Extracellular vesicles from obese and diabetic mouse plasma alter C2C12 myotube glucose uptake and gene expression.

Recent studies have indicated a role for circulating extracellular vesicles (EVs) in the pathogenesis of multiple diseases. However, most in vitro studies have used variable and arbitrary doses of EVs rather than interpreting EVs as an existing component of standard skeletal muscle cell culture media. The current study provides an initial investigation into the effects of circulating EVs on the metabolic phenotype of C2C12 myotubes by replacing EVs from fetal bovine serum with circulating EVs from control mice or mice with obesity and type 2 diabetes (OT2D). We report that EVs associated with OT2D decrease 2-NBDG uptake (a proxy measure of glucose uptake) in the insulin-stimulated state compared to controls. OT2D associated EV treatment also significantly decreased myosin heavy chain type 1 (MHCI) mRNA abundance in myotubes but had no effect on mRNA expression of any other myosin heavy chain isoforms. OT2D-associated circulating EVs also significantly increased lipid accumulation within myotubes without altering the expression of a selection of genes important for lipid entry, synthesis, or catabolism. The data indicate that, in a severely diabetic state, circulating EVs may contribute to insulin resistance and alter gene expression in myotubes in a manner consistent with the skeletal muscle phenotype observed in OT2D.

Loss of NOR-1 represses muscle metabolism through mTORC1-mediated signaling and mitochondrial gene expression in C2C12 myotubes.

Gene expression of the NR4A nuclear orphan receptor NOR-1 is reduced in obesity and in human skeletal muscle during disuse. It has been well established that NOR-1 is highly responsive to both aerobic and resistance exercise and NOR-1 overexpression is coincident with a plethora of metabolic benefits. However, it is unclear whether loss of NOR-1 contributes to inappropriate metabolic signaling in skeletal muscle that could lead to insulin resistance. The purpose of this study was to elucidate the impact of NOR-1 deficiency on C2C12 metabolic signaling. Changes in gene expression after siRNA-mediated NOR-1 knockdown in C2C12 myotubes were determined by qPCR and bioinformatic analysis of RNA-Seq data. Our RNA-Seq data identified several metabolic targets regulated by NOR-1 and implicates NOR-1 as a modulator of mTORC1 signaling via Akt-independent mechanisms. Furthermore, pathway analysis revealed NOR-1 knockdown perturbs the insulin resistance and insulin sensitivity pathways. Taken together, these data suggest skeletal muscle NOR-1 deficiency may contribute to altered metabolic signaling that is consistent with metabolic disease. We postulate that strategies that improve NOR-1 may be important to offset the negative impact that inactivity, obesity, and type 2 diabetes have on mitochondria and muscle metabolism.

Impact of essential amino acid intake, resistance exercise, and aging on the concentration of Achilles peritendinous amino acids and procollagen Iα1 in humans.

Recent studies have shown that consuming amino acid-rich compounds improves tendon collagen content and biomechanical properties. Yet, it is unclear if the consumption of amino acids alters local (peritendinous) amino acid concentrations. If aging or exercise influence local amino acid concentrations in conjunction with an amino acid bolus is also not known. We conducted two studies. In Study 1, young women (n = 7, 25 ± 2 years) completed two identical resistance training sessions with either essential amino acid (EAA) or placebo consumption. In Study 2, an EAA bolus identical to Study 1 was given to younger (n = 7; 27 ± 1 year) and older adults (n = 6; 68 ± 2 years). Microdialysis was used to determine Achilles peritendinous amino acid and pro-collagen Iα1 (a marker of collagen synthesis) concentrations. In Study 1, amino acid consumption increased peritendinous concentrations of all EAA except histidine (p < 0.05). In Study 2, the peritendinous concentration of EAAs except for methionine, histidine, and lysine (p > 0.05) increased with time (p < 0.05). Further, the concentrations of most measured amino acids were greater in older adults (p < 0.05). Pro-collagen Iα1 concentration (p > 0.05) was unaffected by exercise, EAA, or aging (p > 0.05). Our findings demonstrate the following: (1) when not combined with exercise, an oral EAA bolus leads to only modest increases in Achilles peritendinous amino acid concentrations; (2) when combined with resistance exercise, EAA consumption resulted in greater peritendinous amino acid concentrations compared to no exercise; (3) the basal concentrations of most amino acids were greater in older adults, and (4) neither the EAA bolus nor exercise altered peritendinous pro-collagen concentrations.

Mitochondria transplant therapy improves regeneration and restoration of injured skeletal muscle.

