Angiogenesis is the new vasculature formation occurring in adult tissues. It is estimated that growth of any tissue to sizes above 2-3 mm3 requires formation of functional blood vessel network. Angiogenesis is regulated through a complex interplay of many factors, which either activate or inhibit the process. Participation of eicosanoids (large family of lipid mediators derived from arachidonic acid) in such regulation, although recognised as important, was never comparatively investigated in order to quantitatively assess contribution of individual eicosanoid class. In this work, we have determined (using in vitro endothelial cell migration and tube formation assays) that two eicosanoids, prostacyclin (or PGI2) and prostaglandin E2 (or PGE2) are the main activators of angiogenesis acting via their receptors IP or EP4 respectively. The main eicosanoid regulator of angiogenesis is found to be prostacyclin which contributes to overall activation by 80%, whereas PGE2 participates by approximately 20%. Better understanding of angiogenesis regulation could help with design of new drugs to prevent pathological angiogenesis observed in many diseases including cancer.
Microvasc Res. 2015;101:127-34.
Hoang KG1, Allison S2, Murray M2, Petrovic N3.[expand title=”Show Affiliations”]
- School of Pharmacy and Medical Sciences, University of South Australia, Australia.
- Pharmacogenomics and Drug Development Group, Discipline of Pharmacology, School of Medical Sciences, University of Sydney, Australia.
- School of Pharmacy and Medical Sciences, University of South Australia, Australia. Electronic address: [email protected]
Angiogenesis is regulated by numerous activators and inhibitors, including prostanoids. Although many studies have identified their roles in inflammation, regulatory functions of prostanoids in angiogenesis are poorly understood. Here, we compared the activation of angiogenesis in vitro by two prostanoids with important vascular roles: prostaglandin E2 (PGE2) – thought to be the most important prostanoid activator of angiogenesis – and prostaglandin I2 (prostacyclin or PGI2), whose receptors are predominantly expressed in endothelial cells. Both of these prostanoids activate G-protein coupled receptors: EP1, EP2, EP3 and EP4 by PGE2 and IP by prostacyclin. Human umbilical vein endothelial cells (HUVECs) were used to characterize two pivotal pro-angiogenic processes in vitro: cell migration (using the matrigel droplet assay developed in our laboratory) and “tube formation” (a widely accepted method of assessing formation of blood vessel precursors). The suppression of cell migration and tube formation by the IP-specific antagonist CAY10441 was more extensive (~80%) than by the EP4-specific antagonist L-161,982 (~20%). AH6809, an antagonist of EP1, EP2 and EP3 receptors did not significantly suppress angiogenesis. Expression of the pro-angiogenic receptors KDR and Tie-2 in HUVECs was preferentially suppressed by antagonism of IP and EP4 receptors, respectively. EP4 and IP receptor agonists elicited biphasic actions on angiogenic processes in which there was activation at low concentration, and rapid desensitization at high concentrations – a characteristic common to many G-protein coupled receptors. Together these findings suggest that the prostacyclin-IP pathway plays a major role in the regulation of pro-angiogenic processes in HUVECs.
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Figure Legend Human umbilical vein endothelial cell structures used for migration and communication (filopodia, stained by fluorescent cholesterol stain filipin). Unpublished data from the study by Petrovic N. et al. Blood. 2007, 110: 142-150.