Superoxide-Mediated Upregulation of MMP9 Participates in BMPR2 Destabilization and Pulmonary Hypertension Development

BACKGROUND AND AIMS

we previously reported in studies on organoid-cultured bovine pulmonary arteries that pulmonary hypertension (PH) conditions of exposure to hypoxia or endothelin-1 caused a loss of a cartilage oligomeric matrix protein (COMP) stabilization of bone morphogenetic protein receptor-2 (BMPR2) function, a known key process contributing to pulmonary hypertension development. Based on subsequent findings, these conditions were associated with an extracellular superoxide-mediated increase in matrix metalloproteinase 9 (MMP-9) expression. We investigated if this contributed to PH development using mice deficient in MMP9.

RESULTS

wild-type (WT) mice exposed to Sugen/Hypoxia (SuHx) to induce PH had increased levels of MMP9 in their lungs. Hemodynamic measures from MMP9 knockout mice (MMP9 KO) indicated they had attenuated PH parameters compared to WT mice based on an ECHO assessment of pulmonary artery pressure, right ventricular systolic pressure, and Fulton index hypertrophy measurements. In vitro vascular reactivity studies showed impaired endothelium-dependent and endothelium-independent NO-associated vasodilatory responses in the pulmonary arteries of SuHx mice and decreased lung levels of COMP and BMPR2 expression. These changes were attenuated in MMP9 KO mice potentially through preserving COMP-dependent stabilization of BMPR2.

INNOVATION

this study supports a new function of superoxide in increasing MMP9 and the associated impairment of BMPR2 in promoting PH development which could be a target for future therapies.

CONCLUSION

superoxide, through promoting increases in MMP9, mediates BMPR2 depletion and its consequent control of vascular function in response to PH mediators and the SuHx mouse model of PH.

Liposomal nanocarriers of preassembled glycocalyx expeditiously restore endothelial glycocalyx in endotoxemia

The endothelial glycocalyx (EG) is degraded early during sepsis, and currently available treatments are not effective in promptly restoring it. Here, we created liposomal nanocarriers of preassembled glycocalyx (LNPG) by synthesizing glycosylated syndecan-1 and inserting it into the lipid membrane of unilamellar liposomes. We hypothesized that LNPG would fuse with the endothelial cells where EG is degraded and restore EG in sepsis. We induced endotoxemia in C57BL/6J mice using lipopolysaccharides (LPS) and treated them with LNPG, saline, syndecan-1, or liposomes. LNPG significantly prolonged the survival time of LPS-treated mice compared with the other treatments. Immunostaining of en face mesenteric arteries of LPS-treated mice showed that syndecan-1 was fully restored after LNPG administration. In addition, EG height in microvasculature of mouse cremaster muscle was monitored using sidestream dark field imaging. LNPG restored the perfused boundary region (PBR), which is inversely related to EG dimensions, to the control level after LPS administration. Furthermore, flow-induced dilation in isolated mouse mesenteric arterioles was fully recovered after LNPG treatment in LPS-treated mice. In summary, our findings provide evidence of the therapeutic efficacy of LNPG in the LPS-induced mouse model of sepsis, achieved by expeditiously restoring EG through fusion of LNPG with the endothelial plasma membrane and recovery of endothelial function.NEW & NOTEWORTHY Vascular endothelial cells represent the first line of exposure to bacterial endotoxins. Here, we propose a novel therapeutic strategy using liposomes to deliver preassembled glycocalyx to vascular endothelial cell surface and consequently restore endothelial glycocalyx (EG). We tested liposomal nanocarriers of preassembled glycocalyx (LNPG) in vivo and ex vivo to establish for the first time their expeditious therapeutic efficacy in improving survival of lipopolysaccharides (LPS)-treated mice, as achieved by the restoration of EG and recovery of endothelial function.

Overview on Interactive Role of Inflammation, Reactive Oxygen Species, and Calcium Signaling in Asthma, COPD, and Pulmonary Hypertension

Inflammatory signaling is a major component in the development and progression of many lung diseases, including asthma, chronic obstructive pulmonary disorder (COPD), and pulmonary hypertension (PH). This chapter will provide a brief overview of asthma, COPD, and PH and how inflammation plays a vital role in these diseases. Specifically, we will discuss the role of reactive oxygen species (ROS) and Ca²⁺ signaling in inflammatory cellular responses and how these interactive signaling pathways mediate the development of asthma, COPD, and PH. We will also deliberate the key cellular responses of pulmonary arterial (PA) smooth muscle cells (SMCs) and airway SMCs (ASMCs) in these devastating lung diseases. The analysis of the importance of inflammation will shed light on the key questions remaining in this field and highlight molecular targets that are worth exploring. The crucial findings will not only demonstrate the novel roles of essential signaling molecules such as Rieske iron-sulfur protein and ryanodine receptor in the development and progress of asthma, COPD, and PH but also offer advanced insight for creating more effective and new therapeutic targets for these devastating inflammatory lung diseases.

Roles of Genetic Predisposition in the Sex Bias of Pulmonary Pathophysiology, as a Function of Estrogens : Sex Matters in the Prevalence of Lung Diseases

In addition to studies focused on estrogen mediation of sex-different regulation of systemic circulations, there is now increasing clinical relevance and research interests in the pulmonary circulation, in terms of sex differences in the morbidity and mortality of lung diseases such as inherent-, allergic- and inflammatory-based events. Thus, female predisposition to pulmonary artery hypertension (PAH) is an inevitable topic. To better understand the nature of sexual differentiation in the pulmonary circulation, and how heritable factors, in vivo- and/or in vitro-altered estrogen circumstances and changes in the live environment work in concert to discern the sex bias, this chapter reviews pulmonary events characterized by sex-different features, concomitant with exploration of how alterations of genetic expression and estrogen metabolisms trigger the female-predominant pathological signaling. We address the following: PAH (Sect.7.2) is characterized as an estrogenic promotion of its incidence (Sect. 7.2.2), as a function of specific germline mutations, and as an estrogen-elicited protection of its prognosis (Sect.7.2.1). More detail is provided to introduce a less recognized gene of Ephx2 that encodes soluble epoxide hydrolase (sEH) to degrade epoxyeicosatrienic acids (EETs). As a susceptible target of estrogen, Ephx2/sEH expression is downregulated by an estrogen-dependent epigenetic mechanism. Increases in pulmonary EETs then evoke a potentiation of PAH generation, but mitigation of its progression, a phenomenon similar to the estrogen-paradox regulation of PAH. Additionally, the female susceptibility to chronic obstructive pulmonary diseases (Sect. 7.3) and asthma (Sect.7.4), but less preference to COVID-19 (Sect. 7.5), and roles of estrogen in their pathogeneses are briefly discussed.

