Drosophila Models of Tauopathies: What Have We Learned?

Aggregates of the microtubule-associated protein Tau are neuropathological hallmark lesions in Alzheimer's disease (AD) and related primary tauopathies. In addition, Tau is genetically implicated in a number of human neurodegenerative disorders including frontotemporal dementia (FTD) and Parkinson's disease (PD). The exact mechanism by which Tau exerts its neurotoxicity is incompletely understood. Here, we give an overview of how studies using the genetic model organism Drosophila over the past decade have contributed to the molecular understanding of Tau neurotoxicity. We compare the different available readouts for Tau neurotoxicity in flies and review the molecular pathways in which Tau has been implicated. Finally, we emphasize that the integration of genome-wide approaches in human or mice with high-throughput genetic validation in Drosophila is a fruitful approach

Developmental expression of 4-repeat-Tau induces neuronal aneuploidy in Drosophila tauopathy models

Tau-mediated neurodegeneration in Alzheimer's disease and tauopathies is generally assumed to start in a normally developed brain. However, several lines of evidence suggest that impaired Tau isoform expression during development could affect mitosis and ploidy in post-mitotic differentiated tissue. Interestingly, the relative expression levels of Tau isoforms containing either 3 (3R-Tau) or 4 repeats (4R-Tau) play an important role both during brain development and neurodegeneration. Here, we used genetic and cellular tools to study the link between 3R and 4R-Tau isoform expression, mitotic progression in neuronal progenitors and post-mitotic neuronal survival. Our results illustrated that the severity of Tau-induced adult phenotypes depends on 4R-Tau isoform expression during development. As recently described, we observed a mitotic delay in 4R-Tau expressing cells of larval eye discs and brains. Live imaging revealed that the spindle undergoes a cycle of collapse and recovery before proceeding to anaphase. Furthermore, we found a high level of aneuploidy in post-mitotic differentiated tissue. Finally, we showed that overexpression of wild type and mutant 4R-Tau isoform in neuroblastoma SH-SY5Y cell lines is sufficient to induce monopolar spindles. Taken together, our results suggested that neurodegeneration could be in part linked to neuronal aneuploidy caused by 4R-Tau expression during brain development

Distinct phenotypes of three-repeat and four-repeat human tau in a transgenic model of tauopathy.

Tau exists as six closely related protein isoforms in the adult human brain. These are generated from alternative splicing of a single mRNA transcript and they differ in the absence or presence of two N-terminal and three or four microtubule binding domains. Typically all six isoforms have been considered functionally similar. However, their differential involvement in particular tauopathies raises the possibility that there may be isoform-specific differences in physiological function and pathological role. To explore this, we have compared the phenotypes induced by the 0N3R and 0N4R isoforms in Drosophila. Expression of the 3R isoform causes more profound axonal transport defects and locomotor impairments, culminating in a shorter lifespan than the 4R isoform. In contrast, the 4R isoform leads to greater neurodegeneration and impairments in learning and memory. Furthermore, the phosphorylation patterns of the two isoforms are distinct, as is their ability to induce oxidative stress. These differences are not consequent to different expression levels and are suggestive of bona fide physiological differences in isoform biology and pathological potential. They may therefore explain isoform-specific mechanisms of tau-toxicity and the differential susceptibility of brain regions to different tauopathies

Genome-wide, high-content siRNA screening identifies the Alzheimer's genetic risk factor FERMT2 as a major modulator of APP metabolism

Genome-wide association studies (GWASs) have identified 19 susceptibility loci for Alzheimer’s disease (AD). However, understanding how these genes are involved in the pathophysiology of AD is one of the main challenges of the “post-GWAS” era. At least 123 genes are located within the 19 susceptibility loci; hence, a conventional approach (studying the genes one by one) would not be time- and cost-effective. We therefore developed a genome-wide, high-content siRNA screening approach and used it to assess the functional impact of gene under-expression on APP metabolism. We found that 832 genes modulated APP metabolism. Eight of these genes were located within AD susceptibility loci. Only FERMT2 (a β3-integrin co-activator) was also significantly associated with a variation in cerebrospinal fluid Aβ peptide levels in 2886 AD cases. Lastly, we showed that the under-expression of FERMT2 increases Aβ peptide production by raising levels of mature APP at the cell surface and facilitating its recycling. Taken as a whole, our data suggest that FERMT2 modulates the AD risk by regulating APP metabolism and Aβ peptide production

The MAPT H1 Haplotype Is a Risk Factor for Alzheimer's Disease in APOE E4 Non-carriers

