Current Alzheimer Research (v.10, #1)

Evidence that Enzyme Processivity Mediates Differential Aβ Production by PS1 and PS2 by Sean A. Pintchovski, Dale B. Schenk, Guriqbal S. Basi (4-10).
The γ-secretase complex cleaves the carboxy-terminal 99 residue (C99) fragment of the amyloid precursor protein (APP) to generate the amyloid-β (Aβ) peptide. The catalytic activity of this complex is mediated either by the presenilin- 1 (PS1) or the presenilin-2 (PS2) subunit. In vitro and in vivo studies have demonstrated that PS1-containing complexes generate more total Aβ product than PS2-containing complexes, indicating greater cleavage activity by PS1- containing γ-secretase complexes at the APP γ-site. However, it remains untested whether γ-secretase cleavage at the APP -site, which precedes γ-site cleavage and produces the physiologically active APP intracellular domain (AICD), follows the same rule. Using a novel Swedish APP-GVP substrate to facilitate the parallel detection of Aβ and AICD products from PS1-/-/PS2-/- cells co-transfected with either PS1 or PS2, we observed that while PS1 generates more total Aβ product than PS2, consistent with published reports, PS1 and PS2 unexpectedly generate equal amounts of AICD product. We also observed that PS1 and PS2 produce equivalent amounts of Notch intracellular domain (NICD), indicating equal cleavage activity at the Notch S3-site (the corollary of the APP -site). Our findings suggest that processivity differences between PS1 and PS2 underlie the differential production of Aβ peptide. Taken together these findings offer novel insights into γ- secretase biology and have important implications for therapeutically targeting γ-secretase.

Intracellular Accumulation of Toxic Turn Amyloid-β is Associated with Endoplasmic Reticulum Stress in Alzheimer's Disease by Naoko Soejima, Yasumasa Ohyagi, Norimichi Nakamura, Eri Himeno, Kyoko M. Iinuma, Nobutaka Sakae, Ryo Yamasaki, Takeshi Tabira, Kazuma Murakami, Kazuhiro Irie, Noriaki Kinoshita, Frank M. LaFerla, Yutaka Kiyohara, Toru Iwaki, Jun-ichi Kira (11-20).
Amyloid-β protein (Aβ) accumulates in the neurons of Alzheimer’s disease (AD) patients at an early stage of the disease. Recently, we found that Aβ with a toxic turn at positions 22 and 23 accumulates in neurons in AD brain. Here, we studied the accumulation of Aβ, toxic turn Aβ and high-molecular-weight Aβ oligomers in presenilin 1 (PS1) gene-transfected SH-SY5Y cells as well as in the brains of 3xTg-AD mice and AD patients. Immunostaining revealed that accumulation of toxic turn Aβ was promoted in G384A- and I143T-mutant PS1-transfected cells and further enhanced by co-transfection of cells with the Aβ-precursor protein (AβPP) gene. In contrast, accumulation of high-molecular-weight Aβ oligomers was promoted in mutant PS1 cells but attenuated by co-transfection of cells with the AβPP gene. Toxic turn Aβ was detected in the neurons of 3xTg-AD mice aged 2 months, when the mice were cognitively unimpaired. In contrast, high-molecular-weight Aβ oligomers were detected in the neurons of 7-month-old mice, when memory dysfunction is apparent. Furthermore, immunostaining and western blotting for Rab4, Rab6 and GRP78 revealed increased levels of these proteins in mutant PS1 cells and their accumulation in the neurons of 3xTg-AD mice. Remarkably, GRP78 immunoreactivity was increased at 2 months of age. Double-label immunostaining of AD brain revealed an apparent association between toxic turn Aβ and GRP78, an endoplasmic reticulum (ER) stress marker. Intraneuronal accumulation of toxic turn Aβ may be associated with ER stress in the brains of AD model mice and AD patients at an early stage.

