Tau transgenic mice as models for cerebrospinal fluid tau biomarkers

Levels of tau in cerebrospinal fluid (CSF) are elevated in Alzheimer's disease (AD) patients. It is believed this elevation is related to the tau pathology and neurodegeneration observed in AD, but not all tauopathies have increased CSF tau. There has been little pre-clinical work to investigate mechanisms of increased CSF tau due to the difficulty in collecting CSF samples from mice, the most commonly used pre-clinical models. We developed methods to collect CSF from mice without contamination from tau in brain tissue, which is approximately 50,000 fold more abundant in brain than CSF. Using these methods, we measured CSF tau from 3xTg, Tg4510, and Tau Alone transgenic mice. All three lines of mice showed age-dependent increases in CSF tau. They varied in phenotype from undetectable to severe tau pathology and neurodegeneration, suggesting that degenerating neurons are unlikely to be the only source of pathologic CSF tau. Overall, CSF tau levels mirrored expression levels and changes of tau in the brain, but they did not always correlate exactly. CSF tau was often more sensitive to changes in brain transgene expression and pathology. In addition, we also developed ELISA assays specific to different regions of the tau protein. We used these assays to provide evidence that CSF tau exists as fragments, with little intact C-terminus and partial loss of the N-terminus. Taken together, these assays and mouse models may be used to facilitate a deeper understanding of CSF tau in neurodegenerative disease.     

Tyrosine phosphorylation of tau accompanies disease progression in transgenic mouse models of tauopathy

K. Bhaskar, G. A. Hobbs, S‐H. Yen and G. Lee (2010) Neuropathology and Applied Neurobiology 36, 462–477
Tyrosine phosphorylation of tau accompanies disease progression in transgenic mouse models of tauopathy Aim: Tau protein is a prominent component of paired helical filaments in Alzheimer's disease (AD) and other tauopathies. While the abnormal phosphorylation of tau on serine and threonine has been well established in the disease process, its phosphorylation on tyrosine has only recently been described. We previously showed that the Src family non‐receptor tyrosine kinases (SFKs) Fyn and Src phosphorylate tau on Tyr18 and that phospho‐Tyr18‐tau was present in AD brain. In this study, we have investigated the appearance of phospho‐Tyr18‐tau, activated SFK and proliferating cell nuclear antigen (PCNA) during disease progression in a mouse model of human tauopathy. Methods: We have used JNPL3, which expresses human tau with P301L mutation, and antibodies specific for phospho‐Tyr18‐tau (9G3), ser/thr phosphorylated tau (AT8), activated SFK and PCNA. Antibody staining was viewed by either epifluorescence or confocal microscopy. Results: Phospho‐Tyr18‐tau appeared concurrently with AT8‐reactive tau as early as 4 months in JNPL3. Some 9G3‐positive cells also contained activated SFKs and PCNA. We also investigated the triple transgenic mouse model of AD and found that unlike the JNPL3 model, the appearance of 9G3 reactivity did not coincide with AT8 in the hippocampus, suggesting that the presence of APP/presenilin influences tau phosphorylation. Also, Thioflavin S‐positive plaques were 9G3‐negative, suggesting that phospho‐Tyr18‐tau is absent from the dystrophic neurites of the mouse triple transgenic brain. Conclusions: Our results provide evidence for the association of tyrosine‐phosphorylated tau with mechanisms of neuropathogenesis and indicate that SFK activation and cell cycle activation are also involved in JNPL3.     

Decreased axonal transport rates in the Tg2576 APP transgenic mouse: improvement with the gamma‐secretase inhibitor MRK‐560 as detected by manganese‐enhanced MRI

