Dynamin 2 regulates biphasic insulin secretion and plasma glucose homeostasis
Fan Fan, Chen Ji, Yumei Wu, Shawn M. Ferguson, Natalia Tamarina, Louis H. Philipson, Xuelin Lou
Fan Fan, Chen Ji, Yumei Wu, Shawn M. Ferguson, Natalia Tamarina, Louis H. Philipson, Xuelin Lou
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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 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.