Modulation byDLST of the genetic risk of Alzheimer's disease in a very elderly population

Immunity and autoantibodies of a mouse strain with autistic-like behavior

Female and male mice of the BTBR T ⁺ Itpr3 ^tf /J (BTBR) strain have behaviors that resemble autism spectrum disorder. In comparison to C57BL/6 (B6) mice, BTBR mice have elevated humoral immunity, in that they have naturally high serum IgG levels and generate high levels of IgG antibodies, including autoantibodies to brain antigens. This study focused on the specificities of autoantibodies and the immune cells and their transcription factors that might be responsible for the autoantibodies. BTBR IgG autoantibodies bind to neurons better than microglia and with highest titer to nuclear antigens. Two of the antigens identified were alpha-enolase (ENO1) and dihydrolipoyllysine-residue succinyltransferase component of 2-oxoglutarate dehydrogenase complex, mitochondrial (DLST). Surprisingly based on IgG levels, the blood and spleens of BTBR mice have more CD4⁺ and CD8⁺ T cells, but fewer B cells than B6 mice. The high levels of autoantibodies in BTBR relates to their splenic T follicular helper (Tfh) cell levels, which likely are responsible for the higher number of plasma cells in BTBR mice than B6 mice. BTBR mice have increased gene expression of interleukin-21 receptor (I l -21 r) and Paired Box 5 (Pax5), which are known to aid B cell differentiation to plasma cells, and an increased Lysine Demethylase 6B (Kdm6b)/DNA Methyltransferase 1 (Dnmt1) ratio, which increases gene expression. Identification of gene expression and immune activities of BTBR mice may aid understanding of mechanisms associated with autism since neuroimmune network interactions have been posited and induction of autoantibodies may drive the neuroinflammation associated with autism.

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.

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.

Differences in apolipoprotein E3/3 and E4/4 allele-specific gene expression in hippocampus in Alzheimer disease

Apolipoprotein E4 (APOE4) allele is a major risk factor for late-onset familial and sporadic Alzheimer disease (AD). The mechanism of action of APOE in the etiology of AD remains unclear. Using gene expression (microarray) analysis of human hippocampus from APOE3/3 AD and APOE4/4 AD cases, we found different gene transcription patterns between APOE4/4 and APOE3/3 AD cases. The expression of APOE4/4 alleles, in comparison to APOE3/3, is associated with upregulation of multiple gene transcripts encoding cell growth suppresser or arrest, signal transduction, myelinogenesis, cell adhesion and migration, heavy metal metabolism and detoxification. Whereas the APOE4 gene expression is associated with downregulation of gene transcripts involved in mitochondrial oxidative phosphorylation and energy metabolism, synaptic vesicle docking and fusing, and synaptic plasticity compared to APOE3. These mechanisms may contribute increased risk for AD and for cognitive dysfunction in AD patients who carry the APOE4 allele(s).

Cerebrometabolic abnormalities in Alzheimer's disease

Extensive, replicated evidence in patients in vivo and in Alzheimer (AD) tissues in vitro indicates that impaired brain metabolism is one of the cardinal and essentially invariable events in AD. The degree of impairment in brain metabolism is proportional to the degree of clinical disability, both in vivo and in vitro. The 'cerebrometabolic lesion' cannot be attributed to 'slower thinking' or 'brain atrophy', because of quantitative considerations and because the metabolic lesion precedes the development of neuropsychological abnormalities or decreases in brain mass detectable by modern imaging techniques. The causes of the cerebrometabolic lesion in AD are not well defined. Free radicals seem likely to be involved, including free radicals generated from Alzheimer amyloid. Thus, the importance of the cerebrometabolic lesion is entirely compatible with most versions of the widely accepted 'amyloid cascade hypothesis' of AD. A variety of plausible, redundantly documented mechanisms are compatible with the proposal that the cerebrometabolic lesion is a proximate cause of the clinical disability in AD. In agreement with these findings, recent attempts to treat the cerebrometabolic lesion in AD have given encouraging preliminary results. The cerebrometabolic lesion in AD deserves further study.

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.

