Pressure Myography Research Articles

Endothelial TRPA1 Channels Are Activated by Hypoxia in Cerebral Arteries and Protect Against Ischemic Damage

Acute drops in cerebral perfusion can lead to rapid neuronal death, as seen during transient ischemic attacks and ischemic strokes. The extent of brain damage following hypoxia is linked to the ability of collateral blood vessels to adequately supply blood to the peri‐infarct region and thus prevent neuronal loss and infarct expansion. During hypoxia, reactive oxygen species (ROS) are increased and may activate the Ca2+‐permeable transient receptor potential ankyrin 1 (TRPA1) in endothelial cells, promoting vasodilation. Here, we tested the hypothesis that TRPA1 channels in endothelial cells are activated by hypoxia‐derived ROS, leading to cerebral artery dilation and reduced ischemic damage. Using a novel mouse model expressing the Ca2+ indicator GCaMP6f in endothelial cells (Tek:GCaMP6f), we show that 4‐hydroxynonenal (4‐HNE), a lipid peroxide, increased TRPA1 channel activity, detected as elementary Ca2+ influx events (TRPA1 sparklets). The TRPA1 inhibitor A967079 prevented 4‐HNE induction of TRPA1 sparklets in endothelial cells. Acute exposure of cerebral arteries to hypoxia (5% O2, 6% CO2, 89% N2) significantly increased 4‐HNE accumulation in cerebral arteries, which was linked to an increase in TRPA1 sparklets. Hypoxia induction of TRPA1 sparklets was blocked by the TRPA1 inhibitor A967079, and by PEGylated superoxide dismutase (PEG‐SOD), suggesting a role for intracellular generation of ROS. Incubation of arteries with the mitochondria‐targeted antioxidant mitoTEMPO prevented the hypoxia‐induced increase in TRPA1 sparklets, whereas extracellular SOD or the NADPH oxidase inhibitor apocynin had no effect. In pressure myography studies, hypoxia caused endothelium‐dependent dilation of isolated cerebral arteries, an effect that was prevented by the membrane‐permeable SOD mimetic tempol and by mitoTEMPO. Hypoxia‐induced dilation of cerebral arteries was partially inhibited by the TRPA1 antagonist A967079 and was reduced in arteries isolated from endothelial cell‐specific TRPA1 knockout mice (eTRPA1−/− mice). In vivo, loss of TRPA1 channels in endothelial cells increased infarct size following middle cerebral occlusion, a model of ischemic strokes. Reversely, TRPA1 activation with cinnamaldehyde (50 mg/kg) reduced infarct size in wildtype, but not eTRPA1−/−, mice. Together, these data suggest that TRPA1 channels in cerebral artery endothelial cells are early sensors of hypoxia and orchestrate a response that culminates with vasodilation, thereby reducing ischemic damage. Further, pharmacological activation of TRPA1 channels may be a putative therapeutic target to reduce cerebral ischemic damage.Support or Funding InformationSupported by the National Institutes of Health (R01HL091095 to SE) and the American Heart Association (15POST2472002 to PWP)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Chronic administration of an endothelial KCa channel activator (SKA‐31) improves agonist evoked vasodilation in mesenteric arteries of aged rats

Endothelial dysfunction occurs in healthy ageing, and may contribute to the development of cardiovascular complications (e.g. hypertension, atherosclerosis) that are more prevalent in aged individuals. One cause of age‐related endothelial dysfunction is an imbalance in the generation and/or release of vasodilatory and constrictor agents by the vascular endothelium (e.g. reduced NO bioavailability). Ageing may also impact the expression of endothelial proteins involved with vasoactive signaling to the surrounding smooth muscle.The goal of our study was to assess the effects of long term, in vivo administration of SKA‐31, a small molecule activator of KCa 2.x and KCa 3.1 channels, on the functional reactivity of mesenteric arteries in healthy aged rats. Young (225–250 g, 12 weeks of age) and aged (600–700 g, 18 months of age) male Sprague Dawley (SD) rats were treated daily with either vehicle or 10 mg/kg SKA‐31 for 8 weeks, after which mesenteric arteries (i.e. 200–400 μm internal diameter) were isolated and cannulated in an arterial pressure myography chamber. Experimentally, arteries were pressurized to 70 mmHg, preconstricted with 1 μM phenylephrine (PE) and superfused at 6–7 ml/min with Krebs' solution at ~36°C using a peristaltic pump. Vasoactive agents were added directly to the superfusate.The PE‐induced decrease in the intraluminal diameter of pressurized mesenteric arteries (i.e. % change of maximal passive diameter) was significantly greater in aged (44.3 ± 2.7%, n=8) vs. young animals (38.1 ± 3.6%, n=12), whereas chronic SKA‐31 treatment of aged rats reduced the level of vasoconstriction to 36.5 ± 4.0% (n=8).Aged mesenteric arteries dilated less in response to 0.3 μM acetylcholine (ACh), 0.3 μM bradykinin (BK) and 10 μM sodium nitroprusside (SNP) (i.e. inhibition of active tone = 37.0 ± 1.9%, 44.6 ± 4.5%, 55.5 ± 4.8%, respectively; n=4) compared with young arteries (48.3 ± 6.8%, 62.0 ± 7.1%, 68.0 ± 7.9%, respectively, n=4). Chronic treatment of aged SD rats with SKA‐31 improved vasodilation evoked by ACh, BK and SNP (58.5 ± 5.5%, 64.3 ± 5.5%, 76.7 ± 4.4%, respectively; n=4), however, SKA‐31 treatment had no effect on the dilations evoked by either 10 μM adenosine or 5 μM pinacidil.Molecular analysis confirmed that expression of KCa 2.3 and KCa 3.1 channels was significantly decreased in aged mesenteric arteries compared with young vessels. Chronic SKA‐31 administration significantly increased the expression of these channels relative to vehicle‐treated animals (n=3).Collectively, these data demonstrate that chronic SKA‐31 treatment can improve evoked vasodilation in the aged mesenteric microcirculation, in part by enhancing the expression of endothelial KCa 2.3 and KCa 3.1 channels.Support or Funding InformationSupported by research funding to APB from the Canadian Institutes of Health Research. RKM is a recipient of a postdoctoral scholarship from the Libin Cardiovascular Institute and Cumming School of Medicine, Univ. of Calgary.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Acid Sensing Ion Channel 1 Contributes to Endothelium‐Derived Hyperpolarizing Factor Induced Vasodilation in Small Mesenteric Arteries.

