Lipid composition of the canine sperm plasma membrane as markers of sperm motility
The fatty acid composition of the sperm membrane is an important factor involved in the overall sperm quality, including motility. However, in the canine species, the exact composition of the plasma membrane is still unknown. Therefore, the purpose of this study was to evaluate the plasma membrane lipid composition of motile sperm cells and to compare it with asthenospermic samples, as an attempt to determine possible involvements of membrane lipids in dog sperm cell motility. The sperm-rich fraction of ten mature dogs was collected, and samples were subjected to density gradient centrifugation by Percoll®, in order to separate motile and asthenospermic samples. Processed semen samples were evaluated for sperm motility, plasma and acrosome membrane integrity, mitochondrial activity and susceptibility to oxidative stress. Lipid plasma membrane composition was identified by mass spectrometry (MALDI-MS). The motile sperm samples presented the following phospholipids in a high frequency in the plasma membrane: phosphatidylcholine 38:4 (composed of stearic and arachidonic fatty acids), phosphatidylcholine 36:1 (stearic and oleic fatty acids), phosphatidylethanolamine 34:4 (myristic and arachidonic fatty acids), glycerophosphatidic acid 36:4 (palmitic and arachidonic fatty acids), phosphatidylcholine 40:4 plasmanyl and phosphatidylcholine 40:5 plasmenyl. Furthermore, no lipid markers were found in the asthenospermic samples. Results also indicate that differences on plasma membrane composition between motile and asthenospermic samples are crucial factors for determining sperm motility, sperm functionality and susceptibility to oxidative stress. In conclusion, plasma membrane lipid composition varies considerable between motile and asthenospermic samples. Therefore, lipid markers of sperm motility can be considered, such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylcholine plasmanyl, phosphatidylcholine plasmenyl and phosphatidic acid.