Serum soluble urokinase-type plasminogen activator receptor levels and idiopathic FSGS in children: a single-center report

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

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

suPAR: An Inflammatory Mediator for Kidneys

Background

Inflammation is a common feature of many kidney diseases. The implicated inflammatory mediators and their underlying molecular mechanisms however are often not clear.

Summary

suPAR is the soluble form of urokinase-type plasminogen activator receptor (uPAR), associated with inflammation and immune activation. It has evolved into a unique circulating kidney disease factor over the last 10 years. In particular, suPAR has multiple looks due to enzymatic cleavage and alternative transcriptional splicing of the uPAR gene. Most recently, suPAR has emerged as a systemic mediator for COVID-19 infection, associated with lung as well as kidney dysfunction. Like membrane-bound uPAR, suPAR could interact with integrins (e.g., αvβ3 integrin) on podocytes, providing the molecular basis for some glomerular kidney diseases. In addition, there have been numerous studies suggesting that suPAR connects acute kidney injury to chronic kidney disease as a special kidney risk factor. Moreover, the implication of circulating suPAR levels in kidney transplantation and plasmapheresis not only indicates its relevance in monitoring for recurrence but also implies suPAR as a possible therapeutic target. In fact, the therapeutic concept of manipulating suPAR function has been evidenced in several kidney disease experimental models.

Key Messages

The last 10 years of research has established suPAR as a unique inflammatory mediator for kidneys. While open questions remain and deserve additional studies, modulating suPAR function may represent a promising novel therapeutic strategy for kidney disease.

Kidney Transplantation for Focal Segmental Glomerulosclerosis: Can We Prevent Its Recurrence? Personal Experience and Literature Review

Background: Primary focal segmental glomerulosclerosis (FSGS) is associated with a high risk of recurrence after kidney transplantation with a major risk of graft loss despite preventive or curative treatments. Aim: to assess graft survival in FSGS kidney-transplant recipients and to compare those that had a relapse with those that had no relapse. Patients/Methods: we included 17 FSGS kidney-transplant recipients between January 2000 and January 2020, separated retrospectively into two groups (recurrences: n = 8 patients; no recurrences: n = 9 patients). FSGS recurrence was defined as having proteinuria of ≥3 g/g or urinary creatinine of ≥3 g/day. All patients received an induction therapy; maintenance immunosuppressive therapy at post-transplantation relied on tacrolimus/mycophenolate mofetil/steroids. In order to prevent or treat FSGS recurrence, patients received apheresis sessions plus rituximab. Results: FSGS recurrence rate was 47%. All patients that relapsed with a first graft also relapsed with subsequent grafts. Median time to recurrence was 3 (min: 1; max: 4745) days, despite rituximab/apheresis prophylaxis. Mean age was significantly lower in the relapsers (group 1) than in the non-relapsers (group 2); i.e., 47 ± 11 vs. 58 ± 9 years (p = 0.04). Time to progression to stage 5 chronic kidney disease (CKD) and young age at FSGS diagnosis were lower in group 1 compared to group 2; i.e., 5 (min: 1; max: 26) vs. 2 (min: 1; max: 26) years, and 16 (min: 4; max: 55) vs. 34 (min: 6; max 48) years, respectively. There was no difference between the two groups in terms of progression to CKD stage 5 on the native kidneys, averaging 7 years in both groups (p = 0.99). In group 1, seven patients received rituximab/apheresis prophylaxis, although this did not prevent the recurrence of FSGS. Conclusion: pretransplant prophylaxis with plasmapheresis/rituximab did not appear to reduce the risk of recurrence of primary FSGS on the graft, but could allow remission in the event of recurrence.

suPAR, a Circulating Kidney Disease Factor

Urokinase plasminogen activator receptor (uPAR) is a multifaceted, GPI-anchored three-domain protein. Release of the receptor results in variable levels of soluble uPAR (suPAR) in the blood circulation. suPAR levels have been linked to many disease states. In this mini-review, we discuss suPAR as a key circulating molecule mediating kidney disease with a particular focus on differently spliced isoforms.

The glomerular filtration barrier: a structural target for novel kidney therapies

Loss of normal kidney function affects more than 10% of the population and contributes to morbidity and mortality. Kidney diseases are currently treated with immunosuppressive agents, antihypertensives and diuretics with partial but limited success. Most kidney disease is characterized by breakdown of the glomerular filtration barrier (GFB). Specialized podocyte cells maintain the GFB, and structure-function experiments and studies of intercellular communication between the podocytes and other GFB cells, combined with advances from genetics and genomics, have laid the groundwork for a new generation of therapies that directly intervene at the GFB. These include inhibitors of apolipoprotein L1 (APOL1), short transient receptor potential channels (TRPCs), soluble fms-like tyrosine kinase 1 (sFLT1; also known as soluble vascular endothelial growth factor receptor 1), roundabout homologue 2 (ROBO2), endothelin receptor A, soluble urokinase plasminogen activator surface receptor (suPAR) and substrate intermediates for coenzyme Q10 (CoQ₁₀). These molecular targets converge on two key components of GFB biology: mitochondrial function and the actin-myosin contractile machinery. This Review discusses therapies and developments focused on maintaining GFB integrity, and the emerging questions in this evolving field.

Autoimmunity in Focal Segmental Glomerulosclerosis: A Long-Standing Yet Elusive Association

Focal segmental glomerulosclerosis (FSGS) is a histological term that describes a pathologic renal entity affecting both adults and children, with a wide array of possible underlying etiologies. Podocyte damage with scarring, the hallmark of this condition, leads to altered permeability of the glomerular barrier, which may result in massive proteinuria and relentless renal function deterioration. A definite cause of focal segmental glomerulosclerosis can be confirmed in a minority of cases, while most forms have been traditionally labeled as primary or idiopathic. Despite this definition, increasing evidence indicates that primary forms are a heterogenous group rather than a single disease entity: several circulating factors that may affect glomerular permeability have been proposed as potential culprits, and both humoral and cellular immunity have been implicated in the pathogenesis of the disease. Consistently, immunosuppressive drugs are considered as the cornerstone of treatment for primary focal segmental glomerulosclerosis, but response to these agents and long-term outcomes are highly variable. In this review we provide a summary of historical and recent advances on the pathogenesis of primary focal segmental glomerulosclerosis, focusing on implications for its differential diagnosis and treatment.

Serum soluble urokinase plasminogen activator receptor in adolescents: interaction of chronic pain and obesity

Pediatric chronic pain is exacerbated by obesity. Serum soluble urokinase plasminogen activator receptor, a novel inflammation biomarker, was increased in obese adolescents with chronic pain indicating interactive inflammatory conditions.

Introduction:

Obesity in adolescents is increasing in frequency and is associated with short-term and long-term negative consequences that include the exacerbation of co-occurring chronic pain.

Objective:

To determine whether the interaction between chronic pain and obesity would be reflected in changes in serum soluble urokinase plasminogen activator receptor (suPAR) concentrations, a novel marker of systemic inflammation associated with obesity, insulin resistance, and cardiovascular disease.

