Laura Nasarre

Low-density lipoprotein receptor-related protein 1 mediates hypoxia-induced very low density lipoprotein-cholesteryl ester uptake and accumulation in cardiomyocytes

AIMS The myocardium accumulates intracellular lipids under ischaemic conditions, and myocardial fat deposition is closely associated with cardiac dysfunction. Our aims were to analyse the effect of hypoxia on low-density lipoprotein receptor-related protein 1 (LRP1) expression in neonatal rat ventricular myocytes (NRVM) and cardiac-derived HL-1 cells and the molecular mechanisms involved in this effect, to determine the role of LRP1 in the very low density lipoprotein (VLDL) uptake by hypoxic cardiomyocytes, and to study the effect of hypoxia on lipoprotein receptor expression and myocardial lipid profile in an in vivo porcine experimental model of acute myocardial infarction. METHODS AND RESULTS Thin-layer chromatography after lipid extraction showed that VLDL exposure leads to cholesteryl ester (CE) and triglyceride (TG) accumulation in a dose-dependent manner and that hypoxic conditions further increased VLDL-derived intracellular lipid accumulation in HL-1 cells. Knockdown of LRP1 through lentiviral-mediated interfering RNA specifically prevented hypoxia-induced VLDL-CE internalization in HL-1 cells and NRVM. Lipopolysaccharide (LPS)-induced LRP1 overexpression specifically increased VLDL-CE accumulation in NRVM. In addition, using double-radiolabelled [(3)H]CE-[(14)C]TG-VLDL, we found that LRP1 deficiency specifically prevented hypoxia-induced VLDL-[(3)H]CE uptake. Finally, in an in vivo porcine model of infarcted myocardium, ischaemic areas exhibited LRP1 protein up-regulation and intramyocardial CE overaccumulation. CONCLUSION Our results demonstrate that hypoxia increases LRP1 expression through HIF-1α and that LRP1 overexpression mediates hypoxia-induced VLDL-CE uptake and accumulation in cardiomyocytes.

Intratumor cholesteryl ester accumulation is associated with human breast cancer proliferation and aggressive potential: a molecular and clinicopathological study

BackgroundThe metabolic effect of intratumor cholesteryl ester (CE) in breast cancer remains poorly understood. The objective was to analyze the relationship between intratumor CE content and clinicopathological variables in human breast carcinomas.MethodsWe classified 30 breast carcinoma samples into three subgroups: 10 luminal-A tumors (ER+/PR+/Her2-), 10 Her-2 tumors (ER-/PR-/Her2+), and 10 triple negative (TN) tumors (ER-/PR-/Her2-). We analyzed intratumor neutral CE, free cholesterol (FC) and triglyceride (TG) content by thin layer chromatography after lipid extraction. RNA and protein levels of lipid metabolism and invasion mediators were analyzed by real time PCR and Western blot analysis.ResultsGroup-wise comparisons, linear regression and logistic regression models showed a close association between CE-rich tumors and higher histologic grade, Ki-67 and tumor necrosis. CE-rich tumors displayed higher mRNA and protein levels of low-density lipoprotein receptor (LDLR) and scavenger receptor class B member 1 (SCARB1). An increased expression of acetyl-Coenzyme A acetyltransferase 1 (ACAT1) in CE-rich tumors was also reported.ConclusionsIntratumor CE accumulation is intimately linked to proliferation and aggressive potential of breast cancer tumors. Our data support the link between intratumor CE content and poor clinical outcome and open the door to new antitumor interventions.

Lipopolysaccharide downregulates CD91/low-density lipoprotein receptor-related protein 1 expression through SREBP-1 overexpression in human macrophages

Sterol regulatory element-binding proteins (SREBPs) negatively modulate the expression of the CD91/low-density lipoprotein receptor-related protein (LRP1), a carrier and signaling receptor that mediates the endocytosis of more than 40 structurally and functionally distinct ligands. The aim of this work was to analyze whether lipopolysaccharide (LPS) can regulate LRP1 expression through SREBPs in human monocyte-derived macrophages (HMDM). LPS led to LRP1 mRNA and protein inhibition in a dose- and time-dependent manner. Concomitantly, a strong upregulation of SREBP-1 mRNA and SREBP-1 nuclear protein levels was observed in LPS-treated HMDM. The specific silencing of SREBP-1 efficiently prevented LRP1 reduction caused by LPS. SREBP-1 mRNA and nuclear protein levels remained high in HMDM treated with LPS unexposed or exposed to LDL. Native (nLDL) or aggregated LDL (agLDL) per se downregulated SREBP-2 expression levels and increased LRP1 expression. However, lipoproteins did not significantly alter the effect of LPS on SREBP-1 and LRP1 expression. Collectively, these data support that lipoproteins and LPS exert their modulatory effect on LRP1 expression through different SREBP isoforms, SREBP-2 and SREBP-1, respectively. These results highlight a crucial role of SREBP-1 as a mediator of the downregulatory effects of LPS on LRP1 expression in human macrophages, independently of the absence or presence of modified lipoproteins.

