Redox signaling of cardiac HSF1 DNA binding

Untargeted metabolomics analysis of ischemia-reperfusion-injured hearts ex vivo from sedentary and exercise-trained rats

INTRODUCTION

The effects of exercise on the heart and its resistance to disease are well-documented. Recent studies have identified that exercise-induced resistance to arrhythmia is due to the preservation of mitochondrial membrane potential.

OBJECTIVES

To identify novel metabolic changes that occur parallel to these mitochondrial alterations, we performed non-targeted metabolomics analysis on hearts from sedentary and exercise-trained rats challenged with isolated heart ischemia-reperfusion injury (I/R).

METHODS

Eight-week old Sprague-Dawley rats were treadmill trained 5 days/week for 6 weeks (exercise duration and intensity progressively increased to 1 h at 30 m/min up a 10.5% incline, 75-80% VO_2max). The recovery of pre-ischemic function for sedentary rat hearts was 28.8 ± 5.4% (N = 12) compared to exercise trained hearts, which recovered 51.9% ± 5.7 (N = 14) (p < 0.001).

RESULTS

Non-targeted GC-MS metabolomics analysis of (1) sedentary rat hearts; (2) exercise-trained rat hearts; (3) sedentary rat hearts challenged with global ischemia-reperfusion (I/R) injury; and (4) exercise-trained rat hearts challenged with global I/R (10/group) revealed 15 statistically significant metabolites between groups by ANOVA using Metaboanalyst (p < 0.001). Enrichment analysis of these metabolites for pathway-associated metabolic sets indicated a > 10-fold enrichment for ammonia recycling and protein biosynthesis. Subsequent comparison of the sedentary hearts post-I/R and exercise-trained hearts post-I/R further identified significant differences in three metabolites (oleic acid, pantothenic acid, and campesterol) related to pantothenate and CoA biosynthesis (p ≤ 1.24E-05, FDR ≤ 5.07E-4).

CONCLUSIONS

These studies shed light on novel mechanisms in which exercise-induced cardioprotection occurs in I/R that complement both the mitochondrial stabilization and antioxidant mechanisms recently described. These findings also link protein synthesis and protein degradation (protein quality control mechanisms) with exercise-linked cardioprotection and mitochondrial susceptibility for the first time in cardiac I/R.

Mitochondria in the middle: exercise preconditioning protection of striated muscle

Cellular and physiological adaptations to an atmosphere which became enriched in molecular oxygen spurred the development of a layered system of stress protection, including antioxidant and stress response proteins. At physiological levels reactive oxygen and nitrogen species regulate cell signalling as well as intracellular and intercellular communication. Exercise and physical activity confer a variety of stressors on skeletal muscle and the cardiovascular system: mechanical, metabolic, oxidative. Transient increases of stressors during acute bouts of exercise or exercise training stimulate enhancement of cellular stress protection against future insults of oxidative, metabolic and mechanical stressors that could induce injury or disease. This phenomenon has been termed both hormesis and exercise preconditioning (EPC). EPC stimulates transcription factors such as Nrf-1 and heat shock factor-1 and up-regulates gene expression of a cadre of cytosolic (e.g. glutathione peroxidase and heat shock proteins) and mitochondrial adaptive or stress proteins (e.g. manganese superoxide dismutase, mitochondrial KATP channels and peroxisome proliferator activated receptor γ coactivator-1 (PGC-1)). Stress response and antioxidant enzyme inducibility with exercise lead to protection against striated muscle damage, oxidative stress and injury. EPC may indeed provide significant clinical protection against ischaemia-reperfusion injury, Type II diabetes and ageing. New molecular mechanisms of protection, such as δ-opioid receptor regulation and mitophagy, reinforce the notion that mitochondrial adaptations (e.g. heat shock proteins, antioxidant enzymes and sirtuin-1/PGC-1 signalling) are central to the protective effects of exercise preconditioning.

