Extracellular Superoxide Dismutase Protects against Proteinuric Kidney Disease

Extracellular superoxide dismutase (EC-SOD), also known as SOD3, is an antioxidant expressed at high levels in normal adult kidneys. Because oxidative stress contributes to a variety of kidney injuries, we hypothesized that EC-SOD may be protective in CKD progression. To study this hypothesis, we used a murine model of ADR nephropathy characterized by albuminuria and renal dysfunction. We found that levels of EC-SOD diminished throughout the course of disease progression and were associated with increased levels of NADPH oxidase and oxidative stress markers. EC-SOD null mice were sensitized to ADR injury, as evidenced by increases in albuminuria, serum creatinine, histologic damage, and oxidative stress. The absence of EC-SOD led to increased levels of NADPH oxidase and an increase in β-catenin signaling, which has been shown to be pathologic in a variety of kidney injuries. Exposure of EC-SOD null mice to either chronic angiotensin II infusion or to daily albumin injections also caused increased proteinuria. In contrast, EC-SOD null mice subjected to nonproteinuric CKD induced by unilateral ureteral obstruction exhibited no differences compared with wild-type mice. Finally, we also found a decrease in EC-SOD in human CKD biopsy samples, similar to our findings in mice. Therefore, we conclude that EC-SOD is protective in CKDs characterized by proteinuria.     

Pirfenidone Is Renoprotective in Diabetic Kidney Disease

Although several interventions slow the progression of diabetic nephropathy, current therapies do not halt progression completely. Recent preclinical studies suggested that pirfenidone (PFD) prevents fibrosis in various diseases, but the mechanisms underlying its antifibrotic action are incompletely understood. Here, we evaluated the role of PFD in regulation of the extracellular matrix. In mouse mesangial cells, PFD decreased TGF-β promoter activity, reduced TGF-β protein secretion, and inhibited TGF-β–induced Smad2-phosphorylation, 3TP-lux promoter activity, and generation of reactive oxygen species. To explore the therapeutic potential of PFD, we administered PFD to 17-wk-old db/db mice for 4 wk. PFD treatment significantly reduced mesangial matrix expansion and expression of renal matrix genes but did not affect albuminuria. Using liquid chromatography with subsequent electrospray ionization tandem mass spectrometry, we identified 21 proteins unique to PFD-treated diabetic kidneys. Analysis of gene ontology and protein–protein interactions of these proteins suggested that PFD may regulate RNA processing. Immunoblotting demonstrated that PFD promotes dosage-dependent dephosphorylation of eukaryotic initiation factor, potentially inhibiting translation of mRNA. In conclusion, PFD is renoprotective in diabetic kidney disease and may exert its antifibrotic effects, in part, via inhibiting RNA processing.Diabetic nephropathy (DN) is the single major cause of the emerging epidemic of ESRD in the United States,¹ accounting for nearly 50% of all new cases.² Characteristic morphologic lesions of DN include glomerular hypertrophy, thickening of the basement membrane, and mesangial expansion.³ Several interventions, such as tight glycemic control and antihypertensive therapy, especially angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II receptor blockers,^4–9 have been shown to slow the progression of established disease. Nevertheless, DN remains a major long-term complication of both types 1 and 2 diabetes,^10,11 because treatment commenced after the manifestation of overt clinical nephropathy often does not arrest progression to ESRD.¹¹ The annual medical cost for treatment of patients with diabetes ESRD is expected to be $18 to 30 billion (US) during the next decade.^12–15 It is therefore imperative to identify novel drug-therapeutic regimens that can ideally arrest further progression of the disease after manifestation of nephropathy.Pirfenidone (PFD; 5-methyl-1-phenyl-2-(1H)-pyridone) is a low molecular weight synthetic molecule that exerts dramatic antifibrotic properties in cell culture and various animal models of fibrosis.^16,17 PFD has emerged as a promising oral treatment with few adverse effects in open-label clinical studies. A study of hemodialysis patients with a history of sclerosing peritonitis demonstrated that it may not be necessary to adjust dosages of PFD for renal impairment and that the drug is well tolerated even in ESRD.¹⁸ In an open-label study wherein PFD was administered to patients with advanced refractory focal sclerosis, there was a good safety profile in patients with impaired renal function and heavy proteinuria, and PFD slowed the rate of decline of renal function by 25%.¹⁹ In a Phase III trial for patients with idiopathic pulmonary fibrosis in Japan, PFD was reported to promote stabilization and improvement of lung function.²⁰ Of note, there have been no reports that PFD may worsen renal blood flow, lower BP, affect glycemic parameters, or cause hyperkalemia, thereby making this treatment approach truly unique as compared with presently available renin-angiotensin-aldosterone antagonists. Thus, the combined experience with PFD in patients and in animal models of progressive kidney disease suggests that the compound is safe and may provide stabilization of renal function.To determine whether PFD is potentially beneficial in diabetic kidney disease, we studied the effects of PFD in cell culture experiments and in the db/db mouse model of diabetic kidney disease. In cell culture studies, PFD inhibited TGF-β production and TGF-β signaling and reduced TGF-β–induced reactive oxygen species (ROS) production. In the db/db mouse, PFD promoted resolution of mesangial matrix when administered after the onset of nephropathy. For identification of novel pathways of PFD relevant to DN, proteomic studies of the whole kidneys followed by bioinformatic analyses revealed RNA processing as a novel mechanism of PFD action. In support of a role of PFD to affect mRNA translation, PFD was found to regulate the activity of eukaryotic initiation factor (eIF4E), a key mRNA cap-structure binding protein, in mesangial cells in culture.     

