α-Synuclein binds the K(ATP) channel at insulin-secretory granules and inhibits insulin secretion.
α-Synuclein has been studied in numerous cell types often associated with secretory processes. In pancreatic β-cells, α-synuclein might therefore play a similar role by interacting with organelles involved in insulin secretion. We tested for α-synuclein localizing to insulin-secretory granules and characterized its role in glucose-stimulated insulin secretion. Immunohistochemistry and fluorescent sulfonylureas were used to test for α-synuclein localization to insulin granules in β-cells, immunoprecipitation with Western blot analysis for interaction between α-synuclein and K(ATP) channels, and ELISA assays for the effect of altering α-synuclein expression up or down on insulin secretion in INS1 cells or mouse islets, respectively. Differences in cellular phenotype between α-synuclein knockout and wild-type β-cells were found by using confocal microscopy to image the fluorescent insulin biosensor Ins-C-emGFP and by using transmission electron microscopy. The results show that anti-α-synuclein antibodies labeled secretory organelles within β-cells. Anti-α-synuclein antibodies colocalized with K(ATP) channel, anti-insulin, and anti-C-peptide antibodies. α-Synuclein coimmunoprecipitated in complexes with K(ATP) channels. Expression of α-synuclein downregulated insulin secretion at 2.8 mM glucose with little effect following 16.7 mM glucose stimulation. α-Synuclein knockout islets upregulated insulin secretion at 2.8 and 8.4 mM but not 16.7 mM glucose, consistent with the depleted insulin granule density at the β-cell surface membranes observed in these islets. These findings demonstrate that α-synuclein interacts with K(ATP) channels and insulin-secretory granules and functionally acts as a brake on secretion that glucose stimulation can override. α-Synuclein might play similar roles in diabetes as it does in other degenerative diseases, including Alzheimer's and Parkinson's diseases.
Geng
Xuehui
X
Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pennsylvania, USA.
Lou
Haiyan
H
Wang
Jian
J
Li
Lehong
L
Swanson
Alexandra L
AL
Sun
Ming
M
Beers-Stolz
Donna
D
Watkins
Simon
S
Perez
Ruth G
RG
Drain
Peter
P
D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D015536:Down-Regulation / Q000502:physiology; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D007515:Islets of Langerhans / Q000166:cytology; D054086:KATP Channels / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D020133:Reverse Transcriptase Polymerase Chain Reaction; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism*; D051844:alpha-Synuclein / Q000096:biosynthesis / Q000378:metabolism* / Q000494:pharmacology*
D007328:Insulin; D054086:KATP Channels; D051844:alpha-Synuclein; D004247:DNA