Evaluation of Antisense Oligonucleotides Targeting ATXN3 in SCA3 Mouse Models

Abstract

The most common dominantly inherited ataxia, spinocerebellar ataxia type 3 (SCA3), is an incurable neurodegenerative disorder caused by a CAG repeat expansion in the ATXN3 gene that encodes an abnormally long polyglutamine tract in the disease protein, ATXN3. Mice lacking ATXN3 are phenotypically normal; hence, disease gene suppression offers a compelling approach to slow the neurodegenerative cascade in SCA3. Here we tested antisense oligonucleotides (ASOs) that target human ATXN3 in two complementary mouse models of SCA3: yeast artificial chromosome (YAC) MJD-Q84.2 (Q84) mice expressing the full-length human ATXN3 gene and cytomegalovirus (CMV) MJD-Q135 (Q135) mice expressing a human ATXN3 cDNA. Intracerebroventricular injection of ASOs resulted in widespread delivery to the most vulnerable brain regions in SCA3. In treated Q84 mice, three of five tested ASOs reduced disease protein levels by >50% in the diencephalon, cerebellum, and cervical spinal cord. Two ASOs also significantly reduced mutant ATXN3 in the mouse forebrain and resulted in no signs of astrogliosis or microgliosis. In Q135 mice expressing a single ATXN3 isoform via a cDNA transgene, ASOs did not result in similar robust ATXN3 silencing. Our results indicate that ASOs targeting full-length human ATXN3 would likely be well tolerated and could lead to a preventative therapy for SCA3.

Polyglutamine ataxias: From Clinical and Molecular Features to Current Therapeutic Strategies

“…AOs were designed to reduce mutant and wildtype ataxin-3 levels by inducing RNase-H degradation of target mRNA at the AO:RNA duplex. Three of the 5 AOs tests showed a >50% reduction in the disease protein levels in the cerebellum, diencephalon and cervical spinal cord [212]. Although both mutant and wild-type mRNAs are suppressed in this study, it has been found that ataxin-3 knockout mice appear to be normal, which suggests that ataxin-3 may not be essential for viability [213].…”

Oligonucleotide therapy mitigates disease in spinocerebellar ataxia type 3 mice

“…iQ SYBR green quantitative PCR was performed on the diluted cDNA following the manufacturer’s protocol (Bio-Rad, Hercules, CA). Average adjusted relative quantification analysis was performed using previously described primers 6,19 .…”

“…19 In this earlier study, we evaluated a collection of chemically modified ASOs targeting ATXN3 in cellular and mouse models of SCA3. 19 We achieved widespread ASO delivery and efficient silencing of human mutATXN3 throughout affected brain regions, without signs of an adverse immune response to treatment. ASOs were delivered directly into the CNS by intracerebroventricular (ICV) injection, allowing the natural flow of cerebrospinal fluid (CSF) to distribute ASOs throughout the CNS, as supported by histological assessment in ASO-treated rodent and nonhuman primate studies.…”

Deep cerebellar stimulation reduces ataxic motor symptoms in the shaker rat

“…34,35 Although ASOs will likely prove more beneficial than DCS for patients with specific ataxias for which ASOs exist, patients with sporadic ataxias, spinocerebellar ataxias without an ASO, or hereditary ataxias for which the gene is unknown cannot benefit from ASOs. DCS, if translated, may prove a more widely useful therapeutic strategy than pharmaceutical approaches.…”