Using iPSC-Derived Islets to Model the Effect of an ABCC8 Arg1420His Mutation in Fetal and Adult Islets

We previously reported an Arg1420His mutation in ABCC8 in an Indigenous community that resulted in hyperinsulinemic hypoglycemia in infancy in a homozygous carrier and a doubling in type 2 diabetes (T2D) risk in heterozygous carriers (3% of the population). Previous studies of ABCC8 mutations have suggested a loss of pancreatic beta cells as a probable cause of future T2D. To understand the pathomechanism behind the increased risk of T2D due to the Arg1420His mutation, we generated two sets of isogenic iPSCs from two different Indigenous community members. These iPSCs were used to generate pancreatic islets and assess insulin secretion using a dynamic glucose stimulated insulin secretion (D-GSIS) assay when the islets were immature (resembling fetal islets) and during multiple days after maturation (resembling adult islets). In immature islets, the D-GSIS assay confirmed the clinical phenotype of significantly higher insulin secretion in islets with the His-allele under basal conditions (2mM glucose) and a lower response to diazoxide in islets homozygous for the His-allele. Both Arg1420 and His1420 mature islets had lower insulin secretion under basal conditions, however, insulin secretory response to high glucose (20mM) and Tolbutamide (sulphonylurea) was significantly lower in islets heterozygous for the His-allele whereas no response was seen in islets homozygous for the His-allele despite having similar proportion of beta cells as assessed by flow cytometry (~50% cells positive for INS and NKX6-1). This suggests a mechanism other than beta cell loss as the cause of lower insulin secretory response in these impaired islets. Single cell RNA sequencing showed higher expression of G6PC2, which inhibits insulin secretion by opposing the action of GCK, in islets with the His-allele. Our ongoing work includes knockout of G6PC2 in the isogenic iPSCs and using a GCK activator (Dorzagliatin) to correct the insulin secretory response to high glucose in the His-allele carrying islets. Disclosure A.K.Nair: None. K.Barkho: None. M.Traurig: None. R.G.Nelson: None. C.Bogardus: None. L.Baier: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases