NEW FINDINGS: What is the central question of this study? Can short-term 
high-intensity interval training (HIIT) contribute to the reduction of 
ischaemia-reperfusion (IR) injury by enhancing the levels of Klotho and its 
related axes, including myocardial TRPC6 expression, and antioxidant defence as 
novel possible mechanisms of exercise-induced cadioprotection (EICP) against IR 
injury? What is the main finding and its importance? The increase of plasma and 
myocardial levels of Klotho as a result of preconditioning with HIIT and 
prevention of a significant reduction of Klotho during IR injury can promote 
cardioprotection and reduce damage by attenuating myocardial TRPC6 expression 
and increasing antioxidant defence. The present findings may provide a new 
mechanism in EICP and IR injury, and provide the knowledge to develop preventive 
and therapeutic approaches.
ABSTRACT: Cardiovascular disease, especially coronary artery disease, remains a 
major cause of morbidity and mortality in the world, and ischaemia-reperfusion 
(IR) insult is the main pathological cause leading to death. Exercise training 
is associated with a reduced risk of cardiovascular disease and the development 
of cardioprotection against IR injury. Therefore, the purpose of this study was 
to investigate the effect of preconditioning with high-intensity interval 
training (HIIT) on myocardial and plasma levels of Klotho and its related axes 
as novel mechanisms of exercise-induced cardioprotection against IR injury. 
Seventy male Wistar rats were randomly divided into five groups of control, 
HIIT, sham, IR and HIIT group that underwent IR injury (H-IR). The training 
group performed five sessions of HIIT on the treadmill. The cardiac IR injury 
was induced by ligation of the left anterior descending coronary artery for 
30 min followed by 24 h reperfusion. Infarct size and histopathological 
assessment of cardiac tissues were determined through Evans 
Blue-triphenyltetrazolium chloride and haematoxylin-eosin staining, 
respectively. We investigated lipid peroxidation and markers of cardiac injury, 
antioxidant enzymes and the plasma levels of Klotho using enzyme-linked 
immunosorbent assays. Also, myocardial levels of Klotho and TRPC6 expression 
were determined by western blot assays. The results demonstrated a significant 
increase in myocardial and plasma levels of Klotho following HIIT and a 
significant decrease during IR injury. Myocardial TRPC6 channel expression 
increased following IR. HIIT also prevented a significant reduction of Klotho 
during IR and consequently reduced the expression of the TRPC6 channel in the 
H-IR group compared with the IR group. Furthermore, HIIT decreased the infarct 
size, cardiac injury, lipid peroxidation, lactate dehydrogenase, creatine kinase 
myocardial band and cardiac troponin-I, and improved total antioxidant capacity 
and catalase, superoxide dismutase and glutathione peroxidase activities 
following IR injury. The findings of the present study suggest that HIIT 
improves cardioprotection against IR injury and reduces cardiac damages through 
an increase in myocardial and plasma levels of Klotho and its related axes 
(TRPC6 and antioxidant defence). These findings can help to develop preventive 
and therapeutic approaches.