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J Am Soc Nephrol. 2016 Feb;27(2):646-56. doi: 10.1681/ASN.2014111137. Epub 2015 Jun 25.

Activation of the Endogenous Renin-Angiotensin-Aldosterone System or Aldosterone Administration Increases Urinary Exosomal Sodium Channel Excretion.

Author information

1
Departments of Biochemistry.
2
Bioinformatics.
3
Division of Clinical Pharmacology, Department of Medicine, Division of Nephrology, Department of Medicine, and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee James.Luther@Vanderbilt.edu.

Abstract

Urinary exosomes secreted by multiple cell types in the kidney may participate in intercellular signaling and provide an enriched source of kidney-specific proteins for biomarker discovery. Factors that alter the exosomal protein content remain unknown. To determine whether endogenous and exogenous hormones modify urinary exosomal protein content, we analyzed samples from 14 mildly hypertensive patients in a crossover study during a high-sodium (HS, 160 mmol/d) diet and low-sodium (LS, 20 mmol/d) diet to activate the endogenous renin-angiotensin-aldosterone system. We further analyzed selected exosomal protein content in a separate cohort of healthy persons receiving intravenous aldosterone (0.7 μg/kg per hour for 10 hours) versus vehicle infusion. The LS diet increased plasma renin activity and aldosterone concentration, whereas aldosterone infusion increased only aldosterone concentration. Protein analysis of paired urine exosome samples by liquid chromatography-tandem mass spectrometry-based multidimensional protein identification technology detected 2775 unique proteins, of which 316 exhibited significantly altered abundance during LS diet. Sodium chloride cotransporter (NCC) and α- and γ-epithelial sodium channel (ENaC) subunits from the discovery set were verified using targeted multiple reaction monitoring mass spectrometry quantified with isotope-labeled peptide standards. Dietary sodium restriction or acute aldosterone infusion similarly increased urine exosomal γENaC[112-122] peptide concentrations nearly 20-fold, which correlated with plasma aldosterone concentration and urinary Na/K ratio. Urine exosomal NCC and αENaC concentrations were relatively unchanged during these interventions. We conclude that urinary exosome content is altered by renin-angiotensin-aldosterone system activation. Urinary measurement of exosomal γENaC[112-122] concentration may provide a useful biomarker of ENaC activation in future clinical studies.

KEYWORDS:

aldosterone; clinical nephrology; epithelial sodium channel; exosome; hypertension; renin angiotensin system

PMID:
26113616
PMCID:
PMC4731116
DOI:
10.1681/ASN.2014111137
[Indexed for MEDLINE]
Free PMC Article

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