Hypoxia increases Abeta generation by altering beta- and gamma-cleavage of APP

APP as a Protective Factor in Acute Neuronal Insults

Despite its key role in the molecular pathology of Alzheimer’s disease (AD), the physiological function of amyloid precursor protein (APP) is unknown. Increasing evidence, however, points towards a neuroprotective role of this membrane protein in situations of metabolic stress. A key observation is the up-regulation of APP following acute (stroke, cardiac arrest) or chronic (cerebrovascular disease) hypoxic-ischemic conditions. While this mechanism may increase the risk or severity of AD, APP by itself or its soluble extracellular fragment APPsα can promote neuronal survival. Indeed, different animal models of acute hypoxia-ischemia, traumatic brain injury (TBI) and excitotoxicity have revealed protective effects of APP or APPsα. The underlying mechanisms involve APP-mediated regulation of calcium homeostasis via NMDA receptors (NMDAR), voltage-gated calcium channels (VGCC) or internal calcium stores. In addition, APP affects the expression of survival- or apoptosis-related genes as well as neurotrophic factors. In this review, we summarize the current understanding of the neuroprotective role of APP and APPsα and possible implications for future research and new therapeutic strategies.

Acute and Chronic Sustained Hypoxia Do Not Substantially Regulate Amyloid-β Peptide Generation In Vivo

Background

Recent epidemiological evidence has linked hypoxia with the development of Alzheimer disease (AD). A number of in vitro and in vivo studies have reported that hypoxia can induce amyloid-β peptide accumulation through various molecular mechanisms including the up-regulation of the amyloid-β precursor protein, the β-secretase Bace1, or the γγ-secretase complex components, as well as the down-regulation of Aβ-degrading enzymes.

Objectives

To investigate the effects of acute and chronic sustained hypoxia in Aβ generation in vivo.

Methods

2–3 month-old C57/Bl6J wild-type mice were exposed to either normoxia (21% O₂) or hypoxia (9% O₂) for either 4 to 72 h (acute) or 21–30 days (chronic sustained) in a hermetic chamber. Brain mRNA levels of Aβ-related genes were measured by quantitative real-time PCR, whereas levels of Bace1 protein, full length AβPP, and its C-terminal fragments (C99/C88 ratio) were measured by Western blot. In addition, 8 and 14-month-old APP/PS1 transgenic mice were subjected to 9% O₂ for 21 days and levels of Aβ₄₀, Aβ₄₂, full length AβPP, and soluble AβPPα (sAβPPα) were measured by ELISA or WB.

Results

Hypoxia (either acute or chronic sustained) did not impact the transcription of any of the Aβ-related genes in young wild-type mice. A significant reduction of Bace1 protein level was noted with acute hypoxia for 16 h but did not correlate with an increased level of full length AβPP or a decreased C99/C83 ratio. Chronic sustained hypoxia did not significantly alter the levels of Bace1, full length AβPP or the C99/C83 ratio. Last, chronic sustained hypoxia did not significantly change the levels of Aβ₄₀, Aβ₄₂, full length AβPP, or sAβPPα in either young or aged APP/PS1 mice.

Discussion

Our results argue against a hypoxia-induced shift of AβPP proteolysis from the non-amyloidogenic to the amyloidogenic pathways. We discuss the possible methodological caveats of previous in vivo studies.

Chronic Hypoxia-Induced Autophagy Aggravates the Neuropathology of Alzheimer's Disease through AMPK-mTOR Signaling in the APPSwe/PS1dE9 Mouse Model

Alzheimer's disease (AD) is the most common form of dementia with the accumulation of senile plaques and neurofibrillary tangles in the brain. Autophagy is the key machinery for mammalian cells to degrade damaged organelles and abnormal proteins. Enormous evidence suggests that the autophagy pathway is impaired in AD. Our previous study revealed that hypoxia induced autophagic activation leading to more amyloid-β production in vitro. In this study, we investigated whether autophagic dysfunction is involved in the hypoxia mediated-pathogenesis of AD. We used APPSwe/PS1dE9 transgenic (Tg) mice and wildtype (Wt) littermates. We documented that chronic hypoxia caused more and larger senile plaques in the brains of Tg mice. In addition, chronic hypoxia induced activation of autophagy in the brains of both Wt and Tg mice, and compared to the normal autophagic flux in Wt mice, the autophagic flux was impaired in the brains of H-Tg mice with a large amount of autophagic vacuole accumulation and significant high level of P62. In an in vitro study, we showed that hypoxia-induced autophagy significantly elevated the level of hAβ42. Furthermore, we found that chronic hypoxia activated AMPK and further inhibited the mTOR signaling pathway, while inhibition of AMPK attenuated autophagy induction through the enhancement of mTOR phosphorylation. In short, our study provides new insight into the mechanism underlying chronic hypoxia-mediated AD pathogenesis.

Influence of Coding Variability in APP-Aβ Metabolism Genes in Sporadic Alzheimer's Disease

The cerebral deposition of Aβ42, a neurotoxic proteolytic derivate of amyloid precursor protein (APP), is a central event in Alzheimer's disease (AD)(Amyloid hypothesis). Given the key role of APP-Aβ metabolism in AD pathogenesis, we selected 29 genes involved in APP processing, Aβ degradation and clearance. We then used exome and genome sequencing to investigate the single independent (single-variant association test) and cumulative (gene-based association test) effect of coding variants in these genes as potential susceptibility factors for AD, in a cohort composed of 332 sporadic and mainly late-onset AD cases and 676 elderly controls from North America and the UK. Our study shows that common coding variability in these genes does not play a major role for the disease development. In the single-variant association analysis, the main hits, none of which statistically significant after multiple testing correction (1.9e-4 Collapse

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MESH Headings

• Alzheimer Disease/genetics
• Alzheimer Disease/metabolism
• Amyloid beta-Peptides/genetics
• Amyloid beta-Peptides/metabolism
• Amyloid beta-Protein Precursor/genetics
• Amyloid beta-Protein Precursor/metabolism
• Computational Biology
• Exome
• Humans

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Grants

• U24 AG021886 NIA NIH HHS
• P50 AG016574 NIA NIH HHS
• U01 AG052411 NIA NIH HHS
• MR/L016397/1 Medical Research Council
• P01 AG026276 NIA NIH HHS
• Z01 AG000950 Intramural NIH HHS
• G1100695 Medical Research Council
• RF1 AG044546 NIA NIH HHS
• Wellcome Trust
• R01 AG018023 NIA NIH HHS
• U01 AG006786 NIA NIH HHS
• P01 AG003991 NIA NIH HHS
• P50 AG005681 NIA NIH HHS
• Alzheimer’s Research UK
• Wellcome Trust/MRC Joint Call in Neurodegeneration Award
• National Institute for Health Research Biomedical Research Unit in Dementia at University College London Hospitals
• the Big Lottery
• Alzheimer's Research UK
• Intramural Research Programs of the National Institute on Aging and the National Institute of Neurological Disease and Stroke

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Affiliation(s)

