Alzheimer Disease: Nixon RA

Mathews PM, Nixon RA. · No affiliation provided · Neurology. · Pubmed #12847147 No free full text.

This publication has no abstract.

Nixon RA, Yang DS, Lee JH. · Center for Dementia Research, Nathan Kline Institute, New York University School of Medicine, Orangeburg, New York 10962, USA. · Autophagy. · Pubmed #18497567 No free full text.

Abstract: Neuronal survival requires continuous lysosomal turnover of cellular constituents delivered by autophagy and endocytosis. Primary lysosomal dysfunction in inherited congenital "lysosomal storage" disorders is well known to cause severe neurodegenerative phenotypes associated with accumulations of lysosomes and autophagic vacuoles (AVs). Recently, the number of inherited adult-onset neurodegenerative diseases caused by proteins that regulate protein sorting and degradation within the endocytic and autophagic pathways has grown considerably. In this Perspective, we classify a group of neurodegenerative diseases across the lifespan as disorders of lysosomal function, which feature extensive autophagic-endocytic-lysosomal neuropathology and may share mechanisms of neurodegeneration related to degradative failure and lysosomal destabilization. We highlight Alzheimer's disease as a disease within this group and discuss how each of the genes and other risk factors promoting this disease contribute to progressive lysosomal dysfunction and neuronal cell death.

Nixon RA. · Center for Dementia Research, Nathan Kline Institute for Psychiatric Research, Orangeburg, NY 10962, USA. · J Cell Sci. · Pubmed #18032783 links to  free full text

Abstract: Autophagy is the sole pathway for organelle turnover in cells and is a vital pathway for degrading normal and aggregated proteins, particularly under stress or injury conditions. Recent evidence has shown that the amyloid beta peptide is generated from amyloid beta precursor protein (APP) during autophagic turnover of APP-rich organelles supplied by both autophagy and endocytosis. Abeta generated during normal autophagy is subsequently degraded by lysosomes. Within neurons, autophagosomes and endosomes actively form in synapses and along neuritic processes but efficient clearance of these compartments requires their retrograde transport towards the neuronal cell body, where lysosomes are most concentrated. In Alzheimer disease, the maturation of autophagolysosomes and their retrograde transport are impeded, which leads to a massive accumulation of ;autophagy intermediates' (autophagic vacuoles) within large swellings along dystrophic and degenerating neurites. The combination of increased autophagy induction and defective clearance of Abeta-generating autophagic vacuoles creates conditions favorable for Abeta accumulation in Alzheimer disease.

Nixon RA, Cataldo AM. · Center for Dementia Research, Nathan S. Kline Institute, 140 Old Orangeburg Road, Orangeburg, NY 10962, USA. · J Alzheimers Dis. · Pubmed #16914867 No free full text.

Abstract: The identification of cathepsins in amyloid-beta plaques revealed broad dysfunction of the lysosomal system in Alzheimer's disease (AD). Coinciding with the discovery that proteolysis is required to generate the Abeta-peptide, these findings heralded an era of intense investigation on proteases in neurodegeneration. This review traces lysosomal system pathology from its early characterization to its origins within two pathways leading to the lysosome, the endocytic and autophagic pathways. An understanding has grown about how these two pathways are adversely influenced by normal brain aging and by genetic and environmental risk factors for AD, resulting in increased susceptibility of neurons to injury, amyloidogenesis, and neurodegeneration.