Neuropil deposition of beta‐amyloid (Aβ) peptides is believed to be a key event in the neurodegenerative process of Alzheimer’s disease (AD). An early and consistent clinical finding in AD is olfactory dysfunction with associated pathology. Interestingly, transgenic amyloid precursor protein (Tg2576) mice also show early amyloid pathology in olfactory regions. Moreover, a recent study indicates that axonal transport is compromised in the olfactory system of Tg2576 mice, as measured by manganese‐enhanced magnetic resonance imaging (MEMRI). Here we tested whether the putative axonal transport deficit in the Tg2576 mouse model improves in response to a selective gamma‐secretase inhibitor, N‐[cis‐4‐[(4‐chlorophenyl)‐sulfonyl]‐4‐(2,5‐difluorophenyl)cyclohexyl]‐1,1,1‐trifluoromethanesulfonamide (MRK‐560). Tg2576 mice or wild‐type (WT) littermates were treated daily with MRK‐560 (30 μmol/kg) or vehicle for 4 (acute) or 29 days (chronic). The subsequent MEMRI analysis revealed a distinct axonal transport dysfunction in the Tg2576 mice compared with its littermate controls. Interestingly, the impairment of axonal transport could be fully reversed by chronic administration of MRK‐560, in line with the significantly lowered levels of both soluble and insoluble forms of Aβ found in the brain and olfactory bulbs (OBs) following treatment. However, no improvement of axonal transport was observed after acute treatment with MRK‐560, where soluble but not insoluble forms of Aβ were reduced in the brain and OBs. The present results show that axonal transport is impaired in Tg2576 mice compared with WT controls, as measured by MEMRI. Chronic treatment in vivo with a gamma‐secretase inhibitor, MRK‐560, significantly reduces soluble and insoluble forms of Aβ, and fully reverses the axonal transport dysfunction.     

Colocalization of phosphorylated forms of WAVE1, CRMP2, and tau in Alzheimer's disease model mice: Involvement of Cdk5 phosphorylation and the effect of ATRA treatment

Alzheimer's disease (AD) is the most common type of dementia among the elderly. Neurofibrillary tangles (NFTs), a major pathological hallmark of AD, are composed of tau protein that is hyperphosphorylated by cyclin‐dependent kinase 5 (Cdk5) and glycogen synthase kinase 3β (GSK3β). NFTs also contain Wiskott‐Aldrich syndrome protein family verprolin‐homologous protein 1 (WAVE1) and collapsin response‐mediator protein 2 (CRMP2). Although Cdk5 is known to phosphorylate tau, WAVE1, and CRMP2, the significance of this with respect to NFT formation remains to be elucidated. This study examines the involvement of phosphorylated (p‐) CRMP2 and WAVE1 in p‐tau aggregates using a triple‐transgenic (3×Tg; APPswe/PS1M146V/tauP301L) AD mouse model. First, we verified the colocalization of p‐WAVE1 and p‐CRMP2 with aggregated hyperphosphorylated tau in the hippocampus at 23 months of age. Biochemical analysis revealed the inclusion of p‐WAVE1, p‐CRMP2, and tau in the sarkosyl‐insoluble fractions of hippocampal homogenates. To test the significance of phosphorylation of these proteins further, we administered all‐trans‐retinoic acid (ATRA) to the 3×Tg mice, which downregulates Cdk5 and GSK3β activity. In ATRA‐treated mice, fewer and smaller tau aggregates were observed compared with non‐ATRA‐treated mice. These results suggest the possibility of novel therapeutic target molecules for preventing tau pathology. © 2015 Wiley Periodicals, Inc.     

Chronic stress exacerbates tau pathology, neurodegeneration, and cognitive performance through a corticotropin-releasing factor receptor-dependent mechanism in a transgenic mouse model of tauopathy

Because overactivation of the hypothalamic-pituitary-adrenal (HPA) axis occurs in Alzheimer's disease (AD), dysregulation of stress neuromediators may play a mechanistic role in the pathophysiology of AD. However, the effects of stress on tau phosphorylation are poorly understood, and the relationship between corticosterone and corticotropin-releasing factor (CRF) on both β-amyloid (Aβ) and tau pathology remain unclear. Therefore, we first established a model of chronic stress, which exacerbates Aβ accumulation in Tg2576 mice and then extended this stress paradigm to a tau transgenic mouse model with the P301S mutation (PS19) that displays tau hyperphosphorylation, insoluble tau inclusions and neurodegeneration. We show for the first time that both Tg2576 and PS19 mice demonstrate a heightened HPA stress profile in the unstressed state. In Tg2576 mice, 1 month of restraint/isolation (RI) stress increased Aβ levels, suppressed microglial activation, and worsened spatial and fear memory compared with nonstressed mice. In PS19 mice, RI stress promoted tau hyperphosphorylation, insoluble tau aggregation, neurodegeneration, and fear-memory impairments. These effects were not mimicked by chronic corticosterone administration but were prevented by pre-stress administration of a CRF receptor type 1 (CRF(1)) antagonist. The role for a CRF(1)-dependent mechanism was further supported by the finding that mice overexpressing CRF had increased hyperphosphorylated tau compared with wild-type littermates. Together, these results implicate HPA dysregulation in AD neuropathogenesis and suggest that prolonged stress may increase Aβ and tau hyperphosphorylation. These studies also implicate CRF in AD pathophysiology and suggest that pharmacological manipulation of this neuropeptide may be a potential therapeutic strategy for AD.     

