Alzheimer Disease: Bales KR

Bales KR. · Neuroscience Discovery Research, Eli Lilly & Co., Indianapolis, IN 46285, USA. · Exp Neurol. · Pubmed #17662278 No free full text.

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Bales KR, Dodart JC, DeMattos RB, Holtzman DM, Paul SM. · Neuroscience Discovery Research, Lilly Research Laboratories Indianapolis, IN 46285, USA. · Mol Interv. · Pubmed #14993413 links to  free full text

Abstract: Despite important inroads into the molecular pathology of Alzheimer disease, effective long-term treatment for the condition remains elusive. Among the many gene products that are recognized as factors in the disease is apolipoprotein ( (apoE). The risk that specific isoforms of apoE pose with regard to Alzheimer Disease clearly varies, and so the roles that apoE plays in the brain will be crucial to a full understanding of the disease and to efforts to develop effective therapies.

Dodart JC, Mathis C, Bales KR, Paul SM. · Neuroscience Discovery Research, Eli Lilly and Company, Indianapolis, IN 46285, USA. · Genes Brain Behav. · Pubmed #12884970 No free full text.

Abstract: Small animal models that manifest many of the characteristic neuropathological and behavioral features of Alzheimer's disease (AD) have been developed and have proven of great value for studying the pathogenesis of this disorder at the molecular, cellular and behavioral levels. The great progress made in our understanding of the genetic factors that either cause or contribute to the risk of developing AD has prompted many laboratories to create transgenic (tg) mice that overexpress specific genes which cause familial forms of the disease. Several of these tg mice display neuropathological and behavioral features of AD including amyloid beta-peptide (A beta) and amyloid deposits, neuritic plaques, gliosis, synaptic alterations and signs of neurodegeneration as well as memory impairment. Despite these similarities, important differences in neuropathology and behavior between these tg mouse models and AD have also been observed, and to date no perfect animal model has emerged. Moreover, ascertaining which elements of the neuropathological and behavioral phenotype of these various strains of tg mice are relevant to that observed in AD continues to be a challenge. Here we provide a critical review of the AD-like neuropathology and behavioral phenotypes of several well-known and utilized tg mice that express human APP transgenes.

Dodart JC, Bales KR, Paul SM. · Lilly Research Laboratories, Eli Lilly and Company, Neuroscience Discovery Research, Indianapolis, IN 46285, USA. · Trends Mol Med. · Pubmed #12657428 No free full text.

Abstract: Active or passive immunization against the beta-amyloid peptide (Abeta) has been proposed as a method for preventing and/or treating Alzheimer's disease (AD). In addition to lowering brain Abeta and amyloid burden in transgenic mouse models of AD, a beneficial effect of immunization on previously characterized memory impairment(s) has also been reported in these mice. Whether these preclinical data will predict efficacy in AD patients remains to be seen. A clinical trial of active immunization (vaccination) was halted, owing to a serious adverse event (meningoencephalitis), raising questions about the safety of this approach. Two recent reports suggest that immunotherapy-based approaches to treating and preventing AD will require careful antigen and antibody selection, to maximize efficacy and minimize serious adverse events. However, given the potential efficacy of this approach, we believe that immunotherapy for AD should not be prematurely abandoned.

Holtzman DM, Bales KR, Paul SM, DeMattos RB. · Center for the Study of Nervous System Injury, Washington University School of Medicine, St Louis, MO 63110, USA. · Adv Drug Deliv Rev. · Pubmed #12453677 No free full text.

Abstract: Amyloid-beta (Abeta) is a normally soluble 39-43 amino peptide. Genetic and biochemical data strongly suggest that the conversion of Abeta from soluble to insoluble forms with high beta-sheet content and its buildup in the brain is a key step in the pathogenesis of Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). Prevention and/or reversal of this process may serve as a treatment. Methods to prevent or reverse Abeta deposition and its toxic effects would include decreasing its production, preventing its conversion to insoluble forms (e.g. inhibit beta-sheet formation) or in changing the dynamics of extracellular brain Abeta, either locally within the brain or by altering net flux of Abeta between the central nervous system (CNS) and plasma compartment. Transgenic mouse models of AD that develop age-dependent Abeta deposition, damage to the neuropil, and behavioral deficits have enabled researchers to test whether different manipulations can influence these AD-like changes. Recently, active immunization with different forms of the Abeta peptide has been shown to decrease brain Abeta deposition and improve cognitive performance in mouse models of AD. Certain peripherally administered anti-Abeta antibodies have similar effects. The mechanism(s) by which anti-Abeta antibodies result in these effects is just beginning to be elucidated. Abeta-related immune therapies in humans are an exciting new area of AD research. Understanding their detailed mechanism(s) of action and their potential usefulness awaits the results of future animal and human studies.

