Skeletal Muscle Heat Shock Protein Content and the Repeated Bout Effect.

The "Repeated Bout Effect" (RBE) occurs when a skeletal muscle is preconditioned with a few lengthening contractions (LC) prior to exposing the muscle to a greater number of LC. The preconditioning (PC) results in significantly less damage and preservation of force. Since it takes only a few LC to increase muscle heat shock protein (HSP) content, it was of interest to examine the relationship between HSPs and the RBE. To do this, one tibialis anterior (TA) muscle from Sprague-Dawley rats (n = 5/group) was preconditioned with either 0, 5, or 15 lengthening contractions (LC) and exposed to a treatment of 60 LC 48 h later. Preconditioning TA muscles with 15 LC, but not 5 LC, significantly elevated muscle αB-crystallin (p < 0.05), HSP25 (p < 0.05), and HSP72 content (p < 0.001). These preconditioned TA muscles also showed a significantly (p < 0.05) reduced loss of active torque throughout the subsequent 60 LC. While there was a trend for all preconditioned muscles to maintain higher peak torque levels throughout the 60 LC, no significant differences were detected between the groups. Morphologically, preconditioned muscles appeared to show less discernible muscle fiber damage. In conclusion, an elevated skeletal muscle HSP content from preconditioning may contribute to the RBE.

Skeletal muscle metabolism and contraction performance regulation by teneurin C-terminal-associated peptide-1.

Skeletal muscle regulation is responsible for voluntary muscular movement in vertebrates. The genes of two essential proteins, teneurins and latrophilins (LPHN), evolving in ancestors of multicellular animals form a ligand-receptor pair, and are now shown to be required for skeletal muscle function. Teneurins possess a bioactive peptide, termed the teneurin C-terminal associated peptide (TCAP) that interacts with the LPHNs to regulate skeletal muscle contractility strength and fatigue by an insulin-independent glucose importation mechanism in rats. CRISPR-based knockouts and siRNA-associated knockdowns of LPHN-1 and-3 in the C2C12 mouse skeletal cell line shows that TCAP stimulates an LPHN-dependent cytosolic Ca2+ signal transduction cascade to increase energy metabolism and enhance skeletal muscle function via increases in type-1 oxidative fiber formation and reduce the fatigue response. Thus, the teneurin/TCAP-LPHN system is presented as a novel mechanism that regulates the energy requirements and performance of skeletal muscle.

Methacrylic acid-based hydrogels enhance skeletal muscle regeneration after volumetric muscle loss in mice.

Volumetric muscle loss (VML) impairs the regenerative ability of skeletal muscle resulting in scar tissue formation and loss of function. Current treatments are of limited efficacy as they do not fully restore function, i.e., force generation. Regenerative biomaterials, such as those containing methacrylic-acid (MAA), are proposed as a novel approach to enhancing muscle regeneration without added cells, growth factors or drugs. Here, the regenerative effects of two hydrogels were investigated: MAA-poly(ethylene glycol) (MAA-PEG) and MAA-collagen. These hydrogels were used to treat VML injuries in murine tibialis anterior muscles. The MAA-collagen hydrogel significantly increased regenerating muscle fiber size and muscle force production. While both hydrogels increased vascularization, only the MAA-collagen hydrogel increased apparent muscle innervation. The MAA-collagen hydrogel also significantly reduced a pro-inflammatory macrophage (MHCII+CD206-) population. Furthermore, the hydrogels had distinct gene expression profiles indicating that their regenerative abilities were carrier dependent. Overall, this study suggests MAA-collagen as a cell-free and drug-free approach to enhancing skeletal muscle regeneration after traumatic injury.

Leucine-Enriched Essential Amino Acids Improve Recovery from Post-Exercise Muscle Damage Independent of Increases in Integrated Myofibrillar Protein Synthesis in Young Men.

