Increased CYFIP1 dosage alters cellular and dendritic morphology and dysregulates mTOR

Abstract

Rare maternally inherited duplications at 15q11-13 are observed in about 1% of individuals with an Autism Spectrum Disorder (ASD), making it among the most common causes of ASD. 15q11-13 comprises a complex region, and because this CNV encompasses many genes, it is important to explore individual genotypephenotype relationships. Cytoplasmic FMR1 interacting protein 1 (CYFIP1) is of particular interest because of its interaction with FMRP, its upregulation in transformed lymphoblastoid cell lines from patients with duplications at 15q11-13 and ASD, and the presence of smaller overlapping deletions of CYFIP1 in patients with schizophrenia and intellectual disability. Here, we confirm that CYFIP1 is upregulated in transformed lymphoblastoid cell lines, and demonstrate its upregulation in postmortem brain from 15q11-13 duplication patients for the first time. To investigate how increased CYFIP1 dosage might predispose to neurodevelopmental disease, we studied the consequence of its overexpression in multiple systems. We show that overexpression of CYFIP1 results in morphological abnormalities including cellular hypertrophy in SY5Y cells and differentiated mouse neuronal progenitors. We validate these results in vivo by generating a BAC transgenic mouse, which over-expresses CYFIP1 under the endogenous promotor, observing an increase in the proportion of mature dendrite spines and dendritic spine density. Gene expression profiling at embryonic day 15 suggested dysregulation of mTOR signaling, which was confirmed at the protein level. Importantly, similar evidence of mTOR-related dysregulation was seen in brains from 15q11-13 duplication patients with ASD. Finally, treatment of differentiated mouse neuronal progenitors with an mTOR inhibitor (rapamycin) rescued the morphological abnormalities resulting from CYFIP1 overexpression. Together, these data show that CYFIP1 overexpression results in specific cellular phenotypes, and implicate modulation by mTOR signaling, further emphasizing its role as a potential convergent pathway in some forms of ASD.

Collybistin binds and inhibits mTORC1 signaling: a potential novel mechanism contributing to intellectual disability and autism

“…31 In addition, overactivated mTORC1 signaling has also been linked to the pathophysiology of non-syndromic ASD. 10,11,32,33 This hyperactivation of the mTORC1 pathway has been shown to stimulate excessive protein synthesis in neuronal cells, leading to disturbances in neuronal differentiation and morphology, synaptic connectivity, and plasticity. Loss-of-function variants in CB, which are known to reduce GABAergic transmission and alter synaptic plasticity, have been associated with overlapping phenotypes, that is, intellectual disability, epilepsy, anxiety, 15,[22][23][24][25] and now autism, present in the patient here described.…”

“…5 Therefore, dysfunctional mTORC1 signaling and dysregulated protein synthesis in neuronal cells have been associated with several neurodevelopmental disorders with intellectual disability and autism. [6][7][8][9][10][11] mTORC1 signaling modulates assembly of the translation initiation machinery by interacting with the eukaryotic initiation factor eIF3, a scaffold complex that brings all components of the translation initiation process into close proximity, and by coordinating the phosphorylation and activity of key translational regulators S6K1 and 4EBP1. 12 We have recently identified two novel binding partners for eIF3, the neural Rho-GEF collybistin (CB) and the synaptic scaffold protein gephyrin, 13 which are known to be required for GABA A receptors clustering and inhibitory synapse formation.…”

A Subset of Autism-Associated Genes Regulate the Structural Stability of Neurons

“…Interestingly, CYFIP1 mediates FMRP-dependent protein translation to regulate the dendritic complexity and the stability of dendritic spines (Napoli et al, 2008; De Rubeis et al, 2013; Pathania et al, 2014). Overexpression of CYFIP1 results in an increase of dendritic branching and dendritic spine density (Oguro-Ando et al, 2015). Thus, the understanding of the molecular mechanisms regulated by FMRP provides insights into how mutations of FMR1 in ASD may affect neuronal function and contribute to autistic behaviors.…”

mTOR and MAPK: from localized translation control to epilepsy

“…CYFIP is a protein expressed at synapses, displaying multiple functions like local regulation of actin cytoskeleton dynamics and dendritic spine morphology [57]. Interestingly, morphological abnormalities resulting from overexpressed CYFP1 can be rescued by the mTOR inhibitor rapamycin [58] linking mTOR activity with a direct FMRP interactor. Furthermore, it has been shown that elevated levels of phosphorylated mTOR is associated with decreased FMRP [59].…”