Reduction In Oxidative Capacity Research Articles

Time-dependent reduction in oxidative capacity among cultured myotubes from spinal cord injured individuals.

Skeletal muscle adapts in reaction to contractile activity to efficiently utilize energy substrates, primarily glucose and free fatty acids (FA). Inactivity leads to atrophy and a change in energy utilization in individuals with spinal cord injury (SCI). The present study aimed to characterize possible inactivity-related differences in the energy metabolism between skeletal muscle cells cultured from satellite cells isolated 1- and 12-months post-SCI. To characterize inactivity-related disturbances in spinal cord injury, we studied skeletal muscle cells isolated from SCI subjects. Cell cultures were established from biopsy samples from musculus vastus lateralis from subjects with SCI 1 and 12 months after the injury. The myoblasts were proliferated and differentiated into myotubes before fatty acid and glucose metabolism were assessed and gene and protein expressions were measured. The results showed that glucose uptake was increased, while oleic acid oxidation was reduced at 12 months compared to 1 month. mRNA expressions of PPARGC1α, the master regulator of mitochondrial biogenesis, and MYH2, a determinant of muscle fiber type, were significantly reduced at 12 months. Proteomic analysis showed reduced expression of several mitochondrial proteins. In conclusion, skeletal muscle cells isolated from immobilized subjects 12 months compared to 1 month after SCI showed reduced fatty acid metabolism and reduced expression of mitochondrial proteins, indicating an increased loss of oxidative capacity with time after injury.

The role of purine nucleotide metabolism in cardiac failure

Normal cardiac function requires ATP to be synthesized at a sufficient rate to drive the molecular processes underlying electromechanical coupling. Myocardial metabolic dysfunction observed during heart failure leads to reductions in the chemical potential at which ATP is synthesized. We have observed reductions in oxidative capacity, and total adenine nucleotide (TAN) levels in a rat aortic constriction (TAC) induced heart failure model that parallel changes seen in large mammal models and humans with heart failure. Computer simulations of cardiac mechano-energetics also predict a marked increase in inorganic phosphate levels in diseased hearts compared to healthy control hearts. Furthermore, simulations predict that restoring the impaired energetic dysfunction of TAC rats improves systolic function. Metabolomic and proteomic analysis reveal increases in purine degradation by-products and AMP deaminase 3 (AMPD3) levels in failing versus control hearts. AMPD activity has been hypothesized to play a role in skeletal muscle in type 2 diabetes, however, there is still a need to decern the role, if any, of AMPD3 in the heart and in failure. A cardiac ventricle specific AMPD3 conditional knock out (cKO) rat model was developed to test the hypothesis that decreasing AMPD3 activity in the failing heart will lead to a preservation of TAN and improvement in cardiac mechanical function. Cardiac hypertrophy and decomposition were induced by placing a clip (TAC) in three-week old female and male rats. In the cKO model, AMPD3 exon 6 is flanked by loxP sites, and are either heterozygous for cre recombinase driven by the cardiac myosin light chain promoter (cre+/-) or lack the cre enzyme (cre-/-). Tamoxifen was administered to all rats both pre-surgery and post-surgery to induce AMPD3 knock down. Echocardiography was performed at 2- and 18-weeks post-surgery. At 18 weeks post-surgery, hearts were harvested for mitochondrial capacity, metabolite measurements, AMPD activity, and protein and mRNA measurements. Knock down efficiency in cre +/- animals compared to cre -/- was assessed based on enzyme activity, mRNA expression, and protein abundance. There is a 45% decrease in total AMPD activity in the AMPD3 cKO rats, where measured AMPD activity reflects the sum activity of all present AMPD isoforms. Additionally, there is 52% decrease in protein abundance and a 72% reduction in AMPD3 mRNA expression. Preliminary observations reveal significant differences in oxidative capacity and in cardiac function between TAC and sham rats, consistent with the hypothesis that knock down of AMDP3, an enzyme that is upregulated during TAC induced heart failure in rodents, results in preservation of myocardial nucleotide pools and improve cardiac mechanical function. Research is supported by the NIH grants HL144657 and F31-HL154605 (RL). We are grateful for support from the post-baccalaureate research program (2R25GM086262-09), the Systems and Integrative Biology (T32-GM008322) training grant and the Cardiovascular Research and Entrepreneurship training grant (T32-HL125242) and the University of Michigan Rackham Merit Fellowship. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Adult skeletal muscle peroxisome proliferator-activated receptor γ -related coactivator 1 is involved in maintaining mitochondrial content.

The peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1) family of transcriptional coactivators are regulators of mitochondrial oxidative capacity and content in skeletal muscle. Many of these conclusions are based primarily on gain-of-function studies using muscle-specific overexpression of PGC1s. We have previously reported that genetic deletion of both PGC-1α and PGC-1β in adult skeletal muscle resulted in a significant reduction in oxidative capacity with no effect on mitochondrial content. However, the contribution of PGC-1-related coactivator (PRC), the third PGC-1 family member, in regulating skeletal muscle mitochondria is unknown. Therefore, we generated an inducible skeletal muscle-specific PRC knockout mouse (iMS-PRC-KO) to assess the contribution of PRC in skeletal muscle mitochondrial function. We measured mRNA expression of electron transport chain (ETC) subunits as well as markers of mitochondrial content in the iMS-PRC-KO animals and observed an increase in ETC gene expression and mitochondrial content. Furthermore, the increase in ETC gene expression and mitochondrial content was associated with increased expression of PGC-1α and PGC-1β. We therefore generated an adult-inducible PGC-1 knockout mouse in which all PGC-1 family members are deleted (iMS-PGC-1TKO). The iMS-PGC-1TKO animals exhibited a reduction in ETC mRNA expression and mitochondrial content. These data suggest that in the absence of PRC alone, compensation occurs by increasing PGC-1α and PGC-1β to maintain mitochondrial content. Moreover, the removal of all three PGC-1s in skeletal muscle results in a reduction in both ETC mRNA expression and mitochondrial content. Taken together, these results suggest that PRC plays a role in maintaining baseline mitochondrial content in skeletal muscle.

Capillary rarefaction during bed rest is proportionally less than fibre atrophy and loss of oxidative capacity.

Muscle disuse from bed rest or spaceflight results in losses in muscle mass, strength and oxidative capacity. Capillary rarefaction may contribute to muscle atrophy and the reduction in oxidative capacity during bed rest. Artificial gravity may attenuate the negative effects of long-term space missions or bed rest. The aim of the present study was to assess (1) the effects of bed rest on muscle fibre size, fibre type composition, capillarization and oxidative capacity in the vastus lateralis and soleus muscles after 6 and 55days of bed rest and (2) the effectiveness of artificial gravity in mitigating bed-rest-induced detriments to these parameters. Nineteen participants were assigned to a control group (control, n=6) or an intervention group undergoing 30min of centrifugation (n=13). All underwent 55days of head-down tilt bed rest. Vastus lateralis and soleus biopsies were taken at baseline and after 6 and 55days of bed rest. Fibre type composition, fibre cross-sectional area, capillarization indices and oxidative capacity were determined. After just 6days of bed rest, fibre atrophy (-23.2±12.4%, P<0.001) and reductions in capillary-to-fibre ratio (C:F; 1.97±0.57 vs. 1.56±0.41, P<0.001) were proportional in both muscles as reflected by a maintained capillary density. Fibre atrophy proceeded at a much slower rate between 6 and 55days of bed rest (-11.6±12.1% of 6days, P=0.032) and was accompanied by a 19.1% reduction in succinate dehydrogenase stain optical density (P<0.001), without any further significant decrements in C:F (1.56±0.41 vs. 1.49±0.37, P=0.459). Consequently, after 55days of bed rest, the capillary supply-oxidative capacity ratio of a fibre had increased by 41.9% (P<0.001), indicating a capillarization in relative excess of oxidative capacity. Even though the heterogeneity of capillary spacing (LogR SD) was increased after 55days by 12.7% (P=0.004), tissue oxygenation at maximal oxygen consumption of the fibres was improved after 55days bed rest. Daily centrifugation failed to blunt the bed-rest-induced reductions in fibre size and oxidative capacity and capillary rarefaction. The relationship between fibre size and oxidative capacity with the capillary supply of a fibre is uncoupled during prolonged bed rest as reflected by a rapid loss of muscle mass and capillaries, followed at later stages by a more than proportional loss of mitochondria without further capillary loss. The resulting excessive capillary supply of the muscle after prolonged bed rest is advantageous for the delivery of substrates needed for subsequent muscle recovery.

AKT controls protein synthesis and oxidative metabolism via combined mTORC1 and FOXO1 signalling to govern muscle physiology.

