Lung Epithelium Releases Growth Differentiation Factor 15 in Response to Pathogen-mediated Injury

GDF15 (growth differentiation factor 15) is a stress cytokine with several proposed roles, including support of stress erythropoiesis. Higher circulating GDF15 levels are prognostic of mortality during acute respiratory distress syndrome, but the cellular sources and downstream effects of GDF15 during pathogen-mediated lung injury are unclear. We quantified GDF15 in lower respiratory tract biospecimens and plasma from patients with acute respiratory failure. Publicly available data from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were reanalyzed. We used mouse models of hemorrhagic acute lung injury mediated by Pseudomonas aeruginosa exoproducts in wild-type mice and mice genetically deficient for Gdf15 or its putative receptor, Gfral. In critically ill humans, plasma levels of GDF15 correlated with lower respiratory tract levels and were higher in nonsurvivors. SARS-CoV-2 infection induced GDF15 expression in human lung epithelium, and lower respiratory tract GDF15 levels were higher in coronavirus disease (COVID-19) nonsurvivors. In mice, intratracheal P. aeruginosa type II secretion system exoproducts were sufficient to induce airspace and plasma release of GDF15, which was attenuated with epithelial-specific deletion of Gdf15. Mice with global Gdf15 deficiency had decreased airspace hemorrhage, an attenuated cytokine profile, and an altered lung transcriptional profile during injury induced by P. aeruginosa type II secretion system exoproducts, which was not recapitulated in mice deficient for Gfral. Airspace GDF15 reconstitution did not significantly modulate key lung cytokine levels but increased circulating erythrocyte counts. Lung epithelium releases GDF15 during pathogen injury, which is associated with plasma levels in humans and mice and can increase erythrocyte counts in mice, suggesting a novel lung-blood communication pathway.

Association of Hypertensive Disorders of Pregnancy With Coronary Microvascular Dysfunction 8 to 10 Years After Delivery

BACKGROUND

Hypertensive disorders of pregnancy (HDP) are associated with subsequent adverse cardiac remodeling and cardiovascular disease. The role of myocardial microvascular disease among individuals with HDP and left ventricular (LV) remodeling as a potential link to cardiovascular disease is unknown. We aimed to determine whether individuals with HDP history have coronary microvascular dysfunction measured by coronary flow reserve 8 to 10 years after delivery and whether microvascular dysfunction correlates with LV remodeling.

METHODS

Individuals with pregnancies delivered from 2008 to 2010 underwent burst-replenishment myocardial contrast echocardiography (2017-2020) to quantify myocardial perfusion at rest and during dobutamine stress. Video intensity versus time data were used to derive β, the rate of rise of video intensity, a correlate for myocardial blood flow. Coronary flow reserve was calculated as the ratio of β at peak stress to β at rest, averaged across LV myocardial regions of interest.

RESULTS

We studied 91 individuals (aged 38±6 and 9.1±0.9 years postdelivery) and 19 with a history of HDP. Individuals with coronary microvascular dysfunction (coronary flow reserve <2.0; n=13) had a higher proportion of HDP (46.2% versus 16.7%; P=0.026) and higher prepregnancy body mass index, baseline heart rate, and hemoglobin A1c compared with those without microvascular dysfunction. The association of coronary flow reserve and HDP was attenuated after adjusting for cardiometabolic factors (P=0.133). In exploratory subgroup analyses, individuals with both LV remodeling (relative wall thickness >0.42) and HDP (n=12) had the highest proportion of microvascular dysfunction (41.7% versus +HDP-LV remodeling [n=7] 14.3%; -HDP+LV remodeling [n=26] 7.7%; P=0.0498).

CONCLUSIONS

In this small study, HDP history is associated with coronary microvascular dysfunction 1 decade after delivery, findings that may, in part, be driven by metabolic factors including obesity and diabetes. Microvascular dysfunction may contribute to cardiovascular disease among individuals with a history of HDP.

Vitamin E/Coenzyme Q-Dependent "Free Radical Reductases": Redox Regulators in Ferroptosis

Significance: Lipid peroxidation and its products, oxygenated polyunsaturated lipids, act as essential signals coordinating metabolism and physiology and can be deleterious to membranes when they accumulate in excessive amounts. Recent Advances: There is an emerging understanding that regulation of polyunsaturated fatty acid (PUFA) phospholipid peroxidation, particularly of PUFA-phosphatidylethanolamine, is important in a newly discovered type of regulated cell death, ferroptosis. Among the most recently described regulatory mechanisms is the ferroptosis suppressor protein, which controls the peroxidation process due to its ability to reduce coenzyme Q (CoQ). Critical Issues: In this study, we reviewed the most recent data in the context of the concept of free radical reductases formulated in the 1980-1990s and focused on enzymatic mechanisms of CoQ reduction in different membranes (e.g., mitochondrial, endoplasmic reticulum, and plasma membrane electron transporters) as well as TCA cycle components and cytosolic reductases capable of recycling the high antioxidant efficiency of the CoQ/vitamin E system. Future Directions: We highlight the importance of individual components of the free radical reductase network in regulating the ferroptotic program and defining the sensitivity/tolerance of cells to ferroptotic death. Complete deciphering of the interactive complexity of this system may be important for designing effective antiferroptotic modalities. Antioxid. Redox Signal. 40, 317-328.

Pannexin-3 stabilizes the transcription factor Bcl6 in a channel-independent manner to protect against vascular oxidative stress

Targeted degradation regulates the activity of the transcriptional repressor Bcl6 and its ability to suppress oxidative stress and inflammation. Here, we report that abundance of endothelial Bcl6 is determined by its interaction with Golgi-localized pannexin 3 (Panx3) and that Bcl6 transcriptional activity protects against vascular oxidative stress. Consistent with data from obese, hypertensive humans, mice with an endothelial cell-specific deficiency in Panx3 had spontaneous systemic hypertension without obvious changes in channel function, as assessed by Ca2+ handling, ATP amounts, or Golgi luminal pH. Panx3 bound to Bcl6, and its absence reduced Bcl6 protein abundance, suggesting that the interaction with Panx3 stabilized Bcl6 by preventing its degradation. Panx3 deficiency was associated with increased expression of the gene encoding the H2O2-producing enzyme Nox4, which is normally repressed by Bcl6, resulting in H2O2-induced oxidative damage in the vasculature. Catalase rescued impaired vasodilation in mice lacking endothelial Panx3. Administration of a newly developed peptide to inhibit the Panx3-Bcl6 interaction recapitulated the increase in Nox4 expression and in blood pressure seen in mice with endothelial Panx3 deficiency. Panx3-Bcl6-Nox4 dysregulation occurred in obesity-related hypertension, but not when hypertension was induced in the absence of obesity. Our findings provide insight into a channel-independent role of Panx3 wherein its interaction with Bcl6 determines vascular oxidative state, particularly under the adverse conditions of obesity.

Fatty acid nitroalkenes - Multi-target agents for the treatment of sickle cell disease

Sickle cell disease (SCD) is a hereditary hematological disease with high morbidity and mortality rates worldwide. Despite being monogenic, SCD patients display a plethora of disease-associated complications including anemia, oxidative stress, sterile inflammation, vaso-occlusive crisis-related pain, and vasculopathy, all of which contribute to multiorgan dysfunction and failure. Over the past decade, numerous small molecule drugs, biologics, and gene-based interventions have been evaluated; however, only four disease-modifying drug therapies are presently FDA approved. Barriers regarding effectiveness, accessibility, affordability, tolerance, and compliance of the current polypharmacy-based disease-management approaches are challenging. As such, there is an unmet pharmacological need for safer, more efficacious, and logistically accessible treatment options for SCD patients. Herein, we evaluate the potential of small molecule nitroalkenes such as nitro-fatty acid (NO2-FA) as a therapy for SCD. These agents are electrophilic and exert anti-inflammatory and tissue repair effects through an ability to transiently post-translationally bind to and modify transcription factors, pro-inflammatory enzymes and cell signaling mediators. Preclinical and clinical studies affirm safety of the drug class and a murine model of SCD reveals protection against inflammation, fibrosis, and vascular dysfunction. Despite protective cardiac, renal, pulmonary, and central nervous system effects of nitroalkenes, they have not previously been considered as therapy for SCD. We highlight the pathways targeted by this drug class, which can potentially prevent the end-organ damage associated with SCD and contrast their prospective therapeutic benefits for SCD as opposed to current polypharmacy approaches.

Hemin and iron increase synthesis and trigger export of xanthine oxidoreductase from hepatocytes to the circulation

We recently reported a previously unknown salutary role for xanthine oxidoreductase (XOR) in intravascular heme overload whereby hepatocellular export of XOR to the circulation was identified as a seminal step in affording protection. However, the cellular signaling and export mechanisms underpinning this process were not identified. Here, we present novel data showing hepatocytes upregulate XOR expression/protein abundance and actively release it to the extracellular compartment following exposure to hemopexin-bound hemin, hemin or free iron. For example, murine (AML-12 cells) hepatocytes treated with hemin (10 μM) exported XOR to the medium in the absence of cell death or loss of membrane integrity (2.0 ± 1.0 vs 16 ± 9 μU/mL p < 0.0001). The path of exocytosis was found to be noncanonical as pretreatment of the hepatocytes with Vaculin-1, a lysosomal trafficking inhibitor, and not Brefeldin A inhibited XOR release and promoted intracellular XOR accumulation (84 ± 17 vs 24 ± 8 hemin vs 5 ± 3 control μU/mg). Interestingly, free iron (Fe2+ and Fe3+) induced similar upregulation and release of XOR compared to hemin. Conversely, concomitant treatment with hemin and the classic transition metal chelator DTPA (20 μM) or uric acid completely blocked XOR release (p < 0.01). Our previously published time course showed XOR release from hepatocytes likely required transcriptional upregulation. As such, we determined that both Sp1 and NF-kB were acutely activated by hemin treatment (∼2-fold > controls for both, p < 0.05) and that silencing either or TLR4 with siRNA prevented hemin-induced XOR upregulation (p < 0.01). Finally, to confirm direct action of these transcription factors on the Xdh gene, chromatin immunoprecipitation was performed indicating that hemin significantly enriched (∼5-fold) both Sp1 and NF-kB near the transcription start site. In summary, our study identified a previously unknown pathway by which XOR is upregulated via SP1/NF-kB and subsequently exported to the extracellular environment. This is, to our knowledge, the very first study to demonstrate mechanistically that XOR can be specifically targeted for export as the seminal step in a compensatory response to heme/Fe overload.

