Weldon School of Biomedical Engineering, Purdue University . 206 S. Martin Jischke Drive, West Lafayette, Indiana 47906, United States.
Anal Chem. 2017 Apr 18;89(8):4502-4507. doi: 10.1021/acs.analchem.6b04699. Epub 2017 Apr 6.
Dysregulation of lipid metabolism is associated with many diseases including cancer. Lipid droplet (LD), a ubiquitous organelle in mammalian cells, serves as a hub for lipid metabolism. Conventional assays on the measurement of lipid metabolism rely on the quantification of the lipid composition or amount. Such methods cannot distinguish LDs having different biofunctionalities in living cells, and thus could be inaccurate in measuring the instantaneous lipogenesis of the living cells. We applied label-free stimulated Raman scattering microscopy to quantify the LDs' spatial-temporal dynamics, which showed direct links to cellular lipid metabolisms and can separate LDs involved in different metabolic events. In human cancer cells, we found that changes in the maximum displacement of LDs reflected variations in cellular lipogenic activity, and changes in the average speed of LDs revealed alterations in LD size. The LD dynamics analysis allowed for more accurate measurement in the lipogenesis and LD dimensions, and can break the optical diffraction limit to detect small variation in lipid metabolism that was conventionally undetectable. By this method, we revealed changes in the lipogenic activity and LD sizes during glucose starvation of HeLa cells and transforming growth factor beta-induced epithelial-to-mesenchymal transition of SKOV-3 cells. This method opens a way to quantify lipid metabolism in living cells during cellular development and transition.
脂质代谢失调与许多疾病有关，包括癌症。脂滴（LD）是哺乳动物细胞中普遍存在的细胞器，是脂质代谢的中心。传统的脂质代谢测量方法依赖于脂质成分或数量的定量。这些方法无法区分活细胞中具有不同生物功能的 LD，因此在测量活细胞的瞬时脂肪生成时可能不准确。我们应用无标记受激拉曼散射显微镜来定量测量 LD 的时空动力学，这与细胞脂质代谢直接相关，并可分离参与不同代谢事件的 LD。在人类癌细胞中，我们发现 LD 的最大位移变化反映了细胞脂肪生成活性的变化，而 LD 平均速度的变化则揭示了 LD 大小的变化。LD 动力学分析可以更准确地测量脂肪生成和 LD 尺寸，并可以突破光学衍射极限，检测传统上无法检测到的脂质代谢微小变化。通过这种方法，我们揭示了 HeLa 细胞在葡萄糖饥饿和 SKOV-3 细胞转化生长因子β诱导的上皮-间充质转化过程中脂肪生成活性和 LD 大小的变化。这种方法为在细胞发育和转变过程中定量测量活细胞中的脂质代谢开辟了一条途径。
