Liposomal Carrier Conjugated to APP-Derived Peptide for Brain Cancer Treatment.

Brain tumors are hard to treat with the currently available therapy. The major obstacle in the treatment of brain tumors is the lack of therapeutic strategies capable to penetrate the blood-brain barrier (BBB). The BBB is an endothelial interface that separates the brain from the circulatory blood system and prevents the exposure of the central nervous system (CNS) to circulating toxins and potentially harmful compounds. Unfortunately, the BBB prevents also the penetration of therapeutic compounds into the brain. We present here a drug-delivery liposomal carrier, conjugated to a peptide inserted in the liposomal membrane, which is putatively recognized by BBB transporters. The peptide is a short sequence of 5 amino acids (RERMS) present in the amyloid precursor protein (APP). This APP-targeted liposomal system was designed specifically for transporting compounds with anti-cancer activity via the BBB into the brain in an effective manner. This drug-delivery liposomal carrier loaded with the anti-cancer compounds temozolomide (TMZ), curcumin, and doxorubicin crossed the BBB in an in vitro model as well as in vivo (mice model). In the in vitro model, the targeted liposomes crossed the BBB model fourfold higher than the non-targeted liposomes. Labeled targeted liposomes penetrated the brain in vivo 35% more than non-targeted liposomes. Treatment of mice that underwent intracranial injection of human U87 glioblastoma, with the targeted liposomes loaded with the three tested anti-cancer agents, delayed the tumor growth and prolonged the mice survival in a range of 45% -70%. It appears that the targeted liposomal drug-delivery system enables better therapeutic efficacy in a SCID mouse model of glioblastoma compared to the corresponding non-targeted liposomes and the free compounds.

Transmission of amyloid-ß protein pathology from cadaveric pituitary growth hormone.

We previously reported1 the presence of amyloid-ß protein (Aß) deposits in individuals with Creutzfeldt-Jakob disease (CJD) who had been treated during childhood with human cadaveric pituitary-derived growth hormone (c-hGH) contaminated with prions. The marked deposition of parenchymal and vascular Aß in these relatively young individuals with treatment-induced (iatrogenic) CJD (iCJD), in contrast to other prion-disease patients and population controls, allied with the ability of Alzheimer's disease brain homogenates to seed Aß deposition in laboratory animals, led us to argue that the implicated c-hGH batches might have been contaminated with Aß seeds as well as with prions. However, this was necessarily an association, and not an experimental, study in humans and causality could not be concluded. Given the public health importance of our hypothesis, we proceeded to identify and biochemically analyse archived vials of c-hGH. Here we show that certain c-hGH batches to which patients with iCJD and Aß pathology were exposed have substantial levels of Aß40, Aß42 and tau proteins, and that this material can seed the formation of Aß plaques and cerebral Aß-amyloid angiopathy in intracerebrally inoculated mice expressing a mutant, humanized amyloid precursor protein. These results confirm the presence of Aß seeds in archived c-hGH vials and are consistent with the hypothesized iatrogenic human transmission of Aß pathology. This experimental confirmation has implications for both the prevention and the treatment of Alzheimer's disease, and should prompt a review of the risk of iatrogenic transmission of Aß seeds by medical and surgical procedures long recognized to pose a risk of accidental prion transmission2,3.

Effects of Lignans from Schisandra chinensis Rattan Stems against Aß1-42-Induced Memory Impairment in Rats and Neurotoxicity in Primary Neuronal Cells.

