33, Number 2, January 2013
Ling Zhang, Shuli Sheng, Chuan Qin (Handling Associate Editor: Andre Fischer)
The Role of HDAC6 in Alzheimer’s Disease
Abstract: The expression of histone deacetylase 6 (HDAC6)-a versatile enzyme with a known role in epigenetics-increases significantly in the hippocampus and other relevant brain regions in both patients with Alzheimer’s disease (AD) and animal models of AD. However, when and how HDAC6 expression increases during the course of AD progression remains unclear. Whether HDAC6 overexpression is an underlying cause of AD or a condition resulting from AD is controversial. Mounting evidence suggests that increased HDAC6 expression contributes to AD-associated neurodegeneration, although beneficial effects have also been identified. This review article addresses recent research on HDAC6 structure and function, and highlights the potential detrimental and protective roles of HDAC6 overexpression in AD. We hope to shed light on whether HDAC6 overexpression is associated with AD etiopathogenesis or whether it rescues AD-associated neurodegeneration compensatorily. Furthermore, we discuss new evidence showing that HDAC6 may be a therapeutic target for AD.
Patricia L. Fernandez, Gabrielle B. Britton, K.S. Rao
Potential Immunotargets for Alzheimer's Disease Treatment Strategies
Abstract: Alzheimer’s disease (AD) exerts a profound burden on public health worldwide. AD etiology is unknown, and research to understand its underlying pathology has produced agents for the management of symptoms, but not a cure for the disease. Most AD drugs were developed in response to research implicating fibrillar amyloid-β (Aβ) in AD neuropathology but result in only modest short-term improvements in cognitive function, so there is agreement that additional targets need to be investigated. Evidence has implicated the immune system in AD and immunotherapy as a potential approach to AD treatment. Accumulation of microglia and astrocytes has been observed around Aβ deposits and several reports implicate inflammatory mediators in AD pathology. Importantly, Aβ deposition has been found in the brains of AD patients and in aged people without dementia, but signs of neuroinflammation are found only in AD patients and not in normal aged individuals. Animal models suggest a complex role for immunomodulators in AD, namely, these mechanisms are likely to promote the same pathogenic processes that gave rise to them. To date, clinical trials with anti-inflammatories and other immunoregulators have not been successful, but available data strongly favor immunomodulation as a promising disease intervention strategy. This article reviews data that implicate various immunomodulators in AD and considers their potential application in the development of novel AD therapeutics. Currently, a deeper understanding of nervous-immune interactions during normal aging and at all stages of AD is needed. Continued research in AD inflammatory and immunoregulatory processes will increase both our understanding of disease mechanisms and the likelihood of discovering new therapeutic targets for AD.
Robert P. Friedland, Shivani Nandi
A Modest Proposal for a Longitudinal Study of Dementia Prevention (with apologies to Jonathan Swift, 1729)
Abstract: Many studies have documented the role of risk and protective factors for late life dementing illnesses, particularly Alzheimer’s disease. A “Systematic Review” from the US Agency for Healthcare Research and Quality and the National Institute on Aging concluded that because the overall quality of evidence was low, recommendations for public health could not be made. In order to gain evidence for the efficacy of lifestyle interventions, we propose a “Modest Proposal” to study 10,000 subjects over 40 years randomly assigned to groups of low or high saturated fat in the diet, head injury, and high or low levels of mental activity, physical activity, or inactivity as well as smoking or non-smoking. This proposed study cannot be accomplished. The “Modest Proposal” illustrates that the absence of definitive evidence should not restrict physicians from making reasonable recommendations based on the evidence that is available.
Alessandra Berry*, Davide Vacirca*, Sara Capoccia, Veronica Bellisario, Walter Malorni, Elena Ortona#, Francesca Cirulli# *These authors contributed equally to this work. #Both considered as senior authors.
Anti-ATP Synthase Autoantibodies Induce Neuronal Death by Apoptosis and Impair Cognitive Performance in C57BL/6 Mice
Abstract: Previous studies have suggested a pathogenetic role of autoantibodies (Abs) against ATP synthase (ATPs) in patients with Alzheimer’s disease (AD). Using a mouse model, we found that intracerebroventricular administration of anti-ATPs-Abs, purified from AD patients, leads to poor cognitive performance and pronounced cell damage in the hippocampus, a brain region specifically involved in learning and memory processes, which is severely affected in AD. Our results are suggestive of a role of anti-ATPs-Abs in the onset and progression of AD and also provide a fruitful model for the study of memory disturbances in neurodegenerative diseases.
