362-OR: The Role of Intraislet Glucagon in Pulsatile Insulin Secretion

Background: Type 2 diabetes (T2D) is characterised by the loss of pulsatile insulin secretion. We studied mice with β-cell specific loss of the glucagon receptor (GCGRflox/flox X Ins-1 cre) , to investigate the role of intra-islet glucagon signalling on pan-islet calcium oscillations and islet pulsatility. Methods: Frequently sampled intravenous glucose tolerance tests were conducted on GCGRKOβ-cells-/-and littermate controls. Crossing with GCaMP6f (STOP flox) animals allowed for β-cell specific expression of a fluorescent calcium indicator. These islets were functionally imaged in vitro and in vivo. Wild-type mice were transplanted with islets expressing GCaMP6f in β-cells into the anterior eye chamber and placed on a high fat diet. Half of the cohort received a glucagon analogue (GCG-analogue) for 40 days and the control group were fed to achieve weight matching. Calcium imaging was performed regularly during the development of hyperglycaemia and in response to GCG-analogue treatment. Results: GCGRKOβ-cells-/- mice had poorer glucose tolerance in an intraperitoneal glucose tolerance test (control 12.7mmol/L ±0.6 vs. GCGRKOβ-cells-/- 15.4mmol/L ±0.0 at 15 min, p=0.002) ; fasting glycaemia was not different to controls. In vitro, GCGRKOβ-cells-/- islets showed profound loss of synchronised calcium waves in response to glucose which is only partially rescued in vivo. First-phase insulin pulsatility on peripheral blood sampling (n=5) was significantly disordered in GCGRKOβ-cells-/- mice (burst mass GCGRKOβ-cells-/- 0.30 ±0.03 versus 0.84 ±0.23 for controls p=0.04) . Diet induced obesity and hyperglycaemia resulted in a loss of co-ordinated calcium waves in transplanted islets. This was reversed with GCG-analogue treatment, independently of weight-loss (n=8) . Conclusion: These data provide novel evidence for the role of intra-islet glucagon in sustaining synchronised calcium oscillations and support a possible therapeutic role for glucagonergic agents to restore the insulin pulsatility lost in T2D. Disclosure K.Suba: n/a. B.Jones: None. T.M.Tan: Consultant; Zihipp Ltd. B.Owen: None. D.J.Drucker: Consultant; Kallyope, Merck Sharp & Dohme Corp., Novo Nordisk, Pfizer Inc., Other Relationship; Eli Lilly and Company. S.Bloom: None. K.Murphy: None. V.Salem: None. Y.S.Patel: Employee; PerkinElmer. A.Roberts: None. J.V.Shrewsbury: None. S.Chen: None. R.Kwok: None. V.Kalogianni: None. X.Liu: None. G.A.Rutter: Advisory Panel; Sun Pharmaceutical Industries Ltd., Research Support; Sun Pharmaceutical Industries Ltd.