Complement activation and effector pathways in membranous nephropathy

Complement activation has long been recognized as a central feature of membranous nephropathy (MN). Evidence for its role has been derived from the detection of complement products in biopsy tissue and urine from patients with MN and from mechanistic studies primarily based on the passive Heymann nephritis model. Only recently, more detailed insights into the exact mechanisms of complement activation and effector pathways have been gained from patient data, animal models, and in vitro models based on specific target antigens relevant to the human disease. These data are of clinical relevance, as they parallel the recent development of numerous specific complement therapeutics for clinical use. Despite efficient B-cell depletion, many patients with MN achieve only partial remission of proteinuria, which may be explained by the persistence of subepithelial immune complexes and ongoing complement-mediated podocyte injury. Targeting complement, therefore, represents an attractive adjunct treatment for MN, but it will need to be tailored to the specific complement pathways relevant to MN. This review summarizes the different lines of evidence for a central role of complement in MN and for the relevance of distinct complement activation and effector pathways, with a focus on recent developments.

Ofatumumab in Rituximab-Resistant and Rituximab-Intolerant Patients With Primary Membranous Nephropathy: A Case Series

RATIONALE & OBJECTIVE

Rituximab is the first-choice therapy for patients with primary membranous nephropathy (MN) and nephrotic syndrome. However, approximately 30% of patients are treatment-resistant or become treatment-intolerant with hypersensitivity reactions upon repeated drug exposures. We aimed to assess whether ofatumumab, a fully human second-generation anti-CD20 antibody, could be a valuable alternative to rituximab in this population.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

7 rituximab-intolerant and 10 rituximab-resistant patients with MN who consented to receive ofatumumab (50-300mg, single intravenous infusion) and were followed at the nephrology unit of Azienda Socio-Sanitaria Territoriale Papa Giovanni XXIII (Bergamo, Italy) between September 2015 and January 2019.

FINDINGS

Over a median (IQR) follow-up of 5.0 (3.0-9.8) months, all 7 rituximab-intolerant and 3 of the 10 rituximab-resistant patients exhibited complete (proteinuria<0.3g/d) or partial (proteinuria<3.5g/d with≥50% reduction vs baseline) remission of nephrotic syndrome. Circulating B cells were similarly depleted in all patients by 1 week, and serum anti-phospholipase A2 receptor antibody concentrations decreased to<2.7 relative units/mL in 3 of 4 rituximab-intolerant and 4 of 8 rituximab-resistant patients with phospholipase A2 receptor-related disease. Ofatumumab significantly reduced 24-hour urinary protein and immunoglobulin G excretion and increased serum albumin and immunoglobulin G levels. These effects were greater in rituximab-intolerant than in rituximab-resistant patients. Measured glomerular filtration rate significantly increased by an average of 13.4% at 24 months compared with baseline (P=0.036) among all patients in the series. There were 14 nonserious infusion-related adverse events in 9 patients that recovered with temporary infusion interruption.

LIMITATIONS

Retrospective design, limited number of patients.

CONCLUSIONS

Ofatumumab may represent an effective and safe treatment for rituximab-intolerant cases of MN. Larger prospective studies will be needed to validate these preliminary findings and explore the effectiveness of other second-generation anti-CD20 antibodies in this clinical setting.

PLAIN-LANGUAGE SUMMARY

Primary membranous nephropathy (MN) is one of the most frequent causes of nephrotic syndrome (NS) in adults. In this case series, we explored the efficacy of ofatumumab, a fully human second-generation anti-CD20 antibody, in 17 patients with MN and NS who were intolerant or unresponsive to rituximab. All 7 rituximab-intolerant patients exhibited complete or partial clinical remission, compared with only 3 of the 10 rituximab-resistant patients. Autoantibody levels decreased in all patients with phospholipase A2 receptor-related disease. Ofatumumab achieved a significant reduction in urinary protein and immunoglobulin G excretion while increasing serum albumin and immunoglobulin G levels. Ofatumumab may be a promising option for patients with MN who are rituximab-intolerant. Further investigations are warranted to validate these preliminary findings.

Bi-specific autoantigen-T cell engagers as targeted immunotherapy for autoreactive B cell depletion in autoimmune diseases

Introduction

In autoimmune diseases, autoreactive B cells comprise only the 0.1-0.5% of total circulating B cells. However, current first-line treatments rely on non-specific and general suppression of the immune system, exposing patients to severe side effects. For this reason, identification of targeted therapies for autoimmune diseases is an unmet clinical need.

Methods

Here, we designed a novel class of immunotherapeutic molecules, Bi-specific AutoAntigen-T cell Engagers (BiAATEs), as a potential approach for targeting the small subset of autoreactive B cells. To test this approach, we focused on a prototype autoimmune disease of the kidney, membranous nephropathy (MN), in which phospholipase A2 receptor (PLA2R) serves as primary nephritogenic antigen. Specifically, we developed a BiAATE consisting of the immunodominant Cysteine-Rich (CysR) domain of PLA2R and the single-chain variable fragment (scFv) of an antibody against the T cell antigen CD3, connected by a small flexible linker.

Results

BiAATE creates an immunological synapse between autoreactive B cells bearing an CysR-specific surface Ig+ and T cells. Ex vivo, the BiAATE successfully induced T cell-dependent depletion of PLA2R-specific B cells isolated form MN patients, sparing normal B cells. Systemic administration of BiAATE to mice transgenic for human CD3 reduced anti-PLA2R antibody levels following active immunization with PLA2R.

Discussion

Should this approach be confirmed for other autoimmune diseases, BiAATEs could represent a promising off-the-shelf therapy for precision medicine in virtually all antibody-mediated autoimmune diseases for which the pathogenic autoantigen is known, leading to a paradigm shift in the treatment of these diseases.

Quantitative detection and prognostic value of antibodies against M-type phospholipase A2 receptor and its cysteine-rich ricin domain and C-type lectin domains 1 and 6-7-8 in patients with idiopathic membranous nephropathy

BACKGROUND

M-type phospholipase A2 receptor (PLA2R) is the major autoantigen in adult idiopathic membranous nephropathy (IMN). Although reactive epitopes in the PLA2R domains have been identified, the clinical value of these domains recognized by anti-PLA2R antibodies remains controversial. Accordingly, this study aimed to quantitatively detect changes in the concentrations of different antibodies against epitopes of PLA2R in patients with IMN before and after treatment to evaluate the clinical value of epitope spreading.

METHODS

Highly sensitive time-resolved fluorescence immunoassay was used to quantitatively analyze the concentrations of specific IgG and IgG4 antibodies against PLA2R and its epitopes (CysR, CTLD1, CTLD6-7-8) in a cohort of 25 patients with PLA2R-associated membranous nephropathy (13 and 12 in the remission and non-remission groups, respectively) before and after treatment, and the results were analyzed in conjunction with clinical biochemical indicators.

RESULTS

The concentration of specific IgG (IgG4) antibodies against PLA2R and its epitopes (CysR, CTLD1 and CTLD6-7-8) in non-remission group was higher than that in remission group. The multipliers of elevation of IgG (IgG4) antibody were 5.6(6.2) fold, 3.0(24.3) fold, 1.6(9.0) fold, and 4.2(2.6) fold in the non-remission/remission group, respectively. However, the difference in antibody concentrations between the two groups at the end of follow-up was 5.6 (85.2), 1.7 (13.1), 1.0 (5.1), and 1.5 (22.3) times higher, respectively. When detecting concentrations of specific IgG antibodies against PLA2R and its different epitopes, the remission rate was 66.67% for only one epitope at M0 and 36.36% for three epitopes at M0. When detecting concentrations of specific IgG4 antibodies against PLA2R and its different epitopes, the remission rate was 100.00% for only one epitope at M0 and 50.00% for three epitopes at M0. A trivariate logistic regression model for the combined detection of eGFR, anti-CTLD678 IgG4, and urinary protein had an AUC of 100.00%.

CONCLUSION

Low concentrations of anti-CysR-IgG4, anti-CTLD1-IgG4, and anti-CTLD6-7-8-IgG4 at initial diagnosis predict rapid remission after treatment. The use of specific IgG4 against PLA2R and its different epitopes combined with eGFR and urinary protein provides a better assessment of the prognostic outcome of IMN.

