Differential responses of HSPs to heat stress in slow and fast regions of rat gastrocnemius muscle

Effects of preconditioning with heat stress on acute exercise-induced intracellular signaling in male rat gastrocnemius muscle

Heat stress (HS) induces Akt/mTOR phosphorylation and FoxO3a signaling; however, whether a prior increase in heat shock protein 72 (HSP72) expression affects intracellular signaling following eccentric exercise remains unclear. We analyzed the effects of HS pretreatment on intramuscular signaling in response to acute exercise in 10-week-old male Wistar rats (n = 24). One leg of each rat was exposed to HS and the other served as an internal control (CT). Post-HS, rats were either rested or subjected to downhill treadmill running. Intramuscular signaling responses in the red and white regions of the gastrocnemius muscle were analyzed before, immediately after, or 1 h after exercise (n = 8/group). HS significantly increased HSP72 levels in both deep red and superficial white regions. Although HS did not affect exercise-induced mTOR signaling (S6K1/ERK) responses in the red region, mTOR phosphorylation in the white region was significantly higher in CT legs than in HS legs after exercise. Thr308 phosphorylation of Akt showed region-specific alteration with a decrease in the red region and an increase in the white region immediately after downhill running. Overall, a prior increase in HSP72 expression elicits fiber type-specific changes in exercise-induced Akt and mTOR phosphorylation in rat gastrocnemius muscle.

Pre-heating stress associated with acute oral leucine supplementation effects in rat gastrocnemius muscle: Implications for protein synthesis signaling pathways

Skeletal muscle is a highly plastic tissue. The role of heat shock protein 72 (Hsp72) in heat stress-induced skeletal muscle hypertrophy has been well demonstrated; however, the precise mechanisms remain unclear. Essential amino acids, such as leucine, mainly mediate muscle protein synthesis. We investigated the effects of pre-heating and increased Hsp72 expression on the mechanistic target of rapamycin (mTOR) signaling and protein synthesis following leucine administration in rat gastrocnemius muscle. To ensure increased Hsp72 expression in both the red and white portions of the muscle, one leg of male Wistar rats (10-week-old, n = 23) was heat-stressed in 43 °C water for 30 min twice at a 48-h-interval (heat-stressed leg, HS leg). The contralateral leg served as a non-heated internal control (CT leg). After the recovery period (48 h), rats were divided into the pre-administration or oral leucine administration groups. We harvested the gastrocnemius muscle (red and white parts) prior to administration and 30 and 90 min after leucine treatment (n = 7-8 per group) and intramuscular signaling responses to leucine ingestion were determined using western blotting. Heat stress significantly upregulated the expression of Hsp72 and was not altered by leucine administration. Although the phosphorylation levels of mTOR/S6K1 and ERK were similar regardless of heating, 4E-BP1 was less phosphorylated in the HS legs than the CT legs after leucine administration in the red portion of the muscles (P < 0.05). Moreover, c-Myc expression differed significantly after leucine administration in both the red and white portions of the muscles. Our findings indicate that following oral leucine administration, pre-heating partially blunted the muscle protein synthesis signaling response in the rat gastrocnemius muscle.

The impact of Zearalenone on heat-stressed skeletal muscle in pigs

Heat stress (HS) and Zearalenone (ZEN) exposure affect growth, production efficiency, and animal welfare; and, under extreme situations, both can be lethal. Given that both HS and ZEN independently cause oxidative stress, we hypothesized that simultaneous exposure to HS and ZEN would cause greater oxidative stress in porcine skeletal muscle than either condition, alone. To address this hypothesis, crossbred, prepubertal gilts were treated with either vehicle control (cookie dough) or ZEN (40 μg/kg) and exposed to either thermoneutral (TN; 21.0 °C) or 12-h diurnal HS conditions (night: 32.2 °C; day: 35.0 °C) for 7 d. Pigs were euthanized immediately following the environmental challenge and the glycolytic (STW) and oxidative (STR) portions of the semitendinosus muscle were collected for analysis. In STR, malondialdehyde (MDA) concentration, a marker of oxidative stress, tended to increase following ZEN exposure (P = 0.08). HS increased CAT (P = 0.019) and SOD1 (P = 0.049) protein abundance, while ZEN decreased GPX1 protein abundance (P = 0.064) and activity (P = 0.036). In STR, HS did not alter protein expression of HSP27, HSP70, or HSP90. Conversely, in STW, MDA-modified proteins remained similar between all groups. Consistent with STR, ZEN decreased GPX1 (P = 0.046) protein abundance in STW. In STW, ZEN decreased protein abundance of HSP27 (P = 0.032) and pHSP27 (P = 0.0068), while HS increased protein expression of HSP70 (P = 0.04) and HSP90 (P = 0.041). These data suggest a muscle fiber type-specific response to HS or ZEN exposure, potentially rendering STR more susceptible to HS- and/or ZEN-induced oxidative stress, however, the combination of HS and ZEN did not augment oxidative stress.