BACKGROUND: Leucine-enriched essential amino acids (LEAAs) acutely enhance post-exercise myofibrillar protein synthesis (MyoPS), which has been suggested to be important for muscle repair and recovery. However, the ability of LEAAs to concurrently enhance MyoPS and muscle damage recovery in free-living humans has not been studied. METHODS: In a randomized, double-blind, placebo-controlled, parallel-group design, twenty recreationally active males consuming a controlled diet (1.2 g/kg/d of protein) were supplemented thrice daily with 4 g of LEAAs (containing 1.6 g leucine) or isocaloric placebo for four days following an acute bout of lower-body resistance exercise (RE). MyoPS at rest and integrated over 96 h of recovery was measured by D2O. Isometric and isokinetic torque, muscle soreness, Z-band streaming, muscle heat shock protein (HSP) 25 and 72, plasma creatine kinase (CK), and plasma interleukin-6 (IL-6) were measured over 96 h post-RE to assess various direct and indirect markers of muscle damage. RESULTS: Integrated MyoPS increased ~72% over 96 h after RE (p < 0.05), with no differences between groups (p = 0.98). Isometric, isokinetic, and total peak torque decreased ~21% by 48 h after RE (p < 0.05), whereas total peak torque was ~10% greater overall during recovery in LEAAs compared to placebo (p < 0.05). There were moderate to large effects for peak torque in favour of LEAAs. Muscle soreness increased during recovery with no statistical differences between groups but small to moderate effects in favour of LEAAs that correlated with changes in peak torque. Plasma CK, plasma IL-6, and muscle HSP25 increased after RE (p < 0.05) but were not significantly different between groups (p ≥ 0.13). Consistent with a trend toward attenuated Z-band streaming in LEAAs (p = 0.07), muscle HSP72 expression was lower (p < 0.05) during recovery in LEAAs compared with placebo. There were no correlations between MyoPS and any measures of muscle damage (p ≥ 0.37). CONCLUSION: Collectively, our data suggest that LEAAs moderately attenuated muscle damage without concomitant increases in integrated MyoPS in the days following an acute bout of resistance exercise in free-living recreationally active men.

Ovariectomy alters lengthening contraction induced heat shock protein expression.

Estrogen appears to play a role in minimizing skeletal muscle damage as well as regulating the expression of the protective heat shock proteins (HSPs). To clarify the relationship between estrogen, muscle HSP content, and muscle damage, tibialis anterior (TA) muscles from ovary-intact (OVI; n = 12) and ovariectomized (OVX; 3 weeks, n = 12) female Sprague-Dawley rats were subjected to either 20 or 40 lengthening contractions (LCs). Twenty-four hours after stimulation, TA muscles were removed, processed, and assessed for HSP25 and HSP72 content as well as muscle (damage) morphology. No differences in muscle contractile properties were observed in TA muscles between OVI and OVX animals for peak torque during the LCs. In unstressed TA muscles, the basal expression of HSP72 expression was decreased in OVX animals (P < 0.05) while HSP25 content remained unchanged. Following 20 LCs, HSP25 content was elevated (P < 0.05) in TA muscles from OVX animals but unchanged in muscles from OVI animals. Following 40 LCs, HSP25 content was elevated (P < 0.01) in TA muscles from both OVI and OVX animals while HSP72 content was elevated only in TA muscles from OVI animals (P < 0.05). Taken together, these data suggest the loss of ovarian hormones, such as estrogen, may impair the skeletal muscle cellular stress response thereby rendering muscles more susceptible to certain types of contraction induced damage. Novelty Ovariectomy alters muscle HSP72 content. Muscle contractile measures are maintained following ovariectomy.

HSP72 expression is specific to skeletal muscle contraction type.