Oxidative stress, which is caused by Amyloid-ß deposition in brain, plays an important role in Alzheimer's disease. In this study, we found that lignans from Schisandra chinensis rattan stems (rsSCH-L) could reduce the escape latency and the distance travelled by the Aß1-42 injected rats while the crossing platform time was enhanced in the Morris water maze test. Further research demonstrated that lignans from rsSCH-L attenuated Aß1-42-induced neuronal cell injury by increasing the content of SOD and GSH-Px and decreasing the levels of LDH, ROS, and MDA. Moreover, rsSCH-L also inhibited the apoptosis of primary neuronal cells. The mechanisms of the apoptosis were related with the downregulation of caspase-3, caspase-8, Bax, and upregulation of Bcl-2. Taken together, the results show that rsSCH-L can improve cognitive ability in vivo. Meanwhile rsSCH-L exhibit a neuroprotective environment against oxidative stress and apoptosis in vitro. Therefore, rsSCH-L may be a potential therapeutic agent for this neurodegenerative disease.

Mutant APP and amyloid beta-induced defective autophagy, mitophagy, mitochondrial structural and functional changes and synaptic damage in hippocampal neurons from Alzheimer's disease.

The purpose of our study was to determine the toxic effects of hippocampal mutant APP (mAPP) and amyloid beta (Aß) in human mAPP complementary DNA (cDNA) transfected with primary mouse hippocampal neurons (HT22). Hippocampal tissues are the best source of studying learning and memory functions in patients with Alzheimer's disease (AD) and healthy controls. However, investigating immortalized hippocampal neurons that express AD proteins provide an excellent opportunity for drug testing. Using quantitative reverse transcriptase-polymerase chain reaction, immunoblotting & immunofluorescence and transmission electron microscopy, we assessed messenger RNA (mRNA) and protein levels of synaptic, autophagy, mitophagy, mitochondrial dynamics, biogenesis, dendritic protein MAP2 and assessed mitochondrial number and length in mAPP-HT22 cells that express Swedish/Indiana mutations. Mitochondrial function was assessed by measuring the levels of hydrogen peroxide, lipid peroxidation, cytochrome c oxidase activity and mitochondrial adenosine triphosphate. Increased levels of mRNA and protein levels of mitochondrial fission genes, Drp1 and Fis1 and decreased levels fusion (Mfn1, Mfn2 and Opa1) biogenesis (PGC1α, NRF1, NRF2 & TFAM), autophagy (ATG5 & LC3BI, LC3BII), mitophagy (PINK1 & TERT, BCL2 & BNIPBL), synaptic (synaptophysin & PSD95) and dendritic (MAP2) genes were found in mAPP-HT22 cells relative to WT-HT22 cells. Cell survival was significantly reduced mAPP-HT22 cells. GTPase-Drp1 enzymatic activity was increased in mAPP-HT22 cells. Transmission electron microscopy revealed significantly increased mitochondrial numbers and reduced mitochondrial length in mAPP-HT22 cells. These findings suggest that hippocampal accumulation of mAPP and Aß is responsible for abnormal mitochondrial dynamics and defective biogenesis, reduced MAP2, autophagy, mitophagy and synaptic proteins & reduced dendritic spines and mitochondrial structural and functional changes in mAPP hippocampal cells. These observations strongly suggest that accumulation of mAPP and Aß causes mitochondrial, synaptic and autophagy/mitophagy abnormalities in hippocampal neurons, leading to neuronal dysfunction.

Lentivirus-mediated expression of human secreted amyloid precursor protein-alpha prevents development of memory and plasticity deficits in a mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disease driven in large part by accumulated deposits in the brain of the amyloid precursor protein (APP) cleavage product amyloid-ß peptide (Aß). However, AD is also characterised by reductions in secreted amyloid precursor protein-alpha (sAPPα), an alternative cleavage product of APP. In contrast to the neurotoxicity of accumulated Αß, sAPPα has many neuroprotective and neurotrophic properties. Increasing sAPPα levels has the potential to serve as a therapeutic treatment that mitigates the effects of Aß and rescue cognitive function. Here we tested the hypothesis that lentivirus-mediated expression of a human sAPPα construct in a mouse model of AD (APPswe/PS1dE9), begun before the onset of plaque pathology, could prevent later behavioural and electrophysiological deficits. Male mice were given bilateral intra-hippocampal injections at 4 months of age and tested 8-10 months later. Transgenic mice expressing sAPPα performed significantly better than untreated littermates in all aspects of the spatial water maze task. Expression of sAPPα also resulted in partial rescue of long-term potentiation (LTP), tested in vitro. These improvements occurred in the absence of changes in amyloid pathology. Supporting these findings on LTP, lentiviral-mediated expression of sAPPα for 3 months from 10 months of age, or acute sAPPα treatment in hippocampal slices from 18 to 20 months old transgenic mice, completely reversed the deficits in LTP. Together these findings suggest that sAPPα has wide potential to act as either a preventative or restorative therapeutic treatment in AD by mitigating the effects of Aß toxicity and enhancing cognitive reserve.

