Growth Factors In Skeletal Muscle Research Articles

Influence of Pulsing Electromagnetic Field Therapy on Gene Expression in Muscle Cells, Peripheral Circulation, and Metabolic Factors in Aging Adults

This study tested the acute effects of pulsating electromagnetic field (PEMF) therapy session on gene expression in muscle cells, and the changes in cardiovascular and metabolic function in a group of older adults after 12 weeks of treatment. Each therapy session involved 15 minutes of exposure to low frequency pulsating asymmetrical waveforms emitted by the Impulser™ Pro mattress. The treatment was provided five days per week for a total of 60 sessions. Pre and post session muscle biopsies provided tissue for analyses of selected genes. Blood pressure and arterial stiffness was determined for cardiovascular function while cholesterol and glucose levels were evaluated using serum samples. Skin temperature was measured using temperature probes. Fifty-five older men and women (mean age 59.75) completed the entire treatment while six subjects in this group consented to muscle biopsies. The results indicate no change in mRNA content of Ku70 during the single PEMF session however mRNA levels of IL-6 and c-Fos increased. The chronic effects of PEMF treatment include significant reductions in blood pressure, and increases in skin temperature. These findings suggest that due to no change in Ku70 levels, a gene associated with DNA damage, an acute bout of PEMF did not cause acute molecular damage. The increase in IL-6, a gene associated with expression of a glucose transporter, might have an influence on glucose metabolism. The increase in c- Fos, a gene linked to growth factors in skeletal muscle, might influence lose in muscle size associated with aging. The increase in skin temperature is difficult to interpret since it might be linked to either heightened metabolism or improvements in peripheral circulation. More studies are needed to determine if these changes impact the health of aging adults. Keywords: Pulsating electromagnetic field (PEMF) therapy, metabolic function, skin temperature.

Vascular Endothelial Growth Factor in Skeletal Muscle following Glycogen-Depleting Exercise in Humans

Vascular Endothelial Growth Factor in Skeletal Muscle following Glycogen-Depleting Exercise in Humans

Abnormal Regulation of Placental Growth Factor in Skeletal Muscle of Western‐Diet Fed Mice

Diabetics often develop peripheral artery disease (PAD). Arteriogenesis can preserve blood flow distal to occlusion and limit skeletal muscle ischemia in PAD, but is reduced in diabetics by an undefined mechanism. Placental growth factor (PLGF, a VEGF family protein) is a key arteriogenic factor. Therefore, we hypothesized that skeletal muscle PLGF expression and/or regulation could be abnormal in diabetic PAD. We tested this hypothesis in 3 mouse models with varying degrees of metabolic dysfunction: Western diet (WD) fed C57BL/6J (C57‐WD; n=52), control diet (CD) fed ApoE‐/‐ (ApoE‐CD; n=38) and WD fed ApoE‐/‐ (ApoE‐WD; n=32). CD fed C57BL/6J (C57‐CD; n=48) served as controls. Males and females were studied. Metabolic status was characterized by measuring relevant plasma values. After 6 mo on the diets, skeletal muscle PLGF was assessed under baseline conditions (n=58) and 3‐28 d post‐femoral artery occlusion (n=112). VEGF‐A was measured for comparison. Baseline skeletal muscle PLGF protein was decreased in all WD fed groups (p<0.005), with no effect of gender or strain. Regression analysis of PLGF vs metabolic parameters revealed modest correlation with plasma insulin (r2=0.44, p<0.0001). PLGF was sharply elevated in skeletal muscle of C57‐CD mice after femoral occlusion, peaking ~10 d post‐occlusion. This response was decreased and delayed in C57‐WD mice (p<0.05). Even more strikingly, upregulation of PLGF by occlusion was completely abolished in ApoE‐CD and ApoE‐WD mice. We conclude that in skeletal muscle, Western diet‐induced metabolic dysfunction both reduces baseline levels of PLGF and inhibits its upregulation by the physiological stimulus of occlusion. This phenomenon may contribute to the poor arteriogenic response in diabetes. Support: R01 HL084494 (PL).

Alcohol impairs skeletal muscle protein synthesis and mTOR signaling in a time-dependent manner following electrically stimulated muscle contraction.

