Effects of Linoleic Acid on Tether Formation between Monocytes and Endothelial Cells
The fatty acid linoleic acid has been identified as a potential mediator of atherosclerotic plaque development. Treatment of monocytes with linoleic acid leads to an increase in monocyte adhesion to endothelial cells under flow conditions; however, the mechanisms through which linoleic acid affect monocyte adhesion remain unclear. Using a combination of micropipette aspiration techniques and fluorescent microscopy, I tested the hypothesis that linoleic acid increases membrane tether formation between monocytes and endothelial cells.
Treatment of U937 monocytes with free linoleic acid or albumin-bound linoleic acid reduced the cortical tension of the monocytes. The effects of albumin-bound linoleic acid on the membrane were governed by the exchange of linoleic acid from albumin to the membrane and by the removal of fatty acids from the membrane by fatty acid binding sites on albumin.
The frequency of tether formation between U937 monocytes and TNF-α stimulated HUVECs increased following treatment with free linoleic acid or albumin-bound linoleic acid. The increase in tether frequency was not due to an increase in monocyte deformability or adhesion receptor expression. Tether extraction occurred primarily through E-selectin. Treatment with free linoleic acid increased the localization of E-selectin to clathrin-coated pits suggesting an increase in the formation of nanoclusters of E-selectin on HUVECs. The increase in tether frequency was blocked by the U73122 phospholipase C inhibitor indicating that linoleic acid increased monocyte adhesion through a phospholipase C mediated mechanism.
Treatment with free linoleic acid did not affect the threshold force for tether extraction or the effective viscosity of tethers extracted from HUVECs, but it decreased the threshold force for tether extraction from U937 monocytes and increased the effective tether viscosity. Treatment with U73122 blocked the reduction in the threshold force indicating that linoleic acid affected the regulation of the membrane adhesion energy through the hydrolysis of PIP2 by phospholipase C.
The results of the study indicated that linoleic acid promoted membrane tether formation by increasing E-selectin bond formation and reducing the adhesion energy between the U937 plasma membrane and the actin cytoskeleton through the hydrolysis of PIP2 by phospholipase C.
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