Diminished NADPH transhydrogenase activity and mitochondrial redox regulation in human failing myocardium

Ubiquitin-specific peptidase 47 (USP47) regulates cutaneous oxidative injury through nicotinamide nucleotide transhydrogenase (NNT)

Human skin is daily exposed to oxidative stresses in the environment such as physical stimulation, chemical pollutants and pathogenic microorganisms, which are likely to cause skin diseases. As important post-translational modifications, protein ubiquitination and deubiquitination play crucial roles in maintaining cellular homeostasis by the proteolytic removal of oxidized proteins. We have previously reported that the expression of ubiquitin-specific protease 47 (USP47), a kind of deubiquitinating enzymes (DUBs), was significantly elevated in response to oxidative stress. However, the role of USP47 in cutaneous oxidative injury remains unclear. Usp47 wild-type (Usp47+/+) mice and Usp47 knockout (Usp47-/-) mice were used to establish two animal models of oxidative skin damage: (1) radiation- and (2) imiquimod (IMQ)-induced skin injury. Loss of Usp47 consistently aggravated mouse skin damage in vivo. Subsequently, we screened 63 upregulated and 170 downregulated proteins between the skin tissues of wild-type and Usp47-/- mice after 35 Gy electron beam radiation using proteomic analysis. Among the dysregulated proteins, nicotinamide nucleotide transhydrogenase (NNT), which has been reported as a significant regulator of oxidative stress and redox homeostasis, was further investigated in detail. Results showed that NNT was regulated by USP47 through direct ubiquitination mediated degradation and involved in the pathogenesis of cutaneous oxidative injury. Knockdown of NNT expression dramatically limited the energy production ability, with elevated mitochondrial reactive oxygen species (ROS) accumulation and increased mitochondrial membrane potential in irradiated HaCaT cells. Taken together, our present findings illustrate the critical role of USP47 in oxidative skin damage by modulating NNT degradation and mitochondrial homeostasis.

Coenzyme Q10 and nicotinamide nucleotide transhydrogenase: Sentinels for mitochondrial hydrogen peroxide signaling

Mitochondria use hydrogen peroxide (H2O2) as a mitokine for cell communication. H2O2 output for signaling depends on its rate of production and degradation, both of which are strongly affected by the redox state of the coenzyme Q10 (CoQ) pool and NADPH availability. Here, we propose the CoQ pool and nicotinamide nucleotide transhydrogenase (NNT) have evolved to be central modalities for mitochondrial H2O2 signaling. Both factors play opposing yet equally important roles in dictating H2O2 availability because they are connected to one another by two central parameters in bioenergetics: electron supply and Δp. The CoQ pool is the central point of convergence for electrons from various dehydrogenases and the electron transport chain (ETC). The increase in Δp creates a significant amount of protonic backpressure on mitochondria to promote H2O2 genesis through CoQ pool reduction. These same factors also drive the activity of NNT, which uses electrons and the Δp to eliminate H2O2. In this way, electron supply and the magnitude of the Δp manifests as a redox connection between the two sentinels, CoQ and NNT, which serve as opposing yet equally important forces required for budgeting H2O2. Taken together, CoQ and NNT are sentinels linked through mitochondrial bioenergetics to manage H2O2 availability for interorganelle and intercellular redox signaling.

Mitochondrial Integrity Is Critical in Right Heart Failure Development

Molecular processes underlying right ventricular (RV) dysfunction (RVD) and right heart failure (RHF) need to be understood to develop tailored therapies for the abatement of mortality of a growing patient population. Today, the armament to combat RHF is poor, despite the advancing identification of pathomechanistic processes. Mitochondrial dysfunction implying diminished energy yield, the enhanced release of reactive oxygen species, and inefficient substrate metabolism emerges as a potentially significant cardiomyocyte subcellular protagonist in RHF development. Dependent on the course of the disease, mitochondrial biogenesis, substrate utilization, redox balance, and oxidative phosphorylation are affected. The objective of this review is to comprehensively analyze the current knowledge on mitochondrial dysregulation in preclinical and clinical RVD and RHF and to decipher the relationship between mitochondrial processes and the functional aspects of the right ventricle (RV).

Loss of Nicotinamide nucleotide transhydrogenase sensitizes embryos to ethanol-induced neural crest and neural apoptosis via generation of reactive oxygen species

Fetal alcohol spectrum disorders (FASD) are a continuum of birth defects caused by prenatal alcohol exposure. FASD are the most common environmentally induced birth defect and are highly variable. The genetics of an individual influence the severity of their FASD phenotype. However, the genes that sensitize an individual to ethanol-induced birth defects are largely unknown. The ethanol-sensitive mouse substrain, C57/B6J, carries several known mutations including one in Nicotinamide nucleotide transhydrogenase (Nnt). Nnt is a mitochondrial transhydrogenase thought to have an important role in detoxifying reactive oxygen species (ROS) and ROS has been implicated in ethanol teratogenesis. To directly test the role of Nnt in ethanol teratogenesis, we generated zebrafish nnt mutants via CRISPR/Cas9. Zebrafish embryos were dosed with varying concentrations of ethanol across different timepoints and assessed for craniofacial malformations. We utilized a ROS assay to determine if this could be a contributing factor of these malformations. We found that exposed and unexposed mutants had higher levels of ROS compared to their wildtype counterparts. When treated with ethanol, nnt mutants experienced elevated apoptosis in the brain and neural crest, a defect that was rescued by administration of the antioxidant, N-acetyl cysteine (NAC). NAC treatment also rescued most craniofacial malformations. Altogether this research demonstrates that ethanol-induced oxidative stress leads to craniofacial and neural defects due to apoptosis in nnt mutants. This research further supports the growing body of evidence implicating oxidative stress in ethanol teratogenesis. These findings suggest that antioxidants can be used as a potential therapeutic in the treatment of FASD.

An epigenome-wide analysis of socioeconomic position and tumor DNA methylation in breast cancer patients

BACKGROUND

Disadvantaged socioeconomic position (SEP), including lower educational attainment and household income, may influence cancer risk and outcomes. We hypothesized that DNA methylation could function as an intermediary epigenetic mechanism that internalizes and reflects the biological impact of SEP.

METHODS

Based on tumor DNA methylation data from the Illumina 450 K array from 694 breast cancer patients in the Women's Circle of Health Study, we conducted an epigenome-wide analysis in relation to educational attainment and household income. Functional impact of the identified CpG sites was explored in silico using data from publicly available databases.

RESULTS

We identified 25 CpG sites associated with household income at an array-wide significance level, but none with educational attainment. Two of the top CpG sites, cg00452016 and cg01667837, were in promoter regions of NNT and GPR37, respectively, with multiple epigenetic regulatory features identified in each region. NNT is involved in β-adrenergic stress signaling and inflammatory responses, whereas GPR37 is involved in neurological and immune responses. For both loci, gene expression was inversely correlated to the levels of DNA methylation. The associations were consistent between Black and White women and did not differ by tumor estrogen receptor (ER) status.

CONCLUSIONS

In a large breast cancer patient population, we discovered evidence of the significant biological impact of household income on the tumor DNA methylome, including genes in the β-adrenergic stress and immune response pathways. Our findings support biological effects of socioeconomic status on tumor tissues, which might be relevant to cancer development and progression.

Targeting Mitochondrial Metabolism to Save the Failing Heart

Despite considerable progress in treating cardiac disorders, the prevalence of heart failure (HF) keeps growing, making it a global medical and economic burden. HF is characterized by profound metabolic remodeling, which mostly occurs in the mitochondria. Although it is well established that the failing heart is energy-deficient, the role of mitochondria in the pathophysiology of HF extends beyond the energetic aspects. Changes in substrate oxidation, tricarboxylic acid cycle and the respiratory chain have emerged as key players in regulating myocardial energy homeostasis, Ca²⁺ handling, oxidative stress and inflammation. This work aims to highlight metabolic alterations in the mitochondria and their far-reaching effects on the pathophysiology of HF. Based on this knowledge, we will also discuss potential metabolic approaches to improve cardiac function.

