Oxidants differentially regulate the heat shock response

Muscular HSP70 content is higher in elderly compared to young, but is normalized after 12 weeks of strength training

Purpose

Aging is associated with increased myocellular stress and loss of muscle mass and function. Heat shock proteins (HSPs) are upregulated during periods of stress as part of the cells protective system. Exercise can affect both acute HSP regulation and when repeated regularly counteract unhealthy age-related changes in the muscle. Few studies have investigated effects of exercise on HSP content in elderly. The aim of the study was to compare muscular HSP levels in young and elderly and to investigate how training affects HSP content in muscles from aged males and females.

Methods

Thirty-eight elderly were randomized to 12 weeks of strength training (STG), functional strength training (FTG) or a control group (C). To compare elderly to young, 13 untrained young performed 11 weeks of strength training (Y). Muscle biopsies were collected before and after the intervention and analyzed for HSP27, αB-crystallin and HSP70.

Results

Baseline HSP70 were 35% higher in elderly than in young, whereas there were no differences between young and elderly in HSP27 or αB-crystallin. After the training intervention, HSP70 were reduced in STG (− 33 ± 32%; P = 0.001) and FTG (− 28 ± 30%; P = 0.012). The decrease in HSP70 was more pronounced in the oldest. In contrast, Y increased HSP27 (134 ± 1%; P < 0.001) and αB-crystallin (84 ± 94%; P = 0.008).

Conclusion

Twelve weeks of STG or FTG decreased the initial high levels of HSP70 in aged muscles. Thus, regular strength training can normalize some of the increases in cellular stress associated with normal aging, and lead to a healthier cellular environment in aged muscle cells.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-021-04633-4.

Alpha lipoic acid supplementation ameliorates the wrath of simulated tropical heat and humidity stress in male Murrah buffaloes

A supplement which ameliorates temperature-humidity menace in food producing livestock is a prerequisite to develop climate smart agricultural packages. A study was conducted to investigate the heat stress ameliorative efficacy of alpha lipoic acid (ALA) in male Murrah water buffaloes (Bubalus bubalis). Eighteen animals (293.61 ± 4.66Kg Bwt) were randomly allocated into three groups (n = 6); NHSC (non-heat-stressed control), HS (heat-stressed) and HSLA (heat-stressed-supplemented with ALA@32 mg/kg Bwt orally) based on the temperature humidity index (THI) and ALA supplementation. HS and HSLA were exposed to simulated heat challenge in a climatically controlled chamber (40 °C) for 21 consecutive days, 6 h daily. Physiological responses viz. Respiration rate (RR), Pulse rate (PR) and Rectal temperature (RT) were recorded daily before and after heat exposure. Blood samples were collected at the end of heat exposure on days 1, 6, 11, 16, and 21 and on day 28 (7th day post exposure which is considered as recovery) for peripheral blood mononuclear cells (PBMCs) separation, followed by RNA and Protein extraction for Real time quantitative PCR and Western blot analysis respectively, of heat shock proteins (HSPs). Two-way repeated measure ANOVA was performed between groups at different experimental periods. RR (post exposure) in HS and HSLA was significantly higher (P < 0.05) than NHSC from day 1 onwards but HSLA varied significantly from the HS 8th day onwards. Post exposure RT and PR in both HS and HSLA varied (P < 0.05) from NHSC throughout the study; but between HS and HSLA, RT significantly varied on initial 2 days and last 6 days (from days 16 to 21). HSP70 mRNA expression significantly up regulated in high THI groups with respect to the low THI group throughout the experimental period. During chronic stress (days 16 and 21) HSP70 significantly (P < 0.05) increased in HS but not in HSLA (P > 0.05) with respect to NHSC. ALA supplementation up-regulates and sustains (P < 0.05) the expression of HSP90 in HSLA in comparison to the HS and NHSC. HSP105 expression was significantly up-regulated (P < 0.05) in HS on days 16 and 21 (during long-term exposure) but only on day 21 (P < 0.05) in HSLA. HSP70, HSP90, and HSP105 protein expression dynamics were akin to the mRNA transcript data between the study groups. In conclusion, supplementing ALA ameliorates the deleterious effect of heat stress as reflected by improved physiological and cellular responses. ALA supplementation improved cellular antioxidant status and sustained otherwise easily decaying heat shock responses which concertedly hasten the baton change from a limited window of thermo tolerance to long run acclimatization.

