Reduction In Mitochondrial Function Research Articles

Rapid mitochondrial dysfunction mediates TNF-alpha-induced neurotoxicity.

Tumor necrosis factor alpha (TNF-α) is known to exacerbate ischemic brain injury; however, the mechanism is unknown. Previous studies have evaluated the effects of TNF-α on neurons with long exposures to high doses of TNF-α, which is not pathophysiologically relevant. We characterized the rapid effects of TNF-α on basal respiration, ATP production, and maximal respiration using pathophysiologically relevant, post-stroke concentrations of TNF-α. We observed a reduction in mitochondrial function as early as 1.5 h after exposure to low doses of TNF-α, followed by a decrease in cell viability in HT-22 cells and primary neurons. Subsequently, we used the HT-22 cell line to determine the mechanism by which TNF-α causes a rapid and profound reduction in mitochondrial function. Pre-treating with TNF-R1 antibody, but not TNF-R2 antibody, ameliorated the neurotoxic effects of TNF-α, indicating that TNF-α exerts its neurotoxic effects through TNF-R1. We observed an increase in caspase 8 activity and a decrease in mitochondrial membrane potential after exposure to TNF-α which resulted in a release of cytochrome c from the mitochondria into the cytosol. These novel findings indicate for the first time that an acute exposure to pathophysiologically relevant concentrations of TNF-α has neurotoxic effects mediated by a rapid impairment of mitochondrial function. This study focuses on the neurotoxic mechanism of a pro-inflammatory cytokine, tumor necrosis factor alpha (TNF-α). We demonstrate a prompt mitochondrial dysfunction followed by nerve cell loss after exposure to TNF-α. These studies may provide evidence that the immune system can rapidly and adversely affect brain function and that TNF-α signaling may be a target for neuroprotection.

Prohibitin coordinates an anti‐inflammatory/antioxidant feedback loop from mitochondria to nucleus to protect the heart from severe inflammatory stress

Cardiovascular and mitochondrial dysfunctions are well‐known complications of sepsis. Prohibitin (PHB), a mitochondrial protein, has been implicated in experimental models involved in coordinating inflammatory signaling; its mechanisms are unknown. We investigated the role of PHB in the heart during sepsis using an in vivo model (LPS) and in vitro model (TNFα/IL1β) in HL1 cardiomyocytes (HL1c). Sepsis caused reductions in mitochondrial function in both models. In rats, LPS reduced PHB expression in whole heart at 4 and 24 hrs post exposure. While the total cardiac PHB decreased, serum levels spiked 3‐fold and the remainder became concentrated in nucleus. In vitro overexpression of PHB (oPHB) in HL1c attenuated the cytokine‐induced lowers O2 consumption, ATP generation, and Ca2+ retention, and prevented raises in H2O2 in response to these cytokines. oPHB protected the HL1c from TNFα/IL1β‐induced cytotoxicity. oPHB and recombinant PHB to HL1c reduced TNFα/IL1β‐induced NFκB activation and transcription of its downstream targets. These findings uncover a novel role for PHB and suggest that PHB can act as a mobile signal transducer which can suppress inflammation and oxidative stress during sepsis. We anticipate that these findings will lead to novel therapies that exploit the pleiotropic functions of PHB, protecting the heart from diseases in which inflammation and oxidative stress are common.

Mitochondrial Respiration Is Decreased in Rat Kidney Following Fetal Exposure to a Maternal Low-Protein Diet

Maternal protein restriction in rat pregnancy is associated with impaired renal development and age-related loss of renal function in the resulting offspring. Pregnant rats were fed either control or low-protein (LP) diets, and kidneys from their male offspring were collected at 4, 13, or 16 weeks of age. Mitochondrial state 3 and state 4 respiratory rates were decreased by a third in the LP exposed adults. The reduction in mitochondrial function was not explained by complex IV deficiency or altered expression of the complex I subunits that are typically associated with mitochondrial dysfunction. Similarly, there was no evidence that LP-exposure resulted in greater oxidative damage to the kidney, differential expression of ATP synthetase β-subunit, and ATP-ADP translocase 1. mRNA expression of uncoupling protein 2 was increased in adult rats exposed to LP in utero, but there was no evidence of differential expression at the protein level. Exposure to maternal undernutrition is associated with a decrease in mitochondrial respiration in kidneys of adult rats. In the absence of gross disturbances in respiratory chain protein expression, programming of coupling efficiency may explain the long-term impact of the maternal diet.

