NOX1-ROS axis regulates the MAPK signaling pathway and activates caspase-1 to resist Edwardsiella piscicida infection

Abstract

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase serves as a primary generator of reactive oxygen species (ROS) and assumes a critical role in immune responses, cell proliferation or signal transduction processes. The intricate functionality of ROS endows NADPH oxidase with multifaceted roles in host defense mechanisms. However, the specific functions and underlying mechanisms of fish NADPH oxidase during bacterial infections remain largely elusive. In this research, zebrafish were employed as a model organism to investigate the antibacterial function and mechanism of NOX1. Immunofluorescence and subcellular fractionation analyses demonstrated that zebrafish NOX1 was predominantly localized in the cytoplasm. Moreover, upon infection with Edwardsiella piscicida, a significant upregulation of NOX1 expression was observed. Functional assays revealed that zebrafish NOX1 retained the conserved ability to promote ROS generation. This, in turn, suppressed the growth of E. piscicida through the bactericidal activity of ROS. Consequently, the survival rates of zebrafish and cultured cells were enhanced, accompanied by the upregulation of antibacterial genes. Mechanistic investigations further demonstrated that zebrafish NOX1 exerted its antibacterial effects by promoting the expression of critical genes within the MAPK signaling pathway. Simultaneously, zebrafish NOX1 activated caspase-1 via ROS, causing the induction of inflammatory cytokines. Additionally, the NOX1-ROS axis enhanced the transcriptional upregulation of chemokines, including monocyte chemoattractant protein-1 (mcp-1) and C-X-C motif chemokine ligand 8 (cxcl8), which accelerated neutrophil migration, thereby enabling a rapid response to bacterial infection. In summary, this study comprehensively elucidated the function and mechanism of NOX1 during bacterial infection in teleost. These results shed new light on the understanding of fish immunity and offer potential strategies for the prevention and control of fish diseases.