Isolation of glyceraldehyde 3-phosphate dehydrogenase (Gapdh) cDNA from the distal half of mouse chromosome 16: further indication of a link between Alzheimer's disease and glycolysis

Explorative and targeted neuroproteomics in Alzheimer's disease

Alzheimer's disease (AD) is a progressive brain amyloidosis that injures brain regions involved in memory consolidation and other higher brain functions. Neuropathologically, the disease is characterized by accumulation of a 42 amino acid peptide called amyloid β (Aβ42) in extracellular senile plaques, intraneuronal inclusions of hyperphosphorylated tau protein in neurofibrillary tangles, and neuronal and axonal degeneration and loss. Biomarker assays capturing these pathologies have been developed for use on cerebrospinal fluid samples but there are additional molecular pathways that most likely contribute to the neurodegeneration and full clinical expression of AD. One way of learning more about AD pathogenesis is to identify novel biomarkers for these pathways and examine them in longitudinal studies of patients in different stages of the disease. Here, we discuss targeted proteomic approaches to study AD and AD-related pathologies in closer detail and explorative approaches to discover novel pathways that may contribute to the disease. This article is part of a Special Issue entitled: Neuroproteomics: Applications in neuroscience and neurology.

A global single-cell cDNA amplification method for quantitative microarray analysis

We describe here a protocol to faithfully amplify global cDNAs from single cells. The amplified cDNAs retain their sense-antisense orientation and can be easily applied to template preparation for quantitative high-density oligonucleotide microarray analyses. The amplification protocol comprises (1) lysis of a single cell in a tube without purification, (2) first-strand cDNA synthesis with the first primer tailed with oligo dT, (3) elimination of the unreacted first primer, (4) poly (dA) tailing of the cDNA, (5) second-strand cDNA synthesis with the second primer tailed with oligo dT, and (6) 20-cycle, directional PCR with the two primers. To prepare the template for the isothermal linear amplification with T7 RNA polymerase to synthesize labeled cRNAs for microarray hybridization, the promoter sequence is added to the cDNA with another round of PCR. The promoter-tagged cDNA is purified with gel electrophoresis and amplified with one final cycle of PCR.

Spatial correlation between brain aerobic glycolysis and amyloid-β (Aβ ) deposition

Amyloid-β (Aβ) plaque deposition can precede the clinical manifestations of dementia of the Alzheimer type (DAT) by many years and can be associated with changes in brain metabolism. Both the Aβ plaque deposition and the changes in metabolism appear to be concentrated in the brain's default-mode network. In contrast to prior studies of brain metabolism which viewed brain metabolism from a unitary perspective that equated glucose utilization with oxygen consumption, we here report on regional glucose use apart from that entering oxidative phosphorylation (so-called "aerobic glycolysis"). Using PET, we found that the spatial distribution of aerobic glycolysis in normal young adults correlates spatially with Aβ deposition in individuals with DAT and cognitively normal participants with elevated Aβ, suggesting a possible link between regional aerobic glycolysis in young adulthood and later development of Alzheimer pathology.

Global single-cell cDNA amplification to provide a template for representative high-density oligonucleotide microarray analysis

We describe here a protocol for the representative amplification of global mRNAs from typical single mammalian cells to provide a template for high-density oligonucleotide microarray analysis. A single cell is lysed in a tube without purification and first-strand cDNAs are synthesized using a poly(dT)-tailed primer. Unreacted primer is specifically eliminated by exonuclease treatment and second strands are generated with a second poly(dT)-tailed primer after poly(dA) tailing of the first-strand cDNAs. The cDNAs are split into four tubes, which are independently directionally amplified by PCR, and then recombined. The amplified products (approximately 100 ng) show superior representation and reproducibility of original gene expression, especially for genes expressed in more than 20 copies per cell, compared with those obtained by a conventional PCR protocol, and can effectively be used for quantitative PCR and EST analyses. The cDNAs are then subjected to another PCR amplification with primers bearing the T7 promoter sequence. The resultant cDNA products are gel purified, amplified by one final cycle and used for isothermal linear amplification by T7 RNA polymerase to synthesize cRNAs for microarray hybridization. This protocol yields cDNA templates sufficient for more than 80 microarray hybridizations from a single cell, and can be completed in 5-6 days.

