Aβ oligomers trigger and accelerate Aβ seeding

Aggregation of amyloid‐β (Aβ) that leads to the formation of plaques in Alzheimer's disease (AD) occurs through the stepwise formation of oligomers and fibrils. An earlier onset of aggregation is obtained upon intracerebral injection of Aβ‐containing brain homogenate into human APP transgenic mice that follows a prion‐like seeding mechanism. Immunoprecipitation of these brain extracts with anti‐Aβ oligomer antibodies or passive immunization of the recipient animals abrogated the observed seeding activity, although induced Aβ deposition was still evident. Here, we establish that, together with Aβ monomers, Aβ oligomers trigger the initial phase of Aβ seeding and that the depletion of oligomeric Aβ delays the aggregation process, leading to a transient reduction of seed‐induced Aβ deposits. This work extends the current knowledge about the role of Aβ oligomers beyond its cytotoxic nature by pointing to a role in the initiation of Aβ aggregation in vivo. We conclude that Aβ oligomers are important for the early initiation phase of the seeding process.     

Development and Expression of Amyloid‐β Peptide 42 in Retinal Ganglion Cells in Rats

The previous studies have shown that Amyloid‐β peptide (Aβ) was mainly found in neurons of neurodegenerative diseases, such as Alzheimer's disease (AD) and glaucoma and little is known about its expression in normal nerve cells. The aim of the present study was to investigate the expression of amyloid‐β peptide 42 (Aβ‐42) in retinal ganglion cells of the postnatal rats. Rats were divided into seven experimental groups: 3, 6, 13, 15, 25, 60, and 90 days postnatal groups. Rats from 15 and 25 days postnatal groups were further divided into light‐exposure and non light‐exposure group. Cryosections or flat‐mounted retinas of rat eyes were used for testing Aβ‐42 by immunocytochemistry staining. Aβ‐42 expression was not observed in rats within 13 days after birth, but was easily detectable in all groups of rats over 15 days after birth. In addition, the expression of Aβ‐42 in retina was increasing as the rats got older, reached to highest level in 60 days after birth. Furthermore, the expression of Aβ‐42 was not detected in rats kept under dark indicating that light is required for the expression of Aβ‐42 in retina. This is the first report showing that normal retinal ganglion cells express Aβ‐42, and that the expression of Aβ‐42 in retinal ganglion cells requires the exposure to light. These data suggest that Aβ‐42 may play a important role in vision development. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

Effect of active Aβ immunotherapy on neurons in human Alzheimer's disease

Amyloid β peptide (Aβ) immunization of Alzheimer's disease (AD) patients has been reported to induce amyloid plaque removal, but with little impact on cognitive decline. We have explored the consequences of Aβ immunotherapy on neurons in post mortem brain tissue. Eleven immunized (AN1792, Elan Pharmaceuticals) AD patients were compared to 28 non‐immunized AD cases. Immunohistochemistry on sections of neocortex was performed for neuron‐specific nuclear antigen (NeuN), neurofilament protein (NFP) and phosphorylated‐(p)PKR (pro‐apoptotic kinase detected in degenerating neurons). Quantification was performed for pPKR and status spongiosis (neuropil degeneration), NeuN‐positive neurons/field, curvature of the neuronal processes and interneuronal distance. Data were corrected for age, gender, duration of dementia and APOE genotype and also assessed in relation to Aβ42 and tau pathology and key features of AD. In non‐immunized patients, the degree of neuritic curvature correlated with spongiosis and pPKR, and overall the neurodegenerative markers correlated better with tau pathology than Aβ42 load. Following immunization, spongiosis increased, interneuronal distance increased, while the number of NeuN‐positive neurons decreased, consistent with enhanced neuronal loss. However, neuritic curvature was reduced and pPKR was associated with Aβ removal in immunized patients. In AD, associations of spongiosis status, curvature ratio and pPKR load with microglial markers Iba1, CD68 and CD32 suggest a role for microglia in neurodegeneration. After immunization, correlations were detected between the number of NeuN‐positive neurons and pPKR with Iba1, CD68 and CD64, suggesting that microglia are involved in the neuronal loss. Our findings suggest that in established AD this form of active Aβ immunization may predominantly accelerate loss of damaged degenerating neurons. This interpretation is consistent with in vivo imaging indicating an increased rate of cerebral atrophy in immunized AD patients. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

