Altered Phenotype of β-Cells and Other Pancreatic Cell Lineages in Patients With Diffuse Congenital Hyperinsulinism in Infancy Caused by Mutations in the ATP-Sensitive K-Channel

Abstract

Diffuse congenital hyperinsulinism in infancy (CHI-D) arises from mutations inactivating the KATP channel; however, the phenotype is difficult to explain from electrophysiology alone. Here we studied wider abnormalities in the β-cell and other pancreatic lineages. Islets were disorganized in CHI-D compared with controls. PAX4 and ARX expression was decreased. A tendency toward increased NKX2.2 expression was consistent with its detection in two-thirds of CHI-D δ-cell nuclei, similar to the fetal pancreas, and implied immature δ-cell function. CHI-D δ-cells also comprised 10% of cells displaying nucleomegaly. In CHI-D, increased proliferation was most elevated in duct (5- to 11-fold) and acinar (7- to 47-fold) lineages. Increased β-cell proliferation observed in some cases was offset by an increase in apoptosis; this is in keeping with no difference in INSULIN expression or surface area stained for insulin between CHI-D and control pancreas. However, nuclear localization of CDK6 and P27 was markedly enhanced in CHI-D β-cells compared with cytoplasmic localization in control cells. These combined data support normal β-cell mass in CHI-D, but with G1/S molecules positioned in favor of cell cycle progression. New molecular abnormalities in δ-cells and marked proliferative increases in other pancreatic lineages indicate CHI-D is not solely a β-cell disorder.

Atypical Forms of Congenital Hyperinsulinism in Infancy Are Associated With Mosaic Patterns of Immature Islet Cells

“…Tissue samples were fixed in 4% paraformaldehyde and embedded in paraffin wax; 5-µm-thick sections were prepared for immunostaining. Immunohistochemistry and dual immunofluorescence labeling were performed on tissue sections as described previously ( 14, 16, 20 ), using validated and selective primary antibodies to detect the proteins of interest: insulin (1:1000; Abcam, Cambridge, UK), somatostatin (1:300; Zymed, San Francisco, CA), NKX2.2 (1:75; Developmental Studies Hybridoma Bank, Iowa City, IA), and hexokinase I (1:100; Santa Cruz, Dallas, TX). Images were acquired and digitized by a 20×/0.80 Plan Apo objective using the 3DHistech Pannoramic 250 Flash II slide scanner.…”

“…Islets with clear boundaries were selected to quantify the percentage of cells with coexpression of NKX2.2 and somatostatin compared with total islet cell counts. For the quantification of data, islet profiles from CHI-A tissues were directly compared with islets in age-matched tissue from CHI-D (n = 3) as a consequence of ABCC8 gene defects and from neonatal control tissues (n = 3) as previously described ( 14, 16, 20 ).…”

“…In patients with CHI-D, we have recently observed alterations in the ontogenic profile of the islets, suggesting that the tissue is closely aligned with a developmentally naive (fetal-like) pancreas rather than age-matched control tissue ( 16 ). This was defined as the inappropriate expression of NKX2.2 (Nirenberg and Kim 2 homeobox 2) in islet cells.…”

“…NKX2.2 is a transcription factor that is important for insulin-secreting β -cell identity ( 17 ) and normally is suppressed in somatostatin-secreting δ -cells after birth ( 18 ). However, in islets obtained from CHI-D pancreata, there was a more than threefold increase in the coexpression of NKX2.2 with somatostatin in δ -cells ( 16 ). These data imply an increase in both insulin-secreting and insulin-suppressing cellular capacity within the islets.…”

Complexities in the medical management of hypoglycaemia due to congenital hyperinsulinism

“…In β‐cells, these are thought to be coupled to different elements of stimulus secretion coupling mechanisms including the activation of voltage‐dependent K + channels, inhibition of voltage‐dependent Ca 2+ channels and lowering the intracellular concentration of cAMP. The paracrine regulation of glucagon and insulin release by somatostatin is physiologically important as decreased numbers of δ‐cells and immature δ‐cell profiles have been associated with the pathology of CHI.…”