOR activity and CKD. First, XOR activity showed high correlation with the biomarkers of CKD, such as serum creatinine, blood urea nitrogen, uric acid, and estimated glomerular filtration rate. Then, we used least absolute shrinkage and selection operator logical regression algorithm and random forest algorithm to screen CKD molecular markers from differentially expressed genes, and the results of qRT-PCR of XDH, KOX-1, and ROMO1 were in accordance with the results of bioinformatics analyses. In addition, untargeted metabolomics analysis revealed that the purine metabolism pathway was significantly enriched in CKD patients in the simulated models of kidney fibrosis.

The role of toll-like receptors (TLRs) and their therapeutic applications in glomerulonephritis

One of the most important features of innate immunity is the presence of a special group of pattern recognition receptors (PRRs) called toll-like receptors (TLRs), which recognize pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs), resulting in a quick and effective immune response to them. Glomerulonephritis (GN) is one of the most important categories of renal disorders characterized by destructive responses of the immune system to the glomerulus. To date, the association of TLRs as important innate immune system members with GN has been one of the topics that attracted the attention of researchers in this field. However, the exact role of these receptors in the immunopathogenesis of GN has not yet been fully discussed. Therefore, this study aims to overview the role of TLRs in GN and the possibility of using them as a potential therapeutic target.

Immunoglobulin A vasculitis nephritis: Current understanding of pathogenesis and treatment

The clinical spectrum of immunoglobulin A vasculitis nephritis (IgAVN) ranges from the relatively common transitory microscopic hematuria and/or low-grade proteinuria to nephritic or nephrotic syndrome, rapidly progressive glomerulonephritis, or even renal failure. Clinical and experimental studies have shown a multifactor pathogenesis: Infection triggers, impaired glycosylation of IgA1, complement activation, Toll-like-receptor activation and B cell proliferation. This knowledge can identify IgAVN patients at a greater risk for adverse outcome and increase the evidence for treatment recommendations.

End-stage kidney disease: a never healing wound leading to another never healing wound, renal cancer

BACKGROUND

End-stage kidney disease and acquired cystic kidney disease are the final stages of chronic kidney disease, leading to loss of kidney function and frequent development of tumours. It has been suggested that an inflammatory microenvironment may be responsible for the progressive kidney remodelling and cancer development.

METHODS

Our aim was to analyse gene expression suggested to be involved in the remodelling of kidneys in end-stage kidney disease, and in the development of preneoplastic lesions and tumours. Immunohistochemistry was employed to assess the cellular localisation of different genes involved in these pathways on representative tissue sections.

RESULTS

Cellular (αSMA positive naïve activated fibroblasts, endothelial cells, macrophages) and non-cellular components (cytokines IL6, TGFβ, IL1β, CSF2, fibronectin, laminin, and matrix modifier proteases MMP9 and MMP12) of the inflammatory microenvironment were expressed in the kidneys of patients with end-stage kidney disease. IL6 and FN1 expressing naïve activated fibroblasts and recruited inflammatory cells were the most abundant cellular components of the inflammatory microenvironment.

CONCLUSION

The progressive inflammatory and fibrotic processes in end-stage kidney disease have features recalling those of  a never healing wound and may explain the frequent development of kidney cancer.

Usefulness of urinary calprotectin as a novel marker differentiating functional from structural acute kidney injury in the critical care setting

BACKGROUND

Biomarkers are fundamental tools for differentiating between types of acute kidney injury (AKI) and may thus be crucial in management and prognosis. We report on a recently described biomarker, calprotectin, that appears to be a promising candidate in differentiating hypovolemic/functional AKI from intrinsic/structural AKI, whose acknowledgement may play a role in improving outcomes. We aimed to study the efficacy of urinary calprotectin in differentiating these two forms of AKI. The effect of fluid administration on the subsequent clinical course of AKI, its severity and the outcomes were also studied.

METHODOLOGY

Children who presented with conditions predisposing to AKI or with diagnosis of AKI were included. Urine samples for calprotectin analysis were collected and stored at - 20 ºC for analysis at the end of the study. Fluids were administered as per clinical conditions, followed by intravenous furosemide 1 mg/kg, and patients were observed closely for at least 72 h. Children with serum creatinine normalization and clinical improvement were classified as with functional AKI, while those with no response were classified as with structural AKI. Urine calprotectin levels between these two groups were compared. Statistical analysis was performed with SPSS 21.0 software.

RESULTS

Of the 56 children enrolled, 26 were classified as with functional AKI and 30 as with structural AKI. Stage 3 AKI was observed in 48.2% of patients and stage 2 AKI in 33.8%. Mean urine output, creatinine and stage of AKI improved with fluid and furosemide or furosemide alone (OR 6.08, 95% CI 1.65-27.23) (p < 0.01). A positive response to fluid challenge was in favor of functional AKI (OR 6.08, 95% CI 1.65-27.23) (p = 0.008). Presence of edema, sepsis and need for dialysis were hallmarks of structural AKI (p < 0.05). Urine calprotectin/creatinine values were 6 times higher in structural AKI compared to functional AKI. Urine calprotectin/creatinine ratio showed the best sensitivity (63.3%) and specificity (80.7%) at a cut-off value of 1 mcg/mL in differentiating the two types of AKI.

CONCLUSION

Urinary calprotectin is a promising biomarker that may help differentiating structural from functional AKI in children.

Protective effect of IAXO-102 on renal ischemia-reperfusion injury in rats

Ischemia/reperfusion injury (IRI) is a common cause of kidney damage, characterized by oxidative stress and inflammation. In this study, we investigated the potential protective effects of IAXO-102, a chemical compound, on experimentally induced IRI in male rats. The bilateral renal IRI model was used, with 24 adult male rats randomly divided into four groups (N=6): sham group (laparotomy without IRI induction), control group (laparotomy plus bilateral IRI for 30 minutes followed by 2 hours of reperfusion), vehicle group (same as control but pre-injected with the vehicle), and treatment group (similar to control but pre-injected with IAXO-102). We measured several biomarkers involved in IRI pathophysiology using enzyme-linked immunosorbent assay (ELISA), including High mobility group box1 (HMGB1), nuclear factor kappa b-p65 (NF-κB p65), interleukin beta-1 (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), 8-isoprostane, Bcl-2 associated X protein (BAX), heat shock protein 27 (HSP27), and Bcl-2. Statistical analysis was performed using one-way ANOVA and Tukey post hoc tests. Our results showed that IAXO-102 significantly improved kidney function, reduced histological alterations, and decreased the inflammatory response (IL-1, IL-6, and TNF) caused by IRI. IAXO-102 also decreased apoptosis by reducing pro-apoptotic Bax and increasing anti-apoptotic Bcl-2 without impacting HSP27. In conclusion, our findings suggest that IAXO-102 had a significant protective effect against IRI damage in the kidneys.

Complement C3 mediates podocyte injury through TLR4/NFΚB-P65 signaling during ischemia-reperfusion acute kidney injury and post-injury fibrosis

BACKGROUND

The aim of this study was to explore the mechanism of complement C3a mediating podocyte injury during ischemia-reperfusion acute kidney injury (IR-AKI) and post-injury fibrosis.

METHODS

Renal artery clamping was used to establish IR-AKI and post-injury fibrosis model. HE and Masson staining were performed to observe renal fibrosis. The protein abundance levels were measured along with inflammatory markers, renal complement C3. Podocytes were treated with C3a with or without Toll-like receptor 4(TLR4) inhibitor. The effects of TLR4 up-regulation by TLR4 plasmids were examined.

