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Johan Pahlberg, Tian Wang, Jon Cafaro, Greg Darian Field, Alapakkam P Sampath, Jeannie Chen; Analyses Of Retinal Circuits After Rod Rescue In A Mouse Model Of Human Blindness. Invest. Ophthalmol. Vis. Sci. 2016;57(12):604.
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© ARVO (1962-2015); The Authors (2016-present)
Many visual deficits result from the death of photoreceptors, and consequently rods have been major targets in therapeutic approaches for visual restoration. However, rod death is often followed by secondary changes in the inner retina. The extent to which this reorganization obstructs recovery following photoreceptor rescue is not known. Our goal is to determine the possible extent of structural and functional recovery in retinal signaling following the genetic rescue of rods.
We created a mouse model of retinal degeneration caused by loss of expression of the β-subunit of the cyclic nucleotide-gated (CNGβ1) channel. This genetic lesion can be corrected by tamoxifen (TM)-induced Cre recombinase that initiates CNGβ1 expression from the endogenous locus. To assess the structural and biochemical consequences of TM treatment, we used electron microscopy, immunocytochemistry and Western blots. To assess the functional restoration, we used the whole retina electroretinogram, suction electrode recordings, current-clamp recordings from individual rods and rod bipolar cells (RBC), and a large-scale multielectrode array (MEA) system for recordings from hundreds of ganglion cells.
Loss of CNGβ1 expression led to progressive retinal degeneration. The outer nuclear layer thickness decreased progressively as a function of age, reflecting a loss of rod cells. Changes in the outer plexiform layer, including a reduction of synaptic ribbons and less frequent appositions between ribbons and postsynaptic mGluR6 puncta indicated the structure of rod-to-RBC synapse was altered. TM treatment at 1 month halted rod cell death and restored outer segment lengths. It also rescued the structure of the rod-to-RBC synapse. Electrophysiological recordings from TM treated mice exhibited normal rod responses and robust RBC light responses, indicating normal rod function and a nearly full functional recovery of the rod-to-RBC synapse. Preliminary MEA data suggest that restoring CNGβ1 expression and rod function restores some aspects of RGC responses.
These data indicate that early CNGβ1 re-activation in a degenerated retina results in the rescue of rod photoreceptors and retinal circuitry both structurally and functionally. These studies will define a window of opportunity for therapeutic intervention and provide a foundation for future studies aimed at comprehensive treatment of retinal degeneration.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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