Failed upregulation of TFAM protein and mitochondrial DNA in oxidatively deficient fibers of chronic obstructive pulmonary disease locomotor muscle

Skelet Muscle. 2016 Feb 18;6:10. doi: 10.1186/s13395-016-0083-9. eCollection 2016.

Abstract

Background: 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.

Methods: Vastus lateralis biopsies were analyzed from 29 COPD patients and 19 healthy age-matched controls for the presence of mtDNA deletions, levels of oxidatively damaged DNA, mtDNA copy number, and regulators of mitochondrial biogenesis as well the proportion of oxidative-deficient fibers (detected histologically as cytochrome c oxidase-deficient, succinate dehydrogenase positive (COX(-)/SDH(+) )). Additionally, mtDNA copy number and mitochondrial transcription factor A (TFAM) content were measured in laser captured COX(-)SDH(+) and normal single fibers of both COPD and controls.

Results: Compared to controls, COPD muscle exhibited significantly higher levels of oxidatively damaged DNA (8-hydroxy-2-deoxyguanosine (8-OHdG) levels = 387 ± 41 vs. 258 ± 21 pg/mL) and higher prevalence of mtDNA deletions (74 vs. 15 % of subjects in each group), which was accompanied by a higher abundance of oxidative-deficient fibers (8.0 ± 2.1 vs. 1.5 ± 0.4 %). Interestingly, COPD patients with mtDNA deletions had higher levels of 8-OHdG (457 ± 46 pg/mL) and longer smoking history (66.3 ± 7.5 years) than patients without deletions (197 ± 29 pg/mL; 38.0 ± 7.3 years). Transcript levels of regulators of mitochondrial biogenesis and oxidative metabolism were upregulated in COPD compared to controls. However, single fiber analyses of COX(-)/SDH(+) and normal fibers exposed an impairment in mitochondrial biogenesis in COPD; in healthy controls, we detected a marked upregulation of mtDNA copy number and TFAM protein in COX(-)/SDH(+) compared to normal fibers, reflecting the expected compensatory attempt by the oxidative-deficient cells to increase energy levels; in contrast, they were similar between COX(-)/SDH(+) and normal fibers in COPD patients. Taken together, these findings suggest that although the signaling factors regulating mitochondrial biogenesis are increased in COPD muscle, impairment in the translation of these signals prevents the restoration of normal oxidative capacity.

Conclusions: Single fiber analyses provide the first substantive evidence that low muscle oxidative capacity in COPD cannot be explained by physical inactivity alone and is likely driven by the disease pathophysiology.

Keywords: COX deficiency; Chronic obstructive pulmonary disease; Laser capture microscopy; Mitochondrial DNA; Mitochondrial biogenesis; Muscle oxidative impairment; Oxidative stress; TFAM; mtDNA copy number.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Case-Control Studies
  • DNA Damage
  • DNA, Mitochondrial / genetics
  • DNA, Mitochondrial / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Electron Transport Complex IV / genetics
  • Electron Transport Complex IV / metabolism
  • Female
  • Humans
  • Male
  • Middle Aged
  • Mitochondria, Muscle / metabolism*
  • Mitochondria, Muscle / pathology
  • Mitochondrial Proteins / genetics
  • Mitochondrial Proteins / metabolism*
  • Muscle Fibers, Skeletal / metabolism*
  • Muscle Fibers, Skeletal / pathology
  • Organelle Biogenesis
  • Oxidative Stress*
  • Pulmonary Disease, Chronic Obstructive / diagnosis
  • Pulmonary Disease, Chronic Obstructive / genetics
  • Pulmonary Disease, Chronic Obstructive / metabolism*
  • Pulmonary Disease, Chronic Obstructive / physiopathology
  • Quadriceps Muscle / metabolism*
  • Quadriceps Muscle / pathology
  • Quadriceps Muscle / physiopathology
  • Succinate Dehydrogenase / genetics
  • Succinate Dehydrogenase / metabolism
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcription, Genetic
  • Up-Regulation

Substances

  • DNA, Mitochondrial
  • DNA-Binding Proteins
  • Mitochondrial Proteins
  • TFAM protein, human
  • Transcription Factors
  • Succinate Dehydrogenase
  • Electron Transport Complex IV