Astrocytic Aβ1‐42 uptake is determined by Aβ‐aggregation state and the presence of amyloid‐associated proteins

Intracerebral accumulation of amyloid‐β (Aβ) leading to Aβ plaque formation, is the main hallmark of Alzheimer's disease and might be caused by defective Aβ‐clearance. We previously found primary human astrocytes and microglia able to bind and ingest Aβ1‐42 in vitro, which appeared to be limited by Aβ1‐42 fibril formation. We now confirm that astrocytic Aβ‐uptake depends on size and/or composition of Aβ‐aggregates as astrocytes preferably take up oligomeric Aβ over fibrillar Aβ. Upon exposure to either fluorescence‐labelled Aβ1‐42 oligomers (Aβ_oligo) or fibrils (Aβ_fib), a larger (3.7 times more) proportion of astrocytes ingested oligomers compared to fibrils, as determined by flow cytometry. Aβ‐internalization was verified using confocal microscopy and live‐cell imaging. Neither uptake of Aβ_oligo nor Aβ_fib, triggered proinflammatory activation of the astrocytes, as judged by quantification of interleukin‐6 and monocyte‐chemoattractant protein‐1 release. Amyloid‐associated proteins, including α1‐antichymotrypsin (ACT), serum amyloid P component (SAP), C1q and apolipoproteins E (ApoE) and J (ApoJ) were earlier found to influence Aβ‐aggregation. Here, astrocytic uptake of Aβ_fib increased when added to the cells in combination with SAP and C1q (SAP/C1q), but was unchanged in the presence of ApoE, ApoJ and ACT. Interestingly, ApoJ and ApoE dramatically reduced the number of Aβ_oligo‐positive astrocytes, whereas SAP/C1q slightly reduced Aβ_oligo uptake. Thus, amyloid‐associated proteins, especially ApoJ and ApoE, can alter Aβ‐uptake in vitro and hence may influence Aβ clearance and plaque formation in vivo. © 2010 Wiley‐Liss, Inc.     

Enhanced aggregation and β structure of amyloid β peptide after coincubation with C1Q

Several lines of evidence now suggest that aggregation of soluble amyloid β peptide (Aβ) into a cross β sheet configuration may be an important factor in mediating potential neurotoxicity of Aβ. Synthetic Aβ has been shown to self aggregate in vitro. Here, we demonstrate that coincubation of freshly solubilized Aβ with C1q, a complement component known to bind Aβ in vitro and to colocalize with Aβ in vivo, results in as much as a 7-fold enhancement of Aβ aggregation, as well as a 2–4-fold enhancement of β structure within aggregates. The addition of C1q to preformed Aβ aggregates also results in significantly increased resistance to aggregate resolubilization. © 1994 Wiley-Liss, Inc.     

β-Amyloid precursor epitopes in muscle fibers of inclusion body myositis

Sporadic inclusion body myositis (IBM) and hereditary inclusion body myopathy (hIBM) are severe and progressive muscle diseases, characterized pathologically by vacuolated muscle fibers that contain 15- to 21-nm cytoplasmic tubulofilaments (CTFs). Those vacuolated muscle fibers also contain abnormally accumulated ubiquitin and β-amyloid protein (Aβ), and they contain amyloid in β-pleated sheets as indicated by Congo red and crystal violet positivity. Using several well-characterized antibodies, we have now demonstrated that, in addition to Aβ, two other epitopes, N-terminal and C-terminal, of the β-amyloid precursor protein (βPP) are abnormally accumulated in IBM vacuolated muscle fibers and similarly in hIBM. At the light microscopy level, immunoreactivities of N- and C-epitopes of βPP closely colocalized with Aβ and ubiquitin immunoreactivities. However, by immunogold electronmicroscopy, even though N-, C-, and Aβ epitopes of βPP and ubiquitin colocalized at the amorphous and dense floccular structures, only Aβ was localized to the 6- to 10-nm amyloid-like fibrils and only ubiquitin was localized to CTFs. βPP immunoreactive structures were often in proximity to CTFs, but CTFs themselves never contained βPP immunoreactivities. The fact that Aβ but not C- or N-terminal epitopes of βPP localized to the 6- to 10-nm amyloid-like fibrils suggests that free Aβ might be generated during βPP processing and, after aggregation, may be responsible for the amyloid present within IBM muscle fibers. Our study demonstrates that three epitopes of βPP accumulate abnormally in diseased human muscle, and therefore this phenomenon is not unique to Alzheimer's disease, Down's syndrome brain, and Dutch-type cerebrovascular amyloidosis.     

