SHANK3 mutations identified in autism lead to modification of dendritic spine morphology via an actin-dependent mechanism

Abstract

Genetic mutations of SHANK3 have been reported in patients with intellectual disability, autism spectrum disorder (ASD) and schizophrenia. At the synapse, Shank3/ProSAP2 is a scaffolding protein that connects glutamate receptors to the actin cytoskeleton via a chain of intermediary elements. Although genetic studies have repeatedly confirmed the association of SHANK3 mutations with susceptibility to psychiatric disorders, very little is known about the neuronal consequences of these mutations. Here, we report the functional effects of two de novo mutations (STOP and Q321R) and two inherited variations (R12C and R300C) identified in patients with ASD. We show that Shank3 is located at the tip of actin filaments and enhances its polymerization. Shank3 also participates in growth cone motility in developing neurons. The truncating mutation (STOP) strongly affects the development and morphology of dendritic spines, reduces synaptic transmission in mature neurons and also inhibits the effect of Shank3 on growth cone motility. The de novo mutation in the ankyrin domain (Q321R) modifies the roles of Shank3 in spine induction and morphology, and actin accumulation in spines and affects growth cone motility. Finally, the two inherited mutations (R12C and R300C) have intermediate effects on spine density and synaptic transmission. Therefore, although inherited by healthy parents, the functional effects of these mutations strongly suggest that they could represent risk factors for ASD. Altogether, these data provide new insights into the synaptic alterations caused by SHANK3 mutations in humans and provide a robust cellular readout for the development of knowledge-based therapies.

Dendritic spine actin cytoskeleton in autism spectrum disorder

“…Loss of fodrin binding may lead to labile actin filaments leading to alterations in spine density and spine maturation 168 . In non-neuronal cells SHARPIN is known to inhibit integrin activation 169 .…”

“…Furthermore, autism-linked mutations (R12C, arginine to cysteine; L68P, leucine to proline) 168,171,172 in SHANK3 impaired its integrin inhibitory function in non-neuronal cells 170 prompting a new intriguing proposal that at least some of the SHANK ASD-associated mutations alter the integrin activation in neurons.…”

“…Shank3 knockout mice suffer from a loss of cortical actin filaments, in association with reduced Rac1/p21-activated kinase (PAK) activity together with increased activity of cofilin 178 . Overexpression of Shank3 has been found to enhance actin polymerization 168 and increase F-actin levels 179 . The SHANK proteins can regulate Rac1 activity through RhoGEF beta-PIX 163 and RhoGAP RICH2 180 .…”

Autism throughout genetics: Perusal of the implication of ion channels

“…The SHANK proteins are associated with NMDA receptors via the guanylate kinase‐associated protein (GKAP)/postsynaptic density‐95 (PSD‐95) complex and with metabotropic glutamate receptors type 1 (mGluR1) via the neuronal scaffolding protein Homer1. In addition, SHANK proteins can bind to several actin‐regulatory molecules, such as cortactin (Durand et al., 2012). Mutations and CNVs (deletion and duplication) affecting SHANK genes have been associated with ASD.…”

“…Mutations and CNVs (deletion and duplication) affecting SHANK genes have been associated with ASD. These variations resulted in actin accumulation in dendritic spines, which alters the development and the morphology of dendrites (Durand et al., 2012). …”