Celeste Sassi Reta Lila, Weston Research Laboratories, Department of Molecular Neuroscience, UCL Institute of Neurology, London, United Kingdom Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, United States of America Department of Experimental Neurology, Center for Stroke Research Berlin (CSB), Charite’ Universitätmedizin, Berlin, Germany German Center for Neurodegenerative Diseases (DZNE), Berlin site, Germany
Perry G. Ridge Departments of Biology, Neuroscience, Brigham Young University, Provo, UT, United States of America
Michael A. Nalls Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, United States of America
Raphael Gibbs Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, United States of America
Jinhui Ding Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, United States of America
Michelle K. Lupton King's College London Institute of Psychiatry, London, United Kingdom QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia
Claire Troakes King's College London Institute of Psychiatry, London, United Kingdom
Katie Lunnon King's College London Institute of Psychiatry, London, United Kingdom
Safa Al-Sarraj King's College London Institute of Psychiatry, London, United Kingdom
Kristelle S. Brown Translation Cell Sciences-Human Genetics, School of Life Sciences, Queens Medical Centre, University of Nottingham, Nottingham, United Kingdom
Christopher Medway Translation Cell Sciences-Human Genetics, School of Life Sciences, Queens Medical Centre, University of Nottingham, Nottingham, United Kingdom
Jenny Lord Translation Cell Sciences-Human Genetics, School of Life Sciences, Queens Medical Centre, University of Nottingham, Nottingham, United Kingdom
James Turton Translation Cell Sciences-Human Genetics, School of Life Sciences, Queens Medical Centre, University of Nottingham, Nottingham, United Kingdom
ARUK Consortium
Kevin Morgan Translation Cell Sciences-Human Genetics, School of Life Sciences, Queens Medical Centre, University of Nottingham, Nottingham, United Kingdom
John F. Powell King's College London Institute of Psychiatry, London, United Kingdom
John S. Kauwe Departments of Biology, Neuroscience, Brigham Young University, Provo, UT, United States of America
Carlos Cruchaga Washington University, Division of Biology and Biomedical Sciences St. Louis, MO, United States of America
Jose Bras Reta Lila, Weston Research Laboratories, Department of Molecular Neuroscience, UCL Institute of Neurology, London, United Kingdom
Alison M. Goate Icahn School of Medicine at Mount Sinai, Icahn Medical Institute, New York, NY, United States of America
Andrew B. Singleton Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, United States of America
Rita Guerreiro Reta Lila, Weston Research Laboratories, Department of Molecular Neuroscience, UCL Institute of Neurology, London, United Kingdom
John Hardy Reta Lila, Weston Research Laboratories, Department of Molecular Neuroscience, UCL Institute of Neurology, London, United Kingdom

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Cerebrovascular disease in ageing and Alzheimer's disease

Cerebrovascular disease (CVD) and Alzheimer’s disease (AD) have more in common than their association with ageing. They share risk factors and overlap neuropathologically. Most patients with AD have Aβ amyloid angiopathy and degenerative changes affecting capillaries, and many have ischaemic parenchymal abnormalities. Structural vascular disease contributes to the ischaemic abnormalities in some patients with AD. However, the stereotyped progression of hypoperfusion in this disease, affecting first the precuneus and cingulate gyrus, then the frontal and temporal cortex and lastly the occipital cortex, suggests that other factors are more important, particularly in early disease. Whilst demand for oxygen and glucose falls in late disease, functional MRI, near infrared spectroscopy to measure the saturation of haemoglobin by oxygen, and biochemical analysis of myelin proteins with differential susceptibility to reduced oxygenation have all shown that the reduction in blood flow in AD is primarily a problem of inadequate blood supply, not reduced metabolic demand. Increasing evidence points to non-structural vascular dysfunction rather than structural abnormalities of vessel walls as the main cause of cerebral hypoperfusion in AD. Several mediators are probably responsible. One that is emerging as a major contributor is the vasoconstrictor endothelin-1 (EDN1). Whilst there is clearly an additive component to the clinical and pathological effects of hypoperfusion and AD, experimental and clinical observations suggest that the disease processes also interact mechanistically at a cellular level in a manner that exacerbates both. The elucidation of some of the mechanisms responsible for hypoperfusion in AD and for the interactions between CVD and AD has led to the identification of several novel therapeutic approaches that have the potential to ameliorate ischaemic damage and slow the progression of neurodegenerative disease.

Dual-specificity phosphatase 26 (DUSP26) stimulates Aβ42 generation by promoting amyloid precursor protein axonal transport during hypoxia

Amyloid beta peptide (Aβ) is a pathological hallmark of Alzheimer's disease (AD) and is generated through the sequential cleavage of amyloid precursor protein (APP) by β- and γ-secretases. Hypoxia is a known risk factor for AD and stimulates Aβ generation by γ-secretase; however, the underlying mechanisms remain unclear. In this study, we showed that dual-specificity phosphatase 26 (DUSP26) regulates Aβ generation through changes in subcellular localization of the γ-secretase complex and its substrate C99 under hypoxic conditions. DUSP26 was identified as a novel γ-secretase regulator from a genome-wide functional screen using a cDNA expression library. The phosphatase activity of DUSP26 was required for the increase in Aβ42 generation through γ-secretase, but this regulation did not affect the amount of the γ-secretase complex. Interestingly, DUSP26 induced the accumulation of C99 in the axons by stimulating anterograde transport of C99-positive vesicles. Additionally, DUSP26 induced c-Jun N-terminal kinase (JNK) activation for APP processing and axonal transport of C99. Under hypoxic conditions, DUSP26 expression levels were elevated together with JNK activation, and treatment with JNK inhibitor SP600125, or the DUSP26 inhibitor NSC-87877, reduced hypoxia-induced Aβ generation by diminishing vesicle trafficking of C99 to the axons. Finally, we observed enhanced DUSP26 expression and JNK activation in the hippocampus of AD patients. Our results suggest that DUSP26 mediates hypoxia-induced Aβ generation through JNK activation, revealing a new regulator of γ-secretase-mediated APP processing under hypoxic conditions. We propose the role of phosphatase dual-specificity phosphatase 26 (DUSP26) in the selective regulation of Aβ42 production in neuronal cells under hypoxic stress. Induction of DUSP26 causes JNK-dependent shift in the subcellular localization of γ-secretase and C99 from the cell body to axons for Aβ42 generation. These findings provide a new strategy for developing new therapeutic targets to arrest AD progression.

Chronic hypoxia facilitates Alzheimer's disease through demethylation of γ-secretase by downregulating DNA methyltransferase 3b

INTRODUCTION

Environmental factors and epigenetic mechanisms are believed to contribute to Alzheimer's disease (AD). We previously documented that prenatal hypoxia aggravated the cognitive impairment and neuropathology in offspring mice. Here, we investigate the chronic hypoxia-induced epigenetic modifications in AD.

METHODS

The 3-month-old APP(swe)/PS1(dE9) mice were exposed to hypoxic environment 6 hour/day for 30 days, followed by learning and memory tests and biochemical and neuropathology measurement at the age of 4, 6, and 9 months.

RESULTS

We found hypoxia exaggerated the neuropathology and cognitive impairment in AD mice. Chronic hypoxia induced demethylation on genomic DNA and decreased the expression of DNA methyltransferase 3b (DNMT3b) in vivo. We further found that DNMTs inhibition elevated the protein levels of amyloid precursor protein, β- and γ-secretases, whereas overexpression of DNMT3b suppressed the levels of them in vitro.

DISCUSSION

Our study suggests chronic hypoxia can aggravate AD progression through demethylation of genes encoding γ-secretase components by downregulation of DNMT3b.

Induction of cellular prion protein (PrPc) under hypoxia inhibits apoptosis caused by TRAIL treatment

Hypoxia decreases cytotoxic responses to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) protein. Cellular prion protein (PrPc) is regulated by HIF-1α in neurons. We hypothesized that PrPc is involved in hypoxia-mediated resistance to TRAIL-induced apoptosis. We found that hypoxia induced PrPc protein and inhibited TRAIL-induced apoptosis. Thus silencing of PrPc increased TRAIL-induced apoptosis under hypoxia. Overexpression of PrPc protein using an adenoviral vector inhibited TRAIL-induced apoptosis. In xenograft model in vivo, shPrPc transfected cells were more sensitive to TRAIL-induced apoptosis than in shMock transfected cells. Molecular chemo-therapy approaches based on the regulation of PrPc expression need to address anti-tumor function of TRAIL under hypoxia. Molecular chemo-therapy approaches based on the regulation of PrPc expression need to address anti-tumor function of TRAIL under hypoxia.

