What's next for lipoprotein(a)? A national lipid association report from an expert panel discussion.

This is an exciting time in the lipoprotein(a) (Lp(a)) field. Attention to this important lipoprotein and potent cardiovascular risk marker is transitioning from the purview of the specialist to that of the general practitioner. Its clinical adoption as an important test is increasing in momentum. There is evidence that Lp(a) contributes to the pathology of atherothrombotic disease, aortic valve stenosis, and childhood ischemic strokes. Three large, Phase 3, randomized, cardiovascular outcomes trials in which Lp(a) is specifically and substantially lowered by mRNA-directed therapies in secondary prevention settings are in progress and will start to report results as early as 2025. Regardless of outcomes, there remain many unanswered questions about Lp(a), ranging from fundamental unknowns about Lp(a) biology, to the complexity of its measurement, optimal screening strategies, and clinical management in individuals with high Lp(a) levels both with and without overt cardiovascular disease. Accordingly, The National Lipid Association (NLA) convened an Expert Discussion involving clinicians and fundamental researchers to identify knowledge gaps in our understanding of Lp(a) biology and pathogenicity and to discuss approaches in the management of elevated Lp(a) in different clinical settings. (183 words).

Fibrinogen and plasma clot properties are associated with apolipoprotein B and apolipoprotein B-containing lipoproteins in Africans.

BACKGROUND: Case-control, intervention and laboratory studies have demonstrated a link between apolipoprotein B-containing lipoproteins and clot structure and thrombosis. There is, however, limited evidence on population level. OBJECTIVES: We determined the cross-sectional relationship between lipoprotein(a) (Lp(a)), low-density lipoprotein cholesterol (LDL-C), and apolipoprotein B (ApoB) with fibrinogen and plasma clot properties in 1 462 Black South Africans, a population with higher fibrinogen and Lp(a) levels compared with individuals of European descent. METHODS: Data were obtained from participants in the South African arm of the Prospective Urban and Rural Epidemiology study. Clot properties analysed included lag time, slope, maximum absorbance, and clot lysis time (turbidity). Lp(a) was measured in nM using particle-enhanced immunoturbidimetry. General linear models (GLM) were used to determine the associations between ApoB and ApoB-containing lipoproteins with fibrinogen and plasma clot properties. Stepwise regression was used to determine contributors to clot properties and Lp(a) variance. RESULTS: GLM and regression results combined, indicated fibrinogen concentration and rate of clot formation (slope) had the strongest association with Lp(a); clot density associated positively with both Lp(a) and LDL-C; time to clot formation associated negatively with ApoB; and CLT demonstrated strong positive associations with both ApoB and LDL-C, while its association with Lp(a) was fibrinogen concentration dependent. CONCLUSION: These findings suggest that ApoB and the lipoproteins carrying it contribute to prothrombotic clot properties in Africans on epidemiological level and highlight potential novel prothrombotic roles for these (apo)lipoproteins to be considered for the development of targeted therapeutic approaches to address thrombotic conditions related to clot properties.

Lipoprotein(a) and cardiovascular disease.

Elevated plasma levels of lipoprotein(a) (Lp(a)) are a prevalent, independent, and causal risk factor for atherosclerotic cardiovascular disease and calcific aortic valve disease. Lp(a) consists of a lipoprotein particle resembling low density lipoprotein and the covalently-attached glycoprotein apolipoprotein(a) (apo(a)). Novel therapeutics that specifically and potently lower Lp(a) levels are currently in advanced stages of clinical development, including in large, phase 3 cardiovascular outcomes trials. However, fundamental unanswered questions remain concerning some key aspects of Lp(a) biosynthesis and catabolism as well as the true pathogenic mechanisms of the particle. In this review, we describe the salient biochemical features of Lp(a) and apo(a) and how they underlie the disease-causing potential of Lp(a), the factors that determine plasma Lp(a) concentrations, and the mechanism of action of Lp(a)-lowering drugs.

