AUTHOR=Lu Kai , Zhang Xinyu , Chen Xia , Li Yue , Li Wenru , Cheng Yibei , Zhou Jinming , You Keke , Zhou Qiang 

TITLE=Adipokinetic Hormone Receptor Mediates Lipid Mobilization to Regulate Starvation Resistance in the Brown Planthopper, Nilaparvata lugens

JOURNAL=Frontiers in Physiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2018.01730

DOI=10.3389/fphys.2018.01730

ISSN=1664-042X

ABSTRACT=<p>Lipid storage must be efficiently mobilized to sustain the energy demands during processes of exercise or starvation. In insects, adipokinetic hormone (AKH) and brummer lipase are well-known regulators of lipid mobilization. We recently demonstrated that brummer-dependent lipolysis regulates starvation resistance in the brown planthopper, <italic>Nilaparvata lugens</italic>, one of the most destructive rice pests. The present work investigated the roles of the AKH signaling system in lipid mobilization during the starvation process in <italic>N. lugens</italic>. <italic>Nl</italic>AKHR is a typical G protein-coupled receptor (GPCR) and possesses high structure and sequence similarity to other insect AKHRs. Spatial and developmental expression profiles suggested that <italic>Nl</italic>AKH is released from the corpora cardiaca to activate <italic>Nl</italic>AKHR mainly expressed in the fat body. Starvation significantly induced the expression of <italic>NlAKH</italic> and <italic>NlAKHR</italic>, indicating a potential role of the AKH signaling system in starvation resistance. To reveal the functions of the AKH signaling system, a double-stranded RNA (dsRNA)-mediated knockdown of <italic>NlAKHR</italic> and <italic>Nl</italic>AKH peptide injection was performed. The results show <italic>NlAKHR</italic> silencing decreased the levels of 1,2-diacylglycerol (DAG) in the hemolymph and increased triacylglycerol (TAG) levels in the fat body, whereas <italic>Nl</italic>AKH injection led to a critical accumulation of DAG in the hemolymph and a severe reduction of TAG content in the fat body. Knockdown of <italic>NlAKHR</italic> resulted in prolonged lifespan and high levels of whole-body TAG, indicating an inability to mobilize TAG reserves during starvation. Conversely, the <italic>Nl</italic>AKH injection reduced the survival and accelerated TAG mobilization during starvation, which further confirms the role of <italic>Nl</italic>AKH in lipolysis. Moreover, <italic>NlAKHR</italic> silencing caused obesity in <italic>N. lugens</italic>, whereas <italic>Nl</italic>AKH injection depleted organismal TAG reserves <italic>in vivo</italic> and produced a slim phenotype. These results indicate that lipid mobilization is regulated by the AKH signaling system, which is essential for adjusting body lipid homeostasis and ensuring energy supplement during starvation in <italic>N. lugens</italic>.</p>