Phase separation and zinc-induced transition modulate synaptic distribution and association of autism-linked CTTNBP2 and SHANK3

Abstract

Many synaptic proteins form biological condensates via liquid-liquid phase separation (LLPS). Synaptopathy, a key feature of autism spectrum disorders (ASD), is likely relevant to the impaired phase separation and/or transition of ASD-linked synaptic proteins. Here, we report that LLPS and zinc-induced liquid-to-gel phase transition regulate the synaptic distribution and protein-protein interaction of cortactin-binding protein 2 (CTTNBP2), an ASD-linked protein. CTTNBP2 forms self-assembled condensates through its C-terminal intrinsically disordered region and facilitates SHANK3 co-condensation at dendritic spines. Zinc binds the N-terminal coiled-coil region of CTTNBP2, promoting higher-order assemblies. Consequently, it leads to reduce CTTNBP2 mobility and enhance the stability and synaptic retention of CTTNBP2 condensates. Moreover, ASD-linked mutations alter condensate formation and synaptic retention of CTTNBP2 and impair mouse social behaviors, which are all ameliorated by zinc supplementation. Our study suggests the relevance of condensate formation and zinc-induced phase transition to the synaptic distribution and function of ASD-linked proteins.

DRACC1, a major postsynaptic protein, regulates the condensation of postsynaptic proteins via liquid-liquid phase separation

“…DRACC1 has an intrinsically disordered domain (IDR) in its C-terminal end similarly to other proteins that undergo LLPS, such as TDP-43, FMRP, and CTTNBP2 (Shih et al, 2022; Tsang et al, 2019; Zbinden et al, 2020). Dynamics of DRACC1 in neurons observed by time-lapse imaging look similar to that of TLS/FUS (Fujii et al, 2005), which is among the first identified and best characterized RNA-binding proteins in the field of phase separation (Zbinden et al, 2020).…”

The schizophrenia-associated missense variant rs13107325 regulates dendritic spine density

“…Interestingly, a recent study by Tseng et al showed that the human SLC39A8-p.391T missense variant (corresponds to the risk allele of rs13107325) reduced zinc transport (into the cell) in cell models [71], which was consistent with our observations in this study (i.e., zinc concentration was dysregulated in SLC39A8-p.391T knock-in mice compared with wild-types). Zn 2+ has a critical role in the brain, including regulating synaptic plasticity through microtubule stability [72], CTTNBP2 condensates [73], and BDNF signaling Consistent with its important roles in the Zinc concentration has been reported to be associated with several neuropsychiatric disorders [75], including schizophrenia [76,77] and Alzheimer's disease [78]. Zn 2+ is mainly distributed in the central nervous system (CNS) and stored in synaptic vesicles at several glutamatergic nerve terminals, and released upon its neuronal activity [79,80].…”

Liquid–liquid phase separation in synaptopathies

“…ASD-related mutations in cortactin-binding protein 2 alter its condensation and synaptic distribution, leading to social impairment in mice. 68 Rett syndrome is a progressive X-linked neurodevelopmental disorder characterized by severe mental disabilities and autism-like symptoms, mainly caused by loss-of-function mutations in MeCP2. 75 Previous studies have demonstrated that loss or doubling of MeCP2 leads to postnatal neurodevelopment disorders.…”

“…Cortactin‐binding protein 2, an ASD‐linked protein, forms phase‐separated condensates via its C‐terminal IDR and promotes SHANK3 cocondensation in dendritic spines. ASD‐related mutations in cortactin‐binding protein 2 alter its condensation and synaptic distribution, leading to social impairment in mice 68 . Rett syndrome is a progressive X‐linked neurodevelopmental disorder characterized by severe mental disabilities and autism‐like symptoms, mainly caused by loss‐of‐function mutations in MeCP2 75 .…”