Human pluripotent stem cell-derived kidney organoids for personalized congenital and idiopathic nephrotic syndrome modeling.

Nephrotic syndrome (NS) is characterized by severe proteinuria as a consequence of kidney glomerular injury due to podocyte damage. In vitro models mimicking in vivo podocyte characteristics are a prerequisite to resolve NS pathogenesis. The detailed characterization of organoid podocytes resulting from a hybrid culture protocol showed a podocyte population that resembles adult podocytes and was superior compared with 2D counterparts, based on single-cell RNA sequencing, super-resolution imaging and electron microscopy. In this study, these next-generation podocytes in kidney organoids enabled personalized idiopathic nephrotic syndrome modeling, as shown by activated slit diaphragm signaling and podocyte injury following protamine sulfate, puromycin aminonucleoside treatment and exposure to NS plasma containing pathogenic permeability factors. Organoids cultured from cells of a patient with heterozygous NPHS2 mutations showed poor NPHS2 expression and aberrant NPHS1 localization, which was reversible after genetic correction. Repaired organoids displayed increased VEGFA pathway activity and transcription factor activity known to be essential for podocyte physiology, as shown by RNA sequencing. This study shows that organoids are the preferred model of choice to study idiopathic and congenital podocytopathies.

Primary Focal Segmental Glomerulosclerosis Plasmas Increase Lipid Droplet Formation and Perilipin-2 Expression in Human Podocytes.

Many patients with primary focal segmental glomerulosclerosis (FSGS) develop recurrence of proteinuria after kidney transplantation. Several circulating permeability factors (CPFs) responsible for recurrence have been suggested, but were never validated. We aimed to find proteins involved in the mechanism of action of CPF(s) and/or potential biomarkers for the presence of CPF(s). Cultured human podocytes were exposed to plasma from patients with FSGS with presumed CPF(s) or healthy and disease controls. Podocyte proteomes were analyzed by LC-MS. Results were validated using flow cytometry, RT-PCR, and immunofluorescence. Podocyte granularity was examined using flow cytometry, electron microscopy imaging, and BODIPY staining. Perilipin-2 protein expression was increased in podocytes exposed to presumed CPF-containing plasmas, and correlated with the capacity of plasma to induce podocyte granularity, identified as lipid droplet accumulation. Elevated podocyte perilipin-2 was confirmed at protein and mRNA level and was also detected in glomeruli of FSGS patients whose active disease plasmas induced podocyte perilipin-2 and lipid droplets. Our study demonstrates that presumably, CPF-containing plasmas from FSGS patients induce podocyte lipid droplet accumulation and perilipin-2 expression, identifying perilipin-2 as a potential biomarker. Future research should address the mechanism underlying CPF-induced alterations in podocyte lipid metabolism, which ultimately may result in novel leads for treatment.

Novel in vitro assays to detect circulating permeability factor(s) in idiopathic focal segmental glomerulosclerosis.

BACKGROUND: Many patients with idiopathic focal segmental glomerulosclerosis (FSGS) develop recurrence of proteinuria after kidney transplantation (TX). Although several circulating permeability factors (CPFs) responsible for recurrence have been suggested, there is no consensus. To facilitate CPF identification and predict recurrence after TX, there is a need for robust methods that demonstrate the presence of CPFs. METHODS: Cultured human podocytes (hPods) and human and mouse glomerular endothelial cells (ciGEnC, mGEnC) were exposed to plasmas of FSGS patients with presumed CPFs, and of (disease) controls. A visual scoring assay and flow cytometry analysis of side scatter were used to measured changes in cellular granularity after exposure to plasma. RESULTS: Nine out of 13 active disease plasmas of 10 FSGS patients with presumed CPFs induced granularity in hPod in a dose- and time-dependent manner. Corresponding remission plasmas induced no or less granularity in hPod. Similar results were obtained with ciGEnC and mGEnC, although induced granularity was less compared with hPod. Notably, foetal calf serum, healthy plasma and a remission plasma partially blocked FSGS plasma-induced hPod granularity. CONCLUSIONS: We developed a novel assay in which active disease, presumably CPF-containing, FSGS plasmas induced granularity in cultured hPod. Our results may indicate the presence of CPF inhibitor(s) in healthy and remission plasma. We suggest the presence of a delicate balance between CPF and a CPF inhibitory factor, which is disturbed in patients with active disease. Our novel assays can be applied in future research to identify CPF and CPF inhibitors, and possibly to predict recurrence after TX.

Nivolumab-associated Nephrotic Syndrome in a Patient With Renal Cell Carcinoma: A Case Report.

