Progression Of Focal Segmental Glomerulosclerosis Research Articles

INF2 formin variants linked to human inherited kidney disease reprogram the transcriptome, causing mitotic chaos and cell death

Mutations in the human INF2 gene cause autosomal dominant focal segmental glomerulosclerosis (FSGS)—a condition characterized by podocyte loss, scarring, and subsequent kidney degeneration. To understand INF2-linked pathogenicity, we examined the effect of pathogenic INF2 on renal epithelial cell lines and human primary podocytes. Our study revealed an increased incidence of mitotic cells with surplus microtubule-organizing centers fostering multipolar spindle assembly, leading to nuclear abnormalities, particularly multi-micronucleation. The levels of expression of exogenous pathogenic INF2 were similar to those of endogenous INF2. The aberrant nuclear phenotypes were observed regardless of the expression method used (retrovirus infection or plasmid transfection) or the promoter (LTR or CMV) used, and were absent with exogenous wild type INF2 expression. This indicates that the effect of pathogenic INF2 is not due to overexpression or experimental cell manipulation, but instead to the intrinsic properties of pathogenic INF2. Inactivation of the INF2 catalytic domain prevented aberrant nuclei formation. Pathogenic INF2 triggered the translocation of the transcriptional cofactor MRTF into the nucleus. RNA sequencing revealed a profound alteration in the transcriptome that could be primarily attributed to the sustained activation of the MRTF-SRF transcriptional complex. Cells eventually underwent mitotic catastrophe and death. Reducing MRTF-SRF activation mitigated multi-micronucleation, reducing the extent of cell death. Our results, if validated in animal models, could provide insights into the mechanism driving glomerular degeneration in INF2-linked FSGS and may suggest potential therapeutic strategies for impeding FSGS progression.

#1166 ACTION3 pivotal Phase 3 & open-label extension study assessing DMX-200 in adult & paediatric patients with focal segmental glomerulosclerosis (FSGS)

Abstract Background and Aims Focal segmental glomerulosclerosis (FSGS) is a major cause of glomerular disease that affects both adults and children. FSGS can rapidly progress to end-stage kidney disease. Lack of safe and effective treatment represents a significant unmet need for patients with FSGS. Development of treatments has been hampered by complexities including the rare nature of the disease, varying drivers of pathogenesis, and the evolving diagnostic and clinical trial designs, necessitating innovative research approaches. DMX-200 (repagermanium) is a C-C motif chemokine receptor 2 (CCR2) pathway inhibitor. Activation of the angiotensin II type 1 receptor (AT1R) and CCR2 have been independently implicated in the pathogenesis and progression of FSGS. These receptors form a functional complex so inhibition of both receptors may provide an efficient approach to FSGS treatment. In vivo data shows co-administration of DMX-200 and the angiotensin receptor blocker (ARB) irbesartan demonstrated a synergistic reduction in proteinuria, macrophage infiltration, and podocyte loss compared with vehicle or either antagonist alone. A subsequent Phase 2a cross-over study (NCT03649152) in N = 8 patients with biopsy-proven primary FSGS showed that the combination of DMX-200 and irbesartan (compared to placebo) was well tolerated with most patients experiencing a reduction in proteinuria. Based on these data, the global Phase 3 study (ACTION3) was initiated to confirm the proteinuria lowering effects of DMX-200 and assess effects on eGFR decline. ACTION3 is a randomised, placebo-controlled, double-blind, long-duration study of FSGS patients and on completion will provide a resource for the wider nephrology community and advocacy groups on the natural history of FSGS patients and the effects of a CCR2-inhibitor on the background of an ARB. Here we present the baseline data from the first 90 patients enrolled in ACTION3 at 12th January 2024. Method The ACTION3 (NCT05183646) study is a pivotal Phase 3, multicentre study of the efficacy and safety of DMX-200, 120 mg twice daily compared with placebo in adult patients with biopsy-proven FSGS receiving maximal tolerated ARB, with persistent proteinuria >1.5g/ day and eGFR >25 ml/min/1.73 m2. The study plans to enroll approximately 286 patients with primary FSGS, genetic FSGS and FSGS of undetermined cause with the primary objective of evaluating the efficacy of DMX-200 in percent change in 24-hour urine PCR and eGFR slope. The initial 104-week randomized period will be extended in a 2-year open label extension study. A futility analysis by an Independent Data Monitoring Committee following the first 72 patients completing 35 weeks of treatment confirm that continuation of the study is non-futile. Results The study is actively recruiting at 71 sites in 11 countries listed in Table 1. Demographic data of randomised patients is listed in Table 2. Patients are predominantly male (65%), with an average age of 46.6 yrs. and mean eGFR 56.3 ± 27.6 (ml/min/1.73 m2). The study is expanding recruitment into additional countries in the Asia Pacific, Europe, and Latin American regions. Further, the study protocol has sought and received regulatory approval to enroll adolescent patients aged 12-18 in Argentina, Mexico, UK and the US. Conclusion DMX-200 (repagermanium) has shown encouraging signs of safety and efficacy in combination with an ARB for the treatment of FSGS. The contributing countries and baseline characteristics of the patients enrolled in ACTION3 are similar to the populations studied in other recent FSGS trials. No clinically significant safety concerns have been observed in patients enrolled to date in the ACTION3 Phase 3 study.

