PGE₂ MEDIATES OENOCYTOID CELL LYSIS VIA A SODIUM‐POTASSIUM‐CHLORIDE COTRANSPORTER

Abstract

Prostaglandin E2 (PGE2 ) mediates immune responses of the beet armyworm, Spodoptera exigua, including oenocytoid cell lysis (a class of lepidopteran hemocytes: OCL) via its specific membrane receptor to release inactive prophenoloxidase (PPO) into hemolymph. PPO is activated into phenoloxidase in the plasma to play crucial roles in the immune responses of S. exigua. The mechanism of OCL has not been elucidated, however we posed the hypothesis that a rapid accumulation of sodium ions within the oenocytoids allows a massive influx of water by the ion gradient, which leads to the cell lysis. It remains unclear which sodium channel is responsible for the OCL in response to PGE2 . This study identified a specific sodium channel called sodium-potassium-chloride cotransporter 1 (Se-NKCC1) expressed in hemocytes of S. exigua and analyzed its function in the OCL in response to PGE2 . Se-NKCC1 encodes a basic membrane protein (pI value = 8.445) of 1,066 amino acid residues, which contains 12 putative transmembrane domains. Se-NKCC1 was expressed in all developmental stages and tissues. qPCR showed that bacterial challenge significantly induced its expression. A specific inhibitor of NKCC, bumetanide, prevented the OCL in a dose-dependent manner. When RNA interference (RNAi) using double-stranded RNA specific to Se-NKCC1 suppressed its expression, the OCL and PPO activation were significantly inhibited in response to PGE2 . The RNAi treatment also reduced nodule formation to bacterial challenge. These results suggest that Se-NKCC1 is associated with OCL by facilitating inward transport of ions in response to PGE2 .

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

“…We provide evidence that PGE2 promotes oenocytoid lysis in a concentration-dependent manner, where increasing PGE2 concentrations result in increased oenocytoid lysis. This is supported by the role of prostaglandins in mediating the release of PPO through oenocytoid rupture in the beet armyworm S. exigua (6,27,41), although evidence suggests that lysis is independent of the prostaglandin receptor (6,41).…”

An aquaporin mediates cell shape change required for cellular immunity in the beet armyworm, Spodoptera exigua

“…PO activity is required for nodule formation by catalyzing melanization to produce black nodules. It can be induced by the release of its precursor from oenocytoids through cell lysis after water influx 26,27 . Oenocytoid cell lysis resulted in PO activation via PG signaling as seen in PGE 2 treatment (Fig.…”

“…This is because its inactive precursor (PPO) is produced from oenocytoids and released to plasma via cell lysis to be activated by proteases 26,66 . A specific receptor for PGE 2 can mediate cell lysis by activating sodium-potassium-chloride cotransporter to facilitate water influx 27 . These observations support the physiological role of Se-AQP in cellular immune responses by changing cell shape through transmembrane water fluxes.…”

“…PPO is synthesized from a specific hemocyte, oenocytoid, and released into plasma by cell lysis in beet armyworm, Spodoptera exigua 26 . To trigger cell lysis, water should be transported into hemocytes presumably through AQP via an ion gradient established by sodium-potassium-chloride cotransporter activity 27 . Thus, the present study hypothesize that AQP activity is required for cell volume change of hemocytes to perform cellular immune responses.…”

The clotting system in decapod crustaceans: History, current knowledge and what we need to know beyond the models

“…In the spiny lobster P. japonicus, granulocytes are the first cells to respond to Gram negative bacteria and LPS [113,114], in this case, secretory granule exocytosis leads to the release of unknown mediators that bring about clotting and lysis of semi-granulocytes and hyaline cells. In insects, it has been identified several signaling pathways and receptors involved in the lysis of relevant hemocytes and the release of humoral proteins, such as cytoplasmic proPO [115][116][117]. In these species cells lysis can also occur in the absence of microbial elicitors through endogenous mediators [115].…”