Autophagic degradation of aquaporin-2 is an early event in hypokalemia-induced nephrogenic diabetes insipidus.

Abstract

Hypokalemia (low serum potassium level) is a common electrolyte imbalance that can cause a defect in urinary concentrating ability, i.e., nephrogenic diabetes insipidus (NDI), but the molecular mechanism is unknown. We employed proteomic analysis of inner medullary collecting ducts (IMCD) from rats fed with a potassium-free diet for 1 day. IMCD protein quantification was performed by mass spectrometry using a label-free methodology. A total of 131 proteins, including the water channel AQP2, exhibited significant changes in abundance, most of which were decreased. Bioinformatic analysis revealed that many of the down-regulated proteins were associated with the biological processes of generation of precursor metabolites and energy, actin cytoskeleton organization, and cell-cell adhesion. Targeted LC-MS/MS and immunoblotting studies further confirmed the down regulation of 18 selected proteins. Electron microscopy showed autophagosomes/autophagolysosomes in the IMCD cells of rats deprived of potassium for only 1 day. An increased number of autophagosomes was also confirmed by immunofluorescence, demonstrating co-localization of LC3 and Lamp1 with AQP2 and several other down-regulated proteins in IMCD cells. AQP2 was also detected in autophagosomes in IMCD cells of potassium-deprived rats by immunogold electron microscopy. Thus, enhanced autophagic degradation of proteins, most notably including AQP2, is an early event in hypokalemia-induced NDI.

• Authors: Sookkasem Khositseth, Panapat Uawithya, Poorichaya Somparn, Komgrid Charngkaew, Nattakan Thippamom, Jason D Hoffert, Fahad Saeed, D Michael Payne, Shu-Hui Chen, Robert A Fenton, Trairak Pisitkun
• Journal: Scientific reports (Sci Rep) Vol. 5 Pg. 18311 (Dec 17 2015) ISSN: 2045-2322 [Electronic] England
• PMID: 26674602 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Aquaporin 2
• LC3 protein, rat
• Lamp1 protein, rat
• Lysosome-Associated Membrane Glycoproteins
• Microtubule-Associated Proteins
• Proteome

Topics

• Actin Cytoskeleton (metabolism)
• Animals
• Aquaporin 2 (metabolism)
• Autophagy
• Chromatography, Liquid
• Diabetes Insipidus, Nephrogenic (metabolism, physiopathology)
• Hypokalemia (metabolism, physiopathology)
• Immunoblotting
• Kidney Medulla (metabolism)
• Kidney Tubules, Collecting (metabolism, ultrastructure)
• Lysosome-Associated Membrane Glycoproteins (metabolism)
• Male
• Microscopy, Immunoelectron
• Microtubule-Associated Proteins (metabolism)
• Phagosomes (metabolism, ultrastructure)
• Proteome (metabolism)
• Proteomics (methods)
• Rats, Sprague-Dawley
• Tandem Mass Spectrometry
• Time Factors