The role of glucagon- and somatostatin-secreting cells in the regulation of insulin release and beta-cell function in heterotypic pseudoislets.
BACKGROUND
Pseudoislet studies have concentrated on single beta-cell lines or a combination of insulin and glucagon-secreting cells, overlooking the potential role of somatostatin in insulin release. This study sought to evaluate a heterotypic pseudoislet model containing insulin- (MIN6), glucagon- (αTC1.9) and somatostatin (TGP52)-secreting cells of mouse origin and to compare these pseudoislets with traditional monolayer preparations.


METHODS
Cellular viability (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and lactate dehydrogenase assays), proliferation (5-bromo-2-deoxyuridine ELISA), hormone content and functional insulin release in response to a variety of stimuli were measured. Differential expression of E-cadherin, connexin 36 and connexin 43 was assessed by reverse transcriptase-polymerase chain reaction and Western blot to determine a possible role for adherens in insulin release from these pseudoislets.


RESULTS
All pseudoislet cells displayed reduced proliferation coupled with an increase in cell death which may contribute to their static size in culture. While MIN6 and TGP52 cells expressed E-cadherin and showed sustained or improved hormone content when configured as pseudoislets, αTC1.9 lacked E-cadherin and contained less glucagon following pseudoislet formation. MIN6 and αTC1.9 cells expressed connexin 36, but not connexin 43 and TGP52 cells expressed connexin 43 only. In the presence of Alanine, Arginine and glucagon-like peptide-1, heterotypic pseudoislet cultures secreted levels of insulin that were comparable to that of MIN6 pseudoislets. In addition, pseudoislets comprising all three cell lines released more insulin into the surrounding culture medium than MIN6 pseudoislets when studied over a 1-week period.


CONCLUSIONS
The current model may prove useful in studying the role of islet cell interactions in the release of insulin from pancreatic islets.
Kelly
Catriona
C
SAAD Centre for Pharmacy & Diabetes, School of Biomedical Sciences, University of Ulster, Coleraine, UK. catriona.kelly@qub.ac.uk
Parke
Hong Guo
HG
McCluskey
Jane T
JT
Flatt
Peter R
PR
McClenaghan
Neville H
NH
D000409:Alanine / Q000378:metabolism; D000818:Animals; D001120:Arginine / Q000378:metabolism; D015820:Cadherins / Q000032:analysis; D002450:Cell Communication; D049109:Cell Proliferation; D002470:Cell Survival; D002478:Cells, Cultured; D018031:Connexin 43 / Q000032:analysis; D017630:Connexins / Q000032:analysis; D005934:Glucagon / Q000378:metabolism*; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism; D050416:Glucagon-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D013004:Somatostatin / Q000378:metabolism*; D019864:Somatostatin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D000097004:Gap Junction delta-2 Protein
D000409:Alanine; D001120:Arginine; D015820:Cadherins; D018031:Connexin 43; D017630:Connexins; D005934:Glucagon; D052216:Glucagon-Like Peptide 1; D005947:Glucose; D007328:Insulin; D013004:Somatostatin; D000097004:Gap Junction delta-2 Protein