Differential correlations between changes to glutathione redox state, protein ubiquitination, and stress-inducible HSPA chaperone expression after different types of oxidative stress

In primary bovine fibroblasts with an hspa1b/luciferase transgene, we examined the intensity of heat-shock response (HSR) following four types of oxidative stress or heat stress (HS), and its putative relationship with changes to different cell parameters, including reactive oxygen species (ROS), the redox status of the key molecules glutathione (GSH), NADP(H) NAD(H), and the post-translational protein modifications carbonylation, S-glutathionylation, and ubiquitination. We determined the sub-lethal condition generating the maximal luciferase activity and inducible HSPA protein level for treatments with hydrogen peroxide (H2O2), UVA-induced oxygen photo-activation, the superoxide-generating agent menadione (MN), and diamide (DA), an electrophilic and sulfhydryl reagent. The level of HSR induced by oxidative stress was the highest after DA and MN, followed by UVA and H2O2 treatments, and was not correlated to the level of ROS production nor to the extent of protein S-glutathionylation or carbonylation observed immediately after stress. We found a correlation following oxidative treatments between HSR and the level of GSH/GSSG immediately after stress, and the increase in protein ubiquitination during the recovery period. Conversely, HS treatment, which led to the highest HSR level, did not generate ROS nor modified or depended on GSH redox state. Furthermore, the level of protein ubiquitination was maximum immediately after HS and lower than after MN and DA treatments thereafter. In these cells, heat-induced HSR was therefore clearly different from oxidative stress-induced HSR, in which conversely early redox changes of the major cellular thiol predicted the level of HSR and polyubiquinated proteins.

Multivariate modeling of proteins related to trapezius myalgia, a comparative study of female cleaners with or without pain

The prevalence of chronic trapezius myalgia is high in women with high exposure to awkward working positions, repetitive movements and movements with high precision demands. The mechanisms behind chronic trapezius myalgia are not fully understood. The purpose of this study was to explore the differences in protein content between healthy and myalgic trapezius muscle using proteomics. Muscle biopsies from 12 female cleaners with work-related trapezius myalgia and 12 pain free female cleaners were obtained from the descending part of the trapezius. Proteins were separated with two-dimensional differential gel electrophoresis (2D-DIGE) and selected proteins were identified with mass spectrometry. In order to discriminate the two groups, quantified proteins were fitted to a multivariate analysis: partial least square discriminate analysis. The model separated 28 unique proteins which were related to glycolysis, the tricaboxylic acid cycle, to the contractile apparatus, the cytoskeleton and to acute response proteins. The results suggest altered metabolism, a higher abundance of proteins related to inflammation in myalgic cleaners compared to healthy, and a possible alteration of the contractile apparatus. This explorative proteomic screening of proteins related to chronic pain in the trapezius muscle provides new important aspects of the pathophysiology behind chronic trapezius myalgia.

Each to their own: skeletal muscles of different function use different biochemical strategies during aestivation at high temperature

Preservation of muscle morphology depends on a continuing regulatory balance between molecules that protect, and molecules that damage, muscle structural integrity. Excessive disruption of the biochemical balance that favours reactive oxygen species (ROS) in disused muscles may lead to oxidative stress; which in turn is associated with increased atrophic or apoptotic signalling and/or oxidative damage to the muscle and thus muscle disuse atrophy. Increases in rate of oxygen consumption likely increase the overall generation of ROS in vivo. Temperature-induced increases in muscle oxygen consumption rate occur in some muscles of ectotherms undergoing prolonged muscular disuse during aestivation. In the green-striped burrowing frog, Cyclorana alboguttata, both large jumping muscles and small non-jumping muscles undergo atrophy seemingly commensurate with their rate of oxygen consumption during aestivation. However, since the extent of atrophy in these muscles is not enhanced at higher temperatures despite a temperature sensitive rate of oxygen consumption in the jumping muscle, we proposed that muscles are protected by biochemical means that when mobilised at higher temperatures inhibit atrophy. We proposed the biochemical response to temperature would be muscle-specific. We examined the effect of temperature on the antioxidant and heat shock protein systems and evidence of oxidative damage to lipids and proteins in two functionally different skeletal muscles, gastrocnemius (jumping muscle) and iliofibularis (non-jumping muscle), by aestivating frogs at 24 and 30oC for six months. We assayed small molecule antioxidant capacity, mitochondrial and cytosolic SOD and Hsp70 to show that protective mechanisms in disused muscles are differentially regulated both with respect to temperature and aestivation. High aestivation temperature results in an antioxidant response in the metabolically temperature-sensitive jumping muscle. We assayed lipid peroxidation and protein oxidation to show that oxidative damage is apparent during aestivation and its pattern is muscle-specific, but unaffected by temperature. Consideration is given to how the complex responses of muscle biochemistry inform of the different strategies muscles may use in regulating their oxidative environment during extended disuse and disuse at high temperature.

