Heterotypic contact reveals a COX-2-mediated suppression of osteoblast differentiation by endothelial cells: A negative modulatory role for prostanoids in VEGF-mediated cell: cell communication?
In bone, angiogenesis must be initiated appropriately, but limited once remodelling or repair is complete. Our recent findings have supported a role for prostaglandins (PG), known modulators of osteoblast (OB) and endothelial cell (EC) behaviour, in facilitating VEGF-mediated paracrine communication from OBs to 'remotely located' ECs, but the mechanism(s) regulating OB:EC crosstalk when these cells are closely opposed are undefined. In this study we have examined: (i) the effects of exogenous PGE(2) on VEGF-driven events in ECs, and (ii) the role of endogenous COX-2-derived prostanoids in mediating communication between intimately opposed OBs and ECs in direct contact. Exposure of ECs to PGE(2) increased ERK1/2 phosphorylation, COX-2 induction, 6-keto-PGF(1alpha) release and EC proliferation. In contrast, PGE(2) attenuated VEGF(165)-induced VEGFR2/Flk1 phosphorylation, ERK1/2 activation and proliferation of ECs, suggesting that exogenous PGE(2) restricts the actions of VEGF. However, the COX-2-selective inhibitor, NS398, also attenuated VEGF-induced proliferation, implying a distinct role for endogenous COX-2 activity in regulating EC behaviour. To examine the effect of OB:EC proximity and the role of COX-2 products further, we used a confrontational co-culture model. These studies showed that COX-2 blockade with NS398 enhanced EC-dependent increases in OB differentiation, that this effect was reversed by exogenous PGH(2) (immediate COX-2 product), and that exogenous VEGF did not influence EC-dependent OB differentiation under these conditions. Our findings indicate that locally produced prostanoids may serve distinct roles depending on OB:EC proximity and negatively modulate VEGF-mediated changes in EC behaviour when these cells are closely opposed to control angiogenesis during bone (re)modelling.
Clarkin
Claire E
CE
Department of Veterinary Basic Sciences, Royal Veterinary College, University of London, London, UK. claire.clarkin@kcl.ac.uk
Garonna
Elena
E
Pitsillides
Andrew A
AA
Wheeler-Jones
Caroline P D
CP
D015121:6-Ketoprostaglandin F1 alpha / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002450:Cell Communication / Q000502:physiology*; D002454:Cell Differentiation; D002478:Cells, Cultured; D018920:Coculture Techniques; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism*; D016861:Cyclooxygenase Inhibitors / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism; D042783:Endothelial Cells / Q000166:cytology / Q000502:physiology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009578:Nitrobenzenes / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology*; D011453:Prostaglandins / Q000378:metabolism*; D013449:Sulfonamides / Q000378:metabolism; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism
D016861:Cyclooxygenase Inhibitors; D009578:Nitrobenzenes; D011453:Prostaglandins; D013449:Sulfonamides; C080955:N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; D015121:6-Ketoprostaglandin F1 alpha; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D040301:Vascular Endothelial Growth Factor Receptor-2; D048049:Extracellular Signal-Regulated MAP Kinases; D000469:Alkaline Phosphatase; D015232:Dinoprostone