Membranous nephropathy-one morphologic pattern with different diseases

Osteopontin as a Biomarker in Chronic Kidney Disease

Osteopontin (OPN) is a ubiquitously expressed protein with a wide range of physiological functions, including roles in bone mineralization, immune regulation, and wound healing. OPN has been implicated in the pathogenesis of several forms of chronic kidney disease (CKD) where it promotes inflammation and fibrosis and regulates calcium and phosphate metabolism. OPN expression is increased in the kidneys, blood, and urine of patients with CKD, particularly in those with diabetic kidney disease and glomerulonephritis. The full-length OPN protein is cleaved by various proteases, including thrombin, matrix metalloproteinase (MMP)-3, MMP-7, cathepsin-D, and plasmin, producing N-terminal OPN (ntOPN), which may have more detrimental effects in CKD. Studies suggest that OPN may serve as a biomarker in CKD, and while more research is needed to fully evaluate and validate OPN and ntOPN as CKD biomarkers, the available evidence suggests that they are promising candidates for further investigation. Targeting OPN may be a potential treatment strategy. Several studies show that inhibition of OPN expression or activity can attenuate kidney injury and improve kidney function. In addition to its effects on kidney function, OPN has been linked to cardiovascular disease, which is a major cause of morbidity and mortality in patients with CKD.

Membranous nephropathy: new pathogenic mechanisms and their clinical implications

Membranous nephropathy (MN) is characterized histomorphologically by the presence of immune deposits in the subepithelial space of the glomerular filtration barrier; its clinical hallmarks are nephrotic range proteinuria with oedema. In patients with primary MN, autoimmunity is driven by circulating autoantibodies that bind to one or more antigens on the surface of glomerular podocytes. Compared with other autoimmune kidney diseases, the understanding of the pathogenesis of MN has substantially improved in the past decade, thanks to the discovery of pathogenic circulating autoantibodies against phospholipase A₂ receptor 1 (PLA₂R1) and thrombospondin type 1 domain-containing protein 7A (THSD7A). The subsequent identification of more proteins associated with MN, some of which are also endogenous podocyte antigens, might further advance the clinical characterization of MN, including its diagnosis, treatment and prognosis. Insights from studies in patients with MN, combined with the development of novel in vivo and in vitro experimental models, have potential to improve the management of patients with MN. Characterizing the interaction between autoimmunity and local glomerular lesions provides an opportunity to develop more specific, pathogenesis-based treatments.

Establishment of Galectin-3 Time-resolved Fluoroimmunoassay and its Application in Idiopathic Membranous Nephropathy

The aim of this study was to establish a time-resolved fluorescent immunoassay (TRFIA) for the detection of serum Galectin-3 (Gal-3) and apply this method to evaluate the clinical significance of serum Gal-3 in predicting Idiopathic Membranous Nephropathy (IMN) progression. The Gal-3-TRFIA was established using the double antibody sandwich method, with the capture antibodies coated on a 96-well microplate and the detection antibodies chelated with Europium (III) (Eu³⁺). Serum Gal-3 was detected in 81 patients with IMN and 123 healthy controls to further evaluate the value of the Gal-3 in staging of IMN. The sensitivity of the Gal-3-TRFIA assay was 0.85 ng/mL, and the detection range was 0.85-1000 ng/mL. The Gal-3 intra-batch and inter-batch coefficients of variation were 3.45% and 5.12%, respectively. The correlation coefficient (R) between the Gal-3-TRFIA assay and commercially available enzyme-linked immunosorbent assay kits was 0.83. The serum Gal-3 concentration was higher in patients with IMN (65.57 ± 55.90 ng/mL) compared to healthy controls (16.29 ± 9.91 ng/mL, P < 0.0001). In this study, a wide detection range Gal-3-TRFIA assay was developed using lanthanide (Eu³⁺) chelates for the detection of Gal-3 concentrations in serum. Gal-3 concentration is elevated in patients with IMN.

