Structure–function properties of the apoE-dependent COX-2 pathway in vascular smooth muscle cells

Abstract

Apolipoprotein (apoE) E is a multifunctional protein that plays a critical role in atherogenesis, in part by regulating the intimal proliferation of vascular smooth muscle cells. Recently, a novel cyclooxygenase (COX)-2 pathway was shown to contribute to the anti-proliferative action of human apoE3 in vascular smooth muscle cells (VSMC). Here, we provide insight into the structure-function properties by which apoE mediates these effects. ApoE3 is most effective in promoting COX-2 expression as a lipid-free protein and is less active after lipidation. Alterations in the stability of the helix-bundle N-terminal domain of apoE that contains the binding site for the low density lipoprotein (LDL) receptor and heparin do not affect the up-regulation of the COX-2 pathway. In addition, the apoE2, 3, and 4 isoforms are all capable of up-regulating the COX-2 pathway. Finally, the effect of apoE on COX-2 was found to be independent of expression on the VSMC surface of the LDL receptor and heparan sulfate proteoglycans (HSPG). In summary, our data indicates that apoE, particularly in the lipid-free state, can up-regulate COX-2 in murine vascular smooth muscle cells apparently independently of binding to the LDLR, LRP or HSPG.

Cardiovascular Protection by ApoE and ApoE-HDL Linked to Suppression of ECM Gene Expression and Arterial Stiffening

“…S2E vs. S2F). Previously, we reported that apoE3 and its N-terminal domain stimulate the expression of Cox2 mRNA and protein in VSMCs (Ali et al, 2008; Kothapalli et al, 2004). Consistent with these results, the Cox2 inhibitor, nimesulide, prevented suppression of the collagen-I and FN genes by apoE3 in VSMCs whereas the Cox1 inhibitor, SC560, was without effect (Fig.…”

“…3C). Cox2 production in VSMCs leads to the production of PGI 2 , and VSMCs treated with apoE3 have increased amounts of PGI 2 in their conditioned medium (Ali et al, 2008; Kothapalli et al, 2004). The PGI 2 mimetic, cicaprost, phenocopied the effect of apoE3 on collagen-I and FN mRNAs (Fig.…”

“…The best studied apoE receptors are LDL receptor (LDLR), LRP, and heparin sulfate proteoglycan (Boucher et al, 2003; Nimpf and Schneider, 2000; Strickland et al, 2002). Our previous report indicated that Cox2 induction by apoE is likely independent of these receptors (Ali et al, 2008). Downregulation of miR-145 and its bicistronic partner, miR-143, have been implicated in the phenotypic switch of VSMCs from contractile (differentiated) to synthetic (de-differentiated) states (Boettger et al, 2009; Cordes et al, 2009).…”

TNF-α-Induced cPLA2 Expression via NADPH Oxidase/Reactive Oxygen Species-Dependent NF-κB Cascade on Human Pulmonary Alveolar Epithelial Cells

“…COX-2 and cPLA 2 are tightly regulated by various mediators in several species (Beasley, 1999; Ali et al, 2008; Pavicevic et al, 2008). cPLA 2 hydrolyzes the membrane phospholipids, resulting in the release of AA, which is further converted by the constitutive enzyme COX-1 or by the inducible COX-2, and PG synthases to biologically active PGs (DeWitt, 1999).…”

Apoprotein E as a lipid transport and signaling protein in the blood, liver, and artery wall

“…Lipid-free apoE is more effective than the lipid associated protein. Whatever receptor mediates this effect, it does not appear to be the LDL receptor, LRP1, or HSPG (40).…”