Haploinsufficiency of Shank3 Leads to Impairments in Synaptic Transmission and Plasticity

Background: SHANK3 is a synaptic scaffolding protein that is important for glutamate synapse formation/maturation in cultured neurons. Alterations in SHANK3 have been implicated in 22q13 deletion syndrome characterized by developmental delay and severe speech impairment. Recently, rare mutations in SHANK3 as well as copy number variation at this locus have been found to be associated with autism spectrum disorders (ASD). Objectives: In order to clarify the role of SHANK3 involvement in ASD pathogenesis and ASD phenotype, we have developed and characterized Shank3 knockout mice. Methods: Synaptic transmission, plasticity and spine morphology was examined using combined patch-clamp whole-cell recording, two-photon time lapse imaging and extracellular recording of field excitatory postsynaptic potentials at Schaffer collateral-CA1 synapses in acute hippocampal slices prepared from Shank3 heterozygous mice and control littermates. Results: Since all human cases of SHANK3 haploinsufficiency are heterozygotes, we focused our analyses on heterozygotes. In heterozygotes, Shank3 gene expression levels are about half of that of wild type littermates. Heterozygotes and born and grow without any obvious abnormality. Electrophysiological characterization using hippocampal slices prepared from these animals demonstrated that both the amplitude of miniature excitatory postsynaptic currents from hippocampal CA1 pyramidal neurons and the input-output curve for Shank3 heterozygous mice were significantly lower than those in control mice suggesting a reduction in basal transmission due to a postsynaptic effect. However in Shank3 heterozygous mice the frequency of miniature excitatory postsynaptic currents were significantly higher in comparison with the control mice and paired-pulse ratio was decreased which revealed a potential presynaptic role. We next examined the effect of Shank3 deficiency on synaptic plasticity and spine modification. Long-term potentiation (LTP) induced either with theta burst pairing (TBP) or high frequency stimulation was impaired in Shank3 heterozygous mice with no significant change in long-term depression (LTD). Only transient spine expansion was observed in Shank3 heterozygous mice while persistent expansion was seen in spines from control mice after TBP. Conclusions: These results indicate that reducing Shank3 expression level leads to alterations in synaptic transmission and plasticity that would predict behavioral phenotypes, related to learning and memory. Currently, we are characterizing Shank3 heterozygous animals behaviorally. Supported by the Simons Foundation and the Seaver Foundation.