Effect of voluntary exercise on the expression of IGF-I and androgen receptor in three rat skeletal muscles and on serum IGF-I and testosterone levels

The Effect of Voluntary Physical Activity in an Enriched Environment and Combined Exercise Training on the Satellite Cell Pool in Developing Rats

Aim: Postnatal skeletal muscle growth is strongly associated with a satellite cell pool. Early adolescence might be a crucial period when different exercise training interventions have specific consequence on satellite cells. Pax7 and MyoD have been suggested as the leading indicators of satellite cell activation.

Methods: In this study, pre-adolescent male rats (n = 18) were either subjected to an enriched environment that facilitated physical activities or combined training or control for three weeks. The flexor hallucis longus muscle was removed for biochemical and histochemical analysis.

Results: Findings demonstrated that exercise trained rats displayed high levels of serum IGF-1 (p <0.05). There was an increase in Pax7 (p <0.05) and MyoD (p <0.001) mRNA expression. A significant increase in the mean fiber area (p <0.01), satellite cell (p <0.001), and myonuclear numbers (p <0.01) were also observed in both intervention groups. Importantly, enriched rats showed lower corticosterone levels (p <0.05) compared to training ones. Regarding performance, trained and enriched rats had significant improvement in forelimb grip strength (p <0.01) and load-carrying capacity (p <0.05).

Conclusion: Type of physical exercise is an essential part in changing satellite cells pool. Different and frequent physical activities in an enriched environment can be effective for muscle development.

Bone Muscle Crosstalk in Spinal Cord Injuries: Pathophysiology and Implications for Patients' Quality of Life

PURPOSE OF REVIEW

The goal of this review is to provide a comprehensive overview of (i) bone and muscle tissue modifications pathophysiology in spinal cord injury (SCI), (ii) experimental data on the physiopathological mechanisms underpinning these modifications and their similarities with the aging process, and (iii) potential clinical implications in the management of the disabling sequelae of SCI.

RECENT FINDINGS

Several studies attempted to describe the biology underpinning the links between bone and muscle tissues in the setting of highly disabling conditions, such as osteoporosis, sarcopenia, and neurodegenerative disorders, although these bidirectional connections remain still unclear. SCI could be considered an in vivo paradigmatic model of the bone muscle interactions in unloading conditions that might be expanded in the field of neurodegenerative disorders or cancer studies. Future studies should take into consideration the newer insights into bone muscle crosstalk in order to develop multitargeted and therapeutic interventions.

Role of IGF-I signaling in muscle bone interactions

Skeletal muscle and bone rely on a number of growth factors to undergo development, modulate growth, and maintain physiological strength. A major player in these actions is insulin-like growth factor I (IGF-I). However, because this growth factor can directly enhance muscle mass and bone density, it alters the state of the musculoskeletal system indirectly through mechanical crosstalk between these two organ systems. Thus, there are clearly synergistic actions of IGF-I that extend beyond the direct activity through its receptor. This review will cover the production and signaling of IGF-I as it pertains to muscle and bone, the chemical and mechanical influences that arise from IGF-I activity, and the potential for therapeutic strategies based on IGF-I. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Role of IGF-I signaling in muscle bone interactions

Skeletal muscle and bone rely on a number of growth factors to undergo development, modulate growth, and maintain physiological strength. A major player in these actions is insulin-like growth factor I (IGF-I). However, because this growth factor can directly enhance muscle mass and bone density, it alters the state of the musculoskeletal system indirectly through mechanical crosstalk between these two organ systems. Thus, there are clearly synergistic actions of IGF-I that extend beyond the direct activity through its receptor. This review will cover the production and signaling of IGF-I as it pertains to muscle and bone, the chemical and mechanical influences that arise from IGF-I activity, and the potential for therapeutic strategies based on IGF-I. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Treadmill exercise induced functional recovery after peripheral nerve repair is associated with increased levels of neurotrophic factors

