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OBJECTIVE: This study was designed to determine the effect of endurance training on the mitochondrial biogenesis pathway in skeletal muscle of aged rats.
DESIGN: 24 young (5 months) and aged (22 months) male Wistar rats were exercised for 3 weeks following endurance training. The intensity of the training was set at 75% VO2max. Expression analyses were realized in soleus (fiber type I) and gastrocnemius (intermediate fiber type) muscles.
RESULTS: Expression of key transcription factors involved in mitochondrial biogenesis (PGC-1α, NRF-1) and of cytochrome c (a marker of mitochondrial content) increased significantly in response to training in young rat soleus muscle but remained unchanged in aged rats.
Aging is associated with a decrease of protein content of cytochrome c oxidase subunit II (COX II) and an increase of mitochondrial transcription factor A (TFAM) in soleus muscle suggesting a mitochondrial dysfunction. Endurance training didn’t modify COX II and TFAM in both young and aged rats. Neither age nor training altered all theses protein expressions in gastrocnemius muscle.
CONCLUSION: Our study confirmed that fiber type I muscle appears more affected by age-related mitochondrial alterations than intermediate fiber type muscle (Pesce et al. 2005). Short-term endurance training failed to stimulate mitochondrial biogenesis and to reduce mitochondrial dysfunction in skeletal muscle of aged rats. This incapacity to stimulate mitochondrial biogenesis could result from agerelated decrease of AMP kinase activity in skeletal muscle (Reznick et al. 2007).
Pesce, V., A. Cormio, F. Fracasso, A. M. Lezza, P. Cantatore and M. N. Gadaleta. (2005). J Gerontol A Biol Sci Med Sci 60(6): 715-23.
Reznick, R. M., H. Zong, J. Li, K. Morino, I. K. Moore, H. J. Yu, Z. X. Liu, J. Dong, K. J. Mustard, S. A. Hawley, D. Befroy, M. Pypaert, D. G.
Hardie, L. H. Young and G. I. Shulman. (2007). Cell Metab 5(2): 151-6.
CARDIAC STEM CELL ACTIVATION AND ENSUING MYOGENESIS AND ANGIOGENESIS CONTRIBUTE IN CARDIAC ADAPTATION TO INTENSITY-CONTROLLED EXERCISE TRAINING.WARING, C., TORELLA, D., ELLISON, G.
LIVERPOOL JOHN MOORES UNIVERSITYTraditionally, it was thought that exercise improved cardiac function by increasing myocardial mass and contractility through physiological hypertrophy of existing myocytes and enhanced coronary perfusion. Recent data on myocardial cell homeostasis and the identification of cardiac stem cells (CSCs), in the adult mammalian heart, could challenge this concept. We sought to assess if CSC activation and ensuing myocyte and capillary formation participates in cardiac remodeling induced by intensity-controlled exercise training. To this aim, 42 male Wistar rats (226.5±1.5g) were exercised at either a Low (LI; 55-60% VO2 max) or High (HI; 85-90% VO2 max) intensity for 30 mins/day, 4 days/week for up to 4 weeks on motorized treadmills. Fifteen untrained rats acted as age-matched sedentary controls (CTRL). To track myocardial proliferation, BrdU was administered (i.p.) twice daily. Hearts were arrested in diastole and the Left Ventricles (LV) were processed for immunohistochemistry and confocal microscopy analysis. Results showed an increase (P0.05) in average myocyte diameter in the LV following both LI and HI exercise training, compared to CTRL. The distribution of myocytes sizes showed the presence of both larger (hypertrophied) and smaller myocytes (myogenesis) in the ventricular wall of the exercise trained vs. CTRL hearts.
Indeed, there was a significant (P0.05) increase in the % of small myocytes that were BrdU (3.4±0.2 LI, 7.4±0.3 HI) and Ki67 positive (0.8±0.1 LI, 1.0±0.1 HI), following LI and HI exercise training, compared to CTRL (BrdU, 0.01±0.01; Ki67 0.05±0.02). These data document the presence of small newly formed myocytes in the LV of intensity-controlled exercising rats. The number of capillaries in the LV in the LI (2709.8±103.5) and HI (4109.5±347.7) exercise trained animals was significantly (P0.05) greater than CTRL (1531.6±99.5). Many of these capillaries were BrdU positive exhibiting their recent formation. To address the source of new myocytes and capillaries, we evaluated ckit positive (c-kitpos) CSC myocardial activation. The number of c-kitpos CSCs significantly (P0.05) increased in the ventricular wall of the Exercising vs. CTRL rats. Many CSCs were proliferating (BrdU and/or Ki-67 positive) and many expressed the cardiac transcription factor, Nkx2.5, representing myocyte progenitor cells. Also, some CSCs expressed the transcription factor Ets-1, indicative of their differentiation into the endothelial lineage. These data provide a link between a primitive c-kitpos CSC and amplifying myocyte and endothelial progenitors. In conclusion, intensity-controlled treadmill exercise training in adult rats results in myocardial mass remodeling through myocyte hypertrophy, and new myocyte and capillary formation. The latter is due to the activation and ensuing differentiation of CSCs into newlyformed myocytes and capillaries. Finally, these effects were dependent on exercise training intensity.
