Endorepellin, the C-terminal angiostatic module of perlecan, enhances collagen-platelet responses via the α2β1-integrin receptor

Endorepellin, a C-terminal fragment of the vascular basement membrane proteoglycan perlecan, inhibits angiogenesis via the alpha 2 beta 1-integrin receptor. Because this integrin is also implicated in platelet-collagen responses and because endorepellin or its fragments are generated in response to injury and inflammation, we hypothesized that endorepellin could also affect platelet biology. We discovered that endorepellin supported alpha 2 beta 1-dependent platelet adhesion, without appreciably activating or aggregating platelets. Notably, endorepellin enhanced collagen-evoked responses in platelets, in a src kinase-dependent fashion, and enhanced the collagen-inhibitory effect of an alpha 2 beta 1-integrin function-blocking antibody. Collectively, these results suggest that endorepellin/alpha 2 beta 1-integrin interaction and effects are specific and dependent on cell type, differ from those emanated by exposure to collagen, and may be due to cellular differences in alpha 2 beta 1-integrin activation/ligand affinity state. These studies also suggest a heretofore unrecognized role for angiostatic basement membrane fragments in platelet biology. (C) 2007 by The American Society of Hematology.