The Difference of Akt Phosphorylation with Different Strengths of Hemodynamic Forces on the Endothelial Cell

ABSTRACT

PURPOSE: Mechanical forces including shear stress (SS) and cyclic strain (CS) trigger signal transducing events and modulate gene expression in vascular endothelial cells (ECs). However, differences in intracellular events and gene expression depend on the intensity of the forces, which remain unknown. We attempted to clarify the effect of different strengths of SS and CS by determination of the Akt phosphorylation of ECs. METHOD: ECs were exposed to the arterial level of orbital SS with an orbital shaker (210 rpm) or laminar SS (14 dyne/cm2) with a parallel plate or CS (10%) at a frequency of 60 cycles/min. Akt phosphorylation was assessed by immunocytochemical staining and Western blotting with specific antibodies against the phosphorylated Akt. RESULT: Akt demonstrated a time-dependent stimulation of Akt phosphorylation by mechanical forces with a maximal increase up to 2.5-fold after 30 minutes of orbital SS exposure, 3-fold after 2 minutes of laminar SS exposure and 2.3-fold after 30 minutes of CS exposure. Akt phosphorylation in the periphery of the membrane was significantly increased, compared to at the center of the membrane. It was up to 1.4-fold after 30 minutes of orbital SS and up to 2.4-fold after 30 minutes of CS (P<0.05). CONCLUSION: Our results demonstrate that all types of hemodynamic forces phosphorylated Akt in a time-dependent manner and different types of SS may have different effects on the ECs. In addition, the phosphorylation of Akt is dependent on the intensity of the mechanical forces on ECs.