Photoreceptor Transplantation In The Degenerating Retina: Breadth Of Application And Manipulation Of The Microenvironment To Enhance Efficiency

Abstract

Purpose: : Photoreceptor transplantation offers the potential to replace cells lost during disease. We investigated transplanted photoreceptor efficiency in several models of retinal degeneration to examine the breadth of application of this therapy. We examined how disease type and stage affects the formation of outer segments and synapses by transplanted cells. The microenvironment of the degenerating recipient retina was assessed and selectively modulated to enhance integration.

Methods: : FACS-sorted Nrl.GFP+ rod precursor cells were transplanted into 6 mouse models of retinal degeneration (rho-/-, Crb1rd8/rd8, Prph2rds/rds, Prph2+/Δ307, PDE6βrd1/rd1, Gnat1-/-) at different disease stages and assessed 3wks post-transplantation. Glial scarring, outer limiting membrane (OLM) integrity and ONL thickness and density were assessed using immunohistochemistry, western blot and EM. ChABC and siRNA were used to modulate the glial scar and OLM respectively.

Results: : Integration efficiency was significantly influenced both by disease type and disease progression; integration efficiency was significantly higher in Crb1rd8/rd8 recipients and lower in rho-/- recipients compared to wildtype. Significant differences in transplanted photoreceptor outer segment and synapse formation frequency were observed between recipient models. Disease progression differentially affected integration efficiency, with integration decreasing (Gnat1-/-, Crb1rd8/rd8, rho-/-) increasing (Prph2+/Δ307) or remaining stationary (C57BL/6, Prph2rds/rds PDE6βrd1/rd1). Degeneration rate, ONL thickness and density did not correlate with integration success. However, marked changes in glial scaring and OLM integrity were observed and disruption of these factors, using ChABC and siRNA targeted against ZO-1 respectively resulted in increased integration efficiency.

Conclusions: : Disease type and stage have a major impact on transplantation success. We demonstrate that the success of photoreceptor transplantation is heterogenic and that some disease types may be more amenable to cell therapy than others. Large numbers of integrated photoreceptors can be achieved when treating end stage disease in some models. Importantly, where integration efficiency is impaired, a tailored manipulation of the microenvironment can boost integration success.

Keywords: transplantation • photoreceptors • degenerations/dystrophies