Alzheimer's disease and Alzheimer's dementia: distinct but overlapping entities

Much of the controversy about the "amyloid cascade hypothesis" may reflect unrecognized differences in the use of language, including the use of the word "cause." This commentary proposes that the term Alzheimer disease refer to the neuropathological entity and the term Alzheimer dementia to clinical dementia in people who also have Alzheimer neuropathology. The ultimate causes of Alzheimer disease are proposed to be aging, environmental stresses, and genetic predispositions. The fundamental cause of Alzheimer dementia is proposed to be Alzheimer disease, i.e. the neurobiological abnormalities in Alzheimer brain. The neurobiology of Alzheimer disease includes changes that may initially be adaptive but can become excessive and thereby harmful; they include increased expression of APP with accumulation of potentially damaging peptides such as Abeta, inflammation, and increased ROS activity. The neurobiological abnormality that is the proximate cause of Alzheimer dementia appears to be decreases in cerebral metabolic rate. Decreased metabolism occurs not only in this but in essentially all dementias, and impairing brain metabolism induces neuropsychological deficits characteristic of dementias. The immediate cause of Alzheimer dementia is proposed to be deficiencies in signaling, both intracellular and intercellular (neurotransmission), that follow directly from the decrease in cerebrometabolic rate.

Brain metabolism and brain disease: is metabolic deficiency the proximate cause of Alzheimer dementia?

The potential of impairments in oxidative/energy metabolism to cause diseases of the brain had been proposed even before the major pathways of oxidative/energy metabolism were described. Deficiencies associated with disease are known in all the pathways of oxidative/energy metabolism and are associated with some of the most common disorders of the nervous system, including Alzheimer's disease (AD) and Parkinson's disease. A common mechanism in these conditions appears to be a downward mitochondrial spiral, involving abnormalities in energy metabolism, calcium metabolism, and free radicals (reactive oxygen and nitrogen species). In AD, the spiral appears to interact with abnormalities in the metabolism of the Alzheimer amyloid precursor protein (APP) and its Abeta fragment. Several lines of evidence indicate that the mitochondrial spiral may be a proximate cause of the clinical disabilities in AD. Decreases in cerebral metabolic rate (CMR) characteristically occur in AD and in other dementias. Inducing decreases in CMR leads to clinical disabilities characteristically associated with AD and with analogous problems in experimental animals. Treatments directed toward normalizing CMR appear to help at least some patients. Further studies of this possibility and of treatments designed to ameliorate the mitochondrial spiral may prove useful for treating AD and perhaps some other dementing disorders.

No association between DLST gene and Alzheimer's disease or Wernicke-Korsakoff syndrome

Among many candidate genes for the genetically heterogeneous Alzheimer's disease (AD), only apolipoprotein E (ApoE) has been confirmed. Another candidate is the dihydrolipoyl succinyltransferase (DLST) gene, one of three components of thiamine-dependent mitochondrial alpha-ketoglutarate dehydrogenase complex (KGDHC), because KGDHC activity is reported reduced in AD patients. Also characterized by reduced KGDHC activity is another neuropsychiatric disease, Wernicke-Korsakoff syndrome (WKS), which results from thiamine deficiency. Examination of specific DLST gene polymorphism in 247 Japanese AD patients, 53 alcoholic WKS patients, and 368 nondemented Japanese control subjects revealed no significant differences in DLST genotypes and failed to replicate the findings of earlier studies indicating an association between DLST gene polymorphism and AD.

Oxidative metabolism

There is a large body of evidence showing both metabolic defects and oxidative damage in Alzheimer's disease. Studies of cybrid cell lines show reduced cytochrome oxidase. There is also substantial evidence for a defect in alpha-ketoglutarate dehydrogenase. It is therefore possible that therapeutic strategies to improve brain metabolism or ameliorate oxidative damage might be useful in treating Alzheimer's disease.

