Showing papers by "Michel Goedert published in 2014"

A novel in vivo model of tau propagation with rapid and progressive neurofibrillary tangle pathology: the pattern of spread is determined by connectivity, not proximity

Abstract: Intracellular inclusions composed of hyperphosphorylated filamentous tau are a hallmark of Alzheimer’s disease, progressive supranuclear palsy, Pick’s disease and other sporadic neurodegenerative tauopathies. Recent in vitro and in vivo studies have shown that tau aggregates do not only seed further tau aggregation within neurons, but can also spread to neighbouring cells and functionally connected brain regions. This process is referred to as ‘tau propagation’ and may explain the stereotypic progression of tau pathology in the brains of Alzheimer’s disease patients. Here, we describe a novel in vivo model of tau propagation using human P301S tau transgenic mice infused unilaterally with brain extract containing tau aggregates. Infusion-related neurofibrillary tangle pathology was first observed 2 weeks post-infusion and increased in a stereotypic, time-dependent manner. Contralateral and anterior/posterior spread of tau pathology was also evident in nuclei with strong synaptic connections (efferent and afferent) to the site of infusion, indicating that spread was dependent on synaptic connectivity rather than spatial proximity. This notion was further supported by infusion-related tau pathology in white matter tracts that interconnect these regions. The rapid and robust propagation of tau pathology in this model will be valuable for both basic research and the drug discovery process.

Peripheral administration of tau aggregates triggers intracerebral tauopathy in transgenic mice