Defining the threshold: triglyceride to high-density lipoprotein cholesterol (TG/HDL-C) ratio's non-linear impact on tubular atrophy in primary membranous nephropathy

Background

Hyperlipidemia is common in primary membranous nephropathy (PMN) patients, and tubular atrophy (TA) is an unfavorable prognostic factor. However, the correlation between the triglyceride to high-density lipoprotein cholesterol (TG/HDL-C) ratio and TA is controversial. Therefore, our study aimed to investigate the association between the TG/HDL-C ratio and TA in PMN patients.

Methods

We conducted a cross-sectional study and collected data from 363 PMN patients at Shenzhen Second People's Hospital from January 2008 to April 2023. The primary objective was to evaluate the independent correlation between the TG/HDL-C ratio and TA using binary logistic regression model. We used a generalized additive model along with smooth curve fitting and multiple sensitivity analyses to explore the relationship between these variables. Additionally, subgroup analyses were conducted to delve deeper into the results.

Results

Of the 363 PMN patients, 75 had TA (20.66%). The study population had a mean age of 46.598 ± 14.462 years, with 217 (59.78%) being male. After adjusting for sex, age, BMI, hypertension, history of diabetes, smoking, alcohol consumption, UPRO, eGFR, HB, FPG, and ALB, we found that the TG/HDL-C ratio was an independent risk factor for TA in PMN patients (OR=1.29, 95% CI: 1.04, 1.61, P=0.0213). A non-linear correlation was observed between the TG/HDL-C ratio and TA, with an inflection point at 4.25. The odds ratios (OR) on the left and right sides of this inflection point were 1.56 (95% CI: 1.17, 2.07) and 0.25 (95% CI: 0.04, 1.54), respectively. Sensitivity analysis confirmed these results. Subgroup analysis showed a consistent association between the TG/HDL-C ratio and TA, implying that factors such as gender, BMI, age, UPRO, ALB, hypertension and severe nephrotic syndrome had negligible effects on the link between the TG/HDL-C ratio and TA.

Conclusion

Our study demonstrates a non-linear positive correlation between the TG/HDL-C ratio and the risk of TA in PMN patients, independent of other factors. Specifically, the association is more pronounced when the ratio falls below 4.25. Based on our findings, it would be advisable to decrease the TG/HDL-C ratio below the inflection point in PMN patients as part of treatment strategies.

Causal relationship between gut microbiota and kidney diseases: a two-sample Mendelian randomization study

Background

The interplay between gut microbiome genera and inflammatory kidney-related diseases, such as nephrotic syndrome, glomerulonephritis, tubulo-interstitial nephritis, and chronic kidney disease, has been observed. However, the causal relationships between specific bacterial genera and these renal diseases have not been fully elucidated.

Objective

To investigate the potential causal links between different genera of the gut microbiome and the susceptibility to various renal conditions utilizing two-sample Mendelian randomization (MR) analyses.

Materials and methods

Genome-wide association study (GWAS) summary statistics of gut microbiota and inflammatory kidney-related diseases were obtained from published GWASs. Two-sample MR analyses were conducted using methods including inverse-variance weighted (IVW), MR Egger, and others to identify potential causal links between gut microbial genera and renal conditions. Sensitivity analyses, including Cochran's Q test and the MR-PRESSO global test, were performed to validate the robustness of the results and detect horizontal pleiotropy. In addition, a reverse MR analysis was conducted to assess reverse causation possibilities.

Results

By synthesizing insights from both primary and sensitivity analyses, this study unveiled critical associations of 12 bacterial genera with nephrotic syndrome, 7 bacterial genera with membranous nephropathy, 3 bacterial genera with glomerulonephritis, 4 bacterial genera with acute tubulo-interstitial nephritis, 6 bacterial genera with chronic tubulo-interstitial nephritis, and 7 bacterial genera with chronic kidney disease. Various genera were pinpointed as having either positive or negative causal relationships with these renal conditions, as evidenced by specific ranges of IVW-OR values (all P< 0.05). The congruence of the sensitivity analyses bolstered the primary findings, displaying no marked heterogeneity or horizontal pleiotropy. Notably, the reverse MR analysis with nephritis as the exposure did not reveal any causal relationships, thereby strengthening the resilience and validity of the primary associations.

Conclusion

This study explored the causal associations between several gut microbial genera and the risk of several inflammatory kidney-related diseases, uncovering several associations between specific gut microbial genera and nephrotic syndrome, membranous nephropathy, glomerulonephritis, tubulo-interstitial nephritis, and chronic kidney disease. These findings enhance our understanding of the complex interplay between the gut microbiome and kidney diseases, and they will be beneficial for early diagnosis and subsequent treatment.

Association of COVID-19 Versus COVID-19 Vaccination With Kidney Function and Disease Activity in Primary Glomerular Disease: A Report of the Cure Glomerulonephropathy Study

RATIONALE & OBJECTIVE

Patients with glomerular disease (GN) may be at increased risk of severe COVID-19, yet concerns over vaccines causing disease relapse may lead to vaccine hesitancy. We examined the associations of COVID-19 with longitudinal kidney function and proteinuria and compared these with similar associations with COVID-19 vaccination.

STUDY DESIGN

Observational cohort study from July 1, 2021, to January 1, 2023.

SETTING & PARTICIPANTS

A prospective observational study network of 71 centers from North America and Europe (CureGN) with children and adults with primary minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, or IgA nephropathy.

EXPOSURE

COVID-19 and COVID-19 vaccination.

OUTCOME

Repeated measure of estimated glomerular filtration rate (eGFR); recurrent time-to-event outcome of GN disease worsening as defined by doubling of the urinary protein-creatinine ratio (UPCR) to at least 1.5g/g or increase in dipstick urine protein by 2 ordinal levels to 3+(300mg/dL) or above.

ANALYTICAL APPROACH

Interrupted time series analysis for eGFR. Prognostic matched sequential stratification recurrent event analysis for GN disease worsening.

RESULTS

Among 2,055 participants, 722 (35%) reported COVID-19 infection; of these, 92 (13%) were hospitalized, and 3 died (<1%). The eGFR slope before COVID-19 infection was-1.40mL/min/1.73m2 (± 0.29 SD); within 6 months after COVID-19 infection, the eGFR slope was-4.26mL/min/1.73m2 (± 3.02 SD), which was not significantly different (P=0.34). COVID-19 was associated with increased risk of worsening GN disease activity (HR, 1.35 [95% CI, 1.01-1.80]). Vaccination was not associated with a change in eGFR (-1.34mL/min/1.73m2±0.15 SD vs-2.16mL/min/1.73m2±1.74 SD; P=0.6) or subsequent GN disease worsening (HR 1.02 [95% CI, 0.79-1.33]) in this cohort.

LIMITATIONS

Infrequent or short follow-up.

CONCLUSIONS

Among patients with primary GN, COVID-19 infection was severe for 1 in 8 cases and was associated with subsequent worsening of GN disease activity, as defined by proteinuria. By contrast, vaccination against COVID-19 was not associated with change in disease activity or kidney function decline. These results support COVID-19 vaccination for patients with GN.

PLAIN-LANGUAGE SUMMARY

In this cohort study of 2,055 patients with minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, or IgA nephropathy, COVID-19 resulted in hospitalization or death for 1 in 8 cases and was associated with a 35% increase in risk for worsening proteinuria. By contrast, vaccination did not appear to adversely affect kidney function or proteinuria. Our data support vaccination for COVID-19 in patients with glomerular disease.

Machine learning model to estimate probability of remission in patients with idiopathic membranous nephropathy

BACKGROUND

Idiopathic membranous nephropathy (IMN) is a type of nephrotic syndrome and the leading cause of chronic kidney disease. As far as we know, no predictive model for assessing the prognosis of IMN is currently available. This study aims to establish a nomogram to predict remission probability in patients with IMN and assists clinicians to make treatment decisions.

METHODS

A total of 266 patients with histopathology-proven IMN were included in this study. Least absolute shrinkage and selection operator regression was utilized to identify the most important variables. Subsequently, multivariate Cox regression analysis was conducted to construct a nomogram, and bootstrap resampling was employed for internal validation. Receiver operating characteristic and calibration curves and decision curve analysis (DCA) were utilized to assess the performance and clinical utility of the developed model.