Impact of Heatwaves on the Physiology and Retail Meat Quality of Lambs

The experiment investigated the impact of heatwaves (HWs) on the physiology, postmortem muscle metabolism and meat quality of lambs. Seventy-two second-cross lambs (Poll Dorset × (Border Leicester × Merino)) were selected and exposed to either 1, 3 or 5 days of HWs or thermoneutal (TN) (28–38 °C and 40–60% relative humidity, RH; 18–21 °C, 40–55% RH) conditions in climate-controlled chambers. Lambs exposed to 1–5 days of a HW exhibited higher respiration rates (RRs), rectal temperatures (RTs), skin temperatures (STs) and heart rates (HRs) compared to lambs exposed to an equal duration of TN conditions. However, HWs had no significant effects on muscle metabolism (rate and extent of pH decline, muscle glycogen and lactate content) and meat quality (cooking loss and shear force). Similarly, there were limited impacts of 1–5 days of HW on the colour (L*, a*, b* and R630/580) and drip loss of the longissimus thoracis et lumborum (LTL) and semimembranosus (SM) muscles for 4 days’ overwrap retail display. Results suggest that short-duration HWs (1–5 days) had significant negative effects on animal physiology but had no effect on the muscle metabolism and meat quality.

Impact of successive exertional heat injuries on thermoregulatory and systemic inflammatory responses in mice

The purpose of the study was to determine if repeated exertional heat injuries (EHIs) worsen the inflammatory response. We assessed the impact of a single EHI bout (EHI0) or two separate EHI episodes separated by 1 (EHI1), 3 (EHI3), and 7 (EHI7) days in male C57BL/6J mice (n = 236). To induce EHI, mice underwent a forced running protocol until loss of consciousness or core temperature reached ≥ 42.7°C. Blood and tissue samples were obtained 30 min, 3 h, 1 day, or 7 days after the EHI. We observed that mice undergoing repeated EHI (EHI1, EHI3, and EHI7) had longer running distances before collapse (∼528 m), tolerated higher core temperatures (∼0.18°C higher) before collapse, and had higher minimum core temperature (indicative of injury severity) during recovery relative to EHI0 group (∼2.18°C higher; all P < 0.05). Heat resilience was most pronounced when latency was shortest between EHI episodes (i.e., thermal load and running duration highest in EHI1), suggesting the response diminishes with longer recoveries between EHI events. Furthermore, mice experiencing a second EHI exhibited increased serum and liver HSP70, and lower corticosterone, FABP2, MIP-1β, MIP-2, and IP-10 relative to mice experiencing a single EHI typically at 30 min to 3 h after EHI. Our findings indicate that an EHI event may initiate some adaptive processes that provide acute heat resilience to subsequent EHI conditions. NEW & NOTEWORTHY Mice undergoing repeated exertional heat injuries, within 1 wk of an initial heat injury, appear to have some protective adaptations. During the second exertional heat injury, mice were able to run longer and sustain higher body temperatures before collapse. Despite this, the mice undergoing a second exertional heat injury were more resilient to the heat as evidenced by attenuated minimum body temperature, higher HPS70 (serum and liver), lower corticosterone, and lower FABP2.

Heat therapy: mechanistic underpinnings and applications to cardiovascular health

Cardiovascular diseases (CVD) are the leading cause of death worldwide, and novel therapies are drastically needed to prevent or delay the onset of CVD to reduce the societal and healthcare burdens associated with these chronic diseases. One such therapy is "heat therapy," or chronic, repeated use of hot baths or saunas. Although using heat exposure to improve health is not a new concept, it has received renewed attention in recent years as a growing number of studies have demonstrated robust and widespread beneficial effects of heat therapy on cardiovascular health. Here, we review the existing literature, with particular focus on the molecular mechanisms that underscore the cardiovascular benefits of this practice.

