CRISPR, the Gene Editing Tool Improves Huntington’s Disease Symptoms

Our cells have a hard time copying repetitive DNA, and these copying errors can cause repetitive sequences to grow longer with each generation,” said senior study author Gene Yeo, PhD, professor of cellular and molecular medicine at UC San Diego School of Medicine.

“In the Huntingtin gene, these repeats can sometimes grow to many times their normal length, with the resulting repeat-expanded protein tending to aggregate and form toxic clumps in a part of the brain called the striatum that is important for regulating movement. The loss of functional neurons in the striatum ultimately leads to HD symptoms.”

CRISPR in Huntington’s Disease

With colleagues at UC Irvine and Johns Hopkins University, Yeo and his team investigated whether recently described RNA-targeting CRISPR technology could be used to affect RNA (a chemical intermediate between DNA instructions and protein production) accumulation associated with HD.

They used viral vehicles to deliver the therapy to neuronal cultures, which were developed from stem cells derived from patients with HD, and found that the approach not only targeted and destroyed mutant RNA molecules, but also cleared out toxic protein buildup. They also demonstrated that expression of other human genes was generally not disrupted by the therapy.

“Our goal was to engineer a type of therapy that would only target the toxic RNA that causes HD and could keep the rest of the human genome and transcriptome intact,” said co-first author Kathryn Morelli, PhD, a research fellow in Yeo’s lab. “We specifically screened our top therapeutic constructs in HD patient cell lines to make sure of it.”

Development of effective therapies for HD has proven challenging. In 2021, for example, two clinical trials for promising gene therapies were halted following disappointing results performance. Both potential drugs had been touted as game-changers for HD. Currently, no treatments can alter the course of the disease, though medications can lessen some symptoms.

“The Huntington’s community was devastated when the clinical trials failed, primarily due to target specificity and toxic effects,” said Yeo. “But their termination has only re-energized the scientific community to find alternative strategies.”

Yeo’s lab collaborated with Wenzhen Duan, MD, PhD, professor of psychiatry and behavioral sciences, at Johns Hopkins Medicine to conduct preclinical testing in mice. Duan, with co-first author Qian Wu, PhD, found that the therapy improved motor coordination, attenuated striatal degradation and reduced toxic protein levels in a mouse model of HD. The improvements lasted for at least 8 months without adverse effects and minimal off-target effects on other RNA molecules.

Source: Eurekalert