Intra-islet glucagon signalling regulates pulsatile insulin secretion and glucose homeostasis

Suba, K.; Patel, Y.; Alonso, A. M.; Roberts, A.; Hansen, B.; Norton, M.; Shrewsbury, J.; Kwok, R.; Kalogianni, V.; Chen, S.; Liu, X.; Rutter, G. A.; Jones, B.; Minnion, J.; Owen, B. M.; Distaso, W.; Drucker, D. J.; Tan, T. M.; Bloom, S. R.; Murphy, K.; Salem, V.

doi:10.1101/2022.09.01.506223

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bioRxiv · 10.1101/2022.09.01.506223

Intra-islet glucagon signalling regulates pulsatile insulin secretion and glucose homeostasis

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Abstract

BackgroundType 2 diabetes (T2D) is characterised by the loss of pulsatile insulin secretion. We studied mice with {beta}-cell specific loss of the glucagon receptor (Gcgr fl/fl X Ins-1Cre), to investigate the role of intra-islet glucagon receptor signalling on pan-islet calcium oscillations and insulin pulsatility. MethodsFrequently sampled intravenous glucose tolerance tests were conducted on Gcgr {beta}-cell-/- and littermate controls. Crossing with GCaMP6f (STOP flox) animals further allowed for {beta}-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 {beta}-cells into the anterior eye chamber and placed on a high fat diet. Part 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. ResultsGcgr {beta}-cell-/- mice exhibited impaired glucose tolerance following intraperitoneal glucose challenge (control 12.7mmol/L {+/-}0.6 vs. Gcgr {beta}-cell-/- 15.4mmol/L {+/-}0.0 at 15 min, p=0.002); fasting glycaemia was not different to controls. In vitro, Gcgr {beta}-cell-/- islets showed profound loss of synchronised calcium waves in response to glucose which was only partially rescued in vivo. First-phase insulin pulsatility on peripheral blood sampling (n=5) was significantly disordered in Gcgr {beta}-cell-/- mice (burst mass Gcgr {beta}-cell-/- 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 [Ca2+]I waves in transplanted islets. This was reversed with GCG-analogue treatment, independently of weight-loss (n=8). ConclusionThese data provide novel evidence for the role of intra-islet GCGR signalling in sustaining synchronised calcium oscillations and support a possible therapeutic role for glucagonergic agents to restore the insulin pulsatility lost in T2D.

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Suba, K., Patel, Y., Alonso, A. M., Roberts, A., Hansen, B., Norton, M., Shrewsbury, J., Kwok, R., Kalogianni, V., Chen, S., Liu, X., Rutter, G. A., Jones, B., Minnion, J., Owen, B. M., Distaso, W., Drucker, D. J., Tan, T. M., Bloom, S. R., Murphy, K., Salem, V.. 2022-09-03. Intra-islet glucagon signalling regulates pulsatile insulin secretion and glucose homeostasis. https://doi.org/10.1101/2022.09.01.506223

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