Rieske iron-sulfur protein induces FKBP12.6/RyR2 complex remodeling and subsequent pulmonary hypertension through NF-κB/cyclin D1 pathway

Ca2+ signaling in pulmonary arterial smooth muscle cells (PASMCs) plays an important role in pulmonary hypertension (PH). However, the underlying specific ion channel mechanisms remain largely unknown. Here, we report ryanodine receptor (RyR) channel activity and Ca2+ release both are increased, and association of RyR2 by FK506 binding protein 12.6 (FKBP12.6) is decreased in PASMCs from mice with chronic hypoxia (CH)-induced PH. Smooth muscle cell (SMC)-specific RyR2 knockout (KO) or Rieske iron-sulfur protein (RISP) knockdown inhibits the altered Ca2+ signaling, increased nuclear factor (NF)-κB/cyclin D1 activation and cell proliferation, and CH-induced PH in mice. FKBP12.6 KO or FK506 treatment enhances CH-induced PH, while S107 (a specific stabilizer of RyR2/FKBP12.6 complex) produces an opposite effect. In conclusion, CH causes RISP-dependent ROS generation and FKBP12.6/RyR2 dissociation, leading to PH. RISP inhibition, RyR2/FKBP12.6 complex stabilization and Ca2+ release blockade may be potentially beneficial for the treatment of PH.

Proximal tubular-targeted overexpression of the Cyp4a12-20-HETE synthase promotes salt-sensitive hypertension in male mice

20-Hydroxyeicosatetraenoic acid (20-HETE) has been linked to blood pressure (BP) regulation via actions on the renal microvasculature and tubules. We assessed tubular 20-HETE contribution to hypertension by generating transgenic mice overexpressing the CYP4A12-20-HETE synthase (PT-4a12 mice) under the control of the proximal tubule (PT)-specific promoter, phosphoenolpyruvate carboxykinase (PEPCK). 20-HETE levels in the kidney cortex of male (967±210 vs. 249±69 pg/mg protein), but not female (121±15 vs. 92±11 pg/mg protein) PT-4a12 mice, showed a 2.5-fold increase compared to WT. Renal cortical Cyp4a12 mRNA and CYP4A12 protein in male, but not female PT-4a12 mice increased by 2-3-fold compared to WT. Male PT-4a12 mice displayed elevated BP (142±1 vs. 111±4 mmHg, p<0.0001), whereas BP in females PT-4a12 mice was not significantly different from WT (118±2 vs. 117±2 mmHg; p=0.98). In male PT-4a12 mice, BP decreased when transitioned from a control salt (0.4%) to a low-salt diet (0.075%) from 135±4 to 120±6 mmHg (p<0.01) and increased to 153±5 mmHg (p<0.05) when placed on a high-salt diet (4%). Female PT-4a12 mice did not show changes in BP on either low- or high-salt diet. In conclusion, the expression of Cyp4a12 driven by the PEPCK promoter is sex-specific probably due to its X-linkage. The salt-sensitive hypertension seen in PT-4a12 male mice suggests a potential anti-natriuretic activity of 20-HETE that needs to be further explored.

The contribution of chymase-dependent formation of ANG II to cardiac dysfunction in metabolic syndrome of young rats: roles of fructose and EETs

The roles of ACE-independent ANG II production via chymase and therapeutic potential of epoxyeicosatrienoic acids (EETs) in fructose-induced metabolic syndrome (MetS) in the adolescent population remain elusive. Thus we tested the hypothesis that a high-fructose diet (HFD) in young rats elicits chymase-dependent increases in ANG II production and oxidative stress, responses that are reversible by 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), an inhibitor of soluble epoxide hydrolase (sEH) that metabolizes EETs. Three groups of weanling rats (21-day-old) were fed a normal diet, 60% HFD, and HFD with TPPU, respectively, for 30 days. HFD rats developed MetS, characterized by hyperglycemia, hyperinsulinemia, and hypertension and associated with decreases in cardiac output and stroke volume and loss of nitric oxide (NO) modulation of myocardial oxygen consumption; all impairments were normalized by TPPU that significantly elevated circulating 11,12-EET, a major cardiac EET isoform. In the presence of comparable cardiac angiotensin-converting enzyme (ACE) expression/activity among the three groups, HFD rats exhibited significantly greater chymase-dependent ANG II formation in hearts, as indicated by an augmented cardiac chymase content as a function of enhanced mast cell degranulation. The enhanced chymase-dependent ANG II production was paralleled with increases in ANG II type 1 receptor (AT₁R) expression and NADPH oxidase (Nox)-induced superoxide, alterations that were significantly reversed by TPPU. Conversely, HFD-induced downregulation of cardiac ACE2, followed by a lower Ang-(1-7) level displayed in an TPPU-irreversible manner. In conclusion, HFD-driven adverse chymase/ANG II/Nox/superoxide signaling in young rats was prevented by inhibition of sEH via, at least in part, an EET-mediated stabilization of mast cells, highlighting chymase and sEH as therapeutic targets during treatment of MetS.NEW & NOTEWORTHY As the highest fructose consumers, the adolescent population is highly susceptible to the metabolic syndrome, where increases in mast cell chymase-dependent formation of ANG II, ensued by cardiometabolic dysfunction, are reversible in response to inhibition of soluble epoxide hydrolase (sEH). This study highlights chymase and sEH as therapeutic targets and unravels novel avenues for the development of optimal strategies for young patients with fructose-induced metabolic syndrome.

