Elevated hexokinase increases cardiac glycolysis in transgenic mice (original) (raw)
Related papers
Journal of Bioenergetics and Biomembranes, 2009
The hexokinases are fundamental regulators of cardiac glucose uptake; by phosphorylating free intracellular glucose, they maintain the concentration gradient driving myocardial extraction of glucose from the bloodstream. Hexokinases are highly regulated proteins, subject to activation by insulin, hypoxia or ischaemia, and inhibition by their enzymatic product glucose-6-phosphate. In vitro and in many non-cardiac cell types, hexokinases have been shown to bind to the mitochondria, both increasing their phosphorylative capacity, and having a putative role in the anti-apoptotic function of protein kinase B (PKB)/Akt. Whether hexokinase-mitochondrial interaction is a dynamic and responsive process in the heart has been difficult to prove, but there is growing evidence that this association does indeed increase in response to insulin stimulation or ischaemia. In this review I discuss the relevance of hexokinase-mitochondrial interaction to cardiac glycolytic control, our interpretation of 18 FDG cardiac PET scans, and its possible role in protecting the myocardium from ischaemic injury.
Metabolism: clinical and experimental, 2017
Cardiac hexokinase II (HKII) can translocate between cytosol and mitochondria and change its cellular expression with pathologies such as ischemia-reperfusion, diabetes and heart failure. The cardiac metabolic consequences of these changes are unknown. Here we measured energy substrate utilization in cytosol and mitochondria using stabile isotopes and oxygen consumption of the intact perfused heart for 1) an acute decrease in mitochondrial HKII (mtHKII), and 2) a chronic decrease in total cellular HKII. We first examined effects of 200nM TAT (Trans-Activator of Transcription)-HKII peptide treatment, which was previously shown to acutely decrease mtHKII by ~30%. In Langendorff-perfused hearts TAT-HKII resulted in a modest, but significant, increased oxygen consumption, while cardiac performance was unchanged. At the metabolic level, there was a nonsignificant (p=0.076) ~40% decrease in glucose contribution to pyruvate and lactate formation through glycolysis and to mitochondrial citr...
Hexokinases and cardioprotection
Journal of Molecular and Cellular Cardiology, 2015
As mediators of the first enzymatic step in glucose metabolism, hexokinases (HKs) orchestrate a variety of catabolic and anabolic uses of glucose, regulate antioxidant power by generating NADPH for glutathione reduction, and modulate cell death processes by directly interacting with the voltage-dependent anion channel (VDAC), a regulatory component of the mitochondrial permeability transition pore (mPTP). Here we summarize the current state-of-knowledge about HKs and their role in protecting the heart from ischemia/reperfusion (I/R) injury, reviewing: 1) the properties of different HK isoforms and how their function is regulated by their subcellular localization; 2) how HKs modulate glucose metabolism and energy production during I/R; 3) the molecular mechanisms by which HKs influence mPTP opening and cellular injury during I/R; and 4) how different metabolic and HK profiles correlate with susceptibility to I/R injury and cardioprotective efficacy in cancer cells, neonatal hearts, and normal, hypertrophied and failing adult hearts, and how these difference may guide novel therapeutic strategies to limit I/R injury in the heart. This article is part of a Special Issue entitled 'Mitochondria'.
Journal of Biological Chemistry, 2020
The hexosamine biosynthesis pathway (HBP) branches from glycolysis and forms uridine diphosphate-β-N-acetylglucosamine (UDP-GlcNAc), the moiety for O-linked β-N-acetylglucosamine (O-GlcNAc) posttranslational modifications. An inability to directly measure HBP flux has hindered our understanding of the factors regulating protein O-GlcNAcylation. Our goals in this study were to (i) validate a LC-MS method that assesses HBP flux as UDP-GlcNAc (13C)-molar percent enrichment (MPE) and concentration; and (ii) determine whether glucose availability or workload regulate cardiac HBP flux. For (i), we perfused isolated murine working hearts with [U-13C6]glucosamine (1, 10, 50 or 100 µM), which bypasses the rate limiting HBP enzyme. We observed a concentration-dependent increase in UDP-GlcNAc levels and MPE, with the latter reaching a plateau of 56.3±2.9%. For (ii), we perfused isolated working hearts with [U-13C6]glucose (5.5 or 25 mM). Glycolytic efflux doubled with 25 mM [U-13C6]gluco...
