Muscle Heat Shock Protein Research Articles

Inducing Muscle Heat Shock Protein 70 Improves Insulin Sensitivity and Muscular Performance in Aged Mice.

Heat shock proteins (HSPs) are molecular chaperones with roles in longevity and muscular preservation. We aimed to show elevating HSP70 improves indices of health span. Aged C57/BL6 mice acclimated to a western diet were randomized into: geranylgeranylacetone (GGA)-treated (100 mg/kg/d), biweekly heat therapy (HT), or control. The GGA and HT are well-known pharmacological and environmental inducers of HSP70, respectively. Assessments before and after 8 weeks of treatment included glycemic endpoints, body composition, and muscular endurance, power, and perfusion. An HT mice had more than threefold, and GGA mice had a twofold greater HSP70 compared with control. Despite comparable body compositions, both treatment groups had significantly better insulin sensitivity and insulin signaling capacity. Compared with baseline, HT mice ran 23% longer than at study start, which was significantly more than GGA or control. Hanging ability (muscular endurance) also tended to be best preserved in HT mice. Muscle power, contractile force, capillary perfusion, and innervation were not different. Heat treatment has a clear benefit on muscular endurance, whereas HT and GGA both improved insulin sensitivity. Different effects may relate to muscle HSP70 levels. An HSP induction could be a promising approach for improving health span in the aged mice.

Role of small heat shock proteins in muscle under chronic hyperglycemia (1102.42)

Role of small heat shock proteins in muscle under chronic hyperglycemia V. Sudhakar Reddy1, G. Bhanuprakash Reddy1 1Department of Biochemistry, National Institute of Nutrition, Hyderabad, India Objective: To study the expression of small heat shock proteins (sHsp) and their localization in diabetic rat muscle.Methods: Diabetes was induced in rats and maintained on hyperglycemia for a period of 12 weeks. The expression of sHsp and phosphorylated sHsp was analysed by qRT‐PCR, immunoblotting. The translocation of phosphorylated sHsp (pS82‐Hsp27, pS59‐αB‐crystallin; αBC) was analyzed by detergent solubility assay and co‐immunoprecipitation. The cell death was analysed by assessing the levels bcl‐2, bax and cleaved caspase‐3. The interaction of αBC with bax was analyzed by co‐immunoprecipitation Results: Out of 10 sHsp, 7 sHsp were detected in muscle. Among them, increased expression of αBC was seen diabetic muscle. Furthermore, detergent soluble assay and co‐immunoprecipitation studies confirmed the translocation and interaction of phosphorylated sHsp with cytoskeleton (desmin) under diabetic conditions. Diabetes induced the cell death as assessed by the levels of cleaved caspase‐3, bax and bcl‐2. Moreover, diabetes reduced the interaction of αBC with bax.Conclusion: There was increased expression of αBC under hyperglycemic conditions. Further, chronic hyperglycemia induced the translocation of pS82‐Hsp27 and pS59‐αBC from cytoplasm to a striated sarcomere at or near z‐lines and intercalated discs. Altered interaction of αBC with bax seems to influence cell death in diabetic muscle.

Muscle Heat Shock Protein 70 Predicts Insulin Resistance With Aging

Heat shock protein 70 (HSP70) protects cells from accumulating damaged proteins and age-related functional decline. We studied plasma and skeletal muscle (SkM) HSP70 levels in adult vervet monkeys (life span ≈ 25 years) at baseline and after 4 years (≈10 human years). Insulin, glucose, homeostasis model assessment scores, triglycerides, high-density lipoprotein and total plasma cholesterol, body weight, body mass index, and waist circumference were measured repeatedly, with change over time estimated by individual regression slopes. Low baseline SkM HSP70 was a proximal marker for developing insulin resistance and was seen in monkeys whose insulin and homeostasis model assessment increased more rapidly over time. Changes in SkM HSP70 inversely correlated with insulin and homeostasis model assessment trajectories such that a positive change in SkM level was beneficial. The strength of the relationship between changes in SkM HSP70 and insulin remained unchanged after adjustment for all covariates. Younger monkeys drove these relationships, with HSP70 alone being predictive of insulin changes with aging. Plasma and SkM HSP70 were unrelated and HSP70 release from peripheral blood mononuclear cells was positively associated with insulin concentrations in contrast to SkM. Results from aged humans confirmed this positive association of plasma HSP70 and insulin. In conclusion, higher levels of SkM HSP70 protect against insulin resistance development during healthy aging.

