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Vision Restoration with optogenetic tools

Final Report Summary - BLINDOPTOGEN (Vision Restoration with optogenetic tools)

Blindness is one of the most devastating conditions affecting the quality of life, especially in Europe. No treatment is known today for retinal degenerative diseases, such as retinitis pigmentosa or macular degeneration. They are hereditary diseases characterised by the progressive loss of photoreceptors, leading to complete blindness. Recent discoveries of optical neuromodulators, such as channelrhodopsin-2 (ChR2) or halorhodopsin (NpHR), have opened up new possibilities of treating these diseases by imparting light-sensitivity to the remaining retinal neurons after the photoreceptors have died. In a proof-of-concept study (Lagali et al., 2008), I have shown that this approach is feasible: we used a mouse model of retinal degeneration (rd1) and introduced ChR2 specifically in ON bipolar cells of the retina, upon which the animal regained retinal light responses, light-guided behaviour and form vision.

For this project BLINDOPTOGEN, I proposed to follow-up on this study and test several optogenetic strategies of treating blindness in animal models. These strategies included the use of different mouse models for retinal degeneration, and different optical neuromodulators to activate various cell types in the retina, in appreciation of the fact that degenerative diseases are very diverse and a single approach might not work for different conditions. It is hoped that, in the long run, this approach will lead to novel forms of treatment in humans, to alleviate the burdens of blindness of the affected individuals.

The success of vision restoration can be tested and quantified at many levels. The proper expression of the neuromodulator has to be tested and confirmed on the cellular level in the retina. The restored retinal functionality has to be evaluated at the circuitry and tissue level. And finally, on the level of behaviour, it has to be established if the animal regains visual guided behaviour and form vision.

In the European Reintegration Granr (ERG)-funded project BLINDOPTOGEN, I have mainly focused on two parts aspects:

1. Development of an enhanced virtual reality optikinetic drum

The optokinetic reflex manifests itself in an involuntary eye and head movement in response to global image drift. Such compensatory movement can be triggered by presenting a moving regular stripe pattern within a so-called optokinetic drum. An advantage of this reflex-based method is that vision can be tested without any reinforcement training. It has thus become an established method to assess visual performance by varying the parameters of the presented stripe pattern, such as contrast or stripe width. Our new setup ameliorates disadvantages of existing optokinetic drums. The main improvements are:

(1) flexibility of the presented stripe pattern, as we do not use a real rotating drum, but a virtual drum projected on screens surrounding the animal;
(2) automation of the scoring procedure.

All existing optokinetic drums depend on user assessment of the animal's behaviour. Our testing procedure is completely automated, thereby removing user bias from the results, shortening the time required for an experiment, reducing the stress on individual animals, and increasing the experimental throughput.

2. Develop methodology to test optogenetic treatment directly in human retina

Optogenetic treatment of blindness is an extremely fast moving field. The final goal will be to apply this new methodology to human patients. Consequently, a strong emphasis has been laid on testing optogenetic treatment directly in in-vitro human retina. I have set up a collabouration with the University Eye Hospital in Tübingen to receive donated retinal tissue. In the lab, we have successfully established the methodology to record light responses from freshly extracted human retina (leftover tissue from eye surgeries) and to keep fresh or post-mortem human retina in culture in order to transfect it with optogenetic neuromodulators. Preliminary results in this direction are highly promising.

In summary, the ERG-supported project BLINDOPTOGEN has focused both on basic as well as translational research to contribute to successful optogenetic treatment methods of blindness.

Contact details:

Thomas Münch
Retinal Circuits and Optogenetics
Werner Reichardt Centre for Integrative Neuroscience
Otfried-Müller-Str. 25, Room 3.530
72076 Tübingen
Tel: +49-(0)70-712989182