Skeletal Muscle Tissue Inflammation Research Articles

ADAR2 deficiency ameliorates non-alcoholic fatty liver disease and muscle atrophy through modulating serum amyloid A1.

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide. Sarcopenia is a syndrome characterized by progressive and generalized loss of skeletal muscle mass and strength, which is commonly associated with NAFLD. Adenosine-to-inosine editing, catalysed by adenosine deaminase acting on RNA (ADAR), is an important post-transcriptional modification of genome-encoded RNA transcripts. Three ADAR gene family members, including ADAR1, ADAR2 and ADAR3, have been identified. However, the functional role of ADAR2 in obesity-associated NAFLD and sarcopenia remains unclear. ADAR2+/+/GluR-BR/R mice (wild type [WT]) and ADAR2-/-/GluR-BR/R mice (ADAR2 knockout [KO]) were subjected to feeding with standard chow or high-fat diet (HFD) for 20weeks at the age of 5weeks. The metabolic parameters, hepatic lipid droplet, grip strength test, rotarod test, muscle weight, fibre cross-sectional area (CSA), fibre types and protein associated with protein degradation were examined. Systemic and local tissues serum amyloid A1 (SAA1) were measured. The effects of SAA1 on C2C12 myotube atrophy were investigated. ADAR2 KO mice fed with HFD exhibited lower body weight (-7.7%, P<0.05), lower liver tissue weight (-20%, P<0.05), reduced liver lipid droplets in concert with a decrease in hepatic triglyceride content (-24%, P<0.001) and liver injury (P<0.01). ADAR2 KO mice displayed protection against HFD-induced glucose intolerance, insulin resistance and dyslipidaemia. Skeletal muscle mass (P<0.01), muscle strength (P<0.05), muscle endurance (P<0.001) and fibre size (CSA; P<0.0001) were improved in ADAR2 KO mice fed with HFD compared with WT mice fed with HFD. Muscle atrophy-associated transcripts, such as forkhead box protein O1, muscle atrophy F-box/atrogin-1 and muscle RING finger 1/tripartite motif-containing 63, were decreased in ADAR2 KO mice fed with HFD compared with WT mice fed with HFD. ADAR2 deficiency attenuates HFD-induced local liver and skeletal muscle tissue inflammation. ADAR2 deficiency abolished HFD-induced systemic (P<0.01), hepatic (P<0.0001) and muscular (P<0.001) SAA1 levels. C2C12 myotubes treated with recombinant SAA1 displayed a decrease in myotube length (-37%, P<0.001), diameter (-20%, P<0.01), number (-39%, P<0.001) and fusion index (-46%, P<0.01). Myogenic markers (myosin heavy chain and myogenin) were decreased in SAA1-treated myoblast C2C12 cells. These results provide novel evidence that ADAR2 deficiency may be important in obesity-associated sarcopenia and NAFLD. Increased SAA1 might be involved as a regulatory factor in developing sarcopenia in NAFLD.

Effect of Physical Training on Exercise-Induced Inflammation and Performance in Mice.

Acute exercise increases the amount of circulating inflammatory cells and cytokines to maintain physiological homeostasis. However, it remains unclear how physical training regulates exercise-induced inflammation and performance. Here, we demonstrate that acute high intensity exercise promotes an inflammatory profile characterized by increased blood IL-6 levels, neutrophil migratory capacity, and leukocyte recruitment to skeletal muscle vessels. Moreover, we found that physical training amplified leukocyte–endothelial cell interaction induced by acute exercise in skeletal muscle vessels and diminished exercise-induced inflammation in skeletal muscle tissue. Furthermore, we verified that disruption of the gp-91 subunit of NADPH-oxidase inhibited exercise-induced leukocyte recruitment on skeletal muscle after training with enhanced exercise time until fatigue. In conclusion, the training was related to physical improvement and immune adaptations. Moreover, reactive oxygen species (ROS) could be related to mechanisms to limit aerobic performance and its absence decreases the inflammatory response elicited by exercise after training.

