Tumor necrosis factor receptor-associated factor 6 (TRAF6) regulates Aeromonas hydrophila-induced autophagy in yellow catfish (Pelteobagrus fulvidraco).

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a key adaptor protein and E3 ubiquitin ligase involved in immune signaling and autophagy regulation. However, its function in pathogen-induced autophagy in teleost fish remains poorly understood. In this study, a TRAF6 homolog (PfTRAF6) was identified and characterized from yellow catfish (Pelteobagrus fulvidraco). The open reading frame of PfTRAF6 (1617 bp) encodes a 538 amino acid protein containing a conserved Zn-RING domain, zinc finger-TRAF domain, and C-terminal MATH domain. Phylogenetic analysis revealed that PfTRAF6 clustered closely with TRAF6 from other catfish species. PfTRAF6 transcripts were ubiquitously expressed across examined tissues, with the highest level in blood. Following Aeromonas hydrophila infection, both mRNA and protein levels of PfTRAF6 were significantly upregulated in immune-related tissues, particularly in blood and spleen. RNA interference-mediated knockdown of PfTRAF6 in monocytes/macrophages (MO/MΦ) suppressed the conversion of LC3-I to LC3-II, decreased the mRNA expression of pro-inflammatory cytokines and phosphorylation of P62, and reduced the number of autophagosomes observed by transmission electron microscopy. These findings indicate that PfTRAF6 positively regulates A. hydrophila-induced autophagy in yellow catfish. This study provides the first evidence that TRAF6 modulates bacterial infection-triggered autophagy in teleosts, expanding the understanding of the conserved TRAF6-autophagy axis in vertebrate innate immunity.