γ‐Secretase binding sites in aged and Alzheimer's disease human cerebrum: the choroid plexus as a putative origin of CSF Aβ

Deposition of β ‐amyloid (Aβ) peptides, cleavage products of β‐amyloid precursor protein (APP) by β‐secretase‐1 (BACE1) and γ‐secretase, is a neuropathological hallmark of Alzheimer's disease (AD). γ‐Secretase inhibition is a therapeutical anti‐Aβ approach, although changes in the enzyme's activity in AD brain are unclear. Cerebrospinal fluid (CSF) Aβ peptides are thought to derive from brain parenchyma and thus may serve as biomarkers for assessing cerebral amyloidosis and anti‐Aβ efficacy. The present study compared active γ‐secretase binding sites with Aβ deposition in aged and AD human cerebrum, and explored the possibility of Aβ production and secretion by the choroid plexus (CP). The specific binding density of [³H]‐L‐685,458, a radiolabeled high‐affinity γ‐secretase inhibitor, in the temporal neocortex and hippocampal formation was similar for AD and control cases with similar ages and post‐mortem delays. The CP in post‐mortem samples exhibited exceptionally high [³H]‐L‐685,458 binding density, with the estimated maximal binding sites (Bmax) reduced in the AD relative to control groups. Surgically resected human CP exhibited APP, BACE1 and presenilin‐1 immunoreactivity, and β‐site APP cleavage enzymatic activity. In primary culture, human CP cells also expressed these amyloidogenic proteins and released Aβ40 and Aβ42 into the medium. Overall, our results suggest that γ‐secretase activity appears unaltered in the cerebrum in AD and is not correlated with regional amyloid plaque pathology. The CP appears to be a previously unrecognised non‐neuronal contributor to CSF Aβ, probably at reduced levels in AD.     

Conversion of Aβ43 to Aβ40 by the successive action of angiotensin‐converting enzyme 2 and angiotensin‐converting enzyme

The longer and neurotoxic species of amyloid‐β protein (Aβ), Aβ42 and Aβ43, contribute to Aβ accumulation in Alzheimer's disease (AD) pathogenesis and are considered to be the primary cause of the disease. In contrast, the predominant secreted form of Aβ, Aβ40, inhibits amyloid deposition and may have neuroprotective effects. We have reported that angiotensin‐converting enzyme (ACE) converts Aβ42 to Aβ40 and that Aβ43 is the earliest‐depositing Aβ species in the amyloid precursor protein transgenic mouse brain. Here we found that Aβ43 can be converted to Aβ42 and to Aβ40 in mouse brain lysate. We further identified the brain Aβ43‐to‐Aβ42‐converting enzyme as ACE2. The purified human ACE2 converted Aβ43 to Aβ42, and this activity was inhibited by a specific ACE2 inhibitor, DX600. Notably, the combination of ACE2 and ACE could convert Aβ43 to Aβ40. Our results indicate that the longer, neurotoxic forms of Aβ can be converted to the shorter, less toxic or neuroprotective forms of Aβ by ACE2 and ACE. Moreover, we found that ACE2 activity showed a tendency to decrease in the serum of AD patients compared with normal controls, suggesting an association between lower ACE2 activity and AD. Thus, maintaining brain ACE2 and ACE activities may be important for preventing brain amyloid neurotoxicity and deposition in Alzheimer's disease. © 2014 Wiley Periodicals, Inc.     

Plasma Levels of amyloid β proteins Aβ1–40 and Aβ1–42(43) are elevated in Down's syndrome

To investigate the effect of the overexpression of β-amyloid precursor protein (APP) on the production of two major amyloid β protein (Aβ) species, Aβ40 and Aβ42(43), we measured amounts of Aβ1–40 and Aβ1–42(43) in the plasma from 44 patients with Down's syndrome (DS) (age, 19–61 years) and 66 age-matched normal controls using enzyme-linked immunosorbent assays. Plasma concentrations of both Aβ1–40 and Aβ1–42(43) were increased about 3-fold and 2-fold, respectively, in DS patients compared with normal controls. Especially, the increases in plasma Aβ1–40 in DS Patients were statistically higher than the 1.5-fold increase one might predict based on the gene dose of APP in DS. These findings showed that both Aβ1–40 and Aβ1–42(43) are increased in plasma in DS patients, the former more than the latter, suggesting that overexpression of APP and/or other genes may have different effects on the production of these two Aβ species in DS.     

