Increased glyceraldehyde 3-phosphate dehydrogenase levels in the brain of patients with Down's syndrome

Proteomics analysis of human amniotic fluid

Amniotic fluid is a dynamic and complex mixture that reflects the physiological status of the developing fetus. In this study, the human amniotic fluid (AF) proteome of a 16-18-week normal pregnancy was profiled and analyzed to investigate the composition and functions of this fluid. Due to the complexity of AF, we utilized three different fractionation strategies to provide greater coverage. Two types of two-dimensional LC/MS/MS as well as an LC-SDS-PAGE-LC-MS/MS platform were used. A total of 16 AF samples between gestational ages of 16 and 18 weeks from women carrying chromosomally normal fetuses were analyzed by one of the three fractionation methods followed by a common reverse phase LC-MS/MS step. Mascot and The Global Proteome Machine engines were used to search the International Protein Index human database for peptide sequence identification. The list of proteins was generated by combining the results of both engines through the PeptideProphet of Scaffold software. All identified proteins were combined to generate the AF proteome comprising 1,026 unique gene matches or 842 non-redundant proteins. This list includes most of the currently used biomarkers for pregnancy-associated pathologic conditions such as preterm delivery, intra-amniotic infection, and chromosomal anomalies of the fetus. The subcellular localization, tissue expression, functions, and networks of the AF proteome were analyzed by various bioinformatic tools. These data will contribute to the better understanding of amniotic fluid function and to the discovery of novel biomarkers for prenatal diagnosis of fetal abnormalities.

Profiling human brain proteome by multi-dimensional separations coupled with MS

In our initial attempt to analyze the human brain proteome, we applied multi-dimensional protein separation and identification techniques using a combination of sample fractionation, 1-D SDS-PAGE, and MS analysis. The complexity of human brain proteome requires multiple fractionation strategies to extend the range and total number of proteins identified. According to the method of Klose (Methods Mol. Biol. 1999, 112, 67), proteins of the temporal lobe of human brain were fractionated into (i) cytoplasmic and nucleoplasmic, (ii) membrane and other structural, and (iii) DNA-binding proteins. Each fraction was then separated by SDS-PAGE, and the resulting gel line was cut into approximately 50 bands. After trypsin digestion, the resulting peptides from each band were analyzed by RP-LC/ESI-MS/MS using an LTQ spectrometer. The SEQUEST search program, which searched against the IPI database, was used for peptide sequence identification, and peptide sequences were validated by reversed sequence database search and filtered by the Protein Hit Score. Ultimately, 1533 proteins could be detected from the human brain. We classified the identified proteins according to their distribution on cellular components. Among these proteins, 24% were membrane proteins. Our results show that the multiple separation strategy is effective for high-throughput characterization of proteins from complex proteomic mixtures.

Neuroproteomics in neurotrauma

Neurotrauma in the form of traumatic brain injury (TBI) afflicts more Americans annually than Alzheimer's and Parkinson's disease combined, yet few researchers have used neuroproteomics to investigate the underlying complex molecular events that exacerbate TBI. Discussed in this review is the methodology needed to explore the neurotrauma proteome-from the types of samples used to the mass spectrometry identification and quantification techniques available. This neuroproteomics survey presents a framework for large-scale protein research in neurotrauma, as applied for immediate TBI biomarker discovery and the far-reaching systems biology understanding of how the brain responds to trauma. Ultimately, knowledge attained through neuroproteomics could lead to clinical diagnostics and therapeutics to lessen the burden of neurotrauma on society.

Proteomics-driven progress in neurodegeneration research

Proteomics technologies have been widely used in the investigation of neurodegenerative and psychiatric disorders, and in particular in the detection of differences between healthy individuals and patients suffering from such diseases. Thus, brain and cerebrospinal fluid (CSF) samples from patients with Alzheimer's disease, Down syndrome, Pick's disease, Parkinson's disease, schizophrenia, and other disorders as well as brain and CSF from animals serving as models of neurological disorders have been analyzed by proteomics. 2-DE followed by MALDI-TOF-MS has been mainly applied as this proteomics approach provides the possibility of convenient quantification of protein levels and detection of post-translational modifications. About 330 unique proteins with deranged levels and modifications have been detected by proteomics approaches to be related to neurodegeneration and psychiatric disorders. They are mainly involved in metabolism pathways, cytoskeleton formation, signal transduction, guidance, detoxification, transport, and conformational changes. In this article, we provide a summary of the major contributions of proteomics technologies in the study of neurodegenerative and psychiatric diseases, in particular, in the detection of changes in protein levels and modifications related to these disorders.

