Transplanted photoreceptors exchange proteins to host photoreceptors via neurites

Abstract

Purpose : We and others recently reported that transplantation of immature photoreceptors to the adult retina results in reciprocal cytoplasmic protein exchange (material exchange, ME) between transplanted and recipient photoreceptors. Our work aims to define the kinetics and investigate the cellular and molecular mechanisms that regulate this process in transplanted mammalians retinas.

Methods : Transplantations were performed using multiple transgenic donor and recipient models and ME was analyzed at various time-points (3 days to 5 months). Morphology of the transplanted cells and their interaction with the host photoreceptors was analyzed by electron, confocal, light sheet and 2-photon microscopy. A combination of genetic and acute lentiviral gene delivery was used to identify cellular structures and signaling pathways that regulate ME.

Results : The onset of ME coincides with resolution of the surgically-induced retinal injury and persists for several months, indicating that acute transplant-associated death is not a major mechanism of ME. Although donor cells continue to survive, ME is dramatically reduced by 3 months post-transplant, suggesting that transferred material is labile and that ME is a transient process. ME was not enchanced by transplantation of photoreceptors that over produce extracellular vesicles (EV) and was insensitive to pharmacologic inhibition of EV biogenesis and secretion pathways, indicating that EV-mediated transfer is not the major mechanism of ME. Morphological and mechanistic analysis shows that ME requires contact between donor and host cells, and is partially dependent on the neurite outgrowth capacity of the transplanted photoreceptors. Finally, we show that ME is cell specific and involves nuclear, cytoplasmic and membrane proteins.

Conclusions : Material exchange requires cytoplasmic bridges provided by neurites between the transplanted and recipients photoreceptor. The understanding of the mechanisms of material transfer could provide a means to modulate the donor cells and/or the host retina to promote visual rescue in degenerating retinas and could ultimately provide insight on the safety of therapeutic interventions and re-development of current approaches.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.