Rescue of amyotrophic lateral sclerosis phenotype in a mouse model by intravenous AAV9‐ADAR2 delivery to motor neurons

Takenari Yamashita,Kuniko Shimazaki,Shin Kwak,Sayaka Teramoto,Hui Lin Chai,Shoji Tsuji,Shin‐Ichi Muramatsu

doi:10.1002/emmm.201302935

Abstract

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motor neuron disease, and the lack of effective therapy results in inevitable death within a few years of onset. Failure of GluA2 RNA editing resulting from downregulation of the RNA-editing enzyme adenosine deaminase acting on RNA 2 (ADAR2) occurs in the majority of ALS cases and causes the death of motor neurons via a Ca2+-permeable AMPA receptor-mediated mechanism. Here, we explored the possibility of gene therapy for ALS by upregulating ADAR2 in mouse motor neurons using an adeno-associated virus serotype 9 (AAV9) vector that provides gene delivery to a wide array of central neurons after peripheral administration. A single intravenous injection of AAV9-ADAR2 in conditional ADAR2 knockout mice (AR2), which comprise a mechanistic mouse model of sporadic ALS, caused expression of exogenous ADAR2 in the central neurons and effectively prevented progressive motor dysfunction. Notably, AAV9-ADAR2 rescued the motor neurons of AR2 mice from death by normalizing TDP-43 expression. This AAV9-mediated ADAR2 gene delivery may therefore enable the development of a gene therapy for ALS.

Highlights

Amyotrophic lateral sclerosis (ALS) is the most common adult‐ onset motor neuron disease
We explored the possibility of using gene therapy to treat ALS by enhancing adenosine deaminase acting on RNA 2 (ADAR2) activity through delivery of the ADAR2 gene to mouse motor neurons using associated virus serotype 9 (AAV9) as a vector, together with the synapsin I (SYNI) promoter to achieve neuron‐specific expression of the ADAR2 gene
We showed that AAV9‐ADAR2 was successfully delivered to and functioned in motor neurons (Figs 1D and 4 and Supporting Information Fig S3), with a virtual absence of peripheral expression being detected following i.v. administration in the mice

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is the most common adult‐ onset motor neuron disease. The lack of an effective therapy for ALS results in death from respiratory muscle weakness within a few years of onset. Clinical challenges for gene therapy have been observed when using adeno‐ associated virus (AAV) as a vector (Lonergan et al, 2005; Mingozzi & High, 2011). Because motor neurons are widely localized in the cranial motor nerve nuclei in the brainstem and the anterior horns of the entire spinal cord, systemic injection of a vector is preferable to local injection to provide global gene delivery to the motor neurons of ALS patients. To achieve widespread and selective expression of the ADAR2 gene in motor neurons and avoid off‐target delivery, we used AAV9 as a vector and the synapsin I (SYNI) promoter for neuron‐specific expression of ADAR2 cDNA (Supporting Information Fig S1; Iwata et al, 2013)

Methods

Results

Conclusion