Membranous nephropathy in the kidney allograft

Post-Transplant Glomerulonephritis: Challenges and Solutions

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.

Posttransplant nephrotic syndrome resulting from NELL1-positive membranous nephropathy

Membranous nephropathy (MN) constitutes a major cause of nephrotic syndrome (NS) in adults. After kidney transplantation (KTx), both recurrent and de novo MN has been reported. In addition to PLA2R and THSD7A, recent identification of neural EGFL-like-1 protein, NELL1, as a potential disease antigen has enriched our understanding of MN pathogenesis. To date, NELL1-positive MN has only been described in native kidneys, but never been diagnosed in renal allografts. We here report on a 56-year-old male kidney transplant recipient suffering from amyotrophic lateral sclerosis (ALS), who developed NS 25 years after KTx. Allograft biopsy revealed NELL1-positive MN. Using specifically established immunoblotting techniques, we detected new-onset NELL1-IgG1, IgG3, and IgG4 antibodies in the patient´s serum correlating with the course of proteinuria. While primary renal disease was undetermined, MN recurrence seemed unlikely given the long-time span since KTx. By clinical investigation of de novo etiologies, we did not detect an underlying malignancy. However, previous self-medication with dimercaptopropane sulfonate (DMPS) and alpha lipoic acid (ALA) represented a potential trigger and cessation associated with partial remission of proteinuria. This report illustrates the first case of posttransplant NS due to NELL1-positive MN. Monitoring NELL1 antibodies in the serum promise to be a non-invasive diagnostic tool guiding disease management.

Immune-Monitoring Disease Activity in Primary Membranous Nephropathy

Primary membranous nephropathy (MN) is a glomerular disease mediated by autoreactive antibodies, being the main cause of nephrotic syndrome among adult patients. While the pathogenesis of MN is still controversial, the detection of autoantibodies against two specific glomerular antigens, phospholipase A2 receptor (PLA₂R) and thrombospondin type 1 domain containing 7A (THSD7A), together with the beneficial effect of therapies targeting B cells, have highlighted the main role of autoreactive B cells driving this renal disease. In fact, the detection of PLA₂R-specific IgG4 antibodies has resulted in a paradigm shift regarding the diagnosis as well as a better prediction of the progression and recurrence of primary MN. Nevertheless, some patients do not show remission of the nephrotic syndrome or do rapidly recur after immunosuppression withdrawal, regardless the absence of detectable anti-PLA₂R antibodies, thus highlighting the need of other immune biomarkers for MN risk-stratification. Notably, the exclusive evaluation of circulating antibodies may significantly underestimate the magnitude of the global humoral memory immune response since it may exclude the role of antigen-specific memory B cells. Therefore, the assessment of PLA₂R-specific B-cell immune responses using novel technologies in a functional manner may provide novel insight on the pathogenic mechanisms of B cells triggering MN as well as refine current immune-risk stratification solely based on circulating autoantibodies.

Membranous Nephropathy Posttransplantation: An Update of the Pathophysiology and Management

Membranous nephropathy (MN) is a common cause of nephrotic syndrome after transplantation and is associated with an increased risk of allograft loss. MN may occur either as a recurrent or as a de novo disease. As in native kidneys, the pathophysiology of the MN recurrence is in most cases associated with antiphospholipid A2 receptor antibodies. However, the posttransplant course has some distinct features when compared with primary MN, including a lower chance of spontaneous remission and a greater requirement for adjuvant immunosuppressive therapy to induce complete remission. Although the efficacy of rituximab in primary MN is now well established, no randomized studies have assessed its effectiveness in MN after transplant, and there are no specific recommendations for the management of these patients. This review aims to synthesize and update the pathophysiology of posttransplant MN, as well as to address unsolved issues specific to transplantation, including the prognostic value of antiphospholipid A2 receptor, the risk of living-related donation, the link between de novo MN and rejection, and different therapeutic strategies so far deployed in posttransplant MN. Lastly, we propose a management algorithm for patients with MN who are planning to receive a kidney transplant, including pretransplant considerations, posttransplant monitoring, and the clinical approach after the diagnosis of recurrence.

