Regulation of Nrf2/Keap1 signalling in human skeletal muscle during exercise to exhaustion in normoxia, severe acute hypoxia and post-exercise ischaemia: Influence of metabolite accumulation and oxygenation

Abstract

The Nrf2 transcription factor is induced by reactive oxygen and nitrogen species and is necessary for the adaptive response to exercise in mice. It remains unknown whether Nrf2 signalling is activated by exercise in human skeletal muscle. Here we show that Nrf2 signalling is activated by exercise to exhaustion with similar responses in normoxia (P I O 2 : 143 mmHg) and severe acute hypoxia (P I O 2 : 73 mmHg). CaMKII and AMPKα phosphorylation were similarly induced in both conditions. Enhanced Nrf2 signalling was achieved by raising Nrf2 total protein and Ser 40 Nrf2 phosphorylation, accompanied by a reduction of Keap1. Keap1 protein degradation is facilitated by the phosphorylation of p62/SQSTM1 at Ser 349 by AMPK, which targets Keap1 for autophagic degradation. Consequently, the Nrf2-to-Keap1 ratio was markedly elevated and closely associated with a 2-3-fold increase in Catalase protein. No relationship was observed between Nrf2 signalling and SOD1 and SOD2 protein levels. Application of ischaemia immediately at the end of exercise maintained these changes, which were reverted within 1 min of recovery with free circulation. While SOD2 did not change significantly during either exercise or ischaemia, SOD1 protein expression was marginally downregulated and upregulated during exercise in normoxia and hypoxia, respectively. We conclude that Nrf2/Keap1/Catalase pathway is rapidly regulated during exercise and recovery in human skeletal muscle. Catalase emerges as an essential antioxidant enzyme acutely upregulated during exercise and ischaemia. Post-exercise ischaemia maintains Nrf2 signalling at the level reached at exhaustion and can be used to avoid early post-exercise recovery, which is O 2 -dependent.

High intensity muscle stimulation activates a systemic Nrf2-mediated redox stress response

“…The ratio of Nrf2-ARE binding to Keap1 content also illustrates the relationship between Keap1 protein and Nrf2-ARE binding. A recently published paper reported significant decreases in Keap1 content after acute exhaustive exercise in human skeletal muscle and concomitant increases in Nrf2 [17], our data here are in agreement with these results.…”

“…Previous studies on Nrf2 signaling responses to exercise have used whole animal treadmill exercise, measuring Nrf2 in several different tissues [2,15,16,[31][32][33][34][35][36][37], or whole-body exercise in humans [1,17,24,25,[38][39][40]. We have recently shown that basal levels of Nrf2 affect its inducibility to an acute exercise bout in humans [39].…”

“…Furthermore, there is a linear relationship between exercise-induced ROS accumulation and Nrf2 activation [15], which is dependent on the duration of the exercise bout [15,16]. Nrf2 can also be activated in human skeletal muscle in response to supramaximal exercise of shorter duration [17], suggesting that longer durations are not required to induce Nrf2 activity if the intensity of the bout is high enough. High intensity interval training is a popular training method to obtain improvements .…”

Excessive exercise training causes mitochondrial functional impairment and decreases glucose tolerance in healthy volunteers

“…In addition, the transcription factor NF-E2 p45-related factor 2 (Nrf2) and the E3 ligase adaptor Kelch-like ECH-associated protein 1 (KEAP1), which is the primary negative regulator of Nrf2, are both critical players in redox homeostasis, the antioxidative response, and mitochondrial biogenesis. It was recently shown that acute exercise increases the total Nrf2 protein content within minutes after an exercise bout (Gallego-Selles et al, 2020), but less is known regarding the chronic response to training.…”

Role of CaMKII and sarcolipin in muscle adaptations to strength training with different levels of fatigue in the set

“…2,3 CaMKII regulates the expression of the transcription factor coactivator peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), which is a critical regulator of mitochondrial biogenesis. 4 Besides this, CaMKII has been implicated in the regulation of the transcription factor nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), 5,6 which is stimulated by high-intensity exercise 7 and muscle metabolism. [8][9][10] Nevertheless, previous evidence on the role of CaMKII in the regulation of muscle phenotype comes from extreme experimental models and information using physiological models in humans is lacking.…”