The Effects of Disrupting Ca2+ Homeostasis on the ERs and Lipid Metabolism in the Hepatopancreas of Penaeus vannamei Exposed to Ammonia Stress.

Ca2+ homeostasis regulates endoplasmic reticulum (ER) stress and lipid metabolism and is involved in the stress response in mammals. However, how these regulatory pathways respond in aquatic animals exposed to stressful environmental conditions remains unclear. In this study, we used siRNA to inhibit the expression levels of Bip, SERCA, IP3R, and MCU, which are involved in regulating Ca2+ homeostasis in the hepatopancreas of Penaeus vannamei. An ammonia stress experiment was subsequently conducted (stress concentration of 11.3 mg/L) to measure parameters associated with ER stress, Ca2+ homeostasis, and lipid metabolism. This study was performed to verify the roles of Ca2+ homeostasis in regulating ER stress and lipid metabolism in P. vannamei subjected to ammonia stress. Interfering with Bip gene expression limited the unfolded protein reaction (UPR), reduced Ca2+ transport into the ER, and promoted Ca2+ efflux. These findings indicate that Bip plays a critical role in the regulation of ER stress and Ca2+ homeostasis. Interfering with SERCA gene expression exacerbated ER stress responses and promoted the UPR. This interference also reduced ER Ca2+ leakage through IP3R and aggravated the cellular energy deficiency state, indicating that SERCA is crucial for maintaining ER Ca2+ levels and managing energy balance. Reduced IP3R gene expression inhibited ER stress responses by decreasing Ca2+ efflux from the ER. This reduction in Ca2+ transport into the ER and mitochondria resulted in cellular energy deficiency and modulated lipid metabolism, highlighting the role of IP3R in Ca2+ signaling and metabolic regulation. Interfering with MCU gene expression alleviated ROS-induced ERs, led to ER Ca2+ overload, and resulted in cellular energy deficiency while enhancing lipid metabolism. These findings indicate that MCU is vital for regulating mitochondrial Ca2+ uptake and cellular energy metabolism under stress conditions. These results suggest that reducing ER Ca²⁺ efflux and maintaining ER Ca²⁺ homeostasis represent candidate molecular targets whose contributions to ammonia tolerance in shrimp are worth investigating in future studies.