Survival and Axonal Regeneration of Retinal Ganglion Cells in a Mouse Optic Nerve Crush Model After a Delayed Cell-Based Intravitreal Co-Therapy with Ciliary Neurotrophic Factor and Glial Cell Line-Derived Neurotrophic Factor

Abstract

Preclinical studies aimed at preserving retinal ganglion cells (RGCs) under pathological conditions are crucial to finding a cure for optic neuropathies, especially for preventing the progressive RGC death in primary open-angle glaucoma, a globally prevalent disease. This dissertation focused on a cell-based neuroprotective strategy using previously established lentivirally modified clonal neural stem cell (NSC) lines stably overexpressing the neurotrophic factors (NTFs) ciliary neurotrophic factor (referred to as CNTF-NSCs) or glial cell line-derived neurotrophic factor (referred to as GDNF-NSCs). An NSC clone without NTF overexpression was used for control experiments (referred to as control-NSCs). CNTF-NSCs and GDNF-NSCs were intravitreally injected either separately or as a 1:1 mixture (referred to as CNTF/GDNF-NSCs) into a mouse optic nerve crush model. The impact of the treatments on RGC survival was analyzed 14, 28 and 56 days post-lesion (dpl). Axonal regeneration was investigated 28 dpl. While the majority of preclinical studies have started neuroprotective treatments at or even before the time the degeneration of RGCs was induced, glaucoma is usually diagnosed late when the patients experience visual impairment due to a significant loss of RGCs. To more closely mimic the patients’ situation, we therefore injected the NTF-overexpressing NSCs 3 or 5 days after an intraorbital nerve crush when 25% and 57% of the RGC population were already lost, respectively. Both CNTF and GDNF are considered to be potent NTFs for RGCs, and intravitreal administration of CNTF is currently being tested as a potential treatment for glaucoma in clinical trials. However, in the present study, we found that monotherapies with either NTF resulted in only limited RGC survival when treatments were started at advanced stages of RGC loss. In contrast, co-administration of CNTF and GDNF promoted RGC survival in a synergistic manner, and rescued a significant fraction of injured RGCs from cell death. Despite the markedly higher number of surviving RGCs in retinas treated with CNTF/GDNF-NSCs, axonal regeneration was not improved compared to retinas treated with CNTF-NSCs alone. Together, the results indicate that combinatorial neuroprotective treatments merit further research to ultimately establish effective treatments for currently incurable optic neuropathies. The second publication (Part 3, page 45) reviewed recent preclinical studies that aimed to rescue RGCs under pathological conditions and to stimulate axonal regeneration using cell-based neuroprotective strategies, with a focus on cell-based combinatorial neuroprotective approaches.