The effect of heat stress on skeletal muscle contractile properties

An elevated heat-shock protein (HSP) content protects cells and tissues, including skeletal muscles, from certain stressors. We determined if heat stress and the elevated HSP content that results is correlated with protection of contractile characteristics of isolated fast and slow skeletal muscles when contracting at elevated temperatures. To elevate muscle HSP content, one hindlimb of Sprague-Dawley rats (21-28days old, 70-90g) was subjected to a 15min 42°C heat-stress. Twenty-four hours later, both extensor digitorum longus (EDL) and soleus muscles were removed, mounted in either 20°C or 42°C Krebs-Ringer solution, and electrically stimulated. Controls consisted of the same muscles from the contra-lateral (non-stressed) hindlimbs as well as muscles from other (unstressed) animals. Isolated muscles were twitched and brought to tetanus every 5min for 30min. As expected, HSP content was elevated in muscles from the heat-stressed limbs when compared with controls. Regardless of prior treatment, both EDL and soleus twitch tensions were lower at 42°C when compared with 20°C. In addition, when incubated at 42°C, both muscles showed a drop in twitch tension between 5 and 30min. For tetanic tension, both muscles also showed an increase in tension between 5 and 30min when stimulated at 20°C regardless of treatment but when stimulated at 42°C no change was observed. No protective effect of an elevated HSP content was observed for either muscle. In conclusion, although heat stress caused an elevation in HSP content, no protective effects were conferred to isolated contracting muscles.

Skeletal muscle heat shock protein 70: diverse functions and therapeutic potential for wasting disorders

The stress-inducible 70-kDa heat shock protein (HSP70) is a highly conserved protein with diverse intracellular and extracellular functions. In skeletal muscle, HSP70 is rapidly induced in response to both non-damaging and damaging stress stimuli including exercise and acute muscle injuries. This upregulation of HSP70 contributes to the maintenance of muscle fiber integrity and facilitates muscle regeneration and recovery. Conversely, HSP70 expression is decreased during muscle inactivity and aging, and evidence supports the loss of HSP70 as a key mechanism which may drive muscle atrophy, contractile dysfunction and reduced regenerative capacity associated with these conditions. To date, the therapeutic benefit of HSP70 upregulation in skeletal muscle has been established in rodent models of muscle injury, muscle atrophy, modified muscle use, aging, and muscular dystrophy, which highlights HSP70 as a key therapeutic target for the treatment of various conditions which negatively affect skeletal muscle mass and function. This article will review these important findings and provide perspective on the unanswered questions related to HSP70 and skeletal muscle plasticity which require further investigation.

