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Concept: Beta amyloid

318

Amyloidosis is a major problem in over one hundred diseases, including Alzheimer’s disease (AD). Using the iDISCO visualization method involving targeted molecular labeling, tissue clearing, and light-sheet microscopy, we studied plaque formation in the intact AD mouse brain at up to 27 months of age. We visualized amyloid plaques in 3D together with tau, microglia, and vasculature. Volume imaging coupled to automated detection and mapping enables precise and fast quantification of plaques within the entire intact mouse brain. The present methodology is also applicable to analysis of frozen human brain samples without specialized preservation. Remarkably, amyloid plaques in human brain tissues showed greater 3D complexity and surprisingly large three-dimensional amyloid patterns, or TAPs. The ability to visualize amyloid in 3D, especially in the context of their micro-environment, and the discovery of large TAPs may have important scientific and medical implications.

Concepts: Congo red, Disease, Scientific method, Amyloidosis, Human brain, Amyloid, Neuron, Beta amyloid

308

The genetic predispositions which describe a diagnosis of familial Alzheimer’s disease can be considered as cornerstones of the amyloid cascade hypothesis. Essentially they place the expression and metabolism of the amyloid precursor protein as the main tenet of disease aetiology. However, we do not know the cause of Alzheimer’s disease and environmental factors may yet be shown to contribute towards its onset and progression. One such environmental factor is human exposure to aluminium and aluminium has been shown to be present in brain tissue in sporadic Alzheimer’s disease. We have made the first ever measurements of aluminium in brain tissue from 12 donors diagnosed with familial Alzheimer’s disease. The concentrations of aluminium were extremely high, for example, there were values in excess of 10μg/g tissue dry wt. in 5 of the 12 individuals. Overall, the concentrations were higher than all previous measurements of brain aluminium except cases of known aluminium-induced encephalopathy. We have supported our quantitative analyses using a novel method of aluminium-selective fluorescence microscopy to visualise aluminium in all lobes of every brain investigated. The unique quantitative data and the stunning images of aluminium in familial Alzheimer’s disease brain tissue raise the spectre of aluminium’s role in this devastating disease.

Concepts: Protein, Beta amyloid, Dementia, Amyloid precursor protein, Scientific method, Environment, Neuron, Alzheimer's disease

188

The glymphatic system is a recently defined brain-wide paravascular pathway for cerebrospinal fluid (CSF) and interstitial fluid (ISF) exchange that facilitates efficient clearance of solutes and waste from the brain. CSF enters the brain along para-arterial channels to exchange with ISF, which is in turn cleared from the brain along para-venous pathways. Because soluble amyloid β clearance depends on glymphatic pathway function, we proposed that failure of this clearance system contributes to amyloid plaque deposition and Alzheimer’s disease progression. Here we provide proof of concept that glymphatic pathway function can be measured using a clinically relevant imaging technique. Dynamic contrast-enhanced MRI was used to visualize CSF-ISF exchange across the rat brain following intrathecal paramagnetic contrast agent administration. Key features of glymphatic pathway function were confirmed, including visualization of para-arterial CSF influx and molecular size-dependent CSF-ISF exchange. Whole-brain imaging allowed the identification of two key influx nodes at the pituitary and pineal gland recesses, while dynamic MRI permitted the definition of simple kinetic parameters to characterize glymphatic CSF-ISF exchange and solute clearance from the brain. We propose that this MRI approach may provide the basis for a wholly new strategy to evaluate Alzheimer’s disease susceptibility and progression in the live human brain.

Concepts: Neurology, Beta amyloid, Blood-brain barrier, Neuron, Magnetic resonance imaging, Central nervous system, Brain, Cerebrospinal fluid

181

It has been shown that caloric restriction (CR) delays aging and possibly delays the development of Alzheimer’s disease (AD). We conjecture that the mechanism may involve interoceptive cues, rather than reduced energy intake per se. We determined that hunger alone, induced by a ghrelin agonist, reduces AD pathology and improves cognition in the APP-SwDI mouse model of AD. Long-term treatment with a ghrelin agonist was sufficient to improve the performance in the water maze. The treatment also reduced levels of amyloid beta (Aβ) and inflammation (microglial activation) at 6 months of age compared to the control group, similar to the effect of CR. Thus, a hunger-inducing drug attenuates AD pathology, in the absence of CR, and the neuroendocrine aspects of hunger also prevent age-related cognitive decline.