RESULTS

A prognostic nomogram was established, which incorporated creatinine, glomerular_basement_membrane_thickening, gender, IgG_deposition, low-density lipoprotein cholesterol, and fibrinogen. The areas under the curves of the 3-, 12-, 24-month were 0.751, 0.725, and 0.830 in the training set, and 0.729, 0.730, and 0.948 in the validation set respectively. These results and calibration curves demonstrated the good discrimination and calibration of the nomogram in the training and validation sets. Additionally, DCA indicated that the nomogram was useful for remission prediction in clinical settings.

CONCLUSION

The nomogram was useful for clinicians to evaluate the prognosis of patients with IMN in early stage.

The association of serum anti-PLA2R antibody and glomerular PLA2R antigen staining with clinical manifestations and outcomes in membranous nephropathy

BACKGROUND

Phospholipase A2 receptor (PLA2R)-associated membranous nephropathy (MN) was manifested as seropositive for PLA2R antibodies (SAb) and/or glomerular PLA2R antigens' (GAg) deposits. According to the test of SAb and GAg, PLA2R-associated MN can be divided into SAb + /GAg-, SAb-/GAg + , and SAb + /GAg + groups. The clinical characteristics and outcomes of the three groups need to be further evaluated.

METHODS

184 PLA2R-associated MN patients were enrolled. SAb was measured by enzyme-linked immunosorbent assay with a cut-off value of 14 RU/mL. GAg was detected by immunofluorescence using a paraffin section of renal biopsy samples. Clinical characteristics and the decline of eGFR were compared among the 3 groups.

RESULTS

There were 33 SAb + /GAg-, 46 SAb-/GAg +, and 105 SAb + /GAg + PLA2R-associated MN patients reviewed. Clinical characteristics, such as the level of proteinuria, serum albumin, as well as eGFR, were comparable between the SAb + /GAg- and SAb + /GAg + patients. While SAb-/GAg + patients exhibited mild clinical manifestations as evidenced by higher serum albumin (P < 0.001) and lower proteinuria (p = 0.049) compared with SAb + /GAg + patients. After 21.96 ± 7.39 month follow-up, the eGFR decrease was no difference between the SAb + /GAg- and SAb + /GAg + patients. SAb-/GAg + patients had a lower rate of the > 20% eGFR decline as well as a 50% eGFR decline compared with the SAb + /GAg + patients (10.87% vs 30.48%, p = 0.013; 0.00% vs 4.76%, p = 0.324).

CONCLUSIONS

Our study showed that the clinical manifestations of SAb + /Gag- patients were the same as those of double-positive patients, while SAb-/GAg + patients exhibited mild clinical manifestations and slower eGFR decline compared to the double-positive patients.

Varicella-zoster virus infection and primary membranous nephropathy: a Mendelian randomization study

Primary membranous nephropathy (MN) is a rare autoimmune cause of kidney failure. Observational studies have suggested some relationship between virus infection and primary MN, but the association remains unclear. The current study performed a two‑sample Mendelian randomization (MR) analysis to explore the causal association between varicella-zoster virus (VZV) infection (chickenpox and shingles) and primary MN using genome‑wide association studies (GWASs) summary statistics. The exposure datasets containing chickenpox and shingles were obtained from the GWASs conducted by the 23andMe cohort. And summary-level statistics for primary MN were used as the outcome dataset, comprising 2150 cases and 5829 controls from European Ancestry. The inverse variance weighted method was adopted as the main analysis. As a result, we found that both genetically determined chickenpox (odds ratio [95% confidential interval] = 3.61 [1.74-7.50], p = 5.59e-04) and shingles (p = 7.95e-03, odds ratio [95% confidential interval] = 2.49 [1.27-4.91]) were causally associated with an increased risk of developing primary MN. In conclusion, our MR findings provided novel genetic evidence supporting the causal effect of VZV infection on primary MN. Further studies are needed to elucidate the underlying mechanisms mediating the causal association.

Autoantibodies in lupus nephritis useful in distinguishing proliferative nephritis from membranous nephritis

OBJECTIVES

This study was conducted to determine autoantibodies associated with lupus nephritis (LN), especially those useful in diagnosing proliferative and membranous nephritis.

METHODS

A total of 106 patients with LN and 63 patients with systemic lupus erythematosus but no nephritis were enrolled; then, 55 patients were selected from the LN group and were divided into two groups: proliferative nephritis patients (n = 36) and membranous nephritis patients (n = 19). The autoantibody profiles of patients' sera were evaluated using the EUROLINE ANA Profile 3 (IgG) kit.

RESULTS

A higher positivity rate of anti-double-stranded DNA antibody and anti-histone antibody was seen in LN patients compared to nonrenal systemic lupus erythematosus patients. In comparing between proliferative and membranous nephritis, the positivity of anti-nucleosome antibody was higher in proliferative nephritis, although it was not statistically significant. However, anti-nucleosome antibody-positive patients with LN had a higher prevalence of haematuria and pyuria, which are strong indications of proliferative nephritis. Also, a significantly higher positivity rate of anti-RNP70 antibody was seen in membranous nephritis compared to proliferative nephritis.

CONCLUSIONS

Our results showed that anti-nucleosome and anti-RNP70 antibodies may be predictive nonhistological factors for discriminating between proliferative and membranous LN.

The latest model has just arrived! A new experimental mouse model of PLA2R1-associated membranous nephropathy

Much akin to the explosion in number of known target antigens in membranous nephropathy, there has been a rapid expansion in the availability of animal models involving the first 2 antigens discovered in adult disease, phospholipase A2 receptor and thrombospondin type 1 domain-containing 7A. In this issue, Tomas et al. describe a novel mouse model of phospholipase A2 receptor-associated membranous nephropathy that shows great promise for investigating molecular mechanisms of disease and as an experimental system for testing existing and emerging therapies.

Introduction of a novel chimeric active immunization mouse model of PLA2R1-associated membranous nephropathy

The phospholipase A2 receptor 1 (PLA2R1) is the major target antigen in patients with membranous nephropathy (MN), an antibody-mediated autoimmune glomerular disease. Investigation of MN pathogenesis has been hampered by the lack of reliable animal models. Here, we overcome this issue by generating a transgenic mouse line expressing a chimeric PLA2R1 (chPLA2R1) consisting of three human PLA2R1 domains (cysteine-rich, fibronectin type-II and CTLD1) and seven murine PLA2R1 domains (CTLD2-8) specifically in podocytes. Mice expressing the chPLA2R1 were healthy at birth and showed no major glomerular alterations when compared to mice with a wild-type PLA2R1 status. Upon active immunization with human PLA2R1 (hPLA2R1), chPLA2R1-positive mice developed anti-hPLA2R1 antibodies, a nephrotic syndrome, and all major histological features of MN, including granular deposition of mouse IgG and complement components in immunofluorescence and subepithelial electron-dense deposits and podocyte foot process effacement in electron microscopy. In order to investigate the role of the complement system in this model, we further crossed chPLA2R1-positive mice with mice lacking the central complement component C3 (C3-/- mice). Upon immunization with hPLA2R1, chPLA2R1-positive C3-/- mice had substantially less severe albuminuria and nephrotic syndrome when compared to chPLA2R1-positive mice with a wild-type C3 status. In conclusion, we introduce a novel active immunization model of PLA2R1-associated MN and demonstrate a pathogenic role of the complement system in this model.

Histological transition from minimal change disease to THSD7A-associated membranous nephropathy in a patient receiving long-term steroid treatment: A case report

RATIONALE

A predominant Th2 immune response is suggested in the pathogenesis of both minimal change disease (MCD) and membranous nephropathy (MN); however, consecutive development of the 2 diseases in a patient is extremely rare.