Rubinsztein DC, DiFiglia M, Heintz N, Nixon RA, Qin ZH, Ravikumar B, Stefanis L, Tolkovsky A. · Departments of Medical Genetics, University of Cambridge, Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge, UK. · Autophagy. · Pubmed #16874045 links to  free full text

Abstract: Increased numbers of autophagosomes/autophagic vacuoles are seen in a variety of physiological and pathological states in the nervous system. In many cases, it is unclear if this phenomenon is the result of increased autophagic activity or decreased autophagosome-lysosome fusion. The functional significance of autophagy and its relationship to cell death in the nervous system is also poorly understood. In this review, we have considered these issues in the context of acute neuronal injury and a range of chronic neurodegenerative conditions, including the Lurcher mouse, Alzheimer's, Parkinson's, Huntington's and prion diseases. While many issues remain unresolved, these conditions raise the possibility that autophagy can have either deleterious or protective effects depending on the specific situation and stage in the pathological process.

de Grey AD, Alvarez PJ, Brady RO, Cuervo AM, Jerome WG, McCarty PL, Nixon RA, Rittmann BE, Sparrow JR. · Department of Genetics, University of Cambridge, Downing Street, Cambridge CB2 3EH, UK. · Ageing Res Rev. · Pubmed #16040282 No free full text.

Abstract: Several major diseases of old age, including atherosclerosis, macular degeneration and neurodegenerative diseases are associated with the intracellular accumulation of substances that impair cellular function and viability. Moreover, the accumulation of lipofuscin, a substance that may have similarly deleterious effects, is one of the most universal markers of aging in postmitotic cells. Reversing this accumulation may thus be valuable, but has proven challenging, doubtless because substances resistant to cellular catabolism are inherently hard to degrade. We suggest a radically new approach: augmenting humans' natural catabolic machinery with microbial enzymes. Many recalcitrant organic molecules are naturally degraded in the soil. Since the soil in certain environments - graveyards, for example - is enriched in human remains but does not accumulate these substances, it presumably harbours microbes that degrade them. The enzymes responsible could be identified and engineered to metabolise these substances in vivo. Here, we survey a range of such substances, their putative roles in age-related diseases and the possible benefits of their removal. We discuss how microbes capable of degrading them can be isolated, characterised and their relevant enzymes engineered for this purpose and ways to avoid potential side-effects.

Nixon RA. · Department of Psychiatry, NYU School of Medicine, New York, NY 10016, USA. · Neurobiol Aging. · Pubmed #15639316 No free full text.

Abstract: Endocytosis is universally important in cell function. In the brain, the roles of endosomes are relatively more complex due to the unique polar morphology of neurons and specialized needs for inter-cellular communication. New evidence shows that endosome function is altered in a surprising range of neurodegenerative disorders, including in several inherited neurologic disorders where the causative mutations occur in genes that regulate endosome function. In Alzheimer's disease (AD), endosome abnormalities are among the earliest neuropathologic features to develop and have now been closely linked to genetic risk factors for AD, including APP triplication in Trisomy 21 (Down syndrome, DS) and ApoE4 genotype in sporadic AD. Recent findings on endosome regulation and developmental and late-onset neurodegenerative disease disorders are beginning to reveal how endocytic pathway impairment may lead to neuronal dysfunction and cell death in these disorders and may also promote amyloidogenesis in AD.

Nixon RA. · Department of Psychiatry, New York University School of Medicine, Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York 10962, USA. · Am J Pathol. · Pubmed #14982829 links to  free full text

Abstract: Niemann-Pick Type C (NPC) is an inherited neurodegenerative disease of childhood and adolescence that develops from a failure of cholesterol trafficking within the endosomal-lysosomal pathway. Although NPC differs in major respects from Alzheimer's disease (AD), intriguing parallels exist in the cellular pathology of these two diseases, including neurofibrillary tangle formation, prominent lysosome system dysfunction, and influences of apolipoprotein E epsilon4 genotype. Added to these similarities are new findings that some neuronal populations develop abnormalities of endosomes resembling those seen at the earliest stages of AD and also accumulate beta-cleaved amyloid precursor protein (APP) and Abeta peptides within endosomes. In this commentary, the common features of endosome dysfunction are reviewed. Emerging evidence that endosome dysfunction may lead to beta-amyloidogenic APP processing or neurodegeneration by several different means is discussed.

Nixon RA. · Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY 10962, USA. · Ageing Res Rev. · Pubmed #14522243 No free full text.