Alpha-lipoic acid does not alter stress protein response to acute exercise in diabetic brain

Heat shock proteins (HSPs) are molecular chaperones which may act protective in cerebrovascular insults and peripheral diabetic neuropathy. We hypothesized that alpha-lipoic acid (LA), a natural thiol antioxidant, may enhance brain HSP response in diabetes. Rats with or without streptozotocin-induced diabetes were treated with LA or saline for 8 weeks. Half of the rats were subjected to exhaustive exercise to investigate HSP induction, and the brain tissue was analyzed. Diabetes increased constitutive HSC70 mRNA, and decreased HSP90 and glucose-regulated protein 75 (GRP75) mRNA without affecting protein levels. Exercise increased HSP90 protein and mRNA, and also GRP75 and heme oxygenase-1 (HO-1) mRNA only in non-diabetic animals. LA had no significant effect on brain HSPs, although LA increased HSC70 and HO-1 mRNA in diabetic animals and decreased HSC70 mRNA in non-diabetic animals. Eukaryotic translation elongation factor-2, essential for protein synthesis, was decreased by diabetes and suggesting a mechanism for the impaired HSP response related to translocation of the nascent chain during protein synthesis. LA supplementation does not offset the adverse effects of diabetes on brain HSP mRNA expression. Diabetes may impair HSP translation through elongation factors related to nascent chain translocation and subsequent responses to acute stress.

Multifaceted role of heat shock protein 70 in neurons

Heat shock protein 70 (Hsp70) plays important roles in neural protection from stress by assisting cellular protein folding. In this review we discuss the current understanding of inducible and constitutive Hsp70 in maintaining and protecting neuronal synaptic function under normal and stressed conditions.

Edward F. Adolph Distinguished Lecture: Muscle as an endocrine organ: IL-6 and other myokines

Skeletal muscle is an endocrine organ that produces and releases myokines in response to contraction. Some myokines are likely to work in a hormone-like fashion, exerting specific endocrine effects on other organs such as the liver, the brain, and the fat. Other myokines will work locally via paracrine mechanisms, exerting, e.g., angiogenetic effects, whereas yet other myokines work via autocrine mechanisms and influence signaling pathways involved in fat oxidation and glucose uptake. The finding that muscles produce and release myokines creates a paradigm shift and opens new scientific, technological, and scholarly horizons. This finding represents a breakthrough within integrative physiology and contributes to our understanding of why regular exercise protects against a wide range of chronic diseases. Thus the myokine field provides a conceptual basis for the molecular mechanisms underlying, e.g., muscle-fat, muscle-liver, muscle-pancreas, and muscle-brain cross talk.

Effect of continuous high intensity focused ultrasound in a squamous cell carcinoma tumor model compared to muscle tissue evaluated by MRI, histology, and gene expression

The purpose of this study was to investigate the effect of the continuous mode of high intensity focused ultrasound (HIFU) in a mouse head and neck cancer model (SCCVII) compared to muscle tissue. HIFU was applied to SCCVII tumors and to muscle tissue in C3H/Km mice using a dual ultrasound system (imaging 6 MHz/therapeutic 1 MHz). A continuous HIFU mode (total time 20 sec, intensity 6730.6 W/cm(2)) was applied. Three hours after HIFU treatment pre- and post-contrast T1-wt, T2-wt images, and a diffusion-wt STEAM sequence were obtained. After MR imaging, the animals were euthenized and the treated tumor and muscle tissue was taken out for histology and functional genomic analysis. T2 images showed increased signal intensity, post-contrast T1 showed a decreased contrast uptake in the central parts in the tumor tissue as well as in the muscle tissue. In addition a significant higher diffusion coefficient was found in both tissue types. Histological evaluation (H&E, Immunohistochemistry) of the tumors and the muscle tissue revealed areas of significant necrosis. In the tumor tissue 23 genes were up-regulated (> 2 fold change) and 4 genes were down-regulated (< -2 fold change). In the muscle tissue 29 genes were up-regulated and 17 genes down-regulated. Thirteen genes were up-regulated in both tissue types, 8 genes only in the SCCVII tissue, and 11 genes only in the muscle tissue. The use of HIFU treatment on tumor and muscle tissue results in dramatic changes in gene expression. The expression of some genes are tissue specific, the expression of other genes are independent of the tissue type.

Muscle as an endocrine organ: focus on muscle-derived interleukin-6

Skeletal muscle has recently been identified as an endocrine organ. It has, therefore, been suggested that cytokines and other peptides that are produced, expressed, and released by muscle fibers and exert paracrine, autocrine, or endocrine effects should be classified as "myokines." Recent research demonstrates that skeletal muscles can produce and express cytokines belonging to distinctly different families. However, the first identified and most studied myokine is the gp130 receptor cytokine interleukin-6 (IL-6). IL-6 was discovered as a myokine because of the observation that it increases up to 100-fold in the circulation during physical exercise. Identification of IL-6 production by skeletal muscle during physical activity generated renewed interest in the metabolic role of IL-6 because it created a paradox. On one hand, IL-6 is markedly produced and released in the postexercise period when insulin action is enhanced but, on the other hand, IL-6 has been associated with obesity and reduced insulin action. This review focuses on the myokine IL-6, its regulation by exercise, its signaling pathways in skeletal muscle, and its role in metabolism in both health and disease.

