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

Abstract

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.