The spectrum of focal segmental glomerulosclerosis: new insights. Curr Opin Nephrol Hypertens. 2008;17:271-281. [PMID: 18408478 DOI: 10.1097/mnh.0b013e3282f94a96]

Targeting ferroptosis attenuates podocytes injury and delays tubulointerstitial fibrosis in focal segmental glomerulosclerosis

Ferroptosis is a non-apoptotic form of cell death, involved in chronic kidney diseases (CKD) and acute kidney injury (AKI), so far, the role of ferroptosis in focal segmental glomerulosclerosis (FSGS) remains largely unknown. We aimed to investigate the role of ferroptosis in FSGS, in this study, we found the reduced expression of GPX4 in podocytes, as well as tubular epithelial cells (TECs), from patients with FSGS. Treatment with ferrostatin-1 (Fer-1), a potent and selective ferroptosis inhibitor, significantly reduced proteinuria, prevented glomerulosclerosis, attenuated podocyte injury in ADR-induced FSGS murine model. As expected, ADR treatment caused downregulation of GPX4 in human podocytes, treatment with Fer-1 greatly blocked the downregulation of GPX4, restored the GSH level and attenuated cell death. Furthermore, Fer-1 treatment greatly delayed the development of tubulointerstitial fibrosis in ADR-induced FSGS murine model. Taken together, ferroptosis is involved in the pathogenesis of FSGS, targeting ferroptosis is a promising therapeutic option for patients with FSGS.

Current understanding of the molecular mechanisms of circulating permeability factor in focal segmental glomerulosclerosis

The pathogenetic mechanisms underlying the onset and the post-transplant recurrence of primary focal segmental glomerulosclerosis (FSGS) are complex and remain yet to be fully elucidated. However, a growing body of evidence emphasizes the pivotal role of the immune system in both initiating and perpetuating the disease. Extensive investigations, encompassing both experimental models and patient studies, have implicated T cells, B cells, and complement as crucial actors in the pathogenesis of primary FSGS, with various molecules being proposed as potential "circulating factors" contributing to the disease and its recurrence post kidney-transplantation. In this review, we critically assessed the existing literature to identify essential pathways for a comprehensive characterization of the pathogenesis of FSGS. Recent discoveries have shed further light on the intricate interplay between these mechanisms. We present an overview of the current understanding of the engagement of distinct molecules and immune cells in FSGS pathogenesis while highlighting critical knowledge gaps that require attention. A thorough characterization of these intricate immune mechanisms holds the potential to identify noninvasive biomarkers that can accurately identify patients at high risk of post-transplant recurrence. Such knowledge can pave the way for the development of targeted and personalized therapeutic approaches in the management of FSGS.

Generation of human induced pluripotent stem cell line (BCRTi006-A) from a patient with focal segmental glomerulosclerosis disease

Individuals with transient reception potential cation channel 6 (TRPC6) mutation have variable phenotypes, ranging from healthy carriers to focal segmental glomerulosclerosis (FSGS). Human induced pluripotent stem cell (hiPSC) line was generated from the urinary cells of a patient with FSGS with a mutant variant of TRPC6. The cells were reprogrammed with Yamanaka factors (OCT3, SOX2, LIN28, L-MYC, and KLF4) using a commercially available Epi5 Reprogramming Kit. The pluripotency of the hiPSC line was confirmed by the expression of common stem cell markers and by their ability to generate all germ layers in vitro. The line is available and registered in the human pluripotent stem cell registry as BCRTi006-A. The generated line represents a valuable tool for disease modeling and drug development for FSGS.

Renal diseases associated with multiple sclerosis: A narrative review

The mechanisms of renal pathology in multiple sclerosis (MS) can be related to the disease itself or its treatment. Although kidney disease can be associated with MS, not much has been reported in the literature; hence, our study aimed to describe the prevalence and types of renal diseases and discuss their prognosis in patients with MS. A literature search (2012-2022) was performed using the Scale for the Assessment of Narrative Review Articles. The databases searched included MEDLINE (PubMed) and EMBASE. Fourteen articles from these databases met the inclusion criteria. The inclusion criteria were as follows: publications with full-text access. Articles published in English. Original articles related to renal diseases in MS. The prevalence of renal diseases in MS from the articles obtained ranged from 0.74% to 2.49%. Interferon beta (IFN-β)-associated glomerulonephritis was common among the reviewed articles. Significant improvement and resolution of the pathology were observed after the discontinuation of the offending medication. Renal symptoms in 2 out of 4 cases with renal thrombotic microangiopathy (TMA) induced by interferon-beta progressed to chronic kidney disease, even after the drug was stopped. Other studied renal pathologies included nephrolithiasis secondary to urinary retention and urinary catheter use in patients with MS.

Tip-Variant Focal Segmental Glomerulosclerosis in a Patient With Primary Hypothyroidism: A Case Report

Focal segmental glomerulosclerosis (FSGS) is a common cause of nephrotic syndrome (NS) and one of the leading causes of end-stage kidney disease. Endocrinological abnormalities due to the urinary loss of hormone-binding proteins, such as transient hypothyroidism, are well documented in FSGS. Secondary FSGS can arise due to viral infections, drugs, and pre-existing glomerular diseases. Few reports have highlighted the occurrence of FSGS in the background of hypothyroidism. We present a case of a young male with primary hypothyroidism who developed the tip variant of FSGS. A combination of oral corticosteroids and angiotensin-converting enzyme (ACE) inhibitors was successful in causing remission of the FSGS with no relapse.

Diverse alterations of glomerular capillary networks in focal segmental glomerulosclerosis

Introduction

Focal segmental glomerular sclerosis (FSGS) is caused by podocyte injury. It is characterized by obliteration of glomerular capillary tufts with increased extracellular matrix (ECM). Altered communication between podocytes and glomerular endothelial cells (ECs) contributes to sclerosis progression. We focused on EC injury in the FSGS.

Methods

A total of 29 FSGS and 18 control biopsy specimens were assessed for clinicopathologic characteristics. CD34 (a marker for EC)-positive capillaries and ECM accumulation were evaluated quantitatively for each variant using computer-assisted image analysis.

Results

The estimated glomerular filtration rate (eGFR) in the FSGS group was significantly lower than that in the control group. The frequency of FSGS variants was 51.7% for cellular; 13.8% for perihilar (PH), tip, and not otherwise specified (NOS); and 6.9% for collapsing. Regarding sclerotic lesions in all FSGS, narrowing or loss of CD34-positive capillaries was observed. Electron microscopy results showed loss of fenestrae, subendothelial space enlargement, and cytoplasmic swelling, indicating EC injury. Computer-assisted image analysis revealed significantly smaller areas of glomerular capillaries in FSGS with or without sclerotic lesions, with increased ECM. Moreover, in comparison with each variant, narrowed capillaries and ECM accumulation were most prominent in the collapsing variant, whereas the tip variant had the least change.

Conclusion

EC injury was observed in all FSGS cases, not only in sclerotic lesions but also in nonsclerotic lesions. Severity of EC injury may vary in each variant due to diverse alterations of glomerular capillary networks.

Pembrolizumab-induced focal segmental glomerulosclerosis: A case report

RATIONALE

Focal segmental glomerulosclerosis (FSGS) is the most common primary glomerular disorder that leads to end-stage kidney disease. Pembrolizumab, an immune checkpoint inhibitor, is an anti-programmed death 1 (PD-1) immunoglobulin G4 antibody approved for the treatment of advanced melanoma and can cause various renal immune-related adverse events (AEs), including acute kidney injury. Several cases of anti PD-1 therapy-induced glomerulonephritis have been reported so far, but FSGS has seldom been reported.

