Matthew C. Kostek

The Regulation of Skeletal Muscle Protein Turnover during the Progression of Cancer Cachexia in the ApcMin/+ Mouse

Muscle wasting that occurs with cancer cachexia is caused by an imbalance in the rates of muscle protein synthesis and degradation. The ApcMin/+ mouse is a model of colorectal cancer that develops cachexia that is dependent on circulating IL-6. However, the IL-6 regulation of muscle protein turnover during the initiation and progression of cachexia in the ApcMin/+ mouse is not known. Cachexia progression was studied in ApcMin/+ mice that were either weight stable (WS) or had initial (≤5%), intermediate (6–19%), or extreme (≥20%) body weight loss. The initiation of cachexia reduced %MPS 19% and a further ∼50% with additional weight loss. Muscle IGF-1 mRNA expression and mTOR targets were suppressed with the progression of body weight loss, while muscle AMPK phosphorylation (Thr 172), AMPK activity, and raptor phosphorylation (Ser 792) were not increased with the initiation of weight loss, but were induced as cachexia progressed. ATP dependent protein degradation increased during the initiation and progression of cachexia. However, ATP independent protein degradation was not increased until cachexia had progressed beyond the initial phase. IL-6 receptor antibody administration prevented body weight loss and suppressed muscle protein degradation, without any effect on muscle %MPS or IGF-1 associated signaling. In summary, the %MPS reduction during the initiation of cachexia is associated with IGF-1/mTOR signaling repression, while muscle AMPK activation and activation of ATP independent protein degradation occur later in the progression of cachexia. IL-6 receptor antibody treatment blocked cachexia progression through the suppression of muscle protein degradation, while not rescuing the suppression of muscle protein synthesis. Attenuation of IL-6 signaling was effective in blocking the progression of cachexia, but not sufficient to reverse the process.

Muscle Size Responses to Strength Training in Young and Older Men and Women

OBJECTIVES: To examine the possible influences of age and gender on muscle volume responses to strength training (ST).

IL-6 regulation on skeletal muscle mitochondrial remodeling during cancer cachexia in the ApcMin/+ mouse

BackgroundMuscle protein turnover regulation during cancer cachexia is being rapidly defined, and skeletal muscle mitochondria function appears coupled to processes regulating muscle wasting. Skeletal muscle oxidative capacity and the expression of proteins regulating mitochondrial biogenesis and dynamics are disrupted in severely cachectic ApcMin/+ mice. It has not been determined if these changes occur at the onset of cachexia and are necessary for the progression of muscle wasting. Exercise and anti-cytokine therapies have proven effective in preventing cachexia development in tumor bearing mice, while their effect on mitochondrial content, biogenesis and dynamics is not well understood. The purposes of this study were to 1) determine IL-6 regulation on mitochondrial remodeling/dysfunction during the progression of cancer cachexia and 2) to determine if exercise training can attenuate mitochondrial dysfunction and the induction of proteolytic pathways during IL-6 induced cancer cachexia.MethodsApcMin/+ mice were examined during the progression of cachexia, after systemic interleukin (IL)-6r antibody treatment, or after IL-6 over-expression with or without exercise. Direct effects of IL-6 on mitochondrial remodeling were examined in cultured C2C12 myoblasts.ResultsMitochondrial content was not reduced during the initial development of cachexia, while muscle PGC-1α and fusion (Mfn1, Mfn2) protein expression was repressed. With progressive weight loss mitochondrial content decreased, PGC-1α and fusion proteins were further suppressed, and fission protein (FIS1) was induced. IL-6 receptor antibody administration after the onset of cachexia improved mitochondrial content, PGC-1α, Mfn1/Mfn2 and FIS1 protein expression. IL-6 over-expression in pre-cachectic mice accelerated body weight loss and muscle wasting, without reducing mitochondrial content, while PGC-1α and Mfn1/Mfn2 protein expression was suppressed and FIS1 protein expression induced. Exercise normalized these IL-6 induced effects. C2C12 myotubes administered IL-6 had increased FIS1 protein expression, increased oxidative stress, and reduced PGC-1α gene expression without altered mitochondrial protein expression.ConclusionsAltered expression of proteins regulating mitochondrial biogenesis and fusion are early events in the initiation of cachexia regulated by IL-6, which precede the loss of muscle mitochondrial content. Furthermore, IL-6 induced mitochondrial remodeling and proteolysis can be rescued with moderate exercise training even in the presence of high circulating IL-6 levels.