Biochemical and morphological characterization of the AβPP/PS/tau triple transgenic mouse model and its relevance to sporadic Alzheimer's disease

Transgenic (Tg) mouse models of Alzheimer's disease (AD) have been genetically altered with human familial AD genes driven by powerful promoters. However, a Tg model must accurately mirror the pathogenesis of the human disease, not merely the signature amyloid and/or tau pathology, as such hallmarks can arise via multiple convergent or even by pathogenic mechanisms unrelated to human sporadic AD. The 3 × Tg-AD mouse simultaneously expresses 3 rare familial mutant genes that in humans independently produce devastating amyloid-β protein precursor (AβPP), presenilin-1, and frontotemporal dementias; hence, technically speaking, these mice are not a model of sporadic AD, but are informative in assessing co-evolving amyloid and tau pathologies. While end-stage amyloid and tau pathologies in 3 × Tg-AD mice are similar to those observed in sporadic AD, the pathophysiological mechanisms leading to these lesions are quite different. Comprehensive biochemical and morphological characterizations are important to gauge the predictive value of Tg mice. Investigation of AβPP, amyloid-β (Aβ), and tau in the 3 × Tg-AD model demonstrates AD-like pathology with some key differences compared to human sporadic AD. The biochemical dissection of AβPP reveals different cleavage patterns of the C-terminus of AβPP when compared to human AD, suggesting divergent pathogenic mechanisms. Human tau is concomitantly expressed with AβPP/Aβ from an early age while abundant extracellular amyloid plaques and paired helical filaments are manifested from 18 months on. Understanding the strengths and limitations of Tg mouse AD models through rigorous biochemical, pathological, and functional analyses will facilitate the derivation of models that better approximate human sporadic AD.     

Sex Steroid Levels and AD‐Like Pathology in 3xTgAD Mice

Decreases in testosterone and 17β‐oestradiol (E₂) are associated with an increased risk for Alzheimer's disease (AD), which has been attributed to an increase in β‐amyloid and tau pathological lesions. Although recent studies have used transgenic animal models to test the effects of sex steroid manipulations on AD‐like pathology, almost none have systematically characterised the associations between AD lesions and sex steroid levels in the blood or brain in any mutant model. The present study evaluated age‐related changes in testosterone and E₂ concentrations, as well as androgen receptor (AR) and oestrogen receptor (ER) α and β expression, in brain regions displaying AD pathology in intact male and female 3xTgAD and nontransgenic (ntg) mice. We report for the first time that circulating and brain testosterone levels significantly increase in male 3xTgAD mice with age, but without changes in AR‐immunoreactive (IR) cell number in the hippocampal CA1 or medial amygdala. The age‐related increase in hippocampal testosterone levels correlated positively with increases in the conformational tau isoform, Alz50. These data suggest that the over‐expression of human tau up‐regulate the hypothalamic‐pituitary‐gonadal axis in these mice. Although circulating and brain E₂ levels remained stable with age in both male and female 3xTgAD and ntg mice, ER‐IR cell number in the hippocampus and medial amygdala decreased with age in female transgenic mice. Furthermore, E₂ levels were significantly higher in the hippocampus than in serum, suggesting local production of E₂. Although triple transgenic mice mimic AD‐like pathology, they do not fully replicate changes in human sex steroid levels, and may not be the best model for studying the effects of sex steroids on AD lesions.     

