Apolipoprotein(a), through Its Strong Lysine-binding Site in KIV10, Mediates Increased Endothelial Cell Contraction and Permeability via a Rho/Rho Kinase/MYPT1-dependent Pathway

Abstract

Substantial evidence indicates that endothelial dysfunction plays a critical role in atherogenesis. We previously demonstrated that apolipoprotein(a) (apo(a); the distinguishing protein component of the atherothrombotic risk factor lipoprotein(a)) elicits rearrangement of the actin cytoskeleton in human umbilical vein endothelial cells, characterized by increased myosin light chain (MLC) phosphorylation via a Rho/ Rho kinase-dependent signaling pathway. Apo(a) contains kringle (K)IV and KV domains similar to those in plasminogen: apo(a) contains 10 types of plasminogen KIV-like sequences, followed by sequences homologous to the plasminogen KV and protease domains. Several of the apo(a) kringles contain lysinebinding sites (LBS) that have been proposed to contribute to the pathogenicity of Lp(a). Here we demonstrate that apo(a)-induced endothelial barrier dysfunction is mediated via a Rho/ Rho kinase-dependent signaling pathway that results in increased MYPT1 phosphorylation and hence decreased MLC phosphatase activity, thus leading to an increase in MLC phosphorylation, stress fiber formation, cell contraction, and permeability. In addition, studies using recombinant apo(a) variants indicated that these effects of apo(a) are dependent on sequences within the C-terminal half of the apo(a) molecule, specifically, the strong LBS in KIV 10 . In parallel experiments, the apo(a)-induced effects were completely abolished by treatment of the cells with the lysine analogue ⑀-aminocaproic acid and the Rho kinase inhibitor Y27632. Taken together, our findings indicate that the strong LBS in apo(a) KIV 10 mediates all of our observed effects of apo(a) on human umbilical vein endothelial cell barrier dysfunction. Studies are ongoing to further dissect the molecular basis of these findings.Studies have shown that elevated concentrations of plasma lipoprotein(a) (Lp(a)) 2 (Ͼ30 mg/dl or Ͼ100 nM) are a risk factor for a variety of vascular diseases, including coronary heart disease, ischemic stroke, and venous thrombosis (1, 2). Lp(a) is identical to low density lipoprotein (LDL) in both lipid composition as well as the presence of apolipoproteinB-100. However, Lp(a) is clearly distinguishable from LDL by the presence of the unique glycoprotein apolipoprotein(a) (apo(a)) that is disulfide-linked to apolipoproteinB-100 in LDL by a single disulfide bond (3). Apo(a) bears a striking homology with plasminogen and contains multiple repeats of a sequence that resembles plasminogen kringle IV as well as sequences homologous to the kringle V and protease regions of plasminogen (4). The protease domain in apo(a) cannot be activated by activators of plasminogen; therefore, it cannot develop protease activity and hence lacks fibrinolytic activity (5). The kingle IV-like domain in apo(a) is classified into 10 types (KIV 1-10 ); the KIV 2 sequence is present in a variable number of identically repeated copies (from 3 to Ͼ40) giving rise to Lp(a) isoform size heterogeneity (6, 7). Kringle IV types 5-8 (KIV 5-8 ) possess "weak" lysinebinding s...

Apolipoprotein E3 Inhibits Rho to Regulate the Mechanosensitive Expression of Cox2

“…Apolipoprotein(a) rapidly increases Rho-GTP levels and actin stress fibers in endothelial cells and VSMCs [28,29]. Thus, apolipoprotein(a) and apoE3 have opposing effects on Rho-GTP that correspond to their opposing effects on atherosclerosis.…”

Mechanistic insights into Lp(a)-induced IL-8 expression: a role for oxidized phospholipid modification of apo(a)

“…A plausible link between TLR2/CD36 activation and regulation of IL-8 through these factors is supplied by the observations that activation of these receptors induces Once we established that use of a 17K r-apo(a) was a suitable model to study apo(a)-mediated stimulation of IL-8 expression in THP-1 macrophages, we began to probe the mechanism underlying this observation. A number of processes have been reported in which the lysine binding properties of apo(a) KIV 10 is implicated, including the ability of apo(a) to inhibit pericellular plasminogen activation and to increase vascular endothelial cell permeability ( 13,17 ). In these studies, the role of the lysine binding properties had been demonstrated using both the lysine analog, -ACA, as well as an amino acid substitution in the apo(a) KIV 10 domain that abolishes the lysine binding ability of this kringle.…”

“…In cultured vascular endothelial cells, Lp(a)/apo(a) has been shown to induce expression of the cell adhesion molecules, ICAM ( 15 ), E-selectin ( 16 ), and VCAM ( 16 ). Lp(a)/apo(a) also promotes the assembly of actin stress fi bers resulting in cell contraction and increased endothelial cell permeability ( 17 ). Lp(a)/apo(a) has been implicated in pro-infl ammatory processes through its ability to bind to the integrin, Mac-1, on leukocytes, resulting in the Mac-1-dependent promotion of monocyte adhesion and transendothelial migration ( 18 ).…”

Lipoprotein(a)

“…1). These functions include initiation of signaling pathways in macrophages 32 and vascular endothelial cells, 33,34 resulting in proatherogenic changes in cell phenotype and gene expression.…”