Reduced Expression of the Sarcoplasmic Calcium Pump SERCA2 in Skeletal Muscle From Patients With Chronic Obstructive Pulmonary Disease and Low Body Weight

Pathophysiology of muscle dysfunction in COPD

Muscle dysfunction often occurs in patients with chronic obstructive pulmonary disease (COPD) and may involve both respiratory and locomotor (peripheral) muscles. The loss of strength and/or endurance in the former can lead to ventilatory insufficiency, whereas in the latter it limits exercise capacity and activities of daily life. Muscle dysfunction is the consequence of complex interactions between local and systemic factors, frequently coexisting in COPD patients. Pulmonary hyperinflation along with the increase in work of breathing that occur in COPD appear as the main contributing factors to respiratory muscle dysfunction. By contrast, deconditioning seems to play a key role in peripheral muscle dysfunction. However, additional systemic factors, including tobacco smoking, systemic inflammation, exercise, exacerbations, nutritional and gas exchange abnormalities, anabolic insufficiency, comorbidities and drugs, can also influence the function of both respiratory and peripheral muscles, by inducing modifications in their local microenvironment. Under all these circumstances, protein metabolism imbalance, oxidative stress, inflammatory events, as well as muscle injury may occur, determining the final structure and modulating the function of different muscle groups. Respiratory muscles show signs of injury as well as an increase in several elements involved in aerobic metabolism (proportion of type I fibers, capillary density, and aerobic enzyme activity) whereas limb muscles exhibit a loss of the same elements, injury, and a reduction in fiber size. In the present review we examine the current state of the art of the pathophysiology of muscle dysfunction in COPD.

Intrinsic skeletal muscle alterations in chronic heart failure patients: a disease-specific myopathy or a result of deconditioning?

Chronic heart failure (CHF) patients frequently experience impaired exercise tolerance due to skeletal muscle fatigue. Studies suggest that this in part is due to intrinsic alterations in skeletal muscle of CHF patients, often interpreted as a disease-specific myopathy. Knowledge about the mechanisms underlying these skeletal muscle alterations is of importance for the pathophysiological understanding of CHF, therapeutic approach and rehabilitation strategies. We here critically review the evidence for skeletal muscle alterations in CHF, the underlying mechanisms of such alterations and how skeletal muscle responds to training in this patient group. Skeletal muscle characteristics in CHF patients are very similar to what is reported in response to chronic obstructive pulmonary disease (COPD), detraining and deconditioning. Furthermore, skeletal muscle alterations observed in CHF patients are reversible by training, and skeletal muscle of CHF patients seems to be at least as trainable as that of matched controls. We argue that deconditioning is a major contributor to the skeletal muscle dysfunction in CHF patients and that further research is needed to determine whether, and to what extent, the intrinsic skeletal muscle alterations in CHF represent an integral part of the pathophysiology in this disease.

Metabolic derangements in COPD muscle dysfunction

Mitochondrial muscle alterations are common in patients with chronic obstructive pulmonary disease (COPD) and manifest mainly as decreased oxidative capacity and excessive production of reactive oxygen species (ROS). The significant loss of oxidative capacity observed in the quadriceps of COPD patients is mainly due to reduced mitochondrial content in the fibers, a finding consistent with the characteristic loss of type I fibers observed in that muscle. Decreased oxidative capacity does not directly limit maximum performance; however, it is associated with increased lactate production at lower exercise intensity and reduced endurance. Since type I fiber atrophy does not occur in respiratory muscles, the loss of such fibers in the quadriceps could be to the result of disuse. In contrast, excessive production of ROS and oxidative stress are observed in both the respiratory muscles and the quadriceps of COPD patients. The causes of increased ROS production are not clear, and a number of different mechanisms can play a role. Several mitochondrial alterations in the quadriceps of COPD patients are similar to those observed in diabetic patients, thus suggesting a role for muscle alterations in this comorbidity. Amino acid metabolism is also altered. Expression of peroxisome proliferator-activated receptor-γ coactivator-1α mRNA is low in the quadriceps of COPD patients, which could also be a consequence of type I fiber loss; nevertheless, its response to exercise is not altered. Patterns of muscle cytochrome oxidase gene activation after training differ between COPD patients and healthy subjects, and the profile is consistent with hypoxic stress, even in nonhypoxic patients.