The amyloid precursor protein derivative, APP96-110, is efficacious following intravenous administration after traumatic brain injury.

Following traumatic brain injury (TBI) neurological damage is ongoing through a complex cascade of primary and secondary injury events in the ensuing minutes, days and weeks. The delayed nature of secondary injury provides a valuable window of opportunity to limit the consequences with a timely treatment. Recently, the amyloid precursor protein (APP) and its derivative APP96-110 have shown encouraging neuroprotective activity following TBI following an intracerebroventricular administration. Nevertheless, its broader clinical utility would be enhanced by an intravenous (IV) administration. This study assessed the efficacy of IV APP96-110, where a dose-response for a single dose of 0.005mg/kg- 0.5mg/kg APP96-110 at either 30 minutes or 5 hours following moderate-severe diffuse impact-acceleration injury was performed. Male Sprague-Dawley rats were assessed daily for 3 or 7 days on the rotarod to examine motor outcome, with a separate cohort of animals utilised for immunohistochemistry analysis 3 days post-TBI to assess axonal injury and neuroinflammation. Animals treated with 0.05mg/kg or 0.5mg/kg APP96-110 after 30 minutes demonstrated significant improvements in motor outcome. This was accompanied by a reduction in axonal injury and neuroinflammation in the corpus callosum at 3 days post-TBI, whereas 0.005mg/kg had no effect. In contrast, treatment with 0.005m/kg or 0.5mg/kg APP96-110 at 5 hours post-TBI demonstrated significant improvements in motor outcome over 3 days, which was accompanied by a reduction in axonal injury in the corpus callosum. This demonstrates that APP96-110 remains efficacious for up to 5 hours post-TBI when administered IV, and supports its development as a novel therapeutic compound following TBI.

The release and transmission of amyloid precursor protein via exosomes.

Amyloid precursor protein (APP) processing is central in Alzheimer's disease (AD) pathogenesis. The healthy unaffected neurons suffer the transmission of amyloid protein from pathologically affected neurons, which may play an important role in the anatomical spread of the disease. Exosomes are appropriate candidates for transmission of amyloid species, because of their potential role as "intercellular transportation". To address a role of secreted exosomes in neuronal homeostasis in AD, we harvested exosomes from the conditioned medium of HEK293-APP Swe/Ind cells. We have demonstrated that these exosomes contained APP and were capable of efficiently transferring APP to normal primary neurons. Moreover, these exosomes had dose-dependent detrimental effect on cultured neurons. Our results suggest a key mechanism underlying the spread of amyloid protein in the brain and the acceleration of pathology in AD; exosomes secretion serves to amplify and propagate Alzheimer's disease related pathology.

sAßPPα Improves Hippocampal NMDA-Dependent Functional Alterations Linked to Healthy Aging.

This study shows a decrease in soluble amyloid-ß protein precursor-α (sAßPPα) levels, but no change in sAßPPß, in the rat hippocampus during healthy aging, associated with the weaker expression of N-methyl-D-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) in the CA1 area of hippocampal slices. Exogenous application of recombinant sAßPPα increases NMDAR activation in aged animals and could rescue the age-related LTP deficits described. In contrast, it does not affect basal synaptic transmission or glutamate release. These results indicate that improving synaptic sAßPPα availability at synapses helps in reducing the functional NMDAR-related deregulation of hippocampal networks linked to aging.