Identification of heparin interaction sites on thrombin-activatable fibrinolysis inhibitor that modulate plasmin-mediated activation, thermal stability, and antifibrinolytic potential.

Background: Thrombin-activatable fibrinolysis inhibitor (TAFI) is a plasma zymogen that provides a molecular link between coagulation and fibrinolysis. Studies have shown that the presence of glycosaminoglycans accelerates TAFI activation by plasmin and stabilizes activated TAFI (TAFIa). Objectives: We aimed to define the elements of TAFI structure that allow these effects. Methods: Based on crystallographic studies and homology to heparin-binding proteins, we performed mutagenesis of surface-exposed charged residues on TAFI that putatively constitute heparin-binding sites. We determined heparin binding, kinetics of activation by plasmin in the presence or absence of heparin, thermal stability, and antifibrinolytic potential of each variant. Results: Mutagenesis of Lys211 and Lys212 did not impair heparin binding but affected the ability of TAFI to be activated by plasmin. Mutagenesis of Lys306 and His308 did not impair heparin binding, but mutation of His308 had a severe negative effect on TAFI/TAFIa function. Mutation of Arg320 and Lys324 in combination markedly decreased heparin binding but had no effect on heparin-mediated acceleration of TAFI activation by plasmin while somewhat decreasing TAFIa stabilization by heparin. Mutagenesis of Lys327 and Arg330 decreased (but did not eliminate) heparin binding while decreasing the ability of heparin to accelerate plasmin-mediated TAFI activation, stabilize TAFIa, and increase the antifibrinolytic ability of TAFIa. A quadruple mutant of Arg320, Lys324, Lys327, and Arg330 completely lost heparin-binding ability and stabilization of the enzyme by heparin. Conclusion: Basic residues in the dynamic flap of TAFIa define a functionally relevant heparin-binding site, but additional heparin-binding sites may be present on TAFI.

Optimization of plasma-based BioID identifies plasminogen as a ligand of ADAMTS13.

ADAMTS13, a disintegrin and metalloprotease with a thrombospondin type 1 motif, member 13, regulates the length of Von Willebrand factor (VWF) multimers and their platelet-binding activity. ADAMTS13 is constitutively secreted as an active protease and is not inhibited by circulating protease inhibitors. Therefore, the mechanisms that regulate ADAMTS13 protease activity are unknown. We performed an unbiased proteomics screen to identify ligands of ADAMTS13 by optimizing the application of BioID to plasma. Plasma BioID identified 5 plasma proteins significantly labeled by the ADAMTS13-birA* fusion, including VWF and plasminogen. Glu-plasminogen, Lys-plasminogen, mini-plasminogen, and apo(a) bound ADAMTS13 with high affinity, whereas micro-plasminogen did not. None of the plasminogen variants or apo(a) bound to a C-terminal truncation variant of ADAMTS13 (MDTCS). The binding of plasminogen to ADAMTS13 was attenuated by tranexamic acid or ε-aminocaproic acid, and tranexamic acid protected ADAMTS13 from plasmin degradation. These data demonstrate that plasminogen is an important ligand of ADAMTS13 in plasma by binding to the C-terminus of ADAMTS13. Plasmin proteolytically degrades ADAMTS13 in a lysine-dependent manner, which may contribute to its regulation. Adapting BioID to identify protein-interaction networks in plasma provides a powerful new tool to study protease regulation in the cardiovascular system.

A focused update to the 2019 NLA scientific statement on use of lipoprotein(a) in clinical practice.

