Etude de la régulation de l'expression génique du facteur de croissance FGF-1 au cours de la myogénèse

Le FGF1 (fibroblast growth factor 1) est un facteur de croissance connu pour son rôle dans l'angiogenèse, qui est également impliqué dans la myogenèse. Le gène du FGF1 contient quatre promoteurs tissu-spécifiques permettant la synthèse de quatre transcrits possédant des régions 5' non traduite (5'NT) distinctes. Les ARNm issus des promoteurs A et C contiennent un IRES (internal ribosome entry site), élément structural de l'ARN qui permet la traduction de l'ARNm par un mécanisme différent du mécanisme classique dépendant de la coiffe. La première partie de ma thèse a porté sur l'implication du FGF1 au cours de la différenciation des myotubes in vitro, et durant la régénération musculaire in vivo. Nous avons pu démontrer que le FGF1 est induit lors de la différenciation et de la régénération musculaire, et que cette induction est requise pour la différenciation des myoblastes en myotubes. Il apparaît que cette induction est due à une activation coordonnée de la transcription à partir du promoteur A et de la traduction sous contrôle de l'IRES A, suggérant un mécanisme de couplage transcription-traduction. Dans le but d'élucider ce mécanisme, j'ai focalisé la deuxième partie de ma thèse sur la recherche des facteurs protéiques impliqués dans cette régulation au cours de la myogenèse. Par la technologie d'interaction biomoléculaire couplé à la spectrométrie de masse (BIA-MS) et par des expériences de CHIP, nous avons identifié deux protéines candidates, la hnRNPM et p54 nrb/NonO, qui se lient à la fois à l'IRES et au promoteur du FGF1 au cours de la différenciation des myoblastes. Nos résultats démontrent que ces protéines appartiennent à un même complexe qui est transloqué du noyau au cytoplasme spécifiquement au deuxième jour de différenciation myoblastiques, et qu'elles ont la double fonction d'activateur transcriptionnel et traductionnel. De plus, hnRNPM et p54 nrb/NonO se lient au domaine CTD de l'ARN polymérase II, et leur fonction d'activateur de l'IRES nécessite une étape transcriptionnel. Ces données nous permettent de proposer un modèle de couplage transcription-traduction dans lequel les deux protéines se lient au promoteur et activent la transcription, puis sont transférées sur l'ARNm naissant où elles jouent alors le rôle d'ITAF (IRES trans-acting factor). Ainsi nous montrons que la traduction est régulée de manière co-transcriptionnel à l'instar des étapes de maturation de l'ARNm comme l'épissage ou la polyadénylation. De plus, l'inhibition de p54 nrb/NonO bloque l'induction du FGF1 et la formation des myotubes, démontrant la relevance physiologique de ce mécanisme. La troisième partie de ma thèse a été consacrée à l'étude de l'influence de la région 3' non traduite (3'NT) de l'ARNm du FGF1 sur la régulation de ce facteur au cours de la myogenèse. Les résultats montrent que cette région 3'NT joue le rôle d'activateur de l'IRES, particulièrement en présence du promoteur. A l'issue de cette thèse j'ai donc pu démontrer que la régulation de l'expression du FGF1 lors de la myogenèse est très complexe, qu'elle implique un mécanisme de couplage transcription-traduction régulé par des facteurs protéiques, ainsi qu'un dialogue entre l'IRES et la région 3'NT de l'ARNm. En perspective il apparaît qu'un tel mécanisme de couplage pourra certainement se généraliser sur d'autres ARNm de la myogenèse possédant des IRES, ainsi qu'à d'autres processus physiologiques.The FGF1 (fibroblast growth factor 1) is a growth factor known for its role in the angiogenesis, which is also involved in the myogenesis. The gene of the FGF1 contains four promoters tissue specific allowing the synthesis of transcribed four possessing different regions 5 'untranslated region ( UTR). The mRNA from promoters A and C contains one IRES (internal entry ribosome site), structural element which allows the translation of the mRNA by a mechanism different from the classic mechanism dependent on the cap. The first part of my thesis concerned the implication of the FGF1 during the differentiation of the in vitro myotubes, and during the in vivo muscular regeneration. We were able to demonstrate that the FGF1 is involved during the differentiation and during the muscular regeneration, and that this induction is required for the differentiation of myotubes. It seems that this induction is due to a coordinated activation of the transcription from the promoter A and of the translation under control of IRES A, suggesting a coupling mechanism transcription-translation. With the aim of clarifying this mechanism, I focused the second part of my thesis on the research for the protein factors implied in this regulation during the myogenesis. By the technology of biomolecular interaction coupled with the mass spectrometry (BIA-MS) and experiments of CHIP, we identified two candidate proteins, the hnRNPM and p54 nrb / NonO, which are bound at the same time in IRES and to the promoter of the FGF1 during the differentiation of myoblastes. Our results demonstrate that these proteins belong to the same complex which is shuttle in the nucleocytoplasmic specifically in the second day of differentiation myoblastiques, and that they have the double function of transcriptionnel and translation activator. Furthermore, hnRNPM and p54 nrb / NonO are bound in the domain CTD of the polymérase RNA II, and their function of activator of IRES requires a stage transcriptionnel. These data allow us to propose a model of coupling transcription-translation in which both proteins are bound to the promoter and activate the transcription, then are transferred on the rising ARNm where they play then the role of ITAF (IRES trans-acting factor). So we show that the translation is regulated in a way co-transcriptionnel following the example of the stages of maturation of the mRNA as the splicing or the polyadénylation. Furthermore, the inhibition of p54 nrb / NonO blocks the induction of the FGF1 and the training of myotubes, demonstrating the physiological relevance of this mechanism. The third part of my thesis was dedicated to the study of the influence of the region 3 ' untranslated (3'UTR) from the mRNA of the FGF1 on the regulation of this factor during the myogenèse. The results show that this region 3'UTR plays activator's role of IRES, particularly in the presence of the promoter A. Finally I was thus able to demonstrate that the regulation of the expression of the FGF1 during the myogenesis is very complex, that it implies a coupling mechanism transcription-translation regulated by protein factors, as well as a dialogue enters IRES A and the region 3'UTR of the mRNA. In perspective it seems that such a coupling mechanism can certainly become widespread on other mRNA of the myogenesis possessing IRES, as well as in the other physiological processes

