The MAPT H1c risk haplotype is associated with increased expression of tau and especially of 4 repeat containing transcripts

Drosophila Models of Sporadic Parkinson's Disease

Parkinson’s disease (PD) is the most common cause of movement disorders and is characterized by the progressive loss of dopaminergic neurons in the substantia nigra. It is increasingly recognized as a complex group of disorders presenting widely heterogeneous symptoms and pathology. With the exception of the rare monogenic forms, the majority of PD cases result from an interaction between multiple genetic and environmental risk factors. The search for these risk factors and the development of preclinical animal models are in progress, aiming to provide mechanistic insights into the pathogenesis of PD. This review summarizes the studies that capitalize on modeling sporadic (i.e., nonfamilial) PD using Drosophilamelanogaster and discusses their methodologies, new findings, and future perspectives.

The human brainome: network analysis identifies HSPA2 as a novel Alzheimer’s disease target

Our hypothesis is that changes in gene and protein expression are crucial to the development of late-onset Alzheimer’s disease. Previously we examined how DNA alleles control downstream expression of RNA transcripts and how those relationships are changed in late-onset Alzheimer’s disease. We have now examined how proteins are incorporated into networks in two separate series and evaluated our outputs in two different cell lines. Our pipeline included the following steps: (i) predicting expression quantitative trait loci; (ii) determining differential expression; (iii) analysing networks of transcript and peptide relationships; and (iv) validating effects in two separate cell lines. We performed all our analysis in two separate brain series to validate effects. Our two series included 345 samples in the first set (177 controls, 168 cases; age range 65–105; 58% female; KRONOSII cohort) and 409 samples in the replicate set (153 controls, 141 cases, 115 mild cognitive impairment; age range 66–107; 63% female; RUSH cohort). Our top target is heat shock protein family A member 2 (HSPA2), which was identified as a key driver in our two datasets. HSPA2 was validated in two cell lines, with overexpression driving further elevation of amyloid-β40 and amyloid-β42 levels in APP mutant cells, as well as significant elevation of microtubule associated protein tau and phosphorylated-tau in a modified neuroglioma line. This work further demonstrates that studying changes in gene and protein expression is crucial to understanding late onset disease and further nominates HSPA2 as a specific key regulator of late-onset Alzheimer’s disease processes.10.1093/brain/awy215_video1awy215media15824729224001.

Early Gray Matter Volume Loss in MAPT H1H1 de Novo PD Patients: A Possible Association With Cognitive Decline

The MAPT H1 haplotype has been identified as a predictor of cognitive decline in Parkinson's disease (PD). However, its underlying pathological mechanisms have not been fully established. In this work, using a cohort of 120 de novo PD patients with preserved cognition from the Parkinson's Progression Markers Initiative (PPMI) database, we found that patients who were homozygous for MAPT H1 had less gray matter volume (GMV) and greater 1-year GMV loss than patients without this genetic profile. Importantly, these changes were associated with a longitudinal worsening of cognitive indicators. Our findings suggest that early GMV loss in MAPT H1H1 PD patients increases their risk to develop cognitive decline.

Meta-analysis of the association between variants in MAPT and neurodegenerative diseases

Microtubule-associated protein tau (MAPT) gene is compelling among the susceptibility genes of neurodegenerative diseases which include Alzheimer’s disease (AD), Parkinson’s disease (PD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Our meta-analysis aimed to find the association between MAPT and the risk of these diseases. Published literatures were retrieved from MEDLINE and other databases, and 82 case-control studies were recruited. Six haplotype tagging single-nucleotide polymorphisms (rs1467967, rs242557, rs3785883, rs2471738, del-In9 and rs7521) and haplotypes (H2 and H1c) were significantly associated with the above diseases. The odds ratios (ORs) and 95 % confidence intervals (CIs) were evaluated by comparison in minor and major allele frequency using the R software. This study demonstrated that different variants in MAPT were associated with AD (rs2471738: OR= 1.04, 95%CI = 1.00 - 1.09; H2: OR = 0.94, 95% CI = 0.91 - 0.97), PD (H2: OR = 0.76, 95% CI = 0.74 - 0.79), PSP (rs242557: OR = 1. 96, 95% CI = 1. 71 - 2.25; rs2471738: OR = 1. 85, 95% CI = 1. 48 - 2.31; H2: OR = 0.20, 95% CI = 0.18 - 0.23), CBD (rs242557: OR = 2.51, 95%CI = 1. 66 -3.78; rs2471738: OR = 2.07, 95%CI = 1. 32 -3.23; H2: OR = OR = 0.30, 95% CI = 0.23 - 0.41) and ALS (H2: OR = 0.92, 95% CI = 0.86 - 0.98) instead of FTD (H2: OR = 1.02, 95% CI = 0.78 - 1.32). In conclusion, MAPT is associated with risk of neurodegenerative diseases, suggesting crucial roles of tau in neurodegenerative processes.

The associations between the MAPT polymorphisms and Alzheimer's disease risk: a meta-analysis

Published studies revealed that the microtubule-associated protein tau (MAPT) gene polymorphisms increased Alzheimer’s disease (AD) risk; the associations of 4 single nucleotide polymorphisms (SNPs, rs242557G/A, rs2471738C/T, rs3785883G/A and rs1467967A/G) of the MAPT gene with AD risk, however, remain inconclusive. Here, we conducted a meta-analysis to investigate the relationship between the MAPT SNPs and AD risk. A significant association of SNP rs242557 with AD risk was found in a dominant [odds ratio (OR) = 1.05, 95% confidence interval (CI) = 1.01, 1.10, P = 0.025] genetic model, and a suggestive association in an allelic (OR = 1.03, 95% CI = 1.00, 1.06, P = 0.078). When APOE epsilon 4 carrier status was included in stratified analysis, this association was even stronger (allelic model for the APOE epsilon 4 positive individuals: OR = 1.24, 95% CI = 1.08, 1.43, P = 0.003). Furthermore, a significant association of SNP rs2471738 with AD risk was found under all the four models (allelic: OR = 1.11, 95% CI = 1.01, 1.20, P = 0.021; dominant: OR = 1.10, 95% CI = 1.00, 1.21, P = 0.046; recessive: OR = 1.18, 95% CI = 1.05, 1.32, P = 0.004; additive: OR = 1.20, 95% CI = 1.07, 1.34, P = 0.002) models. However, pooled results suggest that the neither rs3785883 nor rs1467967 is associated with AD risk under all the four genetic models. In summary, our study provides further evidence of the associations of the MAPT SNPs with AD risk.

Is it Useful to Classify Progressive Supranuclear Palsy and Corticobasal Degeneration as Different Disorders? No

http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)2330-1619/homepage/mdc312582-sup-v001.htm.

Slowly progressive dementia caused by MAPT R406W mutations: longitudinal report on a new kindred and systematic review

Background

The MAPT c.1216C > T (p.Arg406Trp; R406W) mutation is a known cause of frontotemporal dementia with Parkinsonism linked to chromosome 17 tau with Alzheimer’s disease-like clinical features.

