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Induction of Inflammatory Mediators and Microglial Activation in Mice Transgenic for Mutant Human P301S Tau Protein

2004; Elsevier BV; Volume: 165; Issue: 5 Linguagem: Inglês

10.1016/s0002-9440(10)63421-9

1525-2191

Arianna Bellucci, Andrew J. Westwood, Esther Ingram, Fiorella Casamenti, Michel Goedert, Maria Grazia Spillantini,

S100 Proteins and Annexins

Mice transgenic for human P301S tau protein exhibit many characteristics of the human tauopathies, including the formation of abundant filaments made of hyperphosphorylated tau protein and neurodegeneration leading to nerve cell loss. At 5 months of age, the pathological changes are most marked in brainstem and spinal cord. Here we show that these changes are accompanied by marked neuroinflammation. Many tau-positive nerve cells in brainstem and spinal cord were strongly immunoreactive for interleukin-1β and cyclooxygenase-2, indicating induction and overproduction of proinflammatory cytokines and enzymes. In parallel, numerous activated microglial cells were present throughout brain and spinal cord of transgenic mice, where they concentrated around tau-positive nerve cells. These findings suggest that inflammation may play a significant role in the events leading to neurodegeneration in the tauopathies and that anti-inflammatory compounds may have therapeutic potential. Mice transgenic for human P301S tau protein exhibit many characteristics of the human tauopathies, including the formation of abundant filaments made of hyperphosphorylated tau protein and neurodegeneration leading to nerve cell loss. At 5 months of age, the pathological changes are most marked in brainstem and spinal cord. Here we show that these changes are accompanied by marked neuroinflammation. Many tau-positive nerve cells in brainstem and spinal cord were strongly immunoreactive for interleukin-1β and cyclooxygenase-2, indicating induction and overproduction of proinflammatory cytokines and enzymes. In parallel, numerous activated microglial cells were present throughout brain and spinal cord of transgenic mice, where they concentrated around tau-positive nerve cells. These findings suggest that inflammation may play a significant role in the events leading to neurodegeneration in the tauopathies and that anti-inflammatory compounds may have therapeutic potential. The most common neurodegenerative diseases are characterized by the presence of abnormal filamentous protein inclusions in nerve cells of the brain.1Goedert M Spillantini MG Davies SW Filamentous nerve cell inclusions in neurodegenerative diseases.Curr Opin Neurobiol. 1998; 8: 619-632Crossref PubMed Scopus (226) Google Scholar In Alzheimer's disease (AD), these inclusions are made of hyperphosphorylated tau protein. Together with the extracellular β-amyloid deposits, they constitute the defining neuropathological characteristics of AD. Tau inclusions, in the absence of extracellular deposits, are characteristic of progressive supranuclear palsy, corticobasal degeneration, Pick's disease, argyrophilic grain disease, and frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17).2Lee VMY Goedert M Trojanowski JQ Neurodegenerative tauopathies.Annu Rev Neurosci. 2001; 24: 1121-1159Crossref PubMed Scopus (2087) Google Scholar The identification of mutations in Tau in FTDP-17 has established that dysfunction of tau protein is central to the neurodegenerative process.3Poorkaj P Bird TD Wijsman E Nemens E Garruto RM Anderson L Andreadis A Wiederholt WC Raskind M Schellenberg GD Tau is a candidate gene for chromosome 17 frontotemporal dementia.Ann Neurol. 1998; 43: 815-825Crossref PubMed Scopus (1207) Google Scholar, 4Hutton M Lendon CL Rizzu P Baker M Froelich S Houlden H Pickering-Brown S Chakraverty S Isaacs A Grover A Hackett J Adamson J Lincoln S Dickson D Davies P Petersen RC Stevens M de Graaff E Wauters E van Baren J Hillebrand M Joosse M Kwon JM Nowotny P Che LK Norton J Morris JC Reed LA Trojanowski JQ Basun H Lannfelt L Neystat M Fahn S Dark F Tannenberg T Dodd PR Hayward N Kwok JBJ Schofield PR Andreadis A Snowden J Craufurd D Neary D Owen F Oostra BA Hardy J Goate A van Swieten J Mann D Lynch T Heutink P Association of missense and 5′-splice-site-mutations in tau with the inherited dementia FTDP-17.Nature. 