Ezequiel Surace

Detergent resistant membrane-associated IDE in brain tissue and cultured cells: Relevance to Aβ and insulin degradation

BackgroundInsulin degrading enzyme (IDE) is implicated in the regulation of amyloid β (Aβ) steady-state levels in the brain, and its deficient expression and/or activity may be a risk factor in sporadic Alzheimers disease (AD). Although IDE sub-cellular localization has been well studied, the compartments relevant to Aβ degradation remain to be determined.ResultsOur results of live immunofluorescence, immuno gold electron-microscopy and gradient fractionation concurred to the demonstration that endogenous IDE from brain tissues and cell cultures is, in addition to its other localizations, a detergent-resistant membrane (DRM)-associated metallopeptidase. Our pulse chase experiments were in accordance with the existence of two pools of IDE: the cytosolic one with a longer half-life and the membrane-IDE with a faster turn-over. DRMs-associated IDE co-localized with Aβ and its distribution (DRMs vs. non-DRMs) and activity was sensitive to manipulation of lipid composition in vitro and in vivo. When IDE was mis-located from DRMs by treating cells with methyl-β-cyclodextrin (MβCD), endogenous Aβ accumulated in the extracellular space and exogenous Aβ proteolysis was impaired. We detected a reduced amount of IDE in DRMs of membranes isolated from mice brain with endogenous reduced levels of cholesterol (Chol) due to targeted deletion of one seladin-1 allele. We confirmed that a moderate shift of IDE from DRMs induced a substantial decrement on IDE-mediated insulin and Aβ degradation in vitro.ConclusionOur results support the notion that optimal substrate degradation by IDE may require its association with organized-DRMs. Alternatively, DRMs but not other plasma membrane regions, may act as platforms where Aβ accumulates, due to its hydrophobic properties, reaching local concentration close to its Km for IDE facilitating its clearance. Structural integrity of DRMs may also be required to tightly retain insulin receptor and IDE for insulin proteolysis. The concept that mis-location of Aβ degrading proteases away from DRMs may impair the physiological turn-over of Aβ in vivo deserves further investigation in light of therapeutic strategies based on enhancing Aβ proteolysis in which DRM protease-targeting may need to be taken into account.

Notch signaling proteins HES-1 and Hey-1 bind to insulin degrading enzyme (IDE) proximal promoter and repress its transcription and activity: Implications for cellular Aβ metabolism

Cerebral amyloid β (Aβ) accumulation is pathogenically associated with sporadic Alzheimers disease (SAD). BACE-1 is involved in Aβ generation while insulin-degrading enzyme (IDE) partakes in Aβ proteolytic clearance. Vulnerable regions in AD brains show increased BACE-1 protein levels and enzymatic activity while the opposite occurs with IDE. Another common feature in SAD brains is Notch1 overexpression. Here we demonstrate an increase in mRNA levels of Hey-1, a Notch target gene, and a decrease of IDE transcripts in the hippocampus of SAD brains as compared to controls. Transient transfection of Notch intracellular domain (NICD) in N2aSW cells, mouse neuroblastoma cells (N2a) stably expressing human amyloid precursor protein (APP) Swedish mutation, reduce IDE mRNA levels, promoting extracellular Aβ accumulation. Also, NICD, HES-1 and Hey-1 overexpression result in decreased IDE proximal promoter activity. This effect was mediated by 2 functional sites located at -379/-372 and -310-303 from the first translation start site in the -575/-19 (556 bp) fragment of IDE proximal promoter. By site-directed mutagenesis of the IDE promoter region we reverted the inhibitory effect mediated by NICD transfection suggesting that these sites are indeed responsible for the Notch-mediated inhibition of the IDE gene expression. Intracranial injection of the Notch ligand JAG-1 in Tg2576 mice, expressing the Swedish mutation in human APP, induced overexpression of HES-1 and Hey-1 and reduction of IDE mRNA levels, respectively. Our results support our theory that a Notch-dependent IDE transcriptional modulation may impact on Aβ metabolism providing a functional link between Notch signaling and the amyloidogenic pathway in SAD.

Creation of the Argentina-Alzheimer's Disease Neuroimaging Initiative

The Alzheimers Disease Neuroimaging Initiative (ADNI) is a multisite, longitudinal study that assesses clinical, imaging, genetic, and biospecimen biomarkers through the process of normal aging to mild cognitive impairment and dementia. We present the creation of the Argentina‐ADNI—the first South American ADNI—and its effort to acquire data comparable with those gathered in other worldwide ADNI centers.

