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Background and aims Lipopolysaccharide (LPS) is a main component of the Gram-negative bacterial cell wall and is associated with a greater risk of atherosclerosis development in periodontal disease. LPS has been reported to increase both CD36 and CD204 expression and enhance the uptake of modified low-density lipoprotein (LDL). However, the signaling pathways by which LPS enhances these expression levels and function have not been fully elucidated, although the clarification of these signaling pathways is important for identifying therapeutic targets for atherosclerosis. Methods and results We have shown here that LPS activated the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway, increased both CD204 and CD36 expression, and enhanced the uptake of acetylated-LDL (Ac-LDL) in mouse bone marrow macrophages. The MAPK/ERK kinase (MEK) inhibitors, U0126 (1 μM) and PD0325901 (10 nM), did not affect the expression of either CD36 or CD204 or the uptake of Ac-LDL under normal conditions (no treatment with LPS). In contrast, U0126 (1 μM) and PD0325901 (10 nM) blocked the LPS-induced increase in Ac-LDL uptake and CD204 expression but not CD36 expression. Conclusions These results suggest that LPS may increase Ac-LDL uptake and enhance CD204 expression through MAPK/ERK activation and CD36 expression through an ERK-independent pathway. Since MEK inhibitors block CD204 expression in mouse BM macrophages only under LPS treatment but not under normal conditions, a MEK inhibitor might be a good candidate compound for the treatment of LPS-induced atherosclerosis. [ABSTRACT FROM AUTHOR]

Purpose: Body weight in young growing and young adult animals was reduced by a high dietary density of whey protein concentrate; however, it is unclear whether dietary proteins similarly affect body weight in aging animals. Here, we examined whether whey protein or whey peptide ingestion suppressed body fat accumulation and affected protein expression and phosphorylation in skeletal muscle in aging mice. Methods: Twenty-six male senescence-accelerated mouse prone 6 (SAMP6) mice were assigned randomly to three dietary treatment groups: 18.7 % casein control (CON), 18.7 % whey protein (WPR), and 18.7 % whey peptide (WPE). After 28 weeks of treatment, skeletal tissues were dissected and weighed for analysis. Western blotting was performed to examine the expression of AMP-activated protein kinase (AMPK), acetyl-CoA carboxylase (ACC), and adipose triglyceride lipase (ATGL) in quadriceps muscles. Results: Body (CON: 47.6 ± 2.2 g, WPR: 48.2 ± 2.7 g, WPE: 38.3 ± 2.0 g) and relative white adipose tissue (CON: 38.5 ± 3.5 mg/g, WPR: 43.8 ± 4.0 mg/g, WPE: 21.1 ± 4.4 mg/g) weights were lower in the WPE group compared with the other two groups ( p < 0.05), and no significant differences were observed between the CON and WPR groups. The relative weights of tibialis anterior muscle (CON: 1.04 ± 0.04 mg/g, WPR: 0.97 ± 0.03 mg/g, 1.23 ± 0.05 mg/g) and gastrocnemius muscle (CON: 3.02 ± 0.12 mg/g, WPR: 2.92 ± 0.15 mg/g, WPE: 3.65 ± 0.18 mg/g) were higher in the WPE group compared with the other groups ( p < 0.05). The phosphorylation of AMPK (WPR: 1.03 ± 0.11, WPE: 1.36 ± 0.12; fold change from control) and ACC (WPR: 1.08 ± 0.07, WPE: 1.18 ± 0.05; fold change from control) in WPE was higher than in CON ( p < 0.05). There were no significant differences in the expression levels of ATGL among the three groups. Conclusions: These data suggest that a normal (or moderate excess) dietary density of whey peptide attenuates body fat accumulation via upregulation of fatty acid oxidation in skeletal muscle in aging mice. [ABSTRACT FROM AUTHOR]

