Endothelial Calcium Signaling Research Articles

Contribution Of TRPV4 Channels To Calcium Signaling Profiles Of The Lung Microvascular Endothelium Under Acidic pH

Maintenance of lung endothelial barrier integrity is achieved to a great extent through effcient homeostatic endothelial calcium signaling in the lung microvasculature. The transient receptor potential vanilloid 4 (TRPV4), a non-selective calcium permeable channel has been implicated in several pulmonary pathologies involving lung barrier disruption. These channels are activated by various physical forces and chemical stimuli, but their underlying contribution to inherent and distinct microvascular endothelial Ca2+ signaling profiles are unknown. We previously assessed the role of TRPV4 channels in basal Ca2+ signaling dynamics of the pulmonary microcirculation under differing conditions of stretch and temperature. In the current study, we evaluate the impact of acidic pH (7.1, resembling acidosis) on the distinct endothelial Ca2+ signaling events in the mouse lung microcirculation and examine the participation of TRPV4 channels. Lung slices isolated from the Cdh5-GCaMP8 mice (transgenic mice with Ca2+-dependent fluorescent indicator expressed specifically within vascular endothelial cells) were mounted on Sylgard inserts with HEPES buffer (pH 7.45) and imaged for their basal signaling events using spinning disk confocal microscopy. After an initial baseline recording, the bathing solution was replaced with acidic HEPES buffer (pH 7.1) and recordings were made for approximately two minutes at 5 frames per second. These slices were then treated with the TRPV4 channel inhibitor GSK2193874 (3μM) or vehicle. The recorded image sequences were analyzed by using ImageJ and our custom signal tracking software S8, for quantification of the Ca2+ signaling profiles through event frequency, amplitude, duration and spread. Subjecting the lung slices to pH 7.1 increased the amplitude and spatial spread of the signaling events but the duration and frequency of the events remained relatively constant when compared to baseline recorded events. Addition of the channel blocker diminished the signaling event frequency, amplitude and spatial spread of the lung tissues. The normal pH and vehicle control for the above experiments did not show any relative change from the baseline signaling event profiles. To summarize, treating the lung slices to acidic pH increased the event amplitude and event spatial area distributions, indicating widespread activation of Ca2+ entry events. These increased event parameters were reduced upon addition of the antagonist, suggesting higher contribution of TRPV4 channel induced Ca2+ signaling events under acidic pH. We conclude that the channels contribute minimally to basal dynamics under homeostatic conditions but are activated to a greater extent under stimulations resembling pathological conditions like acidosis or acid aspirations. NIH P01 HL066299, R01 HL155288, NIH S10 0D020149. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

TNFa-TNFRI interaction impairs endothelial calcium signaling and elevates blood pressure in obesity

Endothelial dysfunction in small arteries is a hallmark of obesity-induced hypertension. Recent studies show that the formation of peroxynitrite, a reactive nitrogen species, impairs endothelium-dependent vasodilation. It is well known that inflammatory cytokines promote the formation of cellular peroxynitrite. In this regard, tumor necrosis factor-alpha (TNFα) signaling has been proposed as a contributor to endothelial dysfunction in obesity. Notably, the vascular wall has been proposed as a source of TNFα generation in obesity, although the vascular TNFα signaling mechanisms in obesity are unclear. We hypothesized that vascular wall-derived TNFα acts locally to impair endothelial function in obesity. We previously reported that high-fat diet feeding (60% kcal fat) for 14 weeks elevates blood pressure in mice. Flow cytometry and mRNA expression studies indicated an increase in TNFα levels in freshly isolated SMCs from small mesenteric arteries (MAs) of high-fat diet-fed obese mice compared to normal chow-fed control mice. However, TNFα levels in endothelial cells (ECs) from obese mice were not different from those in ECs from control mice. Tamoxifen-inducible SMC-specific TNFα -/- (TNFα SMC -/- ) mice did not show an increase in blood pressure after high-fat diet feeding. However, tamoxifen-inducible EC-specific TNFα -/- (TNFα EC -/- ) mice showed a similar increase in blood pressure after high-fat diet feeding compared to the control mice. Both TNFα SMC -/- and TNFα EC -/- showed a similar increase in body weight after high-fat diet feeding when compared to control mice, suggesting that differences in weight gain did not contribute to lower blood pressure in obese TNFα SMC -/- mice. Together, these results indicated that SMC TNFα plays a critical role in blood pressure elevation in obesity. The pro-inflammatory effects of TNFα occur mainly through TNFα receptor-I (TNFRI) activation. Therefore, we postulated that TNFα released from SMCs acts locally on EC TNFRI. Endothelium-dependent vasodilation to acetylcholine was improved in obese TNFα SMC -/- mice compared to obese control mice. Previous studies showed that decreased Ca 2+ influx through endothelial TRPV4 (transient receptor potential vanilloid 4) channels contribute to blood pressure elevation in obese mice. The activity of TRPV4 channels is also improved in ECs from obese TNFα SMC -/- mice. Treatment with a selective TNFRI signaling inhibitor (R7050, 10 mg/kg, i.p., once a day for 14 days) reduced the blood pressure to normal levels in obese mice but did not affect blood pressure in control mice. R7050 treatment also restored endothelium-dependent dilation of MAs and the activity of TRPV4 channels in ECs. Collectively, our findings indicate that vascular TNFα impairs endothelial calcium signaling and elevates blood pressure in obesity, highlighting the role of SMCs as a source of TNFα in obesity This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Physiological levels of fluid shear stress modulate vascular function through TRPV4 sparklets.

