Chen-Liaw Alice Y, Hammel Gabrielle, Gomez George
Biology Department, University of Scranton, 800 Linden Street, Scranton, PA, 18510, USA.
Mt. Sinai School of Medicine, New York, NY, USA.
In Vitro Cell Dev Biol Anim. 2017 Sep;53(8):721-727. doi: 10.1007/s11626-017-0181-y. Epub 2017 Jul 13.
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.
非酒精性脂肪肝的特征是肝细胞内甘油三酯异常蓄积，导致肝脏脂肪变性。胰高血糖素样肽1及其类似物艾塞那肽-4可通过诱导体重减轻和减少肝脏甘油三酯蓄积来改善该综合征的某些方面，但尚不清楚这些作用是源于胰高血糖素样肽1对胰腺的作用，还是对肝脏的直接作用。本研究调查了艾塞那肽-4对培养的脂肪变性肝细胞的直接作用及其假定的细胞机制。通过在补充有2 mM亚油酸和油酸的培养基中孵育，在培养的HepG2人肝癌细胞中诱导脂肪变性。然后将脂肪变性肝细胞在蛋白激酶A抑制剂H89中预孵育30分钟，然后用艾塞那肽-4处理24小时。分别通过TUNEL测定和AdipoRed染色来表征细胞活力和甘油三酯含量。我们的结果表明，与瘦对照（25%）相比，脂肪变性细胞维持高水平的细胞内甘油三酯（80%）。艾塞那肽-4处理在12小时后导致细胞内甘油三酯含量显著降低，并持续至24小时，而蛋白激酶A抑制剂消除了艾塞那肽-4的作用。结果表明，艾塞那肽-4在12小时内通过GLP-1受体介导的蛋白激酶A激活诱导脂肪变性肝细胞内甘油三酯部分减少。因此，肝细胞甘油三酯蓄积的减少可能主要是由脂肪生成的下调和游离脂肪酸β-氧化的上调驱动的。
