| Background:Neuroligin is a family of cell-adhesion molecules localized to the postsynaptic membrane and mediates the differentiation of presynaptic and postsynaptic scaffoldings.Different isoforms of neuroligin plays distinct roles in regulating the development and balance of excitatory and inhibitory synapses.Recent studies have reported that many of the susceptibility genes of autism are involved in regulating synapse formation and therefore have the potential to impact excitatory and inhibitory balance.And one of the autism spectrum disorders(ASD)model,neuroligin 3 R451C knockin mice,have cortical interneuron deficits.Morever,deletions or point mutations in neuroligin genes are found in patients with ASD or mental retardations.The dysfunctions of these neuroligin mutants have been verified in multiple neuroligin mouse models,including social interaction deficits,memory impairment and repetitive behaviors.Besides,researchers have also found alternations of the excitatory/inhibitory synapse ratio and the receptor subunit composition in these mice.Objective:To explore the distribution and function of different subtypes of neuroligin in neurons,examine the difference of regulating ways in synapse formation and stability between different types of neurons,and find out the brain region with morphological and functional deficits in these ASD mice models.Furthermore,we also attempted to illustrate the regulatory mechanism of synapse formation and E/I balance,interpret the cause of autism via accurately regulating the expression of neuroligin in neurons,and afford new insights for therapy.Methods:Interference with neuroligin expression in cortical neurons via shRNA was utilized to explore the regulatory mechanism of these proteins upon synapse formation in different subtypes of neurons.We used c-Fos antibody as an indicator of the activity of cells to figure out the brain regions underlying the social novelty deficits of NL3 R451C KI mice,and then injected DCS into these mice to rescue the deficits.Besides,morphological and electrophysiological difference of neurons and synapses were analyzed based on immunocytochemistry,immunohistochemistry,electrophysiological technique and 3D image analyze software.Result:The densities of excitatory synapses in pyramidal neurons and interneurons both significantly decreased due to the reduction of either neuroligin 1 or neuroligin 3 expression.Differently,the inhibitory synapse density in interneurons significantly decreased after neuroligin 1 knock down,but no similar change existed in pyramidal neurons.After the decline of neuroligin 2 expression,the excitatory synapse density significantly decreased in pyramidal neurons,but not in interneurons.The inhibitory synapse densities in pyramidal neurons and interneurons both significantly decreased after neuroligin 2 knock down.The inhibitory synapse density in neither pyramidal neurons nor interneurons significantly changed when the expression of neuroligin 3 was reduced.On the other hand,the c-Fos positive cells in mPFC after three-chamber social test significantly decreased in NL3 R451C KI mice,which can be rescued by DCS injection.The cortical neurons of NL3 R451C KI mice showed overdevelopment in vitro.The density and size of postsynaptic proteins,NMDAR subunit,and electrophysiological results also changed in these cortical neurons in vitro.Conclusion:Neuroligin plays a key role in synapse formation and then regulates the balance of excitatory and inhibitory synapses.An alteration in E/I balance is usually invoked as a possible final common pathway in autism.DCS rescued social novelty deficit and restores decreased c-Fos expressing cells in mPFC of NL3 R451C KI mice.Optogenetic stimulation of PV+ intemeurons altered the social novelty ability and c-Fos expressing cell number in mPFC of mice.Accurate regulation of neuroligin in neurons affords new insights for therapy of autism. |
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