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.     

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.     

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).     

A novel presenilin-1 mutation: Increased β-amyloid and neurofibrillary changes

The prevalence of known mutations in presenilin genes (PS1 and PS2) causing early-onset familial Alzheimer's disease (FAD) was assessed in a population of 98 singleton early-onset AD cases, 29 early-onset FAD cases, and 15 late-onset FAD cases. None of the cases tested positive for the eight mutations initially reported, and none of these mutations were observed in 60 age-matched controls. A novel mutation (R269H) in PS1 was found in a single case of early-onset AD but not in any other AD or control case. Thus, the PS mutations tested are quite rare in early-onset AD. Amyloid β protein (Aβ) deposition was investigated in the temporal cortex of the R269H mutation case using end-specific monoclonal antibodies to detect the presence of Aβ_x?40 and Aβ_x?42 subspecies. Stereologically unbiased tangle and neuropil thread counts were obtained from the same region. R269H PS1 mutation was associated with early age of dementia onset, higher amounts of total Aβ and Aβ_x?42, and increased neuronal cytoskeletal changes. Thus, if the changes observed on this case prove to be typical of PS1 mutations, PS1 mutations may impact both amyloid deposition and neurofibrillary pathology.     

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.     

Aβ-peptide length aid apolipoprotein E genotype in Alzheimer's disease

Apolipoprotein ∈ (ApoE)ε4 allele, a risk factor for the development of Alzheimer's disease (AD), is associated with increased amyloid deposition. We examined cerebral cortex in 68 AD cases using antibodies to βbeta;-amyloid (Aβbeta;) peptides of different length (Aβbeta;_1?40 and Aβbeta;_l?42) and found that the increased plaque frequency observed with ε4 genotypes may be largely attributed to an increase in Aβbeta;_1?40-positive plaques. Indeed, both the number of Aβbeta;_1?40-positive plaques, as well as the ratio of Aβbeta;_I?40/ Aβbeta;_1?42-positive plaques, increased with ε4 dosage. In contrast, the frequency of Aβbeta;_1?42-immunoreactive plaques was similar for ε3/ε3,ε3/ε4 and ε4/ε4 genotypes. ApoE may influence Aβbeta; length by facilitating Aβbeta; _1?40 deposition onto Aβbeta;_1?42-seeded plaques or by modulating the activity of a putative carboxypeptidase that forms Aβbeta;_1?40 from Aβbeta;_1?42 in situ.     

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.     

Acyl ghrelin improves cognition,synaptic plasticity deficits and neuroinflammation following amyloid β (Aβ1‐40) administration in mice

Ghrelin is a metabolic hormone that has neuroprotective actions in a number of neurological conditions, including Parkinson's disease (PD), stroke and traumatic brain injury. Acyl ghrelin treatment in vivo and in vitro also shows protective capacity in Alzheimer's disease (AD). In the present study, we used ghrelin knockout (KO) and their wild‐type littermates to test whether or not endogenous ghrelin is protective in a mouse model of AD, in which human amyloid β peptide 1‐40 (Aβ_1‐40) was injected into the lateral ventricles i.c.v. Recognition memory, using the novel object recognition task, was significantly impaired in ghrelin KO mice and after i.c.v. Aβ_1‐40 treatment. These deficits could be prevented by acyl ghrelin injections for 7 days. Spatial orientation, as assessed by the Y‐maze task, was also significantly impaired in ghrelin KO mice and after i.c.v. Aβ_1‐40 treatment. These deficits could be prevented by acyl ghrelin injections for 7 days. Ghrelin KO mice had deficits in olfactory discrimination; however, neither i.c.v. Aβ_1‐40 treatment, nor acyl ghrelin injections affected olfactory discrimination. We used stereology to show that ghrelin KO and Aβ_1‐40 increased the total number of glial fibrillary acidic protein expressing astrocytes and ionised calcium‐binding adapter expressing microglial in the rostral hippocampus. Finally, Aβ_1‐40 blocked long‐term potentiation induced by high‐frequency stimulation and this effect could be acutely blocked with co‐administration of acyl ghrelin. Collectively, our studies demonstrate that ghrelin deletion affects memory performance and also that acyl ghrelin treatment may delay the onset of early events of AD. This supports the idea that acyl ghrelin treatment may be therapeutically beneficial with respect to restricting disease progression in AD.     

