Frameshift proteins in autosomal dominant forms of Alzheimer disease and other tauopathies

Frameshift (+1) proteins such as APP(+1) and UBB(+1) accumulate in sporadic cases of Alzheimer disease (AD) and in older subjects with Down syndrome (DS). We investigated whether these proteins also accumulate at an early stage of neuropathogenesis in young DS individuals without neuropathology and in early-onset familial forms of AD (FAD), as well as in other tauopathies, such as Pick disease (PiD) or progressive supranuclear palsy (PSP). APP(+1) is present in many neurons and beaded neurites in very young cases of DS, which suggests that it is axonally transported. In older DS patients (>37 years), a mixed pattern of APP(+1) immunoreactivity was observed in healthy looking neurons and neurites, dystrophic neurites, in association with neuritic plaques, as well as neurofibrillary tangles. UBB(+1) immunoreactivity was exclusively present in AD type of neuropathology. A similar pattern of APP(+1) and UBB(+1) immunoreactivity was also observed for FAD and much less explicit in nondemented controls after the age of 51 years. Furthermore, we observed accumulation of +1 proteins in other types of tauopathies, such as PiD, frontotemporal dementia, PSP and argyrophylic grain disease. These data suggest that accumulation of +1 proteins contributes to the early stages of dementia and plays a pathogenic role in a number of diseases that involve the accumulation of tau.

Differential expression of LMO4 protein in Alzheimer's disease

The molecular bases of late-onset and sporadic Alzheimer's disease (AD) still have to be unraveled. Among putative candidates for molecular variations in AD, we propose LMO4 protein, a transcription regulator, involved in multiple protein complexes. We investigated changes in LMO4 immunoreactivity in vulnerable brain regions of AD cases and controls of comparable age. Immunocytochemical analysis revealed a high level of LMO4 expression in the entorhinal cortex (EC) and in the CA1 hippocampal region of the control brains and a consistent decrease in the AD brains, correlated with the amount of neurofibrillary tangles (NFT) degenerating neurones and the severity of senile plaques deposition. The decrease in LMO4 immunoreactivity resulted both from weaker immunoreactive signals and from a loss of immunoreactive neurones. LMO4 immunocytochemical staining appeared not to be colocalized with NFT in a majority of neurones. Its expression was weak in the dentate gyrus and stronger in CA3-4, two regions with no or low numbers of NFT, but there was no decrease in AD compared to control cases. In the frontal cortex, the ventro-infero-median region (area 12) showed a greater LMO4 expression than the polar one (area 9), but no decrease in AD was observed. As LMO4 has been proposed to inhibit cellular differentiation, it can be hypothesized that a reduced expression is associated in EC and CA1 with attempts of diseased neurones to differentiate (e.g. compensatory neuritogenesis). Taken together, these data indicate that LMO4 protein is involved in the complexity of the disease phenotype, at least as a secondary factor.

Permanent cerebral ischemia induces sustained procaspase 9L increase not controlled by Bcl-2

We have investigated how transgenic overexpression of human Bcl-2 (Hu-Bcl-2) modifies cell death proteins activation in the long-term in a model of permanent cerebral ischemia induced by middle cerebral artery occlusion. Hu-Bcl-2, cytochrome c, caspases 9 and 3 expression were examined by immunoblotting and immunohistochemistry. In wild type mice, 1 day after middle cerebral artery occlusion, cytochrome c released from the mitochondria was detected. Middle cerebral artery occlusion induces a lasting activation of caspases in WT mice from day 3 post-injury. Increased level of caspase 3 is accompanied by a decrease in procaspase 3. In contrast, middle cerebral artery occlusion induced a sustained increase of procaspase 9L and a decrease in procaspase 9S concomitant to caspase 9 production. These events were observed in the operated but not in the unoperated hemisphere. Bcl-2 overexpression blocks cytochrome c release and delays caspases activation. Consequently procaspase 3 decrease was no more observed. However, Bcl-2 overexpression did not influence the middle cerebral artery occlusion-induced changes in procaspases 9 L and S. Fourteen days after middle cerebral artery occlusion the apoptotic cascade was no longer blocked in transgenic mice. Caspases 9 and 3 were increased, procaspase 3 was decreased but procaspase 9L and procaspase 9S remained increased and decreased respectively. Hu-Bcl-2 overexpression delays the activation of the cell death molecular machinery but does not control the ischemia-induced change in procaspase 9 L and S. Procaspase 9L increase is a potentially harmful event threatening cells of a rapid destruction when anti-apoptotic treatments by Bcl-2, or caspases inhibitors, are overrun.