1998; 393: 702-705Crossref PubMed Scopus (2855) Google Scholar, 5Spillantini MG Murrell JR Goedert M Farlow MR Klug A Ghetti B Mutation in the tau gene in familial multiple system tauopathy with presenile dementia.Proc Natl Acad Sci USA. 1998; 95: 7737-7741Crossref PubMed Scopus (1294) Google Scholar At an experimental level, the expression of mutant tau in nerve cells is leading to improved models of neurodegeneration.6Lewis J McGowan E Rockwood J Melrose H Nacharaju P van Slegtenhorst M Gwinn-Hardy K Murphy MP Baker M Yu X Duff K Hardy J Corral A Lin WL Yen SH Dickson DW Davies P Hutton M Neurofibrillary tangles, amyotrophy and progressive motor disturbance in mice expressing mutant (P301L) tau protein.Nat Genet. 2000; 25: 402-405Crossref PubMed Scopus (1113) Google Scholar, 7Götz J Chen F Barmettler R Nitsch RM Tau filament formation in transgenic mice expressing P301L tau.J Biol Chem. 2001; 276: 529-534Crossref PubMed Scopus (393) Google Scholar, 8Lim F Hernandez F Lucas JJ Gomez-Ramos P Moran MA Avila J FTDP-17 mutations in tau transgenic mice provoke lysosomal abnormalities and tau filaments in forebrain.Mol Cell Neurosci. 2001; 18: 702-714Crossref PubMed Scopus (177) Google Scholar, 9Tanemura K Murayama M Akagi T Hashikawa T Tominaga T Ichikawa M Yamaguchi H Taskashima A Neurodegeneration with tau accumulation in a transgenic mouse expressing V337M human tau.J Neurosci. 2002; 22: 133-141Crossref PubMed Google Scholar, 10Allen B Ingram E Takao M Smith MJ Jakes R Virdee K Yoshida H Holzer M Craxton M Emson PC Atzori C Migheli A Crowther RA Ghetti B Spillantini MG Goedert M Abundant tau filaments and nonapoptotic neurodegeneration in transgenic mice expressing human P301S tau protein.J Neurosci. 2002; 22: 9340-9351Crossref PubMed Google Scholar, 11Tatebayashi Y Miyasaka T Chui DH Akagi T Mishima KI Iwasaki K Fujiwara M Tanemura K Murayama M Ishiguro K Planel E Sato S Hashikawa T Takashima A Tau filament formation and associative memory deficit in aged mice expressing mutant (R406W) human tau.Proc Natl Acad Sci USA. 2002; 99: 13896-13901Crossref PubMed Scopus (229) Google Scholar, 12Oddo S Caccamo A Shepherd JD Murphy MP Golde TE Kayed R Metherate R Mattson MP Akbari Y LaFerla FM Triple-transgenic model of Alzheimer's disease with plaques and tangles: intracellular Aβ and synaptic dysfunction.Neuron. 2003; 39: 409-421Abstract Full Text Full Text PDF PubMed Scopus (3059) Google Scholar We have described a line of mice transgenic for human P301S tau,10Allen B Ingram E Takao M Smith MJ Jakes R Virdee K Yoshida H Holzer M Craxton M Emson PC Atzori C Migheli A Crowther RA Ghetti B Spillantini MG Goedert M Abundant tau filaments and nonapoptotic neurodegeneration in transgenic mice expressing human P301S tau protein.J Neurosci. 2002; 22: 9340-9351Crossref PubMed Google Scholar a FTDP-17 mutation with strong functional effects and an early age of disease onset.13Bugiani O Murrell JR Giaccone G Hasegawa M Ghigo S Tabaton M Morbin M Primavera A Carella F Solaro C Grisoli M Savoiardo M Spillantini MG Tagliavini F Goedert M Ghetti B Frontotemporal dementia and corticobasal degeneration in a family with a P301S mutation in Tau.J Neuropathol Exp Neurol. 