A Homozygous Missense Mutation in the Ciliary Gene TTC21B Causes Familial FSGS

Several genes, mainly involved in podocyte cytoskeleton regulation, have been implicated in familial forms of primary FSGS. We identified a homozygous missense mutation (p.P209L) in the TTC21B gene in seven families with FSGS. Mutations in this ciliary gene were previously reported to cause nephronophthisis, a chronic tubulointerstitial nephropathy. Notably, tubular basement membrane thickening reminiscent of that observed in nephronophthisis was present in patients with FSGS and the p.P209L mutation. We demonstrated that the TTC21B gene product IFT139, an intraflagellar transport-A component, mainly localizes at the base of the primary cilium in developing podocytes from human fetal tissue and in undifferentiated cultured podocytes. In contrast, in nonciliated adult podocytes and differentiated cultured cells, IFT139 relocalized along the extended microtubule network. We further showed that knockdown of IFT139 in podocytes leads to primary cilia defects, abnormal cell migration, and cytoskeleton alterations, which can be partially rescued by p.P209L overexpression, indicating its hypomorphic effect. Our results demonstrate the involvement of a ciliary gene in a glomerular disorder and point to a critical function of IFT139 in podocytes. Altogether, these data suggest that this homozygous TTC21B p.P209L mutation leads to a novel hereditary kidney disorder with both glomerular and tubulointerstitial damages.     

Podocyte-Specific Deletion of Yes-Associated Protein Causes FSGS and Progressive Renal Failure

FSGS is the most common primary glomerular disease underlying ESRD in the United States and is increasing in incidence globally. FSGS results from podocyte injury, yet the mechanistic details of disease pathogenesis remain unclear. This has resulted in an unmet clinical need for cell-specific therapy in the treatment of FSGS and other proteinuric kidney diseases. We previously identified Yes-associated protein (YAP) as a prosurvival signaling molecule, the in vitro silencing of which increases podocyte susceptibility to apoptotic stimulus. YAP is a potent oncogene that is a prominent target for chemotherapeutic drug development. In this study, we tested the hypothesis that podocyte-specific deletion of Yap leads to proteinuric kidney disease through increased podocyte apoptosis. Yap was selectively silenced in podocytes using Cre-mediated recombination controlled by the podocin promoter. Yap silencing in podocytes resulted in podocyte apoptosis, podocyte depletion, proteinuria, and an increase in serum creatinine. Histologically, features characteristic of FSGS, including mesangial sclerosis, podocyte foot process effacement, tubular atrophy, interstitial fibrosis, and casts, were observed. In human primary FSGS, we noted reduced glomerular expression of YAP. Taken together, these results suggest a role for YAP as a physiologic antagonist of podocyte apoptosis, the signaling of which is essential for maintaining the integrity of the glomerular filtration barrier. These data suggest potential nephrotoxicity with strategies directed toward inhibition of YAP function. Further studies should evaluate the role of YAP in proteinuric glomerular disease pathogenesis and its potential utility as a therapeutic target.     

Deficient Autophagy Results in Mitochondrial Dysfunction and FSGS

FSGS is a heterogeneous fibrosing disease of the kidney, the cause of which remains poorly understood. In most cases, there is no effective treatment to halt or retard progression to renal failure. Increasing evidence points to mitochondrial dysfunction and the generation of reactive oxygen species in the pathogenesis of CKD. Autophagy, a major intracellular lysosomal degradation system, performs homeostatic functions linked to metabolism and organelle turnover. We prevented normal autophagic pathways in nephrons of mice by mutating critical autophagy genes ATG5 or ATG7 during nephrogenesis. Mutant mice developed mild podocyte and tubular dysfunction within 2 months, profound glomerular and tubular changes bearing close similarity to human disease by 4 months, and organ failure by 6 months. Ultrastructurally, podocytes and tubular cells showed vacuolization, abnormal mitochondria, and evidence of endoplasmic reticulum stress, features that precede the appearance of histologic or clinical disease. Similar changes were observed in human idiopathic FSGS kidney biopsy specimens. Biochemical analysis of podocytes and tubules of 2-month-old mutant mice revealed elevated production of reactive oxygen species, activation of endoplasmic reticulum stress pathways, phosphorylation of p38, and mitochondrial dysfunction. Furthermore, cultured proximal tubule cells isolated from mutant mice showed marked mitochondrial dysfunction and elevated mitochondrial reactive oxygen species generation that was suppressed by a mitochondrial superoxide scavenger. We conclude that mitochondrial dysfunction and endoplasmic reticulum stress due to impaired autophagic organelle turnover in podocytes and tubular epithelium are sufficient to cause many of the manifestations of FSGS in mice.     