Benefits of exercise on nerve regeneration and functional recovery have been reported in both central and peripheral nervous system disease models. However, underlying molecular mechanisms of enhanced regeneration and improved functional outcomes are less understood. We used a peripheral nerve regeneration model that has a good correlation between functional outcomes and number of motor axons that regenerate to evaluate the impact of treadmill exercise. In this model, the median nerve was transected and repaired while the ulnar nerve was transected and prevented from regeneration. Daily treadmill exercise resulted in faster recovery of the forelimb grip function as evaluated by grip power and inverted holding test. Daily exercise also resulted in better regeneration as evaluated by recovery of compound motor action potentials, higher number of axons in the median nerve and larger myofiber size in target muscles. Furthermore, these observations correlated with higher levels of neurotrophic factors, glial derived neurotrophic factor (GDNF), brain derived neurotrophic factor (BDNF) and insulin-like growth factor-1 (IGF-1), in serum, nerve and muscle suggesting that increase in muscle derived neurotrophic factors may be responsible for improved regeneration.

Treadmill exercise training prevents myocardial mechanical dysfunction induced by androgenic-anabolic steroid treatment in rats

Elevated concentrations of testosterone and its synthetic analogs may induce changes in cardiovascular function. However, the effects of the combination of anabolic/androgenic steroid (AAS) treatment and exercise training on systolic and diastolic cardiac function are poorly understood. In the present study, we aimed to investigate the effects of low-dose steroid treatment (stanozolol) on cardiac contractile parameters when this steroid treatment was combined with exercise training in rats and the effects of chronic steroid treatment on the Frank-Starling (length-tension curves) relationship. Male Wistar rats were randomly assigned to one of four groups: U (untrained), US (untrained and treated with stanozolol 5 mg/kg/week), T (trained, 16 m/min/1 h) and TS (trained and treated with stanozolol 5 mg/kg/week). Continuous exercise training was conducted 5 days/week for 8 consecutive weeks. The speed of the treadmill was gradually increased to a final setting of 16 m/min/1 h. Experiments were divided into two independent series: 1) central hemodynamic analysis for mean arterial blood pressure (MAP) and cardiac output (CO) measurements and 2) isolated papillary muscle preparation in Krebs solution. Stanozolol treatment significantly increased the MAP and the heart size in untrained and trained rats (U 113±2; T 106±2; US 138±8 and TS 130±7 mmHg). Furthermore, stanozolol significantly decreased developed tension and dT/dt (maximal and minimal) in U rats. However, the developed tension was completely restored by training. The Frank/Starling relationship was impaired in rats treated with stanozolol; however, again, training completely restored diastolic function. Taken together, the present data suggest that AAS treatment is able to decrease cardiac performance (systolic and diastolic functions). The combination of stanozolol and physical training improved cardiac performance, including diastolic and systolic functions, independent of changes in central hemodynamic parameters. Therefore, changes in ventricular myocyte calcium transients may play a cardioprotective role.

Endocrine characterization of the designer steroid methyl-1-testosterone: investigations on tissue-specific anabolic-androgenic potency, side effects, and metabolism

