Rat Plantaris Muscle Research Articles

Endurance training increases mitochondrial myoglobin and enhances its interaction with complex IV in rat plantaris muscle.

Endurance exercise training is known to increase mitochondrial respiration in skeletal muscle. However, the molecular mechanisms behind this are not fully understood. Myoglobin (Mb) is a member of the globin family, which is highly expressed in skeletal and cardiac muscles. We recently found that Mb localizes inside mitochondria in skeletal muscle and interacts with cytochrome c oxidase subunit IV (COXIV), a subunit of mitochondrial complex IV, which regulates respiration by augmenting complex IV activity. In the present study, we investigated the effect of endurance training on Mb-COXIV interaction within mitochondria in rat skeletal muscle. Eight-week-old male Wistar rats were subjected to 6-week treadmill running training. Forty-eight hours after the last training session, the plantaris muscle was removed under anesthesia and used for biochemical analysis. The endurance training increased mitochondrial content in the skeletal muscle. It also augmented complex IV-dependent oxygen consumption and complex IV activity in isolated mitochondria from skeletal muscle. Furthermore, endurance training increased Mb expression at the whole muscle level. Importantly, mitochondrial Mb content and Mb-COXIV binding were increased by endurance training. These findings suggest that an increase in mitochondrial Mb and the concomitant enhancement of Mb interaction with COXIV may contribute to the endurance training-induced upregulation of mitochondrial respiration by augmenting complex IV activity.

Ladder-based resistance training with the progression of training load altered the tibial nerve ultrastructure and muscle fiber area without altering the morphology of the postsynaptic compartment.

Scientific evidence regarding the effect of different ladder-based resistance training (LRT) protocols on the morphology of the neuromuscular system is scarce. Therefore, the present study aimed to compare the morphological response induced by different LRT protocols in the ultrastructure of the tibial nerve and morphology of the motor endplate and muscle fibers of the soleus and plantaris muscles of young adult Wistar rats. Rats were divided into groups: sedentary control (control, n = 9), a predetermined number of climbs and progressive submaximal intensity (fixed, n = 9), high-intensity and high-volume pyramidal system with a predetermined number of climbs (Pyramid, n = 9) and lrt with a high-intensity pyramidal system to exhaustion (failure, n = 9). myelinated fibers and myelin sheath thickness were statistically larger in pyramid, fixed, and failure. myelinated axons were statistically larger in pyramid than in control. schwann cell nuclei were statistically larger in pyramid, fixed, and failure. microtubules and neurofilaments were greater in pyramid than in control. morphological analysis of the postsynaptic component of the plantar and soleus muscles did not indicate any significant difference. for plantaris, the type i myofibers were statistically larger in the pyramid and fixed compared to control. the pyramid, fixed, and failure groups for type ii myofibers had larger csa than control. for soleus, the type i myofibers were statistically larger in the pyramid than in control. pyramid and fixed had larger csa for type ii myofibers than control and failure. the pyramid and fixed groups showed greater mass progression delta than the failure. We concluded that the LRT protocols with greater volume and progression of accumulated mass elicit more significant changes in the ultrastructure of the tibial nerve and muscle hypertrophy without endplate changes.

Temporal expression of mitochondrial life cycle markers during acute and chronic overload of rat plantaris muscles.

Skeletal muscle hypertrophy is generally associated with a fast-to-slow phenotypic adaptation in both human and rodent models. Paradoxically, this phenotypic shift is not paralleled by a concomitant increase in mitochondrial content and aerobic markers that would be expected to accompany a slow muscle phenotype. To understand the temporal response of the mitochondrial life cycle (i.e., biogenesis, oxidative phosphorylation, fission/fusion, and mitophagy/autophagy) to hypertrophic stimuli, in this study, we used the functional overload (FO) model in adult female rats and examined the plantaris muscle responses at 1 and 10weeks. As expected, the absolute plantaris muscle mass increased by ∼12 and 26% at 1 and 10weeks following the FO procedure, respectively. Myosin heavy-chain isoform types I and IIa significantly increased by 116% and 17%, respectively, in 10-week FO plantaris muscles. Although there was a general increase in protein markers associated with mitochondrial biogenesis in acute FO muscles, this response was unexpectedly sustained under 10-week FO conditions after muscle hypertrophy begins to plateau. Furthermore, the early increase in mito/autophagy markers observed under acute FO conditions was normalized by 10weeks, suggesting a cellular environment favoring mitochondrial biogenesis to accommodate the aerobic demands of the plantaris muscle. We also observed a significant increase in the expression of mitochondrial-, but not nuclear-, encoded oxidative phosphorylation (OXPHOS) proteins and peptides (i.e., humanin and MOTS-c) under chronic, but not acute, FO conditions. Taken together, the temporal response of markers related to the mitochondrial life cycle indicates a pattern of promoting biogenesis and mitochondrial protein expression to support the energy demands and/or enhanced neural recruitment of chronically overloaded skeletal muscle.