Journal of Biological Chemistry, 2002
Using adenovirus-mediated gene transfer into FTO-2B cells, a rat hepatoma cell line, we have overexpressed hexokinase I (HK I), glucokinase (GK), liver glycogen synthase (LGS), muscle glycogen synthase (MGS), and combinations of each of the two glucose-phosphorylating enzymes with each one of the GS isoforms. FTO-2B cells do not synthesize glycogen even when incubated with high doses of glucose. Adenovirus-induced overexpression of HK I and/or LGS, two enzymes endogenously expressed by these cells, did not produce a significant increase in the levels of active GS and the total glycogen content. In contrast, GK overexpression led to the glucosedependent activation of endogenous or overexpressed LGS and to the accumulation of glycogen. Similarly overexpressed MGS was efficiently activated by the glucose-6-phosphate (Glc-6-P) produced by either endogenous or overexpressed HK I and by overexpressed GK. These results indicate the existence of at least two pools of Glc-6-P in the cell, one of them is accessible to both isoforms of GS and is replenished by the action of GK, whereas LGS is excluded from the cellular compartment where the Glc-6-P produced by HK I is directed. These findings are interpreted in terms of the metabolic role that the two pairs of enzymes, HK I-MGS in the muscle and GK-LGS in the hepatocyte, perform in their respective tissues.
2000
Limitations to exercise-and maximal insulinstimulated muscle glucose uptake. J. Appl. Physiol. 85(6): [2305][2306][2307][2308][2309][2310][2311][2313] 1998.-The hypothesis of this investigation was that insulin and muscle contraction, by increasing the rate of skeletal muscle glucose transport, would bias control so that glucose delivery to the sarcolemma (and t tubule) and phosphorylation of glucose intracellularly would exert more influence over glucose uptake. Because of the substantial increases in blood flow (and hence glucose delivery) that accompany exercise, we predicted that glucose phosphorylation would become more rate determining during exercise. The transsarcolemmal glucose gradient (TSGG; the glucose concentration difference across the membrane) is inversely related to the degree to which glucose transport determines the rate of glucose uptake. The TSGG was determined by using isotopic methods in conscious rats during euglycemic hyperinsulinemia [Ins; 20 mU/(kg · min); n ϭ 7], during treadmill exercise (Ex, n ϭ 6), and in sedentary, salineinfused rats (Bas, n ϭ 13). Rats received primed, constant intravenous infusions of trace 3-O-[ 3 H]methyl-D-glucose and [U-14 C]mannitol. Then 2-deoxy-[ 3 H]glucose was infused for the calculation of a glucose metabolic index (R g ). At the end of experiments, rats were anesthetized, and soleus muscles were excised. Total soleus glucose concentration and the steady-state ratio of intracellular to extracellular 3-O-[ 3 H]methyl-D-glucose (which distributes on the basis of the TSGG) were used to calculate ranges of possible glucose concentrations ([G]) at the inner and outer sarcolemmal surfaces ([G] im and [G] om , respectively). Soleus R g was increased in Ins and further increased in Ex. In Ins, total soleus glucose, [G] om , and the TSGG were decreased compared with Bas, while [G] im remained near 0. In Ex, total soleus glucose and [G] im were increased compared with Bas, and there was not a decrease in [G] om as was observed in Ins. In addition, accumulation of intracellular free 2-deoxy-[ 3 H]glucose occurred in soleus in both Ex and Ins. Taken together, these data indicate that, in Ex, glucose phosphorylation becomes an important limitation to soleus glucose uptake. In Ins, both glucose delivery and glucose phosphorylation influence the rate of soleus glucose uptake more than under basal conditions. glucose phosphorylation; glucose delivery; countertransport; 3-O-methyl-D-glucose; 2-deoxyglucose GLUCOSE ENTRY into skeletal muscle is determined by membrane permeability to glucose and the transsarcolemmal glucose gradient (TSGG). Membrane permeability is a function of the number of glucose transporters in the sarcolemma [including t tubules
Hexokinase II knockdown results in exaggerated cardiac hypertrophy via increased ROS production
EMBO Molecular Medicine, 2012
Hexokinase-II (HKII) is highly expressed in the heart and can bind to the mitochondrial outer membrane. Since cardiac hypertrophy is associated with a substrate switch from fatty acid to glucose, we hypothesized that a reduction in HKII would decrease cardiac hypertrophy after pressure overload. Contrary to our hypothesis, heterozygous HKII-deficient (HKII þ/À) mice displayed increased hypertrophy and fibrosis in response to pressure overload. The mechanism behind this phenomenon involves increased levels of reactive oxygen species (ROS), as HKII knockdown increased ROS accumulation, and treatment with the antioxidant N-acetylcysteine (NAC) abrogated the exaggerated response. HKII mitochondrial binding is also important for the hypertrophic effects, as HKII dissociation from the mitochondria resulted in de novo hypertrophy, which was also attenuated by NAC. Further studies showed that the increase in ROS levels in response to HKII knockdown or mitochondrial dissociation is mediated through increased mitochondrial permeability and not by a significant change in antioxidant defenses. Overall, these data suggest that HKII and its mitochondrial binding negatively regulate cardiac hypertrophy by decreasing ROS production via mitochondrial permeability.
