L-arginine decreases inflammation and modulates the nuclear factor-κB/matrix metalloproteinase cascade in mdx muscle fibers

Duchenne muscular dystrophy (DMD) is a lethal, X-linked disorder associated with dystrophin deficiency that results in chronic inflammation, sarcolemma damage, and severe skeletal muscle degeneration. Recently, the use of L-arginine, the substrate of nitric oxide synthase (nNOS), has been proposed as a pharmacological treatment to attenuate the dystrophic pattern of DMD. However, little is known about signaling events that occur in dystrophic muscle with L-arginine treatment. Considering the implication of inflammation in dystrophic processes, we asked whether L-arginine inhibits inflammatory signaling cascades. We demonstrate that L-arginine decreases inflammation and enhances muscle regeneration in the mdx mouse model. Classic stimulatory signals, such as proinflammatory cytokines interleukin-1 beta, interieukin-6, and tumor necrosis factor-a, are significantly decreased in mdx mouse muscle, resulting in lower nuclear factor (NF)-kappa B levels and activity. NF-kappa B serves as a pivotal transcription factor with multiple levels of regulation; previous studies have shown perturbation of NF-kappa B signaling in both mdx and DMD muscle. Moreover, L-arginine decreases the activity of metalloproteinase (MMP)-2 and MMP-9, which are transcriptionally activated by NF-kappa B. We show that the inhibitory effect of L-arginine on the NF-kappa B/MMP cascade reduces beta-dystroglycan cleavage and translocates utrophin and nNOS throughout the sarcolemma. Collectively, our results clarify the molecular events by which L-arginine promotes muscle membrane integrity in dystrophic muscle and suggest that NF-kappa B-related signaling cascades could be potential therapeutic targets for DMD management.