Redox regulation of soluble guanylyl cyclase

Soluble guanylyl cyclase: A novel target for the treatment of vascular cognitive impairment?

Vascular cognitive impairment (VCI) describes neurodegenerative disorders characterized by a vascular component. Pathologically, it involves decreased cerebral blood flow (CBF), white matter lesions, endothelial dysfunction, and blood-brain barrier (BBB) impairments. Molecularly, oxidative stress and inflammation are two of the major underlying mechanisms. Nitric oxide (NO) physiologically stimulates soluble guanylate cyclase (sGC) to induce cGMP production. However, under pathological conditions, NO seems to be at the basis of oxidative stress and inflammation, leading to a decrease in sGC activity and expression. The native form of sGC needs a ferrous heme group bound in order to be sensitive to NO (Fe(II)sGC). Oxidation of sGC leads to the conversion of ferrous to ferric heme (Fe(III)sGC) and even heme-loss (apo-sGC). Both Fe(III)sGC and apo-sGC are insensitive to NO, and the enzyme is therefore inactive. sGC activity can be enhanced either by targeting the NO-sensitive native sGC (Fe(II)sGC), or the inactive, oxidized sGC (Fe(III)sGC) and the heme-free apo-sGC. For this purpose, sGC stimulators acting on Fe(II)sGC and sGC activators acting on Fe(III)sGC/apo-sGC have been developed. These sGC agonists have shown their efficacy in cardiovascular diseases by restoring the physiological and protective functions of the NO-sGC-cGMP pathway, including the reduction of oxidative stress and inflammation, and improvement of vascular functioning. Yet, only very little research has been performed within the cerebrovascular system and VCI pathology when focusing on sGC modulation and its potential protective mechanisms on vascular and neural function. Therefore, within this review, the potential of sGC as a target for treating VCI is highlighted.

Oxidized soluble guanylyl cyclase causes erectile dysfunction in alcoholic mice

BACKGROUND AND PURPOSE

Alcohol abuse has been associated with erectile dysfunction (ED), but the implicated molecular mechanisms are unresolved. This study analyses the role of alterations in soluble guanylyl cyclase (sGC) in ED.

EXPERIMENTAL APPROACH

ED was analysed in adult male C57BL/6J mice subjected to the Chronic Intermittent Ethanol (CIE) paradigm. Erectile function was assessed in anaesthetised mice in vivo by evaluating intracavernosal pressure (ICP) and in vitro in isolated mice corpora cavernosa (CC) mounted in a myograph. Protein expression and reactive oxygen species were analysed by western blot and dihydroethidium staining, respectively.

KEY RESULTS

In CIE mice, we observed a significant decrease in the relaxant response of the CC to stimulation of NO release from nitrergic nerves by electrical field stimulation, to NO release from endothelial cells by acetylcholine, to the PDE5 inhibitor sildenafil, and to the sGC stimulator riociguat. Conversely, the response to the sGC activator cinaciguat, whose action is independent of the oxidation state of sGC, was significantly enhanced in these CC. The responses to adenylyl cyclase stimulation with forskolin were unchanged. We found an increase in reactive oxygen species in the CC from CIE mice as well as an increase in CYP2E1 and NOX2 protein expression. In vivo pre-treatment with tempol prevented alcohol-induced erectile dysfunction.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that alcoholic mice show ED in vitro and in vivo due to an alteration in the redox state of sGC and suggest that sGC activators may be effective in ED associated with alcoholism.

Hydrogen sulfide regulates the redox state of soluble guanylate cyclase in CSE-/- mice corpus cavernosum microcirculation

The corpus cavernosum (CC) is a highly vascularized tissue and represents an excellent example of microcirculation. Indeed, erectile dysfunction is considered an early index of cardiovascular disease. Hydrogen sulfide (H2S) at the vascular level is endogenously produced from L-cysteine mainly by the action of cystathionine-γ-lyase (CSE) and plays a role in CC vascular homeostasis. Here we have evaluated the involvement of the endogenous H2S in the regulation of the soluble guanylate cyclase (sCG) redox state. The lack of CSE-derived endogenous H2S, in CSE-/- mice, disrupted the eNOS/NO/sGC/PDE pathway. Indeed, the absence of CSE-derived endogenous H2S caused a significant reduction of the relaxant response to riociguat, an sGC redox-dependent stimulator. Conversely, the response to cinaciguat, an sGC redox-independent activator, was not modified. The relevance of the role played at the redox level of the endogenous H2S was confirmed by the findings that in CC harvested from CSE-/- mice there was a significant reduction of GCβ1 expression coupled with a decrease in CYP5R3, a reductase involved in the regulation of the redox state of sGC. These molecular changes driven by the lack of endogenous H2S translate into a significant reduction in cGMP levels. The replenishment of the lack of H2S with an H2S donor rescued the relaxant response to riociguat in CC of CSE-/- mice. In conclusion, the endogenous CSE-derived H2S plays a physiological key role in the regulation of the redox state of sGC in CC microcirculation.

A natural heme deficiency exists in biology that allows nitric oxide to control heme protein functions by regulating cellular heme distribution

A natural heme deficiency that exists in cells outside of the circulation broadly compromises the heme contents and functions of heme proteins in cells and tissues. Recently, we found that the signaling molecule, nitric oxide (NO), can trigger or repress the deployment of intracellular heme in a concentration-dependent hormetic manner. This uncovers a new role for NO and sets the stage for it to shape numerous biological processes by controlling heme deployment and consequent heme protein functions in biology.

Notch3/Hes5 Induces Vascular Dysfunction in Hypoxia-Induced Pulmonary Hypertension Through ER Stress and Redox-Sensitive Pathways

BACKGROUND

Notch3 (neurogenic locus notch homolog protein 3) is implicated in vascular diseases, including pulmonary hypertension (PH)/pulmonary arterial hypertension. However, molecular mechanisms remain elusive. We hypothesized increased Notch3 activation induces oxidative and endoplasmic reticulum (ER) stress and downstream redox signaling, associated with procontractile pulmonary artery state, pulmonary vascular dysfunction, and PH development.

METHODS

Studies were performed in TgNotch3R169C mice (harboring gain-of-function [GOF] Notch3 mutation) exposed to chronic hypoxia to induce PH, and examined by hemodynamics. Molecular and cellular studies were performed in pulmonary artery smooth muscle cells from pulmonary arterial hypertension patients and in mouse lung. Notch3-regulated genes/proteins, ER stress, ROCK (Rho-associated kinase) expression/activity, Ca2+ transients and generation of reactive oxygen species, and nitric oxide were measured. Pulmonary vascular reactivity was assessed in the presence of fasudil (ROCK inhibitor) and 4-phenylbutyric acid (ER stress inhibitor).

