Multifrequency AFM reveals lipid membrane mechanical properties and the effect of cholesterol in modulating viscoelasticity
Multifrequency AFM reveals lipid membrane mechanical properties and the effect of cholesterol in modulating viscoelasticity
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DOI：
10.1073/pnas.1719065115
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发表时间：
2018-03-13
影响因子：
11.1
通讯作者：
Contera, Sonia
中科院分区：
文献类型：
--
作者：
Al-Rekabi, Zeinab;Contera, Sonia
组成细胞膜的脂质双层的物理性质占据了膜生物学的当前焦点。它们作为被动2D流体的传统表示已逐渐被放弃，转而支持更复杂的图像：各向异性的时间依赖性粘弹性双相材料，能够传输或衰减调节生物过程的机械力。在建立新的模型时，定量实验是必要的，当试图开发合适的动态测量技术。在这里，我们映射的弹性和粘性的模型系统1，2-dipalmitoyl-sn-glycero-3-phosphocholine（DPPC）脂质双层使用多频原子力显微镜（AFM），即调幅-调频（AM-FM）AFM成像在水性环境中。此外，我们研究了胆固醇（Chol）在0至60%浓度下对DPPC双层的影响。AM-AFM定量图表明，在低胆固醇浓度，脂质双层显示出明显的相分离，是弹性的，而在较高的胆固醇浓度，双层出现均匀的，并表现出弹性和粘性的属性。在低胆固醇含量，E-储能模量（弹性）占主导地位。随着Chol插入的增加，更高的能量被耗散;虽然双层变硬（E-存储增加），但粘性分量占主导地位（E-损失）。我们的研究结果提供的证据表明，脂质双层表现出弹性和粘性的性质，由Chol的存在下，这可能会影响传播（弹性）或衰减（粘性）的机械信号通过细胞膜调制。
The physical properties of lipid bilayers comprising the cell membrane occupy the current spotlight of membrane biology. Their traditional representation as a passive 2D fluid has gradually been abandoned in favor of a more complex picture: an anisotropic time-dependent viscoelastic biphasic material, capable of transmitting or attenuating mechanical forces that regulate biological processes. In establishing new models, quantitative experiments are necessary when attempting to develop suitable techniques for dynamic measurements. Here, we map both the elastic and viscous properties of the model system 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers using multifrequency atomic force microscopy (AFM), namely amplitude modulation-frequency modulation (AM-FM) AFM imaging in an aqueous environment. Furthermore, we investigate the effect of cholesterol (Chol) on the DPPC bilayer in concentrations from 0 to 60%. The AM-AFM quantitative maps demonstrate that at low Chol concentrations, the lipid bilayer displays a distinct phase separation and is elastic, whereas at higher Chol concentration, the bilayer appears homogenous and exhibits both elastic and viscous properties. At low-Chol contents, the E-storage modulus (elastic) dominates. As the Chol insertions increases, higher energy is dissipated; and although the bilayer stiffens (increase in E-storage), the viscous component dominates (E-loss). Our results provide evidence that the lipid bilayer exhibits both elastic and viscous properties that are modulated by the presence of Chol, which may affect the propagation (elastic) or attenuation (viscous) of mechanical signals across the cell membrane.