Restoring HSP70 deficiencies improves glucose tolerance in diabetic monkeys

We evaluated heat shock protein 70 (HSP70) changes in diabetes mellitus (DM) in a nonhuman primate model. To this end, two studies were conducted in DM vervet monkeys. 1) Normal control and streptozotocin-induced DM monkeys (Stz-DM) that were differentiated into moderately or poorly controlled DM by judicious insulin administration were evaluated. Liver was collected at 4, 8, 12, 16, and 20 wk after streptozotocin, exposed to ex vivo heat shock at 42°C, and immunoblotted for heat shock factor 1 (HSF1), HSP70, and phosphorylated HSF1. 2) Spontaneous DM monkeys that were not pharmacologically induced were included in a crossover study of the HSP70-inducing drug geranylgeranylacetone (GGA). GGA at 20 mg/kg was given for 14 days with a 6-wk washout period. Glucose tolerance testing and plasma and muscle HSP70 were the primary outcome measurements. In Stz-DM, hyperglycemia reduced hepatic HSP70 in a dose-dependent fashion. HSF1 was increased in livers of monkeys with Stz-DM, but responses to ex vivo heat shock were impaired vs. normal monkeys. Activation of HSF1 appears to be important, because the phosphorylation change with heat stress was nearly perfectly correlated with HSP70 increases. Impaired HSF1 activation was also seen in Stz-DM after chronic hyperglycemia (>12 wk). In naturally occurring DM, increased circulating HSP70 resulted in significantly improved glucose tolerance and significant, positive trends in other measurements of insulin resistance. No change in muscle HSP70 content was observed. We conclude that increasing HSP70, potentially through targeting hyperglycemia-related deficits in HSF1 induction and activation in the liver, is a potent and viable strategy to improve glucose tolerance.

Glutamine preserves skeletal muscle force during an inflammatory insult

The purpose of this study was to test the hypothesis that acute glutamine (GLN) supplementation can counteract skeletal muscle contractile dysfunction occurring in response to inflammation by elevating muscle heat shock protein (Hsp) expression and reducing inflammatory cytokines. Mice received 5 mg/kg lipopolysaccharide (LPS) concurrently with 1 g/kg GLN or vehicle treatments. Plantarflexor isometric force production was measured at 2 hours post-injection. Blood and gastrocnemius muscles were collected, and serum and muscle tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) and muscle Hsp70 and Hsp25 were quantified. Saline/LPS treatment was associated with a 33% reduction in maximal force and elevated serum TNF-alpha and IL-6. GLN completely prevented this force decrement with LPS. GLN was found to reduce muscle Hsp70 and IL-6, but only in the presence of LPS. GLN supplementation provides an effective, novel, clinically applicable means of preserving muscle force during acute inflammation. These data indicate that force preservation is not dependent on reductions in serum cytokines or muscle TNF-alpha, or elevated Hsp levels.

Lipoic acid increases heat shock protein expression and inhibits stress kinase activation to improve insulin signaling in skeletal muscle from high-fat-fed rats

The antioxidant alpha-lipoic acid (LA) has been shown to improve insulin action in high-fat (HF)-fed animal models, yet little is known about its underlying mechanisms of action. We hypothesize that LA acts by inducing heat shock proteins (HSPs), which then inhibit stress kinases known to interfere with insulin signaling intermediates. Male Wistar rats were fed a HF diet (60% calories from fat) for 6 wk, while controls received a chow diet (10% calories from fat). One-half of the rats in each group received daily LA injections (30 mg/kg body wt). In rats fed a HF diet, LA increased expression of HSP72 and activation of HSP25 in soleus muscle, but it had no effect on HSPs in muscle from chow-fed rats. LA treatment reduced phosphorylation of c-Jun NH(2)-terminal kinase (JNK) and inhibitor of kappaB kinase-beta (IKKbeta) activity (IkappaBalpha protein levels) in rats fed a HF diet and effectively restored insulin responsiveness, as seen by insulin-stimulated phosphorylated Akt/Akt and 2-deoxyglucose uptake in soleus muscle. LA also induced activation of p38 MAPK and AMP-activated protein kinase, proteins previously implicated in insulin-independent glucose uptake. In addition, acute LA treatment induced HSPs in vitro in L6 muscle cells and prevented the activation of JNK and IKKbeta with stimulants such as anisomycin and TNF-alpha, respectively. In conclusion, our results suggest chronic LA treatment results in stress kinase inhibition and improved insulin signaling through a HSP-mediated mechanism.

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.