RESULTS

Hypoxia induced a more severe PH phenotype in TgNotch3R169C mice versus controls. TgNotch3R169C mice exhibited enhanced Notch3 activation and expression of Notch3 targets Hes Family BHLH Transcription Factor 5 (Hes5), with increased vascular contraction and impaired vasorelaxation that improved with fasudil/4-phenylbutyric acid. Notch3 mutation was associated with increased pulmonary vessel Ca2+ transients, ROCK activation, ER stress, and increased reactive oxygen species generation, with reduced NO generation and blunted sGC (soluble guanylyl cyclase)/cGMP signaling. These effects were ameliorated by N-acetylcysteine. pulmonary artery smooth muscle cells from patients with pulmonary arterial hypertension recapitulated Notch3/Hes5 signaling, ER stress and redox changes observed in PH mice.

CONCLUSIONS

Notch3 GOF amplifies vascular dysfunction in hypoxic PH. This involves oxidative and ER stress, and ROCK. We highlight a novel role for Notch3/Hes5-redox signaling and important interplay between ER and oxidative stress in PH.

Vascular nitric oxide resistance in type 2 diabetes

Vascular nitric oxide (NO•) resistance, manifested by an impaired vasodilator function of NO• in both the macro- and microvessels, is a common state in type 2 diabetes (T2D) associated with developing cardiovascular events and death. Here, we summarize experimental and human evidence of vascular NO• resistance in T2D and discuss its underlying mechanisms. Human studies indicate a ~ 13-94% decrease in the endothelium (ET)-dependent vascular smooth muscle (VSM) relaxation and a 6-42% reduced response to NO• donors, i.e., sodium nitroprusside (SNP) and glyceryl trinitrate (GTN), in patients with T2D. A decreased vascular NO• production, NO• inactivation, and impaired responsiveness of VSM to NO• [occurred due to quenching NO• activity, desensitization of its receptor soluble guanylate cyclase (sGC), and/or impairment of its downstream pathway, cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG)] are the known mechanisms underlying the vascular NO• resistance in T2D. Hyperglycemia-induced overproduction of reactive oxygen species (ROS) and vascular insulin resistance are key players in this state. Therefore, upregulating vascular NO• availability, re-sensitizing or bypassing the non-responsive pathways to NO•, and targeting key vascular sources of ROS production may be clinically relevant pharmacological approaches to circumvent T2D-induced vascular NO• resistance.

The soluble guanylyl cyclase pathway is inhibited to evade androgen deprivation-induced senescence and enable progression to castration resistance

Castration-resistant prostate cancer (CRPC) is fatal and therapeutically under-served. We describe a novel CRPC-restraining role for the vasodilatory soluble guanylyl cyclase (sGC) pathway. We discovered that sGC subunits are dysregulated during CRPC progression and its catalytic product, cyclic GMP (cGMP), is lowered in CRPC patients. Abrogating sGC heterodimer formation in castration-sensitive prostate cancer (CSPC) cells inhibited androgen deprivation (AD)-induced senescence, and promoted castration-resistant tumor growth. We found sGC is oxidatively inactivated in CRPC. Paradoxically, AD restored sGC activity in CRPC cells through redox-protective responses evoked to protect against AD-induced oxidative stress. sGC stimulation via its FDA-approved agonist, riociguat, inhibited castration-resistant growth, and the anti-tumor response correlated with elevated cGMP, indicating on-target sGC activity. Consistent with known sGC function, riociguat improved tumor oxygenation, decreasing the PC stem cell marker, CD44, and enhancing radiation-induced tumor suppression. Our studies thus provide the first evidence for therapeutically targeting sGC via riociguat to treat CRPC.

Statement of significance

Prostate cancer is the second highest cancer-related cause of death for American men. Once patients progress to castration-resistant prostate cancer, the incurable and fatal stage, there are few viable treatment options available. Here we identify and characterize a new and clinically actionable target, the soluble guanylyl cyclase complex, in castration-resistant prostate cancer. Notably we find that repurposing the FDA-approved and safely tolerated sGC agonist, riociguat, decreases castration-resistant tumor growth and re-sensitizes these tumors to radiation therapy. Thus our study provides both new biology regarding the origins of castration resistance as well as a new and viable treatment option.

BAY58-2667 Activates Different Soluble Guanylyl Cyclase Species by Distinct Mechanisms that Indicate Its Principal Target in Cells is the Heme-Free Soluble Guanylyl Cyclase-Heat Shock Protein 90 Complex

Nitric oxide (NO)-unresponsive forms of soluble guanylyl cyclase (sGC) exist naturally and in disease can disable NO-sGC-cGMP signaling. Agonists like BAY58-2667 (BAY58) target these sGC forms, but their mechanisms of action in living cells are unclear. We studied rat lung fibroblast-6 cells and human airway smooth muscle cells that naturally express sGC and HEK293 cells that we transfected to express sGC and variants. Cells were cultured to build up different forms of sGC, and we used fluorescence and FRET-based measures to monitor BAY58-driven cGMP production and any protein partner exchange or heme loss events that may occur for each sGC species. We found that: (i) BAY58 activated cGMP production by the apo-sGCβ-Hsp90 species after a 5-8 minute delay that was associated with apo-sGCβ exchanging its Hsp90 partner with an sGCα subunit. (ii) In cells containing an artificially constructed heme-free sGC heterodimer, BAY58 initiated an immediate and three times faster cGMP production. However, this behavior was not observed in cells expressing native sGC under any condition. (iii) BAY58 activated cGMP production by ferric heme sGC only after a 30-minute delay, coincident with it initiating a delayed, slow ferric heme loss from sGCβ We conclude that the kinetics favor BAY58 activation of the apo-sGCβ-Hsp90 species over the ferric heme sGC species in living cells. The protein partner exchange events driven by BAY58 account for the initial delay in cGMP production and also limit the speed of subsequent cGMP production in the cells. Our findings clarify how agonists like BAY58 may activate sGC in health and disease. SIGNIFICANCE STATEMENT: A class of agonists can activate cyclic guanosine monophosphate (cGMP) synthesis by forms of soluble guanylyl cyclase (sGC) that do not respond to NO and accumulate in disease, but the mechanisms of action are unclear. This study clarifies what forms of sGC exist in living cells, which of these can be activated by the agonists, and the mechanisms and kinetics by which each form is activated. This information may help to hasten deployment of these agonists for pharmaceutical intervention and clinical therapy.