Diabetes mellitus (DM) has been reported to alter the cardiac response to ischemia-reperfusion (IR). In addition, cardioprotection induced by ischemic preconditioning (IPC) is often impaired in diabetes. We have previously shown that the subcellular localisation of the glycolytic enzyme hexokinase (HK) is causally related to IR injury and IPC protective potential. Especially the binding of HK to mitochondria and prevention of HK solubilisation (HK detachment from mitochondria) during ischemia confers cardioprotection. It is unknown whether diabetes affects HK localisation during IR and IPC as compared to non-diabetes. In this study we hypothesize that DM alters cellular trafficking of hexokinase in response to IR and IPC, possibly explaining the altered response to IR and IPC in diabetic heart. Control (CON) and type I diabetic (DM) rat hearts (65 mg/kg streptozotocin, 4 weeks) were isolated and perfused in Langendorff-mode and subjected to 35 min I and 30 min R with or without IPC (3 times 5 min I). Cytosolic and mitochondrial fractions were obtained at (1) baseline, i.e. after IPC but before I, (2) 35 min I, (3) 5 min R and (4) 30 min R. DM improved rate-pressure product recovery (RPP; 71 ± 10 % baseline (DM) versus 9 ± 1 % baseline (CON) and decreased contracture (end-diastolic pressure: 24 ± 8 mmHg (DM) vs 77 ± 4 mmHg (CON)) after IR as compared to control, and was associated with prevention of HK solubilisation at 35 min I. IPC improved cardiac function in CON but not in DM hearts. IPC in CON prevented HK solubilisation at 35 min I and at 5 min R, with a trend for increased mitochondrial HK. In contrast, the non-effective IPC in DM was associated with solubilisation of HK and decreased mitochondrial HK at early reperfusion and a reciprocal behaviour at late reperfusion. We conclude that type I DM significantly altered cellular HK translocation patterns in the heart in response to IR and IPC, possibly explaining altered response to IR and IPC in diabetes.
Diabetes, 2007
Limitations to exercise-and maximal insulinstimulated muscle glucose uptake. J. Appl. Physiol. 85(6): [2305][2306][2307][2308][2309][2310][2311][2312][2313] 1998.-The hypothesis of this investigation was that insulin and muscle contraction, by increasing the rate of skeletal muscle glucose transport, would bias control so that glucose delivery to the sarcolemma (and t tubule) and phosphorylation of glucose intracellularly would exert more influence over glucose uptake. Because of the substantial increases in blood flow (and hence glucose delivery) that accompany exercise, we predicted that glucose phosphorylation would become more rate determining during exercise. The transsarcolemmal glucose gradient (TSGG; the glucose concentration difference across the membrane) is inversely related to the degree to which glucose transport determines the rate of glucose uptake. The TSGG was determined by using isotopic methods in conscious rats during euglycemic hyperinsulinemia [Ins; 20 mU/(kg · min); n ϭ 7], during treadmill exercise (Ex, n ϭ 6), and in sedentary, salineinfused rats (Bas, n ϭ 13). Rats received primed, constant intravenous infusions of trace 3-O-[ 3 H]methyl-D-glucose and [U-14 C]mannitol. Then 2-deoxy-[ 3 H]glucose was infused for the calculation of a glucose metabolic index (R g ). At the end of experiments, rats were anesthetized, and soleus muscles were excised. Total soleus glucose concentration and the steady-state ratio of intracellular to extracellular 3-O-[ 3 H]methyl-D-glucose (which distributes on the basis of the TSGG) were used to calculate ranges of possible glucose concentrations ([G]) at the inner and outer sarcolemmal surfaces ([G] im and [G] om , respectively). Soleus R g was increased in Ins and further increased in Ex. In Ins, total soleus glucose, [G] om , and the TSGG were decreased compared with Bas, while [G] im remained near 0. In Ex, total soleus glucose and [G] im were increased compared with Bas, and there was not a decrease in [G] om as was observed in Ins. In addition, accumulation of intracellular free 2-deoxy-[ 3 H]glucose occurred in soleus in both Ex and Ins. Taken together, these data indicate that, in Ex, glucose phosphorylation becomes an important limitation to soleus glucose uptake. In Ins, both glucose delivery and glucose phosphorylation influence the rate of soleus glucose uptake more than under basal conditions. glucose phosphorylation; glucose delivery; countertransport; 3-O-methyl-D-glucose; 2-deoxyglucose GLUCOSE ENTRY into skeletal muscle is determined by membrane permeability to glucose and the transsarcolemmal glucose gradient (TSGG). Membrane permeability is a function of the number of glucose transporters in the sarcolemma [including t tubules