The Recent Updates of Therapeutic Approaches Against Aβ for the Treatment of Alzheimer's Disease

One of the main neuropathological lesions observed in brain autopsy of Alzheimer's disease (AD) patients is the extracellular senile plaques mainly composed of amyloid‐beta (Aβ) peptide. Recently, treatment strategies have focused on modifying the formation, clearance, and accumulation of this potentially neurotoxic peptide. β‐ and γ‐secretase are responsible for the cleavage of amyloid precursor protein (APP) and the generation of Aβ peptide. Treatments targeting these two critical secretases may therefore reduce Aβ peptide levels and positive impact on AD. Vaccination is also an advanced approach against Aβ. This review focuses on recent advances of our understanding of this key peptide, with emphasis on Aβ peptide synthesis, accumulation and neurotoxicity, and current therapies including vaccination and two critical secretase inhibitors. MicroRNAs (miRNAs) are a class of conserved endogenous small noncoding RNAs, known to regulate the expression of complementary messenger RNAs, involved in AD development. We therefore address the relationship of miRNAs in the brain and Aβ generation, as a novel therapeutic approach to the treatment of AD while also providing new insights on the etiology of this neurological disorder. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

18F-THK5351 PET Positivity and Longitudinal Changes in Cognitive Function in β-Amyloid-Negative Amnestic Mild Cognitive Impairment

PurposeNeuroinflammation is considered an important pathway associated with several diseases that result in cognitive decline. ¹⁸F-THK5351 positron emission tomography (PET) signals might indicate the presence of neuroinflammation, as well as Alzheimer’s disease-type tau aggregates. β-amyloid (Aβ)-negative (Aβ–) amnestic mild cognitive impairment (aMCI) may be associated with non-Alzheimer’s disease pathophysiology. Accordingly, we investigated associations between ¹⁸F-THK5351 PET positivity and cognitive decline among Aβ– aMCI patients.Materials and MethodsThe present study included 25 amyloid PET negative aMCI patients who underwent a minimum of two follow-up neuropsychological evaluations, including clinical dementia rating-sum of boxes (CDR-SOB). The patients were classified into two groups: ¹⁸F-THK5351-positive and -negative groups. The present study used a linear mixed effects model to estimate the effects of ¹⁸F-THK5351 PET positivity on cognitive prognosis among Aβ– aMCI patients.ResultsAmong the 25 Aβ– aMCI patients, 10 (40.0%) were ¹⁸F-THK5351 positive. The patients in the ¹⁸F-THK5351-positive group were older than those in the ¹⁸F-THK5351-negative group (77.4±2.2 years vs. 70.0±5.5 years; p<0.001). There was no difference between the two groups with regard to the proportion of apolipoprotein E ε4 carriers. Interestingly, however, the CDR-SOB scores of the ¹⁸F-THK5351-positive group deteriorated at a faster rate than those of the ¹⁸F-THK5351-negative group (B=0.003, p=0.033).ConclusionThe results of the present study suggest that increased ¹⁸F-THK5351 uptake might be a useful predictor of poor prognosis among Aβ– aMCI patients, which might be associated with increased neuroinflammation (ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT02656498","term_id":"NCT02656498"}}NCT02656498).     