Exercise is capable of inducing the cellular stress response and increasing skeletal muscle heat shock protein (HSP) content. HSPs function as molecular chaperones and play roles in facilitating protein folding thereby contributing to muscle proteostasis. To determine the relationship between muscle contraction types, muscle damage, and HSP content, one tibialis anterior (TA) muscle from male Sprague-Dawley rats (n = 5/group) was electrically stimulated while actively lengthening (LC), shortening (SC), or remaining to stagnate (IC) for 15 repetitions (3 sets of five). Two additional LC groups underwent 5 and 10 repetitions. Maximal tetanic tension (MTT) was recorded prior to (pre) and at 5 min after (post) the last contraction. Twenty-four hours after stimulation, TA muscles were removed, processed, and assessed for damage and for HSP25 and HSP72 content. Post-MTT was significantly decreased following 15 LCs, (24%; p < 0.05) but not following 15 SCs or 15 ICs. Post-MTT was also decreased by 8% (p < 0.05), and 18% (p < 0.05) for muscles subjected to 5 and 10 LCs, respectively. HSP72 content increased after all LCs conditions but not following ICs or SCs. HSP25 content remained unchanged following all contractions. Similarly, muscle damage was observed only after LCs and not after other contraction types. In conclusion, muscle HSP72 content can be increased with as few as 5 maximal lengthening contractions and appears to be related to muscle damage. This may have important implications for muscle rehabilitation and exercise training programs.

The cellular stress response of rat skeletal muscle following lengthening contractions.

The cellular stress response of the rat tibialis anterior (TA) muscle was investigated following 20, 40, or 60 lengthening contractions (LCs) using an in vivo model of electrical stimulation. Muscles were removed at 0, 1, 3, or 24 h after LCs and assessed for heat shock transcription factor (HSF) activation, heat shock protein (HSP) content, and/or morphological evidence of muscle fibre damage. When compared with the first muscle contraction, peak muscle torque was reduced by 26% (p < 0.05) after 20 LCs and further reduced to 56% and 60% (p < 0.001) after 40 and 60 LCs, respectively. Following 60 LCs, HSF activation was detected at 0, 1, and 3 h but was undetectable at 24 h. Hsp72 content was elevated at 24 h after 20 LCs (2.34 ± 0.37 fold, p < 0.05), 40 LCs (3.02 ± 0.31 fold, p < 0.01), and 60 LCs (3.37 ± 0.21 fold, p < 0.001). Hsp25 content increased after 40 (2.36 ± 0.24 fold, p < 0.01) and 60 LCs (2.80 ± 0.37 fold, p < 0.01). Morphological assessment of TA morphology revealed that very few fibres were damaged following 20 LCs while multiple sets of LCs (40 and 60) caused greater amounts of fibre damage. Electron microscopy showed disrupted Z-lines and sarcomeres were detectable in some muscles fibres following 20 LCs but were more prevalent and severe in muscles subjected to 40 or 60 LCs. These results suggest LCs elevate HSP content by an HSF-mediated mechanism (60 LC) and a single set of 20 LCs is capable of increasing muscle HSP content without causing significant muscle fibre damage.

Hsp25 and Hsp72 content in rat skeletal muscle following controlled shortening and lengthening contractions.

The cytoprotective proteins, Hsp25 and Hsp72, are increased in skeletal muscle after nondamaging, shortening contractions, but the temporal pattern of expression and stimulatory mechanisms remain unclear. Thus, we sought to define the in vivo temporal patterns of expression for Hsp25 and Hsp72 after 2 opposing contractions types. To do this, male Sprague-Dawley rats had 1 tibialis anterior (TA) muscle electrically stimulated (5 sets of 20 repetitions) while being either forcibly lengthened (LC) or shortened (SC). At 2, 8, 24, 48, 72, or 168 h after the contractions both the stimulated and the nonstimulated (contra-lateral control) TA muscles were removed and processed to examine muscle damage (hemotoxylin and eosin staining) and Hsp content (Western blot analyses). Cross-sections from TA muscles subjected to LCs showed muscle fibre damage at 8 h and thereafter. In contrast, no muscle fibre damage was observed at any time point following SCs. When normalized to contra-lateral controls, Hsp25 and Hsp72 content were significantly (P < 0.01) increased at 24 h (3.1- and 3.8-fold, respectively) and thereafter. There were no significant increases in Hsp25 or Hsp72 content at any time point following SC. These data suggest that LCs, but not SCs, result in Hsp accumulation and that the fibre/cellular damage sustained from LCs may be the stimulus for elevating Hsp content.

