Contribution of the Mitochondria to Locomotor Muscle Dysfunction in Patients With COPD

COPD is a significant public health challenge, notably set to become the third leading cause of death and fifth leading cause of chronic disability worldwide by the next decade. Skeletal muscle impairment is now recognized as a disabling, extrapulmonary consequence of COPD that is associated with reduced quality of life and premature mortality. Because COPD typically manifests in older individuals, these clinical features may overlie normal age-associated declines in muscle function and performance. Although physical inactivity, oxidative stress, inflammation, hypoxia, malnutrition, and medications all likely contribute to this comorbidity, a better understanding of the underlying mechanism is needed to develop effective therapies. Mitochondrial alterations have been described; these alterations include reductions in density and oxidative enzyme activity, increased mitochondrial reactive oxygen species production, and induction of muscle proteolysis including autophagy. This review focuses on the perspective that mitochondrial alterations contribute to impaired locomotor muscle performance in patients with COPD by reducing oxidative capacity and thus endurance, as well as by triggering proteolysis and thus contributing to atrophy and weakness. We discuss how the potential underlying mechanisms converge on mitochondria by targeting the peroxisome proliferator-activated receptor γ-coactivator-1α signaling pathway (thereby reducing mitochondrial biogenesis and muscle oxidative capacity and potentially increasing fiber atrophy) and how taking advantage of normal muscle plasticity and mitochondrial biogenesis may reverse this pathophysiology. We propose recent therapeutic strategies aimed at increasing peroxisome proliferator-activated receptor γ-coactivator-1α levels, such as endurance training and exercise mimetic drugs, with the strong rationale for increasing mitochondrial biogenesis and function and thus improving the muscle phenotype in COPD.