Bedding as a variable affecting fasting blood glucose and vascular physiology in mice

Rodent husbandry requires careful consideration of environmental factors that may impact colony performance and subsequent physiological studies. Of note, recent reports have suggested corncob bedding may affect a broad range of organ systems. As corncob bedding may contain digestible hemicelluloses, trace sugars, and fiber, we hypothesized that corncob bedding impacts overnight fasting blood glucose and murine vascular function. Here, we compared mice housed on corncob bedding, which were then fasted overnight on either corncob or ALPHA-dri bedding, a virgin paper pulp cellulose alternative. Male and female mice were used from two noninduced, endothelial-specific conditional knockout strains [Cadherin 5-cre/ERT2, floxed hemoglobin-α1 (Hba1fl/fl) or Cadherin 5-cre/ERT2, floxed cytochrome-B5 reductase 3 (CyB5R3fl/fl)] on a C57BL/6J genetic background. After fasting overnight, initial fasting blood glucose was measured, and mice were anesthetized with isoflurane for measurement of blood perfusion via laser speckle contrast analysis using a PeriMed PeriCam PSI NR system. After a 15-min equilibration, the mice were injected intraperitoneally with the α1-adrenergic receptor agonist, phenylephrine (5 mg/kg), or saline, and monitored for changes in blood perfusion. After a 15-min response period, blood glucose was remeasured postprocedure. In both strains, mice fasted on corncob bedding had higher blood glucose than the pulp cellulose group. In the CyB5R3fl/fl strain, mice housed on corncob bedding displayed a significant reduction in phenylephrine-mediated change in perfusion. In the Hba1fl/fl strain, phenylephrine-induced change in perfusion was not different in the corncob group. This work suggests that corncob bedding, in part due to its ingestion by mice, could impact vascular measurements and fasting blood glucose. To promote scientific rigor and improve reproducibility, bedding type should be routinely included in published methods.NEW & NOTEWORTHY This study demonstrates real-time measurement of changes in perfusion to pharmacological treatment using laser speckle contrast analysis. Furthermore, this investigation revealed that fasting mice overnight on corncob bedding has differential effects on vascular function and that there was increased fasting blood glucose in mice fasted on corncob bedding compared with paper pulp cellulose bedding. This highlights the impact that bedding type can have on outcomes in vascular and metabolic research and reinforces the need for thorough and robust reporting of animal husbandry practices.

Release of hepatic xanthine oxidase (XO) to the circulation is protective in intravascular hemolytic crisis

Xanthine oxidase (XO) catalyzes the catabolism of hypoxanthine to xanthine and xanthine to uric acid, generating oxidants as a byproduct. Importantly, XO activity is elevated in numerous hemolytic conditions including sickle cell disease (SCD); however, the role of XO in this context has not been elucidated. Whereas long-standing dogma suggests elevated levels of XO in the vascular compartment contribute to vascular pathology via increased oxidant production, herein, we demonstrate, for the first time, that XO has an unexpected protective role during hemolysis. Using an established hemolysis model, we found that intravascular hemin challenge (40 μmol/kg) resulted in a significant increase in hemolysis and an immense (20-fold) elevation in plasma XO activity in Townes sickle cell phenotype (SS) sickle mice compared to controls. Repeating the hemin challenge model in hepatocyte-specific XO knockout mice transplanted with SS bone marrow confirmed the liver as the source of enhanced circulating XO as these mice demonstrated 100% lethality compared to 40% survival in controls. In addition, studies in murine hepatocytes (AML12) revealed hemin mediates upregulation and release of XO to the medium in a toll like receptor 4 (TLR4)-dependent manner. Furthermore, we demonstrate that XO degrades oxyhemoglobin and releases free hemin and iron in a hydrogen peroxide-dependent manner. Additional biochemical studies revealed purified XO binds free hemin to diminish the potential for deleterious hemin-related redox reactions as well as prevents platelet aggregation. In the aggregate, data herein reveals that intravascular hemin challenge induces XO release by hepatocytes through hemin-TLR4 signaling, resulting in an immense elevation of circulating XO. This increased XO activity in the vascular compartment mediates protection from intravascular hemin crisis by binding and potentially degrading hemin at the apical surface of the endothelium where XO is known to be bound and sequestered by endothelial glycosaminoglycans (GAGs).

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.

Orai3 and Orai1 mediate CRAC channel function and metabolic reprogramming in B cells

The essential role of store-operated Ca2+ entry (SOCE) through Ca2+ release-activated Ca2+ (CRAC) channels in T cells is well established. In contrast, the contribution of individual Orai isoforms to SOCE and their downstream signaling functions in B cells are poorly understood. Here, we demonstrate changes in the expression of Orai isoforms in response to B cell activation. We show that both Orai3 and Orai1 mediate native CRAC channels in B cells. The combined loss of Orai1 and Orai3, but not Orai3 alone, impairs SOCE, proliferation and survival, nuclear factor of activated T cells (NFAT) activation, mitochondrial respiration, glycolysis, and the metabolic reprogramming of primary B cells in response to antigenic stimulation. Nevertheless, the combined deletion of Orai1 and Orai3 in B cells did not compromise humoral immunity to influenza A virus infection in mice, suggesting that other in vivo co-stimulatory signals can overcome the requirement of BCR-mediated CRAC channel function in B cells. Our results shed important new light on the physiological roles of Orai1 and Orai3 proteins in SOCE and the effector functions of B lymphocytes.

Flipping Off and On the Redox Switch in the Microcirculation

Resistance arteries and arterioles evolved as specialized blood vessels serving two important functions: (a) regulating peripheral vascular resistance and blood pressure and (b) matching oxygen and nutrient delivery to metabolic demands of organs. These functions require control of vessel lumen cross-sectional area (vascular tone) via coordinated vascular cell responses governed by precise spatial-temporal communication between intracellular signaling pathways. Herein, we provide a contemporary overview of the significant roles that redox switches play in calcium signaling for orchestrated endothelial, smooth muscle, and red blood cell control of arterial vascular tone. Three interrelated themes are the focus: (a) smooth muscle to endothelial communication for vasoconstriction, (b) endothelial to smooth muscle cell cross talk for vasodilation, and (c) oxygen and red blood cell interregulation of vascular tone and blood flow. We intend for this thematic framework to highlight gaps in our current knowledge and potentially spark interest for cross-disciplinary studies moving forward.

Abstract 104: Cytochrome B5 Reductase 3 Regulates The Erythropoietin Response To Ischemic Stroke In A Mouse Model Of Chronic Anemia And Oxidative Stress

Introduction: Cytochrome b5 reductase 3 (Cyb5R3) is a heme iron reductase that reverses oxidized soluble guanylate cyclase (sGC) heme iron (Fe 3+ Fe 2+ ) to preserve nitric oxide signaling. Under oxidative stress, such as occurs with sickle cell disease (SCD) and ischemic stroke, Cyb5R3 redox signaling provides resilience against tissue damage. A loss-of-function (roughly 50%) Cyb5R3 missense variant (T117S) occurs with high frequency (0.23 minor allele) in persons of African ancestry, who also suffer a greater burden of sickle cell anemia and ischemic stroke than other races. We hypothesized that Cyb5R3 regulates the erythropoietin response to ischemic stroke in a mouse model of SCD.

Methods: Age-matched male SCD mice with wild-type Cyb5R3 (SS WT ) or T117S Cyb5R3 (SS T117S ) underwent middle cerebral artery occlusion (55 min) and reperfusion (48 hr). Blood was sampled at baseline and 48h reperfusion for hematology measurements. Brains were stained with 2,3,5-triphenyltetrazolium chloride to quantify infarct volume. Erythropoietin (EPO), heme oxygenase 1 (HMOX1) and sGC were assayed by Western blot.

Results: We found brain infarct volume to be greater in SS T117S vs SS WT (63 vs 27 cm 3 , respectively; P=0.003). Red cells, hematocrit and hemoglobin decreased in SS T117S post-stroke, which was opposite to SS WT (red cells: -13% vs 13%, P=0.01; hematocrit: -20% vs 0%, P=0.03; hemoglobin: -18% vs 3%, P=0.02, respectively). In the absence of stroke (age-matched controls), SS WT had elevated HMOX1 protein compared to SS T117S , which normalized in post-stroke SS WT but was unchanged in post-stroke SS T117S . Kidney and plasma EPO levels significantly increased in SS WT post-stroke, but not in SS T117S . In vitro studies using HEK293 cells showed EPO and HMOX1 decrease with Cyb5R3 knockdown by siRNA.

Conclusion: Our findings suggest a modifying role for Cyb5R3 in brain-kidney crosstalk during ischemic stroke, wherein loss of T117S Cyb5R3 activity negatively impacts renal and plasma EPO levels and resilience against infarct of ischemic brain tissue. The Cyb5R3 axis on which the brain-kidney-blood response to stroke in SCD turns represents a novel target for precision medicine approaches to managing stroke risk and pathology in SCD carriers of the T117S variant.

Cytochrome b5 reductases: Redox regulators of cell homeostasis

The cytochrome-b5 reductase (CYB5R) family of flavoproteins is known to regulate reduction-oxidation (redox) balance in cells. The five enzyme members are highly compartmentalized at the subcellular level and function as "redox switches" enabling the reduction of several substrates, such as heme and coenzyme Q. Critical insight into the physiological and pathophysiological significance of CYB5R enzymes has been gleaned from several human genetic variants that cause congenital disease and a broad spectrum of chronic human diseases. Among the CYB5R genetic variants, CYB5R3 is well-characterized and deficiency in expression and activity is associated with type II methemoglobinemia, cancer, neurodegenerative disorders, diabetes, and cardiovascular disease. Importantly, pharmacological and genetic-based strategies are underway to target CYB5R3 to circumvent disease onset and mitigate severity. Despite our knowledge of CYB5R3 in human health and disease, the other reductases in the CYB5R family have been understudied, providing an opportunity to unravel critical function(s) for these enzymes in physiology and disease. In this review, we aim to provide the broad scientific community an up-to-date overview of the molecular, cellular, physiological, and pathophysiological roles of CYB5R proteins.

Loss of cardiomyocyte CYB5R3 impairs redox equilibrium and causes sudden cardiac death

Sudden cardiac death (SCD) in patients with heart failure (HF) is allied with an imbalance in reduction and oxidation (redox) signaling in cardiomyocytes; however, the basic pathways and mechanisms governing redox homeostasis in cardiomyocytes are not fully understood. Here, we show that cytochrome b5 reductase 3 (CYB5R3), an enzyme known to regulate redox signaling in erythrocytes and vascular cells, is essential for cardiomyocyte function. Using a conditional cardiomyocyte-specific CYB5R3-knockout mouse, we discovered that deletion of CYB5R3 in male, but not female, adult cardiomyocytes causes cardiac hypertrophy, bradycardia, and SCD. The increase in SCD in CYB5R3-KO mice is associated with calcium mishandling, ventricular fibrillation, and cardiomyocyte hypertrophy. Molecular studies reveal that CYB5R3-KO hearts display decreased adenosine triphosphate (ATP), increased oxidative stress, suppressed coenzyme Q levels, and hemoprotein dysregulation. Finally, from a translational perspective, we reveal that the high-frequency missense genetic variant rs1800457, which translates into a CYB5R3 T117S partial loss-of-function protein, associates with decreased event-free survival (~20%) in Black persons with HF with reduced ejection fraction (HFrEF). Together, these studies reveal a crucial role for CYB5R3 in cardiomyocyte redox biology and identify a genetic biomarker for persons of African ancestry that may potentially increase the risk of death from HFrEF.