An ancestral inversion of 900 kb on chromosome 17q21, which includes the microtubule-associated protein tau (MAPT) gene, defines two haplotype clades in Caucasians (H1 and H2). The H1 haplotype has been linked inconsistently with AD. In a previous study, we showed that an SNP tagging this haplotype (rs1800547) was associated with AD risk in a large population from the Dementia Genetics Spanish Consortium (DEGESCO) including 4435 cases and 6147 controls. The association was mainly driven by individuals that were non-carriers of the APOE ?4 allele. Our aim was to replicate our previous findings in an independent sample of 4124 AD cases and 3290 controls from Spain (GR@ACE project) and to analyze the effect of the H1 sub-haplotype structure on the risk of AD. The H1 haplotype was associated with AD risk (OR = 1.12; p = 0.0025). Stratification analysis showed that this association was mainly driven by the APOE ?4 non-carriers (OR = 1.15; p = 0.0022). Pooled analysis of both Spanish datasets (n = 17,996) showed that the highest AD risk related to the MAPT H1/H2 haplotype was in those individuals that were the oldest [third tertile (>77 years)] and did not carry APOE ?4 allele (p = 0.001). We did not find a significant association between H1 sub-haplotypes and AD. H1c was nominally associated but lost statistical significance after adjusting by population sub-structure. Our results are consistent with the hypothesis that genetic variants linked to the MAPT H1/H2 are tracking a genuine risk allele for AD. The fact that this association is stronger in APOE ?4 non-carriers partially explains previous controversial results and might be related to a slower alternative causal pathway less dependent on brain amyloid load.ACKNOWLEDGMENTS: The Genome Research at Fundacio ACE/Dementia Genetics Spanish Consortium (GR@ACE/DEGESCO) would like to thank patients and controls who participated in this project. GR@ACE/DEGESCO GWAS program was funded by Grifols SA, Fundacion Bancaria “La Caixa,” and Fundació ACE, Institut Català de Neurociències Aplicades. PS-J and AR have also received support by grant PI16/01861. Accion Estrategica en Salud integrated in the Spanish National ICDCi Plan and financed by Instituto de Salud Carlos III (ISCIII) – Subdireccion General de Evaluacion and the Fondo Europeo de Desarrollo Regional (FEDER – “Una Manera de Hacer Europa”). PS-J was supported by IDIVAL, Instituto de Salud Carlos III [Fondo de Investigacion Sanitario, PI08/0139, PI12/02288, PI16/01652, JPND (DEMTEST PI11/03028)], and the CIBERNED program. We thank Biobanco Valdecilla for their support. LM was supported by Consejería de Salud de la Junta de Andalucía (Grant PI-0001/2017). DEGESCO was also sponsored by the Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED, Spain). Control samples and data from patients included in this study were provided in part by the National DNA Bank Carlos III (www.bancoadn.org, University of Salamanca, Spain) and Hospital Universitario Virgen de Valme (Sevilla, Spain) and they were processed following standard operating procedures with the appropriate approval of the Ethical and Scientific Committee. The genotyping service to generate GR@ACE/DEGESCO GWAS data was carried out at CEGEN-PRB3-ISCIII; it was supported by grant PT17/0019, of the PE ICDCi 2013–2016, funded by ISCIII and ERDF. GR@ACE/DEGESCO consortia would also like to thank to all researchers contributing to this project

Nerve Growth Factor Stimulates Interaction of Cayman Ataxia Protein BNIP-H/Caytaxin with Peptidyl-Prolyl Isomerase Pin1 in Differentiating Neurons

Mutations in ATCAY that encodes the brain-specific protein BNIP-H (or Caytaxin) lead to Cayman cerebellar ataxia. BNIP-H binds to glutaminase, a neurotransmitter-producing enzyme, and affects its activity and intracellular localization. Here we describe the identification and characterization of the binding between BNIP-H and Pin1, a peptidyl-prolyl cis/trans isomerase. BNIP-H interacted with Pin1 after nerve growth factor-stimulation and they co-localized in the neurites and cytosol of differentiating pheochromocytoma PC12 cells and the embryonic carcinoma P19 cells. Deletional mutagenesis revealed two cryptic binding sites within the C-terminus of BNIP-H such that single point mutants affecting the WW domain of Pin1 completely abolished their binding. Although these two sites do not contain any of the canonical Pin1-binding motifs they showed differential binding profiles to Pin1 WW domain mutants S16E, S16A and W34A, and the catalytically inert C113A of its isomerase domain. Furthermore, their direct interaction would occur only upon disrupting the ability of BNIP-H to form an intramolecular interaction by two similar regions. Furthermore, expression of Pin1 disrupted the BNIP-H/glutaminase complex formation in PC12 cells under nerve growth factor-stimulation. These results indicate that nerve growth factor may stimulate the interaction of BNIP-H with Pin1 by releasing its intramolecular inhibition. Such a mechanism could provide a post-translational regulation on the cellular activity of BNIP-H during neuronal differentiation. (213 words

Functional screening of Alzheimer risk loci identifies PTK2B as an in vivo modulator and early marker of Tau pathology

A recent genome-wide association meta-analysis for Alzheimer's disease (AD) identified 19 risk loci (in addition to APOE) in which the functional genes are unknown. Using Drosophila, we screened 296 constructs targeting orthologs of 54 candidate risk genes within these loci for their ability to modify Tau neurotoxicity by quantifying the size of >6000 eyes. Besides Drosophila Amph (ortholog of BIN1), which we previously implicated in Tau pathology, we identified p130CAS (CASS4), Eph (EPHA1), Fak (PTK2B) and Rab3-GEF (MADD) as Tau toxicity modulators. Of these, the focal adhesion kinase Fak behaved as a strong Tau toxicity suppressor in both the eye and an independent focal adhesion-related wing blister assay. Accordingly, the human Tau and PTK2B proteins biochemically interacted in vitro and PTK2B co-localized with hyperphosphorylated and oligomeric Tau in progressive pathological stages in the brains of AD patients and transgenic Tau mice. These data indicate that PTK2B acts as an early marker and in vivo modulator of Tau toxicity

Te Deum / mis en musique par Victor Dourlen

Description complète au fichier de la salle de lecture du Département de la Musiqu