Berta Raposo

Regulation of lysyl oxidase in vascular cells: lysyl oxidase as a new player in cardiovascular diseases.

Lysyl oxidase (LOX) plays a crucial role in the maintenance of extracellular matrix stability and could participate in vascular remodelling associated with cardiovascular diseases. Evidence from in vitro and in vivo studies shows that LOX downregulation is associated with the endothelial dysfunction characteristic of earlier stages of the atherosclerotic process. Conversely, upregulation of this enzyme in vascular cells could induce neointimal thickening in atherosclerosis and restenosis. In fact, LOX is chemotactic for vascular smooth muscle cells and monocytes, is modulated by proliferative stimulus in these cells, and could control other cellular processes such as gene expression and cell transformation. Furthermore, it is conceivable that LOX downregulation could underlie plaque instability and contribute to the destructive remodelling that takes place during aneurysm development. Overall, LOX could play a key role in vascular homeostasis and, hence, it emerges as a new player in cardiovascular diseases. This review addresses the experimental evidence related to the role of LOX in vascular disorders and the potential benefits of controlling its expression and function.

3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Inhibition Prevents Endothelial NO Synthase Downregulation by Atherogenic Levels of Native LDLs: Balance Between Transcriptional and Posttranscriptional Regulation

Abstract—Atherogenic levels of native low density lipoproteins (nLDLs) decrease the bioavailability of endothelium-derived NO and downregulate endothelial NO synthase (eNOS) expression in cultured human endothelial cells. Here, we show that simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, within the therapeutic range (0.01 to 1 &mgr;mol/L) prevented the downregulation of eNOS mRNA and protein promoted by nLDL (180 mg cholesterol/dL, 48 hours) in human umbilical vein endothelial cells. This effect of simvastatin was completely reversed by mevalonate, the product of the reaction, and to a lesser extent by farnesol and geranyl geraniol. Simvastatin significantly stabilized eNOS mRNA in cells treated with nLDL during 48 hours (eNOS mRNA half-life ≈11 hours in controls versus >24 hours in nLDL per 0.1 &mgr;mol/L simvastatin–treated cells). The downregulation of eNOS by nLDL was abrogated by cycloheximide, an inhibitor of protein synthesis, and by N-acetyl-leucyl-leucyl-norleucinal, a protease inhibitor that reduces the catabolism of sterol regulatory element binding proteins. Sterol deprivation increased the downregulation produced by nLDL on eNOS and sterol regulatory element binding protein-2 expression levels. However, no differential modulation of the retardation bands corresponding to the putative sterol-responsive element present in the eNOS promoter was detected by electrophoretic mobility shift assay. Our results suggest that nLDL promote eNOS downregulation operating at a transcriptional level, whereas simvastatin prevents such an effect through a posttranscriptional mechanism.

Modulation of ERG25 expression by LDL in vascular cells

BACKGROUND Plasma low density lipoproteins (LDL) play a key role in the pathogenesis of atherosclerosis. LDL modify gene expression in vascular cells leading to disturbances in the functional state of the vessel wall. METHODS Expression levels of C-4 sterol methyl oxidase gene (ERG25), sterol regulatory element binding protein (SREBP)-1 and -2 were evaluated in porcine aortic endothelial cells (PAEC), porcine and human smooth muscle cells (SMC) and in the vascular wall from normolipemic and hyperlipemic pigs by RT-PCR. SREBP-1 protein levels were assessed by Western blot and SREBP-SRE binding by EMSA. SREBP-2 was overexpressed by transient transfection with lipofectin. RESULTS We have identified expression of the ERG25 in vascular cells and analyzed its regulation by LDL. ERG25, an enzyme involved in cholesterol biosynthesis, is expressed in vascular endothelial and SMC from porcine and human origin and is downregulated by LDL in a time- and dose-dependent manner. Downregulation of ERG25 by LDL was abolished by an inhibitor of neutral cysteine proteases (N-acetyl-leucyl-leucyl-norleucinal) that abrogates SREBP catabolism. LDL downregulated SREBP-2 mRNA levels but not SREBP-1 expression in these cells and both ERG25 and SREBP-2 gene expression was significantly decreased in the vascular wall of diet-induced hypercholesterolemic swine. Finally, in cell transfection experiments SREBP-2 overexpression blocks ERG25 downregulation caused by LDL. CONCLUSIONS Our results indicate that LDL modulate ERG25 expression in the vascular wall and suggest the involvement of SREBP-2 in this mechanism.

Statins normalize vascular lysyl oxidase down-regulation induced by proatherogenic risk factors

AIMS Statins are lipid-lowering drugs widely used in the management of vascular diseases. Clinical and experimental evidence suggest that statins improve endothelial function by both cholesterol-lowering-dependent and -independent mechanisms. We have previously shown that endothelial dysfunction induced by risk factors and proinflammatory cytokines is associated with down-regulation of lysyl oxidase (LOX), a key enzyme modulating extracellular matrix maturation and vascular integrity. Our aim was to analyse whether statins could normalize LOX expression impaired by proatherogenic risk factors. METHODS AND RESULTS We observed that pharmacological concentrations of statins (atorvastatin and simvastatin) modulated LOX transcriptional activity, counteracting the down-regulation of LOX (at the mRNA, protein, and activity level) caused by tumour necrosis factor-alpha (TNFalpha) in porcine, bovine, and human aortic endothelial cells. Geranylgeraniol but not farnesol reversed this effect, suggesting the involvement of geranylgeranylated proteins. In accordance, inhibitors of RhoA/Rho kinase also counteracted LOX down-regulation caused by TNFalpha, and over-expression of a RhoA dominant-negative mutant mimicked statin effects. Statins were also able to counteract the decrease in LOX expression produced by atherogenic concentrations of LDL by a similar mechanism and to partially prevent the increase in endothelial permeability elicited by these lipoproteins. Finally, in the in vivo porcine model of hypercholesterolaemia, we observed that statins abrogated the reduction of vascular LOX expression triggered by high plasma levels of LDL. CONCLUSION These data indicate that statins normalize vascular LOX expression altered by atherogenic risk factors through a RhoA/Rho kinase-dependent mechanism. Thus, modulation of LOX by statins could contribute to vascular protection and to the cardiovascular risk reduction achieved by this therapy.

