Eicosanoid signaling in insect immunology: New genes and unresolved issues

Authors: KIM, YONGGYUN - Andong National University; Stanley, David

Submitted to: Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2021
Publication Date: 2/1/2021
Citation: Kim, Y., Stanley, D.W. 2021. Eicosanoid signaling in insect immunology: New genes and unresolved issues. Genes. 12(2). Article 211. https://doi.org/10.3390/genes12020211.
DOI: https://doi.org/10.3390/genes12020211

Interpretive Summary: Chemical insecticides are effective pest insect management tools, however, negative effects, including environmental contamination and insect resistance to the insecticides attend use of these products. These negative effects drive research into alternative insect management technologies such as biological control based on deploying insect pathogenic microbes, known as microbial control. The problem with microbial insect management is insects have very powerful immune responses to pathogenic microbes, which reduces the efficacy of these microbes. Research is necessary to identify and compromise insect immune mechanisms to improve microbial control effectiveness. In this paper we clarify biochemical signaling that acts in mediating immune reactions to insect pathogenic microbes, and show how research to discover the signals also points to promising directions in future research to compromise insect immune functions. This important information will be used by research teams globally and ultimately benefit citizens of the United States and other countries with improved nutrition and food security.

Technical Abstract: This paper is focused on eicosanoid signaling in insect immunology. We cover 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 AA is 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.