Abstract: Calpains are a family of calcium-dependent cysteine proteases under complex cellular regulation. By making selective limited proteolytic cleavages, they modulate the activity of enzymes, including key signaling molecules, and induce specific cytoskeletal rearrangements, accounting for their roles in cell motility, signal transduction, vesicular trafficking and structural stabilization. Calpain activation has been implicated in various aging phenomena and diseases of late life, including cataract formation, erythrocyte senescence, diabetes mellitus type 2, hypertension, arthritis, and neurodegenerative disorders. The early and pervasive involvement of calpains in Alzheimer's disease potentially influences the development of beta-amyloid and tau disturbances and their consequences for neurodegeneration and neuronal cell loss.

Nixon RA. · Center for Dementia Research, Nathan Kline Institute, 140 Old Orangeburg Rd., Orangeburg, NY 10962, USA. · Ann N Y Acad Sci. · Pubmed #11193788 No free full text.

Abstract: A pathway to Alzheimer's disease (AD) relevant to sporadic AD pathogenesis is described that involves the early and progressive activation of proteolytic systems including, but not limited to, the calpain-calpastatin and endosomal-lysosomal systems. Activation of these proteolytic systems is initiated by normal brain aging and is propelled by the genetic and environmental factors known to increase AD risk. Recent studies show how cathepsins and calpains, acting directly or indirectly through other proteolytic pathways and cellular signaling cascades, may promote beta-amyloidogenesis, neurofibrillary pathology, as well as mediate neurodegeneration in AD.

Nixon RA, Cataldo AM, Mathews PM. · Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York 10962, USA. · Neurochem Res. · Pubmed #11059790 No free full text.

Abstract: A prominent feature of brain pathology in Alzheimer's disease is a robust activation of the neuronal lysosomal system and major cellular pathways converging on the lysosome, namely, endocytosis and autophagy. Recent studies that identify a disturbance of the endocytic pathway as one of the earliest known manifestation of Alzheimer's disease provide insight into how beta-amyloidogenesis might be promoted in sporadic Alzheimer's disease, the most prevalent and least well understood form of the disease. Primary lysosomal dysfunction has historically been linked to neurodegeneration. New data now directly implicate cathepsins as proteases capable of initiating, as well as executing, cell death programs in certain pathologic states. These and other studies support the view that the progressive alterations of lysosomal function observed during aging and Alzheimer's disease contribute importantly to the neurodegenerative process in Alzheimer's disease.

Cataldo AM, Petanceska S, Terio NB, Peterhoff CM, Durham R, Mercken M, Mehta PD, Buxbaum J, Haroutunian V, Nixon RA. · Mailman Research Center, McLean Hospital, 115 Mill Street, Belmont, MA 02478, USA. · Neurobiol Aging. · Pubmed #15465622 No free full text.

Abstract: Early endosomes are a major site of amyloid precursor protein (APP) processing and a convergence point for molecules of pathologic relevance to Alzheimer's disease (AD). Neuronal endosome enlargement, reflecting altered endocytic function, is a disease-specific response that develops years before the earliest stage of AD and Down syndrome (DS). We examined how endocytic dysfunction is related to Abeta accumulation and distribution in early stage AD and DS. We found by ELISA and immunocytochemistry that the appearance of enlarged endosomes coincided with an initial rise in soluble Abeta40 and Abeta42 peptides, which preceded amyloid deposition. Double-immunofluorescence using numerous Abeta antibodies showed that intracellular Abeta localized principally to rab5-positive endosomes in neurons from AD brains and was prominent in enlarged endosomes. Abeta was not detectable in neurons from normal controls and was diminished after amyloid deposition in neuropathologically confirmed AD. These studies support growing evidence that endosomal pathology contributes significantly to Abeta overproduction and accumulation in sporadic AD and in AD associated with DS and may signify earlier disease-relevant disturbances of the signaling functions of endosomes.

Yang DS, Lee JH, Nixon RA. · Center for Dementia Research, Nathan S. Kline Institute, Orangeburg, New York, USA. · Methods Enzymol. · Pubmed #19216904 No free full text.

