Changes in biophysical properties of membranes containing sphingomyelins with very long chain PUFA during cooling

PEÑALVA, D.A.; HOZBOR, F.; AVELDAÑO, M.I.; ANTOLLINI, S.S.

San Luis

Congreso; XLVIII Reunión Anual de la Sociedad Argentina de Biofísica; 2019

Sociedad Argentina de Biofísica

Although the molecular changes that affect the spermatozoa of economically importantanimals, such as bull and ram, are of great research interest, changes regarding plasmamembrane lipid organization as temperature decreases are still poorly understood.Gametes from these mammals contain sphingomyelin (SM) species very long chain n-3polyunsaturated fatty acids (VLCPUFA). (e.g., 30:6 SM, 32:6 SM and 34:6 SM in ram),while in most mammalian cells SM typically contains saturated and monounsaturatedacyl chains (C14 to C24). Also, these spermatozoa have three subclasses of cholineglycerophospholipids (CGP) with docosahexaenoic acid (22:6n-3) ester-bound at the sn-2position of glycerol, the sn-1 position being occupied by a C16 hydrophobic chain boundby an ester, ether o vinyl ether linkage. The aim of this study was to gain informationabout the supramolecular structural organization of these atypical lipids and theirchanges in the segregation, topological and thermodynamic coexistence during cooling.After isolation of these SM species and CGP subclasses from ram sperm by a combinationof chromatographic techniques, large and giant unilamellar vesicles (LUVs and GUVs)were prepared and examined by fluorescence spectroscopy and microscopy. Whereas the3 subclasses of CGP remained in the liquid crystalline state, the SM species 30:6 SM,32:6 SM and 34:6 SM showed gel-liquid crystalline transition temperatures within the 40°C - 5 °C range (5, 15 y 29 °C, respectively). In ternary PC:Cholesterol:SM systems, 32:6SM and 34:6 SM showed propensity to promote cholesterol-SM domain formation duringcooling, although at different temperatures and rates from those of 16:0 SM, here usedas a positive control. In GUVs containing 32:6 SM, the lateral lipid segregation and theprocess of dye efflux started at comparable temperatures. This coincidence did not occurin GUVs containing 16:0 SM. Thus, whereas at physiological temperatures VLCPUFAcontaining SM molecular species are in a fluid state and are not involved in cholesterolrich domains, this state is deeply altered at the low temperatures at which thesegametes are usually preserved, thereby affecting their membrane stability.