背景:游离脂肪酸(FFA)在生物体中作为能源和底物发挥着至关重要的作用;然而,在各种情况下调节FFA水平稳态的分子机制,如喂养和非喂养阶段,没有完全澄清。全代谢昆虫在幼虫摄食阶段消化膳食甘油三酯(TAG),并在停止摄食后的变态过程中降解脂肪体内储存的TAG,这为本研究提供了一个合适的模型。
结果:本研究报道,以鳞翅目昆虫棉铃虫棉铃虫为模型,在取食和非取食阶段,两种脂肪酶受到激素的差异调节,以维持FFA水平的稳态。脂肪酶成员H-A样(Lha样),与人胰脂肪酶(PTL)有关,在喂养阶段在中肠中大量表达,而单酰基甘油脂肪酶ABHD12样(Abhd12样),与人单酰基甘油脂肪酶(MGL)有关,在非进食阶段在脂肪体中大量表达。Lha样通过JH细胞内受体耐甲氧烯1(MET1)被幼体激素(JH)上调,Abhd12样通过叉头盒O(FOXO)转录因子被20-羟基蜕皮激素(20E)上调。敲除Lha样降低了血淋巴中的FFA水平,并降低了脂肪体内的TAG水平。此外,脂滴(LD)很小,大脑形态异常,大脑的大小很小,幼虫表现出延迟化蛹的表型,小蛹,和延迟的组织重塑。Abhd12样的击倒降低了血淋巴中的FFA水平;然而,脂肪体内的TAG水平增加,LDs仍然很大。大脑的发育在幼体阶段被阻止,幼虫表现出延迟化蛹表型和延迟的组织重塑。
结论:不同激素对脂肪酶表达的差异调节决定了FFA在昆虫幼虫生长和变态的非摄食阶段的稳态和脂肪体内不同的TAG水平。FFA的稳态支持昆虫的生长,大脑发育,和变态。
BACKGROUND: Free fatty acids (FFAs) play vital roles as energy sources and substrates in organisms; however, the molecular mechanism regulating the homeostasis of FFA levels in various circumstances, such as feeding and nonfeeding stages, is not fully clarified. Holometabolous insects digest dietary triglycerides (TAGs) during larval feeding stages and degrade stored TAGs in the fat body during metamorphosis after feeding cessation, which presents a suitable model for this study.
RESULTS: This study reported that two lipases are differentially regulated by hormones to maintain the homeostasis of FFA levels during the feeding and nonfeeding stages using the lepidopteran insect cotton bollworm Helicoverpa armigera as a model. Lipase member H-A-like (Lha-like), related to human pancreatic lipase (PTL), was abundantly expressed in the midgut during the feeding stage, while the monoacylglycerol lipase ABHD12-like (Abhd12-like), related to human monoacylglycerol lipase (MGL), was abundantly expressed in the fat body during the nonfeeding stage. Lha-like was upregulated by juvenile hormone (JH) via the JH intracellular receptor methoprene-tolerant 1 (MET1), and Abhd12-like was upregulated by 20-hydroxyecdysone (20E) via forkhead box O (FOXO) transcription factor. Knockdown of Lha-like decreased FFA levels in the hemolymph and reduced TAG levels in the fat body. Moreover, lipid droplets (LDs) were small, the brain morphology was abnormal, the size of the brain was small, and the larvae showed the phenotype of delayed pupation, small pupae, and delayed tissue remodeling. Knockdown of Abhd12-like decreased FFA levels in the hemolymph; however, TAG levels increased in the fat body, and LDs remained large. The development of the brain was arrested at the larval stage, and the larvae showed a delayed pupation phenotype and delayed tissue remodeling.
CONCLUSIONS: The differential regulation of lipases expression by different hormones determines FFAs homeostasis and different TAG levels in the fat body during the feeding larval growth and nonfeeding stages of metamorphosis in the insect. The homeostasis of FFAs supports insect growth, brain development, and metamorphosis.