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International audience; Anacardium occidentale L. (A. occidentale), belonging to Anacardiaceae family, has been documented as traditional plant for the treatment of diabetes and hypertension [1]. Four extracts of A. occidentale were used for this study, namely AOL1 (from cyclohexane), AOL2 (from CH2Cl2), AOL3 (from EtOAc) and AOL4 (from MeOH). The most potent antiradical reactivity was observed in AOL4 with 2023 TE/g of extract compared to chlorogenic acid (2976 TE/g of compound) as positive standard. In the other hand, our data showed a significant inhibitory effect of EtOAc and MeOH extracts on BSA glycoxidation measured in terms of advanced glycation end products (AGEs). In isolated mesenteric artery rings precontracted with phenylephrine [2], AOL1, AOL2, AOL3, and AOL4 induced a concentration-dependant relaxation respectively with IC50 values of 120µg/ml, 100µg/ml, 70µg/ml and 70µg/ml. Exposure of Eahy cells to high glucose for 7 days significantly (p

International audience; Endothelial dysfunction in resistance arteries leads to end organ damages in type 2 diabetes. The capacity of the microcirculation to adapt or remodel in response to changes in blood flow or shear stress is essential for an optimal organ perfusion. Chronic increases in blood flow enhance arterial diameter and endothelium-dependent dilation.Since type 2 diabetes impairs endothelial sensitivity to flow (shear stress) and increases oxidative stress, we hypothesized that Zucker diabetic fatty rats (ZDF) would present an impaired flow-induced remodeling in resistance artery. Aim: The goal of the study was to compare the structural and functional adaptations of mesenteric arteries from lean (LZ) and ZDF rats, to chronic changes in blood flow. Methods: Two mesenteric resistance arteries were ligated in order to increase blood flow in a third artery. This artery was thus submitted, in vivo, to high flow (HF) and compared to normal flow (NF) arteries located at distance. After 3 weeks arteries were studied in vitro (n= 10 rats per group).Results: Arterial diameter (468 vs 394±8µm) and endothelial (acetylcholine)-dependent dilation (91±8 vs 75±6% dilation) were higher in HF than in NF arteries in LZ rats. In ZDF rats, arterial diameter (396±9 vs 440±17µm) and acetylcholine-mediated dilation (42±8 vs 75±7% dilation) were lower in HF than in NF arteries. Nevertheless, endothelial NO-synthase and NADP(H)-oxidase subunits (gp91, p67) expression level and superoxide production were higher in HF than in NF arteries in both LZ and ZDF rats HF suggesting an efficient flow-sensing process in both ZDF and LZ rats. But, in ZDF rats basal oxidative stress was higher compared to LZ rats: a) dihydroethydium staining was higher in both NF and HF arteries in ZDF than in LZ rats and b) acetylcholine-mediated dilation was improved by an acute antioxidant (tempol) in NF and HF arteries from ZDF rats (no effect in LZ rats NF arteries). As a consequence, oxidative stress, slightly increased in LZ rats HF arteries was strongly increased in ZDF rats HF vessels. This led to an excessive superoxide production impairing NO-dependent dilation and HF-remodeling. Finally, a chronic treatment with tempol restored HF arteries diameter (426±13 in NF vs 471±16µm in HF arteries) and endothelium-dependent dilation in ZDF rats. Conclusion: In type 2 diabetic rats increasing blood flow chronically failed to induce outward remodeling and to improve endothelium-dependent dilation; mainly because of superoxide overproduction.

Objective— Notch3, a member of the evolutionary conserved Notch receptor family, is primarily expressed in vascular smooth muscle cells. Genetic studies in human and mice revealed a critical role for Notch3 in the structural integrity of distal resistance arteries by regulating arterial differentiation and postnatal maturation. Methods and Results— We investigated the role of Notch3 in vascular tone in small resistance vessels (tail and cerebral arteries) and large (carotid) arteries isolated from Notch3 -deficient mice using arteriography. Passive diameter and compliance were unaltered in mutant arteries. Similarly, contractions to phenylephrine, KCl, angiotensin II, and thromboxane A2 as well as dilation to acetylcholine or sodium nitroprusside were unaffected. However, Notch3 deficiency induced a dramatic reduction in pressure-induced myogenic tone associated with a higher flow (shear stress)-mediated dilation in tail and cerebral resistance arteries only. Furthermore, RhoA activity and myosin light chain phosphorylation, measured in pressurized tail arteries, were significantly reduced in Notch3 KO mice. Additionally, myogenic tone inhibition by the Rho kinase inhibitor Y27632 was attenuated in mutant tail arteries. Conclusions— Notch3 plays an important role in the control of vascular mechano-transduction, by modulating the RhoA/Rho kinase pathway, with opposite effects on myogenic tone and flow-mediated dilation in the resistance circulation.

The small G protein Rho signaling pathways are recognized as major regulators of cardiovascular functions, and activation of Rho proteins appears to be a common component for the pathogenesis of hypertension and vascular proliferative disorders. Recent evidence suggests that modulation of Rho protein signaling by phosphorylation of Rho proteins provides an additional simple mechanism for coordinating Rho protein functions. Phosphorylation of RhoA by cAMP- or cGMP-activated kinase on Ser188 induces cytosolic sequestration of RhoA through increased interaction with guanine dissociation inhibitor, thereby resulting in inhibition of RhoA-dependent functions. Here we show that stimulation of angiotensin II (Ang II) type 2 receptor (AT 2 R) in vascular smooth muscle cells induces Ser188 phosphorylation of RhoA independently of cAMP- or cGMP-activated kinase. We identify the Ser/Thr kinase Ste20-related kinase SLK as a new kinase phosphorylating RhoA on Ser188. Activation of the signaling cascade involving Src homology 2 domain–containing protein-tyrosine phosphatase 1, casein kinase II and SLK is responsible for RhoA phosphorylation and inhibition of RhoA-mediated arterial contraction induced by AT 2 R activation. These results thus identify the molecular mechanism linking AT 2 R to RhoA inhibition and vasodilation.

