| Greater than 18% of the phospholipid mass in humans is composed of vinyl-ether linked phospholipids, known as plasmalogens. However, their cellular functions are largely not understood. There are two possible functions, for plasmalogens; (1) as a storage sight for polyunsaturated fatty acids (PUFAs) and (2) as a source of these fatty acids during stimulated release. In order to study thew putative functions, mutant cell lines that are defective in plasmalogen synthesis were used. RAW.108 and RAW.12 cells are mutants of the murine macrophage-like cell line RAW 264.7, while NRel-4, NZel-1 and ZR-82 cells are mutants of the hamster fibroblast-like cell line CHO-K1.;In all mutants, fatty acid analysis of the ethanolamine phospholipids (PE), the only lipid class in which plasmalogens contribute significantly, showed significant decreases in the masses of docosapentaenoic acid (DPA; 22:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). Incorporation of labeled DHA into PE was reduced by approximately 50% in the RAW mutants after a 90-minute pulse. Restoration of plasmalogen synthesis by supplementing the growth medium with sn-1-hexadecylglycerol. (HG) completely reversed all of these changes. Pre-existing pools of plasmenylethanolamine were not required for restoration of normal [3H]DHA labeling; addition of HG, only during the labeling period, was sufficient.;Calcium-independent phospholipases A2 (iPLA2) have been implicated in the stimulated release of arachidonic acid (AA) from plasmalogen stores. The iPLA2 inhibitor BEL, completely inhibited lipopolysacharide (LPS) and zymosan stimulated release of [3H]AA in the RAW cells. However, release of [3H]AA in response to LPS, zymosan, or antimycin, was not dependent on the presence of plasmalogens. Although all the phospholipid classes released [3H]AA during zymosan stimulation, NAA was derived predominantly from phosphatidylinositol. In summary, these studies establish that the plasmalogen status of a cell can influence the levels of certain polyunsaturated fatty acids, such as DHA, and that these polyunsaturated My acids can be selectively targeted to plasmalogens. In addition, plasmalogens are not necessary in the stimulated release of [3H]AA, even if this release is inhibitable with BEL. |
