Kidney diseases are among the most prevalent conditions worldwide, impacting over 850 million individuals. They are categorized into acute kidney injury and chronic kidney disease. Current preclinical and clinical trials have demonstrated that endothelin (ET) is linked to the onset and progression of kidney disease. In kidney diseases, pathological conditions such as hyperglycemia, acidosis, insulin resistance, and elevated angiotensin II levels lead to an increase in ET. This elevation activates endothelin receptor type A, resulting in harmful effects like proteinuria and a reduced glomerular filtration rate (GFR). Therefore, to slow the progression of kidney disease, endothelin receptor antagonists (ERAs) have been proposed as promising new therapies. Numerous studies have demonstrated the efficacy of ERAs in significantly reducing proteinuria and improving GFR, thereby slowing the progression of kidney diseases. This review discusses the mechanisms of action of ERAs in treating kidney disease, their efficacy and safety in preclinical and clinical studies, and explores future prospects for ERAs.

Recent studies discovered the prominent presence of anti-nephrin autoantibodies in minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS). However, widely different, and often unconventional autoantibody detection methods were used in these studies, making it challenging to standardize anti-nephrin antibody detection and quantification across different studies.

Here, we compare methods of conventional ELISA, immunoprecipitation (IP)- based on-beads ELISA, immunoprecipitation-Western blotting (IP-WB), and cell- and tissue-based immunofluorescence staining with two cohorts totaling 169 patients and control individuals.

Different assay methods and antigen preparations led to method-specific false-positive and false-negative results. In general, high-quality antigens produced in human cells, combined with IP-based assays, yielded the most robust and reliable results. Among 63 and 24 samples from patients with FSGS or MCD, respectively, two patients with FSGS showed strong antibody signals in both ELISA-based assays and IP-WB, while approximately half of patients with MCD had weak signals detectable only by IP-WB.

These findings highlight the importance of standardizing antibody detection methods.

Disease recurrence after kidney transplantation (KTx) remains a major challenge in patients with primary focal segmental glomerulosclerosis (pFSGS). Antibodies targeting the slit diaphragm protein nephrin have been identified in patients with early disease recurrence. Here, we describe monitoring and effective pre-transplant elimination of anti-nephrin antibodies in an adolescent with pFSGS prior to living-donor KTx.

Anti-nephrin antibodies were assessed in pre- and post-transplant serum samples by ELISA, Western blot and immunoprecipitation using three different nephrin proteins.

Pre-transplant treatment including rituximab and repetitive therapeutic plasma exchanges resulted in effective and sustainable reduction of anti-nephrin antibodies. Allograft function has remained excellent without albuminuria over a follow-up of more than one year. Further analysis showed, that the antibodies were cross-reactive with NEPH3 (filtrin), another key slit diaphragm protein.

Monitoring and pre-transplant elimination of anti-slit diaphragm antibodies may become a standard, personalized approach in patients with pFSGS requiring KTx.

Primary focal segmental glomerulosclerosis is a glomerular disorder associated with a high risk of recurrence after transplantation. Compelling evidence supports the existence of circulating permeability factors whose identity remains elusive. In the current issue of Kidney International, Gupta et al. propose that kidney organoid can respond to these factors in patients with focal segmental glomerulosclerosis and may serve as a potential platform for predicting disease recurrence. Future studies are required to identify the critical factors driving focal segmental glomerulosclerosis recurrence and to develop a standardized organoid platform for predicting clinical outcome.

