Fibrillar amyloid-beta production, accumulation, and recycling in transgenic mice pancreatic acinar cells and macrophages

Endogenous Amyloid-formed Ca2+-permeable Channels in Aged 3xTg AD Mice

Alzheimer's disease (AD), the leading cause of dementia, is characterized by the accumulation of beta-amyloid peptides (Aβ). However, whether Aβ itself is a key toxic agent in AD pathogenesis and the precise mechanism of Aβ-elicited neurotoxicity are still debated. Emerging evidence demonstrates that the Aβ channel/pore hypothesis could explain Aβ toxicity, because Aβ oligomers are able to disrupt membranes and cause edge-conductivity pores that may disrupt cell Ca2+ homeostasis and drive neurotoxicity in AD. However, all available data to support this hypothesis have been collected from "in vitro" experiments using high concentrations of exogenous Aβ. It is still unknown whether Aβ channels can be formed by endogenous Aβ in AD animal models. Here, we report an unexpected finding of the spontaneous Ca2+ oscillations in aged 3xTg AD mice but not in age-matched wild-type mice. These spontaneous Ca2+ oscillations are sensitive to extracellular Ca2+, ZnCl2, and the Aβ channel blocker Anle138b, suggesting that these spontaneous Ca2+ oscillations in aged 3xTg AD mice are mediated by endogenous Aβ-formed channels.

Interplay between Alzheimer's disease and global glucose metabolism revealed by the metabolic profile alterations of pancreatic tissue and serum in APP/PS1 transgenic mice

Increasing evidence suggests that there is a correlation between type 2 diabetes mellitus (T2D) and Alzheimer's disease (AD). Increased Aβ polypeptide production in AD patients would promote metabolic abnormalities, insulin signaling dysfunction and perturbations in glucose utilization, thus leading to the onset of T2D. However, the metabolic mechanisms underlying the interplay between AD and its diabetes-promoting effects are not fully elucidated. Particularly, systematic metabolomics analysis has not been performed for the pancreas tissues of AD subjects, which play key roles in the glucose metabolism of living systems. In the current study, we characterized the dynamic metabolic profile alterations of the serum and the pancreas of APP/PS1 double-transgenic mice (an AD mouse model) using the untargeted metabolomics approaches. Serum and pancreatic tissues of APP/PS1 transgenic mice and wild-type mice were extracted and subjected to NMR analysis to evaluate the functional state of pancreas in the progress of AD. Multivariate analysis of principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were conducted to define the global and the local (pancreas) metabolic features associated with the possible initiation of T2D in the progress of AD. Our results showed the onset of AD-induced global glucose metabolism disorders in AD mice. Hyperglycemia and its accompanying metabolic disorders including energy metabolism down-regulation and oxidative stress were observed in the serum of AD mice. Meanwhile, global disturbance of branched-chain amino acid (BCAA) metabolism was detected, and the change of BCAA (leucine) was positively correlated to the alteration of glucose. Moreover, increased level of glucose and enhanced energy metabolism were observed in the pancreas of AD mice. The results suggest that the diabetes-promoting effects accompanying the progress of AD are achieved by down-regulating the global utilization of glucose and interfering with the metabolic function of pancreas. Since T2D is a risk factor for the pathogenesis of AD, our findings suggest that targeting the glucose metabolism dysfunctions might serve as a supplementary therapeutic strategy for Alzheimer's disease.

Amyloid precursor protein in pancreatic islets

The amyloid precursor protein (APP) has been extensively investigated for its role in the production of amyloid beta (Aβ), a plaque-forming peptide in Alzheimer's disease (AD). Epidemiological evidence suggests type 2 diabetes is a risk factor for AD. The pancreas is an essential regulator of blood glucose levels through the secretion of the hormones insulin and glucagon. Pancreatic dysfunction is a well-characterized consequence of type 1 and type 2 diabetes. In this study, we have examined the expression and processing of pancreatic APP to test the hypothesis that APP may play a role in pancreatic function and the pathophysiology of diabetes. Our data demonstrate the presence of APP within the pancreas, including pancreatic islets in both mouse and human samples. Additionally, we report that the APP/PS1 mouse model of AD overexpresses APP within pancreatic islets, although this did not result in detectable levels of Aβ. We compared whole pancreas and islet culture lysates by Western blot from C57BL/6 (WT), APP^-/- and APP/PS1 mice and observed APP-dependent differences in the total protein levels of GLUT4, IDE and BACE2. Immunohistochemistry for BACE2 detected high levels in pancreatic α cells. Additionally, both mouse and human islets processed APP to release sAPP into cell culture media. Moreover, sAPP stimulated insulin but not glucagon secretion from islet cultures. We conclude that APP and its metabolites are capable of influencing the basic physiology of the pancreas, possibly through the release of sAPP acting in an autocrine or paracrine manner.

A liposome-based therapeutic vaccine against beta -amyloid plaques on the pancreas of transgenic NORBA mice

Immune tolerance to beta-amyloid (Abeta) was broken in NORBA transgenic mice presenting Abeta plaques on their pancreases. Vaccination of Black C57, BALB/c, and NORBA mice with the synthetic Abeta(1-16) sequence modified by covalently attaching two palmitoyl residues at each end of the peptide, subsequently reconstituted in liposomes-Lipid A elicited titers of 1:5,000 of anti-Abeta(1-16) antibodies within 10 weeks after the first inoculation. On direct interaction, sera with antibody titers of 1:5,000 solubilized in vitro up to 80% of preformed Abeta(1-42) aggregates. Cryosections of pancreases of unvaccinated NORBA mice show, on staining with Thioflavin T, extensive areas of high-intensity fluorescence in the acinar cell fields. Quantitation of the average fluorescence intensity in each section indicated that: (i) whereas nonvaccinated NORBA mice develop plaques within 45-60 days after birth, vaccinated 8-week-old NORBA mice did not develop amyloid plaques on their pancreases over a period of 7 months; (ii) cryosections from pancreases of 9- and 15-month-old vaccinated NORBA mice showed less than 50% of the fluorescence shown by cryosections from unvaccinated animals of the same age. The results indicate that palmitoylated Abeta peptides, reconstituted in liposomes-lipid A, are highly immunogenic, eliciting "therapeutic" antibody titers within 3 months of the first inoculation and preventing amyloid plaque formation in young animals or significantly reducing existing plaques in older transgenic mice. Possible implications for the therapy of Alzheimer's disease are discussed.