1999; 58: 667-677Crossref PubMed Scopus (340) Google Scholar, 14Goedert M Jakes R Crowther RA Effects of frontotemporal dementia FTDP-17 mutations on heparin-induced assembly of tau filaments.FEBS Lett. 1999; 450: 306-311Abstract Full Text Full Text PDF PubMed Scopus (215) Google Scholar At 5 to 6 months of age, homozygous animals from this line develop a motor phenotype dominated by a severe paraparesis. Brains and spinal cords of these animals contain abundant neuronal inclusions made of hyperphosphorylated mutant human tau protein in a filamentous state. In the spinal cord, this is accompanied by a large reduction in the number of motor neurons and a marked reactive astrocytosis. In recent years, much work has been devoted to the study of inflammatory processes in neurodegenerative diseases, especially AD.15Akiyama H Barger S Barnum S Bradt B Bauer J Cole GM Cooper NR Eikelenboom P Emmerling M Fiebich BL Finch CE Frautschy S Griffin WST Hampel H Hull M Landreth G Lue LF Mrak R Mackenzie IR McGeer PL O'Banion K Pachter J Pasinetti G Plata-Salaman C Rogers J Rydel R Shen Y Streit W Strohmeyer R Tooyoma I van Muiswinkel FL Veerhuis R Walker D Webster S Wegrzyniak B Wenk G Wyss-Coray T Inflammation and Alzheimer's disease.Neurobiol Aging. 2000; 21: 383-421Abstract Full Text Full Text PDF PubMed Scopus (3585) Google Scholar Neuropathological analysis has revealed many of the hallmarks of inflammation, including microglial cell activation, expression of cytokines and complement, and invasion of immune cells. There has been debate about the relevance of anti-inflammatory drugs for the treatment of AD.16McGeer PL Schulzer M McGeer EG Arthritis and anti-inflammatory agents as possible protective factors for Alzheimer's disease: a review of 17 epidemiologic studies.Neurology. 1996; 47: 425-432Crossref PubMed Scopus (1280) Google Scholar Comparatively little is known about inflammatory processes in diseases with only tau deposits; no information is available about inflammation in experimental animal models of the tauopathies. Here we report that brains and spinal cords from 5-month-old human P301S tau transgenic mice exhibit a strong inflammatory reaction, characterized by interleukin-1β (IL-1β) production and cyclooxygenase-2 (COX-2) induction, as well as by microglial cell activation. Five-month-old homozygous mice transgenic for human P301S tau10Allen B Ingram E Takao M Smith MJ Jakes R Virdee K Yoshida H Holzer M Craxton M Emson PC Atzori C Migheli A Crowther RA Ghetti B Spillantini MG Goedert M Abundant tau filaments and nonapoptotic neurodegeneration in transgenic mice expressing human P301S tau protein.J Neurosci. 2002; 22: 9340-9351Crossref PubMed Google Scholar and age-matched C57BL/6J controls were used. In some experiments, 14-month-old mice transgenic for wild-type human tau (line ALZ17)17Probst A Götz J Wiederhold KH Tolnay M Mistl C Jaton AL Hong M Ishihara T Lee VMY Trojanowski JQ Jakes R Crowther RA Spillantini MG Bürki K Goedert M Axonopathy and amyotrophy in mice transgenic for human four-repeat tau protein.Acta Neuropathol. 2000; 99: 469-481Crossref PubMed Scopus (299) Google Scholar and age-matched controls were used. Polyclonal antibodies specific for IL-1β and COX-2 (Santa Cruz Biotechnology, Santa Cruz, CA) were used at 1:200. A monoclonal anti-actin antibody (Sigma-Aldrich, Poole, UK) was used at 1:1000. Two phosphorylation-dependent anti-tau antibodies were used. AT8 (1:750, Innogenetics, Ghent, Belgium) recognizes human and murine tau phosphorylated at S202 and T205 and AP422 (1:500) recognizes human and murine tau phosphorylated at S422.18Goedert M Jakes R Vanmechelen E Monoclonal antibody AT8 recognises tau protein phosphorylated at both serine 202 and threonine 205.Neurosci Lett. 1995; 189: 167-170Crossref PubMed Scopus (466) Google Scholar, 19Hasegawa M Jakes R Crowther RA Lee VMY Ihara Y Goedert M Characterization of mAb AP422, a novel phosphorylation-dependent monoclonal antibody against tau protein.FEBS Lett. 1996; 384: 25-30Abstract Full Text PDF PubMed Scopus (146) Google Scholar Rat monoclonal antibody OX-42 (1:250; Serotec, Oxford, UK), which binds CD11b receptors, was used to identify microglial cells. Activated microglial cells were detected using monoclonal antibodies OX-6 and M5/114.15.2 (1:200; PharMingen, San Diego, CA), which are directed against major histocompatibility complex class II antigens. Mice were perfused transcardially with 4% paraformaldehyde