PATIENT CONCERN

A Japanese man, who developed nephrotic syndrome in his 50s and was diagnosed with MCD by renal biopsy, experienced a relapse of proteinuria approximately 3 years later during long-term steroid treatment. Since the proteinuria was resistant to increase in steroid dosage, repeat renal biopsy was performed, which revealed a small amount of glomerular subepithelial immune deposits containing immunoglobulin (Ig)G (dominantly IgG4). Immunostaining for thrombospondin-type-1-domain-containing-7A (THSD7A) was positive on the glomerular capillary walls, whereas that for other causative antigens of MN, such as phospholipase A2 receptor or neural epidermal growth factor-like 1 protein, was negative. Detailed examination found no associated condition, including malignancies and allergic diseases.

DIAGNOSIS

The diagnosis of THSD7A-associated idiopathic MN was made.

INTERVENTIONS AND OUTCOMES

He received further increased dose of steroids. Thereafter he maintained clinical improvement because his urinary protein level was decreased.

LESSONS

The present case suggested that histological transition from MCD to MN is possible and repeat biopsy would be crucial for accurate diagnosis.

Altered Intestinal Microbial Flora and Metabolism in Patients with Idiopathic Membranous Nephropathy

INTRODUCTION

Dysbiosis of the intestinal microbiome and related metabolites have been observed in chronic kidney disease, yet their roles in idiopathic membranous nephropathy (IMN) are poorly understood.

METHODS

In this study, we describe the variation of intestinal bacteria and fecal metabolites in patients with IMN in Chinese population. Stool samples were collected from 41 IMN patients at the beginning of diagnosis confirmation and 41 gender- and age-matched healthy control (HC). Microbial communities are investigated by sequencing of 16S rRNA genes and functional profiles predicted using Tax4Fun, and the correlation between intestinal bacteria and IMN clinical characteristics is also analyzed. Untargeted metabolomic analysis is performed to explore the relationship between colon's microbiota and fecal metabolites.

RESULTS

IMN gastrointestinal microbiota demonstrates lower richness and diversity compared to HC, and exhibits a marked taxonomic and inferred functional dysbiosis when compared to HC. Some genera are closely related to the clinical parameters, such as Citrobacter and Akkermansia. Twenty characteristic microbial biomarkers are selected to establish a disease prediction model with a diagnostic accuracy of 93.53%. Fecal metabolomics shows that tryptophan metabolism is reduced in IMN patients but uremic toxin accumulation in feces is not noticeable. Fecal microbiota transplantation demonstrates that gut dysbiosis impairs gut permeability in microbiota-depleted mice and induces NOD-like receptor activation in the kidneys.

CONCLUSIONS

Clarifying the changes in intestinal microbiota in IMN patients will help further know the pathogenesis of this disease, and microbiota-targeted biomarkers will provide a potentially powerful tool for diagnosing and treating IMN.

[Cancer and the Kidney: A Deadly Embrace]

A deadly embrace occurs between cancer and chronic kidney disease. The estimation of kidney function in cancer patients is of utmost interest due to its direct impact on chemotherapy dosing, selection, and eligibility for chemotherapeutics. Overestimating kidney function (determined as estimated glomerular filtration rate -eGFR) can lead to overdosing and drug toxicity, while underestimating kidney function can prevent patients from receiving novel therapies. Notably, the current measures of eGFR are not validated in transplanted patients yet. The field of onconephrology ranges from nephrotoxicity of existing and novel therapeutics, paraproteinemias, and cancer-associated electrolyte imbalance, fluid and acid-base disturbances, the effects of the destruction of cancer cells, and acute and/or chronic kidney injuries. Recently, the therapeutic armamentarium has been enriched with new agents that interfere with specific proteins involved in oncogenesis. These are the so-called target therapies, which although acquired as "targeted" therapies do not have absolute specificity and selectivity and tend to inhibit multiple targets, often involving the kidney. Renal biopsy may be critical in managing these adverse effects. Moreover, primary hematological and oncological disorders can have significant kidney implications in the form of glomerular or nonglomerular diseases presenting with proteinuria, hematuria, hypertension, and kidney function decline, specifically including cast nephropathy or systemic light chain amyloidosis, and paraneoplastic glomerulopathies that occur as a result of occult malignancy, such as Membranous Nephropathy and Minimal Change disease.

Diagnostic utility of serum and urine biomarkers in idiopathic membranous nephropathy: a systematic review and meta-analysis

BACKGROUND

Membranous nephropathy is an autoimmune nephropathy that is one of the most common pathological types of nephrotic syndrome. It is important to find and apply specific biomarkers for the noninvasive diagnosis of idiopathic membranous nephropathy (IMN). However, there are limited data about their diagnostic value. Therefore, an overall meta-analysis helps to identify effective biomarkers for the clinical diagnosis of IMN.

METHODS

A systematic literature search was carried out in PubMed, Embase, Cochrane and Web of Science from inception until December 31, 2020. Two researchers searched for studies that met the inclusion criteria. The results of the joint study were expressed in terms of sensitivity and specificity.

RESULTS

The meta-analysis included 24 studies with biomarkers for the clinical diagnosis of IMN, including antibody against phospholipase A2 receptor (PLA2R-AB), antibody against thrombospondin type I domain-containing 7A (THSD7A-AB), lysosome membrane protein-2 (LIMP-2) and circular RNAs. The diagnostic efficiency of PLA2R-AB for IMN had a combined sensitivity of 60% and a combined specificity of 100%. The diagnostic efficiency of THSD7A-AB for IMN had a combined sensitivity of 3% and a combined specificity of 99%. The diagnostic efficiency of urinary LIMP-2 for IMN was 100%, and the specificity was 100%. The diagnostic efficiency of exosomal circRNAs for IMN was 100%, and the specificity was 100%.

CONCLUSIONS

This meta-analysis shows that PLA2R-AB and THSD7A-AB are of important diagnostic value for IMN. More studies are needed in the future to reveal the diagnostic value of LIMP-2 and circRNAs for IMN.

Elevated circulating CD19+CD24hiCD38hi B cells display pro-inflammatory phenotype in idiopathic membranous nephropathy

CD19+CD24hiCD38hi regulatory B cells exert immunosuppressive functions by producing IL-10, but their role in idiopathic membranous nephropathy (IMN) remains elusive. Here, we investigated the frequency and functional changes of circulating CD19+CD24hiCD38hi B cells and evaluated the correlation of CD19+CD24hiCD38hi B cells with clinical features and T helper cell subsets in IMN patients. Compared with healthy controls (HCs), IMN patients showed an increased frequency of CD19+CD24hiCD38hi B cells, but a significant reduction in the percentage of CD19+CD24hiCD38hi B cells was observed 4 weeks after cyclophosphamide treatment. The frequency of CD19+CD24hiCD38hi B cells was positively correlated with the levels of 24h urinary protein, but negatively correlated with serum total protein and serum albumin, respectively. CD19+CD24hiCD38hi B cells in IMN patients displayed a skewed pro-inflammatory cytokine profile with a higher level of IL-6 and IL-12, but a lower concentration of IL-10 than their healthy counterparts. Accompanied by upregulation of Th2 and Th17 cells in IMN patients, the percentage of CD19+CD24hiCD38hi B cell subset was positively associated with Th17 cell frequency. In conclusion, CD19+CD24hiCD38hi B cells were expanded but functionally impaired in IMN patients. Their altered pro-inflammatory cytokine profile may contribute to the pathogenesis of IMN.

Correlation of Acoustic Radiation Force Impulse Imaging with Chronicity Markers in Native Renal Biopsy

Introduction. Acoustic Radiation Force Impulse (ARFI) is an ultrasound parameter which has shown promise in assessing liver stiffness, but there are limited data on the correlation of ARFI with chronicity markers in renal biopsies. Objectives. Determine ARFI values in ultrasound and correlate with chronicity markers in renal biopsy. Determine whether ARFI can be used as a non-invasive chronicity predictor compared to renal length, Resistive Index (RI), and cortical thickness. Patients and Methods. Two hundred and fifty patients were enrolled in the study. The ultrasound variables ARFI, renal length, RI, and cortical thickness values were assessed by the radiologist prior to renal biopsy. The biopsy slides were graded as per the Mayo Clinic consensus report scoring system by an experienced pathologist. Results. Among 250 study participants, 167 were males and 83 were females. IgA nephropathy was the most common pathology (n=47;19%), followed by diabetic nephropathy (n=42;17%), membranous nephropathy (n=35;14%), FSGS (n=27;11%), and MCD (n=19; 8%). The mean eGFR was 55.9 ± 42.12 ml/min/1.73 m2. The average renal length was 10.086 ± 1.01 cm. The average cortical thickness was 0.707 ± 0.134 cm. Resistive index was 0.68 ± 0.09. Acoustic radiation force impulse had weak negative correlation (r=-0.286; p=0.0001) with total pathological score and weak positive correlation with eGFR (r=0.279; p=0.0001). RI was a better indicator for histologically evaluated chronicity with positive correlation coefficient (r=0.416; p=0.0005) compared to renal length, cortical thickness, and ARFI. Conclusion. ARFI didn't corelate with the pathological score in renal biopsies. RI had better predictive value for chronicity in native renal biopsies.

