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Studies on the mechanisms of neuronal amyloid-β (Aβ) internalisation are crucial for understanding the neuropathological progression of Alzheimer's disease (AD). We here investigated how extracellular Aβ peptides are internalised and focused on three different pathways: (i) via endocytic mechanisms, (ii) via the receptor for advanced glycation end products (RAGE) and (iii) via the pore-forming protein perforin. Both Aβ 40 and Aβ 42 were internalised in retinoic acid differentiated neuroblastoma (RA-SH-SY5Y) cells. A higher concentration was required for Aβ 40 (250 nM) compared with Aβ 42 (100 nM). The internalised Aβ 40 showed a dot-like pattern of distribution whereas Aβ 42 accumulated in larger and distinct formations. By confocal microscopy, we showed that Aβ 40 and Aβ 42 co-localised with mitochondria, endoplasmic reticulum (ER) and lysosomes. Aβ treatment of human primary cortical neurons (hPCN) confirmed our findings in RA-SH-SY5Y cells, but hPCN were less sensitive to Aβ; therefore, a 20 (Aβ 40 ) and 50 (Aβ 42 ) times higher concentration was needed for inducing uptake. The blocking of endocytosis completely inhibited the internalisation of Aβ peptides in RA-SH-SY5Y cells and hPCN, indicating that this is a major pathway by which Aβ enters the cells. In addition, the internalisation of Aβ 42 , but not Aβ 40 , was reduced by 55 % by blocking RAGE. Finally, for the first time we showed that pore formation in cell membranes by perforin led to Aβ internalisation in hPCN. Understanding how Aβ is internalised sheds light on the pathological role of Aβ and provides further ideas of inhibitory strategies for preventing Aβ internalisation and the spreading of neurodegeneration in AD.

Amyloid-β peptide (Aβ) fragment misfolding may play a crucial role in the progression of Alzheimer's disease (AD) pathophysiology as well as epigenetic mechanisms at the DNA and histone level. We hypothesized that histone H3 homeostasis is disrupted in association with the appearance of soluble Aβ at an early stage in AD progression. We identified, localized, and compared histone H3 modifications in multiple model systems (neural-like SH-SY5Y, primary neurons, Tg2576 mice, and AD neocortex), and narrowed our focus to investigate 3 key motifs associated with regulating transcriptional activation and inhibition: acetylated lysine 14, phosphorylated serine 10 and dimethylated lysine 9. Our results in vitro and in vivo indicate that multimeric soluble Aβ may be a potent signaling molecule indirectly modulating the transcriptional activity of DNA by modulating histone H3 homeostasis. These findings reveal potential loci of transcriptional disruption relevant to AD. Identifying genes that undergo significant epigenetic alterations in response to Aβ could aid in the understanding of the pathogenesis of AD, as well as suggesting possible new treatment strategies., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Background: Although genetic and biochemical studies have suggested a cardinal role for β-amyloid (Aβ) in Alzheimer's disease, the underlying mechanism(s) of how Aβ induces neurodegeneration is still unclear. Our objective was to investigate the consequences of Aβ, especially on tau phosphorylation at specific epitopes important for Alzheimer's disease., Methods: We used cortices from Tg2576 mice at 7 days to 15 months of age., Results: MALDI-TOF MS revealed an age-dependent shift in the Aβ isoform pattern. Young animals displayed high cortical levels of the shorter Aβ isoforms (Aβ1-16 and Aβ1-17) compared to 15-month-old Tg2576 mice which mainly expressed Aβ1-40 and Aβ1-42. The Aβ1-42 showed an age-dependent increase, whereas total Aβ1-40 levels remained constant. The highest levels of TBS-soluble Aβ oligomers were found at 90 days of age. Brain Aβ build-up did not affect the phosphorylation of tau at the epitopes investigated., Conclusions: This study provides new information about age-dependent Aβ isoforms and oligomers as well as their effect on site-specific tau phosphorylation in this transgenic mouse model. Our observations suggest that the different human Aβ isoforms do not directly cause increased tau phosphorylation and that the cognitive deficits seen in this mouse model are only related to the Aβ overexpression., (Copyright © 2011 S. Karger AG, Basel.)

Background: Several studies implicate acetylcholinesterase (AChE) in the pathogenesis of Alzheimer's disease (AD), raising the question of whether inhibitors of AChE also might act in a disease-modifying manner. Huprine X (HX), a reversible AChE inhibitor hybrid of tacrine and huperzine A, has shown to affect the amyloidogenic process in vitro. In this study, the aim was to investigate whether HX could affect the AD-related neuropathology in vivo in two mouse models., Methods: Tg2576 (K670M/N671L) (APPswe) and 3xTg-AD (K670M/N671L, PS1M146V, tauP301L) mice were treated with HX (0.12 μmol/kg, i.p., 21 days) or saline at 6-7 months. Human β-amyloid (Aβ) was measured by ELISA, synaptophysin by Western blot and α7 neuronal nicotinic acetylcholine receptors (nAChRs) were analyzed by [(125)I]α-bungarotoxin autoradiography., Results: Treatment with HX reduced insoluble Aβ1-40 (about 40%) in the hippocampus of 3xTg-AD mice, while showing no effect in APPswe mice. Additionally, HX markedly increased cortical synaptophysin levels (about 140%) and decreased (about 30%) the levels of α7 nAChRs in the caudate nucleus of 3xTg-AD mice, while increasing (about 10%) hippocampal α7 nAChRs in APPswe mice., Conclusion: The two mouse models react differently to HX treatment, possibly due to their differences in brain neuropathology. The modulation of Aβ and synaptophysin by HX in 3xTg-AD mice might be due to its suggested interaction with the peripheral anionic site on AChE, and/or via cholinergic mechanisms involving activation of cholinergic receptors. Our results provide further evidence that drugs targeting AChE affect some of the fundamental processes that contribute to neurodegeneration, but whether HX might act in a disease-modifying manner in AD patients remains to be proven., (Copyright © 2010 S. Karger AG, Basel.)