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SNAP23 depletion enables more SNAP25/calcium channel excitosome formation to increase insulin exocytosis in type 2 diabetes
Tao Liang, … , Jeffrey E. Pessin, Herbert Y. Gaisano
Tao Liang, … , Jeffrey E. Pessin, Herbert Y. Gaisano
Published February 13, 2020
Citation Information: JCI Insight. 2020;5(3):e129694. https://doi.org/10.1172/jci.insight.129694.
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Research Article Endocrinology Metabolism

SNAP23 depletion enables more SNAP25/calcium channel excitosome formation to increase insulin exocytosis in type 2 diabetes

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Abstract

SNAP23 is the ubiquitous SNAP25 isoform that mediates secretion in non-neuronal cells, similar to SNAP25 in neurons. However, some secretory cells like pancreatic islet β cells contain an abundance of both SNAP25 and SNAP23, where SNAP23 is believed to play a redundant role to SNAP25. We show that SNAP23, when depleted in mouse β cells in vivo and human β cells (normal and type 2 diabetes [T2D] patients) in vitro, paradoxically increased biphasic glucose-stimulated insulin secretion corresponding to increased exocytosis of predocked and newcomer insulin granules. Such effects on T2D Goto-Kakizaki rats improved glucose homeostasis that was superior to conventional treatment with sulfonylurea glybenclamide. SNAP23, although fusion competent in slower secretory cells, in the context of β cells acts as a weak partial fusion agonist or inhibitory SNARE. Here, SNAP23 depletion promotes SNAP25 to bind calcium channels more quickly and longer where granule fusion occurs to increase exocytosis efficiency. β Cell SNAP23 antagonism is a strategy to treat diabetes.

Authors

Tao Liang, Tairan Qin, Fei Kang, Youhou Kang, Li Xie, Dan Zhu, Subhankar Dolai, Dafna Greitzer-Antes, Robert K. Baker, Daorong Feng, Eva Tuduri, Claes-Goran Ostenson, Timothy J. Kieffer, Kate Banks, Jeffrey E. Pessin, Herbert Y. Gaisano

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Figure 9

Live-cell single-molecule localization and tracking of SNAP25-mScarlet binding to endogenous Cav1.2. (A) SNAP23-knockout (SNAP23-KO) INS-832/13 cells.

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Live-cell single-molecule localization and tracking of SNAP25-mScarlet b...
(B) SNAP23-overexpressing (OE) INS-832/13 cells. Representative live-cell single-molecule image of SNAP25-mScarlet and Cav-mNeonGreen in SNAP23-KO (A, top left) and SNAP23-OE (B, top left) INS-832/13 cells; these images are representative of 4 independent experiments. (A, top left) Endogenous Cav1.2 in SNAP23-KO cells (mTagBFP2) was labeled with mNeonGreen by an MMEJ-mediated knockin method as previously described (54) and shown in detail in Supplemental Figure 9 and described briefly in the Methods. Right: The trajectories of SNAP25-mScarlet were overlaid onto the locations of the endogenous Cav1.2 clusters (indicated in red circles). (A, top right) Representative intensity traces of single SNAP25-mScarlet molecules binding to Cav1.2 clusters (from top to bottom, white circles 1–3 indicated in A, top left). (A, bottom left) Examples of sequential images of the mobility of single SNAP25-mScarlet coming from the cytoplasm (top: corresponds to white circle indicated as event 4 in A, top left) or along the PM (bottom: corresponds to white circle indicated as event 1 in A, top left) traveling to bind a Cav1.2 cluster; the latter trajectory shown in (A, bottom right). Blue rectangle indicates the start, red circle indicates the location of Cav1.2. (B, top left) Cav1.2-knockin INS-832/13 cells were transfected with SNAP23-SNAPf for 24 hours and then incubated with far-red fluorescent substrate, 647-SiR, for imaging. SNAP25-mScarlet was transfected again for 3 to 6 hours before imaging. Trajectories of SNAP25-mScarlet were overlaid onto the locations of endogenous Cav (indicated as red circles). (B, top right) Representative intensity traces (from top to bottom, white circles 1–3 indicated in B, top left). (B, bottom left) Two examples of sequential images showing the mobility of single SNAP25-mScarlet molecules coming from the cytoplasm (top: corresponds to white circle indicated as event 2 in B, top left) or along the PM (bottom: corresponds to white circle indicated as event 4 in B, top left) traveling to bind Cav1.2 clusters; the latter trajectory shown in B, bottom right. (C) Comparison between SNAP23-KO versus WT versus SNAP23-OE. Left: Cumulative dwell time of SNAP25 binding to Cav1.2 per Cav1.2 clusters. Middle: Cumulative frequency of SNAP25 binding to Cav1.2 per Cav1.2 clusters. Right: Travel time histogram of single events of SNAP25 binding to Cav1.2 (n = 10 each from 4 independent experiments). *P < 0.05. Statistical significance was assessed by repeated-measures ANOVA.

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