Causes and pathogenesis of focal segmental glomerulosclerosis

Biomarkers in Primary Focal Segmental Glomerulosclerosis in Optimal Diagnostic-Therapeutic Strategy

Focal segmental glomerulosclerosis (FSGS) involves podocyte injury. In patients with nephrotic syndrome, progression to end-stage renal disease often occurs over the course of 5 to 10 years. The diagnosis is based on a renal biopsy. It is presumed that primary FSGS is caused by an unknown plasma factor that might be responsible for the recurrence of FSGS after kidney transplantation. The nature of circulating permeability factors is not explained and particular biological molecules responsible for inducing FSGS are still unknown. Several substances have been proposed as potential circulating factors such as soluble urokinase-type plasminogen activator receptor (suPAR) and cardiolipin-like-cytokine 1 (CLC-1). Many studies have also attempted to establish which molecules are related to podocyte injury in the pathogenesis of FSGS such as plasminogen activator inhibitor type-1 (PAI-1), angiotensin II type 1 receptors (AT1R), dystroglycan(DG), microRNAs, metalloproteinases (MMPs), forkheadbox P3 (FOXP3), and poly-ADP-ribose polymerase-1 (PARP1). Some biomarkers have also been studied in the context of kidney tissue damage progression: transforming growth factor-beta (TGF-β), human neutrophil gelatinase-associated lipocalin (NGAL), malondialdehyde (MDA), and others. This paper describes molecules that could potentially be considered as circulating factors causing primary FSGS.

Complete remission of tip lesion variant focal segmental glomerulosclerosis (FSGS) with the Janus Kinase (JAK) inhibitor tofacitinib

A 67-year-old woman with transverse myelitis and seizure disorder secondary to suspected central nervous system (CNS) systemic lupus erythematosus (SLE) and seropositive rheumatoid arthritis had two episodes of severe nephrotic syndrome 15 years apart. She underwent a renal biopsy in both episodes, showing tip lesion variant focal segmental glomerulosclerosis (FSGS). The patient responded both times to prednisone treatment, achieving a complete remission within 2 months in the first episode and remission 4 months in the second episode. A year after her second episode, the patient had a third episode of severe nephrotic syndrome. She achieved an equally rapid complete remission in 3 months without steroid treatment, as she was concomitantly treated with the Janus Kinase (JAK) inhibitor tofacitinib for a flare of rheumatoid arthritis. This case report suggests that JAK inhibitors may have therapeutic use in FSGS, which is supported by experimental data in the medical literature.

The Role of Rituximab in Primary Focal Segmental Glomerular Sclerosis of the Adult

Introduction

Primary focal segmental glomerular sclerosis (FSGS) is a rare, likely immune-mediated disease. Rituximab (RTX) may play a role in management, although data in adults are scanty.

Methods

We collected cases of RTX-treated primary FSGS within the Italian Society of Nephrology Immunopathology Working Group and explored response rate (24-hour proteinuria <3.5 g and <50% compared with baseline, stable estimated glomerular filtration rate).

Results

A total of 31 patients were followed for at least 12 months; further follow-up (median 17 months, interquartile range [IQR] 15–33.5) was available for 11. At first RTX administration, median creatinine and 24-hour proteinuria were 1.17 mg/dl (IQR 0.83–1.62) and 5.2 g (IQR 3.3–8.81), respectively. Response rate at 3, 6, and 12 months was 39%, 52%, and 42%, respectively. In the first 12 months, creatinine level remained stable whereas proteinuria and serum albumin level improved, with an increase in the proportion of patients tapering other immunosuppressants. There were 6 patients who were retreated with RTX within 12 months, either for proteinuria increase or refractory disease; only the 2 responders to the first RTX course experienced a further response. At univariate analysis, 6-month response was more frequent in steroid-dependent patients (odds ratio [OR] 7.7 [95% CI 1.16–52.17]) and those with proteinuria <5 g/24 h (OR 8.25 [1.45–46.86]). During long-term follow-up, 4 of 5 responders at 12 months maintained a sustained response, either without further immunosuppression (2 of 4) or with pre-emptive RTX (2 of 4); 1 relapsed and responded to RTX retreatment.

Conclusion

RTX may be an option in primary FSGS, especially in steroid-dependent patients, with 24-hour proteinuria <5 g and previously responders to RTX. Optimal long-term management for responders is unclear, with some patients experiencing sustained remission and others requiring RTX retreatment, either preemptive or after rising proteinuria.

Healthy and unhealthy aging on kidney structure and function: human studies

PURPOSE OF REVIEW

This review is intended to provide an up-to-date analysis of the structural and functional alterations of the kidneys that accompany healthy and unhealthy aging in humans. Macro- and micro- structural changes and glomerular filtration rate (whole kidney and single nephron) accompanying aging will be stressed.

RECENT FINDINGS

Comparative findings concerning distribution of anatomic changes of the kidney healthy and unhealthy aging are reviewed. Challenges concerning definition of chronic kidney disease (CKD) in otherwise healthy aging patients are discussed. The complex interactions of CKD and aging are discussed. The role of podocyte dysbiosis in kidney aging is reviewed.

SUMMARY

Kidney aging is a complex phenomenon often difficult to distinguish from CKD. Nonetheless, phenotypes of healthy and unhealthy aging are evident. Much more information concerning the molecular characteristics of normal kidney aging and its relevance to chronic kidney disease is needed.

Induction of Accelerated Aging in a Mouse Model

With the global increase of the elderly population, the improvement of the treatment for various aging-related diseases and the extension of a healthy lifespan have become some of the most important current medical issues. In order to understand the developmental mechanisms of aging and aging-related disorders, animal models are essential to conduct relevant studies. Among them, mice have become one of the most prevalently used model animals for aging-related studies due to their high similarity to humans in terms of genetic background and physiological structure, as well as their short lifespan and ease of reproduction. This review will discuss some of the common and emerging mouse models of accelerated aging and related chronic diseases in recent years, with the aim of serving as a reference for future application in fundamental and translational research.

Decoding the Mechanism behind the Pathogenesis of the Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a chronic glomerular disease associated with podocyte injury which is named after the pathologic features of the kidney. The aim of this study is to decode the key changes in gene expression and regulatory network involved in the formation of FSGS. Integrated network analysis included Gene Expression Omnibus (GEO) datasets to identify differentially expressed genes (DEGs) between FSGS patients and healthy donors. Bioinformatics analysis was used to identify the roles of the DEGs and included the development of protein-protein interaction (PPI) networks, Gene Ontology (GO), and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses, and the key modules were assured. The expression levels of DEGs were validated using the additional dataset. Eventually, transcription factors and ceRNA networks were established to illuminate the regulatory relationships in the formation of FSGS. 1130 DEGs including 475 upregulated genes and 655 downregulated genes with functional enrichment analysis were determined. Further analysis uncovered that the validated hub genes were defined as candidate genes, including Complement C3a Receptor 1 (C3AR1), C-C Motif Chemokine Receptor 1(CCR1), C-X3-C Motif Chemokine Ligand 1 (CX3CL1), Melatonin Receptor 1A (MTNR1A), and Purinergic Receptor P2Y13 (P2RY13). More importantly, we identified transcription factors and mRNA-miRNA-lncRNA regulatory networks associated with the candidate genes. The candidate genes and regulatory networks discovered in this study can help to comprehend the molecular mechanism of FSGS and supply potential targets for the diagnosis and therapy of FSGS.

Treatment of Focal and Segmental Glomerulosclerosis Secondary to High Altitude Polycythemia with Acetazolamide

Vizcarra-Vizcarra, Cristhian A., Eduardo Chávez-Velázquez, Carmen Asato-Higa, and Abdías Hurtado-Aréstegui. Treatment of focal and segmental glomerulosclerosis secondary to high altitude polycythemia with acetazolamide. High Alt Med Biol 00:000-000, 2022.-Focal segmental glomerulosclerosis (FSGS) is a morphological pattern, caused by glomerular injury and is the leading cause of nephrotic syndrome in adults. We present the case of a 59-year-old female patient, resident of a high-altitude city (3,824 m), who had polycythemia and nephrotic syndrome. A renal biopsy was performed, and the findings were compatible with FSGS. The patient received phlebotomy 500 ml three times, which reduced, partially, the hemoglobin concentration. However, she had refractory proteinuria, despite the use of enalapril and spironolactone. We observed that proteinuria worsened with the increase in hemoglobin levels. So, she was treated with acetazolamide 250 mg bid for 4 months, which reduced proteinuria and hemoglobin. During the coronavirus disease 2019 (COVID-19) pandemic, the patient did not take acetazolamide and again, she had an increase in hemoglobin and proteinuria levels. We conclude that acetazolamide may be an effective treatment in FSGS due to high altitude polycythemia.

