Hyperosmolality activates the integrated stress response in mouse medullary cells

Abstract

The integrated stress response (ISR) is a eukaryotic translation initiation factor‐2 (eIF2a) phosphorylation‐dependent, stress inducible pathway activated by a variety of environmental stresses such as oxidative stress and endoplasmic reticulum stress. However IRS has not been characterized in osmotic stress. In normal conditions, renal medullary cells face high and various interstitial osmolality due to changing concentrations of NaCl and urea. To determine whether hyperosmolality causes IRS, mIMCD3 cells were subjected to hyperosmolality by adding extra NaCl or urea into culture medium. We found that phosphorylated eIF2a increased in the presence of 125, 150 or 200mM NaCl after 0.5, 1, 2 and 3 hours in a dose‐dependent manner. eIF2a phosphorylation also increased in response to 250, 300, 400mM urea at the same time points. High NaCl or urea activated an eIF2a kinase, general regulated non‐depressible‐2 (GCN2), in mIMCD3 cells. 7 day vasopressin infusion into mice raised the osmolality of the renal medulla and increased the mRNA expression of IRS pathway genes ATF3 and ATF4 (2.20 ± 0.37 fold and 1.62 ± 0.03, respectively, P<0.05). We conclude that high concentrations of NaCl or urea activate IRS in renal medullary cells.