Muscle Heat Shock Protein Responses to Altered Levels of Sex Hormones

Sex differences in the HSP response of muscle to various stresses have been reported, but few data on the role of sex hormones on the expression of HSPs exist. Here, young male and female Sprague-Dawley rats were gonadectomized, allowed to recover for 14d and sacrificed after 2 or 12d of hormone administration (testosterone and estradiol for males and females, respectively). A third group (sham) received vehicle only, and was sacrificed after 2 days. Vastus lateralis samples were processed for SDS-PAGE, and immunoblotted for expression of HSP25 & αB Crystallin as well as for the inducible and constitutive isoforms of the 70 kD HSP(HSP70 & HSC70, respectively). Myosin heavy chain (MHC) composition was determined using SDS-PAGE. Differences in HSPs and MHC percentages relative to non-operated controls were determined for males and females (n=5/group). Sham males exhibited a 60% reduction in HSP70, which was reversed by testosterone. In contrast, sham females showed a slight increase in HSP70 (20%), while those receiving estradiol for 2 & 12d showed marked increases (~3-fold) relative to control. HSC70 showed similar, but smaller, patterns of change, and the small HSPs showed no changes in HSPs in any condition for either sex. MHC composition did not differ across groups. Sex hormones appear to modulate resting HSP expression differently in males and females and may reflect sex differences in muscle physiology.

Gender differences in skeletal muscle heat shock proteins induced by diathermy

Heat shock treatments have been used to appreciably increase heat shock protein 70 (Hsp70) and phosphorylation of heat shock protein 27 (Hsp27p). These proteins are believed to be involved in the repair process of myofibrils. The purpose of this investigation was to determine whether diathermy can increase Hsp70 and Hsp27p content in skeletal muscle. Fourteen subjects (n= 7 / group, 18–35 y) received a muscle biopsy from the v. lateralis and then underwent 20 min of diathermy followed by 20 min of hot pack heating on the contralateral leg. Twenty-four hours following treatment, a second muscle biopsy was performed on the treated leg. All samples were analyzed for Hsp70 content using western immunoblotting. Images of the blots were obtained and analyzed via densitometry. A paired t-Test was used to examine differences in heat shock protein content between the treated and untreated legs. Significance was set at P<0.05. Twenty-four hours following the heat treatment, female subjects significantly increased Hsp70 (58%) and Hsp27-p (132%) content compared to the untreated leg. Male subjects had non-significant increases in Hsp70 (35%) and Hsp27-p (68%) skeletal muscle content. These results implicate diathermy as an effective countermeasure to induce Hsp70 & Hsp27-p in female populations. Supported, in part, by a University of Kansas General Research Fund grant (P. Gallagher), and a McNair Scholarship (T. Le).

Changes in markers of muscle damage, inflammation and HSP70 after an Ironman triathlon race

We investigated the effects of an Ironman triathlon race on markers of muscle damage, inflammation and heat shock protein 70 (HSP70). Nine well-trained male triathletes (mean +/- SD age 34 +/- 5 years; VO(2peak) 66.4 ml kg(-1) min(-1)) participated in the 2004 Western Australia Ironman triathlon race (3.8 km swim, 180 km cycle, 42.2 km run). We assessed jump height, muscle strength and soreness, and collected venous blood samples 2 days before the race, within 30 min and 14-20 h after the race. Plasma samples were analysed for muscle proteins, acute phase proteins, cytokines, heat shock protein 70 (HSP70), and clinical biochemical variables related to dehydration, haemolysis, liver and renal functions. Muscular strength and jump height decreased significantly (P < 0.05) after the race, whereas muscle soreness and the plasma concentrations of muscle proteins increased. The cytokines interleukin (IL)-1 receptor antagonist, IL-6 and IL-10, and HSP70 increased markedly after the race, while IL-12p40 and granulocyte colony-stimulating factor (G-CSF) were also elevated. IL-4, IL-1beta and tumour necrosis factor-alpha did not change significantly, despite elevated C-reactive protein and serum amyloid protein A on the day after the race. Plasma creatinine, uric acid and total bilirubin concentrations and gamma-glutamyl transferase activity also changed after the race. In conclusion, despite evidence of muscle damage and an acute phase response after the race, the pro-inflammatory cytokine response was minimal and anti-inflammatory cytokines were induced. HSP70 is released into the circulation as a function of exercise duration.