The Combination of Niacinamide, Vitamin C, and PDRN Mitigates Melanogenesis by Modulating Nicotinamide Nucleotide Transhydrogenase

Nicotinamide nucleotide transhydrogenase (NNT) is involved in decreasing melanogenesis through tyrosinase degradation induced by cellular redox changes. Nicotinamide is a component of coenzymes, such as NAD+, NADH, NADP+, and NADPH, and its levels are modulated by NNT. Vitamin C and polydeoxyribonucleotide (PDRN) are also known to decrease skin pigmentation. We evaluated whether a mixture of nicotinamide, vitamin C, and PDRN (NVP-mix) decreased melanogenesis by modulating mitochondrial oxidative stress and NNT expression in UV-B-irradiated animals and in an in vitro model of melanocytes treated with conditioned media (CM) from UV-B-irradiated keratinocytes. The expression of NNT, GSH/GSSG, and NADPH/NADP+ in UV-B-irradiated animal skin was significantly decreased by UV-B radiation but increased by NVP-mix treatment. The expression of NNT, GSH/GSSG, and NADPH/NADP+ ratios decreased in melanocytes after CM treatment, although they increased after NVP-mix administration. In NNT-silenced melanocytes, the GSH/GSSG and NADPH/NADP+ ratios were further decreased by CM compared with normal melanocytes. NVP-mix decreased melanogenesis signals, such as MC1R, MITF, TYRP1, and TYRP2, and decreased melanosome transfer-related signals, such as RAB32 and RAB27A, in UV-B-irradiated animal skin. NVP-mix also decreased MC1R, MITF, TYRP1, TYRP2, RAB32, and RAB27A in melanocytes treated with CM from UV-irradiated keratinocytes. The expression of MC1R and MITF in melanocytes after CM treatment was unchanged by NNT silencing. However, the expression of TYRP1, TYRP2, RAB32, and RAB27A increased in NNT-silenced melanocytes after CM treatment. NVP-mix also decreased tyrosinase activity and melanin content in UV-B-irradiated animal skin and CM-treated melanocytes. In conclusion, NVP-mix decreased mitochondrial oxidative stress by increasing NNT expression and decreased melanogenesis by decreasing MC1R/MITF, tyrosinase, TYRP1, and TYRP2.

Reversible Thiol Oxidation Increases Mitochondrial Electron Transport Complex Enzyme Activity but Not Respiration in Cardiomyocytes from Patients with End-Stage Heart Failure

Cardiomyocyte dysfunction in patients with end-stage heart failure with reduced ejection fraction (HFrEF) stems from mitochondrial dysfunction, which contributes to an energetic crisis. Mitochondrial dysfunction reportedly relates to increased markers of oxidative stress, but the impact of reversible thiol oxidation on myocardial mitochondrial function in patients with HFrEF has not been investigated. In the present study, we assessed mitochondrial function in ventricular biopsies from patients with end-stage HFrEF in the presence and absence of the thiol-reducing agent dithiothreitol (DTT). Isolated mitochondria exposed to DTT had increased enzyme activity of complexes I (p = 0.009) and III (p = 0.018) of the electron transport system, while complexes II (p = 0.630) and IV (p = 0.926) showed no changes. However, increased enzyme activity did not carry over to measurements of mitochondrial respiration in permeabilized bundles. Oxidative phosphorylation conductance (p = 0.439), maximal respiration (p = 0.312), and ADP sensitivity (p = 0.514) were unchanged by 5 mM DTT treatment. These results indicate that mitochondrial function can be modulated through reversible thiol oxidation, but other components of mitochondrial energy transfer are rate limiting in end-stage HFrEF. Optimal therapies to normalize cardiac mitochondrial respiration in patients with end-stage HFrEF may benefit from interventions to reverse thiol oxidation, which limits complex I and III activities.

Mitochondrial NAD(P)+ Transhydrogenase: From Molecular Features to Physiology and Disease

Significance: Proton-translocating NAD(P)⁺ transhydrogenase, also known as nicotinamide nucleotide transhydrogenase (NNT), catalyzes a reversible reaction coupling the protonmotive force across the inner mitochondrial membrane and hydride (H^-, a proton plus two electrons) transfer between the mitochondrial pools of NAD(H) and NADP(H). The forward NNT reaction is a source of NADPH in the mitochondrial matrix, fueling antioxidant and biosynthetic pathways with reductive potential. Despite the greater emphasis given to the net forward reaction, the reverse NNT reaction that oxidizes NADPH also occurs in physiological and pathological conditions. Recent Advances: NNT (dys)function has been linked to various metabolic pathways and disease phenotypes. Most of these findings have been based on spontaneous loss-of-function Nnt mutations found in the C57BL/6J mouse strain (Nnt^C57BL/6J mutation) and disease-causing Nnt mutations in humans. The present review focuses on recent advances based on the mouse Nnt^C57BL/6J mutation. Critical Issues: Most studies associating NNT function with disease phenotypes have been based on comparisons between different strains of inbred mice (with or without the Nnt^C57BL/6J mutation), which creates uncertainties over the actual contribution of NNT in the context of other potential genetic modifiers. Future Directions: Future research might contribute to understanding the role of NNT in pathological conditions and elucidate how NNT regulates physiological signaling through its forward and reverse reactions. The importance of NNT in redox balance and tumor cell proliferation makes it a potential target of new therapeutic strategies for oxidative-stress-mediated diseases and cancer. Antioxid. Redox Signal. 36, 864-884.

Long-Term Follow-Up of Three Family Members with a Novel NNT Pathogenic Variant Causing Primary Adrenal Insufficiency

Nicotinamide nucleotide transhydrogenase (NNT) deficiency causes primary adrenal insufficiency (PAI) and possibly some extra-adrenal manifestations. A limited number of these patients were previously described. We present the clinical and genetic characteristics of three family members with a biallelic novel pathogenic variant in the NNT gene. The patients were followed until the ages of 21.6, 20.2, and 4.2 years. PAI was diagnosed in the eldest two brothers after an Addisonian crisis and the third was diagnosed at the age of 4.5 months in the asymptomatic stage due to the genetic screening of family members. Whole exome sequencing with a targeted interpretation of variants in genes related to PAI was performed in all the patients. The urinary steroid metabolome was determined by gas chromatography–mass spectrometry in the asymptomatic patient. The three patients, who were homozygous for c.1575dup in the NNT gene, developed isolated glucocorticoid deficiency. The urinary steroid metabolome showed normal excretion of cortisol metabolites. The adolescent patients had slow pubertal progression with low–normal testicular volume, while testicular endocrine function was normal. Bone mineral density was in the range for osteopenia in both grown-up siblings. Echocardiography revealed no structural or functional heart abnormalities. This article is among the first with a comprehensive and chronologically-detailed description of patients with NNT deficiency.

Redox Control of Integrin-Mediated Hepatic Inflammation in Systemic Autoimmunity

Significance: Systemic autoimmunity affects 3%-5% of the population worldwide. Systemic lupus erythematosus (SLE) is a prototypical form of such condition, which affects 20-150 of 100,000 people globally. Liver dysfunction, defined by increased immune cell infiltration into the hepatic parenchyma, is an understudied manifestation that affects up to 20% of SLE patients. Autoimmunity in SLE involves proinflammatory lineage specification in the immune system that occurs with oxidative stress and profound changes in cellular metabolism. As the primary metabolic organ of the body, the liver is uniquely capable to encounter oxidative stress through first-pass derivatization and filtering of waste products. Recent Advances: The traffic of immune cells from their development through recirculation in the liver is guided by cell adhesion molecules (CAMs) and integrins, cell surface proteins that tightly anchor cells together. The surface expression of CAMs and integrins is regulated via endocytic traffic that is sensitive to oxidative stress. Reactive oxygen species (ROS) that elicit oxidative stress in the liver may originate from the mitochondria, the cytosol, or the cell membrane. Critical Issues: While hepatic ROS production is a source of vulnerability, it also modulates the development and function of the immune system. In turn, the liver employs antioxidant defense mechanisms to protect itself from damage that can be harnessed to serve as therapeutic mechanisms against autoimmunity, inflammation, and development of hepatocellular carcinoma. Future Directions: This review is aimed at delineating redox control of integrin signaling in the liver and checkpoints of regulatory impact that can be targeted for treatment of inflammation in systemic autoimmunity. Antioxid. Redox Signal. 36, 367-388.

Computational Modeling of Mitochondria to Understand the Dynamics of Oxidative Stress

Mitochondria are complex organelles that use catabolic metabolism to produce ATP which is the critical energy source for cell function. Oxidative phosphorylation by the electron transport chain, which receives reducing equivalents (NADH and FADH₂) from the tricarboxylic acid cycle, also produces reactive oxygen species (ROS) as a by-product at complex I and III. ROS play a significant role in health and disease. In order to better understand this process, a computational model of mitochondrial energy metabolism and the production of ROS has been developed. The model demonstrates the process regulating ROS production and removal and how different energy substrates can affect ROS production.

S-nitroso-glutathione limits apoptosis and reduces pulmonary vascular dysfunction after bypass

BACKGROUND

During hypoxia or acidosis, S-nitrosoglutathione (GSNO) has been shown to protect the cardiomyocyte from IR injury. In a randomised double blinded control study of a porcine model of paediatric CPB, we aimed to evaluate the effects of two different doses (low and high) of GSNO.

METHODS

Pigs weighing 15-20 kg were exposed to CPB with one hour of aortic cross-clamp. Prior to and during CPB, animals were randomised to receive low dose (up to 20 nmol/kg/min) GSNO (n=8), high dose (up to 60 nmol/kg/min) GSNO (n=6) or normal saline (n=7). Standard cardiac intensive care management was continued for 4 hours post-bypass.

RESULTS

There was a reduction in myocyte apoptosis after administration of GSNO (p=0.04) with no difference between low and high dose GSNO. The low dose GSNO group had lower pulmonary vascular resistance post-CPB (p=0.007). Mitochondrial Complex I activity normalised to citrate synthase activity was higher after GSNO compared to control (p=0.02), with no difference between low and high dose GSNO.

