Long-term rescue of dystrophin expression and improvement in muscle pathology and function in dystrophic mdx mice by peptide-conjugated morpholino.

Exon skipping is capable of correcting frameshift and nonsense mutations in Duchenne muscular dystrophy. Phase 2 clinical trials in the United Kingdom and the Netherlands have reported induction of dystrophin expression in muscle of Duchenne muscular dystrophy patients by systemic administration of both phosphorodiamidate morpholino oligomers (PMO) and 2'-O-methyl phosphorothioate. Peptide-conjugated phosphorodiamidate morpholino offers significantly higher efficiency than phosphorodiamidate morpholino, with the ability to induce near-normal levels of dystrophin, and restores function in both skeletal and cardiac muscle. We examined 1-year systemic efficacy of peptide-conjugated phosphorodiamidate morpholino targeting exon 23 in dystrophic mdx mice. The LD(50) of peptide-conjugated phosphorodiamidate morpholino was determined to be approximately 85 mg/kg. The half-life of dystrophin expression was approximately 2 months in skeletal muscle, but shorter in cardiac muscle. Biweekly injection of 6 mg/kg peptide-conjugated phosphorodiamidate morpholino produced >20% dystrophin expression in all skeletal muscles and ≤5% in cardiac muscle, with improvement in muscle function and pathology and reduction in levels of serum creatine kinase. Monthly injections of 30 mg/kg peptide-conjugated phosphorodiamidate morpholino restored dystrophin to >50% normal levels in skeletal muscle, and 15% in cardiac muscle. This was associated with greatly reduced serum creatine kinase levels, near-normal histology, and functional improvement of skeletal muscle. Our results demonstrate for the first time that regular 1-year administration of peptide-conjugated phosphorodiamidate morpholino can be safely applied to achieve significant therapeutic effects in an animal model.

Whole-genome association studies of sporadic amyotrophic lateral sclerosis: are retroelements involved?

Whole-genome association studies (WGASs) have identified single-nucleotide polymorphisms (SNPs) associated with sporadic amyotrophic lateral sclerosis (sALS). However, WGASs have so far produced results that are not consistent with those obtained from monogenic association studies focused on genes found to be relevant to ALS in functional biological studies. We propose that such inconsistencies might be at least partially alleviated by using approaches that integrate weakly associated SNPs. Several independent studies have detected abnormal reverse transcriptase (RT) activity in sALS patients, suggesting the involvement of retroelements in ALS pathogenesis. Here, we discuss the functions of genes with SNPs or mutations in sALS and consider whether these might implicate the involvement of a putative retroelement associated with sALS pathogenesis. New experimental models for studying retroviral activation and the effects of xenobiotic agents in ALS will be needed to further investigate a potential role of retroelements in the etiology of sALS.