N-Nervonoylsphingomyelin (C24:1) Prevents Lateral Heterogeneity in Cholesterol-Containing Membranes

Abstract

This study was conducted to explore how the nature of the acyl chains of sphingomyelin (SM) influence its lateral distribution in the ternary lipid mixture SM/cholesterol/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), focusing on the importance of the hydrophobic part of the SM molecule for domain formation. Atomic force microscopy (AFM) measurements showed that the presence of a double bond in the 24:1 SM molecule in mixtures with cholesterol (CHO) or in pure bilayers led to a decrease in the molecular packing. Confocal microscopy and AFM showed, at the meso- and nanoscales respectively, that unlike 16:0 and 24:0 SM, 24:1 SM does not induce phase segregation in ternary lipid mixtures with DOPC and CHO. This ternary lipid mixture had a nanomechanical stability intermediate between those displayed by liquid-ordered (Lo) and liquid-disordered (Ld) phases, as reported by AFM force spectroscopy measurements, demonstrating that 24:1 SM is able to accommodate both DOPC and CHO, forming a single phase. Confocal experiments on giant unilamellar vesicles made of human, sheep, and rabbit erythrocyte ghosts rich in 24:1 SM and CHO, showed no lateral domain segregation. This study provides insights into how the specific molecular structure of SM affects the lateral behavior and the physical properties of both model and natural membranes. Specifically, the data suggest that unsaturated SM may help to keep membrane lipids in a homogeneous mixture rather than in separate domains.

The unfavorable lipid environment reduced caveolin-1 expression in apical membranes from human preeclamptic placentas

“…In agreement with Epand et al [54], we also previously showed that when an unsaturated sphingolipid, oleoyl-SM or nervonoyl-SM, is included in a lipid mixture, no lateral phase separation is detected in fluid membranes containing Cho and DOPC (dioleylphophatidylcholine) [33]. Taking into account all these results, we suggest that the increment of SM, specifically the SM 18:1, in preeclamptic-MVM is directly related with the increment of the lipid order and the destabilization of caveolae.…”

“…Thus, SM and Cho, are relevant in determining lipid conformational order and packing [31][32][33]. In this context, in a previous report we demonstrated that independently of the Cho content, SM/PC ratio determines the lipid order of the membrane; as the SM/PC ratio increase, the order of the membrane also increase [33]. In the present paper, membrane order was determined by EPR in normal and preeclamptic-MVM vesicles.…”

“…Cho and SM have both hydrogen-bond donor and acceptor groups that together with the Cho flat and extended hydrophobic structure promote the tight packing of SM and Cho into the liquid-ordered arrangement [53]. Thus, SM and Cho, are relevant in determining lipid conformational order and packing [31][32][33]. In this context, in a previous report we demonstrated that independently of the Cho content, SM/PC ratio determines the lipid order of the membrane; as the SM/PC ratio increase, the order of the membrane also increase [33].…”

“…Instead, SM was the major phospholipid in MVM of preeclamptic placentas. Taking into account that SM/PC ratio determines the lipid order of the membrane [33], this increment in SM may alter this order. In addition, an increase in PS content was also observed in MVM from preeclamptic placentas.…”

“…SM is, together with Cho, relevant in determining lipid conformational order and packing [31][32][33].…”