Mitochondrial reserve capacity in endothelial cells: The impact of nitric oxide and reactive oxygen species

Differences in Glycolysis and Mitochondrial Respiration between Cytotrophoblast and Syncytiotrophoblast In-Vitro: Evidence for Sexual Dimorphism

In the placenta the proliferative cytotrophoblast cells fuse into the terminally differentiated syncytiotrophoblast layer which undertakes several energy-intensive functions including nutrient uptake and transfer and hormone synthesis. We used Seahorse glycolytic and mitochondrial stress tests on trophoblast cells isolated at term from women of healthy weight to evaluate if cytotrophoblast (CT) and syncytiotrophoblast (ST) have different bioenergetic strategies, given their different functions. Whereas there are no differences in basal glycolysis, CT have significantly greater glycolytic capacity and reserve than ST. In contrast, ST have significantly higher basal, ATP-coupled and maximal mitochondrial respiration and spare capacity than CT. Consequently, under stress conditions CT can increase energy generation via its higher glycolytic capacity whereas ST can use its higher and more efficient mitochondrial respiration capacity. We have previously shown that with adverse in utero conditions of diabetes and obesity trophoblast respiration is sexually dimorphic. We found no differences in glycolytic parameters between sexes and no difference in mitochondrial respiration parameters other than increases seen upon syncytialization appear to be greater in females. There were differences in metabolic flexibility, i.e., the ability to use glucose, glutamine, or fatty acids, seen upon syncytialization between the sexes with increased flexibility in female trophoblast suggesting a better ability to adapt to changes in nutrient supply.

Intracellular Lipid Accumulation and Mitochondrial Dysfunction Accompanies Endoplasmic Reticulum Stress Caused by Loss of the Co-chaperone DNAJC3

Recessive mutations in DNAJC3, an endoplasmic reticulum (ER)-resident BiP co-chaperone, have been identified in patients with multisystemic neurodegeneration and diabetes mellitus. To further unravel these pathomechanisms, we employed a non-biased proteomic approach and identified dysregulation of several key cellular pathways, suggesting a pathophysiological interplay of perturbed lipid metabolism, mitochondrial bioenergetics, ER-Golgi function, and amyloid-beta processing. Further functional investigations in fibroblasts of patients with DNAJC3 mutations detected cellular accumulation of lipids and an increased sensitivity to cholesterol stress, which led to activation of the unfolded protein response (UPR), alterations of the ER-Golgi machinery, and a defect of amyloid precursor protein. In line with the results of previous studies, we describe here alterations in mitochondrial morphology and function, as a major contributor to the DNAJC3 pathophysiology. Hence, we propose that the loss of DNAJC3 affects lipid/cholesterol homeostasis, leading to UPR activation, β-amyloid accumulation, and impairment of mitochondrial oxidative phosphorylation.

From OCR and ECAR to energy: Perspectives on the design and interpretation of bioenergetics studies

Biological energy transduction underlies all physiological phenomena in cells. The metabolic systems that support energy transduction have been of great interest due to their association with numerous pathologies including diabetes, cancer, rare genetic diseases, and aberrant cell death. Commercially available bioenergetics technologies (e.g., extracellular flux analysis, high-resolution respirometry, fluorescent dye kits, etc.) have made practical assessment of metabolic parameters widely accessible. This has facilitated an explosion in the number of studies exploring, in particular, the biological implications of oxygen consumption rate (OCR) and substrate level phosphorylation via glycolysis (i.e., via extracellular acidification rate (ECAR)). Though these technologies have demonstrated substantial utility and broad applicability to cell biology research, they are also susceptible to historical assumptions, experimental limitations, and other caveats that have led to premature and/or erroneous interpretations. This review enumerates various important considerations for designing and interpreting cellular and mitochondrial bioenergetics experiments, some common challenges and pitfalls in data interpretation, and some potential "next steps" to be taken that can address these highlighted challenges.

A High Fat/Cholesterol Diet Recapitulates Some Alzheimer's Disease-Like Features in Mice: Focus on Hippocampal Mitochondrial Dysfunction

BACKGROUND

Ample evidence from clinical and pre-clinical studies suggests mid-life hypercholesterolemia as a risk factor for developing Alzheimer's disease (AD) at a later age. Hypercholesterolemia induced by dietary habits can lead to vascular perturbations that increase the risk of developing sporadic AD.

OBJECTIVE

To investigate the effects of a high fat/cholesterol diet (HFCD) as a risk factor for AD by using a rodent model of AD and its correspondent control (healthy animals).

METHODS

We compared the effect of a HFCD in normal mice (non-transgenic mice, NTg) and the triple transgenic mouse model of AD (3xTgAD). We evaluated cognitive performance in relation to changes in oxidative metabolism and neuron-derived nitric oxide (•NO) concentration dynamics in hippocampal slices as well as histochemical staining of markers of the neurovascular unit.

RESULTS

In NTg, the HFCD produced only moderate hypercholesterolemia but significant decline in spatial memory was observed. A tendency for decrease in •NO production was accompanied by compromised mitochondrial function with decrease in spare respiratory capacity. In 3xTgAD mice, a robust increase in plasma cholesterol levels with the HFCD did not worsen cognitive performance but did induce compromise of mitochondrial function and significantly decreased •NO production. We found increased staining of biomarkers for astrocyte endfeet and endothelial cells in 3xTgAD hippocampi, which was further increased by the HFCD.

CONCLUSION

A short term (8 weeks) intervention with HFCD can produce an AD-like phenotype even in the absence of overt systemic hypercholesterolemia and highlights mitochondrial dysfunction as a link between hypercholesterolemia and sporadic AD.

Host bioenergetic parameters reveal cytotoxicity of anti-tuberculosis drugs undetected using conventional viability assays

High attrition rates in tuberculosis (TB) drug development have been largely attributed to safety, which is likely due to the use of endpoint assays measuring cell viability to detect drug cytotoxicity. In drug development for cancer, metabolic, and neurological disorders and for antibiotics, cytotoxicity is increasingly being assessed using extracellular flux (XF) analysis, which measures cellular bioenergetic metabolism in real time. Here, we adopt the XF platform to investigate the cytotoxicity of drugs currently used in TB treatment on the bioenergetic metabolism of HepG2 cells, THP-1 macrophages, and human monocyte-derived macrophages (hMDMs). We found that the XF analysis reveals earlier drug-induced effects on the cells’ bioenergetic metabolism prior to cell death, measured by conventional viability assays. Furthermore, each cell type has a distinct response to drug treatment, suggesting that more than one cell type should be considered to examine cytotoxicity in TB drug development. Interestingly, chemically unrelated drugs with different modes of action on Mycobacterium tuberculosis have similar effects on the bioenergetic parameters of the cells, thus discouraging the prediction of potential cytotoxicity based on chemical structure and mode of action of new chemical entities. The clustering of the drug-induced effects on the hMDM bioenergetic parameters are reflected in the clustering of the effects of the drugs on cytokine production in hMDMs, demonstrating concurrence between the effects of the drugs on the metabolism and functioning of the macrophages. These findings can be used as a benchmark to establish XF analysis as a new tool to assay cytotoxicity in TB drug development.

“SARS-CoV-2 infection of endothelial cell, clinical laboratory and autopsy findings, and outcomes suggest role of hypoxia-inducible factor-1 in COVID-19”

Researchers around the world have experienced the dual nature of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), 'tragically lethal in some people while surprisingly benign in others'. There have been congregating studies of the novel coronavirus disease (COVID-19), a disease that mainly attacks the lungs but also has mystifying effects on the heart, kidneys and brain. Researchers are also gathering information to ascertain why people are dying of COVID-19, whether it is solely a respiratory disorder, a coagulation disorder or multi-organ failure. Alterations in laboratory parameters like lactate, ferritin and albumin have been established as risk factors and are associated with outcomes, yet none have not been sub stantiated with a scientific biochemical rationale. SARSCoV-2 affects the alveolar type II epithelial cells which significantly disturbs its surfactant homeostasis, deprives Na,K-ATPase of ATP, thereby disturbing the alveolar lining fluid which then gradually decreases the alveolar gaseous exchange initiating the intracellular hypoxic conditions. This activates AMP-activated kinase, which further inhibits Na,K-ATPase, which can progressively cause respiratory distress syndrome. The virus may infect endothelial cell (EC) which, being less energetic, cannot withstand the huge energy requirement towards viral replication. There - fore glycolysis, the prime energy generating pathway, must be mandatorily upregulated. This can be achieved by Hypoxia-inducible factor-1 (HIF-1). However, HIF-1 also activates transcription of von Willebrand factor, plasminogen activator inhibitor-1, and suppresses the release of thrombomodulin. This in turn sets off the coagulation cascade that can lead to in-situ pulmonary thrombosis and micro clots. The proposed HIF-1 hypothesis justifies various features, biochemical alteration, laboratory as well as autopsy findings such as respiratory distress syndrome, increased blood ferritin and lactate levels, hypoalbuminemia, endothelial invasion, in-situ pulmonary thrombosis and micro clots, and multi-organ failure in COVID-19.

