Glucose, Metformin, and AICAR Regulate the Expression of G Protein-coupled Receptor Members in INS-1 β Cell

Abstract

Glucagon-like peptide-1 receptor (GLP-1R), glucose-dependent insulinotropic polypeptide receptor (GIPR), and G protein-coupled receptor 40 (GPR40) are members of G protein-coupled receptors (GPCR) family. They are abundantly expressed in islet beta cells, and mediate effects of incretins and fatty acids in beta cells. Glucose and 5-AMP-activated protein kinase (AMPK) are known to be involved in the regulation of beta cell function. Metformin and the potential therapeutic drug for type 2 diabetes, 5-amino-4-imidazolecarboxamide riboside (AICAR), are both known activators of AMPK. Here we studied the effects of glucose, metformin, and AICAR on the expression of GPCR in INS-1 beta cell. INS-1 beta cells were supplemented with different concentrations of glucose, metformin, or AICAR. The expressions of GLP-1R, GIPR, GPR40, and a nuclear transcription factor - peroxisome-proliferator activated receptor alpha (PPARalpha) - were analyzed by real-time RT-PCR and immunoblotting. The time-course of the mRNA degradation of these receptors was also monitored by applying actinomycin D to cells. We demonstrated that the expressions of GLP-1R, GIPR, and PPARalpha were downregulated when INS-1beta cells were treated with glucose, while their expressions were upregulated when treated with metformin or AICAR. Glucose, metformin, or AICAR treatment had no obvious effect on the expression of GPR40. These results indicate that glucose, metformin, and AICAR regulated the expressions of incretin receptors and PPARalpha, but not GPR40 in beta cells. Whether AMPK is a key regulator of these factors mediated receptor regulation remains to be investigated further.

Metformin regulates the incretin receptor axis via a pathway dependent on peroxisome proliferator-activated receptor-α in mice

“…In the second section of our study, we demonstrated that subchronic treatment of mice with metformin leads to enhanced expression of the Glp1r and Gipr genes in murine islets. Pan and colleagues indirectly implicated a role for AMPK in the actions of metformin on islet gene expression via their demonstration that AICAR mimicked the actions of metformin on Glp1r and Gipr mRNA transcripts in INS-1 cells [26]. In contrast, our data demonstrate that AICAR downregulates Glp1r and Gipr mRNA transcripts in INS-1 832/3 beta cells.…”

“…The effect of metformin on islet incretin receptor expression As metformin upregulates the expression of incretin receptors in an islet cell line in vitro [26], we assessed whether metformin modulates pancreatic or islet incretin receptor expression in murine islets. Metformin-treated mice (Fig.…”

Link between metformin and the peroxisome proliferator-activated receptor γ pathway in the uterine tissue of hyperandrogenized prepubertal mice

“…It is known that the uterine PPARg pathway regulates implantation in mice by modulating the 12/15 LOX system (26). These findings, together with the fact that metformin and the PPAR system have been related in a synergistic action (27,28), led us to study the expression of PPARg, 12-LOX, and 15-LOX in uterine tissue from hyperandrogenized mice and their relationship with the metformin treatment.…”

Insulin down-regulates the expression of ubiquitin E3 ligases partially by inhibiting the activity and expression of AMP-activated protein kinase in L6 myotubes

“…We used an AICAR [19] and inhibitor (compound C) [20] to determine the effects of AMPK on the mRNA expression of ubiquitin E3 ligases. When AICAR activates AMPK, we show that the mRNA expression of ubiquitin E3 ligases is enhanced, which is consistent with a previous study [6].…”