Alzheimer Disease: Eckman EA

Eckman CB, Eckman EA. · Department of Neuroscience, Mayo Clinic College of Medicine, Jacksonville, FL 32224, USA. · Neurol Clin. · Pubmed #17659184 No free full text.

Abstract: Alzheimer's disease (AD) is a devastating neurodegenerative disease. To rationally develop novel therapeutic and/or preventative agents for AD, an understanding of the etiology and pathogenesis of this complex disease is necessary. This article examines the evidence for the amyloid hypothesis of AD pathogenesis and discusses how it relates to the neurological and neuropathological features of AD, the known genetic risk factors and causative mutations, and the heightened risk associated with advanced age.

Parkin ET, Watt NT, Hussain I, Eckman EA, Eckman CB, Manson JC, Baybutt HN, Turner AJ, Hooper NM. · Proteolysis Research Group, Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, and Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT, United Kingdom. · Proc Natl Acad Sci U S A. · Pubmed #17573534 links to  free full text

Abstract: Proteolytic processing of the amyloid precursor protein (APP) by beta-secretase, beta-site APP cleaving enzyme (BACE1), is the initial step in the production of the amyloid beta (Abeta) peptide, which is involved in the pathogenesis of Alzheimer's disease. The normal cellular function of the prion protein (PrP(C)), the causative agent of the transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease in humans, remains enigmatic. Because both APP and PrP(C) are subject to proteolytic processing by the same zinc metalloproteases, we tested the involvement of PrP(C) in the proteolytic processing of APP. Cellular overexpression of PrP(C) inhibited the beta-secretase cleavage of APP and reduced Abeta formation. Conversely, depletion of PrP(C) in mouse N2a cells by siRNA led to an increase in Abeta peptides secreted into the medium. In the brains of PrP knockout mice and in the brains from two strains of scrapie-infected mice, Abeta levels were significantly increased. Two mutants of PrP, PG14 and A116V, that are associated with familial human prion diseases failed to inhibit the beta-secretase cleavage of APP. Using constructs of PrP, we show that this regulatory effect of PrP(C) on the beta-secretase cleavage of APP required the localization of PrP(C) to cholesterol-rich lipid rafts and was mediated by the N-terminal polybasic region of PrP(C) via interaction with glycosaminoglycans. In conclusion, this is a mechanism by which the cellular production of the neurotoxic Abeta is regulated by PrP(C) and may have implications for both Alzheimer's and prion diseases.

Eckman EA, Adams SK, Troendle FJ, Stodola BA, Kahn MA, Fauq AH, Xiao HD, Bernstein KE, Eckman CB. · Department of Neuroscience, Mayo Clinic College of Medicine, Jacksonville, Florida 32224, USA. · J Biol Chem. · Pubmed #16912050 links to  free full text

Abstract: The deposition of beta-amyloid in the brain is a pathological hallmark of Alzheimer disease (AD). Normally, the accumulation of beta-amyloid is prevented in part by the activities of several degradative enzymes, including the endothelin-converting enzymes, neprilysin, insulin-degrading enzyme, and plasmin. Recent reports indicate that another metalloprotease, angiotensin-converting enzyme (ACE), can degrade beta-amyloid in vitro and in cellular overexpression experiments. In addition, ACE gene variants are linked to AD risk in several populations. Angiotensin-converting enzyme, neprilysin and endothelin-converting enzyme function as vasopeptidases and are the targets of drugs designed to treat cardiovascular disorders, and ACE inhibitors are commonly prescribed. We investigated the potential physiological role of ACE in regulating endogenous brain beta-amyloid levels for two reasons: first, to determine whether beta-amyloid degradation might be the mechanism by which ACE is associated with AD, and second, to determine whether ACE inhibitor drugs might block beta-amyloid degradation in the brain and potentially increase the risk for AD. We analyzed beta-amyloid accumulation in brains from ACE-deficient mice and in mice treated with ACE inhibitors and found that ACE deficiency did not alter steady-state beta-amyloid concentration. In contrast, beta-amyloid levels are significantly elevated in endothelin-converting enzyme and neprilysin knock-out mice, and inhibitors of these enzymes cause a rapid increase in beta-amyloid concentration in the brain. The results of these studies do not support a physiological role for ACE in the degradation of beta-amyloid in the brain but confirm roles for endothelin-converting enzyme and neprilysin and indicate that reductions in these enzymes result in additive increases in brain amyloid beta-peptide levels.