Oral glutamine supplementation attenuates inflammation and oxidative stress-mediated skeletal muscle protein content degradation in immobilized rats: Role of 70 kDa heat shock protein

Skeletal muscle disuse results in myofibrillar atrophy and protein degradation, via inflammatory and oxidative stress-mediated NF-kB signaling pathway activation. Nutritional interventions, such as l-glutamine (GLN) supplementation have shown antioxidant properties and cytoprotective effects through the modulation on the 70-kDa heat shock protein (HSP70) expression. However, these GLN-mediated effects on cell signaling pathways and biochemical mechanisms that control the myofibrillar protein content degradation in muscle disuse situations are poorly known yet. This study investigated the effects of oral GLN plus l-alanine (ALA; GLN ​+ ​ALA-solution) supplementation, either in their free or dipeptide (L-alanyl-l-glutamine-DIP) form, on GLN-glutathione (GSH) axis and cytoprotection mediated by HSP70 protein expression in the slow-twitch soleus and fast-twitch gastrocnemius skeletal muscle of rats submitted to 14-days of hindlimb immobilization-induced disuse muscle atrophy. Forty-eight Wistar rats were distributed into 6 groups: hindlimb immobilized (IMOB group) and hindlimb immobilized orally supplemented with either GLN (1 g kg^-1) plus ALA (0.61 g kg^-1) ​(GLN ​+ ​ALA-IMOB group) or 1.49 ​g ​kg^-1 of DIP (DIP-IMOB group) and; no-immobilized (CTRL) and no-immobilized supplemented GLN ​+ ​ALA and DIP baselines groups. All animals, including CTRL and IMOB rats (water), were supplemented via intragastric gavage for 14 days, concomitantly to immobilization period. Plasma and muscle GLN levels, lipid (thiobarbituric acid reactive substances-TBARS) and protein (carbonyl) peroxidation, erythrocyte concentration of reduced GSH and GSH disulfide (GSSG), plasma and muscle pro-inflammatory TNF-α levels, muscle IKKα/β-NF-kB signaling pathway and, the myofibrillar protein content (MPC) were measured. The MPC was significantly lower in IMOB rats, compared to CTRL, GLN ​+ ​ALA, and DIP animals (p ​< ​0.05). This finding was associated with reduced plasma and muscle GLN concentration, equally in IMOB animals. Conversely, both GLN ​+ ​ALA and DIP supplementation restored plasma and muscle GLN levels, which equilibrated GSH and intracellular redox status (GSSG/GSH ratio) in erythrocytes and skeletal muscle even as, increased muscle HSP70 protein expression; attenuating oxidative stress and TNF-α-mediated NF-kB pathway activation, fact that reverberated on reduction of MPC degradation in GLN ​+ ​ALA-IMOB and DIP-IMOB animals (p ​< ​0.05). In conclusion, the findings shown herein support the oral GLN ​+ ​ALA and DIP supplementations as a therapeutic and effective nutritional alternative to attenuate the deleterious effects of the skeletal muscle protein degradation induced by muscle disuse.

Heat therapy improves soleus muscle force in a model of ischemia-induced muscle damage

Leg muscle ischemia in patients with peripheral artery disease (PAD) leads to alterations in skeletal muscle morphology and reduced leg strength. We tested the hypothesis that exposure to heat therapy (HT) would improve skeletal muscle function in a mouse model of ischemia-induced muscle damage. Male 42-wk-old C57Bl/6 mice underwent ligation of the femoral artery and were randomly assigned to receive HT (immersion in a water bath at 37°C, 39°C, or 41°C for 30 min) or a control intervention for 3 wk. At the end of the treatment, the animals were anesthetized and the soleus and extensor digitorum longus (EDL) muscles were harvested for the assessment of contractile function and examination of muscle morphology. A subset of animals was used to examine the impact of a single HT session on the expression of genes involved in myogenesis and the regulation of muscle mass. Relative soleus muscle mass was significantly higher in animals exposed to HT at 39°C compared with the control group (control: 0.36 ± 0.01 mg/g versus 39°C: 0.40 ± 0.01 mg/g, P = 0.024). Maximal absolute force of the soleus was also significantly higher in animals treated with HT at 37°C and 39°C (control: 274.7 ± 6.6 mN; 37°C: 300.1 ± 7.7 mN; 39°C: 299.5 ± 10 mN, P < 0.05). In the soleus, but not the EDL muscle, a single session of HT enhanced the mRNA expression of myogenic factors as well as of both positive and negative regulators of muscle mass. These findings suggest that the beneficial effects of HT are muscle specific and dependent on the treatment temperature in a model of PAD. NEW & NOTEWORTHY This is the first study to comprehensively examine the impact of temperature and muscle fiber type composition on the adaptations to repeated heat stress in a model of ischemia-induced muscle damage. Exposure to heat therapy (HT) at 37°C and 39°C, but not at 41°C, improved force development of the isolated soleus muscle. These results suggest that HT may be a practical therapeutic tool to restore muscle mass and strength in patients with peripheral artery disease.

