Statin-Induced Expression of Decay-Accelerating Factor Protects Vascular Endothelium Against Complement-Mediated Injury

Abstract

Abstract-Complement-mediated vascular injury is important in the pathophysiology of atherosclerosis and myocardial infarction. Because recent evidence shows that statins have beneficial effects on endothelial cell (EC) function independent of lipid lowering, we explored the hypothesis that statins modulate vascular EC resistance to complement through the upregulation of complement-inhibitory proteins. Human umbilical vein and aortic ECs were treated with atorvastatin or simvastatin, and decay-accelerating factor (DAF), membrane cofactor protein, and CD59 expression was measured by flow cytometry. A dose-dependent increase in DAF expression of up to 4-fold was seen 24 to 48 hours after treatment. Statin-induced upregulation of DAF required increased steady-state mRNA and de novo protein synthesis. L-Mevalonate and geranylgeranyl pyrophosphate reversed the effect, confirming the role of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibition and suggesting that constitutive DAF expression is negatively regulated by geranylgeranylation. Neither farnesyl pyrophosphate nor squalene inhibited statin-induced DAF expression, suggesting that the effect is independent of cholesterol lowering. Statin-induced DAF upregulation was mediated by the activation of protein kinase C␣ and inhibition of RhoA and was independent of phosphatidylinositol-3 kinase and NO activity. The increased DAF expression was functionally effective, resulting in significant reduction of C3 deposition and complement-mediated lysis of antibody-coated ECs. These observations provide evidence for a novel cytoprotective action of statins on vascular endothelium that is independent of the effect on lipids and results in enhanced protection against complement-mediated injury. Modulation of complement regulatory protein expression may contribute to the early beneficial effects of statins in reducing the morbidity and mortality associated with atherosclerosis.

C-Reactive Protein Upregulates Complement-Inhibitory Factors in Endothelial Cells

“…Incubation with cycloheximide alone led to a superinduction of steady-state DAF mRNA, consistent with previous reports. 12 Addition of both CRP and cycloheximide led to a rise in steady-state DAF mRNA similar to that observed with cycloheximide alone, which was significantly lower than DAF mRNA levels after only CRP treatment ( Figure 2B). Similar results were obtained when examining cell-surface DAF expression ( Figure 2C).…”

“…18 Our data suggest that CRP-induced expression of DAF depends on the synthesis of an intermediate transcriptional activator and that the observed increase in DAF expression is functionally relevant, as indicated by the reduction in complement-mediated cell lysis. However, unlike vascular endothelial growth factor, tumor necrosis factor-␣, interferon-␥, or statins, 12,17,18 CRP was also able to induce the expression of the additional complement inhibitors CD46 and CD59, suggesting that the changes mediated by CRP arise through a combination of signaling pathways. Although not tested, the ability of CRP to activate mitogen-activated protein kinases and the transcription factors nuclear factor-B and activator protein-1, 19 linked to increased complement inhibitor expression, 12,17,18 may be responsible for the increase in DAF, CD46, and CD59 observed after CRP stimulation.…”

“…11 DAF prevents the formation and accelerates the decay of the C3 and C5 convertases that act early within the complement cascade, 11 functioning to maintain vascular integrity as a key protector against complement-mediated cell lysis. 12 The classical pathway of complement may be activated by CRP bound to enzymatically degraded low-density lipoprotein. 13 The effect of CRP on the expression of complementinhibitory factors is unknown.…”

Monitoring the Cellular Effects of HMG-CoA Reductase Inhibitors In Vitro and Ex Vivo

“…For example, statins increase endothelial nitric oxide synthase expression, 14 decrease smooth muscle cell proliferation, 15 reduce matrix metalloproteinase activity and tissue factor production by macrophages, 16,17 increase fibrinolytic activity, 18 and have immunomodulatory and antiinflammatory actions such as increasing resistance to complement 19 and decreasing dendritic cell maturation. 20 Many of these effects are reversed only with geranylgeranyl pyrophosphate and not with farnesyl pyrophosphate, suggesting that inhibition of Rho isoprenylation by statins is the predominant mechanism by which statins exert their antiatherogenic activities.…”

Peripheral tolerance can be modified by altering KLF2-regulated Treg migration

“…Having demonstrated that augmenting KLF2 levels within the Treg compartment is sufficient to promote peripheral tolerance, we next tested if this event could be replicated by simvastatin. Of note, statins have an immunosuppressive effect on endothelial cells, including decreased MHC class II expression, decreased expression of P-selectin and CD40, increased surface expression of complement inhibitory molecules, and increased production of nitric oxide (31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41). Because the endothelial compartment contributes to symptoms of aGVHD (42)(43)(44)(45), these pleiotropic effects precluded the systemic use of simvastatin to test Treg-mediated tolerance.…”