Endothelial calcium (Ca 2+) signaling plays a major role in regulating vasodilation in response to fluid shear stress (FSS) generated by blood flow. Local Ca 2+ influx through single transient receptor potential channel subfamily V member 4 (TRPV4) (termed "sparklets") activated by low concentrations of chemical and biological stimuli has been revealed to modulate vascular function. However, the range in which FSS can initiate TRPV4 sparklets to induce vasodilation is unknown. Here, we assess the activity of TPRV4 sparklets induced by various physiological levels of FSS and investigate the mechanisms involving these Ca 2+ signals in FSS-induced vasodilation. Intact small mesenteric arteries are used for Ca 2+ imaging with a GCaMP2(TRPV4-KO) mouse model and high-speed confocal systems. Markedly increased local Ca 2+ signals are observed in the endothelium under 4-8 dyne/cm 2 FSS, whereas FSS >8 dyne/cm 2 causes global Ca 2+ influx. Further analysis shows that TRPV4 channels form a four-channel group to mediate Ca 2+ sparklets under certain levels of FSS. The large Ca 2+ influx hyperpolarizes endothelial cells by stimulating intermediate (IK)- and small (SK)-conductance Ca 2+-sensitive potassium channels, leading to hyperpolarization of the surrounding smooth muscle cells and ultimately causing endothelium-dependent vasodilation. In conclusion, Ca 2+ influx transits through a small number of endothelial TRPV4 channels opened by certain levels of FSS, which activates the Ca 2+-sensitive IK and SK channels to cause vasodilation.

Abstract P134: Tnfα Impairs Endothelial Calcium Signaling And Elevates Blood Pressure In Obesity.

Endothelial dysfunction in small arteries is a hallmark of obesity-induced hypertension. Recent studies show that endothelial upregulation of inducible nitric oxide synthase (iNOS) and NADPH oxidase 1 (NOX1) plays a critical role in obesity-induced endothelial dysfunction. Endothelial upregulation of iNOS and NOX1 results in excessive formation of peroxynitrite, a reactive nitrogen species, which impairs endothelium-dependent vasodilation. It is well-known that inflammatory mediators elevate cellular iNOS, NOX1, and peroxynitrite levels. In this regard, tumor necrosis factor-alpha (TNFα) signaling has been proposed as a critical contributor to endothelial dysfunction in obesity. Notably, vascular SMCs TNFα levels were increased in heart failure and diabetes. Therefore, we hypothesized that vascular wall-derived TNFα acts locally to impair endothelial function in obesity. Flow cytometry studies showed an increase in TNFα levels in freshly isolated SMCs from small mesenteric arteries (MAs) of high-fat diet-fed obese mice compared to normal chow-fed control mice. However, TNFα levels in ECs from obese mice were not different from those in ECs from control mice. The pro-inflammatory effects of TNFα are mediated mainly through TNFα receptor I activation. Treating the obese mice with a selective inhibitor of TNFα receptor I signaling reduced the blood pressure to normal levels in obese mice but did not affect blood pressure in control mice. Treatment with R7050 also abolished the obesity-induced increase in iNOS and NOX1 expression in endothelial cells. Further, R7050 administration restored acetylcholine-induced, endothelium-dependent vasodilation of MAs in pressure myography experiments. Previous studies showed a decrease in Ca 2+ influx through endothelial TRPV4 channels contributes to blood pressure elevation in obese mice. Notably, R7050 administration restored the Ca 2+ influx signals through endothelial TRPV4 channels in MAs, as studied using high-speed confocal Ca 2+ imaging. Our findings collectively indicate that TNFα signaling contributes to the impairment of endothelial calcium signaling and blood pressure elevation in obesity and highlights the role of SMCs as a source of TNFα in obesity

TNFα signaling impairs endothelial calcium signaling and elevates blood pressure in obesity

