Leucine Enhances Stress Resistance in Honeybees (Apis mellifera L.) by Modulating Sestrin-Dependent Antioxidant Responses

Simple SummaryHoneybees are essential for crop pollination and ecological balance, yet their health is increasingly compromised by environmental stressors such as heavy metals and pesticides. These stressors induce oxidative stress, a cellular imbalance that damages tissues and impairs bee survival. This study investigated whether leucine, a common amino acid in pollen, can enhance the natural antioxidant defenses of honeybees. Our experiments showed that supplementing bees with leucine significantly increased their capacity to counteract oxidative stress, reduced cellular damage, and improved survival under stress conditions. Further analysis revealed that leucine acts by activatingsestrin, which serves as a key regulator of antioxidant responses. Notably, the protective effect of leucine did not primarily depend on the previously recognized TOR pathway. Whensestrinwas experimentally silenced, bees became highly susceptible to stress and developed gut damage, confirming its essential role. Importantly, leucine partially restored resilience even whensestrinwas absent, suggesting additional protective mechanisms. These findings demonstrated that dietary leucine supplementation offers a feasible nutritional strategy to strengthen honeybee health and stress resistance.Environmental stressors such as heavy metals and pesticides pose significant threats to honeybee health by inducing oxidative stress. Enhancing nutritional supply has emerged as a potential strategy for honeybees to enhance stress resistance. However, the underlying molecular mechanisms remain poorly understood. This study investigated the role of leucine (Leu) in regulating antioxidant responses in honeybees (Apis melliferaL.), with a focus on the involvement ofsestrinand the Target of Rapamycin (TOR) signaling pathway. The results showed that Leu supplementation activated the TOR signaling pathway and upregulatedsestrinexpression, leading to enhanced antioxidant capacity and reduced reactive oxygen species (ROS) levels. Silencingsestrindisrupted antioxidant homeostasis, increased stress susceptibility, and caused midgut damage, confirming its essential role in oxidative stress resistance. Notably, inhibition of TOR did not prohibit the protective effects of Leu, suggesting thatsestrin, rather than TOR, serves as a key mediator. Furthermore, Leu fine-tuned antioxidant responses under different stress conditions throughsestrin. Overall, this study demonstrates that Leu andsestrinplay a central role in maintaining antioxidant homeostasis and provide a theoretical basis for nutritional strategies to improve honeybee health and stress resilience.