Daniela Ahl

Imperial College London, Londinium, England, United Kingdom

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Publications (3)24.67 Total impact

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    ABSTRACT: Although Rho-associated kinase (ROCK) activity has been implicated in cardiovascular diseases, the tissue- and isoform-specific roles of ROCKs in the vascular response to injury are not known. To address the role of ROCKs in this process, we generated haploinsufficient Rock1 (Rock1(+/-)) and Rock2 (Rock2(+/-)) mice and performed carotid artery ligations. Following this intervention, we found reduced neointima formation in Rock1(+/-) mice compared with that of WT or Rock2(+/-) mice. This correlated with decreased vascular smooth muscle cell proliferation and survival, decreased levels proinflammatory adhesion molecule expression, and reduced leukocyte infiltration. In addition, thioglycollate-induced peritoneal leukocyte recruitment and accumulation were substantially reduced in Rock1(+/-) mice compared with those of WT and Rock2(+/-) mice. To determine the role of leukocyte-derived ROCK1 in neointima formation, we performed reciprocal bone marrow transplantation (BMT) in WT and Rock1(+/-) mice. Rock1(+/-) to WT BMT led to reduced neointima formation and leukocyte infiltration following carotid ligation compared with those of WT to WT BMT. In contrast, WT to Rock1(+/-) BMT resulted in increased neointima formation. These findings indicate that ROCK1 in BM-derived cells mediates neointima formation following vascular injury and suggest that ROCK1 may represent a promising therapeutic target in vascular inflammatory diseases.
    Journal of Clinical Investigation 06/2008; 118(5):1632-44. · 12.81 Impact Factor
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    ABSTRACT: Mammalian cells respond to bacterial lipopolysaccharide (LPS) through a cognate receptor: Toll-like receptor 4 (TLR4). The signaling pathways, which link TLR4 to the proinflammatory transcription factor nuclear factor kappaB (NF-kappaB), occur through the intracellular docking proteins MyD88 and Trif. We hypothesize that unlike antigen-presenting cells, vascular endothelial cells (ECs) lack the Trif protein TRAM and are therefore incapable of eliciting Trif-dependent immune responses to LPS. Stimulation of wild-type mice with LPS leads to the activation of NF-kappaB in ECs and macrophages in vitro and in vivo. In contrast to macrophages, LPS did not activate endothelial NF-kappaB or NF-kappaB-dependent genes in MyD88(-/-) mice, suggesting the absence of a functional Trif pathway in vascular ECs. Indeed, the Trif-dependent gene cxcl10 was not expressed in ECs after LPS stimulation. This correlated with diminished expression of the Trif accessory TIR protein TRAM in ECs. Overexpression of TRAM cDNA in ECs reconstituted LPS-induced Trif-dependent NF-kappaB activation and cxcl10 promoter activity. The functional absence of TRAM in vascular ECs restricts TLR4 signaling to MyD88-dependent pathway. This is in contrast to macrophages, which respond to LPS via both Trif- and MyD88-dependent pathways. These findings indicate that vascular ECs do not express the Trif-dependent gene subset. This implies that these genes may be dispensable for the endothelial response to bacterial infection and play no role in the endothelial contribution to the development of atherosclerosis.
    Circulation Research 06/2006; 98(9):1134-40. · 11.86 Impact Factor
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    Daniela Ahl
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    ABSTRACT: Kardiovaskuläre Erkrankungen gehören weltweit zu den häufigsten Todesursachen für Männer und Frauen. Jeder zweite Bundesbürger stirbt heute an einer Herz-Kreislauf-Erkrankung. Diese Erkrankung der Arterienwand wird durch ein breites Spektrum an Risikofaktoren begünstigt. Dazu gehören Fettstoffwechselstörungen, insbesondere Hypercholesterinämie, sowie Hypertonie, Hyperglykämie (Diabetes mellitus), Adipositas, Hyperhomocysteinämie und Rauchen, deren Bedeutung in zahlreichen, prospektiv angelegten klinisch-epidemiologischen Studien gesichert werden konnte. Diese Studien haben das Gesamtcholesterin als einen der wichtigsten Risikofaktoren der koronaren Herzkrankheit (KHK) identifiziert. Das LDL-Cholesterin, das als kausaler Faktor der KHK gilt, wird nach derzeitigem Kenntnisstand am effektivsten durch HMG-CoA-Reduktase-Inhibitoren (Statine) gesenkt. Die Hepatische Lipase (HL) hat wichtige Funktionen im Fettstoffwechsel. Sie ist beteiligt bei der Hydrolyse von Triacylglyzeriden und Phospholipiden der HDL2 zu antiatherogenen, cholesterinreichen HDL3 sowie bei der Katalysierung der Hydrolyse von großen triacylglyzeridreichen LDL zu kleinen, dichten und atherogenen LDL-Partikeln. Die Konzentration der kleinen, dichten LDL korreliert positiv mit der Aktivität der HL. Studien, in denen der Einfluss von Statinen auf die HL untersucht wurde, zeigten, dass die Aktivität der HL in vivo durch Statine gesenkt werden kann. In dieser Arbeit wurde untersucht, welcher Mechanismus der Regulation der HL durch Statine zugrunde liegt. Zunächst konnte gezeigt werden, dass die HL in vitro posttranslationell durch Atorvastatin bzw. Lovastatin reguliert