LPS aggravates lung inflammation induced by RSV by promoting the ERK-MMP-12 signaling pathway in mice

BACKGROUND: RSV can lead to persistent airway inflammation and airway hyperresponsiveness (AHR), and is intimately associated with childhood recurrent wheezing and asthma, but the underlying mechanisms remain unclear. Lipopolysaccharide (LPS) is also implicated in the onset and exacerbation of asthma. However, whether inhalation of LPS can boost airway inflammation induced by RSV is not clear. In this study, we utilized an LPS- and RSV-superinfected mouse model to explore underlying pathogenesis. METHODS: Mice were infected with RSV on day 0 and inoculated with LPS from day 35 to day 41, samples were collected on day 42. Inflammatory cells, lung histopathology and AHR were measured. Cytokines were detected by ELISA and ERK, JNK, p38 was determined by western blot. MMP408, PD98059, SP600125 and SB203580 were used to inhibit MMP-12, ERK, JNK and p38 respectively. RESULTS: LPS exposure superimposed on RSV-infected lungs could lead to more vigorous cellular influx, lung structures damage, augmented AHR and higher MMP-12 levels. Inhibition of MMP-12 or ERK signaling pathway in vivo both diminished LPS-driven airway inflammation and AHR. CONCLUSIONS: Exposure to LPS in RSV-infected mice is associated with enhanced increases in ERK-MMP-12 expression that translates into increased lung inflammation and AHR. These findings contribute novel information to the field investigating the onset of post-RSV bronchiolitis recurrent wheezing as a result of LPS exposure.