Rat brain creatine kinase messenger RNA levels are high in primary cultures of brain astrocytes and oligodendrocytes and low in neurons

Association Analysis of Single-Cell RNA Sequencing and Proteomics Reveals a Vital Role of Ca2+ Signaling in the Determination of Skeletal Muscle Development Potential

This study is aimed at exploring the mechanism underlying the homeostasis between myogenesis and adipogenesis in skeletal muscle using a special porcine model with a distinct phenotype on muscle growth rate and intramuscular fat deposition. Differentiation potential of muscle-derived Myo-lineage cells of lean-type pigs was significantly enhanced relative to obese-type pigs, while that of their Adi-lineage cells was similar. Single-cell RNA sequencing revealed that lean-type pigs reserved a higher proportion of Myo-lineage cells in skeletal muscle relative to obese-type pigs. Besides, Myo-lineage cells of the lean-type pig settled closer to the original stage of muscle-derived progenitor cells. Proteomics analysis found that differentially expressed proteins between two sources of Myo-lineage cells are mainly involved in muscle development, cell proliferation and differentiation, ion homeostasis, apoptosis, and the MAPK signaling pathway. The regulation of intracellular ion homeostasis, Ca²⁺ in particular, significantly differed between two sources of Myo-lineage cells. Ca²⁺ concentration in both cytoplasm and endoplasmic reticulum was lower in Myo-lineage cells of lean-type pigs relative to obese-type pigs. In conclusion, a higher proportion and stronger differentiation capacity of Myo-lineage cells are the main causes for the higher capability of myogenic differentiation and lower intramuscular fat deposition. Relative low concentration of cellular Ca²⁺ is advantageous for Myo-lineage cells to keep a potent differentiation potential.

Creatine Enhances Mitochondrial-Mediated Oligodendrocyte Survival After Demyelinating Injury

Chronic oligodendrocyte loss, which occurs in the demyelinating disorder multiple sclerosis (MS), contributes to axonal dysfunction and neurodegeneration. Current therapies are able to reduce MS severity, but do not prevent transition into the progressive phase of the disease, which is characterized by chronic neurodegeneration. Therefore, pharmacological compounds that promote oligodendrocyte survival could be beneficial for neuroprotection in MS. Here, we investigated the role of creatine, an organic acid involved in adenosine triphosphate (ATP) buffering, in oligodendrocyte function. We found that creatine increased mitochondrial ATP production directly in oligodendrocyte lineage cell cultures and exerted robust protection on oligodendrocytes by preventing cell death in both naive and lipopolysaccharide-treated mixed glia. Moreover, lysolecithin-mediated demyelination in mice deficient in the creatine-synthesizing enzyme guanidinoacetate-methyltransferase (Gamt) did not affect oligodendrocyte precursor cell recruitment, but resulted in exacerbated apoptosis of regenerated oligodendrocytes in central nervous system (CNS) lesions. Remarkably, creatine administration into Gamt-deficient and wild-type mice with demyelinating injury reduced oligodendrocyte apoptosis, thereby increasing oligodendrocyte density and myelin basic protein staining in CNS lesions. We found that creatine did not affect the recruitment of macrophages/microglia into lesions, suggesting that creatine affects oligodendrocyte survival independently of inflammation. Together, our results demonstrate a novel function for creatine in promoting oligodendrocyte viability during CNS remyelination.SIGNIFICANCE STATEMENT We report that creatine enhances oligodendrocyte mitochondrial function and protects against caspase-dependent oligodendrocyte apoptosis during CNS remyelination. This work has important implications for the development of therapeutic targets for diseases characterized by oligodendrocyte death, including multiple sclerosis.

Systematic analysis of transcription-level effects of neurodegenerative diseases on human brain metabolism by a newly reconstructed brain-specific metabolic network

Network-oriented analysis is essential to identify those parts of a cell affected by a given perturbation. The effect of neurodegenerative perturbations in the form of diseases of brain metabolism was investigated by using a newly reconstructed brain-specific metabolic network. The developed stoichiometric model correctly represents healthy brain metabolism, and includes 630 metabolic reactions in and between astrocytes and neurons, which are controlled by 570 genes. The integration of transcriptome data of six neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, multiple sclerosis, schizophrenia) with the model was performed to identify reporter features specific and common for these diseases, which revealed metabolites and pathways around which the most significant changes occur. The identified metabolites are potential biomarkers for the pathology of the related diseases. Our model indicated perturbations in oxidative stress, energy metabolism including TCA cycle and lipid metabolism as well as several amino acid related pathways, in agreement with the role of these pathways in the studied diseases. The computational prediction of transcription factors that commonly regulate the reporter metabolites was achieved through binding-site analysis. Literature support for the identified transcription factors such as USF1, SP1 and those from FOX families are known from the literature to have regulatory roles in the identified reporter metabolic pathways as well as in the neurodegenerative diseases. In essence, the reconstructed brain model enables the elucidation of effects of a perturbation on brain metabolism and the illumination of possible machineries in which a specific metabolite or pathway acts as a regulatory spot for cellular reorganization.

Selection of housekeeping genes for normalization of RT-PCR in hypoxic neural stem cells of rat in vitro

Gene expression analysis under various conditions using real-time reverse transcription polymerase chain reaction (RT-PCR) needs reliable control genes. Housekeeping genes are commonly used as the control. However, no validated housekeeping gene is available for study of hypoxic neural stem cell culture. To choose appropriate internal control genes, the expression of eight commonly used housekeeping genes was examined in rat neural stem cell model to find one or more stably expressed genes under hypoxic/ischemic conditions. Two genes, HPRT and RPL13A were identified as the most confidential housekeeping genes in this research by geNorm and NormFinder softwares. As a groundwork, the most stable housekeeping genes for neural stem cells under hypoxic/ischemic conditions are initially investigated and validated in this experiment, which might provide a better understanding for the gene expression study in ischemic and necrotic neural stem cell cultures or in ischemic diseases of the central nervous system (CNS).

Impaired brain creatine kinase activity in Huntington's disease

BACKGROUND

Huntington's disease (HD) is associated with impaired energy metabolism in the brain. Creatine kinase (CK) catalyzes ATP-dependent phosphorylation of creatine (Cr) into phosphocreatine (PCr), thereby serving as readily available high-capacity spatial and temporal ATP buffering.

