Autism-linked mutations of CTTNBP2 reduce social interaction and impair dendritic spine formation via diverse mechanisms

Abstract

Abnormal synaptic formation and signaling is one of the key molecular features of autism spectrum disorders (ASD). Cortactin binding protein 2 (CTTNBP2), an ASD-linked gene, is known to regulate the subcellular distribution of synaptic proteins, such as cortactin, thereby controlling dendritic spine formation and maintenance. However, it remains unclear how ASD-linked mutations of CTTNBP2 influence its function. Here, using cultured hippocampal neurons and knockin mouse models, we screen seven ASD-linked mutations in the short form of the Cttnbp2 gene and identify that M120I, R533* and D570Y mutations impair CTTNBP2 protein–protein interactions via divergent mechanisms to reduce dendritic spine density in neurons. R533* mutation impairs CTTNBP2 interaction with cortactin due to lack of the C-terminal proline-rich domain. Through an N–C terminal interaction, M120I mutation at the N-terminal region of CTTNBP2 also negatively influences cortactin interaction. D570Y mutation increases the association of CTTNBP2 with microtubule, resulting in a dendritic localization of CTTNBP2, consequently reducing the distribution of CTTNBP2 in dendritic spines and impairing the synaptic function of CTTNBP2. Finally, we generated heterozygous M120I knockin mice to mimic the genetic variation of patients and found they exhibit reduced social interaction. Our study elucidates that different ASD-linked mutations of CTTNBP2 result in diverse molecular deficits, but all have the similar consequence of synaptic impairment.

Perineuronal Nets and Metal Cation Concentrations in the Microenvironments of Fast-Spiking, Parvalbumin-Expressing GABAergic Interneurons: Relevance to Neurodevelopment and Neurodevelopmental Disorders

“…Interestingly, cells in the CA1 and CA3 regions of the dorsal hippocampus and basolateral amygdala of the Cttnbp2 knockout mouse showed less-intense C-FOS staining after social stimulation than the wild-type controls. The less-intense C-FOS staining in the Cttnbp2 -/mouse was consistent with gene dosage-dependent effects of Cttnbp2-deficieny on dendritic spines in the dorsal CA1 hippocampal region and other ultrastructural parameters of the excitatory synapse in dorsal hippocampus, such as the size of the postsynaptic density and number of presynaptic vesicles [72]. Cttnbp2 deficiency was associated with reduced synaptic distribution of SHANK2 and SHANK3 scaffold proteins, which suggests that CTTNBP2 has an important role in their synaptic targeting; protein levels of SHANK2 and SHANK3 were not reduced in the total homogenates [72].…”

“…The less-intense C-FOS staining in the Cttnbp2 -/mouse was consistent with gene dosage-dependent effects of Cttnbp2-deficieny on dendritic spines in the dorsal CA1 hippocampal region and other ultrastructural parameters of the excitatory synapse in dorsal hippocampus, such as the size of the postsynaptic density and number of presynaptic vesicles [72]. Cttnbp2 deficiency was associated with reduced synaptic distribution of SHANK2 and SHANK3 scaffold proteins, which suggests that CTTNBP2 has an important role in their synaptic targeting; protein levels of SHANK2 and SHANK3 were not reduced in the total homogenates [72]. Moreover, consistent with their roles as scaffold proteins that are involved in anchoring glutamate receptors at the surface of the postsynaptic membrane of excitatory synapses located on dendritic spines, immunoblotting revealed reduced protein levels of the NMDA receptor subunits GRIN1 and GRIN2A in the synaptosomal fractions of Cttnbp2 -/brains [72].…”

“…Mice with absent or deficient expression of cortactin binding protein 2 (CTTNBP2) (i.e., Cttnbp2 -/and Cttnbp2 +/-, respectively), a regulator of dendritic spine formation, show impairments of social preference, social memory and spatial memory, and cognitive inflexibility in standard behavioral paradigms [72]. Interestingly, cells in the CA1 and CA3 regions of the dorsal hippocampus and basolateral amygdala of the Cttnbp2 knockout mouse showed less-intense C-FOS staining after social stimulation than the wild-type controls.…”

Molecular Mechanisms of Aberrant Neuroplasticity in Autism Spectrum Disorders (Review)

“…Firstly, the effect of these mutations starts still in the process of the nervous system formation in the perinatal period and in early childhood as well. A number of mutations converge on the common path of the nervous system maturation in neurogenesis, axon development, and synapse formation [ 55 ] and these processes play a crucial role in the development of normal neuroplasticity [ 56 ].…”

Glutamatergic Dysfunction and Synaptic Ultrastructural Alterations in Schizophrenia and Autism Spectrum Disorder: Evidence from Human and Rodent Studies

“…The ASD-associated cortactin binding protein 2 (CTTNBP2) is known to regulate the subcellular distribution of synaptic proteins, such as cortactin, thereby controlling dendritic spine formation and maintenance [250]. In the Cttnbp2 −/− mouse model of ASD, in all regions of the dorsal hippocampus, these mice showed a reduction in the length and thickness of PSDs, the count of presynaptic vesicles, and the ratio of vesicle number to PSD length [140].…”