Identification of UBE3A Protein in CSF and Extracellular Space of the Hippocampus Suggest a Potential Novel Function in Synaptic Plasticity

Abstract

Disruptions to the maternally inherited allele UBE3A, encoding for an E3 ubiquitin ligase, leads to the manifestation of Angelman Syndrome (AS). While this disorder is rare, the symptoms are severe and lifelong including but not limited to: intractable seizures, abnormal EEG's, ataxic gait, lack of speech, and most notably an abnormally happy demeanor with easily provoked laughter. Currently, little is known about the neurophysiological underpinnings of UBE3A leading to such globally severe phenotypes. Utilizing the newest AS rat model, comprised of a full UBE3A deletion, we aimed to elucidate novel mechanistic actions and potential therapeutic targets. This report demonstrates for the first time that catalytically active UBE3A protein is detectable within cerebrospinal fluid (CSF) of wild type rats but distinctly absent in AS rat CSF. Microdialysis within the rat hippocampus also showed that UBE3A protein is located in the interstitial fluid of wild type rat brains but absent in AS animals. This protein maintains catalytic activity and appears to be regulated in a dynamic activity‐dependent manner. Lay Summary Angelman syndrome (AS) is a rare genetic disorder caused by the loss of the UBE3A gene within the central nervous system. Although we have identified the gene responsible for AS, we still have a long way to go to fully understand its function in vivo. Here we report that UBE3A is present within normal cerebrospinal fluid (CSF) but distinctly absent in AS CSF. Furthermore, we demonstrate that UBE3A is secreted and that this may occur in a dynamic activity‐dependent fashion. Extracellular UBE3A maintained its ubiquitinating activity, thus suggesting that UBE3A may have a novel role outside of neurons. Autism Res 2021, 14: 645–655. © 2021 International Society for Autism Research and Wiley Periodicals LLC

Loss ofUBE3Aimpacts both neuronal and non-neuronal cells in human cerebral organoids

“…The ChP comprises the brain tissue that produces CSF. Recent human clinical studies also suggest a link between UBE3A and CSF 29,30 . UBE3A has been detected in CSF 30 , and individuals with Autism Spectrum Disorder (which has high comorbidity with AS) exhibit increased extra-axial CSF production 29 .…”

“…Recent human clinical studies also suggest a link between UBE3A and CSF 29,30 . UBE3A has been detected in CSF 30 , and individuals with Autism Spectrum Disorder (which has high comorbidity with AS) exhibit increased extra-axial CSF production 29 . Given this set of experimental and clinical observations, we performed additional experiments to better characterize the phenotypes associated with complete loss of UBE3A as well as identify what phenotypes might arise in organoids generated from a clinically relevant genotype, H9 UBE3A m-/p+ .…”

“…Recent human clinical studies also suggest a link between UBE3A and CSF 29,30 . UBE3A has been detected in CSF 30 We generated H9WT, H9UBE3A m-/p-, and H9UBE3A m-/p+ organoids and observed two discrete morphological phenotypes through brightfield microscopy: large fluid-filled cysts 62,63 and sinuous/invaginated tissue 64 , both characteristic of organoids with ChP tissue (Figures 6A and 6B). Immunostaining for TTR confirmed the ChP identity of the cysts and sinuous tissue (Figure 6C).…”

“…There are also intriguing potential impacts of UBE3A dosage on cerebrospinal fluid (CSF), which is known to regulate both developmental and homeostatic processes of the brain 29,30 .…”

“…Increased extra-axial CSF production has been observed in individuals with autism spectrum disorder 29 , and UBE3A has been found in CSF 30 suggesting UBE3A may affect the choroid plexus (ChP), the brain region responsible for CSF production.…”