Primary Focal Segmental Glomerulosclerosis Recurrence After Pediatric Renal Transplantation

OBJECTIVES

Focal segmental glomerulosclerosis recurrence after renal transplant occurs frequently in pediatric patients and is associated with poor graft survival when patients reach adulthood. We investigated recurrence rates, recurrence risk factors, management strategies, and long-term graft function among pediatric renal transplant recipients with focal segmental glomerulosclerosis as primary disease.

MATERIALS AND METHODS

We retrospectively evaluated medical records of 34 pediatric patients with primary focal segmental glomerulosclerosis who had undergone renal transplant between 2004 and 2019 at our center. Focal segmental glomerulosclerosis recurrence was diagnosed by the presence of nephrotic range proteinuria after transplant and confirmed by graft biopsy. Preoperative prophylactic plasma exchange was administered to pediatric renal transplant recipients with primary focal segmental glomerulosclerosis. Plasma exchange was also used to treat focal segmental glomerulosclerosis recurrence, with rituximab added if the patient did not respond to plasma exchange.

RESULTS

All patients (male-to-female ratio of 19:15) in our group underwent renal transplant. Mean patient age at the time of transplant was 12.72 ± 5.46 years. Twenty-nine patients received living- related donor allografts (85.3%) and 5 received organs from deceased donors (14.7%). We identified focal segmental glomerulosclerosis recurrence in 5 recipients (14.7%). Time from focal segmental glomerulosclerosis diagnosis to end-stage renal disease and duration of dialysis were shorter in the recurrence group than in the nonrecurrence group (48.4 months [range, 2-90 mo] vs 65.1 months [range, 8-123 mo] and 1.41 ± 0.82 vs 3.18 ± 1.88 years, respectively; P < .05). Donor type and transplant age were similar in both groups. Of those with recurrence who had received plasma exchange and rituximab, 3 patients (75%) had complete remission and 1 patient (25%) had partial remission.

CONCLUSIONS

Prophylactic plasma exchange and the combined plasma exchange-rituximab regimen for treatment of focal segmental glomerulosclerosis recurrence resulted in low recurrence and good remission rates in our pediatric cohort.

Histologically resolved small RNA maps in primary focal segmental glomerulosclerosis indicate progressive changes within glomerular and tubulointerstitial regions

Pathological heterogeneity is common in clinical tissue specimens and complicates the interpretation of molecular data obtained from the specimen. As a typical example, a kidney biopsy specimen often contains glomeruli and tubulointerstitial regions with different levels of histological injury, including some that are histologically normal. We reasoned that the molecular profiles of kidney tissue regions with specific histological injury scores could provide new insights into kidney injury progression. Therefore, we developed a strategy to perform small RNA deep sequencing analysis for individually scored glomerular and tubulointerstitial regions in formalin-fixed, paraffin-embedded kidney needle biopsies. This approach was applied to study focal segmental glomerulosclerosis (FSGS), the leading cause of nephrotic syndrome in adults. Large numbers of small RNAs, including microRNAs, 3'-tRFs, 5'-tRFs, and mitochondrial tRFs, were differentially expressed between histologically indistinguishable tissue regions from patients with FSGS and matched healthy controls. A majority of tRFs were upregulated in FSGS. Several small RNAs were differentially expressed between tissue regions with different histological scores in FSGS. Notably, with increasing levels of histological damage, miR-21-5p was upregulated progressively and miR-192-5p was downregulated progressively in glomerular and tubulointerstitial regions, respectively. This study marks the first genome scale molecular profiling conducted in histologically characterized glomerular and tubulointerstitial regions. Thus, substantial molecular changes in histologically normal kidney regions in FSGS might contribute to initiating tissue injury or represent compensatory mechanisms. In addition, several small RNAs might contribute to subsequent progression of glomerular and tubulointerstitial injury, and histologically mapping small RNA profiles may be applied to analyze tissue specimens in any disease.

Histopathological and Clinical Findings of Biopsy-Proven Focal and Segmental Glomerulosclerosis: A Retrospective Study

Background

Focal segmental glomerulosclerosis (FSGS) is characterized by the presence of glomerular damage on histopathological examination. The major defining symptom of FSGS is proteinuria, which indicates damage to the glomerular filtration barrier. Additionally, FSGS is the most common cause of primary nephrotic syndrome. However, in Saudi Arabia, there is a paucity of research on this topic. Therefore, this study was designed to examine the clinical features, laboratory findings, and presence of comorbidities in patients with FSGS to determine their effects on clinical outcomes.

Methods

We retrospectively analyzed the histopathological and clinical data of patients diagnosed with FSGS via biopsy at King Abdulaziz University Hospital, Jeddah, Saudi Arabia, during the period 1989-2020. Biopsy samples were labeled according to the Columbia classification as tip, perihilar, cellular, collapsing, or not otherwise specified (NOS).

Results

We included 39 children and 21 adults. Males accounted for 54.1% of the sample. Hypertension was the most common comorbidity. Regarding FSGS subtypes, 60.9% of the lesions in the adult patients were collapsing lesions, followed by NOS (26.1%). In pediatric patients, 36.8% of the lesions were NOS, followed by collapsing lesions (28.9%). We also observed a very low rate of remission. In both age groups, the most common clinical presentation was nephrotic syndrome.

Conclusion

We found a high prevalence of collapsing and NOS FSGS subtypes in both the adult and pediatric age groups. The most prevalent outcome was the persistence of nephrotic syndrome with low rates of remission.

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.

The Pathology Lesion Patterns of Podocytopathies: How and why?

Podocytopathies are a group of proteinuric glomerular disorders driven by primary podocyte injury that are associated with a set of lesion patterns observed on kidney biopsy, i.e., minimal changes, focal segmental glomerulosclerosis, diffuse mesangial sclerosis and collapsing glomerulopathy. These unspecific lesion patterns have long been considered as independent disease entities. By contrast, recent evidence from genetics and experimental studies demonstrated that they represent signs of repeated injury and repair attempts. These ongoing processes depend on the type, length, and severity of podocyte injury, as well as on the ability of parietal epithelial cells to drive repair. In this review, we discuss the main pathology patterns of podocytopathies with a focus on the cellular and molecular response of podocytes and parietal epithelial cells.

Uncovering Molecular Heterogeneity in the Kidney With Spatially Targeted Mass Spectrometry

The kidney functions through the coordination of approximately one million multifunctional nephrons in 3-dimensional space. Molecular understanding of the kidney has relied on transcriptomic, proteomic, and metabolomic analyses of kidney homogenate, but these approaches do not resolve cellular identity and spatial context. Mass spectrometry analysis of isolated cells retains cellular identity but not information regarding its cellular neighborhood and extracellular matrix. Spatially targeted mass spectrometry is uniquely suited to molecularly characterize kidney tissue while retaining in situ cellular context. This review summarizes advances in methodology and technology for spatially targeted mass spectrometry analysis of kidney tissue. Profiling technologies such as laser capture microdissection (LCM) coupled to liquid chromatography tandem mass spectrometry provide deep molecular coverage of specific tissue regions, while imaging technologies such as matrix assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) molecularly profile regularly spaced tissue regions with greater spatial resolution. These technologies individually have furthered our understanding of heterogeneity in nephron regions such as glomeruli and proximal tubules, and their combination is expected to profoundly expand our knowledge of the kidney in health and disease.

Telomerase is required for glomerular renewal in kidneys of adult mice

Homeostatic renal filtration relies on the integrity of podocytes, which function in glomerular filtration. These highly specialized cells are damaged in 90% of chronic kidney disease, representing the leading cause of end-stage renal failure. Although modest podocyte renewal has been documented in adult mice, the mechanisms regulating this process remain largely unknown and controversial. Using a mouse model of Adriamycin-induced nephropathy, we find that the recovery of filtration function requires up-regulation of the endogenous telomerase component TERT. Previous work has shown that transient overexpression of catalytically inactive TERT (i-TERT^ci mouse model) has an unexpected role in triggering dramatic podocyte proliferation and renewal. We therefore used this model to conduct specific and stochastic lineage-tracing strategies in combination with high throughput sequencing methods. These experiments provide evidence that TERT drives the activation and clonal expansion of podocyte progenitor cells. Our findings demonstrate that the adult kidney bears intrinsic regenerative capabilities involving the protein component of telomerase, paving the way for innovative research toward the development of chronic kidney disease therapeutics.

