Metabolic alterations common to neural and non‐neural cells in alzheimer's disease

The Novel Role of Mitochondrial Citrate Synthase and Citrate in the Pathophysiology of Alzheimer's Disease

Citrate synthase is a key mitochondrial enzyme that utilizes acetyl-CoA and oxaloacetate to form citrate in the mitochondrial membrane, which participates in energy production in the TCA cycle and linked to the electron transport chain. Citrate transports through a citrate malate pump and synthesizes acetyl-CoA and acetylcholine (ACh) in neuronal cytoplasm. In a mature brain, acetyl-CoA is mainly utilized for ACh synthesis and is responsible for memory and cognition. Studies have shown low citrate synthase in different regions of brain in Alzheimer's disease (AD) patients, which reduces mitochondrial citrate, cellular bioenergetics, neurocytoplasmic citrate, acetyl-CoA, and ACh synthesis. Reduced citrate mediated low energy favors amyloid-β (Aβ) aggregation. Citrate inhibits Aβ25-35 and Aβ1-40 aggregation in vitro. Hence, citrate can be a better therapeutic option for AD by improving cellular energy and ACh synthesis, and inhibiting Aβ aggregation, which prevents tau hyperphosphorylation and glycogen synthase kinase-3 beta. Therefore, we need clinical studies if citrate reverses Aβ deposition by balancing mitochondrial energy pathway and neurocytoplasmic ACh production. Furthermore, in AD's silent phase pathophysiology, when neuronal cells are highly active, they shift ATP utilization from oxidative phosphorylation to glycolysis and prevent excessive generation of hydrogen peroxide and reactive oxygen species (oxidative stress) as neuroprotective action, which upregulates glucose transporter-3 (GLUT3) and pyruvate dehydrogenase kinase-3 (PDK3). PDK3 inhibits pyruvate dehydrogenase, which decreases mitochondrial-acetyl-CoA, citrate, and cellular bioenergetics, and decreases neurocytoplasmic citrate, acetyl-CoA, and ACh formation, thus initiating AD pathophysiology. Therefore, GLUT3 and PDK3 can be biomarkers for silent phase of AD.

Formation of reactive oxygen species by human and bacterial pyruvate and 2-oxoglutarate dehydrogenase multienzyme complexes reconstituted from recombinant components

Individual recombinant components of pyruvate and 2-oxoglutarate dehydrogenase multienzyme complexes (PDHc, OGDHc) of human and Escherichia coli (E. coli) origin were expressed and purified from E. coli with optimized protocols. The four multienzyme complexes were each reconstituted under optimal conditions at different stoichiometric ratios. Binding stoichiometries for the highest catalytic efficiency were determined from the rate of NADH generation by the complexes at physiological pH. Since some of these complexes were shown to possess 'moonlighting' activities under pathological conditions often accompanied by acidosis, activities were also determined at pH 6.3. As reactive oxygen species (ROS) generation by the E3 component of hOGDHc is a pathologically relevant feature, superoxide generation by the complexes with optimal stoichiometry was measured by the acetylated cytochrome c reduction method in both the forward and the reverse catalytic directions. Various known affectors of physiological activity and ROS production, including Ca(2+), ADP, lipoylation status or pH, were investigated. The human complexes were also reconstituted with the most prevalent human pathological mutant of the E3 component, G194C and characterized; isolated human E3 with the G194C substitution was previously reported to have an enhanced ROS generating capacity. It is demonstrated that: i. PDHc, similarly to OGDHc, is able to generate ROS and this feature is displayed by both the E. coli and human complexes, ii. Reconstituted hPDHc generates ROS at a significantly higher rate as compared to hOGDHc in both the forward and the reverse reactions when ROS generation is calculated for unit mass of their common E3 component, iii. The E1 component or E1-E2 subcomplex generates significant amount of ROS only in hOGDHc; iv. Incorporation of the G194C variant of hE3, the result of a disease-causing mutation, into reconstituted hOGDHc and hPDHc indeed leads to a decreased activity of both complexes and higher ROS generation by only hOGDHc and only in its reverse reaction.

