Cytotoxicity of Vibrio parahaemolyticus AHPND toxin on shrimp hemocytes, a newly identified target tissue, involves binding of toxin to aminopeptidase N1 receptor

Acute hepatopancreatic necrosis disease (AHPND) caused by PirAB VP -producing strain of Vibrio parahaemolyticus , VP AHPND , has seriously impacted the shrimp production. Although the VP AHPND toxin is known as the VP AHPND virulence factor, a receptor that mediates its action has not been identified. An in-house transcriptome of Litopenaeus vannamei hemocytes allows us to identify two proteins from the aminopeptidase N family, Lv APN1 and Lv APN2, the proteins of which in insect are known to be receptors for Cry toxin. The membrane-bound APN, Lv APN1, was characterized to determine if it was a VP AHPND toxin receptor. The increased expression of Lv APN1 was found in hemocytes, stomach, and hepatopancreas after the shrimp were challenged with either VP AHPND or the partially purified VP AHPND toxin. Lv APN1 knockdown reduced the mortality, histopathological signs of AHPND in the hepatopancreas, and the number of virulent VP AHPND bacteria in the stomach after VP AHPND toxin challenge. In addition, Lv APN1 silencing prevented the toxin from causing severe damage to the hemocytes and sustained both the total hemocyte count (THC) and the percentage of living hemocytes. We found that the r Lv APN1 directly bound to both rPirA VP and rPirB VP toxins, supporting the notion that silencing of Lv APN1 prevented the VP AHPND toxin from passing through the cell membrane of hemocytes. We concluded that the Lv APN1 was involved in AHPND pathogenesis and acted as a VP AHPND toxin receptor mediating the toxin penetration into hemocytes. Besides, this was the first report on the toxic effect of VP AHPND toxin on hemocytes other than the known target tissues, hepatopancreas and stomach.