Upregulation of prostacyclin synthesis-related gene expression by shear stress in vascular endothelial cells

Prostacyclin (prostaglandin I-2, PGI(2)) has a variety of functions, includ ing inhibition of smooth muscle cell proliferation, vasodilation, and antip latelet aggregation. PGI(2) production in endothelial cells has been report ed to increase biphasically after shear loading, but the underlying mechani sm is not well understood. To clarify the mechanism for the second phase of PGI(2) upregulation, we examined the gene expression of the enzymes involv ed in PGI(2) production in human umbilical vein endothelial cells (HUVECs) after shear-stress (24 dyne/cm(2)) loading. The production of 6-keto-PGF(1 alpha), a stable metabolite of PGI(2), increased time-dependently under she ar stress. The arachidonic acid liberation from membrane phospholipids in H UVECs after 12 hours of shear loading was increased significantly compared with the static condition. No change was observed for cytosolic phospholipa se A(2) expression, as detected by reverse transcription-polymerase chain r eaction and Western blotting. Cyclooxygenase (COX)-1 mRNA increased after 1 hour of shear loading, and the increase lasted for 12 hours, the longest t ime tested, whereas COX-2 mRNA increased after 1 hour of shear loading and peaked at 6 hours. An increase of COX-1 expression was detected at 12 hours of shear loading by Western blotting. No expression of COX-2 was detected in the static control, but induced expression was observed at 6 hours after shear loading. PGI(2) synthase was also found to be upregulated. These res ults suggest that the elevated PGI(2) production by shear stress is mediate d by increased arachidonic acid release and a combination of increased expr ession of COXs and PGI(2) synthase.