Amyloid β-protein deposition in the leptomeninges and cerebral cortex

To further investigate the process of amyloid β-protein (Aß) deposition, we determined, using sensitive enzyme immunoassays, the levels of Aβ40 and Aβ42 (Aβs) in the soluble and insoluble fractions of the leptomeninges (containing arachnoid mater and leptomeningeal vessels) and cerebral cortices from elderly control subjects showing various stages of Aβ deposition and from patients affected by Alzheimer's disease (AD). In both locations, insoluble Aβ levels were higher by ordersof magnitude than soluble Aβ levels. Soluble Aβ levels. Soluble Aβ levels in cortices were much lower than those in leptomeninges. In insoluble Aβ in the cortex, Aβ42 was by far the predominant species, and Aβ42 in AD cortices was characterized by the highest degree of modifications in the amino terminus. In contrast, this Aβ42 predominance was not observed in insoluble Aβ in the leptomenings, which were found to be able to accumulate Aβs to an extent similar to that in the cortex, on a weight basis. The levels of insoluble Aβ in the leptomeninges or cortex generally correlated with the degree of cerebral amyloid angiopathy or the abundance of senile plaque, respectively. However, the presence of plaque-free cortical samples showing significant levels of insoluble Aβ42 suggests that biochemically detectable Aβ accumulation precedes immunocytochemically detectable Aβ deposition in the cortex.     

Hereditary cerebral hemorrhage with amyloidosis‐Dutch type

The amyloid β‐protein (Aβ) E22Q mutation of the rare disorder hereditary cerebral hemorrhage with amyloidosis‐Dutch type (HCHWA‐D) causes severe cerebral amyloid angiopathy (CAA) with hemorrhagic strokes of mid‐life onset and dementia. The mutation does not affect total Aβ production but may alter the Aβ1–42:Aβ1–40 ratio, and affect the proteolytic degradation of Aβ and its transport across the blood–brain barrier. Aβ E22Q aggregates faster into more stable amyloid‐like fibrils than wild‐type Aβ. Non‐fibrillar Aβ(x‐42) deposits precede the appearance of fibrils and the deposition of Aβ(x‐40) in the vascular basement membrane. CAA severity tends to increase with age but may vary greatly among patients of comparable ages. Lumenal narrowing of affected blood vessels, leukoencephalopathy, CAA‐associated vasculopathies, and perivascular astrocytosis, microgliosis, and neuritic degeneration complicate the development of HCHWA‐D CAA. Parenchymal Aβ deposition is also enhanced in the HCHWA‐D brain with non‐fibrillar membrane‐bound Aβ(x‐42) deposits evolving into relatively fibrillar diffuse plaques variously associated with reactive astrocytes, activated microglia, and degenerating neurites. Plaque density tends to decrease with age. Neurofibrillary degeneration is absent or limited. HCHWA‐D dementia is associated with CAA severity independently of Braak stage, age, and plaque density. Particularly, microaneurysms may contribute to the development of (small) hemorrhages/infarcts and the latter to cognitive decline in affected subjects. However, the relative importance of cerebral hemorrhages/infarcts, white matter damage and/or other CAA‐ or Aβ‐related factors for cognitive deterioration in HCHWA‐D remains to be determined.     

Active clearance of human amyloid β 1–42 peptide aggregates from the rat ventricular system

A major constituent of SP in the brains of Alzheimer's disease is 39–43 amino acid peptide called β‐amyloid peptide (Aβ). Recent data have demonstrated that Aβ has a strong tendency to form insoluble aggregates and that toxic effects of Aβ is based on its aggregation. In the current study, 100 µg of human synthetic Aβ 1–42 (sAβ 1–42) was infused into the lateral ventricle of rat brain using a short‐term infusion model. At 2 or 7 days following the infusion, sAβ 1–42 was found to form insoluble aggregates, scattering throughout the entire ventricular systems. The sAβ 1–42 aggregates were partially engulfed by phagocytic cells and deposited at the meningeal vessels or the choroid plexuses. However, these deposits mostly disappeared from the ventricles by 28 days post‐infusion. Here, it is reported for the first time that considerable amounts of sAβ 1–42 are almost cleared from the rat ventricular system by the mononuclear phagocytic system.     

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).     