BackgroundSkeletomuscular diseases result in significant muscle loss and decreased performance, paralleled by a loss in mitochondrial and oxidative capacity. Insulin and insulin‐like growth factor‐1 (IGF‐1) are two potent anabolic hormones that activate a host of signalling intermediates including the serine/threonine kinase AKT to influence skeletal muscle physiology. Defective AKT signalling is associated with muscle pathology, including cachexia, sarcopenia, and disuse; however, the mechanistic underpinnings remain unresolved.MethodsTo elucidate the role of AKT signalling in muscle mass and physiology, we generated both congenital and inducible mouse models of skeletal muscle‐specific AKT deficiency. To understand the downstream mechanisms mediating AKT's effects on muscle biology, we generated mice lacking AKT1/2 and FOXO1 (M‐AKTFOXO1TKO and M‐indAKTFOXO1TKO) to inhibit downstream FOXO1 signalling, AKT1/2 and TSC1 (M‐AKTTSCTKO and M‐indAKTTSCTKO) to activate mTORC1, and AKT1/2, FOXO1, and TSC1 (M‐QKO and M‐indQKO) to simultaneously activate mTORC1 and inhibit FOXO1 in AKT‐deficient skeletal muscle. Muscle proteostasis and physiology were assessed using multiple assays including metabolic labelling, mitochondrial function, fibre typing, ex vivo physiology, and exercise performance.ResultsHere, we show that genetic ablation of skeletal muscle AKT signalling resulted in decreased muscle mass and a loss of oxidative metabolism and muscle performance. Specifically, deletion of muscle AKT activity during development or in adult mice resulted in a significant reduction in muscle growth by 30–40% (P < 0.0001; n = 12–20) and 15% (P < 0.01 and P < 0.0001; n = 20–30), respectively. Interestingly, this reduction in muscle mass was primarily due to an ~40% reduction in protein synthesis in both M‐AKTDKO and M‐indAKTDKO muscles (P < 0.05 and P < 0.01; n = 12–20) without significant changes in proteolysis or autophagy. Moreover, a significant reduction in oxidative capacity was observed in both M‐AKTDKO (P < 0.05, P < 0.01 and P < 0.001; n = 5–12) and M‐indAKTDKO (P < 0.05 and P < 0.01; n = 4). Mechanistically, activation and inhibition of mTORC1/FOXO1, respectively, but neither alone, were sufficient to restore protein synthesis, muscle oxidative capacity, and muscle function in the absence of AKT in vivo. In a mouse model of disuse‐induced muscle loss, simultaneous activation of mTORC1 and inhibition of FOXO1 preserved muscle mass following immobilization (~5–10% reduction in casted M‐indFOXO1TSCDKO muscles vs. ~30–40% casted M‐indControl muscles, P < 0.05 and P < 0.0001; n = 8–16).ConclusionsCollectively, this study provides novel insights into the AKT‐dependent mechanisms that underlie muscle protein homeostasis, function, and metabolism in both normal physiology and disuse‐induced muscle wasting.

AMP deamination is sufficient to replicate an atrophy-like metabolic phenotype in skeletal muscle

BackgroundSkeletal muscle atrophy, whether caused by chronic disease, acute critical illness, disuse or aging, is characterized by tissue-specific decrease in oxidative capacity and broad alterations in metabolism that contribute to functional decline. However, the underlying mechanisms responsible for these metabolic changes are largely unknown. One of the most highly upregulated genes in atrophic muscle is AMP deaminase 3 (AMPD3: AMP → IMP + NH3), which controls the content of intracellular adenine nucleotides (AdN; ATP + ADP + AMP). Given the central role of AdN in signaling mitochondrial gene expression and directly regulating metabolism, we hypothesized that overexpressing AMPD3 in muscle cells would be sufficient to alter their metabolic phenotype similar to that of atrophic muscle. MethodsAMPD3 and GFP (control) were overexpressed in mouse tibialis anterior (TA) muscles via plasmid electroporation and in C2C12 myotubes using adenovirus vectors. TA muscles were excised one week later, and AdN were quantified by UPLC. In myotubes, targeted measures of AdN, AMPK/PGC-1α/mitochondrial protein synthesis rates, unbiased metabolomics, and transcriptomics by RNA sequencing were measured after 24 h of AMPD3 overexpression. Media metabolites were measured as an indicator of net metabolic flux. At 48 h, the AMPK/PGC-1α/mitochondrial protein synthesis rates, and myotube respiratory function/capacity were measured. ResultsTA muscles overexpressing AMPD3 had significantly less ATP than contralateral controls (−25%). In myotubes, increasing AMPD3 expression for 24 h was sufficient to significantly decrease ATP concentrations (−16%), increase IMP, and increase efflux of IMP catabolites into the culture media, without decreasing the ATP/ADP or ATP/AMP ratios. When myotubes were treated with dinitrophenol (mitochondrial uncoupler), AMPD3 overexpression blunted decreases in ATP/ADP and ATP/AMP ratios but exacerbated AdN degradation. As such, pAMPK/AMPK, pACC/ACC, and phosphorylation of AMPK substrates, were unchanged by AMPD3 at this timepoint. AMPD3 significantly altered 191 out of 639 detected intracellular metabolites, but only 30 transcripts, none of which encoded metabolic enzymes. The most altered metabolites were those within purine nucleotide, BCAA, glycolysis, and ceramide metabolic pathways. After 48 h, AMPD3 overexpression significantly reduced pAMPK/AMPK (−24%), phosphorylation of AMPK substrates (−14%), and PGC-1α protein (−22%). Moreover, AMPD3 significantly reduced myotube mitochondrial protein synthesis rates (−55%), basal ATP synthase-dependent (−13%), and maximal uncoupled oxygen consumption (−15%). ConclusionsIncreased expression of AMPD3 significantly decreased mitochondrial protein synthesis rates and broadly altered cellular metabolites in a manner similar to that of atrophic muscle. Importantly, the changes in metabolites occurred prior to reductions in AMPK signaling, gene expression, and mitochondrial protein synthesis, suggesting metabolism is not dependent on reductions in oxidative capacity, but may be consequence of increased AMP deamination. Therefore, AMP deamination in skeletal muscle may be a mechanism that alters the metabolic phenotype of skeletal muscle during atrophy and could be a target to improve muscle function during muscle wasting.

