Armand Savioz

Differential Changes in Synaptic Proteins in the Alzheimer Frontal Cortex with Marked Increase in PSD-95 Postsynaptic Protein

We investigated how synaptic plasticity is related to the neurodegeneration process in the human dorsolateral prefrontal cortex. Pre- and postsynaptic proteins of Brodmanns area 9 from patients with Alzheimers disease (AD) and age-matched controls were quantified by immunohistochemical methods and Western blots. The main finding was a significant increase in the expression of postsynaptic density protein PSD-95 in AD brains, revealed on both sections and immunoblots, while the expression of spinophilin, associated to spines, remained quantitatively unchanged despite qualitative changes with age and disease. Presynaptic protein alpha-synuclein indicated an increased immunohistochemical level, while synaptophysin remained unchanged. MAP2, a somatodendritic microtubule protein, as well as AD markers such as amyloid-beta protein and phosphorylated protein tau showed an increased expression on immunosections in AD. Altogether these changes suggest neuritic and synaptic reorganization in the process of AD. In particular, the significant increase in PSD-95 expression suggests a change in NMDA receptors trafficking and may represent a novel marker of functional significance for the disease.

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 diseases 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 Ammons 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. J. Neurosci. Res. 64:61–69, 2001.

Postsynaptic density protein PSD-95 expression in Alzheimer's disease and okadaic acid induced neuritic retraction

In order to understand how plasticity is related to neurodegeneration, we studied synaptic proteins with quantitative immunohistochemistry in the entorhinal cortex from Alzheimer patients and age-matched controls. We observed a significant decrease in presynaptic synaptophysin and an increase in postsynaptic density protein PSD-95, positively correlated with beta amyloid and phosphorylated Tau proteins in Alzheimer cases. Furthermore, Alzheimer-like neuritic retraction was generated in okadaic acid (OA) treated SH-SY5Y neuroblastoma cells with no decrease in PSD-95 expression. However, in a SH-SY5Y clone with decreased expression of transcription regulator LMO4 (as observed in Alzheimers disease) and increased neuritic length, PSD-95 expression was enhanced but did not change with OA treatment. Therefore, increased PSD-95 immunoreactivity in the entorhinal cortex might result from compensatory mechanisms, as in the SH-SY5Y clone, whereas increased Alzheimer-like Tau phosphorylation is not related to PSD-95 expression, as suggested by the OA-treated cell models.

Contribution of neural networks to Alzheimer disease's progression

The neuropathology of Alzheimer disease is characterized by senile plaques, neurofibrillary tangles and cell death. These hallmarks develop according to the differential vulnerability of brain networks, senile plaques accumulating preferentially in the associative cortical areas and neurofibrillary tangles in the entorhinal cortex and the hippocampus. We suggest that the main aetiological hypotheses such as the beta-amyloid cascade hypothesis or its variant, the synaptic beta-amyloid hypothesis, will have to consider neural networks not just as targets of degenerative processes but also as contributors of the diseases progression and of its phenotype. Three domains of research are highlighted in this review. First, the cerebral reserve and the redundancy of the networks elements are related to brain vulnerability. Indeed, an enriched environment appears to increase the cerebral reserve as well as the threshold of diseases onset. Second, diseases progression and memory performance cannot be explained by synaptic or neuronal loss only, but also by the presence of compensatory mechanisms, such as synaptic scaling, at the microcircuit level. Third, some phenotypes of Alzheimer disease, such as hallucinations, appear to be related to progressive dysfunction of neural networks as a result, for instance, of a decreased signal to noise ratio, involving a diminished activity of the cholinergic system. Overall, converging results from studies of biological as well as artificial neural networks lead to the conclusion that changes in neural networks contribute strongly to Alzheimer diseases progression.

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.

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 transcriptaselinked 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.

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

Abstract 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).

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

Abstract 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-XL 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-XL 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-1-, 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-XL-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.

A framework to understand the variations of PSD-95 expression in brain aging and in Alzheimer's disease

The postsynaptic density protein PSD-95 is a major element of synapses. PSD-95 is involved in aging, Alzheimers disease (AD) and numerous psychiatric disorders. However, contradictory data about PSD-95 expression in aging and AD have been reported. Indeed in AD versus control brains PSD-95 varies according to regions, increasing in the frontal cortex, at least in a primary stage, and decreasing in the temporal cortex. In contrast, in transgenic mouse models of aging and AD PSD-95 expression is decreased, in behaviorally aged impaired versus unimpaired rodents it can decrease or increase and finally, it is increased in rodents grown in enriched environments. Different factors explain these contradictory results in both animals and humans, among others concomitant psychiatric endophenotypes, such as depression. The possible involvement of PSD-95 in reactive and/or compensatory mechanisms during AD progression is underscored, at least before the occurrence of important synaptic elimination. Thus, in AD but not in AD transgenic mice, enhanced expression might precede the diminution commonly observed in advanced aging. A two-compartments cell model, separating events taking place in cell bodies and synapses, is presented. Overall these data suggest that AD research will progress by untangling pathological from protective events, a prerequisite for effective therapeutic strategies.

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

Abstract 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 β-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.