Fibrillar Aβ Research Articles

Oligomer-specific Aβ toxicity in cell models is mediated by selective uptake

Alzheimer's disease (AD) is characterized by the aggregation and subsequent deposition of misfolded β-amyloid (Aβ) peptide. Previous studies show that aggregated Aβ is more toxic in oligomeric than in fibrillar form, and that each aggregation form activates specific molecular pathways in the cell. We hypothesize that these differences between oligomers and fibrils are related to their different accessibility to the intracellular space. To this end we used fluorescently labelled Aβ 1–42 and demonstrate that Aβ 1–42 oligomers readily enter both HeLa and differentiated SK‑N‑SH cells whereas fibrillar Aβ 1–42 is not internalized. Oligomeric Aβ 1–42 is internalized by an endocytic process and is transported to the lysosomes. Inhibition of uptake specifically inhibits oligomer but not fibril toxicity. Our study indicates that selective uptake of oligomers is a determinant of oligomer specific Aβ toxicity.

GRK5 deficiency exaggerates inflammatory changes in TgAPPsw mice

BackgroundDeficiency of membrane G-protein coupled receptor (GPCR) kinase-5 (GRK5) recently has been linked to early AD pathogenesis, and has been suggested to contribute to augmented microglial activation in vitro by sensitizing relevant GPCRs. However, GRK5 deficient mice did not show any signs of microgliosis, except for their moderate increase in axonal defects and synaptic degenerative changes during aging. We have speculated that one possible reason for the absence of microgliosis in these animals might be due to lack of an active inflammatory process involving activated GPCR signaling, since GRKs only act on activated GPCRs. The objective of this study was to determine whether the microgliosis is exaggerated in TgAPPsw (Tg2576) mice also deficient in GRK5, in which fibrillar β-amyloid (Aβ) and an active inflammatory process involving activated GPCR signaling are present.MethodsBoth quantitative and qualitative immunochemistry methods were used to evaluate the microgliosis and astrogliosis in these animals. ResultsWe found that inactivation of one copy of the GRK5 gene in the TgAPPsw mice resulted in approximately doubled extent of microgliosis, along with significantly exaggerated astrogliosis, in both hippocampus and cortex of the aged animals. Consistent with previous observations, the activated microglia were located primarily near or surrounding the fibrillar Aβ deposits.ConclusionThe results demonstrate that GRK5 deficiency in vivo significantly exaggerates microgliosis and astrogliosis in the presence of an inflammatory initiator, such as the excess fibrillar Aβ and the subsequent active inflammatory reactions in the TgAPPsw mice.

Toll-like receptor 4-dependent upregulation of cytokines in a transgenic mouse model of Alzheimer's disease

BackgroundAβ deposits in the brains of patients with Alzheimer's disease (AD) are closely associated with innate immune responses such as activated microglia and increased cytokines. Accumulating evidence supports the hypothesis that innate immune/inflammatory responses play a pivotal role in the pathogenesis of AD: either beneficial or harmful effects on the AD progression. The molecular mechanisms by which the innate immune system modulates the AD progression are not well understood. Toll-like receptors (TLRs) are first-line molecules for initiating the innate immune responses. When activated through TLR signaling, microglia respond to pathogens and damaged host cells by secreting chemokines and cytokines and express the co-stimulatory molecules needed for protective immune responses to pathogens and efficient clearance of damaged tissues. We previously demonstrated that an AD mouse model homozygous for a destructive mutation of TLR4 has increases in diffuse and fibrillar Aβ deposits as well as buffer-soluble and insoluble Aβ in the brain as compared with a TLR4 wild-type AD mouse model. Here, we investigated the roles of TLR4 in Aβ-induced upregulation of cytokines and chemokines, Aβ-induced activation of microglia and astrocytes and Aβ-induced immigration of leukocytes.MethodsUsing the same model, levels of cytokines and chemokines in the brain were determined by multiplex cytokine/chemokine array. Activation of microglia and astrocytes and immigration of leukocytes were determined by immunoblotting and immunohistochemistry followed by densitometry and morphometry, respectively.ResultsLevels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-10 and IL-17 in the brains of TLR4 wild-type AD mice were significantly higher than those in TLR4 wild-type non-transgenic littermates. Such increases in cytokines were not found in TLR4 mutant AD mice as compared with TLR4 mutant non-transgenic littermates. Although expression levels of CD11b (a microglia marker) and GFAP (a reactive astrocyte marker) in the brains of TLR4 mutant AD mice were higher than those in TLR4 wild type AD mice, no difference was found in levels of CD45 (common leukocyte antigen).ConclusionThis is the first demonstration of TLR4-dependent upregulation of cytokines in an AD mouse model. Our results suggest that TLR4 signaling is involved in AD progression and that TLR4 signaling can be a new therapeutic target for AD.

