Long Noncoding RNA MIAT Controls Advanced Atherosclerotic Lesion Formation and Plaque Destabilization.

BACKGROUND: Long noncoding RNAs (lncRNAs) are important regulators of biological processes involved in vascular tissue homeostasis and disease development. The present study assessed the functional contribution of the lncRNA myocardial infarction-associated transcript (MIAT) to atherosclerosis and carotid artery disease. METHODS: We profiled differences in RNA transcript expression in patients with advanced carotid artery atherosclerotic lesions from the Biobank of Karolinska Endarterectomies. The lncRNA MIAT was identified as the most upregulated noncoding RNA transcript in carotid plaques compared with nonatherosclerotic control arteries, which was confirmed by quantitative real-time polymerase chain reaction and in situ hybridization. RESULTS: Experimental knockdown of MIAT, using site-specific antisense oligonucleotides (LNA-GapmeRs) not only markedly decreased proliferation and migration rates of cultured human carotid artery smooth muscle cells (SMCs) but also increased their apoptosis. MIAT mechanistically regulated SMC proliferation through the EGR1 (Early Growth Response 1)-ELK1 (ETS Transcription Factor ELK1)-ERK (Extracellular Signal-Regulated Kinase) pathway. MIAT is further involved in SMC phenotypic transition to proinflammatory macrophage-like cells through binding to the promoter region of KLF4 and enhancing its transcription. Studies using Miat-/- and Miat-/-ApoE-/- mice, and Yucatan LDLR-/- mini-pigs, as well, confirmed the regulatory role of this lncRNA in SMC de- and transdifferentiation and advanced atherosclerotic lesion formation. CONCLUSIONS: The lncRNA MIAT is a novel regulator of cellular processes in advanced atherosclerosis that controls proliferation, apoptosis, and phenotypic transition of SMCs, and the proinflammatory properties of macrophages, as well.

Induction of dendritic cell-mediated T-cell activation by modified but not native low-density lipoprotein in humans and inhibition by annexin a5: involvement of heat shock proteins.

OBJECTIVE: Atherosclerosis is an inflammatory disease, where activated immunocompetent cells, including dendritic cells (DCs) and T cells are abundant in plaques. Low-density lipoprotein modified either by oxidation (oxLDL) or by human group X-secreted phospholipase A2 (LDLx) and heat shock proteins (HSP), especially HSP60 and 90, have been implicated in atherosclerosis. We previously reported that Annexin A5 inhibits inflammatory effects of phospholipids, decreases vascular inflammation and improves vascular function in apolipoprotein E(-/-) mice. Here, we focus on the LDLx effects on human DCs and T cells. APPROACH AND RESULTS: Human DCs were differentiated from peripheral blood monocytes, stimulated by oxLDL or LDLx. Naive autologous T cells were cocultured with pretreated DCs. oxLDL and LDLx, in contrast to LDL, induced DC-activation and T-cell proliferation. T cells exposed to LDLx-treated DCs produced interferon-γ, interleukin (IL)-17 but not IL-4 and IL-10. Annexin A5 abrogated LDLx effects on DCs and T cells and increased production of transforming growth factor-ß and IL-10. Furthermore, IL-10 producing T cells suppressed primary T-cell activation via soluble IL-10, transforming growth factor-ß, and cell-cell contact. Lentiviral-mediated shRNA knock-down HSP60 and 90 in DCs attenuated the effect of LDLx on DCs and subsequent T-cell proliferation. Experiments on DC and T cells derived from carotid atherosclerotic plaques gave similar results. CONCLUSIONS: Our data show that modified forms of LDL such as LDLx but not native LDL activate human T cells through DCs. HSP60 and 90 contribute to such T-cell activation. Annexin A5 promotes induction of regulatory T cells and is potentially interesting as a therapeutic agent.

Increased plasma oxidized phospholipid:apolipoprotein B-100 ratio with concomitant depletion of oxidized phospholipids from atherosclerotic lesions after dietary lipid-lowering: a potential biomarker of early atherosclerosis regression.

BACKGROUND: Oxidized phospholipids (OxPL) are pro-inflammatory. We evaluated whether changes in plasma levels of OxPL associated with apolipoprotein B-100 (apoB-100) reflect changes in OxPL content in atherosclerotic plaques during dietary-induced atherosclerosis progression and regression. METHODS AND RESULTS: OxPL content was measured in plasma and immunohistochemically in aortic plaques with antibody E06 in cynomolgus monkeys and New Zealand White rabbits at baseline, after a high-fat/high-cholesterol diet and after reversion to normal chow. The OxPL/apoB ratio, representing the content of OxPL on individual apoB-100 particles, and Total apoB-OxPL (OxPL/apoB multiplied by plasma apoB levels), reflecting the OxPL content on all apoB-100 particles, were measured. Total apoB-OxPL plasma levels increased 3-fold (P<0.0001) during hypercholesterolemia and decreased approximately 75% (P<0.0001) during reversion to normocholesterolemia. In contrast, OxPL/apoB levels decreased significantly (P<0.0001) during hypercholesterolemia and increased significantly (P=0.0002) during reversion to normocholesterolemia. Immunostaining revealed that during atherosclerosis progression OxPL co-localized with apoB-100, whereas during regression OxPL virtually disappeared. CONCLUSIONS: In the setting of overall reduction of plasma OxPL levels after dietary lipid-lowering, increases in the OxPL/apoB ratio reflect reduced content of OxPL in atherosclerotic plaques. These data suggest that changes in the OxPL/apoB ratio may reflect early atherosclerosis regression.

