Le mélanome est un cancer cutané dérivé de la transformation maligne des mélanocytes, cellules responsables de la pigmentation de la peau. Aujourd'hui, il est clairement reconnu que la progression tumorale est le produit d'une interaction dynamique entre les cellules tumorales et leur microenvironnement. Parmi les modes de communication intercellulaire, la sécrétion de nanovésicules appelées exosomes apparaît depuis une vingtaine d'années comme des acteurs majeurs de cette communication. En effet, ils permettent le transport d'un matériel complexe qui pourra impacter le devenir des cellules réceptrices. Bien que différentes données de la littérature aient mis en évidence le rôle des exosomes dans la progression du mélanome ainsi que la résistance aux traitements, les mécanismes moléculaires associés restent peu connus. Le premier objectif de ma thèse a consisté en l'identification du contenu protéique des exosomes de mélanome. Pour cela, nous avons identifié par spectrométrie de masse l'exoprotéome de sept lignées de mélanome d'agressivités différentes. L'analyse de ces résultats nous a permis de mettre en évidence une signature spécifique au niveau des exosomes sécrétés par les cellules les plus agressives. Cette signature a pu être corrélée à des propriétés fonctionnelles portées par ces vésicules. En effet, le traitement de cellules moins agressives par ces vésicules suffit à augmenter leur potentiel migratoire. Ces résultats montrent le rôle joué par les exosomes de mélanome dans la communication entre cellules cancéreuses et la progression tumorale. Parmi les cellules composant le microenvironnement d'un mélanome invasif, les adipocytes présents dans l'hypoderme représentent un acteur émergeant favorisant la progression tumorale. L'équipe dans laquelle j'ai effectué ma thèse a été l'une des premières à montrer, dans un modèle de cancer du sein, l'importance des adipocytes dans l'agressivité tumorale. Bien que différentes études aient montré l'impact des adipocytes sur la progression du mélanome, les mécanismes moléculaires associés restent peu connus. Le second aspect de ma thèse a consisté en l'étude du rôle des adipocytes dans la progression de ce type de tumeurs. Ces derniers stimulent le potentiel migratoire de cellules de mélanome et cet effet est médié par les exosomes sécrétés par les adipocytes (ad-exos). De façon intéressante, nous avons observé que les ad-exos contiennent des protéines impliquées dans chaque étape du métabolisme des acides gras et induisent une reprogrammation métabolique des cellules cancéreuses. L'augmentation de la migration des cellules tumorales induite par les ad-exos est dépendante de ce remodelage métabolique. Ces résultats montrent que les ad-exos participent au dialogue délétère entre mélanome et adipocytes. Ce dialogue pourrait être amplifié dans des conditions d'obésité expliquant le pronostic défavorable observé chez ce sous-groupe de patients. Nous avons montré, qu'en condition d'obésité, la sécrétion d'exosomes par les adipocytes est augmentée. De plus, à quantité égale d'exosomes, l'effet des ad-exos de souris obèses sur la migration des cellules cancéreuses est amplifié. Les ad-exos pourraient donc en partie être responsables du mauvais pronostic observé pour les individus obèses. En conclusion, nous avons montré que les exosomes sont des acteurs majeurs de la progression du mélanome. La signature spécifique que nous avons mise en évidence dans les vésicules sécrétées par les lignées métastatiques pourrait, à terme, être utilisée pour le pronostic de ce cancer. D'autre part, les ad-exos induisent un remodelage métabolique des cellules cancéreuses conduisant à l'augmentation du potentiel migratoire. La compréhension du rôle joué par ces vésicules permettra à terme d'interrompre le dialogue délétère entre adipocytes et cellules tumorales, en particulier chez les individus obèses. / Melanoma is a skin cancer derived from the malignant transformation of melanocytes, cells involved in the skin pigmentation. It is now clearly established that tumor progression results in a dynamic interaction between tumor cells and their microenvironment. Among the different modes of cell communication, the secretion of nanovesicles called exosomes has been extensively studied in the last twenty years and they appear to be major actors in this communication. Indeed, they enable the transport of complex biological material that may impact the behavior of recipient cells. Whereas melanoma exosomes have been implicated in tumor progression and chemoresistance, the mechanisms associated with these processes are little known. The first part of my thesis consisted in the identification of the protein content of melanoma cell exosomes. We identified the exoproteome of seven melanoma lines with various degrees of agressivity using mass spectrometry. The obtained results highlighted