Integrative Urinary Peptidomics in Renal Transplantation Identifies Biomarkers for Acute Rejection

Abstract

Noninvasive methods to diagnose rejection of renal allografts are unavailable. Mass spectrometry followed by multiple-reaction monitoring provides a unique approach to identify disease-specific urine peptide biomarkers. Here, we performed urine peptidomic analysis of 70 unique samples from 50 renal transplant patients and 20 controls (n ϭ 20), identifying a specific panel of 40 peptides for acute rejection (AR). Peptide sequencing revealed suggestive mechanisms of graft injury with roles for proteolytic degradation of uromodulin (UMOD) and several collagens, including COL1A2 and COL3A1. The 40-peptide panel discriminated AR in training (n ϭ 46) and test (n ϭ 24) sets (area under ROC curve Ͼ0.96). Integrative analysis of transcriptional signals from paired renal transplant biopsies, matched with the urine samples, revealed coordinated transcriptional changes for the corresponding genes in addition to dysregulation of extracellular matrix proteins in AR (MMP-7, SERPING1, and TIMP1). Quantitative PCR on an independent set of 34 transplant biopsies with and without AR validated coordinated changes in expression for the corresponding genes in rejection tissue. A six-gene biomarker panel (COL1A2, COL3A1, UMOD, MMP-7, SERPING1, TIMP1) classified AR with high specificity and sensitivity (area under ROC curve ϭ 0.98). These data suggest that changes in collagen remodeling characterize AR and that detection of the corresponding proteolytic degradation products in urine provides a noninvasive diagnostic approach.

Matrix Metalloproteinase-7 as a Surrogate Marker Predicts Renal Wnt/β-Catenin Activity in CKD

“…In that regard, a recent study using a urinary peptidomics approach has identified MMP-7 as one of the biomarkers for acute rejection in renal transplantation. 42 Similarly, plasma MMP-7 is proposed as a potential biomarker in human idiopathic pulmonary fibrosis and as a metastatic marker and survival predictor in patients with renal cell carcinomas. 13,43 Whether plasma MMP-7 level is also elevated in the fibrotic kidney diseases remains to be determined.…”

Derivation and Validation of a Cytokine-Based Assay to Screen for Acute Rejection in Renal Transplant Recipients

“…Of note, all but one of the studies presented results based on the whole cohort of patients recruited, in the absence of internal or external validation. Using a urinary peptide biomarker panel, Ling et al recently reported a sensitivity of 80% and specificity of 83% in detecting acute rejection in a test set of 24 participants; the main caveat was that the nonrejectors were patients with stable renal function or patients with BK nephropathy, a control group relevant for research but not for clinical application of the test (21).…”

Dangers Within

“…THP is the most abundant protein in urine, but its function remains unclear 68 ; it has been implicated as a biomarker of kidney disease and allograft rejection 69,70 and may be a damage signal in renal tubular injury. THP promotes cytokine release 71 and immune cell activation, including DC maturation, 72 but may also have a protective anti-inflammatory role.…”