Skeletal muscle expression of clathrin and mannose 6-phosphate receptor in experimental chloroquine-induced myopathy

[Direct mechanism of action in toxic myopathies]

Toxic myopathies are a large group of disorders generated by surrounding agents and characterized by structural and/or functional disturbances of muscles. The most recurrent are those induced by commonly used medications. Illicit drugs, environmental toxins from animals, vegetables, or produced by micro-organisms as well as chemical products commonly used are significant causes of such disorders. The muscle toxicity results from multiple mechanisms at different biological levels. Many agents can induce myotoxicity through a direct mechanism in which statins, glucocorticoids and ethyl alcohol are the most representative. Diverse mechanisms were highlighted as interaction with macromolecules and induction of metabolic and cellular dysfunctions. Muscle damage can be related to amphiphilic properties of some drugs (chloroquine, hydroxychloroquine, etc.) leading to specific lysosomal disruptions and autophagic dysfunctions. Some agents affect the whole muscle fiber by inducing oxidative stress (ethyl alcohol and some statins) or triggering cell death pathways (apoptosis or necrosis) resulting in extensive alterations. More studies on these mechanisms are needed. They would allow a better knowledge of the intracellular mediators involved in these pathologies in order to develop targeted therapies of high efficiency.

Expression of autophagy-associated genes in skeletal muscle: an experimental model of chloroquine-induced myopathy

OBJECTIVE

Chloroquine modulates autophagocytic protein degradation in the lysosome system, thereby inducing the formation of rimmed vacuoles consisting of autophagosomes and autolysosomes in skeletal muscle. The goal of this study was to investigate the contribution of the lysosomal system, particularly autophagosome formation (an autophagic process) at the molecular level, to the abnormal accumulation of vacuoles in an experimental model of chloroquine-induced myopathy.

METHODS

Histological, immunohistochemical and semiquantitative reverse transcriptase-polymerase chain reaction studies were performed on innervated and denervated rat soleus muscles after treatment with either saline or chloroquine.

RESULTS

Accumulation of rimmed vacuoles was observed only in chloroquine-treated denervated muscles. Microtubule-associated protein-1 light chain-3 (LC3) protein and mRNA levels were significantly increased exclusively in denervated muscles from chloroquine-treated rats, whereas Apg5 and Apg12 mRNA levels did not change significantly. Further, the mRNA levels of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE), which are associated with distal myopathy with rimmed vacuoles showing numerous rimmed vacuoles in its skeletal muscle, were not decreased in denervatedmuscles treated with chloroquine.

CONCLUSIONS

LC3 mRNA may increase in association with rimmed vacuole formation in denervated muscles from chloroquine-treated rats, suggesting an increase in autophagy at the molecular level. Abnormal accumulation of rimmed vacuoles in this myopathy does not appear to be mediated by inhibition of autophagosome-related genes or GNE gene.