[Show abstract][Hide abstract] ABSTRACT: Diminished glucose metabolism accompanies many neurodegenerative diseases including Alzheimer’s disease. An understanding of the relation of these metabolic changes to the disease will enable development of novel therapeutic strategies. Following a metabolic challenge, cells generally conserve energy to preserve viability. This requires activation of many cellular repair/regenerative processes such as mitophagy/autophagy and fusion/fission. These responses may diminish cell function in the long term. Prolonged fission induces mitophagy/autophagy which promotes repair but if prolonged progresses to mitochondrial degradation. Abnormal glucose metabolism alters protein signaling including the release of proteins from the mitochondria or migration of proteins from the cytosol to the mitochondria or nucleus. This overview provides an insight into the different mechanisms of autophagy/mitophagy and mitochondrial dynamics in response to the diminished metabolism that occurs with diseases, especially neurodegenerative diseases such as Alzheimer’s disease. The review discusses multiple aspects of mitochondrial responses including different signaling proteins and pathways of mitophagy and mitochondrial biogenesis. Improving cellular bioenergetics and mitochondrial dynamics will alter protein signaling and improve cellular/mitochondrial repair and regeneration. An understanding of these changes will suggest new therapeutic strategies.
Full-text · Article · Jun 2015 · Neurochemical Research
[Show abstract][Hide abstract] ABSTRACT: Reversible post-translation modifications of proteins are common in all cells and appear to regulate many processes. Nevertheless, the enzyme(s) responsible for the alterations and the significance of the modification are largely unknown. Succinylation of proteins occurs and causes large changes in the structure of proteins; however, the source of the succinyl groups, the targets, and the consequences of these modifications on other proteins are unknown. These studies focused on succinylation of mitochondrial proteins. The results demonstrate that the α-ketoglutarate dehydrogenase complex (KGDHC) can serve as a trans-succinylase that mediates succinylation in an α-ketoglutarate-dependent manner. Inhibition of KGDHC reduced succinylation of both cytosolic and mitochondrial proteins in cultured neurons and in a neuronal cell line. Purified KGDHC can succinylate multiple proteins including other enzymes of the tricarboxylic acid (TCA) cycle leading to modification of their activity. Inhibition of KGDHC also modifies acetylation by modifying the pyruvate dehydrogenase complex. The much greater effectiveness of KGDHC than succinyl CoA suggests that the catalysis due to the E2k succinyltransferase is important. Succinylation appears to be a major signaling system and it can be mediated by KGDHC. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
No preview · Article · Mar 2015 · Journal of Neurochemistry
[Show abstract][Hide abstract] ABSTRACT: Post-transcriptional regulation of mRNA by the RNA-binding protein HuR (encoded by Elavl1) is required in B cells for the germinal center reaction and for the production of class-switched antibodies in response to thymus-independent antigens. Transcriptome-wide examination of RNA isoforms and their abundance and translation in HuR-deficient B cells, together with direct measurements of HuR-RNA interactions, revealed that HuR-dependent splicing of mRNA affected hundreds of transcripts, including that encoding dihydrolipoamide S-succinyltransferase (Dlst), a subunit of the 2-oxoglutarate dehydrogenase (α-KGDH) complex. In the absence of HuR, defective mitochondrial metabolism resulted in large amounts of reactive oxygen species and B cell death. Our study shows how post-transcriptional processes control the balance of energy metabolism required for the proliferation and differentiation of B cells.