RESULTS

C3^-/- resulted in amelioration of renal dysfunction by reducing podocyte damage and renal fibrosis. Immunoblot with renal tissue homogenates from IR-AKI mice revealed that C3^-/- decreased TLR4/Nuclear Factor-κB (NFκB)-P65.

CONCLUSION

Our results indicate that modulating C3/TLR4/NFκB-P65 signaling pathway is a novel therapeutic target for the IR-AKI and post-injury fibrosis.

The long noncoding RNA Meg3 mediates TLR4-induced inflammation in experimental obstructive nephropathy

Kidney inflammation contributes to the progression of chronic kidney disease (CKD). Modulation of Toll-like receptor 4 (TLR4) signaling is a potential therapeutic strategy for this pathology, but the regulatory mechanisms of TLR4 signaling in kidney tubular inflammation remains unclear. Here, we demonstrated that tubule-specific deletion of TLR4 in mice conferred protection against obstruction-induced kidney injury, with reduction in inflammatory cytokine production, macrophage infiltration and kidney fibrosis. Transcriptome analysis revealed a marked down-regulation of long noncoding RNA (lncRNA) Meg3 in the obstructed kidney from tubule-specific TLR4 knockout mice compared with wild-type control. Meg3 was also induced by lipopolysaccharide in tubular epithelial cells via a p53-dependent signaling pathway. Silencing of Meg3 suppressed LPS-induced cytokine production of CCL-2 and CXCL-2 and the activation of p38 MAPK pathway in vitro and ameliorated kidney fibrosis in mice with obstructive nephropathy. Together, these findings identify a proinflammatory role of lncRNA Meg3 in CKD and suggest a novel regulatory pathway in TLR4-driven inflammatory responses in tubular epithelial cells.

The role and mechanism of the gut microbiota in the development and treatment of diabetic kidney disease

Diabetic kidney disease (DKD) is a common complication in patients with diabetes mellitus (DM). Increasing evidence suggested that the gut microbiota participates in the progression of DKD, which is involved in insulin resistance, renin-angiotensin system (RAS) activation, oxidative stress, inflammation and immunity. Gut microbiota-targeted therapies including dietary fiber, supplementation with probiotics or prebiotics, fecal microbiota transplantation and diabetic agents that modulate the gut microbiota, such as metformin, glucagon-like peptide-1 (GLP-1) receptor agonists, dipeptidyl peptidase-4 (DPP-4) inhibitors, and sodium-glucose transporter-2 (SGLT-2) inhibitors. In this review, we summarize the most important findings about the role of the gut microbiota in the pathogenesis of DKD and the application of gut microbiota-targeted therapies.

Chronic Kidney Disease, Urinary Tract Infections and Antibiotic Nephrotoxicity: Are There Any Relationships?

Chronic kidney disease (CKD) has been a constant burden worldwide, with a prevalence of more than 10% of the population and with mortality reaching 1.2 million deaths and 35.8 million disability-adjusted life years (DALYs) in 2017, as it is claimed by the Global Burden of Diseases. Moreover, an increase in its prevalence is expected in the next years due to a rise in the number of people suffering from obesity, diabetes mellitus and hypertension. On the other hand, with cardiovascular morbidity and mortality showing a downward trend, maybe it is time to focus on CKD, to minimize the preventable risk factors involved in its progression toward end-stage kidney disease (ESKD) and to offer a better quality of life. Another major health burden is represented by infectious diseases, particularly urinary tract infections (UTIs), as it is considered that approximately 40-50% of women and 5% of men will have at least one episode during their lifetime. Additionally, CKD consists of a constellation of immunological and metabolical disturbances that lead to a greater risk of UTIs: increased apoptosis of lymphocytes, elevated levels of tumor necrosis factor α and interleukin 6, which lower the function of neutrophils and increased levels of uremic toxins like p-cresyl sulfate and indoxyl sulfate, which alter the adherence and migration of leukocytes to the sites of injury. Moreover, UTIs can lead to a more rapid decline of kidney function, especially in stages G3-G5 of CKD, with all the complications involved. Last, but not least, antibiotherapy is often complicated in this category of patients, as antibiotics can also negatively affect the kidneys. This review will try to focus on the particularities of the urinary microbiome, asymptomatic bacteriuria and UTIs and the subtle balance between the risks of them and the risks of antibiotherapy in the evolution of CKD.

The Importance of Toll-like Receptor 9 Expression on Monocytes and Dendritic Cells in the Context of Epstein–Barr Virus Infection in the Immunopathogenesis of Primary Glomerulonephritis

Toll-like receptor 9 (TLR9) is activated by unmethylated cytosine-phosphate-guanosine (CpG) dinucleotides found in the genomes of pathogens such as Epstein–Barr virus (EBV). The aim of this study was to determine the role of TLR9 in the immunopathogenesis of IgA nephropathy (IgAN) and membranoproliferative glomerulonephritis (MPGN) in the context of Epstein–Barr virus (EBV) infection. For this purpose, the frequency of TLR9-positive monocytes and dendritic cells (DCs, i.e., BDCA-1; myeloid dendritic cells, and BDCA-2; plasmocytoid dendritic cells) was studied, and a quantitative analysis of the concentration of TLR9 in the serum of patients diagnosed with IgAN and MPGN was undertaken. Higher frequencies of TLR9-positive DCs and monocytes in IgAN and MPGN patients were observed as compared with the control group. Patients diagnosed with GN exhibited a higher percentage of BDCA-1+CD19− and BDCA-2+CD123+ DCs than patients in the control group. Moreover, serum TLR9 concentration was shown to be significantly correlated with EBV DNA copy number/µg DNA, IgG, IgM, serum albumin, total protein in 24-h urine collection test and the frequency of BDCA-2+CD123+ DCs in peripheral blood. Our findings confirm that TLR9 may be involved in the development of IgAN and MPGN.

Investigation into the effect and mechanism of dapagliflozin against renal interstitial fibrosis based on transcriptome and network pharmacology

BACKGROUND

Renal interstitial fibrosis (RIF) is the final pathway for chronic kidney diseases (CKD) to end-stage renal disease (ESRD). Dapagliflozin, a selective inhibitor of the sodium glucose co-transporter 2, reduced the risk of renal events in non-diabetic CKD patients in the DAPA-CKD trial. However, the effect and mechanism of dapagliflozin on RIF are not very clear. Currently, we evaluate the effects of dapagliflozin on RIF and systematically explore its mechanism.

METHODS AND RESULTS

Firstly, unilateral ureteral obstruction (UUO) mouse model was established to evaluate effects of dapagliflozin on RIF, and results demonstrated dapagliflozin improved renal function and RIF of UUO mice independent of blood glucose control. Subsequently, transcriptome analysis was performed to explore the potential mechanism of dapagliflozin against RIF, which exhibited the therapeutic effect of dapagliflozin on RIF may be achieved through multiple pathways regulation. Then we verified the potential mechanisms with molecular biology methods, and found that dapagliflozin treatment significantly alleviated inflammation, apoptosis, oxidative stress and mitochondrial injury in kidneys of UUO mice. Furthermore, network pharmacology analysis was used to investigate the potential targets of dapagliflozin against RIF. Moreover, we also applied molecular docking and molecular dynamics simulation to predict the specific binding sites and binding capacity of dapagliflozin and hub target.

CONCLUSIONS

Dapagliflozin had therapeutic effect on RIF independent of blood glucose control, and the protective effects probably mediated by multiple pathways and targets regulation.

