ALS Drug Target Uncovered Through CRISPR Approach

Several genes observed to protect against neuronal toxicity caused by amyotrophic lateral sclerosis.

Through gene editing, researchers may have determined key genetic drivers of amyotrophic lateral sclerosis (ALS), according to a study published by Nature Genetics.

These findings may aid in the development of novel therapeutic targets and represents significant progress towards a cure for the neurodegenerative disease.

ALS impacts how the brain communicates with the body, which makes day-to-day activities difficult. Like other similar conditions, ALS features abnormal aggregates of proteins that cause toxicity to the brain.

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Although the protein aggregates are thought to be toxic to neurons, the process of cell death in ALS is unknown, according to the authors.

“These toxic protein aggregates are what’s likely driving the pathology in the disease, but no one really knows how they cause neuronal cell death. That’s really what we wanted to probe in this study,” said senior author Aaron Gitler, PhD.

In the new study, the authors used CRISPR-Cas9 gene-editing technology to find genes that defend neurons against toxic protein clumps. This investigation resulted in a better understanding of the disease and potential drug targets.

It was previously known that mutations of the C9orf72 gene are common among patients with ALS. In these patients, mutated C9orf72 contains a large segment of DNA that repeats itself. When eroded, the mutated gene is turned into rogue proteins that impact neurons and lead to cell death, according to the authors.

“In a healthy person, you might see 10 to 20 of these DNA repeats,” said co-lead author Michael Haney. “But in ALS, they expand to hundreds or even thousands of repeated segments, and that’s the template for the production of these toxic proteins.”

The goal of the study was to determine how the toxic proteins target healthy neurons and whether there are other genes that protect the brain against the proteins.

The researchers conducted genomewide screening, in which CRISPR-Cas9 was used to change the function of every human gene. They used the approach to determine gene knockouts that could increase toxicity or prevent it, according to the study.

After knocking out every gene and comparing toxicity of ALS proteins in cells, the authors discovered 200 genes that either protected against toxic cells or make it more vulnerable, according to the study.

Two follow-up knock out screenings in mouse neurons indicated that several genes elicited strong protection against ALS, according to the authors.

The analysis revealed that one gene blocks the entrance through which toxic ALS proteins enter the cell to corrupt it.

There was another gene that was able to stave off neural death. The gene codes for Tmx2, and when depleted, nearly 100% of the neurons survived, according to the study. Comparatively, only 10% of normal cells survived.

“We could imagine that Tmx2 might make good drug target candidate,” Haney said. “If you have a small molecule that could somehow impede the function of Tmx2, there might be a therapeutic window there.”

The new findings suggest that Tmx2’s may modulate genes that spark cell death, according to the authors.

This is the first time that CRISPR has been used to investigate a neurodegenerative disease. The authors are currently using the approach to determine additional causes of ALS and other conditions characterized by protein aggregates such as Huntington’s, Parkinson’s, and Alzheimer’s diseases.

“We’re still in early phases, but I think figuring out exactly what Tmx2 normally does in a cell is a good place to start—that would hint at what functions are disturbed when these toxic species kill the cell, and it could point to what pathways we should look into,” said co-lead author Nicholas Kramer.