Exocytosis in insulin secreting cells - role of SNARE-proteins
Author
Summary, in English
Type 2 diabetes is marked by deterioration in pancreatic β-cell function. SNARE-proteins are crucial for the fusion of insulin granules with the plasma membrane, a prerequisite for insulin secretion. The aim of this thesis has been to investigate the exocytotic process in β-cells with a specific focus on the function and significance of the two SNARE-proteins SNAP-25 and syntaxin 1.
SNAP-25 and syntaxin 1 was discovered to be situated in clusters along the plasma membrane. Immunoneutralization of syntaxin 1 and SNAP-25 resulted in a strongly reduced exocytotic response of primed granules in close association with the voltage-dependent calcium channels.
Cholesterol is an essential component of the plasma membrane. Desorption of cholesterol from the plasma membrane in β-cells were accompanied with an overall reduction in the response of β-cells, from insulin secretion to exocytosis. We believe this is due to disturbance of a basic mechanism. Indeed, we found that SNAP-25 migrated from the plasma membrane out to the cytosol.
The stimulating effect of cAMP on insulin secretion is implemented through different pathways. One pathway is through cAMP-GEFII and its downstream affector RIM2. We show that SNAP-25 binds to both cAMP-GEFII and RIM2, and that this binding mediates the effects of cAMP on exocytosis.
The blind-drunk mouse carries a mutation in SNAP-25 that results in increased binding affinities within the SNARE-complex and the consequence in pancreatic β-cells are impaired vesicle recycling and granule exocytosis.
These results together demonstrate the significance of a functional exocytotic machinery for β-cells to respond satisfying to an elevation in blood glucose.
SNAP-25 and syntaxin 1 was discovered to be situated in clusters along the plasma membrane. Immunoneutralization of syntaxin 1 and SNAP-25 resulted in a strongly reduced exocytotic response of primed granules in close association with the voltage-dependent calcium channels.
Cholesterol is an essential component of the plasma membrane. Desorption of cholesterol from the plasma membrane in β-cells were accompanied with an overall reduction in the response of β-cells, from insulin secretion to exocytosis. We believe this is due to disturbance of a basic mechanism. Indeed, we found that SNAP-25 migrated from the plasma membrane out to the cytosol.
The stimulating effect of cAMP on insulin secretion is implemented through different pathways. One pathway is through cAMP-GEFII and its downstream affector RIM2. We show that SNAP-25 binds to both cAMP-GEFII and RIM2, and that this binding mediates the effects of cAMP on exocytosis.
The blind-drunk mouse carries a mutation in SNAP-25 that results in increased binding affinities within the SNARE-complex and the consequence in pancreatic β-cells are impaired vesicle recycling and granule exocytosis.
These results together demonstrate the significance of a functional exocytotic machinery for β-cells to respond satisfying to an elevation in blood glucose.
Department/s
Publishing year
2008
Language
English
Publication/Series
Lund University Faculty of Medicine Doctoral Dissertation Series
Volume
2008:13
Document type
Dissertation
Publisher
Department of Clinical Sciences, Lund University
Topic
- Endocrinology and Diabetes
Keywords
- calcium channel
- cAMP
- syntaxin 1
- SNAP-25
- SNARE
- exocytosis
- Insulin secretion
- pancreatic beta-cells
Status
Published
Research group
- Diabetes - Islet Cell Exocytosis
Supervisor
ISBN/ISSN/Other
- ISSN: 1652-8220
- ISBN: 978-91-85897-66-7
Defence date
29 February 2008
Defence time
09:15
Defence place
Lilla Aulan, Medicinskt Forskningscentrum, ingång 59, Universitetssjukhuset MAS,
Opponent
- Romano Regazzi (Associate Professor)