Methods

We compiled clinical data from a new Swedish kindred with R406W mutation. Seven family members were followed longitudinally for up to 22 years. Radiological examinations were performed in six family members and neuropathological examinations in three. We systematically reviewed the literature and compiled clinical, radiological, and neuropathological data on 63 previously described R406W heterozygotes and 3 homozygotes.

Results

For all cases combined, the median age of onset was 56 years and the median disease duration was 13 years. Memory impairment was the most frequent symptom, behavioral disturbance and language impairment were less common, and Parkinsonism was rare. Disease progression was most often slow. The most frequent clinical diagnosis was Alzheimer’s disease. R406W homozygotes had an earlier age at onset and a higher frequency of behavioral symptoms and Parkinsonism than heterozygotes. In the new Swedish kindred, a consistent imaging finding was ventromedial temporal lobe atrophy, which was evident also in early disease stages as a widening of the collateral sulcus with ensuing atrophy of the parahippocampal gyrus. Unlike previously published R406W carriers, all three autopsied patients from the novel family showed neuropathological similarities with progressive supranuclear palsy, with predominant four-repeat (exon 10+) tau isoform (4R) tauopathy and neurofibrillary tangles accentuated in the basal-medial temporal lobe. Amyloid-β pathology was absent.

Conclusions

Dominance of 4R over three-repeat (exon 10−) tau isoforms contrasts with earlier reports of R406W patients and was not sufficiently explained by the presence of H1/H2 haplotypes in two of the autopsied patients. R406W patients often show a long course of disease with marked memory deficits. Both our neuropathological results and our imaging findings revealed that the ventromedial temporal lobes were extensively affected in the disease. We suggest that this area may represent the point of origin of tau deposition in this disease with relatively isolated tauopathy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0330-2) contains supplementary material, which is available to authorized users.

Scalable Production of iPSC-Derived Human Neurons to Identify Tau-Lowering Compounds by High-Content Screening

Lowering total tau levels is an attractive therapeutic strategy for Alzheimer's disease and other tauopathies. High-throughput screening in neurons derived from human induced pluripotent stem cells (iPSCs) is a powerful tool to identify tau-targeted therapeutics. However, such screens have been hampered by heterogeneous neuronal production, high cost and low yield, and multi-step differentiation procedures. We engineered an isogenic iPSC line that harbors an inducible neurogenin 2 transgene, a transcription factor that rapidly converts iPSCs to neurons, integrated at the AAVS1 locus. Using a simplified two-step protocol, we differentiated these iPSCs into cortical glutamatergic neurons with minimal well-to-well variability. We developed a robust high-content screening assay to identify tau-lowering compounds in LOPAC and identified adrenergic receptors agonists as a class of compounds that reduce endogenous human tau. These techniques enable the use of human neurons for high-throughput screening of drugs to treat neurodegenerative disease.

MAPT Genetic Variation and Neuronal Maturity Alter Isoform Expression Affecting Axonal Transport in iPSC-Derived Dopamine Neurons

The H1 haplotype of the microtubule-associated protein tau (MAPT) locus is genetically associated with neurodegenerative diseases, including Parkinson's disease (PD), and affects gene expression and splicing. However, the functional impact on neurons of such expression differences has yet to be fully elucidated. Here, we employ extended maturation phases during differentiation of induced pluripotent stem cells (iPSCs) into mature dopaminergic neuronal cultures to obtain cultures expressing all six adult tau protein isoforms. After 6 months of maturation, levels of exon 3+ and exon 10+ transcripts approach those of adult brain. Mature dopaminergic neuronal cultures display haplotype differences in expression, with H1 expressing 22% higher levels of MAPT transcripts than H2 and H2 expressing 2-fold greater exon 3+ transcripts than H1. Furthermore, knocking down adult tau protein variants alters axonal transport velocities in mature iPSC-derived dopaminergic neuronal cultures. This work links haplotype-specific MAPT expression with a biologically functional outcome relevant for PD.

Current Understanding of Neurodegenerative Diseases Associated With the Protein Tau

Primary tauopathies are a group of neurodegenerative diseases in which tau is believed to be the major contributing factor of the neurodegenerative process. In primary tauopathies, there is a disassociation between tau (a microtubule-associated protein) and microtubules as a result of tau hyperphosphorylation. This disassociation between tau and microtubules results in tau fibrillization and inclusion formation as well as in microtubule dysfunction. There are different clinical syndromes associated with different primary tauopathies, and some clinical syndromes can be associated with multiple primary tauopathies. Hence, although some clinical syndromes are highly specific and almost diagnostic of a primary tauopathy, many are not, making it difficult to diagnose a primary tauopathy. Recently, radioligands that bind to tau and can be combined with positron emission tomography to detect fibrillary tau antemortem have been developed, although preliminary data suggest that these ligands may not be sensitive in detecting tau associated with many primary tauopathies. Another recent advancement in the field is evidence suggesting that tau may exhibit properties similar to those of prions, although infective transmission has not been shown. There have been a few clinical trials targeting tau and microtubule dysfunction, although none have had any disease-modifying effects. Understanding tau biology is critical to the development of pharmacological agents that could have disease-modifying effects on primary tauopathies.

Evaluating the Patterns of Aging-Related Tau Astrogliopathy Unravels Novel Insights Into Brain Aging and Neurodegenerative Diseases

The term "aging-related tau astrogliopathy" (ARTAG) describes pathological accumulation of abnormally phosphorylated tau protein in astrocytes. We evaluated the correlates of ARTAG types (i.e., subpial, subependymal, white and gray matter, and perivascular) in different neuroanatomical regions. Clinical, neuropathological, and genetic (eg, APOE ε4 allele, MAPT H1/H2 haplotype) data from 628 postmortem brains from subjects were investigated; most of the patients had been longitudinally followed at the University of Pennsylvania. We found that (i) the amygdala is a hotspot for all ARTAG types; (ii) age at death, male sex, and presence of primary frontotemporal lobar degeneration (FTLD) tauopathy are significantly associated with ARTAG; (iii) age at death, greater degree of brain atrophy, ventricular enlargement, and Alzheimer disease (AD)-related variables are associated with subpial, white matter, and perivascular ARTAG types; (iv) AD-related variables are associated particularly with lobar white matter ARTAG; and (v) gray matter ARTAG in primary FTLD-tauopathies appears in areas without neuronal tau pathology. We provide a reference map of ARTAG types and propose at least 5 constellations of ARTAG. Furthermore, we propose a conceptual link between primary FTLD-tauopathy and ARTAG-related astrocytic tau pathologies. Our observations serve as a basis for etiological stratification and definition of progression patterns of ARTAG.

Frontotemporal Dementia

Frontotemporal dementia (FTD) is a heterogeneous disorder with distinct clinical phenotypes associated with multiple neuropathologic entities. Presently, the term FTD encompasses clinical disorders that include changes in behavior, language, executive control, and often motor symptoms. The core FTD spectrum disorders include behavioral variant FTD, nonfluent/agrammatic variant primary progressive aphasia, and semantic variant PPA. Related FTD disorders include frontotemporal dementia with motor neuron disease, progressive supranuclear palsy syndrome, and corticobasal syndrome. In this article, the authors discuss the clinical presentation, diagnostic criteria, neuropathology, genetics, and treatments of these disorders.

