Characterization of amyloid beta peptides from brain extracts of transgenic mice overexpressing the London mutant of human amyloid precursor protein

Alzheimer's disease (AD) is marked by the presence of neurofibrillary tangles and amyloid plaques in the brain of patients. To study plaque formation, we report on further quantitative and qualitative analysis of human and mouse amyloid beta peptides (Abeta) from brain extracts of transgenic mice overexpressing the London mutant of human amyloid precursor protein (APP). Using enzyme-linked immunosorbant assays (ELISAs) specific for either human or rodent Abeta, we found that the peptides from both species aggregated to form plaques. The ratios of deposited Abeta1-42/1-40 were in the order of 2-3 for human and 8-9 for mouse peptides, indicating preferential deposition of Abeta42. We also determined the identity and relative levels of other Abeta variants present in protein extracts from soluble and insoluble brain fractions. This was done by combined immunoprecipitation and mass spectrometry (IP/MS). The most prominent peptides truncated either at the carboxyl- or the amino-terminus were Abeta1-38 and Abeta11-42, respectively, and the latter was strongly enriched in the extracts of deposited peptides. Taken together, our data indicate that plaques of APP-London transgenic mice consist of aggregates of multiple human and mouse Abeta variants, and the human variants that we identified were previously detected in brain extracts of AD patients.     

A transgenic rat expressing human APP with the Swedish Alzheimer's disease mutation

In recent years, transgenic mice have become valuable tools for studying mechanisms of Alzheimer's disease (AD). With the aim of developing an animal model better for memory and neurobehavioural testing, we have generated a transgenic rat model of AD. These animals express human amyloid precursor protein (APP) containing the Swedish AD mutation. The highest level of expression in the brain is found in the cortex, hippocampus, and cerebellum. Starting after the age of 15 months, the rats show increased tau phosphorylation and extracellular Abeta staining. The Abeta is found predominantly in cerebrovascular blood vessels with very rare diffuse plaques. We believe that crossing these animals with mutant PS1 transgenic rats will result in accelerated plaque formation similar to that seen in transgenic mice.     

Antimicrobial activity of human islet amyloid polypeptides: an insight into amyloid peptides' connection with antimicrobial peptides

Abstract Human islet amyloid polypeptide (hIAPP) shows an antimicrobial activity towards two types of clinically relevant bacteria. The potency of hIAPP varies with its aggregation states. Circular dichroism was employed to determine the interaction between hIAPP and bacteria lipid membrane mimic. The antimicrobial activity of each aggregate species is associated with their ability to induce membrane disruption. Our findings provide new evidence revealing the antimicrobial activity of amyloid peptide, which suggest a possible connection between amyloid peptides and antimicrobial peptides.     

Early-onset amyloid deposition and cognitive deficits in transgenic mice expressing a double mutant form of amyloid precursor protein 695

We have created early-onset transgenic (Tg) models by exploiting the synergistic effects of familial Alzheimer's disease mutations on amyloid beta-peptide (Abeta) biogenesis. TgCRND8 mice encode a double mutant form of amyloid precursor protein 695 (KM670/671NL+V717F) under the control of the PrP gene promoter. Thioflavine S-positive Abeta amyloid deposits are present at 3 months, with dense-cored plaques and neuritic pathology evident from 5 months of age. TgCRND8 mice exhibit 3,200-4,600 pmol of Abeta42 per g brain at age 6 months, with an excess of Abeta42 over Abeta40. High level production of the pathogenic Abeta42 form of Abeta peptide was associated with an early impairment in TgCRND8 mice in acquisition and learning reversal in the reference memory version of the Morris water maze, present by 3 months of age. Notably, learning impairment in young mice was offset by immunization against Abeta42 (Janus, C., Pearson, J., McLaurin, J., Mathews, P. M., Jiang, Y., Schmidt, S. D., Chishti, M. A., Horne, P., Heslin, D., French, J., Mount, H. T. J., Nixon, R. A., Mercken, M., Bergeron, C., Fraser, P. E., St. George-Hyslop, P., and Westaway, D. (2000) Nature 408, 979-982). Amyloid deposition in TgCRND8 mice was enhanced by the expression of presenilin 1 transgenes including familial Alzheimer's disease mutations; for mice also expressing a M146L+L286V presenilin 1 transgene, amyloid deposits were apparent by 1 month of age. The Tg mice described here suggest a potential to investigate aspects of Alzheimer's disease pathogenesis, prophylaxis, and therapy within short time frames.     