Baseline Characteristics of Participants in a Randomized Controlled Trial of Metformin for Frailty Prevention

We are conducting a double-blind, randomized controlled trial of metformin for frailty prevention. Participants are adults aged 65+ years with pre-diabetes assessed by 2-hour oral glucose tolerance test (OGTT). Those who are frail (Fried criteria) are excluded. Participants are randomized to metformin (maximum dose of 2,000 mg/day) vs. placebo and followed for 2 years. The primary outcome is frailty (category and score); secondary outcomes are physical performance and function (short physical performance battery, 6-minute walk, lower extremity strength), systemic and skeletal muscle tissue inflammation, muscle insulin signaling, insulin sensitivity (insulin clamp), glucose tolerance (OGTT), and body composition (dual-energy x-ray absorptiometry). Safety assessments occur every 3 months; frailty, systemic inflammation, and OGTT are assessed at baseline and every 6 months, and insulin clamp with muscle biopsies are assessed at baseline and every 12 months. To date, 85 subjects have been randomized; 120 completers are planned. Mean age is 72.8 ± 5.7 years, 55.3% are male, and 43.5% were Hispanic. Mean BMI is 30.2±5.8 kg/m2, waist circumference is 104.4 ±15.5 cm, fasting glucose is 102.3 ± 10.0 mg/dL, Hemoglobin A1c is 5.8 ±0.3, and glucose at 2 hours during OGTT is 167.3 ± 17.8 mg/dL. Metformin is being examined in this study as a potential therapeutic agent to prevent frailty in older adults with pre-diabetes. Findings from this trial may have future implications for the screening and potential treatment of pre-diabetes in older patients with metformin for the prevention of frailty.

Resveratrol alleviates obesity-induced skeletal muscle inflammation via decreasing M1 macrophage polarization and increasing the regulatory T cell population

Resveratrol was reported to inhibit inflammatory responses; however, the role of this polyphenol in obesity-induced skeletal muscle inflammation remains unknown. Mice fed a high fat diet (HFD) were treated with resveratrol for 16 weeks. Resveratrol treatment decreased macrophage infiltration into skeletal muscle of HFD-fed mice. Resveratrol also led to the polarization of macrophages to the M2 direction, as well as decreasing the expression of a number of M1 pro-inflammatory cytokines [tumor necrosis factor α (TNF-α), interleukin 1 β (IL-1β) and interleukin 6 (IL-6)]. In addition, increased infiltration of regulatory T cells (Treg cells) was found following resveratrol treatment in skeletal muscle of mice. Decreased intramyocellular lipid deposition was associated with reduced expression levels of toll-like receptors 2 (TLR2) and TLR4 in resveratrol treated mice. We also found that diminished inflammation in skeletal muscle following resveratrol treatment was accompanied by increasing phosphorylation of 5’-adenosine monophosphate-activated protein kinase (AMPK) and decreasing phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK). Taken together, these findings suggest that resveratrol ameliorates inflammation in skeletal muscle of HFD-induced model of obesity. Therefore, resveratrol might represent a potential treatment for attenuation of inflammation in skeletal muscle tissue.

A RANDOMIZED CONTROLLED TRIAL OF METFORMIN FOR FRAILTY PREVENTION: STUDY DESIGN AND BASELINE CHARACTERISTICS

Inflammation and insulin resistance are major predictors of frailty. Here we describe the study design of an ongoing double-blind, randomized controlled trial of metformin for frailty prevention. Subjects are adults aged 65+ years with pre-diabetes assessed by 2-hour oral glucose tolerance test (OGTT). Those who are frail (Fried criteria) are excluded. Participants are randomized to metformin (maximum dose of 2,000 mg/day) vs. placebo and followed for 2 years. The primary outcome is frailty (category and score); secondary outcomes are physical performance and function (short physical performance battery, 6-minute walk, lower extremity strength), systemic and skeletal muscle tissue inflammation, muscle insulin signaling, insulin sensitivity (insulin clamp), glucose tolerance (OGTT), and body composition (dual-energy x-ray absorptiometry). Safety assessments occur every 3 months; frailty, systemic inflammation, and OGTT are assessed at baseline and every 6 months, and insulin clamp with muscle biopsies are assessed at baseline and every 12 months. To date, 51 subjects have been randomized; 120 completers are planned. Mean age is 73.4 ±5.7 years, 43% are female, and 39% Hispanic. Mean BMI is 30.5 ±5.5 kg/m2, waist circumference is 105 ±13.1 cm, fasting glucose is 102.3 ±8.8 mg/dL, Hemoglobin A1c is 5.8 ±0.3, and glucose at 2 hours during OGTT is 168.5 ±20.4 mg/dL. Metformin is being examined in this study as a potential therapeutic agent to prevent frailty in older adults with pre-diabetes. Findings from this trial may have future implications for the screening and potential treatment of pre-diabetes in older patients with metformin for the prevention of frailty.

