Mitochondrial impairment in the cerebellum of the patients with progressive supranuclear palsy

How can we manage progressive supranuclear palsy syndrome with pharmacotherapy?

INTRODUCTION

Tauopathies are a spectrum of clinicopathological neurodegenerative disorders with increased aggregates included in glia and/or neurons of hyperphosphorylated insoluble tau protein, a microtubule-associated protein. Progressive supranuclear palsy (PSP) is an atypical dopaminergic-resistant parkinsonian syndrome, considered as a primary tauopathy with possible alteration of tau isoform ratio, and tau accumulations characterized by 4 R tau species as the main neuropathological lesions.

AREAS COVERED

In the present review article, we analyzed and discussed viable disease-modifying and some symptomatic pharmacological therapeutics for PSP syndrome (PSPS).

EXPERT OPINION

Pharmacological therapy for PSPS may interfere with the aggregation process or promote the clearance of abnormal tau aggregates. A variety of past and ongoing disease-modifying therapies targeting tau in PSPS included genetic, microtubule-stabilizing compounds, anti-phosphorylation, and acetylation agents, antiaggregant, protein removal, antioxidant neuronal and synaptic growth promotion therapies. New pharmacological gene-based approaches may open alternative prevention pathways for the deposition of abnormal tau in PSPS such as antisense oligonucleotide (ASO)-based drugs. Moreover, kinases and ubiquitin-proteasome systems could also be viable targets.

Mitochondrial Alpha-Keto Acid Dehydrogenase Complexes: Recent Developments on Structure and Function in Health and Disease

The present work delves into the enigmatic world of mitochondrial alpha-keto acid dehydrogenase complexes discussing their metabolic significance, enzymatic operation, moonlighting activities, and pathological relevance with links to underlying structural features. This ubiquitous family of related but diverse multienzyme complexes is involved in carbohydrate metabolism (pyruvate dehydrogenase complex), the citric acid cycle (α-ketoglutarate dehydrogenase complex), and amino acid catabolism (branched-chain α-keto acid dehydrogenase complex, α-ketoadipate dehydrogenase complex); the complexes all function at strategic points and also participate in regulation in these metabolic pathways. These systems are among the largest multienzyme complexes with at times more than 100 protein chains and weights ranging up to ~10 million Daltons. Our chapter offers a wealth of up-to-date information on these multienzyme complexes for a comprehensive understanding of their significance in health and disease.

Mild hypoxia-induced structural and functional changes of the hippocampal network

Hypoxia causes structural and functional changes in several brain regions, including the oxygen-concentration-sensitive hippocampus. We investigated the consequences of mild short-term hypoxia on rat hippocampus in vivo. The hypoxic group was treated with 16% O2 for 1 h, and the control group with 21% O2. Using a combination of Gallyas silver impregnation histochemistry revealing damaged neurons and interneuron-specific immunohistochemistry, we found that somatostatin-expressing inhibitory neurons in the hilus were injured. We used 32-channel silicon probe arrays to record network oscillations and unit activity from the hippocampal layers under anaesthesia. There were no changes in the frequency power of slow, theta, beta, or gamma bands, but we found a significant increase in the frequency of slow oscillation (2.1-2.2 Hz) at 16% O2 compared to 21% O2. In the hilus region, the firing frequency of unidentified interneurons decreased. In the CA3 region, the firing frequency of some unidentified interneurons decreased while the activity of other interneurons increased. The activity of pyramidal cells increased both in the CA1 and CA3 regions. In addition, the regularity of CA1, CA3 pyramidal cells' and CA3 type II and hilar interneuron activity has significantly changed in hypoxic conditions. In summary, a low O2 environment caused profound changes in the state of hippocampal excitatory and inhibitory neurons and network activity, indicating potential changes in information processing caused by mild short-term hypoxia.

The α-Ketoglutarate Dehydrogenase Complex as a Hub of Plasticity in Neurodegeneration and Regeneration

Abnormal glucose metabolism is central to neurodegeneration, and considerable evidence suggests that abnormalities in key enzymes of the tricarboxylic acid (TCA) cycle underlie the metabolic deficits. Significant recent advances in the role of metabolism in cancer provide new insight that facilitates our understanding of the role of metabolism in neurodegeneration. Research indicates that the rate-limiting step of the TCA cycle, the α-ketoglutarate dehydrogenase complex (KGDHC) and its substrate alpha ketoglutarate (KG), serve as a signaling hub that regulates multiple cellular processes: (1) is the rate-limiting step of the TCA cycle, (2) is sensitive to reactive oxygen species (ROS) and produces ROS, (3) determines whether KG is used for energy or synthesis of compounds to support growth, (4) regulates the cellular responses to hypoxia, (5) controls the post-translational modification of hundreds of cell proteins in the mitochondria, cytosol, and nucleus through succinylation, (6) controls critical aspects of transcription, (7) modulates protein signaling within cells, and (8) modulates cellular calcium. The primary focus of this review is to understand how reductions in KGDHC are translated to pathologically important changes that underlie both neurodegeneration and cancer. An understanding of each role is necessary to develop new therapeutic strategies to treat neurodegenerative disease.

Phosphonate analog of 2-oxoglutarate regulates glutamate-glutamine homeostasis and counteracts amyloid beta induced learning and memory deficits in rats

BACKGROUND

Metabolic alteration is a mainstream concept underlying the cognitive decline in neurodegenerative disorders including Alzheimer's disease (AD). Mitochondrial enzyme α-ketoglutarate dehydrogenase complex (α-KGDHC) seems to play a dual-edged sword role in cytotoxic insult. Here, using succinyl phosphonate (SP), a specific α-KGDHC inhibitor, we aimed to examine its potential action on AD progression.

METHODS

Male Wistar rats were assigned to two separate experiments. First, they were bilaterally microinjected into the dorsal CA₁ area by amyloid-beta (Aβ)_25-35 for four consecutive days. Seven days after the last injection, they were trained to acquire Morris Water Maze (MWM) task for three successive days when they were treated with SP after each training session. In the second experiment, SP was administered 30 min after the first Aβ microinjection and behavioral tests were performed one week after the last Aβ administration. The activity of glutamate dehydrogenase (GDH), and glutamine synthetase (GS), as key enzymes involved in glutamate-glutamine homeostasis and histological assays were evaluated in the hippocampi.

RESULTS

Our behavioral results indicated that post-training SP treatment enhanced task acquisition but did not change memory performance in Aβ-treated rats. However, administration of SP at the time of Aβ injection precludes the deteriorative effect of Aβ and neuronal injury on both spatial learning and memory performances indicating its preventive action against Aβ pathology at its early stages. Measurement of enzymes activity shows that α-KGDHC activity was reduced in the Aβ treated group, and SP administration restored its activity; also, GDH and GS activities were increased and decreased respectively due to Aβ, and SP reversed the action of Aβ on these enzymes.

CONCLUSIONS

This study proposes that SP possibly a promising therapeutic approach to improve memory impairment in AD, especially in the early phases of this disease.

Co-expression network analysis of human tau-transgenic mice reveals protein modules associated with tau-induced pathologies

Abnormally accumulated tau protein aggregates are one of the hallmarks of neurodegenerative diseases, including Alzheimer's disease (AD). In order to investigate proteomic alteration driven by tau aggregates, we implemented quantitative proteomics to analyze disease model mice expressing human MAPT P301S transgene (hTau-Tg) and quantified more than 9,000 proteins in total. We applied the weighted gene co-expression analysis (WGCNA) algorithm to the datasets and explored protein co-expression modules that were associated with the accumulation of tau aggregates and were preserved in proteomes of AD brains. This led us to identify four modules with functions related to neuroinflammatory responses, mitochondrial energy production processes (including the tricarboxylic acid cycle and oxidative phosphorylation), cholesterol biosynthesis, and postsynaptic density. Furthermore, a phosphoproteomics study uncovered phosphorylation sites that were highly correlated with these modules. Our datasets represent resources for understanding the molecular basis of tau-induced neurodegeneration, including AD.

