Effects of long-term resistance exercise training on autophagy in rat skeletal muscle of chloroquine-induced sporadic inclusion body myositis

Abstract

Purpose: We examined whether resistance exercise training restores impaired autophagy functions caused by Chloroquine (CQ)-induced Sporadic Inclusion Body Myositis (sIBM) in rat skeletal muscle.

Methods: Male wistar rats were randomly assigned into three groups: Sham (n = 6), CQ (n = 6), and CQ + Exercise (CE, n = 6). To create a rat model of sIBM, rats in the CQ and CE group were intraperitoneally injected with CQ 5 days a week for 16 weeks. Rats in the CE group performed resistance exercise training 3 times a week for 8 weeks in conjunction with CQ starting from week 9 to week 16. During the training period, maximal carrying load, body weight, muscle weight, and relative muscle weight were measured. Autophagy responses were examined by measuring specific markers.

Results: While maximal carrying capacity for resistance exercise training was dramatically increased in the CE group, no significant changes occurred in the skeletal muscle weight as well as in the relative muscle weight of CE compared to the other groups. CQ treatment caused significant increases in the levels of Beclin-1 and p62, and decreases in the levels of LAMP-2 proteins. Interestingly, no significant differences in the LC3-II/I ratio or the LC3-II protein levels were observed. Although CQ-treatment groups suppressed the levels of the potent autophagy inducer, BNIP3, p62 levels were decreased in only the CE group.

Conclusion: Our findings demonstrate that sIBM induced by CQ treatment results in muscle degeneration via impaired autophagy and that resistance exercise training improves movable loading activity. Finally, regular exercise training may provide protection against sIBM by enhancing the autophagy flux through p62 protein.

Keywords: Resistance exercise; autophagy; chloroquine; sIBM; skeletal muscles.

Fig. 1

Increased maximal carrying capacity per resistance training sessions during 8 weeks.

Fig. 2

Protein levels of Beclin-1, Atg7, BNIP3, p62, LC3-II and LC3-II/I ratio in soleus muscles were analyzed as an essential marker involved in processes for the autophagosome formation. A) Representative western blot images of Beclin-1, Atg7, BNIP3, p62, LC3-II, LC3 II/I ratio and α-tubulin among groups. B) Quantification of Beclin-1 protein. C) Quantification of Atg7 protein. D) Quantification of BNIP3 protein. E) Quantification of p62 protein. F) Quantification of LC3-II protein. G) Quantification of LC3-II/I protein ratio. Protein expression comparisons were performed after normalization to α-tubulin. Results are represented as means ± SE (n = 6 rats/group). * p < 0.05, ** p < 0.01, *** p < 0.001 vs. Sham; ^# p < 0.001 vs. CE.

Fig. 3

Protein levels of LAMP-2 and Cathepsin L in soleus muscles were analyzed as a receptor at the lysosomal membrane and a marker of proteolytic capacity of lysosome, respectively. A) Representative western blot images of LAMP-2 and Cathepsin L among groups. Protein expression comparisons were performed after normalization to α-tubulin. B) Quantification of LAMP-2 protein. C) Quantification of Cathepsin L protein. Results are represented as means ± SE (n = 6 rats/group). * p < 0.05, ** p < 0.01 vs. Sham