Mycobacterium tuberculosis SufR responds to nitric oxide via its 4Fe-4S cluster and regulates Fe-S cluster biogenesis for persistence in mice

The persistence of Mycobacterium tuberculosis (Mtb) is a major problem in managing tuberculosis (TB). Host-generated nitric oxide (NO) is perceived as one of the signals by Mtb to reprogram metabolism and respiration for persistence. However, the mechanisms involved in NO sensing and reorganizing Mtb's physiology are not fully understood. Since NO damages iron-sulfur (Fe-S) clusters of essential enzymes, the mechanism(s) involved in regulating Fe-S cluster biogenesis could help Mtb persist in host tissues. Here, we show that a transcription factor SufR (Rv1460) senses NO via its 4Fe-4S cluster and promotes persistence of Mtb by mobilizing the Fe-S cluster biogenesis system; suf operon (Rv1460-Rv1466). Analysis of anaerobically purified SufR by UV-visible spectroscopy, circular dichroism, and iron-sulfide estimation confirms the presence of a 4Fe-4S cluster. Atmospheric O₂ and H₂O₂ gradually degrade the 4Fe-4S cluster of SufR. Furthermore, electron paramagnetic resonance (EPR) analysis demonstrates that NO directly targets SufR 4Fe-4S cluster by forming a protein-bound dinitrosyl-iron-dithiol complex. DNase I footprinting, gel-shift, and in vitro transcription assays confirm that SufR directly regulates the expression of the suf operon in response to NO. Consistent with this, RNA-sequencing of MtbΔsufR demonstrates deregulation of the suf operon under NO stress. Strikingly, NO inflicted irreversible damage upon Fe-S clusters to exhaust respiratory and redox buffering capacity of MtbΔsufR. Lastly, MtbΔsufR failed to recover from a NO-induced non-growing state and displayed persistence defect inside immune-activated macrophages and murine lungs in a NO-dependent manner. Data suggest that SufR is a sensor of NO that supports persistence by reprogramming Fe-S cluster metabolism and bioenergetics.

Autocrine Effects of Brain Endothelial Cell-Produced Human Apolipoprotein E on Metabolism and Inflammation in vitro

Reports of APOE4-associated neurovascular dysfunction during aging and in neurodegenerative disorders has led to ongoing research to identify underlying mechanisms. In this study, we focused on whether the APOE genotype of brain endothelial cells modulates their own phenotype. We utilized a modified primary mouse brain endothelial cell isolation protocol that enabled us to perform experiments without subculture. Through initial characterization we found, that compared to APOE3, APOE4 brain endothelial cells produce less apolipoprotein E (apoE) and have altered metabolic and inflammatory gene expression profiles. Further analysis revealed APOE4 brain endothelial cultures have higher preference for oxidative phosphorylation over glycolysis and, accordingly, higher markers of mitochondrial activity. Mitochondrial activity generates reactive oxygen species, and, with APOE4, there were higher mitochondrial superoxide levels, lower levels of antioxidants related to heme and glutathione and higher markers/outcomes of oxidative damage to proteins and lipids. In parallel, or resulting from reactive oxygen species, there was greater inflammation in APOE4 brain endothelial cells including higher chemokine levels and immune cell adhesion under basal conditions and after low-dose lipopolysaccharide (LPS) treatment. In addition, paracellular permeability was higher in APOE4 brain endothelial cells in basal conditions and after high-dose LPS treatment. Finally, we found that a nuclear receptor Rev-Erb agonist, SR9009, improved functional metabolic markers, lowered inflammation and modulated paracellular permeability at baseline and following LPS treatment in APOE4 brain endothelial cells. Together, our data suggest that autocrine signaling of apoE in brain endothelial cells represents a novel cellular mechanism for how APOE regulates neurovascular function.

Plumbagin Elicits Cell-Specific Cytotoxic Effects and Metabolic Responses in Melanoma Cells

Melanoma is one of the most malignant skin cancers that require comprehensive therapies, including chemotherapy. A plant-derived drug, plumbagin (PLB), exhibits an anticancer property in several cancers. We compared the cytotoxic and metabolic roles of PLB in A375 and SK-MEL-28 cells, each with different aggressiveness. In our results, they were observed to have distinctive mitochondrial respiratory functions. The primary reactive oxygen species (ROS) source of A375 can be robustly attenuated by cell membrane permeabilization. A375 cell viability and proliferation, migration, and apoptosis induction are more sensitive to PLB treatment. PLB induced metabolic alternations in SK-MEL-28 cells, which included increasing mitochondrial oxidative phosphorylation (OXPHOS), mitochondrial ATP production, and mitochondrial mass. Decreasing mitochondrial OXPHOS and total ATP production with elevated mitochondrial membrane potential (MMP) were observed in PLB-induced A375 cells. PLB also induced ROS production and increased proton leak and non-mitochondria respiration in both cells. This study reveals the relationship between metabolism and cytotoxic effects of PLB in melanoma. PLB displays stronger cytotoxic effects on A375 cells, which exhibit lower respiratory function than SK-MEL-28 cells with higher respiratory function, and triggers cell-specific metabolic changes in accordance with its cytotoxic effects. These findings indicate that PLB might serve as a promising anticancer drug, targeting metabolism.

Prenatal air pollution influences neurodevelopment and behavior in autism spectrum disorder by modulating mitochondrial physiology

We investigate the role of the mitochondrion, an organelle highly sensitive to environmental agents, in the influence of prenatal air pollution exposure on neurodevelopment and behavior in 96 children with autism spectrum disorder (ASD) [45 with neurodevelopmental regression (NDR); 76% Male; mean (SD) age 10 y 9 m (3 y 9 m)]. Mitochondrial function was assessed using the Seahorse XFe96 in fresh peripheral blood mononuclear cells. Second and third trimester average and maximal daily exposure to fine air particulate matter of diameter ≤2.5 µm (PM2.5) was obtained from the Environmental Protection Agency's Air Quality System. Neurodevelopment was measured using the Vineland Adaptive Behavior Scale 2nd edition and behavior was assessed using the Aberrant Behavior Checklist and Social Responsiveness Scale. Prenatal PM2.5 exposure influenced mitochondrial respiration during childhood, but this relationship was different for those with (r = 0.25-0.40) and without (r = -0.07 to -0.19) NDR. Mediation analysis found that mitochondrial respiration linked to energy production accounted for 25% (SD = 2%) and 10% (SD = 2%) of the effect of average prenatal PM2.5 exposure on neurodevelopment and behavioral symptoms, respectively. Structural equation models estimated that PM2.5 and mitochondrial respiration accounted for 34% (SD = 4%) and 36% (SD = 3%) of the effect on neurodevelopment, respectively, and that behavior was indirectly influenced by mitochondrial respiration through neurodevelopment but directly influenced by prenatal PM2.5. Our results suggest that prenatal exposure to PM2.5 disrupts neurodevelopment and behavior through complex mechanisms, including long-term changes in mitochondrial respiration and that patterns of early development need to be considered when studying the influence of environmental agents on neurodevelopmental outcomes.

Aconitine induces mitochondrial energy metabolism dysfunction through inhibition of AMPK signaling and interference with mitochondrial dynamics in SH-SY5Y cells

Aconitine, a highly toxic alkaloid derived from Aconitum L., affects the central nervous system and peripheral nervous system. However, the underlying mechanism of aconitine-induced neurotoxicity remains unclear. This study investigates the effects and mechanism of aconitine on mitochondrial energy metabolism in SH-SY5Y cells. Results demonstrated that aconitine exposure suppressed cell proliferation and led to an increase in reactive oxygen species (ROS) and excessive lactate dehydrogenase (LDH) release. Aconitine (400 μmol/L) induced abnormal mitochondrial energy metabolism that quantified by the significant decrease in ATP production, basal respiration, proton leak, maximal respiration, and succinate dehydrogenase (SDH) activity. Phosphorylation of AMPK was significantly reduced in aconitine-treated SH-SY5Y cells. The AMPK activator AIACR pretreatment effectively promoted ATP production to ameliorate mitochondrial energy metabolism disorder caused by aconitine. Mitochondrial biosynthesis was inhibited after treatment with 400 μmol/L aconitine, which was characterized by mitochondria number, TFAM expression, and mtDNA copy number. Moreover, aconitine prompted the down-regulation of mitochondrial fusion proteins OPA1, Mfn1 and Mfn2, and the up-regulation of mitochondrial fission proteins p-Drp1 and p-Mff. These results suggest that aconitine induces mitochondrial energy metabolism dysfunction in SH-SY5Y cells, which may involve the inhibition of AMPK signaling and abnormal mitochondrial dynamics.

Mitochondrial encephalopathy Due to a Novel Pathogenic Mitochondrial tRNAGln m.4349C>T Variant

OBJECTIVE

Mitochondrial diseases are a group of genetic diseases caused by mutations in mitochondrial DNA and nuclear DNA, among which, mutations in mitochondrial tRNA genes possessing prominent status. In most of the cases, however, the detailed molecular pathogenesis of these tRNA gene mutations remains unclear.

METHODS

We performed the clinical emulation, muscle histochemistry, northern blotting analysis of tRNA levels, biochemical measurement of respiratory chain complex activities and mitochondrial respirations in muscle tissue and cybrid cells.

