Developmental changes of the adenine nucleotide translocation in rat brain

The Role of Mitochondrial and Endoplasmic Reticulum Reactive Oxygen Species Production in Models of Perinatal Brain Injury

Significance: Perinatal brain injury is caused by hypoxia-ischemia (HI) in term neonates, perinatal arterial stroke, and infection/inflammation leading to devastating long-term neurodevelopmental deficits. Therapeutic hypothermia is the only currently available treatment but is not successful in more than 50% of term neonates suffering from hypoxic-ischemic encephalopathy. Thus, there is an urgent unmet need for alternative or adjunct therapies. Reactive oxygen species (ROS) are important for physiological signaling, however, their overproduction/accumulation from mitochondria and endoplasmic reticulum (ER) during HI aggravate cell death. Recent Advances and Critical Issues: Mechanisms underlying ER stress-associated ROS production have been primarily elucidated using either non-neuronal cells or adult neurodegenerative experimental models. Findings from mature brain cannot be simply transferred to the immature brain. Therefore, age-specific studies investigating ER stress modulators may help investigate ER stress-associated ROS pathways in the immature brain. New therapeutics such as mitochondrial site-specific ROS inhibitors that selectively inhibit superoxide (O2•-)/hydrogen peroxide (H2O2) production are currently being developed. Future Directions: Because ER stress and oxidative stress accentuate each other, a combinatorial therapy utilizing both antioxidants and ER stress inhibitors may prove to be more protective against perinatal brain injury. Moreover, multiple relevant targets need to be identified for targeting ROS before they are formed. The role of organelle-specific ROS in brain repair needs investigation. Antioxid. Redox Signal. 31, 643-663.

Carnitine regulates myocardial metabolism by Peroxisome Proliferator-Activated Receptor-alpha (PPARalpha) in alcoholic cardiomyopathy

BACKGROUND

Chronic alcohol intake exerts myocardial damage en route to the development of alcoholic cardiomyopathy (ACM), although the precise pathogenesis of ACM is unknown. Carnitine is known to participate in the regulation of metabolism in a number of heart diseases. This study was designed to examine the interplay between myocardial metabolism and carnitine in the development of ACM.

MATERIAL/METHODS

Experimental animals were divided into 3 groups: (i) group A: alcohol-fed. (ii) group B: alcohol/carnitine: (200mg/kg/d, p.o. by mixing carnitine in rat chow). (iii) group C: control. Blood levels of free fatty acid (FFA), total carnitine (TC) and free carnitine (FC) were monitored in rats receiving alcohol with or without carnitine. Mitochondrial adenine nucleotide translocator-1 (ANT1) activity, ATPase activity, high energy phosphate concentration, peroxisome proliferator-activated receptor-α (PPARα), carnitine-palmitoyl transferase I (CPT-I), medium-chain acyl-coenzyme A dehydrogenase (MCAD), ANT1 and ATPase mRNA and protein expression were also monitored in myocardial tissue.

RESULTS

Experimental animals received alcohol with or without carnitine for six 6 months. Our results indicated that FFA increased abruptly. TC and FC were significantly decreased in groups receiving alcohol at 4 months. The concentration of ATP, ADP and AMP in the myocardium decreased following 2 months of alcohol administration. mRNA and protein expression of PPARα, CPT-I, MCAD, ANT1 and ATPase expressions were gradually altered in groups following alcohol feeding.

CONCLUSIONS

These observations suggest that abnormal metabolism is present in the myocardium during the development of ACM. Carnitine may improve myocardial metabolism by elevating the content of PPARα, CPT-I and MCAD.

Modulation of F0F1-ATP synthase activity by cyclophilin D regulates matrix adenine nucleotide levels

