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.     

Function of Nogo‐A/Nogo‐A Receptor in Alzheimer's Disease

Nogo‐A is a protein inhibiting axonal regeneration, which is considered a major obstacle to nerve regeneration after injury in mammals. Rapid progress has been achieved in new physiopathological function of Nogo‐A in Alzheimer's disease in the past decade. Recent research shows that through binding to Nogo‐A receptor, Nogo‐A plays an important role in Alzheimer's disease (AD) pathogenesis. Particularly, Nogo‐A/Nogo‐A receptors modulate the generation of amyloid β‐protein (Aβ), which is thought to be a major cause of AD. This review describes the recent development of Nogo‐A, Nogo‐A receptor, and downstream signaling involved in AD and pharmacological basis of therapeutic drugs. We concluded the Nogo‐A/Nogo‐A receptor provide new insight into potential mechanisms and promising therapy strategies in AD.     

The peripheral messenger RNA expression of glycogen synthase kinase‐3β genes in Alzheimer's disease patients: a preliminary study

Objective: To explore the peripheral leucocytic messenger RNA (mRNA) expression of glycogen synthase kinase‐3β (GSK‐3β) gene in Alzheimer's disease (AD) patients. Methods: Using TaqMan relative quantitative real‐time polymerase chain reaction, we analyzed leucocytic gene expression of GSK‐3β in 48 AD patients and 49 healthy controls. Clinical data of AD patients were also collected. Results: The mRNA expression level of the GSK‐3β gene was significantly higher in the AD group (3.13 ± 0.62) than in the normal group (2.77 ± 0.77). Correlational analyses showed that the mRNA expression level of GSK‐3β gene in AD patients was associated with the age of onset (P= 0.047), age (P= 0.055), and Behavioral Pathology in Alzheimer's Disease Rating Scale total score (P= 0.062) and subscores: aggressiveness score (P= 0.073) and anxieties and phobias score (P= 0.067). Through multivariate regression model, older age, higher anxieties and phobias score and aggressiveness score were associated with higher mRNA expression level of GSK‐3β gene. Conclusion: In AD patients, the mRNA expression level of the GSK‐3β gene is increased and may be related to age and behavioural pathology in AD.     

Endothelins reciprocally regulate VEGF‐A and angiopoietin‐1 production in cultured rat astrocytes: Implications on astrocytic proliferation

Vascular endothelial growth factors (VEGFs) and angiopoietins (ANGs) are involved in pathophysiological responses in damaged nerve tissues. Astrocytes produce VEGFs and ANGs upon brain ischemia and traumatic injury. To clarify the extracellular signals regulating VEGF and ANG production, effects of endothelins (ETs), a family of endothelium‐derived peptides, were examined in cultured rat astrocytes. ET‐1 (100 nM) and Ala^1,3,11,15‐ET‐1 (100 nM), an ET_B receptor agonist, increased VEGF‐A mRNA levels in cultured astrocytes, while ANG‐1 mRNA was decreased by ETs. ET‐1 did not affect astrocytic VEGF‐B, placental growth factor (PLGF), and ANG‐2 mRNA levels. The effects of ET‐1 on VEGF‐A and ANG‐1 mRNAs were inhibited by BQ788, an ET_B antagonist. Release of VEGF‐A proteins from cultured astrocytes was increased by ET‐1. In contrast, ET‐1 reduced release of astrocytic ANG‐1. Exogenous ET‐1 (100 nM) and VEGF₁₆₅ (100 ng/mL), an isopeptide of VEGF‐A, stimulated bromodeoxyuridine (BrdU) incorporation into cultured astrocytes. Treatment with ET‐1 and VEGF₁₆₅ increased the numbers of cyclin D1‐positive astrocytes. Exogenous ANG‐1 (250 ng/mL) did not stimulate the BrdU incorporation. Increases in BrdU incorporation by ET‐1 and VEGF₁₆₅ were not affected by ANG‐1. In 60–70% confluent cultures, SU4312 (10 μM), a VEGF receptor tyrosine kinase inhibitor, partially reduced the effects of ET‐1 on BrdU incorporation and cyclin D1 expression. ET‐induced BrdU incorporation and cyclin D1 expression were reduced by a neutralizing antibody against VEGF‐A. Our findings suggest that ET‐1 is a factor regulating astrocytic VEGF‐A and ANG‐1, and that increased VEGF‐A production potentiates ET‐induced astrocytic proliferation by an autocrine mechanism. © 2012 Wiley Periodicals, Inc.     

