β-Hydroxybutyrate improves glymphatic system function and alleviates cerebral edema in mice after ischemic stroke

Cerebral edema is a severe complication following ischemic stroke. Recent studies have highlighted the crucial role of the glymphatic system (GS) in the clearance of water and macromolecules. GS dysfunction involving the disorders of AQP4 polarization may be crucial in the pathophysiology of cerebral edema. β-Hydroxybutyrate (BHB), the main component of the ketone body, has been shown to alleviate neurological deficits by restoring GS function in subarachnoid hemorrhage models and to reduce Aβ deposition in Alzheimer's disease models. In this study we investigated the effects of BHB on cerebral edema following ischemic stroke and its mechanisms. The mice were fed a ketogenic diet (KD) or a normal diet for 4 weeks before transient middle cerebral artery occlusion (MCAO). Alternatively, the mice received BHB (5 g·kg^-1·d^-1) or vehicle post-MCAO. By using brain section analysis, transcranial macroimaging, two-photon in vivo imaging and MRI, we demonstrated that both KD and BHB treatment significantly enhanced GS function under normal and MCAO conditions. BHB reduced cerebral edema and infarct volume post-MCAO. Notably, delayed BHB treatment initiated 10 h post-MCAO still improved GS function, but did not influence infarct volume. Furthermore, we revealed that BHB increased α1-syntrophin expression and H3K27ac levels in α1-syntrophin (Snta1) enhancer, restoring AQP4 polarization. In addition, BHB also reduced HDAC3 expression and elevated p300 expression. These results suggest that a KD and BHB treatment enhance GS function in mice and that BHB also mitigates brain edema after MCAO. The potentiation of GS function by BHB is likely mediated by the inhibition of HDAC3 activity and the increase in p300 activity, which upregulate α1-syntrophin expression and restore AQP4 polarization.