Amyloid β protein (Aβ) deposition: Aβ42(43) precedes Aβ40 in down Syndrome

The chronological relationship regarding deposition of amyloid β protein (Aβ) species, Aβ40 and Aβ42(43), was investigated in 16 brains from Down syndrome patients aged 31 to 64 years. The frontal cortex was probed with two end-specific monoclonals that recognize Aβ40 or Aβ42(43). All senile plaques detected with an authentic β monoclonal were also Aβ42(43) positive, but only a varying proportion was Aβ40 positive. In young (≤ 50 years old) brains there were many Aβ42(43)-positive, Aβ40-negative diffuse plaques, but only few Aβ40-positive senile plaques (mean, 6.3% of total number of senile plaques). The 2 youngest Down syndrome brains showed only diffuse plaques that were all Aβ42(43) positive but Aβ40 negative. Old (≤ 50 years old) brains contained many mature senile plaques with amyloid cores in addition to diffuse and immature plaques and the proportion of Aβ40-positive senile plaques was increased (mean, 42% of total). Cerebral amyloid angiopathy was more abundant in old Down syndrome brains and was positive for both Aβ40 and Aβ42(43). In cerebral amyloid angiopathy, Aβ40 predominated over Aβ42(43) in both staining intensity and number of positive vessels. These results indicate that (1) the Aβ species intially deposited in the brain as senile plaques is Aβ42(43) and Aβ40 only appears a decade later, and (2) in cerebral amyloid angiopathy Aβ40 appears as early as Aβ42(43).     

Cerebrospinal fluid inhibits Alzheimer β-amyloid fibril formation in vitro

Alzheimer's disease is characterized by the deposition of β-protein (Aβ) as amyloid. Recently, it was found that Aβ is a normal component of serum and cerebrospinal fluid. Synthetic peptides homologous to Aβ form amyloid-like fibrils spontaneously in water or physiological solutions. Using a peptide homologous to Aβ1–40, we find that fibril formation is inhibited by the presence of cerebrospinal fluid.     

Delayed amyloid plaque deposition and behavioral deficits in outcrossed AβPP/PS1 mice

Alzheimer's disease (AD) is a progressive neurodegenerative dementia characterized by amyloid plaque accumulation, synapse/dendrite loss, and cognitive impairment. Transgenic mice expressing mutant forms of amyloid‐β precursor protein (AβPP) and presenilin‐1 (PS1) recapitulate several aspects of this disease and provide a useful model system for studying elements of AD progression. AβPP/PS1 mice have been previously shown to exhibit behavioral deficits and amyloid plaque deposition between 4–9 months of age. We crossed AβPP/PS1 animals with mice of a mixed genetic background (C57BL/6 × 129/SvJ) and investigated the development of AD‐like features in the resulting outcrossed mice. The onset of memory‐based behavioral impairment is delayed considerably in outcrossed AβPP/PS1 mice relative to inbred mice on a C57BL/6 background. While inbred AβPP/PS1 mice develop deficits in radial‐arm water maze performance and novel object recognition as early as 8 months, outcrossed AβPP/PS1 mice do not display defects until 18 months. Within the forebrain, we find that inbred AβPP/PS1 mice have significantly higher amyloid plaque burden at 12 months than outcrossed AβPP/PS1 mice of the same age. Surprisingly, inbred AβPP/PS1 mice at 8 months have low plaque burden, suggesting that plaque burden alone cannot explain the accompanying behavioral deficits. Analysis of AβPP processing revealed that elevated levels of soluble Aβ correlate with the degree of behavioral impairment in both strains. Taken together, these findings suggest that animal behavior, amyloid plaque deposition, and AβPP processing are sensitive to genetic differences between mouse strains. J. Comp. Neurol., 521:1395–1408, 2013. © 2012 Wiley Periodicals, Inc.     