Ischemia-reperfusion injury and hypoglycemia risk in insulin-treated T1DM rats following different modalities of regular exercise

While regular exercise is known to improve cardiovascular function, individuals with type 1 diabetes mellitus (T1DM) have an increased risk for exercise-induced hypoglycemia. Clinical data suggest that higher intensities of acute exercise may alleviate the onset of hypoglycemia; however, the cardiovascular benefit from these forms of exercise in patients with T1DM has yet to be established. The purpose of this study was to investigate the cardiovascular benefit of different regular exercise regimes, while monitoring blood glucose concentrations during the post-exercise period. Fifty rats (8-week-old Sprague-Dawley male) were equally divided into the following groups: nondiabetic sedentary (C), diabetic sedentary (DS), diabetic low-intensity aerobic exercise (DL), diabetic high-intensity aerobic exercise (DH) or diabetic resistance exercise (DR). Diabetes was induced using multiple streptozotocin injections (5×; 20 mg/kg) while subcutaneous insulin pellets maintained glycemia in a range typical for individuals that exercise with T1DM. Exercise consisted of six weeks of treadmill running (DL and DH) or weighted ladder climbs (DR). The cardiovascular benefit of each exercise program was determined by the myocardial recovery from ischemia-reperfusion injury. Exercise-related cardiovascular protection was dependent on the exercise modality, whereby DH demonstrated the greatest protection following an ischemic-reperfusion injury. Each exercise modality caused a significant decline in blood glucose in the post-exercise period; however, blood glucose levels did not reach hypoglycemic concentrations (<3.0 mmol/L) throughout the exercise intervention. These results suggest that elevating blood glucose concentrations prior to exercise allows patients with T1DM to perform exercise that is beneficial to the myocardium without the accompanying risk of hypoglycemia.

Increased immunogenicity is an integral part of the heat shock response following renal ischemia

Renal ischemia increases tubular immunogenicity predisposing to increased risk of kidney allograft rejection. Ischemia-reperfusion not only disrupts cellular homeostasis but also induces the cytoprotective heat shock response that also plays a major role in cellular immune and defense processes. This study therefore tested the hypothesis that upregulation of renal tubular immunogenicity is an integral part of the heat shock response after renal ischemia. Expressions of 70 kDa heat shock protein (Hsp70), major histocompatibility complex (MHC) class II, and intercellular adhesion molecule-1 (ICAM-1) were assessed in normal rat kidney (NRK) cells following ATP depletion (antimycin A for 3 h) and heat (42°C for 24 h). In vitro, transient Hsp70 transfection and heat shock factor-1 (HSF-1) transcription factor decoy treatment were performed. In vivo, ischemic renal cortex was investigated in Sprague-Dawley rats following unilateral renal artery clamping for 45 min and 24 h recovery. Upregulation of Hsp70 was closely and significantly correlated with upregulation of MHC class II and/or ICAM-1 following ATP depletion and heat injury. Bioinformatics analysis searching the TRANSFAC database predicted HSF-1 binding sites in these genes. HSF-1 decoy significantly reduced the expression of immunogenicity markers in stressed NRK cells. In the in vivo rat model of renal ischemia, concordant upregulation of MHC class II molecules and Hsp70 suggests biological relevance of this link. The results demonstrate that upregulation of renal tubular immunogenicity is an integral part of the heat shock response after renal ischemia. Bioinformatic analysis predicted a molecular link to tubular immunogenicity at the level of the transcription factor HSF-1 that was experimentally verified by HSF-1 decoy treatment. Future studies in HSF-1 knockout mice are needed.

Molecular mechanisms in exercise-induced cardioprotection

Physical inactivity is increasingly recognized as modifiable behavioral risk factor for cardiovascular diseases. A partial list of proposed mechanisms for exercise-induced cardioprotection include induction of heat shock proteins, increase in cardiac antioxidant capacity, expression of endoplasmic reticulum stress proteins, anatomical and physiological changes in the coronary arteries, changes in nitric oxide production, adaptational changes in cardiac mitochondria, increased autophagy, and improved function of sarcolemmal and/or mitochondrial ATP-sensitive potassium channels. It is currently unclear which of these protective mechanisms are essential for exercise-induced cardioprotection. However, most investigations focus on sarcolemmal KATP channels, NO production, and mitochondrial changes although it is very likely that other mechanisms may also exist. This paper discusses current information about these aforementioned topics and does not consider potentially important adaptations within blood or the autonomic nervous system. A better understanding of the molecular basis of exercise-induced cardioprotection will help to develop better therapeutic strategies.