Primary over‐expression of AβPP in muscle does not lead to the development of inclusion body myositis in a new lineage of the MCK‐AβPP transgenic mouse

The aim of this study is to determine whether primary over‐expression of AβPP in skeletal muscle results in the development of features of inclusion body myositis (IBM) in a new lineage of the MCK‐AβPP transgenic mouse. Quantitative histological, immunohistochemical and western blotting studies were performed on muscles from 3 to 18 month old transgenic and wild‐type C57BL6/SJL mice. Electron microscopy was also performed on muscle sections from selected animals. Although western blotting confirmed that there was over‐expression of full length AβPP in transgenic mouse muscles, deposition of amyloid‐β and fibrillar amyloid could not be demonstrated histochemically or with electron microscopy. Additionally, other changes typical of IBM such as rimmed vacuoles, cytochrome C oxidase‐deficient fibres, upregulation of MHC antigens, lymphocytic inflammatory infiltration and T cell fibre invasion were absent. The most prominent finding in both transgenic and wild‐type animals was the presence of tubular aggregates which was age‐related and largely restricted to male animals. Expression of full length AβPP in this MCK‐AβPP mouse lineage did not reach the levels required for immunodetection or deposition of amyloid‐β as in the original transgenic strains, and was not associated with the development of pathological features of IBM. These negative results emphasise the potential pitfalls of re‐deriving transgenic mouse strains in different laboratories.     

27‐hydroxycholesterol promotes Aβ accumulation via altering Aβ metabolism in mild cognitive impairment patients and APP/PS1 mice

The oxysterol 27‐hydroxycholesterol (27‐OHC) has been considered to play a key role in the pathogenesis of Alzheimer’s disease (AD). Because β‐amyloid peptide (Aβ) is the pathological hallmark of AD, the aim of this study is to verify whether 27‐OHC could lead to cognitive impairment through modulating Aβ accumulation and deposition. Regulation of Aβ metabolism was explored as the pathogenic mechanism of 27‐OHC. Furthermore, microRNAs (miRNAs) and their relations with 27‐OHC were also detected. In present study, matched case‐control study and APP/PS1 transgenic mice research were conducted. The results showed that the 27‐OHC and Aβ in plasma were increased in mild cognitive impairment patients, and a slight correlation was found between 27‐OHC and Aβ1‐40. This relationship was also proved by the research of APP/PS1 mice. More severe learning and memory impairment and higher Aβ1‐40 expression in brain and plasma were detected in the APP/PS1 mice of 27‐OHC treatment group. In addition, increased amyloid plaques were also found in the hippocampus of 27‐OHC‐treated mice. In order to find out the mechanism of 27‐OHC on regulating Aβ metabolism, the factors of Aβ production (APP, BACE1 and ADAM10), transport (LRP1 and RAGE) and elimination (NEP and IDE) were tested respectively. The gene and protein expressions of APP, BACE1 and RAGE were increased while LRP1 and IDE were decreased in the brain of 27‐OHC‐treated mice. At last, down‐regulated expression of miRNA let‐7g‐5p was found after 27‐OHC treatment. In conclusion, these findings suggested that excessive 27‐OHC could enhance the accumulation and deposition of Aβ both in brain and blood, resulting in a severe impairment of cognition, especially in the modulation of Aβ1‐40. The mechanism might be associated with the regulation of Aβ metabolism, and miRNA let‐7g‐5p was likely to play a vital role in this pathological process induced by 27‐OHC.     

Clusterin levels are increased in Alzheimer's disease and influence the regional distribution of Aβ

