Developmental changes in the protein composition of Manduca sexta lipid droplets

Lipids in Insect Reproduction: Where, How, and Why

Modern insects have inhabited the earth for hundreds of millions of years, and part of their successful adaptation lies in their many reproductive strategies. Insect reproduction is linked to a high metabolic rate that provides viable eggs in a relatively short time. In this context, an accurate interplay between the endocrine system and the nutrients synthetized and metabolized is essential to produce healthy offspring. Lipids guarantee the metabolic energy needed for egg formation and represent the main energy source consumed during embryogenesis. Lipids availability is tightly regulated by a complex network of endocrine signals primarily controlled by the central nervous system (CNS) and associated endocrine glands, the corpora allata (CA) and corpora cardiaca (CC). This endocrine axis provides hormones and neuropeptides that significatively affect tissues closely involved in successful reproduction: the fat body, which is the metabolic center supplying the lipid resources and energy demanded in egg formation, and the ovaries, where the developing oocytes recruit lipids that will be used for optimal embryogenesis. The post-genomic era and the availability of modern experimental approaches have advanced our understanding of many processes involved in lipid homeostasis; therefore, it is crucial to integrate the findings of recent years into the knowledge already acquired in the last decades. The present chapter is devoted to reviewing major recent contributions made in elucidating the impact of the CNS/CA/CC-fat body-ovary axis on lipid metabolism in the context of insect reproduction, highlighting areas of fruitful research.

Sublethal toxicity of sulfoxaflor to parasitoid Binodoxys communis Gahan

Integrated pest management is focused on combining biological and chemical controls. There is evidence of a negative impact of neonicotinoids on biological control, however, sulfoxaflor (SFX), a novel insecticide, its impact on parasitoid natural predator remain limited. Binodoxys communis is an important parasitic natural enemy of Aphis gossypii, which may have direct and indirect toxicity from the insecticides and aphids. Understanding the potential threat of SFX to B. communis is therefore essential to integrated pest management and the conservation of parasitoids. Here, the effects of sublethal doses of SFX on B. communis larvae and adults are presented for the first time. Sublethal SFX doses had a significant negative effect on the survival rate, adult life span, duration of development, and rate of parasitism. Moreover, exposure to sublethal SFX doses also had adverse effects on the biological performance of the next generation of B. communis. Based on the transcriptome analysis, the expression of genes involved in fatty acid metabolism, glycerolipid metabolism, glycerophospholipid metabolism, peroxidase, lysosomes, glutathione metabolism, drug metabolism, and CYP450 were significantly shifted by sublethal SFX exposure. These results indicate that sublethal SFX doses might adversely affect the biological performance of B. communis by altering gene expression related to the function of detoxification systems and energy metabolism. In conclusion, considering the beneficial ecological services of provided by parasitoids and the negative effects of sulfoxaflor across a greater usage scale, we emphasize the importance to optimize pesticide applications in IPM packages, in order to ensure the safety and survival of natural pest parasitoids.

Genome-wide identification, classification, and expression profiling of serine esterases and other esterase-related proteins in the tobacco hornworm, Manduca sexta

Serine esterases (SEs) are hydrolases that catalyze the conversion of carboxylic esters into acids and alcohols. Lipases and carboxylesterases constitute two major groups of SEs. Although over a hundred of insect genomes are known, systematic identification and classification of SEs are rarely performed, likely due to large size and complex composition of the gene family in each species. Considering their key roles in lipid metabolism and other physiological processes, we have categorized 144 M. sexta SEs and SE homologs (SEHs), 114 of which contain a motif of GXSXG. Multiple sequence alignment and phylogenetic tree analysis have revealed 39 neutral lipases (NLs), 3 neutral lipase homologs (NLHs), 11 acidic lipases (ALs), 3 acidic lipase homologs (ALHs), a lipase-3, a triglyceride lipase, a monoglyceride lipase, a hormone-sensitive lipase, and a GDSL lipase. Eighty-three carboxylesterase genes encode 29 α-esterases (AEs), 12 AEHs (e.g., SEH4-1-3), 20 feruloyl esterases (FEs), 2 FEHs, 2 β-esterases (BEs), 2 integument esterases (IEs), 1 IEH, 4 juvenile hormone esterases, 2 acetylcholinesterases, gliotactin, 6 neuroligins, neurotactin, and an uncharacteristic esterase homolog. In addition to these GXSXG proteins, we have identified 26 phospholipases and 13 thioesterases. Expression profiling of these genes in specific tissues and stages has provided insights into their functions including digestion, detoxification, hormone processing, neurotransmission, reproduction, and developmental regulation. In summary, we have established a framework of information on SEs and related proteins in M. sexta to stimulate their research in the model species and comparative investigations in agricultural pests or disease vectors.

