A high speed, high resolution spectral domain optical coherence tomography (SD-OCT) system was used to study in-vivo early morphological changes and optical nerve head (ONH) blood flow in the Long Evans rat retina, induced by administration of sodium iodate (NaIO3). Linear and circular scanned OCT images were acquired at the same location in the retina from healthy control rats and from rats injected with 40mg/kg of NaIO3 solution at 1, 3, 6 12, 24, 72 and 168 hours post drug administration. Morphological OCT images showed changes in the optical reflectance and layer thickness of the photoreceptor IS and OS. The formation of a new low reflective layer between the photoreceptor OS and the RPE was observed in all tested rats. This new layer appeared as early as 1 hour, increased in thickness after 6 hours, and disappeared by 12 hours post NaIO3 injection. The low optical reflectance and the dynamics of this new layer suggest that it was most likely fluid accumulation. Comparison with H&E stained histological sections and IgG immunohistochemistry revealed minimal photoreceptor OS cell swelling at hour 1, detachment of the OS from the RPE by hour 3, and breaking of the blood-retina barrier with significant fluid accumulation by hour 6 post NaIO3 injection. The Doppler Optical Micro-Angiography (DOMAG) algorithm was used to carry out quantitative analysis of the ONH blood flow. Estimation of flow rate on each ONH vessel was done by measurements of the Doppler angle, vessel size and the axial velocity. This study has demonstrated that the capability of UHR-OCT to study optical reflectance and layer thickness changes, rearrangement and detachment of the photoreceptor OS and RPE layers, together with flow rate estimation of retinal blood vessels. Therefore, it can serve as markers in future non-invasive, in-vivo studies of disease or drug induced retinal degeneration in ophthalmic research.

L'épithélium pigmentaire rétinien (EPR) est une monocouche formée de cellules hautement spécialisées et uniques dont les nombreuses fonctions servent à maintenir une vision adéquate. En revanche, ces fonctions spécifiques rendent les cellules de l’EPR particulièrement vulnérables au stress oxydant. Avec le vieillissement, les cellules de l’EPR peuvent dégénérer et devenir non-fonctionnelles, donnant lieu à plusieurs maladies telles que la dégénérescence maculaire liée à l'âge (DMLA). Dans les pays occidentaux, la DMLA est la principale cause de cécité et de déficience visuelle chez les personnes âgées. En fait, environ 90 % des patients atteints de la DMLA souffrent de la forme sèche, pour laquelle il n'existe aucun traitement. Des années de recherche ont établi que le stress oxydant est un contributeur majeur à la pathogenèse de la DMLA sèche. De nombreuses études ont montré que le stress oxydant induit les cellules de l’EPR à libérer des vésicules extracellulaires (VEs). Nos propres travaux ont démontré que les VEs peuvent induire le stress oxydant et la sénescence chez les cellules de l’EPR. Comme d'autres, nous avons constaté que les VEs étaient enrichis en microARNs. Grâce au séquençage d’ARN, nous avons identifié le let-7f comme étant l'un des microARNs les plus abondants contenus dans ces vésicules. L'objectif de ce mémoire a été l’exploration entre la relation let-7f et la dégénérescence des cellules de l’EPR. Nos résultats ont démontré une régulation et une augmentation de l’expression du let-7f dans les cellules de l’EPR sous stress oxydant, in vitro et in vivo. De plus, la surexpression du let-7f a généré un stress oxydant, le dysfonctionnement et la sénescence des cellules humaines de l’EPR (ARPE-19). De plus, l’inhibition du let-7f à protéger ces cellules contre les conséquences néfastes induites par l’iodate de sodium. En somme, les résultats de ce travail suggèrent fortement que le let-7f est impliqué dans la dégénérescence des cellules de l’EPR et pourraient aider à la découverte de nouveaux processus pertinents dans la pathogenèse de la DMLA sèche. / The retinal pigment epithelium (RPE) is a highly specialized and unique monolayer of cells whose many functions are vital for maintaining proper vision. In turn, these specific functions render RPE cells particularly vulnerable to oxidative injury. With age, RPE cells can degenerate and become dysfunctional, giving rise to various disorders such as age-related macular degeneration (AMD). In western countries, AMD is the primary cause of blindness and visual impairments in the elderly. In fact, approximately 90% of all AMD patients suffer from the dry form of the disease, for which there exist no approved treatment. Decades of research have established that chronic oxidative stress is a major contributor to the pathogenesis of dry AMD. Numerous studies have shown that oxidative stress induces RPE cells to release extracellular vesicles (EVs) which participate in cell-to-cell communication. Our recent work has demonstrated that EVs alone were sufficient in inducing oxidative stress and senescence in RPE cells. Consistent with others, we found that EVs released by RPE cells were enriched in microRNAs. RNA-sequencing identified let-7f as one of the most abundant miRNAs contained in these vesicles. Despite being one of the first miRNAs to be discovered, the role of let-7f in RPE cells has remained essentially unexplored. The aim of this dissertation was to investigate the relationship between let-7f and RPE cells in regards to their degeneration and dysfunction. Our results revealed that the expression of let-7f increased and was regulated by oxidative stress in RPE cells, in vitro and in vivo. In addition, let-7f overexpression promoted oxidative stress, cellular dysfunction and senescence in human RPE (ARPE-19) cells. Finally, inhibition of let-7f exhibited protective effects against sodium iodate-induced oxidative injury. Overall, the findings in this work provide strong evidence that let-7f is implicated in the degeneration of RPE cells and further mechanistic investigation may help to uncover novel insights into the genesis of dry AMD.