Purpose: Body weight in young growing and young adult animals was reduced by a high dietary density of whey protein concentrate; however, it is unclear whether dietary proteins similarly affect body weight in aging animals. Here, we examined whether whey protein or whey peptide ingestion suppressed body fat accumulation and affected protein expression and phosphorylation in skeletal muscle in aging mice. Methods: Twenty-six male senescence-accelerated mouse prone 6 (SAMP6) mice were assigned randomly to three dietary treatment groups: 18.7 % casein control (CON), 18.7 % whey protein (WPR), and 18.7 % whey peptide (WPE). After 28 weeks of treatment, skeletal tissues were dissected and weighed for analysis. Western blotting was performed to examine the expression of AMP-activated protein kinase (AMPK), acetyl-CoA carboxylase (ACC), and adipose triglyceride lipase (ATGL) in quadriceps muscles. Results: Body (CON: 47.6 ± 2.2 g, WPR: 48.2 ± 2.7 g, WPE: 38.3 ± 2.0 g) and relative white adipose tissue (CON: 38.5 ± 3.5 mg/g, WPR: 43.8 ± 4.0 mg/g, WPE: 21.1 ± 4.4 mg/g) weights were lower in the WPE group compared with the other two groups ( p < 0.05), and no significant differences were observed between the CON and WPR groups. The relative weights of tibialis anterior muscle (CON: 1.04 ± 0.04 mg/g, WPR: 0.97 ± 0.03 mg/g, 1.23 ± 0.05 mg/g) and gastrocnemius muscle (CON: 3.02 ± 0.12 mg/g, WPR: 2.92 ± 0.15 mg/g, WPE: 3.65 ± 0.18 mg/g) were higher in the WPE group compared with the other groups ( p < 0.05). The phosphorylation of AMPK (WPR: 1.03 ± 0.11, WPE: 1.36 ± 0.12; fold change from control) and ACC (WPR: 1.08 ± 0.07, WPE: 1.18 ± 0.05; fold change from control) in WPE was higher than in CON ( p < 0.05). There were no significant differences in the expression levels of ATGL among the three groups. Conclusions: These data suggest that a normal (or moderate excess) dietary density of whey peptide attenuates body fat accumulation via upregulation of fatty acid oxidation in skeletal muscle in aging mice. [ABSTRACT FROM AUTHOR]

Purpose: Protein ingestion after resistance exercise increases muscle protein synthesis (MPS) in a dose-dependent manner. However, the molecular mechanism(s) for the dose-dependency of MPS remains unclear. This study aimed to determine the dose response of mammalian target of rapamycin (mTOR) signaling in muscle with ingestion of protein after resistance exercise. Methods: Fifteen male subjects performed four sets of six unilateral isokinetic concentric knee extensions. Immediately after exercise, eight subjects consumed water only. The other seven subjects, in a randomized-order crossover design, took either a 10 [3.6 g essential amino acids (EAA)] or 20 g (7.1 g EAA) solution of whey protein. Muscle biopsies from the vastus lateralis muscle were taken 30 min before and 1 h after resistance exercise. Phosphorylation of Akt (Ser473), mTOR (Ser2448), 4E-BP1 (Thr37/46), and S6K1 (Thr389) was measured by western blotting. Results: Concentric knee extension exercise alone did not increase phosphorylation of Akt and mTOR 1 h after exercise, but ingesting protein after exercise significantly increased the phosphorylation of Akt and mTOR in a dose-dependent manner ( P < 0.05). 4E-BP1 phosphorylation significantly decreased after resistance exercise ( P < 0.05), but subjects who took 10 or 20 g of protein after exercise showed increased 4E-BP1 from post-exercise dephosphorylation ( P < 0.05). S6K1 phosphorylation significantly increased after resistance exercise ( P < 0.05), and 20 g of protein further increased S6K1 phosphorylation compared with ingestion of 10 g ( P < 0.05). Conclusions: These findings suggest that whey protein intake after resistance exercise activates mTOR signaling in a dose-dependent manner in untrained men. [ABSTRACT FROM AUTHOR]

In atherosclerosis progression, atherosclerotic plaques develop upon accumulated foam cells derived from macrophages that take up modified low-density lipoprotein (LDL). CD36 and CD204 are the principal scavenger receptors responsible for the uptake of modified LDL. Lipopolysaccharide (LPS) exacerbates atherosclerosis by enhancing the expression of scavenger receptors and thus increasing the uptake of modified LDL into macrophages. However, the signaling pathways that mediate LPS and scavenger receptor expression have not been fully elucidated. We used mouse bone marrow-derived macrophages and investigated the effects of LPS in vitro. LPS enhanced the phosphorylation of extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription-1 (STAT-1). Inhibitors of the mitogen-activated protein kinase (MAPK)/ERK kinase (MEK) pathway (U0126 and PD0325901) suppressed the uptake of acetylated-LDL (Ac-LDL) and the expression of CD204 but not CD36 in LPS-activated macrophages. Inhibitors of the Janus tyrosine kinase (JAK)-STAT pathway (ruxolitinib and tofacitinib) suppressed the uptake of Ac-LDL and the expression of both CD36 and CD204 in LPS-activated macrophages. We next injected LPS into the peritoneal cavity of mice and analyzed the effects of LPS. MEK inhibitor U0126 suppressed the uptake of Ac-LDL and the expression of CD204 but not CD36 in LPS-activated macrophages. JAK inhibitor ruxolitinib suppressed the uptake of Ac-LDL and the expression of both CD36 and CD204 in LPS-activated macrophages. These results suggest that scavenger receptors in LPS-activated mouse macrophages are regulated through a JAK-STAT-dependent pathway. Although further evaluation is necessary, JAK-STAT inhibition could be useful in atherosclerosis therapy, at least for atherosclerosis exacerbated by LPS. [ABSTRACT FROM AUTHOR]