Aristolochic acid I induces proximal tubule injury through ROS/HMGB1/mt DNA mediated activation of TLRs

Aristolochic acids (AAs) are extracted from certain plants as folk remedies for centuries until their nephrotoxicity and carcinogenicity were recognized. Aristolochic acid I (AAI) is one of the main pathogenic compounds, and it has nephrotoxic, carcinogenic and mutagenic effects. Previous studies have shown that AAI acts mainly on proximal renal tubular epithelial cells; however, the mechanisms of AAI‐induced proximal tubule cell damage are still not fully characterized. We exposed human kidney proximal tubule cells (PTCs; HK2 cell line) to AAI in vitro at different time/dose conditions and assessed cell proliferation, reactive oxygen species (ROS) generation, nitric oxide (NO) production, m‐RNA/ protein expressions and mitochondrial dysfunction. AAI exposure decreased proliferation and increased apoptosis, ROS generation / NO production in PTCs significantly at 24 h. Gene/ protein expression studies demonstrated activation of innate immunity (TLRs 2, 3, 4 and 9, HMGB1), inflammatory (IL6, TNFA, IL1B, IL18, TGFB and NLRP3) and kidney injury (LCN2) markers. AAI also induced epithelial‐mesenchymal transition (EMT) and mitochondrial dysfunction in HK2 cells. TLR9 knock‐down and ROS inhibition were able to ameliorate the toxic effect of AAI. In conclusion, AAI treatment caused injury to PTCs through ROS‐HMGB1/mitochondrial DNA (mt DNA)‐mediated activation of TLRs and inflammatory response.

Signaling pathways of chronic kidney diseases, implications for therapeutics

Chronic kidney disease (CKD) is a chronic renal dysfunction syndrome that is characterized by nephron loss, inflammation, myofibroblasts activation, and extracellular matrix (ECM) deposition. Lipotoxicity and oxidative stress are the driving force for the loss of nephron including tubules, glomerulus, and endothelium. NLRP3 inflammasome signaling, MAPK signaling, PI3K/Akt signaling, and RAAS signaling involves in lipotoxicity. The upregulated Nox expression and the decreased Nrf2 expression result in oxidative stress directly. The injured renal resident cells release proinflammatory cytokines and chemokines to recruit immune cells such as macrophages from bone marrow. NF-κB signaling, NLRP3 inflammasome signaling, JAK-STAT signaling, Toll-like receptor signaling, and cGAS-STING signaling are major signaling pathways that mediate inflammation in inflammatory cells including immune cells and injured renal resident cells. The inflammatory cells produce and secret a great number of profibrotic cytokines such as TGF-β1, Wnt ligands, and angiotensin II. TGF-β signaling, Wnt signaling, RAAS signaling, and Notch signaling evoke the activation of myofibroblasts and promote the generation of ECM. The potential therapies targeted to these signaling pathways are also introduced here. In this review, we update the key signaling pathways of lipotoxicity, oxidative stress, inflammation, and myofibroblasts activation in kidneys with chronic injury, and the targeted drugs based on the latest studies. Unifying these pathways and the targeted therapies will be instrumental to advance further basic and clinical investigation in CKD.

Single-cell RNA Sequencing Identified Novel Nr4a1+ Ear2+ Anti-Inflammatory Macrophage Phenotype under Myeloid-TLR4 Dependent Regulation in Anti-Glomerular Basement Membrane (GBM) Crescentic Glomerulonephritis (cGN)

Previously, this study demonstrates the critical role of myeloid specific TLR4 in macrophage-mediated progressive renal injury in anti-glomerular basement membrane (anti-GBM) crescentic glomerulonephritis (cGN); however, the underlying mechanism remains largely unknown. In this study, single-cell RNA sequencing (scRNA-seq), pseudotime trajectories reconstruction, and motif enrichment analysis are used, and macrophage diversity in anti-GBM cGN under tight regulation of myeloid-TLR4 is uncovered. Most significantly, a myeloid-TLR4 deletion-induced novel reparative macrophage phenotype (Nr4a1⁺ Ear2+) with significant upregulated anti-inflammatory and tissue repair-related signaling is discovered, thereby suppressing the M1 proinflammatory responses in anti-GBM cGN. This is further demonstrated in vitro that deletion of TLR4 from bone marrow-derived macrophages (BMDMs) induces the Nr4a1/Ear2-expressing anti-inflammatory macrophages while blocking LPS-stimulated M1 proinflammatory responses. Mechanistically, activation of the Nr4a1/Ear2-axis is recognized as a key mechanism through which deletion of myeloid-TLR4 promotes the anti-inflammatory macrophage differentiation in vivo and in vitro. This is confirmed by specifically silencing macrophage Nr4a1 or Ear2 to reverse the anti-inflammatory effects on TLR4 deficient BMDMs upon LPS stimulation. In conclusion, the findings decode a previously unidentified role for a myeloid-TLR4 dependent Nr4a1/Ear2 negative feedback mechanism in macrophage-mediated progressive renal injury, implying that activation of Nr4a1-Ear2 axis can be a novel and effective immunotherapy for anti-GBM cGN.

Protective Effect of Quercetin 3-O-Glucuronide against Cisplatin Cytotoxicity in Renal Tubular Cells

Quercetin, a flavonoid with promising therapeutic potential, has been shown to protect from cisplatin nephrotoxicity in rats following intraperitoneal injection, but its low bioavailability curtails its prospective clinical utility in oral therapy. We recently developed a micellar formulation (P-quercetin) with enhanced solubility and bioavailability, and identical nephroprotective properties. As a first aim, we herein evaluated the oral treatment with P-quercetin in rats, which displayed no nephroprotection. In order to unravel this discrepancy, quercetin and its main metabolites were measured by HPLC in the blood and urine after intraperitoneal and oral administrations. Whilst quercetin was absorbed similarly, the profile of its metabolites was different, which led us to hypothesize that nephroprotection might be exerted in vivo by a metabolic derivate. Consequently, we then aimed to evaluate the cytoprotective capacity of quercetin and its main metabolites (quercetin 3-O-glucoside, rutin, tamarixetin, isorhamnetin and quercetin 3-O-glucuronide) against cisplatin toxicity, in HK-2 and NRK-52E tubular cell lines. Cells were incubated for 6 h with quercetin, its metabolites or vehicle (pretreatment), and subsequently 18 h in cotreatment with 10-300 μM cisplatin. Immediately after treatment, cell cultures were subject to the MTT technique as an index of cytotoxicity and photographed under light microscopy for phenotypic assessment. Quercetin afforded no direct cytoprotection and quercetin-3-O-glucuronide was the only metabolite partially preventing the effect of cisplatin in cultured tubule cells. Our results identify a metabolic derivative of quercetin contributing to its nephroprotection and prompt to further explore exogenous quercetin-3-O-glucuronide in the prophylaxis of tubular nephrotoxicity.