Brendza RP, Bales KR, Paul SM, Holtzman DM. · Center for the Study of Nervous System Injury, Washington University School of Medicine, St Louis, MO 63110, USA. · Mol Psychiatry. · Pubmed #11840304 links to  free full text

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Zhao L, Lin S, Bales KR, Gelfanova V, Koger D, Delong C, Hale J, Liu F, Hunter JM, Paul SM. · Neuroscience Discovery Research and Integrative Biology, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285, USA. · J Neurosci. · Pubmed #19295164 No free full text.

Abstract: Recent studies suggest that bone marrow-derived macrophages can effectively reduce beta-amyloid (Abeta) deposition in brain. To further elucidate the mechanisms by which macrophages degrade Abeta, we cultured murine macrophages on top of Abeta plaque-bearing brain sections from transgenic mice expressing PDAPP [human amyloid precursor protein (APP) with the APP(717V>F) mutation driven by the platelet-derived growth factor promoter]. Using this ex vivo assay, we found that macrophages from wild-type mice very efficiently degrade both soluble and insoluble Abeta in a time-dependent manner and markedly eliminate thioflavine-S positive amyloid deposits. Because macrophages express and secrete apolipoprotein E (apoE), we compared the efficiency of Abeta degradation by macrophages prepared from apoE-deficient mice or mice expressing human apoE2, apoE3, or apoE4. Macrophages expressing apoE2 were more efficient at degrading Abeta than apoE3-expressing, apoE4-expressing, or apoE-deficient macrophages. Moreover, macrophage-induced degradation of Abeta was effectively blocked by an anti-apoE antibody and receptor-associated protein, an antagonist of the low-density lipoprotein (LDL) receptor family, suggesting involvement of LDL receptors. Measurement of matrix metalloproteinase-9 (MMP-9) activity in the media from human apoE-expressing macrophages cocultured with Abeta-containing brain sections revealed greater levels of MMP-9 activity in apoE2-expressing than in either apoE3- or apoE4-expressing macrophages. Differences in MMP-9 activity appear to contribute to the isoform-specific differences in Abeta degradation by macrophages. These apoE isoform-dependent effects of macrophages on Abeta degradation suggest a novel "peripheral" mechanism for Abeta clearance from brain that may also, in part, explain the isoform-dependent effects of apoE in determining the genetic risk for Alzheimer's disease.

Rohe M, Carlo AS, Breyhan H, Sporbert A, Militz D, Schmidt V, Wozny C, Harmeier A, Erdmann B, Bales KR, Wolf S, Kempermann G, Paul SM, Schmitz D, Bayer TA, Willnow TE, Andersen OM. · Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany. · J Biol Chem. · Pubmed #18362153 links to  free full text

Abstract: Sortilin-related receptor with A-type repeats (SORLA) is a sorting receptor that impairs processing of amyloid precursor protein (APP) to soluble (s) APP and to the amyloid beta-peptide in cultured neurons and is poorly expressed in patients with Alzheimer disease (AD). Here, we evaluated the consequences of Sorla gene defects on brain anatomy and function using mouse models of receptor deficiency. In line with a protective role for SORLA in APP metabolism, lack of the receptor results in increased amyloidogenic processing of endogenous APP and in aggravated plaque deposition when introduced into PDAPP mice expressing mutant human APP. Surprisingly, increased levels of sAPP caused by receptor deficiency correlate with pro-found stimulation of neuronal ERK signaling and with enhanced neurogenesis, providing in vivo support for neurotrophic functions of sAPP. Our data document a role for SORLA not only in control of plaque burden but also in APP-dependent neuronal signaling and suggest a molecular explanation for increased neurogenesis observed in some AD patients.

