Cell Transplantation
(Yvan Arsenijevic)

Retinitis Pigmentosa is a widespread neurodegenerative disorders in the western world. In this disease the photoreceptor layer degenerate and finally leads to the loss of the visual function. The use of cellular therapy aiming at replacing lost cells by a transplantation method seems thus suitable. We use murine models of retinal degeneration mimicking the retinitis pigmentosa. In these models we transplant retinal stem cells (RSCs) into two different locations; the vitreous or the subretinal space of the eye. Such approach allows us to characterize the potential of these cells to differentiate into a natural microenvironment and on the other hand it allows us to evaluate the feasibility of such techniques. In our conditions retinal stem cells injected into the mouse retina exhibited a migratory preference for the ganglion cell layer and a differentiation preference for the glial phenotype. Nevertheless, we observed a slight differentiation of these cells into retinal neurons; ganglion cells and in rare cases into photoreceptors (Canola et al 2007). These results indicate that RSCs preserved the capacity to differentiate into retinal cells. It also appeared that the retina, either during or at a late stage of degeneration, does not provide signals to induce massive differentiation of RSCs into photoreceptors. This suggests that RSCs transplantation may not be sufficient to restore the function of a diseased retina and thus in vitro differentiated photoreceptor transplantation may be more suitable than RSCs to integrate the photoreceptor layer.

 10.08.10

Bioengineering of retinal stem cells
(Meta Djojosubroto)

We have shown that retinal stem cells (RSCs) can be isolated from the newborn mouse retina from the radial glia population (Angénieux et al. 2006, Mehri-Soussi et al. 2006). However, we revealed that cells committed to the photoreceptor fate derived from RSCs  have a poor integration and survival rate after grafting (Canola & Arsenijevic 2007). One possible way to control cell differentiation and circumvent the hostile host environment, thus improving cell survival and engraftment, is by transplanting RSCs in a form of an engineered retinal tissue. In collaboration with the laboratory of Professor Jeffrey Hubbell (Laboratory of regenerative Medicine & Phamacobiology, EPFL), we test synthetic biodegradable polymers, poly(ethylene glycol)(PEG)-based hydrogels, that mimic characteristics of natural extracellular matrices (Lutolf & Hubbell 2003). The polymer is first reacted with cell adhesion peptides, and then formed by cross-linking with peptides that bear cleavage sites for matrix metalloproteinases (MMPs).

We found that with addition of growth factors (EGF and FGF2) and cell adhesion peptides (RGD and/or laminin), radial glia RSCs can survive and proliferate in these 3-dimensional hydrogels. They maintain the expression of Nestin (a neural progenitor cell marker) and Pax6 (a regulator of eye development and RPC proliferation). Our result also showed possibility to differentiate RSCs into retinal neurons. Together, these results are the beginning of potential generation of an enriched biosynthetic tissue of cells committed to the photoreceptor fate that can be used for transplantation studies.

10.08.10