The influence of aging on the effectiveness of heat stress in preventing disuse muscle atrophy

This study examined the aging effect on disuse muscle atrophy prevention using heat stress. Wistar rats aged 7 and 60 weeks were divided into three groups as follows: control, immobilized (Im), and immobilized and heat stressed (ImH). Heat stress was given by immersing the hindlimbs in hot water (42 °C) for 60 min, once in every 3 days and the gastrocnemius (GAS) and soleus (SOL) muscles were extracted after 14 days. Muscle-fiber types were classified using ATPase staining. Heat shock protein 70 (HSP70) was assessed through Western blotting. In GAS muscle of both groups and SOL muscle of 7-week-old rats, the fiber diameter of each muscle type in the ImH group significantly increased compared with that in the Im group. However, this could not be observed in the SOL muscle of the 60-week-old rats. The increased percentage of type-I fibers and variability of types I and II muscle-fiber diameter were evident in the SOL muscle of the 60-week rats. HSP70 was significantly elevated in the ImH group compared with in the Im group in both muscle types of both age groups. Thus, effectiveness of heat stress in the prevention of disuse muscle atrophy appears unsatisfactory in aging muscle fibers.

Heat stress-induced phosphorylation of FoxO3a signalling in rat skeletal muscle

AIM

A recent study demonstrated that FoxO3a was directly induced by the overexpression of Hsp72 in rat soleus muscle. However, whether heat stress treatment induces FoxO3a phosphorylation in rat skeletal muscle remains unclear. This study examined the effects of heat stress on the regulation of the FoxO3a signalling pathway in rat skeletal muscle.

METHODS

Thirty-two male Wistar rats (15 weeks old) were randomly assigned into two groups; sedentary control group (Sed, n = 8) and experimental group (n = 24). After an overnight fast, one leg of each rat (HS leg) in the experimental group was immersed in hot water (43 °C) for 30 min, and the soleus and plantaris muscles in both legs were removed immediately (0 min), 30 min, 60 min, or 24 h after the heat stress (n = 6 each group). The contralateral, non-heated leg in the experimental group served as an internal control (CT leg).

RESULTS

Heat stress treatment resulted in a significant increase in FoxO3a phosphorylation (Ser253) in the soleus and plantaris muscles of heat-stressed legs after 24 h. Hsp72 expression in heat-stressed legs was significantly higher at 60 min and 24 h in these muscles. Activation of the PTEN/Akt and MEK/ERK pathways was also observed in these muscles immediately after stress, but not at 24 h. There were no differences in FoxO1 and AMPKα phosphorylation in either muscle.

CONCLUSION

Heat stress in rat skeletal muscle induces phosphorylation of FoxO3a signalling, and it may be related to Hsp72 upregulation, and the activation of the PTEN/Akt and MEK/ERK pathways.

Effects of static interventions on disuse atrophy of the rat soleus muscle at different sites along its longitudinal axis

[Purpose] The purpose of our study was to verify the inhibitory effects of static intervention (heat load and muscle stretching) on disuse-related adaptation changes in the soleus muscle and to compare these effects across different sites along its longitudinal axis. [Subjects] Forty 8-week-old male Wistar rats. [Methods] The effects of heat load and/or muscle stretching in the rat soleus during hindlimb suspension were evaluated by measuring the cross-sectional area of the muscle fibers, succinate dehydrogenase activity, and number of capillaries in the proximal, middle, and distal regions. [Results] With no intervention the proximal region showed the highest reduction in the cross-sectional area, whereas the distal region showed the highest reduction in succinate dehydrogenase activity and the number of capillaries due to hindlimb suspension. These differences between the proximal and distal regions decreased with both interventions, and the effects were most pronounced with a combination of heat load and muscle stretching. [Conclusion] Differences in the muscle structure between the proximal and distal regions increased due to hindlimb suspension, and this heterogeneity associated with muscle disuse was inhibited by static intervention including heat load and muscle stretching. Furthermore, the combination of heat load and muscle stretching most reduced the heterogeneity.