CONCLUSIONS

In a porcine model of CPB intravenous administration of GSNO limits myocardial apoptosis through preservation of mitochondrial complex I activity, and improves pulmonary vascular resistance. There appears to be a dose dependent effect to this protection.

NNT mediates redox-dependent pigmentation via a UVB- and MITF-independent mechanism

Ultraviolet (UV) light and incompletely understood genetic and epigenetic variations determine skin color. Here we describe an UV- and microphthalmia-associated transcription factor (MITF)-independent mechanism of skin pigmentation. Targeting the mitochondrial redox-regulating enzyme nicotinamide nucleotide transhydrogenase (NNT) resulted in cellular redox changes that affect tyrosinase degradation. These changes regulate melanosome maturation and, consequently, eumelanin levels and pigmentation. Topical application of small-molecule inhibitors yielded skin darkening in human skin, and mice with decreased NNT function displayed increased pigmentation. Additionally, genetic modification of NNT in zebrafish alters melanocytic pigmentation. Analysis of four diverse human cohorts revealed significant associations of skin color, tanning, and sun protection use with various single-nucleotide polymorphisms within NNT. NNT levels were independent of UVB irradiation and redox modulation. Individuals with postinflammatory hyperpigmentation or lentigines displayed decreased skin NNT levels, suggesting an NNT-driven, redox-dependent pigmentation mechanism that can be targeted with NNT-modifying topical drugs for medical and cosmetic purposes.

Mitochondrial function, dynamics and quality control in the pathophysiology of HFpEF

Heart failure (HF) is one of the leading causes of hospitalization for the adult population and a major cause of mortality worldwide. The HF syndrome is characterized by the heart's inability to supply the cardiac output required to meet the body's metabolic requirements or only at the expense of elevated filling pressures. HF without overt impairment of left ventricular ejection fraction (LVEF) was initially labeled as "diastolic HF" until recognizing the coexistence of both systolic and diastolic abnormalities in most cases. Acknowledging these findings, the preferred nomenclature is HF with preserved EF (HFpEF). This syndrome primarily affects the elderly population and is associated with a heterogeneous overlapping of comorbidities that makes its diagnosis challenging. Despite extensive research, there is still no evidence-based therapy for HFpEF, reinforcing the need for a thorough understanding of the pathophysiology underlying its onset and progression. The role of mitochondrial dysfunction in developing the pathophysiological changes that accompany HFpEF onset and progression (low-grade systemic inflammation, oxidative stress, endothelial dysfunction, and myocardial remodeling) has just begun to be acknowledged. This review summarizes our current understanding of the participation of the mitochondrial network in the pathogenesis of HFpEF, with particular emphasis on the signaling pathways involved, which may provide future therapeutic targets.

Loss of Nnt Increases Expression of Oxidative Phosphorylation Complexes in C57BL/6J Hearts

Nicotinamide nucleotide transhydrogenase (NNT) is a proton pump in the inner mitochondrial membrane that generates reducing equivalents in the form of NAPDH, which can be used for anabolic pathways or to remove reactive oxygen species (ROS). A number of studies have linked NNT dysfunction to cardiomyopathies and increased risk of atherosclerosis; however, biallelic mutations in humans commonly cause a phenotype of adrenal insufficiency, with rare occurrences of cardiac dysfunction and testicular tumours. Here, we compare the transcriptomes of the hearts, adrenals and testes from three mouse models: the C57BL/6N, which expresses NNT; the C57BL/6J, which lacks NNT; and a third mouse, expressing the wild-type NNT sequence on the C57BL/6J background. We saw enrichment of oxidative phosphorylation genes in the C57BL/B6J in the heart and adrenal, possibly indicative of an evolved response in this substrain to loss of Nnt. However, differential gene expression was mainly driven by mouse background with some changes seen in all three tissues, perhaps reflecting underlying genetic differences between the C57BL/B6J and -6N substrains.

Role of Oxidative DNA Damage and Repair in Atrial Fibrillation and Ischemic Heart Disease

Atrial fibrillation (AF) and ischemic heart disease (IHD) represent the two most common clinical cardiac diseases, characterized by angina, arrhythmia, myocardial damage, and cardiac dysfunction, significantly contributing to cardiovascular morbidity and mortality and posing a heavy socio-economic burden on society worldwide. Current treatments of these two diseases are mainly symptomatic and lack efficacy. There is thus an urgent need to develop novel therapies based on the underlying pathophysiological mechanisms. Emerging evidence indicates that oxidative DNA damage might be a major underlying mechanism that promotes a variety of cardiac diseases, including AF and IHD. Antioxidants, nicotinamide adenine dinucleotide (NAD⁺) boosters, and enzymes involved in oxidative DNA repair processes have been shown to attenuate oxidative damage to DNA, making them potential therapeutic targets for AF and IHD. In this review, we first summarize the main molecular mechanisms responsible for oxidative DNA damage and repair both in nuclei and mitochondria, then describe the effects of oxidative DNA damage on the development of AF and IHD, and finally discuss potential targets for oxidative DNA repair-based therapeutic approaches for these two cardiac diseases.

Influenza Causes MLKL-Driven Cardiac Proteome Remodeling During Convalescence

RATIONALE

Patients with and without cardiovascular diseases have been shown to be at risk of influenza-mediated cardiac complications. Recent clinical reports support the notion of a direct link between laboratory-confirmed influenza virus infections and adverse cardiac events.

OBJECTIVE

Define the molecular mechanisms underlying influenza virus-induced cardiac pathogenesis after resolution of pulmonary infection and the role of necroptosis in this process.

METHODS AND RESULTS

Hearts from wild-type and necroptosis-deficient (MLKL [mixed lineage kinase domain-like protein]-KO) mice were dissected 12 days after initial influenza A virus (IAV) infection when viral titers were undetectable in the lungs. Immunofluorescence microscopy and plaque assays showed presence of viable IAV particles in the myocardium without generation of interferon responses. Global proteome and phosphoproteome analyses using high-resolution accurate mass-based LC-MS/MS and label-free quantitation showed that the global proteome as well as the phosphoproteome profiles were significantly altered in IAV-infected mouse hearts in a strain-independent manner. Necroptosis-deficient mice had increased survival and reduced weight loss post-IAV infection, as well as increased antioxidant and mitochondrial function, indicating partial protection to IAV infection. These findings were confirmed in vitro by pretreatment of human and rat myocytes with antioxidants or necroptosis inhibitors, which blunted oxidative stress and mitochondrial damage after IAV infection.

CONCLUSIONS

This study provides the first evidence that the cardiac proteome and phosphoproteome are significantly altered post-pulmonary influenza infection. Moreover, viral particles can persist in the heart after lung clearance, altering mitochondrial function and promoting cell death without active replication and interferon responses. Finally, our findings show inhibition of necroptosis or prevention of mitochondrial damage as possible therapeutic interventions to reduce cardiac damage during influenza infections. Graphic Abstract: A graphic abstract is available for this article.

Cellular Redox State Acts as Switch to Determine the Direction of NNT-Catalyzed Reaction in Cystic Fibrosis Cells

The redox states of NAD and NADP are linked to each other in the mitochondria thanks to the enzyme nicotinamide nucleotide transhydrogenase (NNT) which, by utilizing the mitochondrial membrane potential (mΔΨ), catalyzes the transfer of redox potential between these two coenzymes, reducing one at the expense of the oxidation of the other. In order to define NNT reaction direction in CF cells, NNT activity under different redox states of cell has been investigated. Using spectrophotometric and western blotting techniques, the presence, abundance and activity level of NNT were determined. In parallel, the levels of NADPH and NADH as well as of mitochondrial and cellular ROS were also quantified. CF cells showed a 70% increase in protein expression compared to the Wt sample; however, regarding NNT activity, it was surprisingly lower in CF cells than healthy cells (about 30%). The cellular redox state, together with the low mΔΨ, pushes to drive NNT reverse reaction, at the expense of its antioxidant potential, thus consuming NADPH to support NADH production. At the same time, the reduced NNT activity prevents the NADH, produced by the reaction, from causing an explosion of ROS by the damaged respiratory chain, in accordance with the reduced level of mitochondrial ROS in NNT-loss cells. This new information on cellular bioenergetics represents an important building block for further understanding the molecular mechanisms responsible for cellular dysfunction in cystic fibrosis.

Undesirable effects of chemical inhibitors of NAD(P)+ transhydrogenase on mitochondrial respiratory function

NAD(P)⁺ transhydrogenase (NNT) is located in the inner mitochondrial membrane and catalyzes a reversible hydride transfer between NAD(H) and NADP(H) that is coupled to proton translocation between the intermembrane space and mitochondrial matrix. NNT activity has an essential role in maintaining the NADPH supply for antioxidant defense and biosynthetic pathways. In the present report, we evaluated the effects of chemical compounds used as inhibitors of NNT over the last five decades, namely, 4-chloro-7-nitrobenzofurazan (NBD-Cl), N,N'-dicyclohexylcarbodiimide (DCC), palmitoyl-CoA, palmitoyl-l-carnitine, and rhein, on NNT activity and mitochondrial respiratory function. Concentrations of these compounds that partially inhibited the forward and reverse NNT reactions in detergent-solubilized mouse liver mitochondria significantly impaired mitochondrial respiratory function, as estimated by ADP-stimulated and nonphosphorylating respiration. Among the tested compounds, NBD-Cl showed the best relationship between NNT inhibition and low impact on respiratory function. Despite this, NBD-Cl concentrations that partially inhibited NNT activity impaired mitochondrial respiratory function and significantly decreased the viability of cultured Nnt^-/- mouse astrocytes. We conclude that even though the tested compounds indeed presented inhibitory effects on NNT activity, at effective concentrations, they cause important undesirable effects on mitochondrial respiratory function and cell viability.

