Long-chain acyl-CoA synthetase 4 modulates prostaglandin E2 release from human arterial smooth muscle cells

Shelley Barnhart,Deidre L. Golej,Karin E. Bornfeldt,Farah Kramer,Subramaniam Pennathur,Anuradha Vivekanandan-Giri,Bardia Askari

doi:10.1194/jlr.m013292

Abstract

Long-chain acyl-CoA synthetases (ACSLs) catalyze the thioesterification of long-chain FAs into their acyl-CoA derivatives. Purified ACSL4 is an arachidonic acid (20:4)-preferring ACSL isoform, and ACSL4 is therefore a probable regulator of lipid mediator production in intact cells. Eicosanoids play important roles in vascular homeostasis and disease, yet the role of ACSL4 in vascular cells is largely unknown. In the present study, the ACSL4 splice variant expressed in human arterial smooth muscle cells (SMCs) was identified as variant 1. To investigate the function of ACSL4 in SMCs, ACSL4 variant 1 was overexpressed, knocked-down by small interfering RNA, or its enzymatic activity acutely inhibited in these cells. Overexpression of ACSL4 resulted in a markedly increased synthesis of arachidonoyl-CoA, increased 20:4 incorporation into phosphatidylethanolamine, phosphatidylinositol, and triacylglycerol, and reduced cellular levels of unesterified 20:4. Accordingly, secretion of prostaglandin E₂ (PGE₂) was blunted in ACSL4-overexpressing SMCs compared with controls. Conversely, acute pharmacological inhibition of ACSL4 activity resulted in increased release of PGE₂. However, long-term downregulation of ACSL4 resulted in markedly reduced PGE₂ secretion. Thus, ACSL4 modulates PGE₂ release from human SMCs. ACSL4 may regulate a number of processes dependent on the release of arachidonic acid-derived lipid mediators in the arterial wall.

Highlights

Long-chain acyl-CoA synthetases (ACSLs) catalyze the thioesterification of long-chain FAs into their acylCoA derivatives
Free 20:4 is converted by COX-1/COX-2, or lipoxygenases to downstream lipid mediators, including prostaglandin E2 (PGE2), a principal prostaglandin species secreted from human smooth muscle cell (SMC) [9, 10]
By using primers specific for the longer ACSL4_v2 and primers detecting both ACSL4_v1 and ACSL4_v2 (Table 1), the shorter ACSL4_v1 was found to be the primary ACSL4 splice variant expressed in human SMCs (Fig. 1B)

Summary

Introduction

Long-chain acyl-CoA synthetases (ACSLs) catalyze the thioesterification of long-chain FAs into their acylCoA derivatives. Long-chain acyl-CoA synthetase 4 modulates prostaglandin E2 release from human arterial smooth muscle cells. Arachidonic acid (20:4) is an omega-6 FA with a plethora of effects in vascular cells due to its processing by cyclooxygenases (COX-1 and COX-2), lipoxygenases, or cytochrome P450 pathways into lipid mediators with diverse biological activities, such as prostaglandin E2 (PGE2), prostacyclin, leukotrienes, and thromboxanes [1, 2]. These lipid mediators are crucial regulators of vascular homeostasis, and play important roles in vascular disease, including atherosclerosis. ACSL4 undergoes alternative splicing, producing a shorter isoform (variant 1) and a longer isoform (variant 2) containing an additional 41-amino acid N-terminal tail [15, 16]

Methods

Results

Conclusion