Salk scientists have created a new version of the CRISPR/Cas9 genome editing technology that allows them to activate genes without creating breaks in the DNA, potentially circumventing a major hurdle to using gene editing technologies to treat human diseases.
As a proof of concept, the Salk group used their new approach to treat several diseases, including diabetes, acute kidney disease, and muscular dystrophy, in mouse models.
“Although many studies have demonstrated that CRISPR/Cas9 can be applied as a powerful tool for gene therapy, there are growing concerns regarding unwanted mutations generated by the double-strand breaks through this technology,” says Juan Carlos Izpisua Belmonte, a professor in Salk’s Gene Expression Laboratory and senior author of the new paper, published in Cell on December 7, 2017.
In the original CRISPR/Cas9 system, the enzyme Cas9 is coupled with guide RNAs that target it to the right spot in the genome to create DSBs. Recently, some researchers have started using a “Dead” form of Cas9, which can still target specific places in the genome, but no longer cuts DNA. Instead, dCas9 has been coupled with transcriptional activation domains-molecular switches-that turn on targeted genes.
In this way, the technology operates epigenetically, meaning it influences gene activity without changing the DNA sequence.
In the case of kidney disease, they activated two genes known to be involved in kidney function, and observed not only increased levels of the proteins associated with those genes, but improved kidney function following an acute injury.
For muscular dystrophy, the researchers expressed genes that have been previously shown to reverse disease symptoms, including one particularly large gene that cannot easily be delivered via traditional virus-mediated gene therapies.