Gene therapy techniques targeting overactive brain cells show promise in treating drug-resistant forms of the condition
50 million people worldwide have epilepsy. Although the majority of these people are able to use medications to manage and prevent their seizures, about one-third do not respond well to these treatments. In such cases, the only option available to control the seizures is to remove the part of the brain where the seizures occur. But this procedure is extremely dangerous.
Because epileptic seizures are caused by excessive activity of brain cells (neurons) in specific parts of the brain, being able to target and shut down these neurons can prevent seizures from occurring.
Using an innovative gene therapy approach that we developed, we were able to show in cell and animal models that it is possible to specifically target the neurons that cause epileptic seizures. This later prevented them from becoming hyperactive and having future seizures.
The discovery not only has major implications for the treatment of drug-resistant epilepsy, but is likely to be used to treat other neurological conditions caused by overactive neurons, including Parkinson’s disease and migraines. can be used.
Gene therapy works by directly changing a person’s genes to treat a disease or condition. There are a few different ways to do this.
Previous research that has used gene therapy to treat epilepsy in animal models has done so using a virus that has been modified in the laboratory so it is no longer harmful. Researchers will inject the virus into the brain region where seizures occur. The virus will then insert a strand of DNA into the cells, effectively changing the way they work – making them less active and preventing seizures.
Although this technique is much less invasive than brain surgery, the problem with this procedure is that it affects all neurons in the brain region – not just those that cause seizures. It also permanently changes the properties of cells that take up the viral DNA, which can permanently alter brain function.
But our innovative gene therapy tool has shown that it is possible to replace only the brain cells that cause seizures, leaving nearby healthy neurons unaffected. We were able to do this by taking advantage of how gene expression is normally regulated.
Role of promoters
There are 20,000 or more genes in our body, each of which contains instructions for making different proteins and molecules. These genes are usually under the control of neighboring stretches of DNA, called promoters. These determine whether and how much of a particular protein is made. Different cells express different proteins depending on which promoters are active or inactive.
There is also a special type of promoter (called an “activity-dependent” promoter) that will only switch on in response to biochemical signals made by neurons when they fire intensely — such as during a seizure. We took advantage of these activity-dependent promoters, creating a gene therapy that senses and rejects the stimulation of neurons that cause seizures. We linked these activity-dependent promoters to DNA sequences that contain proteins that calm neurons.
We first tested the gene therapy device in neurons grown in a dish, and then in mice with drug-resistant epilepsy. We also tested this technique in lab-grown human “mini-brains.”
Read more: Scientists grow brain tissue with different regions in the lab
In each test, we were able to show that this new gene therapy technique was effective in calming overactive neurons involved in seizures, while not affecting healthy cells.
Although it takes an hour or more to kick in – longer than the typical duration of a seizure – the new gene therapy is highly effective in preventing subsequent seizures. It does this by automatically choosing which neurons to treat and turning them off. It is also able to return neurons to their original state when brain activity returns to normal. The promoter is ready to turn on if seizures occur again.
So the treatment has to be given only once, but has a long-lasting effect – possibly a lifetime. Importantly, the treatment did not affect the mice’s performance on tests of memory and other normal behaviors (such as their anxiety levels, learning and movement).
We are excited by this development, as it could in principle bring the possibility of gene therapy to a wider range of people with drug-resistant epilepsy. But before the therapy is ready to be used in these patients, we will need to conduct several tests to confirm that it can be extended to the larger brain.