in 0.1 mol/L of phosphate buffer, pH 7.2. Brains and spinal cords were removed, postfixed for 2 hours, followed by cryoprotection in 30% sucrose in 0.1 mol/L of phosphate buffer, pH 7.4, for 24 hours. Sagittal brain sections and transverse spinal cord sections (30 μm) were cut on a Leica SM2400 microtome (Leica Microsystems, Bucks, UK), placed in Tris-buffered saline (TBS) containing 0.1% sodium azide, and stored at 4°C. For single-labeling, sections were incubated for 20 minutes at room temperature in 0.1 mol/L of phosphate-buffered saline (PBS), pH 7.4, containing 0.3% Triton X-100, 20% methanol, and 1.5% H2O2, followed by a 30-minute incubation in blocking solution (0.1 mol/L PBS, containing 0.3% Triton X-100, 3% goat serum, and 2 g/L bovine serum albumin). This was followed by the overnight incubation at 4°C in primary antibody in blocking solution. After washing, the sections were incubated in biotinylated secondary antibody (1:1000 in blocking solution, Vectastain; Vector Laboratories, Burlingame, CA). The reaction product was visualized using avidin-biotin and 3′,3′-diaminobenzidine as the chromogen (DAB kit, Vector Laboratories). For double labeling, sections underwent a further cycle of staining and the reaction product was visualized with the Vector NovaRED kit. In control experiments, 20 μg/ml of recombinant IL-1β (Upstate Biotechnology, Lake Placid, NY) was incubated overnight at 4°C with the IL-1β antibody (1:200) before the addition to tissue sections. In additional control experiments, filamentous, sarkosyl-insoluble tau was extracted from human P301S tau transgenic mouse brain10Allen B Ingram E Takao M Smith MJ Jakes R Virdee K Yoshida H Holzer M Craxton M Emson PC Atzori C Migheli A Crowther RA Ghetti B Spillantini MG Goedert M Abundant tau filaments and nonapoptotic neurodegeneration in transgenic mice expressing human P301S tau protein.J Neurosci. 2002; 22: 9340-9351Crossref PubMed Google Scholar and the tau filaments solubilized as described.20Goedert M Spillantini MG Cairns NJ Crowther RA Tau proteins of Alzheimer paired helical filaments: abnormal phosphorylation of all six brain isoforms.Neuron. 1992; 8: 159-168Abstract Full Text PDF PubMed Scopus (885) Google Scholar The dialyzed material (50 μl) was incubated overnight at 4°C with the IL-1β antibody (1:200) or anti-tau antibody AT8 (1:1000), before the addition to tissue sections. For co-localization experiments, sections were incubated for 30 minutes at room temperature with blocking reagent and overnight at 4°C with the primary antibody in blocking solution. After washing, the sections were incubated for 1 hour in the dark with the appropriate fluorescent secondary antibody (Green Alexa, 1:200 in blocking solution; Molecular Probes, Leiden, The Netherlands). Sections were then incubated in the dark with the second primary antibody. After washing, they were incubated in the dark with the second fluorescent secondary antibody (Red Alexa). After washing, the sections were mounted onto slides using Vectashield (Vector Laboratories). Brainstem and spinal cord (10 mg each) from human P301S tau mice and age-matched controls were homogenized in 0.5 ml of cold RIPA buffer (0.1 mol/L PBS, 1% Nonidet P-40, 0.5% sodium deoxycholate, 0.1% sodium dodecyl sulfate, 1 mmol/L phenylmethyl sulfonyl fluoride) containing the complete protease inhibitor cocktail (Roche, Basel, Switzerland). The homogenates were spun for 10 minutes at 10,000 × g and the supernatants used for immunoblotting. Protein concentrations were determined using the Bio-Rad Protein Assay (Hercules, CA) and 25 μg of protein run on 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Gels were blotted overnight at 4°C onto a polyvinylidene difluoride membrane (Pierce, Rockford, IL). Membranes were blocked for 2 hours at 25°C in TBS containing 5% milk and incubated overnight at 4°C with anti-IL-1β or anti-COX-2 antibodies (1:200) in blocking buffer. Membranes were washed in TBS and incubated for 1 hour