Glycogen synthase kinase‐3β (GSK3β) expression in a mouse model of Alzheimer's disease: A light and electron microscopy study

Glycogen synthase kinase‐3β (GSK3β) activity has been previously linked to Alzheimer's disease (AD) by its phosphorylation of tau and activation by amyloid. GSK3β intracellular distribution is important in regulating its activity by restricting access to compartment‐specific substrates. This study investigated regional and intracellular distribution of GSK3β in a mouse model of AD, a bigenic mouse with combined amyloid and tau pathology (BiAT), and controls (FVB). At two different ages, the entire rostrocaudal extent of each brain was examined. Young (6‐months‐old) FVB and BiAT mice did not differ in GSK3β expression and localization. In old (13‐month‐old) BiAT mice, neurons showed increased GSK3β expression only in AD‐relevant brain regions as compared with modest staining in region‐ and age‐matched controls. Two regions with the most robust changes between FVB and BiAT mice, the amygdala and piriform cortex, were quantified at the light microscopic level. In both regions, the density of darkly labeled neurons was significantly greater in the old BiAT mice vs. the old FVB mice. Electron microscopy of the piriform cortex showed neuronal GSK3β labeling in the rough endoplasmic reticulum, on ribosomes, and on microtubules in dendrites in both strains of mice. In old BiAT mice, GSK3β labeling was qualitatively more robust compared to age‐matched controls, and GSK3β also appeared in neurofibrillary tangles. In conclusion, GSK3β expression was increased in specific intracellular locations and was found in tangles in old BiAT mice, suggesting that GSK3β overexpression in specific brain areas may be intrinsic to AD pathology. Synapse, 2013. © 2013 Wiley Periodicals, Inc.     

Cerebrospinal tau,phospho‐tau,and beta‐amyloid and neuropsychological functions in Parkinson's disease

Alzheimer's disease (AD)‐pathology may play a role in Parkinson's disease (PD)‐related dementia (PDD). The aim of this study was to assess cerebrospinal fluid (CSF) levels of tau, phospho‐tau, and beta‐amyloid, proposed AD biomarkers, and their relationship with cognitive function in PD. Forty PD patients [20 nondemented (PDND); 20 PDD] and 30 controls underwent CSF tau, phospho‐tau, and beta‐amyloid analysis using specific ELISA techniques. All PD patients and 15 controls underwent neuropsychological testing of fronto‐subcortical (attention, fluency) and neocortical (memory, naming, visuoperceptive) functions. CSF markers levels were compared between groups, and compared and correlated with neuropsychological measures in PDND and PDD separately and as a continuum (PD). CSF tau and phospho‐tau were higher in PDD than in PDND and controls (P < 0.05). CSF beta‐amyloid ranged from high (controls) to intermediate (PDND) and low (PDD) levels (P < 0.001). In all PD and PDD patients, high CSF tau and phospho‐tau were associated with impaired memory and naming. In PDND, CSF beta‐amyloid was related with phonetic fluency. These findings suggest underlying AD‐pathology in PDD in association with cortical cognitive dysfunction, and that low CSF beta‐amyloid in PDND patients with impaired phonetic fluency can constitute an early marker of cognitive dysfunction. © 2009 Movement Disorder Society     

3R tau expression modifies behavior in transgenic mice

Tauopathy is a group of disorders characterized by the accumulation of hyperphosphorylated tau protein in the brain, resulting in dementia. Here, tau‐related behavior was evaluated in a mouse model with brain overexpression of the shortest human tau isoform (0N3R). Two groups of animals [tau‐transgenic (tau‐tg) and control littermates] were tested for learning and memory at 1 and 7 months. In the Morris water maze, all mice learned the task at 1 month of age and did not learn at 7 months. In contrast, at 7 months, the tau‐tg animals demonstrated better retention of the passive avoidance response compared with their control littermates, which did not learn. In the open field test, no differences were measured between transgenic and nontransgenic young mice, but significantly higher locomotion was observed in the 7‐month‐old tau‐tg mice compared with controls. Behavior during the elevated plus maze test was the same at 1 month, but at 7 months increased entrance to the different arms was observed in the tau‐tg group. Tau expression and phosphorylation levels were analyzed at 8 months. In the subcortical brain region associated with passive avoidance behavior, the tau‐tg mice demonstrated increased brain tau expression coupled with reduced relative phosphorylation. In contrast, increased tau expression and phosphorylation were measured in the cerebral cortex of the tau‐tg mice. In conclusion, 7‐8‐month‐old tau‐tg mice overexpressing nonmutated 0N3R human tau isoform demonstrated enhanced behavior in the passive avoidance test, paralleled by relative tau hypophosphorylation in the subcortical brain region. © 2010 Wiley‐Liss, Inc.     

