Preparation of nuclear matrices from cultured cells: subfractionation of nuclei in situ

Analyses of the different structural systems of the nucleus and the proteins associated with them pose many problems. Because these systems are largely overlapping, in situ localization studies that preserve the in vivo location of proteins and cellular structures often are not satisfactory. In contrast, biochemical cell fractionation may provide artifactual results due to cross-contamination of extracts and structures. To overcome these problems, we have developed a method that combines biochemical cell fractionation and in situ localization and leads to the preparation of a residual cellular skeleton (nuclear matrix and cytoskeletal elements) from cultured cells. This method's main feature is that cell fractionation is performed in situ. Therefore, structures not solubilized in a particular extraction step remain attached to the substrate and retain their morphology. Before and after each extraction step they can be analyzed for the presence and location of the protein under study by using immunological or cytochemical techniques. Thereby the in vivo origin of a protein solubilized in a particular extraction step is determined. The solubilized protein then may be further characterized biochemically. In addition, to allow analyses of proteins associated with the residual cellular skeleton, we have developed conditions for its solubilization that do not interfere with enzymatic and immunological studies

Assembly of Protein 4.1 during Chicken Erythroid Differentiation

Protein 4.1 is a peripheral membrane protein that strengthens the actin-spectrin based membrane skeleton of the red blood cell and also serves to attach this structure to the plasma membrane. In avian erythrocytes it exists as a family of closely related polypeptides that are differentially expressed during erythropoiesis. We have analyzed the synthesis and assembly onto the membrane skeleton of protein 4.1 and in this paper we show that its assembly is extremely rapid and highly efficient since greater than 95% of the molecules synthesized are assembled in less than 1 min. The remaining minor fraction of unassembled protein 4.1 differs kinetically and is either degraded or assembled with slower kinetics. All protein 4.1 variants exhibit a similar kinetic behavior irrespective of the stage of erythroid differentiation. Thus, the amount and the variants ratio of protein 4.1 assembled are determined largely at the transcriptional or at the translational level and not posttranslationally. During erythroid terminal differentiation the molar amounts of protein 4.1 and spectrin assembled change. In postmitotic cells, as compared with proliferative cells, far more protein 4.1 than spectrin is assembled onto the membrane-skeleton. This modulation may permit the assembly of an initially flexible membrane skeleton in mitotic erythroid cells. As cells become postmitotic and undergo the final steps of maturation the membrane skeleton may be gradually stabilized by the assembly of protein 4.1

Expression of complement system components during aging and amyloid deposition in APP transgenic mice

<p>Abstract</p> <p>Background</p> <p>A causal role of the complement system in Alzheimer's disease pathogenesis has been postulated based on the identification of different activated components up to the membrane attack complex at amyloid plaques in brain. However, histological studies of amyloid plaque bearing APP transgenic mice provided only evidence for an activation of the early parts of the complement cascade. To better understand the contribution of normal aging and amyloid deposition to the increase in complement activation we performed a detailed characterization of the expression of the major mouse complement components.</p> <p>Methods</p> <p>APP23 mice expressing human APP751 with the Swedish double mutation as well as C57BL/6 mice were used at different ages. mRNA was quantified by Realtime PCR and the age- as well as amyloid induced changes determined. The protein levels of complement C1q and C3 were analysed by Western blotting. Histology was done to test for amyloid plaque association and activation of the complement cascade.</p> <p>Results</p> <p>High mRNA levels were detected for C1q and some inhibitory complement components. The expression of most activating components starting at C3 was low. Expression of C1q, C3, C4, C5 and factor B mRNA increased with age in control C57BL/6 mice. C1q and C3 mRNA showed a substantial additional elevation during amyloid formation in APP23 mice. This increase was confirmed on the protein level using Western blotting, whereas immunohistology indicated a recruitment of complement to amyloid plaques up to the C3 convertase.</p> <p>Conclusion</p> <p>Early but not late components of the mouse complement system show an age-dependent increase in expression. The response to amyloid deposition is comparatively smaller. The low expression of C3 and C5 and failure to upregulate C5 and downstream components differs from human AD brain and likely contributes to the lack of full complement activation in APP transgenic mice.</p