International audience; AIMS: The link between aging and vascular diseases remains unclear, especially in resistance arteries. As a decreased vasodilator capacity of the endothelium is usually described in aging, we hypothesized that arteriolar remodelling in response to a chronic increase in blood flow might be altered. In addition, we tested the capacity of a vasodilator treatment with hydralazine to restore remodelling, as we have previously shown that hydralazine has a potent effect on the process.METHODS AND RESULTS: Mesenteric resistance arteries (350 microm diameter) from 3- and 24-month-old rats were exposed to high blood flow (HF) and normal blood flow (NF), for 2 weeks by sequential ligating second-order arteries in vivo. In HF arteries, diameter increased by 21% when intraluminal pressure was 100 mmHg, in association with a rise in superoxide production in young rats. On the other hand, both diameter and superoxide levels failed to increase in old rats. Hydralazine restored HF-induced remodelling in old rats in association with an increased superoxide production and a decreased superoxide dismutase (SOD) expression. The SOD-mimetic 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl (TEMPOL) prevented the effect of hydralazine on the arterial diameter. In old rats, hydralazine increased the arterial diameter in HF arteries without increasing eNOS expression. Furthermore, hydralazine also restored HF remodelling in eNOS knockout mice.CONCLUSION: Thus, flow remodelling in resistance arteries failed to occur in aging but it could be restored by hydralazine via a reactive oxygen species-dependent mechanism. These findings may have serious pathophysiological consequences in situations requiring flow-dependent remodelling such as ischaemic and metabolic diseases, more frequent in the elderly.

International audience; Cytoskeletal proteins determine cell shape and integrity and membrane-bound structures connected to extracellular components allow tissue integrity. These structural elements have an active role in the interaction of blood vessels with their environment. Shear stress due to blood flow is the most important force stimulating the endothelium. The role of cytoskeletal proteins in endothelial responses to flow has been studied in resistance arteries using pharmacological tools and transgenic models. Shear stress activates extracellular "flow sensing" elements associated with a thick glycocalyx communicating the signal to membrane-bound complexes (integrins and/or dystrophin-dystroglycans) and to eNOS through a pathway involving the intermediate filament vimentin, the microtubule network and actin. When blood flow increases chronically the endothelium triggers diameter enlargement and medial hypertrophy. This is facilitated by the genetic absence of the intermediate filaments, vimentin and desmin suggesting that these elements oppose the process.

The role of angiotensin II type 2 receptors (AT2R) is not fully understood, especially in vascular diseases. Although its vasodilatory and antitrophic properties are well accepted, in hypertensive rats AT2R stimulation induces vasoconstriction. Abnormalities in the renin-angiotensin system have a key role in cardiovascular disorders associated with the evolution of type II diabetes. Thus, we hypothesized that AT2R function might be altered in diabetic rats resistance arteries. Mesenteric resistance arteries (250 μm diameter) were isolated from type II diabetic Zucker (ZDF) and control rats (LZ) rats receiving the antioxidant tempol (16 mg/kg/day) or water for 3 weeks. Dilation to angiotensin II (due AT2R stimulation) in the presence of candesartan (angiotensin II type 1 receptor blocker) was studied in ring segment of arteries using a wire-myograph mesenteric wall force. AT2R induced endothelium and NO-dependent dilation in LZ (inhibited by L-NAME). It was not affected by cyclooxygenase (indomethacin) or reactive oxygen species (ROS) inhibition (TEMPOL). In ZDF rats AT2R-induced dilation was lower than in LZ rats and independent of NO (not inhibited by L-NAME). It was restored to control level after ROS (tempol) and cycloxygenase inhibition (indomethacin). Cycloxygenase-2 (NS398) and Thromboxane A2 receptor (SQ29548) inhibition also restored AT2R-dilation in ZDF rats to control (LZ) level. Cycloxygenase-2 and ROS were overexpressed (immuno-histological detection using confocal microscopy) in ZDF rats arteries. In ZDF rats chronically treated with the antioxydant Tempol (SOD mimetic) AT2R-induced dilation was equivalent to that in LZ (control) rats and it involved NO and cycloxygenase-2-derivatives in equivalent proportion (dilation inhibited in part by L-NAME and by NS398). In tempol-treated rats SQ29548 had no effect. We conclude that in type II diabetic rats AT2R induced dilation is reduced due to ROS and thromboxane A2-dependent vasoconstriction due to COX-2 activation. Chronic treatment of diabetic rats with tempol restored AT2R-dependent dilation through the suppression of ROS and TxA2 production. These findings might be important to consider in the choice of vasoactive drugs in diabetic patients.

Chronic increases in blood flow increase arterial diameter and NO-dependent dilation in resistance arteries. Because endothelial dysfunction accompanies metabolic syndrome, we hypothesized that flow-mediated remodeling might be impaired in obese rat resistance arteries. Obese and lean Zucker rat mesenteric resistance arteries were exposed to chronic flow increases through arterial ligation in vivo: arteries exposed to high flow were compared with normal flow arteries. Diameter was measured in vitro in cannulated arteries using pressure arteriography. After 7 days, outward remodeling (diameter increased from 346±9 to 412±11 μm at 100 mm Hg) occurred in lean high-flow arteries. Endothelium-dependent tone was reduced in high-flow arteries from obese rats by contrast with lean animals. On the other hand, diameter enlargement occurred similarly in the 2 strains. The involvement of NO in endothelium-dependent dilation (evidenced by NO blockade) and endothelial NO synthase phosphorylation was smaller in obese than in lean rats. Superoxide anion and reduced nicotinamide-adenine dinucleotide phosphate oxidase subunit expression (p67phox and gp91phox) increased in obese rats and were higher in high-flow than in control arteries. Acute Tempol (a catalase mimetic), catalase plus superoxide dismutase, and l -arginine plus tetrahydrobiopterin restored endothelium-dependent dilation in obese rat normal and high-flow arteries to the level found in lean control arteries. Thus, flow-induced remodeling in obese resistance arteries was associated with a reduced endothelium-mediated dilation because of a decreased NO bioavailability and an excessive superoxide production. This dysfunction might have negative consequences in ischemic diseases in patients with obesity or metabolic syndrome.

International audience; The role of angiotensin II type 2 receptors (AT2Rs) remains a matter of controversy. Its vasodilatory and antitrophic properties are well accepted. Nevertheless, in hypertensive rats, AT2R stimulation induces a vasoconstriction counteracting flow-mediated dilation (FMD). This contraction is reversed by hydralazine. Because FMD is also decreased in aging, another risk factor for cardiovascular diseases, we hypothesized that AT2R function might be altered in old-rat resistance arteries. Mesenteric resistance arteries (250 mum in diameter) were isolated from old (24 months) and control (4 months) rats receiving hydralazine (16 mg/kg per day; 2 weeks) or water. FMD, NO-mediated dilation, and endothelial NO synthase expression were lower in old versus control rats. AT2R blockade improved FMD in old rats, suggesting that AT2R stimulation produced vasoconstriction. AT2R expression was higher in old rats and mainly located in the smooth muscle layer. In old rats, AT2R stimulation induced endothelium-independent contraction, which was suppressed by the antioxidant Tempol. Reactive oxygen species level was higher in old-rat arteries than in controls. Hydralazine improved FMD and NO-dependent dilation in old rats without change in AT2R expression and location. In old rats treated with hydralazine, reactive oxygen species level was reduced in endothelial and smooth muscle cells, and AT2R-dependent contraction was abolished. Thus, AT2R stimulation induced vasoconstriction through activation of reactive oxygen species production, contributing to decrease FMD in old-rat resistance arteries. Hydralazine suppressed AT2R-dependent reactive oxygen species production and AT2R-dependent contraction, improving FMD. Importantly, endothelial alterations in aging were reversible. These findings are important to consider in the choice of vasoactive drugs in aging.