Replication of ribosomal DNA in Arabidopsis occurs both inside and outside the nucleolus during S phase progression

ABSTRACT Ribosomal RNA genes (rDNA) have been used as valuable experimental systems in numerous studies. Here, we focus on elucidating the spatiotemporal organisation of rDNA replication in Arabidopsis thaliana. To determine the subnuclear distribution of rDNA and the progression of its replication during the S phase, we apply 5-ethynyl-2′-deoxyuridine (EdU) labelling, fluorescence-activated cell sorting, fluorescence in situ hybridization and structured illumination microscopy. We show that rDNA is replicated inside and outside the nucleolus, where active transcription occurs at the same time. Nascent rDNA shows a maximum of nucleolar associations during early S phase. In addition to EdU patterns typical for early or late S phase, we describe two intermediate EdU profiles characteristic for mid S phase. Moreover, the use of lines containing mutations in the chromatin assembly factor-1 gene fas1 and wild-type progeny of fas1xfas2 crosses depleted of inactive copies allows for selective observation of the replication pattern of active rDNA. High-resolution data are presented, revealing the culmination of replication in the mid S phase in the nucleolus and its vicinity. Taken together, our results provide a detailed snapshot of replication of active and inactive rDNA during S phase progression. Summary: In Arabidopsis, replication of active and inactive rDNA occurs during S phase progression. High-resolution data reveal the culmination of replication in the mid S phase in the nucleolus.

Expresión de la lisil oxidasa (LOX) en la pared vascular: mecanismos implicados en la regulación de la LOX por lipoproteínas de baja densidad

Introduccion La lisil oxidasa (LOX) es una enzima implicada en la estabilizacion de la matriz extracelular que podria ser clave en la disfuncion endotelial desencadenada por factores de riesgo aterosclerotico. Hemos analizado el patron de expresion de las enzimas de la familia de LOX en la pared vascular y determinado los mecanismos implicados en la modulacion de esta enzima por lipoproteinas de baja densidad (LDL) en celulas vasculares. Material y metodos La expresion de la LOX y de otras enzimas de la familia se analizo en arterias coronarias humanas, aorta abdominal porcina, celulas endoteliales de aorta porcina (PAEC) y celulas musculares lisas (CML), mediante inmunohistoquimica, RT-PCR y/o Northern -blot. Resultados Hemos observado grandes diferencias en el patron de expresion de las enzimas de la familia de la LOX en la pared vascular. La LOX se expresa preferentemente en el endotelio y en la adventicia de arterias coronarias humanas y de aorta porcina. El tratamiento con LDL disminuye la expresion de esta enzima en PAEC y CML en cultivo. Este efecto se produce por un mecanismo transcripcional, sin que se vea afectada la estabilidad del mensajero. La esfingosina-1-fosfato (S1P), componente bioactivo de las LDL, no modifico la expresion de la LOX, y la inhibicion de proteinas G sensibles a toxina pertusica no revertio el efecto de las lipoproteinas. Sin embargo, observamos que la inhibicion del procesamiento lisosomal con cloroquina previno la disminucion de la expresion de la LOX causada por las LDL. Conclusiones La disminucion de la expresion de la LOX por LDL requiere el procesamiento lisosomal de la lipoproteina. La regulacion de esta enzima por lipoproteinas y su fuerte expresion en el endotelio vascular apoyan el papel de la LOX en la disfuncion endotelial desencadenada por la hipercolesterolemia y sugieren su contribucion en el proceso aterosclerotico.

Low density lipoproteins downregulate lysyl oxidase in vascular endothelial cells and the arterial wall

Objective—Hypercholesterolemia induces endothelial dysfunction, a hallmark of the atherosclerotic process, modulating the expression of key genes in vascular endothelial cells. Methods and Results—By differential display analysis, we have studied the effect of high concentrations of native low density lipoprotein (LDL) on endothelial gene expression. mRNA levels of lysyl oxidase (LOX), an enzyme involved in collagen and elastin cross-linking, were downregulated by LDL treatment in endothelial cells in a dose- and time-dependent manner (80% of inhibition by 180 mg/dL LDL for 24 hours). This reduction of LOX expression was associated with a decrease in LOX activity (40% and 54% of inhibition after 24 and 48 hours of LDL treatment, respectively). LOX mRNA half-life was not modified by LDL, but transcriptional inhibition blocked the effect of LDL. Inhibition of LOX activity by either LDL or &bgr;-aminopropionitrile, an inhibitor of LOX, increased endothelial permeability (192±0.19- and 3.37±0.74-fold, respectively). Interestingly, a reduction in LOX expression (3.5-fold) was observed in vivo in the vascular wall of hypercholesterolemic pigs. Conclusions—These findings suggest that LDL downregulation of LOX could contribute to the endothelial dysfunction caused by hypercholesterolemia, thus contributing to atherosclerotic plaque formation.