2型糖尿病住院患者糖尿病肾脏疾病的发生率及危险因素分析

目的：分析2型糖尿病住院患者的糖尿病肾脏疾病（DKD）的发生率及危险因素,为临床糖尿病肾脏疾病的防治工作提供理论依据。方法：对2008年1月～2010年8月在上海交通大学附属第六人民医院内分泌代谢科住院的2型糖尿病患者测定血糖、肾功能、血脂谱、24h尿白蛋白等。应用简化肾脏病膳食改良试验（MDRD）公式计算肾小球滤过率（GFRMDRD）。所有患者均由眼科医生进行眼底摄片。按2007年美国肾脏病基金会（NKF）的糖尿病和慢性肾脏疾病的临床诊断治疗指南,将研究人群分为正常组（NCKD）、非糖尿病性肾脏疾病（NDRD）组及DKD组。结果：（1）共入选患者2225例,男1184例,女1041例;平均年龄为（60.5±11.7）岁。本研究人群中,DKD的发生率为15.4%,NDRD的发生率为18.5%。（2）DKD组患者的年龄、糖尿病病程、收缩压、血肌酐、总胆固醇（TC）、低密度胆固醇水平（LDL-C）、24h尿白蛋白量均显著高于NDRD组（P〈0.05）。（3）Logistic回归分析显示：糖尿病病程（OR=1.077,95%CI为1.059～1.096,P〈0.01）、收缩压（OR=1.039,95%CI为1.032～1.047,P〈0.01）、糖化血红蛋白（OR=1.092,95%CI为1.032～1.156,P〈0.01）、TC（OR=1.171,95%CI为1.050～1.306,P〈0.01）、HDL-C（OR=0.558,95%CI为0.369～0.844,P〈0.01）是DKD发生的独立危险因素。结论：为有效地延缓2型糖尿病肾脏病变的发生及发展,临床工作中要严格控制血压、血糖、血脂。     

Metabolomics Reveals a Key Role for Fumarate in Mediating the Effects of NADPH Oxidase 4 in Diabetic Kidney Disease