Endothelial dysfunction in small arteries is a hallmark of obesity‐induced hypertension. Recent studies show that endothelial upregulation of inducible nitric oxide synthase (iNOS) and NADPH oxidase 1 (NOX1) plays a critical role in obesity‐induced endothelial dysfunction. Endothelial upregulation of iNOS and NOX1 results in excessive formation of peroxynitrite, a reactive nitrogen species, which impairs endothelium‐dependent vasodilation. It is well‐known that inflammatory mediators elevate cellular iNOS, NOX1, and peroxynitrite levels. In this regard, tumor necrosis factor alpha (TNFa) signaling has been proposed as a key contributor to endothelial dysfunction in obesity. Notably, vascular smooth muscle cells (SMCs) were shown to generate TNFa in heart failure and diabetes. Therefore, we hypothesized that vascular wall‐derived TNFa acts locally to impair endothelial function in obesity. Flow cytometry studies showed an increase in TNFa levels in freshly isolated SMCs from small mesenteric arteries (MAs) of high‐fat diet‐fed (14 weeks) obese mice compared to normal chow‐fed control mice. However, TNFa levels in endothelial cells (ECs) from obese mice were not different from those in ECs from control mice. The levels of two other cytokines, IL‐1b and IL‐6, were not different between in SMCs and ECs from normal and obese mice. Additionally, qPCR studies in endothelium‐denuded MAs provided further evidence that TNFa expression is increased in SMCs from obese mice compared to control mice. The pro‐inflammatory effects of TNFa are mediated mainly through TNFa receptor I activation. Treating the obese mice with a selective inhibitor of TNFa receptor I signaling (R7050, 10 mg/kg, i.p., once a day for 14 days) reduced the blood pressure to normal levels in obese mice, but had no effect on blood pressure in control mice. Treatment with R7050 also abolished obesity‐induced increase in iNOS and NOX1 expression in endothelial cells. Further, R7050 administration restored acetylcholine‐induced, endothelium‐dependent vasodilation of MAs in pressure myography experiments. Previous studies showed that a decrease in Ca2+ influx through endothelial transient receptor potential vanilloid 4 (TRPV4) channels contributes to blood pressure elevation in obese mice. Notably, R7050 administration restored the Ca2+ influx signals through endothelial TRPV4 channels in MAs, as studied using high‐speed confocal Ca2+ imaging. Collectively, our findings indicate that TNFa signaling contributes to the impairment of endothelial calcium signaling and blood pressure elevation in obesity, and highlight the role of SMCs as a source of TNFa in obesity.

Berberine alleviates NLRP3 inflammasome induced endothelial junction dysfunction through Ca2+ signalling in inflammatory vascular injury

BackgroundBerberine has received rising attention for its application in cardiovascular disease because of its relationship with inflammation. The endothelial NLRP3 inflammasome triggers inflammatory vascular injury which would lead to cardiovascular disease. Endothelial calcium signalling plays a crucial role in both the activation of NLRP3 inflammasome and endothelial cells dysfunction. However, the efficacy of BBR on the endothelial NLRP3 inflammasome in inflammatory vascular injury remains unknown. PurposeIn this study, we focused on the NLRP3 pathway to determine whether BBR regulates endothelial junction function in inflammatory vascular injury. MethodsThe integrity of the junction proteins VE-cadherin (VEC) and zonula occludens‐1 (ZO‐1) detected by immunofluorescence and immunoblotting was used to determine the therapeutic effect of BBR (50, 100, or 200 mg/kg/day) in LPS (100 μg/kg/day)-induced inflammatory vascular injury in mice and mouse microvascular endothelial cells (MECs) treated with LPS (1 μLPS ) and ATP (5 mM). Endothelial permeability was assessed by FITC-labelled dextran and trans-endothelial electrical resistance (TEER) in vitro. The assembly and activation of NLRP3 inflammasomes were detected by western blotting and immunofluorescence. Pharmacophore-based virtual molecular docking studies and calcium imaging analyses were used to determine the interaction of BBR with the ATP-gated Ca2+ channel P2X7R (purinergic P2X receptor 7) in the context of inflammatory vascular injury. ResultsBBR recovered the expression of ZO‐1 and VEC and inhibited endothelial NLRP3 inflammasome activation in coronary microvascular endothelium and in MECs. These results suggested a crucial role of the NLRP3 inflammasome in BBR-regulated endothelial integrity. Further analysis demonstrated that BBR treatment suppressed the binding of TXNIP (thioredoxin interacting protein) with NLRP3. Intriguingly, eliminating extracellular Ca2+ showed a similar effect as BBR. Virtual docking analysis indicated that R574 of P2X7R is a potential target for BBR binding. Ca2+ imaging showed that BBR inhibited the Ca2+ influx in response to ATP, supporting the potential interaction of BBR with P2X7R. ConclusionsThese findings suggest that BBR exhibits potential and specific therapeutic value by targeting calcium signals and the endothelial NLRP3 inflammasome in inflammatory vascular injury.