Eckman EA, Eckman CB. · Department of Neuroscience, Mayo Clinic College of Medicine, Jacksonville, FL, USA. · Biochem Soc Trans. · Pubmed #16246055 No free full text.

Abstract: The accumulation of Abeta (amyloid beta-protein) peptides in the brain is a pathological hallmark of all forms of AD (Alzheimer's disease) and reducing Abeta levels can prevent or reverse cognitive deficits in mouse models of the disease. Abeta is produced continuously and its concentration is determined in part by the activities of several degradative enzymes, including NEP (neprilysin), IDE (insulin-degrading enzyme), ECE-1 (endothelin-converting enzyme 1) and ECE-2, and probably plasmin. Decreased activity of any of these enzymes due to genetic mutation, or age- or disease-related alterations in gene expression or proteolytic activity, may increase the risk for AD. Conversely, increased expression of these enzymes may confer a protective effect. Increasing Abeta degradation through gene therapy, transcriptional activation or even pharmacological activation of the Abeta-degrading enzymes represents a novel therapeutic strategy for the treatment of AD that is currently being evaluated in cell-culture and animal models. In this paper, we will review the roles of NEP, IDE, ECE and plasmin in determining endogenous Abeta concentration, highlighting recent results concerning the regulation of these enzymes and their potential as therapeutic targets.

Farris W, Mansourian S, Leissring MA, Eckman EA, Bertram L, Eckman CB, Tanzi RE, Selkoe DJ. · Department of Neurology, Center for Neurologic Diseases, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA. · Am J Pathol. · Pubmed #15039230 links to  free full text

Abstract: The causes of cerebral accumulation of amyloid beta-protein (Abeta) in most cases of Alzheimer's disease (AD) remain unknown. We recently found that homozygous deletion of the insulin-degrading enzyme (IDE) gene in mice results in an early and marked elevation of cerebral Abeta. Both genetic linkage and allelic association in the IDE region of chromosome 10 have been reported in families with late-onset AD. For IDE to remain a valid candidate gene for late-onset AD on functional grounds, it must be shown that partial loss of function of IDE can still alter Abeta degradation, but without causing early, severe elevation of brain Abeta. Here, we show that naturally occurring IDE missense mutations in a well-characterized rat model of type 2 diabetes mellitus (DM2) result in decreased catalytic efficiency and a significant approximately 15 to 30% deficit in the degradation of both insulin and Abeta. Endogenously secreted Abeta(40) and Abeta(42) are significantly elevated in primary neuronal cultures from animals with the IDE mutations, but there is no increase in steady-state levels of rodent Abeta in the brain up to age 14 months. We conclude that naturally occurring, partial loss-of-function mutations in IDE sufficient to cause DM2 also impair neuronal regulation of Abeta levels, but the brain can apparently compensate for the partial deficit during the life span of the rat. Our findings have relevance for the emerging genetic evidence suggesting that IDE may be a late-onset AD-risk gene, and for the epidemiological relationships among hyperinsulinemia, DM2, and AD.

