Apoptosis is regulated by a conserved gene network across species to maintain homeostasis and stress response. While intracellular apoptotic pathways are well characterized, the extracellular mechanisms governing apoptosis remain largely unexplored, likely due to divergence in species-specific gene sets involved in extracellular regulation. Here we uncover a new extracellular apoptotic mechanism mediated by acetylcholine-binding protein 5 (AChBP5) in the wolf spider Pardosa pseudoannulata. AChBP5 is highly expressed in the spider fat body (midgut diverticula), while other four AChBP genes are abundantly expressed in the tissue brain. Among five AChBP genes, only AChBP5 showed broad transcriptional induction upon exposure to various insecticides, including neonicotinoids and other classes. AChBP5 expression was also upregulated by reactive oxygen species (ROS) including H2O2key triggers of apoptosis. Functional analyzes showed that, in cultured cells, AChBP5 acted as an extracellular sacrificial buffer against oxidative stress to maintain cell viability, and was gradually inactivated by ROS in a concentration-dependent manner. RNAi-mediated silencing of AChBP5 significantly increased spider sensitivity to both induced and direct oxidative stress, underscoring its critical protective function. Collectively, these findings support a model in which lineage-specific genes, AChBP5 may contribute to extracellular modulation of apoptosis and provide a mechanism by which spiders may respond to chemical stressors.
