Ketogenic Diet Modulates Cerebellar AQP4 in an Age-dependent Manner and Parallels Reduced Anxiety-like Behavior in Rats.

Aging is accompanied by neuroinflammation, glial dysfunction, and altered lipid metabolism that contribute to emotional and cognitive decline. Aquaporin-4 (AQP4), the principal astrocytic water channel, supports glymphatic clearance and astroglial homeostasis within neural circuits involved in emotional regulation. The ketogenic diet (KD) has been proposed as a strategy to counteract age-related brain dysfunction; however, its region- and age-specific effects on AQP4 expression and anxiety-like behavior remain unclear. Young (7 weeks) and aged (22 months) male rats were fed either a standard chow or a KD for 10 weeks. Anxiety-like behavior was assessed using the Open Field Test (OFT) and the Elevated Plus Maze (EPM). Serum metabolic markers, including β-hydroxybutyrate (BHB), glucose, lipids, and liver enzymes, were measured. AQP4 protein expression was quantified in the cerebellum and prefrontal cortex. KD induced nutritional ketosis, as reflected by increased BHB levels. Glucose regulation showed a diet × age–dependent pattern, increasing in aged KD-fed rats but decreasing in young KD-fed rats. Lipid responses were also age dependent, with reduced triglycerides in young KD-fed rats and an increased LDL-C: HDL-C ratio in aged KD-fed rats, while liver enzyme values remained within physiological limits. Behaviorally, KD was associated with reduced anxiety-like responses selectively in aged rats, without alterations in general locomotor activity. At the molecular level, KD decreased cerebellar AQP4 expression in aged rats and increased it in young rats, whereas prefrontal cortex AQP4 expression showed a diet-related reduction independent of age. Together, these findings demonstrate that KD exerts age- and region-dependent effects on metabolic state, astroglial AQP4 expression, and anxiety-like behavior. In aged animals, changes in cerebellar AQP4 expression co-occur with reduced anxiety-like behavior, suggesting that cerebellar astroglial adaptations may form part of broader metabolic influences on emotional regulation during aging.