Why most insects have very low proportions of C20 polyunsaturated fatty acids: The oxidative stress hypothesis

Stanley, David; Kim, Yonggyun

doi:10.1002/arch.21622

Cited by 27 publications

(12 citation statements)

References 32 publications

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“…Mammals maintain substantial proportions of AA in PLs, from which it can be hydrolyzed for eicosanoid biosynthesis. Insects tend to maintain very low proportions of AA (often no more than trace amounts) and high proportions of linoleic acid (LA; 18:2n-6) in cellular PLs, which may help reduce oxidative damage to cellular PLs [15]. Elongation/desaturation pathways that convert LA into AA were documented in the 1980s [16], however the research was conducted in a biochemical, rather than a physiological context.…”

Section: Biosynthesis Of Aamentioning

confidence: 99%

Eicosanoid Signaling in Insect Immunology: New Genes and Unresolved Issues

Kim

Stanley

2021

Genes

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This paper is focused on eicosanoid signaling in insect immunology. We begin with eicosanoid biosynthesis through the actions of phospholipase A2, responsible for hydrolyzing the C18 polyunsaturated fatty acid, linoleic acid (18:2n-6), from cellular phospholipids, which is subsequently converted into arachidonic acid (AA; 20:4n-6) via elongases and desaturases. The synthesized AA is then oxygenated into one of three groups of eicosanoids, prostaglandins (PGs), epoxyeicosatrienoic acids (EETs) and lipoxygenase products. We mark the distinction between mammalian cyclooxygenases and insect peroxynectins, both of which convert AA into PGs. One PG, PGI2 (also called prostacyclin), is newly discovered in insects, as a negative regulator of immune reactions and a positive signal in juvenile development. Two new elements of insect PG biology are a PG dehydrogenase and a PG reductase, both of which enact necessary PG catabolism. EETs, which are produced from AA via cytochrome P450s, also act in immune signaling, acting as pro-inflammatory signals. Eicosanoids signal a wide range of cellular immune reactions to infections, invasions and wounding, including nodulation, cell spreading, hemocyte migration and releasing prophenoloxidase from oenocytoids, a class of lepidopteran hemocytes. We briefly review the relatively scant knowledge on insect PG receptors and note PGs also act in gut immunity and in humoral immunity. Detailed new information on PG actions in mosquito immunity against the malarial agent, Plasmodium berghei, has recently emerged and we treat this exciting new work. The new findings on eicosanoid actions in insect immunity have emerged from a very broad range of research at the genetic, cellular and organismal levels, all taking place at the international level.

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Section: Biosynthesis Of Aamentioning

confidence: 99%

Eicosanoid Signaling in Insect Immunology: New Genes and Unresolved Issues

Kim

Stanley

2021

Genes

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“…In particular, long chain-PUFAs (LC-PUFAs: 20 or more carbon atoms) function as signaling molecules to mediate immunity, development, and reproduction 2 . LC-PUFAs are also rich (7–25%) in aquatic insects 3 , but are rare in terrestrial insects due to evolutionary adaptations to prevent oxidative stress 4 . However, terrestrial insects are rich in linoleic acid (LA: 18 carbon atoms) present in phospholipids (PLs), and this fatty acid might be available for the production of LC-PUFAs with the help of elongase and desaturase activities 5 .…”

Section: Introductionmentioning

confidence: 99%

EpOMEs act as immune suppressors in a lepidopteran insect, Spodoptera exigua

Vatanparast

Ahmed

Lee

et al. 2020

Sci Rep

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Epoxyoctadecamonoenoic acids (EpOMEs) are epoxide derivatives of linoleic acid (9,12-octadecadienoic acid) and include 9,10-EpOME and 12,13-EpOME. They are synthesized by cytochrome P450 monooxygenases (CYPs) and degraded by soluble epoxide hydrolase (sEH). Although EpOMEs are well known to play crucial roles in mediating various physiological processes in mammals, their role is not well understood in insects. This study chemically identified their presence in insect tissues: 941.8 pg/g of 9,10-EpOME and 2,198.3 pg/g of 12,13-EpOME in fat body of a lepidopteran insect, Spodoptera exigua. Injection of 9,10-EpOME or 12,13-EpOME into larvae suppressed the cellular immune responses induced by bacterial challenge. EpOME treatment also suppressed the expression of antimicrobial peptide (AMP) genes. Among 139 S. exigua CYPs, an ortholog (SE51385) to human EpOME synthase was predicted and its expression was highly inducible upon bacterial challenge. RNA interference (RNAi) of SE51385 prevented down-regulation of immune responses at a late stage (> 24 h) following bacterial challenge. A soluble epoxide hydrolase (Se-sEH) of S. exigua was predicted and showed specific expression in all development stages and in different larval tissues. Furthermore, its expression levels were highly enhanced by bacterial challenge in different tissues. RNAi reduction of Se-sEH interfered with hemocyte-spreading behavior, nodule formation, and AMP expression. To support the immune association of EpOMEs, urea-based sEH inhibitors were screened to assess their inhibitory activities against cellular and humoral immune responses of S. exigua. 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA) was highly potent in suppressing the immune responses. The addition of AUDA to a pathogenic bacterium significantly increased bacterial pathogenicity by suppressing host immune defense. In sum, this study demonstrated that EpOMEs play a crucial role in facilitating anti-inflammatory responses in S. exigua.

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“…Furthermore, PLA 2 catalyzes the committed step for eicosanoid biosynthesis by releasing AA from phospholipids (Kim et al, 2018 ; Mouchlis and Dennis, 2019 ). Eicosanoids then mediate cellular and humoral immune responses against various microbial pathogens, such as bacteria, fungi, and viruses (Stanley and Kim, 2020 ). Thus, the activation of PLA 2 by Se-DSP1 could upregulate the levels of eicosanoids to mediate immune responses.…”

Section: Discussionmentioning

confidence: 99%

Salicylic Acid, a Plant Hormone, Suppresses Phytophagous Insect Immune Response by Interrupting HMG-Like DSP1

et al. 2021

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Salicylic acid is a plant hormone that can mediate various plant physiological processes. Salicylic acid can bind to human high mobility group box 1 (HMGB1) and interrupt its role in mediating immune responses. Dorsal switch protein 1 (DSP1) is an insect homolog of HMGB1. In this study, a DSP1 (Se-DSP1) encoded in Spodoptera exigua, a phytophagous insect, was characterized, and its potential role in immune response was explored. Upon bacterial challenge, Se-DSP1 was localized in the nucleus and released into the hemolymph. The released Se-DSP1 could mediate both cellular and humoral immune responses by activating eicosanoid biosynthesis. Salicylic acid could bind to Se-DSP1 with a high affinity. The immune responses of S. exigua were significantly interrupted by SA feeding. Larvae reared on tomatoes with high endogenous SA levels became more susceptible to entomopathogens. Taken together, these results suggest a tritrophic defensive role of plant SA against phytophagous insects.

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Why most insects have very low proportions of C20 polyunsaturated fatty acids: The oxidative stress hypothesis

Cited by 27 publications

References 32 publications

Eicosanoid Signaling in Insect Immunology: New Genes and Unresolved Issues

Eicosanoid Signaling in Insect Immunology: New Genes and Unresolved Issues

EpOMEs act as immune suppressors in a lepidopteran insect, Spodoptera exigua

Salicylic Acid, a Plant Hormone, Suppresses Phytophagous Insect Immune Response by Interrupting HMG-Like DSP1

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