Antisense Inhibition of Group VI Ca2+-independent Phospholipase A2 Blocks Phospholipid Fatty Acid Remodeling in Murine P388D1 Macrophages

Abstract

A major issue in lipid signaling relates to the role of particular phospholipase A 2 isoforms in mediating receptor-triggered responses. This has been difficult to study because of the lack of isoform-specific inhibitors. Based on the use of the Group VI Ca 2؉ -independent phospholipase A 2 (iPLA 2 ) inhibitor bromoenol lactone (BEL), we previously suggested a role for the iPLA 2 in mediating phospholipid fatty acid turnover (Balsinde, J., Bianco, I. D., Ackermann, E. J., Conde-Frieboes, K., and Dennis, E. A. (1995) Proc. Natl. Acad. Sci. U. S. A. 92: 8527-8531). We have now further evaluated the role of the iPLA 2 in phospholipid remodeling by using antisense RNA technology. We show herein that inhibition of iPLA 2 expression by a specific antisense oligonucleotide decreases both the steady-state levels of lysophosphatidylcholine and the capacity of the cell to incorporate arachidonic acid into membrane phospholipids. These effects correlate with a decrease in both iPLA 2 activity and protein in the antisense-treated cells. Collectively these data provide further evidence that the iPLA 2 plays a major role in regulating phospholipid fatty acyl turnover in P388D 1 macrophages. In stark contrast, experiments with activated cells confirmed that the iPLA 2 does not play a significant role in receptor-coupled arachidonate mobilization in these cells, as manifested by the lack of an effect of the iPLA 2 antisense oligonucleotide on PAF-stimulated arachidonate release.

The role of phospholipases A2 in schizophrenia

“…21,22 Loss of PLA2G6A function leads to significant reductions in the amount of AA incorporated into the cell membrane. 23 …”

“…[55][56][57] As loss of PLA2G6A function results in reduced cell membrane AA levels, variations in this gene may be responsible for these results. 23 PLA2s and in vivo phospholipid metabolism 31-Phosphorus magnetic resonance imaging ( 31 P MRS) allows measurement of membrane phospholipid dynamics in the living brain. 45 31 P MRS of drugnaïve first episode schizophrenia patients reveals significantly increased breakdown and reduced creation of cellular membranes in never treated patients with schizophrenia.…”

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

“…Hence, inhibition of iPLA 2 results in reduced levels of lysophospholipid acceptors, which in turn leads to a decreased incorporation of AA into PLs under unstimulated conditions (14,(23)(24)(25). When the effect of zymosan on AA incorporation was assayed in monocytes treated with BEL, and hence exhibiting diminished lysophospholipid levels (44), the response was slightly but significantly reduced (Fig.…”

“…Our previous work has indicated that iPLA 2 is a significant contributor to the steady-state lysophospholipid level in resting phagocytic cells (23)(24)(25)43). Hence, inhibition of iPLA 2 results in reduced levels of lysophospholipid acceptors, which in turn leads to a decreased incorporation of AA into PLs under unstimulated conditions (14,(23)(24)(25).…”

“…By means of the former, low concentrations of free AA incorporate into PLs via direct acylation of preexisting PLA 2 -derived lysophospholipids. This pathway is believed to constitute the major pathway for AA incorporation into PLs in a variety of cells under physiological conditions; hence, the availability of lysophospholipid acceptors, particularly lysophosphatidylcholine (lysoPC), is a limiting factor (13,14,(23)(24)(25). The high-capacity/low-affinity pathway incorporates free AA via the de novo route, which ultimately results in the accumulation of AA into triacylglycerol and diarachidonoyl PLs (4,26).…”