Thermal tolerance of contractile function in oxidative skeletal muscle: no protection by antioxidants and reduced tolerance with eicosanoid enzyme inhibition

Mechanisms for the loss of muscle contractile function in hyperthermia are poorly understood. This study identified the critical temperature, resulting in a loss of contractile function in isolated diaphragm (thermal tolerance), and then tested the hypotheses 1) that increased reactive oxygen species (ROS) production contributes to the loss of contractile function at this temperature, and 2) eicosanoid metabolism plays an important role in preservation of contractile function in hyperthermia. Contractile function and passive force were measured in rat diaphragm bundles during and after 30 min of exposure to 40, 41, 42 or 43 degrees C. Between 40 and 42 degrees C, there were no effects of hyperthermia, but at 43 degrees C, a significant loss of active force and an increase in passive force were observed. Inhibition of ROS with the antioxidants, Tiron or Trolox, did not inhibit the loss of contractile force at 43 degrees C. Furthermore, treatment with dithiothreitol, a thiol (-SH) reducing agent, did not reverse the effects of hyperthermia. A variety of global lipoxygenase (LOX) inhibitors further depressed force during 43 degrees C and caused a significant loss of thermal tolerance at 42 degrees C. Cyclooxygenase (COX) inhibitors also caused a loss of thermal tolerance at 42 degrees C. Blockage of phospholipase with phospholipase A(2) inhibitors, bromoenol lactone or arachidonyltrifluoromethyl ketone failed to significantly prevent the loss of force at 43 degrees C. Overall, these data suggest that ROS do not play an apparent role in the loss of contractile function during severe hyperthermia in diaphragm. However, functional LOX and COX enzyme activities appear to be necessary for maintaining normal force production in hyperthermia.

Comparison of continuous vs. pulsed focused ultrasound in treated muscle tissue as evaluated by magnetic resonance imaging, histological analysis, and microarray analysis

The purpose of this study was to investigate the effect of different application modes of high intensity focused ultrasound (HIFU) to muscle tissue. HIFU was applied to muscle tissue of the flank in C3H/Km mice. Two dose regimes were investigated, a continuous HIFU and a short-pulsed HIFU mode. Three hours after HIFU treatment pre- and post-contrast T1-weighted, T2-weighted images and a diffusion-weighted STEAM sequence were obtained. After MR imaging, the animals were euthanized and the treated, and the non-treated tissue was taken out for histology and functional genomic analysis. T2 images showed increased signal intensity and post-contrast T1 showed a decreased contrast uptake in the central parts throughout the tissue of both HIFU modes. A significantly higher diffusion coefficient was found in the muscle tissue treated with continuous wave focused ultrasound. Gene expression analysis revealed profound changes of 54 genes. For most of the analyzed genes higher expression was found after treatment with the short-pulse mode. The highest up-regulated genes encoded for the MHC class III (FC approximately 84), HSP 70 (FC approximately 75) and FBJ osteosarcoma related oncogene (FC approximately 21). Immunohistology and the immunoblot analysis confirmed the presence of HSP70 protein in both applied HIFU modes. The use of HIFU treatment on muscle tissue results in dramatic changes in gene expression; however, the same genes are up-regulated after the application of continuous or pulsed HIFU, indicating that the tissue reaction is independent of the type of tissue damage.

The influence of antioxidant supplementation on markers of inflammation and the relationship to oxidative stress after exercise

Interest in the relationship between inflammation and oxidative stress has increased dramatically in recent years, not only within the clinical setting but also in the fields of exercise biochemistry and immunology. Inflammation and oxidative stress share a common role in the etiology of a variety of chronic diseases. During exercise, inflammation and oxidative stress are linked via muscle metabolism and muscle damage. Because oxidative stress and inflammation have traditionally been associated with fatigue and impaired recovery from exercise, research has focused on nutritional strategies aimed at reducing these effects. In this review, we have evaluated the findings of studies involving antioxidant supplementation on alterations in markers of inflammation (e.g., cytokines, C-reactive protein and cortisol). This review focuses predominantly on the role of reactive oxygen and nitrogen species generated from muscle metabolism and muscle damage during exercise and on the modulatory effects of antioxidant supplements. Furthermore, we have analyzed the influence of factors such as the dose, timing, supplementation period and bioavailability of antioxidant nutrients.

The time-profile of the PBMC HSP70 response to in vitro heat shock appears temperature-dependent

Heat shock proteins (HSPs) are synthesised by cells subsequent to a stress exposure and are known to confer protection to the cell in response to a second challenge. HSP induction and decay are correlated to thermotolerance and may therefore be used as a biomarker of thermal history. The current study tested the temperature-dependent nature of the heat shock response and characterised its time profile of induction. Whole blood from 6 healthy males (Age: 26 +/- (SD) 2 yrs; Body mass 74.2 +/- 3.8 kgs; VO(2max): 49.1 +/- 4.0 ml.kg(-1).min(-1)) were isolated and exposed to in vitro heat shock (HS) at 37, 38, 39, 40, and 41 degrees C for a period of 90 min. After HS the temperature was returned to 37 degrees C and intracellular HSP70 was quantified from the leukocytes at 0, 2, 4, and 6 h after heat treatment. The concentration of HSP70 was not different between temperatures (P > 0.05), but the time-profile of HSP70 synthesis appeared temperature-dependent. At control (37 degrees C) and lower temperatures (38-39 degrees C) the mean HSP70 concentration increased up to 4 h post HS (P < 0.05) and then returned towards baseline values by 6 h post HS. With in vitro hyperthermic conditions (40-41 degrees C), the time-profile was characterised by a sharp rise in HSP70 levels immediately after treatment (P < 0.05 for 40 degrees C at 0 h), followed by a progressive decline over time. The results suggest a temperature-dependent time-profile of HSP70 synthesis. In addition, the temperature at which HSP70 is inducted might be lower than 37 degrees C.