Abstract: Soluble tau forms insoluble aggregates following the intracerebral injection of tau inclusions [3, 4]. This is reminiscent of prions, the intracerebral injection of which induces aggregation of cellular prion protein (PrPC) [9]. Multiple routes of administration can transmit prion diseases, with the intracerebral route being more effective than the intraperitoneal route, which is in turn more effective than the oral route [7]. The oral administration of aggregated apolipoprotein A-II [11] and aggregated amyloid protein A (AA) [8] has also been shown to promote systemic amyloidosis. Moreover, intraperitoneally injected aggregated Aβ-containing extracts increased cerebral β-amyloidosis [5]. Here, we report for the first time that the intraperitoneal injection of tau seeds can also induce intracerebral tauopathy. We used homozygous and heterozygous mice transgenic for human mutant P301S tau [2]. In heterozygous mice, tau aggregation forms later than in homozygous mice, and heterozygous mice live longer than their homozygous counterparts (15 months as opposed to 6 months). Brainstem extracts from 6-month-old homozygous P301S tau transgenic mice (prepared and analysed as previously described [3]) were injected into the peritoneal cavity of 3-month-old heterozygous mice, an age at which they lack tau deposits. The mice were analysed 9 months after the final injection. The number of Gallyas silver-positive cells was assessed using a scanning light microscope. Maps of entire brain sections, along with the annotation of the brain outline and artificially altered areas, were used for the counting of black Gallyas-positive and blue haematoxylin-positive structures (Supplementary Fig. 4). Gallyas per cell nucleus (G/N) ratios were counted, thus reflecting the number of silver-positive cells. G/N ratios were calculated per field of view (20× objective, 661.5 × 372.1 μm). Gauss-blurred ratiometric images (sigma = 70 pixels, pixel edge length = 3.45 μm) were superimposed for the control and experimental groups. Subsequently, a pixel-wise Student’s t test was performed and the probability (p) values were plotted, with the statistically significant portion (p < 0.05) being represented as a colour map (Fig. 2). Our ratiometric approach (G/N) only compares equivalent brain regions to each other. Thus, despite anatomical differences in densities of nuclei, our comparative maps remain unbiased. Fig. 2 Gallyas silver-positive structures per cell nucleus (G/N ratios) in non-injected controls (CO) and in mice injected with aggregated tau-rich homogenate either intraperitoneally (IP) or intracerebrally (IC). a Left panel colour map representing average ... Although groups of mice injected intraperitoneally (IP) with brainstem homogenate from either P301S tau transgenic mice (with tau filaments) or control (CO) mice (without tau filaments) formed Gallyas-positive structures in the brain, there were also significant differences between the two groups (Fig. 1). G/N ratios (Fig. 2a, left panel) showed a marked increase in the number of silver-positive structures in the brainstem and neocortex of mice IP injected with P301S brainstem extract. The probability map (Fig. 2a, right panel) showed large differences in secondary motor cortex, ventral orbital cortex and olfactory nucleus. More ventral regions, including pallidum and lateral preoptic area, showed more silver-positive inclusions in P301S brainstem-injected mice, as did lateral habenular nucleus, thalamic nucleus, pretectal nucleus and mesencephalic reticular formation. In the brainstem, pontine reticular nucleus, gigantocellular reticular nucleus, median vestibular nucleus and solitary tract showed the largest increase in Gallyas-positive inclusions (Supplementary Fig. 2). The hippocampus remained unaffected. At the age of analysis (12 months), brains of heterozygous P301S mice develop neuronal inclusions made of hyperphosphorylated (AT8 positive, pretangles) and aggregated tau (AT100- and Gallyas silver-positive, classical tangles). Both AT8 and AT100 tau immunoreactivity (Supplementary Fig. 3) as well as silver staining in IP-injected mice were increased compared to non-injected mice, but the pattern (brain distribution and morphology) of tau pathology remained unchanged. Age-matched wild-type mice injected intraperitoneally with P301S brainstem extract failed to develop cerebral tauopathy. Fig. 1 Intraperitoneal injection of aggregated tau-rich homogenate increases the number of silver-positive tau inclusions in brain. Gallyas-Braak staining of the brainstem of 12-month-old mice heterozygous for transgenic human mutant P301S tau showed an increase ... We previously showed that the intracerebral injection of silver-positive brainstem extract from mice homozygous for human mutant P301S tau into mice transgenic for human wild-type tau (line ALZ17) induced the formation of silver-positive inclusions [3]. To investigate if this is also true of another mouse model of tauopathy, we injected brainstem extract from homozygous mice transgenic for human mutant P301S tau into the hippocampus and overlying cerebral cortex of 3-month-old heterozygous mice and compared the relative efficiency of intracerebral and intraperitoneal injections after 9 months. Following intracerebral injection, numerous Gallyas-positive structures were present in the CA1 region of the hippocampus and in the secondary motor cortex (Supplementary Fig. 1A). No silver-positive structures were present in these regions following the intraperitoneal injection of control extracts. Heat maps revealed a significant increase in the G/N ratio in the hippocampus following the intracerebral injection of P301S brainstem extract into heterozygous transgenic P301S tau mice (Fig. 2b, left panel). The p maps showed statistically significant differences between groups in the hippocampal area, which was a site of intracerebral injection (Fig. 2b, right panel; Supplementary Fig. 1B). Moreover, the G/N ratio was increased more in brainstem and neocortex following intracerebral than after intraperitoneal injections. Heart, lungs, liver, spleen and kidneys from injected heterozygous P301S tau mice were all silver-negative and tau-negative. No sign of inflammation was detected in either the brain or the periphery. These findings demonstrate that aggregated tau seeds, such as prions and Aβ aggregates, can reach the central nervous system from the periphery. The underlying mechanisms remain to be determined. The replication of peripherally applied prions and their translocation to the brain are dependent on haematopoietic and stromal immune cells, together with the sympathetic innervation of abdominal lymphoid organs [1]. In mouse models of AA-amyloidosis, peripheral blood monocytes transported the aggregates [10]. It therefore appears that amyloid seeds can be carried by blood cells. This may also be true of aggregated tau. Seeding may require the presence of unfolded monomers [6]. It remains to be determined if tau seeds are able to replicate in the peripheral nervous system. Their transport to the brain may not require endogenous tau, which is not expressed by lymphoreticular cells. This is unlike prion propagation, which depends on the expression of PrPC by stromal and haematopoietic cells. Because the central nervous system is affected in clinical tauopathy, the intracerebral route of seed delivery could be expected to be more effective than the intraperitoneal route. This was the case here, where more silver-positive structures formed in brainstem, hippocampus and neocortex following the intracerebral injection of 5 μl brainstem homogenate (0.19 μg of τ/μl of homogenate) than after the intraperitoneal injection of 200 μl homogenate (0.19 μg of τ/μl of homogenate). It follows that, like prion diseases, tauopathies can be seeded in the brain by tau aggregates delivered peripherally, although the intraperitoneal administration was less effective than the intracerebral route. These findings underscore the urgent need for additional work on the aetiology and pathogenesis of tauopathies.

Prion-like mechanisms in the pathogenesis of tauopathies and synucleinopathies.

