Microsphere embolism-induced cortical cholinergic deafferentation and impairments in attentional performance

Ischemic events have been hypothesized to play a critical role on the pathogenesis of dementia and the acceleration of cognitive impairments. This experiment was designed to determine the consequences of microvascular ischemia on the cortical cholinergic input system and associated attention capacities. Injections of microspheres ( approximately 50 microm diameter; approximately 5000 microspheres/100 microL) into the right common carotid artery of rats served as a model of microvascular ischemia and resulted in decreases in the density of cholinergic fibers in the ipsilateral medial prefrontal cortex and frontoparietal areas. Furthermore, dense astrogliosis, indicated by glial fibrillary acidic protein (GFAP) immunohistochemistry, was observed in the globus pallidus, including the areas of origin of cholinergic projections to the cortex. Fluoro-Jade B staining indicated that loss of neurons in the cortex was restricted to areas of microsphere-induced infarcts. Attentional performance was assessed using an operant sustained attention task; performance in this task was previously demonstrated to reflect the integrity and activity of the cortical cholinergic input system. Embolized animals' performance was characterized by a decrease in the animals' ability to detect signals. Their performance in non-signal trials remained unaffected. The residual density of cholinergic axons in prefrontal and frontoparietal areas correlated with the animals' performance. The present data support the hypothesis that microvascular ischemia results in loss of cortical cholinergic inputs and impairs associated attentional performance. Microsphere embolism represents a useful animal model for studying the role of interactions between microvascular disorder and impaired forebrain cholinergic neurotransmission in the manifestation of cognitive impairments.

Deciphering cryptic proteases

Proteases are deeply involved in physiology and pathology. For most, the mechanism is well defined but several fail to display typical protease features (as is the case of the four proteases contained in fibronectin, the inhibitor-resistant mesotrypsin and the proteosomal deubiquitinating enzyme) or have unclear physiological function (such as calpain-like proteins, transthyretin and factor seven activating protease). In other cases, such as in peroxisomal processing proteases, although substrates are defined, the enzyme remains undiscovered. Furthermore, several proteases were identified in pathological conditions, namely secretases in Alzheimer's disease and gross cystic disease fluid protein 15 kDa in breast cancer, when most likely their physiological substrate is still hidden. Lastly, the evolutionary conservation of proteolytic enzymes raises questions related to the origin of biological events, such as the origin of cystein proteases and cell death responses. In this review we will discuss the above cryptic enzymes, as they will probably be relevant in the future.

Executive function deficits in early Alzheimer's disease and their relations with episodic memory

Previous research suggests that patients with Alzheimer's disease (AD) are impaired on executive function early in the course of disease, but negative findings were reported. To evaluate the performance on executive tasks in early AD and to determine the involvement of memory on the outcome of executive tasks. Thirty-six AD patients were divided into two subgroups on the basis of the MMSE: very mild and mild. The comparison with 17 normal controls shows that very mild AD patients had deficits on visuospatial short-term memory, episodic memory, flexibility and self-monitoring abilities, concept formation and reasoning. The mild AD patients showed additional deficits on the Similarities test. Episodic memory and executive deficits occur in the very early stage of AD and precede impairment in constructional praxis, language and sustained attention. With the progression of the disease, additional deficit is observed in abstract thinking. In mild AD, memory failure is also related to executive impairment.

A whole brain MR spectroscopy study from patients with Alzheimer's disease and mild cognitive impairment

