Fibrosis is a pathological feature observed in patients with Duchenne muscular dystrophy (DMD) and in mdx mice, the experimental model of DMD. We evaluated the effect of suramin, a transforming growth factor-beta 1 (TGF-β1) blocker, on fibrosis in mdx mice. mdx mice (6 months old) received suramin for 7 weeks. Suramin- and saline-treated (control) mdx mice performed exercise on a treadmill to worsen disease progression. Immunoblotting showed an increase of TGF-β1 in mdx diaphragm, limb, and cardiac muscles. Suramin decreased creatine kinase in mdx mice and attenuated fibrosis in all muscles studied, except for cardiac muscle. Suramin protected limb muscles against damage and reduced the exercise-induced loss of strength over time. These findings support a role for TGF-β1 in fibrinogenesis and myonecrosis during the later stages of disease in mdx mice. Suramin might be a useful therapeutic alternative for the treatment of dystrophinopathies.

Matsumura CY, Taniguti AP, Pertille A, Santa Neto H, Marques MJ. Stretch-activated calcium channel protein TRPC1 is correlated with the different degrees of the dystrophic phenotype in mdx mice. Am J Physiol Cell Physiol 301: C1344 -C1350, 2011. First published September 7, 2011; doi:10.1152/ajpcell.00056.2011In Duchenne muscular dystrophy (DMD) and in the mdx mouse model of DMD, the lack of dystrophin is related to enhanced calcium influx and muscle degeneration. Stretch-activated channels (SACs) might be directly involved in the pathology of DMD, and transient receptor potential cation channels have been proposed as likely candidates of SACs. We investigated the levels of transient receptor potential canonical channel 1 (TRPC1) and the effects of streptomycin, a SAC blocker, in muscles showing different degrees of the dystrophic phenotype. Mdx mice (18 days old, n ϭ 16) received daily intraperitoneal injections of streptomycin (182 mg/kg body wt) for 18 days, followed by removal of the diaphragm, sternomastoid (STN), biceps brachii, and tibialis anterior muscles. Control mdx mice (n ϭ 37) were injected with saline. Western blot analysis showed higher levels of TRPC1 in diaphragm muscle compared with STN and limb muscles. Streptomycin reduced creatine kinase and prevented exercise-induced increases of total calcium and Evans blue dye uptake in diaphragm and in STN muscles. It is suggested that different levels of the stretch-activated calcium channel protein TRPC1 may contribute to the different degrees of the dystrophic phenotype seen in mdx mice. Early treatment designed to regulate the activity of these channels may ameliorate the progression of dystrophy in the most affected muscle, the diaphragm. dystrophinopaties; streptomycin; Duchenne muscular dystrophy; transient receptor potential canonical channel 1 IN DUCHENNE MUSCULAR DYSTROPHY (DMD) and in the mdx mouse model of DMD, the lack of dystrophin is associated with progressive myonecrosis of skeletal muscles that leads to respiratory failure, the main cause of death in this disease (5,8). Dystrophin is part of the dystrophin-glycoprotein complex, a multisubunit complex that plays a role in maintaining the integrity of the sarcolemma during the stress imposed by muscle contraction (9). Although the mechanisms responsible for myonecrosis are still not completely understood, the chronic increase of cytosolic Ca 2ϩ concentration seen in mdx mice and in DMD (22,29,34) is generally accepted to be closely related to the process of muscle damage, possibly by activating proteases implicated in muscle necrosis (41).Stretch-activated channels (SACs) respond to mechanical stress with increased open probability (19), are permeable to both Na ϩ and Ca 2ϩ (12, 13), and have been suggested to be primarily involved in the pathogenesis of DMD (14, 42, 44). The transient receptor potential (TRP) channels are a family of proteins that regulate calcium entry into cells, and recent findings have suggested that the canonical TRPC1 and TRPC6 channels are key players in muscle m...

In dystrophin-deficient fibers of mdx mice and in Duchenne muscular dystrophy, inflammation and increased production of tumor necrosis factor alpha (TNF-α) contribute to myonecrosis. We examined the effects of eicosapentaenoic acid (EPA) on dystrophic muscle degeneration. Mdx mice (14 days old) received EPA for 16 days. The sternomastoid, diaphragm and biceps brachii muscles were removed. Control mdx mice received vehicle. EPA decreased creatine kinase and myonecrosis and reduced the levels of TNF-α. These results suggest that EPA plays a protective role in dystrophic muscle degeneration, possibly by reducing TNF-α, and support further investigations of EPA as a potential therapy for dystrophinopathies.

Changes in the distribution of acetylcholine receptors have been reported to occur at the neuromuscular junction of mdx mice and may be a consequence of muscle fiber regeneration rather than the absence of dystrophin. In the present study, we examined whether the nerve terminal determines the fate of acetylcholine receptor distribution in the dystrophic muscle fibers of mdx mice. The left sternomastoid muscle of young (1-monthold) and adult (6-month-old) mdx mice was injected with 60 ml lidocaine hydrochloride to induce muscle degeneration-regeneration. Some mice had their sternomastoid muscle denervated at the time of lidocaine injection. After 10 days of muscle denervation, nerve terminals and acetylcholine receptors were labeled with 4-Di-2-ASP and rhodamine-a-bungarotoxin, respectively, for confocal microscopy. In young mdx mice, 75% (n ¼ 137 endplates) of the receptors were distributed in islands. The same was observed in 100% (n ¼ 114 endplates) of the adult junctions. In denervated-regenerated fibers of young mice, the receptors were distributed as branches in 89% of the endplates (n ¼ 90). In denervated-regenerated fibers of adult mice, the receptors were distributed in islands in 100% of the endplates (n ¼ 100). These findings show that nerve-dependent mechanisms are also involved in the changes in receptor distribution in young dystrophic muscles. In older dystrophic muscles, other factors may play a role in receptor distribution. Anat Rec 290: 181-187, 2007. 2007 Wiley-Liss, Inc.Key words: acetylcholine receptors; mdx mice; muscle fiber regeneration; neuromuscular junction remodelingMdx mutant mice are characterized by a marked deficiency in dystrophin (Hoffman et al., 1987;Sicinski et al., 1989). These mice also show acute muscle fiber necrosis followed by regeneration (Tanabe et al., 1986) and therefore provide a model for studying the mechanisms underlying muscle fiber degeneration and regeneration and the effects of a lack of dystrophin on muscle fiber components.Significant structural abnormalities are observed at the neuromuscular junctions of mdx mice, mainly at the postsynaptic site, with a reduction in the number and depth of postsynaptic folds (Torres and Duchen, 1987). Acetylcholine receptors (AChRs) as well as acetylcholinesterase are present in numerous small spots. These changes were found exclusively at the neuromuscular junctions of regenerated muscle fibers (Lyons and Slater, 1991), suggesting that muscle regeneration rather than dystrophin deficiency is responsible for remodeling of the postsynaptic components (Minatel et al., 2001). Controversies exist

This study provides evidence that doxycycline may be a potential therapeutic agent for DMD.