Cyclooxygenase-1 and -2 in the Different Stages of Alzheimers Disease Pathology

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the deposition of beta amyloid (Abeta) protein and the formation of neurofibrillary tangles. In addition, there is an increase of inflammatory proteins in the brains of AD patients. Epidemiological studies, indicating that non-steroidal anti-inflammatory drugs (NSAIDs) decrease the risk of developing AD, have encouraged the study on the role of inflammation in AD. The best-characterized action of most NSAIDs is the inhibition of cyclooxygenase (COX). The expression of the constitutively expressed COX-1 and the inflammatory induced COX-2 has been intensively investigated in AD brain and different disease models for AD. Despite these studies, clinical trials with NSAIDs or selective COX-2 inhibitors showed little or no effect on clinical progression of AD. The expression levels of COX-1 and COX-2 change in the different stages of AD pathology. In an early stage, when low-fibrillar Abeta deposits are present and only very few neurofibrillary tangles are observed in the cortical areas, COX-2 is increased in neurons. The increased neuronal COX-2 expression parallels and colocalizes with the expression of cell cycle proteins. COX-1 is primarily expressed in microglia, which are associated with fibrillar Abeta deposits. This suggests that in AD brain COX-1 and COX-2 are involved in inflammatory and regenerating pathways respectively. In this review we will discuss the role of COX-1 and COX-2 in the different stages of AD pathology. Understanding the physiological and pathological role of cyclooxygenase in AD pathology may facilitate the design of therapeutics for the treatment or prevention of AD.

Selective Contrast Enhancement of Individual Alzheimer’s Disease Amyloid Plaques Using a Polyamine and Gd-DOTA Conjugated Antibody Fragment Against Fibrillar Aβ42 for Magnetic Resonance Molecular Imaging

The lack of an in vivo diagnostic test for AD has prompted the targeting of amyloid plaques with diagnostic imaging probes. We describe the development of a contrast agent (CA) for magnetic resonance microimaging that utilizes the F(ab')2 fragment of a monoclonal antibody raised against fibrillar human Abeta42 This fragment is polyamine modified to enhance its BBB permeability and its ability to bind to amyloid plaques. It is also conjugated with a chelator and gadolinium for subsequent imaging of individual amyloid plaques Pharmacokinetic studies demonstrated this 125I-CA has higher BBB permeability and lower accumulation in the liver and kidney than F(ab')2 in WT mice. The CA retains its ability to bind Abeta40/42 monomers/fibrils and also binds to amyloid plaques in sections of AD mouse brain. Intravenous injection of 125I-CA into the AD mouse demonstrates targeting of amyloid plaques throughout the cortex/hippocampus as detected by emulsion autoradiography. Incubation of AD mouse brain slices in vitro with this CA resulted in selective enhancement on T1-weighted spin-echo images, which co-register with individual plaques observed on spatially matched T2-weighted spin-echo image Development of such a molecular probe is expected to open new avenues for the diagnosis of AD.