Abstract P054: Loss Of The Smooth-muscle-cell-angiotensin Ii-sensitive Lncrna Leads To Smc Hypertrophic And Hypertensive Remodeling Due To Cell Cycle Dysregulation

Vascular smooth muscle cells (SMC) responses to increased levels of Ang II during hypertensive remodeling included enhanced vasoconstriction and hypertrophy due to the enlargement of the SMC on the vessel wall. Hypertrophic SMC usually present defects in cell division and cell polyploidy. However, the molecular mechanisms controlling SMC hypertrophy and polyploidy vs. hyperplasia are still not fully understood. Long-non-coding-RNAs (LncRNAs) are epigenetic regulators of gene expression influencing biological processes, including cell division fidelity. We discovered a novel lncRNA decreased in dedifferentiated SMC, the SMC-Ang II-Sensitive (SAS) lncRNA, which expression is reduced in response to Ang-II in cultured SMC and the aorta of hypertensive mice, suggesting a role in mediating hypertension-induced SMC hypertrophy. Publicly available transcriptional datasets revealed that SAS is preferentially expressed in SMC-rich tissues, including the aorta and renal artery, in humans and mice. Yet, the functional relevance of SAS in SMC has never been investigated. Knockdown of SAS reduces proliferation and migration in SMC treated with Platelet-Derived Growth Factor (PDGF-BB). SAS knockdown was also associated with distinct SMC hypertrophic morphological changes, including enlargement in cell size and polynucleation in vitro. We have generated a SAS KO mouse, and aortas from these mice present a higher number of polynucleated medial SMC than their WT littermates. These data correlate with a cell cycle arrest in G1 and senescence phenotype that SAS deficient SMC present due to dysregulation in cyclins expression. Furthermore, SAS defective cells show mitochondria hyperfusion and increased oxygen consumption that correlates with the observed senescence and arrest on the G1/S checkpoint, and it is exacerbated by treatment with Ang-II. Interestingly, treatment with Losartan, an Ang-II receptor inhibitor, rescues SAS expression on Ang-II treated SMC and diminishes SMC hypertrophy. Together, these observations suggest that a decrease in SAS causes SMC hypertrophy due to defects in cell cycle completion. SAS is a potent regulator of SMC morphology and is required for proper cell division and mitochondria organization.

Immunomodulatory actions of a kynurenine-derived endogenous electrophile

The up-regulation of kynurenine metabolism induces immunomodulatory responses via incompletely understood mechanisms. We report that increases in cellular and systemic kynurenine levels yield the electrophilic derivative kynurenine-carboxyketoalkene (Kyn-CKA), as evidenced by the accumulation of thiol conjugates and saturated metabolites. Kyn-CKA induces NFE2 like bZIP transcription factor 2- and aryl hydrocarbon receptor-regulated genes and inhibits nuclear factor κB- and NLR family pyrin domain containing 3-dependent proinflammatory signaling. Sickle cell disease (SCD) is a hereditary hemolytic condition characterized by basal inflammation and recurrent vaso-occlusive crises. Both transgenic SCD mice and patients with SCD exhibit increased kynurenine and Kyn-CKA metabolite levels. Plasma hemin and kynurenine concentrations are positively correlated, indicating that Kyn-CKA synthesis in SCD is up-regulated during pathogenic vascular stress. Administration of Kyn-CKA abrogated pulmonary microvasculature occlusion in SCD mice, an important factor in lung injury development. These findings demonstrate that the up-regulation of kynurenine synthesis and its metabolism to Kyn-CKA is an adaptive response that attenuates inflammation and protects tissues.

Angiotensin II augments renal vascular smooth muscle soluble GC expression via an AT1 receptor-forkhead box subclass O transcription factor signalling axis

BACKGROUND AND PURPOSE

Reduced renal blood flow triggers activation of the renin-angiotensin-aldosterone system (RAAS) leading to renovascular hypertension. Renal vascular smooth muscle expression of the NO receptor, soluble GC (sGC), modulates the vasodilator response needed to control renal vascular tone and blood flow. Here, we tested if angiotensin II (Ang II) affects sGC expression via an AT₁ receptor-forkhead box subclass O (FoxO) transcription factor dependent mechanism.

EXPERIMENTAL APPROACH

Using a murine two-kidney-one-clip (2K1C) renovascular hypertension model, we measured renal artery vasodilatory function and sGC expression. Additionally, we conducted cell culture studies using rat renal pre-glomerular smooth muscle cells (RPGSMCs) to test the in vitro mechanistic effects of Ang II treatment on sGC expression and downstream function.

KEY RESULTS

Contralateral, unclipped renal arteries in 2K1C mice showed increased NO-dependent vasorelaxation compared to sham control mice. Immunofluorescence studies revealed increased sGC protein expression in 2K1C contralateral renal arteries over sham controls. RPGSMCs treated with Ang II caused a significant up-regulation of sGC mRNA and protein expression as well as downstream sGC-dependent signalling. Ang II signalling effects on sGC expression occurred through an AT₁ receptor and FoxO transcription factor-dependent mechanism at both the mRNA and protein expression levels.

CONCLUSION AND IMPLICATIONS

Renal artery smooth muscle, in vivo and in vitro, up-regulates expression of sGC following RAAS activity. In both cases, up-regulation of sGC leads to increased downstream cGMP signalling, suggesting a previously unrecognized protective mechanism to improve renal blood flow in the uninjured contralateral renal artery.

LINKED ARTICLES

This article is part of a themed issue on cGMP Signalling in Cell Growth and Survival. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.11/issuetoc.

Nrf2 Activation With CDDO-Methyl Promotes Beneficial and Deleterious Clinical Effects in Transgenic Mice With Sickle Cell Anemia

Activation of Nrf2, a major transcription factor that drives the antioxidant defense system, is an emerging therapeutic strategy in Sickle Cell Disease (SCD). In this study, transgenic Sickle Cell Anemia mice (SS mice) treated with CDDO-Methyl (CDDO-Me), a potent Nrf2 activator, showed reduced progression of hemolytic anemia with aging, but surprisingly also showed reduced endothelial function. Pulmonary vessels isolated from SS mice treated for 4 months with CDDO-Me displayed a diminished response to nitric oxide (NO)-induced vasodilation compared to littermates given vehicle. It is unclear what molecular mechanism underly the vascular impairment, however, our in vitro assays revealed that CDDO-Me induced the expression of the endothelin receptor (ETA and ETB) in vascular smooth muscle cells. Endothelin signaling is associated with increased vascular tone and vasoconstriction. This study underscores the importance of pre-clinical benefit-risk investigations of Nrf2 activating compounds which may be used to treat patients with SCD.

Abstract 463: The Smooth-Muscle-Cell-Angiotensin II-Sensitive LncRNA Controls Cell Division Fidelity And Mitochondrial Organization

Reactivation of the cell cycle and increase in proliferation rate (hyperplasia) is a common response of vascular smooth muscle cells (SMC) to modifications of their environment during remodeling. Although SMC hyperplasia is a predominant feature of many vascular diseases, SMC can also increase their mass within the remodeled vessel wall by enlarging their size and becoming hypertrophic. Hypertrophy is usually accompanied by cell cycle defects, cell polyploidy and binucleation, and senescence. However, the molecular mechanisms favoring SMC hypertrophy and their repercussion on SMC phenotype are not fully understood. Long-non-coding-RNAs (LncRNAs) are epigenetic regulators of gene expression, and they have been identified as modulators of cell division. We recently discovered a novel lncRNA, SAS (SMC-Angiotensin II-Sensitive), whose expression was markedly decreased in multiple models of SMC dedifferentiation, suggesting that SAS could regulate SMC phenotype and function. Publicly available transcriptional datasets revealed that SAS is preferentially expressed in SMC-rich tissues, including the aorta, in humans and mice. Yet, the functional relevance of SAS in SMC has never been investigated. Knockdown of SAS reduces proliferation, cell arrest and migration in aortic and renal artery-derived SMC treated with Platelet Derived Growth Factor. SAS knockdown was also associated with distinct SMC morphological changes including increase in cell size and binucleation demonstrating hypertrophy. Together, these observations suggest that decrease in SAS causes SMC hypertrophy due to defects in cell cycle completion and cytokinesis. Interestingly, SAS expression is decreased in response to Angiotensin-II in cultured VSMC and in the aorta of hypertensive mice (2 Kidney-1 Clip model), suggesting a role in mediating hypertension induced SMC hypertrophy. Similarly, to Angiotensin-II treatment, SAS knockdown promoted senescence. Furthermore, SAS deficient cells present mitochondria hyperfusion and increased oxygen consumption that correlates with the observed exacerbated senescence. Altogether, our results indicate that SAS is a potent regulator of VSMC morphology and is required for proper cell division and mitochondria organization.

NF-κB Signaling-Mediated Activation of WNK-SPAK-NKCC1 Cascade in Worsened Stroke Outcomes of Ang II-Hypertensive Mice

BACKGROUND

Worsened stroke outcomes with hypertension comorbidity are insensitive to blood pressure-lowering therapies. In an experimental stroke model with comorbid hypertension, we investigated causal roles of ang II (angiotensin II)-mediated stimulation of the brain WNK (with no lysine [K] kinases)-SPAK (STE20/SPS1-related proline/alanine-rich kinase)-NKCC1 (Na-K-Cl cotransporter) complex in worsened outcomes.

METHODS

Saline- or ang II-infused C57BL/6J male mice underwent stroke induced by permanent occlusion of the distal branches of the middle cerebral artery. Mice were randomly assigned to receive either vehicle dimethyl sulfoxide/PBS (2 mL/kg body weight/day, IP), a novel SPAK inhibitor, 5-chloro-N-(5-chloro-4-((4-chlorophenyl)(cyano)methyl)-2-methylphenyl)-2-hydroxybenzamide (ZT-1a' 5 mg/kg per day, IP) or a NF-κB (nuclear factor-κB) inhibitor TAT-NBD (transactivator of transcription-NEMO-binding domain' 20 mg/kg per day, IP). Activation of brain NF-κB and WNK-SPAK-NKCC1 cascade as well as ischemic stroke outcomes were examined.

