Background: Low density lipoprotein receptor-related protein 1 (LRP1) protects against atherosclerosis by regulating the activation of platelet-derived growth factor receptor β (PDGFRβ) in vascular smooth muscle cells (SMCs). Activated PDGFRβ undergoes tyrosine phosphorylation and subsequently interacts with various signaling molecules, including phosphatidylinositol 3-kinase (PI3K), which binds to the phosphorylated tyrosine 739/750 residues in mice, and thus regulates actin polymerization and cell movement. Methods and Principal Findings: In this study, we found disorganized actin in the form of membrane ruffling and enhanced cell migration in LRP1-deficient (LRP1-/-) SMCs. Marfan syndrome-like phenotypes such as tortuous aortas, disrupted elastic layers and abnormally activated transforming growth factor β (TGFβ) signaling are present in smooth muscle-specific LRP1 knockout (smLRP1-/-) mice. To investigate the role of LRP1-regulated PI3K activation by PDGFRβ in atherogenesis, we generated a strain of smLRP1-/- mice in which tyrosine 739/750 of the PDGFRβ had been mutated to phenylalanines (PDGFRb F2/ F2). Spontaneous atherosclerosis was significantly reduced in the absence of hypercholesterolemia in these mice compared to smLRP1-/- animals that express wild type PDGFR. Normal actin organization was restored and spontaneous SMC migration as well as PDGF-BB-induced chemotaxis was dramatically reduced, despite continued overactivation of TGFβ signaling, as indicated by high levels of nuclear phospho-Smad2. Conclusions and Significance: Our data suggest that LRP1 regulates actin organization and cell migration by controlling PDGFRβ-dependent activation of PI3K. TGFβ activation alone is not sufficient for the expression of the Marfan-like vascular phenotype. Thus, regulation of PI3 Kinase by PDGFRβ is essential for maintaining vascular integrity, and for the prevention of atherosclerosis as well as Marfan syndrome.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Agricultural and Biological Sciences(all)