Membranous nephropathy: a single disease or a pattern of injury resulting from different diseases

Membranous nephropathy (MN) is defined as disease entity characterized by thickening of the glomerular basement membranes due to subepithelial (SE) deposition of immune complexes. It is typically classified into primary MN (70%) when there is no disease association, and secondary MN (30%) when there is an underlying disease association such as lupus, malignancy, infections or drugs. Phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) are target antigens in 70% and 1–5% of primary MN, respectively. The antigens in the remaining MN were not known. Recently, multiple novel proteins/target antigens have been identified in MN. These include exostosin 1/2, neural epidermal growth-like 1 protein, semaphorin 3B, protocadherin 7 and neural cell adhesion molecule 1. Some of these antigens are present in the setting of primary MN, some in secondary MN and some in both, thus blurring the lines between primary and secondary MN. Preliminary studies show that each of the new antigen-associated MN has distinct clinical, kidney biopsy findings and outcome data. We propose that each new protein/antigen-associated MN is a specific disease that results in the common MN pattern of injury characterized by thickened glomerular basement membrane (GBM) with or without spikes or pinholes on light microscopy, granular immunoglobulin G with or without complement 3 on immunofluorescence microscopy and SE electron-dense deposits on electron microscopy. In other words, MN is truly only a pattern of injury resulting from specific diseases that cause deposition of SE immune deposits along the GBM. It is of paramount importance to ascertain the specific disease entity causing the MN pattern not only for precise diagnosis and management, but also for future studies on these newly described diseases.

Multi-Autoantibody Signature and Clinical Outcome in Membranous Nephropathy

BACKGROUND AND OBJECTIVES

Patients with membranous nephropathy can have circulating autoantibodies against membrane-bound (phospholipase A2 receptor 1 [PLA2R1] and thrombospondin type-1 domain containing 7A [THSD7A]) and intracellular (aldose reductase, SOD2, and α-enolase) podocyte autoantigens. We studied their combined association with clinical outcomes.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Serum levels of anti-PLA2R1, anti-THSD7A, anti-aldose reductase, anti-SOD2, and anti-α-enolase autoantibodies were determined in 285 patients at diagnosis and during follow-up using standardized and homemade assays. An eGFR>60 ml/min per 1.73 m² and remission of proteinuria (<0.3/<3.5 g per d) after 12 months were the outcomes of interest.

RESULTS

At diagnosis, 182 (64%), eight (3%), and 95 (33%) patients were anti-PLA2R1⁺, anti-THSD7A⁺, and double negative, respectively. The prevalence of a detectable antibody to at least one intracellular antigen was similarly distributed in patients who were anti-PLA2R1⁺ (n=118, 65%) and double negative (n=64, 67%). Positivity for anti-PLA2R1, anti-SOD2, and anti-α-enolase antibodies and higher titers at diagnosis were associated with poor clinical outcome independently to each other. Combined positivity for anti-PLA2R1, anti-SOD2, and anti-α-enolase was associated with highest risk of poor outcome (odds ratio, 5.5; 95% confidence interval, 1.2 to 24; P=0.01). In Kaplan-Meier analysis, patients who were anti-PLA2R1⁺/anti-SOD2⁺ or anti-PLA2R1⁺/anti-α-enolase⁺ had lower eGFR at 12 months compared with patients who were anti-PLA2R1⁺/anti-SOD2^- or anti-α-enolase^-. Predictive tests (net reclassification index and area under the curve-receiver-operating characteristic analysis) showed that combined assessment of antibodies improved classification of outcome in 22%-34% of cases for partial remission of proteinuria and maintenance of normal eGFR. For patients with nephrotic syndrome at diagnosis, anti-SOD2 positivity and high anti-PLA2R1 titer were associated with a lack of complete remission. Patients who were anti-PLA2R1^-/anti-intracellular antigens^- had the lowest proteinuria and the highest eGFR at diagnosis and the lowest risk of lower eGFR at 12 months. Epitope spreading was present in 81% of patients who were anti-PLA2R1⁺ and was associated with increased positivity for intracellular antigens and poor eGFR at diagnosis and 12 months.

CONCLUSIONS

Combined serological analysis of autoantibodies targeting membrane-bound and intracellular autoantigens identifies patients with poor clinical outcomes.

Effects of CYP3A5 Polymorphisms on Efficacy and Safety of Tacrolimus Therapy in Patients with Idiopathic Membranous Nephropathy

Background

Tacrolimus (TAC) is beneficial for patients with idiopathic membranous nephropathy (IMN). It has a narrow therapeutic concentration range and many factors influence TAC blood concentration. CYP3A5 is the most important enzyme in TAC metabolism. The aim of this study was to analyze the effects of CYP3A5 gene polymorphisms on the efficacy and safety of TAC in IMN patients.