Acid sensing ion channel 1 (ASIC1) belongs to the amiloride‐sensitive degenerin/epithelial sodium channel superfamily, and is permeable to both Na+ and Ca2+. ASIC channels have been found to regulate blood pressure through mechanotransduction in arterial baroreceptors and are also pH sensors in carotid body chemoreceptors. ASIC1 is additionally expressed in vascular smooth muscle and endothelial cells in a variety of vascular beds; yet little is known regarding the role of ASIC1 in the regulation of local vascular resistance. Although extracellular H+ is the recognized activator of ASIC1, we have previously shown this channel can be activated following G protein‐coupled receptor stimulation. In small mesenteric arteries, we found that ASIC1 contributes to acetylcholine (ACh)‐induced endothelial cell Ca2+ entry and vasodilation. However, the mechanisms involved in activating ASIC1 and its downstream effects on vasodilation are unknown. We hypothesized that ACh activates ASIC1‐mediated endothelial cell Ca2+ entry to mediate endothelium‐derived hyperpolarizing factor (EDHF)‐type vasodilation through activation of small (SK) and intermittent (IK) conductance Ca2+‐activated K+ channels. To test this hypothesis, we used pressure myography to study the effects of ASIC1 on ACh‐induced vasodilation (10−9 – 10−5 M) of freshly isolated mesenteric arteries (100–200 μm inner diameter), in the presence of Nω‐nitro‐L‐arginine (nitric oxide synthase inhibitor) and indomethacin (cyclooxygenase inhibitor). ACh‐induced vasodilation was abolished by specific inhibitors of SK and IK channels (apamin and TRAM‐34, respectively), confirming that the ACh‐induced dilation is EDHF‐dependent. The specific ASIC1 antagonist, psalmotoxin 1 (PcTX1; 20 nM) similarly blocks the EDHF‐mediated vasodilatory response, suggesting ASIC1 contributes to ACh‐induced vasodilation through an EDHF‐mediated pathway. Future studies will examine the upstream mechanisms involved in activation of endothelial ASIC1 and subsequent downstream effects to mediate EDHF‐dependent vasodilation. These studies suggest a role for ASIC1 as a novel contributor to agonist‐induced mesenteric vasodilation and cardiovascular homeostasis.Support or Funding InformationSupported by National Heart, Lung, and Blood Institute Grants R01 HL‐111084 (to N.L. Jernigan), T32 HL007736 (to T.C. Resta), and R01 HL132883 (to T.C. Resta).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

AMP‐Activated Protein Kinase (AMPK) Modulates Myoendothelial Junctions (MEJ) in Murine Microvessels

Myoendothelial junctions (MEJ) in microvessels are not only the site of direct cell communication via gap junctions but also represent a signaling microdomain critical for regulating vascular processes such as endothelium dependent hyperpolarization (EDH). The 5′‐adenosine monophosphate‐activated protein kinase (AMPK) has been shown to influence vascular tone. It has not yet been studied, however, whether AMPK could also affect MEJ. Thus, the aim of this project was to elucidate the impact of AMPK on MEJ dynamics and its potential mechanism of action.We studied isolated small mesenteric and skeletal muscle resistance arteries of mice using a pressure myograph system developed in our laboratory. Using confocal and two photon excitation fluorescence microscopy we identified the internal elastic lamina, which in these vessels exhibits small holes that allow direct contact between endothelial and smooth muscle cells. On average, we found that in about 35% of the holes, structures with a bright actin core as assessed by using F‐actin fluorescence in LifeAct mice or by staining with phalloidin which we could define as sites of MEJ. These structures showed expression of Cx37 and Cx43 suggesting that gap junctions (MEGJs) were also localized in these structures. Over observation times of up to 2 hours, we found that the number and localization of these MEJ varied, while they always positioned in the area of holes of IEL only. Thus, for the first time we could investigate MEJ dynamics. AMPK negatively regulates MEJ formation, since in AMPK α1, but not α2 knockout (KO) mice, the number of MEJ was significantly increased. In accordance, in wild type mice, incubation with the AMPK inhibitory compound C (CC) significantly augmented the number of MEJ. Furthermore, KO of AMPK α1, in intact mice as well as in cultured human and porcine smooth muscle cells, went along with an increase in PAI‐1 expression. Accordingly, incubation of arteries with exogenous PAI‐1 also increased the number of MEJ. The negative effect of AMPK on PAI‐1 could be explained by enhanced expression of the silencer of the PAI‐1 gene, small heterodimer partner (SHP). Since MEJ are also involved in EDH, we studied whether an enhanced formation of MEJ correlated with the magnitude of EDH induced vasodilation. Indeed, a higher amount of MEJs in α1 KO mice went along with a left shift of acetylcholine (ACh) ‐induced dilation dose effect curve.This work describes for the first time a role of the α1 subunit of AMPK as a potent modulator of MEJ dynamics which is probably mediated by controlling PAI‐1 expression. Our data also for the first time demonstrate a dynamic regulation of MEJ expression in intact blood vessels.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Insulin Receptor Substrate 2 Controls Insulin-Mediated Vasoreactivity and Perivascular Adipose Tissue Function in Muscle.

