Alzheimer Disease: Apelt J

Baier M, Apelt J, Riemer C, Gültner S, Schwarz A, Bamme T, Burwinkel M, Schliebs R. · Project Neurodegenerative Diseases, Robert-Koch-Institute, Nordufer 20, 13353 Berlin, Germany. · Int J Dev Neurosci. · Pubmed #18662767 No free full text.

Abstract: Neuropathological, epidemiological and experimental data indicate a potential interrelationship between Alzheimer's disease and prion diseases. Proteolytic processing of amyloid precursor protein (APP) by beta-secretase was recently suggested to be controlled by prion protein expression. Here, we characterized the prion infection of Tg2576 mice, which overexpress the human APP(Swe) protein. Prion infection of Tg2576-mice led to an early death of the animals, which was preceded by a relatively short symptomatic stage. However, disease-associated gliosis and deposition of misfolded prion protein PrP(Sc) were identical in infected Tg2576-mice and non-transgenic littermate controls. To analyze the effect of prion infection on APP processing and generation of beta-amyloid we determined cortical levels of SDS- and formic acid (FA)-extractable forms of beta-amyloid (1-40) and (1-42) by ELISA. Formic acid-extractable Abeta (1-42) levels were 10-fold higher in infected versus uninfected Tg2576 mice whereas other forms of Abeta were essentially unaffected by the prion infection. Hence, the experimental model demonstrates that a prion infection of the CNS promotes selectively formation of FA-extractable Abeta(1-42) in Tg2576 mice.

Schliebs R, Heidel K, Apelt J, Gniezdzinska M, Kirazov L, Szutowicz A. · Paul Flechsig Institute for Brain Research, Department of Neurochemistry, University of Leipzig, Leipzig, Germany. · Brain Res. · Pubmed #17026971 No free full text.

Abstract: Increased expression of interleukin (IL)-1beta has been found in Alzheimer brain, raising the question whether plaque-associated up-regulation of IL-1beta may contribute to neurodegeneration. IL-1beta is capable to induce a number of events that also occur in Alzheimer's disease such as stimulation of the amyloidogenic pathway of amyloid precursor protein processing. However, less is known on participation of IL-1beta in specific cholinergic cell loss. To reveal whether IL-1beta affects muscarinic acetylcholine receptor (mAChR)-mediated intracellular signaling, cholinergically differentiated SH-SY5Y cells were exposed to IL-1beta for various periods of time followed by stimulation of mAChR with carbachol for 1 h, and key molecules of cholinergic signaling cascades were determined including phosphoinositide hydrolysis, DNA-binding capacity of NFkappaB and AP-1, and activity of acetylcholinesterase (AChE). Carbachol stimulation of SH-SY5Y cells dose-dependently stimulated the activation of the transcription factors NFkappaB and AP-1 as revealed by electrophoretic mobility shift assay (EMSA), while pre-exposure of SH-SY5Y cells for 24 h with 1 ng/ml IL-1beta completely suppressed the carbachol response. mAChR-mediated enhancements of AChE activity by carbachol were impaired following pre-exposure of SH-SY5Y cells with IL-1beta, already detectable at a concentration of 1 ng/ml and 1 h of exposure time. The data indicate that IL-1beta may interfere with the cholinergic signal transduction cascade by inhibiting transcription factor activation, thus providing another mechanism by which IL-1beta may induce cholinergic dysfunction in Alzheimer's disease.

Apelt J, Bigl M, Wunderlich P, Schliebs R. · Department of Neurochemistry, University of Leipzig, Paul Flechsig Institute for Brain Research, Jahnallee 59, D-04109 Leipzig, Germany. · Int J Dev Neurosci. · Pubmed #15465277 No free full text.