Tauopathy with hippocampal 4-repeat tau immunoreactive spherical inclusions: a report of three cases

Tauopathies are a major group of neurodegenerative proteinopathies characterized by the accumulation of abnormal and hyperphosphorylated tau proteins in the brain. Tau pathology is characterized as 3R (repeat) or 4R predominant or mixed 3R and 4R type. Here we report three cases lacking mutations in the microtubule associated protein tau (MAPT) gene with unusual tau pathology. The age at onset and duration of illness, respectively, were 63 and 20 years (male), 67 and 5 years (female) and 72 and 20 years (female). The clinical presentation was compatible with a diagnosis of progressive supranuclear palsy (PSP) in two subjects and with cognitive decline in all three subjects. Common neuropathological features included neuronal loss in the hippocampus and dentate gyrus associated with spherical basophilic Pick body-like inclusions showing 4R tau immunoreactivity, which was supported by the detection of predominantly 4R tau species by Western blot examination. In addition, accumulation of tau immunoreactive argyrophilic astrocytes in the hippocampus and amygdala and oligodendroglial coiled bodies in the hippocampal white matter were observed. These morphologies appeared in combination with Alzheimer disease-related pathology and subcortical tau pathology compatible with PSP. Together with a single case report in the literature, our observations on these three cases expand the spectrum of previously described tauopathies. We suggest that this tauopathy variant with hippocampal 4R tau immunoreactive spherical inclusions might contribute to the cognitive deficits in the patients reported here. The precise definition of the clinicopathological relevance of these unusual tau pathologies merits further study.

Genome-wide association study identifies MAPT locus influencing human plasma tau levels

OBJECTIVE

To identify genetic loci associated with plasma tau concentrations in healthy elders and individuals with Alzheimer disease.

METHODS

Four hundred sixty-three non-Hispanic white individuals exceeding quality control criteria were included from the Alzheimer's Disease Neuroimaging Initiative (ADNI-1) cohort. Association of plasma tau with genetic polymorphisms was performed with a linear regression model. Significant associations were validated in an independent replication cohort consisting of 431 healthy elders or individuals with mild cognitive impairment recruited from the University of California, San Francisco Memory and Aging Center.

RESULTS

The minor allele (A) of rs242557 in the microtubule-associated protein tau gene (MAPT) was associated with higher plasma tau levels at genome-wide significance (p = 4.85 × 10^-9, empiric family-wise error corrected p = 0.0024) in a dose-dependent fashion. This association was also observed in the replication cohort (p = 1.0 × 10^-5; joint analysis p = 1.2 × 10^-12). Single nucleotide polymorphisms near PARK2 (rs2187213) (p = 6.15 × 10^-6), IL2RA (rs7072793, rs7073236) (p = 7.89 × 10^-6), and an intergenic locus on 9p21.3 (rs7047280) (p = 8.13 × 10^-6) were identified as suggestive loci associated with plasma tau levels.

CONCLUSIONS

MAPT H1c haplotype (rs242557) has previously been identified as a genetic risk factor for progressive supranuclear palsy and corticobasal degeneration. The current findings suggest that plasma tau concentration could be an endophenotype for identifying risk for 4-repeat tauopathies in older individuals.

MAPT haplotype H1G is associated with increased risk of dementia with Lewy bodies

INTRODUCTION

The MAPT H1 haplotype has been associated with several neurodegenerative diseases. We were interested in exploring the role of MAPT haplotypic variation in risk of dementia with Lewy bodies (DLB).

METHOD

We genotyped six MAPT haplotype tagging SNPs and screened 431 clinical DLB cases, 347 pathologically defined high-likelihood DLB cases, and 1049 controls.

RESULT

We performed haplotypic association tests and detected an association with the protective H2 haplotype in our combined series (odds ratio [OR] = 0.75). We fine-mapped the locus and identified a relatively rare haplotype, H1G, that is associated with an increased risk of DLB (OR = 3.30, P = .0017). This association was replicated in our pathologically defined series (OR = 2.26, P = .035).

DISCUSSION

These results support a role for H1 and specifically H1G in susceptibility to DLB. However, the exact functional variant at the locus is still unknown, and additional studies are warranted to fully explain genetic risk of DLB at the MAPT locus.

Gene expression, methylation and neuropathology correlations at progressive supranuclear palsy risk loci

To determine the effects of single nucleotide polymorphisms (SNPs) identified in a genome-wide association study of progressive supranuclear palsy (PSP), we tested their association with brain gene expression, CpG methylation and neuropathology. In 175 autopsied PSP subjects, we performed associations between seven PSP risk variants and temporal cortex levels of 20 genes in-cis, within ±100 kb. Methylation measures were collected using reduced representation bisulfite sequencing in 43 PSP brains. To determine whether SNP/expression associations are due to epigenetic modifications, CpG methylation levels of associated genes were tested against relevant variants. Quantitative neuropathology endophenotypes were tested for SNP associations in 422 PSP subjects. Brain levels of LRRC37A4 and ARL17B were associated with rs8070723; MOBP with rs1768208 and both ARL17A and ARL17B with rs242557. Expression associations for LRRC37A4 and MOBP were available in an additional 100 PSP subjects. Meta-analysis revealed highly significant associations for PSP risk alleles of rs8070723 and rs1768208 with higher LRRC37A4 and MOBP brain levels, respectively. Methylation levels of one CpG in the 3' region of ARL17B associated with rs242557 and rs8070723. Additionally, methylation levels of an intronic ARL17A CpG associated with rs242557 and that of an intronic MOBP CpG with rs1768208. MAPT and MOBP region risk alleles also associated with higher levels of neuropathology. Strongest associations were observed for rs242557/coiled bodies and tufted astrocytes; and for rs1768208/coiled bodies and tau threads. These findings suggest that PSP variants at MAPT and MOBP loci may confer PSP risk via influencing gene expression and tau neuropathology. MOBP, LRRC37A4, ARL17A and ARL17B warrant further assessment as candidate PSP risk genes. Our findings have implications for the mechanism of action of variants at some of the top PSP risk loci.

The Role of MAPT Haplotype H2 and Isoform 1N/4R in Parkinsonism of Older Adults

Background and Objective

Recently, we have shown that the Parkinson’s disease (PD) susceptibility locus MAPT (microtubule associated protein tau) is associated with parkinsonism in older adults without a clinical diagnosis of PD. In this study, we investigated the relationship between parkinsonian signs and MAPT transcripts by assessing the effect of MAPT haplotypes on alternative splicing and expression levels of the most common isoforms in two prospective clinicopathologic studies of aging.

Materials and Methods

using regression analysis, controlling for age, sex, study and neuropathology, we evaluated 976 subjects with clinical, genotyping and brain pathology data for haplotype analysis. For transcript analysis, we obtained MAPT gene and isoform-level expression from the dorsolateral prefrontal cortex for 505 of these subjects.