Brain damage in Alzheimer's disease (AD) and mild cognitive impairment (MCI) is widespread with involvement of large portions of the neocortex and the subcortical white matter. A quantitative measure of neuronal damage of the entire brain might be valuable in the context of large-scale, longitudinal studies of these patients. This study investigated the extent of neuroaxonal injury of patients with AD and MCI using a novel unlocalized proton magnetic resonance spectroscopy ((1)H-MRS) technique, which allows quantification of the concentration of N-acetylaspartate from the whole of the brain tissue (WBNAA). Conventional brain MRI and WBNAA were obtained from 28 AD patients, 27 MCI patients and 25 age-matched controls. Normalized brain volume (NBV) was also measured using an automated segmentation technique. WBNAA and NBV showed a significant heterogeneity between groups (P < 0.001). WBNAA concentration was different between controls and MCI patients (P = 0.003), but not between MCI and AD patients (P = 0.33). NBV differed both between controls and MCI patients (P = 0.02) and between MCI and AD patients (P = 0.03). A multivariate regression model retained WBNAA as the best MRI predictor of the Mini Mental State Examination score (P = 0.001). Significant neuronal damage, which is related to the extent of cognitive decline, can be quantified in the whole brain tissue of patients with AD, using a novel (1)H-MRS approach. The demonstration in patients with MCI of MR structural and metabolic findings, intermediate between those of healthy volunteers and those of AD patients, indicates that neuronal damage is already evident and widespread in individuals with MCI before they are clinically demented.

[Alzheimer's disease versus vascular dementia -- dichotomy or interaction?]

Alzheimer's dementia (AD) and vascular dementia (VD) are the two major forms of dementia in the elderly. They have been separated categorically on the basis of pathophysiological findings and clinical operationalized criteria. However, this strict separation has to be reevaluated in the light of recent data. The risk to develop a neurodegenerative dementia in old age is determined by various susceptibility genes and correlated with aging. In AD, the current understanding of pathophysiology focuses on the amyloid cascade hypothesis as the major endpoint of the complex cellular pathology. In VD, incomplete microangiopathic infarcts due to fibrohyalinosis are regarded as the major pathophysiological event. A controversial discussion exists about the coincidence or interaction of genetically determined risk factors of AD and/or VD. Further interactions between AD and VD exist with regard to perivascular mediators and those factors which impair cerebral blood flow. Based on these and other recent neuropathological and therapeutic findings the hypothesis is proposed that the two specific etiopathologies of AD and VD interact to precipitate clinical dementia in the individual and that the individual phenomenology of these dementias is modified by vascular risk factors. Neither, a categorical separation of AD and VD nor the recent idea to regard AD as a distinct form of vascular dementia, do appear convincing.

Palmitic and stearic fatty acids induce Alzheimer-like hyperphosphorylation of tau in primary rat cortical neurons

Epidemiological studies suggest that high fat diets significantly increase the risk of Alzheimer's disease (AD). In addition, the AD brain is characterized by high fatty acid content compared to that of healthy subjects. Nevertheless, the basic mechanism relating elevated fatty acids and the pathogenesis of AD remains unclear. The present study examines the role of fatty acids in causing hyperphosphorylation of the tau protein, one of the characteristic signatures of AD pathology. Hyperphosphorylation of tau disrupts the cell cytoskeleton and leads to neuronal degeneration. Here, primary rat cortical neurons and astrocytes were treated with saturated free fatty acids (FFAs), palmitic and stearic acids. There was no change in the levels of phosphorylated tau in rat cortical neurons treated directly with these FFAs. The conditioned media from FFA-treated astrocytes, however, caused hyperphosphorylation of tau in the cortical neurons at AD-specific phospho-epitopes. Co-treatment of neurons with N-acetyl cysteine, an antioxidant, reduced FFA-induced hyperphosphorylation of tau. The present results establish a central role of FFAs in causing hyperphosphorylation of tau through astroglia-mediated oxidative stress.

Neuroimaging biomarkers for clinical trials of disease-modifying therapies in Alzheimer's disease

The pathophysiologic process leading to neurodegeneration in Alzheimer's disease (AD) is thought to begin long before clinical symptoms develop. Existing therapeutics for AD improve symptoms, but increasing efforts are being directed toward the development of therapies to impede the pathologic progression of the disease. Although these medications must ultimately demonstrate efficacy in slowing clinical decline, there is a critical need for biomarkers that will indicate whether a candidate disease-modifying therapeutic agent is actually altering the underlying degenerative process. A number of in vivo neuroimaging techniques, which can reliably and noninvasively assess aspects of neuroanatomy, chemistry, physiology, and pathology, hold promise as biomarkers. These neuroimaging measures appear to relate closely to neuropathological and clinical data, such as rate of cognitive decline and risk of future decline. As this work has matured, it has become clear that neuroimaging measures may serve a variety of potential roles in clinical trials of candidate neurotherapeutic agents for AD, depending in part on the question of interest and phase of drug development. In this article, we review data related to the range of neuroimaging biomarkers of Alzheimer's disease and consider potential applications of these techniques to clinical trials, particularly with respect to the monitoring of disease progression in trials of disease-modifying therapies.