Nicotinamide nucleotide transhydrogenase (NNT) regulates mitochondrial ROS and endothelial dysfunction in response to angiotensin II

Endothelial dysfunction is a critical, initiating step in the development of hypertension (HTN) and mitochondrial reactive oxygen species (ROS) are important contributors to endothelial dysfunction. Genome-wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) in the nicotinamide nucleotide transhydrogenase (Nnt) gene that are associated with endothelial dysfunction and increased risk for HTN. NNT is emerging as an important enzyme that regulates mitochondrial NADPH levels and mitochondrial redox balance by supporting the thiol dependent peroxidase systems in the mitochondria. We have previously shown that the absence of NNT in C57Bl/6J animals promotes a more severe hypertensive phenotype through reductions in ^•NO and endothelial dependent vessel dilation. However, the impact of NNT on human endothelial cell function remains unclear. We utilized NNT directed shRNA in human aortic endothelial cells to test the hypothesis that NNT critically regulates mitochondrial redox balance and endothelial function in response to angiotensin II (Ang II). We demonstrate that NNT expression and activity are elevated in response to the mitochondrial dysfunction and oxidative stress associated with Ang II treatment. Knockdown of NNT led to a significant elevation of mitochondrial ROS production and impaired glutathione peroxidase and glutathione reductase activities associated with a reduction in the NADPH/NADP⁺ ratio. Loss of NNT also promoted mitochondrial dysfunction, disruption of the mitochondrial membrane potential, and impaired ATP production in response to Ang II. Finally, we observed that, while the loss of NNT augmented eNOS phosphorylation at Ser¹¹⁷⁷, neither eNOS activity nor nitric oxide production were similarly increased. The results from these studies clearly demonstrate that NNT is critical for the maintenance of mitochondrial redox balance and mitochondrial function. Loss of NNT and disruption of redox balance leads to oxidative stress that compromises eNOS activity that could have a profound effect on the endothelium dependent regulation of vascular tone.

Lack of mitochondrial NADP(H)-transhydrogenase expression in macrophages exacerbates atherosclerosis in hypercholesterolemic mice

The atherosclerosis prone LDL receptor knockout mice (Ldlr-/-, C57BL/6J background) carry a deletion of the NADP(H)-transhydrogenase gene (Nnt) encoding the mitochondrial enzyme that catalyzes NADPH synthesis. Here we hypothesize that both increased NADPH consumption (due to increased steroidogenesis) and decreased NADPH generation (due to Nnt deficiency) in Ldlr-/- mice contribute to establish a macrophage oxidative stress and increase atherosclerosis development. Thus, we compared peritoneal macrophages and liver mitochondria from three C57BL/6J mice lines: Ldlr and Nnt double mutant, single Nnt mutant and wild-type. We found increased oxidants production in both mitochondria and macrophages according to a gradient: double mutant > single mutant > wild-type. We also observed a parallel up-regulation of mitochondrial biogenesis (PGC1a, TFAM and respiratory complexes levels) and inflammatory (iNOS, IL6 and IL1b) markers in single and double mutant macrophages. When exposed to modified LDL, the single and double mutant cells exhibited significant increases in lipid accumulation leading to foam cell formation, the hallmark of atherosclerosis. Nnt deficiency cells showed up-regulation of CD36 and down-regulation of ABCA1 transporters what may explain lipid accumulation in macrophages. Finally, Nnt wild-type bone marrow transplantation into LDLr-/- mice resulted in reduced diet-induced atherosclerosis. Therefore, Nnt plays a critical role in the maintenance of macrophage redox, inflammatory and cholesterol homeostasis, which is relevant for delaying the atherogenesis process.

Differential suitability of reactive oxygen species and the role of glutathione in regulating paradoxical behavior in gliomas: A mathematical perspective

Manipulative strategies of ROS in cancer are often exhibited as changes in the redox and thiol ratio of the cells. Cellular responses to oxidative insults are generated in response to these changes which are triggered due to the rerouting of the metabolic framework to maintain survival under stress. However, mechanisms of these metabolic re-routing are not clearly understood and remained debatable. In the present work, we have designed a context-based dynamic metabolic model to establish that the coordinated functioning of glutathione peroxidase (GTHP), glutathione oxidoreductase (GTHO) and NADPH oxidase (NOX) is crucial in determining cancerous transformation, specifically in gliomas. Further, we propose that the puzzling duality of ROS (represented by changes in h₂o₂ in the present model) in exhibiting varying cellular fates can be determined by considering simultaneous changes in nadph/nadp⁺ and gsh/gssg that occur during the reprogramming of metabolic reactions. This will be helpful in determining the pro-apoptotic or anti-apoptotic fate of gliomas and can be useful in designing effective pro-oxidant and/or anti-oxidant therapeutic approaches against gliomas.

The interplay between oxidative stress and bioenergetic failure in neuropsychiatric illnesses: can we explain it and can we treat it?

Nitro-oxidative stress and lowered antioxidant defences play a key role in neuropsychiatric disorders such as major depression, bipolar disorder and schizophrenia. The first part of this paper details mitochondrial antioxidant mechanisms and their importance in reactive oxygen species (ROS) detoxification, including details of NO networks, the roles of H₂O₂ and the thioredoxin/peroxiredoxin system, and the relationship between mitochondrial respiration and NADPH production. The second part highlights and identifies the causes of the multiple pathological sequelae arising from self-amplifying increases in mitochondrial ROS production and bioenergetic failure. Particular attention is paid to NAD⁺ depletion as a core cause of pathology; detrimental effects of raised ROS and reactive nitrogen species on ATP and NADPH generation; detrimental effects of oxidative and nitrosative stress on the glutathione and thioredoxin systems; and the NAD⁺-induced signalling cascade, including the roles of SIRT1, SIRT3, PGC-1α, the FOXO family of transcription factors, Nrf1 and Nrf2. The third part discusses proposed therapeutic interventions aimed at mitigating such pathology, including the use of the NAD⁺ precursors nicotinamide mononucleotide and nicotinamide riboside, both of which rapidly elevate levels of NAD⁺ in the brain and periphery following oral administration; coenzyme Q₁₀ which, when given with the aim of improving mitochondrial function and reducing nitro-oxidative stress in the brain, may be administered via the use of mitoquinone, which is in essence ubiquinone with an attached triphenylphosphonium cation; and N-acetylcysteine, which is associated with improved mitochondrial function in the brain and produces significant decreases in oxidative and nitrosative stress in a dose-dependent manner.

Comparing Early Eukaryotic Integration of Mitochondria and Chloroplasts in the Light of Internal ROS Challenges: Timing is of the Essence

When trying to reconstruct the evolutionary trajectories during early eukaryogenesis, one is struck by clear differences in the developments of two organelles of endosymbiotic origin: the mitochondrion and the chloroplast. From a symbiogenic perspective, eukaryotic development can be interpreted as a process in which many of the defining eukaryotic characteristics arose as a result of mutual adaptions of both prokaryotes (an archaeon and a bacterium) involved. This implies that many steps during the bacterium-to-mitochondrion transition trajectory occurred in an intense period of dramatic and rapid changes. In contrast, the subsequent cyanobacterium-to-chloroplast development in a specific eukaryotic subgroup, leading to the photosynthetic lineages, occurred in a full-fledged eukaryote. The commonalities and differences in the two trajectories shed an interesting light on early, and ongoing, eukaryotic evolutionary driving forces, especially endogenous reactive oxygen species (ROS) formation. Differences between organellar ribosomes, changes to the electron transport chain (ETC) components, and mitochondrial codon reassignments in nonplant mitochondria can be understood when mitochondrial ROS formation, e.g., during high energy consumption in heterotrophs, is taken into account.IMPORTANCE The early eukaryotic evolution was deeply influenced by the acquisition of two endosymbiotic organelles - the mitochondrion and the chloroplast. Here we discuss the possibly important role of reactive oxygen species in these processes.

