Effect Of Moderate Intensity Aerobic Exercise On Chemerin/CMKLR1 In The Diaphragm Of Mice With COPD

ObjectiveChronic obstructive pulmonary disease(COPD)is primarily caused by smoking and is characterized by chronic inflammation and poorly reversible airflow limitation.The inflammatory response in patients can diffuse from the lungs to the whole body,resulting in the presence of a persistent chronic inflammatory response throughout the body,called systemic inflammation.Systemic inflammation can lead to changes in the morphology and function of the diaphragm,which is a key factor in diaphragmatic dysfunction.Diaphragmatic dysfunction can directly affect the respiratory status of COPD patients and is associated with mortality in COPD.Accordingly,it is hypothesized that effective methods to alleviate inflammation in the body may improve diaphragm dysfunction,delay COPD disease progression and reduce acute exacerbations,and decrease the risk of death.Exercise training is considered to be an effective treatment for diaphragmatic dysfunction in COPD,where aerobic exercise is an easily accepted exercise modality that can effectively improve diaphragmatic function in COPD patients,and the mechanism of action that produces this clinical phenomenon is not fully understood.Exercise training can alleviate the inflammatory response to a variety of chronic diseases.Currently,chemerin and CMKLR1 have been identified as important molecules that are now known to regulate inflammation,have an indispensable role in the inflammatory response in COPD,and are subject to modulation by factors such as exercise.Previous studies have shown that moderate-intensity aerobic exercise appears to have more anti-inflammatory effects compared to low-and high-intensity aerobic exercise.Therefore,the aim of this study was to investigate the effects of moderate intensity aerobic exercise on chemerin and CMKLR1 and inflammatory factors in the diaphragm of mice with cigarette smoke-induced COPD to explore the possible molecular mechanisms that ameliorate diaphragm injury in COPD.MethodsEighteen 8-week-old healthy male C57BL/6J mice were randomly divided into blank control group(CG,n=6),COPD model group(MG,n=6)and COPD moderate-intensity aerobic exercise group(EG,n=6).Mice in the blank control group were routinely housed without any intervention.mice in the COPD model group and the COPD moderate-intensity aerobic exercise group were exposed to cigarette smoke for 25 weeks to establish a COPD mouse model.After successful establishment of the model,the COPD model mice were housed routinely without any exercise intervention;the COPD moderate-intensity aerobic exercise group mice were subjected to a running platform exercise(55% of maximum exercise speed)for 9weeks.At the end of the exercise intervention,lung and diaphragm tissues of mice were stained by hematoxylin-eosin staining(HE),and the mean cross-sectional area(CSA)and mean linear intercept(MLI)of alveoli and CSA of diaphragm muscle fibers were calculated.The expression levels of chemerin,CMKLR1,IL-6,IL-1β and TNF-α proteins in diaphragm muscle were detected by Western blot.Results(1)HE staining of lung tissueThe alveoli of the mice in the blank control group had clear margins,similar size,more uniform,intact tracheal structure,and no abnormal thickening of the tracheal wall,while the alveoli of the mice in the COPD model group had poorly defined margins,and the thickness of the alveolar wall was significantly thinner and ruptured,and multiple alveoli fused to form a pulmonary blister were seen everywhere,and the tracheal wall was significantly thickened.Compared with the COPD model mice,the alveolar wall of COPD exercise group mice had clearer edges and more complete structures,and the thickening of the tracheal wall was also reduced.The mean alveolar CSA was significantly larger in the COPD model group compared to the blank control group(p<0.01).After 9 weeks of moderate intensity aerobic exercise,the mean alveolar CSA in the COPD exercise group was significantly smaller than that in the COPD model group(p<0.05).The alveolar MLI in the COPD model group was significantly larger than that in the blank control group(p<0.05),and the alveolar MLI in the COPD exercise group was smaller than that in the COPD model group,but did not reach a statistical difference(p>0.05).(2)HE staining of diaphragm muscleThe diaphragm fibers of the mice in the blank control group were arranged in a neat and orderly manner,and the CSA of muscle fibers was uniform and similar in size,while the diaphragm fibers of the mice in the COPD model group were arranged in an uncompact and disordered manner,the muscle septum was significantly widened,some muscle fibers were damaged and broken to some extent,the nuclei were significantly reduced,and the mean CSA of muscle fibers was significantly lower than that of the blank control group.After 9 weeks of moderate intensity aerobic exercise,the diaphragm fibers in the COPD exercise group were arranged more neatly and orderly than those in the COPD model group,the septum increased and relieved,the nuclei increased significantly,and the mean CSA of muscle fibers increased significantly(p<0.05).(3)Chemerin and CMKLR1 protein expression in the diaphragmThe expression of chemerin and CMKLR1 protein was significantly higher in the diaphragm of COPD model group mice compared to blank control group mice((p<0.01).Compared to the COPD model group,after 9 weeks of moderate intensity aerobic exercise,the expression levels of chemerin protein in the diaphragm of mice in the COPD exercise group decreased significantly(p<0.01),and the expression of CMKLR1 protein in the diaphragm of mice in the COPD exercise group also decreased,but did not reach statistical differences(p>0.05).(4)TNF-α,IL-6 and IL-1β protein expression in the diaphragmCompared with mice in the blank control group,the expression of TNF-α,IL-6and IL-1β proteins in the diaphragm of mice in the COPD model group increased,among which,only the increase in TNF-α protein expression reached statistical differences(p<0.01).Compared with mice in the COPD model group,the expression levels of the inflammatory factors TNF-α,IL-6 and IL-1β in the diaphragm of mice in the COPD exercise group decreased after 9 weeks of moderate intensity aerobic exercise,but none of them reached statistical significance(p>0.05).ConclusionAfter 9 weeks of moderate intensity aerobic exercise,the pathological damage of lung tissue and diaphragm in COPD mice was improved,and the expression levels of chemerin,CMKLR1 and IL-6,IL-1β and TNF-α proteins in diaphragm were reduced,which alleviated the inflammatory response of mouse diaphragm to some extent.It was hypothesized that the improvement of pathological damage of mouse diaphragm by moderate intensity aerobic exercise was related to the involvement of chemerin/CMKLR1 in regulating the inflammatory response.