Associating Inulin with a Pea Protein Improves Fast-Twitch Skeletal Muscle Mass and Muscle Mitochondrial Activities in Old Rats.

Aging is associated with a decline in muscle mass and function, leading to increased risk for mobility limitations and frailty. Dietary interventions incorporating specific nutrients, such as pea proteins or inulin, have shown promise in attenuating age-related muscle loss. This study aimed to investigate the effect of pea proteins given with inulin on skeletal muscle in old rats. Old male rats (20 months old) were randomly assigned to one of two diet groups for 16 weeks: a 'PEA' group receiving a pea-protein-based diet, or a 'PEA + INU' group receiving the same pea protein-based diet supplemented with inulin. Both groups showed significant postprandial stimulation of muscle p70 S6 kinase phosphorylation rate after consumption of pea proteins. However, the PEA + INU rats showed significant preservation of muscle mass with time together with decreased MuRF1 transcript levels. In addition, inulin specifically increased PGC1-α expression and key mitochondrial enzyme activities in the plantaris muscle of the old rats. These findings suggest that dietary supplementation with pea proteins in combination with inulin has the potential to attenuate age-related muscle loss. Further research is warranted to explore the underlying mechanisms and determine the optimal dosage and duration of intervention for potential translation to human studies.

MOTS‐c protein expression increases following aerobic exercise training and remains elevated during detraining

Mitochondrial open reading frame of the 12S rRNA‐c (MOTS‐c) is a mitochondrial‐derived peptide that is released into the circulation following intense physical activity and, purportedly, has systemic impacts on energy metabolism and insulin sensitivity. Exogenous administration of MOTS‐c in rodent models enhances physical activity / endurance and reduces fat mass in aged mice through the regulation of, in part, the glycolysis / pentose phosphate pathway and amino acid metabolism. Considering that mitochondrial volume and mitochondrial DNA copy number increase following chronic aerobic exercise training, we hypothesized that MOTS‐c expression also would be elevated in exercise‐trained skeletal muscle. MOTS‐c protein expression from phenotypically mixed plantaris muscles of adult female Sprague Dawley rats were compared from six conditions: sedentary (SED; n=11), voluntary exercise training for four (EX4; n=9), six (EX6; n=6), or eight weeks (EX8; n=8), and detraining after four (DETR4) or six (DETR6) weeks, which followed four or six weeks of exercise training, respectively. Total running distances were ~551±61, 371±94, 560±71, 321±44, and 519±27 km for EX4, EX6, EX8, DETR4 and DETR6, respectively. DETR4 rat running distance was significantly lower than EX4, EX8, and DETR6 rats (p<0.01). Total muscle protein homogenate was isolated from mid‐belly muscle chunks and separated using 15% SDS‐PAGE gels (10 μg/sample). Following transfer, membranes were incubated with a custom rabbit anti‐rat MOTS‐c polyclonal antibody, developed, scanned, stripped and re‐probed for GAPDH as a loading control. MOTS‐c protein was significantly elevated from SED (set at 100%) to 188±61, 158±37, 212±27, 168±29, 223±36% in EX4, EX6, EX8, DETR4 and DETR6, respectively (p<0.05). Furthermore, preliminary findings indicate that MOTS‐c is present exclusively within the cytoplasm of skeletal muscle and not compartmentalized within the nuclei or mitochondria. Given that long‐term aerobic exercise augments mitochondrial volume within skeletal muscle, our data suggest that the observed increase in MOTS‐c protein in the present study parallels this mitochondrial adaptation to aerobic physical activity. Taken together, these findings indicate that a more aerobically‐trained individual would have an enhanced MOTS‐c presence within skeletal muscle and, therefore, a greater potential to regulate energy and insulin sensitivity when MOTS‐c is released systemically; additionally, the potential benefits of MOTS‐c are sustained during a period of physical inactivity (e.g., detraining) following exercise training.