the presence of a specific signature in the exosomes secreted by the most aggressive cells. Moreover, this signature was correlated with functional properties of the vesicles. Indeed, incubation of less aggressive cells with these vesicles promoted their migratory abilities. These results show the role of melanoma exosomes in cancer cell communication and in tumor progression. Among the cells composing the microenvironment of invasive melanoma, adipocytes, present in the hypodermis, represent an emerging actor in tumor progression. The group in which I did my PhD was one of the first to highlight the importance of fat cells in breast cancer aggressiveness. Whereas different studies have shown the role of adipocytes in melanoma progression, the mechanisms associated are little known. The second aim of my thesis therefore consisted in the study of the role of adipocytes in melanoma progression. We have shown that adipocytes stimulate the migratory abilities of melanoma cells and that this effect is mediated by exosomes secreted by adipocytes. Interestingly, we observed that these vesicles contain proteins involved in every step of fatty acid metabolism and induce a metabolic reprogramming of cancer cells. The increase in tumor cell migration induced by adipocyte exosomes is dependent on this metabolic remodeling. These results show that adipocyte exosome are actors of the deleterious dialogue between melanoma and adipocytes. This dialogue could be amplified in obese conditions and could explain the poor prognostic of this subtype of patients. We have shown that in obese conditions, exosome secretion by adipocytes is increased. In addition, at equal concentrations in exosomes, the effect of the vesicles secreted by adipocytes from obese mice on cancer cell migration is amplified. Adipocyte exosomes could therefore participate in the poor prognosis of obese patients. In conclusion, we have shown that exosomes represent a major player in melanoma progression. The specific pattern contained in the exosomes from aggressive cells could be used as prognostic biomarkers in melanoma. On the other hand, adipocyte exosomes induce a metabolic reprogramming of cancer cells and this leads to an increase in their migratory abilities. Understanding the role of adipocyte exosomes in tumor progression could help to stop the deleterious dialogue between adipocytes and tumor cells, particularly in obese individuals.

Amyotrophic lateral sclerosis is a relentlessly progressive and fatal neuromuscular disease with no effective biomarkers, treatments or cure. In the early stages of ALS, it can be difficult to provide a diagnosis as patients do not meet diagnostic criteria until they become symptomatic, a sign of neuron degeneration. Early detection is therefore crucial to provide access to therapeutics prior to significant neuron loss. Extracellular vesicles are an ideal source of biomarkers as they contain a mix of proteins and nucleic acids reflective of the physiological state and are released from all cell types. We identified valosin-containing protein, integrin-beta 1 and gelsolin as potential biomarkers for ALS14 through proteomic analysis of EVs isolated from cell lines carrying the ALS-associated VCP-R155H mutation. My results indicate that EVs may serve as a valuable source of protein biomarkers in diagnostic, prognostic and predictive applications.

Endothelial cell dysfunction contributes to sepsis induced initiate immune response and the infiltration of immune cells into organs, resulting in organ injury. Heat shock protein A12B (HSPA12B) is predominantly expressed in endothelial cells. The present study investigated whether endothelial HSPA12B could regulate macrophage pro-inflammatory response during sepsis. Wild type (WT) and endothelial cell-specific HSPA12B deficient (HSPA12B–/–) mice were subjected to CLP sepsis. Mortality and cardiac function were monitored. Higher mortality, worsened cardiac dysfunction, and greater infiltrated macrophages in the myocardium and spleen were observed in HSPA12B–/– septic mice compared with the WT septic mice. The serum levels of TNF-α and IL-1β were higher and the levels of IL-10 were lower in HSPA12B–/– septic mice than in WT septic mice. Importantly, endothelial exosomes contain HSPA12B which can be uptaken by macrophages. Interestingly, endothelial exosomal HSPA12B significantly increases IL-10 levels and decreases TNF-α and IL-1β production in LPS-stimulated macrophages. Mechanistic studies show that endothelial exosomal HSPA12B downregulates NF-κB activation and nuclear translocation in LPS stimulated macrophages. These data suggest that endothelial HSPA12B plays a novel role in the regulation of macrophage pro-inflammatory response via exosomes during sepsis and that sepsis induced cardiomyopathy and mortality are associated with endothelial cell deficiency of HSPA12B.

