Mitochondrial oxidative stress in skeletal muscle alters metabolic signaling responses to acute muscle contraction.

Activation of redox-sensitive signal transduction cascades is an increasingly appreciated mechanism of exercise adaptation in skeletal muscle. Aging and disease are associated with altered redox homeostasis, potentially altering redox responses to muscle contraction, and adaptations to exercise. It is unclear how chronic steady-state changes in redox homeostasis affect contraction-induced signaling cascades. Here we use a novel model of inducible superoxide dismutase 2 knockdown (iSOD2 KD) in skeletal muscle to test how chronic mitochondrial redox perturbations affect subsequent signaling responses to acute fatiguing muscle contraction. After a 12-week doxycycline treatment to knock down SOD2, littermate controls (CON) and iSOD2 KD animals underwent a single acute fatiguing contractile stimulus of the right hindlimb. Muscle tissue was collected immediately after or 3 h after completion of the stimulus followed by redox proteomic and transcriptomic analysis, respectively, and compared to naïve unstimulated controls of each genotype. iSOD2 KD led to decreased protein expression of several key iron-sulfur cluster biosynthesis proteins and increased reversible thiol oxidation of proteins in the mitochondrial compartment in response to muscle contraction. The transcriptomic response to contraction in KD shows activation of apoptosis, oxidative stress, and inflammatory pathways and no significant perturbation in controls. Controls show pathway activation of insulin signaling and glucose metabolism, calcium signaling, and energy stress signaling processes compared to no activation in KD muscle. These results indicate that chronic mitochondrial redox stress shifts acute signaling responses away from metabolic signaling pathways and toward oxidative stress and apoptotic signaling processes which may lead to pathological or maladaptive signaling responses over time.