Purpose: High-intensity neuromuscular electrical stimulation (NMES) training can induce muscle hypertrophy at the whole muscle and muscle fiber levels. However, whether low-intensity NMES training has a similar result is unknown. This study aimed to investigate whether low-intensity NMES training could elicit muscle hypertrophy at the whole muscle and muscle fiber levels in the human skeletal muscle.Methods: Eight untrained young males were subjected to 18 min of unilateral NMES training for 8 weeks. One leg received NMES at maximal tolerable intensity (HIGH); the other leg received NMES at an intensity half of that in the HIGH condition (LOW). Quadriceps muscle thickness (MT), muscle fiber cross-sectional area (CSA), and knee extension strength were measured before and after the training period.Results: The average training intensity throughout the intervention period in the HIGH and LOW conditions were 62.5 ± 4.6% maximal voluntary contraction (MVC) and 32.6 ± 2.6% MVC, respectively. MT, CSA, and muscle strength increased in both exercise conditions (p < 0.05); however, training effects in the LOW condition were lower than those in the HIGH condition (p < 0.05). The average training intensity showed a positive correlation with percent changes in muscle strength (r = 0.797, p = 0.001), MT (r = 0.876, p = 0.001), type I fiber CSA (r = 0.730, p = 0.01), and type II fiber CSA (r = 0.899, p = 0.001).Conclusions: Low-intensity NMES could increase MT, muscle fiber CSA, and muscle strength in healthy human skeletal muscles. However, the magnitude of increase is lower in low-intensity than in high-intensity NMES training. [ABSTRACT FROM AUTHOR]

Muscle fiber composition is associated with physical performance, with endurance athletes having a high proportion of slow-twitch muscle fibers compared to power athletes. Approximately 45% of muscle fiber composition is heritable, however, single nucleotide polymorphisms (SNP) underlying inter-individual differences in muscle fiber types remain largely unknown. Based on three whole genome SNP datasets, we have shown that the rs236448 A allele located near the cyclin-dependent kinase inhibitor 1A (CDKN1A) gene was associated with an increased proportion of slow-twitch muscle fibers in Russian (n = 151; p = 0.039), Finnish (n = 287; p = 0.03), and Japanese (n = 207; p = 0.008) cohorts (meta-analysis: p = 7.9 × 10−5. Furthermore, the frequency of the rs236448 A allele was significantly higher in Russian (p = 0.045) and Japanese (p = 0.038) elite endurance athletes compared to ethnically matched power athletes. On the contrary, the C allele was associated with a greater proportion of fast-twitch muscle fibers and a predisposition to power sports. CDKN1A participates in cell cycle regulation and is suppressed by the miR-208b, which has a prominent role in the activation of the slow myofiber gene program. Bioinformatic analysis revealed that the rs236448 C allele was associated with increased CDKN1A expression in whole blood (p = 8.5 × 10−15) and with greater appendicular lean mass (p = 1.2 × 10−5), whereas the A allele was associated with longer durations of exercise (p = 0.044) reported amongst the UK Biobank cohort. Furthermore, the expression of CDKN1A increased in response to strength (p < 0.0001) or sprint (p = 0.00035) training. Accordingly, we found that CDKN1A expression is significantly (p = 0.002) higher in the m. vastus lateralis of strength athletes compared to endurance athletes and is positively correlated with the percentage of fast-twitch muscle fibers (p = 0.018). In conclusion, our data suggest that the CDKN1A rs236448 SNP may be implicated in the determination of muscle fiber composition and may affect athletic performance. [ABSTRACT FROM AUTHOR]