Polyphenols, present in green tea, grapes, or red wine, have paradoxical properties: they protect against cardiac and cerebral ischemia but inhibit angiogenesis in vitro. So we investigated the effects of polyphenols in vivo on postischemic neovascularization. Rats treated with low (0.2 mg x kg(-1) x day(-1)) or high (20 mg x kg(-1) x day(-1)) doses of red wine polyphenolic compounds (RWPC) were submitted to femoral artery ligature on the left leg. Two wks after ligature, high doses of RWPC (i.e., 7 glasses of red wine) reduced arterial, arteriolar, and capillary densities and blood flow in association with an inhibition of a PI3 kinase-Akt-endothelial NO synthase (eNOS) pathway, decreased VEGF expression, and lower metalloproteinase (MMP) activation. Low doses of RWPC (i.e., 1/10th glass of red wine) increased the left/right (L/R) leg ratio to control level in association with an increased blood flow and microvascular density. This angiogenic effect was associated with an overexpression of PI3 kinase-Akt-eNOS pathway and an increased VEGF production without effect on MMP activation. Thus, low and high doses RWPC have respectively pro- and anti-angiogenic properties on postischemic neovascularization in vivo. This unique dual effect of RWPC offers important perspectives for the treatment and prevention of ischemic diseases (low dose) or cancer growth (high dose).

Background Small resistance arteries regulate peripheral tissue perfusion following variations in arterial pressure and blood flow. An altered flow-mediated dilation (FMD) in response to intraluminal shear stress is the hallmark of early vascular dysfunction. We recently showed that the adaptive flow-dependent arterial remodeling was controlled by the endothelial estrogen receptor alpha (ERa). Our goal was to evaluate the role of ERa in endothelial mechanosensitive mechanisms related to the acute response to flow, by using multiple models of ERa deficiency in male mice, avoiding the hormonal influence of estrogens encountered in females. Methods Evaluation of the FMD was performed on pressurized mesenteric resistance arteries mounted on an arteriograph following step increase in intraluminal flow (6-100 μl/min). Arteries were isolated from wild-type (WT) and ERa genetically modified male mice deficient in either (i) total ERa (ERaKO), (ii) its ligand-dependent transactivation function AF2 (AF2°) and (iii) the plasmic membrane-located ERa following a point mutation of the palmitoylation (C451A) site of the receptor. Results We first observed a selective attenuation of FMD, without any major modification in response to vasodilator agonists (acetylcholine), in mice deficient in ERa (% dilation 50 μl/min: ERaKO: 41 ± 5 vs. WT: 59 ± 4 p Conclusions We thus show, for the first time, that membrane ERa contributes to arterial shear-sensing irrespective of the presence of an agonist or an antagonist. ERa at the membrane could contribute to vascular homeostasis and the regulation of its expression should now be studied.

L’environnement intra-uterin defavorable serait associe au developpement des maladies a l’âge adulte. Ainsi les enfants nes de meres diabetiques ont un risque accru de developper des pathologies telles que l’hypertension arterielle (HTA), le remodelage arteriel constrictif lie a cette HTA etant associe a l’apparition de maladies cardiovasculaires a plus long terme. Objectif Etudier les mecanismes de remodelage suite a l’exposition in utero au diabete maternel. Materiels et methodes Rats soumis in utero a une hyperglycemie maternelle moderee (DMO), developpant une HTA a 6 mois. Le remodelage des grosses et petites arteres, en reponse a cette augmentation de pression, est etudie chez des rats mâles DMO âges de 3 et 18 mois. Le remodelage en reponse a des variations de flux obtenues in vivo par ligatures d’arteres mesenteriques est etudie chez des DMO âges de 3 mois. Resultats En reponse a l’HTA, les DMO ne presentent pas de remodelage des aortes et des arteres mesenteriques. Ces resultats s’expliquent par une augmentation des points d’ancrage des cellules musculaire lisses avec les lames elastiques. Face aux variations de flux obtenues apres ligature, le remodelage expansif du a l’augmentation de flux des arteres mesenteriques des DMO est maintenu, alors que le remodelage constrictif lorsque le flux diminue est absent. Dans ces arteres « bas flux », nous observons une augmentation des activites eNOS et gp91 alors que l’expression de la transglutaminase-2 n’est pas modifiee. Conclusion Nos resultats demontrent que les mecanismes de remodelage sont modifies par l’exposition in utero au diabete maternel.

Small resistance arteries regulate peripheral tissue perfusion following variations in arterial pressure and blood flow. An alteration of the acute flowmediated dilation (FMD) in response to an elevation in intra-arterial shear stress is the hallmark of early vascular dysfunction and ageing. We recently showed that flow-dependent arterial remodeling, an adaptive phenomenon lost with age, was controlled by the endothelial estrogen receptor alpha (ERα). Our goal was thus to evaluate the role of ERαin endothelial mechano-sensitive mechanisms related to the acute response to flow, by using multiple models of ERαdeficiency in male mice, avoiding the hormonal influence of estrogens encountered in females.The evaluation of the FMD was performed on pressurized mesenteric resistance arteries mounted on an arteriograph following step increase in intraluminal flow (6-100 μl/min). Arteries were isolated from wild-type (WT) and ERαgenetically modified male mice deficient in (i) total ERα(ERαKO), (ii) the ligand-dependent transactivation function AF2 (AF2°) or (iii) the plasmic membrane-located ERαfollowing a point mutation of the palmitoylation site of the receptor (C451A).We first observed a selective alteration of FMD, without any major modification in response to vasodilator agonists (acetylcholine), in male mice deficient in total ERα. Interestingly, while the activation of the AF2 function involved in the nuclear action of ERαseemed only partially involved (% dilation 50μl/min: AF2: 49,5+/-11,8 vs. WT: 68,0+/-7,9 p=ns.), a default in receptor membrane addressing in C451A male mice markedly altered FMD (% dilation 50μl/min: C451A:29,4+/-5,1 vs. WT:59,3+/-10,6 ; p