Prevention of apoptotic neuronal death by controlling procaspases? A point of view

In various animal models of neurodegenerative diseases the long-lasting control of cell death by anti-apoptotic therapies is not successful. We present here our view on the control of procaspase expression in a model of cerebral stroke. We have investigated how Hu-Bcl-2 overexpression modifies cell death protein activation in a model of cerebral ischemia induced by permanent middle cerebral artery occlusion (MCAO). In wild type mice MCAO induced release of cytochrome c from the mitochondria, and activation of caspases 9 and 3. In parallel with caspases activation, procaspase 9 and procaspase 3 were, respectively, increased and decreased. In Hu-Bcl-2 transgenic mice cytochrome c release and caspases 9 and 3 activation were blocked. However procaspase 9 increased, like in wt mice, but procaspase 3 remained unchanged. By 2 weeks after MCAO caspases were no longer blocked in Hu-Bcl-2 transgenic mice. Procaspase 9 increase could represent a time bomb in Hu-Bcl-2 mice where caspase 9 activation is blocked. Indeed, cellular accumulation of procaspase 9 is a potentially harmful event able to overcome anti-apoptotic protection by Bcl-2 and threaten cells with rapid destruction. Through understanding of the upstream regulation of procaspase 9, early targets for the pharmacological control of apoptotic cell death may be revealed.

Altered apolipoprotein D expression in the brain of patients with Alzheimer disease

The etiology of late-onset Alzheimer disease is poorly understood. Predisposing factors such as the apolipoprotein E4 allele, as well as protective factors (e.g., antioxidants) have been proposed to play a role in the disease's process. A search for predisposing factors contributing to sporadic late-onset Alzheimer disease was initiated using the differential display technique. RNA expression profiles of the entorhinal cortex and the cerebellum of Alzheimer-diseased and normal patients were compared. The entorhinal cortex is the first brain region to accumulate neurofibrillary tangles during disease progression, whereas the cerebellum is spared. In the Alzheimer cases of this study, one signal showing preferential expression in the entorhinal cortex corresponded to the apolipoprotein D gene. This preferential expression might be genuine at the RNA level as suggested by the in situ hybridization method used. In addition, immunohistochemical experiments showed higher percentages of Apolipoprotein D reactive pyramidal neurons in the entorhinal cortex and region 1 of Ammon's horn in diseased patients. This increase correlated with the number of neurofibrillary tangles in Alzheimer as well as in normal patients. Colocalization of Apolipoprotein D proteins and neurofibrillary tangles in the same neuron was rare. Thus, these results suggest that in Alzheimer disease and aging, apolipoprotein D gene expression is increased in stressed cortical neurons before they possibly accumulate neurofibrillary tangles.

Familial frontotemporal dementia with ubiquitin inclusion bodies and without motor neuron disease

Frontotemporal dementia (FTD) is the second most common degenerative dementia after Alzheimer's disease and its Lewy body variant. Clinical pathology can be subdivided in three main neuropathological subtypes: frontal lobe dementia, Pick's disease and FTD with motor neuron disease (MND), all characterised by distinct histological features. Until recently the presence of ubiquitin-positive intraneuronal inclusions in the dentate gyrus, and the temporal and frontal cortex was usually associated with the MND type. Such inclusions were also observed in a few sporadic cases of FTD without or with parkinsonism (FTDP) in the absence of MND. We present here clinical, neuropathological and immunohistochemical data about a Swiss FTD family with FTDP-like features but without MND. Spongiosis and mild gliosis were observed in the grey matter. No neurofibrillary tangles, Pick bodies, Lewy bodies, senile plaques or prion-positive signals were present. However, ubiquitin-positive intracytoplasmic inclusions were detected in various structures but predominantly in the dentate gyrus. These observations support the existence of a familial form of FTDP with ubiquitin-positive intracytoplasmic inclusions (Swiss FTDP family).

