Muscle wasting and the response to exercise in lung-injured mice is not primarily driven through the glucocorticoid axis.

Background: Muscle wasting is common in patients with acute respiratory distress syndrome (ARDS). We have previously shown that acute lung-injured (ALI) mice develop muscle atrophy driven by muscle E3 ubiquitin ligase muscle RING-finger protein 1 (MuRF1). The muscle atrophy response in ALI mice can be partially alleviated by short durations of moderate-intensity treadmill exercise through unclear mechanisms. Glucocorticoid receptor (GR) signaling has been implicated in muscle wasting and repair, and the MuRF1 promoter contains a glucocorticoid response element. We examined the contribution of muscle GR signaling in ALI-associated muscle wasting and the response to exercise. Methods: Intratracheal lipopolysaccharides were instilled into wild type (WT) mice. Mice exercised for prescribed intensity and duration on a treadmill. GR knockdown was achieved through pharmacologic inhibition and the use of muscle specific GR knockout mice. Muscle structure and function was evaluated using physiologic and histochemical techniques and GR activation was assessed under multiple conditions. Results: Muscle wasting in ALI mice was associated with a GR transcriptional response which was suppressed by exercise. However, neither pharmacological inhibition of muscle GR signaling, nor genetic deletion of muscle GR prevented skeletal muscle wasting or recapitulated the benefits of exercise in WT ALI mice. Moreover, RNAseq of tibialis anterior and diaphragm skeletal muscle in WT mice revealed that exercise influenced genes related to skeletal muscle tissue remodeling, but pathway analysis suggested that this was unrelated to the glucocorticoid axis. Conclusion: GR signaling is dispensable for both ALI muscle wasting and its partial mitigation by exercise in mice.