Heat stress protects against mechanical ventilation-induced diaphragmatic atrophy

Mechanical ventilation (MV) is a life-saving intervention in patients who are incapable of maintaining adequate pulmonary gas exchange due to respiratory failure or other disorders. However, prolonged MV is associated with the development of respiratory muscle weakness. We hypothesized that a single exposure to whole body heat stress would increase diaphragm expression of heat shock protein 72 (HSP72) and that this treatment would protect against MV-induced diaphragmatic atrophy. Adult male Wistar rats (n = 38) were randomly assigned to one of four groups: an acutely anesthetized control group (CON) with no MV; 12-h controlled MV group (CMV); 1-h whole body heat stress (HS); or 1-h whole body heat stress 24 h prior to 12-h controlled MV (HSMV). Compared with CON animals, diaphragmatic HSP72 expression increased significantly in the HS and HSMV groups (P < 0.05). Prolonged MV resulted in significant atrophy of type I, type IIa, and type IIx fibers in the costal diaphragm (P < 0.05). Whole body heat stress attenuated this effect. In contrast, heat stress did not protect against MV-induced diaphragm contractile dysfunction. The mechanisms responsible for this heat stress-induced protection remain unclear but may be linked to increased expression of HSP72 in the diaphragm.

Intramuscular heating through fluidotherapy and heat shock protein response

CONTEXT

Therapeutic modalities that can increase intramuscular temperature commonly are used to treat injuries in the clinical setting. Researchers recently have suggested that the physiologic changes occurring during an increase in temperature also could provide a cytoprotective effect for exercise-induced muscle damage.

OBJECTIVE(S)

To determine if the Fluidotherapy treatment increases the inducible expression of heat shock protein (HSP), to identify the rate of heating that occurs in the lower extremity with Fluidotherapy treatment, and to evaluate the relationship between the inducible expression of HSP and temperature.

DESIGN

Controlled laboratory study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Six male (age = 21.67 ± 1.63 years, height = 180.09 ± 4.83 cm, mass = 87.60 ± 10.51 kg) and 6 female (age = 24.60 ± 4.59 years, height = 151.05 ± 35.76 cm, mass = 55.59 ± 14.58 kg) college-aged students.

INTERVENTION(S)

One lower extremity was randomly selected to receive the heat treatment, and the other extremity received no treatment.

MAIN OUTCOME MEASURE(S)

We measured intramuscular temperature every 10 minutes, determining peak intramuscular temperature by 2 identical sequential measurements, and we analyzed the time to peak temperature. We analyzed the amount of HSP70 expression and HSP27P:T (ratio of HSP27 to the total HSP27 expression) in the gastrocnemius and soleus muscles and measured baseline skinfold thickness and estradiol levels.

RESULTS

Fluidotherapy increased intramuscular temperature by 5.66 ± 0.78°C (t11 = 25.67, P < .001) compared with baseline temperature, with a peak temperature of 39.08°C ± 0.39°C occurring at 84.17 ± 6.69 minutes. We did not find a heat treatment effect for HSP70 or HSP27P:T in the gastrocnemius or soleus muscles (P > .05). Peak temperature and the percentage change of HSP70 were positively correlated for the gastrocnemius and soleus muscles (P < .05). We found no other correlations for skinfold thickness, sex, or estradiol levels (P > .05). No effect of sex for skinfold thickness or estradiol levels at baseline was discovered (P > .05).

CONCLUSIONS

This Fluidotherapy protocol increased the intramuscular temperature to a therapeutic level; however, it did not stimulate inducible HSP70 or HSP27P:T in the soleus and gastrocnemius muscles regardless of sex or skinfold thickness. These data confirmed that Fluidotherapy is an effective heating modality but suggested it is not an effective method for stimulating an HSP response in the lower limb.