Amyloid beta-protein length and cerebral amyloid angiopathy-related haemorrhage

The relationship between amyloid beta-protein (A beta) length and the apolipoprotein E (APOE) epsilon 2 allele, which is over-represented in cerebral amyloid angiopathy-related haemorrhage (CAAH), has not previously been examined. Of 57 CAA patients studied, 37 had CAAH. All patients, particularly those with CAAH had more blood vessels immunoreactive for A beta 40 than A beta 42 in both the leptomeninges and cerebral cortex. CAAH patients had more A beta 40-immunoreactive blood vessels in the leptomeninges (p < 0.001) and cortex (p = 0.027) than had non-haemorrhage patients. Cortical blood vessels, the usual source of haemorrhage in CAAH, were more frequently A beta 42 immunoreactive in APOE epsilon 2 carriers than in non-epsilon 2 carriers (p = 0.022). The APOE epsilon 2 allele may predispose to CAAH by increasing the seeding of cortical blood vessels by A beta 42.     

Amyloid-β plaques may be reduced in advanced stages of cerebral amyloid angiopathy in the elderly

We examined 29 cases in which cerebral amyloid angiopathy (CAA) was detected among routine aged autopsies. Most cases with severe CAA had many amyloid-β (Aβ) plaques in the occipital cortex. Nonetheless, two cases had few Aβ plaques with many small vessels and capillaries with CAA. In the two cases, severe CAA was widely distributed, except in the frontal lobes. Aβ deposits in capillaries often showed the characteristic pattern of dysphoric amyloid angiopathy. A few naked plaques were present. Although Aβ plaques were sparse near small vessels with CAA, there were many Aβ plaques distant from small vessels with CAA. Some of the remaining plaques had a moth-eaten appearance. Based on Aβ-positive star-like appearance and results of double immunohistochemistry for glial fibrillary acidic protein and Aβ_1–42, some astrocytes appeared to contain Aβ. Ionized calcium-binding adapter molecule 1 (Iba1)-positive microglia were scattered within the neuropil, with some present around small vessels with CAA. Iba1-positive microglia also seemed to phagocytose Aβ in several senile plaques by double immunostaining. Neurons and neurites identified with a monoclonal antibody against phosphorylated tau (clone AT8) were occasionally detected in sparse plaque areas, with AT8-identified dot-like structures present around capillaries with CAA. Accumulation of T lymphocytes was detected around vessels in the subarachnoid space in one case. The morphological changes detected in our two cases were similar to those of morphological markers of plaque clearance after Aβ immunotherapy. Nonetheless, our cases did not receive Aβ immunotherapy, but similar pathologies were observed. Overall, advanced CAA cases, including our two cases, may be examples of plaque clearance without Aβ immunotherapy. Further studies are needed to resolve the mechanism of Aβ plaque clearance using these cases.     

Longitudinal study of cerebrospinal fluid levels of tau,Aβ1–40, and Aβ1–42(43) in Alzheimer's disease: A study in Japan

To clarify the alterations of tau, amyloid β protein (Aβ) 1–40 and Aβ1–42(43) in the cerebrospinal fluid (CSF) that accompany normal aging and the progression of Alzheimer's disease (AD), CSF samples of 93 AD patients, 32 longitudinal subjects among these 93 AD patients, 33 patients with non-AD dementia, 56 with other neurological diseases, and 54 normal control subjects from three independent institutes were analyzed by sensitive enzyme-linked immunosorbent assays. Although the tau levels increased with aging, a significant elevation of tau and a correlation between the tau levels and the clinical progression were observed in the AD patients. A significant decrease of the Aβ1–42(43) levels and a significant increase of the ratio of Aβ1–40 to Aβ1–42(43) were observed in the AD patients. The longitudinal AD study showed continuous low Aβ1–42(43) levels and an increase of the ratio of Aβ1–40 to Aβ1–42(43) before the onset of AD. These findings suggest that CSF tau may increase with the clinical progression of dementia and that the alteration of the CSF level of Aβ1–42(43) and the ratio of Aβ1–40 to Aβ1–42(43) may start at early stages in AD. The assays of CSF tau, Aβ1–40, and Aβ1–42(43) provided efficient diagnostic sensitivity (71%) and specificity (83%) by using the production of tau levels and the ratio of Aβ1–40 to Aβ1–42(43), and an improvement in sensitivity (to 91%) was obtained in the longitudinal evaluation.     

