Comparison between gentamycin and exon skipping treatments to restore ryanodine receptor subtype 2 functions in mdx...

In Duchenne muscular dystrophy, a stop-codon mutation in the dystrophin gene induces an impairment of skeletal and smooth muscles contraction. In duodenum from mdx mouse, the disease model, the decrease of contractility was linked with the decrease of calcium signals encoded by ryanodine receptor subtype 2. Aminoglycoside and antisense oligonucleotide strategies were investigated to restore calcium signalling in the mdx mouse. Mdx mice were treated by intraperitoneal injection of gentamycin or 2-O-methyl antisense ribonucleotide directed against exon 23 of dystrophin for 2 weeks. The efficiency of both therapeutic strategies was determined by the level of dystrophin protein expression. The physiological effects of both treatments on ryanodine receptor expression and function were followed by RT-PCR, western blot and calcium measurements. Fourteen days after injection of gentamycin or anti-dystrophin antisense, the expression of dystrophin was recovered in skeletal muscle from treated mdx mice. In duodenum cells, RT-PCR and western blot indicated that the expression of ryanodine receptor subtype 2 was similar in treated mice than in control mice in association with the recovery of caffeine-induced Ca(2+) response. No significant difference was observed in the ryanodine subtype 3-dependent spontaneous Ca(2+) oscillations in untreated and treated mice. Conclusions - these results may help to explain the efficiency of aminoglycoside and anti-dystrophin antisense treatments in smooth muscle. Both treatments could be an interesting therapeutic option to restore smooth muscle contraction in patients with Duchenne muscular dystrophy.