Patients and Methods

Patients with IMN who received oral TAC (0.05-0.075mg/kg/day) combined with prednisone (0.5mg/kg/day) from March 2016 to October 2018 were included. The data of clinical characteristics, therapeutic drugs and adverse reactions of patients were collected at baseline and during 24 weeks of treatment. Patients were divided into two groups according to different CYP3A5 genetic polymorphisms. The significant differences in the efficacy and side effects between the two groups were analyzed.

Results

A total of 76 patients who completed follow-up were divided into CYP3A5 nonexpresser (CYP3A5*3/*3) group and CYP3A5 expresser (CYP3A5 *1/*3) group. The significant association between the CYP3A5 phenotype and TAC metabolism was observed. A total of 43 case-times patients exhibited adverse effects. The infection rate in CYP3A5 nonexpresser group (21.95%) was remarkably higher than the rate in CYP3A5 expresser group (5.71%). Blood concentration and C₀/D levels were risk factors for adverse events through logistic regression analysis. There was no statistical difference between the study groups with respect to the efficacy.

Conclusion

Our results demonstrated that CYP3A5 polymorphisms had important guiding roles in the treatment of IMN with tacrolimus. CYP3A5 expressers required higher daily doses of TAC to achieve the target drug concentration, but with fewer side effects. CYP3A5 genetic polymorphism might be used for TAC dosing adjustment to optimize the treatment for patients with IMN.

Molecular classification of membranous nephropathy

PURPOSE OF REVIEW

Continuous expansion of our knowledge in the pathogenesis of membranous nephropathy possible by the identification of antibodies recognized specific podocytes antigens results in unprecedent patient management strategy.

RECENT FINDINGS

Circulating anti-phospholipase A2 receptor (PLA2R) and anti-thrombospondin domain 7A (THSD7A) antibodies strongly relate with the modifications of podocytes biology leading to the new molecular diagnosis of membranous nephropathy. Immunization against THSD7A involves extra-renal mechanism. However, the pathway of anti-PLA2R immunization still remains unresolved. Experimental data highlight the crucial role of THSD7A in the attachment of podocytes to the glomerular basement membrane, rewarding the THSD7A pathogenicity, whereas the third of Koch's postulates is still not fulfilled for anti-PLA2R antibodies. The anti-PLA2R antibodies epitope spreading will possibly be even more specific marker improving the molecular classification of membranous nephropathy. Two immune epitopes have been identified in the N-terminal tail of THSD7A but without evidence of epitope spreading as for anti-PLA2R.

SUMMARY

In 2019, the Kidney Diseases: Improving Global Outcomes guidelines recognized anti-PLA2R antibodies (but not anti-THSD7A antibodies) as a valuable molecular risk factor for the pejorative evolution of kidney function and recommended their monitoring for the diagnosis and the assessment of membranous nephropathy immune activity. Screening for malignancy is particularly advised in THSD7A-mediated membranous nephropathy.

Novel ELISA for thrombospondin type 1 domain-containing 7A autoantibodies in membranous nephropathy

Autoantibodies against phospholipase A2 receptor 1 (PLA2R1) and thrombospondin type 1 domain-containing 7A (THSD7A) are emerging as biomarkers to classify membranous nephropathy (MN) and to predict outcome or response to treatment. Anti-THSD7A autoantibodies are detected by Western blot and indirect immunofluorescence test (IIFT). Here, we developed a sensitive enzyme-linked immunosorbent assay (ELISA) optimized for quantitative detection of anti-THSD7A autoantibodies. Among 1012 biopsy-proven MN patients from 6 cohorts, 28 THSD7A-positive patients were identified by ELISA, indicating a prevalence of 2.8%. By screening additional patients, mostly referred because of PLA2R1-unrelated MN, we identified 21 more cases, establishing a cohort of 49 THSD7A-positive patients. Twenty-eight patients (57%) were male, and male patients were older than female patients (67 versus 49 years). Eight patients had a history of malignancy, but only 3 were diagnosed with malignancy within 2 years of MN diagnosis. We compared the results of ELISA, IIFT, Western blot, and biopsy staining, and found a significant correlation between ELISA and IIFT titers. Anti-THSD7A autoantibodies were predominantly IgG4 in all patients. Eight patients were double positive for THSD7A and PLA2R1. Levels of anti-THSD7A autoantibodies correlated with disease activity and with response to treatment. Patients with high titer at baseline had poor clinical outcome. In a subgroup of patients with serial titers, persistently elevated anti-THSD7A autoantibodies were observed in patients who did not respond to treatment or did not achieve remission. We conclude that the novel anti-THSD7A ELISA can be used to identify patients with THSD7A-associated MN and to monitor autoantibody titers during treatment.

