Perivascular tissue inhibits rho-kinase-dependent smooth muscle Ca(2+) sensitivity and endothelium-dependent H2 S signalling in rat coronary arteries

Exercise Enhances Anti-contractile Effects of PVAT Through Endogenous H2S in High-Fat Diet-Induced Obesity Hypertension

PURPOSE

Hydrogen sulfide (H2S) secreted by perivascular adipose tissue (PVAT) is a critical vasodilator, which might be involved during the pathogenesis of hypertension. The present study aimed to investigate the exact role of H2S on the regulation of PVAT anti-contraction by long-term exercise in obesity hypertension.

METHODS

After the establishment of obesity hypertension (24 weeks) through a high-fat diet, male Sprague-Dawley rats were randomly assigned to control group (HC), exercise group (HE), cystathionine γ-lyase (CSE) blocking group (HCB), and exercise combined with CSE blocking group (HEB). Exercise and CSE inhibitor regimens were performed throughout 13 weeks.

RESULTS

After 13 weeks of intervention, blood pressure was significantly decreased by long-term exercise (HC vs. HE, P < 0.05) but not by exercise combined with the CSE inhibitor regimen. Meanwhile, the CSE inhibitor significantly blocked the production of H2S in PVAT even after exercise (HE vs. HEB, P < 0.05). Furthermore, long-term exercise altered the expressions of voltage-dependent K+ (Kv) channel subunits 7 (KCNQs), which were diminished by CSE inhibition in mesenteric arteries. As for vascular tension assessment, after incubation with or without KCNQ opener (retigabine), the anti-contractile effect of PVAT (with or without transferred bath solution of PVAT) was significantly enhanced by long-term exercise and eliminated by the CSE inhibitor regimen (P < 0.05); KCNQ inhibitor (XE991) blunted this effect except for HE.

CONCLUSIONS

These results collectively suggest that endogenous H2S is a strong regulator of the anti-contractile effect of PVAT in obesity hypertension by long-term exercise, and KCNQ in the resistance artery might be involved during this process but not the only target channel mediated by H2S.

The Role of Perivascular Adipose Tissue-Derived Hydrogen Sulfide in the Control of Vascular Homeostasis

Significance: Emerging evidence suggests that perivascular adipose tissue (PVAT) has a relevant role in the control of vascular tone in physiology and pathology. Healthy PVAT has anticontractile, anti-inflammatory, and antioxidative actions. Accumulating data from both human and experimental animal models indicate that PVAT dysfunction is conceivably coupled to cardiovascular diseases, and it is associated with vascular inflammation, oxidative stress, and arterial remodeling. Therefore, "healthy" PVAT may constitute a novel therapeutic target for the prevention and treatment of cardiovascular diseases. Recent Advances: Hydrogen sulfide (H₂S) has been recognized as a vascular anti-contractile factor released from PVAT. The enzymes deputed to H₂S biosynthesis are variously expressed in PVAT and strictly dependent on the vascular bed and species. Metabolic and cardiovascular diseases can alter the morphological and secretory characteristics of PVAT, influencing also the H₂S signaling. Here, we discuss the role of PVAT-derived H₂S in healthy conditions and its relevance in alterations occurring in vascular disorders. Critical Issues: We discuss how a better understanding may help in the prevention of vascular dysfunction related to alteration in PVAT-released H₂S as well as the importance of the interplay between PVAT and H₂S. Future Directions: We propose future directions to evaluate the contribution of each enzyme involved in H₂S biosynthesis and their alteration/switch occurring in vascular disorders and the remaining challenges in investigating the role of H₂S. Antioxid. Redox Signal. 37, 84-97.

Coronary Artery Spasm: Risk Factors, Pathophysiological Mechanisms and Novel Diagnostic Approaches

Coronary artery spasm (CAS) is a transient reversible subtotal or complete occlusion induced by coronary hypercontraction and the critical cause of myocardial ischaemia with non-obstructive coronary arteries. During the past decades, our knowledge of the risk factors and pathophysiological mechanisms of CAS have been increasingly progressed, and various diagnostic approaches, including imaging technologies and novel biomarkers, have been proposed to serve well to diagnose CAS clinically. This review aims to summarize these research progresses on the risk factors of CAS and introduce current knowledge about the mechanisms accounting for CAS, including endothelial dysfunction, vascular smooth muscle cell hyperreactivity, and adventitial and perivascular adipose tissue inflammation. We also gathered the recently evolved diagnostic approaches and analyzed their advantages/disadvantages, in purpose of enhancing the diagnostic yield on the basis of ensuring accuracy.