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.     

A critical role of TRPM2 channel in Aβ42‐induced microglial activation and generation of tumor necrosis factor‐α

Amyloid β (Aβ)‐induced neuroinflammation plays an important part in Alzheimer's disease (AD). Emerging evidence supports a role for the transient receptor potential melastatin‐related 2 (TRPM2) channel in Aβ‐induced neuroinflammation, but how Aβ induces TRPM2 channel activation and this relates to neuroinflammation remained poorly understood. We investigated the mechanisms by which Aβ₄₂ activates the TRPM2 channel in microglial cells and the relationships to microglial activation and generation of tumor necrosis factor‐α (TNF‐α), a key cytokine implicated in AD. Exposure to 10–300 nM Aβ₄₂ induced concentration‐dependent microglial activation and generation of TNF‐α that were ablated by genetically deleting (TRPM2 knockout ;TRPM2‐KO) or pharmacologically inhibiting the TRPM2 channel, revealing a critical role of this channel in Aβ₄₂‐induced microglial activation and generation of TNF‐α. Mechanistically, Aβ₄₂ activated the TRPM2 channel via stimulating generation of reactive oxygen species (ROS) and activation of poly(ADPR) polymerase‐1 (PARP‐1). Aβ₄₂‐induced generation of ROS and activation of PARP‐1 and TRPM2 channel were suppressed by inhibiting protein kinase C (PKC) and NADPH oxidases (NOX). Aβ₄₂‐induced activation of PARP‐1 and TRPM2 channel was also reduced by inhibiting PYK2 and MEK/ERK. Aβ₄₂‐induced activation of PARP‐1 was attenuated by TRPM2‐KO and moreover, the remaining PARP‐1 activity was eliminated by inhibiting PKC and NOX, but not PYK2 and MEK/ERK. Collectively, our results suggest that PKC/NOX‐mediated generation of ROS and subsequent activation of PARP‐1 play a role in Aβ₄₂‐induced TRPM2 channel activation and TRPM2‐dependent activation of the PYK2/MEK/ERK signalling pathway acts as a positive feedback to further facilitate activation of PARP‐1 and TRPM2 channel. These findings provide novel insights into the mechanisms underlying Aβ‐induced AD‐related neuroinflammation.     

Relative efficacies of amyloid β peptide (Aβ) binding proteins in Aβ aggregation

The aggregation of amyloid β peptide (Aβ) into its fibrillar, cross β-pleated configuration is generally viewed as a critical event in the pathophysiology of Alzheimer's disease (AD). A diverse group of molecules, the Aβ binding proteins, has been evaluated for their effects on this process. However, most of these studies have used micromolar or greater reagent concentrations, and their different methods have not permitted quantitative comparisons of the efficacy of different Aβ binding proteins in augmenting or inhibiting aggregation. In the present work we have undertaken a coherent analysis using fluorimetry of thioflavin T-stained experimental solutions. The complement protein C1q, serum amyloid P, and transthyretin significantly enhanced the formation of precipitable, cross β-pleated aggregates in solutions of 800 nM Aβ1–42. Under these same experimental conditions, α₁-antichymotrypsin had no significant effect on the aggregation process, and both the E3 and E4 isoforms of apolipoprotein E were significant inhibitors. There was a non-significant trend toward the E3 isoform exhibiting greater inhibition than the E4 isoform. Of the aggregation-facilitating molecules, C1q was substantially and significantly the most potent. © 1996 Wiley-Liss, Inc.     

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.     

