Background: The mechanisms responsible for inappropriate insulin release from β-cells in congenital hyperinsulinism in infancy (CHI) have largely focused upon defects in KATP channels. Little is known about insulin biogenesis, the profiles of insulin in insulin-containing secretory granules or whether the impact of KATP channel defects is the same in diffuse- and focal disease.
Objective and hypotheses: To define the ultrastructural properties of the insulin-containing granules in β-cell different forms of CHI compared to control samples.
Methods: CHI patients were positive for mutations in the KATP channel gene ABCC8 and underwent surgery for the treatment of hypoglycaemia. Morphometric analysis and immuno-gold labelling of insulin (I-Au) was applied to frozen tissue sections of control (n=4) and CHI tissues (diffuse-CHI, n=3; focal-CHI, n=3) and used to identify the insulin-containing granules. Data were acquired using Transmission Electron Microscope from each of the tissue sections; control n=60, diffuse-CHI n=58 and focal-CHI n=61.
Results: Three profiles were defined: mature, dense-core/ crystalline granules; immature secretory granules and secretory granules that were depleted of insulin. Approximately 60% of secretory granules (n=3428) were depleted of insulin in focal-CHI compared to around 10% of granules in diffuse- (n=2258) and control β-cells (n=2577). The percentages of immature granules were significantly lower in focal-CHI (5.7±1.7%) compared with diffuse CHI (45.5±8.7%) and control samples (31.6±3.7%). In contrast, control β-cells had a higher proportions of crystalline granules (62.9±3.1%) compared with focal- (36.6±3.5%) and diffuse-CHI (42.7±1.9%). We also found a higher incidence of multi-vesicular secretory granule structures in focal- (74.7±3.3%) compared to diffuse-CHI and control β-cells (39.5±6.8% vs 27.8±5.6%).
Conclusion: Our data also imply that β-cells in focal-CHI have a greater secretory capacity (increased number multi-vesicular secretory granules and depleted granules) than in diffuse disease, despite the fact that both conditions associate with ABCC8 gene defects.
10 - 12 Sep 2016
European Society for Paediatric Endocrinology