The Vasoactive Effect of Perivascular Adipose Tissue and Hydrogen Sulfide in Thoracic Aortas of Normotensive and Spontaneously Hypertensive Rats

The objective of this study was to investigate the vasoregulatory role of perivascular adipose tissue (PVAT) and its mutual interaction with endogenous and exogenous H₂S in the thoracic aorta (TA) of adult normotensive Wistar rats and spontaneously hypertensive rats (SHRs). In SHRs, hypertension was associated with cardiac hypertrophy and increased contractility. Regardless of the strain, PVAT revealed an anticontractile effect; however, PVAT worsened endothelial-dependent vasorelaxation. Since H₂S produced by both the vascular wall and PVAT had a pro-contractile effect in SHRs, H₂S decreased the sensitivity of adrenergic receptors to noradrenaline in Wistar rats. While H₂S had no contribution to endothelium-dependent relaxation in Wistar rats, in SHRs, H₂S produced by the vascular wall had a pro-relaxant effect. We observed a larger vasorelaxation induced by exogenous H₂S donor in SHRs than in Wistar rats. Additionally, in the presence of PVAT, this effect was potentiated. We demonstrated that PVAT of the TA aggravated endothelial function in SHRs. However, H₂S produced by the TA vascular wall had a pro-relaxation effect, and PVAT revealed anti-contractile activity mediated by the release of an unknown factor and potentiated the vasorelaxation induced by exogenous H₂S. All these actions could represent a form of compensatory mechanism to balance impaired vascular tone regulation.

Arachnoid membrane as a source of sphingosine-1-phosphate that regulates mouse middle cerebral artery tone

Growing evidence indicates that perivascular tissue is critical to modulate vessel function. We hypothesized that the arachnoid membrane surrounding middle cerebral artery (MCA) regulates its function via sphingosine-1-phosphate (S1P)-induced vasoconstriction. The MCA from 3- to 9-month-old male and female wild-type (Oncine France 1 and C57BL/6) mice and sphingosine kinase 2 knockout (SphK2-/-) mice in the C57BL/6 background was mounted in pressure myographs with and without arachnoid membrane. Raman microspectroscopy and imaging were used for in situ detection of S1P. The presence of arachnoid tissue was associated with reduced external and lumen MCA diameters, and with an increase in basal tone regardless of sex and strain background. Strong S1P-positive signals were detected in the arachnoid surrounding the MCA wall in both mice models, as well as in a human post-mortem specimen. Selective S1P receptor 3 antagonist TY 52156 markedly reduced both MCA vasoconstriction induced by exogenous S1P and arachnoid-dependent basal tone increase. Compared to 3-month-old mice, the arachnoid-mediated contractile influence persisted in 9-month-old mice despite a decline in arachnoid S1P deposits. Genetic deletion of SphK2 decreased arachnoid S1P content and vasoconstriction. This is the first experimental evidence that arachnoid membrane regulates the MCA tone mediated by S1P.

Hydrogen sulfide dilates the isolated retinal artery mainly via the activation of myosin phosphatase

AIMS

Hydrogen sulfide (H₂S) is shown in ocular tissues and suggested to involve in the regulation of retinal circulation. However, the mechanism of H₂S-induced relaxation on retinal artery is not clarified yet. Herein, we aimed to evaluate the role of several calcium (Ca²⁺) signaling and Ca²⁺ sensitization mechanisms in the relaxing effect of H₂S donor, NaHS, on retinal arteries.

MATERIALS AND METHODS

Relaxing effects of NaHS (10^-5-3 × 10^-3M) were determined on precontracted retinal arteries in Ca²⁺ free medium as well as in the presence of the inhibitors of Ca²⁺ signaling and Ca²⁺ sensitization mechanisms. Additively, Ca²⁺ sensitivity of the contractile apparatus were evaluated by CaCl₂-induced contractions in the presence of NaHS (3 × 10^-3M). Functional experiments were furtherly assessed by protein and/or mRNA expressions, as appropriate.

KEY FINDINGS

The relaxations to NaHS were preserved in Ca²⁺ free medium while NaHS pretreatment decreased the responsiveness to CaCl₂. The inhibitors of plasmalemmal Ca²⁺-ATPase, sarcoplasmic-endoplasmic reticulum Ca²⁺-ATPase, Na⁺-Ca²⁺ ion-exchanger and myosin light chain kinase (MLCK) unchanged the relaxations to NaHS. Likewise, Ca²⁺ sensitization mechanisms including, rho kinase, protein kinase C and tyrosine kinase were unlikely to mediate the relaxation to NaHS in retinal artery. Whereas, a marked reduction was determined in NaHS-induced relaxations in the presence of MLCP inhibitor, calyculin A. Supportively, NaHS pretreatment significantly reduced phosphorylation of MYPT1-subunit of MLCP.