Neuronal microRNA eeregulation in response to Alzheimer's disease Amyloid-β

Normal brain development and function depends on microRNA (miRNA) networks to fine tune the balance between the transcriptome and proteome of the cell. These small non-coding RNA regulators are highly enriched in brain where they play key roles in neuronal development, plasticity and disease. In neurodegenerative disorders such as Alzheimer's disease (AD), brain miRNA profiles are altered; thus miRNA dysfunction could be both a cause and a consequence of disease. Our study dissects the complexity of human AD pathology, and addresses the hypothesis that amyloid-beta (Abeta) itself, a known causative factor of AD, causes neuronal miRNA deregulation, which could contribute to the pathomechanisms of AD. We used sensitive TaqMan low density miRNA arrays (TLDA) on murine primary hippocampal cultures to show that about half of all miRNAs tested were down-regulated in response to Abeta peptides. Time-course assays of neuronal Abeta treatments show that Abeta is in fact a powerful regulator of miRNA levels as the response of certain mature miRNAs is extremely rapid. Bioinformatic analysis predicts that the deregulated miRNAs are likely to affect target genes present in prominent neuronal pathways known to be disrupted in AD. Remarkably, we also found that the miRNA deregulation in hippocampal cultures was paralleled in vivo by a deregulation in the hippocampus of Abeta42-depositing APP23 mice, at the onset of Abeta plaque formation. In addition, the miRNA deregulation in hippocampal cultures and APP23 hippocampus overlaps with those obtained in human AD studies. Taken together, our findings suggest that neuronal miRNA deregulation in response to an insult by Abeta may be an important factor contributing to the cascade of events leading to AD.N.S. is supported by the Human Frontier Science Program. L.I. is supported by the National Health and Medical Research Council (NHMRC) and the Australian Research Council (ARC), and J.G. is supported by grants from the University of Sydney, the National Health and Medical Research Council (NHMRC), the Australian Research Council (ARC), and the J.O. & J.R. Wicking Trust. Postgraduate scholarship support has been provided by the Wenkart Foundation, GlaxoSmithKline and Alzheimer’s Australia

Expression profiling in APP23 mouse brain: inhibition of Aβ amyloidosis and inflammation in response to LXR agonist treatment

BACKGROUND:Recent studies demonstrate that in addition to its modulatory effect on APP processing, in vivo application of Liver X Receptor agonist T0901317 (T0) to APP transgenic and non-transgenic mice decreases the level of Aß42. Moreover, in young Tg2576 mice T0 completely reversed contextual memory deficits. Compared to other tissues, the regulatory functions of LXRs in brain remain largely unexplored and our knowledge so far is limited to the cholesterol transporters and apoE. In this study we applied T0 to APP23 mice for various times and examined gene and protein expression. We also performed a series of experiments with primary brain cells derived from wild type and LXR knockout mice subjected to various LXR agonist treatments and inflammatory stimuli.RESULTS:We demonstrate an upregulation of genes related to lipid metabolism/transport, metabolism of xenobiotics and detoxification. Downregulated genes are involved in immune response and inflammation, cell death and apoptosis. Additional treatment experiments demonstrated an increase of soluble apolipoproteins E and A-I and a decrease of insoluble Aß. In primary LXRwt but not in LXRa-/-ß-/- microglia and astrocytes LXR agonists suppressed the inflammatory response induced by LPS or fibrillar Aß.CONCLUSION:The results show that LXR agonists could alleviate AD pathology by acting on amyloid deposition and brain inflammation. An increased understanding of the LXR controlled regulation of Aß aggregation and clearance systems will lead to the development of more specific and powerful agonists targeting LXR for the treatment of AD

Amyloid Beta Annular Protofibrils in Cell Processes and Synapses Accumulate with Aging and Alzheimer-Associated Genetic Modification

Amyloid β (Aβ) annular protofibrils (APFs) have been described where the structure is related to that of β barrel pore-forming bacterial toxins and exhibits cellular toxicity. To investigate the relationship of Aβ APFs to disease and their ultrastructural localization in brain tissue, we conducted a pre-embedding immunoelectron microscopic study using anti-annular protofibril antiserum. We examined brain tissues of young- and old-aged amyloid precursor protein transgenic mice (APP23), neprilysin knockout APP23 mice, and nontransgenic littermates. αAPF-immunoreactions tended to be found (1) on plasma membranes and vesicles inside of cell processes, but not on amyloid fibrils, (2) with higher density due to aging, APP transgene, and neprilysin deficiency, and (3) with higher positive rate at synaptic compartments in aged APP23, especially in neprilysin knockout APP23 mice. These findings imply that APFs are distinct from amyloid fibrils, interact with biological membranes, and might be related to synaptic dysfunction in Alzheimer model mouse brains

Memory deficits in APP23/Abca1+/− mice correlate with the level of Aβ oligomers

ABCA1, a member of the ATP-binding cassette family of transporters, lipidates ApoE (apolipoprotein A) and is essential for the generation of HDL (high-density lipoprotein)-like particles in the CNS (central nervous system). Lack of Abca1 increases amyloid deposition in several AD (Alzheimer's disease) mouse models. We hypothesized that deletion of only one copy of Abca1 in APP23 (where APP is amyloid precursor protein) AD model mice will aggravate memory deficits in these mice. Using the Morris Water Maze, we demonstrate that 2-year-old Abca1 heterozygous APP23 mice (referred to as APP23/het) have impaired learning during acquisition, and impaired memory retention during the probe trial when compared with age-matched wild-type mice (referred to as APP23/wt). As in our previous studies, the levels of ApoE in APP23/het mice were decreased, but the differences in the levels of Aβ and thioflavin-S-positive plaques between both groups were insignificant. Importantly, dot blot analysis demonstrated that APP23/het mice have a significantly higher level of soluble A11-positive Aβ (amyloid β protein) oligomers compared with APP23/wt which correlated negatively with cognitive performance. To confirm this finding, we performed immunohistochemistry with the A11 antibody, which revealed a significant increase of A11-positive oligomer structures in the CA1 region of hippocampi of APP23/het. This characteristic region-specific pattern of A11 staining was age-dependent and was missing in younger APP23 mice lacking Abca1. In contrast, the levels of Aβ*56, as well as other low-molecular-mass Aβ oligomers, were unchanged among the groups. Overall, the results of the present study demonstrate that in aged APP23 mice memory deficits depend on Abca1 and are likely to be mediated by the amount of Aβ oligomers deposited in the hippocampus

