Fluid Shear Stress Stimulates Membrane Phospholipid Metabolism in Cultured Human Endothelial Cells

Abstract

There is evidence suggesting that fluid shear stress activates phospholipid turnover in endothelial cells, but it is not clear which phospholipids are involved in the transduction of the flow signal. Cultured human umbilicalvein endothelial cells were prelabeled with [¹⁴C]-arachidonic acid and subjected to laminar shear stresses of 0.4, 1.4 and 22 dyn/cm² for times up to 30 min, after which the distribution of the radioactivity in the phospholipids was determined. We observed decreases in labeled phosphatidylinositol, phosphatidylethanolamine and phosphatidic acid at 10-30 s, and increases in labeled diacylglycerol (DG) and free arachidonate, as well as a simultaneous elevation in inositol 1,4,5-triphosphate (IP₃) levels. A second peak in IP₃ levels was observed 10 min after the onset of shear. This is in contrast with agonist-stimulated endothelial cells, where IP3 levels go back to initial values within a few minutes after stimulation. The flow-induced IP3 response was the same in the presence or absence of ATP and serum in the perfusing medium. These results are consistent with the activation of phospholipase C, phospholipase A₂ and DG lipase by shear stress. This suggests that several phospholipids are involved in the production of free arachidonic acid and DG, which are likely to be important mediators of the shear stress signal. In addition, flow may lead to a chronic stimulation of endothelial-cell metabolism.

Mechanosensitive Ca2+ transients in endothelial cells from human umbilical vein.

“…during Ca2+ influx could be explained by a tiny influx through a Ca2+-selective channel, but an electroneutral mechanism cannot be excluded. This Ca2+ release is accompanied by activation of a Ca2+-independent Cl-conductance that may contribute to stabilization of the driving force for Ca2+ entry and has been described in detail elsewhere (4 Increased synthesis of AA has been observed in endothelial cells from human umbilical vein during stimulation by laminar shear stress (18) …”

State-dependent calcium mobilization by urotensin-II in cultured human endothelial cells

“…At curves and bifurcations, peak wall shear stress may be as high as 100 dyne/ cm 2 . Immediate (milliseconds to seconds) responses to shear stress include increases in ionic conductance [40,48], intracellular Ca 2+ [57,58] and IP3 [8,46]. As a corollary, U-II may facilitate the shear stress-induced increase of [Ca 2+ ] i and/or IP 3 .…”

Mechanotransduction in Response to Shear Stress

“…For example, the PI 3-kinase pathway can lead to the generation of intracellular diacylglycerol and inositol 1,4,5-trisphosphate, and PLC-␥ can activate the protein kinase C pathway. Indeed, inositol 1,4,5-trisphosphate and protein kinase C have been shown to be activated by shear stress (37)(38)(39)(40). Although other stimuli such as growth factors and environmental stresses also activate RTKs (i.e.…”