Role of Histone Acetylation in the Stimulatory Effect of Valproic Acid on Vascular Endothelial Tissue-Type Plasminogen Activator Expression

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Characterization of Human Late Outgrowth Endothelial Progenitor-Derived Cells under Various Flow Conditions.

Background: Endothelial progenitor-derived cells (EPC) are a cell therapy tool in peripheral arterial disease and for re-endothelialization of bypasses and stents. Objective: To assess EPC behavior under flow conditions normally found in vivo. Results: EPC were isolated from human cord blood, cultured on compliant tubes and exposed in an in vitro flow system mimicking hemodynamic environments normally found in medium and large arteries. EPC exposed for 24 h to unidirectional (0.3 ± 0.1 or 6 ± 3 dynes/cm(2)) shear stress oriented along flow direction, while those exposed to bidirectional shear stress (0.3 ± 3 dynes/cm(2)) or static conditions had random orientation. Under bidirectional flow, tissue factor (TF) activity and mRNA expression were significantly increased (2.5- and 7.0-fold) compared to static conditions. Under low shear unidirectional flow TF mRNA increased 4.9 ± 0.5-fold. Similar flow-induced increases were observed for TF in mature umbilical vein-derived endothelial cells. Expression of tissue-type plasminogen activator (t-PA), urokinase (u-PA) and monocyte chemotactic protein 1 (MCP1) were reduced by 40-60% in late outgrowth endothelial progenitor-derived cells (LO-EPC) exposed to any flow environment, while MCP1, but not t-PA or u-PA, was decreased in HUVEC. Conclusions: Flow, in particular bidirectional, modifies the hemostatic balance in LO-EPC with increased TF and decreased plasminogen activator expression

Ex vivo Pulsatile Perfusion of Human Saphenous Veins Induces Intimal Hyperplasia and Increased Levels of the Plasminogen Activator Inhibitor 1.

Vessel wall trauma induces vascular remodeling processes including the development of intimal hyperplasia (IH). To assess the development of IH in human veins, we have used an ex vivo vein support system (EVVSS) allowing the perfusion of freshly isolated segments of saphenous veins in the presence of a pulsatile flow which reproduced arterial conditions regarding shear stress, flow rate and pressure during a period of 7 and 14 days. Compared to the corresponding freshly harvested human veins, histomorphometric analysis showed a significant increase in the intimal thickness which was already maximal after 7 days of perfusion. Expression of the endothelial marker CD31 demonstrated the presence of endothelium up to 14 days of perfusion. In our EVVSS model, the activity as well as the mRNA and protein expression levels of plasminogen activator inhibitor 1, the inhibitor of urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA), were increased after 7 days of perfusion, whereas the expression levels of tPA and uPA were not altered. No major change was observed between 7 and 14 days of perfusion. These data show that our newly developed EVVSS is a valuable setting to study ex vivo remodeling of human veins submitted to a pulsatile flow

Shear stress modulates the expression of the atheroprotective protein Cx37 in endothelial cells

High laminar shear stress (HLSS) is vasculoprotective partly through induction of Kruppel-like factor 2 (KLF2). Connexin37 (Cx37) is highly expressed in endothelial cells (ECs) of healthy arteries, but not in ECs overlying atherosclerotic lesions. Moreover, Cx37 deletion in apolipoprotein E-deficient (ApoE(-/-)) mice increases susceptibility to atherosclerosis. We hypothesized that shear stress, through KLF2 modulation, may affect Cx37 expression in ECs. Cx37 expression and gap-junctional intercellular (GJIC) dye transfer are prominent in the straight portion of carotid arteries of ApoE(-/-) mice, but are reduced at the carotid bifurcation, a region subjected to oscillatory flow. Shear stress-modifying vascular casts were placed around the common carotid artery of ApoE(-/-) mice. Whereas Cx37 expression was conserved in HLSS regions, it was downregulated to ~50% in low laminar or oscillatory flow regions. To study the mechanisms involved, HUVECs or bEnd.3 cells were exposed to flow in vitro. Cx37 and KLF2 expression were increased after 24h of HLSS. Interestingly, shear-dependent Cx37 expression was significantly reduced after silencing of KLF2. Moreover after exposure to simvastatin, a well-known KLF2 inducer, KLF2 binds to the Cx37 promoter region as shown by ChIP. Finally, GJIC dye transfer was highly reduced after KLF2 silencing and was increased after exposure to simvastatin. HLSS upregulates the expression of Cx37 in ECs by inducing its transcription factor KLF2, which increases intercellular communication. Therefore, this effect of shear stress on Cx37 expression may contribute to the synchronization of ECs and participate in the protective effect of HLSS

Lack of association between connexin40 polymorphisms and coronary artery disease.

OBJECTIVE: Cx40 is a gap junction protein important for cell-cell communication in the endothelium. Polymorphisms in the promoter region of the human Cx40 gene, -44G>A and +71A>G, were shown to reduce Cx40 transcription by half. As mice with an endothelial-specific deletion of Cx40 are more susceptible to atherosclerosis, this study was designed to discover a correlation between these polymorphisms and atherosclerosis in European populations.¦METHODS AND RESULTS: 803 patients referred to the Geneva University Hospitals for elective coronary angiography were divided according to the number of significantly stenosed vessels (from 0 to 3) and were genotyped for the Cx40 polymorphisms. Genotype distribution in the control group was -44GG/+71AA=59.8%, -44AG/+71AG=35.1% and -44AA/+71GG=5.2%. Surprisingly, this distribution was similar in the CAD group, with -44GG/+71AA=58.5%, -44AG/+71AG=37.6% and -44AA/+71GG=3.8% (p=0.67). Moreover, no significant association between histological carotid plaque composition of culprit lesions and Cx40 polymorphisms could be detected in 583 Dutch patients of the Athero-Express study.¦CONCLUSIONS: Despite a clear antiatherogenic role of Cx40 in mice, our study could not detect an association of Cx40 promoter polymorphisms and CAD in human. Moreover, a correlation with atherosclerotic plaque stability or hypertension could not be demonstrated either. Connexin polymorphisms affecting channel function may be of greater importance for cardiovascular disease than polymorphisms affecting the expression level of the protein