Chronic pulsatile shear stress impacts synthesis of proteoglycans by endothelial cells: Effect on platelet aggregation and coagulation

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Abstract
Endothelial‐derived proteoglycans are important regulators of the coagulation‐pathway in vivo and our primary objective of this study was to determine whether chronic shear stress affected the synthesis, release, and activity of proteoglycans from bovine aortic endothelial cells (BAEC). BAEC were cultured under shear and proteoglycans were purified from BAEC conditioned media and analyzed using both anionic exchange and size exclusion chromatography. The overall amount of proteoglycans produced per cell was significantly greater for the high shear‐treated samples compared to the low shear‐treated samples indicating that the shear magnitude did impact cell responsiveness. While overall size and composition of the proteoglycans and glycosaminoglycan (GAG) side chains were not altered by shear, the relative proportion of the high and low molecular weight species was inversely related to shear and differed significantly from that found under static tissue culture conditions. Moreover, a unique proteoglycan peak was identified from low shear stress (5 ± 2 dynes/cm2) conditioned media when compared to high shear conditions (23 ± 8 dynes/cm2) via anionic exchange chromatography, suggesting that subtle changes in the GAG structures may impact activity of these molecules. In order to characterize whether these changes impacted proteoglycan function, we studied the effects of shear specific proteoglycans on the inhibition of thrombin‐induced human platelet aggregation as well as on platelet‐fibrin clot dynamics. Proteoglycans from high shear‐treated samples were less effective inhibitors of both platelet aggregation and blood coagulation inhibition than proteoglycans from low shear‐treated samples and both were less effective than proteoglycans isolated from static tissue culture samples. However, due to changes in the overall proteoglycan synthesis and release rate, the high and low shear‐treated sample had essentially identical effects on these activities, suggesting that the cells were able to compensate for stress‐induced proteoglycan changes. Our data suggests that shear stress, by altering proteoglycan synthesis and fine structure, may play a role in maintaining vascular hemodynamics and hemostasis.