Primary focal segmental glomerulosclerosis (pFSGS) is an acquired kidney disorder that frequently leads to kidney failure and confers an elevated risk of recurrence after kidney transplantation, termed recurrent pFSGS. Unfortunately, there is no diagnostic method to foresee recurrence of pFSGS after kidney transplantation. Progress in developing assays to test disease activity is hampered by few preclinical models to replicate disease and inability of in vitro cultured primary podocytes to remain terminally differentiated. In recent years, advancements in kidney organoid biology have led to the development of kidney tissues with glomeruli and major nephron segments including podocytes. To develop a pFSGS model, we studied the effect of plasma from patients diagnosed with pFSGS on kidney organoids differentiated from human pluripotent stem cells. The pFSGS plasma treatment induced podocytopathy, extracellular matrix protein deposition, fibrosis and apoptosis within organoids, whereas non-recurrent plasma did not affect organoid structure. pFSGS plasma also led to loss of normal expression patterns of podocyte specific proteins, nephrin and podocin within podocytes. Further, cytokine array profiling revealed that pFSGS plasma induced secretion of cytokines associated with inflammation and angiogenesis. Additionally, kidney organoids treated with plasma obtained after therapeutic plasma exchange for recurrent pFSGS led to lower cell death in organoids after sequential exchanges with the final exchange showing the least apoptotic cells without morphological abnormality. Overall, our results demonstrate the potential of kidney organoids in advancing kidney disease modeling. These insights could be applied in clinical settings to assist in gauging FSGS recurrence risk prior to kidney transplantation.

Primary Focal Segmental Glomerulosclerosis (FSGS) is an important cause of end-stage renal disease (ESRD). Primary FSGS recurrence rates in transplanted kidneys are high, with 25-50% in first transplants and up to 80% in second transplants, often leading to graft loss. To investigate the molecular and cellular events underlying recurrent primary FSGS (reFSGS), we performed single-nucleus RNA sequencing (snRNA-seq) on kidney transplant biopsies from patients with reFSGS and controls with normal allograft function. Our analysis revealed that podocyte loss in reFSGS is driven by metabolic and structural dysregulation rather than apoptosis. Overexpression of vascular endothelial growth factor (VEGF)-A by podocytes was observed, potentially disrupting glomerular endothelial cell growth and permeability. Parietal epithelial cells (PECs) exhibited dedifferentiation towards a podocyte-like state, potentially compensating for podocyte loss, but this was associated with increased collagen deposition and glomerular sclerosis. Ligand-receptor interactions between glomerular cells and B cells further promoted extracellular matrix deposition and fibrosis. Additionally, tubular cells demonstrated evidence of tubular sclerosis and impaired regenerative potential, accompanied by increased interactions with T cells. These findings provide novel insights into the pathogenesis of reFSGS and identify potential therapeutic targets. This study establishes a foundation for future research to further investigate cell-type-specific interventions in recurrent FSGS.

The structural and functional integrity of glomerular cells is critical for maintaining normal kidney function. Glomerular diseases, which involve chronic histological damage to the kidney, are related to injury to glomerular cells such as endothelial cells, mesangial cells (MCs), and podocytes. When faced with pathogenic conditions, these cells release pro-inflammatory cytokines such as chemokines, inflammatory factors, and adhesion factors. These substances interact with glomerular cells through specific inflammatory pathways, resulting in damage to the structure and function of the glomeruli, ultimately causing glomerular disease. Although the role of inflammation in chronic kidney diseases is well known, the specific molecular pathways that result in glomerular diseases remain largely unclear. For a long time, it has been believed that only immune cells can secrete inflammatory factors. Therefore, targeted therapies against immune cells were considered the first choice for treating inflammation in glomerular disease. However, emerging research indicates that non-immune cells such as glomerular endothelial cells, MCs, and podocytes can also play a role in renal inflammation by releasing inflammatory factors. Similarly, targeted therapies against glomerular cells should be considered. This review aims to uncover glomerular diseases related to inflammation and pathways in glomerular inflammation, and for the first time summarized that non-immune cells in the glomerulus can participate in glomerular inflammatory damage by secreting inflammatory factors, providing valuable references for future strategies to prevent and treat glomerular diseases. More importantly, we emphasized targeted glomerular cell therapy, which may be a key direction for the future treatment of glomerular diseases.