Role of miRNA-671-5p in Mediating Wnt/β-Catenin-Triggered Podocyte Injury

Podocyte injury and proteinuria are the most common features of glomerular disease, which is the leading cause of end-stage renal failure. Hyperactivated Wnt/β-catenin signaling is closely associated with podocyte injury, but the underlying mechanisms are incompletely understood. Here we show that miRNA-671-5p (miR-671-5p) plays a crucial role in mediating β-catenin-triggered podocyte injury by targeting Wilms tumor 1 (WT1). Microarray-based expression profiling revealed that miR-671-5p was the most upregulated miRNA in podocytes after β-catenin activation. MiR-671-5p was colocalized with β-catenin in the glomeruli of proteinuric CKD in vivo. Bioinformatics analyses and luciferase reporter assays confirmed that miR-671-5p targeted WT1 mRNA. Overexpression of miR-671-5p mimics inhibited WT1 and impaired podocyte integrity, whereas miR-671-5p antagomir preserved the expression of WT1 and other podocyte-specific proteins under basal conditions or after β-catenin activation. In mouse remnant kidney model, overexpression of miR-671-5p aggravated podocyte injury, worsened kidney dysfunction and exacerbated renal fibrosis after 5/6 nephrectomy. In contrast, miR-671-5p antagomir alleviated podocyte injury and attenuated proteinuria and renal fibrotic lesions after glomerular injury in vivo. These studies underscore a pivotal role of miR-671-5p in mediating WT1 depletion and podocyte injury induced by β-catenin. Targeting miR-671-5p may serve as a new approach to prevent podocyte injury and proteinuria in proteinuric CKD.

Dexrazoxane Alleviated Doxorubicin-Induced Nephropathy in Rats

INTRODUCTION

Doxorubicin (DOX), an anthracycline antitumor agent, has been widely used against various solid tumors and hematological malignancies. However, the clinical application of DOX is restricted by its multiple organ toxicity including nephrotoxicity. This study investigated the protective effects and mechanisms of dexrazoxane (DZR) against DOX-induced nephropathy in rats.

METHODS

Male Sprague Dawley rats received 2.5 mg/kg DOX once a week for 5 consecutive weeks. 24-h urinary protein and renal function injury biomarkers were determined to evaluate the renal function. Histopathological changes and glomerulosclerosis were examined by hematoxylin and eosin and periodic acid-Schiff staining. The change of renal ultrastructure in the DOX-induced rats was observed by the electron microscopy. The renal apoptosis was detected by TUNEL staining and measured the protein expression of Caspase-3, Bcl-2, and Bax. Renal interstitial fibrosis was determined by Masson staining and immunohistochemistry examination. The levels of vimentin, alpha-smooth muscle actin (α-SMA), and transforming growth factor β (TGF-β) in kidney tissue were detected by Western blot.

RESULTS

DZR pretreatment markedly raised the survival rate and improved the renal dysfunction in DOX-treated rats. DZR ameliorated DOX-induced histopathological lesion of glomerular and tubular and apoptosis. DZR restored the oxidant/antioxidant balance via regulating the levels of MDA, SOD, and TAC. DZR reduced DOX-induced collagen IV deposition and renal interstitial fibrosis and downregulated the fibrosis-related protein expressions of vimentin, α-SMA, and TGF-β1.

CONCLUSION

Our results suggest DZR exerted its protective effects against DOX-induced nephropathy through inhibition of lipid peroxidation, apoptosis, and fibrosis.

CXCR4 induces podocyte injury and proteinuria by activating β-catenin signaling

Background: C-X-C chemokine receptor type 4 (CXCR4) plays a crucial role in mediating podocyte dysfunction, proteinuria and glomerulosclerosis. However, the underlying mechanism remains poorly understood. Here we studied the role of β-catenin in mediating CXCR4-triggered podocyte injury.

Methods: Mouse models of proteinuric kidney diseases were used to assess CXCR4 and β-catenin expression. We utilized cultured podocytes and glomeruli to delineate the signal pathways involved. Conditional knockout mice with podocyte-specific deletion of CXCR4 were generated and used to corroborate a role of CXCR4/β-catenin in podocyte injury and proteinuria.

Results: Both CXCR4 and β-catenin were induced and colocalized in the glomerular podocytes in several models of proteinuric kidney diseases. Activation of CXCR4 by its ligand SDF-1α stimulated β-catenin activation but did not affect the expression of Wnt ligands in vitro. Blockade of β-catenin signaling by ICG-001 preserved podocyte signature proteins and inhibited Snail1 and MMP-7 expression in vitro and ex vivo. Mechanistically, activation of CXCR4 by SDF-1α caused the formation of CXCR4/β-arrestin-1/Src signalosome in podocytes, which led to sequential phosphorylation of Src, EGFR, ERK1/2 and GSK-3β and ultimately β-catenin stabilization and activation. Silencing β-arrestin-1 abolished this cascade of events and inhibited β-catenin in response to CXCR4 stimulation. Podocyte-specific knockout of CXCR4 in mice abolished β-catenin activation, preserved podocyte integrity, reduced proteinuria and ameliorated glomerulosclerosis after Adriamycin injury.

Conclusion: These results suggest that CXCR4 promotes podocyte dysfunction and proteinuria by assembling CXCR4/β-arrestin-1/Src signalosome, which triggers a cascade of signal events leading to β-catenin activation.

Inhibition of Podocytes DPP4 Activity Is a Potential Mechanism of Lobeliae Chinensis Herba in Treating Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease and has become a serious public health problem worldwide. Dipeptidyl peptidase-4 (DPP4) inhibitors, an emerging drug for the treatment of diabetes, have been found to have renoprotective effects in addition to glucose-lowering effects and therefore have the potential to be a treatment modality for DKD. Lobeliae Chinensis Herba (LCH), a traditional Chinese herb widely used in the treatment of diabetes, has recently been found to have a hypoglycaemic mechanism related to the inhibition of DPP4. Firstly, analysis of single-cell sequencing data from mouse kidneys in the National Center for Biotechnology Information (NCBI) database revealed that DPP4 was specifically upregulated in DKD podocytes and was associated with podocyte proliferation. Subsequently, the network pharmacology approach was applied to the screening of compounds. Twelve LCH active ingredients targeting DPP4 were extracted from the Traditional Chinese Medicine System Pharmacology (TCMSP) database. In addition, these 12 compounds and DPP4 were molecularly docked to predict the probability of them affecting DPP4 activity. In vitro, Quercetin, Methyl rosmarinate, Kaempferol, Diosmetin and Acacetin were demonstrated to retard podocyte proliferation by inhibiting DPP4 activity and were the top five compounds predicted by molecular docking to be the most likely to affect DPP4 activity. The half maximal inhibitory concentration (IC₅₀) of the five compounds for DPP4 activity were as follows. Acacetin Log IC₅₀ = −8.349, 95%CI (−9.266, −7.265), Diosmtrin Log IC₅₀ = −8.419, 95%CI (−8.889, −7.950), Log IC₅₀ = −8.349, 95%CI (−9.266, −7.265), Methyl rosmarinate Log IC₅₀ = −8.415, 95%CI (−8.751, −8.085), Kaempferol Log IC₅₀ = −8.297, 95%CI (−9.001, −7.615), Quercetin Log IC₅₀ = −8.864, 95%CI (−9.107, −8.615). Finally, Quercetin, Methyl rosmarinate, Kaempferol, Diosmetin and Acacetin qualified for pharmacokinetic and drug similarity screening and have the potential to be the most promising oral agents for the treatment of DKD.