Correlation Analysis between Intrarenal Small Artery Intimal Thickening and Clinicopathological Features and Prognosis in Primary Membranous Nephropathy Patients

BACKGROUND

Primary membranous nephropathy (PMN) is the most common pathological type of nephrotic syndrome in adults. Intrarenal small artery intimal thickening can be observed in most renal biopsies. The purpose of this study was to investigate the association between intrarenal small artery intimal thickening and clinicopathological features and prognosis in PMN patients.

METHODS

Data were continuously collected from patients who were diagnosed with PMN in Shenzhen Second People's Hospital (The First Affiliated Hospital of Shenzhen University) from 2008 to 2021 for a retrospective cohort study. Regression analysis and survival analysis were used to analyze the relationship between intrarenal small artery intimal thickening and renal prognosis in PMN patients.

RESULTS

300 PMN patients were enrolled in this study, including 165 patients (55%) with intrarenal small artery intimal thickening. Patients with intimal thickening were older, with higher BMI, systolic blood pressure and diastolic blood pressure, serum uric acid, a higher proportion of hypertension, acute kidney injury, nephrotic syndrome, more urine protein, and lower eGFR. Multivariate Cox regression analysis showed that after adjusting for age, gender, hypertension, BMI, urine protein, eGFR, and the use of ACEI/ARB and hormone immunosuppressants, intimal thickening was a risk factor for renal prognosis in PMN patients (HR = 3.68, 95% CI 1.36-9.96, p < 0.05). Kaplan-Meier survival curve analysis showed that the incidence of reaching the renal composite outcome was higher in the intimal thickening group (p < 0.05).

CONCLUSION

The prognosis of PMN patients with intrarenal small artery intimal thickening is worse, so early intervention is very important for these patients.

Tubular basement membrane deposits after allogeneic hematopoietic stem cell transplantation

BACKGROUND

Extraglomerular immune complex deposition is rare and only a few membranous nephropathy cases with tubular basement membrane deposits have been reported following allogeneic hematopoietic stem cell transplantation.

CASE PRESENTATION

We reported a 56-year-old man with increased serum creatinine after allogeneic hematopoietic stem cell transplantation who underwent a renal biopsy. Tubular interstitial nephritis was identified on light microscope. The unique histologic features were diffuse tubular basement membrane immune complex deposition detected by both immunofluorescence and electron microscopy, while the glomerular involvement was inconspicuous. The differential diagnosis from other forms of tubular basement membrane deposition is discussed.

CONCLUSION

Diffuse granular tubular basement membrane immune complex deposition with minimal glomerular involvement is also a manifestation of renal complication in hematopoietic stem cell transplantation recipient. However, the exact mechanism and target antigen remains unknown.

[Clinical significance of the determination of antibodies to thrombospondin type 1 containing domain 7A (THSD7A) in membranous nephropathy]

BACKGROUND

Membranous nephropathy (MN) is an immunocomplex glomerular disease, which is the most common cause of nephrotic syndrome in adults. Numerous studies have established that autoantibodies against the target podocyte autoantigens, including the thrombospondin type 1 domain containing 7A (THSD7A), play a leading role in the development of idiopathic MN.

AIM

To evaluate the prevalence of anti-THSD7A autoantibodies (anti-THSD7A AB) in a group of Russian patients with MN.

MATERIALS AND METHODS

Serum titers of anti-THSD7A AB were tested in 61 patients with biopsy-proven MN and 12 healthy controls.

RESULTS

The prevalence of anti-THSD7A AB was not differing significantly in patients with MN and in the control group (110.9 [71.63; 210.62] and 159.25 [125.64; 231.97] pg/ml, respectively; p=0.111). When comparing subgroups of anti-PLA2R-negative patients and patients who did not receive immunosuppressive therapy with the control group, there were also no statistically significant differences in the Anti-THSD7A AB levels (p>0.05). In the MN group, 1 (1.6%) patient was anti-THSD7A-positive: a 60-year-old man with anti-PLA2R-negative MN and the presence of hormonally inactive adenomas of both adrenal glands and colon polyps (villous adenoma with focal moderate dysplasia, tubulo-villous and tubular adenoma with focal moderate severe dysplasia).

CONCLUSION

THSD7-associated MN is a rare variant of MN and is usually detected in PLA2R-negative patients. Screening for malignancies in THSD7A-positive MN patients is proposed.

[Study of urinary markers of different podocytopathies by proteomic analysis]

BACKGROUND

Focal segmental glomerulosclerosis (FSGS) is a primary podocytopathy characterized by primary podocyte detection and high proteinuria. The search for biomarkers and factors associated with the progression of this disease is an important task nowdays.

AIM

To assess the proteomic profile of urine in patients with FSGS and to isolate urinary biomarkers of podocytopathies.

MATERIALS AND METHODS

The study included 41 patients diagnosed with chronic glomerulonephritis, 27 men and 14 women. According to the morphological study, 28 patients were diagnosed with FSGS, 9 with steroid-sensitive nephrotic syndrome and 14 with steroid-resistant nephrotic syndrome. The comparison group included 13 patients with membranous nephropathy. The study of the urinary proteome was carried out by targeted liquid chromatography-mass spectrometry using multiple reaction monitoring with synthetic stable isotope labelled peptide standards.

RESULTS

The main differences in the protein profile of urine were found in the subgroups of steroid-sensitive (SS) and steroid-resistant (SR) FSGS. In the FSGS SR group, at the onset of the disease, there was a high concentration of proteins reflecting damage to the glomerular filter (apo-lipoprotein A-IV, orosomucoid, cadherin, hemopexin, vitronectin), as well as proteins associated with tubulo-interstitial inflammation and accumulation of extracellular matrix (retinol- and vitamin D-binding proteins, kininogen-1, lumican and neurophilin-2). Compared with the membranous nephropathy group, FSGS patients had significantly higher urinary concentrations of carnosinase, orosomucoid, cadherin-13, tenascin X, osteopontin, and zinc-alpha-2-glycoprotein.

CONCLUSION

Thus, in patients with SR FSGS, the proteomic profile of urine includes more proteins at elevated concentrations, which reflects severe damage to various parts of the nephron compared with patients with SS FSGS and membranous nephropathy.

Prevalence and distribution of primary glomerular diseases in Africa: a systematic review and meta-analysis of observational studies

Glomerulonephritis (GN) is a predominant cause of kidney failure in Africa. The prevalence of primary GNs varies widely across Africa depending on the relative proportion of secondary GNs and genetic predispositions. We assessed the overall and sub-regional prevalence of primary GN and its histologic subtypes in Africa. We searched PubMed, EMBASE and African Journals Online for studies of biopsy-proven primary GNs across all age groups in Africa published between 2010 and 2022. Data for primary GNs [minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MN), mesangioproliferative GN (MesPGN), membranoproliferative GN (MPGN), post-infectious GN (PIGN), IgA Nephropathy (IgAN), and crescentic GN (CresGN)] were extracted. Pooled prevalence was determined using the random effects model. Seventeen eligible articles (n = 6,494 individuals) from 8 African countries met the inclusion criteria. The overall pooled prevalence of FSGS, MCD, MN, MPGN, MesPGN, PIGN, IgAN and CresGN was 26.10%, 22.40%, 8.40%, 6.40%, 6.40%, 2.60%, 2.60%, 1.40%, respectively. Only 4 studies (23.5%) used light microscopy (LM), immunofluorescence (IF), and electron microscopy (EM) for diagnosis. There were significant differences in the distribution of histologic subtypes in the paediatric compared to the adult population and across geographic sub-regions, with West Africa having a higher prevalence of FSGS. Overall, the dominance of FSGS across most regions and age groups has implications for disease diagnosis and ongoing care. Research efforts to understand the impact of this trend on kidney disease outcomes and efforts to improve kidney biopsy practice as a means of early disease detection are needed in Africa.