Increased Risk of Parkinson's Disease in Patients With Obstructive Sleep Apnea: A Population-Based, Propensity Score-Matched, Longitudinal Follow-Up Study

Obstructive sleep apnea (OSA), characterized by repetitive episodes of apnea/hypopnea and hypoxia, is associated with systemic inflammation and induces metabolic, endocrine, and cardiovascular diseases. Inflammation might have an impact on neurodegenerative diseases. This study investigates the possible association between OSA and Parkinson's disease (PD). Random samples out of 1 million individuals were collected from Taiwan's National Health Insurance database. A total of 16,730 patients with newly diagnosed OSA from 2002 to 2008 were recruited and compared with a cohort of 16,730 patients without OSA matched for age, gender, and comorbidities using propensity scoring. All patients were tracked until a diagnosis of PD, death, or the end of 2011.During the mean 5.6-year follow-up period, the incidence rates of PD were 2.30 per 1000 person-years in the OSA cohort and 1.71per 1000 person-years in the comparison group. The incidence rate ratio (IRR) for PD was greater in older patients (≧ 65 years) and male patients with OSA than the controls, respective IRRs being 1.34 and 1.47. After adjustment for the comorbidities, patients with OSA were 1.37 times more likely to have PD than patients without (95% CI = 1.12-1.68, P < 0.05). Subgroup analysis showed that older patients and patients with coronary artery disease, stroke, or chronic kidney disease had a higher risk for PD than their counter parts. Log-rank analysis revealed that patients with OSA had significantly higher cumulative incidence rates of PD than the comparison group (P = 0.0048). Patients with OSA are at an increased risk for subsequent PD, especially elderly male patients.

Basics of neuroanatomy and neurophysiology

This chapter presents an overview of the anatomy and functioning of the central nervous system. We begin the discussion by first examining the cellular basis of neural transmission. Then we present a brief description of the brain's white and gray matter and associated diseases, including a discussion of white-matter lesions. Finally, we place this information into context by discussing how the central nervous system integrates complex information to guide key functional systems, including the visual, auditory, chemosensory, somatic, limbic, motor, and autonomic systems. Where appropriate, we have supplied information pertaining to pathologic and functional outcomes of damage to the central nervous system. Also included is a brief description of important tools and methods used in the study of neuroanatomy and neurophysiology. Overall, this chapter provides a basic review of the concepts required to understand and interpret the clinical disorders and related material presented in the subsequent chapters of this book.

Decreased hemoglobin levels, cerebral small-vessel disease, and cortical atrophy: among cognitively normal elderly women and men

BACKGROUND

Decreased hemoglobin levels increase the risk of developing dementia among the elderly. However, the underlying mechanisms that link decreased hemoglobin levels to incident dementia still remain unclear, possibly due to the fact that few studies have reported on the relationship between low hemoglobin levels and neuroimaging markers. We, therefore, investigated the relationships between decreased hemoglobin levels, cerebral small-vessel disease (CSVD), and cortical atrophy in cognitively healthy women and men.

METHODS

Cognitively normal women (n = 1,022) and men (n = 1,018) who underwent medical check-ups and magnetic resonance imaging (MRI) were enrolled at a health promotion center. We measured hemoglobin levels, white matter hyperintensities (WMH) scales, lacunes, and microbleeds. Cortical thickness was automatically measured using surface based methods. Multivariate regression analyses were performed after controlling for possible confounders.

RESULTS

Decreased hemoglobin levels were not associated with the presence of WMH, lacunes, or microbleeds in women and men. Among women, decreased hemoglobin levels were associated with decreased cortical thickness in the frontal (Estimates, 95% confidence interval, -0.007, (-0.013, -0.001)), temporal (-0.010, (-0.018, -0.002)), parietal (-0.009, (-0.015, -0.003)), and occipital regions (-0.011, (-0.019, -0.003)). Among men, however, no associations were observed between hemoglobin levels and cortical thickness.

CONCLUSION

Our findings suggested that decreased hemoglobin levels affected cortical atrophy, but not increased CSVD, among women, although the association is modest. Given the paucity of modifiable risk factors for age-related cognitive decline, our results have important public health implications.

SUMO1 promotes Aβ production via the modulation of autophagy

Autophagy is one of the main mechanisms in the pathophysiology of neurodegenerative disease. The accumulation of autophagic vacuoles (AVs) in affected neurons is responsible for amyloid-β (Aβ) production. Previously, we reported that SUMO1 (small ubiquitin-like modifier 1) increases Aβ levels. In this study, we explored the mechanisms underlying this. We investigated whether AV formation is necessary for Aβ production by SUMO1. Overexpression of SUMO1 increased autophagic activation, inducing the formation of LC3-II-positive AVs in neuroglioma H4 cells. Consistently, autophagic activation was decreased by the depletion of SUMO1 with small hairpin RNA (shRNA) in H4 cells. The SUMO1-mediated increase in Aβ was reduced by the autophagy inhibitors (3-methyladenine or wortmannin) or genetic inhibitors (siRNA targeting ATG5, ATG7, ATG12, or HIF1A), respectively. Accumulation of SUMO1, ATG12, and LC3 was seen in amyloid precursor protein transgenic mice. Our results suggest that SUMO1 accelerates the accumulation of AVs and promotes Aβ production, which is a key mechanism for understanding the AV-mediated pathophysiology of Alzheimer disease.

Hypoxia Affects Neprilysin Expression Through Caspase Activation and an APP Intracellular Domain-dependent Mechanism

While gene mutations in the amyloid precursor protein (APP) and the presenilins lead to an accumulation of the amyloid β-peptide (Aβ) in the brain causing neurodegeneration and familial Alzheimer's disease (AD), over 95% of all AD cases are sporadic. Despite the pathologies being indistinguishable, relatively little is known about the mechanisms affecting generation of Aβ in the sporadic cases. Vascular disorders such as ischaemia and stroke are well established risk factors for the development of neurodegenerative diseases and systemic hypoxic episodes have been shown to increase Aβ production and accumulation. We have previously shown that hypoxia causes a significant decrease in the expression of the major Aβ-degrading enzyme neprilysin (NEP) which might deregulate Aβ clearance. Aβ itself is derived from the transmembrane APP along with several other biologically active metabolites including the C-terminal fragment (CTF) termed the APP intracellular domain (AICD), which regulates the expression of NEP and some other genes in neuronal cells. Here we show that in hypoxia there is a significantly increased expression of caspase-3, 8, and 9 in human neuroblastoma NB7 cells, which can degrade AICD. Using chromatin immunoprecipitation we have revealed that there was also a reduction of AICD bound to the NEP promoter region which underlies the decreased expression and activity of the enzyme under hypoxic conditions. Incubation of the cells with a caspase-3 inhibitor Z-DEVD-FMK could rescue the effect of hypoxia on NEP activity protecting the levels of AICD capable of binding the NEP promoter. These data suggest that activation of caspases might play an important role in regulation of NEP levels in the brain under pathological conditions such as hypoxia and ischaemia leading to a deficit of Aβ clearance and increasing the risk of development of AD.

Serum amyloid-beta levels are increased in patients with obstructive sleep apnea syndrome

A critical link between amyloid-beta (Aβ) and hypoxia has been demonstrated in in vitro and animal studies but has not yet been proven in humans. Obstructive sleep apnea syndrome (OSAS) is a common disorder that is characterized by nocturnal intermittent hypoxaemia. This study sought to examine the association between the chronic intermittent hypoxia and Aβ in OSAS patients. Forty-five cognitively normal OSAS patients and forty-nine age- and gender-matched subjects diagnosed with simple snoring and not OSAS were included in the present study. Serum Aβ40, Aβ42, total tau and phosphorylated tau 181 (P-tau 181) levels were measured using ELISA kits. All subjects were evaluated with nighttime polysomnography and cognitive tests. Compared with the controls, the OSAS patients exhibited significantly higher serum Aβ40, Aβ42 and total Aβ levels, and each of these levels was positively correlated with the apnea-hypopnea index, the oxygen desaturation index, and the mean and lowest oxyhaemoglobin saturations in the OSAS patients. Moreover, the OSAS patients exhibited strikingly higher serum P-tau 181 levels, and these levels were positively correlated with serum Aβ levels. This study suggests that there is an association between chronic intermittent hypoxia and increased Aβ levels, implying that hypoxia may contribute to the pathogenesis of Alzheimer’s disease.