Gut microbial metabolite TMAO increases peritoneal inflammation and peritonitis risk in peritoneal dialysis patients

Trimethylamine-N-oxide (TMAO), a gut microbiota-produced metabolite, is accumulated in chronic kidney disease (CKD) patients. It is well known to contribute to CKD-related cardiovascular complications. However, the effect of TMAO on peritoneal dialysis (PD)-related peritonitis remains largely unknown. Here, we demonstrate that serum concentrations of TMAO were positively correlated with C-reactive protein levels, and the appearance rate of dialysate IL-6 and PAI-1, in PD patients. During the follow-up period of 28.3 ± 8.0 months, patients with higher TMAO levels (≥50 μM) had a higher risk of new-onset peritonitis (HR, 3.60; 95%CI, 1.18-10.99; P=0.025) after adjusting for sex, age, diabetes, PD duration, BUN, rGFR, C-reactive protein, BMI and β2-M. In CKD rat models, TMAO significantly promoted peritoneal dialysate-induced inflammatory cell infiltration, inflammatory cytokines production in the peritoneum. In vitro study revealed that TMAO directly induced primary peritoneal mesothelial cell necrosis, together with increased production of pro-inflammatory cytokines including CCL2, TNF-α, IL-6, and IL-1β. In addition, TMAO significantly increased TNF-α-induced P-selectin production in mesothelial cells, as well as high glucose-induced TNF-α and CCL2 expression in endothelial cells. In conclusion, our data demonstrate that higher levels of TMAO exacerbate peritoneal inflammation and might be a risk factor of incidence of peritonitis in PD patients.

Dissecting and Evaluating the Therapeutic Targets of Coptis Chinensis Franch in the Treatment of Urinary Tract Infections Induced by Escherichia coli

Coptis chinensis Franch (CCF) is extensively used in the treatment of inflammatory-related diseases. Accumulating studies have previously demonstrated the anti-inflammatory properties of CCF, yet data on its exact targets against urinary tract infections (UTIs) remain largely unknown. Therefore, the present study decodes the potential targets of action of CCF against UTIs by network pharmacology combined with experiment evaluations. Based on the pharmacology network analysis, the current study yielded six core ingredients: quercetin, palmatine (R)-canadine, berlambine, berberine, and berberrubine. The protein–protein interaction network (PPI) was generated by the string database, and then, four targets (IL6, FOS, MYC, and EGFR) were perceived as the major CCF targets using the CytoNCA plug-in. The results of molecular docking showed that the six core constituents of CCF had strong binding affinities toward the four key targets of UTIs after docking into the crystal structure. The enrichment analysis indicated that the possible regulatory mechanisms of CCF against UTIs were based on the modules of inflammation, immune responses, and apoptosis among others. Experimentally, the Escherichia coli (E. coli) strain CFT073 was applied to establish in vivo and in vitro models. In vivo results revealed that the key targets, IL6 and FOS, are significantly upregulated in rat bladder tissues of UTIs, whereas the expression of MYC and EGFR remained steady. Last, in vitro results further confirmed the therapeutic potential of CCF by reducing the expression of IL6 and FOS. In conclusion, IL6 and FOS were generally upregulated in the progression of E. coli–induced UTIs, whereas the CCF intervention exerted a preventive role in host cells stimulated by E. coli, partially due to inhibiting the expression of IL6 and FOS.

Research on the Mechanism of Guizhi to Treat Nephrotic Syndrome Based on Network Pharmacology and Molecular Docking Technology

Objective

Nephrotic syndrome (NS) is a common glomerular disease caused by a variety of causes and is the second most common kidney disease. Guizhi is the key drug of Wulingsan in the treatment of NS. However, the action mechanism remains unclear. In this study, network pharmacology and molecular docking were used to explore the underlying molecular mechanism of Guizhi in treating NS.

Methods

The active components and targets of Guizhi were screened by the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP), Hitpick, SEA, and Swiss Target Prediction database. The targets related to NS were obtained from the DisGeNET, GeneCards, and OMIM database, and the intersected targets were obtained by Venny2.1.0. Then, active component-target network was constructed using Cytoscape software. And the protein-protein interaction (PPI) network was drawn through the String database and Cytoscape software. Next, Gene Ontology (GO) and pathway enrichment analyses of Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed by DAVID database. And overall network was constructed through Cytoscape. Finally, molecular docking was conducted using Autodock Vina.

Results

According to the screening criteria, a total of 8 active compounds and 317 potential targets of Guizhi were chosen. Through the online database, 2125 NS-related targets were identified, and 93 overlapping targets were obtained. In active component-target network, beta-sitosterol, sitosterol, cinnamaldehyde, and peroxyergosterol were the important active components. In PPI network, VEGFA, MAPK3, SRC, PTGS2, and MAPK8 were the core targets. GO and KEGG analyses showed that the main pathways of Guizhi in treating NS involved VEGF, Toll-like receptor, and MAPK signaling pathway. In molecular docking, the active compounds of Guizhi had good affinity with the core targets.

Conclusions

In this study, we preliminarily predicted the main active components, targets, and signaling pathways of Guizhi to treat NS, which could provide new ideas for further research on the protective mechanism and clinical application of Guizhi against NS.

Protective Effect of Ginsenoside Rb1 Nanoparticles Against Contrast-Induced Nephropathy by Inhibiting High Mobility Group Box 1 Gene/Toll-Like Receptor 4/NF-κB Signaling Pathway

With the progress made in the widespread application of interventional radiology procedures, there has been an increasing number of patients who suffer from cardiovascular diseases and go through imaging and interventional treatment with iodine contrast medium (ICM) year by year. In turn, there has been an increasing amount of concern over acute kidney injury (AKI) brought about by ICM. As evidenced by numerous studies, the initiation of inflammatory response plays a critical role in the development of ICM-induced AKI. Correspondingly, the strategy of targeting renal inflammatory response and cytokine release could provide an effective solution to mitigating the ICM-induced AKI. Moreover, Ginsenoside Rb1 (GRb1) constitutes one of the major active components of ginseng and features a wide range of vital biological functions. Judging from the research findings, GRb1 could impose antioxidant and anti-inflammatory effects on cardiovascular diseases, in addition to lung, liver and kidney diseases. However, reports on whether GRb1 could impose a protective effect against contrast-induced nephropathy (CIN) are absent. In this study, we have examined the therapeutic effects imposed by GRb1 as well as the potential molecular mechanism by establishing an in vivo and in vitro model of CIN. In addition, we have set up a mouse model of CIN through sequential intravenous injection of indomethacin, N(ω)-nitro-Larginine methyl ester (L-NAME), and iopromide. To further enhance the bioavailability of GRb1, we have encapsulated GRb1 with polyethylene glycol (PEG)/poly lactic-co-glycolic acid (PLGA) nanocarriers to generate GRb1 nanoparticles (NPs) conducting the in vivo experiments. During the in vitro experiments, we have adopted GRb1 to treat NRK-52E cells or cells transfected with the high mobility group box 1 gene (HMGB1) overexpression plasmid. As shown by the in vivo experimental results, GRb1 NPs could evidently improve the renal dysfunction in CIN, diminish the extent of apoptosis of tubular epithelial cells, and reduce the expression of high mobility group box 1 (HMGB1) and cytokines (tumor necrosis factor (TNF-α), interleukin (IL) 6 and IL-1β). In addition, GRb1 NPs are found to be capable of preventing the activation of Toll-like receptor 4 (TLR4)/NF-κB signaling pathway triggered by contrast medium. The in vitro experimental results have exactly confirmed the findings of the in vivo experiments. In the meantime, through the observation of the in vitro assays, overexpression of HMGB1 can partially counteract the beneficial effects imposed by GRb1. Judging from our research data, GRb1 could impose a protective effect against CIN by inhibiting inflammatory response via HMGB1/TLR4/NF-κB pathway, whereas HMGB1 constitutes a critical molecular target of GRb1.

Toll-Like Receptors Regulate the Development and Progression of Renal Diseases

Background

Stimulated by both microbial and endogenous ligands, toll-like receptors (TLRs) play an important role in the development and progression of renal diseases.

