Insect Fat Body: Energy, Metabolism, and Regulation

Abstract

The fat body plays major roles in the life of insects. It is a dynamic tissue involved in multiple metabolic functions. One of these functions is to store and release energy in response to the energy demands of the insect. Insects store energy reserves in the form of glycogen and triglycerides in the adipocytes, the main fat body cell. Insect adipocytes can store a great amount of lipid reserves as cytoplasmic lipid droplets. Lipid metabolism is essential for growth and reproduction and provides energy needed during extended nonfeeding periods. This review focuses on energy storage and release and summarizes current understanding of the mechanisms underlying these processes in insects. INSECT FAT BODY: AN OVERVIEWThe insect fat body plays an essential role in energy storage and utilization. It is the central storage depot for excess nutrients. In addition, it is an organ of great biosynthetic and metabolic activity (77). Fat body cells not only control the synthesis and utilization of energy reserves-fat and glycogen-but also synthesize most of the hemolymph proteins and circulating metabolites. Large amounts of relevant proteins, such as storage proteins used as an amino acid reservoir for morphogenesis, lipophorins responsible for the lipid transport in circulation, or vitellogenins for egg maturation, are secreted by the fat body (74). Most of the insect's intermediary metabolism takes place in this organ, including lipid and carbohydrate metabolism, protein synthesis, and amino acid and nitrogen metabolism. Some metabolic processes are stage specific such as the synthesis and secretion of storage proteins into the hemolymph that occur in the feeding larva or the synthesis of vitellogenin in adult insects.To perform multiple metabolic functions to fulfill the changing physiological needs of the insect during development, the fat body must be able to integrate signals from other organs. Many of these functions are hormonally regulated, and thus the fat body is the target organ of several hormones (47,107). At the same time, the fat body responds to the metabolic requirements of the organ itself. Therefore, several metabolic processes in the fat body must be tightly coupled to a number of metabolic pathways.Physiological systems to sense nutrient reserves are expected in all organisms, and in insects nutrient sensing itself appears to be the domain of the fat body (87). Studies of Drosophila melanogaster and, more recently, mosquitoes have shown that the fat body specifically expresses aminoacid transporters that function as nutrient sensors (14,61). The level of nutrient reserves accumulated in the fat body modulates several important aspects of the insect's life such as the rate of insect growth, the timing of metamorphosis, and egg development (87). The fat body coordinates insect growth with metamorphosis or reproduction by storing or releasing components central to these events. For example, the synthesis of vitellogenin in the fat body of Aedes aegypti female mosquitoes is NIH Public Access

The African turquoise killifish: A research organism to study vertebrate aging and diapause

“…(b) Selected features of the turquoise killifish that are conserved in human and vertebrate canonical research organisms (zebrafish and house mouse), but are missing in invertebrate canonical research organisms (round worm and fruit fly). References: nervous system: Shimeld and Holland (2000), Freeman and Doherty (2006); Lohr and Hammerschmidt (2011), Oikonomou and Shaham (2011), immune system: Langenau and Zon (2005), Engelmann and Pujol (2010), Buchon, Silverman and Cherry ( 2014); circulatory system: Lehmacher, Abeln and Paululat ( 2012); Stephenson, Adams and Vaccarezza ( 2017); respiratory system: Schottenfeld, Song and Ghabrial ( 2010); skeletal system: Shimeld and Holland (2000); muscular system: Moerman and Williams (2006), Demontis, Piccirillo, Goldberg and Perrimon ( 2013), Piccirillo, Demontis, Perrimon and Goldberg ( 2014), Goody, Carter, Kilroy, Maves and Henry ( 2017); digestive system: McKay, McKay, Avery and Graff ( 2003), Arrese and Soulages (2010), Hashmi et al. ( 2013), Kuraishi, Hori and Kurata ( 2013), Lemaitre and Miguel‐Aliaga (2013), McGhee (2013), Ritter et al.…”

Population dependent effects of photoperiod on diapause related physiological traits in an invasive beetle (Leptinotarsa decemlineata)

“…Therefore insects which diapause as adults typically prepare for overwintering by building large lipid stores in a special organ called the fat body (Hahn & Denlinger 2011). Energy can also be stored in other biochemical forms, for instance as carbohydrates and proteins, but since the energy yield per unit weight in carbohydrates and proteins is much lower than in lipids, lipids are the most common form (Arrese & Soulages 2010). Stored lipids are not only essential for survival during diapause in many species, but also for post-diapause fitness (Hahn & Denlinger 2007) where they act as energy starting capital for, among other, dispersal and development of reproductive tissues , de Kort 1990.…”

“…Stored lipids are not only essential for survival during diapause in many species, but also for post-diapause fitness (Hahn & Denlinger 2007) where they act as energy starting capital for, among other, dispersal and development of reproductive tissues , de Kort 1990. In the fat body, most hemolymph lipids garnered from the breakdown of food are converted into neutral lipids (triglycerides or triacylglycerides) (Arrese & Soulages 2010). Neutral lipids are the main form of storage lipids in the insect fat body, usually constituting more than 90 % of the fat body total lipid mass (Canavoso et al 2001).…”

Variation in lipid synthesis, but genetic homogeneity, among Leptopilina parasitic wasp populations

“…The ability of animals to store energy reserves in the form of fat is essential for both survival and reproduction (Arrese & Soulages, 2010; Hazel, 1995; Turkish & Sturley, 2009). Storage fat can help overcome harsh environmental conditions, such as times at which food is not available, which is an all‐pervasive challenge for many animals (McCue, Terblanche, & Benoit, 2017).…”

“…Lipids are also a critical component of the egg in oviparous animals (Geister, Lorenz, Hoffmann, & Fischer, 2008; Sloggett & Lorenz, 2008; Sotherland & Rahn, 1987), constituting approximately 30%–40% of total macronutrients in insect eggs (Muller et al., 2017). Lipids can further serve as an important energetic substrate fueling flight (Arrese & Soulages, 2010; Kemp & Alcock, 2003; Zera, Sall, & Otto, 1999). The amount of storage lipids available throughout life can thus have major fitness effects, and lipid synthesis is a highly conserved traits (Ballard, Melvin, & Simpson, 2008; Jakob, Marshall, & Uetz, 1993; Kemp & Alcock, 2003).…”