Figure 8.

mTOR Inhibition Affects Stimulus-Secretion Coupling in Cells Exposed to Excess Glucose

(A–D) INS-1 cells or intact mouse islets cultured in physiological glucose were exposed to excess glucose in the presence or absence of KU, transferred to serum-free media, and stimulated with the indicated glucose dose for assessment of insulin secretion. (A) Diagram depicting the media composition and glucose concentrations throughout the different stages of the experimental timeline for (A)–(D). (B) Insulin secretion of INS-1 cells under sub-stimulatory (2 and 4 mM) and stimulatory (8 mM) glucose. (C) Same data shown in (B) but highlighting the effect on secretion at sub-stimulatory glucose. (D) Insulin secretion of freshly isolated mouse islets under sub-stimulatory (3 and 5 mM) and stimulatory (8 mM) glucose. Islets were treated as described in (A), with small adjustments in the glucose concentrations used, which were 6 mM for physiological, 12 mM for excess, and 3 mM for resting glucose. Cells kept in physiological glucose are shown in light gray bars, and cells pre-exposed to excess glucose are shown in dark gray bars, with KU (hatched bars) or without (solid bars). (B,C) Data shown are the secretion normalized by the 2 mM glucose dose and is the average and standard error of four independent experiments with three replicates each. (D) Data shown are the average and standard error from three separate replicas and are representative of three separate experiments.

(E) Potential model to explain the role of mTORC1 hyperactivation in metabolic reprograming due to exposure to excess glucose.