Results

The MAPT H2 haplotype was associated with lower total MAPT expression (p = 1.2x10-14) and global parkinsonism at both study entry (p = 0.001) and proximate to death (p = 0.050). Specifically, haplotype H2 was primarily associated with bradykinesia in both assessments (p<0.001 and p = 0.008). MAPT total expression was associated with age and decreases linearly with advancing age (p<0.001). Analysing MAPT alternative splicing, the expression of 1N/4R isoform was inversely associated with global parkinsonism (p = 0.008) and bradykinesia (p = 0.008). Diminished 1N/4R isoform expression was also associated with H2 (p = 0.001).

Conclusions

Overall, our results suggest that age and H2 are associated with higher parkinsonism score and decreased total MAPT RNA expression. Additionally, we found that H2 and parkinsonism are associated with altered expression levels of specific isoforms. These findings may contribute to the understanding of the association between MAPT locus and parkinsonism in elderly subjects and in some extent to age-related neurodegenerative diseases.

MAPT haplotype diversity in multiple system atrophy

INTRODUCTION

Multiple system atrophy (MSA) is a rare progressive neurodegenerative disorder. MSA was originally considered exclusively sporadic but reports of association with genes such as SNCA, COQ2 and LRRK2 have demonstrated that there is a genetic contribution to the disease. MAPT has been associated with several neurodegenerative diseases and we previously reported a protective association of the MAPT H2 haplotype with MSA in 61 pathologically confirmed cases.

METHODS

In the present study, we assessed the full MAPT haplotype diversity in MSA patients using six MAPT tagging SNPs. We genotyped a total of 127 pathologically confirmed MSA cases, 86 patients with clinically diagnosed MSA and 1312 controls.

RESULTS

We identified four significant association signals in our pathologically confirmed cases, two from the protective haplotypes H2 (MSA:16.2%,

CONTROLS

22.7%, p = 0.024) and H1E (MSA:3.0%,

CONTROLS

9.0%, p = 0.014), and two from the rare risk haplotypes H1x (MSA:3.7%,

CONTROLS

1.3%, p = 0.030) and H1J (MSA:3.0%,

CONTROLS

0.9%, p = 0.021). We evaluated the association of MSA subtypes with the common protective H2 haplotype and found a significant difference with controls for MSA patients with some degree of MSA-C (MSA-C or MSA-mixed), for whom H2 occurred in only 8.6% of patients in our pathologically confirmed series (P < 0.0001).

CONCLUSIONS

Our findings provide further evidence that MAPT variation is associated with risk of MSA. Interestingly, our results suggest a greater effect size in the MSA-C compared to MSA-P for H2. Additional genetic studies in larger pathologically confirmed MSA series and meta-analytic studies will be needed to fully assess the role of MAPT and other genes in MSA.

Comprehensive promoter level expression quantitative trait loci analysis of the human frontal lobe

BACKGROUND

Expression quantitative trait loci (eQTL) analysis is a powerful method to detect correlations between gene expression and genomic variants and is widely used to interpret the biological mechanism underlying identified genome wide association studies (GWAS) risk loci. Numerous eQTL studies have been performed on different cell types and tissues of which the majority has been based on microarray technology.

METHODS

We present here an eQTL analysis based on cap analysis gene expression sequencing (CAGEseq) data created from human postmortem frontal lobe tissue combined with genotypes obtained through genotyping arrays, exome sequencing, and CAGEseq. Using CAGEseq as an expression profiling technique combined with these different genotyping techniques allows measurement of the molecular effect of variants on individual transcription start sites and increases the resolution of eQTL analysis by also including the non-annotated parts of the genome.

RESULTS

We identified 2410 eQTLs and show that non-coding transcripts are more likely to contain an eQTL than coding transcripts, in particular antisense transcripts. We provide evidence for how previously identified GWAS loci for schizophrenia (NRGN), Parkinson's disease, and Alzheimer's disease (PARK16 and MAPT loci) could increase the risk for disease at a molecular level. Furthermore, we demonstrate that CAGEseq improves eQTL analysis because variants obtained from CAGEseq are highly enriched for having a functional effect and thus are an efficient method towards the identification of causal variants.

CONCLUSION

Our data contain both coding and non-coding transcripts and has the added value that we have identified eQTLs for variants directly adjacent to TSS. Future eQTL studies would benefit from combining CAGEseq with RNA sequencing for a more complete interpretation of the transcriptome and increased understanding of eQTL signals.

"New Old Pathologies": AD, PART, and Cerebral Age-Related TDP-43 With Sclerosis (CARTS)

The pathology-based classification of Alzheimer's disease (AD) and other neurodegenerative diseases is a work in progress that is important for both clinicians and basic scientists. Analyses of large autopsy series, biomarker studies, and genomics analyses have provided important insights about AD and shed light on previously unrecognized conditions, enabling a deeper understanding of neurodegenerative diseases in general. After demonstrating the importance of correct disease classification for AD and primary age-related tauopathy, we emphasize the public health impact of an underappreciated AD "mimic," which has been termed "hippocampal sclerosis of aging" or "hippocampal sclerosis dementia." This pathology affects >20% of individuals older than 85 years and is strongly associated with cognitive impairment. In this review, we provide an overview of current hypotheses about how genetic risk factors (GRN, TMEM106B, ABCC9, and KCNMB2), and other pathogenetic influences contribute to TDP-43 pathology and hippocampal sclerosis. Because hippocampal sclerosis of aging affects the "oldest-old" with arteriolosclerosis and TDP-43 pathologies that extend well beyond the hippocampus, more appropriate terminology for this disease is required. We recommend "cerebral age-related TDP-43 and sclerosis" (CARTS). A detailed case report is presented, which includes neuroimaging and longitudinal neurocognitive data. Finally, we suggest a neuropathology-based diagnostic rubric for CARTS.

Inhibitory RNA Aptamers of Tau Oligomerization and Their Neuroprotective Roles against Proteotoxic Stress

Tau is a cytosolic protein that functions in the assembly and stabilization of axonal microtubule networks. Its oligomerization may be the rate-limiting step of insoluble aggregate formation, which is a neuropathological hallmark of Alzheimer's disease (AD) and a number of other tauopathies. Recent evidence indicates that soluble tau oligomers are the toxic species for tau-mediated pathology during AD progression. Herein, we describe novel RNA aptamers that target human tau and were identified through an in vitro selection process. These aptamers significantly inhibited the oligomerization propensity of tau both in vitro and in cultured cell models of tauopathy without affecting the half-life of tau. Tauopathy model cells treated with the aptamers were less sensitized to proteotoxic stress induced by tau overexpression. Moreover, the tau aptamers significantly alleviated synthetic tau oligomer-mediated neurotoxicity and dendritic spine loss in primary hippocampal neurons. Thus, our study demonstrates that delaying tau assembly with RNA aptamers is an effective strategy for protecting cells under various neurodegenerative stresses originating from pathogenic tau oligomerization.

