Secretases Related to Amyloid Precursor Protein Processing

Alzheimer’s disease (AD) is a common neurodegenerative disease whose prevalence increases with age. An increasing number of findings suggest that abnormalities in the metabolism of amyloid precursor protein (APP), a single transmembrane aspartic protein that is cleaved by β- and γ-secretases to produce β-amyloid protein (Aβ), are a major pathological feature of AD. In recent years, a large number of studies have been conducted on the APP processing pathways and the role of secretion. This paper provides a summary of the involvement of secretases in the processing of APP and the potential drug targets that could provide new directions for AD therapy.

Cell line construction and maintenance for Lyso-IP and Endo-IP analysis of amyloid precursor protein processing v1

Lyso-IP is a method that allows for the isolation of lysosomes for proteomics and metabolomics (dx.doi.org/10.17504/protocols.io.bybjpskn; dx.doi.org/10.17504/protocols.io.bx9hpr36). We have developed an analogous approach for purification of early/sorting endosomes (Endo-IP). In addition, we have found that endolysosomal purification via Lyso-IP and Endo-IP can be coupled with a quantitative proteomics workflow to obtain snapshots of Amyloid Precursor Protein (APP) processing to its Aβ products (Park et al. in submission). Here, we describe methods for cell line construction and maintenance of 293 cells with TMEM192-3xHA and 3xFLAG-EEA1, which are used for lysosome and endosome purification, respectively, with the addition of patient mutations to APP promotes processing. Cells with endogenously tagged TMEM192 and stably expressing FLAG-EEA1 are referred to as 293EL cells, for Endo-IP and Lyso-IP. These cells were also prepared in a form that has a deletion of the APP gene (293EL;APP-/-) and the same cells reconstituted with a lentivirus stably expressing APPSw;T700N to allow functional analysis of APP processing.

Changes in cortical gene expression in the muscarinic M1 receptor knockout mouse: potential relevance to schizophrenia, Alzheimer’s disease and cognition

Postmortem and neuroimaging studies show low levels of cortical muscarinic M1 receptors (CHRM1) in patients with schizophrenia which is significant because CHRM signalling has been shown to change levels of gene expression and cortical gene expression is altered in schizophrenia. We decided to identify CHRM1-mediated changes in cortical gene expression by measuring levels of RNA in the cortex of the Chrm1−/− mouse (n = 10), where there would be no signalling by that receptor, and in wild type mouse (n = 10) using the Affymetrix Mouse Exon 1.0 ST Array. We detected RNA for 15,501 annotated genes and noncoding RNA of which 1,467 RNAs were higher and 229 RNAs lower in the cortex of the Chrm1−/− mouse. Pathways and proteins affected by the changes in cortical gene expression in the Chrm1−/− are linked to the molecular pathology of schizophrenia. Our human cortical gene expression data showed 47 genes had altered expression in Chrm1−/− mouse and the frontal pole from patients with schizophrenia with the change in expression of 44 genes being in opposite directions. In addition, genes with altered levels of expression in the Chrm1−/− mouse have been shown to affect amyloid precursor protein processing which is associated with the pathophysiology of Alzheimer’s disease, and 69 genes with altered expression in the Chrm1−/− mouse are risk genes associated with human cognitive ability. Our findings argue CHRM1-mediated changes in gene expression are relevant to the pathophysiologies of schizophrenia and Alzheimer’s disease and the maintenance of cognitive ability in humans.

Therapeutic Effects of Aripiprazole in the 5xFAD Alzheimer’s Disease Mouse Model

Global aging has led to growing health concerns posed by Alzheimer’s disease (AD), the most common type of dementia. Aripiprazole is an atypical FDA-approved anti-psychotic drug with potential against AD. To investigate its therapeutic effects on AD pathology, we administered aripiprazole to 5xFAD AD model mice and examined beta-amyloid (βA)-induced AD-like phenotypes, including βA production, neuroinflammation, and cerebral glucose metabolism. Aripiprazole administration significantly decreased βA accumulation in the brains of 5xFAD AD mice. Aripiprazole significantly modified amyloid precursor protein processing, including carboxyl-terminal fragment β and βA, a disintegrin and metalloproteinase domain-containing protein 10, and beta-site APP cleaving enzyme 1, as determined by Western blotting. Neuroinflammation, as evidenced by ionized calcium binding adapter molecule 1 and glial fibrillary acidic protein upregulation was dramatically inhibited, and the neuron cell layer of the hippocampal CA1 region was preserved following aripiprazole administration. In 18F-fluorodeoxyglucose positron emission tomography, after receiving aripiprazole, 5xFAD mice showed a significant increase in glucose uptake in the striatum, thalamus, and hippocampus compared to vehicle-treated AD mice. Thus, aripiprazole effectively alleviated βA lesions and prevented the decline of cerebral glucose metabolism in 5xFAD AD mice, suggesting its potential for βA metabolic modification and highlighting its therapeutic effect over AD progression.