Sarcopenia is the age-related progressive loss of skeletal muscle (SkM) mass, function, and strength. It has been well elucidated that resistance exercise can attenuate the development of sarcopenia. A population of extracellular vesicles, termed ‘exosomes’ (EXO), can contain microRNA and facilitates intercellular communication, including within SkM, though the response to prolonged training is not well understood. Given the potential role of SkM-derived exosomes in the response to exercise, we examined older adults (n = 30, OLD) before (PRE) and after a 12-week (POST), resistance training program. Healthy, young controls (n = 12, YNG) were used for comparison of baseline measures. Exosomes were isolated from platelet-free plasma using size exclusion chromatography in combination with ultracentrifugation (SEC-UC) and characterized via western blotting, nanoparticle tracking analysis and electron microscopy. To assess exosome biogenesis and miRNA synthesis in skeletal muscle, biopsies were taken from the vastus lateralis. Circulating EXO-enclosed and SkM miRNA expression was measured using RT-PCR. In SEC-UC isolates, EXO-markers CD81 and CD9 were significantly lower in PRE compared to YNG (p<0.05) but did not change with training. At baseline, ALIX, TSG101 and CD63 (markers of exosomes) were not altered with aging as compared to YNG; however, their expression significantly increased with training (p<0.05) Circulating EXO-derived mir-1, -133, -23 and -27a were significantly lower in expression of OLD participants as compared to YNG. Following resistance training, their expression significantly increased (p<0.05), returning to a YNG phenotype. Next, we aimed to investigate the contribution of skeletal muscle in the exosome responses. Our data indicate that a small fraction of circulatory exosomes may originate from skeletal muscle. In addition, in biopsy-derived SkM tissue, expression of proteins involved in EXO and miRNA biogenesis (Alix, XPO-5, DICER) were significantly higher in PRE compared to YNG (p<0.05), and further increased with resistance training (POST, p<0.05). Expression of Rab27a, a marker of exosome trafficking, was significantly higher in PRE (p<0.05) but did not respond to training. In conclusion, here we show alterations in circulating EXO content and cargo with age and resistance training partially restores the values to a younger phenotype. / Thesis / Master of Science in Medical Sciences (MSMS) / Aging is the slow and time-dependent process that our organs, down to the cellular level, deteriorate in function reducing the biological fitness of our bodies. Aging specific to skeletal muscle, or sarcopenia, is especially important because skeletal muscle makes up 40% of our weight, is essential for posture, balance, locomotion and breathing. Sarcopenic individuals have low muscle mass, strength, and function and as a result are associated with low independence in activities of daily living and increased risks of falls and fractures. Exercise, and in particular resistance training, has been shown to be beneficial and cost-effective in treating sarcopenia and delaying aging throughout the body. Part of the underlying mechanism regarding how exercise affects us in a multi-systemic manner is not well understood. We know that skeletal muscle releases a multitude of molecular factors during exercise. Amongst them, extracellular vesicles and specifically exosomes are worth investigating because they have been shown to function in intercellular communication by delivering molecular signals, called microRNAs, from origin cells to recipient cells throughout the body. In this thesis project, we investigate exosomes in circulation of older individuals before and after a 12-week resistance training program. We found that aging alters the exosome pool in circulation as well as their miRNA content. After resistance training, many of miRNAs altered with age, return to levels comparable to young. In addition, we showed that at the skeletal muscle level, aging and resistance training affect exosome biogenesis and miRNA expressions. In conclusion, we provide evidence that aging significantly alters circulatory exosomes and miRNA and show that resistance training normalizes the miRNA profile to levels seen in exosomes derived from young plasma. How exosomes and their molecular signals change with aging and how exercise affects them gives us an insight on how exercise elicits multi-systemic benefits against aging and sarcopenia.