Discordance of light chain isotypes between serum and glomerular deposits in proliferative glomerulonephritis with monoclonal IgG deposits: a case report and review of the literature

BACKGROUND

Proliferative glomerulonephritis with monoclonal immunoglobulin G (IgG) deposits (PGNMID) is a disease entity with nonorganized granular glomerular deposition with monoclonal proteins of both heavy and light chains. Dysproteinemia was observed in only 30% of the patients with PGNMID. We herein report a case of PGNMID with discrepancy between serum and glomerular deposits.

CASE PRESENTATION

The patient was a 50-year-old man who had been followed at a local clinic due to hypertension, type 2 diabetes, hyperlipidemia, hyperuricemia, fatty liver, and obesity. Proteinuria had been noted five years previously, and he had been referred to a hematology department due to hyperproteinemia, high gamma globulin, and κ Bence-Jones protein (BJP) positivity one year previously. Bone marrow aspiration showed 5% plasma cells, and he was referred to the nephrology department to evaluate persistent proteinuria. He was hypertensive, and his estimated glomerular filtration rate was 54.2 ml/min/1.73 m2. His urinary protein level was 0.84 g/g⋅Cr. Urine and serum immunofixation showed BJP-κ type and IgG-κ type, respectively. Kidney biopsy showed an increase in mesangial cells and matrix without nodular lesions under a light microscope. Immunofluorescence microscopy showed granular deposits of IgG and C3 on the capillary wall and weak positivity for C1q. IgG3 was predominant among the IgG subclasses, and intraglomerular κ and λ staining was negative for κ and positive for λ. Direct fast scarlet staining was negative. Electron microscopy showed lumpy deposits without a fibrillar structure in the subepithelial area. Based on the above findings, a diagnosis of membranous nephropathy-type PGNMID was made. Since proteinuria increased gradually after three years of treatment with valsartan (40 mg, daily), oral prednisolone (30 mg, daily) was initiated, which led to decreased proteinuria. The dose of oral prednisolone was gradually tapered to 10 mg per day. At that time, proteinuria was 0.88 g/g⋅Cr. We found 204 cases in 81 articles in the PubMed database, among which 8 showed discrepancy in the heavy and/or light chains between serum and kidney.

CONCLUSIONS

We experienced a case of membranous nephropathy-type PGNMID with discrepancy in light chains between serum and kidney that was successfully treated with oral prednisolone.

Moshen granule ameliorates membranous nephropathy by blocking intrarenal renin-angiotensin system signalling via the Wnt1/β-catenin pathway

BACKGROUND

Membranous nephropathy (MN) is one of the cardinal causes of nephrotic syndrome in adults, but an adequate treatment regimen is lacking.

PURPOSE

We assessed the effect of Moshen granule (MSG) on patients with MN and cationic bovine serum albumin (CBSA)-induced rats. We further identified the bioactive components of MSG and revealed the underlying molecular mechanism of its renoprotective effects.

METHODS

We determined the effect of MSG on patients with MN and CBSA-induced rats and its components on podocyte injury in zymosan-activated serum (ZAS)-elicited podocytes and revealed their regulatory mechanism on the Wnt/β-catenin/renin-angiotensin system (RAS) signalling axis.

RESULTS

MSG treatment improved renal function and reduced proteinuria in MN patients and significantly reduced proteinuria and preserved the protein expression of podocin, nephrin, podocalyxin and synaptopodin in CBSA-induced MN rats. Mechanistically, MSG treatment significantly inhibited the protein expression of angiotensinogen, angiotensin converting enzyme and angiotensin II type 1 receptor, which was accompanied by inhibition of the protein expression of Wnt1 and β-catenin and its downstream gene products, including Snail1, Twist, matrix metalloproteinase-7, plasminogen activator inhibitor-1 and fibroblast-specific protein 1, in CBSA-induced MN rats. We further identified 81 compounds, including astragaloside IV (AGS), calycosin, barleriside A and geniposidic acid, that preserve the podocyte-specific protein expression in ZAS-induced podocytes. Among these four compounds, AGS exhibited the strongest inhibitory effects on podocyte protein expression. AGS treatment significantly inhibited the protein expression of RAS components and Wnt1 and β-catenin and its downstream gene products in ZAS-induced podocytes. In contrast, the inhibitory effect of AGS on podocyte-specific proteins, β-catenin downstream gene products and RAS components was partially abolished in ZAS-induced podocytes treated with ICG-001 and β-catenin siRNA.

CONCLUSION

This study first demonstrates that AGS mitigates podocyte injury by inhibiting the activation of RAS signalling via the Wnt1/β-catenin pathway by both pharmacological and genetic methods. Therefore, AGS might be considered a new β-catenin inhibitor that inhibits the Wnt1/β-catenin pathway to retard MN in patients.

Single-Nephron GFR in Different Glomerular Basement Membrane Stages of Membranous Nephropathy

Key Points

The first study that estimated single-nephron GFR (SNGFR) in patients with membranous nephropathy (MN). Associations of SNGFR with MN staging by electron microscopy and clinicopathologic findings were cross-sectionally investigated. This study illustrates a role for disease-specific GBM structural lesions as determinants of SNGFR in patients with MN.

Background

Alterations in single-nephron dynamics have been demonstrated in animal models of membranous nephropathy (MN). This study applied a recently developed technique to estimate single-nephron parameters in human MN.

Methods

Single-nephron GFR (SNGFR) and single-nephron urinary protein excretion (SNUPE) were calculated by dividing total GFR and UPE by the total estimated number of nonglobally sclerotic glomeruli (NSG). The NSG number per kidney was estimated using cortical volume assessment and biopsy-based stereology. MN staging by electron microscopy was performed using Ehrenreich-Churg (EC) criteria. Single-nephron parameters were analyzed in relation to clinicopathological factors known to associate with disease outcomes.

Results

The study included 109 patients with MN (mean age 65 years; 73% male; eGFR 62 ml/min, 36% on renin-angiotensin-aldosterone system inhibitors prebiopsy). EC stages were I, 19%; II, 49%; III, 26%; and IV, 6%. There was no difference in glomerular volume among EC stage groups. With advancing EC stage, SNGFR and SNUPE decreased from mean 56–42 nl/min and 5.1–3.8 µ g/d, respectively. In multivariable models, EC stage was associated with SNGFR even after adjustment for key clinicopathological factors, such as reduced GFR, serum albumin, UPE, segmental glomerulosclerosis, chronic tubulointerstitial damage, and prebiopsy use of renin-angiotensin-aldosterone system inhibitors. By contrast, EC stage was not associated with glomerular volume and SNUPE after multivariable adjustment.

Conclusions

These results provide the first clinical evidence of alterations in single-nephron dynamics with advancing EC stage of human MN and support a role for disease-specific glomerular basement membrane structural lesions as determinants of SNGFR.

Decay-Accelerating Factor Restrains Complement Activation and Delays Progression of Murine cBSA-Induced Membranous Nephropathy

Key Points

In a murine model of cationic bovine serum albumin (cBSA)–induced membranous nephropathy (MN), complement regulator decay-accelerating factor is upregulated and restrains complement activation. Studies using genetic deletion or pharmacological antagonism of C3aR indicate that the main effector mechanism of complement activation in cBSA-induced MN is C3a/C3aR signaling. C3a formation and/or C3aR-mediated signaling represent promising targets for hypothesis-driven therapies for MN.

Background

Complement activation is believed to play a major pathogenic role in membranous nephropathy (MN), but its effector mechanisms are still unclear. Even less investigated is the role of podocyte-expressed complement regulators, including decay-accelerating factor (DAF) in disease pathophysiology.

