Effects of shear stress on the gene expressions of endothelial nitric oxide synthase, endothelin-1, and thrombomodulin in human retinal microvascular endothelial cells

Physiological shear stress is higher in the retinal microcirculatory network than in other organs. The effects of laminar shear stress on gene expression in human retinal microvascular endothelial cells (HRMECs) was investigated. Cultured HRMECs on glass plates were exposed to a laminar shear stress of 0, 1.5, 6, 15, 30, 60, or 100 dyne/cm(2) for 24 hours and to 60 dyne/cm(2) for 0, 1, 3, 6, 12, 24, or 48 hours. The mRNA expressions of endothelial nitric oxide synthase (eNOS), endothelin-1 (ET-1), and thrombomodulin (TM) in the HRMECs were evaluated using real-time reverse transcription polymerase chain reaction. The HRMECs elongated and aligned parallel with the flow direction based on the shear stress and exposure times. The expression of eNOS mRNA gradually increased and became saturated at 60 dyne/cm(2); ET-1 mRNA expression increased at 1.5 dyne/cm(2) but decreased below that of the static control at shear stresses of 30 dyne/cm(2) or more. TM mRNA expression in response to shear stress increased linearly from 0 to 100 dyne/cm(2). A shear stress of 60 dyne/cm(2) for 6 hours or more promoted eNOS and TM mRNA expression but suppressed ET-1 mRNA expression in HRMECs. Long-term exposure to a physiological shear stress in the retinal arterioles up-regulated eNOS and TM mRNA expressions and downregulated ET-1 mRNA expression in HRMECs. These results suggest that shear stress may be associated with the vasoregulatory and antithrombotic properties of retinal vessels under physiological conditions present during retinal circulation.