Reciprocal actions of constrictor prostanoids and superoxide in chronic hypoxia-induced pulmonary hypertension: roles of EETs

Epoxyeicosatrienoic acids (EETs) are synthesized from arachidonic acid by CYP/epoxygenase and metabolized by soluble epoxide hydrolase (sEH). Roles of EETs in hypoxia-induced pulmonary hypertension (HPH) remain elusive. The present study aimed to investigate the underlying mechanisms, by which EETs potentiate HPH. Experiments were conducted on sEH knockout (sEH-KO) and wild type (WT) mice after exposure to hypoxia (10% oxygen) for three weeks. In normal/normoxic conditions, WT and sEH-KO mice exhibited comparable pulmonary artery acceleration time (PAAT), ejection time (ET), PAAT/ET ratio, and velocity time integral (VTI), along with similar right ventricular systolic pressure (RVSP). Chronic hypoxia significantly reduced PAAT, ET, and VTI, coincided with an increase in RVSP; these impairments were more severe in sEH-KO than WT mice. Hypoxia elicited downregulation of sEH and upregulation of CYP2C9 accompanied with elevation of CYP-sourced superoxide, leading to enhanced pulmonary EETs in hypoxic mice with significantly higher levels in sEH-KO mice. Isometric tension of isolated pulmonary arteries was recorded. In addition to downregulation of eNOS-induced impairment of vasorelaxation to ACh, HPH mice displayed upregulation of thromboxane A₂ (TXA₂) receptor, paralleled with enhanced pulmonary vasocontraction to a TXA₂ analog (U46619) in an sEH-KO predominant manner. Inhibition of COX-1 or COX-2 significantly prevented the enhancement by ∼50% in both groups of vessels, and the remaining incremental components were eliminated by scavenging of superoxide with Tiron. In conclusion, hypoxia-driven increases in EETs, intensified COXs/TXA₂ signaling, great superoxide sourced from activated CYP2C9, and impaired NO bioavailability work in concert, to potentiate HPH development.

Metabolism and Redox in Pulmonary Vascular Physiology and Pathophysiology

Significance: This review considers how some systems controlling pulmonary vascular function are potentially regulated by redox processes to examine how and why conditions such as prolonged hypoxia, pathological mediators, and other factors promoting vascular remodeling contribute to the development of pulmonary hypertension (PH). Recent Advances and Critical Issues: Aspects of vascular remodeling induction mechanisms described are associated with shifts in glucose metabolism through the pentose phosphate pathway and increased cytosolic NADPH generation by glucose-6-phosphate dehydrogenase, increased glycolysis generation of cytosolic NADH and lactate, mitochondrial dysfunction associated with superoxide dismutase-2 depletion, changes in reactive oxygen species and iron metabolism, and redox signaling. Future Directions: The regulation and impact of hypoxia-inducible factor and the function of cGMP-dependent and redox regulation of protein kinase G are considered for their potential roles as key sensors and coordinators of redox and metabolic processes controlling the progression of vascular pathophysiology in PH, and how modulating aspects of metabolic and redox regulatory systems potentially function in beneficial therapeutic approaches.

Extravascular Blood Augments Myogenic Constriction of Cerebral Arterioles: Implications for Hemorrhage-Induced Vasospasm

Background

Subarachnoid hemorrhage is a serious clinical condition that impairs local cerebral blood flow perfusion and consequently initiates neuronal dysfunction. Pressure‐sensitive myogenic vasomotor regulation is an important mechanism involved in the regulation of cerebral blood flow. We hypothesized that extravascular hemolyzed blood enhances arteriolar myogenic constriction, which in vivo may contribute to the reduction of local cerebral blood flow after subarachnoid hemorrhage.

Methods and Results

Arterioles isolated from the middle cerebral artery (MCA arterioles) of mice were cannulated in a perfusion chamber. Arteriolar diameters in response to step increases in intraluminal pressure (20–120 mm Hg) were measured in various experimental conditions. In response to increases in intraluminal pressure, all MCA arterioles exhibited myogenic vasoconstrictions. Compared with controls, the pressure‐induced constriction was significantly enhanced in arterioles (in vitro) exposed to extravascular hemolyzed blood or different concentrations of extracellular erythrocyte lysate (1%, 10%, and 20%) for different exposure durations (1–6 hours). The magnitude of enhancement was proportional to the lysate concentration and exposure duration. In in vivo experiments, 10 μL of autologous blood lysate were injected into the mouse subarachnoid space on the surface of the left MCA. Two hours later, MCA arterioles were isolated and left MCA arterioles displayed enhanced myogenic responses compared with the right MCA. The enhanced myogenic response was prevented by scavenge of superoxide in both in vitro and in vivo experiments.

Conclusions

Extravascular hemolyzed blood, perhaps by promoting vascular production of superoxide, augments myogenic constriction of cerebral arterioles, which plays a crucial role in the subarachnoid hemorrhage–induced cerebral ischemia.