wird. Dies geschieht durch die statininduzierte Aktivierung des Proteasoms, für das das HL-Protein als Substrat zu dienen scheint. Die Kompetition mit einem Hemmer des Proteasoms, MG-132, hebt den vorzeitigen und/oder verstärkten Abbau des Proteins vollständig auf. Neben der posttranslationellen Regulation kann durch die Statine aber auch eine Beeinflussung der Transkription bzw. Translation stattfinden. Es konnte gezeigt werden, dass Atorvastatin und Lovastatin zu einer Abnahme der Menge an mRNA aber auch zu einer geringeren Transkriptionsrate führen. Diese negative Regulation findet nicht in Abhängigkeit voneinander statt, die Abnahme der mRNA ist nicht Folge einer verminderten Transkription. Vielmehr scheinen unterschiedliche Mechanismen verantwortlich zu sein. Schließlich konnte gezeigt werden, dass der Einfluss von Atorvastatin und Lovastatin auf die Transkription durch den Transkriptionsfaktor SREBP, der in Abhängigkeit vom Cholesteringehalt in der Zelle aktiviert wird, erklärt werden könnte. In radioaktiven Bindungsversuchen konnten Bindungsstellen für SREBP im Promotor der HL identifiziert werden. Die nähere Charakterisierung der bindenden Proteine und der Einsatz von in der Bindungsstelle gezielt mutierten Promotorfragmenten zeigen, dass SREBPs möglicherweise an der statinabhängigen Regulation der HL beteiligt sind. Atherosclerosis and its clinical manifestations of heart attack, stroke, and peripheral vascular insufficiency are a major cause of morbidity and mortality among both men and women. Multiple risk factors including hypertension, diabetes mellitus, smoking, and lipoprotein disorders are involved in the pathogenesis of this chronic inflammatory disease of arteries. Plasma lipoproteins are known to play a causative role in atherosclerosis and its clinical manifestation, CHD (coronary heart disease). Raised plasma cholesterol levels, particularly in the LDL fraction, correlate positively with the incidence of CHD, whereas HDL displays a negative association. The risk associated with elevations in plasma triglycerides, which are carried mainly in VLDL remains controversial. However, it is increasingly clear that one way in which this plasma lipid relates to CHD is through its influence on the structure of LDL and HDL, in particular its relation to the subfraction distribution within these density classes. Hepatic lipase (HL) plays a role in the metabolic processing of both HDL and LDL. HL acts to convert large, buoyant HDL2 to small, dense HDL3 by modulating the phospholipids content of the particle. By functioning as a ligand between the lipoprotein and cell surface receptors, HL has been shown to play a role in increased clearance of HDL particles and remnant lipoproteins. HL also catalyzes the hydrolysis of triglycerides and phospholipids in large, buoyant LDL forming small, dense more atherogenic LDL particles. By now therapy with HMG-CoA-Reductase-Inhibitors (statins) is the most effective way to lower elevated levels of cholesterol. Several epidemiological studies have shown that the use of statins results in a decrease of HL activity. The mechanism by which HL is influenced by statins is at the moment still unclear. Aim of this work was to find the mechanism that leads to the observed effect. In a first approach it could be shown that HL is in vitro regulated by Atorvastatin and Lovastatin in a posttranslational way. It is known that statins can activate the proteasome. An explanation for the observed effect on the protein level of HL could be that the HL serves as a substrate for the proteasome. In competition experiments with MG132, a potent inhibitor of the proteasome, the effect of statins alone abolished completely. Besides the posttranslational regulation of HL by Atorvastatin and Lovastatin statins can effect the transcription and/or translation. In order to analyze this possibility we show in another approach that Atorvastatin and Lovastatin lead to a decrease of the amount of HL mRNA in a time-dependent manner. To determine if the statins have an effect on transcription and if there are regulatory elements within the promoter that are affected by statins we used transient transfection assays with HuH7 cells and different promoters of the HL gene. Incubation with Atorvastatin or Lovastatin led to a decreased transcription rate. The negative regulation does not result from a transcription-translation-dependent mechanism. The decrease of the amount of mRNA is not due to the decrease of the transcription-rate. In fact different mechanisms seem to be involved in the observed negative regulation of HL. Statins lower the intracellular content of cholesterol. The following feedback-mechanisms in the cell are mainly started my activation of SREBPs (sterol responsible element binding proteins). These transcription factors are activated against the cholesterol content. By EMSAs (electrophoretic mobility shift assays) we could show that there are several binding sites for SREBP within the promoter of the HL gene. Further characterization of these proteins in western blots and targeted mutation of these binding sites in promoters of the HL gene showed that SREBPs might be involved but not exclusively responsible for the statin-dependent regulation of the HL.