Automated brain tissue assessment in the elderly and demented population: construction and validation of a sub-volume probabilistic brain atlas

OBJECTIVES

To develop an automated imaging assessment tool that accommodates the anatomic variability of the elderly and demented population as well as the registration errors occurring during spatial normalization.

METHODS

20 subjects with Alzheimer's disease (AD), mild cognitive impairment, or normal cognition underwent MRI brain imaging and had their 3D volumetric datasets manually partitioned into 68 regions of interest (ROI) termed sub-volumes. Gray matter (GM), white matter (WM), and cerebral spinal fluid (CSF) voxel counts were then made in the subject's native space for comparison against automated volumetric measures within three sub-volume probabilistic atlas (SVPA) models. The three SVPAs were constructed using 12 parameter affine (12 p), 2nd order (2nd), and 6th order (6th) transforms derived from registering the manually partitioned scans into a Talairach compatible AD population-based target. The three SVPA automated measures were compared to the manually derived measures in the 20 subjects' native space with a "jack-knife" procedure in which each subject was assessed by an SVPA they did not contribute toward constructing.

RESULTS

The mean left and right GM ratio (GM ratio = [GM + CSF] / CSF) "r values" for the 3 SVPAs compared to the manually derived ratios across the 68 ROIs were 0.85 for the 12p SVPA, 0.88 for the 2nd SVPA, and 0.89 for the 6th SVPA. The mean left and right WM ratio (WM ratio = [WM + CSF] / CSF) "r values" for the 3 SVPAs being 0.84 for the 12p SVPA, 0.86 for the 2nd SVPA, and 0.88 for the 6th SVPA.

CONCLUSION

We have constructed, from an elderly and demented cohort, an automated brain volumetric tool that has excellent accuracy compared to a manual gold standard and is capable of regional hypothesis testing and individual patient assessment compared to a population.

[Gap junction-mediated intercellular communication in astrocytes and neuroprotection]

Neuroglial interaction represents a concept that is now more and more integrated in the attempts to understand who does what and how in neuronal processing and survival, in normal as well as in pathological situations. The purpose of the review is to provide an overlook about the role of glial cells, mainly astrocytes, in neuroprotection. Since a typical feature of glia is to be connected by gap junctions that allow them to be organized as a communicating network(s), we will focus this review on what is known about the contribution of astrocyte gap junctions (AGJ) in neuronal survival. As neuroglial interaction and AGJ are both affected during neurodegenerative diseases, we will also consider the above mentioned glial properties in a pathological context with a special interest in Alzheimer's disease.

[Development of automatic extraction of the corpus callosum from magnetic resonance imaging of the head and examination of the early dementia objective diagnostic technique in feature analysis]

We examined the objective diagnosis of dementia based on changes in the corpus callosum. We examined midsagittal head MR images of 17 early dementia patients (2 men and 15 women; mean age, 77.2+/-3.3 years) and 18 healthy elderly controls (2 men and 16 women; mean age, 73.8+/-6.5 years), 35 subjects altogether. First, the corpus callosum was automatically extracted from the MR images. Next, early dementia was compared with the healthy elderly individuals using 5 features of the straight-line methods, 5 features of the Run-Length Matrix, and 6 features of the Co-occurrence Matrix from the corpus callosum. Automatic extraction of the corpus callosum showed an accuracy rate of 84.1+/-3.7%. A statistically significant difference was found in 6 of the 16 features between early dementia patients and healthy elderly controls. Discriminant analysis using the 6 features demonstrated a sensitivity of 88.2% and specificity of 77.8%, with an overall accuracy of 82.9%. These results indicate that feature analysis based on changes in the corpus callosum can be used as an objective diagnostic technique for early dementia.