Cellular assessment of muscle in COPD: case studies of two males

The objective of this paper is to provide an overview of the recent developments in muscle physiology and biochemistry in general, and with respect to chronic obstructive pulmonary disease (COPD) specifically. As a way of illustration, we have presented data on the remodeling that occurs in vastus lateralis in two patients with COPD (COPD #1, forced expiratory volume in one second/forced vital capacity [FEV₁/FVC] = 63%; COPD #2, FEV₁/FVC = 41%) exhibiting differences in muscle wasting as compared to healthy controls (CON; FEV₁/FVC = 111 ± 2.2%, n = 4). Type I fibers percentages were lower in both COPD #1 (16.7) and COPD #2 (24.9) compared to CON (57.3 ± 5.2). Cross sectional area of the type I fibers of the patients ranged between 65%–68% of CON and for the type II subtypes (IIA, IIAX, IIX) between 74% and 89% (COPD #1) and 17%–32% (COPD #2). A lower number of capillary contacts were observed for all fiber types in COPD #1 but not COPD #2. Lower concentrations of adenosine triphosphate (ATP) (24%–26%) and phosphocreatine (18%–20%), but not lactate occurred in COPD. In contrast to COPD #1, who displayed normal glucose transporter content, GLUT1 and GLUT4 were only 71% and 54%, respectively of CON in COPD #2. Lower monocarboxylate contents were found for MCT1 in both COPD #1 (63%) and COPD #2 (41%) and for MCT4 (78%) in COPD #1. Maximal oxidative enzyme activities (V_max) for COPD #2 ranged between 37% (succinic dehydrogenase) and 70% (cytochrome C oxidase) of CON. For the cytosolic enzymes, V_max ranged between 89% (hexokinase) to 31% (pyruvate kinase) of CON. Depressions were also observed in V_max of the Na⁺-K⁺-ATPase for COPD #1 (66% of CON) but not COPD #2 (92% of CON) while V_max of the Ca²⁺-ATPase was near normal in COPD #1 (84% CON). It is concluded that disturbances can occur in muscle to a wide range of excitation, contraction and metabolic processes in COPD.

Abnormal transition pore kinetics and cytochrome C release in muscle mitochondria of patients with chronic obstructive pulmonary disease

Skeletal muscle dysfunction (SMD) is frequent in patients with chronic obstructive pulmonary disease (COPD). Mitochondrial abnormalities appear to play a role in the pathogenesis of SMD. The mitochondrion permeability transition pore (MPTP) facilitates the leakage of mitochondrial matrix constituents, such as cytochrome c (cyto-c), and triggers apoptosis, known to occur in skeletal muscle of patients with COPD. Our objective was to study MPTP kinetics and cyto-c release in skeletal muscle mitochondria of patients with COPD. Mitochondria were isolated from the vastus lateralis (VL), external intercostalis (EI), and latissimus dorsi (LD) in 11 patients with COPD (66 +/- 9 yr; FEV(1) 66 +/- 13%) and 15 smokers with normal lung function (64 +/- 6 yr; FEV(1) 95 +/- 11%) who required thoracic surgery for a localized lung neoplasm. MPTP kinetics were determined spectrophotometrically (time to reach V'max, V'max and mitochondrial swelling) and cyto-c release by enzyme-linked immunosorbent assay. MPTP kinetics and cyto-c release were abnormal in patients with COPD in the three muscles studied. In addition, V'max of VL mitochondria was significantly related (P < 0.01) to BMI (r = -0.75 COPD, -0.67 control) and aerobic capacity (r = -0.70 COPD, -0.60 control) for the COPD group. MPTP kinetics and cyto-c release are abnormal in skeletal and respiratory muscles of patients with moderate COPD, suggesting a systemic mechanism(s) occurring early during the course of the disease.

Abnormal sarcoplasmic reticulum Ca2+-sequestering properties in skeletal muscle in chronic obstructive pulmonary disease

The objective of this study was to investigate the hypothesis that alterations in sarcoplasmic reticulum (SR) Ca2+-cycling properties would occur in skeletal muscle in patients with moderate to severe chronic obstructive pulmonary disease (COPD). To investigate this hypothesis, tissue samples were obtained from the vastus lateralis of 8 patients with COPD [age 65.6 ± 3.2 yr; forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) = 44 ± 2%; mean ± SE] and 10 healthy age-matched controls (CON, age 67.5 ± 2.5 yr; FEV1/FVC = 77 ± 2%), and homogenates were analyzed for a wide range of SR properties. Compared with CON, COPD displayed (in μmol·g protein−1·min−1) a 16% lower maximal Ca2+-ATPase activity [maximal velocity ( Vmax), 158 ± 10 vs. 133 ± 7, P < 0.05] and a 17% lower Ca2+uptake (4.65 ± 0.039 vs. 3.85 ± 0.26, P < 0.05) that occurred in the absence of differences in Ca2+release. The lower Vmaxin COPD was also accompanied by an 11% lower ( P < 0.05) Ca2+sensitivity, as measured by the Hill coefficient (defined as the relationship between Ca2+-ATPase activity and free cytosolic Ca2+concentration for 10–90% Vmax). For the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) isoforms, SERCA1a was 16% higher ( P < 0.05) and SERCA2a was 14% lower ( P < 0.05) in COPD. It is concluded that moderate to severe COPD results in abnormalities in SR Ca2+-ATPase properties that cannot be explained by changes in the SERCA isoform phenotypes. The reduced catalytic properties of SERCA in COPD suggest a disturbance in Ca2+cycling, possibly resulting in impairment in Ca2+-mediated mechanical function and/or second messenger regulated processes.