Summary: Researchers used an RNA-targeting CRISPR system to remove the mutant RNA that drives Huntington’s disease, clearing toxic protein aggregates while largely preserving other human genes and transcripts.
Source: UCSD
Huntington’s disease (HD) is an inherited neurodegenerative disorder marked by progressive loss of movement control, coordination and cognitive abilities. The disease results from a mutation in a single gene called huntingtin (HTT).
Worldwide, more than 200,000 people live with Huntington’s disease; in the United States roughly 30,000 are affected and over a quarter-million are at risk of inheriting the mutation from an affected parent. There is currently no cure.
In a study published December 12, 2022 in Nature Neuroscience, scientists at the University of California San Diego School of Medicine and collaborators report using an RNA-targeting form of CRISPR, Cas13d, to selectively eliminate the toxic RNA produced by the mutant HTT gene. Their approach reduced harmful protein accumulation in cellular and animal models while minimizing disruption of the rest of the genome and transcriptome.
CRISPR is widely known as a genome-editing technology that can add, delete or modify DNA at precise genomic sites. It stems from a bacterial immune mechanism. Traditional DNA-targeting CRISPR tools carry a risk of unintended, permanent edits—insertions or chromosomal alterations that can be inherited. That risk has driven interest in CRISPR systems that target RNA directly, allowing transient and reversible intervention without altering genomic DNA.
Huntington’s disease arises from an expanded stretch of CAG trinucleotide repeats in the HTT gene. Repetitive sequences are prone to copying errors that can lengthen across generations; when CAG repeats exceed the normal range, the resulting huntingtin protein contains an expanded polyglutamine tract that aggregates and becomes toxic to neurons.
“In the huntingtin gene, these repeats sometimes expand far beyond their normal length,” said senior author Gene Yeo, PhD, professor of cellular and molecular medicine at UC San Diego School of Medicine. “The repeat-expanded protein tends to aggregate in the striatum, a brain region essential for movement control. Loss of functional neurons there produces the motor and cognitive symptoms that define HD.”
Yeo’s team, working with researchers at UC Irvine and Johns Hopkins University, tested whether an RNA-targeting CRISPR system could selectively remove the mutant HTT transcripts that drive disease. They engineered a Cas13d construct designed to recognize and destroy expanded CAG-repeat RNA, then delivered the therapy using viral vectors to neuronal cultures derived from stem cells taken from HD patients.
In those patient-derived cell models, the Cas13d treatment selectively degraded mutant HTT RNA and led to clearance of toxic huntingtin protein aggregates. The investigators report that expression of other human genes was generally preserved, reflecting the strategy’s allele sensitivity and transcript-level specificity.
“Our aim was to design a therapy that removes only the toxic RNA species responsible for Huntington’s disease while leaving the rest of the genome and transcriptome intact,” said co-first author Kathryn Morelli, PhD, a research fellow in Yeo’s laboratory. “We screened and validated our top constructs in multiple patient cell lines to ensure specificity.”
Developing effective therapies for Huntington’s disease has been difficult. Several promising gene-based candidates failed in clinical testing, highlighting challenges around target specificity and safety. While current medications can ease some symptoms, none yet change the disease course.
“The HD community was understandably disheartened by earlier trial setbacks, which were largely driven by insufficient target specificity and toxic effects,” Yeo said. “Those outcomes have, however, motivated renewed efforts to explore alternative strategies.”
For preclinical validation, Yeo’s lab collaborated with Wenzhen Duan, MD, PhD, professor of psychiatry and behavioral sciences at Johns Hopkins Medicine. In mouse studies using a well-established HD model, intrastriatal delivery of the Cas13d construct improved motor coordination, reduced striatal degeneration and decreased mutant huntingtin aggregates. These benefits persisted for at least eight months and appeared without observable adverse effects or substantial off-target impacts on other RNA transcripts.
Co-authors on the study include Maya L. Gosztyla, Ryan J. Marina, Kari Lee, Krysten L. Jones, Megan Huang and Allison Li (UC San Diego); Hongshuai Liu, Minmin Yao and Chuangchuang Zhang (Johns Hopkins University); Jiaxu Chen (Beijing University of Chinese Medicine); and Charlene Smith-Geater and Leslie M. Thompson (UC Irvine).
About this CRISPR gene editing research news
Author: Scott LaFee
Source: UCSD
Contact: Scott LaFee – UCSD
Image: The image is credited to Huntington’s Disease News/UCSD
Original Research: Open access. “An RNA-targeting CRISPR–Cas13d system alleviates disease-related phenotypes in Huntington’s disease models” by Gene Yeo et al., Nature Neuroscience.
Abstract
An RNA-targeting CRISPR–Cas13d system alleviates disease-related phenotypes in Huntington’s disease models
Huntington’s disease is a fatal, dominantly inherited neurodegenerative disorder caused by expansion of CAG trinucleotide repeats in exon 1 of the huntingtin (HTT) gene. Reducing the mutant HTT messenger RNA is a validated therapeutic approach.
The researchers developed an allele-sensitive Cas13d system (Cas13d–CAGEX) that targets and eliminates the expanded CAG-repeat RNA. This system effectively removed toxic mutant HTT RNA in fibroblasts from HD patients and in induced pluripotent stem cell-derived neurons.
In vivo, intrastriatal delivery of Cas13d–CAGEX via an adeno-associated viral vector selectively lowered mutant HTT mRNA and protein in the striatum of heterozygous zQ175 mice, an established model of Huntington’s disease. Treated animals showed improved motor performance, less striatal atrophy and fewer mutant HTT protein aggregates. These phenotype improvements persisted for at least eight months with minimal adverse or off-target transcriptomic effects.
Together, these results provide proof of principle that an RNA-targeting CRISPR–Cas13d strategy can selectively reduce pathogenic HTT RNA and improve disease-related phenotypes, offering a potential therapeutic avenue for HD and other dominantly inherited disorders driven by toxic RNA or protein species.