Chronic obstructive pulmonary disease (COPD) is largely caused by smoking, and patient limb muscle exhibits a fast fibre shift and atrophy. We show that this fast fibre shift is associated with type grouping, suggesting recurring cycles of denervation–reinnervation underlie the type shift. Compared to patients with normal fat‐free mass index (FFMI), patients with low FFMI exhibited an exacerbated fibre type shift, marked accumulation of very small persistently denervated muscle fibres, and a blunted denervation‐responsive transcript profile, suggesting failed denervation precipitates muscle atrophy in patients with low FFMI. Sixteen weeks of passive tobacco smoke exposure in mice caused neuromuscular junction degeneration, consistent with a key role for smoke exposure in initiating denervation in COPD.

Eccentric ergometer training (EET) is increasingly being proposed as a therapeutic strategy to improve skeletal muscle strength in various cardiorespiratory diseases, due to the principle that lengthening muscle actions lead to high force-generating capacity at low cardiopulmonary load. One clinical population that may particularly benefit from this strategy is chronic obstructive pulmonary disease (COPD), as ventilatory constraints and locomotor muscle dysfunction often limit efficacy of conventional exercise rehabilitation in patients with severe disease. While the feasibility of EET for COPD has been established, the nature and extent of adaptation within COPD muscle is unknown. The aim of this study was therefore to characterize the locomotor muscle adaptations to EET in patients with severe COPD, and compare them with adaptations gained through conventional concentric ergometer training (CET). Male patients were randomized to either EET (n = 8) or CET (n = 7) for 10 weeks and matched for heart rate intensity. EET patients trained on average at a workload that was three times that of CET, at a lower perception of leg fatigue and dyspnea. EET led to increases in isometric peak strength and relative thigh mass (p < 0.01) whereas CET had no such effect. However, EET did not result in fiber hypertrophy, as morphometric analysis of muscle biopsies showed no increase in mean fiber cross-sectional area (p = 0.82), with variability in the direction and magnitude of fiber-type responses (20% increase in Type 1, p = 0.18; 4% decrease in Type 2a, p = 0.37) compared to CET (26% increase in Type 1, p = 0.04; 15% increase in Type 2a, p = 0.09). EET had no impact on mitochondrial adaptation, as revealed by lack of change in markers of mitochondrial biogenesis, content and respiration, which contrasted to improvements (p < 0.05) within CET muscle. While future study is needed to more definitively determine the effects of EET on fiber hypertrophy and associated underlying molecular signaling pathways in COPD locomotor muscle, our findings promote the implementation of this strategy to improve muscle strength. Furthermore, contrasting mitochondrial adaptations suggest evaluation of a sequential paradigm of eccentric followed by concentric cycling as a means of augmenting the training response and attenuating skeletal muscle dysfunction in patients with advanced COPD.

Key points Mitochondria are frequently implicated in the ageing of skeletal muscle, although the role of denervation in modulating mitochondrial function in ageing muscle is unknown. We show that increased sensitivity to apoptosis initiation occurs prior to evidence of persistent denervation and is thus a primary mitochondrial defect in ageing muscle worthy of therapeutic targeting. However, at more advanced age, mitochondrial function changes are markedly impacted by persistent sporadic myofibre denervation, suggesting the mitochondrion may be a less viable therapeutic target. Abstract Experimental denervation modulates mitochondrial function, where changes in both reactive oxygen species (ROS) and sensitivity to permeability transition are implicated in the resultant muscle atrophy. Notably, although denervation occurs sporadically in ageing muscle, its impact on ageing muscle mitochondria is unknown. Because this information has important therapeutic implications concerning targeting the mitochondrion in ageing muscle, we examined mitochondrial function in skeletal muscle from four groups of humans, comprising two active (mean ± SD age: 23.7 ± 2.7 years and 71.2 ± 4.9 years) and two inactive groups (64.8 ± 3.1 years and 82.5 ± 4.8 years), and compared this with a murine model of sporadic denervation. We tested the hypothesis that, although some alterations of mitochondrial function in aged muscle are attributable to a primary organelle defect, mitochondrial dysfunction would be impacted by persistent denervation in advanced age. Both ageing in humans and sporadic denervation in mice increased mitochondrial sensitivity to permeability transition (humans, P = 0.004; mice, P = 0.01). To determine the contribution of sporadic denervation to mitochondrial function, we pharmacologically inhibited the denervation‐induced ROS response. This reduced ROS emission by 60% ( P = 0.02) in sporadically denervated mouse muscle, which is similar to that seen in humans older than 75 years (–66%, P = 0.02) but not those younger than 75 years. We conclude that an increased sensitivity to permeability transition is a primary mitochondrial defect in ageing muscle. However, at more advanced age, when muscle atrophy becomes more clinically severe, mitochondrial function changes are markedly impacted by persistent sporadic denervation, making the mitochondrion a less viable therapeutic target.