Traumatic brain injury and trichloroethylene exposure interact and produce functional, histological, and mitochondrial deficits

Mitochondria play a pivotal role in the development of pathology associated with Parkinson's disease (PD), traumatic brain injury (TBI), and following exposure to the environmental toxin trichloroethylene (TCE). Evidence from humans indicates that both TBI and TCE can play a role in the development of PD and that each of these insults result in significant mitochondrial dysfunction. In the current studies we hypothesized that exposure to both TCE and TBI would result in increased pathology associated with PD. To test this hypothesis, 16 week old male Fischer 344 rats were administered TCE for either one or two weeks by oral gavage. Following exposure to TCE, rats were subjected to either a sham, mild (1.0mm), or moderate (2.0mm) controlled cortical impact TBI. Given the strong connection between mitochondrial function and PD, TBI, and TCE, tissue from the striatum and substantia nigra were analyzed 6h after the TBI. Neither TCE exposure, TBI, nor the combination of the two insults resulted in mitochondrial deficits at 6h post-TBI in the substantia nigra. Unlike the substantia nigra, the striatum exhibited significant mitochondrial dysfunction. Exposure to TCE alone for two weeks resulted in approximately a 75% reduction in mitochondrial function (p<0.05) in the striatum whereas TBI alone resulted in approximately a 30% reduction in striatal mitochondrial function. Following 1 week exposure to TCE followed by TBI, there was a significant reduction (50%) in mitochondrial function (p<0.05) which required the presence of both insults. Beginning 12days after the injury significant motor impairment was observed with Rotarod testing. Animals exposed to TCE and a moderate TBI exhibited performance which was approximately 50% of controls (p<0.01). Cylinder testing revealed that at 30days post-injury animals exposed to TCE and a moderate TBI also had about a 34% reduction in the usage of the contralateral fore paw and this impairment was significantly worse than both control animals and animals exposed to TCE and a mild TBI (p<0.05). At 30 days post-injury there was a 13–17% reduction in the number of tyrosine hydroxylase (TH) positive neurons in the substantia nigra (p<0.05), which was the result of protein loss and not cell death. Loss of TH positive neurons did not result in changes in striatal TH fiber density or levels of the dopamine transporter or type-2 dopamine receptor. Additionally, exposure to TCE prior to the TBI did not increase the loss of cortical tissue, indicating regional specificity for TCE induced deficits. These studies provide further evidence for the connection between TCE, TBI, and PD and lend support to the concept that PD develops from a multifactorial injury scenario.

Ginkgo extract EGb 761® shields from slowly accumulating neurodegenerative-like changes in a newly developed cell culture model induced by the combined action of low doses of antimycin A1 and 2-deoxy-d-glucose

Different cell culture models were already used to analyze the molecular base of the neuroprotective activities of the Ginkgo biloba extract EGb 761(®) after a single or short-term application. In these previous studies cells were severely injured with agents that promptly induce fatal cellular damage, like vast oxidative stress or mitochondrial dysfunction, and the protective effects of EGb 761(®) on such acute damage were evaluated. Our present study aimed to test EGb 761(®) action in cell cultures, where cellular functions are only moderately impaired by a longer lasting, but relatively modest oxidative stress, reduction of mitochondrial function and reduced intracellular energy levels, thereby causing only slow occurence of cellular damage over a time period of 2weeks. To this end we used neuroblastoma cells (SK-N-MC) that were treated with low doses of a combination of antimycin A1 and 2-deoxy-D: -glucose. Addition of EGb 761(®) to the culture medium efficiently shielded the cells from progressing injury by reduced ATP-levels, oxidized redox state, lipid peroxidation damage and oxidative damage of mitochondrial DNA. As a result the cells were protected from apoptotic death that was observed in cultures without EGb 761(®) after 2weeks of damage occurence. This cell culture system characterizing moderate cellular stress will be applied in future studies to further investigate the mode of action of single EGb 761(®) compounds.