Persistence of Aß seeds in APP null mouse brain.

Cerebral ß-amyloidosis is induced by inoculation of Aß seeds into APP transgenic mice, but not into App(-/-) (APP null) mice. We found that brain extracts from APP null mice that had been inoculated with Aß seeds up to 6 months previously still induced ß-amyloidosis in APP transgenic hosts following secondary transmission. Thus, Aß seeds can persist in the brain for months, and they regain propagative and pathogenic activity in the presence of host Aß.

Follicular fluid Aß40 concentrations may be associated with ongoing pregnancy following in vitro fertilization.

PURPOSE: To determine whether Aß40 levels in the follicular fluid (FF) of infertile women undergoing IVF demonstrate a relationship with IVF cycle parameters and outcome. METHODS: FF Aß40 levels were compared between patients achieving ongoing pregnancy and those with unsuccessful cycles. Clinical data such as ongoing pregnancy rate, implantation rate, number of oocytes retrieved, number of 8 cells embryos with ≤5 % fragmants, ratio of 8 cells embryos with ≤5 % fragmants to total embryos per patient and cleavage rate were compared among three percentile groups of Aß40. CCK-8 method was used to measure the effect of Aß40 on rat granulosa cells proliferation in vitro. RT-PCR was used to detect the mRNA expression levels of steroidogenesis related genes. RESULTS: Patients achieving ongoing pregnancy (n = 26; 50.98%) demonstrated significantly higher FF Aß40 levels compared to those with unsuccessful cycles (n = 25; 49.02%; P = 0.024). No significant differences were observed in APP (amyloid precursor protein) and its other proteolysis products including sAPPα, sAPPßand Aß 42 between the two groups. Statistically significant differences between the three percentile groups of Aß 40 were observed only in the implantation rates and ongoing pregnancy rates. There were no statistically significant differences between the three percentile groups in the age, No. oocytes retrieved, No. 2 pronucleus, No. embryos transferred, No. 8 cells embryos with ≤5% fragmants and cleavage rate. Significantly negative correlation exists between APP and AFC (antral follicle count) (R =-0.360, P = 0.005) and oocytes retrieved (R =-0.378, P = 0.004). There were also significantly positive correlations between Aß40 and Aß42 (R = 0.407, P = 0.000), between AFC and oocytes retrieved (R = 0.476, P = 0.000). Rat granulosa cells treated with Aß40 of different concentrations have improved their proliferative ability. Cells treated with 200 pg/ml Aß40 have the strongest ability of proliferation. 200 pg/ml Aß40 enhanced the expression of key molecules during steroidogenesis such as IGF-1,IGF-1receptor (IGF-1R),FSH receptor (FSHR),P450 aromatase (P450arom),steroidogenic acute regulatory protein (StAR) and cholesterol side-chain cleavage cytochromes P450(P450scc). CONCLUSIONS: Aß40 levels in follicle fluid may be associated with ongoing pregnancy and the moderate expression level of Aß40 is important for oocytes and embryos development.

Soluble amyloid precursor protein-α rescues age-linked decline in neural progenitor cell proliferation.

Neurogenesis is thought to play a role in cognitive function and hippocampal plasticity. Previous studies suggest that neurogenesis declines with aging. However, the onset and mechanism of declined neurogenesis are not fully elucidated. Here we show that the major decline in neurogenesis takes place during adulthood, before aging. Decline in neurogenesis takes place in the subgranular layer of the dentate gyrus and in the subventricular zone, and is primarily due to a reduced number of fast-proliferating neural progenitor cells. Importantly, this decline can be rescued by intraventricular injection of recombinant soluble amyloid precursor protein (sAPPα), which regulates neural progenitor cell proliferation in the adult brain. The counterpart, sAPPß, a product of the amyloidogenic cleavage pathway of amyloid precursor protein, fails to exhibit a proliferative effect in vitro and in vivo, in equimolar concentrations to sAPPα. These observations suggest that adulthood is an appropriate time window for an intervention that upregulates neurogenesis, such as enhancement of sAPPα levels, for the prevention of declining brain plasticity and cognitive function.