Abstract: This chapter describes detailed methods to monitor autophagy in neurodegenerative disorders, especially in Alzheimer's disease. Strategies to assess the competence of autophagy-related mechanisms in disease states ideally incorporate analyses of human disease and control tissues, which may include brain, fibroblasts, or other peripheral cells, in addition to animal and cell models of the neurodegenerative disease pathology and pathobiology. Cross-validation of pathophysiological mechanisms in the diseased tissues is always critical. Because of the cellular heterogeneity of the brain and the differential vulnerability of the neural cells in a given disease state, analyses focus on regional comparisons of affected and unaffected regions or cell populations within a particular brain region and include ultrastructural, immunological, and cell and molecular biological approaches.

Planel E, Krishnamurthy P, Miyasaka T, Liu L, Herman M, Kumar A, Bretteville A, Figueroa HY, Yu WH, Whittington RA, Davies P, Takashima A, Nixon RA, Duff KE. · Taub Institute for Alzheimer's Disease Research, Department of Pathology, Columbia University Medical Center, New York, New York 10032, USA. · J Neurosci. · Pubmed #19036972 links to  free full text

Abstract: In Alzheimer's disease, tau is hyperphosphorylated, which is thought to detach it from microtubules (MTs), induce MT destabilization, and promote aggregation. Using a previously described in vivo model, we investigated whether hyperphosphorylation impacts tau function in wild-type and transgenic mice. We found that after anesthesia-induced hypothermia, MT-free tau was hyperphosphorylated, which impaired its ability to bind MTs and promote MT assembly. MT-bound tau was more resistant to hyperphosphorylation compared with free tau and tau did not dissociate from MTs in wild-type mice. However, 3-repeat tau detached from MT in the transgenic mice. Surprisingly, dissociation of tau from MTs did not lead to overt depolymerization of tubulin, and there was no collapse, or disturbance of axonal MT networks. These results indicate that, in vivo, a subpopulation of tau bound to MTs does not easily dissociate under conditions that extensively phosphorylate tau. Tau remaining on the MTs under these conditions is sufficient to maintain MT network integrity.

Rao MV, Mohan PS, Peterhoff CM, Yang DS, Schmidt SD, Stavrides PH, Campbell J, Chen Y, Jiang Y, Paskevich PA, Cataldo AM, Haroutunian V, Nixon RA. · Center for Dementia Research, Nathan S. Kline Institute, Orangeburg, New York 10962, USA. · J Neurosci. · Pubmed #19020018 links to  free full text

Abstract: Increased activity of calpains is implicated in synaptic dysfunction and neurodegeneration in Alzheimer's disease (AD). The molecular mechanisms responsible for increased calpain activity in AD are not known. Here, we demonstrate that disease progression is propelled by a marked depletion of the endogenous calpain inhibitor, calpastatin (CAST), from AD neurons, which is mediated by caspase-1, caspase-3, and calpains. Initial CAST depletion focally along dendrites coincides topographically with calpain II and ERK 1/2 activation, tau cleavage by caspase-3, and tau and neurofilament hyperphosphorylation. These same changes, together with cytoskeletal proteolysis and neuronal cell death, accompany CAST depletion after intrahippocampal kainic acid administration to mice, and are substantially reduced in mice overexpressing human CAST. Moreover, CAST reduction by shRNA in neuronal cells causes calpain-mediated death at levels of calcium-induced injury that are sublethal to cells normally expressing CAST. Our results strongly support a novel hypothesis that CAST depletion by multiple abnormally activated proteases accelerates calpain dysregulation in AD leading to cytoskeleton disruption and neurodegeneration. CAST mimetics may, therefore, be neuroprotective in AD.