Memantine lowers amyloid‐β peptide levels in neuronal cultures and in APP/PS1 transgenic mice

Memantine is a moderate‐affinity, uncompetitive N‐methyl‐D‐aspartate (NMDA) receptor antagonist that stabilizes cognitive, functional, and behavioral decline in patients with moderate to severe Alzheimer's disease (AD). In AD, the extracellular deposition of fibrillogenic amyloid‐β peptides (Aβ) occurs as a result of aberrant processing of the full‐length Aβ precursor protein (APP). Memantine protects neurons from the neurotoxic effects of Aβ and improves cognition in transgenic mice with high brain levels of Aβ. However, it is unknown how memantine protects cells against neurodegeneration and affects APP processing and Aβ production. We report the effects of memantine in three different systems. In human neuroblastoma cells, memantine, at therapeutically relevant concentrations (1–4 μM), decreased levels of secreted APP and Aβ_1–40. Levels of the potentially amylodogenic Aβ_1–42 were undetectable in these cells. In primary rat cortical neuronal cultures, memantine treatment lowered Aβ_1–42 secretion. At the concentrations used, memantine treatment was not toxic to neuroblastoma or primary cultures and increased cell viability and/or metabolic activity under certain conditions. In APP/presenilin‐1 (PS1) transgenic mice exhibiting high brain levels of Aβ_1–42, oral dosing of memantine (20 mg/kg/day for 8 days) produced a plasma drug concentration of 0.96 μM and significantly reduced the cortical levels of soluble Aβ_1–42. The ratio of Aβ_1–40/Aβ_1–42 increased in treated mice, suggesting effects on the γ‐secretase complex. Thus, memantine reduces the levels of Aβ peptides at therapeutic concentrations and may inhibit the accumulation of fibrillogenic Aβ in mammalian brains. Memantine's ability to preserve neuronal cells against neurodegeneration, to increase metabolic activity, and to lower Aβ level has therapeutic implications for neurodegenerative disorders. © 2009 Wiley‐Liss, Inc.     

Increased frequency of the α‐1‐antichymotrypsin T allele in cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is a process of unknown etiology characterized by amyloid deposition in the wall of small cerebral and meningeal blood vessels. CAA is also a feature of Alzheimer's disease (AD) and of a subgroup of elderly people. α‐1‐Antichymotrypsin (ACT) is a serum glycoprotein frequently associated with vascular and senile plaque amyloid. The ACT gene is known to have a bi‐allele polymorphism that causes a simple amino acid substitution. In an attempt to clarify the possible role of ACT polymorphism in AD and in cases of CAA, the ACT genotype was investigated in AD, CAA, and intellectually intact controls. Representative brain areas (cerebral cortex, hippocampus, putamen, white matter, and gyrus cinguli) from all cases were studied using classical histologic staining techniques (hematoxylin–eosin (HE), Mallory's thrichromic or alkaline congo red stain), and immunohistochemistry for tau and β‐amyloid proteins. There was a significantly increased T allele and TT genotype frequency in the CAA group, but not in the AD group, suggesting a role for the ACT genotype in the development of vascular lesions. The presence of the apolipoprotein E4 allele (ApoE4) did not correlate with the ACT‐A allele, as previously reported, and appeared to be independent of the risk for developing AD.     

Cerebral amyloid angiopathy initially occurs in the meningeal vessels

To clarify the frequency of CAA in the brain parenchyma and subarachnoid space (SAS), we counted sections of blood vessels showing positive staining for Aβ in the SAS, cerebral cortex (CC) and cerebral white matter (WM) using paraffin‐embedded sections of the frontal, temporal and occipital lobes. The specimens had been taken for routine neuropathological examination from the brains of 105 Japanese patients (aged 40–95 years) selected from among 200 consecutive patients autopsied between 1989 and 2015 at our hospital. We examined the anatomical ratios of blood‐vessel sections in the SAS relative to the CC in three selected CAA cases, and those of Aβ‐positive blood‐vessel sections in CAA cases. CAA was found in 53 of the 105 cases (50.5%), and the youngest patient affected was a 51‐year‐old man. The incidence of CAA increased with age. The anatomical ratio of blood vessel sections in the SAS relative to the CC was 1/3.70–1/4.37 (mean: 1/3.94). The ordinary CAA group, in which CAA was seen in both the SAS and CC, included 41 cases (77.4%). In 37 of these cases, the SAS/CC ratio of Aβ‐positive blood vessels was 1/0.05–1/0.66 (mean: 1/0.26), and in the other four cases the ratio was 1/1–1/1.5. In the ordinary CAA group, the SAS/CC ratio of Aβ‐positive blood vessels was smaller than the anatomical ratio. The meningeal CAA group, in which CAA was found only in the SAS, included 12 cases (22.6%). These patients ranged in age from their fifties to their nineties. There was no case in which CAA was limited only to the CC. We concluded that CAA initially develops in the meningeal blood vessels, and not in the cortical blood vessels. CAA in the WM was seen in 10 cases, not only in nine cases that were severe, but also in a mild case.     

