Staging of Alzheimer's Pathology in Triple Transgenic Mice: A Light and Electron Microscopic Analysis

The age-related pathological cascade underlying intraneuronal tau formation in 3xTg-AD mice, which harbor the human APPSwe, PS1M126V , and TauP301L gene mutations, remains unclear. At 3 weeks of age, AT180, Alz50, MC1, AT8, and PHF-1 intraneuronal immunoreactivity appeared in the amygdala and hippocampus and at later ages in the cortex of 3xTg-AD mice. AT8 and PHF-1 staining was fixation dependent in young mutant mice. 6E10 staining was seen at all ages. Fluorescent immunomicroscopy revealed CA1 neurons dual stained for 6E10 and Alz50 and single Alz50 immunoreactive neurons in the subiculum at 3 weeks and continuing to 20 months. Although electron microscopy confirmed intraneuronal cytoplasmic Alz50, AT8, and 6E10 reaction product in younger 3xTg-AD mice, straight filaments appeared at 23 months of age in female mice. The present data suggest that other age-related biochemical mechanisms in addition to early intraneuronal accumulation of 6E10 and tau underlie the formation of tau filaments in 3xTg-AD mice

Staging of Alzheimer\u27s pathology in triple transgenic mice: a light and electron microscopic analysis

The age-related pathological cascade underlying intraneuronal tau formation in 3xTg-AD mice, which harbor the human APP(Swe), PS1(M126V) , and Tau(P301L) gene mutations, remains unclear. At 3 weeks of age, AT180, Alz50, MC1, AT8, and PHF-1 intraneuronal immunoreactivity appeared in the amygdala and hippocampus and at later ages in the cortex of 3xTg-AD mice. AT8 and PHF-1 staining was fixation dependent in young mutant mice. 6E10 staining was seen at all ages. Fluorescent immunomicroscopy revealed CA1 neurons dual stained for 6E10 and Alz50 and single Alz50 immunoreactive neurons in the subiculum at 3 weeks and continuing to 20 months. Although electron microscopy confirmed intraneuronal cytoplasmic Alz50, AT8, and 6E10 reaction product in younger 3xTg-AD mice, straight filaments appeared at 23 months of age in female mice. The present data suggest that other age-related biochemical mechanisms in addition to early intraneuronal accumulation of 6E10 and tau underlie the formation of tau filaments in 3xTg-AD mice

Progression of tau pathology in cholinergic basal forebrain neurons in mild cognitive impairment and Alzheimer\u27s disease

Tau is a microtubule-associated protein that forms neurofibrillary tangles (NFTs) in the selective vulnerable long projection neurons of the cholinergic basal forebrain (CBF) in Alzheimer\u27s disease (AD). Although CBF neurodegeneration correlates with cognitive decline during AD progression, little is known about the temporal changes of tau accumulation in this region. We investigated tau posttranslational modifications during NFT evolution within the CBF neurons of the nucleus basalis (NB) using tissue from subjects with no cognitive impairment, mild cognitive impairment, and AD. The pS422 antibody was used as an early tau pathology marker that labels tau phosphorylated at Ser422; the TauC3 antibody was used to detect later stage tau pathology. Stereologic evaluation of NB tissue immunostained for pS422 and TauC3 revealed an increase in neurons expressing these tau epitopes during disease progression. We also investigated the occurrence of pretangle tau events within cholinergic NB neurons by dual staining for the cholinergic cell marker, p75 NTR, which displays a phenotypic down-regulation within CBF perikarya in AD. As pS422+ neurons increased in number, p75 NTR+ neurons decreased, and these changes correlated with both AD neuropathology and cognitive decline. Also, NFTs developed slower in the CBF compared with previously examined cortical regions. Taken together, these results suggest that changes in cognition are associated with pretangle events within NB cholinergic neurons before frank NFT deposition. © 2011 American Society for Investigative Pathology

Passive immunization with phospho-tau antibodies reduces tau pathology and functional deficits in two distinct mouse tauopathy models.

