Inactivity induces increases in abdominal fat.

Previously, inducing inactivity for 53 h after 21 days of voluntary running resulted in a 25 and 48% increase in epididymal and omental fat pad weights, respectively, while rats continued to eat more than a group that never had access to a running wheel (J Physiol 565: 911-925, 2005). We wanted to test the hypothesis that inactivity, independent of excessive caloric intake, could induce an increase in fat pad mass. Twenty-one-day-old rats were given access to voluntary running wheels for 42-43 days so that they were running approximately 9 km/day in the last week of running, after which wheels were locked for 5, 53, or 173 h (WL5, WL53, WL173) before the rats were killed. During the 53 and 173 h of inactivity, one group of animals was pair fed (PF) to match sedentary controls, whereas the other continued to eat ad libitum (AL). Epididymal and retroperitoneal fat masses were significantly increased in the WL173-PF vs. the WL5 group, whereas epididymal, perirenal, and retroperitoneal fat masses were all significantly increased in the WL173-AL group compared with the WL5 group. Additionally, hyperplasia, and not hypertrophy, of the epididymal fat mass was responsible for the increase at WL173-AL as demonstrated by a significant increase in cell number vs. WL5, with no change in cell diameter or volume. Thus two important findings have been elucidated: 1) increases in measured abdominal fat masses occur in both AL and PF groups at WL173, and 2) adipocyte expansion via hyperplasia occurred with an ad libitum diet following cessation of voluntary running.     

Early depression of Ankrd2 and Csrp3 mRNAs in the polyribosomal and whole tissue fractions in skeletal muscle with decreased voluntary running

The wheel-lock (WL) model for depressed ambulatory activity in rats has shown metabolic maladies ensuing within 53-173 h after WL begins. We sought to determine if WL beginning after 21-23 days of voluntary running in growing female Wistar rats affected the mRNA profile in the polyribosomal fraction from plantaris muscle shortly following WL. In experiment 1, WL occurred at 0200 and muscles were harvested at 0700 daily at 5 h (WL5h, n = 4), 29 h (WL29h, n = 4), or 53 h (WL53h, n = 4) after WL. Affymetrix Rat Gene 1.0 ST Arrays were used to test the initial question as to whether WL affects mRNA occupancy on skeletal muscle polyribosomes. Using a false discovery rate of 15%, no changes in mRNAs in the polyribosomal fraction were observed at WL29h and eight mRNAs (of over 8,200 identified targets) were altered at WL53h compared with WL5h. Interestingly, two of the six downregulated genes included ankyrin repeat domain 2 (Ankrd2) and cysteine-rich protein 3/muscle LIM protein (Csrp3), both of which encode mechanical stretch sensors and RT-PCR verified their WL-induced decline. In experiment 2, whole muscle mRNA and protein levels were analyzed for Ankrd2 and Csrp3 from the muscles of WL5h (4 original samples + 2 new), WL29h (4 original), WL53h (4 original + 2 new), as well as WL173 h (n = 6 new) and animals that never ran (SED, 4-5 new). Relative to WL5h controls, whole tissue Ankrd2 and Csrp3 mRNAs were lower (P < 0.05) at WL53h, WL173h, and SED; Ankrd2 protein tended to decrease at WL53h (P = 0.054) and Csrp3 protein was less in WL173h and SED rats (P < 0.05). In summary, unique early declines in Ankrd2 and Csrp3 mRNAs were identified with removal of voluntary running, which was subsequently followed by declines in Csrp3 protein levels during longer periods of wheel lock.     

Physical inactivity amplifies the sensitivity of skeletal muscle to the lipid-induced downregulation of lipoprotein lipase activity.

