title: Quantitative Spatiotemporal Chemical Profiling of Individual Lipid Droplets by Hyperspectral CARS Microscopy in Living Human Adipose-Derived Stem Cells.
abstract: There is increasing evidence showing that cytosolic lipid droplets, present in all eukaryotic cells, play a key role in many cellular functions. Yet their composition at the individual droplet level and how it evolves over time in living cells is essentially unknown due to the lack of suitable quantitative nondestructive measurement techniques. In this work, we demonstrate the ability of label-free hyperspectral coherent anti-Stokes Raman scattering (CARS) microscopy, together with a quantitative image analysis algorithm developed by us, to quantify the lipid type and content in vol/vol concentration units of individual lipid droplets in living human adipose-derived stem cells during differentiation over 9 days in media supplemented with different fatty acids. Specifically, we investigated the addition of the polyunsaturated linoleic and alpha-linolenic fatty acids into the normal differentiation medium (mostly containing monounsaturated fatty acids). We observe a heterogeneous uptake which is droplet-size dependent, time dependent, and lipid dependent. Cells grown in linoleic-acid-supplemented medium show the largest distribution of lipid content across different droplets at all times during differentiation. When analyzing the average lipid content, we find that adding linoleic or alpha-linolenic fatty acids at day 0 results in uptake of the new lipid components with an exponential time constant of 22 ± 2 h. Conversely, switching lipids at day 3 results in an exponential time constant of 60 ± 5 h. These are unprecedented findings, exemplifying that the quantitative imaging method demonstrated here could open a radically new way of studying and understanding cytosolic lipid droplets in living cells.
authors.affiliation: School of Biosciences, Cardiff University , Cardiff CF10 3AX, United Kingdom.
authors.forename: Claudia
authors.initials: C
authors.lastname: Di Napoli
authors.affiliation: School of Biosciences, Cardiff University , Cardiff CF10 3AX, United Kingdom.
authors.forename: Iestyn
authors.initials: I
authors.lastname: Pope
authors.affiliation: School of Physics and Astronomy, Cardiff University , Cardiff CF10 3AX, United Kingdom.
authors.forename: Francesco
authors.initials: F
authors.lastname: Masia
authors.affiliation: School of Physics and Astronomy, Cardiff University , Cardiff CF10 3AX, United Kingdom.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Langbein
authors.affiliation: School of Biosciences, Cardiff University , Cardiff CF10 3AX, United Kingdom.
authors.forename: Pete
authors.initials: P
authors.lastname: Watson
authors.affiliation: School of Biosciences, Cardiff University , Cardiff CF10 3AX, United Kingdom.
authors.forename: Paola
authors.initials: P
authors.lastname: Borri
mesh_terms: D050156:Adipogenesis; D000273:Adipose Tissue / Q000166:cytology*; D002454:Cell Differentiation; D003470:Culture Media; D005227:Fatty Acids / Q000032:analysis* / Q000737:chemistry; D006801:Humans; D066292:Lipid Droplets / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D013234:Stem Cells / Q000737:chemistry* / Q000166:cytology
chemical_list: D003470:Culture Media; D005227:Fatty Acids