RESUMO
ß-cell dedifferentiation has been accounted as one of the major mechanisms for ß-cell failure; thus, is a cause to diabetes. We study direct impacts of liraglutide treatment on ex vivo human dedifferentiated islets, and its effects on genes important in endocrine function, progenitor states, and epithelial mesenchymal transition (EMT). Human islets from non-diabetic donors, were purified and incubated until day 1 and day 4, and were determined insulin contents, numbers of insulin (INS+) and glucagon (GCG+) cells. The islets from day 3 to day 7 were treated with diabetic drugs, the long acting GLP-1 receptor agonist, liraglutide. As observed in pancreatic islets of type 2 diabetic patients, ex vivo dedifferentiated islets showed more than 50% reduced insulin contents while number of glucagon increased from 10% to about 20%. ß-cell specific genes: PDX1, MAFA, as well as ß-cell functional markers: GLUT1 and SUR1, were significantly depleted more than 40%. Notably, we found increased levels of glucagon regulator, ARX and pre-glucagon transcripts, and remarkably upregulated progenitor expressions: NEUROG3 and ALDH1A identified as ß-cell dysfunction markers in diabetic models. Hyperglucagonemia was often observed in type 2 patients that could lead to over production of gluconeogenesis by the liver. Liraglutide treatments resulted in decreased number of GCG+ cells, increased numbers of GLP-1 positive cells but did not alter elevated levels of EMT marker genes: ACTA2, CDH-2, SNAIL2, and VIM. These effects of liraglutide were blunted when FOXO1 transcripts were depleted. This work illustrates that ex vivo human isolated islets can be used as a tool to study different aspects of ß-cell dedifferentiation. Our novel finding suggests a role of GLP-1 pathway in beta-cell maintenance in FOXO1-dependent manner. Importantly, dedifferentiated islets ex vivo is a useful model that can be utilized to verify the actions of potential drugs to diabetic ß-cell failure.
RESUMO
ß-Cell dysfunction in diabetes results from abnormalities of insulin production, secretion, and cell number. These abnormalities may partly arise from altered developmental programming of ß-cells. Foxo1 is important to maintain adult ß-cells, but little is known about its role in pancreatic progenitor cells as determinants of future ß-cell function. We addressed this question by generating an allelic series of somatic Foxo1 knockouts at different stages of pancreatic development in mice. Surprisingly, ablation of Foxo1 in pancreatic progenitors resulted in delayed appearance of Neurogenin3(+) progenitors and their persistence into adulthood as a self-replicating pool, causing a fourfold increase of ß-cell mass. Similarly, Foxo1 ablation in endocrine progenitors increased their numbers, extended their survival, and expanded ß-cell mass. In contrast, ablation of Foxo1 in terminally differentiated ß-cells did not increase ß-cell mass nor did it affect Neurogenin3 expression. Despite the increased ß-cell mass, islets from mice lacking Foxo1 in pancreatic or endocrine progenitors responded poorly to glucose, resulting in glucose intolerance. We conclude that Foxo1 integrates cues that determine developmental timing, pool size, and functional features of endocrine progenitor cells, resulting in a legacy effect on adult ß-cell mass and function. Our results illustrate how developmental programming predisposes to ß-cell dysfunction in adults and raise questions on the desirability of increasing ß-cell mass for therapeutic purposes in type 2 diabetes.