Hematopoietic Stem Cell Transplant-Membranous Nephropathy Is Associated with Protocadherin FAT1

Abstract

Background: Membranous nephropathy (MN) is a common cause of proteinuria in patients receiving a hematopoietic stem cell transplant (HSCT). The target antigen in HSCT-associated MN is unknown. Methods: We performed laser microdissection and tandem mass spectrometry (MS/MS) of glomeruli of 250 cases of PLA2R-negative MN to detect novel antigens in MN. This was followed by immunohistochemical (IHC)/immunofluorescence microscopy (IF) studies to localize the novel antigen. Western blot analyses were performed using serum and IgG eluted from frozen biopsy tissue to demonstrate IgG binding to the antigen. Results: MS/MS detected a novel protein, protocadherin FAT1 (FAT1), in 9 cases of PLA2R-negative MN. All 9 MN cases developed following allogeneic HSCT (Mayo Clinic discovery cohort). Next, we performed MS/MS in 5 known cases of allogeneic HSCT-associated MN (Cedar Sinai validation cohort). FAT1 was detected in all 5 cases by MS/MS. The total spectral counts for FAT1 ranged from 8 to 39 (mean 20.9 ± 10.1). All 14 cases were negative for known antigens of MN, including PLA2R, THSD7A, NELL1, PCDH7, NCAM1, SEMA3B, and HTRA1. Kidney biopsy showed IgG (2-3+) with mild C3 (0-1+) along the GBM; IgG4 was the dominant IgG subclass. IHC following protease digestion and confocal IF confirmed granular FAT1 deposits along the GBM. Lastly, Western blot analyses detected anti-FAT1 IgG and IgG4 in the eluate obtained from pooled frozen kidney biopsy tissue and in the serum of FAT1-asssociated MN, but not from PLA2R-associated MN. Conclusions: FAT1-associated MN appears to be a unique type of MN associated with HSCT. FAT1-associated MN represents a majority of MN associated with HSCT.

Onconephrology 2022: An Update

“…NELL-1 associated membranous GN following HSCT has also been described 92 . A study published by Sethi et al 93 revealed a novel protein, protocadherin (FAT1), which was detected by microdissection and mass spectrometry in patients with HSCT-associated membranous nephropathy, all of whom were PLA2R antigen negative. The FAT cadherins comprise four members, FAT1-FAT4, and all are large transmembrane proteins of 500-600 kD 94 .…”

Membranous nephropathy: Clearer pathology and mechanisms identify potential strategies for treatment

“…Laser microdissection and mass spectrometry on kidney biopsies of PLA2R-negative PMN has led to the discovery of many more disease antigens such as NELL1, Sema3B, protocadherin 7 (PCDH7), high temperature requirement A serine peptidase 1 (HTRA1), and netrin G1 (NTNG1) ( Figure 1B.3 ). These antigens account for less than 10% of PMN and their associated autoantibodies vary in their predominant IgG subclass, ability to activate complement, and the association of their pathogenic epitope with disulfide bonds based on whether autoantibodies were detected under reducing or non-reducing conditions ( Table 1 ) ( 40 , 41 , 43 – 50 ). Anti-Sema3B autoantibodies correlated with disease activity in a case report of severe pediatric PMN, suggestive of pathogenicity ( 84 ).…”

“…This may be due to EXT1/EXT2-related glycosylation of heparan sulfate, which protects the GBM against immune injury. Contactin 1 (CNTN1) is associated with chronic inflammatory demyelinating polyneuropathy-related MN and protocadherin FAT1 (FAT1) is associated with allogeneic hematopoietic stem cell transplant-related MN ( 49 , 50 ).…”

Bucillamine use for rheumatoid arthritis and type 2 diabetes mellitus are associated with neural epidermal growth factor-like 1 (NELL1)-associated membranous nephropathy

“…Reports of specific antigens for MN began with the identification of M-type phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) . 1,2 From 2019 onwards, the success of combined laser microdissection and mass spectrometry techniques led to the discovery of various antigens including exostosin 1/exostosin 2 (EXT1/EXT2) 3 , neural epidermal growth factor-like 1 protein (NELL1) 4 , semaphorin 3B 5 , neural cell adhesion molecule 1 6 , protocadherin 7 7 , serine protease HTRA1 8 , transforming growth factor beta receptor 3 9 , protocadherin FAT1 10 , contactin 1 11 and netrin G1 12 . As of 2022, it is estimated that the complete picture of the specific antigens of MN is close to being elucidated.…”