In vivo and in vitro manipulation of AGRP expression and carbohydrate response element binding protein by nutrient status.

Abstract

The purpose of this study is to investigate the control of neuropeptide expression associated with nutrient sensing in vivo and in a neuronal cell line GT1-7. We have shown both in vivo and in neuronal cell lines that low nutrient energy status induces AGRP expression and that high nutrient energy status suppresses the expression of AGRP through AMPkinase mechanisms. Since carbohydrate response element binding protein (ChREBP) is a principal transcription factor regulating glucose-responsive genes in the liver, we speculated that this transcription factor may also be involved in the control of AGRP. Rats were fed a 3 h meal each day for 2 weeks and some were killed before the 3 h meal (low-energy status), and the others were killed after the 3 h meal (high-energy status). A comparison was made of brain and liver response to meal feeding a semi-purified diet. mRNA levels were measured by real-time RT-PCR. Expression of glucokinase, ChREBP, NPY, and AGRP were decrease after the meal in the arcuate nucleus but not in other areas of the brain. To mimic the low energy status in vitro, GT1-7 neuronal cells were incubated with low glucose and amino acids overnight. The cells were then “fed” normal levels of glucose and amino acids for 1 h before harvesting the cells. ChREBP levels were enhanced in the refed neuronal cells. It is proposed that the transcription factor ChREBP is involved in glucose suppression of AGRP expression in the brain.