Interphotoreceptor retinoid-binding protein as the physiologically relevant carrier of 11-cis-retinol in the cone visual cycle

J Neurosci. 2011 Mar 23;31(12):4714-9. doi: 10.1523/JNEUROSCI.3722-10.2011.

Abstract

Cones function in constant light and are responsible for mediating daytime human vision. Like rods, cones use the photosensitive molecule 11-cis-retinal to detect light, and in constant illumination, a continuous supply of 11-cis-retinal is needed. A retina visual cycle is thought to provide a privileged supply of 11-cis-retinal to cones by using 11-cis-retinol generated in Müller cells. In the cycle, 11-cis-retinol is transported from Müller cells to cone inner segments, where it is oxidized to 11-cis-retinal. This oxidation step is only performed in cones, thus rendering the cycle cone-specific. Interphotoreceptor retinoid-binding protein (IRBP) is a retinoid-binding protein in the subretinal space that binds 11-cis-retinol endogenously. Cones in Irbp(-/-) mice are retinoid-deficient under photopic conditions, and it is possible that 11-cis-retinol supplies are disrupted in the absence of IRBP. We tested the hypothesis that IRBP facilitates the delivery of 11-cis-retinol to cones by preserving the isomeric state of 11-cis-retinol in light. With electrophysiology, we show that the cone-like photoreceptors of Nrl(-/-) mice use the cone visual cycle similarly to wild-type cones. Then, using oxidation assays in isolated Nrl(-/-)Rpe65(-/-) retinas, we show that IRBP delivers 11-cis-retinol for oxidation in cones and improves the efficiency of the oxidation reaction. Finally, we show that IRBP protects the isomeric state of 11-cis-retinol in the presence of light. Together, these findings suggest that IRBP plays an important role in the delivery of 11-cis-retinol to cones and can facilitate cone function in the presence of light.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carrier Proteins / genetics
  • Chromatography, High Pressure Liquid
  • Electroretinography
  • Eye Proteins / genetics
  • Eye Proteins / metabolism*
  • Light
  • Mice
  • Mice, Knockout
  • Oxidation-Reduction
  • Retinal Cone Photoreceptor Cells / metabolism*
  • Retinoids / chemistry
  • Retinoids / metabolism
  • Retinol-Binding Proteins / metabolism*
  • Vision, Ocular / physiology
  • Vitamin A / metabolism*
  • cis-trans-Isomerases

Substances

  • Carrier Proteins
  • Eye Proteins
  • Retinoids
  • Retinol-Binding Proteins
  • interstitial retinol-binding protein
  • Vitamin A
  • retinoid isomerohydrolase
  • cis-trans-Isomerases