Nox2 as a potential target of mitochondrial superoxide and its role in endothelial oxidative stress

Empowering mitochondrial metabolism: Exploring L-lactate supplementation as a promising therapeutic approach for metabolic syndrome

Mitochondrial dysfunction plays a critical role in the pathogenesis of metabolic syndrome (MetS), affecting various cell types and organs. In MetS animal models, mitochondria exhibit decreased quality control, characterized by abnormal morphological structure, impaired metabolic activity, reduced energy production, disrupted signaling cascades, and oxidative stress. The aberrant changes in mitochondrial function exacerbate the progression of metabolic syndrome, setting in motion a pernicious cycle. From this perspective, reversing mitochondrial dysfunction is likely to become a novel and powerful approach for treating MetS. Unfortunately, there are currently no effective drugs available in clinical practice to improve mitochondrial function. Recently, L-lactate has garnered significant attention as a valuable metabolite due to its ability to regulate mitochondrial metabolic processes and function. It is highly likely that treating MetS and its related complications can be achieved by correcting mitochondrial homeostasis disorders. In this review, we comprehensively discuss the complex relationship between mitochondrial function and MetS and the involvement of L-lactate in regulating mitochondrial metabolism and associated signaling pathways. Furthermore, it highlights recent findings on the involvement of L-lactate in common pathologies of MetS and explores its potential clinical application and further prospects, thus providing new insights into treatment possibilities for MetS.

Role of Mitochondria in the Regulation of Effector Functions of Granulocytes

Granulocytes (neutrophils, eosinophils, and basophils) are the most abundant circulating cells in the innate immune system. Circulating granulocytes, primarily neutrophils, can cross the endothelial barrier and activate various effector mechanisms to combat invasive pathogens. Eosinophils and basophils also play an important role in allergic reactions and antiparasitic defense. Granulocytes also regulate the immune response, wound healing, and tissue repair by releasing of various cytokines and lipid mediators. The effector mechanisms of granulocytes include the production of reactive oxygen species (ROS), degranulation, phagocytosis, and the formation of DNA-containing extracellular traps. Although all granulocytes are primarily glycolytic and have only a small number of mitochondria, a growing body of evidence suggests that mitochondria are involved in all effector functions as well as in the production of cytokines and lipid mediators and in apoptosis. It has been shown that the production of mitochondrial ROS controls signaling pathways that mediate the activation of granulocytes by various stimuli. In this review, we will briefly discuss the data on the role of mitochondria in the regulation of effector and other functions of granulocytes.

Effects of ROS pathway inhibitors and NADH and FADH2 linked substrates on mitochondrial bioenergetics and ROS emission in the heart and kidney cortex and outer medulla

Mitochondria are major sources of reactive oxygen species (ROS), which play important roles in both physiological and pathological processes. However, the specific contributions of different ROS production and scavenging components in the mitochondria of metabolically active tissues such as heart and kidney cortex and outer medulla (OM) are not well understood. Therefore, the goal of this study was to determine contributions of different ROS production and scavenging components and provide detailed comparisons of mitochondrial respiration, bioenergetics, ROS emission between the heart and kidney cortex and OM using tissues obtained from the same Sprague-Dawley rat under identical conditions and perturbations. Specifically, data were obtained using both NADH-linked substrate pyruvate + malate and FADH2-linked substrate succinate followed by additions of inhibitors of different components of the electron transport chain (ETC) and oxidative phosphorylation (OxPhos) and other ROS production and scavenging systems. Currently, there is limited data available for the mitochondria of kidney cortex and OM, the two major energy-consuming tissues in the body only next to the heart, and scarce quantitative information on the interplay between mitochondrial ROS production and scavenging systems in the three tissues. The findings from this study demonstrate significant differences in mitochondrial respiratory and bioenergetic functions and ROS emission among the three tissues. The results quantify the rates of ROS production from different complexes of the ETC, identify the complexes responsible for variations in mitochondrial membrane depolarization and regulations of ROS production, and quantify the contributions of ROS scavenging enzymes towards overall mitochondrial ROS emission. These findings advance our fundamental knowledge of tissue-specific and substrate-dependent mitochondrial respiratory and bioenergetic functions and ROS emission. This is important given the critical role that excess ROS production, oxidative stress, and mitochondrial dysfunction in the heart and kidney cortex and OM play in the pathogenesis of cardiovascular and renal diseases, including salt-sensitive hypertension.

Ultrasound-assisted biomimetic nanobubbles for targeted treatment of atherosclerosis

Cardiovascular disease caused by atherosclerosis remains the main reason of death in the worldwide scale. Although oxidative stress plays a key role in the initiation and progression of atherosclerosis, current antioxidant drugs have limited efficacy. To resolve this problem, we constructed Nox2 siRNA-loaded nanobubbles (PNBs-siNox2) coated with platelet membranes to utilize their antioxidant stress activity and targeting effect for atherosclerosis treatment. After platelet membranes modification, the capacity of PNB to target collagen, foam cells, or human umbilical vein endothelial cells (HUVECs) was significantly increased. Moreover, our study demonstrated that under ultrasonic irradiation, biomimetic nanobubbles were more effective at targeting atherosclerotic plaques and delivering genes into cells. In the present study, we provided a biomimetic gene loading strategy based on nanoplatform for noninvasive, precise and efficient therapy of atherosclerosis, which further improved the efficiency of gene transfection and effectively slowed the progression of atherosclerotic plaques when combined with ultrasound.

Mitochondrial Oxidative Stress and Mitophagy Activation Contribute to TNF-Dependent Impairment of Myogenesis

Many muscular pathologies are associated with oxidative stress and elevated levels of the tumor necrosis factor (TNF) that cause muscle protein catabolism and impair myogenesis. Myogenesis defects caused by TNF are mediated in part by reactive oxygen species (ROS), including those produced by mitochondria (mitoROS), but the mechanism of their pathological action is not fully understood. We hypothesized that mitoROS act by triggering and enhancing mitophagy, an important tool for remodelling the mitochondrial reticulum during myogenesis. We used three recently developed probes—MitoTracker Orange CM-H2TMRos, mito-QC, and MitoCLox—to study myogenesis in human myoblasts. Induction of myogenesis resulted in a significant increase in mitoROS generation and phospholipid peroxidation in the inner mitochondrial membrane, as well as mitophagy enhancement. Treatment of myoblasts with TNF 24 h before induction of myogenesis resulted in a significant decrease in the myoblast fusion index and myosin heavy chain (MYH2) synthesis. TNF increased the levels of mitoROS, phospholipid peroxidation in the inner mitochondrial membrane and mitophagy at an early stage of differentiation. Trolox and SkQ1 antioxidants partially restored TNF-impaired myogenesis. The general autophagy inducers rapamycin and AICAR, which also stimulate mitophagy, completely blocked myogenesis. The autophagy suppression by the ULK1 inhibitor SBI-0206965 partially restored myogenesis impaired by TNF. Thus, suppression of myogenesis by TNF is associated with a mitoROS-dependent increase in general autophagy and mitophagy.

