The Autism Protein Ube3A/E6AP Remodels Neuronal Dendritic Arborization via Caspase-Dependent Microtubule Destabilization

Abstract

gene copy number variation and the resulting overexpression of the protein E6AP is directly linked to autism spectrum disorders (ASDs). However, the underlying cellular and molecular neurobiology remains less clear. Here we report the role of ASD-related increased dosage of Ube3A/E6AP in dendritic arborization during brain development. We show that increased E6AP expression in primary cultured neurons leads to a reduction in dendritic branch number and length. The E6AP-dependent remodeling of dendritic arborization results from retraction of dendrites by thinning and fragmentation at the tips of dendrite branches, leading to shortening or removal of dendrites. This remodeling effect is mediated by the ubiquitination and degradation of XIAP (X-linked inhibitors of aptosis protein) by E6AP, which leads to activation of caspase-3 and cleavage of microtubules. , male and female 2X ASD mice show decreased XIAP levels, increased caspase-3 activation, and elevated levels of tubulin cleavage. Consistently, dendritic branching and spine density are reduced in cortical neurons of 2X ASD mice. In revealing an important role for Ube3A/E6AP in ASD-related developmental alteration in dendritic arborization and synapse formation, our findings provide new insights into the pathogenesis of Ube3A/E6AP-dependent ASD. Copy number variation of the gene and aberrant overexpression of the gene product E6AP protein is a common cause of autism spectrum disorders (ASDs). During brain development, dendritic growth and remodeling play crucial roles in neuronal connectivity and information integration. We found that in primary neurons and in Ube3A transgenic autism mouse brain, overexpression of E6AP leads to significant loss of dendritic arborization. This effect is mediated by the ubiquitination of XIAP (X-linked inhibitor of aptosis protein) by E6AP, subsequent activation of caspases, and the eventual cleavage of microtubules, leading to local degeneration and retraction at the tips of dendritic branches. These findings demonstrate dysregulation in neuronal structural stability as a major cellular neuropathology in ASD.

Autism-linked Cullin3 germline haploinsufficiency impacts cytoskeletal dynamics and cortical neurogenesis through RhoA signaling

“…RhoA is one of the proteins that controls neurite outgrowth, and RhoA upregulation was previously implicated in loss of spines and neurite retraction 6,7,10,17,21 . Previously developed genetic autism mouse models (SETD5, UBE3A, SHANK3, Timothy syndrome) also observed reduced neurite outgrowth, sometimes in concert with reduced synaptic connectivity [21][22][23][24] . The iPSC-derived neurons from Timothy syndrome patients also exhibited dendrite retraction phenotype 21 We attribute observed cytoskeletal and neuronal defects to upregulation of RhoA signaling.…”

Characterizing spine issues: If offers novel therapeutics to Angelman syndrome

“…By two‐photon microscopy, it was showed the normal spine density in layer 2/3 pyramidal neurons from somatosensory cortex and anterior frontal cortex but the spines are less sensitive to sensory experience alternation after Ube3a overdosage (Isshiki et al., 2014). However, through Golgi staining, the spine density in the hippocampus region was found decreased and spines became less mature after Ube3a overdosage on P15 (Khatri et al, 2018).…”

“…The spine density from Ube3a deleted cortical neurons is increased in hippocampus neurons on DIV14 (Sell et al., 2019) but decreased on DIV16 (Wang, Wang, et al, 2019) and DIV18 (Sun et al, 2018) by GFP labeling. After Ube3a dosage elevated, spines from hippocampal neurons became less mature and decreased the density on DIV13 (Khatri et al, 2018) but increased the density on DIV21 (Yi et al., 2015).…”

“…Collectively, in vitro and in vivo evidence strengthened the crucial roles of normal dosage of Ub3a in maintaining spine density and morphology during development, especially the experience‐induced synaptic plasticity and spine modification. Alternation (increase, decrease, and loss) of Ube3a dosage may have no effect on spine/synapse formation (Greer et al, 2010; Yashiro et al., 2009; Kim et al, 2016), but causes deficits of spine maturation, with more thin and long immature spines but less mushroom mature spines (Kim et al, 2016; Khatri et al, 2018; Wang, Wang, et al, 2019). The effects may also depend on the subcellular region like apical and basal (Santo & Stryker, 2010; Yashiro et al., 2009).…”

Impaired proteostasis in rare neurological diseases

“…AS has been studied using in vivo models and hiPSCs. As epigenetic regulation of human UBE3A is conserved in rodents, researchers have generated different AS murine models, including those encompassing one or several exons of UBE3A or even longer deletions affecting the imprinted region, to study this disorder [183][184][185][186].Additionally, generation of an UBE3A reinstatement model has allowed researchers to define neurodevelopmental windows that may rescue AS-related phenotypes: motor deficits were rescued by Ube3a reinstatement in adolescent mice, whereas anxiety, repetitive behavior, and epilepsy were only rescued when Ube3a was reinstated during early development. In contrast, hippocampal synaptic plasticity could be restored at any age [187].…”