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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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 8

Significant reorganization of F-actin in Dnm2 KO β cells and impaired insulin granule recruitment to the PM during GSIS.

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Significant reorganization of F-actin in Dnm2 KO β cells and impaired in...
(A) TIRFM showing a strong fluorescence increase and structural reorganization of the F-actin network (phalloidin) in a Dnm2 KO β cell. Insets show the boxed regions at high magnification. (B) Average fluorescence intensity of F-actin (n = 10 and 11 cells in control and KO; P < 0.01, 2-tailed t test). (C) 3D views of the F-actin network under confocal imaging (at 200 nm z-step). (D) F-actin changes in Dnm2 KO β cells were fully rescued by expressing dynamin 2–RFP. (E) Relative changes of phalloidin fluorescence intensity in control (n = 36), Dnm2 KO (n = 15), and Dnm2 KO cells transfected with dynamin 2–RFP (n = 17 cells; P = 0.002, 1-way ANOVA). (F) The number of insulin granules that were recruited to the PM under TIRFM. Cells were equally stimulated with 20 mM glucose and 10 nM GLP-1 for 1 hour at 37°C and fixed immediately. (G) Significant decrease in the number of insulin granules recruited to the PM after glucose stimulation (n = 25 and 35 cells for control and KO, respectively; P < 0.001, 2-tailed t test). (H) The model depicting dynamin regulation of biphasic GSIS through an actin-dependent mechanism in pancreatic β cells. The dashed line denotes other CME-mediated signaling pathways that may also involved. Scale bars: 5 μm (A and D); 2 μm (F); 1 μm (A, insets). **P < 0.01, ***P < 0.005.