Activation of the Ubiquitin–Proteasome Pathway in the Diaphragm in Chronic Obstructive Pulmonary Disease

Abstract

Rationale: Studies show that the myosin content of the diaphragm in patients with mild to moderate chronic obstructive pulmonary disease (COPD) is reduced, compromising diaphragm contractile performance. The mechanisms for reduced contractile protein content are unknown. In the present study we hypothesized that the loss of contractile protein content is associated with activation of the ubiquitin-proteasome pathway in the diaphragm of patients with mild to moderate COPD. Methods: Proteolytic activity of isolated 20S proteasomes was determined in diaphragm biopsies from patients with and without COPD (predicted mean FEV 1 , 66 and 93%, respectively). In addition, we determined 20S proteasome subunit C8 protein levels by means of Western blotting, ubiquitin-ligase mRNA levels by means of realtime polymerase chain reaction, and caspase-3 activity by determining the hydrolysis of fluorogenic substrates. Results: The 20S proteasome activity was about threefold increased in the diaphragm of patients with COPD. C8 protein levels were not significantly different between COPD and non-COPD diaphragm, indicating increased specific activity of individual proteasomes, rather than an increased number of proteasomes. mRNA levels of the muscle-specific ubiquitin-ligase MAFbx were significantly higher in diaphragm from patients with COPD compared with patients without COPD. Caspase-3-mediated cleavage of actomyosin complexes is considered an initial step in muscle wasting, yielding fragments that can be degraded by the ubiquitin-proteasome pathway. In line with the increased ubiquitin-proteasome activity, caspase-3 activity was higher in diaphragm homogenates from patients with COPD. Conclusions: The present study is the first to demonstrate increased activity of the ubiquitin-proteasome pathway in COPD diaphragm. Importantly, these changes occur in patients with only mild to moderate COPD (Global Initiative for Chronic Obstructive Lung Disease stage I/II).

Respiratory muscle fiber remodeling in chronic hyperinflation: dysfunction or adaptation?

“…Unlike animal experiments, studies on diaphragm fibers from human COPD patients exhibit elevations in caspase-3 activity (67). They also reveal increased 20s proteosome activity and elevated levels of atrogin-1, an E-3 ligase, believed to be involved with the regulation of protein ubiquitination in atrophic muscles (67). Ubiquitination is one of the first steps in degrading damaged proteins via the proteosome or in tagging proteins targeted for degradation in the process of atrophy or fiber shortening.…”

The discordant method: a novel approach for differential correlation

“…In Figure 4b the genes involved in this pathway are highlighted from the rest of the other genes, which total to 17 out of 1667 in the gene set. In previous studies, the ubiquitin protease degradation pathway has been associated with COPD (Ottenheijm et al, 2006).…”

Effects of exercise training on atrophy gene expression in skeletal muscle of mice with chronic allergic lung inflammation

“…However, treadmill training reduced the expression of these genes in all exercised groups, a fact that could be beneficial in cachexia and disuse conditions. Recent studies have shown an increase of molecular markers of muscle atrophy in human COPD (8,9). Doucet and colleagues (8) reported an increase in the activation of muscle atrophy by the up-regulation of atrogin-1 and MuRF1 in the quadriceps muscle of COPD patients.…”

“…www.bjournal.com.br Doucet and colleagues (8) reported an increase in atrogin-1 and MuRF1 (232 and 517%, respectively) mRNA in the quadriceps muscle of patients with COPD. Furthermore, Ottenheijm et al (9) also showed an increase in atrogin-1 gene expression in the diaphragm muscle of patients with mild to moderate COPD. Atrogin-1 and MuRF1 mRNA levels are reliable molecular markers for muscle atrophy by being increased substantially in peripheral skeletal muscle in various muscle-wasting conditions, such as denervation, immobilization, cancer, sepsis, and aging (10)(11)(12).…”