Membranous nephropathy associated with viral infection

An Updated Review of Membranous Nephropathy

Membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome in adults. The discovery of phospholipase A2 receptor (PLA2R) as a target antigen has led to a paradigm shift in the understanding and management of MN. At present, serum PLA2R antibodies are used for diagnosis, prognostication, and guiding treatment. Now, with the discovery of more than 20 novel target antigens, antigen mapping is almost complete. The clinical association of certain antigens provides clues for clinicians, such as the association of nerve epidermal growth factor-like 1 with malignancies and indigenous medicines. Serum antibodies are detected for most target antigens, except exostosin 1 and 2 and transforming growth factor-beta receptor 3, but their clinical utility is yet to be defined. Genome-wide association studies and studies investigating environmental factors, such as air pollution, shed more light on the underpinnings of MN. The standard therapy of MN diversified from cyclical cyclophosphamide and steroids to include rituximab and calcineurin inhibitors over the past decades. Here, we provide a cutting-edge review of MN, focusing on genetics, immune system and environmental factors, novel target antigens and their clinical characteristics, and currently available and emerging novel therapies in MN.

HBx-induced PLA2R overexpression mediates podocyte pyroptosis through the ROS-NLRP3 signaling pathway

INTRODUCTION

Hepatitis B virus-associated glomerulonephritis (HBV-GN) is one of the main types of secondary glomerular diseases, and podocyte injury is an important pathogenic mechanism of HBV-GN, participating in the occurrence and development of HBV-GN. However, the specific mechanism of podocyte injury remains to be studied.

METHODS

Human renal podocytes cultured in vitro were divided into six groups. The podocyte morphology was observed under a transmission electron microscope, and the expression of M-type phospholipase A₂ receptor (M-PLA₂R) on the podocyte membrane was observed by indirect immunofluorescence staining under a fluorescence microscope. The pyroptosis rate and reactive oxygen species (ROS) of podocytes were assessed by FLICA/PI double staining and flow cytometry. Western blot (WB) and quantitative real-time PCR (qPCR) were used to determine the expression of PLA₂R, nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein containing card (ASC), caspase-1, IL-1β, and IL-18.

RESULTS

Hepatitis B virus X (HBx) transfected into human renal podocytes in vitro induced the overexpression of PLA₂R. Moreover, the overexpressed PLA₂R combined with secretory phospholipase A₂ group IB (sPLA₂-IB) aggravated podocyte injury and increased the pyroptosis rate. In addition, the expression of ROS, the NLRP3 inflammasome and downstream inflammatory factors was increased. In contrast, after inhibiting the expression of PLA₂R and ROS, podocyte damage was alleviated, and the pyroptosis rate and the expression of genes related to the ROS-NLRP3 signaling pathway were decreased.

CONCLUSION

HBx-induced PLA₂R overexpression on the podocyte membrane can significantly upregulate the ROS-NLRP3 signaling pathway, thereby mediating podocyte pyroptosis.

Clinical characteristics of membranous nephropathy with spontaneous remission: An analysis of 24 patients

PURPOSE

To investigate the prognosis of patients with spontaneous remission (SR) of phospholipase A2 receptor (PLA2R)-associated membranous nephropathy (MN).

PATIENTS AND METHODS

Patients diagnosed with MN were recruited after examining their renal biopsy in the Renal Department of China-Japan Friendship Hospital between January 2015 and September 2021. Among them, 24 patients with SR were included in this study and follow-up.

RESULTS

Twenty-four patients diagnosed with SR of PLA2R-associated MN were recruited; 11 were male, and 13 were female, with a mean age of 49.5±14.5 years (range, 30-77 years). The initial 24-hour urinary total protein and serum albumin levels were 0.29±0.14g/d and 37.5±4.4g/L, respectively, and the initial serum creatinine was 65.0±15.8μmol/L. During the follow-up of 33.9±19.1 months (range, 6-73 months), 22 (91.7%) patients maintained remission; however, one patient had impaired renal function due to acute coronary syndrome and coronary angiography findings, and one patient experienced a repeated relapse caused by respiratory tract infection, at 50 and 70 months. A systematic review of the relevant literature was conducted, and records of patients with SR of PLA2R-associated MN were retrieved from 16 case reports or case series with a total of 97 cases.

CONCLUSIONS

Most patients with SR of MN had a promising long-term prognosis, with only a few cases of relapse.