Background— We have previously shown that angiotensin II type 2 receptor (AT 2 R) stimulation causes endothelium-dependent vasodilation that does not desensitize after chronic angiotensin II type 1 receptor (AT 1 R) blockade, suggesting a role for AT 2 R in antihypertensive treatment. Methods and Results— We recorded mean arterial pressure (MAP) and investigated AT 2 R by Western blot analysis, immunohistochemistry, and function in isolated mesenteric resistance arteries (205 μm in diameter) from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) receiving the following for 4 weeks in drinking water: placebo, AT 1 R blockade (candesartan; 2 mg/kg per day), ACE inhibitor (perindopril; 3 mg/kg per day), nonselective vasodilator (hydralazine; 16 or 24 mg/kg per day), or candesartan plus hydralazine (16 mg/kg per day). In precontracted isolated arteries, AT 2 R stimulation (angiotensin II in the presence of candesartan) caused vasodilation in WKY rats (MAP=118 mm Hg) and vasoconstriction in SHR (MAP=183 mm Hg). In SHR treated with candesartan (MAP=146 mm Hg) or hydralazine (16 mg/kg per day; MAP=145 mm Hg), AT 2 R-induced contraction was reduced by 50%. In SHR treated with perindopril (MAP=125 mm Hg), AT 2 R stimulation induced vasodilation. In SHR treated with hydralazine (24 mg/kg per day; MAP=105 mm Hg) and in SHR treated with hydralazine (16 mg/kg per day) plus candesartan (MAP=102 mm Hg), an AT 2 R-mediated vasodilation was restored. Immunochemistry and Western blot analysis showed that AT 2 R expression, lower in SHR than in WKY rats, was restored to normal levels by treatments reducing arterial pressure in SHR. Conclusions— Our results suggest that in resistance arteries of SHR, (1) AT 2 R is downregulated by hypertension, and (2) specific and nonspecific antihypertensive treatments restore AT 2 R expression and vasodilator functions.

International audience; Myogenic tone (MT), a fundamental stretch-sensitive vasoconstrictor property of resistance arteries and veins, is a key determinant of local blood flow regulation. We evaluated the pathways involved in MT development. The role of the RhoA/Rho kinase, p38 MAP kinase, and HSP27 in MT was investigated in the rabbit facial vein (RFV), previously shown to possess MT at a pressure level equivalent to 20 mm Hg. Venous MT is poorly understood, although venous diseases affect a large proportion of the population. Stretched RFV are characterized by a temperature-sensitive MT, which is normal at 39 degrees C but fails to develop at 33 degrees C. This allows for the discrimination of the pathways involved in MT from the multiple pathways activated by stretch. Isolated RFV segments were mounted in organ baths and stretched. Temperature was then set at 33 degrees C or 39 degrees C. MT was associated to the translocation of RhoA to the plasma membrane and the Rho kinase inhibitor Y27632 decreased stretch-induced MT by 93.1+/-4.9%. MT was also associated to an increase in p38 (131.0+/-12.5% at 39 degrees C versus 100% at 33 degrees C) and HSP27 phosphorylation (196.1+/-13.3% versus 100%), and the p38 MAP kinase inhibitor SB203580 decreased MT by 36.5+/-8.1%. (39 degrees C, compared with RFV stretched at 33 degrees C). Finally, phosphorylation of p38 was blocked by Y27632 and HSP27 phosphorylation was inhibited by SB203580 and Y27632. Thus, MT and the associated p38 and HSP27 phosphorylation seem to depend on RhoA/Rho kinase activation in stretch RFV.

Flow (shear stress)-mediated dilation (FMD) plays a key role in the local control of vascular diameter and blood flow supply. Although vasodilator treatments improve FMD in diverse models of hypertension, FMD may also change in situations where systemic blood pressure is not affected. In pathological situations such as ischemia, local blood flow and vascular density are increased by vasodilators not affecting systemic blood pressure. As the mechanisms involved remain obscure, we studied FMD in resistance arteries from mice treated chronically (1 month) with hydralazine (200 mg/L in drinking water). Blood flow in mesenteric arteries of mice treated with hydralazine was significantly increased (130 +/- 15 to 169 +/- 27 microl/min, n = 10/group), whereas mean arterial blood pressure was not affected (79 +/- 5 vs 82 +/- 3 mm Hg in controls). Mesenteric resistance arteries (90 microm internal diameter, 75 mm Hg) were isolated and mounted in vitro in an arteriograph. Pressure (myogenic tone)-, phenylephrine-, and KCl-induced contractions, as well as acetylcholine- and sodium nitroprusside-induced dilations, were unaffected by hydralazine. Flow-mediated dilation in arteries from hydralazine-treated mice was significantly increased, especially for low flow values (up to sevenfold). L-NAME-sensitive and indomethacin-sensitive FMD were both increased by hydralazine. Passive arterial diameter increased and arterial wall thickness decreased after chronic hydralazine. This is the first functional evidence that flow (shear stress)-mediated dilation in resistance arteries is improved by a chronic treatment with a nonselective vasodilator. This arteriolar adaptation to a chronic increase in blood flow might be of importance in the pathophysiology of ischemic diseases.

The effect of high NaCl diet on resistance arteries is not yet fully documented. In order to assess the effect of NaCl on myogenic tone and flow-induced dilation independent of arterial blood pressure change, we used normotensive rats which did not develop hypertension upon high NaCl intake. Normotensive Wistar Kyoto Rats received a high (8%) or a normal NaCl diet (0.4%). Mesenteric resistance arteries (150 microm, internal diameter) were cannulated in an arteriograph to allow perfusion of arteries under controlled pressure and flow. Pressure-induced myogenic tone was lower in the high NaCl group than in the control group. Cyclooxygenase inhibition with indomethacin and (N-(2-cyclohexyloxy)-4-nitro-phenyl)-methanesulphonamide, 1 micromol/l) NS 398 (specific cyclooxygenase-2 inhibitor) similarly decreased myogenic tone in rats fed high NaCl but had no effect in those fed a normal NaCl diet. Flow-induced dilation was decreased in the high NaCl group. Inhibition of nitric oxide synthesis with N(G)-nitro-L-arginine methyl ester decreased flow-induced dilation in both groups. Indomethacin and NS 398 did not change flow-induced dilation. As shown by immunofluorescence COX-2 was present in the endothelium of arteries from rats with a high NaCl diet but not in those fed a normal NaCl diet. Thus, chronic high NaCl intake decreased both flow-induced dilation and myogenic tone in resistance arteries. The chronic high NaCl did not affect the participation of nitric oxide on flow-induced dilation, but induced the expression of cyclooxygenase-2, which participates in myogenic tone. These results suggest that high NaCl changes flow and pressure mechanosensing processes and strengthen the hypothesis that sodium ions have an important role in both pressure and flow-mechanotransduction in vascular cells.