RESULTS

We found a novel m.4349C>T mutation in mitochondrial tRNA^Gln gene in a patient present with encephalopathy, epilepsy, and deafness. We demonstrated molecular pathomechanisms of this mutation. This mutation firstly disturbed the translation machinery of mitochondrial tRNA^Gln and impaired mitochondrial respiratory chain complex activities, followed by remarkable mitochondrial dysfunction and ROS production.

INTERPRETATION

This study illustrated the pathogenicity of a novel m.4349C>T mutation and provided a better understanding of the phenotype associated with mutations in mitochondrial tRNA^Gln gene.

Differential Age-Dependent Mitochondrial Dysfunction, Oxidative Stress, and Apoptosis Induced by Neonatal Hypoxia-Ischemia in the Immature Rat Brain

Neonatal hypoxia-ischemia (HI) is among the main causes of mortality and morbidity in newborns. Experimental studies show that the immature rat brain is less susceptible to HI injury, suggesting that changes that occur during the first days of life drastically alter its susceptibility. Among the main developmental changes observed is the mitochondrial function, namely, the tricarboxylic acid (TCA) cycle and respiratory complex (RC) activities. Therefore, in the present study, we investigated the influence of neonatal HI on mitochondrial functions, redox homeostasis, and cell damage at different postnatal ages in the hippocampus of neonate rats. For this purpose, animals were divided into four groups: sham postnatal day 3 (ShP3), HIP3, ShP11, and HIP11. We initially observed increased apoptosis in the HIP11 group only, indicating a higher susceptibility of these animals to brain injury. Mitochondrial damage, as determined by flow cytometry showing mitochondrial swelling and loss of mitochondrial membrane potential, was also demonstrated only in the HIP11 group. This was consistent with the decreased mitochondrial oxygen consumption, reduced TCA cycle enzymes, and RC activities and induction of oxidative stress in this group of animals. Considering that HIP3 and the sham animals showed no alteration of mitochondrial functions, redox homeostasis, and showed no apoptosis, our data suggest an age-dependent vulnerability of the hippocampus to hypoxia-ischemia. The present results highlight age-dependent metabolic differences in the brain of neonate rats submitted to HI indicating that different treatments might be needed for HI newborns with different gestational ages.

PDE5 inhibition rescues mitochondrial dysfunction and angiogenic responses induced by Akt3 inhibition by promotion of PRC expression

Akt3 regulates mitochondrial content in endothelial cells through the inhibition of PGC-1α nuclear localization and is also required for angiogenesis. However, whether there is a direct link between mitochondrial function and angiogenesis is unknown. Here we show that Akt3 depletion in primary endothelial cells results in decreased uncoupled oxygen consumption, increased fission, decreased membrane potential, and increased expression of the mitochondria-specific protein chaperones, HSP60 and HSP10, suggesting that Akt3 is required for mitochondrial homeostasis. Direct inhibition of mitochondrial homeostasis by the model oxidant paraquat results in decreased angiogenesis, showing a direct link between angiogenesis and mitochondrial function. Next, in exploring functional links to PGC-1α, the master regulator of mitochondrial biogenesis, we searched for compounds that induce this process. We found that, sildenafil, a phosphodiesterase 5 inhibitor, induced mitochondrial biogenesis as measured by increased uncoupled oxygen consumption, mitochondrial DNA content, and voltage-dependent anion channel protein expression. Sildenafil rescued the effects on mitochondria by Akt3 depletion or pharmacological inhibition and promoted angiogenesis, further supporting that mitochondrial homeostasis is required for angiogenesis. Sildenafil also induces the expression of PGC-1 family member PRC and can compensate for PGC-1α activity during mitochondrial stress by an Akt3-independent mechanism. The induction of PRC by sildenafil depends upon cAMP and the transcription factor CREB. Thus, PRC can functionally substitute during Akt3 depletion for absent PGC-1α activity to restore mitochondrial homeostasis and promote angiogenesis. These findings show that mitochondrial homeostasis as controlled by the PGC family of transcriptional activators is required for angiogenic responses.

Considerations for using isolated cell systems to understand cardiac metabolism and biology

Changes in myocardial metabolic activity are fundamentally linked to cardiac health and remodeling. Primary cardiomyocytes, induced pluripotent stem cell-derived cardiomyocytes, and transformed cardiomyocyte cell lines are common models used to understand how (patho)physiological conditions or stimuli contribute to changes in cardiac metabolism. These cell models are helpful also for defining metabolic mechanisms of cardiac dysfunction and remodeling. Although technical advances have improved our capacity to measure cardiomyocyte metabolism, there is often heterogeneity in metabolic assay protocols and cell models, which could hinder data interpretation and discernment of the mechanisms of cardiac (patho)physiology. In this review, we discuss considerations for integrating cardiomyocyte cell models with techniques that have become relatively common in the field, such as respirometry and extracellular flux analysis. Furthermore, we provide overviews of metabolic assays that complement XF analyses and that provide information on not only catabolic pathway activity, but biosynthetic pathway activity and redox status as well. Cultivating a more widespread understanding of the advantages and limitations of metabolic measurements in cardiomyocyte cell models will continue to be essential for the development of coherent metabolic mechanisms of cardiac health and pathophysiology.

Mitochondrial Dysfunction in Intervertebral Disc Degeneration: From Pathogenesis to Therapeutic Target

Mitochondria are cytosolic organelles essential for cellular function and survival. The function of mitochondria is maintained by mitochondrial quality control systems including mitochondrial fission and fusion to adapt the altered environment and mitophagy for removal of damaged mitochondria. Mitochondrial dysfunction is closely involved in aging-related diseases. Intervertebral disc (IVD) degeneration, an aging-associated process, is the major contributor to low back pain. Growing evidence has suggested that the mitochondrial function in IVD cells is severely compromised during the degenerative process of IVD, and dysfunctional mitochondria along with impaired mitochondrial dynamics and mitophagy cause a series of cascade reactions that have been implicated in increased oxidative stress, senescence, matrix catabolism, and apoptosis of IVD cells, thereby contributing to the degeneration of IVD. Accordingly, therapies that target mitochondrial dysfunction and related mechanisms, such as ROS generation, mitophagy, and specific molecules and signaling, hold great promise. The present review summarizes the current state of the role of mitochondrial dysfunction in the pathophysiology of IVD degeneration and potential therapeutic strategies that could be developed.

The Relationship Between Reactive Oxygen Species and Endothelial Cell Metabolism

Cardiovascular disease (CVD) has been the leading cause of death for many decades, highlighting the importance of new research and treatments in the field. The role of hypoxia and subsequent free radical production [reactive oxygen species (ROS)] have become an area of particular interest in CVD. Interestingly, our laboratory and other laboratories have recently reported positive roles of subcellular ROS in modulating endothelial cell (EC) metabolism, proliferation, and angiogenesis. This bidirectional relationship between ROS and EC metabolism, as well as functional changes, continues to be an area of active research. Interestingly, ECs have been shown to rely on anaerobic processes for ATP generation, despite their direct access to oxygen. This paradox has proven to be beneficial as the major reliance on glycolysis produces ATP faster, preserves oxygen, and results in reduced ROS levels in contrast to oxidative phosphorylation. This review will address the relationship between ROS and carbohydrate, lipid, and nitrogen metabolism in ECs, and their effects on EC phenotype such as sprouting angiogenesis.

The impact of glucose exposure on bioenergetics and function in a cultured endothelial cell model and the implications for cardiovascular health in diabetes

Cardiovascular disease is the primary driver of morbidity and mortality associated with diabetes. Hyperglycaemia is implicated in driving endothelial dysfunction that might underpin the link between diabetes and cardiovascular disease. This study was designed to determine the impact of chronic preconditioning of cells to hyperglycaemia and transient switching of cultured endothelial cells between hyper- and normo-glycaemic conditions on bioenergetic and functional parameters. Immortalised EA.hy926 endothelial cells were cultured through multiple passages under normoglycaemic (5.5 mM) or hyperglycaemic (25 mM) conditions. Cells were subsequently subjected (48 h) to continued normo- or hyperglycaemic exposure, or were switched to the alternative glycaemic condition, or to an intermediate glucose concentration (12.5 mM) and metabolic activity, together with key markers of function were measured. Cells habituated to hyperglycaemia were energetically quiescent. Functional activity, characterised by the measurement of nitric oxide, endothelin-1, tissue plasminogen activator and plasminogen activator inhibitor-1, was depressed by exposure to high glucose, with the reduction in nitric oxide production being the most notable. Function was more responsive to acute changes in extracellular glucose than were bioenergetic changes. We conclude that glucose is a key determinant of endothelial function. The study highlights the importance of chronic glucose exposure on cell phenotype and emphasises the need to pay close attention to glucose preconditioning in interpreting results under culture conditions.