A deeper understanding of intestinal organoid metabolism revealed by combining fluorescence lifetime imaging microscopy (FLIM) and extracellular flux analyses

Stem cells and the niche in which they reside feature a complex microenvironment with tightly regulated homeostasis, cell-cell interactions and dynamic regulation of metabolism. A significant number of organoid models has been described over the last decade, yet few methodologies can enable single cell level resolution analysis of the stem cell niche metabolic demands, in real-time and without perturbing integrity. Here, we studied the redox metabolism of Lgr5-GFP intestinal organoids by two emerging microscopy approaches based on luminescence lifetime measurement - fluorescence-based FLIM for NAD(P)H, and phosphorescence-based PLIM for real-time oxygenation. We found that exposure of stem (Lgr5-GFP) and differentiated (no GFP) cells to high and low glucose concentrations resulted in measurable shifts in oxygenation and redox status. NAD(P)H-FLIM and O2-PLIM both indicated that at high 'basal' glucose conditions, Lgr5-GFP cells had lower activity of oxidative phosphorylation when compared with cells lacking Lgr5. However, when exposed to low (0.5 mM) glucose, stem cells utilized oxidative metabolism more dynamically than non-stem cells. The high heterogeneity of complex 3D architecture and energy production pathways of Lgr5-GFP organoids were also confirmed by the extracellular flux (XF) analysis. Our data reveals that combined analysis of NAD(P)H-FLIM and organoid oxygenation by PLIM represents promising approach for studying stem cell niche metabolism in a live readout.

Discovery proteomics in aging human skeletal muscle finds change in spliceosome, immunity, proteostasis and mitochondria

A decline of skeletal muscle strength with aging is a primary cause of mobility loss and frailty in older persons, but the molecular mechanisms of such decline are not understood. Here, we performed quantitative proteomic analysis from skeletal muscle collected from 58 healthy persons aged 20 to 87 years. In muscle from older persons, ribosomal proteins and proteins related to energetic metabolism, including those related to the TCA cycle, mitochondria respiration, and glycolysis, were underrepresented, while proteins implicated in innate and adaptive immunity, proteostasis, and alternative splicing were overrepresented. Consistent with reports in animal models, older human muscle was characterized by deranged energetic metabolism, a pro-inflammatory environment and increased proteolysis. Changes in alternative splicing with aging were confirmed by RNA-seq analysis. We propose that changes in the splicing machinery enables muscle cells to respond to a rise in damage with aging.

As humans age, their muscles become weaker, making it increasingly harder for them to move, a condition known as sarcopenia. Analyzing old muscles in other animals revealed that they produce energy inefficiently, they destroy more proteins than younger muscles, and they have high levels of molecules that cause inflammation. These characteristics may be involved in causing muscle weakness.

Proteomics is the study of proteins, the molecules that play many roles in keeping the body working: for example, they accelerate chemical reactions, participate in copying DNA and help cells respond to stimuli. Using proteomics, it is possible to examine a large number of the different proteins in a tissue, which can provide information about the state of that tissue. Ubaida-Mohien et al. used this approach to answer the question of why muscles become weaker with age.

First, they analyzed the levels of all the proteins found in skeletal muscle collected from 58 healthy volunteers between 20 and 87 years of age. This revealed that the muscles of older people have fewer copies of the proteins that make up ribosomes – the cellular machines that produce new proteins – and fewer proteins involved in providing the cell with chemical energy. In contrast, proteins implicated in the immune system, in the maintenance of existing proteins, and in processing other molecules called RNAs were more abundant in older muscles.

Ubaida-Mohien et al. then looked more closely at changes involving RNA processing. Cells make proteins by copying DNA sequences into an RNA template and using this template to instruct the ribosomes on how to make the specific protein. Before the RNA can be ‘read’ by a ribosome, however, some parts must be cut out and others added, which can lead to different versions of the final RNA, also known as alternative transcripts.

In order to check whether the difference in the levels of proteins that process RNAs was affecting the RNAs being produced, Ubaida-Mohien et al. extracted the RNAs from older and younger muscles and compared them. This showed that the RNA in older people had more alternative transcripts, confirming that the change in protein levels was having downstream effects.

Currently, it is not possible to prevent or delay the loss of muscle strength associated with aging. Understanding how the protein make-up of muscles changes as humans grow older may help find new ways to prevent and perhaps even reverse this decline.

Adaptations in Protein Expression and Regulated Activity of Pyruvate Dehydrogenase Multienzyme Complex in Human Systolic Heart Failure

Pyruvate dehydrogenase (PDH) complex, a multienzyme complex at the nexus of glycolytic and Krebs cycles, provides acetyl-CoA to the Krebs cycle and NADH to complex I thus supporting a critical role in mitochondrial energy production and cellular survival. PDH activity is regulated by pyruvate dehydrogenase phosphatases (PDP1, PDP2), pyruvate dehydrogenase kinases (PDK 1-4), and mitochondrial pyruvate carriers (MPC1, MPC2). As NADH-dependent oxidative phosphorylation is diminished in systolic heart failure, we tested whether the left ventricular myocardium (LV) from end-stage systolic adult heart failure patients (n = 26) exhibits altered expression of PDH complex subunits, PDK, MPC, PDP, and PDH complex activity, compared to LV from nonfailing donor hearts (n = 21). Compared to nonfailing LV, PDH activity and relative expression levels of E2, E3bp, E1α, and E1β subunits were greater in LV failure. PDK4, MPC1, and MPC2 expressions were decreased in failing LV, whereas PDP1, PDP2, PDK1, and PDK2 expressions did not differ between nonfailing and failing LV. In order to examine PDK4 further, donor human LV cardiomyocytes were induced in culture to hypertrophy with 0.1 μM angiotensin II and treated with PDK inhibitors (0.2 mM dichloroacetate, or 5 mM pyruvate) or activators (0.6 mM NADH plus 50 μM acetyl CoA). In isolated hypertrophic cardiomyocytes in vitro, PDK activators and inhibitors increased and decreased PDK4, respectively. In conclusion, in end-stage failing hearts, greater expression of PDH proteins and decreased expression of PDK4, MPC1, and MPC2 were evident with higher rates of PDH activity. These adaptations support sustained capacity for PDH to facilitate glucose metabolism in the face of other failing bioenergetic pathways.

Control of the NADPH supply and GSH recycling for oxidative stress management in hepatoma and liver mitochondria

To unveil what controls mitochondrial ROS detoxification, the NADPH supply and GSH/GSSG recycling for oxidative stress management were analyzed in cancer and non-cancer mitochondria. Therefore, proteomic and kinetomic analyses were carried out of the mitochondrial (i) NADPH producing and (ii) GSH/GSSG recycling enzymes associated to oxidative stress management. The protein contents of the eight enzymes analyzed were similar or even higher in AS-30D rat hepatoma mitochondria (HepM) than in rat liver (RLM) and rat heart (RHM) mitochondria, suggesting that the NADPH/GSH/ROS pathway was fully functional in cancer mitochondria. The Vmax values of IDH-2 were much greater than those of GDH, TH and ME, suggesting that IDH-2 is the predominant NADPH producer in the three mitochondrial types; in fact, the GDH reverse reaction was favored. The Vmax values of GR and GPx were lower in HepM than in RLM, suggesting that the oxidative stress management is compromised in cancer mitochondria. The Km values of IDH-2, GR and GPx were all similar among the different mitochondrial types. Kinetic modeling revealed that the oxidative stress management was mainly controlled by GR, GPx and IDH. Modeling and experimentation also revealed that, due to their higher IDH-2 activity and lower GPx activity presumably by acetylation, HepM (i) showed higher steady-state NADPH levels; (ii) required greater peroxide concentrations to achieve reliable steady-state fluxes and metabolite concentration; and (iii) endured higher peroxide concentrations without collapsing their GSH/GSSG ratios. Then, to specifically prompt lower GSH/GSSG ratios under oxidative stress thus compromising cancer mitochondria functioning, GPx should be re-activated.

Aberrant GSH reductase and NOX activities concur with defective CFTR to pro-oxidative imbalance in cystic fibrosis airways

Cystic fibrosis (CF) is associated to impaired Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) channel also causing decreased glutathione (GSH) secretion, defective airway bacterial clearance and inflammation. Here we checked the main ROS-producing and ROS-scavenging enzymes as potential additional factors involved in CF pathogenesis. We found that CFBE41o-cells, expressing F508del CFTR, have increased NADPH oxidase (NOX) activity and expression level, mainly responsible of the increased ROS production, and decreased glutathione reductase (GR) activity, not dependent on GR protein level decrease. Furthermore, defective CFTR proved to cause both extracellular and intracellular GSH level decrease, probably by reducing the amount of extracellular GSH-derived cysteine required for cytosolic GSH synthesis. Importantly, we provide evidence that defective CFTR and NOX/GR activity imbalance both contribute to NADPH and GSH level decrease and ROS overproduction in CF cells.

Enhanced Redox State and Efficiency of Glucose Oxidation With miR Based Suppression of Maladaptive NADPH-Dependent Malic Enzyme 1 Expression in Hypertrophied Hearts

RATIONALE

Metabolic remodeling in hypertrophic hearts includes inefficient glucose oxidation via increased anaplerosis fueled by pyruvate carboxylation. Pyruvate carboxylation to malate through elevated ME1 (malic enzyme 1) consumes NADPH necessary for reduction of glutathione and maintenance of intracellular redox state.

OBJECTIVE

To elucidate upregulated ME1 as a potential maladaptive mechanism for inefficient glucose oxidation and compromised redox state in hypertrophied hearts.

