CX₃CR1 ablation ameliorates motor and respiratory dysfunctions and improves survival of a Rett syndrome mouse model

Rett syndrome (RTT) is a neurodevelopmental disorder caused by loss-of-function mutations in the gene encoding MeCP2, an epigenetic modulator that binds the methyl CpG dinucleotide in target genes to regulate transcription. Previously we and others reported a role of microglia in the pathophysiology of RTT. Because microglia in the Mecp2 knockout (Mecp2KO) mouse model of RTT over-produce neurotoxic mediators glutamate and reactive oxygen species, we hypothesize that blocking neuron-microglia interaction by ablation of CX₃CR1, a chemokine receptor expressed in microglia/myeloid cells mediating such interaction by pairing with its neuronal ligand CX₃CL1, would ameliorate the RTT-like phenotype in Mecp2KO mice. Here we report that CX₃CR1 ablation prolonged the lifespan of Mecp2KO mice from a median survival of 54.5-74days, and significantly improved the body weight gain, symptomatic scores, major respiratory parameters, and motor coordination and performance. CX₃CR1 ablation rectified previously identified histological abnormalities in the Mecp2KO brain such as neuronal soma size in hippocampal CA2, and the number, soma size, and process complexity of microglia. Moreover, CX₃CR1 ablation enhanced the neurotrophic action of microglia in Mecp2KO mice by producing higher amount of insulin-like growth factor 1. Our data support a role of myeloid cells/microglia in RTT and suggest a novel therapeutic approach for RTT by targeting CX₃CR1 with specific antagonists or genetic downregulation.