Long-term outcomes of adults with FSGS in the German Chronic Kidney Disease cohort.

Focal segmental glomerulosclerosis (FSGS) can lead to kidney failure in adults. This study examines the progression of FSGS in the German Chronic Kidney Disease (GCKD) cohort. The GCKD study (N=5217), a prospective cohort, included 159 patients with biopsy-confirmed FSGS recruited from 2010 to 2012. Baseline was defined as the first study visit. Adjudicated endpoints included a composite kidney endpoint (CKE), including an estimated glomerular filtration rate (eGFR) decrease >40%, eGFR <15ml/min/1.73m2 or initiation of kidney replacement therapy and combined major adverse cardiovascular events (MACE), including non-fatal myocardial infarction or stroke and all-cause mortality. Associations between baseline demographics, laboratory data, comorbidity and CKE and MACE were analysed using the Cox proportional hazards regression model. The mean age at baseline was 52.1±13.6years, with a disease duration of 4.72years (quartile 1: 1; quartile 3: 6) before joining the study. The median urinary albumin:creatinine ratio (UACR) at baseline was 0.7g/g (IQR 0.1;1.8), while mean eGFR was 55.8±23ml/min/1.73m2. Based on clinical and pathological features, 69 (43.4%) patients were categorized as primary FSGS, 55 (34.6%) as secondary FSGS and 35 (22%) as indeterminate. Over a follow-up of 6.5years, 44 patients reached the composite kidney endpoint and 16 individuals had at least one MACE. UACR ≥0.7g/g was strongly associated with both the composite kidney endpoint {hazard ratio [HR] 5.27 [95% confidence interval (CI) 2.4-11.5]} and MACE [HR 3.37 (95% CI 1.05-10.82)] compared with <0.7g/g, whereas a higher eGFR at baseline (per 10ml/min) was protective for both endpoints [HR 0.8 (95% CI 0.68-0.95) and HR 0.63 (95% CI 0.46-0.88), respectively]. Patients with secondary FSGS experienced a greater rate of eGFR decline than patients with primary FSGS. Lower eGFR and higher albuminuria are key risk factors for kidney disease progression and cardiovascular events in patients with FSGS.

Rationale and Design of a Phase 2, Double-blind, Placebo-Controlled, Randomized Trial Evaluating AMP Kinase-Activation by Metformin in Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS), the most common primary glomerular disease leading to end-stage kidney disease (ESKD), is characterized by podocyte injury and depletion, whereas minimal change disease (MCD) has better outcomes despite podocyte injury. Identifying mechanisms capable of preventing podocytopenia during injury could transform FSGS to an "MCD-like" state. Preclinical data have reported conversion of an MCD-like injury to one with podocytopenia and FSGS by inhibition of AMP-kinase (AMPK) in podocytes. Conversely, in FSGS, AMPK-activation using metformin (MF) mitigated podocytopenia and azotemia. Observational studies also support beneficial effects of MF on proteinuria and chronic kidney disease (CKD) outcomes in diabetes. A randomized controlled trial (RCT) to test MF in podocyte injury with FSGS has not yet been conducted. We report the rationale and design of phase 2, double-blind, placebo-controlled RCT evaluating the efficacy and safety of MF as adjunctive therapy in FSGS. By randomizing 30 patients with biopsy-confirmed FSGS to MF or placebo (along with standard immunosuppression), we will study mechanistic biomarkers that correlate with podocyte injury or depletion and evaluate outcomes after 6 months. We specifically integrate novel urine, blood, and tissue markers as surrogates for FSGS progression along with unbiased profiling strategies. Our phase 2 trial will provide insight into the potential efficacy and safety of MF as adjunctive therapy in FSGS-a crucial step to developing a larger phase 3 study. The mechanistic assays here will guide the design of other FSGS trials and contribute to understanding AMPK activation as a potential therapeutic target in FSGS. By repurposing an inexpensive agent, our results will have implications for FSGS treatment in resource-poor settings.