Parietal epithelial cells maintain the epithelial cell continuum forming Bowman's space in focal segmental glomerulosclerosis

In the glomerulus, Bowman's space is formed by a continuum of glomerular epithelial cells. In focal segmental glomerulosclerosis (FSGS), glomeruli show segmental scarring, a result of activated parietal epithelial cells (PECs) invading the glomerular tuft. The segmental scars interrupt the epithelial continuum. However, non-sclerotic segments seem to be preserved even in glomeruli with advanced lesions. We studied the histology of the segmental pattern in Munich Wistar Frömter rats, a model for secondary FSGS. Our results showed that matrix layers lined with PECs cover the sclerotic lesions. These PECs formed contacts with podocytes of the uninvolved tuft segments, restoring the epithelial continuum. Formed Bowman's spaces were still connected to the tubular system. In biopsies of patients with secondary FSGS, we also detected matrix layers formed by PECs, separating the uninvolved from the sclerotic glomerular segments. PECs have a major role in the formation of glomerulosclerosis; we show here that in FSGS they also restore the glomerular epithelial cell continuum that surrounds Bowman's space. This process may be beneficial and indispensable for glomerular filtration in the uninvolved segments of sclerotic glomeruli.

Summary: Histological analysis of rat and human kidneys reveals a novel role for parietal epithelial cells (PECs) in glomerulosclerosis. PECs seem to restore the glomerular epithelial continuum, which may avert further loss of glomerular function.

MAD2B-mediated cell cycle reentry of podocytes is involved in the pathogenesis of FSGS

Rationale: Focal segmental glomerulosclerosis (FSGS) is characterized by the dysfunction of “post-mitotic” podocytes. The reentry of podocytes in the cell cycle will ultimately result in cell death. Mitotic arrest deficient 2-like protein 2 (MAD2B), an inhibitor of anaphase-promoting complex (APC)/cyclosome, precisely controls the metaphase to anaphase transition and ordered cell cycle progression. However, the role of MAD2B in FSGS podocyte injury remains unknown.

Methods: To explore MAD2B function in podocyte cell cycle reentry, we used conditional mutant mice lacking MAD2B selectively in podocytes in ADR-induced FSGS murine model. Additionally, KU-55933, a specific inhibitor of ataxia-telangiectasia mutated (ATM) was utilized in vivo and in vitro to explore the role of ATM in regulating MAD2B.

Results: The expression of MAD2B in podocytes was dramatically increased in patients with FSGS and ADR-treated mice along with podocyte cell cycle reentry. Podocyte-specific knockout of MAD2B effectively attenuated proteinuria, podocyte injury, and prevented the aberrant cell cycle reentry. By bioinformatics analysis we revealed that ATM kinase is a key upstream regulator of MAD2B. Furthermore, inhibition of ATM kinase abolished MAD2B-driven cell cycle reentry and alleviated podocyte impairment in FSGS murine model. In vitro studies by site-directed mutagenesis and immunoprecipitation we revealed ATM phosphorylated MAD2B and consequently hampered the ubiquitination of MAD2B in a phosphorylation-dependent manner.

Conclusions: ATM kinase-MAD2B axis importantly contributes to the cell cycle reentry of podocytes, which is a novel pathogenic mechanism of FSGS, and may shed light on the development of its therapeutic approaches.

Kidney Involvement in PSTPIP1 Associated Inflammatory Diseases (PAID): A Case Report and Review of the Literature

Pyogenic arthritis, pyoderma gangrenosum and acne (PAPA) syndrome, and the proline-serine-threonine phosphatase-interacting protein 1 (PSTPIP1)-associated myeloid-related proteinemia inflammatory (PAMI) syndrome are two distinct clinical conditions caused by heterozygous mutations of the PSTPIP1 gene. While skin and joint involvements are shared by both conditions, PAMI is characterized by hepatosplenomegaly, pancytopenia, and growth failure. Kidney involvement is exceptional in PSTPIP1-mediated disorders. The two missense PSTPIP1 variants associated with PAMI syndrome are p.E250K and p.E257K. Long-term treatment with interleukin (IL)-1 inhibitors is effective to control inflammatory manifestations and is usually well-tolerated. We report a case of a patient carrying the PSTPIP1 p.E250K mutation who developed a late-onset kidney involvement despite a long treatment with canakinumab and anakinra. Kidney biopsy showed focal segmental glomerulosclerosis that was treated with tacrolimus (0.1 mg/kg/day in two doses). A literature revision with the aim to assess the proportion and type of kidney involvement in PAMI syndrome revealed that heterogeneous nephropathies may be part of the clinical spectrum. Our study supports the importance of a periodic diagnostic work-up, including kidney laboratory tests and kidney biopsy, in individuals affected with PAMI syndrome. Kidney and liver functions may be impaired regardless of anti-cytokines treatments and additional therapy approaches (i.e., multi-drugs, hematopoietic stem cell transplantation) should be carefully considered.

A systematic review on nephron protective AYUSH drugs as constituents of NEERI-KFT (A traditional Indian polyherbal formulation) for the management of chronic kidney disease

Chronic Kidney Disease (CKD) is a major health problem characterized by kidney dysfunction with progressive segmental glomerulosclerosis to end-stage renal disease (ESRD). Due to lack of scientific data and comprehensive reports, the current systematic review provides an inclusive understanding and prospective associated with phytopharmacology of NEERI-KFT in CKD. The data was collected from more than five databases such as Science Direct, Google Scholar, Elsevier, PubMed, Springer, ACS publication etc using keywords like CKD/Kidney disease, epidemiology/prevalence, modern therapies for CKD management, NEERI-KFT and its role in kidney disease. The study was performed based on scientific reports screened by experts according to inclusion and exclusion criteria. The pre-clinical and clinical findings suggested that NEERI-KFT has promising effects as nephroprotective and considered safe and well effective in primary care of kidney against disease. Phytopharmacological evaluation of NEERI-KFT suggest that it exhibit substantial potential against oxidative and inflammatory stress induced apoptosis by exerting antioxidants, nephroprotective and immunomodulatory effects. Hence, it can be enlighten that NEERI-KFT have potential herbs which exerts significant antioxidants, nephroprotective and immunomodulatory effects in the patients associated with renal dysfunction or CKD thus improving altered renal architecture and renal physiology. Clinically, it is concluded that NEERI-KFT works kidney malfunction and cease ESRD progression or even reduce the number of dialysis.

Glucocorticoids Induce Partial Remission of Focal Segmental Glomerulosclerosis but Not Interstitial Nephritis in COVID-19 Acute Kidney Injury in an APOL1 Low-Risk Genotype White Patient

Patient: Male, 34-year-old

Final Diagnosis: Focal segmental glomerulosclerosis

Symptoms: Acute kidney injury • nephrotic syndrome

Medication: —

Clinical Procedure: Kidney biopsy

Specialty: Nephrology

Formins in Human Disease

Almost 25 years have passed since a mutation of a formin gene, DIAPH1, was identified as being responsible for a human inherited disorder: a form of sensorineural hearing loss. Since then, our knowledge of the links between formins and disease has deepened considerably. Mutations of DIAPH1 and six other formin genes (DAAM2, DIAPH2, DIAPH3, FMN2, INF2 and FHOD3) have been identified as the genetic cause of a variety of inherited human disorders, including intellectual disability, renal disease, peripheral neuropathy, thrombocytopenia, primary ovarian insufficiency, hearing loss and cardiomyopathy. In addition, alterations in formin genes have been associated with a variety of pathological conditions, including developmental defects affecting the heart, nervous system and kidney, aging-related diseases, and cancer. This review summarizes the most recent discoveries about the involvement of formin alterations in monogenic disorders and other human pathological conditions, especially cancer, with which they have been associated. In vitro results and experiments in modified animal models are discussed. Finally, we outline the directions for future research in this field.

Identification of Genetic Causes of Focal Segmental Glomerulosclerosis Increases With Proper Patient Selection

OBJECTIVE

To increase the likelihood of finding a causative genetic variant in patients with a focal segmental glomerulosclerosis (FSGS) lesion, clinical and histologic characteristics were analyzed.

PATIENTS AND METHODS

Individuals 18 years and older with an FSGS lesion on kidney biopsy evaluated at Mayo Clinic from November 1, 1999, through October 31, 2019, were divided into 4 groups based on clinical and histologic characteristics: primary FSGS, secondary FSGS with known cause, secondary FSGS without known cause, and undetermined FSGS. A targeted gene panel and a customized gene panel retrieved from exome sequencing were performed.