Temporal increases in plasma markers of oxidized low-density lipoprotein strongly reflect the presence of acute coronary syndromes.

OBJECTIVES: This study was conducted to test the hypothesis that plasma markers of oxidized low-density lipoprotein (OxLDL) reflect acute coronary syndromes (ACS). BACKGROUND: Oxidized LDL contributes to the pathogenesis of atherosclerosis, but its role in ACS is not established. METHODS: Serial plasma samples were prospectively obtained from patients with an acute myocardial infarction (MI) (n = 8), unstable angina (UA) (n = 15), stable coronary artery disease (CAD) (n = 17), angiographically normal coronary arteries (n = 8), and from healthy subjects (n = 18), at entry into the study, hospital discharge (MI group only), and at 30, 120, and 210 days. Chemiluminescent enzyme-linked immunosorbent assay was used to quantitate plasma levels of: 1) immunoglobulin (Ig)M and IgG OxLDL autoantibody titers (presented as a mean OxLDL autoantibody titer by averaging the results of four distinct epitopes); 2) LDL-autoantibody immune complexes (LDL-IC); and 3) minimally OxLDL measured by antibody E06 (OxLDL-E06), as determined by the content of oxidized phospholipids (OxPL) per apolipoprotein B-100. RESULTS: Baseline OxLDL IgG autoantibody levels were higher in the MI group (p < 0.0001). At 30-day follow-up, the mean IgM OxLDL titers increased by 48% (p < 0.001) and 20% (p < 0.001), and IgM LDL-IC increased by 60% (p < 0.01) and 26% (p < 0.01) in the MI and UA groups, respectively. The OxLDL-E06 levels increased by 54% (p < 0.01) in the MI group at hospital discharge and by 36% at 30 days. No significant changes in any OxLDL markers were noted in the other groups. The OxLDL-E06 levels strongly paralleled the acute rise in lipoprotein(a), or Lp(a), in the MI group, suggesting that toxic OxPL are preferentially bound to Lp(a). Oxidized LDL-E06 also correlated extremely well with Lp(a) in the entire cohort of patients (r = 0.91, p < 0.0001). CONCLUSIONS: Circulating OxLDL-specific markers strongly reflect the presence of ACS, implying immune awareness to newly exposed oxidation-specific epitopes and possible release of OxLDL in the circulation. The OxLDL-E06 measurements provide novel insights into plaque rupture and the potential atherogenicity of Lp(a).

A novel function of lipoprotein [a] as a preferential carrier of oxidized phospholipids in human plasma.

Oxidized phospholipids (OxPLs) on apolipoprotein B-100 (apoB-100) particles are strongly associated with lipoprotein [a] (Lp[a]). In this study, we evaluated whether Lp[a] is preferentially the carrier of OxPL in human plasma. The content of OxPL on apoB-100 particles was measured with monoclonal antibody E06, which recognizes the phosphocholine (PC) headgroup of oxidized but not native phospholipids. To assess whether OxPLs were preferentially bound by Lp[a] as opposed to other lipoproteins, immunoprecipitation and ultracentrifugation experiments, in vitro transfer studies, and chemiluminescent ELISAs were performed. Immunoprecipitation of Lp[a] from human plasma with an apolipoprotein [a] (apo[a])-specific antibody demonstrated that more than 85% of E06 reactivity (i.e., OxPL) coimmunoprecipitated with Lp[a]. Ultracentrifugation experiments showed that nearly all OxPLs were found in fractions containing apo[a], as opposed to other apolipoproteins. In vitro transfer studies showed that oxidized LDL preferentially donates OxPLs to Lp[a], as opposed to LDL, in a time- and temperature-dependent manner, even in aqueous buffer. Approximately 50% of E06 immunoreactivity could be extracted from isolated Lp[a] following exposure of plasma to various lipid solvents. These data demonstrate that Lp[a] is the preferential carrier of PC-containing OxPL in human plasma. This unique property of Lp[a] suggests novel insights into its physiological function and mechanisms of atherogenicity.

