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(Circulation Research. 2006;98:98.)
© 2006 American Heart Association, Inc.

Cellular Biology

Cellular Pathology of Atherosclerosis

Smooth Muscle Cells Promote Adhesion of Platelets to Cocultured Endothelial Cells

Samantha P. Tull, Steve I. Anderson, Sascha C. Hughan, Steve P. Watson, Gerard B. Nash, G. Ed Rainger

From The Centre for Cardiovascular Sciences, The Medical School, The University of Birmingham, Edgbaston, Birmingham, United Kingdom.

Correspondence to Dr G. E. Rainger, Department of Physiology, The Medical School, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom. E-mail g.e.rainger{at}bham.ac.uk

Although platelets do not ordinarily bind to endothelial cells (EC), pathological interactions between platelets and arterial EC may contribute to the propagation of atheroma. Previously, in an in vitro model of atherogenesis, where leukocyte adhesion to EC cocultured with smooth muscle cells was greatly enhanced, we also observed attachment of platelets to the EC layer. Developing this system to specifically model platelet adhesion, we show that EC cocultured with smooth muscle cells can bind platelets in a process that is dependent on EC activation by tumor necrosis factor (TNF)- and transforming growth factor (TGF)-ß₁. Recapitulating the model using EC alone, we found that a combination of TGF-ß₁ and TNF- promoted high levels of platelet adhesion compared with either agent used in isolation. Platelet adhesion was inhibited by antibodies against GPIb-IX-V or _IIbß₃ integrin, indicating that both receptors are required for stable adhesion. Platelet activation during interaction with the EC was also essential, as treatment with prostacyclin or theophylline abolished stable adhesion. Confocal microscopy of the surface of EC activated with TNF- and TGF-ß₁ revealed an extensive matrix of von Willebrand factor that was able to support the adhesion of flowing platelets at wall shear rates below 400 s^–1. Thus, we have demonstrated a novel route of EC activation which is relevant to the atherosclerotic microenvironment. EC activated in this manner would therefore be capable of recruiting platelets in the low-shear environments that commonly exist at points of atheroma formation.

Key Words: smooth muscle cells • endothelial cells • coculture • transforming growth factor-ß₁ • platelet adhesion