Since the 2019 National Lipid Association (NLA) Scientific Statement on Use of Lipoprotein(a) in Clinical Practice was issued, accumulating epidemiological data have clarified the relationship between lipoprotein(a) [Lp(a)] level and cardiovascular disease risk and risk reduction. Therefore, the NLA developed this focused update to guide clinicians in applying this emerging evidence in clinical practice. We now have sufficient evidence to support the recommendation to measure Lp(a) levels at least once in every adult for risk stratification. Individuals with Lp(a) levels <75 nmol/L (30 mg/dL) are considered low risk, individuals with Lp(a) levels ≥125 nmol/L (50 mg/dL) are considered high risk, and individuals with Lp(a) levels between 75 and 125 nmol/L (30-50 mg/dL) are at intermediate risk. Cascade screening of first-degree relatives of patients with elevated Lp(a) can identify additional individuals at risk who require intervention. Patients with elevated Lp(a) should receive early, more-intensive risk factor management, including lifestyle modification and lipid-lowering drug therapy in high-risk individuals, primarily to reduce low-density lipoprotein cholesterol (LDL-C) levels. The U.S. Food and Drug Administration approved an indication for lipoprotein apheresis (which reduces both Lp(a) and LDL-C) in high-risk patients with familial hypercholesterolemia and documented coronary or peripheral artery disease whose Lp(a) level remains ≥60 mg/dL [∼150 nmol/L)] and LDL-C ≥ 100 mg/dL on maximally tolerated lipid-lowering therapy. Although Lp(a) is an established independent causal risk factor for cardiovascular disease, and despite the high prevalence of Lp(a) elevation (∼1 of 5 individuals), measurement rates are low, warranting improved screening strategies for cardiovascular disease prevention.

High levels of lipoprotein(a) in transgenic mice exacerbate atherosclerosis and promote vulnerable plaque features in a sex-specific manner.

BACKGROUND AND AIMS: Despite increased clinical interest in lipoprotein(a) (Lp(a)), many questions remain about the molecular mechanisms by which it contributes to atherosclerotic cardiovascular disease. Existing murine transgenic (Tg) Lp(a) models are limited by low plasma levels of Lp(a) and have not consistently shown a pro-atherosclerotic effect of Lp(a). METHODS: We generated Tg mice expressing both human apolipoprotein(a) (apo(a)) and human apoB-100, with pathogenic levels of plasma Lp(a) (range 87-250 mg/dL). Female and male Lp(a) Tg mice (Tg(LPA+/0;APOB+/0)) and human apoB-100-only controls (Tg(APOB+/0)) (n = 10-13/group) were fed a high-fat, high-cholesterol diet for 12 weeks, with Ldlr knocked down using an antisense oligonucleotide. FPLC was used to characterize plasma lipoprotein profiles. Plaque area and necrotic core size were quantified and immunohistochemical assessment of lesions using a variety of cellular and protein markers was performed. RESULTS: Male and female Tg(LPA+/0;APOB+/0) and Tg(APOB+/0) mice exhibited proatherogenic lipoprotein profiles with increased cholesterol-rich VLDL and LDL-sized particles and no difference in plasma total cholesterol between genotypes. Complex lesions developed in the aortic sinus of all mice. Plaque area (+22%), necrotic core size (+25%), and calcified area (+65%) were all significantly increased in female Tg(LPA+/0;APOB+/0) mice compared to female Tg(APOB+/0) mice. Immunohistochemistry of lesions demonstrated that apo(a) deposited in a similar pattern as apoB-100 in Tg(LPA+/0;APOB+/0) mice. Furthermore, female Tg(LPA+/0;APOB+/0) mice exhibited less organized collagen deposition as well as 42% higher staining for oxidized phospholipids (OxPL) compared to female Tg(APOB+/0) mice. Tg(LPA+/0;APOB+/0) mice had dramatically higher levels of plasma OxPL-apo(a) and OxPL-apoB compared to Tg(APOB+/0) mice, and female Tg(LPA+/0;APOB+/0) mice had higher plasma levels of the proinflammatory cytokine MCP-1 (+3.1-fold) compared to female Tg(APOB+/0) mice. CONCLUSIONS: These data suggest a pro-inflammatory phenotype exhibited by female Tg mice expressing Lp(a) that appears to contribute to the development of more severe lesions with greater vulnerable features.

