Endurance training modulates the muscular transcriptome response to acute exercise

We hypothesized that in untrained individuals (n=6) a single bout of ergometer endurance exercise provokes a concerted response of muscle transcripts towards a slow-oxidative muscle phenotype over a 24-h period. We further hypothesized this response during recovery to be attenuated after six weeks of endurance training. We monitored the expression profile of 220 selected transcripts in muscle biopsies before as well as 1, 8, and 24 h after a 30-min near-maximal bout of exercise. The generalized gene response of untrained vastus lateralis muscle peaked after 8h of recovery (P=0.001). It involved multiple transcripts of oxidative metabolism and glycolysis. Angiogenic and cell regulatory transcripts were transiently reduced after 1h independent of the training state. In the trained state, the induction of most transcripts 8h after exercise was less pronounced despite a moderately higher relative exercise intensity, partially because of increased steady-state mRNA concentration, and the level of metabolic and extracellular RNAs was reduced during recovery from exercise. Our data suggest that the general response of the transcriptome for regulatory and metabolic processes is different in the trained state. Thus, the response is specifically modified with repeated bouts of endurance exercise during which muscle adjustments are establishe

Muscle transcriptome adaptations with mild eccentric ergometer exercise

The muscle has a wide range of possibilities to adapt its phenotype. Repetitive submaximal concentric exercise (i.e., shortening contractions) mainly leads to adaptations of muscle oxidative metabolism and endurance while eccentric exercise (i.e., lengthening contractions) results in muscle growth and gain of muscle strength. Modified gene expression is believed to mediate these exercise-specific muscle adjustments. In the present study, early alterations of the gene expression signature were monitored by a muscle-specific microarray. Transcript profiling was performed on muscle biopsies of vastus lateralis obtained from six male subjects before and in a 24-h time course after a single bout of mild eccentric ergometer exercise. The eccentric exercise consisted of 15min of eccentric cycling at 50% of the individual maximal concentric power output leading to muscle soreness (5.9 on a 0-10 visual analogue scale) and limited muscle damage (1.7-fold elevated creatine kinase activity). Muscle impairment was highlighted by a transient reduction in jumping height after the eccentric exercise. On the gene expression level, we observed a general early downregulation of detected transcripts, followed by a slow recovery close to the control values within the first 24h post exercise. Only very few regulatory factors were increased. This expression signature is different from the signature of a previously published metabolic response after an intensive endurance-type concentric exercise as well as after maximal eccentric exercise. This is the first description of the time course of changes in gene expression as a consequence of a mild eccentric stimulu

Biologically relevant sex differences for fitness-related parameters in active octogenarians

The number of elderly people is growing in western populations, but only few maximal performance data exist for people >75years, in particular for European octogenarians. This study was performed to characterize maximal performance of 55 independently living subjects (32 women, 81.1±3.4years; 23 men, 81.7±2.9years) with a focus on sex differences. Maximal performance was determined in a ramp test to exhaustion on a bicycle ergometer with ergospirometry, electrocardiogram and blood lactate measurements. Maximal isometric extension strength of the legs (MEL) was measured on a force platform in a seated position. Body composition was quantified by X-ray absorptiometry. In >25% of the subjects, serious cardiac abnormalities were detected during the ramp test with men more frequently being affected than women. Maximal oxygen consumption and power output were 18.2±3.2 versus 25.9±5.9mlmin−1kg−1 and 66±12 versus 138±40W for women versus men, with a significant sex difference for both parameters. Men outperformed women for MEL with 19.0±3.8 versus 13.6±3.3Nkg−1. Concomitantly, we found a higher proportion of whole body fat in women (32.1±6.2%) compared to men (20.5±4.4%). Our study extends previously available maximal performance data for endurance and strength to independently living European octogenarians. As all sex-related differences were still apparent after normalization to lean body mass, it is concluded that it is essential to differentiate between female and male subjects when considering maximal performance parameters in the oldest segment of our populatio

