Microglia drive APOE-dependent neurodegeneration in a tauopathy mouse model.

Chronic activation of brain innate immunity is a prominent feature of Alzheimer's disease (AD) and primary tauopathies. However, to what degree innate immunity contributes to neurodegeneration as compared with pathological protein-induced neurotoxicity, and the requirement of a particular glial cell type in neurodegeneration, are still unclear. Here we demonstrate that microglia-mediated damage, rather than pathological tau-induced direct neurotoxicity, is the leading force driving neurodegeneration in a tauopathy mouse model. Importantly, the progression of ptau pathology is also driven by microglia. In addition, we found that APOE, the strongest genetic risk factor for AD, regulates neurodegeneration predominantly by modulating microglial activation, although a minor role of apoE in regulating ptau and insoluble tau formation independent of its immunomodulatory function was also identified. Our results suggest that therapeutic strategies targeting microglia may represent an effective approach to prevent disease progression in the setting of tauopathy.

Novel Treatment Strategies Using TiO2-Nanowired Delivery of Histaminergic Drugs and Antibodies to Tau With Cerebrolysin for Superior Neuroprotection in the Pathophysiology of Alzheimer's Disease.

More than 5.5 million Americans of all ages are suffering from Alzheimer's disease (AD) till today for which no suitable therapy has been developed so far. Thus, there is an urgent need to explore novel therapeutic measures to contain brain pathology in AD. The hallmark of AD includes amyloid-beta peptide (AßP) deposition and phosphorylation of tau in AD brain. Recent evidences also suggest a marked decrease in neurotrophic factors in AD. Thus, exogenous supplement of neurotrophic factors could be one of the possible ways for AD therapy. Human postmortem brain in AD shows alterations in histamine receptors as well, indicating an involvement of the amine in AD-induced brain pathology. In this review, we focused on role of histamine 3 and 4 receptor-modulating drugs in the pathophysiology of AD. Moreover, antibodies to histamine and tau appear to be also beneficial in reducing brain pathology, blood-brain barrier breakdown, and edema formation in AD. Interestingly, TiO2-nanowired delivery of cerebrolysin-a balanced composition of several neurotrophic factors attenuated AßP deposition and reduced tau phosphorylation in AD brain leading to neuroprotection. Coadministration of cerebrolysin with histamine antibodies or tau antibodies has further enhanced neuroprotection in AD. These novel observations strongly suggest a role of nanomedicine in AD that requires further investigation.

Neurodegeneration Enhances the Development of Arthritis.

The prevalence of neurodegenerative disease and arthritis increases with age. Despite both processes being associated with immune activation and inflammation, little is known about the mechanistic interactions between neurodegenerative disease and arthritis. In this article, we show that tau-transgenic (tau-tg) mice that develop neurodegenerative disease characterized by deposition of tau tangles in the brain are highly susceptible to developing arthritis. Already at steady-state conditions, tau-tg mice exhibit peripheral immune activation that is manifested by higher numbers of granulocytes, plasmablasts, and inflammatory Ly6Chi CCR2+ monocytes, as well as increased levels of proinflammatory cytokines, such as TNF-α and IL-17. Upon induction of collagen-induced arthritis (CIA), tau-tg mice displayed an increased incidence and an earlier onset of CIA that was associated with a more pronounced inflammatory cytokine response. Furthermore, induction of CIA led to significantly elevated numbers of Iba-1-expressing cells in the brain, indicative of microglia activation, and the formation of anti-tau Abs in tau-tg mice. These changes were accompanied by the resolution of tau tangles and significantly decreased neurodegenerative pathology. In summary, these data show that neurodegenerative disease enhances the development of arthritis. In addition, arthritis, once induced, triggers innate immune responses in the brain, leading to resolution of neurodegenerative changes.

Plant-based vaccines for Alzheimer's disease: an overview.