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 (21-28 days old, 70-90 g) was subjected to a 15 min 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 5 min for 30 min. 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 30 min. For tetanic tension, both muscles also showed an increase in tension between 5 and 30 min 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.

Isolated hearts treated with skeletal muscle homogenates exhibit altered function.

Skeletal muscle fiber damage and necrosis can result in the release of intracellular molecules into the extracellular environment. These molecules, termed damage-associated molecular patterns (DAMPs), can act as signals capable of initiating immune and/or inflammatory responses through interactions with pattern recognition receptors. To investigate whether skeletal muscle DAMPs interact with the heart and alter cardiac function, isolated rat hearts were perfused for 75 min with buffer containing 1 µg/ml of either soleus (slow), white gastrocnemius (WG, fast), or heat-stressed white gastrocnemius (HSWG) skeletal muscle homogenates. Left ventricular developed pressure (LVDP) and rates of pressure increase/decrease (± dP/dt) were measured using the Langendorff technique. Compared to controls, no changes in LVDP or +dP/dt were observed over the 75-min perfusion when homogenates from the WG muscles were added. In contrast, at 30 min and thereafter, a decreased LVDP and +dP/dt was observed in the hearts treated with soleus muscle homogenates. The hearts treated with HSWG homogenates also showed a decrease in LVDP from 45 min until the end of perfusion. These results suggest that molecules present in slow muscle and heat-stressed muscle are capable of altering cardiac function. Thus, muscle fiber type and/or heat shock protein content of skeletal muscles may be factors that influence cardiac function following skeletal muscle damage.

Mild eccentric exercise increases Hsp72 content in skeletal muscles from adult and late middle-aged rats.

The loss of muscle mass with age or sarcopenia contributes to increased morbidity and mortality. Thus, preventing muscle loss with age is important for maintaining health. Hsp72, the inducible member of the Hsp70 family, is known to provide protection to skeletal muscle and can be increased by exercise. However, ability to increase Hsp72 by exercise is intensity-dependent and appears to diminish with advanced age. Thus, other exercise modalities capable of increasing HSP content and potentially preventing the age related loss of muscle need to be explored. The purpose of this study was to determine if the stress from one bout of mild eccentric exercise was sufficient to elicit an increase in Hsp72 content in the vastus intermedius (VI) and white gastrocnemius (WG) muscles, and if the Hsp72 response differed between adult and late middle-aged rats. To do this, 30 adult (6 months) and late middle-aged (24 months) F344BN rats were randomly divided into three groups (n = 6/group): control (C), level exercise (16 m x min(-1)) and eccentric exercise (16 m x min(-1), 16 degree decline). Exercised animals were sacrificed immediately post-exercise or after 48 hours. Hematoxylin and Eosin staining was used to assess muscle damage, while Western Blotting was used to measure muscle Hsp72 content. A nested ANOVA with Tukey post hoc analysis was performed to determine significant difference (p < 0.05) between groups. Hsp72 content was increased in the VI for both adult and late middle-aged rats 48 hours after eccentric exercise when compared to level and control groups but no differences between age groups was observed. Hsp72 was not detected in the WG following any type of exercise. In conclusion, mild eccentric exercise can increase Hsp72 content in the rat VI muscle and this response is maintained into late middle-age.

NF-κB activation in organs from STZ-treated rats.