Supplementary Data for Berry et al. article (PDF)
Claudia L. Satizabal, Yi-Cheng Zhu, Carole Dufouil, Christophe Tzourio (Handling Associate Editor: Jack de la Torre)
Inflammatory Proteins and the Severity of Dilated Virchow-Robin Spaces in the Elderly
Abstract: Recent studies suggest dilated Virchow-Robin Spaces (dVRS) could be a manifestation of cerebral small-vessel disease, but little is known about their risk factors. As inflammation has been associated with other brain MRI findings, we investigated whether interleukin-6 and C-reactive protein were associated with the severity of dVRS in the eldery. dVRS were assessed in basal ganglia and white matter and rated on a severity scale. We found that elevated interleukin-6 levels were associated with higher severity of dVRS in basal ganglia, suggesting that inflammation might be associated with the burden of dVRS in the elderly.
Supplementary Data for Satizabal et al. article (PDF)
Yan Yang, Delin Ma, Yuping Wang, Teng Jiang, Shuhong Hu, Muxun Zhang, Xuefeng Yu, Cheng-Xin Gong
Intranasal Insulin Ameliorates Tau Hyperphosphorylation in a Rat Model of Type 2 Diabetes
Abstract: Recent studies have demonstrated that insulin plays important roles in the brain, including regulation of glucose metabolism and modulation of learning and memory. We have found dysregulation of brain insulin signaling in both Alzheimer's disease (AD) and type 2 diabetes (T2D), which correlates to hyperphosphorylation of tau, a key abnormal tau modification leading to neurofibrillary tangles. Here, we investigated tau phosphorylation and the two key components of the insulin signaling pathway, protein kinase B (AKT) and glycogen synthase kinase-3β (GSK-3β), in a rat model of T2D produced by a high protein, high glucose, and high fat diet followed by intraperitoneal injection of streptozocin. We found tau hyperphosphorylation, decreased AKT activation, and GSK-3β over-activation in T2D rat brains. Intranasal insulin treatment for four weeks normalized AKT and GSK-3β, as well as reduced tau hyperphosphorylation in T2D rat brains, whereas four-week treatments with subcutaneous insulin had minimal effects on brain GSK-3β and tau phosphorylation. These results suggest decreased brain insulin signaling and tau hyperphosphorylation in the rat model of T2D and demonstrate the efficacy of intranasal insulin treatment to reverse these brain abnormalities. Our findings provide further mechanism by which T2D increases the risk for AD and also support the potential use of intranasal insulin for the treatment of AD.
Alena Opattova*, Peter Filipcik*, Martin Cente, Michal Novak *These authors contributed equally.
Intracellular Degradation of Misfolded Tau Protein Induced by Geldanamycin is Associated with Activation of the Proteasome
Abstract: Misfolded, N- and C-terminally truncated tau protein is the primary constituent of neurofibrillary tangles in brains of patients afflicted with Alzheimer’s disease (AD). Intracellular accumulation of misfolded and truncated tau leads to generation of cytotoxic intermediates; transgenic expression of truncated tau leads to neurological deficits, neurofibrillary degeneration, and premature death of animals. Since no cure for AD or other tauopathies is available yet, we tested the possibility for prevention of pathogenic events elicited by tau, via inhibition of its intracellular accumulation. Using a cell model conditionally expressing truncated and misfolding-prone tau protein, we showed that pathogenic forms of tau are degraded via the proteasome. We have also observed that chymotrypsin-like activity of the proteasome was significantly suppressed (a decrease of ~29.12% in comparison to control cells; p<0.001) as a consequence of truncated tau expression. Interestingly, the activity of the proteasome was enhanced by geldanamycin, a natural inhibitor of Hsp90. This activation resulted in accelerated degradation of misfolded tau. We suggest that non-toxic inhibitors of Hsp90, especially those which can activate the proteasome, are good candidates for the development of molecules that efficiently counteract the damaging effects of pathologically misfolded proteins.
Patricia Natalia Silva, Tatiane Katsue Furuya, Ianna Sampaio Braga, Lucas Trevizani Rasmussen, Roger Willian de Labio, Paulo Henrique Bertolucci, Elizabeth Suchi Chen, Gustavo Turecki, Naguib Mechawar, Spencer Luiz Payao, Jonathan Mill, Marilia Cardoso Smith
CNP and DPYSL2 mRNA Expression and Promoter Methylation Levels in Brain of Alzheimer’s Disease Patients
Abstract: Alzheimer’s disease (AD) is a highly prevalent type of dementia in the elderly population. AD is a complex neurodegenerative disorder. Thus, epigenetic mechanisms that regulate gene expression might have an important role in AD. CNP (2',3'-Cyclic Nucleotide 3' Phosphodiesterase) gene encodes a protein used as an index of myelin alterations. DPYSL2 (Dihydropyrimidinase-like 2) is described as acting in structural and regulatory processes in the central nervous system, such as neural differentiation, neurotransmitter release, and stabilization of microtubules. In this study, we evaluated gene expression and epigenetic regulation of CNP and DPYSL2 genes in three postmortem brain regions (entorhinal and auditory cortices and hippocampus) of AD patients and healthy elderly controls. mRNA quantification was performed using qRT-PCR, and promoter DNA methylation patterns were determined by mass spectrometry using the Sequenom EpiTYPER platform. We observed CNP mRNA downregulation in entorhinal and auditory cortex in relation to the same regions of the control group. CNP alterations in the brain might suggest impairment in myelination leading to a synaptic and cognition loss. No AD-associated differences in CNP and DPYSL2 promoter DNA methylation were observed, suggesting that other mechanisms may be involved in mediating the observed CNP gene expression.