SIGNIFICANCE

The relaxing effect of NaHS in retinal artery is likely to be related to the activation of MLCP and partly, to decrement in Ca²⁺ sensitivity of contractile apparatus.

Coronary artery hypoxic vasorelaxation is augmented by perivascular adipose tissue through a mechanism involving hydrogen sulphide and cystathionine-β-synthase

AIM

Hypoxia causes vasodilatation of coronary arteries which protects the heart from ischaemic damage through mechanisms including the generation of hydrogen sulphide (H₂ S), but the influence of the perivascular adipose tissue (PVAT) and myocardium is incompletely understood. This study aimed to determine whether PVAT and the myocardium modulate the coronary artery hypoxic response and whether this involves hydrogen sulphide.

METHODS

Porcine left circumflex coronary arteries were prepared as cleaned segments and with PVAT intact, myocardium intact or both PVAT and myocardium intact, and contractility investigated using isometric tension recording. Immunoblotting was used to measure levels of H₂ S-synthesizing enzymes: cystathionine-β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulphurtransferase (MPST).

RESULTS

All three H₂ S-synthesizing enzymes were detected in the artery and myocardium, but only CBS and MPST were detected in PVAT. Hypoxia elicited a biphasic response in cleaned artery segments consisting of transient contraction followed by prolonged relaxation. In arteries with PVAT intact, hypoxic contraction was attenuated and relaxation augmented. In arteries with myocardium intact, hypoxic contraction was attenuated, but relaxation was unaffected. In replacement experiments, replacement of dissected PVAT and myocardium attenuated artery contraction and augmented relaxation to hypoxia, mimicking the effect of in situ PVAT and indicating involvement of a diffusible factor(s). In arteries with intact PVAT, augmentation of hypoxic relaxation was reversed by amino-oxyacetate (CBS inhibitor), but not DL-propargylglycine (CSE inhibitor) or aspartate (inhibits MPST pathway).

CONCLUSION

PVAT augments hypoxic relaxation of coronary arteries through a mechanism involving H₂ S and CBS, pointing to an important role in regulation of coronary blood flow during hypoxia.

Acid-base regulation and sensing: Accelerators and brakes in metabolic regulation of cerebrovascular tone

Metabolic regulation of cerebrovascular tone directs blood flow to areas of increased neuronal activity and during disease states partially compensates for insufficient perfusion by enhancing blood flow in collateral blood vessels. Acid-base disturbances frequently occur as result of enhanced metabolism or insufficient blood supply, but despite definitive evidence that acid-base disturbances alter arterial tone, effects of individual acid-base equivalents and the underlying signaling mechanisms are still being debated. H+ is an important intra- and extracellular messenger that modifies cerebrovascular tone. In addition, low extracellular [HCO3-] promotes cerebrovascular contraction through an endothelium-dependent mechanism. CO2 alters arterial tone development via changes in intra- and extracellular pH but it is still controversial whether CO2 also has direct vasomotor effects. Vasocontractile responses to low extracellular [HCO3-] and acute CO2-induced decreases in intracellular pH can counteract H+-mediated vasorelaxation during metabolic and respiratory acidosis, respectively, and may thereby reduce the risk of capillary damage and cerebral edema that could be consequences of unopposed vasodilation. In this review, the signaling mechanisms for acid-base equivalents in cerebral arteries and the mechanisms of intracellular pH control in the arterial wall are discussed in the context of metabolic regulation of cerebrovascular tone and local perfusion.

Murine breast cancer feed arteries are thin-walled with reduced α1A-adrenoceptor expression and attenuated sympathetic vasocontraction

BACKGROUND

Perfusion of breast cancer tissue limits oxygen availability and metabolism but angiogenesis inhibitors have hitherto been unsuccessful for breast cancer therapy. In order to identify abnormalities and possible therapeutic targets in mature cancer arteries, we here characterize the structure and function of cancer feed arteries and corresponding control arteries from female FVB/N mice with ErbB2-induced breast cancer.

METHODS

We investigated the contractile function of breast cancer feed arteries and matched control arteries by isometric myography and evaluated membrane potentials and intracellular [Ca²⁺] using sharp electrodes and fluorescence microscopy, respectively. Arterial wall structure is assessed by transmission light microscopy of arteries mounted in wire myographs and by evaluation of histological sections using the unbiased stereological disector technique. We determined the expression of messenger RNA by reverse transcription and quantitative polymerase chain reaction and studied receptor expression by confocal microscopy of arteries labelled with the BODIPY-tagged α₁-adrenoceptor antagonist prazosin.