Different response to eccentric and concentric training in older men and women

Sarcopenia is the age-related loss of muscle mass and strength and has been associated with an increased risk of falling and the development of metabolic diseases. Various training protocols, nutritional and hormonal interventions have been proposed to prevent sarcopenia. This study explores the potential of continuous eccentric exercise to retard age-related loss of muscle mass and function. Elderly men and women (80.6±3.5years) were randomized to one of three training interventions demanding a training effort of two sessions weekly for 12weeks: cognitive training (CT; n=16), conventional resistance training (RET; n=23) and eccentric ergometer training (EET; n=23). Subjects were tested for functional parameters and body composition. Biopsies were collected from M. vastus lateralis before and after the intervention for the assessment of fiber size and composition. Maximal isometric leg extension strength (MEL: +8.4±1.7%) and eccentric muscle coordination (COORD: −43±4%) were significantly improved with EET but not with RET (MEL: +2.3±2.0%; COORD: −13±3%) and CT (MEL: −2.3±2.5%; COORD: −12±5%), respectively. We observed a loss of body fat (−5.0±1.1%) and thigh fat (−6.9±1.5%) in EET subjects only. Relative thigh lean mass increased with EET (+2.5±0.6%) and RET (+2.0±0.3%) and correlated negatively with type IIX/type II muscle fiber ratios. It was concluded that both RET and EET are beneficial for the elderly with regard to muscle functional and structural improvements but differ in their spectrum of effects. A training frequency of only two sessions per week seems to be the lower limit for a training stimulus to reveal measurable benefit

Hypoxia-induced gene activity in disused oxidative muscle

Hypoxia is an important modulator of the skeletal muscle’s oxidative phenotype. However, little is known regarding the molecular circuitry underlying the muscular hypoxia response and the interaction of hypoxia with other stimuli of muscle oxidative capacity. We hypothesized that exposure of mice to severe hypoxia would promote the expression of genes involved in capillary morphogenesis and glucose over fatty acid metabolism in active or disused soleus muscle of mice. Specifically, we tested whether the hypoxic response depends on oxygen sensing via the alpha-subunit of hypoxia-inducible factor-1 (HIF-1α). Spontaneously active wildtype and HIF-1α heterozygous deficient adult female C57B1/6 mice were subjected to hypoxia (PiO2 70 mmHg). In addition, animals were subjected to hypoxia after 7 days of muscle disuse provoked by hindlimb suspension. Soleus muscles were rapidly isolated and analyzed for transcript level alterations with custom-designed AtlasTM cDNA expression arrays (BD Biosciences) and cluster analysis of differentially expressed mRNAs. Multiple mRNA elevations of factors involved in dissolution and stabilization of blood vessels, glycolysis, and mitochondrial respiration were evident after 24 hours of hypoxia in soleus muscle. In parallel transcripts of fat metabolism were reduced. A comparable hypoxia-induced expression pattern involving complex alterations of the IGF-I axis was observed in reloaded muscle after disuse. This hypoxia response in spontaneously active animals was blunted in the HIF-1α heterozygous deficient mice demonstrating 35% lower HIF-1α mRNA levels. Our molecular observations support the concept that severe hypoxia provides HIF-1-dependent signals for remodeling of existing blood vessels, a shift towards glycolytic metabolism and altered myogenic regulation in oxidative mouse muscle and which is amplified by enhanced muscle use. These findings further imply differential mitochondrial turnover and a negative role of HIF-1α for control of fatty acid oxidation in skeletal muscle exposed to one day of severe hypoxia

Transcriptional reprogramming and ultrastructure during atrophy and recovery of mouse soleus muscle.