A necessary role of DNMT3A in endurance exercise by suppressing ALDH1L1-mediated oxidative stress.

Exercise can alter the skeletal muscle DNA methylome, yet little is known about the role of the DNA methylation machinery in exercise capacity. Here, we show that DNMT3A expression in oxidative red muscle increases greatly following a bout of endurance exercise. Muscle-specific Dnmt3a knockout mice have reduced tolerance to endurance exercise, accompanied by reduction in oxidative capacity and mitochondrial respiration. Moreover, Dnmt3a-deficient muscle overproduces reactive oxygen species (ROS), the major contributors to muscle dysfunction. Mechanistically, we show that DNMT3A suppresses the Aldh1l1 transcription by binding to its promoter region, altering its epigenetic profile. Forced expression of ALDH1L1 elevates NADPH levels, which results in overproduction of ROS by the action of NADPH oxidase complex, ultimately resulting in mitochondrial defects in myotubes. Thus, inhibition of ALDH1L1 pathway can rescue oxidative stress and mitochondrial dysfunction from Dnmt3a deficiency in myotubes. Finally, we show that in vivo knockdown of Aldh1l1 largely rescues exercise intolerance in Dnmt3a-deficient mice. Together, we establish that DNMT3A in skeletal muscle plays a pivotal role in endurance exercise by controlling intracellular oxidative stress.

229-LB: Plasma Lactate and Muscle Aerobic Substrate Oxidation: Does Elevated Lactate Precede Obesity?

Background: The incidence of metabolic diseases is rising and there is a dire need for early detection of risk in order to implement prevention. Fasting plasma lactate concentrations have been shown to be elevated in individuals with obesity and predictive of the development of T2D. An elevated lactate concentration is the product of a shift to glycolysis and a possible reduction in oxidative capacity. However, it is unknown if there are associations between lactate and oxidative capacity in healthy individuals that may predispose them to metabolic disease. Aim: The aim of this study was to determine if fasting lactate concentrations were linked with a reduction in skeletal muscle oxidative capacity in a young healthy population. Methods: Young (age 22 ± 0.5; N=30) lean (BMI (22.4 ± 0.4 kg/m2) women were screened for fasting plasma lactate. Subjects underwent assessments of body composition, aerobic capacity (VO2 peak), skeletal muscle oxidative capacity via near infrared spectroscopy (NIRS) and fasting glucose and insulin were measured for calculating HOMA-IR. Fatty acid oxidation rate was also determined in a subset of samples from skeletal muscle biopsies (vastus lateralis). Results: The women were insulin sensitive (HOMA-IR 1.1 ± 0.1) and had a mean fasting lactate of 0.9 ± 0.1 mmol/L. Time till exhaustion on the VO2 peak test was inversely associated with lactate (R2 = 0.20, p=0.05). Likewise, the rate of deoxygenated hemoglobin (NIRS) (R2 = 0.23, p=0.03) and skeletal muscle fatty acid oxidation (R2 = 0.72, p=0.004) were also inversely associated with fasting lactate. Lactate was inversely correlated with HDL:LDL (R2 = 0.57, p=0.02) and positively correlated with waist:hip (R2 = 0.52, p=0.02). Conclusion: Plasma lactate was inversely related to skeletal muscle oxidative capacity and with metabolic parameters that are risk factors for obesity and T2D. Fasting plasma lactate may thus be a biomarker for identifying healthy individuals at risk for metabolic diseases. Disclosure N.T. Broskey: None. T.E. Jones: None. Z. Yang: None. N. Khang: None. D. Zheng: None. C.J. Tanner: None. R.N. Cortright: None. J.A. Houmard: None. L. Dohm: None. Funding National Institutes of Health (DK56112, DK120296)

Mitochondrial and Nuclear DNA Oxidative Damage in Physiological and Pathological Aging.

Mitochondria play an important role in numerous processes, including energy generation, regulating ion homeostasis, and cell signaling. Mitochondria are also the main source of reactive oxygen species (ROS). Due to the oxidative environment within mitochondria, the macromolecules therein, for example, mtDNA, proteins, and lipids are more susceptible to sustaining damage. During aging, mitochondrial functions decline, partly as a result of an accumulation of mtDNA mutations, decreased mtDNA copy number and protein expression, and a reduction in oxidative capacity. The aim of this study was to summarize the knowledge on DNA oxidative damage in aging and age-related neurodegenerative diseases. It has been hypothesized that various ROS may play an important role not only in physiological senescence but also in the development of neurodegenerative diseases, for example, Alzheimer's disease and Parkinson's disease. Thus, mitochondria seem to be a potential target of novel treatments for neurodegenerative diseases.

