The rat model of COPD skeletal muscle dysfunction induced by progressive cigarette smoke exposure: a pilot study

Background Chronic obstructive pulmonary disease (COPD) skeletal muscle dysfunction is a prevalent malady that significantly affects patients' prognosis and quality of life. Although the study of this disease has attracted considerable attention, a definite animal model is yet to be established. This study investigates whether smoke exposure could lead to the development of a COPD skeletal muscle dysfunction model in rats. Methods Sprague Dawley rats were randomly divided into model (MG, n = 8) and control groups (CG, n = 6). The MG was exposed to cigarette smoke for 16 weeks while the CG was not. The body weight and forelimb grip strength of rats were monitored monthly. The pulmonary function and the strength of tibialis anterior muscle were assessed in vitro and compared after establishing the model. The histological changes in lung and gastrocnemius muscles were observed. The expressions of interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-alpha were detected by ELISA, while the expressions of Atrogin-1 and MuRF1 in the gastrocnemius muscle were determined by Western blotting. Results Smoke exposure slowly increases the body weight and forelimb grip strength of MG rats, compared to CG rats. However, it significantly decreases the pulmonary ventilation function and the skeletal muscle contractility of the MG in vitro. Histologically, the lung tissues of MG show typical pathological manifestations of emphysema, while the skeletal muscles present muscular atrophy. The expressions of IL-6, IL-8, and TNF-alpha in MG rats are significantly higher than those measured in CG rats. Increased levels of Atrogin-1 and MuRF1 were also detected in the gastrocnemius muscle tissue of MG. Conclusion Progressive smoking exposure decreases the contractile function of skeletal muscles, leading to muscular atrophy. It also increases the expressions of inflammatory and muscle protein degradation factors in COPD rats. This indicates that smoke exposure could be used to establish a COPD skeletal muscle dysfunction model in rats.