Targeted Expression of Catalase to Mitochondria Prevents Age-Associated Reductions in Mitochondrial Function and Insulin Resistance

Aging-associated muscle insulin resistance has beenhypothesized to be due to decreased mitochondrial function, secondary to cumulative free radical damage, leading to increased intramyocellular lipid content. To directly test this hypothesis, we examined both invivo and invitro mitochondrial function, intramyocellular lipid content, and insulin action in lean healthy mice with targeted overexpression of the human catalase gene to mitochondria (MCAT mice). Here, we show that MCAT mice are protected from age-induced decrease in muscle mitochondrial function (∼30%), energy metabolism (∼7%), and lipid-induced muscle insulin resistance. This protection from age-induced reduction in mitochondrial function was associated with reduced mitochondrial oxidative damage, preserved mitochondrial respiration and muscle ATP synthesis, and AMP-activated protein kinase-induced mitochondrial biogenesis. Taken together, these data suggest that the preserved mitochondrial function maintained by reducing mitochondrial oxidative damage may prevent age-associated whole-body energy imbalance and muscle insulin resistance.

Mitochondrial DNA alterations and reduced mitochondrial function in aging

Oxidative damage to mitochondrial DNA increases with aging. This damage has the potential to affect mitochondrial DNA replication and transcription which could alter the abundance or functionality of mitochondrial proteins. This review describes mitochondrial DNA alterations and changes in mitochondrial function that occur with aging. Age-related alterations in mitochondrial DNA as a possible contributor to the reduction in mitochondrial function are discussed.

The protective effect of melatonin on methamphetamine-induced calpain-dependent death pathway in human neuroblastoma SH-SY5Y cultured cells

Methamphetamine (METH) is a potent psychostimulant drug that may cause neuronal cell degeneration. The underlying mechanisms of METH-induced neuronal toxicity remains poorly understood. In this study, we investigated an important role of calpain-dependent cascades in methamphetamine-induced toxicity in human dopaminergic neuroblastoma SH-SY5Y cultured cell lines. In addition, the protective effect of melatonin against METH-induced calpain-dependent death pathway was also investigated. The results of this study show that METH significantly decreased cell viability and tyrosine hydroxylase phosphorylation in SH-SY5Y cultured cells. Melatonin reversed the toxic effect of METH by inducing cell viability. In addition, melatonin was able to restore the reduction in mitochondrial function and phosphorylation of tyrosine hydroxylase in SH-SY5Y treated cells. An induction of calpain expression and activity but a reduction of calpain inhibitor (calpastatin) protein levels were observed in SH-SY5Y cells treated with METH but these effects were diminished by melatonin. These results implicated calpain-dependent death pathways in the processes of METH-induced toxicity and also indicated that melatonin has the capacity to reverse this toxic effect in SH-SY5Y cultured cells.

The Effect of Aging on Human Skeletal Muscle Mitochondrial and Intramyocellular Lipid Ultrastructure

The purpose of this study was to determine whether ultrastructural changes in intramyocellular lipid (IMCL) and mitochondria occur with aging. Muscle samples were analyzed from 24 young and 20 old, equally active, individuals for IMCL and mitochondria quantity and size as well as their association. Old men had larger IMCL droplets than all other groups in the total muscle area. Old individuals showed higher IMCL content in the subsarcolemmal area. Young participants had a greater number of mitochondria compared with old participants in both fiber regions and greater enzyme activities of cytochrome c oxidase and citrate synthase. The fraction of IMCL touching mitochondria was lowest in old women in the total area and in old men in the subsarcolemmal region. In summary, older adults have larger IMCL droplets, fewer mitochondria, and a lower proportion of IMCL in contact with mitochondria. These factors likely contribute to age-related reductions in mitochondrial function and lipid metabolism.