Effects of clenbuterol administration on mitochondrial morphology and its regulatory proteins in rat skeletal muscle.

Clenbuterol induces a slow‐to‐fast fiber type transition in skeletal muscle. This muscle fiber transition decreased mitochondrial oxidative capacity and respiratory function. We hypothesized that the clenbuterol‐mediated reduction in oxidative capacity is associated with the alteration in mitochondrial morphology. To verify this hypothesis, we examined whether clenbuterol alters mitochondrial morphology and mitochondrial regulatory proteins in rat skeletal muscle. Clenbuterol was administered to rats via drinking water (30 mg/L) for 3 weeks. Myosin heavy chain (MHC) isoform composition, mitochondrial morphology, and fusion and fission regulatory protein levels in deep region and superficial region in tibialis anterior (TA) muscles were assessed. Clenbuterol induced the fiber type transition from slow to fast in both the regions of TA. The levels of optic atrophy protein 1, mitofusin 2, and mitochondrial fission 1, but not of dynamin‐related protein 1, significantly decreased in deep and superficial muscles after clenbuterol administration (P < 0.01). Also, observation using the transmission electron microscopy showed a decrease in mitochondrial volume (P < 0.05) and an increase in proportion of continuous or interacting mitochondria across Z‐lines (P < 0.05). We showed that clenbuterol administration induces a transition in the muscle fiber type composition toward fast phenotype and causes alterations in mitochondrial morphology with a concomitant decrease in mitochondrial fusion and fission regulatory protein levels. These mitochondrial morphological alterations may influence deleterious effects on skeletal muscle metabolism.

Morphological alterations of mouse skeletal muscles during early ageing are muscle specific.

One of the hallmarks of ageing is muscle wasting that may be preceded by morphological changes, such as capillary rarefaction. Muscle-specific changes in morphology in early ageing may differ between locomotor and respiratory muscles. To investigate this, we compared capillarization, fiber type composition, fiber cross-sectional area (FCSA) and oxidative capacity of individual fibers of the soleus (n = 6/5 for 20- and 79 weeks, respectively), extensor digitorum longus (EDL: n = 3/3) and diaphragm (n = 7/5) muscles in 20- (mature) and 79-week-old (early ageing) CD-1 female mice. There was no significant loss of soleus and EDL mass. The FCSA was larger and the capillary density lower at 79 than 20 weeks in the diaphragm, while in the EDL the opposite was found (both p ≤ 0.002) with no significant ageing-related differences in the soleus. The heterogeneity in capillary spacing, which may negatively impact on muscle oxygenation, was highest in muscles from 20-week-old mice, irrespective of muscle (p ≤ 0.011). Succinate dehydrogenase activity, indicative of oxidative capacity, and capillary to fiber ratio did not significantly change with age in any muscle. At all ages, the capillary supply to a fiber was positively related to FCSA in each muscle. We conclude that despite previously reported early age-related reductions in specific tension in both locomotor and respiratory muscles, morphological changes show a muscle-specific pattern in early ageing CD-1 mice. Specifically, early ageing was associated with 1) diaphragm hypertrophy 2) and fiber atrophy in the EDL that was not accompanied by angiogenesis, capillary rarefaction or reductions in oxidative capacity.

Connecting lysosomes and mitochondria \u2013 a novel role for lipid metabolism in cancer cell death

BackgroundThe understanding of lysosomes has been expanded in recent research way beyond their view as cellular trash can. Lysosomes are pivotal in regulating metabolism, endocytosis and autophagy and are implicated in cancer. Recently it was discovered that the lysosomal V-ATPase, which is known to induce apoptosis, interferes with lipid metabolism in cancer, yet the interplay between these organelles is poorly understood.MethodsLC-MS/MS analysis was performed to investigate lipid distribution in cells. Cell survival and signaling pathways were analyzed by means of cell biological methods (qPCR, Western Blot, flow cytometry, CellTiter-Blue). Mitochondrial structure was analyzed by confocal imaging and electron microscopy, their function was determined by flow cytometry and seahorse measurements.ResultsOur data reveal that interfering with lysosomal function changes composition and subcellular localization of triacylglycerids accompanied by an upregulation of PGC1α and PPARα expression, master regulators of energy and lipid metabolism. Furthermore, cardiolipin content is reduced driving mitochondria into fission, accompanied by a loss of membrane potential and reduction in oxidative capacity, which leads to a deregulation in cellular ROS and induction of mitochondria-driven apoptosis. Additionally, cells undergo a metabolic shift to glutamine dependency, correlated with the fission phenotype and sensitivity to lysosomal inhibition, most prominent in Ras mutated cells.ConclusionThis study sheds mechanistic light on a largely uninvestigated triangle between lysosomes, lipid metabolism and mitochondrial function. Insight into this organelle crosstalk increases our understanding of mitochondria-driven cell death. Our findings furthermore provide a first hint on a connection of Ras pathway mutations and sensitivity towards lysosomal inhibitors.Graphical