Proteomic approaches in the search for disease biomarkers

Significant technological advances in protein chemistry, physics and computer sciences in the last two decades have greatly improved protein separation methodologies, such as electrophoresis and chromatography, and have established mass spectrometry (MS) as an indispensable tool for protein study. The goal of this review is to provide a brief overview of the recent improvements in these methodologies and present examples from their application in proteome analysis and search for disease biomarkers.

Glyceraldehyde-3-phosphate dehydrogenase, apoptosis, and neurodegenerative diseases

Increasing evidence supports the notion that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a protein with multiple functions, including its surprising role in apoptosis. GAPDH is overexpressed and accumulates in the nucleus during apoptosis induced by a variety of insults in diverse cell types. Knockdown of GAPDH using an antisense strategy demonstrates its involvement in the apoptotic cascade in which GAPDH nuclear translocation appears essential. Knowledge concerning the mechanisms underlying GAPDH nuclear translocation and subsequent cell death is growing. Additional evidence suggests that GAPDH may be an intracellular sensor of oxidative stress during early apoptosis. Abnormal expression, nuclear accumulation, changes in physical properties, and loss of glycolytic activity of GAPDH have been found in cellular and transgenic models as well as postmortem tissues of several neurodegenerative diseases. The interaction of GAPDH with disease-related proteins as well as drugs used to treat these diseases suggests that it is a potential molecular target for drug development.

Metalloproteinase ADAMTS-1 but not ADAMTS-5 is manifold overexpressed in neurodegenerative disorders as Down syndrome, Alzheimer's and Pick's disease

ADAMTS-1 is a disintegrin and metalloproteinase with thrombospondin 1 (TSP1)-like motifs with ubiquitous though variable expression. Natural substrates of this protease are proteoglycans as aggrecan and versican and null mutant mice propose a role for growth, fertility, organ structure and function. As the gene for this protein is encoded on chromosome 21 and maybe overexpressed due to the gene dosage hypothesis based upon the presence of a third chromosome in trisomy 21, we decided to study expression in Down syndrome (DS) brain and used brains of patients with Alzheimer's (AD) and Pick's disease (PD) as controls. Frontal cortex of controls, DS, AD and PD were homogenized and extracted proteins were used for immunoblotting using antibodies against ADAMTS-1 and ADAMTS-5. ADAMTS-1-immunoreactivity was manifold increased in brain with DS and neurodegeneration, whereas ADAMTS-5 levels were comparable. Overexpression of this metalloproteinase maybe specifically involved in proteoglycan degradation and handling in brain of patients with neurodegenerative disease which in turn may lead to or reflect pathological lesions in DS, AD and PD brain. The manifold overexpression of ADAMTS-1 may be used as marker protein for neurodegeneration.

Association of late-onset Alzheimer's disease with genetic variation in multiple members of the GAPD gene family

Although several genes have been implicated in the development of the early-onset autosomal dominant form of Alzheimer's disease (AD), the genetics of late-onset AD (LOAD) is complex. Loci on several chromosomes have been linked to the disease, but so far only the apolipoprotein E gene has been consistently shown to be a risk factor. We have performed a large-scale single-nucleotide polymorphism (SNP)-based association study, across the region of linkage on chromosome 12, in multiple case-control series totaling 1,089 LOAD patients and 1,196 control subjects and report association with SNPs in the glyceraldehyde-3-phosphate dehydrogenase (GAPD) gene. Subsequent analysis of GAPD paralogs on other chromosomes demonstrated association with two other paralogs. A significant association between LOAD and a compound genotype of the three GAPD genes was observed in all three sample sets. Individually, these SNPs make differential contributions to disease risk in each of the casecontrol series, suggesting that variants in functionally similar genes may account for series-to-series heterogeneity of disease risk. Our observations raise the possibility that GAPD genes are AD risk factors, a hypothesis that is consistent with the role of GAPD in neuronal apoptosis.

