Characterization of the lipid profile of the equine sperm plasma membrane

Understanding sperm lipidomics is essential to better understand the changes that the sperm membrane undergoes during the cryopreservation process of stallion semen. The permeability of the sperm membrane is linked to and influenced by its lipid composition. The identification of lipids present in the sperm membrane can provide crucial information for better sperm quality after thawing. The objective of this study is to identify and compare the lipid profile of the plasma membrane from stallion sperm resistant (GOOD) and sensitive (BAD) to injuries resulting from the semen freezing process. The semen of 16 stallions was evaluated and classified (Hartwig.et.al. Theriogenology. 2014:81(2):340-6) in two groups: GOOD (n=8) and BAD (n=8). The lipidomic profile of spermatozoa was performed with MALDI-MS with no addition of an extender and with the removal of seminal plasma. The analysis was performed with MetaboAnalyst 2.0 and the discriminating analysis of PLS-DA to demonstrate the variation between BAD and GOOD. The lipid types that were differentially expressed used test T and The Volcano plot was used to compare groups, using the following criteria values of P〈 0.05 and fold-change (FC) ≥1,5. Lipids can affect cellular function depending on their structure and composition. 164 lipids were identified, of which 11 showed differences between the groups, 4 of them with greater abundance in the BAD group: 3 were identified, being glycerophosphoserines, [PS 0-42:5 +109Ag]+, Cholesterol and derivatives [ST 29:3;O +107Ag]+ and the ion 924.4688 m/z could be glycerophosphocholines [PC 29:7 +107Ag]+ or glycerophosphoethanolamine [PE 42:7 +107Ag]+, 424.1616 m/z was not identified. The other 7 showed greater abundance in the group GOOD: 3 glycerophosphoinositols [LPI 18:0 +Na]+, [PI 34:5 +2Na]+, [PI 30:3;O2 +2Na]2+; 2 glycerophosphoserine [PS 35:6 +K]+ and [PS O-38:7 +K]+; and 2 could be glycerophosphocholines: [PC O-29:1+107Ag]+ and [LPC 14:1 +2Na-H]+) or glycerophosphoethanolamines: [PE O-32:1+107Ag]+ and [LPE 17:1+2Na-H]+, respectively 782.4298 m/z and 510.2550 m/z. Spermatozoa in BAD group demonstrated high abundance in lipids with very-long-chain (29-42) and polyunsaturated (3-7 double bonds). While good freezer animals showed greater abundance mainly for glycerophosphoinositols, this family of lipids may be related to greater protection of plasma membrane stability as it is a modulator of the actin cytoskeleton (Corda.et.al. Cellular and Molecular. Life Sciences 2009:66:3449–67). In conclusion, the lipid composition of the sperm membrane differs between stallions with poor and good refrigeration, interfering with sperm quality after thawing, and a good understanding of the lipid composition becomes essential for improving semen, making more research necessary.