NEDD4 activates mitophagy by interacting with LC3 to restrain reactive oxygen species and apoptosis in Apostichopus japonicus challenged with Vibrio splendidus

Mitophagy, the selective degradation of damaged mitochondria by Autophagy, plays a crucial role in the survival of coelomocytes in Apostichopus japonicus following Vibrio splendidus Infection by suppressing the generation of Reactive Oxygen Species (ROS) and attenuating cell Apoptosis. A recent study revealed that reducing the expression of the neural precursor cell-expressed developmentally downregulated gene 4 (NEDD4), an Enzyme 3 (E3) ubiquitin Ligase, significantly affects mitochondrial degradation. Prior to the present study, the functional role of NEDD4 in marine invertebrates was largely unexplored. Therefore, we investigated the role of NEDD4 in the activation of Mitophagy, modulation of ROS levels, and induction of Apoptosis in A. japonicus infected with V. splendidus. The results demonstrated that V. splendidus Infection and lipopolysaccharide (LPS) challenge significantly increased the mRNA levels of NEDD4 in A. japonicus coelomocytes, which was consistent with changes in Mitophagy under the same conditions. Knockdown of AjNEDD4 using specific small interfering RNAs (siRNAs) impaired Mitophagy and caused accumulation of damaged mitochondria, as observed using transmission electron microscopy (TEM) and confocal microscopy. Furthermore, AjNEDD4 was localized to the mitochondria in both coelomocytes and HEK293T cells. Simultaneously, coelomocytes were treated with the inhibitor indole-3-carbinol (I3C) to confirm the regulatory role of AjNEDD4 in Mitophagy. The accumulation of AjNEDD4 in the mitochondria and the level of Mitophagy decreased. Subsequent investigations demonstrated that AjNEDD4 interacts directly with the microtubule-associated protein LIGHT chain 3 (LC3), a key regulator of Autophagy and Mitophagy, indicating its involvement in the Mitophagy pathway. Moreover, AjNEDD4 interference hindered the interaction between AjNEDD4 and LC3, thereby impairing the engulfment and subsequent clearance of damaged mitochondria. Finally, AjNEDD4 interference led to a significant increase in intracellular ROS levels, followed by increased Apoptosis. Collectively, these findings suggest that NEDD4 acts as a crucial regulator of Mitophagy in A. japonicus and plays a vital role in maintaining cellular homeostasis following V. splendidus Infection. NEDD4 suppresses ROS production and subsequent Apoptosis by promoting Mitophagy, thereby safeguarding the survival of A. japonicus under pathogenic conditions. Further investigation of the mechanisms underlying NEDD4-mediated Mitophagy may provide valuable insights into the development of novel strategies for disease control in aquaculture farms.

Apostichopus japonicus; Microtubule-associated protein 1 light chain 3; Mitophagy; Neural precursor cell-expressed developmentally downregulated gene 4; Reactive oxygen species.