Autism-linked neuroligin-3 R451C mutation differentially alters hippocampal and cortical synaptic function

Abstract

Multiple independent mutations in neuroligin genes were identified in patients with familial autism, including the R451C substitution in neuroligin-3 (NL3). Previous studies showed that NL3 R451C knock-in mice exhibited modestly impaired social behaviors, enhanced water maze learning abilities, and increased synaptic inhibition in the somatosensory cortex, and they suggested that the behavioral changes in these mice may be caused by a general shift of synaptic transmission to inhibition. Here, we confirm that NL3 R451C mutant mice behaviorally exhibit social interaction deficits and electrophysiologically display increased synaptic inhibition in the somatosensory cortex. Unexpectedly, however, we find that the NL3 R451C mutation produced a strikingly different phenotype in the hippocampus. Specifically, in the hippocampal CA1 region, the NL3 R451C mutation caused an ∼1.5-fold increase in AMPA receptor-mediated excitatory synaptic transmission, dramatically altered the kinetics of NMDA receptor-mediated synaptic responses, induced an approximately twofold up-regulation of NMDA receptors containing NR2B subunits, and enhanced longterm potentiation almost twofold. NL3 KO mice did not exhibit any of these changes. Quantitative light microscopy and EM revealed that the NL3 R451C mutation increased dendritic branching and altered the structure of synapses in the stratum radiatum of the hippocampus. Thus, in NL3 R451C mutant mice, a single point mutation in a synaptic cell adhesion molecule causes context-dependent changes in synaptic transmission; these changes are consistent with the broad impact of this mutation on murine and human behaviors, suggesting that NL3 controls excitatory and inhibitory synapse properties in a region-and circuit-specific manner.synapse formation A utism spectrum disorders (ASDs) constitute a heterogeneous group of neurodevelopmental diseases with a strong genetic component (1-3). The identification of multiple ASD candidate genes that encode synaptic proteins suggested that ASDs may involve impairments in synaptic transmission (4-12). In particular, numerous mutations in neuroligins, a family of postsynaptic cell adhesion molecules, have been identified in 10,12). Consistent with the hypothesis that synaptic dysfunction contributes to ASD pathogenesis (13, 14), mouse models of two ASD-associated neuroligin mutations exhibit functional changes in synaptic transmission (15, 16).Neuroligins are not critical for the initial establishment of synapses but are required for normal synapse function (17)(18)(19)(20). Deletion of neuroligin-1 or -2 selectively impairs excitatory or inhibitory synaptic transmission, respectively (17,18,21,22), whereas at least in the somatosensory cortex, deletion of neuroligin-3 (NL3) causes no major synaptic phenotype (15). Three ASD-relevant neuroligin mutations were characterized in mouse models: the R451C substitution in NL3 (15, 23), a loss of function mutation of NL4 (24), and a point mutation that was identified in the cytoplasmic tail of NL4 in an ASD patient...

Neurons generated by direct conversion of fibroblasts reproduce synaptic phenotype caused by autism-associated neuroligin-3 mutation

“…The effect of the Nlgn3 R704C-mutation on AMPAR responses is surprisingly strong (∼50% decrease) given the continued presence of other neuroligins that might be redundant. Moreover, no similar effect was observed in Nlgn3 KO neurons (28,29). Together, these observations indicate that the R704C mutation does not operate as a loss-offunction mutation in which AMPARs are insufficiently retained on the neuronal surface but rather as a gain-of-function mutation in which the single amino acid substitution of the R704C mutation induces the removal of AMPARs from the surfaces.…”

“…To examine the pathogenic mechanism of Nlgn3 mutations in ASDs, we previously produced KO mice that lack Nlgn3 expression and knockin mice that contain the ASD-associated point mutations R451C or R704C. These mice exhibit major synaptic phenotypes (21,28,29). Among neuroligin mutations, the R704C mutation (which affects a conserved arginine residue on the cytoplasmic face of the transmembrane region) was arguably the most interesting, in that it produced a selective decrease in AMPA-type glutamate receptor (AMPAR)-mediated responses Significance A major challenge in modeling human diseases is to replicate disease phenotypes in neurons that are differentiated from nonneuronal cells, such as pluripotent stem cells or fibroblasts.…”

The neurexin ligands, neuroligins and leucine-rich repeat transmembrane proteins, perform convergent and divergent synaptic functions in vivo

“…As shown here, their specific roles also will depend on the maturational state of the synapses in which they are localized and the specific circuit in which the synapses function (30).…”

Enhanced synapse remodelling as a common phenotype in mouse models of autism

“…If diverse genetic mutations in these mouse models converge to impairment of activity-dependent stabilization, mice models may show similar enhancement in synapse turnover. An obvious candidate pathway is N-methyl-D-aspartate (NMDA) receptordependent signalling 51 , and previous studies indicated defects in NMDA receptor-dependent synaptic plasticity in ASD mouse models, including NLG R451C mice 52 .…”