Increasing Inhibition of the Rat Brain 2-Oxoglutarate Dehydrogenase Decreases Glutathione Redox State, Elevating Anxiety and Perturbing Stress Adaptation

Specific inhibitors of mitochondrial 2-oxoglutarate dehydrogenase (OGDH) are administered to animals to model the downregulation of the enzyme as observed in neurodegenerative diseases. Comparison of the effects of succinyl phosphonate (SP, 0.02 mmol/kg) and its uncharged precursor, triethyl succinyl phosphonate (TESP, 0.02 and 0.1 mmol/kg) reveals a biphasic response of the rat brain metabolism and physiology to increasing perturbation of OGDH function. At the low (TE)SP dose, glutamate, NAD+, and the activities of dehydrogenases of 2-oxoglutarate and malate increase, followed by their decreases at the high TESP dose. The complementary changes, i.e., an initial decrease followed by growth, are demonstrated by activities of pyruvate dehydrogenase and glutamine synthetase, and levels of oxidized glutathione and citrulline. While most of these indicators return to control levels at the high TESP dose, OGDH activity decreases and oxidized glutathione increases, compared to their control values. The first phase of metabolic perturbations does not cause significant physiological changes, but in the second phase, the ECG parameters and behavior reveal decreased adaptability and increased anxiety. Thus, lower levels of OGDH inhibition are compensated by the rearranged metabolic network, while the increased levels induce a metabolic switch to a lower redox state of the brain, associated with elevated stress of the animals.

Progressive Supranuclear Palsy and Corticobasal Degeneration

Progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are neurodegenerative tauopathies with neuronal and glial lesions composed of tau that is composed predominantly of isomers with four repeats in the microtubule-binding domain (4R tau). The brain regions vulnerable to pathology in PSP and CBD overlap, but there are differences, particularly with respect to distribution of neuronal loss, the relative abundance of neuronal and glial lesions, the morphologic features of glial lesions, and the frequency of comorbid pathology. Both PSP and CBD have a wide spectrum of clinical manifestations, including disorders of movement and cognition. Recognition of phenotypic diversity in PSP and CBD may improve antemortem diagnostic accuracy, which tends to be very good for the most common presentation of PSP (Richardson syndrome), but poor for the most characteristic presentation of CBD (corticobasal syndrome: CBS). Development of molecular and imaging biomarkers may improve antemortem diagnostic accuracy. Currently, multidisciplinary symptomatic and supportive treatment with pharmacological and non-pharmacological strategies remains the standard of care. In the future, experimental therapeutic trials will be important to slow disease progression.

Progressive supranuclear palsy: Advances in diagnosis and management

Progressive supranuclear palsy (PSP) is a complex clinicopathologic disease with no current cure or disease modulating therapies that can only be definitively confirmed at autopsy. Growing understanding of the phenotypic diversity of PSP has led to expanded clinical criteria and new insights into etiopathogenesis that coupled with improved in vivo biomarkers makes increased access to current clinical trials possible. Current standard-of-care treatment of PSP is multidisciplinary, supportive and symptomatic, and several trials of potentially disease modulating agents have already been completed with disappointing results. Current ongoing clinical trials target the abnormal aggregation of tau through a variety of mechanisms including immunotherapy and gene therapy offer a more direct method of treatment. Here we review PSP clinicopathologic correlations, in vivo biomarkers including MRI, PET, and CSF biomarkers. We additionally review current pharmacologic and non-pharmacologic methods of treatment, prior and ongoing clinical trials in PSP. Newly expanded clinical criteria and improved specific biomarkers will aid in identifying patients with PSP earlier and more accurately and expand access to these potentially beneficial clinical trials.

The biology of Lonp1: More than a mitochondrial protease

Initially discovered as a protease responsible for degradation of misfolded or damaged proteins, the mitochondrial Lon protease (Lonp1) turned out to be a multifaceted enzyme, that displays at least three different functions (proteolysis, chaperone activity, binding of mtDNA) and that finely regulates several cellular processes, within and without mitochondria. Indeed, LONP1 in humans is ubiquitously expressed, and is involved in regulation of response to oxidative stress and, heat shock, in the maintenance of mtDNA, in the regulation of mitophagy. Furthermore, its proteolytic activity can regulate several biochemical pathways occurring totally or partially within mitochondria, such as TCA cycle, oxidative phosphorylation, steroid and heme biosynthesis and glutamine production. Because of these multiple activities, Lon protease is highly conserved throughout evolution, and mutations occurring in its gene determines severe diseases in humans, including a rare syndrome characterized by Cerebral, Ocular, Dental, Auricular and Skeletal anomalies (CODAS). Finally, alterations of LONP1 regulation in humans can favor tumor progression and aggressiveness, further highlighting the crucial role of this enzyme in mitochondrial and cellular homeostasis.

Exclusive neuronal detection of KGDHC-specific subunits in the adult human brain cortex despite pancellular protein lysine succinylation

The ketoglutarate dehydrogenase complex (KGDHC) consists of three different subunits encoded by OGDH (or OGDHL), DLST, and DLD, combined in different stoichiometries. DLD subunit is shared between KGDHC and pyruvate dehydrogenase complex, branched-chain alpha-keto acid dehydrogenase complex, and the glycine cleavage system. Despite KGDHC's implication in neurodegenerative diseases, cell-specific localization of its subunits in the adult human brain has never been investigated. Here, we show that immunoreactivity of all known isoforms of OGDHL, OGDH, and DLST was detected exclusively in neurons of surgical human cortical tissue samples identified by their morphology and visualized by double labeling with fluorescent Nissl, while being absent from glia expressing GFAP, Aldhl1, myelin basic protein, Olig2, or IBA1. In contrast, DLD immunoreactivity was evident in both neurons and glia. Specificity of anti-KGDHC subunits antisera was verified by a decrease in staining of siRNA-treated human cancer cell lines directed against the respective coding gene products; furthermore, immunoreactivity of KGDHC subunits in human fibroblasts co-localized > 99% with mitotracker orange, while western blotting of 63 post-mortem brain samples and purified recombinant proteins afforded further assurance regarding antisera monospecificity. KGDHC subunit immunoreactivity correlated with data from the Human Protein Atlas as well as RNA-Seq data from the Allen Brain Atlas corresponding to genes coding for KGDHC components. Protein lysine succinylation, however, was immunohistochemically evident in all cortical cells; this was unexpected, because this posttranslational modification requires succinyl-CoA, the product of KGDHC. In view of the fact that glia of the human brain cortex lack succinate-CoA ligase, an enzyme producing succinyl-CoA when operating in reverse, protein lysine succinylation in these cells must exclusively rely on propionate and/or ketone body metabolism or some other yet to be discovered pathway encompassing succinyl-CoA.

Benfotiamine treatment activates the Nrf2/ARE pathway and is neuroprotective in a transgenic mouse model of tauopathy

Impaired glucose metabolism, decreased levels of thiamine and its phosphate esters, and reduced activity of thiamine-dependent enzymes, such as pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and transketolase occur in Alzheimer's disease (AD). Thiamine deficiency exacerbates amyloid beta (Aβ) deposition, tau hyperphosphorylation and oxidative stress. Benfotiamine (BFT) rescued cognitive deficits and reduced Aβ burden in amyloid precursor protein (APP)/PS1 mice. In this study, we examined whether BFT confers neuroprotection against tau phosphorylation and the generation of neurofibrillary tangles (NFTs) in the P301S mouse model of tauopathy. Chronic dietary treatment with BFT increased lifespan, improved behavior, reduced glycated tau, decreased NFTs and prevented death of motor neurons. BFT administration significantly ameliorated mitochondrial dysfunction and attenuated oxidative damage and inflammation. We found that BFT and its metabolites (but not thiamine) trigger the expression of Nrf2/antioxidant response element (ARE)-dependent genes in mouse brain as well as in wild-type but not Nrf2-deficient fibroblasts. Active metabolites were more potent in activating the Nrf2 target genes than the parent molecule BFT. Docking studies showed that BFT and its metabolites (but not thiamine) bind to Keap1 with high affinity. These findings demonstrate that BFT activates the Nrf2/ARE pathway and is a promising therapeutic agent for the treatment of diseases with tau pathology, such as AD, frontotemporal dementia and progressive supranuclear palsy.

