Targeting of nitric oxide synthase to endothelial cell caveolae via palmitoylation: implications for nitric oxide signaling

CAVIN-2 positively correlates with diabetic PAD and promotes LDL transcytosis by inhibiting eNOS activation

OBJECTIVE

Caveolae are closely linked to the onset and progression of atherosclerosis. The pivotal involvement of caveolin-1 (CAV1) within the caveolae in atherosclerosis development has been consistently supported. However, the potential contributions of additional caveolae proteins to atherosclerosis necessitate further exploration. Therefore, this research aimed to afford clinical evidence linking CAVIN-2 to diabetic peripheral artery disease (PAD) and its role in low-density lipoprotein (LDL) transcytosis.

METHODS

Blood samples were collected from a total of 115 participants, including 36 patients without diabetes (ND), 26 patients with type 2 diabetes mellitus (T2DM), and 53 patients with T2DM and PAD (DM-PAD). The plasma levels of CAV1, CAVIN-1, and CAVIN-2 were measured by ELISA. The correlation between CAV1, CAVIN-1, CAVIN-2, and diabetic PAD was examined using Spearman correlation analysis. The predictive effect of CAV1 and CAVIN-2 were analyzed by receiver operating characteristic (ROC) curves. Cellular experiments were used to investigate the effect and mechanism of CAVIN-2 on LDL transcytosis.

RESULTS

Elevated CAV1 and CAVIN-2 levels were observed in T2DM and DM-PAD groups, with a positive correlation to DM-PAD and PAD severity. Both CAV1 and CAVIN-2 emerged as predictors of DM-PAD. In vitro, CAVIN-2 knockdown decreased LDL transcytosis, while CAVIN-2 overexpression increased it. Additionally, CAVIN-2 was found to inhibit eNOS activation and nitric oxide (NO) production, thereby promoting LDL transcytosis and atherosclerosis progression.

CONCLUSION

CAVIN-2 was positively correlated with DM-PAD and promoted LDL transcytosis through the inhibition of eNOS activation, contributing to atherosclerosis development. This study provided clinical evidence linking CAVIN-2 to diabetic PAD and suggested its potential as a biomarker for disease progression.

The Ever-Expanding Influence of the Endothelial Nitric Oxide Synthase

Nitric oxide (NO) generated by the endothelial NO synthase (eNOS) plays an essential role in the maintenance of vascular homeostasis and the prevention of vascular inflammation. There are a myriad of mechanisms that regulate the activity of the enzyme that may prove to represent interesting therapeutic opportunities. In this regard, the kinases that phosphorylate the enzyme and regulate its activity in situations linked to vascular disease seem to be particularly promising. Although the actions of NO were initially linked mainly to the activation of the guanylyl cyclase and the generation of cyclic GMP in vascular smooth muscle cells and platelets, it is now clear that NO elicits the majority of its actions via its ability to modify redox-activated cysteine residues in a process referred to as S-nitrosylation. The more wide spread use of mass spectrometry to detect S-nitrosylated proteins has helped to identify just how large the NO sphere of influence is and just how many cellular processes are affected. It may be an old target, but the sheer impact of eNOS on vascular health really justifies a revaluation of therapeutic options to maintain and protect its activity in situations associated with a high risk of developing cardiovascular disease.

Caveolin and oxidative stress in cardiac pathology

Caveolins interact with signaling molecules within caveolae and subcellular membranes. Dysregulation of caveolin function and protein abundance contributes to cardiac pathophysiological processes, driving the development and progression of heart disease. Reactive oxygen species (ROS) play a critical role in maintaining cellular homeostasis and are key contributors to the pathophysiological mechanisms of cardiovascular disorders. Caveolins have been shown to modulate oxidative stress and regulate redox homeostasis. However, the specific roles of caveolins, particularly caveolin-1 and caveolin-3, in regulating ROS production during cardiac pathology remain unclear. This mini-review article highlights the correlation between caveolins and oxidative stress in maintaining cardiovascular health and modulating cardiac diseases, specifically in myocardial ischemia, heart failure, diabetes-induced metabolic cardiomyopathy, and septic cardiomyopathy. A deeper understanding of caveolin-mediated mechanisms may pave the way for innovative therapeutic approaches to treat cardiovascular diseases.

Sickle Trait and Alpha Thalassemia Increase NOS-Dependent Vasodilation of Human Arteries Through Disruption of Endothelial Hemoglobin-eNOS Interactions

BACKGROUND

Severe malaria is associated with impaired nitric oxide (NO) synthase (NOS)-dependent vasodilation, and reversal of this deficit improves survival in murine models. Malaria might have selected for genetic polymorphisms that increase endothelial NO signaling and now contribute to heterogeneity in vascular function among humans. One protein potentially selected for is alpha globin, which, in mouse models, interacts with endothelial NOS (eNOS) to negatively regulate NO signaling. We sought to evaluate the impact of alpha globin gene deletions on NO signaling and unexpectedly found human arteries use not only alpha but also beta globin to regulate eNOS.

METHODS

The eNOS-hemoglobin complex was characterized by multiphoton imaging, gene expression analysis, and coimmunoprecipitation studies of human resistance arteries. Novel contacts between eNOS and hemoglobin were mapped using molecular modeling and simulation. Pharmacological or genetic disruption of the eNOS-hemoglobin complex was evaluated using pressure myography. The association between alpha globin gene deletion and blood pressure was assessed in a population study.

RESULTS

Alpha and beta globin transcripts were detected in the endothelial layer of the artery wall. Imaging colocalized alpha and beta globin proteins with eNOS at myoendothelial junctions. Immunoprecipitation demonstrated that alpha globin and beta globin form a complex with eNOS and cytochrome b5 reductase. Modeling predicted negatively charged glutamic acids at positions 6 and 7 of beta globin to interact with positively charged arginines at positions 97 and 98 of eNOS. Arteries from donors with a glutamic acid-to-valine substitution at beta globin position 6 (sickle trait) exhibited increased NOS-dependent vasodilation. Alpha globin gene deletions were associated with decreased arterial alpha globin expression, increased NOS-dependent vasodilation, and lower blood pressure. Mimetic peptides that targeted the interactions between hemoglobin and eNOS recapitulated the effects of these genetic variants on human arterial vasoreactivity.

CONCLUSIONS

Alpha and beta globin subunits of hemoglobin interact with eNOS to restrict NO signaling in human resistance arteries. Malaria-protective genetic variants that alter the expression of alpha globin or the structure of beta globin are associated with increased NOS-dependent vasodilation. Targeting the hemoglobin-eNOS interface could potentially improve NO signaling in diseases of endothelial dysfunction such as severe malaria or chronic cardiovascular conditions.

Subcellular Localization Guides eNOS Function

Nitric oxide synthases (NOS) are enzymes responsible for the cellular production of nitric oxide (NO), a highly reactive signaling molecule involved in important physiological and pathological processes. Given its remarkable capacity to diffuse across membranes, NO cannot be stored inside cells and thus requires multiple controlling mechanisms to regulate its biological functions. In particular, the regulation of endothelial nitric oxide synthase (eNOS) activity has been shown to be crucial in vascular homeostasis, primarily affecting cardiovascular disease and other pathophysiological processes of importance for human health. Among other factors, the subcellular localization of eNOS plays an important role in regulating its enzymatic activity and the bioavailability of NO. The aim of this review is to summarize pioneering studies and more recent publications, unveiling some of the factors that influence the subcellular compartmentalization of eNOS and discussing their functional implications in health and disease.

Liquid plasma promotes angiogenesis through upregulation of endothelial nitric oxide synthase-induced extracellular matrix metabolism: potential applications of liquid plasma for vascular injuries

BACKGROUND

Applications of nonthermal plasma have expanded beyond the biomedical field to include antibacterial, anti-inflammatory, wound healing, and tissue regeneration. Plasma enhances epithelial cell repair; however, the potential damage to deep tissues and vascular structures remains under investigation.