METHODS AND RESULTS

ME1 expression was selectively inhibited, in vivo, via non-native miR-ME1 (miRNA specific to ME1) in pressure-overloaded rat hearts. Rats subjected to transverse aortic constriction (TAC) or Sham surgery received either miR-ME1 or PBS. Effects of ME1 suppression on anaplerosis and reduced glutathione (GSH) content were studied in isolated hearts supplied ¹³C-enriched substrate: palmitate, glucose, and lactate. Human myocardium collected from failing and nonfailing hearts during surgery enabled RT-qPCR confirmation of elevated ME1 gene expression in clinical heart failure versus nonfailing human hearts (P<0.04). TAC induced elevated ME1 content, but ME1 was lowered in hearts infused with miR-ME1 versus PBS. Although Sham miR-ME1 hearts showed no further reduction of inherently low anaplerosis in normal heart, miR-ME1 reduced anaplerosis in TAC to baseline: TAC miR-ME1=0.034±0.004; TAC PBS=0.081±0.005 (P<0.01). Countering elevated anaplerosis in TAC shifted pyruvate toward oxidation in the tricarboxylic acid cycle. Importantly, via the link to NADPH consumption by pyruvate carboxylation, ME1 suppression in TAC restored GSH content, reduced lactate production, and ultimately improved contractility.

CONCLUSIONS

A maladaptive increase in anaplerosis via ME1 in TAC is associated with reduced GSH content. Suppressing increased ME1 expression in hypertrophied rat hearts, which is also elevated in failing human hearts, reduced pyruvate carboxylation thereby normalizing anaplerosis, restoring GSH content, and reducing lactate accumulation. Reducing ME1 induced favorable metabolic shifts for carbohydrate oxidation, improving intracellular redox state and enhanced cardiac performance in pathological hypertrophy.

NAD(H) and NADP(H) Redox Couples and Cellular Energy Metabolism

SIGNIFICANCE

The nicotinamide adenine dinucleotide (NAD⁺)/reduced NAD⁺ (NADH) and NADP⁺/reduced NADP⁺ (NADPH) redox couples are essential for maintaining cellular redox homeostasis and for modulating numerous biological events, including cellular metabolism. Deficiency or imbalance of these two redox couples has been associated with many pathological disorders. Recent Advances: Newly identified biosynthetic enzymes and newly developed genetically encoded biosensors enable us to understand better how cells maintain compartmentalized NAD(H) and NADP(H) pools. The concept of redox stress (oxidative and reductive stress) reflected by changes in NAD(H)/NADP(H) has increasingly gained attention. The emerging roles of NAD⁺-consuming proteins in regulating cellular redox and metabolic homeostasis are active research topics.

CRITICAL ISSUES

The biosynthesis and distribution of cellular NAD(H) and NADP(H) are highly compartmentalized. It is critical to understand how cells maintain the steady levels of these redox couple pools to ensure their normal functions and simultaneously avoid inducing redox stress. In addition, it is essential to understand how NAD(H)- and NADP(H)-utilizing enzymes interact with other signaling pathways, such as those regulated by hypoxia-inducible factor, to maintain cellular redox homeostasis and energy metabolism.

FUTURE DIRECTIONS

Additional studies are needed to investigate the inter-relationships among compartmentalized NAD(H)/NADP(H) pools and how these two dinucleotide redox couples collaboratively regulate cellular redox states and cellular metabolism under normal and pathological conditions. Furthermore, recent studies suggest the utility of using pharmacological interventions or nutrient-based bioactive NAD⁺ precursors as therapeutic interventions for metabolic diseases. Thus, a better understanding of the cellular functions of NAD(H) and NADP(H) may facilitate efforts to address a host of pathological disorders effectively. Antioxid. Redox Signal. 28, 251-272.

Nicotinamide nucleotide transhydrogenase (NNT) deficiency dysregulates mitochondrial retrograde signaling and impedes proliferation

To study the physiological roles of NADH and NADPH homeostasis in cancer, we studied the effect of NNT knockdown on physiology of SK-Hep1 cells. NNT knockdown cells show limited abilities to maintain NAD⁺ and NADPH levels and have reduced proliferation and tumorigenicity. There is an increased dependence of energy production on oxidative phosphorylation. Studies with stable isotope tracers have revealed that under the new steady-state metabolic condition, the fluxes of TCA and glycolysis decrease while that of reductive carboxylation increases. Increased [α-ketoglutarate]/[succinate] ratio in NNT-deficient cells results in decrease in HIF-1α level and expression of HIF-1α regulated genes. Reduction in NADPH level leads to repression of HDAC1 activity and an increase in p53 acetylation. These findings suggest that NNT is essential to homeostasis of NADH and NADPH pools, anomalies of which affect HIF-1α- and HDAC1-dependent pathways, and hence retrograde response of mitochondria.

C57BL/6 Substrains Exhibit Different Responses to Acute Carbon Tetrachloride Exposure: Implications for Work Involving Transgenic Mice

Biological differences exist between strains of laboratory mice, and it is becoming increasingly evident that there are differences between substrains. In the C57BL/6 mouse, the primary substrains are called 6J and 6N. Previous studies have demonstrated that 6J and 6N mice differ in response to many experimental models of human disease. The aim of our study was to determine if differences exist between 6J and 6N mice in terms of their response to acute carbon tetrachloride (CCl4) exposure. Mice were given CCl4 once and were euthanized 12 to 96 h later. Relative to 6J mice, we found that 6N mice had increased liver injury but more rapid repair. This was because of the increased speed with which necrotic hepatocytes were removed in 6N mice and was directly related to increased recruitment of macrophages to the liver. In parallel, enhanced liver regeneration was observed in 6N relative to 6J mice. Hepatic stellate cell activation occurred earlier in 6N mice, but there was no difference in matrix metabolism between substrains. Taken together, these data demonstrate specific and significant differences in how the C57BL/6 substrains respond to acute CCl4, which has important implications for all mouse studies utilizing this model.

Dissecting the role of myeloid and mesenchymal fibroblasts in age-dependent cardiac fibrosis

Aging is associated with increased cardiac interstitial fibrosis and diastolic dysfunction. Our previous study has shown that mesenchymal fibroblasts in the C57BL/6J (B6J) aging mouse heart acquire an inflammatory phenotype and produce higher levels of chemokines. Monocyte chemoattractant protein-1 (MCP-1) secreted by these aged fibroblasts promotes leukocyte uptake into the heart. Some of the monocytes that migrate into the heart polarize into M2a macrophages/myeloid fibroblasts. The number of activated mesenchymal fibroblasts also increases with age, and consequently, both sources of fibroblasts contribute to fibrosis. Here, we further investigate mechanisms by which inflammation influences activation of myeloid and mesenchymal fibroblasts and their collagen synthesis. We examined cardiac fibrosis and heart function in three aged mouse strains; we compared C57BL/6J (B6J) with two other strains that have reduced inflammation via different mechanisms. Aged C57BL/6N (B6N) hearts are protected from oxidative stress and fibroblasts derived from them do not develop an inflammatory phenotype. Likewise, these mice have preserved diastolic function. Aged MCP-1 null mice on the B6J background (MCP-1KO) are protected from elevated leukocyte infiltration; they develop moderate but reduced fibrosis and diastolic dysfunction. Based on these studies, we further delineated the role of resident versus monocyte-derived M2a macrophages in myeloid-dependent fibrosis and found that the number of monocyte-derived M2a (but not resident) macrophages correlates with age-related fibrosis and diastolic dysfunction. In conclusion, we have found that ROS and inflammatory mediators are necessary for activation of fibroblasts of both developmental origins, and prevention of either led to better functional outcomes.

Analyses of caspase-1-regulated transcriptomes in various tissues lead to identification of novel IL-1β-, IL-18- and sirtuin-1-independent pathways

BACKGROUND

It is well established that caspase-1 exerts its biological activities through its downstream targets such as IL-1β, IL-18, and Sirt-1. The microarray datasets derived from various caspase-1 knockout tissues indicated that caspase-1 can significantly impact the transcriptome. However, it is not known whether all the effects exerted by caspase-1 on transcriptome are mediated only by its well-known substrates. Therefore, we hypothesized that the effects of caspase-1 on transcriptome may be partially independent from IL-1β, IL-18, and Sirt-1.

METHODS

To determine new global and tissue-specific gene regulatory effects of caspase-1, we took novel microarray data analysis approaches including Venn analysis, cooperation analysis, and meta-analysis methods. We used these statistical methods to integrate different microarray datasets conducted on different caspase-1 knockout tissues and datasets where caspase-1 downstream targets were manipulated.

RESULTS

We made the following important findings: (1) Caspase-1 exerts its regulatory effects on the majority of genes in a tissue-specific manner; (2) Caspase-1 regulatory genes partially cooperates with genes regulated by sirtuin-1 during organ injury and inflammation in adipose tissue but not in the liver; (3) Caspase-1 cooperates with IL-1β in regulating less than half of the genes involved in cardiovascular disease, organismal injury, and cancer in mouse liver; (4) The meta-analysis identifies 40 caspase-1 globally regulated genes across tissues, suggesting that caspase-1 globally regulates many novel pathways; and (5) The meta-analysis identified new cooperatively and non-cooperatively regulated genes in caspase-1, IL-1β, IL-18, and Sirt-1 pathways.

