Shank3‐deficient thalamocortical neurons show HCN channelopathy and alterations in intrinsic electrical properties

Abstract

SHANK3 is a scaffolding protein that is highly enriched in excitatory synapses. Mutations in the SHANK3 gene have been linked to neuropsychiatric disorders especially the autism spectrum disorders. SHANK3 deficiency is known to cause impairments in synaptic transmission, but its effects on basic neuronal electrical properties that are more localized to the soma and proximal dendrites remain unclear. Here we confirmed that in heterologous expression systems two different mouse Shank3 isoforms, Shank3A and Shank3C, significantly increase the surface expression of the mouse hyperpolarization-activated, cyclic-nucleotide-gated (HCN) channel. In Shank3 knockout mice, which lack exons 13-16 in the Shank3 gene (both Shank3A and Shank3C are removed) and display a severe behavioural phenotype, the expression of HCN2 is reduced to an undetectable level. The thalamocortical (TC) neurons from the ventrobasal (VB) complex of Shank3 mice demonstrate reduced I current amplitude and correspondingly increased input resistance, negatively shifted resting membrane potential, and abnormal spike firing in both tonic and burst modes. Impressively, these changes closely resemble those of HCN2-/- TC neurons but not of the TC neurons from Shank3 mice, which lack exons 4-9 in the Shank3 gene (Shank3C still exists) and demonstrate moderate behavioural phenotypes. Additionally, Shank3 deficiency increases the ratio of excitatory/inhibitory balance in VB neurons but has a limited impact on the electrical properties of connected thalamic reticular (RTN) neurons. These results provide new understanding about the role of HCN channelopathy in mediating detrimental effects downstream from Shank3 deficiency.

Photodynamic Modification of Native HCN Channels Expressed in Thalamocortical Neurons

“…Indeed, Shank3 deficiency led to a reduction in HCN expression and produced a similar trend of changes in RMP, R in , and AP firing between Shank3−/− and HCN2−/− neurons. 33 Here we extend our previous investigations of heterologously expressed HCN channels to native HCN channels expressed in VB and VTA neurons. We found that PDM with FITC-cAMP as the photosensitizer resulted in a long-lasting increase in I inst and a corresponding decrease in I h .…”

“…[28][29][30] Importantly, Shank3deficient hippocampal neurons displayed reduced I h current, which resulted in increased R in and decreased RMP. [31][32][33] Both Shank3 and HCN2 are expressed at high levels in the thalamus. Although the thalamus plays a crucial role in processing sensory information and structural and functional abnormalities have been identified in the thalamus of ASD patients, less is known regarding how the thalamus contributes to ASD symptoms at the cellular level.…”

Shank3 Mice Carrying the Human Q321R Mutation Display Enhanced Self-Grooming, Abnormal Electroencephalogram Patterns, and Suppressed Neuronal Excitability and Seizure Susceptibility

“…Importantly, SHANK3 mutations have been shown to account for ∼1% of all ASD cases (Leblond et al, 2014). Multiple lines of Shank3 -mutant mice and, more recently, rats that carry global, conditional and point mutations in Shank3 , have been generated and characterized, providing information about normal and disease-related functions of Shank3 (Bozdagi et al, 2010; Peca et al, 2011; Wang et al, 2011; Schmeisser et al, 2012; Yang et al, 2012; Han et al, 2013; Kouser et al, 2013; Lee et al, 2015; Speed et al, 2015; Jaramillo et al, 2016, 2017; Mei et al, 2016; Wang et al, 2016; Zhou et al, 2016; Harony-Nicolas et al, 2017; Vicidomini et al, 2017; Amal et al, 2018; Berg et al, 2018; Bey et al, 2018; Drapeau et al, 2018; Engineer et al, 2018; Fourie et al, 2018; Heise et al, 2018; Jin et al, 2018; Ma et al, 2018; Qin et al, 2018; Yoo et al, 2018; Zhu et al, 2018; Balaan et al, 2019; Rendall et al, 2019). These animals display diverse synaptic, neuronal, circuit and behavioral abnormalities, providing substantial insight into how Shank3 mutations lead to various phenotypic abnormalities in mice (Jiang and Ehlers, 2013; Harony-Nicolas et al, 2015; Sala et al, 2015; Ferhat et al, 2017; Monteiro and Feng, 2017; Mossa et al, 2017; Tan and Zoghbi, 2018).…”

Network-Based Integrative Analysis of Genomics, Epigenomics and Transcriptomics in Autism Spectrum Disorders

“…These channels establish the slow native pacemaker currents contributing to membrane resting potentials, input resistance, dendritic integration, synaptic transmission, and neuronal excitability. Interestingly, it seems that SHANK3 , strongly linked to ASDs, works in organization of HCN-channels [29] and that its expression negatively influences those of HCN2 [30], so variations in the SHANK3 gene are reflected in pacemaker current abnormalities. In addition, variants in HCN1 , another member of the HCN family, were detected in patients with epileptic encephalopathy and clinical features of Dravet syndrome, intellectual disability, and autistic features [31].…”