The mitochondrial 2-oxoadipate and 2-oxoglutarate dehydrogenase complexes share their E2 and E3 components for their function and both generate reactive oxygen species

Herein are reported unique properties of the novel human thiamin diphosphate (ThDP)-dependent enzyme 2-oxoadipate dehydrogenase (hE1a), known as dehydrogenase E1 and transketolase domain-containing protein 1 that is encoded by the DHTKD1 gene. It is involved in the oxidative decarboxylation of 2-oxoadipate (OA) to glutaryl-CoA on the final degradative pathway of L-lysine and is critical for mitochondrial metabolism. Functionally active recombinant hE1a has been produced according to both kinetic and spectroscopic criteria in our toolbox leading to the following conclusions: (i) The hE1a has recruited the dihydrolipoyl succinyltransferase (hE2o) and the dihydrolipoyl dehydrogenase (hE3) components of the tricarboxylic acid cycle 2-oxoglutarate dehydrogenase complex (OGDHc) for its activity. (ii) 2-Oxoglutarate (OG) and 2-oxoadipate (OA) could be oxidized by hE1a, however, hE1a displays an approximately 49-fold preference in catalytic efficiency for OA over OG, indicating that hE1a is specific to the 2-oxoadipate dehydrogenase complex. (iii) The hE1a forms the ThDP-enamine radical from OA according to electron paramagnetic resonance detection in the oxidative half reaction, and could produce superoxide and H₂O₂ from decarboxylation of OA in the forward physiological direction, as also seen with the 2-oxoglutarate dehydrogenase hE1o component. (iv) Once assembled to complex with the same hE2o and hE3 components, the hE1o and hE1a display strikingly different regulation: both succinyl-CoA and glutaryl-CoA significantly reduced the hE1o activity, but not the activity of hE1a.

Postmortem studies on mitochondria in schizophrenia

The aim of this paper is to provide a brief review of mitochondrial structure as it relates to function and then present abnormalities in mitochondria in postmortem schizophrenia with a focus on ultrastructure. Function, morphology, fusion, fission, motility, ΔΨmem, ATP production, mitochondrial derived vesicles, and mitochondria-associated ER membranes will be briefly covered. Pathology in mitochondria has long been implicated in schizophrenia, as shown by genetic, proteomic, enzymatic and anatomical abnormalities. The cortex and basal ganglia will be reviewed. In the anterior cingulate cortex, the number of mitochondria per neuronal somata in layers 5/6 in schizophrenia is decreased by 43%. There are also fewer mitochondria in terminals forming axospinous synapses. In the caudate and putamen the number of mitochondria is abnormal in both glial cells and neurons in schizophrenia subjects, the extent of which depends on treatment, response and predominant lifetime symptoms. Treatment-responsive schizophrenia subjects had about a 40% decrease in the number of mitochondria per synapse in the caudate nucleus and putamen, while treatment resistant cases had normal values. A decrease in mitochondrial density in the neuropil distinguishes paranoid from undifferentiated schizophrenia. The appearance, size and density of mitochondria were normal in the nucleus accumbens. In the substantia nigra, COX subunits were affected in rostral regions. Mitochondrial hyperplasia occurs within axon terminals that synapse onto dopamine neurons, but mitochondria in dopamine neuronal somata are similar in size and number. In schizophrenia, mitochondria are differentially affected depending on the brain region, cell type, subcellular location, treatment status, treatment response and symptoms.

The human Krebs cycle 2-oxoglutarate dehydrogenase complex creates an additional source of superoxide/hydrogen peroxide from 2-oxoadipate as alternative substrate

Recently, we reported that the human 2-oxoglutarate dehydrogenase (hE1o) component of the 2-oxoglutarate dehydrogenase complex (OGDHc) could produce the reactive oxygen species superoxide and hydrogen peroxide (detected by chemical means) from its substrate 2-oxoglutarate (OG), most likely concurrently with one-electron oxidation by dioxygen of the thiamin diphosphate (ThDP)-derived enamine intermediate to a C2α-centered radical (detected by Electron Paramagnetic Resonance) [Nemeria et al., 2014 [17]; Ambrus et al. 2015 [18]]. We here report that hE1o can also utilize the next higher homologue of OG, 2-oxoadipate (OA) as a substrate according to multiple criteria in our toolbox: (i) Both E1o-specific and overall complex activities (NADH production) were detected using OA as a substrate; (ii) Two post-decarboxylation intermediates were formed by hE1o from OA, the ThDP-enamine and the C2α-hydroxyalkyl-ThDP, with nearly identical rates for OG and OA; (iii) Both OG and OA could reductively acylate lipoyl domain created from dihydrolipoyl succinyltransferase (E2o); (iv) Both OG and OA gave α-ketol carboligaton products with glyoxylate, but with opposite chirality; a finding that could be of utility in chiral synthesis; (v) Dioxygen could oxidize the ThDP-derived enamine from both OG and OA, leading to ThDP-enamine radical and generation of superoxide and H₂O₂. While the observed oxidation-reduction with dioxygen is only a side reaction of the predominant physiological product glutaryl-CoA, the efficiency of superoxide/ H₂O₂ production was 7-times larger from OA than from OG, making the reaction of OGDHc with OA one of the important superoxide/ H₂O₂ producers among 2-oxo acid dehydrogenase complexes in mitochondria.

Human dihydrolipoamide dehydrogenase (E3) deficiency: Novel insights into the structural basis and molecular pathomechanism

This review summarizes our present view on the molecular pathogenesis of human (h) E3-deficiency caused by a variety of genetic alterations with a special emphasis on the moonlighting biochemical phenomena related to the affected (dihydro)lipoamide dehydrogenase (LADH, E3, gene: dld), in particular the generation of reactive oxygen species (ROS). E3-deficiency is a rare autosomal recessive genetic disorder frequently presenting with a neonatal onset and premature death; the highest carrier rate of a single pathogenic dld mutation (1:94-1:110) was found among Ashkenazi Jews. Patients usually die during acute episodes that generally involve severe metabolic decompensation and lactic acidosis leading to neurological, cardiological, and/or hepatological manifestations. The disease owes its severity to the fact that LADH is the common E3 subunit of the alpha-ketoglutarate (KGDHc), pyruvate (PDHc), and branched-chain α-keto acid dehydrogenase complexes and is also part of the glycine cleavage system, hence the malfunctioning of LADH simultaneously incapacitates several central metabolic pathways. Nevertheless, the clinical pictures are usually not unequivocally portrayed through the loss of LADH activities and imply auxiliary mechanisms that exacerbate the symptoms and outcomes of this disorder. Enhanced ROS generation by disease-causing hE3 variants as well as by the E1-E2 subcomplex of the hKGDHc likely contributes to selected pathogeneses of E3-deficiency, which could be targeted by specific drugs or antioxidants; lipoic acid was demonstrated to be a potent inhibitor of ROS generation by hE3 in vitro. Flavin supplementation might prove to be beneficial for those mutations triggering FAD loss in the hE3 component. Selected pathogenic hE3 variants lose their affinity for the E2 component of the hPDHc, a mechanism which warrants scrutiny also for other E3-haboring complexes.

Plasma metabolomics reveals a diagnostic metabolic fingerprint for mitochondrial aconitase (ACO2) deficiency

Mitochondrial respiratory chain dysfunction has been identified in a number of neurodegenerative disorders. Infantile cerebellar-retinal degeneration associated with mutations in the mitochondrial aconitase 2 gene (ACO2) has been recently described as a neurodegenerative disease of autosomal recessive inheritance. To date there is no biomarker for ACO2 deficiency and diagnosis relies on genetic analysis. Here we report global metabolic profiling in eight patients with ACO2 deficiency. Using an LC-MS-based metabolomics platform we have identified several metabolites with affected plasma concentrations including the tricarboxylic acid cycle metabolites cis-aconitate, isocitrate and alpha-ketoglutarate, as well as phosphoenolpyruvate and hydroxybutyrate. Taken together we report a diagnostic metabolic fingerprint for mitochondrial aconitase 2 deficiency.

