TNF-α-mediated podocyte injury via the apoptotic death receptor pathway in a mouse model of IgA nephropathy

BackgroundIgA nephropathy (IgAN) is the most common primary glomerular disease worldwide and it is characterized by mesangial IgA deposits. Proteinuria is a common clinical feature of IgAN, which has a critical connection to podocyte injury and has been used as a clinical prognostic factor for IgAN. Evidence has shown that TNF-α released from mesangial cells may lead to podocyte apoptosis.MethodsForty male BALB/c mouse were randomly divided into the control group and IgAN group. A mice model of IgAN was developed by oral administration of bovine serum albumin (BSA) combined with Staphylococcus Enterotoxin B (SEB) tail vein injection. Urinary protein concentrations, renal function, renal morphological, IgA deposition, apoptosis situation, and the mRNA and protein expression of nephrin, podocin, TNF-α, TNFR1, caspase-8 and caspase-3, were detected after 12 weeks.ResultsBSA and SEB can successfully establish an IgAN mouse model, and the main pathological changes are the IgA immune complex deposition in the mesangial area. The gene and protein expression levels of nephrin and podocin were found to be downregulated, and death receptor pathway-related indicators were upregulated, and they were involved in TNF-α-activated podocyte injury and apoptosis in IgAN mice.ConclusionTNF-α may play an important role in the pathogenesis of podocyte apoptosis in IgAN, and its effects may be mediated through the apoptotic death receptor pathway.     

补肾活血方保护FSGS小鼠足细胞的实验研究

[目的]观察补肾活血方对局灶性节段性肾小球硬化(FSGS)小鼠足细胞骨架蛋白desmin,足细胞裂孔膜蛋白nephrin及肾母细胞瘤wt1的影响,探讨此组方保护足细胞的作用机制。[方法]以阿霉素诱导方式完成FSGS肾病模型制备,在1周之后以补肾活血方开展治疗(设为治疗组),时间持续6周。然后再设空白对照组与模型组。针对3组的尿、血及肾组织等进行收集,并检测体质量、血清白蛋白(ALB)、24 h尿白蛋白排泄率(UAER)以及尿白蛋白/尿肌酐比值(UACR)等。通过光镜针对肾组织形态变化情况进行观察分析,以免疫荧光完成小鼠的肾组织nephrin荧光强度测定工作;采用逆转录-聚合酶链反应(RT-PCR)检测3组肾组织当中的desmin、wt1表达水平。[结果]模型组UAER、UACR显著高于空白对照组与治疗组(P0.01),模型组体质量和ALB显著低于空白对照组和治疗组(P0.01)。空白对照组nephrin免疫荧光表达具有连续性特征,而模型组则是具有少量点状或者片状特征,较空白对照组和治疗组表达明显减少。模型组当中的wt1 mRNA表达水平明显低于治疗组、空白对照组(P0.01),而desmin mRNA表达水平明显超过空白对照组、治疗组(P0.01)。[结论]采用补肾活血组方可以降低FSGS小鼠蛋白尿,同时有可能和wt1、nephrin表达水平上调,以及desmin表达水平下调存在关系。     

B7–1 Is Not Induced in Podocytes of Human and Experimental Diabetic Nephropathy

The incidence of progressive kidney disease associated with diabetes continues to rise worldwide. Current standard therapy with angiotensin–converting enzyme inhibitors and/or angiotensin receptor blockers achieves only partial renoprotection, increasing the need for novel therapeutic approaches. Previous studies described B7–1 induction in podocytes of patients with proteinuria, including those with FSGS and type 2 diabetic nephropathy (DN). These findings sparked great excitement in the renal community, implying that abatacept, a costimulatory inhibitor that targets B7–1, could be a novel therapy for diabetic renal disease. Given previous concerns over the value of B7–1 immunostaining and the efficacy of abatacept in patients with recurrent FSGS after renal transplantation, we investigated B7–1 expression in human and experimental DN before embarking on clinical studies of the use of B7–1 targeting strategies to treat proteinuria in DN. Immunohistochemical analysis of kidney specimens using different antibodies revealed that B7–1 is not induced in podocytes of patients with DN, independent of disease stage, or BTBR ob/ob mice, a model of type 2 diabetes. These results do not support the use of abatacept as a therapeutic strategy for targeting podocyte B7–1 for the prevention or treatment of DN.     