Supplementary Data for Silva et al. article (PDF)
Simona Capsoni, Anne-Sophie Carlo, Domenico Vignone, Gianluca Amato, Chiara Criscuolo, Thomas E. Willnow, Antonino Cattaneo
SorLA Deficiency Dissects Amyloid Pathology from Tau and Cholinergic Neurodegeneration in a Mouse Model of Alzheimer’s Disease
Abstract: Sortilin-related receptor with A-type repeats (SorLA, also known as LR11) has been implicated in Alzheimer’s disease (AD). Thus, genetic studies associated SorLA gene variants with the risk of sporadic AD. Also, in vitro and in vivo studies showed that SorLA impairs processing of the amyloid-β protein precursor (AβPP) to amyloid-β. In particular, it has been found that loss of SorLA accelerates senile plaque deposition in mouse models overexpressing mutant forms of human AβPP and presenilin 1. Here we tested the possibility that SorLA deficiency also interferes with behavioral and neuropathological endpoints in an alternative murine AD model, the AD10 anti-nerve growth factor (NGF) mouse, in which amyloid-β accumulation derives from the altered processing of endogenous AβPP. In addition to alterations in AβPP processing, AD10 mice also show cholinergic deficit and tau hyperphosphorylation resulting in behavioral deficits in learning and memory paradigms. We found that the loss of SorLA not only exacerbates early amyloid pathology but, at the same time, protects from cholinergic deficit and from early phospho-tau mislocalization. The results show that in the AD10 anti-NGF mouse model the AβPP processing-related aspects of neurodegeneration can be dissociated from those related to tau posttranslational processing and to cholinergic phenotypic maintenance by modulation of SorLA expression. We suggest that SorLA regulates different aspects of neurodegeneration in a complex way, supporting the hypothesis that SorLA expression might be critical not only for amyloid-related pathology but also for other cellular processes altered in AD.
Sid E. O’Bryant, Leigh Johnson, Valerie Balldin, Melissa Edwards, Robert Barber, Benjamin Williams, Michael Devous, Blair Sushing, Janice Knebl, James Hall
Characterization of Mexican Americans with Mild Cognitive Impairment and Alzheimer’s Disease
Abstract: The purpose of the study was to provide characterization of Mexican Americans who meet criteria for Alzheimer’s disease (AD) and mild cognitive impairment (MCI). For the study, 1,069 participants ages 40 and above who self-identified as either non-Hispanic white (n=633) or Mexican American (n=436) were recruited using a community-based participatory research approach. Global cognition was assessed via the Mini-Mental State Examination (MMSE), dementia severity by the Clinical Dementia Rating Scale, and depression via the Geriatric Depression Scale 30-item version. Age, gender, education, ApoE e4 allele frequency, and diabetic diagnoses were also analyzed. The findings showed that Mexican Americans (normal controls, MCI, and AD) were younger, less highly educated, performed more poorly on the MMSE, endorsed more symptoms of depression, were more likely to be diagnosed with diabetes, and possessed the ApoE e4 allele less frequently. Age was the only significant risk factor for cognitive dysfunction (AD/MCI) among Mexican Americans (OR=1.06, 95% CI = 1.03-1.09). Age (B=0.07, std=0.02, p<0.001) and ApoE e4 presence (B=0.9, std=0.4, p=0.02) were significantly related to increased disease severity. Given the rapidly growing and aging Mexican American population, there is a substantial need for research into cognitive aging, MCI, and AD among this ethnic group. The current findings hold important implications for both clinic and research settings and point to additional research needs.
Audrey Gabelle, Florence Richard, Laure-Anne Gutierrez, Susanna Schraen, Fleur Delva, Olivier Rouaud, Luc Buee, Jean-Francois Dartigues, Jacques Touchon, Jean-Charles Lambert, Claudine Berr
Plasma Amyloid-β Levels and Prognosis in Incident Dementia Cases of the 3-City Study
Abstract: Studies of plasma amyloid-β (Aβ) levels as potential biomarkers for incident Alzheimer’s disease (AD) have yielded contradictory results. We explored the associations between plasma Aβ40, Aβ42, and truncated Aβ levels, and prognosis of dementia in participants of the prospective 3-City Study. 120 aged individuals diagnosed with 2-year incident dementia were followed up for seven years. The associations between Aβ plasma levels and baseline cognitive score, cognitive decline, and death were examined. A higher level of baseline plasma Aβ was associated with worse cognitive status two years prior to incident dementia diagnosis. In incident AD patients, the association was only significant for Aβ40 and Aβn-42. In the fast cognitive decliners group, especially in AD cases, a higher level of 5 pg/ml of baseline Aβ42, Aβn-42,Aβn-42/Aβn-40, and Aβ42/Aβ40 ratios were associated with a lower risk of fast cognitive decline based on the Isaacs Set Test score. There was no association between peptide levels and mortality in demented subjects. When assayed at prodromal stage, plasma Aβ levels may be potentially useful markers of fast cognitive decline in individuals who subsequently become demented.