Investigating the Effects of Four Weeks of Spinal Nerve Ligation After a Period of Combined Training on the Expression of Involved Genes in Calcium Current in Plantaris Muscle of Male Wistar Rats

Aims This study aims to investigate the effect of spinal nerve ligation (SNL) after a period of combined training on the expression of some genes that are involved in the calcium flow in the plantaris muscle of male Wistar rats. Methods & Materials A total of 16 adult male Wistar rats were randomly divided into 2 groups, namely the control-SNL (n=8) and combined training-SNL (n=8). The animals in the training group participated in a training program for 6 weeks. After this period, the protocol of spinal SNL was performed on the research groups for 4 weeks. Finally, the rats were dissected and the plantaris muscle was removed. Real-time polymerase chain reaction was used to measure the mRNA expression of STIM1, ORAI1, and MG29 genes. Findings In the combined training-SNL group, an increase in the expression of STIM1 (P=0.01), ORAI1 (P=0.002), and MG29 (P=0.02) was observed when compared to the control-SNL group. Conclusion The results of the present study showed that SNL reduces the expression of STIM1, ORAI1, and MG29 in the plantaris muscle. Meanwhile, combined training before SNL has a compensatory effect in this regard.

X-ray Diffraction Analysis to Explore Molecular Traces of Eccentric Contraction on Rat Skeletal Muscle Parallelly Evaluated with Signal Protein Phosphorylation Levels.

We performed X-ray diffraction analyses on rat plantaris muscle to determine if there are strain-specific structural changes at the molecular level after eccentric contraction (ECC). ECC was elicited in situ by supramaximal electrical stimulation through the tibial nerve. One hour after a series of ECC sessions, the structural changes that remained in the sarcomere were evaluated using X-ray diffraction. Proteins involved in cell signaling pathways in the muscle were also examined. ECC elicited by 100, 75, and 50 Hz stimulation respectively developed peak tension of 1.34, 1.12 and 0.79 times the isometric maximal tetanus tension. The series of ECC sessions phosphorylated the forkhead box O proteins (FoxO) in a tension-time integral-dependent manner, as well as phosphorylated the mitogen-activated protein kinases (MAPK) and a protein in the mammalian target of rapamycin (mTOR) pathway in a maximal tension dependent manner. Compared to isometric contractions, ECC was more efficient in phosphorylating the signaling proteins. X-ray diffraction revealed that the myofilament lattice was preserved even after intense ECC stimulation at 100 Hz. Additionally, ECC < 75 Hz preserved the molecular alignment of myoproteins along the myofilaments, while 75-Hz stimulation induced a slight but significant decrease in the intensity of meridional troponin reflection at 1/38 nm−1, and of myosin reflection at 1/14.4 nm−1. These two reflections demonstrated no appreciable decrease with triple repetitions of the standard series of ECC sessions at 50 Hz, suggesting that the intensity decrease depended on the instantaneous maximal tension development rather than the total load of contraction, and was more likely linked with the phosphorylation of MAPK and mTOR signaling proteins.

Functional Isolation of Single Motor Units of Rat Medial Gastrocnemius Muscle.

This work outlines functional isolation of motor units (MUs), a standard electrophysiological method for determining characteristics of motor units in hindlimb muscles (such as the medial gastrocnemius, soleus, or plantaris muscle) in experimental rats. A crucial element of the method is the application of electrical stimuli delivered to a motor axon isolated from the ventral root. The stimuli may be delivered at constant or variable inter-pulse intervals. This method is suitable for experiments on animals at varying stages of maturity (young, adult or old). Moreover, this protocol can be used in experiments studying variability and plasticity of motor units evoked by a large spectrum of interventions. The results of these experiments may both augment basic knowledge in muscle physiology and be translated into practical applications. This procedure focuses on the surgical preparation for the recording and stimulation of MUs, with an emphasis on the necessary steps to achieve preparation stability and reproducibility of results.

Commentaries on Viewpoint: The interaction between SARS-CoV-2 and ACE2 may have consequences for skeletal muscle viral susceptibility and myopathies.

Commentaries on Viewpoint: The interaction between SARS-CoV-2 and ACE2 may have consequences for skeletal muscle viral susceptibility and myopathies.

Fast repetitive stretch suppresses denervation-induced muscle fibrosis.