Hypoxia induces metalloproteinase-9 activation and human vascular smooth muscle cell migration through low-density lipoprotein receptor-related protein 1-mediated Pyk2 phosphorylation.

Objective—Hypoxia disturbs vascular function by promoting extracellular matrix remodeling. Extracellular matrix integrity and composition are modulated by metalloproteinases (MMPs). Our aim was to investigate the role of low-density lipoprotein receptor–related protein 1 (LRP1) in regulating MMP-9/MMP-2 activation and vascular smooth muscle cells (VSMCs) migration in response to hypoxia, and to elucidate the LRP1-signaling pathways involved in this process. Approach and Results—Western blot analysis showed that hypoxia induced a sustained phosphorylation of proline-rich tyrosine kinase 2 concomitantly with LRP1 overexpression in human VSMCs (hVSMCs). Deletion of LRP1 using small-interfering RNA technology or treatment of hVSMCs with the Src family kinase inhibitor PP2 impaired hypoxia-induced phosphorylation of proline-rich tyrosine kinase 2 levels. Coimmunoprecipitation experiments showed that the higher amounts of phosphorylation of proline-rich tyrosine kinase 2/LRP1&bgr; immunoprecipitates in hypoxic hVSMCs were abolished in PP2-treated hVSMCs. Both LRP1 silencing and PP2 treatment were highly effective in the prevention of hypoxia-induced MMP-9 activation and hVSMC migration. Cellular subfractionation experiments revealed that PP2 effects may be caused by impairment of hypoxia-induced nuclear factor-&kgr;&bgr; translocation to the nucleus. ELISA measurements showed that LRP1 silencing but not PP2 treatment increased interleukin-1&bgr;, interleukin-6, and monocyte chemoattractant protein-1 secretion by hypoxic hVSMCs. Conclusions—Our findings determine a crucial role of LRP1-mediated Pyk2 phosphorylation on hypoxia-induced MMP-9 activation and hVSMC migration and therefore in hypoxia-induced vascular remodeling. Both LRP1 silencing and PP2 treatments also influence hypoxia-induced proinflammatory effects in hVSMCs. Therefore, further studies are required to establish therapeutical strategies that efficiently modulate vascular remodeling and inflammation associated with hypoxia-vascular diseases.

Lipid Loading of Human Vascular Smooth Muscle Cells Induces Changes in Tropoelastin Protein Levels and Physical Structure

Aggregated low-density lipoprotein (agLDL), one of the main LDL modifications in the arterial intima, contributes to massive intracellular cholesteryl ester (CE) accumulation in human vascular smooth muscle cells (VSMC), which are major producers of elastin in the vascular wall. Our aim was to analyze the levels, physical structure, and molecular mobility of tropoelastin produced by agLDL-loaded human VSMC (agLDL-VSMC) versus that produced by control VSMC. Western blot analysis demonstrated that agLDL reduced VSMC-tropoelastin protein levels by increasing its degradation rate. Moreover, our results demonstrated increased levels of precursor and mature forms of cathepsin S in agLDL-VSMC. Fourier transform infrared analysis revealed modifications in the secondary structures of tropoelastin produced by lipid-loaded VSMCs. Thermal and dielectric analyses showed that agLDL-VSMC tropoelastin has decreased glass transition temperatures and distinct chain dynamics that, in addition to a loss of thermal stability, lead to strong changes in its mechanical properties. In conclusion, agLDL lipid loading of human vascular cells leads to an increase in cathepsin S production concomitantly with a decrease in cellular tropoelastin protein levels and dramatic changes in secreted tropoelastin physical structure. Therefore, VSMC-lipid loading likely determines alterations in the mechanical properties of the vascular wall and plays a crucial role in elastin loss during atherosclerosis.

K Domain CR9 of Low Density Lipoprotein (LDL) Receptor-related Protein 1 (LRP1) Is Critical for Aggregated LDL-induced Foam Cell Formation from Human Vascular Smooth Muscle Cells