Physical inactivity is a risk factor for lipoprotein disorders and the metabolic syndrome. Physical inactivity has a powerful effect on suppressing lipoprotein lipase (LPL) activity in skeletal muscle, the rate-limiting enzyme for hydrolysis of triglyceride (TG)-rich lipoproteins. We tested the ability of several compounds to prevent the decrease in LPL. The present study minimized standing and ordinary light nonexercise movements in rats to compare the effects of inactivity and nonexercise activity thermogenesis (NEAT) on LPL activity. The key new insight was that the typically quick decrease in LPL activity of oxidative muscle caused by physical inactivity was prevented by nicotinic acid (NA), whereas inhibitors of TNF-alpha, inducible nitric oxide synthase, and NF-kappaB had no such effect. NA was administered at a dose known to acutely impede the appearance of plasma TG from the liver and free fatty acids from adipose tissue, and it was effective at intentionally lowering plasma lipid concentrations to the same level in active and inactive groups. As measured from heparin-releasable LPL activity, LPL in the microvasculature of the most oxidative muscles was approximately 90% lower in the inactive group compared with controls, and this suppression was completely blocked by NA. In contrast to inactivity, NA did not raise muscle LPL in ambulatory controls, whereas a large exogenous fat delivery did decrease LPL activity. In vitro control studies revealed that NA did not have a direct effect on skeletal muscle LPL activity. In conclusion, physical inactivity amplifies the ability of plasma lipids to suppress muscle LPL activity. The light ambulatory contractions responsible for NEAT are sufficient for mitigating these deleterious effects.     

Skeletal muscle and heart LKB1 deficiency causes decreased voluntary running and reduced muscle mitochondrial marker enzyme expression in mice

LKB1 has been identified as a component of the major upstream kinase of AMP-activated protein kinase (AMPK) in skeletal muscle. To investigate the roles of LKB1 in skeletal muscle, we used muscle-specific LKB1 knockout (MLKB1KO) mice that exhibit low expression of LKB1 in heart and skeletal muscle, but not in other tissues. The importance of LKB1 in muscle physiology was demonstrated by the observation that electrical stimulation of the muscle in situ increased AMPK phosphorylation and activity in the wild-type (WT) but not in the muscle-specific LKB1KO mice. Likewise, phosphorylation of acetyl-CoA carboxylase (ACC) was markedly attenuated in the KO mice. The LKB1KO mice had difficulty running on the treadmill and exhibited marked reduction in distance run in voluntary running wheels over a 3-wk period (5.9 +/- 0.9 km/day for WT vs. 1.7 +/- 0.7 km/day for MLKB1KO mice). The MLKB1KO mice anesthetized at rest exhibited significantly decreased phospho-AMPK and phospho-ACC compared with WT mice. KO mice exhibited lower levels of mitochondrial protein expression in the red and white regions of the quadriceps. These observations, along with previous observations from other laboratories, clearly demonstrate that LKB1 is the major upstream kinase in skeletal muscle and that it is essential for maintaining mitochondrial marker proteins in skeletal muscle. These data provide evidence for a critical role of LKB1 in muscle physiology, one of which is maintaining basal levels of mitochondrial oxidative enzymes. Capacity for voluntary running is compromised with muscle and heart LKB1 deficiency.     

Positive Effects of Voluntary Running on Metabolic Syndrome-Related Disorders in Non-Obese Hereditary Hypertriacylglycerolemic Rats

While metabolic syndrome is often associated with obesity, 25% of humans suffering from it are not obese and the effect of physical activity remains unclear in such cases. Therefore, we used hereditary hypertriaclyglycerolemic (HHTg) rats as a unique model for studying the effect of spontaneous physical activity [voluntary running (VR)] on metabolic syndrome-related disorders, such as dyslipidemia, in non-obese subjects. Adult HHTg males were fed standard (CD) or high-sucrose (HSD) diets ad libitum for four weeks. Within both dietary groups, some of the rats had free access to a running wheel (CD+VR, HSD+VR), whereas the controls (CD, HSD) had no possibility of extra physical activity. At the end of the four weeks, we measured the effects of VR on various metabolic syndrome-associated parameters: (i) biochemical parameters, (ii) the content and composition of triacylglycerols (TAG), diacylglycerols (DAG), ceramides and membrane phospholipids, and (iii) substrate utilization in brown adipose tissue. In both dietary groups, VR led to various positive effects: reduced epididymal and perirenal fat depots; increased epididymal adipose tissue lipolysis; decreased amounts of serum TAG, non-esterified fatty acids and insulin; a higher insulin sensitivity index. While tissue ceramide content was not affected, decreased TAG accumulation resulted in reduced and modified liver, heart and skeletal muscle DAG. VR also had a beneficial effect on muscle membrane phospholipid composition. In addition, compared with the CD group, the CD+VR rats exhibited increased fatty acid oxidation and protein content in brown adipose tissue. Our results confirm that physical activity in a non-obese model of severe dyslipidemia has many beneficial effects and can even counteract the negative effects of sucrose consumption. Furthermore, they suggest that the mechanism by which these effects are modulated involves a combination of several positive changes in lipid metabolism.     