Alternations of central insulin‐like growth factor‐1 sensitivity in APP/PS1 transgenic mice and neuronal models

Although many post‐mortem studies have found evidence of central insulin resistance in Alzheimer's disease (AD) patients, results on changes of central insulin‐like growth factor‐1 (IGF‐1) signaling in the pathological process of AD remain controversial. In the present study, we observed the activation states of IGF‐1 downstream signaling in brain slices of transgenic mice carrying APPswe/PS1dE9 mutations (APP/PS1 mice) at both early and late stages (ex vivo) and further investigated the involvement of oligomeric β‐amyloid (Aβ) and Aβ‐enriched culture medium (CM) on IGF‐1 sensitivity employing neuronal models (in vitro). In 6‐ and 18‐month‐old APP/PS1 mice, the phosphorylations of IGF‐1 receptor (IGF‐1R) and Akt in response to IGF‐1 stimulation were significantly reduced in the hippocampal and cortical slices, whereas IGF‐1R protein expression and mRNA levels of IGF‐1 and IGF‐1R in the hippocampal slices were significantly higher than that in wild‐type mice. In agreement with these results, reduced IGF‐1 sensitivity was verified in APP and PS1 double stably transfected CHO cells; moreover, IGF‐1 stimulated phosphorylations of IGF‐1R and Akt were also markedly weakened by oligomeric Aβ or Aβ‐enriched CM posttreatment in CHO cells without APP/PS1‐transfected (K1 cells) and primary hippocampal neurons. These observations indicate that the impaired central IGF‐1 sensitivity at early and late stages of APP/PS1 transgenic mice might be attributable, at least partially, to the overproduced Aβ, especially the oligomeric Aβ. These findings may shed new light on the mechanisms underlying the defective IGF‐1 signaling in AD pathogenesis and provide important clues for AD drug discovery. © 2013 Wiley Periodicals, Inc.     

Amyloid β‐protein suppressed nicotinic acetylcholine receptor‐mediated currents in acutely isolated rat hippocampal CA1 pyramidal neurons

Amyloid β protein (Aβ) is responsible for the deficits of learning and memory in Alzheimer's disease (AD). The high affinity between Aβ and nicotinic acetylcholine receptors (nAChRs) suggests that the impairment of cognitive function in AD might be involved in the Aβ‐induced damage of nAChRs. This study investigated the effects of Aβ fragments on nAChR‐mediated membrane currents in acutely isolated rat hippocampal pyramidal neurons by using whole‐cell patch clamp technique. The results showed that: (1) nonspecific nAChR agonist nicotine, selective α7 nAChR agonist choline, and α4β2 nAChR agonist epibatidine all effectively evoked inward currents in CA1 neurons at normal resting membrane potential, with different desensitization characteristics; (2) acute application of different concentrations (pM–μM) of Aβ25‐35, Aβ31‐35, or Aβ35‐31 alone did not trigger any membrane current, but pretreatment with 1 μM Aβ25‐35 and Aβ31‐35 similarly and reversibly suppressed the nicotine‐induced currents; (3) further, choline‐ and epibatidine‐induced currents were also reversibly suppressed by the Aβ pretreatment, but more prominent for the choline‐induced response. These results demonstrate that the functional activity of both α7 and α4β2 nAChRs in the membrane of acutely isolated hippocampal neurons was significantly downregulated by Aβ treatment, suggesting that nAChRs, especially α7 nAChRs, in the brain may be the important biological targets of neurotoxic Aβ in AD. In addition, the similar suppression of nAChR currents by Aβ25‐35 and Aβ31‐35 suggests that the sequence 31‐35 in Aβ molecule may be a shorter active center responsible for the neurotoxicity of Aβ in AD. Synapse, 2013. © 2012 Wiley Periodicals, Inc.     