Alcohol (EtOH) decreases protein synthesis and mammalian target of rapamycin (mTOR)-mediated signaling and blunts the anabolic response to growth factors in skeletal muscle. The purpose of the current investigation was to determine whether acute EtOH intoxication antagonizes the contraction-induced increase in protein synthesis and mTOR signaling in skeletal muscle. Fasted male mice were injected intraperitoneally with 3 g/kg EtOH or saline (control), and the right hindlimb was electrically stimulated (10 sets of 6 contractions). The gastrocnemius muscle complex was collected 30 min, 4 h, or 12 h after stimulation. EtOH decreased in vivo basal protein synthesis (PS) in the nonstimulated muscle compared with time-matched Controls at 30 min, 4 h, and 12 h. In Control, but not EtOH, PS was decreased 15% after 30 min. In contrast, PS was increased in Control 4 h poststimulation but remained unchanged in EtOH. Last, stimulation increased PS 10% in Control and EtOH at 12 h, even though the absolute rate remained reduced by EtOH. The stimulation-induced increase in the phosphorylation of S6K1 Thr(421)/Ser(424) (20-52%), S6K1 Thr(389) (45-57%), and its substrate rpS6 Ser(240/244) (37-72%) was blunted by EtOH at 30 min, 4 h, and 12 h. Phosphorylation of 4E-BP1 Ser(65) was also attenuated by EtOH (61%) at 4 h. Conversely, phosphorylation of extracellular signal-regulated kinase Thr(202)/Tyr(204) was increased by stimulation in Control and EtOH mice at 30 min but only in Control at 4 h. Our data indicate that acute EtOH intoxication suppresses muscle protein synthesis for at least 12 h and greatly impairs contraction-induced changes in synthesis and mTOR signaling.

TWEAK promotes exercise intolerance by decreasing skeletal muscle oxidative phosphorylation capacity

BackgroundProinflammatory cytokine tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and its receptor Fn14 are the major regulators of skeletal muscle mass in many catabolic conditions. However, their role in muscle metabolism remains largely unknown. In the present study, we investigated the role of TWEAK on exercise capacity and skeletal muscle mitochondrial content and oxidative metabolism.MethodsWe employed wild-type and TWEAK-knockout (KO) mice and primary myotube cultures and performed biochemical, bioenergetics, and morphometric assays to evaluate the effects of TWEAK on exercise tolerance and muscle mitochondrial function and angiogenesis.ResultsTWEAK-KO mice showed improved exercise tolerance compared to wild-type mice. Electron microscopy analysis showed that the abundance of subsarcolemmal and intermyofibrillar mitochondria is significantly increased in skeletal muscle of TWEAK-KO mice compared to wild-type mice. Furthermore, age-related loss in skeletal muscle oxidative capacity was rescued in TWEAK-KO mice. Expression of a key transcriptional regulator peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and several other molecules involved in oxidative metabolism were significantly higher in skeletal muscle of TWEAK-KO mice. Moreover, treatment of primary myotubes with soluble TWEAK inhibited the expression of PGC-1α and mitochondrial genes and decreased mitochondrial respiratory capacity. Deletion of TWEAK also improved angiogenesis and transcript levels of vascular endothelial growth factor in skeletal muscle of mice.ConclusionsThese results demonstrate that TWEAK decreases mitochondrial content and oxidative phosphorylation and inhibits angiogenesis in skeletal muscle. Neutralization of TWEAK is a potential approach for improving exercise capacity and oxidative metabolism in skeletal muscle.

The expression of vascular endothelial growth factor in skeletal muscle of patients with sleep disorders

An increased capillary network has been observed in skeletal muscle of patients with restless legs syndrome (RLS) and obstructive sleep apnea syndrome (OSAS). This finding could be due to upregulation of growth factors responsible for angiogenesis. The aim of the study was to examine the occurrence and localization of VEGF and capillary proliferation in skeletal muscle of RLS (n = 12) and OSAS (n = 12) patients and controls (n = 11). Double-immunofluorescence staining for capillaries (CD31) and VEGF, and proliferating cells (Ki-67), was carried out on biopsies taken from the tibialis anterior. The percentage of capillaries expressing VEGF (CD31,VEGF(+)) was significantly higher in OSAS and RLS patients compared with controls. The percentage of proliferating capillaries (CD31,Ki-67(+)) was significantly higher in OSAS patients compared with controls. Our study shows the occurrence of proliferation of endothelial cells in skeletal muscle in RLS and OSAS, supporting an upregulation of VEGF located in capillaries, probably due to local hypoxia.

