Relation entre la phosphorylation de Tau et la fragmentation de l'appareil de Golgi

Dans la maladie d’Alzheimer (MA), il y a deux lésions neuropathologiques majeures, les plaques séniles composées du peptide amyloïde-bêta et les enchevêtrements neurofibrillaires formés de la protéine Tau hyperphosphorylée et agrégée. L’une des caractéristiques cellulaires de la MA est la fragmentation de l’appareil de Golgi (AG). Cette fragmentation est observée tôt dans la MA, et peut être induite par le peptide amyloïde-bêta extracellulaire. Cependant, plusieurs études laissent croire que la protéine Tau hyperphosphorylée pourrait également contribuer à la fragmentation de l’AG. Nous avons donc examiné si la Tau hyperphosphorylée pouvait induire une fragmentation de l’AG lors de sa surexpression dans les cellules HeLa. Nos résultats montrent que la surexpression d’une forme hyperphosphorylée de Tau induit plus rapidement une fragmentation Golgienne qu’une forme non-phosphorylable de Tau. La protéine Tau peut être sécrétée dans l’espace extracellulaire, la tau hyperphosphorylée étant la forme de tau la plus sécrétée. Nous avons donc examiné la capacité de la protéine Tau extracellulaire à pouvoir induire une fragmentation Golgienne. La Tau hyperphosphorylée extracellulaire a été la seule forme de Tau à induire une fragmentation de l’AG. Nous nous sommes ensuite demandés si ce phénomène était du à la plus importante phosphorylation de cette forme de Tau ou bien à sa plus grande quantité dans le milieu extracellulaire. Nos expériences de dilution du milieu ont permis de démontrer une relation dose-dépendante entre la quantité de Tau hyperphosphorylée extracellulaire et la fragmentation Golgienne. Ensuite nous avons tenté d’identifier le domaine de Tau impliqué dans cette fragmentation. Nos résultats ont révélé que la séquence de Tau inductrice de la fragmentation Golgienne se trouve dans sa partie C-terminale qui contient les séquences répétées impliquées dans sa liaison avec les microtubules (MTBD). Toutefois, nos résultats indiquent que l’effet de Tau sur l’AG ne fait pas intervenir de modification microtubulaire, ce qui nous laisse à croire que la Tau intracellulaire n’est pas responsable de la fragmentation Golgienne. Finalement, nous avons vérifié si l’AG demeurait fonctionnel suite à la surexpression de Tau en examinant le transport de la protéine VSVG. Nos expériences indiquent que la surexpression de Tau n’affecte pas le transport de VSVG. En conclusion, nous avons démontré que la Tau extracellulaire peut induire une fragmentation de l’AG. Cependant, le lien entre ces deux évènements demeure inconnu. Sachant que la fragmentation de l’AG peut affecter le fonctionnement neuronal, la Tau extracellulaire pourrait devenir une cible thérapeutique pour la MA.Alzheimer’s disease (AD) is characterized by two neuropathological lesions, senile plaques composed of Abeta peptide and neurofibrillary tangles formed by hyperphosphorylated and aggregated Tau protein. Interestingly, in AD, a fragmentation of Golgi apparatus is noted at early stages of the disease. It was recently shown that the extracellular pool of Abeta peptide can induce a fragmentation of the Golgi. However, several studies indicated that hyperphosphorylated Tau could also contribute to this fragmentation. We therefore examined whether hyperphosphorylated Tau could induce a fragmentation of the Golgi by overexpressing it in HeLa cells. Our results revealed that a Tau mutant mimicking hyperphophosphorylation induced an earlier fragmentation of the Golgi than a non-phosphorylable Tau mutant. We previously demonstrated that Tau can be secreted in the extracellular space, the mutant mimicking hyperphosphorylation being the most secreted. We then examined whether extracellular Tau was able to induce a fragmentation of the Golgi as noted for extracellular Abeta. Interestingly, the mutant mimicking Tau hyperphosphorylation was the sole form of Tau that could induce a Golgi fragmentation when it was present in the medium. We then determine whether the induction of the fragmentation by extracellular hyperphosphorylated Tau was linked to its phosphorylation state and/or to its high amount in the medium. Our results indicate that the Golgi fragmentation induced by hyperphosphorylated Tau was caused by its high levels in the medium. We also investigated which domain of Tau was involved in the induction of the Golgi fragmentation. Our results revealed that the sequence of Tau responsible the Golgi fragmentation is located in its C-terminal where the repeated sequences (MTBD) involved in its association with microtubules are found. However, no alteration of the microtubules was noted in the HeLa overexpressing Tau indicating that the microtubules would not be involved in Tau-induced Golgi fragmentation. This supports the fact that extracellular not intracellular Tau is responsible for the fragmentation of the Golgi. Finally, by examining the trafficking of the VSVG protein, we showed that the Golgi remained functional upon the overexpression of Tau in HeLa cells. In conclusions, our results demonstrated that extracellular tau is the main pool of Tau responsible for its induction of the Golgi fragmentation. The link between extracellular Tau and the fragmentation of the Golgi remains to be elucidated. Knowing that the Golgi fragmentation could become detrimental to neurons, extracellular Tau could be a therapeutic target for AD

