Written by Lucy Job: https://www.linkedin.com/in/lucyjob/

Caenorhabditis elegans is a type of tiny soil-dwelling worm, found to accept certain human genes into their own genome [1]. These ‘humanised’ worms are a very useful tool to study human disease, with researchers at the University of Liverpool now using them to study human epilepsy and discover new anti-epileptic drugs [1] [2].

“C. elegans, model organism in life sciences” by ZEISS Microscopy

What is epilepsy?

Epilepsy is one of the most common conditions affecting the brain, shaping the lives of an estimated 50 million people worldwide [3]. In the UK alone, there are an estimated 600,000 epilepsy patients, which is almost 1 in every 100 people, with 87 people diagnosed every day [4]. There are a lot of different causes of epilepsy, and it can affect people of all ages [5].

Known causes of epilepsy, adapted from the World Health Organisation Infographics of Epilepsy [5]

Those with epilepsy suffer from recurrent seizures, which is caused by sudden bursts of electrical activity within the brain. The most well-known seizure type affects movement, causing muscle jerking, twitching, and/or weakness. Lesser known seizures affect the person’s awareness to their surroundings and can cause changes in sensation or emotion [6].

Currently, there are over 20 anti-epileptic drugs available with many different drug targets [7]. These drugs try to stop the sudden uncontrolled bursts of electrical activity within the brain. However, these anti-epileptic drugs do not work for one third of patients, named ‘refractory epilepsy’, with the reason for this not fully understood [8]. Therefore, new drugs are desperately needed for those patients with refractory epilepsy.

Why worms for drug development?

Making new drugs is controversial as testing on mammals, like mice and primates, has many ethical and financial issues. As these worms are invertebrates, less complex animals, they do not require extensive ethical training for use [9]. Also, these worms have a short reproduction time (~3 days) and lifespan (~3 weeks) and do not need expensive equipment take care of them, making them a much cheaper alternative [10]. Therefore, it is beneficial to test new drugs on less complex animals first, and then move onto more complex animals later in the drug development process. However, it is hard to justify using tiny soil-dwelling worms to test drugs for humans when we are so different [9].

Humanising the worm

To tackle this, researchers led by Professor Alan Morgan at the University of Liverpool have created humanised worms to study severe forms of epilepsy, such as Ohtahara syndrome [1]. This was achieved, in part, using the highly specialised gene editing process CRIPSR-Cas9 and which is used to insert, delete, or substitute target genes, to fix or introduce gene mutations [11].

Brief summary of CRISPR-Cas9. The Cas9 enzyme cuts the target genetic code, causing a DNA break. Once broken, a DNA repair process, leads to the desired insertion, deletions, or substitution at the target site.

GABA is a neurotransmitter (a biological chemical) which can prevent sudden electrical activity in the human brain. Studies by multiple different research teams have found GABA mutations (more specifically GABAA receptors) in patients with a spectrum of epileptic encephalopathies, such as Lennox-Gastaut syndrome and West syndrome [12].

In this project we aim to introduce mutated human GABAA receptor genes found in epilepsy patients into worms. We will then induce seizures in the worms and test a range of new anti-seizure drugs to see which compounds are most effective. Therefore, we will be able to assess the effect the new anti-seizure drugs may have in humans with the same genetic mutations.

Humanised worms used to study anti-epileptic drugs at the University of Liverpool.

Using these humanised worms as a first step in drug development is beneficial as it gives researchers the opportunity to fast-track the selection process, whittling down large numbers of drug candidates to a select few in a short space of time [2].

References

1.              Zhu, B., et al., Functional analysis of epilepsy-associated variants in STXBP1/Munc18-1 using humanized Caenorhabditis elegans. Epilepsia, 2020. 61(4): p. 810-821.

2.              Wong, S.Q., et al., A Caenorhabditis elegans assay of seizure-like activity optimised for identifying antiepileptic drugs and their mechanisms of action. J Neurosci Methods, 2018. 309: p. 132-142.

3.              Organization, W.H., Epilepsy: a public health imperative. 2019: World Health Organization,.

4.              Action, E. What is epilepsy? 2019 2019 [cited 2020 29.06.2020]; Available from: https://www.epilepsy.org.uk/info/what-is-epilepsy.

5.              Organization, W.H. Infographics on epilepsy. 2016-2017  [cited 2020 29.06.2020]; Available from: https://www.who.int/mediacentre/infographic/mental-health/epilepsy/en/.

6.              NHS. Symptoms – Epilepsy. 2017  [cited 2020 29.06.2020]; Available from: https://www.nhs.uk/conditions/epilepsy/symptoms/.

7.              Loscher, W., et al., New avenues for anti-epileptic drug discovery and development. Nat Rev Drug Discov, 2013. 12(10): p. 757-76.

8.              Kwan, P. and M.J. Brodie, Early identification of refractory epilepsy. N Engl J Med, 2000. 342(5): p. 314-9.

9.              Cunliffe, V.T., et al., Epilepsy research methods update: Understanding the causes of epileptic seizures and identifying new treatments using non-mammalian model organisms. Seizure, 2015. 24: p. 44-51.

10.            Chen, X., et al., Using C. elegans to discover therapeutic compounds for ageing-associated neurodegenerative diseases. Chem Cent J, 2015. 9: p. 65.

11.            Zhang, F., Y. Wen, and X. Guo, CRISPR/Cas9 for genome editing: progress, implications and challenges. Hum Mol Genet, 2014. 23(R1): p. R40-6.

12.            O’Reilly, L.P., et al., C. elegans in high-throughput drug discovery. Adv Drug Deliv Rev, 2014. 69-70: p. 247-53.

13.            Hernandez, C.C. and R.L. Macdonald, A structural look at GABAA receptor mutations linked to epilepsy syndromes. Brain Res, 2019. 1714: p. 234-247.

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