Accelerated amyloid deposition, neurofibrillary degeneration and neuronal loss in double mutant APP/tau transgenic mice

Even though the idea that amyloid beta peptide accumulation is the primary event in the pathogenesis of Alzheimer's disease has become the leading hypothesis, the causal link between aberrant amyloid precursor protein processing and tau alterations in this type of dementia remains controversial. We further investigated the role of beta-amyloid production/deposition in tau pathology and neuronal cell death in the mouse brain by crossing Tg2576 and VLW lines expressing human mutant amyloid precursor protein and human mutant tau, respectively. The resulting double transgenic mice showed enhanced amyloid deposition accompanied by neurofibrillary degeneration and overt neuronal loss in selectively vulnerable brain limbic areas. These findings challenge the idea that tau pathology in Alzheimer's disease is merely a downstream effect of amyloid production/deposition and suggest that reciprocal interactions between beta-amyloid and tau alterations may take place in vivo.     

Lysosomal LAMP1 immunoreactivity exists in both diffuse and neuritic amyloid plaques in the human hippocampus

Lysosomal vesicles around neuritic plaques are thought to drive Alzheimer's disease by providing ideal microenvironments for generation of amyloid‐β. Although lysosomal vesicles are present at every amyloid plaque in mouse models of Alzheimer's disease, the number of amyloid plaques that contain lysosomal vesicles in the human brain remains unknown. This study aimed to quantify lysosomal vesicles at amyloid plaques in the human hippocampus. Lysosome‐associated membrane protein 1 (LAMP1)‐positive vesicles accumulated in both diffuse (Aβ42‐positive/AT8‐negative) and neuritic (Aβ42‐positive/AT8‐positive) plaques in all regions were analysed. In contrast to mouse models of Alzheimer's disease, however, not all amyloid plaques accumulated LAMP1‐positive lysosomal vesicles. Even at neuritic plaques, LAMP1 immunoreactivity was more abundant than phospho‐tau (AT8). Further, lysosomal vesicles colocalised weakly with phospho‐tau such that accumulation of lysosomal vesicles and phospho‐tau appeared to be spatially distinct events that occurred within dystrophic neurites. This quantitative study shows that diffuse plaques, as well as neuritic plaques, contain LAMP1 immunoreactivity in the human hippocampus.     

Characterization of a 3xTg‐AD mouse model of Alzheimer's disease with the senescence accelerated mouse prone 8 (SAMP8) background

No model fully recapitulates the neuropathology of Alzheimer's disease (AD). Although the triple‐transgenic mouse model of AD (3xTg‐AD) expresses Aβ plaques and tau‐laden neurofibrillary tangles, as well as synaptic and behavioral deficits, it does not display frank neuronal loss. Because old age is the most important risk factor in AD, senescence‐related interactions might be lacking to truly establish an AD‐like environment. To investigate this hypothesis, we bred the 3xTg‐AD mouse with the senescence‐accelerated mouse prone 8 (SAMP8), a model of accelerated aging. We generated four groups of heterozygous mice with either the SAMP8 or SAMR1 (senescence‐resistant‐1) genotype, along with either the 3xTg‐AD or non‐transgenic (NonTg) genotype. Despite no differences among groups in total latency to escape the Barnes maze, a greater number of errors were noticed before entering the target hole in 19‐month‐old P8/3xTg‐AD mice at day 5, compared to other groups. Postmortem analyses revealed increased cortical levels of phospho‐tau (Thr231) in female P8/3xTg‐AD mice (+277% vs. R1/3xTg‐AD mice), without other tau‐related changes. Female P8/3xTg‐AD mice exhibited higher cortical soluble Aβ40 and Aβ42 concentrations (Aβ40, +85%; Aβ42, +35% vs. R1/3xTg‐AD), whereas insoluble forms remained unchanged. Higher Aβ42 load coincided with increased astroglial activation in female P8/3xTg‐AD mice, as measured with glial fibrillary acidic protein (GFAP) (+57% vs. R1/3xTg‐AD mice). To probe neuronal degeneration, concentrations of neuronal nuclei (NeuN) were measured, but no differences were detected between groups. Altogether, the SAMP8 genotype had deleterious effects on spatial memory and exerted female‐specific aggravation of AD neuropathology without overt neurodegeneration in 3xTg‐AD mice.     