Wahrle SE, Jiang H, Parsadanian M, Kim J, Li A, Knoten A, Jain S, Hirsch-Reinshagen V, Wellington CL, Bales KR, Paul SM, Holtzman DM. · Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. · J Clin Invest. · Pubmed #18202749 links to  free full text

Abstract: APOE genotype is a major genetic risk factor for late-onset Alzheimer disease (AD). ABCA1, a member of the ATP-binding cassette family of active transporters, lipidates apoE in the CNS. Abca1(-/-) mice have decreased lipid associated with apoE and increased amyloid deposition in several AD mouse models. We hypothesized that mice overexpressing ABCA1 in the brain would have increased lipidation of apoE-containing lipoproteins and decreased amyloid deposition. To address these hypotheses, we created PrP-mAbca1 Tg mice that overexpress mouse Abca1 throughout the brain under the control of the mouse prion promoter. We bred the PrP-mAbca1 mice to the PDAPP AD mouse model, a transgenic line overexpressing a mutant human amyloid precursor protein. PDAPP/Abca1 Tg mice developed a phenotype remarkably similar to that seen in PDAPP/Apoe(-/-) mice: there was significantly less amyloid beta-peptide (Abeta) deposition, a redistribution of Abeta to the hilus of the dentate gyrus in the hippocampus, and an almost complete absence of thioflavine S-positive amyloid plaques. Analyses of CSF from PrP-mAbca1 Tg mice and media conditioned by PrP-mAbca1 Tg primary astrocytes demonstrated increased lipidation of apoE-containing particles. These data support the conclusions that increased ABCA1-mediated lipidation of apoE in the CNS can reduce amyloid burden and that increasing ABCA1 function may have a therapeutic effect on AD.

Costa DA, Cracchiolo JR, Bachstetter AD, Hughes TF, Bales KR, Paul SM, Mervis RF, Arendash GW, Potter H. · Johnnie B. Byrd Sr. Alzheimer's Center and Research Institute, Tampa, FL 33647, USA. · Neurobiol Aging. · Pubmed #16730391 No free full text.

Abstract: Lifelong cognitive stimulation is associated with a lower risk of Alzheimer's disease (AD), but causality is difficult to prove. We therefore sought to investigate the preventative potential of environmental enrichment (EE) using mice expressing both human mutant presenilin-1 and the amyloid precursor protein (PS1/PDAPP). At weaning, mice were placed into either an enriched or standard housing environment. Behavioral testing at 4.5-6 months showed that environmentally enriched PS1/PDAPP mice outperformed mice in standard housing, and were behaviorally indistinguishable from non-transgenic mice across multiple cognitive domains. PS1/PDAPP mice exposed to both environmental enrichment and behavioral testing, but not to EE alone, showed 50% less brain beta-amyloid without improved dendritic morphology. Microarray analysis revealed large enrichment-induced changes in hippocampal expression of genes/proteins related to Abeta sequestration and synaptic plasticity. These results indicate that EE protects against cognitive impairment in AD transgenic mice through a dual mechanism, including both amyloid dependent and independent mechanisms.

Bales KR, Tzavara ET, Wu S, Wade MR, Bymaster FP, Paul SM, Nomikos GG. · Neuroscience Discovery Research, Eli Lilly and Company, Indianapolis, Indiana 46285, USA. · J Clin Invest. · Pubmed #16498501 links to  free full text

Abstract: Disruption of cholinergic neurotransmission contributes to the memory impairment that characterizes Alzheimer disease (AD). Since the amyloid cascade hypothesis of AD pathogenesis postulates that amyloid beta (A beta) peptide accumulation in critical brain regions also contributes to memory impairment, we assessed cholinergic function in transgenic mice where the human A beta peptide is overexpressed. We first measured hippocampal acetylcholine (ACh) release in young, freely moving PDAPP mice, a well-characterized transgenic mouse model of AD, and found marked A beta-dependent alterations in both basal and evoked ACh release compared with WT controls. We also found that A beta could directly interact with the high-affinity choline transporter which may impair steady-state and on-demand ACh release. Treatment of PDAPP mice with the anti-A beta antibody m266 rapidly and completely restored hippocampal ACh release and high-affinity choline uptake while greatly reducing impaired habituation learning that is characteristic of these mice. Thus, soluble "cholinotoxic" species of the A beta peptide can directly impair cholinergic neurotransmission in PDAPP mice leading to memory impairment in the absence of overt neurodegeneration. Treatment with certain anti-A beta antibodies may therefore rapidly reverse this cholinergic dysfunction and relieve memory deficits associated with early AD.

