Hydroxycarboxylic Acid Receptor 2 Mediates β-hydroxybutyrate's Antiseizure Effect in Mice

The ketogenic diet, a high-fat, low-carbohydrate regimen, is often used to treat drug-resistant seizures and is being studied for Alzheimer's disease and other neuropsychiatric disorders. However, its mechanism of action remains unclear. β-hydroxybutyrate, a primary circulating ketone body produced by the ketogenic diet, may mediate its effects on seizures by binding to a recently identified Gi-coupled receptor: hydrocarboxylic acid receptor 2 (HCAR2).

RNAscope in situ hybridization assay and real-time quantitative polymerase chain reaction were used to assess HCAR2 expression in the mouse brain. We generated HCAR2^-/^- using the CRISPR-Cas technique on an S129 mouse background. Whole-cell current-clamp was performed to measure the passive and active membrane properties of hippocampal dentate granule cells. The voltage-clamp was performed to record synaptic currents. Two complementary in vivo mouse models-continuous hippocampal stimulation to induce status epilepticus (SE) and kindling-were used to induce seizures.

HCAR2 was localized in dentate granule cells and microglia. In mice with HCAR2, β-hydroxybutyrate reduced neuronal excitability by hyperpolarizing the resting membrane potential, raising the action potential threshold, and reducing the firing frequency of dentate granule cells. β-hydroxybutyrate suppressed excitatory synaptic transmission. These effects were nullified in HCAR2^-/^- mice. HCAR2^-/^- mice showed no cognitive impairment. Moreover, β-hydroxybutyrate did not affect seizures in HCAR2^-/^- mice. However, it diminished both the duration and severity of seizures in HCAR2⁺/⁺ mice.

These findings demonstrate that HCAR2 mediates β-hydroxybutyrate's antiseizure effects by regulating neuronal excitability and synaptic transmission. These studies propose a new mechanism for the antiseizure action of the ketogenic diet. ANN NEUROL 2026;99:809-824.