Trypanosoma cruzi modulates lipid metabolism and highjacks phospholipids from the midgut of Rhodnius prolixus

Chagas disease is potentially life-threatening and caused by the protozoan parasite Trypanosoma cruzi. The parasite cannot synthesize some lipids and depends on the uptake of these lipids from its vertebrate and invertebrate hosts. To achieve this, T. cruzi may need to modify the physiology of the insect host for its own benefit. In this study, we investigated the interaction of T. cruzi (Y strain) with its insect vector Rhodnius prolixus and how it manipulates the vector lipid metabolism. We observed a physiological change in lipid flux in of infected insects. In the fat body of infected insects, triacylglycerol levels decreased by 80.6% and lipid storage droplet-1(LSD-1) mRNA levels were lower, when compared to controls. Lipid sequestration by infected midguts led to increased levels of 5' AMP-activated protein kinase (AMPK) phosphorylation and activation in the fat body, inhibiting the synthesis of fatty acids and stimulating their oxidation. This led to reduced lipid levels in the fat body of infected insets, despite the fact that T. cruzi does not colonize this tissue. There was a 3-fold increase, in lipid uptake and synthesis in the midgut of infected insects. Finally, our results suggest that the parasite modifies the lipid flux and metabolism of its vector R. prolixus through the increase in lipid delivery from the fat body to midgut that are then scavenge by T cruzi.

An insight on the future therapeutic application potential of Stevia rebaudiana Bertoni for atherosclerosis and cardiovascular diseases

Stevia rebaudiana Bertoni is a native plant to Paraguay. The extracts have been used as a famous sweetening agent, and the bioactive components derived from stevia possess a broad spectrum of therapeutical potential for various illnesses. Among its medicinal benefits are anti-hypertensive, anti-tumorigenic, anti-diabetic, and anti-hyperlipidemia. Statins (3-hydro-3-methylglutaryl-coenzyme A reductase inhibitor) are a class of drugs used to treat atherosclerosis. Statins are explicitly targeting the HMG-CoA reductase, an enzyme in the rate-limiting step of cholesterol biosynthesis. Despite being widely used in regulating plasma cholesterol levels, the adverse effects of the drug are a significant concern among clinicians and patients. Hence, steviol glycosides derived from stevia have been proposed as an alternative in replacing statins. Diterpene glycosides from stevia, such as stevioside and rebaudioside A have been evaluated for their efficacy in alleviating cholesterol levels. These glycosides are a potential candidate in treating and preventing atherosclerosis provoked by circulating lipid retention in the sub-endothelial lining of the artery. The present review is an effort to integrate the pathogenesis of atherosclerosis, involvement of lipid droplets biogenesis and its associated proteins in atherogenesis, current approaches to treat atherosclerosis, and pharmacological potential of stevia in treating the disease.

A look into Colorado potato beetle lipid metabolism through the lens of lipid storage droplet proteins

The Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) inflicts serious damage to potato plants by feeding ravenously on their leaves. Adult L.decemlineata have a photoperiod-induced dormancy response, also known as diapause, which allows them to survive severe winter conditions by digging into soil. Most insects that undergo diapause accumulate abundant lipid reserves prior to diapause and utilize most of them during the diapause. This process is likely to be governed by the interplay of lipid storage droplet proteins (LSDs), also known as perilipins, with the help of other proteins. Here, genes encoding L. decemlineata LSD1 and LSD2 were identified. Both were expressed primarily in the fat body with LdLSD1 and LdLSD2 being primarily expressed in adult and larval stages, respectively. LdLSD1 was up-regulated in starving larvae, while LdLSD2 was primarily expressed in feeding larvae. The expression pattern of LdLSD1 in adults during feeding, diapause and post-diapause contrasted to the total body fat levels, while the expression pattern of LdLSD2 was positively correlated with total body fat levels. RNA interference (RNAi) of LdLSD2 in larvae suggested a core role for LSD2 in the protection/assembly of storage lipids as this treatment reduced overall lipid droplet volume. These data shed light on the functions of these proteins in L. decemlineata and their roles in both diapause and during starvation.

