Aerobic exercise ameliorates particulate matter-induced lung injury in aging rats

Particulate matter 2.5 (PM_2.5) is an inflammatory-inducing factor that is considered to be related to many adverse respiratory problems, especially in the elderly. This study aimed to examine whether pre-exercise training could prevent pulmonary injury induced by urban PM_2.5 in aging rats and investigate its relationship with inflammatory pathways. Male Wistar rats (aged 16 months) were randomly divided into four groups: sedentary, exercise, sedentary + PM_2.5 exposure, and exercise + PM_2.5 exposure. All rats in exercise-related groups were treadmill-trained for 8 weeks (65%-75% VO_2max for 30 min every other day). Sedentary groups' rats lived freely in cages without exercise intervention. Rats in the PM-related groups were exposed to ambient PM_2.5 (4 h day^-1) for 2 weeks after an 8-week exercise intervention or sedentary treatment. Finally, all rats' pulmonary function, lung morphology, degree of inflammation, and relevant protein and mRNA transcript expression levels were examined. The results indicated that PM_2.5 exposure induced lung injury in the sedentary + PM_2.5 exposure group, as evidenced by the deterioration of pulmonary function, histopathological characteristics, and inflammatory changes. Aerobic exercise alleviated PM_2.5-induced airway obstruction, deterioration of pulmonary function, bronchial mucosal exfoliation, and inflammatory responses in aging rats. These effects in exercise groups were associated with the increased expression of intracellular 70 kDa heat shock protein (iHSP70) and the suppression of nuclear transcription factor-κB (NF-κB) activation, as confirmed by increased expression of inhibitor of NF-κB (IκBα) and a reduction in phospho-IKBα (p-IκBα), which is regulated by inhibiting kappa B kinase beta (IKKβ). Taken together, aerobic pre-exercise had protective effects on lung injury and reduced vulnerability to inflammation induced by PM_2.5 exposure, possibly through the toll-like receptor 4 (TLR4)/NF-κB signaling pathways mediated by the extracellular-to-intracellular HSP70 ratio. Pre-exercise training may be an effective way to protect against PM_2.5-induced lung toxicity in aging individuals.