White matter hypoperfusion and damage in dementia: post-mortem assessment

Neuroimaging has revealed a range of white matter abnormalities that are common in dementia, some that predict cognitive decline. The abnormalities may result from structural diseases of the cerebral vasculature, such as arteriolosclerosis and amyloid angiopathy, but can also be caused by nonstructural vascular abnormalities (eg, of vascular contractility or permeability), neurovascular instability or extracranial cardiac or vascular disease. Conventional histopathological assessment of the white matter has tended to conflate morphological vascular abnormalities with changes that reflect altered interstitial fluid dynamics or white matter ischemic damage, even though the latter may be of extracranial or nonstructural etiology. However, histopathology is being supplemented by biochemical approaches, including the measurement of proteins involved in the molecular responses to brain ischemia, myelin proteins differentially susceptible to ischemic damage, vessel-associated proteins that allow rapid measurement of microvessel density, markers of blood-brain barrier dysfunction and axonal injury, and mediators of white matter damage. By combining neuroimaging with histopathology and biochemical analysis, we can provide reproducible, quantitative data on the severity of white matter damage, and information on its etiology and pathogenesis. Together these have the potential to inform and improve treatment, particularly in forms of dementia to which white matter hypoperfusion makes a significant contribution.

Dissecting the Contribution of Vascular Alterations and Aging to Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive decline that afflicts as many as 45 % of individuals who survive past the age of 85. AD has been associated with neurovascular dysfunction and brain accumulation of amyloid-β peptide, as well as tau phosphorylation and neurodegeneration, but the pathogenesis of the disease is still somewhat unclear. According to the amyloid cascade hypothesis of AD, accumulation of amyloid-β peptide (Aβ) aggregates initiates a sequence of events leading to neuronal injury and loss, and dementia. Alternatively, the vascular hypothesis of AD incorporates the vascular contribution to the disease, stating that a primary insult to brain microcirculation (e.g., stroke) not only contributes to amyloidopathy but initiates a non-amyloidogenic pathway of vascular-mediated neuronal dysfunction and injury, which involves blood-brain barrier compromise, with increased permeability of blood vessels, leakage of blood-borne components into the brain, and, consequently, neurotoxicity. Vascular dysfunction also includes a diminished brain capillary flow, causing multiple focal ischemic or hypoxic microinjuries, diminished amyloid-β clearance, and formation of neurotoxic oligomers, which lead to neuronal dysfunction. Here we present and discuss relevant findings on the contribution of vascular alterations during aging to AD, with the hope that a better understanding of the players in the "orchestra" of neurodegeneration will be useful in developing therapies to modulate the "symphony".

Impaired Aβ clearance: a potential link between atherosclerosis and Alzheimer's disease

Alzheimer’s Disease (AD) and atherosclerosis remain two of the largest public health burdens in the world today. Although traditionally considered distinct pathological entities, mounting epidemiologic, clinical and experimental evidence suggests that cerebrovascular atherosclerosis and AD interact reciprocally to disrupt brain structure and function. Whereas the hypoperfusion and hypoxia caused by atherosclerosis of cerebral vessels may enhance the production of amyloid-β peptide (Aβ), a peptide central to AD pathology, Aβ, in turn, may promote formation of atherosclerotic lesions through vascular oxidative stress and endothelial dysfunction leading to additional vascular damage. Here, we briefly review evidence suggesting that impaired clearance of Aβ is an additional, simultaneously occurring mechanism by which AD and cerebrovascular disease may be causally linked. We examine the literature supporting mechanisms by which flow-limiting large-artery stenosis, arterial stiffening and microvascular dysfunction could contribute to AD pathophysiology by impairing Aβ clearance and elevating brain levels of Aβ. Finally, we highlight the need for further research to improve our understanding of the complex interactions of AD and atherosclerosis with Aβ clearance, which may ultimately serve to guide the development of novel diagnostic and therapeutic approaches for this devastating and highly prevalent condition.

Synaptic protein levels altered in vascular dementia

Introduction

Cerebral ischaemia is the defining pathophysiological abnormality in most forms of vascular dementia (VAD), but the pathogenesis of the dementia remains poorly understood. In Alzheimer's disease (AD), there is early loss of synaptic proteins, but these have been little studied in VAD.

Materials and Methods

We measured synaptophysin, postsynaptic density protein 95 (PSD-95), drebrin, synaptosomal-associated protein 25 (SNAP-25) and vascular endothelial growth factor (VEGF) by enzyme-linked immunosorbent assays in superior temporal cortex from 11 patients with VAD and, initially, 11 non-dementia controls. We corrected for neuronal content by measurement of neuron-specific enolase. A further 11 controls were subsequently used in a validation study. Simulation of post-mortem delay found that PSD-95 was stable at 4°C but declined slightly at RT. SNAP-25 and drebrin showed good post-mortem stability. Previous studies had shown good post-mortem preservation of synaptophysin and VEGF.

Results

The VAD cases had lower synaptophysin (but P > 0.05 in initial study), significantly lower SNAP-25 (P = 0.024) and significantly higher drebrin (P = 0.020). On comparison with the second control group, the reduction in synaptophysin was significant (P = 0.008), and the other results were confirmed.

Conclusion

There is probably a reduction in presynaptic proteins in the temporal cortex in VAD, although not as marked as in AD. In VAD, there is also an increase in drebrin, which may be a response to reduced synaptic input.

Differential roles of Aβ processing in hypoxia-induced axonal damage

Axonopathy is a common and early phase in neurodegenerative and traumatic CNS diseases. Recent work suggests that amyloid β (Aβ) produced from amyloid precursor protein (APP) may be a critical downstream mediator of CNS axonopathy in CNS diseases, particularly those associated with hypoxia. We critically tested this hypothesis in an adult retinal explant system that preserves the three-dimensional organization of the retina while permitting direct imaging of two cardinal features of early-stage axonopathy: axonal structural integrity and axonal transport capacity. Using this system, we found via pharmacological inhibition and genetic deletion of APP that production of Aβ is a necessary step in structural compromise of retinal ganglion cell (RGC) axons induced by the disease-relevant stressor hypoxia. However, identical blockade of Aβ production was not sufficient to protect axons from associated hypoxia-induced reduction in axonal transport. Thus, Aβ mediates distinct facets of hypoxia-induced axonopathy and may represent a functionally selective pharmacological target for therapies directed against early-stage axonopathy in CNS diseases.

Post-mortem assessment of hypoperfusion of cerebral cortex in Alzheimer's disease and vascular dementia

Perfusion is reduced in the cerebral neocortex in Alzheimer's disease. We have explored some of the mechanisms, by measurement of perfusion-sensitive and disease-related proteins in post-mortem tissue from Alzheimer's disease, vascular dementia and age-matched control brains. To distinguish physiological from pathological reduction in perfusion (i.e. reduction exceeding the decline in metabolic demand), we measured the concentration of vascular endothelial growth factor (VEGF), a protein induced under conditions of tissue hypoxia through the actions of hypoxia-inducible factors, and the myelin associated glycoprotein to proteolipid protein 1 (MAG:PLP1) ratio, which declines in chronically hypoperfused brain tissue. To evaluate possible mechanisms of hypoperfusion, we also measured the levels of amyloid-β40, amyloid-β42, von Willebrand factor (VWF; a measure of microvascular density) and the potent vasoconstrictor endothelin 1 (EDN1); we assayed the activity of angiotensin I converting enzyme (ACE), which catalyses the production of another potent vasoconstrictor, angiotensin II; and we scored the severity of arteriolosclerotic small vessel disease and cerebral amyloid angiopathy, and determined the Braak tangle stage. VEGF was markedly increased in frontal and parahippocampal cortex in Alzheimer's disease but only slightly and not significantly in vascular dementia. In frontal cortex the MAG:PLP1 ratio was significantly reduced in Alzheimer's disease and even more so in vascular dementia. VEGF but not MAG:PLP1 increased with Alzheimer's disease severity, as measured by Braak tangle stage, and correlated with amyloid-β42 and amyloid-β42: amyloid-β40 but not amyloid-β40. Although MAG:PLP1 tended to be lowest in cortex from patients with severe small vessel disease or cerebral amyloid angiopathy, neither VEGF nor MAG:PLP1 correlated significantly with the severity of structural vascular pathology (small vessel disease, cerebral amyloid angiopathy or VWF). However, MAG:PLP1 showed a significant negative correlation with the level of EDN1, which we previously showed to be elevated in the cerebral cortex Alzheimer's disease. These finding are in contrast with the previously demonstrated reduction in EDN1, and positive correlation with MAG:PLP1, in the hypoperfused white matter in Alzheimer's disease. The decline in MAG:PLP1 strongly suggests pathological hypoperfusion of the frontal cortex in Alzheimer's disease. Although severe small vessel disease or cerebral amyloid angiopathy may contribute in some cases, abnormal vascular contractility mediated by EDN1 is likely to be a more important overall contributor. Both amyloid-β accumulation and hypoperfusion are likely to cause the upregulation of VEGF.