PATIENT CONCERNS

46-year old woman presented to our hospital with generalized edema.

DIAGNOSES

Laboratory examination revealed features of nephrotic syndrome, and kidney biopsy confirmed FSGS. After other etiological factors of secondary FSGS were ruled out, she was diagnosed with FSGS caused by pembrolizumab.

INTERVENTIONS

She did not resume treatment with pembrolizumab and was treated with irbesartan and furosemide according to the American Society of Clinical Oncology Practice guidelines.

OUTCOMES

After 2 months, the features of nephrotic syndrome resolved.

LESSONS

This case provides valuable insight into the etiology of FSGS that can occur as a renal immune-related AE of PD-1 inhibitor therapy. Therefore, patients should undergo evaluation for renal function and urinalysis at baseline and after treatment. If patients treated with PD-1 inhibitors present with renal injury and/or unexplained proteinuria >1 g/day, we would recommend a kidney biopsy to determine the underlying cause and establish an appropriate therapeutic plan.

Clinicopathologic characteristics, pathology, and prognosis of 77 dogs with focal segmental glomerulosclerosis

BACKGROUND

Focal segmental glomerulosclerosis (FSGS) is a common cause of nonimmune complex glomerulopathy and the prognosis and clinicopathologic findings associated with this condition have not been described in dogs.

OBJECTIVE

To characterize the presentation and identify clinical factors associated with the survival of dogs with FSGS.

ANIMALS

Seventy-seven dogs diagnosed with FSGS based on evaluation of renal biopsy samples submitted to the International Veterinary Renal Pathology Service.

METHODS

Retrospective review of medical records of dogs biopsied for evaluation of proteinuria between January 2015 and May 2017.

RESULTS

The incidence of FSGS among all dogs biopsied for proteinuria was 26%. Significantly more females (48; 62.3%) than males (29; 37.7%) were affected (P = .04). At the time of biopsy, median serum creatinine concentration (SCr) was 1.2 mg/dL (range, 0.3-8.7), median serum albumin concentration (Alb) was 2.8 g/dL (range, 1.1-4.6), median systolic blood pressure was 153.5 mm Hg (range, 95-260), and median urine protein : creatinine ratio was 5.9 (range, 1.4-22). Median survival time after biopsy was 258 days (range, 26-1003) for dogs that died from all causes (n = 32). Factors that were associated with a shorter survival time included SCr ≥ 2.1 mg/dL (P < .01) and Alb < 2 g/dL (P < .01).

CONCLUSIONS AND CLINICAL IMPORTANCE

Most dogs with FSGS were female, and although commonly hypertensive, azotemia, severe hypoalbuminemia and ascites or edema were observed infrequently. Variables significantly associated with survival time were SCr and Alb.

ARHGEF7 (β-PIX) Is Required for the Maintenance of Podocyte Architecture and Glomerular Function

BACKGROUND

Previous studies showed that Cdc42, a member of the prototypical Rho family of small GTPases and a regulator of the actin cytoskeleton, is critical for the normal development and health of podocytes. However, upstream regulatory mechanisms for Cdc42 activity in podocytes are largely unknown.

METHODS

We used a proximity-based ligation assay, BioID, to identify guanine nucleotide exchange factors that activate Cdc42 in immortalized human podocytes. We generated podocyte-specific ARHGEF7 (commonly known as β-PIX) knockout mice by crossing β-PIX floxed mice with Podocin-Cre mice. Using shRNA, we established cultured mouse podocytes with β-PIX knockdown and their controls.

RESULTS

We identified β-PIX as a predominant guanine nucleotide exchange factor that interacts with Cdc42 in human podocytes. Podocyte-specific β-PIX knockout mice developed progressive proteinuria and kidney failure with global or segmental glomerulosclerosis in adulthood. Glomerular podocyte density gradually decreased in podocyte-specific β-PIX knockout mice, indicating podocyte loss. Compared with controls, glomeruli from podocyte-specific β-PIX knockout mice and cultured mouse podocytes with β-PIX knockdown exhibited significant reduction in Cdc42 activity. Loss of β-PIX promoted podocyte apoptosis, which was mediated by the reduced activity of the prosurvival transcriptional regulator Yes-associated protein.

CONCLUSIONS

These findings indicate that β-PIX is required for the maintenance of podocyte architecture and glomerular function via Cdc42 and its downstream Yes-associated protein activities. This appears to be the first evidence that a Rho-guanine nucleotide exchange factor plays a critical role in podocytes.

Biological applications of knowledge graph embedding models

Complex biological systems are traditionally modelled as graphs of interconnected biological entities. These graphs, i.e. biological knowledge graphs, are then processed using graph exploratory approaches to perform different types of analytical and predictive tasks. Despite the high predictive accuracy of these approaches, they have limited scalability due to their dependency on time-consuming path exploratory procedures. In recent years, owing to the rapid advances of computational technologies, new approaches for modelling graphs and mining them with high accuracy and scalability have emerged. These approaches, i.e. knowledge graph embedding (KGE) models, operate by learning low-rank vector representations of graph nodes and edges that preserve the graph's inherent structure. These approaches were used to analyse knowledge graphs from different domains where they showed superior performance and accuracy compared to previous graph exploratory approaches. In this work, we study this class of models in the context of biological knowledge graphs and their different applications. We then show how KGE models can be a natural fit for representing complex biological knowledge modelled as graphs. We also discuss their predictive and analytical capabilities in different biology applications. In this regard, we present two example case studies that demonstrate the capabilities of KGE models: prediction of drug-target interactions and polypharmacy side effects. Finally, we analyse different practical considerations for KGEs, and we discuss possible opportunities and challenges related to adopting them for modelling biological systems.

Genetic studies of focal segmental glomerulosclerosis: a waste of scientific time?

Many genetic causes of focal segmental glomerulosclerosis (FSGS) have been described. A paradox is that the science in the molecular biology, which generally appears of high quality, is not mirrored by a similarly critical analysis of the renal pathology. FSGS has been applied to such a wide range of conditions that it can reasonably be said to have no useful meaning. Attempts to refine the term have been largely ignored. Study of 252 papers on genetic causes of FSGS found various clinical features. Many papers took the reported diagnosis without question. Few papers reported a pathological review, almost half reported FSGS and up to six other conditions caused by any particular gene, some reported FSGS with recognisable glomerular disorders, over 80% did not apply the Columbia classification, and in nearly all with photomicrographs, the images were not useful for refinement of FSGS. Some workers commented on a lack of genotype-phenotype correlation. One reason is a disregard of the principle that scientific investigation requires an unambiguous definition of the condition studied, to allow others to replicate or refute the findings. Genetic studies of FSGS should use a similarly rigorous approach to renal pathology to that used in molecular biology.

Human podocyte injury in the early course of hypertensive renal injury

BACKGROUND

Hypertension is prevalent in the general population and is regarded as the second leading cause of renal damage and dysfunction, outnumbered only by diabetes. However, the mechanisms remain unclear.

AIM

To investigate podocyte injury induced by hypertension in the early course without massive proteinuria or renal dysfunction.

METHODS

The hypertension group comprised 18 patients with hypertension accompanied by microalbuminuria, diagnosed with hypertensive renal injury according to biopsy results. For a comparison of pathological changes in renal tissue, control group 1 comprised 10 healthy volunteers, and control group 2 comprised 16 patients who underwent surgery for renal trauma.