HIV-Associated Nephropathy in 2022

Background

HIV-associated nephropathy (HIVAN) is a renal parenchymal disease that occurs exclusively in people living with HIV. It is a serious kidney condition that may possibly lead to end-stage kidney disease, particularly in the HIV-1 seropositive patients.

Summary

The African-American population has increased susceptibility to this comorbidity due to a strong association found in the APOL1 gene, specifically two missense mutations in the G1 allele and a frameshift deletion in the G2 allele, although a "second-hit" event is postulated to have a role in the development of HIVAN. HIVAN presents with proteinuria, particularly in the nephrotic range, as with other kidney diseases. The diagnosis requires biopsy and typically presents with collapsing subtype focal segmental glomerulosclerosis and microcyst formation in the tubulointerstitial region. Gaps still exist in the definitive treatment of HIVAN - concurrent use of antiretroviral therapy and adjunctive management with like renal-angiotensin-aldosterone system inhibitors, steroids, or renal replacement therapy showed benefits.

Key Message

This study reviews the current understanding of HIVAN including its epidemiology, mechanism of disease, related genetic factors, clinical profile, and pathophysiologic effects of management options for patients.

Intrarenal Single-Cell Sequencing of Hepatitis B Virus Associated Membranous Nephropathy

To date, the pathogenesis of hepatitis B virus (HBV)-associated membranous nephropathy (MN) remains elusive. This study aimed to decipher the etiopathogenesis of HBV-associated MN by performing single-cell RNA sequencing (scRNA-seq) of kidney biopsy specimens from a patient with HBV-associated MN and two healthy individuals. We generated 4,114 intrarenal single-cell transcriptomes from the HBV-associated MN patient by scRNA-seq. Compared to healthy individuals, podocytes in the HBV-associated MN patient showed an increased expression of extracellular matrix formation-related genes, including HSPA5, CTGF, and EDIL3. Kidney endothelial cells (ECs) in the HBV-associated MN were enriched in inflammatory pathways, including NF-kappa B signaling, IL-17 signaling, TNF signaling and NOD-like receptor signaling. Gene ontology (GO) functional enrichment analysis and Gene Set Variation Analysis (GSVA) further revealed that differentially expressed genes (DEGs) of ECs from the HBV-associated MN patients were enriched in apoptotic signaling pathway, response to cytokine and leukocyte cell-cell adhesion. The up-regulated DEGs in glomerular ECs of HBV-associated MN patients were involved in biological processes such as viral gene expression, and protein targeting to endoplasmic reticulum. We further verified that the overexpressed genes in ECs from HBV-associated MN were mainly enriched in regulation of protein targeting to endoplasmic reticulum, exocytosis, viral gene expression, IL-6 and IL-1 secretion when compared with anti-phospholipase A2 receptor (PLA2R)-positive idiopathic membranous nephropathy (IMN). The receptor-ligand crosstalk analysis revealed potential interactions between endothelial cells and other cells in HBV-associated-MN. These results offer new insight into the pathogenesis of HBV-associated MN and may identify new therapeutic targets for HBV-associated MN.

Renal autoimmunity: The role of bacterial and viral infections, an extensive review

Autoimmunity is a process by which the loss of self-tolerance results in an immune attack against the body own tissues and organs. For autoimmunity to occur, various elements serving as triggers were described by which infections are considered one of the leading factors. In turn, renal involvement in autoimmune diseases, whether by an organ-specific attack, or as part of a systemic disease process, is well known. As bacterial and viral infections are considered to be common triggers for autoimmunity in general, we aimed to study their association with renal autoimmunity in particular. We performed an extensive search of the recent and relevant medical literature regarding renal autoimmunity syndromes such as infection-associated glomerulonephritis and vasculitis, associated with bacterial and viral infections. By utilizing PubMed and Google Scholar search engines, over 200 articles and case reports were reviewed. Among other mechanisms, direct infection of the renal parenchyma, molecular mimicry, induction of B-cells or secretion of superantigens, bacterial and viral pathogens were found to correlate with the development of renal autoimmunity. Nevertheless, this was not true for all pathogens, as some mimic autoimmune diseases and others show a surprisingly protective effect. The exact immunopathogenesis is yet to be determined, however. For conclusion, bacterial and viral infections are linked to renal autoimmunity by both direct damage and as mediators of systemic diseases. Further research particularly on the immunopathogenetic mechanisms of renal autoimmunity associated with infections is required.