Background: Skeletal muscle fiber type distribution has implications for human health, muscle function, and performance. This knowledge has been gathered using labor-intensive and costly methodology that limited these studies. Here, we present a method based on muscle tissue RNA sequencing data (totRNAseq) to estimate the distribution of skeletal muscle fiber types from frozen human samples, allowing for a larger number of individuals to be tested. Methods: By using single-nuclei RNA sequencing (snRNAseq) data as a reference, cluster expression signatures were produced by averaging gene expression of cluster gene markers and then applying these to totRNAseq data and inferring muscle fiber nuclei type via linear matrix decomposition. This estimate was then compared with fiber type distribution measured by ATPase staining or myosin heavy chain protein isoform distribution of 62 muscle samples in two independent cohorts (n = 39 and 22). Results: The correlation between the sequencing-based method and the other two were rATPas = 0.44 [0.13–0.67], [95% CI], and rmyosin = 0.83 [0.61–0.93], with p = 5.70 × 10–3 and 2.00 × 10–6, respectively. The deconvolution inference of fiber type composition was accurate even for very low totRNAseq sequencing depths, i.e., down to an average of ~ 10,000 paired-end reads. Conclusions: This new method (https://github.com/OlaHanssonLab/PredictFiberType) consequently allows for measurement of fiber type distribution of a larger number of samples using totRNAseq in a cost and labor-efficient way. It is now feasible to study the association between fiber type distribution and e.g. health outcomes in large well-powered studies. [ABSTRACT FROM AUTHOR]

We investigated whether time-of-day dependent changes in the rat soleus (SOL) muscle size, after eccentric exercises, operate via the mechanistic target of rapamycin (mTOR) signaling pathway. For our first experiment, we assigned 9-week-old male Wistar rats randomly into four groups: light phase (zeitgeber time; ZT6) non-trained control, dark phase (ZT18) non-trained control, light phase-trained, and dark phase-trained. Trained animals performed 90 min of downhill running once every 3 d for 8 weeks. The second experiment involved dividing 9-week-old male Wistar rats to control and exercise groups. The latter were subjected to 15 min of downhill running at ZT6 and ZT18. The absolute (+12.8%) and relative (+9.4%) SOL muscle weights were higher in the light phase-trained group. p70S6K phosphorylation ratio was 42.6% higher in the SOL muscle of rats that had exercised only in light (non-trained ZT6). Collectively, the degree of muscle hypertrophy in SOL is time-of-day dependent, perhaps via the mTOR/p70S6K signaling. [ABSTRACT FROM AUTHOR]

Abstract: α-Actinins are actin-binding proteins, and two isoforms (α-actinin-2 and -3) are major structural components of the sarcomeric Z line in mammalian skeletal muscle. Based on human and knockout mice studies, α-actinin-3 is thought to be associated with muscle force output and high contraction velocities. However, fiber-type specific expression of α-actinin isoforms is not well understood and may vary among species. In this study, we investigated the expression of α-actinin isoforms and the difference between fiber types in rat skeletal muscle and compared it with those of humans and mice from previous reports. Soleus and plantaris muscles were analyzed immunohistochemically to identify muscle fiber types and α-actinin protein expression. α-Actinin-2 was stained in all muscle fibers in both the soleus and plantaris muscles; i.e., all α-actinin-3 co-expressed with α-actinin-2 in rat skeletal muscles. The proportions of α-actinin-3 expression, regardless of fiber type, were significantly higher in the plantaris (75.8±0.6%) than the soleus (8.0±1.7%). No α-actinin-3 expression was observed in type I fibers, whereas all type IIx+b fibers expressed α-actinin-3. α-Actinin-3 was also expressed in type IIa fibers; however, approximately 75% of type IIa fibers were not stained by α-actinin-3, and the proportion varied between muscles. The proportion of α-actinin-3 expression in type IIa fibers was significantly higher in the soleus muscle than the plantaris muscle. Our results showed that fiber-type specific expression of α-actinin isoforms in rats is more similar to that in humans compared to that of the mouse, whereas the proportion of α-actinin-3 protein varied between muscles. [Copyright &y& Elsevier]

Abstract: Alpha (α)-actinin-3 is located in the skeletal muscle Z-line and forms actin–actin crosslinks. An interesting property of α-actinin-3 is its expression pattern, which is restricted to fast type II skeletal muscle fibers. However, little is known about the response of α-actinin-3 levels to changes in skeletal muscle such as fiber type transformation. This study examined α-actinin-3 levels in the soleus muscles of rats subjected to hindlimb unloading, which causes a slow-to-fast fiber transformation in the soleus muscle. After unloading, type II myosin heavy chain (MyHC) and fast myosin levels increased significantly (P <0.0001 for type II MyHC, P <0.005 for fast myosin). Along with these increases in fast fibers, α-actinin-3 expression levels increased significantly (P <0.0007) and dramatically. These results indicate that α-actinin-3 levels increase concomitantly with increases in skeletal muscle fast fibers. [Copyright &y& Elsevier]