The utility of phospholipase A2 receptor autoantibody in membranous nephropathy after kidney transplantation

Membranous nephropathy (MN) is estimated to cause end-stage renal disease in ∼ 5% of patients, in whom renal transplantation is the therapy of choice. Among patients receiving a transplant for MN, the disease will recur in the graft in 30–50%; among these, graft loss will occur in 50% within 10 years. Several studies have suggested that phospholipase A2 receptor autoantibody (aPLA2R) levels before transplantation might be useful in predicting recurrence, and their titration after transplantation is clinically relevant to assess the risk of recurrence and progression, to guide treatment indications and to monitor treatment response. In this review we describe the evolving role of aPLA2R as a biomarker in primary MN and its current usefulness in predicting recurrence of this autoimmune podocytopathy after renal transplantation.

miR-217 Is a Useful Diagnostic Biomarker and Regulates Human Podocyte Cells Apoptosis via Targeting TNFSF11 in Membranous Nephropathy

Background

MicroRNAs have recently been verified as useful diagnostic biomarkers in various diseases. In this study, we investigated whether miR-217 is a useful diagnostic biomarker and the possible pathological mechanism of miR-217 in this disease.

Methods

Patients with focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MN), and diabetic nephropathy (DN) and control patients were enrolled in this study. The miR-217 inhibitor and mimics were transfected into human podocyte cells to investigate the pathological mechanism of miR-217 in this disease. Relevant indicators were detected and tested.

Results

Compared with control patients, miR-217 was significantly downregulated and TNFSF11 was significantly upregulated in MN. Then, miR-217 had obvious separation between patients with MN and control patients, with an AUC of 0.941, a cutoff value of <750.0 copies/ul, and sensitivity and specificity of 88.9% and 75.9%. In addition, the TNFSF11 was confirmed to be the target gene of miR-217. Finally, in in vitro experiments, the upregulation of miR-217 could decrease the expression of TNFSF11 and not induce human podocyte cells apoptosis; however, the downregulation of miR-217 could bring about an opposite change.

Conclusions

miR-217 is a useful diagnostic biomarker and is involved in human podocyte cells apoptosis via targeting TNFSF11 in membranous nephropathy.

Primary Membranous Nephropathy

Membranous nephropathy (MN) is a unique glomerular lesion that is the most common cause of idiopathic nephrotic syndrome in nondiabetic white adults. About 80% of cases are renal limited (primary MN, PMN) and 20% are associated with other systemic diseases or exposures (secondary MN). This review focuses only on PMN. Most cases of PMN have circulating IgG4 autoantibody to the podocyte membrane antigen PLA2R (70%), biopsy evidence PLA2R staining indicating recent immunologic disease activity despite negative serum antibody levels (15%), or serum anti-THSD7A (3%-5%). The remaining 10% without demonstrable anti-PLA2R/THSd7A antibody or antigen likely have PMN probably secondary to a different, still unidentified, anti-podocyte antibody. Considerable clinical and experimental data now suggests these antibodies are pathogenic. Clinically, 80% of patients with PMN present with nephrotic syndrome and 20% with non-nephrotic proteinuria. Untreated, about one third undergo spontaneous remission, especially those with absent or low anti-PLA2R levels, one-third progress to ESRD over 10 years, and the remainder develop nonprogressive CKD. Proteinuria can persist for months after circulating anti-PLA2R/THSD7A antibody is no longer detectable (immunologic remission). All patients with PMN should be treated with supportive care from the time of diagnosis to minimize protein excretion. Patients with elevated anti-PLA2R/THSD7A levels and proteinuria >3.5 g/d at diagnosis, and those who fail to reduce proteinuria to <3.5 g after 6 months of supportive care or have complications of nephrotic syndrome, should be considered for immunosuppressive therapy. Accepted regimens include steroids/cyclophosphamide, calcineurin inhibitors, and B cell depletion. With proper management, only 10% or less will develop ESRD over the subsequent 10 years.