Is Amyloid Binding Alcohol Dehydrogenase a Drug Target for Treating Alzheimer's Disease? by Eva Borger, Laura Aitken, Heng Du, Wenshen Zhang, Frank J Gunn-Moore, Shirley Shi Du Yan (21-29).
Current strategies for the treatment of Alzheimer's disease (AD) involve tackling the formation or clearance of the amyloid-beta peptide (Aβ) and/or hyper-phosphorylated tau, or the support and stabilization of the remaining neuronal networks. However, as we gain a clearer idea of the large number of molecular mechanisms at work in this disease, it is becoming clearer that the treatment of AD should take a combined approach of dealing with several aspects of the pathology. The concept that we also need to protect specific sensitive targets within the cell should also be considered. In particular the role of protecting the function of a specific mitochondrial protein, amyloid binding alcohol dehydrogenase (ABAD), will be the focus of this review. Mitochondrial dysfunction is a well-recognized fact in the progression of AD, though until recently the mechanisms involved could only be loosely labeled as changes in ‘metabolism’. The discovery that Aβ can be present within the mitochondria and specifically bind to ABAD, has opened up a new area of AD research. Here we review the evidence that the prevention of Aβ binding to ABAD is a drug target for the treatment of AD.

Characterization of Myelin Pathology in the Hippocampal Complex of a Transgenic Mouse Model of Alzheimer's Disease by Larry C. Schmued, James Raymick, Merle G. Paule, Melanie Dumas, Sumit Sarkar (30-37).
We have characterized the myelin changes observed within the hippocampal complex (HC) of a transgenic (Tg) mouse model of Alzheimer's disease (AD). Individual myelinated fibers were labeled with Black-Gold II while amyloid plaques were labeled with either Congo Red or Pan-A-beta immunofluoresence. Myelinated fibers were never seen passing through amyloid plaques in any region, while conspicuous myelin pathology was seen within, and immediately adjacent to, the amyloid plaques in the HC of the AD-Tg mouse. This pathology consisted of a complete disruption of myelinated fibers passing through the plaque and the region immediately adjacent to the plaques exhibited an edematous swelling of the fibers. This pathology was most frequently observed within the molecular and polymorph layers of the dentate gyrus and the molecular layer of Ammon's horn. The remaining layers of Ammon's horn exhibited minimal myelin pathology, while moderate myelinopathy was observed in the subiculum. Since the HC is integral for memory function, these findings may help account for the memory problems so characteristic of the disease process. Because the molecular layers of the dentate gyrus and Ammon's horn are the sites of inputs to the HC, the extensive myelin pathology observed in these regions would imply functional deafferentation of the HC. The appearance of some Black-Gold II positive debris within the plaques may reflect a possible cascade mechanism whereby the presence of plaques results in myelin degeneration, some of which is incorporated within the plaque, causing it to further expand in a self-perpetuating fashion.

Brief but Chronic Increase in Allopregnanolone Cause Accelerated AD Pathology Differently in Two Mouse Models by Sara K. Bengtsson, Maja Johansson, Torbjorn Backstrom, Roger M. Nitsch, Mingde Wang (38-47).
Previously, we have shown that chronic treatment with allopregnanolone (ALLO) for three months impaired learning function in the Swe/PS1 mouse model. ALLO is a neurosteroid, produced in the CNS and a GABAA receptor agonist. ALLO modulates the general inhibitory system in the CNS by enhancing the effect of GABA. Chronic treatment with other GABAA receptor active compounds, such as benzodiazepines, ethanol and medroxy-progesterone acetate has been associated to cognitive decline and/or increased risk for dementia. In this study, we sufficed with a treatment period of one month for the Swe/PS1 mouse, and included another Alzheimer's disease mouse model; the Swe/Arc model. We found that one month of chronic treatment with elevated ALLO levels within physiological range impaired learning and memory function in the Swe/Arc female and male mice. Male Swe/PS1 mice also showed marginally impaired function, while the female mice did not. Furthermore, the chronic ALLO treatment caused increased levels of soluble Aβ in the Swe/PS1 mouse model while the levels were unchanged in the Swe/Arc model. Therefore, both Swe/Arc and Swe/PS1 mice showed signs of accelerated disease progression. Still, further studies are required to determine the mechanisms behind the cognitive impairment and the increased Aβ-levels caused by mildly elevated ALLO-levels.

