Prolonged hypokalemia induces a decrease of urinary concentrating ability via down-regulation of aquaporin 2 (AQP2); however, the precise mechanisms remain unknown. To investigate the role of autophagy in the degradation of AQP2, we generated the principal cell-specific Atg7 deletion (Atg7 Δpc ) mice. In hypokalemic Atg7-floxed (Atg7 f/f ) mice, huge irregular shaped LC3-positive autophagic vacuoles accumulated mainly in inner medullary collecting duct (IMCD) cells. Total- and pS261-AQP2 were redistributed from apical and subapical domains into these vacuoles, which were not co-localized with RAB9. However, in the IMCD cells of hypokalemic Atg7 Δpc mice, these canonical autophagic vacuoles were markedly reduced, whereas numerous small regular shaped LC3-negative/RAB9-positive non-canonical autophagic vacuoles were observed along with diffusely distributed total- and pS261-AQP2 in the cytoplasm. The immunoreactivity of pS256-AQP2 in the apical membrane of IMCD cells was markedly decreased, and no redistribution was observed in both hypokalemic Atg7 f/f and Atg7 Δpc mice. These findings suggest that AQP2 down regulation in hypokalemia was induced by reduced phosphorylation of AQP2, resulting in a reduction of apical plasma labeling of pS256-AQP2 and degradation of total- and pS261-AQP2 via an LC3/ATG7-dependent canonical autophagy pathway.
Bibliographical noteFunding Information:
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2012R1A2A2A01045884, NRF-2016R1D1A1B03932970, NRF-2018R1A2B6003440 and NRF-2016R1A6A3A11931412) and MRC for Cancer Evolution Research Center (NRF-2012R1A5A2047939).
© 2019, The Author(s).