OBJECTIVE

Substantial evidence supports a specific role of the Cr/PCr system in neurodegenerative diseases. In the brain, the Cr/PCr ATP-buffering system is established by a concerted operation of the brain-specific cytosolic enzyme BB-CK and ubiquitous mitochondrial uMt-CK. It is not yet established whether the activity of these CK isoenzymes is impaired in HD.

METHODS

We measured PCr, Cr, ATP and ADP in brain extracts of 3 mouse models of HD - R6/2 mice, N171-82Q and HdhQ(111) mice - and the activity of CK in cytosolic and mitochondrial brain fractions from the same mice.

RESULTS

The PCr was significantly increased in mouse HD brain extracts as compared to nontransgenic littermates. We also found an approximately 27% decrease in CK activity in both cytosolic and mitochondrial fractions of R6/2 and N171-82Q mice, and an approximately 25% decrease in the mitochondria from HdhQ(111) mice. Moreover, uMt-CK and BB-CK activities were approximately 63% lower in HD human brain samples as compared to nondiseased controls.

CONCLUSION

Our findings lend strong support to the role of impaired energy metabolism in HD, and point out the potential importance of impairment of the CK-catalyzed ATP-buffering system in the etiology of HD.

Inhibition of creatine kinase activity by lysine in rat cerebral cortex

Accumulation of lysine (Lys) in tissues and biochemical fluids is the biochemical hallmark of patients affected by familial hyperlysinemia (FH) and also by other inherited neurometabolic disorders. In the present study, we investigated the in vitro effect of Lys on various parameters of energy metabolism in cerebral cortex of 30-day-old Wistar rats. We verified that total (tCK) and cytosolic creatine kinase activities were significantly inhibited by Lys, in contrast to the mitochondrial isoform which was not affected by this amino acid. Furthermore, the inhibitory effect of Lys on tCK activity was totally prevented by reduced glutathione, suggesting a possible role of reactive species oxidizing critical thiol groups of the enzyme. In contrast, Lys did not affect (14)CO(2) production from [U-(14)C] glucose (aerobic glycolytic pathway) and [1-(14)C] acetic acid (citric acid cycle activity) neither the various activities of the electron transfer chain and synaptic Na(+)K(+)-ATPase at concentrations as high as 5.0 mM. Considering the importance of creatine kinase (CK) activity for brain energy metabolism homeostasis and especially ATP transfer and buffering, our results suggest that inhibition of this enzyme by Lys may contribute to the neurological signs presented by symptomatic patients affected by FH and other neurodegenerative disorders in which Lys accumulates.

Reactive oxygen species generation is modulated by mitochondrial kinases: correlation with mitochondrial antioxidant peroxidases in rat tissues

Mitochondrial hexokinase (mt-HK) and creatine kinase (mt-CK) activities have been recently proposed to reduce the rate of mitochondrial ROS generation through an ADP re-cycling mechanism. Here, we determined the role of mt-HK and mt-CK activities in regulate mitochondrial ROS generation in rat brain, kidney, heart and liver, relating them to the levels of classical antioxidant enzymes. The activities of both kinases were significantly higher in the brain than in other tissues, whereas the activities of catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR) were higher in both liver and kidney mitochondria. In contrast, manganese superoxide dismutase (Mn-SOD) activity was not significantly different among these tissues. Activation of mitochondrial kinases by addition of their substrates increased the ADP re-cycling and thus the respiration by enhancing the oxidative phosphorylation. Succinate induced hydrogen peroxide (H(2)O(2)) generation was higher in brain than in kidney and heart mitochondria, and the lowest in liver mitochondria. Mitochondrial membrane potential (DeltaPsi(m)) and H(2)O(2) production, decreased with additions of 2-DOG or Cr to respiring brain and kidney mitochondria but not to liver. The inhibition of H(2)O(2) production by 2-DOG and Cr correspond to almost 100% in rat brain and about 70% in kidney mitochondria. Together our data suggest that mitochondrial kinases activities are potent preventive antioxidant mechanism in mitochondria with low peroxidase activities, complementing the classical antioxidant enzymes against oxidative stress.

Creatine treatment promotes differentiation of GABA-ergic neuronal precursors in cultured fetal rat spinal cord

Creatine is a substrate of cytosolic and mitochondrial creatine kinases. Its supplementation augments cellular levels of creatine and phosphocreatine, the rate of ATP resynthesis, and improves the function of the creatine kinase energy shuttle. High cytoplasmatic total creatine levels have been reported to be neuroprotective by inhibiting apoptosis. In addition, creatine has direct antioxidant effects, which may be of importance in amyotrophic lateral sclerosis. In the present study, we investigated the effects of creatine [5 mM] on survival and differentiation of cultured GABA-immunoreactive (-ir) and choline acetyltransferase (ChAT)-ir rat spinal cord neurons. Furthermore, we addressed the neuroprotective potential of creatine supplementation against 3-nitropropionic acid (3-NP) induced toxicity. General cell survival and total neuronal cell density were not altered by chronic creatine treatment. We found, however, after chronic creatine and short-term creatine exposure a significantly higher density of GABA-ir neurons hinting to a differentiation-inducing mechanism of creatine. This notion is further supported by a significant higher content of GAD after creatine exposure. Creatine supplementation also exerted a partial, but significant neuroprotection for GABA-ir neurons against 3-NP induced toxicity. Interestingly, chronic creatine treatment did not alter cell density of ChAT-ir neurons but promoted their morphologic differentiation. Cell soma size and number of primary neurites per neuron were increased significantly after creatine supplementation. Taken together, creatine supplementation promoted the differentiation or the survival of GABAergic neurons and resulted in partial neuroprotection against 3-NP induced toxicity. The data suggest that creatine may play a critical role during development of spinal cord neurons.