CYB5R3 in type II alveolar epithelial cells protects against lung fibrosis by suppressing TGF-β1 signaling

Type II alveolar epithelial cell (AECII) redox imbalance contributes to the pathogenesis of idiopathic pulmonary fibrosis (IPF), a deadly disease with limited treatment options. Here, we show that expression of membrane-bound cytochrome B5 reductase 3 (CYB5R3), an enzyme critical for maintaining cellular redox homeostasis and soluble guanylate cyclase (sGC) heme iron redox state, is diminished in IPF AECIIs. Deficiency of CYB5R3 in AECIIs led to sustained activation of the pro-fibrotic factor TGF-β1 and increased susceptibility to lung fibrosis. We further show that CYB5R3 is a critical regulator of ERK1/2 phosphorylation and the sGC/cGMP/protein kinase G axis that modulates activation of the TGF-β1 signaling pathway. We demonstrate that sGC agonists (BAY 41-8543 and BAY 54-6544) are effective in reducing the pulmonary fibrotic outcomes of in vivo deficiency of CYB5R3 in AECIIs. Taken together, these results show that CYB5R3 in AECIIs is required to maintain resilience after lung injury and fibrosis and that therapeutic manipulation of the sGC redox state could provide a basis for treating fibrotic conditions in the lung and beyond.

An acute bout of prolonged sitting blunts popliteal endothelium-independent dilation in young, healthy adults

A single bout of prolonged uninterrupted sitting increases oxidative stress, reduces popliteal blood flow-induced shear stress, and diminishes endothelium-dependent, flow-mediated dilation (FMD). The FMD response is also influenced by the sensitivity of vascular smooth muscle cells to nitric oxide (i.e., endothelium-independent dilation), which is also attenuated by elevated oxidative stress. However, it is currently unknown whether prolonged sitting impacts popliteal endothelium-independent dilation responses, which may uncover a novel mechanism associated with sitting-induced vascular dysfunction. This study tested the hypothesis that prolonged sitting attenuates both popliteal FMD and endothelium-independent, nitroglycerin-mediated dilation responses (NMD, 0.4 mg sublingual dose). Popliteal blood flow (mL/min), relative FMD (%), and NMD (%) were assessed via duplex ultrasonography before and after a ∼3-h bout of sitting in 14 young, healthy adults (8♀; 22 ± 2 yr). Prolonged sitting attenuated resting blood flow (57 ± 23 to 32 ± 16 mL/min, P < 0.001), relative FMD (4.6 ± 2.8% to 2.2 ± 2.5%; P = 0.001), and NMD (7.3 ± 4.0% to 4.6 ± 3.0%; P = 0.002). These novel findings demonstrate that both endothelium-dependent and independent mechanisms contribute to the adverse vascular consequences associated with prolonged bouts of sitting.NEW & NOTEWORTHY We demonstrate that lower-limb vascular smooth muscle function is attenuated in young, healthy adults after an acute bout of prolonged sitting. These data indicate that prolonged sitting-induced vascular dysfunction involves both endothelium-dependent and -independent mechanisms.

Cellular Factors That Shape the Activity or Function of Nitric Oxide-Stimulated Soluble Guanylyl Cyclase

NO-stimulated guanylyl cyclase (SGC) is a hemoprotein that plays key roles in various physiological functions. SGC is a typical enzyme-linked receptor that combines the functions of a sensor for NO gas and cGMP generator. SGC possesses exclusive selectivity for NO and exhibits a very fast binding of NO, which allows it to function as a sensitive NO receptor. This review describes the effect of various cellular factors, such as additional NO, cell thiols, cell-derived small molecules and proteins on the function of SGC as cellular NO receptor. Due to its vital physiological function SGC is an important drug target. An increasing number of synthetic compounds that affect SGC activity via different mechanisms are discovered and brought to clinical trials and clinics. Cellular factors modifying the activity of SGC constitute an opportunity for improving the effectiveness of existing SGC-directed drugs and/or the creation of new therapeutic strategies.

Dental Pulp Inflammation Initiates the Occurrence of Mast Cells Expressing the α1 and β1 Subunits of Soluble Guanylyl Cyclase

The binding of nitric oxide (NO) to heme in the β₁ subunit of soluble guanylyl cyclase (sGC) activates both the heterodimeric α₁β₁ and α₂β₁ isoforms of the enzyme, leading to the increased production of cGMP from GTP. In cultured human mast cells, exogenous NO is able to inhibit mast cell degranulation via NO-cGMP signaling. However, under inflammatory oxidative or nitrosative stress, sGC becomes insensitive to NO. The occurrence of mast cells in healthy and inflamed human tissues and the in vivo expression of the α₁ and β₁ subunits of sGC in human mast cells during inflammation remain largely unresolved and were investigated here. Using peroxidase and double immunohistochemical incubations, no mast cells were found in healthy dental pulp, whereas the inflammation of dental pulp initiated the occurrence of several mast cells expressing the α₁ and β₁ subunits of sGC. Since inflammation-induced oxidative and nitrosative stress oxidizes Fe²⁺ to Fe³⁺ in the β₁ subunit of sGC, leading to the desensitization of sGC to NO, we hypothesize that the NO- and heme-independent pharmacological activation of sGC in mast cells may be considered as a regulatory strategy for mast cell functions in inflamed human dental pulp.

New Opportunities in Heart Failure with Preserved Ejection Fraction: From Bench to Bedside… and Back

Heart failure with preserved ejection fraction (HFpEF) is a growing public health problem in nearly 50% of patients with heart failure. Therefore, research on new strategies for its diagnosis and management has become imperative in recent years. Few drugs have successfully improved clinical outcomes in this population. Therefore, numerous attempts are being made to find new pharmacological interventions that target the main mechanisms responsible for this disease. In recent years, pathological mechanisms such as cardiac fibrosis and inflammation, alterations in calcium handling, NO pathway disturbance, and neurohumoral or mechanic impairment have been evaluated as new pharmacological targets showing promising results in preliminary studies. This review aims to analyze the new strategies and mechanical devices, along with their initial results in pre-clinical and different phases of ongoing clinical trials for HFpEF patients. Understanding new mechanisms to generate interventions will allow us to create methods to prevent the adverse outcomes of this silent pandemic.

Cigarette smoke induces pulmonary arterial dysfunction through an imbalance in the redox status of the soluble guanylyl cyclase

Chronic obstructive pulmonary disease (COPD), whose main risk factor is cigarette smoking (CS), is one of the most common diseases globally. Some COPD patients also develop pulmonary hypertension (PH), a severe complication that leads to premature death. Evidence suggests reactive oxygen species (ROS) involvement in COPD and PH, especially regarding pulmonary artery smooth muscle cells (PASMC) dysfunction. However, the effects of CS-driven oxidative stress on the pulmonary vasculature are not completely understood. Herein we provide evidence on the effects of CS extract (CSE) exposure on PASMC regarding ROS production, antioxidant response and its consequences on vascular tone dysregulation. Our results indicate that CSE exposure promotes mitochondrial fission, mitochondrial membrane depolarization and increased mitochondrial superoxide levels. However, this superoxide increase did not parallel a counterbalancing antioxidant response in human pulmonary artery (PA) cells. Interestingly, the mitochondrial superoxide scavenger mitoTEMPO reduced mitochondrial fission and membrane potential depolarization caused by CSE. As we have previously shown, CSE reduces PA vasoconstriction and vasodilation. In this respect, mitoTEMPO prevented the impaired nitric oxide-mediated vasodilation, while vasoconstriction remained reduced. Finally, we observed a CSE-driven downregulation of the Cyb5R3 enzyme, which prevents soluble guanylyl cyclase oxidation in PASMC. This might explain the CSE-mediated decrease in PA vasodilation. These results provide evidence that there might be a connection between mitochondrial ROS and altered vasodilation responses in PH secondary to COPD, and strongly support the potential of antioxidant strategies specifically targeting mitochondria as a new therapy for these diseases.