EETs promote hypoxic pulmonary vasoconstriction via constrictor prostanoids

To test the hypothesis that epoxyeicosatrienoic acids (EETs) facilitate pulmonary responses to hypoxia, male wild-type (WT) and soluble-epoxide hydrolase knockout (sEH-KO) mice, and WT mice chronically fed a sEH inhibitor (t-TUCB; 1 mg·kg^-1·day^-1) were used. Right ventricular systolic pressure (RVSP) was recorded under control and hypoxic conditions. The control RVSP was comparable among all groups. However, hypoxia elicited increases in RVSP in all groups with predominance in sEH-KO and t-TUCB-treated mice. 14,15-EEZE (an EET antagonist) attenuated the hypoxia-induced greater elevation of RVSP in sEH-deficient mice, suggesting an EET-mediated increment. Exogenous 5,6-; 8,9-, or 14,15-EET (0.05 ng/g body wt) did not change RVSP in any conditions, but 11,12-EET enhanced RVSP under hypoxia. Isometric tension was recorded from pulmonary arteries isolated from WT and sEH-KO mice, vessels that behaved identically in their responsiveness to vasoactive agents and vessel stretch. Hypoxic pulmonary vasoconstriction (HPV, expressed as increases in hypoxic force) was significantly greater in vessels of sEH-KO than WT vessels; the enhanced component was inhibited by EEZE. Treatment of WT vessels with 11,12-EET enhanced HPV to the same level as sEH-KO vessels, confirming EETs as primary players. Inhibition of cyclooxygenases (COXs) significantly enhanced HPV in WT vessels, but attenuated HPV in sEH-KO vessels. Blocking/inhibiting COX-1, prostaglandin H₂ (PGH₂)/thromboxane A₂ (TXA₂) receptors and TXA synthase prevented the enhanced HPV in sEH-KO vessels but had no effects on WT vessels. In conclusion, an EET-dependent alteration in PG metabolism that favors the action of vasoconstrictor PGH₂ and TXA₂ potentiates HPV and hypoxia-induced elevation of RVSP in sEH-deficient mice.

Chymase-dependent production of angiotensin II: an old enzyme in old hearts

Age-dependent alteration of the renin-angiotensin system (RAS) and generation of angiotensin II (Ang II) are well documented. By contrast, RAS-independent generation of Ang II in aging and its responses to exercise have not been explored. To this end, we examined the effects of chymase, a secretory serine protease, on the angiotensin-converting enzyme (ACE)-independent conversion of Ang I to Ang II. We hypothesized that age-dependent alteration of cardiac Ang II formation is chymase dependent in nature and is prevented by exercise training. Experiments were conducted on hearts isolated from young (3 mo), aged sedentary (24 mo), and aged rats chronically exercised on a treadmill. In the presence of low Ang I levels and downregulation of ACE expression/activity, cardiac Ang II levels were significantly higher in aged than young rats, suggesting an ACE-independent response. Aged hearts also displayed significantly increased chymase expression and activity, as well as upregulation of tryptase, a biological marker of mast cells, confirming a mast cell-sourced increase in chymase. Coincidently, cardiac superoxide produced from NADPH oxidase (Nox) was significantly enhanced in aged rats and was normalized by exercise. Conversely, a significant reduction in cardiac expression of ACE2 followed by lower Ang 1-7 levels and downregulation of the Mas receptor (binding protein of Ang 1-7) in aged rats were completely reversed by exercise. In conclusion, local formation of Ang II is increased in aged hearts, and chymase is primarily responsible for this increase. Chronic exercise is able to normalize the age-dependent alterations via compromising chymase/Ang II/angiotensin type 1 receptor/Nox actions while promoting ACE2/Ang 1-7/MasR signaling.

NEW & NOTEWORTHY

Aging increases angiotensin-converting enzyme (ACE)-independent production of cardiac angiotensin II (Ang II), a response that is driven by chymase in an exercise-reversible manner. These findings highlight chymase, in addition to ACE, as an important therapeutic target in the treatment and prevention of Ang II-induced deterioration of cardiac function in the elderly.

Sexually dimorphic adaptation of cardiac function: roles of epoxyeicosatrienoic acid and peroxisome proliferator-activated receptors

Epoxyeicosatrienoic acids (EETs) are cardioprotective mediators metabolized by soluble epoxide hydrolase (sEH) to form corresponding diols (DHETs). As a sex‐susceptible target, sEH is involved in the sexually dimorphic regulation of cardiovascular function. Thus, we hypothesized that the female sex favors EET‐mediated potentiation of cardiac function via downregulation of sEH expression, followed by upregulation of peroxisome proliferator‐activated receptors (PPARs). Hearts were isolated from male (M) and female (F) wild‐type (WT) and sEH‐KO mice, and perfused with constant flow at different preloads. Basal coronary flow required to maintain the perfusion pressure at 100 mmHg was significantly greater in females than males, and sEH‐KO than WT mice. All hearts displayed a dose‐dependent decrease in coronary resistance and increase in cardiac contractility, represented as developed tension in response to increases in preload. These responses were also significantly greater in females than males, and sEH‐KO than WT. 14,15‐EEZE abolished the sex‐induced (F vs. M) and transgenic model‐dependent (KO vs. WT) differences in the cardiac contractility, confirming an EET‐driven response. Compared with M‐WT controls, F‐WT hearts expressed downregulation of sEH, associated with increased EETs and reduced DHETs, a pattern comparable to that observed in sEH‐KO hearts. Coincidentally, F‐WT and sEH‐KO hearts exhibited increased PPARα expression, but comparable expression of eNOS, PPARβ, and EET synthases. In conclusion, female‐specific downregulation of sEH initiates an EET‐dependent adaptation of cardiac function, characterized by increased coronary flow via reduction in vascular resistance, and promotion of cardiac contractility, a response that could be further intensified by PPARα.

EETs Elicit Direct Increases in Pulmonary Arterial Pressure in Mice

OBJECTIVE

The biological role of epoxyeicosatrienoic acids (EETs) in the regulation of pulmonary circulation is currently under debate. We hypothesized that EETs initiate increases in right ventricular systolic pressure (RVSP) via perhaps, pulmonary vasoconstriction.

METHODS

Mice were anesthetized with isoflurane. Three catheters, inserted into the left jugular vein, the left carotid artery, and the right jugular vein, were used for infusing EETs, monitoring blood pressure (BP), and RVSP respectively. BP and RVSP were continuously recorded at basal conditions, in response to administration of 4 regioisomeric EETs (5,6-EET; 8,9-EET; 11,12-EET, and 14,15-EET; 1, 2, 5 and 10 ng/g body weight (BW) for each EET), and during exposure of mice to hypoxia.