Search for a mutation in the tau gene in a Swiss family with frontotemporal dementia

Frontotemporal dementia (FTD) is considered to have a heterogeneous aetiology. To date the tau gene located on chromosome 17 has been shown to be implicated in the pathogenesis of several FTD families with parkinsonism, the so called FTDP-17 families. The mutations reported so far are located within exons 9 to 13, a region coding for the microtubule-binding sites. They are causing various cytoskeletal disturbances. We are describing here the main clinical and neuropathological features of a Swiss FTD family with members presenting a FTDP-like clinical phenotype. However, if we except two silent polymorphic sites at position 227 and 255 in exon 9, neither a known FTDP-17 mutation nor a novel one was detected in this region of the tau gene. Thus, the existence of a yet unknown mechanism of neurodegeneration, other than via mutations near or within the microtubule-binding sites, or the exon 10 splice sites of the tau gene, has to be considered to explain dementia in this family. A mutation in another gene is still possible.

No detected mutations in the genes for the amyloid precursor protein and presenilins 1 and 2 in a swiss early-onset Alzheimer's disease family with a dominant mode of inheritance

Mutations have been found in more than a hundred early-onset families with Alzheimer's disease (AD) in the genes for the amyloid precursor protein, presenilin 1 and presenilin 2. The object of our investigation was to identify if these mutations or novel ones were operating in a Swiss early-onset AD family (mean age of onset: 53.3 years) with 7 members available, all neuropathologically confirmed. No known or new mutations were detected. Thus, our data support the existence of a yet unknown mutation, or other genes, contributing to familial early-onset AD. CopyrightCopyright 1999S.KargerAG,Basel

Differential distribution of presenilin-1, Bax, and Bcl-X(L) in Alzheimer's disease and frontotemporal dementia

We have previously reported that presenilin-1 (PS-1)-immunoreactive neurons survive in late-onset sporadic Alzheimer's disease (AD). To examine if this is also the case in other dementing conditions, and if it is associated with changes in the expression of the main apoptosis-related proteins, a quantitative immunocytochemical study of presenilin-1, Bax, and Bcl-X(L) in the cerebral cortex of non-demented and AD patients, and patients with frontotemporal dementia (FTD) was performed. In non-demented cases, the frequency of neurons showing PS-1 immunoreactivity was 25-60%, Bax immunoreactivity 36-54%, and Bcl-X(L) immunoreactivity 26-63% depending on the cortical area. The frequency of NFT-free neurons which contained PS-1 or Bax was consistently increased in all of the areas in AD. In FTD cases, the percentage of PS-I-, but not Bax-immunoreactive neurons was increased only in areas displaying a substantial neuronal loss. Conversely, there was no difference in the densities of Bcl-X(L)-containing neurons among the three diagnosis groups. These data suggest that surviving neurons in affected cortical areas in AD show a high expression of PS-1 and Bax, indicating that these proteins play a key role in the mechanisms of cell death in this disorder. In FTD, neurons containing PS-1 are preserved, further supporting a neuroprotective role for this protein in other neurodegenerative disorders.

Expression of leptin receptor mRNA (long form splice variant) in the human cerebellum

Primers specific to the long isoform of leptin receptor (OB-Rb) mRNA were used in reverse transcriptase-linked polymerase chain reactions (RT-PCR) to investigate the expression of this receptor in the hypothalamus and cerebellum of human and rat. For both regions, we observed RT-PCR cDNAs as well as restriction enzyme cleavage fragments of expected sizes. Additionally, in situ hybridization of human cerebellum using two independent [35S]oligonucleotide probes complementary to the OB-Rb mRNA sequence revealed a prominent hybridization signal within the granular layer. Overall, our findings demonstrate the expression of OB-Rb mRNA in the cerebellum and suggest that in such a location, leptin receptors may mediate a function presumably not linked to body weight homeostasis.