Extracellular heat shock protein 72 is a marker of the stress protein response in acute lung injury

Previous studies have shown that heat shock protein 72 (Hsp72) is found in the extracellular space (eHsp72) and that eHsp72 has potent immunomodulatory effects. However, whether eHsp72 is present in the distal air spaces and whether eHsp72 could modulate removal of alveolar edema is unknown. The first objective was to determine whether Hsp72 is released within air spaces and whether Hsp72 levels in pulmonary edema fluid would correlate with the capacity of the alveolar epithelium to remove alveolar edema fluid in patients with ALI/ARDS. Patients with hydrostatic edema served as controls. The second objective was to determine whether activation of the stress protein response (SPR) caused the release of Hsp72 into the extracellular space in vivo and in vitro and to determine whether SPR activation and/or eHsp72 itself would prevent the IL-1beta-mediated inhibition of the vectorial fluid transport across alveolar type II cells. We found that eHsp72 was present in plasma and pulmonary edema fluid of ALI patients and that eHsp72 was significantly higher in pulmonary edema fluid from patients with preserved alveolar epithelial fluid clearance. Furthermore, SPR activation in vivo in mice and in vitro in lung endothelial, epithelial, and macrophage cells caused intracellular expression and extracellular release of Hsp72. Finally, SPR activation, but not eHsp72 itself, prevented the decrease in alveolar epithelial ion transport induced by exposure to IL-1beta. Thus SPR may protect the alveolar epithelium against oxidative stress associated with experimental ALI, and eHsp72 may serve as a marker of SPR activation in the distal air spaces of patients with ALI.

Releasing signals, secretory pathways, and immune function of endogenous extracellular heat shock protein 72

Heat shock proteins (Hsp) were first characterized as intracellular proteins, which function to limit protein aggregation, facilitate protein refolding, and chaperone proteins. During times of cellular stress, intracellular Hsp levels increase to provide cellular protection. Recently, it has been recognized that Hsp, particularly Hsp72, are also found extracellularly (eHsp72), where they exhibit potent immunomodulatory effects on innate and acquired immunity. Circulating eHsp72 levels also greatly increase during times of stress (i.e., when an organism is exposed to a physical/psychological stressor or suffers from various pathological conditions). It has been proposed that elevated eHsp72 serves a protective role by facilitating immunological responses during times of increased risk of pathogenic challenge and/or tissue damage. This review focuses on the in vivo releasing signals and immunomodulatory function(s) of endogenous eHsp72. In addition, we present data that emphasize the importance of caution when conducting in vitro immunological tests of Hsp72 function.

Vitamin E isoform-specific inhibition of the exercise-induced heat shock protein 72 expression in humans

Increased levels of reactive oxygen and nitrogen species, as seen in response to exercise, challenge the cellular integrity. Important protective adaptive changes include induction of heat shock proteins (HSPs). We hypothesized that supplementation with antioxidant vitamins C (ascorbic acid) and E (tocopherol) would attenuate the exercise-induced increase of HSP72 in the skeletal muscle and in the circulation. Using randomization, we allocated 21 young men into three groups receiving one of the following oral supplementations: RRR-alpha-tocopherol 400 IU/day + ascorbic acid (AA) 500 mg/day (CEalpha), RRR-alpha-tocopherol 290 IU/day + RRR-gamma-tocopherol 130 IU/day + AA 500 mg/day (CEalphagamma), or placebo (Control). After 28 days of supplementation, the subjects performed 3 h of knee extensor exercise at 50% of the maximal power output. HSP72 mRNA and protein content was determined in muscle biopsies obtained from vastus lateralis at rest (0 h), postexercise (3 h), and after a 3-h recovery (6 h). In addition, blood was sampled for measurements of HSP72, alpha-tocopherol, gamma-tocopherol, AA, and 8-iso-prostaglandin-F2alpha (8-PGF2alpha). Postsupplementation, the groups differed with respect to plasma vitamin levels. The marker of lipid peroxidation, 8-iso-PGF2alpha, increased from 0 h to 3 h in all groups, however, markedly less (P < 0.05) in CEalpha. In Control, skeletal muscle HSP72 mRNA content increased 2.5-fold (P < 0.05) and serum HSP72 protein increased 4-fold (P < 0.05) in response to exercise, whereas a significant increase of skeletal muscle HSP72 protein content was not observed (P = 0.07). In CEalpha, skeletal muscle HSP72 mRNA, HSP72 protein, and serum HSP72 were not different from Control in response to exercise. In contrast, the effect of exercise on skeletal muscle HSP72 mRNA and protein, as well as circulating HSP72, was completely blunted in CEalphagamma. The results indicate that gamma-tocopherol comprises a potent inhibitor of the exercise-induced increase of HSP72 in skeletal muscle as well as in the circulation.