THE EFFECT OF HIGH INTENSITY RUNNING ON INFLAMMATION, IRON STATUS AND HEPCIDIN ACTIVITY IN MODERATELY TRAINED ENDURANCE ATHLETES.PEELING, P., DAWSON, B., SWINKELS, D., TRINDER, D.
THE UNIVERSITY OF WESTERN AUSTRALIAHepcidin is a liver produced hormone that acts to internalise and degrade the iron transport channels in the intestine and on the cell surface of macrophages, ultimately reducing the absorption and transport of iron in the body. Hepcidin expression is controlled by the level of circulating IL-6 and the current iron status of the body. To date, it is unknown as to the effect of high intensity exercise on the activity of this hormone within 24 h of recovery. As such, this investigation examined effect of high intensity running on inflammatory markers, iron status, and urinary hepcidin activity in male and female athletes at 3 and 24 h post-exercise.
Eleven moderately trained runners (6 male and 5 female) participated in three laboratory testing sessions including: (1) A graded-exercise test to determine maximal oxygen consumption (VO2max) and peak heart rate (HRpeak). (2) A 60-min trial of running (RUN) involving 15 min at 75-80% HRpeak and 45 min at 85-90% HRpeak. (3) A 60-min trial of seated rest (REST). The RUN and REST trials were applied in a randomised, counterbalanced order, and were separated by a minimum of 28 days, ensuring all female participants were in the follicular phase of the menstrual cycle.
Throughout the RUN and REST trials, venous blood and urine samples were collected pre-trial, immediately post-trial, and at 3 and 24 h post-trial. Blood samples were analysed for circulating levels of Interleukin-6 (IL-6), C-Reactive Protein (CRP), serum iron and serum ferritin.
Urine samples were analysed for urinary hepcidin concentration. A repeated measures ANOVA for time, trial and time*trial effects was conducted between the RUN and REST trials, with post-hoc, paired samples t-tests applied in the event of a significant main effect. The alpha level was accepted at p0.05.
Blood analysis revealed that three participants were classified as iron deficient, and were therefore removed from the analysis. For the remaining eight healthy iron status subjects, the immediate post-RUN levels of IL-6 and 24 h post-RUN levels of CRP were significantly increased from baseline, and when compared to REST (p0.05). Hepcidin levels in the RUN trial after 3 and 24 h of recovery were significantly greater than the pre- and immediate post-RUN levels, and also when compared to the 3 h time point of REST (p0.05). Serum iron was significantly increased post-RUN from baseline (p0.05), but had returned to normal by 3 h of recovery. There were no significant changes in serum ferritin levels.
This study has shown that urinary hepcidin levels are significantly elevated post-exercise in moderately trained athletes with a healthy iron status. Here, elevated hepcidin activity occurred approximately 3 h subsequent to an increase in IL-6 and serum iron. As such, it is possible that the post-exercise activity of this hormone is driven by inflammation and hemolysis.
A ROLE FOR SATELLITE CELLS IN THE ETIOLOGY AND TREATMENT OF SARCOPENIA?VERDIJK, L.B., VAN LOON, L.J.C.
MAASTRICHT UNIVERSITYSatellite cells (SC) are the only source for the generation of new myonuclei in skeletal muscle tissue. As such, SC play a key role in muscle fiber atrophy and/or hypertrophy. We suggest that SC represent an important factor in the etiology and treatment of the age-related decline in muscle mass and strength, or sarcopenia.