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.     

A fast and simple clearing and swelling protocol for 3D in-situ imaging of the kidney across scales

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Podocyte changes upon induction of albuminuria in Thy-1.1 transgenic mice.

BACKGROUND: Thy-1.1 transgenic mice, characterized by ectopic expression of the Thy-1.1 protein on podocytes, spontaneously develop proteinuria and focal glomerulosclerosis (FGS). Injection of a monoclonal antibody (mAb) directed against the Thy-1.1 protein in young transgenic mice induces a massive albuminuria that is followed by an accelerated FGS within 3 weeks. This albuminuria is complement and leukocyte independent. The time course of proteinuria, the pathogenesis of the acute proteinuria and the dose dependency of FGS are unknown. METHODS: Albuminuria was measured in Thy-1.1 transgenic mice after injection of different doses of anti-Thy-1.1 mAb and at different time points within the first 24 h after injection. Podocytic foot processes and slit pore diameter were quantitated by electron microscopy. Changes in expression of slit pore constituents (podocin, CD2AP, nephrin and ZO-1), cytoskeleton-associated proteins (actin, alpha-actinin, ezrin and synaptopodin), the GDH-podocyte adhesion molecules alpha(3)-integrin, and heparan sulfate were studied by immunofluorescence. FGS was scored by light microscopy at 3 weeks after induction of albuminuria. RESULTS: Albuminuria in Thy-1.1 transgenic mice was observed within 10 min after anti-Thy-1.1 mAb injection. This rapid development of albuminuria was accompanied by a reduction in number of podocytic foot processes from 20.0 +/- 0.7/10 microm glomerular basement membrane (GBM) in saline-treated transgenic mice to 8.0 +/- 0.5 and 2.2 +/- 0.2 in anti-Thy-1.1-treated mice, at 10 min and 8 h after treatment, respectively. In addition, we observed a significant decrease in width of remaining slit pores, from 32.7 +/- 1.1 to 26.8 +/- 1.4 nm at 10 min after mAb injection. By immunofluorescence, we did not observe major changes in the expression pattern of any of the proteins studied. There was no correlation between the injected dose of the anti-Thy-1.1 mAb and the acute albuminuria. In contrast, the percentage of FGS at 3 weeks correlated with the dose, and a significant correlation between the percentage of FGS and the time-averaged albuminuria over the 3 week study period (P < 0.001) was found. CONCLUSION: Injection of mAb directed against the Thy-1.1 protein, in young non-albuminuric Thy-1.1 transgenic mice, induced an acute albuminuria within 10 min, which was accompanied by foot process effacement. Notably, we observed a decrease in slit pore width although the expression of slit pore proteins was unchanged. Also, the acute albuminuria could not be related to alterations in cytoskeleton-associated proteins, the GBM adhesion molecule alpha(3)-integrin or heparan sulfate in the GBM. The dose-dependent development of FGS and the correlation between the percentage FGS and time-averaged albuminuria suggest that, in our model, FGS is a consequence of podocyte injury. However, the data leave open the possibility that albuminuria itself contributes to FGS development. The Thy-1.1 transgenic mouse model is an excellent model to study further the relationship between podocytic injury, albuminuria and the development of FGS.     

