Tau seeding without tauopathy.

Neurodegenerative tauopathies such as Alzheimer's disease (AD) are caused by brain accumulation of tau assemblies. Evidence suggests tau functions as a prion, and cells and animals can efficiently propagate unique, transmissible tau pathologies. This suggests a dedicated cellular replication machinery, potentially reflecting a normal physiologic function for tau seeds. Consequently, we hypothesized that healthy control brains would contain seeding activity. We have recently developed a novel monoclonal antibody (MD3.1) specific for tau seeds. We used this antibody to immunopurify tau from the parietal and cerebellar cortices of 19 healthy subjects without any neuropathology, ranging 19 to 65 years. We detected seeding in lysates from the parietal cortex, but not in the cerebellum. We also detected no seeding in brain homogenates from wildtype or human tau knockin mice, suggesting that cellular/genetic context dictates development of seed-competent tau. Seeding did not correlate with subject age or brain tau levels. We confirmed our essential findings using an orthogonal assay, real-time quaking-induced conversion, which amplifies tau seeds in vitro. Dot blot analyses revealed no AT8 immunoreactivity above background levels in parietal and cerebellar extracts and ∼1/100 of that present in AD. Based on binding to a panel of antibodies, the conformational characteristics of control seeds differed from AD, suggesting a unique underlying assembly, or structural ensemble. Tau's ability to adopt self-replicating conformations under nonpathogenic conditions may reflect a normal function that goes awry in disease states.

SNCA genetic lowering reveals differential cognitive function of alpha-synuclein dependent on sex.

Antisense oligonucleotide (ASO) therapy for neurological disease has been successful in clinical settings and its potential has generated hope for Alzheimer's disease (AD). We previously described that ablating SNCA encoding for α-synuclein (αSyn) in a mouse model of AD was beneficial. Here, we sought to demonstrate whether transient reduction of αSyn expression using ASOSNCA could be therapeutic in a mouse model of AD. The efficacy of the ASOSNCA was measured via immunocytochemistry, RT-qPCR and western blotting. To assess spatial learning and memory, ASOSNCA or PBS-injected APP and non-transgenic (NTG) mice, and separate groups of SNCA-null mice, were tested on the Barnes circular maze. Hippocampal slice electrophysiology and transcriptomic profiling were used to explore synaptic function and differential gene expression between groups. Reduction of SNCA transcripts alleviated cognitive deficits in male transgenic animals, but surprisingly, not in females. To determine the functional cause of this differential effect, we assessed memory function in SNCA-null mice. Learning and memory were intact in male mice but impaired in female animals, revealing that the role of αSyn on cognitive function is sex-specific. Transcriptional analyses identified a differentially expressed gene network centered around EGR1, a central modulator of learning and memory, in the hippocampi of SNCA-null mice. Thus, these novel results demonstrate that the function of αSyn on memory differs between male and female brains.

Tau seeding in cases of multiple sclerosis.

Relapsing remitting multiple sclerosis (MS) is an inflammatory demyelinating disorder of the central nervous system that in many cases leads to progressive MS, a neurodegenerative disease. Progressive MS is untreatable and relentless, and its cause is unknown. Prior studies of MS have documented neuronal accumulation of phosphorylated tau protein, which characterizes another heterogeneous group of neurogenerative disorders, the tauopathies. Known causes of tauopathy are myriad, and include point mutations within the tau gene, amyloid beta accumulation, repeated head trauma, and viral infection. We and others have proposed that tau has essential features of a prion. It forms intracellular assemblies that can exit a cell, enter a secondary cell, and serve as templates for their own replication in a process termed "seeding." We have previously developed specialized "biosensor" cell systems to detect and quantify tau seeds in brain tissues. We hypothesized that progressive MS is a tauopathy, potentially triggered by inflammation. We tested for and detected tau seeding in frozen brain tissue of 6/8 subjects with multiple sclerosis. We then evaluated multiple brain regions from a single subject for whom we had detailed clinical history. We observed seeding outside of MS plaques that was enriched by immunopurification with two anti-tau antibodies (HJ8.5 and MD3.1). Immunohistochemistry with AT8 and MD3.1 confirmed prior reports of tau accumulation in MS. Although larger studies are required, our data suggest that progressive MS may be considered a secondary tauopathy.

Bidirectional modulation of Alzheimer phenotype by alpha-synuclein in mice and primary neurons.

α-Synuclein (αSyn) histopathology defines several neurodegenerative disorders, including Parkinson's disease, Lewy body dementia, and Alzheimer's disease (AD). However, the functional link between soluble αSyn and disease etiology remains elusive, especially in AD. We, therefore, genetically targeted αSyn in APP transgenic mice modeling AD and mouse primary neurons. Our results demonstrate bidirectional modulation of behavioral deficits and pathophysiology by αSyn. Overexpression of human wild-type αSyn in APP animals markedly reduced amyloid deposition but, counter-intuitively, exacerbated deficits in spatial memory. It also increased extracellular amyloid-ß oligomers (AßOs), αSyn oligomers, exacerbated tau conformational and phosphorylation variants associated with AD, and enhanced neuronal cell cycle re-entry (CCR), a frequent prelude to neuron death in AD. Conversely, ablation of the SNCA gene encoding for αSyn in APP mice improved memory retention in spite of increased plaque burden. Reminiscent of the effect of MAPT ablation in APP mice, SNCA deletion prevented premature mortality. Moreover, the absence of αSyn decreased extracellular AßOs, ameliorated CCR, and rescued postsynaptic marker deficits. In summary, this complementary, bidirectional genetic approach implicates αSyn as an essential mediator of key phenotypes in AD and offers new functional insight into αSyn pathophysiology.

