Synthesis of Ether Lipids and Phosphatidylethanolamine by Ejaculated Human Spermatozoa

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Abstract
Ether lipids are the 1-O-alkyl derivatives of phospholipids. In contrast to nongerminal tissues where the plasma membrane content of ether lipids is low, over 40% of the phospholipids present in sperm plasma membranes are ether lipids. This study was undertaken to determine whether ejaculated human serm could synthesize ether lipids either through reacylation of 1-alkyl-sn-2-lysophosphatidylcholine or through direct incorporation of 1-hexadecanol into diacyl phosphatidylcholine or diacyl phosphatidylethanolamine. The ability of sperm to reacylate 1-acyl-sn-2-lysophosphatidylethanolamine was also assessed. In these experiments, freshly ejaculated sperm were unable to reacylate a phosphocholine lyso ether lipid with either palmitic (16:0) or docosahexaenoic (22:6) acids. In contrast, sperm readily incorporated both 16:0 and 22:6 into 1-acyl lysophosphatidylethanolamine. Similarly, sperm freely incorporated 1-hexadecanol into diacyl phosphatidylethanolamine thus forming a 1-alkyl phosphoethanolamine ether lipid. Diacyl phosphatidylcholine could not serve as a substrate in this reaction. It is apparent, based on these data, that human spermatozoa can directly synthesize phosphoethanolamine ether lipids that may subsequently undergo exhaustive methylation to form phosphocholine ether lipids.