Dynamin 1 depletion and memory deficits in rats treated with Aβ and cerebral ischemia

Alzheimer's disease (AD) is progressive dementia with senile plaques composed of β‐amyloid (Aβ). Recent studies suggest that synaptic dysfunction is one of the earliest events in the pathogenesis of AD. Here we provide the first experimental evidence that a change in the level of dynamin 1 induced by Aβ correlates with memory impairment in vivo. We treated rats with transient cerebral ischemia with oligomeric forms of Aβ (Aβ oligomers), including dimers, trimers, and tetramers, intracerebroventricularly. The combination of Aβ oligomers and cerebral ischemia, but not cerebral ischemia alone, significantly impaired memory and decreased the level of dynamin 1, which plays a critical role in synaptic vesicle recycling, but did not affect the levels of other synaptic proteins, such as synaptophysin and synaptobrevin, in the hippocampus. Furthermore, the N‐methyl‐D ‐aspartate (NMDA) receptor antagonist memantine prevented memory impairment and dynamin 1 degradation, suggesting that these changes might be mediated by NMDA receptors. These results suggest that Aβ oligomers induce memory impairment via dynamin 1 degradation, which may imply that dynamin 1 degradation is one of the causes of synaptic dysfunction in AD. © 2010 Wiley‐Liss, Inc.     

Cyclin‐Dependent kinase 5 targeting prevents β‐Amyloid aggregation involving glycogen synthase kinase 3β and phosphatases

Inappropriate activation of cyclin‐dependent kinase 5 (CDK5) resulting from proteolytic release of the activator fragment p25 from the membrane contributes to the formation of neurofibrillary tangles, β‐amyloid (βA) aggregation, and chronic neurodegeneration. At 18 months of age, 3× Tg‐AD mice were sacrificed after either 3 weeks (short term) or 1 year (long term) of CDK5 knockdown. In short‐term‐treated animals, CDK5 knockdown reversed βA aggregation in the hippocampi via inhibitory phosphorylation of glycogen synthase kinase 3β Ser9 and activation of phosphatase PP2A. In long‐term‐treated animals, CDK5 knockdown induced a persistent reduction in CDK5 and prevented βA aggregation, but the effect on amyloid precursor protein processing was reduced, suggesting that yearly booster therapy would be required. These findings further validate CDK5 as a target for preventing or blocking amyloidosis in older transgenic mice. © 2015 Wiley Periodicals, Inc.     

Binding and uptake of Aβ1‐42 by primary human astrocytes in vitro

Clearance of the amyloid‐β peptide (Aβ) as a remedy for Alzheimer's disease (AD) is a major target in on‐going clinical trials. In vitro studies confirmed that Aβ is taken up by rodent astrocytes, but knowledge on human astrocyte‐mediated Aβ clearance is sparse. Therefore, by means of flow cytometry and confocal laser scanning microscopy (CLSM), we evaluated the binding and internalization of Aβ1‐42 by primary human fetal astrocytes and adult astrocytes, isolated from nondemented subjects (n = 8) and AD subjects (n = 6). Furthermore, we analyzed whether α1‐antichymotrypsin (ACT), which is found in amyloid plaques and can influence Aβ fibrillogenesis, affects the Aβ uptake by human astrocytes. Upon over night exposure of astrocytes to FAM‐labeled Aβ1‐42 (10 μM) preparations, (80.7 ± 17.7)% fetal and (52.9 ± 20.9)% adult Aβ‐positive astrocytes (P = 0.018) were observed. No significant difference was found in Aβ1‐42 uptake between AD and non‐AD astrocytes, and no influence of ApoE genotype on Aβ1‐42 uptake was observed in any group. There was no difference in the percentage of Aβ‐positive cells upon exposure to Aβ1‐42 (10 μM) combined with ACT (1,000:1, 100:1, and 10:1 molar ratio), versus Aβ1‐42 alone. CLSM revealed binding of Aβ1‐42 to the cellular surfaces and cellular internalization of smaller Aβ1‐42 fragments. Under these conditions, there was no increase in cellular release of the proinflammatory chemokine monocyte‐chemoattractant protein 1, as compared with nontreated control astrocytes. Thus, primary human astrocytes derived from different sources can bind and internalize Aβ1‐42, and fetal astrocytes were more efficient in Aβ1‐42 uptake than adult astrocytes. © 2008 Wiley‐Liss, Inc.     