No description available.

Breast cancer (BC) is the second most diagnosed cancer in Canadian women. Early detection of this cancer is critical to improve patient survival and prognoses. Exosomes are proposed to be involved in tumor proliferation through the transfer of diverse biomolecules, including metabolites. The use of exosomes as biomarkers for early diagnosis of BC has recently garnered interest due to them having unique biomolecules in diseased cohorts. Hence, an untargeted metabolomic analysis of BC exosomes was performed using nano high-performance liquid chromatography coupled to tandem mass spectrometry (nLC-MS/MS) for BC diagnostic biomarker discovery. A total of 9 independent metabolite samples from non-tumorogenic MCF10A and highly metastatic MDA-MB-231 cell lines were analyzed. Bioinformatic analysis revealed 27 potential metabolite candidates unique to MDA-MB-231. Amongst 4 metabolites tested, one, N-Acetyl-L-Phenylalanine, was successfully validated. Overall, this study reveals that exosomes possess metabolites that can be candidates for early BC diagnosis.

Suprachiasmatic nuclei (SCN) is the master circadian pacemaker that generates coordinated rhythms and drives oscillations in other peripheral tissues. Extracellular vesicles (exosomes) have been implicated in cell-to-cell communication and the regulation of circadian clock. However, mammalian clock-derived exosomes have not been characterized. This thesis examine the contents of exosome released from SCN2.2 cells in vitro using a combination of proteomics, next-generation sequencing, and bioinformatic analyses. SCN2.2 cells-derived exosomes, that carry unique microRNAs and proteins, could be taken up by fibroblast cells in vitro. Interestingly, several unique microRNAs and proteins found in SCN2.2 cells-derived exosomes have shown circadian rhythmicity in other cells. In addition, differential expressed microRNAs secreted by SCN cells were also observed outside of exosomes. Taken together, these studies demonstrate that exosomes, containing small RNAs, RNAs and proteins, are released from SCN2.2 cells and likely have a biological role in circadian regulation of metabolism in downstream cells.

La maladie de Parkinson (MP) est une maladie neurodégénérative invalidante pour laquelle le diagnostic ne peut être donné qu’une fois la dégénérescence neuronale bien entamée, rendant impérative la découverte d’un biomarqueur ; un outil biologique permettant de prédire l’apparition de la pathologie ou d’évaluer sa progression. Mon projet de maîtrise visait donc l’étude des vésicules extracellulaires (VE) issues du sang comme test diagnostique ou comme marqueur de la progression de la MP. La quantification des VE effectuée par cytométrie de flux à haute sensibilité a révélé une augmentation spécifique des VE dérivées d’érythrocytes (VEE) chez les parkinsoniens comparés à leurs contrôles, ainsi qu’une forte corrélation avec la progression de la maladie. L’analyse quantitative de l’alphasynucléine (α-Syn), principale protéine impliquée dans la pathologie de la maladie, a montré un niveau similaire entre les individus. Cependant, l’analyse protéomique des VEE a révélé une modulation de certaines protéines entre les patients et les donneurs sains. Nos résultats suggèrent que les VEE pourraient conduire au développement d’un marqueur pour suivre l’évolution de la maladie ainsi que l’effet de nouvelles thérapies. / 341812 Parkinson’s disease (PD) is a debilitating neurodegenerative disease for which the diagnosis can only be confirmed once the degeneration state is very advanced, making imperative the discovery of a biomarker: a biological tool to predict the onset of pathology or its progression. My master’s project was designed to study extracellular vesicles (EV) from the blood in order to discover if they could be used as a diagnostic test or as a marker of disease progression. Quantification of EV performed by high-sensitivity flow cytometry demonstrated an increase in PD patients compared to their controls and a strong correlation with the progression of the disease only in EV derived from erythrocytes (EEV). Quantitative analysis of α-Syn, the main protein involved into PD pathogenesis, showed a similar level between individuals. However, analysis of the EEV proteome reveals a modulation of some proteins between patients and healthy donors. Our results suggest that EEV have the potential to lead to the development of a marker abled to track disease course as well as measuring the effect of new therapies.