Summary

As a highly conserved large family, TLRs have 11 members in humans (TLR1∼TLR11) and 13 members in mouse (TLR1∼TLR13). It has been widely reported that TLR2 and TLR4 signaling, activated by both exogenous and endogenous ligands, promote disease progression in both renal ischemia-reperfusion injury and diabetic nephropathy. TLR4 also vitally functions in CKD and infection-associated renal diseases such as pyelonephritis induced by urinary tract infection. Stimulation of intracellular TLR7/8 and TLR9 by host-derived nucleic acids also plays a key role in systemic lupus erythematosus. Given that certain microRNAs with GU-rich sequence have recently been found to be able to serve as TLR7/8 ligands, these microRNAs may initiate pro-inflammatory signal via activating TLR signal. Moreover, as microRNAs can be transferred across different organs via cell-secreted exosomes or protein-RNA complex, the TLR signaling activated by the miRNAs released by other injured organs may also result in renal dysfunction.

Key Messages

In this review, we sum up the recent progress in the role of TLRs in various forms of glomerulonephritis and discuss the possible prevention or therapeutic strategies for clinic treatment to renal diseases.

Toll-like receptor 4: An attractive therapeutic target for acute kidney injury

Acute kidney injury (AKI) is a progressive renal complication which significantly affects the patient's life with huge economic burden. Untreated acute kidney injury eventually progresses to a chronic form and end-stage renal disease. Although significant breakthroughs have been made in recent years, there are still no effective pharmacological therapies for the treatment of acute kidney injury. Toll-like receptor 4 (TLR4) is a well-characterized pattern recognition receptor, and increasing evidence has shown that TLR4 mediated inflammatory response plays a pivotal role in the pathogenesis of acute kidney injury. The expression of TLR4 has been seen in resident renal cells, including podocytes, mesangial cells, tubular epithelial cells and endothelial cells. Activation of TLR4 signaling regulates the transcription of numerous pro-inflammatory cytokines and chemokines, resulting in renal inflammation. Therefore, targeting TLR4 and its downstream effectors could serve as an effective therapeutic intervention to prevent renal inflammation and subsequent kidney damage. For the first time, this review summarizes the literature on acute kidney injury from the perspective of TLR4 from year 2010 to 2020. In the current review, the role of TLR4 signaling pathway in AKI with preclinical evidence is discussed. Furthermore, we have highlighted several compounds of natural and synthetic origin, which have the potential to avert the renal TLR4 signaling in preclinical AKI models and have shown protection against AKI. This scientific review provides new ideas for targeting TLR4 in the treatment of AKI and provides strategies for the drug development against AKI.

TrkC Is Essential for Nephron Function and Trans-Activates Igf1R Signaling

BACKGROUND

Injury to kidney podocytes often results in chronic glomerular disease and consecutive nephron malfunction. For most glomerular diseases, targeted therapies are lacking. Thus, it is important to identify novel signaling pathways contributing to glomerular disease. Neurotrophic tyrosine kinase receptor 3 (TrkC) is expressed in podocytes and the protein transmits signals to the podocyte actin cytoskeleton.

METHODS

Nephron-specific TrkC knockout (TrkC-KO) and nephron-specific TrkC-overexpressing (TrkC-OE) mice were generated to dissect the role of TrkC in nephron development and maintenance.

RESULTS

Both TrkC-KO and TrkC-OE mice exhibited enlarged glomeruli, mesangial proliferation, basement membrane thickening, albuminuria, podocyte loss, and aspects of FSGS during aging. Igf1 receptor (Igf1R)-associated gene expression was dysregulated in TrkC-KO mouse glomeruli. Phosphoproteins associated with insulin, erb-b2 receptor tyrosine kinase (Erbb), and Toll-like receptor signaling were enriched in lysates of podocytes treated with the TrkC ligand neurotrophin-3 (Nt-3). Activation of TrkC by Nt-3 resulted in phosphorylation of the Igf1R on activating tyrosine residues in podocytes. Igf1R phosphorylation was increased in TrkC-OE mouse kidneys while it was decreased in TrkC-KO kidneys. Furthermore, TrkC expression was elevated in glomerular tissue of patients with diabetic kidney disease compared with control glomerular tissue.

CONCLUSIONS

Our results show that TrkC is essential for maintaining glomerular integrity. Furthermore, TrkC modulates Igf-related signaling in podocytes.

HIF in Nephrotoxicity during Cisplatin Chemotherapy: Regulation, Function and Therapeutic Potential

Simple Summary

Cisplatin is a widely used chemotherapy drug, but its use and efficacy are limited by its nephrotoxicity. HIF has protective effects against kidney injury during cisplatin chemotherapy, but it may attenuate the anti-cancer effect of cisplatin. In this review, we describe the role and regulation of HIF in cisplatin-induced nephrotoxicity and highlight the therapeutic potential of targeting HIF in chemotherapy.

Abstract

Cisplatin is a highly effective, broad-spectrum chemotherapeutic drug, yet its clinical use and efficacy are limited by its side effects. Particularly, cancer patients receiving cisplatin chemotherapy have high incidence of kidney problems. Hypoxia-inducible factor (HIF) is the “master” transcription factor that is induced under hypoxia to trans-activate various genes for adaptation to the low oxygen condition. Numerous studies have reported that HIF activation protects against AKI and promotes kidney recovery in experimental models of cisplatin-induced acute kidney injury (AKI). In contrast, little is known about the effects of HIF on chronic kidney problems following cisplatin chemotherapy. Prolyl hydroxylase (PHD) inhibitors are potent HIF inducers that recently entered clinical use. By inducing HIF, PHD inhibitors may protect kidneys during cisplatin chemotherapy. However, HIF activation by PHD inhibitors may reduce the anti-cancer effect of cisplatin in tumors. Future studies should test PHD inhibitors in tumor-bearing animal models to verify their effects in kidneys and tumors.

Molecular determinants of disease severity in urinary tract infection

The most common and lethal bacterial pathogens have co-evolved with the host. Pathogens are the aggressors, and the host immune system is responsible for the defence. However, immune responses can also become destructive, and excessive innate immune activation is a major cause of infection-associated morbidity, exemplified by symptomatic urinary tract infections (UTIs), which are caused, in part, by excessive innate immune activation. Severe kidney infections (acute pyelonephritis) are a major cause of morbidity and mortality, and painful infections of the urinary bladder (acute cystitis) can become debilitating in susceptible patients. Disease severity is controlled at specific innate immune checkpoints, and a detailed understanding of their functions is crucial for strategies to counter microbial aggression with novel treatment and prevention measures. One approach is the use of bacterial molecules that reprogramme the innate immune system, accelerating or inhibiting disease processes. A very different outcome is asymptomatic bacteriuria, defined by low host immune responsiveness to bacteria with attenuated virulence. This observation provides the rationale for immunomodulation as a new therapeutic tool to deliberately modify host susceptibility, control the host response and avoid severe disease. The power of innate immunity as an arbitrator of health and disease is also highly relevant for emerging pathogens, including the current COVID-19 pandemic.

Biomarkers of Immune Activation and Incident Kidney Failure With Replacement Therapy: Findings From the African American Study of Kidney Disease and Hypertension

RATIONALE & OBJECTIVE

Immune activation is fundamental to the pathogenesis of many kidney diseases. Innate immune molecules such as soluble urokinase-type plasminogen activator receptor (suPAR) have been linked to the incidence and progression of chronic kidney disease (CKD). Whether other biomarkers of immune activation are associated with incident kidney failure with replacement therapy (KFRT) in African Americans with nondiabetic kidney disease is unclear.