Comparison of AT8 immunoreactivity in the locus ceruleus and hippocampus of 154 brains from routine autopsies

We compared semiquantitatively AT8 immunoreactivity in the locus ceruleus (LC) and hippocampus of 154 brains from routine autopsies to investigate the initial sites of phosphorylated tau (phospho‐tau) development. The numbers of AT8‐positive neurons and the severity of AT8‐positive neuropil threads (NTs) in the LC were strongly associated: there were no cases with AT8‐positive neurons that lacked NTs and 20 cases (13%) had only NTs in the LC. Phospho‐tau pathologies in the LC were almost equally on both sides, although some cases (7.8%) showed unilateral predominance. The numbers of AT8‐positive neurons in the LC and the numbers of AT8‐positive neurons and NTs in the hippocampus were also strongly associated. There were only two cases with AT8‐positive neurons in the LC that lacked phospho‐tau pathology in the hippocampus, and 21 cases (13.6%) with phospho‐tau pathology in the hippocampus that lacked AT8‐positive neurons in the LC. The numbers of AT8‐positive NTs in the LC and AT8‐positive neurons and NTs in the hippocampus were also strongly associated. There were seven cases (4.5%) with AT8‐positive NTs in the LC that lacked phospho‐tau pathology in the hippocampus, and five cases (3.2 %) with phospho‐tau pathologies in the hippocampus that lacked AT8‐positive NTs in the LC. In this study, we could not confirm that phospho‐tau pathologies begin in the LC. We suspect their simultaneous occurrences in both hippocampal regions and in LC.     

l-Theanine attenuates cadmium-induced neurotoxicity through the inhibition of oxidative damage and tau hyperphosphorylation

Cadmium (Cd) has long been known to induce neurological degenerative disorders. We studied effects of l-theanine, one of the major amino acid components in green tea, on Cd-induced brain injury in mice. Male ICR mice were intraperitoneally injected with l-theanine (100 or 200 mg/kg/day) or saline and after one hour these mice were orally administrated with CdCl₂ (3.75–6 mg/kg). The treatment was conducted for 8 weeks. l-Theanine significantly reduced Cd level in the mouse brain and plasma. Cd-induced neuronal cell death in the mouse cortex and hippocampus were apparently inhibited by l-theanine treatment. l-Theanine also decreased the levels of malondialdehyde (MDA) and ROS, and obviously elevated the levels of glutathione (GSH) and activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) in the mouse brain. Hyperphosphorylation of tau protein is proposed to be an early event for the evolution of tau pathology, and may play an important role in Cd-induced neurodegeneration. Our results showed that l-theanine significantly suppressed Cd-induced tau protein hyperphosphorylation at Ser199, Ser202, and Ser396. Mechanism study showed that l-theanine inhibited the activation of glycogen synthase kinase-3β (GSK-3β) which contributed to the hyperphosphorylation of tau and Cd-induced cytotoxicity. Furthermore, l-theanine reduced Cd-induced cytotoxicity possibly by interfering with the Akt/mTOR signaling pathway. In conclusion, our study indicated that l-theanine protected mice against Cd-induced neurotoxicity through reducing brain Cd level and relieved oxidative damage and tau hyperphosphorylation. Our foundings provide a novel insight into the potential use of l-theanine as prophylactic and therapeutic agents for Cd-induced neurodegenerative diseases.     

