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Jesse Peterson, Amitavo Mitra, Minzhong Yu, Edward Dudek, Jinsong Yang, Neal Peachey, Janis Lem; Regulation of Synaptic and Gap Junctional Proteins in the Retina by Rhodopsin-Regulated Protein Kinase D. Invest. Ophthalmol. Vis. Sci. 2013;54(15):699.
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Protein kinase D (PKD) in the retina forms complexes with α-catenin, β-catenin and cadherin in a rhodopsin- and light-dependent manner. These proteins colocalize primarily to synaptic layers of the retina, namely the outer limiting membrane, outer and inner plexiform and ganglion cell layers. Cadherin/catenin complexes are implicated in regulation of synaptic strength at chemical synapses (Murase S, Neuron 2002) and in electrical gap junctions (Shaw RM, Cell 2007). We test the hypothesis that PKD regulates synaptic changes in response to light.
Synaptic changes were assessed in synaptosomal preparations isolated from photoreceptor-specific PKD knockout, PKD kinase-dead mutant mice and WT control retinas. Changes in α-catenin, β-catenin, cadherin and the synapse proteins PSD95, ribeye, synaptophysin and synaptic vesicle 2 (SV2) were analyzed by Western blot analysis. Gap junctional changes were assessed by neurobiotin labeling after cut-loading (Choi HJ, JOVE 2012). ERGs were used to test for physiological changes.
Western blot analysis of synaptosomal preparations showed statistically significant decreased levels of α-catenin, β-catenin and cadherin in PKD KO and kinase-dead retina compared to control retina. Furthermore, the synaptic proteins PSD95, ribeye, synaptophysin and SV2 were significantly decreased. Levels of protein were unchanged in total retina lysate. Neurobiotin tracer studies revealed a significant decrease in light-mediated amacrine cell coupling in PKD KO and kinase-dead retinas compared to WT retinas. ERGs of PKD mutant mice were normal.
Our data suggest that PKD acts downstream of rhodopsin to alter the distribution of synaptic adherens proteins and affects both chemical and electrical synapses. This suggests that rhodopsin modifies synaptic plasticity in the retina. Further studies are required to determine the precise molecular mechanism of this light-regulated event as well as its physiological consequence.
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