Translatome profiling reveals opposing alterations in inhibitory and excitatory neurons of fragile X mice and identifies EPAC2 as a therapeutic target

Symptoms of fragile X syndrome (FXS), the leading monogenic cause of intellectual disability and autism, are thought to arise from an excitation/inhibition (E/I) imbalance. Here, we leverage cell-type-specific mRNA sequencing to profile molecular alterations in cortical excitatory (Camk2) and inhibitory (Pvalb) neurons in Fmr1 knockout (KO) mice, integrating transcriptomic results with circuit and behavioral readouts to prioritize novel therapeutic targets. We uncovered significant genotype-by-cell type interactions for differential gene expression in Camk2a and Pvalb translatomes, and, strikingly, the underlying signaling pathways were often altered in opposite directions. Among the 184 differentially expressed genes that were concordantly dysregulated across both cell types, only Rapgef4 (a.k.a., exchange protein direftly activated by cAMP 2 [Epac2]; upregulated in Fmr1 KO) was also a fragile X messenger ribonucleoprotein (FMRP) target, brain-enriched, and associated with neurodevelopmental disorders. Treatment of Fmr1 KO mice with a specific EPAC2 antagonist restored cortical circuit function and ameliorated multiple behavioral phenotypes. Thus, EPAC2 should be considered a potential therapeutic target for FXS.