How Times Have Changed! A Cornucopia of Antigens for Membranous Nephropathy

The identification of the major target antigen phospholipase A2 receptor (PLA2R) in the majority of primary (idiopathic) cases of membranous nephropathy (MN) has been followed by the rapid identification of numerous minor antigens that appear to define phenotypically distinct forms of disease. This article serves to review all the known antigens that have been shown to localize to subepithelial deposits in MN, as well as the distinctive characteristics associated with each subtype of MN. We will also shed light on the novel proteomic approaches that have allowed identification of the most recent antigens. The paradigm of an antigen normally expressed on the podocyte cell surface leading to in-situ immune complex formation, complement activation, and subsequent podocyte injury will be discussed and challenged in light of the current repertoire of multiple MN antigens. Since disease phenotypes associated with each individual target antigens can often blur the distinction between primary and secondary disease, we encourage the use of antigen-based classification of membranous nephropathy.

Primary membranous glomerulonephritis with negative serum PLA2R in haemophilia A successfully managed with rituximab - case report and review of the literature

BACKGROUND

Hepatitis C virus (HCV) and human immunodeficiency virus (HIV) cause a wide range of glomerular pathologies. In people with haemophilia, transfusion-associated infections with these viruses are common and definitive pathological diagnosis in this population is complicated by the difficulty of safely obtaining a renal biopsy. Membranous nephropathy (MN) is a common cause of adult onset nephrotic syndrome occurring in both primary and secondary forms. Primary MN is associated with podocyte autoantibodies, predominantly against phospholipase A2 receptor (PLA2R). Secondary disease is often associated with viral infection; however, infrequently with HIV or HCV. Distinguishing these entities from each other and other viral glomerular disease is vital as treatment strategies are disparate.

CASE PRESENTATION

We present the case of a 48-year-old man with moderate haemophilia A and well-controlled transfusion-associated HCV and HIV coinfection who presented with sudden onset nephrotic range proteinuria. Renal biopsy demonstrated grade two membranous nephropathy with associated negative serum PLA2R testing. Light and electron microscopic appearances were indeterminant of a primary or secondary cause. Given his extremely stable co-morbidities, treatment with rituximab and subsequent angiotensin receptor blockade was initiated for suspected primary MN and the patient had sustained resolution in proteinuria over the following 18 months. Subsequent testing demonstrated PLA2R positive glomerular immunohistochemistry despite multiple negative serum results.

CONCLUSIONS

Pursuing histological diagnosis is important in complex cases of MN as the treatment strategies between primary and secondary vary significantly. Serum PLA2R testing alone may be insufficient in the presence of multiple potential causes of secondary MN.

The COVID-19 Epidemic: Management and Outcomes of Hemodialysis and Peritoneal Dialysis Patients in Stockholm, Sweden

BACKGROUND

The COVID-19 outbreak has been associated with a high morbidity, mortality, and a risk of long-term sequelae, and patients with severe COVID-19 are at increased risk of acute kidney injury. CKD patients are at high risk of being exposed to COVID-19 and suffer complications and poor outcome. In Sweden, mitigation strategies did not include lockdown. During March-April of 2020, wide-spread infection occurred in Stockholm.

METHODS

Management and outcomes in forty hemodialysis (HD) patients and 4 peritoneal dialysis (PD) patients, with symptomatic COVID-19 in greater Stockholm during March and April of 2020 are reported.

RESULTS

Twenty-four HD patients (60%) required medical care and hospitalization, whereas 16 patients (40%) were treated at home. Nine patients died (mortality rate of 22.5%), of whom 8 were men. The median age in non-survivors (78 years) was significantly higher than in survivors (p = 0.003). The median time in dialysis (11.5 years) was also significantly longer in non-survivors (p = 0.01). C-reactive protein (CRP) at diagnosis in 7 of non-survivors (median 213 mg/L, range 86-329 mg/L) was significantly higher than the CRP in 25 survivors (median 87 mg/L, range 1-328 mg/L) (p = 0.0003). Maximum CRP also indicated poorer outcome among hospitalized patients (p = 0.0004). The gender imbalance was striking with only men dying apart from 1 elderly woman. Only 4 PD patients were hospitalized with symptomatic COVID-19. One patient died, 2 were discharged, and 1 was treated at the intensive care unit and survived.

CONCLUSION

HD patients >70 years were reported with longer dialysis vintage, higher CRP, and males were at an increased risk of dying from COVID-19, whereas those <70 years seemed to have a milder disease. Mitigation strategies to reduce rates of infection in high-risk populations remain essential. Follow-up focusing on long-term prognosis for extrapulmonary manifestations is likely to be important also in dialysis patients.