Diurnal Regulation Of Exercise-induced Interleukin-6 Signaling

Abstract

BACKGROUND: Exercise induced production of specific myokines, namely Interluekin-6 (IL-6), is essential in protecting the heart against cardiac ischemia-reperfusion (IR) injury in mice. Interestingly, IL-6 production in skeletal muscle has been shown to have a circadian rhythm in vitro, which also influences the magnitude of exercise-induced IL-6 in the blood in humans. However, how the circadian rhythm affects the exercise-mediated IL-6 signaling pathways in the heart is not currently known. PURPOSE: It was the purpose of this study to investigate how time-of-day affects exercise induced IL-6 signaling in the heart. METHODS: We assessed activation of the IL-6 signaling pathway in cardiac muscle following exercise at two times of day; Zeitgeber time (ZT) 0 (beginning of light/rest phase) and ZT12 (beginning of dark/active phase). 21-week-old male C57/BL6 mice (n=38) were habituated to treadmill exercise for 5 days under red light during the active phase and allowed to recover for 2 days. Following a single 60-minute bout of treadmill exercise at 10 m/min, mice were sacrificed at 3 time points; pre-exercise (SED), immediately post-exercise (POST), and 1-hour post-exercise (1HR). Hearts were cleared of blood and rapidly snap frozen in LN2. IL-6 signaling was assessed via western blotting of phosphorylated Signal Transducer and Activator of Transcription 3 (pSTAT3). Statistical analyses was performed using SPSS 25 (SPSS Inc., Chicago, IL, USA). Differences in p-STAT3 at the various time points was analyzed using 2x3 factorial ANOVA and significance accepted at p < 0.05. RESULTS: Values are presented as (Mean ± SD), fold change from sedentary mice at ZT0. No difference was observed in p-STAT3 (Tyr705) between sedentary mice at ZT0 and ZT12 (1.00 ± 0.35 vs 0.95 ± 0.60). A significant interaction effect revealed that p-STAT3 (Tyr705) levels were significantly increased following exercise performed at ZT0 (POST; 4.45 ± 1.30, and 1HR; 2.70 ± 1.35, p < 0.05), while exercise at ZT12 had no effect on IL-6 (POST; 1.42 ± 0.52), and 1HR; 1.32 ± 0.56, p < 0.05). CONCLUSIONS: Exercise-induced myocardial IL-6-signaling was strongly activated at ZT0 compared to exercise at ZT12. Induction of IL-6 activation in cardiac tissue by exercise is time-of-day dependent. Funding: Work was supported by NV INBRE Pilot Grant to Dr. McGinnis