A Lipidomic Perspective of the Action of Group IIA Secreted Phospholipase A2 on Human Monocytes: Lipid Droplet Biogenesis and Activation of Cytosolic Phospholipase A2α.

Juan P Rodríguez,María A Balboa,Elbio Leiguez,Catarina Teixeira,Carlos Guijas,Jesús Balsinde,Bruno Lomonte,José M Gutiérrez

doi:10.3390/biom10060891

Abstract

Phospholipase A2s constitute a wide group of lipid-modifying enzymes which display a variety of functions in innate immune responses. In this work, we utilized mass spectrometry-based lipidomic approaches to investigate the action of Asp-49 Ca2+-dependent secreted phospholipase A2 (sPLA2) (MT-III) and Lys-49 sPLA2 (MT-II), two group IIA phospholipase A2s isolated from the venom of the snake Bothrops asper, on human peripheral blood monocytes. MT-III is catalytically active, whereas MT-II lacks enzyme activity. A large decrease in the fatty acid content of membrane phospholipids was detected in MT III-treated monocytes. The significant diminution of the cellular content of phospholipid-bound arachidonic acid seemed to be mediated, in part, by the activation of the endogenous group IVA cytosolic phospholipase A2α. MT-III triggered the formation of triacylglycerol and cholesterol enriched in palmitic, stearic, and oleic acids, but not arachidonic acid, along with an increase in lipid droplet synthesis. Additionally, it was shown that the increased availability of arachidonic acid arising from phospholipid hydrolysis promoted abundant eicosanoid synthesis. The inactive form, MT-II, failed to produce any of the effects described above. These studies provide a complete lipidomic characterization of the monocyte response to snake venom group IIA phospholipase A2, and reveal significant connections among lipid droplet biogenesis, cell signaling and biochemical pathways that contribute to initiating the inflammatory response.

Highlights

The phospholipase A2 (PLA2) superfamily consists of a broad range of enzymes defined by their ability to catalyze the hydrolysis of the ester bond at the sn-2 position of glycerophospholipids.The hydrolysis products of this reaction, free fatty acid and lysophospholipid, serve as precursors for a variety of bioactive lipid mediators with important biological roles [1]
Phospholipids were isolated and their fatty acid content was measured by Gas Chromatography/Mass Spectrometry (GC/MS)
We show here that the catalytic activity of group IIA secreted PLA2s (sPLA2) is required for lipid droplet formation to occur, it probably being the only factor involved, since inactive MT-II does not reproduce the effect

Summary

Introduction

The phospholipase A2 (PLA2) superfamily consists of a broad range of enzymes defined by their ability to catalyze the hydrolysis of the ester bond at the sn-2 position of glycerophospholipids.The hydrolysis products of this reaction, free fatty acid and lysophospholipid, serve as precursors for a variety of bioactive lipid mediators with important biological roles [1]. An alternative classification exists that groups these enzymes into six major classes on the basis of biochemical similarities and/or cell regulation properties These are the Ca2+-dependent cytosolic PLA2s, the Ca2+-dependent secreted PLA2s (sPLA2), the Ca2+-independent cytosolic PLA2s, the platelet-activating factor acetyl hydrolases, the lysosomal PLA2, and the adipose-specific PLA2 [2]. A variety of biological activities have been described for sPLA2s, including digestive actions, toxic activities (neurotoxic, myotoxic, hypotensive, etc.) and immune roles. In this regard, group IIA sPLA2 was defined as a pro-inflammatory PLA2, since its gene induction and synthesis were observed after cell stimulation by endotoxin and cytokines [3,4,5]. Another member of the family, the group V enzyme, is described as anti-inflammatory in some models [6,7,8]

Methods

Results

Discussion

Conclusion