The journal of pharmacology and experimental therapeutics

Background Huntington’s disease is an autosomal-dominant neurodegenerative disease caused by CAG trinucleotide repeat expansion in HTT, resulting in a mutant huntingtin protein. IONIS-HTTR...

https://www.nejm.org/doi/pdf/10.1056/NEJMoa1900907

Targeting Huntingtin Expression in Patients with Huntington’s Disease

Huntington's disease is a neurodegenerative disorder caused by a polyglutamine repeat in the Huntingtin gene (HTT). Although suppressing the expression of mutant HTT (mHTT) has been explored as a therapeutic strategy to treat Huntington's disease, considerable efforts have gone into developing allele-specific suppression of mHTT expression, given that loss of Htt in mice can lead to embryonic lethality. It remains unknown whether depletion of HTT in the adult brain, regardless of its allele, could be a safe therapy. Here, we report that permanent suppression of endogenous mHTT expression in the striatum of mHTT-expressing mice (HD140Q-knockin mice) using CRISPR/Cas9-mediated inactivation effectively depleted HTT aggregates and attenuated early neuropathology. The reduction of mHTT expression in striatal neuronal cells in adult HD140Q-knockin mice did not affect viability, but alleviated motor deficits. Our studies suggest that non-allele-specific CRISPR/Cas9-mediated gene editing could be used to efficiently and permanently eliminate polyglutamine expansion-mediated neuronal toxicity in the adult brain.

/pdf/crispr-cas9-mediated-gene-editing-ameliorates-neurotoxicity-bg6mqtkvwo.pdf

CRISPR/Cas9-mediated gene editing ameliorates neurotoxicity in mouse model of Huntington’s disease

Adeno-associated viral (AAV) vectors are a rapidly emerging gene therapy platform for the treatment of neurological diseases. In preclinical studies, transgenes encoding therapeutic proteins, microRNAs, antibodies or gene-editing machinery have been successfully delivered to the central nervous system with natural or engineered viral capsids via various routes of administration. Importantly, initial clinical studies have demonstrated encouraging safety and efficacy in diseases such as Parkinson disease and spinal muscular atrophy, as well as durability of transgene expression. Here, we discuss key considerations and challenges in the future design and development of therapeutic AAV vectors, highlighting the most promising targets and recent clinical advances.

Gene therapy for neurological disorders: progress and prospects

The dominantly inherited spinocerebellar ataxias (SCAs) are a large and diverse group of neurodegenerative diseases. The most prevalent SCAs (SCA1, SCA2, SCA3, SCA6 and SCA7) are caused by expansion of a glutamine-encoding CAG repeat in the affected gene. These SCAs represent a substantial portion of the polyglutamine neurodegenerative disorders and provide insight into this class of diseases as a whole. Recent years have seen considerable progress in deciphering the clinical, pathological, physiological and molecular aspects of the polyglutamine SCAs, with these advances establishing a solid base from which to pursue potential therapeutic approaches.

/pdf/polyglutamine-spinocerebellar-ataxias-from-genes-to-9ssomkz9cg.pdf

Polyglutamine spinocerebellar ataxias — from genes to potential treatments

CRISPR/Cas9 Editing of the Mutant Huntingtin Allele In Vitro and In Vivo

RNA-targeting approaches are emerging as viable therapeutics that offer an alternative method to modulate traditionally 'undrugable' targets. In the case of dominantly inherited neurodegenerative diseases, gene suppression strategies can target the underlying cause of these intractable disorders. Polyglutamine diseases are caused by CAG expansions in discrete genes, making them ideal candidates for gene suppression therapies. Here, we discuss the current state of gene suppression approaches for Huntington's disease and the spinocerebellar ataxias, including the use of antisense oligonucleotides, short-interfering RNAs, as well as viral vector-mediated delivery of short hairpin RNAs and artificial microRNAs. We focus on lessons learned from preclinical studies investigating gene suppression therapies for these disorders, particularly in rodent models of disease and in non-human primates. In animal models, recent advances in gene suppression technologies have not only prevented disease progression in a number of cases, but have also reversed existing disease, providing evidence that reducing the expression of disease-causing genes may be of benefit in symptomatic patients. Both allele- and non-allele-specific approaches to gene suppression have made great strides over the past decade, showing efficacy and safety in both small and large animal models. Advances in delivery techniques allow for broad and durable suppression of target genes, have been validated in non-human primates and in some cases, are currently being evaluated in human patients. Finally, we discuss the challenges of developing and delivering gene suppression constructs into the CNS and recent advances of potential therapeutics into the clinic.