Differential effects of hydrogen peroxide and ascorbic acid on the aerobic thermosensitivity of yeast cells grown under aerobic and anoxic conditions

We have previously demonstrated that in aerobically-grown cells of the yeast Saccharomyces cerevisiae, hydrogen peroxide (H(2)O(2)) increases and ascorbic acid decreases cellular thermosensitivity, as determined by the inducibility of a heat shock (HS)-reporter gene. In this work, we reveal that the aerobic thermosensitivity of anaerobically-grown yeast cells also increases in the presence of H(2)O(2), albeit differentially between cells with two different lipid profiles. In comparison to aerobically-grown fermenting cells treated with the same H(2)O(2) concentration, both these types of anaerobically-grown cells were found to be considerably less sensitive to aerobic heat shock and considerably more thermotolerant. Paradoxically, and in contrast to ascorbate-pretreated aerobically-grown yeast cells, when anaerobically-grown cells were heat-shocked aerobically in the presence of the same ascorbic acid concentration, they exhibited increased thermosensitivity and decreased intrinsic thermotolerance with respect to their untreated counterparts. These findings are discussed with respect to what is currently known about the redox and physiological status of yeast cells grown aerobically and cells reoxygenated following anoxic growth.

Transduction of redox signaling by electrophile-protein reactions

Over the last 50 years, the posttranslational modification (PTM) of proteins has emerged as a central mechanism for cells to regulate metabolism, growth, differentiation, cell-cell interactions, and immune responses. By influencing protein structure and function, PTM leads to a multiplication of proteome diversity. Redox-dependent PTMs, mediated by environmental and endogenously generated reactive species, induce cell signaling responses and can have toxic effects in organisms. PTMs induced by the electrophilic by-products of redox reactions most frequently occur at protein thiols; other nucleophilic amino acids serve as less favorable targets. Advances in mass spectrometry and affinity-chemistry strategies have improved the detection of electrophile-induced protein modifications both in vitro and in vivo and have revealed a high degree of amino acid and protein selectivity of electrophilic PTM. The identification of biological targets of electrophiles has motivated further study of the functional impact of various PTM reactions on specific signaling pathways and how this might affect organisms.

Heat shock proteins and exercise: a primer

Heat shock proteins (HSPs) are, in general, prosurvival molecules within the cellular environment, and the overexpression of even just 1 family of HSPs can lead to protection against and improvements after a variety of stressors. Not surprisingly, a fertile area of study has grown out of efforts to exploit the innate biologic behaviour of HSPs. Exercise, because of the inherent physiologic stresses associated with it, is but 1 stimulus that can result in a robust increase in various HSPs in several tissues, not the least of which happen to be the heart and skeletal muscle. The purpose of this review is to introduce the reader to the major HSP families, the control of their expression, and some of their biologic functions, specifically with respect to the influence of exercise. Moreover, as the first in a series of reviews from a common symposium, we will briefly introduce the concepts presented by the other authors, which include the effects of different exercise paradigms on skeletal muscle HSPs in the adult and aged systems, HSPs as regulators of inflammation, and the ion channel stabilizing effects of HSPs.

Increased temperature and protein oxidation lead to HSP72 mRNA and protein accumulation in the in vivo exercised rat heart

Expression of myocardial heat shock protein 72 (HSP72), mediated by its transcription factor, heat shock factor 1 (HSF1), increases following exercise. However, the upstream stimuli governing exercise-induced HSF1 activation and subsequent Hsp72 gene expression in the whole animal remain unclear. Exercise-induced increases in body temperature may promote myocardial radical production, leading to protein oxidation. Conceivably, myocardial protein oxidation during exercise may serve as an important signal to promote nuclear HSF1 migration and activation of Hsp72 expression. Therefore, these experiments tested the hypothesis that prevention of exercise-induced increases in body temperature attenuates cardiac protein oxidation, diminishes HSF1 activation and decreases HSP72 expression in vivo. To test this hypothesis, in vivo exercise-induced changes in body temperature were manipulated by exercising male rats in either cold (4 degrees C) or warm ambient conditions (22 degrees C). Warm exercise increased both body temperature (+3 degrees C) and myocardial protein oxidation, whereas these changes were attenuated by cold exercise. Interestingly, exercise in both conditions did not significantly increase myocardial nuclear localized phosphorylated HSF1. Nonetheless, warm exercise elevated left-ventricular HSP72 mRNA by ninefold and increased myocardial HSP72 protein levels by threefold compared with cold-exercised animals. Collectively, these data indicate that elevated body temperature and myocardial protein oxidation promoted exercise-induced cardiac HSP72 mRNA expression and protein accumulation following in vivo exercise. However, these results suggest that exercise-induced myocardial HSP72 protein accumulation is not a result of nuclear-localized, phosphorylated HSF1, indicating that other transcriptional or post-transcriptional regulatory mechanisms are involved in exercise-induced HSP72 expression.

