Positional specificity of lysosomal phospholipase A2

Akira Abe,Miki Hiraoka,James A Shayman

doi:10.1194/jlr.m600183-jlr200

Akira Abe, Miki Hiraoka + Show 1 more

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https://doi.org/10.1194/jlr.m600183-jlr200

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Abstract

Lysosomal phospholipase A(2) (Lpla2) is highly expressed in alveolar macrophages and may mediate the phospholipid metabolism of surfactant. Studies on the properties of this phospholipase are consistent with the presence of both phospholipase A(1) and phospholipase A(2) activities. These activities were studied through the production of O-acyl compounds, produced by the transacylase activity of Lpla2. Liposomes containing POPC and N-acetylsphingosine (NAS) were incubated with the soluble fraction obtained from MDCK cells stably transfected with the mouse Lpla2 gene. Two 1-O-acyl-NASs, 1-O-palmitoyl-NAS and 1-O-oleoyl-NAS, were produced by Lpla2. The formation rate of 1-O-oleoyl-NAS was 2.5-fold that of 1-O-palmitoyl-NAS. When 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC) was used, the formation rate of 1-O-oleoyl-NAS was 5-fold higher than that of 1-O-palmitoyl-NAS. Thus, Lpla2 can act on acyl groups at both sn-1 and sn-2 positions of POPC and OPPC. When 1-palmitoyl-2-unsaturated acyl-sn-glycero-3-phosphocholines were used as acyl donors, the transacylation of the acyl group from the sn-2 position to NAS was preferred to that of the palmitoyl group from the sn-1 position. An exception was observed for 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC), for which the formation rate of 1-O-palmitoyl-NAS from PAPC was 4-fold greater than that of 1-O-arachidonoyl-NAS. Thus, Lpla2 has broad positional specificity for the sn-1 and sn-2 acyl groups in phosphatidylcholine and phosphatidylethanolamine.

Highlights

Lysosomal phospholipase A2 (Lpla2) is highly expressed in alveolar macrophages and may mediate the phospholipid metabolism of surfactant
The soluble fraction of alveolar macrophages (AMs) from Lpla21/1 mice was assayed under acidic conditions with liposomes consisting of 1-palmitoyl-2-[14C]oleoyl-sn-glycero-3-phosphocholine and dicetyl phosphate (Fig. 1A–D). 1-Hydroxy-2[14C]oleoyl-sn-glycero-3-phosphocholine (2-[14C]oleoyllysoPC) as well as 14C-labeled oleic acid were produced
The difference in phospholipase A activity between Lpla21/1 and Lpla22/2 mouse AMs is thought to be primarily attributable to Lpla2, because the null mouse has a systemic deficiency of Lpla2

Summary

Introduction

Lysosomal phospholipase A2 (Lpla2) is highly expressed in alveolar macrophages and may mediate the phospholipid metabolism of surfactant. We previously identified a lysosomal phospholipase A2 (Lpla2) with specificity toward phosphatidylcholine (PC) and phosphatidylethanolamine (PE) [1]. Granulocyte macrophage colony-stimulating factor (GMCSF)-deficient mice are known to be a model of impaired surfactant catabolism and develop progressive accumulation of surfactant lipids and proteins in lung [5]. Acidic phospholipase A activity has been suggested to play an important role in pulmonary surfactant phospholipid catabolism [7]. To better understand the biological function of Lpla and its potential role in surfactant catabolism, Lpla2-deficient (Lpla22/2) mice were created by double conditional gene targeting using Cre/ loxP and Flp/FRT systems [8]. This article is available online at http://www.jlr.org

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