The influence of chronic cerebral hypoperfusion on cognitive function and amyloid ß metabolism in APP overexpressing mice.

BACKGROUND AND PURPOSE: Cognitive impairment resulting from cerebrovascular insufficiency has been termed vascular cognitive impairment, and is generally accepted to be distinct from Alzheimer's disease resulting from a neurodegenerative process. However, it is clear that this simple dichotomy may need revision in light of the apparent occurrence of several shared features between Alzheimer's disease and vascular cognitive impairment. Nevertheless, it still remains largely unknown whether the burden of vascular- and Alzheimer-type neuropathology are independent or interdependent. Therefore, we investigated whether chronic cerebral hypoperfusion influences cognitive ability or amyloid ß deposition in amyloid precursor protein (APP) overexpressing transgenic mice. METHODS: Two months old mice overexpressing a mutant form of the human APP bearing both the Swedish and Indiana mutations (APP(Sw/Ind)-Tg mice), or their wild-type littermates, were subjected to chronic cerebral hypoperfusion with bilateral common carotid artery stenosis (BCAS) using microcoils or sham operation. Barnes maze test performance and histopathological findings were analyzed at eight months old by 2 × 2 factorial experimental designs with four groups. RESULTS: BCAS-operated APP(Sw/Ind)-Tg mice showed significantly impaired learning ability compared to the other three groups of mice. Two-way repeated measures analysis of variance showed a synergistic interaction between the APP genotype and BCAS operation in inducing learning impairment. The cognitive performances were significantly correlated with the neuronal densities. BCAS significantly reduced the density of Nissl-stained neurons and silver-stained cored plaques in the hippocampus of APP(Sw/Ind)-Tg mice but increased the amount of filter-trap amyloid ß in the extracellular-enriched soluble brain fraction, compared to those from sham operated mice. CONCLUSIONS: The results suggest interaction between chronic cerebral hypoperfusion and APP(Sw/Ind) overexpression in cognitive decline in mice through enhanced neuronal loss and altered amyloid ß metabolism.

Changed clathrin regulatory proteins in the brains of Alzheimer's disease patients and animal models.

In the study, the expression of clathrin regulatory proteins dynamin I, AP180, and synaptic vesicle protein synaptophysin in multiple brain regions of the patients with Alzheimer's disease (AD), the transgenic mice carrying the Swedish mutation of amyloid-ß protein precursor (AßPP) 670/671 (AßPPSWE), and the rats injected by bilateral hippocampus with amyloid-ß peptide (Aß)1-42 were examined by immunohistochemistry and Nissl staining, Western blotting, and Real-time PCR, respectively. Spatial learning and memory of the rats were evaluated by Morris Water Maze test, and the ability of endocytosis in the cultured rat hippocampal neurons was detected by FM1-43 fluorescence imaging. Significant decreases in protein levels of dynamin I, AP180, and synaptophysin were observed in both AD patients and mice with AßPPSWE as compared to controls. Obvious declines of dynamin I and synaptophysin at protein and mRNA levels and impaired learning and spatial memory ability were found in the rats injected with Aß1-42 as compared to controls. In addition, deposits of Aß localized in the hippocampus around the sites of Aß1-42 injection and the decreased numbers of Nissl bodies in neurons were found. Moreover, the disrupted synaptic vesicle endocytosis and decreased dynamin I protein were detected in stimulated hippocampal neurons treated with Aß1-42. These findings imply a malfunctioning clathrin-mediated endocytosis during AD pathological processes, which might be relevant to the mechanism underlying the cognitive deficit associated with AD.