Glyceraldehyde-3-phosphate dehydrogenase activity as an independent modifier of methylglyoxal levels in diabetes

Methylglyoxal (MG) may be an important cause of diabetic complications. Its primary source is dihydroxyacetone phosphate (DHAP) whose levels are partially controlled by glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Using a human red blood cell (RBC) culture, we examined the effect of modifying GAPDH activity on MG production. With the inhibitor koningic acid (KA), we showed a linear, concentration-dependent GAPDH inhibition, with 5 microM KA leading to a 79% reduction of GAPDH activity and a sixfold increase in MG. Changes in redox state produced by elevated pH also resulted in a 2.4-fold increase in MG production at pH 7.5 and a 13.4-fold increase at pH 7.8. We found substantial inter-individual variation in DHAP and MG levels and an inverse relationship between GAPDH activity and MG production (R=0.57, P=0.005) in type 2 diabetes. A similar relationship between GAPDH activity and MG was observed in vivo in type 1 diabetes (R=0.29, P=0.0018). Widely varying rates of progression of diabetic complications are seen among individuals. We postulate that modification of GAPDH by environmental factors or genetic dysregulation and the resultant differences in MG production could at least partially account for this observation.

New insights into an old protein: the functional diversity of mammalian glyceraldehyde-3-phosphate dehydrogenase

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was considered a classical glycolytic protein examined for its pivotal role in energy production. It was also used as a model protein for analysis of protein structure and enzyme mechanisms. The GAPDH gene was utilized as a prototype for studies of genetic organization, expression and regulation. However, recent evidence demonstrates that mammalian GAPDH displays a number of diverse activities unrelated to its glycolytic function. These include its role in membrane fusion, microtubule bundling, phosphotransferase activity, nuclear RNA export, DNA replication and DNA repair. These new activities may be related to the subcellular localization and oligomeric structure of GAPDH in vivo. Furthermore, other investigations suggest that GAPDH is involved in apoptosis, age-related neurodegenerative disease, prostate cancer and viral pathogenesis. Intriguingly, GAPDH is also a unique target of nitric oxide. This review discusses the functional diversity of GAPDH in relation to its protein structure. The mechanisms through which mammalian cells may utilize GAPDH amino acid sequences to provide these new functions and to determine its intracellular localization are considered. The interrelationship between new GAPDH activities and its role in cell pathologies is addressed.

Purification of a dichlorophenol-indophenol oxidoreductase from rat and bovine synaptic membranes: tight complex association of a glyceraldehyde-3-phosphate dehydrogenase isoform, TOAD64, enolase-gamma and aldolase C

NADH-dichlorophenol-indophenol oxidoreductases (PMOs) were purified from synaptic plasma membranes or synaptic vesicles (small recycling vesicles) from both bovine and rat brains and from a neuroblastoma cell line, NB41A3. Several isoforms could be identified in purified plasma membranes and vesicles. Purification of the enzyme activity involved protein extraction with detergents, (NH4)2SO4 precipitation, chromatography under stringent conditions and native PAGE. PMO activity could be attributed to a very tight complex of several proteins that could not be separated except by SDS/PAGE. SDS/PAGE resolved the purified complex into at least five proteins, which could be micro-sequenced and identified unambiguously as hsc70, TOAD64 and glyceraldehyde-3-phosphate dehydrogenase tightly associated with the brain-specific proteins aldolase C and enolase-gamma. Enzyme activity could be purified from both synaptic plasma membranes and recycling vesicles, yields being much greater from the latter source. Highly purified plasma membranes (prepared from a neuroblastoma cell line NB41A3 by iminobiotinylation of intact cells and affinity purification with avidin and anti-avidin antibodies under very stringent conditions) also displayed PMO activity tightly associated with TOAD64. The association of PMO in a tight complex was confirmed by its immunoprecipitation from cellular and membrane extracts of NB41A3 using antibodies directed against any component protein of the complex followed by immunodetection with antibodies directed against the other members. Antibodies also inhibited the enzyme activity synergistically. In addition, induction of the different components of the complex during dichlorophenol-indophenol stress was demonstrated by the S1 RNase-protection assay in synchronized NB41A3 cells. The role of the complex in membrane fusion and cellular response to extracellular oxidative stress during growth and development is discussed.

Glyceraldehyde-3-phosphate dehydrogenase is over-expressed during apoptotic death of neuronal cultures and is recognized by a monoclonal antibody against amyloid plaques from Alzheimer's brain

The age-induced apoptotic death of cerebellar neurons in culture is associated with over-expression of a 38-kDa particulate protein identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Both the age-induced apoptosis and the 38-kDa protein overexpression were effectively suppressed by the presence of tetrahydroaminoacridine, an antidementia drug, or aurintricarboxylic acid. This over-expressed 38-kDa protein and purified GAPDH were found to react with a monoclonal antibody (mAb), Am-3, which was raised against amyloid plaques from Alzheimer's brain, but not with mAb, AmT-1, which was produced using synthetic amyloid beta peptide. These results raise the possibility that GAPDH is also involved in the neurodegeneration during the development of Alzheimer's disease.