Signaling Role for Lysophosphatidylcholine Acyltransferase 3 in Receptor-Regulated Arachidonic Acid Reacylation Reactions in Human Monocytes

Abstract

Cellular availability of free arachidonic acid (AA) is an important step in the production of pro- and anti-inflammatory eicosanoids. Control of free AA levels in cells is carried out by the action of phospholipase A2s and lysophospholipid acyltransferases, which are responsible for the reactions of deacylation and incorporation of AA from and into the sn-2 position of phospholipids, respectively. In this work, we have examined the pathways for AA incorporation into phospholipids in human monocytes stimulated by zymosan. Our data show that stimulated cells exhibit an enhanced incorporation of AA into phospholipids that is not secondary to an increased availability of lysophospholipid acceptors due to phospholipase A2 activation but rather reflects the receptor-regulated nature of the AA reacylation pathway. In vitro activity measurements indicate that the receptor-sensitive step of the AA reacylation pathway is the acyltransferase using lysophosphatidylcholine (lysoPC) as acceptor, and inhibition of the enzyme lysoPC acyltransferase 3 by specific small interfering RNA results in inhibition of the stimulated incorporation of AA into phospholipids. Collectively, these results define lysoPC acyltransferase 3 as a novel-signal–regulated enzyme that is centrally implicated in limiting free AA levels in activated cells.

Polarization of Macrophages toward M2 Phenotype Is Favored by Reduction in iPLA2β (Group VIA Phospholipase A2)

“…Many components of the immune system, including macrophages (50 -54), monocytes (55), neutrophils (56,57), mast cells (58), and T-cells and B-cells (59), express iPLA 2 ␤ activity. Among its proposed roles in macrophages, iPLA 2 ␤ has been implicated in playing a major role in free fatty acid accumulation in macrophages (60 -63) leading to apoptosis.…”

Simultaneous activation of p38 and JNK by arachidonic acid stimulates the cytosolic phospholipase A2-dependent synthesis of lipid droplets in human monocytes

“…Cells were scraped twice with 0.1% Triton X-100 in PBS, and total lipids were extracted according to the method of Bligh and Dyer (33), reconstituted in chloroform/methanol (2:1, v/v), and separated by thin-layer chromatography with n -hexane/ether/acetic acid (70:30:1, v/v/v). The spots corresponding to TAG were cut out, and the plate and analyzed for radioactivity by liquid scintillation counting (36)(37)(38). (10,(20)(21)(22).…”

Altered Arachidonate Distribution in Macrophages from Caveolin-1 Null Mice Leading to Reduced Eicosanoid Synthesis

“…Phospholipids and neutral lipids were separated with hexane/ether/ acetic acid (70:30:1, v/v/v) as a mobile phase. The spots were cut out and analyzed for radioactivity by liquid scintillation counting (26). For analysis of the molecular species into which the exogenous fatty acid was incorporated, [ Macrophage Stimulation-Cells were placed in serum-free medium for 30 min before addition of zymosan (1 mg/ml) for the time indicated.…”