Farris W, Mansourian S, Chang Y, Lindsley L, Eckman EA, Frosch MP, Eckman CB, Tanzi RE, Selkoe DJ, Guenette S. · Center for Neurologic Diseases, Department of Neurology, Brigham and Women's Hospital, Boston, MA 02115, USA. · Proc Natl Acad Sci U S A. · Pubmed #12634421 links to  free full text

Abstract: Two substrates of insulin-degrading enzyme (IDE), amyloid beta-protein (Abeta) and insulin, are critically important in the pathogenesis of Alzheimer's disease (AD) and type 2 diabetes mellitus (DM2), respectively. We previously identified IDE as a principal regulator of Abeta levels in neuronal and microglial cells. A small chromosomal region containing a mutant IDE allele has been associated with hyperinsulinemia and glucose intolerance in a rat model of DM2. Human genetic studies have implicated the IDE region of chromosome 10 in both AD and DM2. To establish whether IDE hypofunction decreases Abeta and insulin degradation in vivo and chronically increases their levels, we characterized mice with homozygous deletions of the IDE gene (IDE --). IDE deficiency resulted in a >50% decrease in Abeta degradation in both brain membrane fractions and primary neuronal cultures and a similar deficit in insulin degradation in liver. The IDE -- mice showed increased cerebral accumulation of endogenous Abeta, a hallmark of AD, and had hyperinsulinemia and glucose intolerance, hallmarks of DM2. Moreover, the mice had elevated levels of the intracellular signaling domain of the beta-amyloid precursor protein, which was recently found to be degraded by IDE in vitro. Together with emerging genetic evidence, our in vivo findings suggest that IDE hypofunction may underlie or contribute to some forms of AD and DM2 and provide a mechanism for the recently recognized association among hyperinsulinemia, diabetes, and AD.

Eckman EA, Watson M, Marlow L, Sambamurti K, Eckman CB. · Mayo Clinic Jacksonville, Florida 32224, USA. · J Biol Chem. · Pubmed #12464614 links to  free full text

Abstract: The abnormal accumulation of beta-amyloid (Abeta) in the brain is an early and invariant feature in Alzheimer's disease (AD) and is believed to play a pivotal role in the etiology and pathogenesis of the disease. As such, a major focus of AD research has been the elucidation of the mechanisms responsible for the generation of Abeta. As with any peptide, however, the degree of Abeta accumulation is dependent not only on its production but also on its removal. In cell-based and in vitro models we have previously characterized endothelin-converting enzyme-1 (ECE-1) as an Abeta-degrading enzyme that appears to act intracellularly, thus limiting the amount of Abeta available for secretion. To determine the physiological significance of this activity, we analyzed Abeta levels in the brains of mice deficient for ECE-1 and a closely related enzyme, ECE-2. Significant increases in the levels of both Abeta40 and Abeta42 were found in the brains of these animals when compared with age-matched littermate controls. The increase in Abeta levels in the ECE-deficient mice provides the first direct evidence for a physiological role for both ECE-1 and ECE-2 in limiting Abeta accumulation in the brain and also provides further insight into the factors involved in Abeta clearance in vivo.

Yager D, Watson M, Healy B, Eckman EA, Eckman CB. · Mayo Clinic Jacksonville, FL 32224, USA. · J Mol Neurosci. · Pubmed #12212770 No free full text.

Abstract: Alzheimer's disease (AD) is the most common form of dementia in the elderly. Without a treatment that significantly delays the progression of the disease over 14 million Americans are likely to be affected with AD by the middle of the 21st Century, presenting an enormous economic and social burden. Evidence gathered over the last two decades has implicated the abnormal accumulation of A beta, in particular the longer more amyloidogenic form A beta42, as a potential causative agent in the disease. To screen for compounds that reduce A beta accumulation we have established several high throughput, cell based screens capable of the sensitive and selective detection of A beta40 and A beta42. Using these screens we have analyzed a proprietary library of natural product extracts for their ability to influence A beta accumulation. Using this approach, we have identified several agents capable of influencing total A beta concentration. In addition, we have identified one extract that selectively reduces A beta42. Intracerebroventricular administration of this agent to mice results in a selective reduction in A beta42 in the brain.

Haugabook SJ, Yager DM, Eckman EA, Golde TE, Younkin SG, Eckman CB. · Mayo Clinic Jacksonville, Birdsall Building Room 253, 4500 San Pablo Road, Jacksonville, FL 32224, USA. · J Neurosci Methods. · Pubmed #11478976 No free full text.