Low mitochondrial content and oxidative capacity are well-established features of locomotor muscle dysfunction, a prevalent and debilitating systemic occurrence in patients with chronic obstructive pulmonary disease (COPD). Although the exact cause is not firmly established, physical inactivity and oxidative stress are among the proposed underlying mechanisms. Here, we assess the impact of COPD pathophysiology on mitochondrial DNA (mtDNA) integrity, biogenesis, and cellular oxidative capacity in locomotor muscle of COPD patients and healthy controls. We hypothesized that the high oxidative stress environment of COPD muscle would yield a higher presence of deletion-containing mtDNA and oxidative-deficient fibers and impaired capacity for mitochondrial biogenesis.

The multifactorial functional limitation of COPD increasingly demonstrates the need for an integrated circulatory assessment. In this study cardiac output (Qc) derived from non-inert (CO2-RB), inert (N2O-RB) gas rebreathing approaches and bioimpedance were compared to examine the limitations of currently available non-invasive techniques for exercise Qc determination in patients with chronic lung disease. Thirteen COPD patients (GOLD II-III) completed three constant cycling bouts at 20, 35, and 50% of peak work on two occasions to assess Qc with bioimpedance as well as using CO2-RB and N2O-RB for all exercise tests. Results showed significantly lower Qc using the N2O-RB or end-tidal CO2-derived Qc compared to the PaCO2-derived CO2-RB or the bioimpedance at rest and for all exercise intensities. End-tidal CO2-derived values are however not statistically different from those obtained using inert-gas rebreathing. This study show that in COPD patients, CO2-rebreathing Qc values obtained using PaCO2 contents which account for any gas exchange impairment or inadequate gas mixing are similar to those obtained using thoracic bioimpedance. Alternately, the lower values for N2O rebreathing derived Qc indicates the inability of this technique to account for gas exchange impairment in the computation of Qc. These findings indicate that the choice of a gas rebreathing technique to measure Qc in patients must be dictated by the ability to include in the derived computations a correction for either gas exchange inadequacies and/or a vascular shunt.

Altered mitochondrial function has been implicated in aging muscle atrophy. If this is a primary effect or secondary to sporadic denervation that occurs in aging is unclear. To address this question we examined four groups of human males: young active (YA, 24 yrs), old active (OA, 71yrs), old inactive (OI, 65 yrs) and very old inactive (VOI, 83yrs). We demonstrated that activity and age modified mitochondrial function in myofibres (respiration coupling YA 4.0±0.2 vs OA 3.3±0.2 vs OI 2.9±0.2 vs VOI 2.5±0.1 & calcium retention capacity YA 0.9±0.2 vs OA 0.4±0.1 vs OI 0.3 ±0.01 vs VOI 0.3 ±0.1). To better isolate the impact of denervation on mitochondrial function we used a model of sporadic denervation (sarco mice who have unstable neuromuscular junctions) and a pharmacological approach (arachidonyl trifluoromethyl ketone (AACOCF3)) to block the denervation-induced mitochondrial ROS (mtROS) signal. Sarco mice treated with AACOCF3 had significantly reduced mtROS emissions compared to vehicle treated myofibers (vehicle, 0.11±0.03 vs. AACOCF3, 0.05±0.03) but not wild type mice, demonstrating that denervation modulates mtROS. In humans, AACOCF3 reduced mtROS in the over 75s (vehicle, 0.7±0.1 vs. AACOCF3, 0.2±0.1) but not in younger subjects. We conclude that while some alterations in mitochondrial function are age related, others are in part, secondary to accumulation of denervated myofibres. This has implications for therapeutic targeting of mitochondria to ameliorate aging muscle atrophy. CIHR MOP119583 & 125986