Resveratrol decreases inflammation and increases utrophin gene expression in the mdx mouse model of duchenne muscular dystrophy

BACKGROUND & AIMS Duchenne muscular dystrophy (DMD) is a lethal genetic disease with no cure. Reducing inflammation or increasing utrophin expression can alleviate DMD pathology. Resveratrol can reduce inflammation and activate the utrophin promoter. The aims of this study were to identify an active dose of resveratrol in mdx mice and examine if this dose decreased inflammation and increased utrophin expression. METHODS 5-week old mdx mice were given 0, 10, 100, or 500 mg/kg of resveratrol everyday for 10 days. Sirt1 was measured by qRT-PCR and used to determine the most active dose. Muscle inflammation was measured by H&E staining, CD45 and F4/80 immunohistochemistry. IL-6, TNFα, PGC-1α, and utrophin gene expression were measured by qRT-PCR. Utrophin, Sirt1, and PGC-1α protein were quantified by western blot. RESULTS The 100 mg/kg dose of resveratrol, the most active dose, increased Sirt1 mRNA 60 ± 10% (p < 0.01), reduced immune cell infiltration 21 ± 6% (H&E) and 42 ± 8% (CD45 immunohistochemistry (p < 0.05)), reduced macrophage infiltration 48 ± 10% (F4/80 immunohistochemistry (p < 0.05)), and increased IL-6, PGC-1α, and utrophin mRNA 247 ± 77%, 27 ± 17%, and 43 ± 23% respectively (p ≤ 0.05). Utrophin, Sirt1, and PGC-1α protein expression did not change. CONCLUSIONS Resveratrol may be a therapy for DMD by reducing inflammation.

Can dual energy X-ray absorptiometry provide a valid assessment of changes in thigh muscle mass with strength training in older adults?

Objective:To determine how dual-energy X-ray absorptiometry (DXA) compares to computed tomography (CT) for measuring changes in total thigh skeletal muscle (SM) mass with strength training (ST) in older adults.Subjects:Fifty previously sedentary, relatively healthy older men (n=23, 60 (s.d.=7.5) years) and women (n=27, 60 (s.d.=9.3) years).Results:Results indicate that there was a significant increase in thigh SM mass with ST measured by both CT (3.9±0.4%) and DXA (2.9±0.6%) methods (both P<0.001), and there was not a significant difference in percent change between the two methods, although there was a substantial absolute difference (∼2 kg) at baseline between the two methods. Although Bland–Altman plots indicate overall agreement between the percent thigh SM mass changes of DXA vs CT methods, the 3.4% error associated with DXA was greater than the thigh SM mass change from DXA. However, the CT measured change in thigh SM mass was greater than its error (0.6%).Conclusions:DXA overestimates baseline and after ST thigh SM mass, and may not be able to detect small changes in thigh SM mass with ST due to its higher error. Although DXA has certain advantages that warrant is used in epidemiologic and intervention studies, improvements to DXA are needed for the accurate assessment of small changes in thigh SM mass.

Blood Pressure Response to Strength Training May Be Influenced by Angiotensinogen A–20C and Angiotensin II Type I Receptor A1166C Genotypes in Older Men and Women

Objectives: To determine the influence of angiotensinogen (AGT) A–20C, M235 T, and angiotensin II type 1 receptor (AGTR1) A1166C genotypes on resting blood pressure (BP) response to strength training (ST) in older men and women.

