Urinary Prognostic Biomarkers and Classification of IgA Nephropathy by High Resolution Mass Spectrometry Coupled with Liquid Chromatography

Abstract

IgA nephropathy is the most common cause of primary glomerulonephritis. There are different pathologic biopsy-based scoring systems in use, but there is no consensus among nephrologists yet regarding the best classification method. Our aim was to test urine proteomics as a non-invasive method for classification of IgA nephropathy. This aim was pursued by discovering novel prognostic protein biomarkers in urine, and linking them to pathogenesis of the disease through known signaling and metabolic pathways. 13 urine samples of the patients with biopsy-proven IgA nephropathy were analyzed via two proteomics approaches: nanoflow LC-MS/MS and GeLC-MS/MS. The results of label-free quantification were subjected to multivariate statistical analysis, which could classify patients into two groups, broadly corresponding to the primary and advance stages. The proteome classification correlated well with biopsy-based scoring systems, especially endocapillary hypercellularity score of the Oxford’s classification. Differentially excreted candidate proteins were found as potential prognostic biomarkers: afamin, leucine-rich alpha-2-glycoprotein, ceruloplasmin, alpha-1-microgolbulin, hemopexin, apolipoprotein A-I, complement C3, vitamin D-binding protein, beta-2-microglobulin, and retinol-binding protein 4. Pathway analysis suggested impairment of Extra Cellular Matrix (ECM)-Receptor Interaction pathways as well as activation of complement and coagulation pathway in progression of IgA nephropathy.

Complement Activation and Kidney Injury Molecule-1–Associated Proximal Tubule Injury in Severe Preeclampsia

“…Changes in the urinary excretion of B2M, cystatin C, osteopontin, and uromodulin have been associated with varying forms of kidney injury, 27,33,[50][51][52][53][54][55]231 but were not different between preeclampsia cases and controls. Increased urine NGAL has been associated with acute kidney injury, 51,56,57 but we found levels to be decreased in preeclampsia.…”

Penalized Regression Versus Random Forest Model in Analyzing High Dimensional Proteomic Data: Diagnosis of IgA Nephropathy

“…They reported a positive correlation between CD44 expression and degree of proteinuria as well as degree of renal damage (26). There is evidence on decreased urinary excretion of CD44 in advanced stage of IgA nephropathy compared with the primary stage (28). However, decreased urinary excretion of this protein was significant in the current study and helped to discriminate the case from the control group.…”

Biomarkers and targeted new therapies for IgA nephropathy

“…The proteomic investigation in biofluids of patients with IgAN has detected several biomarkers of inflammation and progression, most of them belonging to the complement and coagulation pathways [11,41]. Several old and new data have indicated the role of complement dysregulation in IgAN, as complement factor deposits in association with IgA, particularly C5b-9, mannose binding lectin, ficolin, and C4b, indicating the prevalence of the lectin pathway activation [41][42][43].…”

“…Several old and new data have indicated the role of complement dysregulation in IgAN, as complement factor deposits in association with IgA, particularly C5b-9, mannose binding lectin, ficolin, and C4b, indicating the prevalence of the lectin pathway activation [41][42][43]. The presence of glomerular C4d deposition has been proposed to be an early biomarker for progressive IgAN [44].…”