Increased generation of alternatively cleaved beta-amyloid peptides in cells expressing mutants of the amyloid precursor protein defective in endocytosis

The subcellular location of the secretases processing the beta-amyloid precursor protein (APP) is not established yet. We analyzed the generation of the beta-amyloid peptide (Abeta) in human embryonic kidney 293 cell lines stably expressing wild-type and noninternalizing mutants of human APP. APP lacking the entire cytoplasmic domain or with both tyrosine residues of the motif GYENPTY mutated to alanine showed at least fivefold reduced endocytosis. In these cell lines, the production of Abeta1-40 was substantially reduced, but accompanied by the appearance of two prominent alternative Abeta peptides differing at the amino-termini. Based on antibody reactivity and mobility in high-resolution gels in comparison with defined Abeta fragments, these peptides were identified as Abeta3-40 and Abeta5-40. Notably, these alternative Abeta peptides were not generated when the APP mutants were retained in the early secretory pathway by treatment with brefeldin A. These results indicate that the alternative processing is the result of APP accumulation at the plasma membrane and provide evidence of distinct beta-secretase activities. Cleavage amino-terminal to position 1 of Abeta occurs predominantly in endosomes, whereas the processing at positions 3 or 5 takes place at the plasma membrane.     

Transgenic mice expressing hamster prion protein produce species-specific scrapie infectivity and amyloid plaques

Three transgenic mouse lines designated Tg 69, 71, and 81 were produced harboring a Syrian hamster (Ha) prion protein (PrP) gene; all expressed the cellular HaPrP isoform in their brains. Inoculation of Tg 81 mice or hamsters with Ha prions caused scrapie in integral of 75 days; nontransgenic control mice failed to develop scrapie after greater than 500 days. Tg 71 mice inoculated with Ha prions developed scrapie in integral of 170 days. Both Tg 71 and Tg 81 mice exhibited spongiform degeneration and reactive astrocytic gliosis, and they produced the scrapie HaPrP isoform in their brains. Tg 81 brains also showed HaPrP amyloid plaques characteristic of Ha scrapie and contained integral of 10(9) ID50 units of Ha prions based on Ha bioassays. Our findings argue that the PrP gene modulates scrapie susceptibility, incubation times, and neuropathology; furthermore, they demonstrate synthesis of infectious scrapie prions programmed by a recombinant DNA molecule.     

Genetic background determines the extent of islet amyloid formation in human islet amyloid polypeptide transgenic mice

Genetic background is important in determining susceptibility to metabolic abnormalities such as insulin resistance and beta-cell dysfunction. Islet amyloid is associated with reduced beta-cell mass and function and develops in the majority of our C57BL/6J x DBA/2J (F(1)) male human islet amyloid polypeptide (hIAPP) transgenic mice after 1 yr of increased fat feeding. To determine the relative contribution of each parental strain, C57BL/6J (BL6) and DBA/2J (DBA2), to islet amyloid formation, we studied male hIAPP mice on each background strain (BL6, n = 13; and DBA2 n = 11) and C57BL/6J x DBA/2J F(1) mice (n = 17) on a 9% (wt/wt) fat diet for 1 yr. At the end of 12 mo, islet amyloid deposition was quantified from thioflavin S-stained pancreas sections. The majority of mice in all groups developed islet amyloid (BL6: 91%, F(1): 76%, DBA2: 100%). However, the prevalence (%amyloid-positive islets; BL6: 14 +/- 3%, F(1): 44 +/- 8%, DBA2: 49 +/- 9%, P < 0.05) and severity (%islet area occupied by amyloid; BL6: 0.03 +/- 0.01%, F(1): 9.2 +/- 2.9%, DBA2: 5.7 +/- 2.3%, p < or = 0.01) were significantly lower in BL6 than F(1) and DBA2 mice. Increased islet amyloid severity was negatively correlated with insulin-positive area per islet, in F(1) (r(2) = 0.75, P < 0.001) and DBA2 (r(2) = 0.87, P < 0.001) mice but not BL6 mice (r(2) = 0.07). In summary, the extent of islet amyloid formation in hIAPP transgenic mice is determined by background strain, with mice expressing DBA/2J genes (F(1) and DBA2 mice) being more susceptible to amyloid deposition that replaces beta-cell mass. These findings underscore the importance of genetic and environmental factors in studying metabolic disease.     