Endocannabinoids, FOXO and the metabolic syndrome: Redox, function and tipping point – The view from two systems

The endocannabinoid system (ECS) was only ‘discovered’ in the 1990s. Since then, many new ligands have been identified, as well as many new intracellular targets – ranging from the PPARs, to mitochondria, to lipid rafts. It was thought that blocking the CB-1 receptor might reverse obesity and the metabolic syndrome. This was based on the idea that the ECS was dysfunctional in these conditions. This has met with limited success. The reason may be that the ECS is a homeostatic system, which integrates energy seeking and storage behaviour with resistance to oxidative stress. It could be viewed as having thrifty actions. Thriftiness is an innate property of life, which is programmed to a set point by both environment and genetics, resulting in an epigenotype perfectly adapted to its environment. This thrifty set point can be modulated by hormetic stimuli, such as exercise, cold and plant micronutrients. We have proposed that the physiological and protective insulin resistance that underlies thriftiness encapsulates something called ‘redox thriftiness’, whereby insulin resistance is determined by the ability to resist oxidative stress. Modern man has removed most hormetic stimuli and replaced them with a calorific sedentary lifestyle, leading to increased risk of metabolic inflexibility. We suggest that there is a tipping point where lipotoxicity in adipose and hepatic cells induces mild inflammation, which switches thrifty insulin resistance to inflammation-driven insulin resistance. To understand this, we propose that the metabolic syndrome could be seen from the viewpoint of the ECS, the mitochondrion and the FOXO group of transcription factors. FOXO has many thrifty actions, including increasing insulin resistance and appetite, suppressing oxidative stress and shifting the organism towards using fatty acids. In concert with factors such as PGC-1, they also modify mitochondrial function and biogenesis. Hence, the ECS and FOXO may interact at many points; one of which may be via intracellular redox signalling. As cannabinoids have been shown to modulate reactive oxygen species production, it is possible that they can upregulate anti-oxidant defences. This suggests they may have an ‘endohormetic’ signalling function. The tipping point into the metabolic syndrome may be the result of a chronic lack of hormetic stimuli (in particular, physical activity), and thus, stimulus for PGC-1, with a resultant reduction in mitochondrial function and a reduced lipid capacitance. This, in the context of a positive calorie environment, will result in increased visceral adipose tissue volume, abnormal ectopic fat content and systemic inflammation. This would worsen the inflammatory-driven pathological insulin resistance and inability to deal with lipids. The resultant oxidative stress may therefore drive a compensatory anti-oxidative response epitomised by the ECS and FOXO. Thus, although blocking the ECS (e.g. via rimonabant) may induce temporary weight loss, it may compromise long-term stress resistance. Clues about how to modulate the system more safely are emerging from observations that some polyphenols, such as resveratrol and possibly, some phytocannabinoids, can modulate mitochondrial function and might improve resistance to a modern lifestyle.

N-3 HUFAs affect fat deposition, susceptibility to oxidative stress, and apoptosis in Atlantic salmon visceral adipose tissue