Different fibrillar Aβ 1–42 concentrations induce adult hippocampal neurons to reenter various phases of the cell cycle

In Alzheimer's disease (AD) cell cycle reentry precedes neuronal death, which could be induced by many cytotoxic factors. It is believed that beta amyloid (Aβ), the major component of extracellular plaques in AD, is potent in inducing neurons to reenter cell cycle. In AD brains, neurons expressing cell cycle markers are reported in many brain regions without any plaque formation, although very low levels of Aβ may still be detected. In the other side, because cell cycle reentry is not an immediate cause of apoptosis, neurons may remain in cell cycle phases for some time prior to their final death. In this study we examined if very low concentrations of Aβ 1–42 (picomolar) can trigger the adult neurons to reenter the cell cycle, and the effect of different Aβ concentrations on neuronal progression through different cell cycle phases. Primary adult neurons were treated with Aβ 1–42 at 2 × 10 − 6 , 2 × 10 − 5 , 2 × 10 − 4 , 0.5 and 2.5 µM concentrations. Cyclin D1 and cyclin B1 (the markers for G1 and G2 phases of the cell cycle, respectively) and apoptosis were assessed. Treatment with Aβ at 2.5 µM induced apoptosis. At lower levels however, Aβ promoted neurons entering G1 and G2 phases without apoptosis, with 0.5 µM of Aβ inducing neurons into G2, and 2 × 10 − 5, 2 × 10 − 4 into G1 phases. Our results suggested that lower concentrations of Aβ induced neurons to reenter the cell cycle, and different concentrations had differential abilities to promote neurons into various cell cycle phases or trigger their death.

Examining the levels of ganglioside and cholesterol in cell membrane on attenuation the cytotoxicity of beta-amyloid peptide

The deposition of β-amyloid (Aβ) on cell membranes is considered as one of the primary factors in having Alzheimer's disease (AD). Recent studies have suggested that certain components of plasma membrane, ganglioside and cholesterol could accelerate the accumulation of Aβ on the plasma membranes. However, the effect of cholesterol and ganglioside (GM1) on Aβ cytotoxicity is still a controversial issue. The aim of this study is to understand the roles of GM1 and cholesterol in AD by using PC12, a neuron-like cell. The effects of the sequence, conformation, and concentration of Aβ on cytotoxicity were also investigated. Monomeric Aβ could attack the plasma membrane resulting in cytotoxicity, however, fibrillar Aβ was found to be less toxic. Our results showed that Aβ (1–40) was more toxic than Aβ (25–35) and the cytotoxicity of Aβ was proportional to its concentration. Besides, the depletion of GM1 from plasma membrane, it would block the Aβ-induced cytotoxicity. Decreasing the cholesterol level by around 30% could attenuate the cytotoxicity of Aβ. These findings validate our idea that the cholesterol could stabilize the lateral pressure derived from the formation of GM1-Aβ complex on the membrane surface. Furthermore, both GM1 and cholesterol are essential in mechanism of Aβ accumulation and could modulate the cytotoxicity of monomeric Aβ.

Stabilization of a β-hairpin in monomeric Alzheimer's amyloid-β peptide inhibits amyloid formation

According to the amyloid hypothesis, the pathogenesis of Alzheimer's disease is triggered by the oligomerization and aggregation of the amyloid-beta (Abeta) peptide into protein plaques. Formation of the potentially toxic oligomeric and fibrillar Abeta assemblies is accompanied by a conformational change toward a high content of beta-structure. Here, we report the solution structure of Abeta(1-40) in complex with the phage-display selected affibody protein Z(Abeta3), a binding protein of nanomolar affinity. Bound Abeta(1-40) features a beta-hairpin comprising residues 17-36, providing the first high-resolution structure of Abeta in beta conformation. The positions of the secondary structure elements strongly resemble those observed for fibrillar Abeta. Z(Abeta3) stabilizes the beta-sheet by extending it intermolecularly and by burying both of the mostly nonpolar faces of the Abeta hairpin within a large hydrophobic tunnel-like cavity. Consequently, Z(Abeta3) acts as a stoichiometric inhibitor of Abeta fibrillation. The selected Abeta conformation allows us to suggest a structural mechanism for amyloid formation based on soluble oligomeric hairpin intermediates.

