蛋白酶体抑制剂MG-132抑制慢性阻塞性肺疾病大鼠模型膈肌萎缩的研究

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

目的研究蛋白酶体抑制剂MG-132抑制烟草烟雾所致慢性阻塞性肺疾病（简称慢阻肺）大鼠模型骨骼肌萎缩的可能机制。方法采用反复烟草烟雾暴露联合气管内注入脂多糖法成功制备成年雄性sD大鼠慢阻肺模型，分为非十预组、高剂量组（MG-132 0．1mg·kg^-1·d^-1）和低剂量组（MG-1320．05mg·kg^-1·d^-1），每组12只，另设对照组。各组分别于实验1周和4周处死6只大鼠，分离大鼠膈肌并称重，采用酶联免疫吸附试验法测定大鼠血清和膈肌中肿瘤坏死因子-α（TNF—α）的表达，逆转录-PCR法和Western blot法检测大鼠膈肌内的肌萎缩F—box蛋白（MAFbx）、核因子-κB p65和抑制性因子κB—α（IKB-α）mRNA和蛋白表达。多组间比较采用方差分析，两组问比较采用t检验，相关性检验采用Pearson直线相关性分析。结果实验1周和4周非干预组[（0．83±0．09）mg和（1．01±0．06）mg]、高剂量组[（0．85±0．02）mg和（1．11±0．06）mg]及低剂量组[（0．83±0．03）mg和（1．04±0．02）mg]大鼠的膈肌重量均低于对照组[（0．99±0．06）mg和（1．20±0．04）mg]，高剂量组和低剂量组大鼠膈肌重量下降程度均小于非干预组，高剂量组干预4周时更明显；实验4周时在高剂量组和低剂量组膈肌中TNF-α含量[（106±8）ng／L和（122±7）ng／L]显著低于非干预组[（143±24）ng／L]，高剂量组膈肌中核因子-κBp65和MAFbx蛋白表达水平（1．13±0．04和1．27±0．05）及mRNA含量（2．17±0．42和1．74±0．14）显著低于非干预组（1．32±0．04和1．44±0．07及2．81±0．31和4．87±0．34），IKB—α基因和蛋白表达水平（0．96±0．08和0．83±0．06）显著高于非干预组（0．25±0．02和0．58±0．06），差异均有统计学意义（t值为1．57—24．9，P〈0．05）。各组大鼠血清和膈肌中TNF-α表达水平与膈肌中核因子-κBp65蛋白和mRNA表达水平呈显著正相关（r值为0．672～0．875，均P〈0．01），与IκB—α蛋白和mRNA表达水平呈显著负相关（r值为-0．656～-0．927，均P〈0．01）。结论蛋白酶体抑制剂MG-132可能通过抑制IκB—α的泛素化降解，从而稳定核因子-κB活性，抑制泛素蛋白酶体途径介导的慢阻肺大鼠膈肌萎缩。

Objective 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. Methods 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 Westeru 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. Results 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 d 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 ） . Conclusions 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.