Coupling of phagocytic NADPH oxidase activity and mitochondrial superoxide production

Superoxide radical plays an important role in redox cell signaling and physiological processes; however, overproduction of superoxide or insufficient activity of antioxidants leads to oxidative stress and contributes to the development of pathological conditions such as endothelial dysfunction and hypertension. Meanwhile, the studies of superoxide in biological systems represent unique challenges associated with short lifetime of superoxide, insufficient reactivity of the superoxide probes, and lack of site-specific detection of superoxide. In this work we have developed 15N-and deuterium-enriched spin probe 15N-CAT1H for high sensitivity and site-specific detection of extracellular superoxide. We have tested simultaneous tracking of extracellular superoxide by 15N-CAT1H and intramitochondrial superoxide by conventional 14N-containing spin probe mitoTEMPO-H in immune cells isolated from spleen, splenocytes, under basal conditions or stimulated with inflammatory cytokines IL-17A and TNFα, NADPH oxidase activator PMA, or treated with inhibitors of mitochondrial complex I rotenone or complex III antimycin A. 15N-CAT1H provides two-fold increase in sensitivity and improves detection since EPR spectrum of 15N-CAT1 nitroxide does not overlap with biological radicals. Furthermore, concurrent use of cell impermeable 15N-CAT1H and mitochondria-targeted 14N-mitoTEMPO-H allows simultaneous detection of extracellular and mitochondrial superoxide. Analysis of IL-17A- and TNFα-induced superoxide showed parallel increase in 15N-CAT1 and 14N-mitoTEMPO signals suggesting coupling between phagocytic NADPH oxidase and mitochondria. The interplay between mitochondrial superoxide production and activity of phagocytic NADPH oxidase was further investigated in splenocytes isolated from Sham and angiotensin II infused C57Bl/6J and Nox2KO mice. Angiotensin II infusion in wild-type mice increased the extracellular basal splenocyte superoxide which was further enhanced by complex III inhibitor antimycin A, mitochondrial uncoupling agent CCCP and NADPH oxidase activator PMA. Nox2 depletion attenuated angiotensin II mediated stimulation and inhibited both extracellular and mitochondrial PMA-induced superoxide production. These data indicate that splenocytes isolated from hypertensive angiotensin II-infused mice are "primed" for enhanced superoxide production from both phagocytic NADPH oxidase and mitochondria. Our data demonstrate that novel 15N-CAT1H provides high sensitivity superoxide measurements and combination with mitoTEMPO-H allows independent and simultaneous detection of extracellular and mitochondrial superoxide. We suggest that this new approach can be used to study the site-specific superoxide production and analysis of important sources of oxidative stress in cardiovascular conditions.

Oxidative Stress in Preterm Newborns

Preterm babies are highly susceptible to oxidative stress (OS) due to an imbalance between the oxidant and antioxidant systems. The generation of free radicals (FR) induces oxidative damage to multiple body organs and systems. OS is the main factor responsible for the development of typical premature infant diseases, such as bronchopulmonary dysplasia, retinopathy of prematurity, necrotizing enterocolitis, intraventricular hemorrhage, periventricular leukomalacia, kidney damage, eryptosis, and also respiratory distress syndrome and patent ductus arteriosus. Many biomarkers have been detected to early identify newborns at risk of developing a free radical-mediated disease and to investigate new antioxidant strategies. This review reports the current knowledge on OS in the preterm newborns and the newest findings concerning the use of OS biomarkers as diagnostic tools, as well as in implementing antioxidant therapeutic strategies for the prevention and treatment of these diseases and their sequelae.

Avocado Oil Prevents Kidney Injury and Normalizes Renal Vasodilation after Adrenergic Stimulation in Hypertensive Rats: Probable Role of Improvement in Mitochondrial Dysfunction and Oxidative Stress

Hypertension impairs the function of the kidney and its vasculature. Adrenergic activation is involved in these processes by promoting oxidative stress and mitochondrial dysfunction. Thus, the targeting of mitochondrial function and mitochondrial oxidative stress may be an approach to alleviate hypertensive kidney damage. Avocado oil, a source of oleic acid and antioxidants, improves mitochondrial dysfunction, decreases mitochondrial oxidative stress, and enhances vascular function in hypertensive rats. However, whether avocado oil improves the function of renal vasculature during the adrenergic stimulation, and if this is related to improvement in renal damage and enhancement of mitochondrial activity is unknown. Thus, the effects of avocado oil on renal vascular responses to adrenergic stimulation, mitochondrial dysfunction, oxidative stress, and renal damage were compared with prazosin, an antagonist of α₁-adrenoceptors, in hypertensive rats induced by L-NAME. Avocado oil or prazosin decreased blood pressure, improved endothelium-dependent renal vasodilation, prevented mitochondrial dysfunction and kidney damage in hypertensive rats. However, avocado oil, but not prazosin, decreased mitochondrial ROS generation and improved the redox state of mitochondrial glutathione. These results suggest that avocado oil and prazosin prevented hypertensive renal damage due to the improvement in mitochondrial function.

Reactive Oxygen Species: Not Omnipresent but Important in Many Locations

Reactive oxygen species (ROS), such as the superoxide anion or hydrogen peroxide, have been established over decades of research as, on the one hand, important and versatile molecules involved in a plethora of homeostatic processes and, on the other hand, as inducers of damage, pathologies and diseases. Which effects ROS induce, strongly depends on the cell type and the source, amount, duration and location of ROS production. Similar to cellular pH and calcium levels, which are both strictly regulated and only altered by the cell when necessary, the redox balance of the cell is also tightly regulated, not only on the level of the whole cell but in every cellular compartment. However, a still widespread view present in the scientific community is that the location of ROS production is of no major importance and that ROS randomly diffuse from their cellular source of production throughout the whole cell and hit their redox-sensitive targets when passing by. Yet, evidence is growing that cells regulate ROS production and therefore their redox balance by strictly controlling ROS source activation as well as localization, amount and duration of ROS production. Hopefully, future studies in the field of redox biology will consider these factors and analyze cellular ROS more specifically in order to revise the view of ROS as freely flowing through the cell.

Is Oxidative Stress the Link Between Cerebral Small Vessel Disease, Sleep Disruption, and Oligodendrocyte Dysfunction in the Onset of Alzheimer's Disease?

Oxidative stress is an early occurrence in the development of Alzheimer’s disease (AD) and one of its proposed etiologic hypotheses. There is sufficient experimental evidence supporting the theory that impaired antioxidant enzymatic activity and increased formation of reactive oxygen species (ROS) take place in this disease. However, the antioxidant treatments fail to stop its advancement. Its multifactorial condition and the diverse toxicological cascades that can be initiated by ROS could possibly explain this failure. Recently, it has been suggested that cerebral small vessel disease (CSVD) contributes to the onset of AD. Oxidative stress is a central hallmark of CSVD and is depicted as an early causative factor. Moreover, data from various epidemiological and clinicopathological studies have indicated a relationship between CSVD and AD where endothelial cells are a source of oxidative stress. These cells are also closely related to oligodendrocytes, which are, in particular, sensitive to oxidation and lead to myelination being compromised. The sleep/wake cycle is another important control in the proliferation, migration, and differentiation of oligodendrocytes, and sleep loss reduces myelin thickness. Moreover, sleep plays a crucial role in resistance against CSVD, and poor sleep quality increases the silent markers of this vascular disease. Sleep disruption is another early occurrence in AD and is related to an increase in oxidative stress. In this study, the relationship between CSVD, oligodendrocyte dysfunction, and sleep disorders is discussed while focusing on oxidative stress as a common occurrence and its possible role in the onset of AD.

Redox signaling in heart failure and therapeutic implications

Heart failure is a growing health burden worldwide characterized by alterations in excitation-contraction coupling, cardiac energetic deficit and oxidative stress. While current treatments are mostly limited to antagonization of neuroendocrine activation, more recent data suggest that also targeting metabolism may provide substantial prognostic benefit. However, although in a broad spectrum of preclinical models, oxidative stress plays a causal role for the development and progression of heart failure, no treatment that targets reactive oxygen species (ROS) directly has entered the clinical arena yet. In the heart, ROS derive from various sources, such as NADPH oxidases, xanthine oxidase, uncoupled nitric oxide synthase and mitochondria. While mitochondria are the primary source of ROS in the heart, communication between different ROS sources may be relevant for physiological signalling events as well as pathologically elevated ROS that deteriorate excitation-contraction coupling, induce hypertrophy and/or trigger cell death. Here, we review the sources of ROS in the heart, the modes of pathological activation of ROS formation as well as therapeutic approaches that may target ROS specifically in mitochondria.