RESULTS

Breast cancer feed arteries are thin-walled and produce lower tension than control arteries of similar diameter in response to norepinephrine, thromboxane-analog U46619, endothelin-1, and depolarization with elevated [K⁺]. Fewer layers of similarly-sized vascular smooth muscle cells explain the reduced media thickness of breast cancer arteries. Evidenced by lower media stress, norepinephrine-induced and thromboxane-induced tension development of breast cancer arteries is reduced more than is explained by the thinner media. Conversely, media stress during stimulation with endothelin-1 and elevated [K⁺] is similar between breast cancer and control arteries. Correspondingly, vascular smooth muscle cell depolarizations and intracellular Ca²⁺ responses are attenuated in breast cancer feed arteries during norepinephrine but not during endothelin-1 stimulation. Protein expression of α₁-adrenoceptors and messenger RNA levels for α_1A-adrenoceptors are lower in breast cancer arteries than control arteries. Sympathetic vasocontraction elicited by electrical field stimulation is inhibited by α₁-adrenoceptor blockade and reduced in breast cancer feed arteries compared to control arteries.

CONCLUSION

Thinner media and lower α₁-adrenoceptor expression weaken contractions of breast cancer feed arteries in response to sympathetic activity. We propose that abnormalities in breast cancer arteries can be exploited to modify tumor perfusion and thereby either starve cancer cells or facilitate drug and oxygen delivery during chemotherapy or radiotherapy.

Regulation of vascular tone homeostasis by NO and H2S: Implications in hypertension

Nitric oxide (NO) and hydrogen sulfide (H2S) are two gasotransmitters that are produced in the vasculature and contribute to the regulation of vascular tone. NO and H2S are synthesized in both vascular smooth muscle and endothelial cells; NO functions primarily through the sGC/cGMP pathway, and H2S mainly through activation of the ATP-dependent potassium channels; both leading to relaxation of vascular smooth muscle cells. A deficit in the NO/H2S homeostasis is involved in the pathogenesis of various cardiovascular diseases, especially hypertension. It is now becoming increasingly clear that there are important interactions between NO and H2S and that have a profound impact on vascular tone and this may provide insights into the new therapeutic interventions. The aim of this review is to provide a better understanding of individual and interactive roles of NO and H2S in vascular biology. Overall, available data indicate that both NO and H2S contribute to vascular (patho)physiology and in regulating blood pressure. In addition, boosting NO and H2S using various dietary sources or donors could be a hopeful therapeutic strategy in the management of hypertension.

Increased Contractile Function of Human Saphenous Vein Grafts Harvested by "No-Touch" Technique

Saphenous vein grafts are the most common conduits used for coronary artery bypass grafting (CABG); however, no more than 60% of vein grafts remain open after 10 years and graft failure is associated with poor clinical outcome. The “no-touch” harvesting technique—where a sheet of perivascular tissue is retained around the vein—improves graft patency to over 80% after 16 years of follow-up, but the mechanism for the improved patency rate is unclear. In this study, we investigated acute functional differences between vein grafts harvested conventionally and by “no-touch” technique and explored the importance of perivascular tissue for reducing surgical trauma, minimizing excessive distension, and releasing vasoactive paracrine factors. Segments of human saphenous veins were obtained from CABG surgery and their functional properties investigated by isometric and isobaric myography. We found a broad diameter-tension relationship for human saphenous veins, with peak capacity for active tension development at diameters corresponding to transmural pressures around 60 mmHg. Across the investigated transmural pressure range between 10 and 120 mmHg, maximal tension development was higher for “no-touch” compared to conventionally harvested saphenous veins. Contractile responses to serotonin, noradrenaline, and depolarization induced with elevated extracellular [K⁺] were significantly larger for saphenous veins harvested by “no-touch” compared to conventional technique. Conventional vein grafts are routinely pressurized manually in order to test for leaks; however, avoiding this distension procedure did not change the acute contractile function of the conventionally excised saphenous veins. In contrast, even though surgical removal of perivascular tissue during conventional harvesting was associated with a substantial decrease in force development, removal of perivascular tissue by careful dissection under a stereomicroscope only marginally affected contractile responses of veins harvested by “no-touch” technique. In conclusion, we show that saphenous veins harvested by “no-touch” technique have greater contractile capacity than veins harvested by conventional technique. The different capacity for smooth muscle contraction is not due to vasoactive substances released by the perivascular tissue. Instead, we propose that the larger tension development of saphenous veins harvested by “no-touch” technique reflects reduced surgical damage, which may have long-term consequences that contribute to the superior graft patency.

