Behaviour of Retinal Precursor Cells Transplanted into the Subretinal Space of Normal and Degenerated Adult Mouse Retina

Abstract

Abstract: : Purpose: In order to reveal whether expanded retinal precursor cells (RPCs) can integrate a degenerated retina we transplanted RPCs in 8 month old VPP transgenic mice that mimic human Retinitis Pigmentosa and in C57/Bl6 control mice. Methods: Up to 75’000 RPCs expanded in vitro and labelled with the PKH26 dye, isolated from DBA2J newborns, were injected into the subretinal space of adult C57/Bl6 and VPP eyes without any immunosuppression. We analysed the eye slices by microscopy and immunohistochemistry after different post–transplantation times. Results: Although the injection is allogenic, no immuno–reaction has been observed and 100% of the animals survived. The injected cells covered an area of up to 10% of the total retina. Only 6% of the transplanted cells die postinjection. Cell migration was observed only in damaged areas and rare cells differentiated into neurons. In comparison to wild–type mice, transplanted retinas of VPP mice show greater migration. RPCs have a tendency to align themselves in the GCL, instead of the site where degeneration occurred, which is not the case in control mice injected with living or dead cells. Moreover these cells are in some cases positive for a ganglion cell marker, NeuN. Positive cells for NeuN were also observed in rare events in healthy retinas. It seems that RPCs have a propensity to commit to the ganglion cell phenotype. On the other hand, no recoverin positive cells were observed in either retina type, suggesting that the microenvironment in late stages of degeneration do not confer appropriate conditions to induce photoreceptor differentiation.. Conclusions: Few grafted cells can migrate into the various layers of a healthy retina. In VPP retinas the migration is remarkably enhanced, but surprisingly the cells align themselves in the GCL. This behaviour may suggest that the degeneration also affects the GCL. Further experiments are needed to confirm either that the RPCs converge where the degeneration occurs at the moment of injection or that the cells used cannot differentiate into photoreceptors due to the stress of the microenvironment, thus indicating that more differentiated cells are needed.

Keywords: retina • transplantation • ganglion cells