Methods:

We measured serum suPAR levels in 146 adolescent males and females with no pain or obesity (healthy controls; n = 40), chronic pain with healthy weight (n = 37), obesity alone (n = 41), and the combination of chronic pain and obesity (n = 28).

Results:

Serum suPAR (median [interquartile range]) was not increased by chronic pain alone (2.2 [1.8–2.4] ng/mL) or obesity alone (2.2 [2.0–2.4] ng/mL) but was increased significantly with the combination of chronic pain and obesity (2.4 [2.1–2.7] ng/mL; P < 0.019). This finding confirms the proposition that pain and obesity are inflammatory states that display a classic augmenting interaction.

Conclusion:

We propose that measurement of serum suPAR can be added to the armamentarium of serum biomarkers useful in the evaluation of mechanisms of inflammation in adolescent obesity and chronic pain.

Idiopathic nephrotic syndrome and serum permeability factors: a molecular jigsaw puzzle

Nephrotic syndrome is traditionally defined using the triad of edema, hypoalbuminemia, and proteinuria, but this syndrome is very heterogeneous and difficult to clarify. Its idiopathic form (INS) is probably the most harmful and essentially comprises two entities: minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS). We will consider some hypotheses regarding the mechanisms underlying INS: (i) the presence of several glomerular permeability factors in the sera of patients that alter the morphology and function of podocytes leading to proteinuria, (ii) the putative role of immune cells. Thanks to recent data, our understanding of these disorders is evolving towards a more multifactorial origin. In this context, circulating factors may be associated according to sequential kinetic mechanisms or micro-environmental changes that need to be determined. In addition, the resulting proteinuria may trigger more proteinuria enhancing the glomerular destabilization.

Soluble Urokinase Receptor Levels in Secondary Focal Segmental Glomerulosclerosis

Background

Soluble urokinase receptor (suPAR) has been reported to be a possible permeability factor causing primary focal segmental glomerulosclerosis (FSGS) in recent years. We investigated the plasma and urinary suPAR levels in patients with 3 common types of secondary FSGS: Alport's syndrome (Alport-FSGS), obesity-related FSGS, and diabetic nephropathy.

Methods

Fifty-two secondary FSGS patients diagnosed by kidney biopsy, including 8 with Alport-FSGS, 20 with obesity-related FSGS, and 24 with diabetic nephropathy, were enrolled in the study in the period from January 2008 to June 2014 at the Renal Division, Peking University First Hospital. Fifty-six healthy donors and 74 patients with primary FSGS, 14 with minimal-change disease, and 29 with membranous nephropathy were used as healthy controls and disease controls, respectively. Plasma and urinary suPAR concentrations were measured with commercial ELISA kits, and their correlations with clinical and pathological data were analyzed.

Results

Both plasma and urinary suPAR levels in the total secondary FSGS group were significantly higher than in healthy controls (p < 0.0001 and p< 0.001, respectively). There was no significant difference in levels of plasma and urinary suPAR in the Alport-FSGS, obesity-related FSGS, and diabetic nephropathy groups (p = 0.64 and p = 0.72, respectively). The plasma suPAR level was not correlated with estimated glomerular filtration rate and urine protein.

Conclusions

The levels of plasma and urinary suPAR in patients with Alport-FSGS, obesity-related FSGS, and diabetic nephropathy were increased. Plasma suPAR might be a pathogenetic participation factor or a useful marker of glomerular diseases with FSGS-associated podocytopathy but is not necessarily a circulating permeability factor.

Association between Soluble Urokinase-Type Plasminogen Activator Receptor Levels and Chronic Kidney Disease: A Systematic Review and Meta-Analysis

Background

Chronic kidney disease (CKD) has become a global public health problem with a high prevalence and mortality. There is no sensitive and effective markers for chronic kidney disease. Previous studies proposed suPAR as an early predict biomarker for chronic kidney disease, but the results are controversial. Therefore, the purpose of the current meta-analysis is to evaluate the association between suPAR and CKD.

Methods

We searched the PubMed, Embase, Cochrane Library databases, and Web of Science before May 1, 2019. The search was based on the key words including suPAR and CKD. Data are extracted independently according to standard format, and quality analysis is performed. We extracted the concentration of suPAR and hazard rate (HR) values of mortality, cardiovascular disease, and end-stage renal disease.

Results

There were 14 studies fulfilling the criteria. The concentration of suPAR was higher in patients with CKD than that in the control group (P < 0.001; SMD: −2.17; 95% CI: −2.71, −1.63; I² = 67.4%). SuPAR had a higher risk of mortality (P=0.001; HR: 1.72; 95% CI: 1.24, 2.39; I² = 68.0%). The higher suPAR level increased the risk of cardiovascular disease (P < 0.001; HR: 3.06; 95% CI: 2.21, 4.22; I² = 0.0%) and the risk of end-stage renal disease (P < 0.001; HR: 1.40; 95% CI: 1.22, 1.60; I² = 0.0%).

Conclusions

Monitoring suPAR concentrations may be used for early diagnosis and prognosis for patients with CKD, and the higher suPAR increased the risk of mortality, cardiovascular events, and end-stage renal disease.

Serum soluble urokinase type plasminogen activated receptor and focal segmental glomerulosclerosis: a systematic review and meta-analysis

OBJECTIVES

Soluble urokinase plasminogen activated receptor (suPAR) is a biomarker that may predict the occurrence of focal segmental glomerulosclerosis (FSGS); however, there is still controversy about whether suPAR can predict FSGS. In this study, we performed a systematic evaluation and meta-analysis to prove whether suPAR can predict FSGS, and to detect a threshold concentration of suPAR that can be used to diagnose FSGS. In addition, a threshold concentration of suPAR for the diagnosis of FSGS was proposed.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

We systematically searched PubMed, Embase, Cochrane Library, Web of Science and China Biology Medicine databases for studies published from the inception dates to 1 December 2018. ELIGIBILITY CRITERIA: (1) Data involving the suPAR level were from blood samples; (2) FSGS was diagnosed by biopsy; and (3) randomised controlled trials, cohort studies, case-control studies and cross-sectional studies.

DATA EXTRACTION AND SYNTHESIS

Initially, a total of 364 studies were searched, among which 29 studies were finally included. In addition, seven studies described the cut-off value of suPAR, which ranged from 2992.6 to 5500 pg/mL.

RESULTS

The results showed that the suPAR levels in the primary FSGS group were significantly higher when compared with that in the normal control group (p<0.001; standard mean difference (SMD): 2.56; 95% CI 1.85 to 3.28), and significant differences were observed in the secondary FSGS and in the normal control group (p<0.001; SMD: 1.68; 95% CI 1.37 to 1.98). A suPAR concentration of 3000 pg/mL may be the best threshold for the diagnosis of primary FSGS (sensitivity=0.72; specificity=0.88; area under the curve=0.85).