SOLUBLE GUANYLYL CYCLASE ACTIVATION RESCUES HYPEROXIA-INDUCED DYSFUNCTION OF VASCULAR RELAXATION

ABSTRACT

Introduction: Perioperative alterations in perfusion lead to ischemia and reperfusion injury, and supplemental oxygen is administered during surgery to limit hypoxic injury but can lead to hyperoxia. We hypothesized that hyperoxia impairs endothelium-dependent and endothelium-independent vasodilation but not the vasodilatory response to heme-independent soluble guanylyl cyclase activation. Methods: We measured the effect of oxygen on vascular reactivity in mouse aortas. Mice were ventilated with 21% (normoxia), 60% (moderate hyperoxia), or 100% (severe hyperoxia) oxygen during 30 minutes of renal ischemia and 30 minutes of reperfusion. After sacrifice, the thoracic aorta was isolated, and segments mounted on a wire myograph. We measured endothelium-dependent and endothelium-independent vasodilation with escalating concentrations of acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, and we measured the response to heme-independent soluble guanylyl cyclase activation with cinaciguat. Vasodilator responses to each agonist were quantified as the maximal theoretical response ( Emax ) and the effective concentration to elicit 50% relaxation (EC 50 ) using a sigmoid model and nonlinear mixed-effects regression. Aortic superoxide was measured with dihydroethidium probe and high-performance liquid chromatography quantification of the specific superoxide product 2-hydroxyethidium. Results: Hyperoxia impaired endothelium-dependent (ACh) and endothelium-independent (SNP) vasodilation compared with normoxia and had no effect on cinaciguat-induced vasodilation. The median ACh Emax was 76.4% (95% confidence interval = 69.6 to 83.3) in the normoxia group, 53.5% (46.7 to 60.3) in the moderate hyperoxia group, and 53.1% (46.3 to 60.0) in the severe hyperoxia group ( P < 0.001, effect across groups), while the ACh EC 50 was not different among groups. The SNP Emax was 133.1% (122.9 to 143.3) in normoxia, 128.3% (118.1 to 138.6) in moderate hyperoxia, and 114.8% (104.6 to 125.0) in severe hyperoxia ( P < 0.001, effect across groups), and the SNP EC 50 was 0.38 log M greater in moderate hyperoxia than in normoxia (95% confidence interval = 0.18 to 0.58, P < 0.001). Cinaciguat Emax and EC 50 were not different among oxygen treatment groups (median range Emax = 78.0% to 79.4% and EC 50 = -18.0 to -18.2 log M across oxygen groups). Aorta 2-hydroxyethidium was 1419 pmol/mg of protein (25th-75th percentile = 1178-1513) in normoxia, 1993 (1831-2473) in moderate hyperoxia, and 2078 (1936-2922) in severe hyperoxia ( P = 0.008, effect across groups). Conclusions: Hyperoxia, compared with normoxia, impaired endothelium-dependent and endothelium-independent vasodilation but not the response to heme-independent soluble guanylyl cyclase activation, and hyperoxia increased vascular superoxide production. Results from this study could have important implications for patients receiving high concentrations of oxygen and at risk for ischemia reperfusion-mediated organ injury.

Soluble guanylate cyclase activator BAY 54-6544 improves vasomotor function and survival in an accelerated ageing mouse model

DNA damage is a causative factor in ageing of the vasculature and other organs. One of the most important vascular ageing features is reduced nitric oxide (NO)soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) signaling. We hypothesized that the restoration of NO-sGC-cGMP signaling with an sGC activator (BAY 54-6544) may have beneficial effects on vascular ageing and premature death in DNA repair-defective mice undergoing accelerated ageing. Eight weeks of treatment with a non-pressor dosage of BAY 54-6544 restored the decreased in vivo microvascular cutaneous perfusion in progeroid Ercc1^∆/- mice to the level of wild-type mice. In addition, BAY 54-6544 increased survival of Ercc1^∆/- mice. In isolated Ercc1^∆/- aorta, the decreased endothelium-independent vasodilation was restored after chronic BAY 54-6544 treatment. Senescence markers p16 and p21, and markers of inflammation, including Ccl2, Il6 in aorta and liver, and circulating IL-6 and TNF-α were increased in Ercc1^∆/- , which was lowered by the treatment. Expression of antioxidant genes, including Cyb5r3 and Nqo1, was favorably changed by chronic BAY 54-6544 treatment. In summary, BAY 54-6544 treatment improved the vascular function and survival rates in mice with accelerated ageing, which may have implication in prolonging health span in progeria and normal ageing.

Riociguat attenuates left ventricular proteome and microRNA profile changes after experimental aortic stenosis in mice

BACKGROUND AND PURPOSE

Development and progression of heart failure (HF) involve endothelial and myocardial dysfunction as well as a dysregulation of the nitric oxide - soluble guanylyl cyclase - cyclic guanosine monophosphate (NO-sGC-cGMP) signalling pathway. Recently, we reported that the sGC stimulator riociguat (RIO) has beneficial effects on cardiac remodelling and progression of HF in response to chronic pressure overload. Here, we examined if these favourable RIO effects are also reflected in alterations of the myocardial proteome and microRNA profiles.

EXPERIMENTAL APPROACH

Male C57BL/6N mice underwent transverse aortic constriction (TAC) and sham operated mice served as controls. TAC and sham animals were randomised and treated with either RIO or vehicle for five weeks, starting three weeks post-surgery when cardiac hypertrophy was established. Afterwards we performed mass spectrometric proteome analyses and microRNA sequencing of proteins and RNAs, respectively, isolated from left ventricles (LV).

KEY RESULTS

TAC-induced changes of the LV proteome were significantly reduced by RIO treatment. Bioinformatics analyses revealed that RIO improved TAC-induced cardiovascular disease related pathways, metabolism and energy production, e.g. reversed alterations in the levels of myosin heavy chain 7 (MYH7), cardiac phospholamban (PLN), and ankyrin repeat domain-containing protein 1 (ANKRD1). RIO also attenuated TAC-induced changes of microRNA levels in the LV.

CONCLUSION AND IMPLICATIONS

The sGC stimulator RIO has beneficial effects on cardiac structure and function during pressure overload, which is accompanied by a reversal of TAC-induced changes of the cardiac proteome and microRNA profile. Our data support the potential of RIO as a novel HF therapeutic.