Coordinated regulation of endothelial calcium signaling and shear stress-induced nitric oxide production by PKCβ and PKCη

BackgroundProtein Kinase C (PKC) is a promiscuous serine/threonine kinase regulating vasodilatory responses in vascular endothelial cells. Calcium-dependent PKCbeta (PKCβ) and calcium-independent PKCeta (PKCη) have both been implicated in the regulation and dysfunction of endothelial responses to shear stress and agonists. ObjectiveWe hypothesized that PKCβ and PKCη differentially modulate shear stress-induced nitric oxide (NO) production by regulating the transduced calcium signals and the resultant eNOS activation. As such, this study sought to characterize the contribution of PKCη and PKCβ in regulating calcium signaling and endothelial nitric oxide synthase (eNOS) activation after exposure of endothelial cells to ATP or shear stress. MethodsBovine aortic endothelial cells were stimulated in vitro under pharmacological inhibition of PKCβ with LY333531 or PKCη targeting with a pseudosubstrate inhibitor. The participation of PKC isozymes in calcium flux, eNOS phosphorylation and NO production was assessed following stimulation with ATP or shear stress. ResultsPKCη proved to be a robust regulator of agonist- and shear stress-induced eNOS activation, modulating calcium fluxes and tuning eNOS activity by multi-site phosphorylation. PKCβ showed modest influence in this pathway, promoting eNOS activation basally and in response to shear stress. Both PKC isozymes contributed to the constitutive and induced phosphorylation of eNOS. The observed PKC signaling architecture is intricate, recruiting Src to mediate a portion of PKCη's control on calcium entry and eNOS phosphorylation. Elucidation of the importance of PKCη in this pathway was tempered by evidence of a single stimulus producing concurrent phosphorylation at ser1179 and thr497 which are antagonistic to eNOS activity. ConclusionsWe have, for the first time, shown in a single species in vitro that shear stress- and ATP-stimulated NO production are differentially regulated by classical and novel PKCs. This study furthers our understanding of the PKC isozyme interplay that optimizes NO production. These considerations will inform the ongoing design of drugs for the treatment of PKC-sensitive cardiovascular pathologies.

8‐oxoguanine glycosylase (OGG1) is a determinant of endothelial dysfunction via calcium and nitric oxide signaling

Diabetes mellitus is a chronic disease that hinders the body's ability to produce or respond to the hormone insulin, resulting in abnormal metabolism and elevated glucose levels. Type II diabetes has been characterized by a two-to-four-fold increase in cardiovascular disease, such as carotid artery stenosis, generally attributed to the adverse effects of hyperglycemia and oxidative stress on vascular biology. With it being a very common and significant health complication, understanding the pathology and the mechanisms by which diabetes-induced oxidative stress serves as a precursor to several notable vascular diseases is paramount, and is the overall objective of this study. Endothelial dysfunction (ED) is a vascular phenomenon attributed to a reduction in nitric oxide (NO) bioactivity and an increase in oxygen free radical formation with subsequent oxidative stress, thus leading to impaired vasodilation, and compromised vascular function. ED tends to be a consistent finding in diabetes. A major source of oxidative stress is the abnormal production of reactive oxygen species (ROS) in the context of diabetic inflammation. Increased ROS production leads to mitochondrial DNA (mt DNA) damage and aberrant cell signaling. Typically, mt DNA damage is repaired through the base excision repair (BER) pathway. However, during chronic inflammation in diabetes, this repairing capability is ineffective due to downregulation of key BER enzymes, namely 8-oxoguanine glycosylase (OGG1). Given this rational, we hypothesized that the BER pathway is an important determinant of endothelial dysfunction via impaired calcium and NO signaling. To test this hypothesis, we examined the effect of BER defects on endothelial calcium signaling and NO production using carotid arteries isolated from mice deficient in OGG1. Opened artery measurements of endothelial calcium and NO signaling were performed using a custom-designed parallel plate flow chamber. Briefly, segments of carotid arteries (~200 µm in diameter) were isolated from OGG1 deficient (KO) and wild type (WT) mice and cut open lengthwise to expose the endothelial surface. The isolated vessels were then stained with a loading solution composed of Pluronic acid (Fischer), Cal-520 (AAT bio) calcium indicator dye and DAR-4M (Calbiochem), a fluorescent probe for NO. Time lapse signal measurements were collected via confocal microscopy and were then analyzed and processed with S8, a custom automated solution to signal analysis based on noise filtering and object tracking, which computed dynamic amplitude, frequency, duration, and spatial spread. We discovered that although the number of calcium signals detected within the measurement interval were similar between KO and WT (10 ± 3 vs 9 ± 3, µ ± SEM, respectively), the spatial spread of signals within the KO (19.95 ± 3.78 µm2, µ ± SEM) was greater than WT (9.65 ± 2.7 µm2, p = 0.057 via Welch's unpaired t-test). These data suggest that OGG1 may be a determinant of normal endothelial calcium signaling and might serve as a therapeutic target for preventing the adverse effects of endothelial dysfunction present in diabetes.

