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Statins, inhibitors of HMG-CoA reductase, elicit various actions on vascular cells including the modulation of proliferation and migration of smooth muscle cells (SMCs). Here, we have elucidated the mechanism by which statins, in particular pitavastatin, attenuate the migration activity of SMCs. The expression of LR11, a member of the LDL receptor family and an enhancer of cell surface localization of urokinase-type plasminogen activator receptor (uPAR), is increased in cultured SMCs by treatment with PDGF-BB. Pitavastatin attenuates the PDGF-BB -induced surface expression of LR11 and uPAR. The increased migration of SMCs observed both upon overexpression of LR11 and via stimulation of secretion of soluble LR11 is not reversed by pitavastatin. In vivo studies showed that the SMCs expressing LR11 in plaques are almost congruent with intimal cells expressing nonmuscle myosin heavy chain (SMemb). Pitavastatin reduced the expression of LR11 and SMemb, and the levels of LR11, uPAR, and SMemb in cultured intimal SMCs were reduced to those seen in medial SMCs. We propose that this statin reduces PDGF-induced migration through the attenuation of the LR11/uPAR system in SMCs. Modulation of the LR11/uPAR system with statins suggests a novel treatment strategy for atherogenesis based on suppression of intimal SMC migration.

Objective: Studies on the involvement of low-density lipoprotein receptor relatives (LRs) in atherosclerosis have recently gained new focus because of the specific expression of certain of these receptors in the thickened intima. Here, we show that LRP1B, a member of LRs, modulates the migration of smooth muscle cells (SMCs) by increasing the degradation of membrane receptors, urokinase-type plasminogen activator receptor (uPAR), and platelet-derived growth factor receptor (PDGFR) beta., Methods and Results: Immunohistochemistry showed that LRP1B expression in human coronary arteries is localized to the intimal SMCs near the plaque surface as well as to medial SMCs. LRP1B expression levels in cultured SMCs increase at the late phase of proliferation. Cell surface and internalization assays, in combination with coimmunoprecipitation experiments, showed that LRP1B binds and internalizes uPAR. Metabolic labeling analysis demonstrated that anti-LRP1B IgY decreased the catabolism of uPAR. In addition, the anti-LRP1B antibody raised PDGFRbeta protein and PDGFR-mediated phosphorylation levels of ERK1/2. Finally, the anti-LRP1B IgY enhanced the migration and invasion of SMCs in the presence of PDGF-BB., Conclusions: LRP1B modulates the catabolism of uPAR and PDGFR, affecting the migration of SMCs. This functional characterization of LRP1B opens novel avenues for elucidating the (patho)physiological significance of SMC migration in atheromatous plaques.

LR11, a member of the LDL receptor family, is highly expressed in vascular smooth muscle cells (SMCs) of the hyperplastic intima, and induces enhanced migration of SMCs in vitro via its upregulation of urokinase-type plasminogen activator receptor (uPAR) expression. In this study, we have delineated the mechanism by which LR11 elevates the expression levels of uPAR in SMCs. Secretion of soluble LR11 is induced in SMCs during the rapidly proliferating phase, and the secreted LR11 induces the migration activities of SMCs. Both the cell-anchored and secreted forms of LR11 have the capacity to bind to and form complexes with uPAR. LR11-overexpressing cells show significantly enhanced uPAR binding, but decreased uPAR internalization. LR11 colocalizes with uPAR on the cell surface and inhibits the LDL receptor-related protein (LRP)-mediated binding and internalization of uPAR. Thus, LR11 mediates the uPAR localization to the plasma membrane. LR11 is highly expressed in the atheromatous plaque areas of apoE knockout mice, particularly in the intimal SMCs at the border between intima and media. The neutralization of LR11 function with anti-LR11 antibody reduced cuff-induced intimal thickness in mice. The novel mechanism of regulation of uPAR localization in SMCs accompanied with enhanced migration activity possibly constitutes an important factor in the process of atherosclerosis and arterial remodeling.

Background: LR11, a member of the LDL receptor family, is highly expressed in vascular smooth muscle cells (SMCs) of the hyperplastic intima but not media. To further clarify the involvement of LR11 in the process of atherosclerosis, we have characterized the migration and invasion activities of LR11-overexpressing SMCs., Methods and Results: LR11 cDNA was transfected into the rat SMC line A7r5. Compared with mock cells (C-1), in the presence of platelet-derived growth factor-BB, the transfected cells (R-1 and R-2) showed 3.5- to 4.0-fold higher expression of LR11 protein, 1.7- to 1.8-fold increased migration, and 2.0- to 2.2-fold elevated invasion activities, respectively. The increases were essentially abolished by the addition of receptor-associated protein, anti-LR11 antibodies, or apolipoprotein E. Immunological analyses showed that urokinase-type plasminogen activator receptor (uPAR) levels were increased in LR11-overexpressing cells. Anti-urokinase-type plasminogen activator (uPA) and anti-uPAR antibodies reduced the migration and invasion activities of R-1 and R-2 cells to baseline levels. Receptor-associated protein, anti-LR11 antibodies, and apolipoprotein E decreased uPAR expression in the LR11-overexpressing cells by approximately 50%. Cellular catabolism of uPAR was significantly decreased in R-1 and R-2 cells compared with control. Cultured SMCs isolated from intima of atherosclerotic rabbit aortas showed increased expression levels of LR11 and uPAR and enhanced migration and invasion compared with SMCs from medial layers., Conclusions: Overexpression of LR11 induces enhanced migration and invasion activities of intimal SMCs in vitro, probably through its regulation of the uPA/uPAR system.