This study investigated the use of the hindlimb suspension (HS) and reloading model of mice for the mapping of ultrastructural and gene expressional alterations underlying load-dependent muscular adaptations. Mice were hindlimb suspended for 7 days or kept as controls (n = 12). Soleus muscles were harvested after HS (HS7, n = 23) or after resuming ambulatory cage activity (reloading) for either 1 day (R1, n = 13) or 7 days (R7, n = 9). Using electron microscopy, a reduction in mean fiber area (-37%) and in capillary-to-fiber ratio (from 1.83 to 1.42) was found for HS7. Subsequent reloading caused an increase in interstitial cells (+96%) and in total capillary length (+57%), whereas mean fiber area and capillary-to-fiber ratio did not significantly change compared with HS. Total RNA in the soleus muscle was altered with both HS (-63%) and reloading (+108% in R7 compared with control). This is seen as an important adaptive mechanism. Gene expression alterations were assessed by a muscle-specific low-density cDNA microarray. The transcriptional adjustments indicate an early increase of myogenic factors during reloading together with an overshoot of contractile (MyHC I and IIa) and metabolic (glycolytic and oxidative) mRNA amounts and suggest mechano-sensitivity of factors keeping the sarcomeres in register (desmin, titin, integrin-beta1). Important differences to published data from former rat studies were found with the mouse HS model for contractile and glycolytic enzyme expression. These species-specific differences need to be considered when transgenic mice are used for the elucidation of monogenetic factors in mechano-dependent muscle plasticity

Muscle transcriptome adaptations with mild eccentric ergometer exercise

The muscle has a wide range of possibilities to adapt its phenotype. Repetitive submaximal concentric exercise (i.e., shortening contractions) mainly leads to adaptations of muscle oxidative metabolism and endurance while eccentric exercise (i.e., lengthening contractions) results in muscle growth and gain of muscle strength. Modified gene expression is believed to mediate these exercise-specific muscle adjustments. In the present study, early alterations of the gene expression signature were monitored by a muscle-specific microarray. Transcript profiling was performed on muscle biopsies of vastus lateralis obtained from six male subjects before and in a 24-h time course after a single bout of mild eccentric ergometer exercise. The eccentric exercise consisted of 15 min of eccentric cycling at 50% of the individual maximal concentric power output leading to muscle soreness (5.9 on a 0-10 visual analogue scale) and limited muscle damage (1.7-fold elevated creatine kinase activity). Muscle impairment was highlighted by a transient reduction in jumping height after the eccentric exercise. On the gene expression level, we observed a general early downregulation of detected transcripts, followed by a slow recovery close to the control values within the first 24 h post exercise. Only very few regulatory factors were increased. This expression signature is different from the signature of a previously published metabolic response after an intensive endurance-type concentric exercise as well as after maximal eccentric exercise. This is the first description of the time course of changes in gene expression as a consequence of a mild eccentric stimulus

Transient induction of cyclin A in loaded chicken skeletal muscle.

Cell proliferation is believed to contribute to the increased synthesis rate during load-induced growth of avian anterior latissimus dorsi (ALD) skeletal muscle, but the relative contribution of different cell types to this proliferative response and the time course of cell activation are not well documented. The present investigation measured the abundance and localization of cyclin A protein, which is uniquely present in proliferating cells and required for the entry of vertebrate cells into the DNA synthesis phase during the time course of chicken ALD loading. Total protein content in 1.5-, 7-, and 13-day loaded ALD increased by 60, 191, and 294%, respectively. Immunoblotting analysis identified that cyclin A protein per total protein was dramatically increased in ALD muscle after 1.5 days of loading but returned to control level at 7 days. In vitro kinase assays demonstrated a corresponding massive activation of the cyclin A-regulated, cyclin-dependent kinase 2 but not of cyclin-dependent kinase 2 protein level in muscle homogenates after 1.5 days of muscle loading. Immunofluorescence experiments demonstrated that the increase of cyclin A in 1.5 days of loaded ALD was primarily confined to nuclei of interstitial cells (92%) but was also found in fiber-associated cells (8%). In situ hybridization demonstrated an increased number of nuclei of interstitial cells expressing collagen I transcripts after 1.5 days of loading. These data show that the cell cycle protein cyclin A is induced in fiber-associated cells during the early growth response in loaded ALD but also implicate an activation of interstitial cells as playing an early role in this model for muscle growth