Cu(II) Binding to Monomeric, Oligomeric, and Fibrillar Forms of the Alzheimer’s Disease Amyloid-β Peptide

Copper has been proposed to play a role in Alzheimer's disease through interactions with the amyoid-beta (Abeta) peptide. The coordination environment of bound copper as a function of Cu:Abeta stoichiometry and Abeta oligomerization state are particularly contentious. Using low-temperature electron paramagnetic resonance (EPR) spectroscopy, we spectroscopically distinguish two Cu(II) binding sites on both soluble and fibrillar Abeta (for site 1, A parallel = 168 +/- 1 G and g parallel = 2.268; for site 2, A parallel = 157 +/- 2 G and g parallel = 2.303). When fibrils that have been incubated with more than 1 equiv of Cu(II) are washed, the second Cu(II) ion is removed, indicating that it is only weakly bound to the fibrils. No change in the Cu(II) coordination environment is detected by EPR spectroscopy of Cu(II) with Abeta (1:1 ratio) collected as a function of Abeta fibrillization time, which indicates that the Cu(II) environment is independent of Abeta oligomeric state. The initial Cu(II)-Abeta complexes go on to form Cu(II)-containing Abeta fibrils. Transmission electron microscopy images of Abeta fibrils before and after Cu(II) addition are the same, showing that once incorporated, Cu(II) does not affect fibrillar structure; however, the presence of Cu(II) appears to induce fibril-fibril association. On the basis of our results, we propose a model for Cu(II) binding to Abeta during fibrillization that is independent of peptide oligomeric state.

η-Secretase: Reduction of Amyloid Precursor Protein η-Site Cleavage in Alzheimers Disease

The accumulation and deposition of fibrillar Abeta is thought the primary cause of Alzheimer's disease (AD). Abeta is generated by sequential proteolytic processing involving beta- and gamma-secretase on Amyloid beta protein precursor (APP). Recently, gamma-secretase was shown to cleave near the cytoplasmic membrane boundary of APP, called epsilon-site cleavage, as well as in the middle of the membrane domain, called gamma-site cleavage. Recent findings indicate that gamma- and epsilon-site cleavage are regulated independently. In this review, the reduction of epsilon-site cleavage in AD and the importance of epsilon-site cleavage are discussed.

Apoptosis in Transgenic Mice Expressing the P301L Mutated Form of Human Tau

The rTg4510 mouse is a tauopathy model, characterized by massive neurodegeneration in Alzheimer's disease (AD)-relevant cortical and limbic structures, deficits in spatial reference memory, and progression of neurofibrillary tangles (NFT). In this study, we examined the role of apoptosis in neuronal loss and associated tau pathology. The results showed that DNA fragmentation and caspase-3 activation are common in the hippocampus and frontal cortex of young rTg4510 mice. These changes were associated with cleavage of tau into smaller intermediate fragments, which persist with age. Interestingly, active caspase-3 was often co-localized with cleaved tau. In vitro, fibrillar Abeta(1-42) resulted in nuclear fragmentation, caspase activation, and caspase-3-induced cleavage of tau. Notably, incubation with the antiapoptotic molecule tauroursodeoxycholic acid abrogated apoptosis-mediated cleavage of tau in rat cortical neurons. In conclusion, caspase-3-cleaved intermediate tau species occurred early in rTg54510 brains and preceded cell loss in Abeta-exposed cultured neurons. These results suggest a potential role of apoptosis in neurodegeneration.

