Confocal Microscopy Image Analysis of Pancreatic beta-Cells K-ATP Channel Proteins in Congenital Hyperinsulinism (CHI)

Abstract

Background: CHI is a life-threatening disorder of glucose metabolism of neonates characterized by serum insulin levels unresponsive to blood glucose concentrations. Pancreatic ß-cells regulates insulin secretion through ATP sensitive potassium channels (K ATP channel) formed by sulfonylurea receptor 1 (SUR1) and potassium inward rectifying 6.2 (Kir 6.2) proteins. The ß-cell K ATP channel dependent CHI is classically associated with loss-of-function mutations of these subunits genes. In a previous study [1], no mutations in the Kir6.2 gene and in the 33-37 exons hot spot region of the SUR1 gene were identified in these patients. The aim of this study is to investigate if these subunits were present in the ß-cells of CHI patients. Design: Pancreatic surgical paraffin tissue from 7 neonates (3F/4M, 4-13 mo) with CHI and 8 autopsy pancreatic control tissue (5F/3M, 4-11 mo) were included in the study. Confocal microscopy double-staining immuno fluorescence (insulin/SUR1 and insulin/Kir6.2) was performed in order to detect each protein specifically in the ß-cells. All sections were analyzed under a Zeiss 510 Meta confocal laser scanning microscope (63x). At least 10 different endocrine islets were captured to evaluate the expression of either Kir6.2 or SUR1 (green-488nm) and insulin (red-633nm). Co-expression of insulin/SUR1 and insulin/Kir6.2 was analysed visually (green x red→yellow) and through correlation Pearson’s coefficient(PC) that estimates the goodness of rate association of the two fluorochromes. PC was compared among cases and controls using a nonparametric method (Mann-Whitney). Results: Visual observation clearly revealed the presence of Kir6.2 and SUR1 in a granular cytoplasmic pattern in the ß-cells of cases and controls. Nevertheless, overlap of insulin/Kir6.2 and insulin/SUR1 seemed to be more constant and uniformin controls than in CHI cases, confirmed by the analysis through PC showing a statistically significant decrease in Kir6.2 ( P = 0.0084) and SUR1 ( P = 0.041) in the ß-cells of CHI patients. Conclusions: This is the first demonstration of K ATP channels subunits Kir6.2 and SUR1 in the pancreatic ß-cells of CHI patients using an in situ method. Our results show that both subunits were present in the ß-cells, but are under-expressed in CHI patients compared to controls, adding a new information to this rare condition with a complex pathogenesis.