Dihydronicotinamide riboside promotes cell-specific cytotoxicity by tipping the balance between metabolic regulation and oxidative stress

Nicotinamide adenine dinucleotide (NAD⁺), the essential cofactor derived from vitamin B3, is both a coenzyme in redox enzymatic processes and substrate in non-redox events; processes that are intimately implicated in all essential bioenergetics. A decrease in intracellular NAD⁺ levels is known to cause multiple metabolic complications and age-related disorders. One NAD⁺ precursor is dihydronicotinamide riboside (NRH), which increases NAD⁺ levels more potently in both cultured cells and mice than current supplementation strategies with nicotinamide riboside (NR), nicotinamide mononucleotide (NMN) or vitamin B3 (nicotinamide and niacin). However, the consequences of extreme boosts in NAD⁺ levels are not fully understood. Here, we demonstrate the cell-specific effects of acute NRH exposure in mammalian cells. Hepatocellular carcinoma (HepG3) cells show dose-dependent cytotoxicity when supplemented with 100–1000 μM NRH. Cytotoxicity was not observed in human embryonic kidney (HEK293T) cells over the same dose range of NRH. PUMA and BAX mediate the cell-specific cytotoxicity of NRH in HepG3. When supplementing HepG3 with 100 μM NRH, a significant increase in ROS was observed concurrent with changes in the NAD(P)H and GSH/GSSG pools. NRH altered mitochondrial membrane potential, increased mitochondrial superoxide formation, and induced mitochondrial DNA damage in those cells. NRH also caused metabolic dysregulation, altering mitochondrial respiration. Altogether, we demonstrated the detrimental consequences of an extreme boost of the total NAD (NAD⁺ + NADH) pool through NRH supplementation in HepG3. The cell-specific effects are likely mediated through the different metabolic fate of NRH in these cells, which warrants further study in other systemic models.

Forces, fluxes, and fuels: tracking mitochondrial metabolism by integrating measurements of membrane potential, respiration, and metabolites

Assessing mitochondrial function in cell-based systems is a central component of metabolism research. However, the selection of an initial measurement technique may be complicated given the range of parameters that can be studied and the need to define the mitochondrial (dys)function of interest. This methods-focused review compares and contrasts the use of mitochondrial membrane potential measurements, plate-based respirometry, and metabolomics and stable isotope tracing. We demonstrate how measurements of 1) cellular substrate preference, 2) respiratory chain activity, 3) cell activation, and 4) mitochondrial biogenesis are enriched by integrating information from multiple methods. This manuscript is meant to serve as a perspective to help choose which technique might be an appropriate initial method to answer a given question, as well as provide a broad "roadmap" for designing follow-up assays to enrich datasets or resolve ambiguous results.

Myeloperoxidase: A versatile mediator of endothelial dysfunction and therapeutic target during cardiovascular disease

Myeloperoxidase (MPO) is a prominent mammalian heme peroxidase and a fundamental component of the innate immune response against microbial pathogens. In recent times, MPO has received considerable attention as a key oxidative enzyme capable of impairing the bioactivity of nitric oxide (NO) and promoting endothelial dysfunction; a clinically relevant event that manifests throughout the development of inflammatory cardiovascular disease. Increasing evidence indicates that during cardiovascular disease, MPO is released intravascularly by activated leukocytes resulting in its transport and sequestration within the vascular endothelium. At this site, MPO catalyzes various oxidative reactions that are capable of promoting vascular inflammation and impairing NO bioactivity and endothelial function. In particular, MPO catalyzes the production of the potent oxidant hypochlorous acid (HOCl) and the catalytic consumption of NO via the enzyme's NO oxidase activity. An emerging paradigm is the ability of MPO to also influence endothelial function via non-catalytic, cytokine-like activities. In this review article we discuss the implications of our increasing knowledge of the versatility of MPO's actions as a mediator of cardiovascular disease and endothelial dysfunction for the development of new pharmacological agents capable of effectively combating MPO's pathogenic activities. More specifically, we will (i) discuss the various transport mechanisms by which MPO accumulates into the endothelium of inflamed or diseased arteries, (ii) detail the clinical and basic scientific evidence identifying MPO as a significant cause of endothelial dysfunction and cardiovascular disease, (iii) provide an up-to-date coverage on the different oxidative mechanisms by which MPO can impair endothelial function during cardiovascular disease including an evaluation of the contributions of MPO-catalyzed HOCl production and NO oxidation, and (iv) outline the novel non-enzymatic mechanisms of MPO and their potential contribution to endothelial dysfunction. Finally, we deliver a detailed appraisal of the different pharmacological strategies available for targeting the catalytic and non-catalytic modes-of-action of MPO in order to protect against endothelial dysfunction in cardiovascular disease.

Angiogenesis in gynecological cancers and the options for anti-angiogenesis therapy

Angiogenesis is required in cancer, including gynecological cancers, for the growth of primary tumors and secondary metastases. Development of anti-angiogenesis therapy in gynecological cancers and improvement of its efficacy have been a major focus of fundamental and clinical research. However, survival benefits of current anti-angiogenic agents, such as bevacizumab, in patients with gynecological cancer, are modest. Therefore, a better understanding of angiogenesis and the tumor microenvironment in gynecological cancers is urgently needed to develop more effective anti-angiogenic therapies, either or not in combination with other therapeutic approaches. We describe the molecular aspects of (tumor) blood vessel formation and the tumor microenvironment and provide an extensive clinical overview of current anti-angiogenic therapies for gynecological cancers. We discuss the different phenotypes of angiogenic endothelial cells as potential therapeutic targets, strategies aimed at intervention in their metabolism, and approaches targeting their (inflammatory) tumor microenvironment.

Reduced mitochondrial translation prevents diet-induced metabolic dysfunction but not inflammation

The contribution of dysregulated mitochondrial gene expression and consequent imbalance in biogenesis is not well understood in metabolic disorders such as insulin resistance and obesity. The ribosomal RNA maturation protein PTCD1 is essential for mitochondrial protein synthesis and its reduction causes adult-onset obesity and liver steatosis. We used haploinsufficient Ptcd1 mice fed normal or high fat diets to understand how changes in mitochondrial biogenesis can lead to metabolic dysfunction. We show that Akt-stimulated reduction in lipid content and upregulation of mitochondrial biogenesis effectively protected mice with reduced mitochondrial protein synthesis from excessive weight gain on a high fat diet, resulting in improved glucose and insulin tolerance and reduced lipid accumulation in the liver. However, inflammation of the white adipose tissue and early signs of fibrosis in skeletal muscle, as a consequence of reduced protein synthesis, were exacerbated with the high fat diet. We identify that reduced mitochondrial protein synthesis and OXPHOS biogenesis can be recovered in a tissue-specific manner via Akt-mediated increase in insulin sensitivity and transcriptional activation of the mitochondrial stress response.

Mitochondrial Markers in Aging and Primary Open-Angle Glaucoma

This review focuses on recent progress in understanding the role of mitochondrial markers in the context of mitochondrial dysfunction in glaucoma and discussing new therapeutic approaches to modulate mitochondrial function and potentially lead to improved outcomes in glaucoma.

Mitochondrial spare respiratory capacity: Mechanisms, regulation, and significance in non-transformed and cancer cells

Mitochondrial metabolism must constantly adapt to stress conditions in order to maintain bioenergetic levels related to cellular functions. This absence of proper adaptation can be seen in a wide array of conditions, including cancer. Metabolic adaptation calls on mitochondrial function and draws on the mitochondrial reserve to meet increasing needs. Among mitochondrial respiratory parameters, the spare respiratory capacity (SRC) represents a particularly robust functional parameter to evaluate mitochondrial reserve. We provide an overview of potential SRC mechanisms and regulation with a focus on its particular significance in cancer cells.

Mycobacterium tuberculosis SufR Responds to Nitric oxide via its 4Fe-4S cluster and Regulates Fe-S cluster Biogenesis for Persistence in Mice.. [DOI: 10.1101/2020.08.10.245365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The persistence of Mycobacterium tuberculosis (Mtb) is a major problem in managing tuberculosis. Host–generated nitric oxide (NO) is perceived as one of the signals by Mtb to reprogram metabolism and respiration for persistence. However, the mechanisms involved in NO sensing and reorganizing Mtb′s physiology are not fully understood. Since NO damages iron–sulfur (Fe–S) clusters of essential enzymes, the mechanism(s) involved in regulating Fe–S cluster biogenesis could help Mtb persist in host tissues. Here, we show that a transcription factor SufR (Rv1460) senses NO via its 4Fe–4S cluster and promotes persistence of Mtb by mobilizing the Fe-S cluster biogenesis system; suf operon (Rv1460–Rv1466). Analysis of anaerobically purified SufR by UV-visible spectroscopy, circular dichroism, and iron-sulfide estimation confirms the presence of a 4Fe–4S cluster. Atmospheric O2 and H2O2 gradually degrade the 4Fe–4S cluster of SufR. Furthermore, electron paramagnetic resonance (EPR) analysis demonstrates that NO directly targets SufR 4Fe–4S cluster by forming a protein-bound dinitrosyl–iron–dithiol complex. DNase I footprinting, gel–shift, and in vitro transcription assays confirm that SufR directly regulates the expression of the suf operon in response to NO. Consistent with this, RNA–sequencing of Mtb ΔsufR demonstrates deregulation of the suf operon under NO stress. Strikingly, NO inflicted irreversible damage upon Fe–S clusters to exhaust respiratory and redox buffering capacity of MtbΔsufR. Lastly, Mtb ΔsufR failed to recover from a NO-induced non-growing state and displayed persistence defect inside immune–activated macrophages and murine lungs in a NO–dependent manner. Data suggest that SufR is a sensor of NO that supports persistence by reprogramming Fe–S cluster metabolism and bioenergetics.

