In nature, cells are not randomly clustered to form tissues. The tissue is a more complicated system with functions that go beyond what any single cell type could accomplish. While studying single-cell mechanics and dynamics is relevant from an investigative point of view, this approach loses, or fail to gather information about the tissue. The tissue investigated in this study is the neurosensory retina which seeing as extension of the brain is a very convenient model for the central nervous system due to its accessibility. The retina is constantly subjected to different mechanical stresses from development to adulthood. Although the majority of the phenomena where mechanical stresses are involved are well-studied, the mechanics behind them is not well understood. However, knowledge about the ability of the retina to adjust to mechanical stresses is essential, for example, for improving retinal surgery. Establishing a method to mechanically probe the retina is a challenge due to the extremely delicate nature of this multilayered neural tissue and to the short-time survival ex vivo. The organotypic tissue culture is a powerful tool because it allows to maintain with high accuracy the complex multicellular anatomy and the microenvironment of the original tissue. One of the limitations of the organotypic culture techniques has been until recently due to the ability to use only post-natal/juvenile tissues for long-term culture. The importance of using adult tissue is incontestable when the investigation focuses on age-related pathologies such as vitreous shrinkage or macula degeneration. In this work, TiO2 nanotube arrays are presented as the innovative substrate for long-term organotypic culture of adult neural tissue. The retinal whole-mount of adult guinea pig and the brain slices of adult mouse were cultures for 14 days without showing any sign of edema or swelling. Furthermore, in order to study the behavior of the retinal tissue under shear stress new set-ups were designed. For the first time, the behavior of the retinal layers were observed showing that the retina does not act as an homogeneous material in response to an applied stress. The methods developed here can be used for future quantitative studies, to provide an exact knowledge of retinal biomechanics which will help retinal surgeons to optimize their methods.

In nature, cells are not randomly clustered to form tissues. The tissue is a more complicated system with functions that go beyond what any single cell type could accomplish. While studying single-cell mechanics and dynamics is relevant from an investigative point of view, this approach loses, or fail to gather information about the tissue. The tissue investigated in this study is the neurosensory retina which seeing as extension of the brain is a very convenient model for the central nervous system due to its accessibility. The retina is constantly subjected to different mechanical stresses from development to adulthood. Although the majority of the phenomena where mechanical stresses are involved are well-studied, the mechanics behind them is not well understood. However, knowledge about the ability of the retina to adjust to mechanical stresses is essential, for example, for improving retinal surgery. Establishing a method to mechanically probe the retina is a challenge due to the extremely delicate nature of this multilayered neural tissue and to the short-time survival ex vivo. The organotypic tissue culture is a powerful tool because it allows to maintain with high accuracy the complex multicellular anatomy and the microenvironment of the original tissue. One of the limitations of the organotypic culture techniques has been until recently due to the ability to use only post-natal/juvenile tissues for long-term culture. The importance of using adult tissue is incontestable when the investigation focuses on age-related pathologies such as vitreous shrinkage or macula degeneration. In this work, TiO2 nanotube arrays are presented as the innovative substrate for long-term organotypic culture of adult neural tissue. The retinal whole-mount of adult guinea pig and the brain slices of adult mouse were cultures for 14 days without showing any sign of edema or swelling. Furthermore, in order to study the behavior of the retinal tissue under shear stress new set-ups were designed. For the first time, the behavior of the retinal layers were observed showing that the retina does not act as an homogeneous material in response to an applied stress. The methods developed here can be used for future quantitative studies, to provide an exact knowledge of retinal biomechanics which will help retinal surgeons to optimize their methods.

La maladie de Parkinson (MP) est caractérisée par une dégénérescence des neurones dopaminergiques de la voie nigrostriée. La thérapie cellulaire, par transplantation intranigrale de cellules fœtales issues de mésencéphale ventral (MV), assure un rétablissement anatomique et fonctionnel de cette voie. Des molécules de guidage axonal (MGA) joueraient ainsi un rôle dans la reconnexion axonale des cellules transplantées. Pour tester cette hypothèse, nous avons étudié l'expression de MGA dans le cerveau adulte intact et dans des cellules destinées à la transplantation, ainsi que dans le cerveau adulte d'un modèle murin de la MP après transplantation. Dans le tissu intact, nous avons montré que semaphorin7A (Sema7A) et Sema3A et leurs récepteurs, plexinC1 et neuropilin1, conservent leur expression protéique. De plus, grâce à l'utilisation de puces à ADN, nous avons montré que les récepteurs Robo2, neuropilin1, neuropilin2, EphA5 et DCC sont exprimés de manière différentielle dans les deux populations cellulaires utilisées pour la transplantation. Ceci suggère que ces molécules seraient impliquées dans la restauration fonctionnelle observée. Enfin, dans le tissu lésé, nous avons observé, par RT-qPCR, des variations d'expression de l'ARNm de ces MGA après transplantation intranigrale des cellules fœtales du MV, suggérant plus particulièrement l'implication de Sema3A, Sema3F et Sema7A dans la reconstruction de la voie. Ce travail met en lumière l'action de sémaphorines dans le guidage axonal des cellules transplantées. L'intégration de ces MGA dans les procédures de transplantation pourrait aider à optimiser les procédures de thérapie cellulaire dans la MP. / Parkinson's disease (PD) is characterised by the degeneration of the dopaminergic nigrostriatal pathway. Cell therapy using intranigral transplantation of foetal ventral mesencephalon (VM) cells in a mouse model of PD results in anatomical and functional reconstruction of the pathway. This suggests a role for axon guidance molecules (GMs) in reconnecting transplanted cells to their striatal target. To test this hypothesis, we studied the expression of axon GMs in the intact adult brain, on cells used for transplantation and in a mouse model of PD after cell therapy. In the intact brain, we showed that GMs as semaphorin7A (Sema7A) and Sema3A and their corresponding receptors, plexinC1 and neuropilin1, retain an expression at the protein level, therefore showing a possible role for these guidance cues in the adult brain. Moreover, using microarray, we studied GM receptor expression profiles in two types of cells used for transplantation and exhibiting different functional ameliorations. Robo2, neuropilin1, neuropilin2, EphA5 and DCC receptors showed differential expression between the two cellular populations, indicating their possible contribution to the different functional outcomes observed. In the lesioned mouse brain, we observed, using RT-qPCR, variations of mRNA expression of these axon GMs after intranigral transplantation of foetal VM derived cells, thus suggesting the implication of Sema3A, Sema3F, and Sema7A in the reconstruction of the pathway. Overall, this work highlights particular importance of semaphorins in the nigrostriatal pathway reconstruction. Integrating these cues in transplantation procedures can possibly optimize cell therapy for PD patients.