Lipoprotein(a) induces caspase-1 activation and IL-1 signaling in human macrophages.

Introduction: Lipoprotein(a) (Lp(a)) is an LDL-like particle with an additional apolipoprotein (apo)(a) covalently attached. Elevated levels of circulating Lp(a) are a risk factor for atherosclerosis. A proinflammatory role for Lp(a) has been proposed, but its molecular details are incompletely defined. Methods and results: To explore the effect of Lp(a) on human macrophages we performed RNA sequencing on THP-1 macrophages treated with Lp(a) or recombinant apo(a), which showed that especially Lp(a) induces potent inflammatory responses. Thus, we stimulated THP-1 macrophages with serum containing various Lp(a) levels to investigate their correlations with cytokines highlighted by the RNAseq, showing significant correlations with caspase-1 activity and secretion of IL-1ß and IL-18. We further isolated both Lp(a) and LDL particles from three donors and then compared their atheroinflammatory potentials together with recombinant apo(a) in primary and THP-1 derived macrophages. Compared with LDL, Lp(a) induced a robust and dose-dependent caspase-1 activation and release of IL-1ß and IL-18 in both macrophage types. Recombinant apo(a) strongly induced caspase-1 activation and IL-1ß release in THP-1 macrophages but yielded weak responses in primary macrophages. Structural analysis of these particles revealed that the Lp(a) proteome was enriched in proteins associated with complement activation and coagulation, and its lipidome was relatively deficient in polyunsaturated fatty acids and had a high n-6/n-3 ratio promoting inflammation. Discussion: Our data show that Lp(a) particles induce the expression of inflammatory genes, and Lp(a) and to a lesser extent apo(a) induce caspase-1 activation and IL-1 signaling. Major differences in the molecular profiles between Lp(a) and LDL contribute to Lp(a) being more atheroinflammatory.

Profibrinolytic effects of rivaroxaban are mediated by thrombin-activatable fibrinolysis inhibitor and are attenuated by a naturally occurring stabilizing mutation in enzyme.

Rivaroxaban is a direct factor Xa inhibitor, recently implemented as a favorable alternative to warfarin in anticoagulation therapy. Rivaroxaban effectively reduces thrombin generation, which plays a major role in the activation of thrombin activatable fibrinolysis inhibitor (TAFI) to TAFIa. Based on the antifibrinolytic role of TAFIa, we hypothesized that rivaroxaban would consequently induce more rapid clot lysis. In vitro clot lysis assays were used to explore this hypothesis and additionally determine the effects of varying TAFI levels and a stabilizing Thr325Ile polymorphism (rs1926447) in the TAFI protein on the effects of rivaroxaban. Rivaroxaban was shown to decrease thrombin generation, resulting in less TAFI activation, thus enhancing lysis. These effects were also shown to be less substantial in the presence of greater TAFI levels or the more stable Ile325 enzyme. These findings suggest a role for TAFI levels and the Thr325Ile polymorphism in the pharmacodynamics and pharmacogenomics of rivaroxaban.

Assays to quantify fibrinolysis: strengths and limitations. Communication from the International Society on Thrombosis and Haemostasis Scientific and Standardization Committee on fibrinolysis.

Fibrinolysis is a series of enzymatic reactions that degrade insoluble fibrin. Plasminogen activators convert the zymogen plasminogen to the active serine protease plasmin, which cleaves and solubilizes crosslinked fibrin clots into fibrin degradation products. The quantity and quality of fibrinolytic enzymes, their respective inhibitors, and clot structure determine overall fibrinolysis. The quantity of protein can be measured by antigen-based assays, and both quantity and quality can be assessed using functional assays. Furthermore, variations of commonly used assays have been reported, which are tailored to address the role(s) of specific fibrinolytic factors and cellular elements (eg, platelets, neutrophils, and red blood cells). Although the concentration and/or activity of a protein can be quantified, how these individual components contribute to the overall fibrinolysis outcome can be challenging to determine. This difficulty is due to temporal changes within and around the thrombi during the clot breakdown, particularly the fibrin matrix structure, and composition. Furthermore, terms such as "fibrinolytic activity/potential," "plasminogen activation," and "plasmin activity" are often used interchangeably despite having different definitions. The purpose of this review is to 1) summarize the assays measuring fibrinolysis activity and potential, 2) facilitate the interpretation of data generated by these assays, and 3) summarize the strengths and limitations of these assays.

