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Heat-induced endoplasmic reticulum stress in soleus and gastrocnemius muscles and differential response to UPR pathway in rats.

ABSTRACT: The present study aimed to investigate the differential response of oxidative (soleus) and glycolytic (gastrocnemius) muscles to heat-induced endoplasmic reticulum (ER) stress. It was hypothesized that due to compositional and functional differences, both muscles respond differently to acute heat stress. To address this, male Sprague Dawley rats (12/group) were subjected to thermoneutral (25 °C) or heat stress (42 °C) conditions for 1 h. Soleus and gastrocnemius muscles were removed for analysis post-exposure. A significant increase in body temperature and free radical generation was observed in both the muscles following heat exposure. This further caused a significant increase in protein carbonyl content, AOPP, and lipid peroxidation in heat-stressed muscles. These changes were more pronounced in heat-stressed soleus compared to the gastrocnemius muscle. Accumulation of unfolded, denatured proteins results in ER stress, causing activation of unfolded protein response (UPR) pathway. The expressions of UPR transducers were significantly higher in soleus as compared to the gastrocnemius muscle. A significant elevation in resting intracellular calcium ion was also observed in heat-stressed soleus muscle. Overloading of cells with misfolded proteins in soleus muscle activated ER-induced apoptosis as indicated by significant upregulation of C/EBP homologous protein and Caspase12. The study provides a detailed mechanistic representation of the differential response of muscles toward UPR under heat stress. Data suggests that soleus majorly being an oxidative muscle is more prone to heat stress-induced insult indicated by enhanced apoptosis. This study may aid in devising mitigation strategies to improve muscle performance under heat stress.

SUBMITTER: Sharma S

PROVIDER: S-EPMC7925797 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Genes can be activated or inhibited by signals within the tissues in response to an acute bout of exercise. It is unclear how a particular aerobic exercise bout may influence two muscles with similar actions to the activity. Therefore, the purposes of this investigation was to determine the gene response of selected genes involved in the "stress" response of the gastrocnemius (fast-twitch) and soleus (slow-twitch) muscles to a single two hour aerobic exercise bout in female Sprague-Dawley Rats at the 1 hour time point after the exercise. Exercised rats were run (n=8) for 2 hours at 20 m.min(-1) and one hour after the completion of the bout had their soleus (S) and gastrocnemius (G) muscles removed. Age and timed matched sedentary control rats had both S and G muscles removed also. RNA was isolated from all muscles. Real-time PCR analysis was performed on the following genes: NFκB, TNFα, and Atf3. GAPDH was used as the housekeeping gene for both muscles. S muscle showed more genes altered (n = 52) vs G (n = 26). NFκB gene expression was 0.83 ± 0.14 in the exercised S but was + 1.36 ± 0.58 in the exercised G and was not significantly different between the muscles. TNFα was altered 1.30 ± 0. 34 in the exercised S and 1.36 ± 0.71 in the exercised G and was not significantly different between the muscles. The gene Atf3 was significantly altered at 4.97 ± 1.01 in the exercised S, while it was not significantly altered in the exercised G (0.70 ± 0.55). This study demonstrates that an acute bout of aerobic exercise can alter gene expression to a different extent in both the S and G muscles. It is highly likely that muscle recruitment was a factor which influenced the gene expression in theses muscles. It is interesting to note that some genes were similarly activated in these two muscles but other genes may demonstrate a varied response to the same exercise bout depending on the type of muscle. Key pointsThe soleus (primarily slow twitch) and the gastrocnemius (primarily fast type) do not respond the same to a given exercise bout.There are gene transcription differences in stress genes between the 2 muscles.The results of exercise studies should be carefully viewed as the muscle used in measurements may not provide an adequate representation of all skeletal muscles.