Cyclophilin D was recently shown to bind to and decrease the activity of F(0)F(1)-ATP synthase in submitochondrial particles and permeabilized mitochondria [Giorgio V et al. (2009) J Biol Chem, 284, 33982-33988]. Cyclophilin D binding decreased both ATP synthesis and hydrolysis rates. In the present study, we reaffirm these findings by demonstrating that, in intact mouse liver mitochondria energized by ATP, the absence of cyclophilin D or the presence of cyclosporin A led to a decrease in the extent of uncoupler-induced depolarization. Accordingly, in substrate-energized mitochondria, an increase in F(0)F(1)-ATP synthase activity mediated by a relief of inhibition by cyclophilin D was evident in the form of slightly increased respiration rates during arsenolysis. However, the modulation of F(0)F(1)-ATP synthase by cyclophilin D did not increase the adenine nucleotide translocase (ANT)-mediated ATP efflux rate in energized mitochondria or the ATP influx rate in de-energized mitochondria. The lack of an effect of cyclophilin D on the ANT-mediated adenine nucleotide exchange rate was attributed to the ∼ 2.2-fold lower flux control coefficient of the F(0)F(1)-ATP synthase than that of ANT, as deduced from measurements of adenine nucleotide flux rates in intact mitochondria. These findings were further supported by a recent kinetic model of the mitochondrial phosphorylation system, suggesting that an ∼ 30% change in F(0)F(1)-ATP synthase activity in fully energized or fully de-energized mitochondria affects the ADP-ATP exchange rate mediated by the ANT in the range 1.38-1.7%. We conclude that, in mitochondria exhibiting intact inner membranes, the absence of cyclophilin D or the inhibition of its binding to F(0)F(1)-ATP synthase by cyclosporin A will affect only matrix adenine nucleotides levels.

Changes in dihydrolipoamide dehydrogenase expression and activity during postnatal development and aging in the rat brain

Brain energy metabolism is increased during postnatal development and diminished in neurodegenerative diseases linked to senescence. The objective of this study was to determine if these conditions could involve postnatal or senescence-related shifts in activity or expression of dihydrolipoamide dehydrogenase (DLDH), a key mitochondrial oxidoreductase. Rats ranging from 10 to 60 days of age were used in studies of postnatal development, whereas rats aged 5 or 30 months were used in the aging studies. The expression of DLDH was determined by Western blot analysis using anti-DLDH antibodies and DLDH diaphorase activity was measured by an in-gel activity staining method using nitroblue tetrazolium (NBT)/NADH. Activity of DLDH dehydrogenase was measured as NAD+ oxidation of dihydrolipoamide. When these measures were considered in separate groups of 10-, 20-, 30-, or 60-day-old rats, all three showed an increase between 10 and 20 days of age. However, dehydrogenase activity of DLDH showed a further, progressive increase from 20 days to adulthood, in the absence of any further change in DLDH expression or diaphorase activity. No age-related decline in DLDH activity or expression was evident over the period from 5 to 30 months of age. Moreover, aging did not render DLDH more susceptible to oxidative inactivation by mitochondria-generated reactive oxygen species (ROS). Taken together, results of the present study indicate that (1) brain DLDH expression and activity undergo independent postnatal maturational increases; (2) senescence does not confer any detectable change in the activity of DLDH or its susceptibility to inactivation by mitochondrial oxidative stress.

Cloning, expression, and transcription analysis of L-arabinose isomerase gene from Mycobacterium smegmatis SMDU

The L-arabinose metabolic gene cluster, araA, araB, araD, araG, araH and araR, encoding L-arabinose isomerase (L-AI) and its accessory proteins was cloned from Mycobacterium smegmatis SMDU and sequenced. The deduced amino acid sequence of araA displayed highest identity with that of Bacillus subtilis (52%). These six genes comprised the L-arabinose operon, and its genetic arrangement was similar to that of B. subtilis. The L-AI gene (araA), encoding a 501 amino acid protein with a calculated molecular mass of 54,888 Da, was expressed in Escherichia coli. The productivity and overall enzymatic properties of the recombinant L-AI were almost same as the authentic L-AI from M. smegmatis. Although the recombinant L-AI showed high substrate specificity, as did L-AI from other organisms, this enzyme catalyzed not only isomerization of L-arabinose-L-ribulose and D-galactose-D-tagatose but also isomerization of L-altrose-L-psicose and L-erythrulose-L-threose. In combination with L-AI from M. smegmatis, L-threose and L-altrose can be produced from cheap and abundant erythritol and D-fructose respectively, indicating that this enzyme has great potential for biological application in rare sugar production. Transcription analysis using various sugars revealed that this enzyme was significantly induced not only by L-arabinose and D-galactose but also by L-ribose, galactitol, L-ribulose, and L-talitol. This different result of transcription mediated by sugars from that of E. coli suggests that the transcriptional regulation of araA from M. smegmatis against sugar is loose compared with that from E. coli, and that it depends on the hydroxyl configuration at C2, C3 and C4 positions of sugars.