Premature centromere division of metaphase chromosomes in peripheral blood lymphocytes of Alzheimer's disease patients: relation to gender and age

Chromosomal alterations are a feature of both aging and Alzheimer's disease (AD). This study examined if premature centromere division (PCD), a chromosomal instability indicator increased in AD, is correlated with aging or, instead, represents a de novo chromosomal alteration due to accelerating aging in AD. PCD in peripheral blood lymphocytes was determined in sporadic AD patients and gender and age-matched unaffected controls. Metaphase nuclei were analyzed for chromosomes showing PCD, X chromosomes with PCD (PCD,X), and acrocentric chromosomes showing PCD. AD patients, regardless of age, demonstrated increased PCD on any chromosome and PCD on acrocentric chromosomes in both genders, whereas an increase in frequency of PCD,X was expressed only in women. This cytogenetic analysis suggests that PCD is a feature of AD, rather than an epiphenomenon of chronological aging, and may be useful as a physiological biomarker that can be used for disease diagnosis.

Association of Omi/HtrA2 with γ-secretase in mitochondria

Omi/HtrA2, a mitochondrial serine protease with chaperone activity, is involved in varied intracellular processes. Dysfunctional Omi/HtrA2 has thus been implicated in various neurodegenerative disorders. Previously, we have shown that γ-secretase complexes are present and active in mitochondria. Here, we demonstrate that peptide corresponding to C-terminus of presenilin-1, as previously reported to activate Omi/HtrA2, interacts with Omi/HtrA2 in isolated mitochondria. Moreover, we show that Omi/HtrA2 interacts with presenilin in active γ-secretase complexes located to mitochondria. Using a biotinylated γ-secretase inhibitor and confocal microscopy, we could further confirm the association of γ-secretase complexes with mitochondrial Omi/HtrA2. Furthermore, determination of γ-secretase complex topology in isolated mitochondria revealed an association of γ-secretase complexes with the outer membrane of mitochondria with the extreme PS1 C-terminus facing the inter-membrane space. We have also studied the impact of Omi/HtrA2 on γ-secretase activity, measuring APP intracellular domain (AICD) production. We found reduced AICD production in mitochondria isolated from Omi/HtrA2 knockout mouse embryonic fibroblasts, indicating a significant role of Omi/HtrA2 on γ-secretase activity. Thus, our results provide information for understanding the interplay between mitochondrial Omi/HtrA2 and γ-secretase complexes in AD.

A metabolomic study of the CRND8 transgenic mouse model of Alzheimer's disease

Alzheimer's disease is the most common neurodegenerative disease of the central nervous system characterized by a progressive loss in memory and deterioration of cognitive functions. In this study the transgenic mouse TgCRND8, which encodes a mutant form of the amyloid precursor protein 695 with both the Swedish and Indiana mutations and develops extracellular amyloid beta-peptide deposits as early as 2-3 months, was investigated. Extract from eight brain regions (cortex, frontal cortex, cerebellum, hippocampus, olfactory bulb, pons, midbrain and striatum) were studied using (1)H NMR spectroscopy. Analysis of the NMR spectra discriminated control from APP695 tissues in hippocampus, cortex, frontal cortex, midbrain and cerebellum, with hippocampal and cortical region being most affected. The analysis of the corresponding loading plots for these brain regions indicated a decrease in N-acetyl-L-aspartate, glutamate, glutamine, taurine (exception hippocampus), gamma-amino butyric acid, choline and phosphocholine (combined resonances), creatine, phosphocreatine and succinate in hippocampus, cortex, frontal cortex (exception gamma-amino butyric acid) and midbrain of affected animals. An increase in lactate, aspartate, glycine (except in midbrain) and other amino acids including alanine (exception frontal cortex), leucine, iso-leucine, valine and water soluble free fatty acids (0.8-0.9 and 1.2-1.3 ppm) were observed in the TgCRND8 mice. Our findings demonstrate that the perturbations in metabolism are more widespread and include the cerebellum and midbrain. Furthermore, metabolic perturbations are associated with a wide range of metabolites which could improve the diagnosis and monitoring of the progression of Alzheimer's disease.

Systemic and brain metabolic dysfunction as a new paradigm for approaching Alzheimer's dementia

Since its definition Alzheimer's disease has been at the centre of consideration for neurologists, psychiatrists, and pathologists. With John P. Blass it has been disclosed a different approach Alzheimer's disease neurodegeneration understanding not only by the means of neurochemistry but also biochemistry opening new scenarios in the direction of a metabolic system degeneration. Nowadays, the understanding of the role of cholesterol, insulin, and adipokines among the others in Alzheimer's disease etiopathogenesis is clarifying approaches valuable not only in preventing the disease but also for its therapy.