We aimed to examine the influence of different speeds of stretching on denervation-induced skeletal muscle fibrosis. Stretching was passively applied to rat plantaris muscle denervated by sciatic nerve excision in three different cycles of 0.5, 3, or 12 cycles/min, for 20 min/d for 2 weeks. Gene analysis results showed greater expression of fibrosis-related factors with fast stretching compared with non-stretched muscle. Laser Doppler blood flow analysis indicated reduced intramuscular blood flow during stretching. Histological analysis demonstrated fibrotic area decreases in 12 cycles/min stretched muscle compared with non-stretched muscle. Slower stretching induced greater mRNA expression of collagen and fibroblasts and greater decrement of blood flow. Histologically, faster stretching suppressed fibrosis. These results suggest that fast repetitive stretching of denervated muscle might suppress processes of muscle fibrosis.

Photobiomodulation modulates the expression of inflammatory cytokines during the compensatory hypertrophy process in skeletal muscle.

Compensatory hypertrophy (CH) occurs due to excessive mechanical load on a muscle, promoting an increase in the size of muscle fibers. In clinical practice, situations such as partial nerve injuries, denervation, and muscle imbalance caused by trauma to muscles and nerves or diseases that promote the loss of nerve conduction can induce CH in muscle fibers. Photobiomodulation (PBM) has demonstrated beneficial effects on muscle tissue during CH. The aim of the present study was to evaluate the effect of PBM on the inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) as well as type 2 metalloproteinases (MMP-2) during the process of CH due to excessive load on the plantaris muscle in rats. Forty-five Wistar rats weighing 250g were divided into three groups: control group (n = 10), hypertrophy (H) group (n = 40), and H + PBM group (n = 40). CH was induced through the ablation of synergist muscles of the plantaris muscle. The tendons of the gastrocnemius and soleus muscles were isolated and sectioned to enable the partial removal of each of muscle. The preserved plantaris muscle below the removed muscles was submitted to excessive functional load. PBM was performed with low-level laser (AsGaAl, λ = 780nm; 40mW; energy density: 10J/cm2; 10s on each point, 8 points; 3.2J). Animals from each group were euthanized after 7 and 14days. The plantaris muscles were carefully removed and sent for analysis of the gene and protein expression of IL-6 and TNF-α using qPCR and ELISA, respectively. MMP-2 activity was analyzed using zymography. The results were submitted to statistical analysis (ANOVA + Tukey's test, p < 0.05). The protein expression analysis revealed an increase in IL-6 levels in the H + PBM group compared to the H group and a reduction in the H group compared to the control group. A reduction in TNF-α was found in the H and H + PBM groups compared to the control group at 7days. The gene expression analysis revealed an increase in IL-6 in the H + PBM group compared to the H group at 14days as well as an increase in TNF-α in the H + PBM group compared to the H group at 7days. Increases in MMP-2 were found in the H and H + PBM groups compared to the control group at both 7 and 14days. Based on findings in the present study, it is concluded that PBM was able to modulate pro-inflammatory cytokines that are essential for the compensatory hypertrophy process. However, it has not shown a modulation effect directly in MMP-2 activity during the same period evaluated.

Added mass in rat plantaris muscle causes a reduction in mechanical work.

Most of what we know about whole muscle behaviour comes from experiments on single fibres or small muscles that are scaled up in size without considering the effects of the additional muscle mass. Previous modelling studies have shown that tissue inertia acts to slow the rate of force development and maximum velocity of muscle during shortening contractions and decreases the work and power per cycle during cyclic contractions; however, these results have not yet been confirmed by experiments on living tissue. Therefore, in this study we conducted in situ work-loop experiments on rat plantaris muscle to determine the effects of increasing the mass of muscle on mechanical work during cyclic contractions. We additionally simulated these experimental contractions using a mass-enhanced Hill-type model to validate our previous modelling work. We found that greater added mass resulted in lower mechanical work per cycle relative to the unloaded trials in which no mass was added to the muscle (P=0.041 for both 85 and 123% increases in muscle mass). We additionally found that greater strain resulted in lower work per cycle relative to unloaded trials at the same strain to control for length change and velocity effects on the work output, possibly due to greater accelerations of the muscle mass at higher strains. These results confirm that tissue mass reduces muscle mechanical work at larger muscle sizes, and that this effect is likely amplified for lower activations.