CONCLUSION

Our results suggested that suPAR might be a potential biomarker for predicting primary and secondary FSGS. In addition, our data showed that a suPAR concentration of 3000 pg/mL might be used as a threshold for the diagnosis of FSGS.

TRIAL REGISTRATION NUMBER

CRD42019120948.

Clinical value of soluble urokinase type plasminogen activator receptors in chronic kidney disease

Chronic kidney disease (CKD) will progress to end stage without treatment, the decline off renal function may not linear. A sensitive marker such as soluble urokinase-type plasminogen activator receptors (suPARs) may allow potential intervention and treatment in earlier stages of CKD.

OBJECTIVES

This study was designed to measure plasma (suPAR) in patients with CKD with different stages and to find its correlation with the disease severity.

METHODS

This study was conducted on 114 subjects, 84 were patients with different stages and different causes of CKD, and 30 healthy subjects as controls. Blood urea, serum creatinine, serum high-sensitive C-reactive protein, estimated glomerular filtration rate, and 24 hours proteinuria were measured, renal biopsy was done for all patients, and plasma (suPAR) was measured using enzyme-linked immunosorbent assay.

RESULTS

suPAR plasma levels were significantly higher in patients with CKD (7.9 ± 3.82 ng/mL) than controls (1.76 ± 0.77 ng/mL, P < .001). suPAR correlated with the disease severity. In stage 1 to 2 group, it was 3.7 ± 1.5 ng/mL, in stage 3 to 4, it was 10.10 ± 1.22 ng/mL, and in stage 5 group, it was 12.34 ± 0.88 ng/mL; the difference between the 3 groups was highly significant (P < .001). A cutoff point 2.5 ng/mL of suPAR was found between controls and stage 1 group. According to the cause of CKD, although patients with obstructive cause and those with focal glomerulosclerosis had the higher levels 9.11 ± 3.32 ng/mL and 8.73 ± 3.19 ng/mL, respectively, but there was no significant difference between patients with CKD according to the cause of the CKD.

CONCLUSION

Plasma (suPAR) increased in patients with CKD and correlated with disease severity.

Recurrent and de novo Glomerulonephritis After Kidney Transplantation

The prevalence, pathogenesis, predictors, and natural course of patients with recurrent glomerulonephritis (GN) occurring after kidney transplantation remains incompletely understood, including whether there are differences in the outcomes and advances in the treatment options of specific GN subtypes, including those with de novo GN. Consequently, the treatment options and approaches to recurrent disease are largely extrapolated from the general population, with responses to these treatments in those with recurrent or de novo GN post-transplantation poorly described. Given a greater understanding of the pathogenesis of GN and the development of novel treatment options, it is conceivable that these advances will result in an improved structure in the future management of patients with recurrent or de novo GN. This review focuses on the incidence, genetics, characteristics, clinical course, and risk of allograft failure of patients with recurrent or de novo GN after kidney transplantation, ascertaining potential disparities between “high risk” disease subtypes of IgA nephropathy, idiopathic membranous glomerulonephritis, focal segmental glomerulosclerosis, and membranoproliferative glomerulonephritis. We will examine in detail the management of patients with high risk GN, including the pre-transplant assessment, post-transplant monitoring, and the available treatment options for disease recurrence. Given the relative paucity of data of patients with recurrent and de novo GN after kidney transplantation, a global effort in collecting comprehensive in-depth data of patients with recurrent and de novo GN as well as novel trial design to test the efficacy of specific treatment strategy in large scale multicenter randomized controlled trials are essential to address the knowledge deficiency in this disease.

Clinical features and outcomes of kidney transplant recipients with focal segmental glomerulosclerosis recurrence

AIM

Focal segmental glomerulosclerosis recurs in up to 30% and up to 80% of adult and pediatric kidney transplant recipients, respectively. There is no standard of care treatment. The purpose of this study was to evaluate clinical characteristics, treatments and outcomes of patients with focal segmental glomerulosclerosis recurrence (FSGSr).

METHODS

This was a retrospective single-center cohort study including FSGSr patients treated with plasmapheresis (PP) and combinations of high dose steroids, cyclosporine and rituximab.

RESULTS

Among 61 patients included in this analysis the median time to diagnosis was 19 days. The incidence of first biopsy-confirmed FSGSr was 18% reaching 52.4% with follow-up biopsies. During PP treatment 54% of the patients developed infectious complications. PP was discontinued in 37% of patients due to treatment failure (no remission or graft loss) and in 26% due to an adverse event. All patients who discontinued PP due to adverse event did not show clinical response or lost the allograft. The incidence of acute rejection was 34.4%. The incidences of partial and complete remissions were 16.4% and 27.8%, respectively. Overall 6-years patient and graft survivals were 90.7% and 64.5%, respectively.

CONCLUSION

This analysis confirms the low, variable and unpredictable rate of FSGSr remission, inconsistencies among available therapeutic options and its high rate of adverse events, and the negative impact on graft survival.

Increased Serum Soluble Urokinase-Type Plasminogen Activator Receptor (suPAR) Levels in FSGS: A Meta-Analysis

Introduction

The soluble urokinase-type plasminogen activator receptor (suPAR) has been found to be elevated in primary focal segmental glomerulosclerosis (pFSGS). However, its usefulness as a biomarker for FSGS remains controversial. We conducted a meta-analysis aiming at investigating the significance of suPAR in diagnosing pFSGS.

Methods

Electronic databases (PubMed and EMBASE) were searched to identify studies comparing suPAR levels in FSGS patients and controls, from the earliest available date to May 1, 2018. A random-effects model with standardized mean difference (SMD) was used for meta-analyses. Risk of bias was assessed using the Newcastle-Ottawa quality assessment scale.

Results

A total of 187 articles were screened, and the final analysis included 13 articles. In comparison to healthy controls, serum suPAR levels were significantly increased in pFSGS patients (SMD, 1.07, 95% confidence interval (CI) 0.65 to 1.48; participants = 814; studies = 9, I ² = 85%). Higher suPAR levels were also found in patients with pFSGS compared to those with minimal change disease (SMD 0.53, 95% CI 0.22 to 0.84). Of note, such a difference was not found in pediatric groups (SMD 0.42, 95% CI -0.13 to 0.96) while it was more evidently noted in adult patients (SMD 1.32, 95% CI 0.90 to 1.74). Serum suPAR levels did not differ between pFSGS patients in remission compared to those in active proteinuric state (SMD 0.29, 95% CI -0.30 to 0.88). Comparison with membranous nephropathy and IgA nephropathy showed no significant difference.

Conclusions

Our meta-analysis demonstrated that, in comparison to both healthy controls and controls with minimal change disease, suPAR levels were significantly higher in adult patients with pFSGS. suPAR levels did not differ between pFSGS patients during the initial period of diagnosis and those in remission.

