Astragaloside IV alleviates post-traumatic cytotoxic edema via inhibition of AQP4 expression and subcellular localization.

Abstract

BACKGROUND: Cytotoxic edema is one of the major causes of neurological impairment and even death following traumatic brain injury (TBI). Upregulation and altered subcellular localization of aquaporin-4 (AQP4) are key factors contributing to post-traumatic cytotoxic edema. Early intervention to mitigate cytotoxic edema can significantly improve patient outcomes. Astragaloside IV (AS-IV) has shown potential therapeutic effects against cerebral edema in related studies. PURPOSE: To determine whether AS-IV alleviates post-traumatic cytotoxic edema and to investigate its mechanism in reducing cytotoxic edema by inhibiting AQP4 expression and subcellular localization. METHODS: The controlled cortical impact (CCI) model was used to induce moderate traumatic brain injury in mice. Magnetic resonance imaging (MRI) was performed on days 1, 3, and 7 after TBI to evaluate the efficacy of AS-IV by characterizing the nature and volume of cerebral edema, and Sodium Aeschate(SA) was used as a positive control. Blood-brain barrier (BBB) integrity was assessed via transmission electron microscopy (TEM), and Cy5.5-labeled AS-IV was injected for in vivo fluorescence imaging to evaluate its ability to cross the BBB. Histopathological examination and TEM were conducted on day 3 to observe cellular and organelle-level changes in the edematous area. Neurological severity score (NSS), rotarod test, open-field test, grip strength test, and adhesive removal test were used to comprehensively assess the motor function. Western blotting (WB), ELISA, molecular docking, and immunofluorescence were applied to investigate the optimal administration concentration of AS-IV and to determine the expression and distribution of related proteins. RESULTS: Cerebral edema in mice was primarily cytotoxic on days 1 and 3 after TBI. The volume of cytotoxic edema increased, and the motor dysfunction worsened in days 1-3. Cytotoxic edema had partially resolved and turned into infarct foci on day 7. AS-IV significantly reduced cytotoxic edema and improved motor dysfunction in CCI mice, with efficacy comparable to that of SA. Further experiments indicated that AS-IV downregulates AQP4 expression via the Akt/FoxO3a/AQP4 pathway and inhibits AQP4 subcellular localization through the TRPV4/cAMP/PKA pathway. CONCLUSION: AS-IV alleviates post-traumatic cytotoxic edema by inhibiting the expression of AQP4 via the Akt/FoxO3a/AQP4 pathway and the subcellular localization of AQP4 via the TRPV4/cAMP/PKA pathway.