Yang DS, Kumar A, Stavrides P, Peterson J, Peterhoff CM, Pawlik M, Levy E, Cataldo AM, Nixon RA. · Center for Dementia Research, Nathan Kline Institute, New York University School of Medicine, 140 Old Orangeburg Rd., Bldg. 39, Orangeburg, NY 10962, USA. · Am J Pathol. · Pubmed #18688038 links to  free full text

Abstract: Mechanisms of neuronal loss in Alzheimer's disease (AD) are poorly understood. Here we show that apoptosis is a major form of neuronal cell death in PS/APP mice modeling AD-like neurodegeneration. Pyknotic neurons in adult PS/APP mice exhibited apoptotic changes, including DNA fragmentation, caspase-3 activation, and caspase-cleaved alpha-spectrin generation, identical to developmental neuronal apoptosis in wild-type mice. Ultrastructural examination using immunogold cytochemistry confirmed that activated caspase-3-positive neurons also exhibited chromatin margination and condensation, chromatin balls, and nuclear membrane fragmentation. Numbers of apoptotic profiles in both cortex and hippocampus of PS/APP mice compared with age-matched controls were twofold to threefold higher at 6 months of age and eightfold higher at 21 to 26 months of age. Additional neurons undergoing dark cell degeneration exhibited none of these apoptotic features. Activated caspase-3 and caspase-3-cleaved spectrin were abundant in autophagic vacuoles, accumulating in dystrophic neurites of PS/APP mice similar to AD brains. Administration of the cysteine protease inhibitor, leupeptin, promoted accumulation of autophagic vacuoles containing activated caspase-3 in axons of PS/APP mice and, to a lesser extent, in those of wild-type mice, implying that this pro-apoptotic factor is degraded by autophagy. Leupeptin-induced autophagic impairment increased the number of apoptotic neurons in PS/APP mice. Our findings establish apoptosis as a mode of neuronal cell death in aging PS/APP mice and identify the cross talk between autophagy and apoptosis, which influences neuronal survival in AD-related neurodegeneration.

Trinchese F, Fa' M, Liu S, Zhang H, Hidalgo A, Schmidt SD, Yamaguchi H, Yoshii N, Mathews PM, Nixon RA, Arancio O. · Department of Pathology and Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University, New York, New York, USA. · J Clin Invest. · Pubmed #18596919 links to  free full text

Abstract: Calpains are calcium-dependent enzymes that determine the fate of proteins through regulated proteolytic activity. Calpains have been linked to the modulation of memory and are key to the pathogenesis of Alzheimer disease (AD). When abnormally activated, calpains can also initiate degradation of proteins essential for neuronal survival. Here we show that calpain inhibition through E64, a cysteine protease inhibitor, and the highly specific calpain inhibitor BDA-410 restored normal synaptic function both in hippocampal cultures and in hippocampal slices from the APP/PS1 mouse, an animal model of AD. Calpain inhibition also improved spatial-working memory and associative fear memory in APP/PS1 mice. These beneficial effects of the calpain inhibitors were associated with restoration of normal phosphorylation levels of the transcription factor CREB and involved redistribution of the synaptic protein synapsin I. Thus, calpain inhibition may prove useful in the alleviation of memory loss in AD.

Boland B, Kumar A, Lee S, Platt FM, Wegiel J, Yu WH, Nixon RA. · Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York 10962, USA. · J Neurosci. · Pubmed #18596167 links to  free full text

