Department of Plant Medicals, Andong National University, Andong, 36720, Korea.
Department of Plant Medicals, Andong National University, Andong, 36720, Korea.
J Invertebr Pathol. 2024 Jun;204:108095. doi: 10.1016/j.jip.2024.108095. Epub 2024 Mar 16.
Epoxyoctadecamonoenoic acids (EpOMEs) are produced from linoleic acid by a cytochrome P450 monooxygenase (CYP) and play a crucial role in terminating excessive and unnecessary immune responses during the late infection stage in insects. This suggests that an increase in the EpOME level may enhance the virulence of insect pathogens against pests. This study tested this hypothesis using a specific inhibitor against soluble epoxide hydrolase (sEH) to degrade EpOMEs, which leads to elevated endogenous EpOME levels. A baculovirus, Autographa californica multiple nucleopolyhedrovirus (AcMNPV), was used to infect three different lepidopteran insects (Spodoptera exigua, Maruca vitrata, and Plutella xylostella) by oral feeding or hemocoelic injection treatments. Within one hour, the viral infection induced the expression of three different phospholipase A (PLA) genes and, after 12 h, up-regulated the expressions of CYP and sEH genes in Spodopera exigua. As expected, AcMNPV virulence was suppressed by the addition of arachidonic acid (a catalytic product of PLA) but was enhanced by the addition of either of the EpOME regioisomers. In addition, treatment with a specific sEH inhibitor (AUDA) increased AcMNPV virulence against three different lepidopteran insects, presumably by increasing endogenous EpOME levels. This enhanced effect of EpOMEs on virulence was further supported by specific RNA interference (RNAi), in which RNAi specific to CYP expression decreased AcMNPV virulence while a specific RNAi against sEH expression significantly enhanced virulence. In response to AcMNPV infection, TUNEL assay results showed that S. exigua larvae exhibited apoptosis in the midgut, fat body, and epidermis. Inhibition of apoptosis by a pan-caspase inhibitor, Z-VAD-FMK, significantly increased virulence. Similarly, the addition of AUDA to the viral treatment suppressed the gene expression of five inducible caspases and cytochrome C to suppress apoptosis, which led to a significant increase in the tissue viral titers. These results indicate that EpOMEs play a role in terminating excessive and unnecessary immune responses against viral infection during the late stage by down-regulating antiviral apoptosis in lepidopteran insects.
环氧十八碳单烯酸（EpOMEs）是由细胞色素 P450 单加氧酶（CYP）从亚油酸产生的，在昆虫晚期感染阶段对终止过度和不必要的免疫反应起着至关重要的作用。这表明 EpOME 水平的增加可能会增强昆虫病原体对害虫的毒力。本研究使用一种针对可溶性环氧化物水解酶（sEH）的特异性抑制剂来降解 EpOMEs，从而导致内源性 EpOME 水平升高，以此来验证这一假设。研究使用杆状病毒——棉铃虫多核多角体病毒（AcMNPV）通过口服或血腔注射处理来感染三种不同的鳞翅目昆虫（斜纹夜蛾、菜粉蝶和小菜蛾）。在一小时内，病毒感染诱导了三种不同的磷脂酶 A（PLA）基因的表达，12 小时后，上调了斜纹夜蛾中 CYP 和 sEH 基因的表达。正如预期的那样，添加花生四烯酸（PLA 的一种催化产物）抑制了 AcMNPV 的毒力，但添加 EpOME 的任一同位异构体都增强了 AcMNPV 的毒力。此外，用一种特异性的 sEH 抑制剂（AUDA）处理增加了 AcMNPV 对三种不同鳞翅目昆虫的毒力，推测是通过增加内源性 EpOME 水平。EpOMEs 对毒力的增强作用进一步得到了特异性 RNA 干扰（RNAi）的支持，其中 CYP 表达的特异性 RNAi 降低了 AcMNPV 的毒力，而 sEH 表达的特异性 RNAi 则显著增强了毒力。对 AcMNPV 感染的 TUNEL 检测结果表明，斜纹夜蛾幼虫的中肠、脂肪体和表皮出现凋亡。用泛半胱天冬酶抑制剂 Z-VAD-FMK 抑制凋亡显著增加了毒力。同样，在病毒处理中添加 AUDA 抑制了五个诱导型半胱天冬酶和细胞色素 C 的基因表达，以抑制凋亡，从而导致组织病毒滴度显著增加。这些结果表明，EpOMEs 通过下调鳞翅目昆虫对病毒感染的过度和不必要的免疫反应，在晚期发挥作用，从而终止抗病毒凋亡。