Exercise-induced expression of angiogenic growth factors in skeletal muscle and in capillaries of healthy and diabetic mice

BackgroundDiabetes has negative, and exercise training positive, effects on the skeletal muscle vasculature, but the mechanisms are not yet fully understood. In the present experiment the effects of running exercise on the mRNA expression of pro- and antiangiogenic factors were studied in healthy and diabetic skeletal muscle. The responses in capillaries and muscle fibers, collected from the muscle with laser capture microdissection, were also studied separately.MethodsHealthy and streptozotocin-induced diabetic mice were divided into sedentary and exercise groups. Exercise was a single bout of 1 h running on a treadmill. Gastrocnemius muscles were harvested 3 h and 6 h post exercise, and angiogenesis-related gene expressions were analyzed with real-time PCR. In addition to muscle homogenates, capillaries and muscle fibers were collected from the muscle with laser capture microdissection method and analyzed for vascular endothelial growth factor-A (VEGF-A) and thrombospondin-1 (TSP-1) mRNA expression.ResultsOf the proangiogenic factors, VEGF-A and VEGF receptor-2 (VEGFR-2) mRNA expression increased significantly (P < 0.05) in healthy skeletal muscle 6 h post exercise. VEGF-B also showed a similar trend (P = 0.08). No significant change was observed post exercise in diabetic muscles in the expression of VEGF-A, VEGFR-2 or VEGF-B. The expression of angiogenesis inhibitor TSP-1 and angiogenic extracellular matrix protein Cyr61 were significantly increased in diabetic muscles (P < 0.05–0.01). Capillary mRNA expression resembled that in the muscle homogenates, however, the responses were greater in capillaries compared to muscle homogenates and pure muscle fibers.ConclusionThe present study is the first to report the effects of a single bout of exercise on the expression of pro- and antiangiogenic factors in diabetic skeletal muscle, and it provides novel data about the separate responses in capillaries and muscle fibers to exercise and diabetes. Diabetic mice seem to have lower angiogenic responses to exercise compared to healthy mice, and they show markedly increased expression of angiogenesis inhibitor TSP-1. Furthermore, exercise-induced VEGF-A expression was shown to be greater in capillaries than in muscle fibers.

A Comparison of Aerobic Exercise and Resistance Training in Patients With and Without Chronic Kidney Disease

The morbidity and mortality associated with chronic kidney disease (CKD) are primarily caused by atherosclerosis and cardiovascular disease, which may be in part caused by inflammation and oxidative stress. Aerobic exercise and resistance training have been proposed as measures to combat obesity, inflammation, endothelial dysfunction, oxidative stress, insulin resistance, and progression of CKD. In non-CKD patients, aerobic exercise reduces inflammation, increases insulin sensitivity, decreases microalbuminuria, facilitates weight loss, decreases leptins, and protects against oxidative injury. In nondialysis CKD, aerobic exercise decreases microalbuminuria, protects from oxidative stress, and may increase the glomerular filtration rate (GFR). Aerobic exercise in hemodialysis patients has been reported to enhance insulin sensitivity, improve lipid profile, increase hemoglobin, increase strength, decrease blood pressure, and improve quality of life. Resistance training, in the general population, decreases C-reactive protein, increases insulin sensitivity, decreases body fat content, increases insulin-like growth factor-1 (IGF-1), and decreases microalbuminuria. In the nondialysis CKD population, resistance training has been reported to reduce inflammation, increase serum albumin, maintain body weight, increase muscle strength, increase IGF-1, and increase GFR. Resistance training in hemodialysis increases muscle strength, increases physical functionality, and improves IGF-1 status. Combined aerobic exercise and resistance training during dialysis improves muscle strength, work output, cardiac fitness, and possibly dialysis adequacy. There is a need for more investigation on the role of exercise in CKD. If the benefits of aerobic exercise and strength training in non-CKD populations can be shown to apply to CKD patients as well, renal rehabilitation will begin to play an important role in the approach to the treatment, prevention, and slowed progression of CKD.