Supplementary Data for Gabelle et al. article (PDF)
John E. Lewis, H. Reginald McDaniel, Marc E. Agronin, David A. Loewenstein, Jorge Riveros, Rafael Mestre, Mairelys Martinez, Niurka Colina, Dahlia Abreu, Janet Konefal, Judi M. Woolger, Karriem H. Ali
The Effect of an Aloe Polymannose Multinutrient Complex on Cognitive and Immune Functioning in Alzheimer’s Disease
Abstract: Alzheimer’s disease (AD) is a leading killer of Americans, imparts a significant toll on the quality of life of the patient and primary caregiver, and results in inordinate costs in an already overburdened medical system. Prior studies on cholinesterase inhibitors among AD patients have shown minimal amelioration of disease symptoms and/or restoration of lost cognitive functioning. The effect of improved nutrition, particularly with dietary supplements, on cognitive functioning may offer an alternative strategy compared to standard treatment. The present pilot study investigated the effect of an aloe polymannose multinutrient complex (APMC) formula on cognitive and immune functioning over 12 months among adults diagnosed with AD. Subjects participated in an open-label trial and consumed 4 teaspoons per day of the APMC. The ADAS-cog, MMSE, ADCS-ADL, and SIB were administered at baseline and 3, 6, 9, and 12 months follow-up. Cytokines and lymphocyte and monocyte subsets were assessed at baseline and 12 months. The mean ADAS-cog cognition score significantly improved at 9 and 12 months from baseline, and 46% of our sample showed clinically-significant improvement (>4-point change) from baseline to 12 months. Participants showed significant decreases in tumor necrosis factor-α, vascular endothelial growth factor, and interleukins-2 and -4. CD90+, CD95+CD3+, CD95+CD34+, CD95+CD90+, CD14+CD34+, CD14+CD90+, and CD14+CD95+ decreased significantly, whereas CD14+ significantly increased. Participants tolerated the APMC supplement with few, temporary adverse reactions. Our results showed improvements in both clinical and physiological outcomes for a disease that otherwise has no standard ameliorative remedy.
Elaine K. Hebda-Bauer, Tracy A. Simmons, Andrew Sugg, Eren Ural, James A. Stewart, James L. Beals, Qiang Wei, Stanley J. Watson, Huda Akil
3xTg-AD Mice Exhibit an Activated Central Stress Axis during Early-Stage Pathology
Abstract: Activation of the hypothalamic-pituitary-adrenal (HPA) axis occurs in response to the organism’s innate need for homeostasis. The glucocorticoids (GCs) that are released into the circulation upon acute activation of the HPA axis perform stress-adaptive functions and provide negative feedback to turn off the HPA axis, but can be detrimental when in excess. Long-term activation of the HPA axis (such as with chronic stress) enhances susceptibility to neuronal dysfunction and death, and increases vulnerability to Alzheimer’s disease (AD). However, little is known how components of the HPA axis, upstream of GCs, impact vulnerability to AD. This study examined basal gene expression of stress-related molecules in brains of 3xTg-AD mice during early-stage pathology. Basal GC levels and mRNA expression of the glucocorticoid receptor (GR), mineralocorticoid receptor (MR), and corticotropic releasing hormone (CRH) in several stress- and emotionality-related brain regions were measured in 3-4-month-old 3xTg-AD mice. Despite normal GC levels, young 3xTg-AD mice exhibit an activated central HPA axis, with altered mRNA levels of MR and GR in the hippocampus, GR and CRH in the paraventricular nucleus of the hypothalamus, GR and CRH in the central nucleus of the amygdala, and CRH in the bed nucleus of the stria terminalis. This HPA axis activation is present during early-stage neuropathology when 3xTg-AD mice show mild behavioral changes, suggesting an ongoing neuroendocrine regulation that precedes the onset of severe AD-like pathology and behavioral deficits.