Generation of mice expressing the human glucagon receptor with a direct replacement vector

The process of evaluating the in vivo efficacy of non–peptidyl receptor antagonists in animal models is frequently complicated by failure of compounds displaying high affinity against the human receptors to show measurable affinity at the corresponding rodent receptors. In order to generate a suitable animal model in which to evaluate the in vivo activity of non–peptidyl glucagon receptor antagonists, we have utilized a direct targeting approach to replace the murine glucagon receptor with the human glucagon receptor gene by homologous recombination. Specific expression of the human glucagon receptor (GR) in the livers of transgenic mice was confirmed with an RNase protection assay, and the pharmacology of the human GRs expressed in the livers of these mice parallels that of human GR in a recombinant CHO cell line with respect to both binding of ¹²⁵I–glucagon and the ability of glucagon to stimulate cAMP production. L–168,049, a non–peptidyl GR antagonist selective for the human GR shows a 3.5 fold higher affinity for liver membrane preparations of human GR expressing mice (IC₅₀=172±98nM) in the presence of MgCl₂ in marked contrast to the measured affinity of the murine receptor (IC₅₀=611±97nM) for this non–peptidyl antagonist. The human receptors expressed are functional as measured by the ability of glucagon to stimulate cAMP production and the selectivity of this antagonist for the human receptor is further verified by its ability to block glucagon–stimulated cyclase activity with 5 fold higher potency (IC₅₀=97.2±13.9nM) than for the murine receptor (IC₅₀=504±247nM). Thus we have developed a novel animal model for evaluating GR antagonists in vivo. These mice offer the advantage that the regulatory sequences which direct tissue specific and temporal expression of the GR have been unaltered and thus expression of the human gene in these mice remains in the normal chromosomal context.     

Interaction of dipeptydil peptidase IV with amyloid peptides

The aggregates of amyloid beta peptides (Aβs) are regarded as one of the main pathological hallmarks of Alzheimer’s disease (AD). An imbalance between the rates of synthesis and clearance of Aβs is considered to be a possible cause for the onset of AD. Dipeptidyl peptidases II and IV (DPPII and DPPIV) are serine proteases removing N-terminal dipeptides from polypeptides and proteins with proline or alanine on the penultimate position. Alanine is an N-terminal penultimate residue in Аβs, and we presumed that DPPII and DPPIV could cleave them. The results of present in vitro research demonstrate for the first time the ability of DPPIV to truncate the commercial Aβ40 and Aβ42 peptides, to hinder the fibril formation by them and to participate in the disaggregation of preformed fibrils of these peptides. The increase of absorbance at 334 nm due to complex formation between primary amines with o-phtalaldehyde was used to show cleaving of Aβ40 and Aβ42. The time-dependent increase of the quantity of primary amines during incubation of peptides in the presence of DPPIV suggested their truncation by DPPIV, but not by DPPII. The parameters of the enzymatic breakdown by DPPIV were determined for Aβ40 (K_m = 37.5 μM, k_cat/K_m = 1.7 × 10³ M⁻¹sec⁻¹) and Aβ42 (K_m = 138.4 μM, k_cat/K_m = 1.90 × 10² M⁻¹sec⁻¹). The aggregation-disaggregation of peptides was controlled by visualization on transmission electron microscope and by Thioflavin-T fluorescence on spectrofluorimeter and fluorescent microscope. DPPIV hindered the peptide aggregation/fibrillation during 3-4 days incubation in 20 mM phosphate buffer, pH 7.4, 37 °C by 50–80%. Ovalbumin, BSA and DPPII did not show this effect. In the presence of DPPIV, the preformed fibrils were disaggregated by 30–40%. Conclusion: for the first time it was shown that the Aβ40 and Aβ42 are substrates of DPPIV. DPPIV prohibits the fibrillation of peptides and promotes disaggregation of their preformed aggregates.     