RESULT

This study assessed whether liquid plasma (LP) increased nitric oxide (NO) production in human umbilical vein endothelial cells by modulating endothelial NO synthase (eNOS) phosphorylation and potential signaling pathways. First, we developed a liquid plasma product and confirmed the angiogenic effect of LP using the Matrigel plug assay. We found that the NO content increased in plasma-treated water. NO in plasma-treated water promoted cell migration and angiogenesis in scratch and tube formation assays via vascular endothelial growth factor mRNA expression. In addition to endothelial cell proliferation and migration, LP influenced extracellular matrix metabolism and matrix metalloproteinase activity. These effects were abolished by treatment with NG-L-monomethyl arginine, a specific inhibitor of NO synthase. Furthermore, we investigated the signaling pathways mediating the phosphorylation and activation of eNOS in LP-treated cells and the role of LKB1-adenosine monophosphate-activated protein kinase in signaling. Downregulation of adenosine monophosphate-activated protein kinase by siRNA partially inhibited LP-induced eNOS phosphorylation, angiogenesis, and migration.

CONCLUSION

The present study suggests that LP treatment may be a novel strategy for promoting angiogenesis in vascular damage. Video Abstract.

Unraveling the Cave: A Seventy-Year Journey into the Caveolar Network, Cellular Signaling, and Human Disease

In the mid-1950s, a groundbreaking discovery revealed the fascinating presence of caveolae, referred to as flask-shaped invaginations of the plasma membrane, sparking renewed excitement in the field of cell biology. Caveolae are small, flask-shaped invaginations in the cell membrane that play crucial roles in diverse cellular processes, including endocytosis, lipid homeostasis, and signal transduction. The structural stability and functionality of these specialized membrane microdomains are attributed to the coordinated activity of scaffolding proteins, including caveolins and cavins. While caveolae and caveolins have been long appreciated for their integral roles in cellular physiology, the accumulating scientific evidence throughout the years reaffirms their association with a broad spectrum of human disorders. This review article aims to offer a thorough account of the historical advancements in caveolae research, spanning from their initial discovery to the recognition of caveolin family proteins and their intricate contributions to cellular functions. Furthermore, it will examine the consequences of a dysfunctional caveolar network in the development of human diseases.

Endothelin-1 acutely increases nitric oxide production via the calcineurin mediated dephosphorylation of Caveolin-1

Endothelin (ET)-1 is an endothelial-derived peptide that exerts biphasic effects on nitric oxide (NO) levels in endothelial cells such that acute exposure stimulates-while sustained exposure attenuates-NO production. Although the mechanism involved in the decrease in NO generation has been identified but the signaling involved in the acute increase in NO is still unresolved. This was the focus of this study. Our data indicate that exposing pulmonary arterial endothelial cells (PAEC) to ET-1 led to an increase in NO for up to 30min after which levels declined. These effects were attenuated by ET receptor antagonists. The increase in NO correlated with significant increases in pp60Src activity and increases in eNOS phosphorylation at Tyr83 and Ser1177. The ET-1 mediated increase in phosphorylation and NO generation were attenuated by the over-expression of a pp60Src dominant negative mutant. The increase in pp60Src activity correlated with a reduction in the interaction of Caveolin-1 with pp60Src and the calcineurin-mediated dephosphorylation of caveolin-1 at three previously unidentified sites: Thr91, Thr93, and Thr95. The calcineurin inhibitor, Tacrolimus, attenuated the acute increase in pp60Src activity induced by ET-1 and a calcineurin siRNA attenuated the ET-1 mediated increase in eNOS phosphorylation at Tyr83 and Ser1177 as well as the increase in NO. By using a Caveolin-1 celluSpot peptide array, we identified a peptide targeting a sequence located between aa 41-56 as the pp60Src binding region. This peptide fused to the TAT sequence was found to decrease caveolin-pp60Src interaction, increased pp60Src activity, increased eNOS pSer1177 and NO levels in PAEC and induce vasodilation in isolated aortic rings in wildtype but not eNOS knockout mice. Together, our data identify a novel mechanism by which ET-1 acutely increases NO via a calcineurin-mediated dephosphorylation of caveolin-1 and the subsequent stimulation of pp60Src activity, leading to increases in phosphorylation of eNOS at Tyr83 and Ser1177.

Modulation of the nitric oxide/cGMP pathway in cardiac contraction and relaxation: Potential role in heart failure treatment

Evidence exists that heart failure (HF) has an overall impact of 1-2 % in the global population being often associated with comorbidities that contribute to increased disease prevalence, hospitalization, and mortality. Recent advances in pharmacological approaches have significantly improved clinical outcomes for patients with vascular injury and HF. Nevertheless, there remains an unmet need to clarify the crucial role of nitric oxide/cyclic guanosine 3',5'-monophosphate (NO/cGMP) signalling in cardiac contraction and relaxation, to better identify the key mechanisms involved in the pathophysiology of myocardial dysfunction both with reduced (HFrEF) as well as preserved ejection fraction (HFpEF). Indeed, NO signalling plays a crucial role in cardiovascular homeostasis and its dysregulation induces a significant increase in oxidative and nitrosative stress, producing anatomical and physiological cardiac alterations that can lead to heart failure. The present review aims to examine the molecular mechanisms involved in the bioavailability of NO and its modulation of downstream pathways. In particular, we focus on the main therapeutic targets and emphasize the recent evidence of preclinical and clinical studies, describing the different emerging therapeutic strategies developed to counteract NO impaired signalling and cardiovascular disease (CVD) development.

Lost in traffic: consequences of altered palmitoylation in neurodegeneration

One of the first molecular events in neurodegenerative diseases, regardless of etiology, is protein mislocalization. Protein mislocalization in neurons is often linked to proteostasis deficiencies leading to the build-up of misfolded proteins and/or organelles that contributes to cellular toxicity and cell death. By understanding how proteins mislocalize in neurons, we can develop novel therapeutics that target the earliest stages of neurodegeneration. A critical mechanism regulating protein localization and proteostasis in neurons is the protein-lipid modification S-acylation, the reversible addition of fatty acids to cysteine residues. S-acylation is more commonly referred to as S-palmitoylation or simply palmitoylation, which is the addition of the 16-carbon fatty acid palmitate to proteins. Like phosphorylation, palmitoylation is highly dynamic and tightly regulated by writers (i.e., palmitoyl acyltransferases) and erasers (i.e., depalmitoylating enzymes). The hydrophobic fatty acid anchors proteins to membranes; thus, the reversibility allows proteins to be re-directed to and from membranes based on local signaling factors. This is particularly important in the nervous system, where axons (output projections) can be meters long. Any disturbance in protein trafficking can have dire consequences. Indeed, many proteins involved in neurodegenerative diseases are palmitoylated, and many more have been identified in palmitoyl-proteomic studies. It follows that palmitoyl acyl transferase enzymes have also been implicated in numerous diseases. In addition, palmitoylation can work in concert with cellular mechanisms, like autophagy, to affect cell health and protein modifications, such as acetylation, nitrosylation, and ubiquitination, to affect protein function and turnover. Limited studies have further revealed a sexually dimorphic pattern of protein palmitoylation. Therefore, palmitoylation can have wide-reaching consequences in neurodegenerative diseases.

