The Modulation Of AMPA Receptor GluA1 Subunit By M1 Acetycholine Receptor And Its Effect On Learning And Memory Function

Muscarinic acetylcholine receptors(m ACh Rs)are G protein-coupled receptors and important for multiple cognitive activities such as learning and memory.Among the m ACh Rs,M1 receptor is most abundantly expressed in the hippocampus(accounting for about 50%of the total m ACh Rs density)and the main subtype of m ACh Rs implicated in cognitive functions.Defects of M1 receptors have been implicated in the cognitive impairments of patients with Alzheimer's disease(AD).Ionic glutamate receptors AMPARs(?-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors)mediate the most majority of fast excitatory transmission in the mammalian brain and their trafficking into and out of synapses is a key factor in determining synaptic plasticity.However,whether or not M1 receptor regulates AMPAR trafficking and the regulatory mechanism remains to be defined.The study may help to further understand the physiological mechanisms of synaptic plasticity and learning and memory,and might provide potential drug targets for the therapy of the impaired cognitive function in AD.Our previous study suggested that M1 receptor could regulate the phosphorylation of AMPAR subunits so as to regulate their trafficking.In current study,we further investigated the modulation of AMPA receptor subunit GluA1 by M1 acetylcholine receptor and its effect on learning and memory function.The antagonism or knockdown of M1 receptor experiments were used to investigate the role of basal M1 receptor activity in maintaining GluA1 in WT mice hippocampus.Biotinylation,live-cell imaging and immunofluorescence experiments were used to investigate the regulation of M1 receptor activation on AMPAR GluA1 subunit trafficking to hippocampal neuronal surface and synapses,and GluA1-S845A mutant(in which Ser⁸⁴⁵ was mutated to Ala)was employed to explore the role of Ser845phosphorylation in GluA1 trafficking regulated by M1 receptor activation.Furthermore,inhibitors of signaling pathways were applied to explore the underlying mechanism of GluA1 trafficking regulated by M1 receptor activation.Further,the effect of M1 receptor activation on cognitive improvement was evaluated in GluA1-S845A mutant mice.The results showed that:1.Basal M1 receptor activity modulated the expression and Ser845 phosphorylation of GluA1 subunit in hippocampus of WT mice,and antagonism of M1 receptor impaired the synaptic insertion of GluA1 subunit induced by hippocampal-dependent spatial reference memory.2.M1 receptor activation increased the cell surface and synaptic insertion of GluA1.3.M1 receptor modulated GluA1 trafficking through the phosphorylation of GluA1 at Ser845.4.M1 receptor activation regulated the phosphorylation of GluA1 at Ser845 through a c AMP-PKA-PI3K-Akt-m TOR signaling pathway.5.The phosphorylation of GluA1 at Ser845 was essential for the M1 receptor-mediated rescue of spatial reference learning and memory impaired by A?_25-35 in mice.The above results suggest that basal M1 receptor activity could maintain the expression of AMPA receptor GluA1 subunit,and M1 receptor activation facilitates the process of GluA1 trafficking to neuronal surface,especially spines.Furthermore,the study clarifies the molecular mechanism of GluA1 phosphorylation at Ser845regulated by M1 receptor,and defines the function of GluA1 phosphorylation at Ser845 in the rescue of learning and memory impaired by A?_25-35.In summary,the study reveals a new molecular mechanism of M1 receptor and AMPA receptor-mediated cognition,provides new insights into pathophysiology of AD and potential targets for the AD therapy.