Abnormalities of mitochondrial functioning can partly explain the metabolic disorders encountered in sarcopenic gastrocnemius

Aging triggers several abnormalities in muscle glycolytic fibers including increased proteolysis, reactive oxygen species (ROS) production and apoptosis. Since the mitochondria are the main site of substrate oxidation, ROS production and programmed cell death, we tried to know whether the cellular disorders encountered in sarcopenia are due to abnormal mitochondrial functioning. Gastrocnemius mitochondria were extracted from adult (6 months) and aged (21 months) male Wistar rats. Respiration parameters, opening of the permeability transition pore and ROS production, with either glutamate (amino acid metabolism) or pyruvate (glucose metabolism) as a respiration substrate, were evaluated at different matrix calcium concentrations. Pyruvate dehydrogenase and respiratory complex activities as well as their contents measured by Western blotting analysis were determined. Furthermore, the fatty acid profile of mitochondrial phospholipids was also measured. At physiological calcium concentration, state III respiration rate was lowered by aging in pyruvate conditions (-22%), but not with glutamate. The reduction of pyruvate oxidation resulted from a calcium-dependent inactivation of the pyruvate dehydrogenase system and could provide for the well-known proteolysis encountered during sarcopenia. Matrix calcium loading and aging increased ROS production. They also reduced the oxidative phosphorylation. This was associated with lower calcium retention capacities, suggesting that sarcopenic fibers are more prone to programmed cell death. Aging was also associated with a reduced mitochondrial superoxide dismutase activity, which does not intervene in toxic ROS overproduction but could explain the lower calcium retention capacities. Despite a lower content, cytochrome c oxidase displayed an increased activity associated with an increased n-6/n-3 polyunsaturated fatty acid ratio of mitochondrial phospholipids. In conclusion, we propose that mitochondria obtained from aged muscle fibers display several functional abnormalities explaining the increased proteolysis, ROS overproduction and vulnerability to apoptosis exhibited by sarcopenic muscle. These changes appear to be related to modifications of the fatty acid profile of mitochondrial lipids.     

Moderate exercise training is more effective than resveratrol supplementation for ameliorating lipid metabolic complication in skeletal muscle of high fat diet-induced obese mice

[Purpose]

The aim of this study was to compare the effectiveness of moderate exercise training or resveratrol supplementation with a low fat diet on lipid metabolism in the skeletal muscle of high fat diet-induced obese mice.

[Methods]

C57BL/6J mice (5 weeks old, n = 30) were fed a high fat diet (45% fat) for 8 weeks first to make them obese. Afterward, all the mice were fed a low fat diet during 8 weeks of intervention with moderate exercise training and resveratrol supplementation. Before the intervention, the mice were separated into 3 groups: low-fat diet control (HLC; n = 10), low fat diet with resveratrol (HLR; n = 10) or low fat diet with exercise (HLE n = 10). The exercise group (HLE) performed treadmill running for 30-60 min/day at 10-22 m/min, 0% grade, 5 times/week for 8 weeks, while the resveratrol group (HLR) received a daily dose of resveratrol (10 mg/kg of body weight), 5 days/week for 8 weeks.

[Results]

Body weight was significantly reduced in HLE. Further, the lipogenesis marker SREBP and the inflammatory cytokine TNF-α were significant reduced in HLE. However, there was no significant effect from resveratrol supplementation with a low fat diet. Taken together, exercise training with a low fat diet has the positive effect of ameliorating lipid disturbance in the skeletal muscle of high fat diet-induced obese mice.

[Conclusion]

These findings suggest that exercise training with a low fat diet is most effective to improve lipid metabolism by reducing lipogenesis and inflammation in the skeletal muscle of high fat diet-induced obese mice.     

The ameliorating effects of 2,3-dihydroxy-4-methoxyacetophenone on scopolamine-induced memory impairment in mice and its neuroprotective activity

We isolated 2,3-dihydroxy-4-methoxyacetophenone, a neuroprotective compound from Cynenchum paniculatum in our previous study.The present study was conducted to investigate the possible neuroprotective effect of 2,3-dihydroxy-4-methoxyacetophenone that has been previously isolated from Cynenchum paniculatum on hippocampal neuronal cell line, HT22 cells and its possible cognitive-enhancing effect on scopolamine-induced amnesia in mice.Neuroprotective effect against glutamate-induced neurotoxicity in HT22 cells was evaluated by MTT assay. Also, cognitive enhancing effect against scopolamine (1 mg/kg, ip) induced learning and memory deficit was measured by Morris water maze test. Oral administered of 2,3-dihydroxy-4-methoxyacetophenone (1, 10, 20, 40 and 50 mg/kg) to amnesic mice induced by scopolamine. In Morris water maze test, 2,3-dihydroxy-4-methoxyacetophenone (50 mg/kg) improved the impairment of spatial memory induced by scopolamine. 2,3-Dihydroxy-4-methoxyacetophenone protect HT22 cells on glutamate induced cell-death in a dose-dependent manner (EC₅₀ value: 10.94 μM). Furthermore, 2,3-dihydroxy-4-methoxyacetophenone was found to inhibit [Ca²⁺] accumulation in HT22 cells and had antioxidantive activity. The results showed that 2,3-dihydroxy-4-methoxyacetophenone exert neuroprotective and cognitive-enhancing activities through its antioxidant activity. We suggest that 2,3-dihydroxy-4-methoxyacetophenone improves cognitive function and may be helpful for the treatment of Alzheimer’s disease.     