Alcohol alters skeletal muscle heat shock protein gene expression in rats: these effects are moderated by sex, raised endogenous acetaldehyde, and starvation

Alcoholic myopathy is a common pathology characterized by wasting due to reduced protein synthesis, although the mechanisms involved remain unclear. Women are particularly sensitive and malnutrition exacerbates the myopathy. This study aimed to address (i) whether long-term alcohol feeding alters expression of heat shock proteins (HSPs) in male and female rats; (ii) the effect of immediate alcohol dosing with or without raised levels of endogenous acetaldehyde; and (iii) the effect of starvation. To address this, (i) male and female rats were fed alcohol in the long-term (6-7 weeks as 35% of energy in a liquid diet) and compared to controls fed the same diet with isoenergetic glucose; (ii) male rats given an immediate bolus (75 mmol ethanol per kilogram body weight intraperitoneally) 2.5 hours before sacrifice and compared to controls given a dose of saline (with or without pretreatment with cyanamide—an acetaldehyde dehydrogenase inhibitor which raises endogenous acetaldehyde); (iii) male rats starved for 1 or 2 days then immediately dosed with alcohol. Protein levels of HSP 27, HSP 60, and HSP 70 were measured in muscles of male rats fed alcohol and pair-fed control rats by SDS-PAGE and Western blotting in study I. Levels of HSP 27, HSP 60, HSP 70, and HSP 90 mRNA were analyzed in hind limb skeletal muscle by reverse transcription–polymerase chain reaction with an endogenous internal standard, glyceraldehyde-3-phosphate-dehydrogenase. (i) Long-term alcohol dosage reduced HSP 27 in male rats but not in females, whereas HSP 90 mRNA increased in long-term alcohol-fed female rats but not in male rats. These changes were reflected by a similar trend in HSP protein content, although statistical significance was not achieved. (ii) There was no effect on any of the HSP mRNAs in rats dosed immediately with alcohol or in combination with cyanamide. (iii) Starvation per se for 2 days was associated with an increase in HSP 27 mRNA. Alcohol administration after 2 days starvation caused a blunting of the increased HSP 27 mRNA in starvation alone. This suggests that long-term alcohol exposure affects HSP gene expression and that this effect is moderated by sex and starvation. This may contribute to, or reflect, the biochemical lesion in alcoholic myopathy.

Response and function of skeletal muscle heat shock protein 70

In response to stress, cells produce a series of heat shock proteins (Hsps). One of the most prominent Hsps, is the 70 kDa Hsp (Hsp70). Hsp70 is a highly conserved and essential protein against stress. The skeletal muscle responds to a diverse group of stress signals namely, muscle contraction linked energy and milieu challenges, ischemia and exercise by producing Hsp70. The extent of this Hsp70 response in skeletal muscle depends on the type and intensity of the signal, and is characterized in a muscle fiber specific manner by a special time course. Hsp70 in the skeletal muscle is regulated at transcriptional, translational and posttranslational levels. Hsp70 serves as an indicator for cellular stress as a molecular chaperone, plays pivotal role in maintaining cellular homeostasis by preventing apoptosis, influences energy metabolism, facilitates cellular processes in terms of muscular adaptation and interacts with other signalling pathways. This review summarizes our current knowledge on the skeletal muscle Hsp70 response.

Skeletal muscle HSP72 and norepinephrine response to static magnetic field in rat

The present work was undertaken in order to investigate the noradrenergic system and skeletal muscle heat shock protein 72 (HSP72) response to static magnetic field (MF) in male rats. At thermoneutrality (25 degrees C), the exposition of rats 1 hour/day for 5 consecutive days to MF of 128 mT (m tesla) induced an increase in norepinephrine content in gastrocnemius muscle (+25%, p < 0.05) but had no effect at 67 mT (+1%, p > 0.05), indicating a stimulatory effect of sub-acute MF exposure on the noradrenergic system activity. Moreover, exposed rats to MF displayed a non-significant increase of HSP72 levels in gastrocnemius muscles (+29%, p > 0.05). The results indicate that noradrenergic systems in rat's gastrocnemius muscles are affected by MF exposure. Interestingly, sub-acute exposure insufficiency increased HSP72 levels in gastrocnemius muscles.

