Mechanisms of U46619-induced contraction in mouse intrarenal artery

Investigating the Mechanisms Underlying U46619-Induced Contraction on Porcine Lower Esophageal Sphincter

Gastroesophageal reflux disease (GERD) is associated with an incompetent lower esophageal sphincter (LES), resulting in the reflux of gastric contents into the esophagus. U46619, a thromboxane A2 (TXA2) receptor agonist, induces contractions in various smooth muscles. Therefore, this study aimed to investigate the effects and mechanisms of action of U46619 on the porcine LES. To achieve this, contractions of the clasp and sling strips of the porcine LES, induced by U46619, were measured using isometric transducers. Furthermore, the contractile mechanism of U46619 in the porcine LES was investigated by pretreating the strips with atropine (a muscarinic receptor antagonist), tetrodotoxin (a neuronal sodium channel blocker), nifedipine (a calcium channel blocker), and Ca2+-free Krebs-Henseleit solution. Additionally, reverse transcription polymerase chain reaction (PCR) and immunohistochemistry (IHC) were performed to determine the presence of the TXA2 receptor in porcine LES. The results of this study demonstrated that U46619 caused marked concentration-dependent contractions in both porcine sling and clasp strips. The mechanism of U46619-induced contraction of the porcine LES was found to be related to calcium channels. Furthermore, the reverse transcription PCR analysis and IHC revealed that the TXA2 receptor was expressed in the clasp and sling fibers of porcine LES. Consequently, this study suggests that U46619 mediates the contraction of porcine LES through calcium channels and has potential as a therapeutic approach for treating GERD. SIGNIFICANCE STATEMENT: This study establishes that U46619 induces concentration-dependent contractions in porcine LES, primarily mediated by calcium channels. The presence of the TXA2 receptor in LES clasp and sling fibers is confirmed. These findings highlight U46619's potential as a GERD therapeutic by targeting calcium channels for LES contraction modulation.

Pharmacological study on the enhancing effects of U46619 on guinea pig urinary bladder smooth muscle contraction induced by acetylcholine and α,β-methylene ATP and the possible involvement of protein kinase C

We examined whether U46619 (a prostanoid TP receptor agonist) could enhance the contractions of guinea pig urinary bladder smooth muscle (UBSM) in response to acetylcholine (ACh) and an ATP analog (α,β-methylene ATP (αβ-MeATP)) through stimulation of the UBSM TP receptor and whether protein kinase C (PKC) is involved. U46619 (10-7 M) markedly enhanced UBSM contractions induced by electrical field stimulation and ACh/αβ-MeATP (3 × 10-6 M each), the potentiation of which was completely suppressed by SQ 29,548 (a TP receptor antagonist, 6 × 10-7 M). PKC inhibitors did not attenuate the ACh-induced contractions enhanced by U46619 although they partly suppressed the U46619-enhanced, αβ-MeATP-induced contractions. While phorbol 12-myristate 13-acetate (PMA, a PKC activator, 10-6 M) did not enhance ACh-induced contractions, it enhanced αβ-MeATP-induced contractions, an effect that was completely suppressed by PKC inhibitors. αβ-MeATP-induced contractions, both with and without U46619 enhancement, were strongly inhibited by diltiazem. U46619/PMA enhanced 50 mM KCl-induced contractions, the potentiation of which was partly/completely attenuated by PKC inhibitors. These findings suggest that U46619 potentiates parasympathetic nerve-associated UBSM contractions by stimulating UBSM TP receptors. PKC-increased Ca2+ influx through voltage-dependent Ca2+ channels may partially play a role in purinergic receptor-mediated UBSM contractions enhanced by TP receptor stimulation.

The integrin ligand SVEP1 regulates GPCR-mediated vasoconstriction via integrins α9β1 and α4β1

BACKGROUND AND PURPOSE

Vascular tone is regulated by the relative contractile state of vascular smooth muscle cells (VSMCs). Several integrins directly modulate VSMC contraction by regulating calcium influx through L-type voltage-gated Ca²⁺ channels (VGCCs). Genetic variants in ITGA9, which encodes the α9 subunit of integrin α9β1, and SVEP1, a ligand for integrin α9β1, associate with elevated blood pressure; however, neither SVEP1 nor integrin α9β1 has reported roles in vasoregulation. We determined whether SVEP1 and integrin α9β1 can regulate VSMC contraction.