Cirrito JR, Yamada KA, Finn MB, Sloviter RS, Bales KR, May PC, Schoepp DD, Paul SM, Mennerick S, Holtzman DM. · Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. · Neuron. · Pubmed #16364896 No free full text.

Abstract: Aggregation of the amyloid-beta (Abeta) peptide in the extracellular space of the brain is central to Alzheimer's disease pathogenesis. Abeta aggregation is concentration dependent and brain region specific. Utilizing in vivo microdialysis concurrently with field potential recordings, we demonstrate that Abeta levels in the brain interstitial fluid are dynamically and directly influenced by synaptic activity on a timescale of minutes to hours. Using an acute brain slice model, we show that the rapid effects of synaptic activity on Abeta levels are primarily related to synaptic vesicle exocytosis. These results suggest that synaptic activity may modulate a neurodegenerative disease process, in this case by influencing Abeta metabolism and ultimately region-specific Abeta deposition. The findings also have important implications for treatment development.

Cirrito JR, Deane R, Fagan AM, Spinner ML, Parsadanian M, Finn MB, Jiang H, Prior JL, Sagare A, Bales KR, Paul SM, Zlokovic BV, Piwnica-Worms D, Holtzman DM. · Department of Neurology, Washington University Medical School, St. Louis, Missouri 63110, USA. · J Clin Invest. · Pubmed #16239972 links to  free full text

Abstract: Accumulation of amyloid-beta (Abeta) within extracellular spaces of the brain is a hallmark of Alzheimer disease (AD). In sporadic, late-onset AD, there is little evidence for increased Abeta production, suggesting that decreased elimination from the brain may contribute to elevated levels of Abeta and plaque formation. Efflux transport of Abeta across the blood-brain barrier (BBB) contributes to Abeta removal from the brain. P-glycoprotein (Pgp) is highly expressed on the luminal surface of brain capillary endothelial cells and contributes to the BBB. In Pgp-null mice, we show that [I]Abeta40 and [I]Abeta42 microinjected into the CNS clear at half the rate that they do in WT mice. When amyloid precursor protein-transgenic (APP-transgenic) mice were administered a Pgp inhibitor, Abeta levels within the brain interstitial fluid significantly increased within hours of treatment. Furthermore, APP-transgenic, Pgp-null mice had increased levels of brain Abeta and enhanced Abeta deposition compared with APP-transgenic, Pgp WT mice. These data establish a direct link between Pgp and Abeta metabolism in vivo and suggest that Pgp activity at the BBB could affect risk for developing AD as well as provide a novel diagnostic and therapeutic target.

Wahrle SE, Jiang H, Parsadanian M, Hartman RE, Bales KR, Paul SM, Holtzman DM. · Program in Neurosciences, Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. · J Biol Chem. · Pubmed #16207708 links to  free full text

Abstract: Apolipoprotein E (apoE) genotype has a major influence on the risk for Alzheimer disease (AD). Different apoE isoforms may alter AD pathogenesis via their interactions with the amyloid beta-peptide (Abeta). Mice lacking the lipid transporter ABCA1 were found to have markedly decreased levels and lipidation of apoE in the central nervous system. We hypothesized that if Abca1-/- mice were bred to the PDAPP mouse model of AD, PDAPP Abca1-/ mice would have a phenotype similar to that of PDAPP Apoe+/- and PDAPP Apoe-/- mice, which develop less amyloid deposition than PDAPP Apoe+/+ mice. In contrast to this prediction, 12-month-old PDAPP Abca -/- mice had significantly higher levels of hippocampal Abeta, and cerebral amyloid angiopathy was significantly more common compared with PDAPP Abca1+/+ mice. Amyloid precursor protein (APP) C-terminal fragments were not different between Abca1 genotypes prior to plaque deposition in 3-month-old PDAPP mice, suggesting that deletion of Abca1 did not affect APP processing or Abeta production. As expected, 3-month-old PDAPP Abca1-/- mice had decreased apoE levels, but they also had a higher percentage of carbonate-insoluble apoE, suggesting that poorly lipidated apoE is less soluble in vivo. We also found that 12-month-old PDAPP Abca1-/- mice had a higher percentage of carbonate-insoluble apoE and that apoE deposits co-localize with amyloid plaques, demonstrating that poorly lipidated apoE co-deposits with insoluble Abeta. Together, these data suggest that despite substantially lower apoE levels, poorly lipidated apoE produced in the absence of ABCA1 is strongly amyloidogenic in vivo.

