Depolymerization of aquaporin-4 orthogonal array particles via the A25Q mutation does not cause behavioral deficits but confers resilience to chronic unpredictable mild stress.

Abstract

Aquaporin-4 (AQP4) formed orthogonal array particles (OAPs) is critical for brain water homeostasis and astrocytic function, but whether OAP structural integrity influences behavior or stress susceptibility is unknown. Using knock-in mice carrying the AQP4-A25Q mutation, which depolymerizes OAPs without altering AQP4 expression, we investigated baseline behavior and responses to chronic unpredictable mild stress (CUMS). Naïve AQP4-A25Q mice showed no anxiety- or depression-like behavior differences from wild-type (WT) mice, indicating OAP disassembly alone does not cause behavior deficit disorders. However, after CUMS, AQP4-A25Q mice exhibited significant resilience: reduced immobility in the tail suspension and forced swimming tests, preserved locomotor activity and central-zone exploration in the open field, and decreased anxiety-like responses in elevated plus maze compared to post stress WT mice. CUMS induced marked astrocytic (GFAP, S100β) and microglial (Iba-1, CD68) activation in WT hippocampus, but these responses were largely absent in mutants. Consistently, CUMS elevated pro-inflammatory cytokine (IL-1β, IL-6, TNF-α) in WT but not mutant mice. Although CUMS reduced the pAkt/Akt ratio in both genotypes, AQP4-A25Q mice maintained significantly higher pAkt levels after stress. Moreover, CUMS caused neuronal damage in WT hippocampus and cortex, whereas AQP4-A25Q mice were protected and even showed increased hippocampal neuronal density after stress. Collectively, OAP depolymerization does not intrinsically disrupt behavior but confers resilience to chronic stress by attenuating glial activation, neuroinflammation, and pAkt decline, preserving neuronal integrity. This identifies AQP4 OAP structure as a novel molecular determinant of stress susceptibility and highlights therapeutic potential for targeting OAP assembly in stress-related neuropsychiatric disorders.