Potential in vivo amelioration by N‐acetyl‐L‐cysteine of oxidative stress in brain in human double mutant APP/PS‐1 knock‐in mice: Toward therapeutic modulation of mild cognitive impairment

Alzheimer's disease (AD) is the most prevalent form of dementia among the elderly. Although the underlying cause has yet to be established, numerous data have shown that oxidative stress is implicated in AD as well as in preclinical stages of AD, such as mild cognitive impairment (MCI). The oxidative stress observed in brains of subjects with AD and MCI may be due, either fully or in part, to increased free radicals mediated by amyloid‐β peptide (Aβ). By using double human mutant APP/PS‐1 knock‐in mice as the AD model, the present work demonstrates that the APP/PS‐1 double mutation results in elevated protein oxidation (as indexed by protein carbonyls), protein nitration (as indexed by 3‐nitrotyrosine), as well as lipid peroxidation (as indexed by protein‐bound 4‐hydroxy‐2‐nonenal) in brains of mice aged 9 months and 12 months. APP/PS‐1 mice also exhibited lower levels of brain glutathione peroxidase (GPx) in both age groups studied, whereas glutathione reductase (GR) levels in brain were unaffected by the mutation. The activities of both of these antioxidant enzymes were significantly decreased in APP/PS‐1 mouse brains, whereas the activity of glucose‐6‐phosphate dehydrogenase (G6PDH) was increased relative to controls in both age groups. Levels of peptidyl prolyl isomerase 1 (Pin1) were significantly decreased in APP/PS‐1 mouse brain aged 9 and 12 months. Administration of N‐acetyl‐L‐cysteine (NAC), a glutathione precursor, to APP/PS‐1 mice via drinking water suppressed increased protein oxidation and nitration and also significantly augmented levels and activity of GPx in brain from both age groups. Oral administration of NAC also increased the diminished activity of GR and protected against lipid peroxidation in brains of 9‐month‐old APP/PS‐1 mice only. Pin1 levels, GR levels, and G6PDH activity in brain were unaffected by oral administration of NAC in both age groups. These results are discussed with reference to the therapeutic potential of this brain‐accessible glutathione precursor in the treatment of MCI and AD. © 2010 Wiley‐Liss, Inc.     

Melatonin protects against amyloid‐β‐induced impairments of hippocampal LTP and spatial learning in rats

Alzheimer's disease (AD), the most prevalent neurodegenerative disease in the elderly, leads to progressive loss of memory and cognitive deficits. Amyloid‐β protein (Aβ) in the brain is thought to be the main cause of memory loss in AD. Melatonin, an indole hormone secreted by the pineal gland, has been reported to produce neuroprotective effects. We examined whether melatonin could protect Aβ‐induced impairments of hippocampal synaptic plasticity, neuronal cooperative activity, and learning and memory. Rats received bilateral intrahippocampal injection of Aβ1‐42 or Aβ31‐35 followed by intraperitoneal application of melatonin for 10 days, and the effects of chronic melatonin treatment on in vivo hippocampal long‐term potentiation (LTP) and theta rhythm and Morris water maze performance were examined. We showed that intrahippocampal injection of Aβ1‐42 or Aβ31‐35 impaired hippocampal LTP in vivo, while chronic melatonin treatment reversed Aβ1‐42‐ or Aβ31‐35‐induced impairments in LTP induction. Intrahippocampal injection of Aβ31‐35 impaired spatial learning and decreased the power of theta rhythm in the CA1 region induced by tail pinch, and these synaptic, circuit, and learning deficits were rescued by chronic melatonin treatment. These results provide evidence for the neuroprotective action of melatonin against Aβ insults and suggest a strategy for alleviating cognition deficits of AD. Synapse 67:626–636, 2013 . © 2013 Wiley Periodicals, 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.     

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.     

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.     

