Potentiation of group III metabotropic glutamate receptors positively affects neurophysiological features in a mouse model of Rett syndrome.

Abstract

Rett syndrome (RTT) is a neurodevelopmental disorder primarily caused by loss-of-function mutations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene. Genetic restoration of MECP2 in mice can reverse phenotypes, providing hope for disease-modifying therapies in the disease. Studies in people with and mouse models of RTT have identified neurophysiological features, such as auditory event-related potentials (AEPs), that correlate with disease severity, suggesting potential as translatable biomarkers. We have identified reductions in the expression and function of the group III metabotropic glutamate receptor 7 (mGlu₇), a G protein-coupled receptor regulating presynaptic neurotransmitter release, in both human and mouse RTT brains. Additionally, treatment of RTT mice with a positive allosteric modulator (PAM) of the group III mGlu receptors (VU0422288) improves behavioral phenotypes, most likely via mGlu₇ potentiation. To evaluate whether VU0422288 treatment modulates neurophysiological biomarkers, we acutely treated RTT mice with VU0422288 at 3,10, and 30 mg/kg and assessed neurophysiological features. VU0422288 treatment caused increases in AEP peak amplitudes in RTT mice but not in wild-type controls, with no effect on basal electroencephalogram power. Treatment with a different compound, ADX88178, a PAM that activates the mGlu_{4, 6and 8} receptors, did not affect neurophysiological assessments, suggesting that the target of VU0422288 is likely mGlu₇. These findings suggest that neurophysiological features, like AEP, have potential as sensitive and quantitative biomarkers that may be useful in evaluating mGlu₇ PAMs and other pharmacological interventions as novel RTT treatment strategies. SIGNIFICANCE STATEMENT: Correlations between neurophysiological features and disease severity in Rett syndrome suggest their potential as translatable biomarkers sensitive to pharmacological modulation. This study demonstrates that potentiation of group III metabotropic glutamate receptors improves neurophysiological features in Rett syndrome mice.