We have investigated how n-3 highly unsaturated fatty acids (HUFAs) in the diet affect fatty acid (FA) utilization, fat storage and oxidative stress (OS) in Atlantic salmon (Salmo salar) white adipose tissue (WAT). Four groups of Atlantic salmon were fed for 21 weeks on one of the four diets supplemented with 23% (of dry matter) lipid. Docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3) levels increased from 10% of total FAs in the rapeseed oil (RO) diet, to 20% in the fish oil (FO) diet, and to 50% and 55% in the DHA-enriched and EPA-enriched diets, respectively. Increased dietary levels of n-3 HUFAs resulted in lower fat percentage in WAT. Furthermore, mitochondrial FA beta-oxidation activity was higher in the FO group than it was in the RO group. The relative levels of DHA and EPA in phospholipids (PLs) from WAT and mitochondrial membranes increased with the increasing dietary levels of these HUFAs. In general, the mitochondrial membrane PLs were characterised by lower relative levels of n-3 HUFAs and higher relative levels of linoleic acid (LA; 18:2 n-6) than WAT membrane PLs. The predominance of LA relative to n-3 HUFAs in mitochondrial membrane PLs may help to protect these PLs from peroxidation. Cytochrome c oxidase measurements revealed higher incidence of disrupted mitochondrial membranes in the DHA and EPA dietary groups than in the FO and RO dietary groups. This disruption further affected the mitochondrial function, resulting in a marked reduction in FA beta-oxidation capacities. The reduction in mitochondrial function and the increase in the activity of superoxide dismutase (SOD) in the DHA and EPA groups showed that high dietary dose of DHA and EPA resulted in oxidative stress (OS). The increased activity of caspase 3 in the high n-3 HUFA groups suggested the induction of apoptosis and increased incidence of cell death in WAT, which may be one of the factors explaining the lower fat percentage found in these groups.

Disruption of a mitochondrial RNA-binding protein gene results in decreased cytochrome b expression and a marked reduction in ubiquinol–cytochrome c reductase activity in mouse heart mitochondria

Mice homozygous for a defect in the PTCD2 (pentatricopeptide repeat domain protein 2) gene were generated in order to study the role of this protein in mitochondrial RNA metabolism. These mice displayed specific but variable reduction of ubiquinol-cytochrome c reductase complex activity in mitochondria of heart, liver and skeletal muscle due to a decrease in the expression of mitochondrial DNA-encoded cytochrome b, the catalytic core of the complex. This reduction in mitochondrial function has a profound effect on the myocardium, with replacement of ventricular cardiomyocytes by fibro-fatty tissue. Northern blotting showed a reduction in the mRNA for the mitochondrial DNA encoded proteins cytochrome b (cytb) and ND5 (NADH dehydrogenase subunit 5) and an elevation in a combined pre-processed ND5-CYTB transcript. This suggests that the PTCD2 protein is involved in processing RNA transcripts involving cytochrome b derived from mitochondrial DNA. This defines the site for PTCD2 action in mammalian mitochondria and suggests a possible role for dysfunction of this protein in the aetiology of heart failure.

Age-related changes in H2O2 production and bioenergetics in rat brain synaptosomes

Detrimental changes to mitochondrial function have been shown to occur with age. In this study we examined the levels of H2O2 production, in situ mitochondrial membrane potential (Δψm), oxygen consumption (JO2) and electron transport chain (ETC) enzyme activities in synaptosomes isolated from rats of two age groups, 6 and 18 months. The rate of H2O2 production in synaptosomes was found to be higher in the 18-month old group compared to that of 6-month old. Δψm was found to be significantly lower in synaptosomes from the older rats, which also correlated with a reduction in JO2. Measurement of the individual electron transport chain enzyme activities revealed that reduced complex II/III and complex IV activities were the possible contributors to the reduced bioenergetic function in synaptosomes from the older rats. These data suggest that ageing may lead to increased nerve terminal H2O2 production while simultaneous deleterious effects on bioenergetic function occur in in situ synaptosomal mitochondria. In addition, Ca2+-independent glutamate release was found to be increased at lower levels of complex I inhibition in the synaptosomes from older rats, suggesting that reduction of mitochondrial function may potentiate excitotoxic conditions in the ageing brain.

