Functional deletion of α7 nicotinic acetylcholine receptor impairs Ca 2+ -dependent glutamatergic synaptic transmission by affecting both presynaptic and postsynaptic protein expression and function

Beatrice Cannata^1,2Laura Sposito¹Martina Albini¹Giuseppe Aceto^1,2Giulia Puliatti¹Giacomo Lazzarino^3,4Cristian Ripoli^1,2Maria Rosaria Tropea⁵Daniela Puzzo^5,6Roberto Piacentini^1,2*Claudio Grassi^1,2

• ¹Department of Neuroscience, Universita Cattolica del Sacro Cuore, Milan, Italy
• ²Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, Italy
• ³Saint Camillus International University of Health and Medical Sciences, Rome, Italy
• ⁴IRCCS Ospedale San Camillo, Venice, Italy
• ⁵Department of Biomedical and Biotechnological Sciences, Universita degli Studi di Catania, Catania, Italy
• ⁶IRCCS Associazione OASI Maria SS, Troina, Italy

Alpha7 nicotinic acetylcholine receptors (α7-nAChRs) are ionotropic, Ca²⁺-permeable receptors highly expressed in brain regions involved in memory formation, such as the hippocampus. Their activation induces cation influx and neuronal depolarization, which in turn promotes glutamate release-highlighting a crucial interplay between cholinergic and glutamatergic signaling in the healthy brain.Interestingly, the genetic deletion of α7-nAChRs in mice (α7-KO mice) leads to an Alzheimer's disease (AD)like phenotype characterized by aberrant amyloid-β accumulation, tau phosphorylation, and neuroinflammation in aged (> 12 months) mice. However, glutamatergic transmission in these mice prior to the onset of the AD-like phenotype has been poorly investigated. We thus studied molecular and functional properties of glutamatergic transmission in 4-6 months-old α7-KO mice, representing a prodromal phase of the AD-like neuropathology. We found that hippocampal CA1 neurons in brain slices from α7-KO mice showed a reduced frequency of the spontaneous excitatory post-synaptic currents (sEPSCs) compared to those of wild-type (WT) mice. On the contrary, the amplitude of sEPSCs was not affected, although in α7-KO neurons these currents displayed a longer rise time than in WT. CA1 neurons from α7-KO mice also exhibited a significantly smaller evoked NMDA currents than WT neurons, whereas AMPA currents were unaffected. From a molecular point of view, hippocampal neurons of α7-KO mice exhibited an increased expression of the presynaptic protein Synapsin-1 and of the NMDA subunits GluN2A and GluN2B, but no modifications in the expression of AMPA receptor subunits (GluA1 and GluA2) were found.Importantly, selective re-expression of the α7-nAChRs in neurons of α7-KO mice restored the evoked NMDA current amplitude and the rise time of sEPSCs, but it did not rescue the frequency of sEPSCs, thus suggesting that post-synaptic integrity depends on neuronal α7-nAChRs.