INTRODUCTION: Immune checkpoint inhibitors have taken an important place in the treatment of different types of malignancies. These drugs are known to have specific immune-mediated adverse events. We describe a case of severe nephrotic syndrome secondary to treatment with nivolumab in a patient with renal cell carcinoma. CASE PRESENTATION: A 62-year-old man was treated with nivolumab for papillary renal cell carcinoma type 2 for 8 weeks when he was admitted to the hospital with a severe nephrotic syndrome and acute kidney injury. Renal biopsy showed focal segmental glomerulosclerosis. Treatment with high-dose corticosteroids had insufficient effect, but the addition of mycophenolate mofetil resulted in remission of the nephrotic syndrome and recovery of renal function. Proteinuria subsequently relapsed during corticosteroid tapering. CONCLUSIONS: The time course in this patient strongly suggests that the nephrotic syndrome occurred as an adverse drug reaction to nivolumab treatment. If during nivolumab treatment renal insufficiency, hypoalbuminemia, or proteinuria develops, further analysis for a possible nephrotic syndrome is warranted for early detection and treatment of this life-threatening complication.

The Clinical Course of Minimal Change Nephrotic Syndrome With Onset in Adulthood or Late Adolescence: A Case Series.

BACKGROUND: Few studies have examined the treatment and outcome of adult-onset minimal change nephrotic syndrome (MCNS). We retrospectively studied 125 patients who had MCNS with onset in either adulthood or late adolescence. Presenting characteristics, duration of initial treatment and response to treatment, relapse patterns, complications, and long-term outcome were studied. STUDY DESIGN: Case series. SETTING & PARTICIPANTS: Patients with new-onset nephrotic syndrome 16 years or older and a histologic diagnosis of MCNS in 1985 to 2011 were identified from pathology records of 10 participating centers. OUTCOMES: Partial and complete remission, treatment resistance, relapse, complications, renal survival. RESULTS: Corticosteroids were given as initial treatment in 105 (84%) patients. After 16 weeks of corticosteroid treatment, 92 (88%) of these patients had reached remission. Median time to remission was 4 (IQR, 2-7) weeks. 7 (6%) patients initially received cyclophosphamide with or without corticosteroids, and all attained remission after a median of 4 (IQR, 3-11) weeks. 13 (10%) patients reached remission without immunosuppressive treatment. One or more relapses were observed in 57 (54%) patients who received initial corticosteroid treatment. Second-line cyclophosphamide resulted in stable remission in 57% of patients with relapsing MCNS. Acute kidney injury was observed in 50 (40%) patients. Recovery of kidney function occurred almost without exception. Arterial or venous thrombosis occurred in 11 (9%) patients. At the last follow-up, 113 (90%) patients were in remission and had preserved kidney function. 3 patients with steroid-resistant MCNS progressed to end-stage renal disease, which was associated with focal segmental glomerulosclerosis lesions on repeat biopsy. LIMITATIONS: Retrospective design, variable treatment protocols. CONCLUSIONS: The large majority of patients who had MCNS with onset in adulthood or late adolescence were treated with corticosteroids and reached remission, but many had relapses. Cyclophosphamide resulted in stable remission in many patients with relapses. Significant morbidity was observed due to acute kidney injury and other complications. Progression to end-stage renal disease occurred in a few patients and was explained by focal segmental glomerulosclerosis.

Minimal change disease and idiopathic FSGS: manifestations of the same disease.

Minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) are the key histological findings in patients with idiopathic nephrotic syndrome (INS). Although MCD and idiopathic FSGS are often considered to represent separate entities based on differences in their presenting characteristics, histology and outcomes, little evidence exists for this separation. We propose that MCD and idiopathic FSGS are different manifestations of the same progressive disease. The gradual development of FSGS in patients with non-remitting or relapsing INS has been well documented. Moreover, FSGS is the uniform result of substantial podocyte loss in animal models, and a common feature of virtually all progressive human glomerulopathies. As evidence suggests a common aetiology, the pathogenesis of MCD and idiopathic FSGS should be studied together. In clinical trials, idiopathic FSGS should be considered to represent an advanced stage of disease progression that is less likely to respond to treatment than the earlier stage of disease, which is usually defined as MCD.

Permeability factors in idiopathic nephrotic syndrome: historical perspectives and lessons for the future.

The term idiopathic nephrotic syndrome (iNS) traditionally covers minimal change disease and primary focal segmental glomerulosclerosis (FSGS), now thought to be separate disease entities. Clinical and experimental evidence suggest that circulating permeability factors are involved in their pathogenesis. In the past four decades, many investigators have searched for the responsible factors, thus far with little success. The recent report of the soluble urokinase plasminogen activator receptor as a causative factor in FSGS has received much attention, but again the initially promising findings were not confirmed. We describe the history of the search for permeability factors, discuss the pitfalls that are likely responsible for the lack of success and propose criteria that should be used in future studies when evaluating candidate permeability factors.