Mitochondrial Creatine Kinase Activity Prevents Reactive Oxygen Species Generation

As recently demonstrated by our group (da-Silva, W. S., Gómez-Puyou, A., Gómez-Puyou, M. T., Moreno-Sanchez, R., De Felice, F. G., de Meis, L., Oliveira, M. F., and Galina, A. (2004) J. Biol. Chem. 279, 39846-39855) mitochondrial hexokinase activity (mt-HK) plays a preventive antioxidant role because of steady-state ADP re-cycling through the inner mitochondrial membrane in rat brain. In the present work we show that ADP re-cycling accomplished by the mitochondrial creatine kinase (mt-CK) regulates reactive oxygen species (ROS) generation, particularly in high glucose concentrations. Activation of mt-CK by creatine (Cr) and ATP or ADP, induced a state 3-like respiration in isolated brain mitochondria and prevention of H(2)O(2) production obeyed the steady-state kinetics of the enzyme to phosphorylate Cr. The extension of the preventive antioxidant role of mt-CK depended on the phosphocreatine (PCr)/Cr ratio. Rat liver mitochondria, which lack mt-CK activity, only reduced state 4-induced H(2)O(2) generation when 1 order of magnitude more exogenous CK activity was added to the medium. Simulation of hyperglycemic conditions, by the inclusion of glucose 6-phosphate in mitochondria performing 2-deoxyglucose phosphorylation via mt-HK, induced H(2)O(2) production in a Cr-sensitive manner. Simulation of hyperglycemia in embryonic rat brain cortical neurons increased both DeltaPsi(m) and ROS production and both parameters were decreased by the previous inclusion of Cr. Taken together, the results presented here indicate that mitochondrial kinase activity performed a key role as a preventive antioxidant against oxidative stress, reducing mitochondrial ROS generation through an ADP-recycling mechanism.

Lipid Peroxidation During Human Cerebral Myelination

The critical period of human cerebral myelination is characterized by rapid production of cellular membranes. We hypothesize that this period is subject to the "physiological" generation of free radicals resulting in lipid peroxidation (LPO). In this study, oxidative markers were examined in developing human parietal white matter using 4-hydroxy-2-nonenal (HNE) protein adducts as an indicator of LPO. Immunocytochemistry showed an increase in HNE-positive glia from 40 gestational weeks to 1.5 postnatal years encompassing the peak period of myelin sheath synthesis at this site. Western blots showed a distinct pattern of HNE-modified proteins at fetal/term ages 26 to 42 gestational weeks and a second, different pattern at 45 gestational weeks to 2.5 postnatal years. Proteins modified by HNE in the latter period, corresponding to active myelination, were identified using mass spectrometry. The most prominent category of HNE modification included cytoskeletal proteins such as tubulins and neurofilaments. Other categories included cell type-specific proteins for mature oligodendrocytes and astrocytes and proteins involved in cell cycle and energy metabolism. We conclude that human brain development involves basal levels of oxidative stress and resulting LPO and that these processes target different proteins in an age-specific manner, thereby likely playing distinct roles during different periods of brain maturation.

Decrease in creatine kinase messenger RNA expression in the hippocampus and dorsolateral prefrontal cortex in bipolar disorder

OBJECTIVES

Bipolar disorder (BPD) affects more than 2 million adults in the USA and ranks among the top 10 causes of worldwide disabilities. Despite its prevalence, very little is known about the etiology of BPD. Recent evidence suggests that cellular energy metabolism is disturbed in BPD. Mitochondrial function is altered, and levels of high-energy phosphates, such as phosphocreatine (PCr), are reduced in the brain. This evidence has led to the hypothesis that deficiencies in energy metabolism could account for some of the pathophysiology observed in BPD. To further explore this hypothesis, we examined levels of creatine kinase (CK) mRNA, the enzyme involved in synthesis and metabolism of PCr, in the hippocampus (HIP) and dorsolateral prefrontal cortex (DLPFC) of control, BPD and schizophrenia subjects.

METHODS

Tissue was obtained from the Harvard Brain Tissue Resource Center. Real-time quantitative polymerase chain reaction (HIP, DLPFC) and gene expression microarrays (HIP) were employed to compare the brain and mitochondrial 1 isoforms of CK.

RESULTS

Both CK isoforms were downregulated in BPD. Furthermore, mRNA transcripts for oligodendrocyte-specific proteins were downregulated in the DLPFC, whereas the mRNA for the neuron-specific protein microtubule-associated protein 2 was downregulated in the HIP.

CONCLUSION

Although some of the downregulation of CK might be explained by cell loss, a more general mechanism seems to be responsible. The downregulation of CK transcripts, if translated into protein levels, could explain the reduction of high-energy phosphates previously observed in BPD.

A proteome analysis of the anterior cingulate cortex gray matter in schizophrenia

The Anterior Cingulate Cortex (ACC, Brodmans Area 24) is implicated in the pathogenesis of schizophrenia due to its normal functions and connectivity together with reports of structural, morphological and neurotransmitter aberrations within this brain area in the disease state. Two-dimensional gel electrophoresis (2DE) was employed to scan and compare the ACC gray matter proteomes between schizophrenia (n = 10) and control (n = 10) post-mortem human tissue. This proteomic approach has detected 42 protein spots with altered levels in the schizophrenia cohort, which to our knowledge is the first proteomic analysis of the ACC in schizophrenia. Thirty nine of these proteins were subsequently identified using mass spectrometry and functionally classified into metabolism and oxidative stress, cytoskeletal, synaptic, signalling, trafficking and glial-specific groups. Some of the identified proteins have previously been implicated in the disease pathogenesis and some offer new insights into schizophrenia. Investigating these proteins, the genes encoding these proteins, their functions and interactions may shed light on the molecular mechanisms underlying the heterogeneous symptoms characteristic of schizophrenia.

Transcription of brain creatine kinase in U87-MG glioblastoma is modulated by factor AP2

Our previous studies established in U87-MG glioblastoma cells that elevated cAMP increased transcription of the endogenous as well as a transiently-transfected brain creatine kinase (CKB) gene, despite the absence of a cAMP response element (CRE) in the CKB proximal promoter. This report employed transfection to show that the transcription of CKB in U87 cells is induced by transcription factor AP2alpha, which is known to be activated by cAMP. Dominant-negative forms of AP2alpha not only prevented the AP2alpha-mediated activation of CKB but also blocked the cAMP-mediated increase in CKB transcription caused by forskolin treatment. The mutation of the four potential AP2 elements within the CKB proximal promoter showed that induction of CKB by AP2 was mediated principally through the AP2 element located at -50 bp in the promoter. Electromobility shift assays revealed a protein in U87 nuclear extracts that bound to a consensus AP2alpha element as well as to the (-50) AP2 element in CKB. Interestingly, the CKB (-50) AP2 element contains GCCAATGGG which also bound NF-Y, the CCAAT-binding protein, suggesting that interplay between AP2 and NF-Y may modulate CKB transcription. This is the first report of a role for AP2 in the regulation of CKB transcription and of an AP2 element within which an NF-Y site is located.

