Expression of Human Myeloperoxidase by Macrophages Promotes Atherosclerosis in Mice

Increased myeloperoxidase (MPO) levels and activity are associated with increased cardiovascular risk among individuals with chronic kidney disease (CKD). However, a lack of good animal models for examining the presence and catalytic activity of MPO in vascular lesions has impeded mechanistic studies into CKD-associated cardiovascular diseases. Here, we show for the first time that exaggerated atherosclerosis in a pathophysiologically relevant CKD mouse model is associated with increased macrophage-derived MPO activity. Male 7-week-old LDL receptordeficient mice underwent sham (control mice) or 5/6 nephrectomy and were fed either a low-fat or high-fat, high-cholesterol diet for 24 weeks, and the extents of atherosclerosis and vascular reactivity were assessed. MPO expression and oxidation products, and the protein-bound oxidized tyrosine moieties 3-chlorotyrosine, 3-nitrotyrosine, and o,o′-dityrosine were examined with immunoassays and confirmed with mass spectrometry (MS). As anticipated, the CKD mice had significantly higher plasma creatinine, urea nitrogen, and intact parathyroid hormone along with lower hematocrit and body weight. On both the diet regimens, CKD mice did not have hypertension but had lower cholesterol and triglyceride levels than the control mice. Despite the lower cholesterol levels, CKD mice had increased aortic plaque areas, fibrosis, and luminal narrowing. They also exhibited increased MPO expression and activity (i.e., increased oxidized tyrosines) that co-localized with infiltrating lesional macrophages and diminished vascular reactivity. In summary, unlike non-CKD mouse models of atherosclerosis, CKD mice exhibit increased MPO expression and catalytic activity in atherosclerotic lesions, which colocalize with lesional macrophages. These results implicate macrophage-derived MPO in CKDaccelerated atherosclerosis.Chronic kidney disease (CKD) affects 15% of Americans, and cardiovascular disease (CVD) continues to be the leading cause of mortality in Myeloperoxidase oxidizes artery proteins in kidney disease2 these patients (>10-fold mortality compared to the general population) (1-6). An increased risk for CVD is evident even in milder and non-albuminuric forms of CKD and cannot be fully explained by traditional risk factors (7-10). Furthermore, control of established risk factors such as hyperlipidemia results in substantially lower risk reduction in CKD patients compared to the general population (11). Recent evidence supports the key role of nontraditional risk factors (e.g., oxidative stress) in the pathogenesis of CVD in CKD (12-17), suggesting that CKD-specific mechanisms are responsible for CVD in kidney patients.Atherosclerosis, the major cause of CVD, is a chronic inflammatory disease characterized by the infiltration of lipids and inflammatory cells, such as monocyte-derived macrophages and Tlymphocytes, into the artery wall (18). While elevated levels of low-density lipoprotein (LDL) are known to increase the risk of atherosclerosis greatly (19), in vitro studies sugges...

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Myeloperoxidase-derived oxidants damage artery wall proteins in an animal model of chronic kidney disease–accelerated atherosclerosis

Zeng

Mathew

Byun

et al. 2018

“…Elevated levels of chlorotyrosine and nitrotyrosine, two characteristic products of MPO, have been detected in HDL from human atherosclerotic lesions (42,43,86,87). Moreover, when MPO is expressed in macrophages, atherosclerosis increases in LDL receptor-deficient mice (88), raising the possibility that the heme enzyme promotes atherosclerosis by targeting apoA-I for oxidative damage.…”