EXPERIMENTAL APPROACH

SVEP1 and integrin binding were confirmed by immunoprecipitation and cell binding assays. Human induced pluripotent stem cell-derived VSMCs were used in in vitro [Ca²⁺ ]_i studies, and aortas from a Svep1^+/- knockout mouse model were used in wire myography to measure vessel contraction.

KEY RESULTS

We confirmed the ligation of SVEP1 to integrin α9β1 and additionally found SVEP1 to directly bind to integrin α4β1. Inhibition of SVEP1, integrin α4β1 or α9β1 significantly enhanced [Ca²⁺ ]_i levels in isolated VSMCs to Gα_q/11 -vasoconstrictors. This response was confirmed in whole vessels where a greater contraction to U46619 was seen in vessels from Svep1^+/- mice compared to littermate controls or when integrin α4β1 or α9β1 was inhibited. Inhibition studies suggested that this effect was mediated via VGCCs, PKC and Rho A/Rho kinase dependent mechanisms.

CONCLUSIONS AND IMPLICATIONS

Our studies reveal a novel role for SVEP1 and the integrins α4β1 and α9β1 in reducing VSMC contractility. This could provide an explanation for the genetic associations with blood pressure risk at the SVEP1 and ITGA9 loci.

PM2.5 causes vascular hyperreactivity through the upregulation of the thromboxane A2 receptor and activation of MAPK pathways

Airborne fine particulate matter (PM_2.5) is a major cardiovascular disease environmental risk factor. However, the underlying mechanism of action is not fully understood. Thromboxane is widely known as an important vasoconstrictor substance that binds to G-protein-coupled receptors (GPCR) in arteries and is involved in various cardiovascular diseases. This study examined the effect of PM_2.5 on thromboxane A₂ receptor (TP) in the mesenteric arteries and the underlying intracellular signal mechanisms (by focusing on the mitogen-activated protein kinase (MAPK) pathway). Rat mesenteric artery segments were exposed to PM_2.5 in the presence of MAPK pathway inhibitors. The contractile reactivity of mesenteric arteries was analyzed using wire myography. The mRNA and protein expression of TP receptor and MAPK pathway molecules were detected by real-time PCR and Western blot. Mesenteric artery receptor localization was assessed by immunohistochemistry. The results showed that TP receptor-mediated maximum contraction response was achieved after exposing arteries to 1.0 μg/mL PM_2.5 for 16 h (Emax: 228 ± 16% of K⁺). Moreover, inhibitor U0126 (ERK1/2 inhibitor), SB203580 (p38 inhibitor), and SP600125 (JNK inhibitor) depressed the increased TP receptor-mediated contractile responses (reduced rage were 17.9 ~ 59.6%). These inhibitors also decreased the increased mRNA expression and protein of the TP receptor induced by PM_2.5 (reduced by more than 50% and 46%, respectively). The immunoreactivity of increased TP receptor expression was primarily localized in the cytoplasm. In addition, phosphorylation quantitative analysis showed that in the presence of MAPK inhibitors, the PM_2.5-induced phosphorylation of ERK1/2, p38, and JNK protein increased by more than 30.0 ~ 130.3%. These results suggest that PM_2.5 upregulates the TP receptor of rat mesenteric arteries through activation of the ERK1/2, p38, and JNK MAPK pathways.

VEGFR2 in vascular smooth muscle cells mediates H2S-induced dilation of the rat cerebral basilar artery

INTRODUCTION

The aim of present study was to study whether the vascular endothelial growth factor receptor 2 (VEGFR₂) mediates hydrogen sulfide (H₂S)-induced relaxation of the rat cerebral vasculature.