Les vésicules extracellulaires (VE) sont des « fragments » de cellules activement libérés dans tous les fluides biologiques. Elles transitent dans la circulation corporelle et transmettent leur contenu bioactif à d’autres cellules. Le lait est le fluide qui contient le plus de VE et celles-ci encapsulent plusieurs éléments bioactifs qui ont des effets anticancéreux, anti-inflammatoire et diminuent notamment les symptômes de la polyarthrite rhumatoïde in vivo. Durant ma thèse j’ai exploré la diversité des VE présentes dans le lait bovin commercial et j’ai étudié leurs activités biologiques dans le cadre des maladies inflammatoires chroniques de l’intestin (MICI). Les résultats que j’ai obtenus démontrent l’existence de plusieurs populations de VE dans le lait bovin commercial que j’ai pu discriminer grâce à l’utilisation du citrate de sodium pour leur isolation. J’ai découvert qu’elles étaient capables de survivre lors de la digestion in vitro durant laquelle elles protègent leur contenu bioactif, notamment des microARN. Après avoir décrit en détail les différents microARN et protéines encapsulées dans ces VE, j’ai pu trouver des marqueurs spécifiques pour certains sous-ensembles de VE du lait. J’ai aussi montré le transfert de miR-223 bovin à des cellules humaines in vitro et son activité biologique sur l’expression d’un gène rapporteur. J’ai alors exploré l’activité biologique des VE du lait dans un modèle murin de colite induite par le Dextran sulfate sodium (DSS). La prise orale de VE du lait a diminué les symptômes de la maladie, restauré en partie le microbiote intestinal et rétabli la barrière digestive et les niveaux de mucines. J’ai aussi découvert que différentes populations de VE du lait ont différents effets sur l’inflammation du côlon, notamment en modulant le niveau de certains microARN impliqués dans le développement des MICI. Le lait contient donc différentes VE avec des activités biologiques différentes capables de moduler l’inflammation et le développement de pathologies digestives. L’étude des mécanismes qui sous-tendent leur bioactivité pourrait impacter la prise en charge des maladies inflammatoires, permettrait une amélioration des formulations de lait pour les nouveau-nés et serait d’importance pour la santé publique et le traitement industriel du lait commercial. / Extracellular vesicles (EVs) are cellular “fragments” actively released in all biological fluids. They are transported through body circulation and transmit their bioactive content to remote recipient cells. Milk is the biological fluid most enriched in EVs and these encapsulate several bioactive elements with anti-cancer and anti-inflammatory effects and reduce the symptoms of rheumatoid arthritis in vivo. During my thesis, I explored the diversity of EVs present in commercial bovine milk and studied their biological activities in the context of inflammatory bowel diseases (IBD). The results I obtained demonstrate the existence of several EV subsets in commercial bovine milk that I could discriminate using sodium citrate for their isolation. I found these EVs can survive during in-vitro digestion and protect their bioactive content, including microRNAs. After detailing the different microRNAs and proteins encapsulated in these EVs, I found specific markers for certain populations of milk EVs. I also reported the transfer of vesicular bovine miR-223 to human cells in vitro and its biological activity on the expression of a reporter gene. I then explored the biological activities of milk EVs in a mouse model of DSS-induced colitis. The oral intake of milk EVs decreased the symptoms of the disease, restored part of the intestinal microbiota, restored the intestinal barrier and replenished mucin levels. Also, different populations of milk EVs differentially modulated inflammation in the colon, notably by regulating the level of certain IBD-associated microRNAs. Milk therefore contains different EV subsets with different biological activities capable of modulating inflammation and the development of digestive pathologies. Studying the mechanisms underlying their bioactivity could impact the management of inflammatory diseases, improve milk formulations for newborns, and be of importance to public health and industrial milk processing.