Section: Discussionmentioning

confidence: 99%

Exchange of Apolipoprotein A-I between Lipid-associated and Lipid-free States

Cavigiolio¹,

Geier²,

Shao

et al. 2010

Self Cite

An important event in cholesterol metabolism is the efflux of cellular cholesterol by apolipoprotein A-I (apoA-I), the major protein of high density lipoproteins (HDL). Lipid-free apoA-I is the preferred substrate for ATP-binding cassette A1, which promotes cholesterol efflux from macrophage foam cells in the arterial wall. However, the vast majority of apoA-I in plasma is associated with HDL, and the mechanisms for the generation of lipid-free apoA-I remain poorly understood. In the current study, we used fluorescently labeled apoA-I that exhibits a distinct fluorescence emission spectrum when in different states of lipid association to establish the kinetics of apoA-I transition between the lipid-associated and lipid-free states. This approach characterized the spontaneous and rapid exchange of apoA-I between the lipid-associated and lipid-free states. In contrast, the kinetics of apoA-I exchange were significantly reduced when apoA-I on HDL was cross-linked with a bi-functional reagent or oxidized by myeloperoxidase. Our observations support the hypothesis that oxidative damage to apoA-I by myeloperoxidase limits the ability of apoA-I to be liberated in a lipid-free form from HDL. This impairment of apoA-I exchange reaction may be a trait of dysfunctional HDL contributing to reduced ATP-binding cassette A1-mediated cholesterol efflux and atherosclerosis.Apolipoprotein A-I (apoA-I), 4 the primary protein constituent of HDL, inhibits atherosclerosis in hypercholesterolemic mice (1-3). Moreover, increasing evidence indicates that HDL is cardioprotective in humans (4). The ability of HDL to promote cholesterol efflux from cholesteryl ester-laden macrophage foam cells is of central importance to the initiation and progression of atherosclerosis (5-7).In plasma, the vast majority of apoA-I associates with spherical HDL, a complex of apolipoproteins, phospholipids, triglycerides, free cholesterol, and cholesterol esters (8). However, the primary acceptor of cholesterol and phospholipids from macrophages is lipid-free or lipid-poor apoA-I (containing up to four phospholipid molecules (9)), which is the preferred substrate of the plasma membrane transporter ATP-binding cassette A1 (ABCA1) (10 -15). Circulating HDL is remodeled by the action of proteins and enzymes (16) such as cholesteryl ester transfer protein (17), lechitin:cholesterol acyltransferase (LCAT) (18, 19), phospholipid transfer protein (20, 21), and hepatic lipase (22). Plasma HDL remodeling can result in the destabilization of HDL and the release of lipid-free/lipid-poor apoA-I. Furthermore, the selective uptake of lipids from HDL through scavenger receptor B, type 1 can yield lipid-poor apoA-I (23).We hypothesized that the production of lipid-free/lipid-poor apoA-I from mature HDL and relipidation by ABCA1 is a dynamic process in the arterial wall, which is critical in protecting macrophages from cholesteryl ester accumulation. Previously, we showed that lipid-free/lipid-poor apoA-I is released from reconstituted HDL (rHDL) by long term (3-7 days) incu...

“…Additionally, only low levels of 3-chlorotyrosine, a characteristic product of myeloperoxidase, are detectable by mass spectrometry in mouse atherosclerotic tissue (22). Importantly, recent studies demonstrate that expression of human myeloperoxidase in macrophages promotes atherosclerosis in mice, providing direct evidence of the enzyme's causal role in atherogenesis (23).…”

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confidence: 99%

Myeloperoxidase Generates 5-Chlorouracil in Human Atherosclerotic Tissue

Takeshita

Byun

Nhan

et al. 2006

Self Cite

Somatic mutations induced by oxidative damage of DNA might play important roles in atherogenesis. However, the underlying mechanisms remain poorly understood. Myeloperoxidase, a heme protein expressed by select populations of artery wall macrophages, initiates one potentially mutagenic pathway by generating hypochlorous acid. This potent chlorinating agent reacts rapidly with primary amines to yield long-lived, selectively reactive N-chloramines. In the current studies, we demonstrate that myeloperoxidase produced by human macrophages differentiated in the presence of granulocyte macrophage colony-stimulating factor generates 5-chlorouracil, a mutagenic thymine analog. The primary amine taurine fails to block the reaction, suggesting that N-haloamines produced by macrophages might oxidize uracil. Model system studies demonstrated that N-chloramines convert uracil to 5-chlorouracil. Interestingly, the tertiary amine nicotine dramatically enhances uracil chlorination, suggesting that cigarette smoke might promote nucleobase oxidation by N-chloramines. To look for evidence that myeloperoxidase promotes uracil oxidation in vivo, we measured 5-chlorouracil levels in human aortic tissue, using isotope dilution gas chromatography-mass spectrometry. The level of 5-chlorouracil was 10-fold higher in atherosclerotic aortic tissue obtained during vascular surgery than in normal aortic tissue, suggesting that halogenated nucleobases produced by macrophages might contribute to atherogenesis. Because 5-chlorouracil can be incorporated into nuclear DNA, our observations raise the possibility that halogenation reactions initiated by phagocytes provide one pathway for mutagenesis, phenotypic modulation, and cytotoxicity during atherogenesis.