Samantha Davenward, Peter Bentham, Jan Wright, Peter Crome, Deborah Job, Anthony Polwart, Christopher Exley
Silicon-Rich Mineral Water as a Non-Invasive Test of the ‘Aluminum Hypothesis’ in Alzheimer’s Disease
Abstract: There has been a plausible link between human exposure to aluminum and Alzheimer’s disease for several decades. We contend that the only direct and ethically acceptable experimental test of the ‘aluminum hypothesis’, which would provide unequivocal data specific to the link, is to test the null hypothesis that a reduction in the body burden of aluminum to its lowest practical limit would have no influence upon the incidence, progression, or severity of Alzheimer’s disease. Herein we are testing the hypothesis that silicon-rich mineral waters can be used as non-invasive methods to reduce the body burden of aluminum in individuals with Alzheimer’s disease and a control group consisting of their carers and partners. We have shown that drinking up to 1L of a silicon-rich mineral water each day for 12 weeks facilitated the removal of aluminum via the urine in both patient and control groups without any concomitant affect upon the urinary excretion of the essential metals, iron and copper. We have provided preliminary evidence that over 12 weeks of silicon-rich mineral water therapy the body burden of aluminum fell in individuals with Alzheimer’s disease and, concomitantly, cognitive performance showed clinically relevant improvements in at least 3 out of 15 individuals. This is a first step in a much needed rigorous test of the ‘aluminum hypothesis of Alzheimer’s disease’ and a longer term study involving many more individuals is now warranted.
Yu Zhang, Maria Carmela Tartaglia, Norbert Schuff, Gloria C. Chiang, Christopher Ching, Howard J. Rosen, Maria Luisa Gorno-Tempini, Bruce L. Miller, Michael W. Weiner (Handling Associate Editor: J. Wesson Ashford)
MRI Signatures of Brain Macrostructural Atrophy and Microstructural Degradation in Frontotemporal Lobar Degeneration Subtypes
Abstract: Brain magnetic resonance imaging (MRI) studies have demonstrated regional patterns of brain macrostructural atrophy and white matter microstructural alterations separately in the three major subtypes of frontotemporal lobar degeneration (FTLD), which includes behavioral variant frontotemporal dementia (bvFTD), semantic dementia (SD), and progressive nonfluent aphasia (PNFA). This study was to investigate to what extent the pattern of white matter microstructural alterations in FTLD subtypes mirrors the pattern of brain atrophy, and to compare the ability of various diffusion tensor imaging (DTI) indices in characterizing FTLD patients, as well as to determine whether DTI measures provide greater classification power for FTLD than measuring brain atrophy. Twenty-five patients with FTLD (13 with bvFTD, 6 with SD, and 6 with PNFA) and 19 healthy age-matched control subjects underwent both structural MRI and DTI scans. Measurements of regional brain atrophy were based on T1-weighted MRI data and voxel-based morphometry. Measurements of regional white matter degradation were based on voxelwise as well as regions-of-interest tests of DTI variations, expressed as fractional anisotropy, axial diffusivity, and radial diffusivity. Compared to controls, bvFTD, SD, and PNFA patients each exhibited characteristic regional patterns of brain atrophy and white matter damage. DTI overall provided significantly greater accuracy for FTLD classification than brain atrophy. Moreover, radial diffusivity was more sensitive in assessing white matter damage in FTLD than other DTI indices. The findings suggest that DTI in general and radial diffusivity in particular are more powerful measures for the classification of FTLD patients from controls than brain atrophy.
Supplementary Data for Zhang et al. article (PDF)
Eran P. Klein, Jeffrey Kaye (Handling Associate Editor: Peter Whitehouse)
Dementia Specialists and Early Adoption of Amyloid Imaging
Abstract: The goal of this study was to describe the attitudes of U.S. neurologists specializing in dementia toward the use of amyloid imaging in the diagnosis of Alzheimer’s disease (AD). A cross-sectional electronic physician survey of dementia specialists at U.S. medical schools was performed. The response rate for the survey was 51.9% (135/260). Greater than 83% of respondents plan to use amyloid imaging to evaluate patients for AD. Most respondents intend to use amyloid imaging as an adjunctive diagnostic modality to confirm (77%) or rule-out (73%) a diagnosis of AD; 24% plan to use amyloid imaging to screen asymptomatic individuals for evidence of cerebral amyloid. Specialists who do not intend to use amyloid imaging (16%) express concern about the cost (73%), the usefulness (55%), and likelihood of patient (55%) and clinician (59%) misinterpretation of findings. The need for patient pre-test counseling was endorsed by a large percentage (92%) of dementia specialists (higher than for genetic testing (82%)). In conclusion, dementia specialists, particularly young specialists, are likely to be early adopters of amyloid imaging. Assuming ready availability, this new technology would be used as a confirmatory test in the evaluation of AD, as well as a screening tool for asymptomatic pathology. Specialists recognize the complexity of interpreting amyloid imaging findings and the need for patient counseling before undergoing testing.
