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Chez les vertébrés, la perception de la lumière est possible grâce à la transformation de l'énergie des photons en un signal électrochimique dans les photorécepteurs. La photo-isomérisation du chromophore RAL-11-cis en RAL-tout-trans déclenche une cascade d'événements de transduction du signal et conduit à la perte de la sensibilité à la lumière des photorécepteurs, un processus de recyclage du chromophore visuel entre alors en jeu afin de rétablir cette sensibilité, c'est le cycle visuel de rétinoïdes. Le cycle visuel s'effectue dans les photorécepteurs et l'épithélium pigmentaire rétinien et fait intervenir plusieurs protéines. L'étape limitante de ce cycle est catalysée par la protéine spécifique de l'EPR RPE65. Mieux comprendre la régulation de cette étape permettra d'ouvrir des pistes thérapeutiques pour différentes pathologies liées l'activité du cycle visuel. Notre laboratoire a montré que FATP1, une protéine du métabolisme lipidique, inhibe l'activité de RPE65 in vitro. Dans ce travail, nous avons évalué l'effet de l'absence de FATP1 sur l'activité du cycle visuel et la fonction visuelle dans un modèle murin. La souris ko FATP1 est caractérisée par une baisse des amplitudes des ondes a et b de l'ERG, un retard de régénérescence de l'ERG et d'accumulation de rétinylesters après éblouissement. La formation du RAL-11-cis reste comparable à celle des souris sauvages. Les souris FATP-/- montrent une plus grande susceptibilité aux effets du vieillissement : des anomalies de structure ont été observées au niveau des photorécepteurs, de la membrane de Brüch et de la choroïde, sans accumulation excessive de lipides ou de lipofuscine ni de dégénérescence rétinienne. La perturbation de la fonction visuelle observé en l'absence de FATP1 chez la souris pourrait avoir un effet plus accru chez l'homme qui vie plus longtemps et dont la rétine reçoit plus de lumière. En conclusion, FATP1 pourrait être une composante importante pour le vieillissement de la rétine chez l'homme. / In vertebrates, perception of light is made possible through the conversion of photon energy into an electrochemical signal in photoreceptors. The photo-isomerization of the chromophore 11-cis-RAL into all-trans-RAL triggers a cascade of signal transduction and leads to loss of light sensitivity of photoreceptors, thus, a recycling process of chromophore called the rétinal visual cycle is involved to restore this sensitivity. The visual cycle takes place in the photoreceptors and retinal pigment epithelium and involves several proteins. The limiting step of this cycle is catalyzed by RPE-specific protein RPE65. Better understanding the regulation of this step might open up new ways for treatment of various pathologies related to the visual cycle activity. Our laboratory has shown that FATP1, a protein involved in lipid metabolism, inhibits the activity of RPE65 in vitro. In this study, we evaluated the effect of the lack of FATP1 on the activity of the visual cycle and visual function in a mouse model. FATP1 ko mice are characterized by lower a and b amplitudes of the elctroretinogram, delayed ERG and retinylesters accumulation recovery after bleache. 11-cis-RAL synthesis rates are similar to those of wt mice. FATP1 ko mice show a greater susceptibility to the aging effects: structural abnormalities were observed in the photoreceptors, Bruch's membrane and choroid without excessive accumulation of lipid or lipofuscin or retinal degeneration. The disturbance of visual function which accopagne the lack of FATP1 in mice could have a more increased effect in human who live longer and wich the retina receives more light. In conclusion, FATP1 might be an important component for the aging of the retina in humans.

All cells depend on properly folded proteins for survival and function. Misfolding of proteins results in loss of critical functions and may trigger the misfolding of other nearby proteins leading to toxic aggregation. While many proteins can fold on their own, others with complicated domain structures require assistance from protein folding machines called chaperones. The most complex and highly specialized of all chaperones is the eukaryotic chaperonin complex CCT which is necessary for the folding of a wide variety of essential proteins. These include the cytoskeletal proteins actin and tubulin as well as the Gβ subunit of the G protein heterotrimer. However, CCT activity can also drive diseases such as cancer and viral infections and could represent a high value therapeutic target if the mechanisms by which it folds its different client proteins were better understood. To this end, we identified and characterized an interaction between CCT and the RNA-dependent RNA polymerase of SARS-CoV-2, the virus responsible for the deadly global pandemic that began in 2019. We showed that SARS-CoV-2 replication is impaired by loss of CCT and that the polymerase, designated Nsp12, interacts with CCT upon synthesis and quickly releases - the hallmark pattern of a CCT substrate. Furthermore, we solved a 3.3 Å cryo-EM structure of Nsp12 bound to open CCT showing Nsp12 binding between the two rings of CCT and extending up through of the folding chambers and out of CCT. At 107 kD, Nsp12 is the largest substrate ever visualized inside of CCT and answers a long-standing question in the field of how CCT could accommodate substrates larger than its 70 kD folding chamber. Given that CCT is known to fold proteins with WD40-repeat domains, we also investigated a potential relationship between CCT and RPE65. RPE65, which contains a WD40 domain, is the retinyl ester isomerase that converts all-trans retinyl esters into 11-cis retinol, a key step in the visual cycle, and its mutation is a common cause of hereditary retinal dystrophies. We showed that CCT interacts with RPE65 and that nascent RPE65 binds and releases from CCT albeit with relatively slow kinetics. However, RPE65 is not dependent on CCT for expression or activity. This suggests that the relationship between RPE65 and CCT may represent a novel CCT function distinct from the canonical obligate substrate dynamic.

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