Nuclear factor kappa B (NF-κB) is a ubiquitously expressed transcription factor comprised of various subunits (p50 (NF-κB1), p52 (NF-κB2), p65 (RelA), RelB, and c-Rel). Activation of certain NF-κB subunits appears to foster an inflammatory state that may promote the development of disease. Thus characterizing the specific NF-κB subunits may provide insight into the pathogenesis of certain diseases. The purpose of this study was to determine if 1 month of a diabetic state, induced by streptozotocin (STZ) treatment, alters the constitutive level of NF-κB activation, its subunit composition, or the content of NF-κB-related proteins in rodent liver, kidney, spleen, and heart. Diabetes was induced in male Sprague-Dawley rats by a single tail vein injection of STZ (55 mg·kg-1 body weight). After 30 days, the heart, liver, spleen, and kidney were assessed for NF-κB activation and subunit composition with electrophoretic mobility shift assay (EMSA), and p50 and p65 subunit content was assessed with Western blotting. In diabetic animals, the constitutive level of NF-κB activation was reduced in liver, but was unchanged in kidney, spleen, and heart. EMSA supershifts showed the predominant subunit in the activated NF-κB complexes from both diabetic and control animals to be p50, although the p65 subunit was detected in NF-κB complexes from diabetic hearts. The content of p50 was unaltered in all diabetic tissues examined, whereas the content of p65 was increased only in hearts from diabetic animals. These findings support the idea that a diabetic state may induce specific changes in NF-κB subunit composition in certain tissues.

Acute exercise activates myocardial nuclear factor kappa B.

The myocardial stress response to exercise is dependent on exercise intensity and thus understanding the molecular responses between various exercise intensity levels might aid in exercise prescription. Nuclear factor kappa B (NF-κB) is a ubiquitous transcription factor that mediates a variety of cellular processes including inflammation, immune responses, apoptosis and cell growth/development. NF-κB can be comprised of homo- and/or heterodimers formed from five distinct proteins: p50 (NF-κB1), p52 (NF-κB2), RelA (p65), c-Rel, and RelB. NF-κB is located in the cytoplasm and kept inactive by inhibitory proteins but following the exposure to a myriad of stimuli, an activated NF-κB dimer translocates to the nucleus and exerts transcriptional effects on upwards of 150 genes. To examine the activation of NF-κB in the myocardium following exercise, male Sprague-Dawley rats (n = 24) were exercised by treadmill running at 20 m/min for 30 min or 30 m/min for 20 min. At 0, 2, or 24 h following exercise, animals were anesthetized, hearts excised and immediately frozen in liquid nitrogen. Portions of hearts were homogenized, protein concentrations determined and extracts assayed for NF-κB activation (DNA binding activity) using electrophoretic mobility shift assays (EMSA). Visual examination of EMSA autoradiographs revealed an enhanced NF-κB activation in the hearts from exercised animals when compared with non-running controls. Subsequent supershift analyses using antibodies specific for NF-κB subunits showed the higher intensity exercise was associated with p65 (RelA) in the activated NF-κB complex while the NF-κB complex in hearts from animals exercised at the lower intensity was comprised primarily of p50. These data suggest exercise is capable of activating myocardial NF-κB and that a threshold for the activation of specific NF-κB subunits may exist.

Diabetes-induced atrophy is associated with a muscle-specific alteration in NF-kappaB activation and expression.

NF-kappaB is a transcription factor implicated in pathological responses that develop during diabetes mellitus, including skeletal muscle atrophy. Given that NF-kappaB activation, protein composition, and content within diabetic skeletal muscle remain generally uncharacterized, a streptozotocin (STZ) model was used to assess NF-kappaB activation, composition, and content. Sprague-Dawley rats were injected with STZ (55 mg/kg) and after 30 days the soleus (SOL), plantaris (PL), red gastrocnemius (RG), and white gastrocnemius (WG) muscles were assessed by electrophoresis mobility shift assay and western blotting. NF-kappaB activation was detected in all muscles examined, but was reduced in RG muscles from diabetic animals. Supershifts indicated NF-kappaB was composed primarily of p50 in diabetic and control animals. The content of both p65 and p52 was elevated in SOL and PL muscles, while p52 was decreased in RG. The coactivating protein, Bcl-3, was increased in WG and RG, but decreased in PL. Both p50 and RelB remained unchanged in all tissues examined. All muscles from diabetic animals demonstrated reduced mass when compared to controls, but only the gastrocnemius demonstrated atrophy as reflected by a reduced muscle-to-body mass ratio. In conclusion, diabetic alterations to the contents and activation of the NF-kappaB protein were tissue-specific, but did not appear to alter dimer composition of constitutively bound NF-kappaB. These results indicate that diabetes may alter NF-kappaB activity and expression in a muscle-specific manner.