We have previously shown that angiotensin II (Ang II) and pressure increase extracellular signal-regulated kinase (ERK) 1/2 activity synergistically in intact, pressurized resistance arteries in vitro. However, the mechanisms by which pressure and Ang II activate ERK1/2 in intact resistance arteries remain to be determined. The purpose of the present study was to investigate the involvement of Rho-kinase and the actin filament network in Ang II- and pressure-induced ERK1/2 activation, as well as in the contractile response induced by Ang II. Mesenteric resistance arteries (200 to 300 microm) were isolated, mounted in an arteriograph, and stimulated by pressure, Ang II, or both. Activation of ERK1/2 was then measured by an in-gel assay. In mesenteric resistance arteries maintained at 70 mm Hg, Ang II (0.1 micromol/L) induced contraction (29+/-1.4% of phenylephrine, 10 micromol/L-induced contraction) and significantly increased ERK1/2 activity. Selective inhibition of Rho-kinase by Y-27632 (10 micromol/L) and selective disruption of the actin filament network by cytochalasin B (10 micromol/L) both decreased the Ang II-induced contraction by 78+/-1.2% and 87+/-1.9%, respectively, and significantly diminished ERK1/2 activity. In the absence of Ang II, increasing intraluminal pressure from 0 to 70 or 120 mm Hg increased ERK1/2 activity. ERK1/2 activity at 120 mm Hg was similar to that observed at 70 mm Hg in the presence of Ang II. Pressure-induced ERK1/2 activation was markedly attenuated by cytochalasin B but not by Y-27632. These results indicate that whereas pressure-induced ERK1/2 activation requires an intact actin filament network, but not Rho-kinase, the activation of ERK1/2 and the contraction induced by Ang II require both Rho-kinase and an intact actin filament network in isolated, intact mesenteric resistance arteries.

Abstract —Increased steady intraluminal pressure in blood vessels activates the extracellular signal–regulated kinase (ERK)1/2 pathway. However, signal transduction of pulsatile stretch has not been elucidated. Using an organ culture model of rabbit aorta, we studied ERK1/2 activation by pulsatility in vessels maintained at 80 mm Hg for 24 hours. ERK1/2 activity was evaluated by in-gel kinase assays and by Western blot. Compared with control aortas without pulsatility, aortas submitted to a pulsatile 10% variation in vessel diameter displayed a significant increase in ERK1/2 activity (207±12%, P 2 − levels in freshly isolated vessels were equivalent to the levels found in pulsatile vessels. In conclusion, pulsatile stretch activates ERK1/2 in the arterial wall via pathways different from those induced by steady overstretch. Pulsatility might be considered a physiological stimulus that maintains a certain degree of ERK1/2 activation via oxygen-derived free radical production.

Hypertension is one of the most frequent pathology in the industrialized world. Although it is recognized to be dependent on a combination of genetic and environmental factors, its molecular basis remains elusive. A possible candidate is the monomeric G protein RhoA which activates Rho kinase. However, how it is activated and whether it has a causative role in hypertension is still unknown. By in vitro experiments, we provide evidence that Arhgef1 is the RhoA guanine exchange factor specifically responsible for Angiotensin II (Ang II)-induced RhoA/Rho kinase activation in arterial smooth muscle cells. To analyze in vivo the role of Arhgef1, we generated mice lacking Arhgef1 specifically in smooth muscle cells (SM-Arhgef1-KO). We used Arhgef1lox/lox mice, which were mated to SMMHC-CreERT2 to produce SMMHC-CreERT2 ; Arhgef1lox/lox mice (SM-Arhgef1lox/lox). SM-Arhgef1-KO mice were then obtained by treating SM-Arhgef1lox/lox mice with tamoxifen. Remarkably, SM-Arhgef1-KO mice were resistant to hypertension induced by chronic Ang II infusion (sub-cutaneous osmotic pump, 1 μg/kg/min). Furthermore, Arhgef1 deletion after induction of hypertension by Ang II restored normal arterial pressure level. Basal arterial pressure and responses to vasoconstrictors other than Ang II (phenylephrine, U46619, endotheline) were not modified in SM-Arhgef1-KO mice. Our results show that Arhgef1 activation and its downstream RhoA/Rho kinase signaling are central to the development of Ang IIdependent hypertension. We identify Arhgef1 as an alternative potential target for the treatment of hypertension.

Abstract —Pressure-induced tone (myogenic, MT) and flow (shear stress)–induced dilation (FD) are potent modulators of resistance artery tone. We tested the hypothesis that locally produced angiotensin II interacts with MT and FD. Rat mesenteric resistance arteries were perfused in situ. Arterial diameter was measured by intravital microscopy after a bifurcation on 2 distal arterial branches equivalent in size (150 μm, n=7 per group). One was ligated distally and thus submitted to pressure only (MT, no FD). The second branch was submitted to flow and pressure (MT and FD). The difference in diameter between the 2 vessels was considered to be FD. Flow-diameter-pressure relationship was established in the absence and then in the presence of 1 of the following agents. In the nonligated segment (MT+FD), angiotensin II type 1 (AT 1 ) receptor blockade (losartan) had no significant effect, whereas angiotensin II type 2 (AT 2 ) receptor blockade (PD123319) or saralasin (AT 1 +AT 2 blocker) decreased the diameter significantly, by 9±1 and 10±0.8 μm, respectively. Angiotensin II in the presence of losartan increased the diameter by 18±0.6 μm (inhibited by PD123319). PD123319 or saralasin had no effect after NO synthesis blockade or after endothelial disruption. In the arterial segment ligated distally (MT only), AT 1 or AT 2 receptor blockade had no significant effect. AT 2 -dependent dilation represented 20% to 39% of FD (shear stress from 22 to 37 dyn/cm 2 ), and AT 2 -receptor mRNA was found in mesenteric resistance arteries. Thus, resistance arterial tone was modulated in situ by locally produced angiotensin II, which might participate in flow-induced dilation through endothelial AT 2 receptor activation of NO release.

Resistance arteries have a key role in the control of local blood flow. They are able to remodel in response to chronic increases in flow during growth, exercising or in ischemic diseases. Flow-mediated remodelling is governed by the endothelium. The incidence of metabolic syndrome increases with age and these 2 risk factors reduce endothelium integrity, because of an inflammatory process. We hypothesized that inflammation possibly through the induction of cycloxygenase-2 (COX2), might affect remodeling in old obese rats. In 12-month old obese and lean Zucker rats mesenteric resistance arteries were alternatively ligated in vivo so that one artery was submitted to high flow (HF), compare to normal flow (NF) vessels.After 21 days, outward hypertrophic remodelling in HF arteries occurred in obese rats (498±20 in HF arteries vs 443±18μm in NF arteries, P

