Chapter 4In oculo transplantation studies involving the neural retina and its pigment epithelium

Mechanical injury increases bFGF and CNTF mRNA expression in the mouse retina

We characterized the survival-factor response of the normal mouse retina to mechanical injury by examining the expression of mRNAs for basic fibroblast growth factor (bFGF), ciliary neurotrophic factor (CNTF), and their receptors, FGF receptor-1 (FGFR-1) and CNTF receptor alpha (CNTFR-alpha). The retina was injured by making an incision through the choroid and retinal pigment epithelium that penetrated the subretinal space of each eye of an adult BALB/c mouse. Retinas were taken 6 hr, 12 hr, 1, 2, 4, 7, 10 and 16 days post-injury. Control animals were without injury. Northern blot analysis was performed to determine bFGF, CNTF and their receptor mRNA levels. A significant increase in bFGF and CNTF mRNAs was observed after injury, along with an increase in glial fibrillary acidic protein (GFAP) expression. More than 2-fold of upregulation of bFGF mRNA was seen as early as 6 hr after injury. This increase reached a maximum of more than 5-fold at day 2 post-injury and then declined slowly, and was still about 2.5-fold of the control level by day 16. Expression of CNTF showed a small increase of about 1.6-fold at 6 hr after injury. The upregulation reached a peak level of about 2.7-fold at day 4 after injury, then declined to control level by day 16. There was only a very small increase in FGFR-1 at 6, 12 and 24 hr after injury, and no significant increases in FGFR-1 at time points longer than 1 day post-injury. Expression of GFAP followed a time course similar to that of bFGF. We conclude that mechanical injury induces bFGF, CNTF, and GFAP expression in the mouse retina with time courses similar to the upregulation of these molecules in rat retina. Compared to the upregulation in rat retina, however, the injury-induced upregulation of bFGF and GFAP is much less in the mouse retina. In addition, there was only a very small induction of FGFR-1 expression in the mouse retina. These findings may explain, at least in part, the lack of injury-induced photoreceptor protection in the mouse retina.

Neurophysiology of central retinal degeneration in cat

Receptive fields of ganglion cells have been studied in cats possessing a chronic, arrested lesion of central retinal degeneration. Lesions were characterized by an ophthalmoscopically sharp border separating apparently normal retina from the region of the lesion. Under direct ophthalmoscopic guidance, a succession of recordings was obtained from ganglion cells having cell bodies at various positions relative to the lesion. Cells located more than 1 deg outside the ophthalmoscopic border had normal visual sensitivity as assessed by area-threshold experiments. Inside the lesion cells within 1 deg of the border had reduced sensitivity which often precluded functional classification by the usual visual tests. Ganglion cells located more than 1 deg inside the border of large lesions were blind and some had abnormal patterns of maintained discharge of action potentials. Nevertheless, the antidromic latencies of these blind cells fell into the familiar conduction groups (T1/T2/T3). Receptive-field maps of cells near the border of the lesion often appeared truncated, with the missing portion of the field covered by the lesion. These observations were consistent with the abnormal form of area-threshold curves. Although the responsiveness of cells near the lesion was abnormally low for grating stimuli, cutoff spatial frequency and orientation bias of these cells were within normal limits.

Maintenance of opsin and S-antigen gene expression in RCS dystrophic rats following RPE transplantation

The effects of retinal pigment epithelium (RPE) transplantation in rescuing photoreceptor cells (PRC) were studied in RCS rats bearing the rdy mutation. RPE preparations from Long-Evans rats were transplanted into the subretinal space of post-natal (P) 17-19-day-old RCS rats. Age-matched RCS animals in the control group received injections of the transplantation vehicle buffer alone. The animals were killed at various post-natal ages after RPE transplantation. Immunocytochemical studies using antibodies to opsin and S-antigen indicated intact photoreceptor cells in the transplanted retinas. In contrast age-matched sham-injected animals did not show any rescue of photoreceptor cells at P90. Single RPE transplantation of 60,000 cells in each eye resulted in restoration of near normal mRNA levels for opsin, and S-antigen proteins. Comparisons of mRNA levels of two visual proteins using cDNA probes demonstrated a therapeutic effect of RPE transplantation in preventing a progressive decline in mRNA levels due to retinal degeneration. In contrast, P109 sham-injected controls showed no detectable mRNA levels for these proteins. In vitro protein synthesis in RPE-transplanted retinas implied further competence of these retinas. These data suggest that RPE transplantation not only rescues photoreceptors from degeneration, but more importantly, it allows normal transcription and translation in these cells rendering them capable of participating in the visual and signal transduction cascade.

