The response of endothelial cells to wall shear stress alterations:the effect of erythrocyte aggregation

Vascular endothelial cells are the primary cell types exposed to shear stress originating from blood flow. They regulate the production of autocrine and paracrine vasoactive factors both acutely and chronically in relation with the effect of shear stress. It is well known that shear stress selectively regulates the expression of many different genes and contributes the pathophysiology of vascular wall. Mechanical forces which have in vivo effects on endothelial cells are originated from blood flow and they are called wall shear stress: magnitude of wall shear stress is determined by multiplying the velocity of fluid adjacent to vessel wall (wall shear stress) with viscosity of the fluid. In several studies it was shown that alterations on hemodynamic conditions or wall shear stress may have effects on NO-synthesizing mechanisms of vessel endothelium. Fluidity of blood is a major determinant of wall shear stress. In rats, increased erythrocyte aggregation reduces the expression and function of endothelial nitric oxide synthase (eNOS) while it increases the blood pressure. It has been shown that eNOS which is a potential receptor of the l shear stress, plays a role in sensing of the alterations in shear stress by endothelial cells. In the present study we wanted to investigate the alterations of NO-dependent mechanisms in endothelial cells that are settled in capillary tubes, in response to a reduction in wall shear stress resulting from an increase in erythrocyte aggregation. In this study, we have located human umbilical cord originated venous endothelial cells into glass capillary tubes with a special technique. Endothelial cells cultured in glass capillary tubes were perfused with blood samples of different characteristics in constant pressure. Perfusion of capillaries covered with endothelial cells is realized by use of following three samples; normal human blood, blood which has increased erythrocyte aggregation due to changed plasma content (dextran group), and blood which has modified aggregation due to changed erythrocyte surface attributes (F98 group). Capillary tubes of study groups filled with endothelial cells were perfused for 30 minutes or 6 hours with appropriate erythrocyte suspensions. After the perfusion, eNOS protein levels and mRNA expression were measured in endothelium cells. Nitrite-nitrate levels of endothelial cells were also measured. It is observed that both NO production and eNOS serin 1177 expression increased in the cultured endothelial cells inside glass capillary tubes in response to flow. Perfusion of capillary tubes with blood samples whose erythrocyte aggregation was increased, decreased the NO production and eNOS serin 1177 expression. This experimental data show that alterations in wall shear stress caused by modification in erythrocyte aggregation can be monitored with NO-dependent mechanisms. Key words: Wall shear stres, endothelial nitric oxide synthase, nitric oxide