LPA disruption with AAV-CRISPR potently lowers plasma apo(a) in transgenic mouse model: A proof-of-concept study.

Lipoprotein(a) (Lp(a)) represents a unique subclass of circulating lipoprotein particles and consists of an apolipoprotein(a) (apo(a)) molecule covalently bound to apolipoprotein B-100. The metabolism of Lp(a) particles is distinct from that of low-density lipoprotein (LDL) cholesterol, and currently approved lipid-lowering drugs do not provide substantial reductions in Lp(a), a causal risk factor for cardiovascular disease. Somatic genome editing has the potential to be a one-time therapy for individuals with extremely high Lp(a). We generated an LPA transgenic mouse model expressing apo(a) of physiologically relevant size. Adeno-associated virus (AAV) vector delivery of CRISPR-Cas9 was used to disrupt the LPA transgene in the liver. AAV-CRISPR nearly completely eliminated apo(a) from the circulation within a week. We performed genome-wide off-target assays to determine the specificity of CRISPR-Cas9 editing within the context of the human genome. Interestingly, we identified intrachromosomal rearrangements within the LPA cDNA in the transgenic mice as well as in the LPA gene in HEK293T cells, due to the repetitive sequences within LPA itself and neighboring pseudogenes. This proof-of-concept study establishes the feasibility of using CRISPR-Cas9 to disrupt LPA in vivo, and highlights the importance of examining the diverse consequences of CRISPR cutting within repetitive loci and in the genome globally.

Understanding the ins and outs of lipoprotein (a) metabolism.

PURPOSE OF REVIEW: This review summarizes our current understanding of the processes of apolipoprotein(a) secretion, assembly of the Lp(a) particle and removal of Lp(a) from the circulation. We also identify existing knowledge gaps that need to be addressed in future studies. RECENT FINDINGS: The Lp(a) particle is assembled in two steps: a noncovalent, lysine-dependent interaction of apo(a) with apoB-100 inside hepatocytes, followed by extracellular covalent association between these two molecules to form circulating apo(a).The production rate of Lp(a) is primarily responsible for the observed inverse correlation between apo(a) isoform size and Lp(a) levels, with a contribution of catabolism restricted to larger Lp(a) isoforms.Factors that affect apoB-100 secretion from hepatocytes also affect apo(a) secretion.The identification of key hepatic receptors involved in Lp(a) clearance in vivo remains unclear, with a role for the LDL receptor seemingly restricted to conditions wherein LDL concentrations are low, Lp(a) is highly elevated and LDL receptor number is maximally upregulated. SUMMARY: The key role for production rate of Lp(a) [including secretion and assembly of the Lp(a) particle] rather than its catabolic rate suggests that the most fruitful therapies for Lp(a) reduction should focus on approaches that inhibit production of the particle rather than its removal from circulation.

Beyond fibrinolysis: The confounding role of Lp(a) in thrombosis.

Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are a causal risk factor for the development of atherothrombotic disorders including coronary heart disease. However, the pathological mechanisms underlying this causal relationship remain incompletely defined. Lp(a) consists of a lipoprotein particle in which apolipoproteinB100 is covalently linked to the unique glycoprotein apolipoprotein(a) (apo(a)). The remarkable homology between apo(a) and the fibrinolytic proenzyme plasminogen strongly suggests an antifibrinolytic role: apo(a) contains a strong lysine binding site and can block the sites on fibrin and cellular receptors required for plasminogen activation, but itself lacks proteolytic activity. While numerous in vitro and animal model studies indicate that apo(a) can inhibit plasminogen activation and fibrinolysis, this activity may not be preserved in Lp(a). Moreover, elevated Lp(a) does not reduce the efficacy of thrombolytic therapy and is not a risk factor for some non-atherosclerotic thrombotic disorders such as venous thromboembolism. Accordingly, different prothrombotic mechanisms for Lp(a) must be contemplated. Evidence exists that Lp(a) binds to and inactivates tissue factor pathway inhibitor and stimulates expression of tissue factor by monocytes. Moreover, some studies have shown that Lp(a) promotes platelet activation and aggregation, at least in response to some agonists. Lp(a) alters the structure of the fibrin network to make it less permeable and more resistant to lysis. Finally, Lp(a) may promote the development of a vulnerable plaque phenotype that is more prone to rupture and hence the precipitation of atherothrombotic events. Further study, especially in animal models of thrombosis, is required to clarify the prothrombotic effects of Lp(a).

Oxidized phospholipid modification of lipoprotein(a): Epidemiology, biochemistry and pathophysiology.

Oxidized phospholipids (OxPL) are key mediators of the pro-atherosclerotic effects of oxidized lipoproteins. They are particularly important for the pathogenicity of lipoprotein(a) (Lp(a)), which is the preferred lipoprotein carrier of phosphocholine-containing OxPL in plasma. Indeed, elevated levels of OxPL-apoB, a parameter that almost entirely reflects the OxPL on Lp(a), are a potent risk factor for atherothrombotic diseases as well as calcific aortic valve stenosis. A substantial fraction of the OxPL on Lp(a) are covalently bound to the KIV10 domain of apo(a), and the strong lysine binding site (LBS) in this kringle is required for OxPL addition. Using apo(a) species lacking OxPL modification - by mutating the LBS - has allowed direct assessment of the role of apo(a) OxPL in Lp(a)-mediated pathogenesis. The OxPL on apo(a) account for numerous harmful effects of Lp(a) on monocytes, macrophages, endothelial cells, smooth muscle cells, and valve interstitial cells documented both in vitro and in vivo. In addition, the mechanisms underlying these effects have begun to be unraveled by identifying the cellular receptors that respond to OxPL, the intracellular signaling pathways turned on by OxPL, and the changes in gene and protein expression evoked by OxPL. The emerging picture is that the OxPL on Lp(a) are central to its pathobiology. The OxPL modification may explain why Lp(a) is such a potent risk factor for cardiovascular disease despite being present at concentrations an order of magnitude lower than LDL, and they account for the ability of elevated Lp(a) to cause both atherothrombotic disease and calcific aortic valve stenosis.

Sortilin enhances secretion of apolipoprotein(a) through effects on apolipoprotein B secretion and promotes uptake of lipoprotein(a).

Elevated plasma lipoprotein(a) (Lp(a)) is an independent, causal risk factor for atherosclerotic cardiovascular disease and calcific aortic valve stenosis. Lp(a) is formed in or on hepatocytes from successive noncovalent and covalent interactions between apo(a) and apoB, although the subcellular location of these interactions and the nature of the apoB-containing particle involved remain unclear. Sortilin, encoded by the SORT1 gene, modulates apoB secretion and LDL clearance. We used a HepG2 cell model to study the secretion kinetics of apo(a) and apoB. Overexpression of sortilin increased apo(a) secretion, while siRNA-mediated knockdown of sortilin expression correspondingly decreased apo(a) secretion. Sortilin binds LDL but not apo(a) or Lp(a), indicating that its effect on apo(a) secretion is likely indirect. Indeed, the effect was dependent on the ability of apo(a) to interact noncovalently with apoB. Overexpression of sortilin enhanced internalization of Lp(a), but not apo(a), by HepG2 cells, although neither sortilin knockdown in these cells or Sort1 deficiency in mice impacted Lp(a) uptake. We found several missense mutations in SORT1 in patients with extremely high Lp(a) levels; sortilin containing some of these mutations was more effective at promoting apo(a) secretion than WT sortilin, though no differences were found with respect to Lp(a) internalization. Our observations suggest that sortilin could play a role in determining plasma Lp(a) levels and corroborate in vivo human kinetic studies which imply that secretion of apo(a) and apoB are coupled, likely within the hepatocyte.