Clusterin, also known as apoJ, is a lipoprotein abundantly expressed within the CNS. It regulates Aβ fibril formation and toxicity and facilitates amyloid‐β (Aβ) transport across the blood‐brain barrier. Genome‐wide association studies have shown variations in the clusterin gene (CLU) to influence the risk of developing sporadic Alzheimer''s disease (AD). To explore whether clusterin modulates the regional deposition of Aβ, we measured levels of soluble (NP40‐extracted) and insoluble (guanidine‐HCl‐extracted) clusterin, Aβ40 and Aβ42 by sandwich ELISA in brain regions with a predilection for amyloid pathology—mid‐frontal cortex (MF), cingulate cortex (CC), parahippocampal cortex (PH), and regions with little or no pathology—thalamus (TH) and white matter (WM). Clusterin level was highest in regions with plaque pathology (MF, CC, PH and PC), approximately mirroring the regional distribution of Aβ. It was significantly higher in AD than controls, and correlated positively with Aβ42 and insoluble Aβ40. Soluble clusterin level rose significantly with severity of cerebral amyloid angiopathy, and in MF and PC regions was highest in APOE ɛ4 homozygotes. In the TH and WM (areas with little amyloid pathology) clusterin was unaltered in AD and did not correlate with Aβ level. There was a significant positive correlation between the concentration of clusterin and the regional levels of insoluble Aβ42; however, the molar ratio of clusterin : Aβ42 declined with insoluble Aβ42 level in a region‐dependent manner, being lowest in regions with predilection for Aβ plaque pathology. Under physiological conditions, clusterin reduces aggregation and promotes clearance of Aβ. Our findings indicate that in AD, clusterin increases, particularly in regions with most abundant Aβ, but because the increase does not match the rising level of Aβ42, the molar ratio of clusterin : Aβ42 in those regions falls, probably contributing to Aβ deposition within the tissue.     

Cerebrovascular miRNAs correlate with the clearance of Aβ through perivascular route in younger 3xTg‐AD mice

The “two‐hit vascular hypothesis for Alzheimer's disease (AD)” and amyloid‐β (Aβ) oligomer hypothesis suggest that impaired soluble Aβ oligomers clearance through the cerebral vasculature may be an initial step of the AD process. Soluble Aβ oligomers are driven into perivascular spaces from the brain parenchyma and toward peripheral blood flow. The underlying vascular‐based mechanism, however, has not been defined. Given that microRNAs (miRNAs), emerging as novel modulators, are involved in numerous physiological and pathological processes, we hypothesized that cerebrovascular miRNAs may regulate the activities of brain blood vessels, which further affects the concentration of Aβ in the AD brain. In this study, perivascular Aβ deposits, higher vascular activation, increased pericyte coverage and up‐regulated capillaries miRNAs at 6 months old (6 mo) were found to correlate with the lower Aβ levels of middle AD stage (9 mo) in 3xTg‐AD (3xTg) mice. It is implicated that at the early stage of AD when intracellular Aβ appeared, higher expression of vessel‐specific miRNAs, elevated pericyte coverage, and activated endothelium facilitate Aβ oligomer clearance through the perivascular route, resulting in a transient reduction of Aβ oligomers at 9 mo. Additionally, ghrelin‐induced upregulation of capillary miRNAs and increased pericyte coverage attenuated Aβ burden at 9 mo, in further support of the relationship between vascular miRNAs and Aβ clearance. This work suggests a cerebral microvessel miRNA may boost endothelial highly activated phenotypes to promote elimination of Aβ oligomers through the perivascular drainage pathway and contribute to AD progression. The targeting of brain vessel‐specific miRNAs may provide a new rationale for the development of innovative therapeutic strategies for AD treatment.     

Oligomeric Aβ in Alzheimer's Disease: Relationship to Plaque and Tangle Pathology,APOE Genotype and Cerebral Amyloid Angiopathy

