Identification of a prostaglandin E2 receptor that regulates mosquito oenocytoid immune cell function in limiting bacteria and parasite infection

Abstract

Lipid-derived signaling molecules known as eicosanoids have integral roles in mediating immune and inflammatory processes across metazoans. This includes the function of prostaglandins and their cognate G protein-coupled receptors (GPCRs) to employ their immunological actions. In insects, prostaglandins have been implicated in the regulation of both cellular and humoral immune responses, yet studies have been limited by the absence of a described prostaglandin receptor. Here, we characterize a prostaglandin E2 receptor (AgPGE2R) in the mosquito Anopheles gambiae and examine its contributions to innate immunity. AgPGE2R expression is most abundant in circulating hemocytes where it is primarily localized to oenocytoid immune cell populations. Through the administration of prostaglandin E2 (PGE2) and AgPGE2R-silencing by RNAi, we demonstrate that PGE2 signaling regulates the expression of a subset of prophenoloxidases (PPOs) and antimicrobial peptides (AMPs). PGE2 priming via the AgPGE2R significantly limited bacterial replication and suppressed Plasmodium oocyst survival. Additional experiments establish that PGE2 priming increases phenoloxidase (PO) activity through the increased expression of PPO1 and PPO3, which significantly influence Plasmodium oocyst survival. We also provide evidence that PGE2 priming is concentration-dependent, where high concentrations of PGE2 promote oenocytoid lysis, negating the protective effects of PGE2 priming on anti-Plasmodium immunity. Taken together, our results characterize the AgPGE2R and the role of prostaglandin signaling on immune cell function, providing new insights into the role of PGE2 on anti-bacterial and anti-Plasmodium immune responses in the mosquito host.

Single-cell analysis of mosquito hemocytes identifies signatures of immune cell subtypes and cell differentiation

“…This directly contrasts previous suggestions that mosquito PPOs are only constitutively expressed in oenocytoid populations (Castillo et al, 2006;Hillyer and Strand, 2014;Strand, 2008), yet is supported by recent evidence that phagocytic granulocyte populations in mosquitoes significantly contribute to PPO production (Kwon and Smith, 2019;Smith et al, 2016). Furthermore, the enriched expression of PPO1, PPO8, and (to a lesser extent) PPO3 in oenocytoids is supported by recent studies examining prostaglandin signaling on PPO expression in mosquito oenocytoid populations (Kwon et al, 2020). (Gulley et al, 2013;Kanost and Jiang, 2015).…”

“…Recent studies of prostaglandin signaling in An. gambiae have also implicated the regulation of PPO1, PPO3, and PPO8 in oenocytoid populations (Kwon et al, 2020), providing further support that a subset of PPOs are specifically regulated in oenocytoids. In addition, several lines of evidence support that granulocyte populations also contribute to PPO expression in An.…”

“…Traditional classifications of mosquito hemocytes describe three cell types: prohemocyte precursors, phagocytic granulocytes, and oenocytoids that have primary roles in melanization (Castillo et al, 2006). However, recent studies have begun to challenge these traditional immune cell classifications, demonstrating the existence of multiple types of phagocytic cells (Kwon and Smith, 2019;Severo et al, 2018) and that both granulocytes and oenocytoids contribute to prophenoloxidase expression (Bryant and Michel, 2016;Kwon et al, 2020;Kwon and Smith, 2019;Severo et al, 2018;Smith et al, 2016). Together, this suggests that there is additional complexity to mosquito immune cells that are not accurately represented by the traditional classification of mosquito hemocytes into three cell types.…”

Single-cell analysis of mosquito hemocytes identifies signatures of immune cell subtypes and cell differentiation

“…This directly contrasts previous suggestions that mosquito PPOs are only constitutively expressed in oenocytoid populations (Castillo et al, 2006;Hillyer and Strand, 2014;Strand, 2008), yet is supported by recent evidence that phagocytic granulocyte populations in mosquitoes significantly contribute to PPO production (Kwon and Smith, 2019;Smith et al, 2016). Furthermore, the enriched expression of PPO1, PPO8, and (to lesser extent) PPO3 in oenocytoids is supported by recent studies examining prostaglandin signaling on PPO expression in mosquito oenocytoid populations (Kwon et al, 2020).…”

Eicosanoid Signaling in Insect Immunology: New Genes and Unresolved Issues

“…Kwon et al [ 68 ] posted a preprint on the Biorxiv preprint server, in which they report on a PGE 2 receptor (AgPGE 2 R) that regulates mosquito, A. gambiae , oenocytoid immune cell function. The receptor is expressed in midgut, fat body, ovary, Malpighian tubules and hemocytes.…”