Abstract: The molecular mechanisms of beta-amyloidogenesis in sporadic Alzheimer's disease are still poorly understood. To reveal whether aging-associated increases in brain oxidative stress and inflammation may trigger onset or progression of beta-amyloid deposition, a transgenic mouse (Tg2576) that express the Swedish double mutation of human amyloid precursor protein (APP) was used as animal model to study the developmental pattern of markers of oxidative stress and APP processing. In Tg2576 mouse brain, cortical levels of soluble beta-amyloid (1-40) and (1-42) steadily increased with age, but significant deposition of fibrillary beta-amyloid in cortical areas did not occur before postnatal age of 10 months. The slope of increase in cerebral cortical beta-secretase (BACE1) activities in Tg2576 mice between ages of 9 and 13 months was significantly higher as compared to that of the alpha-secretase, while the expression level of BACE1 protein and mRNA did not change with age. The activities of superoxide dismutase and glutathione peroxidase in cortical tissue from Tg2576 mice steadily increased from postnatal age 9-12 months. The levels of cortical nitric oxide, and reactive nitrogen species demonstrated peak values around 9 months of age, while the level of interleukin-1beta steadily increased from postnatal month 13 onwards. The developmental temporal coincidence of increased levels of reactive nitrogen species and antioxidative enzymes with the onset of beta-amyloid plaque deposition provides further evidence that developmentally and aging-induced alterations in brain oxidative status exhibit a major factor in triggering enhanced production and deposition of beta-amyloid, and potentially predispose to Alzheimer's disease.

Blasko I, Beer R, Bigl M, Apelt J, Franz G, Rudzki D, Ransmayr G, Kampfl A, Schliebs R. · Department of Psychiatry, University Hospital of Innsbruck, Innsbruck, Austria. · J Neural Transm. · Pubmed #15057522 No free full text.

Abstract: Traumatic brain injury (TBI) is a risk factor for the development of Alzheimer's disease (AD). After a traumatic brain injury depositions of amyloid beta (Abeta) in the brain parenchyma were found. In this study we investigated the expression pattern of beta-secretase (BACE-1) in ipsi- or contralateral hippocampus and cortex following controlled cortical TBI in rats. BACE-1 mRNA levels, estimated by real time RT-PCR, were elevated 24 h post injury, and persisting up to 72 h, in the ipsi- and contralateral hippocampus and cerebral cortex as compared to the sham-treated animals (p<0.01). The TBI-induced changes in BACE-1 mRNA are due to enhanced hippocampal and cortical expression of BACE-1 mRNA in neurons and reactive astrocytes as revealed by in situ hybridization. The alterations in hippocampal BACE-1 mRNA levels are accompanied by corresponding increases in BACE-1 protein levels in ipsi- and contralateral hippocampus and ipsilateral cortex as demonstrated by Western blot analysis. In contrast, in the contralateral cortex only a weak increase of traumatically induced BACE-1 protein production was found. The activity of BACE-1 as measured by the formation of the cleavage product of amyloid beta precursor protein, transiently increased up to 48 h after injury, but returned to basal level 7 days post injury. This study demonstrates that the beta-secretase is stimulated following TBI and may suggest a mechanism for the temporal increase of Abeta levels observed in patients with brain trauma.

Klingner M, Apelt J, Kumar A, Sorger D, Sabri O, Steinbach J, Scheunemann M, Schliebs R. · Department of Neurochemistry, Paul Flechsig Institute for Brain Research, University of Leipzig, Jahnallee 59, D-04109 Leipzig, Germany. · Int J Dev Neurosci. · Pubmed #14599482 No free full text.

Abstract: Cholinergic deficits in Alzheimer's disease are accompanied by a number of alterations in other transmitter systems including glutamate, noradrenaline and serotonin, suggesting the involvement also of other neurotransmitter systems in the pathogenesis of the disease. To address the question whether beta-amyloid may contribute to these deficits, brain tissue from transgenic Tg2576 mice with Alzheimer plaque pathology at ages of 5 (still no significant plaque load) and 17 months (moderate to high cortical beta-amyloid plaque load) were examined for a number of cholinergic and non-cholinergic markers. Transgenic mice with no significant plaque load demonstrated reduced hemicholinium-3 (HCh-3) binding to choline uptake sites in anterior brain regions as compared to non-transgenic littermates, while in aged transgenic mice with high number of plaque deposits decreased HCh-3 binding levels were accompanied by increased vesicular acetylcholine transporter binding in selected cortical brain regions. In aged transgenic mice GABA(A), NMDA, AMPA, kainate, and beta-adrenergic as well 5-HT(1A)- and 5-HT(2A)-receptor binding levels were hardly affected, whereas alpha(1)- and alpha(2)-adrenoceptor binding was increased in selected cerebral cortical regions as compared to non-transgenic littermates. The development of changes in both cholinergic and non-cholinergic markers in transgenic Tg2576 mouse brain already before the onset of progressive plaque deposition provides in vivo evidence of a modulatory role of soluble beta-amyloid on cortical neurotransmission and may be referred to the deficits in learning and memory observed in these mice also before significant plaque load.