Myocardial Heat Shock Protein 70 Expression in Young and Old Rats After Identical Exercise Programs

Synthesis of inducible heat shock protein 70 (HSP70) is impaired in aged animals following acute stresses including exercise. In this study we determined whether aging affects expression of this cytoprotective protein following chronic exercise participation. Male Fischer 344 rats, final ages 6 and 24 months, exercised identically for 10 weeks on a treadmill (15 degrees incline, 15 m/min for up to 60 minutes, 5 days/week). In 6-month-old animals, exercise increased HSP70 in heart (44%), liver (216%), and skeletal muscle (126%) (p <.05 vs sedentary). In 24-month-old animals, exercise increased HSP70 in muscle (69%), but not in heart or liver. In heart, antioxidant enzyme activities and HSP70 messenger RNA were measured and found to be unaffected by exercise at both ages. Our results indicate an age-related decrease in HSP70 production in heart and liver following chronic exercise. Furthermore, the aged heart does not increase its antioxidant enzyme defenses to compensate for the HSP70 deficit.

Molecular Cloning of Bovine Cardiac Muscle Heat-Shock Protein 70 kDa and Its Phosphorylation by cAMP-Dependent Protein Kinase in Vitro

The 70-kDa heat-shock protein (Hsp70) has been cloned and sequenced from bovine cardiac muscle. On the basis of sequence features, the gene corresponds to the cytoplasmic form of Hsp70. This cardiac Hsp70 cDNA clone has an open reading frame of 1926 bp coding for 641 amino acids and a predicted molecular mass of 70.25 kDa. Comparison of the amino acid sequence revealed an extensive sequence identity with other species of Hsp70. Escherichia coli expressed cardiac Hsp70 stimulated a 2-fold increase in calcineurin (CaN) activity. Notably, we observed that Hsp70 directly interacts with CaN using a pull-down assay. Furthermore, expressed cardiac-specific Hsp70 was phosphorylated in vitro by cAMP-dependent protein kinase. Phosphorylation resulted in the incorporation of 0.1 mol of phosphate per mol of Hsp70. The phosphorylated Hsp70 was unable to activate the phosphatase activity of CaN. This is the first demonstration that Hsp70 is phosphorylated by cAMP-dependent protein kinase and provides an on/off switch for the regulation of CaN signaling by Hsp70.

Arm Muscle HSP70 Response to Strenght Training

2182 Heat shock protein 70 (HSP70) expression in skeletal muscle is involved in a variety of muscular changes including myopathy, muscle atrophy, muscle hypertrophy and ischemia.HSP70 plays an important role in muscular adaptation to training and can serve as an indicator for cellular stress. It is known that HSP70 expression and HSP70 response to exercise are related to muscle fiber type. Up to date, data on HSP70 response to training in human muscles have been derived from leg muscles and there is no study reporting HSP70 response in arm muscles. PURPOSE: To investigate HSP70 response to strength training in arm muscle. METHODS: Twelve male volunteers performed either a 6-week strength training (3d/w) with maximum contractions (Max group) or combination training of maximum contractions, ballistic and strech-shortening movements (Combi group). Muscle samples were taken from m. triceps brachii before and after training by fine needle biopsy technique. HSP70 (from 2.5 μg total protein loaded) was measured with Western Blot with reference to a series of standard HSP70. HSP70 mRNA was determined using quantitative real-time RT-PCR in relation to a house-keeping (HPRT) gene. RESULTS: Strength training produced a significant increase in 1 RM in both groups (5.6 kg for Max group and 5.0 kg for Combi group, respectively), and combined strength training led an additional improvement in maximum movement velocity (0.1 m/s, p<0.05). HSP70 (median) increased after training from 15.2 to 58.9 ng, (P<0.01) in Max group and 15.5 to 54.2 ng, (P<0.01) in Combi group. There was also a significant difference of the copy numbers of HSP70 mRNA before and after training in Max group (2.59 vs. 10.1, P<0.01) and Combi group (1.93 vs. 10.57, P<0.01). CONCLUSION: In response to physical training, HSP70 can be induced in human arm muscles. In our study different training programs with comparable training intensity and volume seem not to affect HSP70 expression. Based on its universal role as “molecular chaperone” HSP70 can have important impact on the adaptation to strength training in arm muscle composed predominantly of fast muscle fibers.