Predicting the risks of progression to chronic kidney disease (CKD) stage 5 in idiopathic nephrotic syndrome (NS) and recurrence of the disease (rNS) following kidney transplantation (KT) is a key assessment to provide essential management information. NS has been categorized etiologically as genetic and immune-based. A genetic cause can be identified in ~ 30% of children with steroid-resistant NS (SRNS), a finding associated with a very low risk of rNS following KT. In immune-based NS, clinical overlap is observed among steroid-sensitive NS, secondary-resistant NS, and SRNS not associated with disease-causing genetic variants (non-monogenic SRNS). While ~ 50% of SRNS patients with no identified monogenic disease respond to intensified immunosuppressive treatments, the ones that do not respond to this therapy have a high risk of progression to CKD stage 5 and post-KT rNS. Secondary-resistant patients who progress to CKD stage 5 display the highest risk of post-KT rNS. The proposed shared underlying mechanism of the immune-based NS associated with post-KT rNS is based on a systemic circulating factor (CF) that affects glomerular permeability by inducing foot process effacement and focal segmental glomerulosclerosis. However, identifying patients without a detected genetic form who will recur post-KT is a major challenge. Extensive efforts, therefore, have been made to identify CFs and biomarkers potentially capable of predicting the risk of progression to CKD stage 5 and post-KT rNS. This review discusses the in vitro and in vivo approaches employed to date to identify and characterize potential CFs and CF-induced biomarkers of recurrent NS and offers an assessment of their potential to improve outcomes of KT in this patient population.

Podocytes express large-conductance Ca2+-activated K+ channels (BK channels) and at least two different pore-forming KCa1.1 subunit C-terminal splice variants, known as VEDEC and EMVYR, along with auxiliary β and γ subunits. Podocyte KCa1.1 subunits interact directly with TRPC6 channels and BK channels become active in response to Ca2+ influx through TRPC6. Here, we confirmed that Ca2+ influx through TRPC channels is reduced following the blockade of BK channels by paxilline. The overall abundance of KCa1.1 subunits, as well as that of β4 and γ3 subunits, were increased in glomeruli isolated from Sprague Dawley rats during chronic puromycin aminonucleoside (PAN) nephrosis. Exposing cultured mouse podocytes for 24 h to recombinant TNFα, a circulating factor implicated in pediatric nephrotic syndromes, did not affect the total abundance of KCa1.1, but did evoke significant increases in both β4 and γ3. However, TNFα evoked a marked increase in the surface abundance of KCa1.1 subunits, similar to that of its previously reported effects on TRPC6 channels. The effect of TNFα on the surface expression of KCa1.1 was eliminated following siRNA knockdown of the β4 subunits, suggesting a role for this subunit in KCa1.1 trafficking to the cell surface. By contrast, treating podocytes with suPAR did not affect the total or surface expression of KCa1.1. The coordinated activation of KCa1.1 channels may promote Ca2+ influx through TRPC channels during normal and abnormal podocyte function by maintaining a membrane potential that allows for the efficient permeation of divalent cations through TRPC pores.

Primary Focal and Segmental glomerulosclerosis (FSGS) is one of the most common causes of idiopathic nephrotic syndrome. Our aim was to describe a large cohort of patients with primary FSGS, identify risk factors associated with worse renal survival and assess the impact of different immunosuppressive regiments on renal survival.

This was a historical cohort study of adults who were diagnosed with primary FSGS from March 26, 1982, to September 16, 2020. The primary outcome was progression to ESRD.

We included 579 patients. The mean age was 46 (±15) years of age, with 378 (65%) males and median 24-hour proteinuria was 3.8 (2-6) g. In multivariable analysis only eGFR (HR: 0.97 per ml/min increase, 95% CIs 0.95-0.98) and remission status (complete remission (HR: 0.03, 95% CIs 0.003-0.22) and partial remission (HR: 0.28, 95% CIs 0.13-0.61) compared to no remission) were associated with renal survival. Among patients who received immunosuppression compared to those that did not, there was a higher percentage of complete remission (121 (41%) vs. 40 (24%), p<0.001), and higher percentage of relapses (135 (64%) vs. 27 (33%), p<0.001). Immunosuppression and its type (glucocorticoids vs. cyclosporine ± glucocorticoids) were not associated with renal survival.

In primary FSGS, complete and partial remission were associated with improved renal survival. Further randomized studies are needed to assess the efficacy of different therapeutic agents and guide treatment.

