Insulin Promotes the Expression of the Gluconeogenic Rate-Limiting Enzymes Phosphoenolpyruvate Carboxykinase (Pepck) and Glucose 6-Phosphatase (G6pase) through PI3k/Akt/mTOR Signaling Pathway in Goose Hepatocytes

Xp Xiong,Sh Wei,Q Song,F He,Hh Liu,Hy Xu,W Gan,Cc Han

doi:10.1590/1806-9061-2015-0080

Xp Xiong, Sh Wei + Show 6 more

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https://doi.org/10.1590/1806-9061-2015-0080

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Abstract

To identify what makes insulin have an activating or inhibiting role in gluconeogenesis in goose hepatocytes and whether insulin regulates PEPCK and G6Pase through the PI3k/Akt/mTOR pathway or not, goose primary hepatocytes were isolated and cultured in vitro. After 12h cultured in serum-free medium, hepatocytes were incubated for 24 h in the medium with no addition (control) or with the addition of50, 100, and 150 nM of insulin, 1000 nM NVP-BEZ235, or co-addition of 150nM insulin and 1000nM NVP-BEZ235. Glucose concentration and PEPCK and G6Pase expression were determined. The results showed that PEPCK and G6Pase mRNA levels and activities were up regulated in the 50, 100, and 150nM insulin treatments, while glucose concentration was not significantly altered (p> 0.05). Compared with the activation role of 150nM insulin alone, the co-treatment with1000nM NVP-BEZ235 and 150nM insulin significantly down regulated PEPCK mRNA level and G6Pase protein activity (p< 0.05). However, there is a different result on mRNA level of G6Pase. In conclusion, G6Pase and PEPCK are up regulated by insulin through PI3k/Akt/mTOR pathway in goose hepatocytes. However, G6Pase mRNA and protein levels may be regulated by insulin through different signaling pathways.

Highlights

Insulin, secreted from pancreatic β cells, is a known primary regulator of glucose metabolism, by counter regulatory glucagon and growth hormone (Cryer,1993; Saltiel & Kahn,2001)
The concentration of 50 nM insulin showed maximum up regulation of mRNA expression of G6Pase and PEPCK, and the 150nM insulin treatment group has the strongest effect on the increase of G6Paseprotein activity
Many previous studies have shown that insulin strongly inhibited the expression of G6Pase and PEPCK (O’Brien & Granner, 1996; Argaud et al, 1996), another study showed that insulin failed to inhibit

Summary

Introduction

Insulin, secreted from pancreatic β cells, is a known primary regulator of glucose metabolism, by counter regulatory glucagon and growth hormone (Cryer,1993; Saltiel & Kahn,2001). As the only hormone that lowers blood glucose in vivo, insulin plays an important role in hepatic glucose production. Insulin action is impaired, resulting in increased hepatic glucose production (Prasad et al, 2005). Many studies indicated that insulin has a close relationship with gluconeogenesis. Donkin & Armentano (1995) showed that insulin reduced gluconeogenesis and increased glycogenesis from propionate and lactate in hepatocytes of pre-ruminating calves, but had no effect on the hepatocytes of ruminating calves. A study showed that modulated gluconeogenesis by inhibiting of the coactivator TORC2 (Dentin et al, 2007)

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