Metabolic Pathways Involved in Formation of Spontaneous and Lipopolysaccharide-Induced Neutrophil Extracellular Traps (NETs) Differ in Obesity and Systemic Inflammation

Obesity manifests itself with low-grade chronic inflammation that shapes immune responses during infection. Albeit obese individuals are at risk of higher mortality due to comorbidities, they are better protected from systemic inflammation. Recently, we showed that in the vasculature of obese mice kept on high-fat diet (HFD), neutrophils produce less neutrophil extracellular traps (NETs) than in lean controls (normal diet, ND). NETs are used by neutrophils to counteract severe infection, but they also cause collateral damage. Hardly anything is known about metabolic requirements for their formation, especially in the context of obesity and/or sepsis. Thus, we aimed to study the immunometabolism of NET formation by application of ex vivo neutrophil analyses (Seahorse analyzer, selective inhibitors, confocal imaging) and intravital microscopy. The obtained data show that glycolysis and/or pentose phosphate pathway are involved in NETs release by ND neutrophils in both physiological and inflammatory conditions. In contrast, such cells of septic HFD mice utilize these routes only to spontaneously cast NETs, while after secondary ex vivo activation they exhibit so called "exhausted phenotype", which manifests itself in diminished NET release despite high glycolytic potential and flexibility to oxidize fatty acids. Moreover, impact of ATP synthase inhibition on NET formation is revealed. Overall, the study shows that the neutrophil potential to cast NETs depends on both the metabolic and inflammatory state of the individual.

Differential ROS-Mediated Phosphorylation of Drp1 in Mitochondrial Fragmentation Induced by Distinct Cell Death Conditions in Cerebellar Granule Neurons

Reactive oxygen species (ROS) production has been associated with neuronal death. ROS are also involved in mitochondrial fission, which is mediated by Dynamin-related protein 1 (Drp1). The regulation of mitochondrial fragmentation mediated by Drp1 and its relationship to mitochondrial ROS (mtROS) in neuronal death have not been completely clarified. The aim of this study is to evaluate the role of mtROS in cell death and their involvement in the activation of Drp1 and mitochondrial fission in a model of cell death of cultured cerebellar granule neurons (CGN). Neuronal death of CGN induced by potassium deprivation (K5) and staurosporine (ST) triggers mitochondrial ROS production and mitochondrial fragmentation. K5 condition evoked an increase of Drp1 phosphorylation at Ser616, but ST treatment led to a decrease of Drp1 phosphorylation. Moreover, the death of CGN induced by both K5 and ST was markedly reduced in the presence of MitoTEMPO; however, mitochondrial morphology was not recovered. Here, we show that the mitochondria are the initial source of ROS involved in the neuronal death of CGN and that mitochondrial fragmentation is a common event in cell death; however, this process is not mediated by Drp1 phosphorylation at Ser616.

COVID-19 and Oxidative Stress

Pathogenesis of the novel coronavirus infection COVID-19 is the subject of active research around the world. COVID-19 caused by the SARS-CoV-2 is a complex disease in which interaction of the virus with target cells, action of the immune system and the body’s systemic response to these events are closely intertwined. Many respiratory viral infections, including COVID-19, cause death of the infected cells, activation of innate immune response, and secretion of inflammatory cytokines. All these processes are associated with the development of oxidative stress, which makes an important contribution to pathogenesis of the viral infections. This review analyzes information on the oxidative stress associated with the infections caused by SARS-CoV-2 and other respiratory viruses. The review also focuses on involvement of the vascular endothelium in the COVID-19 pathogenesis.

STING, the Endoplasmic Reticulum, and Mitochondria: Is Three a Crowd or a Conversation?

The anti-viral pattern recognition receptor STING and its partnering cytosolic DNA sensor cGAS have been increasingly recognized to respond to self DNA in multiple pathologic settings including cancer and autoimmune disease. Endogenous DNA sources that trigger STING include damaged nuclear DNA in micronuclei and mitochondrial DNA (mtDNA). STING resides in the endoplasmic reticulum (ER), and particularly in the ER-mitochondria associated membranes. This unique location renders STING well poised to respond to intracellular organelle stress. Whereas the pathways linking mtDNA and STING have been addressed recently, the mechanisms governing ER stress and STING interaction remain more opaque. The ER and mitochondria share a close anatomic and functional relationship, with mutual production of, and inter-organelle communication via calcium and reactive oxygen species (ROS). This interdependent relationship has potential to both generate the essential ligands for STING activation and to regulate its activity. Herein, we review the interactions between STING and mitochondria, STING and ER, ER and mitochondria (vis-à-vis calcium and ROS), and the evidence for 3-way communication.

NETosis: Molecular Mechanisms, Role in Physiology and Pathology

NETosis is a program for formation of neutrophil extracellular traps (NETs), which consist of modified chromatin decorated with bactericidal proteins from granules and cytoplasm. Various pathogens, antibodies and immune complexes, cytokines, microcrystals, and other physiological stimuli can cause NETosis. Induction of NETosis depends on reactive oxygen species (ROS), the main source of which is NADPH oxidase. Activation of NADPH oxidase depends on increase in the concentration of Ca²⁺ in the cytoplasm and in some cases on the generation of ROS in mitochondria. NETosis includes release of the granule components into the cytosol, modification of histones leading to chromatin decondensation, destruction of the nuclear envelope, as well as formation of pores in the plasma membrane. In this review, basic mechanisms of NETosis, as well as its role in the pathogenesis of some diseases including COVID-19 are discussed.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

Mitochondrial Isolevuglandins Contribute to Vascular Oxidative Stress and Mitochondria-Targeted Scavenger of Isolevuglandins Reduces Mitochondrial Dysfunction and Hypertension

Hypertension remains a major health problem in Western Societies, and blood pressure is poorly controlled in a third of patients despite use of multiple drugs. Mitochondrial dysfunction contributes to hypertension, and mitochondria-targeted agents can potentially improve treatment of hypertension. We have proposed that mitochondrial oxidative stress produces reactive dicarbonyl lipid peroxidation products, isolevuglandins, and that scavenging of mitochondrial isolevuglandins improves vascular function and reduces hypertension. To test this hypothesis, we have studied the accumulation of mitochondrial isolevuglandins-protein adducts in patients with essential hypertension and Ang II (angiotensin II) model of hypertension using mass spectrometry and Western blot analysis. The therapeutic potential of targeting mitochondrial isolevuglandins was tested by the novel mitochondria-targeted isolevuglandin scavenger, mito2HOBA. Mitochondrial isolevuglandins in arterioles from hypertensive patients were 250% greater than in arterioles from normotensive subjects, and ex vivo mito2HOBA treatment of arterioles from hypertensive subjects increased deacetylation of a key mitochondrial antioxidant, SOD2 (superoxide dismutase 2). In human aortic endothelial cells stimulated with Ang II plus TNF (tumor necrosis factor)-α, mito2HOBA reduced mitochondrial superoxide and cardiolipin oxidation, a specific marker of mitochondrial oxidative stress. In Ang II-infused mice, mito2HOBA diminished mitochondrial isolevuglandins-protein adducts, raised Sirt3 (sirtuin 3) mitochondrial deacetylase activity, reduced vascular superoxide, increased endothelial nitric oxide, improved endothelium-dependent relaxation, and attenuated hypertension. Mito2HOBA preserved mitochondrial respiration, protected ATP production, and reduced mitochondrial permeability pore opening in Ang II-infused mice. These data support the role of mitochondrial isolevuglandins in endothelial dysfunction and hypertension. We conclude that scavenging of mitochondrial isolevuglandins may have therapeutic potential in treatment of vascular dysfunction and hypertension.

