C-reactive protein (CRP) is a pluripotent mediator of inflammation and is present at sites of vascular injury and in atherosclerotic lesions. CRP stimulates endothelial cell adhesion molecule expression and monocyte migration, thereby contributing to the development and progression of vascular lesion formation. In addition, chronic exposure to CRP is known to inhibit angiogenesis and endothelial cell (EC) proliferation.
Aim: Whether CRP also affects EC migration, however, has yet to be determined. The present study investigates how long-term exposure to CRP interacts with vascular endothelial growth factor (VEGF) -induced EC migration.
Methods and results: Using a Transwell chamber migration assay, VEGF (20 ng/mL, 5 h incubation)-induced migration of human umbilical vein EC was significantly inhibited in cells pretreated with CRP (10 microg/mL) for 24 h by more than 75%. EC migration in response to VEGF is known to require activation of the protein kinase B (Akt)/endothelial NO synthase (eNOS)- and the extracellular signal-regulated protein kinase 1/2 (ERK1/2) pathway. We therefore investigated the long-term effects of CRP on these signalling events. Immunoblotting with phosphospecific antibodies revealed rapid and transient activation/phosphorylation of the protein kinase Akt within 20 minutes after stimulation with VEGF, which was inhibited by 86% in EC pretreated with CRP (10 microg/mL, 24 h, p<0.05). Subsequent VEGF-induced phosphorylation of eNOS downstream of Akt was completely inhibited in CRP-treated EC. In contrast, CRP-pretreatment did not affect VEGF-induced phosphorylation of ERK1/2. Interestingly, stimulation of EC with CRP for 16-24 h induced marked expression of the phosphatase and tensin homolog (PTEN), which functions as a negative regulator of phosphatidylinositol 3 kinase (PI3K) -->Akt signalling.
Conclusion: The observed time course for CRP-mediated PTEN upregulation corresponds to the exposure time needed for inhibition of Akt phosphorylation and migration and may therefore constitute a potential mechanism by which CRP inhibits inducible Akt phosphorylation and EC migration.