Comparison of Glomerular and Podocyte mRNA Profiles in Streptozotocin-Induced Diabetes

Evaluating the mRNA profile of podocytes in the diabetic kidney may indicate genes involved in the pathogenesis of diabetic nephropathy. To determine if the podocyte-specific gene information contained in mRNA profiles of the whole glomerulus of the diabetic kidney accurately reflects gene expression in the isolated podocytes, we crossed Nos3^−/− IRG mice with podocin-rtTA and TetON-Cre mice for enhanced green fluorescent protein labeling of podocytes before diabetic injury. Diabetes was induced by streptozotocin, and mRNA profiles of isolated glomeruli and sorted podocytes from diabetic and control mice were examined 10 weeks later. Expression of podocyte-specific markers in glomeruli was downregulated in diabetic mice compared with controls. However, expression of these markers was not altered in sorted podocytes from diabetic mice. When mRNA levels of glomeruli were corrected for podocyte number per glomerulus, the differences in podocyte marker expression disappeared. Analysis of the differentially expressed genes in diabetic mice also revealed distinct upregulated pathways in the glomeruli (mitochondrial function, oxidative stress) and in podocytes (actin organization). In conclusion, our data suggest reduced expression of podocyte markers in glomeruli is a secondary effect of reduced podocyte number, thus podocyte-specific gene expression detected in the whole glomerulus may not represent that in podocytes in the diabetic kidney.     

Focal Segmental Glomerulosclerosis Associated with Mitochondrial Cytopathy: Report of Two Cases with Special Emphasis on Podocytes

We report two children with focal segmental glomerulosclerosis (FSGS) associated with mitochondrial cytopathy (MC). Case 1 was diagnosed as MC with the findings of ptosis, ophthalmoplegia, failure to thrive, high serum lactate and pyruvate levels, ragged red fibers in muscle biopsy and the common 4.9 kb deletion in mtDNA when she was four years old. She subsequently developed FSGS four years later. Case 2 was a four month-old girl presenting with feeding difficulty from birth, with vomiting, seizures and nystagmoid eye movements, nephrotic proteinuria and hematuria. Renal biopsy revealed FSGS. Ultrastructural study demonstrated markedly pleomorphic mitochondria in podocytes with a severe effacement of foot processes. The analyses of muscle biopsy and skin fibroblasts for respiratory chain enzymes were found to be normal, while mitochondrial DNA analysis revealed the population of a single deleted mtDNA in the heteroplasmic state. The present cases illustrate FSGS as a rare renal complication of mitochondrial disease and provide further evidence of podocytes possessing abnormal mitochondria which may cause glomerular epithelial cell damage leading to glomerulosclerosis.     

BDNF repairs podocyte damage by microRNA‐mediated increase of actin polymerization

Idiopathic focal segmental glomerulosclerosis (FSGS) is a progressive and proteinuric kidney disease that starts with podocyte injury. Podocytes cover the external side of the glomerular capillary by a complex web of primary and secondary ramifications. Similar to dendritic spines of neuronal cells, podocyte processes rely on a dynamic actin‐based cytoskeletal architecture to maintain shape and function. Brain‐derived neurotrophic factor (BDNF) is a pleiotropic neurotrophin that binds to the tropomyosin‐related kinase B receptor (TrkB) and has crucial roles in neuron maturation, survival, and activity. In neuronal cultures, exogenously added BDNF increases the number and size of dendritic spines. In animal models, BDNF administration is beneficial in both central and peripheral nervous system disorders. Here we show that BDNF has a TrkB‐dependent trophic activity on podocyte cell processes; by affecting microRNA‐134 and microRNA‐132 signalling, BDNF up‐regulates Limk1 translation and phosphorylation, and increases cofilin phosphorylation, which results in actin polymerization. Importantly, BDNF effectively repairs podocyte damage in vitro, and contrasts proteinuria and glomerular lesions in in vivo models of FSGS, opening a potential new perspective to the treatment of podocyte disorders. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Vitamin D attenuates proteinuria by inhibition of heparanase expression in the podocyte

The glomerular filtration barrier consists of podocytes, the glomerular basement membrane, and endothelial cells covered with a glycocalyx. Heparan sulphate (HS) in the glomerular filtration barrier is reduced in patients with proteinuria, which is associated with increased expression of the HS‐degrading enzyme heparanase. Previously, we showed that heparanase is essential for the development of proteinuria in experimental diabetic nephropathy. Vitamin D supplementation reduces podocyte loss and proteinuria in vitro and in vivo. Therefore, we hypothesize that vitamin D reduces proteinuria by reducing glomerular heparanase. Adriamycin‐exposed rats developed proteinuria and showed increased heparanase expression, which was reduced by 1,25‐dihydroxyvitamin D₃ (1,25‐D₃) treatment. In vitro, adriamycin increased heparanase mRNA in the podocyte, which could be corrected by 1,25‐D₃ treatment. In addition, 1,25‐D₃ treatment reduced transendothelial albumin passage after adriamycin stimulation. In line with these results, we showed direct binding of the vitamin D receptor to the heparanase promoter, and 1,25‐D₃ dose‐dependently reduced heparanase promoter activity. Finally, 1,25‐D₃‐deficient 25‐hydroxy‐1α‐hydroxylase knockout mice developed proteinuria and showed increased heparanase, which was normalized by 1,25‐D₃ treatment. Our data suggest that the protective effect of vitamin D on the development of proteinuria is mediated by inhibiting heparanase expression in the podocyte. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