The soluble urokinase receptor is not a clinical marker for focal segmental glomerulosclerosis.

The soluble urokinase receptor (suPAR) promotes proteinuria and induces focal segmental glomerulosclerosis (FSGS)-like lesions in mice. A serum suPAR concentration cutoff of 3000 pg/ml has been proposed as a clinical biomarker for patients with FSGS. Interestingly, several studies in patients with glomerulopathy found an inverse correlation between the estimated glomerular filtration rate (eGFR) and suPAR. As patients with FSGS present at different eGFRs, we studied the relationship between eGFR and suPAR in a cohort of 476 non-FSGS patients and 54 patients with biopsy-proven idiopathic FSGS. In the non-FSGS patients, eGFR was the strongest significant determinant of suPAR. The proposed cutoff for suPAR in FSGS patients was exceeded in 17%, 39%, and 88% in patients with eGFRs of more than 60, 45-60, and 30-45 ml/min per 1.73 m(2), respectively. In patients with eGFR of <30 ml/min per 1.73 m(2), suPAR exceeded the cutoff in 95% of patients. Levels of suPAR in patients with idiopathic FSGS overlapped with non-FSGS controls and for any given eGFR did not discriminate FSGS cases from non-FSGS controls. In the overall cohort, there was a negative association between idiopathic FSGS and suPAR, and idiopathic FSGS was not an independent predictor of FSGS concentration over 3000 pg/ml. Thus, this study does not support an absolute, eGFR-independent, suPAR concentration cutoff as a biomarker for underlying FSGS pathology and questions the validity of relative, eGFR-dependent suPAR cutoff values.

Serum suPAR in patients with FSGS: trash or treasure?

The urokinase-type plasminogen activator receptor (uPAR) has important functions in cell migration. uPAR can be shed from the cell membrane resulting in soluble uPAR (suPAR). Further cleavage gives rise to shorter fragments with largely unknown functions. Recent studies have demonstrated that both overexpression of uPAR on podocytes and the administration of suPAR cause proteinuria in mice. The common pathogenic mechanism involves the activation of podocyte ß3-integrin. Increased activation of ß3-integrin is also observed in patients with focal and segmental glomerulosclerosis (FSGS). These observations form the basis for the hypothesis that suPAR may be the circulating factor causing FSGS. A recent study fosters this idea by demonstrating increased suPAR levels in the serum of patients with FSGS and reporting an association with recurrence after transplantation and response to plasmapheresis. However, this study was heavily biased, and subsequent studies have given conflicting results. Although the experimental work is very suggestive, at present there is no proof that any known human suPAR fragment causes FSGS in humans. We therefore suggest that the measurement of suPAR using currently available assays has absolutely no value at the present time in decision-making in routine clinical practice.

A retrospective study of focal segmental glomerulosclerosis: clinical criteria can identify patients at high risk for recurrent disease after first renal transplantation.

BACKGROUND: Focal segmental glomerulosclerosis (FSGS) is a frequent cause of end-stage renal disease. Renal transplantation in patients with FSGS is often complicated by disease recurrence, which is associated with poor outcome. There are no tests that reliably predict recurrence of FSGS after transplantation. The aim of this study was to evaluate if clinical criteria can identify patients at high risk for recurrent disease. METHODS: We retrospectively studied 94 patients who received a first renal transplant at a median age of 37 years (range 5-69 years). Patients were assigned to one of three groups: familial or genetic FSGS (group I; n=18), secondary FSGS (group II; n=10) and idiopathic FSGS (group III; n=66). Pretransplant clinical characteristics were analyzed to determine predictors of a recurrence after transplantation. RESULTS: FSGS only recurred in patients with idiopathic FSGS (group III; 42%). Patients with a recurrence had a significantly lower serum albumin, higher 24-hour proteinuria and higher estimated glomerular filtration rate at diagnosis. Serum albumin at diagnosis was the only independent predictor of a recurrence in patients with idiopathic FSGS. Patients with recurrent FSGS had more acute rejection episodes (54% vs. 27%, P =0.02) and lower five year graft survival compared to patients without a recurrence (50 vs. 82%, P <0.01). CONCLUSIONS: Clinical criteria allow identification of patients at high risk of recurrent FSGS after renal transplantation. This information can be used in the counseling and management of patients with FSGS.