Investigation of the Iron Oxide Nanoparticle Effects on Amyloid Precursor Protein Processing in Hippocampal Cells

Introduction: Iron oxide nanoparticles (Fe2O3-NPs) are small magnetic particles that widely used in different aspects of biology and medicine in modern life. Fe2O3-NP accumulated in the living cells due to absence of active system to excrete the iron ions so damages cellular organelles by highly reactivity. Method: Herein cytotoxic effects of Fe2O3-NP with 50 nm size were investigated on primary culture of neonatal rat hippocampus by MTT assay. Pathophysiological signs of Alzheimer disease such as amyloid precursor protein (APP) expression, Aβ aggregation, soluble APPα and APPβ secretion also were investigated in hippocampal cells treated by various concentration of NP for different exposure time. Results: Our results revealed, Fe2O3-NP treatment causes oxidative stress in cells that accompanied by upregulation of the APP and Aβ in a concentration dependent manner. NP exposing also leads to more secretion of sAPPβ rather than sAPPα that concluded to increased activation of β-secretase in NP received cells. All of the harmful effects accumulate in neurons that could not be renovated so lead to neurodegeneration in Alzheimer disease. Conclusion: This study approved iron-based NPs could help to develop the Alzheimer and related neurological disorders and explained why some of the iron chelators have therapeutic potential in Alzheimer disease.

Dysregulated Wnt Signalling in the Alzheimer’s Brain

The Wnt signalling system is essential for both the developing and adult central nervous system. It regulates numerous cellular functions ranging from neurogenesis to blood brain barrier biology. Dysregulated Wnt signalling can thus have significant consequences for normal brain function, which is becoming increasingly clear in Alzheimer’s disease (AD), an age-related neurodegenerative disorder that is the most prevalent form of dementia. AD exhibits a range of pathophysiological manifestations including aberrant amyloid precursor protein processing, tau pathology, synapse loss, neuroinflammation and blood brain barrier breakdown, which have been associated to a greater or lesser degree with abnormal Wnt signalling. Here we provide a comprehensive overview of the role of Wnt signalling in the CNS, and the research that implicates dysregulated Wnt signalling in the ageing brain and in AD pathogenesis. We also discuss the opportunities for therapeutic intervention in AD via modulation of the Wnt signalling pathway, and highlight some of the challenges and the gaps in our current understanding that need to be met to enable that goal.

Effects of Radiofrequency Electromagnetic Fields and Ionizing Radiation on Amyloid Precursor Protein Processing and Cell Death

The growing concerns regarding the adverse biological effects of radiofrequency electromagnetic fields (RF-EMFs), which are generated by common electronic devices, on the human brain led us to investigate their impact on Alzheimer’s disease (AD). We aimed to establish the effects of RF-EMF on the expression of molecular markers associated with amyloid precursor protein (APP), cell death, and clonogenic survival in HT22 and APP-overexpressing 7w-PSML cells. We compared the effects of RF-EMF at a high specific absorption rate (SAR) level with the neuronal-cell-death-inducing effects of ionizing radiation (IR). RF-EMF exposure (8 W/kg SAR) promoted the protein expression of ADAM10 (α-secretase) in the HT22 cells (<i>p</i> < 0.05) and downregulated the APP mRNA level in the 7w-PSML cells (<i>p</i> < 0.01). In contrast, IR (10 Gy) significantly reduced the APP and a disintegrin and metalloproteinase 10 (ADAM10) levels without altering their respective mRNA levels in these cells. Interestingly, IR exposure significantly upregulated BACE1 (α-secretase) at both the protein and mRNA levels, suggesting adverse effects in AD. IR induced cell death and reduced clonogenic survival in both cell lines. Although RF-EMF (high SAR level) influenced APP processing, it did not induce any deleterious change in either cell line. Thus, further studies are necessary to clarify the influence of RF-EMF on AD.