METHODS

Relaxation of cerebral basilar artery (CBA) and vascular smooth muscle cells (VSMCs) was measured by using a pressure myograph system and image analysis system, respectively. The intracellular calcium concentration ([Ca²⁺]_i) in VSMCs was detected using fluorescence imaging analysis.

RESULTS

We found that H₂S donor NaHS induced significant relaxation of VSMCs from the CBA of wild type rat, but in VEGFR₂ knockdown VSMCs, NaHS-induced relaxation reduced markedly. In addition, NaHS-induced vasodilation of rat CBA also attenuated obviously when the expression of VEGFR₂ was knocked down in vivo. In addition, pretreatment with the VEGFR₂ blocker SU5416 likewise lowered the NaHS-induced relaxation of rat CBA. Nevertheless, the VEGFR₂ agonist, vascular endothelial growth factor 164 (VEGF164), induced a concentration-dependent relaxation of CBA, which is similar to the effect of NaHS. Furthermore, we found that both NaHS and VEGF164 significantly inhibited the U₄₆₆₁₉-induced increase of [Ca²⁺]_i fluorescence intensity in the VSMCs. However, the inhibitory effect of NaHS on the [Ca²⁺]_i fluorescence intensity in VSMCs was markedly inhibited by pretreatment with SU5416 or VEGFR₂ knockdown.

CONCLUSION

These findings indicated that H₂S-induced CBA dilation and reduction of [Ca²⁺]_i in VSMCs occur by acting on VEGFR₂.

Signalling pathway of U46619-induced vascular smooth muscle contraction in mouse coronary artery

BACKGROUND

Thromboxane A2 (TXA2 ) participates in many pathophysiological processes of coronary artery disease. However, its mechanism of TXA2 -induced contraction in the coronary artery remains to be clarified. A multi myograph system was used to measure the isometric tension of the mouse coronary arteries and identify the effect and pathway of TXA2 analogues U46619. Confocal laser scanning microscopy was used to measure the intracellular calcium concentration ([Ca2+ ]i ) in mouse coronary artery smooth muscle cells. Results from the experiment had shown that contraction in coronary artery was generated by U46619 in a concentration-dependent manner, which was completely abolished by a specific TXA2 receptor blocker, GR32191. PI-PLC inhibitors U73122 and D609 and Rho-Kinase inhibitor Y-27632 can block the U46619 elicited coronary artery contraction in a dose-dependent manner. Then, the vasoconstriction response to U46619 was obviously inhibited by two pan-PKC inhibitors chelerythrine or Gӧ6983, and a selective PKCδ inhibitor rottlerin, but was not blocked by a selective PKCζ inhibitor PKC-PS or a selective PKCβ inhibitor hispidin. Meanwhile, the PKC activator PDBu-induced vasoconstriction was significantly inhibited by 1 μmol/L nifedipine, then mostly inhibited by 100 μmol/L 2-APB and 10 μmol/L Y27632. We further found that the response to U46619 was inhibited, respectively, by three calcium channel blockers nifedipine, SKF96356 or 2-APB in a concentration-dependent manner. Although Store-operated Ca2+ (SOC) channels generated the increase of [Ca2+ ]i in mouse coronary artery smooth muscle cells, SOC channels did not contribute to the vasoconstriction in mouse coronary arteries. Caffeine-induced sarcoplasmic reticulum (SR) Ca2+ release could obviously induce coronal vasoconstriction. In addition, NPPB, a cell membrane Ca2+ activated C1- channel blocker, could obviously inhibit the U46619-induced vasoconstriction. The U46619-induced mouse coronary artery contraction was involved in the increase in [Ca2+ ]i mediated by Cav1.2, TRPC channels and SR release through the activation of G-protein-coupled TP receptors and the kinases signalling pathway in TP downstream proteins, while SOC channels did not participate in the vasoconstriction.

