Stem cells as tools in regenerative therapy for retinal degeneration

Abstract

Objective: To describe the use of stem cells (SCs) for regeneration of retinal degenerations. Regenerative medicine intends to provide therapies for severe injuries or chronic diseases where endogenous repair does not sufficiently restore the tissue. Pluripotent SCs, with their capacity to give rise to specialized cells, are the most promising candidates for clinical application. Despite encouraging results, a combination with up-to-date tissue engineering might be critical for ultimate success.

Design: The focus is on the use of SCs for regeneration of retinal degenerations. Cell populations include embryonic, neural, and bone marrow-derived SCs, and engineered grafts will also be described.

Results: Experimental approaches have successfully replaced damaged photoreceptors and retinal pigment epithelium using endogenous and exogenous SCs.

Conclusions: Stem cells have the potential to significantly impact retinal regeneration. A combination with bioengineering may bear even greater promise. However, ethical and scientific issues have yet to be solved.

Figure 1. Population of CD45⁻ TCSC

(A) Hierarchy of stem cell development and potential under physiological () and culture () conditions. (B) Rare events cell sorting is a useful tool to select candidate stem cell populations. TCSC are Sca-1⁺/CD45⁻/lin⁻ as shown.

Figure 2. Expression of RPE markers RPE-65 and MITF

Autofluorescence in flat mount whole eye preparations of control (D) and NaIO₃ treated mice (A – C and E, F). The top row (A – C) compared different doses of NaIO₃ at 7d post injection (PI): (A) 35 mg/kg, (B) 50 mg/kg, and (C) 70 mg/kg body weight. E, B and F compare different times PI at the same dose (50 mg/kg): (E) 3d PI; (B) 7d PI; and (F) 21d PI. Beginning on 3d PI a patchy loss of RPE can be detected by the decrease in autofluorescence (black areas). The total area bare of RPE (autofluorescent areas) is dose dependent and increased over time (magnification 1,000×).

Figure 3. Immunocytochemical staining of vertical sections of a GFP chimeric mouse eye four weeks after NaIO₃ treatment and BMC mobilization

GFP⁺ BMC were stained with anti-GFP (green fluorescence) and anti-MITF (red fluorescence). The merged Nomarski image shows a monolayer of MITF⁺ GFP⁺ BMC (yellow) on Bruch’s membrane. The monolayer of BMC is adjacent to pigmented host RPE cells (arrows) outlined with white dashes.

Figure 4. Co-culture with RPE cells for two weeks leads to the expression of RPE-specific markers on sorted Sca-1⁺ BMSC

(A) GFP⁺ BMSC are stained with anti-RPE65 (Cy3 – red) and (B) with anti-GFP (green). (C) Cell nuclei are shown in blue (DAPI). Arrows indicate similar positions in the panels. (D) A merge of the top two panels is shown. Overlapping expression of red and green indicates BMSC that express RPE markers; red cells, which are not green, correspond to RPE cells in the co-culture.

Figure 5. Cross section of a mouse eye six weeks after NaIO₃ injection and i.v. transplantation of EGFP⁺ BMSC

The donor cells were stained with anti-GFP and anti-RPE-65. The panel shows a merged image combined with Nomarski optics to visualize the location in the subretinal space (scale bar = 5 µm). There is a cluster of cells with yellow fluorescence representing transplanted BMSC (arrow) that indicates co-localization of GFP (green fluorescence) and RPE-65 (red fluorescence). The remaining host RPE (asterisks) has been damaged by NaIO₃ treatment, as well as the sensory retina.