RESULTS

All 4 EETs initiated dose-dependent increases in RVSP, though reduced BP. 11,12-EET elicited the greatest increment in RVSP among all EET isoforms. To clarify the direct elevation of RVSP in a systemic BP-independent manner, equivalent amounts of 14,15-EET were injected over 1 and 2 minutes respectively. One-minute injection of 14,15-EET elicited significantly faster and greater increases in RVSP than the 2-minute injection, whereas their BP changes were comparable. Additionally, direct injection of low doses of 14,15-EET (0.1, 0.2, 0.5, and 1 ng/g BW) into the right ventricle caused significant increases in RVSP without effects on BP, confirming that systemic vasodilation-induced increases in venous return are not the main cause for the increased RVSP. Acute exposure of mice to hypoxia significantly elevated RVSP, as well as 14,15-EET-induced increases in RVSP.

CONCLUSIONS

EETs directly elevate RVSP, a response that may play an important role in the development of hypoxia-induced pulmonary hypertension (PH).

Female-favorable attenuation of coronary myogenic constriction via reciprocal activations of epoxyeicosatrienoic acids and nitric oxide

Epoxyeicosatrienoic acids (EETs) are metabolites of arachidonic acid via CYP/epoxygenases, which are catabolized by soluble epoxide hydrolase (sEH) and known to possess cardioprotective properties. To date, the role of sEH in the modulation of pressure-induced myogenic response/constriction in coronary arteries, an important regulatory mechanism in the coronary circulation, and the issue as to whether the disruption of the sEH gene affects the myogenic response sex differentially have never been addressed. To this end, experiments were conducted on male (M) and female (F) wild-type (WT) and sEH-knockout (KO) mice. Pressure-diameter relationships were assessed in isolated and cannulated coronary arteries. All vessels constricted in response to increases in intraluminal pressure from 60 to 120 mmHg. Myogenic vasoconstriction was significantly attenuated, expressed as an upward shift in the pressure-diameter curve of vessels, associated with higher cardiac EETs in M-KO, F-WT, and F-KO mice compared with M-WT controls. Blockade of EETs via exposure of vessels to 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) prevented the attenuated myogenic constriction in sEH-KO mice. In the presence of 14,15-EEZE, pressure-diameter curves of females presented an upward shift from those of males, exhibiting a sex-different phenotype. Additional administration of N(ω)-nitro-l-arginine methyl ester eliminated the sex difference in myogenic responses, leading to four overlapped pressure-diameter curves. Cardiac sEH was downregulated in F-WT compared with M-WT mice, whereas expression of endothelial nitric oxide synthase and CYP4A (20-HETE synthase) was comparable among all groups. In summary, in combination with NO, the increased EET bioavailability as a function of genetic deletion and/or downregulation of sEH accounts for the female-favorable attenuation of pressure-induced vasoconstriction.

EET-dependent potentiation of pulmonary arterial pressure: sex-different regulation of soluble epoxide hydrolase

We tested the hypothesis that suppression of epoxyeicosatrienoic acid (EET) metabolism via genetic knockout of the gene for soluble epoxide hydrolase (sEH-KO), or female-specific downregulation of sEH expression, plays a role in the potentiation of pulmonary hypertension. We used male (M) and female (F) wild-type (WT) and sEH-KO mice; the latter have high pulmonary EETs. Right ventricular systolic pressure (RVSP) and mean arterial blood pressure (MABP) in control and in response to in vivo administration of U46619 (thromboxane analog), 14,15-EET, and 14,15-EEZE [14,15-epoxyeicosa-5(z)-enoic acid; antagonist of EETs] were recorded. Basal RVSP was comparable among all groups of mice, whereas MABP was significantly lower in F-WT than M-WT mice and further reduced predominantly in F-KO compared with M-KO mice. U46619 dose dependently increased RVSP and MABP in all groups of mice. The increase in RVSP was significantly greater and coincided with smaller increases in MABP in M-KO and F-WT mice compared with M-WT mice. In F-KO mice, the elevation of RVSP by U46619 was even higher than in M-KO and F-WT mice, associated with the least increase in MABP. 14,15-EEZE prevented the augmentation of U46619-induced elevation of RVSP in sEH-KO mice, whereas 14,15-EET-induced pulmonary vasoconstriction was comparable in all groups of mice. sEH expression in the lungs was reduced, paralleled with higher levels of EETs in F-WT compared with M-WT mice. In summary, EETs initiate pulmonary vasoconstriction but act as vasodilators systemically. High pulmonary EETs, as a function of downregulation or deletion of sEH, potentiate U46619-induced increases in RVSP in a female-susceptible manner.

Sexually dimorphic phenotype of arteriolar responsiveness to shear stress in soluble epoxide hydrolase-knockout mice

We hypothesized that potentiating the bioavailability of endothelial epoxyeicosatrienoic acids (EETs) via deletion of the gene for soluble epoxide hydrolase (sEH), or downregulation of sEH expression, enhances flow/shear stress-induced dilator responses (FID) of arterioles. With the use of male (M) and female (F) wild-type (WT) and sEH-knockout (KO) mice, isolated gracilis muscle arterioles were cannulated and pressurized at 80 mmHg. Basal tone and increases in diameter of arterioles as a function of perfusate flow (5, 10, 15, 20, and 25 μl/min) were recorded. The magnitude of FID was significantly smaller and associated with a greater arteriolar tone in M-WT than F-WT mice, revealing a sex difference in FID. This sex difference was abolished by deletion of the sEH gene, as evidenced by an enhanced FID in M-KO mice to a level comparable with those observed in F-KO and F-WT mice. These three groups of mice coincidentally exhibited an increased endothelial sensitivity to shear stress (smaller WSS50) and were hypotensive. Endothelial EETs participated in the mediation of enhanced FID in M-KO, F-KO, and F-WT mice, without effects on FID of M-WT mice. Protein expression of sEH was downregulated by approximately fourfold in vessels of F-WT compared with M-WT mice, paralleled with greater vascular EET levels that were statistically comparable with those observed in both male and female sEH-KO mice. In conclusion, sex-different regulation of sEH accounts for sex differences in flow-mediated dilation of microvessels in gonadally intact mice.

