Purpose: To evaluate the neuroprotective potential of glial cell line-derived neurotrophic factor (GDNF) in the retinal degeneration (rd/rd) mouse model of human retinitis pigmentosa.
Methods: Subretinal injections of GDNF were made into rd/rd mice at 13 and 17 days of age and electroretinograms (ERGs) recorded at 22 days. Control mice received saline vehicle injections or underwent no procedure. At 23 days of age, retinas from treated and control mice were fixed and processed for wholemount immunohistochemistry using an anti-rod opsin antibody, and rod numbers were estimated using an unbiased stereological systematic random approach. Subsequent to counting, immunolabeled retinas were re-embedded and sectioned in a transverse plane and the numbers of rods recalculated.
Results: Although ERGs could not be recorded from sham-operation or nonsurgical rd/rd mice at 22 days of age, detectable responses (both a- and b-waves) were observed in 4 of 10 GDNF-treated mice. Stereological assessment of immunolabeled rods at 23 days showed that control rd/rd retinas contained 41,880+/-3,890 (mean +/- SEM; n = 6), phosphate-buffered saline (PBS)-injected retinas contained 61,165+/-4,932 (n = 10; P < 0.001 versus control retinas) and GDNF-injected retinas contained 89,232+/-8,033 (n = 10; P < 0.001 versus control retinas, P < 0.002 versus PBS). This increase in rod numbers after GDNF treatment was confirmed by cell counts obtained from frozen sections.
Conclusions: GDNF exerts both histologic and functional neuroprotective effects on rod photoreceptors in the rd/rd mouse. Thus rescue was demonstrated in an animal model of inherited retinal degeneration in which the gene defect was located within the rods themselves, similar to most forms of human retinitis pigmentosa. GDNF represents a candidate neurotrophic factor for palliating some forms of hereditary human blindness.