STUDY DESIGN

Prospective cohort.

SETTING & PARTICIPANTS

African American Study of Kidney Disease and Hypertension (AASK) participants with available baseline serum samples for biomarker measurement.

PREDICTORS

Baseline serum levels of soluble tumor necrosis factor receptor 1 (sTNFR1), sTNFR2, tumor necrosis factor α (TNF-α), and interferon γ (IFN-γ).

OUTCOMES

Incident KFRT, all-cause mortality.

ANALYTICAL APPROACH

Cox proportional hazards models.

RESULTS

Among 500 participants with available samples, mean glomerular filtration rate was 44.7mL/min/1.73m², and median urinary protein-creatinine ratio was 0.09g/g at baseline. Over a median follow up of 9.6 years, there were 161 (32%) KFRT and 113 (23%) death events. In models adjusted for demographic and clinical factors and baseline kidney function, each 2-fold higher baseline level of sTNFR1, sTNFR2, and TNF-α was associated with 3.66-fold (95% CI, 2.31-5.80), 2.29-fold (95% CI, 1.60-3.29), and 1.35-fold (95% CI, 1.07-1.71) greater risks of KFRT, respectively; in comparison, each doubling of baseline suPAR concentration was associated with 1.39-fold (95% CI, 1.04-1.86) greater risk of KFRT. sTNFR1, sTNFR2, and TNF-α were also significantly associated with death (up to 2.2-fold higher risks per 2-fold higher baseline levels; P≤0.01). IFN-γ was not associated with either outcome. None of the biomarkers modified the association of APOL1 high-risk status (genetic risk factors for kidney disease among individuals of African ancestry) with KFRT (P>0.05 for interaction).

LIMITATIONS

Limited generalizability to other ethnic groups or causes of CKD.

CONCLUSIONS

Among African Americans with CKD attributed to hypertension, baseline levels of sTNFR1, sTNFR2, and TNF-α but not IFN-γ were associated with KFRT and mortality.

Toll-like Receptors as Potential Therapeutic Targets in Kidney Diseases

Toll-like Receptors (TLRs) are members of pattern recognition receptors and serve a pivotal role in host immunity. TLRs response to pathogen-associated molecular patterns encoded by pathogens or damage-associated molecular patterns released by dying cells, initiating an inflammatory cascade, where both beneficial and detrimental effects can be exerted. Accumulated evidence has revealed that TLRs are closely associated with various kidney diseases but their roles are still not well understood. This review updated evidence on the roles of TLRs in the pathogenesis of kidney diseases including urinary tract infection, glomerulonephritis, acute kidney injury, transplant allograft dysfunction and chronic kidney diseases.

Ellagic Acid Ameliorates Renal Ischemic-Reperfusion Injury Through NOX4/JAK/STAT Signaling Pathway

Ellagic acid (EA), a natural polyphenolic compound, has been proved to possess multiple biological activities including alleviating ischemic-reperfusion (I/R) injury. The aim of this current study was to investigate whether EA alleviates I/R injury via regulating inflammatory signaling pathway. Rats were subjected to ischemic-reperfusion (I/R) injury and given orally with different doses of EA before surgery. H&E staining, ELISA assay, and biochemical index analysis were performed to evaluate renal injury and inflammatory factors. Oxidative stress level was detected by DCFH-DA staining and corresponding assay kits. In addition, TUNEL assay and flow cytometric assay were applied for exploring the apoptosis of tissue and cells, respectively. Western blot assay was used to assess protein expressions in tissue and cells. The results showed that EA attenuated the renal I/R injury and reserved renal cell function in vivo. The levels of TNF-a, IL-1β, IL-6, and MCP-1, oxidative stress level, and apoptosis were suppressed in EA-treated rats. Mechanistic studies showed that EA suppressed the phosphorylation of JAK1, JAK2, and STAT1 and reduced the NOX4 level. EA reduced apoptosis, hypoxia-induced inflammatory response, and ROS levels. Moreover, overexpression of NOX4 reversed the protective function with NOX4 inhibition, indicating that the effect of EA against renal IRI or cell hypoxia/reoxygenation might mainly depend on NOX4. The results suggest that EA exerts the renoprotective effect via suppressing NOX4/JAK/STAT signaling pathway, which may be a novel potential therapy for the treatment of acute kidney injury in clinic.

LPS-Induced Acute Kidney Injury Is Mediated by Nox4-SH3YL1

Cytosolic proteins are required for regulation of NADPH (nicotinamide adenine dinucleotide phosphate) oxidase (Nox) isozymes. Here we show that Src homology 3 (SH3) domain-containing YSC84-like 1 (SH3YL1), as a Nox4 cytosolic regulator, mediates lipopolysaccharide (LPS)-induced H₂O₂ generation, leading to acute kidney injury. The SH3YL1, Ysc84p/Lsb4p, Lsb3p, and plant FYVE proteins (SYLF) region and SH3 domain of SH3YL1 contribute to formation of a complex with Nox4-p22^phox. Interaction of p22^phox with SH3YL1 is triggered by LPS, and the complex induces H₂O₂ generation and pro-inflammatory cytokine expression in mouse tubular epithelial cells. After LPS injection, SH3YL1 knockout mice show lower levels of acute kidney injury biomarkers, decreased secretion of pro-inflammatory cytokines, decreased infiltration of macrophages, and reduced tubular damage compared with wild-type (WT) mice. The results strongly suggest that SH3YL1 is involved in renal failure in LPS-induced acute kidney injury (AKI) mice. We demonstrate that formation of a ternary complex of p22^phox-SH3YL1-Nox4, leading to H₂O₂ generation, induces severe renal failure in the LPS-induced AKI model.

The Emerging Role of Innate Immunity in Chronic Kidney Diseases

Renal fibrosis is a common fate of chronic kidney diseases. Emerging studies suggest that unsolved inflammation will progressively transit into tissue fibrosis that finally results in an irreversible end-stage renal disease (ESRD). Renal inflammation recruits and activates immunocytes, which largely promotes tissue scarring of the diseased kidney. Importantly, studies have suggested a crucial role of innate immunity in the pathologic basis of kidney diseases. This review provides an update of both clinical and experimental information, focused on how innate immune signaling contributes to renal fibrogenesis. A better understanding of the underlying mechanisms may uncover a novel therapeutic strategy for ESRD.

Selective nanoparticle-mediated targeting of renal tubular Toll-like receptor 9 attenuates ischemic acute kidney injury

We developed an innovative therapy for ischemic acute kidney injury with discerning kidney-targeted delivery of a selective Toll-like receptor 9 (TLR9) antagonist in mice subjected to renal ischemia reperfusion injury. Our previous studies showed that mice deficient in renal proximal tubular TLR9 were protected against renal ischemia reperfusion injury demonstrating a critical role for renal proximal tubular TLR9 in generating ischemic acute kidney injury. Herein, we used 300-400 nm polymer-based mesoscale nanoparticles that localize to the renal tubules after intravenous injection. Mice were subjected to sham surgery or 30 minutes renal ischemia and reperfusion injury after receiving mesoscale nanoparticles encapsulated with a selective TLR9 antagonist (unmethylated CpG oligonucleotide ODN2088) or mesoscale nanoparticles encapsulating a negative control oligonucleotide. Mice treated with the encapsulated TLR9 antagonist either six hours before renal ischemia, at the time of reperfusion or 1.5 hours after reperfusion were protected against ischemic acute kidney injury. The ODN2088-encapsulated nanoparticles attenuated renal tubular necrosis, inflammation, decreased proinflammatory cytokine synthesis. neutrophil and macrophage infiltration and apoptosis, decreased DNA fragmentation and caspase 3/8 activation when compared to the negative control nanoparticle treated mice. Taken together, our studies further suggest that renal proximal tubular TLR9 activation exacerbates ischemic acute kidney injury by promoting renal tubular inflammation, apoptosis and necrosis after ischemia reperfusion. Thus, our studies suggest a potential promising therapy for ischemic acute kidney injury with selective kidney tubular targeting of TLR9 using mesoscale nanoparticle-based drug delivery.