Heat stress enhances mTOR signaling after resistance exercise in human skeletal muscle

This study investigated the effect of heat stress (HS) on mammalian target of rapamycin (mTOR) signaling involved in translation initiation after resistance exercise in human skeletal muscle. Eight young male subjects performed four sets of six maximal repetitions of knee extension exercises, with or without HS, in a randomized crossover design. HS was applied to the belly of the vastus lateralis by using a microwave therapy unit prior to and during exercise. Muscle biopsies were taken from the vastus lateralis before, immediately after, and 1 h after exercise. HS significantly increased the phosphorylation of Akt/PKB, mTOR, and ribosomal protein S6 at 1 h after exercise (P < 0.05), and the 4E-BP1 phosphorylation level, which had initially decreased with exercise, had recovered by 1 h after exercise with HS. In addition, the phosphorylation of ribosomal S6 kinase 1 was significantly increased immediately after exercise with HS (P < 0.05). These results indicate that HS enhances mTOR signaling after resistance exercise in human skeletal muscle.

Heat shock proteins (chaperones) in fish and shellfish and their potential role in relation to fish health: a review

Heat shock proteins (HSPs), also known as stress proteins and extrinsic chaperones, are a suite of highly conserved proteins of varying molecular weight (c. 16-100 kDa) produced in all cellular organisms when they are exposed to stress. They develop following up-regulation of specific genes, whose transcription is mediated by the interaction of heat shock factors with heat shock elements in gene promoter regions. HSPs function as helper molecules or chaperones for all protein and lipid metabolic activities of the cell, and it is now recognized that the up-regulation in response to stress is universal to all cells and not restricted to heat stress. Thus, other stressors such as anoxia, ischaemia, toxins, protein degradation, hypoxia, acidosis and microbial damage will also lead to their up-regulation. They play a fundamental role in the regulation of normal protein synthesis within the cell. HSP families, such as HSP90 and HSP70, are critical to the folding and assembly of other cellular proteins and are also involved in regulation of kinetic partitioning between folding, translocation and aggregation within the cell. HSPs also have a wider role in relation to the function of the immune system, apoptosis and various facets of the inflammatory process. In aquatic animals, they have been shown to play an important role in health, in relation to the host response to environmental pollutants, to food toxins and in particular in the development of inflammation and the specific and non-specific immune responses to bacterial and viral infections in both finfish and shrimp. With the recent development of non-traumatic methods for enhancing HSP levels in fish and shrimp populations via heat, via provision of exogenous HSPs or by oral or water administration of HSP stimulants, they have also, in addition to the health effects, been demonstrated to be valuable in contributing to reducing trauma and physical stress in relation to husbandry events such as transportation and vaccination.

Skeletal Muscle for Endomyocardial Biopsy: Comparable Stress Response in Doxorubicin Cardio-myopathy

In the present study, we compared the cell damage response in skeletal and cardiac muscle tissue when exposed to doxorubicin. This was carried out by means of a less invasive informative substitute to endomyocardiac biopsy based on Hsp70 immunodetection and a subcellular analysis of the nucleolus. Male Sprague Dawley rats (62 g body weight) were randomly distributed into 3 group, the control and doxorubicin I and doxorubicin II groups, in which 15 and 25 mg/kg body weight of doxorubicin (0.1 ml, i.v.) was administered, respectively. After 15, 30, 45 and 60 minutes, portions of the left and right ventricle wall and interventricle wall, together with skeletal muscle from the posterior and anterior member, were prepared for Hsp70 immunodetection by Western blot analysis and ultrastructural study using the thin cut technique. Differential cell response between the control and treated groups was observed in Hsp70 immunodetection and at the subcellular level. In the control group, the Hsp70 recognition levels and typical normal nucleolar morphology were similar, while the treated groups showed variable-dependent Hsp70 recognition and segregation of nucleolar components, forming ring-like figures of a variable-independent nature. Comparison of cardiac and skeletal muscle tissue cell response to doxorubicin toxic aggression revealed parallelism in terms of Hsp70 accumulation in certain regions of both tissues (15 mg/kg body weight of doxorubicin), which suggests that replacing endomyocardiac biopsy analysis with skeletal muscle analysis may be a safe option.

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.