Clinical heterogeneity of neuro-inflammatory PET profiles in early Alzheimer’s disease

The relationship between neuroinflammation and cognition remains uncertain in early Alzheimer’s disease (AD). We performed a cross-sectional study to assess how neuroinflammation is related to cognition using TSPO PET imaging and a multi-domain neuropsychological assessment. A standard uptake value ratio (SUVR) analysis was performed to measure [18F]-DPA-714 binding using the cerebellar cortex or the whole brain as a (pseudo)reference region. Among 29 patients with early AD, the pattern of neuroinflammation was heterogeneous and exhibited no correlation with cognition at voxel-wise, regional or whole-brain level. The distribution of the SUVR values was independent of sex, APOE phenotype, early and late onset of symptoms and the presence of cerebral amyloid angiopathy. However, we were able to demonstrate a complex dissociation as some patients with similar PET pattern had opposed neuropsychological profiles while other patients with opposite PET profiles had similar neuropsychological presentation. Further studies are needed to explore how this heterogeneity impacts disease progression

Clinical heterogeneity of neuro-inflammatory PET profiles in early Alzheimer’s disease

International audienceThe relationship between neuroinflammation and cognition remains uncertain in early Alzheimer's disease (AD). We performed a cross-sectional study to assess how neuroinflammation is related to cognition using TSPO PET imaging and a multidomain neuropsychological assessment. A standard uptake value ratio (SUVR) analysis was performed to measure [ 18 F]-DPA-714 binding using the cerebellar cortex or the whole brain as a (pseudo)reference region. Among 29 patients with early AD, the pattern of neuroinflammation was heterogeneous and exhibited no correlation with cognition at voxel-wise, regional or whole-brain level. The distribution of the SUVR values was independent of sex, APOE phenotype, early and late onset of symptoms and the presence of cerebral amyloid angiopathy. However, we were able to demonstrate a complex dissociation as some patients with similar PET pattern had opposed neuropsychological profiles while other patients with opposite PET profiles had similar neuropsychological presentation. Further studies are needed to explore how this heterogeneity impacts disease progression.</div

Clinical heterogeneity of neuro-inflammatory PET profiles in early Alzheimer’s disease

International audienceThe relationship between neuroinflammation and cognition remains uncertain in early Alzheimer's disease (AD). We performed a cross-sectional study to assess how neuroinflammation is related to cognition using TSPO PET imaging and a multidomain neuropsychological assessment. A standard uptake value ratio (SUVR) analysis was performed to measure [ 18 F]-DPA-714 binding using the cerebellar cortex or the whole brain as a (pseudo)reference region. Among 29 patients with early AD, the pattern of neuroinflammation was heterogeneous and exhibited no correlation with cognition at voxel-wise, regional or whole-brain level. The distribution of the SUVR values was independent of sex, APOE phenotype, early and late onset of symptoms and the presence of cerebral amyloid angiopathy. However, we were able to demonstrate a complex dissociation as some patients with similar PET pattern had opposed neuropsychological profiles while other patients with opposite PET profiles had similar neuropsychological presentation. Further studies are needed to explore how this heterogeneity impacts disease progression.</div

Translocator protein (TSPO) genotype does not change cerebrospinal fluid levels of glial activation, axonal and synaptic damage markers in early Alzheimer’s disease

Background: PET imaging of the translocator protein (TSPO) is used to assess in vivo brain inflammation. One of the main methodological issues with this method is the allelic dependence of the radiotracer affinity. In Alzheimer’s disease (AD), previous studies have shown similar clinical and patho-biological profiles between TSPO genetic subgroups. However, there is no evidence regarding the effect of the TSPO genotype on cerebrospinal-fluid biomarkers of glial activation, and synaptic and axonal damage. Method: We performed a trans-sectional study in early AD to compare cerebrospinal-fluid levels of GFAP, YKL-40, sTREM2, IL-6, IL-10, NfL and neurogranin between TSPO genetic subgroups. Results: We recruited 33 patients with early AD including 16 (48%) high affinity binders, 13 (39%) mixed affinity binders, and 4/33 (12%) low affinity binders. No difference was observed in terms of demographics, and cerebrospinal fluid levels of each biomarker for the different subgroups. Conclusion: TSPO genotype is not associated with a change in glial activation, synaptic and axonal damage in early AD. Further studies with larger numbers of participants will be needed to confirm that the inclusion of specific TSPO genetic subgroups does not introduce selection bias in studies and trials of AD that combine TSPO imaging with cerebrospinal fluid biomarkers