Chronic antioxidant enzyme mimetic treatment differentially modulates hyperthermia-induced liver HSP70 expression with aging

One postulated mechanism for the reduction in stress tolerance with aging is a decline in the regulation of stress-responsive genes, such as inducible heat shock protein 72 (HSP70). Increased levels of oxidative stress are also associated with aging, but it is unclear what impact a prooxidant environment might have on HSP70 gene expression. This study utilized a superoxide dismutase/catalase mimetic (Eukarion-189) to evaluate the impact of a change in redox environment on age-related HSP70 responses to a physiologically relevant heat challenge. Results demonstrate that liver HSP70 mRNA and protein levels are reduced in old compared with young rats at selected time points over a 48-h recovery period following a heat-stress protocol. While chronic systemic administration of Eukarion-189 suppressed hyperthermia-induced liver HSP70 mRNA expression in both age groups, HSP70 protein accumulation was blunted in old rats but not in their young counterparts. These data suggest that a decline in HSP70 mRNA levels may be responsible for the reduction in HSP70 protein observed in old animals after heat stress. Furthermore, improvements in redox status were associated with reduced HSP70 mRNA levels in both young and old rats, but differential effects were manifested on protein expression, suggesting that HSP70 induction is differentially regulated with aging. These findings highlight the integrated mechanisms of stress protein regulation in eukaryotic organisms responding to environmental stress, which likely involve interactions between a wide range of cellular signals.

Heat stress facilitates the recovery of atrophied soleus muscle in rat

Effects of heat stress on the recovery of atrophied soleus muscle were studied in rats. Ten-week-old male Wistar rats were randomly divided into cage control (CC) and 5-day hindlimb suspension group (HS). The half of the rats in group HS was exposed to heat stress (41 degrees C for 60 min) in an incubator immediately after the hindlimb suspension (HS-H) and the other group of rats was not heat stressed (HS-C) prior to 10 days of ambulation recovery. One group of cage control rats (CH) was also exposed to heat similarly. The soleus muscles were dissected at four time points, i.e., immediately after the suspension (or heat stress), and 3, 5, and 10 days after the recovery (n=8 per group at each time point). The absolute wet weight and water and protein content of whole soleus muscle in group HS-C were approximately 36, 27, and 8 mg less than CC (p <0.05). Thus, the percentage contribution of water and protein loss to the decrease in muscle weight was 75 and 22%, respectively. Although water content, as well as muscle weight, was elevated within 3 days, the increase of protein was delayed. Heat exposure prior to recovery accelerated the increase in protein content even in the control group. These phenomena were closely associated with 72-kD heat shock protein (HSP72) content. It is suggested that heat stress applied at the end of hindlimb unloading facilitated the recovery of atrophied soleus muscle of rat, through possibly HSP72-related events of protein metabolism. The data also indicated that the combination of heat and mechanical stress evoked larger and long lasting HSP72 response than does heat or mechanical stress alone.

Overexpression of manganese superoxide dismutase promotes the survival of prostate cancer cells exposed to hyperthermia

It has been hypothesized that exposure of cells to hyperthermia results in an increased flux of reactive oxygen species (ROS), primarily superoxide anion radicals, and that increasing antioxidant enzyme levels will result in protection of cells from the toxicity of these ROS. In this study, the prostate cancer cell line, PC-3, and its manganese superoxide dismutase (MnSOD)-overexpressing clones were subjected to hyperthermia (43 degrees C, 1 h). Increased expression of MnSOD increased the mitochondrial membrane potential (MMP). Hyperthermic exposure of PC-3 cells resulted in increased ROS production, as determined by aconitase inactivation, lipid peroxidation, and H2O2 formation with a reduction in cell survival. In contrast, PC-3 cells overexpressing MnSOD had less ROS production, less lipid peroxidation, and greater cell survival compared to PC-3 Wt cells. Since MnSOD removes superoxide, these results suggest that superoxide free radical or its reaction products are responsible for part of the cytotoxicity associated with hyperthermia and that MnSOD can reduce cellular injury and thereby enhance heat tolerance.