/pdf/gene-suppression-strategies-for-dominantly-inherited-bnpd2c2iqw.pdf

Gene suppression strategies for dominantly inherited neurodegenerative diseases: lessons from Huntington's disease and spinocerebellar ataxia

Viral vectors are a promising tool for effective delivery of genetic material into cells. They take advantage of the natural ability of a virus to deliver a genetic payload into cells while being genetically modified such that their ability to replicate is crippled or removed. Here, an updated overview of routinely used viral vectors, including adeno-associated viruses (AAV), retroviruses/lentiviruses, and adenoviruses (Ads), is provided, as well as perspectives on their advantages and disadvantages in research and gene therapy. © 2018 by John Wiley & Sons, Inc.

Viral Vectors for Gene Transfer.

Objective: Spinocerebellar ataxia type 1 is an autosomal dominant fatal neurodegenerative disease caused by a polyglutamine expansion in the coding region of ATXN1. We showed previously that partial suppression of mutant ataxin-1 (ATXN1) expression, using virally-expressed RNAi triggers, could prevent disease symptoms in a transgenic mouse model and a knock in mouse model of the disease, using a single dose of virus. Here, we set out to test if RNAi triggers targeting ATXN1 could not only prevent, but also reverse disease readouts when delivered after symptom onset.

Methods: We administered recombinant adeno-associated virus (rAAV) expressing miS1, an artificial miRNA targeting human ATXN1 mRNA (rAAV.miS1) to a mouse model of SCA1 (B05 mice). Viruses were delivered prior to or after symptom onset at multiple doses. Control B05 mice were treated with rAAVs expressing a control artificial miRNA, or with saline. Animal behavior, molecular phenotypes, neuropathology and magnetic resonance spectroscopy were done on all groups and data were compared to wildtype littermates.

Results: We found that SCA1 phenotypes could be reversed by partial suppression of human mutant ATXN1 mRNA by rAAV.miS1 when delivered after symptom onset. We also identified the therapeutic range of rAAV.miS1 that could prevent or reverse disease readouts.

Interpretation: SCA1 disease may be reversible by RNAi therapy, and the doses required for advancing this therapy to humans are delineated. This article is protected by copyright. All rights reserved.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/ana.24789

RNAi prevents and reverses phenotypes induced by mutant human ataxin-1.

Polyglutamine (polyQ) repeat diseases are a class of neurodegenerative disorders caused by CAG-repeat expansion There are diverse cellular mechanisms behind the pathogenesis of polyQ disorders, including transcriptional dysregulation Interestingly, we find that levels of the long isoform of nuclear paraspeckle assembly transcript 1 (Neat1L) are elevated in the brains of mouse models of spinocerebellar ataxia types 1, 2, 7 and Huntington's disease (HD) Neat1L was also elevated in differentiated striatal neurons derived from HD knock-in mice and in HD patient brains The elevation was mutant Huntingtin (mHTT) dependent, as knockdown of mHTT in vitro and in vivo restored Neat1L to normal levels In additional studies, we found that Neat1L is repressed by methyl CpG binding protein 2 (MeCP2) by RNA-protein interaction but not by occupancy of MeCP2 at its promoter We also found that NEAT1L overexpression protects from mHTT-induced cytotoxicity, while reducing it enhanced mHTT-dependent toxicity Gene set enrichment analysis of previously published RNA sequencing data from mouse embryonic fibroblasts and cells derived from HD patients shows that loss of NEAT1L impairs multiple cellular functions, including pathways involved in cell proliferation and development Intriguingly, the genes dysregulated in HD human brain samples overlap with pathways affected by a reduction in NEAT1, confirming the correlation of NEAT1L and HD-induced perturbations Cumulatively, the role of NEAT1L in polyQ disease model systems and human tissues suggests that it may play a protective role in CAG-repeat expansion diseases

Megan S. Keiser

Papers

CRISPR/Cas9 Editing of the Mutant Huntingtin Allele In Vitro and In Vivo

Gene suppression strategies for dominantly inherited neurodegenerative diseases: lessons from Huntington's disease and spinocerebellar ataxia

Viral Vectors for Gene Transfer.

RNAi prevents and reverses phenotypes induced by mutant human ataxin-1.

The long non-coding RNA NEAT1 is elevated in polyglutamine repeat expansion diseases and protects from disease gene-dependent toxicities.