A journey into the world of insect lipid metabolism

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.

The Puzzling Conservation and Diversification of Lipid Droplets from Bacteria to Eukaryotes

Membrane compartments are amongst the most fascinating markers of cell evolution from prokaryotes to eukaryotes, some being conserved and the others having emerged via a series of primary and secondary endosymbiosis events. Membrane compartments comprise the system limiting cells (one or two membranes in bacteria, a unique plasma membrane in eukaryotes) and a variety of internal vesicular, subspherical, tubular, or reticulated organelles. In eukaryotes, the internal membranes comprise on the one hand the general endomembrane system, a dynamic network including organelles like the endoplasmic reticulum, the Golgi apparatus, the nuclear envelope, etc. and also the plasma membrane, which are linked via direct lateral connectivity (e.g. between the endoplasmic reticulum and the nuclear outer envelope membrane) or indirectly via vesicular trafficking. On the other hand, semi-autonomous organelles, i.e. mitochondria and chloroplasts, are disconnected from the endomembrane system and request vertical transmission following cell division. Membranes are organized as lipid bilayers in which proteins are embedded. The budding of some of these membranes, leading to the formation of the so-called lipid droplets (LDs) loaded with hydrophobic molecules, most notably triacylglycerol, is conserved in all clades. The evolution of eukaryotes is marked by the acquisition of mitochondria and simple plastids from Gram-positive bacteria by primary endosymbiosis events and the emergence of extremely complex plastids, collectively called secondary plastids, bounded by three to four membranes, following multiple and independent secondary endosymbiosis events. There is currently no consensus view of the evolution of LDs in the Tree of Life. Some features are conserved; others show a striking level of diversification. Here, we summarize the current knowledge on the architecture, dynamics, and multitude of functions of the lipid droplets in prokaryotes and in eukaryotes deriving from primary and secondary endosymbiosis events.

Manduca sexta Perilipin 1B: A new PLIN1 isoform linked to fat storage prior to pupation

Perilipins (PLINs) are proteins that associate with lipid droplets (LDs) and play roles in the control of triglycerides (TG) metabolism. Two types of PLINs - 1 and 2- occur in insects. Following previous work on MsPLIN1A (a 42 kDa protein formerly called MsLsd1), here we report a new PLIN1 isoform, MsPLIN1B. MsPLIN1B cDNA was cloned and the 1835bp cDNA contains an ORF encoding a 47.9 kDa protein whose expression was confirmed by mass spectrometry. Alternative transcripts A and B, which differ in the alternative use of exon 1, were the most abundant PLIN1 transcripts in the fat body. These transcripts encode nearly identical proteins except that the B isoform contains 59 additional residues in its amino terminus. No conserved domain was identified in the extra region of MsPLIN1B. The novel PLIN1 isoform is found in lepidopteran species. In Manduca, PLIN1B was expressed only in the 5th instar larva and its levels correlated with fat storage. Furthermore, PLIN1B levels increased with the fat content of the diet in insects of the same age confirming a direct relationship between PLIN1B and TG storage irrespective of development. The nutritional status impacted PLIN1B levels, which decreased in starvation and increased with subsequent re-feeding. Altogether data support a link between PLIN1B and TG storage in caterpillars prior to pupation. The combined findings suggest distinct roles for PLIN1A, PLIN1B and PLIN2. MsPLIN1A abundance correlates with mobilization of TG stores, MsPLIN2 with the synthesis of new LDs and MsPLIN1B abundance correlates with high levels of TG storage and large LD sizes at the end of the last feeding period.

Lipid Droplets in Health and Disease

Lipids are essential building blocks synthesized by complex molecular pathways and deposited as lipid droplets (LDs) in cells. LDs are evolutionary conserved organelles found in almost all organisms, from bacteria to mammals. They are composed of a hydrophobic neutral lipid core surrounding by a phospholipid monolayer membrane with various decorating proteins. Degradation of LDs provide metabolic energy for divergent cellular processes such as membrane synthesis and molecular signaling. Lipolysis and autophagy are two main catabolic pathways of LDs, which regulate lipid metabolism and, thereby, closely engaged in many pathological conditons. In this review, we first provide an overview of the current knowledge on the structural properties and the biogenesis of LDs. We further focus on the recent findings of their catabolic mechanism by lipolysis and autophagy as well as their connection ragarding the regulation and function. Moreover, we discuss the relevance of LDs and their catabolism-dependent pathophysiological conditions.