Developmental expression of the murine Mobp gene

In this report we describe the developmental expression of the murine (Mobp) gene encoding myelin-associated oligodendrocytic basic protein. We have characterized three Mobp cDNA clones which have been used as probes. Murine Mobp splice variant-1 (mmsv-1), a portion of 3' untranslated region (UTR), is homologous to 3' UTR sequences found in the rat Mobp splice variants rOP1, Mobp81-A and Mobp-99. The mmsv-2 sequence, encoding 81 amino acids, closely resembles the rat Mobp81-A splice variant. The mmsv-3 cDNA, encoding 170 amino acids corresponding closely to the rat rOPRP1 splice variant, detects a single mRNA species present in low levels from E12 onward, suggesting this MOBP may have a function alternative or additional to involvement in myelin formation. The mmsv-1 probe detects an mRNA species abundantly expressed in the postnatal central nervous system (CNS) but barely detectable at E18. This mRNA is located initially in the cell bodies of oligodendrocytes, moving distally into their processes as myelination proceeds. The most abundant mmsv(s) in the adult CNS are present at detectable levels after expression of the myelin basic protein (Mbp) gene and marginally after or coincident with the proteolipid protein (Plp) gene. The level of the abundant, late-expressed mRNA correlates closely with the capacity to form myelin and the maturity of oligodendrocytes, as shown in two hypomyelinated mutants, rumpshaker and jimpy, which represent mildly and severely affected phenotypes, respectively.

A method for the extraction of genomic DNA from human brain tissue fixed and stored in formalin for many years

We report a method providing access to high molecular weight, polymerase chain reaction (PCR)-amplifiable genomic DNA from brains stored in formalin for many years. It consists mainly of an intensive proteinase K treatment of ground tissue previously embedded in agarose plugs, followed by a washing and an elution step. The method was tested on brains fixed and stored in formalin for up to 46 years. All extracted DNA show an identical pattern of degradation ranging from well-preserved (more than 20 kb) to 400-bp-long fragments. This was demonstrated for DNA extracted from the cerebellums of elderly psychiatric and geriatric patients (of more than 60 years of age), male and female, demented or not, with postmortem delays longer than 1 h and shorter than 1 day. In all these cases PCR amplification of a 838-bp-long beta-actin product was successfully performed when proteinase K treatment was sufficiently effective to generate pure DNA. Thus, high molecular weight, PCR-amplifiable genomic DNA can be extracted from brains stored in formalin for almost half a century.

Sequence analysis of 497 mouse brain ESTs expressed in the substantia nigra

The use of subtracted, region-specific cDNA libraries combined with single-pass cDNA sequencing allows the discovery of novel genes and facilitates molecular description of the tissue or region involved. We report the sequence of 497 mouse expressed sequence tags (ESTs) from two subtracted libraries enriched for cDNAs expressed in the substantia nigra, a brain region with important roles in movement control and Parkinson disease. Of these, 238 ESTs give no database matches and therefore derive from novel genes. A further 115 ESTs show sequence similarity to ESTs from other organisms, which themselves do not yield any significant database matches to genes of known function. Fifty-six ESTs show sequence similarity to previously identified genes whose mouse homologues have not been reported. The total number of ESTs reported that are new for the mouse is 407, which, together with the 90 ESTs corresponding to known mouse genes or cDNAs, contributes to the molecular description of the substantia nigra.