Role of Perivascular Adipose Tissue in Health and Disease

Perivascular adipose tissue (PVAT) is cushion of fat tissue surrounding blood vessels, which is phenotypically different from other adipose tissue depots. PVAT is composed of adipocytes and stromal vascular fraction, constituted by different populations of immune cells, endothelial cells, and adipose-derived stromal cells. It expresses and releases an important number of vasoactive factors with paracrine effects on vascular structure and function. In healthy individuals, these factors elicit a net anticontractile and anti-inflammatory paracrine effect aimed at meeting hemodynamic and metabolic demands of specific organs and regions of the body. Pathophysiological situations, such as obesity, diabetes or hypertension, induce changes in its amount and in the expression pattern of vasoactive factors leading to a PVAT dysfunction in which the beneficial paracrine influence of PVAT is shifted to a pro-oxidant, proinflammatory, contractile, and trophic environment leading to functional and structural cardiovascular alterations and cardiovascular disease. Many different PVATs surrounding a variety of blood vessels have been described and exhibit regional differences. Both protective and deleterious influence of PVAT differs regionally depending on the specific vascular bed contributing to variations in the susceptibility of arteries and veins to vascular disease. PVAT therefore, might represent a novel target for pharmacological intervention in cardiovascular disease. © 2018 American Physiological Society. Compr Physiol 8:23-59, 2018.

Pro-contractile effects of perivascular fat in health and disease

Perivascular adipose tissue (PVAT) is now recognized as an active player in vascular homeostasis. The expansion of PVAT in obesity and its possible role in vascular dysfunction have attracted much interest. In terms of the regulation of vascular tone and blood pressure, PVAT has been shown to release vasoactive mediators, for instance, angiotensin peptides, reactive oxygen species, chemokines and cytokines. The secretory profile of PVAT is altered by obesity, hypertension and other cardiovascular diseases, leading to an imbalance between its pro-contractile and anti-contractile effects. PVAT adipocytes represent an important source of the mediators, but infiltrating immune cells may become more important under conditions of hypoxia and inflammation. This review describes recent advances in the effects of PVAT on the regulation of vascular tone, highlighting the evidence for a pro-contractile action in health and disease. The role of the endothelium, vascular smooth muscle, immune cells and probably perivascular nerves in PVAT function is also discussed.

LINKED ARTICLES

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue - Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc.

Crosstalk between cardiomyocyte-rich perivascular tissue and coronary arteries is reduced in the Zucker Diabetic Fatty rat model of type 2 diabetes mellitus

AIM

We tested the hypothesis that crosstalk between cardiomyocyte-rich perivascular tissue (PVT) and coronary arteries is altered in diabetes.

METHODS

We studied the vasoactive effects of PVT in arteries from the Zucker Diabetic Fatty (ZDF) rat model of type 2 diabetes, streptozotocin (STZ)-treated Wistar rats with type 1 diabetes, and corresponding - heterozygous Zucker Lean (ZL) or vehicle-treated Wistar - control rats. Vasocontractile and vasorelaxant functions of coronary septal arteries with and without PVT were investigated using wire myography.

RESULTS

After careful removal of PVT, vasoconstriction in response to serotonin and thromboxane analogue U46619 was similar in arteries from ZDF and ZL rats, whereas depolarization-induced vasoconstriction - caused by elevating extracellular [K⁺ ] - was reduced in arteries from ZDF compared to ZL rats. PVT inhibited serotonin-, U46619- and depolarization-induced vasoconstriction in arteries from ZL rats, but this anticontractile influence of PVT was attenuated in arteries from ZDF rats. Methacholine-induced vasorelaxation was smaller in arteries from ZDF than ZL rats both with and without PVT, and the antirelaxant influence of PVT was comparable between arteries from ZDF and ZL rats. We observed no differences in vasoconstriction, vasorelaxation or PVT-dependent vasoactive effects between arteries from STZ- and vehicle-treated Wistar rats.

CONCLUSION

Anticontractile influences of PVT are attenuated in coronary arteries from ZDF rats but unaffected in arteries from STZ-treated rats. Signs of endothelial dysfunction are evident in coronary septal arteries - with and without PVT - from ZDF rats but not STZ-treated rats. We propose that altered signalling between cardiomyocyte-rich PVT and coronary arteries can contribute to cardiovascular complications in type 2 diabetes mellitus.