A journey into the world of insect lipid metabolism

Abstract

Lipid metabolism is fundamental to life. In insects, it is critical, during reproduction, flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. Fat body contains various different cell types; however, adipocytes and oenocytes are the primary cells related to lipid metabolism. Lipid metabolism starts with the hydrolysis of dietary lipids, absorption of lipid monomers, followed by lipid transport from midgut to the fat body, lipogenesis or lipolysis in the fat body, and lipid transport from fat body to other sites demanding energy. Lipid metabolism is under the control of hormones, transcription factors, secondary messengers and posttranscriptional modifications. Primarily, lipogenesis is under the control of insulin‐like peptides that activate lipogenic transcription factors, such as sterol regulatory element‐binding proteins, whereas lipolysis is coordinated by the adipokinetic hormone that activates lipolytic transcription factors, such as forkhead box class O and cAMP‐response element‐binding protein. Calcium is the primary–secondary messenger affecting lipid metabolism and has different outcomes depending on the site of lipogenesis or lipolysis. Phosphorylation is central to lipid metabolism and multiple phosphorylases are involved in lipid accumulation or hydrolysis. Although most of the knowledge of insect lipid metabolism comes from the studies on the model Drosophila; other insects, in particular those with obligatory or facultative diapause, also have great potential to study lipid metabolism. The use of these models would significantly improve our knowledge of insect lipid metabolism.

Two calcium‐binding chaperones from the fat body of the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) involved in diapause

“…Starvation-related downregulation of LdCrT is in accordance with the facts that (i) CrT deficiency reduces ER Ca 2+ store capacity (W. A. Wang et al, 2017), (ii) reduced ER Ca 2+ levels leads to lipid hydrolysis in insect fat body adipocytes (Baumbach et al, 2014;Subramanian et al, 2013;Toprak et al, 2020), (iii) lipids are the primary energy source during starvation which leads to lipid mobilization (Lee & Park, 2004), and (iv) fat body is one of the primary sites of LdCrT expression at the larval stage (current study). These findings suggest that CrT might be also involved in lipid metabolism.…”

Impact of high-fat diet on lifespan, metabolism, fecundity and behavioral senescence inDrosophila

“…Although several of the DILPs are involved in lipid metabolism in flies (Broughton et al, 2005;Musselman and Kühnlein, 2018;Toprak et al, 2020), we found that transcript levels of dilp1-dilp3, dilp5, and dilp6 displayed no significant changes with short of long-term exposure to HFD. Similar findings were presented in previous reports (Jung et al, 2018;Woodcock et al, 2015).…”

“…No differences were detected for transcripts of five different insulin-like peptides (dilp1-dilp3, dilp5, and dilp6). AKH is known to induce mobilization of lipids in insects, including Drosophila (Gäde and Auerswald, 2003;Grönke et al, 2007;Musselman and Kühnlein, 2018;Toprak et al, 2020;Van der Horst, 2003), but also to allocate carbohydrate as energy to fuel food search in hungry flies (Bharucha et al, 2008;Isabel et al, 2005;Lee and Park, 2004;Yu et al, 2016). AKH signaling has also been shown to regulate lifespan in flies (Katewa et al, 2012;Post et al, 2018;Waterson et al, 2014).…”

“…Drosophila has also been employed to model certain human diseases based on the fact that about 65% of human disease-related genes have functional orthologs in flies [see (Ugur et al, 2016;Yamamoto et al, 2014)]. Recently studies have emerged on the effect of HFD on health and physiology of Drosophila (Birse et al, 2010;Driver and Cosopodiotis, 1979;Heier and Kühnlein, 2018;Heinrichsen and Haddad, 2012;Huang et al, 2020;Jung et al, 2018;Musselman and Kühnlein, 2018;Rivera et al, 2019;Stobdan et al, 2019;Tatar et al, 2014;Toprak et al, 2020;Trinh and Boulianne, 2013;von Frieling et al, 2020;Woodcock et al, 2015). Most of these studies have investigated effects of relatively short exposure to HFD, ranging between one and three weeks, although some determined the effect of HFD on total lifespan (Heinrichsen and Haddad, 2012;Rivera et al, 2019;Woodcock et al, 2015).…”

The Diapause Lipidomes of Three Closely Related Beetle Species Reveal Mechanisms for Tolerating Energetic and Cold Stress in High-Latitude Seasonal Environments

“…This is reflective of patterns found also in other studies ( Irwin and Lee, 2003 ; Williams et al, 2012 ; Fründ et al, 2013 ; Lehmann et al, 2016 ) and probably highlights the effect of metabolic suppression ( Sinclair, 2015 ). It is of course also possible that other substrates are used for energy production than lipid, even though lipid seems most commonly used ( Hahn and Denlinger, 2007 ; Toprak et al, 2020 ). In the CPB it has for instance been shown that large quantities of a storage protein called Diapause Protein 1 is sequestered prior to diapause ( Lehmann et al, 2014b ).…”