Inhibition of soluble epoxide hydrolase increases coronary perfusion in mice

Roles of soluble epoxide hydrolase (sEH), the enzyme responsible for hydrolysis of epoxyeicosatrienoic acids (EETs) to their diols (DHETs), in the coronary circulation and cardiac function remain unknown. We tested the hypothesis that compromising EET hydrolysis/degradation, via sEH deficiency, lowers the coronary resistance to promote cardiac perfusion and function. Hearts were isolated from wild type (WT), sEH knockout (KO) mice and WT mice chronically treated with t-TUCB (sEH inhibitor), and perfused with constant flow at different pre-loads. Compared to WT controls, sEH-deficient hearts required significantly greater basal coronary flow to maintain the perfusion pressure at 100 mmHg and exhibited a greater reduction in vascular resistance during tension-induced heart work, implying a better coronary perfusion during cardiac performance. Cardiac contractility, characterized by developed tension in response to changes in preload, was potentially increased in sEH-KO hearts, manifested by an enlarged magnitude at each step-wise increase in end-diastolic to peak-systolic tension. 14,15-EEZE (EET antagonist) prevented the adaptation of coronary circulation in sEH null hearts whereas responses in WT hearts were sensitive to the inhibition of NO. Cardiac expression of EET synthases (CYP2J2/2C29) was comparable in both genotypic mice whereas, levels of 14,15-, 11,12- and 8,9-EETs were significantly higher in sEH-KO hearts, accompanied with lower levels of DHETs. In conclusion, the elevation of cardiac EETs, as a function of sEH deficiency, plays key roles in the adaptation of coronary flow and cardiac function.

Long-term methionine-diet induced mild hyperhomocysteinemia associated cardiac metabolic dysfunction in multiparous rats

Mild hyperhomocysteinemia (HHcy, clinically defined as less than 30 μmol/L) is an independent cardiovascular disease (CVD) risk factor, and is associated with many complications during pregnancy, such as preeclampsia (PE). The aim of this study was to assess the effect of long-term mild HHcy on cardiac metabolic function of multiparous rats. Female rats were mated 3 to 4 times and were fed with methionine in drinking water to increase plasma Hcy (2.9 ± 0.3 to 10.5 ± 2.3 μmol/L) until termination. This caused significant increase of heart weight/body weight (0.24 ± 0.01 to 0.27 ± 0.01 g/100 g) and left ventricle weight (0.69 ± 0.03 to 0.78 ± 0.01 g). Superoxide production was increased by 2.5-fold in HHcy hearts using lucigenin chemiluminescence. The ability of bradykinin and carbachol to regulate myocardial oxygen consumption (MVO₂) in vitro was impaired by 59% and 66% in HHcy heart, and it was restored by ascorbic acid (AA), tempol, or apocynin (Apo). Protein expression of p22^phox subunit of NAD(P)H oxidase was increased by 2.6-fold, but there were no changes in other NAD(P)H oxidase subunits, NOSs or SODs. Microarray revealed 1518 genes to be differentially regulated (P < 0.05). The mRNA level of NAD(P)H oxidase subunits, NOSs or SODs remained unchanged. In conclusion, long-term mild HHcy increases cardiac superoxide mainly through regulation of p22^phox component of the NAD(P)H oxidase and impairs the ability of NO to regulate MVO₂ in heart of multiparous mothers.

Role of homocysteinylation of ACE in endothelial dysfunction of arteries

The direct impact of de novo synthesis of homocysteine (Hcy) and its reactive metabolites, Hcy-S-S-Hcy and Hcy thiolactone (HCTL), on vascular function has not been fully elucidated. We hypothesized that Hcy synthesized within endothelial cells affects activity of angiotensin-converting enzyme (ACE) by direct homocysteinylation of its amino- and/or sulfhydryl moieties. This covalent modification enhances ACE reactivity toward angiotensin II (ANG II)-NADPH oxidase-superoxide-dependent endothelial dysfunction. Mesenteric and coronary arteries isolated from normal rats were incubated for 3 days with or without exogenous methionine (Met, 0.1-0.3 mM), a precursor to Hcy. Incubation of arteries in Met-free media resulted in time-dependent decreases in vascular Hcy formation. By contrast, vessels incubated with Met produced Hcy in a dose-dependent manner. There was a notably greater de novo synthesis of Hcy from endothelial than from smooth muscle cells. Enhanced levels of Hcy production significantly impaired shear stress-induced dilation and release of nitric oxide, events that are associated with elevated production of vascular superoxide. Each of these processes was attenuated by ANG II type I receptor blocker or ACE and NADPH oxidase inhibitors. In addition, in vitro exposure of purified ACE to Hcy-S-S-Hcy/HCTL resulted in formation of homocysteinylated ACE and an enhanced ACE activity. The enhanced ACE activity was confirmed in isolated coronary and mesenteric arteries that had been exposed directly to Hcy-S-S-Hcy/HCTL or after Met incubation. In conclusion, vasculature-derived Hcy initiates endothelial dysfunction that, in part, may be mediated by ANG II-dependent activation of NADPH oxidase in association with homocysteinylation of ACE.

