Molecular dissection of PLA2R1-related membranous nephropathy: towards a portfolio of new clinical biomarkers – MNaims

Membranous nephropathy (MN) is a rare autoimmune kidney disease, yet a major cause of nephrotic syndrome, with ~1,300 and 10,000 new cases per year in France and Europe, respectively. It is characterized by the accumulation of immune deposits on podocytes. Considerable advances have occurred in the understanding of MN pathophysiology with the successive identification of three antigens by Partners 1 and 3 (P1/P3), including neutral endopeptidase (NEP, NEJM, 2002) in neonatal MN, and the phospholipase A2 receptor (PLA2R1, NEJM, 2009, 1 patent) and thrombospondin type-1 domain-containing 7A (THSD7A, NEJM, 2014, 1 patent) in adult MN. All three antigens are expressed on podocytes where they serve as targets for circulating antibodies (Ab) to produce immune deposits, leading to podocyte injury and kidney dysfunction.
PLA2R1-related MN is the major form of the disease, with anti-PLA2R1 Ab detected in about 70% of patients. Our discoveries already have a major impact on diagnosis, prognosis and monitoring, with the first commercial blood tests available.
However, the etiology of MN is complex and the clinical outcome of patients is highly variable, from spontaneous remission to end-stage kidney disease. For instance, we still cannot explain which genetic and immunological factors trigger the autoimmune response and what really happens at the podocyte surface. There is thus a need to better understand these mechanisms towards more personalized patients' care from diagnosis to prognosis, and for an effective and safe therapy.
Our project on MN aims (MNaims) to analyze two important missing links in PLA2R1-related MN pathogenesis: i) the genetics and immunological features leading to an autoimmune response to PLA2R1, and ii) the molecular mechanisms of PLA2R1 proteolytic processing leading to immune deposits.
Towards these goals, the consortium assembles 3 Partners from Sophia Antipolis and Paris with complementary expertise from molecular biology to clinical investigation.
The project focuses on PLA2R1-related MN with 3 scientific workpackages:
WP1. Immunological analysis of PLA2R1 autoimmune response. We will identify B and T cell epitopes by multiple approaches. P1 has identified B-cell PLA2R1 epitope-containing domains and has shown a mechanism of epitope spreading associated with disease worsening (JASN 2016, 1 patent). P3 has characterized B and T cell subpopulations in MN during treatment (KI 2017). Our objective is to establish a portfolio of epitopes recognized by immune cells in vivo.
WP2. Genetic analysis of PLA2R1-related MN. We will study PLA2R1 gene clusters of coding and non-coding SNPs that appear to be associated with MN by functional and epigenetic approaches. P3 has identified multiple SNPs in PLA2R1-related MN next to the above epitopes (NEJM, 2011; JASN 2013). Our objective is to identify variants and promoter methylation sites linked to PLA2R1 expression and cell biology.
WP3. Analysis of PLA2R1 shedding in MN. We have found that membrane-bound PLA2R1 can be cleaved by proteases from the regulated intramembrane proteolysis (RIP) pathway to generate a soluble form of PLA2R1 and a corresponding intracellular domain. We hypothesize that this mechanism is at the basis of immune deposit formation. We will study the proteolytic processing of PLA2R1 in details, both in vitro and in vivo. P2 has an internationally recognized expertise in RIP in the context of Alzheimer's disease.
The overall objective of this project is to better understand genetic, immunological and biological events at the basis of initiation and progression of MN, in research areas not carefully investigated so far.
The MNaims project is conceptually and methologically innovative, and our consortium is ideally placed to achieve the objectives. We hope to take an important step forward in understanding the molecular mechanisms of the disease and thus to provide new clinical biomarkers (genetic, blood and urine tests) towards more precision medicine.