Background: LRP1 plays a major role in foam cell formation from human vascular smooth muscle cells (hVSMCs). Results: Antibodies generated against the C-terminal half of cluster II CR9 domain (Gly1127–Cys1140) efficiently prevented hVSMC foam cell formation. Conclusion: CR9 is key for AgLDL binding and internalization. Significance: Our results open new avenues for treating vascular lipid deposition in atherosclerosis. Low density lipoprotein receptor-related protein (LRP1) mediates the internalization of aggregated LDL (AgLDL), which in turn increases the expression of LRP1 in human vascular smooth muscle cells (hVSMCs). This positive feedback mechanism is thus highly efficient to promote the formation of hVSMC foam cells, a crucial vascular component determining the susceptibility of atherosclerotic plaque to rupture. Here we have determined the LRP1 domains involved in AgLDL recognition with the aim of specifically blocking AgLDL internalization in hVSMCs. The capacity of fluorescently labeled AgLDL to bind to functional LRP1 clusters was tested in a receptor-ligand fluorometric assay made by immobilizing soluble LRP1 “minireceptors” (sLRP1-II, sLRP1-III, and sLRP1-IV) recombinantly expressed in CHO cells. This assay showed that AgLDL binds to cluster II. We predicted three well exposed and potentially immunogenic peptides in the CR7–CR9 domains of this cluster (termed P1 (Cys1051–Glu1066), P2 (Asp1090–Cys1104), and P3 (Gly1127–Cys1140)). AgLDL, but not native LDL, bound specifically and tightly to P3-coated wells. Rabbit polyclonal antibodies raised against P3 prevented AgLDL uptake by hVSMCs and were almost twice as effective as anti-P1 and anti-P2 Abs in reducing intracellular cholesteryl ester accumulation. Moreover, anti-P3 Abs efficiently prevented AgLDL-induced LRP1 up-regulation and counteracted the down-regulatory effect of AgLDL on hVSMC migration. In conclusion, domain CR9 appears to be critical for LRP1-mediated AgLDL binding and internalization in hVSMCs. Our results open new avenues for an innovative anti-VSMC foam cell-based strategy for the treatment of vascular lipid deposition in atherosclerosis.

Inverse relationship between raft LRP1 localization and non-raft ERK1,2/MMP9 activation in idiopathic dilated cardiomyopathy: Potential impact in ventricular remodeling

BACKGROUND Idiopathic dilated cardiomyopathy (IDCM) is characterized by adverse ventricular remodeling attributed to altered activity of extracellular matrix metalloproteinase (MMP). MMP overactivation is linked to changes in extracellular signal-regulated kinases (ERK), reportedly modulated by the low-density lipoprotein receptor-related protein 1 (LRP1) receptor. The aim of this work was to compare the levels, membrane distribution and interactions of LRP1, ERK1,2 and MMP2/9 in control and IDCM myocardium. METHODS Left ventricle samples from IDCM patients and control subjects were collected to analyze gene and protein expression by Real-time PCR and Western blot, respectively. Fractions enriched in cholesterol, Flotillin-1 and Caveolin-3 (rafts) were isolated from the remaining membrane (non-rafts) by sucrose gradient ultracentrifugation. We assessed the formation of LRP1-ERK1,2 complexes and MMP activity by immunoprecipitation and zymography, respectively. RESULTS In control myocardium, LRP1 was exclusively found in non-rafts while activation of ERK1,2 was preferentially detected in rafts. LRP1/p-ERK1,2 complexes were almost undetectable in rafts and non-rafts. In contrast, in IDCM myocardium, LRP1 moved to rafts and ERK1,2 activation was found in raft and non-raft fractions. Moreover, LRP1/p-ERK1,2 complexes were also found in both membrane fractions, although the amount was higher in non-rafts where MMP9 overactivation was exclusively detected. CONCLUSIONS The presented findings demonstrate a differential membrane compartmentalisation of ERK signaling in IDCM myocardium. The movement of LRP1 to rafts and the concomitant increase in non-raft-related ERK1,2/MMP9 activation may have crucial clinical implications in the progression of disease.

Hypoxia-driven sarcoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA2) downregulation depends on low-density lipoprotein receptor-related protein 1 (LRP1)-signalling in cardiomyocytes.

The maintenance of sarcoplasmic reticulum Ca(2+) ATPase (SERCA2) activity is crucial for cardiac function and SERCA2 is dramatically reduced in the heart exposed to hypoxic/ischemic conditions. Previous work from our group showed that hypoxia upregulates the phosphorylated form of the Ca(2+)-dependent nonreceptor protein tyrosine kinase (PTK) proline-rich tyrosine kinase 2 (pPyk2) protein levels in a low-density lipoprotein receptor-related protein (LRP1)-dependent manner. Pyk2 in turn may modulate SERCA2 in cardiomyocytes although this remains controversial. We therefore aimed to investigate the role of LRP1 on hypoxia-induced SERCA2 depletion in cardiomyocytes and to establish LRP1 signalling mechanisms involved. Western blot analysis showed that hypoxia reduced SERCA2 concomitantly with a sustained increase in LRP1 and pPyk2 protein levels in HL-1 cardiomyocytes. By impairing hypoxia-induced Pyk2 phosphorylation and HIF-1α accumulation, LRP1 deficiency prevented SERCA2 depletion and reduction of the sarcoplasmic reticulum calcium content in cardiomyocytes. Moreover, the inhibition of Pyk2 phosphorylation (with the Src-family inhibitor PP2) or the specific silencing of Pyk2 (with siRNA-anti Pyk2) preserved low HIF-1α and high SERCA2 levels in HL-1 cardiomyocytes exposed to hypoxia. We determined that the LRP1/Pyk2 axis represses SERCA2 mRNA expression via HIF-1α since HIF-1α overexpression abolished the protective effect of LRP1 deficiency on SERCA2 depletion. Our findings show a crucial role of LRP1/Pyk2/HIF-1α in hypoxia-induced cardiomyocyte SERCA2 downregulation, a pathophysiological process closely associated with heart failure.

