Functional, Ultrastructural, and Transcriptomic Changes in Rat Diaphragms with Different Durations of Cigarette Smoke Exposure

Exercise Attenuate Diaphragm Atrophy in COPD Mice via Inhibiting the RhoA/ROCK Signaling

Background

Exercise is an indispensable component of pulmonary rehabilitation with strong anti-inflammatory effects. However, the mechanisms by which exercise prevents diaphragmatic atrophy in COPD (chronic obstructive pulmonary disease) remain unclear.

Methods

Forty male C57BL/6 mice were assigned to the control (n=16) and smoke (n=24) groups. Mice in the smoke group were exposed to the cigarette smoke (CS) for six months. They were then divided into model and exercise training groups for 2 months. Histological changes were observed in lung and diaphragms. Subsequently, agonist U46639 and antagonist Y27632 of RhoA/ROCK were subjected to mechanical stretching in LPS-treated C2C12 myoblasts. The expression levels of Atrogin-1, MuRF-1, MyoD, Myf5, IL-1β, TNF-α, and RhoA/ROCK were determined by Western blotting.

Results

Diaphragmatic atrophy and increased RhoA/ROCK expression were observed in COPD mice. Exercise training attenuated diaphragmatic atrophy, decreased the expression of MuRF-1, and increased MyoD expression in COPD diaphragms. Exercise also affects the upregulation of RhoA/ROCK and inflammation-related proteins. In in vitro experiments with C2C12 myoblasts, LPS remarkably increased the level of inflammation and protein degradation, whereas Y27632 or combined with mechanical stretching prevented this phenomenon considerably.

Conclusion

RhoA/ROCK plays an important role in the prevention of diaphragmatic atrophy in COPD.

Changes in diaphragm contractility in cigarette smoking-exposed and smoking cessation rats are associated with alterations in mitochondrial morphology and homeostasis

The effects of cigarette smoking (CS) cessation on the diaphragm are unknown, as are the CS-induced diaphragmatic mitochondrial changes. We examined the changes in diaphragm contractility, as well as alterations in mitochondrial morphology, function and homoeostasis during CS exposure and after cessation. Rats were randomly divided into CS exposure and CS cessation groups: 3-month CS (S3), 6-month CS (S6), 6-month CS followed by 3-month cessation (S6N3). The changes in the diaphragm were investigated, including contractile properties, the ultrastructure, mitochondrial function and the expression of markers of mitochondrial homoeostasis. CS caused irreversible histological disruption and functional depression in the lungs, along with significantly declines in diaphragmatic contractility and more severely in extensor digitorum longus muscular contractility. Such declines were recovered after 3-month CS cessation. CS exposure disrupted the diaphragmatic mitochondrial morphology and function (S6), which was significantly alleviated in the S6N3 group. The mitochondrial homoeostasis was depressed (S6), as indicated by the downregulation of Pink1 and Mfn1. Interestingly, the Mfn1 level was recovered after smoking cessation (S6N3). In conclusion, smoking cessation eased CS-induced diaphragmatic dysfunction and mitochondrial deregulation, which are likely associated with deregulated mitochondrial homoeostasis.

Effect of Oxidative Stress on Diaphragm Dysfunction and Exercise Intervention in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) can cause extrapulmonary injury such as diaphragm dysfunction. Oxidative stress is one of the main factors causing diaphragm dysfunction in COPD. Exercise plays a positive role in the prevention and treatment of diaphragm dysfunction in COPD, and the changes in diaphragm structure and function induced by exercise are closely related to the regulation of oxidative stress. Therefore, on the basis of the review of oxidative stress and the changes in diaphragm structure and function in COPD, this article analyzed the effects of exercise on oxidative stress and diaphragm dysfunction in COPD and explored the possible mechanism by which exercise improves oxidative stress. Studies have found that diaphragm dysfunction in COPD includes the decline of muscle strength, endurance, and activity. Oxidative stress mainly affects the structure and function of the diaphragm in COPD through protein oxidation, protease activation and calcium sensitivity reduction. The effects of exercise on oxidative stress level and diaphragm dysfunction may differ depending on the intensity, duration, and style of exercise. The mechanism of exercise on oxidative stress in the diaphragm of COPD may include improving antioxidant capacity, reducing oxidase activity and improving mitochondrial function.