Effects of genetic selection and voluntary activity on the medial gastrocnemius muscle in house mice.

In a previous study, we found that in house mice both genetic selection (10 generations of artificial selection for high voluntary activity on running wheels) and access to running wheels (7-8 weeks) elicited a modest increase in maximal oxygen consumption. Based on these results, we hypothesized that genetic selection would affect the changes in endurance and oxidative capacity of the medial gastrocnemius (MG) muscle induced by wheel access (training response). Wheel access increased the isotonic endurance of the MG in both genetically selected and random-bred (control) mice. However, this exercise-induced improvement in isotonic endurance of the MG was similar between genetically selected and control mice. Wheel access also increased the succinate dehydrogenase activity of MG muscle fibers in both selected and control lines. However, this exercise-induced increase in succinate dehydrogenase activity was comparable between genetically selected and control animals. Taken together, these results indicate that the modest increase in maximal oxygen consumption associated with genetic selection is not reflected by the training-induced changes in oxidative capacity and endurance of MG muscle fibers.     

Hypoglycemic effects of brassinosteroid in diet-induced obese mice

The prevalence of obesity is increasing globally, and obesity is a major risk factor for metabolic diseases such as type 2 diabetes. Previously, we reported that oral administration of homobrassinolide (HB) to healthy rats triggered a selective anabolic response that was associated with lower blood glucose. Therefore, the aim of this study was to evaluate the effects of HB administration on glucose metabolism, insulin sensitivity, body composition, and gluconeogenic gene expression profiles in liver of C57BL/6J high-fat diet-induced obese mice. Acute oral administration of 50-300 mg/kg HB to obese mice resulted in a dose-dependent decrease in fasting blood glucose within 3 h of treatment. Daily chronic administration of HB (50 mg/kg for 8 wk) ameliorated hyperglycemia and improved oral glucose tolerance associated with obesity without significantly affecting body weight or body composition. These changes were accompanied by lower expression of two key gluconeogenic enzymes, phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G-6-Pase), and increased phosphorylation of AMP-activated protein kinase in the liver and muscle tissue. In vitro, HB treatment (1-15 μM) inhibited cyclic AMP-stimulated but not dexamethasone-stimulated upregulation of PEPCK and G-6-Pase mRNA levels in H4IIE rat hepatoma cells. Among a series of brassinosteroid analogs related to HB, only homocastasterone decreased glucose production in cell culture significantly. These results indicate the antidiabetic effects of brassinosteroids and begin to elucidate their putative cellular targets both in vitro and in vivo.     

Effect of metformin on nitric oxide synthase in genetically obese (ob/ob) mice.

Genetically obese (ob/ob) mice were employed for the study of the effect of metformin on activity and expression of nitric oxide synthase (NOS ) in vitro and in vivo. For in vitro analysis, mouse liver extracts were used. For the in vivo study, (ob/ob) and their control litter mates (ob/c) mice were injected with specified amounts of metformin and the expression of NOS in the adipose tissue and hypothalamus was measured by Western blotting. Results show that metformin exhibited a biphasic effect on NOS activity in vitro. Expression of metformin was differentially altered in the hypothalamus and adipose tissues of the normal and ob/ob animals that were treated with metformin. Further, a significant decrease in food intake occurred in the (ob/ob) mice that received metformin. This decrease in food intake was not accompanied by changes in serum glucose. At inhibitory concentrations, hypothalamic NOS expression changes differentially in normal and ob/ob mice. In normal mice, metformin stimulated NOS expression, while in ob/ob mice there was an inhibition. NOS expression increased in brown adipose tissue of metformin treated control mice, while no such increase was observed in ob/ob mice. No effect of metformin was observed in white adipose tissue of control or obese mice. Thus, metformin may produce anorectic effects through modulation of NOS.     

