Analysis Of Skeletal Muscle Atrophy In A COPD Rat Model By Expressions Of Caspase-3,8,9 Proteases

Objective: To investigate the involvement of apoptosis in skeletal muscle wasting of patients with chronic obstructive pulmonary disease (COPD) based on rats model, and suggest possible apoptotic signaling pathways by measuring the expression levels of several key caspase proteases.Methods: A rat model of COPD was established by passive smoking and instillation of Porcine Pancreatic Elastase (PPE) into the airways. Randomly, 18 rats were selected from COPD-positive rats without apparent weight loss for Group B, and 18 rats were selected from COPD-positive underweighted rats for Group C. Additionally, 18 healthy rats were selected as controls. Biopsy specimens of extensor digitorum longus and diaphragmatic muscle from all the rats in 3 groups were made for examination. Terminal deoxynucleotidyl Transferase Biotin-dUTP Nick End Labeling (TUNEL) and immunohistrochemistry techniques were applied to observe DNA fragmentation and to assess the activities of caspase-3,-8,-9 in these specimens respectively.Results:The percentages of apoptotic myonucleus in muscle biopsies from COPD-positive underweighted rats are 53.9% and 44.4%, respectively determined by TUNEL and caspase-3 immunohistrochemistry technique. The concordance between the two techniques in the assessment of apoptosis was excellent (r=0.923). Apoptosis rates has significant negative relative to masses of extensor digitorum longus which is a stable index to muscle atrophy(r=-0.89). Expressions of caspase-8/-9 can only be observed in biopsies from COPD-positive underweighted rats. The average optical density and integral optical density of caspase-8 in extensor digitorum longus muscle were significantly higher than that in diaphragmatic muscle (0.58±0.07vs0.35±0.06,980.2±79.3vs313.2±25.9, P<0.01). However, the AOD and IOD of caspase-9 in extensor digitorum longus muscle were much lower than that in diaphragmatic muscle (0.39±0.05vs0.48±0.08, 430.2±42.5vs1010.2±106.3, P<0.01).Conclusions: 1 .There exist links between apoptosis and muscle fiber atrophy in the rat model of COPD. 2. The numbers of caspase-3-positive myonucleus and TUNEL-positive myonucleus are at the same level. It suggests the apoptotic pathway in COPD skeletal muscle atrophy would be caspase-dependent. 3. Expressions of caspase 8 suggest that apoptosis of skeletal muscles in the rat model of COPD would be triggered by external receptor. 4. Experiments showed significant differences existing in the expression of Caspase-8/-9 between extensor digitorum longus and diaphragmatic muscle. These differences suggest mitochondria contribute more in the apoptosis of diaphragmatic muscle.