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Inhibition of exendin-4-induced steatosis by protein kinase A in cultured HepG2 human hepatoma cells

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Abstract

Nonalcoholic fatty liver is characterized by the abnormal accumulation of triglycerides within hepatocytes, resulting in a steatotic liver. Glucagon-like peptide 1 and its analog exendin-4 can ameliorate certain aspects of this syndrome by inducing weight loss and reducing hepatic triglyceride accumulation, but it is unclear whether these effects result from the effects of glucagon-like peptide 1 on the pancreas, or from direct action on the liver. This study investigated the direct action and putative cellular mechanism of exendin-4 on steatotic hepatocytes in culture. Steatosis was induced in cultured HepG2 human hepatoma cells by incubation in media supplemented with 2 mM each of linoleic acid and oleic acid. Steatotic hepatocytes were then pre-incubated in the protein kinase A inhibitor H89 for 30 min, then treated with exendin-4 over a period of 24 h. Cell viability and triglyceride content were characterized by a TUNEL assay and AdipoRed staining, respectively. Our results showed that steatotic cells maintained high levels of intracellular triglycerides (80%) compared to lean controls (25%). Exendin-4 treatment caused a significant reduction in intracellular triglyceride content after 12 h that persisted through 24 h, while protein kinase A inhibitors abolished the effects of exendin-4. The results demonstrate the exendin-4 induces a partial reduction in triglycerides in steatotic hepatocytes within 12 h via the GLP-1 receptor-mediated activation of protein kinase A. Thus, the reduction in hepatocyte triglyceride accumulation is likely driven primarily by downregulation of lipogenesis and upregulation of β-oxidation of free fatty acids.

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Acknowledgements

This work was pioneered by AC as part of the Cellular Bioengineering Summer Undergraduate Research Program at Rutgers University (supported by the NSF EEC 1262924). This work was supported by the Ellen Miller Casey Award to AC, Research as a High Impact Practice student funding program awarded to GH, and internal funds from the University of Scranton awarded to GG.

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Author notes

  1. Alice Y. Chen-Liaw

    Present address: Mt. Sinai School of Medicine, New York, NY, USA

Authors and Affiliations

  1. Biology Department, University of Scranton, 800 Linden Street, Scranton, PA, 18510, USA

    Alice Y. Chen-Liaw, Gabrielle Hammel & George Gomez

  2. Loyola Science Center 395, 204 Monroe Ave, Scranton, PA, 18510, USA

    George Gomez

Authors
  1. Alice Y. Chen-Liaw
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  2. Gabrielle Hammel
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  3. George Gomez
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Correspondence to George Gomez.

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Editor: Tetsuji Okamoto

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Chen-Liaw, A.Y., Hammel, G. & Gomez, G. Inhibition of exendin-4-induced steatosis by protein kinase A in cultured HepG2 human hepatoma cells. In Vitro Cell.Dev.Biol.-Animal 53, 721–727 (2017). https://doi.org/10.1007/s11626-017-0181-y

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  • DOI: https://doi.org/10.1007/s11626-017-0181-y

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