Efavirenz induces alterations in lipid metabolism through AMPK activation

Summary of results EFV produced an immediate reduction of mitochondrialfunction, evident by the significant and dose-dependentinhibition of mitochondrial O2 consumption and thedecrease of intracellular ATP and Δψm. This metabolicstress promoted the activation of AMPK, triggering severalof its signalling pathways, as EFV induced an increment inCD36 mRNA expression and in intracellular lipid content,which could have been a result of the formation of lipiddroplets. This intracellular lipid increase was not presentin cells treated with Compound C, which points to a keyrole for AMPK in these mechanisms. Conclusion Given that EFV treatment is usually prolonged, thesemechanisms may effect the general regulation of lipidmetabolism and could cause the alterations that are char-acteristic of lipoatrophy.

In vitro effects of the active metabolite of leflunomide, A77 1726, on feline herpesvirus–1

To determine whether the active metabolite of leflunomide, A77 1726 (A77), inhibits replication of feline herpesvirus-1 (FHV-1) in cell culture. Crandell Rees feline kidney (CRFK) cell cultures. Cell cultures were inoculated with FHV-1 and treated simultaneously with concentrations of A77 ranging from 0 to 200microM. The antiviral effect of A77 was determined by use of conventional plaque reduction assays. The effect of A77 on viral load was determined via real-time PCR analysis, and transmission electron microscopy was used to evaluate the effect of A77 on viral morphology. To determine whether the antiviral effect was attributable to alterations in CRFK cell viability and number, CRFK cells were treated with various concentrations of A77 and stained with Annexin V and propidium iodide to assess apoptosis and a mitochondrial function assay was used to determine cell viability. Concentrations of A77 > or = 20microM were associated with substantial reduction in plaque number and viral load. Concentrations > or = 100microM were associated with complete suppression of plaque formation. At low concentrations of A77, clusters of intracytoplasmic virus particles that appeared to lack tegument and an external membrane were detected. Treatment of uninfected CRFK cell monolayers with A77 was associated with reduction in mitochondrial function with minimal evidence of apoptosis. Leflunomide may be an alternative to current calcineurin-based immunosuppressive protocols used in feline organ transplantation because of its antiherpesviral activity.

Aging-Associated Reductions in AMP-Activated Protein Kinase Activity and Mitochondrial Biogenesis

SummaryRecent studies have demonstrated a strong relationship between aging-associated reductions in mitochondrial function, dysregulated intracellular lipid metabolism, and insulin resistance. Given the important role of the AMP-activated protein kinase (AMPK) in the regulation of fat oxidation and mitochondrial biogenesis, we examined AMPK activity in young and old rats and found that acute stimulation of AMPK-α2 activity by 5′-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) and exercise was blunted in skeletal muscle of old rats. Furthermore, mitochondrial biogenesis in response to chronic activation of AMPK with β-guanidinopropionic acid (β-GPA) feeding was also diminished in old rats. These results suggest that aging-associated reductions in AMPK activity may be an important contributing factor in the reduced mitochondrial function and dysregulated intracellular lipid metabolism associated with aging.

Changes in Hsp60 Level of the Failing Heart Following Acute Myocardial Infarction and the Effect of Long-Term Treatment with Trandolapril

Changes in heat shock protein (Hsp) 60 of the viable left ventricular muscle (viable LV) after myocardial infarction in rats and the effect of the angiotensin I-converting enzyme inhibitor (ACEI) trandolapril were examined. Myocardial infarction was induced in rats by ligation of the left coronary artery. The coronary artery-ligated (CAL) and sham-operated (Sham) rats were orally treated with 3 mg/kg/d trandolapril from the 2nd to 8th week after surgery. Hemodynamic parameters and tissue weights of the left and right ventricles of the animals at the 8th week after CAL (8w-CAL rats) showed signs indicating chronic heart failure. An increase in Hsp60 content, a decrease in mitochondrial oxygen consumption rate (OCR), and an increase in the mitochondrial thiobarbiturate-reacting substance (TRS) of the viable LV were detected. Eight weeks after CAL. Long-term treatment of the CAL rats with trandolapril improved the hemodynamic parameters, attenuated the CAL-induced increase in Hsp60 content, the decrease in mitochondrial OCR, and the increase in the mitochondrial TRS content of the viable LV at the 8th week after myocardial infarction. The increase in Hsp60 content was closely related to the decrease in the mitochondrial OCR and to a rise in the LVEDP of the CAL animal at the 8th week after myocardial infarction. These results suggest that a series of pathophysiological alterations, including a reduction in mitochondrial function, appearance of reactive oxygen stress, and production of Hsp60 is involved in the development of cardiac failure and that trandolapril is beneficial for preventing these alterations.