Dehydroepiandrosterone promotes pulmonary artery relaxation by NADPH oxidation-elicited subunit dimerization of protein kinase G 1α

The activity of glucose-6-phosphate dehydrogenase (G6PD) controls a vascular smooth muscle relaxing mechanism promoted by the oxidation of cytosolic NADPH, which has been associated with activation of the 1α form of protein kinase G (PKG-1α) by a thiol oxidation-elicited subunit dimerization. This PKG-1α-activation mechanism appears to contribute to responses of isolated endothelium-removed bovine pulmonary arteries (BPA) elicited by peroxide, cytosolic NADPH oxidation resulting from G6PD inhibition, and hypoxia. Dehydroepiandrosterone (DHEA) is a steroid hormone with pulmonary vasodilator activity, which has beneficial effects in treating pulmonary hypertension. Because multiple mechanisms have been suggested for the vascular effects of DHEA and one of the known actions of DHEA is inhibiting G6PD, we investigated whether it promoted relaxation associated with NADPH oxidation, PKG-1α dimerization, and PKG activation detected by increased vasodilator-stimulated phosphoprotein (VASP) phosphorylation. Relaxation of BPA to DHEA under aerobic or hypoxic conditions was associated with NADPH oxidation, PKG-1α dimerization, and increased VASP phosphorylation. The vasodilator activity of DHEA was markedly attenuated in pulmonary arteries and aorta from a PKG knockin mouse containing a serine in place of a cysteine involved in PKG dimerization. DHEA promoted increased PKG dimerization in lungs from wild-type mice, which was not detected in the PKG knockin mouse model. Thus PKG-1α dimerization is a major contributing factor to the vasodilator actions of DHEA and perhaps its beneficial effects in treating pulmonary hypertension.

Roles for cytosolic NADPH redox in regulating pulmonary artery relaxation by thiol oxidation-elicited subunit dimerization of protein kinase G1α

The activity of glucose-6-phosphate dehydrogenase (G6PD) appears to control a vascular smooth muscle relaxing mechanism regulated through cytosolic NADPH oxidation. Since our recent studies suggest that thiol oxidation-elicited dimerization of the 1α form of protein kinase G (PKG1α) contributes to the relaxation of isolated endothelium-removed bovine pulmonary arteries (BPA) to peroxide and responses to hypoxia, we investigated whether cytosolic NADPH oxidation promoted relaxation by PKG1α dimerization. Relaxation of BPA to G6PD inhibitors 6-aminonicotinamide (6-AN) and epiandrosterone (studied under hypoxia to minimize basal levels of NADPH oxidation and PKG1α dimerization) was associated with increased PKG1α dimerization and PKG-mediated vasodilator-stimulated phosphoprotein (VASP) phosphorylation. Depletion of PKG1α by small inhibitory RNA (siRNA) inhibited relaxation of BPA to 6-AN and attenuated the increase in VASP phosphorylation. Relaxation to 6-AN did not appear to be altered by depletion of soluble guanylate cyclase (sGC). Depletion of G6PD, thioredoxin-1 (Trx-1), and Trx reductase-1 (TrxR-1) in BPA with siRNA increased PKG1α dimerization and VASP phosphorylation and inhibited force generation under aerobic and hypoxic conditions. Depletion of TrxR-1 with siRNA inhibited the effects of 6-AN and enhanced similar responses to peroxide. Peroxiredoxin-1 depletion by siRNA inhibited PKG dimerization to peroxide, but it did not alter PKG dimerization under hypoxia or the stimulation of dimerization by 6-AN. Thus regulation of cytosolic NADPH redox by G6PD appears to control PKG1α dimerization in BPA through its influence on Trx-1 redox regulation by the NADPH dependence of TrxR-1. NADPH regulation of PKG dimerization may contribute to vascular responses to hypoxia that are associated with changes in NADPH redox.

Roles for redox mechanisms controlling protein kinase G in pulmonary and coronary artery responses to hypoxia

We previously reported that isolated endothelium-removed bovine pulmonary arteries (BPAs) contract to hypoxia associated with removal of peroxide- and cGMP-mediated relaxation. In contrast, bovine coronary arteries (BCAs) relax to hypoxia associated with cytosolic NADPH oxidation coordinating multiple relaxing mechanisms. Since we recently found that H(2)O(2) relaxes BPAs through PKG activation by both soluble guanylate cyclase (sGC)/cGMP-dependent and cGMP-independent thiol oxidation/subunit dimerization mechanisms, we investigated if these mechanisms participate in BPA contraction and BCA relaxation to hypoxia. The contraction of BPA (precontracted with 20 mM KCl) to hypoxia was associated with decreased PKG dimerization and PKG-mediated vasodilator-stimulated phosphoprotein (VASP) phosphorylation. In contrast, exposure of 20 mM KCl-precontracted endothelium-removed BCAs to hypoxia caused relaxation and increased dimerization and VASP phosphorylation. Depletion of sGC by organoid culture of BPAs with an oxidant of the sGC heme (10 μM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) increased aerobic force generation, decreased VASP phosphorylation, and inhibited further contraction to hypoxia and changes in VASP phosphorylation. Thiol reduction with dithiothreitol increased aerobic force in BPAs and decreased PKG dimerization, VASP phosphorylation, and the contraction to hypoxia. Furthermore, PKG-1α and sGC β(1)-subunit small interfering RNA-transfected BPAs demonstrated increased aerobic K(+) force and inhibition of further contraction to hypoxia, associated with an attenuation of H(2)O(2)-elicited relaxation and VASP phosphorylation. Thus, decreases in both a sGC/cGMP-dependent and a dimerization-dependent activation of PKG by H(2)O(2) appear to contribute to the contraction of BPAs elicited by hypoxia. In addition, stimulation of PKG activation by dimerization may be important in the relaxation of coronary arteries to hypoxia.