The Search for Biomarkers to Aid in Diagnosis, Differentiation, and Prognosis of Childhood Idiopathic Nephrotic Syndrome

Identification of genes associated with childhood-onset nephrotic syndrome has significantly advanced our understanding of the pathogenesis of this complex disease over the past two decades, however the precise etiology in many cases remains unclear. At this time, we still rely on invasive kidney biopsy to determine the underlying cause of nephrotic syndrome in adults. In children, response to steroid therapy has been shown to be the best indicator of prognosis, and therefore all children are treated initially with corticosteroids. Because this strategy exposes a large number of children to the toxicities of steroids without providing any benefit, many researchers have sought to find a marker that could predict a patient's response to steroids at the time of diagnosis. Additionally, the identification of such a marker could provide prognostic information about a patient's response to medications, progression to end stage renal disease, and risk of disease recurrence following transplantation. Major advances have been made in understanding how genetic biomarkers can be used to predict a patient's response to therapies and disease course, especially after transplantation. Research attempting to identify urine- and serum-based biomarkers which could be used for the diagnosis, differentiation, and prognosis of nephrotic syndrome has become an area of emphasis. In this review, we explore the most exciting biomarkers and their potential clinical applications.

Can components of the plasminogen activation system predict the outcome of kidney transplants?

Proteolytic and antiproteolytic enzymes play a critical role in the physiology and pathology of different stages of human life. One of the important members of the proteolytic family is the plasminogen activation system (PAS), which includes several elements crucial for this review: the 50 kDa glycoprotein plasminogen activator inhibitor 1 (PAI-1) that inhibits tissue-type (tPA) and urokinase-type plasminogen activator (uPA). These two convert plasminogen into its active form named plasmin that can lyse a broad spectrum of proteins. Urokinase receptor (uPAR) is the binding site of uPA. This glycoprotein on the cell surface facilitates urokinase activation of plasminogen, creating high proteolytic activity close to the cell surface. PAS activities have been reported to predict the outcome of kidney transplants. However, reports on expression of PAS in kidney transplants seem to be controversial. On the one hand there are reports that impaired proteolytic activity leads to induction of chronic allograft nephropathy, while on the other hand treatment with uPA and tPA can restore function of acute renal transplants. In this comprehensive review we describe the complexity of the PAS as well as biological effects of the PAS on renal allografts, and provide a possible explanation of the reported controversy.

Nephronectin (NPNT) and the prediction of nephrotic syndrome response to steroid treatment

Steroid-resistant nephrotic syndrome represents about 10-20% of pediatrics' nephrotic syndrome. The regeneration of glomerular barrier seems pivotal for cessation of proteinuria. Nephronectin (NPNT) plays a major role in nephrogenesis, signal transduction, and epithelial-mesenchymal interactions. This study aims to preliminary assess NPNT as potential noninvasive biomarker of glomerular regeneration and its ability to identify steroid resistance. In this case control study, 80 retrospectively selected patients with nephrotic syndrome were enrolled in addition to 40 healthy controls. Forty patients were steroid sensitive (SSNS) and the other 40 patients were steroid-resistant (SRNS), NPTN concentration was measured using ELISA and NPNT mRNA expression was assayed using real-time PCR. NPTN concentrations were significantly higher in SSNS than both SRNS and controls (The means were 4.64 ± 3.05, 0.69 ± 0.44, and 1.63 ± 0.59, respectively). Moreover, NPTN concentrations were significantly lower in SRNS than controls. NPTN was significantly overexpressed in SSNS compared to both SRNS and controls (the means were 10.82 ± 7.39, 1.19 ± 0.94, and 1.04 ± 0.10, respectively) with no statistically significant difference between SRNS and controls. ROC curves analysis showed that both NPNT expression and NPNT serum level are of promising diagnostic performance (ROC_AUC 0.948 and 0.896, respectively). Regression analysis showed that both NPNT expression and NPNT serum level can be independent predictors of steroid resistance. The present study shows for the first time an enhanced expression of NPNT in steroid-sensitive nephrotic syndrome patients suggesting NPNT as a marker of glomerular regeneration. Also, serum NPNT can be a useful noninvasive biomarker of steroid resistance.

[Current insights about recurrence of glomerular diseases after renal transplantation]

Recurrence of glomerular disease after renal transplantation is a frequent cause of graft loss. Incidence, risk factors and outcome of recurrence are widely due to the underlying glomerular disease. Graft biopsy analysis is required to confirm the definitive diagnosis of recurrence and to start an appropriate therapy that, in some cases, remains challenging to prevent graft failure. Increased use of protocol biopsy and recent advances in our understanding of the pathogenesis of some glomerular diseases with the identification of some relevant biomarkers provide a unique opportunity to initiate kidney-protective therapy at early stages of recurrence on the graft. This review summarizes our current knowledge on the management of many recurrent primary and secondary glomerulonephritis after kidney transplantation.

Steroid-resistant nephrotic syndrome: a persistent challenge for pediatric nephrology

Steroid-resistant nephrotic syndrome remains a challenge to treat, but various efforts are underway to better understand the pathogenesis and improve patient outcomes. This review provides an update on the newer advances in understanding the molecular etiologies for a variety of podocyte abnormalities, potential circulating factors that may initiate and sustain the steroid-resistant state, genetic mutations, and precision medicine treatment modalities in this continuously perplexing disorder.

Soluble Urokinase Receptors in Focal Segmental Glomerulosclerosis: A Review on the Scientific Point of View

Focal segmental glomerulosclerosis (FSGS) is one of the primary glomerular disorders in both children and adults which can progress to end-stage renal failure. Although there are genetic and secondary causes, circulating factors have also been regarded as an important factor in the pathogenesis of FSGS, because about 40% of the patients with FSGS have recurrence after renal transplantation. Soluble urokinase-type plasminogen activator receptor (suPAR) is a soluble form of uPAR, which is a membrane-bound protein linked to GPI in various immunologically active cells, including podocytes. It has recently been suggested as a potential circulating factor in FSGS by in vitro podocyte experiments, in vivo mice models, and human studies. However, there have also been controversies on this issue, because subsequent studies showed conflicting results. suPAR levels were also increased in patients with other glomerular diseases and were inversely correlated with estimated glomerular filtration rate. Nevertheless, there has been no balanced review on this issue. In this review, we compare the conflicting data on the involvement of suPAR in the pathogenesis of FSGS and shed light on interpretation by taking into account many points and the potential variables and confounders influencing serum suPAR levels.

Activation of the IL-2 Receptor in Podocytes: A Potential Mechanism for Podocyte Injury in Idiopathic Nephrotic Syndrome?