RESULTS

The hypertension group had significantly higher blood pressure (P = 0.000) and microalbuminuria (P = 0.000) compared with control group 1. In the hypertension group, urinary podocytes were detected following positive staining of podocyte-specific nephrin and/or CD2-associated protein (CD2AP) in urine sediment. Podocyte foot process fusion and a significant decrease in nephrin and/or CD2AP expression in glomeruli were observed in the hypertension group compared with control group 2. This indicated that hypertension caused podocyte injury and detachment from the glomerular basement membrane, which was consistent with urinary detection of podocytes.

CONCLUSION

Our results suggest that podocyturia appears early in the course of hypertensive renal injury, and may be a sensitive marker for early prediction of hypertensive renal injury.

Ectopic expression of CLDN2 in podocytes is associated with childhood onset nephrotic syndrome

BACKGROUND

Animal models of nephrotic syndrome (NS) revealed that tight junction (TJ)-like structures are generated together with a concomitant decrease in slit diaphragms (SDs). Claudins (CLDNs) are capable of forming TJ strands and thereby the backbone of TJs. We showed the ectopic expression of CLDN2 in podocytes in pediatric NS, and detected its localization.

METHODS

Renal frozen specimens were obtained by biopsy from 49 pediatric patients: 21 subjects with MCD, 18 with FSGS, and 10 with IgA nephritis (IgA-N). CLDN2 expression was observed by immunohistochemistry and the CLDN2-positive area was calculated. Moreover, its localization was detected using immunoelectron microscopy.

RESULTS

CLDN2 is ectopically detected in cases with MCD and FSGS before remission. The CLDN2-stained region in MCD and FSGS glomeruli before remission was significantly greater than that after remission as well as in IgA-N patients. Immunoelectron microscopy revealed that CLDN2 was concentrated along newly formed TJs in podocytes.

CONCLUSION

The same pathological findings in terms of ectopic CLDN2 expression in podocytes were shown in cases with MCD and FSGS before remission. Immunofluorescence and immunoelectron studies of CLDN2 appear to afford a powerful tool for the diagnosis of primary NS. In addition, CLDN2 expression level may be related to disease status.

Circulating CASK is associated with recurrent focal segmental glomerulosclerosis after transplantation

Introduction

Focal and Segmental GlomeruloSclerosis (FSGS) can cause nephrotic syndrome with a risk of progression to end-stage renal disease. The idiopathic form has a high rate of recurrence after transplantation, suggesting the presence of a systemic circulating factor that causes glomerular permeability and can be removed by plasmapheresis or protein-A immunoadsorption.

Results

To identify this circulating factor, the eluate proteins bound on therapeutic immunoadsorption with protein-A columns were analyzed by comparative electrophoresis and mass spectrometry. A soluble form of calcium/calmodulin-dependent serine protein kinase (CASK) was identified. CASK was immunoprecipitated only in the sera of patients with recurrent FSGS after transplantation and not in control patients. Recombinant-CASK (rCASK) induced the reorganization of the actin cytoskeleton in immortalized podocytes, a redistribution of synaptopodin, ZO-1,vinculin and ENA. rCASK also induced alterations in the permeability of a monolayer of podocytes and increased the motility of pdodocytes in vitro. The extracellular domain of CD98, a transmembrane receptor expressed on renal epithelial cells, has been found to co-immunoprecipitated with rCASK. The invalidation of CD98 with siRNA avoided the structural changes of rCask treated cells suggesting its involvement in physiopathology of the disease. In mice, recombinant CASK induced proteinuria and foot process effacement in podocytes.

Conclusion

Our results suggest that CASK can induce the recurrence of FSGS after renal transplantation.

Autophagy activity and expression pattern of autophagy-related markers in the podocytes of patients with lupus nephritis: association with pathological classification

OBJECTIVE

To identify the significance of autophagy in lupus nephritis (LN).

METHODS

The number of autophagosomes in podocytes was counted and the expression of multiple molecular markers associated with autophagy was evaluated in LN specimens: in renal biopsy specimens from 90 patients with LN and 15 healthy controls, autophagosomes in podocytes were counted using transmission electron microscopy and the expression levels of four autophage related proteins including Beclin-1, microtubule-associated protein light chain 3 (LC3), autophagy-related gene 7 (Atg7), and UNC-51-like kinase 1 (ULK1) were measured using immunohistochemistry.

RESULTS

The number of autophagosomes in patients with LN types III, IV, and combined V-IV type were significantly higher than in controls (p < 0.0001; p < 0.0001; p = 0.009, respectively). However, the autophagosomes numbers in patients with II and V types LN were significantly lower than controls (both p < 0.0001). Various levels of marker expression were identified, and they correlated significantly with LN pathology classifications. Moreover, the percentage of marker expression in LN types III, IV and V-IV were significantly higher than controls (p < 0.05), while that in types II and V were lower than controls, although the difference for LC3 and ULK1 was not statistically significant.

CONCLUSIONS

Autophagy activity and expression pattern of autophagy-related markers in podocytes were significantly positively correlated with LN of types III, IV, and V-IV, but negatively correlated with II and V types. Therefore autophagy could be a useful predictor of LN pathology type, and be informative and helpful in the development of treatment strategies in clinical settings.

Intrinsic tumor necrosis factor-α pathway is activated in a subset of patients with focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is frequently found in biopsies of patients with steroid resistant nephrotic syndrome (SRNS). The pathogenesis of SRNS/FSGS is often unknown and the disease will recur in up to 50% of patients post-transplant, indicating the presence of circulating podocyte-toxic factor(s). Several studies have reported clinical improvement after anti-TNFα therapy. However, prediction of the clinical outcome in SRNS/FSGS is difficult, and novel predictive biomarkers are needed. An image-based assay, which measures disassembly of focal adhesion complexes in cultured podocytes, was used to ascertain the presence of podocyte toxic activity in SRNS/FSGS sera. Expression of TNFα pathway genes was analysed in the Nephroseq FSGS cohort and in cultured podocytes treated with SRNS/FSGS sera. Podocyte toxic activity was detected in 48/96 SRNS/FSGS patients. It did not correlate with serum TNFα levels, age, sex, ethnicity or glomerular filtration rate. In ~25% of the toxic samples, the toxicity was strongly inhibited by blockade of TNFα signaling. Transcriptional profiling of human FSGS biopsies and podocytes treated with FSGS sera revealed significant increases in expression of TNFα pathway genes. We identified patients with serum podocyte toxic activity who may be at risk for FSGS recurrence, and those patients in whom serum podocyte toxicity may be reversed by TNFα blockade. Activation of TNFα pathway genes occurs in podocytes of FSGS patients suggesting a causative effect of this pathway in response to circulating factor(s). In vitro analyses of patient sera may stratify patients according to prognostic outcomes and potential responses to specific clinical interventions.

Puromycin aminonucleoside triggers apoptosis in podocytes by inducing endoplasmic reticulum stress

Background

Puromycin aminonucleoside (PAN) is a known podocytotoxin. PAN-induced nephrosis is a widely used animal model for studying human idiopathic nephrotic syndrome. Abnormal protein accumulation associated with podocyte-specific endoplasmic reticulum (ER) stress damages cells structurally and functionally, which in turn induces apoptosis and severe proteinuria. In the present study, we investigated the effect of PAN on ER stress and apoptosis in podocytes in vitro.