Application of proteomics technologies in the investigation of the brain

Approximately 30-50% of the genes in mammals are expressed in the nervous system. A differential expression of genes in distinct patterns is necessary for the generation of the large variety of neuronal phenotypes. Proteomic analysis of brain compartments may be useful to understand the complexity, to investigate disorders of the central nervous system, and to search for corresponding early markers. Up to now, proteomics has mainly studied the identity and levels of the abundant human, rat, and mouse brain proteins as well as changes of their levels and the modifications that result from various neurological disorders, like Alzheimer's disease and Down's syndrome in humans and in animal models of those diseases. The proteins, for which altered levels in these disorders have been observed, exert mainly neurotransmission, guidance, and signal-transduction functions, or are involved in detoxification, metabolism, and conformational changes. Some of those proteins may be potential drug targets. Further improvement of proteomics technologies to increase sensitivity and efficiency of detection of certain protein classes is necessary for a more detailed analysis of the brain proteome. In this review, a description of the proteomics technologies applied in the investigation of the brain, the major findings that resulted from their application, and the potential and limitations of the current technologies are discussed.

Chemically induced neuronal damage and gliosis: enhanced expression of the proinflammatory chemokine, monocyte chemoattractant protein (MCP)-1, without a corresponding increase in proinflammatory cytokines(1)

Enhanced expression of proinflammatory cytokines and chemokines has long been linked to neuronal and glial responses to brain injury. Indeed, inflammation in the brain has been associated with damage that stems from conditions as diverse as infection, multiple sclerosis, trauma, and excitotoxicity. In many of these brain injuries, disruption of the blood-brain barrier (BBB) may allow entry of blood-borne factors that contribute to, or serve as the basis of, brain inflammatory responses. Administration of trimethyltin (TMT) to the rat results in loss of hippocampal neurons and an ensuing gliosis without BBB compromise. We used the TMT damage model to discover the proinflammatory cytokines and chemokines that are expressed in response to neuronal injury. TMT caused pyramidal cell damage within 3 days and a substantial loss of these neurons by 21 days post dosing. Marked microglial activation and astrogliosis were evident over the same time period. The BBB remained intact despite the presence of multiple indicators of TMT-induced neuropathology. TMT caused large increases in whole hippocampal-derived monocyte chemoattractant protein (MCP)-1 mRNA (1,000%) by day 3 and in MCP-1 (300%) by day 7. The mRNA levels for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-6, cytokines normally expressed during the earliest stage of inflammation, were not increased up to 21 days post dosing. Lipopolysaccharide, used as a positive control, caused large inductions of cytokine mRNA in liver, as well as an increase in IL-1beta in hippocampus, but it did not result in the induction of astrogliosis. The data suggest that enhanced expression of the proinflammatory cytokines, TNF-alpha, IL-1beta and IL-6, is not required for neuronal and glial responses to injury and that MCP-1 may serve a signaling function in the damaged CNS that is distinct from its role in proinflammatory events.

Subcellular alteration of glyceraldehyde-3-phosphate dehydrogenase in Alzheimer's disease fibroblasts

The regulation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been implicated both in age-related neurodegenerative disease and in apoptosis. Previous in vitro studies suggest an interaction between GAPDH and the beta-amyloid precursor protein (beta-APP), a protein directly involved in Alzheimer's disease (AD). New studies indicate that GAPDH is a multidimensional protein with diverse membrane, cytoplasmic, and nuclear functions; each is distinct from its role in glycolysis. The nuclear functions of GAPDH include a role in apoptosis that requires its translocation to the nucleus. Accordingly, beta-APP-GAPDH interactions, altering GAPDH structure in vivo, may affect energy generation, inducing hypometabolism, a characteristic AD phenotype. Because GAPDH is a multifunctional protein, pleiotropic effects may also occur in a variety of fundamental cellular pathways in AD cells. This may include unique GAPDH-RNA interactions. We report here the identification of a high-molecular-weight (HMW) GAPDH species present exclusively in the postnuclear fraction of AD cells. The latter is characterized by reduced GAPDH activity. The HMW GAPDH species was not detected in postnuclear age-matched control (AMC) fractions nor in AD whole-cell preparations. Each is characterized by normal GAPDH activity. By definition, the preparation of whole-cell extracts entails the destruction of subcellular structure. The latter findings indicate that the dissociation of the GAPDH protein from the HMW species restores its enzymatic activity. Thus, these results reveal a new, unique intracellular phenotype in AD cells. The functional consequences of subcellular alteration in GAPDH structure in AD cells are considered.

Alteration of intracellular structure and function of glyceraldehyde-3-phosphate dehydrogenase: a common phenotype of neurodegenerative disorders?