The Effects of Eccentric Contraction Preconditioning on Ischemia- Reperfusion Injury in Mouse Skeletal Muscle

2013 Endurance exercise-induced increase in cardiac heat shock protein (HSP) is associated with reductions in ischemia-reperfusion (I-R) injury in the heart. Eccentrically biased exercise is associated with increases in skeletal muscle HSP and protection from exercise-induced muscle injury in subsequent bouts. PURPOSE: To ascertain whether preconditioning of mouse anterior crural muscle with eccentric contractions protects the muscle against I-R injury. The left anterior crural muscles of mice performed either 150 passive concentric or 150 eccentric contractions in vivo. METHODS: I-R injury was induced 2 wks later by placing a tourniquet around the left upper thigh for 2 h. Peak isometric torque as a function of stimulation frequency (20–400 Hz) was measured immediately before and after the preconditioning exercise and I-R injury, and at 7, 14 and 21 d after ischemia. At 21 d, the injured and contralateral control EDL muscles were dissected free for in vitro contractile measurements. RESULTS: Peak isometric torques (20–400 Hz) were decreased immediately (91–52%) after eccentric contraction-induced injury. Immediately prior to I-R injury there were no differences between groups for peak isometric torques at frequencies (20–400 Hz). I-R injury resulted in significant, and similar, reductions in peak isometric torques in both groups immediately after injury (99–100%), and at 7 d (84–90%), 14 d (40–48%) and 21 d (30–35%). There were no differences between groups for peak isometric twitch and tetanic forces, specific force, and wet weight for injured EDL muscles 21 d after I-R injury. CONCLUSION: Preconditioning mouse skeletal muscle with a single bout of eccentric contractions does not appear to protect the muscle against I-R injury.

The Effects of Eccentric Contraction Preconditioning on Ischemia- Reperfusion Injury in Mouse Skeletal Muscle

2013 Endurance exercise-induced increase in cardiac heat shock protein (HSP) is associated with reductions in ischemia-reperfusion (I-R) injury in the heart. Eccentrically biased exercise is associated with increases in skeletal muscle HSP and protection from exercise-induced muscle injury in subsequent bouts. PURPOSE: To ascertain whether preconditioning of mouse anterior crural muscle with eccentric contractions protects the muscle against I-R injury. The left anterior crural muscles of mice performed either 150 passive concentric or 150 eccentric contractions in vivo. METHODS: I-R injury was induced 2 wks later by placing a tourniquet around the left upper thigh for 2 h. Peak isometric torque as a function of stimulation frequency (20–400 Hz) was measured immediately before and after the preconditioning exercise and I-R injury, and at 7, 14 and 21 d after ischemia. At 21 d, the injured and contralateral control EDL muscles were dissected free for in vitro contractile measurements. RESULTS: Peak isometric torques (20–400 Hz) were decreased immediately (91–52%) after eccentric contraction-induced injury. Immediately prior to I-R injury there were no differences between groups for peak isometric torques at frequencies (20–400 Hz). I-R injury resulted in significant, and similar, reductions in peak isometric torques in both groups immediately after injury (99–100%), and at 7 d (84–90%), 14 d (40–48%) and 21 d (30–35%). There were no differences between groups for peak isometric twitch and tetanic forces, specific force, and wet weight for injured EDL muscles 21 d after I-R injury. CONCLUSION: Preconditioning mouse skeletal muscle with a single bout of eccentric contractions does not appear to protect the muscle against I-R injury.