Cognitive reserve and Aβ1-42 in mild cognitive impairment (Argentina-Alzheimer’s Disease Neuroimaging Initiative)

Background The purpose of this study was to investigate the relationship between cognitive reserve and concentration of Aβ1-42 in the cerebrospinal fluid (CSF) of patients with mild cognitive impairment, those with Alzheimer’s disease, and in control subjects. Methods Thirty-three participants from the Argentina-Alzheimer’s Disease Neuroimaging Initiative database completed a cognitive battery, the Cognitive Reserve Questionnaire (CRQ), and an Argentinian accentuation reading test (TAP-BA) as a measure of premorbid intelligence, and underwent lumbar puncture for CSF biomarker quantification. Results The CRQ significantly correlated with TAP-BA, education, and Aβ1-42. When considering Aβ1-42 levels, significant differences were found in CRQ scores; higher levels of CSF Aβ1-42 were associated with higher CRQ scores. Conclusion Reduced Aβ1-42 in CSF is considered as evidence of amyloid deposition in the brain. Previous results suggest that individuals with higher education, higher occupational attainment, and participation in leisure activities (cognitive reserve) have a reduced risk of developing Alzheimer’s disease. Our results support the notion that enhanced neural activity has a protective role in mild cognitive impairment, as evidenced by higher CSF Aβ1-42 levels in individuals with more cognitive reserve.

Predicting episodic memory performance using different biomarkers: results from Argentina-Alzheimer's Disease Neuroimaging Initiative.

Purpose Argentina-Alzheimer’s Disease Neuroimaging Initiative (Arg-ADNI) is the first ADNI study to be performed in Latin America at a medical center with the appropriate infrastructure. Our objective was to describe baseline characteristics and to examine whether biomarkers related to Alzheimer’s disease (AD) physiopathology were associated with worse memory performance. Patients and methods Fifteen controls and 28 mild cognitive impairment and 13 AD dementia subjects were included. For Arg-ADNI, all biomarker parameters and neuropsychological tests of ADNI-II were adopted. Results of positron emission tomography (PET) with fluorodeoxyglucose and 11C-Pittsburgh compound-B (PIB-PET) were available from all participants. Cerebrospinal fluid biomarker results were available from 39 subjects. Results A total of 56 participants were included and underwent baseline evaluation. The three groups were similar with respect to years of education and sex, and they differed in age (F=5.10, P=0.01). Mean scores for the baseline measurements of the neuropsychological evaluation differed significantly among the three groups at P<0.001, showing a continuum in their neuropsychological performance. No significant correlations were found between the principal measures (long-delay recall, C-Pittsburgh compound-B scan, left hippocampal volume, and APOEε4) and either age, sex, or education (P>0.1). Baseline amyloid deposition and left hippocampal volume separated the three diagnostic groups and correlated with the memory performance (P<0.001). Conclusion Cross-sectional analysis of baseline data revealed links between cognition, structural changes, and biomarkers. Follow-up of a larger and more representative cohort, particularly analyzing cerebrospinal fluid and brain biomarkers, will allow better characterization of AD in our country.

Argentina ADNI: Preliminary report on CSF biomarkers

Background: The majority of individuals referred to a Memory Clinic have subtle symptoms of cognitive impairment and from a clinical point of view most of them are not demented. Eventually, many of these individuals develop a form of dementia that is clinically detectable but some of them may remain stable for years, and the concern may even disappear. The EEG diagnostic tool presented here is designed to help the clinician to evaluate possible progress of the cognitive symptoms in MCI subjects over time. Methods: In an EEG database EEGs from 342 mild AD subjects and 181 MCI individuals have been entered. The EEG data from the MCI individuals was collected over a period of 7 years (20052011). Over the course of 8 years these MCI individuals have been followed up. The MCI individuals were divided into three subgroups according to their clinical status at follow up: prodromal AD (pAD), stable MCI (sMCI), and other. The pAD and sMCI groups were compared by constructing a classifier by applying statistical pattern recognition to a large set of EEG features. Results: Of the 181 MCI individuals 70 were diagnosed with AD 1-7.7 years after the EEG measurement with a mean of 2 years. 79 remainedMCI for at least 3 years, with a mean of 4.75 years and standard deviation of 1.00 year. The remaining 32 individuals had developed other types of dementia at follow up. The pAD-sMCI classifier indicates that using EEG it is possible to predict which of the MCI individuals will at a later time develop AD with accuracy of about 80%. Conclusions: Following amore substantial clinical validation and an easy access to the methodology, we expect this application of clinical EEG in support for differential diagnosis of mild cognitive impairment to become a realistic first step in the full clinical workup of patients who visit a memory clinic. The underlying technology is well known, widely available and inexpensive in relation to other imaging techniques.

