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M.-P. G. Agbaga, R. S. Brush, M. A. Mandal, K. Henry, M. H. Elliott, R. E. Anderson; ELOVL4 Protein and Biosynthesis of Very Long Chain Fatty Acids. Invest. Ophthalmol. Vis. Sci. 2008;49(13):765.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations in Elongation of Very Long Chain fatty acids (ELOVL4) gene have been shown to cause Stargardt-like macular dystrophy. Other members of the ELO gene family have been shown to catalyze fatty acid elongation; ELOVL4 mutant mice have deficiencies in very long chain fatty acids in the skin and retina. However, definitive evidence that ELOVL4 is involved in fatty acid elongation and the specific step in the elongation process it may catalyze have not been presented. We hypothesized that the ELOVL4 protein may be an enzyme or a co-enzyme involved in fatty acid elongation. In this study, we investigated the role of ELOVL4 in the biosynthesis of very long chain fatty acids (VLCFAs) in rat neonatal cardiac myocytes and a human retina epithelium cell line (ARPE-19).
ELOVL4 protein was expressed in neonatal rat cardiomyocytes and ARPE-19 cells using an adenoviral delivery system. Non-transduced cells and GFP-expressing cells were used as controls. Transduction efficiency was confirmed by real-time PCR, immunocytochemistry, and Western blot analysis. Transduced and control cells were treated with 24:0, 20:5n3, or 22:5n3, all precursors of VLCFAs (≥ 26 carbons). Cells were collected and total lipids were extracted and converted to fatty acid methyl esters, which were analyzed by gas chromatography-mass spectrometry (GC-MS).
Transduction efficiencies of cardiomyocytes and ARPE-19 cells were greater than 90%. Both transduced and control cells internalized all three fatty acids. 24:0 was elongated to 26:0 in all cells. However, only ELOVL4-expressing cells further elongated 26:0 to 28:0 and 30:0 compared to control cells. Likewise, only ELOVL4-expressing cells elongated 20:5n3 and 22:5n3 to C30 - C36 polyunsaturated fatty acids (PUFA). These findings demonstrate that ELOVL4 is a component of a fatty acid elongation system that catalyzes the synthesis of VLCFAs.
We have shown, for the first time, the specific steps in fatty acid metabolism catalyzed by ELOVL4. We propose that these steps are important in the retina for synthesis of very long chain (C30-C36) PUFA that are esterified in phosphatidylcholine in rod outer segment membranes.
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