Recent studies of the ketogenic diet, an extremely high-fat diet with extremely low carbohydrates, suggest that it changes the energy metabolism properties of skeletal muscle. However, ketogenic diet effects on muscle metabolic characteristics are diverse and sometimes countervailing. Furthermore, ketogenic diet effects on skeletal muscle performance are unknown. After male Wistar rats (8 weeks of age) were assigned randomly to a control group (CON) and a ketogenic diet group (KD), they were fed for 4 weeks respectively with a control diet (10% fat, 10% protein, 80% carbohydrate) and a ketogenic diet (90% fat, 10% protein, 0% carbohydrate). After the 4-week feeding period, the extensor digitorum longus (EDL) muscle was evaluated ex vivo for twitch force, tetanic force, and fatigue. We also analyzed the myosin heavy chain composition, protein expression of metabolic enzymes and regulatory factors, and citrate synthase activity. No significant difference was found between CON and KD in twitch or tetanic forces or muscle fatigue. However, the KD citrate synthase activity and the protein expression of Sema3A, citrate synthase, succinate dehydrogenase, cytochrome c oxidase subunit 4, and 3-hydroxyacyl-CoA dehydrogenase were significantly higher than those of CON. Moreover, a myosin heavy chain shift occurred from type IIb to IIx in KD. These results demonstrated that the 4-week ketogenic diet improves skeletal muscle aerobic capacity without obstructing muscle contractile function in sedentary male rats and suggest involvement of Sema3A in the myosin heavy chain shift of EDL muscle. [ABSTRACT FROM AUTHOR]

The mechanisms involved in unloading-induced skeletal muscle loss may be age-specific, and the evidence for exercise preconditioning-induced protection against disuse muscle atrophy in aged rats is limited. Therefore, in this study, we investigated age-related differences in the activation of the HDAC4/Gadd45α pathway following hindlimb unloading (HU). We also assessed the protective effect of preconditioning exercise on this pathway in young and old rat gastrocnemius muscle. Three-month-old (young, n = 18) and 24-month-old (old, n = 18) male Wistar rats were assigned to the following groups: control group (n = 6), seven days of HU group (n = 6), and a bout of exercise preconditioning prior to HU (Ex+HU) group (n = 6). Rats of both ages in the Ex + HU group ran continuously on a motor-driven treadmill (0° slope, 20 m/min, 15 min) prior to HU. The gastrocnemius muscles were removed after 7 days of HU and analyzed for protein content and mRNA expression. Gastrocnemius muscle weight was significantly higher in the Ex+HU group than in the HU group of old rats, but not in young rats. Levels of HDAC4 protein and mRNA were significantly increased in the old HU group. However, the increase was significantly suppressed in the old Ex+HU group. Moreover, the protective effect of exercise preconditioning had a positive effect on Gadd45α mRNA and protein levels only in the old Ex+HU group. No exercise preconditioning-related protection was observed in the young rats. Our data indicated that a single bout of preconditioning exercise prior to HU may exert a protective effect in disuse muscle atrophy in old rats and that these effects may be partially mediated by the HDAC4/Gadd45α axis. • Exercise preconditioning attenuates HU-induced gastrocnemius muscle atrophy. • Preconditioning exercise elicits age-specific protective effects against muscle atrophy. • The effects may be partially mediated by the HDAC4/Gadd45α axis. [ABSTRACT FROM AUTHOR]