Acute resistance exercise increases skeletal muscle angiogenic growth factor expression

Acute aerobic exercise promotes skeletal muscle angiogenesis and increases the expression of several angiogenic growth factors in skeletal muscle and in the circulation. Resistance exercise can promote skeletal muscle angiogenesis, though the increase is less robust than the response to aerobic exercise. PURPOSE: To determine if acute resistance exercise increases angiogenic growth factor (VEGF and angiopoietin) expression in skeletal muscle and plasma. METHODS: Six young men began by performing a progressive two legged, knee extensor resistance exercise test to determine one repetition maximum (1-RM). Following the determination of 1-RM, subjects performed 3 sets of ten repetitions (3 × 10) at 60–80% of 1-RM. Vastus lateralis muscle biopsies and plasma samples were obtained prior to the initiation of the 1-RM test and at 0, 2, and 4 hr following the completion of the last resistance exercise set. mRNA was analyzed by rtPCR and proteins by ELISA. RESULTS: In muscle, VEGF, KDR, neuropilin 1, and Tie2 mRNA were significantly (p < 0.05) increased by resistance exercise, while VEGF protein and Flt-1 mRNA tended (p < 0.1) to be increased by exercise. In the plasma, VEGF and sFlt-1 protein tended (p < 0.1) to be increased by exercise. Neither angiopoietin 1 or 2 mRNA in skeletal muscle was increased by exercise at the time points investigated. CONCLUSIONS: Similar to aerobic exercise, resistance exercise increases angiogenic growth factor expression. The lack of an angiopoietin 2 response may be responsible for the less robust angiogenic response to resistance compared to aerobic exercise. Supported by NIH AG-21891 and Mid-Atlantic AHA 0465415U.

Effect of Exercise on mRNA Levels for Growth Factors in Skeletal Muscle of Hemodialysis Patients

Muscle mass and muscle mRNA levels for certain growth factors are reduced in maintenance hemodialysis (MHD) patients. This study tested the hypothesis that in MHD patients endurance exercise training (EET) increases mRNA levels for insulin-like growth factors and reduces myostatin mRNA. Biopsies of the right vastus lateralis muscle were performed before and at the end of 8.9 +/- 0.9 (SEM) weeks of EET in MHD patients. Muscle tissue was analyzed histologically by electron microscopy and for fiber cross-sectional area, and, in 8 pairs of biopsies, muscle was examined for mRNA levels for the following proteins: myostatin, insulin-like growth factor-I (IGF-I), IGF-I receptor (IGF-IR), IGF binding proteins (IGFBPs)-1, -2, -3, -4, and -5, and IGF-binding protein-related protein-1 (IGFBP-rP1). Outpatient MHD centers. This was a pilot study conducted in sedentary clinically stable MHD patients undergoing EET with no control group. EET that was carefully supervised by exercise trainers. Skeletal muscle mRNA levels, especially myostatin mRNA. With EET, skeletal muscle myostatin mRNA decreased by 51%, mRNA levels increased significantly for IGF-IR (by 41%), IGFBP-2, -4, and -5, and IGFBP-rP1. IGF-I mRNA increased by 35%; this change was not significant. IGFBP-3 mRNA did not change, and IGFBP-1 mRNA was undetectable. There were mild to moderate alterations in skeletal muscle ultrastructure that did not change significantly with EET. Muscle fiber size, measured in 5 patients, did not change. In MHD patients who undergo approximately 9 weeks of EET, skeletal muscle mRNA for myostatin decreases and mRNA for IGF-IR, IGFBPs -2, -4, and -5 and IGFBP-rP1 increases. These changes may indicate mechanisms by which EET improves muscle exercise capacity in MHD patients.