Longitudinal liver stiffness assessment in patient with chronic hepatitis C undergoing antiviral therapy.

BACKGROUND/AIMS:Liver stiffness (LS) measurement by means of transient elastography (TE) is accurate to predict fibrosis stage. The effect of antiviral treatment and virologic response on LS was assessed and compared with untreated patients with chronic hepatitis C (CHC). METHODS: TE was performed at baseline, and at weeks 24, 48, and 72 in 515 patients with CHC. RESULTS: 323 treated (62.7%) and 192 untreated patients (37.3%) were assessed. LS experienced a significant decline in treated patients and remained stable in untreated patients at the end of study (P<0.0001). The decline was significant for patients with baseline LS ≥ 7.1 kPa (P<0.0001 and P 0.03, for LS ≥ 9.5 and ≥ 7.1 kPa vs lower values, respectively). Sustained virological responders and relapsers had a significant LS improvement whereas a trend was observed in nonresponders (mean percent change -16%, -10% and -2%, for SVR, RR and NR, respectively, P 0.03 for SVR vs NR). In multivariate analysis, high baseline LS (P<0.0001) and ALT levels, antiviral therapy and non-1 genotype were independent predictors of LS improvement. CONCLUSIONS: LS decreases during and after antiviral treatment in patients with CHC. The decrease is significant in sustained responders and relapsers (particularly in those with high baseline LS) and suggests an improvement in liver damage

A randomized, double-blind, placebo-controlled phase 2 study to assess safety, tolerability, and efficacy of RT001 in patients with amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE: RT001 is a deuterated synthetic homologue of linoleic acid, which makes membrane polyunsaturated fatty acids resistant to lipid peroxidation, a process involved in motor neuron degeneration in amyotrophic lateral sclerosis (ALS). METHODS: We conducted a randomized, multicenter, placebo-controlled clinical trial. Patients with ALS were randomly allocated to receive either RT001 or placebo for 24 weeks. After the double-blind period, all patients received RT001 during an open-label phase for 24 weeks. The primary outcome measures were safety and tolerability. Key efficacy outcomes included the ALS Functional Rating Scale (ALSFRS-R), percent predicted slow vital capacity, and plasma neurofilament light chain concentration. RESULTS: In total, 43 patients (RT001 = 21; placebo = 22) were randomized. RT001 was well tolerated; one patient required dose reduction due to adverse events (AEs). Numerically, there were more AEs in the RT001 group compared to the placebo group (71% versus 55%, p = 0.35), with gastrointestinal symptoms being the most common (43% in RT001, 27% in placebo, p = 0.35). Two patients in the RT001 group experienced a serious AE, though unrelated to treatment. The least-squares mean difference in ALSFRS-R total score at week 24 of treatment was 1.90 (95% confidence interval = -1.39 to 5.19) in favor of RT001 (p = 0.25). The directions of other efficacy outcomes favored RT001 compared to placebo, although no inferential statistics were performed. CONCLUSIONS: Initial data indicate that RT001 is safe and well tolerated. Given the exploratory nature of the study, a larger clinical trial is required to evaluate its efficacy