Are mitochondria critical in the pathogenesis of Alzheimer's disease?

This review summarizes recent findings that suggest a causal connection between mitochondrial abnormalities and sporadic Alzheimer's disease (AD). Genetic causes of AD are known only for a small proportion of familial AD patients, but for a majority of sporadic AD patients, genetic causal factors are still unknown. Currently, there are no early detectable biomarkers for sporadic AD, and there is a lack of understanding of the pathophysiology of the disease. Findings from recent genetic studies of AD pathogenesis suggest that mitochondrial defects may play an important role in sporadic AD progression, and that mitochondrial abnormalities and oxidative damage may play a significant role in the progression of familial AD. Findings from biochemical studies, in vitro studies, gene expression studies, and animal model studies of AD are reviewed, and the possible contribution of mitochondrial mutations to late-onset sporadic AD is discussed.

Progress in clinical neurosciences: cognitive markers of progression in Alzheimer's disease

The objective of this review is to summarize the literature on Alzheimer's disease progression utilizing cognitive batteries to track change over time. Studies published in English and obtained through PubMed searches (1983-2004) were included (i) if they had a longitudinal design and followed probable Alzheimer's patients diagnosed by National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association or Diagnostic and Statistical Manual III/IV criteria, and (ii) if the techniques used for serial assessment were well-established in terms of validity and reliability. Longitudinal studies examining Alzheimer's disease progression report highly variable annual rates of change in decline rate. It remains unclear if this reflects disease subgroups or stage-related rate of decline. In conclusion a combination of stage-appropriate cognitive tests such as the Mattis Dementia Rating Scale and the Severe Impairment Battery, along with appropriate statistical methods to account for individual variability in decline rates, can capture the progression of Alzheimer disease and may be useful in further investigation.

The C-terminal Tail of Presenilin Regulates Omi/HtrA2 Protease Activity

Presenilin mutations are responsible for most cases of autosomal dominant inherited forms of early onset Alzheimer disease. Presenilins play an important role in amyloid beta-precursor processing, NOTCH receptor signaling, and apoptosis. However, the molecular mechanisms by which presenilins regulate apoptosis are not fully understood. Here, we report that presenilin-1 (PS1) regulates the proteolytic activity of the serine protease Omi/HtrA2 through direct interaction with its regulatory PDZ domain. We show that a peptide corresponding to the cytoplasmic C-terminal tail of PS1 dramatically increases the proteolytic activity of Omi/HtrA2 toward the inhibitor of apoptosis proteins and beta-casein and induces cell death in an Omi/HtrA2-dependent manner. Consistent with these results, ectopic expression of full-length PS1, but not PS1 lacking the C-terminal PDZ binding motif, potentiated Omi/HtrA2-induced cell death. Our results suggest that the C terminus of PS1 is an activation peptide ligand for the PDZ domain of Omi/HtrA2 and may regulate the protease activity of Omi/HtrA2 after its release from the mitochondria during apoptosis. This mechanism of Omi/HtrA2 activation is similar to the mechanism of activation of the related bacterial DegS protease by the outer-membrane porins.

Gene expression profiles of transcripts in amyloid precursor protein transgenic mice: up-regulation of mitochondrial metabolism and apoptotic genes is an early cellular change in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by the impairment of cognitive functions and by beta amyloid (Abeta) plaques in the cerebral cortex and the hippocampus. Our objective was to determine genes that are critical for cellular changes in AD progression, with particular emphasis on changes early in disease progression. We investigated an established amyloid precursor protein (APP) transgenic mouse model (the Tg2576 mouse model) for gene expression profiles at three stages of disease progression: long before (2 months of age), immediately before (5 months) and after (18 months) the appearance of Abeta plaques. Using cDNA microarray techniques, we measured mRNA levels in 11 283 cDNA clones from the cerebral cortex of Tg2576 mice and age-matched wild-type (WT) mice at each of the three time points. This gene expression analysis revealed that the genes related to mitochondrial energy metabolism and apoptosis were up-regulated in 2-month-old Tg2576 mice and that the same genes were up-regulated at 5 and 18 months of age. These microarray results were confirmed using northern blot analysis. Results from in situ hybridization of mitochondrial genes-ATPase-6, heat-shock protein 86 and programmed cell death gene 8-suggest that the granule cells of the hippocampal dentate gyrus and the pyramidal neurons in the hippocampus and the cerebral cortex are up-regulated in Tg2576 mice compared with WT mice. Results from double-labeling in situ hybridization suggest that in Tg2576 mice only selective, over-expressed neurons with the mitochondrial gene ATPase-6 undergo oxidative damage. These results, therefore, suggest that mitochondrial energy metabolism is impaired by the expression of mutant APP and/or Abeta, and that the up-regulation of mitochondrial genes is a compensatory response. These findings have important implications for understanding the mechanism of Abeta toxicity in AD and for developing therapeutic strategies for AD.