Plasma Acetylcholinesterase Activity Correlates with Intracerebral β-Amyloid Load by Adi Alkalay, Gil D. Rabinovici, Gabriel Zimmerman, Neha Agarwal, Daniela Kaufer, Bruce L. Miller, William J Jagust, Hermona Soreq (48-56).
Background: Previous studies have demonstrated alterations in the peripheral cholinergic system in Alzheimer's disease (AD), though results have been inconsistent and not linked to in vivo biomarkers of pathology. We examined the relationship between amyloid-beta (Aβ) plaques and plasma cholinesterase activity in a heterogeneous dementia population. Methods: 29 participants with clinical AD and 35 with non-AD diagnoses underwent positron emission tomography (PET) with the amyloid ligand [11C] PIB and plasma measurements of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activity. Multi-linear regression was used to evaluate the relationship between AChE or BChE activity and PIB binding (adjusted for age, sex, apolipoprotein E4 and vascular risk), applying voxel-wise and region of interest (ROI) approaches. AChE activity was further adjusted for cholinesterase inhibitor (ChE-I) use. Global amyloid load was measured using a PIB Index, representing mean tracer binding in frontal, parietal, lateral temporal and cingulate cortex. Results: AChE activity was correlated with PIB Index (β=0.39, p < 0.001) and with regional PIB binding in frontal, temporal, parietal and occipital lobes, precuneus and posterior cingulate on both voxel-wise (p < 0.001 uncorrected) and ROI (β=0.26-0.41, p < 0.005) analysis. Correlations remained significant after covarying clinical diagnosis (β=0.42, p=0.001), and among participants naive to ChE-I (β=0.51, p=0.005). No correlation was found between BChE activity and PIB. Among AD participants, disease severity was not correlated with AChE, BChE or PIB Index. Conclusion: AChE activity in plasma is correlated with brain Aβ load. Activation of the ‘anti-inflammatory cholinergic pathway’ may provide the link between Aβ plaques and peripheral cholinergic measures.

Elevated Plasma Levels of Soluble TNFRs and TACE Activity in Alzheimer's Disease Patients of Northern Han Chinese Descent by Lin Bai, Ning Song, Jintai Yu, Lan Tan, Yong Shen, Junxia Xie, Hong Jiang (57-62).
Background: We recently reported elevated cerebrospinal fluid (CSF) levels of soluble tumor necrosis factor (TNF) receptors and TNF-α converting enzyme (TACE) activity in subjects with Alzheimer's disease (AD) in a Caucasian population. The TNF receptor-mediated signaling pathway contributes to the production of Aβ and the subsequent cytotoxicity that is observed in AD brains. However, whether the plasma levels of soluble TNF receptors (sTNFRs) are changed is still unclear in AD patients of Han descent. Methods: In the present study, we analyzed the plasma sTNFR levels using commercially available immunoassay kits in 76 AD patients and 40 age- and sex-matched control subjects of Northern Han Chinese descent. Furthermore, the TACE activity was measured using a solution-based assay containing a fluorescently labeled TACE substrate. Results: AD patients exhibited higher levels of both sTNFR and TACE activity in their plasma compared with age- and sex-matched control subjects. The levels of sTNFR1 strongly correlated with the levels of sTNFR2 (rs =0.526, P < 0.001). In addition, the levels of sTNFR1 were significantly correlated with TACE activity (rs = 0.308, P < 0.01). Conclusion: These results suggest that sTNFRs and TACE activity might serve as potential peripheral diagnostic candidate biomarkers in AD.

The Association of ACT -17 A/T Polymorphism with Alzheimer's Disease: A Meta-Analysis by Chao Dou, Jiyuan Zhang, Yang Sun, Xin Zhao, Qihan Wu, Chaoneng Ji, Shaohua Gu, Yi Xie, Yumin Mao (63-71).
Association studies between Alpha-1-antichymotrypsin (ACT)-17(A > T) polymorphisms and Alzheimer's disease (AD) susceptibility have shown conflicting results. In this investigation, we performed a meta-analysis to assess the purported associations. Subgroup analyses based on ethnicity (Caucasians, East-Asian and American mixed) were also performed including a total of 5,676 AD patients and 5,460 controls for ACT-17. Overall, allele contrast (A vs. T) of ACT -17 polymorphism produced significant results in the worldwide population [Pheterogeneity=0.01, random-effects (RE) odds ratio (OR) 1.12; 95% CI 1.04-1.21, P=0.003] and in the Caucasian population [Pheterogeneity=0.03, RE OR1.11 95% CI 1.01-1.24, P=0.04]. Meta-analyses of other genetic contrasts suggested that the A allele carriers are associated with increased susceptibility to AD in variant populations. No significant association was observed in the East-Asian subgroup analysis. In conclusion, ACT-17 variation presents a risk factor for AD in the worldwide population, especially in the Caucasian population.