Introduction: Insulin signaling in adipose tissue has been shown to regulate insulin's effects in muscle. In muscle, perivascular adipose tissue (PVAT) and vascular insulin signaling regulate muscle perfusion. Insulin receptor substrate (IRS) 2 has been shown to control adipose tissue function and glucose metabolism, and here we tested the hypothesis that IRS2 mediates insulin's actions on the vessel wall as well as the vasoactive properties of PVAT.Methods: We studied PVAT and muscle resistance arteries (RA) from littermate IRS2+/+ and IRS2−/− mice and vasoreactivity by pressure myography, vascular insulin signaling, adipokine expression, and release and PVAT morphology. As insulin induced constriction of IRS2+/+ RA in our mouse model, we also exposed RA's of C57/Bl6 mice to PVAT from IRS2+/+ and IRS2−/− littermates to evaluate vasodilator properties of PVAT.Results: IRS2−/− RA exhibited normal vasomotor function, yet a decreased maximal diameter compared to IRS2+/+ RA. IRS2+/+ vessels unexpectedly constricted endothelin-dependently in response to insulin, and this effect was absent in IRS2−/− RA due to reduced ERK1/2activation. For evaluation of PVAT function, we also used C57/Bl6 vessels with a neutral basal effect of insulin. In these experiments insulin (10.0 nM) increased diameter in the presence of IRS2+/+ PVAT (17 ± 4.8, p = 0.014), yet induced a 10 ± 7.6% decrease in diameter in the presence of IRS2−/− PVAT. Adipocytes in IRS2−/− PVAT (1314 ± 161 μm2) were larger (p = 0.0013) than of IRS2+/+ PVAT (915 ± 63 μm2). Adiponectin, IL-6, PAI-1 secretion were similar between IRS2+/+ and IRS2−/− PVAT, as were expression of pro-inflammatory genes (TNF-α, CCL2) and adipokines (adiponectin, leptin, endothelin-1). Insulin-induced AKT phosphorylation in RA was similar in the presence of IRS2−/− and IRS2+/+ PVAT.Conclusion: In muscle, IRS2 regulates both insulin's vasoconstrictor effects, mediating ERK1/2-ET-1 activation, and its vasodilator effects, by mediating the vasodilator effect of PVAT. The regulatory role of IRS2 in PVAT is independent from adiponectin secretion.

Obesity-induced Endothelial Dysfunction is Prevented by Neutrophil Extracellular Trap Inhibition

Endothelial dysfunction precedes atherosclerosis and may constitute a critical link between obesity-related inflammation and cardiovascular disease. Neutrophil extracellular traps (NETs) have been shown to promote vascular damage in murine models of autoimmune disease and atherosclerosis. The impact of NETs towards endothelial dysfunction associated with obesity is unknown. Using a diet-induced obesity (DIO) mouse model, this study investigated whether the inhibition or degradation of NETs could reduce the endothelial dysfunction observed in DIO mice. Following induction of DIO, there were elevated plasma concentrations of monocyte chemoattractant protein-1 (MCP-1) and impairment of mesenteric arteriolar vasorelaxation in response to acetylcholine as measured by pressure myography. A marker of NET formation, cathelicidin-related antimicrobial peptide (CRAMP), was markedly increased in mesenteric arterial walls of DIO mice compared to mice on standard chow. Prevention of NET formation with Cl-amidine or dissolution of NETs with DNase restored endothelium-dependent vasodilation to the mesenteric arteries of DIO mice. These findings suggest an instrumental role for NETs in obesity-induced endothelial dysfunction.

