Effect of aryl-hydrocarbon receptor activity on lipid accumulation, insulin content and secretion from clonal pancreatic beta-cells
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OBJECTIVE: The aryl hydrocarbon receptor (AhR) translocates to the nucleus and binds to the aryl hydrocarbon receptor nuclear translocator (ARNT) to regulate biological responses upon ligand activation. The aim of this study was to measure the effects of activation or inhibition of AhR activity on basal and glucose-stimulated insulin secretion (GSIS) from clonal pancreatic β-cells (INS-1) cultured under normal and glucolipotoxic (GLT) conditions (high glucose and fatty acid). METHODS: Insulin content and secretion were measured utilizing homogenous time-resolved fluorescence (HTRF) insulin assay kit (cisbio). Cells cultured in RPMI media containing 5 mM and 11 mM glucose were pre-incubated with the receptor agonist FICZ or antagonist CH223191 for 96 hours. Insulin secretion over 2 hours was reported as ng/million cells. Intracellular lipid was measured by fluorescence after Nile red staining. RESULTS: Incubation of INS-1 cells with 11 mM glucose and fatty acid increased lipid droplets, basal insulin secretion and inhibited GSIS compared to cells cultured in 4 mM glucose, characteristic of GLT. Incubation of INS-1 cells with 11 mM glucose alone also exhibited GLT characteristics. INS-1 cells cultured at 11 mM glucose and treated with antagonist (1.25 - 10 μM) had decreased lipid content and improved insulin secretion compared to cells cultured in 11 mM glucose alone. INS-1 cells cultured in 5 mM glucose and treated with the AhR agonist (1.25 - 10 μM) exhibited increased intracellular lipid and impaired insulin secretion. CONCLUSION: The AhR may play a mediatory role in the development of GLT in pancreatic β-cells cultured in excess nutrients and β-cell specific activator or inhibitor ligands of this receptor could potentially be a targeted therapeutic treatment of diabetes.