Humanized animal exercise model for clinical implication

Exercise Regulation of Cognitive Function and Neuroplasticity in the Healthy and Diseased Brain

Regular exercise broadly enhances physical and mental health throughout the lifespan. Animal models have provided us with the tools to gain a better understanding of the underlying biochemical, physiological, and morphological mechanisms through which exercise exerts its beneficial cognitive effects. One brain region in particular, the hippocampus, is especially responsive to exercise. It is critically involved in learning and memory and is one of two regions in the mammalian brain that continues to generate new neurons throughout life. Exercise prevents the decline of the hippocampus from aging and ameliorates many neurodegenerative diseases, in part by increasing adult hippocampal neurogenesis but also by activating a multitude of molecular mechanisms that promote brain health. In this chapter, we first describe some rodent models used to study effects of exercise on the brain. Then we review the rodent work focusing on the mechanisms behind which exercise improves cognition and brain health in both the normal and the diseased brain, with emphasis on the hippocampus.

Voluntary exercise delays heart failure onset in rats with pulmonary artery hypertension

Increased physical activity is recommended for the general population and for patients with many diseases because of its health benefits but can be contraindicated if it is thought to be a risk for serious cardiovascular events. One such condition is pulmonary artery hypertension (PAH). PAH and right ventricular failure was induced in rats by a single injection of monocrotaline (MCT). MCT rats with voluntary access to a running wheel ran on average 2 km/day. The time for half the animals to develop heart failure signs (median survival time) was 28 days (exercise failure group), significantly longer than sedentary animals (sedentary failure group, 23 days). The contractility of single failing myocytes in response to increasing demand (stimulation frequency) was significantly impaired compared with that in both sedentary control and exercising control myocytes. However, myocytes from exercising MCT rats, tested at 23 days (exercise + MCT group), showed responses intermediate to the control (sedentary control and exercising control) and failing (sedentary failure and exercise failure) groups. We conclude that voluntary exercise is beneficial to rats with heart failure induced by PAH, and this is evidence to support the consideration of appropriate exercise regimes for potentially vulnerable groups.

Low intensity training of mdx mice reduces carbonylation and increases expression levels of proteins involved in energy metabolism and muscle contraction

High intensity training induces muscle damage in dystrophin-deficient mdx mice, an animal model for Duchenne muscular dystrophy. However, low intensity training (LIT) rescues the mdx phenotype and even reduces the level of protein carbonylation, a marker of oxidative damage. Until now, beneficial effects of LIT were mainly assessed at the physiological level. We investigated the effects of LIT at the molecular level on 8-week-old wild-type and mdx muscle using 2D Western blot and protein-protein interaction analysis. We found that the fast isoforms of troponin T and myosin binding protein C as well as glycogen phosphorylase were overcarbonylated and downregulated in mdx muscle. Some of the mitochondrial enzymes of the citric acid cycle were overcarbonylated, whereas some proteins of the respiratory chain were downregulated. Of functional importance, ATP synthase was only partially assembled, as revealed by Blue Native PAGE analysis. LIT decreased the carbonylation level and increased the expression of fast isoforms of troponin T and of myosin binding protein C, and glycogen phosphorylase. In addition, it increased the expression of aconitate hydratase and NADH dehydrogenase, and fully restored the ATP synthase complex. Our study demonstrates that the benefits of LIT are associated with lowered oxidative damage as revealed by carbonylation and higher expression of proteins involved in energy metabolism and muscle contraction. Potentially, these results will help to design therapies for DMD based on exercise mimicking drugs.