The renal podocyte plays an important role in maintaining the structural integrity of the glomerular basement membrane. We have previously reported that patients with idiopathic nephrotic syndrome (INS) have increased IL-2 production. We hypothesized that podocytes express an IL-2 receptor (IL-2R) and signaling through this receptor can result in podocyte injury. To confirm the presence of the IL-2R, we tested a conditionally immortalized murine podocyte cell line by flow cytometry, qPCR, and Western blot. To test for the presence of the IL-2R in vivo, immunohistochemical staining was performed on human renal biopsies in children with FSGS and control. Podocytes were stimulated with IL-2 in vitro, to study signaling events via the JAK/STAT pathway. The results showed that stimulation with IL-2 resulted in increased mRNA and protein expression of STAT 5a, phosphorylated STAT 5, JAK 3, and phosphorylated JAK 3. We then investigated for signs of cellular injury and the data showed that pro-apoptotic markers Bax and cFLIP were significantly increased following IL-2 exposure, whereas LC3 II was decreased. Furthermore, mitochondrial depolarization and apoptosis were both significantly increased following activation of the IL-2R. We used a paracellular permeability assay to monitor the structural integrity of a podocyte monolayer following IL-2 exposure. The results showed that podocytes exposed to IL-2 have increased albumin leakage across the monolayer. We conclude that murine podocytes express the IL-2R, and that activation through the IL-2R results in podocyte injury.

Recurrence of Focal and Segmental Glomerulosclerosis After Transplantation

Focal segmental glomerulosclerosis, which is a common glomerular disorder, manifests clinically with a nephrotic syndrome and has a high propensity for recurrence after kidney transplantation. The pathophysiology is currently unknown, and podocytes appear to be the target of one or several circulating factor(s) that lead to the recurrence of proteinuria after kidney transplantation. Identifying these circulating factor(s) and cells involved in its synthesis remains elusive; however, recently, our research on podocyte cytoskeleton biology has opened a new era of treatment. This review will highlight recent progress in the physiopathology of focal segmental glomerulosclerosis recurrence after transplantation and its treatment.

FSGS: Diagnosis and Diagnostic Work-Up

Focal segmental glomerulosclerosis is a histologic lesion, rather than a clinical disease. FSGS is common cause of nephrotic syndrome in both adults and children worldwide. In the United States it is the most common primary glomerular disease resulting in end-stage renal disease and recent reports have suggested that its incidence might be on the rise. Currently the incidence is estimated to be 7 per million. The podocyte is the cellular target cell in FSGS and in recent years substantial insight in the pathogenesis and genetics of FSGS have accumulated. Furthermore the discovery of potential novel biomarkers to diagnose FSGS and monitor disease activity has renewed interest in this disease. In this review article we will focus on the clinical presentation and diagnosis of FSGS.

Primary glomerulonephritides

Most glomerulonephritides, even the more common types, are rare diseases. They are nevertheless important since they frequently affect young people, often cannot be cured, and can lead to chronic kidney disease, including end-stage renal failure, with associated morbidity and cost. For example, in young adults, IgA nephropathy is the most common cause of end-stage renal disease. In this Seminar, we summarise existing knowledge of clinical signs, pathogenesis, prognosis, and treatment of glomerulonephritides, with a particular focus on data published between 2008 and 2015, and the most common European glomerulonephritis types, namely IgA nephropathy, membranous glomerulonephritis, minimal change disease, focal segmental glomerulosclerosis, membranoproliferative glomerulonephritis, and the rare complement-associated glomerulonephritides such as dense deposit disease and C3 glomerulonephritis.

Circulating Permeability Factors in Primary Focal Segmental Glomerulosclerosis: A Review of Proposed Candidates

Primary focal segmental glomerulosclerosis (FSGS) is a major cause of the nephrotic syndrome and often leads to end-stage renal disease. This review focuses on circulating permeability factors in primary FSGS that have been implicated in the pathogenesis for a long time, partly due to the potential recurrence in renal allografts within hours after transplantation. Recently, three molecules have been proposed as a potential permeability factor by different groups: the soluble urokinase plasminogen activator receptor (suPAR), cardiotrophin-like cytokine factor-1 (CLCF-1), and CD40 antibodies. Both CLCF-1 and CD40 antibodies have not been validated by independent research groups yet. Since the identification of suPAR, different studies have questioned the validity of suPAR as a biomarker to distinguish primary FSGS from other proteinuric kidney diseases as well as suPAR's pathogenic role in podocyte damage. Researchers have suggested that cleaved molecules of suPAR have a pathogenic role in FSGS but further studies are needed to determine this role. In future studies, proposed standards for the research of the permeability factor should be carefully followed. The identification of the permeability factor in primary FSGS would be of great clinical relevance as it could influence potential individual treatment regimen.

Circulating suPAR as a biomarker of disease severity in children with proteinuric glomerulonephritis

BACKGROUND

The increase of circulating urokinase plasminogen activator receptor (suPAR) was demonstrated in various diseases showing its prognostic value as well as the link to the inflammatory reaction. In glomerular diseases, suPAR was considered a causative factor of proteinuria. In the present study we aimed to evaluate serum concentration of suPAR in children with primary and secondary glomerulonephritis (GN) and its association with disease severity.

METHODS

The study involved 22 children with minimal change disease (MCD), nine with primary focal segmental glomerulosclerosis (FSGS), seven with Henoch-Schönlein nephritis, seven with lupus nephritis (LN) and 16 controls.

RESULTS

Serum suPAR was significantly higher in children with FSGS and LN than controls (4.47±1.39 ng/mL vs. 3.23±0.76 ng/mL; P=0.011 and 6.17±1.12 ng/mL vs. 3.23±0.76 ng/mL, respectively; P<0.0001). Further, suPAR was increased in LN when compared to FSGS (P=0.031). In the total group suPAR showed negative correlation with eGFR, serum complement C3 and positive with left ventricular mass index. In children with MCD and FSGS the inverse association of suPAR with eGFR was also shown.

CONCLUSIONS

In children with primary and secondary glomerulonephritis suPAR levels are not associated with proteinuria. In primary GN elevated suPAR levels may result from reduced eGFR reflecting renal damage. In LN circulating suPAR can be increased further indicating both multi-organ involvement and systemic inflammation reflecting disease severity.

Update on the treatment of focal segmental glomerulosclerosis in renal transplantation

Focal segmental glomerulosclerosis (FSGS) represents one of the most severe glomerular diseases, with frequent progression to end-stage renal disease and a high rate of recurrence in renal allografts (30%-50%). Recurrent FSGS portends a negative outcome, with the hazard ratio of graft failure being two-fold higher then that of other glomerulonephritis. Two patterns of clinical presentations are observed: Early recurrence, which is characterized by massive proteinuria within hours to days after implantation of the renal graft, and late recurrence, which occurs several months or years after the transplantation. Many clinical conditions have been recognized as risk factors for recurrence, including younger age, rapid progression of the disease to end-stage renal disease on native kidneys, and loss of previous renal allografts due to recurrence. However, much less is known about the incidence and risk factors of the so-called “de novo” type of FSGS, for which sufferers are transplanted patients without disease on native kidneys; but, rapid development of allograft failure is frequently observed. Management of both forms is challenging, and none of the approaches proposed to date have been demonstrated as consistently beneficial or effective. In the present review we report an update on the available therapeutic strategies for FSGS in renal transplantation within the context of a critical overview of the current literature.

