Antisense oligonucleotide therapy for spinocerebellar ataxia type 2

Abstract

There are no disease-modifying treatments for adult human neurodegenerative diseases. Here we test RNA-targeted therapies in two mouse models of spinocerebellar ataxia type 2 (SCA2), an autosomal dominant polyglutamine disease. Both models recreate the progressive adult-onset dysfunction and degeneration of a neuronal network that are seen in patients, including decreased firing frequency of cerebellar Purkinje cells and a decline in motor function. We developed a potential therapy directed at the ATXN2 gene by screening 152 antisense oligonucleotides (ASOs). The most promising oligonucleotide, ASO7, downregulated ATXN2 mRNA and protein, which resulted in delayed onset of the SCA2 phenotype. After delivery by intracerebroventricular injection to ATXN2-Q127 mice, ASO7 localized to Purkinje cells, reduced cerebellar ATXN2 expression below 75% for more than 10 weeks without microglial activation, and reduced the levels of cerebellar ATXN2. Treatment of symptomatic mice with ASO7 improved motor function compared to saline-treated mice. ASO7 had a similar effect in the BAC-Q72 SCA2 mouse model, and in both mouse models it normalized protein levels of several SCA2-related proteins expressed in Purkinje cells, including Rgs8, Pcp2, Pcp4, Homer3, Cep76 and Fam107b. Notably, the firing frequency of Purkinje cells returned to normal even when treatment was initiated more than 12 weeks after the onset of the motor phenotype in BAC-Q72 mice. These findings support ASOs as a promising approach for treating some human neurodegenerative diseases.

Oligonucleotide therapy mitigates disease in spinocerebellar ataxia type 3 mice

“…Importantly, sustained ASO-5 exposure was not accompanied by evidence of induced gliosis or apoptosis in vulnerable brain regions, and no adverse events were observed even at the highest ASO doses. These results further support the growing evidence from preclinical animal and human clinical ASO trials demonstrating sustained, widespread, and well-tolerated ASO delivery to the CNS following longitudinal ICV or intrathecal delivery 20,22 . In support of the tolerability of ASOs for SCA3, recent elegant work from Toonen et al, assessed exon-skipping of the CAG repeat containing exon 10 in ATXN3 18 .…”

“…Although the molecular mechanism causing slowed firing in Q84/WT mice was not explored here, previous experiments have suggested that impairment of K v 3 family potassium channels in this mouse model 25 contribute to spiking abnormalities, and Purkinje neurons from K v 3.3 knockout mice show slower firing and a deeper AHP 45 . Moreover, the rescue of motor impairment through pharmacologic targeting of ion channels in SCA1 mice 46 and ASO treatment in SCA2 mice 22 is associated with normalizing of Purkinje neuron firing frequency, suggesting that ASO treatment in SCA3 mice improves Purkinje neuron physiology in a behaviorally relevant manner. That said, the neural circuitry underlying motor activity is far more complex than simply the regulation of Purkinje neuron firing.…”

Therapeutic reduction of ataxin-2 extends lifespan and reduces pathology in TDP-43 mice

“…Both ASOs were developed and synthesized by Ionis Pharmaceuticals. ASOs were synthesized as described 26 and were 20 bp in length, with five 2′- O -methoxyethyl (MOE) modified nucleotides at each end of the oligonucleotide, and ten DNA nucleotides in the center. The backbone of the ASOs consists of a mixture of phosphorothioate (PS) and phosphodiester (PO) linkages: 1-PS, 4-PO, 10-PS, 2-PO and 2-PS (5′ to 3′).…”

“…We screened a collection of ASOs for safety and efficacy (Extended Data Fig. 7 and 26 ), and used the most effective and well-tolerated ASO for further studies. Intracerebroventricular (ICV) injection of 4 μg of the Atxn2 ASO at P1 did not affect the home-cage behavior or grip strength of WT mice (Extended Data Fig.…”

Progression of spinocerebellar ataxia type 2. What do we need to know?

“…A reduction of ataxin-2 expression by the anti-sense oligonucleotide (ASO) therapy can be a promising future therapeutic approach for the disease. This ASO has been tested in SCA2 mouse models and improved motor performance and Purkinje cells firing rate of the animals 3 . In recent years, many therapeutic attempts have been developed to repair or replace the abnormal protein generated by the genetic mutation.…”