Survival and Axonal Regeneration of Retinal Ganglion Cells in a Mouse Optic Nerve Crush Model After a Cell-Based Intravitreal Co-Administration of Ciliary Neurotrophic Factor and Glial Cell Line-Derived Neurotrophic Factor at Different Post-Lesion Time Points.

We recently showed, in a mouse optic nerve crush model, that a sustained cell-based intravitreal administration of ciliary neurotrophic factor (CNTF) and glial cell line-derived neurotrophic factor (GDNF) synergistically slowed the lesion-induced degeneration of retinal ganglion cells (RGCs), resulting in the presence of approximately 35% viable RGCs eight months after the lesion. However, the combinatorial neuroprotective treatment was initiated shortly after the lesion. To mimic a more clinically relevant situation, we co-administered both factors either three or five days after an intraorbital nerve crush when approximately 35% or 57% of the RGCs were degenerated, respectively. Analyses of the retinas at different time points after the lesion consistently revealed the presence of significantly more surviving RGCs in retinas co-treated with CNTF and GDNF than in retinas treated with either factor alone. For example, when the neurotrophic factors were administered five days after the nerve crush and the animals were analyzed two months after the lesion, retinas co-treated with CNTF and GDNF contained approximately 40% of the RGCs present at the start of treatment. In comparison, monotherapy with either CNTF or GDNF protected only about 15% or 10% of the RGCs present at baseline, respectively. The number of regenerating axons in the distal nerve stumps was similar in CNTF- and CNTF/GDNF-treated animals, despite the significantly higher number of rescued RGCs in the latter group. These findings have potential implications for studies aimed at developing neuroprotective treatments for optic neuropathies such as glaucoma.