Genetic Risk Factors for Depression in Alzheimer`s Disease Patients by Sonke Arlt, Cuneyt Demiralay, Bjorn Tharun, Olga Geisel, Niels Storm, Martin Eichenlaub, Jan T. Lehmbeck, Klaus Wiedemann, Boris Leuenberger, Holger Jahn (72-81).
Objective: Alzheimer's Disease (AD) is often associated with depressive symptoms developing at any time before and after AD onset. The aetiology of depression in AD has not sufficiently been characterized, but biological aspects due to neurodegeneration and/ or genetic risk factors may play a plausible role and may distinguish it from common depressive disorders. Method: To investigate the possible relationship between genetic risk factors and depression in AD, we assessed genetic polymorphisms reported to be associated with depression (MAOA VNTR, ACE 288bp Insertion/ Deletion, 5HTTLPR, COMT Val158Met, BDNF Val66Met, TPH1 A218C, HTR2A T102C, P2RX7 Q460R, FKBP5 rs1360780 and CRHR1 rs242941) in a cross-sectional study on 246 AD patients with or without clinically significant major depressive disorder (MDD) according to DSM-IV. Results: Significant associations between AD and MDD have been found for three polymorphisms mainly in females (TPH1 A218C, MAOA VNTR and BDNF Val66Met) and one polymorphism in the total population only (FKBP5 rs1360780). There was an increased risk of having MDD in homozygous female carriers of the TPH1 A-allele (odds ratio: 4.35) and homozygous carriers of the MAOA VNTR low activity allele 3R (odds ratio: 3.37). Conclusion: We detected allelic or genotypic associations of MAOA, TPH1, FKBP5 and BDNF in clinically significant MDD in AD. Odds-ratios were generally higher in female AD-patients, which might be due to the composition of the study population. Further studies on the neurotransmitter systems affected by the genetic polymorphisms found to be associated with MDD in AD may help to elucidate the underlying pathomechanisms of MDD.

The Usefulness of Amyloid Imaging in Predicting the Clinical Outcome After Two Years in Subjects with Mild Cognitive Impairment by Timo Grimmer, Carolin Wutz, Alexander Drzezga, Stefan Forster, Hans Forstl, Marion Ortner, Robert Perneczky, Alexander Kurz (82-85).
Background: Mild cognitive impairment (MCI) is a syndrome heterogeneous with regards to etiology and prognosis. Amyloid imaging enables to visualize a hallmark pathology of Alzheimer's disease (AD). Therefore we aimed to assess the usefulness of [11C]PiB PET for predicting clinical outcome of MCI patients after an interval of 2 years. Methods: In 28 MCI participants with a global CDR rating at baseline of 0.5 a baseline examination including clinical assessments and [11C]PiB PET imaging and a clinical follow-up examination after a planned interval of 24 months were performed. Predictive values and accuracy of amyloid-positive and negative scans for conversion to dementia of any type and to dementia due to AD were calculated and compared to neuropsychological tests and ApoE genotyping. Results: Of 17 MCI patients who were amyloid-positive at baseline converted 9 to dementia all of the AD type. 3 of the 11 amyloid-negative MCI subjects converted to dementia but none to dementia due to AD. PPV, NPV and accuracy (to dementia: 0.53, 0.73 and 0.61; to AD: 0.53, 1.00 and 0.70) was comparable to neuropsychological tests and superior to ApoE genotyping. Conclusion: All MCI subjects who converted to dementia due to AD were amyloid-positive. However, only 50% of these MCI due to AD, intermediate likelihood, patients developed manifest dementia due to AD after 24 months limiting the usefulness of [11C]PiB PET for individual prediction of clinical outcome.

