Epilepsy and Autism Spectrum disorders (ASD) are both complex neurodevelopmental disorders which share approximately 30% comorbidity. Epilepsy is characterized by unprovoked recurrent seizures and affects ~1% of the population while ASDs are characterized by deficits in language, social, and behavior and found 1 in 68 people. Variants in synaptic genes suggest disruptions in synaptic regulation underlie both conditions. PRICKLE1 and PRICKLE2 are known core WNT/ PCP genes implicated in Progressive myoclonic epilepsy in families and in the general population. Humans, mice, zebrafish, and Drosophila with disrupted Prickle exhibit epileptic behavior and other neurological deficits. Prickle is implicated in several aspects of neuronal development and mutated proteins display aberrant activity in vivo and in vitro.
Recently, variations in PRICKLE1 were associated with ASDs in humans. The mechanisms by which PRICKLE could contribute to ASDs are unknown. Results presented here show Prickle1+/- mice exhibit ASD-like behavior. Prickle1 associates with Synapsin I; a phosphoprotein important for synaptogenesis, axonogenesis, and neurotransmitter release. Mutant R104QPRICKLE1 protein causes a reduction in sizes of dense-core vesicles in neuronal-like PC12 cells. Results indicate PRICKLE1 may be associated with ASDs and possibly involved in synaptic homeostasis.
Prickle deregulation has also been associated with neural tube defects and cancers. The mechanism(s) by which Prickle is regulated is incompletely understood. To further elucidate the role of PRICKLE in disease, immunoprecipitates from PRICKLE-expressing stable tetracycline-regulated neuronal-like PC12 cells were identified by mass spectrometry. The deubiquitinating enzyme USP9X was identified as a novel interacting PRICKLE protein. USP9X is a substrate-specific deubiquitinating enzyme implicated in several aspects of neuronal development, associated with X-linked intellectual disability and a candidate gene for epilepsy. Results show that USP9X robustly deubiquitinates and protects PRICKLE from proteasomal degradation. USP9X variants found in the ARRA ASD cohort directly associates USP9X with ASDs. The identified USP9X mutations delete the PRICKLE-interacting domain and provide a possible mechanism for PRICKLE deregulation. Already a target for treating cancer, USP9X can serve as a therapeutic target to regulate PRICKLE levels.