Gudheti Manasa V, Mlodzianoski Michael, Hess Samuel T
Department of Physics and Astronomy, University of Maine, Orono, ME 04469, USA.
Biophys J. 2007 Sep 15;93(6):2011-23. doi: 10.1529/biophysj.106.103374. Epub 2007 May 18.
Unsaturated trans fatty acids have been linked to a higher incidence of coronary artery disease, but not enough is known about the effect of trans lipids on membrane properties. Liquid-ordered (l(o)) and liquid-disordered (l(d)) membrane domains are implicated in various biological processes, such as endocytosis, adhesion, signaling, protein transport, apoptosis, and disease pathogenesis. The physical forces that induce domain formation and thus orchestrate cell function need to be further addressed and quantified. Here, we test the effect of trans DOPC (dielaidoyl phosphatidylcholine or DEPC) on the morphology of giant unilamellar vesicles (GUVs, used as a biomembrane model) made by electroformation with varying compositions of egg sphingomyelin, trans DOPC, cis DOPC, and cholesterol. GUVs were imaged by confocal fluorescence microscopy and then analyzed for changes in membrane morphology and properties such as l(o)/l(d) phase coexistence and area fractions, distribution of meridional curvature, and fluorescent-probe intensity distribution. BODIPY-FL-C(12)-sphingomyelin, Lissamine rhodamine B dioleoylphosphatidylethanolamine and BODIPY-TR-C(12)-sphingomyelin were used as fluorescent probes to differentially label the l(o) and l(d) phases. Trans DOPC induces some vesicles to form multidomain, invaginated morphologies that differ from the typical two-domain circular and truncated spherical shapes observed in its absence. Trans DOPC also alters the membrane curvature distribution; this is more pronounced in the l(o) phase near the phase boundary, where significantly negative curvatures (<-0.5 microm(-1)) are observed. A narrower distribution of meridional curvatures in GUVs with trans DOPC is suggestive of higher membrane bending rigidity. The ratio of average fluorescent intensities in the l(d)/l(o) phases indicates a greater concentration or brightness of the probes BODIPY-FL-C(12)-sphingomyelin and BODIPY-TR-C(12)-sphingomyelin in the l(o) phase in the presence of trans DOPC. Addition of trans DOPC does not alter the l(o)/l(d) area fractions, indicating that it does not act like egg sphingomyelin, a saturated lipid. These changes in membrane properties seen in the presence of trans lipids could significantly impact cell function.
不饱和反式脂肪酸与冠状动脉疾病的较高发病率有关，但关于反式脂质对膜特性的影响，我们所知尚少。液态有序（l(o)）和液态无序（l(d)）膜结构域参与了各种生物过程，如内吞作用、黏附、信号传导、蛋白质运输、细胞凋亡和疾病发病机制。诱导结构域形成从而协调细胞功能的物理力需要进一步研究和量化。在此，我们测试了反式二油酰磷脂酰胆碱（dielaidoyl phosphatidylcholine，或DEPC）对通过电形成法制备的、含有不同比例的卵鞘磷脂、反式二油酰磷脂酰胆碱、顺式二油酰磷脂酰胆碱和胆固醇的巨型单层囊泡（GUVs，用作生物膜模型）形态的影响。通过共聚焦荧光显微镜对GUVs成像，然后分析膜形态和特性的变化，如l(o)/l(d)相共存和面积分数、子午线曲率分布以及荧光探针强度分布。使用BODIPY-FL-C(12)-鞘磷脂、丽丝胺罗丹明B二油酰磷脂酰乙醇胺和BODIPY-TR-C(12)-鞘磷脂作为荧光探针来分别标记l(o)相和l(d)相。反式二油酰磷脂酰胆碱会诱导一些囊泡形成多结构域、内陷的形态，这与在不存在反式二油酰磷脂酰胆碱时观察到的典型双结构域圆形和截头球形不同。反式二油酰磷脂酰胆碱还会改变膜曲率分布；在靠近相界的l(o)相中这种变化更为明显，在那里观察到显著的负曲率（<-0.5微米⁻¹）。含有反式二油酰磷脂酰胆碱的GUVs中子午线曲率分布更窄，这表明膜的弯曲刚性更高。l(d)/l(o)相中的平均荧光强度比值表明，在存在反式二油酰磷脂酰胆碱的情况下，BODIPY-FL-C(12)-鞘磷脂和BODIPY-TR-C(12)-鞘磷脂探针在l(o)相中的浓度或亮度更高。添加反式二油酰磷脂酰胆碱不会改变l(o)/l(d)面积分数，这表明它的作用与饱和脂质卵鞘磷脂不同。在存在反式脂质的情况下观察到的这些膜特性变化可能会对细胞功能产生重大影响。
