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 β cells, and mediate effects of incretins and fatty acids in β cells. Glucose and 5-AMP-activated protein kinase (AMPK) are known to be involved in the regulation of β 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 β cell. INS-1 β 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 α (PPARα) – 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 PPARα were downregulated when INS-1β 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 PPARα, but not GPR40 in β cells. Whether AMPK is a key regulator of these factors mediated receptor regulation remains to be investigated further.

Key words

beta cells - glucose - incretins - metformin

References

• 1 Del Prato S, Marchetti P. Beta- and alpha-cell dysfunction in type 2 diabetes.  Horm Metab Res. 2004;  36 775-781
• 2 Brown AJ, Jupe S, Briscoe CP. A family of fatty acid binding receptors.  DNA Cell Biol. 2005;  24 54-61
• 3 Yamada Y, Seino Y. Physiology of GIP – a lesson from GIP receptor knockout mice.  Horm Metab Res. 2004;  36 771-774
• 4 Meier JJ, Nauck MA. GIP as a potential therapeutic agent?.  Horm Metab Res. 2004;  36 859-866
• 5 Itoh Y, Kawamata Y, Harada M, Kobayashi M, Fujii R, Fukusumi S, Ogi K, Hosoya M, Tanaka Y, Uejima H, Tanaka H, Maruyama M, Satoh R, Okubo S, Kizawa H, Komatsu H, Matsumura F, Noguchi Y, Shinohara T, Hinuma S, Fujisawa Y, Fujino M. Free fatty acids regulate insulin secretion from pancreatic beta cells through GPR40.  Nature. 2003;  422 173-176
• 6 Briscoe CP, Tadayyon M, Andrews JL, Benson WG, Chambers JK, Eilert MM, Ellis C, Elshourbagy NA, Goetz AS, Minnick DT, Murdock PR, Sauls HR, Shabon U, Spinage LD, Strum JC, Szekeres PG, Tan KB, Way JM, Ignar DM, Wilson S, Muir AI. The orphan G protein-coupled receptor GPR40 is activated by medium and long chain fatty acids.  J Biol Chem. 2003;  278 11303-11311
• 7 Shapiro H, Shachar S, Sekler I, Hershfinkel M, Walker MD. Role of GPR40 in fatty acid action on the beta cell line INS-1E, Biochem.  Biophys Res Commun. 2005;  335 97-104
• 8 Schnell S, Schaefer M, Schofl C. Free fatty acids increase cytosolic free calcium and stimulate insulin secretion from beta-cells through activation of GPR40.  Mol Cell Endocrinol. 2007;  263 173-180
• 9 Steneberg P, Rubins N, Bartoov-Shifman R, Walker MD, Edlund H. The FFA receptor GPR40 links hyperinsulinemia, hepatic steatosis, and impaired glucose homeostasis in mouse.  Cell Metab. 2005;  1 245-258
• 10 Bensellam M, Van Lommel L, Overbergh L, Schuit FC, Jonas JC. Cluster analysis of rat pancreatic islet gene mRNA levels after culture in low-, intermediate- and high-glucose concentrations.  Diabetologia. 2009;  52 463-476
• 11 Hardie DG, Hawley SA, Scott JW. AMP-activated protein kinase-development of the energy sensor concept.  J Physiol. 2006;  574 7-15
• 12 Lynn FC, Thompson SA, Pospisilik JA, Ehses JA, Hinke SA, Pamir N, McIntosh CH, Pederson RA. A novel pathway for regulation of glucose-dependent insulinotropic polypeptide (GIP) receptor expression in beta cells.  FASEB J. 2003;  17 91-93
• 13 Ling Z, Kiekens R, Mahler T, Schuit FC, Pipeleers-Marichal M, Sener A, Kloppel G, Malaisse WJ, Pipeleers DG. Effects of chronically elevated glucose levels on the functional properties of rat pancreatic β-cells.  Diabetes. 1996;  45 1774-1782