Münch G, Apelt J, Rosemarie-Kientsch-Engel, Stahl P, Lüth HJ, Schliebs R. · Neuroimmunological Cell Biology Unit, Interdisciplinary Center for Clinical Research, Leipzig, Germany. · J Neurochem. · Pubmed #12871569 No free full text.

Abstract: Increased expression and altered processing of the amyloid precursor protein (APP) and generation of beta-amyloid peptides is important in the pathogenesis of amyloid plaques in Alzheimer's disease (AD). Transgenic Tg2576 mice overexpressing the Swedish mutation of human APP exhibit beta-amyloid deposition in the neocortex and limbic areas, accompanied by gliosis and dystrophic neurites. However, murine plaques appear to be less cross-linked and the mice show a lower degree of inflammation and neurodegeneration than AD patients. 'Advanced glycation endproducts (AGEs)', formed by reaction of proteins with reactive sugars or dicarbonyl compounds, are able to cross-link proteins and to activate glial cells, and are thus contributing to plaque stability and plaque-induced inflammation in AD. In this study, we analyze the tissue distribution of AGEs and the pro-inflammatory cytokines IL-1beta and TNF-alpha in 24-month-old Tg2576 mice, and compare the AGE distribution in these mice with a younger age group (13 months old) and a typical Alzheimer's disease patient. Around 70% of the amyloid plaque cores in the 24-month-old mice are devoid of AGEs, which might explain their solubility in physiological buffers. Plaque associated glia, which express IL-1beta and TNF-alpha, contain a significant amount of AGEs, suggesting that plaques, i.e. Abeta as its major component, can induce intracellular AGE formation and the expression of the cytokines on its own. In the 13-month-old transgenic mice, AGEs staining can neither be detected in plaques nor in glial cells. In contrast, AGEs are present in high amounts in both plaques and glia in the human AD patient. The data obtained in this show interesting differences between the transgenic mouse model and AD patients, which should be considered using the transgenic approach to test therapeutical strategies to eliminate plaques or to attenuate the inflammatory response in AD.

Lüth HJ, Apelt J, Ihunwo AO, Arendt T, Schliebs R. · Paul Flechsig Institute for Brain Research, Department of Neurochemistry, University of Leipzig, Jahnallee 59, D-04109 Leipzig, Germany. · Brain Res. · Pubmed #12788508 No free full text.

Abstract: Cholinergic dysfunction is a consistent feature of Alzheimer's disease, and the interrelationship between beta-amyloid deposits, inflammation and early cholinergic cell loss is still not fully understood. To characterize the mechanisms by which beta-amyloid and pro-inflammatory cytokines may exert specific degenerating actions on cholinergic cells ultrastructural investigations by electron microscopy were performed in brain sections from transgenic Tg2576 mice that express the Swedish double mutation of the human amyloid precursor protein and progressively develop beta-amyloid plaques during aging. Both light and electron microscopical investigations of the cerebral cortex of 19-month-old transgenic mice revealed a number of pathological tissue responses in close proximity of beta-amyloid plaques, such as activated microglia, astroglial proliferation, increased number of fibrous astrocytes, brain edema, degeneration of nerve cells, dendrites and axon terminals. Ultrastructural detection of choline acetyl transferase (ChAT)-immunostaining in cerebral cortical sections of transgenic mice clearly demonstrated degeneration of ChAT-immunoreactive fibres in the environment of beta-amyloid plaques and activated glial cells suggesting a role of beta-amyloid and/or inflammation in specific degeneration of cholinergic synaptic structures.