Full-text · Article · Feb 2015 · Nature Immunology
[Show abstract][Hide abstract] ABSTRACT: Thiamine dependent enzymes are diminished in Alzheimer's disease (AD). Thiamine deficiency in vitro and in rodents is a useful model of this reduction. Thiamine interacts with cellular calcium stores. To directly test the relevance of the thiamine dependent changes to dynamic processes in AD, the interactions must be studied in cells from patients with AD. These studies employed fibroblasts. Mitochondrial dysfunction including reductions in thiamine dependent enzymes and abnormalities in calcium homeostasis and oxidative processes occur in fibroblasts from Alzheimer's Disease (AD) patients. Bombesin-releasable calcium stores (BRCS) from the endoplasmic reticulum (ER) are exaggerated in fibroblasts from patients with AD bearing a presenilin-1 (PS-1) mutation and in control fibroblasts treated with oxidants. ER calcium regulates calcium entry into the cell through capacitative calcium entry (CCE), which is reduced in fibroblasts and neurons from mice bearing PS-1 mutations. Under physiological conditions, mitochondria and ER play important and interactive roles in the regulation of Ca(2+) homeostasis. Thus, the interactions of mitochondria and oxidants with CCE were tested. Inhibition of ER Ca(2+)-ATPase by cyclopiazonic acid (CPA) stimulates CCE. CPA-induced CCE was diminished by inhibition of mitochondrial Ca(2+) export (-60 %) or import (-40 %). Different aspects of mitochondrial Ca(2+) coupled to CPA-induced-CCE were sensitive to select oxidants. The effects were very different when CCE was examined in the presence of InsP3, a physiological regulator of ER calcium release, and subsequent CCE. CCE under these conditions was only mildly reduced (20-25 %) by inhibition of mitochondrial Ca(2+) export, and inhibition of mitochondrial Ca(2+) uptake exaggerated CCE (+53 %). However, t-BHP reversed both abnormalities. The results suggest that in the presence of InsP3, mitochondria buffer the local Ca(2+) released from ER following rapid activation of InsP3R and serve as a negative feedback to the CCE. The results suggest that mitochondrial Ca(2+) modifies the depletion and refilling mechanism of ER Ca(2+) stores.
[Show abstract][Hide abstract] ABSTRACT: A decline in α-ketoglutarate dehydrogenase complex (KGDHC) activity has been associated with neurodegeneration. Provision of succinyl-CoA by KGDHC is essential for generation of matrix ATP (or GTP) by substrate-level phosphorylation catalyzed by succinyl-CoA ligase. Here, we demonstrate ATP consumption in respiration-impaired isolated and in situ neuronal somal mitochondria from transgenic mice with a deficiency of either dihydrolipoyl succinyltransferase (DLST) or dihydrolipoyl dehydrogenase (DLD) that exhibit a 20-48% decrease in KGDHC activity. Import of ATP into the mitochondrial matrix of transgenic mice was attributed to a shift in the reversal potential of the adenine nucleotide translocase toward more negative values due to diminished matrix substrate-level phosphorylation, which causes the translocase to reverse prematurely. Immunoreactivity of all three subunits of succinyl-CoA ligase and maximal enzymatic activity were unaffected in transgenic mice as compared to wild-type littermates. Therefore, decreased matrix substrate-level phosphorylation was due to diminished provision of succinyl-CoA. These results were corroborated further by the finding that mitochondria from wild-type mice respiring on substrates supporting substrate-level phosphorylation exhibited ∼30% higher ADP-ATP exchange rates compared to those obtained from DLST+/- or DLD+/- littermates. We propose that KGDHC-associated pathologies are a consequence of the inability of respiration-impaired mitochondria to rely on "in-house" mitochondrial ATP reserves.-Kiss, G., Konrad, C., Doczi, J., Starkov, A. A., Kawamata, H., Manfredi, G., Zhang, S. F., Gibson, G. E., Beal, M. F., Adam-Vizi, V., Chinopoulos, C. The negative impact of α-ketoglutarate dehydrogenase complex deficiency on matrix substrate-level phosphorylation.
No preview · Article · Mar 2013 · The FASEB Journal
[Show abstract][Hide abstract] ABSTRACT: Reduced glucose metabolism is an invariant feature of Alzheimer's Disease (AD) and an outstanding biomarker of disease progression. Glucose metabolism may be an attractive therapeutic target, whether the decline initiates AD pathophysiology or is a critical component of a cascade. The cause of cerebral regional glucose hypometabolism remains unclear. Thiamine-dependent processes are critical in glucose metabolism and are diminished in brains of AD patients at autopsy. Further, the reductions in thiamine-dependent processes are highly correlated to the decline in clinical dementia rating scales. In animal models, thiamine deficiency exacerbates plaque formation, promotes phosphorylation of tau and impairs memory. In contrast, treatment of mouse models of AD with the thiamine derivative benfotiamine diminishes plaques, decreases phosphorylation of tau and reverses memory deficits. Diabetes predisposes to AD, which suggests they may share some common mechanisms. Benfotiamine diminishes peripheral neuropathy in diabetic humans and animals. In diabetes, benfotiamine induces key thiamine-dependent enzymes of the pentose shunt to reduce accumulation of toxic metabolites including advanced glycation end products (AGE). Related mechanisms may lead to reversal of plaque formation by benfotiamine in animals. If so, the use of benfotiamine could provide a safe intervention to reverse biological and clinical processes of AD progression. This article is part of a Special Issue entitled 'Mitochondrial function'.
