title: Quantification of Lipid Metabolism in Living Cells through the Dynamics of Lipid Droplets Measured by Stimulated Raman Scattering Imaging.
abstract: 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.
authors.affiliation: Weldon School of Biomedical Engineering, Purdue University . 206 S. Martin Jischke Drive, West Lafayette, Indiana 47906, United States.
authors.forename: Chi
authors.identifier: 0000-0002-7735-5614
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Weldon School of Biomedical Engineering, Purdue University . 206 S. Martin Jischke Drive, West Lafayette, Indiana 47906, United States.
authors.forename: Junjie
authors.initials: J
authors.lastname: Li
authors.affiliation: Weldon School of Biomedical Engineering, Purdue University . 206 S. Martin Jischke Drive, West Lafayette, Indiana 47906, United States.
authors.forename: Lu
authors.initials: L
authors.lastname: Lan
authors.affiliation: Weldon School of Biomedical Engineering, Purdue University . 206 S. Martin Jischke Drive, West Lafayette, Indiana 47906, United States.
authors.forename: Ji-Xin
authors.initials: JX
authors.lastname: Cheng
mesh_terms: D045744:Cell Line, Tumor; D058750:Epithelial-Mesenchymal Transition / Q000187:drug effects; D005947:Glucose / Q000172:deficiency; D006367:HeLa Cells; D006801:Humans; D066292:Lipid Droplets / Q000737:chemistry*; D050356:Lipid Metabolism; D000073758:Nonlinear Optical Microscopy; D016212:Transforming Growth Factor beta / Q000494:pharmacology
chemical_list: D016212:Transforming Growth Factor beta; D005947:Glucose