Product(s) used in this publication: Reference Peptides for Targeted Proteomics - SpikeTides™ & SpikeMix™
Angiotensin-II (Ang II) mediates progression of autosomal-dominant polycystickidney disease (ADPKD) and otherchronickidneydiseases (CKD). However, markers of kidney Ang II activity are lacking. We previously defined 83 Ang II-regulatedproteins in vitro, which reflected kidney Ang II activity in vivo.
In this study, we developed selectedreactionmonitoring (SRM) assays for quantification of Ang II-regulatedproteins in urine of ADPKD and CKD patients. We demonstrated that 47 of 83 Ang II-regulated transcripts were differentially expressed in cystic compared to normal kidney tissue. We then developed SRM assays for 18 Ang II-regulatedproteins overexpressed in cysts and/or secreted in urine. Methods that yielded CV ≤ 6 % for control proteins, and recovery ~100 % were selected. Heavy-labeled peptides corresponding to 13 identified Ang II-regulated peptides were spiked into urine samples of 17 ADPKD patients, 9 patients with CKD predicted to have high kidney Ang II activity and 11 healthy subjects. Samples were then digested and analyzed on triple-quadrupole mass spectrometer in duplicates.
Calibration curves demonstrated linearity (R(2) > 0.99) and within-run CVs < 9 % in the concentration range of 7/13 peptides. Peptide concentrations were normalized by urine creatinine. Deamidated peptide forms were monitored, and accounted for <15 % of the final concentrations. Urine excretion rates of proteins BST1, LAMB2, LYPA1, RHOB and TSP1 were significantly different (p < 0.05, one-way ANOVA) between patients with CKD, those with ADPKD and healthy controls. Urine protein excretion rates were highest in CKD patients and lowest in ADPKD patients. Univariate analysis demonstrated significant association between urine protein excretion rates of most proteins and disease group (p < 0.05, ANOVA) as well as sex (p < 0.05, unpaired t test). Multivariate analysis across protein concentration, age and sex demonstrated good separation between ADPKD and CKD patients.
We have optimized methods for quantification of Ang II-regulatedproteins, and we demonstrated that they reflected differences in underlying kidney disease in this pilot study. High urine excretion of Ang II-regulatedproteins in CKD patients likely reflects high kidney Ang II activity. Low excretion in ADPKD appears related to lack of communication between cysts and tubules. Future studies will determine whether urine excretion rate of Ang II-regulatedproteins correlates with kidney Ang II activity in larger cohorts of chronickidney disease patients.
Angiotensin II; Autosomal dominant polycystickidney disease; Chronickidney disease; Polycystickidney disease; Proteomics; Renin angiotensin system; Selectedreactionmonitoring; Urine