Thiamine deficiency induces endoplasmic reticulum stress and oxidative stress in human neurons derived from induced pluripotent stem cells

Thiamine (vitamin B1) deficiency (TD) plays a major role in the etiology of Wernicke's encephalopathy (WE) which is a severe neurological disorder. TD induces selective neuronal cell death, neuroinflammation, endoplasmic reticulum (ER) stress and oxidative stress in the brain which are commonly observed in many aging-related neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and progressive supranuclear palsy (PSP). However, the underlying cellular and molecular mechanisms remain unclear. The progress in this line of research is hindered due to the lack of appropriate in vitro models. The neurons derived for the human induced pluripotent stem cells (hiPSCs) provide a relevant and powerful tool for the research in pharmaceutical and environmental neurotoxicity. In this study, we for the first time used human induced pluripotent stem cells (hiPSCs)-derived neurons (iCell neurons) to investigate the mechanisms of TD-induced neurodegeneration. We showed that TD caused a concentration- and duration-dependent death of iCell neurons. TD induced ER stress which was evident by the increase in ER stress markers, such as GRP78, XBP-1, CHOP, ATF-6, phosphorylated eIF2α, and cleaved caspase-12. TD also triggered oxidative stress which was shown by the increase in the expression 2,4-dinitrophenyl (DNP) and 4-hydroxynonenal (HNE). ER stress inhibitors (STF-083010 and salubrinal) and antioxidant N-acetyl cysteine (NAC) were effective in alleviating TD-induced death of iCell neurons, supporting the involvement of ER stress and oxidative stress. It establishes that the iCell neurons are a novel tool to investigate cellular and molecular mechanisms for TD-induced neurodegeneration.

Mitochondrial Quality Control Proteases in Neuronal Welfare

The functional integrity of mitochondria is a critical determinant of neuronal health and compromised mitochondrial function is a commonly recognized factor that underlies a plethora of neurological and neurodegenerative diseases. Metabolic demands of neural cells require high bioenergetic outputs that are often associated with enhanced production of reactive oxygen species. Unopposed accumulation of these respiratory byproducts over time leads to oxidative damage and imbalanced protein homeostasis within mitochondrial subcompartments, which in turn may result in cellular demise. The post-mitotic nature of neurons and their vulnerability to these stress factors necessitate strict protein homeostatic control to prevent such scenarios. A series of evolutionarily conserved proteases is one of the central elements of mitochondrial quality control. These versatile proteolytic enzymes conduct a multitude of activities to preserve normal mitochondrial function during organelle biogenesis, metabolic remodeling and stress. In this review we discuss neuroprotective aspects of mitochondrial quality control proteases and neuropathological manifestations arising from defective proteolysis within the mitochondrion.

A Review of Treatment Options for Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) is an atypical parkinsonian condition characterized by a symmetric akinetic-rigid syndrome, early falls, supranuclear gaze palsy, and a frontotemporal behavioral syndrome. The typical phenotype is termed Richardson's syndrome, but numerous other phenotypes have been described. The pathophysiology of PSP is not fully understood, but dysfunction of the tau protein seems to play a central role. Despite exciting new knowledge on the pathophysiology of PSP, there is still no highly effective symptomatic or disease-modifying treatment. We review the evidence on pharmacotherapy and experimental therapies in PSP and provide levels of recommendation for the off-label use of commonly used drugs in this disorder.

Relationship between uric acid levels and progressive supranuclear palsy

INTRODUCTION

The pathophysiology of both PD and PSP is characterized by a pro-oxidant state. Uric acid is an oxidative stress marker. High uric acid blood levels have been associated with a reduced risk of PD and a decreased rate of disease progression. We investigated whether a low serum concentration of uric acid is also associated with PSP.

METHODS

We measured serum uric acid concentrations in a subsample of the ENGENE PSP Cohort that included 75 cases and 75 frequency-matched-by-sex healthy controls (69 spouses, 6 in-laws) from four centers willing to participate (Case Western, Rush University, University of Utah, and University of Louisville). Case severity was characterized using the total PSP-Rating Scale, UPDRS, and Mattis Dementia Rating Scale. Unconditional logistic regression, Pearson's chi-squared test, and analysis of variance were used, as appropriate.

RESULTS

The mean uric acid level among cases (4.0 mg/dL) was not significantly lower than that of controls (4.1 mg/dL). When controlling for sex, there were no between-group statistical differences in uric acid levels. Uric acid levels were not correlated with disease severity.

CONCLUSIONS

The results of this study do not provide evidence of uric acid having a protective role in PSP, even if oxidative injury is important in the pathophysiology of this disorder. The lack of statistical significance suggests that there is no direct association between uric acid levels and PSP. However, a small inverse association cannot be excluded. © 2016 Movement Disorder Society.

Quantitative assessment of cerebral gray matter density change in progressive supranuclear palsy using voxel based morphometry analysis and cerebral MR T1-weighted FLAIR imaging

PURPOSE

To investigate the gray matter (GM) atrophy in Progressive supranuclear palsy (PSP) using T1-weighted Fluid-Attenuated Inversion Recovery (FLAIR) images based on voxel based morphometry (VBM) method.

MATERIALS AND METHODS

In this study, we firstly modified the conventional VBM method to make it can process the T1-weighted FLAIR brain images. Then, we used this method on the 24 PSP patients and 23 healthy age- and sex-matched control subjects to find the local gray matter density changes of PSP patients.

RESULTS

Compared with healthy controls, GM reductions of PSP patients mainly located in the thalamus, basal ganglia, pons, midbrain, insular cortex, frontal cortex, temporal lobe, cerebellum, cingulate cortex and hippocampus.

CONCLUSION

We used the modified VBM technique into T1 FLAIR data to study the brain gray matter atrophy in PSP, and found some new atrophy areas, including pallidum, middle and posterior cingulum, lingual, fusiform gyrus and the post part of inferior temporal gyrus. These areas have not been described in the former VBM studies, but they revealed abnormity in the pathologic and other studies on PSP. Our results might be expected to provide significant underlining neurology information and diagnostic value for PSP.

The Role of Mitochondrial DNA in Mediating Alveolar Epithelial Cell Apoptosis and Pulmonary Fibrosis

Convincing evidence has emerged demonstrating that impairment of mitochondrial function is critically important in regulating alveolar epithelial cell (AEC) programmed cell death (apoptosis) that may contribute to aging-related lung diseases, such as idiopathic pulmonary fibrosis (IPF) and asbestosis (pulmonary fibrosis following asbestos exposure). The mammalian mitochondrial DNA (mtDNA) encodes for 13 proteins, including several essential for oxidative phosphorylation. We review the evidence implicating that oxidative stress-induced mtDNA damage promotes AEC apoptosis and pulmonary fibrosis. We focus on the emerging role for AEC mtDNA damage repair by 8-oxoguanine DNA glycosylase (OGG1) and mitochondrial aconitase (ACO-2) in maintaining mtDNA integrity which is important in preventing AEC apoptosis and asbestos-induced pulmonary fibrosis in a murine model. We then review recent studies linking the sirtuin (SIRT) family members, especially SIRT3, to mitochondrial integrity and mtDNA damage repair and aging. We present a conceptual model of how SIRTs modulate reactive oxygen species (ROS)-driven mitochondrial metabolism that may be important for their tumor suppressor function. The emerging insights into the pathobiology underlying AEC mtDNA damage and apoptosis is suggesting novel therapeutic targets that may prove useful for the management of age-related diseases, including pulmonary fibrosis and lung cancer.

Glyphosate, pathways to modern diseases III: Manganese, neurological diseases, and associated pathologies

Manganese (Mn) is an often overlooked but important nutrient, required in small amounts for multiple essential functions in the body. A recent study on cows fed genetically modified Roundup(®)-Ready feed revealed a severe depletion of serum Mn. Glyphosate, the active ingredient in Roundup(®), has also been shown to severely deplete Mn levels in plants. Here, we investigate the impact of Mn on physiology, and its association with gut dysbiosis as well as neuropathologies such as autism, Alzheimer's disease (AD), depression, anxiety syndrome, Parkinson's disease (PD), and prion diseases. Glutamate overexpression in the brain in association with autism, AD, and other neurological diseases can be explained by Mn deficiency. Mn superoxide dismutase protects mitochondria from oxidative damage, and mitochondrial dysfunction is a key feature of autism and Alzheimer's. Chondroitin sulfate synthesis depends on Mn, and its deficiency leads to osteoporosis and osteomalacia. Lactobacillus, depleted in autism, depend critically on Mn for antioxidant protection. Lactobacillus probiotics can treat anxiety, which is a comorbidity of autism and chronic fatigue syndrome. Reduced gut Lactobacillus leads to overgrowth of the pathogen, Salmonella, which is resistant to glyphosate toxicity, and Mn plays a role here as well. Sperm motility depends on Mn, and this may partially explain increased rates of infertility and birth defects. We further reason that, under conditions of adequate Mn in the diet, glyphosate, through its disruption of bile acid homeostasis, ironically promotes toxic accumulation of Mn in the brainstem, leading to conditions such as PD and prion diseases.