Islet amyloid development in a mouse strain lacking endogenous islet amyloid polypeptide (IAPP) but expressing human IAPP

BACKGROUND: Several mouse strains expressing human islet amyloid polypeptide (IAPP) have been created to study development of islet amyloid and its impact on islet cell function. The tendency to form islet amyloid has varied strongly among these strains by factors that have not been elucidated. Because some beta cell granule components are known to inhibit IAPP fibril formation in vitro, we wanted to determine whether a mouse strain expressing human IAPP but lacking the nonamyloidogenic mouse IAPP is more prone to develop islet amyloidosis. MATERIALS AND METHODS: Such a strain was created by cross-breeding a transgenic mouse strain and an IAPP null mouse strain. RESULTS: When fed a fat-enriched diet, male mice expressing only human IAPP developed islet amyloid earlier and to a higher extent than did mice expressing both human and mouse IAPP. Supporting these results, we found that mouse IAPP dose-dependently inhibits formation of fibrils from human IAPP. CONCLUSIONS: Female mice did not develop amyloid deposits, although small extracellular amorphous IAPP deposits were found in some islets. When cultivated in vitro, amyloid deposits occurred within 10 days in islets from either male or female mice expressing only human IAPP. The study shows that formation of islet amyloid may be dependent on the environment, including the presence or absence of fibril inhibitors or promoters.     

Synergistic effects of amyloid peptides and lead on human neuroblastoma cells

Aggregated amyloid peptides (AP), major components of senile plaques, have been considered to play a very important and crucial role in the development and neuro-pathogenesis of Alzheimer's disease (AD). In the present in vitro, study the synergistic effects of Pb(2+), a heavy metal, and AP on the human neuroblastoma SH-SY5Y cells were investigated. The cells treated with Pb(2+) (0.01-10 μM) alone exhibited a significant decrease in viability and IC(50) was 5 μM. A similar decrease in viability was also observed when the cells were exposed to AP, Aβ1-40 (20-120 μM) and Aβ25-35 (2.5-15 μM) for 48 hrs. The IC(50) values were 60 μM and 7.5 μM for Aβ1-40 and Aβ25-35 respectively. To assess the synergistic effects the cells were exposed to IC(50) of both AP and Pb(2+), which resulted in further reduction of the viability. The study was extended to determine the lactate dehydrogenase (LDH) release to assess the cytotoxic effects, 8-isoprostane for extent of oxidative damage, COX 1 and 2 for inflammation related changes, p53 protein for DNA damage and protein kinases A and C for signal transduction. The data suggest that the toxic effects of AP were most potent in the presence of Pb(2+), resulting in an aggravated clinical pathological condition. This could be attributed to the oxidative stress, inflammation neuronal apoptosis and an alteration in the activities of the signaling enzymes.     

The Arctic Alzheimer mutation favors intracellular amyloid-beta production by making amyloid precursor protein less available to alpha-secretase

Mutations within the amyloid-beta (Abeta) domain of the amyloid precursor protein (APP) typically generate hemorrhagic strokes and vascular amyloid angiopathy. In contrast, the Arctic mutation (APP E693G) results in Alzheimer's disease. Little is known about the pathologic mechanisms that result from the Arctic mutation, although increased formation of Abeta protofibrils in vitro and intraneuronal Abeta aggregates in vivo suggest that early steps in the amyloidogenic pathway are facilitated. Here we show that the Arctic mutation favors proamyloidogenic APP processing by increased beta-secretase cleavage, as demonstrated by altered levels of N- and C-terminal APP fragments. Although the Arctic mutation is located close to the alpha-secretase site, APP harboring the Arctic mutation is not an inferior substrate to a disintegrin and metalloprotease-10, a major alpha-secretase. Instead, the localization of Arctic APP is altered, with reduced levels at the cell surface making Arctic APP less available for alpha-secretase cleavage. As a result, the extent and subcellular location of Abeta formation is changed, as revealed by increased Abeta levels, especially at intracellular locations. Our findings suggest that the unique clinical symptomatology and neuropathology associated with the Arctic mutation, but not with other intra-Abeta mutations, could relate to altered APP processing with increased steady-state levels of Arctic Abeta, particularly at intracellular locations.     

