Gene Therapy Targets Cryptic Exons in ALS Treatment

In a significant advancement for targeting neurodegenerative diseases, recent research has highlighted the potential of using cryptic exons. This innovative approach, which aims to treat conditions such as amyotrophic lateral sclerosis (ALS), leverages precise genetic modifications to address the underlying deficits associated with these disorders.

Understanding Cryptic Exons

ALS is a debilitating neurodegenerative disease that is primarily influenced by age, typically manifesting around the average age of 55 years. The disease is characterized by the degeneration of motor neurons, leading to loss of muscle control and functionality. Recent studies have shown that ALS is often associated with the dysfunction of the protein TDP-43, which plays a crucial role in maintaining proper RNA transcription.

During the transcription process, genes are converted into RNA, which consists of exons (coding sequences) and introns (non-coding sequences). Occasionally, introns may contain sequences that resemble exons—known as cryptic exons—which can disrupt the final RNA product, resulting in faulty proteins. In ALS, TDP-43 normally prevents these cryptic exons from being expressed incorrectly. However, when TDP-43 becomes dysfunctional, the delicate balance of protein synthesis is compromised, triggering a cascade of cellular issues.

The Novel Gene Therapy Approach

Given that ALS affects only a fraction of neurons—estimated at less than 0.00001% of the total cell population—targeting therapy with high specificity is essential. In a groundbreaking study published in Science, researchers from the Francis Crick Institute and the UCL Queen Square Institute of Neurology have developed a method to precisely target these affected cells.

The research team created viral vectors designed to carry both therapeutic genes (such as functional TDP-43) and specific cryptic exon sequences found in the gene AARS1. Importantly, the viral vectors only express the therapeutic cargo in cells where TDP-43 is functioning poorly, allowing for a targeted treatment approach.

Findings and Results

In initial experiments, researchers incorporated a fluorescent protein, mCherry, within the viral vectors to evaluate the specificity of their construct. The results showed a substantial increase in mCherry expression correlating with cryptic exon expression in cells lacking functional TDP-43. Although some leaky expression was detected in normal cells, adjusting the construct to include additional cryptic exons resulted in enhanced specificity for cells with deficient TDP-43.

The researchers further validated their approach by mimicking ALS-like conditions using human embryonic kidney cells. In this setup, the viral vectors displayed similar activation patterns, strongly suggesting that this method could be effectively applied to ALS patients.

Precision and Future Directions

One of the study's notable experimental features involved using vectors containing DNA-editing tools. These tools were able to successfully eliminate cryptic splice sites exclusively in compromised cells, showcasing the precision of this gene therapy method. Additionally, vectors carrying a less aggregation-prone version of TDP-43 were tested, reinforcing the potential for tailored therapeutic interventions.

As Dr. Claire Le Pichon from the Eunice Kennedy Shriver National Institute of Child Health and Human Development noted, “Gene therapy holds promise for treating neurodegenerative diseases like ALS and FTD, which are relatively common but for which there are few treatments.” This emphasis on correcting TDP-43 functionality only in affected cells represents a crucial development in achieving safer and more efficient precision medicine for neurodegenerative diseases.

“Disease-induced activation of gene therapies at single-cell resolution could help mitigate the potential risks of permanent transgene expression in patients.” – Research excerpt

By focusing on precision targeting, this research opens new avenues for therapies that not only aim to treat existing conditions but also to intervene in at-risk individuals before clinical symptoms arise. Such innovative strategies could play a pivotal role in the future of ALS and the broader category of neurodegenerative disease therapies.

Literature Cited

[1] Wilkins, O. G., et al. (2024). Creation of de novo cryptic splicing for ALS and FTD precision medicine. Science.

[2] Scotter, E. L., et al. (2015). TDP-43 proteinopathy and ALS: insights into disease mechanisms and therapeutic targets. Neurotherapeutics, 12(2), 352-363.

[3] McAleese, K. E., et al. (2017). TDP‐43 pathology in Alzheimer’s disease, dementia with Lewy bodies and ageing. Brain pathology, 27(4), 472-479.

[4] Lifespan.io