Direct, pleiotropic protective effect of cyclosporin A against simulated ischemia-induced injury in isolated cardiomyocytes

Cyclosporin A is an immunosuppressor that prolongs graft survival but its use is limited by cardiotoxicity. The effects of cyclosporin A on several functional and biological characteristics were thus evaluated in rat cardiomyocytes in normal conditions and in a substrate-free, hypoxia-reoxygenation model of ischemia-reperfusion. Cyclosporin A (100 and 1000 ng/ml) did not induce cardiocytotoxicity in basal conditions. Simulated ischemia gradually decreased and then blocked the spontaneous electromechanical activity. Cyclosporin A at 100 and 1000 ng/ml permitted the maintenance of electromechanical functions that were abolished in control cells. Cyclosporin A also improved the post-"ischemic" functional recovery. Cyclosporin A reduced the "ischemia"-induced lactate dehydrogenase and troponine I releases and the successive rises in heat shock protein mRNA observed after "ischemia" and reoxygenation. Moreover, cyclosporin A improved the resumption of the mitochondrial function. To conclude, cyclosporin A displayed a direct, pleiotropic protection of isolated cardiomyocytes against physiological, metabolic, structural and stress signaling changes induced by ischemia-reperfusion mimicked in vitro.

Heat shock protein 70 gene therapy combined with hyperthermia using magnetic nanoparticles

Heat shock proteins (HSPs) are recognized as significant participants in immune reactions. We previously reported that expression of HSP70 in response to hyperthermia, produced using our original magnetite cationic liposomes (MCLs), induces antitumor immunity. In the present study, we examine whether the antitumor immunity induced by hyperthermia is enhanced by hsp70 gene transfer. A human hsp70 gene mediated by cationic liposomes was injected into a B16 melanoma nodule in C57BL/6 mice in situ. At 24 hours after the injection of the hsp70 gene, MCLs were injected into melanoma nodules in C57BL/6 mice, which were subjected to an alternating magnetic field for 30 minutes. The temperature at the tumor reached 43 degrees C and was maintained by controlling the magnetic field intensity. The combined treatment strongly arrested tumor growth over a 30-day period, and complete regression of tumors was observed in 30% (3/10) of mice. Systemic antitumor immunity was induced in the cured mice. This study demonstrates that this novel therapeutic strategy combining the use of hsp70 gene therapy and hyperthermia using MCLs may be applicable to patients with advanced malignancies.

The Effect of Exercise in Cool, Control and Hot Environments on Cardioprotective HSP70 Induction

A number of environmental and metabolic stimuli rapidly induce the expression of several highly conserved proteins such as heat shock proteins (HSPs) or stress proteins. The purpose of this study was to investigate the effects of a single bout of submaximal exercise in varying ambient temperatures on cardiac and skeletal muscle. Adult male Sprague-Dawley rats were randomly placed in one of three ambient temperature groups; control (23 degrees C), hot (41 degrees C) and cool (11 degrees C). Each exercise bout consisted of treadmill running at 17 m/min and 0% grade. Tissue HSP70 levels for all groups were determined using analysis of variance in two factorial design (2 x 3). Baseline rectal temperature was similar for all three groups. In the control and hot temperature groups, final rectal temperatures differed from the baseline values (p<.05). The rectal temperature from the control/exercise group were 38.5+/-0.3 degrees C at rest and 39.8+/-0.3 degrees C at exhaustion, the hot/exercise group were 38.4+/-0.3 degrees C at rest and 41.2+/-0.9 degrees C at exhaustion and the cool/exercise group were 38.2+/-0.3 degrees C at rest and 38.5+/-0.2 degrees C at exhaustion. The running time was 102.0+/-39.5 min at the control/exercise group, 44.1+/-18.0 min at the hot/exercise group, and 55.4+/-11.9 min at the cool/exercise group. The level of soleus, cardiac and extensor digitorium longus (EDL) HSP70 in cool temperature does not change during a single bout of submaximal exercise. Whereas a single bout of submaximal exercise in hot and control ambient temperatures increases HSP70 accumulation in locomotor muscles, such as the soleus and cardiac, but not in the EDL tissue. This study shows that the changes of HSP70 level induced by a single bout of submaximal exercise at various ambient temperatures (control, hot and cool) depend on the rectal temperature.

Stimulation of glycogen synthesis by heat shock in L6 skeletal-muscle cells: regulatory role of site-specific phosphorylation of glycogen-associated protein phosphatase 1