Targeting protein modifications in metabolic diseases: molecular mechanisms and targeted therapies

The ever-increasing prevalence of noncommunicable diseases (NCDs) represents a major public health burden worldwide. The most common form of NCD is metabolic diseases, which affect people of all ages and usually manifest their pathobiology through life-threatening cardiovascular complications. A comprehensive understanding of the pathobiology of metabolic diseases will generate novel targets for improved therapies across the common metabolic spectrum. Protein posttranslational modification (PTM) is an important term that refers to biochemical modification of specific amino acid residues in target proteins, which immensely increases the functional diversity of the proteome. The range of PTMs includes phosphorylation, acetylation, methylation, ubiquitination, SUMOylation, neddylation, glycosylation, palmitoylation, myristoylation, prenylation, cholesterylation, glutathionylation, S-nitrosylation, sulfhydration, citrullination, ADP ribosylation, and several novel PTMs. Here, we offer a comprehensive review of PTMs and their roles in common metabolic diseases and pathological consequences, including diabetes, obesity, fatty liver diseases, hyperlipidemia, and atherosclerosis. Building upon this framework, we afford a through description of proteins and pathways involved in metabolic diseases by focusing on PTM-based protein modifications, showcase the pharmaceutical intervention of PTMs in preclinical studies and clinical trials, and offer future perspectives. Fundamental research defining the mechanisms whereby PTMs of proteins regulate metabolic diseases will open new avenues for therapeutic intervention.

Nitric Oxide Acts as a Key Signaling Molecule in Plant Development under Stressful Conditions

Nitric oxide (NO), a colorless gaseous molecule, is a lipophilic free radical that easily diffuses through the plasma membrane. These characteristics make NO an ideal autocrine (i.e., within a single cell) and paracrine (i.e., between adjacent cells) signalling molecule. As a chemical messenger, NO plays a crucial role in plant growth, development, and responses to biotic and abiotic stresses. Furthermore, NO interacts with reactive oxygen species, antioxidants, melatonin, and hydrogen sulfide. It regulates gene expression, modulates phytohormones, and contributes to plant growth and defense mechanisms. In plants, NO is mainly produced via redox pathways. However, nitric oxide synthase, a key enzyme in NO production, has been poorly understood recently in both model and crop plants. In this review, we discuss the pivotal role of NO in signalling and chemical interactions as well as its involvement in the mitigation of biotic and abiotic stress conditions. In the current review, we have discussed various aspects of NO including its biosynthesis, interaction with reactive oxygen species (ROS), melatonin (MEL), hydrogen sulfide, enzymes, phytohormones, and its role in normal and stressful conditions.

The Importance of the Plasma Membrane in Atherogenesis

Atherosclerotic cardiovascular diseases are an important medical problem due to their high prevalence, impact on quality of life and prognosis. The pathogenesis of atherosclerosis is an urgent medical and social problem, the solution of which may improve the quality of diagnosis and treatment of patients. Atherosclerosis is a complex chain of events, which proceeds over many years and in which many cells in the bloodstream and the vascular wall are involved. A growing body of evidence suggests that there are complex, closely linked molecular mechanisms that occur in the plasma membranes of cells involved in atherogenesis. Lipid transport, innate immune system receptor function, and hemodynamic regulation are linked to plasma membranes and their biophysical properties. A better understanding of these interrelationships will improve diagnostic quality and treatment efficacy.

A Role of Caveolae in Trabecular Meshwork Mechanosensing and Contractile Tone

Polymorphisms in the CAV1/2 gene loci impart increased risk for primary open-angle glaucoma (POAG). CAV1 encodes caveolin-1 (Cav1), which is required for biosynthesis of plasma membrane invaginations called caveolae. Cav1 knockout mice exhibit elevated intraocular pressure (IOP) and decreased outflow facility, but the mechanistic role of Cav1 in IOP homeostasis is unknown. We hypothesized that caveolae sequester/inhibit RhoA, to regulate trabecular meshwork (TM) mechanosensing and contractile tone. Using phosphorylated myosin light chain (pMLC) as a surrogate indicator for Rho/ROCK activity and contractile tone, we found that pMLC was elevated in Cav1-deficient TM cells compared to control (131 ± 10%, n = 10, p = 0.016). Elevation of pMLC levels following Cav1 knockdown occurred in cells on a soft surface (137 ± 7%, n = 24, p < 0.0001), but not on a hard surface (122 ± 17%, n = 12, p = 0.22). In Cav1-deficient TM cells where pMLC was elevated, Rho activity was also increased (123 ± 7%, n = 6, p = 0.017), suggesting activation of the Rho/ROCK pathway. Cyclic stretch reduced pMLC/MLC levels in TM cells (69 ± 7% n = 9, p = 0.002) and in Cav1-deficient TM cells, although not significantly (77 ± 11% n = 10, p = 0.059). Treatment with the Cav1 scaffolding domain mimetic, cavtratin (1 μM) caused a reduction in pMLC (70 ± 5% n = 7, p = 0.001), as did treatment with the scaffolding domain mutant cavnoxin (1 μM) (82 ± 7% n = 7, p = 0.04). Data suggest that caveolae differentially regulate RhoA signaling, and that caveolae participate in TM mechanotransduction. Cav1 regulation of these key TM functions provide evidence for underlying mechanisms linking polymorphisms in the Cav1/2 gene loci with increased POAG risk.

Increased Fetal Cardiovascular Disease Risk: Potential Synergy Between Gestational Diabetes Mellitus and Maternal Hypercholesterolemia

Cardiovascular diseases (CVD) remain a major cause of death worldwide. Evidence suggests that the risk for CVD can increase at the fetal stages due to maternal metabolic diseases, such as gestational diabetes mellitus (GDM) and maternal supraphysiological hypercholesterolemia (MSPH). GDM is a hyperglycemic, inflammatory, and insulin-resistant state that increases plasma levels of free fatty acids and triglycerides, impairs endothelial vascular tone regulation, and due to the increased nutrient transport, exposes the fetus to the altered metabolic conditions of the mother. MSPH involves increased levels of cholesterol (mainly as low-density lipoprotein cholesterol) which also causes endothelial dysfunction and alters nutrient transport to the fetus. Despite that an association has already been established between MSPH and increased CVD risk, however, little is known about the cellular processes underlying this relationship. Our knowledge is further obscured when the simultaneous presentation of MSPH and GDM takes place. In this context, GDM and MSPH may substantially increase fetal CVD risk due to synergistic impairment of placental nutrient transport and endothelial dysfunction. More studies on the separate and/or cumulative role of both processes are warranted to suggest specific treatment options.

Diversity of Lipid Function in Atherogenesis: A Focus on Endothelial Mechanobiology

Atherosclerosis is one of the most important problems in modern medicine. Its high prevalence and social significance determine the need for a better understanding of the mechanisms of the disease's development and progression. Lipid metabolism and its disorders are one of the key links in the pathogenesis of atherosclerosis. Lipids are involved in many processes, including those related to the mechanoreception of endothelial cells. The multifaceted role of lipids in endothelial mechanobiology and mechanisms of atherogenesis are discussed in this review. Endothelium is involved in ensuring adequate vascular hemodynamics, and changes in blood flow characteristics are detected by endothelial cells and affect their structure and function.

Nitric Oxide as a Central Molecule in Hypertension: Focus on the Vasorelaxant Activity of New Nitric Oxide Donors

Cardiovascular diseases include all types of disorders related to the heart or blood vessels. High blood pressure is an important risk factor for cardiac complications and pathological disorders. An increase in circulating angiotensin-II is a potent stimulus for the expression of reactive oxygen species and pro-inflammatory cytokines that activate oxidative stress, perpetuating a deleterious effect in hypertension. Studies demonstrate the capacity of NO to prevent platelet or leukocyte activation and adhesion and inhibition of proliferation, as well as to modulate inflammatory or anti-inflammatory reactions and migration of vascular smooth muscle cells. However, in conditions of low availability of NO, such as during hypertension, these processes are impaired. Currently, there is great interest in the development of compounds capable of releasing NO in a modulated and stable way. Accordingly, compounds containing metal ions coupled to NO are being investigated and are widely recognized as having great relevance in the treatment of different diseases. Therefore, the exogenous administration of NO is an attractive and pharmacological alternative in the study and treatment of hypertension. The present review summarizes the role of nitric oxide in hypertension, focusing on the role of new NO donors, particularly the metal-based drugs and their protagonist activity in vascular function.