The implications of genetic studies on the pathogenesis of Alzheimer's disease

Current research in molecular genetics and molecular cell biology has disclosed that Alzheimer's disease (AD) is composed of a number of etiologically heterogenous disorders. In dominantly inherited early onset AD, the missense mutations found in the genes encoding amyloid precursor protein (APP), presenilin-1, and/or presenilin-2, are all known to increase the production and secretion of Aβ_1–42(43). The abnormal deposition of Aβ_1–42 is currently considered to play a key role in triggering a pathological array of symptoms in AD. Investigation of the molecular mechanism causing dominant AD provides a powerful model to understand the etiology of sporadic late-onset AD, whose mechanism remains unknown.     

Reduction of β-amyloid peptide42 in the cerebrospinal fluid of patients with Alzheimer's disease

In this clinical study, the cerebrospinal fluid (CSF) level of a Novemberel form of the β-amyloid peptide (Aβ) extending to position 42 (Aβ₄₂) was determined in patients with Alzheimer's disease (AD) as well as controls. In addition to measurement of CSF Aβ₄₂ levels, total Aβ peptides, microtubule-associated protein τ, and apolipoprotein E (ApoE) genotype were also assessed. It is interesting that CSF Aβ₄₂ levels were found to be significantly lower in AD patients relative to controls, whereas total Aβ levels were not. Aβ₄₂ has recently been shown to preferentially deposit in the brain tissue of patients with AD, suggesting that diminished clearance may account for its reduction in CSF. As previously reported, τ levels were increased in AD patients; however, neither Aβ₄₂ nor τ levels were apparently influenced by the ApoE genotype.     

Long‐term oral intake of aluminium or zinc does not accelerate Alzheimer pathology in AβPP and AβPP/tau transgenic mice

Whether or not the oral intake of metals such as aluminium (Al) and zinc (Zn) is a risk for Alzheimer's disease (AD) has been a matter of controversy. Lack of AD pathology in patients with Al encephalopathy indicates Al does not cause AD. On the other hand, some epidemiological studies have suggested high Al increases the occurrence of AD. Our purpose is to test if high Al in drinking water is a risk factor for AD. We administered Al and Zn in drinking water to Tg2576, a transgenic mouse model for amyloid β‐protein (Aβ) deposition with the Aβ precursor protein (AβPP) mutations (K670N/M671L), and Tg2576/tau(P301L), a model for Aβ and tau deposition. Deionized water was given to the control Tg2576 and Tg2576/tau. After administration for 4–10 months of approximately 100 mg/kg body weight Al or Zn per day, we were not able to find by quantitative immunohistochemical analyses differences in the deposition of Aβ and tau between the treated and untreated groups. Nor did the Al or Zn treatment affect the amount of soluble Aβ and Aβ*56, an Aβ oligomer, measured by ELISA or immunoblot. The oral intake of excess Al or Zn does not accelerate AD pathology in the transgenic mouse models for Aβ and tau accumulation. Such results do not seem to support the notion that excessive oral intake of Al or Zn is a risk factor for AD.     

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.     

CSF Aβ42 and tau in Parkinson's disease with cognitive impairment

We tested the hypothesis that the CSF biomarker signature associated with Alzheimer's disease (AD) is present in a subset of individuals with Parkinson's disease and Dementia (PD‐D) or with PD and Cognitive Impairment, Not Dementia (PD‐CIND). We quantified CSF Aβ₄₂, total tau (T‐tau), and phospho‐tau (P181‐tau) using commercially available kits. Samples were from 345 individuals in seven groups (n): Controls ≤50 years (35), Controls >50 years (115), amnestic Mild Cognitive Impairment (aMCI) (24), AD (49), PD (49), PD‐CIND (62), and PD‐D (11). We observed expected changes in AD or aMCI compared with age‐matched or younger controls. CSF Aβ₄₂ was reduced in PD‐CIND (P < 0.05) and PD‐D (P < 0.01), whereas average CSF T‐tau and P181‐tau were unchanged or decreased. One‐third of PD‐CIND and one‐half of PD‐D patients had the biomarker signature of AD. Abnormal metabolism of Aβ₄₂ may be a common feature of PD‐CIND and PD‐D. © 2010 Movement Disorder Society     

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.     

