Subcellular Translocation of Fatty Acid-Binding Protein 5 (FABP5) in Glucose-Dependent Insulinotropic Polypeptide (GIP)-Producing K-Cells: Re-Emerging Role of Transmission Electron Microscope

Presentation Number: SAT 578
Date of Presentation: April 1st, 2017

Kimitaka Shibue*1, Yotsapon Thewjitcharoen2, Shunsuke Yamane2, Norio Harada2, Takanari Harada2, Yuta Fujiwara2, Kazuyo Suzuki2, Yu Wang2, Keiko Furuta3, Yuji Owada4 and Nobuya Inagaki1
1Kyoto University Graduate School of Medicine, Kyoto, Japan, 2Graduate School of medicine ,Kyoto University, Kyoto, Japan, 3Graduate School of Medicine, Kyoto University, Kyoto, Japan, 4Tohoku University,Sendai, Sendai, Japan

Abstract

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone that not only potentiates insulin secretion but also links over-nutrition to obesity. Due to scarcity of enteroendocrine K-cells (less than 0.1% of all intestinal epithelial cells in upper small intestine), it had been very difficult to localize and study K-cells in details. Previously, we established GIP-green fluorescent protein (GFP) knock-in (GIP-GFP) mice that enable us to visualize K-cells by detecting GFP fluorescence and recently we demonstrated that fatty acid-binding protein 5 (FABP5), an intracellular lipid chaperone, is localized in K-cells and involved in GIP secretion. To elucidate the role of FABP5 in GIP secretion, we used a pre-embedding immunonanogold-labeling technique for transmission electron microscopy (TEM) to connect a visible structure of K-cell with a specific in situ localization and distribution of FABP5 molecules at a high resolution. Our study revealed that FABP5 translocated from nucleus to attach with GIP-producing secretory vesicles in response to acute fat ingestion. Measuring distances between vesicles and gold particles was evaluated and showed greater distances in fasted state when compared with those in fed state (3.9±2.1 nm VS. 1.5±0.6 nm) and the mean number of gold particles were 2 particles per one granule in fasted state compared with 6 particles per one granule in fed state. Both conditions confirmed that FABP5 did not incorporate into vesicles. From these results, we hypothesize that FABP5 may be involved in the latter stage of the GIP secretion pathway inside K-cells and the nucleocytoplasmic shuttling of FABP5 might be necessary to increase efflux of nuclear FABP5 into cytoplasm. Therefore, FABP5 might be moved bi-directionally depending on the level of lipid stimulation. Taken together, we successfully demonstrated the utility of TEM approach with anti-FABP5 antibody as a specific marker for gut K-cells and revealed subcellular translocalization of FABP5 in the pathway of GIP secretion. Re-emerging role of TEM could expand our knowledge on structure-function relationships into not only gut K-cells physiology but also the regulation of secretion by other enteroendocrine cell populations.

 

Nothing to Disclose: KS, YT, SY, NH, TH, YF, KS, YW, KF, YO, NI