Behind the curtain of tauopathy: a show of multiple players orchestrating tau toxicity

tau, a microtubule-associated protein, directly binds with microtubules to dynamically regulate the organization of cellular cytoskeletons, and is especially abundant in neurons of the central nervous system. Under disease conditions such as Pick's disease, progressive supranuclear palsy, frontotemporal dementia, parkinsonism linked to chromosome 17 and Alzheimer's disease, tau proteins can self-assemble to paired helical filaments progressing to neurofibrillary tangles. In these diseases, collectively referred to as "tauopathies", alterations of diverse tau modifications including phosphorylation, metal ion binding, glycosylation, as well as structural changes of tau proteins have all been observed, indicating the complexity and variability of factors in the regulation of tau toxicity. Here, we review our current knowledge and hypotheses from relevant studies on tau toxicity, emphasizing the roles of phosphorylations, metal ions, folding and clearance control underlining tau etiology and their regulations. A summary of clinical efforts and associated findings of drug candidates under development is also presented. It is hoped that a more comprehensive understanding of tau regulation will provide us with a better blueprint of tau networking in neuronal cells and offer hints for the design of more efficient strategies to tackle tau-related diseases in the future.

The Genetic Basis of Cognitive Impairment and Dementia in Parkinson's Disease

Cognitive dysfunction is a common feature of Parkinson's disease (PD) with mild cognitive impairment affecting around a quarter of patients in the early stages of their disease, and approximately half developing dementia by 10 years from diagnosis. However, the pattern of cognitive impairments and their speed of evolution vary markedly between individuals. While some of this variability may relate to extrinsic factors and comorbidities, inherited genetic heterogeneity is also known to play an important role. A number of common genetic variants have been identified, which contribute to cognitive function in PD, including variants in catechol-O-methyltransferase, microtubule-associated protein tau, and apolipoprotein E. Furthermore, rarer mutations in glucocerebrosidase and α-synuclein and are strongly associated with dementia risk in PD. This review explores the functional impact of these variants on cognition in PD and discusses how such genotype-phenotype associations provide a window into the mechanistic basis of cognitive heterogeneity in this disorder. This has consequent implications for the development of much more targeted therapeutic strategies for cognitive symptoms in PD.

Genetic overlap between Alzheimer's disease and Parkinson's disease at the MAPT locus

We investigated the genetic overlap between Alzheimer's disease (AD) and Parkinson's disease (PD). Using summary statistics (P-values) from large recent genome-wide association studies (GWAS) (total n=89 904 individuals), we sought to identify single nucleotide polymorphisms (SNPs) associating with both AD and PD. We found and replicated association of both AD and PD with the A allele of rs393152 within the extended MAPT region on chromosome 17 (meta analysis P-value across five independent AD cohorts=1.65 × 10(-7)). In independent datasets, we found a dose-dependent effect of the A allele of rs393152 on intra-cerebral MAPT transcript levels and volume loss within the entorhinal cortex and hippocampus. Our findings identify the tau-associated MAPT locus as a site of genetic overlap between AD and PD, and extending prior work, we show that the MAPT region increases risk of Alzheimer's neurodegeneration.

Early maturation and distinct tau pathology in induced pluripotent stem cell-derived neurons from patients with MAPT mutations

Tauopathies, such as Alzheimer's disease, some cases of frontotemporal dementia, corticobasal degeneration and progressive supranuclear palsy, are characterized by aggregates of the microtubule-associated protein tau, which are linked to neuronal death and disease development and can be caused by mutations in the MAPT gene. Six tau isoforms are present in the adult human brain and they differ by the presence of 3(3R) or 4(4R) C-terminal repeats. Only the shortest 3R isoform is present in foetal brain. MAPT mutations found in human disease affect tau binding to microtubules or the 3R:4R isoform ratio by altering exon 10 splicing. We have differentiated neurons from induced pluripotent stem cells derived from fibroblasts of controls and patients with N279K and P301L MAPT mutations. Induced pluripotent stem cell-derived neurons recapitulate developmental tau expression, showing the adult brain tau isoforms after several months in culture. Both N279K and P301L neurons exhibit earlier electrophysiological maturation and altered mitochondrial transport compared to controls. Specifically, the N279K neurons show abnormally premature developmental 4R tau expression, including changes in the 3R:4R isoform ratio and AT100-hyperphosphorylated tau aggregates, while P301L neurons are characterized by contorted processes with varicosity-like structures, some containing both alpha-synuclein and 4R tau. The previously unreported faster maturation of MAPT mutant human neurons, the developmental expression of 4R tau and the morphological alterations may contribute to disease development.

Frontotemporal lobar degeneration: old knowledge and new insight into the pathogenetic mechanisms of tau mutations

Frontotemporal lobar degeneration (FTLD) is a group of heterogeneous neurodegenerative diseases which includes tauopathies. In the central nervous system (CNS) tau is the major microtubule-associated protein (MAP) of neurons, promoting assembly and stabilization of microtubules (MTs) required for morphogenesis and axonal transport. Primary tauopathies are characterized by deposition of abnormal fibrils of tau in neuronal and glial cells, leading to neuronal death, brain atrophy and eventually dementia. In genetic tauopathies mutations of tau gene impair the ability of tau to bind to MTs, alter the normal ratio among tau isoforms and favor fibril formation. Recently, additional functions have been ascribed to tau and different pathogenetic mechanisms are then emerging. In fact, a role of tau in DNA protection and genome stability has been reported and chromosome aberrations have been found associated with tau mutations. Furthermore, newly structurally and functionally characterized mutations have suggested novel pathological features, such as a tendency to form oligomeric rather than fibrillar aggregates. Tau mutations affecting axonal transport and plasma membrane interaction have also been described. In this article, we will review the pathogenetic mechanisms underlying tau mutations, focusing in particular on the less common aspects, so far poorly investigated.

Invited review: Drug development for tauopathies

Many different approaches to treating tauopathies are currently being explored, with a few compounds already in clinical development (including small molecules such as anti-aggregation compound LMTX and active vaccines AADvac1 and ACI-35). This review aims to summarize the status of the clinical candidates and to highlight the emerging areas of research that hold promise for drug development. Tau is post-translationally modified in several different ways (phosphorylated, acetylated, glycosylated and truncated). The extent of these modifications can be manipulated to influence tau aggregation state and pathogenesis and the enzymes involved provide tractable targets for drug intervention. In addition, modulation of tau expression levels is an attractive therapeutic approach. Finally, the recently described prion-like spreading of tau between cells opens up novel avenues from the tau drug development perspective. The review compares the merits of small-molecule and antibody-based therapies and emphasizes the need for amenable clinical biomarkers for drug development, particularly PET imaging.

