Shank3 Deficiency Induces NMDA Receptor Hypofunction via an Actin-Dependent Mechanism

Abstract

Shank3, which encodes a scaffolding protein at glutamatergic synapses, is a genetic risk factor for autism. In this study, we examined the impact of Shank3 deficiency on the NMDA-type glutamate receptor, a key player in cognition and mental illnesses. We found that knockdown of Shank3 with a small interfering RNA (siRNA) caused a significant reduction of NMDAR-mediated ionic or synaptic current, as well as the surface expression of NR1 subunits, in rat cortical cultures. The effect of Shank3 siRNA on NMDAR currents was blocked by an actin stabilizer, and was occluded by an actin destabilizer, suggesting the involvement of actin cytoskeleton. Since actin dynamics is regulated by the GTPase Rac1 and downstream effector p21-activated kinase (PAK), we further examined Shank3 regulation of NMDARs when Rac1 or PAK was manipulated. We found that the reducing effect of Shank3 siRNA on NMDAR currents was mimicked and occluded by specific inhibitors for Rac1 or PAK, and was blocked by constitutively active Rac1 or PAK. Immunocytochemical data showed a strong reduction of F-actin clusters after Shank3 knockdown, which was occluded by a PAK inhibitor. Inhibiting cofilin, the primary downstream target of PAK and a major actin depolymerizing factor, prevented Shank3 siRNA from reducing NMDAR currents and F-actin clusters. Together, these results suggest that Shank3 deficiency induces NMDAR hypofunction by interfering with the Rac1/PAK/cofilin/actin signaling, leading to the loss of NMDAR membrane delivery or stability. It provides a potential mechanism for the role of Shank3 in cognitive deficit in autism.

Dendritic spine actin cytoskeleton in autism spectrum disorder

“…SHANK3 was found to directly interact with Arp2/3 and to increase F-actin levels in the Shank3 transgenic mice, and treating the mice with the moodstabilizing drug valproate, but not lithium, ameliorated the manic-like behavior 179 . Consistent with previous results showing that NMDA receptor membrane delivery and stability depend on the integrity of actin cytoskeleton 331 , these findings further highlight that the dysregulation of synaptic actin filaments and the loss of synaptic NMDA receptors contribute to the manifestation of autism-like phenotypes, and thus provide strategies for the treatment of autism 178 .…”

Deficiency of Shank2 causes mania-like behavior that responds to mood stabilizers

“…For instance, it is well-known that inhibition of NMDAR function through pharmacologic or genetic manipulation can lead to hyperactivity in the open field (40,61,62). Since both Shank2 and Shank3 mutant mice have alterations in NMDAR subunit expression and NMDA responses (1,(63)(64)(65), comparative studies between these lines of mutant mice may reveal whether the same neural circuitry and molecular mechanisms modulate their abnormal behaviors.…”

The role of glutamate and its receptors in autism and the use of glutamate receptor antagonists in treatment

“…NMDA receptor dysfunction is a common feature of several models, including SHANK3 (Duffney et al 2013), NLGN1 (Blundell et al 2010), FXS knockout mouse (Eadie et al 2010) and MeCP2 transgenic mice (Asaka et al 2006). NLGN1 knockout mice do not exhibit many behavioral deficits characteristic of autism, although increased repetitive behaviors are observed (Blundell et al 2010).…”