Nrf2 and NF-kB signalling, and antioxidant enzyme adaptations to sprint interval training are potentiated by brief ischaemia application during the recovery periods

Abstract

INTRODUCTION: Reactive oxygen and nitrogen species (RONS) stimulate signalling pathways essential for the adaptative response to exercise. Nrf2 and NFkB transcription factors regulate over 150 genes involved in redox homeostasis, inflammation, and the antioxidant response. High intensity exercise increases RONS and activates Nrf2, NFkB, and CaMKII signalling in human skeletal muscle (HSM), an effect potentiated by immediate ischaemia application (PMID: 32863217). It remains unknown how sprint interval training (SIT) modulates antioxidant enzyme expression and regulatory transcription factors. It is uncertain whether additional metabolic and RONS-mediated stress could further stimulate the adaptive response to SIT. We hypothesized that SIT would upregulate the basal and exercise-induced Nrf2 and NFkB signal ling, with this effect being exacerbated by post-exercise ischaemia. METHODS: Ten active subjects were tested before and after SIT (4-6 30s sprints, 4min recovery, 6 sessions in 2 weeks). Immediately after each sprint, the circulation of one leg was instantaneously occluded (300mmHg) for 30-50s. The main PRE and POST-training tests consist ed of an incremental exercise to exhaustion (IE) followed by 90min rest and 6 bouts of supramaximal exercise to exhaustion at 120%VO2max (SPE) interspaced with 20s recovery, during which circulation of both legs was fully occluded. In addition, VL biopsies were taken at rest, 90 min after IE, and immediately after SPE unilaterally at PRE and bilaterally at POST from the leg training with free circula tion (FCL) and the leg training with ischaemia (IS) for Western Blotting. Statistics: repeated-measures ANOVA RESULTS: After SIT, basal protein levels of pSer536p65, IkBalpha, IkBbeta, pSer40Nrf2, Nrf2, Nrf2/Keap1 ratio, Catalase, SOD1, GR, pThr287CaMKII, and CaMKII were largely increased (~2.3-fold) solely in IS (p<0.05). Besides, SIT increased basal protein levels significantly more in IS for pSer176/180IKK, p50, p65 (~1.9-fold vs. FCL) (p<0.05). The acute upregulation following SPE observed at PRE and after SIT in FCL was blunted in IS (p<0.05) for pThr287CaMKII, IkBbeta, TrxR1, Nrf2, pSer40Nrf2, p65, pSer536p65, pSer176/180 IKK and pTyr705STAT3. CONCLUSION: These findings show that Nrf2 and NFkB signalling and their downstream antioxidant enzymes are largely upregulated by additional time under oxidative stress during 2 weeks of SIT in HSM. Furthermore, we have shown that a marked elevation of the basal antioxidant response with training suppresses the acute exercise-induced activation of Nrf2 and NFkB signalling otherwise required in the non-trained state. This was achieved by employing a novel experimental approach where immediate ischaemia is applied after each bout in only one leg, exacerbating RONS and metabolite build-up, which may enhance the antioxidant capacity of HSM. Whether these adaptations are beneficial for performance or long-term adaptation to training remains to be evaluated.