Identification of M ₄ muscarinic acetylcholine receptor expressing astrocytes that regulate locomotion and survival in murine prion disease

Whilst there has been much focus on the function of neuronally expressed members of the muscarinic acetylcholine receptor family (mAChR) less attention has been paid to the expression profile and role of the five members of this family (M ₁ -M ₅ mAChRs) in non-neuronal cells of the brain. Using genetically engineered mice we identify a previously unappreciated sub-population of astrocytes expressing the M ₄ mAChR subtype. These are located in various brain regions that include the brainstem, hypothalamus and, most abundantly, the cerebellum. Signalling and proteomic analysis of M ₄ mAChR positive astrocytes from the cerebellum established the functional expression of this receptor subtype and its role in the regulation of protein expression. Genetic ablation of M ₄ mAChR positive astrocytes in mice revealed a specific role in locomotion behaviour. Importantly, in the context of murine prion disease, a model of terminal neurodegeneration associated with profound neuroinflammation, we observed a significant expansion of M ₄ mAChR positive astrocytes and report ablation experiments that established that this astrocyte sub-population has a detrimental effect on late-stage disease. Together we provide evidence of a sub-population of M ₄ mAChR expressing astrocytes that play a specific role in normal neurophysiology and the progression of inflammatory neurodegenerative disease.