Genetics of Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative syndrome that is clinically characterized by progressive postural instability, supranuclear gaze palsy, parkinsonism and cognitive decline. Pathologically, diagnosis of PSP is based on characteristic features, such as neurofibrillary tangles, neutrophil threads, tau-positive astrocytes and their processes in basal ganglia and brainstem, and the accumulation of 4 repeat tau protein. PSP is generally recognized as a sporadic disorder; however, understanding of genetic background of PSP has been expanding rapidly. Here we review relevant publications to outline the genetics of PSP. Although only small number of familial PSP cases have been reported, the recognition of familial PSP has been increasing. In some familial cases of clinically probable PSP, PSP pathologies were confirmed based on NINDS neuropathological diagnostic criteria. Several mutations in MAPT, the gene that causes a form of familial frontotemporal lobar degeneration with tauopathy, have been identified in both sporadic and familial PSP cases. The H1 haplotype of MAPT is a risk haplotype for PSP, and within H1, a sub-haplotype (H1c) is associated with PSP. A recent genome-wide association study on autopsyproven PSP revealed additional PSP risk alleles in STX6 and EIF2AK3. Several heredodegenerative parkinsonian disorders are referred to as PSP-look-alikes because their clinical phenotype, but not their pathology, mimics PSP. Due to the fast development of genomics and bioinformatics, more genetic factors related to PSP are expected to be discovered. Undoubtedly, these studies will provide a better understanding of the pathogenesis of PSP and clues for developing therapeutic strategies.

A geographical cluster of progressive supranuclear palsy in northern France

OBJECTIVE

To describe a cluster of progressive supranuclear palsy (PSP) in northern France. PSP has not been reported in geographical, temporal, or occupational clusters. A unit of Neurology and Neurogeriatrics opened in 2005 at the Centre Hospitalier de Wattrelos, serving the population of Wattrelos and Leers (combined population 51,551) and parts of neighboring towns. For most of the 20th century, this area was a center for chromate and phosphate ore processing, textile dyeing, and tanning. Significant industrial waste persists close to residential areas.

METHODS

From 2005 to 2014, 92 patients with PSP at Centre Hospitalier de Wattrelos were identified and studied. Detailed residential data were available in the medical records. Eighty cases have had magnetic resonance head scanning and 60 have died, of whom 13 have been examined neuropathologically.

RESULTS

The ratio of observed to expected PSP incidence over the period 2005 to 2012 was 12.3 (95% confidence interval: 7.4-35.9). Mean onset age was 74.3 years. The Richardson syndrome/PSP-parkinsonism ratio was 43%/42%. Four other phenotypes each occurred in 2% to 5%. Onset was gait/balance difficulty in 52%. None of the 92 affected patients were relatives and 7 were of North African ancestry. MRI was compatible with a clinical diagnostic of PSP in all cases. Histopathologic examination confirmed neurofibrillary degeneration and tufted astrocytes in all autopsied cases. Western blots revealed a typical tau 4R doublet. The tau H1 haplotype occurred in 95.8% of cases' chromosomes.

CONCLUSIONS

We have identified a cluster of PSP in a geographical area with severe environmental contamination by industrial metals.

Regulation of human MAPT gene expression

The number of known pathologies involving deregulated Tau expression/metabolism is increasing. Indeed, in addition to tauopathies, which comprise approximately 30 diseases characterized by neuronal aggregation of hyperphosphorylated Tau in brain neurons, this protein has also been associated with various other pathologies such as cancer, inclusion body myositis, and microdeletion/microduplication syndromes, suggesting its possible function in peripheral tissues. In addition to Tau aggregation, Tau deregulation can occur at the expression and/or splicing levels, as has been clearly demonstrated in some of these pathologies. Here, we aim to review current knowledge regarding the regulation of human MAPT gene expression at the DNA and RNA levels to provide a better understanding of its possible deregulation. Several aspects, including repeated motifs, CpG island/methylation, and haplotypes at the DNA level, as well as the key regions involved in mRNA expression and stability and the splicing patterns of different mRNA isoforms at the RNA level, will be discussed.

SNCA Gene, but Not MAPT, Influences Onset Age of Parkinson's Disease in Chinese and Australians

Background. α-Synuclein (SNCA) and microtubule-associated protein tau (MAPT) are the two major genes independently, but not jointly, associated with susceptibility for Parkinson's disease (PD). The SNCA gene has recently been identified as a major modifier of age of PD onset. Whether MAPT gene synergistically influences age of onset of PD is unknown. Objective. To investigate independent and joint effects of MAPT and SNCA on PD onset age. Methods. 412 patients with PD were recruited from the Australian PD Research Network (123) and the Neurology Department, Ruijin Hospital Affiliated to Shanghai Jiaotong University, China (289). MAPT (rs17650901) tagging H1/H2 haplotype and SNCA (Rep1) were genotyped in the Australian cohort, and MAPT (rs242557, rs3744456) and SNCA (rs11931074, rs894278) were genotyped in the Chinese cohort. SPSS regression analysis was used to test genetic effects on age at onset of PD in each cohort. Results. SNCA polymorphisms associated with the onset age of PD in both populations. MAPT polymorphisms did not enhance such association in either entire cohort. Conclusion. This study suggests that, in both ethnic groups, SNCA gene variants influence the age at onset of PD and α-synuclein plays a key role in the disease course of PD.

Association between MAPT haplotype and memory function in patients with Parkinson's disease and healthy aging individuals

Genetic variation is associated with differences in the function of the brain as well as its susceptibility to disease. The common H1 haplotypic variant of the microtubule-associated protein tau gene (MAPT) has been related to an increased risk for Parkinson's disease (PD). Furthermore, among PD patients, H1 homozygotes have an accelerated progression to dementia. We investigated the neurocognitive correlates of MAPT haplotypes using functional magnetic resonance imaging. Thirty-seven nondemented patients with PD (19 H1/H1, 18 H2 carriers) and 40 age-matched controls (21 H1/H1, 19 H2 carriers) were scanned during performance of a picture memory encoding task. Behaviorally, H1 homozygosity was associated with impaired picture recognition memory in PD patients and control subjects. These impairments in the H1 homozygotes were accompanied by an altered blood-oxygen level-dependent response in the medial temporal lobe during successful memory encoding. Additional age-related differences in blood-oxygen level-dependent response were observed in the medial temporal lobes of H1 homozygotes with PD. These results suggest that common variation in MAPT is not only associated with the dementia of PD but also differences in the neural circuitry underlying aspects of cognition in normal aging.

Impaired intracellular trafficking defines early Parkinson's disease

Parkinson's disease (PD) is an insidious and incurable neurodegenerative disease, and represents a significant cost to individuals, carers, and ageing societies. It is defined at post-mortem by the loss of dopamine neurons in the substantia nigra together with the presence of Lewy bodies and Lewy neurites. We examine here the role of α-synuclein and other cellular transport proteins implicated in PD and how their aberrant activity may be compounded by the unique anatomy of the dopaminergic neuron. This review uses multiple lines of evidence from genetic studies, human tissue, induced pluripotent stem cells, and refined animal models to argue that prodromal PD can be defined as a disease of impaired intracellular trafficking. Dysfunction of the dopaminergic synapse heralds trafficking impairment.

