Abstract: TH-PO566
Patients with IgA Nephropathy (IgAN) or IgA Vasculitis (IgAV) Have Significantly Higher Serum Levels of α1-Microglobulin IgA Complexes
Session Information
- Glomerular Diseases: Omics, Biomarkers, and Tools
October 24, 2024 | Location: Exhibit Hall, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Glomerular Diseases
- 1401 Glomerular Diseases: Mechanisms, including Podocyte Biology
Authors
- Lardinois, Olivier, National Institute of Environmental Health Sciences, Mass Spectrometry Research and Support Group, Research Triangle Park, North Carolina, United States
- Deterding, Leesa, National Institute of Environmental Health Sciences, Mass Spectrometry Research and Support Group, Research Triangle Park, North Carolina, United States
- Williams, Jason G., National Institute of Environmental Health Sciences, Mass Spectrometry Research and Support Group, Research Triangle Park, North Carolina, United States
- Nachman, Patrick H., University of Minnesota, Division of Renal Diseases and Hypertension, Minneapolis, Minnesota, United States
Background
The cause of IgAN and IgAV remains unknown. Patients with IgAN and IgAV who develop nephritis have elevated levels of circulatory IgA1-containing complexes, which contain galactose-deficient IgA1, IgG antibodies and some unidentified proteins. Identification of the key constituents of these protein-protein complexes and the nature of the chemical bonds within the complexes may lead to better understanding of the pathophysiology of IgAN/V.
Methods
Low and high molecular mass IgA forms were isolated from serum of 32 patients with IgAN/V and 12 healthy controls (HC) by affinity-capture on peptide M agarose beads. Various molecular forms of IgA1 were size-separated by gel electrophoresis. Proteins were visualized by Coomassie blue staining or by Western blotting using appropriate antibodies. The relative abundance of each protein within the complexes was estimated by mass spectrometry using a Tandem Mass Tag (TMT) quantification approach. A sensitive and efficient method for mapping protein disulfide bonds was used to identify the inter-chain disulfide bonds within the complexes.
Results
Immunoblotting demonstrated 1:1 complexes between IgA and albumin, α1-antitrypsin, or α1-microglobulin. Mapping of protein disulfide bonds demonstrated that 1) complexes of albumin and α1-antitrypsin with IgA monomer are disulfide-bound to penultimate C-terminal cysteine on the tailpiece of IgA and 2) α1-microglobulin is linked to IgA by a non-reducible covalent thioether bond to the same cysteine. Of 146 identified proteins, 86 were robustly quantified in the protein complexes using TMT-based quantification, and 15 showed significantly different levels in patients with IgAN/V and healthy controls. The relative abundance of IgA-α1-microglobulin complexes was significantly higher in patients than HC. The association of IgA-α1-microglobulin complexes level and IgAN had an area under the curve (AUC) value of 0.912 (C.I. = 0.840-0.984), significantly higher than other serum candidate diagnostic biomarkers under investigation.
Conclusion
We confirmed the presence of increased levels of IgA-α1-microglobulin complexes in the serum of patients with IgAN compared to HC. The specificity of the complex for IgAN or IgAV is under investigation. IgA-α1-microglobulin complexes could serve as a non-invasive biomarker of IgAN/V.
Funding
- Other NIH Support