RESULTS

The overall rate of detection of a monogenic cause was 42.9% (21/49). Individuals with undetermined FSGS had the highest rate of positivity (87.5%; 7/8) followed by secondary FSGS without an identifiable cause (61.5%; 8/13) and secondary FSGS with known cause (33.3%; 5/15). Four of 5 (80%) individuals in the latter group who had positive genetic testing results also had a family history of kidney disease. Univariate analysis showed that family history of kidney disease (odds ratio [OR], 13.8; 95% CI, 3.7 to 62.4; P<.001), absence of nephrotic syndrome (OR, 8.2; 95% CI, 1.9 to 58.1; P=.004), and female sex (OR, 5.1; 95% CI, 1.5 to 19.9; P=.01) were strong predictors of finding a causative genetic variant in the entire cohort. The most common variants were in the collagen genes (52.4%; 11/21), followed by the podocyte genes (38.1%; 8/21).

CONCLUSION

In adults with FSGS lesions, proper selection of patients increases the rate of positive genetic testing significantly. The majority of individuals with undetermined FSGS in whom the clinical presentation and histologic parameters are discordant had a genetic diagnosis.

Rituximab for recurrence of primary focal segmental glomerulosclerosis after kidney transplantation: Results of a nationwide study

Rituximab (RTX) therapy for primary focal segmental glomerulosclerosis recurrence after kidney transplantation (KT) has been extensively debated. We aimed to assess the benefit of adding RTX to plasmapheresis (PP), corticosteroids, and calcineurin inhibitors (standard of care, SOC). We identified 148 adult patients who received KT in 12/2004-12/2018 at 21 French centers: 109 received SOC (Group 1, G1), and 39 received immediate RTX along with SOC (Group 2, G2). In G1, RTX was introduced after 28 days of SOC in the event of failure (G1a, n = 19) or PP withdrawal (G1b, n = 12). Complete remission (CR) was achieved in 46.6% of patients, and partial remission (PR) was achieved in 33.1%. The 10-year graft survival rates were 64.7% and 17.9% in responders and nonresponders, respectively. Propensity score analysis showed no difference in CR+PR rates between G1 (82.6%) and G2 (71.8%) (p = .08). Following the addition of RTX (G1a), 26.3% of patients had CR, and 31.6% had PR. The incidence of severe infections was similar between patients treated with and without RTX. In multivariable analysis, infection episodes were associated with hypogammaglobulinemia <5 g/L. RTX could be used in cases of SOC failure or remission for early discontinuation of PP without increasing the risk of infection.

Genotype/Phenotype Interactions and First Steps Toward Targeted Therapy for Sphingosine Phosphate Lyase Insufficiency Syndrome

Sphingosine-1-phosphate lyase insufficiency syndrome (SPLIS) is a rare metabolic disorder caused by a deficiency in sphingosine-1-phosphate lyase (SPL), the final enzyme in the sphingolipid degradative pathway. Inactivating mutations of SGPL1-the gene encoding SPL-lead to a deficiency of its downstream products, and buildup of sphingolipid intermediates, including its bioactive substrate, sphingosine-1-phosphate (S1P), the latter causing lymphopenia, a hallmark of the disease. Other manifestations of SPLIS include nephrotic syndrome, neuronal defects, and adrenal insufficiency, but their pathogenesis remains unknown. In this report, we describe the correlation between SGPL1 genotypes, age at diagnosis, and patient outcome. Vitamin B6 serves as a cofactor for SPL. B6 supplementation may aid some SPLIS patients by overcoming poor binding kinetics and promoting proper folding and stability of mutant SPL proteins. However, this approach remains limited to patients with a susceptible allele. Gene therapy represents a potential targeted therapy for SPLIS patients harboring B6-unresponsive missense mutations, truncations, deletions, and splice-site mutations. When Sgpl1 knockout (SPLKO) mice that model SPLIS were treated with adeno-associated virus (AAV)-mediated SGPL1 gene therapy, they showed profound improvement in survival and kidney and neurological function compared to untreated SPLKO mice. Thus, gene therapy appears promising as a universal, potentially curative treatment for SPLIS.

Therapeutic trials in adult FSGS: lessons learned and the road forward

Focal segmental glomerulosclerosis (FSGS) is not a specific disease entity but a lesion that primarily targets the podocyte. In a broad sense, the causes of the lesion can be divided into those triggered by a presumed circulating permeability factor, those that occur secondary to a process that might originate outside the kidneys, those caused by a genetic mutation in a podocyte or glomerular basement membrane protein, and those that arise through an as yet unidentifiable process, seemingly unrelated to a circulating permeability factor. A careful attempt to correctly stratify patients with FSGS based on their clinical presentation and pathological findings on kidney biopsy is essential for sound treatment decisions in individual patients. However, it is also essential for the rational design of therapeutic trials in FSGS. Greater recognition of the pathophysiology underlying podocyte stress and damage in FSGS will increase the likelihood that the cause of an FSGS lesion is properly identified and enable stratification of patients in future interventional trials. Such efforts will facilitate the identification of effective therapeutic agents.

Role of autophagy and evaluation the effects of microRNAs 214, 132, 34c and prorenin receptor in a rat model of focal segmental glomerulosclerosis

AIMS

Focal segmental glomerulosclerosis (FSGS) is the common cause of chronic renal disease worldwide. Although there are many etiologic factors which have common theme of podocyte injury conclusive etiology is not clearly understood. In this study, we aimed to explore the role of autophagy in the pathogenesis of podocyte injury, which is the key point in disease progression, and the roles of intrarenal microRNAs and the prorenin receptor (PRR) in the 5/6 nephrectomy and adriamycin nephropathy models of FSGS.

MAIN METHODS

For experimental FSGS model, 5/6 nephrectomy and adriamycin nephropathy models were created and characterized in adult Sprague Dawley rats. Microarray analysis was performed on FSGS and control groups that was confirmed by q-RT-PCR. Beclin1, LC3B, PRR, ATG7 and ATG5 expression were evaluated by western blotting and immunohistochemistry. Also, Beclin1 and PRR expression were measured by ELISA. Glomerular podocyte isolation was performed and autophagic activity was evaluated in podocytes before and after transfection with miRNA mimic and antagonists.

KEY FINDINGS

Glomerular expression of Beclin1, LC3B, PRR, ATG7 and ATG5 were significantly lower in the 5/6 nephrectomy than adriamycin nephropathy group and in both groups lower when compared to control groups. Western blot results were consistent with immunohistochemical data. Electron microscopy revealed signs of impaired autophagy in FSGS. Autophagic activity decreased significantly after miR-214, miR-132 and miR-34c mimics and increased after transfection with antagonists.

SIGNIFICANCE

These results showed that the role of autophagic activity and decreased expression of PRR in FSGS pathogenesis and miR-34c, miR-132 and miR-214 could be a potential treatment strategy by regulating autophagy.

Mechanisms of Scarring in Focal Segmental Glomerulosclerosis

BACKGROUND

Focal segmental glomerulosclerosis (FSGS) is a histologic pattern characterized by focal glomerular scarring, which often progresses to systemic and diffuse glomerulosclerosis. Previous studies have emphasized that the initiation of classic FSGS occurs in podocytes. The dysfunction and loss of podocytes have been associated with the development of proteinuria and the progression of various diseases. In addition, primary, secondary, and genetic FSGS are caused by different mechanisms of podocyte injury.

SUMMARY

The potential sources and mechanism of podocyte supplementation are the focus of our current research. Increasing attention has been paid to the role played by parietal epithelial cells (PECs) during the progression of FSGS. PECs are not only the primary influencing factors in glomerulosclerosis lesions but also have repair abilities, which remain a focus of debate. Notably, other resident glomerular cells also play significant roles in the progression of this disease.

KEY MESSAGE

In this review, we focus on the mechanism of scarring in FSGS and discuss current and potential therapeutic strategies.