Supplementary Data for Klein and Kaye article (PDF)
Alex Bahar-Fuchs, Victor Villemagne, Kevin Ong, Gael Chetelat, Fiona Lamb, Cornelia B. Reininger, Michael Woodward, Christopher C. Rowe
Prediction of Amyloid-β Pathology in Amnestic Mild Cognitive Impairment with Neuropsychological Tests
Abstract: Assessment of disease biomarkers, particularly the in vivo assessment of amyloid-β (Aβ) burden with positron emission tomography (PET), is gradually becoming central to the diagnosis of mild cognitive impairment (MCI) due to Alzheimer’s disease (AD). However, the incorporation of biomarker evidence to the diagnostic process is currently restricted mainly to research settings. The identification of memory measures that are associated with Aβ is of clinical relevance as this may enhance the confidence in making a diagnosis of MCI due to AD in clinical settings. Forty one persons with amnestic MCI underwent Aβ imaging with 18F- Florbetaben PET, magnetic resonance imaging, and a comprehensive neuropsychological assessment. All measures of episodic memory were significantly correlated with Aβ burden, but regression analyses revealed a strong and selective association between story recall and Aβ over and beyond the effects of age, education, global cognition, hippocampal volume, or other memory tests. Analyses of sensitivity and specificity of memory measures to detect high versus low Aβ scans suggested that word-list recall performed better when high sensitivity was preferred, whereas story recall performed better when high specificity was preferred. In conclusion, a measure of story recall may increase the confidence in making a diagnosis of MCI due to AD in clinical settings.
Stefanie K. Forest, Christopher M. Acker, Cristina d’Abramo, Peter Davies (Handling Associate Editor: Gregory Jicha)
Methods for Measuring Tau Pathology in Transgenic Mouse Models
Abstract: In Alzheimer’s disease (AD) and tauopathies, tau becomes hyperphosphorylated, undergoes a conformational change, and becomes aggregated and insoluble. There are three methods commonly used to study the insoluble tau fraction, two that utilize detergents (Sarkosyl and RIPA) and another that does not (insoluble). However, these methods require large amounts of homogenate for a relatively low yield of the insoluble fraction, which can be problematic when dealing with small tissue samples. Furthermore, the most common way of analyzing this material is through densitometry of immunoblots, offering only semiquantitative measurements. We provide a comparison of the three methods commonly used (Sarksoyl, RIPA, and insoluble) through immunoblot and ELISA analyses. Finally, we tested a new method to determine aggregated tau levels, utilizing a monoantibody tau ELISA. The insoluble fractions of four different mouse models (P301L, htau, wild type, and knockout) as well as human AD and control brains were examined. There were significant correlations between the three insoluble methods for both total tau and pS396/404 tau measured by immunoblot or ELISA analyses. Additionally, the results from the ELISA method correlated significantly with those from immunoblot analyses. Finally, the monoantibody assay on the lysate significantly correlated with the total tau ELISAs performed on the three insoluble preparations. Taken together, these results suggest that all three insoluble preparation methods offer similar results for measuring insoluble tau in either mouse or human brains. In addition the new monoantibody ELISA offers a simple quantitative method to measure the amount of aggregated tau in both human and mouse brains.
Belinda Yew, Suvarna Alladi, Mekala Shailaja, John R. Hodges, Michael Hornberger (Handling Associate Editor: Paulo Caramelli)
Lost and Forgotten? Orientation versus Memory in Alzheimer’s Disease and Frontotemporal Dementia
Abstract: Recent studies suggest that significant memory problems are not specific to Alzheimer’s disease (AD) but can be also observed in other neurodegenerative conditions, such as behavioral variant frontotemporal dementia (bvFTD). We investigated whether orientation (spatial & temporal) information is a better diagnostic marker for AD compared to memory and whether their atrophy correlates of orientation and memory differ. A large sample (n = 190) of AD patients (n=73), bvFTD patients (n= 54), and healthy controls (n = 63) underwent testing. A subset of the patients (n = 72) underwent structural imaging using voxel-based morphometry analysis of magnetic resonance brain imaging. Orientation and memory scores from the Addenbrooke’s Cognitive Examination showed that AD patients had impaired orientation and memory, while bvFTD patients performing at control level for orientation but had impaired memory. A logistic regression showed that 78% of patients could be classified on the basis of orientation and memory scores alone at clinic presentation. Voxel-based morphometry analysis was conducted using orientation and memory scores as covariates, which showed that the neural correlates for orientation and memory also dissociated with posterior hippocampus cortex being related to orientation in AD, while the anterior hippocampus was associated with memory performance in the AD and bvFTD patients. Orientation and memory measures discriminate AD and bvFTD to a high degree and tap into different hippocampal regions. Disorientation and posterior hippocampus appears therefore specific to AD and will allow clinicians to discriminate AD patients from other neurodegenerative conditions with similar memory deficits at clinic presentation.
