Abstract
Purpose: :
To investigate the fate of in vitro differentiated RSCs transplanted into a developing retina affected by retinal degeneration in order to characterize the potential of RSC–derived cells to integrate the photoreceptor layer.
Methods: :
RSCs were isolated from mice expressing GFP and expanded in EGF and FGF2 for an extensive period of time. After expansion, cells were differentiated into retinal cells in a two–step procedure to commit them to a photoreceptor fate, and then transplanted intravitreally into the eye of newborn Rho–/– mice (P0 – P3). Retinas were studied at different time–points after transplantation.
Results: :
Acquisition of the photoreceptor fate was ascertained by several parameters prior to transplantation. Although the majority of the transplanted cells, which were previously differentiated, remained in a cluster form in close contact with the ganglion cell layer (GCL) or the lens, some grafted cells have incorporated the GCL. This limited migration occurred early after injection. By 3 days post–surgery, incorporated cells presented complex arborescence with processes ending in the plexiform layer. By 5, 7, 14 and 30 days after injection, cells had not migrated deeper in the retina. In vitro, differentiated cells express specific retinal markers of photoreceptor, amacrine, and Müller cells and some of them retain the expression of nestin. However, after transplantation, the clusters of donor cells as well as incorporated cells do not express markers of retinal neurons. Cells integrated in the retina express preferentially GFAP which may reflect a differentiation process of the RSCs, which includes a transitional state, before acquiring neuronal fate, hypothesis that is under investigation. Nonetheless, a subpopulation of these GFAP–expressing cells expresses glutamine synthetase, a Müller cell specific marker.
Conclusions: :
Integrated cells clearly adopt ganglion cell–like morphologies but express GFAP instead of retinal ganglion cell markers. These results indicate that the cells differentiated into neurons in vitro may not survive transplantation procedure, unlike undifferentiated ones. It is thus important to improve RSC differentiation to obtain higher rates of photoreceptor production and the appropriate level of maturation in order to obtain a more homogeneous population to determine if these cells have the capacity to migrate and incorporate into the ONL.
Keywords: transplantation • retina • differentiation