Cardiomyocyte intracellular cholesteryl ester accumulation promotes tropoelastin physical alteration and degradation Role of LRP1 and cathepsin S

Dyslipemia has a direct impact on cardiac remodeling by altering extracellular matrix (ECM) components. One of the main ECM components is elastin, a proteic three-dimensional network that can be efficiently degraded by cysteine proteases or cathepsins. Dyslipemic status in insulin resistance and combined hyperlipoproteinemia diseases include raised levels of very low density lipoproteins (VLDL), triglyceride (TG)-cholesteryl ester (CE)-rich lipoproteins. Enhanced VLDL concentration promotes cardiomyocyte intracellular cholesteryl ester (CE) accumulation in a LRP1-dependent manner. The aim of this work was to analyze the effect of cardiomyocyte intracellular CE accumulation on tropoelastin (TE) characteristics and to investigate the role of LRP1 and cathepsin S (CatS) on these effects. Molecular studies showed that LRP1 deficiency impaired CE selective uptake and accumulation from TG-CE-rich lipoproteins (VLDL+IDL) and CE-rich lipoproteins (aggregated LDL, agLDL). Biochemical and confocal microscopic studies showed that LRP1-mediated intracellular CE accumulation increased CatS mature protein levels and induced an altered intracellular TE globule structure. Biophysical studies evidenced that LRP1-mediated intracellular CE accumulation caused a significant drop of Tg2 glass transition temperature of cardiomyocyte secreted TE. Moreover, CatS deficiency prevented the alterations in TE intracellular globule structure and on TE glass transition temperature. These results demonstrate that LRP1-mediated cardiomyocyte intracellular CE accumulation alters the structural and physical characteristics of secreted TE through an increase in CatS mature protein levels. Therefore, the modulation of LRP1-mediated intracellular CE accumulation in cardiomyocytes could impact pathological ventricular remodeling associated with insulin-resistance and combined hyperlipoproteinemia, pathologies characterized by enhanced concentrations of TG-CE-rich lipoproteins.

Translating the microRNA signature of microvesicles derived from human coronary artery smooth muscle cells in patients with familial hypercholesterolemia and coronary artery disease

AIMS To analyze the impact of atherogenic lipoproteins on the miRNA signature of microvesicles derived from human coronary artery smooth muscle cells (CASMC) and to translate these results to familial hypercholesterolemia (FH) and coronary artery disease (CAD) patients. METHODS Conditioned media was collected after exposure of CASMC to atherogenic lipoproteins. Plasma samples were collected from two independent populations of diagnosed FH patients and matched normocholesterolemic controls (Study population 1, N=50; Study population 2, N=24) and a population of patients with suspected CAD (Study population 3, N=50). Extracellular vesicles were isolated and characterized using standard techniques. A panel of 30 miRNAs related to vascular smooth muscle cell (VSMC) (patho-)physiology was analyzed using RT-qPCR. RESULTS Atherogenic lipoproteins significantly reduced levels of miR-15b-5p, -24-3p, -29b-3p, -130a-3p, -143-3p, -146a-3p, -222-3p, -663a levels (P<0.050) in microvesicles (0.1μm-1μm in diameter) released by CASMC. Two of these miRNAs, miR-24-3p and miR-130a-3p, were reduced in circulating microvesicles from FH patients compared with normocholesterolemic controls in a pilot study (Study population 1) and in different validation studies (Study populations 1 and 2) (P<0.050). Supporting these results, plasma levels of miR-24-3p and miR-130a-3p were also downregulated in FH patients compared to controls (P<0.050). In addition, plasma levels of miR-130a-3p were inversely associated with coronary atherosclerosis in a cohort of suspected CAD patients (Study population 3) (P<0.050). CONCLUSIONS Exposure to atherogenic lipoproteins modifies the miRNA profile of CASMC-derived microvesicles and these alterations are reflected in patients with FH. Circulating miR-130a-3p emerges as a potential biomarker for coronary atherosclerosis.