NEPHROSIN

Primary Nephrotic Syndrome (pNS) is a rare kidney disease characterized by massive proteinuria and hypoalbuminemia. The pathogenesis is poorly understood but recent findings suggest the implication of autoantibodies, highlighting pNS as an autoimmune kidney disease. The discovery of circulating anti-nephrin antibodies whose titers correlate with disease activity in a small subset of patients that for most, were treated with steroids, led us to hypothesize that pNS is caused by autoantibodies targeting slit diaphragm proteins including nephrin and other unknown podocyte proteins. Our aim is to demonstrate the presence of autoantibodies against nephrin and other podocyte antigens, to better understand the pathophysiology, and to assess the clinical utility of these autoantibodies as diagnostic and prognostic biomarkers. Based on the clinical data and samples from well-phenotyped cohorts of pediatric and adult patients with pNS, we will assess the true prevalence of anti-nephrin antibodies and correlate their titers with disease activity. To better understand the pathophysiology, we will 1) identify the nephrin epitopes involved by testing the reactivity of patients’ antibodies against deletion mutants of nephrin and search for related intronic variants resulting in increased immunogenicity, 2) establish experimental models (animal and glomerulus-on-chip) to demonstrate the pathogenicity of human anti-nephrin antibodies, 3) identify autoantibodies targeting other podocyte antigens by WB analysis on potential candidates (UCHL1, NEPH-1, NEPH-2, NEPH-3, podocin) and on protein extracts from microdissected human glomeruli incubated with patients' serum, followed by mass spectrometry identification of the reactive bands, and 4) correlate the level of antibodies and antigen-specific memory B cells with clinical activity and assess its ability to stratify the risk of relapse in 2 prospective cohorts of children and adults with pNS. We will develop new diagnostic and prognostic tests capable of measuring antibodies against nephrin and other antigens characteristic of pNS. This project aims to better understand the mechanisms involved in pNS pathophysiology, to provide new diagnostic and prognostic assays to improve patients’ care, and to pave the way for future clinical trials investigating non-invasive diagnostic strategies and personalized therapeutic management.