Recent evidence reveals that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is not simply a classical glycolytic protein of little interest. Instead, it is a multifunctional protein with diverse cytoplasmic, membrane and nuclear activities. Significantly, each activity is separate and distinctfrom its role in energy production. Its nuclear activities include its emerging role in apoptosis especially in neuronal cells. GAPDH translocates into the nucleus during programmed cell death. Introduction of antisense GAPDH sequences reduces apoptosis and prevents its nuclear translocation. Independent analyses demonstrate that GAPDH may be involved in the cellular phenotype of age-related neurodegenerative disorders. GAPDH binds uniquely in vitro to the beta-amyloid precursor protein (betaAPP), to huntingtin as well as to other triplet repeat neuronal disorder proteins. In Parkinson's disease (PD) cells, immunofluorescent data suggests the co-l localization of GAPDH and alpha-synuclein in Lewy bodies. Drugs used to treat PD bind specifically to GAPDH. Our recent findings (Mazzola and Sirover, 2001) demonstrate a subcellular reduction in GAPDH glycolytic activity in Alzheimer's disease (AD) and in Huntington's disease (HD) cells. The latter may be due to intracellular alteration of GAPDH structure (Mazzola and Sirover 2002). We discuss the hypothesis that the intracellularformation of GAPDH: neuronal protein complexes may represent an emerging cellular phenotype of neurodegenerative disorders. The cytoplasmic binding of neuronal proteins to GAPDH could affect energy production. Nuclear interactions could affect its apoptotic activity. Other functions of this multidimensional protein may also be inhibited. Experimental paradigms to test this hypothesis are considered.

Carbohydrate handling enzymes in fetal Down syndrome brain

Impaired glucose metabolism in adult Down Syndrome (DS) has been well-documented in vivo and information on the underlying biochemical defect i.e. aberrant glucose handling enzymes is already available. Nothing is known on carbohydrate handling, however, in early life of DS patients, when no secondary phenomena as e.g. Alzheimer-like neuropathology occur in the brain yet. We therefore determined a series of key enzymes of carbohydrate metabolism in fetal control and DS brain during the early second trimenon. We used two-dimensional electrophoresis with subsequent MALDI characterization and specific software for quantification of protein spots. We observed comparable levels of phosphoglycerate mutase, phosphoglycerate kinase 1; fructose-biphosphate aldolase A, fructose bisphosphate aldolase C; ribose-phosphate pyrophosphokinase 1; D-phosphoglycerate dehydrogenase, 6-phosphogluconolactonase; aflatoxin B1 aldehyde reductase 1, aldose reductase; inosine-5'-monophosphate dehydrogenase 2; galactokinase, in brain of fetal controls and DS. We conclude that our biochemical findings point to the fact that DS patients start early life with unchanged glucose handling, pentose phosphate shunt, glycolysis, sugar aldehyde, guanine nucleotide- and ribonucleoside formation and galactose metabolism.

Alteration of gene expression in Down's syndrome (DS) brains: its significance in neurodegeneration

Several groups have reported pro-apoptotic alteration of gene expression in Down's syndrome (DS) brains. Aged DS brains manifest a similar neuropathology to Alzheimer's disease (AD), including the presence of senile plaques (SP) and neurofibrillary tangles (NFT). Although it is controversial if neurodegenerative processes play a pathological role in DS brains, evidence such as cortical neurons from fetal DS brains showing vulnerability to cell death when compared with neurons from control subjects supports this point of view. In this chapter, we review the reports that demonstrate pro-apoptotic alteration of gene expression in DS brains. In addition to the pathogenic genes on chromosome 21, such as amyloid precursor protein (APP) and CuZn-superoxide dismutase (SOD1), other genes which associate with p53, or with processes for protein folding have been frequently found.

Beta-amyloid precursor protein, ETS-2 and collagen alpha 1 (VI) chain precursor, encoded on chromosome 21, are not overexpressed in fetal Down syndrome: further evidence against gene dosage effect

