Novel lipofuscin bisretinoids prominent in human retina and in a model of recessive Stargardt disease

J Biol Chem. 2009 Jul 24;284(30):20155-66. doi: 10.1074/jbc.M109.021345. Epub 2009 May 28.

Abstract

Bisretinoid adducts accumulate as lipofuscin in retinal pigment epithelial (RPE) cells of the eye and are implicated in the pathology of inherited and age-related macular degeneration. Characterization of the bisretinoids A2E and the all-trans-retinal dimer series has shown that these pigments form from reactions in photoreceptor cell outer segments that involve all-trans-retinal, the product of photoisomerization of the visual chromophore 11-cis-retinal. Here we have identified two related but previously unknown RPE lipofuscin compounds. By high performance liquid chromatography-electrospray ionization-tandem mass spectrometry, we determined that the first of these compounds is a phosphatidyl-dihydropyridine bisretinoid; to indicate this structure and its formation from two vitamin A-aldehyde (A2), we will refer to it as A2-dihydropyridine-phosphatidylethanolamine (A2-DHP-PE). The second pigment, A2-dihydropyridine-ethanolamine, forms from phosphate hydrolysis of A2-DHP-PE. The structure of A2-DHP-PE was corroborated by Fourier transform infrared spectroscopy, and density functional theory confirmed the presence of a dihydropyridine ring. This lipofuscin pigment is a fluorescent compound with absorbance maxima at approximately 490 and 330 nm, and it was identified in human, mouse, and bovine eyes. We found that A2-DHP-PE forms in reaction mixtures of all-trans-retinal and phosphatidylethanolamine, and in mouse eyecups we observed an age-related accumulation. As compared with wild-type mice, A2-DHP-PE is more abundant in mice with a null mutation in Abca4 (ATP-binding cassette transporter 4), the gene causative for recessive Stargardt macular degeneration. Efforts to clarify the composition of RPE lipofuscin are important because these compounds are targets of gene-based and drug therapies that aim to alleviate ABCA4-related retinal disease.

Publication types

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

MeSH terms

  • ATP-Binding Cassette Transporters / genetics
  • Age Factors
  • Animals
  • Cattle
  • Chromatography, High Pressure Liquid
  • Diterpenes
  • Humans
  • Lipofuscin / analogs & derivatives
  • Lipofuscin / analysis*
  • Lipofuscin / isolation & purification
  • Lipofuscin / metabolism*
  • Macular Degeneration / genetics
  • Macular Degeneration / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Models, Molecular
  • Molecular Structure
  • Pigment Epithelium of Eye / chemistry*
  • Retina / chemistry*
  • Retinaldehyde / metabolism
  • Spectroscopy, Fourier Transform Infrared
  • Tandem Mass Spectrometry
  • Vitamin A / analogs & derivatives
  • Vitamin A / analysis
  • Vitamin A / isolation & purification
  • Vitamin A / metabolism

Substances

  • ATP-Binding Cassette Transporters
  • Diterpenes
  • Lipofuscin
  • vitamin A-aldehyde-dihydropyridine-ethanolamine
  • vitamin A-aldehyde-dihydropyridine-phosphatidylethanolamine
  • Vitamin A
  • Retinaldehyde