Inhaled nitric oxide improves post-cardiac arrest outcomes via guanylate cyclase-1 in bone marrow-derived cells

RATIONALE

Nitric oxide (NO) exerts its biological effects primarily via activation of guanylate cyclase (GC) and production of cyclic guanosine monophosphate. Inhaled NO improves outcomes after cardiac arrest and cardiopulmonary resuscitation (CPR). However, mechanisms of the protective effects of breathing NO after cardiac arrest are incompletely understood.

OBJECTIVE

To elucidate the mechanisms of beneficial effects of inhaled NO on outcomes after cardiac arrest.

METHODS

Adult male C57BL/6J wild-type (WT) mice, GC-1 knockout mice, and chimeric WT mice with WT or GC-1 knockout bone marrow were subjected to 8 min of potassium-induced cardiac arrest to determine the role of GC-1 in bone marrow-derived cells. Mice breathed air or 40 parts per million NO for 23 h starting at 1 h after CPR.

RESULTS

Breathing NO after CPR prevented hypercoagulability, cerebral microvascular occlusion, an increase in circulating polymorphonuclear neutrophils and neutrophil-to-lymphocyte ratio, and right ventricular dysfunction in WT mice, but not in GC-1 knockout mice, after cardiac arrest. The lack of GC-1 in bone marrow-derived cells diminished the beneficial effects of NO breathing after CPR.

CONCLUSIONS

GC-dependent signaling in bone marrow-derived cells is essential for the beneficial effects of inhaled NO after cardiac arrest and CPR.

Soluble GC stimulators and activators: Past, present and future

The discovery of soluble GC (sGC) stimulators and sGC activators provided valuable tools to elucidate NO-sGC signalling and opened novel pharmacological opportunities for cardiovascular indications and beyond. The first-in-class sGC stimulator riociguat was approved for pulmonary hypertension in 2013 and vericiguat very recently for heart failure. sGC stimulators enhance sGC activity independent of NO and also act synergistically with endogenous NO. The sGC activators specifically bind to, and activate, the oxidised haem-free form of sGC. Substantial research efforts improved on the first-generation sGC activators such as cinaciguat, culminating in the discovery of runcaciguat, currently in clinical Phase II trials for chronic kidney disease and diabetic retinopathy. Here, we highlight the discovery and development of sGC stimulators and sGC activators, their unique modes of action, their preclinical characteristics and the clinical studies. In the future, we expect to see more sGC agonists in new indications, reflecting their unique therapeutic potential.

cGMP and mitochondrial K+ channels-Compartmentalized but closely connected in cardioprotection

The 3',5'-cGMP pathway triggers cytoprotective responses and improves cardiomyocyte survival during myocardial ischaemia and reperfusion (I/R) injury. These beneficial effects were attributed to NO-sensitive GC induced cGMP production leading to activation of cGMP-dependent protein kinase I (cGKI). cGKI in turn phosphorylates many substrates, which eventually facilitate opening of mitochondrial ATP-sensitive potassium channels (mitoK_ATP ) and Ca²⁺ -activated potassium channels of the BK type (mitoBK). Accordingly, agents activating mitoK_ATP or mitoBK provide protection against I/R-induced damages. Here, we provide an up-to-date summary of the infarct-limiting actions exhibited by the GC/cGMP axis and discuss how mitoK_ATP and mitoBK, which are present at the inner mitochondrial membrane, confer mito- and cytoprotective effects on cardiomyocytes exposed to I/R injury. In view of this, we believe that the functional connection between the cGMP cascade and mitoK⁺ channels should be exploited further as adjunct to reperfusion therapy in myocardial infarction.

Inactivation of soluble guanylyl cyclase in living cells proceeds without loss of haem and involves heterodimer dissociation as a common step

BACKGROUND AND PURPOSE

Nitric oxide (NO) activates soluble guanylyl cyclase (sGC) for cGMP production, but in disease, sGC becomes insensitive towards NO activation. What changes occur to sGC during its inactivation in cells is not clear.

EXPERIMENTAL APPROACH

We utilized HEK293 cells expressing sGC proteins to study the changes that occur regarding its haem content, heterodimer status and sGCβ protein partners when the cells were given the oxidant ODQ or the NO donor NOC12 to inactivate sGC. Haem content of sGCβ was monitored in live cells through use of a fluorescent-labelled sGCβ construct, whereas sGC heterodimer status and protein interactions were studied by Western blot analysis. Experiments with purified proteins were also performed.

KEY RESULTS

ODQ- or NOC12-driven inactivation of sGC in HEK293 cells was associated with haem oxidation (by ODQ), S-nitrosation of the sGCβ subunit (by NOC12), sGC heterodimer breakup and association of the freed sGCβ subunit with cell chaperone Hsp90. These changes occurred without detectable loss of haem from the sGCβ reporter construct. Treating a purified ferrous haem-containing sGCβ with ODQ or NOC12 caused it to bind with Hsp90 without showing any haem loss.

CONCLUSION AND IMPLICATIONS

Oxidative (ODQ) or nitrosative (NOC12) inactivation of cell sGC involves sGC heterodimer dissociation and rearrangement of the sGCβ protein partners without any haem loss from sGCβ. Clarifying what changes do and do not occur to sGC during its inactivation in cells may direct strategies to preserve or recover NO-dependent cGMP signalling in health and disease.

Peripheral arteriopathy caused by Notch3 gain-of-function mutation involves ER and oxidative stress and blunting of NO/sGC/cGMP pathway

Notch3 mutations cause Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL), which predisposes to stroke and dementia. CADASIL is characterised by vascular dysfunction and granular osmiophilic material (GOM) accumulation in cerebral small vessels. Systemic vessels may also be impacted by Notch3 mutations. However vascular characteristics and pathophysiological processes remain elusive. We investigated mechanisms underlying the peripheral vasculopathy mediated by CADASIL-causing Notch3 gain-of-function mutation. We studied: (i) small arteries and vascular smooth muscle cells (VSMCs) from TgNotch3R169C mice (CADASIL model), (ii) VSMCs from peripheral arteries from CADASIL patients, and (iii) post-mortem brains from CADASIL individuals. TgNotch3R169C vessels exhibited GOM deposits, increased vasoreactivity and impaired vasorelaxation. Hypercontractile responses were normalised by fasudil (Rho kinase inhibitor) and 4-phenylbutyrate (4-PBA; endoplasmic-reticulum (ER) stress inhibitor). Ca2+ transients and Ca2+ channel expression were increased in CADASIL VSMCs, with increased expression of Rho guanine nucleotide-exchange factors (GEFs) and ER stress proteins. Vasorelaxation mechanisms were impaired in CADASIL, evidenced by decreased endothelial nitric oxide synthase (eNOS) phosphorylation and reduced cyclic guanosine 3',5'-monophosphate (cGMP) levels, with associated increased soluble guanylate cyclase (sGC) oxidation, decreased sGC activity and reduced levels of the vasodilator hydrogen peroxide (H2O2). In VSMCs from CADASIL patients, sGC oxidation was increased and cGMP levels decreased, effects normalised by fasudil and 4-PBA. Cerebral vessels in CADASIL patients exhibited significant oxidative damage. In conclusion, peripheral vascular dysfunction in CADASIL is associated with altered Ca2+ homoeostasis, oxidative stress and blunted eNOS/sGC/cGMP signaling, processes involving Rho kinase and ER stress. We identify novel pathways underlying the peripheral arteriopathy induced by Notch3 gain-of-function mutation, phenomena that may also be important in cerebral vessels.