Interplay between extracellular matrix components and cellular and molecular mechanisms in kidney fibrosis

Chronic kidney disease (CKD) is characterized by pathological accumulation of extracellular matrix (ECM) proteins in renal structures. Tubulointerstitial fibrosis is observed in glomerular diseases as well as in the regeneration failure of acute kidney injury (AKI). Therefore, finding antifibrotic therapies comprises an intensive research field in Nephrology. Nowadays, ECM is not only considered as a cellular scaffold, but also exerts important cellular functions. In this review, we describe the cellular and molecular mechanisms involved in kidney fibrosis, paying particular attention to ECM components, profibrotic factors and cell-matrix interactions. In response to kidney damage, activation of glomerular and/or tubular cells may induce aberrant phenotypes characterized by overproduction of proinflammatory and profibrotic factors, and thus contribute to CKD progression. Among ECM components, matricellular proteins can regulate cell-ECM interactions, as well as cellular phenotype changes. Regarding kidney fibrosis, one of the most studied matricellular proteins is cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), currently considered as a fibrotic marker and a potential therapeutic target. Integrins connect the ECM proteins to the actin cytoskeleton and several downstream signaling pathways that enable cells to respond to external stimuli in a coordinated manner and maintain optimal tissue stiffness. In kidney fibrosis, there is an increase in ECM deposition, lower ECM degradation and ECM proteins cross-linking, leading to an alteration in the tissue mechanical properties and their responses to injurious stimuli. A better understanding of these complex cellular and molecular events could help us to improve the antifibrotic therapies for CKD.

Central odontogenic fibroma in association with brown tumor of hyperparathyroidism in a patient with neurofibromatosis type 1

We present a patient with bone abnormalities and a myriad of lesions secondary to his redeveloping renal failure and neurofibromatosis type 1 (NF1). A 21-year-old male renal transplant recipient with NF1 presented with painless masses and large, irregular radiolucent lesions in the maxilla and mandible. After histologic examination, the lesion was diagnosed as a central odontogenic fibroma (COdF) in association with a central giant cell lesion, most consistent with brown tumor of hyperparathyroidism. The bone changes were interpreted to be highly suggestive of renal osteodystrophy. Around 30 cases of hybrid central giant cell granuloma-like lesion in association with central odontogenic fibroma have been reported. This, to our knowledge, is the first reported case of brown tumor in association with COdF. Our case provides further evidence of the giant cell component as the initiating entity in these hybrid lesions.

Immunohistochemical Expression of FOXP3+ Regulatory T Cells in Proteinuric Primary Glomerulopathies

FOXP3+ regulatory T-cell (Tregs) detection in renal allograft biopsies has been associated with a less intense immune response. Data about FOXP3+ Tregs' presence and role in primary glomerulopathies of native kidneys are minimal. We comparatively studied the immunohistochemical expression of FOXP3+ Tregs, CD4+ and CD3+ T cells in IgA nephropathy (IgAN), focal segmental glomerulosclerosis (FSGS), and membranous glomerulopathy (MGN). We retrospectively reviewed 71 renal biopsies (28 from patients with IgAN, 22 from patients with FSGS and 21 from patients with MGN) performed with proteinuria as the main indication. FOXP3+ Tregs and CD4+ and CD3+ T cells in inflammatory cell infiltrates of the interstitial tissue and periglomerular space were automatically counted using image analysis software. Univariable and multivariable logistic regressions were applied for statistical analysis. Nuclear FOXP3+ immunohistochemical expression was observed in T cells in 64% of IgAN cases, 77% of FSGS cases, and 76% of MGN cases (p > 0.05). Absolute FOXP3+ Tregs count in the interstitial tissue was higher in patients without arteriolar hyalinosis than in those with arteriolar hyalinosis (1.814 ± 2.160 vs. 831 ± 696; p = 0.029). In patients with a high FOXP3+/CD4+ ratio in the interstitial tissue, the odds ratio for CKD-EPI eGFR ≥60 ml/min/1.73 m² at biopsy was 4.80 (95% CI: 1.29-17.91; p = 0.019). FOXP3+ Tregs intrarenal infiltration in primary glomerulopathies is common. FOXP3+ Tregs' increased expression may be associated with milder histological lesions. High FOXP3+/CD4+ ratio in the interstitial tissue may have prognostic significance for renal function preservation.

Simulations of Glomerular Shear and Hoop Stresses in Diabetes, Hypertension, and Reduced Renal Mass using a Network Model of a Rat Glomerulus

A novel anatomically accurate model of rat glomerular filtration is used to quantify shear stresses on the glomerular capillary endothelium and hoop stresses on the glomerular capillary walls. Plasma, erythrocyte volume, and plasma protein mass are distributed at network nodes using pressure differentials calculated taking into account volume loss to filtration, improving on previous models which only took into account blood apparent viscosity in calculating pressures throughout the network. Filtration is found to be heterogeneously distributed throughout the glomerular capillary network and is determined by concentration of plasma proteins and surface area of the filtering capillary segments. Hoop stress is primarily concentrated near the afferent arteriole, whereas shear stress is concentrated near the efferent arteriole. Using parameters from glomerular micropuncture studies, conditions of diabetes mellitus (DM), 5/6‐Nephrectomy (5/6‐Nx), and Angiotensin II‐induced hypertension (HTN) are simulated and compared to their own internal controls to assess the changes in mechanical stresses. Hoop stress is increased in all three conditions, while shear stress is increased in 5/6‐Nx, decreased in HTN, and maintained at control levels in DM by the hypertrophic response of the glomerular capillaries. The results indicate that these alterations in mechanical stresses and the consequent release of cytokines by or injury of the glomerular cells may play a significant role in the progression of glomerulopathy in these disease conditions.

Simulations of increased glomerular capillary wall strain in the 5/6-nephrectomized rat

Objective

Chronic glomerular hypertension is associated with glomerular injury and sclerosis; however, the mechanism by which increases in pressure damage glomerular podocytes remains unclear. We tested the hypothesis that increases in glomerular pressure may deleteriously affect podocyte structural integrity by increasing the strain of the glomerular capillary walls, and that glomerular capillary wall strain may play a significant role in the perpetuation of glomerular injury in disease states that are associated with glomerular hypertension.

Methods

We developed an anatomically accurate mathematical model of a compliant, filtering rat glomerulus to quantify the strain of the glomerular capillary walls in a remnant glomerulus of the 5/6‐nephrectomized rat model of chronic kidney disease. In terms of estimating the mechanical stresses and strains in the glomerular capillaries, this mathematical model is a substantial improvement over previous models which do not consider pressure‐induced alterations in glomerular capillary diameters in distributing plasma and erythrocytes throughout the network.

Results

Using previously reported data from experiments measuring the change of glomerular volume as a function of perfusion pressure, we estimated the Young's modulus of the glomerular capillary walls in both control and 5/6‐nephrectomized conditions. We found that in 5/6‐nephrectomized conditions, the Young's modulus increased to 8.6 MPa from 7.8 MPa in control conditions, but the compliance of the capillaries increased in 5/6‐nephrectomized conditions due to a 23.3% increase in the baseline glomerular capillary diameters. We found that glomerular capillary wall strain was increased approximately threefold in 5/6‐nephrectomized conditions over control, which may deleteriously affect both mesangial cells and podocytes. The magnitudes of strain in model simulations of 5/6‐nephrectomized conditions were consistent with magnitudes of strain that elicit podocyte hypertrophy and actin cytoskeleton reorganization in vitro.

Conclusions

Our findings indicate that glomerular capillary wall strain may deleteriously affect podocytes directly, as well as act in concert with other mechanical changes and environmental factors inherent to the in vivo setting to potentiate glomerular injury in severe renoprival conditions.

Targeting Canonical and Non-Canonical STAT Signaling Pathways in Renal Diseases

Signal transducer and activator of transcription (STAT) plays an essential role in the inflammatory reaction and immune response of numerous renal diseases. STATs can transmit the signals of cytokines, chemokines, and growth factors from the cell membrane to the nucleus. In the canonical STAT signaling pathways, upon binding with their cognate receptors, cytokines lead to a caspase of Janus kinases (JAKs) and STATs tyrosine phosphorylation and activation. Besides receptor-associated tyrosine kinases JAKs, receptors with intrinsic tyrosine kinase activities, G-protein coupled receptors, and non-receptor tyrosine kinases can also activate STATs through tyrosine phosphorylation or, alternatively, other post-translational modifications. Activated STATs translocate into the nucleus and mediate the transcription of specific genes, thus mediating the progression of various renal diseases. Non-canonical STAT pathways consist of preassembled receptor complexes, preformed STAT dimers, unphosphorylated STATs (U-STATs), and non-canonical functions including mitochondria modulation, microtubule regulation and heterochromatin stabilization. Most studies targeting STAT signaling pathways have focused on canonical pathways, but research extending into non-canonical STAT pathways would provide novel strategies for treating renal diseases. In this review, we will introduce both canonical and non-canonical STAT pathways and their roles in a variety of renal diseases.

