SummaryLipid bodies, hpid-rich cytoplasmic inclusions, are characteristically abundant in vivo in leukocytes associated with inflammation. Because lipid bodies are potential reservoirs of esterified arachidohate and sites at which eicosanoid-forming enzymes may localize, we evaluated mechanisms of lipid body formation in neutrophils (PMN). Among receptor-mediated agonists, platelet-activating factor (PAF), but not C5a, formyl-methyl-phenylalanine, interleukin 8, or leukotriene (LT) B4, induced the rapid formation of lipid bodies in PMN. This action of PAF was receptor mediated, as it was dose dependently inhibited by the PAF receptor antagonist WEB 2086 and blocked by pertussis toxin. Lipid body induction by PAF required 5-lipoxygenase (LO) activity and was inhibited by the 5-1ipoxygenase-activating protein antagonist MK 886 and the 5-LO inhibitor zileuton, but not by cyclooxygenase inhibitors. Corroborating the dependency of PAF-induced lipid body formation on 5-LO, PMN and macrophages from wild-type mice, but not from 5-LO genetically deficient mice, formed lipid bodies on exposure to PAF both in vitro and in vivo within the pleural cavity. The 5-LO product inducing lipid body formation was not LTB4 but was 5(S)-hydroxyeicosatetraenoic acid [5(S)-HETE], which was active at 10-fold lower concentrations than PAF and was also inhibited by pertussis toxin but not by zileuton or WEB 2086. Furthermore, 5-HETE was equally effective in inducing lipid body formation in both wild-type and 5-LO genetically deficient mice. Both PAF-and 5(S)-HETE-induced lipid body formation were inhibited by the protein kinase C (PKC) inhibitors staurosporine and chelerythrine, the phosphotipase C (PLC) inhibitors D609 and U-73122, and by actinomycin D and cycloheximide. Prior stimulation of human PMN with PAF to form lipid bodies enhanced eicosanoid production in response to submaximal stimulation with the calcium ionophore A23187; and the levels of both prostaglandin (PG) E 2 and LTB 4 correlated with the number of lipid bodies. Furthermore, pretreatment of cells with actinomycin D or cycloheximide inhibited not only the induction of lipid body formation by PAF, but also the PAF-induced "priming" for enhanced PGE 2 and LTB 4 in PMN. Thus, the compartmentalization of lipids to form lipid bodies in PMN is dependent on specific cellular responses that can be PAF receptor mediated, involves signaling through 5-LO to form 5-HETE and then through PKC and PLC, and requires new protein synthesis. Since increases in lipid body numbers correlated with priming for enhanced PGE 2 and LTB4 production in PMN, the induction of lipid bodies may have a role in the formation of eicosanoid mediators by leukocytes involved in inflammation.
Leukotrienes have been implicated in the regulation of immune responses, including inflammation and immediate hypersensitivity reactions. Here, we describe the phenotypic analysis of leukotriene-deficient mice generated by inactivation of the 5-lipoxygenase (SLO) gene. These 5LO(-/-) mice were unable to synthesize detectable levels of leukotrienes and were more resistant to lethal anaphylaxis induced by platelet-activating factor. The intensity of an acute inflammatory response induced by arachidonic acid was similar in 5LO(-/-) mice and controls. However, the response in 5LO(-/-) mice, but not in controls, could be virtually eliminated by a cyclooxygenase inhibitor. These data suggest that inflammatory responses are modulated by arachidonic acid metabolites through a variety of interconnected mechanisms. This has important implications for understanding the early events of an inflammatory response and for designing drugs for use in therapeutic intervention.
Leukotrienes are potent inflammatory mediators synthesized from arachidonic acid (AA) predominately by cells of myeloid origin. The synthesis of these lipids is believed to be dependent not only on the expression of the enzyme 5-lipoxygenase (5-LO), which catalyzes the first steps in the synthesis of leukotrienes, but also on expression of a nuclear membrane protein termed the 5-LO–activating protein (FLAP). To study the relationship of these two proteins in mediating the production of leukotrienes in vivo and to determine whether the membrane protein FLAP has additional functions in various inflammatory processes, we have generated a mouse line deficient in this protein. FLAP-deficient mice develop normally and are healthy. However, an array of assays comparing inflammatory reactions in FLAP-deficient mice and in normal controls revealed that FLAP plays a role in a subset of these reactions. Although examination of DTH and IgE-mediated passive anaphylaxis showed no difference between wild-type and FLAP-deficient animals, mice without FLAP possessed a blunted inflammatory response to topical AA and had increased resistance to platelet-activating factor–induced shock compared to controls. Also, edema associated with Zymosan A–induced peritonitis was markedly reduced in animals lacking FLAP. To determine whether these differences relate solely to a deficit in leukotriene production, or whether they reflect an additional role for FLAP in inflammation, we compared the FLAP-deficient mice to 5-LO–deficient animals. Evaluation of mice lacking FLAP and 5-LO indicated that production of leukotrienes during inflammatory responses is dependent upon the availability of FLAP and did not support additional functions for FLAP beyond its role in leukotriene production.