BACKGROUND: Injection of exogenous mitochondria has been shown to improve the ischaemia-damaged myocardium, but the effect of mitochondrial transplant therapy (MTT) to restore skeletal muscle mass and function has not been tested following neuromuscular injury. Therefore, we tested the hypothesis that MTT would improve the restoration of muscle function after injury. METHODS: BaCl2 was injected into the gastrocnemius muscle of one limb of 8-12-week-old C57BL/6 mice to induce damage without injury to the resident stem cells. The contralateral gastrocnemius muscle was injected with phosphate-buffered saline (PBS) and served as the non-injured intra-animal control. Mitochondria were isolated from donor mice. Donor mitochondria were suspended in PBS or PBS without mitochondria (sham treatment) and injected into the tail vein of BaCl2 injured mice 24 h after the initial injury. Muscle repair was examined 7, 14 and 21 days after injury. RESULTS: MTT did not increase systemic inflammation in mice. Muscle mass 7 days following injury was 21.9 ± 2.1% and 17.4 ± 1.9% lower (P < 0.05) in injured as compared with non-injured intra-animal control muscles in phosphate-buffered saline (PBS)- and MTT-treated animals, respectively. Maximal plantar flexor muscle force was significantly lower in injured as compared with uninjured muscles of PBS-treated (-43.4 ± 4.2%, P < 0.05) and MTT-treated mice (-47.7 ± 7.3%, P < 0.05), but the reduction in force was not different between the experimental groups. The percentage of collagen and other non-contractile tissue in histological muscle cross sections, was significantly greater in injured muscles of PBS-treated mice (33.2 ± 0.2%) compared with MTT-treated mice (26.5 ± 0.2%) 7 days after injury. Muscle wet weight and maximal muscle force from injured MTT-treated mice had recovered to control levels by 14 days after the injury. However, muscle mass and force had not improved in PBS-treated animals by 14 days after injury. The non-contractile composition of the gastrocnemius muscle tissue cross sections was not different between control, repaired PBS-treated and repaired MTT-treated mice 14 days after injury. By 21 days following injury, PBS-treated mice had fully restored gastrocnemius muscle mass of the injured muscle to that of the uninjured muscle, although maximal plantar flexion force was still 19.4 ± 3.7% (P < 0.05) lower in injured/repaired gastrocnemius as compared with uninjured intra-animal control muscles. CONCLUSIONS: Our results suggest that systemic mitochondria delivery can enhance the rate of muscle regeneration and restoration of muscle function following injury.

The Impact of Obesity on C1q/TNF-Related Protein-9 Expression and Endothelial Function following Acute High-Intensity Interval Exercise vs. Continuous Moderate-Intensity Exercise.

C1q-TNF-related protein-9 (CTRP9) increases endothelial nitric oxide synthase and reduces vasoconstrictors. There is limited information regarding exercise-mediated CTRP9 in obesity. The purpose of this study was to compare high-intensity interval exercise (HIIE) and continuous moderate-intensity exercise (CME) on the CTRP9 response and an indicator of endothelial function (FMD) in obese participants. Sixteen young male participants (9 obese and 7 normal-weight) participated in a counterbalanced and caloric equated experiment: HIIE (30 min, 4 intervals of 4 min at 80-90% of VO2 max with 3 min rest between intervals) and CME (38 min at 50-60% VO2 max). Serum CTRP9 and FMD were measured prior to, immediately following exercise, and 1 h and 2 h into recovery. CTRP9 was significantly increased immediately following acute HIIE and CME in both groups (p = 0.003). There was a greater CME-induced FMD response at 2 h into recovery in obese participants (p = 0.009). A positive correlation between CTRP9 and FMD percent change was observed in response to acute CME when combined with both obese and normal-weight participants (r = 0.589, p = 0.016). The novel results from this study provide a foundation for additional examination of the mechanisms of exercise-mediated CTRP9 on endothelial function in individuals with obesity.

An exploratory investigation of apoptotic and autophagic responses in peripheral blood mononuclear cells following maximal aerobic exercise in obese individuals.

Autophagy is a critical molecular process in promoting cell survival against apoptosis. This study examined whether maximal aerobic exercise-mediated apoptosis in obesity might be underlying the involvement of autophagy in the peripheral blood mononuclear cells (PBMCs). Twelve healthy male subjects (6 obese and 6 normal-weight) were recruited to participate in a maximal graded exercise test on a treadmill. Obese subjects exhibited a significantly lower Bax, but a higher Bcl-2 protein level in conjunction with a reduced Bax/Bcl-2 AUCi compared to normal-weight subjects following exercise. Furthermore, a greater LC3-II/LC3-I ratio and LC3-II/LC3-I AUCi was observed in obese subjects compared to normal-weight subjects. LC3-II/LC3-I AUCi was also positively associated with obesity-associated parameters (BMI, waist/hip circumference, and fasting insulin level), but was negatively correlated with Bax/Bcl-2 AUCi. These findings demonstrate that maximal aerobic exercise differentially mediates the intrinsic apoptotic pathway and autophagic activity in human PBMCs isolated from obese compared to normal-weight individuals.