1,25-(OH)2D3对局灶节段性肾小球硬化大鼠尿足细胞排泄及肾小球WT-1分布的影响

目的 探讨1,25-(OH)2D3对局灶节段性肾小球硬化(FSGS)大鼠尿足细胞(UPC)排泄及肾小球WT-1蛋白分布的影响.方法 24只SD大鼠分为3组:对照组、FSGS组、1,25-(OH)2D3组.采用左肾摘除,阿霉素重复注射诱导FSGS大鼠模型.1,25-(OH)2D3组在第1次给予阿霉素后1周埋植渗透性微量泵按0.03 ng/(g·d)皮下给予1,25-(OH)2D3.实验10周末检测尿白蛋白排泄率(UAER)、尿转化生长因子-β1(TGF-β1)及结缔组织生长因子(CTGF).免疫荧光法检测尿沉渣足细胞特异性标志蛋白Wflm's tumor-1(WT-1),观察肾小球WT-1的分布.尿WT-1荧光细胞即为尿液足细胞.结果 FSGS组UPC、UAER、TGF-β1、CTGF、肾小球细胞数及细胞外基质(ECM)/肾小球毛细血管襻面积均较对照组明显升高(P<0.01).与FSGS组相比,1,25-(OH)2D3组UAER、ECM/肾小球毛细血管襻面积显著降低(P<0.01),UPC、TGF-β1、肾小球细胞数亦降低(P<0.05),CTGF无统计学意义(P>0.05).肾小球荧光染色示WT-1在对照组正常,FSGS组呈节段性缺失,1,25-(OH)2D3组缺失较轻.UPC与UAER呈正相关(r.=0.42,P<0.05),TGF-β1与CTGF亦呈正相关(r.=0.47,P<0.05).结论 尿液中脱落足细胞检测可作为判断.FSGS病情活动性的标志之一.1,25-(OH)2D3可减轻FSGS大鼠UPC、UAER、TGF-β1的排泄,抑制肾小球细胞数及ECM增殖,恢复肾组织WT1-表达而有肾保护作用.     

Investigational drugs in development for focal segmental glomerulosclerosis

Introduction: Focal segmental glomerulosclerosis is an important cause of end stage kidney disease and is a paradigm for the study of glomerular scarring. There are no FDA approved treatments for this condition. Current therapies, assessed based on reduction in proteinuria, are generally effective in a subset of patients which suggests that FSGS is a heterogeneous group of glomerular disorders or podocytopathies that converge on a common histopathological phenotype.

Areas covered: We searched for investigational drugs agents that target different pathophysiological pathways using the key words ‘FSGS’ and ‘podocyte’ in American and European clinical trial registers (clinicaltrials.gov; clinicaltrialsregister.eu). Published articles were searched in PubMed, Medline, the Web of Science and the Cochrane Central Register of Controlled Trials Library.

Expert opinion: Progress is being made in defining the mechanism of action of subtypes of FSGS. Current and investigational therapies for FSGS target these different pathways of injury. It is anticipated that advances in systems biology will further refine the classification of FSGS by subdividing the disease based on the primary mechanism of glomerular injury, identify biomarkers to discriminate between different subtypes, and enable appropriate selection of appropriate therapy for each individual in accordance with the goals of precision medicine.     

环孢素对足细胞尿激酶型纤溶酶原激活剂受体表达的影响

目的观察环孢素对脂多糖诱导的足细胞尿激酶型纤溶酶原激活剂受体(uPAR)表达的影响。方法建立体内脂多糖诱导小鼠蛋白尿模型和体外脂多糖足细胞损伤模型,2种模型均分为正常对照组、脂多糖组和脂多糖+环孢素组。通过测量尿蛋白-尿肌酐比值观察各组小鼠尿蛋白的变化情况,通过免疫荧光激光共聚焦、RT-PCR及流式细胞术观察各组小鼠肾组织及足细胞uPAR基因和蛋白水平。结果脂多糖组小鼠尿蛋白-尿肌酐比值高于正常对照组(P<0.01),脂多糖+环孢素组低于脂多糖组(P<0.05)。脂多糖+环孢素组小鼠肾组织中uPAR的表达弱于脂多糖组。足细胞脂多糖组uPAR蛋白荧光信号明显强于正常对照组,给予环孢素后荧光信号减弱。足细胞脂多糖+环孢素组uPAR蛋白表达率和Plaur mRNA为(20.10±10.70)%和0.872±0.167,均低于脂多糖组[(65.17±13.04)%和1.341±0.287,P<0.05],与正常对照组无显著差异[(18.06±7.78)%和1.025±0.167,P>0.05]。结论环孢素可能通过抑制足细胞uPAR的表达,从而稳定和保护足细胞起到降蛋白尿作用。