Effects of antiparkinsonian agents on β‐amyloid and α‐synuclein oligomer formation in vitro

The aggregation of β‐amyloid protein (Aβ) and α‐synuclein (αS) are hypothesized to be the key pathogenic event in Alzheimer's disease (AD) and Lewy body diseases (LBD), with oligomeric assemblies thought to be the most neurotoxic. Inhibitors of oligomer formation, therefore, could be valuable therapeutics for patients with AD and LBD. Here, we examined the effects of antiparkinsonian agents (dopamine, levodopa, trihexyphenidyl, selegiline, zonisamide, bromocriptine, peroxide, ropinirole, pramipexole, and entacapone) on the in vitro oligomer formation of Aβ40, Aβ42, and αS using a method of photo‐induced cross‐linking of unmodified proteins (PICUP), electron microscopy, and atomic force microscopy. The antiparkinsonian agents except for trihexyphenidyl inhibited both Aβ and αS oligomer formations, and, among them, dopamine, levodopa, pramipexole, and entacapone had the stronger in vitro activity. Circular dichroism and thioflavin T(S) assays showed that secondary structures of Aβ and αS assemblies inhibited by antiparkinsonian agents were statistical coil state and that their seeding activities had disappeared. The antiparkinsonian agents could be potential therapeutic agents to prevent or delay AD and LBD progression. © 2013 Wiley Periodicals, Inc.     

Loss of endosomal/lysosomal membrane impermeability is an early event in amyloid Aβ1-42 pathogenesis

Previous studies have implicated the failure to degrade aggregated Aβ1-42 in late endosomes or secondary lysosomes as a mechanism for the accumulation of β-amyloid in Alzheimer's disease. We examined the consequences of intracellular accumulation of Aβ1-42 on the integrity of the endosomal/lysosomal compartment by monitoring Lucifer Yellow fluorescence and the release of lysosomal hydrolases into the soluble, cytosolic fraction. In control cells, the Lucifer Yellow fluorescence is observed as punctate staining in a perinuclear distribution with no apparent cytoplasmic fluorescence, consistent with its localization in late endosomes or secondary lysosomes. After incubation with Aβ1-42 for 6 hr, a loss of lysosomal membrane impermeability is observed as evidenced by redistribution of the fluorescence to a diffuse, cytoplasmic pattern. The loss of lysosomal membrane impermeability is correlated with Aβ1-42 accumulation, since incubation of the cells with the nonaccumulating isoform of amyloid, Aβ1-40, does not induce leakage. The same results were obtained using the release of soluble lysosomal hydrolases, cathepsin D and β-hexosaminidase, into the cytosol as an assay for the leakage of lysosomal contents. Together, our results suggest that the loss of lysosomal membrane impermeability may be an early event in Aβ pathogenesis, and provide an explanation for the miscompartmentalization of extracellular and cytoplasmic components observed in Alzheimer's disease (AD). The release of hydrolases may further cause the breakdown of the cytoskeleton and the blebbing of the plasma membrane, and the leakage of heparan sulfate glycosaminoglycans from the lysosome may ultimately promote the assembly of tau into neurofibrillary tangles (NFT). J. Neurosci. Res. 52:691–698, 1998. © 1998 Wiley-Liss, Inc.     

Cerebrospinal fluid levels of amyloid β-protein in alzheimer's disease: Inverse correlation with severity of dementia and effect of apolipoprotein e genotype

Alzheimer's disease (AD) is characterized by formation in brain of neurofibrillary tangles and of amyloid deposits. The major protein component of the former is τ, while the latter are composed of amyloid β-peptides (Aβ), which are derived by proteolytic cleavage of the amyloid β-protein precursor (APP). Both β and various secretory APP derivatives including Aβ and APP^s are present in human cerebrospinal fluid (CSF). To investigate whether clinical signs of AD are paralleled by changes in CSF levels of these proteins, we correlated quantitative measures of dementia severity with CSF concentrations of Aβ, of APP^s, and of τ We found that levels of Aβ in CSF of AD patients were inversely correlated both to cognitive and to functional measures of dementia severity. In contrast, levels of APP^s and of τ did not correlate with dementia severity. Apolipoprotein E (apoE) genotype did not influence CSF levels of Aβ, APP^s, or τ, which were similar among AD patients with Apo E ε3/3, ε3/4, and ε4/4 alleles. These data indicate that CSF levels of Aβ decrease with advancing severity of dementia in AD and suggest that they are independent of a patient's Apo E genotype.     