Serum Aβ is predictive for short-term neurological deficits after acute ischemic stroke

Mounting evidence suggests that ischemic stroke (IS) is associated with Alzheimer's disease (AD). IS and vascular risk factors increase the risk for AD. However, whether AD pathologies exist in IS and the effects of these pathologies on stroke remain unknown. In the present study, we aimed to investigate the alterations of serum Aβ after acute IS (AIS), and its correlations with the neurological deficits, infarction volume, and site after stroke. AIS patients (n = 35) were recruited within 24 h of symptom onset. Age- and gender-matched AD patients (n = 48) and cognitively normal controls (NC, n = 37) were also enrolled. Serum Aβ40 and Aβ42 and the National Institute of Health Stroke Scale Score (NIHSS) were measured on day 1, 3, and 7 after stroke onset. We found that serum Aβ40 and Aβ42 levels were increased at day 1 and reached peak levels at day 3, and decreased to pre-stroke levels at day 7. Serum Aβ40 levels at day 1 were correlated with the NIHSS scores and infarction volume of AIS patients. Serum Aβ42 levels at day 1 were significantly higher in IS patients with dominant gray matter infarction. Serum Aβ40 levels at day 1 were predictive for NIHSS at day 7. Our results indicate that AIS can induce the generation of Aβ in the brain, which may in turn be involved in the pathogenesis of neurological deficits after stroke. Serum Aβ might be predictive for the short-term neurological deficits after AIS.

Cytoprotective effects of fisetin against hypoxia-induced cell death in PC12 cells

Fisetin protects cells under hypoxia through ROS scavenging and the HIF1α-, MAPK/ERK-, p38 MAPK- and PI3 K/Akt-dependent pathways in PC12 cells.

From chronic cerebral hypoperfusion to Alzheimer-like brain pathology and neurodegeneration

Chronic cerebral hypoperfusion (CCH) is a common consequence of various cerebral vascular disorders and hemodynamic and blood changes. Recent studies have revealed an important role of CCH in neurodegeneration and dementia, including vascular dementia and Alzheimer's disease (AD). This article reviews the recent advances in understanding CCH-induced neurodegeneration and AD-related brain pathology and cognitive impairment. We discuss the causes and assessment of CCH, the possible mechanisms by which CCH promotes Alzheimer-like pathology and neurodegeneration, and animal models of CCH. It appears that CCH promotes neurodegeneration and AD through multiple mechanisms, including induction of oxidative stress, Aβ accumulation and aggravation, tau hyperphosphorylation, synaptic dysfunction, neuronal loss, white matter lesion, and neuroinflammation. Better understanding of the mechanisms of CCH will help develop therapeutic strategies for preventing and treating neurodegeneration, including sporadic AD and vascular dementia, caused by CCH.

CD36 upregulation mediated by intranasal LV-NRF2 treatment mitigates hypoxia-induced progression of Alzheimer's-like pathogenesis

AIMS

There is extensive evidence that oxidative stress induces cellular dysfunction in the brain and plays a critical role in Alzheimer's disease (AD) pathogenesis. Hypoxia increases factors involved in oxidative stress injury and contributes to the onset and progression of AD. Nuclear factor erythroid 2-related factor 2 (NRF2), a major component regulating antioxidant response, is attenuated in the AD brain. Importantly, NRF2 directly regulates the alternative first exons of CD36, an important participant in oxidative and inflammatory processes. To explore the effects of hypoxia-induced deterioration of AD-like pathogenesis and investigate the correlation between hypoxia-induced NRF2 signal alterations and CD36 expression, we examined the NRF2 signaling, CD36, and oxidative stress events in hypoxia-treated APPswe/PSEN1dE9 (APP/PS1) mice brain.

RESULTS

We observed that hypoxia treatment increased oxidative stress, exacerbated inflammation, and aggravated learning defects in aged APP/PS1 mice. Microglia from hypoxia-treated mice brain exhibited marked reduction in CD36 expression and inhibition of β-amyloid (Aβ) degradation. Accordingly, hypoxia treatment caused a decrease in transactivation of NRF2 target genes in the aging mouse brain. Intranasal administration with a lentiviral vector encoding human NRF2 increased CD36 expression, ameliorated the weak antioxidant response triggered by hypoxia, diminished Aβ deposition, and improved spatial memory defects.

INNOVATION

In this study, we demonstrated for the first time that NRF2 intranasal treatment-induced increases of CD36 could enhance Aβ clearance in AD transgenic mouse.

CONCLUSION

These results suggest that targeting NRF2-mediated CD36 expression might provide a beneficial intervention for cognitive impairment and oxidative stress in AD progression.

Impact of sleep on the risk of cognitive decline and dementia

PURPOSE OF REVIEW

Trouble falling or staying asleep, poor sleep quality, and short or long sleep duration are gaining attention as potential risk factors for cognitive decline and dementia, including Alzheimer's disease. Sleep-disordered breathing has also been linked to these outcomes. Here, we review recent observational and experimental studies investigating the effect of poor sleep on cognitive outcomes and Alzheimer's disease, and discuss possible mechanisms.

RECENT FINDINGS

Observational studies with self-report and objective sleep measures (e.g. wrist actigraphy, polysomnography) support links between disturbed sleep and cognitive decline. Several recently published studies demonstrate associations between sleep variables and measures of Alzheimer's disease pathology, including cerebrospinal fluid measures of Aβ and PET measures of Aβ deposition. In addition, experimental studies suggest that sleep loss alters cerebrospinal fluid Aβ dynamics, decrements in slow-wave sleep may decrease the clearance of Aβ from the brain, and hypoxemia characteristic of sleep-disordered breathing increases Aβ production.

SUMMARY

Findings indicate that poor sleep is a risk factor for cognitive decline and Alzheimer's disease. Although mechanisms underlying these associations are not yet clear, healthy sleep appears to play an important role in maintaining brain health with age, and may play a key role in Alzheimer's disease prevention.

New therapeutic approaches for Alzheimer's disease and cerebral amyloid angiopathy

Accumulating evidence has shown a strong relationship between Alzheimer’s disease (AD), cerebral amyloid angiopathy (CAA), and cerebrovascular disease. Cognitive impairment in AD patients can result from cortical microinfarcts associated with CAA, as well as the synaptic and neuronal disturbances caused by cerebral accumulations of β-amyloid (Aβ) and tau proteins. The pathophysiology of AD may lead to a toxic chain of events consisting of Aβ overproduction, impaired Aβ clearance, and brain ischemia. Insufficient removal of Aβ leads to development of CAA and plays a crucial role in sporadic AD cases, implicating promotion of Aβ clearance as an important therapeutic strategy. Aβ is mainly eliminated by three mechanisms: (1) enzymatic/glial degradation, (2) transcytotic delivery, and (3) perivascular drainage (3-“d” mechanisms). Enzymatic degradation may be facilitated by activation of Aβ-degrading enzymes such as neprilysin, angiotensin-converting enzyme, and insulin-degrading enzyme. Transcytotic delivery can be promoted by inhibition of the receptor for advanced glycation end products (RAGE), which mediates transcytotic influx of circulating Aβ into brain. Successful use of the RAGE inhibitor TTP488 in Phase II testing has led to a Phase III clinical trial for AD patients. The perivascular drainage system seems to be driven by motive force generated by cerebral arterial pulsations, suggesting that vasoactive drugs can facilitate Aβ clearance. One of the drugs promoting this system is cilostazol, a selective inhibitor of type 3 phosphodiesterase. The clearance of fluorescent soluble Aβ tracers was significantly enhanced in cilostazol-treated CAA model mice. Given that the balance between Aβ synthesis and clearance determines brain Aβ accumulation, and that Aβ is cleared by several pathways stated above, multi-drugs combination therapy could provide a mainstream cure for sporadic AD.