A New Method to Measure Cellular Toxicity of Non-Fibrillar and Fibrillar Alzheimer's Aβ Using Yeast

The 42 amino acid amyloid-beta (Abeta) can exist in multiple physical states including oligomers and fibrils. This study shows that fibril formation is hastened by the biological buffers required to support the growth of mammalian cells, but is prevented if Abeta is maintained in water. Here we describe a method to produce Abeta in oligomeric form and the comparison of stable fibrillar and non-fibrillar forms in cell toxicity studies in water, achieved through the use of yeast. We show that extracellular, non-fibrillar Abeta causes a dose dependent loss of cell viability while fibrillar Abeta has low toxicity.

Ligand‐Induced Flocculation of Neurotoxic Fibrillar Aβ(1–42) by Noncovalent Crosslinking

Aggregation of the amyloid-beta (Abeta) peptides has a pivotal role in Alzheimer's disease (AD). Small molecules and short peptides/peptidomimetics can exert their full protective effects against Abeta within a short time-frame, but the exact mechanism of action is unclear. Time-dependent NMR spectroscopic binding and replacement experiments were carried out for peptide LPFFD and thioflavine T (ThT) on neurotoxic fibrillar Abeta(1-42), which revealed transient binding behavior for both compounds, and complex time-dependent features in the replacement experiments. The results of particle size measurements through the use of diffuse light-scattering and transmission electron microscopy support the conclusions that the studied ligands induced interfibrillar association on a short timescale, which explains the NMR spectroscopic binding and replacement results. zeta-Potential measurements revealed a slightly increased electrostatic stability of the Abeta fibrils upon ligand binding; this suggests that the interfibrillar assembly is driven by specific noncovalent cross-linking interactions. A specific surface and mobility decrease due to the ligand-induced flocculation of the Abeta fibrils can explain the neuroprotective effects.

Aβ peptide conformation determines uptake and interleukin-1α expression by primary microglial cells

Microglia clear amyloid beta (Aβ) after immunization. The interaction of Aβ with the microglial cell surface also results in cytokine expression. Soluble oligomers and protofibrils of Aβ may be more neurotoxic than Aβ fibrils. We investigated the effects of oligomeric, protofibrillar and fibrillar Aβ40 and Aβ42 peptides on uptake and IL-1α expression by primary microglia. Aβ peptide assemblies were extensively characterized. Primary microglial cells were exposed to different Aβ40 and Aβ42 assemblies and IL-1α expression was quantified. To study uptake, microglial cells were exposed to different assemblies of Cy3-labeled Aβ. We found that Aβ42 and Aβ40 oligomers and fibrils induced IL-1α expression, but protofibrils did not. We also observed that all forms of Aβ42 (oligomer, protofibril and fibril) and Aβ40 fibrils were taken up by the microglial cells. These results demonstrate that microglial cells can take up non-fibrillar Aβ and that oligomeric peptide induces an inflammatory response. The uptake of oligomeric and protofibrillar Aβ by microglia merits further investigation as a potential means for removing these neurotoxic species from the brain.

Involvement of calpain and p25 of CDK5 pathway in ginsenoside Rb1's attenuation of β-amyloid peptide 25–35-induced tau hyperphosphorylation in cortical neurons

Increasing evidence have shown that β-amyloid (Aβ) induced hyperphosphorylation of tau, which eventually resulted in the disruption of microtubule (MT) integrity. Cyclin-dependent kinase 5 (CDK5) and its activator p35 are required for neurite outgrowth. The cleavage of p35 to p25, mediated by calpain and calcium, caused CDK5 dislocation and subsequently p25/CDK5-induced tau hyperphosphorylation, which disrupted the cytoskeleton and resulted in neuronal death. In the present study we investigated the effects of ginsenoside Rb1 on fibrillar Aβ 25–35-induced tau hyperphosphorylation in primary cultured cortical neurons and also the potential involvement of Ca 2+-calpain-CDK5 signal pathway. The present study suggests that Ca 2+, calpain, and p25 in CDK5 pathway may play important roles in Aβ 25–35-induced tau hyperphosphorylation.

