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Doctoral thesis
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New insight into insulin secretion and blood glucose homeostasis in mice lacking islet non-β-cells

Number of pages245
Imprimatur date2022-02-23
Defense date2022-02-23
Abstract

The pancreas is an accessory gland of the digestive system. It fulfils two functions, exocrine and endocrine. The exocrine compartment (95-99%) consists of acinar and ductal cells producing and secreting enzymes involved in food digestion. The endocrine part is organized in cell clusters scattered throughout the exocrine parenchyma called islet of Langerhans (1-5%). In humans, islets contain five hormone-releasing cell types: • • α-cells secrete glucagon in response to low blood glucose levels, • • β-cells secrete insulin in response to high circulating glucose levels, • • δ-cells secrete somatostatin, which modulates insulin and glucagon release, • • γ-cells secrete pancreatic polypeptide (PPY), which regulates both endocrine and exocrine functions, • • ε-cells secrete ghrelin; these cells are mainly present during pancreas development. Insulin promotes glucose uptake in most tissues, thus lowering blood sugar levels. Defects in insulin secretion are at the core of nutrient metabolism impairment and diabetes onset. Intraislet local communication between islet cells takes place through direct cell-cell contacts or via the release of soluble factors. It is assumed that a complex network of interactions exists between the different islet cell types, which would be essential to assure a proper regulation of insulin secretion. However, it is unclear whether α-, δ-, and γ-cell-derived signals are a requisite for proper β-cell function and thus for the homeostasis of blood glucose. To address this question, we generated a new transgenic mouse model, named nonβ-DTR, in which the ablation of islet α-, δ- and γ-cells can be induced with diphtheria toxin (DT) administration. We found that the lack of islet nonβ-cells has no detrimental impact on β-cell function nor on the regulation of circulating glucose levels in adult mice. We instead observed a moderate amelioration of glucose tolerance and insulin sensitivity, as well as a resistance to gain body weight under high-fat diet. We also report that both β-cell identity and transcriptome were preserved after nonβ-cell loss in DT-treated nonβ-DTR mice. Moreover, the dynamics of insulin secretion in islets devoid of non-β-cells remained unchanged relative to intact islets. All these observations constitute a notable gain in fundamental knowledge and represent a valuable proof-of-principle supporting current research in Type 1 diabetes. This includes the development of treatments based on the generation of transplantable functional cell clusters containing surrogate β-like cells only, and lacking non-β-cells.

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Citation (ISO format)
ABATE, Maria Valentina. New insight into insulin secretion and blood glucose homeostasis in mice lacking islet non-β-cells. 2022. doi: 10.13097/archive-ouverte/unige:160176
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Creation04/03/2022 5:07:00 PM
First validation04/03/2022 5:07:00 PM
Update time04/03/2023 12:08:26 PM
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