Comparative proteomic analysis of glomerular proteins in IgA nephropathy and IgA vasculitis with nephritis

Abstract

Abstract Background: IgA nephropathy (IgAN) and IgA vasculitis with nephritis (IgAVN) are related glomerular diseases characterized by marked similarities in immunological and histological findings. We herein performed a comparative proteomic analysis of glomerular proteins in IgAN and IgAVN. Methods: We used renal biopsy specimens from 6 IgAN patients without nephrotic syndrome (NS) (IgAN-I subgroup), 6 IgAN patients with NS (IgAN-II subgroup), 6 IgAVN patients with <10% of glomeruli with crescent formation (IgAVN-I subgroup), 6 IgAVN patients with ≥20% of glomeruli with crescent formation (IgAVN-II subgroup), and 5 control cases. Proteins were extracted from laser microdissected glomeruli and analyzed using mass spectrometry. The relative abundance of proteins was then compared between groups. An immunohistochemical validation study was also performed. Results: More than 850 proteins with high confidence were identified. A principal component analysis revealed a clear separation between IgAN and IgAVN patients and control cases. In further analyses, 546 proteins that were matched with ≥2 peptides were selected. In comparisons with the control group, higher levels (>2.6 fold) of immunoglobulins (IgA, IgG, and IgM), complements (C3, C4A, C5, and C9), complement factor H-related proteins (CFHR) 1 and 5, vitronectin, fibrinogen chains, and transforming growth factor-β inducible gene-h3 were observed in the IgAN and IgAVN subgroups, whereas lower levels (<0.3 fold) of hornerin were noted in the IgAN and IgAVN subgroups. Furthermore, the abundance of C9 and CFHR1 was significantly higher in the IgAN group than in the IgAVN group. The abundance of some podocyte-associated proteins was significantly lower in the IgAN group than in the IgAVN group. The abundance of some podocyte-associated proteins and glomerular basement membrane (GBM) proteins was also significantly lower in the IgAN-II subgroup than in the IgAN-I subgroup. Among the IgAN and IgAVN subgroups, talin 1 was not detected in the IgAN-II subgroup. This result was supported by immunohistochemical findings. Conclusions: The present results suggest shared molecular mechanisms for glomerular injury in IgAN and IgAVN, except for enhanced glomerular complement activation and podocyte injury in IgAN. Differences in the protein abundance of podocyte-associated and GBM proteins between the IgAN subgroups may be associated with the severity of proteinuria.