Concepts: Amyloid, Memory, Inclusion body myositis, Pathology, Senescence, Cognition, Beta amyloid, Alzheimer's disease

172

Over the past two decades, it has become increasingly apparent that Alzheimer’s disease neuropathology is characterized by activated microglia (brain resident macrophages) as well as the classic features of amyloid plaques and neurofibrillary tangles. The intricacy of microglial biology has also become apparent, leading to a heightened research interest in this particular cell type. Over the years a number of different microglial cell culturing techniques have been developed to study either primary mammalian microglia, or immortalized cell lines. Each microglial system has advantages and disadvantages and should be selected for its appropriateness in a particular research context. This review summarizes several of the most common microglial cell culture systems currently being employed in Alzheimer’s research including primary microglia; BV2 and N9 retroviral immortalized microglia; human immortalized microglia (HMO6); and spontaneously immortalized rodent microglial lines (EOC lines and HAPI cells). Particularities of cell culture requirements and characteristics of microglial behavior, especially in response to applied inflammogen stimuli, are compared and discussed across these cell types.

Concepts: Neurology, Cell culture, Neurofibrillary tangle, Microglia, Cell biology, Beta amyloid, Alzheimer's disease, Cell

167

Alzheimer’s disease is a worldwide metabolic disease and an economically costly diseases to society, so more medicines need to be developed to treat this disease. Huperzine A, a novel lycopodium alkaloid isolated from tranditional Chinese medicine Huperzia serrata (Qian Ceng Ta), has been shown to possess multiple neuroprotective effects for Alzheimer’s disease, but the precise pharmacological mechanism of huperzine A is unclear and need to be further investigated. In this study, proteins from untreated N2a cells (Con group), cells pre-incubated with huperzine A followed by Aβ (1-42) oligomers treatment (HupA group) and cells treated with Aβ (1-42) oligomers (Aβ group) with 5 biological replicates in each cohort, were processed in centrifugal proteomic reactor and quantified by label-free quantitation. A total of 2860 proteins were quantified with high confidence, and 198 proteins were significantly changed (with P-value <0.05) between HupA and Aβ cohorts. The pathway and direct protein-protein interaction network analysis showed that huperzine A protects N2a cells against Aβ oligomer-induced cell death by down-regulation of cellular tumor antigen p53 (Trp53) expression.

Concepts: Proteomics, Medicine, Cancer, Beta amyloid, Huperzine A, Acetylcholinesterase inhibitor, Huperzia serrata, Protein

112

Alzheimer’s disease (AD) is characterized by accumulation of the β-amyloid peptide (Aβ), which is generated through sequential proteolysis of the amyloid precursor protein (APP), first by the action of β-secretase, generating the β-C-terminal fragment (βCTF), and then by the Presenilin 1 (PS1) enzyme in the γ-secretase complex, generating Aβ. γ-Secretase is an intramembranous protein complex composed of Aph1, Pen2, Nicastrin, and Presenilin 1. Although it has a central role in the pathogenesis of AD, knowledge of the mechanisms that regulate PS1 function is limited. Here, we show that phosphorylation of PS1 at Ser367 does not affect γ-secretase activity, but has a dramatic effect on Aβ levels in vivo. We identified CK1γ2 as the endogenous kinase responsible for the phosphorylation of PS1 at Ser367. Inhibition of CK1γ leads to a decrease in PS1 Ser367 phosphorylation and an increase in Aβ levels in cultured cells. Transgenic mice in which Ser367 of PS1 was mutated to Ala, show dramatic increases in Aβ peptide and in βCTF levels in vivo. Finally, we show that this mutation impairs the autophagic degradation of βCTF, resulting in its accumulation and increased levels of Aβ peptide and plaque load in the brain. Our results demonstrate that PS1 regulates Aβ levels by a unique bifunctional mechanism. In addition to its known role as the catalytic subunit of the γ-secretase complex, selective phosphorylation of PS1 on Ser367 also decreases Aβ levels by increasing βCTF degradation through autophagy. Elucidation of the mechanism by which PS1 regulates βCTF degradation may aid in the development of potential therapies for Alzheimer’s disease.