Receptor-dependent cell stress and amyloid accumulation in systemic amyloidosis

Accumulation of fibrils composed of amyloid A in tissues resulting in displacement of normal structures and cellular dysfunction is the characteristic feature of systemic amyloidoses. Here we show that RAGE, a multiligand immunoglobulin superfamily cell surface molecule, is a receptor for the amyloidogenic form of serum amyloid A. Interactions between RAGE and amyloid A induced cellular perturbation. In a mouse model, amyloid A accumulation, evidence of cell stress and expression of RAGE were closely linked. Antagonizing RAGE suppressed cell stress and amyloid deposition in mouse spleens. These data indicate that RAGE is a potential target for inhibiting accumulation of amyloid A and for limiting cellular dysfunction induced by amyloid A.     

Interpreting the aggregation kinetics of amyloid peptides

Amyloid fibrils are insoluble mainly beta-sheet aggregates of proteins or peptides. The multi-step process of amyloid aggregation is one of the major research topics in structural biology and biophysics because of its relevance in protein misfolding diseases like Alzheimer's, Parkinson's, Creutzfeld-Jacob's, and type II diabetes. Yet, the detailed mechanism of oligomer formation and the influence of protein stability on the aggregation kinetics are still matters of debate. Here a coarse-grained model of an amphipathic polypeptide, characterized by a free energy profile with distinct amyloid-competent (i.e. beta-prone) and amyloid-protected states, is used to investigate the kinetics of aggregation and the pathways of fibril formation. The simulation results suggest that by simply increasing the relative stability of the beta-prone state of the polypeptide, disordered aggregation changes into fibrillogenesis with the presence of oligomeric on-pathway intermediates, and finally without intermediates in the case of a very stable beta-prone state. The minimal-size aggregate able to form a fibril is generated by collisions of oligomers or monomers for polypeptides with unstable or stable beta-prone state, respectively. The simulation results provide a basis for understanding the wide range of amyloid-aggregation mechanisms observed in peptides and proteins. Moreover, they allow us to interpret at a molecular level the much faster kinetics of assembly of a recently discovered functional amyloid with respect to the very slow pathological aggregation.     

Thiocyanate supplementation decreases atherosclerotic plaque in mice expressing human myeloperoxidase

Abstract

Elevated levels of the heme enzyme myeloperoxidase (MPO) are associated with adverse cardiovascular outcomes. MPO predominantly catalyzes formation of the oxidants hypochlorous acid (HOCl) from Cl^?, and hypothiocyanous acid (HOSCN) from SCN^?, with these anions acting as competitive substrates. HOSCN is a less powerful and more specific oxidant than HOCl, and selectively targets thiols; such damage is largely reversible, unlike much HOCl-induced damage. We hypothesized that increased plasma SCN^?, and hence HOSCN formation instead of HOCl, may decrease artery wall damage. This was examined using high-fat fed atherosclerosis-prone LDLR^–/– mice transgenic for human MPO, with and without SCN^? (10 mM) added to drinking water. Serum samples, collected fortnightly, were analyzed for cholesterol, triglycerides, thiols, MPO, and SCN^?; study-long exposure was calculated by area under the curve (AUC). Mean serum SCN^? concentrations were elevated in the supplemented mice (200–320 μM) relative to controls (< 120 μM). Normalized aortic root plaque areas at sacrifice were 26% lower in the SCN^?-supplemented mice compared with controls (P = 0.0417), but plaque morphology was not appreciably altered. Serum MPO levels steadily increased in mice on the high-fat diet, however, comparison of SCN^?-supplemented versus control mice showed no significant changes in MPO protein, cholesterol, or triglyceride levels; thiol levels were decreased in supplemented mice at one time-point. Plaque areas increased with higher cholesterol AUC (r = 0.4742; P = 0.0468), and decreased with increasing SCN^? AUC (r = ? 0.5693; P = 0.0134). These data suggest that increased serum SCN^? levels, which can be achieved in humans by dietary manipulation, may decrease atherosclerosis burden.     