Redox regulation of guanylate cyclase and protein kinase G in vascular responses to hypoxia

The production of cGMP by the soluble form of guanylate cyclase (sGC) in bovine pulmonary arteries (BPA) is controlled by cytosolic NADPH maintaining reduced thiol and heme sites on sGC needed for activation by NO, and the levels of Nox oxidase-derived superoxide and peroxide that influence pathways regulating sGC activity. Our recent studies in BPA suggest that the activities of peroxide metabolizing pathways in vascular smooth muscle potentially determine the balance between sGC stimulation by peroxide and a cGMP-independent activation of cGMP-dependent protein kinase (PKG) by a disulfide-mediated subunit dimerization. Cytosolic NADPH oxidation also appears to function in BPA through its influence on protein thiol redox control as an additional mechanism promoting vascular relaxation through PKG activation. These processes regulating PKG may participate in decreases in peroxide and increases in NADPH associated with contraction of BPA to hypoxia and in cytosolic NADPH oxidation potentially mediating bovine coronary artery relaxation to hypoxia.

Roles for soluble guanylate cyclase and a thiol oxidation-elicited subunit dimerization of protein kinase G in pulmonary artery relaxation to hydrogen peroxide

We have previously provided evidence that hydrogen peroxide (H(2)O(2)) stimulates soluble guanylate cyclase (sGC) under conditions where it relaxes isolated endothelium-removed bovine pulmonary arteries (BPAs). Since it was recently reported that H(2)O(2) induces coronary vasorelaxation associated with a nitric oxide/cGMP-independent thiol oxidation/subunit dimerization-elicited activation of protein kinase G (PKG), we investigated whether this mechanism participates in the relaxation of BPAs to H(2)O(2). BPAs precontracted with serotonin (incubated under hypoxia to lower endogenous H(2)O(2)) were exposed to increasing concentrations of H(2)O(2). It was observed that 0.1-1 mM H(2)O(2) caused increased PKG dimerization and relaxation. These responses were associated with increased phosphorylation of vasodilator-stimulated phosphoprotein (VASP) at the serine-239 site known to be mediated by PKG. Treatment of BPAs with 1 mM DTT attenuated PKG dimerization, VASP phosphorylation, and relaxation to H(2)O(2). An organoid culture of BPAs for 48 h with 10 μM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a heme oxidant inhibitor of sGC activation, depleted sGC expression by 85%, associated with a 67% attenuation of VASP phosphorylation and 48% inhibition of relaxation elicited by 100 μM H(2)O(2). Thus both a sGC activation/cGMP-dependent and a thiol oxidation subunit dimerization/cGMP-independent activation of PKG appear to contribute to the relaxation of BPAs elicited by H(2)O(2).

Roles for Nox4 in the contractile response of bovine pulmonary arteries to hypoxia

Hypoxia appears to promote contraction [hypoxic pulmonary vasoconstriction (HPV)] of bovine pulmonary arteries (BPA) through removal of a peroxide-mediated relaxation. This study examines the roles of BPA Nox oxidases and mitochondria in the HPV response. Inhibitors of Nox2 (0.1 mM apocynin and 50 muM gp91-dstat) and mitochondrial electron transport (10 muM antimycin and rotenone) decreased superoxide generation in BPA without affecting contraction to 25 mM KCl or the HPV response. Transfection of BPA with small inhibitory RNA (siRNA) for Nox2 and Nox4 decreased Nox2 and Nox4 protein expression, respectively, associated with an attenuation of superoxide detection, without affecting 25 mM KCl contraction. However, Nox4 siRNA, but not Nox2, attenuated HPV in BPA. A Nox4 inhibitor plumbagin (10 muM) increased basal force, decreased superoxide detection and peroxide release, and caused BPA to relax under hypoxia. Although acute removal of peroxide with 0.1 mM ebselen increased 25 mM KCl contraction and decreased hypoxic contraction, prolonged treatment with ebselen only decreased hypoxic contraction without affecting 25 mM KCl contraction, suggesting basal peroxide levels also maintain a contractile mechanism not removed by acute hypoxia. Organ culture of BPA with transforming growth factor (TGF)-beta1 (4 nM) increased Nox4 expression, superoxide, peroxide, and the HPV response. Thus Nox2 and mitochondria are sources for superoxide generation in BPA, which do not appear to influence the HPV response. However, peroxide derived from superoxide generated by Nox4 appears to maintain a basal relaxation in BPA under normoxic conditions, which is removed under hypoxia leading to HPV. Peroxide generated by Nox4 may also function to maintain a contractile mechanism, which is not reversed by acute hypoxia.

Heme oxygenase-1 induction modulates hypoxic pulmonary vasoconstriction through upregulation of ecSOD

Endothelium-denuded bovine pulmonary arteries (BPA) contract to hypoxia through a mechanism potentially involving removing a superoxide-derived hydrogen peroxide-mediated relaxation. BPA organ cultured for 24 h with 0.1 mM cobalt chloride (CoCl(2)) to increase the expression and activity of heme oxygenase-1 (HO-1) is accompanied by a decrease in 5 microM lucigenin-detectable superoxide and an increase in horseradish peroxidase-luminol detectable peroxide levels. Force development to KCl in BPA was not affected by increases in HO-1, but the hypoxic pulmonary vasoconstriction (HPV) response was decreased. Organ culture with a HO-1 inhibitor (10 microM chromium mesoporphyrin) reversed the effects of HO-1 on HPV and peroxide. Treatment of HO-1-induced BPA with extracellular catalase resulted in reversal of the attenuation of HPV without affecting the force development to KCl. Increasing intracellular peroxide scavenging with 0.1 mM ebselen increased force development to KCl and partially reversed the decrease in HPV seen on induction of HO-1. HO-1 induction increases extracellular (ec) superoxide dismutase (SOD) expression without changing Cu,Zn-SOD and Mn-SOD levels. HO-1-induced BPA rings treated with the copper chelator 10 mM diethyldithiocarbamate to inactivate ecSOD and Cu,Zn-SOD showed increased superoxide and decreased peroxide to levels equal to non-HO-1-induced rings, whereas the addition of SOD to freshly isolated BPA rings attenuated HPV similar to HO-1 induction with CoCl(2). Therefore, HO-1 induction in BPA increases ecSOD expression associated with enhanced generation of peroxide in amounts that may not be adequately removed during hypoxia, leading to an attenuation of HPV.