Testosterone is Key to Increase the Muscle Capillary Density of Old and Trained Rats

Introduction It is indicated that aging reduces muscular vascularity. Thus, strategies that aim to reverse or decrease the progression of these changes are suggested. Therefore, the present study aimed to analyze the blood capillary density of the plantaris muscle (PL) of aged rats submitted to strength training and exogenous testosterone use. Methods A total of 30 rats were divided equally into the following groups: EA: 20 months old; OLD: 24 months old; OLD + S: testosterone; ST: strength training; and ST + S: strength training + testosterone. Strength training was performed 3 times a week for 15 weeks. Testosterone administration was performed by the intraperitoneal method 2 times a week at a dose of 10mg/kg. All of the morphological parameters were analyzed using morphoquantitative techniques. Results A significant increase in the capillaries numerical density of the OLD + S and ST + S groups. The OLD + S and ST + S groups demonstrated a higher ratio of capillaries per myofiber than the EA, OLD and ST groups. The OLD and ST groups had a higher ratio than the EA group. The OLD + S, ST and ST + S groups presented a statistically significant increase in the cross-sectional area in the type I fibers when compared with the EA and OLD groups. However, the ST group showed a significant increase compared with the OLD group. In type II fibers, the ST and ST + S groups showed a greater cross-sectional area than the EA group. As for the mean cross-sectional area, the ST and ST + S groups presented significantly larger areas than the other groups. Conclusion Anabolic steroid administration is crucial to increase the blood capillary density of the plantaris muscle of old rats, independently of the effects of strength training.

Hyperglycaemia correlates with skeletal muscle capillary regression and is associated with alterations in the murine double minute-2/forkhead box O1/thrombospondin-1 pathway in type 1 diabetic BioBreeding rats.

Type 1 diabetes can have deleterious effects on skeletal muscle and its microvasculature. Our laboratory has recently identified murine double minute-2 as a master regulator of muscle microvasculature by controlling expression levels of two key molecular actors of the angio-adaptive process: the pro-angiogenic vascular endothelial growth factor-A and the anti-angiogenic thrombospondin-1. Here, we show for the first time that in the soleus and plantaris muscles of the diabetes-prone BioBreeding rats, a rodent model of autoimmune type 1 diabetes, murine double minute-2 protein levels are significantly decreased, coinciding with elevated protein levels of thrombospondin-1 and its transcription factor forkhead box O1. Significant capillary regression was observed to similar extent in soleus and plantaris muscles of type 1 diabetic rats. Elevated blood glucose levels were correlated with the loss of capillaries, the reduction in murine double minute-2 expression and with the elevations in thrombospondin-1. Vascular endothelial growth factor-A protein levels were unaltered or even increased in diabetic animals, yet type 1 diabetic animals had less vascular endothelial growth factor receptor-2 abundance. The vascular endothelial growth factor-A/thrombospondin-1 ratio, a good indicator of skeletal muscle angio-adaptive environment, was decreased in type 1 diabetic muscle. Our results suggest that the murine double minute-2-forkhead box O1-thrombospondin-1 pathway plays an important role in angio-regulation of the skeletal muscle in the pathophysiological context of type 1 diabetes.

PO-245 Exercise at the lactate threshold (LT) and above the LT increases phosphorylation of AMPK and Akt in rat skeletal muscle

&#x0D; Objective A single bout of exercise can enhance glucose uptake in skeletal muscle. It is well established that AMP-activated protein kinase (AMPK) activation is required for stimulation of glucose uptake by exercise. After the initial phosphorylation of glucose by hexokinase, glucose is further utilized to mitochondrial oxidation during exercise. The direct or functional interaction between hexokinase and Akt may act to integrate glucose metabolism in working muscle. Hence, AMPK and Akt activation would be cooperatively regulated exercise-induced activation of glucose metabolism. Although exercise at the lactate threshold (LT) and above the LT sharply increase glucose uptake via increasing AMPK activity, whether LT exercise can also increase Akt activity is still unknown. Therefore, we examined the AMPK and Akt activity immediately after several intensities of exercise.&#x0D; Methods Male wistar rats (250-270 g) were randomly assigned to 3 groups: Resting control (sedentary, n=16), Low-intensity exercise (LIE: 10 m/min for 30 min, n=8), LT intensity exercise 1 (LTE1: 17.5 m/min for 30 min, n=8), LT intensity exercise 2 (LTE2: 22.5 m/min for 30 min, n=8), and High-intensity exercise (HE: 27.5 m/min for 30 min, n=8). Immediately after each treadmill exercise, plantaris and soleus muscles were dissected.&#x0D; Results LIE exercise did not changed AMPK phosphorylation site (Thr172), indicator of AMPK activity, and Akt phosphorylation site (Ser473, Thr308), indicator of Akt activity, in these muscles compared with resting control. At and above LTE1 exercise increased the phosphorylation of AMPK in these tissues. At and above LTE2 exercise increased the phosphorylation of Akt in these tissues. Therefore, increasing AMPK and Akt activity immediately after LT exercise possibly involved with regulating glucose metabolism.&#x0D; Conclusions Phosphorylation of AMPK and Akt is increased immediately after at and above LT exercise in rat soleus and plantaris muscle.&#x0D;