EH Domain-Containing 2 Deficiency Restricts Adipose Tissue Expansion and Impairs Lipolysis in Primary Inguinal Adipocytes

Lipid uptake can be facilitated via caveolae, specific plasma membrane invaginations abundantly expressed in adipocytes. The dynamin-related protein EH domain-containing 2 (EHD2) stabilizes caveolae at the cell surface. Here, we have examined the importance of EHD2 for lipid handling using primary adipocytes isolated from EHD2 knockout (Ehd2^−/−) C57BL6/N mice. Following high-fat diet (HFD) feeding, we found a clear impairment of epididymal, but not inguinal, adipose tissue expansion in Ehd2^−/− compared with Ehd2^+/+ (WT) mice. Cell size distribution analysis revealed that Ehd2^−/− mice had a lower proportion of small adipocytes, and an accumulation of medium-sized adipocytes in both epididymal and inguinal adipose tissue. Further, PPARγ activity, FABP4 and caveolin-1 expression were decreased in adipocytes isolated from Ehd2^−/− mice. Inguinal adipocytes isolated from Ehd2^−/− mice displayed reduced lipolysis in response to beta adrenergic receptor agonist, which was associated with reduced phosphorylation of perilipin-1 and hormone sensitive lipase (HSL). This impairment could not be rescued using a cAMP analog, indicating that impaired lipolysis in Ehd2^−/− primary adipocytes likely occurs at the level of, or downstream of, protein kinase A (PKA). Altogether, these findings pinpoint the importance of EHD2 for maintained intracellular lipid metabolism, and emphasize differences in mechanisms regulating lipid handling in various adipose-tissue depots.

Harnessing polyphenol power by targeting eNOS for vascular diseases

Vascular diseases arise due to vascular endothelium dysfunction in response to several pro-inflammatory stimuli and invading pathogens. Thickening of the vessel wall, formation of atherosclerotic plaques consisting of proliferating smooth muscle cells, macrophages and lymphocytes are the major consequences of impaired endothelium resulting in atherosclerosis, hypercholesterolemia, hypertension, type 2 diabetes mellitus, chronic renal failure and many others. Decreased nitric oxide (NO) bioavailability was found to be associated with anomalous endothelial function because of either its reduced production level by endothelial NO synthase (eNOS) which synthesize this potent endogenous vasodilator from L-arginine or its enhanced breakdown due to severe oxidative stress and eNOS uncoupling. Polyphenols are a group of bioactive compounds having more than 7000 chemical entities present in different cereals, fruits and vegetables. These natural compounds possess many OH groups which are largely responsible for their strong antioxidative, anti-inflammatory antithrombotic and anti-hypersensitive properties. Several flavonoid-derived polyphenols like flavones, isoflavones, flavanones, flavonols and anthocyanidins and non-flavonoid polyphenols like tannins, curcumins and resveratrol have attracted scientific interest for their beneficial effects in preventing endothelial dysfunction. This article will focus on in vitro as well as in vivo and clinical studies evidences of the polyphenols with eNOS modulating activity against vascular disease condition while their molecular mechanism will also be discussed.

Red Blood Cell and Endothelial eNOS Independently Regulate Circulating Nitric Oxide Metabolites and Blood Pressure

BACKGROUND

Current paradigms suggest that nitric oxide (NO) produced by endothelial cells (ECs) through endothelial nitric oxide synthase (eNOS) in the vessel wall is the primary regulator of blood flow and blood pressure. However, red blood cells (RBCs) also carry a catalytically active eNOS, but its role is controversial and remains undefined. This study aimed to elucidate the functional significance of RBC eNOS compared with EC eNOS for vascular hemodynamics and nitric oxide metabolism.

METHODS

We generated tissue-specific loss- and gain-of-function models for eNOS by using cell-specific Cre-induced gene inactivation or reactivation. We created 2 founder lines carrying a floxed eNOS (eNOSflox/flox) for Cre-inducible knockout (KO), and gene construct with an inactivated floxed/inverted exon (eNOSinv/inv) for a Cre-inducible knock-in (KI), which respectively allow targeted deletion or reactivation of eNOS in erythroid cells (RBC eNOS KO or RBC eNOS KI mice) or in ECs (EC eNOS KO or EC eNOS KI mice). Vascular function, hemodynamics, and nitric oxide metabolism were compared ex vivo and in vivo.

RESULTS

The EC eNOS KOs exhibited significantly impaired aortic dilatory responses to acetylcholine, loss of flow-mediated dilation, and increased systolic and diastolic blood pressure. RBC eNOS KO mice showed no alterations in acetylcholine-mediated dilation or flow-mediated dilation but were hypertensive. Treatment with the nitric oxide synthase inhibitor Nγ-nitro-l-arginine methyl ester further increased blood pressure in RBC eNOS KOs, demonstrating that eNOS in both ECs and RBCs contributes to blood pressure regulation. Although both EC eNOS KOs and RBC eNOS KOs had lower plasma nitrite and nitrate concentrations, the levels of bound NO in RBCs were lower in RBC eNOS KOs than in EC eNOS KOs. Reactivation of eNOS in ECs or RBCs rescues the hypertensive phenotype of the eNOSinv/inv mice, whereas the levels of bound NO were restored only in RBC eNOS KI mice.

CONCLUSIONS

These data reveal that eNOS in ECs and RBCs contribute independently to blood pressure homeostasis.

Implications of Oxidative and Nitrosative Post-Translational Modifications in Therapeutic Strategies against Reperfusion Damage

Post-translational modifications based on redox reactions "switch on-off" the biological activity of different downstream targets, modifying a myriad of processes and providing an efficient mechanism for signaling regulation in physiological and pathological conditions. Such modifications depend on the generation of redox components, such as reactive oxygen species and nitric oxide. Therefore, as the oxidative or nitrosative milieu prevailing in the reperfused heart is determinant for protective signaling, in this review we defined the impact of redox-based post-translational modifications resulting from either oxidative/nitrosative signaling or oxidative/nitrosative stress that occurs during reperfusion damage. The role that cardioprotective conditioning strategies have had to establish that such changes occur at different subcellular levels, particularly in mitochondria, is also presented. Another section is devoted to the possible mechanism of signal delivering of modified proteins. Finally, we discuss the possible efficacy of redox-based therapeutic strategies against reperfusion damage.