Abstract: Macroautophagy, a major pathway for organelle and protein turnover, has been implicated in the neurodegeneration of Alzheimer's disease (AD). The basis for the profuse accumulation of autophagic vacuoles (AVs) in affected neurons of the AD brain, however, is unknown. In this study, we show that constitutive macroautophagy in primary cortical neurons is highly efficient, because newly formed autophagosomes are rapidly cleared by fusion with lysosomes, accounting for their scarcity in the healthy brain. Even after macroautophagy is strongly induced by suppressing mTOR (mammalian target of rapamycin) kinase activity with rapamycin or nutrient deprivation, active cathepsin-positive autolysosomes rather than LC3-II-positive autophagosomes predominate, implying efficient autophagosome clearance in healthy neurons. In contrast, selectively impeding late steps in macroautophagy by inhibiting cathepsin-mediated proteolysis within autolysosomes with cysteine- and aspartyl-protease inhibitors caused a marked accumulation of electron-dense double-membrane-limited AVs, containing cathepsin D and incompletely degraded LC3-II in perikarya and neurites. Similar structures accumulated in large numbers when fusion of autophagosomes with lysosomes was slowed by disrupting their transport on microtubules with vinblastine. Finally, we find that the autophagic vacuoles accumulating after protease inhibition or prolonged vinblastine treatment strongly resembled AVs that collect in dystrophic neurites in the AD brain and in an AD mouse model. We conclude that macroautophagy is constitutively active and highly efficient in healthy neurons and that the autophagic pathology observed in AD most likely arises from impaired clearance of AVs rather than strong autophagy induction alone. Therapeutic modulation of autophagy in AD may, therefore, require targeting late steps in the autophagic pathway.

Cataldo AM, Mathews PM, Boiteau AB, Hassinger LC, Peterhoff CM, Jiang Y, Mullaney K, Neve RL, Gruenberg J, Nixon RA. · Laboratory for Molecular Neuropathology, Mailman Research Center, McLean Hospital, 115 Mill St., Belmont, MA 02478, USA. · Am J Pathol. · Pubmed #18535180 links to  free full text

Abstract: Endocytic dysfunction is an early pathological change in Alzheimer's disease (AD) and Down's syndrome (DS). Using primary fibroblasts from DS individuals, we explored the interactions among endocytic compartments that are altered in AD and assessed their functional consequences in AD pathogenesis. We found that, like neurons in both AD and DS brains, DS fibroblasts exhibit increased endocytic uptake, fusion, and recycling, and trafficking of lysosomal hydrolases to rab5-positive early endosomes. Moreover, late endosomes identified using antibodies to rab7 and lysobisphosphatidic acid increased in number and appeared as enlarged, perinuclear vacuoles, resembling those in neurons of both AD and DS brains. In control fibroblasts, similar enlargement of rab5-, rab7-, and lysobisphosphatidic acid-positive endosomes was induced when endocytosis and endosomal fusion were increased by expression of either a rab5 or an active rab5 mutant, suggesting that persistent endocytic activation results in late endocytic dysfunction. Conversely, expression of a rab5 mutant that inhibits endocytic uptake reversed early and late endosomal abnormalities in DS fibroblasts. Our results indicate that DS fibroblasts recapitulate the neuronal endocytic dysfunction of AD and DS, suggesting that increased trafficking from early endosomes can account, in part, for downstream endocytic perturbations that occur in neurons in both AD and DS brains.

Mi W, Pawlik M, Sastre M, Jung SS, Radvinsky DS, Klein AM, Sommer J, Schmidt SD, Nixon RA, Mathews PM, Levy E. · Nathan S. Kline Institute, Orangeburg, New York 10962, USA. · Nat Genet. · Pubmed #18026100 No free full text.

Abstract: Using transgenic mice expressing human cystatin C (encoded by CST3), we show that cystatin C binds soluble amyloid-beta peptide and inhibits cerebral amyloid deposition in amyloid-beta precursor protein (APP) transgenic mice. Cystatin C expression twice that of the endogenous mouse cystatin C was sufficient to substantially diminish amyloid-beta deposition. Thus, cystatin C has a protective role in Alzheimer's disease pathogenesis, and modulation of cystatin C concentrations may have therapeutic implications for the disease.

Battaglia F, Wang HY, Ghilardi MF, Gashi E, Quartarone A, Friedman E, Nixon RA. · City University of New York [CUNY] School of Medicine, Nathan Kline Institute, Orangeburg, New York, USA. · Biol Psychiatry. · Pubmed #17651702 No free full text.

