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Characterizing CGI-94 (comparative gene identification-94) which is down-regulated in the hippocampus of early stage Alzheimer's disease brain.

The treatment of Alzheimer's disease (AD) remains a major challenge because of the incomplete understanding of the triggering events that lead to the selective neurodegeneration characteristic of AD brains. Here we describe a new protein, CGI-94, that is down-regulated at the mRNA level in the hippocampus of early stage AD brain. Transfection experiments with CGI-94 as a green fluorescent protein (GFP)-fusion-protein show that this protein is translocated into the nucleus of the cell. The finding that this protein, which has a bipartite nuclear localization signal, is also observed in the cytoplasm and extracellular space points to a multifunctional protein. Immunohistochemical analyses reveal that CGI-94 is mainly expressed in neurons of the hippocampal formation and the cortex but not in the cerebellar nucleus. In conclusion, the expression of the nucleolar phosphoprotein CGI-94 appears to be disturbed in early processes of neuronal degeneration.

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Elevated levels of an exocrine pancreatic secretory protein in Alzheimer disease brain.

We identified by a monoclonal antibody-based immunoradiometric assay high concentrations of an exocrine pancreatic protein called pancreatic thread protein (PTP) in several areas of Alzheimer disease (AD) brain. The saline-extractable soluble immunoreactivity shares at least three epitopes in common with the native pancreatic form of the protein; the Mr varies from approximately 17,000 to 20,000. Quantitative measurements of PTP immunoreactivity in various regions of several AD brains revealed levels varying from 12 to 295 ng/g of tissue (mean, 116 ng/g) compared with 1-11 ng/g of tissue (mean, 5 ng/g) found in comparable areas of control brains. Immunocytochemistry performed with the anti-PTP monoclonal antibodies demonstrate PTP immunoreactivity within large pyramidal neurons--many of which contain neurofibrillary tangles in both AD and Down syndrome. Less accumulation was observed in astrocytes, and some PTP immunoreactivity was found extracellularly. The highest number of labeled cells in AD and Down syndrome was seen in the hippocampal formation. Fewer positive-staining cells were noted in normal and disease control brains. We conclude, therefore, that an exocrine pancreatic protein is present in the central nervous system of normal individuals at low levels; in AD brain concentrations of this protein are much higher.

Alzheimer Disease↗

Metallothionein (MT)-III: generation of polyclonal antibodies, comparison with MT-I+II in the freeze lesioned rat brain and in a bioassay with astrocytes, and analysis of Alzheimer's disease brains.

Metallothionein-III is a low molecular weight, heavy-metal binding protein expressed mainly in the central nervous system. First identified as a growth inhibitory factor (GIF) of rat cortical neurons in vitro, it has subsequently been shown to be a member of the metallothionein (MT) gene family and renamed as MT-III. In this study we have raised polyclonal antibodies in rabbits against recombinant rat MT-III (rMT-III). The sera obtained reacted specifically against recombinant zinc-and cadmium-saturated rMT-III, and did not cross-react with native rat MT-I and MT-II purified from the liver of zinc injected rats. The specificity of the antibody was also demonstrated in immunocytochemical studies by the elimination of the immunostaining by preincubation of the antibody with brain (but not liver) extracts, and by the results obtained in MT-III null mice. The antibody was used to characterize the putative differences between the rat brain MT isoforms, namely MT-I+II and MT-III, in the freeze lesion model of brain damage, and for developing an ELISA for MT-III suitable for brain samples. In the normal rat brain, MT-III was mostly present primarily in astrocytes. However, lectin staining indicated that MT-III immunoreactivity was also present in microglia, monocytes and/or macrophages in the leptomeninges and lying adjacent to major vessels. In freeze lesioned rats, both MT-I+II and MT-III immunoreactivities increased in the ipsilateral cortex. The pattern of MT-III immunoreactivity significantly differed from that of MT-I+II, since the latter was evident in both the vicinity of the lesioned tissue and deeper cortical layers, whereas that of the former was located only in the deeper cortical layers. This suggests different roles for these MT isoforms, and indeed in a new bioassay measuring astrocyte migration in vitro, rMT-III promoted migration to a higher extent than MT-I+II. Thus, MT-III could not only affect neuronal sprouting as previously suggested, but also astrocyte function. Finally, MT-III protein levels of patients with Alzheimer's disease (AD) were, if anything, increased when compared with similarly aged control brains, which was in agreement with the significantly increased MT-III mRNA levels of AD brains.

