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Elena Braginskaja, Jessica Gumerson, Muriel Perron, Anand Swaroop, Jerome E Roger; Glycogen Synthase Kinases 3 control photoreceptor development and homeostasis by modulating NRL stability. Invest. Ophthalmol. Vis. Sci. 2017;58(8):348.
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© ARVO (1962-2015); The Authors (2016-present)
Gene regulatory network required for photoreceptor development and homeostasis is dependent on intrinsic factor expression. Posttranslational modifications bring in additional level of regulation allowing rapid and reversible modifications of targeted factors in response to changing microenvironment. Among the modifying enzymes are Glycogen Synthase Kinases 3 (GSK3s), key regulators of brain development and homeostasis. One of their main modes of action is the control of protein stability. GSK3s deregulation is involved in many pathologies of the central nervous system. However, their role is poorly understood in the retina. We aimed at delineating the function of GSK3s and at identifying their critical targets in photoreceptors.
Gsk3α and Gsk3β-floxed mice were mated with Crx::Cre line for conditional deletion in photoreceptor precursors. The phenotype was evaluated by immunohistochemistry and electroretinogram (ERG). Gene expression was assessed by qPCR and immunoblotting. The impact of GSK3-dependent phosphorylation on protein stability was investigated in transfected cells.
Lack of GSK3s in photoreceptor precursors led to progressive photoreceptor loss from P18 onwards. Scotopic and photopic ERG responses were significantly decreased before the onset of degeneration. Further analysis demonstrated impairment in photoreceptor maturation and reduced opsin expression. However, expression of key photoreceptor specific transcription factors was not significantly affected at the transcriptional level. Interestingly, while CRX and NR2E3 protein amount was unchanged, the absence of GSK3s led to an increase in NRL protein level associated with a reduced number of phosphorylated isoforms. In vitro experiments established a GSK3-dependent phosphorylation altering NRL protein stability. Preliminary proteome and transcriptome analyses revealed deregulation of only a subset of NRL target genes critical for photoreceptor function.
Lack of GSK3s in photoreceptor precursors impairs their differentiation and leads to degeneration. Photoreceptor death in the absence of GSK3 may arise from the change of NRL phosphorylation and stability leading to an aberrant expression of a subset of NRL target genes. Our findings should also shed more light on disease mechanisms of NRL mutation-associated retinitis pigmentosa for which altered NRL phosphorylation has been reported.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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