Oxidized phospholipids predict the presence and progression of carotid and femoral atherosclerosis and symptomatic cardiovascular disease: five-year prospective results from the Bruneck study.

OBJECTIVES: The purpose of this work was to determine the predictive value of oxidized phospholipids (OxPLs) present on apolipoprotein B-100 particles (apoB) in carotid and femoral atherosclerosis. BACKGROUND: The OxPLs are pro-inflammatory and pro-atherogenic and may be detected using the antibody E06 (OxPL/apoB). METHODS: The Bruneck study is a prospective population-based survey of 40- to 79-year-old men and women initiated in 1990. Plasma levels of OxPL/apoB and lipoprotein (a) [Lp(a)] were measured in 765 of 826 (92.6%) and 671 of 684 (98.1%) subjects alive in 1995 and 2000, respectively, and correlated with ultrasound measures of carotid and femoral atherosclerosis. RESULTS: The distribution of the OxPL/apoB levels was skewed to lower levels and nearly identical to Lp(a) levels. The OxPL/apoB and Lp(a) levels were highly correlated (r = 0.87, p < 0.001), and displayed long-term stability and lacked correlations with most cardiovascular risk factors and lifestyle variables. The number of apolipoprotein (a) kringle IV-2 repeats was inversely related to Lp(a) mass (r = -0.48, p < 0.001) and OxPL/apoB levels (r = -0.46, p < 0.001). In multivariable analysis, OxPL/apoB levels were strongly and significantly associated with the presence, extent, and development (1995 to 2000) of carotid and femoral atherosclerosis and predicted the presence of symptomatic cardiovascular disease. Both OxPL/apoB and Lp(a) levels showed similar associations with atherosclerosis severity and progression, suggesting a common biological influence on atherogenesis. CONCLUSIONS: This study suggests that pro-inflammatory oxidized phospholipids, present primarily on Lp(a), are significant predictors of the presence and extent of carotid and femoral atherosclerosis, development of new lesions, and increased risk of cardiovascular events. The OxPL biomarkers may provide valuable insights into diagnosing and monitoring cardiovascular disease.

Mechanical aortic injury in apoE-deficient mice as a model for development of atherosclerosis: demonstration of leukocyte rolling early after injury.

A mouse model of aortic endothelium regeneration following mechanical injury was studied in wild-type and apoE-deficient (apoE0) animals. The injury induced a topologically nonuniform and complex reparative response. Compared to wild-type animals, apoE0 mice had unaltered ability to regenerate endothelium. Despite the pro-coagulative state of the apoE0 mice, no arterial thromboses were detected. Only deeper arterial injury with damage to the internal elastic membrane was associated with the development of atherosclerotic lesions in apoE0 mice. During the limited observation period of 7 days, superficial arterial injury in apoE0 mice was inconsequential. In addition, for the first time in vivo, rolling of polymorphonuclear leukocytes over the damaged endothelium was documented.

Lysine-phosphatidylcholine adducts in kringle V impart unique immunological and potential pro-inflammatory properties to human apolipoprotein(a).

Lipoprotein(a), Lp(a), an athero-thrombotic risk factor, reacts with EO6, a natural monoclonal autoantibody that recognizes the phophorylcholine (PC) group of oxidized phosphatidylcholine (oxPtdPC) either as a lipid or linked by a Schiff base to lysine residues of peptides/proteins. Here we show that EO6 reacts with free apolipoprotein(a) apo(a), its C-terminal domain, F2 (but not the N-terminal F1), kringle V-containing fragments obtained by the enzymatic digestion of apo(a) and also kringle V-containing apo(a) recombinants. The evidence that kringle V is critical for EO6 reactivity is supported by the finding that apo(a) of rhesus monkeys lacking kringle V did not react with EO6. Based on the previously established EO6 specificity requirements, we hypothesized that all or some of the six lysines in human kringle V are involved in Schiff base linkage with oxPtdPC. To test this hypothesis, we made use of a recombinant lysine-containing apo(a) fragment, rIII, containing kringle V but not the protease domain. EO6 reacted with rIII before and after reduction to stabilize the Schiff base and also after extensive ethanol/ether extraction that yielded no lipids. On the other hand, delipidation of the saponified product yielded an average of two mol of phospholipids/mol of protein consistent with direct analysis of inorganic phosphorous on the non-saponified rIII. Moreover, only two of the six theoretical free lysine amino groups per mol of rIII were unavailable to chemical modification by 2,4,6-trinitrobenzene sulfonic acid. Finally, rIII, like human apo(a), stimulated the production of interleukin 8 in THP-1 macrophages in culture. Together, our studies provide evidence that in human apo(a), kringle V is the site that reacts with EO6 via lysine-oxPtdPC adducts that may also be involved in the previously reported pro-inflammatory effect of apo(a) in cultured human macrophages.