Lower Stearoyl-CoA Desaturase and Hormone Sensitive Lipase Gene Expression in Superficial Subcutaneous Adipose Tissue of Male, but Not Female, Patients with Type 2 Diabetes

Mitochondrial gene expression in visceral (VAT) and lipogenesis in abdominal subcutaneous adipose tissue (SAT) are lower in insulin resistance (IR). Humans with hormone sensitive lipase (HSL) gene mutations are prone to type 2 diabetes (T2D). SAT is divided into deep (DSAT) and superficial SAT (SSAT). SSAT was speculated to be protective in T2D, but gender specificity is unknown. We hypothesized lower mitochondrial efficiency as well as lower markers of lipogenesis and lipolysis in SSAT only in male T2D patients vs. glucose-tolerant humans (CON), which may characterize dysfunctional SSAT. In 20 T2D and 20 CON matched for sex, BMI and age (female/male: 6/14 per group; 32±1 vs. 31±1 kg/m2, 52±2 vs. 54±2 years), we assessed M-values by euglycemic-hyperinsulinemic clamps, liver fat content (HCL) and VAT by MRS. In biopsies of SSAT, mitochondrial oxidative capacity was measured by respirometry, lipogenesis assessed from stearoyl-CoA desaturase (SCD) mRNA, lipolysis from adipocyte triglyceride lipase (ATGL) and HSL mRNA by RTqPCR. The insulin resistant T2D had 63% and 22% higher HCL (p&amp;lt;0.01) and VAT (p&amp;lt;0.05) than CON. In SSAT, T2D featured 20%, 50%, 70%, 49% reductions in oxidative capacity, SCD, ATGL and HSL mRNA (all p&amp;lt;0.05). Gender segregated analyzes showed higher oxidative capacity only in females, whereas only ATGL was also lower in female T2D vs. CON. In T2D, VAT was 22% lower (p&amp;lt;0.01) and HSL mRNA 70% higher (both p&amp;lt;0.001) in female than in male participants. In conclusion, lower lipogenesis and lipolysis in SSAT of male T2D patients may lead to inadequate lipid storage in SSAT, thereby promoting ectopic fat storage as HCL and VAT. Disclosure K. Bódis: None. J. Lundbom: None. T. Jelenik: None. D.F. Markgraf: None. A. Strom: None. O.P. Zaharia: None. Y. Karusheva: None. V. Burkart: None. K. Müssig: None. Y. Kupriyanova: None. M. Ouni: None. J. Hwang: None. D. Ziegler: None. A. Schuermann: None. M. Roden: Speaker's Bureau; Self; Boehringer Ingelheim GmbH. Research Support; Self; Boehringer Ingelheim GmbH. Consultant; Self; Poxel SA. Research Support; Self; Danone Nutricia Early Life Nutrition, GlaxoSmithKline plc., Nutricia Advanced Medical Nutrition, Sanofi. J. Szendroedi: None.

Cancer-induced cardiac cachexia: Pathogenesis and impact of physical activity

Cachexia is a wasting syndrome observed in many patients suffering from several chronic diseases including cancer. In addition to the progressive loss of skeletal muscle mass, cancer cachexia results in cardiac function impairment. During the severe stage of the disease, patients as well as animals bearing cancer cells display cardiac atrophy. Cardiac energy metabolism is also impeded with disruption of mitochondrial homeostasis and reduced oxidative capacity, although the available data remain equivocal. The release of inflammatory cytokines by tumor is a key mechanism in the initiation of heart failure. Oxidative stress, which results from the combination of chemotherapy, inadequate antioxidant consumption and chronic inflammation, will further foster heart failure. Protein catabolism is due to the concomitant activation of proteolytic systems and inhibition of protein synthesis, both processes being triggered by the deactivation of the Akt/mammalian target of rapamycin pathway. The reduction in oxidative capacity involves AMP-activated protein kinase and peroxisome proliferator-activated receptor gamma coactivator1α dysregulation. The nuclear factor-κB transcription factor plays a prominent role in the coordination of these alterations. Physical exercise appears as an interesting non-pharmaceutical way to counteract cancer cachexia-induced-heart failure. Indeed, aerobic training has anti-inflammatory effects, increases anti-oxidant defenses, prevents atrophy and promotes oxidative metabolism. The present review points out the importance of better understanding the concurrent structural and metabolic changes within the myocardium during cancer and the protective effects of exercise against cardiac cachexia.