No preview · Article · Sep 2012 · Molecular and Cellular Neuroscience
[Show abstract][Hide abstract] ABSTRACT: Understanding the molecular sequence of events that culminate in multiple abnormalities in brains from patients that died with Alzheimer's disease (AD) will help to reveal the mechanisms of the disease and identify upstream events as therapeutic targets. The activity of the mitochondrial α-ketoglutarate dehydrogenase complex (KGDHC) in homogenates from autopsy brain declines with AD. Experimental reductions in KGDHC in mouse models of AD promote plaque and tangle formation, the hallmark pathologies of AD. We hypothesize that deficits in KGDHC also lead to the abnormalities in endoplasmic reticulum (ER) calcium stores and cytosolic calcium following K(+) depolarization that occurs in cells from AD patients and transgenic models of AD. The activity of the mitochondrial enzyme KGDHC was diminished acutely (minutes), long-term (days), or chronically (weeks). Acute inhibition of KGDHC produced effects on calcium opposite to those in AD, while the chronic or long-term inhibition of KGDHC mimicked the AD-related changes in calcium. Divergent changes in proteins released from the mitochondria that affect endoplasmic reticulum calcium channels may underlie the selective cellular consequences of acute versus longer term inhibition of KGDHC. The results suggest that the mitochondrial abnormalities in AD can be upstream of those in calcium.
Full-text · Article · Dec 2011 · Neurobiology of aging
[Show abstract][Hide abstract] ABSTRACT: The activity of the α-ketoglutarate dehydrogenase complex (KGDHC), a mitochondrial enzyme complex that mediates the oxidative decarboxylation of α-ketoglutarate in the TCA cycle, is reduced in Alzheimer's disease. We investigated the metabolic effects of a partial KGDHC activity reduction on brain glucose metabolism using mice with disrupted expression of dihydrolipoyl succinyltransferase (DLST; gene encoding the E2k subunit of KGDHC). Brain tissue extracts from cortex and cerebellum of 6-week-old heterozygote DLST knockout mice (DLST+/-) and corresponding wild-type mice injected with [U-(13) C]glucose and decapitated 15 min later were analyzed. An increase in the concentration of glucose in cortex suggested a decrease in the cortical utilization of glucose in DLST+/- mice. Furthermore, the concentration and (13) C labelling of aspartate in cortex were reduced in DLST+/- mice. This decline was likely caused by a decrease in the pool of oxaloacetate. In contrast to results from cell culture studies, no indications of altered glycolysis or GABA shunt activity were found. Glucose metabolism in the cerebellum was unaffected by the decrease in KGDHC activity. Among metabolites not related to glucose metabolism, the concentration of taurine was decreased in the cortex, and that of tyrosine was increased in the cerebellum. These results imply that diminished KGDHC activity has the potential to induce the reduction in glucose utilization that is seen in several neurodegenerative diseases.
Full-text · Article · Dec 2011 · Journal of Neuroscience Research
[Show abstract][Hide abstract] ABSTRACT: J. Neurochem. (2011) 118, 440–448.
These experiments reveal for the first time that microRNAs (miRNAs) mediate oxidant regulated expression of a mitochondrial tricarboxylic acid cycle gene (mdh2). mdh2 encoded malate dehydrogenase (MDH) is elevated by an unknown mechanism in brains of patients that died with Alzheimer’s disease. Oxidative stress, an early and pervasive event in Alzheimer’s disease, increased MDH activity and mRNA level of mdh2 by 19% and 22%, respectively, in a mouse hippocampal cell line (HT22). Post-transcriptional events underlie the change in mRNA because actinomycin D did not block the elevated mdh2 mRNA. Since miRNAs regulate gene expression post-transcriptionally, the expression of miR-743a, a miRNA predicted to target mdh2, was determined and showed a 52% reduction after oxidant treatment. Direct interaction of miR-743a with mdh2 was demonstrated with a luciferase based assay. Over-expression or inhibition of miR-743a led to a respective reduction or increase in endogenous mRNA and MDH activity. The results demonstrate that miR-743a negatively regulates mdh2 at post-transcriptional level by directly targeting the mdh2 3′UTR. The findings are consistent with the suggestion that oxidative stress can elevate the activity of MDH through miR-743a, and provide new insights into possible roles of miRNA in oxidative stress and neurodegeneration.