Distinct cellular expressions of creatine synthetic enzyme GAMT and creatine kinases uCK-Mi and CK-B suggest a novel neuron-glial relationship for brain energy homeostasis

The creatine/phosphocreatine shuttle system, as catalysed reversibly by creatine kinases, is thought to be essential for the storing and buffering of high phosphate-bound energy in tissues with high energy demand. In the present study, we aimed to clarify the cellular system of creatine biosynthesis and its energy metabolism in the mouse brain by immunohistochemistry for creatine biosynthetic enzyme S-adenosylmethionine:guanidinoacetate N-methyltransferase (GAMT), ubiquitous mitochondrial creatine kinase (uCK-Mi) and brain-type cytoplasmic creatine kinase (CK-B). GAMT was expressed highly in oligodendrocytes and olfactory ensheathing glia and moderately in astrocytes, whereas GAMT was very low in neurons and microglia. By contrast, uCK-Mi was expressed selectively in neurons and localized in their mitochondria in dendrites, cell bodies, axons and terminals. The distinct and almost complementary distribution of GAMT and uCK-Mi suggests that the creatine in neuronal mitochondria is derived not only from the circulation, but also from local glial cells associated with these neuronal elements. By contrast, CK-B was selective to astrocytes among glial populations, and was exclusive to inhibitory neurons among neuronal populations. Interestingly, these cells with high CK-B immunoreactivity are known to be highly resistant to acute energy loss, such as hypoxia and hypoglycemia. Considering that phosphocreatine generates ATP much faster than the processes of glycolysis and oxidative phosphorylation, the highly regulated cellular expressions of creatine biosynthetic and metabolic enzymes suggest that the creatine/phosphocreatine shuttle system plays a role in brain energy homeostasis through a novel neuron-glial relationship.

L-2-hydroxyglutaric acid inhibits mitochondrial creatine kinase activity from cerebellum of developing rats

L-2-Hydroxyglutaric acid (LGA) is the biochemical hallmark of patients affected by the neurometabolic disorder known as L-2-hydroxyglutaric aciduria (LHGA). Although this disorder is predominantly characterized by severe neurological findings and pronounced cerebellum atrophy, the neurotoxic mechanisms of brain injury are virtually unknown. In the present study, we investigated the effect of LGA, at 0.25-5mM concentrations, on total creatine kinase (tCK) activity from cerebellum, cerebral cortex, cardiac muscle and skeletal muscle homogenates of 30-day-old Wistar rats. CK activity was measured also in the cytosolic (Cy-CK) and mitochondrial (Mi-CK) fractions from cerebellum. We verified that tCK activity was significantly inhibited by LGA in the cerebellum, but not in cerebral cortex, cardiac muscle and skeletal muscle. Furthermore, CK activity from the mitochondrial fraction was inhibited by LGA, whereas that from the cytosolic fraction of cerebellum was not affected by the acid. Kinetic studies revealed that the inhibitory effect of LGA on Mi-CK was non-competitive in relation to phosphocreatine. Finally, we verified that the inhibitory effect of LGA on tCK was fully prevented by pre-incubation of the homogenates with reduced glutathione (GSH), suggesting that this inhibition is possibly mediated by oxidation of essential thiol groups of the enzyme. Considering the importance of creatine kinase activity for energy homeostasis, our results suggest that the selective inhibition of this enzyme activity by increased levels of LGA could be possibly related to the cerebellar degeneration characteristically found in patients affected by L-2-hydroxyglutaric aciduria.

Fatty acid synthesizing enzymes intrinsic to myelin

A recent study showing incorporation of acetyl groups from neuronal N-acetylaspartate into myelin lipids suggested the presence of fatty acid synthesizing enzymes in myelin that utilize the acetyl groups liberated by myelin-associated aspartoacylase [J. Neurochem. 78 (2001) 736]. We report here detection of the fatty acid synthase (FAS) complex and acetyl-CoA carboxylase (ACC) in purified myelin. The activity of myelin FAS was approximately half that of cytosolic FAS and, unlike the latter, required detergent for activation. Intrinsic association of FAS with myelin was indicated by failure to remove the activity with NaCl or Na-taurocholate. Myelin-associated ACC was approximately 10% of cytosolic ACC in myelin isolated by gradient centrifugation, and this was reduced by half following osmotic shock; this suggested bimodal distribution of myelin ACC, some being loosely associated within inter-lamellar cytoplasmic spaces and the remainder more firmly associated in a manner that resists NaCl/Na-taurocholate treatments. These results, in combination with earlier findings, provide a possible mechanism for the observed incorporation of neuronal NAA acetyl groups into myelin lipids.

Expression of creatine kinase isoenzyme genes during postnatal development of rat brain cerebellum: evidence for transcriptional regulation

Transcription and accumulation of brain-type creatine kinase (CKB) mRNA and its protein was examined during postnatal development of rat brain cerebellum, the brain region containing highest CKB mRNA in the adult. CKB protein was extremely low at day 1, increased about 10-fold until week 4 and remained constant until week 10. This time course was paralleled by cerebellar CKB mRNA, which was also extremely low at day 1 and increased 5-fold during the first 3 weeks and then remained constant. High levels of CKB protein were also detected in cultured primary cerebellar granular neurons. Nuclear run-on assays directly showed that CKB mRNA accumulation during postnatal cerebellar development was due to increased transcription. When compared with cerebrum and whole brain, cerebellar CKB mRNA accumulation during postnatal development was temporally delayed. Analysis of myocyte enhancer factor (MEF)-2 and Sp1, factors known to initiate or sustain CKB transcription in tissues other than brain, revealed that MEF-2 in cerebellum was low at week 1 but increased 3.5-fold by week 7, while Sp1 remained unchanged. The increase in CKB protein during cerebellar postnatal development was coincident with that of the ubiquitous mitochondrial CK protein and mRNA, indicating that a functional phosphocreatine energy shuttle probably exists for efficient ATP regeneration in the cerebellum. This should be beneficial for the many energy-demanding requirements during cerebellar development, as indicated by the observed temporal co-expression of CKB with myelin basic protein, which is involved in axon myelination by oligodendrocytes.

