Abstract
Purpose :
Photoreceptor transplantation could be a future treatment for patients with retinal degeneration, however controversy exists over whether transplanted donor cells integrate or fuse with the host retina. Cell fusion – the merging of two separate lipid bilayer plasma membranes – results in the transfer of cytoplasmic contents, including organelles and proteins between fused cells, and occurs in development, homeostasis, disease and regeneration. We tested the hypothesis that cytoplasmic transfer occurs between donor photoreceptor precursors and mature host photoreceptors using an experimental model of heterologous photoreceptor transplantation.
Methods :
To study the occurrence of cytoplasmic transfer between donor and host photoreceptor cells, we transplanted fluorescence-activated cell sorted Nrl.GFP donor photoreceptor precursors into the subretinal space of adult host mice without retinal degeneration in which DsRed was expressed ubiquitously. We analyzed the co-localization of green fluorescent protein (GFP) and DsRed fluorescence 3 weeks following transplantation. We also computed the Manders overlap coefficient (MOC) to measure the co-distribution GFP and DsRed in perinuclear photoreceptor cytoplasm in the host outer nuclear layer (ONL).
Results :
We detected extensive cytoplasmic colocalization of DsRed and GFP in cells located in the host ONL. We found that 93.8 ± 4.1% (mean ± SEM, N = 3 eyes) of morphologically normal GFP+ photoreceptor cells in the host retina colocalised DsRed. The median MOC value was 0.9.
Conclusions :
The appearance of well-formed fluorescence-labeled donor photoreceptor cells in the host retina following transplantation is most commonly due to cytoplasmic transfer between donor and host retinal cells, instead of migration of donor cells into the host outer nuclear layer. These findings are consistent with donor-host cell fusion. The clinical consequences of photoreceptor fusion are currently unknown, however this mechanism may also be useful therapeutically.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.