Preview · Article · May 2011 · Journal of Neurochemistry
[Show abstract][Hide abstract] ABSTRACT: Reduced brain metabolism is an invariant feature of Alzheimer Disease (AD) that is highly correlated to the decline in brain
functions. Decreased activities of key tricarboxylic acid cycle (TCA) cycle enzymes may underlie this abnormality and are
highly correlated to the clinical state of the patient. The activity of the α-ketoglutarate dehydrogenase complex (KGDHC),
an arguably rate-limiting enzyme of the TCA cycle, declines with AD, but the mechanism of inactivation and whether it can
be reversed remains unknown. KGDHC consists of multiple copies of three subunits. KGDHC is sensitive to oxidative stress,
which is pervasive in AD brain. The present studies tested the mechanism for the peroxynitrite-induced inactivation and subsequent
reactivation of purified and cellular KGDHC. Peroxynitrite inhibited purified KGDHC activity in a dose-dependent manner and
reduced subunit immunoreactivity and increased nitrotyrosine immunoreactivity. Nano-LC-MS/MS showed that the inactivation
was related to nitration of specific tyrosine residues in the three subunits. GSH diminished the nitrotyrosine immunoreactivity
of peroxynitrite-treated KGDHC, restored the activity and the immunoreactivity for KGDHC. Nano-LC-MS/MS showed this was related
to de-nitration of specific tyrosine residues, suggesting KGDHC may have a denitrase activity. Treatment of N2a cells with
peroxynitrite for 5 min followed by recovery of cells for 24 h reduced KGDHC activity and increased nitrotyrosine immunoreactivity.
Increasing cellular GSH in peroxynitrite-treated cells rescued KGDHC activity to the control level. The results suggest that
restoring KGDHC activity is possible and may be a useful therapeutic approach in neurodegenerative diseases.
No preview · Article · May 2011 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: Images of brain metabolism and measurements of activities of components of the electron transport chain support earlier studies that suggest that brain glucose oxidation is inherently abnormal in a significant proportion of persons with schizophrenia. Therefore, we measured the activities of enzymes of the tricarboxylic (TCA) cycle in dorsolateral-prefrontal-cortex from schizophrenia patients (N=13) and non-psychiatric disease controls (N=13): the pyruvate dehydrogenase complex (PDHC), citrate synthase (CS), aconitase, isocitrate dehydrogenase (ICDH), the alpha-ketoglutarate dehydrogenase complex (KGDHC), succinate thiokinase (STH), succinate dehydrogenase (SDH), fumarase and malate dehydrogenase (MDH). Activities of aconitase (18.4%, p<0.05), KGDHC (26%) and STH (28.2%, p<0.05), enzymes in the first half of the TCA cycle, were lower, but SDH (18.3%, p<0.05) and MDH (34%, p<0.005), enzymes in the second half, were higher than controls. PDHC, CS, ICDH and fumarase activities were unchanged. There were no significant correlations between enzymes of TCA cycle and cognitive function, age or choline acetyl transferase activity, except for aconitase activity which decreased slightly with age (r=0.55, p=003). The increased activities of dehydrogenases in the second half of the TCA cycle may reflect a compensatory response to reduced activities of enzymes in the first half. Such alterations in the components of TCA cycle are adequate to alter the rate of brain metabolism. These results are consistent with the imaging studies of hypometabolism in schizophrenia. They suggest that deficiencies in mitochondrial enzymes can be associated with mental disease that takes the form of schizophrenia.
No preview · Article · Mar 2011 · European neuropsychopharmacology: the journal of the European College of Neuropsychopharmacology
[Show abstract][Hide abstract] ABSTRACT: Reduced brain metabolism is an invariant feature of Alzheimer Disease (AD) that is highly correlated to the decline in brain functions. Decreased activities of key tricarboxylic acid cycle (TCA) cycle enzymes may underlie this abnormality and are highly correlated to the clinical state of the patient. The activity of the α-ketoglutarate dehydrogenase complex (KGDHC), an arguably rate-limiting enzyme of the TCA cycle, declines with AD, but the mechanism of inactivation and whether it can be reversed remains unknown. KGDHC consists of multiple copies of three subunits. KGDHC is sensitive to oxidative stress, which is pervasive in AD brain. The present studies tested the mechanism for the peroxynitrite-induced inactivation and subsequent reactivation of purified and cellular KGDHC. Peroxynitrite inhibited purified KGDHC activity in a dose-dependent manner and reduced subunit immunoreactivity and increased nitrotyrosine immunoreactivity. Nano-LC-MS/MS showed that the inactivation was related to nitration of specific tyrosine residues in the three subunits. GSH diminished the nitrotyrosine immunoreactivity of peroxynitrite-treated KGDHC, restored the activity and the immunoreactivity for KGDHC. Nano-LC-MS/MS showed this was related to de-nitration of specific tyrosine residues, suggesting KGDHC may have a denitrase activity. Treatment of N2a cells with peroxynitrite for 5 min followed by recovery of cells for 24 h reduced KGDHC activity and increased nitrotyrosine immunoreactivity. Increasing cellular GSH in peroxynitrite-treated cells rescued KGDHC activity to the control level. The results suggest that restoring KGDHC activity is possible and may be a useful therapeutic approach in neurodegenerative diseases.
