Expression of a miRNA targeting mutated SOD1 in astrocytes induces motoneuron plasticity and improves neuromuscular function in ALS mice

In familial forms of amyotrophic lateral sclerosis (ALS) caused by mutations in superoxide dismutase-1 (SOD1) gene, both cell-autonomous and non-cell-autonomous mechanisms lead to the selective degeneration of motoneurons. Gene-targeted deletion of mutated SOD1 in mature astrocytes has been shown to slow down disease progression. However, the potential therapeutic application of targeting astrocytes has not been evaluated yet. Here, an AAV vector encoding an artificial microRNA is used to deliver RNA interference against mutated SOD1 by targeting astrocytes in ALS mice. In mice expressing the mutated SOD1G93A protein, we found that the treatment leads to the progressive rescue of neuromuscular junction occupancy, to the recovery of the compound muscle action potential in the gastrocnemius muscle, and significantly improves neuromuscular function. In the spinal cord, gene therapy targeting astrocytes protects a small pool of fast-fatigable motoneurons until disease end stage. In the gastrocnemius muscle of the treated SOD1G93A mice, the fast-twitch type IIb muscle fibers are preserved from atrophy. Axon collateral sprouting is observed together with muscle fiber type grouping indicative of denervation/re-innervation events. The transcriptome profiling of spinal cord motoneurons shows changes in the expression levels of factors regulating the dynamics of microtubules. Gene therapy delivering RNA interference against mutated SOD1 in astrocytes provides therapeutic effects enhancing motoneuron plasticity and improving neuromuscular function in ALS mice. Overall design: SOD1-G93A mutant mice were ICV injected at P2 either with the AAV-miR SOD1 vector which drives expression of an artificial anti-human SOD1 miR in astrocytes or with AAV-miR ctrl. An additional group of non-injected SOD1-G93A littermate mice was included in the experiment. At day 65, a transcriptomic analysis was performed on motoneurons captured by laser microdissection in the ventral horn.