Various products containing rarely characterized anabolic steroids are nowadays marketed as dietary supplements. Herein, the designer steroid methyl-1-testosterone (M1T) (17β-hydroxy-17α-methyl-5α-androst-1-en-3-one) was identified, and its biological activity, potential adverse effects, and metabolism were investigated. The affinity of M1T toward the androgen receptor (AR) was tested in vitro using a yeast AR transactivation assay. Its tissue-specific androgenic and anabolic potency and potential adverse effects were studied in a Hershberger assay (sc or oral), and tissue weights and selected molecular markers were investigated. Determination of M1T and its metabolites was performed by gas chromatography mass spectrometry. In the yeast AR transactivation assay, M1T was characterized as potent androgen. In rats, M1T dose-dependently stimulated prostate and levator ani muscle weight after sc administration. Oral administration had no effect but stimulated proliferation in the prostate and modulated IGF-I and AR expression in the gastrocnemius muscle in a dose-dependent manner. Analysis of tyrosine aminotransferase expression provided evidence for a strong activity of M1T in the liver (much higher after oral administration). In rat urine, 17α-methyl-5α-androstane-3α,17β-diol, M1T, and a hydroxylated metabolite were identified. In humans, M1T was confirmed in urine in addition to its main metabolites 17α-methyl-5α-androst-1-ene-3α,17β-diol and 17α-methyl-5α-androstane-3α,17β-diol. Additionally, the corresponding 17-epimers as well as 17β-hydroxymethyl-17α-methyl-18-nor-5α-androsta-1,13-dien-3-one and its 17-epimer were detected, and their elimination kinetics was monitored. It was demonstrated that M1T is a potent androgenic and anabolic steroid after oral and sc administration. Obviously, this substance shows no selective AR modulator characteristics and might exhibit liver toxicity, especially after oral administration.

Combined exercise and insulin-like growth factor-1 supplementation induces neurogenesis in old rats, but do not attenuate age-associated DNA damage

We have investigated the effects of 2 weeks of insulin-like growth factor-1 (IGF-1) supplementation (5 μg/kg per day) and 6 weeks of exercise training (60% of the maximal oxygen consumption [VO₂ max]) on neurogenesis, DNA damage/repair, and sirtuin content in the hippocampus of young (3 months old) and old (26 months old) rats. Exercise improved the spatial memory of the old group, but IGF-1 supplementation eliminated this effect. An age-associated decrease in neurogenesis was attenuated by exercise and IGF-1 treatment. Aging increased the levels of 8-oxo-7,8-dihydroguanine (8-oxoG) and the protein Ku70, indicating the role of DNA damage in age-related neuropathology. Acetylation of 8-oxoguanine DNA glycosylase (OGG1) was detected in vivo, and this decreased with aging. However, in young animals, exercise and IGF-1 treatment increased acetylated (ac) OGG1 levels. Sirtuin 1 (SIRT1) and SIRT3, as DNA damage-associated lysine deacetylases, were measured, and SIRT1 decreased with aging, resulting in a large increase in acetylated lysine residues in the hippocampus. On the other hand, SIRT3 increased with aging. Exercise-induced neurogenesis might not be a causative factor of increased spatial memory, because IGF-1 plus exercise can induce neurogenesis in the hippocampus of older rats. Data revealed that the age-associated increase in 8-oxoG levels is due to decreased acetylation of OGG1. Age-associated decreases in SIRT1 and the associated increase in lysine acetylation, in the hippocampus, could have significant impact on function and thus, could suggest a therapeutic target.

Molecular aspects involved in swimming exercise training reducing anhedonia in a rat model of depression

Patients suffering from depression frequently display hyperactivity of the hypothalamic-pituitary-adrenal axis (HPA) resulting in elevated cortisol levels. One main symptom of this condition is anhedonia. There is evidence that exercise training can be used as a rehabilitative intervention in the treatment of depressive disorders. In this scenario, the aim of the present study was to assess the effect of an aerobic exercise training protocol on the depressive-like behavior, anhedonia, induced by repeated dexamethasone administration. The study was carried out on adult male Wistar rats randomly divided into four groups: the "control group" (C), "exercise group" (E), "dexamethasone group" (D) and the "dexamethasone plus exercise group" (DE). The exercise training consisted of swimming (1 h/d, 5 d/wk) for 3 weeks, with an overload of 5% of the rat body weight. Every day rats were injected with either dexamethasone (D/DE) or saline solution (C/E). Proper positive controls, using fluoxetine, were run in parallel. Decreased blood corticosterone levels, reduced adrenal cholesterol synthesis and adrenal weight (HPA disruption), reduced preference for sucrose consumption and increased immobility time (depressive-like behavior), marked hippocampal DNA oxidation, increased IL-10 and total brain-derived neurotrophic factor (BDNF; pro-plus mature-forms) and a severe loss of body mass characterized the dexamethasone-treated animals. Besides increasing testosterone blood concentrations, the swim training protected depressive rats from the anhedonic state, following the same profile as fluoxetine, and also from the dexamethasone-induced impaired neurochemistry. The data indicate that physical exercise could be a useful tool in preventing and treating depressive disorders.