Ferroptosis is involved in focal segmental glomerulosclerosis in rats

To explore whether ferroptosis is involved in focal segmental glomerulosclerosis (FSGS) and its mechanism. The FSGS rat model was constructed by single nephrectomy combined with fractional tail vein injection of doxorubicin. 24-hour urine protein, serum biochemistry, HE, PAS and Masson pathological staining were measured to assess renal injury. Glomerular and morphological changes of ferroptosis were observed by transmission electron microscopy. Iron content in renal tissue was assessed by Prussian blue staining and iron detection. GSH/GSSG kit was used to detect the content and proportion of reduced/oxidized glutathione. Lipid peroxidation related proteins including MDA expression was assessed by colorimetry. The iron metabolism biomarkers such as hepcidin, ferroportin and TFR, ferroptosis biomarkers such as GPX4, ACSL4, and ferritinophagy biomarkers such as LC3II/LC3I, NCOA4, and FTH1 were detected by Western blot. Significant urinary protein, hyperlipidemia, azotemia, increased serum creatinine and hypoproteinemia were observed in FSGS rats. Histology and electron microscopy showed segmental sclerosis of glomeruli, compensatory enlargement of some glomeruli, occlusion of capillary lumen, balloon adhesion, increased mesangial matrix, atrophy of some tubules, and renal interstitial fibrosis in renal tissue of FSGS rats. The morphology of glomerular foot processes disappeared; the foot processes were extensively fused and some foot processes detached. Mitochondria became smaller, membrane density increased, and mitochondrial cristae decreased or disappeared. In addition, iron deposition was observed in renal tissue of FSGS rats. Compared with the control group, the levels of GSH, GSH/GSSG, GPX4, and ferroportin were reduced and the expression of GSSG, MDA, ACSL4, hepcidin, and TFR was increased in the renal tissue of FSGS rats; meanwhile, the expression of LC3II/LC3I and NCOA4 was increased and the expression of FTH1 was decreased. Ferroptosis is involved in the pathological progression of FSGS, which is probably associated with activation of ferritinophagy. This represents a potential therapeutic target for FSGS.

Research on Rare Diseases in Germany - Using small fish and super-resolution microscopy to track down a rare disease.

Focal segmental glomerulosclerosis (FSGS) is a rare disease, or damage to the filtering units of the kidney, the glomeruli, about of which there is only limited knowledge and few treatment options. The STOP-FSGS consortium has set itself the goal to expand our knowledge of this disease and develop new treatment options. Through intensive research and the use of state-of-the-art techniques such as super-resolution microscopy, AI-based imaging and single-cell research, the consortium aims to gain a deeper understanding of the mechanisms of FSGS. This will allow the disease to be diagnosed more accurately and thus enable targeted and more effective treatment of patients. Another focus is on the search for drugs that slow down or even cure the disease. By establishing a rapid animal model, i.e. zebrafish larva, potential substances/drugs were identified that can alleviate FSGS. Moreover, super-resolution microscopy was used to precisely quantify the structural changes in the kidney by determining the so-called 'filtration slit density' (FSD) and to identify a marker allowing a personalised prognosis and assessment of the course of the disease. The results obtained help to better recognise the progression of FSGS and to optimally adapt treatment in order to improve the quality of life of the afflicted individuals and avoid renal replacement therapies.

Btg2 Promotes Focal Segmental Glomerulosclerosis via Smad3-Dependent Podocyte-Mesenchymal Transition.

Podocyte injury plays a critical role in the progression of focal segmental glomerulosclerosis (FSGS). Here, it is reported that B-cell translocation gene 2 (Btg2) promotes Adriamycin (ADR)-induced FSGS via Smad3-dependent podocyte-mesenchymal transition. It is found that in FSGS patients and animal models, Btg2 is markedly upregulated by podocytes and correlated with progressive renal injury. Podocyte-specific deletion of Btg2 protected against the onset of proteinuria and glomerulosclerosis in ADR-treated mice along with inhibition of EMT markers such as α-SMA and vimentin while restoring epithelial marker E-cadherin. In cultured MPC5 podocytes, overexpression of Btg2 largely promoted ADR and TGF-β1-induced EMT and fibrosis, which is further enhanced by overexpressing Btg2 but blocked by disrupting Btg2. Mechanistically, Btg2 is rapidly induced by TGF-β1 and then bound Smad3 but not Smad2 to promote Smad3 signaling and podocyte EMT, which is again exacerbated by overexpressing Btg2 but blocked by deleting Btg2 in MPC5 podocytes. Interestingly, blockade of Smad3 signaling with a Smad3 inhibitor SIS3 is also capable of inhibiting Btg2 expression and Btg2-mediated podocyte EMT, revealing a TGF-β/Smad3-Btg2 circuit mechanism in Btg2-mediated podocyte injury in FSGS. In conclusion, Btg2 is pathogenic in FSGS and promotes podocyte injury via a Smad3-dependent EMT pathway.