Review: sporadic cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) may result from focal to widespread amyloid-β protein (Aβ) deposition within leptomeningeal and intracortical cerebral blood vessels. In addition, pericapillary Aβ refers to Aβ depositions in the glia limitans and adjacent neuropil, whereas in capillary CAA Aβ depositions are present in the capillary wall. CAA may cause lobar intracerebral haemorrhages and microbleeds. Hypoperfusion and reduced vascular autoregulation due to CAA might cause infarcts and white matter lesions. CAA thus causes vascular lesions that potentially lead to (vascular) dementia and may further contribute to dementia by impeding the clearance of solutes out of the brain and transport of nutrients across the blood brain barrier. Severe CAA is an independent risk factor for cognitive decline. The clinical diagnosis of CAA is based on the assessment of associated cerebrovascular lesions. In addition, perivascular spaces in the white matter and reduced concentrations of both Aβ(40) and Aβ(42) in cerebrospinal fluid may prove to be suggestive for CAA. Transgenic mouse models that overexpress human Aβ precursor protein show parenchymal Aβ and CAA, thus corroborating the current concept of CAA pathogenesis: neuronal Aβ enters the perivascular drainage pathway and may accumulate in vessel walls due to increased amounts and/or decreased clearance of Aβ, respectively. We suggest that pericapillary Aβ represents early impairment of the perivascular drainage pathway while capillary CAA is associated with decreased transendothelial clearance of Aβ. CAA plays an important role in the multimorbid condition of the ageing brain but its contribution to neurodegeneration remains to be elucidated.     

Theory of Mind in Parkinson's disease

Amyloid-beta peptide (Aβ) is believed to be central in the pathogenesis of Alzheimer's disease (AD) characterized by cognitive deficits. However, it remains uncertain which form(s) of Aβ pathology is responsible for the cognitive deficits in AD. In the present study, the cognitive deficits and the profiles of Aβ pathology were characterized in the 12-month-old APPswe/PS1dE9 double transgenic mice, and their correlations were examined. Compared with non-transgenic littermates, the middle-aged APPswe/PS1dE9 mice exhibited spatial learning and memory deficits in the water maze test and long-term contextual memory deficits in the step-down passive avoidance test. Among the middle-aged APPswe/PS1dE9 mice, hippocampal soluble Aβ1-40 and Aβ1-42 levels were highly correlated with spatial learning deficits and long-term contextual memory deficits, as well as cortical and hippocampal soluble Aβ1-40 and Aβ1-42 levels were strongly correlated with spatial memory deficits. By contrast, no significant correlations were observed between three measures of cognitive functions and amyloid plaque burden (total Aβ plaque load and fibrillar Aβ plaque load), total Aβ levels (Aβ1-40 and Aβ1-42), as well as insoluble Aβ levels (Aβ1-40 and Aβ1-42). Stepwise multiple regression analysis identified hippocampal soluble Aβ1-40 and Aβ1-42 levels as independent factors for predicting the spatial learning deficits and the long-term contextual memory deficits, as well as hippocampal and cortical soluble Aβ1-40 and Aβ1-42 levels as independent factors for predicting the spatial memory deficits in transgenic mice. These results demonstrate that cognitive deficits are highly related to the levels of soluble Aβ in middle-aged APPswe/PS1dE9 mice, in which soluble Aβ levels are only a tiny fraction of the amount of total Aβ levels. Consequently, our findings provide further evidence that soluble Aβ might primarily contribute to cognitive deficits in AD, suggesting that reducing the levels of soluble Aβ species would be a therapeutic intervention for AD patients even with large deposits of aggregated, insoluble Aβ.     