Abstract: Evidence gathered over the last two decades suggests that beta amyloid (Abeta), the predominant proteinaceous component of senile plaques, plays an early and critical role in the etiology and pathogenesis of Alzheimer's disease (AD). Thus, it is reasonable to hypothesize that compounds capable of reducing the accumulation of Abeta may be of value therapeutically. Additionally, compounds that influence Abeta accumulation may be useful as tools to further dissect the cellular pathways that regulate Abeta production and accumulation. To screen for compounds that affect Abeta levels, we have established high throughput, cell-based assays capable of the sensitive and selective detection of Abeta40 in parallel with the more amyloidogenic form of the peptide, Abeta42. To validate the approach, we examined the effects of several compounds previously identified to influence Abeta accumulation. Analysis of peptide accumulation following treatment with these compounds showed results similar to those previously published. Currently, we are using this assay to screen drugs that have already received FDA approval for the treatment of other diseases and over-the-counter natural product extracts. If compounds such as these can be identified that lower Abeta in the brain, they may represent one of the fastest and most cost effective methods to therapy.

Eckman EA, Reed DK, Eckman CB. · Mayo Clinic Jacksonville, 4500 San Pablo Road, Jacksonville, FL 32224, USA. · J Biol Chem. · Pubmed #11337485 links to  free full text

Abstract: Deposition of beta-amyloid (Abeta) peptides in the brain is an early and invariant feature of all forms of Alzheimer's disease. As with any secreted protein, the extracellular concentration of Abeta is determined not only by its production but also by its catabolism. A major focus of Alzheimer's research has been the elucidation of the mechanisms responsible for the generation of Abeta. Much less, however, is known about the mechanisms responsible for Abeta removal in the brain. In this report, we describe the identification of endothelin-converting enzyme-1 (ECE-1) as a novel Abeta-degrading enzyme. We show that treatment of endogenous ECE-expressing cell lines with the metalloprotease inhibitor phosphoramidon causes a 2-3-fold elevation in extracellular Abeta concentration that appears to be due to inhibition of intracellular Abeta degradation. Furthermore, we show that overexpression of ECE-1 in Chinese hamster ovary cells, which lack endogenous ECE activity, reduces extracellular Abeta concentration by up to 90% and that this effect is completely reversed by treatment of the cells with phosphoramidon. Finally, we show that recombinant soluble ECE-1 is capable of hydrolyzing synthetic Abeta40 and Abeta42 in vitro at multiple sites.

Haugabook SJ, Le T, Yager D, Zenk B, Healy BM, Eckman EA, Prada C, Younkin L, Murphy P, Pinnix I, Onstead L, Sambamurti K, Golde TE, Dickson D, Younkin SG, Eckman CB. · Mayo Clinic Jacksonville, Jacksonville, Florida 32224, USA. · FASEB J. · Pubmed #11099491 links to  free full text

Abstract: The abnormal accumulation of the amyloid beta protein (Abeta) has been implicated as an early and critical event in the etiology and pathogenesis of Alzheimer's disease (AD). Compounds that reduce Abeta accumulation may therefore be useful therapeutically. In cell-based screens we detected a significant reduction in Abeta concentration after treatment with the phosphatidylinositol kinase inhibitors wortmannin and LY294002. To determine the effect of this class of compounds on in vivo Abeta accumulation, we administered wortmannin to the Tg2576 mouse model of AD. Oral administration of wortmannin over four months resulted in a significant, non-overlapping 40%-50% reduction in the number of senile plaques, one of the pathological hallmarks of AD. Sandwich ELISA analysis of formic acid extractable Abeta in the brain of treated animals indicates that both Abeta40 and the longer, more amyloidogenic form of the peptide, Abeta42, were significantly reduced. These data provide the first direct evidence that compounds identified by their ability to reduce Abeta concentration in vitro can reduce Abeta accumulation and deposition in the brain, thus establishing a basic paradigm for the identification and evaluation of additional compounds that lower Abeta accumulation.