Glucose/mitochondria in neurological conditions

Impairments of glucose and mitochondrial function are important causes of brain dysfunction and therefore of brain disease. Abnormalities have been found in association with disease of the nervous system in most of the components of glucose/mitochondrial metabolism. In many, molecular genetic abnormalities have been defined. Brain glucose oxidation is abnormal in common diseases of the nervous system, including Alzheimer disease and other dementias, Parkinson disease, delirium, probably schizophrenia and other psychoses, and of course cerebrovascular disease. Defects in a single component and even a single mutation can be associated with different clinical phenotypes. The same clinical phenotype can result from different genotypes. The complex relationship between biological abnormality in brain glucose utilization and clinical disorder is similar to that in other disorders that have been intensively studied at the genetic level. Genes for components of the pathways of brain glucose oxidation are good candidate genes for disease of the brain. Preliminary data support the proposal that treatments to normalize abnormalities in brain glucose oxidation may benefit many patients with common brain diseases.

Effects of 60 Hz electromagnetic field exposure on APP695 transcription levels in differentiating human neuroblastoma cells

Epidemiological studies have suggested that workers with primary occupation that are likely to have resulted in the medium-to-high extremely low frequency (ELF) electromagnetic field (EMF) exposure are at increased risk of Alzheimer's disease (AD) pathogenesis. As a first step in investigating the possibility of an association between the ELF-EMF exposure and AD at the cellular level, we have used the differentiating IMR-32 neuroblastoma cells. In double-blind experiments, IMR-32 cells were exposed to the magnetic field intensities of 50, 100, and 200 microT at a frequency of 60 Hz for a period of 4 h at the three ages of differentiation (2, 10, and 16 days after incubation in differentiation medium). We used a custom-made Helmholtz coil setup driven by a 60-Hz sinusoidal signal from a function generator and an in-house built power amplifier. Total RNA extracted from the exposed cells was separated by the agarose gel electrophoresis and transferred to a nylon membrane for the northern hybridization. Digoxygenin-labeled APP695 RNA probes were used to detect changes in the APP695 mRNA levels in response to the ELF-EMF exposure. The results reported herein provided no support for any relationship between the APP695 gene transcription and IMR-32 differentiation age, as well as the magnetic field exposure. This study constitutes the first step towards investigating the possibility of an association between the ELF-EMF exposure and AD manifestations at the cellular level.

Selective antibody-induced cholinergic cell and synapse loss produce sustained hippocampal and cortical hypometabolism with correlated cognitive deficits

The physiological interrelationships between cognitive impairments, neurotransmitter loss, amyloid processing and energy metabolism changes in AD, cholinergic dementia and Down's syndrome are largely unknown to date. This report contains novel studies into the association between cognitive function and cerebral metabolism after long-term selective CNS cholinergic neuronal and synaptic loss in a rodent model. We measured local cerebral rates of glucose utilization ((14)C-2-deoxyglucose) throughout the brains of awake rats 4.5 months after bilateral intraventricular injections of a cholinotoxic antibody directed against the low-affinity NGF receptor (p75 NGF) associated with cholinergic neurons (192 IgG-saporin). Permanent cholinergic synapse loss was demonstrated by [(3)H]-vesamicol in vitro autoradiography defining presynaptic vesicular acetylcholine (ACh) transport sites. While other metabolic studies have defined acute and transient glucose use changes after relatively nonspecific lesions of anatomical regions containing cholinergic neurons, our results show sustained reductions in glucose utilization in brain regions impacted by cholinergic synapse loss, including frontal cortical and hippocampal regions, relative to glucose use levels in control rats. In the same animals, impaired cognitive spatial performance in a Morris water maze was correlated with reduced glucose use rates in the cortex and hippocampus at this time point, which is consistent with increased postmortem cortical and hippocampal amyloid precursor protein (APP) levels (45, 46). These results are consistent with the view of cholinergic influence over metabolism, APP processing, and cognition in the cortex and hippocampus.

