Proceedings of The Physiological Society

Experimental Models (Exeter, UK) (2018) Proc Physiol Soc 40, C07

Oral Communications

Male AKR1D1 (5β-reductase) knockout mice have altered pancreatic islet morphology and hormone secretion

S. Harris1, L. Gathercole1,2, R. Ramracheya1, A. Forhead2,3, J. Tomlinson1

1. OCDEM, University of Oxford, Oxford, Oxon, United Kingdom. 2. Department of Biological and Medical Sciences, Oxford Brookes University, Oxford, United Kingdom. 3. Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom.

The enzyme 5β-reductase (AKR1D1) catalyses an essential step in bile acid synthesis, but in addition, controls intra-cellular steroid hormone availability by inactivation and the generation of 5β-reduced dihydrosteroid metabolites. Steroid hormones and bile acids are regulators of global lipid and carbohydrate metabolism. As disturbances in steroid hormone and bile acid metabolism have potent effects on metabolic health, we hypothesize that AKR1D1 may play a role in metabolic homeostasis. Secretion of the pancreatic hormones, insulin and glucagon, are dysregulated in metabolic disorders and the role of AKR1D1 in regulating glucose homeostasis and pancreatic function remains unexplored. We generated a global AKR1D1 knockout (KO) mouse. After euthanasia, the pancreas was removed and weighed. Immunohistochemical and stereological techniques were used to define whole pancreas and islet morphology in KO (n=5) mice at 12 weeks of age (12w) compared against wild-type (WT; n=5) controls. Additionally, pancreatic islets were isolated from male WT (n=3) and KO (n=3) mice at 30w and insulin and glucagon secretion were assessed in static incubations. Data (mean±SEM) were assessed by Student's t-test. At 12w, relative pancreas mass was decreased in AKR1D1 KO male mice compared to WT controls (g/kg: WT: 12.7±1.3, KO: 7.5±1.0, P<0.05), while there was no change in pancreatic mass in female mice. Pancreatic islet volume and relative beta-cell mass were decreased in male KO mice only, however, there was no alteration in alpha-cell mass. At 30w, insulin secretion was increased in isolated KO islets upon treatment with 1mM (basal) glucose (mean as % islet content: WT: 0.07±0.01, KO: 0.12±0.01, P<0.05), without any change in total islet insulin content. However, in response to 20mM glucose, the increase in insulin secretion was lower in KO islets when expressed relative to basal levels (WT: 3.5-fold change, KO: 2.6-fold change, P=0.08). Compared to WT controls, the KO islets failed to suppress glucagon release in the presence of 20mM glucose (mean as % change in glucagon secretion: WT: -29±20, KO: 61±14). Indeed, we observed a paradoxical increase in glucagon secretion with increasing glucose concentration (1mM glucose; WT: 5.8±1.1, KO: 7.4±3.9 pg/islet/hr. 20mM glucose; WT: 4.0±0.7, KO: 8.7±3.0 pg/islet/hr). Whilst endogenous expression of AKR1D1 in the murine pancreatic islet is very low, alterations in steroid hormone and bile acid exposure have been shown to modify pancreatic islet cell function; AKR1D1 KO male mice have a dysregulation of insulin and glucagon secretion, which may have profound effects on normal glucose homeostasis. The mechanisms underpinning the changes observed remain to be determined. Further characterization is warranted to define the role of AKR1D1 and to determine whether it has potential as a therapeutic target in metabolic disease.

Where applicable, experiments conform with Society ethical requirements