Myostatin Expression And Apoptosis Of Diaphragmatic Muscle Cell In Chronic Obstructive Pulmonary Disease Rats

ObjectiveTo investigate myostatin expression in diaphragm of chronic obstructive pulmonarydisease（COPD）rats and analyse the correlation between myostatin and apoptosis ofdiaphragmatic muscle cell,thus to understand the mechanism of diaphragm dysfunction，develop an effective way to prevention and treatment strategy of COPD.MethodsThirty-five SD rats were randomly divided into a normal control group（n=15），aCOPD group（n=20）.Rat models of COPD were established by exposure to cigarette smokedaily for20weeks．Lung function was measured by small animal pulmonary functiontesting system in half rats of every group．The total cell counts,neutrophil counts andneutrophil proportion in bronchoalveolar lavage fluid(BALF) were measured．Lung tissuresection stained by hematoxylin and eosin(HE) was observed to study the morphologicalchanges． Mean linear intercept(MLI) and mean alveolar numbers(MAN) weremeasured． Diaphragm tissure section stained by HE was observed to study themorphological changes, the ultrastructure injury of diaphragm was observed by thetransmission electron microscopy，and terminal deoxynucleotidyl transferase-mediateddUTP nick end labeling(TUNEL) methods were carried out to examined apoptosis ofdiaphragmatic muscle cell.The protein level of myostatin in diaphragm was measured byWestern blot. The mRNA level of myostatin in diaphragm was measured by means ofreverse transcription-polymerase chain reaction(RT-PCR).Results（1）Compared with the normal control group，FEV0.3/FVC and PEF were lower inCOPD group(P<0.05).（2）The total cell counts,neutrophil counts and neutrophil proportion in BALF werehigher in COPD group than in the normal control group(all P<0.05). （3）Under the light microscopy,morphology detection of lung tissues showedsignificant enlarged airspace，disruption of alveolar septum and formation of emphysema inCOPD group．（4）MLI in COPD group was higher than that in the normal control group(P<0.05)while MAN was decreased on the contrary(P<0.05),compared with the normal controlgroup(P<0.05).（5）Under the transmission electron microscopy, COPD group showed diaphrag-matic muscle fiber size was different, part of the muscle fibers atrophy, part of the musclefibers appeared irregular contraction area, abnormal arrangement of sarcomere, fractureand dissolution of focal muscular wire intrafusal muscle fiber, mitochondria swelling andmitochondrial extensive vacuoles.（6）Compared with the normal control group，diaphragm weight was lower in COPDgroup(P<0.05).（7）Compared with the normal control group，COPD group showed higher apoptosisindex(AI) in diaphragm(P<0.05).（8）Compared with the normal control group，the protein and mRNA expressions ofmyostatin in diaphragm increased significantly in COPD group(P<0.05).（9）The protein and mRNAof myostatin expression in diaphragm of COPD groupwere negatively correlated with diaphragm weight (respectively r=-0.764，P<0.05；r=-0.885，P<0.05)，and were positively correlated with apoptosis of diaphragmatic musclecell(respectively r=0.857，P<0.05；r=0.865，P<0.05)．Conclusions（1）Improved cigarette smoke could establish COPD model of diaphragmatic muscledamage in rats，this rat model owned high similarity to human COPD．（2）Myostatin expression in diaphragm increase significantly in COPD rat, maycause apoptosis of diaphragmatic muscle cell and diaphragm atrophy，participate in thedevelopment of dysfunction of respiratory muscle in COPD.