Fusion pore regulation by cAMP/Epac2 controls cargo release during insulin exocytosis
Abstract
Regulated exocytosis establishes a narrow fusion pore as initial aqueous connection to the extracellular space, through which small transmitter molecules such as ATP can exit. Co-release of polypeptides and hormones like insulin requires further expansion of the pore. There is evidence that pore expansion is regulated and can fail in diabetes and neurodegenerative disease. Here we report that the cAMP-sensor Epac2 (Rap-GEF4) controls fusion pore behavior by acutely recruiting two pore-restricting proteins, amisyn and dynamin-1, to the exocytosis site in insulin-secreting beta-cells. cAMP elevation restricts and slows fusion pore expansion and peptide release, but not when Epac2 is inactivated pharmacologically or in Epac2-/- (Rapgef4-/-) mice. Consistently, overexpression of Epac2 impedes pore expansion. Widely used antidiabetic drugs (GLP-1 receptor agonists and sulfonylureas) activate this pathway and thereby paradoxically restrict hormone release. We conclude that Epac2/cAMP controls fusion pore expansion and thus the balance of hormone and transmitter release during insulin granule exocytosis.
Data availability
Source data file has been provided for Fig 7. All raw data are available on the Dryad Digital Repository (https://doi.org/10.5061/dryad.6b604g8).
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Data from: Fusion pore regulation by cAMP/Epac2 controls cargo release during insulin exocytosisDryad Digital Repository, doi:10.5061/dryad.6b604g8.
Article and author information
Author details
Funding
Swedish Research Council (2014-02575)
- Anders Tengholm
- Sebastian Barg
Norwegian Research Council
- Marit Bakke
Helse-Bergen
- Marit Bakke
Olga Jönssons stipend
- Alenka Guček
P O Zetterlingsstiftelse
- Alenka Guček
Swedish Research Council (2017-00956)
- Anders Tengholm
- Sebastian Barg
Swedich Research Council (2018-02871)
- Anders Tengholm
- Sebastian Barg
European Foundation for the Study of Diabetes
- Anders Tengholm
- Sebastian Barg
Diabetes Wellness Network Sweden
- Anders Tengholm
- Sebastian Barg
Swedish Diabetes Society
- Anders Tengholm
- Sebastian Barg
Swedish Society for Medical Research
- Nikhil R Gandasi
Hjärnfonden
- Sebastian Barg
NovoNordisk
- Nikhil R Gandasi
- Anders Tengholm
- Sebastian Barg
Family Ernfors Foundation
- Alenka Guček
- Anders Tengholm
- Sebastian Barg
European Foundation for the Study of Diabetes
- Nikhil R Gandasi
- Anders Tengholm
- Sebastian Barg
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: This study was performed in strict accordance with European and Swedish legislation, fundamental ethical principles and approved by the Regional Ethics Board Uppsala (license number 31, 1-32).
Copyright
© 2019, Guček et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Further reading
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- Cell Biology
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Long thought to have little relevance to ovarian physiology, the rete ovarii may have a role in follicular dynamics and reproductive health.
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- Cell Biology
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The rete ovarii (RO) is an appendage of the ovary that has been given little attention. Although the RO appears in drawings of the ovary in early versions of Gray’s Anatomy, it disappeared from recent textbooks, and is often dismissed as a functionless vestige in the adult ovary. Using PAX8 immunostaining and confocal microscopy, we characterized the fetal development of the RO in the context of the mouse ovary. The RO consists of three distinct regions that persist in adult life, the intraovarian rete (IOR), the extraovarian rete (EOR), and the connecting rete (CR). While the cells of the IOR appear to form solid cords within the ovary, the EOR rapidly develops into a convoluted tubular epithelium ending in a distal dilated tip. Cells of the EOR are ciliated and exhibit cellular trafficking capabilities. The CR, connecting the EOR to the IOR, gradually acquires tubular epithelial characteristics by birth. Using microinjections into the distal dilated tip of the EOR, we found that luminal contents flow toward the ovary. Mass spectrometry revealed that the EOR lumen contains secreted proteins potentially important for ovarian function. We show that the cells of the EOR are closely associated with vasculature and macrophages, and are contacted by neuronal projections, consistent with a role as a sensory appendage of the ovary. The direct proximity of the RO to the ovary and its integration with the extraovarian landscape suggest that it plays an important role in ovary development and homeostasis.