Role of aromatic interactions in amyloid formation by peptides derived from human Amylin

Numerous polypeptides and proteins form amyloid deposits in vivo or in vitro. The mechanism of amyloid formation is not well-understood particularly in the case where unstructured polypeptides assemble to form amyloid. Aromatic-aromatic interactions are known to be important in globular proteins, and the possibility that they might play a key role in amyloid formation has been raised. The results of Ala-scanning experiments on short polypeptides derived from Amylin have suggested that aromatic interactions could be particularly important for this system. Here, we examine a set of Amylin-derived polypeptides in which the single aromatic residue has been substituted with a Leu and Ala. A peptide corresponding to residues 21-29 with a Phe-23 to Leu substitution, a free N terminus, and amidated C terminus readily forms amyloid. Shorter peptides derived from the putative minimal amyloid-forming segment of Amylin, residues 22-27, also form amyloid when Phe-23 is replaced by Leu. Amyloid formation is more facile when the N terminus is deprotonated and the peptide is uncharged. Substitution of the Phe with Ala results in a peptide that is noticeably less prone to form amyloid. A peptide corresponding to residues 10-19 of human Amylin with blocked termini and the sole aromatic residue, Phe-15, substituted by Leu readily forms amyloid. A Phe-15 to Ala substitution reduces significantly the ability to form amyloid. These results indicate that an aromatic residue is not required for amyloid formation in these systems and indicates that other factors such as size, beta-sheet propensity, and hydrophobicity of the side chain in question are also important.     

Neuronal alpha-synucleinopathy with severe movement disorder in mice expressing A53T human alpha-synuclein

alpha-Synucleinopathies are neurodegenerative disorders that range pathologically from the demise of select groups of nuclei to pervasive degeneration throughout the neuraxis. Although mounting evidence suggests that alpha-synuclein lesions lead to neurodegeneration, this remains controversial. To explore this issue, we generated transgenic mice expressing wild-type and A53T human alpha-synuclein in CNS neurons. Mice expressing mutant, but not wild-type, alpha-synuclein developed a severe and complex motor impairment leading to paralysis and death. These animals developed age-dependent intracytoplasmic neuronal alpha-synuclein inclusions paralleling disease onset, and the alpha-synuclein inclusions recapitulated features of human counterparts. Moreover, immunoelectron microscopy revealed that the alpha-synuclein inclusions contained 10-16 nm wide fibrils similar to human pathological inclusions. These mice demonstrate that A53T alpha-synuclein leads to the formation of toxic filamentous alpha-synuclein neuronal inclusions that cause neurodegeneration.     

Establishment of a transgenic mouse model specifically expressing human serum amyloid A in adipose tissue

Obesity and obesity co-morbidities are associated with a low grade inflammation and elevated serum levels of acute phase proteins, including serum amyloid A (SAA). In the non-acute phase in humans, adipocytes are major producers of SAA but the function of adipocyte-derived SAA is unknown. To clarify the role of adipocyte-derived SAA, a transgenic mouse model expressing human SAA1 (hSAA) in adipocytes was established. hSAA expression was analysed using real-time PCR analysis. Male animals were challenged with a high fat (HF) diet. Plasma samples were subjected to fast protein liquid chromatography (FPLC) separation. hSAA, cholesterol and triglyceride content were measured in plasma and in FPLC fractions. Real-time PCR analysis confirmed an adipose tissue-specific hSAA gene expression. Moreover, the hSAA gene expression was not influenced by HF diet. However, hSAA plasma levels in HF fed animals (37.7±4.0 µg/mL, n = 7) were increased compared to those in normal chow fed animals (4.8±0.5 µg/mL, n = 10; p<0.001), and plasma levels in the two groups were in the same ranges as in obese and lean human subjects, respectively. In FPLC separated plasma samples, the concentration of hSAA peaked in high-density lipoprotein (HDL) containing fractions. In addition, cholesterol distribution over the different lipoprotein subfractions as assessed by FPLC analysis was similar within the two experimental groups. The established transgenic mouse model demonstrates that adipose tissue produced hSAA enters the circulation, resulting in elevated plasma levels of hSAA. This new model will enable further studies of metabolic effects of adipose tissue-derived SAA.