Supplementary Data for Yew et al. article (PDF)
Marco Bozzali, Valentina Battistoni, Enrico Premi, Antonella Alberici, Giovanni Giulietti, Silvana Archetti, Marinella Turla, Roberto Gasparotti, Mara Cercignani, Alessandro Padovani, Barbara Borroni (Handling Associate Editor: Francesca Baglio)
Structural Brain Signature of FTLD Driven by Granulin Mutation
Abstract: Several causative gene mutations have been identified in frontotemporal lobar degeneration (FTLD), including mutations within Granulin (GRN) genes. It was recently shown that FTLD patients carriers of GRN Thr272fs mutation [FTLD-GRN(m+)] exhibit more severe abnormalities, as assessed by magnetic resonance imaging (MRI), than those with sporadic FTLD [FTLD-GRN(m-)]. The aim of this study was to investigate the relationship between grey (GM) and white matter (WM) microstructural damage in FTLD patients, carriers, and non-carriers of the mutation. Twenty-three FTLD patients [6 GRN(m+) and 17 GRN(m-)] and 12 healthy subjects received an MRI scan including volumetric and diffusion imaging. GM was assessed using voxel-based morphometry, while the corpus callosum was reconstructed using diffusion tractography. Mean diffusivity and fractional anisotropy of the corpus callosum were compared between groups. FTLD patients showed widespread GM atrophy and altered diffusion indices in the corpus callosum when compared to healthy subjects. When contrasting GRN(m+) against GRN(m-) patients, the former group had more atrophy in the left frontal GM, and reduced fractional anisotropy and increased mean diffusivity in the left anterior part of the corpus callosum. Significant correlations between the GM and WM damage were found in GRN(m+) patients. This pattern of damage was able to predict some of the additional neuropsychological deficits observed in GRN(m+) as compared to GRN(m-) patients. A more prominent involvement of WM in GRN(m+) patients is consistent with the knowledge that GRN genes are expressed in the microglia. This involvement might be responsible for the accrual of additional GM atrophy via disconnection mechanisms.
Javier Olazaran, Juan Antonio Hernandez-Tamames, Elena Molina, Pablo Garcia-Polo, Jose Luis Dobato, Juan Alvarez-Linera, Pablo Martinez-Martin, AD Research Unit Investigators
Clinical and Anatomical Correlates of Gait Dysfunction in Alzheimer’s Disease
Abstract: We conducted a cross-sectional study to investigate the clinical and anatomical correlates of gait dysfunction in advanced Alzheimer’s disease (AD). A comprehensive clinical protocol that included cognitive, functional, behavioral, and motor variables was administered to patients with probable AD (n=100), possible AD (n=17), and AD with cerebrovascular disease (AD+CVD) (n=27). Gait dysfunction was evaluated with the Rating Scale for Gait Evaluation in Cognitive Deterioration and magnetic resonance imaging was analyzed in 94 patients (volumetry study) and 78 patients (diffusion tensor imaging study). Univariate correlations, multivariate regression, and statistical parametric mapping analyses were conducted in the total sample and in the subsample of patients with probable AD. Mean age was 82.5 (SD 6.3, range 56 to 98), 83.3% were female patients, and 95.1% displayed moderate to severe dementia. Parkinsonism, patient setting (nursing home), dementia severity, apathy, and (worse) cognitive performance significantly predicted gait dysfunction in the total sample (p<0.05, R2=0.58), whereas parkinsonism, patient setting, and limb weakness due to non-AD conditions predicted gait dysfunction in probable AD (p<0.05, R2=0.57). Gait dysfunction was related to atrophy in the motor cortex, the middle cingulate, the anterior insula, the right caudate (probable AD only), and the anterior lobe of the cerebellum (p<0.01, corrected). Significant correlations were also observed between gait dysfunction and damage in several white matter locations (p<0.001, uncorrected). The present results are congruent with a model of multi-system gray matter degeneration, with progressive damage to critical regions (i.e., motor cortex, cingulate, insula, and cerebellum) producing gait dysfunction and, eventually, gait loss in AD.
Wei-Li Xu, Barbara Caracciolo, Hui-Xin Wang, Giola Santoni, Bengt Winblad, Laura Fratiglioni
Accelerated Progression from Mild Cognitive Impairment to Dementia among APOE ε4ε4 Carriers
Abstract: The impact of APOE ε4 on mild cognitive impairment (MCI) and its progression to dementia remain controversial. We aimed to examine the association of APOE ε4 with MCI, and to verify the hypothesis that ε4 accelerates progression from MCI to dementia. In the Kungsholmen Project, 756 cognitively healthy participants and 212 people with MCI aged >75 years were identified at baseline. Amnestic MCI (aMCI) and other cognitive impairment no dementia (oCIND) as two subtypes of MCI were assessed based on standard definitions. The two cohorts were followed for 9 years to detect incident cases of MCI and dementia following international criteria. APOE genotypes were assessed at baseline. Data were analyzed using Cox models. During the follow-up, in the cognitively healthy cohort, 165 people developed MCI (40 aMCI and 125 oCIND) and 176 developed dementia; in the MCI cohort, 118 persons progressed to dementia. Compared with APOE ε3ε3, the hazard ratios (HRs) (95% CIs) of ε2ε4/ε3εε were 2.24 (1.10-4.57) for aMCI and 1.78 (1.15-2.75) for oCIND, while the ε4ε4 was related to dementia with a HR of 4.35 (1.97-9.63) in the cognitively healthy cohort. In the MCI cohort, the ε4ε4 genotype led to a multi-adjusted HR of 2.89 (1.12-7.48) for dementia and accelerated the progression to dementia by 3.36 years. The APOE ε4 heterozygotes are associated with an increased risk of aMCI and oCIND. The ε4 homozygote substantially accelerates progression from MCI to dementia, and anticipate dementia occurrence by more than 3 years in people with MCI.
