Exercise training attenuates neutrophil infiltration and elastase expression in adipose tissue of high-fat-diet-induced obese mice

The innate immune system is associated with the development of local inflammation. Neutrophils play an essential role in the development of the adipose tissue (AT) inflammation associated with obesity by producing elastase, which can promote the activation and infiltration of macrophages. Exercise training attenuates AT inflammation via suppression of macrophage infiltration. However, the mechanisms driving this phenomenon remains to be elucidated. Here, we evaluated the effects of exercise training on the infiltration of neutrophils and elastase expression in an obese mouse model. Four-week-old male C57BL/6J mice were randomly assigned to one of three groups that either received a normal diet (ND) plus sedentary activity (n = 15), a high-fat diet (HFD) plus sedentary activity (n = 15), or a HFD plus exercise training (n = 15). Mice were fed the ND or HFD from the age of 4 weeks until 20 weeks. Mice in the exercise group ran on a treadmill for 60 min/day, 5 days/week over the same experimental period. Mice fed with the HFD had increased content of macrophages in the AT and increased inflammatory cytokine mRNA levels, which were reduced by exercise training. Similarly, AT from the HFD sedentary mice contained more neutrophils than AT from the ND mice, and the amount of neutrophils in this tissue in HFD-fed mice was lowered by exercise training. The mRNA levels of neutrophil elastase in AT were lower in the HFD exercise-trained mice than those in the HFD sedentary mice. These results suggest that exercise training plays a critical role in reducing macrophage infiltration and AT inflammation by regulating the infiltration of neutrophils.