Calcium Signal Profiles in Vascular Endothelium from Cdh5-GCaMP8 and Cx40-GCaMP2 Mice

Introduction: Studies in Cx40-GCaMP2 mice, which express calcium biosensor GCaMP2 in the endothelium under connexin 40 promoter, have identified the unique properties of endothelial calcium signals. However, Cx40-GCaMP2 mouse is associated with a narrow dynamic range and lack of signal in the venous endothelium. Recent studies have proposed many GCaMPs (GCaMP5/6/7/8) with improved properties although their performance in endothelium-specific calcium studies is not known. Methods: We characterized a newly developed mouse line that constitutively expresses GCaMP8 in the endothelium under the VE-cadherin (Cdh5-GCaMP8) promoter. Calcium signals through endothelial IP3 receptors and TRP vanilloid 4 (TRPV4) ion channels were recorded in mesenteric arteries (MAs) and veins from Cdh5-GCaMP8 and Cx40-GCaMP2 mice. Results: Cdh5-GCaMP8 mice showed lower baseline fluorescence intensity, higher dynamic range, and higher amplitudes of individual calcium signals than Cx40-GCaMP2 mice. Importantly, Cdh5-GCaMP8 mice enabled the first recordings of discrete calcium signals in the intact venous endothelium and revealed striking differences in IP3 receptor and TRPV4 channel calcium signals between MAs and mesenteric veins. Conclusion: Our findings suggest that Cdh5-GCaMP8 mice represent significant improvements in dynamic range, sensitivity for low-intensity signals, and the ability to record calcium signals in venous endothelium.

Mitochondria Amplify TRPV4‐dependent Calcium Dynamics within the Pulmonary Microvascular Endothelium

Acute respiratory distress syndrome (ARDS) is an inflammatory lung disease common in critically ill patients marked by diffuse alveolar damage and increased pulmonary endothelial barrier permeability. A large body of evidence supports the role of mitochondrial dysfunction in ARDS, which has been shown to mediate endothelial permeability. For example, in cultured rat pulmonary microvascular endothelial cells (PMVECs), the mitochondrial complex I inhibitor rotenone increases endothelial permeability and in isolated perfused lung studies, rotenone increases the pulmonary vascular filtration coefficient. In both cell culture and isolated perfused lungs, the amphipathic quinone coenzyme Q1 (CoQ1) rescues rotenone‐dependent increases in endothelial permeability by bypassing complex I to restore mitochondrial bioenergetics.The transient receptor potential vanilloid protein 4 (TRPV4), a mechanically gated calcium channel, has also been implicated in mediating endothelial permeability by increasing intracellular calcium in response to high pressure ventilation. The phorbol ester 4α‐phorbol‐12,13‐didecanoate (4αPDD) provides a pharmacological means of TRPV4 activation and stimulates endothelial permeability responses in both cell culture and animal models of lung injury. Given that mitochondria actively participate in calcium buffering, we hypothesized that TRPV4‐dependent calcium signals may be compartmentalized by mitochondria. To test this hypothesis, we used confocal microscopy to measure calcium signals in PMVECs in response to TRPV4 activation via 4αPDD (5 μM) after treatment with vehicle, rotenone (0.5 μM), or rotenone in combination with CoQ1 (10 μM), and developed a sensitive, automated technique for intracellular calcium signal transient analysis.Using our novel analysis approach, we found that rotenone significantly decreased the number of calcium signal transients stimulated by 4αPDD over a 15 minute interval (mean ± SEM: 22 ± 4 rotenone vs 96 ± 14 vehicle, p <0.01), and that CoQ1 in combination with rotenone reversed this effect (60 ± 15, p = n.s. vs vehicle). Rotenone also dampened the amplitude of calcium responses to TRPV4, an effect that was partially restored by CoQ1. These findings support the hypothesis that mitochondria regulate TRPV4‐mediated calcium dynamics by amplifying calcium signals, and that mitochondrial dysfunction impairs this phenomenon. This suggests that mitochondrial regulation of endothelial calcium signaling is essential to the maintenance of barrier integrity and provides a possible therapeutic target in ARDS.Support or Funding InformationNIH K25HL136869 and NIH P01 HL066299‐17

S100A6 is a positive regulator of PPP5C-FKBP51-dependent regulation of endothelial calcium signaling.

ISOC is a cation current permeating the ISOC channel. In pulmonary endothelial cells, ISOC activation leads to formation of inter-endothelial cell gaps and barrier disruption. The immunophilin FK506-binding protein 51 (FKBP51), in conjunction with the serine/threonine protein phosphatase 5C (PPP5C), inhibits ISOC . Free PPP5C assumes an autoinhibitory state, which has low "basal" catalytic activity. Several S100 protein family members bind PPP5C increasing PPP5C catalytic activity in vitro. One of these family members, S100A6, exhibits a calcium-dependent translocation to the plasma membrane. The goal of this study was to determine whether S100A6 activates PPP5C in pulmonary endothelial cells and contributes to ISOC inhibition by the PPP5C-FKBP51 axis. We observed that S100A6 activates PPP5C to dephosphorylate tau T231. Following ISOC activation, cytosolic S100A6 translocates to the plasma membrane and interacts with the TRPC4 subunit of the ISOC channel. Global calcium entry and ISOC are decreased by S100A6 in a PPP5C-dependent manner and by FKBP51 in a S100A6-dependent manner. Further, calcium entry-induced endothelial barrier disruption is decreased by S100A6 dependent upon PPP5C, and by FKBP51 dependent upon S100A6. Overall, these data reveal that S100A6 plays a key role in the PPP5C-FKBP51 axis to inhibit ISOC and protect the endothelial barrier against calcium entry-induced disruption.