Alzheimer Disease↗

Characterization of an O-glycosylated plaque-associated protein from Alzheimer disease brain.

In this work we characterized a 90-kDa glycoprotein from Alzheimer disease (9OAzgp) brain extracts that is recognized by the GalNAc-specific lectin from Amaranthus leucocarpus (ALL), as determined through Western blot. The 90Azgp was purified by electro-elution, and its amino acid sequence determined from peptides obtained after trypsin digestion through MALDI-TOF (Matrix-assisted laser desorption ionization-time of flight), and compared with the relative values obtained from the NCBInr (Swiss-Prot 10/01/2001) database. The 90Azgp showed 32% and 42% homology with the KIAA0310 protein from human brain and the human gastric mucin, respectively. Presence of O-glycosidically linked glycans in the proteins recognized by ALL was confirmed by inhibition of the lectin-glycoprotein interaction through hapten-inhibition assays and also by elimination of the O-glycosidically linked glycans after treatment with O-glycanase from Diplococcus pneumoniae. Electron transmission microscopy confirmed that the receptor recognized by the lectin is processed in the Golgi apparatus of AD neurons. Although the specific role of this glycoprotein has not been identified, considering that the presence of this lectin receptor co-localized with neuritic plaques and in AD sprouting neurons, it could suggest that the O-glycosyl-protein identified by the A. leucocarpus lectin participates in the pathogenesis of neurodegenerative diseases.

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Selenium and selenoproteins in the brain and brain diseases.

Over the past three decades, selenium has been intensively investigated as an antioxidant trace element. It is widely distributed throughout the body, but is particularly well maintained in the brain, even upon prolonged dietary selenium deficiency. Changes in selenium concentration in blood and brain have been reported in Alzheimer's disease and brain tumors. The functions of selenium are believed to be carried out by selenoproteins, in which selenium is specifically incorporated as the amino acid, selenocysteine. Several selenoproteins are expressed in brain, but many questions remain about their roles in neuronal function. Glutathione peroxidase has been localized in glial cells, and its expression is increased surrounding the damaged area in Parkinson's disease and occlusive cerebrovascular disease, consistent with its protective role against oxidative damage. Selenoprotein P has been reported to possess antioxidant activities and the ability to promote neuronal cell survival. Recent studies in cell culture and gene knockout models support a function for selenoprotein P in delivery of selenium to the brain. mRNAs for other selenoproteins, including selenoprotein W, thioredoxin reductases, 15-kDa selenoprotein and type 2 iodothyronine deiodinase, are also detected in the brain. Future research directions will surely unravel the important functions of this class of proteins in the brain.

Animals↗

Activation of caspase-8 in the Alzheimer's disease brain.

Recent studies support the activation of apoptotic pathways in the Alzheimer's disease (AD) brain. Neurons committed to apoptosis may do so by either activation of a receptor-mediated pathway employing caspase-8 or through an alternative mitochondrial pathway involving oxidative stress. In the present study, the role of caspase-8 in the AD brain was examined by designing a caspase-cleavage site-directed antibody to one of the active fragments of caspase-8. In vitro analysis with this antibody, termed CASP-8p18, demonstrated that it recognized the active 18-kDa fragment of caspase-8 but not the precursor protein. In vivo immunohistochemical analysis using hippocampal tissue sections from AD or aged-matched control brains demonstrated CASP-8p18 immunolabeling of neurons in all AD cases, whereas little staining was observed in controls. These results were confirmed using a commercially available antibody that, like the CASP-8p18 antibody reacts only with the 18-kDa fragment of caspase-8 and not full-length caspase-8. As with CASP-8p18 antibody, the commercial antibody-labeled neurons in all AD cases, while showing a relative paucity of staining in representative control cases. Labeling of CASP-8p18 within tangle-bearing neurons was observed in double-labeling studies with AT8 or PHF-1, both markers for neurofibrillary tangles (NFTs). In addition, using a caspase-cleavage site-directed antibody that recognizes cleavage products of caspase-3 showed colocalization of this antibody with the CASP-8p18 antibody within NFTs. These results suggest a role for caspase-8 and the receptor-mediated apoptotic pathway as a mechanism leading to the activation of caspase-3 within neurons of the AD brain.

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