Endocrine Abstracts (2019) 65 OP3.4 | DOI: 10.1530/endoabs.65.OP3.4

Mice with a gain-of function G[alpha]11 mutation have autosomal dominant hypocalcaemia, but not impaired glucose metabolism

Anna Gluck1, Kate Lines1, Caroline Gorvin1, Valerie Babinsky1, Sian Piret1, Stefan Sarbu2, Michelle Stewart3, Liz Bentley3, Sara Wells3, Roger Cox3, Rupert Ecker2, Isabella Ellinger4, Fadil Hannan1 & Rajesh Thakker1

1OCDEM, University of Oxford, Oxford, UK; 2Research and Development Department of TissueGnostics GmbH, Vienna, Austria; 3Medical Research Council Mammalian Genetics Unit and Mary Lyon Centre, Medical Research Council Harwell Institute, Harwell Science and Innovation Campus, Didcot, UK; 4Institute of Pathophysiology and Allergy Research, Medical University of Vienna, Vienna, Austria

The calcium-sensing-receptor (CaSR) is a G-protein-coupled receptor that plays a fundamental role in extracellular calcium homeostasis, but is also implicated in non-calcitropic disorders including colon cancer and asthma. In addition, CaSR is highly expressed in pancreatic islets where it has a role in insulin secretion. Patients with gain-of-function CaSR mutations, and mice (referred to as Nuf) with a gain-of-function CaSR mutation (Leu723Gln), develop autosomal dominant hypocalcaemia type-1. Nuf mice also have impaired glucose tolerance, reduced insulin secretion, and decreased pancreatic islet size and proliferation, indicating a role for CaSR in pancreatic islets. Patients with gain-of-function mutations of the Gα11 protein, which mediates CaSR signalling, and mice (referred to as Dsk7) with a gain-of-function Gα11 mutation (Ile62Val), develop ADH2. We therefore investigated Dsk7 mice for defects in glucose metabolism and islet architecture. Wild-type (n=21), heterozygous (n=24) and homozygous (n=9) Dsk7 mice were aged for 14 weeks and intraperitoneal glucose tolerance tests were performed. Heterozygous and homozygous Dsk7 mice, compared to wild-type, were confirmed to have hypocalcaemia (plasma adjusted-calcium of 2.06±0.08 and 1.72±0.08 mmol/l, and 2.37±0.09 mmol/l respectively, P<0.0001), consistent with ADH2. However, significant differences in glucose tolerance were not observed. Pancreatic islet size and number, assessed by haematoxylin and eosin staining of paraffin-embedded tissue sections, did not differ between wild-type (n=10), heterozygous (n=8) and homozygous (n=9) Dsk7 mice. Islet architecture was further studied by immunofluorescence microscopy using antibodies against insulin, glucagon and the proliferation marker Ki-67. Image analyses of >144 islets per genotype (n=8 mice) revealed no difference in α- and β-cell number and proliferation. In conclusion, our findings indicate that Gα11 gain-of-function does not influence glucose homeostasis or pancreatic islet architecture. Thus, the glucose phenotype observed in the Nuf mice is likely transduced by G-proteins other than Gα11, or is due to G-protein independent mechanisms.