Concepts: Protein, Beta amyloid, Enzyme, Signal transduction, Peptide, Presenilin, Amyloid precursor protein, Alzheimer's disease

105

Alzheimer’s disease is the most common form of dementia in the western world, however there is no cure available for this devastating neurodegenerative disorder. Despite clinical and experimental evidence implicating the intestinal microbiota in a number of brain disorders, its impact on Alzheimer’s disease is not known. To this end we sequenced bacterial 16S rRNA from fecal samples of Aβ precursor protein (APP) transgenic mouse model and found a remarkable shift in the gut microbiota as compared to non-transgenic wild-type mice. Subsequently we generated germ-free APP transgenic mice and found a drastic reduction of cerebral Aβ amyloid pathology when compared to control mice with intestinal microbiota. Importantly, colonization of germ-free APP transgenic mice with microbiota from conventionally-raised APP transgenic mice increased cerebral Aβ pathology, while colonization with microbiota from wild-type mice was less effective in increasing cerebral Aβ levels. Our results indicate a microbial involvement in the development of Abeta amyloid pathology, and suggest that microbiota may contribute to the development of neurodegenerative diseases.

Concepts: Gene expression, Beta amyloid, Neurodegenerative disorders, Molecular biology, Alzheimer's disease, Gut flora, Bacteria, Neurology

101

Alzheimer’s disease (AD) is a devastating condition with no known effective treatment. AD is characterized by memory loss as well as impaired locomotor ability, reasoning, and judgment. Emerging evidence suggests that the innate immune response plays a major role in the pathogenesis of AD. In AD, the accumulation of β-amyloid (Aβ) in the brain perturbs physiological functions of the brain, including synaptic and neuronal dysfunction, microglial activation, and neuronal loss. Serum levels of soluble ST2 (sST2), a decoy receptor for interleukin (IL)-33, increase in patients with mild cognitive impairment, suggesting that impaired IL-33/ST2 signaling may contribute to the pathogenesis of AD. Therefore, we investigated the potential therapeutic role of IL-33 in AD, using transgenic mouse models. Here we report that IL-33 administration reverses synaptic plasticity impairment and memory deficits in APP/PS1 mice. IL-33 administration reduces soluble Aβ levels and amyloid plaque deposition by promoting the recruitment and Aβ phagocytic activity of microglia; this is mediated by ST2/p38 signaling activation. Furthermore, IL-33 injection modulates the innate immune response by polarizing microglia/macrophages toward an antiinflammatory phenotype and reducing the expression of proinflammatory genes, including IL-1β, IL-6, and NLRP3, in the cortices of APP/PS1 mice. Collectively, our results demonstrate a potential therapeutic role for IL-33 in AD.

Concepts: Beta amyloid, Memory, Cognition, Brain, Neuron, Innate immune system, Alzheimer's disease, Immune system

86

In Alzheimer’s disease, aggregates of Aβ and tau in amyloid plaques and neurofibrillary tangles spread progressively across brain tissues following a characteristic pattern, implying a tissue-specific vulnerability to the disease. We report a transcriptional analysis of healthy brains and identify an expression signature that predicts-at ages well before the typical onset-the tissue-specific progression of the disease. We obtain this result by finding a quantitative correlation between the histopathological staging of the disease and the expression patterns of the proteins that coaggregate in amyloid plaques and neurofibrillary tangles, together with those of the protein homeostasis components that regulate Aβ and tau. Because this expression signature is evident in healthy brains, our analysis provides an explanatory link between a tissue-specific environmental risk of protein aggregation and a corresponding vulnerability to Alzheimer’s disease.

Concepts: Transcription, Peptide, Histopathology, Gene, Neurofibrillary tangle, Beta amyloid, Alzheimer's disease