Wheel-running exercise alters rat diaphragm action potentials and their regulation by K+ channels.

Endurance exercise modifies regulatory systems that control skeletal muscle Na+ and K+ fluxes, in particular Na+-K+-ATPase-mediated transport of these ions. Na+ and K+ ion channels also play important roles in the regulation of ionic movements, specifically mediating Na+ influx and K+ efflux that occur during contractions resulting from action potential depolarization and repolarization. Whether exercise alters skeletal muscle electrophysiological properties controlled by these ion channels is unclear. The present study tested the hypothesis that endurance exercise modifies diaphragm action potential properties. Exercised rats spent 8 wk with free access to running wheels, and they were compared with sedentary rats living in conventional rodent housing. Diaphragm muscle was subsequently removed under anesthesia and studied in vitro. Resting membrane potential was not affected by endurance exercise. Muscle from exercised rats had a slower rate of action potential repolarization than that of sedentary animals (P = 0.0098), whereas rate of depolarization was similar in the two groups. The K+ channel blocker 3,4-diaminopyridine slowed action potential repolarization and increased action potential area of both exercised and sedentary muscle. However, these effects were significantly smaller in diaphragm from exercised than sedentary rats. These data indicate that voluntary running slows diaphragm action potential repolarization, most likely by modulating K+ channel number or function.     

Metabolic adaptations in skeletal muscle overexpressing GLUT4: effects on muscle and physical activity.

To understand the long-term metabolic and functional consequences of increased GLUT4 content, intracellular substrate utilization was investigated in isolated muscles of transgenic mice overexpressing GLUT4 selectively in fast-twitch skeletal muscles. Rates of glycolysis, glycogen synthesis, glucose oxidation, and free fatty acid (FFA) oxidation as well as glycogen content were assessed in isolated EDL (fast-twitch) and soleus (slow-twitch) muscles from female and male MLC-GLUT4 transgenic and control mice. In male MLC-GLUT4 EDL, increased glucose influx predominantly led to increased glycolysis. In contrast, in female MLC-GLUT4 EDL increased glycogen synthesis was observed. In both sexes, GLUT4 overexpression resulted in decreased exogenous FFA oxidation rates. The decreased rate of FFA oxidation in male MLC-GLUT4 EDL was associated with increased lipid content in liver, but not in muscle or at the whole body level. To determine how changes in substrate metabolism and insulin action may influence energy balance in an environment that encouraged physical activity, we measured voluntary training activity, body weight, and food consumption of MLC-GLUT4 and control mice in cages equipped with training wheels. We observed a small decrease in body weight of MLC-GLUT4 mice that was paradoxically accompanied by a 45% increase in food consumption. The results were explained by a marked fourfold increase in voluntary wheel exercise. The changes in substrate metabolism and physical activity in MLC-GLUT4 mice were not associated with dramatic changes in skeletal muscle morphology. Collectively, results of this study demonstrate the feasibility of altering muscle substrate utilization by overexpression of GLUT4. The results also suggest that as a potential treatment for type II diabetes mellitus, increased skeletal muscle GLUT4 expression may provide benefits in addition to improvement of insulin action.     