No preview · Article · Mar 2011 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: Diminished thiamine (vitamin B1) dependent processes and oxidative stress accompany Alzheimer's disease (AD). Thiamine deficiency in animals leads to oxidative stress. These observations suggest that thiamin may act as an antioxidant. The current experiments first tested directly whether thiamin could act as an antioxidant, and then examined the physiological relevance of the antioxidant properties on oxidant sensitive, calcium dependent processes that are altered in AD. The first group of experiments examined whether thiamin could diminish reactive oxygen species (ROS) or reactive nitrogen species (RNS) produced by two very divergent paradigms. Dose response curves determined the concentrations of t-butyl-hydroperoxide (t-BHP) (ROS production) or 3-morpholinosydnonimine ((SIN-1) (RNS production) to induce oxidative stress within cells. Concentrations of thiamine that reduced the RNS in cells did not diminish the ROS. The second group of experiments tested whether thiamine alters oxidant sensitive aspects of calcium regulation including endoplasmic reticulum (ER) calcium stores and capacitative calcium entry (CCE). Thiamin diminished ER calcium considerably, but did not alter CCE. Thiamine did not alter the actions of ROS on ER calcium or CCE. On the other hand, thiamine diminished the effect of RNS on CCE. These data are consistent with thiamine diminishing the actions of the RNS, but not ROS, on physiological targets. Thus, both experimental approaches suggest that thiamine selectively alters RNS. Additional experiments are required to determine whether diminished thiamine availability promotes oxidative stress in AD or whether the oxidative stress in AD brain diminishes thiamine availability to thiamine dependent processes.
Preview · Article · Dec 2010 · Neurochemical Research
[Show abstract][Hide abstract] ABSTRACT: Alzheimer's disease (AD) is defined by senile plaques made of amyloid-beta peptide (Abeta), neurofibrillary tangles made of hyperphosphorylated tau proteins, and memory deficits. Thus, the events initiating the cascade leading to these end points may be more effective therapeutic targets than treating each facet individually. In the small percentage of cases of AD that are genetic (or animal models that reflect this form of AD), the factor initiating AD is clear (e.g., genetic mutations lead to high Abeta1-42 or hyperphosphorylated tau proteins). In the vast majority of AD cases, the cause is unknown. Substantial evidence now suggests that abnormalities in glucose metabolism/mitochondrial function/oxidative stress (GMO) are an invariant feature of AD and occur at an early stage of the disease process in both genetic and non-genetic forms of AD. Indeed, decreases in brain glucose utilization are diagnostic for AD. Changes in calcium homeostasis also precede clinical manifestations of AD. Abnormal GMO can lead to plaques, tangles, and the calcium abnormalities that accompany AD. Abnormalities in GMO diminish the ability of the brain to adapt. Therapies targeting mitochondria may ameliorate abnormalities in plaques, tangles, calcium homeostasis, and cognition that comprise AD.
Preview · Article · Jan 2010 · Journal of Alzheimer's disease: JAD
[Show abstract][Hide abstract] ABSTRACT: Presenilin-1 (PS1) and -2 (PS2), which when mutated cause familial Alzheimer disease, have been localized to numerous compartments of the cell, including the endoplasmic reticulum, Golgi, nuclear envelope, endosomes, lysosomes, the plasma membrane, and mitochondria. Using three complementary approaches, subcellular fractionation, gamma-secretase activity assays, and immunocytochemistry, we show that presenilins are highly enriched in a subcompartment of the endoplasmic reticulum that is associated with mitochondria and that forms a physical bridge between the two organelles, called endoplasmic reticulum-mitochondria-associated membranes. A localization of PS1 and PS2 in mitochondria-associated membranes may help reconcile the disparate hypotheses regarding the pathogenesis of Alzheimer disease and may explain many seemingly unrelated features of this devastating neurodegenerative disorder.
Full-text · Article · Nov 2009 · American Journal Of Pathology