Resistin secreted by porcine alveolar macrophages leads to endothelial cell dysfunction during <i>Haemophilus parasuis</i> infection

Abstract

<i>Haemophilus parasuis</i> (<i>H. parasuis</i>) causes exudative inflammation, implying endothelial dysfunction during pathogen infection. However, so far, the molecular mechanism of endothelial dysfunction caused by <i>H. parasuis</i> has not been clarified. By using the transwell-based cell co-culture system, we demonstrate that knocking out <i>resistin</i> in porcine alveolar macrophages (PAMs) dramatically attenuated endothelial monolayer damage caused by <i>H. parasuis</i>. The resistin secreted by PAMs inhibited the expression of the tight junction proteins claudin-5 and occludin rather than the adherens junction protein VE-cadherin in co-cultured porcine aortic endothelial cells (PAECs). Furthermore, we demonstrate that resistin regulated claudin-5 and occludin expression and monolayer PAEC permeability in an LKB1/AMPK/mTOR pathway-dependent manner. Additionally, we reveal that the outer membrane lipoprotein gene <i>lppA</i> in <i>H. parasuis</i> induced resistin expression in PAMs, as deleting <i>lppA</i> reduced <i>resistin</i> expression in <i>H. parasuis</i>-infected PAMs, causing a significant change in LKB1/AMPK/mTOR pathway activity in co-cultured PAECs, thereby restoring tight junction protein levels and endothelial monolayer permeability. Thus, we postulate that the <i>H. parasuis lppA</i> gene enhances resistin production in PAMs, disrupting tight junctions in PAECs and causing endothelial barrier dysfunction. These findings elucidate the pathogenic mechanism of exudative inflammation caused by <i>H. parasuis</i> for the first time and provide a more profound angle of acute exudative inflammation caused by bacteria.