Transforming Growth Factor Beta Receptor 3 (TGFBR3)–Associated Membranous Nephropathy

Abstract

Background: Membranous lupus nephritis (MLN) comprises 10-15 percent of lupus nephritis and increases morbidity and mortality of patients with systemic lupus erythematosus (SLE) through complications of nephrotic syndrome and chronic kidney failure. Identification of the target antigens in MLN may enable non-invasive monitoring of disease activity, inform treatment decisions, and aid in prognostication, as is now possible for idiopathic MN caused by antibodies against the phospholipase A2 receptor. Here, we show evidence for type III transforming growth factor-beta receptor (TGFBR3) as a novel biomarker expressed in a subset of patients with membranous lupus nephritis. Methods: We utilized mass spectrometry for protein discovery through enrichment of glomerular proteins by laser capture microdissection and through elution of immune complexes within MLN biopsies. Co-localization with IgG within glomerular immune deposits from patients and disease controls was evaluated by confocal microscopy. Immunostaining of consecutive case series was used to determine the overall frequency in MN and MLN. Results: TGFBR3 was found to be enriched in glomeruli and co-immunoprecipitated with IgG within a subset of MLN biopsies by mass spectrometry. Staining of consecutive MN cases without clinical evidence of SLE did not show TGFBR3 expression (0/104), but showed a 5.5% prevalence in MLN (11/199 cases). TGFBR3 co-localized with IgG along the glomerular basement membranes in TGFBR3-associated MN, but not in control cases. Conclusions: Positive staining for TGFBR3 within glomerular immune deposits represents a distinct form of membranous nephropathy, substantially enriched in membranous lupus nephritis. A diagnosis of TGFBR3-associated MN can alert the clinician to search for an underlying autoimmune disease.

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

“…TGFBR3 is positive within 5.5% of MLN biopsies and is not identified in primary MN cases (33). Patients with TGFBR3associated MN had a mean age of 39.6 ± 16.1 years and were predominantly female.…”

“…In the field of MN, the use of sequential methods of LCM followed by MS has allowed the discovery of multiple new autoantigens including the exostosin 1/2 complex (EXT1/2) (21), neural epidermal growth factor-like 1 (NELL1) (22), semaphorin 3B (SEMA3B) (30), and protocadherin 7 (PCDH7) (31). It was also utilized as an ancillary technique in confirmation of the new autoantigens serine protease HTRA1 (HTRA1) (23), neural cell adhesion molecule 1 (NCAM1) (32), and type III transforming growth factor-beta receptor (TGFBR3) (33). Additionally, the LCM-MS methodology confirmed the appropriate target antigen in cases of PLA2R-and THSD7Aassociated MN cases, validating its utility for all known subtypes of MN.…”

“…To date, three autoantigens have been described in membranous lupus nephritis, which together comprise approximately 1/3 of all MLN cases. These include the exostosin 1/exostosin 2 complex (EXT1/2) (21), neural cell adhesion-molecule 1 (NCAM1) (32), and transforming growth factor b receptor 3 (TGFBR3) (33). PLA2R positivity can be rarely seen in MLN (in up to 5.3% of cases) (84).…”

“…EXT1/EXT2-positive MN appears tightly associated with autoimmunity, with 70% of patients having a positive ANA, 35% having a clinical diagnosis of SLE and 12% of patients having mixed connective tissue disease at the time of biopsy (21). The frequency of EXT1/EXT2 positivity in MLN is 17.0-38.4% (33,87,88). From the largest cohort of 374 patients with MLN, 32.6% had EXT1/EXT2-positivity.…”

“…The type III transforming growth factor-beta receptor (TGFBR3) was identified as a putative target in MLN by tissue-based proteomics utilizing LCM and tissue IP (33). TGFBR3 is an accessory receptor for TGF-b signaling and is involved in negative regulation of T-cell dependent antibody responses through reducing CD4 + T-cell specification to the Th1 lineage (92).…”