Effect of resistance exercise on muscle steroidogenesis

Circulating testosterone is elevated acutely following resistance exercise (RE) and is an important anabolic hormone for muscle adaptations to resistance training. The purpose of this study was to examine the acute effect of heavy RE on intracrine muscle testosterone production in young resistance-trained men and women. Fifteen young, highly resistance-trained men ( n = 8; 21 ± 1 yr, 175.3 ± 6.7 cm, 90.8 ± 11.6 kg) and women ( n = 7; 24 ± 5 yr, 164.6 ± 6.7 cm, 76.4 ± 15.6 kg) completed 6 sets of 10 repetitions of Smith machine squats with 80% of their 1-repetition maximum. Before RE and 10 and 70 min after RE, muscle biopsies were obtained from the vastus lateralis. Before RE, after 3 and 6 sets of squats, and 5, 15, 30, and 70 min into recovery from RE, blood samples were obtained using venipuncture from an antecubital vein. Muscle samples were analyzed for testosterone, 17β-hydroxysteroid dehydrogenase (HSD) type 3, and 3β-HSD type 1 and 2 content. Blood samples were analyzed for glucose and lactate concentrations. No changes were found for muscle testosterone, 3β-HSD type 1 and 2, and 17β-HSD type 3 concentrations. However, a change in protein migration in the Bis-Tris gel was observed for 17β-HSD type 3 postexercise; this change in migration indicated an ∼2.8 kDa increase in molecular mass. These findings indicate that species differences in muscle testosterone production may exist between rats and humans. In humans, muscle testosterone concentrations do not appear to be affected by RE. This study expands on the current knowledge obtained from animal studies by examining resting and postexercise concentrations of muscle testosterone and steroidogenic enzymes in humans.

Alteration of gene expression in rat colon mucosa after exercise

The development of colon cancer is highly influenced by lifestyle factors such as nutrition and physical inactivity. Detailed biological mechanisms are thus far unclear. The purpose of this study was to investigate the effects of regular treadmill exercise on gene expression in rat colon mucosa. For this purpose, 6-week-old male Wistar rats completed a stress-free voluntary treadmill exercise period of 12 weeks. Sedentary rats served as a control group. In the colon mucosa, steady-state mRNA expression levels of approximately 10,000 genes were compared between both groups by micro-array analysis (MWG rat 10K array). A total of 8846 mRNAs were detected above background level. Regular exercise led to a decreased expression of 47 genes at a threshold-factor of 2.0. Three genes were found to be up-regulated in the exercise group. The identified genes encode proteins involved in signal transduction (n=11), transport (n=8), immune system (n=7), cytoskeleton (n=6), protein targeting (n=6), metabolism (n=5), transcription (n=3) and vascularization (n=2). Among the genes regulated by regular exercise, the betaine-homocysteine methyltransferase 2 (BHMT2) seems to be of particular interest. Physical activity may protect against aberrant methylation by repressing the BHMT2 gene and thus contribute to a decreased risk of developing colon cancer. We have also identified vascular endothelial growth factor (VEGF), angiopoietin-2 (ANG-2) and calcium-independent phospholipase a2 (iPL-A2), all of them with markedly reduced transcript levels in the mucosa of active rats. In summary, our experiment presents the first gene expression pattern in rat colon mucosa following regular treadmill activity and represents an important step in understanding the molecular mechanisms responsible for the preventive effect of physical activity on the development of colon cancer.

