Disruption of Nrf2/ARE signaling impairs antioxidant mechanisms and promotes cell degradation pathways in aged skeletal muscle

Age-associated decline in antioxidant potential and accumulation of reactive oxygen/nitrogen species are primary causes for multiple health problems, including muscular dystrophy and sarcopenia. The role of the nuclear erythroid-2-p45-related factor-2 (Nrf2) signaling has been implicated in antioxidant gene regulation. Here, we investigated the loss-of-function mechanisms for age-dependent regulation of Nrf2/ARE (Antioxidant Response Element) signaling in skeletal muscle (SM). Under basal physiological conditions, disruption of Nrf2 showed minimal effects on antioxidant defenses in young (2 months) Nrf2−/− mice. Interestingly, mRNA and protein levels of NADH Quinone Oxidase-1 were dramatically (*P < 0.001) decreased in Nrf2−/− SM when compared to WT at 2 months of age, suggesting central regulation of NQO1 occurs through Nrf2. Subsequent analysis of the Nrf2-dependent transcription and translation showed that the aged mice (> 24 months) had a significant increase in ROS along with a decrease in glutathione (GSH) levels and impaired antioxidants in Nrf2−/− when compared to WT SM. Further, disruption of Nrf2 appears to induce oxidative stress (increased ROS, HNE-positive proteins), ubiquitination and pro-apoptotic signals in the aged SM of Nrf2−/− mice. These results indicate a direct role for Nrf2/ARE signaling on impairment of antioxidants, which contribute to muscle degradation pathways upon aging. Our findings conclude that though the loss of Nrf2 is not amenable at younger age; it could severely affect the SM defenses upon aging. Thus, Nrf2 signaling might be a potential therapeutic target to protect the SM from age-dependent accumulation of ROS by rescuing redox homeostasis to prevent age-related muscle disorders such as sarcopenia and myopathy.

► Nrf2-Keap1 pathway is conserved in skeletal muscle.
► Abrogation of Nrf2 has a minimal role on SM redox state in younger age.
► Loss of Nrf2 down regulates transcription of ARE-antioxidants upon aging.
► Impaired antioxidant mechanisms induce oxidative stress in aged Nrf2−/− mice.
► Disruption of Nrf2 increases ubiquitination and apoptosis upon aging.