Autophagy alleviates neurodegeneration caused by mild impairment of oxidative metabolism

Thiamine deficiency (TD) causes mild impairment of oxidative metabolism and region-selective neuronal loss in the brain, which may be mediated by neuronal oxidative stress, endoplasmic reticulum (ER) stress, and neuroinflammation. TD-induced brain damage is used to model neurodegenerative disorders, and the mechanism for the neuronal death is still unclear. We hypothesized that autophagy might be activated in the TD brain and play a protective role in TD-induced neuronal death. Our results demonstrated that TD induced the accumulation of autophagosomes in thalamic neurons measured by transmission electron microscopy, and the up-regulation of autophagic markers LC3-II, Atg5, and Beclin1 as measured with western blotting. TD also increased the expression of autophagic markers and induced LC3 puncta in SH-SY5Y neuroblastoma cells. TD-induced expression of autophagic markers was reversed once thiamine was re-administered. Both inhibition of autophagy by wortmannin and Beclin1 siRNA potentiated TD-induced death of SH-SY5Y cells. In contrast, activation of autophagy by rapamycin alleviated cell death induced by TD. Intraperitoneal injection of rapamycin stimulated neuronal autophagy and attenuated TD-induced neuronal death and microglia activation in the submedial thalamus nucleus (SmTN). TD inhibited the phosphorylation of p70S6 kinase, suggesting mTOR/p70S6 kinase pathway was involved in the TD-induced autophagy. These results suggest that autophagy is neuroprotective in response to TD-induced neuronal death in the central nervous system. This opens a potential therapeutic avenue for neurodegenerative diseases caused by mild impairment of oxidative metabolism. Autophagy is neuroprotective in response to thiamine deficiency (TD)-induced neuronal death. TD caused neuronal damage and induced the formation of autophagosome, and increased the expression of autophagy-related proteins. Autophagy sequestered damaged and dysfunctional organelles/protein, and transported them to lysosomes for degradation/recycling. This process provided nutrients for injured neurons. Wortmannin and knockdown of Beclin1 inhibited autophagy, and exacerbated TD-induced cell death, while activation of autophagy by rapamycin offered protection against TD neurotoxicity.

Molecular basis of asbestos-induced lung disease

Asbestos causes asbestosis and malignancies by molecular mechanisms that are not fully understood. The modes of action underlying asbestosis, lung cancer, and mesothelioma appear to differ depending on the fiber type, lung clearance, and genetics. After reviewing the key pathologic changes following asbestos exposure, we examine recently identified pathogenic pathways, with a focus on oxidative stress. Alveolar epithelial cell apoptosis, which is an important early event in asbestosis, is mediated by mitochondria- and p53-regulated death pathways and may be modulated by the endoplasmic reticulum. We review mitochondrial DNA (mtDNA)-damage and -repair mechanisms, focusing on 8-oxoguanine DNA glycosylase, as well as cross talk between reactive oxygen species production, mtDNA damage, p53, OGG1, and mitochondrial aconitase. These new insights into the molecular basis of asbestos-induced lung diseases may foster the development of novel therapeutic targets for managing degenerative diseases (e.g., asbestosis and idiopathic pulmonary fibrosis), tumors, and aging, for which effective management is lacking.

Oxidative stress and pulmonary fibrosis

Oxidative stress is implicated as an important molecular mechanism underlying fibrosis in a variety of organs, including the lungs. However, the causal role of reactive oxygen species (ROS) released from environmental exposures and inflammatory/interstitial cells in mediating fibrosis as well as how best to target an imbalance in ROS production in patients with fibrosis is not firmly established. We focus on the role of ROS in pulmonary fibrosis and, where possible, highlight overlapping molecular pathways in other organs. The key origins of oxidative stress in pulmonary fibrosis (e.g. environmental toxins, mitochondria/NADPH oxidase of inflammatory and lung target cells, and depletion of antioxidant defenses) are reviewed. The role of alveolar epithelial cell (AEC) apoptosis by mitochondria- and p53-regulated death pathways is examined. We emphasize an emerging role for the endoplasmic reticulum (ER) in pulmonary fibrosis. After briefly summarizing how ROS trigger a DNA damage response, we concentrate on recent studies implicating a role for mitochondrial DNA (mtDNA) damage and repair mechanisms focusing on 8-oxoguanine DNA glycosylase (Ogg1) as well as crosstalk between ROS production, mtDNA damage, p53, Ogg1, and mitochondrial aconitase (ACO2). Finally, the association between ROS and TGF-β1-induced fibrosis is discussed. Novel insights into the molecular basis of ROS-induced pulmonary diseases and, in particular, lung epithelial cell death may promote the development of unique therapeutic targets for managing pulmonary fibrosis as well as fibrosis in other organs and tumors, and in aging; diseases for which effective management is lacking. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Behavioral improvement after chronic administration of coenzyme Q10 in P301S transgenic mice

Coenzyme Q10 is a key component of the electron transport chain which plays an essential role in ATP production and also has antioxidant effects. Neuroprotective effects of coenzyme Q10 have been reported in both in vitro and in vivo models of neurodegenerative diseases. However, its effects have not been studied in cells or in animals with tau induced pathology. In this report, we administered coenzyme Q10 to transgenic mice with the P301S tau mutation, which causes fronto-temporal dementia in man. These mice develop tau hyperphosphorylation and neurofibrillary tangles in the brain. Coenzyme Q10 improved survival and behavioral deficits in the P301S mice. There was a modest reduction in phosphorylated tau in the cortex of P301S mice. We also examined the effects of coenzyme Q10 treatment on the electron transport chain enzymes, the mitochondrial antioxidant enzymes, and the tricarboxylic acid cycle. There was a significant increase in complex I activity and protein levels, and a reduction in lipid peroxidation. Our data show that coenzyme Q10 significantly improved behavioral deficits and survival in transgenic mice with the P301S tau mutation, upregulated key enzymes of the electron transport chain, and reduced oxidative stress.

An update on the role of mitochondrial α-ketoglutarate dehydrogenase in oxidative stress

The activity of mitochondrial alpha-ketoglutarate dehydrogenase complex (KGDHC) is severely reduced in human pathologies where oxidative stress is traditionally thought to play an important role, such as familial and sporadic forms of Alzheimer's disease and other age-related neurodegenerative diseases. This minireview is focused on substantial data that were accumulated over the last 2 decades to support the concept that KGDHC can be a primary mitochondrial target of oxidative stress and at the same time a key contributor to it by producing reactive oxygen species. This article is part of a Special Issue entitled 'Mitochondrial function and dysfunction in neurodegeneration'.

Mitochondrial aconitase knockdown attenuates paraquat-induced dopaminergic cell death via decreased cellular metabolism and release of iron and H₂O₂

Mitochondrial oxidative stress is a contributing factor in the etiology of numerous neuronal disorders. However, the precise mechanism(s) by which mitochondrial reactive oxygen species modify cellular targets to induce neurotoxicity remains unknown. In this study, we determined the role of mitochondrial aconitase (m-aconitase) in neurotoxicity by decreasing its expression. Incubation of the rat dopaminergic cell line, N27, with paraquat (PQ(2+) ) resulted in aconitase inactivation, increased hydrogen peroxide (H(2) O(2) ) and increased ferrous iron (Fe(2+) ) at times preceding cell death. To confirm the role of m-aconitase in dopaminergic cell death, we knocked down m-aconitase expression via RNA interference. Incubation of m-aconitase knockdown N27 cells with PQ(2+) resulted in decreased H(2) O(2) production, Fe(2+) accumulation, and cell death compared with cells expressing basal levels of m-aconitase. To determine the metabolic role of m-aconitase in mediating neuroprotection, we conducted a complete bioenergetic profile. m-Aconitase knockdown N27 cells showed a global decrease in metabolism (glycolysis and oxygen consumption rates) which blocked PQ(2+) -induced H(+) leak and respiratory capacity deficiency. These findings suggest that dopaminergic cells are protected from death by decreasing release of H(2) O(2) and Fe(2+) in addition to decreased cellular metabolism.