The usage of population and disease registries as pre-screening tools for clinical trials, a systematic review

Abstract Objective This systematic review aims to outline the use of population and disease registries for clinical trial pre-screening. Materials and methods The search was conducted in the time period of January 2014 to December 2022 in three databases: MEDLINE, Embase, and Web of Science Core Collection. References were screened using the Rayyan software, firstly based on titles and abstracts only, and secondly through full text review. Quality of the included studies was assessed using the List of Included Studies and quality Assurance in Review tool, enabling inclusion of publications of only moderate to high quality. Results The search originally identified 1430 citations, but only 24 studies were included, reporting the use of population and/or disease registries for trial pre-screening. Nine disease domains were represented, with 54% of studies using registries based in the USA, and 62.5% of the studies using national registries. Half of the studies reported usage for drug trials, and over 478,679 patients were identified through registries in this review. Main advantages of the pre-screening methodology were reduced financial burden and time reduction. Discussion and conclusion The use of registries for trial pre-screening increases reproducibility of the pre-screening process across trials and sites, allowing for implementation and improvement of a quality assurance process. Pre-screening strategies seem under-reported, and we encourage more trials to use and describe their pre-screening processes, as there is a need for standardized methodological guidelines

A Bayesian two-stage biomass model for stock assessment of data-limited species: An application to cuttlefish ( Sepia officinalis ) in the English Channel

Cuttlefish is a key commercial species in the English Channel fishery in terms of landings and value. Age-based assessment methods are limited by time-consuming age determination with statoliths and the lack of stock assessment models tailored to this data-limited species. A two-stage biomass model is developed in the Bayesian state-space modelling framework that allows inferences to be made on the stock biomass at the start, middle and end of each fishing seasons between 1992 and 2014, while accounting for both process and measurement errors and to assimilate various sources of information. A method that uses ancillary length-frequency data is developed to provide an informative prior distribution for the biomass growth rate parameter g (E = 0.89) and its annual variability (CV = 0.1). The new model is a substantial improvement on the existing stock assessment method used by the International Council for the Exploration of the Seas. Taking into consideration a time-varying g parameter provides a more ecologically meaningful model with regard to the sensitivity of the cuttlefish population dynamics to environmental fluctuations and improves model fit. The model also provides predictions of the unexploited biomass in winter, which is based on survey data, and helps manage the stock in the event of strong depletion

Stock assessment models for short-lived species in data-limited situations. Case study of the English Channel stock of cuttlefish.

Among the English Channel fishery, the importance of cuttlefish stock has increased, following the cephalopods global landings and market trend. The stock is currently managed at regional scale but not by European regulations, although it is a shared species targeted by French and British fishing fleets at several stages of its life-cycle and across much of its distributional range. An assessment of this stock was conducted in June 2014 by fitting a two-stage biomass model on a 22 years’ time-series (1992-2013). As the assumptions of the model are based on a simplified life-cycle, it would be appropriate to compare the results with outputs from other models in order to obtain reliable biomass estimations. The final aim is to produce reliable management rules to assure a sustainable harvest rate. The use of a Bayesian framework is particularly adapted for decision making, allowing the propagation of uncertainty in the model and the use of prior knowledge on some parameter distributions. Therefore, we implemented the two-stage biomass model into a Bayesian framework and compared the results with the outputs of the initial fit. We also applied a multi-annual generalized depletion model to the English Channel cuttlefish stock. We found similar trends of biomass estimates for both models. The Bayesian model outputs showed a smaller range of variation than the initial fit. These results allow a first comparison of the initial model outputs. But the Bayesian model could be improved and particular attention should be paid to the growth parameter g because of the high sensitivity of model outputs to its value

Update of the English Channel cuttlefish stock assessment with a Bayesian two-stage biomass model.