Eicosanoid blood vessel regulation in physiological and pathological states

Arachidonic acid can be metabolized in blood vessels by three primary enzymatic pathways; cyclooxygenase (COX), lipoxygenase (LO), and cytochrome P450 (CYP). These eicosanoid metabolites can influence endothelial and vascular smooth muscle cell function. COX metabolites can cause endothelium-dependent dilation or constriction. Prostaglandin I2 (PGI2) and thromboxane (TXA2) act on their respective receptors exerting opposing actions with regard to vascular tone and platelet aggregation. LO metabolites also influence vascular tone. The 12-LO metabolite 12S-hydroxyeicosatrienoic acid (12S-HETE) is a vasoconstrictor whereas the 15-LO metabolite 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA) is an endothelial-dependent hyperpolarizing factor (EDHF). CYP enzymes produce two types of eicosanoid products: EDHF vasodilator epoxyeicosatrienoic acids (EETs) and the vasoconstrictor 20-HETE. The less-studied cross-metabolites generated from arachidonic acid metabolism by multiple pathways can also impact vascular function. Likewise, COX, LO, and CYP vascular eicosanoids interact with paracrine and hormonal factors such as the renin-angiotensin system and endothelin-1 (ET-1) to maintain vascular homeostasis. Imbalances in endothelial and vascular smooth muscle cell COX, LO, and CYP metabolites in metabolic and cardiovascular diseases result in vascular dysfunction. Restoring the vascular balance of eicosanoids by genetic or pharmacological means can improve vascular function in metabolic and cardiovascular diseases. Nevertheless, future research is necessary to achieve a more complete understanding of how COX, LO, CYP, and cross-metabolites regulate vascular function in physiological and pathological states.

Effect of mitochondrial complex III inhibitors on the regulation of vascular tone in porcine coronary artery

In order to gain insight into the regulation of vascular tone by mitochondria, the effects of mitochondrial complex III inhibitors on contractile responses in porcine isolated coronary arteries were investigated. Segments of porcine coronary arteries were set up for isometric tension recording and concentration response curves to contractile agents were carried out in the absence or presence of the complex III inhibitors antimycin A or myxothiazol. Activity of AMP kinase was determined by measuring changes in phosphorylation of AMP kinase at Thr172. Pre-incubation with 10 μM antimycin A (Q_i site inhibitor), or myxothiazol (Q_o site inhibitor) led to inhibition of the contraction to the thromboxane receptor agonist U46619. Similar effects were seen on contractile responses to extracellular calcium, and the L-type calcium channel opener BAY K 8644, suggesting that both antimycin A and myxothiazol inhibit calcium-dependent contractions. The inhibitory effect of antimycin A was still seen in the absence of extracellular calcium, indicating an additional effect on a calcium independent pathway. The AMP kinase inhibitor dorsomorphin (10 μM) prevented the inhibitory of antimycin A but not myxothiazol. Furthermore, antimycin A increased the phosphorylation of AMP kinase, indicating an increase in activity, suggesting that antimycin A also acts through this pathway. These data indicate that inhibition of complex III attenuates contractile responses through inhibition of calcium influx. However, inhibition of the Q_i site can also inhibit the contractile response through activation of AMP kinase.

NO-induced vasodilation correlates directly with BP in smooth muscle-Na/Ca exchanger-1-engineered mice: elevated BP does not attenuate endothelial function