at 25°C with peroxidase-conjugated anti-rabbit antibody (DakoCytomation, Glostrup, Denmark) (1:2000) in blocking buffer. After washing in TBS, the membranes were incubated for 1 hour at 25°C with a monoclonal anti-actin antibody (1:1000) in TBS. This was followed by washing and a 1-hour incubation at 25°C with peroxidase-conjugated anti-mouse antibody (1:2000, DakoCytomation) in blocking buffer. Blots were developed using enhanced chemiluminescence (Amersham Biosciences, Arlington Heights, IL), followed by the scanning of the bands. Numerous IL-1β-positive cells with a neuronal morphology were present throughout the central nervous system of 5-month-old human P301S tau transgenic mice. They were particularly abundant in brainstem and spinal cord (Figure 1, A and C). Nerve cell processes were also stained, particularly in spinal cord, where the majority of proximal dendrites was immunoreactive. In age-matched control mice, only a few nerve cells were weakly IL-1β-immunoreactive (Figure 1, B and D). In transgenic mice, numerous COX-2-immunoreactive nerve cell bodies and processes were present in cerebral cortex, hippocampus, brainstem, cerebellum, and spinal cord (Figure 2; A, C to F). In control mice, a proportion of nerve cells was positive for COX-2 (Figure 2B). Double-labeling immunofluorescence showed co-localization of IL-1β and COX-2 with staining for the phosphorylation-dependent anti-tau antibody AT8 (Figure 3, Figure 4). IL-1β staining was completely abolished after preincubation of the primary antibody with recombinant IL-1β. It was not changed after preincubation of the IL-1β antibody with hyperphosphorylated tau protein extracted from the brains of human P301S tau transgenic mice. Preincubation with the latter totally abolished staining with anti-tau antibody AT8. Microglial cells were not immunoreactive for IL-1β or COX-2. By immunoblotting, the levels of proIL-1β, IL-1β and COX-2 were markedly increased in brainstem and spinal cord from human P301S tau transgenic mice, when compared with age-matched controls (Figure 5). Immunoblotting with an anti-actin antibody was used to ensure equal loading.Figure 2COX-2 immunoreactivity in brain and spinal cord of human P301S tau transgenic mice. Strongly stained nerve cells and processes (arrows) in brainstem (A), spinal cord (C), cerebral cortex (D), hippocampus (E), and cerebellum (F) of 5-month-old human P301S tau transgenic mice. B: COX-2 immunoreactivity in brainstem of an age-matched control mouse. Note the strong staining of some nerve cell bodies and processes in A, C, D–F. Scale bars: 150 μm (B, also representative for A); 85 μm (C); 80 μm (D); 170 μm (E); 70 μm (F).View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 3Double-labeling immunofluorescence staining for IL-1β (green) and tau phosphorylated at S202 and T205 (antibody AT8) (red) in brainstem and spinal cord of human P301S tau transgenic mice. A and B: Brainstem stained for IL-1β (A) and phosphorylated tau (B). C: Merged images shown in A and B. D and E: Spinal cord stained for IL-1β (D) and phosphorylated tau (E). F: Merged images shown in D and E. Co-localization is indicated by the yellow color. Scale bars: 60 μm (C, also representative for A, B); 125 μm (F, also representative for D, E).View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 4Double-labeling immunofluorescence staining for COX-2 (green) and tau phosphorylated at S202 and T205 (antibody AT8) (red) in brainstem and spinal cord of human P301S tau transgenic mice. A and B: Brainstem stained for COX-2 (A) and phosphorylated tau (B). C: Merged images shown in A and B. D and E: Spinal cord stained for COX-2 (D) and phosphorylated tau (E). F: Merged images shown in D and E. Co-localization is indicated by the yellow color. Scale bars: 45 μm (C, also representative for A, B); 40 μm (F, also representative for D, E).View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 5Immunoblotting for IL-1β and COX-2 of spinal cord (left) and brainstem (right) from three human P301S tau transgenic mice and three age-matched controls. Immunoblotting for actin was used to ensure equal loading. Note the increased levels of proIL-1β, IL-1β and COX-2 in tissues from the transgenic mice.View Large Image Figure ViewerDownload Hi-res image Download (PPT) In transgenic human P301S tau mice, numerous strongly OX-42-immunoreactive microglial cells were present, particularly in close proximity to AP422-positive nerve cells in brainstem, cerebral cortex, hippocampus, and spinal cord (Figure 6; A, C, E). Some had the morphology of activated cells, in that they were characterized by a bushy appearance with swollen cell bodies and intensely stained, thickened, and branched processes. In the remainder of the brain, OX-42-immunoreactive cells were characterized by a more ramified morphology, even when showing features of activation. In brain and spinal cord from control mice, microglial cells were only weakly OX-42-immunoreactive and displayed a sessile morphology, with thin, finely branching processes extending radially from small, oblong cell bodies (Figure 6, B and D). In transgenic mice, double-labeling immunohistochemistry with OX-42 and IL-1β or COX-2 antibodies gave the same staining pattern as that obtained using OX-42 and AP422 antibodies, with OX-42-positive, activated microglial cells concentrated around anti-IL-1β and COX-2-positive cells (not shown). Major histocompatibility complex class II-positive microglial cells were numerous in the spinal cord of human P301S tau mice, as evidenced by staining with antibodies OX-6 and M5/114.15.2 (Figure 6, Figure 7). Double-labeling immunohistochemistry showed the presence of OX-6-positive microglial cells around AP422-positive nerve cells (Figure 6F). The microglia had the morphology of activated cells, as evidenced by an amoeboid, bushy appearance with large, round cell bodies and short, thick processes. In some instances, several microglial cells clustered around a single tau-positive cell. Mice transgenic for wild-type human tau from the ALZ17 line and control mice showed no specific immunoreactivity for OX-6 (not shown) or M5/114.15.2 (Figure 7; B to D). The present findings demonstrate that the intraneuronal accumulation of human P301S tau protein is associated with the activation of inflammatory processes. The latter were characterized by increased IL-1β and COX-2 staining of nerve cells and the activation of microglial cells. In age-matched control brains, only a small number of nerve cells was weakly immunoreactive for IL-1β and COX-2, in agreement with previous findings.21Lechan R Toni R Clark B Cannon J Shaw A Dinarello C Reichlin S Immunoreactive interleukin-1β localization in the rat forebrain.Brain Res. 1990; 514: 135-140Crossref PubMed Scopus (331) Google Scholar, 22Yamagata K Andreasson KI Kaufmann WE Barnes CA Worley PF Expression of a mitogen-inducible cyclooxygenase in brain neurons: regulation by synaptic activity and glucocorticoids.Neuron. 1993; 11: 371-386Abstract Full Text PDF PubMed Scopus (1083) Google Scholar By immunoblotting, markedly increased levels of IL-1β and COX-2 were present in brainstem and spinal cord from human P301S tau transgenic mice. Cells strongly immunoreactive for IL-1β and COX-2 were also stained by the phosphorylation-dependent anti-tau antibodies AT8 and AP422, which recognize both soluble and filamentous tau proteins. This indicates that the accumulation of abnormal mutant human tau protein triggers the production of proinflammatory cytokines and enzymes in nerve cells. These findings are reminiscent of work on transgenic animal models of amyotrophic lateral sclerosis (ALS) resulting from the overexpression of mutant superoxide dismutase, in which IL-1β and COX-2 were expressed at abnormally high levels in motor neurons.23Li M Ona VO Guégan C Chen M Jackson-Lewis V Andrews LJ Olszewski AJ Stieg PE Lee JP Przedborski S Friedlander RM Functional role of caspase-1 and caspase-3 in an ALS transgenic mouse model.Science. 