Abstract P007: Association of Plasma Lactate with Incident Atrial Fibrillation in the ARIC Study

Introduction: Atrial fibrillation (AF) is the most common cardiac arrhythmia, affecting up to six million persons in the United States. The mechanism underlying AF has been extensively investigated in recent years. Reduction in oxidative capacity has been described as a contributor to several aging-related diseases including hypertension and diabetes mellitus. In vitro studies of atrial myocardium have described mitochondrial dysfunction related to reduced oxidative capacity in patients with AF. We sought to evaluate the association of plasma lactate, a marker of impaired oxidative capacity, with incident AF in a large population-based cohort. Methods: The Atherosclerotic Risk in Communities (ARIC) study has followed 15,792 men and women from 4 US communities since 1987. We identified 11,191 participants at the 4 th visit (1996-1998) without prevalent AF for whom plasma lactate levels were available. Incident AF was identified using hospital discharge codes and death certificates. The association of plasma lactate with incident AF was evaluated using Cox proportional hazards models. Results: During a mean follow-up of 13.1 years, there were 1498 cases of incident AF. In unadjusted analysis, there was a statistically significant difference in incident AF when comparing plasma lactate by quartiles and continuously (Model 1). This association remained significant in adjusted models including age, gender, race, body-mass index, smoking, alcohol use, history of cardiovascular disease, aspirin use, statin use, total cholesterol, and glomerular filtration rate (Models 2 and 3). When adjusting for diabetes or hypertension alone, potential mediators to which reduced oxidative capacity may contribute, this association was strongly attenuated (HR per standard deviation of log(lactate) 1.04, 95% CI: 0.99, 1.10 and 1.04, 95% CI: 0.99, 1.09 respectively). Conclusion: Plasma lactate is independently associated with incident AF, and its contribution to AF may be, at least in part, mediated by diabetes and/or hypertension.

Maternal Creatine Supplementation during Pregnancy Prevents Long-Term Changes in Diaphragm Muscle Structure and Function after Birth Asphyxia.

Using a model of birth asphyxia, we previously reported significant structural and functional deficits in the diaphragm muscle in spiny mice, deficits that are prevented by supplementing the maternal diet with 5% creatine from mid-pregnancy. The long-term effects of this exposure are unknown. Pregnant spiny mice were fed control or 5% creatine-supplemented diet for the second half of pregnancy, and fetuses were delivered by caesarean section with or without 7.5 min of in-utero asphyxia. Surviving pups were raised by a cross-foster dam until 33±2 days of age when they were euthanized to obtain the diaphragm muscle for ex-vivo study of twitch tension and muscle fatigue, and for structural and enzymatic analyses. Functional analysis of the diaphragm revealed no differences in single twitch contractile parameters between any groups. However, muscle fatigue, induced by stimulation of diaphragm strips with a train of pulses (330ms train/sec, 40Hz) for 300sec, was significantly greater for asphyxia pups compared with controls (p<0.05), and this did not occur in diaphragms of creatine + asphyxia pups. Birth asphyxia resulted in a significant increase in the proportion of glycolytic, fast-twitch fibres and a reduction in oxidative capacity of Type I and IIb fibres in male offspring, as well as reduced cross-sectional area of all muscle fibre types (Type I, IIa, IIb/d) in both males and females at 33 days of age. None of these changes were observed in creatine + asphyxia animals. Thus, the changes in diaphragm fatigue and structure induced by birth asphyxia persist long-term but are prevented by maternal creatine supplementation.

Single-Blind, Randomized, Controlled Clinical Trial of Exercise in Ambulatory Spinal Muscular Atrophy: Why are the Results Negative?

Background:The benefits of exercise on long-term health and well-being are well established. The possible benefits of exercise in Spinal Muscular Atrophy (SMA) have not been explored in a controlled clinical trial format.Objective:To assess the effects of exercise on measures of function, strength, and exercise capacity in ambulatory SMA patients.Methods:Fourteen participants, ages 10–48 years, were randomized to control and exercise cohorts after a 1 month lead-in period. The exercise group received 6 months of intervention. Thereafter, both groups received the intervention for the remaining 12 months. Participants were monitored for a total of 19 months. Exercise included individualized home-based cycling and strengthening. The primary outcome measure was distance walked during the six-minute walk test (6MWT). Secondary outcomes included strength, function, exercise capacity, quality of life and fatigue.Results:Twelve participants completed the first 7 months of the study, and 9 completed all 19 months. At baseline, the groups were similar on all clinical variables. There were no group changes at any time point in the 6MWT, fatigue, or function. Percent-predicted VO2 max improved 4.9% in all participants in 6 months (p = 0.036) (n = 10).Conclusion:Daily exercise is safe in ambulatory SMA and should be encouraged. We did not uncover any deleterious effects on strength, function, or fatigue. Our study documented a reduction in oxidative capacity and a blunted conditioning response to exercise possibly representing an important insight into underlying pathophysiological mechanisms. These findings also may be linked causally to mitochondrial depletion in SMA and warrant further study.

Daily heat stress treatment rescues denervation-activated mitochondrial clearance and atrophy in skeletal muscle.