Muscle type-specific RNA polymerase II recruitment during PGC-1α gene transcription after acute exercise in adult rats.

Epigenetic regulation of gene expression differs between fast- and slow-twitch skeletal muscles in adult rats, although the precise mechanisms are still unknown. The present study investigates the differences in responses of RNA polymerase II (Pol II) and histone acetylation during transcriptional activation in the plantaris and soleus muscles of adult rats after acute treadmill running. We targeted the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) gene to analyze epigenomic changes by chromatin immunoprecipitation. The mRNA expression of the PGC-1α-b isoform was significantly upregulated in both plantaris and soleus muscles 2 h after acute running, although the magnitude of the upregulation was more pronounced in the plantaris muscle. The sequences of proximal exons of the PGC-1α locus were expressed more in the plantaris muscle after acute running. Accumulation of Pol II was noted near the alternative exon 1 in both plantaris and soleus muscles in association with the enhanced distribution of acetylated histone 3. Accumulation of Pol II was also observed at the transcription start site, exon 2, and exon 3 in the plantaris muscle, but not the soleus muscle. It was noted that in the soleus muscle, acetylation of histone 3 at lysine 27 was enhanced throughout the PGC-1α locus in response to transcriptional activation, suggesting that elongating Pol II was capable of traveling through to the end of the locus. These results indicate that the mobility of Pol II during PGC-1α transcription differed between fast- and slow-twitch skeletal muscles, affecting the strength of the transcriptional activity.NEW & NOTEWORTHY Fast- and slow-twitch skeletal muscles have distinct characteristics in both force production and metabolism. Epigenetic regulations also largely differ in these muscles. Here we show that RNA polymerase II is distributed extensively at the proximal regions downstream of transcription start site during the transcriptional activation of PGC-1α in fast-twitch muscles, but it accumulates at the first exon in slow-twitch muscles. These findings will provide a basis to understand type-specific mechanisms in skeletal muscle.

Amount of daily exercise is an essential stimulation to alter the epigenome of skeletal muscle in rats.

Long-term running training causes epigenetic changes in the skeletal muscles. Here we tested the effects of the total amount or duration of running training on the distribution of histones in the rat plantaris muscle. Post-weaned young rats were assigned to 3 different training groups: Run-1, 30 min/day running exercise for 8 wk using an animal treadmill at 24 m/min; Run-2, 15 min/day for 8 wk; and Run-3, 60 min/day for 4 wk. Citrate synthase activity was not significantly changed by running training, although the slight increase was observed in Run-3. Genes that were previously defined as showing the typical responses to running training were targeted to measure the distribution of histones using chromatin immunoprecipitation. The distribution of acetylated histone 3 was elevated in Run-2 and Run-3, but not in Run-1. Incorporation of H3.3 into the nucleosome was stimulated in Run-1, whereas H3.3 distribution was unchanged in Run-2 or downregulated in Run-3. Significant downregulation of H3.3 expression was also detected in Run-3. We further checked the responses of the target genes during acute running. Target genes were transcriptionally activated and histone acetylation was stimulated at the loci in response to acute running. These results suggested that the exchange of the histone component to H3.3 was stimulated by running training, inhibiting the accumulation of acetylated histones in Run-1. Additionally, it was further suggested that the enhanced daily amount of running caused changes in the H3.3 expression, affecting the rate of the histone exchange in Run-3. NEW & NOTEWORTHY Chromatin remodeling in the skeletal muscle is a potent mechanism preventing disuse atrophy in later life that can be acquired via long-term exercise training. Here we demonstrated in rats that daily exercise amount is a key factor in the development of epigenetic changes in the skeletal muscle. To acquire a health benefit, our research suggests the importance of considering the time endurance for daily exercise bouts.

