# Acute Dehydration Drives Organ-Specific Modulation of Phosphorylated AQP4ex in Brain and Kidney

## TL;DR

This study shows how dehydration affects a water channel protein differently in the brain and kidney, revealing a new way the body controls water balance.

## Contribution

The paper identifies phosphorylation of AQP4ex as a rapid, tissue-specific regulatory mechanism for water transport during dehydration.

## Key findings

- Phosphorylated AQP4ex levels increased in the kidney medulla during dehydration.
- Phosphorylated AQP4ex levels decreased in the cerebral cortex during dehydration.
- Phosphorylation of AQP4ex is tissue-specific and adjusts water flux according to organ needs.

## Abstract

Water deprivation triggers coordinated physiological responses to preserve body fluid balance, yet the molecular mechanisms that regulate aquaporin-mediated water transport under dehydration remain incompletely understood. Aquaporin-4 (AQP4), the main water channel in the brain and a basolateral water pathway in the kidney collecting duct, exists in multiple isoforms, including the translational readthrough variant AQP4ex, whose regulatory role is only beginning to be defined. Here, we investigated the effects of acute water deprivation (6–12 h) on AQP4 isoform expression and phosphorylation in a mouse kidney and brain. While total AQP4 and AQP4ex protein levels remained largely unchanged in both tissues, dehydration induced a marked and divergent regulation of the phosphorylated form of AQP4ex. Levels increased in the kidney medulla, consistent with enhanced antidiuretic water transport, but decreased in the cerebral cortex, suggesting a protective reduction in perivascular water permeability. No changes were detected in the cerebellum. These findings identify phosphorylation of AQP4ex as a rapid, tissue-specific regulatory mechanism that adjusts water flux according to the physiological needs of each organ, revealing an additional layer of control in systemic water homeostasis and highlighting AQP4ex as a potential target in dehydration-related and osmotic disorders. Future studies could explore the signaling pathways regulating AQP4ex phosphorylation and investigate its potential involvement in pathological conditions, such as diabetes insipidus or cerebral edema.