Epinephrine Induces von Willebrand Factor Release from Cultured Endothelial Cells: Involvement of Cyclic AMP-dependent Signalling in Exocytosis

Abstract

Summaryvon Willebrand factor (vWf) is released from endothelial cell storage granules after stimulation with thrombin, histamine and several other agents that induce an increase in cytosolic free calcium ([Ca2+]i). In vivo, epinephrine and the vasopressin analog DDAVP increase vWf plasma levels, although they are thought not to induce vWf release from endothelial cells in vitro. Since these agents act via a cAMP-dependent pathway in responsive cells, we examined the role of cAMP in vWf secretion from cultured human umbilical vein endothelial cells. vWf release increased by 50% in response to forskolin, which activates adenylate cyclase. The response to forskolin was much stronger when cAMP degradation was blocked with IBMX, an inhibitor of phosphodiesterases (+200%), whereas IBMX alone had no effect. vWf release could also be induced by the cAMP analogs dibutyryl-cAMP (+40%) and 8-bromo-cAMP (+25%); although their effect was weak, they clearly potentiated the response to thrombin. Epinephrine (together with IBMX) caused a small, dose-dependent increase in vWf release, maximal at 10-6 M (+50%), and also potentiated the response to thrombin. This effect is mediated by adenylate cyclase-coupled β-adrenergic receptors, since it is inhibited by propranolol and mimicked by isoproterenol. In contrast to thrombin, neither forskolin nor epinephrine caused an increase in [Ca2+]j as measured by fura-2 fluorescence. In addition, the effects of forskolin and thrombin were additive, suggesting that they act through distinct signaling pathways. We found a close correlation between cellular cAMP content and vWf release after stimulation with epinephrine and forskolin. These results demonstrate that cAMP-dependent signaling events are involved in the control of exocytosis from endothelial cells (an effect not mediated by an increase in [Ca2+]i) and provide an explanation for epinephrine-induced vWf release.

Differential regulation of endothelial exocytosis of P-selectin and von Willebrand factor by protease-activated receptors and cAMP

“…Inhibition of protein synthesis with cycloheximide caused a small decrease in the basal release of VWF but did not decrease forskolin-, PAR1-, or PAR2-APmediated release of VWF and caused a small increase in VWF release, which is consistent with previous studies conducted with forskolin ( Figure 5C). 25 …”

“…24 In addition, agents that elevate intracellular cAMP such as vasopressin receptor agonists, purine nucleotides, epinephrine, and forskolin can also trigger the release of VWF. [25][26][27] The time course of cAMPstimulated VWF release is delayed compared with agonists that increase intracellular Ca 2ϩ . By inference, stimulation of VWF release should also occur in tandem with translocation of P-selectin to the cell surface, because both factors are located in the same secretory granule.…”

Exercise prescription and thrombogenesis

“…Augmentation of shearinduced platelet aggregation during strenuous exercise is likely related to increased endogenous release of epinephrine. Strenuous exercise promotes the release of epinephrine [35], which can induce the release of vWF from endothelial cells [36] and enhance shear-induced platelet aggregation via activating platelet a 2 -adrenergic receptors [37]. Epinephrine can synergize with hear stress to induce platelet aggregation, and this synergistic response depends on both vWF-GPIb interaction and functional GPIIb/IIIb complexes [38].…”

Hypertensive stretch regulates endothelial exocytosis of Weibel-Palade bodies through VEGF receptor 2 signaling pathways

“…Thus, the regulation of endothelial exocytosis has been extensively studied. The regulation of WPB exocytosis involves the activation of canonical pathways mediated by second messengers, such as calcium and cAMP [3,4], and the induction of a negative pathway executed by nitric oxide (NO), which inhibits the exocytosis of WPBs by the S-nitrosylation of N-ethylmaleimide-sensitive factor (NSF), a component of the membrane fusion and exocytotic machinery [5,6]. So far, however, the vast majority of our knowledge on the regulation of WPB exocytosis has been obtained from the studies conducted with chemical agonists, such as thrombin, histamine and VEGF.…”