Discovering genes with localised expression in the mouse brain: cDNAs specific to the substantia nigra

Many important phenomena of normal brain physiology and disease are likely to be related to the function of genes expressed in localised regions of the brain. We show that subtracted libraries enriched in clones corresponding to rare mRNAs, which must include genes with very localised and neuron-specific expression, can easily be produced from single-stranded directional cDNA libraries after hybridization to excess photobiotinylated opposite-stranded cDNA (or RNA) from another brain region, followed by the removal of biotinylated molecules. We also demonstrate the use of heterologous probes from anatomically precise small regions of bovine brain to identify cDNA clones that putatively represent mRNAs present at significantly higher levels in a substantia nigra mRNA population enriched for pars compacta mRNA than in the total ventral midbrain or cerebellar mRNA population. Some of these cDNAs may identify genes that play important roles in the specific molecular biology of dopaminergic neurons, including susceptibility to Parkinson's disease.

Cloning and sequencing of a murine cDNA encoding the proteasome component C5

A cDNA encoding the mouse homologue to the rat and human component C5 of proteasome was isolated from a mouse ventral midbrain library. The deduced amino acid sequence shows 93% and 97.5% identity to the human and rat C5 component respectively.

Enhanced access to rare brain cDNAs by prescreening libraries: 207 new mouse brain ESTs

To use single-pass cDNA sequencing to characterize low-frequency cDNA clones from a region of the brain that includes the primary site of neurodegeneration in human Parkinson disease, we have developed a prescreening procedure using single brain region first-strand cDNA probes. Selection of cDNA clones giving low hybridization signals allowed the elimination of clones resulting from abundant messages and enrichment for clones corresponding to low-copy messages. Comparative sequencing of standard and prescreened cDNA libraries (191 and 124 clones, respectively) showed that this procedure raised the frequency of novel sequences encountered from 54 to 81%. The increased proportion of novel ESTs justifies the labor of prescreening. Automation of this procedure will accelerate the molecular description of genes expressed in any brain region, or any tissue, and represents a way to maximize access to cDNA sequences for human and mouse genome characterization. In total, the comparative sequencing experiments generated 207 new mouse and 11 new rat brain ESTs.

Reverse genetics of the mouse central nervous system: targeted genetic analysis of neuropeptide function and reverse genetic screens for genes involved in human neurodegenerative disease

The development of gene targeting technology in mouse embryonic stem cells allows reverse genetics to be used to investigate the function of any cloned gene in the developing and adult brain. Promoter-trap, replacement and insertion vector strategies can be used to generate defined mutations in the chromosomal copy of a cloned gene in embryonic stem cells. These cells can be used to make chimaeric mice, some of which transmit the in vitro mutation via the germline to transgenic offspring. The phenotype of complete loss-of-function mutations (gene knock-outs) can be studied at molecular, cell biological, neurophysiological and behavioural levels, and allows inferences about gene function to be made. Precise small mutations can also be made using integrative vector or two-step replacement vector strategies, allowing specific questions to be asked about regulation and protein structure-function relationships. Reverse genetics can therefore be used as an alternative or additional approach to pharmacology for the study of molecular functions in the central nervous system. Reverse genetic studies of the involvement of particular molecules in neurological disease syndromes may be superior to pharmacological studies to the extent that the syndrome is determined by genetic predisposition. The general ways in which reverse genetics of the mouse can be used to ask questions about molecules in the central nervous system are illustrated by examples from ongoing work of this laboratory. Neuropeptides are an important class of transmitters in the brain, but only in very few cases have specific CNS functions been assigned to a particular neuropeptide. Targeted mutation of neuropeptide precursor and receptor genes offers a rapid way to learn about neuropeptide function. Complete loss-of-function mutations will provide information on any developmental roles of a neuropeptide and on overall behavioural and physiological effects of loss-of-function. More specific targeted mutations allow dissection of the individual roles of multiple neuropeptides that derive from a common precursor protein, and allow in vivo studies of the functional importance of particular amino acids. Experimental progress towards targeted mutation of the neurotensin receptor is described as an example. Recent technological improvements makes targeted mutation of a number of genes possible. This allows reverse genetic screening to be undertaken for genes involved in particular neurobiological phenomena: genes are identified on the basis of molecular criteria (e.g. expression pattern), and gene-targeting used to check their relevance to a phenotype. Neurodegenerative disease is an important aspect of the human phenotype.(ABSTRACT TRUNCATED AT 400 WORDS)