Traumatic nerve injury or nerve disease leads to denervation and severe muscle atrophy. Recent evidence shows that mitochondrial loss could be a key mediator of skeletal muscle atrophy. Here, we show that daily heat stress treatment rescues denervation-induced loss of mitochondria and concomitant muscle atrophy. We also found that denervation-activated autophagy-dependent mitochondrial clearance (mitophagy) was suppressed by daily heat stress treatment. The molecular basis of this observation is explained by our results showing that heat stress treatment attenuates the increase of key proteins that regulate the tagging step for mitochondrial clearance and the intermediate step of autophagosome formation in denervated muscle. These findings contribute to the better understanding of mitochondrial quality control in denervated muscle from a translational perspective and provide a mechanism behind the attenuation of muscle wasting by heat stress. Traumatic nerve injury or motor neuron disease leads to denervation and severe muscle atrophy. Recent evidence indicates that loss of mitochondria and the related reduction in oxidative capacity could be key mediators of skeletal muscle atrophy. As our previous study showed that heat stress increased the numbers of mitochondria in skeletal muscle, we evaluated whether heat stress treatment could have a beneficial impact on denervation-induced loss of mitochondria and subsequent muscle atrophy. Here, we report that daily heat stress treatment (mice placed in a chamber with a hot environment; 40°C, 30minday(-1) , for 7days) rescues the following parameters: (i)muscle atrophy (decreased gastrocnemius muscle mass); (ii)loss of mitochondrial content (decreased levels of ubiquinol-cytochrome c reductase core proteinII, cytochrome c oxidase subunitsI and IV and voltage-dependent anion channel protein); and (iii)reduction in oxidative capacity (reduced maximal activities of citrate synthase and 3-hydroxyacyl-CoA dehydrogenase) in denervated muscle (produced by unilateral sciatic nerve transection). In order to gain a better understanding of the above mitochondrial adaptations, we also examined the effects of heat stress on autophagy-dependent mitochondrial clearance (mitophagy). Daily heat stress normalized denervation-activated induction of mitophagy (increased mitochondrial microtubule-associated protein 1A/1B-light chain3-II (LC3-II) with and without blocker of autophagosome clearance). The molecular basis of this observation was explained by the results that heat stress attenuated the denervation-induced increase in key proteins that regulate the following steps: (i)the tagging step of mitochondrial clearance (increased mitochondrial Parkin, ubiquitin-conjugated, P62/sequestosome 1 (P62/SQSTM1)); and (ii)the elongation step of autophagosome formation (increased Atg5-Atg12 conjugate and Atg16L). Overall, our results contribute to the better understanding of mitochondrial quality control and the mechanisms behind the attenuation of muscle wasting by heat stress in denervated skeletal muscle.

Chronic Binge Alcohol (CBA) Decreases Skeletal Muscle Oxidative Capacity in Simian Immunodeficiency Virus (SIV)‐Infected Macaques

Chronic HIV infection is associated with insulin resistance and increased lipodystrophy. Skeletal muscle (SKM) represents a major site for glucose and lipid oxidation. Acute and chronic alcohol exposure inhibits skeletal muscle glucose metabolism and potentially promotes insulin resistance. We sought to determine the effects of daily CBA or isocaloric sucrose (SUC) administration to male SIV-infected rhesus macaques on SKM muscle fiber type and oxidative capacity. SKM samples (quadriceps) were collected at necropsy after 11 months of SIV infection from CBA/SIV (n=5) or SUC/SIV (n=3) macaques. Serial cross sections (10 μm) were stained for myosin ATPase to determine fiber type population and succinate dehydrogenase (SDH) to measure oxidative capacity. Both SUC/SIV and CBA/SIV animals had decreased (33.2 and 28.2%) number of type 1 (oxidative) fibers and a larger proportion of type 2b (glycolytic) fibers compared to naïve uninfected animals (42%) (n=2). SDH activity, measured by optical density, was significantly lower in the type 1 fibers of both SUC/SIV (OD=87.8) and CBA/SIV (OD=90.7) when compared to controls (OD=120.7). Analysis of SDH activity across all muscle fibers demonstrated a significant reduction in total oxidative capacity in CBA/SIV (OD=146.6) compared to naïve (OD=268.3) and SUC/SIV (OD=195.4) groups. These results demonstrate a reduction in the oxidative capacity of SKM fibers in SIV-infected animals that is further exacerbated by CBA. This research was supported by grants AA07577, AA09803 and AA11290 from the NIAAA/NIH

Muscle dysfunction in COPD

Although it has been well characterized that COPD muscle dysfunction is the result of the complex interaction between systemic and local factors, the etiology of muscle dysfunction remains to be fully identified. Interestingly, while hyperinflation and an increased work of breathing appear to be the main contributing events to respiratory muscle dysfunction, deconditioning seems to play a major role in the dysfunction of peripheral muscles in COPD. Other factors such as cigarette smoke, nutritional abnormalities, exacerbations, drugs, hypoxia, hypercapnia, comorbidities, and physical activity also influence muscle mass and function in COPD patients (1-3; 5; 9; 15). Besides, derangements of key molecular and cellular processes such as redox imbalance, mitochondrial dysfunction, enhanced protein catabolism and reduced protein anabolism, structural alterations, and systemic inflammation also modify muscle phenotype and function in COPD patients.