Aβ degradation or cerebral perfusion? Divergent effects of multifunctional enzymes

There is increasing evidence that deficient clearance of β-amyloid (Aβ) contributes to its accumulation in late-onset Alzheimer disease (AD). Several Aβ-degrading enzymes, including neprilysin (NEP), endothelin-converting enzyme (ECE), and angiotensin-converting enzyme (ACE) reduce Aβ levels and protect against cognitive impairment in mouse models of AD. In post-mortem human brain tissue we have found that the activity of these Aβ-degrading enzymes rise with age and increases still further in AD, perhaps as a physiological response that helps to minimize the build-up of Aβ. ECE-1/-2 and ACE are also rate-limiting enzymes in the production of endothelin-1 (ET-1) and angiotensin II (Ang II), two potent vasoconstrictors, increases in the levels of which are likely to contribute to reduced blood flow in AD. This review considers the possible interdependence between Aβ-degrading enzymes, ischemia and Aβ in AD: ischemia has been shown to increase Aβ production both in vitro and in vivo, whereas increased Aβ probably enhances ischemia by vasoconstriction, mediated at least in part by increased ECE and ACE activity. In contrast, NEP activity may help to maintain cerebral perfusion, by reducing the accumulation of Aβ in cerebral blood vessels and lessening its toxicity to vascular smooth muscle cells. In assessing the role of Aβ-degrading proteases in the pathogenesis of AD and, particularly, their potential as therapeutic agents, it is important to bear in mind the multifunctional nature of these enzymes and to consider their effects on other substrates and pathways.

Behavioral and neuropathological consequences of transient global ischemia in APP/PS1 Alzheimer model mice

Alzheimer's disease (AD) typically manifests in elderly people with several co-morbidities, especially cardiovascular, whereas transgenic mouse models of this disease usually employ middle-aged animals that have a good general health status. To assess the combined effect of compromised cerebral blood circulation and brain amyloid pathology we induced transient (17min) global ischemia (TGI) to young adult APPswe/PS1dE9 (APdE9) mice modeling AD amyloid pathology, and assessed the outcome on behavior two weeks and on histopathology five weeks after the ischemic insult. Ischemic injury resulted in reduced motor coordination and impaired spatial learning and memory. Neuropathological examination revealed circumscribed sites of neuronal loss in ischemic mice, including hippocampal CA2, lateral CA3 and medial CA1 pyramidal cell layer, and superficial layers of cortical patches. Notably, Fluoro-Jade staining revealed dying neurons as late as five weeks after the initial insult, and staining for active microglia and astrocytes confirmed the presence of inflammatory reaction. The extent of neuronal loss in CA2 and CA1 correlated significantly with impairment in spatial memory. There was no genotype difference in either behavioral or neuropathological consequences of TGI. However, the post-operative survival of transgenic animals was greatly reduced compared to wild type animals. APdE9 mice at a pre-plaque age appear to be more sensitive than wild-type mice to TGI in terms of post-operative recovery but the surviving APdE9 mice do not display more severe neurological deficits than wild-type mice.

Nontranscriptional role of Hif-1α in activation of γ-secretase and notch signaling in breast cancer

γ-Secretase is composed of four proteins that are obligatory for protease activity: presenilin, nicastrin, Aph1, and Pen-2. Despite the progress toward understanding the function of these individual subunits, there is no information available pertaining to the modulation of γ-secretase in response to environmental changes in cells. Here, we show that hypoxia upregulates γ-secretase activity through a direct interaction with Hif-1α, revealing an unconventional function for Hif-1α as an enzyme subunit, which is distinct from its canonical role as a transcription factor. Moreover, hypoxia-induced cell invasion and metastasis are alleviated by either γ-secretase inhibitors or a dominant-negative Notch coactivator, indicating that γ-secretase/Notch signaling plays an essential role in controlling these cellular processes. The present study reveals a mechanism in which γ-secretase can achieve temporal control through conditional interactions with regulatory proteins, such as Hif-1α, under select physiological and pathological conditions.

Hypoxia-up-regulated mitochondrial movement regulator does not contribute to the APP/PS1 double transgenic mouse model of Alzheimer's disease

BACKGROUND/AIMS

It has been demonstrated that mitochondrial dysfunction is associated with Alzheimer's disease (AD); meanwhile, hypoxia-up-regulated mitochondrial movement regulator (HUMMR) plays an important role in regulating mitochondrial function. The present study aimed to confirm the association between HUMMR and mitochondrial function in AD.

METHODS

We detected the expression of HUMMR at transcriptional and translational levels in APP/PS1 double transgenic mice using real-time quantitative RT-PCR and Western blotting. Age- and gender-matched wild-type (WT) littermates were used as controls. Mitochondrial morphology was observed in the hippocampus and cortex of APP/PS1 double transgenic mice using transmission electron microscopy.

RESULTS

Damage to mitochondrial morphology in the hippocampus and cortex of APP/PS1 double transgenic mice was found, including swelling and cavitations. Our analysis showed no statistical differences in the expression of HUMMR between APP/PS1 double transgenic mice and WT littermates (p > 0.05). These results showed that there was no association between HUMMR and mitochondrial dysfunction in APP/PS1 transgenic mice.

CONCLUSION

These results indicate that HUMMR does not play a key role in mitochondrial dysfunction in the APP/PS1 double transgenic AD mouse.

UV irradiation accelerates amyloid precursor protein (APP) processing and disrupts APP axonal transport

Overexpression and/or abnormal cleavage of amyloid precursor protein (APP) are linked to Alzheimer's disease (AD) development and progression. However, the molecular mechanisms regulating cellular levels of APP or its processing, and the physiological and pathological consequences of altered processing are not well understood. Here, using mouse and human cells, we found that neuronal damage induced by UV irradiation leads to specific APP, APLP1, and APLP2 decline by accelerating their secretase-dependent processing. Pharmacological inhibition of endosomal/lysosomal activity partially protects UV-induced APP processing implying contribution of the endosomal and/or lysosomal compartments in this process. We found that a biological consequence of UV-induced γ-secretase processing of APP is impairment of APP axonal transport. To probe the functional consequences of impaired APP axonal transport, we isolated and analyzed presumptive APP-containing axonal transport vesicles from mouse cortical synaptosomes using electron microscopy, biochemical, and mass spectrometry analyses. We identified a population of morphologically heterogeneous organelles that contains APP, the secretase machinery, molecular motors, and previously proposed and new residents of APP vesicles. These possible cargoes are enriched in proteins whose dysfunction could contribute to neuronal malfunction and diseases of the nervous system including AD. Together, these results suggest that damage-induced APP processing might impair APP axonal transport, which could result in failure of synaptic maintenance and neuronal dysfunction.

Increased γ-secretase activity in idiopathic normal pressure hydrocephalus patients with β-amyloid pathology

The potential similarity between the brain pathology of idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer disease (AD) is intriguing and thus further studies focusing on the underlying molecular mechanisms may offer valuable information for differential diagnostics and the development of treatments for iNPH. Here, we investigated β- and γ-secretase activities in relation to amyloid-β (Aβ) pathology in the brain tissue samples collected from iNPH and AD patients. β- and γ-secretase activities were measured from the frontal cortical biopsies of 26 patients with suspected iNPH as well as post-mortem tissue samples from the inferior temporal cortex of 74 AD patients and eight subjects without neurofibrillary pathology. In iNPH samples with detectable Aβ plaques, γ-secretase activity was significantly increased (∼1.6-fold) when compared to iNPH samples without Aβ plaques (p = 0.009). In the AD samples, statistically significant differences in the γ-secretase activity were not observed with respect to disease severity (mild, moderate and severe AD according to neurofibrillary pathology). Conversely, β-secretase activity was unaltered in iNPH samples with or without Aβ plaques, while it was significantly increased in relation to disease severity in the AD patients. These results show for the first time increased γ-secretase but not β-secretase activity in the biopsy samples from the frontal cortex of iNPH patients with AD-like Aβ pathology. Conversely, the opposite was observed in these secretase activities in AD patients with respect to neurofibrillary pathology. Despite the resemblances in the Aβ pathology, iNPH and AD patients appear to have marked differences in the cellular mechanisms responsible for the production of Aβ.