Alzheimer's disease and the 'ABSENT' hypothesis: mechanism for amyloid beta endothelial and neuronal toxicity

Alzheimer's disease [AD] is the most common cause of dementia among people age 65 and older. One of the biggest stumbling blocks in developing effective drug therapy for Alzheimer's disease has been the lack of a comprehensive hypothesis that explains the mechanism behind all of the histopathological changes seen in patients suffering from Alzheimer's disease. An overview of the currently popular 'amyloid' and 'vascular' hypotheses for AD demonstrates that neither hypothesis by itself can explain all the known histopathological and biochemical lesions seen in Alzheimer's disease. The paper presents a hypothesis that tries to explain the mechanism behind almost all the histopathological changes, and varying clinical manifestations seen in both diagnosed AD and Vascular Dementia [VaD]. The new hypothesis is based on the known dual toxicity of beta amyloid to both vascular and neuronal tissues, their synergy and the resultant net effect on the onset and progression of AD. The new hypothesis therefore will be known as the Amyloid Beta Synergistic Endothelial and Neuronal Toxicity [ABSENT] hypothesis. The ABSENT hypothesis will try to show the common chemical mechanism behind almost all of the pathological changes seen in AD. According to the ABSENT hypothesis, beta amyloid itself generates all the free radicals that cause both vascular dysfunction and the neuronal damage seen in AD. The chemical mechanism proposed is based on evidence from physical chemistry experiments, calculations as well as in vitro/in vivo experiments. The ABSENT hypothesis does not favor one mode of beta amyloid-induced brain damage over the other, rather it considers the net effects of the neuronal stress/damage caused by both the cerebrovascular dysfunction and direct neurotoxicity caused by beta amyloid. The hypothesis states that each patient has a different balance of predisposing factors that modulate the extent of neurotoxicity and cerebrovascular dysfunction caused by beta amyloid and thereby explains the wide range and mixed nature of damage and dysfunction seen in the studies done on patients diagnosed with AD, VaD or 'mixed dementias'. According to the hypothesis, beta amyloid peptides are necessary if not sufficient to cause AD, VaD and mixed senile dementias. The hypothesis, therefore, proposes the term Beta Amyloid Dementias [BAD] to describe the conditions currently covered by the diagnoses of 'AD', 'VaD' and 'Mixed [senile] Dementias'. Finally, the ABSENT hypothesis tries to put forth a direct chemical mechanism behind the apparent synergy and increased association between old age, pre- and coexisting vascular disease, diabetes and AD.

Amyloid beta-peptide(1-42) and hydrogen peroxide-induced toxicity are mediated by TRPM2 in rat primary striatal cultures

Amyloid beta-peptide (Abeta) is the main component of senile plaques which characterize Alzheimer's disease and may induce neuronal death through mechanisms which include oxidative stress. To date, the signalling pathways linking oxidant stress, a component of several neurodegenerative diseases, to cell death in the CNS are poorly understood. Melastatin-like transient receptor potential 2 (TRPM2) is a Ca(2+)-permeant non-selective cation channel, which responds to increases in oxidative stress levels in the cell and is activated by oxidants such as hydrogen peroxide. We demonstrate here that Abeta and hydrogen peroxide both induce death in cultured rat striatal cells which express TRPM2 endogenously. Transfection with a splice variant that acts as a dominant negative blocker of TRPM2 function (TRPM2-S) inhibited both hydrogen peroxide- and Abeta-induced increases in intracellular-free Ca(2+) and cell death. Functional inhibition of TRPM2 activation by the poly(ADP-ribose)polymerase inhibitor SB-750139, a modulator of intracellular pathways activating TRPM2, attenuated hydrogen peroxide- and Abeta-induced cell death. Furthermore, a small interfering RNA which targets TRPM2, reduced TRPM2 mRNA levels and the toxicity induced by hydrogen peroxide and Abeta. These data demonstrate that activation of TRPM2, functionally expressed in primary cultures of rat striatum, contributes to Abeta- and oxidative stress-induced striatal cell death.

