Interleukin-6 and Exercise-Induced Cardioprotection

Abstract

Ischemia-Reperfusion (IR) injury is the leading cause of death in the US and industrialized nations. Exercise preconditioning has emerged as a unique method to reduce the injury associated with IR, yet the mechanisms have not been fully elucidated. The purpose of this study was to examine the potential of the cytokine Interleukin-6 (IL-6) as an exercise-induced mediator of cardioprotection. Wild type (C57) and IL-6 knockout (IL-6-/-) mice (n=32 for both groups) underwent treadmill habituation, and three days of cardioprotective exercise for 60 minutes at 18 m*min-1 and 0% grade. Aim 1, animals were sacrificed PRE, POST, 30, and 60 minutes post-exercise on the third session, and serum, skeletal muscles and hearts were analyzed for indices of IL-6 signaling via PCR and western blotting. Aim 2, mice were separated into Sedentary (C57 SED and IL-6-/- SED), Exercised (C57 EX and IL-6-/- EX), and Sham (SH, C57 mice only) groups (C57 n=24; IL-6-/-=16), and received a surgically induced in vivo IR surgery. Hearts were excised and incubated in TTC for myocardial necrosis. Ischemic and perfused tissues were collected and analyzed for indices of apoptosis and autophagy via PathScan analysis and conventional western blotting. Aim 1: Exercise increased IL-6 and sIL-6R in the blood, as well as IL-6R mRNA and protein in the gastrocnemius and myocardium. IL-6R protein was increased only in the C57 mice. P-STAT3 was similarly increased in gastrocnemius and heart in both C57 and IL-6-/- mice post exercise. Myocardial iNOS mRNA and protein were decreased by exercise, while COX-2 mRNA and protein were unchanged. Aim 2: Exercise protected C57 EX mice against IR induced arrhythmias and necrosis, while C57 SED, IL-6-/- SED and IL-6-/- EX mice had significantly higher arrhythmia scores, and significantly greater % infarct area compared to SH. C57 EX mice had increased p44/42 MAPK and p38 MAPK phosphorylation compared to IL-6-/- EX mice, suggesting protection was dependent upon these pathways. This is the first study to show that exercise exerts cardioprotection via IL-6, and strongly implicates protective signaling originating from the exercised skeletal muscle.