Reversible Dissolution of Microdomains in Detergent-Resistant Membranes at Physiological Temperature

The formation of lipid microdomains (“rafts”) is presumed to play an important role in various cellular functions, but their nature remains controversial. Here we report on microdomain formation in isolated, detergent-resistant membranes from MDA-MB-231 human breast cancer cells, studied by atomic force microscopy (AFM). Whereas microdomains were readily observed at room temperature, they shrunk in size and mostly disappeared at higher temperatures. This shrinking in microdomain size was accompanied by a gradual reduction of the height difference between the microdomains and the surrounding membrane, consistent with the behaviour expected for lipids that are laterally segregated in liquid ordered and liquid disordered domains. Immunolabeling experiments demonstrated that the microdomains contained flotillin-1, a protein associated with lipid rafts. The microdomains reversibly dissolved and reappeared, respectively, on heating to and cooling below temperatures around 37°C, which is indicative of radical changes in local membrane order close to physiological temperature.

脂质微区（lipid microdomains，又称脂筏（rafts））的形成被认为在多种细胞功能中发挥关键作用，但其本质仍存在争议。本研究报道了从MDA-MB-231人乳腺癌细胞中分离得到的去污剂抗性膜（detergent-resistant membranes）内的微区形成过程，并采用原子力显微镜（atomic force microscopy，AFM）进行观测分析。实验结果表明，微区在室温下易于被清晰观测到，但在较高温度下其尺寸会发生收缩，且最终大多消失。伴随微区尺寸收缩的是其与周围膜之间的高度差逐渐降低，这与侧向分离为液晶有序域（liquid ordered domains）与液晶无序域（liquid disordered domains）的脂质的预期行为相符。免疫标记实验证实，该微区包含flotillin-1，一种与脂筏相关的蛋白。当加热至约37℃附近时，微区发生可逆性溶解；而冷却至该温度以下时，微区则重新出现，这一现象表明，在接近生理温度的区间内，局部膜的有序性会发生显著改变。