This study examined the effect of changes in body temperature during exercise on signal transduction-related glucose uptake in the skeletal muscle of type 2 diabetic rats. Otsuka Long-Evans Tokushima Fatty rats (25 weeks of age), which have type 2 diabetes, were divided into the following four weight-matched groups; control (CON, n = 6), exercised under warm temperature (WEx, n = 8), exercised under cold temperature (CEx, n = 8), and heat treatment (HT, n = 6). WEx and CEx animals were subjected to running on a treadmill at 20 m/min for 30 min under warm (25°C) or cold (4°C) temperature. HT animals were exposed to single heat treatment (40–41°C for 30 min) in a heat chamber. Rectal and muscle temperatures were measured immediately after exercise and heat treatment, and the gastrocnemius muscle was sampled under anesthesia. Rectal and muscle temperatures increased significantly in rats in the WEx and HT, but not the CEx, groups. The phosphorylation levels of Akt, AS160, and TBC1D1 (Thr590) were significantly higher in the WEx and HT groups than the CON group (p < 0.05). In contrast, the phosphorylation levels of AMP-activated protein kinase, ACC, and TBC1D1 (Ser660) were significantly higher in rats in the WEx and CEx groups than the CON group (p < 0.05) but did not differ significantly between rats in the WEx and CEx groups. Body temperature elevation by heat treatment did not activate the AMPK signaling. Our data suggest that body temperature elevation during exercise is essential for activating the Akt signaling pathway in the skeletal muscle of rats with type 2 diabetic rats. [ABSTRACT FROM AUTHOR]

We examined the effect of repeated heat stress on muscle atrophy, and apoptotic and proteolytic regulation in unloaded rat slow- and fast-type skeletal muscles. Forty male Wistar rats (11 week-old) were divided into control ( CT), hindlimb unweighting ( HU), intermittent weight-bearing during HU ( HU + IWB), and intermittent weight-bearing with heat stress during HU (41-41.5°C for 30 min; HU + IWB + HS) groups. The HU + IWB + HS and HU + IWB groups were released from unloading for 1 h every second day, during which the HU + IWB + HS group underwent the heating. Our results revealed that repeated bouts of heat stress resulted in protection against disuse muscle atrophy in both soleus and plantaris muscles. This heat stress-induced protection against disuse-induced muscular atrophy may be partially due to reduced apoptotic activation in both muscles, and decreased ubiquitination in only the soleus muscle. We concluded that repeated heat stress attenuated skeletal muscle atrophy via suppressing apoptosis but the response to proteolytic systems depend on the muscle phenotype. [ABSTRACT FROM AUTHOR]

Human skeletal muscle fiber is heterogenous due to its diversity of slow- and fast-twitch fibers. In human, slow-twitched fiber gene expression is correlated to MOTS-c, a mitochondria-derived peptide that has been characterized as an exercise mimetic. Within the MOTS-c open reading frame, there is an East Asian-specific m.1382A>C polymorphism (rs111033358) that changes the 14th amino acid of MOTS-c (i.e., K14Q), a variant of MOTS-c that has less biological activity. Here, we examined the influence of the m.1382A>C polymorphism causing MOTS-c K14Q on skeletal muscle fiber composition and physical performance. The myosin heavy chain (MHC) isoforms (MHC-I, MHC-IIa, and MHC-IIx) as an indicator of muscle fiber composition were assessed in 211 Japanese healthy individuals (102 men and 109 women). Muscular strength was measured in 86 physically active young Japanese men by using an isokinetic dynamometer. The allele frequency of the m.1382A>C polymorphism was assessed in 721 Japanese athletes and 873 ethnicity-matched controls. The m.1382A>C polymorphism genotype was analyzed by TaqMan SNP Genotyping Assay. Individuals with the C allele of the m.1382A>C exhibited a higher proportion of MHC-IIx, an index of fast-twitched fiber, than the A allele carriers. Men with the C allele of m.1382A>C exhibited significantly higher peak torques of leg flexion and extension. Furthermore, the C allele frequency was higher in the order of sprint/power athletes (6.5%), controls (5.1%), and endurance athletes (2.9%). Additionally, young male mice were injected with the MOTS-c neutralizing antibody once a week for four weeks to mimic the C allele of the m.1382A>C and assessed for protein expression levels of MHC-fast and MHC-slow. Mice injected with MOTS-c neutralizing antibody showed a higher expression of MHC-fast than the control mice. These results suggest that the C allele of the East Asian-specific m.1382A>C polymorphism leads to the MOTS-c K14Q contributes to the sprint/power performance through regulating skeletal muscle fiber composition. • There is an East Asian-specific m.1382A>C polymorphism in the mtDNA that changes the 14th amino acid of MOTS-c (i.e., K14Q). • C allele of the MOTS-c m.1382A>C showed a higher percentage of MHC-IIx and muscular strength than the A allele. • C allele frequency of the MOTS-c m.1382A>C polymorphism overrepresented in the sprint/power athletes. • MOTS-c neutralizing, mimicking C allele, showed lower and higher expression of MHC-slow and -fast than controls. [ABSTRACT FROM AUTHOR]