The Efficacy and Safety of Pulmonary Vasodilators in Pediatric Pulmonary Hypertension (PH): A Systematic Review and Meta-analysis

Background: We performed a meta-analysis to evaluate the efficacy and safety of pulmonary vasodilators in pediatric pulmonary hypertension (PH) patients. Methods: We searched electronic databases including PubMed, EMBASE, and the Cochrane Library up to May 2020, and conducted a subgroup analysis for pulmonary vasodilators or underlying disease. Results: Fifteen studies with 719 pediatric PH patients were included in the meta-analysis. Adverse events did not differ (p = 0.11, I ² = 15%) between the pulmonary vasodilators group and the control group, neither in the subgroups. In total, compared with the control group treatment, pulmonary vasodilators significantly decreased the mortality (p = 0.002), mean pulmonary artery pressure (mPAP, p = 0.02), and mechanical ventilation duration (p = 0.03), also improved the oxygenation index (OI, p = 0.01). In the persistent pulmonary hypertension of the newborn (PPHN) subgroup, phosphodiesterase type 5 inhibitors (PDE5i) significantly reduced mortality (p = 0.03), OI (p = 0.007) and mechanical ventilation duration (p = 0.004). Administration of endothelin receptor antagonists (ERAs) improved OI (p = 0.04) and mechanical ventilation duration (p < 0.00001) in PPHN. We also found that in the pediatric pulmonary arterial hypertension (PPAH) subgroup, mPAP was pronouncedly declined with ERAs (p = 0.006). Systolic pulmonary artery pressure (sPAP, p < 0.0001) and pulmonary arterial/aortic pressure (PA/AO, p < 0.00001) were significantly relieved with PDE5i, partial pressure of arterial oxygen (PaO₂) was improved with prostacyclin in postoperative PH (POPH) subgroup (p = 0.001). Compared with the control group, pulmonary vasodilators could significantly decrease PA/AO pressure (p < 0.00001) and OI (p < 0.00001) in the short-term (duration <7 days) follow-up subgroup, improve mPAP (p = 0.03) and PaO₂ (p = 0.01) in the mid-term (7-30 days) follow-up subgroup, also decrease mortality, mPAP (p = 0.0001), PA/AO pressure (p = 0.0007), duration of mechanical ventilation (p = 0.004), and ICU stay (p < 0.00001) in the long-term follow subgroup (>30 days). Conclusion: Pulmonary vasodilators decrease the mortality in pediatric PH patients, improve the respiratory and hemodynamic parameters, reduce the mechanical ventilation duration.

Physiologic Consequences of Caveolin-1 Ablation in Conventional Outflow Endothelia

Purpose

Polymorphisms at the caveolin-1/2 locus are associated with glaucoma and IOP risk and deletion of caveolin-1 (Cav1) in mice elevates IOP and reduces outflow facility. However, the specific location/cell type responsible for Cav1-dependent regulation of IOP is unclear. We hypothesized that endothelial Cav1 in the conventional outflow (CO) pathway regulate IOP via endothelial nitric oxide synthase (eNOS) signaling.

Methods

We created a mouse with targeted deletion of Cav1 in endothelial cells (Cav1ΔEC) and evaluated IOP, outflow facility, outflow pathway distal vascular morphology, eNOS phosphorylation, and tyrosine nitration of iridocorneal angle tissues by Western blotting.

Results

Endothelial deletion of Cav1 resulted in significantly elevated IOP versus wild-type mice but not a concomitant decrease in outflow facility. Endothelial Cav1 deficiency did not alter the trabecular meshwork or Schlemm's canal morphology, suggesting that the effects observed were not due to developmental deformities. Endothelial Cav1 deletion resulted in eNOS hyperactivity, modestly increased protein nitration, and significant enlargement of the drainage vessels distal to Schlemm's canal. L-Nitro-arginine methyl ester treatment reduced outflow in Cav1ΔEC but not wild-type mice and had no effect on the size of drainage vessels. Endothelin-1 treatment decrease the outflow and drainage vessel size in both wild-type and Cav1ΔEC mice.

Conclusions

Our results suggest that hyperactive eNOS signaling in the CO pathway of both Cav1ΔEC and global Cav1 knockout mice results in chronic dilation of distal CO vessels and protein nitration, but that Cav1 expression in the trabecular meshwork is sufficient to rescue CO defects reported in global Cav1 knockout mice.

Dual Role of Caveolin-1 in β-Catenin Signaling During Fracture Healing Induced by Low-Intensity Pulsed Ultrasound in Rabbits

We did this research to observe the effect of LIPUS on long bone fracture repair and caveolin-1, β-catenin signaling expression in the radius defects of rabbits, to explore its possible molecular mechanisms. 24 male New Zealand rabbits with bilateral radial bone defects were divided into 4 groups randomly, n = 6. The right side had daily LIPUS exposure for 20 minutes, while the left received sham treatment. After 7, 14, 21, 28 days, respectively, fracture healing was observed by X-ray imaging and Dual Energy X-ray Absorptiometry (DXA) scan, specimens were harvested for histology, immunohistochemistry, and gene expression analysis. We found that LIPUS brought forward endochondral ossification, increased the bone callus size without changes in Bone Mineral Density (BMD). The caveolin-1 expression increased first then decreased, while the β-catenin kept growing during the process. These demonstrated that caveolin-1 participated in fracture healing accelerated by LIPUS, which was speculated to play a dual role in β-catenin signaling expression.

Endothelial caveolin and its scaffolding domain in cancer

Since the initial reports implicating caveolin-1 (CAV1) in neoplasia, the scientific community has made tremendous strides towards understanding how CAV1-dependent signaling and caveolae assembly modulate solid tumor growth. Once a solid neoplastic tumor reaches a certain size, it will increasingly rely on its stroma to meet the metabolic demands of the rapidly proliferating cancer cells, a limitation typically but not exclusively addressed via the formation of new blood vessels. Landmark studies using xenograft tumor models have highlighted the importance of stromal CAV1 during neoplastic blood vessel growth from preexisting vasculature, a process called angiogenesis, and helped identify endothelium-specific signaling events regulated by CAV1, such as vascular endothelial growth factor (VEGF) receptors as well as the endothelial nitric oxide (NO) synthase (eNOS) systems. This chapter provides a glimpse into the signaling events modulated by CAV1 and its scaffolding domain (CSD) during endothelial-specific aspects of neoplastic growth, such as vascular permeability, angiogenesis, and mechanotransduction.

Intracellular Sources of ROS/H2O2 in Health and Neurodegeneration: Spotlight on Endoplasmic Reticulum

Reactive oxygen species (ROS) are produced continuously throughout the cell as products of various redox reactions. Yet these products function as important signal messengers, acting through oxidation of specific target factors. Whilst excess ROS production has the potential to induce oxidative stress, physiological roles of ROS are supported by a spatiotemporal equilibrium between ROS producers and scavengers such as antioxidative enzymes. In the endoplasmic reticulum (ER), hydrogen peroxide (H2O2), a non-radical ROS, is produced through the process of oxidative folding. Utilisation and dysregulation of H2O2, in particular that generated in the ER, affects not only cellular homeostasis but also the longevity of organisms. ROS dysregulation has been implicated in various pathologies including dementia and other neurodegenerative diseases, sanctioning a field of research that strives to better understand cell-intrinsic ROS production. Here we review the organelle-specific ROS-generating and consuming pathways, providing evidence that the ER is a major contributing source of potentially pathologic ROS.

The vital role for nitric oxide in intraocular pressure homeostasis

Catalyzed by endothelial nitric oxide (NO) synthase (eNOS) activity, NO is a gaseous signaling molecule maintaining endothelial and cardiovascular homeostasis. Principally, NO regulates the contractility of vascular smooth muscle cells and permeability of endothelial cells in response to either biochemical or biomechanical cues. In the conventional outflow pathway of the eye, the smooth muscle-like trabecular meshwork (TM) cells and Schlemm's canal (SC) endothelium control aqueous humor outflow resistance, and therefore intraocular pressure (IOP). The mechanisms by which outflow resistance is regulated are complicated, but NO appears to be a key player as enhancement or inhibition of NO signaling dramatically affects outflow function; and polymorphisms in NOS3, the gene that encodes eNOS modifies the relation between various environmental exposures and glaucoma. Based upon a comprehensive review of past foundational studies, we present a model whereby NO controls a feedback signaling loop in the conventional outflow pathway that is sensitive to changes in IOP and its oscillations. Thus, upon IOP elevation, the outflow pathway tissues distend, and the SC lumen narrows resulting in increased SC endothelial shear stress and stretch. In response, SC cells upregulate the production of NO, relaxing neighboring TM cells and increasing permeability of SC's inner wall. These IOP-dependent changes in the outflow pathway tissues reduce the resistance to aqueous humor drainage and lower IOP, which, in turn, diminishes the biomechanical signaling on SC. Similar to cardiovascular pathogenesis, dysregulation of the eNOS/NO system leads to dysfunctional outflow regulation and ocular hypertension, eventually resulting in primary open-angle glaucoma.

