Several studies documented the key role of oxidative stress and abnormal production of reactive oxygen species (ROS) in the pathophysiology of muscular dystrophies (MDs). The sources of ROS, however, are still controversial as well as their major molecular targets. This study investigated whether ROS produced in mitochondria by monoamine oxidase (MAO) contributes to MD pathogenesis. Pargyline, an MAO inhibitor, reduced ROS accumulation along with a beneficial effect on the dystrophic phenotype of Col6a1(-/-) mice, a model of Bethlem myopathy and Ullrich congenital MD, and mdx mice, a model of Duchenne MD. Based on our previous observations on oxidative damage of myofibrillar proteins in heart failure, we hypothesized that MAO-dependent ROS might impair contractile function in dystrophic muscles. Indeed, oxidation of myofibrillar proteins, as probed by formation of disulphide cross-bridges in tropomyosin, was detected in both Col6a1(-/-) and mdx muscles. Notably, pargyline significantly reduced myofiber apoptosis and ameliorated muscle strength in Col6a1(-/-) mice. This study demonstrates a novel and determinant role of MAO in MDs, adding evidence of the pivotal role of mitochondria and suggesting a therapeutic potential for MAO inhibition.
Autophagy is crucial in the turnover of cell components, and clearance of damaged organelles by the autophagic-lysosomal pathway is essential for tissue homeostasis. Defects of this degradative system have a role in various diseases, but little is known about autophagy in muscular dystrophies. We have previously found that muscular dystrophies linked to collagen VI deficiency show dysfunctional mitochondria and spontaneous apoptosis, leading to myofiber degeneration. Here we demonstrate that this persistence of abnormal organelles and apoptosis are caused by defective autophagy. Skeletal muscles of collagen VI-knockout (Col6a1(-/-)) mice had impaired autophagic flux, which matched the lower induction of beclin-1 and BCL-2/adenovirus E1B-interacting protein-3 (Bnip3) and the lack of autophagosomes after starvation. Forced activation of autophagy by genetic, dietary and pharmacological approaches restored myofiber survival and ameliorated the dystrophic phenotype of Col6a1(-/-) mice. Furthermore, muscle biopsies from subjects with Bethlem myopathy or Ullrich congenital muscular dystrophy had reduced protein amounts of beclin-1 and Bnip3. These findings indicate that defective activation of the autophagic machinery is pathogenic in some congenital muscular dystrophies.
Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy are inherited muscle disorders caused by mutations of genes encoding the extracellular matrix protein collagen VI (ColVI). Mice lacking ColVI (Col6a1(-/-)) display a myopathic phenotype associated with ultrastructural alterations of mitochondria and sarcoplasmic reticulum, mitochondrial dysfunction with abnormal opening of the permeability transition pore (PTP) and increased apoptosis of muscle fibers. Treatment with cyclosporin (Cs) A, a drug that desensitizes the PTP by binding to cyclophilin (Cyp)-D, was shown to rescue myofiber alterations in Col6a1(-/-) mice and in UCMD patients, suggesting a correlation between PTP opening and pathogenesis of ColVI muscular dystrophies. Here, we show that inactivation of the gene encoding for Cyp-D rescues the disease phenotype of ColVI deficiency. In the absence of Cyp-D, Col6a1(-/-) mice show negligible myofiber degeneration, rescue from mitochondrial dysfunction and ultrastructural defects, and normalized incidence of apoptosis. These findings (i) demonstrate that lack of Cyp-D is equivalent to its inhibition with CsA at curing the mouse dystrophic phenotype; (ii) establish a cause-effect relationship between Cyp-D-dependent PTP regulation and pathogenesis of the ColVI muscular dystrophy and (iii) validate Cyp-D and the PTP as pharmacological targets for the therapy of human ColVI myopathies.
Related JoVE Video
Journal of Visualized Experiments
What is Visualize?
JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.
How does it work?
We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.
Video X seems to be unrelated to Abstract Y...
In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.