The Rush Memory and Aging Project: study design and baseline characteristics of the study cohort

The long-term objective of the Rush Memory and Aging Project is to identify the postmortem indices linking genetic and environmental risk factors to the development of Alzheimer's disease (AD). The overall study design involves a detailed assessment of risk factors for AD in older persons without known dementia who agree to annual clinical evaluation and organ donation at the time of death. In contrast to other clinical-pathologic studies which are conducted on special populations, the Rush Memory and Aging Project enrolled a cohort with much greater diversity in terms of educational attainment, in addition to gender, race, and ethnicity. From September of 1997 through April of 2005, more than 1,000 older persons without known dementia from more than 30 residential facilities across the Chicago metropolitan area agreed to participate. Their mean age was 81 years, about a third had 12 or fewer years of education, a third were men, and about 10% were members of a racial or ethnic minority group. More than 950 already have completed their baseline clinical evaluation.

Atrophy rate in medial temporal lobe during progression of Alzheimer disease

OBJECTIVE

To establish the progression of brain atrophy rates in patients with a known date of onset of Alzheimer disease (AD).

METHODS

Each of 18 subjects had two high-resolution T1-weighted three-dimensional MRI examinations. The two MRIs were coregistered and the annual rate of brain tissue atrophy was derived both for the entire brain and regionally for the left and right medial temporal lobe (MTL). Time since onset (TSO) of AD, defined as the interval between the date of onset and the midpoint of MRI dates, ranged from -2.9 to 4.2 years.

RESULTS

In patients with AD, TSO was a correlate of the atrophy rate for both the left MTL (R2 = 0.58, p = 0.001) and right MTL (R2 = 0.30, p = 0.03). When serial measurements were applied to a control group of 21 cognitively normal elderly subjects, MTL atrophy rate classified the group membership (AD vs normal cognition) with an accuracy of 92.3%.

CONCLUSION

Increased annual atrophy rate in the medial temporal lobe is a potential diagnostic marker of the progression of Alzheimer disease.

N-acteyl cysteine alleviates oxidative damage to central nervous system of ApoE-deficient mice following folate and vitamin E-deficiency

Oxidative stress is an early neurodegenerative insult in Alzheimer's disease (AD). Antioxidant mechanisms, including elements of the glutathione (GSH) pathway, undergo at least a transient compensatory increase that is apparently insufficient due to continued oxidative damage during disease progression. Mice deficient in apolipoprotein E, which provide a model for some aspects of AD, undergo increased oxidative damage to brain tissue and cognitive decline when maintained on a folate-free diet, despite a compensatory increase in glutathione synthase transcription and activity as well as increased levels of GSH. Dietary supplementation with N-acetyl cysteine (1 g/kg diet), a cell-permeant antioxidant and GSH precursor, alleviated oxidative damage and cognitive decline, and restored glutathione synthase and GSH levels in ApoE-deficient mice deprived of folate to those of normal mice maintained in the presence of folate. These data support the administration of antioxidant precursors to buffer oxidative damage in neurodegenerative disorders.

Differential loss of synaptic proteins in Alzheimer's disease: implications for synaptic dysfunction

The objective of our research was to determine synaptic protein levels in brain specimens from AD subjects and age-matched control subjects. Further, to determine whether presynaptic or postsynaptic compartments of neurons are preferentially affected in AD patients, we studied 3 presynaptic vesicle proteins (synaptotagmin, synaptophysin, and Rab 3A), 2 synaptic membrane proteins (Gap 43 and synaptobrevin), and 2 postsynaptic proteins (neurogranin and synaptopodin) in specimens from AD and age-matched control brains. Two brain regions--the frontal and parietal cortices--were assessed for protein levels by immunoblotting analysis. We found a loss of both presynaptic vesicle proteins and postsynaptic proteins in all brain specimens from AD patients compared to those from age-matched control subjects. Further, we found that the loss of synaptic proteins was more severe in the frontal cortex brain specimens than in the parietal cortex brain specimens from the AD subjects compared to those from the control subjects, suggesting that the frontal brain may be critical for synaptic function in AD. Using immunohistochemistry techniques, we also determined the distribution pattern of all synaptic proteins in both the frontal and parietal cortices brain specimens from control subjects. Of the 7 synaptic proteins studied, the presynaptic proteins synaptophysin and rab 3A and the postsynaptic protein synaptopodin were the most down-regulated. Our study suggests that postsynaptic proteins and presynaptic proteins are important for synaptic function and may be related to cognitive impairments in AD.