Methods

Mouse podocytes were cultured and treated with various concentrations of PAN. ER stress markers were then evaluated by western blotting, and apoptosis was evaluated by fluorescence-activated cell sorting (FACS) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays.

Results

PAN treatment increased ER stress markers such as activating transcription factor (ATF) 6α and caspase-12 in a dose-dependent manner at 12 and 24 hours, respectively. These markers were reduced by chemical chaperones, such as sodium 4-phenylbutyric acid and tauroursodeoxycholic acid. PAN treatment also increased 78 kD glucose-regulated protein (GRP78)/binding immunoglobulin protein (BiP) at the earlier stage of 12 hours. PAN significantly induced podocyte apoptosis in concentration- and time-dependent manners, as seen using FACS and TUNEL assays. This result was improved by Nox4 siRNA, ATF6 siRNA, and chemical chaperones. LY294002, a PI3-kinase inhibitor, significantly boosted ER stress and apoptosis. PAN-induced ER stress increased oxidative stress and subsequently induced apoptosis, and could be mitigated by inhibition of PI3-kinase signaling.

Conclusion

Our findings suggest that PAN induces ER stress in podocytes mainly through the GRP78/BiP, ATF6α, and caspase-12 pathways, which trigger apoptosis via induction of oxidative stress. This stress is mitigated by inhibiting PI3-kinase signaling.

The Spectrum of Focal Segmental Glomerulosclerosis from Eastern India: Is It Different?

Focal segmental glomerulosclerosis (FSGS) is a disease that is defined entirely by its histopathological appearance. The recent Columbian classification has grouped this disease into various types based on the light microscopic description. There is a paucity of data describing the distribution of its various subtypes from the Indian subcontinent. This study was undertaken with the aim to throw light on the epidemiology and clinical features of primary FSGS in Eastern India. This retrospective study includes our cohort of biopsy-proven FSGS who presented to us from June 2009 to July 2011 and the analysis of their presenting clinical and histopathological features from our center in East India. Out of 347 patients diagnosed with FSGS in this period, 224 patients were included in the study. A total of 167 cases were of not otherwise specified (NOS) variant (74.5%), 30 tip variant (13.39%), 14 perihilar (6.25%), 8 cellular (3.57%), and 5 to the collapsing variant (2.23%). The maximum proteinuria at presentation was seen with the tip variant (7.98 ± 6.6 g/24 h), and the renal functions were most deranged at presentation with the collapsing variant. These findings were different from those described in other populations including higher prevalence of the tip and the perihilar variant, significant difference in the degree of hypertension, proteinuria, and renal dysfunction among the different variants. The Columbian classification has helped to stratify the outcomes of this glomerular disease with respect to its clinical presentation as well as histopathological features. However, the characteristics of the various variants do show a distinctive pattern in various populations based on ethnicities.

Recent advances of animal model of focal segmental glomerulosclerosis

In the last decade, great advances have been made in understanding the genetic basis for focal segmental glomerulosclerosis (FSGS). Animal models using specific gene disruption of the slit diaphragm and cytoskeleton of the foot process mirror the etiology of the human disease. Many animal models have been developed to understand the complex pathophysiology of FSGS. Therefore, we need to know the usefulness and exact methodology of creating animal models. Here, we review classic animal models and newly developed genetic animal models. Classic animal models of FSGS involve direct podocyte injury and indirect podocyte injury due to adaptive responses. However, the phenotype depends on the animal background. Renal ablation and direct podocyte toxin (PAN, adriamycin) models are leading animal models for FSGS, which have some limitations depending on mice background. A second group of animal models were developed using combinations of genetic mutation and toxin, such as NEP25, diphtheria toxin, and Thy1.1 models, which specifically injure podocytes. A third group of animal models involves genetic engineering techniques targeting podocyte expression molecules, such as podocin, CD2-associated protein, and TRPC6 channels. More detailed information about podocytopathy and FSGS can be expected in the coming decade. Different animal models should be used to study FSGS depending on the specific aim and sometimes should be used in combination.

Response of Renal Podocytes to Excessive Hydrostatic Pressure: a Pathophysiologic Cascade in a Malignant Hypertension Model

BACKGROUND/AIMS

Renal injuries induced by increased intra-glomerular pressure coincide with podocyte detachment from the glomerular basement membrane (GBM). In previous studies, it was demonstrated that mesangial cells have a crucial role in the pathogenesis of malignant hypertension. However, the exact pathophysiological cascade responsible for podocyte detachment and its relationship with mesangial cells has not been fully elucidated yet and this was the aim of the current study.

METHODS

Rat renal mesangial or podocytes were exposed to high hydrostatic pressure in an in-vitro model of malignant hypertension. The resulted effects on podocyte detachment, apoptosis and expression of podocin and integrinβ1 in addition to Angiotensin-II and TGF-β1 generation were evaluated. To simulate the paracrine effect podocytes were placed in mesangial cell media pre-exposed to pressure, or in media enriched with Angiotensin-II, TGF-β1 or receptor blockers.

RESULTS

High pressure resulted in increased Angiotensin-II levels in mesangial and podocyte cells. Angiotensin-II via the AT1 receptors reduced podocin expression and integrinβ1, culminating in detachment of both viable and apoptotic podocytes. Mesangial cells exposed to pressure had a greater increase in Angiotensin-II than pressure-exposed podocytes. The massively increased concentration of Angiotensin-II by mesangial cells, together with increased TGF-β1 production, resulted in increased apoptosis and detachment of non-viable apoptotic podocytes. Unlike the direct effect of pressure on podocytes, the mesangial mediated effects were not related to changes in adhesion proteins expression.

CONCLUSIONS

Hypertension induces podocyte detachment by autocrine and paracrine effects. In a direct response to pressure, podocytes increase Angiotensin-II levels. This leads, via AT1 receptors, to structural changes in adhesion proteins, culminating in viable podocyte detachment. Paracrine effects of hypertension, mediated by mesangial cells, lead to higher levels of both Angiotensin-II and TGF-β1, culminating in apoptosis and detachment of non-viable podocytes.

Compound effects of aging and experimental FSGS on glomerular epithelial cells

Advanced age portends a poorer prognosis in FSGS. To understand the impact of age on glomerular podocytes and parietal epithelial cells (PECs), experimental FSGS was induced in 3m-old mice (20-year old human age) and 27m-old mice (78-year old human age) by abruptly depleting podocytes with a cytopathic anti-podocyte antibody. Despite similar binding of the disease-inducing antibody, podocyte density was lower in aged FSGS mice compared to young FSGS mice. Activated PEC density was higher in aged versus young FSGS mice, as was the percentage of total activated PECs. Additionally, the percentage of glomeruli containing PECs with evidence of phosphorylated ERK and EMT was higher in aged FSGS mice. Extracellular matrix, measured by collagen IV and silver staining, was higher in aged FSGS mice along Bowman's capsule. However, collagen IV accumulation in the glomerular tufts alone and in glomeruli with both tuft and Bowman's capsule accumulation were similar in young FSGS and aged FSGS mice. Thus, the major difference in collagen IV staining in FSGS was along Bowman's capsule in aged mice. The significant differences in podocytes, PECs and extracellular matrixaccumulation between young mice and old mice with FSGS might explain the differences in outcomes in FSGS based on age.