The effect of inversion at 8p23 on BLK association with lupus in Caucasian population

To explore the potential influence of the polymorphic 8p23.1 inversion on known autoimmune susceptibility risk at or near BLK locus, we validated a new bioinformatics method that utilizes SNP data to enable accurate, high-throughput genotyping of the 8p23.1 inversion in a Caucasian population. Methods: Principal components analysis (PCA) was performed using markers inside the inversion territory followed by k-means cluster analyses on 7416 European derived and 267 HapMaP CEU and TSI samples. A logistic regression conditional analysis was performed. Results: Three subgroups have been identified; inversion homozygous, heterozygous and non-inversion homozygous. The status of inversion was further validated using HapMap samples that had previously undergone Fluorescence in situ hybridization (FISH) assays with a concordance rate of above 98%. Conditional analyses based on the status of inversion were performed. We found that overall association signals in the BLK region remain significant after controlling for inversion status. The proportion of lupus cases and controls (cases/controls) in each subgroup was determined to be 0.97 for the inverted homozygous group (1067 cases and 1095 controls), 1.12 for the inverted heterozygous group (1935 cases 1717 controls) and 1.36 for non-inverted subgroups (924 cases and 678 controls). After calculating the linkage disequilibrium between inversion status and lupus risk haplotype we found that the lupus risk haplotype tends to reside on non-inversion background. As a result, a new association effect between non-inversion status and lupus phenotype has been identified ((p = 8.18×10⁻⁷, OR = 1.18, 95%CI = 1.10–1.26). Conclusion: Our results demonstrate that both known lupus risk haplotype and inversion status act additively in the pathogenesis of lupus. Since inversion regulates expression of many genes in its territory, altered expression of other genes might also be involved in the development of lupus.

Paclitaxel-induced neuropathy: potential association of MAPT and GSK3B genotypes

Background

Paclitaxel treatment produces dose-limiting peripheral neurotoxicity, which adversely affects treatment and long-term outcomes. In the present study, the contribution of genetic polymorphisms to paclitaxel-induced neurotoxicity were assessed in 21 patients, focusing on polymorphisms involved in the tau-microtubule pathway, an important target of paclitaxel involved in neurotoxicity development.

Methods

Polymorphisms in the microtubule-associated protein tau (MAPT) gene (haplotype 1 and rs242557 polymorphism) and the glycogen synthase kinase-3β (GSK3β) gene (rs6438552 polymorphism) were investigated. Neurotoxicity was assessed using neuropathy grading scales, neurophysiological studies and patient questionnaires.

Results

A significant relationship between the GSK-3B rs6438552 polymorphism and paclitaxel-induced neurotoxicity was evident.

Conclusions

Polymorphisms in tau-associated genes may contribute to the development of paclitaxel-induced neurotoxicity, although larger series will be necessary to confirm these findings.

Role of the extended MAPT haplotype in the worsening of psychotic symptoms and treatment response in Alzheimer disease

INTRODUCTION

There is evidence that neurofibrillary tangle (NFT) burden is associated with psychotic symptoms in Alzheimer disease (AD). However, it is not clear whether this association is direct or mediated through the increased cognitive impairment associated with NFTs.

METHODS

We sought to determine whether the extended MAPT haplotype was associated with the worsening of delusions and hallucinations in a combined cohort of 95 patients who participated in 2 clinical trials of treatment with memantine.

RESULTS

After controlling for baseline dementia severity, exposure to memantine, and antipsychotics, analysis shows that carriers of at least one H2 allele had a 5.4-fold (P = .03) increased risk of worsening hallucinations. There was some evidence of association with worsening delusions but only in analysis by allele.

CONCLUSION

These results are the first to indicate that the H2 allele of the extended MAPT haplotype negatively affects the course of psychotic symptoms in AD independently of disease severity. It will be important for future research to examine MAPT transcription in people with AD with and without psychotic symptoms to understand the exact mechanisms underlying these findings.

Association of MAPT haplotypes with Alzheimer's disease risk and MAPT brain gene expression levels

Introduction

MAPT encodes for tau, the predominant component of neurofibrillary tangles that are neuropathological hallmarks of Alzheimer’s disease (AD). Genetic association of MAPT variants with late-onset AD (LOAD) risk has been inconsistent, although insufficient power and incomplete assessment of MAPT haplotypes may account for this.

Methods

We examined the association of MAPT haplotypes with LOAD risk in more than 20,000 subjects (n-cases = 9,814, n-controls = 11,550) from Mayo Clinic (n-cases = 2,052, n-controls = 3,406) and the Alzheimer’s Disease Genetics Consortium (ADGC, n-cases = 7,762, n-controls = 8,144). We also assessed associations with brain MAPT gene expression levels measured in the cerebellum (n = 197) and temporal cortex (n = 202) of LOAD subjects. Six single nucleotide polymorphisms (SNPs) which tag MAPT haplotypes with frequencies greater than 1% were evaluated.

Results

H2-haplotype tagging rs8070723-G allele associated with reduced risk of LOAD (odds ratio, OR = 0.90, 95% confidence interval, CI = 0.85-0.95, p = 5.2E-05) with consistent results in the Mayo (OR = 0.81, p = 7.0E-04) and ADGC (OR = 0.89, p = 1.26E-04) cohorts. rs3785883-A allele was also nominally significantly associated with LOAD risk (OR = 1.06, 95% CI = 1.01-1.13, p = 0.034). Haplotype analysis revealed significant global association with LOAD risk in the combined cohort (p = 0.033), with significant association of the H2 haplotype with reduced risk of LOAD as expected (p = 1.53E-04) and suggestive association with additional haplotypes. MAPT SNPs and haplotypes also associated with brain MAPT levels in the cerebellum and temporal cortex of AD subjects with the strongest associations observed for the H2 haplotype and reduced brain MAPT levels (β = -0.16 to -0.20, p = 1.0E-03 to 3.0E-03).

Conclusions

These results confirm the previously reported MAPT H2 associations with LOAD risk in two large series, that this haplotype has the strongest effect on brain MAPT expression amongst those tested and identify additional haplotypes with suggestive associations, which require replication in independent series. These biologically congruent results provide compelling evidence to screen the MAPT region for regulatory variants which confer LOAD risk by influencing its brain gene expression.

Using the neanderthal and denisova genetic data to understand the common MAPT 17q21 inversion in modern humans

The polymorphic inversion on 17q21, that includes the MAPT gene, represents a unique locus in the human genome characterized by a large region with strong linkage disequilibrium. Two distinct haplotypes, H1 and H2, exist in modern humans, and H1 has been unequivocally related to several neurodegenerative disorders. Recent data indicate that recurrent inversions of this genomic region have occurred through primate evolution, with the H2 haplotype being the ancestral state. Neandertals harbored the H1 haplotype; however, until now, no data were available for the Denisova hominin. Neandertals and Denisovans are sister groups that share a common ancestor with modern humans. We analyzed the MAPT sequence and assessed the differences between modern humans, Neandertals, Denisovans, and great apes. Our analysis indicated that the Denisova hominin carried the H1 haplotype, and the Neandertal and Denisova common ancestor probably shared the same subhaplotype (H1j). We also found 68 intronic variants within the MAPT gene, 23 exclusive to Denisova hominin, 6 limited to Neandertals, and 24 exclusive to present-day humans. Our results reinforce previous data; this suggests that the 17q21 inversion arose within the modern human lineage. The data also indicate that archaic hominins that coexisted in Eurasia probably shared the same MAPT subhaplotype, and this can be found in almost 2% of chromosomes from European ancestry.