Reduced vascular endothelial growth factor and capillary density in the occipital cortex in dementia with Lewy bodies

In dementia with Lewy bodies (DLB), blood flow tends to be reduced in the occipital cortex. We previously showed elevated activity of the endothelin and angiotensin pathways in Alzheimer's disease (AD). We have measured endothelin-1 (ET-1) level and angiotensin-converting enzyme (ACE) activity in the occipital cortex in DLB and control brains. We also measured vascular endothelial growth factor (VEGF); factor VIII-related antigen (FVIIIRA) to indicate microvessel density; myelin-associated glycoprotein (MAG), a marker of ante-mortem hypoperfusion; total α-synuclein (α-syn) and α-synuclein phosphorylated at Ser129 (α-syn-p129). In contrast to findings in AD, ACE activity and ET-1 level were unchanged in DLB compared with controls. VEGF and FVIIIRA levels were, however, significantly lower in DLB. VEGF correlated positively with MAG concentration (in keeping with a relationship between reduction in VEGF and hypoperfusion), and negatively with α-syn and α-syn-p129 levels. Both α-syn and α-syn-p129 levels increased in human SH-SY5Y neuroblastoma cells after oxygen-glucose deprivation (OGD), and VEGF level was reduced in SH-SY5Y cells overexpressing α-syn. Taken together, our findings suggest that reduced microvessel density rather than vasoconstriction is responsible for lower occipital blood flow in DLB, and that the loss of microvessels may result from VEGF deficiency, possible secondary to the accumulation of α-syn.

Epigenetic modifications of chronic hypoxia-mediated neurodegeneration in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder affecting the elderly people. AD is characterized by progressive and gradual decline in cognitive function and memory loss. While familial early-onset AD is usually associated with gene mutations, the etiology of sporadic late-onset form of AD is largely unknown. It has been reported that environmental factors and epigenetic alterations significantly contribute to the process of AD. Our previous studies have documented that chronic hypoxia is one of the environmental factors that may trigger the AD development and aggravate the disease progression. In this review, we will summarize the pathological effects of chronic hypoxia on the onset and development of AD and put forward the possible molecule mechanisms underlying the chronic hypoxia mediated AD pathogenesis. Finally, we propose that epigenetic regulations may represent new opportunity for the therapeutic intervention of this disease.

Valproic acid reduces neuritic plaque formation and improves learning deficits in APP(Swe) /PS1(A246E) transgenic mice via preventing the prenatal hypoxia-induced down-regulation of neprilysin

AIMS

Previously, we have documented that prenatal hypoxia can aggravate the cognitive impairment and Alzheimer's disease (AD) neuropathology in APP(Swe) /PS1(A246E) (APP/PS1) transgenic mice, and valproic acid (VPA) can prevent hypoxia-induced down-regulation of β-amyloid (Aβ) degradation enzyme neprilysin (NEP) in primary neurons. In this study, we have investigated the molecular mechanisms of VPA's anti-AD effects and found that VPA can reduce the prenatal hypoxia-induced neuritic plaque formation and improve the learning deficits in the AD mouse model.

METHODS

The pregnant APP/PS1 transgenic mice were exposed in a hypobaric chamber. Neuritic plaque staining, Morris water maze, and enzyme-linked immunosorbent assay (ELISA) were used to detect the effects of VPA on Aβ neuropathology, learning, and memory. Chromatin immunoprecipitation (ChIP) assays and real-time PCR (RT-PCR) were used to determine the effect of VPA on the histone3 acetylation (H3-Ace).

RESULTS

We found that VPA can inhibit neuritic plaque formation and improve the learning and memory in the prenatal hypoxic APP/PS1 transgenic mice. In addition, VPA treatment can decrease the soluble and insoluble Aβ42 levels and increase the NEP expression via up-regulation of H3-Ace in the APP/PS1 transgenic mice.

CONCLUSION

Valproic acid is able to attenuate the prenatal hypoxia-induced Aβ neuropathology and learning and memory deficits via inhibiting the activation of histone deacetylase 1 (HDAC1), preventing the decrease in H3-Ace in the NEP promoter regions and reducing the down-regulation of NEP.

Cell-specific blood-brain barrier regulation in health and disease: a focus on hypoxia

The blood-brain barrier (BBB) is a complex vascular structure consisting of microvascular endothelial cells that line the vessel wall, astrocyte end-feet, pericytes, as well as the basal lamina. BBB cells act in concert to maintain the characteristic impermeable and low paracellular flux of the brain vascular network, thus ensuring a homeostatic neuronal environment. Alterations in BBB stability that occur during injury have dire consequences on disease progression and it is clear that BBB cell-specific responses, positive or negative, must make a significant contribution to injury outcome. Reduced oxygenation, or hypoxia, is a characteristic of many brain diseases that significantly increases barrier permeability. Recent data suggest that hypoxia-inducible factor (HIF-1), the master regulator of the hypoxic response, probably mediates many hypoxic effects either directly or indirectly via its target genes. This review discusses current knowledge of physiological cell-specific regulation of barrier function, their responses to hypoxia as well as consequences of hypoxic- and HIF-1-mediated mechanisms on barrier integrity during select brain diseases. In the final sections, the potential of current advances in targeting HIF-1 as a therapeutic strategy will be overviewed.

Carnosic acid suppresses the production of amyloid-β 1-42 and 1-43 by inducing an α-secretase TACE/ADAM17 in U373MG human astrocytoma cells

Amyloid beta (Aβ) peptides are key molecules in the pathogenesis of Alzheimer's disease (AD). The sequential cleavage of amyloid precursor protein (APP) by the β- and γ-secretases generates Aβ peptides; however, the alternate cleavage of APP by the α- and γ-secretases decreases Aβ production. We previously reported that carnosic acid (CA), a phenolic diterpene compound found in the labiate herbs rosemary and sage, suppresses Aβ (1-40 and 1-42) production by activating α-secretase in cultured SH-SY5Y human neuroblastoma cells (Neurosci. Res. 2013; 75: 94-102). Here, we investigated the effect of CA on the production of Aβ peptides (1-40, 1-42 and 1-43) in U373MG human astrocytoma cells. The treatment of cells with CA suppressed Aβ40/42/43 release (55-71% decrease at 50μM). CA treatment enhanced the mRNA expressions of an α-secretase TACE (tumor necrosis factor-α-converting enzyme, also called a disintegrin and metalloproteinase-17, ADAM17); however, the β-secretase BACE1 (β-site APP-cleaving enzyme-1) was not increased by CA. Knockdown of TACE by siRNA reduced soluble-APPα release enhanced by CA and partially recovered the CA-suppressed Aβ40/42/43 release. These results suggest that CA reduces Aβ production, at least partially, by activating TACE in human astroglial cells. The use of CA may have a potential in the prevention of Aβ-mediated diseases.

Neuropathologic changes associated with atrial fibrillation in a population-based autopsy cohort

BACKGROUND

Atrial fibrillation (AF) is associated with higher risk of dementia and Alzheimer's disease. To better understand the mechanism, we examined neuropathologic changes seen with AF.

METHODS

We analyzed data from an autopsy series arising from a population-based, prospective cohort study set within Group Health, an integrated health care delivery system. Participants were people aged 65 and older, community-dwelling, and nondemented at study enrollment, who died during follow-up and underwent autopsy. AF was defined from medical records. Permanent AF was defined as having two or more electrocardiograms showing AF between 6 and 36 months apart with no evidence of sinus rhythm in between. The primary study outcomes were gross infarcts, neuritic plaques, and neurofibrillary tangles, ascertained using consensus guidelines. Adjusted relative risks and 95% CIs were calculated using modified Poisson regression, weighted to account for selection into the autopsy cohort.

