Purpose: To examine the protective effect of glial cell line-derived neurotrophic factor (GDNF) on retinal detachment (RD)-induced photoreceptor damage by using gene delivery.
Methods: Gene delivery to photoreceptors was achieved by subretinal injection of recombinant adeno-associated virus expressing GDNF (rAAV-GDNF) in the right eyes and AAV expressing Escherichia coli LacZ (rAAV-LacZ) in the left eyes of Lewis rats. RD in bilateral eyes was induced with subretinal injection of high-density vitreous substitute in the temporal retina 3 weeks after gene delivery. The synthesis and accumulation of GDNF within the retina was monitored 3 weeks after RD by immunohistochemistry and enzyme-linked immunosorbent assay (ELISA), respectively. The rescue of photoreceptors was evaluated by monitoring the preservation of the thickness of photoreceptor outer segment (OS) and outer nuclear layer (ONL). Apoptosis in the photoreceptors was studied using the TdT-dUTP terminal nick-end labeling (TUNEL) method 2 days after RD. Müller cell activity was checked using the immunohistochemistry with glial fibrillary acidic protein (GFAP) antibody 28 days after RD.
Results: Gene delivery was demonstrated by immunohistochemical study. The results of ELISA confirmed that high levels of neurotrophic factors were produced in retinas. Photoreceptor OS degeneration and the gradual shortening of the ONL were noted after RD in all the eyes. However, rAAV-GDNF-treated eyes retained longer OS than rAAV-LacZ-treated eyes 7 (P = 0.012) and 28 days (P = 0.008) after RD. ONL was also longer in rAAV-GDNF-treated eyes than in rAAV-LacZ-treated eyes 7 (P = 0.012) and 28 days (P = 0.008) after RD. GDNF-treated eyes had statistically less apoptotic cells than control eyes in photoreceptor layer (P = 0.043). Subretinal proliferation of Müller cells was suppressed in the GDNF-treated group, indicating less scar formation.
Conclusions: GDNF is a potential factor that can protect photoreceptors from degeneration. In addition to preserving the OS and ONL structures, GDNF may exert its protective action by preventing the apoptosis of photoreceptors after RD. GDNF gene therapy may be a valuable adjuvant to current treatments in certain complicated forms of RD.