Abstract
Abstract: :
Purpose: To demonstrate engraftment and differentiation of adult neural progenitor cells (NPCs) in an optic nerve (ON) crush model of ganglion cell injury and a model of chronically-elevated IOP. Methods: A well-characterized source of NPCs derived from the adult rat hippocampus and expressing GFP (gift of Dr. F. Gage) was used. ON crush was made by approaching the ON from the orbit through a conjunctival incision along the superior fornix and crushing it at a distance of 4-5 mm from the posterior pole for 30 seconds using small suture tie forceps. Alternatively, to establish chronically-elevated IOP, three episcleral veins were severed by a standard cautery. At various times following ON crush or episcleral vein cautery, dissociated NPCs (3 ml of 5×103- 5×104 cells) were transplanted into the subretinal space using a trans-scleral approach. Some animals also received subretinal delivery of sustained-release BDNF microspheres (100ng/ml). Rats were allowed to recover for 2-6 wk, at which times they were sacrificed. Eyes were removed, and retinas were cryosectioned for analyses. Sections were stained for retinal cell type-specific markers including rhodopsin, recoverin, PKC, calbindin, calretinin, parvalbumin and Thy1.1, using the appropriate Cy3-conjugated secondary antibody. Results: Successful ON crush was achieved with intact retinal blood flow. Following episcleral vein cautery, the IOP remained elevated for at least 6wk (26 ± 3.9 mmHg) compared to the fellow eyes (18.7 ± 3.7 mmHg). In both injury models, by 2 wk post-transplant, numerous GFP-expressing cells had engrafted into the host retina, migrated to the inner retina and extended processes. At 4-6 wk, many GFP-expressing cells were present throughout the INL and displayed horizontal-, bipolar- and amacrine cell-like morphologies. GFP-expressing cells were also present in the GCL with fibers that extended into the NFL. In some rats, GFP-expressing fibers were also present in the ON. In rats co-transplanted with sustained-release BDNF microspheres, we observed that GFP-expressing cells appeared more differentiated, extending longer, more-varicose processes; also some GFP-expressing cells in the GCL co-localized with Thy1.1. Conclusions: NPCs transplanted to the subretinal space readily engraft into a host retina that has undergone ON crush or episcleral vein cautery. Cells migrate to specific retinal layers and undergo morphological differentiation reminiscent of retinal neurons. Furthermore, concomitant sustained release of BDNF appears to enhance the differentiation of transplanted cells.
Keywords: transplantation • intraocular pressure • ganglion cells