Use of SyCatCh for the restoration of light signals in the retina of mice with photoreceptor degeneration

• Applicant: Dr. Michaela Fuchs
• Subject Area: Cognitive, Systems and Behavioural Neurobiology
• Term: from 2014 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 267355644

The retina is the first stage in the processing of light signals in the visual system. Highly specialized light-sensing neurons, the rod and cone photoreceptors, convert light into neural signals and transmit these to the post-receptoral retinal network. The retina performs considerable processing and filtering of the visual information before these signals are transmitted to the higher visual centers in the brain.Many retinal degenerative diseases involve the degeneration of photoreceptors and often lead to complete blindness. The prevention of vision loss or even the restoration of visual function are important goals in vision research. A promising strategy for the restoration of vision is optogenetics, which involves the introduction of genes encoding light-sensitive proteins (like channelrhodopsins) into neurons downstream of the photoreceptors. Upon light stimulation, these proteins generate electrical signals in neurons which are not intrinsically light-sensitive.The rd1 mouse is a widely used model of early onset retinal degeneration. It was previously demonstrated that expression of channelrhodopsin-2 in inner retinal cells of these mice can restore photosensitivity at the retinal and cortical level, proving the potential use of optogenetics in the restoration of vision. However, very high light intensities were needed for stimulation, which could ultimately cause photodamage to the retina. This might be overcome by using genetically engineered variants with altered properties.Our aim is to test a new optogenetic strategy for restoring light-sensitivity to the retinal circuitry following photoreceptor degeneration. This strategy is based on specifically controlling synaptic activity by light, by virally introducing the light-activated calcium channel CatCh into synaptic terminals of ON bipolar cells.Stimulation with blue light should lead to an influx of calcium ions and directly result in vesicle fusion at the highly specialized bipolar cell ribbon synapse, both of which we will measure using genetically encoded reporters of synaptic activity in combination with multiphoton imaging. We will use electrophysiological recordings with multi-electrode arrays to test whether the light signals are transmitted to the ganglion cells to generate spikes. All this will tell us directly how well CatCh expression in ON bipolar cells restores synaptic transmission in the retina of rd1 mice. We will test whether the light signals are transmitted to the higher visual centers in the brain by measuring optomotor responses and by imaging neural activity in the visual cortex.With our approach we will hopefully be able to restore visual function in mice with photoreceptor degeneration. We think that using CatCh will require significantly reduced light levels for activation of ON bipolar cells in comparison with previously used channelrhodopsins, thereby eliminating the concern that high intensity light induces photodamage in the retina.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom
• Host: Professor Dr. Leon Lagnado