Interleukin‐18 and transforming growth factor‐beta 1 plasma levels in Alzheimer’s disease and vascular dementia

Inflammation has been involved in the development of dementia in cerebrovascular diseases. To investigate the cellular activation of the peripheral immune system in patients with Alzheimer’s disease (AD) and vascular dementia (VaD), we determined the presence of IL‐18 and TGF‐β1 in the plasma by using ELISA. The levels of IL‐18 and TGF‐β1 were significantly elevated in patients with AD and VaD compared to non‐demented, age‐matched subjects. We found an inverse correlation between the levels of IL‐18 and TGF‐β1 in AD patients. In VaD patients, the correlation between IL‐18 and TGF‐β1 reached a borderline positive value. Whereas, in the non‐demented, age‐matched subjects, a positive correlation between IL‐18 and TGF‐β1 levels was observed. These findings indicate that IL‐18 and TGF‐β1 elevation is associated with AD and VaD patients, confirming that the immune system might exert a remarkable role in the development and progression of neurodegenerative disorders. Moreover, as different modifications were detected in the patients affected by AD and VaD, we propose that IL‐18 and TGF‐ β1 plasma levels might represent possible differential biomarkers.     

TGF‐β1 Pathway as a New Target for Neuroprotection in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder that affects more than 37 million people worldwide. Current drugs for AD are only symptomatic, but do not interfere with the underlying pathogenic mechanisms of the disease. AD is characterized by the presence of ß‐amyloid (Aβ) plaques, neurofibrillary tangles, and neuronal loss. The identification of the molecular determinants underlying AD pathogenesis is a fundamental step to design new disease‐modifying drugs. Recently, a specific impairment of transforming‐growth‐factor‐β1 (TGF‐β1) signaling pathway has been demonstrated in AD brain. The deficiency of TGF‐β1 signaling has been shown to increase both Aβ accumulation and Aβ‐induced neurodegeneration in AD models. The loss of function of TGF‐ß1 pathway seems also to contribute to tau pathology and neurofibrillary tangle formation. Growing evidence suggests a neuroprotective role for TGF‐β1 against Aβ toxicity both in vitro and in vivo models of AD. Different drugs, such as lithium or group II mGlu receptor agonists are able to increase TGF‐β1 levels in the central nervous system (CNS), and might be considered as new neuroprotective tools against Aβ‐induced neurodegeneration. In the present review, we examine the evidence for a neuroprotective role of TGF‐β1 in AD, and discuss the TGF‐β1 signaling pathway as a new pharmacological target for the treatment of AD.     

Tripchlorolide protects neuronal cells from microglia‐mediated β‐amyloid neurotoxicity through inhibiting NF‐κB and JNK signaling

Recent research has focused on soluble oligomeric assemblies of β‐amyloid peptides (Aβ) as the proximate cause of neuroinflammation, synaptic loss, and the eventual dementia associated with Alzheimer's disease (AD). In this study, tripchlorolide (T₄), an extract of Tripterygium wilfordii Hook. F (TWHF), was studied as a novel agent to suppress neuroinflammatory process in microglial cells and to protect neuronal cells against microglia‐mediated oligomeric Aβ toxicity. T₄ significantly attenuated oligomeric Aβ(1‐42)‐induced release of inflammatory productions such as tumor necrosis factor‐α, interleukin‐1β, nitric oxide (NO), and prostaglandin E₂. It also downregulated the protein levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase‐2 (COX‐2) in microglial cells. Further molecular mechanism study demonstrated that T₄ inhibited the nuclear translocation of nuclear factor‐κB (NF‐κB) without affecting I‐κBα phosphorylation. It repressed Aβ‐induced JNK phosphorylation but not ERK or p38 MAPK. The inhibition of NF‐κB and JNK by T₄ is correlated with the suppression of inflammatory mediators in Aβ‐stimulated microglial cells. These results suggest that T₄ protects neuronal cells by blocking inflammatory responses of microglial cells to oligomeric Aβ(1‐42) and that T₄ acts on the signaling of NF‐κB and JNK, which are involved in the modulation of inflammatory response. Therefore, T₄ may be an effective agent in modulating neuroinflammatory process in AD. © 2009 Wiley‐Liss, Inc.     