We have previously shown that high blood flow (HF)-induced remodeling in mesenteric resistance arteries (MRA) failed to occur in aging. Heme oxygenase (HO)-1 is known to be induced by hemodynamic forces in VSM and endothelial cells. The aim of this work was to evaluate: i) the physiological role of HO activity in HF remodeling in MRA, and ii) the effect of systemic HO-1 induction on altered HF remodeling in MRA of aged rats. First-order MRA from 3- and 18-months-old rats were exposed to HF for 2 (young) or 14 days (young and old) by alternate ligation of 2nd-order arteries. I. Outward hypertrophic remodeling in HF arteries of young control rats (increased diameter and medial cross-sectional area) was associated with a profound increase in the expression of HO-1 mRNA two days after the ligation. II. HO inhibition with Sn-protoporphyrin (50 μmol/kg/day, i.p.) significantly inhibited diameter enlargement in HF arteries. III. HO-1 protein was barely detected in MRA from both young and old rats but was markedly increased after treatment with the HO-1 inducer Co-protoporphyrin (CoPP, 5 mg/kg, twice a week, s.c.). In old rats, CoPP decreased mean arterial blood pressure to a level similar to that in young animals (80±2.5 vs 101.5±2 mmHg, compared with untreated old rats) suggesting that CoPP may act as vasodilator. Moreover, HO-1 induction restored HF remodeling in old animals (17±2 vs 3±3 % increase in diameter, and 18440±2192 vs 13805±323μm2 for medial cross-sectional area when compared to HF in control old rats ; pressure=75mmHg). IV. This latter data was supported by the ability of CoPP to restore HF remodeling in eNOS-KO mice. These novel data show the pivotal role of HO activity in HF-induced remodeling in MRA. This likely occurs via its action on diameter enlargement in parallel with MMPs-dependent matrix degradation, downstream eNOS. Thus, selective HO-1 induction can be used as a new therapeutic approach to ameliorate the prognosis of cardiovascular injury associated with altered adaptation capacity of small arteries to chronic changes in local blood flow such as in ischemic and metabolic diseases or in hypertension, more frequent in the elderly.

Background —Dystrophin has a key role in striated muscle mechanotransduction of physical forces. Although cytoskeletal elements play a major role in the mechanotransduction of pressure and flow in vascular cells, the role of dystrophin in vascular function has not yet been investigated. Thus, we studied endothelial and muscular responses of arteries isolated from mice lacking dystrophin (mdx mice). Methods and Results —Carotid and mesenteric resistance arteries 120 μm in diameter were isolated and mounted in vitro in an arteriograph to control intraluminal pressure and flow. Blood pressure was not affected by the absence of dystrophin. Pressure-induced (myogenic), phenylephrine-induced, and KCl-induced forms of tone were unchanged. Flow (shear stress)–induced dilation in arteries isolated from mdx mice was decreased by 50% to 60%, whereas dilation to acetylcholine or sodium nitroprusside was unaffected. NG-nitro-L-arginine methyl ester–sensitive flow dilation was also decreased in arteries from mdx mice. Thus, the absence of dystrophin was associated with a defect in signal transduction of shear stress. Dystrophin was present in vascular endothelial and smooth muscle cells, as shown by immunolocalization, and localized at the level of the plasma membrane, as seen by confocal microscopy of perfused isolated arteries. Conclusions —This is the first functional study of arteries lacking the gene for dystrophin. Vascular reactivity was normal, with the exception of flow-induced dilation. Thus, dystrophin could play a specific role in shear-stress mechanotransduction in arterial endothelial cells. Organ damage in such diseases as Duchenne dystrophy might be aggravated by such a defective arterial response to flow.

BACKGROUND Whereas dystrophin has a key role in striated muscle mechanotransduction, its role in vascular functions is not fully understood. In mice lacking dystrophin (mdx) both flow (shear stress)-mediated dilation (FMD) and vascular wall remodelling are decreased, suggesting a low capacity of the vasculature to adapt to metabolic needs. OBJECTIVE AND DESIGN We assessed the capacity of a systemic vasodilator treatment to improve vascular remodelling and blood flow in mdx mice. We measured vascular structure and function in mesenteric resistance arteries (MRA) from control and mdx mice treated for 1 month with hydralazine. RESULTS Although hydralazine did not significantly affect blood pressure, mesenteric blood flow was increased in control and mdx mice (150+/-25 to 194+/-30 and 110+/-26 to 143+/-18 microl/min; respectively; n=10/group). MRA (90 microm internal diameter, 75 mmHg) were isolated in vitro in arteriographs. Arterial diameter and FMD were significantly increased by hydralazine in control but not in mdx mice. Hydralazine also increased N-nitro-L-arginine methyl ester (L-NAME)-sensitive FMD in control mice, not in mdx mice. Pressure-, phenylephrine-, serotonin- and calcium-induced contraction, as well as acetylcholine- and sodium nitroprusside-induced dilation, were not affected by hydralazine whatever the strain. CONCLUSION This study provides functional evidence that local blood flow could be improve by hydralazine in mdx mice despite a lack of vascular adaptation to flow. This study brings a new insight in the pathophysiology of dystrophin-related myopathies. Nevertheless, the consequences of an increased blood flow in non-adapted arteries remain unknown.

International audience; Backgroung/ Objectives: maternal obesity impacts vascular functions linked to metabolic disorders in offspring, leading to cardiovascular diseases during adulthood. Even if the relation between prenatal conditioning of cardiovascular diseases by maternal obesity and the vascular function begins to be documented, little is known about resistance arteries. They are of particular interest because of their specific role in the regulation of local blood flow. Then our study aims to determine if maternal obesity can directly program fetal vascular dysfunction of resistance arteries, independently of metabolic disorders.Methods: with a model of rats exposed in utero to mild maternal diet-induced obesity (OMO), we investigated third-order mesenteric arteries of 4-month old rats in absence of metabolic disorders. The methylation profile of these vessels was determined by Reduced Representation Bisulfite Sequencing (RRBS). Vascular structure and reactivity were investigated using histomorphometry analysis and wire-myography. Metabolic function was evaluated by insulin and glucose tolerance tests, plasma lipid profile and adipose tissue analysis.Results: at 4 months of age, small mesenteric arteries of OMO presented specific epigenetic modulations of matrix metalloproteinases (MMPs), collagens, and potassium channels genes in association with an outward remodeling and perturbations in the endothelium-dependent vasodilation pathways (greater contribution of EDHFs pathway in OMO males compared to control rats, and greater implication of PGI2 in OMO females compared to control rats). These vascular modifications were detected in absence of metabolic disorders.Conclusion: our study reports a specific methylation profile of resistance arteries associated to vascular remodeling and vasodilation balance perturbations in offspring exposed in utero to maternal obesity, in absence of metabolic dysfunctions.