A two-stage biomass model is developed in the Bayesian framework that allows us to assimilate various sources of information. A method that makes use of ancillary length frequency data is developed to provide an informative prior distribution for the intrinsic biomass growth rate parameter and its annual variability. The new Bayesian model provides substantial improvement to the existing stock assessment method used by ICES. Considering a time-varying g parameter improves model fit and improves the ecological realisms of the model according to the sensitivity of the cuttlefish population dynamics to environmental fluctuations. We present results of the English Channel cuttlefish stock assessment updated with the new Bayesian model. The model also provides predictions of the unexploited biomass in winter based on survey data, and help managing the stock in case of strong depletion

A Bayesian two-stage biomass model applied to the English Channel stock of cuttlefish (Sepia officinalis)

Among the English Channel fishery, the importance of cuttlefish stock has increased, following the cephalopods global landings and market trend. An adapted stock assessment model is needed in order to give good management advice with accurate uncertainties. Age based methods in this species are hampered by time consuming age determination with statoliths. A model requiring few data and adapted to the species life-history is therefore proposed. An assessment of this stock was conducted in June 2015 by fitting a two-stage biomass model on a 22 years’ time-series (1992-2014). The use of a Bayesian framework is particularly adapted for decision making, allowing the propagation of uncertainty in the model. It also permits the use of different sources of information, and is particularly well suited to face the lack of data. In this exercise we implement the two-stage biomass model into a Bayesian framework. We also improve the Bayesian model by using length frequency data and a mortality model to better estimate the biomass growth parameter g. We compare results of two models: one with fixed g and one with time-varying g. The last one is more realistic and model fit is better

Stock assessment of the English Channel stock of cuttlefish with a two-stage biomass model

Among the English Channel fishery, the importance of cuttlefish stock has increased, following the cephalopods global landings and market trend. The stock is currently managed at regional scale but not by European regulations, although it is a shared species targeted by French and British fishing fleets at several stages of its life-cycle and across much of its distributional range. An assessment of this stock was conducted in June 2014 by fitting a two-stage biomass model on a 22 years’ time-series (1992-2013). We present the last update of cuttlefish stock assessment using the same model on years 1992-2014. As the outputs of the model are sensitive to a fix growth parameter, we explore possibilities to improve the model. The use of a Bayesian framework is particularly adapted for decision making, allowing the propagation of uncertainty in the model and the use of prior knowledge on some parameter distributions. Therefore, we implemented the two-stage biomass model into a Bayesian framework and compared the results with the outputs of the initial fit. We found similar trends of biomass estimates for both models. The Bayesian model outputs showed a smaller range of variation than the initial fit. These results are only a first step toward an improvement of the two-stage biomass model currently used for cuttlefish stock assessment in the English Channel. The Bayesian model could indeed be improved and particular attention should be paid to the growth parameter g because of the high sensitivity of model outputs to its value. We discuss future directions of this work

DETERMINATE and LATE FLOWERING Are Two TERMINAL FLOWER1/CENTRORADIALIS Homologs That Control Two Distinct Phases of Flowering Initiation and Development in Pea

Genes in the TERMINAL FLOWER1 (TFL1)/CENTRORADIALIS family are important key regulatory genes involved in the control of flowering time and floral architecture in several different plant species. To understand the functions of TFL1 homologs in pea, we isolated three TFL1 homologs, which we have designated PsTFL1a, PsTFL1b, and PsTFL1c. By genetic mapping and sequencing of mutant alleles, we demonstrate that PsTFL1a corresponds to the DETERMINATE (DET) gene and PsTFL1c corresponds to the LATE FLOWERING (LF) gene. DET acts to maintain the indeterminacy of the apical meristem during flowering, and consistent with this role, DET expression is limited to the shoot apex after floral initiation. LF delays the induction of flowering by lengthening the vegetative phase, and allelic variation at the LF locus is an important component of natural variation for flowering time in pea. The most severe class of alleles flowers early and carries either a deletion of the entire PsTFL1c gene or an amino acid substitution. Other natural and induced alleles for LF, with an intermediate flowering time phenotype, present no changes in the PsTFL1c amino acid sequence but affect LF transcript level in the shoot apex: low LF transcript levels are correlated with early flowering, and high LF transcript levels are correlated with late flowering. Thus, different TFL1 homologs control two distinct aspects of plant development in pea, whereas a single gene, TFL1, performs both functions in Arabidopsis. These results show that different species have evolved different strategies to control key developmental transitions and also that the genetic basis for natural variation in flowering time may differ among plant species