Human muscle fiber composition is heterogeneous and mainly determined by genetic factors. A previous study reported that experimentally induced iron deficiency in rats increases the proportion of fast-twitch muscle fibers. Iron status has been reported to be affected by genetic factors. As the TMPRSS6 rs855791 T/C and HFE rs1799945 C/G polymorphisms are strongly associated with iron status in humans, we hypothesized that the genotype score (GS) based on these polymorphisms could be associated with the muscle fiber composition in humans. Herein, we examined 214 Japanese individuals, comprising of 107 men and 107 women, for possible associations of the GS for iron status with the proportion of myosin heavy chain (MHC) isoforms (I, IIa, and IIx) as markers of muscle fiber composition. No statistically significant correlations were found between the GS for iron status and the proportion of MHC isoforms in all participants. When the participants were stratified based on sex, women showed positive and negative correlations of the GS with MHC-IIa (age-adjusted p = 0.020) and MHC-IIx (age-adjusted p = 0.011), respectively. In contrast, no correlation was found in men. In women, a 1-point increase in the GS was associated with 2.42% higher MHC-IIa level and 2.72% lower MHC-IIx level. Our results suggest that the GS based on the TMPRSS6 rs855791 T/C and HFE rs1799945 C/G polymorphisms for iron status is associated with muscle fiber composition in women. [ABSTRACT FROM AUTHOR]

Abstract: Macroautophagy (autophagy) is an intracellular catalytic process. We examined the effect of running exercise, which stimulates cardiac work physiologically, on the expression of microtubule-associated protein 1 light chain 3 (LC3)-II, an indicator of autophagy, as well as some autophagy-related proteins in rat cardiac muscle. The left ventricles were taken from rats immediately (0h), and at 0.5h, 1h or 3h after a single bout of running exercise on a treadmill for 30min and also from rats in a rest condition. In these samples, we evaluated the level of LC3-II and p62, and the phosphorylation level of mammalian target of rapamycin (mTOR), Akt and AMP-activated protein kinase alpha (AMPKα) by Western blotting. The exercise produced a biphasic change in LC3-II, with an initial decrease observed immediately after the exercise and a subsequent increase 1h thereafter. LC3-II then returned to the rest level at 3h after the exercise. A negative correlation was found between the LC3-II expression and mTOR phosphorylation, which plays a role in inhibiting autophagy. The exercise increased phosphorylation of AMPKα, which stimulates autophagy via suppression of mTOR phosphorylation, immediately after exercise. The level of p62 and phosphorylated Akt was not altered significantly by the exercise. These results suggest for the first time that a single bout of running exercise induces a biphasic change in autophagy in the cardiac muscle. The exercise-induced change in autophagy might be partially mediated by mTOR in the cardiac muscle. [Copyright &y& Elsevier]

The present study was performed to investigate the involvement of SNARK in physical activity levels in mice. To examine the acute effect of SNARK deficiency on voluntary running, Snark-deficient mice (Snark+/-: n = 16) and their wild-type counterparts (Snark+/+: n = 16) were assigned to sedentary or exercise (1 wk voluntary wheel running) groups. In addition, to clarify the differences in voluntary running activity and its effect between genotypes, mice (Snark+/+: n = 16; Snark+/-: n = 16) were also kept in individual cages with/without a running wheel for 5 mo. Unexpectedly, in both voluntary running experiments, running distances were increased in Snark+/- mice compared with Snark+/+ mice. Under sedentary conditions, body and white adipose tissue weights were increased significantly in Snark+/- mice. However, no significant differences were observed between the two genotypes under exercise conditions, and the values were significantly less than those under sedentary conditions in the long-term experiment. In the short-term experiment, serum interleukin-6 level in exercised Snark+/+ mice was the same as that in sedentary Snark+/+ mice, whereas that in sedentary Snark+/- mice was significantly lower than in the other groups. In contrast, serum leptin level was reduced significantly in exercised Snark+/- mice compared with sedentary Snark+/- mice. The results of this study demonstrated that exposure to an environment that allows voluntary exercise promotes increased running activity and prevents obesity in Snark-deficient mice. [ABSTRACT FROM AUTHOR]