RESULTS

Stroke triggered a 2- to 5-fold increase of WNK (isoforms 1, 2, 4), SPAK/OSR1 (oxidative stress-responsive kinase 1), and NKCC1 protein in the ang II-infused hypertensive mouse brains at 24 hours after stroke, which was associated with increased nuclear translocation of phospho-NF-κB protein in the cortical neurons (a Pearson correlation r of 0.77, P<0.005). The upregulation of WNK-SPAK-NKCC1 cascade proteins resulted from increased NF-κB recruitment on Wnk1, Wnk2, Wnk4, Spak, and Nkcc1 gene promoters and was attenuated by NF-κB inhibitor TAT-NBD. Poststroke administration of SPAK inhibitor ZT-1a significantly reduced WNK-SPAK-NKCC1 complex activation, brain lesion size, and neurological function deficits in the ang II-hypertensive mice without affecting blood pressure and cerebral blood flow.

CONCLUSIONS

The ang II-induced stimulation of NF-κB transcriptional activity upregulates brain WNK-SPAK-NKCC1 cascade and contributes to worsened ischemic stroke outcomes, illustrating the brain WNK-SPAK-NKCC1 complex as a therapeutic target for stroke with comorbid hypertension.

Benign prostatic hyperplasia/obstruction ameliorated using a soluble guanylate cyclase activator

Benign prostatic hyperplasia (BPH) is a feature of ageing males. Up to half demonstrate bladder outlet obstruction (BOO) with associated lower urinary tract symptoms (LUTS) including bladder overactivity. Current therapies to reduce obstruction, such as α1-adrenoceptor antagonists and 5α-reductase inhibitors, are not effective in all patients. The phosphodiesterase-5 inhibitor (PDE5I) tadalafil is also approved to treat BPH and LUTS, suggesting a role for nitric oxide (NO• ), soluble guanylate cyclase (sGC), and cGMP signalling pathways. However, PDE5I refractoriness can develop for reasons including nitrergic nerve damage and decreased NO• production, or inflammation-related oxidation of the sGC haem group, normally maintained in a reduced state by the cofactor cytochrome-b5-reductase 3 (CYB5R3). sGC activators, such as cinaciguat (BAY 58-2667), have been developed to enhance sGC activity in the absence of NO• or when sGC is oxidised. Accordingly, their effects on the prostate and LUT function of aged mice were evaluated. Aged mice (≥24 months) demonstrated a functional BPH/BOO phenotype, compared with adult animals (2-12 months), with low, delayed voiding responses and elevated intravesical pressures as measured by telemetric cystometry. This was consistent with outflow tract histological and molecular data that showed urethral constriction, increased prostate weight, greater collagen deposition, and cellular hyperplasia. All changes in aged animals were attenuated by daily oral treatment with cinaciguat for 2 weeks, without effect on serum testosterone levels. Cinaciguat had only transient (1 h) cardiovascular effects with oral gavage, suggesting a positive safety profile. The benefit of cinaciguat was suggested by its reversal of an overactive cystometric profile in CYB5R3 smooth muscle knockout mice that mirrors a profile of oxidative dysfunction where PDE5I may not be effective. Thus, the aged male mouse is a suitable model for BPH-induced BOO and cinaciguat has a demonstrated ability to reduce prostate-induced obstruction and consequent effects on bladder function. © 2021 The Pathological Society of Great Britain and Ireland.

SOD2 V16A amplifies vascular dysfunction in sickle cell patients by curtailing mitochondria complex IV activity

Superoxide dismutase 2 (SOD2) catalyzes the dismutation of superoxide to hydrogen peroxide in mitochondria, limiting mitochondrial damage. The SOD2 amino acid valine-to-alanine substitution at position 16 (V16A) in the mitochondrial leader sequence is a common genetic variant among patients with sickle cell disease (SCD). However, little is known about the cardiovascular consequences of SOD2V16A in SCD patients or its impact on endothelial cell function. Here, we show SOD2V16A associates with increased tricuspid regurgitant velocity (TRV), systolic blood pressure, right ventricle area at systole, and declined 6-minute walk distance in 410 SCD patients. Plasma lactate dehydrogenase, a marker of oxidative stress and hemolysis, significantly associated with higher TRV. To define the impact of SOD2V16A in the endothelium, we introduced the SOD2V16A variant into endothelial cells. SOD2V16A increases hydrogen peroxide and mitochondrial reactive oxygen species (ROS) production compared with controls. Unexpectedly, the increased ROS was not due to SOD2V16A mislocalization but was associated with mitochondrial complex IV and a concomitant decrease in basal respiration and complex IV activity. In sum, SOD2V16A is a novel clinical biomarker of cardiovascular dysfunction in SCD patients through its ability to decrease mitochondrial complex IV activity and amplify ROS production in the endothelium.

Histone deacetylase inhibitors (HDACi) increase expression of KCa2.3 (SK3) in primary microvascular endothelial cells

The small conductance calcium-activated potassium channel (KCa2.3) has long been recognized for its role in mediating vasorelaxation through the endothelium-derived hyperpolarization (EDH) response. Histone deacetylases (HDACs) have been implicated as potential modulators of blood pressure and histone deacetylase inhibitors (HDACi) are being explored as therapeutics for hypertension. Herein, we show that HDACi increase KCa2.3 expression when heterologously expressed in HEK cells and endogenously expressed in primary cultures of human umbilical vein endothelial cells (HUVECs) and human intestinal microvascular endothelial cells (HIMECs). When primary endothelial cells were exposed to HDACi, KCa2.3 transcripts, subunits, and functional current are increased. Quantitative RT-PCR (qPCR) demonstrated increased KCa2.3 mRNA following HDACi, confirming transcriptional regulation of KCa2.3 by HDACs. By using pharmacological agents selective for different classes of HDACs, we discriminated between cytoplasmic and epigenetic modulation of KCa2.3. Biochemical analysis revealed an association between the cytoplasmic HDAC6 and KCa2.3 in immunoprecipitation studies. Specifically inhibiting HDAC6 increases expression of KCa2.3. In addition to increasing the expression of KCa2.3, we show that nonspecific inhibition of HDACs causes an increase in the expression of the molecular chaperone Hsp70 in endothelial cells. When Hsp70 is inhibited in the presence of HDACi, the magnitude of the increase in KCa2.3 expression is diminished. Finally, we show a slower rate of endocytosis of KCa2.3 as a result of exposure of primary endothelial cells to HDACi. These data provide the first demonstrated approach to increase KCa2.3 channel number in endothelial cells and may partially account for the mechanism by which HDACi induce vasorelaxation.

FoxO4 controls sGCβ transcription in vascular smooth muscle

Nitric oxide (NO) binds soluble guanylyl cyclase β (sGCβ) to produce cGMP and relax vascular smooth muscle cells (SMCs) needed for vasodilation. Although the regulation of NO-stimulated sGC activity has been well characterized at the posttranslational level, the mechanisms that govern sGC transcription remain incompletely understood. Recently, we identified Forkhead box subclass O (FoxO) transcription factors as essential for expression of sGC; however, the specific FoxO family member responsible for the expression of sGCβ in SMC remains unknown. Using FoxO shRNA knockdown adenovirus treatment in rat aortic SMCs, we show that FoxO1 or FoxO3 knockdown causes greater than twofold increases in Gucy1a3 and Gucy1b3 mRNA expression, without changes in NO-dependent cGMP production or cGMP-dependent phosphorylation. FoxO4 knockdown produced a 50% decrease in Gucy1a3 and Gucy1b3 mRNA with 70% loss of sGCα and 50% loss of sGCβ protein expression. Knockdown of FoxO4 expression decreased cGMP production and downstream protein kinase G-dependent phosphorylation more than 50%. Triple FoxO knockdown exacerbated loss of sGC-dependent function, phenocopying previous FoxO inhibition studies. Using promoter luciferase and chromatin immunoprecipitation assays, we find that FoxO4 acts as a transcriptional activator by directly binding several FoxO DNA motifs in the promoter regions of GUCY1B3 in human aortic SMCs. Collectively, our data show FoxO4 is a critical transcriptional regulator of sGCβ expression in SMC.NEW & NOTEWORTHY One of the key mechanisms of vascular smooth muscle cell (SMC) dilation occurs through nitric oxide (NO)-dependent induction of soluble guanylyl cyclase (sGC) by means of its β-subunit. Herein, we are the first to identify Forkhead box subclass O protein 4 (FoxO4) as a key transcriptional regulator of GUCY1B3 expression, which codes for sGCβ protein in human and animal SMCs. This discovery will likely have important implications for the future usage of antihypertensive and vasodilatory therapies which target NO production, sGC, or FoxO transcription factors.

Association of N-Terminal Pro-Brain Natriuretic Peptide Concentration in Early Pregnancy With Development of Hypertensive Disorders of Pregnancy and Future Hypertension

IMPORTANCE

Hypertensive disorders of pregnancy are associated with future cardiovascular disease, perhaps because of subclinical cardiac dysfunction before pregnancy leading to impaired adaptation to pregnancy. Natriuretic peptides are promising biomarkers for detecting subclinical cardiac dysfunction outside of pregnancy.

OBJECTIVE

To investigate whether higher concentrations of N-terminal pro-brain natriuretic peptide (NT-proBNP) in early pregnancy would be associated with hypertensive disorders of pregnancy and hypertension 2 to 7 years post partum.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study used data from the The Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be Heart Health Study, a prospective multicenter observational study. A total of 4103 nulliparous women with complete data and no prepregnancy hypertension or diabetes who were treated at 8 clinical sites were included. Women were followed up with for 2 to 7 years after pregnancy. Data were collected from October 2010 to October 2017, and data were analyzed from August 2020 to November 2021.

EXPOSURES

NT-proBNP concentration, measured using an electrochemiluminescence immunoassay from a first-trimester blood sample.

MAIN OUTCOMES AND MEASURES

Hypertensive disorders of pregnancy and incident hypertension (systolic blood pressure of 130 mm Hg or diastolic blood pressure of 80 mm Hg or use of antihypertensive agents) at follow-up visit.

RESULTS

A total of 4103 women met inclusion criteria; the mean (SD) age was 27.0 (5.6) years. Among these women, 909 (22.2%) had an adverse pregnancy outcome, and 817 (19.9%) had hypertension at the follow-up visit. Higher NT-proBNP concentrations were associated with a lower risk of hypertensive disorders of pregnancy (adjusted odds ratio per doubling, 0.81; 95% CI, 0.73-0.91), which persisted after adjustment for age, self-reported race and ethnicity, early-pregnancy body mass index, smoking, and aspirin use. Similarly, higher NT-proBNP concentration in early pregnancy was also associated with a lower risk of incident hypertension 2 to 7 years after delivery (adjusted odds ratio per doubling, 0.84; 95% CI, 0.77-0.93), an association that persisted after controlling for confounders, including hypertensive disorders of pregnancy.