2000; 288: 335-339Crossref PubMed Scopus (631) Google Scholar, 24Almer G Guégan C Teismann P Naini A Rosoklija G Hays AP Chen C Przedborski S Increased expression of the pro-inflammatory enzyme cyclooxygenase-2 in amyotrophic lateral sclerosis.Ann Neurol. 2001; 49: 176-185Crossref PubMed Scopus (244) Google Scholar It suggests that the induction of proinflammatory cytokines and enzymes may be a general response of neurons to the intracellular accumulation of aggregation-prone proteins.25Rockwell P Yuan H Magnusson R Figueiredo-Pereira ME Proteasome inhibition in neuronal cells induces a proinflammatory response manifested by upregulation of cyclooxygenase-2, its accumulation as ubiquitin conjugates, and production of the prostaglandin PGEs.Arch Biochem Biophys. 2000; 374: 25-33Crossref Scopus (121) Google Scholar IL-1β levels are elevated in AD brain26Griffin WS Stanley LC Ling C White L MacLeod V Perrot LJ White CL Araoz C Brain interleukin 1 and S-100 immunoreactivity are elevated in Down syndrome and Alzheimer disease.Proc Natl Acad Sci USA. 1989; 86: 7611-7615Crossref PubMed Scopus (1624) Google Scholar and COX-2 expression is increased in tangle-bearing nerve cells.27Pasinetti GM Aisen PS Cyclooxygenase-2 expression is increased in frontal cortex of Alzheimer's disease brain.Neuroscience. 1998; 87: 319-324Crossref PubMed Scopus (408) Google Scholar, 28Oka A Takashima A Induction of cyclooxygenase-2 in brains of patients with Down's syndrome and dementia of Alzheimer type: specific localization in affected neurones and axons.Neuroreport. 1997; 8: 1161-1164Crossref PubMed Scopus (143) Google Scholar In addition, COX-2 protein expression is induced in nerve cells after ischemia, with COX-2 selective inhibitors preventing ischemia-induced delayed nerve cell death.29Nakayama M Uchimura K Zhu RL Nagayama T Rose ME Stetler RA Isakson PC Chen J Graham SH Cyclooxygenase-2 inhibition prevents delayed death of CA1 hippocampal neurons following global ischemia.Proc Natl Acad Sci USA. 1998; 95: 10954-10959Crossref PubMed Scopus (316) Google Scholar Cytokines, such as IL-1β, are known to induce COX-2 expression in nerve cells,30Serou MJ DeCoster MA Bazan NG Interleukin-1 beta activates expression of cyclooxygenase-2 and inducible nitric oxide synthase in primary hippocampal neuronal culture: platelet-activating factor as a preferential mediator of cyclooxygenase-2 expression.J Neurosci Res. 1999; 58: 593-598Crossref PubMed Scopus (96) Google Scholar, 31Hoozemans JJM Veerhuis R Janssen I Rozemuller AJM Eikelenboom P Interleukin-1β induced cyclooxygenase 2 expression and prostaglandin E2 secretion by human neuroblastoma cells: implications for Alzheimer's disease.Exp Gerontol. 2001; 36: 559-570Crossref PubMed Scopus (69) Google Scholar suggesting that IL-1β expression may have triggered COX-2 induction in the human P301S tau transgenic mice. It remains to be determined whether IL-1β was produced by neuronal or glial cells. COX-2-derived prostanoids may play a role in the cascade of events that leads to the death of motor neurons and other nerve cells in the human P301S tau transgenic mice. Neuronal overexpression of COX-2 has been shown to lead to nerve cell death and signs of cognitive impairment.32Andreasson KI Savonenko A Vidensky S Goellner JJ Zheng Y Shaffer A Kaufmann WE Worley PF Isakson P Markowska AL Age-dependent cognitive deficits and neuronal apoptosis in cyclooxygenase-2 transgenic mice.J Neurosci. 2001; 21: 8198-8209Crossref PubMed Google Scholar Conversely, inhibition of COX-2 in mice transgenic for mutant human superoxide dismutase delayed neurodegeneration and the appearance of clinical symptoms,33Drachman DB Frank K Dykes-Hoberg M Teismann P Almer G Przedborski S Rothstein JD Cyclooxygenase-2 inhibition protects motor neurons and prolongs survival in a transgenic mouse model of ALS.Ann Neurol. 