Hydrogen Sulfide Attenuates Hypertensive Inflammation via Regulating Connexin Expression in Spontaneously Hypertensive Rats

BackgroundHydrogen sulfide (H2S) has anti-inflammatory and anti-hypertensive effects, and connexins (Cxs) are involved in regulation of immune homeostasis. In this study, we explored whether exogenous H2S prevents hypertensive inflammation by regulating Cxs expression of T lymphocytes in spontaneously hypertensive rats (SHR).Material/MethodsWe treated SHR with sodium hydrosulfide (NaHS) for 9 weeks. Vehicle-treated Wistar-Kyoto rats (WKYs) were used as a control. The arterial pressure was monitored by the tail-cuff method, and vascular function in basilar arteries was examined by pressure myography. Hematoxylin and eosin staining was used to show vascular remodeling and renal injury. The percentage of T cell subtypes in peripheral blood, surface expressions of Cx40/Cx43 on T cell subtypes, and serum cytokines level were determined by flow cytometry or ELISA. Expression of Cx40/Cx43 proteins in peripheral blood lymphocytes was analyzed by Western blot.ResultsChronic NaHS treatment significantly attenuated blood pressure elevation, and inhibited inflammation of target organs, vascular remodeling, and renal injury in SHR. Exogenous NaHS also improved vascular function by attenuating KCl-stimulated vasoconstrictor response in basilar arteries of SHR. In addition, chronic NaHS administration significantly suppressed inflammation of peripheral blood in SHR, as evidenced by the decreased serum levels of IL-2, IL-6, and CD4/CD8 ratio and the increased IL-10 level and percentage of regulatory T cells. NaHS treatment decreased hypertension-induced Cx40/Cx43 expressions in T lymphocytes from SHR.ConclusionsOur data demonstrate that H2S reduces hypertensive inflammation, at least partly due to regulation of T cell subsets balance by Cx40/Cx43 expressions inhibition.

AT1 Receptor Antagonism Improves Structural, Functional, and Biomechanical Properties in Resistance Arteries in a Rodent Chronic Kidney Disease Model.

The renin-angiotensin system, in particular Angiotensin II (AngII), plays a significant role in the pathogenesis of hypertension in chronic kidney disease (CKD). Effects of chronic AT1 receptor antagonism were investigated in a genetic hypertensive rat model of CKD, the Lewis polycystic kidney (LPK) rat. Mixed-sex LPK and Lewis control rats (total n = 31) were split between treated (valsartan 60 mg/kg/day p.o. from 4 to 18 weeks) and vehicle groups. Animals were assessed for systolic blood pressure and urine biochemistry, and after euthanasia, blood collected for urea and creatinine analysis, confirming the hypertensive and renal phenotype. Mesenteric resistance vasculature was assessed using pressure myography and histology. Valsartan treatment improved vascular structure in LPK rats, increasing internal and external diameter values and reducing wall thickness (untreated vs. treated LPK: 53.19 ± 3.29 vs. 33.93 ± 2.17 μm) and wall-lumen ratios (untreated vs. treated LPK: 0.52 ± 0.09 vs. 0.16 ± 0.01, all P < 0.0001). Endothelium dysfunction, as measured by maximal response to acetylcholine (Rmax), was normalized with treatment (untreated vs. treated LPK: 69.56 ± 4.34 vs. 103.05 ± 4.13, P < 0.05), increasing the relative contributions of nitric oxide and endothelium-derived hyperpolarization to vasorelaxation while downregulating the prostanoid contribution. Biomechanical properties also improved with treatment, as indicated by an increase in compliance, decrease in intrinsic stiffness and alterations in the artery wall composition, which included decreases in collagen density and collagen/elastin ratio. Our results highlight the importance of AngII as a driver of resistance vessel structural, functional, and biomechanical dysfunction and provide insight as to how AT1 receptor blockade exerts therapeutic efficacy in CKD.

Epithelial Na+ channel differentially contributes to shear stress-mediated vascular responsiveness in carotid and mesenteric arteries from mice.

A potential "new player" in arteries for mediating shear stress responses is the epithelial Na+ channel (ENaC). The contribution of ENaC as shear sensor in intact arteries, and particularly different types of arteries (conduit and resistance), is unknown. We investigated the role of ENaC in both conduit (carotid) and resistance (third-order mesenteric) arteries isolated from C57Bl/6J mice. Vessel characteristics were determined at baseline (60 mmHg, no flow) and in response to increased intraluminal pressure and shear stress using a pressure myograph. These protocols were performed in the absence and presence of the ENaC inhibitor amiloride (10 µM) and after inhibition of endothelial nitric oxide synthase (eNOS) by Nω-nitro-l-arginine methyl ester (l-NAME; 100 µM). Under no-flow conditions, amiloride increased internal and external diameters of carotid (13 ± 2%, P < 0.05) but not mesenteric (0.5 ± 0.9%, P > 0.05) arteries. In response to increased intraluminal pressure, amiloride had no effect on the internal diameter of either type of artery. However, amiloride affected the stress-strain curves of mesenteric arteries. With increased shear stress, ENaC-dependent effects were observed in both arteries. In carotid arteries, amiloride augmented flow-mediated dilation (9.2 ± 5.3%) compared with control (no amiloride, 6.2 ± 3.3%, P < 0.05). In mesenteric arteries, amiloride induced a flow-mediated constriction (-11.5 ± 6.6%) compared with control (-2.2 ± 4.5%, P < 0.05). l-NAME mimicked the effect of ENaC inhibition and prevented further amiloride effects in both types of arteries. These observations indicate that ENaC contributes to shear sensing in conduit and resistance arteries. ENaC-mediated effects were associated with NO production but may involve different (artery-dependent) downstream signaling pathways. NEW & NOTEWORTHY The epithelial Na+ channel (ENaC) contributes to shear sensing in conduit and resistance arteries. In conduit arteries ENaC has a role as a vasoconstrictor, whereas in resistance arteries ENaC contributes to vasodilation. Interaction of ENaC with endothelial nitric oxide synthase/nitric oxide signaling to mediate the effects is supported; however, cross talk with other shear stress-dependent signaling pathways cannot be excluded.