Follicular helper T (Tfh) cells have been implicated in the pathophysiology of numerous diseases. This study investigated the hypothetical function of peripheral blood IL-21+ Tfh cells in the etiology of focal segmental glomerulosclerosis (FSGS). Tfh cell subsets were identified via flow cytometry in PBMCs from 15 patients with FSGS and 9 healthy controls (HCs). Moreover, a cytometric bead array (CBA) was used to determine the level of IL-21 in the serum. The proportions of IL-21+ cTfh cells, IL-21+ PD-1+ cTfh cells and serum IL-21 were lower in FSGS patients than in HCs. In FSGS patients, the serum IL-21 concentration was positively correlated with the frequency of IL-21+ cTfh cells and IL-21+ PD-1+ cTfh cells. The frequencies of IL-21+ cTfh cells and IL-21+ PD-1+ cTfh cells were negatively associated with 24-h urine protein but positively correlated with eGFR, serum albumin and serum IgG. CONCLUSIONS: An aberrant frequency of IL-21+ Tfh cells was detected in FSGS patients, which may provide a better understanding of FSGS pathogenesis.

Circulating anti-podocyte antibodies have been proposed as potential factors contributing to increased permeability in primary podocytopathies, such as Minimal Change Disease (MCD) and Focal Segmental Glomerulosclerosis (FSGS). The aim of the study was to to assess the levels of antibodies targeting synaptopodin and annexin 1 in the blood serum of patients diagnosed with nephrotic syndrome, with the aim of evaluating their potential utility in diagnosing primary podocytopathies and predicting therapeutic response.

The study included a total of 72 patients diagnosed with nephrotic syndrome, alongside 21 healthy subjects for comparison. Among the patients, 38 were diagnosed with FSGS, 12 with MCD, and 22 with MN. The levels of anti-synaptopodin and anti-annexin-1 antibodies were quantified using Enzyme-Linked Immunosorbent Assay.

The levels of antibodies to annexin 1 and anti-synaptopodin in the blood were found to be higher in patients diagnosed with MCD and FSGS compared to those with MN and healthy individuals. The elevated levels of antibodies to annexin 1 and synaptopodin showed area under the curve values of 0.826 (95% CI 0.732-0.923) and 0.827 (95% CI 0.741-0.879), respectively. However, a model incorporating both antibodies demonstrated higher sensitivity (80.9%) and specificity (81.3%) with an AUC of 0.859 (95% CI 0.760-0.957). Notably, serum levels of annexin 1 and anti-synaptopodin antibodies did not predict the response to prednisolone and/or CNI therapy.

Levels of antibodies targeting synaptopodin and annexin 1 were notably elevated in patients diagnosed with MCD and FSGS compared to those with MN and healthy controls. A panel comprising both antibodies demonstrated moderate to high sensitivity and specificity for diagnosis MCD or FSGS.

The etiologies of podocyte dysfunction that lead to pediatric nephrotic syndrome (NS) are vast and vary with age at presentation. The discovery of numerous novel genetic podocytopathies and the evolution of diagnostic technologies has transformed the investigation of steroid-resistant NS while simultaneously promoting the replacement of traditional morphology-based disease classifications with a mechanistic approach. Podocytopathies associated with primary and secondary steroid-resistant NS manifest as diffuse mesangial sclerosis, minimal change disease, focal segmental glomerulosclerosis, and collapsing glomerulopathy. Molecular testing, once an ancillary option, has become a vital component of the clinical investigation and when paired with kidney biopsy findings, provides data that can optimize treatment and prognosis. This review focuses on the causes including selected monogenic defects, clinical phenotypes, histopathologic findings, and age-appropriate differential diagnoses of nephrotic syndrome in the pediatric population with an emphasis on podocytopathies.