La choroïde est l'une des structures essentielles de l'œil humain, jouant un rôle crucial dans la fonction visuelle. Située dans la partie postérieure de l'œil, entre la rétine et la sclère, la choroïde est une couche vasculaire riche en vaisseaux sanguins. Elle remplit plusieurs fonctions vitales pour la santé de l'œil comme l'approvisionnement en nutriments et en oxygène à la rétine externe, ce qui favorise le bon fonctionnement de ce tissu essentiel à la vision. La choroïde est majoritairement composée de cellules pigmentées nommées mélanocytes qui absorbent la lumière excédentaire via la mélanine présente dans les mélanosomes. Ce pigment piégeur de radicaux libres et d'ions métalliques possède également une activité antioxydante. Tout déséquilibre dans la physiologie des mélanocytes peut donc avoir des conséquences sur la santé oculaire et conduire à des pathologies telles que le mélanome uvéal ou la dégénérescence maculaire liée à l'âge. La transformation des mélanocytes de l'uvée peut conduire au développement d'une tumeur oculaire nommée mélanome uvéal. Ce dernier est le cancer intraoculaire primaire le plus fréquent chez l'adulte et est associé au développement de métastases chez 50% des patients au bout de 15 ans. La dissémination de cellules cancéreuses au niveau de sites métastasiques comme le foie (89%) diminue l'espérance de vie des patients car les traitements actuels contre les métastases sont peu efficaces. En 2019, l'équipe de la Pre Solange Landreville a montré *in vivo* l'existence d'une corrélation entre la communication intercellulaire des cellules cancéreuses avec les cellules stellaires hépatiques et la formation de métastases hépatiques. Nous avons émis l'hypothèse que des vésicules extracellulaires dérivées des cellules cancéreuses du mélanome uvéal jouent un rôle dans l'établissement d'une niche pré-métastatique hépatique. Le premier objectif de mon doctorat était de caractériser les vésicules extracellulaires mélanomiques et d'étudier leur rôle dans le remodelage des niches primaire et métastatique. Nous avons montré que les cellules métastatiques du mélanome uvéal sécrétaient davantage de vésicules extracellulaires comparativement aux cellules non-métastatiques ou aux mélanocytes choroïdiens sains. De plus, l'ajout de vésicules extracellulaires mélanomiques sur des cellules stellaires hépatiques a permis de confirmer l'activation de ces cellules et leurs rôles pro-fibrotiques et pro-angiogéniques sur les cellules endothéliales et hépatiques. Enfin, nous avons démontré que la rigidité du stroma hépatique joue un rôle essentiel au développement de la niche pré-métastatique du mélanome uvéal; les vésicules extracellulaires étaient internalisées à une faible rigidité, ce qui modifiait le transcriptome des cellules stellaires hépatiques. Les recherches sur la dégénérescence maculaire liée à l'âge ont corrélé une augmentation du stress oxydatif avec la dégénérescence de l'épithélium pigmentaire rétinien et des photorécepteurs de la rétine et donc la perte partielle de la fonction visuelle. En collaboration avec le laboratoire de la Pre Stéphanie Proulx, le laboratoire de la Pre Solange Landreville a obtenu des résultats préliminaires démontrant que la présence de mélanocytes choroïdiens réduisait le niveau de stress oxydatif dans les cellules de l'épithélium pigmentaire rétinien. Au sein de cette thèse, nous avons émis l'hypothèse que les mélanocytes choroïdiens sécrètent des vésicules extracellulaires pour établir une communication intercellulaire et ainsi participer au maintien de l'homéostasie de la choroïde et de l'épithélium pigmentaire rétinien adjacent. Le deuxième objectif de mon doctorat était de caractériser les vésicules extracellulaires mélanocytaires et d'étudier leurs rôles dans la choroïde. Nos résultats ont confirmé l'internalisation des vésicules extracellulaires des mélanocytes choroïdiens par les cellules environnantes (i.e. fibroblastes, cellules endothéliales et cellules de l'épithélium pigmentaire rétinien). Nous avons aussi démontré que les vésicules extracellulaires mélanocytaires engendraient des modifications du transcriptome et de l'expression de phosphokinases et de protéines angiogéniques dans les cellules endothéliales choroïdiennes et l'épithélium pigmentaire rétinien. Le développement de réseaux endothéliaux et la migration des cellules endothéliales étaient augmentés post-internalisation des vésicules extracellulaires. Nos études protéomiques ont démontré que les vésicules extracellulaires mélanocytaires étaient enrichies de protéines angiogéniques. Mes deux projets de doctorat ont permis de mettre en évidence l'importance des vésicules extracellulaires dans la communication intercellulaire dans des conditions saines ou pathologiques