β-hydroxybutyrate restores social deficits by suppressing HDAC9 in the ACC of Shank3B-deficient mice.

Autism spectrum disorder (ASD) is characterized by core deficits in social behavior, yet effective interventions remain limited. Ketogenic diet (KD) shows behavioral benefits in ASD, but the underlying mechanisms remain unclear. Here, using Shank3B knockout (KO) mice, we found that KD ameliorates social deficits and induces systemic ketosis with marked elevation of β-hydroxybutyrate (BHB) in KO mice. Oral BHB alone recapitulates KD's prosocial effects, restoring social interaction and neuronal activity in the anterior cingulate cortex (ACC). Mechanistically, we identified HDAC9 as a region- specific epigenetic target upregulated in ACC neurons of Shank3B KO mice and suppressed by BHB. HDAC9 overexpression in ACC neurons induces social and synaptic deficits, while class IIa HDAC inhibition phenocopies BHB effects. BHB also restores dendritic complexity, excitatory transmission, and AMPA receptor expression. These findings uncover a metabolite-driven epigenetic mechanism linking ketogenic metabolism to the rescue of social behavior via the ACC, and identify HDAC9 as a potential therapeutic target for ASD-related social deficits.