Heat shock protein accumulation and heat shock transcription factor activation in rat skeletal muscle during compensatory hypertrophy

AIM

To assess the stress/heat shock protein (HSP) and heat shock factor activation response in overloaded (hypertrophied) plantaris muscles.

METHODS

Male Sprague-Dawley rats (n = 5 per time point) underwent unilateral removal of the left gastrocnemius muscle. After 1, 2, 3, 5, 7, 14 and 28 days, plantaris muscles were removed, weighted rapidly frozen in liquid nitrogen. Total protein content was determined and HSP 25 and HSP 72 contents were assessed by Western blotting. Heat shock transcription factor (HSF) activation was assessed by electrophoretic mobility shift assay (EMSA).

RESULTS

While plantaris muscle mass was significantly increased 3 days after the imposition of overload and remained elevated thereafter confirming muscle hypertrophy, muscle protein content was not increased until 7 days after the imposition of overload. HSP 72 content was significantly increased at 3 days, while HSP 25 content was not significantly increased until 7 days after synergistic muscle removal. HSF activation was detected at 1, 2 and 3 days of overload but undetectable thereafter. The addition of HSF1- and HSF2-specific antibodies to extracts prior to EMSA failed to supershift the HSF-heat shock element complex.

CONCLUSION

The temporal pattern of both HSF activation and HSP expression in skeletal muscle undergoing hypertrophy suggests the increased level of the observed HSPs may be both a consequence of both the immediate stress of overload and the hypertrophic process. The inability of HSF1- and HSF2-specific antibodies to cause supershifts suggests the HSF detected during overload may not be HSF1 or HSF2.

Elevated core and muscle temperature to levels comparable to exercise do not increase heat shock protein content of skeletal muscle of physically active men

AIM

Exercise-associated hyperthermia is routinely cited as the signal responsible for inducing an increased production of heat shock proteins (HSPs) following exercise. This hypothesis, however, has not been tested in human skeletal muscle. The aim of the present study was to therefore investigate the role of increased muscle and core temperature in contributing to the exercise-induced production of the major HSP families in human skeletal muscle.

METHODS

Seven physically active males underwent a passive heating protocol of 1 h duration during which the temperature of the core and vastus lateralis muscle were increased to similar levels to those typically occurring during moderately demanding aerobic exercise protocols. One limb was immersed in a tank containing water maintained at approximately 45 degrees C whilst the contra-lateral limb remained outside the tank and was not exposed to heat stress. Muscle biopsies were obtained from the vastus lateralis of both legs immediately prior to and at 48 h and 7 days post-heating.

RESULTS

The heating protocol induced significant increases (P < 0.05) in rectal (1.5 +/- 0.2 degrees C) and muscle temperature of the heated leg (3.6 +/- 0.5 degrees C). Muscle temperature of the non-heated limb showed no significant change (P > 0.05) following heating (pre: 36.1 +/- 0.5, post: 35.7 +/- 0.2 degrees C). Heating failed to induce a significant increase (P > 0.05) in muscle content of HSP70, HSC70, HSP60, HSP27, alphaB-crystallin, MnSOD protein content or in the activity of superoxide dismutase and catalase.

CONCLUSIONS

These data demonstrate that increases in both systemic and local muscle temperature per se do not appear to mediate the exercise-induced production of HSPs in human skeletal muscle and suggest that non-heat stress factors associated with contractile activity are of more importance in mediating this response.

Age-related alterations in expression of apoptosis regulatory proteins and heat shock proteins in rat skeletal muscle

Aging of skeletal muscle is often accompanied by muscle atrophy and it appears that apoptosis plays an important role in this process. The detailed mechanism(s) is not completely understood, however. In this study, we examined expression of the apoptosis regulatory proteins as well as the heat shock proteins, which have been shown to modulate the apoptotic process in certain cell types, in order to more completely elucidate apoptotic signaling in aged skeletal muscle. To more specifically identify alterations that are likely to be the result of aging, we compared 16-month-old middle-aged (MD) and 29-month-old senescent (SE) male Fischer 344 x Brown Norway rats in our study. Our results show that the degree of DNA laddering was higher in SE compared to MD rats. Using total tissue homogenates we examined the level of expression of several apoptosis-related proteins in two categories: mitochondria-associated proteins and caspases. Of the mitochondria-associated proteins, the levels of p53 showed a significant increase in SE compared to MD rats. There was also a significant increase in the expression of Bax, Bcl-2 and Apaf-1 in SE rats over that of MD rats; cytochrome c and AIF levels remained unchanged, however. Regarding the caspases, there were increases in the levels of pro-caspases-12 and -7 and cleaved caspase-9, although the levels of pro- and cleaved caspase-3 as well as cleaved caspase-12 remained unchanged. Furthermore, our results showed significant increases in HSP27, HSP60, and the inducible HSP70. These data show that in rat skeletal muscle increased apoptosis occurs between middle-age and senescence, indicating an aging-related increase in apoptosis in skeletal muscle. The involvement of different apoptotic pathways in the aging process is suggested by the selective alterations in the apoptosis regulatory proteins. The increased expression of the HSPs suggests a relationship between HSPs and the aging-related apoptotic process.

