Airborne Fine Particulate Matter Causes Murine Bronchial Hyperreactivity via MAPK Pathway- Mediated M3 Muscarinic Receptor Upregulation

摘要

Regarding the human health effects, airborne fine particulate matter 2.5 (PM_(2.5)) is an important environmental risk factor. However, the underlying molecular mechanisms are largely unknown. The present study examined the hypothesis that PM_(2.5) causes bronchial hyperreactivity by upregulated muscarinic receptors via the mitogen-activated protein kinase (MAPK) pathway. The isolated rat bronchi segments were cultured with different concentration of PM_(2.5) for different time. The contractile response of the bronchi segments were recorded by a sensitive myograph. The mRNA and protein expression levels of M_3 muscarinic receptors were studied by quantitative real-time PCR and immunohistochemistry, respectively. The muscarinic receptors agonist, carbachol induced a remarkable contractile response on fresh and DMSO cultured bronchial segments. Compared with the fresh or DMSO culture groups, 1.0 µg/ mL of PM_(2.5) cultured for 24 h significantly enhanced muscarinic receptor-mediated contractile responses in bronchi with a markedly increased maximal contraction. In addition, the expression levels of mRNA and protein for M_3 muscarinic receptors in bronchi of PM_(2.5) group were higher than that of fresh or DMSO culture groups. SB203580 (p38 inhibitor) and U0126 (MEK1/2 inhibitor) significantly inhibited the PM_(2.5)-induced enhanced contraction and increased mRNA and protein expression of muscarinic receptors. However, JNK inhibitor SP600125 had no effect on PM25-induced muscarinic receptor upregulation and bronchial hyperreactivity. In conclusion, airborne PM_(2.5) upregulates muscarinic receptors, which causes subsequently bronchial hyperreactivity shown as enhanced contractility in bronchi. This process may be mediated by p38 and MEK1/2 MAPK pathways.