Prostaglandin catabolism in Spodoptera exigua, a lepidopteran insect

Abstract

Several prostaglandins (PGs) and PG-synthesizing enzymes have been identified from insects. PGs mediate cellular and humoral immune responses. However, uncontrolled and prolonged immune responses might have adverse effects on survival. PG catabolism in insects has not been reported. Here, using a transcriptomic analysis, we predicted two PG-degrading enzymes, PG dehydrogenase (SePGDH) and PG reductase (SePGR), in Spodoptera exigua, a lepidopteran insect. SePGDH and SePGR expression levels were upregulated after immune challenge. However, their expression peaks occurred after those of PG biosynthesis genes such as PGE2 synthase or PGD2 synthase. SePGDH and SePGR expression levels were upregulated after injection with PGE2 or PGD2. In contrast, such upregulated expression was not detected after injection with leukotriene B4, an eicosanoid inflammatory mediator. RNA interference (RNAi) using double-stranded RNAs specific to SePGDH or SePGR suppressed their expression levels. The RNAi treatment resulted in an excessive and fatal melanization of larvae even after a non-pathogenic bacterial infection. Phenoloxidase (PO) activity mediating the melanization in larval plasma was induced by bacterial challenge or PGE2 injection. Although the induced PO activity decreased after 8 h in control, larvae treated with dsRNAs specific to PG-degrading enzyme genes kept the high PO activities for a longer period compared to control larvae. These results suggest that SePGDH and SePGR are responsible for PG degradation at a late phase of immune responses.

Eicosanoid Signaling in Insect Immunology: New Genes and Unresolved Issues

“…Two PG-degrading enzymes, PG dehydrogenase ( SePGDH ) and PG reductase ( SePGR ), act in S. exigua . [ 30 ]. SePGDH and SePGR expression levels are upregulated after immune challenge.…”

“…Here is the question whether the small G proteins including Rac1 activate the actin-associating factors in the hemocyte spreading. Based on Fascin, a molecular component of PGE 2 signaling pathway in D. melanogaster [52], proteinprotein interactions were predicted using the computer modeling program, STRING (http://version10a.string-db.org), and showed that Fascin interacts with 20 proteins including another Rho family small G protein, Cdc42 [30]. In the binding model, Cdc42 interacts with several actin-associated factors including actin monomer, actin-related proteins (Arp2/3) and profilin.…”

“…In the binding model, Cdc42 interacts with several actin-associated factors including actin monomer, actin-related proteins (Arp2/3) and profilin. With an addition of cofilin due to its function in actin remodeling [58], fascin, Arp2, profilin and Cdc42 were predicted as actin-associated factors that could lead to hemocyte spreading behavior in response to PGE 2 [30]. Under individual RNAi treatments, the hemocyte spreading behavior was significantly impaired, except for dsRNA treatment against cofilin, an actin-depolymerizing factor.…”

“…Arp2, profilin and Cdc42 were predicted as actin-associated factors that could lead to he-mocyte spreading behavior in response to PGE2 [30]. Under individual RNAi treatments, the hemocyte spreading behavior was significantly impaired, except for dsRNA treatment against cofilin, an actin-depolymerizing factor.…”

Genome-Wide Analysis Indicates a Complete Prostaglandin Pathway from Synthesis to Inactivation in Pacific White Shrimp, Litopenaeus vannamei

“…In humans, PGs are produced by the serial metabolic cascades of phospholipids cyclooxygenase (COX) and prostaglandin synthases (PGSs) and finally inactivated by 15hydroxyprostaglandin dehydrogenase (PGDH). The synthesis and inactivation pathways of PGs are conserved in mammals but partially missing in other animal groups, such as fish [14] and insects [15,16]. However, little is known regarding the PG synthesis and inactivation pathways of crustaceans.…”