The NADPH oxidase (NOX) isoform NOX4 has been linked with diabetic kidney disease (DKD). However, a mechanistic understanding of the downstream effects of NOX4 remains to be established. We report that podocyte-specific induction of NOX4 in vivo was sufficient to recapitulate the characteristic glomerular changes noted with DKD, including glomerular hypertrophy, mesangial matrix accumulation, glomerular basement membrane thickening, albuminuria, and podocyte dropout. Intervention with a NOX1/NOX4 inhibitor reduced albuminuria, glomerular hypertrophy, and mesangial matrix accumulation in the F1 Akita model of DKD. Metabolomic analyses from these mouse studies revealed that tricarboxylic acid (TCA) cycle–related urinary metabolites were increased in DKD, but fumarate levels were uniquely reduced by the NOX1/NOX4 inhibitor. Expression of fumarate hydratase (FH), which regulates urine fumarate accumulation, was reduced in the diabetic kidney (in mouse and human tissue), and administration of the NOX1/NOX4 inhibitor increased glomerular FH levels in diabetic mice. Induction of Nox4 in vitro and in the podocyte-specific NOX4 transgenic mouse led to reduced FH levels. In vitro, fumarate stimulated endoplasmic reticulum stress, matrix gene expression, and expression of hypoxia-inducible factor-1α (HIF-1α) and TGF-β. Similar upregulation of renal HIF-1α and TGF-β expression was observed in NOX4 transgenic mice and diabetic mice and was attenuated by NOX1/NOX4 inhibition in diabetic mice. In conclusion, NOX4 is a major mediator of diabetes-associated glomerular dysfunction through targeting of renal FH, which increases fumarate levels. Fumarate is therefore a key link connecting metabolic pathways to DKD pathogenesis, and measuring urinary fumarate levels may have application for monitoring renal NOX4 activity.     

Effect of Spironolactone on Urinary Protein Excretion in Patients with Chronic Kidney Disease

Aim.?To investigate antiproteinuric effect of spironolactone in patients with chronic kidney disease (CKD) treated with angiotensin-converting enzyme (ACE) inhibitors and/or angiotensin II type 1 receptor blockers (ARBs).?Methods.?This study was performed in 33 CKD patients with proteinuria. 24 h urinary protein excretion and biochemical parameters were obtained before the therapy. Then, spironolactone (25 mg/d) was added to the therapy. The antiproteinuric effect of spironolactone was examined for eight weeks.?Results.?At eight weeks, there was a significant decrease in proteinuria (p < 0.001, 47.9% decrease). Systolic and diastolic blood pressures were significantly decreased (p < 0.004, p < 0.001, respectively). However, no correlation was detected between the reductions in systolic and diastolic BP and the reduction in proteinuria (p = 0.464, p = 0.239, respectively). Serum potassium level increased significantly (p < 0.001).?Conclusions.?Our study suggests that spironolactone significantly reduces urinary protein excretion. This strategy may be useful to slow the progression of CKD. However, hyperkalemia is the most important side effect of treatment, and it is necessary to monitor potassium level. Further studies are needed to determine the efficacy of spironolactone on proteinuria.     

Crumbs2 Is an Essential Slit Diaphragm Protein of the Renal Filtration Barrier

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ADAM10-Mediated Ectodomain Shedding Is an Essential Driver of Podocyte Damage

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Sphingomyelinase-Like Phosphodiesterase 3b Expression Levels Determine Podocyte Injury Phenotypes in Glomerular Disease

Diabetic kidney disease (DKD) is the most common cause of ESRD in the United States. Podocyte injury is an important feature of DKD that is likely to be caused by circulating factors other than glucose. Soluble urokinase plasminogen activator receptor (suPAR) is a circulating factor found to be elevated in the serum of patients with FSGS and causes podocyte αVβ₃ integrin-dependent migration in vitro. Furthermore, αVβ₃ integrin activation occurs in association with decreased podocyte-specific expression of acid sphingomyelinase-like phosphodiesterase 3b (SMPDL3b) in kidney biopsy specimens from patients with FSGS. However, whether suPAR-dependent αVβ₃ integrin activation occurs in diseases other than FSGS and whether there is a direct link between circulating suPAR levels and SMPDL3b expression in podocytes remain to be established. Our data indicate that serum suPAR levels are also elevated in patients with DKD. However, unlike in FSGS, SMPDL3b expression was increased in glomeruli from patients with DKD and DKD sera-treated human podocytes, where it prevented αVβ₃ integrin activation by its interaction with suPAR and led to increased RhoA activity, rendering podocytes more susceptible to apoptosis. In vivo, inhibition of acid sphingomyelinase reduced proteinuria in experimental DKD but not FSGS, indicating that SMPDL3b expression levels determined the podocyte injury phenotype. These observations suggest that SMPDL3b may be an important modulator of podocyte function by shifting suPAR-mediated podocyte injury from a migratory phenotype to an apoptotic phenotype and that it represents a novel therapeutic glomerular disease target.     

Corticosteroid treatment exacerbates nephrotic syndrome in a zebrafish model of magi2a knockout

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