Injury-induced actin cytoskeleton reorganization in podocytes revealed by super-resolution microscopy

The architectural integrity of tissues requires complex interactions, both between cells and between cells and the extracellular matrix. Fundamental to cell and tissue homeostasis are the specific mechanical forces conveyed by the actomyosin cytoskeleton. Here we used super-resolution imaging methods to visualize the actin cytoskeleton in the kidney glomerulus, an organized collection of capillaries that filters the blood to make the primary urine. Our analysis of both mouse and human glomeruli reveals a network of myosin IIA-containing contractile actin cables within podocyte cell bodies and major processes at the outer aspects of the glomerular tuft. These likely exert force on an underlying network of myosin IIA-negative, noncontractile actin fibers present within podocyte foot processes that function to both anchor the cells to the glomerular basement membrane and stabilize the slit diaphragm against the pressure of fluid flow. After injuries that disrupt the kidney filtration barrier and cause foot process effacement, the podocyte's contractile actomyosin network relocates to the basolateral surface of the cell, manifesting as sarcomere-like structures juxtaposed to the basement membrane. Our findings suggest a new model of the podocyte actin cytoskeleton in health and disease and suggest the existence of novel mechanisms that regulate podocyte architecture.

Characterization of NPHS2 gene polymorphisms associated to steroid resistance nephrotic syndrome in Indian children

Nephrotic syndrome (NS) is the common glomerular disease in children. These children are treated with steroids, depending upon their behavior. They are either steroid sensitive (SSNS) or steroid resistant (SRNS). NPHS2 gene mutants are linked to the risk of autosomal recessive SRNS and in some cases to SSNS. The present study has been performed to screen single nucleotide polymorphisms (SNPs) of the NPHS2 gene in a group of 90 Indian children suffering with NS (30 SSNS, 30 SRNS and 30 Controls) by PCR method followed by direct exon sequencing. Effect of SNPs on fold expression changes at transcript level of podocin was checked using quantitative real time PCR (qRT-PCR). SNPs identified through sequencing helps to carry out in-silico analysis. Overall 17 SNPs were identified in NPHS2 gene where 6 were found novel. Three missense SNPs p.R299Q, p.P20L and p.G35D were also identified in this population where SNP, p.G35D was found novel. In addition to sequencing analysis, results of in silico analysis shows that a mutant with these three missense SNPs has least ligand binding efficiency compared to native model. Moreover the significant observation of this study included two intronic SNPs c.451+23C>T and c.451+58A>T present in SRNS group of patients. These SNPs has shown high level of clinical significance within genomic and allelic frequency along with haplotypes and linkage disequilibrium count. The qRT-PCR analysis shows, down expression of podocin protein at transcript level in SRNS patients compared to SSNS patients. All these results support the fact that SNPs present in this population could affect the protein structural stability. Thus it is concluded that the polymorphisms predicted in this study might be disease causing in the NPHS2 gene and may have influence on the therapeutic response of NS patients.

Genetics of hereditary nephrotic syndrome: a clinical review

Advances in podocytology and genetic techniques have expanded our understanding of the pathogenesis of hereditary steroid-resistant nephrotic syndrome (SRNS). In the past 20 years, over 45 genetic mutations have been identified in patients with hereditary SRNS. Genetic mutations on structural and functional molecules in podocytes can lead to serious injury in the podocytes themselves and in adjacent structures, causing sclerotic lesions such as focal segmental glomerulosclerosis or diffuse mesangial sclerosis. This paper provides an update on the current knowledge of podocyte genes involved in the development of hereditary nephrotic syndrome and, thereby, reviews genotype-phenotype correlations to propose an approach for appropriate mutational screening based on clinical aspects.

Renoprotection: focus on TRPV1, TRPV4, TRPC6 and TRPM2

Members of the transient receptor potential (TRP) cation channel receptor family have unique sites of regulatory function in the kidney which enables them to promote regional vasodilatation and controlled Ca²⁺ influx into podocytes and tubular cells. Activated TRP vanilloid 1 receptor channels (TRPV1) have been found to elicit renoprotection in rodent models of acute kidney injury following ischaemia/reperfusion. Transient receptor potential cation channel, subfamily C, member 6 (TRPC6) in podocytes is involved in chronic proteinuric kidney disease, particularly in focal segmental glomerulosclerosis (FSGS). TRP vanilloid 4 receptor channels (TRPV4) are highly expressed in the kidney, where they induce Ca²⁺ influx into endothelial and tubular cells. TRP melastatin (TRPM2) non-selective cation channels are expressed in the cytoplasm and intracellular organelles, where their inhibition ameliorates ischaemic renal pathology. Although some of their basic properties have been recently identified, the renovascular role of TRPV1, TRPV4, TRPC6 and TRPM2 channels in disease states such as obesity, hypertension and diabetes is largely unknown. In this review, we discuss recent evidence for TRPV1, TRPV4, TRPC6 and TRPM2 serving as potential targets for acute and chronic renoprotection in chronic vascular and metabolic disease.

Clinical Significance of IgM and C3 Glomerular Deposition in Primary Focal Segmental Glomerulosclerosis

BACKGROUND AND OBJECTIVES

Glomerular IgM deposition is commonly shown in primary FSGS and sometimes accompanied by C3 deposition. Clinical presentation and treatment outcomes of these patients are not investigated in detail.

DESIGN, SETTING, PARTICIPANTS, &MEASUREMENTS

One hundred six consecutive patients with biopsy-proven primary FSGS from 2004 to 2014 were enrolled retrospectively. Clinical features and treatment outcomes were compared between patients with and without IgM/C3 deposition.

RESULTS

Fifty-eight (54.7%) patients presented with IgM glomerular deposition on sclerotic segments. C3 and C1q depositions were shown exclusively in patients with IgM deposition (34.5% versus 0.0%; P<0.001 and 8.6% versus 0.0%; P=0.04, respectively). Patients with IgM deposition were younger (median; range: 24.5; 18.8-39.0 versus 46.5; 26.0-64.0 years old; P=0.001), had higher level of serum IgM (142.5; 96.3-206.0 versus 107.0; 71.0-140.0 mg/dl; P=0.01), and had higher level of eGFR (median; range 97.7; 48.0-135.8 versus 62.1; 33.7-93.9 ml/min per 1.73 m(2); P=0.01) at the time of kidney biopsy. The percentage of sclerosis lesions was significantly higher in patients with C3 deposition (median; range: 21.7%; 15.3%-31.1% versus 9.2%; 6.6%-20.0%; P=0.002). Although patients received comparable immunosuppressive treatments during 58.9 (29.5-81.1) months of follow-up, a significantly higher prevalence of refractory cases (no response or steroid dependent) occurred in patients with combined IgM and C3 deposition compared with patients with IgM deposition alone or without IgM deposition (58.8% versus 22.2% versus 15.6%, respectively; P=0.004). Multivariate analysis identified combined IgM and C3 deposition (odds ratio, 11.32; 95% confidence interval, 2.26 to 56.65; P=0.003) as an independent risk factor for refractory patients; 19 of 98 patients developed renal dysfunction when their serum creatinine levels increased >30% from baseline and reached >1.5 mg/dl. Combined IgM and C3 deposition (hazard ratio, 5.67; 95% confidence interval, 1.34 to 23.84; P=0.02) was identified as an independent risk factor for renal dysfunction.

CONCLUSIONS

Patients with primary FSGS and IgM and C3 deposition showed unfavorable therapeutic responses and worse renal outcomes, which indicate that IgM and C3 deposition might involve disease progression via complement activation.

