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6-Ketocholestanol suppresses lipid accumulation by decreasing FASN gene expression through SREBP-dependent regulation in HepG2 cells

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Abstract

Nuclear receptors, such as liver X receptors (LXRs) and sterol regulatory element-binding proteins (SREBPs), are key regulators of lipogenic genes, including fatty acid synthase (FASN). It has been reported that several oxycholesterols (OCs) act as LXR ligands; however, it is unclear whether all OC molecular species act as ligands. We previously demonstrated that the absorption rate of dietary 6-ketocholestanol (6-keto), an oxycholesterol, is the highest of all the OCs using thoracic lymph duct-cannulated rats. However, limited information is available about the physiological significance of 6-keto. In this study, we investigated whether treatment with 6-keto increases intracellular triacylglycerol (TAG) levels through up-regulation of lipogenic gene expression in HepG2 cells. 6-Keto treatment significantly reduced intracellular TAG levels through down-regulation of lipogenic genes including FASN. Although 6-keto significantly suppressed FASN gene promoter activities, the action was completely diminished when mutations were present in the SREBP promoter site. TO901317 (TO) significantly increased FASN gene promoter activities, whereas simultaneous treatment with TO and 6-keto significantly reduced this activity. We also compared the effects of several OCs that are oxidized at the carbon-6 and -7 in the B-ring of cholesterol on FASN gene promoter activities. Similar to 6-keto, 6α-OH and 6β-OH significantly reduced the activity of the FASN gene promoter, which suggests that oxidation of carbon-6 in the B-ring may play an important role in the reduction of FASN expression. Our results indicate that 6-keto suppresses lipid accumulation by decreasing FASN gene expression through SREBP-dependent regulation in HepG2 cells.

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Acknowledgements

This work was supported by JSPS KAKENHI Grant Number 21580144. The authors thank Editage (www.editage.jp) for English language editing.

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Authors and Affiliations

  1. Laboratory of Nutrition Chemistry, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan

    Bungo Shirouchi, Shuhei Yanagi, Chinami Okawa, Maiko Koga & Masao Sato

Authors
  1. Bungo Shirouchi
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  2. Shuhei Yanagi
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  3. Chinami Okawa
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  4. Maiko Koga
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  5. Masao Sato
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Contributions

BS wrote the manuscript. SY, CO, and MK participated in the experimental work and collected and analyzed data. BS and MS contributed to the study design, supervised the study, and commented on the manuscript. All authors have read and approved the final version of the manuscript.

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Correspondence to Masao Sato.

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Supplemental Fig. 1.

The sequence of the human FASN promoter region. Underlines indicate selected regulatory elements. LXRE, liver X receptor response element; SRE, sterol response element; SREBP, sterol regulatory element-binding protein. Supplemental Fig. 2. The sequences of wild type and mutant LXRE and SREBP elements from the rat Fasn promoter region. Underlines indicate selected regulatory elements. Dotted bases indicate mutations in the LXRE and SREBP elements. LXRE, liver X receptor response element; SRE, sterol response element; SREBP, sterol regulatory element-binding protein. (PPTX 52 kb)

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Shirouchi, B., Yanagi, S., Okawa, C. et al. 6-Ketocholestanol suppresses lipid accumulation by decreasing FASN gene expression through SREBP-dependent regulation in HepG2 cells. Cytotechnology 72, 175–187 (2020). https://doi.org/10.1007/s10616-019-00368-5

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  • DOI: https://doi.org/10.1007/s10616-019-00368-5

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