Impact of acute high-intensity interval exercise on plasma pentraxin 3 and endothelial function in obese individuals-a pilot study.

PURPOSE: Pentraxin 3 (PTX3) has been shown to be a predictor of endothelial dysfunction in patients with increased risk of cardiovascular disease (CVD) (e.g., obesity). Circulating PTX3 concentrations are dysregulated in obese individuals and are elevated following acute aerobic exercise. High-intensity interval exercise (HIIE) has been demonstrated to be as effective as continuous moderate-intensity exercise in improving endothelial function, as indicated by brachial artery flow-mediated dilation (BAFMD), in patients with CVD. Therefore, the purpose of this study was to examine the effect of acute HIIE on plasma PTX3 and BAFMD responses in obese individuals. METHODS: Eight obese and six normal-weight young males participated in acute HIIE (4 intervals of 4 min at 80-90% of VO2max; 3 min of active recovery at 50-60% VO2max). Plasma PTX3 and BAFMD were measured prior to, immediately following exercise, and one and 2 hours into recovery. RESULTS: Plasma PTX3 concentrations significantly increased following HIIE, yet the PTX3 response to HIIE was significantly blunted in obese compared to normal-weight participants. While the kinetic responses of BAFMD were also significantly different in obese compared to normal-weight participants, similar increases above the baseline were observed 2 hours into recovery in both groups. Finally, plasma PTX3 concentrations were not associated with BAFMD at baseline or in response to HIIE. CONCLUSION: The utilization of HIIE may serve as a time-efficient exercise prescription strategy to transiently improve endothelial function, independent of elevated plasma PTX3 concentrations, in obese individuals.

Transcriptome Analysis of Skeletal Muscle Reveals Altered Proteolytic and Neuromuscular Junction Associated Gene Expressions in a Mouse Model of Cerebral Ischemic Stroke.

Stroke is a leading cause of mortality and long-term disability in patients worldwide. Skeletal muscle is the primary systemic target organ of stroke that induces muscle wasting and weakness, which predominantly contribute to functional disability in stroke patients. Currently, no pharmacological drug is available to treat post-stroke muscle morbidities as the mechanisms underlying post-stroke muscle wasting remain poorly understood. To understand the stroke-mediated molecular changes occurring at the transcriptional level in skeletal muscle, the gene expression profiles and enrichment pathways were explored in a mouse model of cerebral ischemic stroke via high-throughput RNA sequencing and extensive bioinformatic analyses. RNA-seq revealed that the elevated muscle atrophy observed in response to stroke was associated with the altered expression of genes involved in proteolysis, cell cycle, extracellular matrix remodeling, and the neuromuscular junction (NMJ). These data suggest that stroke primarily targets muscle protein degradation and NMJ pathway proteins to induce muscle atrophy. Collectively, we for the first time have found a novel genome-wide transcriptome signature of post-stroke skeletal muscle in mice. Our study will provide critical information to further elucidate specific gene(s) and pathway(s) that can be targeted to mitigate accountable for post-stroke muscle atrophy and related weakness.

Acute high-intensity interval exercise induces comparable levels of circulating cell-free DNA and Interleukin-6 in obese and normal-weight individuals.

AIMS: Obesity is associated with lipid aggregation in adipocytes and macrophage infiltration, leading to increased oxidative stress and inflammation. Increased cell-free DNA (cfDNA) concentrations have been observed in clinical conditions of systemic inflammation. While the beneficial effects of regular physical activity on the release of circulating cfDNA still remain unknown, acute intense exercise has been shown to increase inflammatory cytokines and cfDNA concentrations in normal-weight individuals. Therefore, the primary purpose of this study was to examine the effect of acute high-intensity interval Exercise (HIIE) on plasma cfDNA and interleukin-6 (IL-6) responses in obese and normal-weight subjects. MAIN METHODS: Fourteen male subjects (7 obese and 7 normal-weight) participated in an acute HIIE protocol (30 min, 4x4min @ 80% - 90% of VO2max) on a treadmill. Between HIIE intervals, subjects performed 3 min of active recovery at 50-60% VO2max. Blood samples were collected prior to, immediately following exercise, and one hour into recovery for measurements of plasma cfDNA and IL-6. KEY FINDINGS: Our results demonstrated a significant elevation in plasma cfDNA immediately following acute HIIE in both obese and normal-weight subjects. A comparable elevation in the concentration of plasma IL-6 was also found between two groups in response to acute HIIE. Furthermore, the level of plasma cfDNA was not correlated with IL-6 either at baseline or in response to acute HIIE. SIGNIFICANCE: These findings may support the utilization of HIIE as a time-efficient exercise protocol to understand the obesity-associated cfDNA and inflammatory responses.