Abstract: Neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease, are characterized by the abnormal aggregation of a small number of intracellular proteins, with tau and α-synuclein being the most commonly affected. Until recently, the events leading to aggregate formation were believed to be entirely cell-autonomous, with protein misfolding occurring independently in many cells. It is now believed that protein aggregates form in a small number of brain cells, from which they propagate intercellularly through templated recruitment, reminiscent of the mechanisms by which prions spread through the nervous system.

Tau silencing by siRNA in the P301S mouse model of tauopathy.

Abstract: Suppression of tau protein expression has been shown to improve behavioral deficits in mouse models of tauopathies, offering an attractive therapeutic approach. Experimentally this had been achieved by switching off the promoters controlling the transgenic human tau gene (MAPT), which is not possible in human patients. The aim of the present study was therefore to evaluate the effectiveness of small interfering RNAs (siRNAs) and their cerebral delivery to suppress human tau expression in vivo, which might be a therapeutic option for human tauopathies. We used primary cortical neurons of transgenic mice expressing P301S-mutated human tau and Lund human mesencephalic (LUHMES) cells to validate the suppressive effect of siRNA in vitro. For measuring the effect in vivo, we stereotactically injected siRNA into the brains of P301S mice to reveal the suppression of tau by immunochemistry (AT180, MC1, and CP13 antibodies). We found that the Accell™ SMART pool siRNA against MAPT can effectively suppress tau expression in vitro and in vivo without a specific delivery agent. The siRNA showed a moderate distribution in the hippocampus of mice after single injection. NeuN, GFAP, Iba-1, MHC II immunoreactivities and the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay showed neither signs of neurotoxicity or neuroinflammation nor apoptosis when MAPT siRNA is present in the hippocampus. Our data suggest that siRNA against MAPT can serve as a potential tool for gene therapy in tauopathies.

The novel MAPT mutation K298E: Mechanisms of mutant tau toxicity, brain pathology and tau expression in induced fibroblast-derived neurons

Abstract: Frontotemporal lobar degeneration (FTLD) consists of a group of neurodegenerative diseases characterized by behavioural and executive impairment, language disorders and motor dysfunction. About 20–30 % of cases are inherited in a dominant manner. Mutations in the microtubule-associated protein tau gene (MAPT) cause frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17T). Here we report a novel MAPT mutation (K298E) in exon 10 in a patient with FTDP-17T. Neuropathological studies of post-mortem brain showed widespread neuronal loss and gliosis and abundant deposition of hyperphosphorylated tau in neurons and glia. Molecular studies demonstrated that the K298E mutation affects both protein function and alternative mRNA splicing. Fibroblasts from a skin biopsy of the proband taken at post-mortem were directly induced into neurons (iNs) and expressed both 3-repeat and 4-repeat tau isoforms. As well as contributing new knowledge on MAPT mutations in FTDP-17T, this is the first example of the successful generation of iNs from skin cells retrieved post-mortem.

Piericidin A aggravates Tau pathology in P301S transgenic mice.

Abstract: Objective The P301S mutation in exon 10 of the tau gene causes a hereditary tauopathy. While mitochondrial complex I inhibition has been linked to sporadic tauopathies. Piericidin A is a prototypical member of the group of the piericidins, a class of biologically active natural complex I inhibitors, isolated from streptomyces spp. with global distribution in marine and agricultural habitats. The aim of this study was to determine whether there is a pathogenic interaction of the environmental toxin piericidin A and the P301S mutation. Methods Transgenic mice expressing human tau with the P301S-mutation (P301S+/+) and wild-type mice at 12 weeks of age were treated subcutaneously with vehicle (N = 10 P301S+/+, N = 7 wild-type) or piericidin A (N = 9 P301S+/+, N = 9 wild-type mice) at a dose of 0.5 mg/kg/d for a period of 28 days via osmotic minipumps. Tau pathology was measured by stereological counts of cells immunoreative with antibodies against phosphorylated tau (AD2, AT8, AT180, and AT100) and corresponding Western blot analysis. Results Piericidin A significantly increased the number of phospho-tau immunoreactive cells in the cerebral cortex in P301S+/+ mice, but only to a variable and mild extent in wild-type mice. Furthermore, piericidin A led to increased levels of pathologically phosphorylated tau only in P301S+/+ mice. While we observed no apparent cell loss in the frontal cortex, the synaptic density was reduced by piericidin A treatment in P301S+/+ mice. Discussion This study shows that exposure to piericidin A aggravates the course of genetically determined tau pathology, providing experimental support for the concept of gene-environment interaction in the etiology of tauopathies.