Rationale and Study Design of a Randomized Clinical Trial of Metformin to Prevent Frailty in Older Adults With Prediabetes.

Frailty is a geriatric syndrome that leads to poor health outcomes with aging. Previous studies have demonstrated that insulin resistance and inflammation predict frailty onset. Metformin is a widely used, well-tolerated drug that improves insulin sensitivity and displays anti-inflammatory properties. It is also known to prevent diabetes onset in adults with prediabetes. We hypothesize that metformin in older adults with prediabetes will promote healthy aging and prevent frailty. Here we describe an ongoing placebo-controlled, double-blinded clinical trial of metformin for the prevention of frailty in older adults with prediabetes. Older adults aged more than 65 years are randomized to metformin or placebo and are followed for 2 years. Prediabetes, required for inclusion, is assessed by 2-hour oral glucose tolerance test. Exclusion criteria are baseline frailty (Fried criteria), diabetes, dementia, untreated depression, active malignancy, or severe cardiovascular, pulmonary, and neurologic diseases. Primary outcome is frailty; secondary outcomes are physical function (Short Physical Performance Battery), systemic and skeletal muscle tissue inflammation, muscle insulin signaling, insulin sensitivity (insulin clamp), glucose tolerance (oral glucose tolerance test), and body composition (dual-energy x-ray absorptiometry). Subjects are followed every 3 months for safety assessments and every 6 months for frailty assessment (Fried criteria) and oral glucose tolerance test, and every 12 or 24 months for secondary outcomes. Enrollment of 120 subjects (completers) will take place over a 2-year period. Metformin is being examined in this study as a potential therapeutic agent to prevent frailty in older adults with prediabetes. Findings from this trial may have future implications for the screening and potential treatment of prediabetes in older patients with metformin for the prevention of frailty.

Alteration of inflammatory cytokines, energy metabolic regulators, and muscle fiber type in the skeletal muscle of postweaning piglets.

This study was conducted to determine the alterations of inflammatory cytokines, energy metabolic regulators, and muscle fiber type in the LM of the piglets postweaning. Crossbred piglets (Landrace × Large White) weaned at 14 d age were randomly selected from 8 litters and slaughtered at 0 (W0), 1 (W1), 3 (W3), 5 (W5), or 7 (W7) days postweaning. The glycogen content, free glucose concentration, and enzyme activities, including ATPase (Na/K, Ca/Mg), creatine kinase, and lactic dehydrogenase (LDH), were detected in the skeletal muscle tissue. Concentrations of proinflammatory cytokines, including IL-1β, IL-6, and tumor necrosis factor-α (TNF-α), and anti-inflammatory cytokines, including IL-10 and transforming growth factor-β1 (TGF-β1), were measured in serum. The mRNA abundance of the above cytokines, energy metabolic regulators, and muscle fiber type related genes were determined via real-time quantitative PCR analysis. The adenosine monophosphate-activated protein kinase α (AMPKα) signaling was measured by Western blot analysis. Our results showed ATPase activities were lower on W7 d but LDH activity was higher on W3 d after weaning ( < 0.05). Serum TNF-α concentration was markedly increased on W1 d, then returned to the value of preweaning ( < 0.05), and almost all the values of inflammatory cytokines were reduced to a low point on W5 d after weaning. Additionally, the IL-6 mRNA abundance was upregulated during W3 to W7 d, but cytokine TNF-α was upregulated just on W7 d ( < 0.05). The mRNA abundance of AMPKα and uncoupling protein (UCP) 3 were both higher on W1 and W3 d, and UCP2 was higher on W7 d postweaning ( < 0.05). Myosin heavy chain (MyHC) I and MyHC IIx-type fibers were enhanced on W1 d, then returned to the value of preweaning, and the MyHC IIb-type fiber was significantly increased on W5 and W7 d ( < 0.05). Meanwhile, the value of P-AMPKα/T-AMPKα increased on W3 d postweaning ( < 0.05) compared with that on W0 d. These results indicate that weaning stress induced inflammation in skeletal muscle tissue during at least 7 d postweaning. It upregulated the expression of proinflammatory cytokines, which then stimulated the AMPKα and UCP involved in energy metabolism events, accompanied by significant alterations in muscle fiber type.

