Identification of microtubule-associated protein tau isoforms in Alzheimer's paired helical filaments

Structural characterization of polysaccharide purified from Hericium erinaceus fermented mycelium and its pharmacological basis for application in Alzheimer's disease: Oxidative stress related calcium homeostasis

The purified polysaccharides from Hericium erinaceus fermented mycelium entitled with PHEB was analyzed and it was mainly composed of six glycosidic bonds. It has been confirmed to show the relieving activity against Alzheimer's Disease (AD)- just as behaviors of B6C3-Tg (APPswePSEN1d E9)/Nju double transgenic [Genotype: (Appswe)T, (Psen1) T] (APP/PS1) mice. Six-week PHEB administration significantly improved the cognitive behavior of mice. Brain injury, amyloid beta deposition and tau hyperphosphorylation were alleviated in PHEB-treated AD mice without changes in other tissues. PHEB alleviated the oxidative stress in brains of AD mice via regulation the Nrf2 and its downstream kinase, which further improved the cholinergic system function. Proteomics and bioinformatics analysis showed that the therapeutic effect of PHEB is achieved by regulating calcium homeostasis mediated by oxidative stress. Furthermore, PHEB regulated the CaMK II/IV to achieve the calcium homeostasis in brains; and ultimately to show the anti-AD property.

Phospho-Tau Protein Expression in the Cell Cycle of SH-SY5Y Neuroblastoma Cells: A Morphological Study

It has been reported that the main function of tau protein is to stabilize microtubules and promote the movement of organelles through the axon in neurons. In Alzheimer's disease, tau protein is the major constituent of the paired helical filament, and it undergoes post-translational modifications including hyperphosphorylation and truncation. Whether other functions of tau protein are involved in Alzheimer's disease is less clear. We used SH-SY5Y human neuroblastoma cells as an in vitro model to further study the functions of tau protein. We detected phosphorylated tau protein as small dense dots in the cell nucleus, which strongly colocalize with intranuclear speckle structures that were also labelled with an antibody to SC35, a protein involved in nuclear RNA splicing. We have shown further that tau protein, phosphorylated at the sites recognized by pT231, TG-3, and AD2 antibodies, is closely associated with cell division. Different functions may be characteristic of phosphorylation at specific sites. Our findings suggest that the presence of tau protein is involved in separation of sister chromatids in anaphase, and that tau protein also participates in maintaining the integrity of the DNA (pT231, prophase) and chromosomes during cell division (TG-3).

Selectively increased oxidative modifications mapped to detergent‐insoluble forms of Aβ and β‐III tubulin in Alzheimer's disease

Deleterious post-translational modifications (PTMs) to the neuronal cytoskeleton are a proposed mechanistic link between accumulation of amyloid (A) beta peptides and subsequent abnormalities of tau and neurodegeneration in Alzheimer's disease (AD). Here we tested the hypothesis that PTMs on neuronal tubulins selectively accumulate in a pathological protein fraction in AD. We used new software, P-MOD, to identify comprehensively and map PTMs using mass spectral data from soluble (normal) and detergent-insoluble (pathological) protein fractions from AD, as well as total extracts from controls, for selected proteins: Abeta, tau, apolipoprotein (apo) E, glial fibrillary acidic protein (GFAP), alpha-III tubulin, and beta-III tubulin. Our results confirmed direct observations of others by identifying methionine (M) sulfoxides at Abeta position 35 and numerous sites of tau phosphorylation in detergent-insoluble protein from AD, while no PTMs were enriched on primarily astrocyte-derived apoE or GFAP in this fraction. P-MOD mapped several abundant M sulfoxides to neuron-enriched beta-III tubulin but not its heterodimeric partner, neuron-enriched alpha-III tubulin, a result confirmed by selective suppression of CNBr-mediated cleavage of beta-III tubulin. These findings are the first comprehensive assessment of PTMs in AD and point to oxidative modification of beta-III tubulin as a potential contributor to the neuronal cytoskeletal disruption that is characteristic of AD.

Characterisation of cytoskeletal abnormalities in mice transgenic for wild-type human tau and familial Alzheimer's disease mutants of APP and presenilin-1

To study the role of Abeta amyloid deposits in the generation of cytoskeletal lesions, we have generated a transgenic mouse line coexpressing in the same neurons a wild-type human tau isoform (0N3R), a mutant form of APP (751SL) and a mutant form of PS1 (M146L). These mice developed early cerebral extracellular deposits of Abeta, starting at 2.5 months. A somatodendritic neuronal accumulation of transgenic tau protein was observed in tau only and in tau/PS1/APP transgenic mice, including in neurons adjacent to Abeta deposits. The phosphorylation status of this somatodendritic tau was similar in the two transgenic lines. The Abeta deposits were surrounded by a neuritic reaction composed of axonal dystrophic processes, immunoreactive for many phosphotau epitopes and for the human tau transgenic protein. Ultrastructural observation showed in these dystrophic neurites a disorganisation of the microtubule and the neurofilament network but animals that were observed up to 18 months of age did not develop neurofibrillary tangles. These results indicate that overexpression of mutant PS1, mutant APP and of wild-type human tau were not sufficient per se to drive the formation of neurofibrillary tangles in a transgenic model. The Abeta deposits, however, were associated to marked changes in cytoskeletal organisation and in tau phosphorylation in adjacent dystrophic neurites.

