Decorin Signalling in Endothelial Cells

Introduction: Angiogenesis is integral to oral disease and wound healing. Therefore, investigation of its control mechanisms is essential. Decorin is a proteoglycan of the extracellular matrix of e.g. periodontal ligament, gingiva and bone. While not expressed by quiescent endothelial cells, it is upregulated during angiogenesis, where autocrine decorin signalling upregulates the cyclin dependent kinase inhibitors p21 and p27, enhancing cell survival. Decorin upregulates p21 via the IGFR and Akt, however the mechanism of p27 upregulation is unknown.

Objectives: This study aims to elucidate the role of decorin signalling in endothelial cells, particularly in migration and adhesion; integrin-mediated events essential to angiogenesis.

Methods: Endothelial cells (EA.hy926) cultured on collagen or fibronectin were incubated with decorin (purified under native conditions) or integrin inhibitors, and focal adhesion kinase (FAK) phosphorylation was compared by Western blotting. Migration was investigated using a spheroid migration assay, and effects on stress fibres were visualised by fluorescence microscopy. The electrophoretic mobility shift assay (EMSA) was utilised to investigate transcription factor activity.

Results: Decorin has been described as an inhibitor of cell migration and adhesion, and to signal through α₂β₁ integrin on platelets. However, decorin effects contrast to those of Rhodoectin (α₂β₁ integrin inhibitor). Decorin increases cell migration on fibronectin and collagen, while Rhodocetin and cyclic RGD peptides (α_vβ₃ integrin inhibitor), decrease migration. Decorin has no effect on FAK autophosphorylation, while Rhodocetin decreases it. Rhodocetin affects stress fibres in a manner distinct from decorin. EMSA studies support evidence for decorin activating multiple signalling pathways, since decorin transiently activates Akt, but also activates FoxO transcription factors, which are inhibited by Akt, but increase p27 transcription.

Conclusions: This study supports a role for decorin in control of angiogenesis through modulation of cell migration, and of cell fate. This also indicates decorin as a potential component for manipulating angiogenesis in tissue engineering.