Cortical thickness, brain metabolic activity, and in vivo amyloid deposition in asymptomatic, middle-aged offspring of patients with late-onset Alzheimer's disease

The natural history of preclinical late-onset Alzheimers disease (LOAD) remains obscure and has received less attention than that of early-onset AD (EOAD), in spite of accounting for more than 99% of cases of AD. With the purpose of detecting early structural and functional traits associated with the disorder, we sought to characterize cortical thickness and subcortical grey matter volume, cerebral metabolism, and amyloid deposition in persons at risk for LOAD in comparison with a similar group without family history of AD. We obtained 3T T1 images for gray matter volume, FDG-PET to evaluate regional cerebral metabolism, and PET-PiB to detect fibrillar amyloid deposition in 30 middle-aged, asymptomatic, cognitively normal individuals with one parent diagnosed with LOAD (O-LOAD), and 25 comparable controls (CS) without family history of neurodegenerative disorders (CS). We observed isocortical thinning in AD-relevant areas including posterior cingulate, precuneus, and areas of the prefrontal and temporoparietal cortex in O-LOAD. Unexpectedly, this group displayed increased cerebral metabolism, in some cases overlapping with the areas of cortical thinning, and no differences in bilateral hippocampal volume and hippocampal metabolism. Given the importance of age in this sample of individuals potentially developing early AD-related changes, we controlled results for age and observed that most differences in cortical thickness and metabolism became nonsignificant; however, greater deposition of β-amyloid was observed in the right hemisphere including temporoparietal cortex, postcentral gyrus, fusiform inferior and middle temporal and lingual gyri. If replicated, the present observations of morphological, metabolic, and amyloid changes in cognitively normal persons with family history of LOAD may bear important implications for the definition of very early phenotypes of this disorder.

Argentina-Alzheimer's disease neuroimaging initiative (Arg-ADNI): neuropsychological evolution profile after one-year follow up

The Argentina-Alzheimers disease neuroimaging initiative (Arg-ADNI) study is a longitudinal prospective cohort of 50 participants at a single institution in Buenos Aires, Argentina. Longitudinal assessments on a neuropsychological test battery were performed on 15 controls, 24 mild cognitive impairment (MCI) patients and 12 Alzheimers disease (AD) dementia patients. In our study population, there was a high prevalence of positive AD biomarkers in the AD group, 92.3% (12/13); and a low prevalence in the normal controls, 20%; almost half (48%) of the patients diagnosed with MCI had positive amyloid detection. After a one year, the significant differences found at baseline on neuropsychological testing were similar at the follow-up assessment even though the AD group had significantly altered its functional performance (FAQ and CDR). The exception was semantic fluency, which showed greater impairment between the AD group and MCI and normal controls respectively. For these tests, the addition of AD biomarkers as a variable did not significantly alter the variations previously found for the established clinical groups model. Finally, the one-year conversion rate to dementia was 20% in the MCI cohort.

THE A/T/N CLASSIFICATION IN THE PROGNOSIS OF MILD COGNITIVE IMPAIRMENT IN THE ARGENTINE-ALZHEIMER’S DISEASE NEUROIMAGING INITIATIVE COHORT

patients were classified based on their baseline CSF biomarker levels as biomarker (BM)-positive or BM-negative. Clinical decline was determined by following the patients over a period of 24 months, based on Mini-Mental State Examination (MMSE) and Clinical Dementia Rating-Sum of Boxes (CDR-SB) and Functional Activities Questionnaire (FAQ) scores. The ability of the CSF biomarkers and ratios to separate patients with higher versus lower change in clinical scores was estimated based on a multivariable linear mixed effects model. Time-to-event analyses, including Kaplan-Meier curves, were performed for outcome dementia (follow-up of up to 72 months). Results:MMSE scores showed a significantly stronger decrease in BM-positive compared with BM-negative patients (Table 1, Figure 1). pTau/Ab42 and tTau/ Ab42 ratios performed better as predictors of clinical decline than single biomarkers (Table 1). Similar results were obtained for the other scores (Table 1). Although no clear optimum for the biomarker cut-offs could be identified, good separation was observed between patients with lower and higher risk of progression to dementia for the biomarkers (Figure 2). Conclusions:

CORTICAL THICKNESS FOLLOW-UP AFTER ONE YEAR IN ADNI-ARGENTINA COHORT

P1-451 CORTICALTHICKNESS FOLLOW-UP AFTER ONE YEAR IN ADNI-ARGENTINA COHORT Ismael Luis Calandri, Ignacio Demey, Patricio Alexis Chrem Mendez, Gabriela Cohen, Maria Julieta Russo, Ezequiel Surace, Horacio Martinetto, Federico Nahas, Maria Eugenia Martin, Paula Harris, Jorge Campos, Gustavo Sevlever, Silvia Vazquez, Allegri F. Ricardo, Ra ul Carrea Institute for Neurological Research (FLENI), Buenos Aires, Argentina; Hospital Brit anico de Buenos Aires, Buenos Aires, Argentina; Ra ul Carrea Institute for Neurological Research (FLENI), Buenos Aires, Argentina. Contact e-mail: ismaelcalandri@gmail.com