Dynamin 2 regulates biphasic insulin secretion and plasma glucose homeostasis
Fan Fan, … , Louis H. Philipson, Xuelin Lou
Fan Fan, … , Louis H. Philipson, Xuelin Lou
Published September 28, 2015
Citation Information: J Clin Invest. 2015;125(11):4026-4041. https://doi.org/10.1172/JCI80652.
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Research Article Endocrinology

Dynamin 2 regulates biphasic insulin secretion and plasma glucose homeostasis

Abstract

Alterations in insulin granule exocytosis and endocytosis are paramount to pancreatic β cell dysfunction in diabetes mellitus. Here, using temporally controlled gene ablation specifically in β cells in mice, we identified an essential role of dynamin 2 GTPase in preserving normal biphasic insulin secretion and blood glucose homeostasis. Dynamin 2 deletion in β cells caused glucose intolerance and substantial reduction of the second phase of glucose-stimulated insulin secretion (GSIS); however, mutant β cells still maintained abundant insulin granules, with no signs of cell surface expansion. Compared with control β cells, real-time capacitance measurements demonstrated that exocytosis-endocytosis coupling was less efficient but not abolished; clathrin-mediated endocytosis (CME) was severely impaired at the step of membrane fission, which resulted in accumulation of clathrin-coated endocytic intermediates on the plasma membrane. Moreover, dynamin 2 ablation in β cells led to striking reorganization and enhancement of actin filaments, and insulin granule recruitment and mobilization were impaired at the later stage of GSIS. Together, our results demonstrate that dynamin 2 regulates insulin secretory capacity and dynamics in vivo through a mechanism depending on CME and F-actin remodeling. Moreover, this study indicates a potential pathophysiological link between endocytosis and diabetes mellitus.

Authors

Fan Fan, Chen Ji, Yumei Wu, Shawn M. Ferguson, Natalia Tamarina, Louis H. Philipson, Xuelin Lou

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Figure 3

Dynamin 2 regulates biphasic insulin secretion induced by 20 mM glucose.

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Dynamin 2 regulates biphasic insulin secretion induced by 20 mM glucose....
(A) 20 mM glucose induced biphasic insulin secretion from both control and Dnm2 KO islets (n = 5 independent experiments for each group, n = 30–50 islets per experiment per genotype). (B) 30 mM KCl induced insulin secretion after 10 minutes rest from the same islet samples in A. (C and D) AUC analysis for the first phase (10–20 minutes, n = 5 each; P = 0.17, 2-tailed t test) and the second phase (20–40 minutes, n = 5 each, P = 0.016, 2-tailed t test) of GSIS shown in A. (E) AUC analysis of insulin secretion (P = 0.07, 2-tailed t test) induced by 30 mM KCl from B. (F) Time-lapse live-cell TIRFM of a representative fusion event in a control β cell expressing NPY-pHluorin (20 Hz). (G) Total granule fusion events under TIRFM during the first phase (during the first 0–6 minutes) and the second phase (during minutes 7–20) of GSIS under 20 mM glucose stimulation. Each square in the images marked a single fusion event. (H) The average number of fusion events in the first phase (n = 8 and 14 for control and KO cells, respectively; P = 0.30, 2-tailed t test) and second phase of GSIS (n = 7 and 6 for control and KO cells, respectively; P = 0.01, 2-tailed t test). Scale bars: 1 μm (F); 2 μm (G). **P < 0.01.