In the retina, visual information is quickly segregated into pathways that respond to increases and decreases in light intensity. At the first retinal synapse, the tonic release of glutamate from photoreceptor terminals maintains a high synaptic concentration in darkness that rapidly decreases in response to light. Two types of postsynaptic cells, the ON- and OFF-bipolar cells (BPCs), respond with opposite polarity to glutamate released by photoreceptors, thus establishing the opposing visual pathways that are maintained throughout the rest of the visual system. The basis of signaling in OFF-BPCs, which relies on the activation of ionotropic glutamate receptors, is well understood;the signaling pathway that generates the light response in ON-BPCs, however, is more complex, and the molecular mechanisms remain to be elucidated. The ON-BPC signaling pathway originates with a unique metabotropic glutamate receptor, mGluR6, which is found exclusively on the dendrites of ON-BPCs. mGluR6 acts via a G-protein, GO, to regulate the activity of an unidentified cation channel such that the light-induced decrease in glutamate opens the channel and depolarizes the cell. In many ways, this sequence of events resembles the well-studied signal transduction pathway of photoreceptor outer segments, in which photoexcitation of rhodopsin is coupled via the G-protein, transducin, to the closure of a cGMP-gated cation channel. In the outer segment, the kinetics of the light response is largely determined by the lifetime of activated transducin. Deactivation of transducin occurs upon hydrolysis of GTP by the transducin alpha subunit, and this reaction is accelerated by interaction with the G?5-RGS9-R9AP complex. Mutations in the gene encoding any one of these three proteins severely impair vision by slowing recovery after light flashes. We have identified two similar complexes, G?5-RGS7 and G?5-RGS11, in ON-BPC dendrites suggesting a similar mechanism of deactivation of the ON-BPC signal transduction pathway. We hypothesize that the RGS- G?5 complexes are critical components of the mGluR6 signal transduction pathway in ON-BPC dendrites. Using a combination of biochemical, immunohistochemical, and electrophysiological approaches, we will test this hypothesis by answering the following questions: 1. How do RGS-G?5 complexes shape the response of ON-BPCs to light? 2. How are these RGS complexes anchored in the ON-BPC dendrites and how does this affect their function? 3. What other proteins in the mGluR6 pathway interact with G?5-RGS7 and G?5-RGS11? The data from this study will contribute to the elucidation of the signaling pathway in the ON-bipolar cell, a fundamental, yet poorly understood, step in visual processing.

Public Health Relevance

The proposed research into the intracellular biochemical pathways generating the light response of retinal ON-bipolar cells is of relevance to the development of cures for blindness, including the design of visual prosthetics and gene therapy. Moreover, because G protein-coupled receptors and pathways are the target of the majority of pharmaceutical drugs, this research will have broad relevance to the development of therapeutic interventions for numerous neurological and cardiovascular diseases.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY018625-04
Application #
8312621
Study Section
Biology and Diseases of the Posterior Eye Study Section (BDPE)
Program Officer
Greenwell, Thomas
Project Start
2009-09-01
Project End
2014-07-31
Budget Start
2012-08-01
Budget End
2014-07-31
Support Year
4
Fiscal Year
2012
Total Cost
$369,278
Indirect Cost
$103,451
Name
Oregon Health and Science University
Department
Ophthalmology
Type
Schools of Medicine
DUNS #
096997515
City
Portland
State
OR
Country
United States
Zip Code
97239
Neuillé, Marion; Morgans, Catherine W; Cao, Yan et al. (2015) LRIT3 is essential to localize TRPM1 to the dendritic tips of depolarizing bipolar cells and may play a role in cone synapse formation. Eur J Neurosci 42:1966-75
Brown, R Lane; Xiong, Wei-Hong; Peters, James H et al. (2015) TRPM3 expression in mouse retina. PLoS One 10:e0117615
Xiong, Wei-Hong; Pang, Ji-Jie; Pennesi, Mark E et al. (2015) The Effect of PKCα on the Light Response of Rod Bipolar Cells in the Mouse Retina. Invest Ophthalmol Vis Sci 56:4961-74
Xiong, Wei-Hong; Brown, R Lane; Reed, Brian et al. (2015) Voriconazole, an antifungal triazol that causes visual side effects, is an inhibitor of TRPM1 and TRPM3 channels. Invest Ophthalmol Vis Sci 56:1367-73
Stempel, Andrew J; Morgans, Catherine W; Stout, J Timothy et al. (2014) Simultaneous visualization and cell-specific confirmation of RNA and protein in the mouse retina. Mol Vis 20:1366-73
Dalal, Monica D; Morgans, Catherine W; Duvoisin, Robert M et al. (2013) Diagnosis of occult melanoma using transient receptor potential melastatin 1 (TRPM1) autoantibody testing: a novel approach. Ophthalmology 120:2560-4
Lu, Bin; Morgans, Catherine W; Girman, Sergey et al. (2013) Retinal morphological and functional changes in an animal model of retinitis pigmentosa. Vis Neurosci 30:77-89
Xiong, Wei-Hong; Duvoisin, Robert M; Adamus, Grazyna et al. (2013) Serum TRPM1 autoantibodies from melanoma associated retinopathy patients enter retinal on-bipolar cells and attenuate the electroretinogram in mice. PLoS One 8:e69506
Reed, Brian T; Morgans, Catherine W; Duvoisin, Robert M (2013) Differential modulation of retinal ganglion cell light responses by orthosteric and allosteric metabotropic glutamate receptor 8 compounds. Neuropharmacology 67:88-94
Morgans, Catherine W; Brown, Ronald Lane; Duvoisin, Robert M (2010) TRPM1: the endpoint of the mGluR6 signal transduction cascade in retinal ON-bipolar cells. Bioessays 32:609-14

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