#2519 THE EFFECT OF TRPC5 AND PALLADIN EXPRESSION ON TREATMENT RESPONSE AND RENAL OUTCOME IN FOCAL SEGMENTAL GLOMERULOSCLEROSIS

Abstract Background and Aims Focal segmental glomerulosclerosis (FSGS) is a disease that is among the primary glomerulopathies and often progresses to chronic renal failure. Despite advances in immunosuppressive therapy for the treatment of glomerular diseases, some FSGS patients are resistant to single or combination immunosuppressive regimens containing; glucocorticoids, cyclophosphamide, calcineurin inhibitors, mycophenolate mofetil (MMF), and/or rituximab. FSGS-related nephrotic syndrome, the degree of proteinuria and response to steroid therapy are the most important factors associated with long-term prognosis, independent of histological findings. Failure to respond to immunosuppressive therapy, including corticosteroids, has been evaluated as one of the most important markers of the risk of developing renal failure. Unfortunately, there is no reliable marker that can predict steroid response. One of the earliest manifestations of podocyte damage is cytoskeletal remodeling, known as deletion of foot ridges. It was recently shown that transient receptor potential channel 5 (TRPC5) plays an important role in initiating this process. However, the role of TRPC5 in disease progression is unknown. It is thought that calcium influx caused by sustained TRPC5 activation in the chronic disease setting may lead to calcium toxicity and podocyte death. It is known that the actin regulatory protein palladin, which is highly expressed here, is also highly related to podocyte function and podocytopathies, and plays an important role in the stability of the actin cytoskeleton. The aim of our study was to define the frequency of TRPC5 and palladin renal expressions in podocytes in focal segmental glomerulosclerosis (FSGS) and its relationship with prognosis and treatment response. Method A total of 182 patients were enrolled for baseline clinical and histopathological features and 103 patients with a clinical follow-up for more than 2 years were evaluated for outcomes. Immunohistochemical staining was performed with TRPC5 and palladin antibodies on kidney biopsies and glomerular staining was evaluated. Results Baseline characteristics, and health parameters were similar between TRPC5+/TRPC5− and palladin+/palladin− groups. TRPC5 expression was observed in 69% of the patient biopsies and palladin expression in 73%. We found that TRPC5 and palladin expression was a significant predictor of FSGS severity and poor treatment response (both p&amp;lt;0.05). In addition, TRPC5 expression was significantly associated with the development of end-stage renal disease and ongoing proteinuria. Conclusion The development of proven treatments that delay the progression of FSGS is critical to patient survival. The development of new treatments is possible only by knowing the underlying pathophysiological mechanism of the disease. Podocyte loss is a critical step in the development of irreversible glomerulosclerosis, which causes chronic kidney disease. Therefore, blocking TRPC5 channel and palladin may be an effective treatment strategy, especially in treatment-resistant FSGS patients with positive staining on biopsy. Our study is the first in the literature to show these two antigens in kidney tissue in FSGS and to associate them with disease prognosis. TRPC5 and palladin expression may serve as a biomarker to facilitate diagnosis and choose new treatment regimens of proteinuric kidney diseases in the future.

Perturbations in podocyte transcriptome and biological pathways induced by FSGS associated circulating factors.

Focal segmental glomerulosclerosis (FSGS) is frequently associated with heavy proteinuria and progressive renal failure requiring dialysis or kidney transplantation. However, primary FSGS also has a ~40% risk of recurrence of disease in the transplanted kidney (rFSGS). Multiple circulating factors have been identified to contribute to the pathogenesis of primary and rFSGS including soluble urokinase-type plasminogen activator receptor (suPAR) and patient-derived CD40 autoantibody (CD40autoAb). However, the downstream effector pathways specific to individual factors require further study. The tumor necrosis factor, TNF pathway activation by one or more circulating factors present in the sera of patients with FSGS has been supported by multiple studies. A human in vitro model was used to study podocyte injury measured as the loss of actin stress fibers. Anti-CD40 autoantibody was isolated from FSGS patients (recurrent and non-recurrent) and control patients with ESRD due to non-FSGS related causes. Two novel human antibodies-anti-uPAR (2G10) and anti-CD40 antibody (Bristol Meyer Squibb, 986090) were tested for their ability to rescue podocyte injury. Podocytes treated with patient derived antibody were transcriptionally profiled using whole human genome microarray. Here we show that podocyte injury caused by sera from FSGS patients is mediated by CD40 and suPAR and can be blocked by human anti-uPAR and anti-CD40 antibodies. Transcriptomic studies to compare the molecules and pathways activated in response to CD40 autoantibody from rFSGS patients (rFSGS/CD40autoAb) and suPAR, identified unique inflammatory pathways associated with FSGS injury. We identified several novel and previously described genes associated with FSGS progression. Targeted blockade of suPAR and CD40 pathways with novel human antibodies showed inhibition of podocyte injury in FSGS.