Nasal vaccination with a proteosome-based adjuvant and glatiramer acetate clears beta-amyloid in a mouse model of Alzheimer disease

Amyloid beta-peptide (Abeta) appears to play a key pathogenic role in Alzheimer disease (AD). Immune therapy in mouse models of AD via Abeta immunization or passive administration of Abeta antibodies markedly reduces Abeta levels and reverses behavioral impairment. However, a human trial of Abeta immunization led to meningoencephalitis in some patients and was discontinued. Here we show that nasal vaccination with a proteosome-based adjuvant that is well tolerated in humans plus glatiramer acetate, an FDA-approved synthetic copolymer used to treat multiple sclerosis, potently decreases Abeta plaques in an AD mouse model. This effect did not require the presence of antibody, as it was observed in B cell-deficient (Ig mu-null) mice. Vaccinated animals developed activated microglia that colocalized with Abeta fibrils, and the extent of microglial activation correlated strongly with the decrease in Abeta fibrils. Activation of microglia and clearing of Abeta occurred with the adjuvant alone, although to a lesser degree. Our results identify a novel approach to immune therapy for AD that involves clearing of Abeta through the utilization of compounds that have been safely tested on or are currently in use in humans.

A Rapid Label-Free Electrochemical Detection and Kinetic Study of Alzheimer's Amyloid Beta Aggregation

We present the first electrochemical detection, characterization, and kinetic study of the aggregation of Alzheimer's disease (AD) amyloid beta peptides (Abeta-40, Abeta-42) using three different voltammetric techniques at a glassy carbon electrode (GCE). This method is based on detecting changes in the oxidation signal of tyrosine (Tyr) residue. As the peptides aggregate, there are structure conformational changes, which affect the degree of exposure of Tyr to the molecular surface of the peptides. The results show significant differences in the aggregation process between the two peptides, and these correlate highly with established techniques. The method is rapid and label-free, and the principle can be universally applied to other protein aggregation studies related to diseases, such as Huntington's, Parkinson's, and Creutzfeldt Jacob (CJD). This method could also be explored in screening for the effectiveness of AD therapies.

Monitoring disease progression in transgenic mouse models of Alzheimer's disease with proton magnetic resonance spectroscopy

Currently no definitive biomarker of Alzheimer's disease (AD) is available, and this impedes both clinical diagnosis in humans and drug discovery in transgenic animal models. Proton magnetic resonance spectroscopy ((1)H MRS) provides a noninvasive way to investigate in vivo neurochemical abnormalities. Each observable metabolite can potentially provide information about unique in vivo pathological processes at the molecular or cellular level. In this study, the age-dependent 1H MRS profile of transgenic AD mice was compared to that of wild-type mice. Twenty-seven APP-PS1 mice (which coexpress mutated human presenilin 1 and amyloid-beta precursor protein) and 30 wild-type mice age 66-904 days were examined, some repeatedly. A reduction in the levels of N-acetylaspartate and glutamate, compared with total creatine levels, was found in APP-PS1 mice with advancing age. The most striking finding was a dramatic increase in the concentration of myo-inositol with age in APP-PS1 mice, which was not observed in wild-type mice. The age-dependent neurochemical changes observed in APP-PS1 mice agree with results obtained from in vivo human MRS studies. Among the different transgenic mouse models of AD that have been studied with 1H MRS, APP-PS1 mice seem to best match the neurochemical profile exhibited in human AD. 1H MRS could serve as a sensitive in vivo surrogate indicator of therapeutic efficacy in trials of agents designed to reduce neurotoxicity due to microglial activation. Because of its noninvasive and repeatable nature, MRS in transgenic models of AD could substantially accelerate drug discovery for this disease.

