Comparative proteomic analysis of glomerular proteins in primary and bucillamine-induced membranous nephropathy

Anti-phospholipase A2 receptor autoantibody (PLA2R Ab)-associated membranous nephropathy (MN) is the most common form of primary MN (pMN). On the other hand, bucillamine (BCL), an antirheumatic drug developed in Japan, was reported to cause a rare form of secondary MN (sMN). Between these MN forms, comparative proteomic analysis of glomerular proteins has not been performed.

We used renal biopsy specimens from 6 patients with PLA2R Ab (+) pMN, 6 patients with PLA2R Ab (‒) pMN, 6 patients with BCL-induced sMN, and 5 control cases (time 0 transplant biopsies). Proteins were extracted from laser-microdissected glomeruli and analyzed using mass spectrometry. The quantification values of protein abundance in each MN group were compared with those in the control group.

More than 800 proteins with high confidence were identified. Principal component analysis revealed a different distribution between the pMN and sMN groups. For further analysis, 441 proteins matched with ≥ 3 peptides were selected. Among the pMN and sMN groups, we compared the profiles of several protein groups based on the structural and functional characteristics, such as immunoglobulins, complements, complement-regulating proteins, podocyte-associated proteins, glomerular basement membrane proteins, and several proteins that are known to be associated with kidney diseases, including MN. In all MN groups, increased levels of immunoglobulins (IgG, IgA, and IgM), complements (C3, C4, and C9), complement factor H-related protein 5, type XVIII collagen, calmodulin, polyubiquitin, and ubiquitin ligase were observed. For some proteins, such as type VII collagen and nestin, the fold-change values were significantly different between the pMN and sMN groups.

Between the pMN and BCL-induced sMN groups, we observed common and different alterations in protein levels such as known disease-associated proteins and potential disease marker proteins.