Andersen OM, Reiche J, Schmidt V, Gotthardt M, Spoelgen R, Behlke J, von Arnim CA, Breiderhoff T, Jansen P, Wu X, Bales KR, Cappai R, Masters CL, Gliemann J, Mufson EJ, Hyman BT, Paul SM, Nykjaer A, Willnow TE. · Max Delbrueck Center for Molecular Medicine, D-13125 Berlin, Germany. · Proc Natl Acad Sci U S A. · Pubmed #16174740 links to  free full text

Abstract: sorLA (Sorting protein-related receptor) is a type-1 membrane protein of unknown function that is expressed in neurons. Its homology to sorting receptors that shuttle between the plasma membrane, endosomes, and the Golgi suggests a related function in neuronal trafficking processes. Because expression of sorLA is reduced in the brain of patients with Alzheimer's disease (AD), we tested involvement of this receptor in intracellular transport and processing of the amyloid precursor protein (APP) to the amyloid beta-peptide (Abeta), the principal component of senile plaques. We demonstrate that sorLA interacts with APP in vitro and in living cells and that both proteins colocalize in endosomal and Golgi compartments. Overexpression of sorLA in neurons causes redistribution of APP to the Golgi and decreased processing to Abeta, whereas ablation of sorLA expression in knockout mice results in increased levels of Abeta in the brain similar to the situation in AD patients. Thus, sorLA acts as a sorting receptor that protects APP from processing into Abeta and thereby reduces the burden of amyloidogenic peptide formation. Consequently, reduced receptor expression in the human brain may increase Abeta production and plaque formation and promote spontaneous AD.

Fryer JD, Demattos RB, McCormick LM, O'Dell MA, Spinner ML, Bales KR, Paul SM, Sullivan PM, Parsadanian M, Bu G, Holtzman DM. · Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. · J Biol Chem. · Pubmed #15888448 links to  free full text

Abstract: Apolipoprotein E (apoE), a chaperone for the amyloid beta (Abeta) peptide, regulates the deposition and structure of Abeta that deposits in the brain in Alzheimer disease (AD). The primary apoE receptor that regulates levels of apoE in the brain is unknown. We report that the low density lipoprotein receptor (LDLR) regulates the cellular uptake and central nervous system levels of astrocyte-derived apoE. Cells lacking LDLR were unable to appreciably endocytose astrocyte-secreted apoE-containing lipoprotein particles. Moreover, cells overexpressing LDLR showed a dramatic increase in apoE endocytosis and degradation. We also found that LDLR knock-out (Ldlr-/-) mice had a significant, approximately 50% increase in the level of apoE in the cerebrospinal fluid and extracellular pools of the brain. However, when the PDAPP mouse model of AD was bred onto an Ldlr-/- background, we did not observe a significant change in brain Abeta levels either before or after the onset of Abeta deposition. Interestingly, human APOE3 or APOE4 (but not APOE2) knock-in mice bred on an Ldlr-/- background had a 210% and 380% increase, respectively, in the level of apoE in cerebrospinal fluid. These results demonstrate that central nervous system levels of both human and murine apoE are directly regulated by LDLR. Although the increase in murine apoE caused by LDLR deficiency was not sufficient to affect Abeta levels or deposition by 10 months of age in PDAPP mice, it remains a possibility that the increase in human apoE3 and apoE4 levels caused by LDLR deficiency will affect this process and could hold promise for therapeutic targets in AD.

Fryer JD, Simmons K, Parsadanian M, Bales KR, Paul SM, Sullivan PM, Holtzman DM. · Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. · J Neurosci. · Pubmed #15772340 links to  free full text

Abstract: Alzheimer's disease (AD) is characterized by the aggregation and deposition of the normally soluble amyloid-beta (Abeta) peptide in the extracellular spaces of the brain as parenchymal plaques and in the walls of cerebral vessels as cerebral amyloid angiopathy (CAA). CAA is a common cause of brain hemorrhage and is found in most patients with AD. As in AD, the epsilon4 allele of the apolipoprotein E (apoE) gene (APOE) is a risk factor for CAA. To determine the effect of human apoE on CAA in vivo, we bred human APOE3 and APOE4 "knock-in" mice to a transgenic mouse model (Tg2576) that develops amyloid plaques as well as CAA. The expression of both human apoE isoforms resulted in a delay in Abeta deposition of several months relative to murine apoE. Tg2576 mice expressing the more fibrillogenic murine apoE develop parenchymal amyloid plaques and CAA by 9 months of age. At 15 months of age, the expression of human apoE4 led to substantial CAA with very few parenchymal plaques, whereas the expression of human apoE3 resulted in almost no CAA or parenchymal plaques. Additionally, young apoE4-expressing mice had an elevated ratio of Abeta 40:42 in brain extracellular pools and a lower 40:42 ratio in CSF, suggesting that apoE4 results in altered clearance and transport of Abeta species within different brain compartments. These findings demonstrate that, once Abeta fibrillogenesis occurs, apoE4 favors the formation of CAA over parenchymal plaques and suggest that molecules or treatments that increase the ratio of Abeta 40:42 may favor the formation of CAA versus parenchymal plaques.

