Intracellular Fatty Acids Imaged by Scanning X-Ray Fluorescence Microscopy

Fatty acid metabolism abnormality is closely involved with many diseases, so many biochemical research results have been reported. In such a setting, intracellular imaging of fatty acids was thought difficult to achieve because of the difficulty in labelling small molecules of fatty acid. In actuality, labelling big fluorescence molecules greatly inhibits fatty acid metabolism. Observation of unlabelled cells with mass spectrometry or Raman microscope was beneficial, but it was difficult to observe them at the cellular or organelle level.

A joint research group of researchers at The University of Tokyo Graduate School of Medicine, Centre national de la recherche scientifique (CNRS), Osaka University Graduate School of Engineering, RIKEN Spring-8 Centre, Waseda University Department of Applied Chemistry, and the Research Institute National Centre for Global Health and Medicine developed a method for labelling fatty acids with bromine (Br) and applied scanning X-ray fluorescence microscopy (SXFM) at the large synchrotron radiation facility Spring-8. This is the first method for achieving high-resolution imaging of intracellular fatty acids.

In the mice-derived CHO-K1 cells used in this study, labelled element signals from cells were observed around a cell nucleus, exhibiting a distribution similar to that of endoplasmic reticulum and Golgi body. Many enzymes to synthesize intercellular fatty acids were common in that area, so it was expected that many fatty acids would be observed.

Major cell toxicity was not observed in the course of the experiment. In the biochemical study, it was clarified that most element-labelled fatty acids taken up by cells were metabolized into phosphatide. From this, it is thought that the obtained element distribution was that of intracellular-labelled phosphatide. This group also succeeded in visualizing the spot-like distribution of Br of about 1μ in diameter in the cytoplasm with a resolution of some 250 nm, a world first. SXFM can visualize intracellular labelled fatty acid structures sized 1μ or less providing the organelle-level resolution.

It will become possible to clarify changes in lipid metabolism through visualization of intracellular localization at an organelle level by performing single-element labelling on various fatty acids. It is expected that the use of SXFM will develop research on various life phenomena and various disorders, including inflammation, vascular impairment, and neurological disorders.

Reference: 
Shimura, M., Shindou, H., Szyrwiel, L., Tokuoka, S. M., Hamano, F., Matsuyama, S., Shimizu, T. (2016). Imaging of intracellular fatty acids by scanning x-ray fluorescence microscopy. The FASEB Journal, 30(12), 4149–4158. doi:10.1096/fj.201600569r

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