Plasmalogen status influences docosahexaenoic acid levels in a macrophage cell line: insights using ether lipid-deficient variants

Previously, this laboratory reported the isolation of variants, RAW.12 and RAW.108, from the macrophagelike cell line RAW 264.7 that are defective in plasmalogen biosynthesis [Zoeller; R.A. et al. 1992, J. Biol, Chem. 267: 82 99-8306]. Fatty acid analysis showed significant changes in the mutants in the ethanolamine phospholipids (PE), the only phospholipid class in which t he plasmalogen species, plasmenylethanolamine, contributes significantly. W ithin the PE fraction, docosapentaenoic (DPA; 22:5n-3) and docosahexaenoic (DHA; 22:6n-3) acids were reduced by approximately 50% in the variants whil e the levels of arachidonic acid (AA; 20:4n-6) remained unaffected. The dec rease in DHA was accompanied by a 50% decrease in labeling PE with [H-3]DHA over a 90-min period, Restoration of plasmenylethanolamine by supplementin g the growth medium with sn-1-hexadecylglycerol (HG) completely reversed th ese changes in RAW.108, Pre-existing pools of plasmenylethanolamine were no t required for restoration of normal [H-3]DHA labeling; addition of HG only during the labeling period was sufficient. Due to the loss of Delta 1'-des aturase in RAW.12, HG supplementation resulted in the accumulation of plasm enylethanolamine's immediate biosynthetic precursor, plasmanylethanolamine. Even though this latter phospholipid contained only the ether functionalit y (lacking the vinyl ether double bond) it was sufficient to restore wild t ype-like fatty acid composition and DHA labeling of the ethanolamine phosph olipids, identifying the ether bond as a structural determinant for this sp ecificity.jlr In summary, we have used these mutants to establish that the plasmalogen status of a cell can influence the levels of certain polyunsatu rated fatty acids. These results support the notion that certain polyunsatu rated fatty acids, such as DHA, can be selectively targeted to plasmalogens and that this targeting occurs during de novo biosynthesis, or shortly the reafter, through modification of nascent plasmalogen pools.