Clues on the function of Manduca sexta perilipin 2 inferred from developmental and nutrition-dependent changes in its expression

Cellular triglycerides (TG) are stored in cytosolic lipid droplets (LDs). Perilipins (PLIN) are a group of LD-proteins that play important roles in the assembly and transport of LDs and in TG metabolism. Two members of the PLIN family are found in insects (PLIN1 & 2 or Lsd1 & 2). We have cloned and expressed Manduca sexta PLIN2 (MsPLIN2), and studied developmental and nutritional changes in the expression of PLIN2. Nutritional changes induced fast alterations in PLIN2 mRNA and protein levels in fat body and midgut of the feeding larvae. The relationship observed between PLIN2 expression and TG synthesis in both larval fat body and midgut suggests that PLIN2 is needed when tissues are accumulating TG. However, when the fat body was storing TG at maximal capacity, MsPLIN2 levels declined. This unexpected finding suggests the occurrence of alternative mechanism/s to shield TG from the action of lipases in M. sexta LDs. In addition, it implies that the cellular level of lipid storage could be modulating MsPLIN2 expression and/or degradation. The study also confirmed that MsPLIN2 was most abundant in the adult fat body, which is characterized by a high rate of TG hydrolysis and lipid mobilization. Whether MsPLIN2 is directly involved in lipolysis and/or the secretion of lipids in the fat body of adult of M. sexta is unknown at this time. Nonetheless, the coexistence of high PLIN2 and lipolysis levels suggests a complex role for MsPLIN2. Altogether, we found that MsPLIN2 is needed when the synthesis of glycerides, DG and TG, is active even if the insect is accumulating or consuming TG.

Lipids in Insect Oocytes: From the Storage Pathways to Their Multiple Functions

In insect physiology, the mechanisms involved in the buildup and regulation of yolk proteins in developing oocytes have been thoroughly researched during the last three decades. Comparatively, the study of lipid metabolism in oocytes had received less attention. The importance of this issue lies in the fact that lipids make up to 40% of the dry weight of an insect egg, being the most important supply of energy for the developing embryo. Since the oocyte has a very limited capacity to synthesize lipids de novo, most of the lipids in the mature eggs arise from the circulation. The main lipid carriers in the insect circulatory system are the lipoproteins lipophorin and vitellogenin. In some species, the endocytosis of lipophorin and vitellogenin may account for about 10% of the lipids present in mature eggs. Thus, most of the lipids are transferred by a lipophorin-mediated pathway, in which the lipoprotein unloads its lipid cargo at the surface of oocytes without internalization. This chapter recapitulates the current status on lipid storage and its utilization in insect oocytes and discusses the participation of key factors including lipoproteins, transfer proteins, lipolytic enzymes, and dynamic organelles such as lipid droplets. The new findings in the field of lipophorin receptors are presented in the context of lipid accumulation during egg maturation, and the roles of lipids beyond energy source are summarized from the perspective of oogenesis and embryogenesis. Finally, prospective and fruitful areas of future research are suggested.

As the fat flies: The dynamic lipid droplets of Drosophila embryos

Research into lipid droplets is rapidly expanding, and new cellular and organismal roles for these lipid-storage organelles are continually being discovered. The early Drosophila embryo is particularly well suited for addressing certain questions in lipid-droplet biology and combines technical advantages with unique biological phenomena. This review summarizes key features of this experimental system and the techniques available to study it, in order to make it accessible to researchers outside this field. It then describes the two topics most heavily studied in this system, lipid-droplet motility and protein sequestration on droplets, discusses what is known about the molecular players involved, points to open questions, and compares the results from Drosophila embryo studies to what it is known about lipid droplets in other systems.

Lipid Droplets as Signaling Platforms Linking Metabolic and Cellular Functions

The main cells of the adipose tissue of animals, adipocytes, are characterized by the presence of large cytosolic lipid droplets (LDs) that store triglyceride (TG) and cholesterol. However, most cells have LDs and the ability to store lipids. LDs have a well-known central role in storage and provision of fatty acids and cholesterol. However, the complexity of the regulation of lipid metabolism on the surface of the LDs is still a matter of intense study. Beyond this role, a number of recent studies have suggested that LDs have major functions in other cellular processes, such as protein storage and degradation, infection, and immunity. Thus, our perception of LDs has been radically transformed from simple globules of fat to highly dynamic organelles of unexpected complexity. Here, we compiled some recent evidence supporting the emerging view that LDs act as platforms connecting a number of relevant metabolic and cellular functions.