Kinga Szigeti, Deepika Lal, Yanchun Li, Rachelle S. Doody, Kirk Wilhelmsen, Li Yan, Song Liu, Changxing Ma and the Texas Alzheimer Research and Care Consortium
Genome-Wide Scan for Copy Number Variation Association with Age at Onset of Alzheimer’s Disease
Abstract: Alzheimer’s disease (AD) is a progressive neurodegenerative disease with high prevalence, which imposes a substantial public health problem. The heritability of AD is estimated at 60-80% forecasting the potential use of genetic biomarkers for risk stratification in the future. Several large scale genome-wide association studies using high frequency variants identified 10 loci accountable for only a fraction of the estimated heritability. To find the missing heritability, systematic assessment of various mutational mechanisms needs to be performed. This copy number variation (CNV) genome-wide association study with age at onset (AAO) of AD identified 5 CNV regions that may contribute to the heritability of AAO of AD. Two CNV events are intragenic causing a deletion in CPNE4. In addition, to further study the mutational load at the 10 known susceptibility loci, CNVs overlapping with these loci were also catalogued. We identified rare small events overlapping CR1 and BIN1 in AD and normal controls with opposite CNV dosage. The CR1 events are consistent with previous reports. Larger scale studies with deeper genotyping specifically addressing CNV are needed to evaluate the significance of these findings.
Supplementary Data for Szigeti et al. article (PDF)
Sonia Bonně, Federica Lupo, Emanuele Lo Gerfo, Alessandro Martorana, Roberta Perri, Carlo Caltagirone, Giacomo Koch (Handling Associate Editor: Marco Bozzali)
Altered Parietal-Motor Connections in Alzheimer’s Disease Patients
Abstract: Alzheimer’s disease (AD) is characterized by altered functional cortico-cortical connectivity likely due to loss of afferent and efferent connections between different cortical areas. Here we explored parieto-frontal functional connectivity in 15 AD patients and 12 healthy control subjects by means of bifocal transcranial magnetic stimulation (TMS). Conditioning stimuli were applied over the right posterior parietal cortex (PPC) at different intensities (90% and 110% of resting motor threshold, RMT). Motor evoked potentials (MEPs) were then recorded from the ipsilateral primary motor cortex at different interstimulus intervals (ISIs) ranging between 2 and 15 ms.Results showed that in healthy subjects, a conditioning TMS pulse applied over the ipsilateral PPC at 90%, but not at 110%, of RMT intensity was able to increase the excitability of the right M1. This functional interaction peaked at ISI=6 ms. Conversely, in AD patients the facilitatory pattern of parieto-motor connections was evident only when TMS was delivered at an intensity of 110% of RMT with a peak at ISI=8 ms. Moreover in AD patients, treatment with cholinesterase inhibitors did not induce any significant modification in the strength of the connection. In subsequent analyses, we found that, in AD patients, the effects induced by PPC conditioning at 110% RMT correlated with neuropsychological measures of episodic memory and executive functions, implying that patients with better cognitive performance had less impaired connectivity. Our findings reveal that parieto-frontal cortico-cortical functional connectivity is altered in AD patients, providing further evidence for a disconnection-based interpretation of AD symptoms.
Joan Vilalta-Franch, Laia Calvo-Perxas, Josep Garre-Olmo, Oriol Turro-Garriga, Secundino Lopez-Pousa (Handling Associate Editor: Barbara Caracciolo)
Apathy Syndrome in Alzheimer’s Disease Epidemiology: Prevalence, Incidence, Persistence, and Risk and Mortality Factors
Abstract: The objective of this paper was to assess the prevalence, incidence, persistence, and risk and mortality factors for Apathy Syndrome in Alzheimer’s disease (ASAD) in a clinical sample. This was a cohort study of 491 patients with probable Alzheimer’s disease (AD). CAMDEX, NPI-10, RDRS-2, and Zarit Burden Interview (ZBI) were administered, and all patients were reevaluated after 12 months. Baseline ASAD diagnosis was made using specific diagnostic criteria. ASAD prevalence and incidence/year were 21.0% and 10.6%, respectively. After one year, ASAD persisted in 61.2% of patients. At baseline, patients with ASAD scored lower on the CAMCOG and higher on the Blessed, RDRS-2, and ZBI. Antipsychotic use was the only risk factor for ASAD (RR=3.159; 95% CI: 1.247-8.003). ASAD was related to an increased functional disability, but no relationship with cognitive impairment or increased caregiver burden was detected. Finally, ASAD was associated with an increased risk of mortality (HR=1.987; 95% CI: 1.145-3.450; p=0.014). ASAD suggests a more severe AD clinical profile, with poorer functional progression and increased mortality risk. Antipsychotic use seems to be the only risk factor for ASAD.