Superoxide and Non-ionotropic Signaling in Neuronal Excitotoxicity

Excitotoxicity is classically attributed to Ca²⁺ influx through NMDA receptors (NMDAr), leading to production of nitric oxide by neuronal nitric oxide synthase and superoxide by mitochondria, which react to form highly cytotoxic peroxynitrite. More recent observations warrant revision of the classic view and help to explain some otherwise puzzling aspects of excitotoxic cell injury. Studies using pharmacological and genetic approaches show that superoxide produced by NMDAr activation originates primarily from NADPH oxidase rather than from mitochondria. As NADPH oxidase is localized to the plasma membrane, this also provides an explanation for the extracellular release of superoxide and cell-to-cell “spread” of excitotoxic injury observed in vitro and in vivo. The signaling pathway linking NMDAr to NADPH oxidase involves Ca²⁺ influx, phosphoinositol-3-kinase, and protein kinase Cζ, and interventions at any of these steps can prevent superoxide production and excitotoxic injury. Ca²⁺ influx specifically through NMDAr is normally required to induce excitotoxicity, through a mechanism presumed to involve privileged Ca²⁺ access to local signaling domains. However, experiments using selective blockade of the NMDAr ion channel and artificial reconstitution of Ca²⁺ by other routes indicate that the special effects of NMDAr activation are attributable instead to concurrent non-ionotropic NMDAr signaling by agonist binding to NMDAr. The non-ionotropic signaling driving NADPH oxidase activation is mediated in part by phosphoinositol-3-kinase binding to the C-terminal domain of GluN2B receptor subunits. These more recently identified aspects of excitotoxicity expand our appreciation of the complexity of excitotoxic processes and suggest novel approaches for limiting neuronal injury.

Nicotinamide Adenine Dinucleotide Phosphate Oxidase and Neurodegenerative Diseases: Mechanisms and Therapy

Significance: The growing incidence of neurodegenerative diseases significantly impacts the individuals who suffer from these disorders and is a major health concern globally. Although the specific mechanisms of neurodegenerative diseases are still far from being acknowledged, it is becoming clear that oxidative stress and neuroinflammation are critical contributing factors to the progression of neurodegeneration. Thus, it is conceivable that the inhibition of oxidative stress and neuroinflammation may represent promising therapeutic targets for the treatment of neurodegenerative diseases. Recent Advances: Recently, the strategy for neurodegenerative disease therapy has shifted from the use of antioxidants and conventional anti-inflammatory targets to upstream mediators due to the failure of most antioxidants and nonsteroidal anti-inflammatory drugs in clinical trials. Nicotinamide adenine dinucleotide phosphate oxidases (NOXs), a family of superoxide-producing enzyme complexes, have been identified as an upstream factor that controls both oxidative stress and neuroinflammation. Genetic inactivation or pharmacological inhibition of NOX enzymes displays potent neuroprotective effects in a broad spectrum of neurodegenerative disease models. Critical Issues: The detailed mechanisms of how NOX enzymes regulate oxidative stress and neuroinflammation still remain unclear. Moreover, the currently available inhibitors of NOX enzymes exhibit nonspecificity, off-target effects, unsuitable pharmacokinetic properties, and even high toxicity, markedly limiting their potential clinical applications. Future Directions: This review provides novel insights into the roles of NOXs in neurodegenerative pharmacology, and indicates the types of NOX enzyme inhibitors that should be identified and developed as candidates for future applications, which might reveal novel neurodegenerative disease therapies based on NOXs.

Inhibition of Fatty Acid Oxidation Promotes Macrophage Control of Mycobacterium tuberculosis

Macrophage activation involves metabolic reprogramming to support antimicrobial cellular functions. How these metabolic shifts influence the outcome of infection by intracellular pathogens remains incompletely understood. Mycobacterium tuberculosis (Mtb) modulates host metabolic pathways and utilizes host nutrients, including cholesterol and fatty acids, to survive within macrophages. We found that intracellular growth of Mtb depends on host fatty acid catabolism: when host fatty acid β-oxidation (FAO) was blocked chemically with trimetazidine, a compound in clinical use, or genetically by deletion of the mitochondrial fatty acid transporter carnitine palmitoyltransferase 2 (CPT2), Mtb failed to grow in macrophages, and its growth was attenuated in mice. Mechanistic studies support a model in which inhibition of FAO generates mitochondrial reactive oxygen species, which enhance macrophage NADPH oxidase and xenophagy activity to better control Mtb infection. Thus, FAO inhibition promotes key antimicrobial functions of macrophages and overcomes immune evasion mechanisms of Mtb.IMPORTANCEMycobacterium tuberculosis (Mtb) is the leading infectious disease killer worldwide. We discovered that intracellular Mtb fails to grow in macrophages in which fatty acid β-oxidation (FAO) is blocked. Macrophages treated with FAO inhibitors rapidly generate a burst of mitochondria-derived reactive oxygen species, which promotes NADPH oxidase recruitment and autophagy to limit the growth of Mtb. Furthermore, we demonstrate the ability of trimetazidine to reduce pathogen burden in mice infected with Mtb. These studies will add to the knowledge of how host metabolism modulates Mtb infection outcomes.

Signaling pathways targeting mitochondrial potassium channels

In this review, we describe key signaling pathways regulating potassium channels present in the inner mitochondrial membrane. The signaling cascades covered here include phosphorylation, redox reactions, modulation by calcium ions and nucleotides. The following types of potassium channels have been identified in the inner mitochondrial membrane of various tissues: ATP-sensitive, Ca²⁺-activated, voltage-gated and two-pore domain potassium channels. The direct roles of these channels involve regulation of mitochondrial respiration, membrane potential and synthesis of reactive oxygen species (ROS). Changes in channel activity lead to diverse pro-life and pro-death responses in different cell types. Hence, characterizing the signaling pathways regulating mitochondrial potassium channels will facilitate understanding the physiological role of these proteins. Additionally, we describe in this paper certain regulatory mechanisms, which are unique to mitochondrial potassium channels.

Distinct dual roles of p-Tyr42 RhoA GTPase in tau phosphorylation and ATP citrate lyase activation upon different Aβ concentrations

Both the accumulation of Amyloid-β (Aβ) in plaques and phosphorylation of Tau protein (p-Tau) in neurofibrillary tangles have been identified as two major symptomatic features of Alzheimer's disease (AD). Despite of critical role of Aβ and p-Tau in AD progress, the interconnection of signalling pathways that Aβ induces p-Tau remains elusive. Herein, we observed that a popular AD model mouse (APP/PS1) and Aβ-injected mouse showed an increase in p-Tyr42 Rho in hippocampus of brain. Low concentrations of Aβ (1 μM) induced RhoA-mediated Ser422 phosphorylation of Tau protein (p-Ser422 Tau), but reduced the expression of ATP citrate lyase (ACL) in the HT22 hippocampal neuronal cell line. In contrast, high concentrations of Aβ (10 μM) along with high levels of superoxide production remarkably attenuated accumulation of p-Ser422 Tau, but augmented ACL expression and activated sterol regulatory element-binding protein 1 (SREBP1), leading to cellular senescence. Notably, a high concentration of Aβ (10 μM) induced nuclear localization of p-Tyr42 Rho, which positively regulated NAD kinase (NADK) expression by binding to the NADK promoter. Furthermore, severe AD patient brain showed high p-Tyr42 Rho levels. Collectively, our findings indicate that both high and low concentrations of Aβ are detrimental to neurons via distinct two p-Tyr42 RhoA-mediated signalling pathways in Ser422 phosphorylation of Tau and ACL expression.

Pro- and antitumor effects of mitochondrial reactive oxygen species

In cancer, mitochondrial functions are commonly altered. Directly involved in metabolic reprogramming, mitochondrial plasticity confers to cancer cells a high degree of adaptability to a wide range of stresses and to the harsh tumor microenvironment. Lack of nutrients or oxygen caused by altered perfusion, metabolic needs of proliferating cells, co-option of the microenvironment, control of the immune system, cell migration and metastasis, and evasion of exogenous stress (e.g., chemotherapy) are all, at least in part, influenced by mitochondria. Mitochondria are undoubtedly one of the key contributors to cancer development and progression. Understanding their protumoral (dys)functions may pave the way to therapeutic strategies capable of turning them into innocent entities. Here, we will focus on the production and detoxification of mitochondrial reactive oxygen species (mtROS), on their impact on tumorigenesis (genetic, prosurvival, and microenvironmental effects and their involvement in autophagy), and on tumor metastasis. We will also summarize the latest therapeutic approaches involving mtROS.