au niveau de la choroïde. Mes travaux contribuent à l'avancement des connaissances dans la compréhension de pathologies telles que la dégénérescence maculaire liée à l'âge ou le mélanome uvéal, ce qui permet d'envisager de nouvelles perspectives pour le diagnostic ou le pronostic de ces maladies, ainsi que l'amélioration des traitements offerts à ces patients. / The choroid is one of the essential structures of the human eye, playing a crucial role in visual function. Located in the posterior part of the eye, between the retina and the sclera, the choroid is a vascular layer rich in blood vessels. It serves several vital functions for eye health, such as supplying nutrients and oxygen to the outer retina, which promotes the proper functioning of this tissue essential for vision. The choroid is mainly composed of pigmented cells called melanocytes that absorb excess light through the melanin present in melanosomes. This pigment, a scavenger of free radicals and metal ions, also possesses antioxidant activity. Any imbalance in the physiology of melanocytes can therefore have consequences on ocular health and lead to pathologies such as uveal melanoma or age-related macular degeneration. The transformation of uveal melanocytes can lead to the development of an ocular tumor called uveal melanoma. This is the most common intraocular cancer in adults and is associated with the development of metastases in 50% of patients. The spread of tumor cells to metastatic sites like the liver (89%) decreases the life expectancy of patients because current treatments against metastases are ineffective. In 2019, the team led by Professor Solange Landreville demonstrated *in vivo* the existence of a correlation between intercellular communication of tumor cells with hepatic stellate cells and the formation of hepatic metastases. We hypothesized that extracellular vesicles derived from uveal melanoma tumor cells play a role in establishing a pre-metastatic hepatic niche. The first objective of my doctoral thesis was to characterize melanoma-derived extracellular vesicles and study their role in remodeling the primary and metastatic niches. We showed that metastatic uveal melanoma cells secreted more extracellular vesicles compared to non-metastatic cells or healthy choroidal melanocytes. Furthermore, the addition of melanoma-derived extracellular vesicles to hepatic stellate cells confirmed the activation of these cells and their pro-fibrotic and pro-angiogenic roles on endothelial and hepatic cells. Finally, we demonstrated that hepatic stromal stiffness plays an essential role in the development of the pre-metastatic niche of uveal melanoma; extracellular vesicles were internalized at low rigidity, which altered the transcriptome of hepatic stellate cells. Research on age-related macular degeneration has correlated an increase in oxidative stress with the degeneration of the retinal pigment epithelium and photoreceptors of the retina, leading to partial loss of visual function. In collaboration with Professor Stéphanie Proulx's laboratory, Professor Solange Landreville's laboratory obtained preliminary results demonstrating that the presence of choroidal melanocytes reduced the level of oxidative stress in retinal pigment epithelial cells. Within this thesis, we hypothesized that choroidal melanocytes secrete extracellular vesicles to establish intercellular communication and thus participate in maintaining the homeostasis of the choroid and adjacent retinal pigment epithelium. The second objective of my doctoral thesis was to characterize melanocytic extracellular vesicles and study their roles in the choroid. Our results confirmed the internalization of choroidal melanocyte-derived extracellular vesicles by surrounding cells (i.e., fibroblasts, endothelial cells, and retinal pigment epithelial cells). We also demonstrated that melanocytic extracellular vesicles induced changes in the transcriptome and expression of phosphokinases and angiogenic proteins in choroidal endothelial cells and retinal pigment epithelium. The development of endothelial networks and the migration of choroidal endothelial cells were increased post-internalization of extracellular vesicles. Our proteomic studies showed that the extracellular vesicles were enriched with angiogenic proteins. My two doctoral projects have highlighted the importance of extracellular vesicles in intercellular communication in both healthy and pathological conditions in the choroid. My work contributes to advancing knowledge in understanding pathologies such as age-related macular degeneration or uveal melanoma, which opens new perspectives for the diagnosis or prognosis of these diseases, as well as the improvement of treatments offered to these patients.