Dual pathways mediate β‐amyloid stimulated glutathione release from astrocytes

Oxidative stress plays an important role in the progression of Alzheimer's disease (AD) and other neurodegenerative conditions. Glutathione (GSH), the major antioxidant in the central nervous system, is primarily synthesized and released by astrocytes. We determined if β‐amyloid (Aβ42), crucially involved in Alzheimer's disease, affected GSH release. Monomeric Aβ (mAβ) stimulated GSH release from cultured cortical astrocytes more effectively than oligomeric Aβ (oAβ) or fibrillary Aβ (fAβ). Monomeric Aβ increased the expression of the transporter ABCC1 (also referred to as MRP1) that is the main pathway for GSH release. GSH release from astrocytes, with or without mAβ stimulation, was reduced by pharmacological inhibition of ABCC1. Astrocytes robustly express connexin proteins, especially connexin43 (Cx43), and mAβ also stimulated Cx43 hemichannel‐mediated glutamate and GSH release. Aβ‐stimulation facilitated hemichannel opening in the presence of normal extracellular calcium by reducing astrocyte cholesterol level. Aβ treatment did not alter the intracellular concentration of reduced or oxidized glutathione. Using a mouse model of AD with early onset Aβ deposition (5xFAD), we found that cortical ABCC1 was significantly increased in temporal register with the surge of Aβ levels in these mice. ABCC1 levels remained elevated from 1.5 to 3.5 months of age in 5xFAD mice, before plunging to subcontrol levels when amyloid plaques appeared. Similarly, in cultured astrocytes, prolonged incubation with aggregated Aβ, but not mAβ, reduced induction of ABCC1 expression. These results support the hypothesis that in the early stage of AD pathogenesis, less aggregated Aβ increases GSH release from astrocytes (via ABCC1 transporters and Cx43 hemichannels) providing temporary protection from oxidative stress which promotes AD development. GLIA 2015;63:2208–2219     

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.     

Enhanced generation of intracellular Aβ42 amyloid peptide by mutation of presenilins PS1 and PS2

The accumulation of amyloid β‐peptide (Aβ) in the brain is a critical pathological process in Alzheimer's disease (AD). Recent studies have implicated intracellular Aβ in neurodegeneration in AD. To investigate the generation of intracellular Aβ, we established human neuroblastoma SH‐SY5Y cells stably expressing wild‐type amyloid precursor protein (APP), Swedish mutant APP, APP plus presenilin 1 (PS1) and presenilin 2 (PS2; wild‐type or familial AD‐associated mutant), and quantified intracellular Aβ40 and Aβ42 in formic acid extracts by sensitive Western blotting. Levels of both intracellular Aβ40 and Aβ42 were 2–3‐fold higher in cells expressing Swedish APP, compared with those expressing wild‐type APP. Intracellular Aβ42/Aβ40 ratios were approximately 0.5 in these cells. These ratios were increased markedly in cells expressing mutant PS1 or PS2 compared with those expressing their wild‐type counterparts, consistent with the observed changes in secreted Aβ42/Aβ40 ratios. High total levels of intracellular Aβ were observed in cells expressing mutant PS2 because of a marked elevation of Aβ42. Immunofluorescence staining additionally revealed more intense Aβ42 immunoreactivity in mutant PS2‐expressing cells than in wild‐type cells, which was partially colocalized with immunoreactivity for the trans‐Golgi network and endosomes. The data collectively indicate that PS mutations promote the accumulation of intracellular Aβ42, which appears to be localized in multiple subcellular compartments.     

Amyloid (Aβ) deposition in chromosome 1–linked Alzheimer's disease: The volga german families

Amyloid β protein (Aβ) deposition was investigated in the frontal cortex of 6 cases of (genetically confirmed) chromosome 1–linked Alzheimer's disease (AD) (PS-2 gene mutation) among the Volga German families using the end-specific monoclonal antibodies BA27 and BC05 to detect the presence of Aβ₄₀ and Aβ₄₂₍₄₃₎, respectively. In all patients, Aβ₄₂₍₄₃₎ was the predominant peptide species present, although the total amount of Aβ₄₀ and Aβ₄₂₍₄₃₎ deposited in plaques did not differ from that seen in sporadic AD and was significantly lower than that occurring in AD due to PS-1 gene mutations. Therefore, mutations in the PS-2 gene, like those in the presenilin-1 (PS-1) and amyloid precursor protein (APP) genes, are associated with an initial and preferential deposition of Aβ₄₂₍₄₃₎ within the brain. Although the mechanisms(s) whereby the PS-1 and PS-2 gene mutations operate remains unclear, it seems from the present study that the effect of the PS-2 gene mutation on the brain is muuch less severe, at least as far as Aβ deposition is concerned, than that of the PS-1 mutation, which seems to confer a much earlier and a much more aggressive development of AD.     

