Assay for cell migration and invasion of vascular smooth muscle cells

Chemotaxis is a critical event in the development of atherosclerotic lesions and in the restenosis that often occurs after surgical intervention and angioplasty (1). Chemokines involved in atherogenesis include colony-stimulating factors (2), oxidized low-density lipoproteins (3), transforming growth factor-β (4) and fibroblast growth factor (5), which induce chemotaxis of monocytes and endothelial cells. Other growth factors, such as platelet-derived growth factor (PDGF) (6) and insulin-like growth factor-1, induce chemotaxis of vascular smooth muscle cells (VSMCs) (7), which play a major role in the formation of atherosclerotic lesions (8,9). In normal human arteries, VSMC-reside mainly in the tunica media in a quiescent state and express a variety of differentiation-specific genes important to maintain the physiological regulation of vessel tone and blood pressure (10). Under pathological conditions, such as vessel injury or atherosclerotic plaque development, VSMCs become exposed to certain growth factors and cytokines, such as PDGF, which induce a transformation from the contractile to a synthetic state (7,11-13). Only in the latter state, VSMCs acquire the ability to migrate from the tunica media to the tunica intima. In vivo, VSMCs are surrounded by and embedded in a variety of extracellular matrices (ECMs) that must be traversed during migration. In the intact vessel, one of the main ECM barriers to cell movement is the basement membrane (BM) that surrounds each VSMC and separates the VSMC-containing medial cell layer from the endothelium (14). Migrating VSMCs have been shown to digest BM (14,15), an invasion process that is mediated by tightly regulated proteases (16). Within this group of proteases, the family of matrix metalloproteinases (MMPs) are essential for the digestion of ECM components such as collagens, gelatins, or proteoglycans (17,18).