Generation of New Cone and Rod Photoreceptors in Models of Retinal Degeneration by Transplantation of Crx-Positive Precursor Cells

Abstract

Purpose: : The irreversible loss of photoreceptors during retinal degeneration is a leading cause of blindness in the developed world. Repair of such damage by retinal cell therapy may be a feasible treatment option, as transplanted rod precursor cells have been shown to integrate into diseased retinae and restore some visual function. As human vision is cone dependent, we investigated the competency of early photoreceptor precursors to give rise to both rod and cone photoreceptors after transplantation into mouse models of retinal degeneration.

Methods: : Crx (cone-rod homeobox), a key regulator of vertebrate photoreceptor development, is expressed in post-mitotic rod and cone cells. Immature photoreceptors expressing a Crx.gfp transgene were isolated from embryonic and postnatal retinae by flow cytometry. GFP⁺ cells were transplanted sub-retinally in adult wildtype and degenerating retinae (RetGC1^-/-, Crb1^rd8/rd8; models of Leber’s congenital amaurosis). Three weeks after transplantation, GFP⁺ photoreceptors in the recipient outer nuclear layer (ONL) were counted and cones identified by immunohistochemistry for RxR_gamma and cone arrestin.

Results: : Crx⁺ precursors efficiently integrated into wildtype and degenerating retinae. The transplanted Crx.gfp cells acquired mature photoreceptor morphologies in the ONL of the recipient retina. Whilst the majority of integrated cells adopted a rod fate, a proportion of embryonic donor cells developed into cone photoreceptors. These cone cells displayed characteristic features (cone pedicles, nuclear structure, position within ONL) and expressed RxR_gamma and cone arrestin. A significant increase in cone integration efficiency was observed after transplantation in the cone-deficient RetGC1^-/- retina.

Conclusions: : Embryonic Crx.gfp donor cells develop into cone and rod photoreceptors after transplantation into the adult wildtype and degenerating retina.

Keywords: retina • photoreceptors • transplantation