Altered zinc transport disrupts mitochondrial protein processing/import in fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder that affects individuals who are carriers of small CGG premutation expansions in the fragile X mental retardation 1 (FMR1) gene. Mitochondrial dysfunction was observed as an incipient pathological process occurring in individuals who do not display overt features of FXTAS (1). Fibroblasts from premutation carriers had lower oxidative phosphorylation capacity (35% of controls) and Complex IV activity (45%), and higher precursor-to-mature ratios (P:M) of nDNA-encoded mitochondrial proteins (3.1-fold). However, fibroblasts from carriers with FXTAS symptoms presented higher FMR1 mRNA expression (3-fold) and lower Complex V (38%) and aconitase activities (43%). Higher P:M of ATPase β-subunit (ATPB) and frataxin were also observed in cortex from patients that died with FXTAS symptoms. Biochemical findings observed in FXTAS cells (lower mature frataxin, lower Complex IV and aconitase activities) along with common phenotypic traits shared by Friedreich's ataxia and FXTAS carriers (e.g. gait ataxia, loss of coordination) are consistent with a defective iron homeostasis in both diseases. Higher P:M, and lower ZnT6 and mature frataxin protein expression suggested defective zinc and iron metabolism arising from altered ZnT protein expression, which in turn impairs the activity of mitochondrial Zn-dependent proteases, critical for the import and processing of cytosolic precursors, such as frataxin. In support of this hypothesis, Zn-treated fibroblasts showed a significant recovery of ATPB P:M, ATPase activity and doubling time, whereas Zn and desferrioxamine extended these recoveries and rescued Complex IV activity.

Inactivation and reactivation of the mitochondrial α-ketoglutarate dehydrogenase complex

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.

Behavioral impact of the regulation of the brain 2-oxoglutarate dehydrogenase complex by synthetic phosphonate analog of 2-oxoglutarate: implications into the role of the complex in neurodegenerative diseases

Decreased activity of the mitochondrial 2-oxoglutarate dehydrogenase complex (OGDHC) in brain accompanies neurodegenerative diseases. To reveal molecular mechanisms of this association, we treated rats with a specific inhibitor of OGDHC, succinyl phosphonate, or exposed them to hypoxic stress. In males treated with succinyl phosphonate and in pregnancy-sensitized females experiencing acute hypobaric hypoxia, we revealed upregulation of brain OGDHC (within 24 hours), with the activity increase presumably representing the compensatory response of brain to the OGDHC inhibition. This up-regulation of brain OGDHC was accompanied by an increase in exploratory activity and a decrease in anxiety of the experimental animals. Remarkably, the hypoxia-induced elevation of brain OGDHC and most of the associated behavioral changes were abrogated by succinyl phosphonate. The antagonistic action of hypoxia and succinyl phosphonate demonstrates potential therapeutic significance of the OGDHC regulation by the phosphonate analogs of 2-oxoglutarate.

Mitochondrial viability in mouse and human postmortem brain

Neuronal function in the brain requires energy in the form of ATP, and mitochondria are canonically associated with ATP production in neurons. The electrochemical gradient, which underlies the mitochondrial transmembrane potential (DeltaPsi(mem)), is harnessed for ATP generation. Here we show that DeltaPsi(mem) and ATP-production can be engaged in mitochondria isolated from human brains up to 8.5 h postmortem. Also, a time course of postmortem intervals from 0 to 24 h using mitochondria isolated from mouse cortex reveals that DeltaPsi(mem) in mitochondria can be reconstituted beyond 10 h postmortem. It was found that complex I of the mitochondrial electron transport chain was affected adversely with increasing postmortem intervals. Mitochondria isolated from postmortem mouse brains maintain the ability to produce ATP, but rates of production decreased with longer postmortem intervals. Furthermore, we show that postmortem brain mitochondria retain their DeltaPsi(mem) and ATP-production capacities following cryopreservation. Our finding that DeltaPsi(mem) and ATP-generating capacity can be reinitiated in brain mitochondria hours after death indicates that human postmortem brains can be an abundant source of viable mitochondria to study metabolic processes in health and disease. It is also possible to archive these mitochondria for future studies.

Oxidative inactivation of mitochondrial aconitase results in iron and H2O2-mediated neurotoxicity in rat primary mesencephalic cultures

BACKGROUND

Mitochondrial oxidative stress is a contributing factor in the etiology of numerous neuronal disorders. However, the precise mechanism(s) by which mitochondrial reactive oxygen species (ROS) modify cellular targets to induce the death of neurons remains unknown. The goal of this study was to determine if oxidative inactivation of mitochondrial aconitase (m-aconitase) resulted in the release of redox-active iron (Fe2+) and hydrogen peroxide (H2O2) and whether this contributes to cell death.

METHODOLOGY/PRINCIPAL FINDINGS

Incubation of rat primary mesencephalic cultures with the redox cycling herbicide paraquat (PQ2+) resulted in increased production of H2O2 and Fe2+ at times preceding cell death. To confirm the role of m-aconitase as a source of Fenton reagents and death, we overexpressed m-aconitase using an adenoviral construct thereby increasing the target available for inactivation by ROS. Co-labeling studies identified astrocytes as the predominant cell type expressing transduced m-aconitase although neurons were identified as the primary cell type dying. Oxidative inactivation of m-aconitase overexpressing cultures resulted in exacerbation of H2O2 production, Fe2+ accumulation and increased neuronal death. Increased cell death in m-aconitase overexpressing cultures was attenuated by addition of catalase and/or a cell permeable iron chelator suggesting that neuronal death occurred in part via astrocyte-derived H2O2.

CONCLUSIONS

These results suggest a role of ROS-sensitive m-aconitase as a source of Fe2+ and H2O2 and as a contributing factor to neurotoxicity.

Mice deficient in dihydrolipoyl succinyl transferase show increased vulnerability to mitochondrial toxins

The activity of a key mitochondrial tricarboxylic acid cycle enzyme, alpha-ketoglutarate dehydrogenase complex (KGDHC), declines in many neurodegenerative diseases. KGDHC consists of three subunits. The dihydrolipoyl succinyl transferase (DLST) component is unique to KGDHC. DLST(+/-) mice showed reduced mRNA and protein levels and decreased brain mitochondrial KGDHC activity. Neurotoxic effects of mitochondrial toxins were exacerbated in DLST(+/-) mice. MPTP produced a significantly greater reduction of striatal dopamine and tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta of DLST(+/-) mice. DLST deficiency enhanced the severity of lipid peroxidation in the substantia nigra after MPTP treatment. Striatal lesions induced by either malonate or 3-nitropropionic acid (3-NP) were significantly larger in DLST(+/-) mice than in wildtype controls. DLST deficiency enhanced the 3-NP inhibition of mitochondria enzymes, and 3-NP induced protein and DNA oxidations. These observations support the hypothesis that reductions in KGDHC may impair the adaptability of the brain and contribute to the pathogenesis of neurodegenerative diseases.

Ethanol promotes thiamine deficiency-induced neuronal death: involvement of double-stranded RNA-activated protein kinase

BACKGROUND

Heavy alcohol consumption causes cerebellar degeneration, and the underlying mechanism is unclear. Chronic alcoholism is usually associated with thiamine deficiency (TD) which is known to induce selective neurodegeneration in the brain. However, the role of TD in alcohol-induced cerebellar degeneration remains to be elucidated. The double-stranded RNA-activated protein kinase (PKR) is a potent antiviral protein. Viral infection or binding to dsRNA causes PKR autophosphorylation and subsequent phosphorylation of the alpha-subunit of eukaryotic translation factor-2alpha, leading to inhibition of translation or apoptosis. PKR can also be activated by cellular stresses.

METHODS

In this study, we used an in vitro model, cultured cerebellar granule neurons (CGNs), to investigate the interaction between TD and ethanol and evaluate the contribution of their interaction to neuronal loss. TD was induced by treatment with amprolium in association with ethanol. Cell viability was determined by 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide assay. PKR expression/phosphorylation and subcellular distribution was analyzed with immunoblotting and immunocytochemistry.

