The proteasome inhibitor MG132 attenuates skeletal muscle atrophy in a rat model of chronic obstructive pulmonary disease

Abstract

To investigate the effect of the proteasome inhibitor MG-132 on skeletal muscle atrophy in a rat model of chronic obstructive pulmonary disease (COPD) and its potential mechanisms. The COPD rat model was established by instillation of LPS and exposure to the cigarette smoke. Then the COPD rats were randomly divided into 3 groups (each group n = 12): COPD model control group, MG-132 high dose group (MG-132 0.1 mg·kg(-1)·d(-1)) and low dose group (MG-132 0.05 mg·kg(-1)·d(-1)), and normal control group. After 1 week and 4 week, 6 rats of each group were sacrificed, and then the following parameters were determined: the weight of the diaphragm muscle, the concentration of TNF-α in the serum and diaphragm via enzyme-linked immunosorbent assay (ELISA). Muscle atrophy F-box protein (MAFbx), NF-κBp65, and IκB-α mRNA levels were determined by RT-PCR. The protein levels of MAFbx, NF-κBp65 and IκB-α in diaphragm were measured by Western blot. The single factor analysis of variance was used for statistical analysis among the groups, while t test was used for comparison between 2 groups, and Pearson linear correlation analysis was also performed. The weight of diaphragm muscle from 1 week and 4 week normal control group [(0.99 ± 0.06) mg and (1.20 ± 0.04) mg] were reduced as compared to those of COPD model control group [(0.83 ± 0.09) mg and (1.01 ± 0.06) mg], high dose group [(0.85 ± 0.02) mg and (1.11 ± 0.06) mg], and low dose group [(0.83 ± 0.03) mg and (1.04 ± 0.02) mg]. The reduction of diaphragm muscle weight in the high dose group and the low dose group was significantly less than that in the COPD model control group, with a more marked difference as compared with the 4 week high dose group. The TNF-α levels in diaphragm from 4 week high dose group [(106 ± 8) ng/L] and low dose group [(122 ± 7) ng/L] were decreased as compared to that of the COPD model control group [(143 ± 24) ng/L]. The levels of NF-κBp65 and MAFbx mRNA from the 4 week high dose group (2.17 ± 0.42) and low dose group (1.74 ± 0.14) and the protein expression (1.13 ± 0.04 and 1.27 ± 0.05) were also decreased as compared to those of the COPD model control group (mRNA 2.81 ± 0.31 and 4.87 ± 0.34, protein expression 1.32 ± 0.04 and 1.44 ± 0.07). The levels of IκB-α mRNA and protein expression (0.96 ± 0.08 and 0.83 ± 0.06) were higher than those of the COPD model control group (0.25 ± 0.02 and 0.58 ± 0.06), (t = 1.57-24.9, P < 0.05). The levels of the TNF-α levels in serum and diaphragm were correlated positively with the levels of MAFbx and NF-κBp65 mRNA and protein expression (r = 0.672-0.875, P < 0.01), but negatively with the levels of IκB-α mRNA and protein expression (r = -0.656--0.927, P < 0.01). The proteasome inhibitor MG-132 significantly inhibited IκB-α degradation thus preventing NF-κB activation. This effect resulted in preventing skeletal muscle atrophy in the COPD rats.