The Cytotoxic Enterotoxin ofAeromonas hydrophilaInduces Proinflammatory Cytokine Production and Activates Arachidonic Acid Metabolism in Macrophages

Open Access
Publisher Website
Google Scholar
Abstract
An aerolysin-related cytotoxic enterotoxin (Act) ofAeromonas hydrophilapossesses multiple biological activities, which include its ability to lyse red blood cells, destroy tissue culture cell lines, evoke a fluid secretory response in ligated intestinal loop models, and induce lethality in mice. The role of Act in the virulence of the organism has been demonstrated. In this study, we evaluated the potential of Act to induce production of proinflammatory cytokines associated with Act-induced tissue injury and Act's capacity to activate in macrophages arachidonic acid (AA) metabolism that leads to production of eicosanoids (e.g., prostaglandin E2[PGE2]). Our data indicated that Act stimulated the production of tumor necrosis factor alpha and upregulated the expression of genes encoding interleukin-1β (IL-1β) and IL-6 in the murine macrophage cell line RAW264.7. Act also activated transcription of the gene encoding inducible nitric oxide synthase. Act evoked the production of PGE2coupled to the cyclooxygenase-2 (COX-2) pathway. AA is a substrate for PGE2, and Act produced AA from phospholipids by inducing group V secretory phospholipase A2. We also demonstrated that Act increased cyclic AMP (cAMP) production in macrophages. cAMP, along with PGE2, could potentiate fluid secretion in animal models because of infiltration and activation of macrophages resulting from Act-induced tissue injury. After Act treatment of RAW cells, we detected an increased translocation of NF-κB and cAMP-responsive element binding protein (CREB) to the nucleus using gel shift assays. Act also upregulated production of antiapoptotic protein Bcl-2 in macrophages, suggesting a protective role for Bcl-2 against cell death induced by proinflammatory cytokines. The increased expression of genes encoding the proinflammatory cytokines, COX-2, and Bcl-2 appeared correlated with the activation of NF-κB and CREB. This is the first report of the detailed mechanisms of action of Act fromA. hydrophila.