Maturation, inactivation, and recovery mechanisms of soluble guanylyl cyclase

Soluble guanylate cyclase (sGC) is a heme-containing heterodimeric enzyme that generates many molecules of cGMP in response to its ligand nitric oxide (NO); sGC thereby acts as an amplifier in NO-driven biological signaling cascades. Because sGC helps regulate the cardiovascular, neuronal, and gastrointestinal systems through its cGMP production, boosting sGC activity and preventing or reversing sGC inactivation are important therapeutic and pharmacologic goals. Work over the last two decades is uncovering the processes by which sGC matures to become functional, how sGC is inactivated, and how sGC is rescued from damage. A diverse group of small molecules and proteins have been implicated in these processes, including NO itself, reactive oxygen species, cellular heme, cell chaperone Hsp90, and various redox enzymes as well as pharmacologic sGC agonists. This review highlights their participation and provides an update on the processes that enable sGC maturation, drive its inactivation, or assist in its recovery in various settings within the cell, in hopes of reaching a better understanding of how sGC function is regulated in health and disease.

Nitric Oxide in Post-cardiac Arrest Syndrome

Sudden cardiac arrest is a leading cause of death worldwide. Although the methods of cardiopulmonary resuscitation have been improved, mortality is still unacceptably high, and many survivors suffer from lasting neurological deficits due to the post-cardiac arrest syndrome (PCAS). Pathophysiologically, generalized vascular endothelial dysfunction accompanied by platelet activation and systemic inflammation has been implicated in the pathogenesis of PCAS. Because endothelial-derived nitric oxide (NO) plays a central role in maintaining vascular homeostasis, the role of NO-dependent signaling has been a focus of the intense investigation. Recent preclinical studies showed that therapeutic interventions that increase vascular NO bioavailability may improve outcomes after cardiac arrest complicated with PCAS. In particular, NO inhalation therapy has been shown to improve neurological outcomes and survival in multiple species. Clinical studies examining the safety and efficacy of inhaled NO in patients sustaining PCAS are warranted.

Preserved activity of soluble guanylate cyclase (sGC) in iliac artery from middle-aged rats: Role of sGC modulators

Vascular aging leads to structural and functional changes. Iliac arteries (IA) provide blood flow to lower urinary tract and pelvic ischemia has been reported as an important factor for bladder remodeling and overactivity. Dysfunction of the nitric oxide (NO)-cyclic guanosine monophosphate pathway (cGMP) is one factor involved in the development of lower urinary tract (LUT) disorders. Therefore, we hypothesized that ageing-associated LUT disorders is a consequence of lower cGMP productions due to an oxidation of soluble guanylate cylase (sGC) that results in local ischemia. In the present study IA from middle-aged and young rats were isolated and the levels of NO, reactive oxygen species (ROS), the gene expression of the enzymes involved in the NO-pathway and concentration-response curves to the soluble guanylate (sGC) stimulator (BAY 41-2272), sGC activator (BAY 58-2667), tadalafil, acetylcholine (ACh) and sodium nitroprusside (SNP) were determined. In IA from middle-aged rats the gene expression for endothelial nitric oxide synthase and the ROS were lower and higher, respectively than the young group. The relaxations induced by ACh and SNP were significantly lower in IA from middle-aged rats. In IA from middle-aged rats the mRNA expression of PDE5 was 55% higher, accompanied by lower relaxation induced by tadalafil. On the other hand, the gene expression for sGCα1 were similar in IA from both groups. Both BAY 41-2272 and BAY 58-2667 produced concentration-dependent relaxations in IA from both groups, however, the latter was 9-times more potent than BAY 41-2272 and produced similar relaxations in IA in both middle-aged and young groups. Yet, the sGC oxidant, ODQ increased the relaxation and the cGMP levels induced by BAY 58-2667. On the other hand, in tissues stimulated with SNP, tadalafil and BAY-2272, the intracellular levels of cGMP were lower in IA from middle-aged than young rats. In conclusion, our results clearly showed that the relaxations induced by the endothelium-dependent and -independent agents, by the PDE5 inhibitor and by sGC stimulator were impaired in IA from aged rats, while that induced by sGC activator was preserved. It suggests that sGC activator may be advantageous in treating ischemia-related functional changes in the lower urinary tract organs in situations where the NO levels are reduced.

An inherent dysfunction in soluble guanylyl cyclase is present in the airway of severe asthmatics and is associated with aberrant redox enzyme expression and compromised NO-cGMP signaling

A subset of asthmatics develop a severe form of the disease whose etiology involves airway inflammation along with inherent drivers that remain ill-defined. To address this, we studied human airway smooth muscle cells (HASMC), whose relaxation drives airway bronchodilation and whose dysfunction contributes to airway obstruction and hypersensitivity in severe asthma. Because HASMC relaxation can be driven by the NO-soluble guanylyl cyclase (sGC)-cGMP signaling pathway, we questioned if HASMC from severe asthma donors might possess inherent defects in their sGC or in redox enzymes that support sGC function. We analyzed HASMC primary lines derived from 17 severe asthma and 16 normal donors and corresponding lung tissue samples regarding sGC activation by NO or by pharmacologic agonists, and also determined expression levels of sGC α1 and β1 subunits, supporting redox enzymes, and related proteins. We found a majority of the severe asthma donor HASMC (12/17) and lung samples primarily expressed a dysfunctional sGC that was NO-unresponsive and had low heterodimer content and high Hsp90 association. This sGC phenotype correlated with lower expression levels of the supporting redox enzymes cytochrome b5 reductase, catalase, and thioredoxin-1, and higher expression of heme oxygenases 1 and 2. Together, our work reveals that severe asthmatics are predisposed toward defective NO-sGC-cGMP signaling in their airway smooth muscle due to an inherent sGC dysfunction, which in turn is associated with inherent changes in the cell redox enzymes that impact sGC maturation and function.

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The etiology of severe asthma involves airway inflammation and inherent drivers that remain ill-defined.

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Airway smooth muscle cells of severe asthmatics display a NO-unresponsive and dysfunctional sGC which persists in culture.

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Their inherent sGC dysfunction is associated with low CYB5R3 expression and altered expression of other redox enzymes.

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That airway sGC dysfunction and redox enzyme changes cluster within severe asthma is unexpected and may help guide therapy.