CONCLUSIONS

Our findings suggest that caspase-1 regulates many new signaling pathways potentially via its known substrates and also via transcription factors and other proteins that are yet to be identified.

Cardiac Ryanodine Receptor (Ryr2)-mediated Calcium Signals Specifically Promote Glucose Oxidation via Pyruvate Dehydrogenase

Cardiac ryanodine receptor (Ryr2) Ca²⁺ release channels and cellular metabolism are both disrupted in heart disease. Recently, we demonstrated that total loss of Ryr2 leads to cardiomyocyte contractile dysfunction, arrhythmia, and reduced heart rate. Acute total Ryr2 ablation also impaired metabolism, but it was not clear whether this was a cause or consequence of heart failure. Previous in vitro studies revealed that Ca²⁺ flux into the mitochondria helps pace oxidative metabolism, but there is limited in vivo evidence supporting this concept. Here, we studied heart-specific, inducible Ryr2 haploinsufficient (cRyr2Δ50) mice with a stable 50% reduction in Ryr2 protein. This manipulation decreased the amplitude and frequency of cytosolic and mitochondrial Ca²⁺ signals in isolated cardiomyocytes, without changes in cardiomyocyte contraction. Remarkably, in the context of well preserved contractile function in perfused hearts, we observed decreased glucose oxidation, but not fat oxidation, with increased glycolysis. cRyr2Δ50 hearts exhibited hyperphosphorylation and inhibition of pyruvate dehydrogenase, the key Ca²⁺-sensitive gatekeeper to glucose oxidation. Metabolomic, proteomic, and transcriptomic analyses revealed additional functional networks associated with altered metabolism in this model. These results demonstrate that Ryr2 controls mitochondrial Ca²⁺ dynamics and plays a specific, critical role in promoting glucose oxidation in cardiomyocytes. Our findings indicate that partial RYR2 loss is sufficient to cause metabolic abnormalities seen in heart disease.

Three-Dimensional Model of Human Nicotinamide Nucleotide Transhydrogenase (NNT) and Sequence-Structure Analysis of its Disease-Causing Variations

Defective mitochondrial proteins are emerging as major contributors to human disease. Nicotinamide nucleotide transhydrogenase (NNT), a widely expressed mitochondrial protein, has a crucial role in the defence against oxidative stress. NNT variations have recently been reported in patients with familial glucocorticoid deficiency (FGD) and in patients with heart failure. Moreover, knockout animal models suggest that NNT has a major role in diabetes mellitus and obesity. In this study, we used experimental structures of bacterial transhydrogenases to generate a structural model of human NNT (H‐NNT). Structure‐based analysis allowed the identification of H‐NNT residues forming the NAD binding site, the proton canal and the large interaction site on the H‐NNT dimer. In addition, we were able to identify key motifs that allow conformational changes adopted by domain III in relation to its functional status, such as the flexible linker between domains II and III and the salt bridge formed by H‐NNT Arg882 and Asp830. Moreover, integration of sequence and structure data allowed us to study the structural and functional effect of deleterious amino acid substitutions causing FGD and left ventricular non‐compaction cardiomyopathy. In conclusion, interpretation of the function–structure relationship of H‐NNT contributes to our understanding of mitochondrial disorders.

NNT mutations: a cause of primary adrenal insufficiency, oxidative stress and extra-adrenal defects

OBJECTIVE

Nicotinamide nucleotide transhydrogenase (NNT), one of the several genes recently discovered in familial glucocorticoid deficiencies (FGD), is involved in reactive oxygen species detoxification, suggesting that extra-adrenal manifestations may occur, due to the sensitivity to oxidative stress of other organs rich in mitochondria. Here, we sought to identify NNT mutations in a large cohort of patients with primary congenital adrenal insufficiency without molecular etiology and evaluate the degree of adrenal insufficiency and onset of extra-adrenal damages.

METHODS

Sanger or massive parallel sequencing of NNT and patient monitoring.

RESULTS

Homozygous or compound heterozygous NNT mutations occurred frequently (26%, 13 unrelated families, 18 patients) in our cohort. Seven new mutations were identified: p.Met337Val, p.Ala863Glu, c.3G>A (p.Met1?), p.Arg129*, p.Arg379*, p.Val665Profs*29 and p.Ala704Serfs*19. The most frequent mutation, p.Arg129*, was found recurrently in patients from Algeria. Most patients were diagnosed belatedly (8-18 months) after presenting severe hypoglycemia; others experiencing stress conditions were diagnosed earlier. Five patients also had mineralocorticoid deficiency at onset. One patient had congenital hypothyroidism and two cryptorchidism. In follow-up, we noticed gonadotropic and genitalia impairments (precocious puberty, testicular inclusions, interstitial Leydig cell adenoma, azoospermia), hypothyroidism and hypertrophic cardiomyopathy. Intrafamilial phenotype heterogeneity was also observed.

CONCLUSIONS

NNT should be sequenced, not only in FGD, but also in all primary adrenal insufficiencies for which the most frequent etiologies have been ruled out. As NNT is involved in oxidative stress, careful follow-up is needed to evaluate mineralocorticoid biosynthesis extent, and gonadal, heart and thyroid function.

Cigarette toxicity triggers Leber's hereditary optic neuropathy by affecting mtDNA copy number, oxidative phosphorylation and ROS detoxification pathways

Leber's hereditary optic neuropathy (LHON), the most frequent mitochondrial disease, is associated with mitochondrial DNA (mtDNA) point mutations affecting Complex I subunits, usually homoplasmic. This blinding disorder is characterized by incomplete penetrance, possibly related to several genetic modifying factors. We recently reported that increased mitochondrial biogenesis in unaffected mutation carriers is a compensatory mechanism, which reduces penetrance. Also, environmental factors such as cigarette smoking have been implicated as disease triggers. To investigate this issue further, we first assessed the relationship between cigarette smoke and mtDNA copy number in blood cells from large cohorts of LHON families, finding that smoking was significantly associated with the lowest mtDNA content in affected individuals. To unwrap the mechanism of tobacco toxicity in LHON, we exposed fibroblasts from affected individuals, unaffected mutation carriers and controls to cigarette smoke condensate (CSC). CSC decreased mtDNA copy number in all cells; moreover, it caused significant reduction of ATP level only in mutated cells including carriers. This implies that the bioenergetic compensation in carriers is hampered by exposure to smoke derivatives. We also observed that in untreated cells the level of carbonylated proteins was highest in affected individuals, whereas the level of several detoxifying enzymes was highest in carriers. Thus, carriers are particularly successful in reactive oxygen species (ROS) scavenging capacity. After CSC exposure, the amount of detoxifying enzymes increased in all cells, but carbonylated proteins increased only in LHON mutant cells, mostly from affected individuals. All considered, it appears that exposure to smoke derivatives has a more deleterious effect in affected individuals, whereas carriers are the most efficient in mitigating ROS rather than recovering bioenergetics. Therefore, the identification of genetic modifiers that modulate LHON penetrance must take into account also the exposure to environmental triggers such as tobacco smoke.

Reversal of Mitochondrial Transhydrogenase Causes Oxidative Stress in Heart Failure

Mitochondrial reactive oxygen species (ROS) play a central role in most aging-related diseases. ROS are produced at the respiratory chain that demands NADH for electron transport and are eliminated by enzymes that require NADPH. The nicotinamide nucleotide transhydrogenase (Nnt) is considered a key antioxidative enzyme based on its ability to regenerate NADPH from NADH. Here, we show that pathological metabolic demand reverses the direction of the Nnt, consuming NADPH to support NADH and ATP production, but at the cost of NADPH-linked antioxidative capacity. In heart, reverse-mode Nnt is the dominant source for ROS during pressure overload. Due to a mutation of the Nnt gene, the inbred mouse strain C57BL/6J is protected from oxidative stress, heart failure, and death, making its use in cardiovascular research problematic. Targeting Nnt-mediated ROS with the tetrapeptide SS-31 rescued mortality in pressure overload-induced heart failure and could therefore have therapeutic potential in patients with this syndrome.

Different Blood Cell-Derived Transcriptome Signatures in Cows Exposed to Vaccination Pre- or Postpartum

Periparturient cows have been found to reveal immunosuppression, frequently associated with increased susceptibility to uterine and mammary infections. To improve understanding of the causes and molecular regulatory mechanisms accounting for this phenomenon around calving, we examined the effect of an antigen challenge on gene expression modulation on cows prior to (BC) or after calving (AC) using whole transcriptome sequencing (RNAseq). The transcriptome analysis of the cows’ blood identified a substantially higher number of loci affected in BC cows (2,235) in response to vaccination compared to AC cows (208) and revealed a divergent transcriptional profile specific for each group. In BC cows, a variety of loci involved in immune defense and cellular signaling processes were transcriptionally activated, whereas protein biosynthesis and posttranslational processes were tremendously impaired in response to vaccination. Furthermore, energy metabolism in the blood cells of BC cows was shifted from oxidative phosphorylation to the glycolytic system. In AC cows, the number and variety of regulated pathways involved in immunomodulation and maintenance of immnunocompetence are considerably lower after vaccination, and upregulation of arginine degradation was suggested as an immunosuppressive mechanism. Elevated transcript levels of erythrocyte-specific genes involved in gas exchange processes were a specific transcriptional signature in AC cows pointing to hematopoiesis activation. The divergent and substantially lower magnitude of transcriptional modulation in response to vaccination in AC cows provides evidence for a suppressed immune capacity of early lactating cows on the molecular level and demonstrates that an efficient immune response of cows is related to their physiological and metabolic status.