Parkin reverses intracellular β‐amyloid accumulation and its negative effects on proteasome function

The significance of intracellular β‐amyloid (Aβ₄₂) accumulation is increasingly recognized in Alzheimer's disease (AD) pathogenesis. Aβ removal mechanisms that have attracted attention include IDE/neprilysin degradation and antibody‐mediated uptake by immune cells. However, the role of the ubiquitin‐proteasome system (UPS) in the disposal of cellular Aβ has not been fully explored. The E3 ubiquitin ligase Parkin targets several proteins for UPS degradation, and Parkin mutations are the major cause of autosomal recessive Parkinson's disease. We tested whether Parkin has cross‐function to target misfolded proteins in AD for proteasome‐dependent clearance in SH‐SY5Y and primary neuronal cells. Wild‐type Parkin greatly decreased steady‐state levels of intracellular Aβ₄₂, an action abrogated by proteasome inhibitors. Intracellular Aβ₄₂ accumulation decreased cell viability and proteasome activity. Accordingly, Parkin reversed both effects. Changes in mitochondrial ATP production from Aβ or Parkin did not account for their effects on the proteasome. Parkin knock‐down led to accumulation of Aβ. In AD brain, Parkin was found to interact with Aβ and its levels were reduced. Thus, Parkin is cytoprotective, partially by increasing the removal of cellular Aβ through a proteasome‐dependent pathway. © 2009 Wiley‐Liss, Inc.     

Scavenging of Alzheimer's amyloid β-protein by microglia in culture

Deposits of amyloid β-protein (Aβ) form the cores of the pathological plaques which characterize Alzheimer's disease. The mechanism of formation of the deposits is unknown; one possibility is failure of a clearance mechanism that would normally remove the protein from brain parenchyma. This study has investigated the capacity of the central nervous system (CNS) phagocytes, microglia cells, to clear exogenous Aβ_1–42 from their environment. Cultured microglia from adult rat CNS have a high capacity to remove Aβ from serum-free medium, shown by immunoblotting experiments. Aβ from incubation medium was attached to the cell surface and could be identified by immunocytochemistry at the light or electron microscopic (EM) level; by EM, Aβ also appeared in phagosome-like intracellular vesicles. Light microscopic immunocytochemistry combined with computer-assisted image analysis showed that cells accumulated Aβ within 24 hr. from culture medium containing from 1 to 20 μg/ml Aβ. Microglial accumulation of Aβ was substantially reduced in the presence of fetal bovine serum. Addition of the protease inhibitor leupeptin to incubation medium with serum resulted in accumulation of Aβ in a membrane-bound intracellular compartment, but not at the cell surface. The increase in intracellular accumulation in the presence of the protease inhibitor indicates a microglial capacity for intracellular degradation of Aβ in the absence of inhibition. The change from predominantly cell-surface accumulation in serum-free medium to predominantly intracellular accumulation with serum may be explained by the presence in serum of carrier proteins that complex with Aβ and target it to cell surface receptors capable of stimulating endocytosis. Microglia were also cultured on unfixed cryostat sections of human brain tissue containing Alzheimer's plaques. Very little Aβ from the tissue was accumulated by the cells, although cultured microglia were found in direct contact with anti-Aβ immunopositive plaques. Possibly Aβ in tissue sections was complexed with other proteins which either inhibited its uptake by microglia or enhanced its proteolysis, preventing cellular accumulation of immunostainable Aβ. The results indicate that cultured microglia effectively remove Aβ from tissue culture medium and from the surface of the dish and concentrate monomer and aggregates of Aβ either on the cell surface or intracellularly. This process may be modified by proteins present in Alzheimer's brain sections. © 1996 Wiley-Liss, Inc.     

Apolipoproteins E and J interfere with amyloid‐beta uptake by primary human astrocytes and microglia in vitro

Defective clearance of the amyloid‐β peptide (Aβ) from the brain is considered a strong promoter in Alzheimer's disease (AD) pathogenesis. Astrocytes and microglia are important mediators of Aβ clearance and Aβ aggregation state and the presence of amyloid associated proteins (AAPs), such as Apolipoproteins E and J (ApoE and ApoJ), may influence Aβ clearance by these cells. Here we set out to investigate whether astrocytes and microglia differ in uptake efficiency of Aβ oligomers (Aβ_oligo) and Aβ fibrils (Aβ_fib), and whether the Aβ aggregation state and/or presence of AAPs affect Aβ uptake in these cells in vitro. Adult human primary microglia and astrocytes, isolated from short delay post‐mortem brain tissue, were exposed to either Aβ_oligo or Aβ_fib alone or combined with a panel of certain AAPs whereafter Aβ‐positive cells were quantified using flow cytometry. Upon exposure to Aβ combined with ApoE, ApoJ, α1‐antichymotrypsin (ACT) and a combination of serum amyloid P and complement C1q (SAP‐C1q), a clear reduction in astrocytic but not microglial Aβ_oligo uptake, was observed. In contrast, Aβ_fib uptake was strongly reduced in the presence of AAPs in microglia, but not in astrocytes. These data provide the first evidence of distinct roles of microglia and astrocytes in Aβ clearance. More importantly we show that Aβ clearance by glial cells is negatively affected by AAPs like ApoE and ApoJ. Thus, targeting the association of Aβ with AAPs, such as ApoE and ApoJ, could serve as a therapeutic strategy to increase Aβ clearance by glial cells. GLIA 2014;62:493–503     

