Novel Lipofuscin Bisretinoids Prominent in Human Retina and in a Model of Recessive Stargardt Disease

• Published in: The Journal of biological chemistry 2009-07, Vol.284 (30), p.20155-20166
• Main Authors: Wu, Yalin, Fishkin, Nathan E., Pande, Ajay, Pande, Jayanti, Sparrow, Janet R.
• Format: Article
• Language: English
• Subjects: Age Factors; Animals; ATP-Binding Cassette Transporters - genetics; Cattle; Chromatography, High Pressure Liquid; Diterpenes; Humans; Lipofuscin - analogs & derivatives; Lipofuscin - analysis; Lipofuscin - isolation & purification; Lipofuscin - metabolism; Macular Degeneration - genetics; Macular Degeneration - metabolism; Metabolism and Bioenergetics; 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
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M109.021345

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-elec tro spray 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-phosphatidyleth a nol amine (A2-DHP-PE). The second pigment, A2-dihydropyridine-eth a nol amine, 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 ∼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 phosphatidyleth a nol amine, 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.