Long-term overexpression of heme oxygenase 1 promotes tau aggregation in mouse brain by inducing tau phosphorylation

Intracellular tau aggregates composed of neurofibrillary tangles (NFTs) are a defining feature of Alzheimer's disease (AD). Increased expression of heme oxygenase-1 (HO-1) is a common phenomenon in AD. Interestingly, the spatial distribution of HO-1 expression is essentially identical to that of pathological accumulation of tau in AD. In this study, we developed a new transgenic mouse overexpressing HO-1, called CAG-HO-1 Tg mice, to explore the relationship between HO-1 and tau aggregation. In this model, we found that long-term overexpression of HO-1 significantly promoted tau aggregation in brain, by analyzing changes in morphology and insoluble tau expression levels. Moreover, our research provides the first in vivo evidence that HO-1 can enhance iron loading and tau (Ser199/202/396) phosphorylation in brains of transgenic mice. Cellular evidence indicates that HO-1 can induce the phosphorylation of tau through iron accumulation in Neuro2a cells stably transfected with HO-1. Our data suggest that long-term overexpression of HO-1 can promote tau aggregation. This mechanism involves excessive iron production mediated by HO-1 overexpression, which induces tau phosphorylation. Our results provide a potential pathway for the pathogenesis of tauopathies, which remains largely unknown.     

Neurofibrillary tangle formation by introducing wild-type human tau into APP transgenic mice

Senile plaques comprised of Aβ aggregates and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau filaments are the hallmarks of Alzheimer’s disease (AD). A number of amyloid precursor protein (APP) transgenic (Tg) mice harboring APP mutations have been generated as animal models of AD. These mice successfully display amyloid plaque formation and subsequent tau hyperphosphorylation, but seldom induce NFT formations. We have demonstrated that the APP_OSK-Tg mice, which possess the E693Δ (Osaka) mutation in APP and thereby accumulate Aβ oligomers without plaques, exhibit tau hyperphosphorylation at 8 months, but not NFT formation even at 24 months. We assumed that APP-Tg mice, including ours, failed to form NFTs because NFT formation requires human tau. To test this hypothesis, we crossbred APP_OSK-Tg mice with tau-Tg mice (tau264), which express low levels of 3-repeat and 4-repeat wild-type human tau without any pathology. The resultant double Tg mice displayed tau hyperphosphorylation at 6 months and NFT formation at 18 months in the absence of tau mutations. Importantly, these NFTs contained both 3-repeat and 4-repeat human tau, similar to those in AD. Furthermore, the double Tg mice exhibited Aβ oligomer accumulation, synapse loss, and memory impairment at 6 months and neuronal loss at 18 months, all of which appeared earlier than in the parent APP_OSK-Tg mice. These results suggest that Aβ and human tau synergistically interact to accelerate each other’s pathology, that the presence of human tau is critical for NFT formation, and that Aβ oligomers can induce NFTs in the absence of amyloid plaques.     

Overexpression of human S100B exacerbates cerebral amyloidosis and gliosis in the Tg2576 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most common progressive dementia and is pathologically characterized by brain deposition of amyloid‐β (Aβ) peptide as senile plaques. Inflammatory and immune response pathways are chronically activated in AD patient brains at low levels, and likely play a role in disease progression. Like microglia, activated astrocytes produce numerous acute‐phase reactants and proinflammatory molecules in the AD brain. One such molecule, S100B, is highly expressed by reactive astrocytes in close vicinity of β‐amyloid deposits. We have previously shown that augmented and prolonged activation of astrocytes has a detrimental impact on neuronal survival. Furthermore, we have implicated astrocyte‐derived S100B as a candidate molecule responsible for this deleterious effect. To evaluate a putative relationship between S100B and AD pathogenesis, we crossed transgenic mice overexpressing human S100B (TghuS100B mice) with the Tg2576 mouse model of AD, and examined AD‐like pathology. Brain parenchymal and cerebral vascular β‐amyloid deposits and Aβ levels were increased in bigenic Tg2576‐huS100B mice. These effects were associated with increased cleavage of the β‐C‐terminal fragment of amyloid precursor protein (APP), elevation of the N‐terminal APP cleavage product (soluble APPβ), and activation of β‐site APP cleaving enzyme 1. In addition, double transgenic mice showed augmented reactive astrocytosis and microgliosis, high levels of S100 expression, and increased levels of proinflammatory cytokines as early as 7–9 months of age. These results provide evidence that (over)‐expression of S100B acts to accelerate AD‐like pathology, and suggest that inhibiting astrocytic activation by blocking S100B biosynthesis may be a promising therapeutic strategy to delay AD progression. © 2009 Wiley‐Liss, Inc.     

