The pore-forming protein Aep1 is an innate immune molecule that prevents zebrafish from bacterial infection

Following the Aeromonas hydrophila aerolysin, various aerolysin-like pore-forming proteins have been identified from bacteria to vertebrates. We have recently reported the mechanism of receptor recognition and in vitro pore-formation of a zebrafish aerolysin-like protein Dln1/Aep1. However, the physiological function of Aep1 remains unknown. Here we detected that aep1 gene is constitutively expressed in various immune-related tissues of adult zebrafish; and moreover, its expression is significantly up-regulated upon bacterial challenge, indicating its involvement in antimicrobial infection. Pre-injection of recombinant Aep1 into the infected zebrafish greatly accelerated the clearance of bacteria, resulting in significantly increased survival rate. Meanwhile, the induced expression of cytokines such as interleukin IL-1β and tumor necrosis factor TNF-α in zebrafish upon injection of recombinant Aep1 suggested that Aep1 may be a pro-inflammatory protein that triggers the antimicrobial immune responses. However, compared to the overproduction of these cytokines in the infected zebrafish, pre-injection of Aep1 could significantly reduce the expression level of these cytokines, accompanying with a reduced bacterial load. Moreover, the expression profiles through the developmental stages of zebrafish demonstrated that aep1 is activated at the very early stage prior to the maturation of adaptive immune system. Altogether, our findings proved that Aep1 is an innate immune molecule that prevents the bacterial infection.