Adh Promotes Actinobacillus pleuropneumoniae Survival in Porcine Alveolar Macrophages by Inhibiting CHAC2-Mediated Respiratory Burst and Inflammatory Cytokine Expression

Actinobacillus pleuropneumoniae (A. pleuropneumoniae) causes porcine pleuropneumonia that seriously endangers pig’s health. Adh, located in the head region of trimeric autotransporter adhesion of A. pleuropneumoniae, affects bacterial adhesion and pathogenicity. However, how Adh mediates A. pleuropneumoniae immune invasion is still unclear. Here, we established the A. pleuropneumoniae strain L20 or L20 ΔAdh-infected porcine alveolar macrophages (PAM) model, and applied protein overexpression, RNA interference, qRT-PCR, Western blot and immunoflourescence techniques to dissect the effects of Adh on PAM during A. pleuropneumoniae infection. We found that Adh could increase the A. pleuropneumoniae adhesion and intracellular survival in PAM. Gene chip analysis of piglet lungs further showed that Adh significantly induced cation transport regulatory-like protein 2 (CHAC2) expression, whose overexpression suppressed the phagocytic capacity of PAM. Furthermore, CHAC2 overexpression dramatically increased glutathione (GSH) expression, decreased reactive oxygen species (ROS), and promoted A. pleuropneumoniae survival in PAM, while the knockdown of CHAC2 reversed these phenomena. Meanwhile, CHAC2 silence activated the NOD1/NF-κB pathway, resulting in an increase in IL-1β, IL-6, and TNF-α expression, whereas this effect was weakened by CHAC2 overexpression and addition of NOD1/NF-κB inhibitor ML130. Moreover, Adh enhanced the secretion of LPS of A. pleuropneumoniae, which regulated the expression of CHAC2 via TLR4. In conclusion, through a LPS-TLR4-CHAC2 pathway, Adh inhibits respiratory burst and inflammatory cytokines expression to promote A. pleuropneumoniae survival in PAM. This finding may provide a novel target for the prevention and treatment of A. pleuropneumoniae.