Mitochondrial permeability transition pore is involved in oxidative burst and NETosis of human neutrophils

Neutrophils release neutrophil extracellular traps (NETs) in response to numerous pathogenic microbes as the last suicidal resource (NETosis) in the fight against infection. Apart from the host defense function, NETs play an essential role in the pathogenesis of various autoimmune and inflammatory diseases. Therefore, understanding the molecular mechanisms of NETosis is important for regulating aberrant NET release. The initiation of NETosis after the recognition of pathogens by specific receptors is mediated by an increase in intracellular Ca²⁺ concentration, therefore, the use of Ca²⁺ ionophore A23187 can be considered a semi-physiological model of NETosis. Induction of NETosis by various stimuli depends on reactive oxygen species (ROS) produced by NADPH oxidase, however, NETosis induced by Ca²⁺ ionophores was suggested to be mediated by ROS produced in mitochondria (mtROS). Using the mitochondria-targeted antioxidant SkQ1 and specific inhibitors of NADPH oxidase, we showed that both sources of ROS, mitochondria and NADPH oxidase, are involved in NETosis induced by A23187 in human neutrophils. In support of the critical role of mtROS, SkQ1-sensitive NETosis was demonstrated to be induced by A23187 in neutrophils from patients with chronic granulomatous disease (CGD). We assume that Ca²⁺-triggered mtROS production contributes to NETosis either directly (CGD neutrophils) or by stimulating NADPH oxidase. The opening of the mitochondrial permeability transition pore (mPTP) in neutrophils treated by A23187 was revealed using the electron transmission microscopy as a swelling of the mitochondrial matrix. Using specific inhibitors, we demonstrated that the mPTP is involved in mtROS production, NETosis, and the oxidative burst induced by A23187.

Redox Signaling from Mitochondria: Signal Propagation and Its Targets

Progress in mass spectroscopy of posttranslational oxidative modifications has enabled researchers to experimentally verify the concept of redox signaling. We focus here on redox signaling originating from mitochondria under physiological situations, discussing mechanisms of transient redox burst in mitochondria, as well as the possible ways to transfer such redox signals to specific extramitochondrial targets. A role of peroxiredoxins is described which enables redox relay to other targets. Examples of mitochondrial redox signaling are discussed: initiation of hypoxia-inducible factor (HIF) responses; retrograde redox signaling to PGC1α during exercise in skeletal muscle; redox signaling in innate immune cells; redox stimulation of insulin secretion, and other physiological situations.

Nanotherapeutic modulation of excitotoxicity and oxidative stress in acute brain injury

Excitotoxicity is a primary pathological process that occurs during stroke, traumatic brain injury (TBI), and global brain ischemia such as perinatal asphyxia. Excitotoxicity is triggered by an overabundance of excitatory neurotransmitters within the synapse, causing a detrimental cascade of excessive sodium and calcium influx, generation of reactive oxygen species, mitochondrial damage, and ultimately cell death. There are multiple potential points of intervention to combat excitotoxicity and downstream oxidative stress, yet there are currently no therapeutics clinically approved for this specific purpose. For a therapeutic to be effective against excitotoxicity, the therapeutic must accumulate at the disease site at the appropriate concentration at the right time. Nanotechnology can provide benefits for therapeutic delivery, including overcoming physiological obstacles such as the blood–brain barrier, protect cargo from degradation, and provide controlled release of a drug. This review evaluates the use of nano-based therapeutics to combat excitotoxicity in stroke, TBI, and hypoxia–ischemia with an emphasis on mitigating oxidative stress, and consideration of the path forward toward clinical translation.

Mitochondrial Deacetylase Sirt3 Reduces Vascular Dysfunction and Hypertension While Sirt3 Depletion in Essential Hypertension Is Linked to Vascular Inflammation and Oxidative Stress

RATIONALE

Hypertension represents a major risk factor for stroke, myocardial infarction, and heart failure and affects 30% of the adult population. Mitochondrial dysfunction contributes to hypertension, but specific mechanisms are unclear. The mitochondrial deacetylase Sirt3 (Sirtuin 3) is critical in the regulation of metabolic and antioxidant functions which are associated with hypertension, and cardiovascular disease risk factors diminish Sirt3 level.

OBJECTIVE

We hypothesized that reduced Sirt3 expression contributes to vascular dysfunction in hypertension, but increased Sirt3 protects vascular function and decreases hypertension.

METHODS AND RESULTS

To test the therapeutic potential of targeting Sirt3 expression, we developed new transgenic mice with global Sirt3OX (Sirt3 overexpression), which protects from endothelial dysfunction, vascular oxidative stress, and hypertrophy and attenuates Ang II (angiotensin II) and deoxycorticosterone acetate-salt induced hypertension. Global Sirt3 depletion in Sirt3^-/- mice results in oxidative stress due to hyperacetylation of mitochondrial superoxide dismutase (SOD2), increases HIF1α (hypoxia-inducible factor-1), reduces endothelial cadherin, stimulates vascular hypertrophy, increases vascular permeability and vascular inflammation (p65, caspase 1, VCAM [vascular cell adhesion molecule-1], ICAM [intercellular adhesion molecule-1], and MCP1 [monocyte chemoattractant protein 1]), increases inflammatory cell infiltration in the kidney, reduces telomerase expression, and accelerates vascular senescence and age-dependent hypertension; conversely, increased Sirt3 expression in Sirt3OX mice prevents these deleterious effects. The clinical relevance of Sirt3 depletion was confirmed in arterioles from human mediastinal fat in patients with essential hypertension showing a 40% decrease in vascular Sirt3, coupled with Sirt3-dependent 3-fold increases in SOD2 acetylation, NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activity, VCAM, ICAM, and MCP1 levels in hypertensive subjects compared with normotensive subjects.

CONCLUSIONS

We suggest that Sirt3 depletion in hypertension promotes endothelial dysfunction, vascular hypertrophy, vascular inflammation, and end-organ damage. Our data support a therapeutic potential of targeting Sirt3 expression in vascular dysfunction and hypertension.

Comparison of Mitochondrial Superoxide Detection Ex Vivo/In Vivo by mitoSOX HPLC Method with Classical Assays in Three Different Animal Models of Oxidative Stress

Background: Reactive oxygen and nitrogen species (RONS such as H₂O₂, nitric oxide) are generated within the organism. Whereas physiological formation rates confer redox regulation of essential cellular functions and provide the basis for adaptive stress responses, their excessive formation contributes to impaired cellular function or even cell death, organ dysfunction and severe disease phenotypes of the entire organism. Therefore, quantification of RONS formation and knowledge of their tissue/cell/compartment-specific distribution is of great biological and clinical importance. Methods: Here, we used a high-performance/pressure liquid chromatography (HPLC) assay to quantify the superoxide-specific oxidation product of the mitochondria-targeted fluorescence dye triphenylphosphonium-linked hydroethidium (mitoSOX) in biochemical systems and three animal models with established oxidative stress. Type 1 diabetes (single injection of streptozotocin), hypertension (infusion of angiotensin-II for 7 days) and nitrate tolerance (infusion of nitroglycerin for 4 days) was induced in male Wistar rats. Results: The usefulness of mitoSOX/HPLC for quantification of mitochondrial superoxide was confirmed by xanthine oxidase activity as well as isolated stimulated rat heart mitochondria in the presence or absence of superoxide scavengers. Vascular function was assessed by isometric tension methodology and was impaired in the rat models of oxidative stress. Vascular dysfunction correlated with increased mitoSOX oxidation but also classical RONS detection assays as well as typical markers of oxidative stress. Conclusion: mitoSOX/HPLC represents a valid method for detection of mitochondrial superoxide formation in tissues of different animal disease models and correlates well with functional parameters and other markers of oxidative stress.

