Low shear stress up-regulation of proinflammatory gene expression in human retinal microvascular endothelial cells

The vascular endothelium responds to shear stress generated by blood flow and changes functions to regulate blood flow and maintain tissue homeostasis. Recently, we found that arteriolar high shear stress leads to increased expression of vasodilatory and antithrombotic genes in human retinal microvascular endothelial cells (HRMECs). However, it is unknown whether low shear stress, which is induced by hypoperfusion particularly in the retinal venules where leukocyte-endothelial interactions mainly occur, affects the retinal endothelial function. We studied the effect of low shear stress on proinflammatory gene expression in HRMECs. The cells were cultured on glass plates and exposed to laminar shear stresses of 0 (static), 1.5 (relatively low flow), and 15 dyne/cm2 (relatively high flow) for 24 h using parallel plate-type flow-loading devices. The mRNA expressions of adhesion molecules, cytokines and chemokines, and procoagulant factors were evaluated using real-time reverse-transcription polymerase chain reaction. HRMECs exposed to 1.5 dyne/cm2 significantly up-regulated the mRNA expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin. The cells exposed to 1.5 dyne/cm2 of stress also had increased cytokine/chemokine mRNA expression, i.e., interleukin (IL)-6, IL-8, platelet-derived growth factor-B, and monocyte chemotactic protein-1. Procoagulant factors, i.e., tissue factor and plasminogen activator inhibitor-1 mRNA, increased significantly with exposure to 1.5 dyne/cm2 of stress. Our results showed that relatively low shear stress causes up-regulation of proinflammatory genes in HRMECs, suggesting that decreased shear stress due to vascular hypoperfusion might change the phenotypic characterization of the retinal vascular endothelium and be associated with leukocyte-endothelial interactions.