Influence of starvation on heart contractility and corticosterone level in rats

The physiological changes, including cardiac modification, that occur during starvation are not yet completely understood. The purpose of this study is to examine the effects of a 2-week starvation period on heart contractility, muscle mass, and irisin and corticosterone levels in rats. Rats in the starved group showed a significant reduction in the body, heart, kidney, and muscle weight (n = 23, p < 0.05). Blood glucose, total protein, and albumin showed a 44, 17.5, and 10.3 % reduction, respectively (p < 0.05). Lipid reserves, such as total lipid, triglyceride, and free fatty acid, were also comparably reduced (p < 0.05). However, the bilirubin, creatinine, blood urea nitrogen, and creatine kinase levels were higher than in the control group (p < 0.05). The blood irisin level was unchanged, but the stress-related corticosterone level was significantly higher in the starved group. The differences observed in M-mode echocardiography were further compared with the body-weight-matched control group. Starvation reduced the left ventricle mass; however, this difference was not significant compared with the body-weight-matched group (p > 0.05). In the starvation group, the impairment of cardiac output was dependent on the reduction in stroke volume and heart rate. Starvation induced a severe reduction in ejection fraction and fractional shortening when compared with the body-weight-matched control group (p < 0.05). In summary, prolonged starvation, which leads to a deficiency of available nutrition, increases the stress-related corticosterone level, impairs the cardiac output, and is associated with changes in cardiac morphogeometry.

The rat adequately reflects human responses to exercise in blood biochemical profile: a comparative study

Animal models are widely used in biology and the findings of animal research are traditionally projected to humans. However, recent publications have raised concerns with regard to what extent animals and humans respond similar to physiological stimuli. Original data on direct in vivo comparison between animals and humans are scarce and no study has addressed this issue after exercise. We aimed to compare side by side in the same experimental setup rat and human responses to an acute exercise bout of matched intensity and duration. Rats and humans ran on a treadmill at 86% of maximal velocity until exhaustion. Pre and post exercise we measured 30 blood chemistry parameters, which evaluate iron status, lipid profile, glucose regulation, protein metabolism, liver, and renal function. ANOVA indicated that almost all biochemical parameters followed a similar alteration pattern post exercise in rats and humans. In fact, there were only 2/30 significant species × exercise interactions (in testosterone and globulins), indicating different responses to exercise between rats and humans. On the contrary, the main effect of exercise was significant in 15/30 parameters and marginally nonsignificant in other two parameters (copper, P = 0.060 and apolipoprotein B, P = 0.058). Our major finding is that the rat adequately mimics human responses to exercise in those basic blood biochemical parameters reported here. The physiological resemblance of rat and human blood responses after exercise to exhaustion on a treadmill indicates that the use of blood chemistry in rats for exercise physiology research is justified.

Ursolic Acid-induced elevation of serum irisin augments muscle strength during resistance training in men

Ursolic acid (UA), a type of pentacyclic triterpenoid carboxylic acid purified from natural plants, can promote skeletal muscle development. We measured the effect of resistance training (RT) with/without UA on skeletal muscle development and related factors in men. Sixteen healthy male participants (age, 29.37±5.14 years; body mass index=27.13±2.16 kg/m²) were randomly assigned to RT (n=7) or RT with UA (RT+UA, n=9) groups. Both groups completed 8 weeks of intervention consisting of 5 sets of 26 exercises, with 10~15 repetitions at 60~80% of 1 repetition maximum and a 60~90-s rest interval between sets, performed 6 times/week. UA or placebo was orally ingested as 1 capsule 3 times/day for 8 weeks. The following factors were measured pre-and post-intervention: body composition, insulin, insulin-like growth factor-1 (IGF-1), irisin, and skeletal muscle strength. Body fat percentage was significantly decreased (p<0.001) in the RT+UA group, despite body weight, body mass index, lean body mass, glucose, and insulin levels remaining unchanged. IGF-1 and irisin were significantly increased compared with baseline levels in the RT+UA group (p<0.05). Maximal right and left extension (p<0.01), right flexion (p<0.05), and left flexion (p<0.001) were significantly increased compared with baseline levels in the RT+UA group. These findings suggest that UA-induced elevation of serum irisin may be useful as an agent for the enhancement of skeletal muscle strength during RT.