Apelt J, Ach K, Schliebs R. · Paul Flechsig Institute for Brain Research, Department of Neurochemistry, University of Leipzig, Jahnallee 59, D-04109 Leipzig, Germany. · Neurosci Lett. · Pubmed #12633883 No free full text.

Abstract: Pathological accumulation of cortical beta-amyloid is an early and consistent feature of Alzheimer's disease. Brain level of beta-amyloid is determined both by its production and by its catabolism. Neprilysin, a zinc metalloproteinase has been suggested as potential candidate of beta-amyloid-degrading enzyme in vivo. To address the question whether pathological accumulation of beta-amyloid peptides in transgenic Tg2576 mice with Alzheimer-like pathology may affect beta-amyloid catabolism, the expression of neprilysin was studied during postnatal maturation and aging. Neprilysin protein but mRNA levels decreased in mouse cerebral cortex with age (2-22 months), independently of transgene status. Immunocytochemistry revealed few neprilysin-positive dystrophic neurites around beta-amyloid plaques and an upregulation of neprilysin in plaque-surrounding reactive astrocytes which may suggest a role of plaque-mediated astrogliosis in beta-amyloid degradation.

Bigl M, Apelt J, Eschrich K, Schliebs R. · Institute of Biochemistry, University of Leipzig, Leipzig, Germany. · J Neural Transm. · Pubmed #12541014 No free full text.

Abstract: Alzheimer's disease is associated with markedly impaired cerebral glucose metabolism as detected by reduced cortical desoxyglucose utilization, by altered activities of key glycolytic enzymes or by reduced densities of cortical glucose transporter subtypes. To determine whether formation and/or deposition of beta-amyloid plays a role in the pathology of glucose metabolism, transgenic Tg2576 mice that overexpress the Swedish mutation of the human amyloid precursor protein and demonstrate a progressive, age-related cortical and hippocampal deposition of beta-amyloid plaques, were used to study expression and activity of key enzymes of brain glycolysis (phosphofructokinase, PFK) and glyconeogenesis (fructose1,6-bisphosphatase; FbPase). Quantitative RT-PCR revealed high expression levels of both C- and M-type PFK mRNA in non-transgenic mouse cerebral cortex, whilst there was little expression of the L-type. In 24-month-old transgenic Tg2576 mouse cortex, but not in 7-, 13-, and 17-month-old mice, the copy number of PFK-C mRNA was significantly reduced in comparison to non-transgenic littermates, while the mRNA level of the other PFK isoforms and FbPase did not differ between transgenic and non-transgenic tissue samples. In situ hybridization in brain sections from aged Tg2576 mice revealed reduced PFK-C mRNA expression in beta-amyloid plaque-associated neurons and upregulation in reactive astrocytes surrounding beta-amyloid deposits. The decreased PFK-C protein level detected by Western analysis in cerebral cortical tissue from 24-month-old transgenic Tg2576 mice was accompanied by reduced enzyme activity of PFK in comparison to non-transgenic littermates. Our data demonstrate that impairment of cerebral cortical glucose metabolism occurs only due to the long-lasting high beta-amyloid burden. This results from a reduction in glycolytic activity in beta-amyloid plaque-associated neurons and a concomitant upregulation in reactive, plaque-surrounding astrocytes.

Hartlage-Rübsamen M, Zeitschel U, Apelt J, Gärtner U, Franke H, Stahl T, Günther A, Schliebs R, Penkowa M, Bigl V, Rossner S. · Department of Neurochemistry, Paul Flechsig Institute for Brain Research, University of Leipzig, Leipzig, Germany. · Glia. · Pubmed #12509807 No free full text.

