Figure 3: Cholesterol accumulation in pancreatic beta cells and its effect on GLP-1R mediated potentiation of GSIS.

(A) The cells were incubated with 160 μM cholesterol for 1 h or 12 h following which total cholesterol is measured. Data are normalized as μg/mg protein and presented as mean ± SEM of 3 independent experiments. (B) Time-course analysis of GLP-1R internalization in control and cholesterol enriched BRIN-BD11 pancreatic beta cells. Cells were transfected with GFP tagged GLP-1R and stimulated with 1 μM GLP-1Tmr for 0 min and 30 min and visualized by confocal microscopy. Images are representative of three independent experiments.(Scale: 7.5 μm) (C) Insulin exocytosis from BRIN-BD11 pancreatic beta cells following 1 h treatment with soluble cholesterol in presence of 0.1 mM glucose and 16.7 mM glucose. Insulin secretion was measured as ng insulin /mg protein and the data was expressed as fold increase over untreated control (basal insulin secretion at 0.1 mM glucose as well as basal insulin secretion at 16.7 mM glucose is considered as 1 fold and the respective cholesterol mediated insulin exocytosis is compared). (D) GLP-1R mediated potentiation of GSIS in cholesterol enriched pancreatic beta cells. Control and cholesterol enriched BRIN-BD11 cells were treated with GLP-1R agonist Exendin-4(Ex-4) in presence of 16.7 mM glucose and insulin secretion was measured as ng insulin/mg protein for a period of 30 min. Insulin secretion from untreated cells in presence of 0.1 mM glucose is considered as basal. Data are expressed as fold increase of insulin secretion over basal secretion and presented as mean ± SEM of 4 independent experiments.