Epigenetic reprogramming in metabolic disorders: nutritional factors and beyond

Environmental factors (e.g., malnutrition and physical inactivity) contribute largely to metabolic disorders including obesity, type 2 diabetes, cardiometabolic disease and nonalcoholic fatty liver diseases. The abnormalities in metabolic activity and pathways have been increasingly associated with altered DNA methylation, histone modification and noncoding RNAs, whereas lifestyle interventions targeting diet and physical activity can reverse the epigenetic and metabolic changes. Here we review recent evidence primarily from human studies that links DNA methylation reprogramming to metabolic derangements or improvements, with a focus on cross-tissue (e.g., the liver, skeletal muscle, pancreas, adipose tissue and blood samples) epigenetic markers, mechanistic mediators of the epigenetic reprogramming, and the potential of using epigenetic traits to predict disease risk and intervention response. The challenges in epigenetic studies addressing the mechanisms of metabolic diseases and future directions are also discussed and prospected.     

Differential vulnerability of skeletal muscle feed arteries to dysfunction in insulin resistance: impact of fiber type and daily activity

Functional and structural heterogeneity exists among skeletal muscle vascular beds related, in part, to muscle fiber type composition. This study was designed to delineate whether the vulnerability to vascular dysfunction in insulin resistance is uniformly distributed among skeletal muscle vasculatures and whether physical activity modifies this vulnerability. Obese, hyperphagic Otsuka Long-Evans Tokushima fatty rats (20 wk old) were sedentary (OSED) or physically active (OPA; access to running wheels) and compared with age-matched sedentary Long-Evans Tokushima Otsuka (LSED) rats. Vascular responses were determined in isolated, pressurized feed arteries from fast-twitch gastrocnemius (GFAs) and slow-twitch soleus (SFAs) muscles. OSED animals were obese, insulin resistant, and hypertriglyceridemic, traits absent in LSED and OPA rats. GFAs from OSED animals exhibited depressed dilation to ACh, but not sodium nitroprusside, and enhanced vasoconstriction to endothelin-1 (ET-1), but not phenylephrine, compared with those in LSED. Immunoblot analysis suggests reduced endothelial nitric oxide synthase phosphorylation at Ser1177 and endothelin subtype A receptor expression in OSED GFAs. Physical activity prevented reduced nitric oxide-dependent dilation to ACh, but not enhanced ET-1 vasoconstriction, in GFA from OPA animals. Conversely, vasoreactivity of SFAs to ACh and ET-1 were principally similar in all groups, whereas dilation to sodium nitroprusside was enhanced in OSED and OPA rats. These data demonstrate, for the first time, that SFAs from insulin-resistant rats exhibit reduced vulnerability to dysfunction versus GFAs and that physical activity largely prevents GFA dysfunction. We conclude that these results demonstrate that vascular dysfunction associated with insulin resistance is heterogeneously distributed across skeletal muscle vasculatures related, in part, to muscle fiber type and activity level.     

Daily exercise increases hepatic fatty acid oxidation and prevents steatosis in Otsuka Long-Evans Tokushima Fatty rats

Exercise training is commonly prescribed for treatment of nonalcoholic fatty liver disease (NAFLD). We sought to determine whether exercise training prevents the development of NAFLD in Otsuka Long-Evans Tokushima Fatty (OLETF) rats and to elucidate the molecular mechanisms underlying the effects of exercise on hepatic steatosis. Four-week-old OLETF rats were randomly assigned to either a sedentary control group (Sed) or a group given access to voluntary running wheels for 16 wk (Ex). Wheels were locked 2 days before euthanasia in the Ex animals, and both groups were euthanized at 20 wk old. Voluntary wheel running attenuated weight gain and reduced serum glucose, insulin, free fatty acids, and triglycerides in Ex animals compared with Sed (P < 0.001). Ex animals exhibited significantly reduced hepatic triglyceride levels and displayed fewer lipid droplets (Oil Red O staining) and reduced lipid droplet size compared with Sed. Wheel running increased by threefold the percent of palmitate oxidized completely to CO(2) in the Ex animals but did not alter AMP-activated protein kinase-alpha (AMPKalpha) or AMPK phosphorylation status. However, fatty acid synthase and acetyl-coenzyme A carboxylase (ACC) content were significantly reduced (approximately 70 and approximately 35%, respectively), and ACC phosphorylation and cytochrome c content were significantly elevated (approximately 35 and approximately 30%, respectively) in the Ex animals. These results unequivocally demonstrate that daily physical activity attenuates hepatic steatosis and NAFLD in an obese rodent model and suggest that this effect is likely mediated, in part, through enhancement of hepatic fatty acid oxidation and reductions in key protein intermediates of fatty acid synthesis.     

