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C. M. Craft, B. M. Brown, R. M. Yetemian; Proteomic Analysis Reveals Potential Unstable Isoforms of Glycolytic Enzymes and Peroxiredoxin 6 in Age-Related Cone Degeneration. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4407.
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To examine cone phototransduction proteins contributing to shutoff, light adaptation and recovery, we used the Neural retina leucine zipper transcription factor knockout [Nrl-/-] genetic background provided by Mears & Swaroop and verified that the G-protein receptor kinase 1 (Grk1-/-, C.K. Chen) was essential for mouse cone opsin phosphorylation and shutoff. Later, we observed a light independent, age-related cone dystrophy in the Grk1-/-Nrl-/- double knockout mice (DKO). What is the molecular mechanisms of this degeneration, and when visual arrestins are knocked out, do the cones also die?
Proteomic analysis with 2D gel electrophoresis and EttanTM DIGE overlay technology was followed by identification with mass spectrometry of retinal proteins of age-matched Nrl-/- mice compared to Grk1-/-, Arr1-/- [J. Chen], or Arr4-/-. Using retinal homogenates, we tested specific proteins with enzymatic assays, phosphorylation studies, and oxidative/reduction modifications. AffymetrixTM analysis of retinal RNA examined gene regulation.
When comparing the DKO proteomic profiles, few retinal proteins are modified. In Nrl-/-Grk1-/-, two isoforms of phosphoglucose isomerase (Pgi)1 and phosphoglycerate mutase1 (Pgm1) were identified. When Nrl-/-Arr1-/- proteins are compared with Nrl-/-, a more acidic or oxidized form was observed in DKOs of a bifunctional enzyme: Peroxiredoxin6 (Prdx6) or calcium independent Phospholipase A2. Prdx6 is not modified in either Grk1-/-Nrl-/- or Arr4-/-Nrl-/-. Neither Pgi, Pgm1, or Prdx6 mRNA was up- or down-regulated in the AffymetrixTM analysis. Specific posttranslational and covalent modifications of these identified proteins may lead to the involvement of chaperones for targeted degradation.
Multiple isoforms of two glycolytic enzymes are post-translationally modified in the oxidative stress response and may be lysosomally targeted and lead to degeneration in the Grk1Nrl DKO. Although retinal expression of the glycolytic enzymes was reduced when either visual arrestin is not expressed, Prdx6 was the major observed variation only in Arr1-/-Nrl-/- and may be a protective mechanism used to up-regulate the enzyme’s antioxidant function. By controlling the accumulation of terminally degraded marked proteins and/or increasing Prdx6's oxidation, effective treatments may be developed for preventing age-related retinal degeneration.1Yetemian, RM et al., IOVS 2007:48, E-abstract 4695
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