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Jennifer Chen and Jenny E Gunton

Islet transplantation, a therapeutic option to treat type 1 diabetes, is not yet as successful as whole-pancreas transplantation as a treatment for diabetes. Mouse models are commonly used for islet research. However, it is clear disparities exist between islet transplantation outcomes in mice and humans. Given the shortage of transplant-grade islets, it is crucial that we further our understanding of factors that determine long-term islet survival and function post-transplantation. In turn, that may lead to new therapeutic targets and strategies that to improve transplant outcomes. Here, we summarise the current landscape in clinical transplantation, highlight underlying similarities and differences between mouse and human islets, and review interventions that are being considered to create a new pool of β-cells for clinical application.

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Jennifer H Stern, Gordon I Smith, Shiuwei Chen, Roger H Unger, Samuel Klein, and Philipp E Scherer

Hyperglucagonemia, a hallmark in obesity and insulin resistance promotes hepatic glucose output, exacerbating hyperglycemia and thus predisposing to the development type 2 diabetes. As such, glucagon signaling is a key target for new therapeutics to manage insulin resistance. We evaluated glucagon homeostasis in lean and obese mice and people. In lean mice, fasting for 24 h caused a rise in glucagon. In contrast, a decrease in serum glucagon compared to baseline was observed in diet-induced obese mice between 8 and 24 h of fasting. Fasting decreased serum insulin in both lean and obese mice. Accordingly, the glucagon:insulin ratio was unaffected by fasting in obese mice but increased in lean mice. Re-feeding (2 h) restored hyperglucagonemia in obese mice. Pancreatic perfusion studies confirm that fasting (16 h) decreases pancreatic glucagon secretion in obese mice. Consistent with our findings in the mouse, a mixed meal increased serum glucagon and insulin concentrations in obese humans, both of which decreased with time after a meal. Consequently, fasting and re-feeding less robustly affected glucagon:insulin ratios in obese compared to lean participants. The glucoregulatory disturbance in obesity may be driven by inappropriate regulation of glucagon by fasting and a static glucagon:insulin ratio.