The glomerular permeability factors in idiopathic nephrotic syndrome

It is currently postulated that steroid-sensitive idiopathic nephrotic syndrome (SSNS) and steroid-resistant idiopathic nephrotic syndrome (SRNS), which are not related to the mutation of a gene coding for podocyte structures or for glomerular basement membrane proteins, result from a circulating factor affecting podocyte shape and function. T lymphocytes have for a long time been suspected to be involved in the pathophysiology of these diseases. The successful treatment of steroid-dependant nephrotic syndrome with rituximab suggests a potential role for B lymphocytes. Clinical and experimental data indicate roles for cytokines IL-13, TNFα, circulating cardiotrophin-like cytokine factor 1 (member of the IL-6 family), circulating hemopexin, radical oxygen species, and the soluble urokinase-type plasminogen activator receptor (suPAR) in the development of nephrotic syndrome. Podocyte metabolism modifications-leading to the overexpression of the podocyte B7-1antigen (CD 80), hypoactivity of the podocyte enzyme sphingomyelin phosphodiesterase acid-like 3 b (SMPDL3b), and to the podocyte production of a hyposialylated form of the angiopoietin-like 4 (Angptl4)-are mechanisms possibly involved in the changes in the podocyte cytoskeleton leading to SSNS and or SRNS. Different multifactorial pathophysiological mechanisms can be advocated for SSNS and SRNS. The present paper reviews the experimental and clinical data upon which the different hypotheses are based and reports their possible clinical applications.

Long-term Outcomes of Childhood Onset Nephrotic Syndrome

There are limited studies on long-term outcomes of childhood onset nephrotic syndrome (NS). A majority of children with NS have steroid-sensitive nephrotic syndrome (SSNS). Steroid-resistant nephrotic syndrome (SRNS) is associated with a high risk of developing end-stage renal disease. Biomarkers and analysis of genetic mutations may provide new information for prognosis in SRNS. Frequently relapsing and steroid-dependent NS is associated with long-term complications, including dyslipidemia, cataracts, osteoporosis and fractures, obesity, impaired growth, and infertility. Long-term complications of SSNS are likely to be under-recognized. There remain many gaps in our knowledge of long-term outcomes of childhood NS, and further study is indicated.

Full-length soluble urokinase plasminogen activator receptor down-modulates nephrin expression in podocytes

Increased plasma level of soluble urokinase-type plasminogen activator receptor (suPAR) was associated recently with focal segmental glomerulosclerosis (FSGS). In addition, different clinical studies observed increased concentration of suPAR in various glomerular diseases and in other human pathologies with nephrotic syndromes such as HIV and Hantavirus infection, diabetes and cardiovascular disorders. Here, we show that suPAR induces nephrin down-modulation in human podocytes. This phenomenon is mediated only by full-length suPAR, is time-and dose-dependent and is associated with the suppression of Wilms’ tumor 1 (WT-1) transcription factor expression. Moreover, an antagonist of αvβ3 integrin RGDfv blocked suPAR-induced suppression of nephrin. These in vitro data were confirmed in an in vivo uPAR knock out Plaur^−/− mice model by demonstrating that the infusion of suPAR inhibits expression of nephrin and WT-1 in podocytes and induces proteinuria. This study unveiled that interaction of full-length suPAR with αvβ3 integrin expressed on podocytes results in down-modulation of nephrin that may affect kidney functionality in different human pathologies characterized by increased concentration of suPAR.

A circulating permeability factor in focal segmental glomerulosclerosis: the hunt continues

Primary focal segmental glomerulosclerosis (FSGS) is one of the major causes of steroid-resistant nephrotic syndrome, and renal prognosis in patients with steroid-resistant FSGS is poor. It has been long speculated that a circulating permeability factor should be implicated in the pathogenesis of the disease because a substantial portion of the patients with primary FSGS experience recurrence shortly after transplantation. Although molecules such as cardiotrophin-like cytokine 1 (CLC-1) and anti-CD40 antibody have been proposed to be potential circulating permeability factors, a definitive factor remains to be discovered. Soluble urokinase-type plasminogen activator receptor (suPAR) has attracted substantial attention and garnered scrutiny by renal researchers since Reiser's group suggested that it was linked to the pathogenesis of primary FSGS and that it might be useful as a diagnostic biomarker. A number of different cohort studies have shown that serum suPAR levels are negatively associated with renal function and can scarcely differentiate FSGS from the other glomerular/renal diseases. In contrast to initial studies, several in vivo studies investigating the effects of forced suPAR upregulation could not show the induction of proteinuria or podocyte injury. Currently it is suggested that a different form of suPAR, which cannot be measured by presently available enzyme-linked immunosorbent assay, might be the culprit; however, it remains to be determined whether this is the case. Because a circulating permeability factor might be a useful biomarker for diagnosing FSGS as well as a potent therapeutic target for primary and recurrent FSGS, further dedicated work will be needed.

Urokinase plasminogen activator receptor and its soluble form in common biopsy-proven kidney diseases and in staging of diabetic nephropathy

OBJECTIVES

Soluble urokinase plasminogen activator receptor (suPAR), derived from membrane bound uPAR, is associated with inflammatory diseases. In the present study, we explored the expression of uPAR/suPAR in common biopsy-proven kidney diseases and the relationship between suPAR and staging of type 2 diabetic nephropathy (DN).

DESIGN AND METHODS

Serum samples for suPAR and renal tissues for uPAR staining were investigated in various common kidney diseases. The levels of serum suPAR were measured and adequate cut-off values of different stage of DN were calculated by receiver operating characteristic (ROC) curve.

RESULTS

In our results, the expression of uPAR on renal tissues was pronounced in the majority of kidney diseases. Comparing of expression of uPAR among different kidney diseases, it was strongest in minimal change disease (MCD) and weakest in chronic interstitial nephritis. Serum suPAR in most kidney diseases, except of MCD, was significantly elevated and was highest in DN. As for DN and suPAR, we found that suPAR progressively increased with staging of DN. Moreover, suPAR was linearly and negatively related to estimated glomerular filtration rate and positively related to the amount of proteinuria. By ROC curve, the cut-off values of suPAR in DN for assessing development increased with the progression of the disease.

CONCLUSIONS

We concluded that uPAR/suPAR is elevated in most kidney diseases and that suPAR is a useful biomarker for assessing stages of DN.

A case report of adrenocorticotropic hormone to treat recurrent focal segmental glomerular sclerosis post-transplantation and biomarker monitoring

Background: Recurrent focal segmental glomerular sclerosis (rFSGS) in renal transplant recipients (RTR) is difficult to predict and treat. Early rFSGS is likely from circulating factors and preformed antibodies.