Altered fibre types in gastrocnemius muscle of high wheel-running selected mice with mini-muscle phenotypes

Selective breeding of mice for high voluntary wheel running has favoured characteristics that facilitate sustained, aerobically supported activity, including a "mini-muscle" phenotype with markedly reduced hind limb muscle mass, increased mass-specific activities of oxidative enzymes, decreased % myosin heavy chain IIb, and, in the medial gastrocnemius, reduced twitch speed, reduced mass-specific isotonic power, and increased fatigue resistance. To evaluate whether selection has altered fibre type expression in mice with either "mini" or normal muscle phenotypes, we examined fibre types of red and white gastrocnemius. In both the medial and lateral gastrocnemius, the mini-phenotype increased activities of oxidative enzymes and decreased activities of glycolytic enzymes. In red muscle samples, the mini-phenotype markedly changed fibre types, with the % type I and type IIA fibres and the surface area of type IIA fibres increasing; in addition, mice from selected lines in general had an increased % type IIA fibres and larger type I fibres as compared with mice from control lines. White muscle samples from mini-mice showed dramatic structural alterations, with an atypical distribution of extremely small, unidentifiable fibres surrounded by larger, more oxidative fibres than normally present in white muscle. The increased proportion of oxidative fibres and these atypical small fibres together may explain the reduced mass and increased mitochondrial enzyme activities in mini-muscles. These and previous results demonstrate that extension of selective breeding beyond the time when the response of the selected trait (i.e. distance run) has levelled off can still modify the mechanistic underpinnings of this behaviour.     

二甲双胍对D-半乳糖诱导雄性中年小鼠衰老的干预作用*

目的:探讨二甲双胍(Met)对D-半乳糖(D-gal)诱导雄性中年小鼠衰老的干预作用。方法:50只ICR 9月龄雄性小鼠,在SPF级实验环境饲养,自由摄食与饮水。随机分5组:对照组,模型组,二甲双胍低、中、高剂量(Met 50 mg/kg,Met 100 mg/kg,Met 200 mg/kg)组,每组10只。Met组和模型组小鼠每日颈背部皮下注射D-gal 100 mg/ kg,同时分别给予Met(50、100、200 mg/kg)或等体积NS灌胃。对照组注射和灌胃等体积NS。连续8周给药。检测小鼠一般状态,体重,空腹血糖,血清和肝脏超氧化物歧化酶(SOD)活性、丙二醛(MDA)含量水平;水迷宫实验检测学习记忆能力;HE染色观察小鼠海马组织结构。结果:每日Met 200 mg/kg干预,能减少模型小鼠的体重。Met干预对模型鼠正常空腹血糖无影响。每日Met 50、100、200 mg/kg剂量干预,与模型组相比,均能显著提升模型小鼠血清和肝组织的SOD活性(P＜0.05)、降低血清MDA含量(P＜0.05),改善学习记忆能力测试的大部分指标(P＜0.05),HE染色显示海马齿状回核固缩、深染的神经元明显减少。Met干预在大部分指标上呈剂量-效应依赖关系。结论:每日Met 50～200 mg/kg长期处理,以Met 200 mg/kg为显著,能延缓D-gal 诱导的雄性中年衰老模型小鼠的衰老进程,机制可能与降低小鼠体重与增强机体抗氧化水平有关。     

Differential effects of ozone on airway and tissue mechanics in obese mice.

Obesity is an important risk factor for asthma. We recently reported increased ozone (O(3))-induced hyperresponsiveness to methacholine in obese mice (Shore SA, Rivera-Sanchez YM, Schwartzman IN, and Johnston RA. J Appl Physiol 95: 938-945, 2003). The purpose of this study was to determine whether this increased hyperresponsiveness is the result of changes in the airways, the lung tissue, or both. To that end, we examined the effect of O(3) (2 parts/million for 3 h) on methacholine-induced changes in lung mechanics with the use of a forced oscillation technique in wild-type C57BL/6J mice and mice obese because of a genetic deficiency in leptin (ob/ob mice). In ob/ob mice, O(3) increased baseline values for all parameters measured in the study: airway resistance (Raw), lung tissue resistance (Rtis), lung tissue damping (G) and elastance (H), and lung hysteresivity (eta). In contrast, no effect of O(3) on baseline mechanics was observed in wild-type mice. O(3) exposure significantly increased Raw, Rtis, lung resistance (Rl), G, H, and eta responses to methacholine in both groups of mice. For G, Rtis, and Rl there was a significant effect of obesity on the response to O(3). Our results demonstrate that both airways and lung tissue contribute to the hyperresponsiveness that occurs after O(3) exposure in wild-type mice. Our results also demonstrate that changes in the lung tissue rather than the airways account for the amplification of O(3)-induced hyperresponsiveness observed in obese mice.     

