The Value of Urinary RBP4 in The Diagnosis of FSGS and other Renal Diseases.

Abstract

BackgroundFocal segmental glomerulosclerosis (FSGS) is the leading cause of chronic renal failure worldwide. Unequivocal diagnosis of FSGS can only be made with a renal biopsy, which is an invasive, risk-associated medical procedure. The discovery of non-invasive molecular biomarkers for the diagnosis of FSGS still remains an important scientific goal. This study examines the urinary proteome profile of FSGS patients and reference groups, in order to identify urinary protein expression alterations indicative of FSGS. Methods Urine samples were collected from subjects representing FSGS, IgA nephropathy (IgAN), clear cell renal cell carcinoma (ccRCC), chromophobe renal cell carcinoma (chRCC), and healthy control group, respectively. The samples were pooled and subjected to SWATH-MS proteomics analysis. ELISA was utilized to validate the expression level of Retinol-binding protein 4 (uRBP4) in 130 urine supernatant samples (21 FSGS, 20 IgAN, 31 ccRCC, 21 chRCC, 7 prostate cancer patients and 30 healthy volunteers).ResultsThe MS study identified 194 (FSGS), 179 (IgAN), 271 (ccRCC), 255 (chRCC), and 275 (healthy controls) urinary proteins. The comparative proteomic analysis revealed that Retinol-binding protein 4 clearly discriminates FSGS from the rest of the groups. Increased levels of uRBP4 in FSGS urine specimens were also detected by ELISA (FSGS vs IgAN p=0.0244, FSGS vs ccRCC p=0.004, FSGS vs chRCC p=0.013, FSGS vs prostate cancer p=0.02, FSGS vs healthy controls p<0.00001). Significantly elevated levels of uRBP4 were also observed for IgAN, ccRCC and chRCC versus healthy individuals.ConclusionsUrinary RBP4 protein is significantly upregulated in FSGS in comparison to IgAN, ccRCC, chRCC, prostate cancer patients and healthy subjects. Determining FSGS diagnosis based on uRBP4 expression alone is not possible. Specific uRBP4 concentration cut-off can be applied to accurately distinguish individuals with renal disorder (in general) from healthy subjects. Thus, urinary RBP4 could serve as a screening biomarker identifying people at risk of renal disorders, who should undergo more detailed diagnostics.