This study examined whether the exercise-increased extracellular heat shock protein 72 (eHsp72) levels in rats was associated with body temperature elevation during exercise. In all, 26 female Sprague-Dawley rats (3 mo old) were assigned randomly to control (CON; n = 8), exercise under warm temperature (WEx; n = 9), or exercise under cold temperature (CEx; n = 9). The WEx and CEx were trained at 25°C or 4°C, respectively, for nine days using a treadmill. Before and immediately after the final exercise bout, the colonic temperatures were measured as an index of body temperature. The animals were subsequently anesthetized, and blood samples were collected and centrifuged. Plasma samples were obtained to assess their eHsp72 levels. Only the colonic temperature in WEx was increased significantly (P < 0.05) by exercise. The eHsp72 level in WEx was significantly higher (P < 0.05) than that of either the CON or CEx. However, no significant difference was found between CON and CEx. Regression analyses revealed that the eHsp72 level increased as a function of the body temperature. In another experiment, the eHsp72 level of animals with body temperature that was passively elevated through similar kinetics to those of the exercise was studied. Results of this experiment showed that mere body temperature elevation was insufficient to induce eHsp72 responses. Collectively, our results suggest that body temperature elevation during exercise is important for induction of exercise-increased eHsp72. In addition, the possible role of body temperature elevation is displayed when the exercise stressor is combined with it. [ABSTRACT FROM AUTHOR]

PPARGC1A rs8192678 G/A (Gly482Ser) and NRF1 rs6949152 A/G polymorphisms have been associated with endurance athlete status, endurance performance phenotypes, and certain health-related markers of different pathologies such as metabolic syndrome, diabetes, and dyslipidemia. We hypothesized that they could be considered interesting candidates for explaining inter-individual variations in muscle fiber composition in humans. We aimed to examine possible associations of these polymorphisms with myosin heavy-chain (MHC) isoforms as markers of muscle fiber compositions in vastus lateralis muscle in a population of 214 healthy Japanese subjects, aged between 19 and 79 years. No significant associations were found in men for any measured variables. In contrast, in women, the PPARGC1A rs8192678 A/A genotype was significantly associated with a higher proportion of MHC-I (p = 0.042) and with a lower proportion of MHC-IIx (p = 0.033), and the NRF1 rs6949152 AA genotype was significantly associated with a higher proportion of MHC-I (p = 0.008) and with a lower proportion of MHC IIx (p = 0.035). In women, the genotype scores of the modes presenting the most significant results for PPARGC1A rs8192678 G/A (Gly482Ser) and NRF1 rs6949152 A/G polymorphisms were significantly associated with MHC-I (p = 0.0007) and MHC IIx (p = 0.0016). That is, women with combined PPARGC1A A/A and NRF1 A/A genotypes presented the highest proportion of MHC-I and the lowest proportion of MHC-IIx, in contrast to women with combined PPARGC1A GG+GA and NRF1 AG+GG genotypes, who presented the lowest proportion of MHC-I and the highest proportion of MHC-IIx. Our results suggest possible associations between these polymorphisms (both individually and in combination) and the inter-individual variability observed in muscle fiber composition in women, but not in men. [ABSTRACT FROM AUTHOR]

Changes in histone acetylation and methylation status with aging affect gene expression and phenotype in several tissues; however, age-related changes in histone modification in the skeletal muscle have not been elucidated yet. This study investigated age-related global changes in histone modification in rat gastrocnemius muscle. Male Wistar rats (n = 28) were assigned to one of four age groups (n = 7 per group) corresponding to different life stages: 3 months old (3-mo; young), 6 months old (adult), 12 months old (12-mo; middle-aged), and 24 months old (24-mo; old). The gastrocnemius muscle was removed and global histone modification (acetylation and tri-methylation) at K9 and K27 was evaluated by western blotting. Relative muscle mass decreased in the 12- and 24-mo rats accompanied with reduction in type IIb myosin heavy chain isoforms and Myh4 (MHC IIB) mRNA expression. Histone H3 acetylation decreased in an age-dependent manner, with lower levels in 12- and 24-mo groups than in the 3-mo group. K9 and K27 acetylation decreased with age. Although there was no significant change in K27 tri-methylation, K9 tri-methylation showed an age-dependent decline. Histone modification status (acetylation at K9 and K27 and tri-methylation at K9) was positively associated with relative gastrocnemius muscle weight, the percentage of type IIb myosin heavy chain isoform, myosin heavy chain type IIb protein expression, and the level of Myh4 mRNA. Thus, global histone H3 methylation and acetylation decrease with age, and the latter might be associated with age-related muscle atrophy of rat gastrocnemius muscle. • Global histone H3 methylation and acetylation decrease with age. • SIRT1 accumulation in nuclei presumably could induce H3K9 and H3K27 deacetylation. • Changes may be linked to age-related type IIb fiber atrophy in rat skeletal muscle. [ABSTRACT FROM AUTHOR]