Attenuation of β‐amyloid‐induced tauopathy via activation of CK2α/SIRT1: Targeting for cilostazol

β‐Amyloid (Aβ) deposits and hyperphosphorylated tau aggregates are the chief hallmarks in the Alzheimer's disease (AD) brains, but the strategies for controlling these pathological events remain elusive. We hypothesized that CK2‐coupled SIRT1 activation stimulated by cilostazol suppresses tau acetylation (Ac‐tau) and tau phosphorylation (P‐tau) by inhibiting activation of P300 and GSK3β. Aβ was endogenously overproduced in N2a cells expressing human APP Swedish mutation (N2aSwe) by exposure to medium containing 1% fetal bovine serum for 24 hr. Increased Aβ accumulation was accompanied by increased Ac‐tau and P‐tau levels. Concomitantly, these cells showed increased P300 and GSK3β P‐Tyr216 expression; their expressions were significantly reduced by treatment with cilostazol (3–30 μM) and resveratrol (20 μM). Moreover, decreased expression of SIRT1 and its activity by Aβ were significantly reversed by cilostazol as by resveratrol. In addition, cilostazol strongly stimulated CK2α phosphorylation and its activity, and then stimulated SIRT1 phosphorylation. These effects were confirmed by using the pharmacological inhibitors KT5720 (1 μM, PKA inhibitor), TBCA (20 μM, inhibitor of CK2), and sirtinol (20 μM, SIRT1 inhibitor) as well as by SIRT1 gene silencing and overexpression techniques. In conclusion, increased cAMP‐dependent protein kinase‐linked CK2/SIRT1 expression by cilostazol can be a therapeutic strategy to suppress the tau‐related neurodegeneration in the AD brain. © 2013 Wiley Periodicals, Inc.     

Amyloid‐β induces sleep fragmentation that is rescued by fatty acid binding proteins in Drosophila

Disruption of sleep/wake activity in Alzheimer's disease (AD) patients significantly affects their quality of life and that of their caretakers and is a major contributing factor for institutionalization. Levels of amyloid‐β (Aβ) have been shown to be regulated by neuronal activity and to correlate with the sleep/wake cycle. Whether consolidated sleep can be disrupted by Aβ alone is not well understood. We hypothesize that Aβ42 can increase wakefulness and disrupt consolidated sleep. Here we report that flies expressing the human Aβ42 transgene in neurons have significantly reduced consolidated sleep compared with control flies. Fatty acid binding proteins (Fabp) are small hydrophobic ligand carriers that have been clinically implicated in AD. Aβ42 flies that carry a transgene of either the Drosophila Fabp or the mammalian brain‐type Fabp show a significant increase in nighttime sleep and long consolidated sleep bouts, rescuing the Aβ42‐induced sleep disruption. These studies suggest that alterations in Fabp levels and/or activity may be associated with sleep disturbances in AD. Future work to determine the molecular mechanisms that contribute to Fabp‐mediated rescue of Aβ42‐induced sleep loss will be important for the development of therapeutics in the treatment of AD. © 2016 Wiley Periodicals, Inc.     

The two‐hydrophobic domain tertiary structure of reticulon proteins is critical for modulation of β‐secretase BACE1

β‐Site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is a membrane‐bound protease that is essential for the production of β‐amyloid protein (Aβ). Given the crucial role of Aβ accumulation in Alzheimer's disease (AD), inhibition of BACE1 activity may represent a feasible therapeutic strategy in the treatment of AD. Recently, we and others identified reticulon 3 (RTN3) and reticulon 4‐B/C (RTN4‐B/C or Nogo‐B/C) as membrane proteins that interact with BACE1 and inhibit its ability to produce Aβ. In this study, we employed various mutants of RTN3 and RTN4‐C and C. elegans RTN to investigate the molecular mechanisms by which RTNs regulate BACE1. We found that RTN3 mutants lacking the N‐terminal or C‐terminal or loop domain as well as a RTN4‐C mutant lacking the C‐terminal domain bound to BACE1 comparably to wild‐type RTN3 and RTN4‐C. Furthermore, overexpression of wild‐type RTN3, RTN4‐C, and these RTN mutants similarly reduced Aβ40 and Aβ42 secretion by cells expressing Swedish mutant APP. C. elegans RTN, which has low homology to human RTNs, also interacted with BACE1 and inhibited Aβ secretion. In contrast, two RTN3 mutants containing deletions of the first or second potential transmembrane domains and an RTN3 swap mutant of the second transmembrane domain bound BACE1 but failed to inhibit Aβ secretion. Collectively, these results suggest that the two‐transmembrane‐domain tertiary structure of RTN proteins is critical for the ability of RTNs to modulate BACE1 activity, whereas N‐terminal, C‐terminal and loop regions are not essential for this function. © 2009 Wiley‐Liss, Inc.     