Protection of cultured oligodendrocytes against tumor necrosis factor-alpha by the antioxidants coenzyme Q(10) and N-acetyl cysteine

Tumor necrosis factor-alpha (TNF-alpha) retards the rate of terminal maturation of oligodendrocytes in vitro. The following respective compounds were used along with TNF-alpha in order to try and restore the normal rate of maturation: (1). the antioxidant, coenzyme Q(10) (CoQ(10)); (2). the antioxidant, N-acetyl cysteine (NAC); (3). creatine, which helps to preserve cellular energy; and (4) S-adenosyl methionine (SAM), which contributes to the biosynthesis of lipids and proteins. Of these compounds, only CoQ(10) or NAC was able to restore the numbers of mature myelin basic protein-positive cells and the ability of the oligodendrocytes to form membrane sheets. If TNF-alpha treatment causes oxidative damage by compromising oxidative metabolism in oligodendrocytes, increasing products of lipid peroxidation and/or generating radical oxygen species that can interfere with maturation signals, CoQ(10) and NAC may protect oligodendrocytes by reversing one or more of those destructive processes during terminal maturation.

On the mechanisms of neuroprotection by creatine and phosphocreatine

Creatine and phosphocreatine were evaluated for their ability to prevent death of cultured striatal and hippocampal neurons exposed to either glutamate or 3-nitropropionic acid (3NP) and to inhibit the mitochondrial permeability transition in CNS mitochondria. Phosphocreatine (PCr), and to a lesser extent creatine (Cr), but not (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK801), dose-dependently ameliorated 3NP toxicity when applied simultaneously with the 3NP in Mg2+-free media. Pre-treatment of PCr for 2 or 5 days and Cr for 5 days protected against glutamate excitotoxicity equivalent to that achieved by MK801 post-treatment. The combination of PCr or Cr pre-treatment and MK801 post-treatment did not provide additional protection, indicating that both prevented the toxicity attributable to secondary glutamate release. To determine if Cr or PCr directly inhibited the permeability transition, mitochondrial swelling and depolarization were assayed in isolated, purified brain mitochondria. PCr reduced the amount of swelling induced by calcium by 20%. Cr decreased mitochondrial swelling when inhibitors of creatine kinase octamer-dimer transition were present. However, in brain mitochondria prepared from rats fed a diet supplemented with 2% creatine for 2 weeks, the extent of calcium-induced mitochondrial swelling was not altered. Thus, the neuroprotective properties of PCr and Cr may reflect enhancement of cytoplasmic high-energy phosphates but not permeability transition inhibition.

Protective effect of the energy precursor creatine against toxicity of glutamate and beta-amyloid in rat hippocampal neurons

The loss of ATP, which is needed for ionic homeostasis, is an early event in the neurotoxicity of glutamate and beta-amyloid (A(beta)). We hypothesize that cells supplemented with the precursor creatine make more phosphocreatine (PCr) and create larger energy reserves with consequent neuroprotection against stressors. In serum-free cultures, glutamate at 0.5-1 mM was toxic to embryonic hippocampal neurons. Creatine at >0.1 mM greatly reduced glutamate toxicity. Creatine (1 mM) could be added as late as 2 h after glutamate to achieve protection at 24 h. In association with neurotoxic protection by creatine during the first 4 h, PCr levels remained constant, and PCr/ATP ratios increased. Morphologically, creatine protected against glutamate-induced dendritic pruning. Toxicity in embryonic neurons exposed to A(beta) (25-35) for 48 h was partially prevented by creatine as well. During the first 6 h of treatment with A(beta) plus creatine, the molar ratio of PCr/ATP in neurons increased from 15 to 60. Neurons from adult rats were also partially protected from a 24-h exposure to A(beta) (25-35) by creatine, but protection was reduced in neurons from old animals. These results suggest that fortified energy reserves are able to protect neurons against important cytotoxic agents. The oral availability of creatine may benefit patients with neurodegenerative diseases.

Conditions providing enhanced transfection efficiency in rat pheochromocytoma PC12 cells permit analysis of the activity of the far-upstream and proximal promoter of the brain creatine kinase gene

While brain creatine kinase (CKB) is expressed at highest levels in the brain, where it functions in regenerating ATP, the gene elements and protein factors regulating CKB transcription in neuronal and glial cells have not been identified. To investigate the regulation of CKB in neuronal cells, we examined the expression of the promoter proximal and 5' far-upstream regions of the rat CKB gene transiently transfected into rat PC12 pheochromocytoma cells. Initially, these experiments were hampered by the extremely low transfection efficiency of PC12 cells. We increased efficiency by greater than 200-fold by employing CaPO4-precipitated DNA transfection into PC12 cells which were optimized for transient transfection by: (i) culturing cells in polylysine-coated dishes to insure attachment throughout transfection; (ii) exposing cells to transfected DNA for an optimal time and employing a glycerol shock; and, most importantly, (iii) dissociating the characteristic self-adhesive clumps of PC12 into mostly single cells. Use of the plasmid expressing green fluorescent protein allowed identification of the transfected cells that averaged 10-20% of the total. Analyses of CKB promoter-CAT gene constructs showed that in PC12 cells expression of the proximal (0.2 kb) CKB promoter was low while expression of the 1.4 kb promoter was three fold higher and the 2.9 kb promoter was ten fold higher, suggesting the presence of at least two upstream cis-acting, positive regulatory elements. In agreement, the steady-state CKB mRNA level was higher in PC12 than in other neuronal cell lines examined, possibly reflecting the effects of positive upstream factors. The results are discussed in relation to how this economical and straightforward transfection procedure may be useful in identify factors regulating the transcription of CKB and other genes expressed in neuronal cells.