Serum amyloid β protein in young and elderly depression: a pilot study

Background: Depression may increase the risk of developing Alzheimer's disease (AD). Recent large cohort studies have also shown that a low plasma amyloid β (Aβ)‐42 level combined with a high Aβ40 level increases the risk of developing AD, suggesting plasma Aβ42/40 ratio as useful for identifying risk of developing mild cognitive impairment and AD. Although several studies have examined Aβ levels in the peripheral blood of elderly individuals with depression, results have been inconsistent. Furthermore, no results have been described for younger depression. Methods: Serum Aβ40, Aβ42 level and Aβ40/42 ratio were evaluated using enzyme‐linked immunosorbent assay in 60 patients with major depressive disorder (MDD) and 60 healthy controls. The results were analyzed in two age groups (young, <60 years; elderly, ≥60 years). Results: Serum Aβ40 level was significantly higher in young MDD patients compared to young controls (P < 0.001), but it was not significantly deferent in the elderly group. Serum Aβ42 level did not differ significantly in both young and elderly groups. Aβ40/42 ratio was significantly higher in both young (P < 0.001) and elderly (P < 0.001) patients with MDD compared to controls. Conclusions: Serum Aβ40/42 ratio was significantly higher in MDD patients than in controls, and this difference was seen for both elderly and young subjects. This may suggest that even young subjects with MDD undergo pathological changes in the very early stage of amyloid deposition.     

The production ratios of AICDε51 and Aβ42 by intramembrane proteolysis of βAPP do not always change in parallel

Background: During intramembrane proteolysis of β‐amyloid protein precursor (βAPP) by presenilin (PS)/γ‐secretase, ε‐cleavages at the membrane‐cytoplasmic border precede γ‐cleavages at the middle of the transmembrane domain. Generation ratios of Aβ42, a critical molecule for Alzheimer's disease (AD) pathogenesis, and the major Aβ40 species might be associated with ε48 and ε49 cleavages, respectively. Medicines to downregulate Aβ42 production have been investigated by many pharmaceutical companies. Therefore, the ε‐cleavages, rather than the γ‐cleavage, might be more effective upstream targets for decreasing the relative generation of Aβ42. Thus, one might evaluate compounds by analyzing the generation ratio of the βAPP intracellular domain (AICD) species (ε‐cleavage‐derived), instead of that of Aβ42. Methods: Cell‐free γ‐secretase assays were carried out to observe de novo AICD production. Immunoprecipitation/MALDI‐TOF MS analysis was carried out to detect the N‐termini of AICD species. Aβ and AICD species were measured by ELISA and immunoblotting techniques. Results: Effects on the ε‐cleavage by AD‐associated pathological mutations around the ε‐cleavage sites (i.e., βAPP V642I, L648P and K649N) were analyzed. The V642I and L648P mutations caused an increase in the relative ratio of ε48 cleavage, as expected from previous reports. Cells expressing the K649N mutant, however, underwent a major ε‐cleavage at the ε51 site. These results suggest that ε51, as well as ε48 cleavage, is associated with Aβ42 production. Only AICDε51, though, and not Aβ42 production, dramatically changed with modifications to the cell‐free assay conditions. Interestingly, the increase in the relative ratio of the ε51 cleavage by the K649N mutation was not cancelled by these changes. Conclusion: Our current data show that the generation ratio of AICDε51 and Aβ42 do not always change in parallel. Thus, to identify compounds that decrease the relative ratio of Aβ42 generation, measurement of the relative level of Aβ42‐related AICD species (i.e., AICDε48 and AICDε51) might not be useful. Further studies to reveal how the ε‐cleavage precision is decided are necessary before it will be possible to develop drugs targeting ε‐cleavage as a means for decreasing Aβ42 production.