Chronic Hypoxia Enhances Expression and Activity of Mitochondrial Creatine Kinase and Hexokinase in the Rat Ventricular Myocardium

Abstract

Background: Creatine kinase (CK) and hexokinase (HK) play a key role in myocardial energy homeostasis. We aimed to determine CK and HK expression and enzyme activity in the left (LV) and right (RV) ventricles of rats adapted for 3 weeks to normobaric hypoxia (10 % O₂) either continuously (CNH) or intermittently with 1-h or 16-h normoxic episode per day. Methods: The Real-Time RT-PCR, Western blot, and enzyme-coupled assays were used. In addition, the effect of CNH on the HK co-localization with mitochondria, which can inhibit apoptosis, was assessed using immunofluorescence techniques. Results: CK and HK activities increased in the LV during all hypoxic adaptations, which was consistent with elevated protein levels of mitochondrial mtCKs, cytosolic CKB, HK1, and HK2 isoforms. Enzyme activities also increased in the hypoxic RV, but only CKB protein was elevated. No effect of CNH on HK1 or HK2 co-localization with mitochondria was observed. Conclusion: Up-regulation of mtCKs and HK isoforms may stimulate the respiratory chain and help to maintain energy homeostasis of chronically hypoxic myocardium and prevent oxidative stress. In this way, CK and HK enzymes can possibly participate in the establishment of ischemia-resistant phenotype of chronically hypoxic hearts.

Alterations in antioxidant system, mitochondrial biogenesis and autophagy in preeclamptic myometrium

“…Indeed, VDAC1 (the level of which was also higher in the loPE group) may serve as a platform for ubiquitination and mitochondria selection in a Δψ-dependent manner during autophagy [47], [48], [67]. Thus, we suggest that increases in HK1 and VDAC1 levels in the loPE group could be linked to glucose metabolism, probably due to hypoxia or the activity of exogenous agents [68], and also to autophagy activation in loPE myometrium.…”

TRAP1 Provides Protection Against Myocardial Ischemia-Reperfusion Injury by Ameliorating Mitochondrial Dysfunction

“…A recent study showed that the activities of creatine kinase (CK) and hexokinase (HK), which are essential for the production of ATP by oxidative phosphorylation, increased in response to hypoxia. Therefore, future studies should assess the activity of CK and HK in response to myocardial I/R injury in relation to TRAP1 expression [26]. …”

Cardioprotective adaptation of rats to intermittent hypobaric hypoxia is accompanied by the increased association of hexokinase with mitochondria

“…The HK activity can be also modulated by its substrate availability and product concentration. It has been reported that hypoxia can increase the glucose flux into cardiomyocytes (9,10,35) as well as the HK activity (6,37,47). In addition, the HK activity rises due to an increase of HK association with mitochondria (28).…”

“…These data suggest that hypoxic adaptation, which is associated with ROS-dependent signaling (16), may lead to the activation of prosurvival pathways that can involve binding of HK to mitochondria. The present model of chronic hypoxia corresponding to the altitude of 7,000 m represents rather extreme conditions in terms of adaptive potential compared with the moderate continuous normobaric hypoxia used in our previous study (47). However, this model still provides cardiac phenotype characterized by increased resistance to I/R injury (16,26), despite the fact that it is associated with oxidative stress as indicated by a decreased GSH/GSSG ratio and increased content of lipofuscin-like pigments (16).…”

“…The specific enzyme HK activity was expressed as units per gram protein (U/g; Units of Enzyme Activity, 1979). The detailed procedure was described earlier (47).…”