Plants are considered advantageous platforms for biomanufacturing recombinant vaccines. This constitutes a field of intensive research and some plant-derived vaccines are expected to be marketed in the near future. In particular, plant-based production of immunogens targeting molecules with implications on the pathology of Alzheimer's has been explored over the last decade. These efforts involve targeting amyloid beta and ß-secretase with several immunogen configurations that have been evaluated in test animals. The results of these developments are analyzed in this review. Perspectives on the topic are identified, such as exploring additional antigen configurations and adjuvants in order to improve immunization schemes, characterizing in detail the elicited immune responses, and immunological considerations in the achievement of therapeutic humoral responses via mucosal immunization. Safety concerns related to these therapies will also be discussed.

Investigating interventions in Alzheimer's disease with computer simulation models.

Progress in the development of therapeutic interventions to treat or slow the progression of Alzheimer's disease has been hampered by lack of efficacy and unforeseen side effects in human clinical trials. This setback highlights the need for new approaches for pre-clinical testing of possible interventions. Systems modelling is becoming increasingly recognised as a valuable tool for investigating molecular and cellular mechanisms involved in ageing and age-related diseases. However, there is still a lack of awareness of modelling approaches in many areas of biomedical research. We previously developed a stochastic computer model to examine some of the key pathways involved in the aggregation of amyloid-beta (Aß) and the micro-tubular binding protein tau. Here we show how we extended this model to include the main processes involved in passive and active immunisation against Aß and then demonstrate the effects of this intervention on soluble Aß, plaques, phosphorylated tau and tangles. The model predicts that immunisation leads to clearance of plaques but only results in small reductions in levels of soluble Aß, phosphorylated tau and tangles. The behaviour of this model is supported by neuropathological observations in Alzheimer patients immunised against Aß. Since, soluble Aß, phosphorylated tau and tangles more closely correlate with cognitive decline than plaques, our model suggests that immunotherapy against Aß may not be effective unless it is performed very early in the disease process or combined with other therapies.

Development of a sensitive ELISA for quantification of three- and four-repeat tau isoforms in tauopathies.

Tau protein plays an important role in stabilising and assembling neuronal microtubules. Pathological changes in expression and aggregation of tau isoforms containing three (3R-tau) and four (4R-tau) microtubule-binding repeat domains are associated with several tauopathies. This paper describes novel sandwich ELISAs for quantification of 3R- and 4R-tau in brain. The assays are constructed using well-characterised isoform-specific antibodies (RD3 and RD4) as capture antibodies and an affinity-purified HRP-anti-tau peptide antibody and biotin-tyramide amplification for detection. For 3R-tau, we achieved a minimal detection limit in buffer of 460 pg mL(-1) and a recovery of 81.0% using 500 pg mL(-1) recombinant 3R-tau spiked in diluted brain homogenate. Mean intra- and inter-assay variation of the 3R-tau ELISA was 8.8 and 10.5%, respectively. For 4R-tau, the detection limit was 780 pg mL(-1) and the recovery of 5 ng mL(-1) spiked recombinant 4R-tau was 86.0% and the mean intra- and inter-assay variation was 10.4 and 15.6%, respectively. With these assays, we showed that in progressive supranuclear palsy (PSP) brains, 4R-tau is significantly increased in frontal cortex and caudate, the two regions that are usually associated with 4R-tau-dominant pathology. This increase was not observed in occipital lobe, a region that is spared of tau inclusions. No differences in 3R-tau levels were found between PSP and control brains in all regions tested. With this, we have for the first time developed ELISAs for quantification of 3R- and 4R-tau isoforms in pathological samples. These could prove useful in the pathological investigation and differential diagnosis of tauopathies.

Characterization of mitotic neurons derived from adult rat hypothalamus and brain stem.

