The CRISPR-Cas9 gene-editing tool, also known for acting like a pair of ‘scissors’, is delivered to brain cells to cut out the disease-causing DNA sequence. Illustration by Rita Félix

A study, carried out by a team from the Centre for Neuroscience and Cell Biology at the University of Coimbra (CNC-UC) and GeneT – Gene Therapy Centre of Excellence, reveals new findings that may contribute to the development of therapeutic approaches for Machado-Joseph disease. This disease affects the brain and motor skills, with the highest prevalence in the Azores (on the island of Flores, Wheel it affects between one in 140 and one in 239 adults) and in the central region of the country.

In this study, the team from the University of Coimbra, which has been investigating a new therapeutic strategy for this disease, used extracellular vesicles (small particles secreted by cells) as a delivery vehicle for gene-editing tools in the context of this disease.

The vesicles were used to encapsulate the CRISPR-Cas9 system—which functions as a set of genetic “scissors”—which is then delivered to the neurons in the brain. Through this process, it was possible to inactivate the mutant ATXN3 gene, which, in Machado-Joseph disease, is altered by excessive repetitions of CAG sequences in the genetic code.

The use of these vesicles is an innovative approach because it enables the genetic editing system to reach the target cells rapidly. Their use has demonstrated advantages in the rapid delivery of the CRISPR-Cas9 system, which may bring researchers ever closer to developing a safer therapeutic strategy for the Machado-Joseph disease.

This proposed therapeutic approach is based on gene therapy, a type of treatment that involves editing the genome (or DNA) and which opens possibilities for curing many rare genetic diseases that remain, to this day, incurable.

“With this study, we aimed to understand whether it would be possible to use extracellular vesicles to achieve transient exposure to the gene-editing machinery and minimize unwanted edits. We have been testing extracellular vesicles because they overcome some of the limitations of conventional viral vectors, ensuring a lower immune response, greater encapsulation capacity and transient expression of the gene-editing tools”, explains Kevin Leandro, a researcher at CNC-UC and the article’s first author.

The CNC-UC/GeneT team (from left to right): Kevin Leandro, David Machado and Luís Pereira de Almeida

The scientists have also developed a light-controlled delivery system, using a photocleavable—that is, light-activated—protein which contributes to the efficiency of genetic editing. This is one of the first international studies to demonstrate the effectiveness of this approach using extracellular vesicles in the context of Machado-Joseph disease.

Machado-Joseph disease, also known as spinocerebellar ataxia type 3, is one of a group of conditions known as spinocerebellar ataxias, which are genetic and hereditary neurodegenerative diseases. They cause significant suffering to those affected, who experience progressive impairment of motor function, speech, swallowing and fine motor skills (ataxia), whilst retaining all their cognitive and intellectual functions.

The study Extracellular vesicle-mediated delivery of SpCas9 RNPs for therapeutic gene editing in Spinocerebellar Ataxia Type 3, published in the journal Biomaterials, is available here.

Inês Amado da Silva with Catarina Ribeiro (UC)