Selective lowering of synapsins induced by oligomeric α-synuclein exacerbates memory deficits.

Mounting evidence indicates that soluble oligomeric forms of amyloid proteins linked to neurodegenerative disorders, such as amyloid-ß (Aß), tau, or α-synuclein (αSyn) might be the major deleterious species for neuronal function in these diseases. Here, we found an abnormal accumulation of oligomeric αSyn species in AD brains by custom ELISA, size-exclusion chromatography, and nondenaturing/denaturing immunoblotting techniques. Importantly, the abundance of αSyn oligomers in human brain tissue correlated with cognitive impairment and reductions in synapsin expression. By overexpressing WT human αSyn in an AD mouse model, we artificially enhanced αSyn oligomerization. These bigenic mice displayed exacerbated Aß-induced cognitive deficits and a selective decrease in synapsins. Following isolation of various soluble αSyn assemblies from transgenic mice, we found that in vitro delivery of exogenous oligomeric αSyn but not monomeric αSyn was causing a lowering in synapsin-I/II protein abundance. For a particular αSyn oligomer, these changes were either dependent or independent on endogenous αSyn expression. Finally, at a molecular level, the expression of synapsin genes SYN1 and SYN2 was down-regulated in vivo and in vitro by αSyn oligomers, which decreased two transcription factors, cAMP response element binding and Nurr1, controlling synapsin gene promoter activity. Overall, our results demonstrate that endogenous αSyn oligomers can impair memory by selectively lowering synapsin expression.

Soluble Conformers of Aß and Tau Alter Selective Proteins Governing Axonal Transport.

UNLABELLED: Despite the demonstration that amyloid-ß (Aß) can trigger increased tau phosphorylation and neurofibrillary tangle (NFT) formation in vivo, the molecular link associating Aß and tau pathologies remains ill defined. Here, we observed that exposure of cultured primary neurons to Aß trimers isolated from brain tissue of subjects with Alzheimer's disease led to a specific conformational change of tau detected by the antibody Alz50. A similar association was supported by postmortem human brain analyses. To study the role of Aß trimers in vivo, we created a novel bigenic Tg-Aß+Tau mouse line by crossing Tg2576 (Tg-Aß) and rTg4510 (Tg-Tau) mice. Before neurodegeneration and amyloidosis, apparent Aß trimers were increased by ∼2-fold in 3-month-old Tg-Aß and Tg-Aß+Tau mice compared with younger mice, whereas soluble monomeric Aß levels were unchanged. Under these conditions, the expression of soluble Alz50-tau conformers rose by ∼2.2-fold in the forebrains of Tg-Aß+Tau mice compared with nontransgenic littermates. In parallel, APP accumulated intracellularly, suggestive of a putative dysfunction of anterograde axonal transport. We found that the protein abundance of the kinesin-1 light chain (KLC1) was reduced selectively in vivo and in vitro when soluble Aß trimers/Alz50-tau were present. Importantly, the reduction in KLC1 was prevented by the intraneuronal delivery of Alz50 antibodies. Collectively, our findings reveal that specific soluble conformers of Aß and tau cooperatively disrupt axonal transport independently from plaques and tangles. Finally, these results suggest that not all endogenous Aß oligomers trigger the same deleterious changes and that the role of each assembly should be considered separately. SIGNIFICANCE STATEMENT: The mechanistic link between amyloid-ß (Aß) and tau, the two major proteins composing the neuropathological lesions detected in brain tissue of Alzheimer's disease subjects, remains unclear. Here, we report that the trimeric Aß species induce a pathological modification of tau in cultured neurons and in bigenic mice expressing Aß and human tau. This linkage was also observed in postmortem brain tissue from subjects with mild cognitive impairment, when Aß trimers are abundant. Further, this modification of tau was associated with the intracellular accumulation of the precursor protein of Aß, APP, as a result of the selective decrease in kinesin light chain 1 expression. Our findings suggest that Aß trimers might cause axonal transport deficits in AD.

The stable carbon isotope ratio of some components of an eelgrass, Zostera marina, bed.

Living and dead Zostera marina blades, plankton samples, sediments, and several animal components of an eelgrass bed near Beaufort, N.C. were collected and analyzed for 13C/12C ratios (δ 13C). The δ 13C values of producer and consumer organisms were compared in order to examine the possible origins of organic matter present in the consumers. Living and dead eelgrass blades displayed similar δ13C values,-12.2 and-10.6 per mil ‰ respectively, while the epiphytic community growing on the grass blades had a mean isotope ratio of-16.0‰. Animal components analyzed represented five major feeding-mode categories: invertebrates living on grass blades an presumably feeding on the epibiota (-15.1‰), deposit feeding invertebrates (-15.0‰), predatory and omnivorous invertebrates (-16.7‰), suspension and surface feeding invertebrates (-18.3‰) and omnivorous fish (-16.8‰).Organisms commonly found on the grass blades appeared to feed primarily on the epibiota growing on the blades. It is hypothesized that the epibiota derive some of their carbon from DOC released by the Zostera blade. The urchin, Lytechinus variegatus, and the brittle star, Ophioderma brevispinum, both deposit feeders, appeared to derive a major proportion of their carbon from eelgrass. With the exception of the shrimp, Alpheus heterochaelis, and the pipefish, Syngnathus floridae, the majority of other organisms analyzed appeared to be linked more directly to a plankton-carbon food chanin than to a seagrass-carbon system in this relatively young eelgrass bed.