Abstract
Abstract: :
Purpose: To determine the extent of engraftment, migration and differentiation of adult neural stem cells transplanted into the subretinal space following transient retinal ischemia. Methods: These studies used a well-characterized source of neural progenitor cells derived from the adult rat hippocampus and labeled with GFP (gift of Dr. F. Gage). Retinal ischemia was induced under visual control by insertion into the anterior chamber of a 30 G needle attached to an i.v. saline drip and raising the intraocular pressure for 90-120 min. Some animals then received subretinal transplantation of a suspension of GFP-labeled cells (10 µl of 1.5 X 107 cells/ml) via a trans-scleral approach. Rats were allowed to recover for 6 hr-4 wk, at which times they were perfused with 4% PFA. Eyes were removed, and retinas were cryosectioned for analyses. Sections from untransplanted retinas underwent TUNEL analysis to determine the time course of ischemic cell death. Sections from transplanted retinas were stained for retinal cell type-specific markers including rhodopsin, recoverin, PKC, calbindin, calretinin or parvalbumin, using the appropriate Cy3-conjugated secondary antibody. Results:TUNEL revealed that ischemic cell death peaked at 24 hr. By 72 hr the inner nuclear layer (INL) and ganglion cell layer (GCL) were obliterated in central retina, sparing far peripheral regions. In transplanted rats, by 2 wk numerous GFP-labeled cells had engrafted into the host retina and formed a mass in the outer retina. In addition, some cells had migrated to the inner retina and extended processes. This was especially apparent near the graft margins. At 3 and 4 wk post-transplant, many GFP-labeled cells were present at various strata of the INL and displayed morphological characteristics of horizontal, bipolar and amacrine cells. GFP-labeled cells were also present in the GCL, and numerous labeled fibers were seen in the nerve fiber layer, approaching the optic nerve head. In double label studies, however, no GFP-labeled cells were observed to express retinal phenotypic markers. Conclusion:Adult neural progenitor cells transplanted to the subretinal space are readily engrafted into a host retina which has undergone ischemic injury. In addition, many cells migrate to specific retinal layers where they undergo morphological differentiation to resemble known populations of retinal neurons. These studies suggest that certain developmental cues are recapitulated following injury, and they demonstrate the potential utility of adult stem cell transplantation for retinal neurodegenerative disease.
Keywords: 448 ischemia • 607 transplantation