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.

Cordycepin protects renal ischemia/reperfusion injury through regulating inflammation, apoptosis, and oxidative stress

Cordycepin (3'-deoxyadenosine) is a naturally occurring adenosine analog and one of the bioactive constituents isolated from Cordyceps sinensis, species of the fungal genus Cordyceps. It has traditionally been a prized Chinese folk medicine for the human well-being. However, the actions of cordycepin against renal ischemia/reperfusion injury (I/R) are still unknown. In the present study, rats were subject to I/R and cordycepin was intragastrically administered for seven consecutive days before surgery to investigate the effects and mechanisms of cordycepin against renal I/R injury. The test results of kidney and peripheral blood samples of experimental animals showed that cordycepin significantly decreased serum blood urea nitrogen and creatinine levels and markedly attenuated cell injury. Mechanistic studies showed that cordycepin significantly regulated inflammation, apoptosis, and oxidative stress. These data provide new insights for investigating the natural product with the nephroprotective effect against I/R, which should be developed as a new therapeutic agent for the treatment of I/R in the future.

Mechanisms and therapeutic targets of ischemic acute kidney injury

Acute kidney injury (AKI) due to renal ischemia reperfusion (IR) is a major clinical problem without effective therapy and is a significant and frequent cause of morbidity and mortality during the perioperative period. Although the pathophysiology of ischemic AKI is not completely understood, several important mechanisms of renal IR-induced AKI have been studied. Renal ischemia and subsequent reperfusion injury initiates signaling cascades mediating renal cell necrosis, apoptosis, and inflammation, leading to AKI. Better understanding of the molecular and cellular pathophysiological mechanisms underlying ischemic AKI will provide more targeted approach to prevent and treat renal IR injury. In this review, we summarize important mechanisms of ischemic AKI, including renal cell death pathways and the contribution of endothelial cells, epithelial cells, and leukocytes to the inflammatory response during ischemic AKI. Additionally, we provide some updated potential therapeutic targets for the prevention or treatment of ischemic AKI, including Toll-like receptors, adenosine receptors, and peptidylarginine deiminase 4. Finally, we propose mechanisms of ischemic AKI-induced liver, intestine, and kidney dysfunction and systemic inflammation mainly mediated by Paneth cell degranulation as a potential explanation for the high mortality observed with AKI.

Treatment with toll-like receptor 2 inhibitor ortho-vanillin alleviates lipopolysaccharide-induced acute kidney injury in mice

Reducing inflammation is a promising approach for the prevention and treatment of septic acute kidney injury (AKI), since AKI is characterized by excessive inflammation in the kidney. Previous studies have demonstrated that toll-like receptor 2 (TLR2) is overstimulated, which promotes inflammation by activating the NF-κB signaling pathway, in a lipopolysaccharide (LPS)-induced model of AKI mice. For the present study, it was hypothesized that TLR2 inhibition could reduce inflammation and consequently prevent septic AKI. Therefore, the potential renal protective effects of ortho-vanillin (OV), an inhibitor of TLR2, were investigated in the present study in vitro and in vivo. In vitro treatment with OV on LPS-stimulated mouse podocyte cell line MPC5 did not affect TLR2 expression but interrupted the interaction between TLR2 and its downstream adaptor MyD88, resulting in the reduction of inflammatory cytokines IL-6 and TNF-α expression. In vivo OV treatment in an LPS-challenged mouse model effectively alleviated LPS-induced kidney injury as indicated by histology analysis and the significantly reduced blood urea nitrogen and serum creatinine levels. Additionally, inflammatory cytokines TNF-α, IL-6 and IL-1β expression were also significantly reduced in mice with OV treatment. Signaling pathway analysis further demonstrated that OV treatment did not affect the expression of TLR2 and p65 but suppressed p65 phosphorylation. Taken together, data from the present study demonstrated that OV was effective in protecting renal function against LPS-induced AKI through the inhibition of TLR2/NF-κB signaling and subsequent inflammatory cytokine production. These findings indicated that OV or targeting TLR2 signaling in general, represents a novel therapeutic approach for use in the prevention and treatment of AKI.

NLRP2 Regulates Proinflammatory and Antiapoptotic Responses in Proximal Tubular Epithelial Cells

Nod-like Receptor Pyrin domain containing proteins (NLRPs) expressed by resident renal cells may contribute to the pathogenesis of multiple renal diseases. Cystinosis is a genetic disorder that affects kidney and particularly proximal tubular epithelial cells (PTEC). Here, we investigated the expression of NLRP family members in human control and cystinotic conditionally immortalized PTEC. Among all the NLRPs tested, we found that NLRP2 is highly expressed in cystinostic PTEC, but not in PTEC from healthy subjects. The NLRP2 overexpression was confirmed in primary PTEC and in kidney biopsies from cystinotic patients. In order to elucidate the role of NLRP2 in PTEC, we stably transfected control PTEC with an NLRP2-containing plasmid. We showed that NLRP2 markedly increases the production of several NF-κB regulated cytokines and chemokines. Accordingly, we demonstrated that NLRP2 interacts with IKKa and positively regulates the DNA-binding activity of p50 and p65 NF-κB, by modulating the p65 NF-κB phosphorylation status in Serine 536. Transcriptome analysis revealed that NLRP2 also upregulates the expression of profibrotic mediators and reduces that of several interferon-inducible genes. Finally, NLRP2 overexpression decreased the apoptotic cell rate. Consistently, silencing of NLRP2 by small-interfering RNA in cystinotic PTEC resulted in a significant decrease in cytokine and chemokine production as well as in an increase in the apoptosis rate. Altogether, our data reveals a previously unrecognized role for NLRP2 in regulating proinflammatory, profibrotic and antiapoptotic responses in PTEC, through NF-κB activation. Moreover, our findings unveil a novel potential mechanism involving NLRP2 overexpression in the pathogenesis of cystinosis.

A glance at molecular mechanisms underlying cisplatin-induced nephrotoxicity and possible renoprotective strategies: a narrative review

Cisplatin is a platinum-based drug that is usually used for the treatment of many carcinomas. However, it comes with several devastating side effects, including nephrotoxicity. Cisplatin toxicity is a very complex process, which is exacerbated by the accumulation of cisplatin in renal tubular cells via passive diffusion and transporter-mediated processes. Once cisplatin enters these cells, it induces the formation of reactive oxygen species that cause cellular damage, including DNA damage, inflammation, and eventually cell death. On a small scale, these damages can be mitigated by cellular antioxidant defense mechanism. However, on a large scale, such as in chemotherapy, this defense mechanism may fail, resulting in nephrotoxicity. The current article reviews the molecular mechanisms underlying cisplatin-induced nephrotoxicity and possible renoprotective strategies to determine novel therapeutic interventions for alleviating this toxicity.