Recent evidence suggests that glycogen-associated protein phosphatase 1 (PP-1(G)) is essential for basal and exercise-induced glycogen synthesis, which is mediated in part by dephosphorylation and activation of glycogen synthase (GS). In the present study, we examined the potential role of site-specific phosphorylation of PP-1(G) in heat-shock-induced glycogen synthesis. L6 rat skeletal-muscle cells were stably transfected with wild-type PP-1(G) or with PP-1(G) mutants in which site-1 (S1) Ser(48) and site-2 (S2) Ser(67) residues were substituted with Ala. Cells expressing wild-type and PP-1(G) mutants, S1, S2 and S1/S2, were examined for potential alterations in glycogen synthesis after a 60 min heat shock at 45 degrees C, followed by analysis of [(14)C]glucose incorporation into glycogen at 37 degrees C. PP-1(G) S1 mutation caused a 90% increase in glycogen synthesis on heat-shock treatment, whereas the PP-1(G) S2 mutant was not sensitive to heat stress. The S1/S2 double mutant was comparable with wild-type, which showed a 30% increase over basal. Heat-shock-induced glycogen synthesis was accompanied by increased PP-1 and GS activities. The highest activation was observed in S1 mutant. Heat shock also resulted in a rapid and sustained Akt/ glycogen synthase kinase 3 beta (GSK-3 beta) phosphorylation. Wortmannin blocked heat-shock-induced Akt/GSK-3 beta phosphorylation, prevented 2-deoxyglucose uptake and abolished the heat-shock-induced glycogen synthesis. Muscle glycogen levels regulate GS activity and glycogen synthesis and were found to be markedly depleted in S1 mutant on heat-shock treatment, suggesting that PP-1(G) S1 Ser phosphorylation may inhibit glycogen degradation during thermal stimulation, as S1 mutation resulted in excessive glycogen synthesis on heat-shock treatment. In contrast, PP-1(G) S2 Ser phosphorylation may promote glycogen breakdown under stressful conditions. Heat-shock-induced glycogenesis appears to be mediated via phosphoinositide 3-kinase/Akt-dependent GSK-3 beta inactivation as well as phosphoinositide 3-kinase-independent PP-1 activation.

Heat shock proteins: modifying factors in physiological stress responses and acquired thermotolerance

Cells from virtually all organisms respond to a variety of stresses by the rapid synthesis of a highly conserved set of polypeptides termed heat shock proteins (HSPs). The precise functions of HSPs are unknown, but there is considerable evidence that these stress proteins are essential for survival at both normal and elevated temperatures. HSPs also appear to play a critical role in the development of thermotolerance and protection from cellular damage associated with stresses such as ischemia, cytokines, and energy depletion. These observations suggest that HSPs play an important role in both normal cellular homeostasis and the stress response. This mini-review examines recent evidence and hypotheses suggesting that the HSPs may be important modifying factors in cellular responses to a variety of physiologically relevant conditions such as hyperthermia, exercise, oxidative stress, metabolic challenge, and aging.

HSP72 gene expression progressively increases in human skeletal muscle during prolonged, exhaustive exercise

To examine the effect of exercise on heat shock protein (HSP) 72 mRNA expression in skeletal muscle, five healthy humans (20 +/- 1 yr; 64 +/- 3 kg; peak O(2) uptake of 2.55 +/- 0.2 l/min) cycled until exhaustion at a workload corresponding to 63% peak O(2) uptake. Muscle was sampled from the vastus lateralis, and muscle temperature was measured at rest (R), 10 min of exercise (Min10), approximately 40 min before fatigue (F-40 = 144 +/- 7 min), and fatigue (F = 186 +/- 15 min). Muscle samples were analyzed for HSP72 mRNA expression, as well as glycogen and lactate concentration. Muscle temperature increased (P < 0.05) during the first 10 min of exercise but then remained constant for the duration of the exercise. Similarly, lactate concentration increased (P < 0.05) when Min10 was compared with R but decreased (P < 0.05) thereafter, such that concentrations at F-40 and F were not different from those at R. In contrast, muscle glycogen concentration fell progressively throughout exercise (486 +/- 74 vs. 25 +/- 7 mmol/kg dry weight for R and F, respectively; P < 0.05). HSP72 mRNA was detected at R but did not increase by Min10. However, HSP72 mRNA increased (P < 0.05) 2.2 +/- 0.5- and 2.6 +/- 0.9-fold, respectively, when F-40 and F were compared with R. These data demonstrate that HSP72 mRNA increases progressively during acute cycling, suggesting that processes that take place throughout concentric exercise are capable of initiating a stress response.

Lens-specific regulation of the thioredoxin-1 gene, but not thioredoxin-2, upon in vivo photochemical oxidative stress in the Emory mouse

Thioredoxin (TRX)-1 and TRX-2 redox-regulatory genes were analyzed in the lens and some other tissues of the Emory mouse, a model for age-related human cataract. The cDNA transcripts of mRNAs encoding TRX-1 and TRX-2 genes were isolated and cloned by RT-PCR from the lens, liver, kidney, and tail, and the cDNA sequences were similar to the reported sequences of murine TRX-1 and TRX-2 genes. In vivo photochemical oxidative stress to the Emory mice resulted in fivefold upregulation of the lens TRX-1 gene at 3 weeks and declined thereafter. Western blot analysis revealed a fourfold increase of TRX-1 protein in the lens at 3 weeks after oxidative stress. The TRX-2 gene in the lens was not changed up to 5 weeks and decreased by 50% thereafter. However, the expressions of these genes in the liver, kidney, and tail were not changed. Fluorescent light or riboflavin alone did not affect the expressions of TRX-1 and TRX-2 genes in the lens. Thus, we show the expressions of TRX-1 and TRX-2 genes in the lens, liver, kidney, and tail and lens-specific upregulation of the TRX-1 gene and protein expressions, possibly as a protective response to the altered redox state of the lens after in vivo oxidative stress to the Emory mouse.