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.
Mesh Terms:
Animals, Cytoplasm, DNA, Down-Regulation, Immunohistochemistry, Immunoprecipitation, Insulin, Insulin-Secreting Cells, Islets of Langerhans, KATP Channels, Mice, Mice, Inbred C57BL, Mice, Knockout, Microscopy, Confocal, Microscopy, Electron, Transmission, Microscopy, Fluorescence, Reverse Transcriptase Polymerase Chain Reaction, Secretory Vesicles, alpha-Synuclein
Animals, Cytoplasm, DNA, Down-Regulation, Immunohistochemistry, Immunoprecipitation, Insulin, Insulin-Secreting Cells, Islets of Langerhans, KATP Channels, Mice, Mice, Inbred C57BL, Mice, Knockout, Microscopy, Confocal, Microscopy, Electron, Transmission, Microscopy, Fluorescence, Reverse Transcriptase Polymerase Chain Reaction, Secretory Vesicles, alpha-Synuclein
Am. J. Physiol. Endocrinol. Metab.
Date: Feb. 01, 2011
PubMed ID: 20858756
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