RESULTS

Thiamine deficiency caused death of CGNs but ethanol did not. However, TD plus ethanol induced a much greater cell loss than TD alone. TD-induced PKR phosphorylation and ethanol exposure significantly promoted TD-induced PKR phosphorylation as well as its nuclear translocation. A selective PKR inhibitor not only protected CGNs against TD toxicity, but also abolished ethanol potentiation of TD-induced loss of CGNs.

CONCLUSIONS

Ethanol promoted TD-induced PKR activation and neuronal death. PKR may be a convergent protein that mediates the interaction between TD and ethanol.

Senescence accelerated mouse strain is sensitive to neurodegeneration induced by mild impairment of oxidative metabolism

Neuronal loss and impairment of oxidative metabolism are frequently observed in aging associated neurodegenerative diseases. Thiamine deficiency (TD) induces the region selective neuronal loss in the brain, which has been used to model neurodegeneration, accompanied by mild impairment of oxidative metabolism. C57BL/6 mice were commonly used animals for TD experiments; however, the individual variations among C57BL/6 mice in response to TD limited the consistence of brain pathology. The senescence accelerated prone 8 (SAMP8) mouse strain exhibits age-related morphological changes in the brain and deficits in learning and memory. In this study, we compared the effects of TD on SAMP8 mice, senescence accelerated resistant 1 (SAMR1) mice and C57BL/6 mice. TD-induced body weight loss in SAMP8 mice was much greater than in SAMR1 and C57BL/6 mice. In addition, earlier and more severe loss of neurons in the submedial thalamic nucleus (SmTN) of the thalamus was detected in the SAMP8 mice. After 8 days of TD (TD8), the loss of NeuN-positive neurons in the SmTN of SAMP8, SAMR1 and C57BL/6 mice was 65%, 50%, and 36%, respectively. TD also caused accumulation of amyloid precursor protein (APP) in the thalamus. After TD10, APP immunoreactivity in the thalamus of SAMP8 was much more intense than that of SAMR1 and C57BL/6 mice. These results suggest that SAMP8 mice are sensitive to TD and therefore offer a useful model for studying aging related neurodegeneration caused by the impairment of oxidative metabolism.

The neurodegenerative mitochondriopathies

Mitochondria are physically or functionally altered in many neurodegenerative diseases. This is the case for very rare neurodegenerative disorders as well as extremely common age-related ones such as Alzheimer's disease and Parkinson's disease. In some disorders very specific patterns of altered mitochondrial function or systemic mitochondrial dysfunction are demonstrable. Some disorders arise from mitochondrial DNA mutation, some from nuclear gene mutation, and for some the etiology is not definitively known. This review classifies neurodegenerative diseases using mitochondrial dysfunction as a unifying feature, and in doing so defines a group of disorders called the neurodegenerative mitochondriopathies. It discusses what mitochondrial abnormalities have been identified in various neurodegenerative diseases, what is currently known about the mitochondria-neurodegeneration nexus, and speculates on the significance of mitochondrial function in some disorders not classically thought of as mitochondriopathies.

Susceptibility of mitochondrial superoxide dismutase to aluminium induced oxidative damage

Aluminium has been implicated in various neurodegenerative diseases but exact mechanism of action is still not known. Mitochondria being a major site of reactive oxygen species production are considered to be target of oxidative stress and it seems that the oxidative damage to mitochondrial proteins may underlie the pathogenesis of aluminium induced neurodegeneration. Thus, the present study was undertaken to reveal the effects of chronic aluminium exposure (10mg/kg b.wt, intragastrically for 12 weeks) on the oxidative damage to mitochondrial proteins in male albino Wistar rats. Chronic aluminium exposure resulted in decrease in the activity of mitochondrial superoxide dismutase (MnSOD) and aconitase in different regions of rat brain suggesting increased oxidative stress. This decrease in MnSOD activity in turn might be responsible for the increased protein oxidation as observed in our study. All these processes taken together may cause increased oxidative damage to mitochondrial proteins in general. By taking the advantage of recent immunochemical probe for oxidatively modified proteins, we identified MnSOD to be susceptible to oxidative damage in aluminium treated animals. The quantitative RT-PCR analysis for Lon protease, a protease involved in the removal of oxidatively modified proteins from mitochondria, showed decreased mRNA expression suggesting increased oxidative damage and decreased removal of mitochondrial proteins. The identification of specific proteins as targets of oxidative damage may provide new therapeutic measures to reverse the effects of aluminium induced neurodegeneration.

Novel functions of the alpha-ketoglutarate dehydrogenase complex may mediate diverse oxidant-induced changes in mitochondrial enzymes associated with Alzheimer's disease

Measures in autopsied brains from Alzheimer's Disease (AD) patients reveal a decrease in the activity of alpha-ketoglutarate dehydrogenase complex (KGDHC) and an increase in malate dehydrogenase (MDH) activity. The present experiments tested whether both changes could be caused by the common oxidant H(2)O(2) and to probe the mechanism underlying these changes. Since the response to H(2)O(2) is modified by the level of the E2k subunit of KGDHC, the interaction of MDH and KGDHC was studied in cells with varying levels of E2k. In cells with only 23% of normal E2k protein levels, one-hour treatment with H(2)O(2) decreased KGDHC and increased MDH activity as well as the mRNA level for both cytosolic and mitochondrial MDH. The increase in MDH did not occur in cells with 100% or 46% of normal E2k. Longer treatments with H(2)O(2) inhibited the activity of both enzymes. Glutathione is a major regulator of cellular redox state and can modify enzyme activities. H(2)O(2) converts reduced glutathione (GSH) to oxidized glutathione (GSSG), which reacts with protein thiols. Treatment of purified KGDHC with GSSG leads to glutathionylation of all three KGDHC subunits. Thus, cellular glutathione level was manipulated by two means to determine the effect on KGDHC and MDH activities. Both buthionine sulfoximine (BSO), which inhibits glutathione synthesis without altering redox state, and H(2)O(2) diminished glutathione to a similar level after 24 h. However, H(2)O(2), but not BSO, reduced KGDHC and MDH activities, and the reduction was greater in the E2k-23 line. These findings suggest that the E2k may mediate diverse responses of KGDHC and MDH to oxidants. In addition, the differential response of activities to BSO and H(2)O(2) together with the in vitro interaction of KGDHC with GSSG suggests that glutathionylation is one possible mechanism underlying oxidative stress-induced inhibition of the TCA cycle enzymes.

Activation of double-stranded RNA-activated protein kinase by mild impairment of oxidative metabolism in neurons

Thiamine (vitamin B1) deficiency (TD) causes mild and chronic impairment of oxidative metabolism and induces neuronal death in specific brain regions. The mechanisms underlying TD-induced cell death, however, remain unclear. The double-stranded RNA-activated protein kinase (PKR), has been well known for its anti-viral function. Upon activation by viral infection or double-stranded RNA, PKR phosphorylates its substrate, the alpha-subunit of eukaryotic initiation factor-2 (eIF2alpha), leading to inhibition of translation. In response to various cellular stresses, PKR can also be stimulated by its protein activators, or its mouse homologue, PKR activator (RAX). We demonstrated that TD in mice induced phosphorylation of PKR at Thr446 and Thr451 and phosphorylation of eIF2alpha at Ser51 in the cerebellum and the thalamus. TD caused phosphorylation of PKR and eIF2alpha, as well as nuclear translocation of PKR in primary cultures of cerebellar granule neurons. PKR phosphorylation is necessary for its nuclear translocation because TD failed to induce nuclear translocation of a T446A/T451A PKR mutant. Both PKR inhibitor and dominant-negative PKR mutant protected cerebellar granule neurons against TD-induced cell death. TD promoted the association between RAX and PKR. Antioxidant vitamin E dramatically decreased the RAX/PKR association and ameliorated TD-induced cell death. Our results indicate that TD-induced neuronal death is at least partially mediated by the activation of PKR.

Rash from Antiepileptic Drugs: Influence by Gender, Age, and Learning Disability

PURPOSE

Cutaneous adverse reactions from antiepileptic drugs (AEDs) are common, but have received little scientific attention from a clinical point of view. We wanted to study the incidence of skin reactions of current AEDs and to explore their relation to clinical parameters such as gender, age, and learning disability.