Effects of macrophage and retinal pigment epithelial cell transplants on photoreceptor cell rescue in RCS rats

The effects of macrophage transplants on photoreceptor cell survival in retinas of Royal College of Surgeons (RCS) dystrophic rats were contrasted with RPE-cell transplants, sham-injection and surgical controls. The effects of these different treatments on the thickness and total area of the outer nuclear layer (ONL) were evaluated by light and electron microscopy at 1, 2 and 5 months after transplantation or surgical manipulations. Macrophage transplants into dystrophic retinas, although significantly reducing the debris zone thickness (p less than 0.01), had little effect on photoreceptor cell survival (2-3 cells thick ONL) after two months. In contrast, two months after RPE-cell transplantation, retinas exhibited an 8-10 cell thick ONL. Also, inner and outer segments of rescued photoreceptor cells were present, especially in areas directly beneath RPE-cell transplants. At the same time period, retinas injected with saline had a 2-3 cell thick ONL with no organized inner or outer segments. Furthermore, the affected ONL area in macrophage-transplanted or saline-injected retinas was significantly smaller than that seen in RPE-cell transplanted retinas (p less than 0.0001). Surviving photoreceptor cells were found only in the RPE-cell transplanted retinas five months after treatment. No effect on photoreceptor cell survival was seen in saline-injected, needle-inserted or incision-only retinas. Thus, transplantation of healthy RPE cells is an effective long-term therapeutic approach to correct the genetic defect in retinas of RCS dystrophic rats.

Transplantation to the diseased and damaged retina

Retinas of Royal College of Surgeons (RCS) dystrophic rats undergo a dramatic loss of photoreceptor cells as a result of defective retinal pigment epithelial (RPE) cells. These retinas are therefore a valuable model in the investigation of the role of the RPE on photoreceptor-cell survival and development. Also, rat retinas damaged by excessive light serve as a suitable environment to study survival of transplanted photoreceptor cells. Even though photoreceptor cells are lost in these retinas, a normal inner retinal structure is retained. Both models have recently been used in successful RPE-cell and/or photoreceptor-cell transplantation studies designed to replace defective or lost cells due to retinal disease or damage. These new approaches in the field of retinal transplantation offer unique and novel opportunities for the development of possible therapeutic strategies in human eye disease, and for improving our understanding of the normal relationships between retinal cells.

Optimal conditions for long-term photoreceptor cell rescue in RCS rats: the necessity for healthy RPE transplants

Retinal pigment epithelial (RPE) cells from normal Long-Evans, healthy Royal College of Surgeons (RCS) pigmented congenic (rdy+p+) and RCS pigmented dystrophic rats were transplanted into retinas of RCS non-pigmented dystrophic rats at post-natal days 17 and 26 (P17 and P26). When examined at P60, rescued photoreceptor cells were found in all transplanted groups. In addition, a small, but significant increase in the outer nuclear layer (ONL) thickness was detected in retinas injected with vehicle (sham control); however, the ONL thickness was reduced to control levels by 3-5 months after injections in both the sham controls and the group grafted with RCS pigmented dystrophic RPE cells. Likewise, large volumes of vehicle were injected into the subretinal space resulting in no long lasting beneficial effects. Also, there was no significant difference between the ONL thickness in retinas grafted with RCS congenic RPE and those grafted with Long-Evans RPE. When donor RPE cells from Long-Evans rats at neonatal and adult stages were transplanted into P26 RCS hosts, photoreceptor cell rescue could be found; however, the younger RPE cells affected a better rescue than those derived from adult eyes. In addition, when RPE cells from 6- to 9-day-old Long-Evans rats were transplanted into retinas of RCS dystrophic rats at 10, 17 and 26 days, significant rescue of photoreceptor cells was observed. Of these transplantation times, day 17 appeared to affect the best rescue of photoreceptor cells up to 1 yr. In contrast, little or no rescue was observed in the retinas of those RCS dystrophic rats when RPE cell transplantation was performed at P38, P43 and P48. The photoreceptor cell rescue was also found to be dependent on the concentration of RPE cells injected, which was maximal at 60,000-120,000 cells microliters-1. These findings lead us to conclude that in order to affect long-term, up to 1 yr, rescue of photoreceptor cells in the RCS rat, young, healthy RPE cells are required and transplantation needs to be performed at early stages of the disease process.