Nitric Oxide Mediated Degradation of CYP2A6 via the Ubiquitin-Proteasome Pathway in Human Hepatoma Cells

Several cytochrome P450 enzymes are known to be down-regulated by nitric oxide (NO). CYP2A6 is responsible for the metabolism of nicotine and several other xenobiotics, but its susceptibility to down-regulation by NO has not been reported. To address this question, we used Huh7 human hepatoma cell lines to express CYP2A6 with a C-terminal V5 tag (CYP2A6V5). NO donor treatment [dipropylenetriamine NONOate (DPTA)] down-regulated CYP2A6 protein to approximately 40% of control levels in 4 hours. An NO scavenging agent protected CYP2A6 from down-regulation by DPTA in a concentration-dependent manner, demonstrating that the down-regulation is NO-dependent. Experiments with the protein synthesis inhibitor cycloheximide showed that CYP2A6 protein down-regulation occurs posttranslationally. In the presence of proteasome inhibitors MG132 or bortezomib, NO-treated cells showed an accumulation of a high molecular mass signal, whereas autophagy inhibitors chloroquine and 3-methyladenine and the lysosomal and calpain inhibitor E64d had no effect. Immunoprecipitation of CYP2A6 followed by Western blotting with an antiubiquitin antibody showed that the high molecular mass species contain polyubiquitinated CYP2A6 protein. This suggests that NO led to the degradation of protein via the ubiquitin-proteasome pathway. The down-regulation by NO was blocked by the reversible CYP2A6 inhibitor pilocarpine but not by the suicide inhibitor methoxsalen, demonstrating that down-regulation requires NO access to the active site but does not require catalytic activity of the enzyme. These findings provide novel insights toward the regulation of CYP2A6 in a human cell line and can influence our understanding of CYP2A6-related drug metabolism. SIGNIFICANCE STATEMENT: This study demonstrates that the nicotine metabolizing enzyme CYP2A6 is down-regulated by nitric oxide, a molecule produced in large amounts in the context of inflammation and that is also inhaled from cigarette smoke. This occurs via ubiquitination and proteasomal degradation, and does not require catalytic activity of the enzyme. This work adds to the growing knowledge of the selective effect and mechanism of action of nitric oxide (NO) on cytochrome P450 enzymes and suggests a possible novel mode of interaction between nicotine and NO in cigarette smokers.

Stimulation of soluble guanylate cyclase improves donor organ function in rat heart transplantation

Heart transplantation remains the definitive therapy of end-stage heart failure. Ischemia-reperfusion injury occurring during transplantation is a primary determinant of long-term outcome of heart transplantation and primary graft insufficiency. Modification of the nitric oxide/soluble guanylate cyclase/cyclic guanosine monophosphate signaling pathway appears to be one of the most promising among the pharmacological interventional options. We aimed at characterizing the cardio-protective effects of the soluble guanylate cyclase stimulator riociguat in a rat model of heterotopic heart transplantation. Donor Lewis rats were treated orally with either riociguat or placebo for two days (n = 9) in each transplanted group and (n = 7) in donor groups. Following explantation, hearts were heterotopically transplanted. After one hour reperfusion, left ventricular pressure-volume relations and coronary blood flow were recorded. Molecular biological measurements and histological examination were also completed. Left ventricular contractility (systolic pressure: 117 ± 13 vs. 48 ± 5 mmHg, p < 0.001; dP/dt_max: 2963 ± 221 vs. 1653 ± 159 mmHg/s, p < 0.001), active relaxation (dP/dt_min: −2014 ± 305 vs. −1063 ± 177 mmHg/s, p = 0.02; all at 120 µl of left ventricular volume), and alteration of coronary blood flow standardized to heart weight (2.55 ± 0.32 vs. 1.67 ± 0.22 ml/min/g, p = 0.03) were markedly increased following preconditioning with riociguat. Myocardial apoptosis markers were also significantly reduced in the riociguat pretreated group as well as the antioxidant markers were elevated. Pharmacological preconditioning with riociguat decreases ischemia-reperfusion injury and improves donor organ function in our animal model of heart transplantation. Therefore, riociguat might be a potential cardioprotective agent.

Guanylyl Cyclase-cGMP Signaling Pathway in Melanocytes: Differential Effects of Altered Gravity in Non-Metastatic and Metastatic Cells

Human epidermal melanocytes as melanin producing skin cells represent a crucial barrier against UV-radiation and oxidative stress. It was shown that the intracellular signaling molecule cyclic guanosine-3′,5′-monophosphate (cGMP), generated by the guanylyl cyclases (GCs), e.g., the nitric oxide (NO)-sensitive soluble GC (sGC) and the natriuretic peptide-activated particulate GC (GC-A/GC-B), plays a role in the melanocyte response to environmental stress. Importantly, cGMP is involved in NO-induced perturbation of melanocyte–extracellular matrix interactions and in addition, increased NO production during inflammation may lead to loss of melanocytes and support melanoma metastasis. Further, the NO-sensitive sGC is expressed predominantly in human melanocytes and non-metastatic melanoma cells, whereas absence of functional sGC but up-regulated expression of GC-A/GC-B and inducible NO synthase (iNOS) are detected in metastatic cells. Thus, suppression of sGC expression as well as up-regulated expression of GC-A/GC-B/iNOS appears to correlate with tumor aggressiveness. As the cGMP pathway plays important roles in melanocyte (patho)physiology, we present an overview on the differential effects of altered gravity (hypergravity/simulated microgravity) on the cGMP signaling pathway in melanocytes and melanoma cells with different metastatic potential. We believe that future experiments in real microgravity may benefit from considering cGMP signaling as a possible factor for melanocyte transformation and in medication.

cGMP: a unique 2nd messenger molecule - recent developments in cGMP research and development

Cyclic guanosine monophosphate (cGMP) is a unique second messenger molecule formed in different cell types and tissues. cGMP targets a variety of downstream effector molecules and, thus, elicits a very broad variety of cellular effects. Its production is triggered by stimulation of either soluble guanylyl cyclase (sGC) or particulate guanylyl cyclase (pGC); both enzymes exist in different isoforms. cGMP-induced effects are regulated by endogenous receptor ligands such as nitric oxide (NO) and natriuretic peptides (NPs). Depending on the distribution of sGC and pGC and the formation of ligands, this pathway regulates not only the cardiovascular system but also the kidney, lung, liver, and brain function; in addition, the cGMP pathway is involved in the pathogenesis of fibrosis, inflammation, or neurodegeneration and may also play a role in infectious diseases such as malaria. Moreover, new pharmacological approaches are being developed which target sGC- and pGC-dependent pathways for the treatment of various diseases. Therefore, it is of key interest to understand this pathway from scratch, beginning with the molecular basis of cGMP generation, the structure and function of both guanylyl cyclases and cGMP downstream targets; research efforts also focus on the subsequent signaling cascades, their potential crosstalk, and also the translational and, ultimately, the clinical implications of cGMP modulation. This review tries to summarize the contributions to the "9th International cGMP Conference on cGMP Generators, Effectors and Therapeutic Implications" held in Mainz in 2019. Presented data will be discussed and extended also in light of recent landmark findings and ongoing activities in the field of preclinical and clinical cGMP research.