Methods

We induced MN by serial injections of cationic bovine serum albumin (cBSA) in WT, DAF−/−, and C3aR−/− BALB/c mice and measured disease severity (by albuminuria, BUN, serum albumin, and glomerular histologic changes) and signs of complement activation in the glomeruli (immunofluorescence for C1q, C3b, and membrane attack complex). We also treated DAF−/− mice with cBSA-induced MN with a selective C3aR antagonist and measured the same readouts.

Results

cBSA-induced MN was associated with increased glomerular expression of DAF. Genetic deletion of DAF resulted in increased complement activation and higher disease severity than in WT animals. Treating cBSA-injected DAF−/− mice with a C3aR antagonist reduced disease severity. Similarly, C3aR−/− animals were protected from cBSA-induced MN, despite IgG deposition in the glomeruli and complement activation. Evidence of C1q and C3b deposition in the glomeruli of these mice suggest that IgG-cBSA immune complex formation in the glomeruli activates complement through the classical pathway.

Conclusions

On cBSA-induced injury, podocytes upregulate DAF expression, which restrains complement activation. However, after prolonged injury, complement activation overcomes DAF regulatory effects leading to the formation of soluble anaphylatoxin C3a that, by signaling through C3aR, promotes glomerular injury and cBSA-induced MN disease progression. Considering the growing number of complement targeting therapies, our findings may have major translational effect on the treatment of patients with MN.

Shared genetic risk across different presentations of gene test-negative idiopathic nephrotic syndrome

BACKGROUND

Idiop athic nephrotic syndrome (INS) is classified in children according to response to initial corticosteroid therapy into steroid-sensitive (SSNS) and steroid-resistant nephrotic syndrome (SRNS), and in adults according to histology into minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS). However, there is well-recognised phenotypic overlap between these entities. Genome-wide association studies (GWAS) have shown a strong association between SSNS and variation at HLA, suggesting an underlying immunological basis. We sought to determine whether a risk score generated from genetic variants associated with SSNS could be used to gain insight into the pathophysiology of INS presenting in other ways.

METHODS

We developed an SSNS genetic risk score (SSNS-GRS) from the five variants independently associated with childhood SSNS in a previous European GWAS. We quantified SSNS-GRS in independent cohorts of European individuals with childhood SSNS, non-monogenic SRNS, MCD, and FSGS, and contrasted them with SSNS-GRS quantified in individuals with monogenic SRNS, membranous nephropathy (a different immune-mediated disease-causing nephrotic syndrome), and healthy controls.

RESULTS

The SSNS-GRS was significantly elevated in cohorts with SSNS, non-monogenic SRNS, MCD, and FSGS compared to healthy participants and those with membranous nephropathy. The SSNS-GRS in all cohorts with non-monogenic INS were also significantly elevated compared to those with monogenic SRNS.

CONCLUSIONS

The shared genetic risk factors among patients with different presentations of INS strongly suggests a shared autoimmune pathogenesis when monogenic causes are excluded. Use of the SSNS-GRS, in addition to testing for monogenic causes, may help to classify patients presenting with INS. A higher resolution version of the Graphical abstract is available as Supplementary information.

Membranous Nephropathy in Syphilis is Associated with Neuron-Derived Neurotrophic Factor

SIGNIFICANCE STATEMENT

Syphilis is a common worldwide sexually transmitted infection. Proteinuria may occur in patients with syphilis. Membranous nephropathy (MN) is the most common cause of proteinuria in syphilis. The target antigen of MN in syphilis is unknown. This study shows that MN in syphilis is associated with a novel target antigen called neuron-derived neurotrophic factor (NDNF). NDNF-associated MN has distinctive clinical and pathologic manifestations and NDNF appears to be the target antigen in syphilis-associated MN.

BACKGROUND

Syphilis is a common sexually transmitted infection. Membranous nephropathy (MN) is a common cause of proteinuria in syphilis. The target antigen is not known in most cases of syphilis-associated MN.

METHODS

We performed laser microdissection of glomeruli and mass spectrometry (MS/MS) in 250 cases (discovery cohort) of phospholipase A2 receptor-negative MN to identify novel target antigens. This was followed by immunohistochemistry/confocal microscopy to localize the target antigen along the glomerular basement membrane (GBM). Western blot analyses using IgG eluted from frozen biopsy tissue were performed to detect binding to target antigen.

RESULTS

MS/MS studies of the discovery cohort revealed high total spectral counts of a novel protein, neuron-derived neurotrophic factor (NDNF), in three patients: one each with syphilis and hepatitis B, HIV (syphilis status not known), and lung tumor. Next, MS/MS studies of five cases of syphilis-MN (validation cohort) confirmed high total spectral counts of NDNF (average 45±20.4) in all (100%) cases. MS/MS of 14 cases of hepatitis B were negative for NDNF. All eight cases of NDNF-associated MN were negative for known MN antigens. Electron microscopy showed stage I MN in all cases, with superficial and hump-like deposits without GBM reaction. IgG1 was the dominant IgG subtype on MS/MS and immunofluorescence microscopy. Immunohistochemistry/confocal microscopy showed granular staining and colocalization of NDNF and IgG along GBM. Western blot analyses using eluate IgG of NDNF-MN showed binding to both nonreduced and reduced NDNF, while IgG eluate from phospholipase A2 receptor-MN showed no binding.

CONCLUSION

NDNF is a novel antigenic target in syphilis-associated MN.

Negative Modulation of B Cell Activation by Melanocortin 1 Receptor Signaling Protects against Membranous Nephropathy

SIGNIFICANCE STATEMENT

Emerging evidence suggests that melanocortin neuropeptides-specifically adrenocorticotropic hormone-offer a novel, steroidogenic-independent therapeutic modality for membranous nephropathy (MN). The molecular mechanism underlying this beneficial effect, however, remains largely elusive. To investigate whether melanocortins modulate humoral immunity, the authors induced passive Heymann nephritis, a model of human MN, in wild-type and melanocortin 1 receptor (MC1R) knockout rats and treated them with melanocortin agents. Additional rats received adoptive transfer of bone marrow-derived cells beforehand from wild-type or MC1R knockout rats. The findings indicate that MC1R signaling plays a key role in negative modulation of B-cell activation and thereby suppresses humoral immune responses in passive Heymann nephritis, and suggest that MC1R signaling might offer a novel B cell-targeted therapeutic strategy for MN.

BACKGROUND

Emerging evidence suggests that the pituitary neuropeptide melanocortins-specifically, adrenocorticotropic hormone-offer a novel nonsteroidogenic therapeutic modality for membranous nephropathy (MN). However, the mechanism(s) of action remains elusive.

METHODS

To investigate whether melanocortins modulate humoral immunity, we induced passive Heymann nephritis (PHN), a model of MN, in wild-type (WT) and melanocortin 1 receptor (MC1R) knockout (KO) rats. We treated the animals with melanocortin agents-repository corticotropin injection, the nonsteroidogenic pan-melanocortin receptor agonist [Nle 4 , DPhe 7 ]-α-melanocyte stimulating hormone, the selective MC1R agonist MS05, vehicle gel, or phosphate-buffered saline-and evaluated kidney function, histology, and molecular changes. Additional rats received adoptive transfer of syngeneic bone marrow-derived cells beforehand from WT or MC1R KO rats.

RESULTS

KO of MC1R worsened PHN and this was associated with increased deposition of autologous immunoglobulin G (IgG) and complement C5b-9 in glomeruli and higher circulating levels of autologous IgG-evidence of a sensitized humoral immune response. Melanocortin therapy ameliorated PHN in WT rats, coinciding with reduced glomerular deposition of autologous IgG and C5b -9. The beneficial efficacy of melanocortins was blunted in KO rats but restored by adoptive transfer of syngeneic bone marrow-derived cells derived from WT rats. Mechanistically, MC1R was expressed in B lymphocytes and was negatively associated with B cell activation. MC1R agonism triggered the expression of microphthalmia-associated transcription factor in activated B cells in a cAMP-dependent mode and also repressed the expression of interferon regulatory factor 4 (a lymphoid transcription factor essential for B-cell development and maturation), resulting in suppressed plasma cell differentiation and IgG production.

