Alamandine and Its Receptor MrgD Pair Up to Join the Protective Arm of the Renin-Angiotensin System

Only a few years ago, alamandine was found to be a member of the protective arm of the renin-angiotensin system. It turned out to be an endogenous ligand of the G protein-coupled receptor MrgD. So far, MrgD had predominantly been studied in a neuronal context. The expression of the receptor in non-neuronal tissue showed hitherto unknown effects mediated by MrgD, most strikingly alamandine-induced vasodilation. Alamandine being a part of the non-classical renin-angiotensin system, a protective role of receptor activation seemed natural. This review summarizes the different effects of MrgD activation by alamandine in vasculature, in the central nervous system, and in organs as kidney and heart. Alamandine and MrgD are promising novel drug targets to protect the kidney and heart through anti-hypertensive actions

Genetically Encoded Calcium Indicators: A New Tool in Renal Hypertension Research

Hypertension is ranked as the third cause of disability-adjusted life-years. The percentage of the population suffering from hypertension will continue to increase over the next years. Renovascular disease is one of the most common causes of secondary hypertension. Vascular changes seen in hypertension are partially based on dysfunctional calcium signaling. This signaling can be studied using calcium indicators (loading dyes and genetically encoded calcium indicators; GECIs). Most progress in development has been seen in GECIs, which are used in an increasing number of publications concerning calcium signaling in vasculature and the kidney. The use of transgenic mouse models expressing GECIs will facilitate new possibilities to study dysfunctional calcium signaling in a cell type-specific manner, thus helping to identify more specific targets for treatment of (renal) hypertension

Role of Ryanodine Type 2 Receptors in Elementary Ca 2+ Signaling in Arteries and Vascular Adaptive Responses

Background: Hypertension is the major risk factor for cardiovascular disease, the most common cause of death worldwide. Resistance arteries are capable of adapting their diameter independently in response to pressure and flow-associated shear stress. Ryanodine receptors (RyRs) are major Ca2+-release channels in the sarcoplasmic reticulum membrane of myocytes that contribute to the regulation of contractility. Vascular smooth muscle cells exhibit 3 different RyR isoforms (RyR1, RyR2, and RyR3), but the impact of individual RyR isoforms on adaptive vascular responses is largely unknown. Herein, we generated tamoxifen-inducible smooth muscle cell-specific RyR2-deficient mice and tested the hypothesis that vascular smooth muscle cell RyR2s play a specific role in elementary Ca2+ signaling and adaptive vascular responses to vascular pressure and/or flow. Methods and Results: Targeted deletion of the Ryr2 gene resulted in a complete loss of sarcoplasmic reticulum-mediated Ca2+-release events and associated Ca2+-activated, large-conductance K+ channel currents in peripheral arteries, leading to increased myogenic tone and systemic blood pressure. In the absence of RyR2, the pulmonary artery pressure response to sustained hypoxia was enhanced, but flow-dependent effects, including blood flow recovery in ischemic hind limbs, were unaffected. Conclusions: Our results establish that RyR2-mediated Ca2+-release events in VSCM s specifically regulate myogenic tone (systemic circulation) and arterial adaptation in response to changes in pressure (hypoxic lung model), but not flow. They further suggest that vascular smooth muscle cell-expressed RyR2 deserves scrutiny as a therapeutic target for the treatment of vascular responses in hypertension and chronic vascular diseases