Increased Vascular Contractility in Hypertension Results From Impaired Endothelial Calcium Signaling.

Endothelial cells line all blood vessels and are critical regulators of vascular tone. In hypertension, disruption of endothelial function alters the release of endothelial-derived vasoactive factors and results in increased vascular tone. Although the release of endothelial-derived vasodilators occurs in a Ca2+-dependent manner, little is known on how Ca2+ signaling is altered in hypertension. A key element to endothelial control of vascular tone is Ca2+ signals at specialized regions (myoendothelial projections) that connect endothelial cells and smooth muscle cells. This work describes disruption in the operation of this key Ca2+ signaling pathway in hypertension. We show that vascular reactivity to phenylephrine is increased in hypertensive (spontaneously hypertensive rat) when compared with normotensive (Wistar Kyoto) rats. Basal endothelial Ca2+ activity limits vascular contraction, but that Ca2+-dependent control is impaired in hypertension. When changes in endothelial Ca2+ levels are buffered, vascular contraction to phenylephrine increased, resulting in similar responses in normotension and hypertension. Local endothelial IP3(inositol trisphosphate)-mediated Ca2+ signals are smaller in amplitude, shorter in duration, occur less frequently, and arise from fewer sites in hypertension. Spatial control of endothelial Ca2+ signaling is also disrupted in hypertension: local Ca2+ signals occur further from myoendothelial projections in hypertension. The results demonstrate that the organization of local Ca2+ signaling circuits occurring at myoendothelial projections is disrupted in hypertension, giving rise to increased contractile responses.

Human myometrial artery function and endothelial cell calcium signalling are reduced by obesity: Can this contribute to poor labour outcomes?

Determining how obesity affects function in human myometrial arteries, to help understand why childbirth has poor outcomes in obese women. Myometrial arteries were studied from 84 biopsies. Contraction (vasopressin and U-46619) and relaxation (carbachol, bradykinin, SNAP) was assessed using wire myography. eNOS activity was assessed using L-NAME. Cholesterol was reduced using methyl-β-cyclodextrin to determine whether it altered responses. Differences in endothelial cell intracellular Ca2+ signalling were assessed using confocal microscopy. The effects of BMI on relaxation were agonist specific and very marked; all vessels, irrespective of BMI, relaxed to bradykinin but 0% of vessels (0/13) from obese women relaxed to carbachol, compared to 59% (10/17) from normal weight women. Cholesterol-lowering drugs did not restore carbachol responses (n=6). All vessels, irrespective of BMI, relaxed when NO was directly released by SNAP (n=19). Inhibition of eNOS with L-NAME had a significant effect in normal but not overweight/obese vessels. Compared to bradykinin, a lower proportion of endothelial cells responded to carbachol and the amplitude of the calcium response was significantly less, in all vessels. Furthermore, a significantly lower proportion of endothelial cells responded to carbachol in the overweight/obese group compared to control. In contrast to relaxation, the effect of contractile agonists was unchanged with increasing BMI. The ability of human myometrial arteries to relax is significantly impaired with obesity, and our data suggest this is due to a deficit in endothelial calcium signalling. This inability to recover following compression during contractions, might contribute to poor labours in obese women.

Endothelial Calmodulin and CaMKII Play a Role in Leukocyte Transmigration

Inflammation results in the dilation of blood vessels and recruitment of circulating leukocytes into damaged tissues for repair. A transient increase in endothelial cytosolic free calcium (↑[Ca2+]i) is required for leukocyte transendothelial migration (TEM). We have also found that IQ‐domain GTPase‐activating protein 1 (IQGAP1) is essential for TEM. Specifically, the calmodulin‐binding isoleucine‐glutamine (IQ) motif domain is critical for its function during TEM. Calmodulin (CaM) is an intracellular calcium‐binding protein, however, its role in TEM is undescribed. Therefore, we hypothesized that it is involved in the endothelial calcium signaling cascade essential for supporting leukocyte transmigration.In endothelial cells IQGAP1 knockdown reduced TEM substantially. Re‐expressing IQGAP1 truncation mutants containing both the actin‐binding and IQ‐motif domains rescued TEM but truncation mutants lacking the IQ motif domain but did not support TEM.Human endothelial cells treated with the calmodulin inhibitor trifluoperazine (TFP) demonstrated a marked reduction in leukocyte TEM. Only 13% of leukocytes transmigrated through endothelial monolayers pretreated with 100 mM TFP compared to 84% TEM in control, untreated monolayers (p<0.05). We also looked at the role of calmodulin kinase II (CaMKII). Treating endothelial monolayers with 10 mM KN‐93, a CaMKII inhibitor, substantially reduced leukocyte TEM. Here 22% of leukocytes transmigrated which was significantly reduced compared to control TEM rates (p<0.05). Calmodulin pulldowns also showed that without the IQ‐motif domain IQGAP1 cannot substantially interact with calmodulin further suggesting a link between endothelial calcium, IQGAP1 and CaM.Current experiments focus on inhibiting CaM and CaMKII in endothelial cells using genetically encoded selective inhibitory peptides and inducible endothelial‐specific CaMKII‐deficient mice. Identifying the mechanism by which endothelial Ca2+ influx mediates TEM will provide novel insight into the signaling and also provide potential targets for anti‐inflammatory therapy.Support or Funding InformationR01 HL046849, R01 HL064774, F30 HL134202This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Automated Intracellular Calcium Profiles Extraction from Endothelial Cells Using Digital Fluorescence Images.