Transient Hypertension after Spinal Cord Injury Leads to Cerebrovascular Endothelial Dysfunction and Fibrosis.

We aimed to create a clinically relevant pre-clinical model of transient hypertension, and then evaluate the pathophysiological cerebrovascular processes resulting from this novel stimulus, which has recently been epidemiologically linked to cerebrovascular disease. We first developed a clinically relevant model of transient hypertension, secondary to induced autonomic dysreflexia after spinal cord injury and demonstrated that in both patients and rats, this stimulus leads to drastic acute cerebral hyperperfusion. For this, iatrogenic urodynamic filling/penile vibrostimulation was completed while measuring beat-by-beat blood pressure and cerebral blood flow (CBF) in patients. We then developed a rodent model mimicking the clinical reality by performing colorectal distention (to induce autonomic dysreflexia) using pre-clinical beat-by-beat blood pressure and CBF assessments. We then performed colorectal distension in rats for four weeks (6x/day) to evaluate the long-term cerebrovascular consequences of transient hypertension. Outcome measures included middle cerebral artery endothelial function, remodeling, profibrosis and perivascular innervation; measured via pressure myography, immunohistochemistry, molecular biology, and magnetic resonance imaging. Our model demonstrates that chronic repetitive cerebral hyperperfusion secondary to transient hypertension because of autonomic dysreflexia: (1) impairs cerebrovascular endothelial function; (2) leads to profibrotic cerebrovascular stiffening characterized by reduced distensibility and increased collagen deposition; and (3) reduces perivascular sympathetic cerebrovascular innervation. These changes did not occur concurrent to hallmark cerebrovascular changes from chronic steady-state hypertension, such as hypertrophic inward remodeling, or reduced CBF. Chronic exposure to repetitive transient hypertension after spinal cord injury leads to diverse cerebrovascular impairment that appears to be unique pathophysiology compared with steady-state hypertension in non-spinal cord injured models.

Microvascular insulin resistance in skeletal muscle and brain occurs early in the development of juvenile obesity in pigs.

Impaired microvascular insulin signaling may develop before overt indices of microvascular endothelial dysfunction and represent an early pathological feature of adolescent obesity. Using a translational porcine model of juvenile obesity, we tested the hypotheses that in the early stages of obesity development, impaired insulin signaling manifests in skeletal muscle (triceps), brain (prefrontal cortex), and corresponding vasculatures, and that depressed insulin-induced vasodilation is reversible with acute inhibition of protein kinase Cβ (PKCβ). Juvenile Ossabaw miniature swine (3.5 mo of age) were divided into two groups: lean control ( n = 6) and obese ( n = 6). Obesity was induced by feeding the animals a high-fat/high-fructose corn syrup/high-cholesterol diet for 10 wk. Juvenile obesity was characterized by excess body mass, hyperglycemia, physical inactivity (accelerometer), and marked lipid accumulation in the skeletal muscle, with no evidence of overt atherosclerotic lesions in athero-prone regions, such as the abdominal aorta. Endothelium-dependent (bradykinin) and -independent (sodium nitroprusside) vasomotor responses in the brachial and carotid arteries (wire myography), as well as in the skeletal muscle resistance and 2A pial arterioles (pressure myography) were unaltered, but insulin-induced microvascular vasodilation was impaired in the obese group. Blunted insulin-stimulated vasodilation, which was reversed with acute PKCβ inhibition (LY333-531), occurred alongside decreased tissue perfusion, as well as reduced insulin-stimulated Akt signaling in the prefrontal cortex, but not the triceps. In the early stages of juvenile obesity development, the microvasculature and prefrontal cortex exhibit impaired insulin signaling. Such adaptations may underscore vascular and neurological derangements associated with juvenile obesity.

Nitric Oxide-Dependent Feedback Loop Regulates Transient Receptor Potential Vanilloid 4 (TRPV4) Channel Cooperativity and Endothelial Function in Small Pulmonary Arteries.

BackgroundRecent studies demonstrate that spatially restricted, local Ca2+ signals are key regulators of endothelium‐dependent vasodilation in systemic circulation. There are drastic functional differences between pulmonary arteries (PAs) and systemic arteries, but the local Ca2+ signals that control endothelium‐dependent vasodilation of PAs are not known. Localized, unitary Ca2+ influx events through transient receptor potential vanilloid 4 (TRPV4) channels, termed TRPV4 sparklets, regulate endothelium‐dependent vasodilation in resistance‐sized mesenteric arteries via activation of Ca2+‐dependent K+ channels. The objective of this study was to determine the unique functional roles, signaling targets, and endogenous regulators of TRPV4 sparklets in resistance‐sized PAs.Methods and ResultsUsing confocal imaging, custom image analysis, and pressure myography in fourth‐order PAs in conjunction with knockout mouse models, we report a novel Ca2+ signaling mechanism that regulates endothelium‐dependent vasodilation in resistance‐sized PAs. TRPV4 sparklets exhibit distinct spatial localization in PAs when compared with mesenteric arteries, and preferentially activate endothelial nitric oxide synthase (eNOS). Nitric oxide released by TRPV4‐endothelial nitric oxide synthase signaling not only promotes vasodilation, but also initiates a guanylyl cyclase‐protein kinase G‐dependent negative feedback loop that inhibits cooperative openings of TRPV4 channels, thus limiting sparklet activity. Moreover, we discovered that adenosine triphosphate dilates PAs through a P2 purinergic receptor‐dependent activation of TRPV4 sparklets.ConclusionsOur results reveal a spatially distinct TRPV4‐endothelial nitric oxide synthase signaling mechanism and its novel endogenous regulators in resistance‐sized PAs.