Exercise alters the immune profile in Tg2576 Alzheimer mice toward a response coincident with improved cognitive performance and decreased amyloid

BackgroundInflammation is associated with Aβ pathology in Alzheimer's disease (AD) and transgenic AD models. Previously, it has been demonstrated that chronic stimulation of the immune response induces pro-inflammatory cytokines IL-1β and TNF-α which contribute to neurodegeneration. However, recent evidence has shown that inducing the adaptive immune response reduces Aβ pathology and is neuroprotective. Low concentrations of IFN-γ modulate the adaptive immune response by directing microglia to differentiate to antigen presenting cells. Our objective was to determine if exercise could induce a shift from the immune profile in aged (17–19 months) Tg2576 mice to a response that reduces Aβ pathology.MethodsTG (n = 29) and WT (n = 27) mice were divided into sedentary (SED) and exercised (RUN) groups. RUN animals were provided an in-cage running wheel for 3 weeks. Tissue was harvested and hippocampus and cortex dissected out. Quantitative data was analyzed using 2 × 2 ANOVA and student's t-tests.ResultsIL-1β and TNF-α were significantly greater in hippocampi from sedentary Tg2576 (TGSED) mice than in wildtype (WTSED) (p = 0.04, p = 0.006). Immune response proteins IFN-γ and MIP-1α are lower in TGSED mice than in WTSED (p = 0.03, p = 0.07). Following three weeks of voluntary wheel running, IL-1β and TNF-α decreased to levels indistinguishable from WT. Concurrently, IFN-γ and MIP-1α increased in TGRUN. Increased CD40 and MHCII, markers of antigen presentation, were observed in TGRUN animals compared to TGSED, as well as CD11c staining in and around plaques and vasculature. Additional vascular reactivity observed in TGRUN is consistent with an alternative activation immune pathway, involving perivascular macrophages. Significant decreases in soluble Aβ40 (p = 0.01) and soluble fibrillar Aβ (p = 0.01) were observed in the exercised transgenic animals.ConclusionExercise shifts the immune response from innate to an adaptive or alternative response. This shift in immune response coincides with a decrease in Aβ in advanced pathological states.

A transgenic rat model of Alzheimer's disease with extracellular Aβ deposition

Many transgenic mouse models of Alzheimer's disease (AD) that deposit amyloid (Aβ) have been produced, but development of an Aβ-depositing rat model has not been successful. Here, we describe a rat model with extracellular fibrillar Aβ deposition. Two lines of Sprague Dawley rats with transgenes expressing human amyloid precursor protein (APP) with the familial AD (FAD) mutations K670N/M671L and K670N/M671L/V717I were crossed. Aβ production in the double homozygous rats was sufficient for deposition by 17–18 months of age. The age of onset of Aβ deposition was reduced by crossing in a third rat line carrying a human presenilin-1 (PS-1) transgene with the FAD M146V mutation. The triple homozygous line had an onset of Aβ deposition by 7 months of age. Deposits appeared similar to those observed in the mouse models and displayed surrounding glial and phosphorylated tau reactivity. Aβ levels measured by ELISA were comparable to those reported in mouse models, suggesting that substantially greater amounts of soluble Aβ are not required in the rat to generate Aβ deposition.

Native and oxidized low-density lipoproteins modulate the vasoactive actions of soluble β-amyloid peptides in rat aorta

