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

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.

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.

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.

Expresión de la lisil oxidasa (LOX) en la pared vascular: mecanismos implicados en la regulación de la LOX por lipoproteínas de baja densidad / Lysyl oxidase (LOX) expression in the vascular wall: mechanisms involved in LOX regulation by low density lipoproteins

Introducción. La lisil oxidasa (LOX) es una enzima implicada en la estabilización de la matriz extracelular que podría ser clave en la disfunción endotelial desencadenada por factores de riesgo aterosclerótico. Hemos analizado el patrón de expresión de las enzimas de la familia de LOX en la pared vascular y determinado los mecanismos implicados en la modulación de esta enzima por lipoproteínas de baja densidad (LDL) en células vasculares. Material y métodos. La expresión de la LOX y de otras enzimas de la familia se analizó en arterias coronarias humanas, aorta abdominal porcina, células endoteliales de aorta porcina (PAEC) y células musculares lisas (CML), mediante inmunohistoquímica, RT-PCR y/o Northern-blot. Resultados. Hemos observado grandes diferencias en el patrón de expresión 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 expresión 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 modificó la expresión de la LOX, y la inhibición de proteínas G sensibles a toxina pertúsica no revertió el efecto de las lipoproteínas. Sin embargo, observamos que la inhibición del procesamiento lisosomal con cloroquina previno la disminución de la expresión de la LOX causada por las LDL. Conclusiones. La disminución de la expresión de la LOX por LDL requiere el procesamiento lisosomal de la lipoproteína. La regulación de esta enzima por lipoproteínas y su fuerte expresión en el endotelio vascular apoyan el papel de la LOX en la disfunción endotelial desencadenada por la hipercolesterolemia y sugieren su contribución en el proceso aterosclerótico (AU)

Introduction. Lysyl oxidase (LOX) is an enzyme involved in extracellular matrix stabilization that could play a key role in endothelial dysfunction triggered by atherosclerotic risk factors. We analyzed the expression pattern of LOX isoenzymes in the vascular wall and determined the molecular mechanisms involved in low density lipoproteins (LDL)-mediated LOX modulation in vascular cells. Material and methods. LOX isoenzyme expression was analyzed in human coronary arteries, porcine abdominal aorta, porcine aortic endothelial cells (PAEC) and vascular smooth muscle cells (VSMC) by immunohistochemistry, RT-PCR and/or Northern-blot. Results. We observed marked differences in the vascular expression pattern of LOX isoenzymes. LOX was preferentially expressed in endothelium and adventitia in human coronary arteries and in porcine abdominal aorta. LDL decreased LOX expression in both PAEC and VSMC in culture. This effect was due to a transcription mechanism that did not seem to alter mRNA stability. Sphingosine-1-phosphate (S1P), an LDL bioactive component, did not modify LOX expression, and inhibition of pertussis toxin-sensitive G-proteins did not prevent the effect of lipoproteins. Finally, we observed that inhibition of lysosomal processing with chloroquine abolished the LDL-induced LOX downregulation. Conclusions. LOX downregulation by LDL requires lipoprotein lysosomal processing. Both LOX regulation by lipoproteins and its strong endothelial expression support the role of this enzyme in endothelial dysfunction triggered by hypercholesterolemia and suggest that it contributes to the atherosclerotic process (AU)

High levels of homocysteine inhibit lysyl oxidase (LOX) and downregulate LOX expression in vascular endothelial cells.

BACKGROUND: Hyperhomocysteinemia, an independent risk factor for cardiovascular disease and atherothrombosis, alters endothelial function through a mechanism not fully understood. Downregulation of lysyl oxidase (LOX), an enzyme involved in extracellular matrix maturation, impairs the endothelial barrier function and could be involved in homocysteine (HC)-induced endothelial dysfunction. OBJECTIVE: The aim of this study was to analyze the effect of HC on LOX regulation in vascular endothelial cells. RESULTS: HC at pathophysiological concentrations (35 microM) inhibited LOX activity in porcine aortic endothelial cells. Homocysteine thiolactone and related molecules containing sulfhydryl groups (cysteine), but not methionine or homocystine (non-containing thiol-group) inhibited LOX. In addition, the blockade of HC-sulfhydryl group by N-ethylmaleimide abrogated HC-induced LOX downregulation. This process was triggered by oxidative stress since superoxide dismutase and vitamin C reverted LOX inhibition caused by HC. On the contrary, the effect was not mediated through the induction of endoplasmic reticulum stress. Finally, higher doses of HC (200 microM), common in severe hyperhomocysteinemia, decreased LOX mRNA levels ( approximately 2-fold) and LOX promoter activity in transient transfection experiments. CONCLUSIONS: These findings suggest that LOX inhibition contributes to the endothelial dysfunction associated with hyperhomocysteinemia. This effect was dependent on a mechanism involving both an inhibition of LOX activity and a reduction of LOX expression.

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 beta-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.