Résumé: Some of vascular endothelial dysfunction are caused by an impairment in nitric oxide biodisponibility, involving resistance arteries and leading to increase the systemic blood pressure and thus to rise hypertension. Hence antihypertensive agents that reverse endothelial dysfunction and lowers blood pressure might improve the prog nosis of patients with hypertension. Many studies investigated the underlying mechanism of Nebivolol® NEB-induced vasodilation and reported that is a highly selective β1 adrenoceptor blocker with additional vasodilating properties, but the mechanism that mediates these actions remain controversial. This review presents an overview of the NEB signaling pathway. Many hypothesizes in the literature suggest an endothelium-dependent liberation of NO induced by NEB in static conditions, and this NO production is due to stimulation of β3-adrenoreceptors and oestrogen receptors and was dependent from e-NOS activation so implicating PI3-K and Akt signaling pathway. Other findings reported an endothelium independent mechanism so independent from Ca+2/Calmodulin, e-NOS and β-adrenoreceptor pathway. Our studies concern the endothelium-dependent liberation of NO induced by NEB. We found that NEB induces up regulation of NO production in dose dependent manner. This increase in NO production is accompanied with a translocation of e-NOS from cellular membrane to peri nuclear region of the cell, these results suggest that hypertensive properties of the NEB are dependent from an eNOS mechanism thus from an endothelium dependent mechanism.

Résumé: Almost all of the cells of the human body are subjected to mechanical stresses. In endothelial cells, mechanical stresses can vary from some milli -Pascal (shear stress) to some Pascal (hydrostatic pres sure). Today it is know that mechanical stresses have a decisive part in cellular physiology. However, if the main biological effects of mechanical stress are well documentated, the mechanisms between mechanical forces to physiological phenomenon remain nearly unknown (mechanotransduction phe nomenon). In this work, through personal results and published works, the authors considers the effects of mechanical stresses and possible hypothesis.

Résumé: Tissue engineering requires the response of the cells to different stimuli inducing the synthesis of the extracellular matrix (ECM). It was been shown that mechanical and biochemical stimuli acted on the synthesis of ECM, particulary type I and III collagens. Growth factors implied in transduction pathways are multiple, but the main is TGF-. Member of the transforming growth factor- (TGF-) family bind to type II and type I serine/threonine kinase receptors, which initiate intracellular signals through activation of SMADs proteins. Receptor regulated SMADs are anchored to the cell membrane by interaction with membrane-bound proteins, including SMAD anchor for receptor activation (SARA). Upon ligand stimulation, SMAD2/3 are phosphorylated by the receptors and form oligomeric complexes with common-partner SMADs (SMAD4). The oligomeric SMAD complexes then translocate into the nucleus, where they regulate the transcription of target genes by direct binding to DNA. A third class of SMADs, inhibitory SMADs (SMAD7), plays a crucial role in a negative feedback loop to control TGF- activity. SMAD7 constitutively formed a complex with the TGF- receptors and interferes with the phosphorylation of SMAD2/3. Nevertheless the effect of mechanical stress of this pathway remain unknown. The aim of this work was to study the pathway of TGF- via the proteins SMADs under mechanical (stretching) and biochemical (TGF-) stimulations. Endogenous SMADs expression and its modulation by biochemical and mechanical stimulations were evaluated by both flow cytometry and confocal microscopy. Our results show that stretching as well as TGF-stimulation applied during 15 min decrease significantly the expression of SMAD2/3 and SMAD2/3p. After 1h of stimulation, the expression of SMAD2/3 and SMAD2/3p was restored. The double-stained sections revealed co-localization of SMAD2/3p-SMAD4 in both cytoplasme and nucleus, this co-localization desappeared after 15 min of biochemical or mechanical stimulation and SMAD4 conserve a constant and nuclear localization. The present results demonstrate that 10ng of TGF- and stretching (5%, 1HZ) Applied during 15min induced a negative feed back loop which blocks the signaling pathway to control TGF- activity. This inhibition effect was raised after 1h of stimulation. Nevertheless, these preliminary studies should be continued by study of expression and localization of inhibitory SMADs (SMAD7).

Résumé: Endothelial cells (ECs) form the interface between the blood and vessel wall. ECs perform many important functions such as: decrease of platelet aggregation, anti-thrombogenic and anti-adhesive effects, inhibition of vascular smooth muscle cells (SMCs) proliferation and regulation of their contraction and the arterial tonicity, via secretion of vasodilators or vasoconstrictors molecules such as nitric oxide (NO), endothelin I, prostacyclin and angiotensin II. This secretion is strongly influenced by mechanical forces imposed on the ECs. ECs are able to convert mechanical stimuli into intracellular signals that affect cellular functions (proliferation, apoptosis, migration, permeability as well as gene expression). Many of human diseases such as hypercholesterolemia, diabetes and hypertension are strongly linked to a disturbance of the production of several vasodilators or vasoconstrictors molecules such as NO. NO has been proved to play a key role in the control of vascular homeostasis and cardiovascular system function. NO is generated by endothelial nitric oxide synthase (e-NOS) using L-arginine as substrate and forming L-citrulline as a « side product ». NO diffuses from ECs to SMCs and increases intracellular cyclic guanosine monophosphate (cGMP), thus leading to the SMCs relaxation. Reducing of NO production is directly involved in hypertension disorder. Therefore, many drugs focusing the regulation of NO are used against this household disease. The aim of this in-vitro work was to evaluate the endothelial cells behaviour, when they are sheared by an unidirectional laminar flow rate (20 dynes/cm2) for 6 hours. e-NOS expression was evaluated by confocal microscopy and by RT-PCR. This work was carried out in order to study the arterial hypertension disorder. We found that the shear stress up-regulated the expression of e-NOS without changing its cytoplasmic localization. Shear stress also affected cells rearrangement by inducing their reorientation. In the early stage cells are not totally oriented parallel to the flow direction, which implied there that it is a consequent reduction of intracellular stress.