Experimental Models Used to Assess Lymphatic Contractile Function

Recent years have seen a renewed interest in studies of the lymphatic system. This review addresses the differences between in vivo and ex vivo methods for visualization and functional studies of lymphatic networks, with an emphasis on studies of collecting lymphatic vessels. We begin with a brief summary of the historical uses of both approaches. For the purpose of detailed comparisons, we subdivide in vivo methods into those visualizing lymphatic networks through the intact skin and those using surgically opened skin. We subdivide ex vivo methods into isobaric studies (using a pressure myograph) or isometric studies (using a wire myograph). For all four categories, we compile a comprehensive list of the advantages, disadvantages, and limitations of each preparation, with the goal of informing the research community as to the appropriate kinds of experiments best suited, and ill suited, for each.

Increased myoendothelial feedback is associated with increased connexin37 and IK1 channel expression in mesenteric arteries of diet-induced hyperhomocysteinemic mice.

Previously, we found that diet-induced HHcy in mice caused decreased eNOS expression and signaling in mesenteric arteries, but greatly enhanced non-NOS, non-prostacyclin-dependent vasodilation, which involves MEJ communication. To further assess whether HHcy enhances MEJ communication, this study examined endothelium-dependent attenuation of phenylephrine-induced vasoconstriction (myoendothelial feedback) and key molecules involved. Myoendothelial feedback was examined in isolated mouse mesenteric arteries, after 6-weeks diet-induced HHcy, using pressure myography. Gap junction (Cx37, Cx40, Cx43), NOS (eNOS, nNOS, iNOS), and potassium channel (IK1) protein expression were measured with immunoblots, and connexin mRNAs with real-time PCR. Contribution of nNOS+iNOS to vasomotor responses was assessed using the drug TRIM. Myoendothelial feedback was significantly (P<.05) enhanced in HHcy arteries compared to control, coincident with significantly greater Cx37 and IK1 protein and Cx37 mRNA. Cx43 protein, but not mRNA, was significantly less in HHcy, and Cx40 was not different. eNOS protein was significantly less in HHcy. nNOS and iNOS were not different. TRIM had little effect on vasomotor function. Diet-induced HHcy enhanced myoendothelial feedback, and increased Cx37 and IK1 expression may contribute. nNOS or iNOS did not upregulate to compensate for decreased eNOS, and they had little involvement in vasomotor function.

Loss of Female Sex Hormones Exacerbates Cerebrovascular and Cognitive Dysfunction in Aortic Banded Miniswine Through a Neuropeptide Y-Ca2+-Activated Potassium Channel-Nitric Oxide Mediated Mechanism.

BackgroundPostmenopausal women represent the largest cohort of patients with heart failure with preserved ejection fraction, and vascular dementia represents the most common form of dementia in patients with heart failure with preserved ejection fraction. Therefore, we tested the hypotheses that the combination of cardiac pressure overload (aortic banding [AB]) and the loss of female sex hormones (ovariectomy [OVX]) impairs cerebrovascular control and spatial memory.Methods and ResultsFemale Yucatan miniswine were separated into 4 groups (n=7 per group): (1) control, (2) AB, (3) OVX, and (4) AB‐OVX. Pigs underwent OVX and AB at 7 and 8 months of age, respectively. At 14 months, cerebral blood flow velocity and spatial memory (spatial hole‐board task) were lower in the OVX groups (P<0.05), with significant impairments in the AB‐OVX group (P<0.05). Resting carotid artery β stiffness and vascular resistance during central hypovolemia were increased in the AB‐OVX group (P<0.05), and blood flow recovery after central hypovolemia was reduced in both OVX groups (P<0.05). Isolated pial artery (pressure myography) vasoconstriction to neuropeptide Y was greatest in the AB‐OVX group (P<0.05), and vasodilation to the Ca2+‐activated potassium channel α‐subunit agonist NS‐1619 was impaired in both AB groups (P<0.05). The ratio of phosphorylated endothelial nitric oxide synthase:total endothelial nitric oxide synthase was depressed and Ca2+‐activated potassium channel α‐subunit protein was increased in AB groups (P<0.05).ConclusionsMechanistically, impaired cerebral blood flow control in experimental heart failure may be the result of heightened neuropeptide Y–induced vasoconstriction along with reduced vasodilation associated with decreased Ca2+‐activated potassium channel function and impaired nitric oxide signaling, the effects of which are exacerbated in the absence of female sex hormones.

Endothelial Mineralocorticoid Receptor Mediates Parenchymal Arteriole and Posterior Cerebral Artery Remodeling During Angiotensin II-Induced Hypertension.

