Edwardsiella piscicida T3SS effector EseJ regulates PPARγ production to promote colonization in macrophages

The Type III secretion system (T3SS) and its effector proteins are crucial virulence factors in the pathogenesis of bacterial pathogens. A dozen of T3SS effector proteins have been identified in Edwardsiella piscicida, a bacterial pathogen threatening aquaculture industries, but the specific role of EseJ, a specific effector with large molecular weight (1 358 aa and 146 kDa) essential for infection processes, remains unclear. This study revealed that PPARγ expression was upregulated during the infection of J774A.1 macrophages by E. piscicida, whereas the T3SS-deficient mutant (ΔT3SS) did not alter PPARγ expression. Screening of several deletion mutants of T3SS effectors further validated that EseJ promotes PPARγ expression in J774A.1 cells. During E. piscicida infection, EseJ-induced PPARγ expression suppressed the secretion of pro-inflammatory cytokines, enhanced the production of anti-inflammatory cytokines, reduced the release of mitochondrial reactive oxygen species (ROS), and alleviated mitochondrial damages. The upregulation of PPARγ contributed to E. piscicida colonization within J774A.1 cells. Additionally, pull-down assays highlighted 77 host proteins potentially interacting with EseJ and bacterial two-hybrid assays confirmed the direct interaction between EseJ and the ubiquinone oxidoreductase subunit 7 (NDUFA7). In conclusion, our study provides new insights into the role of T3SS effector EseJ in the pathogenesis of E. piscicida, providing potential targets for the prevention and control of E. piscicida infections.