Sarcopenia is characterized by the loss of type I and II muscle fibers, and specific type II muscle fiber atrophy. In accordance, recent data from our lab show that type II muscle fiber atrophy is accompanied by a specific reduction in type II muscle fiber SC content in elderly versus young males. However, it remains to be elucidated whether muscle fiber characteristics are predictive of the actual amount of skeletal muscle mass and strength in the elderly. Therefore, we correlated various skeletal muscle fiber characteristics (from muscle biopsies) with muscle mass (CT) and strength (1RM) within a population of 41 healthy, elderly males (65y). Greater muscle fiber crosssectional area (CSA) was associated with more myonuclei and more SC per muscle fiber (0.50≤r≤0.56 for type I and II
14 ANNUAL CONGRESS OF THE EUROPEAN COLLEGE OF SPORT SCIENCETH Thursday, June 25th, 2009 fibers). The number of myonuclei per fiber correlated with the number of SC per muscle fiber (r=0.40 for type I and II fibers). Furthermore, type I and II muscle fiber CSA correlated with leg muscle strength, and with quadriceps CSA. These data imply that muscle fiber size is predictive of muscle mass and strength. Furthermore, SC content is closely related to myonuclear content and is predictive of muscle fiber size. The latter provides further support to the idea that SC content is a key regulator of muscle fiber size and, as such, muscle mass and strength. Thus, to enable a substantial increase in muscle mass and strength, it seems imperative to effectively increase SC content. The latter was achieved following 3 months of resistance type exercise training in 13 healthy, elderly males. Substantial improvements in muscle mass, strength, and type II muscle fiber size were accompanied by a type II muscle fiber specific increase in SC content.
Collectively, our findings suggest that the muscle fiber type-specific decline in SC content represents a key factor in the gradual loss of muscle mass and strength with aging. The latter can, at least partly, be reversed by resistance type exercise training. Future studies should focus on optimizing SC activation, proliferation, and differentiation. The latter will be instrumental to define more effective exercise, nutritional, and/or pharmacological interventions to counteract the loss of muscle mass and function with aging.
INFLUENCE OF ACE I/D AND ACTN3 R/X POLYMORPHISMS ON MUSCLE FUNCTION AND BODY COMPOSITION OF
OLDER CAUCASIAN MENMCCAULEY, T., FOLLAND, J.P., MASTANA, S.S.
LOUGHBOROUGH UNIVERSITYAdvancing age is associated with a progressive decline in muscle strength and function largely due to sarcopenia. Healthy older individuals have age related deficits in muscle power that are even greater than muscle strength (1) leading to compromised mobility and an increased risk of falls. ACE I/D and ACTN3 R/X polymorphisms have been suggested to influence variations in skeletal muscle function (2,3) and body composition (4). ACTN3 has been proposed as a metabolically thrifty gene thought to improve energetic efficiency (5), promote energy storage and fat accumulation. This study investigated the influence of ACE and ACTN3 genotypes on body composition and muscle function phenotypes in older Caucasian men.
Following ethical approval a range of muscle function measurements were taken from 100 healthy non strength trained UK males (60yrs) on two occasions. A conventional strength testing chair was used to measure maximal isometric knee extensor and elbow flexor strength. Maximum twitches were electrically evoked (Digitimer DS7AH, UK) in the quadriceps to assess time to peak tension (TPT) and half relaxation time (HRT). Isokinetic knee extensor peak torque was measured at three velocities (0, 30 and 240º.s-¹) using isokinetic dynamometry (Cybex Norm, USA). Relative strength at high velocity (240º.s-¹:30º.s-¹) was calculated. A Dual-energy X-ray Absorptiometry (DXA) scan (Lunar Prodigy Advance DXA machine, GE Lunar, Madison, WI) was used to assess non-skeletal lean mass and fat mass. ACE I/D and ACTN3 R/X genotype were determined from whole blood samples using polymerase chain reaction, and serum ACE using spectrophotometry.
ACE and ACTN3 genotype distributions were in Hardy Weinberg Equilibrium (II 25, ID 48, DD 27; RR 43, RX 41, XX 16). Physical characteristics were independent of ACE genotype (height, body mass, lean body mass, body mass index). ACTN3 XX genotype individuals had a higher fat mass (P = 0.04), and a trend for greater body mass (P=0.09) than RR individuals. The muscle function phenotypes assessed were found to be independent of ACE and ACTN3 genotypes. Serum ACE activity was negatively correlated with the relative torque at high velocity (R =-0.23; P =0.03). There were trends for serum ACE to correlate with quadriceps (R=0.19; P=0.07) and elbow flexor (R=0.20;
P=0.06) isometric strength.