Insulin regulates human pancreatic endocrine cell differentiation in vitro.

OBJECTIVE: The consequences of mutations in genes associated with monogenic forms of diabetes on human pancreas development cannot be studied in a time-resolved fashion in vivo. More specifically, if recessive mutations in the insulin gene influence human pancreatic endocrine lineage formation is still an unresolved question. METHODS: To model the extremely reduced insulin levels in patients with recessive insulin gene mutations, we generated a novel knock-in H2B-Cherry reporter human induced pluripotent stem cell (iPSC) line expressing no insulin upon differentiation to stem cell-derived (SC-) ß cells in vitro. Differentiation of iPSCs into the pancreatic and endocrine lineage, combined with immunostaining, Western blotting and proteomics analysis phenotypically characterized the insulin gene deficiency in SC-islets. Furthermore, we leveraged FACS analysis and confocal microscopy to explore the impact of insulin shortage on human endocrine cell induction, composition, differentiation and proliferation. RESULTS: Interestingly, insulin-deficient SC-islets exhibited low insulin receptor (IR) signaling when stimulated with glucose but displayed increased IR sensitivity upon treatment with exogenous insulin. Furthermore, insulin shortage did not alter neurogenin-3 (NGN3)-mediated endocrine lineage induction. Nevertheless, lack of insulin skewed the SC-islet cell composition with an increased number in SC-ß cell formation at the expense of SC-α cells. Finally, insulin deficiency reduced the rate of SC-ß cell proliferation but had no impact on the expansion of SC-α cells. CONCLUSIONS: Using iPSC disease modelling, we provide first evidence of insulin function in human pancreatic endocrine lineage formation. These findings help to better understand the phenotypic impact of recessive insulin gene mutations during pancreas development and shed light on insulin gene function beside its physiological role in blood glucose regulation.

Human Islet Morphology Revisited: Human and Rodent Islets Are Not So Different After All.

There has been great interest in understanding how human islets differ from rodent islets. Three major issues about human islet morphology have remained controversial over recent decades: 1) the proportion of the islet made up of ß-cells; 2) whether islet cell types have a non-random mantle-core pattern, as seen in rodents, or are randomly scattered throughout the islet; 3) the relation of the different cell types to the blood vessels within the islet, which has implications for intraislet function. We re-examined these issues on immunostained sections of non-diabetic adult human pancreas. The composition of the islets can vary by the analysis method (number vs volume) and by the sampling of islets by size. The majority of adult human islets have clear, non-random clustering of ß-cells and blood vessels that penetrate into the ß-cell cores. We conclude that although there is far more variability in islet composition both within each human pancreas and among different human pancreas than in rodent pancreas, the islet architecture is not so different between the species. The intrapancreatic variability raises important questions about how islets evolve and function throughout life and how this might relate to the pathogenesis of diabetes.