Resistance training, and IGF involvement in the maintenance of muscle mass during the aging process

Sarcopenia is the decline of muscle mass and strength with age. Sarcopenia leads to significant impairment in the ability to carry out normal daily function and thus there is a great need for interventions that will lead to muscle regeneration and repair in the aging population. Age-related sarcopenia in humans, characterized by loss of type I and type II muscle fibers and a decrease in fiber cross-sectional area primarily in type II fibers, can be attenuated by mechanical load on the muscle, which increases cross-sectional area of the remaining fibers, but does not restore fiber numbers characteristic of young muscle. Considerable evidence also implicates age-related declines in muscle insulin-like growth factor action in sarcopenia. IGF-I promotes myoblast proliferation, differentiation, and protein accretion in muscle through multiple signaling mechanisms, including the PI3-kinase, MAP kinase and calcineurin pathways. Exercise and injury induce increases in IGF-I, IGF-I receptors and IGF-I-activated signaling pathways. Although there is evidence that aging muscle retains the ability to synthesize IGF-I, there is also evidence that aging may be associated with attenuation of the ability of exercise to induce an isoform of IGF-I that promotes satellite cell proliferation. Moreover, aging muscle may be resistant to IGF-I, an effect that is reversed by exercise. However, it is clear that over-expression of IGF-I in muscle can protect against age-related sarcopenia.

Adiponectin is regulated differently by chronic exercise than by weight-matched food restriction in hyperphagic and obese OLETF rats

This study was intended to investigate the effects of chronic exercise on blood adiponectin level. Male Otsuka Long Evans Tokushima Fatty (OLETF) rats (26 weeks old) were divided to undergo either regular 12-week wheel running exercise (EX) or to have food restriction (FR) that resulted in body weight reduction similar to that in EX. Both EX and FR induced similar reductions in body weight, abdominal fat volume and plasma leptin concentration compared with ad libitum control. At the end of the study, although plasma adiponectin level was increased in FR, the adiponectin level did not change in EX. Plasma testosterone level was higher in EX than in either of the other two groups. A significant inverse relationship existed between plasma levels of adiponectin and testosterone for all groups. Our results suggested that 12-week voluntary wheel running exercise induces different effects on plasma adiponectin level than does food restriction, despite similar reduction in body weight, fat tissue mass and plasma leptin concentration. We speculate that the elevated plasma testosterone concentration might offset any hyperadiponectinemic effect of body weight and fat volume reduction in exercising rats.

Short-term endurance training results in a muscle-specific decrease of myostatin mRNA content in the rat

AIM

Myostatin has been characterized as a negative regulator of skeletal muscle growth. To examine a probable function of myostatin during the adaptation of skeletal muscle in response to training, we analysed the effect of short-term endurance training on myostatin and insulin-like growth factor-I (IGF-I) mRNA contents in rat skeletal muscles. To assess the impact of the training stimulus, mRNA levels of metabolic genes were analysed simultaneously.

METHODS

Male Wistar rats were trained for 5 days by swimming, while another group remained untrained. Myostatin, IGF-I, glucose transporter 4 (GLUT4), hexokinase II (HK II) and hydroxyacyl-CoA dehydrogenase (HAD) mRNA levels were determined by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) in gastrocnemius, vastus lateralis and soleus muscles. A time course experiment was conducted, in order to examine transient changes of myostatin mRNA contents in gastrocnemius 7 and 24 h after one-swimming session as well as 24 h after a 3-day swimming training.

RESULTS

No significant changes in IGF-I and GLUT4 mRNA levels were found in any of the muscles analysed. mRNA contents of myostatin were significantly reduced in gastrocnemius and vastus lateralis but not in soleus. In agreement to this pattern, we found significantly higher mRNA levels of HK II and HAD in the trained group. The time course experiment revealed significantly reduced myostatin mRNA contents in gastrocnemius 7 but not 24 h post-exercise. The 3-day swimming training resulted also in significantly lower myostatin mRNA levels in the trained group.

CONCLUSION

This study demonstrated that short-term endurance training may modulate myostatin mRNA levels, implying a probable role of myostatin in remodelling of skeletal muscle in response to training.