Abstract: The beta-site APP-cleaving enzyme (BACE1) is a prerequisite for the generation of beta-amyloid peptides, which give rise to cerebrovascular and parenchymal beta-amyloid deposits in the brain of Alzheimer's disease patients. BACE1 is neuronally expressed in the brains of humans and experimental animals such as mice and rats. In addition, we have recently shown that BACE1 protein is expressed by reactive astrocytes in close proximity to beta-amyloid plaques in the brains of aged transgenic Tg2576 mice that overexpress human amyloid precursor protein carrying the double mutation K670N-M671L. To address the question whether astrocytic BACE1 expression is an event specifically triggered by beta-amyloid plaques or whether glial cell activation by other mechanisms also induces BACE1 expression, we used six different experimental strategies to activate brain glial cells acutely or chronically. Brain sections were processed for the expression of BACE1 and glial markers by double immunofluorescence labeling and evaluated by confocal laser scanning microscopy. There was no detectable expression of BACE1 protein by activated microglial cells of the ameboid or ramified phenotype in any of the lesion paradigms studied. In contrast, BACE1 expression by reactive astrocytes was evident in chronic but not in acute models of gliosis. Additionally, we observed BACE1-immunoreactive astrocytes in proximity to beta-amyloid plaques in the brains of aged Tg2576 mice and Alzheimer's disease patients.

Apelt J, Lessig J, Schliebs R. · Paul Flechsig Institute for Brain Research, Department of Neurochemistry, University of Leipzig, Jahnallee 59, 04109 Leipzig, Germany. · Neurosci Lett. · Pubmed #12161274 No free full text.

Abstract: To study the relationship of beta-amyloid-mediated micro- and astrogliosis and inflammation-induced proteins including intercellular adhesion molecule (ICAM-1), brain tissue from transgenic Tg2576 mice expressing the Swedish mutation of the human amyloid precursor protein were examined for ICAM-1 expression. Immunocytochemistry demonstrated a diffuse immunostaining of ICAM-1 in the corona around fibrillary beta-amyloid plaques and an upregulation of ICAM-1 in activated microglial cells located in close proximity to the plaques, an ICAM-1 distribution pattern that partly mimics the situation in the brain of Alzheimer patients. The developmental time course revealed that the rate of cortical ICAM-1 induction was somewhat behind that of the progression of beta-amyloid plaque deposition. The microglial expression of ICAM-1 is a further indicator of the presence of inflammatory reactions in aged transgenic Tg2576 mouse brain, and may be a result of plaque-mediated astrocytic interleukin-1beta upregulation.

Rossner S, Apelt J, Schliebs R, Perez-Polo JR, Bigl V. · Paul Flechsig Institute for Brain Research, Department of Neurochemistry, University of Leipzig, Jahnallee 59, D-04109 Leipzig, Germany. · J Neurosci Res. · Pubmed #11391698 No free full text.

Abstract: We measured tissue distribution and expression pattern of the beta-site amyloid precursor protein (APP)-cleaving enzyme (BACE) in the brains of transgenic Tg2576 mice that show amyloid pathology. BACE protein was expressed at high levels in brain; at lower levels in heart and liver; and at very low levels in pancreas, kidney, and thymus and was almost absent in spleen and lung when assayed by Western blot analysis. We observed strictly neuronal expression of BACE protein in the brains of nontransgenic control mice, with the most robust immunocytochemical labeling present in the cerebral cortex, hippocampal formation, thalamus, and cholinergic basal forebrain nuclei. BACE protein levels did not differ significantly between control and transgenic mice or as a result of aging. However, in the aged, 17-month-old Tg2576 mice there was robust amyloid plaque formation, and BACE protein was also present in reactive astrocytes present near amyloid plaques, as shown by double immunofluorescent labeling and confocal laser scanning microscopy. The lack of astrocytic BACE immunoreactivity in young transgenic Tg2576 mice suggests that it is not the APP overexpression but rather the amyloid plaque formation that stimulates astrocytic BACE expression in Tg2576 mice. Our data also suggest that the neuronal overexpression of APP does not induce the overexpression of its metabolizing enzyme in neurons. Alternatively, the age-dependent accumulation of amyloid plaques in the Tg2576 mice does not require increased neuronal expression of BACE. Our data support the hypothesis that neurons are the primary source of beta-amyloid peptides in brain and that astrocytic beta-amyloid generation may contribute to amyloid plaque formation at later stages or under conditions when astrocytes are activated.

Hartlage-Rübsamen M, Apelt J, Schliebs R. · Paul Flechsig Institute for Brain Research, Department of Neurochemistry, University of Leipzig, Jahnallee 59, D-04109, Leipzig, Germany. · Neurosci Lett. · Pubmed #11290390 No free full text.