Brendza RP, Bacskai BJ, Cirrito JR, Simmons KA, Skoch JM, Klunk WE, Mathis CA, Bales KR, Paul SM, Hyman BT, Holtzman DM. · Department of Neurology and Hope Center for Neurological Disorders, Washington University School of Medicine, St. Louis, Missouri 63110, USA. · J Clin Invest. · Pubmed #15668737 links to  free full text

Abstract: Neuritic plaques are a defining feature of Alzheimer disease (AD) pathology. These structures are composed of extracellular accumulations of amyloid-beta peptide (Abeta) and other plaque-associated proteins, surrounded by large, swollen axons and dendrites (dystrophic neurites) and activated glia. Dystrophic neurites are thought to disrupt neuronal function, but whether this damage is static, dynamic, or reversible is unknown. To address this, we monitored neuritic plaques in the brains of living PDAPP;Thy-1:YFP transgenic mice, a model that develops AD-like pathology and also stably expresses yellow fluorescent protein (YFP) in a subset of neurons in the brain. Using multiphoton microscopy, we observed and monitored amyloid through cranial windows in PDAPP;Thy-1:YFP double-transgenic mice using the in vivo amyloid-imaging fluorophore methoxy-X04, and individual YFP-labeled dystrophic neurites by their inherent fluorescence. In vivo studies using this system suggest that amyloid-associated dystrophic neurites are relatively stable structures in PDAPP;Thy-1:YFP transgenic mice over several days. However, a significant reduction in the number and size of dystrophic neurites was seen 3 days after Abeta deposits were cleared by anti-Abeta antibody treatment. This analysis suggests that ongoing axonal and dendritic damage is secondary to Abeta and is, in part, rapidly reversible.

Costa DA, Nilsson LN, Bales KR, Paul SM, Potter H. · Department of Biochemistry and Molecular Biology and Suncoast Gerontology Center, University of South Florida, Tampa, FL 33620, USA. · J Alzheimers Dis. · Pubmed #15505373 No free full text.

Abstract: To determine the role of apolipoprotein E (apoE) in the deposition of different forms of Alzheimer amyloid deposit, we studied mice expressing both mutant human amyloid beta-protein precursor (AbetaPP) and presenilin 1 (PS1) that, in addition, were either normal or knocked-out for apoE. By 7 months of age, extensive deposits of amorphous amyloid beta (Abeta) had developed equally in both lines, indicating that, when present in high amounts, Abeta alone is sufficient for such deposition to occur. In contrast, filamentous, thioflavine S-positive amyloid deposition in AbetaPP/PS mice was catalyzed at least 3000 fold by apoE. Electron micrographs further illustrated the filamentous nature of Abeta deposits in mice expressing apoE. These and other behavior data indicate that the primary function of apoE in Alzheimer's disease is to promote the polymerization of Abeta into mature, beta pleated sheet filaments, a process that is necessary for inducing cognitive decline. Thus, preventing apoE from binding to Abeta may prove to be an effective means of therapeutic intervention.