Rapid Progression of Focal Segmental Glomerulosclerosis in Patients with High-Risk APOL1 Genotypes.

FSGS is a heterogeneous diagnosis with a guarded prognosis. Polymorphisms in the apolipoprotein L1 ( APOL1 ) gene are associated with developing FSGS and faster progression to kidney failure in affected patients. Better understanding the natural history of patients with FSGS and APOL1 risk alleles is essential to improve patient care and support the design and interpretation of interventional studies. The objective of this study was to evaluate the quantitative association between APOL1 and kidney disease progression and the interaction with other clinical and laboratory factors. CureGN cohort study participants with biopsy diagnosis of FSGS, regardless of self-identified race, were included. The exposure of interest was two APOL1 risk alleles (high risk) versus zero to one risk alleles (low risk). The primary outcome was eGFR slope categorized as rapid progressor (eGFR slope ≤-5 ml/min per year), intermediate progressor (slope between 0 and -5), or nonprogressor (slope ≥0). Multivariable ordinal logistic and linear regressions were used for adjusted analyses. Missing data were addressed using multiple imputation. Of 650 participants, 476 (73%) had genetic testing, among whom 87 (18%) were high risk. High-risk participants were more likely to have lower median eGFR (62 [interquartile range, 36-81] versus low-risk participants 76 ml/min per 1.73 m 2 [interquartile range, 44-106]; P <0.01). In adjusted analysis, the odds of more rapid progression of eGFR was 2.75 times higher (95% confidence interval, 1.67 to 4.53; P <0.001) in the high-risk versus low-risk groups. In patients with FSGS, high-risk APOL1 genotype is the predominant factor associated with more rapid loss of kidney function.

The Angiogenesis Inhibitor Isthmin-1 (ISM1) Is Overexpressed in Experimental Models of Glomerulopathy and Impairs the Viability of Podocytes.

Focal segmental glomerulosclerosis (FSGS) is a major cause of end-stage renal disease and remains without specific treatment. To identify new events during FSGS progression, we used an experimental model of FSGS associated with nephroangiosclerosis in rats injected with L-NAME (Nω-nitro-L-arginine methyl ester). After transcriptomic analysis we focused our study on the role of Isthmin-1 (ISM1, an anti-angiogenic protein involved in endothelial cell apoptosis. We studied the renal expression of ISM1 in L-NAME rats and other models of proteinuria, particularly at the glomerular level. In the L-NAME model, withdrawal of the stimulus partially restored basal ISM1 levels, along with an improvement in renal function. In other four animal models of proteinuria, ISM1 was overexpressed and localized in podocytes while the renal function was degraded. Together these facts suggest that the glomerular expression of ISM1 correlates directly with the progression-recovery of the disease. Further in vitro experiments demonstrated that ISM1 co-localized with its receptors GRP78 and integrin αvβ5 on podocytes. Treatment of human podocytes with low doses of recombinant ISM1 decreased cell viability and induced caspase activation. Stronger ISM1 stimuli in podocytes dropped mitochondrial membrane potential and induced nuclear translocation of apoptosis-inducing factor (AIF). Our results suggest that ISM1 participates in the progression of glomerular diseases and promotes podocyte apoptosis in two different complementary ways: one caspase-dependent and one caspase-independent associated with mitochondrial destabilization.

Therapeutic Potential Targeting Podocyte Mitochondrial Dysfunction in Focal Segmental Glomerulosclerosis.

Podocytes are essential components of the glomerular filtration barrier and essential for the proper filtration function of the glomerulus. Podocyte injury under various stress conditions is the primary pathogenesis and key determinant of focal segmental glomerulosclerosis (FSGS) with prominent clinical manifestations of proteinuria or nephrotic syndrome. Under physiological conditions, a highly coordinated mitochondrial quality control system, including antioxidant defenses, mitochondrial dynamics (fusion, fission, and mitophagy), and mitochondrial biogenesis, guarantees the sophisticated structure and various functions of podocytes. However, under FSGS pathological conditions, mitochondria encounter oxidative stress, dynamics disturbances, and defective mitochondrial biogenesis. Moreover, mutations in mitochondrial DNA and mitochondria-related genes are also strongly associated with FSGS. Based on these pieces of evidence, bioactive agents that function to relieve mitochondrial oxidative stress and promote mitochondrial biogenesis have been proven effective in preclinical FSGS models. Targeting the mitochondrial network is expected to provide new therapeutic strategies for the treatment of FSGS and delay its progression to end-stage renal disease. Mitochondrial dysfunction plays a key role in podocyte injury and FSGS progression. This review summarized recent advances in the study of mitochondrial homeostatic imbalance and dysfunction in FSGS and discussed the potential of mitochondria-targeted therapeutics in improving FSGS and retarding its progression to end-stage renal disease.