Despite accumulating evidence of a central role for oligomeric amyloid β (Aβ) in the pathogenesis of Alzheimer''s Disease (AD), there is scant information on the relationship between the levels and distribution of oligomeric Aβ and those of other neurodegenerative abnormalities in AD. In the present study, we have found oligomeric Aβ to be associated with both diffuse and neuritic plaques (mostly co‐localized with Aβ_1–42) and with cerebrovascular deposits of Aβ in paraffin sections of formalin‐fixed human brain tissue. The amount of oligomeric Aβ that was labeled in the sections correlated with total Aβ plaque load, but not phospho‐tau load, cerebral amyloid angiopathy (CAA) severity or APOE genotype. Although soluble, oligomeric and insoluble Aβ levels were all significantly increased in AD brain homogenates, case‐to‐case variation and overlap between AD and controls were considerable. Over the age‐range studied (43–98 years), the levels of soluble Aβ, oligomeric Aβ₄₂, oligomeric Aβ₄₀ and insoluble Aβ did not vary significantly with age. Oligomeric Aβ_1–42 and insoluble Aβ levels were significantly higher in women. Overall, the level of insoluble Aβ, but neither oligomeric nor soluble Aβ, was associated with Braak stage, CAA severity and APOEε4 frequency, raising questions as to the role of soluble and oligomeric Aβ in the progression of AD.     

Rapid amyloid‐β oligomer and protofibril accumulation in traumatic brain injury

Deposition of amyloid‐β (Aβ) is central to Alzheimer's disease (AD) pathogenesis and associated with progressive neurodegeneration in traumatic brain injury (TBI). We analyzed predisposing factors for Aβ deposition including monomeric Aβ40, Aβ42 and Aβ oligomers/protofibrils, Aβ species with pronounced neurotoxic properties, following human TBI. Highly selective ELISAs were used to analyze N‐terminally intact and truncated Aβ40 and Aβ42, as well as Aβ oligomers/protofibrils, in human brain tissue, surgically resected from severe TBI patients (n = 12; mean age 49.5 ± 19 years) due to life‐threatening brain swelling/hemorrhage within one week post‐injury. The TBI tissues were compared to post‐mortem AD brains (n = 5), to post‐mortem tissue of neurologically intact (NI) subjects (n = 4) and to cortical biopsies obtained at surgery for idiopathic normal pressure hydrocephalus patients (iNPH; n = 4). The levels of Aβ40 and Aβ42 were not elevated by TBI. The levels of Aβ oligomers/protofibrils in TBI were similar to those in the significantly older AD patients and increased compared to NI and iNPH controls (P < 0.05). Moreover, TBI patients carrying the AD risk genotype Apolipoprotein E epsilon3/4 (APOE ε3/4; n = 4) had increased levels of Aβ oligomers/protofibrils (P < 0.05) and of both N‐terminally intact and truncated Aβ42 (P < 0.05) compared to APOE ε3/4‐negative TBI patients (n = 8). Neuropathological analysis showed insoluble Aβ aggregates (commonly referred to as Aβ plaques) in three TBI patients, all of whom were APOE ε3/4 carriers. We conclude that soluble intermediary Aβ aggregates form rapidly after TBI, especially among APOE ε3/4 carriers. Further research is needed to determine whether these aggregates aggravate the clinical short‐ and long‐term outcome in TBI.     

The binding of pullulan modified cholesteryl nanogels to Aβ oligomers and their suppression of cytotoxicity

Among various hydrogels able to form monodisperse and stable nanoparticles (20–30 nm) are those with pullulan-bearing cholesteryl moieties (CHP). These nanoparticles can interact with soluble proteins through hydrophobic bonding. The objectives of this study were to investigate whether CHP nanogels would interact with oligomeric forms of the 42 amino acid variant of β-amyloid (Aβ_1–42) and if the formation of CHP-Aβ_1–42 oligomer entities will reduce cytotoxicity of Aβ_1–42 in primary cortical cells and microglial (N9) cells. By employing fluorescent CHP analogs with different charges we provide evidence that, (i) both neutral and positively charged CHP nanoparticles interact with Aβ_1–42 monomers and oligomers, (ii) neutral CHP is non-toxic, but positively charged derivatives (CHPNH2) are toxic, particularly in primary cortical cultures, and (iii) binding of both monomeric and oligomeric Aβ_1–42 to CHP significantly reduces Aβ_1–42 toxicity in both the primary cortical and microglial cells. These results suggest that CHP nanogels could provide a valid complementary approach to antibody immunotherapy in neurological disorders characterized by the formation of soluble toxic aggregates, such as those in Alzheimer's disease (AD).     