Mitochondrion as a Target for Heart Failure Therapy- Role of Protein Lysine Acetylation

Heart failure is a leading cause of death worldwide. Despite medical advances, the dismal prognosis of heart failure has not been improved. The heart is a high energy-demanding organ. Impairments of cardiac energy metabolism and mitochondrial function are intricately linked to cardiac dysfunction. Mitochondrial dysfunction contributes to impaired myocardial energetics and increased oxidative stress in heart failure, and the opening of mitochondrial permeability transition pore triggers cell death and myocardial remodeling. Therefore, there has been growing interest in targeting mitochondria and metabolism for heart failure therapy. Recent developments suggest that mitochondrial protein lysine acetylation modulates the sensitivity of the heart to stress and hence the propensity to heart failure. This article reviews the role of mitochondrial dysfunction in heart failure, with a special emphasis on the regulation of the nicotinamide adenine dinucleotide (NAD(+)/NADH) ratio and sirtuin-dependent lysine acetylation by mitochondrial function. Strategies for targeting NAD(+)-sensitive mechanisms in order to intervene in protein lysine acetylation and, thereby, improve stress tolerance, are described, and their usefulness in heart failure therapy is discussed.

Differentiating between apparent and actual rates of H2O2 metabolism by isolated rat muscle mitochondria to test a simple model of mitochondria as regulators of H2O2 concentration

Mitochondria are often regarded as a major source of reactive oxygen species (ROS) in animal cells, with H2O2 being the predominant ROS released from mitochondria; however, it has been recently demonstrated that energized brain mitochondria may act as stabilizers of H2O2 concentration (Starkov et al. [1]) based on the balance between production and the consumption of H2O2, the later of which is a function of [H2O2] and follows first order kinetics. Here we test the hypothesis that isolated skeletal muscle mitochondria, from the rat, are able to modulate [H2O2] based upon the interaction between the production of ROS, as superoxide/H2O2, and the H2O2 decomposition capacity. The compartmentalization of detection systems for H2O2 and the intramitochondrial metabolism of H2O2 leads to spacial separation between these two components of the assay system. This results in an underestimation of rates when relying solely on extramitochondrial H2O2 detection. We find that differentiating between these apparent rates found when using extramitochondrial H2O2 detection and the actual rates of metabolism is important to determining the rate constant for H2O2 consumption by mitochondria in kinetic experiments. Using the high rate of ROS production by mitochondria respiring on succinate, we demonstrate that net H2O2 metabolism by mitochondria can approach a stable steady-state of extramitochondrial [H2O2]. Importantly, the rate constant determined by extrapolation of kinetic experiments is similar to the rate constant determined as the [H2O2] approaches a steady state.

Impact of a novel homozygous mutation in nicotinamide nucleotide transhydrogenase on mitochondrial DNA integrity in a case of familial glucocorticoid deficiency

BACKGROUND

Familial Glucocorticoid Deficiency (FGD) is a rare autosomal recessive disorder that is characterized by isolated glucocorticoid deficiency. Recently, mutations in the gene encoding for the mitochondrial nicotinamide nucleotide transhydrogenase (NNT) have been identified as a causative gene for FGD; however, no NNT activities have been reported in FGD patients carrying NNT mutations.

METHODS

Clinical, biochemical and molecular analyses of lymphocytes from FDG homozygous and heterozygous carriers for the F215S NNT mutation.

RESULTS

In this study, we described an FGD-affected Japanese patient carrying a novel NNT homozygous mutation (c.644T>C; F215S) with a significant loss-of-function (NNT activity = 31% of healthy controls) in peripheral blood cells' mitochondria. The NNT activities of the parents, heterozygous for the mutation, were 61% of controls.

CONCLUSIONS

Our results indicated that (i) mitochondrial biogenesis (citrate synthase activity) and/or mtDNA replication (mtDNA copy number) were affected at ≤60% NNT activity because these parameters were affected in individuals carrying either one or both mutated alleles; and (ii) other outcomes (mtDNA deletions, protein tyrosine nitration, OXPHOS capacity) were affected at ≤30% NNT activity as also observed in murine cerebellar mitochondria from C57BL/6J (NNT^-/-) vs. C57BL/6JN (NNT^+/+) substrains.

GENERAL SIGNIFICANCE

By studying a family affected with a novel point mutation in the NNT gene, a gene-dose response was found for various mitochondrial outcomes providing for novel insights into the role of NNT in the maintenance of mtDNA integrity beyond that described for preventing oxidative stress.

Vitex agnus-castus L. (Verbenaceae) Improves the Liver Lipid Metabolism and Redox State of Ovariectomized Rats

Vitex agnus-castus (VAC) is a plant that has recently been used to treat the symptoms of menopause, by its actions on the central nervous system. However, little is known about its actions on disturbances in lipid metabolism and nonalcoholic fat liver disease (NAFLD), frequently associated with menopause. Ovariectomized (OVX) rats exhibit increased adiposity and NAFLD 13 weeks after ovary removal and were used as animal models of estrogen deficiency. The rats were treated with crude extract (CE) and a butanolic fraction of VAC (ButF) and displayed the beneficial effects of a reduction in the adiposity index and a complete reversion of NAFLD. NAFLD reversion was accompanied by a general improvement in the liver redox status. The activities of some antioxidant enzymes were restored and the mitochondrial hydrogen peroxide production was significantly reduced in animals treated with CE and the ButF. It can be concluded that the CE and ButF from Vitex agnus-castus were effective in preventing NAFLD and oxidative stress, which are frequent causes of abnormal liver functions in the postmenopausal period.

Mitochondrial mechanisms of redox cycling agents implicated in Parkinson's disease

Environmental agents have been implicated in Parkinson's disease (PD) based on epidemiological studies and the ability of toxicants to replicate features of PD. However, the precise mechanisms by which toxicants induce dopaminergic toxicity observed in the idiopathic form of PD remain to be fully understood. The roles of ROS and mitochondria are strongly suggested in the mechanisms by which these toxicants exert dopaminergic toxicity. There are marked differences and similarities shared by the toxicants in increasing steady-state levels of mitochondrial ROS. Furthermore, toxicants increase steady-state mitochondrial ROS levels by stimulating the production, inhibiting the antioxidant pathways of both. This review will focus on the role of mitochondria and ROS in PD associated with environmental exposures to redox-based toxicants.

Mitochondria-derived reactive oxygen species mediate caspase-dependent and -independent neuronal deaths

Mitochondrial dysfunction and oxidative stress are implicated in many neurodegenerative diseases. Mitochondria-targeted drugs that effectively decrease oxidative stress, protect mitochondrial energetics, and prevent neuronal loss may therefore lend therapeutic benefit to these currently incurable diseases. To investigate the efficacy of such drugs, we examined the effects of mitochondria-targeted antioxidants MitoQ10 and MitoE2 on neuronal death induced by neurotrophin deficiency. Our results indicate that MitoQ10 blocked apoptosis by preventing increased mitochondria-derived reactive oxygen species (ROS) and subsequent cytochrome c release, caspase activation, and mitochondrial damage in nerve growth factor (NGF)-deprived sympathetic neurons, while MitoE2 was largely ineffective. In this paradigm, the most proximal point of divergence was the ability of MitoQ10 to scavenge mitochondrial superoxide (O2(-)). MitoQ10 also prevented caspase-independent neuronal death in these cells demonstrating that the mitochondrial redox state significantly influences both apoptotic and nonapoptotic pathways leading to neuronal death. We suggest that mitochondria-targeted antioxidants may provide tools for delineating the role and significance of mitochondrial ROS in neuronal death and provide a new therapeutic approach for neurodegenerative conditions involving trophic factor deficits and multiple modes of cell death.

Damaged mitochondria in Fanconi anemia - an isolated event or a general phenomenon?

Fanconi anemia (FA) is known as an inherited bone marrow failure syndrome associated with cancer predisposition and susceptibility to a number of DNA damaging stimuli, along with a number of clinical features such as upper limb malformations, increased diabetes incidence and typical anomalies in skin pigmentation. The proteins encoded by FA-defective genes (FANC proteins) display well-established roles in DNA damage and repair pathways. Moreover, some independent studies have revealed that mitochondrial dysfunction (MDF) is also involved in FA phenotype. Unconfined to FA, we have shown that other syndromes featuring DNA damage and repair (such as ataxia-telangiectasia, AT, and Werner syndrome, WS) display MDF-related phenotypes, along with oxidative stress (OS) that, altogether, may play major roles in these diseases. Experimental and clinical studies are warranted in the prospect of future therapies to be focused on compounds scavenging reactive oxygen species (ROS) as well as protecting mitochondrial functions.