Increased light damage susceptibility at night does not correlate with RPE65 levels and rhodopsin regeneration in rats

https://doi.org/10.1016/S0014-4835(03)00059-9Get rights and content

Abstract

The susceptibility of rats to light-induced retinal degeneration is increased at night. In mice, an important determinant of light damage susceptibility is the efficacy of rhodopsin regeneration after bleaching. The rate of rhodopsin regeneration is at least partly controlled by RPE65, a protein expressed in the retinal pigment epithelium. We therefore tested a potential involvement of RPE65 and rhodopsin regeneration in the increased light damage susceptibility of rats at night. For this purpose, rats were exposed to visible light at noon or at midnight and extent of light damage was determined by retinal morphology and TUNEL staining. Rpe65 gene expression was analyzed by semiquantitative RT-PCR and levels of RPE65 protein were determined by Western blotting. Rhodopsin regeneration kinetics was determined by measuring rhodopsin content immediately after a strong bleach and after different times of recovery in darkness.

Rats were more susceptible to light damage at night as described by Organisciak and collegues [Invest. Ophthalmol. Vis. Sci. 41 (2000) 3694]. Rpe65 gene expression followed a day–night rhythm with highest steady-state mRNA levels at the beginning and lowest levels at the end of the day period. However, RPE65 protein levels remained constant. Rhodopsin regeneration kinetics did not differ during day and night. We conclude that levels of RPE65 protein and rhodopsin regeneration kinetics do not correlate with the increased light damage susceptibility observed in rats at night. Additional genetic or physiologic modifiers may exist in rats that regulate the retinal responsiveness to acute light exposure.

Introduction

Light absorption by the visual pigment rhodopsin is required to initiate the phototransduction cascade (Pepe, 2001). Absorption of excessive amounts of light, however, may eventually lead to photoreceptor degeneration by an apoptotic process (Grimm et al., 2000b, Remé et al., 1998). Increasing epidemiological and experimental evidence suggests that light may be an important exogenous co-factor for the development and severity of retinal degenerations as they occur during the course of age related macular degeneration (AMD) and retinitis pigmentosa (RP) (Cideciyan et al., 1998, Cruickshanks et al., 1993, Cruickshanks et al., 2001, Simons, 1993, Taylor et al., 1990). In addition, the progression of retinal degeneration is enhanced by light in an increasing number of animal models for human retinal diseases (Chen et al., 1999a, Chen et al., 1999b, LaVail et al., 1999, Organisciak et al., 1999, Sanyal and Hawkins, 1986, Wang et al., 1997). Light damage susceptibility is at least partially controlled by genetic factors in different mouse strains (LaVail et al., 1987a). One factor has been identified as a sequence variation in the Rpe65 gene (Danciger et al., 2000). The variation was shown to influence steady-state levels of the RPE65 protein in the mouse and to correlate with rhodopsin regeneration kinetics in the visual cycle (Wenzel et al., 2001). RPE65 is specifically expressed in the pigment epithelium (Seeliger et al., 2001) and is essential for the re-isomerization of all-trans retinal during the visual cycle and thus for the regeneration of rhodopsin after bleaching (Redmond et al., 1998). Rhodopsin regeneration is an important factor determining light damage susceptibility in different mouse strains (Wenzel et al., 2001). Inhibition of the visual cycle leads to strong protection against light-induced photoreceptor apoptosis (Keller et al., 2001). Strain differences in light damage susceptibility have been observed also in rats (Borges et al., 1990, Iseli et al., 2002). However, in rats, RPE65 protein and rhodopsin regeneration do not seem to be the main determinants for the observed strain differences (Iseli et al., 2002) suggesting that other genetic factors may determine damage after light exposure in different rat strains. Furthermore, as an exogenous component determining damage susceptibility, a photostatic adjustment to environmental illuminance levels was found (Penn and Williams, 1986). It has been shown that light damage susceptibility in a specific rat strain varies with the time of day (Duncan and O'Steen, 1985, Organisciak et al., 2000, White and Fisher, 1987). The mechanism for this observation is unclear but may involve a diurnal/circadian-dependent expression of intrinsic factor(s). For example a rhythmic variation of molecules involved in phototransduction was observed (Brann and Cohen, 1987, Farber et al., 1991, Korenbrot and Fernald, 1989, McGinnis et al., 1992, Organisciak et al., 1991, Tosini and Menaker, 1996, Wiechmann and Sinacola, 1997). One of the factors might be RPE65 which may influence efficiency of rhodopsin regeneration during day- or night-time. Therefore, we tested expression of the Rpe65 gene during night and day and analyzed potential effects on rhodopsin regeneration and light damage susceptibility.