Endothelial cells perform a wide variety of fundamental functions for the cardiovascular system, their proliferation and migration being strongly regulated by their intracellular calcium concentration. Hence it is extremely important to carefully measure endothelial calcium signals under different stimuli. A proposal to automate the intracellular calcium profiles extraction from fluorescence image sequences is presented. Digital image processing techniques were combined with a multi-target tracking approach supported by Kalman estimation. The system was tested with image sequences from two different stimuli. The first one was a chemical stimulus, that is, ATP, which caused small movements in the cells trajectories, thereby suggesting that the bath application of the agonist does not generate significant artifacts. The second one was a mechanical stimulus delivered by a glass microelectrode, which caused major changes in cell trajectories. The importance of the tracking block is evidenced since more accurate profiles were extracted, mainly for cells closest to the stimulated area. Two important contributions of this work are the automatic relocation of the region of interest assigned to the cells and the possibility of data extraction from big image sets in efficient and expedite way. The system may adapt to different kind of cell images and may allow the extraction of other useful features.

CORM-401 induces calcium signalling, NO increase and activation of pentose phosphate pathway in endothelial cells.

Carbon monoxide-releasing molecules (CO-RMs) induce nitric oxide (NO) release (which requires NADPH), and Ca2+ -dependent signalling; however, their contribution in mediating endothelial responses to CO-RMs is not clear. Here, we studied the effects of CO liberated from CORM-401 on NO production, calcium signalling and pentose phosphate pathway (PPP) activity in human endothelial cell line (EA.hy926). CORM-401 induced NO production and two types of calcium signalling: a peak-like calcium signal and a gradual increase in cytosolic calcium. CORM-401-induced peak-like calcium signal, originating from endoplasmic reticulum, was reduced by thapsigargin, a SERCA inhibitor, and by dantrolene, a ryanodine receptors (RyR) inhibitor. In contrast, the phospholipase C inhibitor U73122 did not significantly affect peak-like calcium signalling, but a slow and progressive CORM-401-induced increase in cytosolic calcium was dependent on store-operated calcium entrance. CORM-401 augmented coupling of endoplasmic reticulum and plasmalemmal store-operated calcium channels. Interestingly, in the presence of NO synthase inhibitor (l-NAME) CORM-401-induced increases in NO and cytosolic calcium were both abrogated. CORM-401-induced calcium signalling was also inhibited by superoxide dismutase (poly(ethylene glycol)-SOD). Furthermore, CORM-401 accelerated PPP, increased NADPH concentration and decreased the ratio of reduced to oxidized glutathione (GSH/GSSG). Importantly, CORM-401-induced NO increase was inhibited by the PPP inhibitor 6-aminonicotinamide (6-AN), but neither by dantrolene nor by an inhibitor of large-conductance calcium-regulated potassium ion channel (paxilline). The results identify the primary role of CO-induced NO increase in the regulation of endothelial calcium signalling, that may have important consequences in controlling endothelial function.

P2 The action of endothelial–derived acetylcholine is impaired in diabetes

The endothelium is highly sensitive to acetylcholine and responds to the neurotransmitter by releasing vasodilators that control smooth muscle tone. However, acetylcholine is not expected to reach the endothelium through the vessel wall or via blood. Here, by studying calcium signalling in large areas of the endothelium of intact arteries, we show: (1) the endothelium itself is a source of acetylcholine, (2) acetylcholine release from the endothelium underlies flow-mediated vascular responses; and (3) flow-mediated responses are all but abolished in a rat model of diabetes. Calcium signalling was studied in large fields of intact endothelia (~150 cells) of carotid and mesenteric arteries from healthy and diabetic rats (Sprague-Dawley, 150–250 g). In both carotid and mesenteric arteries, flow evoked repeatable endothelial calcium signalling. Importantly, flow-mediated calcium responses could be manipulated by modulating cholinergic signalling pathways: the muscarinic receptor blocker, atropine (100 nM), and the acetylcholine hydrolase, acetylcholinesterase (4 U/ml), each abolished flow-induced calcium activity, whilst the acetylcholinesterase inhibitor, neostigmine (10 µM), enhanced calcium activity, and the choline acetyltransferase inhibitor, bromoacetylcholine (50?µM), attenuated responses. Significantly, responses were reduced in diabetic, compared to control, endothelia. Indeed, the number of diabetic endothelial cells responding to flow was 45% of control, and the peak and time-averaged magnitude of calcium signals was reduced to 54% and 12% of control, respectively. These results identify the endothelium as a source of non-neuronal acetylcholine release and thus demonstrate the reason for the endothelium’s sensitivity to acetylcholine. Significantly, reduced acetylcholine release may underlie the pathophysiology and endothelial dysfunction that occurs in diabetes.