In Alzheimer's disease (AD), an extensive accumulation of extracellular amyloid plaques and intraneuronal tau tangles, along with neuronal loss, is evident in distinct brain regions. Staging of tau pathology by postmortem analysis of AD subjects suggests a sequence of initiation and subsequent spread of neurofibrillary tau tangles along defined brain anatomical pathways. Further, the severity of cognitive deficits correlates with the degree and extent of tau pathology. In this study, we demonstrate that phospho-tau (p-tau) antibodies, PHF6 and PHF13, can prevent the induction of tau pathology in primary neuron cultures. The impact of passive immunotherapy on the formation and spread of tau pathology, as well as functional deficits, was subsequently evaluated with these antibodies in two distinct transgenic mouse tauopathy models. The rTg4510 transgenic mouse is characterized by inducible over-expression of P301L mutant tau, and exhibits robust age-dependent brain tau pathology. Systemic treatment with PHF6 and PHF13 from 3 to 6 months of age led to a significant decline in brain and CSF p-tau levels. In a second model, injection of preformed tau fibrils (PFFs) comprised of recombinant tau protein encompassing the microtubule-repeat domains into the cortex and hippocampus of young P301S mutant tau over-expressing mice (PS19) led to robust tau pathology on the ipsilateral side with evidence of spread to distant sites, including the contralateral hippocampus and bilateral entorhinal cortex 4 weeks post-injection. Systemic treatment with PHF13 led to a significant decline in the spread of tau pathology in this model. The reduction in tau species after p-tau antibody treatment was associated with an improvement in novel-object recognition memory test in both models. These studies provide evidence supporting the use of tau immunotherapy as a potential treatment option for AD and other tauopathies

Age-dependent changes in tau pathology in rTg4510 mice.

<p><b>A.</b> AT8 p-tau staining in 3- and 6-month old rTg4510 brain sections. Scale bar = 500 μm. <b>B-E.</b> Age-dependent change in <b>B.</b> hippocampal soluble total tau, <b>C.</b> hippocampal soluble AT8 p-tau, <b>D.</b> hippocampal insoluble total tau, and <b>E.</b> hippocampal insoluble AT8 p-tau. Individual comparisons were vs. 3.5-month old mice using ANOVA with a Dunnett’s post-hoc test (*p<0.05, ** p<0.01, *** p<0.001; n = 7–11 per group). <b>F.</b> Hippocampal soluble AT8 levels normalized to total tau levels were correlated with AT8 staining scores from immunohistochemistry (R² = 0.51, p<0.001).</p

PHF13 reduces EC tau pathology and rescues NOR performance in PS19 mice injected with K18PL PFFs.

<p>K18PL PFFs were injected into the hippocampus and mice evaluated following treatment with PHF13 or IgG2b for 4 weeks. <b>A.</b> Hippocampal area occupied by AT8 immunostaining on the ipsilateral (Ipsi) and contralateral (Contra) sides following treatment with 30 mg/Kg i.p. IgG2b or PHF13. <b>B.</b> AT8-positive cell counts within the EC of IgG2b- and PHF13-treated mice. <b>C.</b> MC1-positive cell counts within the EC of IgG2b- and PHF13-treated mice. <b>D.</b> Percent time spent on the novel object in a NOR assay. Statistical analyses were performed using a t-test comparison between IgG2b and PHF13 treatment groups (* p<0.05, ** p<0.01; n = 10-12/group).</p

Model of antibody engagement of tau in-vivo.

<p>A compartmental model depicting tau and antibody (IgG) levels in brain, interstitial fluid (ISF), cerebrospinal fluid (CSF) and plasma. CSF tau is truncated with levels of ~1 nM, while tau in ISF exists as a full-length molecule with levels of 3–5 nM (4-5x greater than in CSF) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125614#pone.0125614.ref047" target="_blank">47</a>]. Concentrations of p-tau are estimated to be about 1–10% of total tau levels. Tau antibody concentrations are 1–3 nM in CSF and ISF [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125614#pone.0125614.ref044" target="_blank">44</a>]. Antibody engagement of p-tau in CSF and ISF would enable clearance of tau via a variety of antibody-mediated mechanisms. Full-length tau is indicated as a molecule containing N-terminal (orange line), mid-domain (blue line), microtubule-binding repeat region (black box), and C-terminal (grey line) regions, whereas truncated tau in the CSF compartment is indicated by the mid-domain and N-terminal fragments.</p