Section snippets

Animals and rearing conditions

All procedures concerning animals adhered to the ARVO statement for the use of animals in ophthalmic and vision research. Albino rats (Sprague–Dawly) were purchased and reared for additional 10–15 days in a light/dark cycle (lights on: 6 a.m., lights off: 6 p.m.) with 60–100 lux within the cages. Experiments were performed at the age of 6–8 weeks. Water and rodent food were provided ad libitum. Animals that were exposed at midnight were taken from the regular light-dark cycle. Therefore, these

Increased light damage susceptibility at night

Earlier work has shown that susceptibility to light damage varies with the time of day (Duncan and O'Steen, 1985, Organisciak et al., 2000, White and Fisher, 1987). In most of these experiments repetitive light exposure over several days had been used (Duncan and O'Steen, 1985, White and Fisher, 1987), or light damage was induced with green light (Organisciak et al., 2000). Therefore, we verified a diurnal dependent light damage susceptibility in our system by exposing albino rats at noon or at

Discussion

Light damage susceptibility is increased during the night in animals kept under a light–dark cycle of 12 hr:12 hr (Organisciak et al., 2000). Here we tested whether this difference might correlate with levels of RPE65 protein and/or rhodopsin regeneration. These two parameters have recently been shown to correlate with light damage susceptibility in different mouse strains (Wenzel et al., 2001). We show that in rats, Rpe65 gene expression, RPE65 protein levels and rhodopsin regeneration do not

Acknowledgements

The authors like to thank Coni Imsand, Dora Greuter and Gabi Hoegger for skilled technical assistance and Ulli Busse for administrative help. This work was supported by the Swiss National Science Foundation, the Bruppacher Foundation, the German Research Council and the Velux Foundation.

References (42)

  • S. Sanyal et al.

    Development and degeneration of retina in rds mutant mice: effects of light on the rate of degeneration in albino and pigmented homozygous and heterozygous mutant and normal mice

    Vision Res.

    (1986)
  • M.P. White et al.

    Degree of light damage to the retina varies with time of day of bright light exposure

    Physiol. Behav.

    (1987)
  • A.F. Wiechmann et al.

    Diurnal expression of recoverin in the rat retina

    Brain Res. Mol. Brain Res.

    (1997)
  • R.W. Young

    Shedding of discs from rod outer segments in the rhesus monkey

    J. Ultrastruct. Res.

    (1971)
  • J.M. Borges et al.

    A comparative study of photic injury in four inbred strains of albino rats

    Curr. Eye Res.

    (1990)
  • M.R. Brann et al.

    Diurnal expression of transducin mRNA and translocation of transducin in rods of rat retina

    Science

    (1987)
  • C.K. Chen et al.

    Abnormal photoresponses and light-induced apoptosis in rods lacking rhodopsin kinase

    Proc. Nat. Acad. Sci. USA

    (1999)
  • J. Chen et al.

    Increased susceptibility to light damage in an arrestin knockout mouse model of Oguchi disease (stationary night blindness)

    Invest. Ophthalmol. Vis. Sci.

    (1999)
  • A.V. Cideciyan et al.

    Disease sequence from mutant rhodopsin allele to rod and cone photoreceptor degeneration in man

    Proc. Nat. Acad. Sci. USA

    (1998)
  • K.J. Cruickshanks et al.

    Sunlight and age-related macular degeneration. The beaver dam eye study

    Arch. Ophthalmol.

    (1993)
  • K.J. Cruickshanks et al.

    Sunlight and the 5-year incidence of early age-related maculopathy: the beaver dam eye study

    Arch. Ophthalmol.

    (2001)
  • Cited by (11)

    • Cell death mechanisms in retinal phototoxicity

      2023, Journal of Photochemistry and Photobiology
    • Identification of susceptibility loci for light-induced visual impairment in rats

      2021, Experimental Eye Research
      Citation Excerpt :

      Wenzel et al. showed that Rpe65 Leu450Met variation increased RPI resistance in various mouse strains by slowing rhodopsin regeneration (Wenzel et al., 2001). Iseli et al. demonstrated that Wistar rats were more susceptible to RPI than Lewis rats (Iseli et al., 2002), but Rpe65 expression and rhodopsin regeneration could not be the main factors controlling RPI susceptibility in rats (Beatrice et al., 2003). These findings indicated that different genetic factors between mice and rats might be involved in the mechanism of onset and/or progression of RPI.

    • Retinal light damage: Mechanisms and protection

      2010, Progress in Retinal and Eye Research
      Citation Excerpt :

      In the ONL, c-fos is normally elevated at night, while its expression in the inner retina, particularly in ganglion cells, is transiently enhanced at light onset (Yoshida et al., 1993). In rats, RPE-65 mRNA levels are also highest at the beginning of the day, but RPE-65 protein levels do not correlate with circadian dependent light damage susceptibility (Beatrice et al., 2003). Other evidence indicates that melanopsin, a protein located within a subset of ganglion cells, serves as a retinal circadian irradiance detector (Provencio et al., 2000; Hattar et al., 2002; Berson et al., 2002).

    • Photoreceptor organisation and phenotypic characterization in retinas of two diurnal rodent species: Potential use as experimental animal models for human vision research

      2008, Vision Research
      Citation Excerpt :

      The presence of both rods and cones in their retina will greatly facilitate comparison of the two populations in the face of stress and injury, and in their responses to prospective neuroprotective treatments. For example, the cellular and molecular mechanisms underlying phototoxic damage of rods has been quite extensively examined, providing knowledge on parameters such as light intensity, duration, spectral quality, circadian timing and genetic variants (Beatrice, Wenzel, Remé, & Grimm, 2003; Organisciak, Darrow, Barsalou, Kutty, & Wiggert, 2000; Wenzel, Grimm, Samardzija, & Remé, 2005; Wenzel et al., 2007). The data for cones are very limited, and give conflicting results demonstrating either increased (Cortina, Gordon, Lukiw, & Bazan, 2003) or decreased (Cicerone, 1976) vulnerability compared to rods.

    • Circadian effects on retinal light damage

      2014, The Retina and Circadian Rhythms
    View all citing articles on Scopus
    View full text