Smad ubiquitination regulatory factor‐2 in progressive supranuclear palsy

M. Nakamura, H. Ito, Y. Nakamura, R. Wate, S. Kaneko, S. Nakano, S. Matsumoto and H. Kusaka (2011) Neuropathology and Applied Neurobiology 37, 307–314
Smad ubiquitination regulatory factor‐2 in progressive supranuclear palsy Aims: Smad ubiquitination regulatory factor‐2 (Smurf2) is an E3 ligase that belongs to the HECT domain ubiquitin ligase family. Smurf2 can interact with Smad proteins and promote their ubiquitin‐dependent degradation, thereby controlling the cellular levels of these signalling mediators. Phosphorylated Smad2/3 (pSmad2/3) was recently identified in phosphorylated tau (phospho‐tau) inclusions in patients with progressive supranuclear palsy (PSP). As Smurf2 is the E3 ligase of pSmad2, we aimed at investigating the relationship among Smurf2, pSmad2/3 and phospho‐tau in this study. Methods: The brains of six PSP and three control patients without neurological disorder were investigated by immunohistochemical analysis. Results: In the control subjects, Smurf2 immunoreactivity was not demonstrable in the neurones and glial cells, and that for pSmad2/3 was observed exclusively in neuronal and glial nuclei. In PSP patients, the pathognomonic neuronal and glial phospho‐tau inclusions were immunopositive for both Smurf2 and pSmad2/3. The intensity of pSmad2/3 immunosignals of neuronal and glial nuclei containing phospho‐tau inclusions was less than that for the cells without the inclusions. Triple immunofluorescence staining for Smurf2, pSmad2/3 and phospho‐tau revealed co‐localization of these proteins within the neuronal and glial inclusions; and in some globose neurofibrillary tangles, the Smurf2 immunoreactivity appeared more centrally distributed than that of pSmad2/3 and phospho‐tau. Conclusions: This is the first demonstration of the presence of Smurf2 immunoreactivity in the phospho‐tau inclusions in PSP. These findings suggest that Smurf2 plays a significant role in the pathomechanism of PSP by causing abnormal redistribution of neuronal nuclear pSmad2/3 to the cytoplasm.     

Microsomal prostaglandin E synthase‐1 is induced in alzheimer's disease and its deletion mitigates alzheimer's disease‐like pathology in a mouse model

Epidemiological studies have suggested that long‐term use of nonsteroidal anti‐inflammatory drugs that inhibit cyclooxygenase (COX) activity can moderate the onset or progression of Alzheimer's disease (AD). Thus it has been suggested that prostaglandin E₂ (PGE₂), a major end‐product of COX, may play a pathogenic role in AD, but the involvement of PGE synthase (PGES), a terminal enzyme downstream from COX, has not been fully elucidated. Here we found that, among three PGES enzymes, only microsomal PGES‐1 (mPGES‐1) is induced, and its expression is associated with β‐amyloid (Aβ) plaques in the cerebral cortex in human AD patients and in Tg2576 mice, a transgenic AD mouse model. Furthermore, to investigate whether mPGES‐1 contributes to AD‐like pathology, we bred mPGES‐1‐deficient mice with Tg2576 mice. We found that mPGES‐1 deletion reduced the accumulation of microglia around senile plaques and attenuated learning impairments in Tg2576 mice. These results indicated that mPGES‐1 is induced in the AD brain and thus plays a role in AD pathology. Blockage of mPGES‐1 could form the basis for a novel therapeutic strategy for patients with AD. Inc. © 2013 Wiley Periodicals, Inc.