Production and increased detection of amyloid β protein and amyloidogenic fragments in brain microvessels,meningeal vessels and choroid plexus in Alzheimer's disease

Recent advances indicate soluble amyloid β (Aβ) protein is produced constitutively during normal metabolism of the amyloid precursor protein (APP). This has not been directly examined in human brain vascular tissues. Using a panel of well-characterized antibodies, here we show that increased amounts of soluble Aβ were found in isolated vascular tissues from AD subjects compared to age-matched controls without significant Alzheimer pathology. Immunocytochemical analyses of isolated vessel preparations showed characteristic transverse patterns of Aβ deposits in large vessels with smooth muscle, however, fine Aβ deposits were apparent even in capillaries. A proportion of such Aβ protein and potentially amyloidogenic carboxyl terminal fragments were released by solubilization and disruption of the vascular basement membrane by collagenase treatments. We further demonstrated by in vitro metabolic labelling that soluble Aβ or an Aβ-like peptide is associated and produced by cerebral microvessels, meningeal vessels and the choroid plexus isolated postmortem from human as well as rat brain. Compared to those from young rats, cerebral microvessels from aging rats showed increased release of carboxyl terminal fragments of APP and Aβ-like peptide. Our observations provide the first direct demonstration that human vascular tissues produce soluble Aβ, a product of the secretory pathway in APP processing. Our findings also suggest that aging associated alterations in the basement membranes are a factor in Aβ accumulation that results in vascular amyloid deposition, the principal feature of cerebral amyloid angiopathy.     

Characteristics of dyshoric capillary cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) affects brain parenchymal and leptomeningeal arteries and arterioles but sometimes involves capillaries (capCAA) with spread of the amyloid into the surrounding neuropil, that is, dyshoric changes. We determined the relationship between capCAA and larger vessel CAA, β amyloid (Aβ) plaques, neurofibrillary changes, inflammation, and apolipoprotein E (APOE) in 22 cases of dyshoric capCAA using immunohistochemistry. The dyshoric changes contained predominantly Aβ1-40, whereas dense bulblike deposits adjacent to the capillary wall contained mostly Aβ1-42. There was an inverse local correlation between Aβ plaque load and capCAA severity (p = 0.01), suggesting that Aβ transport between the neuropil and the circulation may be mechanistically involved. Deposits of hyperphosphorylated tau and ubiquitin and clusters of activated microglia, resembling the changes around Aβ plaques, were found around capCAA but were absent around larger vessel CAA. In 14 cases for which APOE genotype was available, there was a high APOE-ε4 allele frequency (54%; 43% homozygous). The severity of CapCAA increased with the number of ε4-alleles; and APOE4 seemed to colocalize with capCAA by immunohistochemistry. These results suggest that capCAA is pathologically and possibly pathogenetically distinct from larger vessel CAA, and that it is associated with a high APOE-ε4 allele frequency.     

Macrophage colony stimulating factor is associated with excretion of amyloid‐β peptides from cerebrospinal fluid to peripheral blood

Background: The process of aggregation of brain amyloid‐β peptides (Aβ) is thought to be associated with the pathogenesis of Alzheimer's disease (AD). Amyloid‐β peptides are produced by sequential endoproteolysis by β‐site amyloid‐β protein precursor‐cleaving enzyme (BACE) followed by presenilin (PS)/γ‐secretase. There are several species of Aβ due to cleavage diversity of PS/γ‐secretase. The predominant species in human cerebrospinal fluid (CSF) or plasma is Aβ40, whereas Aβ42 is much more aggregatable and accumulated in senile plaques. The level of Aβ in the brain is determined by the balance between the generation and clearance of Aβ, including transport across the brain–blood barrier (BBB). Although the processes of Aβ generation and degradation have been studied in some detail, knowledge of the Aβ transport process across the BBB is limited. So far, low‐density lipoprotein receptor‐related protein (LRP1), P‐glycoprotein (P‐gp), and insulin‐like growth factor‐1 (IGF‐1) have been identified to modify the excretion of brain Aβ to the blood. Methods: To investigate whether macrophage colony stimulating factor (M‐CSF) has a role in the Aβ transport process, human Aβ was injected into the lateral ventricle of the brain of M‐CSF‐deficient (op/op) mice. Then, plasma and brain Aβ levels were measured by ELISA to determine the time‐course of Aβ movement from the brain to the plasma. Result: When human Aβ40 was injected into mouse lateral ventricles, the efflux of Aβ from the CSF to the blood was transiently decreased and delayed in M‐CSF‐deficient mice. Moreover, endogenous plasma Aβ40 levels were lower in M‐CSF‐deficient mice. Conclusion: The results indicate that M‐CSF deficiency impairs excretion of human‐type Aβ40 from the CSF to blood. We propose that M‐CSF may be a novel factor that facilitates the excretion of Aβ from the CSF to the blood via the BBB.