β-Arrestin2 Couples Metabotropic Glutamate Receptor 5 to Neuronal Protein Synthesis and Is a Potential Target to Treat Fragile X

Synaptic protein synthesis is essential for modification of the brain by experience and is aberrant in several genetically defined disorders, notably fragile X (FX), a heritable cause of autism and intellectual disability. Neural activity directs local protein synthesis via activation of metabotropic glutamate receptor 5 (mGlu(5)), yet how mGlu(5) couples to the intracellular signaling pathways that regulate mRNA translation is poorly understood. Here, we provide evidence that beta-arrestin2 mediates mGlu(5)-stimulated protein synthesis in the hippocampus and show that genetic reduction of beta-arrestin2 corrects aberrant synaptic plasticity and cognition in the Fmr1(-ly) mouse model of FX. Importantly, reducing beta-arrestin2 does not induce psychotomimetic activity associated with full mGlu(5) inhibitors and does not affect G(q) signaling. Thus, in addition to identifying a key requirement for mGlu(5)-stimulated protein synthesis, these data suggest that beta-arrestin2-biased negative modulators of mGlu(5) offer significant advantages over first-generation inhibitors for the treatment of FX and related disorders.