Down syndrome (DS) is the most common human chromosomal abnormality caused by an extra copy of chromosome 21 and characterized clinically by somatic anomalies, mental retardation and precocious dementia. The phenotype of DS is thought to result from overexpression of a gene or genes located on the triplicated chromosome or chromosome region. Reports that challenge this notion, however, have been published. To add to this body of evidence, the expression of beta-amyloid precursor protein (APP), ETS-2 and collagen alpha1 (VI) chain precursor, encoded on chromosome 21, was investigated in fetal brain by western blot and two-dimensional electrophoresis (2-DE). Western blot detected APP and ETS-2 that migrated at approximately 75 and 50kDa, respectively. Subsequent densitometric analysis of APP and ETS-2 immunoreactivity did not produce any significant change between controls and DS. Since the metabolic fate of APP determines the propensity of amyloid beta production, the expression of the secreted forms of APP (sAPP) had been examined. Neither the expression of sAPPalpha nor sAPPbeta showed any detectable changes among the two groups. Collagen alpha1 (VI) chain precursor, a protein resolved as a single spot on 2D gel was identified by matrix associated laser desorption ionization mass spectroscopy. Quantitative analysis of this spot using the 2D Image Master software revealed a significant decrease in fetal DS (P < 0.01) compared to controls. Linear regression analysis did not show any correlation between protein levels and age. The current data suggest that overexpression per se can not fully explain the DS phenotype.

Differential expression of molecular chaperones in brain of patients with Down syndrome

Heat shock proteins (HSPs) in their molecular capacity as chaperones have been reported to regulate the apoptotic pathway and also play a critical role in protein conformational diseases such as Alzheimer's disease (AD). As all Down syndrome (DS) brains display AD-like neuropathology, neuronal loss in DS was shown to be mediated by apoptosis. We decided to investigate the expression patterns of HSPs in seven brain regions of adults with DS using two-dimensional polyacrylamide gel electrophoresis (2-DE). Following 2-DE, approximately 120 protein spots were successfully identified by matrix-assisted laser desorption/ionization--mass spectrometry (MALDI-MS) followed by quantification of the identified proteins. We unambiguously identified and quantified nine different chaperone proteins. Accordingly, all but three chaperone proteins did exhibit a significant change in expression. HSP 70 RY, heat shock cognate (HSC) 71 and glucose-regulated protein (GRP) 75 showed a significant decrease (P < 0.05) in DS temporal cortex whereas HSP 70.1 and GRP 78 were significantly increased (P<0.05) in cerebellum. Whilst T-complex 1 (TCP-1) epsilon subunit showed a significant decrease (P< 0.05) in parietal cortex, a similar extent of increase (P<0.05) as that observed in cerebellum was obtained in parietal levels of GRP 78. Alpha-crystallin B, HSP 60 and GRP 94 did not show any detectable changes in expression patterns. This report presents the first approach to quantify nine different chaperones simultaneously at the protein level in different brain regions and provides evidence for aberrant chaperone expression patterns in DS. The relevance of this aberrant expression patterns are discussed in relation to the biochemical and neuropathological abnormalities in DS brain.

Decreased brain levels of 2',3'-cyclic nucleotide-3'-phosphodiesterase in Down syndrome and Alzheimer's disease

In Down syndrome (DS) as well as in Alzheimer's disease (AD) oligodendroglial and myelin alterations have been reported. 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase) and carbonic anhydrase II (CA II) are widely accepted as markers for oligodendroglia and myelin. However, only data on CNPase activity have been available in AD and DS brains so far. In our study we determined the protein levels of CNPase and CA II in DS, AD and in control post mortem brain samples in order to assess oligodendroglia and myelin alterations in both diseases. We used two dimensional electrophoresis to separate brain proteins that were subsequently identified by matrix assisted laser desorption and ionization mass-spectroscopy (MALDI-MS). Seven brain areas were investigated (frontal, temporal, occipital and parietal cortex, cerebellum, thalamus and caudate nucleus). In comparison to control brains we detected significantly decreased CNPase protein levels in frontal and temporal cortex of DS patients. The level of CA II protein in DS was unchanged in comparison to controls. In AD brains levels of CNPase were decreased in frontal cortex only. The level of CA II in all brain areas in AD group was comparable to controls. Changes of CNPase protein levels in DS and AD are in agreement with the previous finding of decreased CNPase activity in DS and AD brain. They probably reflect decreased oligodendroglial density and/or reduced myelination. These can be secondary to disturbances in axon/oligodendroglial communication due to neuronal loss present in both diseases. Alternatively, reduced CNPase levels in DS brains may be caused by impairment of glucose metabolism and/or alterations of thyroid functions.