Arterial smooth muscle Na+/Ca2+ exchanger-1 (SM-NCX1) promotes vasoconstriction or vasodilation by mediating, respectively, Ca2+ influx or efflux. In vivo, SM-NCX1 mediates net Ca2+ influx to help maintain myogenic tone (MT) and neuronally activated constriction. SM-NCX1-TG (overexpressing transgenic) mice have increased MT and mean blood pressure (MBP; +13.5 mmHg); SM-NCX1-KO (knockout) mice have reduced MT and MBP (-11.1 mmHg). Endothelium-dependent vasodilation (EDV) is often impaired in hypertension. We tested whether genetically engineered SM-NCX1 expression and consequent BP changes similarly alter EDV. Isolated, pressurized mesenteric resistance arteries with MT from SM-NCX1-TG and conditional SM-NCX1-KO mice, and femoral arteries in vivo from TG mice were studied. Acetylcholine (ACh)-dilated TG arteries with MT slightly more than control or KO arteries, implying that SM-NCX1 overexpression does not impair EDV. In preconstricted KO, but not TG mouse arteries, however, ACh- and bradykinin-triggered vasodilation was markedly attenuated. To circumvent the endothelium, phenylephrine-constricted resistance arteries were tested with Na-nitroprusside [SNP; nitric oxide (NO) donor] and cGMP. This endothelium-independent vasodilation was augmented in TG but attenuated in KO arteries that lack NCX1-mediated Ca2+ clearance. Baseline cytosolic Ca2+ ([Ca2+]cyt) was elevated in TG femoral arteries in vivo, supporting the high BP; furthermore, SNP-triggered [Ca2+]cyt decline and vasodilation were augmented as NO and cGMP promote myocyte polarization thereby enhancing NCX1-mediated Ca2+ efflux. The TG mouse data indicate that BP elevation does not attenuate endothelium-dependent vasodilation. Thus, in essential hypertension and many models the endothelial impairment that supports the hypertension apparently is not triggered by BP elevation but by extravascular mechanisms.NEW & NOTEWORTHY Endothelium-dependent, ACh-induced vasodilation (EDV) is attenuated, and arterial myocyte Na+/Ca2+ exchangers (NCX1) are upregulated in many forms of hypertension. Surprisingly, mildly hypertensive smooth muscle-specific (SM)-NCX1 transgenic mice exhibited modestly enhanced EDV and augmented endothelium-independent vasodilation (EIV). Conversely, mildly hypotensive SM-NCX1-knockout mice had greatly attenuated EIV. These adaptations help compensate for NCX1 expression-induced alterations in cytosolic Ca2+ and blood pressure (BP) and belie the view that elevated BP, itself, causes the endothelial dysregulation in hypertension.

Mechanism of thromboxane receptor-induced vasoconstriction in human saphenous vein

Saphenous vein (SV) is one of the most widely used graft material in patients undergoing coronary artery bypass graft surgery (CABG). Thromboxane A2 (TXA2) is implicated in graft failure by inducing vasoconstriction and platelet aggregation. The aim of this study is to investigate the mechanism involved in TXA2-induced vasoconstriction in human SV. The role of different inhibitors and blockers on U46619 (TXA2-mimetic)-induced vasoconstriction is investigated by using an isolated organ bath system. Relaxation responses to several mediators are evaluated in SV pre-contracted with U46619 and compared with those pre-contracted with phenylephrine. Our results demonstrate that U46619-induced contraction is completely blocked by myosin light chain kinase inhibitor ML-9 or TP receptor antagonist BAY u3405. Furthermore, U46619-induced contraction is partially inhibited by phospholipase C inhibitor U73122, protein kinase C inhibitor calphostin C, Rho-kinase inhibitor Y-27632, L-type calcium channel blocker nifedipine, store-operated channel inhibitor SKF96365 or removal of extracellular calcium. Relaxation responses to NO donor (sodium nitroprusside), guanylate cyclase (GC) stimulator (riociguat), phosphodiesterase (PDE) inhibitors (sildenafil, IBMX), adenylate cyclase (AC) activator (forskolin) and acetylcholine (ACh) are markedly reduced when U46619 is used as a pre-contraction agent. Our results demonstrate that influx of extracellular Ca2+ (through L-type calcium channels and store-operated calcium channels) and intracellular Ca2+ release together with Ca2+ sensitization (through Rho-kinase activation) are necessary components for TXA2-induced vasoconstriction in SV. Moreover, more pronounced decrease in vasorelaxation induced by several mediators (SNP, riociguat, sildenafil, IBMX, forskolin, and ACh) in the presence of U46619 when compared with phenylephrine suggests that there is a crosstalk between the TP receptor signaling pathway and PDE, AC, GC enzymes. We believe that the investigation of mechanism of the TXA2-induced vasoconstriction in SV will provide additional information for the prevention of SV graft failure.