Insulin sensitivity linked skeletal muscle Nr4a1 DNA methylation is programmed by the maternal diet and modulated by voluntary exercise in mice

Perinatal maternal high-fat consumption is known to increase the obesity and type 2 diabetes susceptibility and to impair exercise performance in the offspring. We hypothesize that epigenetic modifications in the skeletal muscle are partly responsible for this phenotype. To detect skeletal muscle genes affected by maternal nutrition, male offspring of low-fat (LF) and high-fat (HF) diet fed dams (BL6 mice) received LF diet upon weaning and were sacrificed at 6 or 25 weeks of age. Gene expression of Musculus quadriceps was investigated by microarray analysis revealing an up-regulation of the nuclear receptor Nr4a1 by maternal HF feeding. This was accompanied by promoter hypomethylation of CpG_-1408 which correlated with increased Nr4a1 gene expression at both ages. Offspring voluntary exercise training (by supplying running wheels from 7 to 25 weeks of age) normalized Nr4a1 methylation and gene expression respectively, and ameliorated the negative effects of maternal HF feeding on insulin sensitivity. Overall, Nr4a1 gene expression in skeletal muscle correlated with higher insulin levels during an oral glucose tolerance test and could, therefore, be involved in programming type 2 diabetes susceptibility in offspring exposed to perinatal high fat diet.     

Voluntary running, skeletal muscle gene expression, and signaling inversely regulated by orchidectomy and testosterone replacement

Declines in skeletal muscle size and strength, often seen with chronic wasting diseases, prolonged or high-dose glucocorticoid therapy, and the natural aging process in mammals, are usually associated with reduced physical activity and testosterone levels. However, it is not clear whether the decline in testosterone and activity are causally related. Using a mouse model, we found that removal of endogenous testosterone by orchidectomy results in an almost complete cessation in voluntary wheel running but only a small decline in muscle mass. Testosterone replacement restored running behavior and muscle mass to normal levels. Orchidectomy also suppressed the IGF-I/Akt pathway, activated the atrophy-inducing E3 ligases MuRF1 and MAFBx, and suppressed several energy metabolism pathways, and all of these effects were reversed by testosterone replacement. The study also delineated a distinct, previously unidentified set of genes that is inversely regulated by orchidectomy and testosterone treatment. These data demonstrate the necessity of testosterone for both speed and endurance of voluntary wheel running in mice and suggest a potential mechanism for declined activity in humans where androgens are deficient.     

Obesity‐Related Knowledge,Attitudes, and Behaviors in Obese and Non‐obese Urban Philadelphia Female Adolescents

Objectives: To examine relationships between knowledge, attitudinal and behavioral factors, and obesity and to determine how these factors influence obesity status in west Philadelphia female adolescents. Research Methods and Procedures: A matched‐pairs study was conducted with 32 stature‐ and age‐matched pairs of obese (body mass index and triceps skinfold ≥95th percentile of National Health and Nutrition Examination Survey I) and non‐obese (body mass index and triceps skinfold between the 15th and 85th percentiles of National Health and Nutrition Examination Survey I) female African American adolescents (aged 11 to 15 years), selected from a school‐based study sample, based on obesity status and matching criteria. Adolescents were compared on the following measures: physical activity, inactivity, dietary intake, eating attitudes, health behavior knowledge, body image, self‐esteem, and maturation status. Differences between obese and non‐obese females were tested using paired t tests and Wilcoxon matched‐pairs signed‐rank tests. Results: Physical activity, inactivity, and perception of ideal body size emerged as the most important contributory factors to obesity status. There were no statistically significant matched‐pair differences in macronutrient and micronutrient intakes, self‐esteem, eating attitudes, health behavior knowledge, or maturation status of these adolescents. Obese adolescents had significantly lower levels of physical activity, higher inactivity, and a larger perception of ideal body size than non‐obese adolescents. Discussion: Knowledge and attitudinal factors (with the exception of perception of ideal body size) had far less association with obesity than activity‐related behavioral factors. These findings suggest that future intervention strategies should pay particular attention to physical activity, inactivity, and body image attitudes.     