Molecular Mechanisms of Insulin Resistance in Humans and Their Potential Links With Mitochondrial Dysfunction

Recent studies using magnetic resonance spectroscopy have shown that decreased insulin-stimulated muscle glycogen synthesis due to a defect in insulin-stimulated glucose transport activity is a major factor in the pathogenesis of type 2 diabetes. The molecular mechanism underlying defective insulin-stimulated glucose transport activity can be attributed to increases in intramyocellular lipid metabolites such as fatty acyl CoAs and diacylglycerol, which in turn activate a serine/threonine kinase cascade, thus leading to defects in insulin signaling through Ser/Thr phosphorylation of insulin receptor substrate (IRS)-1. A similar mechanism is also observed in hepatic insulin resistance associated with nonalcoholic fatty liver, which is a common feature of type 2 diabetes, where increases in hepatocellular diacylglycerol content activate protein kinase C-epsilon, leading to reduced insulin-stimulated tyrosine phosphorylation of IRS-2. More recently, magnetic resonance spectroscopy studies in healthy lean elderly subjects and healthy lean insulin-resistant offspring of parents with type 2 diabetes have demonstrated that reduced mitochondrial function may predispose these individuals to intramyocellular lipid accumulation and insulin resistance. Further analysis has found that the reduction in mitochondrial function in the insulin-resistant offspring can be mostly attributed to reductions in mitochondrial density. By elucidating the cellular and molecular mechanisms responsible for insulin resistance, these studies provide potential new targets for the treatment and prevention of type 2 diabetes.

Last Word: Point:Counterpoint authors respond to commentaries on “Hypoxic pulmonary vasoconstriction is/is not mediated by increased production of reactive oxygen species”