CONCLUSIONS AND RELEVANCE

In this cohort study, higher NT-proBNP concentrations in early pregnancy were associated with a lower risk of hypertensive disorders of pregnancy and hypertension 2 to 7 years post partum. These findings suggest that normal early-pregnancy cardiovascular physiology, as assessed by NT-proBNP concentration, may provide biologic insights into both pregnancy outcome and cardiovascular disease risk.

Endothelial superoxide dismutase 2 is decreased in sickle cell disease and regulates fibronectin processing

Sickle cell disease (SCD) is a genetic red blood cell disorder characterized by increased reactive oxygen species (ROS) and a concordant reduction in antioxidant capacity in the endothelium. Superoxide dismutase 2 (SOD2) is a mitochondrial-localized enzyme that catalyzes the dismutation of superoxide to hydrogen peroxide. Decreased peripheral blood expression of SOD2 is correlated with increased hemolysis and cardiomyopathy in SCD. Here, we report for the first time that endothelial cells exhibit reduced SOD2 protein expression in the pulmonary endothelium of SCD patients. To investigate the impact of decreased SOD2 expression in the endothelium, SOD2 was knocked down in human pulmonary microvascular endothelial cells (hPMVECs). We found that SOD2 deficiency in hPMVECs results in endothelial cell dysfunction, including reduced cellular adhesion, diminished migration, integrin protein dysregulation, and disruption of permeability. Furthermore, we uncover that SOD2 mediates changes in endothelial cell function via processing of fibronectin through its inability to facilitate dimerization. These results demonstrate that endothelial cells are deficient in SOD2 expression in SCD patients and suggest a novel pathway for SOD2 in regulating fibronectin processing.

Abstract WMP112: Cyb5r3 Provides Resilience Against Cerebral Infarct And Hemorrhagic Transformation In Mice Following Stroke

Introduction: Cytochrome B5 reductase 3 (CYB5R3) is a heme reductase, ubiquitously expressed in red cells and somatic cells. We discovered a novel role for smooth muscle cell (SMC) CYB5R3 in reducing oxidized heme (Fe 3+ ) of soluble guanylate cyclase back to its reduced form (Fe 2+ ) to enable nitric oxide signaling for cyclic guanosine monophosphate production and vessel dilation. We have published higher systemic and pulmonary artery pressures in mice with conditional SMC-specific CYB5R3 knockdown. While there are over 40 CYB5R3 variants, the T117S loss-of-function (~50%) variant is interesting as it is enriched (0.23 minor allele) in persons of African ancestry. We hypothesized that the T117S variant increases risk for stroke with poor outcomes.

Methods: We studied transient middle cerebral artery occlusion (50 min) in mice with CRISPR-Cas9 induced T117S CYB5R3 (T117S), Cre/Lox induced endothelial cell-specific CYB5R3 knockdown (EC-KD), Cre/Lox induced SMC-specific CYB5R3 knockdown (SMC-KD), global CYB5R3 overexpression (OE), and wild-type (WT) mice; all were adult males on a C57Bl6 background. Cerebral infarct volume (mm 3 ) was determined 24 hr later using 2,3,5-Triphenyltetrazolium chloride (TTC) and ImageJ.

Results: Infarct volume was larger in T117S (132 vs 71; P=0.002) versus WT controls, which SMC-KD replicated (123 vs 70; P=0.01) and OE reversed (49 vs 100; P=0.02); EC-KD had little effect (88 vs 72). Hemorrhagic transformation was greatest in EC-KD (7/8 vs 5/9) and SMC-KD (3/6 vs 1/6), whereas there was no effect for T117S or OE.

Conclusion: A congenital global point mutation causing CYB5R3 loss-of-function (T117S) enhances area at risk for cerebral infarct after stroke, while conditional deletion of EC and SMC CYB5R3 contribute to hemorrhagic transformation. Determining T117S carrier status of patients may help predict stroke risk and allow CYB5R3-targeted precision therapy approaches to stroke management.

Smooth muscle cell CYB5R3 preserves cardiac and vascular function under chronic hypoxic stress

Chronic hypoxia is a major driver of cardiovascular complications, including heart failure. The nitric oxide (NO) - soluble guanylyl cyclase (sGC) - cyclic guanosine monophosphate (cGMP) pathway is integral to vascular tone maintenance. Specifically, NO binds its receptor sGC within vascular smooth muscle cells (SMC) in its reduced heme (Fe²⁺) form to increase intracellular cGMP production, activate protein kinase G (PKG) signaling, and induce vessel relaxation. Under chronic hypoxia, oxidative stress drives oxidation of sGC heme (Fe²⁺→Fe³⁺), rendering it NO-insensitive. We previously showed that cytochrome b5 reductase 3 (CYB5R3) in SMC is a sGC reductase important for maintaining NO-dependent vasodilation and conferring resilience to systemic hypertension and sickle cell disease-associated pulmonary hypertension. To test whether CYB5R3 may be protective in the context of chronic hypoxia, we subjected SMC-specific CYB5R3 knockout mice (SMC CYB5R3 KO) to 3 weeks hypoxia and assessed vascular and cardiac function using echocardiography, pressure volume loops and wire myography. Hypoxic stress caused 1) biventricular hypertrophy in both WT and SMC CYB5R3 KO, but to a larger degree in KO mice, 2) blunted vasodilation to NO-dependent activation of sGC in coronary and pulmonary arteries of KO mice, and 3) decreased, albeit still normal, cardiac function in KO mice. Overall, these data indicate that SMC CYB5R3 deficiency potentiates bilateral ventricular hypertrophy and blunts NO-dependent vasodilation under chronic hypoxia conditions. This implicates that SMC CYB5R3 KO mice post 3-week hypoxia have early stages of cardiac remodeling and functional changes that could foretell significantly impaired cardiac function with longer exposure to hypoxia.

A primer for measuring cGMP signaling and cGMP-mediated vascular relaxation

Soluble guanylyl cyclase (sGC, also called GC1) is the main receptor for nitric oxide (NO) that catalyzes the production of the second messenger molecule, 3'5' cyclic guanosine monophosphate (cGMP) leading to vasorelaxation, and inhibition of leukocyte recruitment and platelet aggregation. Enhancing cGMP levels, through sGC agonism or inhibition of cGMP breakdown via phosphodiesterase inhibition, has yielded FDA approval for several cGMP modifier therapies for treatment of cardiovascular and pulmonary diseases. While basic research continues to improve our understanding of cGMP signaling and as new therapies evolve to elevate cGMP levels, we provide a short methodological primer for measuring cGMP and cGMP-mediated vascular relaxation for investigators.

Cooperation between CYB5R3 and NOX4 via coenzyme Q mitigates endothelial inflammation

NADPH oxidase 4 (NOX4) regulates endothelial inflammation by producing hydrogen peroxide (H₂O₂) and to a lesser extent O₂^•-. The ratio of NOX4-derived H₂O₂ and O₂^•- can be altered by coenzyme Q (CoQ) mimics. Therefore, we hypothesize that cytochrome b5 reductase 3 (CYB5R3), a CoQ reductase abundant in vascular endothelial cells, regulates inflammatory activation. To examine endothelial CYB5R3 in vivo, we created tamoxifen-inducible endothelium-specific Cyb5r3 knockout mice (R3 KO). Radiotelemetry measurements of systolic blood pressure showed systemic hypotension in lipopolysaccharides (LPS) challenged mice, which was exacerbated in R3 KO mice. Meanwhile, LPS treatment caused greater endothelial dysfunction in R3 KO mice, evaluated by acetylcholine-induced vasodilation in the isolated aorta, accompanied by elevated mRNA expression of vascular adhesion molecule 1 (Vcam-1). Similarly, in cultured human aortic endothelial cells (HAEC), LPS and tumor necrosis factor α (TNF-α) induced VCAM-1 protein expression was enhanced by Cyb5r3 siRNA, which was ablated by silencing the Nox4 gene simultaneously. Moreover, super-resolution confocal microscopy indicated mitochondrial co-localization of CYB5R3 and NOX4 in HAECs. APEX2-based electron microscopy and proximity biotinylation also demonstrated CYB5R3's localization on the mitochondrial outer membrane and its interaction with NOX4, which was further confirmed by the proximity ligation assay. Notably, Cyb5r3 knockdown HAECs showed less total H₂O₂ but more mitochondrial O₂^•-. Using inactive or non-membrane bound active CYB5R3, we found that CYB5R3 activity and membrane translocation are needed for optimal generation of H₂O₂ by NOX4. Lastly, cells lacking the CoQ synthesizing enzyme COQ6 showed decreased NOX4-derived H₂O₂, indicating a requirement for endogenous CoQ in NOX4 activity. In conclusion, CYB5R3 mitigates endothelial inflammatory activation by assisting in NOX4-dependent H₂O₂ generation via CoQ.

Human and rodent red blood cells do not demonstrate xanthine oxidase activity or XO-catalyzed nitrite reduction to NO

A number of molybdopterin enzymes, including xanthine oxidoreductase (XOR), aldehyde oxidase (AO), sulfite oxidase (SO), and mitochondrial amidoxime reducing component (mARC), have been identified as nitrate and nitrite reductases. Of these enzymes, XOR has been the most extensively studied and reported to be a substantive source of nitric oxide (NO) under inflammatory/hypoxic conditions that limit the catalytic activity of the canonical NOS pathway. It has also been postulated that XOR nitrite reductase activity extends to red blood cell (RBCs) membranes where it has been immunohistochemically identified. These findings, when combined with countervailing reports of XOR activity in RBCs, incentivized our current study to critically evaluate XOR protein abundance/enzymatic activity in/on RBCs from human, mouse, and rat sources. Using various protein concentrations of RBC homogenates for both human and rodent samples, neither XOR protein nor enzymatic activity (xanthine → uric acid) was detectable. In addition, potential loading of RBC-associated glycosaminoglycans (GAGs) by exposing RBC preparations to purified XO before washing did not solicit detectable enzymatic activity (xanthine → uric acid) or alter NO generation profiles. To ensure these observations extended to absence of XOR-mediated contributions to overall RBC-associated nitrite reduction, we examined the nitrite reductase activity of washed and lysed RBC preparations via enhanced chemiluminescence in the presence or absence of the XOR-specific inhibitor febuxostat (Uloric®). Neither addition of inhibitor nor the presence of the XOR substrate xanthine significantly altered the rates of nitrite reduction to NO by RBC preparations from either human or rodent sources confirming the absence of XO enzymatic activity. Furthermore, examination of the influence of the age (young cells vs. old cells) of human RBCs on XO activity also failed to demonstrate detectable XO protein. Combined, these data suggest: 1) that XO does not contribute to nitrite reduction in/on human and rodent erythrocytes, 2) care should be taken to validate immuno-detectable XO by demonstrating enzymatic activity, and 3) XO does not associate with human erythrocytic glycosaminoglycans or participate in nonspecific binding.