Fagan AM, Christopher E, Taylor JW, Parsadanian M, Spinner M, Watson M, Fryer JD, Wahrle S, Bales KR, Paul SM, Holtzman DM. · Department of Neurology and Center for the Study of Nervous System Injury, Alzheimer's Disease Research Center, Washington University School of Medicine, 660 S. Euclid Ave., Box 8111, St. Louis, MO 63110, USA. · Am J Pathol. · Pubmed #15466405 links to  free full text

Abstract: Epidemiological studies suggest links between cholesterol metabolism and Alzheimer's disease (AD), with hypercholesterolemia associated with increased AD risk, and use of cholesterol-lowering drugs associated with decreased risk. Animal models using cholesterol-modifying dietary or pharmacological interventions demonstrate similar findings. Proposed mechanisms include effects of cholesterol on the metabolism of amyloid-beta (Abeta), the protein that deposits in AD brain. To investigate the effect of genetic alterations in plasma cholesterol on Abeta pathology, we crossed the PDAPP transgenic mouse model of AD-like cerebral amyloidosis to apolipoprotein AI-null mice that have markedly reduced plasma cholesterol levels due to a virtual absence of high density lipoproteins, the primary lipoprotein in mice. Interestingly and in contrast to models using non-physiological high fat diets or cholesterol-lowering drugs to modify plasma cholesterol, we observed no differences in Abeta pathology in PDAPP mice of the various apoAI genotypes despite robust differences in plasma cholesterol levels between the groups. Absence of apoAI also resulted in reductions in brain but not cerebrospinal fluid cholesterol, but had no effect on brain apolipoprotein E levels. These and other data suggest that it is perhaps the level of brain apolipoprotein E, not cholesterol per se, that plays a primary role in brain Abeta metabolism.

Nilsson LN, Arendash GW, Leighty RE, Costa DA, Low MA, Garcia MF, Cracciolo JR, Rojiani A, Wu X, Bales KR, Paul SM, Potter H. · Department of Biochemistry and Molecular Biology, Suncoast Gerontology Center, University of South Florida, 12901 Bruce B. Downs Blvd., Tampa, FL 33612, USA. · Neurobiol Aging. · Pubmed #15312961 No free full text.

Abstract: Biochemical and genetic studies indicate that the inflammatory proteins, apolipoprotein E (ApoE) and alpha(1)-antichymotrypsin (ACT) are important in the pathogenesis of Alzheimer's disease (AD). Using several lines of multiply transgenic/knockout mice we show here that murine ApoE and human ACT separately and synergistically facilitate both diffuse A beta immunoreactive and fibrillar amyloid deposition and thus also promote cognitive impairment in aged PDAPP(V717F) mice. The degree of cognitive impairment is highly correlated with the ApoE- and ACT-dependent hippocampal amyloid burden, with PDAPP mice lacking ApoE and ACT having little amyloid and little learning disability. A analysis of young mice before the onset of amyloid formation shows that steady-state levels of monomeric A beta peptide are unchanged by ApoE or ACT. These data suggest that the process or product of amyloid formation is more critical than monomeric A beta for the neurological decline in AD, and that the risk factors ApoE and ACT participate primarily in disease processes downstream of APP processing.

Leighty RE, Nilsson LN, Potter H, Costa DA, Low MA, Bales KR, Paul SM, Arendash GW. · Memory and Aging Research Laboratory, SCA 110, University of South Florida, Tampa, FL 33620, USA. · Behav Brain Res. · Pubmed #15219712 No free full text.

Abstract: Behavioral assessment of genetically-manipulated mouse lines for Alzheimer's disease has become an important index for determining the efficacy of therapeutic interventions and examining disease pathogenesis. However, the potential for higher level statistical analyses to assist in these goals remains largely unexplored. The present study thus involved multimetric statistical analyses of behavioral and beta-amyloid (Abeta) deposition measures from four PDAPP-derived transgenic mouse lines that differ in extent of Abeta deposition. For all four lines, multiple behavioral measures obtained from a comprehensive task battery administered at 15-16 months of age were collectively examined by correlation, factor, and discriminant function analyses. In addition, both compact and total beta-amyloid (Abeta) histologic measures were determined from the same animals. Widespread intra- and inter-task correlations were evident, with impairment in all three water tasks (Morris maze, platform recognition, and radial arm water maze) correlating extensively with Abeta deposition in hippocampus and cerebral cortex. By elucidating the underlying relationships among measures, factor analysis revealed a single primary factor (Factor 1) that loaded most cognitive measures, particularly those for working memory and recognition. Abeta deposition measures loaded exclusively on this primary factor. In individual animals, only factor scores derived from this primary factor were correlated with Abeta deposition. Both of these findings again underscore the association between cognitive impairment and Abeta deposition. Finally, discriminant function analysis (step-wise forward method) was able to distinguish between all four AD transgenic lines based on behavioral performance alone, as well as when Abeta deposition measures were included. Our results demonstrate the utility of higher level, multimetric analysis of behavioral measures from AD transgenic mice. Analyses such as these will be very beneficial for the functional evaluation of therapeutic interventions against AD and for finding behavioral measures that can serve as predictors of pathology.