Protecting glomerulus: role of angiotensin-II type 2 receptor.

Podocyte injury due to either drug, toxin, infection, or metabolic abnormality is a great concern as it increases the risk of developing focal segmental glomerulosclerosis (FSGS) and proteinuric kidney diseases. The direct podocyte injury due to doxorubicin is associated with an increase in proinflammatory cytokines and induction of cathepsin L. The increased activity of cathepsin L in turn may degrade the glomerular slit diaphragm resulting in proteinuric kidney injury. The angiotensin-II type 2 receptor (AT2R) has earlier been reported to be associated with the preservation of slit diaphragm proteins and prevention of proteinuria. Recent in vivo findings by Zhang and colleagues further support the anti-proteinuric role of AT2R in preventing podocyte injury via down-regulating cytokines ccl2, and hence, cathepsin L, thereby, limiting the progression of FSGS.

Blocking ribosomal protein S6 phosphorylation inhibits podocyte hypertrophy and focal segmental glomerulosclerosis

Ribosomal protein S6 (rpS6) phosphorylation mediates the hypertrophic growth of kidney proximal tubule cells. However, the role of rpS6 phosphorylation in podocyte hypertrophy and podocyte loss during the pathogenesis of focal segmental glomerulosclerosis (FSGS) remains undefined. Here, we examined rpS6 phosphorylation levels in kidney biopsy specimens from patients with FSGS and in podocytes from mouse kidneys with Adriamycin-induced FSGS. Using genetic and pharmacologic approaches in the mouse model of FSGS, we investigated the role of rpS6 phosphorylation in podocyte hypertrophy and loss during development and progression of FSGS. Phosphorylated rpS6 was found to be markedly increased in the podocytes of patients with FSGS and Adriamycin-induced FSGS mice. Genetic deletion of the Tuberous sclerosis 1 gene in kidney glomerular podocytes activated mammalian target of rapamycin complex 1 signaling to rpS6 phosphorylation, resulting in podocyte hypertrophy and pathologic features similar to those of patients with FSGS including podocyte loss, leading to segmental glomerulosclerosis. Since protein phosphatase 1 is known to negatively regulate rpS6 phosphorylation, treatment with an inhibitor increased phospho-rpS6 levels, promoted podocyte hypertrophy and exacerbated formation of FSGS lesions. Importantly, blocking rpS6 phosphorylation (either by generating congenic rpS6 knock-in mice expressing non-phosphorylatable rpS6 or by inhibiting ribosomal protein S6 kinase 1-mediated rpS6 phosphorylation with an inhibitor) significantly blunted podocyte hypertrophy, inhibited podocyte loss, and attenuated formation of FSGS lesions. Thus, our study provides genetic and pharmacologic evidence indicating that specifically targeting rpS6 phosphorylation can attenuate the development of FSGS lesions by inhibiting podocyte hypertrophy and associated podocyte depletion.

Role of fibroblast specific protein 1 expression in the progression of adriamycin-induced glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a commonly occurring cause of steroid-resistant nephrotic syndrome and frequently progresses to renal failure. Podocyte epithelial-mesenchymal transition (EMT) is thought to induce podocyte detachment in glomerular diseases, and severe degeneration and shedding of glomerular podocytes plays a major role in the progression of FSGS. We showed that fibroblast specific protein 1 (FSP1), an EMT marker, is strongly expressed in podocytes of FSGS patients, but the significance of podocyte expression of FSP1 to the pathophysiology of FSGS remained unclear. Here, we investigated FSP1 expression in podocytes from mice with adriamycin (ADR)-induced nephropathy, a murine model of FSGS. The number of FSP1-positive (FSP1+) podocytes was increased in ADR-treated mice and positively correlated with the degree of proteinuria and glomerulosclerosis in ADR-treated mice. ADR-induced FSGS and the attendant proteinuria were significantly ameliorated in FSP1 knockout mice as compared to wild type mice. These findings indicate that podocyte expression of FSP1 plays a crucial role in the pathogenesis of FSGS, which makes FSP1 a potential target for treatment of FSGS.