ABSTRACTIntroduction: The effect of eccentric (ECC) versus concentric (CON) training on metabolic properties in skeletal muscle is understood poorly. We determined the responses in oxidative capacity and mitochondrial H2O2 production after eccentric (ECC) versus concentric (CON) training performed at similar mechanical power. Methods: Forty‐eight rats performed 5‐ or 20‐day eccentric (ECC) or concentric (CON) training programs. Mitochondrial respiration, H2O2 production, citrate synthase activity (CS), and skeletal muscle damage were assessed in gastrocnemius (GAS), soleus (SOL) and vastus intermedius (VI) muscles. Results: Maximal mitochondrial respiration improved only after 20 days of concentric (CON) training in GAS and SOL. H2O2 production increased specifically after 20 days of eccentric ECC training in VI. Skeletal muscle damage occurred transiently in VI after 5 days of ECC training. Conclusions: Twenty days of ECC versus CON training performed at similar mechanical power output do not increase skeletal muscle oxidative capacities, but it elevates mitochondrial H2O2 production in VI, presumably linked to transient muscle damage. Muscle Nerve 50: 803–811, 2014

Although prior studies have examined mitochondrial function in COPD muscle, none have compared cachectic versus non-cachectic patients, nor have they compared patients with type II shift versus those who are not shifted. Since mitochondrial dysfunction is thought to contribute to muscle atrophy in COPD, we hypothesized that mitochondrial alterations would be greater in cachectic patients. Similarly, we hypothesized that an impaired muscle oxidative capacity, an increase in mitochondrial ROS emission and an insensitivity to permeability transition would be greater in COPD patients with a shift towards greater type II fiber abundance. Strikingly, our results show that although there is a greater reduction in mitochondrial oxidative capacity in cachectic patients, both ROS emission and sensitivity to permeability transition are similar in cachectic versus non-cachectic patients. In regard to our second hypothesis, whereas there were no differences in oxidative capacity or ROS emission between COPD patients with type II fiber shift, a lower sensitivity to permeability transition was seen in COPD patients with a type II fiber shift. As such, our analysis reveals that fiber type shift per se is unlikely to account for the lower muscle oxidative capacity and increase in mitochondrial ROS emission seen in COPD muscle, but could explain the lower sensitivity to permeability transition. Overall, our results suggest that mitochondrial involvement in COPD is primarily to reduce oxidative capacity of COPD muscle, but as some changes are dissociated from a fiber type shift, these changes may constitute dysfunction even if they are not contributing to development of cachexia.

Rationale: Locomotor muscle atrophy develops in patients with chronic obstructive pulmonary disease (COPD) partly because of increased protein degradation by the ubiquitin-proteasome system. It is not known if autophagy also contributes to protein degradation.Objectives: To investigate whether autophagy is enhanced in locomotor muscles of stable patients with COPD, to quantify autophagy-related gene expression in these muscles, and to identify mechanisms of autophagy induction.Methods: Muscle biopsies were obtained from two cohorts of control subjects and patients with COPD and the numbers of autophagosomes in the vastus lateralis and tibialis anterior muscles, the levels of LC3B protein lipidation, and the expression of autophagy-related genes were measured in the vastus lateralis muscle. To investigate potential pathways that might induce the activation of autophagy, measures were taken of protein kinase B (AKT), mTORC1, and AMPK pathway activation, transcription factor regulation, proteasome activation, and oxidative stress.Measurements and Main Results: Autophagy is enhanced in the locomotor muscles of patients with COPD as shown by significantly higher numbers of autophagosomes in affected muscles as compared with control subjects. Autophagosome number inversely correlates with FEV1. In the vastus lateralis, LC3B protein lipidation is increased by COPD and the expression of autophagy-related gene expressions is up-regulated. LC3B lipidation inversely correlates with thigh cross-sectional area, FEV1, and FEV1/FVC ratio. Enhanced autophagy is associated with activation of the AMPK pathway and FOXO transcription factors, inhibition of the mTORC1 and AKT pathways, and the development of oxidative stress.Conclusions: Autophagy is significantly enhanced in locomotor muscles of stable patients with COPD. The degree of autophagy correlates with severity of muscle atrophy and lung function impairment.