The Role of Structure and Biophysical Properties in the Pleiotropic Effects of Statins

Statins are a class of drugs used to lower low-density lipoprotein cholesterol and are amongst the most prescribed medications worldwide. Most statins work as a competitive inhibitor of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGR), but statin intolerance from pleiotropic effects have been proposed to arise from non-specific binding due to poor enzyme-ligand sensitivity. Yet, research into the physicochemical properties of statins, and their interactions with off-target sites, has not progressed much over the past few decades. Here, we present a concise perspective on the role of statins in lowering serum cholesterol levels, and how their reported interactions with phospholipid membranes offer a crucial insight into the mechanism of some of the more commonly observed pleiotropic effects of statin administration. Lipophilicity, which governs hepatoselectivity, is directly related to the molecular structure of statins, which dictates interaction with and transport through membranes. The structure of statins is therefore a clinically important consideration in the treatment of hypercholesterolaemia. This review integrates the recent biophysical studies of statins with the literature on the physiological effects and provides new insights into the mechanistic cause of statin pleiotropy, and prospective means of understanding the cholesterol-independent effects of statins.

The NOS/NO system in an example of extreme adaptation: The African lungfish

African dipnoi (lungfish) are aestivating fish and obligate air breathers that, throughout their complex life cycle, undergo remarkable morpho-functional organ readjustment from biochemical to morphological level. In the present review we summarize the changes of the NOS/NO (Nitric Oxide Synthase/Nitric Oxide) system occurring in lungs, gills, kidney, heart, and myotomal muscle of African lungfish of the genus Protopterus (P. dolloi and P. annectens), in relation to the switch from freshwater to aestivation, and vice-versa. In particular, the expression and localization patterns of NOS, and its protein partners Akt, Hsp-90 and HIF-1α, have been discussed, together with the apoptosis rate, evaluated by TUNEL technique. We hypothesize that all these molecular components are crucial in signalling transduction/integration networks induced by environmental challenges (temperature, dehydration, inactivity)experienced at the beginning, during, and at the end of the dry season.

It takes more than two to tango: mechanosignaling of the endothelial surface

The endothelial surface is a highly flexible signaling hub which is able to sense the hemodynamic forces of the streaming blood. The subsequent mechanosignaling is basically mediated by specific structures, like the endothelial glycocalyx building the top surface layer of endothelial cells as well as mechanosensitive ion channels within the endothelial plasma membrane. The mechanical properties of the endothelial cell surface are characterized by the dynamics of cytoskeletal proteins and play a key role in the process of signal transmission from the outside (lumen of the blood vessel) to the interior of the cell. Thus, the cell mechanics directly interact with the function of mechanosensitive structures and ion channels. To precisely maintain the vascular tone, a coordinated functional interdependency between endothelial cells and vascular smooth muscle cells is necessary. This is given by the fact that mechanosensitive ion channels are expressed in both cell types and that signals are transmitted via autocrine/paracrine mechanisms from layer to layer. Thus, the outer layer of the endothelial cells can be seen as important functional mechanosensitive and reactive cellular compartment. This review aims to describe the known mechanosensitive structures of the vessel building a bridge between the important role of physiological mechanosignaling and the proper vascular function. Since mutations and dysfunction of mechanosensitive proteins are linked to vascular pathologies such as hypertension, they play a potent role in the field of channelopathies and mechanomedicine.

Endothelial lipase increases eNOS activating capacity of high-density lipoprotein

Endothelial lipase (EL) changes structural and functional properties of high-density lipoprotein (HDL). HDL is a relevant modulator of endothelial nitric oxide synthase (eNOS) activity, but the effect of EL on HDL induced eNOS-activation has not yet been investigated. Here, we examined the impact of EL-modified HDL (EL-HDL) on eNOS activity, subcellular trafficking, and eNOS- dependent vasorelaxation. EL-HDL and empty virus (EV)-HDL as control were isolated from human serum incubated with EL-overexpressing or EV infected HepG2 cells. EL-HDL exhibited higher capacity to induce eNOS phosphorylation at Ser1177 and eNOS activity in EA.hy 926 cells, as well as eNOS-dependent vasorelaxation of mouse aortic rings compared to control HDL. As revealed by confocal and structured illumination-microscopy EL-HDL-driven induction of eNOS was accompanied by an increased eNOS-GFP targeting to the plasma membrane and a lower eNOS-GFP colocalization with Golgi and mitochondria. Widefield microscopy of filipin stained cells revealed that EL-HDL lowered cellular free cholesterol (FC) and as found by thin-layer chromatography increased cellular cholesterol ester (CE) content. Additionally, cholesterol efflux capacity, acyl-coenzyme A: cholesterol acyltransferase activity, and HDL particle uptake were comparable between EL-HDL and control HDL. In conclusion, EL increases eNOS activating capacity of HDL, a phenomenon accompanied by an enrichment of the plasma membrane eNOS pool, a decreased cell membrane FC and increased cellular CE content.

Pathophysiological Role of Caveolae in Hypertension

Caveolae, flask-shaped cholesterol-, and glycosphingolipid-rich membrane microdomains, contain caveolin 1, 2, 3 and several structural proteins, in particular Cavin 1-4, EHD2, pacsin2, and dynamin 2. Caveolae participate in several physiological processes like lipid uptake, mechanosensitivity, or signaling events and are involved in pathophysiological changes in the cardiovascular system. They serve as a specific membrane platform for a diverse set of signaling molecules like endothelial nitric oxide synthase (eNOS), and further maintain vascular homeostasis. Lack of caveolins causes the complete loss of caveolae; induces vascular disorders, endothelial dysfunction, and impaired myogenic tone; and alters numerous cellular processes, which all contribute to an increased risk for hypertension. This brief review describes our current knowledge on caveolae in vasculature, with special focus on their pathophysiological role in hypertension.

Extracellular l-arginine Enhances Relaxations Induced by Opening of Calcium-Activated SKCa Channels in Porcine Retinal Arteriole

We investigated whether the substrate for nitric oxide (NO) production, extracellular l-arginine, contributes to relaxations induced by activating small (SKCa) conductance Ca²⁺-activated potassium channels. In endothelial cells, acetylcholine increased ³H-l-arginine uptake, while blocking the SKCa and the intermediate (IKCa) conductance Ca²⁺-activated potassium channels reduced l-arginine uptake. A blocker of the y+ transporter system, l-lysine also blocked ³H-l-arginine uptake. Immunostaining showed co-localization of endothelial NO synthase (eNOS), SKCa3, and the cationic amino acid transporter (CAT-1) protein of the y+ transporter system in the endothelium. An opener of SKCa channels, cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA) induced large currents in endothelial cells, and concentration-dependently relaxed porcine retinal arterioles. In the presence of l-arginine, concentration-response curves for CyPPA were leftward shifted, an effect unaltered in the presence of low sodium, but blocked by l-lysine in the retinal arterioles. Our findings suggest that SKCa channel activity regulates l-arginine uptake through the y+ transporter system, and we propose that in vasculature affected by endothelial dysfunction, l-arginine administration requires the targeting of additional mechanisms such as SKCa channels to restore endothelium-dependent vasodilatation.