Circulating Leukocytes and Oxidative Stress in Cardiovascular Diseases: A State of the Art

Increased oxidative stress from both mitochondrial and cytosolic sources contributes to the development and the progression of cardiovascular diseases (CVDs), and it is a target of therapeutic interventions. The numerous efforts made over the last decades in order to develop tools able to monitor the oxidative stress level in patients affected by CVDs rely on the need to gain information on the disease state. However, this goal has not been satisfactorily accomplished until now. Among others, the isolation of circulating leukocytes to measure their oxidant level offers a valid, noninvasive challenge that has been tested in few pathological contexts, including hypertension, atherosclerosis and its clinical manifestations, and heart failure. Since leukocytes circulate in the blood stream, it is expected that they might reflect quite closely both systemic and cardiovascular oxidative stress and provide useful information on the pathological condition. The results of the studies discussed in the present review article are promising. They highlight the importance of measuring oxidative stress level in circulating mononuclear cells in different CVDs with a consistent correlation between degree of oxidative stress and severity of CVD and of its complications. Importantly, they also point to a double role of leukocytes, both as a marker of disease condition and as a direct contributor to disease progression. Finally, they show that the oxidative stress level of leukocytes reflects the impact of therapeutic interventions. It is likely that the isolation of leukocytes and the measurement of oxidative stress, once adequately developed, may represent an eligible tool for both research and clinical purposes to monitor the role of oxidative stress on the promotion and progression of CVDs, as well as the impact of therapies.

LRRK2 activation in idiopathic Parkinson's disease

Missense mutations in leucine-rich repeat kinase 2 (LRRK2) cause familial Parkinson's disease (PD). However, a potential role of wild-type LRRK2 in idiopathic PD (iPD) remains unclear. Here, we developed proximity ligation assays to assess Ser1292 phosphorylation of LRRK2 and, separately, the dissociation of 14-3-3 proteins from LRRK2. Using these proximity ligation assays, we show that wild-type LRRK2 kinase activity was selectively enhanced in substantia nigra dopamine neurons in postmortem brain tissue from patients with iPD and in two different rat models of the disease. We show that this occurred through an oxidative mechanism, resulting in phosphorylation of the LRRK2 substrate Rab10 and other downstream consequences including abnormalities in mitochondrial protein import and lysosomal function. Our study suggests that, independent of mutations, wild-type LRRK2 plays a role in iPD. LRRK2 kinase inhibitors may therefore be useful for treating patients with iPD who do not carry LRRK2 mutations.

Say NO to ROS: Their Roles in Embryonic Heart Development and Pathogenesis of Congenital Heart Defects in Maternal Diabetes

Congenital heart defects (CHDs) are the most prevalent and serious birth defect, occurring in 1% of all live births. Pregestational maternal diabetes is a known risk factor for the development of CHDs, elevating the risk in the child by more than four-fold. As the prevalence of diabetes rapidly rises among women of childbearing age, there is a need to investigate the mechanisms and potential preventative strategies for these defects. In experimental animal models of pregestational diabetes induced-CHDs, upwards of 50% of offspring display congenital malformations of the heart, including septal, valvular, and outflow tract defects. Specifically, the imbalance of nitric oxide (NO) and reactive oxygen species (ROS) signaling is a major driver of the development of CHDs in offspring of mice with pregestational diabetes. NO from endothelial nitric oxide synthase (eNOS) is crucial to cardiogenesis, regulating various cellular and molecular processes. In fact, deficiency in eNOS results in CHDs and coronary artery malformation. Embryonic hearts from diabetic dams exhibit eNOS uncoupling and oxidative stress. Maternal treatment with sapropterin, a cofactor of eNOS, and antioxidants such as N-acetylcysteine, vitamin E, and glutathione as well as maternal exercise have been shown to improve eNOS function, reduce oxidative stress, and lower the incidence CHDs in the offspring of mice with pregestational diabetes. This review summarizes recent data on pregestational diabetes-induced CHDs, and offers insights into the important roles of NO and ROS in embryonic heart development and pathogenesis of CHDs in maternal diabetes.

Crosstalk Between Mitochondrial Hyperacetylation and Oxidative Stress in Vascular Dysfunction and Hypertension

Significance: Vascular dysfunction plays a key role in the development of arteriosclerosis, heart disease, and hypertension, which causes one-third of deaths worldwide. Vascular oxidative stress and metabolic disorders contribute to vascular dysfunction, leading to impaired vasorelaxation, vascular hypertrophy, fibrosis, and aortic stiffening. Mitochondria are critical in the regulation of metabolic and antioxidant functions; therefore, mitochondria-targeted treatments could be beneficial. Recent Advances: Vascular dysfunction is crucial in hypertension pathophysiology and exhibits bidirectional relationship. Metabolic disorders and oxidative stress contribute to the pathogenesis of vascular dysfunction and hypertension, which are associated with mitochondrial impairment and hyperacetylation. Mitochondrial deacetylase Sirtuin 3 (Sirt3) is critical in the regulation of metabolic and antioxidant functions. Clinical studies show that cardiovascular disease risk factors reduce Sirt3 level and Sirt3 declines with age, paralleling the increased incidence of cardiovascular disease and hypertension. An imbalance between mitochondrial acetylation and reduced Sirt3 activity contributes to mitochondrial dysfunction and oxidative stress. We propose that mitochondrial hyperacetylation drives a vicious cycle between metabolic disorders and mitochondrial oxidative stress, promoting vascular dysfunction and hypertension. Critical Issues: The mechanisms of mitochondrial dysfunction are still obscure in human hypertension. Mitochondrial hyperacetylation and oxidative stress contribute to mitochondrial dysfunction; however, regulation of mitochondrial acetylation, the role of GCN5L1 (acetyl-CoA-binding protein promoting acetyltransferase protein acetylation) acetyltransferase, Sirt3 deacetylase, and acetylation of specific proteins require further investigations. Future Directions: There is an urgent need to define molecular mechanisms and the pathophysiological role of mitochondrial hyperacetylation, identify novel pharmacological targets, and develop therapeutic approaches to reduce this phenomenon.

Biochemical basis and metabolic interplay of redox regulation

Accumulated evidence strongly indicates that oxidative stress, characterized by an imbalance between reactive oxygen species (ROS) production and antioxidants in favor of oxidants, plays an important role in disease pathogenesis. However, ROS can act as signaling molecules and fulfill essential physiological functions at basal levels. Each ROS would be different in the extent to stimulate and contribute to different pathophysiological effects. Importantly, multiple ROS generators can be activated either concomitantly or sequentially by relevant signaling molecules for redox biological functions. Here, we summarized the current knowledge related to chemical and biochemical features of primary ROS species and corresponding antioxidants. Metabolic pathways of five major ROS generators and five ROS clearance systems were described, including their ROS products, specific ROS enriched tissue, cell and organelle, and relevant functional implications. We provided an overview of ROS generation and induction at different levels of metabolism. We classified 11 ROS species into three types based on their reactivity and target selectivity and presented ROS homeostasis and functional implications in pathological and physiological status. This article intensively reviewed and refined biochemical basis, metabolic signaling and regulation, functional insights, and provided guidance for the identification of novel therapeutic targets.

Chemical Probes for Redox Signaling and Oxidative Stress

SIGNIFICANCE

Cellular reactive oxygen species (ROS) mediate redox signaling cascades that are critical to numerous physiological and pathological processes. Analytical methods to monitor cellular ROS levels and proteomic platforms to identify oxidative post-translational modifications (PTMs) of proteins are critical to understanding the triggers and consequences of redox signaling. Recent Advances: The prevalence and significance of redox signaling has recently been illuminated through the use of chemical probes that allow for sensitive detection of cellular ROS levels and proteomic dissection of oxidative PTMs directly in living cells.

CRITICAL ISSUES

In this review, we provide a comprehensive overview of chemical probes that are available for monitoring ROS and oxidative PTMs, and we highlight the advantages and limitations of these methods.

FUTURE DIRECTIONS

Despite significant advances in chemical probes, the low levels of cellular ROS and low stoichiometry of oxidative PTMs present challenges for accurately measuring the extent and dynamics of ROS generation and redox signaling. Further improvements in sensitivity and ability to spatially and temporally control readouts are essential to fully illuminate cellular redox signaling.