Effects of aluminum on activity of krebs cycle enzymes and glutamate dehydrogenase in rat brain homogenate

Aluminum is a neurotoxic agent for animals and humans that has been implicated as an etiological factor in several neurodegenerative diseases and as a destabilizer of cell membranes. Due to its high reactivity, Al3+ is able to interfere with several biological functions, including enzymatic activities in key metabolic pathways. In this paper we report that, among the enzymes that constitute the Krebs cycle, only two are activated by aluminum: alpha-ketoglutarate dehydrogenase and succinate dehydrogenase. In contrast, aconitase, shows decreased activity in the presence of the metal ion. Al3+ also inhibits glutamate dehydrogenase, an allosteric enzyme that is closely linked to the Krebs cycle. A possible correlation between aluminum, the Krebs cycle and aging processes is discussed.

Inherent abnormalities in energy metabolism in Alzheimer disease. Interaction with cerebrovascular compromise

Alzheimer disease (AD) is a form of the dementia syndrome. AD appears to have a variety of fundamental etiologies that lead to the neuropathological manifestations which define the disease. Patients who are at high risk to develop AD typically show impairments of cerebral metabolic rate in vivo even before they show any evidence of the clinical disease on neuropsychological, electrophysiological, and neuroimaging examinations. Therefore, impairment in energy metabolism in AD can not be attributed to loss of brain substance or to electrophysiological abnormalities. Among the characteristic abnormalities in the AD brain are deficiencies in several enzyme complexes which participate in the mitochondrial oxidation of substrates to yield energy. There include the pyruvate dehydrogenase complex (PDHC), the alpha-ketoglutarate dehydrogenase complex (KGDHC), and Complex IV of the electron transport chain (COX). The deficiency of KGDHC may be due to a mixture of causes including damage by free radicals and perhaps to genetic variation in the DLST gene encoding the core protein of this complex. Inherent impairment of glucose oxidation by the AD brain may reasonably be expected to interact synergistically with an impaired supply of oxygen and glucose to the AD brain, in causing brain damage. These considerations lead to the hypothesis that cerebrovascular compromise and inherent abnormalities in the brain's ability to oxidize substrates can interact to favor the development of AD, in individuals who are genetically predisposed to develop neuritic plaques.

Catecholamines potentiate amyloid beta-peptide neurotoxicity: involvement of oxidative stress, mitochondrial dysfunction, and perturbed calcium homeostasis

Oxidative stress and mitochondrial dysfunction are implicated in the neuronal cell death that occurs in physiological settings and in neurodegenerative disorders. In Alzheimer's disease (AD) degenerating neurons are associated with deposits of amyloid beta-peptide (A beta), and there is evidence for increased membrane lipid peroxidation and protein oxidation in the degenerating neurons. Cell culture studies have shown that A beta can disrupt calcium homeostasis and induce apoptosis in neurons by a mechanism involving oxidative stress. We now report that catecholamines (norepinephrine, epinephrine, and dopamine) increase the vulnerability of cultured hippocampal neurons to A beta toxicity. The catecholamines were effective in potentiating A beta toxicity at concentrations of 10-200 microM, with the higher concentrations (100-200 microM) themselves inducing cell death. Serotonin and acetylcholine were not neurotoxic and did not modify A beta toxicity. Levels of membrane lipid peroxidation, and cytoplasmic and mitochondrial reactive oxygen species, were increased following exposure to neurons to A beta, and catecholamines exacerbated the oxidative stress. Subtoxic concentrations of catecholamines exacerbated decreases in mitochondrial energy charge and transmembrane potential caused by A beta, and higher concentrations of catecholamines alone induced mitochondrial dysfunction. Antioxidants (vitamin E, glutathione, and propyl gallate) protected neurons against the damaging effects of A beta and catecholamines, whereas the beta-adrenergic receptor antagonist propanolol and the dopamine (D1) receptor antagonist SCH23390 were ineffective. Measurements of intracellular free Ca2+ ([Ca2+]i) showed that A beta induced a slow elevation of [Ca2+]i which was greatly enhanced in cultures cotreated with catecholamines. Collectively, these data indicate a role for catecholamines in exacerbating A beta-mediated neuronal degeneration in AD and, when taken together with previous findings, suggest roles for oxidative stress induced by catecholamines in several different neurodegenerative conditions.