TRPC-mediated Ca2+ signaling and control of cellular functions

Canonical members of the TRP superfamily of ion channels have long been recognized as key elements of Ca²⁺ handling in a plethora of cell types. The emerging role of TRPC channels in human physiopathology has generated considerable interest in their pharmacological targeting, which requires detailed understanding of their molecular function. Although consent has been reached that receptor-phospholipase C (PLC) pathways and generation of lipid mediators constitute the prominent upstream signaling process that governs channel activity, multimodal sensing features of TRPC complexes have been demonstrated repeatedly. Downstream signaling by TRPC channels is similarly complex and involves the generation of local and global cellular Ca²⁺ rises, which are well-defined in space and time to govern specific cellular functions. These TRPC-mediated Ca²⁺ signals rely in part on Ca²⁺ permeation through the channels, but are essentially complemented by secondary mechanisms such as Ca²⁺ mobilization from storage sites and Na⁺/Ca²⁺ exchange, which involve coordinated interaction with signaling partners. Consequently, the control of cell functions by TRPC molecules is critically determined by dynamic assembly and subcellular targeting of the TRPC complexes. The very recent availability of high-resolution structure information on TRPC channel complexes has paved the way towards a comprehensive understanding of signal transduction by TRPC channels. Here, we summarize current concepts of cation permeation in TRPC complexes, TRPC-mediated shaping of cellular Ca²⁺ signals and the associated control of specific cell functions.

Role of the Endocytosis of Caveolae in Intracellular Signaling and Metabolism

Caveolae are 60-80 nm invaginated plasma membrane (PM) nanodomains, with a specific lipid and protein composition, which assist and regulate multiple processes in the plasma membrane-ranging from the organization of signalling complexes to the mechanical adaptation to changes in PM tension. However, since their initial descriptions, these structures have additionally been found tightly linked to internalization processes, mechanoadaptation, to the regulation of signalling events and of endosomal trafficking. Here, we review caveolae biology from this perspective, and its implications for cell physiology and disease.

Dietary Fatty Acid Saturation Modulates Sphingosine-1-Phosphate-Mediated Vascular Function

Sphingolipids, modified by dietary fatty acids, are integral components of plasma membrane and caveolae that are also vasoactive compounds. We hypothesized that dietary fatty acid saturation affects vasoconstriction to sphingosine-1-phosphate (S1P) through caveolar regulation of rho kinase. Wild type (WT) and caveolin-1-deficient (cav-1 KO) mice which lack vascular caveolae were fed a low-fat diet (LF), 60% high-saturated fat diet (lard, HF), or 60% fat diet with equal amounts of lard and n-3 polyunsaturated menhaden oil (MO). Weight gain of WT on HF and MO diets was similar while markedly blunted in cav-1 KO. Neither high-fat diet affected the expression of cav-1, rho, or rho kinase in arteries from WT. In cav-1 KO, MO increased the vascular expression of rho but had no effect on rho kinase. HF had no effect on rho or rho kinase expression in cav-1 KO. S1P produced a concentration-dependent constriction of gracilis arteries from WT on LF that was reduced with HF and restored to normal with MO. Constriction to S1P was reduced in cav-1 KO and no longer affected by a high-saturated fat diet. Inhibition of rho kinase which reduced constriction to PE independent of diet in arteries from WT and cav-1 KO only reduced constriction to S1P in arteries from WT fed MO. The data suggest that dietary fatty acids modify vascular responses to S1P by a caveolar-dependent mechanism which is enhanced by dietary n-3 polyunsaturated fats.

Endothelial NOS: perspective and recent developments

Endothelial NOS (eNOS), and its product NO, are vital components of the control of vasomotor function and cardiovascular homeostasis. In the present review, we will take a deep dive into eNOS enzymology, function and mechanisms regulating endothelial NO. The mechanisms regulating eNOS and NO synthesis discussed here include alterations to transcriptional, post-translational modifications and protein-protein regulations. Also, we will discuss the phenotypes associated with various eNOS mutants and the consequences of a disrupted eNOS/NO cascade, highlighting the importance of eNOS function and vascular homeostasis. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.

The Molecular Regulation and Functional Roles of NOX5

NOX (NADPH oxidases) are a family of NADPH-dependent transmembrane enzymes that synthesize superoxide and other reactive oxygen species. There are seven isoforms (NOX1-5 and DUOX1-2) which derive from a common ancestral NOX. NOX enzymes are distinguished by different modes of activation, the types of ROS that are produced, the cell types where they are expressed, and distinct functional roles. NOX5 was one of the earliest eukaryotic Nox enzymes to evolve and ironically the last isoform to be discovered in humans. In the time since its discovery, our knowledge of the regulation of NOX5 has expanded tremendously, and we now have a more comprehensive understanding of the molecular mechanisms underlying NOX5-dependent ROS production. In contrast, the cell types where NOX5 is robustly expressed and its functional significance in health and disease remain an underdeveloped area. The goal of this chapter is to provide an up-to-date overview of the mechanisms regulating NOX5 function and its importance in human physiology and pathophysiology.

Sources of Vascular Nitric Oxide and Reactive Oxygen Species and Their Regulation

Nitric oxide (NO) is a small free radical with critical signaling roles in physiology and pathophysiology. The generation of sufficient NO levels to regulate the resistance of the blood vessels and hence the maintenance of adequate blood flow is critical to the healthy performance of the vasculature. A novel paradigm indicates that classical NO synthesis by dedicated NO synthases is supplemented by nitrite reduction pathways under hypoxia. At the same time, reactive oxygen species (ROS), which include superoxide and hydrogen peroxide, are produced in the vascular system for signaling purposes, as effectors of the immune response, or as byproducts of cellular metabolism. NO and ROS can be generated by distinct enzymes or by the same enzyme through alternate reduction and oxidation processes. The latter oxidoreductase systems include NO synthases, molybdopterin enzymes, and hemoglobins, which can form superoxide by reduction of molecular oxygen or NO by reduction of inorganic nitrite. Enzymatic uncoupling, changes in oxygen tension, and the concentration of coenzymes and reductants can modulate the NO/ROS production from these oxidoreductases and determine the redox balance in health and disease. The dysregulation of the mechanisms involved in the generation of NO and ROS is an important cause of cardiovascular disease and target for therapy. In this review we will present the biology of NO and ROS in the cardiovascular system, with special emphasis on their routes of formation and regulation, as well as the therapeutic challenges and opportunities for the management of NO and ROS in cardiovascular disease.

Failure to reabsorb the primary cilium induces cellular senescence

Aurora kinase A (AURKA) is necessary for proper primary cilium disassembly before mitosis. We found that depletion of caveolin-1 expression promotes primary cilia formation through the proteasomal-dependent degradation of aurora kinase A and induces premature senescence in human fibroblasts. Down-regulation of intraflagellar transport-88, a protein essential for ciliogenesis, inhibits premature senescence induced by the depletion of caveolin-1. In support of these findings, we showed that alisertib, a pharmacological inhibitor of AURKA, causes primary cilia formation and cellular senescence by irreversibly arresting cell growth. Suppression of primary cilia formation limits cellular senescence induced by alisertib. The primary cilium must be disassembled to free its centriole to form the centrosome, a necessary structure for mitotic spindle assembly and cell division. We showed that the use of the centriole to form primary cilia blocks centrosome formation and mitotic spindle assembly and prevents the completion of mitosis in cells in which cellular senescence is caused by the inhibition of AURKA. We also found that AURKA is down-regulated and primary cilia formation is enhanced when cellular senescence is promoted by other senescence-inducing stimuli, such as oxidative stress and UV light. Thus, we propose that impaired AURKA function induces premature senescence by preventing reabsorption of the primary cilium, which inhibits centrosome and mitotic spindle formation and consequently prevents the completion of mitosis. Our study causally links the inability of the cell to disassemble the primary cilium, a microtubule-based cellular organelle, to the development of premature senescence, a functionally and pathologically relevant cellular state.-Jeffries, E. P., Di Filippo, M., Galbiati, F. Failure to reabsorb the primary cilium induces cellular senescence.