Oxidative stress creates a unique, CaMKII-mediated substrate for atrial fibrillation in heart failure

The precise mechanisms by which oxidative stress (OS) causes atrial fibrillation (AF) are not known. Since AF frequently originates in the posterior left atrium (PLA), we hypothesized that OS, via calmodulin-dependent protein kinase II (CaMKII) signaling, creates a fertile substrate in the PLA for triggered activity and reentry. In a canine heart failure (HF) model, OS generation and oxidized-CaMKII-induced (Ox-CaMKII-induced) RyR2 and Nav1.5 signaling were increased preferentially in the PLA (compared with left atrial appendage). Triggered Ca2+ waves (TCWs) in HF PLA myocytes were particularly sensitive to acute ROS inhibition. Computational modeling confirmed a direct relationship between OS/CaMKII signaling and TCW generation. CaMKII phosphorylated Nav1.5 (CaMKII-p-Nav1.5 [S571]) was located preferentially at the intercalated disc (ID), being nearly absent at the lateral membrane. Furthermore, a decrease in ankyrin-G (AnkG) in HF led to patchy dropout of CaMKII-p-Nav1.5 at the ID, causing its distribution to become spatially heterogeneous; this corresponded to preferential slowing and inhomogeneity of conduction noted in the HF PLA. Computational modeling illustrated how conduction slowing (e.g., due to increase in CaMKII-p-Nav1.5) interacts with fibrosis to cause reentry in the PLA. We conclude that OS via CaMKII leads to substrate for triggered activity and reentry in HF PLA by mechanisms independent of but complementary to fibrosis.

A Flow Cytometry-based Assay for Measuring Mitochondrial Membrane Potential in Cardiac Myocytes After Hypoxia/Reoxygenation

Timely and efficient reperfusion of the occluded coronary artery is the best strategy for decreasing myocardial infarct size in patients with a ST-segment elevated myocardial infarction. However, reperfusion per se can result in further cardiomyocyte death, a phenomenon known as reperfusion injury. The opening of the mitochondrial permeability transition pore (mPTP), with the decrease of the mitochondrial membrane potential (MMP), or mitochondrial depolarization, is universally recognized as the final step of reperfusion injury and is responsible for mitochondrial and cardiomyocyte death. JC-1 is a lipophilic cationic dye that accumulates in mitochondria depending on the value of MMP. The higher the MMP is, the more JC-1 accumulates in the mitochondria. The increasing amounts of JC-1 in mitochondria can be reflected by a fluorescence emission shift from green (~530 nm) to red (~590 nm). Therefore, the reduction of the red/green fluorescence intensity ratio can indicate the depolarization of mitochondria. Here, we take advantage of JC-1 to measure MMP, or the opening of mPTP in human cardiac myocytes after hypoxia/reoxygenation, detected by flow cytometry.

Hsp70 Suppresses Mitochondrial Reactive Oxygen Species and Preserves Pulmonary Microvascular Barrier Integrity Following Exposure to Bacterial Toxins

Pneumonia is a leading cause of death in children and the elderly worldwide, accounting for 15% of all deaths of children under 5 years old. Streptococcus pneumoniae is a common and aggressive cause of pneumonia and can also contribute to meningitis and sepsis. Despite the widespread use of antibiotics, mortality rates for pneumonia remain unacceptably high in part due to the release of bacterial toxins. Pneumolysin (PLY) is a cholesterol-dependent toxin that is produced by Streptococcus, and it is both necessary and sufficient for the development of the extensive pulmonary permeability edema that underlies acute lung injury. The mechanisms by which PLY disrupts the pulmonary endothelial barrier are not fully understood. Previously, we found that reactive oxygen species (ROS) contribute to the barrier destructive effects of PLY and identified an unexpected but potent role of Hsp70 in suppressing ROS production. The ability of Hsp70 to influence PLY-induced barrier dysfunction is not yet described, and the goal of the current study was to identify whether Hsp70 upregulation is an effective strategy to protect the lung microvascular endothelial barrier from G⁺ bacterial toxins. Overexpression of Hsp70 via adenovirus-mediated gene transfer attenuated PLY-induced increases in permeability in human lung microvascular endothelial cells (HLMVEC) with no evidence of cytotoxicity. To adopt a more translational approach, we employed a pharmacological approach using geranylgeranylacetone (GGA) to acutely upregulate endogenous Hsp70 expression. Following acute treatment (6 h) with GGA, HLMVECs exposed to PLY displayed improved cell viability and enhanced endothelial barrier function as measured by both Electric Cell-substrate Impedance Sensing (ECIS) and transwell permeability assays compared to control treated cells. PLY promoted increased mitochondrial ROS, decreased mitochondrial oxygen consumption, and increased caspase 3 cleavage and cell death, which were collectively improved in cells pretreated with GGA. In mice, IP pretreatment with GGA 24 h prior to IT administration of PLY resulted in significantly less Evans Blue Dye extravasation compared to vehicle, indicating preserved endothelial barrier integrity and suggesting that the acute upregulation of Hsp70 may be an effective therapeutic approach in the treatment of lung injury associated with pneumonia.

Mitochondria and cardiovascular diseases-from pathophysiology to treatment

Mitochondria are the source of cellular energy production and are present in different types of cells. However, their function is especially important for the heart due to the high demands in energy which is achieved through oxidative phosphorylation. Mitochondria form large networks which regulate metabolism and the optimal function is achieved through the balance between mitochondrial fusion and mitochondrial fission. Moreover, mitochondrial function is upon quality control via the process of mitophagy which removes the damaged organelles. Mitochondrial dysfunction is associated with the development of numerous cardiac diseases such as atherosclerosis, ischemia-reperfusion (I/R) injury, hypertension, diabetes, cardiac hypertrophy and heart failure (HF), due to the uncontrolled production of reactive oxygen species (ROS). Therefore, early control of mitochondrial dysfunction is a crucial step in the therapy of cardiac diseases. A number of anti-oxidant molecules and medications have been used but the results are inconsistent among the studies. Eventually, the aim of future research is to design molecules which selectively target mitochondrial dysfunction and restore the capacity of cellular anti-oxidant enzymes.

Endothelial AIP1 Regulates Vascular Remodeling by Suppressing NADPH Oxidase-2

Objective: AIP1 expression is downregulated in human atherosclerotic plaques and global deletion of AIP1 in mice exacerbates atherosclerosis in ApoE-KO mouse models. However, the direct role of AIP1 in endothelium, vascular remodeling and associated vascular diseases has not been determined. Approach and Results: We used endothelial cell (EC)-specific AIP1-deficient (AIP1-ECKO) mice to define the role of AIP1 in vascular remodeling and intima-media thickening in a mouse carotid artery ligation model characterized by both neointimal hyperplasia and inward vessel remodeling. Compared to WT littermates, AIP1-ECKO mice had 2.2-fold larger intima area and 4.4-fold thicker intima as measured by intima/media ratio in arteries with more proliferating vascular smooth muscle cells (VSMCs) at week 2-4 post-injury. Increased reactive oxygen species (ROS) in endothelium at early time points induced inflammation and vessel dysfunction in AIP1-ECKO prior to VSMC accumulations. Moreover, knockdown of AIP1 in human EC enhanced ROS generation which was attenuated by co-silencing of NOX2. Mechanistically, AIP1 via its proline-rich region binds to the SH3 domain of cytosolic subunit p47phox to disrupt formation of an active NOX2 complex, attenuating ROS production. Conclusion: Our study supports that AIP1 regulates vascular remodeling with intima-media thickening by suppressing endothelial NOX2-dependent oxidative stress. Highlights: •In a carotid ligation model, endothelial cell (EC)-specific AIP1-deficient (AIP1-ECKO) mice had much larger media area, thicker vessel wall and augmented neointima formation.•Increased production of reactive oxygen species in vascular EC at early time points concomitant with vessel dysfunction in AIP1-ECKO.•AIP1 via its proline-rich region binds to the SH3 domain of cytosolic subunit p47phox to disrupt formation of an active NOX2 complex, attenuating ROS production.