Establishment and characterization of a novel conditionally immortalized human parietal epithelial cell line

Parietal epithelial cells (PECs) are epithelial cells in the kidney, surrounding Bowman's space. When activated, PECs increase in cell volume, proliferate, migrate to the glomerular tuft and excrete extracellular matrix. Activated PECs are crucially involved in the formation of sclerotic lesions, seen in focal segmental glomerulosclerosis (FSGS). In FSGS, a number of glomeruli show segmental sclerotic lesions. Further disease progression will lead to increasing number of involved glomeruli and gradual destruction of the affected glomeruli. Although the involvement of PECs in FSGS has been acknowledged, little is known about the molecular processes driving PEC activation. To get more insights in this process, accurate in vivo and in vitro models are needed. Here, we describe the development and characterization of a novel conditionally immortalized human PEC (ciPEC) line. We demonstrated that ciPECs are differentiated when grown under growth-restrictive conditions and express important PEC-specific markers, while lacking podocyte and endothelial markers. In addition, ciPECs showed PEC-like morphology and responded to IL-1β treatment. We therefore conclude that we have successfully generated a novel PEC line, which can be used for future studies on the role of PECs in FSGS.

Adiponectin protects obesity-related glomerulopathy by inhibiting ROS/NF-κB/NLRP3 inflammation pathway

BACKGROUND

Adiponectin is an adipocytokine that plays a key regulatory role in glucose and lipid metabolism in obesity. The prevalence of obesity has led to an increase in the incidence of obesity-related glomerulopathy (ORG). This study aimed to identify the protective role of adiponectin in ORG.

METHODS

Small-interfering RNA (siRNA) against the gene encoding adiponectin was transfected into podocytes. The oxidative stress level was determined using a fluorometric assay. Apoptosis was analyzed by flow cytometry. The expressions of podocyte markers and pyrin domain containing protein 3 (NLRP3) inflammasome-related proteins were measured by qRT-PCR, immunohistochemistry, and Western blot.

RESULTS

Podocytes treated with palmitic acid (PA) showed downregulated expressions of podocyte markers, increased apoptosis, upregulated levels of NLRP3 inflammasome-related proteins, increased production of inflammatory cytokines (IL-18 and IL-1β), and induced activation of NF-κB as compared to the vehicle-treated controls. Decreased adiponectin expression was observed in the serum samples from high fat diet (HFD)-fed mice. Decreased podocin expression and upregulated NLRP3 expression were observed in the kidney samples from high fat diet (HFD)-fed mice. Treatment with adiponectin or the NLRP3 inflammasome inhibitor, MCC950, protected cultured podocytes against podocyte apoptosis and inflammation. Treatment with adiponectin protected mouse kidney tissues against decreased podocin expression and upregulated NLRP3 expression. The knockout of adiponectin gene by siRNA increased ROS production, resulting in the activation of NLRP3 inflammasome and the phosphorylation of NF-κB in podocytes. Pyrrolidine dithiocarbamate, an NF-κB inhibitor, prevented adiponectin from ameliorating FFA-induced podocyte injury and NLRP3 activation.

CONCLUSIONS

Our study showed that adiponectin ameliorated PA-induced podocyte injury in vitro and HFD-induced injury in vivo via inhibiting the ROS/NF-κB/NLRP3 pathway. These data suggest the potential use of adiponectin for the prevention and treatment of ORG.

Generation of 20 human induced pluripotent stem cell lines from patients with focal segmental glomerulosclerosis (FSGS)

Focal segmental glomerulosclerosis (FSGS) is a major cause of familial nephrotic syndrome. We generated 20 induced pluripotent stem cell lines from patients diagnosed with FSGS. The iPSC lines include 8 female and 12 male lines and cover a donor age range from 31 to 78. The lines were generated from peripheral blood mononuclear cells by integration-free reprogramming using Sendai virus vectors. Cell lines were fully characterized regarding their pluripotency and differentiation potential, and quality controlled for karyotypic integrity, identity and clearance of reprogramming vectors. The generated cell lines represent a valuable tool for disease modelling and drug development for FSGS.

Gene Expression as a Guide to the Development of Novel Therapies in Primary Glomerular Diseases

Despite improvements in understanding the pathogenic mechanisms of primary glomerular diseases, therapy still remains nonspecific. We sought to identify novel therapies targeting kidney-intrinsic injury of distinct primary glomerulonephritides through computational systems biology approaches. We defined the unique transcriptional landscape within kidneys from patients with focal segmental glomerulosclerosis (FSGS), minimal change disease (MCD), immunoglobulin A nephropathy (IgAN), membranous nephropathy (MN) and thin basement membrane nephropathy (TBMN). Differentially expressed genes were functionally annotated with enrichment analysis, and distinct biological processes and pathways implicated in each primary glomerular disease were uncovered. Finally, we identified novel drugs and small-molecule compounds that may reverse each glomerulonephritis phenotype, suggesting they should be further tested as precise therapy in primary glomerular diseases.

Dissecting the Involvement of Ras GTPases in Kidney Fibrosis

Many different regulatory mechanisms of renal fibrosis are known to date, and those related to transforming growth factor-β1 (TGF-β1)-induced signaling have been studied in greater depth. However, in recent years, other signaling pathways have been identified, which contribute to the regulation of these pathological processes. Several studies by our team and others have revealed the involvement of small Ras GTPases in the regulation of the cellular processes that occur in renal fibrosis, such as the activation and proliferation of myofibroblasts or the accumulation of extracellular matrix (ECM) proteins. Intracellular signaling mediated by TGF-β1 and Ras GTPases are closely related, and this interaction also occurs during the development of renal fibrosis. In this review, we update the available in vitro and in vivo knowledge on the role of Ras and its main effectors, such as Erk and Akt, in the cellular mechanisms that occur during the regulation of kidney fibrosis (ECM synthesis, accumulation and activation of myofibroblasts, apoptosis and survival of tubular epithelial cells), as well as the therapeutic strategies for targeting the Ras pathway to intervene on the development of renal fibrosis.

Cyclosporine A Treatment of Proteinuria in a New Case of MAFB-Associated Glomerulopathy without Extrarenal Involvement: A Case Report

The MAFB gene encodes an important basic leucine zipper transcription factor that functions in glomerular podocytes, macrophages, and osteoclasts. Recently, MAFB was identified as the gene that was responsible for causing nephropathy with focal segmental glomerulosclerosis (FSGS) with multicentric carpotarsal osteolysis (MCTO) or Duane retraction syndrome (DRS). Here, we describe a patient with nephropathy associated with FSGS who exhibited a novel stop-gain variant in the MAFB gene (NM_005461:c.590C>A (p.Ser197Ter)). The patient's father exhibited proteinuria with FSGS with possible DRS, whereas the patient exhibited nephropathy with FSGS and nearly normal eye movement and hearing function, as well as intact bone structure in the extremities. Conventional oral steroids or immunosuppressive drugs have not demonstrated effectiveness for patients with nephropathy who exhibit pathogenic variants in MAFB, except for a patient with nephropathy with FSGS and MCTO who experienced attenuated proteinuria within the subnephrotic range in response to cyclosporine A (CyA) treatment for at least 4 years. Thus, we attempted administration of CyA in our patient. Unexpectedly, the patient demonstrated good and rapid responses to CyA, including a partial reduction in proteinuria from approximately 2.0 g/g Cr to proteinuria within the subnephrotic range (0.27 g/g Cr) after 13 months of observation. Our findings suggest that CyA may be a suitable treatment option for patients with nephropathy with FSGS who exhibit pathogenic MAFB variants.

Protective Role of the M-Sec-Tunneling Nanotube System in Podocytes

BACKGROUND

Podocyte dysfunction and loss are major determinants in the development of proteinuria. FSGS is one of the most common causes of proteinuria, but the mechanisms leading to podocyte injury or conferring protection against FSGS remain poorly understood. The cytosolic protein M-Sec has been involved in the formation of tunneling nanotubes (TNTs), membrane channels that transiently connect cells and allow intercellular organelle transfer. Whether podocytes express M-Sec is unknown and the potential relevance of the M-Sec-TNT system in FSGS has not been explored.

METHODS

We studied the role of the M-Sec-TNT system in cultured podocytes exposed to Adriamycin and in BALB/c M-Sec knockout mice. We also assessed M-Sec expression in both kidney biopsies from patients with FSGS and in experimental FSGS (Adriamycin-induced nephropathy).