Cerebrovascular accumulation of Abeta (beta-amyloid) occurs in aging and AD (Alzheimer's disease). Hypercholesterolaemia, which is associated with raised plasma LDL (low-density lipoprotein), may predispose to AD. Soluble Abeta is found in the circulation and enhances vasoconstriction. Under conditions that may favour the formation of short Abeta oligomers, as opposed to more severe polymerization leading to Abeta fibrillogenesis, we investigated the influence of LDLs on the vasoactive actions of soluble Abeta. Thus the actions of Abeta40 and Abeta42 in combination with native or oxidized LDL on vasoconstriction to NA (noradrenaline) and vasodilatation to ACh (acetylcholine) were examined in rat aortic rings. LDL, particularly when oxidized, potentiated NA-induced constriction when combined with soluble Abeta40 and, especially, Abeta42. Soluble Abeta40 reduced relaxation induced by ACh, but Abeta42 was ineffective. Native and oxidized LDL also attenuated relaxation. Synergism occurred between oxidized LDL and Abeta with respect to ACh-induced relaxation, but not between native LDL and Abeta. We have shown for the first time that, under conditions that may result in Abeta oligomer formation, LDL, particularly when oxidized, modulates the vascular actions of soluble Abeta to extents greater than those reported previously for fibrillar Abeta preparations. Mechanisms whereby a treatable condition, namely hypercholesterolaemia, might contribute to the development of the cerebrovascular component of AD are indicated.

Fibrillar beta-amyloid (Aβ) (1–42) elevates extracellular Aβ in cultured hippocampal neurons of adult rats

Alzheimer's disease (AD) is a chronic disorder with progressive neurodegeneration associated with aging and is characterized by fibrillar beta-amyloid (Aβ) deposits in the brain. Although the increased production of Aβ seems to play a noticeable role in AD pathogenesis and its progression, all the mechanisms which are involved in this extracellular Aβ elevation are not known completely. In the present study, we used adult hippocampal neuronal culture as an in vitro model which is favorable for adult neurodegenerative diseases' studies. We introduced a toxic concentration for fibrillar Aβ1–42 in adult neurons which was much lower from the toxic concentration in embryonic neurons. To determine the effect of fibrillar Aβ1–42 which is the most toxic part of amyloid plaques, on extracellular Aβ1–40, as the main part of βAPP proteolysis products, we treated the neurons with fibrillar Aβ1–42 at nontoxic concentrations of 2 × 10 − 6 , 2 × 10 − 5 and 2 × 10 − 4 μM and measured extracellular Aβ1–40. Our findings show that even very low levels of fibrillar Aβ1–42 can contribute to subsequent extracellular Aβ elevation in a dose dependent manner. These results suggest that even low levels of fibrillar Aβ may have deleterious actions if it remains in extracellular space for a period of time.

Induction of complement proteins in a mouse model for cerebral microvascular Aβ deposition

The deposition of amyloid β-protein (Aβ) in cerebral vasculature, known as cerebral amyloid angiopathy (CAA), is a common pathological feature of Alzheimer's disease and related disorders. In familial forms of CAA single mutations in the Aβ peptide have been linked to the increase of vascular Aβ deposits accompanied by a strong localized activation of glial cells and elevated expression of neuroinflammatory mediators including complement proteins. We have developed human amyloid-β precursor protein transgenic mice harboring two CAA Aβ mutations (Dutch E693Q and Iowa D694N) that mimic the prevalent cerebral microvascular Aβ deposition observed in those patients, and the Swedish mutations (K670N/M671L) to increase Aβ production. In these Tg-SwDI mice, we have reported predominant fibrillar Aβ along microvessels in the thalamic region and diffuse plaques in cortical region. Concurrently, activated microglia and reactive astrocytes have been detected primarily in association with fibrillar cerebral microvascular Aβ in this model. Here we show that three native complement components in classical and alternative complement pathways, C1q, C3, and C4, are elevated in Tg-SwDI mice in regions rich in fibrillar microvascular Aβ. Immunohistochemical staining of all three proteins was increased in thalamus, hippocampus, and subiculum, but not frontal cortex. Western blot analysis showed significant increases of all three proteins in the thalamic region (with hippocampus) as well as the cortical region, except C3 that was below detection level in cortex. Also, in the thalamic region (with hippocampus), C1q and C3 mRNAs were significantly up-regulated. These complement proteins appeared to be expressed largely by activated microglial cells associated with the fibrillar microvascular Aβ deposits. Our findings demonstrate that Tg-SwDI mice exhibit elevated complement protein expression in response to fibrillar vascular Aβ deposition that is observed in patients with familial CAA.