AQP2 in human urine is predominantly localized to exosomes with preserved water channel activities

作者：Miyazawa Yuko; Mikami Saki; Yamamoto Keiko; Sakai Masaki; Saito Tatsuya; Yamamoto Tadashi; Ishibashi Kenichi; Sasaki Sei^*

来源：Clinical and Experimental Nephrology, 2018, 22(4): 782-788.

DOI：10.1007/s10157-018-1538-6

• Aquaporin-2
• Urine concentration
• Proteomics
• Kidney
• Biomarker
• ESCRT

AQP2 water channel is critical for urinary concentration in the kidney. Interestingly, AQP2 is abundantly excreted in the urine as extracellular vesicles (EVs), which is known to be a useful biomarker for water-balance disorders although the character of AQP2-enriched EVs is poorly understood including water channel function.
Human urine EVs were obtained by a differential centrifugation method. AQP2-bearing EVs were isolated by immunoprecipitation with an AQP2-specific antibody, and the proteins in the EVs were analyzed by LC-MS/MS proteomic analysis. Osmotic water permeability (Pf) of the AQP2-rich EVs was measured by a stopped-flow method monitoring scattered light intensity in response to outwardly directed osmotic gradient.
Sequential centrifugation of human urine showed that AQP2 was present predominantly (80%) in low-density EVs (160,000 g), whereas negligible amount in high-density EVs (17,000 g). Proteomic analysis of the AQP2-bearing EVs identified 137 proteins, mostly in the endosome pathway, including the components of ESCRT (endosomal sorting complex required transporter)-I, II, III. Pf value of the 160,000 g EVs was 4.75 +/- 0.38 x 10(-4) cm s(-1) (mean +/- SE) with the activation energy of 3.51 kcal mol(-1) which was inhibited with 0.3 mM HgCl2 by 63%, suggesting a channel-mediated water transport. Moreover, Pf value showed a significant correlation with the abundance of AQP2 protein in EVs.
Taken together, AQP2 is localized predominantly to urinary exosomes with preserved water channel activities.

• 出版日期2018-8