Scientists have used a CRISPR-Cas9 gene editing system to lessen repetitive behavior characteristics in mice with a form of fragile X syndrome (FXS), the most common known single-gene cause of autism spectrum disorder (ASD). What’s more the Cas9 was delivered into the brain on gold nanoparticles, a method called CRISPR-Gold, eliminating the potentially dangerous use of a virus delivery system. The research was done by University of Texas scientists and published in Nature Biomedical Engineering.
Although single-gene autism disorders like FXS are relatively rare compared to cases with multiple genetic mutations, they present an advantage for researchers seeking to pinpoint causes and potential treatments for ASD.
In the current experiment, mice with FXS were injected with CRISPR-Gold carrying the Cas9 complex in the striatum of the brain. This region is known to mediate habit formation and is related to repetitive behaviors common to ASD. The Cas9 targeted an excitatory receptor, called the metabotropic glutamate receptor 5 (mGluR5), that is involved in neuronal communication and is dysregulated in FXS. This led to dampening of the exaggerated signaling between cells and lessened the repetitive behavior.
Repetitive digging and leaping were both observed in the mice prior to and following treatment and it was noted that obsessive digging was reduced by approximately 30%, while leaping went down 70%. The researchers correlated this decrease to the approximately 50% of mGluR5 genes in the striatum that were edited, cutting the receptors by half.
Not only did this study confirm that mGluR5 receptor in the striatum is involved in exaggerated repetitive behavior, it also demonstrated the possibility for safe genome editing in the brain using the CRISPR-gold method.
According to the researchers, this is the first study to demonstrate that Cas9 protein can be ferried into the brain with gold nanoparticles for therapeutic effect. "If you inject CRISPR DNA using a virus, you can't control how much Cas9 protein and guide RNA are expressed, so injecting it via a virus has a potential problem," said study leader Hye Young Lee, an assistant professor of cellular and integrative physiology at the University of Texas Health Science Center at San Antonio. "I think the CRISPR-Gold method is very cool because we can control the amount we wish to inject and that probably minimizes the side effects of using CRISPR, for example off-target effects."
Image: Researchers injected gold nanoparticles (upper right) carrying CRISPR-Cas9 into the brains of mice with fragile X syndrome to edit DNA (scissors) and knock out a neurotransmitter receptor, which reduced exaggerated repetitive behavior typical of autism spectrum disorder. Image courtesy of the University of Texas Health Science Center at San Antonio.