Role of Myeloid-Derived Suppressor Cells in Glucocorticoid-Mediated Amelioration of FSGS

The mechanism by which glucocorticoids alleviate renal inflammatory disorders remains incompletely understood. Here, we report that the efficacy of glucocorticoids in ameliorating FSGS depends on the capacity to expand myeloid-derived suppressor cells (MDSCs). After glucocorticoid treatment, the frequency of CD11b⁺HLA-DR⁻CD14⁻CD15⁺ MDSCs in peripheral blood rapidly increased in patients with glucocorticoid-sensitive FSGS but remained unchanged in patients with glucocorticoid-resistant FSGS. The frequency of CD11b⁺Gr-1⁺ MDSCs in mouse peripheral blood, bone marrow, spleen, kidney-draining lymph nodes (KDLNs), and kidney also increased after glucocorticoid treatment. The induced MDSCs from glucocorticoid-treated mice strongly suppressed T cells, dendritic cells, and macrophages but induced regulatory T cells in spleen, KDLNs, and kidney. Moreover, glucocorticoid treatment suppressed doxorubicin-induced T cell proliferation, dendritic cell and macrophage infiltration, and proinflammatory cytokine production, whereas this protective effect was largely abolished by depleting MDSCs using anti–Gr-1 antibody. Finally, the adoptive transfer of induced MDSCs into the doxorubicin-treated mice not only confirmed the protective role of MDSCs in doxorubicin-induced renal injury but also showed that the transferred MDSCs rapidly migrated into the lymphocyte-accumulating organs, such as the spleen and KDLNs, where they suppressed T cell proliferation. Taken together, these results demonstrate that glucocorticoid treatment ameliorates FSGS by expanding functional MDSCs and that this rapid elevation of MDSCs in peripheral blood may serve as an indicator for predicting the efficacy of glucocorticoid treatment.     

A Rare Autosomal Dominant Variant in Regulator of Calcineurin Type 1 (RCAN1) Gene Confers Enhanced Calcineurin Activity and May Cause FSGS

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Exclusion of homozygous PLCE1 (NPHS3) mutations in 69 families with idiopathic and hereditary FSGS

Focal and segmental glomerulosclerosis (FSGS) is the most common glomerular cause of end-stage kidney disease (ESKD). Although the etiology of FSGS has not been fully elucidated, recent results from the positional cloning of genes mutated in nephrotic syndromes are now beginning to provide insight into the pathogenesis of these diseases. Mutations in PLCE1/NPHS3 have recently been reported as a cause of nephrotic syndrome characterized by diffuse mesangial sclerosis (DMS) histology. One single family with a missense mutation had late onset of the disease that was characterized by FSGS. To further define the role of PLCE1 mutations in the etiology of FSGS, we performed mutational analysis in 69 families with FSGS. A total of 69 families with 231 affected individuals were examined. The median age of disease onset was 26 years (range 1–66 years). Onset of ESKD was at a median age of 35.5 years. Seven variants leading to non-synonymous changes were found, of which only two are new variants (exon 4 c.1682 G>A R561Q, exon 31 c.6518A>G K2173R). No known disease-causing mutations were identified in the families screened. PLCE1/NPHS3 mutations are not a cause of FSGS in this cohort. The absence of mutations in PLCE1/NPHS3 in this study indicates that there are additional genetic causes of FSGS and that hereditary FSGS is a heterogeneous disease. Kindreds appropriate for genome-wide screening are currently being subjected to analysis with the aim of identifying other genetic causes of FSGS.     