[Membranous glomerulonephritis : An example of individualized medicine in nephrology]

BACKGROUND

Membranous glomerulonephritis (MGN) is the most frequent cause of a nephrotic syndrome in adults. It is an autoimmune disease caused by binding of autoantibodies to endogenous proteins expressed on glomerular podocytes. Antibody binding and activation of inflammatory mediators result in the onset of proteinuria. Recently, two endogenous podocytic target antigens in MGN have been characterized and their clinical role is a main focus of research in nephrology.

OBJECTIVE

The discovery that antibodies against phospholipase A2 receptor 1 (PLA₂R1) and thrombospondin type 1 domain containing 7A (THSD7A) mediate the pathogenesis of MGN leads to the question of what clinical role these antibodies have in patients with MGN.

MATERIAL AND METHODS

Evidence published in recent years on the role of the described antigens is analyzed and critically discussed. The clinical conclusions derived for patients with MGN are presented.

RESULTS

Antibodies against PLA₂R1 are detectable in approximately 80% of patients with MGN, while 2-3% of patients have antibodies against THSD7A. Serum analyses of antibodies and immunohistological staining in kidney biopsies enable an almost 100% certain diagnosis of PLA₂R1 and THSD7A-mediated MGN. Serum levels of PLA₂R1 antibodies are predictors for the response to therapy, determine the prognosis and allow an exact individualized monitoring of treatment. The THSD7A antibodies are associated with an increased prevalence of malignant tumors and play a pathogenetic role in the genesis of this secondary form of MGN.

CONCLUSION

The characterization of the antibodies responsible for the development of MGN is an example of precision medicine in nephrology and the foundation for the development of new, curative treatments.

Characterization of autoantibodies in primary membranous nephropathy and their clinical significance

Introduction: Membranous nephropathy (MN) is the most common cause of a nephrotic syndrome in Caucasian adults. The identification of target antigens in MN in the last decade has had a major impact on the clinical approach to these patients. Areas covered: Since the discoveries in animal models in the 1980s that circulating autoantibodies induce disease upon in situ binding to glomerular podocytes, many attempts have been undertaken to define the human antigens responsible for disease induction. Only in 2009 was Phospholipase A₂ Receptor 1 described as the major antigen responsible for MN onset in about 70% of patients. Subsequently, in 2014, Thrombospondin Type-1 Domain-Containing 7A was identified as a second antigen, accounting for 2-3% of patients with MN. The knowledge of the role of these antibodies in MN has improved the diagnosis and management of patients and helped to better define the need for immunosuppressive treatment. Expert commentary: These discoveries over the last 10 years in the discipline of nephrology have clearly shown the improvements a better understanding of disease pathogenesis can bring for patient care.

The role of osteopontin in kidney diseases

BACKGROUND

Osteopontin (OPN) is a pleiotropic glycoprotein expressed in various cell types in animals and in humans, including bone, immune, smooth muscle, epithelial and endothelial cells. Moreover, OPN is found in kidneys (in the thick ascending limbs of the loop of Henle and in distal nephrons) and urine. The protein plays an important role in mineralization and bone resorption. In addition, OPN is involved in the regulation of immunity and inflammation, angiogenesis and apoptosis. It was demonstrated that OPN and some OPN gene polymorphic variants are associated with the pathogenesis and progression of multiple disorders, such as cancer, autoimmune, neurodegenerative and cardiovascular diseases. Moreover, recent studies suggested that OPN is associated with the pathogenesis of renal failure.

METHODS

In this review, I briefly discussed the role of OPN and its gene polymorphisms in kidney physiology, as well as in various kidney diseases.

FINDINGS AND CONCLUSION

Most studies reported that OPN expression is elevated in urolithiasis, and also in acute and chronic kidney diseases, and in renal allograft dysfunction. Moreover, it was demonstrated that polymorphic variants of the OPN gene may be associated with renal failure. However, some reports suggested that OPN is essential for tubulogenesis, and that it inhibits calcium oxalate crystal formation and retention, nitric oxide synthesis, cell apoptosis and promotes cell regeneration. Thus, further studies are required to fully understand the role of OPN in kidney physiology and pathology. Eventually, these studies may result in the identification of OPN as a valuable marker for renal dysfunction prognosis and treatment.