Changes in the brain protein levels following administration of kainic acid

Kainic acid (KA), a potent neurotoxin and excitatory amino acid, leads to derangements and modulation of brain proteins. No global brain protein expression pattern induced by KA-treatment has been reported yet. We therefore studied the effect of systemic KA administration on the levels of brain proteins. Rats were injected placebo or KA intraperitoneally and brain was taken after one week. The mitochondrial and cytosolic fractions of the brain proteins were analyzed by proteomics technologies and the levels of selected proteins were quantified using specific software. Heat shock protein HSP 27 was exclusively detected in brains of animals treated with KA, whereas the glucose regulated protein GRP 78 was downregulated. The levels of neurofilaments and alpha-internexin were significantly decreased and a fragment of tubulin alpha-1 chain was manifold increased in KA-brains. The mitochondrial enzymes dihydrolipoamide dehydrogenase, ATP synthase beta chain and isocitrate dehydrogenase were reduced and pyruvate kinase M1 was increased following KA treatment. We conclude that the concomitant determination of the brain proteins indicates altered regulation of heat shock proteins, neuronal death, cytoskeletal disruption, and mitochondrial derangement by systemic KA administration. This report confirms and extends previous studies on the effect of KA on the expression of brain proteins and suggests that our analytical system can serve as a model for neurotoxicological, neurobiological, and neuropathological proteome studies.

Glyceraldehyde-3-phosphate dehydrogenase in neurodegeneration and apoptosis signaling

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a well-studied glycolytic enzyme that plays a key role in energy metabolism. GAPDH catalyzes the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate in the glycolytic pathway. As part of the conversion, GAPDH converts NAD+ to the high-energy electron carrier NADH. GAPDH has been referred to as a "housekeeping" protein and based on the view that GAPDH gene expression remains constant under changing cellular conditions, the levels of GAPDH mRNA have frequently been used to normalize northern blots. In recent years, that view has changed since GAPDH is now known to contribute to a number of diverse cellular functions unrelated to glycolysis. Normative functions of GAPDH now include nuclear RNA export, DNA replication, DNA repair, exocytotic membrane fusion, cytoskeletal organization and phosphotransferase activity. Pathologically, GAPDH has been implicated in apoptosis, neurodegenerative disease, prostate cancer and viral pathogenesis (see Sirover (1999) for a recent review of GAPDH functions). Most recently, it has been shown that GAPDH is a target for deprenyl related compounds (Carlile et al., 2000; Kragten et al., 1998) and may contribute to the neuroprotection offered by those compounds.

Reduction of glyceraldehyde-3-phosphate dehydrogenase activity in Alzheimer's disease and in Huntington's disease fibroblasts

New functions have been identified for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) including its role in neurodegenerative disease and in apoptosis. GAPDH binds specifically to proteins implicated in the pathogenesis of a variety of neurodegenerative disorders including the beta-amyloid precursor protein and the huntingtin protein. However, the pathophysiological significance of such interactions is unknown. In accordance with published data, our initial results indicated there was no measurable difference in GAPDH glycolytic activity in crude whole-cell sonicates of Alzheimer's and Huntington's disease fibroblasts. However, subcellular-specific GAPDH-protein interactions resulting in diminution of GAPDH glycolytic activity may be disrupted or masked in whole-cell preparations. For that reason, we examined GAPDH glycolytic activity as well as GAPDH-protein distribution as a function of its subcellular localization in 12 separate cell strains. We now report evidence of an impairment of GAPDH glycolytic function in Alzheimer's and Huntington's disease subcellular fractions despite unchanged gene expression. In the postnuclear fraction, GAPDH was 27% less glycolytically active in Alzheimer's cells as compared with age-matched controls. In the nuclear fraction, deficits of 27% and 33% in GAPDH function were observed in Alzheimer's and Huntington's disease, respectively. This evidence supports a functional role for GAPDH in neurodegenerative diseases. The possibility is considered that GAPDH:neuronal protein interaction may affect its functional diversity including energy production and as well as its role in apoptosis.

Postmortem changes in the level of brain proteins

A systematic study on postmortem changes of brain proteins has not been performed so far and information is limited to basic principles of specific or nonspecific proteolysis or proteolysis of individual proteins. We studied protein level alterations in rat brain of animals kept at 23 degrees C for several postmortem times up to 72 h. Brain tissue protein extracts were analyzed by two-dimensional electrophoresis and the proteins with different levels were identified by matrix-assisted laser desorption ionization mass spectrometry. The changes observed mainly concerned structural proteins and enzymes. The levels of dihydropyrimidinase-related protein-2 decreased within 6 h and two new spots were detected representing shorter forms of the protein. Most of the other alterations appeared about 48 h postmortem. The most significant were reduced levels of neurofilament, alpha-internexin, synaptosomal-associated protein 25, glial fibrillary acidic protein, heat shock proteins, and dynamin-1; increased levels of 14-3-3 proteins and spectrin; and generation of shorter forms of certain proteins, such as tubulins, actin, and serum albumin. The results may be useful in neuropathology and brain protein studies.