Impaired endothelial calcium signaling is responsible for the defective dilation of mesenteric resistance arteries from db/db mice to acetylcholine

We aimed at assessing the role of endothelial cell calcium for the endothelial dysfunction of mesenteric resistance arteries of db/db mice (a model of type 2 diabetes) and determine whether treatment with sulfaphenazole, improves endothelial calcium signaling and function. Pressure myography was used to study acetylcholine (ACh) -induced vasodilation. Intracellular calcium ([Ca2+]i) transients was measured by confocal laser scanning microscopy and smooth muscle membrane potential with sharp microelectrodes. The impaired dilation to ACh observed in mesenteric resistance arteries from db/db mice was improved by treatment of the mice with sulfaphenazole for 8 weeks. The impaired dilation to ACh was associated with decreased endothelial [Ca2+]i and smooth muscle hyperpolarization. Sulfaphenazole applied in vitro improved endothelial mediated dilation of arteries from db/db mice both in the absence and the presence of inhibitors of nitric oxide and cyclooxygenase. Sulfaphenazole also increased the percentage of endothelial cells with ACh induced increases of [Ca2+]i. The study shows that impaired endothelial [Ca2+]i control can explain the reduced endothelial function in arteries from diabetic mice and that sulfaphenazole treatment improves endothelial [Ca2+]i responses to ACh and consequently endothelium-dependent vasodilation. These observations provide mechanistic insight into endothelial dysfunction in diabetes.

Genetic deficit of KCa 3.1 channels protects against pulmonary circulatory collapse induced by TRPV4 channel activation.

The intermediate conductance calcium/calmodulin-regulated K+ channel KCa 3.1 produces hyperpolarizing K+ currents that counteract depolarizing currents carried by transient receptor potential (TRP) channels, and provide the electrochemical driving force for Cl- and fluid movements. We investigated whether a deficiency in KCa 3.1 (KCa 3.1-/- ) protects against fatal pulmonary circulatory collapse in mice after pharmacological activation of the calcium-permeable TRP subfamily vanilloid type 4 (TRPV4) channels. An opener of TRPV4 channels, GSK1016790A, was infused in wild-type (wt) and KCa 3.1-/- mice; haemodynamic parameters, histology and pulmonary vascular reactivity were measured; and patch clamp was performed on pulmonary arterial endothelial cells (PAEC). In wt mice, GSK1016790A decreased right ventricular and systemic pressure leading to a fatal circulatory collapse that was accompanied by increased protein permeability, lung haemorrhage and fluid extravasation. In contrast, KCa 3.1-/- mice exhibited a significantly smaller drop in pressure to GSK1016790A infusion, no haemorrhage and fluid water extravasation, and the mice survived. Moreover, the GSK1016790A-induced relaxation of pulmonary arteries of KCa 3.1-/- mice was significantly less than that of wt mice. GSK1016790A induced TRPV4 currents in PAEC from wt and KCa 3.1-/- mice, which co-activated KCa 3.1 and disrupted membrane resistance in wt PAEC, but not in KCa 3.1-/- PAEC. Our findings show that a genetic deficiency of KCa 3.1 channels prevented fatal pulmonary circulatory collapse and reduced lung damage caused by pharmacological activation of calcium-permeable TRPV4 channels. Therefore, inhibition of KCa 3.1channels may have therapeutic potential in conditions characterized by abnormal high endothelial calcium signalling, barrier disruption, lung oedema and pulmonary circulatory collapse.

0168 : Endothelium dependent relaxation and T-type voltage-gated calcium channels

T-type voltage-gated calcium channels (T-VGCC) are involved in the regulation of pulmonary arterial tone. Besides their roles in smooth muscle cell contraction, we investigate if T-VGCC could control vascular relaxation via endothelial calcium signaling regulation in mouse pulmonary arteries. Immunofluorescence labeling indicates that endothelial cells (as well as smooth muscle cells) express T-VGCC proteins (Cav3.1 and Cav3.2 isotypes). We show that nitric oxide (NO)-dependent relaxation induced by acetylcholine is reduced in the presence of T-VGCC antagonists (mibefradil, NNC 55- 0396) and in Cav3.1 knock-out mice. Acetylcholine induces an endothelial intracellular calcium increase which is reduced by the same types of inhibitors. By contrast, endothelium dependent relaxation induced by beta 2 adrenergic stimulation (with procaterol), which is calcium independent, is not inhibited by mibefradil or in Cav3.1 knock-out mice. Furthermore, in pathological condition (pulmonary hypertension induced by a chronic hypoxia), acetylcholine-mediated relaxation is reduced and even more in Cav3.1 knockout mice. In summary, in mice pulmonary arteries, acetylcholine and calciumdependent dilatation require T-VGCC. The present findings suggest that calcium influx through T-VGCC mediate a dual effect in pulmonary artery: a contraction when it occurred in smooth muscle cells and a dilatation when it occurred in endothelial cells.