Hypoxic Preconditioning Mitigates Diaphragmatic Skeletal Muscle Fatigue during Reoxygenation via ROS and ERK Signaling

Abstract

Reoxygenation of skeletal muscle after hypoxia has been shown to induce tissue damage and lead to muscle dysfunction. For instance, oxygen levels are depleted during periods of intense exercise and the subsequent flow of oxygenated blood can induce oxidative stress. However, the mechanism for reoxygenation-induced fatigue or injury in skeletal muscle has not been fully elucidated. In addition, limited research has focused on the potential of hypoxic preconditioning (HPC; alternating periods of hypoxia and normoxia) as an effective method for reducing muscle fatigue during reoxygenation. PURPOSE: This study investigated the hypothesis that HPC protects diaphragmatic muscle function during reoxygenation through ROS and ERK signaling. METHODS: Isolated mouse diaphragm muscle strips were either non-treated (n = 10), treated with HPC (n = 7), or exposed to a combination of the antioxidants Tiron and N-acetyl cysteine (NAC) (1mM each, n = 4) or an ERK inhibitor (PD98059, 100 μM, n = 5) prior to HPC treatment followed by a 30 min hypoxic period (PO2 = 5 Torr) and subsequent reoxygenation. The muscle strips were electrically stimulated in a myograph device containing Ringer’s solution during reoxygenation. Data were analyzed using a multi-way ANOVA, and expressed as means ± SE. P < 0.05 was the criterion level for significance. RESULTS: Our results demonstrated that HPC significantly increases muscle function during reoxygenation (37.7 ± 8.5% for treated vs. 9.8 ± 2.5% for control, P < 0.05; expressed as percent of the maximal force at the end of the contraction protocol). Inhibition of ROS signaling (5.22 ± 0.2% for treated vs. 9.8 ± 2.5% for control) and ERK activation (13.4 ± 4.4% for treated vs. 9.8 ± 2.5% for control) abolished the protective HPC effect on the muscle force development. CONCLUSION: We propose that HPC may reduce diaphragmatic skeletal muscle fatigue during reoxygenation through ROS signaling and the activation of the ERK pathway.