Methods: We present the case of a 23-year-old white man who presented with rFSGS and acute renal failure, requiring dialysis 9-months after a 1-haplotype matched living-related transplant. We retrospectively analyzed serum samples from various clinical stages for rFSGS biomarkers: serum glomerular albumin permeability (P_alb), soluble urokinase-type plasminogen activator receptor (suPAR) serum level with suPAR-β3 integrin signaling on human podocytes, and angiotensin II type I receptor-antibody (AT1R-Ab) titer.

Results: All biomarkers were abnormal at 1-year pre-transplant prior to initiation of dialysis and at the time of transplant. After initiation of hemodialysis, β3 integrin activity on human podocytes, in response to patient serum, as well as AT1R-Ab were further elevated. At the time of biopsy-proven recurrence, all biomarkers were abnormally high. One week after therapy with aborted plasmapheresis (secondary to intolerance), and high dose steroids, the P_alb and suPAR-β3 integrin activity remained significantly positive. After 12-weeks of treatment with high-dose steroids, rituximab, and galactose, the patient remained hemodialysis-dependent. Three-months after his initial presentation, we commenced adrenocorticotropic hormone (ACTH, Acthar^® Gel), 80 units subcutaneously twice weekly. Four-weeks later, he was able to discontinue dialysis. After 8-months of maintenance ACTH therapy, his serum creatinine stabilized at 1.79 mg/dL with <1 g of proteinuria.

Conclusion: ACTH therapy was associated with improvement in renal function within 4 weeks. The use of rFSGS biomarkers may aid in predicting development of rFSGS.

Recent advances in the understanding of immune-mediated nephrotic syndrome: diagnostic and prognostic implications

Glomerular diseases with severe defects in glomerular permeability give rise to heavy proteinuria and can present as nephrotic syndrome. There are many different causes of the nephrotic syndrome and a renal biopsy is nearly always needed to elucidate the underlying disease. During the last decade, substantial advances have occurred in the understanding of the pathophysiological mechanisms involved in immune-mediated glomerular diseases. Here, we review the diagnostic and prognostic implications of recent progress on the understanding of membranous nephropathy, minimal change disease, focal segmental glomerulosclerosis, amyloidosis, IgA nephropathy and membranoproliferative glomerulonephritis.

Novel therapies for FSGS: preclinical and clinical studies

Focal segmental glomerulosclerosis (FSGS) is a rare but important cause of end-stage kidney disease in children and adults. Current therapy, consisting of corticosteroids and calcineurin inhibitors, fails to achieve a sustained remission in most patients. Therefore, there is a pressing need to develop new treatments for this glomerulopathy. Traditional approaches have focused on agents that modulate the immune system. In this review, we summarize preclinical and clinical data with newer agents that may ameliorate FSGS. We focus on drugs that inhibit immune injury or inflammation, such as abatacept, rituximab, adalimumab, and stem cells. The potential of agents that block the glomerular action of circulating permeability factors such as soluble urokinase receptor is reviewed. Finally, because fibrosis represents the final common pathway of glomerular damage in FSGS, the experience with a wide range of antifibrotic agents is presented. Despite extensive research on the podocyte dysfunction in the pathogenesis of FSGS, there are few agents that directly target podocyte structure or viability. We conclude that FSGS is a heterogeneous disorder and that intensified translational research is vital to improve our understanding of distinct subtypes that have a defined prognosis and predictable response to targeted therapeutic interventions.

Serum suPAR levels help differentiate steroid resistance from steroid-sensitive nephrotic syndrome in children

BACKGROUND

Soluble urokinase plasminogen activator receptor (suPAR) has been regarded as a permeability factor in proteinuria, though its role in primary nephrotic syndrome remains to be elucidated further.

METHODS

Plasma samples and clinical information from 176 children with primary nephrotic syndrome were collected and concentrations of suPAR were measured. We evaluated the correlation between suPAR concentrations and clinical features, and the value of the plasma suPAR level in predicting steroid-resistant nephrotic syndrome (SRNS).

RESULTS

There is a significant difference in plasma suPAR concentration between SRNS and steroid-sensitive nephrotic syndrome (SSNS) groups (3,744.1 ± 2,226.0 vs. 2,153.5 ± 1,167.0, p < 0.05). The area under the curve (AUC) was 0.80, with p < 0.001 for the receiver operating characteristic (ROC) curve analysis using suPAR to predict SRNS. The suspicious range for predicting SRNS was estimated to be 1,907.0 pg/ml to 3,043.5 pg/ml (χ(2) = 14.775, p = 0.001).

CONCLUSIONS

From ROC curve analysis, we demonstrated the significance of the suPAR level in predicting SRNS with a high specificity but low sensitivity. However, the clinical value of suPAR to predict steroid resistance and guide therapy remains to be investigated further.

Clinical significance of serum and urinary soluble urokinase receptor (suPAR) in primary nephrotic syndrome and MPO-ANCA-associated glomerulonephritis in Japanese

BACKGROUND

The soluble urokinase receptor (suPAR) has been implicated as a cause of primary focal segmental glomerulosclerosis (FSGS). However, the clinical significance of suPAR in glomerular diseases currently remains unclear.

METHODS

In this retrospective single-center cohort study, we investigated serum (s-) and urinary (u-) suPAR in patients with primary nephrotic syndrome (NS) (serum/urine: 37/32 cases) and MPO-ANCA-associated glomerulonephritis (ANCA-GN) (serum/urine: 13/11 cases).

RESULTS

In pretreatment s- and u-suPAR, no significant differences were observed between the primary NS and ANCA-GN groups or among the pathological types of primary NS. An inverse correlation was noted between pretreatment s-suPAR and eGFR in the primary NS and ANCA-GN groups. A positive correlation was noted between pretreatment u-suPAR and proteinuria in the primary NS group. Furthermore, time-course changes in s- and u-suPAR over 2 months after therapy were associated with the therapeutic responsiveness of primary NS, particularly the differentiation of MCNS from FSGS (s-suPAR: AUC-ROC = 0.905, p = 0.007; u-suPAR: AUC-ROC = 0.816, p = 0.048). In the ANCA-GN group, a positive correlation was found between pretreatment s-suPAR and clinical severity or crescent formation, whereas u-suPAR was not correlated with these parameters.

CONCLUSION

S- and u-suPAR after therapy may serve as clinical markers to judge the treatment response of untreated NS and differentiate MCNS from FSGS, but not in pretreatment patients. S-, but not u-suPAR may predict the severity of and crescent formation in ANCA-GN.

Causes and pathogenesis of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) describes both a common lesion in progressive kidney disease, and a disease characterized by marked proteinuria and podocyte injury. The initial injuries vary widely. Monogenetic forms of FSGS are largely due to alterations in structural genes of the podocyte, many of which result in early onset of disease. Genetic risk alleles in apolipoprotein L1 are especially prevalent in African Americans, and are linked not only to adult-onset FSGS but also to progression of some other kidney diseases. The recurrence of FSGS in some transplant recipients whose end-stage renal disease was caused by FSGS points to circulating factors in disease pathogenesis, which remain incompletely understood. In addition, infection, drug use, and secondary maladaptive responses after loss of nephrons from any cause may also cause FSGS. Varying phenotypes of the sclerosis are also manifest, with varying prognosis. The so-called tip lesion has the best prognosis, whereas the collapsing type of FSGS has the worst prognosis. New insights into glomerular cell injury response and repair may pave the way for possible therapeutic strategies.