Telbivudine antagonizes TLR4 to inhibit the epithelial-to-mesenchymal transition in human proximal tubular epithelial cells in vitro

The antiviral drug Telbivudine (LdT) has an extrahepatic pharmaceutical effect that improves renal inflammation and tubulointerstitial fibrosis. However, the exact mechanism of action requires further investigation. Toll-like receptor 4 (TLR4) is involved in several physiological processes, including inflammation, fibrosis, innate immunity, and hepatitis B virus-associated glomerulonephritis. The epithelial-to-mesenchymal transition (EMT) is the characteristic pathological change in tubulointerstitial fibrosis. In this study, we used transforming growth factor-β (TGF-β) to stimulate human proximal tubular epithelial (HK-2) cells to investigate the effects of LdT in EMT. In addition, we treated HK-2 cells with a TLR4 agonist, lipopolysaccharide, to determine the effect of LdT on TLR4. The results indicated that LdT inhibited the expression of TLR4 and its downstream proteins. It also decreased the release of inflammatory factors, downregulated the TGF-β/Smad signaling pathway, and reversed the EMT changes seen in HK-2 cells. In conclusion, LdT antagonized TLR4 to inhibit EMT in proximal tubular epithelial cells.

Tetramethylpyrazine guards against cisplatin-induced nephrotoxicity in rats through inhibiting HMGB1/TLR4/NF-κB and activating Nrf2 and PPAR-γ signaling pathways

Cisplatin-induced acute renal injury is the most common and serious side effect, sometimes requiring discontinuation of the treatment. Thus, the development of new protective strategies is essential. The present study aimed to investigate the potential nephroprotective effect of tetramethylpyrazine (TMP) against acute renal damage induced by cisplatin in rats. Rats were administered 50 and 100 mg/kg TMP intraperitoneally before cisplatin (7 mg/kg). Acute nephrotoxicity was evident in cisplatin-treated rats where relative kidney weight, BUN and serum creatinine were markedly elevated. Cisplatin administration resulted in enhanced oxidative stress, evidenced by depleted GSH level as well as catalase and superoxide dismutase activities. Also, lipid peroxidation was boosted in comparison to the control. This was associated with inhibition of Nrf2 defense pathway. Moreover, cisplatin increased the expression of pro-inflammatory mediators in the kidney tissues. Cisplatin-induced apoptosis was depicted by elevated Bax mRNA expression and caspase-3 activity, as well as decreased Bcl2 mRNA expression. In addition, high mobility group box 1/toll-like receptor 4/nuclear factor-kappa B (HMGB1/TLR4/NF-κB) signaling pathway was significantly upregulated, while peroxisome proliferator-activated receptor-gamma (PPAR-γ) expression was significantly diminished in cisplatin-treated rats. Cisplatin-induced nephrotoxicity, oxidative stress, inflammation, apoptosis and the effect on Nrf2 defense pathway and HMGB1/TLR4/NF-κB as well as PPAR-γ expression were markedly ameliorated by TMP administration. Given the major nephrotoxicity of cisplatin cancer chemotherapy, TMP might be a potential candidate for neoadjuvant chemotherapy due to its antioxidant, anti-inflammatory and anti-apoptotic effects, in addition to its effect on Nrf2, HMGB1/TLR4/NF-κB signaling pathway and PPAR-γ expression.

Urinary tract infections (UTIs) or genital tract infections (GTIs)? It's the diagnostics that count

Urinary tract infections (UTIs) and genital tract infections (GTIs) are both very common infectious diseases. Thus, accuracy and rapidity in recognition and treatment of sexually transmitted urogenital tract infections (ST-UGTIs) is a major concern in global public health systems. The application of reliable, accurate diagnostic tools is the key to definite detection, identification and treatment. This literature review focused on different characteristics of UGTIs in patients and the importance of diagnostic methodologies.

The articles published and indexed from 1980 through October 2018 in the databases of PubMed and MEDLINE, as well as the Google Scholar web search engine, were collected and studied. MeSH keywords of “Sexual intercourse”, “Urinary Tract Infections”, “Genital Tract Infections” and “Toll-Like Receptors” were used for searching articles. Then, the proper articles (original and review articles) were subjected to a very rigorous selection process.

The clinical symptoms and signs or asymptomatic properties of UTIs and GTIs are similar and often overlap. In many cases, the lack of suitable diagnostic techniques leads to misdiagnosed/undignosed GTIs and overdiagnosed UTIs. The outcome of poor diagnostics is failure of definite identification and treatment.

The application of advanced techniques comprising PCR, microarray and next-generation sequencing promises to be more effective, together with the use of the microbial pattern of the individual’s UGT to provide reliable detection, identification and definite treatment. This will be an option in the near future.

Indispensable role of β-arrestin2 in the protection of remifentanil preconditioning against hepatic ischemic reperfusion injury

Our previous study demonstrated that remifentanil, an opioid agonist, conferred profound liver protection during hepatic ischemia reperfusion injury (HIRI), in which Toll-like receptors (TLRs) played a crucial role in mediating the inflammatory responses. β-arrestin2, a well-known mu opioid receptor desensitizer, is also a negatively regulator of Toll-like receptor 4 (TLR4)-mediated inflammatory reactions in a mitogen-activated protein kinase (MAPK)-dependent manner. Using the rodent models of hepatic ischemia reperfusion injury both in wild type and TLR4 knockout (TLR4 KO) mice, we found that remifentanil preconditioning could inhibit the expression of TLR4 and reduce the inflammatory response induced by HIRI in wild type but not in TLR4 KO mice. For the in-vitro study, LPS was used to treat RAW264.7 macrophage cells to mimic the inflammatory response induced by HIRI. Remifentanil increased β-arrestin2 expression both in vivo and in vitro, while after silencing β-arrestin2 RNA, the effect of remifentanil in reducing cell death and apoptosis, as well as decreasing phosphorylation of ERK and JNK were abolished in RAW264.7 cells. These data suggested that remifentanil could ameliorate mice HIRI through upregulating β-arrestin2 expression, which may function as a key molecule in bridging opioid receptor and TLR4 pathway.

Epithelial innate immunity mediates tubular cell senescence after kidney injury

Acute kidney injury (AKI) is a common clinical condition of growing incidence. Patients who suffer severe AKI have a higher risk of developing interstitial fibrosis, chronic kidney disease, and end-stage renal disease later in life. Cellular senescence is a persistent cell cycle arrest and altered gene expression pattern evoked by multiple stressors. The number of senescent cells increases with age and even in small numbers these cells can induce chronic inflammation and fibrosis; indeed, in multiple organs including kidneys, the accumulation of such cells is a hallmark of aging. We hypothesized that cellular senescence might be induced in the kidney after injury and that this might contribute to progressive organ fibrosis. Testing this hypothesis, we found that tubular epithelial cells (TECs) in mice senesce within a few days of kidney injury and that this response is mediated by epithelial Toll-like and interleukin 1 receptors (TLR/IL-1R) of the innate immune system. Epithelial cell-specific inhibition of innate immune signaling in mice by knockout of myeloid differentiation 88 (Myd88) reduced fibrosis as well as damage to kidney tubules, and also prevented the accumulation of senescent TECs. Importantly, although inactivation of Myd88 after injury ameliorated fibrosis, it did not reduce damage to the tubules. Selectively induced apoptosis of senescent cells by two different approaches only partially reduced kidney fibrosis, without ameliorating damage to the tubules. Our data reveal a cell-autonomous role for epithelial innate immunity in controlling TEC senescence after kidney injury, and additionally suggest that early therapeutic intervention is required for effective reduction of long-term sequelae of AKI.

How Tubular Epithelial Cell Injury Contributes to Renal Fibrosis

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