2002; 52: 771-778Crossref PubMed Scopus (268) Google Scholar, 34Pompl PN Ho L Bianchi M McManus T Qin W Pasinetti GM A therapeutic role for cyclooxygenase-2 inhibitors in a transgenic model of amyotrophic lateral sclerosis.FASEB J. 2003; 17: 725-727Crossref PubMed Scopus (118) Google Scholar possibly through a reduction of glutamate release.35Drachman DB Rothstein JD Inhibition of cyclooxygenase-2 protects motor neurons in an organotypic model of amyotrophic lateral sclerosis.Ann Neurol. 2000; 48: 792-795Crossref PubMed Scopus (108) Google Scholar In the light of the present findings, inhibition of COX-2 may be a potential therapeutic target for the human tauopathies. Brain and spinal cord of 5-month-old human P301S tau transgenic mice exhibited large numbers of OX42-immunoreactive microglial cells. They were much larger in number and more strongly immunoreactive for CD11b receptors than microglia from age-matched controls. In tissues from transgenic mice, a proportion of OX42-positive cells had the morphological appearance of activated microglia. These cells, which were concentrated around nerve cells immunoreactive for phosphorylated tau, IL-1β, and COX-2, were immunoreactive for major histocompatibility complex class II antigens. Activated microglial cells were not present in the spinal cord of mice from line ALZ17, which accumulate wild-type human tau in nerve cells, but do not develop filamentous tau deposits or nerve cell death.17Probst A Götz J Wiederhold KH Tolnay M Mistl C Jaton AL Hong M Ishihara T Lee VMY Trojanowski JQ Jakes R Crowther RA Spillantini MG Bürki K Goedert M Axonopathy and amyotrophy in mice transgenic for human four-repeat tau protein.Acta Neuropathol. 2000; 99: 469-481Crossref PubMed Scopus (299) Google Scholar They express a four-repeat human brain tau isoform (441 amino acids) under the control of the murine Thy1 promoter. Expression levels of human tau in brainstem and spinal cord are very similar between line ALZ17 and the line transgenic for human P301S tau protein.10Allen B Ingram E Takao M Smith MJ Jakes R Virdee K Yoshida H Holzer M Craxton M Emson PC Atzori C Migheli A Crowther RA Ghetti B Spillantini MG Goedert M Abundant tau filaments and nonapoptotic neurodegeneration in transgenic mice expressing human P301S tau protein.J Neurosci. 2002; 22: 9340-9351Crossref PubMed Google Scholar, 17Probst A Götz J Wiederhold KH Tolnay M Mistl C Jaton AL Hong M Ishihara T Lee VMY Trojanowski JQ Jakes R Crowther RA Spillantini MG Bürki K Goedert M Axonopathy and amyotrophy in mice transgenic for human four-repeat tau protein.Acta Neuropathol. 2000; 99: 469-481Crossref PubMed Scopus (299) Google Scholar It follows that activation of microglial cells in the human P301S tau mice was linked to tau filament formation and neurodegeneration and was not the mere consequence of the overexpression of human tau. These findings mirror what has been described in AD,15Akiyama H Barger S Barnum S Bradt B Bauer J Cole GM Cooper NR Eikelenboom P Emmerling M Fiebich BL Finch CE Frautschy S Griffin WST Hampel H Hull M Landreth G Lue LF Mrak R Mackenzie IR McGeer PL O'Banion K Pachter J Pasinetti G Plata-Salaman C Rogers J Rydel R Shen Y Streit W Strohmeyer R Tooyoma I van Muiswinkel FL Veerhuis R Walker D Webster S Wegrzyniak B Wenk G Wyss-Coray T Inflammation and Alzheimer's disease.Neurobiol Aging. 2000; 21: 383-421Abstract Full Text Full Text PDF PubMed Scopus (3585) Google Scholar, 36McGeer PL Akiyama H Itagaki S McGeer EG Immune system response in Alzheimer's disease.Can J Neurol Sci. 1989; 16: 516-527Crossref PubMed Scopus (429) Google Scholar, 37Haga S Akai K Ishii T Demonstration of microglial cells in and around senile (neuritic) plaques in the Alzheimer brain. 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However, it may well play an important role in the series of events leading to neurodegeneration. It will be interesting to determine whether anti-inflammatory compounds can have a beneficial effect on the neurodegenerative process. We thank Professor G. Pepeu for helpful advice and insightful discussions.