The brain is highly susceptible to injury caused by hypertension because the increased blood pressure causes artery remodeling that can limit cerebral perfusion. Mineralocorticoid receptor (MR) antagonism prevents hypertensive cerebral artery remodeling, but the vascular cell types involved have not been defined. In the periphery, the endothelial MR mediates hypertension-induced vascular injury, but cerebral and peripheral arteries are anatomically distinct; thus, these findings cannot be extrapolated to the brain. The parenchymal arterioles determine cerebrovascular resistance. Determining the effects of hypertension and MR signaling on these arterioles could lead to a better understanding of cerebral small vessel disease. We hypothesized that endothelial MR signaling mediates inward cerebral artery remodeling and reduced cerebral perfusion during angiotensin II (AngII) hypertension. The biomechanics of the parenchymal arterioles and posterior cerebral arteries were studied in male C57Bl/6 and endothelial cell-specific MR knockout mice and their appropriate controls using pressure myography. AngII increased plasma aldosterone and decreased cerebral perfusion in C57Bl/6 and MR-intact littermates. Endothelial cell MR deletion improved cerebral perfusion in AngII-treated mice. AngII hypertension resulted in inward hypotrophic remodeling; this was prevented by MR antagonism and endothelial MR deletion. Our studies suggest that endothelial cell MR mediates hypertensive remodeling in the cerebral microcirculation and large pial arteries. AngII-induced inward remodeling of cerebral arteries and arterioles was associated with a reduction in cerebral perfusion that could worsen the outcome of stroke or contribute to vascular dementia.

Red/near infrared light stimulates release of an endothelium dependent vasodilator and rescues vascular dysfunction in a diabetes model

Peripheral artery disease (PAD) is a morbid condition whereby ischemic peripheral muscle causes pain and tissue breakdown. Interestingly, PAD risk factors, e.g. diabetes mellitus, cause endothelial dysfunction secondary to decreased nitric oxide (NO) levels, which could explain treatment failures. Previously, we demonstrated 670nm light (R/NIR) increased NO from nitrosyl-heme stores, therefore we hypothesized R/NIR can stimulate vasodilation in healthy and diabetic blood vessels. Vasodilation was tested by ex vivo pressure myography in wild type C57Bl/6, endothelial nitric oxide synthase (eNOS) knockout, and db/db mice (10mW/cm2 for 5min with 10min dark period). NOS inhibition with N-Nitroarginine methyl ester (L-NAME) or the NO scavenger Carboxy-PTIO (c-PTIO) tested the specificity of NO production. 4,5-Diaminofluorescein diacetate (DAF-2) measured NO in human dermal microvascular endothelial cells (HMVEC-d). R/NIR significantly increased vasodilation in wild type and NOS inhibited groups, however R/NIR dilation was totally abolished with c-PTIO and blood vessel denudation. Interestingly, the bath solution from intact R/NIR stimulated vessels could dilate light naïve vessels in a NO dependent manner. Characterization of the bath identified a NO generating substance suggestive of S-nitrosothiols or non heme iron nitrosyl complexes. Consistent with the finding of an endothelial source of NO, intracellular NO increased with R/NIR in HMVEC-d treated with and without L-NAME (1mM), yet c-PTIO (100µm) reduced NO production. R/NIR significantly dilated db/db blood vessels. In conclusion, R/NIR stimulates vasodilation by release of NO bound substances from the endothelium. In a diabetes model of endothelial dysfunction, R/NIR restores vasodilation, which lends the potential for new treatments for diabetic vascular disease.

Maternal high-fat diet programs cerebrovascular remodeling in adult rat offspring

Maternal environmental factors such as diet have consequences on later health of the offspring. We found that maternal high-fat diet (HFD) exposure renders adult offspring brain more susceptible to ischemic injury. The present study was further to investigate whether HFD consumption during rat pregnancy and lactation influences the cerebral vasculature in adult male offspring. Besides the endothelial damage observed in the transmission electron microscopy, the MCAs of offspring from fat-fed dams fed with control diet (HFD/C) also displayed increased wall thickness and media/lumen ratio, suggesting that cerebrovascular hypertrophy or hyperplasia occurs. Moreover, smaller lumen diameter and elevated myogenic tone of the MCAs over a range of intralumenal pressures indicate inward cerebrovascular remodeling in HFD/C rats, with a concomitant increase in vessel stiffness. More importantly, both wire and pressure myography demonstrated that maternal HFD intake also enhanced the MCAs contractility to ET-1, accompanied by increases in ET types A receptor (ETAR) but not B (ETBR) density in the arteries. Furthermore, ETAR antagonism but not ETBR antagonism restored maternal HFD-induced cerebrovascular dysfunction in adult offspring. Taken together, maternal diet can substantially influence adult offspring cerebrovascular health, through remodeling of both structure and function, at least partially in an ET-1 manner.