Exercise, oxidative stress and hormesis

Physical inactivity leads to increased incidence of a variety of diseases and it can be regarded as one of the end points of the exercise-associated hormesis curve. On the other hand, regular exercise, with moderate intensity and duration, has a wide range of beneficial effects on the body including the fact that it improves cardio-vascular function, partly by a nitric oxide-mediated adaptation, and may reduce the incidence of Alzheimer's disease by enhanced concentration of neurotrophins and by the modulation of redox homeostasis. Mechanical damage-mediated adaptation results in increased muscle mass and increased resistance to stressors. Physical inactivity or strenuous exercise bouts increase the risk of infection, while moderate exercise up-regulates the immune system. Single bouts of exercise increases, and regular exercise decreases the oxidative challenge to the body, whereas excessive exercise and overtraining lead to damaging oxidative stress and thus are an indication of the other end point of the hormetic response. Based upon the genetic setup, regular moderate physical exercise/activity provides systemic beneficial effects, including improved physiological function, decreased incidence of disease and a higher quality of life.

Increased temperature, not cardiac load, activates heat shock transcription factor 1 and heat shock protein 72 expression in the heart

The expression of myocardial heat shock protein 72 (HSP72) postexercise is initiated by the activation of heat shock transcription factor 1 (HSF1). However, it remains unknown which physiological stimuli govern myocardial HSF1 activation during exercise. These experiments tested the hypothesis that thermal stress and mechanical load, concomitant with simulated exercise, provide independent stimuli for HSF1 activation and ensuing cardiac HSP72 gene expression. To elucidate the independent roles of increased temperature and cardiac workload in the exercise-mediated upregulation of left-ventricular HSP72, hearts from adult male Sprague-Dawley rats were randomly assigned to one of five simulated exercise conditions. Upon reaching a surgical plane of anesthesia, each experimental heart was isolated and perfused using an in vitro working heart model, while independently varying temperatures (i.e., 37°C vs. 40°C) and cardiac workloads (i.e., low preload and afterload vs. high preload and afterload) to mimic exercise responses. Results indicate that hyperthermia, independent of cardiac workload, promoted an increase in nuclear translocation and phosphorylation of HSF1 compared with normothermic left ventricles. Similarly, hyperthermia, independent of workload, resulted in significant increases in cardiac levels of HSP72 mRNA. Collectively, these data suggest that HSF1 activation and HSP72 gene transcriptional competence during simulated exercise are linked to elevated heart temperature and are not a direct function of increased cardiac workload.

Can the different heat shock response thresholds found in fermenting and respiring yeast cells be attributed to their differential redox states?

In this study we used a heat-shock (HS) reporter gene to demonstrate that respiring cells are intrinsically less sensitive (by 5 degrees C) than their fermenting counterparts to a sublethal heat shock. We also used an oxidant-sensitive fluorescent probe to demonstrate that this correlates with lower levels of sublethal reactive oxygen species (ROS) accumulation in heat-stressed respiring cells. Moreover, this relationship between HS induction of the reporter gene and ROS accumulation extends to respiring cells that have had their ROS levels modified by treatment with the anti-oxidant ascorbic acid and the pro-oxidant H(2)O(2). Thus, by demonstrating that the ROS/HSR correlation previously demonstrated in fermenting cells also holds for respiring cells (despite their greater HS insensitivity and higher level of intrinsic thermotolerance), we provide evidence that the intracellular redox state may influence both the sensitivity of the heat-shock response (HSR) and stress tolerance in the yeast Saccharomyces cerevisiae.

Heat shock response and acute lung injury

All cells respond to stress through the activation of primitive, evolutionarily conserved genetic programs that maintain homeostasis and assure cell survival. Stress adaptation, which is known in the literature by a myriad of terms, including tolerance, desensitization, conditioning, and reprogramming, is a common paradigm found throughout nature, in which a primary exposure of a cell or organism to a stressful stimulus (e.g., heat) results in an adaptive response by which a second exposure to the same stimulus produces a minimal response. More interesting is the phenomenon of cross-tolerance, by which a primary exposure to a stressful stimulus results in an adaptive response whereby the cell or organism is resistant to a subsequent stress that is different from the initial stress (i.e., exposure to heat stress leading to resistance to oxidant stress). The heat shock response is one of the more commonly described examples of stress adaptation and is characterized by the rapid expression of a unique group of proteins collectively known as heat shock proteins (also commonly referred to as stress proteins). The expression of heat shock proteins is well described in both whole lungs and in specific lung cells from a variety of species and in response to a variety of stressors. More importantly, in vitro data, as well as data from various animal models of acute lung injury, demonstrate that heat shock proteins, especially Hsp27, Hsp32, Hsp60, and Hsp70 have an important cytoprotective role during lung inflammation and injury.

