Exercise‐induced Increase in Hexokinase II‐mitochondria Association Reduces Cardiac Ischemia‐Reperfusion Injury in Rats

Abstract

IntroductionExercise‐training has been shown to modulate signaling pathways that contribute to improved mitochondrial function in the heart. AKT, a serine/threonine protein kinase pathway is a critical regulator of a variety of cellular functions and its activation is implicated in cardioprotection from ischemia‐reperfusion (I/R) injury. Importantly, the AKT pathway has been shown to be upregulated in exercise. However, the interplay between AKT signaling, mitochondrial function and cardio‐protection in exercise remains to be well elucidated.AIMHerein, we investigated the role of exercise‐induced AKT/Hexokinase II (HKII)‐signaling as a potential mechanism in preserving mitochondrial function and thereby, contribute to cardioprotection against I/R injury.MethodsIsolated hearts from rats, randomly assigned to either sedentary (SED) group or 6–8 weeks treadmill trained (TRN) group, were subjected to 30 min global ischemia and 5 min reperfusion. Mitochondria were isolated immediately after reperfusion and the effects of exercise on cardiac mitochondrial bioenergetics, including changes in O2 consumption rate, mitochondrial membrane potential (ΔΨm), and mitochondrial calcium retention capacity (CRC) was examined. Western blot was performed to quantify the total AKT, p‐AKT and p‐HKII. In addition, we checked the subcellular distributions of HKII and examined the regulation of apoptotic markers at the mitochondrial level. In some hearts, cardiac functional variables and infarct size were also assessed after 120 min reperfusion in SED and TRN rats.ResultsWe found that exercise increased the phosphorylation of AKT in TRN rat hearts, which was associated, concomitantly, with increased phosphorylation of HKII and increased translocation to mitochondria following IR. TRN rats also showed a decreased expression of Bax and DRP1 in mitochondrial fraction and inhibition of caspase‐3 activation. Furthermore, exercise preserved the mitochondrial bioenergetics with significantly higher respiratory control index and more normalized ΔΨm compared to SED rats (see schematic). CRC was greater in TRN rats compared to SED rats (226.6 ± 13.3 nmol /mg protein vs 173.3 ± 13.3 nmol /mg protein). These improvements in mitochondrial function in TRN rats correlated with improved cardiac function during reperfusion.ConclusionThe results indicate that AKT‐mediated HKII‐mitochondrial interaction due to exercise protects mitochondria by inhibiting mitochondrial apoptotic cascades and likely contributes to the increased cardioprotection against IR injury.Support or Funding InformationThis work was supported by NIH grant R01 HL131673‐01A1 to AKSC and WMKSchematic diagram for exercise‐induced activation of AKT‐HKII signaling pathway during IR injury (A). Time course of the mitochondrial O2 consumption, membrane potential (B) and calcium retention capacity (C) in SED and TRN rats after IR stress.Figure 1