ATP7A Maintains Bactericidal Function of Neutrophils and Macrophages via Regulating the Formation and Activation of Phagolysosomes

ABSTRACT Neutrophils and macrophages are indispensable phagocytic immune cells, critically responsible for fish's ability to combat pathogens. Studies unveil that ATP7A is essential for copper trafficking to the lysosome in the cells, a process that is fundamental for their antibacterial functions in vitro. However, its antibacterial role in vivo and the underlying mechanisms have been insufficiently explored. In this study, we have demonstrated that atp7a −/− mutant larvae are significantly more susceptible to Aeromonas hydrophila (AH) infection and possess fewer neutrophils and macrophages compared to their wild‐type (WT) counterparts, and these mutants show a pronounced delay in the migration of the cells in response to infection. Atp7a deficiency leads to a marked downregulation of key phagosomal and lysosomal proteins, which impairs the formation of phagolysosomes and impairs lysosomal acidification and reactive oxygen species (ROS) elevation, then results in the ultimately impaired phagocytic activity and the attenuated release of phagolysosomal inflammatory and chemotactic signals such as il‐1β / 6 / 8 , underscoring the impaired immune function of the mutants. Furthermore, Atp7a is shown to interact with proteins Lamp1 and Ctsb to facilitate copper trafficking and with Rabep1 and Rabgef1, to shield these proteins from degradation. Meanwhile, Atp7a‐dependent copper trafficking is essential in Rabgef1 ubiquitination and the consequent activation of Rab5 and Rab7. These thereby enhance phagolysosomal activity and reinforce the immune response of neutrophils and macrophages against AH infection. In conclusion, this study compellingly establishes the pivotal role of Atp7a in sustaining the bactericidal capacities of immune cells in fish, while also illuminating the potential immune‐related implications for individuals with ATP7A deficiency.