Memantine protects rat cortical cultured neurons against β‐amyloid‐induced toxicity by attenuating tau phosphorylation

It has been suggested that accumulation of beta‐amyloid (Aβ) peptide triggers neurodegeneration, at least in part, via glutamate‐mediated excitotoxicity in Alzheimer’s disease (AD) brain. This is supported by observations that toxicity induced by Aβ peptide in cultured neurons and in adult rat brain is known to be mediated by activation of glutamatergic N‐methyl‐d ‐aspartate (NMDA) receptors. Additionally, recent clinical studies have shown that memantine, a noncompetitive NMDA receptor antagonist, can significantly improve cognitive functions in some AD patients. However, very little is currently known about the potential role of memantine against Aβ‐induced toxicity. In the present study, we have shown that Aβ_1–42‐induced toxicity in rat primary cortical cultured neurons is accompanied by increased extracellular and decreased intracellular glutamate levels. We subsequently demonstrated that Aβ toxicity is induced by increased phosphorylation of tau protein and activation of tau kinases, i.e. glycogen synthase kinase‐3β and extracellular signal‐related kinase 1/2. Additionally, Aβ treatment induced cleavage of caspase‐3 and decreased phosphorylation of cyclic AMP response element binding protein, which are critical in determining survival of neurons. Memantine treatment significantly protected cultured neurons against Aβ‐induced toxicity by attenuating tau‐phosphorylation and its associated signaling mechanisms. However, this drug did not alter either conformation or internalization of Aβ_1–42 and it was unable to attenuate Aβ‐induced potentiation of extracellular glutamate levels. These results, taken together, provide new insights into the possible neuroprotective action of memantine in AD pathology.     

Abnormal fronto-parietal coupling of brain rhythms in mild Alzheimer's disease: a multicentric EEG study

Cholinergic deafferentation/recovery in rats mainly impinges on the fronto‐parietal coupling of brain rhythms [D. P. Holschneider et al. (1999) Exp. Brain Res., 126 , 270–280]. Is this reflected by the functional coupling of fronto‐parietal cortical rhythms at an early stage of Alzheimer's disease (mild AD)? Resting electroencephalographic (EEG) rhythms were studied in 82 patients with mild AD and in control subjects, such as 41 normal elderly (Nold) subjects and 25 patients with vascular dementia (VaD). Patients with AD and VaD had similar mini‐mental state evaluation scores of 17–24. The functional coupling was estimated by means of the synchronization likelihood (SL) of the EEG data at electrode pairs, accounting for linear and non‐linear components of that coupling. Cortical rhythms of interest were delta (2–4 Hz), theta (4–8 Hz), alpha (1 8–10.5 Hz), alpha 2 (10.5–13 Hz), beta 1 (13–20 Hz), beta 2 (20–30 Hz) and gamma (30–40 Hz). A preliminary data analysis (Nold) showed that surface Laplacian transformation of the EEG data reduced the values of SL, possibly because of the reduction of influences due to head volume conduction. Therefore, the final analysis was performed on Laplacian‐transformed EEG data. The SL was dominant at alpha 1 band in all groups. Compared with the Nold subjects, patients with VaD and mild AD presented a marked reduction of SL at both fronto‐parietal (delta–alpha) and inter‐hemispherical (delta–beta) electrode pairs. The feature distinguishing the patients with mild AD with respect to patients with VaD groups was a more prominent reduction of fronto‐parietal alpha 1 SL. These results suggest that mild AD is characterized by an abnormal fronto‐parietal coupling of the dominant human cortical rhythm at 8–10.5 Hz.