Wavelength- and irradiance-dependent changes in intracellular nitric oxide level

SIGNIFICANCE

Photobiomodulation (PBM) refers to the beneficial effects of low-energy light absorption. Although there is a large body of literature describing downstream physiological benefits of PBM, there is a limited understanding of the molecular mechanisms underlying these effects. At present, the most popular hypothesis is that light absorption induces release of nitric oxide (NO) from the active site of cytochrome c oxidase (COX), allowing it to bind O2 instead. This is believed to increase mitochondrial respiration, and result in greater overall health of the cell due to increased adenosine triphosphate production.

AIM

Although NO itself is a powerful signaling molecule involved in a host of biological responses, less attention has been devoted to NO mechanisms in the context of PBM. The purpose of our work is to investigate wavelength-specific effects on intracellular NO release in living cells.

APPROACH

We have conducted in-depth dosimetry analyses of NO production and function in an in vitro retinal model in response to low-energy exposure to one or more wavelengths of laser light.

RESULTS

We found statistically significant wavelength-dependent elevations (10% to 30%) in intracellular NO levels following laser exposures at 447, 532, 635, or 808 nm. Sequential or simultaneous exposures to light at two different wavelengths enhanced the NO modulation up to 50% of unexposed controls. Additionally, the immediate increases in cellular NO levels were independent of the function of NO synthase, depended greatly on the substrate source of electrons entering the electron transport chain, and did not result in increased levels of cyclic guanosine monophosphate.

CONCLUSIONS

Our study concludes the simple model of light-mediated release of NO from COX is unlikely to explain the wide variety of PBM effects reported in the literature. Our multiwavelength method provides a novel tool for studying immediate and early mechanisms of PBM as well as exploring intracellular NO signaling networks.

The diabetic microenvironment causes mitochondrial oxidative stress in glomerular endothelial cells and pathological crosstalk with podocytes

BACKGROUND

In the setting of diabetes mellitus, mitochondrial dysfunction and oxidative stress are important pathogenic mechanisms causing end organ damage, including diabetic kidney disease (DKD), but mechanistic understanding at a cellular level remains obscure. In mouse models of DKD, glomerular endothelial cell (GEC) dysfunction precedes albuminuria and contributes to neighboring podocyte dysfunction, implicating GECs in breakdown of the glomerular filtration barrier. In the following studies we wished to explore the cellular mechanisms by which GECs become dysfunctional in the diabetic milieu, and the impact to neighboring podocytes.

METHODS

Mouse GECs were exposed to high glucose media (HG) or 2.5% v/v serum from diabetic mice or serum from non-diabetic controls, and evaluated for mitochondrial function (oxygen consumption), structure (electron microscopy), morphology (mitotracker), mitochondrial superoxide (mitoSOX), as well as accumulation of oxidized products (DNA lesion frequency (8-oxoG, endo-G), double strand breaks (γ-H2AX), endothelial function (NOS activity), autophagy (LC3) and apoptotic cell death (Annexin/PI; caspase 3). Supernatant transfer experiments from GECs to podocytes were performed to establish the effects on podocyte survival and transwell experiments were performed to determine the effects in co-culture.

RESULTS

Diabetic serum specifically causes mitochondrial dysfunction and mitochondrial superoxide release in GECs. There is a rapid oxidation of mitochondrial DNA and loss of mitochondrial biogenesis without cell death. Many of these effects are blocked by mitoTEMPO a selective mitochondrial anti-oxidant. Secreted factors from dysfunctional GECs were sufficient to cause podocyte apoptosis in supernatant transfer experiments, or in co-culture but this did not occur when GECs had been previously treated with mitoTEMPO.

CONCLUSION

Dissecting the impact of the diabetic environment on individual cell-types from the kidney glomerulus indicates that GECs become dysfunctional and pathological to neighboring podocytes by increased levels of mitochondrial superoxide in GEC. These studies indicate that GEC-signaling to podocytes contributes to the loss of the glomerular filtration barrier in DKD. Video abstract.

Mitochondrial superoxide contributes to oxidative stress exacerbated by DNA damage response in RAD51-depleted ovarian cancer cells

Ovarian cancer is the most lethal gynecological malignancy. Abnormal homologous recombination repair, high level of reactive oxygen species (ROS) and upregulation of antioxidant genes are characteristic features of ovarian cancer. However, the molecular mechanisms governing the redox homeostasis in ovarian cancer cells remain to be fully elucidated. We here demonstrated a critical role of RAD51, a protein essential for homologous recombination, in the maintenance of redox homeostasis. We found that RAD51 is overexpressed in high grade serous ovarian cancer and is associated with poor prognosis. Depletion or inhibition of RAD51 results in G2/M arrest, increased production of reactive oxygen species and accumulation of oxidative DNA damage. Importantly, antioxidant N-acetylcysteine (NAC) significantly attenuated the induction of DNA damage and the perturbation of proliferation caused by RAD51 depletion. We further demonstrated that RAD51 inhibition or depletion led to elevated production of mitochondrial superoxide and increased accumulation of mitochondria. Moreover, CHK1 activation is required for the G2/M arrest and the generation of mitochondrial stress in response to RAD51 depletion. Together, our results indicate that nuclear DNA damage caused by RAD51 depletion may trigger mitochondria-originated redox dysregulation. Our findings suggest that a vicious cycle of nuclear DNA damage, mitochondrial accumulation and oxidative stress may contribute to the tumor-suppressive effects of RAD51 depletion or inhibition.

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RAD51 is overexpressed in ovarian cancer and is associated with poor prognosis.

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Depletion of RAD51 leads to increased mitochondrial superoxide production and oxidative DNA damage.

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Increased production of mitochondrial ROS requires CHK1-mediated G2/M arrest.

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mROS increase is independent of mtDNA.

Context-dependent regulation of endothelial cell metabolism: differential effects of the PPARβ/δ agonist GW0742 and VEGF-A

Peroxisome proliferator activated receptor β/δ (PPARβ/δ) has pro-angiogenic functions, but whether PPARβ/δ modulates endothelial cell metabolism to support the dynamic phenotype remains to be established. This study characterised the metabolic response of HUVEC to the PPARβ/δ agonist, GW0742, and compared these effects with those induced by VEGF-A. In HUVEC monolayers, flux analysis revealed that VEGF-A promoted glycolysis at the expense of fatty acid oxidation (FAO), whereas GW0742 reduced both glycolysis and FAO. Only VEGF-A stimulated HUVEC migration and proliferation whereas both GW0742 and VEGF-A promoted tubulogenesis. Studies using inhibitors of PPARβ/δ or sirtuin-1 showed that the tubulogenic effect of GW0742, but not VEGF-A, was PPARβ/δ- and sirtuin-1-dependent. HUVEC were reliant on glycolysis and FAO, and inhibition of either pathway disrupted cell growth and proliferation. VEGF-A was a potent inducer of glycolysis in tubulogenic HUVEC, while FAO was maintained. In contrast, GW0742-induced tubulogenesis was associated with enhanced FAO and a modest increase in glycolysis. These novel data reveal a context-dependent regulation of endothelial metabolism by GW0742, where metabolic activity is reduced in monolayers but enhanced during tubulogenesis. These findings expand our understanding of PPARβ/δ in the endothelium and support the targeting of PPARβ/δ in regulating EC behaviour and boosting tissue maintenance and repair.

Piscidin-1 Induces Apoptosis via Mitochondrial Reactive Oxygen Species-Regulated Mitochondrial Dysfunction in Human Osteosarcoma Cells

Osteosarcoma (OSA) is the most common type of cancer that originates in the bone and usually occurs in young children. OSA patients were treated with neoadjuvant chemotherapy and surgery, and the results were disappointing. Marine antimicrobial peptides (AMPs) have been the focus of antibiotic research because they are resistant to pathogen infection. Piscidin-1 is an AMP from the hybrid striped bass (Morone saxatilis × M. chrysops) and has approximately 22 amino acids. Research has shown that piscidin-1 can inhibit bacterial infections and has antinociception and anti-cancer properties; however, the regulatory effects of piscidin-1 on mitochondrial dysfunction in cancer cells are still unknown. We aimed to identify the effects of piscidin-1 on mitochondrial reactive oxygen species (mtROS) and apoptosis in OSA cells. Our analyses indicated that piscidin-1 has more cytotoxic effects against OSA cells than against lung and ovarian cancer cells; however, it has no effect on non-cancer cells. Piscidin-1 induces apoptosis in OSA cells, regulates mtROS, reduces mitochondrial antioxidant manganese superoxide dismutase and mitochondrial transmembrane potential, and decreases adenosine 5′-triphosphate production, thus leading to mitochondrial dysfunction and apoptosis. The mitochondrial antioxidant, mitoTempo, reduces the apoptosis induced by piscidin-1. Results suggest that piscidin-1 has potential for use in OSA treatment.