Neuronal cell death in Down's syndrome

Down's syndrome (DS), occurring in 0.8 out of 1,000 live births, is a genetic disorder in which an extra portion of chromosome 21 leads to several abnormalities. With respect to the nervous system, it causes mental retardation. It is conceived that abnormal neuronal cell death in development is involved, but there is no direct evidence yet. In addition to developmental brain abnormalities, almost all DS brains over 40 years old manifest a similar pathology to Alzheimer's disease (AD), including the presence of senile plaques (SP) and neurofibrillary tangles (NFT). Although there was a debate to segregate dementia from underlying mental retardation, at least some portion of DS patients exhibit deteriorated mental status with aging. The mechanism underlying these abnormalities at the molecular level remains to be elucidated. Recently there have been several reports suggesting abnormalities reflecting increased risk to apoptosis in DS brains. Increased expression of several apoptosis-related genes (p53, fas, ratio of bax to bcl-2, GAPDH) in DS brains has been reported. Cultured neurons from both patients and model animals are reportedly more vulnerable to apoptosis. Overproduction of reactive oxygen species and its causative roles for increased apoptosis in DS tissues are suggested. One possible hypothesis is an increased susceptibility to apoptosis due to p53 overactivation in DS brains. A beta 42, a critical peptide for AD pathology from amyloid precursor protein (APP), can be detected in DS brains. A beta 42 is deposited in SP from an early stage, suggesting common molecular mechanisms in DS and AD. Animal models for DS are important in the search of molecular mechanisms. Several types of models are now available. Future DS studies are expected to integrate information from animal models and human tissues.

Differences in protein level between neonatal and adult brain

Age is a physiological condition that affects protein expression. We investigated differences in protein level between newborn and adult brains. Brain tissue extracts from male and female adult and neonatal rats were analyzed by two-dimensional gel electrophoresis. Gel comparison revealed the presence of many differences, of qualitative and quantitative nature, between a neonatal and adult brain. The most significant age-related difference concerned alpha-fetoprotein, which was detected in the brain of neonatal rats only. The levels of 22 proteins, including dihydropyrimidinase-related proteins 1,3, and 4 and 14-3-3 proteins, were higher in the neonatal brain, whereas the levels of 28 proteins, including dihydropyrimidinase-related protein 2, dynamin-1 and many enzymes were higher in the adult brain. We did not detect a consistent sex-related difference in the brain proteins. An inconsistency was observed in the location of the spot representing glial fibrillary acidic protein in the male brain.

Rat brain proteins: two-dimensional protein database and variations in the expression level

A two-dimensional database of rat brain proteins was constructed. Brain samples from newborn animals were analyzed by two-dimensional electrophoresis and the proteins were identified by matrix-assisted laser desorption/ionization mass spectrometry. The database comprises 210 different proteins, the majority of which are structural components, heat shock proteins and enzymes with various catalytic activities. Several minor differences in the expression level were detected, mainly of quantitative nature, which most likely represent allelic differences. The map may be useful in studies of neurological disorders in animal models of human diseases.

Enrichment of human brain proteins by heparin chromatography

Detection of low-abundance proteins is essential for the identification of novel drug targets by differential protein expression studies. We studied the enrichment of human fetal brain proteins by heparin chromatography. Total soluble brain proteins were fractionated on Heparin-Actigel and the fractions collected were analyzed by two-dimensional electrophoresis. The proteins were identified by matrix-assisted laser desorption ionization mass spectrometry. Approximately 300 protein spots were analyzed, representing 70 different polypeptides, 50 of which were bound to the heparin matrix. Eighteen brain proteins were identified for the first time. The proteins enriched by heparin chromatography include both minor and major components of the brain protein extract. The enriched proteins belong to several classes, including proteasome components, dihydropirimidinase-related proteins, T-complex protein 1 components and enzymes with various catalytic activities. The results include a two-dimensional map of the soluble brain proteins and a list of the proteins enriched by heparin chromatography. These may be useful in the design of protein purification protocols and in studies of neurological disorders.