RESULTS

Podocytes can form TNTs in a M-Sec-dependent manner. Consistent with the notion that the M-Sec-TNT system is cytoprotective, podocytes overexpressed M-Sec in both human and experimental FSGS. Moreover, M-Sec deletion resulted in podocyte injury, with mitochondrial abnormalities and development of progressive FSGS. In vitro, M-Sec deletion abolished TNT-mediated mitochondria transfer between podocytes and altered mitochondrial bioenergetics. Re-expression of M-Sec reestablishes TNT formation and mitochondria exchange, rescued mitochondrial function, and partially reverted podocyte injury.

CONCLUSIONS

These findings indicate that the M-Sec-TNT system plays an important protective role in the glomeruli by rescuing podocytes via mitochondrial horizontal transfer. M-Sec may represent a promising therapeutic target in FSGS, and evidence that podocytes can be rescued via TNT-mediated horizontal transfer may open new avenues of research.

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

Podocyte injury and subsequent detachment are hallmarks of progressive glomerulosclerosis. In addition to cell injury, unknown mechanical forces on the injured podocyte may promote detachment. To identify the nature of these mechanical forces, we studied the dynamics of podocyte detachment using sequential ultrastructural geometry analysis by transmission electron microscopy in NEP25, a mouse model of podocytopathy induced by anti-Tac(Fv)-PE38 (LMB2), a fusion protein attached to Pseudomonas exotoxin A, targeting CD25 on podocytes. After LMB2 injection, foot process effacement occurred on day three but detachment commenced on day eight and extended to day ten, reaching toward the urinary pole in clusters. Podocyte detachment was associated with foot process effacement covering over 60% of the glomerular basement membrane length. However, approximately 25% of glomeruli with diffuse (over 80%) foot process effacement showed no detachment. Blocking glomerular filtration via unilateral ureteral obstruction resulted in diffuse foot process effacement but no pseudocysts or detachment, whereas uninephrectomy increased pseudocysts and accelerated detachment, indicating that glomerular filtrate drives podocyte detachment via pseudocyst formation as a forerunner. Additionally, more detachment was observed in juxtamedullary glomeruli than in superficial glomeruli. Thus, glomerular filtrate drives the dynamics of podocyte detachment in this model of podocytopathy. Hence, foot process effacement may be a prerequisite allowing filtrate to generate local mechanical forces that expand the subpodocyte space forming pseudocysts, promote podocyte detachment and subsequent segmental sclerosis.

Therapeutic Options for Recurrence of Primary Focal Segmental Glomerulonephritis (FSGS) in the Renal Allograft: Single-Center Experience

Focal Segmental Glomerulosclerosis (FSGS) recurrence after kidney transplantation (KTx) is relatively frequent and is associated with poor graft survival. The aim of this study was to investigate which management strategies were associated with better outcomes in our cohort of KTx recipients with primary FSGS. We retrospectively collected data on patients with primary FSGS who received a KTx between 1993 and 2019. A history of biopsy proven FSGS in native kidneys and new onset of significant proteinuria early post-KTx led to the diagnosis of recurrence, which was confirmed by graft biopsy. From 1993 to 2019 we performed 46 KTxs in patients with primary FSGS. We identified 26 episodes of recurrence in 25 patients, 67% of them occurring in males. They were younger at the time of KTx (33.8 vs. 41.1 years old, p = 0.067) and had progressed to end stage renal disease (ESRD) faster after FSGS diagnosis (61.4 vs. 111.2 months, p = 0.038), while they were less likely to have received prophylactic plasmapheresis (61.5% vs. 90%, p = 0.029). 76.7% of recurrences were found early, after a median of 0.5 months (IQR 0.1-1) with a median proteinuria was 8.5 (IQR 4.9-11.9) g/day. All patients with recurrence were treated with plasmapheresis, while 8 (30.7%) additionally received rituximab, 1 (3.8%) abatacept, and 4 (15.4%) ACTH. 7 (27%) patients experienced complete and 11 (42.3%) partial remission after a mean time of 3 (±1.79) and 4.4 (±2.25) months, respectively. Prognosis was worse for patients who experienced a recurrence. Eleven (42.3%) patients lost their graft from FSGS in a median time of 33 (IQR 17.5-43.3) months. In this series of patients, primary FSGS recurred frequently after KTx. Prophylacic plasmapheresis was shown efficacious in avoiding FSGS recurrence, while timely diagnosis and plasmapheresis-based regimens induced remission in more than half of the patients.

Lysosome function in glomerular health and disease

The lysosome represents an important regulatory platform within numerous vesicle trafficking pathways including the endocytic, phagocytic, and autophagic pathways. Its ability to fuse with endosomes, phagosomes, and autophagosomes enables the lysosome to break down a wide range of both endogenous and exogenous cargo, including macromolecules, certain pathogens, and old or damaged organelles. Due to its center position in an intricate network of trafficking events, the lysosome has emerged as a central signaling node for sensing and orchestrating the cells metabolism and immune response, for inter-organelle and inter-cellular signaling and in membrane repair. This review highlights the current knowledge of general lysosome function and discusses these findings in their implication for renal glomerular cell types in health and disease including the involvement of glomerular cells in lysosomal storage diseases and the role of lysosomes in nongenetic glomerular injuries.

Nephrotic syndrome with focal segmental glomerular lesions unclassified by Columbia classification; Pathology and clinical implication

Background

The Columbia classification is widely used for diagnosis of focal segmental glomerulosclerosis (FSGS). In practice, we occasionally encounter segmental glomerular lesions unclassified as Columbia classification. We analyzed the clinical implication of unclassified segmental lesions comparing with Columbia-classified FSGS.

Methods

A retrospective cohort study from 13 local hospitals in Japan. From 172 biopsy cases diagnosed with FSGS or minimal change disease (MCD)/FSGS spectrum with unclassified segmental lesions, adult patients with nephrotic syndrome who received immunosuppressive therapies were included. The cases are classified by pathology, i.e., typical FSGS lesions sufficiently classified into subgroups of Columbia classification: collapsing (COL), tip (TIP), cellular (CEL), perihilar (PH), and not otherwise specified (NOS), and unclassified by the Columbia classification into three subgroups: “endothelial damage,”; “simple attachment,”; and “minor cellular lesion,”. The response to immunosuppressive treatment and 30% decline of eGFR were compared.

Results

Among 48 eligible cases, all were Japanese, 34 were typical FSGS; 13 TIP, 15 CEL, 6 NOS, and no COL or PH cases. Fourteen were unclassified cases: endothelial damage (n = 6), simple attachment (n = 5), and minor cellular lesion (n = 3). The median age of overall patients was 60 years old and the median of eGFR and urinary protein creatinine ratio was 51.5 mL/min/1.73m² and 7.35, respectively. They received similar therapeutic regimen. Kaplan-Meier analysis revealed no significant difference in treatment response between typical FSGS and unclassified cases. Evaluating among the subgroups, endothelial damage, simple attachment and minor cellular lesion showed similar treatment response to TIP or CEL. No significant difference was also observed in the 30% decline of eGFR.

Conclusions

Japanese adult patients with nephrotic syndrome showing unclassified segmental lesions as Columbia classification may be equivalent clinical impact as Columbia classification of FSGS.

NPHS2 gene polymorphism aggravates renal damage caused by focal segmental glomerulosclerosis with COL4A3 mutation

Focal segmental glomerulosclerosis (FSGS), a type of primary glomerular disease, is the leading cause of end-stage renal disease (ESRD). Several studies have revealed that certain single-gene mutations are involved in the pathogenesis of FSGS; however, the main cause of FSGS has not been fully elucidated. Homozygous mutations in the glomerular basement membrane gene can lead to early renal failure, while heterozygous carriers develop renal failure symptoms late. Here, molecular genetic analysis of clinical information collected from clinical reports and medical records was performed. Results revealed that nephrosis 2 (NPHS2) gene polymorphism aggravated renal damage in three FSGS families with heterozygous COL4A3 mutation, leading to early renal failure in index patients. Our findings suggest that COL4A3 and NPHS2 may have a synergistic effect on renal injury caused by FSGS. Further analysis of the glomerular filtration barrier could help assess the cause of kidney damage. Moreover, a detailed analysis of the glomerular basement membrane-related genes and podocyte structural proteins may help us better understand FSGS pathogenesis and provide insights into the prognosis and treatment of hereditary glomerulonephropathy.