Heat stress inhibits skeletal muscle hypertrophy.

Heat shock proteins (Hsps) are molecular chaperones that aid in protein synthesis and trafficking and have been shown to protect cells/tissues from various protein damaging stressors. To determine the extent to which a single heat stress and the concurrent accumulation of Hsps influences the early events of skeletal muscle hypertrophy, Sprague-Dawley rats were heat stressed (42 degrees C, 15 minutes) 24 hours prior to overloading 1 plantaris muscle by surgical removal of the gastrocnemius muscle. The contralateral plantaris muscles served as controls. Heat-stressed and/or overloaded plantaris muscles were assessed for muscle mass, total muscle protein, muscle protein concentration, Type I myosin heavy chain (Type I MHC) content, as well as Hsp72 and Hsp25 content over the course of 7 days following removal of the gastrocnemius muscle. As expected, in non-heat-stressed animals, muscle mass, total muscle protein and MHC I content were significantly increased (P < 0.05) following overload. In addition, Hsp25 and Hsp72 increased significantly after 2 and 3 days of overload, respectively. A prior heat stress-elevated Hsp25 content to levels similar to those measured following overload alone, but heat stress-induced Hsp72 content was increased significantly greater than was elicited by overload alone. Moreover, overloaded muscles from animals that experienced a prior heat stress showed a lower muscle mass increase at 5 and 7 days; a reduced total muscle protein elevation at 3, 5, and 7 days; reduced protein concentration; and a diminished Type I MHC content accumulation at 3, 5, and 7 days relative to nonheat-stressed animals. These data suggest that a prior heat stress and/or the consequent accumulation of Hsps may inhibit increases in muscle mass, total muscle protein content, and Type I MHC in muscles undergoing hypertrophy.

Heat shock protein expression in rat skeletal muscle after repeated applications of pulsed and continuous ultrasound.

OBJECTIVE: To determine whether repeated ultrasound treatments are capable of increasing the expression of heat shock protein (HSP) 72 and HSP 25 in rat skeletal muscles. DESIGN: In vivo, experimental, controlled study. SETTING: Animal laboratory. ANIMALS: Male Sprague-Dawley rats (n=9). INTERVENTIONS: Ultrasound (1MHz, 15 min, 2.0 cm2 transducer) continuous at 1.0 W/cm2 spatial average temporal average intensity (CONTUS) or pulsed at 2.0 W/cm2 spatial average temporal peak intensity 50% duty cycle (PULS50) was applied on 4 consecutive days to the lower leg muscles of 1 hindlimb in each rat (n=9). MAIN OUTCOME MEASURES: Twenty-four hours after the final ultrasound application, hindlimb muscles were removed, weighed, and assessed for HSP 72 and HSP 25 content by Western blotting. Bands from blots were quantified and data were assessed using t tests (alpha=.05). RESULTS: Ultrasound did not affect core or contralateral hindlimb muscle temperature. Average muscle temperatures during the final day ultrasound treatments were 38.71 degrees +/-0.30 degrees C when using PULS50 and 38.16 degrees +/-0.57 degrees C when using CONTUS. PULS50 significantly increased HSP 25 content in the plantaris and soleus muscles and HSP 72 content in the plantaris muscles. CONTUS significantly increased HSP 72 content in the white gastrocnemius muscle. CONCLUSIONS: HSPs can be induced in skeletal muscle when ultrasound is used on a repeated basis to treat soft tissue.

Altered heat stress response following streptozotocin-induced diabetes.