Embryonic or neonatal rat neurons retain plasticity and are readily grown in tissue culture, but neurons of the adult brain were thought to be terminally differentiated and therefore difficult to culture. Recent studies, however, suggest that it may be possible to culture differentiated neurons from the hippocampus of adult rats. We modified these procedures to grow differentiated neurons from adult rat hypothalamus and brain stem. At day 7 in tissue culture and beyond, the predominant cell types in hypothalamic and brain stem cultures had a stellate morphology and could be subdivided into two distinct groups, one of which stained with antibodies to the immature neuron marker alpha-internexin, while the other stained with the astrocyte marker GFAP. The alpha-internexin positive cells were mitotic and grew to form a characteristic two-dimensional cellular network. These alpha-internexin positive cells coimmunostained for the neuronal markers MAP2, type III beta-tubulin, and tau, and also bound tetanus toxin, but were negative for the oligodendrocyte marker GalC and also for the neurofilament triplet proteins NF-L, NF-M, and NF-H, markers of more mature neurons. Patch-clamp analysis of these alpha-internexin positive cells revealed small Ca(2+) currents with a peak current of -0.5 +/- 0.1 pA/pF at a membrane potential of -20 mV (n = 5) and half-maximal activation at -30 mV (n = 5). Na(+) currents with a peak current density of -154.5 +/- 49.8 pA/pF at a membrane potential of -15 mV (n = 5) were also present. We also show that these cells can be frozen and regrown in tissue culture and that they can be efficiently infected by viral vectors. These cells therefore have the immunological and electrophysiological properties of immature mitotic neurons and should be useful in a variety of future studies of neuronal differentiation and function.

Glycosylation of microtubule-associated protein tau in Alzheimer's disease brain.

In the neurofibrillary pathology of Alzheimer's disease (AD), neurofibrillary tangles (NFTs) contain paired helical filaments (PHFs) as their major fibrous component. Abnormally hyperphosphorylated, microtubule-associated protein tau is the major protein subunit of PHFs. A recent in vitro study showed that PHF tangles from AD brains are highly glycosylated, whereas no glycan is detected in normal tau. Deglycosylation of PHF tangles converts them into bundles of straight filaments and restores their accessibility to microtubules. We showed that PHF tangles from AD brain tissue were associated with specific glycan molecules by double immunostaining with peroxidase and alkaline phosphatase labeling. Intracellular tangles and dystrophic neurites in a neuritic plaque with abnormally hyperphosphorylated tau, detected with the monoclonal antibodies AT-8 and anti-tau-2, were also positive with lectin Galanthus nivalis agglutinin (GNA) which recognizes both the N- and O-glycosidically linked saccharides. Colocalization was not seen in the extracellular tangles and amyloid deposition, suggesting that the glycosylation of tau might be associated with the early phase of insoluble NFT formation. Thus, although abnormal phosphorylation might promote aggregation of tau and inhibition of the assembly of microtubules, glycosylation mediated by a GNA-positive glycan appears to be responsible for the formation of the PHF structures in vivo.

Recognition of the minimal epitope of monoclonal antibody Tau-1 depends upon the presence of a phosphate group but not its location.

The major constituent of the paired helical filaments (PHFs) of Alzheimer's disease is the abnormally phosphorylated form of the microtubule-associated protein, tau. Monoclonal antibody (mAb) Tau-1 is used extensively to stain normal human tau, and tau isolated from the brains of Alzheimer's disease patients after dephosphorylation. We used a panel of 6 synthetic peptides to localize the minimal epitope of Tau-1 between amino acids 192-204. All 4 serine residues within this fragment were later phosphorylated individually by chemical methods, and it was shown that none of the peptides carrying a single phosphate group were recognized by the antibody. The serines included those that are probably not transformed in AD and consequently, conclusions drawn about malfunctioning kinase activity, based on Tau-1 immunoreactivity, can be extremely misleading. The recognition was restored at a decreased level when one of the serines was replaced by an alanine residue. mAb AT8 was made by immunizing with the PHFs and was reported to recognize the same region of the protein in a phosphorylated form. AT8 did not, however, cross-react with any of the singly phosphorylated peptides, indicating that the recognition site of the two antibodies are not entirely complementary or the binding to AT8 needs multiple phosphorylation of the antigen. The abolished recognition of the phosphorylated peptides cannot be attributed to a conformational change due to phosphorylation, since all peptides exhibited reverse-turn secondary structures, as indicated by circular dichroism (CD) spectroscopy. Anti-tau mAbs may distinguish between phosphorylated and non-phosphorylated forms of epitopes regardless of the location of the phosphate group.