METHODS

Consecutive patients with epilepsy were studied retrospectively. A detailed survey of medical records concerning all treatment with AEDs was performed.

RESULTS

A total of 663 patients were included with altogether 2,567 exposures to 15 different AEDs. Skin reactions were found in 14% of the patients and in 5% of the exposures. Ninety-seven percent of the reactions occurred to either carbamazepine (CBZ, 11%), phenytoin (PHT, 8%), lamotrigine (LTG, 8%), oxcarbazepine (8%), or phenobarbital (2%). Skin reactions developed significantly more often in females than in males (19% vs. 8%), and significantly less often in patients with learning disability than in other patients (7% vs. 16%). These differences were significant for CBZ, PHT, and LTG when analyzed separately. Females displayed higher rash frequency during the reproductive years, while men experienced less frequent rash in the same phase of life.

CONCLUSIONS

Fertile females have a higher risk for skin reactions compared to males, probably due to hormonal factors. Patients with learning disability appeared to have a lower risk than other patients in this study. Hygiene factors may possibly be underlying.

Apoptotic neuronal death in Parkinson's disease: Involvement of nitric oxide

Apoptosis of nigral dopaminergic neurons by various mechanisms is an emerging phenomenon involved in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Both extrinsic and intrinsic pathways seems to be involved in death of nigral neurons, intrinsic pathway however, seems to be more important due to the energy crisis. Apoptosis by intrinsic pathway is executed by several initiators and effector caspases, which have been found activated in PD patients, experimental models as well as in neuronal cultures. Nitric oxide (NO) seems to be a central molecule due to its ability to modulate both pro and antiapoptotic phenomenon. The review focuses on the diverse extrinsic and intrinsic factors, signaling pathways and their modulation by NO leading to the death of dopaminergic neurons.

Responses of the mitochondrial alpha-ketoglutarate dehydrogenase complex to thiamine deficiency may contribute to regional selective vulnerability

Thiamine-dependent enzymes are diminished in multiple neurodegenerative diseases. Thiamine deficiency (TD) reduces the activity of thiamine dependent-enzymes [e.g., the alpha-ketoglutarate dehydrogenase complex (KGDHC)], induces regional selective neurodegeneration and serves as a model of a mild impairment of oxidative metabolism. The current experiments tested whether changes in KGDHC protein subunits (E1k, E2k and E3) or activity or message levels underlie the selective loss of neurons in particular brain regions. Thus, TD-induced changes in these variables in the brain region most vulnerable to TD [the sub-medial thalamic nucleus (SmTN)] were compared to those in a region that is relatively resistant to TD (cortex) at stages of TD when the neuron loss in SmTN is not present, minimal or severe. Impaired motor performance on rotarod was apparent by 8 days of TD (-32%) and was severe by 10 days of TD (-97%). At TD10, the overall KGDHC activity measured by an in situ histochemical staining method declined 52% in SmTN but only 20% in cortex. Reductions in the E2k and E3 mRNA in SmTN occurred as early as TD6 (-28 and -18%, respectively) and were more severe by TD10 (-61 and -66%, respectively). On the other hand, the level of E1k mRNA did not decline in SmTN until TD10 (-48%). In contrast, TD did not alter mRNA levels of the subunits in cortex at late stages. Western blots and immunocytochemistry revealed different aspects of the changes in protein levels. In SmTN, the immunoreactivity of E1k and E3 by Western blotting increased 34 and 40%, respectively, only at TD8. In cortex, the immunoreactivity of the three subunits was not altered. Immunocytochemical staining of brain sections from TD10 mice indicated a reduction in the immunoreactivity of all subunits in SmTN, but not in cortex. These findings demonstrate that the response of the KGDHC activity, mRNA and immunoreactivity of E1k, E2k and E3 to TD is region and time dependent. Loss of KGDHC activity in cortex is likely related to post-translational modification rather than a loss of protein, whereas in SmTN transcriptional and post-translational modifications may account for diminished KGDHC activity. Moreover, the earlier detection in TD induced-changes of the transcripts of KGDHC indicates that transcriptional modification of the two subunits (E2k and E3) of KGDHC may be one of the early events in the cascade leading to selective neuronal death.

Thiamine deficiency induces endoplasmic reticulum stress in neurons

Thiamine (vitamin B1) deficiency (TD) causes region selective neuronal loss in the brain; it has been used to model neurodegeneration that accompanies mild impairment of oxidative metabolism. The mechanisms for TD-induced neurodegeneration remain incompletely elucidated. Inhibition of protein glycosylation, perturbation of calcium homeostasis and reduction of disulfide bonds provoke the accumulation of unfolded proteins in the endoplasmic reticulum (ER), and cause ER stress. Recently, ER stress has been implicated in a number of neurodegenerative models. We demonstrated here that TD up-regulated several markers of ER stress, such as glucose-regulated protein (GRP) 78, growth arrest and DNA-damage inducible protein or C/EBP-homologus protein (GADD153/Chop), phosphorylation of eIF2alpha and cleavage of caspase-12 in the cerebellum and the thalamus of mice. Furthermore, ultrastructural analysis by electron microscopic study revealed an abnormality in ER structure. To establish an in vitro model of TD in neurons, we treated cultured cerebellar granule neurons (CGNs) with amprolium, a potent inhibitor of thiamine transport. Exposure to amprolium caused apoptosis and the generation of reactive oxygen species in CGNs. Similar to the observation in vivo, TD up-regulated markers for ER stress. Treatment of a selective inhibitor of caspase-12 significantly alleviated amprolium-induced death of CGNs. Thus, ER stress may play a role in TD-induced brain damage.

Gene expression changes in thalamus and inferior colliculus associated with inflammation, cellular stress, metabolism and structural damage in thiamine deficiency

Identification of gene expression changes that promote focal neuronal death and neurological dysfunction can further our understanding of the pathophysiology of these disease states and could lead to new pharmacological and molecular therapies. Impairment of oxidative metabolism is a pathogenetic mechanism underlying neuronal death in many chronic neurodegenerative diseases as well as in Wernicke's encephalopathy (WE), a disorder induced by thiamine deficiency (TD). To identify functional pathways that lead to neuronal damage in this disorder, we have examined gene expression changes in the vulnerable thalamus and inferior colliculus of TD rats using Affymetrix Rat Genome GeneChip analysis in combination with gene ontology and functional categorization assessment utilizing the NetAffx GO Mining Tool. Of the 15 927 transcripts analysed, 125 in thalamus and 141 in inferior colliculus were more abundantly expressed in TD rats compared with control animals. In both regions, the major functional categories of transcripts that were increased in abundance after TD were those associated with inflammation (approximately 33%), stress (approximately 20%), cell death and repair ( approximately 26%), and metabolic perturbation (approximately 19%), together constituting approximately 98% of all transcripts up-regulated. These changes occurred against a background of neuronal cell loss and reactive astro- and microgliosis in both structures. Our results indicate that (i) TD produces changes in gene expression that are consistent with the observed dysfunction and pathology, and (ii) similar alterations in expression occur in thalamus and inferior colliculus, brain regions previously considered to differ in pathology. These findings provide important new insight into processes responsible for lesion development in TD, and possibly WE.

Calcium, mitochondria and oxidative stress in neuronal pathology. Novel aspects of an enduring theme

The interplay among reactive oxygen species (ROS) formation, elevated intracellular calcium concentration and mitochondrial demise is a recurring theme in research focusing on brain pathology, both for acute and chronic neurodegenerative states. However, causality, extent of contribution or the sequence of these events prior to cell death is not yet firmly established. Here we review the role of the alpha-ketoglutarate dehydrogenase complex as a newly identified source of mitochondrial ROS production. Furthermore, based on contemporary reports we examine novel concepts as potential mediators of neuronal injury connecting mitochondria, increased [Ca2+]c and ROS/reactive nitrogen species (RNS) formation; specifically: (a) the possibility that plasmalemmal nonselective cationic channels contribute to the latent [Ca2+]c rise in the context of glutamate-induced delayed calcium deregulation; (b) the likelihood of the involvement of the channels in the phenomenon of 'Ca2+ paradox' that might be implicated in ischemia/reperfusion injury; and (c) how ROS/RNS and mitochondrial status could influence the activity of these channels leading to loss of ionic homeostasis and cell death.