Endothelial damage and dysfunction in acute graft-versus-host disease

Altres ajuts: Deutsche Forschungsgemeinschaft (DFG) TRR221 (B11 Z02), TRR225 (B08)Clinical studies have suggested a potential involvement of endothelial dysfunction and damage in the development and severity of acute graft-versus-host disease (aGvHD). Accordingly, we found an increased percentage of apoptotic caspase 3 positive blood vessels in duodenal and colonic mucosa biopsies of patients with severe aGvHD. In murine experimental aGvHD, we detected severe microstructural endothelial damage and reduced endothelial pericyte coverage accompanied by reduced expression of endothelial tight junction proteins leading to increased endothelial leakage in aGvHD target organs. During intestinal aGvHD, colonic vasculature structurally changed, reflected by increased vessel branching and vessel diameter. As recent data demonstrated an association of endothelium-related factors and steroid refractory aGvHD (SR-aGvHD), we analyzed human biopsies and murine tissues from SR-aGvHD. We found extensive tissue damage but low levels of alloreactive T-cell infiltration in target organs, providing the rationale for T-cell independent SR-aGvHD treatment strategies. Consequently, we tested the endothelium-protective PDE5 inhibitor sildenafil, which reduced apoptosis and improved metabolic activity of endothelial cells in vitro. Accordingly, sildenafil treatment improved survival and reduced target organ damage during experimental SR-aGvHD. Our results demonstrate extensive damage, structural changes, and dysfunction of the vasculature during aGvHD. Therapeutic intervention by endothelium-protecting agents is an attractive approach for SR-aGvHD complementing current anti-inflammatory treatment options

The role of KCNQ channels in the regulation of arterial vascular tone

Adipositashypertonie ist die häufigste sekundäre Hypertonie im Menschen. Die Mechanismen des zugrundeliegenden erhöhten systemischen arteriellen Widerstandes sind nicht ausreichend bekannt. Im Rahmen dieser Arbeit wurde 1) die Rolle von Kv-Kanälen des KCNQ-Subtyps bei der periadventitiellen Gefäßregulation durch das perivaskuläre Fettgewebe (PVAT) untersucht, 2) welche Rolle endogener Schwefelwasserstoff (H2S) und 3) Spinophilin (SPL) als Regulator des G-Protein-gekoppelten-Rezeptoren (GPCR)-Signalwegs bei der Gefäßregulation spielen. Die Untersuchungen fokussierten sich auf Cystathionin-γ-Lyase (CSE), die die Bildung von H2S aus L-Cystein im PVAT katalysiert, und neuartige KCNQ-Kanalöffner. Es wurden isometrische Kontraktionsmessungen an systemischen Arterien von Ratten und Mäusen sowie telemetrische Blutdruckmessungen durchgeführt. Die Öffnung von KCNQ-Kanälen stellte sich als potenter Mechanismus für die Auslösung einer Vasorelaxation in systemischen Arterien von Ratten und Mäusen heraus, auch spielen die Kanäle eine bedeutende Rolle in der parakrinen Kontrolle des vaskulären Tonus durch PVAT. Eine partielle Modulation durch H2S scheint vorzuliegen, denn im Falle einer reduzierten H2S-Freisetzung aus dem PVAT konnten die parakrinen Effekte durch synthetische KCNQ-Kanalöffner nachgeahmt werden. Synthetische KCNQ- Kanalöffner senkten den systemischen Blutdruck in normotensiven und adipösen (New Zealand Obese) Mäusen. CSE-H2S scheint den ADRF-Effekt nur in Ratten-, nicht aber in Mausaorten zu modulieren. Abwesenheit von SPL induzierte eine sympathisch vermittelte arterielle Hypertonie in SPL-gendefizienten (SPL-/-) Mäusen. Hier zeigte sich, dass SPL die Angiotensin II (AngII)-vermittelte Aktivierung des sympathischen Nervensystems einschränkt und die vaskuläre Gefäßkontraktion auf AngII nicht beeinflusst. Die vorliegenden Ergebnisse tragen zum besseren Verständnis von Mechanismen der systemischen Gefäßregulation bei und eröffnen neue Forschungsansätze für zukünftige Studien zu Mechanismen der Adipositashypertonie.Obesity-induced hypertension is the most common cause of secondary hypertension in humans. The underlying mechanisms of increased systemic arterial resistance are not fully understood. In this thesis, the role of Kv channel subtype KCNQ in the regulation of vascular tone by periadventitial fat tissue (PVAT) was analyzed (1), as well as the role of hydrogen sulfide (H2S) (2) and Spinophilin (SPL) as regulator of G-protein-coupled receptor signaling pathway (3) in the control of vascular tone. The experiments focused on the enzyme cystathionine-γ-lyase (CSE), which catalyzes the formation of H2S from L-cysteine in PVAT, and novel KCNQ channel openers. Isometric contractility measurements were performed on sytemic arteries of rats and mice. Blood pressure was assessed by telemetry in mice. KCNQ channel opening proved to be a powerful mechanism for inducing vasorelaxation of systemic arteries in rats and mice. The channels also play an important role in the paracrine regulation of vascular tone by PVAT. A partial modulation by H2S seems to be present, as the paracrine effects could be mimicked by synthetic KCNQ channel openers in conditions of reduced H2S release. Synthetic KCNQ channel openers also reduced systemic blood pressure in normotensive and obese (New Zealand Obese) mice. CSE-H2S seems to modulate the ADRF effect only in rat, but not in mouse aorta. Absence of SPL induced a sympathetically mediated arterial hypertension in SPL-deficient (SPL-/-) mice. It was shown that SPL attenuates angiotensin II- mediated activation of the sympathetic nervous system while the vasoconstriction to angiotensin II is not affected. These results provide a better understanding on mechanisms involving systemic vascular regulation. Furthermore, this will expand this area of research for future studies leading to a better understanding on the mechanisms of obesity-induced hypertension