Rapamycin Ameliorates Dystrophic Phenotype in mdx Mouse Skeletal Muscle

Duchenne muscular dystrophy (DMD) is an X-linked, lethal, degenerative disease that results from mutations in the dystrophin gene, causing necrosis and inflammation in skeletal muscle tissue. Treatments that reduce muscle fiber destruction and immune cell infiltration can ameliorate DMD pathology. We treated the mdx mouse, a model for DMD, with the immunosuppressant drug rapamycin (RAPA) both locally and systemically to examine its effects on dystrophic mdx muscles. We observed a significant reduction of muscle fiber necrosis in treated mdx mouse tibialis anterior (TA) and diaphragm (Dia) muscles 6 wks post-treatment. This effect was associated with a significant reduction in infiltration of effector CD4(+) and CD8(+) T cells in skeletal muscle tissue, while Foxp3(+) regulatory T cells were preserved. Because RAPA exerts its effects through the mammalian target of RAPA (mTOR), we studied the activation of mTOR in mdx TA and Dia with and without RAPA treatment. Surprisingly, mTOR activation levels in mdx TA were not different from control C57BL/10 (B10). However, mTOR activation was different in Dia between mdx and B10; mTOR activation levels did not rise between 6 and 12 wks of age in mdx Dia muscle, whereas a rise in mTOR activation level was observed in B10 Dia muscle. Furthermore, mdx Dia, but not TA, muscle mTOR activation was responsive to RAPA treatment.

Nitro‐aspirin improves high‐fat diet induced insulin resistance in mice by attenuation of iNOS induction in skeletal muscle tissue

Nitric oxide (NO) plays a pivotal role in the regulation of glucose homeostasis. In insulin resistant humans and high-fat diet (HFD) fed mice, the inducible form of NO synthase (iNOS) is upregulated in skeletal muscle, where it contributes to insulin resistance, as evidenced by protection against HFD-induced insulin resistance in iNOS knockout mice. Conversely, there is evidence that slow releasing NO donors improve insulin sensitivity in HFD-fed mice, but the mechanism is unknown. We hypothesized that it may do so by attenuating iNOS induction in skeletal muscle. We, therefore, studied the effects of nitro-aspirin (100 mg/kg/day during wk 8) on glucose uptake in vivo (hyperinsulinemic clamp) in C57BL6 mice fed with HFD for 8 wks. In additional mice, we studied the effects of nitro-aspirin on iNOS protein and RNA expression (RT-PCR) in skeletal muscle. As expected, glucose infusion rate during the steady state of the clamp was significantly lower in HFD- than normal chow fed mice (68.1±14.9 vs. 93.3±15.7 mg/kg per min, P<0.01). Nitro-aspirin partially restored insulin sensitivity in HFD fed mice (80.8±9.9 mg/kg per min, P=0.03 vs. vehicle), whereas aspirin had no effect. Most, importantly, nitro aspirin, but not aspirin, abolished (P<0.02) the HFD-induced increase in iNOS protein expression, and attenuated (P<0.04) the increase in RNA expression in skeletal muscle. These findings provide the very first evidence that a slow releasing NO-donor prevents iNOS induction and inflammation in skeletal muscle tissue and improves glucose homeostasis in insulin-resistant HFD-fed mice.

High specificity of myositis specific autoantibodies for myositis compared with other neuromuscular disorders

Myositis specific autoantibodies (MSAs) are proven to be specific for myositis compared with other inflammatory connective tissue diseases. Their specificity compared, however, with other neuromuscular disorders, which are included in the differential diagnosis of patients in whom the diagnosis myositis is under consideration, is unknown. We prospectively screened sera from 107 patients with various neuromuscular disorders for the most common MSAs and compared the results with the findings in a group of 97 myositis patients, published previously. Special attention was paid to patients with facioscapulohumeral muscular dystrophy (FSHD), an autosomal dominant muscle disease with marked inflammation in skeletal muscle tissue. Only one patient in the neuromuscular disorders group tested positive for an MSA, compared with 41 in the myositis group, resulting in a specificity of 99%. None of the FSHD patients tested positive. We conclude that the tested MSAs are highly specific for myositis and that they are not merely associated with muscle inflammation.