The combination of NRF1 and Nrf2 activators in myoblasts stimulate mechanisms of proteostasis without changes in mitochondrial respiration

Abstract

Persistent oxidative stress contributes to hallmarks of aging, including impaired proteostasis and mitochondrial dysfunction, while acute oxidative challenges resolved swiftly contribute to beneficial adaptations. Adaptive homeostasis is where acute exposures to sub-toxic stimuli kindle transient expansion of responses necessary to reestablish homeostasis. Elucidating mechanisms underlying adaptive homeostasis will provide novel targets for healthspan extension. Nuclear erythroid-related factor 2 (Nrf2) is a key regulator of cytoprotective gene transcription for redox homeostasis; nuclear respiratory factor 1 (NRF1) is a transcription factor that regulates expression of genes necessary for mitochondrial function. Regulation of both is compromised with advancing age. We hypothesized that NRF1 (NRF1a) and Nrf2 (Nrf2a) activators might improve adaptive homeostasis in C2C12 myoblasts by promoting mitochondrial proteome maintenance and function. Using stable isotope tracing, we assessed protein synthesis over a 16-hr treatment with NRF1a, Nrf2a, or both, with and without a hydrogen peroxide (H₂O₂) stress. We assessed mitochondrial function using high-resolution respirometry. Co-treatment of NRF1a and Nrf2a under H₂O₂ stress favored proteostatic maintenance (p<0.05). H₂O₂ stress decreased mitochondrial respiration and this decrease was not altered by NRF1a/Nrf2a co-treatment. These results suggest that simultaneously targeting Nrf2 and NRF1 may be a viable approach for reestablishing mitochondrial protein homeostasis following a stress, but that this adaptation may not improve respiratory capacity.