Deletion of tumor necrosis factor death receptor inhibits amyloid β generation and prevents learning and memory deficits in Alzheimer's mice

The tumor necrosis factor type 1 death receptor (TNFR1) contributes to apoptosis. TNFR1, a subgroup of the TNFR superfamily, contains a cytoplasmic death domain. We recently demonstrated that the TNFR1 cascade is required for amyloid β protein (Aβ)–induced neuronal death. However, the function of TNFR1 in Aβ plaque pathology and amyloid precursor protein (APP) processing in Alzheimer's disease (AD) remains unclear. We report that the deletion of the TNFR1 gene in APP23 transgenic mice (APP23/TNFR1−/−) inhibits Aβ generation and diminishes Aβ plaque formation in the brain. Genetic deletion of TNFR1 leads to reduced β-secretase 1 (BACE1) levels and activity. TNFR1 regulates BACE1 promoter activity via the nuclear factor-κB pathway, and the deletion of TNFR1 in APP23 transgenic mice prevents learning and memory deficits. These findings suggest that TNFR1 not only contributes to neurodegeneration but also that it is involved in APP processing and Aβ plaque formation. Thus, TNFR1 is a novel therapeutic target for AD

Selective vulnerability of different types of commissural neurons for amyloid β-protein-induced neurodegeneration in APP23 mice correlates with dendritic tree morphology

The amyloid β-protein (Aβ) is the main component of Alzheimer's disease-related senile plaques. Although Aβ is associated with the development of Alzheimer's disease, it has not been shown which forms of Aβ induce neurodegeneration in vivo and which types of neurons are vulnerable. To address these questions, we implanted DiI crystals into the left frontocentral cortex of APP23 transgenic mice overexpressing mutant human APP (amyloid precursor protein gene) and of littermate controls. Traced commissural neurons in layer III of the right frontocentral cortex were quantified in 3-, 5-, 11- and 15-month-old mice. Three different types of commissural neurons were traced. At 3 months of age no differences in the number of labelled commissural neurons were seen in APP23 mice compared with wild-type mice. A selective reduction of the heavily ramified type of neurons was observed in APP23 mice compared with wild-type animals at 5, 11 and 15 months of age, starting when the first Aβ-deposits occurred in the frontocentral cortex at 5 months. The other two types of commissural neurons did not show alterations at 5 and 11 months. At 15 months, the number of traced sparsely ramified pyramidal neurons was reduced in addition to that of the heavily ramified neurons in APP23 mice compared with wild-type mice. At this time Aβ-deposits were seen in the neo- and allocortex as well as in the basal ganglia and the thalamus. In summary, our results show that Aβ induces progressive degeneration of distinct types of commissural neurons. Degeneration of the most vulnerable neurons starts in parallel with the occurrence of the first fibrillar Aβ-deposits in the neocortex, that is, with the detection of aggregated Aβ. The involvement of additional neuronal subpopulations is associated with the expansion of Aβ-deposition into further brain regions. The vulnerability of different types of neurons to Aβ, thereby, is presumably related to the complexity of their dendritic morpholog

Sex‐specific genetic factors affect the risk of early‐onset periodontitis in Europeans

Aims: Various studies have reported that young European women are more likely to develop early-onset periodontitis compared to men. A potential explanation for the observed variations in sex and age of disease onset is the natural genetic variation within the autosomal genomes. We hypothesized that genotype-by-sex (G × S) interactions contribute to the increased prevalence and severity. Materials and methods: Using the case-only design, we tested for differences in genetic effects between men and women in 896 North-West European early-onset cases, using imputed genotypes from the OmniExpress genotyping array. Population-representative 6823 controls were used to verify that the interacting variables G and S were uncorrelated in the general population. Results: In total, 20 loci indicated G × S associations (P < 0.0005), 3 of which were previously suggested as risk genes for periodontitis (ABLIM2, CDH13, and NELL1). We also found independent G × S interactions of the related gene paralogs MACROD1/FLRT1 (chr11) and MACROD2/FLRT3 (chr20). G × S-associated SNPs at CPEB4, CDH13, MACROD1, and MECOM were genome-wide-associated with heel bone mineral density (CPEB4, MECOM), waist-to-hip ratio (CPEB4, MACROD1), and blood pressure (CPEB4, CDH13). Conclusions: Our results indicate that natural genetic variation affects the different heritability of periodontitis among sexes and suggest genes that contribute to inter-sex phenotypic variation in early-onset periodontitis