Abstract: BACKGROUND: The aim of this study was to determine whether neocortical long-term potentiation (LTP) is deficient in patients with Alzheimer's disease (AD) and in amyloid precursor protein (APP)/presenilin-1 (PS1) mice, an AD animal model. We then ascertained whether this deficit might be paralleled by functional abnormalities of N-methyl-D-aspartate (NMDAR) glutamate receptors. METHODS: We studied neocortical LTP-like plasticity in 10 patients with mild-to-moderate AD and 10 age-matched normal controls using paired associative stimulation (PAS). We assessed neocortical (medial prefrontal cortex and primary motor cortex) and hippocampal LTP in brain slices of symptomatic APP/PS1 mice. NMDAR composition and signaling as well as synaptic calcium influx were determined in motor, prefrontal and hippocampal cortices of APP/PS1 mice. RESULTS: Both AD patients and transgenic animals showed a deficit in NMDAR-dependent forms of neocortical plasticity. Biochemical analysis showed impaired NMDAR function in symptomatic APP/PS1 mice. CONCLUSIONS: Neocortical plasticity is impaired in both patients with AD and APP/PS1 mice. The results of our biochemical studies point to impaired NMDAR function as the most likely cause for the neocortical plasticity deficit in AD.

Gandy S, Zhang YW, Ikin A, Schmidt SD, Bogush A, Levy E, Sheffield R, Nixon RA, Liao FF, Mathews PM, Xu H, Ehrlich ME. · Farber Institute for Neurosciences and the Department of Neurology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA. · J Neurochem. · Pubmed #17630980 No free full text.

Abstract: Studies in continuously cultured cells have established that familial Alzheimer's disease (FAD) mutant presenilin 1 (PS1) delays exit of the amyloid precursor protein (APP) from the trans-Golgi network (TGN). Here we report the first description of PS1-regulated APP trafficking in cerebral neurons in culture and in vivo. Using neurons from transgenic mice or a cell-free APP transport vesicle biogenesis system derived from the TGN of those neurons, we demonstrated that knocking-in an FAD-associated mutant PS1 transgene was associated with delayed kinetics of APP arrival at the cell surface. Apparently, this delay was at least partially attributable to impaired exit of APP from the TGN, which was documented in the cell-free APP transport vesicle biogenesis assay. To extend the study to APP and carboxyl terminal fragment (CTF) trafficking to cerebral neurons in vivo, we performed subcellular fractionation of brains from APP transgenic mice, some of which carried a second transgene encoding an FAD-associated mutant form of PS1. The presence of the FAD mutant PS1 was associated with a slight shift in the subcellular localization of both holoAPP and APP CTFs toward iodixanol density gradient fractions that were enriched in a marker for the TGN. In a parallel set of experiments, we used an APP : furin chimeric protein strategy to test the effect of artificially forcing TGN concentration of an APP : furin chimera that could be a substrate for beta- and gamma-cleavage. This chimeric substrate generated excess Abeta42 when compared with wildtype APP. These data indicate that the presence of an FAD-associated mutant human PS1 transgene is associated with redistribution of the APP and APP CTFs in brain neurons toward TGN-enriched fractions. The chimera experiment suggests that TGN-enrichment of a beta-/gamma-secretase substrate may play an integral role in the action of mutant PS1 to elevate brain levels of Abeta42.

Liang J, Yin C, Doong H, Fang S, Peterhoff C, Nixon RA, Monteiro MJ. · Graduate Program in Molecular Medicine, and Institute for Neurodegenerative Diseases, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201, USA. · J Cell Sci. · Pubmed #16968747 links to  free full text