Distinct pH homeostatic features in lymphoblasts from Alzheimer's disease patients

Epstein-Barr-transformed lymphocytes from Alzheimer's disease patients showed the following distinct features in controlling the intracellular pH compared with cells from normal age-matched controls: (1) The alphaIgM-induced intracellular acidification was more pronounced in Alzheimer's disease than control cells and this effect appears to be associated with a loss of effectiveness of a Ca2+/calmodulin-dependent mechanism in controlling the activity of the Na+/H+ exchanger; and (2) the intracellular H+-buffering capacity and the rate of proton efflux in response to an acid load were both decreased in Alzheimer's disease cells. It is concluded that the amplitude of the intracellular pH changes under acid-loading conditions will always be greater in Alzheimer's disease than in control cells.

Neuroprotective efficacy and mechanisms of novel pyrrolopyrimidine lipid peroxidation inhibitors in the gerbil forebrain ischemia model

A brief period of bilateral carotid occlusion (BCO)-induced forebrain ischemia in gerbils triggers neuronal degeneration and the subsequent expression of amyloid precursor protein (APP), b-amyloid protein (b-AP), and apolipoprotein E (APO-E) in the selectively vulnerable CA1 region of the hippocampus. The increase in immunoreactivity is secondary to the postischemic degeneration of the CA1 neurons and is largely astrocyte-derived as evidenced by a simultaneous increase in glial fibrillary acidic protein (GFAP) staining. Oxygen radical-induced lipid peroxidation has been strongly suggested to play a role in postischemic neuronal damage and Alzheimer's disease. Recent literature suggests a possible link between early oxidative stress and APP overexpression. Therefore, the present investigation examined the effect of two novel brain-penetrating pyrrolopyrimidine lipid peroxidation inhibitors (PNU-101033E and PNU-104067F) on CA1 neurodegeneration and the subsequent increase in APP, b-AP, APO-E, and GFAP immunostaining at 4 days after a 5-minute episode of forebrain ischemia. Using an antibody for lipid peroxidation-derived malondialdehyde (MDA)-modified proteins, the authors also examined the effects of PNU-104067F on MDA immunostaining 2 days after ischemia, before completion of the neuronal loss. At 2 days, the authors also evaluated microglial activation using an antibody to surface major histocompatibility complex class II antigen expressed by activated microglia. Gerbils were treated at 30 mg/kg orally 30 minutes before the BCO and 2 hours after ischemia, followed by daily dosing for the next day (microglia and MDA) and the successive 3 days for APP, b-AP, APO-E, and GFAP immunostaining. APP and APO-E staining was significantly suppressed by 50% and 66%, respectively, with either compound. b-AP immunoreactivity was decreased 56% with both compounds, and GFAP expression was significantly decreased 53% (PNU-101033E) and 60.5% (PNU-104067F). There was a concomitant partial sparing of the CA1 hippocampal neurons by both PNU-101033E and PNU-104067F (P < .01) as determined by cresyl violet histochemistry. PNU-104067F significantly inhibited lipid peroxidation-derived MDA immunostaining and microglia activation (P < .05) at 48 hours after ischemia. Brain-penetrable lipid peroxidation inhibitors may provide attenuation of various glial response proteins after ischemic injury, probably secondary to neuronal protection.

Calbindin D28k blocks the proapoptotic actions of mutant presenilin 1: reduced oxidative stress and preserved mitochondrial function

Mutations in the presenilin 1 (PS-1) gene account for many cases of early-onset autosomal dominant inherited forms of Alzheimer's disease. Recent findings suggest that PS-1 mutations may sensitize neurons to apoptosis induced by trophic factor withdrawal and exposure to amyloid beta-peptide (Abeta). We now report that overexpression of the calcium-binding protein calbindin D28k prevents apoptosis in cultured neural cells expressing mutant PS-1 (L286V and M146V missense mutations). Elevations of the intracellular Ca2+ concentration and generation of reactive oxygen species induced by Abeta, and potentiated by mutant PS-1, were suppressed in calbindin-overexpressing cells. Impairment of mitochondrial function by Abeta (which preceded apoptosis) was exacerbated by PS-1 mutations and was largely prevented by calbindin. These findings suggest that PS-1 mutations render neurons vulnerable to apoptosis by a mechanism involving destabilization of cellular calcium homeostasis, which leads to oxidative stress and mitochondrial dysfunction.