Rab proteins implicated in lipid storage and mobilization

Abnormal intracellular accumulation or transport of lipids contributes greatly to the pathogenesis of human diseases. In the liver, excess accumulation of triacylglycerol (TG) leads to fatty liver disease encompassing steatosis, steatohepatitis and fibrosis. This places individuals at risk of developing cirrhosis, hepatocellular carcinoma or hepatic decompensation and also contributes to the emergence of insulin resistance and dyslipidemias affecting many other organs. Excessive accumulation of TG in adipose tissue contributes to insulin resistance as well as to the release of cytokines attracting leucocytes leading to a pro-inflammatory state. Pathological accumulation of cholesteryl ester (CE) in macrophages in the arterial wall is the progenitor of atherosclerotic plaques and heart disease. Overconsumption of dietary fat, cholesterol and carbohydrates explains why these diseases are on the increase yet offers few clues for how to prevent or treat individuals. Dietary regimes have proven futile and barring surgery, no realistic alternatives are at hand as effective drugs are few and not without side effects. Overweight and obesity-related diseases are no longer restricted to the developed world and as such, constitute a global problem. Development of new drugs and treatment strategies are a priority yet requires as a first step, elucidation of the molecular pathophysiology underlying each associated disease state. The lipid droplet (LD), an up to now overlooked intracellular organelle, appears at the heart of each pathophysiology linking key regulatory and metabolic processes as well as constituting the site of storage of both TGs and CEs. As the molecular machinery and mechanisms of LDs of each cell type are being elucidated, regulatory proteins used to control various cellular processes are emerging. Of these and the subject of this review, small GTPases belonging to the Rab protein family appear as important molecular switches used in the regulation of the intracellular trafficking and storage of lipids.

TGL-mediated lipolysis in Manduca sexta fat body: possible roles for lipoamide-dehydrogenase (LipDH) and high-density lipophorin (HDLp)

Triglyceride-lipase (TGL) is a major fat body lipase in Manduca sexta. The knowledge of how TGL activity is regulated is very limited. A WWE domain, presumably involved in protein-protein interactions, has been previously identified in the N-terminal region of TGL. In this study, we searched for proteins partners that interact with the N-terminal region of TGL. Thirteen proteins were identified by mass spectrometry, and the interaction with four of these proteins was confirmed by immunoblot. The oxidoreductase lipoamide-dehydrogenase (LipDH) and the apolipoprotein components of the lipid transporter, HDLp, were among these proteins. LipDH is the common component of the mitochondrial α-keto acid dehydrogenase complexes whereas HDLp occurs in the hemolymph. However, subcellular fractionation demonstrated that these two proteins are relatively abundant in the soluble fraction of fat body adipocytes. The cofactor lipoate found in typical LipDH substrates was not detected in TGL. However, TGL proved to have critical thiol groups. Additional studies with inhibitors are consistent with the notion that LipDH acting as a diaphorase could preserve the activity of TGL by controlling the redox state of thiol groups. On the other hand, when TG hydrolase activity of TGL was assayed in the presence of HDLp, the production of diacylglycerol (DG) increased. TGL-HDLp interaction could drive the intracellular transport of DG. TGL may be directly involved in the lipoprotein assembly and loading with DG, a process that occurs in the fat body and is essential for insects to mobilize fatty acids. Overall the study suggests that TGL occurs as a multi-protein complex supported by interactions through the WWE domain.

The proteomics of lipid droplets: structure, dynamics, and functions of the organelle conserved from bacteria to humans

Lipid droplets are cellular organelles that consists of a neutral lipid core covered by a monolayer of phospholipids and many proteins. They are thought to function in the storage, transport, and metabolism of lipids, in signaling, and as a specialized microenvironment for metabolism in most types of cells from prokaryotic to eukaryotic organisms. Lipid droplets have received a lot of attention in the last 10 years as they are linked to the progression of many metabolic diseases and hold great potential for the development of neutral lipid-derived products, such as biofuels, food supplements, hormones, and medicines. Proteomic analysis of lipid droplets has yielded a comprehensive catalog of lipid droplet proteins, shedding light on the function of this organelle and providing evidence that its function is conserved from bacteria to man. This review summarizes many of the proteomic studies on lipid droplets from a wide range of organisms, providing an evolutionary perspective on this organelle.