Koistinaho M, Lin S, Wu X, Esterman M, Koger D, Hanson J, Higgs R, Liu F, Malkani S, Bales KR, Paul SM. · Neuroscience Discovery Research, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285, USA. · Nat Med. · Pubmed #15195085 No free full text.

Abstract: We have previously shown that apolipoprotein E (Apoe) promotes the formation of amyloid in brain and that astrocyte-specific expression of APOE markedly affects the deposition of amyloid-beta peptides (Abeta) in a mouse model of Alzheimer disease. Given the capacity of astrocytes to degrade Abeta, we investigated the potential role of Apoe in this astrocyte-mediated degradation. In contrast to cultured adult wild-type mouse astrocytes, adult Apoe(-/-) astrocytes do not degrade Abeta present in Abeta plaque-bearing brain sections in vitro. Coincubation with antibodies to either Apoe or Abeta, or with RAP, an antagonist of the low-density lipoprotein receptor family, effectively blocks Abeta degradation by astrocytes. Phase-contrast and confocal microscopy show that Apoe(-/-) astrocytes do not respond to or internalize Abeta deposits to the same extent as do wild-type astrocytes. Thus, Apoe seems to be important in the degradation and clearance of deposited Abeta species by astrocytes, a process that may be impaired in Alzheimer disease.

Brendza RP, Simmons K, Bales KR, Paul SM, Goldberg MP, Holtzman DM. · Center for the Study of Nervous System Injury, Washington University School of Medicine, St. Louis, MO 63110, USA. · Neurobiol Aging. · Pubmed #14643378 No free full text.

Abstract: Neuritic plaques are one of the defining neuropathological features of Alzheimer's disease (AD). These structures are composed of a buildup of fibrils of the amyloid-beta (Abeta) peptide (amyloid) surrounded by activated glial cells and degenerating nerve processes (dystrophic neurites). To study neuritic plaques and possible abnormalities associated with dendrites, axons, and synaptic structures, we have developed an acute slice preparation model using PDAPP, yellow fluorescent protein (YFP) double transgenic mice (a mouse model with AD-like pathology that stably expresses YFP in a subset of neurons in the brain). With laser scanning confocal microscopy, we have imaged living brain slices from PDAPP, YFP double transgenic mice as old as 20 months and have been able to visualize axons, dendrites, dendritic spines, and dystrophic neurites for many hours. Our initial studies suggest that dystrophic axons and dendrites within neuritic plaques are fairly stable structures in the absence of exogenous perturbations. This acute slice preparation model should prove to be a useful tool to explore the pathophysiology of Abeta-related axonal, dendritic, and synaptic dysfunction.

Cirrito JR, May PC, O'Dell MA, Taylor JW, Parsadanian M, Cramer JW, Audia JE, Nissen JS, Bales KR, Paul SM, DeMattos RB, Holtzman DM. · Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. · J Neurosci. · Pubmed #14523085 links to  free full text

Abstract: Soluble amyloid-beta (Abeta) peptide converts to structures with high beta-sheet content in Alzheimer's disease (AD). Soluble Abeta is released by neurons into the brain interstitial fluid (ISF), in which it can convert into toxic aggregates. Because assessment of ISF Abeta levels may provide unique insights into Abeta metabolism and AD, an in vivo microdialysis technique was developed to measure it. Our Abeta microdialysis technique was validated ex vivo with human CSF and then in vivo in awake, freely moving mice. Using human amyloid precursor protein (APP) transgenic mice, we found that, before the onset of AD-like pathology, ISF Abeta in hippocampus and cortex correlated with levels of APP in those tissues. After the onset of Abeta deposition, significant changes in the ISF Abeta40/Abeta42 ratio developed without changes in Abeta1-x. These changes differed from changes seen in tissue lysates from the same animals. By rapidly inhibiting Abeta production, we found that ISF Abeta half-life was short ( approximately 2 hr) in young mice but was twofold longer in mice with Abeta deposits. This increase in half-life, without an increase in steady-state levels, suggests that inhibition of Abeta synthesis reveals a portion of the insoluble Abeta pool that is in dynamic equilibrium with ISF Abeta. This now measurable in vivo pool is a likely target for new diagnostic and therapeutic strategies.