Effect of hindlimb unloading and reloading on the soleus and plantaris muscles in diabetic rats.

[Purpose] This study aimed to induce disuse muscle atrophy in Goto-Kakizaki rats, a type 2 diabetes model, to investigate the effects of reloading on the soleus and plantaris muscles. [Materials and Methods] Wistar and Goto-Kakizaki (GK) rats were divided into 6 groups: Wistar Control (WC), GK Control (GC), Wistar Tail suspension (WS), GK Tail suspension (GS), and Wistar Reload (WR), GK Reload (GR). [Results] Investigation of myofiber cross-sectional area in Goto-Kakizaki rat soleus muscles indicated that the GS group showed significantly lower values than the GC and GR groups. No significant differences were observed between the GC and GR groups. However, investigation of plantaris muscles in Goto-Kakizaki rats indicated that the GS and GR groups showed a significant decrease compared to the GC group. No significant differences were found between the GS and GR groups. [Conclusion] Investigation of muscle weight/body weight ratios and myofiber cross-sectional area in tail suspension groups confirmed the induction of muscular atrophy. The differences in the degree of atrophy and recovery in terms of myofiber cross-sectional area observed in Goto-Kakizaki rat plantaris muscles may be influenced by the myofiber type and diabetes.

アイシング処置がラット損傷筋の回復過程に及ぼす影響

Although icing treatment has been well accepted as aftercare in sports fields, the detailed mechanisms of the treatment is not fully understood. In this study, we investigated the effect of icing treatment on the recovery process of rat plantaris muscles with artificially induced muscle damage. Sixty male Wistar rats (8-weeks-old) were randomly assigned to three groups; control (CTL), bupivacaine-injected (BPVC), and icing treatment after BPVC (ICE). Icing treatment was applied for 20 min immediately after BPVC, and the treatment was used once per day for 3 days. The plantaris muscles were removed at 3, 7, 15, and 28 days after the muscle damage, then immunohistochemical and real time RT-PCR analysis were performed. In histochemical analysis, although significant changes were found in the relative muscle weight, cross-sectional area of muscle fiber, percentage of muscle fiber with central nuclei, and expressed immature myosin heavy chain isoforms after muscle damage, as compared to the CTL group, no differences were found between BPVC and ICE groups. In mRNA expression analysis, the ICE group had a significantly lower value of MyoD than the BPVC group at 3 days after the damage. Expression of IL-6 mRNA, which relates to muscle inflammation, indicated significantly higher value in BPVC, but not in ICE, than CTL groups at 7days after the damage. Furthermore, BKB2 receptor, which relates to acute muscle soreness, indicated a significantly higher expression in BPVC than ICE groups at 3 days after the damage. These results suggest that icing treatment is effective to suppress muscle inflammation and soreness at an early stage of recovery from damage, but not effective for muscle regeneration at a later stage.

Alternate-Day High-Fat Diet Induces an Increase in Mitochondrial Enzyme Activities and Protein Content in Rat Skeletal Muscle.

Long-term high-fat diet increases muscle mitochondrial enzyme activity and endurance performance. However, excessive calorie intake causes intra-abdominal fat accumulation and metabolic syndrome. The purpose of this study was to investigate the effect of an alternating day high-fat diet on muscle mitochondrial enzyme activities, protein content, and intra-abdominal fat mass in rats. Male Wistar rats were given a standard chow diet (CON), high-fat diet (HFD), or alternate-day high-fat diet (ALT) for 4 weeks. Rats in the ALT group were fed a high-fat diet and standard chow every other day for 4 weeks. After the dietary intervention, mitochondrial enzyme activities and protein content in skeletal muscle were measured. Although body weight did not differ among groups, the epididymal fat mass in the HFD group was higher than those of the CON and ALT groups. Citrate synthase and beta-hydroxyacyl CoA dehydrogenase activities in the plantaris muscle of rats in HFD and ALT were significantly higher than that in CON rats, whereas there was no difference between HFD and ALT groups. No significant difference was observed in muscle glycogen concentration or glucose transporter-4 protein content among the three groups. These results suggest that an alternate-day high-fat diet induces increases in mitochondrial enzyme activities and protein content in rat skeletal muscle without intra-abdominal fat accumulation.