Apo(a) and ApoB Interact Noncovalently Within Hepatocytes: Implications for Regulation of Lp(a) Levels by Modulation of ApoB Secretion.

BACKGROUND: Elevated plasma Lp(a) (lipoprotein(a)) levels are associated with increased risk for atherosclerotic cardiovascular disease and aortic valve stenosis. However, the cell biology of Lp(a) biosynthesis remains poorly understood, with the locations of the noncovalent and covalent steps of Lp(a) assembly unclear and the nature of the apoB-containing particle destined for Lp(a) unknown. We, therefore, asked if apo(a) and apoB interact noncovalently within hepatocytes and if this impacts Lp(a) biosynthesis. METHODS: Using human hepatocellular carcinoma cells expressing 17K (17 kringle) apo(a), or a 17KΔLBS7,8 variant with a reduced ability to bind noncovalently to apoB, we performed coimmunoprecipitation, coimmunofluorescence, and proximity ligation assays to document intracellular apo(a):apoB interactions. We used a pulse-chase metabolic labeling approach to measure apo(a) and apoB secretion rates. RESULTS: Noncovalent complexes containing apo(a)/apoB are present in lysates from cells expressing 17K but not 17KΔLBS7,8, whereas covalent apo(a)/apoB complexes are absent from lysates. 17K and apoB colocalized intracellularly, overlapping with staining for markers of endoplasmic reticulum trans-Golgi, and early endosomes, and less so with lysosomes. The 17KΔLBS7,8 had lower colocalization with apoB. Proximity ligation assays directly documented intracellular 17K/apoB interactions, which were dramatically reduced for 17KΔLBS7,8. Treatment of cells with PCSK9 (proprotein convertase subtilisin/kexin type 9) enhanced, and lomitapide reduced, apo(a) secretion in a manner dependent on the noncovalent interaction between apo(a) and apoB. Apo(a) secretion was also reduced by siRNA-mediated knockdown of APOB. CONCLUSIONS: Our findings explain the coupling of apo(a) and Lp(a)-apoB production observed in human metabolic studies using stable isotopes as well as the ability of agents that inhibit apoB biosynthesis to lower Lp(a) levels.

Lipoprotein Proteomics and Aortic Valve Transcriptomics Identify Biological Pathways Linking Lipoprotein(a) Levels to Aortic Stenosis.

Lipoprotein(a) (Lp(a)) is one of the most important risk factors for the development of calcific aortic valve stenosis (CAVS). However, the mechanisms through which Lp(a) causes CAVS are currently unknown. Our objectives were to characterize the Lp(a) proteome and to identify proteins that may be differentially associated with Lp(a) in patients with versus without CAVS. Our second objective was to identify genes that may be differentially regulated by exposure to high versus low Lp(a) levels in explanted aortic valves from patients with CAVS. We isolated Lp(a) from the blood of 21 patients with CAVS and 22 volunteers and performed untargeted label-free analysis of the Lp(a) proteome. We also investigated the transcriptomic signature of calcified aortic valves from patients who underwent aortic valve replacement with high versus low Lp(a) levels (n = 118). Proteins involved in the protein activation cascade, platelet degranulation, leukocyte migration, and response to wounding may be associated with Lp(a) depending on CAVS status. The transcriptomic analysis identified genes involved in cardiac aging, chondrocyte development, and inflammation as potentially influenced by Lp(a). Our multi-omic analyses identified biological pathways through which Lp(a) may cause CAVS, as well as key molecular events that could be triggered by Lp(a) in CAVS development.