Metabolic Syndrome Mediates ROS-miR-193b-NFYA-Dependent Downregulation of Soluble Guanylate Cyclase and Contributes to Exercise-Induced Pulmonary Hypertension in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Many patients with heart failure with preserved ejection fraction have metabolic syndrome and develop exercise-induced pulmonary hypertension (EIPH). Increases in pulmonary vascular resistance in patients with heart failure with preserved ejection fraction portend a poor prognosis; this phenotype is referred to as combined precapillary and postcapillary pulmonary hypertension (CpcPH). Therapeutic trials for EIPH and CpcPH have been disappointing, suggesting the need for strategies that target upstream mechanisms of disease. This work reports novel rat EIPH models and mechanisms of pulmonary vascular dysfunction centered around the transcriptional repression of the soluble guanylate cyclase (sGC) enzyme in pulmonary artery (PA) smooth muscle cells.

METHODS

We used obese ZSF-1 leptin-receptor knockout rats (heart failure with preserved ejection fraction model), obese ZSF-1 rats treated with SU5416 to stimulate resting pulmonary hypertension (obese+sugen, CpcPH model), and lean ZSF-1 rats (controls). Right and left ventricular hemodynamics were evaluated using implanted catheters during treadmill exercise. PA function was evaluated with magnetic resonance imaging and myography. Overexpression of nuclear factor Y α subunit (NFYA), a transcriptional enhancer of sGC β1 subunit (sGCβ1), was performed by PA delivery of adeno-associated virus 6. Treatment groups received the SGLT2 inhibitor empagliflozin in drinking water. PA smooth muscle cells from rats and humans were cultured with palmitic acid, glucose, and insulin to induce metabolic stress.

RESULTS

Obese rats showed normal resting right ventricular systolic pressures, which significantly increased during exercise, modeling EIPH. Obese+sugen rats showed anatomic PA remodeling and developed elevated right ventricular systolic pressure at rest, which was exacerbated with exercise, modeling CpcPH. Myography and magnetic resonance imaging during dobutamine challenge revealed PA functional impairment of both obese groups. PAs of obese rats produced reactive oxygen species and decreased sGCβ1 expression. Mechanistically, cultured PA smooth muscle cells from obese rats and humans with diabetes or treated with palmitic acid, glucose, and insulin showed increased mitochondrial reactive oxygen species, which enhanced miR-193b-dependent RNA degradation of nuclear factor Y α subunit (NFYA), resulting in decreased sGCβ1-cGMP signaling. Forced NYFA expression by adeno-associated virus 6 delivery increased sGCβ1 levels and improved exercise pulmonary hypertension in obese+sugen rats. Treatment of obese+sugen rats with empagliflozin improved metabolic syndrome, reduced mitochondrial reactive oxygen species and miR-193b levels, restored NFYA/sGC activity, and prevented EIPH.

CONCLUSIONS

In heart failure with preserved ejection fraction and CpcPH models, metabolic syndrome contributes to pulmonary vascular dysfunction and EIPH through enhanced reactive oxygen species and miR-193b expression, which downregulates NFYA-dependent sGCβ1 expression. Adeno-associated virus-mediated NFYA overexpression and SGLT2 inhibition restore NFYA-sGCβ1-cGMP signaling and ameliorate EIPH.

Redox Switches Controlling Nitric Oxide Signaling in the Resistance Vasculature and Implications for Blood Pressure Regulation: Mid-Career Award for Research Excellence 2020

The arterial resistance vasculature modulates blood pressure and flow to match oxygen delivery to tissue metabolic demand. As such, resistance arteries and arterioles have evolved a series of highly orchestrated cell-cell communication mechanisms between endothelial cells and vascular smooth muscle cells to regulate vascular tone. In response to neurohormonal agonists, release of several intracellular molecules, including nitric oxide, evokes changes in vascular tone. We and others have uncovered novel redox switches in the walls of resistance arteries that govern nitric oxide compartmentalization and diffusion. In this review, we discuss our current understanding of redox switches controlling nitric oxide signaling in endothelial and vascular smooth muscle cells, focusing on new mechanistic insights, physiological and pathophysiological implications, and advances in therapeutic strategies for hypertension and other diseases.

Notch2 Suppression Mimicking Changes in Human Pulmonary Hypertension Modulates Notch1 and Promotes Endothelial Cell Proliferation

Pulmonary arterial hypertension (PAH) is a fatal cardiopulmonary disease characterized by increased vascular cell proliferation with resistance to apoptosis and occlusive remodeling of the small pulmonary arteries in humans. The Notch family of proteins are proximal signaling mediators of an evolutionarily conserved pathway that effect cell proliferation, fate determination, and development. In endothelial cells (ECs), Notch receptor 2 (Notch2) has been shown to promote endothelial apoptosis. However, a pro- or anti-proliferative role for Notch2 in pulmonary endothelial proliferation and ensuing PAH is unknown. Herein, we postulated that suppressed Notch2 signaling drives pulmonary endothelial proliferation in the setting of PAH. We observed that levels of Notch2 are ablated in lung and PA tissue samples from PAH patients compared to non-PAH controls. Interestingly, Notch2 expression was attenuated in human pulmonary artery endothelial cells (hPAECs) exposed to vasoactive factors including hypoxia, TGFβ, ET-1, and IGF-1. Gene silencing of Notch2 increased EC proliferation and reduced apoptosis. At the molecular level, Notch2-deficient hPAECs activated Akt, Erk1/2 and anti-apoptotic protein Bcl-2, and reduced levels of p21^cip and Bax. Intriguingly, loss of Notch2 elicits a paradoxical activation of Notch1 and transcriptional upregulation of canonical Notch target genes Hes1, Hey1 and Hey2. Further, reduction in Rb and increased E2F1 binding to the Notch1 promoter appear to explain the upregulation of Notch1. In aggregate, our results demonstrate that loss of Notch2 derepresses Notch1 and elicits aberrant EC hallmarks of PAH. The data underscore a novel role for Notch in the maintenance of endothelial cell homeostasis.

CoenzymeQ in cellular redox regulation and clinical heart failure

Coenzyme Q (CoQ) is ubiquitously embedded in lipid bilayers of various cellular organelles. As a redox cycler, CoQ shuttles electrons between mitochondrial complexes and extramitochondrial reductases and oxidases. In this way, CoQ is crucial for maintaining the mitochondrial function, ATP synthesis, and redox homeostasis. Cardiomyocytes have a high metabolic rate and rely heavily on mitochondria to provide energy. CoQ levels, in both plasma and the heart, correlate with heart failure in patients, indicating that CoQ is critical for cardiac function. Moreover, CoQ supplementation in clinics showed promising results for treating heart failure. This review provides a comprehensive view of CoQ metabolism and its interaction with redox enzymes and reactive species. We summarize the clinical trials and applications of CoQ in heart failure and discuss the caveats and future directions to improve CoQ therapeutics.

Abstract P726: Cytochrome B5 Reductase 3 Modifies The Brain-Blood Axis Response To Ischemic Stroke In Mice With Sickle Cell Disease

Introduction: Stroke and silent infarcts are serious complications of sickle cell disease (SCD), occurring frequently in children. Decreased nitric oxide bioavailability and responsiveness contribute to neurovascular disease. Cytochrome b5 reductase 3 (Cyb5R3) is a heme iron reductase that reduces oxidized soluble guanylate cyclase heme iron (Fe 3+ --> Fe 2+ ) to preserve nitric oxide signaling. A loss-of-function Cyb5R3 missense variant (T117S) occurs with high frequency (0.23 minor allele) in persons of African ancestry.

Hypothesis: We hypothesized that impaired reductase function of T117S Cyb5R3 exacerbates brain damage after ischemic stroke in SCD.

Methods: Bone marrow transplant was used to create male SCD mice with wild type (SS/WT) or T117S (SS/T117S) Cyb5R3. Blood was sampled before and after middle cerebral artery occlusion (55 minutes occlusion, 48 hours reperfusion). Infarct volume (IV) was determined by 2,3,5-triphenyltetrazolium chloride. Intravascular hemolysis and correlation (Pearson’s R) of hematology changes with IV were determined. Baseline Walk-PHaSST (NCT00492531) data were analyzed for stroke occurrence.

Results: Brain IV (63 vs 27 cm 3 , P=0.003) and mortality (3/6 vs 0/8) were greater in SS/T117S vs SS/WT. Red blood cells, hemoglobin and hematocrit declined as IV increased. Plasma oxyhemoglobin increased in parallel with IV (r = 0.74, P=0.09). There were different signatures to hematologic changes that occurred with IV in SCD. Relative to wild type, T117S contracted the erythroid compartment (red blood cell: -13% vs 13%, P=0.003; hematocrit: -20% vs 1%, P=0.008; hemoglobin: -18% vs 2%, P=0.007). Mean platelet volume correlated with IV in SS/T117S (r = 0.87, P=0.06), while the inverse occurred in SS/WT (r = -0.63, P=0.09) Monocytes increased in parallel with IV in SS/T117S (r = 0.73, P=0.16), but followed the opposite trajectory in SS/WT (r = -0.77, P=0.04). WalkPHaSST participants with T117S Cyb5R3 self-reported more ischemic stroke (7.4% vs 5.1%) relative to wild type.

Conclusion: Cyb5R3 is an important modifier of the evolution and outcome of ischemic brain injury in SCD and its hematologic consequences. Our findings indicate a bidirectional relationship between stroke and anemia in SCD that may axially turn on Cyb5R3 activity.

Xanthine Oxidase Drives Hemolysis and Vascular Malfunction in Sickle Cell Disease

OBJECTIVE

Chronic hemolysis is a hallmark of sickle cell disease (SCD) and a driver of vasculopathy; however, the mechanisms contributing to hemolysis remain incompletely understood. Although XO (xanthine oxidase) activity has been shown to be elevated in SCD, its role remains unknown. XO binds endothelium and generates oxidants as a byproduct of hypoxanthine and xanthine catabolism. We hypothesized that XO inhibition decreases oxidant production leading to less hemolysis. Approach and Results: Wild-type mice were bone marrow transplanted with control (AA) or sickle (SS) Townes bone marrow. After 12 weeks, mice were treated with 10 mg/kg per day of febuxostat (Uloric), Food and Drug Administration-approved XO inhibitor, for 10 weeks. Hematologic analysis demonstrated increased hematocrit, cellular hemoglobin, and red blood cells, with no change in reticulocyte percentage. Significant decreases in cell-free hemoglobin and increases in haptoglobin suggest XO inhibition decreased hemolysis. Myographic studies demonstrated improved pulmonary vascular dilation and blunted constriction, indicating improved pulmonary vasoreactivity, whereas pulmonary pressure and cardiac function were unaffected. The role of hepatic XO in SCD was evaluated by bone marrow transplanting hepatocyte-specific XO knockout mice with SS Townes bone marrow. However, hepatocyte-specific XO knockout, which results in >50% diminution in circulating XO, did not affect hemolysis levels or vascular function, suggesting hepatocyte-derived elevation of circulating XO is not the driver of hemolysis in SCD.