Proximal promoter of the rat brain creatine kinase gene lacks a consensus CRE element but is essential for the cAMP-mediated increased transcription in glioblastoma cells

Our previous studies have shown that transcription of brain creatine kinase (CKB) mRNA in U87-MG glioblastoma cells is stimulated by a forskolin-mediated increase in cyclic AMP (cAMP) via a pathway involving protein kinase A (PKA) and the activation of Galphas proteins. In this report, we have employed transient transfection to investigate the rat CKB gene elements essential for the cAMP-mediated induction of rat CKB transcription in human U87 cells and have mapped the transcription start site of the induced CKB transcripts. We found that the level of induced transcription from the transfected genomic rat CKB gene was the same whether transcription was driven by 2.9 kb of CKB promoter plus 5' flanking sequence or the 0.2 kb CKB promoter, suggesting that the proximal CKB promoter was essential. Also, the level of induced transcription of the chloramphenicol acetyl transferase (CAT) reporter gene driven by the 2.9 kb CKB promoter was the same as with the 0.2 kb CKB promoter. Analyses of a series of 5' deletions of the 0.2 kb proximal CKB promoter showed that the sequences between -80 bp and +1 bp were essential for the cAMP-mediated induction of CKB transcription, despite the absence of a consensus cAMP response element (CRE) sequence in that region. In agreement, gel mobility shift assays showed that nuclear extracts from U87 cells contained a protein(s) which bound specifically to a [32P]CKB DNA probe containing the -60 bp to +1 bp sequence. Mapping the 5' end of the CKB transcripts showed that the initiation of the cAMP-induced transcription occurred almost exclusively from the downstream transcription start site, apparently under the initiation direction of the nonconsensus (-28) TTAA element and not the consensus (-60) TATAAATA element. The results are discussed with regard to nuclear protein factors which may be involved, and the possible cAMP-mediated increase in CKB transcription during myelinogenesis, since the differentiation of oligodendrocytes has previously been shown to be accelerated by increased intracellular cAMP.

Arginine kinase expression and localization in growth cone migration

Migrating neuronal growth cones exert traction forces that are generated by ATP-driven F-actin/myosin interactions. Sustained generation of these forces may require an energy supply mediated by the guanidino kinases, creatine kinase and arginine kinase. We cloned and sequenced grasshopper arginine kinase and examined its expression during embryogenesis and its subcellular localization in vivo and in vitro. During the first half of embryogenesis, arginine kinase is expressed selectively in a small percentage of ectodermal cells (dorsal closure cells), in a small percentage of mesodermal cells (muscle pioneers), and throughout the developing CNS. Most of these cell types are motile, including nascent neurons, muscle pioneers, dorsal closure cells, and many CNS glia. Neuroblasts also strongly express arginine kinase; they are nonmotile but are undergoing repeated rounds of (ATP-dependent) mitosis. Arginine kinase is colocalized with F-actin in a narrow band along the leading edges of lamellipodia of migrating glia. In neurons undergoing axonogenesis, arginine kinase is concentrated in growth cones and extends to the tips of filopodia. The amount of arginine kinase varies widely between growth cones, even between different growth cones of the same neuron. Energy for growth cone migration appears to be mobilized by (1) selective expression of arginine kinase by neurons, (2) localization of arginine kinase within growth cones, and (3) concentration of arginine kinase within specific growth cones, depending on the traction forces being generated. Mobilization of guanidino kinases may participate in the selective growth of specific growth cones.

The expression of creatine kinase isoenzymes in neocortex of patients with neurodegenerative disorders: Alzheimer's and Pick's disease

Creatine kinase (CK) activity was found decreased in the brains of patients with Alzheimer's disease (AD) and Pick's disease (PD). However, the decrease of total CK activity in AD was more pronounced than in PD. Analysis of the activity of two CK isoforms, BCK and ubiquitous mitochondrial CK, demonstrated that the decrease of total CK activity in AD and PD was related to the decrease of BCK activity. The decline of CK activity both in AD and PD correlated well with the decline of the content of immunoreactive BCK in brain extracts. The BCK mRNA level in AD and PD was not significantly different from control patients and could not be the primary reason for decreases in CK content and activity. The decreased level of BCK in AD and PD brains might be caused by posttranscriptional events, which could affect the translation of BCK mRNA and/or lead to the inactivation and degradation of the enzyme. Because CK is sensitive to oxidative modification, it is possible that the changes observed in this study result from free radical damage.

Creatine kinase-B mRNA levels in brain regions from male and female rats

The creatine kinase-B (CKB) enzyme is proposed to have a pivotal role in the regeneration of ATP in the nervous system. In the present study, the steady-state levels of CKB mRNA were determined by RNase protection assay in seventeen separate brain regions obtained from rats during the initial interval of the light period or period of inactivity in rats. The antisense probe used specifically hybridizes to CKB mRNA and discriminates CKB from CKM mRNA. The results show that brain regions from Wistar rats differ in CKB mRNA content. Highest levels of CKB mRNA were detected in the male and female cerebellum. High levels of CKB mRNA were observed in the spinal cord, brain stem and its structures (medulla, pons and midbrain) and olfactory bulb of the male rats. Female rats also contained high levels of CKB mRNA in the brain stem. In both male and female rats, the frontal cortex, occipital cortex, hippocampus and striatum exhibited lower levels of CKB mRNA relative to the complete brain. Statistical analyses demonstrated a significant difference between the male and female CKB mRNA profiles. However, CKB mRNA levels in brain regions with estrogen receptors (hypothalamus, hippocampus) were similar in male and female rats. Differential CKB mRNA levels in various brain regions may suggest diverse physiological significance of the CKB system in the regulation of brain energy metabolism.

Prostaglandin E1, E2, and cholera toxin increase transcription of the brain creatine kinase gene in human U87 glioblastoma cells

The creatine kinase isoenzymes play an important role in maintaining ATP levels in some cell types during times of high energy demand. We have previously shown in primary cell cultures from rat brain that glial cells express much higher levels of brain creatine kinase (CKB) mRNA than neurons. In a separate earlier study we observed that transcription of CKB mRNA in glial cells can be stimulated by a forskolin-mediated increase in cAMP via a pathway involving protein kinase A (PKA). In this report, we show that the level of CKB mRNA in human U87 glioblastoma cells can be increased by either prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), or cholera toxin (an activator of G alpha s proteins). The induction of CKB mRNA occurs rapidly (with maximal induction after 6 h), is at the level of transcription, and is mediated specifically through PKA. In addition, the results indicate that both PGE1 and PGE2 use the same or related signal transduction pathways to increase CKB transcription. These results suggest that in glial cells CKB mRNA can be regulated by extracellular signals acting through G-protein-coupled receptors. This study may contribute to an understanding of the mechanisms underlying the previously-reported, early postnatal increase in CKB enzyme activity in rat brain. The results are also discussed with regard to the potential involvement of the expression of prostaglandins and CKB during hypoxia and ischemia.