A Comparative Analysis of the Lipoprotein(a) and Low-Density Lipoprotein Proteomic Profiles Combining Mass Spectrometry and Mendelian Randomization.

BACKGROUND: Lipoprotein(a) (Lp[a]), which consists of a low-density lipoprotein (LDL) bound to apolipoprotein(a), is one of the strongest genetic risk factors for atherosclerotic cardiovascular diseases. Few studies have performed hypothesis-free direct comparisons of the Lp(a) and the LDL proteomes. Our objectives were to compare the Lp(a) and the LDL proteomic profiles and to evaluate the effect of lifelong exposure to elevated Lp(a) or LDL cholesterol levels on the plasma proteomic profile. METHODS: We performed a label-free analysis of the Lp(a) and LDL proteomic profiles of healthy volunteers in a discovery (n = 6) and a replication (n = 9) phase. We performed inverse variance weighted Mendelian randomization to document the effect of lifelong exposure to elevated Lp(a) or LDL cholesterol levels on the plasma proteomic profile of participants of the INTERVAL study. RESULTS: We identified 15 proteins that were more abundant on Lp(a) compared with LDL (serping1, pi16, itih1, itih2, itih3, pon1, podxl, cd44, cp, ptprg, vtn, pcsk9, igfals, vcam1, and ttr). We found no proteins that were more abundant on LDL compared with Lp(a). After correction for multiple testing, lifelong exposure to elevated LDL cholesterol levels was associated with the variation of 18 plasma proteins whereas Lp(a) did not appear to influence the plasma proteome. CONCLUSIONS: Results of this study highlight marked differences in the proteome of Lp(a) and LDL as well as in the effect of lifelong exposure to elevated LDL cholesterol or Lp(a) on the plasma proteomic profile.

CONTEXTE: La lipoprotéine(a) (Lp[a]), qui est constituée d'une lipoprotéine de basse densité (LDL) liée à une apolipoprotéine(a), est l'un des plus importants facteurs de risque génétiques de survenue d'une maladie cardiovasculaire athéroscléreuse. Peu d'études comparatives directes sans hypothèse ont porté sur le protéome de la Lp(a) et celui des LDL. Nos objectifs étaient de comparer les profils protéomiques de la Lp(a) et des LDL et d'évaluer l'effet d'une exposition à vie à un taux élevé de Lp(a) ou de cholestérol LDL sur le profil protéomique plasmatique. MÉTHODOLOGIE: Nous avons réalisé une analyse sans marquage des profils protéomiques de la Lp(a) et des LDL chez des volontaires en bonne santé dans le cadre d'une phase de découverte (n = 6) et d'une phase de réplication (n = 9). Pour rendre compte de l'effet d'une exposition à vie à un taux élevé de Lp(a) ou de cholestérol des LDL sur le profil protéomique plasmatique des participants de l'étude INTERVAL, nous avons utilisé une analyse de randomisation Mendélienne avec pondération par l'inverse de la variance. RÉSULTATS: Nous avons relevé 15 protéines associées en plus grande abondance à la Lp(a) qu'aux LDL (serping1, pi16, itih1, itih2, itih3, pon1, podxl, cd44, cp, ptprg, vtn, pcsk9, igfals, vcam1 et ttr). Nous n'avons noté aucune protéine associée en plus grande abondance aux LDL qu'à la Lp(a). Après correction pour tenir compte de la multiplicité des tests, l'exposition à vie à un taux élevé de cholestérol LDL a été associée à la variation de 18 protéines plasmatiques, tandis que le taux de Lp(a) ne semblait pas influencer le protéome plasmatique. CONCLUSIONS: Les résultats de notre étude font ressortir les différences marquées entre le protéome de la Lp(a) et celui des LDL, ainsi qu'entre l'effet sur le profil protéomique plasmatique de l'exposition à vie à un taux élevé de cholestérol LDL et celui de l'exposition à vie à un taux élevé de Lp(a).