SRT1720 Administration Attenuates Albuminuria and Renal Fibrosis on Adriamycin‐Induced Glomerulosclerosis

The focal segmental glomerulosclerosis (FSGS) is the leading cause of progression of chronic kidney disease (CKD) and its responsible for the increasing number of cases of dialysis and kidney transplants worldwide. The lack of knowledge about the mechanisms underlying the progression of FSGS makes it difficult to develop therapeutic approaches with regarding the proteinuria and CKD progression. The aim of the study is to investigate the role of SIRT1 on FSGS induced by adriamycin, focusing on renoprotective responses. For this we used a synthetic SIRT1 agonist, the SRT1720. Male Balb/c mice aged 5 weeks were organized into two treatment groups: 48h and 14 days, being thus distributed in four experimental conditions: control (vehicle), adriamycin (ADR, 10 mg/kg), treated with SRT1720 (20 mg/kg/day) and treated with ADR+SRT1720. After the treatment, physiological parameters such as body weight, renal weight, weight gain, and plasma parameters such as creatinine, urea and osmolarity were evaluated. The glomerulosclerosis index was assessed by quantifying the renal sections stained with periodic acid-schiff (PAS). Urinary albumin was detected after staining the SDS-polyacrylamide gel. For the 48h group, the expression of mRNA was performed by quantitative real time PCR. For the 14-day group, GRP78, claudin-1, phospho eIF2αSer51 and phospho AMPKαThr172 protein expression were evaluated by immunoblotting. Type-IV collagen and nephrin staining were verified by immunofluorescence using confocal microscopy. The results indicate that for the ADR 48h group there was a decrease in final body weight, renal weight and an increase in plasma creatinine concentration compared to the control group. Administration of SRT1720 mitigates part of these effects, improving renal function. Our data indicate that although there is no positive stain for glomerulosclerosis in PAS or differences in the gene expression of Kim1, Tnf and Nphs1, the animals already have significant albuminuria within 48 hours after ADR administration in comparison to control, group, which suggests an initial damage on glomerular ultrafiltration barrier. Regarding the 14-day group, a decrease in final weight, an increase in renal weight, an increase in plasma creatinine, a significant increase in urinary albumin and the glomerulosclerosis index for ADR animals are observed, and this effect was clearly reversed by administration of SRT1720. There were no changes in creatinine clearance between groups after 14 days of treatment, despite an increase in urinary flow for the ADR + SRT1720 group. Although there were no significant differences on GRP78, phospho eIF2αSer51 or claudin-1 protein expression, the ADR+SRT1720 group showed an increase on phospho AMPKαThr172. Type IV collagen deposition was observed in ADR mice, as well as an important reduction in glomerular nephrin marking. These effects were partially reversed by the administration of the SRT1720. In conclusion, our data indicate that SRT1720 administration, a synthetic SIRT1 agonist, can improve renal function, mainly by partially preserving the glomerular ultrafiltration barrier and inhibiting renal fibrosis.

Nuclear exclusion of YAP exacerbates podocyte apoptosis and disease progression in Adriamycin-induced focal segmental glomerulosclerosis

AbstractFocal segmental glomerulosclerosis (FSGS) is a chronic glomerular disease with poor clinical outcomes. Podocyte loss via apoptosis is one important mechanism underlying the pathogenesis of FSGS. Recently, Yes-associated-protein (YAP), a key downstream protein in the Hippo pathway, was identified as an activator for multiple gene transcriptional factors in the nucleus to control cell proliferation and apoptosis. To investigate the potential role of YAP in the progression of FSGS, we examined kidney samples from patients with minimal change disease or FSGS and found that increases in podocyte apoptosis is positively correlated with the cytoplasmic distribution of YAP in human FSGS. Utilizing an established mT/mG transgenic mouse model and primary cultured podocytes, we found that YAP was distributed uniformly in nucleus and cytoplasm in the podocytes of control animals. Adriamycin treatment induced gradual nuclear exclusion of YAP with enhanced phospho-YAP/YAP ratio, accompanied by the induction of podocyte apoptosis both in vivo and in vitro. Moreover, we used verteporfin to treat an Adriamycin-induced FSGS mouse model, and found YAP inhibition by verteporfin induced nuclear exclusion of YAP, thus increasing podocyte apoptosis and accelerating disease progression. Therefore, our findings suggest that YAP nuclear distribution and activation in podocytes is an important endogenous anti-apoptotic mechanism during the progression of FSGS.An increase in podocyte apoptosis is positively correlated with the cytoplasmic distribution of YAP in focal segmental glomerulosclerosis (FSGS). YAP inhibition by verteporfin induces nuclear exclusion of YAP, thus increasing the podocyte apoptosis and accelerating disease progression. Therefore, this study suggests that YAP activation and nuclear distribution in podocytes is an endogenous anti-apoptotic mechanism during the progression of FSGS.

ECM Characterization Reveals a Massive Activation of Acute Phase Response during FSGS.