The intermediate filament desmin has a key role in the integrity and contractility of skeletal and cardiac myocytes. Its absence or aggregation leads to cardiomyopathies. In arteries desmin is distributed heterogeneously; vascular disorders might also occur in its absence. We studied endothelial and muscular functions in arteries from mice lacking desmin (des-/-), compared with control (des+/+). Carotid and mesenteric resistance arteries were mounted in vitro in arteriographs. Desmin was located exclusively in smooth muscle cells. In arteries from des-/- mice, pressure-induced (myogenic) tone was unchanged, but agonist-induced tone decreased in resistance arteries (no change in large arteries). Flow (shear stress)- and acetylcholine-induced, endothelium-dependent dilation, as well as endothelium-independent dilation, were also decreased in resistance arteries. To our knowledge, this is the first study of vascular contractile and dilatory functions in arteries lacking desmin. Although vascular reactivity was normal in large arteries, it decreased strongly in small resistance arteries. Thus, desmin is required in vascular smooth muscle cells and in resistance arteries, for efficient control of vascular tone and consequently for an optimal blood flow supply. This microvascular defect found in the absence of desmin might play a major role in myopathies seen in desmin-related diseases.

End-organs perfusion is altered in metabolic diseases due in part to a decreased endothelium-mediated relaxation in resistance arteries (RA). Infl ammatory factors including cyclooxygenase-2 (COX2) derived agents affect the endothelium to different degrees in aging and obesity but the effect of their association on the endothelium is not fully understood. We hypothesized that COX2 derivatives might reduce endothelium-mediated relaxation in aging associated with obesity. RA from 4 and 12 month-old obese Zucker rats RA were isolated to measure acetylcholine (endothelium)-mediated relaxation (AMR), in vitro, using wire-myography. Impaired with obesity in young rats, AMR was further reduced with aging in old obese rats (89 versus 77 % maximal relaxation, young versus old lean rats and 72 versus 51 %, old young versus old obese rats). Endothelial NO-synthase (eNOS) blockade (L-NAME) was reduced in old obese rats although eNOS expression level was unaffected. However, indomethacin improved AMR in old obese rats only, suggesting that vasoconstrictor prostanoids were involved. Similarly, COX2 inhibition (NS398) and TxA2/PGH2 receptor blockade (SQ29548) increased AMR in arteries from old obese rats only. Old obese rats presented the highest levels of blood TxB2 (TxA2 metabolite) associated with an increased COX2 immunostaining and expression level. Chronic inhibition of COX2 with NS398 (3 weeks) restored AMR in old obese rats (78 % versus 57 % in control obese rats) to the level observed in solventtreated old lean rats (84 %). Taken together, these data show that obesity in old rats is associated with a reduced endothelium-mediated relaxation due to an excessive production of COX-2 derivatives, most probably TxA2.

Resistance arteries (RA) have a key role in the control of local blood flow. They undergo outward expansive remodeling in response to a chronic increase in blood flow as seen in post-ischemic collateral arteries growth. This remodeling is associated with improved endothelium-dependent dilation. We hypothesized that estrogens play a role in flow-mediated improvement of endothelium-dependent dilation. Local increase in blood flow in one mesenteric artery was obtained local surgery in three-month old ovariectomized female rats treated or not with 17-b-estradiol (E2). Changes in arterial function and structure were measured after 2 weeks. After 2 weeks, arterial diameter increased in high flow (HF) compared to normal flow (NF) arteries in ovariectomized rats treated with E2, not in untreated rats. Acetylcholine-mediated relaxation was higher in HF than in NF arteries in control and OVX rats treated with E2. In untreated rats, the relaxation was lower in HF than in NF vessels. eNOS expression level was higher in HF than in NF vessels in E2-treated rats only. Acetylcholine-mediated relaxation was fully dependent on the production of NO in E2-treated rats (total inhibition by the NO-synthesis blocker L-NAME). In untreated OVX rats L-NAME blocked only partly the relaxation. Endothelium-independent relaxation (sodium nitroprusside) was not affect by OVX or by E2. Serotoninand phenylephrine-mediated contraction was higher in HF than in NF arteries in both treated and untreated OVX rats. Thus, we demonstrated the essential role of endogenous E2 in flowmediated improvement of endothelium (NO)-mediated dilation in mesenteric resistance arteries.

SRF est un facteur de transcription implique dans la reponse adaptative des cellules musculaires lisses (CMLs) aux conditions pathologiques comme l’atherosclerose ou l’hypertension. Nous etudions le role de ce gene grâce a un modele Cre-Lox d’inactivation de SRF chez la souris cible dans les CMLs et inductible au tamoxifene (TAM) (souche SM22-CreERT2). Les analyses en RT-PCR et immunohistochimiques revelent une diminution de 45 % de l’expression de SRF au niveau des gros vaisseaux, accompagnee d’une reduction significative des isoformes musculaires lisses de l’actine, de la myosine et de SM22. L’histologie montre une elongation des noyaux des CMLs dans l’axe circonferentiel des vaisseaux. Une analyse transcriptomique a ete realisee en puces Affymetrix sur des aortes de souris controles et mutantes 8 jours apres inactivation de SRF. 169 genes sont sousexprimes chez le mutant, essentiellement impliques dans les processus d’adhesion cellulaire et d’organisation du cytosquelette, tandis que 349 genes sont sur-exprimes parmi lesquels la NOS3 et des genes impliques dans la reponse inflammatoire. Sur le plan fonctionnel, les souris mutantes femelles presentent une diminution significative de la pression arterielle (PA) systolique mesuree a la queue 10 jours apres la premiere injection de TAM. Ces resultats ont ete confirmes sur un groupe ovariectomise afin de s’affranchir des interactions potentielles du TAM avec l’action de l’œstradiol sur la PA. Suite a l’observation d’une augmentation de la NOS3 chez le mutant, une administration en aigu de L-NAME (100 mg/kg) a ete realisee a J14 afin d’inhiber la voie du NO. Le L-NAME induit une augmentation de la PAS de 37,5 ± 5,7 (mmHg) en moyenne chez les controles versus 22,9 ± 8 chez les mutants (p = 0.011). En revanche, a meme augmentation de PA, on observe une plus grande augmentation du diametre carotidien par rapport aux animaux controles. L’ensemble de nos resultats montre une alteration de la voie du NO ainsi que des proprietes structurales de la paroi musculaire avec des consequences fonctionnelles sur le controle de la pression arterielle.