Review of the next generation of Alzheimer's disease therapeutics: challenges for drug development

1. AD is believed to stem from dysfunctional cholinergic signaling in the regions of the brain associated with memory and cognition. 2. The occurrence of AD in afflicted individuals correlates with an increase in the accumulation of A beta-rich senile plaques and neurofibrillary tangles in the brain. 3. Currently, the only FDA-approved AD therapies are a group of acetylcholinesterase inhibitors which slow the turnover of the neurotransmitter acetylcholine in the synapse. 4. Many other compounds which target other aspects of the disease, such as reducing neuronal damage and limiting oxidation, are in clinical trials. These include monoamine oxidase (MAO-B) inhibitors, NSAIDs, antioxidants and estrogen, among others. 5. Recent research discoveries have more completely defined the molecular nature of AD, and are generating new approaches for treatment. One idea is to limit the ability of the protein tau to become phosphorylated in hopes that this will limit the formation of neurofibrillary tangles in the brain. 6. A separate approach that is being pursued is to prevent formation and accumulation of A beta plaques. This may be accomplished by either regulating gamma-secretase activity, or using anti-beta-amyloid antibodies to reduce the size of existing plaques. 7. Employing improved procedural and technological approaches during clinical trials, such as bridging studies, dynabridge studies and PET analysis, promises to streamline the drug development process. 8. The use of biomarkers and MRI analysis may be an effective means by which to identify the disease early. Consequently, early intervention treatment therapies may be an effective way of delaying onset of the disease. 9. Long term AD studies, particularly those focusing on the MCI population, are likely to provide statistically valid results using a smaller study population.

Genetic epidemiology of Alzheimer's disease

The genetics of Alzheimer's disease is one of the most complex topics to study from an epidemiological point of view, particularly in population-based studies on polymorphisms of genes. The present review focuses primarily on some conflicting results on genetic epidemiology of Alzheimer's disease, and the major difficulties met in such studies.

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.

The alpha-ketoglutarate dehydrogenase complex in neurodegeneration

Altered energy metabolism is characteristic of many neurodegenerative disorders. Reductions in the key mitochondrial enzyme complex, the alpha-ketoglutarate dehydrogenase complex (KGDHC), occur in a number of neurodegenerative disorders including Alzheimer's Disease (AD). The reductions in KGDHC activity may be responsible for the decreases in brain metabolism, which occur in these disorders. KGDHC can be inactivated by several mechanisms, including the actions of free radicals (Reactive Oxygen Species, ROS). Other studies have associated specific forms of one of the genes encoding KGDHC (namely the DLST gene) with AD, Parkinson's disease, as well as other neurodegenerative diseases. Reductions in KGDHC activity can be plausibly linked to several aspects of brain dysfunction and neuropathology in a number of neurodegenerative diseases. Further studies are needed to assess mechanisms underlying the sensitivity of KGDHC to oxidative stress and the relation of KGDHC deficiency to selective vulnerability in neurodegenerative diseases.

A polymorphism in the tau gene associated with risk for Alzheimer's disease

Searching for tau genetic variations which could be associated with risk for Alzheimer's disease (AD), we have performed a mutational analysis of a region containing the whole exon 11 of the tau gene, which encodes a microtubule binding region critical for tau self-assembly, and we have found a biallelic polymorphism at position +34 of intron 11 (IVS11 + 34G/A). We have analyzed the allelic frequencies of this polymorphism in a case-control sample (167 clinically diagnosed AD and 194 controls) and found that the presence of any G allele (genotypes AG + GG) is associated with a five-fold AD risk in individuals carrying the apolipoprotein E4 allele, strongly suggesting that the combined effect of tau and apoE is relevant in relation with AD pathogenesis.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

A DLST genotype associated with reduced risk for Alzheimer's disease

Recent studies suggest that variants of the DLST gene alter the risk of AD. DLST encodes the core subunit of the mitochondrial alpha-ketoglutarate dehydrogenase complex, which is deficient in AD. The authors report that in 247 US white subjects, homozygosity for DLST A19,117, T19,183 was associated with a reduced risk of AD (odds ratio [OR] = 0.35, p = 0.018). The reduced risk was marked in subjects who did not carry the apolipoprotein (APOE)-4 allele (OR = 0.16, p = 0.014). Further study of DLST in AD appears warranted.