The glomerular basement membrane (GBM) and extra-cellular matrix (ECM) are essential to maintain a functional interaction between the glomerular podocytes and the fenestrated endothelial cells in the formation of the slit diaphragm for the filtration of blood. Dysregulation of ECM homeostasis can cause Focal segmental glomerulosclerosis (FSGS). Despite this central role, alterations in ECM composition during FSGS have not been analyzed in detail yet. Here, we characterized the ECM proteome changes in miR-193a-overexpressing mice, which suffer from FSGS due to suppression of Wilms’ tumor 1 (WT1). By mass spectrometry we identified a massive activation of the acute phase response, especially the complement and fibrinogen pathways. Several protease inhibitors (ITIH1, SERPINA1, SERPINA3) were also strongly increased. Complementary analysis of RNA expression data from both miR-193a mice and human FSGS patients identified additional candidate genes also mainly involved in the acute phase response. In total, we identified more than 60 dysregulated, ECM-associated genes with potential relevance for FSGS progression. Our comprehensive analysis of a murine FSGS model and translational comparison with human data offers novel targets for FSGS therapy.

Mechanisms of Scarring in Focal Segmental Glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) presents with scar in parts of some glomeruli and often progresses to global and diffuse glomerulosclerosis. Podocyte injury is the initial target in primary FSGS, induced by a circulating factor. Several gene variants, for example, APOL1, are associated with increased susceptibility to FSGS. Primary FSGS may be due to genetic mutation in key podocyte genes. Increased work stress after loss of nephrons, epigenetic mechanisms, and various profibrotic pathways can contribute to progressive sclerosis, regardless of the initial injury. The progression of FSGS lesions also involves crosstalk between podocytes and other kidney cells, such as parietal epithelial cells, glomerular endothelial cells, and even tubular epithelial cells. New insights related to these mechanisms could potentially lead to new therapeutic strategies to prevent progression of FSGS.

EET Analogs and the Dual‐Inhibition of sEH/COX‐2 for the Treatment of Focal Segmental Glomerular Sclerosis

Focal segmental glomerulosclerosis (FSGS) is the single most common form of kidney disease. This devastating disorder can lead to end stage renal disease (ESRD), a terminal diagnosis in the absence of a kidney transplant. The progression of FSGS is defined by sclerotic damage to the glomerulus, the filtering unit of blood in the kidney. Epoxyeicosatrienoic acids (EETs) are a family of arachidonic acid metabolites important to glomerular function. EETs are metabolized by enzymes such as soluble epoxide hydrolase (sEH) and cyclooxygenase (COX), and we have developed a novel dual‐ligand drug (PTUPB) that inhibits both sEH and COX‐2. We hypothesize that EET analogs and the dual‐inhibition of sEH and COX‐2 will mitigate glomerular damage caused by FSGS. The long‐term goal of this research is to better understand the role of 8,9‐EET and its metabolites on glomerular function so that we can develop new therapies to treat FSGS and other nephropathies.MethodsGlomerular Permeability Assay: Glomeruli were pre‐incubated in 5% albumin (50kDa dialyzed BSA), followed by a bath exchange to 1% albumin. Under normal conditions the glomeruli are non‐permeable to albumin, and as a result, when the 5% albumin bath is exchanged for 1% albumin, water is taken up into the intra‐glomerular space due to the rapid change in oncotic pressure. Glomerular permeability was tested using our non‐hydrolyzable 8,9‐EET analog (1μM), our non‐hydrolyzable 14,15‐EET analog (EET‐A, 1μM) or PTUPB (1μM) with isolated SD rat glomeruli in the presence or absence of angiotensin II (AngII, 10μM), a known glomerular permeabilizing agent. 3D‐Confocal imaging (72μm z‐depth, 27‐layer z‐stack) was utilized to measure the relative changes in glomerular volume.ResultsGlomerular permeability to albumin (Palb) is derived from the albumin reflection coefficient (σalb), where a value of 1 indicates high permeability to albumin, and 0 indicates low permeability (relative to control). A baseline response to a 5% to 1% albumin exchange resulted in very low albumin permeability (Palb = −0.21 ± 0.21, n=6). Conversely, the presence of AngII resulted high albumin permeability (Palb = 1.21 ± 0.12, n=15). Our 8,9‐EET analog, in the presence of AngII, mitigated the effects of AngII‐induced permeability (Palb = 0.13 ± 0.18, n=7), as did our dual sEH/COX2 inhibitor, PTUPB, under the same Ang‐II stimulation (Palb = 0.71% ± 0.35, n=7), but not the 14,15‐EET analog (Palb = 0.99% ± 0.21, n=4) . All values are mean ± SEM.ConclusionFSGS is complex multi‐model disease, and glomerular damage/dysfunction are at the core of this condition. The ability of our 8,9‐EET analog and PUTPB to decrease AngII‐associated glomerular permeability suggest and important role for EETs and their metabolism. Future work will investigate not only the effects of 8,9‐EET analogs and PTUPB on glomerular health, but also the consequences of EET metabolites and other EET‐analogs, on both glomerular and mesangial function using cell and animal models.Support or Funding InformationR01 DK103616‐01 (John D. Imig). Dr. Ralph and Marian Falk Medical Research Trust ‐ Phase II (John D. Imig)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.