Author:

Keywords:

Retina, Neuroprotection, Superior colliculus, Retinal ganglion cell, Optogenetics

Abstract:

Glaucoma is a neurodegenerative disease characterized by a progressive loss of the retinal ganglion cells (RGCs). The central brain targets of the RGCs are well-known to be important for the survival and activity of their retinal connections. To investigate this two-way connection between the brain and the RGCs as a neuroprotective strategy in glaucoma, a series of experiments was performed in which the major retinal projection in the mouse, the superior colliculus (SC), was optogenetically activated in an established experimental mouse glaucoma model. Optogenetic activation of the SC was performed via injection of an adeno-associated viral vector coding for the stable step-function opsin (SSFO). The SSFO is a channelrhodopsin 2 mutant with slow closing kinetics, thus facilitating prolonged neuronal activation. Transgene expression was shown to cover a large area of the SC. After optic fiber implantation, animals were subjected to the previously reported laser-induced ocular hypertension model (OHT), which induces glaucoma-like RGC loss. Starting one day before OHT induction, the experimental group received light stimulation twice daily until the animals were sacrificed at 14 dpi. Neuronal activation of the SC was validated via immunostaining for the immediate-early gene c-Fos and behavioral analysis. Activation of the SC is known to induce specific behavioral changes, such as turning, freezing and running, which were all observed upon repeated optogenetic stimulation. Behavioral changes lasted for 20 - 30 minutes, coinciding with the SSFO kinetics. Together, these data show that repeated optogenetic stimulation of the SC is possible. Following semi-automated quantification of RGCs on Brn3a-stained retinal flatmounts, the optogentically stimulated group showed an significant increase in RGC survival, with 91% (± 4% SEM, N=21) survival versus 75% (± 6% SEM, N=16) in the non-stimulated group, compared to untreated eyes. Our data clearly reveal that repeated stimulation of central brain targets can contribute to neuroprotection of RGCs. Ongoing work includes elucidation of a possible mechanism, with a focus on neurotrophins. In conclusion, these results unveil exciting new possible treatment paradigms for glaucoma and other optic neuropathies.