RESULTS

Three hundred and twenty-eight participants underwent autopsy; 134 (41%) had AF. People with AF were more likely to have gross infarcts than those without AF (45% vs 31%; relative risk 1.82, 95% CI 1.23-2.71); in 30%, these infarcts were not clinically recognized before death. Alzheimer's disease neuropathologic changes were not associated with ever having AF but were more common in people with permanent AF. Adjusted relative risks for frequent neuritic plaques and neurofibrillary tangles were 1.47 (0.96-2.28) and 1.40 (0.79-2.49), respectively, for people with permanent AF versus no AF.

CONCLUSIONS

AF is associated with gross infarcts. Permanent AF may contribute to Alzheimer's disease neuropathologic changes, but more study is needed.

Hypoxia-triggered m-calpain activation evokes endoplasmic reticulum stress and neuropathogenesis in a transgenic mouse model of Alzheimer's disease

BACKGROUND

Previous studies have demonstrated that endoplasmic reticulum (ER) stress is activated in Alzheimer's disease (AD) brains. ER stress-triggered unfolded protein response (UPR) leads to tau phosphorylation and neuronal death.

AIMS

In this study, we tested the hypothesis that hypoxia-induced m-calpain activation is involved in ER stress-mediated AD pathogenesis.

METHOD

We employed a hypoxic exposure in APP/PS1 transgenic mice and SH-SY5Y cells overexpressing human Swedish mutation APP (APPswe).

RESULTS

We observed that hypoxia impaired spatial learning and memory in the APP/PS1 mouse. In the transgenic mouse brain, hypoxia increased the UPR, upregulated apoptotic signaling, enhanced the activation of calpain and glycogen synthase kinase-3β (GSK3β), and increased tau hyperphosphorylation and β-amyloid deposition. In APPswe cells, m-calpain silencing reduced hypoxia-induced cellular dysfunction and resulted in suppression of GSK3β activation, ER stress and tau hyperphosphorylation reduction as well as caspase pathway suppression.

CONCLUSION

These findings demonstrate that hypoxia-induced abnormal calpain activation may increase ER stress-induced apoptosis in AD pathogenesis. In contrast, a reduction in the expression of the m-calpain isoform reduces ER stress-linked apoptosis that is triggered by hypoxia. These findings suggest that hypoxia-triggered m-calpain activation is involved in ER stress-mediated AD pathogenesis. m-calpain is a potential target for AD therapeutics.

Assessing white matter ischemic damage in dementia patients by measurement of myelin proteins

White matter ischemia is difficult to quantify histologically. Myelin-associated glycoprotein (MAG) is highly susceptible to ischemia, being expressed only adaxonally, far from the oligodendrocyte cell body. Myelin-basic protein (MBP) and proteolipid protein (PLP) are expressed throughout the myelin sheath. We compared MAG, MBP, and PLP levels in parietal white matter homogenates from 17 vascular dementia (VaD), 49 Alzheimer's disease (AD), and 33 control brains, after assessing the post-mortem stability of these proteins. Small vessel disease (SVD) and cerebral amyloid angiopathy (CAA) severity had been assessed in paraffin sections. The concentration of MAG remained stable post-mortem, declined with increasing SVD, and was significantly lower in VaD than controls. The concentration of MBP fell progressively post-mortem, limiting its diagnostic utility in this context. Proteolipid protein was stable post-mortem and increased significantly with SVD severity. The MAG/PLP ratio declined significantly with SVD and CAA severity. The MAG and PLP levels and MAG/PLP did not differ significantly between AD and control brains. We validated the utility of MAG and MAG/PLP measurements on analysis of 74 frontal white matter samples from an Oxford cohort in which SVD had previously been scored. MAG concentration and the MAG/PLP ratio are useful post-mortem measures of ante-mortem white matter ischemia.

Dysregulation of hypoxia-inducible factor by presenilin/γ-secretase loss-of-function mutations

Presenilin (PSEN) 1 and 2 are the catalytic components of the γ-secretase complex, which cleaves a variety of proteins, including the amyloid precursor protein (APP). Proteolysis of APP leads to the formation of the APP intracellular domain (AICD) and amyloid β that is crucially involved in the pathogenesis of Alzheimer's disease. Prolyl-4-hydroxylase-domain (PHD) proteins regulate the hypoxia-inducible factors (HIFs), the master regulators of the hypoxic response. We previously identified the FK506 binding protein 38 (FKBP38) as a negative regulator of PHD2. Genetic ablation of PSEN1/2 has been shown to increase FKBP38 protein levels. Therefore, we investigated the role of PSEN1/2 in the oxygen sensing pathway using a variety of genetically modified cell and mouse lines. Increased FKBP38 protein levels and decreased PHD2 protein levels were found in PSEN1/2-deficient mouse embryonic fibroblasts and in the cortex of forebrain-specific PSEN1/2 conditional double knock-out mice. Hypoxic HIF-1α protein accumulation and transcriptional activity were decreased, despite reduced PHD2 protein levels. Proteolytic γ-secretase function of PSEN1/2 was needed for proper HIF activation. Intriguingly, PSEN1/2 mutations identified in Alzheimer patients differentially affected the hypoxic response, involving the generation of AICD. Together, our results suggest a direct role for PSEN in the regulation of the oxygen sensing pathway via the APP/AICD cleavage cascade.

Death by a thousand cuts in Alzheimer's disease: hypoxia--the prodrome

A wide range of clinical consequences may be associated with obstructive sleep apnea (OSA) including systemic hypertension, cardiovascular disease, pulmonary hypertension, congestive heart failure, cerebrovascular disease, glucose intolerance, impotence, gastroesophageal reflux, and obesity, to name a few. Despite this, 82 % of men and 93 % of women with OSA remain undiagnosed. OSA affects many body systems, and induces major alterations in metabolic, autonomic, and cerebral functions. Typically, OSA is characterized by recurrent chronic intermittent hypoxia (CIH), hypercapnia, hypoventilation, sleep fragmentation, peripheral and central inflammation, cerebral hypoperfusion, and cerebral glucose hypometabolism. Upregulation of oxidative stress in OSA plays an important pathogenic role in the milieu of hypoxia-induced cerebral and cardiovascular dysfunctions. Strong evidence underscores that cerebral amyloidogenesis and tau phosphorylation--two cardinal features of Alzheimer's disease (AD), are triggered by hypoxia. Mice subjected to hypoxic conditions unambiguously demonstrated upregulation in cerebral amyloid plaque formation and tau phosphorylation, as well as memory deficit. Hypoxia triggers neuronal degeneration and axonal dysfunction in both cortex and brainstem. Consequently, neurocognitive impairment in apneic/hypoxic patients is attributable to a complex interplay between CIH and stimulation of several pathological trajectories. The framework presented here helps delineate the emergence and progression of cognitive decline, and may yield insight into AD neuropathogenesis. The global impact of CIH should provide a strong rationale for treating OSA and snoring clinically, in order to ameliorate neurocognitive impairment in aged/AD patients.

Prenatal hypoxia may aggravate the cognitive impairment and Alzheimer's disease neuropathology in APPSwe/PS1A246E transgenic mice

Most cases of Alzheimer's disease (AD) arise through interactions between genetic and environmental factors. It is believed that hypoxia is an important environmental factor influencing the development of AD. Our group has previously demonstrated that hypoxia increased β-amyloid (Aβ) generation in aged AD mice. Here, we further investigate the pathological role of prenatal hypoxia in AD. We exposed the pregnant APP(Swe)/PS1(A246E) transgenic mice to high-altitude hypoxia in a hypobaric chamber during days 7-20 of gestation. We found that prenatal hypoxic mice exhibited a remarkable deficit in spatial learning and memory and a significant decrease in synapses. We also documented a significantly higher level of amyloid precursor protein, lower level of the Aβ-degrading enzyme neprilysin, and increased Aβ accumulation in the brain of prenatal hypoxic mice. Finally, we demonstrated striking neuropathologic changes in prenatal hypoxic AD mice, showing increased phosphorylation of tau, decreased hypoxia-induced factor, and enhanced activation of astrocytes and microglia. These data suggest that although the characteristic features of AD appear later in life, hypoxemia in the prenatal stage may contribute to the pathogenesis of the disease, supporting the notion that environmental factors can trigger or aggravate AD.