The heat shock response involves activation of heat shock transcription factor 1 (Hsf1) followed by the rapid synthesis of the protective heat shock proteins (Hsps). To determine if the stress experienced during streptozotocin (STZ)-induced diabetes altered the heat shock response, male Sprague-Dawley rats (n = 33; 280-300 g) were assigned to 4 groups: (1) control, (2) diabetic (30 days after 55 mg/kg STZ i.v.), (3) heat stressed (42 degrees C for 15 minutes), and (4) diabetic heat-stressed group (heat stressed 42 degrees C for 15 minutes, 30 days after 55 mg/kg STZ i.v.). The content of Hsp72, Hsp25, and Hsf1 in skeletal muscles, heart, kidney, and liver was assessed by Western blotting, while electrophoretic mobility shift gel analysis was used to assess Hsf activation. Without heat stress, the constitutive expression of Hsp25, Hsp72, and Hsf1 in tissues from diabetic animals and controls was similar. However, 24 hours following heat stress, the heart, kidney, and liver from diabetic animals showed an increased Hsp72 and Hsp25 content compared to the same tissues from heat-stressed nondiabetic animals (P < 0.05). The white gastrocnemius and plantaris muscles from heat-stressed animals (diabetic and nondiabetic) both showed significant and similar elevations in Hsp72 content. Interestingly, while all muscles from nondiabetic animals showed significant (P < 0.05) increase in Hsp25 content after heat stress, no increase in Hsp25 content was detected in muscles from heat-stressed diabetic animals. As expected, Hsf activation was undetectable in all tissues from non-heat-stressed animals but was detectable in tissues from both diabetic and nondiabetic animals following heat stress with the exception of diabetic skeletal muscle, where it was attenuated. Hsf1 content was unaltered in all tissues examined except in the white gastrocnemius muscles from heat-stressed diabetic animals, where it was undetectable. These results suggest that when tissues from STZ-induced diabetic animals are heat stressed, the Hsp/stress response is altered in a tissue-specific manner. This impaired ability to activate the stress response may explain, at least in part, the selective atrophy of certain muscles or muscle fiber types during diabetes.

Preservation of heat stress induced myocardial hsp 72 in aged animals following caloric restriction.

The major stress inducible Heat Shock Protein (HSP 72) confers myocardial protection from ischemia. A decreased ability to express HSP 72 during homeostatic disruptions has been suggested as a possible mechanism for the increased susceptibility of aged hearts to ischemic stress. Given that Caloric Restriction (CR) has been reported to reverse or delay age-associated cellular senescence, we examined the effect of CR on the ability of aged hearts to induce and accumulate HSP 72. Adult (6 months), aged (22 months) and CR aged (22 months) Fisher 344 rats were heat stressed by raising core temperature to 41 degrees C for 10 min. Immediately after heat stress, or 24 h later, the myocardium was examined for either activation of the heat shock transcription factor (HSF) or HSP 72 accumulation. Hearts from heat stressed CR animals demonstrated an increased HSF activation and an increased HSP 72 content when compared to hearts from heat stressed aged animals. The HSF response and HSP 72 content of the hearts from heat stressed aged CR animals was comparable to that observed in hearts from heat stressed adult animals. These results suggest CR may preserve the ability of the aged myocardium to activate and/or express HSP 72.

Tissue-specific expression of inducible and constitutive Hsp70 isoforms in the western painted turtle.

Expression of Hsp73 and Hsp72 in four tissues of the naturally anoxia-tolerant western painted turtle (Chrysemys picta) was investigated in response to a 24 h forced dive and following 1 h recovery. Of the tissues examined, brain and liver displayed approximately threefold and sevenfold higher basal Hsp73 expression than heart and skeletal muscle. Basal Hsp72 expression was relatively low in all tissues examined. After the 24 h forced dive and 1 h recovery, Hsp73 expression did not differ significantly from basal expression with the exception of liver, where expression decreased significantly after 1 h recovery. Hsp72 expression was unchanged in liver following a 24 h dive; however, it increased twofold in brain and threefold in heart and skeletal muscle. Dive-induced Hsp72 expression was found to correlate inversely with basal Hsp73 expression. Following 1 h recovery, Hsp72 expression was significantly elevated in all tissues above levels in dived animals. These data indicate a tissue-specific pattern of Hsp73 and Hsp72 expression in the western painted turtle during both unstressed and stressed conditions.