Loss Of Schizophrenia-associated Mir-501-3p In Mice Impairs Sociability And Memory In Mice By Enhancing MGluR5-mediated Glutamatergic Transmission

Background and objectiveSchizophrenia is a complex neuropsychiatric disorder that is characterized by a complex range of symptoms and cognitive imopairment and involves disturbances in neural circuity and synaptic plasticity.Although the estimate heritability of schizophrenia is high(60-80%),non-Mendelian features including a concordance rate in monozygotic twins reaching 50%,indicating that the interplay between genetic and epigenetic or environmental factors plays an important role in mediating phenotypic heterogeneity and disease susceptibility.Of the major epigenetic factor,a class of small noncoding RNA molecules known as microRNAs(miRNAs),usually～22 nucleotides in length,engage in post-transcriptional repression or mRNA destabilization of many target genes by base pairing to the target mRNAs.Since miRNAs are thought to organize neuronal development and plasticity by modulating complex gene networks,the clinical implications of an abnormality or disturbance of these networks are substantial,particularly if such abnormality occurs during development of the central nervous.Glutamine is an excitatory neurotransmitter in the central nervous system and elicits fast excitatory synaptic responses by activating ionotropic and metabotropic receptors.Ionotropic glutamate receptors(iGluRs),including N-methyl-D-aspartate receptors(NMDARs),alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors(AMPARs)and kainite receptors,are ligand-gated cation channels.Metabotropic glutamate receptors(mGluRs)are G protein-coupled receptors composed of eight mGluR subtypes(mGluR1-8).Several studies have demonstrated that miRNAs play regulatory roles in synaptic plasticity by directly targeting synaptic receptors or their downstream targets.However,due to the large numbers of miRNAs and their target genes,the regulatory molecular mechanism contributing to pathogenesis and development is largely unknown.Materials and methodsIn this study,we employed schizophrenia-discordant monozygotic twins(MZ)(SDCs)twins to screen 15 DE-miRNAs associated with individual differences in the phenotype and disease susceptibility of MZ twins.As phenotype-discordant MZ twins share a common genetic background,genetic variants may not lead directly to phenotype changes but may affect phenotype variability through changes in epigenetic profiles.10 of 15 DE-miRNAs remained consistently altered in schizophrenia after four HCC twin pairs were included to control for the nonpsychiatric-related trait differences between MZ twins.Morover,we further validation one of the downregulated miRNAs,miR-501-3p,expression level in the sporadic case of schizophrenia.We then mimicked one of the downregulated miRNAs,miR-501-3p,observed in MZ twin patients by generating a miR-501 conditional allele in mice to investigate the impact of miR-5013p loss of function in vivo.Moreover,we employed large-scale proteomic analysis to discover the in vivo taregets of miR-501-3p,and futher inhibited or knockdown its activity to ameliorate the abnormal behaviors causes by the loss of miR-501.Results and discussionIn this study,we performed transcriptomic analysis of peripheral blood RNA from MZ discordant for schizophrenia and identified a schizophrenia-associated downregulated microRNAs,miR-501-3p,which showed cinsistently schizophrenia associated downregulation in independent PBMCs and postmortem brain cohorts contributes to schizophrenia risk by regulating neural-related pathways.We showed that the loss of miR-501-3p in germline knockout(KO)mice resulted in dendritic structure defects,glutamatergic transmission enhancement and abnormal behaviors including social deficits,memory impairments,and sensorimotor gating disruption,which were attenuated when miR-501 expression was conditionally restored in the nervous system.Combining the results of proteomic analyses with the known genes linked to schizophrenia revealed that metabotropic glutamate receptor 5(mGluR5)was one of the miR-501-3p targets and was elevated in vivo upon loss of miR-501.Treatment with the mGluR5 negative allosteric modulator MTEP or the NMDAR antagonist AP5 ameliorated the deficits observed in Mir501-KO mice.Altogether,our finding that the association of dysregulated microRNA expression with phenotypic variations of monozygotic twins discordant for schizophrenia and loss of schizophrenia-associated miR-501-3p in male mice induced sociability,memory and sensorimotor gating disruption through mGluR5-mediated excitatory glutamatergic transmission enhancement.The epigenetic and pathophysiological mechanism that links miR-5013p to the modulation of excitatory glutamatergic transmission provides etiological implications for schizophrenia.