The identification and characterization of excitotoxic nerve-endings in Alzheimer disease

Regionally specific neuronal loss is a distinguishing feature of Alzheimer disease (AD). Excitotoxicity is a mechanism commonly invoked to explain this. We review the accumulating evidence for such a hypothesis, particularly the altered expression and pharmacology of glutamate receptors and transporters in pathologically susceptible regions of the AD brain. Loss of neurons would be expected to lead to the retrograde degeneration of their afferents, which should be reflected in a loss of presynaptic markers such as synaptophysin. We discuss the possibility that neurons may be destroyed locally, but that glutamatergic presynaptic terminals may remain, or even re-proliferate. The reduced glutamate uptake site density in AD brain may signify a loss of the transporters on otherwise intact terminals, rather than the loss of glutamatergic afferents. Neuronal death may follow if cells are exposed to excessive amounts of glutamate; the loss of transporters from functioning, but defective, glutamate terminals would mean they could continue to release glutamate to exacerbate excitotoxicity. We discuss experimental methods to quantitate synapses, which are crucial for deciding between the various possibilities.

mTOR/p70S6k signalling alteration by Abeta exposure as well as in APP-PS1 transgenic models and in patients with Alzheimer's disease

In Alzheimer's disease, neuropathological hallmarks include the accumulation of beta-amyloid peptides (Abeta) in senile plaques, phosphorylated tau in neurofibrillary tangles and neuronal death. Abeta is the major aetiological agent according to the amyloid cascade hypothesis. Translational control includes phosphorylation of the kinases mammalian target of rapamycin (mTOR) and p70S6k which modulate cell growth, proliferation and autophagy. It is mainly part of an anti-apoptotic cellular signalling. In this study, we analysed modifications of mTOR/p70S6k signalling in cellular and transgenic models of Alzheimer's disease, as well as in lymphocytes of patients and control individuals. Abeta 1-42 produced a rapid and persistent down-regulation of mTOR/p70S6k phosphorylation in murine neuroblastoma cells associated with caspase 3 activation. Using western blottings, we found that phosphorylated forms of mTOR and p70S6k are decreased in the cortex but not in the cerebellum (devoid of plaques) of double APP/PS1 transgenic mice compared with control mice. These results were confirmed by immunohistochemical methods. Finally, the expression of phosphorylated p70S6k was significantly reduced in lymphocytes of Alzheimer's patients, and levels of phosphorylated p70S6k were statistically correlated with Mini Mental Status Examination (MMSE) scores. Taken together, these findings demonstrate that the mainly anti-apoptotic mTOR/p70S6k signalling is altered in cellular and transgenic models of Alzheimer's disease and in peripheral cells of patients, and could contribute to the pathogenesis of the disease.

Structural and mutational analyses of the molecular interactions between the catalytic domain of factor XIa and the Kunitz protease inhibitor domain of protease nexin 2

Factor XIa (FXIa) is a serine protease important for initiating the intrinsic pathway of blood coagulation. Protease nexin 2 (PN2) is a Kunitz-type protease inhibitor secreted by activated platelets and a physiologically important inhibitor of FXIa. Inhibition of FXIa by PN2 requires interactions between the two proteins that are confined to the catalytic domain of the enzyme and the Kunitz protease inhibitor (KPI) domain of PN2. Recombinant PN2KPI and a mutant form of the FXI catalytic domain (FXIac) were expressed in yeast, purified to homogeneity, co-crystallized, and the structure of the complex was solved at 2.6 angstroms (Protein Data Bank code 1ZJD). In this complex, PN2KPI has a characteristic, disulfide-stabilized double loop structure that fits into the FXIac active site. To determine the contributions of residues within PN2KPI to its inhibitory activity, selected point mutations in PN2KPI loop 1 11TGPCRAMISR20 and loop 2 34FYGGC38 were tested for their ability to inhibit FXIa. The P1 site mutation R15A completely abolished its ability to inhibit FXIa. IC50 values for the wild type protein and the remaining mutants were as follows: PN2KPI WT, 1.28 nM; P13A, 5.92 nM; M17A, 1.62 nM; S19A, 1.86 nM; R20A, 5.67 nM; F34A, 9.85 nM. The IC50 values for the M17A and S19A mutants were not significantly different from those obtained with wild type PN2KPI. These functional studies and activated partial thromboplastin time analysis validate predictions made from the PN2KPI-FXIac co-crystal structure and implicate PN2KPI residues, in descending order of importance, Arg15, Phe34, Pro13, and Arg20 in FXIa inhibition by PN2KPI.