Abstract P277: Mineralocorticoid Receptor Signaling Regulates TRPV4-mediated Vasodilation of Parenchymal Arterioles

Hypertension impairs endothelium-dependent dilation of the parenchymal arterioles (PA) that regulate white matter perfusion. In the periphery, mineralocorticoid receptor (MR) activation facilitates hypertension-associated artery dysfunction; the role of MR signaling in PA dysfunction has not been defined. We hypothesized that Angiotensin II (AngII)-hypertension impairs TRPV4-mediated dilation in an MR-dependent manner. 16 week old male C57bl/6 mice were treated with AngII (800ng/kg/min) ± the MR antagonist, eplerenone (EPL; 100mg/kg/day) for 4 weeks; Sham mice served as control. PAs were isolated and studied by pressure myography. Data are presented as mean ± SEM; n=4-6 per group. AngII increased systolic blood pressure, an effect not blunted by EPL (Sham:147 ± 3; AngII: 177* ± 3; AngII+EPL: 182* ± 6mmHg; *=p&lt;0.05 vs. Sham). However, EPL prevented the increased myogenic tone (31±1 vs 48*±4 vs 35±3 % tone; *=p&lt;0.05 vs. Sham) and the impaired carbachol (CbCh)-induced dilation (51±3 vs 24*±2 vs 49±3 %dilation; Sham vs. AngII vs. AngII+EPL; *=p&lt;0.05 vs. Sham) caused by AngII infusion. CbCh-induced dilation was unaltered by L-NAME (10 -5 M) and indomethacin (10 -4 M) in all groups (Sham: 51±3 vs. 53±2; AngII:24±2 vs. 28±2; AngII+EPL 49±3 vs. 47±3% dilation; CbCh vs. CbCh+L-NAME+Indomethacin) implicating endothelium-derived hyperpolarization (EDH). In contrast, the TRPV4 antagonist, GSK2193874 (GSK2, 10 -7 M) blunted the CbCh-induced dilation in all groups (Sham: 51±3 vs 13*±8; AngII: 24±2 vs 7*±2; AngII+EPL: 49±3 vs 16*±4 % dilation; CbCh vs CbCh+GSK2 ;*=p&lt;0.05). In the AngII and AngII+EPL mice, TRPV4 inhibition reduced myogenic tone (AngII: 16±3; AngII+EPL: 17±6 %tone loss; p&lt;0.05), an effect that was not observed in the Sham mice (2±3 %tone loss). AngII infusion decreased cerebral perfusion; EPL prevented this decrease (Sham: 938±32; AngII:596*±53; AngII+EPL:793±36 perfusion units; *=p&lt;0.05 vs. Sham). MR activation regulates TRPV4 signaling in PAs during AngII-infusion, independent of hypertension. Impaired TRPV4 function plays a critical role in AngII-hypertension-associated changes in PA reactivity and may increase the risk of small vessel disease.

Abstract P243: Smooth Muscle Cullin-3 Deficiency Causes Severe Early Onset Hypertension and Nitric Oxide Resistance

Mutations in Cullin-3 ( Cul3 ) resulting in exon 9 skipping (CUL3α9) cause human hypertension. We demonstrated that selective expression of CUL3α9 in smooth muscle causes arterial stiffness and hypertension. We hypothesized that deletion of CUL3 in smooth muscle causes severe hypertension. Mice carrying a conditional allele of CUL3 were bred with mice expressing a tamoxifen-inducible CRE-recombinase driven by a smooth muscle promoter. Mice were administered tamoxifen i.p. (75 mg/kg) for 5 consecutive days to generate smooth muscle CUL3 knockout (S-CUL3KO). CUL3 protein was undetectable whereas Cullin-1 protein was preserved in aorta from S-CUL3KO mice. We assessed vascular function in the cerebral basilar artery and aorta using pressurized and wire myograph, respectively. Blood pressure (BP) was measured by radiotelemetry. S-CUL3KO mice exhibited significantly increased systolic BP (SBP) at 2 weeks and 4 weeks post tamoxifen compared to corn oil controls (2 wks SBP mmHg: 145±1 vs 115±2, p&lt;0.001; 4 weeks SBP: 169±1 vs 115±3, p&lt;0.001). Pulse wave velocity was also increased in S-CUL3KO mice (3.7±0.1 m/s vs 2.2±0.1, P&lt;0.001), suggesting increased arterial stiffness. Aorta from S-CUL3KO mice exhibited severely impaired vasorelaxation to acetylcholine (ACh) compared to controls (at 100 μM: 1.0±3% vs 77±5%, p&lt;0.0001), and to the nitric oxide donor sodium nitroprusside (SNP) (at 100 μM: 15±4% vs 96±1%, p&lt;0.001). In agreement with data from aorta, cerebral basilar artery from S-CUL3KO mice also exhibited significant impairment to ACh- and SNP-mediated vasorelaxation. Conversely, S-CUL3KO aorta retained an ability to relax in response to a cGMP analogue (8-pCPT-cGMP, at 100 μμ: 8-pCPT-cGMP 70±3%) and to the heme-independent soluble guanylate cyclase activator (BAY 58-2667, at 10 μμ: BAY 58-2667 94±2%), indicating that downstream mechanisms controlled by cGMP remain intact in the absence of CUL3. Captopril (120 mg/kg/day) was sufficient to normalized BP in S-CUL3KO mice to pre-tamoxifen levels (change in SBP mmHg: -50.2±1.9 S-CUL3KO vs -25.0±2 control, P&lt;0.0001). We conclude that smooth muscle CUL3 is a major BP determinant, and identifying novel CUL3 substrates in smooth muscle would be beneficial as therapeutic targets in the treatment of hypertension.