Exercise Protects Lung Injury Induced by PM_2.5 Exposure in Rats: Mediated by GSK3β on Extracellular to Intracellular HSP70 Ratio

To explore the protective effects of long-term exercise on lung injury induced by PM_2.5 and the mechanism of extracellular to intracellular HSP70 ratio mediated by GSK3β. Male Wistar rats(aged 8 weeks) were randomly divided into four groups:Sedentary(S), exercise(E), sedentary+PM_2.5 exposure(S+PM_2.5) and exercise+PM_2.5 exposure(E+PM_2.5). All rats in exerciserelated groups were trained by running on a treadmill for 8 weeks(60 min/time, 5 times/week). Rats in the PM-related groups were exposed to ambient PM_2.5(7 times/week, 6 h/time) for 3 weeks after an 8-week exercise intervention or sedentary treatment. Finally,all rats' pulmonary function, lung morphology, degree of inflammation, and relevant protein expression levels were examined. It was found that PM_2.5 exposure led to neutrophil infiltration, alveolar hemorrhage, and alveolar septal thickening. Compared with S group,the significant decrease of MV, TV, EF50, PIF, PEF, iHSP70, IκBα, HSF1 and p-GSK3^βser9 were observed, but the obvious increase of PAU, Te, TNF-α, IL-1α, IL-6, eHSP70, TLR-4, NFκB p65, p-IκBα, IKKβ, p-IKKβ, GSK3β, p-P38 and p-HSF1^ser303 were presented in S+PM_2.5 group. The lung injury was significantly improved in the E+PM_2.5 group compared with that of S+PM_2.5 group.Compared with S+PM_2.5 group, the MV, TV, EF50, PIF, PEF, iHSP70, IκBα, HSF1 and p-GSK3^βser9 were significantly increased, but the PAU, Te, TNF-α, IL-1α, IL-6, e HSP70, TLR-4, NFκB p65, p-IκBα, IKKβ, p-IKKβ, GSK3β, p-P38 and p-HSF1^ser303 were obviously decreased in E+PM_2.5 group. 8-week exercise training expressed protective effects on lung injury and reduced vulnerability to inflammation induced by PM_2.5 exposure, it was possibly through the P38 MAPK/GSK3β/HSF1 signaling pathways mediated by the extracellular-to-intracellular HSP70 ratio.