The Metabolic Remodelling in Lung Cancer and Its Putative Consequence in Therapy Response

Lung cancer is the leading cause of cancer-related deaths worldwide in both men and women. Conventional chemotherapy has failed to provide long-term benefits for many patients and in the past decade, important advances were made to understand the underlying molecular/genetic mechanisms of lung cancer, allowing the unfolding of several other pathological entities. Considering these molecular subtypes, and the appearance of promising targeted therapies, an effective personalized control of the disease has emerged, nonetheless benefiting a small proportion of patients. Although immunotherapy has also appeared as a new hope, it is still not accessible to the majority of patients with lung cancer.The metabolism of energy and biomass is the basis of cellular survival. This is true for normal cells under physiological conditions and it is also true for pathophysiologically altered cells, such as cancer cells. Thus, knowledge of the metabolic remodelling that occurs in cancer cells in the sense of, on one hand, surviving in the microenvironment of the organ in which the tumour develops and, on the other hand, escaping from drugs conditioned microenvironment, is essential to understand the disease and to develop new therapeutic approaches.

A precision medicine approach to defining the impact of doxorubicin on the bioenergetic-metabolite interactome in human platelets

Non-invasive measures of the response of individual patients to cancer therapeutics is an emerging strategy in precision medicine. Platelets offer a potential dynamic marker for metabolism and bioenergetic responses in individual patients since they have active glycolysis and mitochondrial oxidative phosphorylation and can be easily isolated from a small blood sample. We have recently shown how the bioenergetic-metabolite interactome can be defined in platelets isolated from human subjects by measuring metabolites and bioenergetics in the same sample. In the present study, we used a model system to assess test the hypothesis that this interactome is modified by xenobiotics using exposure to the anti-cancer drug doxorubicin (Dox) in individual donors. We found that unsupervised analysis of the metabolome showed clear differentiation between the control and Dox treated group. Dox treatment resulted in a concentration-dependent decrease in bioenergetic parameters with maximal respiration being most sensitive and this was associated with significant changes in over 166 features. A metabolome-wide association study of Dox was also conducted, and Dox was found to have associations with metabolites in the glycolytic and TCA cycle pathways. Lastly, network analysis showed the impact of Dox on the bioenergetic-metabolite interactome and revealed profound changes in the regulation of reserve capacity. Taken together, these data support the conclusion that platelets are a suitable platform to predict and monitor therapeutic efficacy as well as anticipate susceptibility to toxicity in the context of precision medicine.

Bioenergetics and translational metabolism: implications for genetics, physiology and precision medicine

It is now becoming clear that human metabolism is extremely plastic and varies substantially between healthy individuals. Understanding the biochemistry that underlies this physiology will enable personalized clinical interventions related to metabolism. Mitochondrial quality control and the detailed mechanisms of mitochondrial energy generation are central to understanding susceptibility to pathologies associated with aging including cancer, cardiac and neurodegenerative diseases. A precision medicine approach is also needed to evaluate the impact of exercise or caloric restriction on health. In this review, we discuss how technical advances in assessing mitochondrial genetics, cellular bioenergetics and metabolomics offer new insights into developing metabolism-based clinical tests and metabolotherapies. We discuss informatics approaches, which can define the bioenergetic-metabolite interactome and how this can help define healthy energetics. We propose that a personalized medicine approach that integrates metabolism and bioenergetics with physiologic parameters is central for understanding the pathophysiology of diseases with a metabolic etiology. New approaches that measure energetics and metabolomics from cells isolated from human blood or tissues can be of diagnostic and prognostic value to precision medicine. This is particularly significant with the development of new metabolotherapies, such as mitochondrial transplantation, which could help treat complex metabolic diseases.

Closing the Mitochondrial Permeability Transition Pore in hiPSC-Derived Endothelial Cells Induces Glycocalyx Formation and Functional Maturation

Human induced pluripotent stem cells (hiPSCs) are used to study organogenesis and model disease as well as being developed for regenerative medicine. Endothelial cells are among the many cell types differentiated from hiPSCs, but their maturation and stabilization fall short of that in adult endothelium. We examined whether shear stress alone or in combination with pericyte co-culture would induce flow alignment and maturation of hiPSC-derived endothelial cells (hiPSC-ECs) but found no effects comparable with those in primary microvascular ECs. In addition, hiPSC-ECs lacked a luminal glycocalyx, critical for vasculature homeostasis, shear stress sensing, and signaling. We noted, however, that hiPSC-ECs have dysfunctional mitochondrial permeability transition pores, resulting in reduced mitochondrial function and increased reactive oxygen species. Closure of these pores by cyclosporine A improved EC mitochondrial function but also restored the glycocalyx such that alignment to flow took place. These results indicated that mitochondrial maturation is required for proper hiPSC-EC functionality.

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hiPSC-ECs lack a functional glycocalyx and fail to align to flow

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hiPSC-ECs have reduced mitochondrial function and increased leakage of ROS

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Closing the mPTP with cyclosporine A induces mitochondrial maturation

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Improved mitochondrial function restores the glycocalyx and alignment to flow

Persistent Mitochondrial Dysfunction Linked to Prolonged Organ Dysfunction in Pediatric Sepsis

OBJECTIVES

Limited data exist about the timing and significance of mitochondrial alterations in children with sepsis. We therefore sought to determine if alterations in mitochondrial respiration and content within circulating peripheral blood mononuclear cells were associated with organ dysfunction in pediatric sepsis.

DESIGN

Prospective observational study SETTING:: Single academic PICU.

PATIENTS

One-hundred sixty-seven children with sepsis/septic shock and 19 PICU controls without sepsis, infection, or organ dysfunction.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Mitochondrial respiration and content were measured in peripheral blood mononuclear cells on days 1-2, 3-5, and 8-14 after sepsis recognition or once for controls. Severity and duration of organ dysfunction were determined using the Pediatric Logistic Organ Dysfunction score and organ failure-free days through day 28. Day 1-2 maximal uncoupled respiration (9.7 ± 7.7 vs 13.7 ± 4.1 pmol O2/s/10 cells; p = 0.02) and spare respiratory capacity (an index of bioenergetic reserve: 6.2 ± 4.3 vs 9.6 ± 3.1; p = 0.005) were lower in sepsis than controls. Mitochondrial content, measured by mitochondrial DNA/nuclear DNA, was higher in sepsis on day 1-2 than controls (p = 0.04) and increased in sepsis patients who had improving spare respiratory capacity over time (p = 0.005). Mitochondrial respiration and content were not associated with day 1-2 Pediatric Logistic Organ Dysfunction score, but low spare respiratory capacity was associated with higher Pediatric Logistic Organ Dysfunction score on day 3-5. Persistently low spare respiratory capacity was predictive of residual organ dysfunction on day 14 (area under the receiver operating characteristic, 0.72; 95% CI, 0.61-0.84) and trended toward fewer organ failure-free days although day 28 (β coefficient, -0.64; 95% CI, -1.35 to 0.06; p = 0.08).

CONCLUSIONS

Mitochondrial respiration was acutely decreased in peripheral blood mononuclear cells in pediatric sepsis despite an increase in mitochondrial content. Over time, a rise in mitochondrial DNA tracked with improved respiration. Although initial mitochondrial alterations in peripheral blood mononuclear cells were unrelated to organ dysfunction, persistently low respiration was associated with slower recovery from organ dysfunction.

The role of glycolysis and mitochondrial respiration in the formation and functioning of endothelial tip cells during angiogenesis

During sprouting angiogenesis, an individual endothelial tip cell grows out from a pre-existing vascular network and guides following and proliferating stalk cells to form a new vessel. Metabolic pathways such as glycolysis and mitochondrial respiration as the major sources of adenosine 5'-triphosphate (ATP) for energy production are differentially activated in these types of endothelial cells (ECs) during angiogenesis. Therefore, we studied energy metabolism during angiogenesis in more detail in tip cell and non-tip cell human umbilical vein ECs. Small interfering RNA was used to inhibit transcription of glycolytic enzymes PFKFB3 or LDHA and mitochondrial enzyme PDHA1 to test whether inhibition of these specific pathways affects tip cell differentiation and sprouting angiogenesis in vitro and in vivo. We show that glycolysis is essential for tip cell differentiation, whereas both glycolysis and mitochondrial respiration occur during proliferation of non-tip cells and in sprouting angiogenesis in vitro and in vivo. Finally, we demonstrate that inhibition of mitochondrial respiration causes adaptation of EC metabolism by increasing glycolysis and vice versa. In conclusion, our studies show a complex but flexible role of the different metabolic pathways to produce ATP in the regulation of tip cell and non-tip cell differentiation and functioning during sprouting angiogenesis.

