Date Published: April 23, 2019
Publisher: Public Library of Science
Author(s): Yeranuhi Hovhannisyan, Gagik Melikyan, Nathalie Mougenot, Jacqueline Gao-Li, Bertrand Friguet, Denise Paulin, Zhenlin Li, Arnaud Ferry, Onnik Agbulut, Aldrin V. Gomes.
Previous studies have shown that proteasome inhibition can have beneficial effects in dystrophic mouse models. In this study, we have investigated the effects of a new selective proteasome inhibitor, CLi, a strong caspase-like inhibitor of the 20S proteasome, on skeletal and cardiac muscle functions of mdx mice. In the first series of experiments, five-month-old male mdx mice (n = 34) were treated with 2 different doses (20 and 100 μg/kg) of CLi and in the second series of experiments, five-month-old female mdx (n = 19) and wild-type (n = 24) mice were treated with 20 μg/kg CLi and Velcade (1 mg/kg) for 1-month. All animals were treadmill exercised twice a week to worsen the dystrophic features. In the first series of experiments, our results demonstrated that 20 μg/kg CLi did not significantly increase absolute and specific maximal forces in skeletal muscle from male mdx mice. Moreover, the higher susceptibility to contraction induced skeletal muscle injury was worsened by 100 μg/kg CLi since the force drop following lengthening contractions was increased with this high dose. Furthermore, we found no differences in the mRNA levels of the molecular markers implicated in dystrophic features. Concerning cardiac function, CLi had no effect on left ventricular function since ejection and shortening fractions were unchanged in male mdx mice. Similarly, CLi did not modify the expression of genes implicated in cardiac remodeling. In the second series of experiments, our results demonstrated an improvement in absolute and specific maximal forces by CLi, whereas Velcade only increased specific maximal force in female mdx mice. In addition, exercise tolerance was not improved by CLi. Taken together, our results show that CLi treatment can only improve maximal force production in exercised female mdx mice without affecting either exercice tolerance capacity or cardiac function. In conclusion, selective inhibition of caspase-like activity of proteasome with CLi has no compelling beneficial effect in dystrophic mdx mice.
Duchenne muscular dystrophy is a fatal genetic disorder affecting both skeletal and cardiac muscles. It is caused by dystrophin deficiency. Dystrophin is a subsarcolemmal protein, thought to play a role in force transmission, sarcolemma stability, localization and function of different proteins that trigger damage process in its absence. The mdx mouse is a widely used mouse model for Duchenne muscular dystrophy, it exhibits muscle weakness, i.e. reduced specific maximal force (absolute maximal force generated relative to muscle cross-sectional area or weight) [1–5] as well as muscle degeneration and regeneration. The muscle of Mdx mice is also more susceptible to damage caused by lengthening (eccentric) contractions. Thus, less than 10 lengthening contractions cause an immediate marked force drop in mdx mice but not in wild-type mice [6–9]. In addition to these skeletal muscle dystrophic features, the heart of mdx mice also exhibits signs of cardiomyopathy that are more pronounced in old as compared to young mdx mice [10,11].
Mdx mice exhibit increased proteasome activity and proteasome inhibition has been previously shown to rescue the expression of the dystrophin glycoprotein complex, to improve histological dystrophic features in skeletal muscle and to restore cardiac sodium current in dystrophin deficient mice [12–14,16,21–22]. Moreover, exercise increases proteasome activity in both skeletal and cardiac muscles, at least in healthy mice [23,24]. Therefore, in the present study we sought to determine whether inhibition of the 20S proteasome caspase-like activity by CLi would be beneficial for skeletal and cardiac muscle functions in exercised dystrophic mdx mice. CLi (1,1-dimethyl furo[4-benzylamino]pyridine-3-one), a derivative of nor-cerpegin, is a strong caspase-like inhibitor of the 20S constitutive proteasome . Our results demonstrate that both 20 μg/kg and 100 μg/kg CLi treatments inhibit selectively the caspase-like activity of the 20S proteasome in skeletal muscle. One-month after treatment, our results showed that inhibition of the 20S proteasome caspase-like activity with the selective nor-cerpegin family proteasome inhibitor slightly improved maximal force production in exercised mdx mice without affecting either exercice tolerance capacity or cardiac function. In conclusion, selective inhibition of caspase-like activity of the proteasome with CLi has no compelling beneficial effect in dystrophic mdx mice.