Serum suPAR levels are modulated by immunosuppressive therapy of minimal change nephrotic syndrome

BACKGROUND

Soluble urokinase-type plasminogen activator receptor (suPAR) could be a causative factor in idiopathic focal segmental glomerulosclerosis (FSGS). It is currently unknown to what extent suPAR levels could be affected by treatment with immunosuppressive drugs such as cyclosporin A (CsA) and mycophenolate mofetil (MMF). Treatment with CsA, but not MMF, is accompanied by nephrotoxicity, and since suPAR levels correlate with glomerular filtration rate (GFR), treatment with these drugs could indirectly modulate suPAR levels by their effect on renal function.

METHODS

We measured suPAR levels in a recent prospective multicenter crossover trial comparing the efficacy of MMF and CsA in pediatric patients with minimal change disease (MCD) and frequently relapsing steroid-sensitive nephrotic syndrome (FR-SSNS). All patients had biopsy-proven MCD and normal renal function; they were treated with each drug for 1 year in a crossover study design. Serum suPAR levels were measured before and after 1 year of therapy with MMF (n = 40) and CsA (n = 35).

RESULTS

The suPAR levels decreased after 1 year of treatment with MMF (p < 0.05). Conversely, suPAR levels increased after 1 year of treatment with CsA in the same patients (p = 0.01). These changes in suPAR levels were not correlated to the estimated glomerular filtration rate (eGFR) or changes in the GFR.

CONCLUSIONS

Data from this prospective randomized trial suggest that treatment with MMF and CsA is associated with different effects on suPAR levels in children with MCD and that these are independent of their effects on GFR.

A reassessment of soluble urokinase-type plasminogen activator receptor in glomerular disease

It has been suggested that soluble urokinase receptor (suPAR) is a causative circulating factor for and a biomarker of focal and segmental glomerulosclerosis (FSGS). Here we undertook validation of these assumptions in both mouse and human models. Injection of recombinant suPAR in wild-type mice did not induce proteinuria within 24 hours. Moreover, a disease phenotype was not seen in an inducible transgenic mouse model that maintained elevated suPAR concentrations for 6 weeks. Plasma and urine suPAR concentrations were evaluated as clinical biomarkers in 241 patients with glomerular disease from the prospective, longitudinal multi-center observational NEPTUNE cohort. The serum suPAR concentration at baseline inversely correlated with estimated glomerular filtration rate (eGFR) and the urine suPAR/creatinine ratio positively correlated with the urine protein/creatinine ratio. After adjusting for eGFR and urine protein, neither the serum nor urine suPAR level was an independent predictor of FSGS histopathology. A multivariable mixed-effects model of longitudinal data evaluated the association between the change in serum suPAR concentration from baseline with eGFR. After adjusting for baseline suPAR concentration, age, gender, proteinuria and time, the change in suPAR from baseline was associated with eGFR, but this association was not different for patients with FSGS as compared to other diagnoses. Thus, these results do not support a pathological role for suPAR in FSGS.

Relationship between serum soluble urokinase plasminogen activator receptor level and steroid responsiveness in FSGS

BACKGROUND AND OBJECTIVES

Soluble urokinase plasminogen activator receptor (suPAR) was initially proposed as a pathogenic and predictive biomarker of primary FSGS, but the findings were controversial. This study aimed to clarify the clinical implications of suPAR.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The study enrolled 109 patients with biopsy-proven primary FSGS who were administered prednisone between January 2011 and May 2013 and followed up for 6-24 months (median duration of follow-up, 12 months). Ninety-six healthy volunteers, 20 patients with minimal-change disease (MCD), and 22 patients with membranous nephropathy (MN) served as controls. Serum suPAR levels were measured using ELISA.

RESULTS

suPAR levels in patients with FSGS (median, 3512 [interquartile range (IQR), 2232-4231] pg/ml) were significantly higher than in healthy controls (median, 1823 [IQR, 1563-2212] pg/ml; P<0.001), patients with MCD (median, 1678 [IQR, 1476-2182] pg/ml; P<0.001), and patients with MN (median, 1668 [IQR, 1327-2127] pg/ml; P<0.001). With 3000 pg/ml used as a threshold, suPAR levels were elevated in 48.6% of patients with FSGS, in contrast to 5% of patients with MCD and 4.5% of those with MN. suPAR levels were independently associated with steroid response in patients with FSGS (odds ratio, 85.02; P=0.001). Patients who were sensitive to steroids had significantly higher suPAR levels than nonsensitive patients (median, 3426 [IQR, 2670-5655] pg/ml versus 2523 [IQR, 1977-3460] pg/ml; P=0.001). A suPAR level of 3400 pg/ml was chosen as the optimal cutoff value for steroid response. At the 6-month follow-up in 84 patients with FSGS, suPAR levels were significantly decreased in those with suPAR level ≥ 3400 pg/ml (median, 4553 [IQR, 3771-6120] pg/ml versus 3149 [IQR, 2278-3953]; P=0.002) but were unchanged in patients with suPAR level <3400 pg/ml (median, 2359 [IQR, 2023-2842] pg/ml versus 2490 [IQR, 1916-3623] pg/ml; P=0.09).

CONCLUSIONS

suPAR is specifically elevated in some patients with FSGS, which differs from the finding in patients with MCD and MN. A suPAR assay may help predict steroid response in patients with primary FSGS.

Decreased glomerular filtration as the primary factor of elevated circulating suPAR levels in focal segmental glomerulosclerosis

BACKGROUND

Circulating factor(s) has been thought to be the underlying cause of focal segmental glomerulosclerosis (FSGS), and recent studies foster this idea by demonstrating increased soluble urokinase receptor (suPAR) levels in the serum of FSGS patients.

METHODS

To explore the possible contribution of suPAR in FSGS pathogenesis, we analyzed serum suPAR levels in 17 patients with FSGS and compared them with those in patients with steroid-sensitive nephrotic syndrome, chronic glomerulonephritis, or non-glomerular kidney diseases.

RESULTS

Serum suPAR levels in patients with FSGS were higher than those in patients with steroid-sensitive nephrotic syndrome or chronic glomerulonephritis, but not higher than those in patients with non-glomerular kidney diseases. suPAR levels negatively correlate with estimated glomerular filtration rate and were decreased after renal transplantation in patients with FSGS as well as in those with non-glomerular kidney diseases. Furthermore, 6 FSGS patients with post-transplant recurrence demonstrated that suPAR levels were not high during the recurrence.

CONCLUSIONS

Based on our results, elevated suPAR levels in FSGS patients were attributed mainly to decreased glomerular filtration. These data warrant further analysis for involvement of possible circulating factor(s) in FSGS pathogenesis.