Different molecular and structural adaptations with eccentric and conventional strength training in elderly men and women

Reprogramming of gene expression contributes to structural and functional adaptation of muscle tissue in response to altered use. The aim of this study was to investigate mechanisms for observed improvements in leg extension strength, gain in relative thigh muscle mass and loss of body and thigh fat content in response to eccentric and conventional strength training in elderly men (n = 14) and women (n = 14; average age of the men and women: 80.1 ± 3.7 years) by means of structural and molecular analyses. Biopsies were collected from m. vastus lateralis in the resting state before and after 12 weeks of training with two weekly resistance exercise sessions (RET) or eccentric ergometer sessions (EET). Gene expression was analyzed using custom-designed low-density PCR arrays. Muscle ultrastructure was evaluated using EM morphometry. Gain in thigh muscle mass was paralleled by an increase in muscle fiber cross-sectional area (hypertrophy) with RET but not with EET, where muscle growth is likely occurring by the addition of sarcomeres in series or by hyperplasia. The expression of transcripts encoding factors involved in muscle growth, repair and remodeling (e.g., IGF-1, HGF, MYOG, MYH3) was increased to a larger extent after EET than RET. MicroRNA 1 expression was decreased independent of the training modality, and was paralleled by an increased expression of IGF-1 representing a potential target. IGF-1 is a potent promoter of muscle growth, and its regulation by microRNA 1 may have contributed to the gain of muscle mass observed in our subjects. EET depressed genes encoding mitochondrial and metabolic transcripts. The changes of several metabolic and mitochondrial transcripts correlated significantly with changes in mitochondrial volume density. Intramyocellular lipid content was decreased after EET concomitantly with total body fat. Changes in intramyocellular lipid content correlated with changes in body fat content with both RET and EET. In the elderly, RET and EET lead to distinct molecular and structural adaptations which might contribute to the observed small quantitative differences in functional tests and body composition parameters. EET seems to be particularly convenient for the elderly with regard to improvements in body composition and strength but at the expense of reducing muscular oxidative capacity

Different response to eccentric and concentric training in older men and women

Sarcopenia is the age-related loss of muscle mass and strength and has been associated with an increased risk of falling and the development of metabolic diseases. Various training protocols, nutritional and hormonal interventions have been proposed to prevent sarcopenia. This study explores the potential of continuous eccentric exercise to retard age-related loss of muscle mass and function. Elderly men and women (80.6 +/- 3.5 years) were randomized to one of three training interventions demanding a training effort of two sessions weekly for 12 weeks: cognitive training (CT; n = 16), conventional resistance training (RET; n = 23) and eccentric ergometer training (EET; n = 23). Subjects were tested for functional parameters and body composition. Biopsies were collected from M. vastus lateralis before and after the intervention for the assessment of fiber size and composition. Maximal isometric leg extension strength (MEL: +8.4 +/- 1.7%) and eccentric muscle coordination (COORD: -43 +/- 4%) were significantly improved with EET but not with RET (MEL: +2.3 +/- 2.0%; COORD: -13 +/- 3%) and CT (MEL: -2.3 +/- 2.5%; COORD: -12 +/- 5%), respectively. We observed a loss of body fat (-5.0 +/- 1.1%) and thigh fat (-6.9 +/- 1.5%) in EET subjects only. Relative thigh lean mass increased with EET (+2.5 +/- 0.6%) and RET (+2.0 +/- 0.3%) and correlated negatively with type IIX/type II muscle fiber ratios. It was concluded that both RET and EET are beneficial for the elderly with regard to muscle functional and structural improvements but differ in their spectrum of effects. A training frequency of only two sessions per week seems to be the lower limit for a training stimulus to reveal measurable benefits