Mitochondrial oncobioenergetics of prostate tumorigenesis

Mitochondria are emerging as key players in the tumorigenic process of cells by maintaining the biosynthetic and energetic capabilities of cancer cells. It is now evident that mitochondria are involved in the malignant transformation, cell proliferation, aggression and metastatic behavior of prostate cancer (PC). Recent comprehensive analysis of the mitochondrial oncobioenergetic (MOB) profile of PC cells using microplate-based high resolution respirometry has clearly demonstrated that characteristic MOB alterations occur at different stages of PC development. Additionally, studies have reported that modification of the MOB profile significantly inhibits the growth of malignant cells. This observation suggests that dynamic alterations in the MOB function are a critical component in the development of malignant disease of the prostate. Therefore, quantification of MOB function may be a good marker for the prediction of tumor stage. Future studies may develop novel approaches to measure oncobioenergetics of tumors with minimal invasive procedures effectively in men to determine the general prostate health and tumor staging, and to predict whether a tumor will proceed to malignancy in patients. Additionally, since PC is a slow growing tumor, modulating the MOB profile at specific stages of tumor development may be a novel approach to treat or prevent PC.

IL-17A-stimulated endothelial fatty acid β-oxidation promotes tumor angiogenesis

AIMS

Tumor growth is an angiogenesis-dependent process that requires sustained new vessel growth. Interleukin-17 (IL-17A) is a key cytokine that modulates tumor progression. However, whether IL-17A affects the metabolism of endothelial cells is unknown.

MAIN METHODS

A xenograft model was established by implanting H460 (human lung cancer cell line) cells transfected with IL-17A-expressing or control vector. The effects of IL-17A on sprouting and tube formation of human umbilical vein endothelial cells (HUVECs) were measured. After treatment with IL-17A, the proliferation and migration of HUVECs were examined. Liquid chromatography-mass spectrometry (LC-MS) and Seahorse were used to detect the effects of IL-17A on mitochondrial respiration and fatty acid β-oxidation (FAO) in HUVECs. Western blotting was used to examine signaling pathways.

KEY FINDINGS

Herein, we found that IL-17A promoted H460 tumor growth and angiogenesis in vivo and in vitro. Moreover, IL-17A stimulated angiogenesis by enhancing FAO, increasing mitochondrial respiration of endothelial cells. The AMP-activated protein kinase (AMPK) signaling pathway was activated to promote FAO. Finally, IL-17A-induced angiogenesis was blocked when FAO was inhibited using etomoxir.

SIGNIFICANCE

In summary, these results indicate that IL-17A stimulates angiogenesis by promoting FAO. Thus, our study might provide a new therapeutic target for angiogenic vascular disorders.

Lymphatic and blood systems: Identical or fraternal twins?

Blood and lymphatic systems work in close collaboration to ensure their respective physiological functions. The lymphatic vessel network is being extensively studied, but has been overlooked as compared to the blood vasculature mainly due to the problematic discrimination of lymphatic vessels from the blood ones. This issue has been fortunately resolved in the past decade leading to the emergence of a huge amount of data in lymphatic biology revealing many shared features with the blood vasculature. However, this likeliness between the two vascular systems may lead to a simplistic view of lymphatics and a direct transcription of what is known for the blood system to the lymphatic one, thereby neglecting the lymphatic specificities. In this context, this review aims to clarify the main differences between the two vascular systems focusing on recently discovered lymphatic features.

Danggui Buxue Tang, a Chinese Herbal Decoction Containing Astragali Radix and Angelicae Sinensis Radix, Modulates Mitochondrial Bioenergetics in Cultured Cardiomyoblasts

Danggui Buxue Tang (DBT) is an ancient herbal mixture containing Astragali Radix and Angelicae Sinensis Radix, and which are commonly consumed for "qi-invigorating" (i.e., stimulating vital energy/energy metabolism) as traditional Chinese medicine (TCM). The pharmacological activities of DBT in anti-oxidation, estrogenic, hematopoietic, and immunogenic have been reported; however, the role of DBT in cellular energy metabolism has not been determined. Here, we employed an extracellular flux analyzer to evaluate the mitochondrial respiration of cultured H9C2 cardiomyoblasts in present of DBT. The herbal extract of DBT was qualified chemically for the major ingredients, i.e. astragaloside, calycosin, formononetin, Z-ligustilide, and ferulic acid. The anti-oxidant activities of DBT, as well as its major ingredients, were determined by Folin-Ciocalteu assay, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, and protective effect in tert-butyl hydroperoxide (tBHP)-treated cultured cardiomyoblasts. In addition, a real-time oxygen consumption rate (OCR) in herbal extract-treated cultured cardiomyoblasts was revealed by using a Seahorse extracellular flux analyzer. In addition, the transcript expressions of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PCG-1α) and other genes relating to mitochondria biogenesis were determined in cardiomyoblasts under different herbal treatments. DBT possessed the strongest anti-oxidant activity and protective effects on the oxidatively stressed cardiomyoblasts. By revealing the OCR in mitochondria, the health state of cultured cardiomyoblasts under DBT was improved via increase of basal respiration, proton leak, non-mitochondria, and adenosine triphosphate (ATP) production. Furthermore, the transcriptional activities of genes responsible for mitochondrial biogenesis and DNA replication were stimulated by application of DBT in cultures.

Acute increases in O-GlcNAc indirectly impair mitochondrial bioenergetics through dysregulation of LonP1-mediated mitochondrial protein complex turnover

The attachment of O-linked β-N-acetylglucosamine (O-GlcNAc) to the serine and threonine residues of proteins in distinct cellular compartments is increasingly recognized as an important mechanism regulating cellular function. Importantly, the O-GlcNAc modification of mitochondrial proteins has been identified as a potential mechanism to modulate metabolism under stress with both potentially beneficial and detrimental effects. This suggests that temporal and dose-dependent changes in O-GlcNAcylation may have different effects on mitochondrial function. In the current study, we found that acutely augmenting O-GlcNAc levels by inhibiting O-GlcNAcase with Thiamet-G for up to 6 h resulted in a time-dependent decrease in cellular bioenergetics and decreased mitochondrial complex I, II, and IV activities. Under these conditions, mitochondrial number was unchanged, whereas an increase in the protein levels of the subunits of several electron transport complex proteins was observed. However, the observed bioenergetic changes appeared not to be due to direct increased O-GlcNAc modification of complex subunit proteins. Increases in O-GlcNAc were also associated with an accumulation of mitochondrial ubiquitinated proteins; phosphatase and tensin homolog induced kinase 1 (PINK1) and p62 protein levels were also significantly increased. Interestingly, the increase in O-GlcNAc levels was associated with a decrease in the protein levels of the mitochondrial Lon protease homolog 1 (LonP1), which is known to target complex IV subunits and PINK1, in addition to other mitochondrial proteins. These data suggest that impaired bioenergetics associated with short-term increases in O-GlcNAc levels could be due to impaired, LonP1-dependent, mitochondrial complex protein turnover.

Differential Effects of Yeast NADH Dehydrogenase (Ndi1) Expression on Mitochondrial Function and Inclusion Formation in a Cell Culture Model of Sporadic Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder that exhibits aberrant protein aggregation and mitochondrial dysfunction. Ndi1, the yeast mitochondrial NADH dehydrogenase (complex I) enzyme, is a single subunit, internal matrix-facing protein. Previous studies have shown that Ndi1 expression leads to improved mitochondrial function in models of complex I-mediated mitochondrial dysfunction. The trans-mitochondrial cybrid cell model of PD was created by fusing mitochondrial DNA-depleted SH-SY5Y cells with platelets from a sporadic PD patient. PD cybrid cells reproduce the mitochondrial dysfunction observed in a patient's brain and periphery and form intracellular, cybrid Lewy bodies comparable to Lewy bodies in PD brain. To improve mitochondrial function and alter the formation of protein aggregates, Ndi1 was expressed in PD cybrid cells and parent SH-SY5Y cells. We observed a dramatic increase in mitochondrial respiration, increased mitochondrial gene expression, and increased PGC-1α gene expression in PD cybrid cells expressing Ndi1. Total cellular aggregated protein content was decreased but Ndi1 expression was insufficient to prevent cybrid Lewy body formation. Ndi1 expression leads to improved mitochondrial function and biogenesis signaling, both processes that could improve neuron survival during disease. However, other aspects of PD pathology such as cybrid Lewy body formation were not reduced. Consequently, resolution of mitochondrial dysfunction alone may not be sufficient to overcome other aspects of PD-related cellular pathology.

3-Mercaptopyruvate sulfurtransferase supports endothelial cell angiogenesis and bioenergetics

BACKGROUND AND PURPOSE

During angiogenesis, quiescent endothelial cells (ECs) are activated by various stimuli to form new blood vessels from pre-existing ones in physiological and pathological conditions. Many research groups have shown that hydrogen sulfide (H₂ S), the newest member of the gasotransmitter family, acts as a proangiogenic factor. To date, very little is known about the regulatory role of 3-mercaptopyruvate sulfurtransferase (3-MST), an important H₂ S-producing enzyme in ECs. The aim of our study was to explore the potential role of 3-MST in human EC bioenergetics, metabolism, and angiogenesis.

EXPERIMENTAL APPROACH

To assess in vitro angiogenic responses, we used EA.hy926 human vascular ECs subjected to shRNA-mediated 3-MST attenuation and pharmacological inhibition of proliferation, migration, and tube-like network formation. To evaluate bioenergetic parameters, cell respiration, glycolysis, glucose uptake, and mitochondrial/glycolytic ATP production were measured. Finally, global metabolomic profiling was performed to determine the level of 669 metabolic compounds.

KEY RESULTS

3-MST-attenuated ECs subjected to shRNA or pharmacological inhibition of 3-MST significantly reduced EC proliferation, migration, and tube-like network formation. 3-MST silencing also suppressed VEGF-induced EC migration. From bioenergetic and metabolic standpoints, 3-MST attenuation decreased mitochondrial respiration and mitochondrial ATP production, increased glucose uptake, and perturbed the entire EC metabolome.

CONCLUSION AND IMPLICATIONS

3-MST regulates bioenergetics and morphological angiogenic functions in human ECs. The data presented in the current report support the view that 3-MST pathway may be a potential candidate for therapeutic modulation of angiogenesis.

LINKED ARTICLES

This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.

The second genome: Effects of the mitochondrial genome on cancer progression

The role of genetics in cancer has been recognized for centuries, but most studies elucidating genetic contributions to cancer have understandably focused on the nuclear genome. Mitochondrial contributions to cancer pathogenesis have been documented for decades, but how mitochondrial DNA (mtDNA) influences cancer progression and metastasis remains poorly understood. This lack of understanding stems from difficulty isolating the nuclear and mitochondrial genomes as experimental variables, which is critical for investigating direct mtDNA contributions to disease given extensive crosstalk exists between both genomes. Several in vitro and in vivo models have isolated mtDNA as an independent variable from the nuclear genome. This review compares and contrasts different models, their advantages and disadvantages for studying mtDNA contributions to cancer, focusing on the mitochondrial-nuclear exchange (MNX) mouse model and findings regarding tumor progression, metastasis, and other complex cancer-related phenotypes.

Mitochondrial ATP production provides long-range control of endothelial inositol trisphosphate-evoked calcium signaling

Endothelial cells are reported to be glycolytic and to minimally rely on mitochondria for ATP generation. Rather than providing energy, mitochondria in endothelial cells may act as signaling organelles that control cytosolic Ca2+ signaling or modify reactive oxygen species (ROS). To control Ca2+ signaling, these organelles are often observed close to influx and release sites and may be tethered near Ca2+ transporters. In this study, we used high-resolution, wide-field fluorescence imaging to investigate the regulation of Ca2+ signaling by mitochondria in large numbers of endothelial cells (∼50 per field) in intact arteries from rats. We observed that mitochondria were mostly spherical or short-rod structures and were distributed widely throughout the cytoplasm. The density of these organelles did not increase near contact sites with smooth muscle cells. However, local inositol trisphosphate (IP3)-mediated Ca2+ signaling predominated near these contact sites and required polarized mitochondria. Of note, mitochondrial control of Ca2+ signals occurred even when mitochondria were far from Ca2+ release sites. Indeed, the endothelial mitochondria were mobile and moved throughout the cytoplasm. Mitochondrial control of Ca2+ signaling was mediated by ATP production, which, when reduced by mitochondrial depolarization or ATP synthase inhibition, eliminated local IP3-mediated Ca2+ release events. ROS buffering did not significantly alter local Ca2+ release events. These results highlight the importance of mitochondrial ATP production in providing long-range control of endothelial signaling via IP3-evoked local Ca2+ release in intact endothelium.

Mitochondrial localization of St14-encoding transmembrane serine protease is involved in neural stem/progenitor cell bioenergetics through binding to F0F1-ATP synthase complex

Knockdown of the suppression of tumorigenicity 14-encoding type II transmembrane serine protease matriptase (MTP) in neural stem/progenitor (NS/P) cells impairs cell mobility, response to chemo-attractants, and neurovascular niche interaction. In the present study, we showed by Western blot that a portion of MTP can be detected in the mitochondrial fraction of mouse NS/P cells by immunostaining that it is co-stained with the mitochondrial dye MitoTracker (Thermo Fisher Scientific, Waltham, MA, USA) inside the cells. Co-immunoprecipitation showed that MTP is bound to the β subunit of mitochondrial F₀F₁-ATP synthase complex (ATP-β). Cyto-immunofluorescence staining and an in situ proximity ligation assay further confirmed a physical interaction between MTP and ATP-β. This interaction relied on the presence of both Cls/Clr urchin embryonic growth factor, bone morphogenic protein 1 and low-density lipoprotein receptor motifs of MTP. We found that NS/P cell mitochondrial membrane potential is impaired by MTP knockdown, and ATP synthesis and oxygen consumption rate are significantly reduced in MTP-knockdown NS/P cells. Among the oxidative phosphorylation functions, the greatest effect of MTP knockdown is the reduction by over 50% in the mitochondrial energy reserve capacity. This made MTP-knockdown NS/P cells unable to overcome hydrogen peroxide stress, which leads to cessation of cell growth. This work identifies 2 previously unknown functions for MTP: first as a binding protein in the mitochondrial F₁F₀-ATP synthase complex and second as a regulatory mechanism of mitochondrial bioenergetics. Mitochondrial MTP may serve a protective function for NS/P cells in response to stress.-Fang, J.-D., Tung, H.-H., Lee, S.-L. Mitochondrial localization of St14-encoding transmembrane serine protease is involved in neural stem/progenitor cell bioenergetics through binding to F₀F₁-ATP synthase complex.

Cellular Abnormalities and Emerging Biomarkers in Alcohol-Associated Liver Disease

Alcohol-associated liver disease (AALD) is the third most common preventable cause for disease burden and mortality in the US. AALD, including alcoholic hepatitis (AH), contributes to half of admissions from decompensated liver disease and 20% of all liver transplants in the US. Peripheral blood cells contribute to systemic inflammation, oxidative stress, mitochondrial dysfunction, and fibrosis in AALD and AH. Alcohol dysregulates function of lymphocytes, neutrophils, monocytes, and tissue macrophages of the innate immune system. These alterations in turn can modulate adaptive immune responses. In this review, we describe these disruptive effects of alcohol on cells of the innate and adaptive immune system and focus on cellular-based emerging biomarkers on diagnosis and prognosis of patients with AALD and AH.

The brominated flame retardant BDE 47 upregulates purine metabolism and mitochondrial respiration to promote adipocyte differentiation

Adipocyte differentiation is closely associated with obesity and obesity-induced metabolic disorders. Epidemiological studies have demonstrated the association of obesity with environmental pollutants, such as polybrominated diphenyl ethers (PBDEs), common flame retardants in various consumer products. However, their obesogenic effects and mechanism are underexplored. We employed non-targeted metabolomics studies based on liquid chromatography-high resolution mass spectrometry to determine how 2,2',4,4'-tetra-brominated biphenyl ether (BDE 47), one of the main congeners of PBDEs detected in human tissue, promotes adipocyte differentiation of mouse preadipocyte 3 T3-L1 cells. The promoting effects of BDE 47 exposure (5 or 10 μM) on adipocyte differentiation were confirmed by enhancing lipid accumulation and expression levels of biomarkers of adipogenesis. For the first time, we demonstrated that BDE 47 upregulated purine metabolism and altered glutathione metabolism to promote oxidative stress and uric acid production in adipocytes. BDE 47 also elevated mitochondrial respiration and glycolysis in adipocytes to induce more ATP to combat oxidative stress. Antioxidant treatments, including the suppression of xanthine oxidase, inhibited the effects of BDE 47 on inducing oxidative stress and lipid accumulation. BDE 47 may be a potential environmental obesogen by providing a permissive oxidative environment to induce adipocyte differentiation.

ALDH2 Activity Reduces Mitochondrial Oxygen Reserve Capacity in Endothelial Cells and Induces Senescence Properties

Endothelial cells (ECs) are dynamic cells that turn from growth into senescence, the latter being associated with cellular dysfunction, altered metabolism, and age-related cardiovascular diseases. Aldehyde dehydrogenase 2 (ALDH2) is a mitochondrial enzyme metabolizing acetaldehyde and other toxic aldehydes, such as 4-hydroxynonenal (4-HNE). In conditions in which lipid peroxidation products and reactive oxygen species (ROS) are accumulated, ECs become dysfunctional and significantly contribute to the progression of vascular-dependent diseases. The aim of the present study has been to investigate whether inhibition of ALDH2 alters endothelial functions together with the impairment of bioenergetic functions, accelerating the acquisition of a senescent phenotype. HUVECs transfected with siRNA targeting ALDH2 or treated with daidzin, an ALDH2 inhibitor, were used in this study. We observed an alteration in cell morphology associated with endothelial dysfunctions. Loss of ALDH2 reduced cell proliferation and migration and increased paracellular permeability. To assess bioenergetic function in intact ECs, extracellular flux analysis was carried out to establish oxygen consumption rates (OCR). We observed a decrease in mitochondrial respiration and reserve capacity that coincided with SA-β-Gal accumulation and an increase in p21 and p53 expression in siALDH2 or daidzin-treated HUVECs. Treatment with N-acetyl-L-cysteine (NAC) reduced endothelial dysfunctions mediated by siALDH2, indicating that oxidative stress downstream to siALDH2 plays an instrumental role. Our results highlight that ALDH2 impairment accelerates the acquisition of a premature senescent phenotype, a change likely to be associated with the observed reduction of mitochondrial respiration and reserve capacity.