Abstract: Ubiquitin regulator-X (UBX) is a discrete protein domain that binds p97/valosin-containing protein (VCP), a molecular chaperone involved in diverse cell processes, including endoplasmic-reticulum-associated protein degradation (ERAD). Here we characterize a human UBX-containing protein, UBXD2, that is highly conserved in mammals, which we have renamed erasin. Biochemical fractionation, immunofluorescence and electron microscopy, and protease protection experiments suggest that erasin is an integral membrane protein of the endoplasmic reticulum and nuclear envelope with both its N- and C-termini facing the cytoplasm or nucleoplasm. Localization of GFP-tagged deletion derivatives of erasin in HeLa cells revealed that a single 21-amino-acid sequence located near the C-terminus is necessary and sufficient for localization of erasin to the endoplasmic reticulum. Immunoprecipitation and GST-pulldown experiments confirmed that erasin binds p97/VCP via its UBX domain. Additional immunoprecipitation assays indicated that erasin exists in a complex with other p97/VCP-associated factors involved in ERAD. Overexpression of erasin enhanced the degradation of the ERAD substrate CD3delta, whereas siRNA-mediated reduction of erasin expression almost completely blocked ERAD. Erasin protein levels were increased by endoplasmic reticulum stress. Immunohistochemical staining of brain tissue from patients with Alzheimer's disease and control subjects revealed that erasin accumulates preferentially in neurons undergoing neurofibrillary degeneration in Alzheimer's disease. These results suggest that erasin may be involved in ERAD and in Alzheimer's disease.

Salehi A, Delcroix JD, Belichenko PV, Zhan K, Wu C, Valletta JS, Takimoto-Kimura R, Kleschevnikov AM, Sambamurti K, Chung PP, Xia W, Villar A, Campbell WA, Kulnane LS, Nixon RA, Lamb BT, Epstein CJ, Stokin GB, Goldstein LS, Mobley WC. · Department of Neurology and Neurological Sciences, Stanford University, Stanford, California 94305, USA. · Neuron. · Pubmed #16815330 No free full text.

Abstract: Degeneration of basal forebrain cholinergic neurons (BFCNs) contributes to cognitive dysfunction in Alzheimer's disease (AD) and Down's syndrome (DS). We used Ts65Dn and Ts1Cje mouse models of DS to show that the increased dose of the amyloid precursor protein gene, App, acts to markedly decrease NGF retrograde transport and cause degeneration of BFCNs. NGF transport was also decreased in mice expressing wild-type human APP or a familial AD-linked mutant APP; while significant, the decreases were less marked and there was no evident degeneration of BFCNs. Because of evidence suggesting that the NGF transport defect was intra-axonal, we explored within cholinergic axons the status of early endosomes (EEs). NGF-containing EEs were enlarged in Ts65Dn mice and their App content was increased. Our study thus provides evidence for a pathogenic mechanism for DS in which increased expression of App, in the context of trisomy, causes abnormal transport of NGF and cholinergic neurodegeneration.

Yu WH, Cuervo AM, Kumar A, Peterhoff CM, Schmidt SD, Lee JH, Mohan PS, Mercken M, Farmery MR, Tjernberg LO, Jiang Y, Duff K, Uchiyama Y, Näslund J, Mathews PM, Cataldo AM, Nixon RA. · Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY 10962, USA. · J Cell Biol. · Pubmed #16203860 links to  free full text

Abstract: Macroautophagy, which is a lysosomal pathway for the turnover of organelles and long-lived proteins, is a key determinant of cell survival and longevity. In this study, we show that neuronal macroautophagy is induced early in Alzheimer's disease (AD) and before beta-amyloid (Abeta) deposits extracellularly in the presenilin (PS) 1/Abeta precursor protein (APP) mouse model of beta-amyloidosis. Subsequently, autophagosomes and late autophagic vacuoles (AVs) accumulate markedly in dystrophic dendrites, implying an impaired maturation of AVs to lysosomes. Immunolabeling identifies AVs in the brain as a major reservoir of intracellular Abeta. Purified AVs contain APP and beta-cleaved APP and are highly enriched in PS1, nicastrin, and PS-dependent gamma-secretase activity. Inducing or inhibiting macroautophagy in neuronal and nonneuronal cells by modulating mammalian target of rapamycin kinase elicits parallel changes in AV proliferation and Abeta production. Our results, therefore, link beta-amyloidogenic and cell survival pathways through macroautophagy, which is activated and is abnormal in AD.