Ca2+ storage capacity of rat brain mitochondria declines during the postnatal development without change in ROS production capacity

Ca2+ overload of mitochondria and oxidants are considered as crucial factors inducing the opening of the permeability transition pore (PTP) in mitochondria. The interdependence between permeability transition (PT), calcium retention capacity (CRC), and reactive oxygen species (ROS) generation was studied in mitochondria from immature and mature rat brain. Brain mitochondria isolated from 1-day- and 1-week-old rats are much more resistant to Ca2+-triggered PT in phosphate-containing incubation medium than mitochondria from adult brain, since the CRC decreases with development. CRC of mitochondria from 1-week-old rat brain was higher than for adult rat brain (450 +/- 112 vs. 175 +/- 35 nmol Ca2+ per mg of protein). In contrast, for ROS generation there was no age difference. In immature and mature mitochondria, basal, respiratory chain-inhibited or glutathione-depleted ROS generations were similar. In addition, the extent of the Ca2+ load was without effect on the basal ROS generation before mitochondria underwent PT. In summary, ROS generation does not crucially affect the ability of immature mitochondria to buffer high levels of extramitochondrial Ca2+ without undergoing PT. However, we hypothesize that the high resistance of immature mitochondria is related to the low content of some PTP complex constituents, such as creatine kinase.

Developmental changes in expression and subcellular localization of the DNA repair glycosylase, MYH, in the rat brain

Mammalian cells employ a network of DNA repair pathways. DNA repair is required during development to ensure accuracy of DNA replication in the rapidly dividing embryonic cells and to maintain genomic integrity in the mature organism. An enzyme involved in repair of replication errors generated on either normal or oxidatively damaged DNA templates, is the mammalian ortholog of the Escherichia coli MutY DNA glycosylase (MYH). We show that levels of MYH isoform, detected at the E14 embryonic stage, decrease during embryonic and neonatal rat development, while new isoforms appear and gradually increase in the neonate and adult brain. The temporally declining expression of embryonic MYH resembles the pattern of proliferating cell nuclear antigen (PCNA) decline during this period. Immunohistochemical analyses of the embryonic brain show that cells staining for MYH initially coincide with cells staining for PCNA. At later stages PCNA declines, while MYH is detected primarily outside the nucleus. MutY-like glycosylase activity for adenines misincorporated opposite oxidized guanines is detected in both, embryonic and adult brain extracts. Together, these findings suggest that in proliferating embryonic cells, MYH might be primarily involved in post replicative repair of nuclear DNA, whereas in post mitotic neurons, in the repair of mitochondrial DNA.

Developmental changes in the Ca2+-regulated mitochondrial aspartate-glutamate carrier aralar1 in brain and prominent expression in the spinal cord

Aralar1 and citrin are two isoforms of the mitochondrial carrier of aspartate-glutamate (AGC), a calcium regulated carrier, which is important in the malate-aspartate NADH shuttle. The expression and cell distribution of aralar1 and citrin in brain cells has been studied during development in vitro and in vivo. Aralar1 is the only isoform expressed in neurons and its levels undergo a marked increase during in vitro maturation, which is higher than the increase in mitochondrial DNA in the same time window. The enrichment in aralar1 per mitochondria during neuronal maturation is associated with a prominent rise in the function of the malate-aspartate NADH shuttle. Paradoxically, during in vivo development of rat or mouse brain there is very little postnatal increase in total aralar1 levels per mitochondria. This is explained by the fact that astrocytes develop postnatally, have aralar1 levels much lower than neurons, and their increase masks that of aralar1. Aralar1 mRNA and protein are widely expressed throughout neuron-rich areas in adult mouse CNS with clear enrichments in sets of neuronal nuclei in the brainstem and, particularly, in the ventral horn of the spinal cord. These aralar1-rich neurons represent a subset of the cytochrome oxidase-rich neurons in the same areas. The presence of aralar1 could reflect a tonic activity of these neurons, which is met by the combination of high malate-aspartate NADH shuttle and respiratory chain activities.