Characteristics of podocyte injury in malignant hypertensive nephropathy of rats (MSHRSP/Kpo strain)

Proteinuria is not only a hallmark of renal complication in malignant hypertension, but is also a major deteriorating factor for the progression to end-stage renal disease. Podocyte injury plays a crucial role in the renal damage associated with hypertensive nephropathy, but the underlying mechanism remains unclear. Malignant stroke-prone spontaneously hypertensive rats (MSHRSP/Kpo) represent an original and useful model of human malignant hypertension. In this study, we disclosed the glomerular injuries in the MSHRSP/Kpo. MSHRSP/Kpo exhibited elevated blood pressure at 6 weeks along with renal dysfunction and proteinuria. Histological analysis of the MSHRSP/Kpo glomeruli revealed a severe atrophy, but no change was found in the podocyte number. The expression levels of podocyte-specific proteins, nephrin, podocin, and synaptopodin were decreased in the MSHRSP/Kpo glomeruli, though another podocyte-specific protein, CD2AP, in the MSHRSP/Kpo glomeruli exhibited a similar extent of staining as in normotensive WKY/Kpo rats. Furthermore, desmin was not markedly detected in the WKY/Kpo glomeruli, but was strongly positive in MSHRSP/Kpo. By electron microscopy, well-formed foot processes (FP) were replaced by effacement in MSHRSP/Kpo. An original malignant hypertension strain MSHRSP/Kpo exhibits podocyte injuries associated with the decrease of some podocyte-specific proteins and the upregulation of desmin, along with FP effacement and proteinuria.

Obesity-related glomerulopathy: clinical and pathologic characteristics and pathogenesis

The prevalence of obesity-related glomerulopathy is increasing in parallel with the worldwide obesity epidemic. Glomerular hypertrophy and adaptive focal segmental glomerulosclerosis define the condition pathologically. The glomerulus enlarges in response to obesity-induced increases in glomerular filtration rate, renal plasma flow, filtration fraction and tubular sodium reabsorption. Normal insulin/phosphatidylinositol 3-kinase/Akt and mTOR signalling are critical for podocyte hypertrophy and adaptation. Adipokines and ectopic lipid accumulation in the kidney promote insulin resistance of podocytes and maladaptive responses to cope with the mechanical forces of renal hyperfiltration. Although most patients have stable or slowly progressive proteinuria, up to one-third develop progressive renal failure and end-stage renal disease. Renin-angiotensin-aldosterone blockade is effective in the short-term but weight loss by hypocaloric diet or bariatric surgery has induced more consistent and dramatic antiproteinuric effects and reversal of hyperfiltration. Altered fatty acid and cholesterol metabolism are increasingly recognized as key mediators of renal lipid accumulation, inflammation, oxidative stress and fibrosis. Newer therapies directed to lipid metabolism, including SREBP antagonists, PPARα agonists, FXR and TGR5 agonists, and LXR agonists, hold therapeutic promise.

Practical Application of Columbia Classification for Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a heterogeneous clinicopathological entity. Two frameworks for the classification of FSGS have been described: etiologic and morphologic. The etiologic classification is distinguished among genetic, adaptive, virus-associated, drug-induced, and idiopathic types. Morphologic classification is commonly referred to as the Columbia classification published in 2004, which distinguishes five variants: collapsing, tip, cellular, perihilar, and not otherwise specified (NOS). This classification is based on light microscopic patterns with rigorously defined specific criteria, which can be applied to primary and secondary forms of FSGS, and has been widely used over the past 10 years both as a diagnostic and as a prognostic clinical tool. This paper defines common histopathological features of FSGS, distinguished characters among five variants, and points out the confusion about terminology of variants, because most were proposed in the past with different definitions. Despite good interobserver reproducibility of this classification system, difficulty in its application may arise in the interpretation of lesions with mixed features of more than one variant in the same tissue specimen and with late lesions, because other variants may evolve into the NOS variant over time.

Pathology of Podocytopathies Causing Nephrotic Syndrome in Children

Nephrotic syndrome (NS) in children includes a diverse group of diseases that range from genetic diseases without any immunological defects to causes that are primarily due to immunological effects. Recent advances in molecular and genomic studies have resulted in a plethora of genetic defects that have been localized to the podocyte, the basic structure that is instrumental in normal filtration process. Although the disease can manifest from birth and into adulthood, the primary focus of this review would be to describe the novel genes and pathology of primary podocyte defects that cause NS in children. This review will restrict itself to the pathology of congenital NS, minimal change disease (MCD), and its variants and focal segmental glomerulosclerosis (FSGS). The two major types of congenital NS are Finnish type characterized by dilated sausage shaped tubules morphologically and diffuse mesangial sclerosis characterized by glomerulosclerosis. MCD has usually normal appearing biopsy features on light microscopy and needs electron microscopy for diagnosis, whereas FSGS in contrast has classic segmental sclerosing lesions identified in different portions of the glomeruli and tubular atrophy. This review summarizes the pathological characteristics of these conditions and also delves into the various genetic defects that have been described as the cause of these primary podocytopathies. Other secondary causes of NS in children, such as membranoproliferative and membranous glomerulonephritis, will not be covered in this review.

Novel unbiased assay for circulating podocyte-toxic factors associated with recurrent focal segmental glomerulosclerosis

Focal segmental glomerular sclerosis (FSGS) is an irreversible renal pathology characterized by podocyte detachment from the glomerular basement membrane, hyalinosis, and sclerosis. Clinically, it manifests with proteinuria and progressive loss of glomerular filtration. Primary idiopathic FSGS can occur in isolation and frequently progresses to end-stage renal disease, requiring dialysis or kidney transplantation. In 30-50% of these patients, proteinuria and FSGS recur in the renal allograft, suggesting the presence of a podocyte-toxic factor(s) in the recipient's serum. Currently, there is no reliable way to quantify the serum activity or predict the subset of FSGS patients at risk for recurrence after transplantation. We describe a novel in vitro method that measures the podocyte-toxic activity of sera from FSGS patients using cultured human podocytes; we compare this with the effect of compounds such as adriamycin. Using immunofluorescence microscopy followed by computerized image-processing analysis, we show that incubation of human podocytes with adriamycin leads to a dose-dependent disassembly of focal adhesion complexes (FACs). We then demonstrate that sera from patients with posttransplant recurrent or idiopathic FSGS cause a similar FAC disturbance. In contrast, sera from nonrecurrent FSGS patients do not affect FACs. In some FSGS patients, toxic effects of serum can be prevented by blockade of the tumor necrosis factor-α pathway. We propose that this method may be useful as a diagnostic tool to identify FSGS patients with serum podocyte-toxic activity that presumably places them at increased risk for recurrence in the renal allograft.

Aging in the Canine Kidney

Given the irreversible nature of nephron loss, aging of the kidney is of special interest to diagnostic and toxicologic pathologists. There are many similarities among histologic lesions in aged human and canine kidneys, including increased frequency of glomerulosclerosis, interstitial fibrosis, and tubular atrophy. Unfortunately, there are few studies in which renal tissue from aged healthy dogs was adequately examined with advanced diagnostics—namely, transmission electron microscopy and immunofluorescence—so age-associated changes in canine podocytes and glomerular basement membranes are poorly characterized. An age-associated decrease in the glomerular filtration rate in humans and dogs (specifically small breed dogs) has been documented. Although lesions in aged rats and mice differ somewhat from those of aged dogs and humans, the knowledge gained from rodent models is still vital to elucidating the pathogenesis of age-associated renal disease. Many novel molecules implicated in renal aging have been identified through genetically modified rodent models and transcriptomic and proteomic analysis of human kidneys. These molecules represent intriguing therapeutic targets and diagnostic biomarkers. Likewise, influencing critical pathways of cellular aging, such as telomere shortening, cellular senescence, and autophagy, could improve renal function in the elderly.