Mitochondrial dysfunction is implicated in skeletal muscle atrophy and dysfunction with aging, with strong support for an increased mitochondrial‐mediated apoptosis in sedentary rodent models. Whether this applies to aged human muscle is unknown, nor is it clear whether these changes are caused by sedentary behavior. Thus, we examined mitochondrial function [respiration, reactive oxygen species (ROS) emission, and calcium retention capacity (CRC)] in permeabilized myofibers obtained from vastus lateralis muscle biopsies of healthy physically active young (23.7±2.7 yr; mean±sd) and older (71.2±4.9 yr) men. Although mitochondrial ROS and maximal respiratory capacity were unaffected, the acceptor control ratio was reduced by 18% with aging, suggesting mild uncoupling of oxidative phosphorylation. CRC was reduced by 50% with aging, indicating sensitization of the mitochondrial permeability transition pore (mPTP) to apoptosis. Consistent with the mPTP sensitization, older muscles showed a 3‐fold greater fraction of endonuclease G (a mitochondrial proapoptotic factor)‐positive myonuclei. Aged muscles also had lower mitophagic potential, based on a 43% reduction in Parkin to the voltage‐dependent anion channel (VDAC) protein ratio. Collectively, these results show that mitochondrial‐mediated apoptotic signaling is increased in older human muscle and suggest that accumulation of dysfunctional mitochondria with exaggerated apoptotic sensitivity is due to impaired mitophagy.—Gouspillou, G., Sgarioto, N., Kapchinsky, S., Purves‐Smith, F., Norris, B., Pion, C. H., Barbat‐Artigas, S., Lemieux, R, Taivassalo, T., Morais, J. A., Aubertin‐Leheudre, M., Hepple, R. T. Increased sensitivity to mitochondrial permeability transition and myonuclear translocation of endonuclease G in atrophied muscle of physically active older humans. FASEB J. 28, 28–1621 (1633). www.fasebj.org

In healthy subjects, the metabolic cost of negative work (eccentric exercise, ECC) is much less than that of positive work (concentric exercise, CON) at the same absolute power output. However, whether this reduction in metabolic and ventilatory requirements persists in COPD patients, particularly at higher exercise intensities, has not been evaluated. Therefore, we assessed the metabolic and ventilatory responses of severe COPD patients while exercising at the same absolute workrate and at symptom-limited peak power during ECC and CON incremental cycling.

Since in eccentric exercise greater force is produced at a reduced oxygen cost, this modality of exercise could be attractive for pulmonary rehabilitation of severe COPD patients. Objective: To estimate the extent to which eccentric compared to concentric exercise training produces greater increases in quadriceps force, and leads to better improvements in hamstring force, exercise capacity and physical activity. Methods: Pilot randomized clinical trial in which COPD patients were randomly assigned to either a concentric(CON) or eccentric(ECC) cycling protocol, 3 sessions/week for 10 weeks. In the CON group, target training intensity was set as 80% of peak work rate (Wmax) while in the ECC group the target intensity was set as 4-times 80% of baseline Wmax. Lung function, muscle strength(Biodex), maximal work capacity(Wmax) and physical activity(Armband) were assessed. Results: Preliminary analysis included 11 male COPD patients(69±6 years; FEV1:41±10%pred; BMI: 27±6 Kg.m-2). After 10 weeks of training, isometric quadriceps force was 14%(20Nm)[95%CI: 2-26%,p=0.03] and concentric hamstring force was 27%(14Nm)[95%CI:2-50%,p=0.03] higher in the ECC. A trend for greater improvements in concentric quadriceps force was observed only in the ECC group (ECC=16% of change, p=0.06 vs CON=1%,p=0.6). Both ECC and CON training yielded similar improvements in Wmax (ECC 18%,p=0.01 vs CON 16%; p= 0.03). Steps/day remained unchanged (p>.05) in both groups. Conclusion: Preliminary results show a trend for greater improvements in quadriceps muscle force with ECC compared to CON training in severe COPD patients. Funding:McGill Health Centre Research Institute/pilot project and Edith Strauss.