Pro-atherosclerotic disturbed flow disrupts caveolin-1 expression, localization, and function via glycocalyx degradation

BACKGROUND

Endothelial-dependent atherosclerosis develops in a non-random pattern in regions of vessel bending and bifurcations, where blood flow exhibits disturbed flow (DF) patterns. In contrast, uniform flow (UF), normal endothelium, and healthy vessel walls co-exist within straight vessels. In clarifying how flow protectively or atherogenically regulates endothelial cell behavior, involvement of the endothelial surface glycocalyx has been suggested due to reduced expression in regions of atherosclerosis development. Here, we hypothesized that pro-atherosclerotic endothelial dysfunction occurs as a result of DF-induced reduction in glycocalyx expression and subsequently impairs endothelial sensitivity to flow. Specifically, we propose that glycocalyx degradation can induce pro-atherosclerotic endothelial dysfunction through decreased caveolin-1 and endothelial nitric oxide synthase expression and localization.

METHODS

We studied endothelial cells in atherosclerotic-prone DF and atherosclerotic-resistant UF conditions in parallel plate flow culture and in C57Bl/6 mice. The effects of flow conditioning on endothelial cell behavior were quantified using immunocytochemistry. The glycocalyx was fluorescently labeled for wheat germ agglutinin, which serves as a general glycocalyx label, and heparan sulfate, a major glycocalyx component. Additionally, mechanosensitivity was assessed by immunocytochemical fluorescence expression and function of caveolin-1, the protein that forms the mechanosignaling caveolar invaginations on the endothelial surface, total endothelial-type nitric oxide synthase (eNOS), which synthesizes nitric oxide, and serine 1177 phosphorylated eNOS (eNOS-pS1177), which is the active form of eNOS. Caveolin function and eNOS expression and activation were correlated to glycocalyx expression. Heparinase III enzyme was used to degrade a major glycocalyx component, HS, to identify the role of the glycocalyx in caveoin-1 and eNOS-pS1177 regulation.

RESULTS

Results confirmed that DF reduces caveolin-1 expression and abolishes most of its subcellular localization preferences, when compared to the effect of UF. DF down-regulates caveolin-1 mechanosignaling, as indicated by its reduced colocalization with serine 1177 phosphorylated endothelial-type nitric oxide synthase (eNOS-pS1177), a vasoregulatory signaling molecule whose activity is regulated by its residence in caveolae. As expected, DF inhibited glycocalyx expression compared to UF. In the absence of heparan sulfate, a major glycocalyx component, UF-conditioned endothelial cells exhibited near DF-like caveolin-1 expression, localization, and colocalization with eNOS-pS1177.

CONCLUSIONS

This is the first demonstration of a flow-defined role of the glycocalyx in caveolae expression and function related to vasculoprotective endothelial mechanosensitivity that defends against atherosclerosis. The results suggest that a glycocalyx-based therapeutic targeted to areas of atherosclerosis development could prevent disease initiation and progression.

Posttranslational Modifications of RAS Proteins

The three human RAS genes encode four proteins that play central roles in oncogenesis by acting as binary molecular switches that regulate signaling pathways for growth and differentiation. Each is subject to a set of posttranslational modifications (PTMs) that modify their activity or are required for membrane targeting. The enzymes that catalyze the various PTMs are potential targets for anti-RAS drug discovery. The PTMs of RAS proteins are the focus of this review.

Cells respond to deletion of CAV1 by increasing synthesis of extracellular matrix

A range of cellular functions have been attributed to caveolae, flask-like invaginations of the plasma membrane. Here, we have used RNA-seq to achieve quantitative transcriptional profiling of primary embryonic fibroblasts from caveolin 1 knockout mice (CAV1-/- MEFs), and thereby to gain hypothesis-free insight into how these cells respond to the absence of caveolae. Components of the extracellular matrix were decisively over-represented within the set of genes displaying altered expression in CAV1-/- MEFs when compared to congenic wild-type controls. This was confirmed biochemically and by imaging for selected examples. Up-regulation of components of the extracellular matrix was also observed in a second cell line, NIH-3T3 cells genome edited to delete CAV1. Up-regulation of components of the extracellular matrix was detected in vivo by assessing collagen deposition and compliance of CAV1-/- lungs. We discuss the implications of these findings in terms of the cellular function of caveolae.

Effect of spatial heterogeneity and colocalization of eNOS and capacitative calcium entry channels on shear stress-induced NO production by endothelial cells: A modeling approach

Introduction

Colocalization of endothelial nitric oxide synthase (eNOS) and capacitative Ca²⁺ entry (CCE) channels in microdomains such as cavaeolae in endothelial cells (ECs) has been shown to significantly affect intracellular Ca²⁺ dynamics and NO production, but the effect has not been well quantified.

Methods

We developed a two-dimensional continuum model of an EC integrating shear stress-mediated ATP production, intracellular Ca²⁺ mobilization, and eNOS activation to investigate the effects of spatial colocalization of plasma membrane eNOS and CCE channels on Ca²⁺ dynamics and NO production in response to flow-induced shear stress. Our model examines the hypothesis that subcellular colocalization of cellular components can be critical for optimal coupling of NO production to blood flow.

Results

Our simulations predict that heterogeneity of CCE can result in formation of microdomains with significantly higher Ca²⁺ compared to the average cytosolic Ca²⁺. Ca²⁺ buffers with lower or no mobility further enhanced Ca²⁺ gradients relative to mobile buffers. Colocalization of eNOS to CCE channels significantly increased NO production.

Conclusions

Our results provide quantitative understanding for the role of spatial heterogeneity and the compartmentalization of signals in regulation of shear stress-induced NO production.

Potential pitfalls in analyzing structural uncoupling of eNOS: aging is not associated with increased enzyme monomerization

Homodimer formation is essential for the normal activity of endothelial nitric oxide synthase (eNOS). Structural uncoupling of eNOS, with generation of enzyme monomers, is thought to contribute to endothelial dysfunction in several vascular disorders, including aging. However, low-temperature SDS-PAGE of healthy arteries has revealed considerable variation between studies in the relative expression of eNOS dimers and monomers. While assessing structural uncoupling of eNOS in aging arteries, we identified methodological pitfalls that might contribute to such variation. Therefore, using human cultured aortic endothelial cells and aortas from young and aged Fischer-344 rats, we investigated optimal approaches for analyzing the expression of eNOS monomers and dimers. The results demonstrated that published differences in treatment of cell lysates can significantly impact the relative expression of several eNOS species, including denatured monomers, partially folded monomers, dimers, and higher-order oligomers. In aortas, experiments initially confirmed a large increase in eNOS monomers in aging arteries, consistent with structural uncoupling. However, these monomers were actually endogenous IgG, which, under these conditions, has mobility similar to eNOS monomers. Increased IgG levels in aged aortas likely reflect the aging-induced disruption of endothelial junctions and increased arterial penetration of IgG. After removal of the IgG signal, there were low levels of eNOS monomers in young arteries, which were not significantly different in aged arteries. Therefore, structural uncoupling of eNOS is not a prominent feature in young healthy arteries, and the process is not increased by aging. The study also identifies optimal approaches to analyze eNOS dimers and monomers. NEW & NOTEWORTHY Structural uncoupling of endothelial nitric oxide synthase (eNOS) is considered central to endothelial dysfunction. However, reported levels of eNOS dimers and monomers vary widely, even in healthy arteries. We demonstrate that sample processing can alter relative levels of eNOS species. Moreover, endothelial dysfunction in aging aortas results in IgG accumulation, which, because of similar mobility to eNOS monomers, could be misinterpreted as structural uncoupling. Indeed, enzyme monomerization is not prominent in young or aging arteries.