World Small Animal Veterinary Association Renal Pathology Initiative: Classification of Glomerular Diseases in Dogs

Evaluation of canine renal biopsy tissue has generally relied on light microscopic (LM) evaluation of hematoxylin and eosin-stained sections ranging in thickness from 3 to 5 µm. Advanced modalities, such as transmission electron microscopy (TEM) and immunofluorescence (IF), have been used sporadically or retrospectively. Diagnostic algorithms of glomerular diseases have been extrapolated from the World Health Organization classification scheme for human glomerular disease. With the recent establishment of 2 veterinary nephropathology services that evaluate 3-µm sections with a panel of histochemical stains and routinely perform TEM and IF, a standardized objective species-specific approach for the diagnosis of canine glomerular disease was needed. Eight veterinary pathologists evaluated 114 parameters (lesions) in renal biopsy specimens from 89 dogs. Hierarchical cluster analysis of the data revealed 2 large categories of glomerular disease based on the presence or absence of immune complex deposition: The immune complex-mediated glomerulonephritis (ICGN) category included cases with histologic lesions of membranoproliferative or membranous patterns. The second category included control dogs and dogs with non-ICGN (glomerular amyloidosis or focal segmental glomerulosclerosis). Cluster analysis performed on only the LM parameters led to misdiagnosis of 22 of the 89 cases-that is, ICGN cases moved to the non-ICGN branch of the dendrogram or vice versa, thereby emphasizing the importance of advanced diagnostic modalities in the evaluation of canine glomerular disease. Salient LM, TEM, and IF features for each pattern of disease were identified, and a preliminary investigation of related clinicopathologic data was performed.

Understanding multicellular function and disease with human tissue-specific networks

Tissue and cell-type identity lie at the core of human physiology and disease. Understanding the genetic underpinnings of complex tissues and individual cell lineages is crucial for developing improved diagnostics and therapeutics. We present genome-wide functional interaction networks for 144 human tissues and cell types developed using a data-driven Bayesian methodology that integrates thousands of diverse experiments spanning tissue and disease states. Tissue-specific networks predict lineage-specific responses to perturbation, reveal genes’ changing functional roles across tissues, and illuminate disease-disease relationships. We introduce NetWAS, which combines genes with nominally significant GWAS p-values and tissue-specific networks to identify disease-gene associations more accurately than GWAS alone. Our webserver, GIANT, provides an interface to human tissue networks through multi-gene queries, network visualization, analysis tools including NetWAS, and downloadable networks. GIANT enables systematic exploration of the landscape of interacting genes that shape specialized cellular functions across more than one hundred human tissues and cell types.

Huaier Cream Protects against Adriamycin-Induced Nephropathy by Restoring Mitochondrial Function via PGC-1α Upregulation

The mechanism by which Huaier, a Chinese traditional medicine, protects podocytes remains unclear. We designed the present study to examine whether mitochondrial function restored by PGC-1α serves as the major target of Huaier cream in protecting ADR nephropathy. After ADR administration, the podocytes exhibited remarkable cell injury and mitochondrial dysfunction. Additionally, ADR also reduced PGC-1α both in vivo and in vitro. Following the Huaier treatment, the notable downregulation of PGC-1α and its downstream molecule mitochondrial transcription factor A (TFAM) were almost entirely blocked. Correspondingly, Huaier markedly ameliorated ADR-induced podocyte injury and mitochondrial dysfunction in both rat kidneys and incubated cells as it inhibited the decrease of nephrin and podocin expression, mtDNA copy number, MMP, and ATP content. Transmission electron microscopy result also showed that Huaier protected mitochondria against ADR-induced severe mitophagy and abnormal changes of ultrastructural morphology. In conclusion, Huaier can protect podocytes against ADR-induced cytotoxicity possibly by reversing the dysfunction of mitochondria via PGC-1α overexpression, which may be a novel therapeutic drug target in glomerular diseases.

The Evidence-Based Approach to Adult-Onset Idiopathic Nephrotic Syndrome

Adult-onset nephrotic syndrome (NS) differs from its pediatric counterpart in several important ways. Most importantly, NS in adults is more etiologically heterogeneous compared to children, and thus treatment approaches rely heavily on the histological diagnosis provided by renal biopsy. The evidence-based approach to treatment of adult NS has been critically examined by the Kidney Disease Improving Global Outcomes (KDIGO) guidelines in glomerulonephritis, published in 2012. Here, we examine the strengths and limits of those guidelines and review recent work that expands the evidence-based approach.

Resolution of proteinuria after transarterial embolization of aberrant renal artery in a patient with focal segmental glomerulosclerosis

A 24-year-old man was admitted to our hospital for persistent proteinuria. He was born with a low birth weight but had grown up uneventful until the age of 20 when he was found to have proteinuria. Because his body mass index was 30.9 kg/m² at that time, he was diagnosed as obesity-related nephropathy. However, weight reduction and administration of ACE inhibitor were minimally effective for the amelioration of proteinuria. Ultrasound-guided percutaneous renal biopsy at the lower pole of right kidney was performed. As serious bleeding occurred from the right aberrant renal artery soon after biopsy, he was treated with transarterial embolization (TAE). The day after TAE, proteinuria completely disappeared. Renal biopsy showed benign nephrosclerosis with secondary focal segmental glomerulosclerosis (FSGS). Proteinuria could be induced by increased blood flow and pressure due to abnormal blood supply from aberrant renal artery. This is the first report of resolution of proteinuria after TAE of aberrant renal artery in a patient with FSGS.

The Impact of Histologic Variants on FSGS Outcomes

Focal segmental glomerulosclerosis (FSGS) is the most common glomerular disease leading to end-stage renal disease. The clinical course is highly variable with disparate responses to therapeutic intervention and rates of progression. Histologic variant subtype has been commonly used as a prognostic and therapeutic guide in the clinical management of FSGS. The tip lesion is widely considered to portend the most favorable prognosis and to be the most responsive to steroid therapy. Conversely, the collapsing lesion, more prevalent in patients of African descent, is associated with steroid resistance and higher risk of disease progression. In the 10 years since the Columbia classification system for FSGS was published, some retrospective and one prospective study explored the impact of histologic variants at the time of biopsy on FSGS outcomes. The results largely validate its clinical predictive value with respect to treatment response, though its utility in cases recurring after kidney transplantation is still unknown. Sampling and interpretation errors are additional sources of caution. More research is needed to fully define reproducible prognostic and therapeutic markers for this polymorphic disorder.