Vitamin D receptor FokI genotype influences bone mineral density response to strength training, but not aerobic training

To determine the influence of the vitamin D receptor (VDR) gene FokI and BsmI genotype on bone mineral density response to two exercise training modalities, 206 healthy men and women (50–81 years old) were studied before and after ∼5–6 months of either aerobic exercise training (AT) or strength training (ST). A totla of 123 subjects completed AT (51 men, 72 women) and 83 subjects completed ST (40 men, 43 women). DNA was extracted from blood samples of all subjects and genotyping was performed at the VDR FokI and BsmI locus to determine its association to training response. Total body, greater trochanter and femoral neck bone mineral density (BMD) were measured before and after both training programmes using dual‐energy X‐ray absorptiometry. VDR BsmI genotype was not significantly related to BMD at baseline or after ST or AT. However, VDR FokI genotype was significantly related to ST‐ but not AT‐induced changes in femoral neck BMD (P < 0.05). The heterozygotes (Ff) in the ST group approached a significantly greater increase in femoral neck BMD (P= 0.058) compared to f homozygotes. There were no significant genotype relationships in the AT group. These data indicate that VDR FokI genotype may influence femoral neck BMD response to ST, but not AT.

IL-6 signaling blockade increases inflammation but does not affect muscle function in the mdx mouse

BackgroundIL-6 is a pleiotropic cytokine that modulates inflammatory responses and plays critical roles in muscle maintenance and remodeling. In the mouse model (mdx) of Duchenne Muscular Dystrophy, IL-6 and muscle inflammation are elevated, which is believed to contribute to the chronic inflammation and failure of muscle regeneration in DMD. The purpose of the current study was to examine the effect of blocking IL-6 signaling on the muscle phenotype including muscle weakness and pathology in the mdx mouse.MethodsA monoclonal antibody against the IL-6 receptor (IL-6r mAb) that blocks local and systemic IL-6 signaling was administered to mdx and BL-10 mice for 5 weeks and muscle function, histology, and inflammation were examined.ResultsIL-6r mAb treatment increased mdx muscle inflammation including total inflammation score and ICAM-1 positive lumens in muscles. There was no significant improvement in muscle strength nor muscle pathology due to IL-6r mAb treatment in mdx mice.ConclusionsThese results showed that instead of reducing inflammation, IL-6 signaling blockade for 5 weeks caused an increase in muscle inflammation, with no significant change in indices related to muscle regeneration and muscle function. The results suggest a potential anti-inflammatory instead of the original hypothesized pro-inflammatory role of IL-6 signaling in the mdx mice.

Comparison of acute responses to isotonic or isokinetic eccentric muscle action: differential outcomes in skeletal muscle damage and implications for rehabilitation.

Both isotonic and isokinetic eccentric muscle contractions are commonly used in muscle research laboratories to induce muscle damage, yet, the muscle damage outcomes between these 2 modes of eccentric contraction have not been compared. The purpose of this study was to compare modes of contraction for differences in muscle damage. 16 men were placed in the isotonic (IT: 110% of maximal isometric torque) or the isokinetic (IK: 120°/s) group, with each group performing 200 eccentric muscle actions of the knee extensors. Isometric peak torque, perceived soreness and CK activity were measured immediately pre and post exercise, and 48-h post exercise. Mean total work (~1700 J) and peak torque per set (~265 Nm) decreased over the 200 repetitions (p<0.01), and was not different between groups. Damage markers changed 48-h post exercise (p<0.05): peak isometric torque (-13%), creatine kinase activity (+200%) and self-perceived muscular soreness (+4 unit change). Significant group×time interactions (p<0.01) indicated that peak isometric torque was 22% lower, and creatine kinase and self-perceived muscular soreness were 330% and 3 unit difference higher in the IT as compared to the IK groups, 48-h post exercise. When equating for total work, skeletal muscle damage markers are higher during IT vs. IK modes. This reflects differences inherent in contraction type and suggests that this should be taken into account during physical rehabilitation.

Age-Related Changes in Adult Muscle Morphology

Skeletal muscle undergoes numerous morphological changes from early adulthood to old age including muscle size, configuration, and structure. This review discusses these changes, considers the limitations in interpreting studies, addresses the potential health implications, and describes some mechanisms and interventions to ameliorate aging-related changes in skeletal muscle. Discussion in each section focuses on measurement and analysis techniques of muscle morphology, limitations of human research, and the discussion uses animal work to support findings in humans. We examine the discrepancies in the study of fiber type distribution with age, and special emphasis is given to two topics: fiber-type distribution and intra- and intercellular fat. Finally, training adaptations and health implications are briefly discussed. The focus of the current review is the morphological changes that occur in skeletal muscle during the normal aging process, with emphasis on human studies.