Yoko Saigo

Protection of photoreceptor cells from phototoxicity by transplanted retinal pigment epithelial cells expressing different neurotrophic factors.

Transplantation of cells or tissues and the intravitreal injection of neurotrophic factors are two methods that have been used to treat retinal diseases. The purpose of this study was to examine the effects of combining both methods: the transplantation of retinal pigment epithelial (RPE) cells expressing different neurotrophic factors. The neutrophic factors were Axokine, brain derived-neurotrophic factor (BDNF), and basic fibroblast growth factor (bFGF). The enhanced green fluorescence protein (eGFP) gene was used as a reporter gene. These genes were transduced into RPE cells by lipofection, selected by antibiotics, and transplanted into the subretinal space of 108 rats. The rats were examined at 1 week and 3 months after the transplantation to determine whether the transduced cells were present, were expressing the protein, and were able to protect photoreceptors against phototoxicity. The survival of the transplanted cells was monitored by the presence of eGFP. The degree of protection was determined by the thickness of the outer nuclear layer. Our results showed that the degree of photoreceptor protection was different for the different types of neurotrophic factors at 1 week. After 3 months, the number of surviving transplanted cell was markedly reduced, and protection was observed only with the BDNF-transduced RPE cells. A significant degree of rescue was also observed by BDNF-transduced RPE cells in the nontransplanted area of the retina at both the early and late times. Lymphocytic infiltration was not detected in the vitreous, retina, and choroid at any time. We conclude that the transplantation of BDNF-transduced RPE cells can reduce the photoreceptor damage induced by phototoxicity in the transplanted area and weakly in the nontransplanted area.

Limited Neural Differentiation of Retinal Pigment Epithelium

The retinal pigment epithelial (RPE) cell shares its origin with the neural retina as an anterior neural plate derivative. Recently RPE cell was reported on its capacity of transdifferentiating into a neuron-like cell in mammals.2,2 Neurotrophic factors have reported to play essential roles. Some of these factors are basic fibroblast growth factor (bFGF) for transdifferentiation of RPE into neural cells2,3 or epithelial growth factor (EGF) for proliferation of neural progenitor cells.4

Transgenic rd mice harboring axokine gene by Rpe65 gene promoter does not rescue photoreceptor degeneration.

Neurotrophic factors have reported to rescue photoreceptor degeneration in dystrophic rats (Faktorovich et al., 1990), and variable strains of mice showing hereditary photoreceptor degeneration (LaVail et al., 1998). Axokine is a modified form of human CNTF to enhance its specific activity (Panayotatos et al., 1993) and its signaling pathway is reported in retinal neurons and glia via CNTF receptor (CNTFRa) (Peterson et al., 2000). In this study, we introduced Axokine gene in rd/rd mice, a mice reported to have mutation in s subunit of phosphodiesterase (PDE) gene (Pittler and Baehr, 1991) and examined its effect for retinal degeneration. The Axokine gene was introduced into retinal pigment epithelium (RPE) by Rpr65 promoter, which has acitivity of RPE specific expression