Subcellular Reactive Oxygen Species (ROS) in Cardiovascular Pathophysiology

There exist two opposing perspectives regarding reactive oxygen species (ROS) and their roles in angiogenesis and cardiovascular system, one that favors harmful and causal effects of ROS, while the other supports beneficial effects. Recent studies have shown that interaction between ROS in different sub-cellular compartments plays a crucial role in determining the outcomes (beneficial vs. deleterious) of ROS exposures on the vascular system. Oxidant radicals in one cellular organelle can affect the ROS content and function in other sub-cellular compartments in endothelial cells (ECs). In this review, we will focus on a critical fact that the effects or the final phenotypic outcome of ROS exposure to EC are tissue- or organ-specific, and depend on the spatial (subcellular localization) and temporal (duration of ROS exposure) modulation of ROS levels.

Thioredoxin reverses age-related hypertension by chronically improving vascular redox and restoring eNOS function

The incidence of high blood pressure with advancing age is notably high, and it is an independent prognostic factor for the onset or progression of a variety of cardiovascular disorders. Although age-related hypertension is an established phenomenon, current treatments are only palliative but not curative. Thus, there is a critical need for a curative therapy against age-related hypertension, which could greatly decrease the incidence of cardiovascular disorders. We show that overexpression of human thioredoxin (TRX), a redox protein, in mice prevents age-related hypertension. Further, injection of recombinant human TRX (rhTRX) for three consecutive days reversed hypertension in aged wild-type mice, and this effect lasted for at least 20 days. Arteries of wild-type mice injected with rhTRX or mice with TRX overexpression exhibited decreased arterial stiffness, greater endothelium-dependent relaxation, increased nitric oxide production, and decreased superoxide anion (O₂^•-) generation compared to either saline-injected aged wild-type mice or mice with TRX deficiency. Our study demonstrates a potential translational role of rhTRX in reversing age-related hypertension with long-lasting efficacy.

Hypoxia-reoxygenation enhances murine afferent arteriolar vasoconstriction by angiotensin II

We tested the hypothesis that hypoxia-reoxygenation (H/R) augments vasoreactivity to angiotensin II (ANG II). In particular, we compared an in situ live kidney slice model with isolated afferent arterioles (C57Bl6 mice) to assess the impact of tubules on microvessel response. Hematoxylin and eosin staining was used to estimate slice viability. Arterioles in the slices were located by differential interference contrast microscopy, and responses to vasoactive substances were assessed. Cytosolic calcium transients and NADPH oxidase (NOX) mRNA expression were studied in isolated afferent arterioles. SOD activity was measured in live slices. Both experimental models were subjected to control and H/R treatment (60 min). Slices were further analyzed after 30-, 60-, and 90-min hypoxia followed by 10- or 20-min reoxygenation (H/R). H/R resulted in enhanced necrotic tissue damage compared with control conditions. To characterize the slice model, we applied ANG II (10^-7 M), norepinephrine (NE; 10^-5 M), endothelin-1 (ET-1; 10^-7 M), and ATP (10^-4 M), reducing the initial diameter to 44.5 ± 2.8, 50.0 ± 2.2, 45.3 ± 2.6, and 74.1 ± 1.8%, respectively. H/R significantly increased the ANG II response compared with control in live slices and in isolated afferent arterioles, although calcium transients remained similar. TEMPOL incubation prevented the H/R effect on ANG II responses. H/R significantly increased NOX2 mRNA expression in isolated arterioles. SOD activity was significantly decreased after H/R. Enhanced arteriolar responses after H/R occurred independently from the surrounding tissue, indicating no influence of tubules on vascular function in this model. The mechanism of increased ANG II response after H/R might be increased oxidative stress and increased calcium sensitivity of the contractile apparatus.

Uncoupling Protein 2: A Key Player and a Potential Therapeutic Target in Vascular Diseases

Uncoupling protein 2 (UCP2) is an inner mitochondrial membrane protein that belongs to the uncoupling protein family and plays an important role in lowering mitochondrial membrane potential and dissipating metabolic energy with prevention of oxidative stress accumulation. In the present article, we will review the evidence that UCP2, as a consequence of its roles within the mitochondria, represents a critical player in the predisposition to vascular disease development in both animal models and in humans, particularly in relation to obesity, diabetes, and hypertension. The deletion of the UCP2 gene contributes to atherosclerosis lesion development in the knockout mice, also showing significantly shorter lifespan. The UCP2 gene downregulation is a key determinant of higher predisposition to renal and cerebrovascular damage in an animal model of spontaneous hypertension and stroke. In contrast, UCP2 overexpression improves both hyperglycemia- and high-salt diet-induced endothelial dysfunction and ameliorates hypertensive target organ damage in SHRSP. Moreover, drugs (fenofibrate and sitagliptin) and several vegetable compounds (extracts from Brassicaceae, berberine, curcumin, and capsaicin) are able to induce UCP2 expression level and to exert beneficial effects on the occurrence of vascular damage. As a consequence, UCP2 becomes an interesting therapeutic target for the treatment of common human vascular diseases.

Crosstalk of mitochondria with NADPH oxidase via reactive oxygen and nitrogen species signalling and its role for vascular function

Cardiovascular diseases are associated with and/or caused by oxidative stress. This concept has been proven by using the approach of genetic deletion of reactive species producing (pro-oxidant) enzymes as well as by the overexpression of reactive species detoxifying (antioxidant) enzymes leading to a marked reduction of reactive oxygen and nitrogen species (RONS) and in parallel to an amelioration of the severity of diseases. Likewise, the development and progression of cardiovascular diseases is aggravated by overexpression of RONS producing enzymes as well as deletion of antioxidant RONS detoxifying enzymes. Thus, the consequences of the interaction (redox crosstalk) of superoxide/hydrogen peroxide produced by mitochondria with other ROS producing enzymes such as NADPH oxidases (Nox) are of outstanding importance and will be discussed including the consequences for endothelial nitric oxide synthase (eNOS) uncoupling as well as the redox regulation of the vascular function/tone in general (soluble guanylyl cyclase, endothelin-1, prostanoid synthesis). Pathways and potential mechanisms leading to this crosstalk will be analysed in detail and highlighted by selected examples from the current literature including hypoxia, angiotensin II-induced hypertension, nitrate tolerance, aging and others. The general concept of redox-based activation of RONS sources via "kindling radicals" and enzyme-specific "redox switches" will be discussed providing evidence that mitochondria represent key players and amplifiers of the burden of oxidative stress.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Dysfunction of Kidney Endothelium after Ischemia/Reperfusion and Its Prevention by Mitochondria-Targeted Antioxidant

One of the most important pathological consequences of renal ischemia/reperfusion (I/R) is kidney malfunctioning. I/R leads to oxidative stress, which affects not only nephron cells but also cells of the vascular wall, especially endothelium, resulting in its damage. Assessment of endothelial damage, its role in pathological changes in organ functioning, and approaches to normalization of endothelial and renal functions are vital problems that need to be resolved. The goal of this study was to examine functional and morphological impairments occurring in the endothelium of renal vessels after I/R and to explore the possibility of alleviation of the severity of these changes using mitochondria-targeted antioxidant 10-(6'-plastoquinonyl)decylrhodamine 19 (SkQR1). Here we demonstrate that 40-min ischemia with 10-min reperfusion results in a profound change in the structure of endothelial cells mitochondria, accompanied by vasoconstriction of renal blood vessels, reduced renal blood flow, and increased number of endothelial cells circulating in the blood. Permeability of the kidney vascular wall increased 48 h after I/R. Injection of SkQR1 improves recovery of renal blood flow and reduces vascular resistance of the kidney in the first minutes of reperfusion; it also reduces the severity of renal insufficiency and normalizes permeability of renal endothelium 48 h after I/R. In in vitro experiments, SkQR1 provided protection of endothelial cells from death provoked by oxygen-glucose deprivation. On the other hand, an inhibitor of NO-synthases, L-nitroarginine, abolished the positive effects of SkQR1 on hemodynamics and protection from renal failure. Thus, dysfunction and death of endothelial cells play an important role in the development of reperfusion injury of renal tissues. Our results indicate that the major pathogenic factors in the endothelial damage are oxidative stress and mitochondrial damage within endothelial cells, while mitochondria-targeted antioxidants could be an effective tool for the protection of tissue from negative effects of ischemia.