Study led by Duke-NUS Medical School and National Neuroscience Institute (NNI) uncovers role of specific ion channel in epileptic seizures.
Autism spectrum disorder is a lifelong developmental disability with varying degrees of severity. Approximately one in every 150 children in Singapore are diagnosed with this disorder and one percent of the population is affected worldwide. A syndromic form of autism spectrum disorder is known as Angelman syndrome (AS). It is a genetic, neurodevelopmental disorder that affects about one in 15,000 births worldwide. Some signs and symptoms include intellectual disability, seizures, and ataxia just to name a few.
At present there are no treatments beside medication that can subside seizures and symptomatic therapy. However, research has shown that there is association between AS and the deletion of chromosome 15q11-13 which is where the gene that codes for Ubiquitin Protein Ligase E3A (UBE3A) is located. Despite this the mechanism by which underlies epilepsy in AS was yet to be found.
In a joint research by a team from both Duke-NUS Medical School and NNI, the researchers discovered that UBE3A prevents hyperexcitability of neurons in voltage-dependent big potassium channels by ubiquitination of these channels. Using human induced neurons and human cortical organoids, the researchers were able to compare the neuro-conductivity between wildtype UBE3A gene and knockout UBE3A gene neurons. The CRISPR-Cas9 gene editing system was used to achieve the knockout neurons.
“Findings from mouse models of AS have been hard to translate into human trials because of key differences between human and mouse neurons, resulting in an inability to identify a clear mechanism that can lead to effective therapeutics,” explained Associate Professor Hyunsoo Shawn Je, from Duke-NUS’ Neuroscience and Behavioural Disorders Programme, senior author of the study.
“We found that dysfunction of a specific molecule, known as the large conductance calcium-activated potassium (BK) channel, was misregulated in neurons derived from AS patients’ cells, and this change seems to be responsible for frequent seizures in AS patients,” Dr Alfred Sun, Junior Principal Investigator at NNI and co-first author of the study, elaborated.
The research team from Duke-NUS and NNI, together with collaborators from the Genome Institute of Singapore (GIS), the Singapore Bioimaging Consortium (SBIC), the Agency for Science, Technology and Research (A*STAR), the National University of Singapore (NUS), and Duke University focused on studying the functional changes of human neurons induced from AS patient-derived iPSCs at both the individual cell and the network ensemble levels with the use of functionally mature two-dimensional (2D) human neuronal cultures as well as three-dimensional (3D) human cortical organoids, or mini brains.
“The integrative data analysis obtained from functionally mature 2D neurons and 3D organoids using a combination of genetic, biochemical, electrophysiological, and imaging assays represents an advanced platform for investigating neuronal phenotypes in vitro. This approach may be applicable to disease modelling studies performed in other tissues or organs,” Dr Qiang Yuan, co-first author from Duke-NUS, highlighted.
Identifying the role of potassium channelopathy in causing epilepsy in AS still provide essential basis for the mechanism of neuronal hyperactivity and also could lead to the discovery of therapeutic options for AS and similar conditions.
The researchers will next be developing a high-throughput drug-screening platform to screen current US Food and Drug Administration approved drugs that can potentially be repurposed for treatment of epilepsy in AS patients. [APBN]