• 14 Päth G, Opel A, Knoll A, Seufert J. Nuclear protein p8 is associated with glucose-induced pancreatic beta-cell growth.  Diabetes. 2004;  53 ((Suppl 1)) S82-S85
• 15 Holst JJ, Gromada J, Nauck MA. The pathogenesis of NIDDM involves a defective expression of the GIP receptor.  Diabetologia. 1997;  40 984-986
• 16 Lynn FC, Pamir N, Ng EH, McIntosh CH, Kieffer TJ, Pederson RA. Defective glucose-dependent insulinotropic polypeptide receptor expression in diabetic fatty Zucker rats.  Diabetes. 2001;  50 1004-1011
• 17 Nauck MA, Heimesaat MM, Orskov C, Holst JJ, Ebert R, Creutzfeldt W. Preserved incretin activity of glucagon-like peptide 1 [7-36amide] but not of synthetic human gastric inhibitory polypeptide in patients with type-2 diabetes mellitus.  J Clin Invest. 1993;  91 301-307
• 18 Kjems LL, Holst JJ, Volund A, Madsbad S. The influence of GLP-1 on glucose-stimulated insulin secretion: effects on beta-cell sensitivity in type 2 and nondiabetic subjects.  Diabetes. 2003;  52 380-386
• 19 Valverde I, Wang GS, Burghardt K, Kauri LM, Redondo A, Acitores A, Villanueva-Penacarrillo ML, Courtois P, Sener A, Cancelas J, Malaisse WJ, Scott FW. Bioactive GLP-1 in gut, receptor expression in pancreas and insulin response to GLP-1 in diabetes-prone rats.  Endocrine. 2004;  23 77-84
• 20 Xu G, Kaneto H, Laybutt DR, Duvivier-Kali VF, Trivedi N, Suzuma K, King GL, Weir GC, Bonner-Weir S. Downregulation of GLP-1 and GIP receptor expression by hyperglycemia: possible contribution to impaired incretin effects in diabetes.  Diabetes. 2007;  56 1551-1558
• 21 Da S, X, Leclerc I, Varadi A, Tsuboi T, Moule SK, Rutter GA. Role for AMP-activated protein kinase in glucose-stimulated insulin secretion and preproinsulin gene expression.  Biochem J. 2003;  371 761-774
• 22 Kefas BA, Cai Y, Kerckhofs K, Ling Z, Martens G, Heimberg H, Pipeleers D, Van de CM. Metformin-induced stimulation of AMP-activated protein kinase in beta-cells impairs their glucose responsiveness and can lead to apoptosis.  Biochem Pharmacol. 2004;  68 409-416
• 23 Kefas BA, Cai Y, Ling Z, Heimberg H, Hue L, Pipeleers D, Van de CM. AMP-activated protein kinase can induce apoptosis of insulin-producing MIN6 cells through stimulation of c-Jun-N-terminal kinase.  J Mol Endocrinol. 2003;  30 151-161
• 24 Kefas BA, Heimberg H, Vaulont S, Meisse D, Hue L, Pipeleers D, Van de CM. AICA-riboside induces apoptosis of pancreatic beta cells through stimulation of AMP-activated protein kinase.  Diabetologia. 2003;  46 250-254
• 25 Pold R, Jensen LS, Jessen N, Buhl ES, Schmitz O, Flyvbjerg A, Fujii N, Goodyear LJ, Gotfredsen CF, Brand CL, Lund S. Long-term AICAR administration and exercise prevents diabetes in ZDF rats.  Diabetes. 2005;  54 928-934
• 26 Roche E, Farfari S, Witters LA, Assimacopoulos-Jeannet F, Thumelin S, Brun T, Corkey BE, Saha AK, Prentki M. Long-term exposure of beta-INS cells to high glucose concentrations increases anaplerosis, lipogenesis, and lipogenic gene expression.  Diabetes. 1998;  47 1086-1094
• 27 Kahn BB, Alquier T, Carling D, Hardie DG. AMP-activated protein kinase: ancient energy gauge provides clues to modern understanding of metabolism.  Cell Metab. 2005;  1 15-25
• 28 Ravnskjaer K, Boergesen M, Dalgaard LT, Mandrup S. Glucose-induced repression of PPARalpha gene expression in pancreatic beta-cells involves PP2A activation and AMPK inactivation.  J Mol Endocrinol. 2006;  36 289-299

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