LETTERS TO THE EDITORLast Word: Point:Counterpoint authors respond to commentaries on “Hypoxic pulmonary vasoconstriction is/is not mediated by increased production of reactive oxygen species”E. Kenneth Weir, and Stephen L. ArcherE. Kenneth Weir, and Stephen L. ArcherPublished Online:01 Sep 2006https://doi.org/10.1152/japplphysiol.00707.2006This is the final version - click for previous versionMoreSectionsPDF (29 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat To the Editor: Regarding the pro-con debate on reactive oxygen species (ROS) and hypoxic pulmonary vasoconstriction (HPV), Dr. Aaronson (1) raises questions about oxygen sensing, ROS/redox state, and HPV in the mice that lack the gp91 component of NADPH oxidase (2). We agree that the ROS levels measured at the lung surface in these mice are markedly diminished, indicating that the ROS measured by this technique are largely generated by NADPH oxidase and do not control HPV. This leaves ROS production by mitochondria and the cellular redox state as potential sensors. The paper showed that HPV was still present in mice lacking the isoform of NADPH oxidase that contains the gp91 subunit. It should not be interpreted to say that the mitochondria in the resistance pulmonary arteries of these mice do not produce ROS. We provide considerable evidence in the debate that mitochondrial production of ROS is likely to play an important role in normoxic pulmonary vasodilatation.Dr. Aaronson (1) also suggests that the intracellular milieu in most cells is relatively reduced, leaving little room for hypoxia to reduce it further. The pulmonary artery smooth muscle cells live at a much higher oxygen tension than systemic smooth muscle cells, so redox conditions may be different. Certainly hypoxia has been shown to make the lungs more reduced in terms of NAD(P)H-to-NAD(P) ratios (4, 5) and GSH (6). Thus changes in redox status and/or mitochondrial ROS, and/or other NADPH oxidase isoforms could act as oxygen sensors.In regard to the letter from Professors Acker and Fandrey (1), we discussed hypoxia-inducible factor (HIF) in the setting of the fawn-hooded rat, in which we show that a reduction in mitochondrial function and ROS result in activation of HIF. This can be reversed by exogenous H2O2, suggesting that a decrease in ROS signals this effect of hypoxia.Our main difference of opinion with Dr. Packer (1) relates to the assertion that H2O2 causes constriction in all vessels. The reference restriction prevents us from documenting the many papers that have demonstrated H2O2 to cause vasodilatation. The reader should refer to the section on vasodilatation in a recent review (3) or enter “hydrogen peroxide and vasodilatation” in PubMed.REFERENCES1 Aaronson PI, Berchner-Pfannschmidt U, Acker H, Fandrey J, Gupte SA, Wolin MS, Packer CS, Peleaz NJ, Evans AM, and Gonzalez C. Comments on Point:Counterpoint series “Hypoxic pulmonary vasoconstriction is/is not mediated by increased production of reactive oxygen species.” J Appl Physiol 101: 1001–1002, 2006.Google Scholar2 Archer S, Reeve H, Michelakis E, Puttagunta L, Waite R, Nelson DP, Dinauer MC, and Weir EK. O2 sensing is preserved in mice lacking the gp91 phox subunit of NADPH oxidase. Proc Natl Acad Sci USA 96: 7944–7949, 1999.Crossref | PubMed | ISI | Google Scholar3 Cai H. Hydrogen peroxide regulation of endothelial function: origins, mechanisms, and consequences. Cardiovasc Res 68: 26–36, 2005.Crossref | PubMed | ISI | Google Scholar4 Chander A, Dhariwal K, and Viswanathan R. Pyridine nucleotides in lung and liver of hypoxic rats. Life Sci 26: 1935–1945, 1980.Crossref | PubMed | ISI | Google Scholar5 Leach R, Hill H, Snetkov V, Robertson T, and Ward J. Divergent roles of glycolysis and the mitochondrial electron transport chain in hypoxic pulmonary vasoconstriction of the rat: identity of the hypoxic sensor. J Physiol 536: 211–124, 2001.Crossref | PubMed | ISI | Google Scholar6 Reeve H, Michelakis E, Nelson D, Weir E, and Archer S. Alterations in a redox oxygen sensing mechanism in chronic hypoxia. J Appl Physiol 90: 2249–2256, 2001.Link | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 101Issue 3September 2006Pages 1005-1005 Copyright & PermissionsCopyright © 2006 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00707.2006History Published online 1 September 2006 Published in print 1 September 2006 Metrics

Mitochondrial dysfunction and increased sensitivity to excitotoxicity in mice deficient in DNA mismatch repair

The expression profile in the hippocampus of mice lacking one allele of the MutS homologue (Msh2), gene, which is one of the most representative components of the DNA mismatch repair system, was analysed to understand whether defects in the repair or in response to DNA damage could impact significantly on brain function. The overall results suggested a reduction in mitochondrial function as indicated by gene expression analysis, biochemical and behavioural studies. In the hippocampus of Msh2+/- mice, array data, validated by RT-PCR and western blot analysis, showed reduced expression levels of genes for cytochrome c oxidase subunit 2 (CoxII), ATP synthase subunit beta and superoxide dismutase 1. Biochemically, mitochondria from the hippocampus and cortex of these mice show reduced CoxII and increased aconitase activity. Behaviourally, these alterations resulted in mice with increased vulnerability to kainic acid-induced epileptic seizures and hippocampal neuronal loss. These data suggest that lack of an efficient system involved in recognizing and repairing DNA damage may generate a brain mitochondriopathy.