Abstract
Immortal hepatocyte cell lines are widely used to elucidate insulin-dependent signalling pathways and regulation of hepatic metabolism, although the often tumorigenic origin might not represent the metabolic state of healthy hepatocytes. We aimed to investigate if murine cell line AML12 and human cell line THLE-2, which are derived from healthy liver cells, are comparable to hepatoma cell line HepG2 for studying acute insulin signalling and expression of gluconeogenic enzymes and hepatokines. Insulin responsiveness of AML12 and THLE-2 cells was impaired when cells were cultured in the recommended growth medium, but comparable with HepG2 cells by using insulin-deficient medium. THLE-2 cells showed low abundance of insulin receptor, while protein levels in HepG2 and AML12 were comparable. AML12 and THLE-2 cells showed only low or non-detectable transcript levels of G6PC and PCK1. Expression of ANGPTL4 was regulated similarly in HepG2 and AML12 cells upon peroxisome proliferator-activated receptor δ activation but only HepG2 cells resemble the in vivo regulation of hepatic ANGPTL4 by cAMP. Composition of the culture medium and protein expression levels of key signalling proteins should be considered when AML12 and THLE-2 are used to study insulin signalling. With regard to gluconeogenesis and hepatokine expression, HepG2 cells appear to be closer to the in vivo situation despite the tumorigenic origin.
Highlights
The liver plays a key role in energy homoeostasis by regulation of glucose and lipid metabolism and synthesis of hepatokines
Withdrawal of insulin from the growth medium for 24 h led to significant increase of AKT phosphorylation on both sites after acute insulin stimulation compared with insulin-stimulated cells that were cultured in normal growth medium
Human primary hepatocytes represent the ‘gold standard’ for studying hepatic insulin signalling and metabolic regulation on the cellular level [25]. Due to their limited availability, high costs when purchased, variation in quality due to variations in preparation and unstable phenotype, permanent cell lines such as HepG2 that are derived from a hepatocellular carcinoma are often used
Summary
The liver plays a key role in energy homoeostasis by regulation of glucose and lipid metabolism and synthesis of hepatokines. Postprandial glucose is taken up into the liver and hepatic insulin signalling via the AKT pathway leads to various effects such as glycogen storage, inhibition of gluconeogenesis, promotion of lipogenesis and protein synthesis, and activation of pro-survival pathways. Hepatokines are liver-derived proteins that regulate metabolic pathways in other tissues and have attracted much interest in the last few years since they are in focus for the development of drugs targeting diabetes [1,2]. The comprehensive understanding of the signalling pathways that regulate the metabolic functions in the liver is highly important to target the disturbances in pathological states.
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