Limited expression of heparan sulphate proteoglycans associated with Aβ deposits in the APPswe/PS1dE9 mouse model for Alzheimer's disease

N. M. Timmer, M. K. Herbert, J. W. Kleinovink, A. J. Kiliaan, R. M. W. de Waal and M. M. Verbeek (2010) Neuropathology and Applied Neurobiology 36, 478–486
Limited expression of heparan sulphate proteoglycans associated with Aβ deposits in the APPswe/PS1dE9 mouse model for Alzheimer's disease Aims: Alzheimer's disease (AD) is characterized by deposition of the amyloid beta (Aβ) peptide in brain parenchyma and vasculature. Several proteins co‐deposit with Aβ, including heparan sulphate proteoglycans (HSPG). HSPG have been suggested to contribute to Aβ aggregation and deposition, and may influence plaque formation and persistence by stimulating Aβ fibrillization and by protecting Aβ against degradation. Mouse models for AD, expressing the human amyloid precursor protein (APP), produce Aβ deposits similar to humans. These models may be used to study disease pathology and to develop new therapeutic interventions. We aimed to investigate whether co‐deposition of HSPG in AD brains can be replicated in the APPswe/PS1dE9 mouse model for AD and if a temporal association of HSPG with Aβ exists. Methods: We studied the co‐deposition of several HSPG and of the glycosaminoglycan side chains of HSPG in the APPswe/PS1dE9 model at different ages by immunohistochemistry. Results: We found that, although APPswe/PS1dE9 mice did develop severe Aβ pathology with age, co‐deposition of HS glycosaminoglycan chains and the various HSPG (agrin, perlecan and glypican‐1) was scarce (<10–30% of the Aβ deposits were stained). Conclusions: Our data suggest that the molecular composition of Aβ deposits in the APPswe/PS1dE9 mouse, with respect to the several HSPG investigated in this study, does not accurately reflect the human situation. The near absence of HSPG in Aβ deposits in this transgenic mouse model may, in turn, hinder the translation of preclinical intervention studies from mice to men.     

Analysis of β‐amyloid (Aβ) deposition in the temporal lobe in Alzheimer's disease using Fourier (spectral) analysis

R. A. Armstrong and N. J. Cairns (2010) Neuropathology and Applied Neurobiology 36, 248–257
Analysis of β‐amyloid (Aβ) deposition in the temporal lobe in Alzheimer's disease using Fourier (spectral) analysis Aim: To determine the spatial pattern of β‐amyloid (Aβ) deposition throughout the temporal lobe in Alzheimer's disease (AD). Methods: Sections of the complete temporal lobe from six cases of sporadic AD were immunolabelled with antibody against Aβ. Fourier (spectral) analysis was used to identify sinusoidal patterns in the fluctuation of Aβ deposition in a direction parallel to the pia mater or alveus. Results: Significant sinusoidal fluctuations in density were evident in 81/99 (82%) analyses. In 64% of analyses, two frequency components were present with density peaks of Aβ deposits repeating every 500–1000 µm and at distances greater than 1000 µm. In 25% of analyses, three or more frequency components were present. The estimated period or wavelength (number of sample units to complete one full cycle) of the first and second frequency components did not vary significantly between gyri of the temporal lobe, but there was evidence that the fluctuations of the classic deposits had longer periods than the diffuse and primitive deposits. Conclusions: (i) Aβ deposits exhibit complex sinusoidal fluctuations in density in the temporal lobe in AD; (ii) fluctuations in Aβ deposition may reflect the formation of Aβ deposits in relation to the modular and vascular structure of the cortex; and (iii) Fourier analysis may be a useful statistical method for studying the patterns of Aβ deposition both in AD and in transgenic models of disease.