Transcriptional Levels of Growth Factors in Skeletal Muscle of Maintenance Hemodialysis Patients

This study was performed to assess the mRNA levels in skeletal muscle of maintenance hemodialysis (MHD) patients. Fifty-one sedentary MHD patients and 21 sedentary normal adults of similar age, gender distribution, and racial/ethnic mix as the patients were examined. The subjects had needle muscle biopsy to measure mRNA levels. They were assessed in right vastus lateralis muscle for insulinlike growth factor I (IGF-IEa and IGF-IEc), IGF-II, the IGF-I receptor, the IGF-II receptor, and myostatin. mRNA was measured by real-time polymerase chain reaction amplification of reverse transcribed cDNA. The results showed that in the MHD patients, as compared with the normal control patients, skeletal muscle mRNA levels for IGF-IEa, IGF-II, and the IGF-I receptor were significantly reduced, whereas mRNA for IGF-IEc, IGF-II receptor, and myostatin were not different than normal. We conclude that sedentary MHD patients show reductions in mRNA levels in the right vastus lateralis muscle for certain growth factor proteins, notably IGF-IEa, IGF-II, and the IGF-I receptor. These abnormalities may contribute to the sarcopenia and impaired endurance capacity, strength, and physical performance that occur in MHD patients.

Stem cells to build muscles

Beginning on page 909, De Bari et al. describe a cell- based therapeutic strategy for Duchenne muscular dystrophy (DMD), the most common lethal genetic disorder in children. Although clinical studies are still a long way off, the results highlight the importance of secondary events in the pathogenesis of DMD and demonstrate the potential of a novel source of human adult stem cells. Figure Human cells derived from a stem cell transplant (red) can repopulate a mouse muscle. DMD is caused by a lack of dystrophin at the sarcolemma of muscle fibers, resulting in irreversible degeneration of skeletal muscle once the satellite cells needed for regeneration have been depleted. Having identified a population of mesenchymal stem cells that can be cultured from the synovial membranes of adult human donors, the authors tested the muscle-regenerating capacity of the cells in two mouse models. When transplanted into nude mice, the stem cells contribute to the formation of myofibers and give rise to functional satellite cells. Molecular markers suggest that the differentiation of the stem cells recapitulates embryonic myogenesis. Implanting the stem cells into mdx mice, a model of DMD, results in the appearance of human dystrophin at the sarcolemma and the expression of mouse mechano growth factor in skeletal muscle, a surrogate marker for the restoration of muscle contractility. Direct replacement of dystrophin expression has yielded less than spectacular results. In contrast, the success of the stem cell approach reinforces the idea that the clinical progression of DMD is at least partly due to loss of stem cells—a secondary effect of the loss of dystrophin. Thus, restoring satellite cell populations, even while a patient retains a defect in dystrophin, could be an effective treatment strategy. The authors are now characterizing the existing synovial membrane–derived human stem cells in detail, in the hopes of identifying a cell population with predictable and reproducible biological behavior for use in human patients. Additional studies will focus on analyzing muscle function in mdx mice directly over long periods, rather than relying on surrogate markers. ▪

Factors affecting production of luciferase and epitope-tagged IGF-I in porcine muscle after DNA injection.

Direct DNA injection into porcine skeletal muscle was investigated as an approach for studying roles of locally produced IGF-I on IGF-binding protein (IGFBP) production. To determine parameters for maximal reporter gene expression, and to investigate the effects of dose, time and weaning on exogenous DNA expression, plasmid DNA encoding firefly luciferase under control of a constitutive promoter and enhancer was injected in skeletal muscle of pigs. Results indicate that injected DNA does not migrate beyond 9 mm from injection sites and that 100 microg DNA injections resulted in optimal luciferase activity. Maximum amounts of recombinant protein were observed 3 days after injection, and were reduced by weaning. Using these data, a second DNA injection study was performed using plasmid DNA containing a cDNA insert for epitope-tagged insulin-like growth factor-I (TIGF-I). Significant quantities of TIGF-I were detected by ELISA and confirmed by western blotting. Both IGFBP-2 and IGFBP-2 mRNA were increased in treated muscle compared with controls. We conclude that increased expression of IGF-I in muscle results in increased IGFBP-2. Furthermore, these data indicate that this in vivo approach of gene transfer results in biologically active recombinant protein production in porcine skeletal muscle, and provides an excellent in vivo model for studying the autocrine and (or) paracrine effects of locally produced growth factors in skeletal muscle.