Uteroplacental insufficiency alters cerebral mitochondrial gene expression and DNA in fetal and juvenile rats

Uteroplacental insufficiency increases the risk of perinatal and long-term neurologic morbidity by depriving the fetus of oxidative substrate and causing intrauterine growth retardation. Skeletal muscle and liver from growth retarded fetal and juvenile rats respond to this deprivation by altering mitochondrial gene expression and function. The objective of this study was to determine whether cerebral mitochondrial mRNA is similarly altered in fetal and juvenile growth retarded rats and to correlate these alterations with mitochondrial DNA and marker protein levels. To fulfill this objective, mRNA levels of four important mitochondrial proteins were quantified using RT-PCR in growth retarded and sham-operated control fetal and juvenile rat brains; these proteins were NADH-ubiquinone oxireductase subunit 4, subunit C of the F1F0-ATPase, and the adenine nucleotide transporters 1 and 2. Mitochondrial DNA/nuclear DNA ratios and mitochondrial 60 kD marker protein levels were also quantified in growth retarded and sham-operated control fetal and juvenile rat brains using PCR and Western Blotting, respectively. Cerebral mRNA levels of all four proteins were increased in the IUGR fetuses and decreased in the IUGR juvenile animals. Cerebral mitochondrial/nuclear DNA ratios and mitochondrial marker protein levels were not significantly altered in the IUGR fetuses; however, both were significantly diminished in IUGR juvenile pups. These studies suggest that the metabolic stresses associated with uteroplacental insufficiency in the rat cause altered fetal and postnatal cerebral mitochondrial mRNA and DNA levels.

Differences in the activation of the mitochondrial permeability transition among brain regions in the rat correlate with selective vulnerability

Mitochondria from different regions of the brain were prepared, and the activation of the mitochondrial permeability transition (MPT) by calcium was investigated by monitoring the associated mitochondrial swelling. In general, the properties of the MPT in brain mitochondria were found to be qualitatively similar to those observed in liver and heart mitochondria. Thus, swelling was inhibited by adenine nucleotides (AdNs) and low pH (<7.0), whereas thiol reagents and alkalosis facilitated swelling. Cyclosporin A and its nonimmunosuppressive analogue N-methyl-Val-4-cyclosporin A (PKF 220-384) both inhibited swelling and prevented the translocation of cyclophilin D from the matrix to the membranes of cortical mitochondria. However, the calcium sensitivity of the MPT differed in mitochondria from three brain regions (hippocampus > cortex > cerebellum) and is correlated with the susceptibility of these regions to ischemic damage. Depleting mitochondria of AdNs by treatment with pyrophosphate ions sensitized the MPT to [Ca2+] and abolished regional differences, implying regional differences in mitochondrial AdN content. This was confirmed by measurements showing significant differences in AdN content among regions (cerebellum > cortex > hippocampus). Our data add to recent evidence that the MPT may be involved in neuronal death.

Alteration of the ADP/ATP translocase isoform pattern improves ATP expenditure in developing rat liver mitochondria

The expression of adenine nucleotide translocase isoforms (AAC) during perinatal development of the rat was studied by measuring mRNA transcript levels of AAC1 and AAC2 genes in liver, heart and brain tissue. In contrast to heart and brain, AAC1 mRNA is not present in adult liver tissue, but is transiently expressed around birth. AAC1 expression in liver did not respond to cold stress (examined with adult rats), therefore a possible involvement of AAC1 in the liver thermogenesis of newborns is excluded. Measurement of the [3H]ADP uptake by liver mitochondria revealed that the molecular activity of the AAC protein was significantly higher in mitochondria from 4-day-old neonates compared with adults. We suggest that the transient AAC1 gene expression in the perinatal liver helps to accommodate the mitochondrial ATP supply to the increased cytosolic ATP consumption initiated at birth.

Expression of the ADP/ATP carrier and expansion of the mitochondrial (ATP + ADP) pool contribute to postnatal maturation of the rat heart

The role of the ADP/ATP carrier (AAC), a key protein of the mitochondrial ATP-generating system, is not clear during postnatal rat heart development. To elucidate this role, the phosphorylating respiration (state 3), the activity and the content of AAC, the size of the exchangeable mitochondrial (ATP + ADP) pool and the control of AAC over respiration at state 3 were measured in mitochondria isolated from rat hearts at various postnatal ages. There was a 5-fold increase in the AAC activity from newborn to aged rat hearts, which was paralleled by a 1.5-fold increase in state 3 respiration. At birth, the AAC and the F0F1-ATP synthase exerted about 80% of the control over phosphorylating respiration (state 3: flux control coefficients 0.39 +/- 0.04 and 0.38 +/- 0.08). The strong increase in the AAC activity was partly caused by the doubling of the protein content. In addition, the turnover number of AAC increased by a factor of 2.5 due to the expansion of the (ATP + ADP) pool from 3.4 +/- 0.9 to 10.6 +/- 1.5 nmol.mg protein-1. The data strongly indicate that the increase in the AAC activity is an essential step in the postnatal maturation of rat heart mitochondria.