Gene-environment interplay in neurogenesis and neurodegeneration

Factors associated with predisposition and vulnerability to neurodegenerative disorders may be described usefully within the context of gene-environment interplay. There are many identified genetic determinants for so-called genetic disorders, and it is possible to duplicate many elements of recognized human neurodegenerative disorders in either knock-in or knock-out mice. However, there are similarly, many identifiable environmental influences on outcomes of the genetic defects; and the course of a progressive neurodegenerative disorder can be greatly modified by environmental elements. Constituent cellular defense mechanisms responsive to the challenge of increased reactive oxygen species represent only one crossroad whereby environment can influence genetic predisposition. In this paper we highlight some of the major neurodegenerative disorders and discuss possible links of gene-environment interplay. The process of adult neurogenesis in brain is also presented as an additional element that influences gene-environment interplay. And the so-called priming processes (i.e., production of receptor supersensitization by repeated drug dosing), is introduced as yet another process that influences how genes and environment ultimately and co-dependently govern behavioral ontogeny and outcome. In studies attributing the influence of genetic alteration on behavioral phenotypy, it is essential to carefully control environmental influences.

Transgenic expression of the shortest human tau affects its compartmentalization and its phosphorylation as in the pretangle stage of Alzheimer's disease

We have generated transgenic mice expressing the shortest human tau protein, the microtubule-associated protein that composes paired helical filaments in Alzheimer's disease. Transgenic tau transcripts and proteins were strongly expressed in neurons in the developing and adult brain. In contrast to the endogenous tau that progressively disappeared from neuronal cell bodies during development, the human transgenic tau remained abundant in cell bodies and dendrites of a subset of neurons in the adult. This somatodendritic transgenic tau was immunoreactive with antibodies to tau phosphorylated on Thr181 and Thr231 and with the conformation-dependent Alz50 antibody. A few astrocytes expressing the transgenic tau were strongly immunoreactive with antibodies to additional tau phosphorylation sites, ie, at Ser262/ 356 and Ser396/404. All of these phosphorylation sites have been identified in paired helical filaments-tau proteins. In electron microscopy, the transgenic tau was detected into microtubules in axons and in dendrites but not in cell bodies. Neurofibrillary tangles were not detected in transgenic animals examined up to the age of 19 months. These results indicate that transgenic manipulation of tau expression and intracellular targeting is sufficient per se to affect tau compartmentalization, phosphorylation, and conformation partly as it is observed at the pretangle stage in Alzheimer's disease.

Assembled tau filaments differ from native paired helical filaments as determined by scanning transmission electron microscopy (STEM)

Paired helical filaments (PHF) are abnormal, approximately 20-25-nm wide periodically twisted filaments, which accumulate in Alzheimer's disease (AD) brain and other neurodegenerative disorders, including corticobasal degeneration (CBD). PHF are primarily composed of highly phosphorylated tau protein. However, both phosphorylated and non-phosphorylated forms of tau are able to assemble in vitro into filaments similar in the ultrastructural appearance to PHF. In the present study, filaments were assembled in vitro from unmodified recombinant human tau and the physical mass per unit length of filaments and the mass density were determined using scanning transmission electron microscopy (STEM). Two general types of filaments were observed. One type was composed of 11.4 nm-wide, 10-75 nm long, frequently twisted and PHF-like filaments, with a mass per unit length (44 kDa/nm) approximately one third of that observed in isolated AD filaments. The other were straight filaments, approximately 6.8-nm wide and 0.2-2 microm long, which often formed parallel clusters of two or more filaments. Triple clusters were 19. 2-nm wide and had a mass per unit length (70 kDa/nm) approximately two thirds of that seen in isolated AD filaments. Despite different morphology, both twisted and straight filaments had mass densities between 0.48-0.55 kDa/nm3. These values are significantly higher than those reported for PHF found either in AD (0.40 kDa/nm3) or CBD (0.33 kDa/nm3). These results suggest that the packing of tau differs in vivo from that observed in vitro and that specific tau isoform content, elongation of tau molecules by phosphorylation or other factors may be required to reproduce pathological assembly. Therefore mass density determinations appear to be an important criterion in comparing various filaments.