In situ hybridization analysis of CHOT1, a creatine transporter, in the rat central nervous system

A putative choline transporter (CHOT1) has been cloned from rat brain and is reported to express a high-affinity, sodium-dependent, hemicholinium-3-insensitive choline transporter in oocytes. A second transporter (OCCREATRA) cloned from rabbit brain is 98% homologous to CHOT1 and is reported to transport creatine. We examined the distribution of CHOT1 mRNA in rat brain by in situ hybridization, using a 48 base oligonucleotide probe. In adult rats, the hybridization signal was widespread, but with a distinct pattern. High levels of expression were detected in the cerebellum (Purkinje and granule cell layers), choroid plexus, medial habenula, pontine nuclei, several brainstem nuclei, and hippocampus (pyramidal cell layer). Moderate signal was detected in cortex, globus pallidus, corpus callosum, and most other white matter tracts. Very low levels were present in striatum, nucleus accumbens, hippocampus molecular layer, and cerebellar molecular layer. Emulsion autoradiography indicated cellular localization to both neurons and glia. CHOT1 mRNA was relatively abundant in some cholinergic regions, including the medial habenula, the medial septum, and several brainstem nuclei. However, the overall pattern was distinctly different from that expected for cholinergic markers and correlated well with the localization of creatine kinase. The widespread distribution and poor correlation with cholinergic markers indicates that the CHOT1 gene does not encode the classical choline transporter known to be associated with acetylcholine synthesis. It is possible that CHOT1 is associated with cholinergic neurotransmission in some brain regions. However, it appears to encode that the rat creatine transporter, and its widespread and heterogeneous distribution suggests regions where creatine phosphate is an important energy source.

Mouse p53 represses the rat brain creatine kinase gene but activates the rat muscle creatine kinase gene

The creatine kinases (CK) regenerate ATP for cellular reactions with a high energy expenditure. While muscle CK (CKM) is expressed almost exclusively in adult skeletal and cardiac muscle, brain CK (CKB) expression is more widespread and is highest in brain glial cells. CKB expression is also high in human lung tumor cells, many of which contain mutations in p53 alleles. We have recently detected high levels of CKB mRNA in HeLa cells and, in this study, have tested whether this may be due to the extremely low amounts of p53 protein present in HeLa cells. Transient transfection experiments showed that wild-type mouse p53 severely repressed the rat CKB promoter in HeLa but not CV-1 monkey kidney cells, suggesting that, in HeLa but not CV-1 cells, p53 either associates with a required corepressor or undergoes a posttranslational modification necessary for CKB repression. Conversely, mouse wild-type p53 strongly activated the rat CKM promoter in CV-1 cells but not in HeLa cells, suggesting that, in CV-1 cells, p53 may associate with a required coactivator or is modified in a manner necessary for CKM activation. The DNA sequences required for p53-mediated modulations were found to be within bp -195 to +5 of the CKB promoter and within bp -168 to -97 of the CKM promoter. Moreover, a 112-bp fragment from the proximal rat CKM promoter (bp -168 to -57), which contained five degenerate p53-binding elements, was capable of conferring p53-mediated activation on a heterologous promoter in CV-1 cells. Also, this novel p53 sequence, when situated in the native 168-bp rat CKM promoter, conferred p53-mediated activation equal to or greater than that of the originally characterized far-upstream (bp -3160) mouse CKM p53 element. Therefore, CKB and CKM may be among the few cellular genes which could be targets of p53 in vivo. In addition, we analyzed a series of missense mutants with alterations in conserved region II of p53. Mutations affected p53 transrepression and transactivation activities differently, indicating that these activities in p53 are separable. The ability of p53 mutants to transactivate correlated well with their ability to inhibit transformation of rat embryonic fibroblasts by adenovirus E1a and activated Ras.

Mouse p53 represses the rat brain creatine kinase gene but activates the rat muscle creatine kinase gene

The creatine kinases (CK) regenerate ATP for cellular reactions with a high energy expenditure. While muscle CK (CKM) is expressed almost exclusively in adult skeletal and cardiac muscle, brain CK (CKB) expression is more widespread and is highest in brain glial cells. CKB expression is also high in human lung tumor cells, many of which contain mutations in p53 alleles. We have recently detected high levels of CKB mRNA in HeLa cells and, in this study, have tested whether this may be due to the extremely low amounts of p53 protein present in HeLa cells. Transient transfection experiments showed that wild-type mouse p53 severely repressed the rat CKB promoter in HeLa but not CV-1 monkey kidney cells, suggesting that, in HeLa but not CV-1 cells, p53 either associates with a required corepressor or undergoes a posttranslational modification necessary for CKB repression. Conversely, mouse wild-type p53 strongly activated the rat CKM promoter in CV-1 cells but not in HeLa cells, suggesting that, in CV-1 cells, p53 may associate with a required coactivator or is modified in a manner necessary for CKM activation. The DNA sequences required for p53-mediated modulations were found to be within bp -195 to +5 of the CKB promoter and within bp -168 to -97 of the CKM promoter. Moreover, a 112-bp fragment from the proximal rat CKM promoter (bp -168 to -57), which contained five degenerate p53-binding elements, was capable of conferring p53-mediated activation on a heterologous promoter in CV-1 cells. Also, this novel p53 sequence, when situated in the native 168-bp rat CKM promoter, conferred p53-mediated activation equal to or greater than that of the originally characterized far-upstream (bp -3160) mouse CKM p53 element. Therefore, CKB and CKM may be among the few cellular genes which could be targets of p53 in vivo. In addition, we analyzed a series of missense mutants with alterations in conserved region II of p53. Mutations affected p53 transrepression and transactivation activities differently, indicating that these activities in p53 are separable. The ability of p53 mutants to transactivate correlated well with their ability to inhibit transformation of rat embryonic fibroblasts by adenovirus E1a and activated Ras.