Insights into the renal pathogenesis in Schimke immuno-osseous dysplasia: A renal histological characterization and expression analysis

Schimke immuno-osseous dysplasia (SIOD) is a pleiotropic disorder caused by mutations in the SWI/SNF2-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like-1 (SMARCAL1) gene, with multiple clinical features, notably end-stage renal disease. Here we characterize the renal pathology in SIOD patients. Our analysis of SIOD patient renal biopsies demonstrates the tip and collapsing variants of focal segmental glomerulosclerosis (FSGS). Additionally, electron microscopy revealed numerous glomerular abnormalities most notably in the podocyte and Bowman's capsule. To better understand the role of SMARCAL1 in the pathogenesis of FSGS, we defined SMARCAL1 expression in the developing and mature kidney. In the developing fetal kidney, SMARCAL1 is expressed in the ureteric epithelium, stroma, metanephric mesenchyme, and in all stages of the developing nephron, including the maturing glomerulus. In postnatal kidneys, SMARCAL1 expression is localized to epithelial tubules of the nephron, collecting ducts, and glomerulus (podocytes and endothelial cells). Interestingly, not all cells within the same lineage expressed SMARCAL1. In renal biopsies from SIOD patients, TUNEL analysis detected marked increases in DNA fragmentation. Our results highlight the cells that may contribute to the renal pathogenesis in SIOD. Further, we suggest that disruptions in genomic integrity during fetal kidney development contribute to the pathogenesis of FSGS in SIOD patients.

The role of survivin in podocyte injury induced by puromycin aminonucleoside

Objective

Survivin is a member of the inhibitor of apoptosis protein family, which uniquely promotes mitosis and regulates apoptosis in cancer cells. Recent studies have demonstrated that survivin also expresses in several normal adult cells. In the present study, we aimed to investigate the function of survivin in the terminally differentiated epithelial cells, podocytes.

Methods

Survivin expression and location were detected by Quantitative Real-Time PCR, western blot and fluorescence confocal microscopy methods in normal and injured mouse podocytes. Cyto-protection function of survivin was also studied in cultured podocyte injured by puromycin aminonucleoside (PAN), transfected with survivin siRNA to down-regulate survivin expression, or with survivin plasmid to transiently over-express survivin.

Results

In podocytes, PAN stimulated expressions of survivin and the apoptosis related molecule caspase 3. Knockdown of survivin expression by siRNA increased the activation of caspase 3, induced podocyte apoptosis and remarkable rearrangement of actin cytoskeleton. Moreover, over-expression of survivin inhibited PAN-induced podocyte apoptosis and cytoskeleton rearrangement.

Conclusion

Our data provides the evidence that survivin plays an important role in protecting podocytes from apoptosis induced by PAN. The mechanism of survivin related anti-apoptosis may, at least partially, be through the activation of caspase 3.

Dipping your feet in the water: podocytes in urine

Podocyte injury and loss plays an important role in the pathogenesis and progression of many kidney diseases. Studies have shown that podocyte-related markers and products can be detected in the urine of patients with glomerular diseases such as focal segmental glomerulosclerosis, IgA nephropathy, lupus nephritis, diabetic nephropathy and pre-eclampsia. Therefore, detecting the loss of podocytes in the urine provides a useful noninvasive technique of gathering information about the disease type and/or activity of glomerular diseases. Currently, urine podocyte-related protein markers, mRNA, microRNA and exosomes have been used with varying degrees of success to study glomerular diseases. The determination of urinary podocyte loss may become an important noninvasive tool in the evaluation of glomerular diseases.

Clinical features and outcomes of focal segmental glomerulosclerosis pathologic variants in Korean adult patients

BACKGROUND

Many studies have shown that clinical characteristics and outcomes differ depending on pathologic variants of focal segmental glomerulosclerosis (FSGS). However, these are not well defined in Asian populations.

METHODS

This retrospective study evaluated clinical features and outcomes of pathologic FSGS variants in 111 adult patients between January 2004 and December 2012. Primary outcome was the composite of doubling of baseline serum creatinine concentrations (D-SCr) or onset of end-stage renal disease (ESRD). Secondary outcome included complete (CR) or partial remission (PR).

RESULTS

There were 70 (63.1%), 20 (18.0%), 17 (15.3%), 3 (2.7%), and 1 (0.9%) patients with not-otherwise specified (NOS), tip, perihilar, cellular, and collapsing variants, respectively. At presentation, nephrotic-range proteinuria occurred more commonly in tip lesion than in other variants. The overall 5-year renal survival rate was 76.8%. During a median follow-up of 34.5 months, only 1 (5.0%) patient with a tip lesion reached the composite end point compared to 2 (11.8%) and 12 (17.1%) patients in perihilar and NOS variants, but this difference was not statistically significant in an adjusted Cox model. However, tip lesion was associated with a significantly increased probability of achieving CR (P = 0.044).

CONCLUSION

Similar to other populations, Korean adult patients with FSGS have distinct clinical features with the exception of a rare frequency of cellular and collapsing variants. Although pathologic variants were not associated with overall outcome, the tip variant exhibited favorable outcome in terms of achieving remission. Further studies are required to delineate long-term outcome and response to treatment of the pathologic variants.

Angiotensin II activation of TRPC6 channels in rat podocytes requires generation of reactive oxygen species

Angiotensin II (AII) plays a major role in the progression of chronic kidney diseases. Podocytes are essential components of the ultrafiltration apparatus, and are targets for AII signaling. AII has been shown to increase generation of reactive oxygen species (ROS) in podocytes. Canonical transient receptor potential-6 (TRPC6) channels stimulate Ca(2+) influx in podocytes, and have been implicated in glomerular disease. We observed that AII increased cationic currents in rat podocytes in an isolated glomerulus preparation in which podocytes are still attached to the underlying capillary. This effect was completely blocked by SKF-96365, by micromolar La(3+) , and by siRNA knockdown of TRPC6, indicating that TRPC6 is the primary source of Ca(2+) influx mobilized by endogenously expressed angiotensin II receptors in these cells. These responses were also blocked by the AT1R antagonist losartan, the phospholipase C inhibitor D-609, and by inhibition of G protein signaling. The pan-protein kinase C inhibitor chelerythrine had no effect. Importantly, pretreating podocytes with the ROS quencher manganese (III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) eliminated AII activation of TRPC6. Significant reductions of AII effects on podocyte TRPC6 were also observed after pretreatment with NADPH oxidase inhibitors apocynin or diphenylene iodonium (DPI). These data suggest that ROS production permits activation of TRPC6 channels by G protein and PLC-dependent cascades initiated by AII acting on AT1Rs in podocytes. This pathway also provides a basis whereby two forms of cellular stress-oxidative stress and Ca(2+) overload-converge on common pathways relevant to disease.

Mitochondrial dysfunction in the pathophysiology of renal diseases

Mitochondrial dysfunction has gained recognition as a contributing factor in many diseases. The kidney is a kind of organ with high energy demand, rich in mitochondria. As such, mitochondrial dysfunction in the kidney plays a critical role in the pathogenesis of kidney diseases. Despite the recognized importance mitochondria play in the pathogenesis of the diseases, there is limited understanding of various aspects of mitochondrial biology. This review examines the physiology and pathophysiology of mitochondria. It begins by discussing mitochondrial structure, mitochondrial DNA, mitochondrial reactive oxygen species production, mitochondrial dynamics, and mitophagy, before turning to inherited mitochondrial cytopathies in kidneys (inherited or sporadic mitochondrial DNA or nuclear DNA mutations in genes that affect mitochondrial function). Glomerular diseases, tubular defects, and other renal diseases are then discussed. Next, acquired mitochondrial dysfunction in kidney diseases is discussed, emphasizing the role of mitochondrial dysfunction in the pathogenesis of chronic kidney disease and acute kidney injury, as their prevalence is increasing. Finally, it summarizes the possible beneficial effects of mitochondrial-targeted therapeutic agents for treatment of mitochondrial dysfunction-mediated kidney injury-genetic therapies, antioxidants, thiazolidinediones, sirtuins, and resveratrol-as mitochondrial-based drugs may offer potential treatments for renal diseases.