May 2008
Volume 49, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2008
SUMOylation of Retinal Proteins in Aroused vs. Torpid Ground Squirrels
Author Affiliations & Notes
  • J. M. Tonne
    Biology, University of Wisconsin Oshkosh, Oshkosh, Wisconsin
  • K. A. Linberg
    Neuroscience Research Institute, University of California Santa Barbara, Santa Barbara, California
  • D. Eisenschink
    Biology, University of Wisconsin Oshkosh, Oshkosh, Wisconsin
  • M. K. Traub
    Neuroscience Research Institute, University of California Santa Barbara, Santa Barbara, California
  • T. Rytz
    Biology, University of Wisconsin Oshkosh, Oshkosh, Wisconsin
  • T. Thomas
    Biology, University of Wisconsin Oshkosh, Oshkosh, Wisconsin
  • G. P. Lewis
    Neuroscience Research Institute, University of California Santa Barbara, Santa Barbara, California
  • D. K. Vaughan
    Biology, University of Wisconsin Oshkosh, Oshkosh, Wisconsin
  • S. K. Fisher
    Neuroscience Research Institute, University of California Santa Barbara, Santa Barbara, California
  • Footnotes
    Commercial Relationships  J.M. Tonne, None; K.A. Linberg, None; D. Eisenschink, None; M.K. Traub, None; T. Rytz, None; T. Thomas, None; G.P. Lewis, None; D.K. Vaughan, WiSys Technology Foundation Inc., P; S.K. Fisher, None.
  • Footnotes
    Support  UW Oshkosh Graduate Collaborative Grant (UWO), NSF-REU Grant (UWO), WiSys-ARG (UWO), NIH Grant EY00888 (UCSB)
Investigative Ophthalmology & Visual Science May 2008, Vol.49, 2060. doi:https://doi.org/
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      J. M. Tonne, K. A. Linberg, D. Eisenschink, M. K. Traub, T. Rytz, T. Thomas, G. P. Lewis, D. K. Vaughan, S. K. Fisher; SUMOylation of Retinal Proteins in Aroused vs. Torpid Ground Squirrels. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2060. doi: https://doi.org/.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: : The Small Ubiquitin-Like Modifier (SUMO) is a 100 amino acid protein that is covalently bound to target proteins by the Ubc9 enzyme. Thus, "SUMOylation" is a post-translational modification that draws upon a pre-existing pool of free SUMO. SUMOylation is hypothesized to spare protein conjugates from proteasomal degradation. SUMOylation of brain proteins is up-regulated during hibernation torpor in the 13-lined ground squirrel (GS), which naturally tolerates a repeated ischemia-reperfusion cycle over several months (Lee et al. J. Cereb. Blood Flow Metab. 2007). Protein sparing by SUMOylation might thus be a key neuroprotective strategy in the CNS. We tested the hypothesis that SUMOylation of retinal proteins would be similarly up-regulated during torpor in the cone-dominant GS retina.

Methods: : Young of the year GSs from the UW Oshkosh captive colony were used. Hibernation-naïve (aroused) GSs were sacrificed in August, October and November, whereas first-hibernation (torpid) GSs were sacrificed in October and December. Retinas were processed for in situ immunolabelling, Western blotting, and reverse transcriptase-PCR. Immunoprobes (gifts of Dr. Lee) and primers that distinguished SUMO-1 from SUMO-2/3 were used.

Results: : Messenger RNAs for SUMO-1 and SUMO-2/3 were detected in retinas from aroused and torpid GSs. Compared to blots from aroused GSs, blots from torpid GSs demonstrated down-regulated free SUMO-2/3 (Mr 16 kD) alongside up-regulated SUMO-2/3 protein conjugates (Mr 60-200 kD). A similar but less-robust response was seen on blots probed with anti-SUMO-1. Retinal SUMO conjugates were not identical to those identified in brain (Lee et al. 2007). In situ immunoreactivity (IR) for both types of SUMO in August/aroused GS retina was observed in the RPE and all retinal layers except for two regions in photoreceptors: their outer segments and ellipsoid mitochondria. SUMO-IR in November/aroused and December/torpid GS retinas was reduced, relative to that seen in August/aroused retinas, particularly sclerad of the inner plexiform layer.

Conclusions: : Our Western blot data support the hypothesis that SUMOylation of retinal proteins is upregulated during torpor when the GS brain exhibits resilience to repeated ischemia-reperfusion cycles. Reduced in situ SUMO-IR during torpor may reflect epitope masking resulting from this upregulated SUMOylation of protein targets, combined with their cross-linking by aldehyde fixation.

Keywords: neuroprotection • protein modifications-post translational • retina 
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