α-Defensins Induce a Post-translational Modification of Low Density Lipoprotein (LDL) That Promotes Atherosclerosis at Normal Levels of Plasma Cholesterol

Abstract

Approximately one-half of the patients who develop clinical atherosclerosis have normal or only modest elevations in plasma lipids, indicating that additional mechanisms contribute to pathogenesis. In view of increasing evidence that inflammation contributes to atherogenesis, we studied the effect of human neutrophil ␣-defensins on low density lipoprotein (LDL) trafficking, metabolism, vascular deposition, and atherogenesis using transgenic mice expressing human ␣-defensins in their polymorphonuclear leukocytes (Def ؉/؉ ). Accelerated Def Atherosclerosis and its thrombotic sequel, "atherothrombosis," are likely to remain the predominant cause of death in "developed" countries for decades to come. The etiology of this syndrome is multifactorial, and current predictors provide an incomplete estimate of the risk and opportunity for intervention. In a pooled analysis of over 87,000 persons with diagnosed coronary heart disease, one in five lacked any of the conventional risk factors: hypertension, smoking, high cholesterol, or diabetes (1). Furthermore, half of all cardiovascular events occur in patients with normal lipid levels (2). These data reveal the need to identify and mitigate as yet undescribed, but clinically relevant, risk factors for cardiovascular disease beyond those targeted in current practice.This problem is compounded by the lack of animal models that closely simulate human disease. Animal models used to study atherosclerosis, including its hyperlipidemic (3, 4) and inflammatory (5) components, are often characterized by striking elevations in plasma cholesterol, reaching plasma concentrations of 1500 -2200 mg/dl in LDLR Ϫ/Ϫ and 400 -450 mg/dl in ApoE Ϫ/Ϫ mice fed a high fat diet (3, 4), and most of the cholesterol is found in the VLDL fraction (3, 4). Neither these levels of lipids nor this distribution of lipoproteins is representative of findings in the vast majority of patients with atherosclerosis. Thus, there continues to be a need for new models to identify novel risk factors and novel approaches to intervention.We have identified human ␣-defensins 1-4, also known as human neutrophil peptides (HNPs), 2 as potentially having a role in the development of atherosclerosis. ␣-Defensins are antimicrobial proteins that constitute ϳ5% of the total protein in polymorphonuclear leukocytes (PMNs). ␣-Defensins are released from a subset of azurophilic granules when the PMNs are activated by a variety of agonists (6, 7). ␣-Defensins are abundant in human atherosclerotic coronary and carotid arteries (8, 9), and there is a significant correlation between the deposition of ␣-defensins in skin tissue and the severity of coronary artery disease (10). ␣-Defensins inhibit the degradation of low density lipoprotein (LDL) and Lp(a) by vascular cells (11), increase their binding and retention in extracellular matrix (12), and inhibit tissue-type plasminogen activator (tPA)-mediated fibrinolysis (13, 14).These observations have been confirmed and extended by others. Increased plasma levels of ␣-defensins are assoc...

Human neutrophil peptides inhibit cleavage of von Willebrand factor by ADAMTS13: a potential link of inflammation to TTP

“…presentation support the potential contribution of HNP-mediated inhibition of ADAMTS13 activity to the pathogenesis of acquired autoimmune TTP and identifies a potential new therapeutic target such as colchicine to inhibit the release of HNPs 33 in the treatment and prevention of disease relapse.…”

“…by guest www.bloodjournal.org From induce a post-translational modification of low-density lipoprotein that promotes atherosclerosis at normal levels of plasma cholesterol. 33 Here, we show that HNPs inhibit the proteolytic cleavage of the minimal substrate VWF73 and multimeric VWF by ADAMTS13 under diverse conditions (Figures 1 and 2). This inhibitory activity appeared to be mediated by high-affinity binding of HNPs to the central A2 domain of VWF (ie, VWF73) through the RRY motif (Figure 3).…”

“…Local release, binding, and retention of HNPs at sites of vascular injury are likely to exceed expectations based on plasma levels. 33 Lastly, studies under way in mice transgenic for neutrophil expression of HNP1 33,46 are needed to more definitively assess the role of these peptides in propagating thrombosis in the setting of antibody-mediated deficiency of ADAMTS13 activity. 47,48 In summary, we demonstrate that HNPs are potent inhibitors of ADAMTS13-dependent VWF proteolysis in vitro.…”

Opposing effects of HNP1 (α-defensin-1) on plasma cholesterol and atherogenesis

“…More specifically, results from several groups using diverse approaches suggest that human α-defensins (α-defs) 1-4, also known as human neutrophil peptides (HNPs), [2] contribute to this process [5,6,[8][9][10][11]. We recently examined the mechanism by which α-defensins released from activated neutrophils may promote formation of lipid streaks in the vasculature using HNP-1tg/tg Def +/+ (Def +/+ ) mice fed a high fat diet (HFD) [12]. We found that α-defensin-1 (α-def-1) forms complexes with LDL, accelerating lipoprotein clearance from the circulation by the liver, leading to hypocholesterolemia [12].…”

“…We recently examined the mechanism by which α-defensins released from activated neutrophils may promote formation of lipid streaks in the vasculature using HNP-1tg/tg Def +/+ (Def +/+ ) mice fed a high fat diet (HFD) [12]. We found that α-defensin-1 (α-def-1) forms complexes with LDL, accelerating lipoprotein clearance from the circulation by the liver, leading to hypocholesterolemia [12]. In line with this, plasma levels of total cholesterol (TCH) and LDL were lower in Def +/+ mice than in wild type control animals [12].…”