Membrane Stretch and Angiotensin II type 1a Receptor: Causes and Role in the Myogenic Response

The ligand-independent activation of Angiotensin II type 1 receptors following vascular stretch plays very important (patho) physiological roles. Indeed, recent studies have implicated this mechanism in cardiac hypertrophy under conditions of pressure overload and it has shown to be indispensable in the regulation of the myogenic response in smooth muscle cells of small resistance arteries, as well as mesenteric and renal resistance arteries. The information discussed in here will highlight the involvement of the mechanoactivation of the Angiotensin II type I receptors in the development of the myogenic response and the molecular mechanisms modulating them following activation

Differential Effects of Cystathionine-γ-lyase–Dependent Vasodilatory H₂S in Periadventitial Vasoregulation of Rat and Mouse Aortas

<div><h3>Background</h3><p>Hydrogen sulfide (H₂S) is a potent vasodilator. However, the complex mechanisms of vasoregulation by H₂S are not fully understood. We tested the hypotheses that (1) H₂S exerts vasodilatory effects by opening KCNQ-type voltage-dependent (K_v) K⁺ channels and (2) that H₂S-producing cystathionine-γ-lyase (CSE) in perivascular adipose tissue plays a major role in this pathway.</p> <h3>Methodology/Principal Findings</h3><p>Wire myography of rat and mouse aortas was used. NaHS and 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione (ADTOH) were used as H₂S donors. KCNQ-type K_v channels were blocked by XE991. 4-Propargylglycine (PPG) and ß-cyano-l-alanine (BCA), or 2-(aminooxy)-acetic acid (AOAA) were used as inhibitors of CSE or cystathionine-ß-synthase (CBS), respectively. NaHS and ADTOH produced strong vasorelaxation in rat and mouse aortas, which were abolished by KCNQ channel inhibition with XE991. Perivascular adipose tissue (PVAT) exerted an anticontractile effect in these arteries. CSE inhibition by PPG and BCA reduced this effect in aortas from rats but not from mice. CBS inhibition with AOAA did not inhibit the anticontractile effects of PVAT. XE991, however, almost completely suppressed the anticontractile effects of PVAT in both species. Exogenous l-cysteine, substrate for the endogenous production of H₂S, induced vasorelaxation only at concentrations >5 mmol/l, an effect unchanged by CSE inhibition.</p> <h3>Conclusions/Signficance</h3><p>Our results demonstrate potent vasorelaxant effects of H₂S donors in large arteries of both rats and mice, in which XE991-sensitive KCNQ-type channel opening play a pivotal role. CSE-H₂S seems to modulate the effect of adipocyte-derived relaxing factor in rat but not in mouse aorta. The present study provides novel insight into the interaction of CSE-H₂S and perivascular adipose tissue. Furthermore, with additional technical advances, a future clinical approach targeting vascular H₂S/KCNQ pathways to influence states of vascular dysfunction may be possible.</p> </div

Schematic illustration on differential effects of cystathionine-γ-lyase (CSE)–dependent vasodilatory H₂S in periadventitial vasoregulation of rat and mouse aortas.

<p>4-AP, 4-aminopyridine.</p