Laser printing of single cells: statistical analysis, cell viability, and stress

Methods to print patterns of mammalian cells to various substrates with high resolution offer unique possibilities to contribute to a wide range of fields including tissue engineering, cell separation, and functional genomics. This manuscript details experiments demonstrating that BioLP Biological Laser Printing, can be used to rapidly and accurately print patterns of single cells in a noncontact manner. Human osteosarcoma cells were deposited into a biopolymer matrix, and after 6 days of incubation, the printed cells are shown to be 100% viable. Printing low numbers of cells per spot by BioLP is shown to follow a Poisson distribution, indicating that the reproducibility for the number of cells per spot is therefore determined not by the variance in printed volume per drop but by random sampling statistics. Potential cell damage during the laser printing process is also investigated via immunocytochemical studies that demonstrate minimal expression of heat shock proteins by printed cells. Overall, we find that BioLP is able to print patterns of osteosarcoma cells with high viability, little to no heat or shear damage to the cells, and at the ultimate single cell resolution.

Calcineurin and heat shock protein 72 in functionally overloaded rat plantaris muscle

The involvement of calcineurin (CaN) and heat shock protein (Hsp) 72 in the regulation of fiber size and/or phenotype in response to functional overload (FO) was investigated. In one FO group, the plantaris muscle was overloaded by cutting the distal tendons (5-10 mm length) of the soleus and gastrocnemius of 3-week-old male Wistar rats. Cyclosporin A (CsA), a CaN inhibitor, was injected daily (5 mg/kg body weight, i.p.) in a second group of FO rats (FO+CsA group) for a 2-week period. Compared to age-matched controls (Con), the absolute and relative plantaris weights were increased in both FO groups: the hypertrophic response was attenuated in FO+CsA rats. The mean cross-sectional area of each fiber type was increased (approximately 2.0-fold) in the plantaris of FO rats: CsA treatment attenuated this effect, although the fibers were still larger than in Con rats. The percent composition of myosin heavy chain (MHC) IIb decreased from 54% in Con to 19% in FO rats, whereas types I, IIa, and IIx MHC increased in the FO rats. CsA treatment blunted the shifts in MHC isoforms: the FO+CsA group showed a smaller decrease in type IIb and a smaller increase in type IIx MHC than the FO group. The levels of CaN-A and -B proteins were higher (approximately 2.5-fold) in FO than Con rats, whereas these values were similar in Con and FO+CsA rats. Hsp72 protein levels were higher in FO (3.6-fold) and FO+CsA (5.2-fold) than Con rats, with the values being significantly higher in the FO+CsA than FO rats. CsA treatment in Con rats had no effects on muscle mass, fiber size, MHC composition, and Hsp72 or CaN levels. Combined, these results suggest that CaN levels are related to changes in both fiber size and phenotype, and that Hsp72 levels are more related to the levels of stress added to the muscle rather than to increases in the slow fiber phenotype in functionally overloaded rat plantaris muscles.

Heat shock proteins and neuromuscular disease

The heat shock proteins are families of proteins with known activities that include chaperoning nascent peptides within the cell and cytoprotection. Most work on the nervous system has related to the role of heat shock proteins in neuroprotection from either hypoxic-ischemic or traumatic injury. The role of these proteins during normal physiological activity and injury is still under investigation. Heat shock proteins in neuromuscular disease have been investigated to some extent but were largely neglected until recently. The goal of this review is to summarize the evidence linking heat shock proteins with neuromuscular disease and to provide some insight into the roles or functions of these proteins in disease states.