Ursolic acid increases skeletal muscle and brown fat and decreases diet-induced obesity, glucose intolerance and fatty liver disease

Skeletal muscle Akt activity stimulates muscle growth and imparts resistance to obesity, glucose intolerance and fatty liver disease. We recently found that ursolic acid increases skeletal muscle Akt activity and stimulates muscle growth in non-obese mice. Here, we tested the hypothesis that ursolic acid might increase skeletal muscle Akt activity in a mouse model of diet-induced obesity. We studied mice that consumed a high fat diet lacking or containing ursolic acid. In skeletal muscle, ursolic acid increased Akt activity, as well as downstream mRNAs that promote glucose utilization (hexokinase-II), blood vessel recruitment (Vegfa) and autocrine/paracrine IGF-I signaling (Igf1). As a result, ursolic acid increased skeletal muscle mass, fast and slow muscle fiber size, grip strength and exercise capacity. Interestingly, ursolic acid also increased brown fat, a tissue that shares developmental origins with skeletal muscle. Consistent with increased skeletal muscle and brown fat, ursolic acid increased energy expenditure, leading to reduced obesity, improved glucose tolerance and decreased hepatic steatosis. These data support a model in which ursolic acid reduces obesity, glucose intolerance and fatty liver disease by increasing skeletal muscle and brown fat, and suggest ursolic acid as a potential therapeutic approach for obesity and obesity-related illness.     

Effects of long-term physical exercise on skeletal muscles in senescence-accelerated mice (SAMP8)

We examined the effect of long-term exercise on the prevention of sarcopenia using a senescence-accelerated-prone mice (SAMP8) model. Mice were housed in a wheel cage for 25 weeks to increase voluntary exercise. At week 23, endurance running capacity was examined using a treadmill. In a treadmill running test, the wheel cage group had increased endurance running capacity, which suggests that aging-related loss of muscle function was recovered by long-term exercise. Mice were sacrificed and microarray analysis revealed that genes involved in protein synthesis and degradation were upregulated in the skeletal muscles of the wheel cage group, suggesting accelerated protein turnover. Total body and adipose tissue weights decreased following the use of the wheel cage. Thus, long-term, spontaneous physical exercise may assist in recovering from aging-related sarcopenia (loss of muscle function) and obesity.     

Parallel and divergent adaptations of rat soleus and plantaris to chronic exercise and hypergravity

It has been demonstrated that endurance exercise and chronic acceleration, i.e., hypergravity, produce comparable adaptations in a variety of physiological systems, including decreased adiposity, increased energy metabolism, and altered intermediary metabolism. Similar adaptations have not been demonstrated for skeletal muscle per se. To further differentiate between these general responses with respect to gravity and exercise, this study tested the hypothesis that chronic exercise (voluntary wheel running) and chronic acceleration (2 G via centrifugation) will induce similar changes in muscle myosin heavy chain (MHC) isoform expression in rat plantaris, a fast extensor, and in rat soleus, a slow "antigravity" extensor. The experimental design involved four groups of mature male rats (n = 8/group): 1 G and 2 G with running wheels, and 1 G and 2 G controls without running wheels. The primary observations from the study were as follows: 1) 8 wk of 2 G are an adequate stimulus for MHC compositional changes in rat plantaris and soleus muscle; 2) both exercise and +G caused an increase in the slow MHC1 isoform in soleus muscle, suggesting that loading is a primary stimulus for this shift; and 3) 2 G and exercise appeared to have differential effects on the plantaris muscle MHC isoforms, with 2 G causing an increase in MHC2b, and exercise causing a decrease in MHC2b with a concomitant increase in MHC1, suggesting that factors other than enhanced loading, possibly locomotor activity levels, are the primary stimulus for this shift.