Proteomic Analysis Identified Urine Proteins Predictive of Chronic Allograft Injury.

Abstract

Aim: To correlate early urine protein biomarkers with long term kidney transplant histology and function; to assess biomarker potential to predict subsequent allograft dysfunction and chronic interstitial fibrosis. Method: Patient cohort was selected from a single center within the GoCAR study who had urine samples at 3 and 12 months and protocol biopsies at 0, 3, and 12 months post transplant. Patients were grouped by chronic damage scores using Banff and Chronic Allograft Damage Index (CADI) from 12 month biopsies or change in estimated glomerular filtration rate (eGFR). Urine proteins at 3 and 12 months associated with chronic damage at 12 months were identified by two-dimensional differential in gel electrophoresis (2D-DIGE) and tandem mass spectrometry. Differential protein abundance was calculated using DeCyder software and further interrogated using the STRING network program. Results: Delayed graft function occurred in 25% and biopsy proven acute rejection in 17% of patients. Acute and chronic damage scores were low at 3 months. Proteinuria or eGFR were not significantly different between chronic damage analysis groups. From the 3 month urine, 9 proteins including kininogen, MASP2 and cystatin M correlated to fibrosis at 12 months (5 with Banff, 4 with CADI) and 2 proteins correlated with change in eGFR. The top KEGG pathway in the STRING network were coagulation and complement cascades. Follow up 12 month urine analysis based on the same chronic damage groups revealed 11 proteins, 4 identified in the previous 3 month analysis and 7 new proteins, including CD14 and β2 microglobulin. The top KEGG pathway at 12 months was antigen processing and presentation. Conclusion: Using traditional proteomic techniques, we have identified potential non-invasive biomarkers that are predictive of chronic allograft damage. The dominant urine proteome alters between 3 and 12 months expressing a different panel of proteins. While early urine protein signatures predict subsequent damage, validation in larger and more diverse cohorts is required.