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Diabetologia. 2017 Jun;60(6):1033-1042. doi: 10.1007/s00125-017-4239-x. Epub 2017 Mar 9.

Paracrine GABA and insulin regulate pancreatic alpha cell proliferation in a mouse model of type 1 diabetes.

Author information

1
Robarts Research Institute, Rome: 7240, University of Western Ontario, 1151 Richmond Street North, London, ON, N6A 5B7, Canada.
2
Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada.
3
Robarts Research Institute, Rome: 7240, University of Western Ontario, 1151 Richmond Street North, London, ON, N6A 5B7, Canada. wlu53@uwo.ca.
4
Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada. wlu53@uwo.ca.

Abstract

AIMS/HYPOTHESIS:

This study aimed to elucidate the mechanism of increased proliferation of alpha cells in recent-onset type 1 diabetes. Pancreatic beta cells express GAD and produce γ-aminobutyric acid (GABA), which inhibits alpha cell secretion of glucagon. We explored the roles of GABA in alpha cell proliferation in conditions corresponding to type 1 diabetes in a mouse model and in vitro.

METHODS:

Type 1 diabetes was induced by injecting the mice with streptozotocin (STZ). Some of the STZ-injected mice were treated with GABA (10 mg/kg daily) for 12 days. Isolated pancreatic islets were treated with STZ or STZ together with GABA for 2 days. The effects of GABA treatment on STZ-induced alpha cell proliferation in vivo and in vitro were assessed. The effect of muscimol, a GABA receptor agonist, on αTC1-6 cell proliferation was also examined.

RESULTS:

STZ injection substantially decreased levels of GAD, GABA and insulin in pancreatic beta cells 12 h after injection; this was followed by an upsurge of phosphorylated mechanistic target of rapamycin (p-mTOR) in the alpha cells at day 1, and a significant increase in alpha cell mass at day 3. Treating STZ-injected mice with GABA largely restored the immunodetectable levels of insulin and GAD in the beta cells and significantly decreased the number of aldehyde dehydrogenase 1 family, member A3 (ALDH1a3)-positive cells, alpha cell mass and hyperglucagonaemia. STZ treatment also increased alpha cell proliferation in isolated islets, which was reversed by co-treatment with GABA. Muscimol, together with insulin, significantly lowered the level of cytosolic Ca2+ and p-mTOR, and decreased the proliferation rate of αTC1-6 cells.

CONCLUSIONS/INTERPRETATION:

GABA signalling critically controls the alpha cell population in pancreatic islets. Low intraislet GABA may contribute to alpha cell hyperplasia in early type 1 diabetes.

KEYWORDS:

Alpha cell; Beta cell; Diabetes; GAD; Glucagon; Insulin; Proliferation; Streptozotocin; Transdifferentiation; γ-Aminobutyric acid

PMID:
28280900
DOI:
10.1007/s00125-017-4239-x
[Indexed for MEDLINE]

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