An epigenetic signature in peripheral blood associated with the haplotype on 17q21.31, a risk factor for neurodegenerative tauopathy

Little is known about how changes in DNA methylation mediate risk for human diseases including dementia. Analysis of genome-wide methylation patterns in patients with two forms of tau-related dementia--progressive supranuclear palsy (PSP) and frontotemporal dementia (FTD)--revealed significant differentially methylated probes (DMPs) in patients versus unaffected controls. Remarkably, DMPs in PSP were clustered within the 17q21.31 region, previously known to harbor the major genetic risk factor for PSP. We identified and replicated a dose-dependent effect of the risk-associated H1 haplotype on methylation levels within the region in blood and brain. These data reveal that the H1 haplotype increases risk for tauopathy via differential methylation at that locus, indicating a mediating role for methylation in dementia pathophysiology.

New perspectives on the role of tau in Alzheimer's disease. Implications for therapy

Alzheimer's disease (AD) and related dementias constitute a major public health issue due to an increasingly aged population as a consequence of generally improved medical care and demographic changes. Current drug treatment of AD, the most prevalent dementia, with cholinesterase inhibitors or NMDA antagonists have demonstrated very modest, symptomatic efficacy, leaving an unmet medical need for new, more effective therapies. While drug development efforts in the last two decades have primarily focused on the amyloid cascade hypothesis, so far with disappointing results, tau-based strategies have received little attention until recently despite that the presence of extensive tau pathology is central to the disease. The discovery of mutations within the tau gene that cause fronto-temporal dementia demonstrated that tau dysfunction, in the absence of amyloid pathology, was sufficient to cause neuronal loss and clinical dementia. Abnormal levels and hyperphosphorylation of tau protein have been reported to be the underlying cause of a group of neurodegenerative disorders collectively known as 'tauopathies'. The detrimental consequence is the loss of affinity between this protein and the microtubules, increased production of fibrillary aggregates and the accumulation of insoluble intracellular neurofibrillary tangles. However, it has become clear in recent years that tau is not only a microtubule interacting protein, but rather has additional roles in cellular processes. This review focuses on emerging therapeutic strategies aimed at treating the underlying causes of the tau pathology in tauopathies and AD, including some novel approaches on the verge of providing new treatment paradigms within the coming years.

Assessment of common variability and expression quantitative trait loci for genome-wide associations for progressive supranuclear palsy

Progressive supranuclear palsy is a rare parkinsonian disorder with characteristic neurofibrillary pathology consisting of hyperphosphorylated tau protein. Common variation defining the microtubule associated protein tau gene (MAPT) H1 haplotype strongly contributes to disease risk. A recent genome-wide association study (GWAS) revealed 3 novel risk loci on chromosomes 1, 2, and 3 that primarily implicate STX6, EIF2AK3, and MOBP, respectively. Genetic associations, however, rarely lead to direct identification of the relevant functional allele. More often, they are in linkage disequilibrium with the causative polymorphism(s) that could be a coding change or affect gene expression regulatory motifs. To identify any such changes, we sequenced all coding exons of those genes directly implicated by the associations in progressive supranuclear palsy cases and analyzed regional gene expression data from control brains to identify expression quantitative trait loci within 1 Mb of the risk loci. Although we did not find any coding variants underlying the associations, GWAS-associated single-nucleotide polymorphisms at these loci are in complete linkage disequilibrium with haplotypes that completely overlap with the respective genes. Although implication of EIF2AK3 and MOBP could not be fully assessed, we show that the GWAS single-nucleotide polymorphism rs1411478 (STX6) is a strong expression quantitative trait locus with significantly lower expression of STX6 in white matter in carriers of the risk allele.

Antisense reduction of tau in adult mice protects against seizures

Tau, a microtubule-associated protein, is implicated in the pathogenesis of Alzheimer's Disease (AD) in regard to both neurofibrillary tangle formation and neuronal network hyperexcitability. The genetic ablation of tau substantially reduces hyperexcitability in AD mouse lines, induced seizure models, and genetic in vivo models of epilepsy. These data demonstrate that tau is an important regulator of network excitability. However, developmental compensation in the genetic tau knock-out line may account for the protective effect against seizures. To test the efficacy of a tau reducing therapy for disorders with a detrimental hyperexcitability profile in adult animals, we identified antisense oligonucleotides that selectively decrease endogenous tau expression throughout the entire mouse CNS--brain and spinal cord tissue, interstitial fluid, and CSF--while having no effect on baseline motor or cognitive behavior. In two chemically induced seizure models, mice with reduced tau protein had less severe seizures than control mice. Total tau protein levels and seizure severity were highly correlated, such that those mice with the most severe seizures also had the highest levels of tau. Our results demonstrate that endogenous tau is integral for regulating neuronal hyperexcitability in adult animals and suggest that an antisense oligonucleotide reduction of tau could benefit those with epilepsy and perhaps other disorders associated with tau-mediated neuronal hyperexcitability.

An inflection point in gene discovery efforts for neurodegenerative diseases: from syndromic diagnoses toward endophenotypes and the epigenome

We are at an inflection point in our study of the human genome as it relates to neurodegenerative disease. The sequencing of the human genome, and its associated cataloging of human genetic variation and technological as well as methodological development, introduced a period of rapid gene discovery over the past decade. These efforts have yielded many new insights and will continue to uncover the genetic architecture of syndromically defined neurodegenerative diseases in the coming decades. More recently, these successful study designs have been applied to the investigation of intermediate traits that relate to and inform our understanding of clinical syndromes and to exploration of the epigenome, the higher-order structure of DNA that dictates the expression of a given genetic risk factor. While still nascent, given the challenges of accumulating large numbers of subjects with detailed phenotypes and technological hurdles in characterizing the state of chromatin, these efforts represent key investments that will enable the study of the functional consequences of a genetic risk factor and, eventually, its contribution to the clinical manifestations of a given disease. As a community of investigators, we are therefore at an exciting inflection point at which gene discovery efforts are transitioning toward the functional characterization of implicated genetic variation; this transition is crucial for understanding the molecular, cellular, and systemic events that lead to a syndromic diagnosis for a neurodegenerative disease.

Biochemistry and cell biology of tau protein in neurofibrillary degeneration

Tau represents the subunit protein of one of the major hallmarks of Alzheimer disease (AD), the neurofibrillary tangles, and is therefore of major interest as an indicator of disease mechanisms. Many of the unusual properties of Tau can be explained by its nature as a natively unfolded protein. Examples are the large number of structural conformations and biochemical modifications (phosphorylation, proteolysis, glycosylation, and others), the multitude of interaction partners (mainly microtubules, but also other cytoskeletal proteins, kinases, and phosphatases, motor proteins, chaperones, and membrane proteins). The pathological aggregation of Tau is counterintuitive, given its high solubility, but can be rationalized by short hydrophobic motifs forming β structures. The aggregation of Tau is toxic in cell and animal models, but can be reversed by suppressing expression or by aggregation inhibitors. This review summarizes some of the structural, biochemical, and cell biological properties of Tau and Tau fibers. Further aspects of Tau as a diagnostic marker and therapeutic target, its involvement in other Tau-based diseases, and its histopathology are covered by other chapters in this volume.