May 2008
Volume 49, Issue 13
ARVO Annual Meeting Abstract  |   May 2008
Retinoid Processing in Müller Cells
Author Affiliations & Notes
  • J. Kaylor
    Jules Stein Eye Institute, UCLA, Los Angeles, California
  • R. Radu
    Jules Stein Eye Institute, UCLA, Los Angeles, California
  • A. Miu
    Jules Stein Eye Institute, UCLA, Los Angeles, California
  • G. Travis
    Jules Stein Eye Institute, UCLA, Los Angeles, California
  • Footnotes
    Commercial Relationships  J. Kaylor, None; R. Radu, None; A. Miu, None; G. Travis, None.
  • Footnotes
    Support  NIH R01-EY11713
Investigative Ophthalmology & Visual Science May 2008, Vol.49, 3521. doi:
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      J. Kaylor, R. Radu, A. Miu, G. Travis; Retinoid Processing in Müller Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3521. doi:

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

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Purpose: : The visual cycle for the regeneration of rhodopsin is well defined in RPE cells. However, several lines of evidence suggest that cones may regenerate visual pigments by a mechanism independent of the RPE that might involve Müller cells. Prior work from our laboratory indicated the existence of a retinoid isomerase (distinct from Rpe65) in chicken and ground-squirrel retinas that catalyzes the direct conversion of all-trans-retinol (all-trans-ROL) to 11-cis-retinol (11-cis-ROL). This ‘isomerase-2’ activity is coupled to a palmitoyl coenzyme A (palm CoA) dependent retinyl-ester synthase (ARAT), to yield 11-cis-retinyl palmitate (11-cis-RP) as a final product. A strong candidate for ARAT is acyl CoA:diacylglyerol acyltransferase type-1 (DGAT1). We are working to understand the role of Müller cells in the processing of visual retinoids.

Methods: : Primary Müller cell cultures were prepared from chicken retinas. We measured expression of several visual cycle mRNA’s by quantitative real-time PCR. We determined the levels of visual retinoids synthesized in vivo by incubation of the Müller cells with all-trans-ROL added to the medium. The media and cells were separated for analysis. We also used cell homogenates as an enzyme source to assay in vitro the activities of isomerase-2 and ARAT in Müller cells. Retinoids in samples were extracted with hexane and analyzed by liquid chromatography.

Results: : Cultured chicken Müller cells expressed the mRNA’s for several retinoid-processing proteins including cellular retinaldehyde binding protein (CRALBP), DGAT1, and RGR-opsin. Addition of all-trans-ROL to the culture medium resulted in the synthesis of all-trans-retinyl palmitate (all-trans-RP) and all-trans-retinaldehyde by the Müller cells. Addition of 11-cis-ROL to the medium resulted in the synthesis of 11-cis-RP and 11-cis-retinaldehyde by the cells. In the presence of palm CoA, Müller cell homogenates synthesized all-trans-RP and 11-cis-RP from all-trans-ROL and 11-cis-ROL substrates, respectively. In contrast to RPE homogenates, we observed very low palm CoA-independent synthesis of retinyl esters by Müller cell homogenates. Significantly, we observed synthesis of 11-cis-RP from all-trans-ROL and palm CoA substrates by Müller homogenates in the dark, indicating the presence of isomerase-2 activity in these cells.

Conclusions: : Cultured chicken Müller cells contain robust ARAT activity, which is probably mediated by DGAT1. In contrast, lecithin:retinol acyl-transferase (LRAT) activity is virtually undetectable in these cells. The Müller cells also contain isomerase-2 activity, indicated by palm CoA-dependent synthesis of 11-cis-RP from all-trans-ROL.

Keywords: Muller cells • retinoids/retinoid binding proteins • retinal glia 

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