BRI2 (ITM2b) inhibits Abeta deposition in vivo.

Analyses of the biologic effects of mutations in the BRI2 (ITM2b) and the amyloid beta precursor protein (APP) genes support the hypothesis that cerebral accumulation of amyloidogenic peptides in familial British and familial Danish dementias and Alzheimer's disease (AD) is associated with neurodegeneration. We have used somatic brain transgenic technology to express the BRI2 and BRI2-Abeta1-40 transgenes in APP mouse models. Expression of BRI2-Abeta1-40 mimics the suppressive effect previously observed using conventional transgenic methods, further validating the somatic brain transgenic methodology. Unexpectedly, we also find that expression of wild-type human BRI2 reduces cerebral Abeta deposition in an AD mouse model. Additional data indicate that the 23 aa peptide, Bri23, released from BRI2 by normal processing, is present in human CSF, inhibits Abeta aggregation in vitro and mediates its anti-amyloidogenic effect in vivo. These studies demonstrate that BRI2 is a novel mediator of Abeta deposition in vivo.

Induction of tau pathology by intracerebral infusion of amyloid-beta -containing brain extract and by amyloid-beta deposition in APP x Tau transgenic mice.

Alzheimer's disease presents morphologically with senile plaques, primarily made of extracellular amyloid-beta (A beta) deposits, and neurofibrillary lesions, which consist of intracellular aggregates of hyperphosphorylated tau protein. To study the in vivo induction of tau pathology, dilute brain extracts from aged A beta-depositing APP23 transgenic mice were intracerebrally infused in young B6/P301L tau transgenic mice. Six months after the infusion, tau pathology was induced in the injected hippocampus but also in brain regions well beyond the injection sites such as the entorhinal cortex and amygdala, areas with neuronal projection to the injection site. No or only modest tau induction was observed when brain extracts from aged nontransgenic control mice and aged tau-depositing B6/P301L transgenic mice were infused. To further study A beta-induced tau lesions B6/P301L tau transgenic mice were crossed with APP23 mice. Although A beta deposition in double-transgenic mice did not differ from single APP23 transgenic mice, double-transgenic mice revealed increased tau pathology compared to single B6/P301L tau transgenic mice predominately in areas with high A beta plaque load. The present results suggest that both extract-derived A beta species and deposited fibrillary A beta can induce the formation of tau neurofibrillary pathology. The observation that infused A beta can trigger the tau pathology in the absence of A beta deposits provides an explanation for the discrepancy between the neuroanatomical location of A beta deposits and the development and spreading of tau lesions in Alzheimer's disease brain.

Exogenous induction of cerebral beta-amyloidogenesis is governed by agent and host.

Protein aggregation is an established pathogenic mechanism in Alzheimer's disease, but little is known about the initiation of this process in vivo. Intracerebral injection of dilute, amyloid-beta (Abeta)-containing brain extracts from humans with Alzheimer's disease or beta-amyloid precursor protein (APP) transgenic mice induced cerebral beta-amyloidosis and associated pathology in APP transgenic mice in a time- and concentration-dependent manner. The seeding activity of brain extracts was reduced or abolished by Abeta immunodepletion, protein denaturation, or by Abeta immunization of the host. The phenotype of the exogenously induced amyloidosis depended on both the host and the source of the agent, suggesting the existence of polymorphic Abeta strains with varying biological activities reminiscent of prion strains.

Effects of intrahippocampal CT105, a carboxyl terminal fragment of beta-amyloid precursor protein, alone/with inflammatory cytokines on working memory in rats.