尿足细胞及其相关分子在肾小球疾病中的表达

目的：探讨尿液检测局灶节段性肾小球硬化足细胞损伤与其他足细胞病之间的特点和差异。方法：入选原发性局灶节段性肾小球硬化（KSGS）患者54例,膜性肾病（MN）23例及微小病变（MCD）12例,正常对照20例。免疫荧光法计数尿足细胞,荧光实时定量PCR法定量尿沉渣足细胞相关分子nephrin、podocin、synaptopodin mRNA的表达水平,Western印迹法检测尿液WilmsTumor1（WT1）蛋白水平,免疫荧光法检测肾脏组织podocalyxin的表达及分布。结果：（1）FSGS组、MN组、MCD组和对照组尿足细胞阳性率分别是63％、34．8％、33．3％和0,FSGS组与其余各组相比差异均有统计学意义（P〈0．05）。FSGS组足细胞脱落数目显著高于MCD组、MN组和对照组（P〈0．05）,伴足细胞尿FSGS患者与不伴足细胞尿FS—GS患者相比,24h尿蛋白和血清白蛋白（Alb）差异均有统计学意义（P〈0．05）。（2）FSGS组尿沉渣足细胞nephrin mRNA表达水平显著高于MCD和MN组（P〈0．05）;FSGS组尿沉渣足细胞podocinmRNA表达显著高于MCD组（P〈0．05）,与MN组相比有升高趋势但差异无统计学意义;尿沉渣足细胞synaptopodin mRNA表达各组间差异无统计学意义。尿沉渣足细胞nephrin、podocin．synaptopodin mRNA的表达与24h蛋白尿无相关性。（3）FSGS组尿WT1蛋白量显著高于MCD和MN组。部分足细胞阴性患者尿液检测到WT1分子。（4）FSC-S患者肾组织podocalyxin较对照组、MCD和MN有明显的节段缺失。结论：局灶节段性肾小球硬化病患者足细胞损伤严重,尿足细胞与FSGS疾病活动相关。尿沉渣足细胞nephrin mRNA表达可以把FSGS与MCD和MN区分开来,尿WT1蛋白可能是足细胞早期损伤指标。     

Increase of Integrin-Linked Kinase Activity in Cultured Podocytes upon Stimulation with Plasma from Patients with Recurrent FSGS

Recurrent focal segmental glomerulosclerosis (FSGS) is a major challenge in the field of transplantation. Integrin-linked kinase (ILK) has emerged as a key mediator of podocyte–glomerular basement membrane (GBM) interactions. To clarify the involvement of plasma factors in FSGS recurrence, we examined the effects of plasma from FSGS patients with or without posttransplant recurrence on cultured podocytes, focusing particularly on ILK activity. Podocytes from a conditionally immortalized mouse podocyte cell line were treated with plasma from 11 FSGS patients, and ILK activity was determined using an immune complex kinase assay. Treatment with plasma from three patients with recurrence induced an increase in ILK activity. In contrast, no increase in ILK activity was observed in cultured podocytes treated with plasma from the remaining three patients with recurrence and five patients without recurrence. Cultured podocytes treated with plasma that induced ILK activity showed alterations of focal contact and detachment from the laminin matrix. In conclusion, this preliminary study provides experimental evidence suggesting the possible presence of circulating toxic factors in the plasma of some patients with recurrent FSGS, which induce an increase in podocyte ILK activity that may lead to the detachment of podocytes from the GBM.     

Glomerular filtrate affects the dynamics of podocyte detachment in a model of diffuse toxic podocytopathy

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

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Preemptive Plasmapheresis and Recurrence of FSGS in High-Risk Renal Transplant Recipients

Recurrent focal segmental glomerulosclerosis (FSGS) following transplantation is ascribed to the presence of a circulating FSGS permeability factor (FSPF). Plasmapheresis (PP) can induce remission of proteinuria in recurrent FSGS. This study addressed the efficacy of pre-transplant PP in decreasing the incidence of recurrence in high-risk patients. Ten patients at high-risk for FSGS recurrence because of rapid progression to renal failure (n = 4) or prior transplant recurrence of FSGS (n = 6) underwent a course of 8 PP treatments in the peri-operative period. Recurrences were identified by proteinuria >3 g/day and confirmed by biopsy. Seven patients, including all 4 with first grafts and 3 of 6 with prior recurrence, were free of recurrence at follow-up (238-1258 days). Final serum creatinine in 8 patients with functioning kidneys averaged 1.53 mg/dL. FSGS recurred within 3 months in 3 patients, each of whom had lost prior transplants to recurrent FSGS. Two of these progressed to end-stage renal disease (ESRD) and the third has significant renal dysfunction. Based on inclusion criteria, recurrence rates of 60% were expected if no treatment was given. Therefore, PP may decrease the incidence of recurrent FSGS in high-risk patients. Definitive conclusions regarding optimal management can only be drawn from larger, randomized, controlled studies.