Abstract: Transgenic mice (Tg2576) that express the Swedish double mutation of human amyloid precursor protein and develop Alzheimer-like beta-amyloid deposits in the aged brain, were used to study the effect of beta-amyloid deposition on expression of both neuronal (nNOS) and inducible nitric oxide synthase (iNOS) in cells surrounding beta-amyloid plaques. Nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry and double immunofluorescent labeling revealed that most of the fibrillary, thioflavine-S-positive cortical beta-amyloid deposits in 13-, 17-, and 21-month-old transgenic animals were closely associated with dystrophic nNOS-positive neurons, while nNOS-bearing neurons located more distal to plaques appeared to be unaffected. There was no significant expression of iNOS in transgenic mouse brain. The data suggest enhanced vulnerability of nNOS-containing neocortical neurons to beta-amyloid toxicity. Alternatively, expression of nNOS may also be a response to plaque-mediated damage of neurons, consistent with a neuroprotective role of nitric oxide.

Apelt J, Schliebs R. · Paul Flechsig Institute for Brain Research, Department of Neurochemistry, University of Leipzig, Jahnallee 59, D-04109, Leipzig, Germany. · Brain Res. · Pubmed #11245811 No free full text.

Abstract: To elucidate the mechanisms involved in beta-amyloid-mediated inflammation in Alzheimer's disease, transgenic Tg2576 mice containing as transgene the Swedish double mutation of human amyloid precursor protein 695, were examined for the expression pattern of various cytokines using double immunocytochemistry and laser scanning microscopy. Tg2576 mice studied at postnatal ages of 13, 16 and 19 months demonstrated an age-related accumulation of both senile and diffuse beta-amyloid plaques in neocortex and hippocampus. Reactive interleukin (IL)-1beta-immunoreactive astrocytes were found in close proximity to both fibrillary and diffuse beta-amyloid deposits detectable at very early stages of plaque development, while activated microglia appeared in and around fibrillary beta-amyloid plaques only. Subpopulations of reactive astrocytes also demonstrated immunolabeling for transforming growth factor (TGF)-beta1, TGF-beta3, and IL-10, already detectable in 13-month-old transgenic mouse brain, while a few IL-6-immunoreactive astrocytes were observed only at later stages of plaque development. The early beta-amyloid-mediated upregulation of IL-1beta, TGF-beta, and IL-10 in surrounding reactive astrocytes indicates the induction of both pro- and anti-inflammatory mechanisms. The transgenic approach used in this study may thus provide a useful tool to further disclose the in vivo mechanisms by which pro- and anti-inflammatory cytokines interact and/or contribute to the progression of Alzheimer's disease.

Bigl M, Apelt J, Luschekina EA, Lange-Dohna C, Rossner S, Schliebs R. · Institute of Biochemistry, University of Leipzig, Liebigstrasse 16, D-04103 Leipzig, Germany. · Neurosci Lett. · Pubmed #10998560 No free full text.

Abstract: On the basis of the recent cloning of the beta-secretase, the beta-site amyloid precursor protein (APP)-cleaving enzyme (BACE), (Science, 286 (1999) 735), digoxigenin-labelled riboprobes were generated to localize the cellular expression pattern of BACE mRNA in brain sections of transgenic Tg2576 mice, overexpressing the Swedish mutation of the APP695 isoform. Non-radioactive in situ hybridization in combination with immunohistochemistry to identify the cell types and beta-amyloid deposits revealed strong BACE mRNA hybridization signals in neurons of the cerebral cortex, hippocampal formation, thalamus and cholinergic basal forebrain nuclei, while astrocytes did not display any labeling. Neurons surrounding beta-amyloid deposits did not demonstrate altered expression level of BACE mRNA as compared to neurons in cortical areas that are free of beta-amyloid deposits, and the regional expression pattern of BACE mRNA did not correlate with the distribution of beta-amyloid deposits. These data suggest that high level of expression of BACE mRNA is not necessarily related to enhanced deposition of beta-amyloid plaques. To elucidate those factors that contribute to beta-amyloid plaque deposition in a particular region, the transgenic Tg2576 mouse may represent an appropriate tool.