CONCLUSIONS

Ten weeks of febuxostat treatment significantly decreased hemolysis and improved pulmonary vasoreactivity in a mouse model of SCD. Although hepatic XO accounts for >50% of circulating XO, it is not the source of XO driving hemolysis in SCD.

Abstract P093: Cytochrome B5 Reductase 3 And Xanthine Oxidase Coordinately Regulate Soluble Guanylyl Cyclase Physiological Redox State

In cardiovascular disease, oxidative stress can drive soluble guanylyl cyclase (sGC) heme oxidation resulting in the loss of the sGC heme (apo-sGC), the impairment of nitric oxide (NO) binding and cGMP production, and vasoconstriction. Consequently, a new class of therapeutic compounds sGC activators have been developed which target oxidized and apo-sGC to cause irreversible, NO-independent reactivation of cGMP production and vasodilation. While sGC activators have had varied clinical success, surprisingly few studies have defined the impact of NO-independent sGC activation on vascular physiology in healthy conditions. We found mesenteric and pulmonary arteries are two log orders more sensitive to NO-independent sGC activator BAY 58-2667 induced vasodilation than aorta; no difference in NO-dependent sGC vasodilation between vessels was observed. These data indicate the presence of an activatable physiological pool of oxidized and/or apo-sGC in pulmonary and mesenteric arteries. We recently published that smooth muscle cell cytochrome b5 reductase 3 (CYB5R3) acts to reduce oxidized heme sGC back to its NO-sensitive reduced heme state during vascular disease. We found transgenic CYB5R3 overexpression (CYB5R3 OE) mice were more resistant to BAY 58-2667 mesenteric artery vasodilation and blood pressure lowering compared to wild-type controls (n=5-9) under physiologic conditions. Also, healthy CYB5R3 OE pulmonary arteries had a near complete loss of BAY 58-2667 vasodilation suggesting both mesenteric and pulmonary arteries contain a pool of oxidized sGC. We next asked if physiological H 2 O 2 production accounts for changes in BAY 58-2667 responsiveness. We found using mitochondrial-specific catalase overexpression mice, that BAY 58-2667 vasodilation did not differ from controls in any vascular bed (n=4-6). We next tested whether xanthine oxidase (XO), which can produce H 2 O 2 at the endothelial cell surface of vessels, can impact physiological BAY 58-2667 vasodilation. We found that Febuxostat, a XO inhibitor, led to a significant decrease in mesenteric artery BAY 58-2667 induced vasodilation from ~70% to ~30% (n=6). Combined, these data provide evidence for CYB5R3 and XO as regulators of physiological sGC resistance artery vasodilation.

Abstract MP19: Smooth Muscle Cell Cytochrome B5 Reductase 3 Causes Heart Failure With Reduced Ejection Fraction Under Hypoxic Stress

Pulmonary hypertension causes increased pulmonary vascular resistance and right heart failure. Nitric oxide (NO) binds to its receptor soluble guanylyl cyclase (sGC) within vascular smooth muscle cells in its reduced heme (Fe 2+ ) form to increase intracellular cGMP production, activate protein kinase G signaling, and induce vessel relaxation. In pulmonary hypertension, endothelial damage leading to decreased NO bioavailability combined with oxidation of the sGC heme (Fe 3+ ) in vascular smooth muscle cells rendering it NO-insensitive results in vasonstriction. Notably, we have previously shown that cytochrome b5 reductase 3 (CYB5R3) in vascular smooth muscle cells is an sGC reductase (Fe 3+ to Fe 2+ ) that maintains NO-dependent vasodilation in vascular disease. We therefore hypothesized that CYB5R3 confers protection in pulmonary hypertension. To test this, we subjected smooth muscle cell-specific CYB5R3 knockout mice (SMC CYB5R3 KO) to 21 days of continuous hypoxia (10% O 2 ) and assessed vascular and cardiac function. We found that SMC CYB5R3 KO led to enhanced cardiac hypertrophy when compared to wild-type (WT) controls (n=8/ group). Specifically, SMC CYB5R3 KO mice had a larger right ventricle per tibia size, left ventricle mass, and Fulton index compared to WT (n=8/ group). Moreover, SMC CYB5R3 KO mice had a significantly impaired ejection fraction and fractional shortening, and increased left ventricular posterior wall pressure (n=3-5/group). No differences in right heart function or overall cardiac fibrosis were observed between groups (n=3-5/group). With respect to vascular function, hypoxic pulmonary arteries from SMC CYB5R3 KO mice also had a blunted response to sodium nitroprusside induced NO-dependent vasodilation though no difference in sGC activator BAY 58-2667 induced NO-independent vasodilation was observed as compared to WT (n=8-11/ group). No differences in pulmonary arterial sGC levels or medial area were observed between groups (n=6-7). Combined, these data implicate that loss of SMC CYB5R3 exacerbates cardiomyocyte hypertrophy and reduces cardiac function independent of pulmonary pressure differences.

Excessive dietary salt promotes aortic stiffness in murine renovascular hypertension

Renovascular hypertension is characterized by activation of the renin-angiotensin-aldosterone system, blunted natriuretic responses, and elevated sympathetic nerve activity. Excess dietary salt intake exaggerates arterial blood pressure (ABP) in multiple models of experimental hypertension. The present study tested whether a high-salt diet exaggerated ABP and vascular dysfunction in a 2-kidney, 1-clip (2K1C) murine model. Male C57BL/6J mice (8-12 wk) were randomly assigned, and fed a 0.1% or 4.0% NaCl diet, and instrumented with telemetry units to measure ABP. Then, the 2K1C model was produced by placing a cuff around the right renal artery. Systolic, diastolic, and mean ABP were significantly higher in mice fed 4.0% vs. 0.1% NaCl at 1 wk but not after 3 wk. Interestingly, 2K1C hypertension progressively increased arterial pulse pressure in both groups; however, the magnitude was significantly greater in mice fed 4.0% vs. 0.1% NaCl at 3 wk. Moreover, pulse wave velocity was significantly greater in 2K1C mice fed 4.0% vs. 0.1% NaCl diet or sham-operated mice fed either diet. Histological assessment of aortas indicated no structural differences among groups. Finally, endothelium-dependent vasodilation was significantly and selectively attenuated in the aorta but not mesenteric arteries of 2K1C mice fed 4.0% NaCl vs. 0.1% NaCl or sham-operated control mice. The findings suggest that dietary salt loading transiently exaggerates 2K1C renovascular hypertension but promotes chronic aortic stiffness and selective aortic vascular dysfunction.NEW & NOTEWORTHY High dietary salt exaggerates hypertension in multiple experimental models. Here we demonstrate that a high-salt diet produces a greater increase in arterial blood pressure at 1 wk after induction of 2-kidney, 1-clip (2K1C) hypertension but not at 3 wk. Interestingly, 2K1C mice fed a high-salt diet displayed an exaggerated pulse pressure, elevated pulse wave velocity, and reduced endothelium-dependent vasodilation of the aorta but not mesenteric arteries. These findings suggest that dietary salt may interact with underlying cardiovascular disease to promote selective vascular dysfunction and aortic stiffness.

Ultrasound-Targeted Microbubble Cavitation with Sodium Nitrite Synergistically Enhances Nitric Oxide Production and Microvascular Perfusion

Microvascular obstruction is a common repercussion of percutaneous coronary intervention for distal microembolization, ischemia-reperfusion injury and inflammation, which increases post-myocardial infarction heart failure and mortality. Ultrasound-targeted microbubble cavitation (UTMC) may resolve microvascular obstruction while activating endothelial nitric oxide synthase (eNOS) and increasing endothelium-derived nitric oxide (NO) bioavailability. Nitrite, a cardioprotective agent, offers an additional source of NO and potential synergy with UTMC. UTMC and nitrite co-therapy increased microvascular perfusion and NO concentration in a rat hindlimb model. Using N-nitro-L-arginine methyl ester for eNOS blockade, we found a three-way interaction effect between nitrite, UTMC and eNOS on microvascular perfusion and NO production. Modulating ultrasound peak negative acoustic pressure (0.33-1.5 MPa) significantly affected outcomes, while microbubble dosage (2 × 108 bubbles/mL, 1.5 mL/h to 1 × 109 bubbles/mL, 3 mL/h) did not. Nitrite co-therapy also protected against oxidative stress. Comparison of nitrite to sodium nitroprusside with UTMC revealed synergistic effects were specific to nitrite. Synergy between UTMC and nitrite holds therapeutic potential for cardiovascular disease.

Nitrite elicits divergent NO-dependent signaling that associates with outcome in out of hospital cardiac arrest

Brain and heart injury cause most out-of-hospital cardiac arrest deaths but limited pharmacotherapy exists to protect these tissues. Nitrite is a nitric oxide precursor that is protective in pre-clinical models of ischemic injury and safe in Phase I testing. Protection may occur by cGMP generation via the sGC pathway or through S-nitrosothiol and nitrated conjugated linoleic acid (NO₂-CLA) formation. We hypothesized that nitrite provided during CPR signals through multiple pathways and that activation of signals is associated with OHCA outcome. To this end, we performed a secondary analysis of a phase 1 study of intravenous nitrite administration during resuscitation in adult out-of-hospital cardiac arrest. Associations between whole blood nitrite and derived plasma signals (cGMP and NO₂-CLA) with patient characteristics and outcomes were defined using Chi-square or t-tests and multiple logistic regression. Whole blood nitrite levels correlated inversely with plasma NO₂-CLA (p = 0.039) but not with cGMP. Patients with shockable rhythms had higher cGMP (p = 0.027), NO₂-CLA (p < 0.0001) and trended towards lower nitrite (p = 0.077). Importantly, plasma cGMP and NO₂-CLA levels were higher in survivors (p = 0.033 and 0.019) and in those with good neurological outcome (p = 0.046 and 0.021). Nitrite was lower in patients with good neurologic outcome (p = 0.029). cGMP (OR 4.02; 95% CI 1.04–15.54; p = 0.044) and NO₂-CLA (OR 3.74; 95% CI 1.11–12.65; p = 0.034) were associated with survival. Nitrite (OR 0.20; 95% CI 0.05–0.08; p = 0.026) and NO₂-CLA (OR 3.96; 95% CI 1.01–15.60; p = 0.049) were associated with favorable neurologic outcome. In summary, nitrite administration was associated with increased plasma cGMP and NO₂-CLA formation in selected OHCA patients. Furthermore, patients with the highest levels of cGMP and NO₂-CLA were more likely to survive and experience better neurological outcomes.