17Beta-estradiol attenuates oxidative impairment of synaptic Na+/K+-ATPase activity, glucose transport, and glutamate transport induced by amyloid beta-peptide and iron

Synapse loss, deposits of amyloid beta-peptide (Abeta), impaired energy metabolism, and cognitive deficits are defining features of Alzheimer's disease (AD). Estrogen replacement therapy reduces the risk of developing AD in postmenopausal women. Because synapses are likely sites for initiation of neurodegenerative cascades in AD, we tested the hypothesis that estrogens act directly on synapses to suppress oxidative impairment of membrane transport systems. Exposure of rat cortical synaptosomes to Abeta25-35 (Abeta) and FeSO4 induced membrane lipid peroxidation and impaired the function of the plasma membrane Na+/K+-ATPase, glutamate transporter, and glucose transporter. Pretreatment of synaptosomes with 17beta-estradiol or estriol largely prevented impairment of Na+/K+-ATPase activity, glutamate transport, and glucose transport; other steroids were relatively ineffective. 17Beta-estradiol suppressed membrane lipid peroxidation induced by Abeta and FeSO4, but did not prevent impairment of membrane transport systems by 4-hydroxynonenal (a toxic lipid peroxidation product), suggesting that an antioxidant property of 17beta-estradiol was responsible for its protective effects. By suppressing membrane lipid peroxidation in synaptic membranes, estrogens may prevent impairment of transport systems that maintain ion homeostasis and energy metabolism, and thereby forestall excitotoxic synaptic degeneration and neuronal loss in disorders such as AD and ischemic stroke.

Transglutaminase-catalyzed inactivation of glyceraldehyde 3-phosphate dehydrogenase and alpha-ketoglutarate dehydrogenase complex by polyglutamine domains of pathological length

Several adult-onset neurodegenerative diseases are caused by genes with expanded CAG triplet repeats within their coding regions and extended polyglutamine (Qn) domains within the expressed proteins. Generally, in clinically affected individuals n >/= 40. Glyceraldehyde 3-phosphate dehydrogenase binds tightly to four Qn disease proteins, but the significance of this interaction is unknown. We now report that purified glyceraldehyde 3-phosphate dehydrogenase is inactivated by tissue transglutaminase in the presence of glutathione S-transferase constructs containing a Qn domain of pathological length (n = 62 or 81). The dehydrogenase is less strongly inhibited by tissue transglutaminase in the presence of constructs containing shorter Qn domains (n = 0 or 10). Purified alpha-ketoglutarate dehydrogenase complex also is inactivated by tissue transglutaminase plus glutathione S-transferase constructs containing pathological-length Qn domains (n = 62 or 81). The results suggest that tissue transglutaminase-catalyzed covalent linkages involving the larger poly-Q domains may disrupt cerebral energy metabolism in CAG/Qn expansion diseases.

Isolation, characterization, and mapping of gene encoding dihydrolipoyl succinyltransferase (E2k) of human alpha-ketoglutarate dehydrogenase complex

We have isolated and sequenced cDNAs representing the full-length (2987-bp) gene for dihydrolipoyl succinyltransferase (E2k component) of the human alpha-ketoglutarate dehydrogenase complex (KGDHC) from a human fetal brain cDNA library. The E2k cDNA was mapped to human chromosome 14 using a somatic cell hybrid panel, and more precisely to band 14q24.3 by in situ hybridization. This cDNA also cross-hybridized to an apparent E2k pseudogene on chromosome 1p31. Northern analysis revealed the E2k gene to be ubiquitously expressed in peripheral tissues and brain. Interestingly, chromosome 14q24.3 has recently been reported to contain gene defects for an early-onset form of familial Alzheimer's disease and for Machado-Joseph disease. Future studies will be necessary to determine whether the E2k gene plays a role in either of these two disorders.

The cultured fibroblast model

Cultured skin fibroblasts have been successfully used to elucidate the molecular and biochemical bases of a large number of inborn errors of metabolism which cause neurological disease. The fibroblast model is now being extended to studies of genetic diseases of the nervous system with later clinical onset, including Alzheimer's Disease (AD). Persistence in the cultured cells of an abnormality found in AD brain provides evidence that the abnormality in brain is not simply a reflection of anatomic or chemical damage in the clinically affected tissue. Biochemical and cell biological studies of AD fibroblasts are succeeding in implicating molecules which warrant further study at the molecular genetic level. In neurological diseases with an important genetic component, including AD, studies of fibroblasts can be a useful adjunct to studies of brain.