Nutritional stress is a common environmental challenge for insects in nature. As a central organ of energy metabolism, the fat body plays a crucial role in maintaining energy homeostasis. However, the mechanisms by which the fat body regulates programmed cell death (PCD) during energy crises remain unclear. In this study, the fat body of Bombyx mori was used as a model to investigate the regulatory mechanisms underlying PCD transitions induced by sustained energy depletion. The results indicated that starvation caused a significant reduction in adenosine triphosphate (ATP), rapid depletion of glycogen and triglycerides, and marked inhibition of the endoplasmic reticulum (ER) calcium pump enzyme SERCA. Concurrently, it upregulated the expression of the calcium channel IP3R. These combined effects led to Ca2+ efflux from the ER calcium stores and cytoplasmic Ca2+ overload. Intracellular Ca2+ levels significantly increased, followed by a decrease during prolonged starvation, paralleling changes in calpain activity and accompanied by the upregulation of the proapoptotic protein NtATG5. Short-term starvation promoted autophagy by significantly increasing LC3-II and ATG5 expression, whereas prolonged starvation promoted calpain-mediated cleavage of ATG5 to generate NtATG5 and activated caspase-3, leading to apoptosis. Furthermore, the IP3R inhibitor 2-APB significantly suppressed starvation-induced calcium signaling, autophagy, and apoptosis. This study reveals the regulatory mechanism by which the Bombyx mori fat body modulates PCD under starvation stress via the ER-Ca2+-calpain signaling pathway, providing crucial insights into how nutritional deprivation causes physiological damage in insects.
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