The integration of lateral gastrocnemius muscle function and kinematics in running turkeys

Animals commonly move over a range of speeds, and encounter considerable variation in habitat structure, such as inclines. Hindlimb kinematics and muscle function in diverse groups of vertebrates are affected by these changes in behavior and habitat structure, providing a fruitful source of variation for studying the integration of kinematics and muscle function. While it has been observed in a variety of vertebrates that muscle length change can be minimal during locomotion, it is unclear how, and to what degree, in vivo muscle length change patterns are integrated with kinematics. We tested the hypothesis that the length of the turkey lateral gastrocnemius (LG), a biarticular muscle that has moments at the ankle and knee, is not solely affected by changes in joint kinematics. We recorded in vivo muscle length changes (using sonomicrometry) and hindlimb movements (using high-speed video) of wild turkeys running on various inclines, and at different speeds. We quantified the relationship between joint angle (knee and ankle separately) and muscle length in freshly euthanized specimens, and then applied an empirically derived correction for changes in pennation angle and tendon strain during locomotion to improve the accuracy of our predicted lengths. We estimated muscle length at four points during each stride and then compared these values with those measured directly. Other than during swing, the predicted changes in muscle length calculated from the changes in joint kinematics did not correspond with our measured values of LG length. Therefore, the lengths at which the LG operates in turkeys are not determined entirely by kinematics. In addition to strain in series elastic components, we hypothesize that heterogeneous strain within muscles, interactions between muscles and muscle pennation angle all contribute to the nonlinear relationship between muscle length changes and kinematics.     

Effect of thyroidectomy on fast and slow muscle fibres of rat gastrocnemius muscle

A combined histochemical, biochemical and electrophoretic study with respect to the enzymes succnic dehydrogenase(SDH), myofibrillar adenosine triphosphatase (m-ATPase), lactate dehydrogenase (LDH) isozymes and myosin light chains was carried out to investigate the response of rat gastrocnemius muscle (medial head). Twelve weeks after thyroidectomy, the results indicated a shift from fast to slow type pattern of LDH isozymes, fibre type transformation from Type II to Type I and a decrease in SDH and m-ATPase activity. The results suggest, possible thyroidal involvement in determining the phenotypic properties of skeletal muscle.     

Genomic imprinting and genetic effects on muscle traits in mice

ABSTRACT: BACKGROUND: Genomic imprinting refers to parent-of-origin dependent gene expression caused by differential DNA methylation of the paternally and maternally derived alleles. Imprinting is increasingly recognized as an important source of variation in complex traits, however, its role in explaining variation in muscle and physiological traits, especially those of commercial value, is largely unknown compared with genetic effects. RESULTS: We investigated both genetic and genomic imprinting effects on key muscle traits in mice from the Berlin Muscle Mouse population, a key model system to study muscle traits. Using a genome scan, we first identified loci with either imprinting or genetic effects on phenotypic variation. Next, we established the proportion of phenotypic variation explained by additive, dominance and imprinted QTL and characterized the patterns of effects. In total, we identified nine QTL, two of which show large imprinting effects on glycogen content and potential, and body weight. Surprisingly, all imprinting patterns were of the bipolar type, in which the two heterozygotes are different from each other but the homozygotes are not. Most QTL had pleiotropic effects and explained up to 40% of phenotypic variance, with individual imprinted loci accounting for 4-5% of variation alone. CONCLUSION: Surprisingly, variation in glycogen content and potential was only modulated by imprinting effects. Further, in contrast to general assumptions, our results show that genomic imprinting can impact physiological traits measured at adult stages and that the expression does not have to follow the patterns of paternal or maternal expression commonly ascribed to imprinting effects.     

Effect of chronic metformin treatment of hepatic and muscle glycogen metabolism in KK mice.

Noninsulin-dependent diabetic KK mice, aged 90-100 days, with hyperinsulinemia and insulin resistance were treated with either metformin (N = 13) or water (control, N = 10) orally at a concentration of 50 mg/kg twice daily for 28 weeks. Age-matched nondiabetic Swiss Webster (SW) mice were also similarly treated. Liver and skeletal muscle glycogen synthase and phosphorylase enzymes were determined in all groups of mice. Both enzymes were significantly lower in control KK than in control SW mice. Metformin did not influence either of these enzymes in nondiabetic SW mice. However, it significantly increased the active form of glycogen synthase (a form) in both the liver and muscle of KK mice. Metformin also increased the active form of phosphorylase (a form) in the liver but not in the muscle of these mice. Hepatic glycogen content was similar in both control and metformin-treated KK mice. However, the muscle glycogen content was significantly higher in metformin-treated than in control KK mice. These data suggest that metformin preferentially stimulates glycogen synthesis in skeletal muscle, and this seems to be responsible for the observed improvement in fasting glucose and glucose response to an oral glucose load in KK mice.