In this study, we examined the effects of a 105 amino acid carboxyl terminal fragment of beta-amyloid precursor protein (CT105) and inflammatory cytokines on working memory in rats, by using a three-panel runway set-up. CT105 at 10 nmol/side significantly impaired working memory when it was administered bilaterally into the hippocampus. Furthermore, to elucidate the interaction of CT105 with inflammatory cytokines, we co-administered tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in combination with CT105. Concurrent injections of CT105 (1.0 nmol/side) and TNF-alpha (100 ng/side) produced a synergistic deficit of working memory, whereas IL-1beta (100 ng/side) combined with CT105 (1.0 nmol/side) did not affect the working memory performance. These results indicate that the CT105-induced impairment of working memory is strongly aggravated by an increase in the level of the inflammatory cytokine TNF-alpha, which may occur in the brains of patients with Alzheimer's disease.

Exogenous induction of cerebral beta-amyloidosis in betaAPP-transgenic mice.

A key commonality of most age-related neurodegenerative diseases is the accumulation of aggregation-prone proteins in the brain. Except for the prionoses, the initiation and propagation of these proteopathies in vivo remains poorly understood. In a previous study, we found that the deposition of the amyloidogenic peptide Abeta can be induced by injection of dilute extracts of Alzheimeric neocortex into the brains of Tg2576 transgenic mice overexpressing the human beta-amyloid precursor protein. The present study was undertaken to assess the pathology after long-term (12 months) incubation, and to clarify the distinctive anatomical distribution of seeded Abeta-immunoreactivity. All mice were injected at 3 months of age; 5 months later, as expected, Abeta deposits were concentrated mostly in the injected hemisphere. After 12 months, abundant, transgene-derived Abeta deposits were present bilaterally in the forebrain, but plaque load was still clearly greater in the extract-injected hemisphere. There was also evidence of tau hyperphosphorylation in axons of the corpus callosum that had been injured by the injection, most prominently in transgenic mice, but also, to a lesser degree, in non-transgenic mice. Five months following injection of AD-extract, an isolated cluster of Abeta-immunoreactive microglia was sometimes evident in the ipsilateral entorhinal cortex; the strong innervation of the hippocampus by entorhinal cortical neurons suggests the possible spread of seeded pathology from the injection site via neuronal transport mechanisms. Finally, using India Ink to map the local dispersion of injectate, we found that Abeta induction is especially potent in places where the injectate is sequestered. The AD-seeding model can illuminate the emergence and spread of cerebral beta-amyloidosis and tau hyperphosphorylation, and thus could enhance our understanding of AD and its pathogenic commonalties with other cerebral proteopathies.

Use-dependent effects of amyloidogenic fragments of (beta)-amyloid precursor protein on synaptic plasticity in rat hippocampus in vivo.

The Alzheimer's disease-related beta-amyloid precursor protein (beta-APP) is metabolized to a number of potentially amyloidogenic peptides that are believed to be pathogenic. Application of relatively low concentrations of the soluble forms of these peptides has previously been shown to block high-frequency stimulation-induced long-term potentiation (LTP) of glutamatergic transmission in the hippocampus. The present experiments examined how these peptides affect low-frequency stimulation-induced long-term depression (LTD) and the reversal of LTP (depotentiation). We discovered that beta-amyloid peptide (Abeta1-42) and the Abeta-containing C -terminus of beta-APP (CT) facilitate the induction of LTD in the CA1 area of the intact rat hippocampus. The LTD was frequency- and NMDA receptor-dependent. Thus, although low-frequency stimulation alone was ineffective, after intracerebroventricular injection of Abeta1-42, it induced an LTD that was blocked by d-(-)-2-amino-5-phosphonopentanoic acid. Furthermore, an NMDA receptor-dependent depotentiation was induced in a time-dependent manner, being evoked by injection of CT 10 min, but not 1 hr, after LTP induction. These use- and time-dependent effects of the amyloidogenic peptides on synaptic plasticity promote long-lasting reductions in synaptic strength and oppose activity-dependent strengthening of transmission in the hippocampus. This will result in a profound disruption of information processing dependent on hippocampal synaptic plasticity.