Neuropsychiatric Symptoms in Amnestic Mild Cognitive Impairment: Increased Risk and Faster Progression to Dementia by Johanne Somme, Manuel Fernandez-Martínez, Ana Molano, Juan Jose Zarranz (86-94).
Introduction. Neuropsychiatric symptoms (NPS) are common in mild cognitive impairment (MCI) but its role as a predictive factor for the progression to dementia is still not clear. The objective of this study is to identify NPS that predict the progression from amnestic MCI (a-MCI) to dementia using an easy to administer screening tool for NPS. Material and Methods. 132 patients with a-MCI were assessed for NPS by the Neuropsychiatric Inventory (NPI) and followed to detect progression to dementia. Results. The mean follow-up time was 3.5±2.9 years and rate of progression to dementia 28.8%. Two items of NPI were found to be independent risk factors for progression, nighttime behavioural disturbance (hazard ratio(HR)=2.2, 95%CI=1.10-4.43), anxiety (HR=2.5, 95%CI=1.01-6.20) and apathy (HR=2.2, 95%CI=1.003-4.820). The risk of progression increased with higher score on NPI (HR=1.046 per point, 95%CI=1.019- 1.073), and with a higher number of items of NPI affected (HR=3.6 per item, 95%CI=2.0-6.4). Faster progression to dementia was observed in patients with either nighttime behavioural disturbance, apathy or anxiety (4.6 vs. 8.3 years, 5.3 vs. 8.4 years and 3.0 vs. 7.7 years respectively, p < 0.01) as well as in those with a higher number of items affected (no items = 9.2 years, 1-3 items = 6.6 years and > 3 items = 2.9 years, p < 0.001). Conclusions. Assessing a broad spectrum of NPS can help identify patients with a-MCI presenting a higher risk for progression to dementia. This can be useful to select patients for closer follow-up, clinical trials and future therapeutic interventions.

Background: Many early-stage Alzheimer's disease (AD) patients suffer from spatial navigational impairment even in familiar environments. Growing evidence shows that the retrosplenial cortex (RSC) is more damaged in youngonset AD patients (YOAD, onset age before 65) than in late-onset AD (LOAD) in the early-stage of AD. Impaired translation between egocentric and allocentric representations of the environment, as a cause for spatial navigational impairment, usually occurs in people with lesions in the RSC. Objective: To test translational ability between spatial representations in early-stage YOAD and LOAD patients. Methods Tests deemed sensitive to translation of spatial representations were used to evaluate 29 AD (14 YOAD, 15 LOAD) and 27 cognitively healthy controls (14 younger NC and 13 older NC). Results: Younger NC outperformed YOAD in the tests of translation of spatial representations in spite of their equal basic visuoperceptual abilities and distance estimation. No such difference existed between LOAD and older NC. Conclusion: The translation of egocentric-allocentric representation ability, as a principal function of RSC, does not deteriorate equally in early-stage AD patients of different onset age. That early-stage YOAD show more deviations in translation of their spatial representation ability deserves our attention because it may endanger their daily activities.

Microdose Lithium Treatment Stabilized Cognitive Impairment in Patients with Alzheimer's Disease by Marielza Andrade Nunes, Tania Araujo Viel, Hudson Sousa Buck (104-107).
A lower incidence of dementia in bipolar patients treated with lithium has been described. This metal inhibits the phosphorylation of glycogen-synthase-kinase 3-α and β, which are related to amyloid precursor protein processing and tau hyperphosphorylation in pathological conditions, respectively. Following the same rationale, a group just found that lithium has disease-modifying properties in amnestic mild cognitive impairment with potential clinical implications for the prevention of Alzheimer's Disease (AD) when a dose ranging from 150 to 600 mg is used. As lithium is highly toxic in regular doses, our group evaluated the effect of a microdose of 300&#x3BC;g, administered once daily on AD patients for 15 months. In the evaluation phase, the treated group showed no decreased performance in the mini-mental state examination test, in opposition to the lower scores observed for the control group during the treatment, with significant differences starting three months after the beginning of the treatment, and increasing progressively. This data suggests the efficacy of a microdose lithium treatment in preventing cognitive loss, reinforcing its therapeutic potential to treat AD using very low doses.

Despite over one hundred years of intense effort studying Alzheimer's disease (AD), we still do not understand its cause(s) and this adversely affects our ability to develop strongly effective treatments and means to prevent it. This is because our research efforts are not aligned to decipher this age-related disorder that, well after its discovery, has become a major cause of death throughout the world. We are therefore recommending a process to analyze some of the principal factors that hinder our progress in this field of research. Recognizing these barriers — and acting on such a recognition by seeking to resolve them experimentally and garnering societal support to do so — will constitute critical steps towards establishing strategies that will lead to a sorely needed paradigm shift in AD research, and ultimately to the prevention and the effective treatment of this devastating condition. This will probably also spur progress in many related neuropsychiatric disorders, and in that sense act as a seminal endeavor with far-reaching consequences. In order to accomplish this complex task, the biomedical community must acknowledge and come to a consensus about the factors that limit our progress, and then work together to generate new algorithms to tackle these fundamental issues rationally, effectively and deliberately.