Schisandrin B induced antioxidant response is partly mediated by cytochrome P-4502E1 catalyzed reaction in mouse liver

In order to explore the role of cytochrome P-450 (CYP) 2E1 in schisandrin B (Sch B)-induced antioxidant and heat shock responses, the effects of Sch B treatment on hepatic mitochondrial glutathione antioxidant status (mtGAS) and heat shock protein (Hsp)25/70 expression were compared between wild-type and cyp2e1 knock-out C57B/6N mice. Cyp2e1 knock-out mice exhibited a significantly smaller degree of Sch B-induced enhancement in hepatic mtGAS when compared with the wild-type counterpart. But Hsp25/70 expression induced by Sch B was not affected. Sch B-induced enhancement of mtGAS was corroborated by the increase in hepatic mitochondrial antioxidant capacity, as assessed by in vitro measurement of oxidant production, with the enhancing effect being slightly reduced in the knock-out mice. Using liver microsomes prepared from wild-type and knock-out mice as a source of CYP, Sch B was found to be a good co-substrate for the CYP-catalyzed reaction, with the rate of NADPH oxidation observable in microsomes prepared from knock-out mice being slower. The CYP-catalyzed reaction with Sch B was associated with a concomitant production of oxidant species, with the extent of oxidant production being reduced in cyp2e1 knock-out mouse microsomes. Taken together, the results indicate that CYP2E1 is partly responsible for the hepatic metabolism of Sch B that may trigger the antioxidant response in vivo.

Exercise-induced cardioprotection--biochemical, morphological and functional evidence in whole tissue and isolated mitochondria

Myocardial injury is a major contributor to the morbidity and mortality associated with coronary artery disease. Regular exercise has been confirmed as a pragmatic countermeasure to protect against cardiac injury. Specifically, endurance exercise has been proven to provide cardioprotection against cardiac insults in both young and old animals. Proposed mechanisms to explain the cardioprotective effects of exercise are mediated, at least partially, by redox changes and include the induction of myocardial heat shock proteins, improved cardiac antioxidant capacity, and/or elevation of other cardioprotective molecules. Understanding the molecular basis for exercise-induced cardioprotection is important in developing exercise strategies to protect the heart during and after insults. Data suggest that these positive modulator effects occur at different levels of cellular organization, being mitochondria fundamental organelles that are sensitive to disturbances imposed by exercise on basal homeostasis. At present, which of these protective mechanisms is essential for exercise-induced cardioprotection remains unclear. This review analyzes the biochemical, morphological and functional outcomes of acute and chronic exercise on the overall cardiac muscle tissue and in isolated mitochondria. Some redox-based mechanisms behind the cross-tolerance effects particularly induced by endurance training, against certain stressors responsible for the impairments in cardiac homeostasis caused by aging, diabetes, drug administration or ischemia-reperfusion are also outlined. Further work should be addressed in order to clarify the precise regulatory mechanisms by which physical exercise augments heart tolerance against many cardiotoxic agents.

Role of cytochrome P-450 in schisandrin B-induced antioxidant and heat shock responses in mouse liver

In order to explore the role of cytochrome P-450 (P-450) in schisandrin B (Sch B)-induced antioxidant and heat shock responses, the effect of 1-aminobenzotriazole (ABT, a broad spectrum inhibitor of P-450) on hepatic mitochondrial glutathione antioxidant status (mtGAS) and heat shock protein (Hsp)25/70 expression was examined in Sch B-treated mice. The non-specific and partial inhibition of cytochrome P-450 (P-450) by ABT pretreatment significantly caused a protraction in the time-course of Sch B-induced enhancement in hepatic mitGAS and Hsp25/70 expression in mice. Using mouse liver microsomes as a source of P-450, Sch B, but not dimethyl diphenyl bicarboxylate (a non-hepatoprotective analog of Sch B), was found to serve as a co-substrate for the P-450-catalyzed NADPH oxidation reaction, with a concomitant production of oxidant species. Taken together, the results suggest that oxidant species generated from P-450-catalyzed reaction with Sch B may trigger the antioxidant and heat shock responses in mouse liver.