Autism-Associated Mutations in ProSAP2/Shank3 Impair Synaptic Transmission and Neurexin–Neuroligin-Mediated Transsynaptic Signaling

Abstract

Mutations in several postsynaptic proteins have recently been implicated in the molecular pathogenesis of autism and autism spectrum disorders (ASDs), including Neuroligins, Neurexins, and members of the ProSAP/Shank family, thereby suggesting that these genetic forms of autism may share common synaptic mechanisms. Initial studies of ASD-associated mutations in ProSAP2/Shank3 support a role for this protein in glutamate receptor function and spine morphology, but these synaptic phenotypes are not universally penetrant, indicating that other core facets of ProSAP2/Shank3 function must underlie synaptic deficits in patients with ASDs. In the present study, we have examined whether the ability of ProSAP2/Shank3 to interact with the cytoplasmic tail of Neuroligins functions to coordinate pre/postsynaptic signaling through the Neurexin-Neuroligin signaling complex in hippocampal neurons of Rattus norvegicus. Indeed, we find that synaptic levels of ProSAP2/Shank3 regulate AMPA and NMDA receptor-mediated synaptic transmission and induce widespread changes in the levels of presynaptic and postsynaptic proteins via Neurexin-Neuroligin transsynaptic signaling. ASD-associated mutations in ProSAP2/Shank3 disrupt not only postsynaptic AMPA and NMDA receptor signaling but also interfere with the ability of ProSAP2/Shank3 to signal across the synapse to alter presynaptic structure and function. These data indicate that ASD-associated mutations in a subset of synaptic proteins may target core cellular pathways that coordinate the functional matching and maturation of excitatory synapses in the CNS.

Shank mutant mice as an animal model of autism

“…In fact, another study includes a similar deletion, which excised exon 4 to 7 (Shank3 e4 -7 ), although the majority of the results from that study refer to a downstream deletion of exons 13-16, resulting in the knockout of many shorter isoforms not affected in the other studies [72]. In addition, two recent studies have used gene expression in cultured hippocampal neurons to look at the subcellular mechanisms of Shank3, and the effect of point mutations in the ankyrin repeats domain associated with autism ( [14,73]; tables 3 and 4).…”

“…The Shank proteins bind neuroligins, suggesting that understanding the functional roles of this interaction may give insights into the underlying pathology of at least some forms of ASD. In this context, an intriguing recent study has shown that the overexpression of Shank3 results in alterations not just in postsynaptic function but also in presynaptic function and that this effect is mediated by the interaction between neuroligins and neurexins [73]. The introduction of ASD mutations in Shank3 (R87C, R375C, Q396R and InsG) impaired both pre-and postsynaptic function at glutamatergic synapses.…”

Shank3 Is Part of a Zinc-Sensitive Signaling System That Regulates Excitatory Synaptic Strength

“…They are considered central regulators of postsynaptic function, interacting with a large number of postsynaptic molecules including glutamate receptors, structural proteins, and the actin cytoskeleton (Boeckers et al, 2002;Kreienkamp, 2008). Shank3 also interacts with the C-terminal tails of Neuroligin 1 and 3 (Meyer et al, 2004) and thus couples changes in postsynaptic reception with presynaptic neurotransmitter release via the trans-synaptic Neurexin/Neuroligin complex (Arons et al, 2012). Both knock-down of endogenous Shank3 and overexpression of autism spectrum disorder (ASD)-associated Shank3 variants interfere with trans-synaptic signaling, indicating that presynaptic and postsynaptic coupling are likely targeted by ASD mutations (Kumar and Christian, 2009;Miles, 2011;Arons et al, 2012).…”

“…Shank3 also interacts with the C-terminal tails of Neuroligin 1 and 3 (Meyer et al, 2004) and thus couples changes in postsynaptic reception with presynaptic neurotransmitter release via the trans-synaptic Neurexin/Neuroligin complex (Arons et al, 2012). Both knock-down of endogenous Shank3 and overexpression of autism spectrum disorder (ASD)-associated Shank3 variants interfere with trans-synaptic signaling, indicating that presynaptic and postsynaptic coupling are likely targeted by ASD mutations (Kumar and Christian, 2009;Miles, 2011;Arons et al, 2012). Shank3-deficient mice show deficits in glutamatergic excitatory synaptic transmission, decreased LTP expression, and altered social interaction and anxietyrelated behaviors (Bozdagi et al, 2010;Kouser et al, 2013;Duffney et al, 2015;Lee et al, 2015;Speed et al, 2015).…”

“…Moreover, we find that Shank3 is essential for zinc-dependent modulation of AMPAR-mediated synaptic transmission. Intriguingly, an ASD-associated Shank3 variant (Shank3 R87C ) that impairs synaptic signaling (Arons et al, 2012) remains responsive to zinc and, while still supporting zincdependent increases in synaptic transmission, it fails to mediate trans-synaptic signals that modulate the reliability of presynaptic neurotransmitter release. These data support the concept that Shank3 is a crucial regulator of zinc-dependent signaling at excitatory synapses.…”