CONCLUSIONS

MC1R signaling negatively modulates B cell activation and suppresses humoral immune responses in PHN, suggesting that MC1R signaling might offer a novel therapeutic target for MN.

Pathogenicity of Human Anti-PLA 2 R1 Antibodies in Minipigs: A Pilot Study

SIGNIFICANCE STATEMENT

Membranous nephropathy (MN) is an autoimmune kidney disease characterized by immune deposits in the glomerular basement membrane. Circulating anti-phospholipase A 2 receptor 1 (PLA 2 R1) antibodies are detectable in 70%-80% of patients with MN, but experimental evidence of pathogenicity has been lacking. This study demonstrates the pathogenicity of human anti-PLA 2 R1 antibodies in minipigs, a model for MN that intrinsically expresses PLA 2 R1 on podocytes. After passive transfer of human anti-PLA 2 R1 antibody-containing plasma from patients with PLA 2 R1-associated MN to minipigs, antibodies were detected in the minipig glomeruli, but not in response to plasma from healthy controls. The minipigs developed histomorphological characteristics of MN, local complement activation in the glomeruli, and low-level proteinuria within 7 days, showing that human anti-PLA 2 R1 antibodies are pathogenic.

BACKGROUND

Primary membranous nephropathy (MN) is an autoimmune kidney disease in which immune complexes are deposited beneath the epithelium in the glomeruli. The condition introduces a high risk for end-stage kidney disease. Seventy percent to 80% of patients with MN have circulating antibodies against phospholipase A 2 receptor 1 (PLA 2 R1), and levels correlate with treatment response and prognosis. However, experimental evidence that human anti-PLA 2 R1 antibodies induce MN has been elusive.

METHODS

In passive transfer experiments, minipigs received plasma or purified IgG from patients with PLA 2 R1-associated MN or from healthy controls. Anti-PLA 2 R1 antibodies and proteinuria were monitored using Western blot, ELISA, and Coomassie staining. Kidney tissues were analyzed using immunohistochemistry, immunofluorescence, electron microscopy, and proteomic analyses.

RESULTS

Minipigs, like humans, express PLA 2 R1 on podocytes. Human anti-PLA 2 R1 antibodies bound to minipig PLA 2 R1 in vitro and in vivo . Passive transfer of human anti-PLA 2 R1 antibodies from patients with PLA 2 R1-associated MN to minipigs led to histological characteristics of human early-stage MN, activation of components of the complement cascade, and low levels of proteinuria. We observed development of an autologous, later phase of disease.

CONCLUSIONS

A translational approach from humans to minipigs showed that human anti-PLA 2 R1 antibodies are pathogenic in MN, although in the heterologous phase of disease only low-level proteinuria developed.

Discovery of seven novel putative antigens in membranous nephropathy and membranous lupus nephritis identified by mass spectrometry

Multiple autoantigens have been identified in membranous nephropathy (MN) by tissue-based proteomics. However, antigenic targets of disease are unknown for over 10% of patients with MN and over half of those with membranous lupus nephritis (MLN). Here, we identified multiple new targets in PLA2R-/THSD7A-/EXT-/NELL1-quadruple negative MN biopsies through mass spectrometry of immune complexes recovered from biopsy tissue of patients with MN. Patients with MN negative for these four antigens were identified from Arkana Laboratories case archives. Protein G immunoprecipitation recovered immune complexes from frozen biopsy tissue from 142 quadruple-negative cases and 278 cases of known antigen type, followed by interrogation by mass spectrometry. Potential putative antigens were confirmed through paraffin immunofluorescence and co-localization with IgG within immune deposits. Consecutive series of 165 cases of PLA2R-negative MN and 142 MLN biopsies were screened to determine the frequency for each potential antigen. Seven putative antigens were discovered within immune complexes from biopsies of patients with MN including FCN3, CD206, EEA1, SEZ6L2, NPR3, MST1, and VASN. Peptides from these proteins were not enriched in the 278 cases of known antigen type. Between three to 30 unique peptides were detected for each new target. Frequencies of each biomarker, determined by staining consecutive case series, ranged from under 1 to 4.9%. NPR3 and CD206 were only positive in index cases. All cases showed co-localization of IgG within the immune deposits. Thus, seven putative antigens were newly identified in MN and MLN. Due to the number of antigens identified, it is becoming impractical to type PLA2R-negative MN or MLN cases through immunostaining alone. A multiplex approach is needed for subtyping of these diseases.

Gut Microbiota Alterations and Primary Glomerulonephritis in Children: A Review

The article summarizes the current evidence on the impact of microbiota alterations on immune-mediated primary glomerulonephritis in children. In particular, the focus is on the link between dysbiosis and the onset or recurrence of idiopathic nephrotic syndrome, immunoglobulin A nephropathy, and membranous nephropathy. The aim is to describe possible pathomechanisms, differences in gut microbiota composition between pediatric patients and healthy controls, and possible usage of microbiota manipulations in supportive therapy. On this basis, we attempt to indicate directions for further research in that field.

Membranous nephropathy: Clearer pathology and mechanisms identify potential strategies for treatment

Primary membranous nephropathy (PMN) is one of the common causes of adult-onset nephrotic syndrome and is characterized by autoantibodies against podocyte antigens causing in situ immune complex deposition. Much of our understanding of the disease mechanisms underpinning this kidney-limited autoimmune disease originally came from studies of Heymann nephritis, a rat model of PMN, where autoantibodies against megalin produced a similar disease phenotype though megalin is not implicated in human disease. In PMN, the major target antigen was identified to be M-type phospholipase A2 receptor 1 (PLA2R) in 2009. Further utilization of mass spectrometry on immunoprecipitated glomerular extracts and laser micro dissected glomeruli has allowed the rapid discovery of other antigens (thrombospondin type-1 domain-containing protein 7A, neural epidermal growth factor-like 1 protein, semaphorin 3B, protocadherin 7, high temperature requirement A serine peptidase 1, netrin G1) targeted by autoantibodies in PMN. Despite these major advances in our understanding of the pathophysiology of PMN, treatments remain non-specific, often ineffective, or toxic. In this review, we summarize our current understanding of the immune mechanisms driving PMN from animal models and clinical studies, and the implications on the development of future targeted therapeutic strategies.

Hepatitis B virus-associated cryoglobulinaemia diffuse endocapillary proliferative glomerulonephritis: a case report and literature review

Cryoglobulinaemia can manifest as fatigue, purpura, and joint pain, and can involve the kidneys and peripheral nervous system. Type II and mixed cryoglobulinemia cases are usually associated with hepatitis C virus infection and autoimmune diseases, and most cases reported outside China have been related to hepatitis C virus. The pathological manifestation of cryoglobulinaemia glomerulonephritis is always membranous proliferative glomerulonephritis or membranous nephropathy; other pathological types are rare. This current case report describes a female patient with hepatitis B virus (HBV)-associated cryoglobulinaemic glomerulonephritis. The patient had hepatitis B complicated with purpura, abnormal urinalysis and renal function. She was positive for rheumatoid factor and had decreased complement, and her blood cryoglobulin level was positive. The pathological findings were consistent with late-stage capillary proliferative glomerulonephritis, which improved after steroid, immunosuppressant and anti-HBV treatment.

The role of the complement system in primary membranous nephropathy: A narrative review in the era of new therapeutic targets

Primary membranous nephropathy (MN) is an important cause of nephrotic syndrome and chronic kidney disease (CKD) in the adult population. Although the discovery of different autoantibodies against glomerular/podocytic antigens have highlighted the role of B cells in the pathogenesis of MN, suboptimal response or even resistance to B cell-directed therapies occurs, suggesting that other pathophysiological mechanisms are involved in mediating podocyte injury. The complement system plays an important role in the innate immune response to infection, and dysregulation of the complement system has been observed in various kidney diseases. There is compelling evidence of complement cascade activation in primary MN, with the mannose-binding lectin (MBL) and alternative pathways particularly implicated. With appropriate validation, assays of complements and associated activation products could hold promise as adjunctive tools for non-invasive disease monitoring and prognostication. While there is growing interest to target the complement system in MN, there is concern regarding the risk of infection due to encapsulated organisms and high treatment costs, highlighting the need for clinical trials to identify patients most likely to benefit from complement-directed therapies.