Abstract
Skeletal muscle weakness is a prominent feature in patients with rheumatoid arthritis (RA). In this study, we investigated whether neuromuscular electrical stimulation (NMES) training protects against skeletal muscle dysfunction in rats with adjuvant-induced arthritis (AIA). AIA was produced by intraarticular injection of complete Freund’s adjuvant into the knees of Wistar rats. For NMES training, dorsiflexor muscles were stimulated via a surface electrode (0.5 ms pulse, 50 Hz, 2 s on/4 s off). NMES training was performed every other day for three weeks and consisted of three sets produced at three min intervals. In each set, the electrical current was set to achieve 60% of the initial maximum isometric torque and the current was progressively increased to maintain this torque; stimulation was stopped when the 60% torque could no longer be maintained. After the intervention period, extensor digitorum longus (EDL) muscles were excised and used for physiological and biochemical analyses. There was a reduction in specific force production (i.e. force per cross-sectional area) in AIA EDL muscles, which was accompanied by aggregation of the myofibrillar proteins actin and desmin. Moreover, the protein expressions of the pro-oxidative enzymes NADPH oxidase, neuronal nitric oxide synthase, p62, and the ratio of the autophagosome marker LC3bII/LC3bI were increased in AIA EDL muscles. NMES training prevented all these AIA-induced alterations. The present data suggest that NMES training prevents AIA-induced skeletal muscle weakness presumably by counteracting the formation of actin and desmin aggregates. Thus, NMES training can be an effective treatment for muscle dysfunction in patients with RA.
Highlights
Rheumatoid cachexia occurs in approximately 10–50% of patients with rheumatoid arthritis (RA) and is characterized by the loss of muscle strength [1, 2]
Torque traces were displayed on a monitor, and the stimulation intensity was progressively increased throughout the stimulation period in order to maintain a peak torque corresponding to 60% of the initial maximum isometric torque, which was measured in every neuromuscular electrical stimulation (NMES) training sessions
We further investigated the underling mechanisms of arthritis-induced muscle dysfunction and found that desmin as well as actin are aggregated in adjuvant-induced arthritis (AIA) extensor digitorum longus (EDL) muscles
Summary
Rheumatoid cachexia occurs in approximately 10–50% of patients with rheumatoid arthritis (RA) and is characterized by the loss of muscle strength [1, 2]. Helliwell et al [3] reported a 60% reduction in grip strength despite only a 10% reduction in cross-sectional area.
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