Recent studies discovered the prominent presence of anti-nephrin autoantibodies in minimal change disease, steroid-sensitive nephrotic syndrome and/or post-transplant recurrent focal segmental glomerulosclerosis (FSGS). However, widely different, and often unconventional autoantibody detection methods were used among these studies, making it challenging to assess the pathogenic role for the antibodies. Here we examined methods of conventional ELISA, magnetic on-beads ELISA, immunoprecipitation-immunoblotting (IP-IB), and cell- and tissue-based antibody assays with 127 plasma samples of kidney and non-kidney diseases. On the antigen side, we compared commercially available recombinant human nephrin extracelluar domain (ECD) produced from human or mouse cell lines, as well as lab-made full length, ECD, and series of ECD truncates for measuring autoantibody reactivity and specificity. Surprisingly, different assay methods and different antigen preparations led to observation of assay-specific false-positive and false-negative results. In general, a set of tests that combines magnetic beads-enhanced ELISA, followed by IP-IB, and epitope mapping showed the most robust results for anti-nephrin autoantibodies, detected in two primary FSGS patients among all cases tested. It is interesting to note that cell/tissue-based results, also supported by antigen truncation studies, clearly suggest steric hindrance of reactive epitopes, as in full length nephrin that forms compact self-associated complexes. In conclusion, anti-nephrin positivity is rare among the tested patients (2/127), including those with FSGS (2/42), and autoantibody results can be affected by the choice of detection methods.

Glomeruli can be damaged in several conditions after kidney transplantation, with a potential impact on the graft function and survival. Primary glomerulonephritis, a group of glomerular immunological damage that results in variable histological patterns and clinical phenotypes, can occur in kidney transplant recipients as a recurrent or de novo condition. Specific immunologic conditions associated with kidney transplantation, such as acute rejection episodes, can act as an additional trigger after transplantation, impacting the incidence of these glomerulopathies. The post-transplant GN recurrence ranges from 3% to 15%, varying according to the GN subtype and post-transplant time, mainly occurring after 3-5 years of kidney transplantation. Advances in the knowledge of glomerulonephritis pathophysiology have provided new approaches to pre-transplant risk evaluation and post-transplant monitoring. Glomeruli can be affected by several systemic viral infections, such as human immunodeficiency virus (HIV), hepatitis C virus (HCV), hepatitis B virus (HBV), severe acute respiratory syndrome coronavirus 2 (SARS-COV-2), cytomegalovirus (CMV), and BK virus. The diagnosis of these infections, as well as the identification of possible complications associated with them, are important to minimize the negative impacts of these conditions on kidney transplant recipients' outcomes.

Recurrent forms of primary focal segmental glomerulosclerosis (FSGS) pose an unmet challenge to nephrologists, both in terms of understanding the underlying pathophysiology and in terms of identifying an effective management strategy of this disease, which frequently leads to kidney graft loss. In the past few decades, experimental observations both in patients and in animal models have led to the hypothesis of the existence of circulating factors driving the loss of integrity of the glomerular filtration barrier in FSGS. Although different circulating factor candidates have been postulated, none has been unequivocally shown to be pathogenic. In the current study, Shirai et al. propose a new candidate for this role by identifying circulating anti-nephrin autoantibodies in a cohort of patients with post-transplant recurrence of primary FSGS. Recent evidence by Watts et al. has also identified anti-nephrin autoantibodies in the circulation and in the kidney biopsies of patients with minimal change disease. If confirmed, the identification of these autoantibodies would both contribute to identifying the elusive circulating factor in FSGS and increase our understanding of the spectrum of proteinuric glomerular lesions, spanning from minimal change disease to FSGS. The quest for the Holy Grail is perhaps closer to completion.

Focal segmental glomerulosclerosis (FSGS) is a histological pattern of glomerular damage that includes idiopathic conditions as well as genetic and non-genetic forms. Among these various etiologies, different phenotypes within the spectrum of congenital anomalies of the kidney and urinary tract (CAKUT) have been associated with FSGS.

Until recently, the main pathomechanism of how congenital kidney and urinary tract defects lead to FSGS was attributed to a reduced number of nephrons, resulting in biomechanical stress on the remaining glomeruli, detachment of podocytes, and subsequent inability to maintain normal glomerular architecture. The discovery of deleterious single-nucleotide variants in PAX2, a transcription factor crucial in normal kidney development and a known cause of papillorenal syndrome, in individuals with adult-onset FSGS without congenital kidney defects has shed new light on developmental defects that become evident during podocyte injury.

In this mini-review, we challenge the assumption that FSGS in CAKUT is caused by glomerular hyperfiltration alone and hypothesize a multifactorial pathogenesis that includes overlapping cellular mechanisms that are activated in both damaged podocytes as well as nephron progenitor cells.