JQ1 Epigenetic Modulation of Pancreatic β-Cells (INS-1) Normalizes Glucose Sensitivity under Hyperglycemia: Therapeutic Preventive Implications for Type II Diabetes Mellitus

Abstract

Chronic hyperinsulinemia and insulin resistance are prequels to type II diabetes mellitus (T2D), a disease that affects over 10% of Americans and is closely associated with obesity, as nearly 90% of diabetic patients are overweight or obese. Chronic excess nutrient exposure leads to glucolipotoxicity in pancreatic {beta}-cells, which is characterized by a left shift in glucose concentration-dependent insulin secretion. Previous studies from our laboratory have demonstrated that the Bromodomain and Extra-Terminal (BET) protein inhibitor JQ1 (400 nM) increases fatty acid (FA) oxidation in clonal pancreatic {beta}-cells (INS-1), leading to a partial reversal of glucolipotoxicity. The present research investigates the effect of JQ1 on the glucose sensitivity of INS-1 cells under hyperglycemic conditions. INS-1 cells were pre-treated with dimethyl sulfoxide-based 400 nM JQ1 for 3 days and cultured for 5 days in RPMI 1640 media (11 mM glucose). Subsequently, INS-1 cells were pre-incubated in a modified Krebs-Henseleit buffer (1 mM glucose) before adding test solutions (1-12 mM glucose). Samples for insulin release and cellular content were measured using a Homogeneous Time-Resolved Fluorescence insulin assay kit. Insulin secretion from INS-1 cells cultured in 11 mM glucose was maximally stimulated at 4 mM glucose. Treatment with JQ1 for one day right-shifted maximal glucose-stimulated insulin secretion (GSIS) to 6 mM glucose compared to control but did not prevent stimulated insulin secretion at 4 mM glucose. Three-day treatment with JQ1 reduced secretion at 4 mM glucose to basal level (1 mM) while maintaining the right-shifted concentration-dependent GSIS, an effect described herein for the first time. Total insulin content (TIC) and release as its percentage were also measured, indicating a higher TIC and lower percentage use in JQ1-treated cells. Additionally, lipid concentration was photographically fluorescent analyzed, showing significant depletion of lipid droplets in JQ1-treated cells. Results imply that epigenetic modulation of pancreatic {beta}-cells with JQ1 beneficially alters signal transduction pathways that maintain insulin-glucose homeostasis by ameliorating glucolipotoxicity through the preservation of a low GSIS basal level, increment of GSIS maximum capacity, delay of GSIS cuspid level at 12 mM glucose, more efficient spend of total insulin content resources, and diminished lipid accumulation due to increased FA oxidation--thereby suggesting JQ1 returning hyperglycemic {beta}-cells to physiological conditions. Suggested future directions include improving the efficacy and accuracy of JQ1 and similar small-molecule BET inhibitors through tests in human subjects isolated islets, as this presents an innovative course of research for the prevention of T2D and comorbidities.