Project description:1. The effect of hypocaloric feeding (25% of normal food intake for 21 days) of rats on the enzymic and metabolic adaptations in the gastrocnemius, plantaris and soleus muscles was studied. 2. In control and hypocaloric rats the muscle relaxation rates at 100 Hz were 35.76 and 11.38% force loss/10 ms respectively. Control rats exhibited enhanced force of muscle contraction as the frequency of stimulation increased from 10 to 100 Hz, with maximum force being at 100 Hz. Hypocaloric rats exhibited a decrease in the increment of force being exerted at high frequencies, with maintenance of force at lower stimulatory frequencies. 3. In muscles of hypocaloric rats, there were significant decreases in the maximal activities of hexokinase (17.6-37.0%), 6-phosphofructokinase (22.7-34.2%), pyruvate kinase (21.2-36.0%), citrate synthase (34.1-41.5%), oxoglutarate dehydrogenase (29.4-52.4%) and 3-hydroxyacyl-CoA dehydrogenase (26.7-32.1%), whereas the activities of glycogen phosphorylase increased (23.8-43.4%) compared with control values. 4. In soleus-muscle strip preparations of hypocaloric rats, there were significant decreases in the rates of lactate production (28.1%) and glucose oxidation (32.6%) compared with control preparations. 5. Mitochondrial preparations from muscles of hypocaloric rats incubated with various substrates exhibited decreased rates of oxygen uptake compared with control preparations. 6. In muscles of hypocaloric rats (gastrocnemius and soleus), there were significant decreases in the concentrations of glycogen (P less than 0.001) and phosphocreatine (P less than 0.001) and increases in those of pyruvate (P less than 0.001), lactate (P less than 0.001) and ADP (P less than 0.001), whereas those of ATP and AMP remained unchanged. 7. Calculated [lactate]/[pyruvate] and [ATP]/[ADP] ratios exhibited significant increases (P less than 0.05) and decreases (P less than 0.05) in muscles of hypocaloric rats respectively. 8. The results are discussed in relation to the genesis of muscle dysfunction caused by malnutrition.

Project description:BackgroundFibromyalgia (FM) is a chronic musculoskeletal pain disorder, characterized by chronic widespread pain and bodily tenderness and is often accompanied by affective disturbances, however often with unknown etiology. According to recent reports, physical and psychological stress trigger FM. To develop new treatments for FM, experimental animal models for FM are needed to be development and characterized. Using a mouse model for FM including intermittent cold stress (ICS), we hypothesized that ICS leads to morphological alterations in skeletal muscles in mice.MethodsMale and female ICS mice were kept under alternating temperature (4 °C/room temperature [22 °C]); mice constantly kept at room temperature served as control. After scarification, gastrocnemius and soleus muscles were removed and snap-frozen in liquid nitrogen-cooled isopentane or fixed for electron microscopy.ResultsIn gastrocnemius/soleus muscles of male ICS mice, we found a 21.6% and 33.2% decrease of fiber cross sectional area (FCSA), which in soleus muscle concerns the loss of type IIa and IIx FCSA. This phenomenon was not seen in muscles of female ICS mice. However, this loss in male ICS mice was associated with an increase in gastrocnemius of the density of MIF+ (8.6%)-, MuRF+ (14.7%)-, Fbxo32+ (17.8%)-cells, a 12.1% loss of capillary contacts/muscle fiber as well as a 30.7% increase of damaged mitochondria in comparison with male control mice. Moreover, significant positive correlations exist among densities (n/mm(2)) of MIF+, MuRF+, Fbxo32+-cells in gastrocnemius/ soleus muscles of male ICS mice; these cell densities inversely correlate with FCSA especially in gastrocnemius muscle of male ICS mice.ConclusionThe ICS-induced decrease of FCSA mainly concerns gastrocnemius muscle of male mice due to an increase of inflammatory and atrogenic cells. In soleus muscle of male ICS and soleus/gastrocnemius muscles of female ICS mice morphological alterations seem to occur not at all or delayed. The sex-specificity of findings, which is not easily reconciled with the epidemiology of FM (female predominance), implicate that gastrocnemius muscle of male ICS mice should preferentially be used for future investigations with FM. Moreover, we suggest to investigate morphological and/or molecular alterations at different time-points (up to two weeks) after ICS.

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Heat-induced endoplasmic reticulum stress in soleus and gastrocnemius muscles and differential response to UPR pathway in rats.

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