Nowadays, cardiovascular diseases are the leading cause of death in the world. Their consequences on human body are well known. However, mechanisms involved in these pathologies are not totally established. Mitochondria has been widely studied in these pathologies. Mitochondrial dynamics’ dysfunctions have been widely established on cardiac pathologies but not on vascular pathologies. Thus, in this work, we investigated the role of mitochondrial dynamics in arterial hypertension and aortic aneurysm. First, we investigated impacts of OPA1 mutation on arterial hypertension. By using an Opa1+/- heterozygote mouse model, we demonstrated the protective role of OPA1 in arterial hypertension. Indeed, Opa1+/- mice treated with L-NAME developed hypertension more severe than control mice.The second study aimed to investigate mitochondrial dynamics’ modulation in aortic aneurysm. First, we show aortic aneurysm remodelling in Opa1+/- mice treated with angiotensin II. Then,we demonstrated a modification of mitochondrial dynamics’ gene expression in our aneurysm model (Ldlr-/-, HFD, AngII).To conclude, this work demonstrated, for the first time, a protective role of OPA1 in arterial hypertension and a deregulation of mitochondrial dynamics in aortic aneurysm., De nos jours, les pathologies cardiovasculaires représentent la première cause de mortalité dans le monde. Aujourd’hui, leurs conséquences sur l’Homme sont bien décrites. En revanche, il est souvent difficile de connaître avec précision les mécanismes à l’origine de certaines de ces pathologies. La place de la mitochondrie dans celles-ci a largement été étudiée. Des dysfonctions de la dynamique mitochondriale ont notamment été mises en évidence dans des pathologies cardiaques. En revanche, sa place dans les pathologies vasculaires reste encore inconnue. C’est pourquoi notre premier objectif a consisté à comprendre la place de la dynamique mitochondriale dans l’un des principaux facteurs de risque des pathologies cardiovasculaires, l’hypertension artérielle. Cette première étude a mis en évidence une aggravation de l’hypertension artérielle dans un modèle murin hétérozygote pour la protéine de fusion mitochondriale OPA1 (Opa1+/-),soumis à un traitement au L-NAME. Notre deuxième objectif a consisté à étudier la place de la dynamique mitochondriale dans l’une des pathologies vasculaires les plus mortelles, l’anévrisme de l’aorte. Dans un premier temps, nous avons mis en évidence un remodelage anévrismal des aortes provenant de souris Opa1+/- soumises à un traitement hypertenseur à l’angiotensine II. En parallèle, nous avons observé une modification d’expression des gènes codants pour les protéines de la dynamique mitochondriale dans un modèle reconnu d’anévrisme (Ldlr-/-, HFD, AngII). Pour conclure, ce travail a montré pour la première fois, le rôle protecteur d’OPA1 dans l’hypertension artérielle et la dérégulation de la dynamique mitochondriale dans l’anévrisme aortique.

The myogenic tone (MT) is the ability of the resistance arteries to contract in response to an increase in intraluminal pressure. MT protects capillaries against excessive rises in pressure, and regulates local blood flow. Due to its role in the development of pathologies, MT is an interesting therapeutic target. However the molecular mechanisms involved in MT still remain to be elucidated. The RhoA/Rho-kinase pathway plays an important role in the MT in particular via its role in the calcium sensitization of the contractile apparatus. Thus, we were particularly interested in determining factors that can modulate or be modulated by this pathway. First, we demonstrated that MT requires RhoA to be localized at the cellular membrane, where it interacts with caveolin-1 and activates its effectors such as Rho-kinase. Furthermore the activation of RhoA by the pressure is regulated by the Notch3 receptor, so occurring as a mechanosensor. Our works also showed the role of the serum response factor (SRF) in the MT via the regulation of the cytoskeleton and the activity of mecanosensitive channels. Finally, we showed in sildenafil treated rats, that the inhibition of RhoA activity induced a overexpression of it, that is responsible to an increase of the MT and an hypertension after this treatment. These works bring new and additional knowledges on the implication of proteins such as RhoA, Notch3 and SRF in the MT providing a better understanding of this mechanism and its regulation. These new elements offer new therapeutic targets for the treatment of pathologies involving vascular dysfonctions., Le tonus myogénique (TM) est la capacité des artères de résistance à se contracter suite à une élévation de la pression intraluminale. Il permet la protection des capillaires contre une augmentation excessive de pression, et régule les débits sanguins locaux. L'implication du TM dans le développement de certaines pathologies fait de lui une cible thérapeutique intéressante. Cela nécessite une identification précise des protagonistes moléculaires. La voie RhoA/Rho-kinase joue un rôle important dans le TM en régulant la sensibilisation au calcium de l'appareil contractile. Nous nous sommes donc particulièrement intéressés à des éléments pouvant moduler ou être modulés par cette voie. Ainsi, nous avons mis en évidence que l'intervention de la voie RhoA/Rho-kinase dans le TM implique tout d'abord une localisation membranaire de RhoA, afin d'interagir avec la cavéoline-1 et d'activer ses effecteurs tels que Rho-kinase. De plus l'activation de RhoA par la pression est régulée par le récepteur Notch3 intervenant ainsi comme un mécanosenseur. Nos travaux montrent aussi le rôle du facteur de réponse au sérum (SRF) dans le TM via la régulation du cytosquelette et de l'activité des canaux mécanosensibles. Pour finir, l'inhibition de l'activité de RhoA, lors d'un traitement avec du Sildénafil, entraine une surexpression de RhoA qui est responsable d'une élévation du TM et d'une hypertension à l'arrêt du traitement. Cette thèse apporte de nouvelles connaissances sur l'implication de RhoA, Notch3 et SRF dans le TM permettant une meilleure compréhension de ce mécanisme. Cela offre de nouvelles cibles thérapeutiques pour combattre les pathologies impliquant des dysfonctions vasculaires.

International audience; BACKGROUND: Dystrophin has a key role in striated muscle mechanotransduction of physical forces. Although cytoskeletal elements play a major role in the mechanotransduction of pressure and flow in vascular cells, the role of dystrophin in vascular function has not yet been investigated. Thus, we studied endothelial and muscular responses of arteries isolated from mice lacking dystrophin (mdx mice). METHODS AND RESULTS: Carotid and mesenteric resistance arteries 120 micrometer in diameter were isolated and mounted in vitro in an arteriograph to control intraluminal pressure and flow. Blood pressure was not affected by the absence of dystrophin. Pressure-induced (myogenic), phenylephrine-induced, and KCl-induced forms of tone were unchanged. Flow (shear stress)-induced dilation in arteries isolated from mdx mice was decreased by 50% to 60%, whereas dilation to acetylcholine or sodium nitroprusside was unaffected. NG-nitro-L-arginine methyl ester-sensitive flow dilation was also decreased in arteries from mdx mice. Thus, the absence of dystrophin was associated with a defect in signal transduction of shear stress. Dystrophin was present in vascular endothelial and smooth muscle cells, as shown by immunolocalization, and localized at the level of the plasma membrane, as seen by confocal microscopy of perfused isolated arteries. CONCLUSIONS:-This is the first functional study of arteries lacking the gene for dystrophin. Vascular reactivity was normal, with the exception of flow-induced dilation. Thus, dystrophin could play a specific role in shear-stress mechanotransduction in arterial endothelial cells. Organ damage in such diseases as Duchenne dystrophy might be aggravated by such a defective arterial response to flow.