Loss of smooth muscle CYB5R3 amplifies angiotensin II-induced hypertension by increasing sGC heme oxidation

Nitric oxide regulates BP by binding the reduced heme iron (Fe2+) in soluble guanylyl cyclase (sGC) and relaxing vascular smooth muscle cells (SMCs). We previously showed that sGC heme iron reduction (Fe3+ → Fe2+) is modulated by cytochrome b5 reductase 3 (CYB5R3). However, the in vivo role of SMC CYB5R3 in BP regulation remains elusive. Here, we generated conditional smooth muscle cell-specific Cyb5r3 KO mice (SMC CYB5R3-KO) to test if SMC CYB5R3 loss affects systemic BP in normotension and hypertension via regulation of the sGC redox state. SMC CYB5R3-KO mice exhibited a 5.84-mmHg increase in BP and impaired acetylcholine-induced vasodilation in mesenteric arteries compared with controls. To drive sGC oxidation and elevate BP, we infused mice with angiotensin II. We found that SMC CYB5R3-KO mice exhibited a 14.75-mmHg BP increase, and mesenteric arteries had diminished nitric oxide-dependent vasodilation but increased responsiveness to sGC heme-independent activator BAY 58-2667 over controls. Furthermore, acute injection of BAY 58-2667 in angiotensin II-treated SMC CYB5R3-KO mice showed greater BP reduction compared with controls. Together, these data provide the first in vivo evidence to our knowledge that SMC CYB5R3 is an sGC heme reductase in resistance arteries and provides resilience against systemic hypertension development.

17β-Estradiol nongenomically induces vascular endothelial H2S release by promoting phosphorylation of cystathionine γ-lyase

Estrogen exerts its cardiovascular protective role at least in part by regulating endothelial hydrogen sulfide (H₂S) release, but the underlying mechanisms remain to be fully elucidated. Estrogen exerts genomic effects, i.e. those involving direct binding of the estrogen receptor (ER) to gene promoters in the nucleus, and nongenomic effects, mediated by interactions of the ER with other proteins. Here, using human umbilical vein endothelial cells (HUVECs), immunological detection, MS-based analyses, and cGMP and H₂S assays, we show that 17β-estradiol (E2) rapidly enhances endothelial H₂S release in a nongenomic manner. We found that E2 induces phosphorylation of cystathionine γ-lyase (CSE), the key enzyme in vascular endothelial H₂S generation. Mechanistically, E2 enhanced the interaction of membrane ERα with the Gα subunit Gαi-2/3, which then transactivated particulate guanylate cyclase-A (pGC-A) to produce cGMP, thereby activating protein kinase G type I (PKG-I). We also found that PKG-Iβ, but not PKG-Iα, interacts with CSE, leading to its phosphorylation, and rapidly induces endothelial H₂S release. Furthermore, we report that silencing of either CSE or pGC-A in mice attenuates E2-induced aorta vasodilation. These results provide detailed mechanistic insights into estrogen's nongenomic effects on vascular endothelial H₂S release and advance our current understanding of the protective activities of estrogen in the cardiovascular system.

The Redox architecture of physiological function

The ability of organisms to accommodate variations in metabolic need and environmental conditions is essential for their survival. However, an explanation is lacking as to how the necessary accommodations in response to these challenges are organized and coordinated from (sub)cellular to higher-level physiological functions, especially in mammals. We propose that the chemistry that enables coordination and synchronization of these processes dates to the origins of Life. We offer a conceptual framework based upon the nature of electron exchange (Redox) processes that co-evolved with biological complexification, giving rise to a multi-layered system in which intra/intercellular and inter-organ exchange processes essential to sensing and adaptation stay fully synchronized. Our analysis explains why Redox is both the lingua franca and the mechanism that enable integration by connecting the various elements of regulatory processes. We here define these interactions across levels of organization as the 'Redox Interactome'. This framework provides novel insight into the chemical and biological basis of Redox signalling and may explain the recent convergence of metabolism, bioenergetics, and inflammation as well as the relationship between Redox stress and human disease.

Chronological Change of Vascular Reactivity to cGMP Generators in the Balloon-Injured Rat Carotid Artery

BACKGROUND/AIMS

Soluble guanylate cyclase (sGC) exists as reduced, oxidized, and heme-free forms. Currently, it is unclear whether endovascular mechanical stenosis has an impact on vascular tone control by drugs targeting sGC, namely cGMP generators.

METHODS

Pharmacological responses to acidified sodium nitrite (reduced sGC stimulant) and BAY 60-2770 (oxidized/heme-free sGC stimulant) were studied in balloon-injured rat carotid arteries at several time points. In addition, sGC expression was detected by immunohistochemistry.

RESULTS

At 1 day after injury, acidified sodium nitrite-induced relaxation was attenuated in the injured artery, whereas BAY 60-2770-induced relaxation was augmented. Similar attenuation of response to acidified sodium nitrite was seen at 7 and 14 days after injury. On the other hand, the augmentation of response to BAY 60-2770 disappeared at 7 and 14 days after injury. At 1 day after injury, the immunohistochemical expression pattern of sGC in the smooth muscle layer of the injured artery was not different from that of the uninjured artery. However, in the injured artery, the intensity of sGC staining was weak at 7 and 14 days after injury.

CONCLUSION

Balloon injury alters vascular responsiveness to cGMP generators, which seems to be associated with the form and/or expression of sGC.

Dysregulation of stress systems and nitric oxide signaling underlies neuronal dysfunction in Alzheimer's disease

Stress is a multimodal response involving the coordination of numerous body systems in order to maximize the chance of survival. However, long term activation of the stress response results in neuronal oxidative stress via reactive oxygen and nitrogen species generation, contributing to the development of depression. Stress-induced depression shares a high comorbidity with other neurological conditions including Alzheimer's disease (AD) and dementia, often appearing as one of the earliest observable symptoms in these diseases. Furthermore, stress and/or depression appear to exacerbate cognitive impairment in the context of AD associated with dysfunctional catecholaminergic signaling. Given there are a number of homologous pathways involved in the pathophysiology of depression and AD, this article will highlight the mechanisms by which stress-induced perturbations in oxidative stress, and particularly NO signaling, contribute to neurodegeneration.

Fe in biosynthesis, translocation, and signal transduction of NO: toward bioinorganic engineering of dinitrosyl iron complexes into NO-delivery scaffolds for tissue engineering

The ubiquitous physiology of nitric oxide enables the bioinorganic engineering of [Fe(NO)₂]-containing and NO-delivery scaffolds for tissue engineering.