Nrf2 activation protects against lithium-induced nephrogenic diabetes insipidus

Lithium (Li) is the mainstay pharmacotherapeutic mood stabilizer in bipolar disorder. Its efficacious use is complicated by acute and chronic renal side effects, including nephrogenic diabetes insipidus (NDI) and progression to chronic kidney disease (CKD). The nuclear factor erythroid-derived 2-related factor 2 (Nrf2) pathway senses and coordinates cellular responses to oxidative and electrophilic stress. Here, we identify that graded genetic activation of Nrf2 protects against Li-induced NDI (Li-NDI) and volume wasting via an aquaporin 2-independent mechanism. Renal Nrf2 activity is differentially expressed on functional segments of the nephron, and its activation along the distal tubule and collecting duct directly modulates ion transporter expression, mimicking paradoxical effects of diuretics in mitigating Li-NDI. In addition, Nrf2 reduces cyclooxygenase expression and vasoactive prostaglandin biosynthesis. Pharmacologic activation of Nrf2 confers protective effects, confirming this pathway as a potentially novel druggable target for the prevention of acute and chronic renal sequelae of Li therapy.

Smooth muscle cytochrome b5 reductase 3 deficiency accelerates pulmonary hypertension development in sickle cell mice

Pulmonary and systemic vasculopathies are significant risk factors for early morbidity and death in patients with sickle cell disease (SCD). An underlying mechanism of SCD vasculopathy is vascular smooth muscle (VSM) nitric oxide (NO) resistance, which is mediated by NO scavenging reactions with plasma hemoglobin (Hb) and reactive oxygen species that can oxidize soluble guanylyl cyclase (sGC), the NO receptor. Prior studies show that cytochrome b5 reductase 3 (CYB5R3), known as methemoglobin reductase in erythrocytes, functions in VSM as an sGC heme iron reductase critical for reducing and sensitizing sGC to NO and generating cyclic guanosine monophosphate for vasodilation. Therefore, we hypothesized that VSM CYB5R3 deficiency accelerates development of pulmonary hypertension (PH) in SCD. Bone marrow transplant was used to create SCD chimeric mice with background smooth muscle cell (SMC)-specific tamoxifen-inducible Cyb5r3 knockout (SMC R3 KO) and wild-type (WT) control. Three weeks after completing tamoxifen treatment, we observed 60% knockdown of pulmonary arterial SMC CYB5R3, 5 to 6 mm Hg elevated right-ventricular (RV) maximum systolic pressure (RVmaxSP) and biventricular hypertrophy in SS chimeras with SMC R3 KO (SS/R3KD) relative to WT (SS/R3WT). RV contractility, heart rate, hematological parameters, and cell-free Hb were similar between groups. When identically generated SS/R3 chimeras were studied 12 weeks after completing tamoxifen treatment, RVmaxSP in SS/R3KD had not increased further, but RV hypertrophy relative to SS/R3WT persisted. These are the first studies to establish involvement of SMC CYB5R3 in SCD-associated development of PH, which can exist in mice by 5 weeks of SMC CYB5R3 protein deficiency.

Sickle cell disease: at the crossroads of pulmonary hypertension and diastolic heart failure

Sickle cell disease (SCD) is caused by a single point mutation in the gene that codes for beta globin synthesis, causing haemoglobin polymerisation, red blood cell stiffening and haemolysis under low oxygen and pH conditions. Downstream effects include widespread vasculopathy due to recurring vaso-occlusive events and haemolytic anaemia, affecting all organ systems. Cardiopulmonary complications are the leading cause of death in patients with SCD, primarily resulting from diastolic heart failure (HF) and/or pulmonary hypertension (PH). HF in SCD often features biventricular cardiac hypertrophy and left ventricular (LV) diastolic dysfunction. Among HF cases in the general population, approximately half occur with preserved ejection fraction (HFpEF). The insidious evolution of HFpEF differs from the relatively acute evolution of HF with reduced ejection fraction. The PH of SCD has diverse origins, which can be pulmonary arterial (precapillary), pulmonary venous (postcapillary) or pulmonary thromboembolic. It is also appreciated that patients with SCD can develop both precapillary and postcapillary PH, with elevations in LV diastolic pressures, as well as elevations in transpulmonary pressure gradient and pulmonary vascular resistance. Regardless of the cause of PH in SCD, its presence significantly reduces functional capacity and increases mortality. PH that occurs in the presence of HFpEF is usually of postcapillary origin. This review aims to assemble what has been learnt from clinical and animal studies about the manifestation of PH-HFpEF in SCD, specifically the contributions of LV diastolic dysfunction and myocardial fibrosis, in an attempt to gain an understanding of its evolution.

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.

Abstract P139: Cytochrome B5 Reductase 3 Biases Activation of Soluble Guanylyl Cyclase in Resistance Arteries

Soluble guanylyl cyclase (sGC) heme oxidation (Fe 3+ ) leading to apo-sGC formation diminishes the ability of nitric oxide (NO) to bind sGC and generate intracellular cGMP levels needed for downstream protein kinase G activation and vessel relaxation. While several studies suggest that pathological oxidative stress drives sGC heme oxidation and apo-sGC formation, we report for the first time that resistance arteries, but not conduit arteries, contain a previously unrecognized pool of heme oxidized and/or apo-sGC in non-stressed conditions that can be activated independent of NO. Specifically, our vascular reactivity studies indicate that systemic resistance and pulmonary arteries are responsive to NO-independent sGC activator BAY 58-2667 at 2-3 log-fold lower concentrations than that of conduit aorta and renal arteries (n=4-5/ vascular bed). Further, mesenteric arteries treated with 1μM MitoTempol, a superoxide dismutase mimetic and mitochondrial anti-oxidant, show a decreased responsiveness to BAY 58-2667 (n=3-5/group). Notably, we have published evidence that cytochrome b5 reductase 3 (CYB5R3) acts as an sGC heme reductase (Fe 3+ -> Fe 2+ ) in cultured vascular smooth muscle cells. We recently performed vasoreactivity studies in transgenic CYB5R3 overexpression (OE CYB5R3) mice and show these mice have a significantly decreased responsiveness to BAY 58-2667 compared to controls irrespective of vascular bed (n=4-6/ group). Additionally, OE CYB5R3 mice exhibit a ~7mmHg decrease in pulse pressure and impaired blood pressure reduction in response to an acute injection of BAY 58-2667 as compared to controls (n=5/ group). Combined, these data indicate that mitochondria derived-reactive oxygen species and expression of CYB5R3 serve as a rheostat for modulating sensitivity to sGC activator BAY 58-2667 and vascular responsiveness in resistance arteries. Importantly, these results provide valuable insight into sGC activator therapy for treatment of hypertension and other cardiovascular related diseases.

Abstract 575: Loss of Function Variant in CYB5R3 Associates With Exacerbated Cardiac Hypertrophy in Mice

African Americans (AA) are 20 times more likely to be diagnosed with heart failure (HF) before the age of 50 and 2 times more likely to die from heart failure. Previous reports have shown AA with HF have diminished nitric oxide (NO) signaling, a pathway critical for cardiac contractility. NO signals, in part, via binding reduced heme iron (Fe 2+ ) in soluble guanylyl cyclase (sGC) leading to cyclic guanosine monophosphate (cGMP) generation. Recently, our lab reported that cytochrome b5 reductase 3 (Cyb5R3) reduces oxidized sGC heme-iron from the oxidized (Fe 3+ ) to the reduced (Fe 2+ ) state, thereby sensitizing sGC to NO. However, the role of Cyb5R3 in the setting of HF remains elusive. It is known that a high frequency Cyb5R3 T117S single nucleotide polymorphism (23% minor allele frequency) exists and is enriched in individuals with African ancestry. To determine the impact of T117S in HF outcomes, we completed a retrospective study from AHEFT and GRACE trials. Our data show that Cyb5R3 T117S carriers have significantly accelerated time to death/transplant. Additionally, biobank HF samples from AA samples show an enrichment of Cyb5R3 T117S carriers from 0.23 to 0.4. To assess the impact of Cyb5R3 T117S on sGC/cGMP signaling in the heart, ventricular cGMP levels in AA with HF were examined. Pooled Cyb5R3 T117S carriers have significantly decreased cGMP relative to non-carriers. Next, we determined if this variant impacts sGC heme redox state. Using purified protein activity assays, we found that Cyb5R3 T117S results in a 60% loss-of-function and an inability to reduce oxidized sGC. Lastly, to test the in vivo impact of the Cyb5R3 T117S variant in heart failure, we generated a novel Cyb5R3 T117S mouse. Transverse aortic constriction (TAC) studies in Cyb5R3 T117S mice show significantly accelerates cardiac hypertrophy relative to wild-type TAC controls. Taken together, these data suggest Cyb5R3 T117S may be a disease modifying variant that augments hypertrophic signaling through an sGC-dependent mechanism.

Nitric Oxide-Independent Soluble Guanylate Cyclase Activation Improves Vascular Function and Cardiac Remodeling in Sickle Cell Disease

Sickle cell disease (SCD) is associated with intravascular hemolysis and oxidative inhibition of nitric oxide (NO) signaling. BAY 54-6544 is a small-molecule activator of oxidized soluble guanylate cyclase (sGC), which, unlike endogenous NO and the sGC stimulator, BAY 41-8543, preferentially binds and activates heme-free, NO-insensitive sGC to restore enzymatic cGMP production. We tested orally delivered sGC activator, BAY 54-6544 (17 mg/kg/d), sGC stimulator, BAY 41-8543, sildenafil, and placebo for 4-12 weeks in the Berkeley transgenic mouse model of SCD (BERK-SCD) and their hemizygous (Hemi) littermate controls (BERK-Hemi). Right ventricular (RV) maximum systolic pressure (RVmaxSP) was measured using micro right-heart catheterization. RV hypertrophy (RVH) was determined using Fulton's index and RV corrected weight (ratio of RV to tibia). Pulmonary artery vasoreactivity was tested for endothelium-dependent and -independent vessel relaxation. Right-heart catheterization revealed higher RVmaxSP and RVH in BERK-SCD versus BERK-Hemi, which worsened with age. Treatment with the sGC activator more effectively lowered RVmaxSP and RVH, with 90-day treatment delivering superior results, when compared with other treatments and placebo groups. In myography experiments, acetylcholine-induced (endothelium-dependent) and sodium-nitroprusside-induced (endothelium-independent NO donor) relaxation of the pulmonary artery harvested from placebo-treated BERK-SCD was impaired relative to BERK-Hemi but improved after therapy with sGC activator. By contrast, no significant effect for sGC stimulator or sildenafil was observed in BERK-SCD. These findings suggest that sGC is oxidized in the pulmonary arteries of transgenic SCD mice, leading to blunted responses to NO, and that the sGC activator, BAY 54-6544, may represent a novel therapy for SCD-associated pulmonary arterial hypertension and cardiac remodeling.