ABSTRACT
In the kidney, final urinary acidification is achieved by V-ATPases expressed in type A intercalated cells. The B1 subunit of the V-ATPase is required for maximal urinary acidification, while the role of the homologous B2 subunit is less clear. Here we examined the effect of acute acid/alkali loading in humans on B1 and B2 subunit abundance in urinary exosomes in normal individuals and of acid loading in patients with distal renal tubular acidosis (dRTA). Specificities of B1 and B2 subunit antibodies were verified by yeast heterologously expressing human B1 and B2 subunits, and murine wild-type and B1-deleted kidney lysates. Acute ammonium chloride loading elicited systemic acidemia, a drop in urinary pH, and increased urinary ammonium excretion. Nadir urinary pH was achieved at four to five hours, and exosomal B1 abundance was significantly increased at two through six hours after ammonium chloride loading. After acute equimolar sodium bicarbonate loading, blood and urinary pH rose rapidly, with a concomitant reduction of exosomal B1 abundance within two hours, which remained lower throughout the test. In contrast, no change in exosomal B2 abundance was found following acid or alkali loading. In patients with inherited or acquired distal RTA, the urinary B1 subunit was extremely low or undetectable and did not respond to acid loading in urine, whereas no change in B2 subunit was found. Thus, both B1 and B2 subunits of the V-ATPase are detectable in human urinary exosomes, and acid and alkali loading or distal RTA cause changes in the B1 but not B2 subunit abundance in urinary exosomes.
Subject(s)
Acidosis, Renal Tubular/enzymology , Exosomes/enzymology , Kidney Tubules/enzymology , Vacuolar Proton-Translocating ATPases/urine , Water-Electrolyte Balance , Acidosis, Renal Tubular/genetics , Acidosis, Renal Tubular/physiopathology , Acidosis, Renal Tubular/urine , Adult , Ammonium Chloride/administration & dosage , Animals , Bicarbonates/administration & dosage , Exosomes/drug effects , Humans , Hydrogen-Ion Concentration , Kidney Tubules/drug effects , Kidney Tubules/physiopathology , Male , Mice, Knockout , Middle Aged , Mutation , Saccharomyces cerevisiae/enzymology , Saccharomyces cerevisiae/genetics , Vacuolar Proton-Translocating ATPases/genetics , Vacuolar Proton-Translocating ATPases/metabolism , Water-Electrolyte Balance/drug effects , Young AdultABSTRACT
The (pro)renin receptor [(P)RR] binds to renin and its precursor prorenin to activate the tissue renin-angiotensin system. It is cleaved to generate soluble (P)RR and M8-9, a residual hydrophobic truncated protein. The (pro)renin receptor also functions as an intracellular accessory protein of vacuolar-type H+-ATPase, which plays an essential role in controlling the intracellular vesicular acid environment. Thus, in the kidney, (P)RR may play a role in transporting H+ to urine in the collecting duct. Although blood soluble (P)RR has been recognized as a biomarker reflecting the status of the tissue renin-angiotensin system and/or tissue (P)RR, the significance of urinary soluble (P)RR excretion has not been determined. Therefore, this study aimed to investigate the characteristics of urinary soluble (P)RR excretion. Urinary soluble (P)RR excretion was measured, and its association with background factors was investigated in 441 patients. Relationships between changes in urine pH due to vitamin C treatment, which reduce urine pH, and urinary soluble (P)RR excretion were investigated in 10 healthy volunteers. Urinary soluble (P)RR excretion was 1.46 (0.44-2.92) ng/gCre. Urine pH showed a significantly positive association with urinary soluble (P)RR excretion, independent of other factors. Changes in urine pH and urinary soluble (P)RR excretion due to vitamin C treatment were significantly and positively correlated (ρ = 0.8182, p = 0.0038). These data showed an association between urinary soluble (P)RR excretion and urine pH in humans, suggesting that (P)RR in the kidney might play a role in urine pH regulation.
Subject(s)
Hypertension/urine , Kidney/metabolism , Renin/urine , Vacuolar Proton-Translocating ATPases/urine , Adult , Biological Transport/genetics , Humans , Hydrogen-Ion Concentration , Hypertension/pathology , Kidney/pathology , Kidney Tubules, Collecting/metabolism , Middle Aged , Receptors, Cell Surface , Renin-Angiotensin System/genetics , Vacuolar Proton-Translocating ATPases/geneticsABSTRACT
BACKGROUND AND OBJECTIVES: Obstructive nephropathy is a leading cause of CKD in children. The assessment of severity of renal impairment and the prediction of which children will progress to renal failure are, however, challenging. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This case-control study measured the urinary excretion of candidate biomarkers in 27 prevalent case-patients with posterior urethral valves (PUVs) and 20 age-matched controls, correlated their urinary concentration with GFR, and analyzed receiver-operating characteristic (ROC) curve and regression analyses to assess their performance as tests for low GFR. RESULTS: The median urinary protein-to-creatinine ratio was higher in children with PUV (45 g/mol; range, 5-361 g/mol) than in controls (7 g/mol; range, 3-43 g/mol) (P<0.01) and correlated inversely with renal function (r = -0.44; P<0.05). In whole urine, excretion of aquaporin-2 was significantly decreased, whereas that of TGFß and L1 cell adhesion molecule (L1CAM) was significantly increased. Whole-urine TGFß excretion correlated inversely with GFR (r = -0.53; P<0.05). As tests for low GFR, whole-urine TGFß, L1CAM, and urinary protein-to-creatinine ratio performed best, with areas under the ROC curves of 0.788, 0.795, and 0.814, respectively. By linear regression analysis, whole-urine TGFß, L1CAM, and urinary protein-to-creatinine ratio were associated with low GFR in the case-patients. CONCLUSIONS: Candidate biomarkers of obstructive nephropathy can be readily measured in whole urine and in urine exosomes. In boys with PUV, these biomarkers correlate with GFR.