Transcription of the brain creatine kinase gene in glial cells is modulated by cyclic AMP-dependent protein kinase

The brain creatine kinase (CKB) gene is expressed in a variety of tissues with highest expression seen in the brain. We have previously shown in primary rat brain cell cultures that CKB mRNA levels are high in oligodendrocytes and astrocytes and low in neurons (Molloy et al.: J Neurochem 59:1925-1932, 1992). In this report we show that treatment of human U87 glioblastoma cells with forskolin and IBMX, to elevate intracellular cAMP, induces expression of CKB mRNA from the transiently transfected rat CKB gene by 14-fold and also increases expression from the endogenous human CKB gene. This induction of CKB mRNA i) is due to increased transcription; ii) occurs rapidly (with maximal induction after 6 hr; iii) requires the activity of protein kinase A (PKA), but iv) does not require de novo protein synthesis and, in fact, is superinduced in the presence of cycloheximide. Given the role of oligodendrocytes in the energy-demanding process of myelination and of astrocytes in ion transport, these results have physiological significance, since they suggest that changes in cellular energy requirements in the brain during events, such as glial cell differentiation and increased neuronal activity, may in part be met by a cAMP-mediated modulation of CKB gene expression. Of particular importance is the possible modulation of CKB gene expression during myelinogenesis, since oligodendrocyte differentiation has been shown previously to be stimulated by increases in cAMP.

Creatine kinase in non-muscle tissues and cells

Over the past years, a concept for creatine kinase function, the 'PCr-circuit' model, has evolved. Based on this concept, multiple functions for the CK/PCr-system have been proposed, such as an energy buffering function, regulatory functions, as well as an energy transport function, mostly based on studies with muscle. While the temporal energy buffering and metabolic regulatory roles of CK are widely accepted, the spatial buffering or energy transport function, that is, the shuttling of PCr and Cr between sites of energy utilization and energy demand, is still being debated. There is, however, much circumstantial evidence, that supports the latter role of CK including the distinct, isoenzyme-specific subcellular localization of CK isoenzymes, the isolation and characterization of functionally coupled in vitro microcompartments of CK with a variety of cellular ATPases, and the observed functional coupling of mitochondrial oxidative phosphorylation with mitochondrial CK. New insight concerning the functions of the CK/PCr-system has been gained from recent M-CK null-mutant transgenic mice and by the investigation of CK localization and function in certain highly specialized non-muscle tissues and cells, such as electrocytes, retina photoreceptor cells, brain cells, kidney, salt glands, myometrium, placenta, pancreas, thymus, thyroid, intestinal brush-border epithelial cells, endothelial cells, cartilage and bone cells, macrophages, blood platelets, tumor and cancer cells. Studies with electric organ, including in vivo 31P-NMR, clearly reveal the buffer function of the CK/PCr-system in electrocytes and additionally corroborate a direct functional coupling of membrane-bound CK to the Na+/K(+)-ATPase. On the other hand, experiments with live sperm and recent in vivo 31P-NMR measurements on brain provide convincing evidence for the transport function of the CK/PCr-system. We report on new findings concerning the isoenzyme-specific cellular localization and subcellular compartmentation of CK isoenzymes in photoreceptor cells, in glial and neuronal cells of the cerebellum and in spermatozoa. Finally, the regulation of CK expression by hormones is discussed, and new developments concerning a connection of CK with malignancy and cancer are illuminated. Most interesting in this respect is the observed upregulation of CK expression by adenoviral oncogenes.

Creatine kinase isoenzymes in chicken cerebellum: specific localization of brain-type creatine kinase in Bergmann glial cells and muscle-type creatine kinase in Purkinje neurons

Creatine kinase isoenzymes were localized in the chicken cerebellum by the use of isoenzyme-specific anti-chicken creatine kinase antibodies. Brain-type creatine kinase was found in high amounts in the molecular layer, particularly in Bergmann glial cells but also in other cells of the cerebellar cortex, e.g. in astrocytes and in the glomerular structures, as well as in cells of the deeper nuclei. A mitochondrial creatine kinase isoform was primarily localized to the glomerular structures in the granule cell layer and was also identified in Purkinje neurons. Surprisingly, a small amount of the muscle-type creatine kinase isoform was identified in cerebellar extracts by immunoprecipitation, immunoblotting and native enzyme electrophoresis, and was shown to be localized exclusively in Purkinje neurons. Cell type-specific expression of brain- and muscle-type creatine kinase in Bergmann glial cells and Purkinje neurons, respectively, may serve to adapt cellular ATP regeneration to the different energy requirements in these specialized cell types. The presence of brain-type creatine kinase in Bergmann glial cells and astrocytes is discussed within the context of the energy requirements for ion homeostasis (K+ resorption), as well as for metabolite and neurotransmitter trafficking. In addition, the presence of muscle-type creatine kinase in Purkinje neurons, which also express other muscle-specific proteins, is discussed with respect to the unique calcium metabolism of these neurons and their role in cerebellar motor learning.

Expression of the rat brain creatine kinase gene in C6 glioma cells

We have recently shown that while brain creatine kinase (CKB) mRNA was detectable in RNA from cultured primary rat brain neurons, CKB mRNA was about 15-fold higher in primary astrocytes and 17-fold higher in oligodendrocytes (Molloy et al., J Neurochem 59:1925-1932, 1992). To begin to understand the molecular mechanisms responsible for brain glial cells containing the highest levels of CKB mRNA in the body, we have examined the expression of rat CKB mRNA in established C6 glioma cells. RNase-protection analysis showed the endogenous CKB mRNA levels in exponentially growing C6 were high and measured 50% of that in total RNA from rat brain lysate and 60% of that in cultured primary astrocytes and oligodendrocytes. The 5' and 3' ends of CKB mRNA in C6 were mapped to the same nucleotides as CKB mRNA from rat brain, indicating that the sites of in vivo transcription initiation and termination/polyadenylation of CKB mRNA in C6 are the same as in total rat brain RNA. The level of CKB enzyme activity in C6 whole cell lysates was among the highest of the glial cell lines which we measured. All creatine kinase enzyme activity present in C6 was found in the dimeric CKB isoform (BB), which is characteristic of CKB expression in the brain. A 2.9 kb gene fragment containing the basal CKB promoter and far-upstream 5' sequences was cloned upstream of the chloramphenicol acetyltransferase (CAT) gene and transfected into C6 cells. CAT activity was readily detectable in C6 and mapping of the 5' end of the CAT mRNA showed that transcription was directed from the correct initiation site. Since we found C6 cells were difficult to transfect, conditions were established which both maximized transfection efficiency and maintained normal C6 cell morphology. These results should permit the future identification of the nuclear trans-acting factors and the cognate cis-acting regulatory elements responsible for high CKB mRNA expression in brain glial cells.