Fibroblast Growth Factor-2 Potentiates Vascular Smooth Muscle Cell Migration to Platelet-Derived Growth Factor

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Abstract
Fibroblast growth factor-2 (FGF-2) has been implicated in vascular smooth muscle cell (SMC) migration, a key process in vascular disease. We demonstrate here that FGF-2 promotes SMC motility by altering β 1 integrin–mediated interactions with the extracellular matrix (ECM). FGF-2 significantly increased surface expression of α 2 β 1 , α 3 β 1 , and α 5 β 1 integrins on human SMCs, as assessed by flow cytometry. The greatest increase was for the collagen-binding α 2 β 1 integrin. Despite this, FGF-2 did not increase SMC adhesion to type I collagen but instead promoted SMC elongation and SMC motility. The latter was evaluated by using a microchemotaxis chamber and by digital time-lapse video microscopy. Although FGF-2 was not chemotactic for human SMCs, cells preincubated with FGF-2 displayed a 3.1-fold increase in migration to the undersurface of porous type I collagen–coated membranes and a 2.1-fold increase in migration speed on collagen. Furthermore, chemotaxis to platelet-derived growth factor-BB on collagen was significantly greater in SMCs exposed to FGF-2. FGF-2–induced elongation and migration on collagen were inhibited by a blocking anti-α 2 β 1 antibody; however, SMC adhesion to collagen was unaffected. SMC migration on fibronectin was also enhanced by FGF-2, although less prominently: migration through porous membranes increased 1.8-fold, and migration speed increased 1.3-fold. Also, FGF-2 completely disassembled the smooth muscle α-actin–containing stress fiber network contemporaneously with the change in integrin expression and cell shape. We conclude that (1) exogenous FGF-2 promotes SMC migration and potentiates chemotaxis to PDGF-BB; (2) the promigratory effect of FGF-2 is especially prominent on type I collagen and is mediated by upregulation of α 2 β 1 integrin; and (3) FGF-2 disassembles actin stress fibers, which may promote differential utilization of α 2 β 1 integrin for motility but not adhesion. This dynamic SMC-ECM interplay may be an important mechanism by which FGF-2 facilitates SMC motility in vivo.