Common Impact of Chronic Kidney Disease and Brain Microhemorrhages on Cerebral Aβ Pathology in SHRSP

While chronic kidney disease seems to be an independent risk factor for cognitive decline, its impact on cerebral amyloid‐β (Aβ) depositions, one hallmark of Alzheimer's Disease (AD) pathology, has not been investigated. Utilizing 80 male nontransgenic spontaneously hypertensive stroke prone rats (SHRSP) at various ages (12 to 44 weeks), tubulointerstitial renal damage, prevalence of cerebral microhemorrhages and Aβ accumulations were quantified. Using age‐adjusted general linear models we investigated the main and interaction effects of renal damage and cerebral microhemorrhages on cerebral Aβ load. In addition, using post mortem human brain tissue of 16 stroke patients we examined the co‐localization of perivascular Aβ deposits and small vessel wall damage. Statistical models revealed an age‐independent main effect of tubulointerstitial kidney damage on brain Aβ accumulations, which was reinforced by the consecutive presence of cerebral microhemorrhages. Moreover, cerebral microhemorrhages independently predicted brain Aβ burden in SHRSP. In up to 69% of all human cases perivascular Aβ deposits were detected in the direct vicinity of small vessel wall damage. Our results support the associations between vascular pathology and Aβ deposition, and demonstrate a relationship between chronic kidney disease and cerebral Aβ pathology. Hence, our data suggest that prevention of chronic renal damage may reduce cerebral Aβ pathology.     

轻度认知障碍患者EEG动力学特征提取与分类方法研究进展

脑电图可用于对轻度认知障碍的病理性变化进行评估。近年来,脑电领域的特征提取和分类方法广泛地应用到对轻度认知障碍疾病的诊断中。首先从局部耦合与全局同步两个方面,深入分析轻度认知障碍患者脑电信号特征提取方法的应用情况及其优势和不足,而后对当前轻度认知障碍患者脑电信号特征进行分类的多种方法进行详细总结与分析,如支持向量机、k均值以及近年来应用广泛的卷积神经网络等,最后对该领域脑电动力学特征提取与分类方法的未来发展趋势进行展望。     

Increased Amoeboid Microglial Density in the Olfactory Bulb of Parkinson's and Alzheimer's Patients

The olfactory bulb (OB) is affected early in both Parkinson's (PD) and Alzheimer's disease (AD), evidenced by the presence of disease‐specific protein aggregates and an early loss of olfaction. Whereas previous studies showed amoeboid microglia in the classically affected brain regions of PD and AD patients, little was known about such changes in the OB. Using a morphometric approach, a significant increase in amoeboid microglia density within the anterior olfactory nucleus (AON) of AD and PD patients was observed. These amoeboid microglia cells were in close apposition to β‐amyloid, hyperphosphorylated tau or α‐synuclein deposits, but no uptake of pathological proteins by microglia could be visualized. Subsequent analysis showed (i) no correlation between microglia and α‐synuclein (PD), (ii) a positive correlation with β‐amyloid (AD), and (iii) a negative correlation with hyperphosphorylated tau (AD). Furthermore, despite the observed pathological alterations in neurite morphology, neuronal loss was not apparent in the AON of both patient groups. Thus, we hypothesize that, in contrast to the classically affected brain regions of AD and PD patients, within the AON rather than neuronal loss, the increased density in amoeboid microglial cells, possibly in combination with neurite pathology, may contribute to functional deficits.     

老年DM2患者认知功能障碍与C型利钠肽的关系

目的:研究老年2型糖尿病(DM2)患者认知障碍与C型利钠肽(C-type natriuretic peptide,CNP)的关系,进一步探讨糖尿病认知障碍的发病机制.方法 80例60岁以上的DM2患者,根据蒙特利尔认知评估量表(Montreal Cognitive Assessment,MoCA)分为认知障碍组(31例...