To identify the E-prostanoid (EP) receptors that mediate the hemodynamic actions of PGE2, we studied acute vascular responses to infusions of PGE2using lines of mice in which each of four EP receptors (EP1 through EP4) have been disrupted by gene targeting. In mixed groups of males and females, vasodepressor responses after infusions of PGE2were significantly diminished in the EP2 −/− and EP4 −/− lines but not in the EP1 −/− or EP3 −/− lines. Because the actions of other hormonal systems that regulate blood pressure differ between sexes, we compared the roles of individual EP receptors in males and females. We found that the relative contribution of each EP-receptor subclass was strikingly different in males from that in females. In females, the EP2 and EP4 receptors, which signal by stimulating adenylate cyclase, mediate the major portion of the vasodepressor response to PGE2. In males, the EP2 receptor has a modest effect, but most of the vasodepressor effect is mediated by the phospholipase C-coupled EP1receptor. Finally, in male mice, the EP3 receptor actively opposes the vasodepressor actions of PGE2. Thus the hemodynamic actions of PGE2 are mediated through complex interactions of several EP-receptor subtypes, and the role of individual EP receptors differs dramatically in males from that in females. These differences may contribute to sexual dimorphism of blood pressure regulation.
The transition to pulmonary respiration following birth requires rapid alterations in the structure of the mammalian cardiovascular system. One dramatic change that occurs is the closure and remodeling of the ductus arteriosus (DA), an arterial connection in the fetus that directs blood flow away from the pulmonary circulation. A role for prostaglandins in regulating the closure of this vessel has been supported by pharmacological and genetic studies. The production of prostaglandins is dependent on two cyclooxygenases (COX-1 and COX-2), which are encoded by separate genes. We report here that the absence of either or both COX isoforms in mice does not result in premature closure of the DA in utero. However, 35% of COX-2(؊͞؊) mice die with a patent DA within 48 h of birth. In contrast, the absence of only the COX-1 isoform does not affect closure of the DA. The mortality (35%) and patent DA incidence due to absence of COX-2 is, however, significantly increased (79%) when one copy of the gene encoding COX-1 is also inactivated. Furthermore, 100% of the mice deficient in both isoforms die with a patent DA within 12 h of birth, indicating that in COX-2-deficient mice, the contribution of COX-1 to DA closure is gene dosage-dependent. Together, these data establish roles for COX-1, and especially for COX-2, in the transition of the cardiopulmonary circulation at birth. T he ductus arteriosus (DA) is an arterial connection in the fetus between the pulmonary artery and the aorta. The DA directs deoxygenated blood away from the pulmonary circulation toward the descending aorta and to the umbilicoplacental circulation where oxygenation occurs. The DA plays a critical role in the cardiovascular physiology of the fetus and newborn (for review see ref. 1). In utero patency of the DA is essential for proper fetal health, and premature DA closure causes pulmonary hypertension, congestive heart failure, and edema. In contrast, failure of the DA to close after birth, designated patent DA, compromises postnatal health by contributing to respiratory complications, including pulmonary hypertension and edema (2).A family of lipid mediators known as prostaglandins (PGs) are among the factors that have been shown to influence the tone of the DA. The initial reaction in the synthesis of all PGs is catalyzed by prostaglandin G͞H synthase, also known as cyclooxygenase (COX), two isoforms of which have been identified. Both COX-1 and COX-2 catalyze the synthesis of PGH 2 , a product required for the formation of the various biologically active PGs (3). Individual PGs act through specific receptors to mediate their biological effects. The role for PGs in regulation of DA tone was initially determined from the observation that nonsteroidal anti-inflammatory drugs (NSAIDs), which act by inhibiting COX (4), modulate DA tone in utero and following birth (1).The dilation of the DA in utero is an active process maintained primarily by PGE 2 . The PG receptors that may have a role in dilation of the DA include the PGE 2 receptors, EP2 (5) and EP...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.