Pseudomonas aeruginosa promoters which contain a conserved GG-N10-GC motif but appear to be RpoN-independent

The proC gene of Pseudomonas aeruginosa encodes the constitutive delta 1-pyrroline 5-carboxylate reductase (the third enzyme of proline biosynthesis) and ranks among the numerous Pseudomonas genes which are poorly transcribed in Escherichia coli. The promoters of the proC gene were located by deletion mapping. The 5' ends of the proC transcripts originating from one promoter were determined by primer extension. This promoter has a GG-N10-GC motif with a 16 bp spacing between the GC doublet and the transcription start site. Such spacing is unusually long for sigma 54-dependent promoters. In rpoN mutants of P. aeruginosa and P. putida a proC'--'lacZ fusion was expressed at wild-type levels, suggesting that sigma 54 RNA polymerase is not involved in proC transcription. The expression of another P. aeruginosa gene, anr (for anaerobic regulation of nitrate respiration and anaerobic arginine degradation), also appeared to be independent of RpoN in Pseudomonas and occurred at a very low level in E. coli. The proC and anr promoters have sequence similarities in addition to the conserved GG--N10--GC motif and may also be related to some alg (alginate) promoters of P. aeruginosa. We propose that the proC and anr promoters are activated by proteins, including perhaps an alternative sigma factor, which are present in Pseudomonas but absent from E. coli.

Comparison of proC and other housekeeping genes of Pseudomonas aeruginosa with their counterparts in Escherichia coli

In a comparative study of housekeeping genes of Pseudomonas aeruginosa and Escherichia coli, the nucleotide sequence of a proline biosynthetic gene, proC, of P. aeruginosa has been determined. The subunit molecular mass (approximately 29 kDa) and the N-terminal amino acid sequence of purified delta 1-pyrroline 5-carboxylate reductase, the proC gene product, were in agreement with the proC nucleotide sequence. A survey of pairs of isofunctional genes from P. aeruginosa and E. coli reveals that within each pair, translated genes (including proC) have diverged more strongly than have untranslated genes specifying ribosomal or transfer RNAs. The translated genes, but not the untranslated ones, have a G + C content that is typical of the respective genomic G + C contents.

Genetic structure, function and regulation of the transposable element IS21

The IncP plasmid R68.45 and other plasmids carrying tandem repeats of the insertion sequence IS21 [= (IS21)2] produce replicon fusions via transposition at high frequencies in Escherichia coli and other gram-negative bacteria, whereas plasmids with a single IS21 copy, e.g. R68, give replicon fusions rarely. The 2131 bp nucleotide sequence of IS21 was determined; at the ends there were 11 bp inverted repeats with one mismatch. Two adjacent open reading frames, istA and istB, were located on one DNA strand of IS21. In E. coli maxicells, polypeptides of 46 kDa (the istA gene product) and 30 kDa (the istB gene product) were expressed by (IS21)2 plasmids, but not by IS21 plasmids. Genetic analysis of (IS21)2 plasmids indicates that the IS21-IS21 junctions form a promoter, which initiates transcription of the istAB operon in one of the two IS21 elements. A single IS21 element fused to an inducible external tac promoter expressed both proteins after induction, but did not promote effective replicon fusion, unless an IS21-IS21 junction (the preferred site for IS21 transposase action) was also present on the plasmid carrying the tac-IS21 construct. The sequences located between the IS21 elements in (IS21)2, 3 bp in R68.45 or 2 bp in pME28, were not recovered in the replicon fusion products. Homologous recombination between the directly oriented IS21 elements in the fusion products led to plasmids with a single IS21 insertion. Analysis of the latter showed that IS21 had a low, but not totally random specificity of insertion and created target duplications of 4 bp (occasionally 5 bp).(ABSTRACT TRUNCATED AT 250 WORDS)