(Proline3)PP, or (P³)PP, is an enzymatically stable, neuropeptide Y4 receptor (NPY4R)-selective, pancreatic polypeptide (PP) analogue with established weight-lowering and pancreatic islet morphology benefits in obesity-diabetes. In the current study, we now investigate the impact of twice-daily (P³)PP administration (25 nmol/kg) for 11 days on islet cell lineage, using streptozotocin (STZ) diabetic Ins1^Cre/+;Rosa26-eYFP and Glu^CreERT2;Rosa26-eYFP transgenic mice with enhanced yellow fluorescent protein (eYFP) labelling of beta-cell and alpha-cells, respectively. (P³)PP had no obvious impact on body weight or blood glucose levels in STZ-diabetic mice at the dose tested, but did return food intake towards control levels in Ins1^Cre/+;Rosa26-eYFP mice. Notably, pancreatic insulin content was augmented by (P³)PP treatment in both Ins1^Cre/+;Rosa26-eYFP and Glu^CreERT2;Rosa26-eYFP mice, alongside enhanced beta-cell area and reduced alpha-cell area. Beneficial (P³)PP-induced changes on islet morphology were consistently associated with decreased beta-cell apoptosis, while (P³)PP also augmented beta-cell proliferation in Ins1^Cre/+;Rosa26-eYFP mice. Alpha-cell turnover rates were returned towards healthy control levels by (P³)PP intervention in both mouse models. In terms of islet cell lineage, increased transition of alpha- to beta-cells as well as decreased beta- to alpha-cell differentiation were shown to contribute towards the enhancement of beta-cell area in (P³)PP-treated mice. Together these data reveal, for the first time, sustained NPY4R activation positively modulates beta-cell turnover, as well as islet cell plasticity, to help preserve pancreatic islet architecture following STZ-induced metabolic stress.

Glucagon receptor (GCGR) antagonism elicits antihyperglycemic effects in rodents and humans. The present study investigates whether the well characterised peptide-based GCGR antagonist, desHis¹Pro⁴Glu⁹-glucagon (Lys¹²PAL), alters alpha-cell turnover or identity in mice. Multiple low-dose streptozotocin (STZ) treated (50 mg/kg bw, 5 days) transgenic Glu^CreERT2;ROSA26-eYFP mice were employed. STZ mice received twice daily administration of saline vehicle or desHis¹Pro⁴Glu⁹-glucagon (Lys¹²PAL), at low- or high-dose (25 and 100 nmol/kg, respectively) for 11 days. No GCGR antagonist induced changes in food or fluid intake, body weight or glucose homeostasis were observed. As expected, STZ dramatically reduced (P < 0.001) islet numbers and increased (P < 0.01) alpha-to beta-cell ratio, which was linked to elevated (P < 0.05) levels of beta-cell apoptosis. Whilst treatment with desHis¹Pro⁴Glu⁹-glucagon (Lys¹²PAL) decreased (P < 0.05-P < 0.001) alpha- and beta-cell areas, it also helped restore the classic rodent islet alpha-cell mantle in STZ mice. Interestingly, low-dose desHis¹Pro⁴Glu⁹-glucagon (Lys¹²PAL) increased (P < 0.05) alpha-cell apoptosis rates whilst high dose decreased (p < 0.05) this parameter. This difference reflects substantially increased (P < 0.001) alpha-to beta-cell transdifferentiation following high dose desHis¹Pro⁴Glu⁹-glucagon (Lys¹²PAL) treatment, which was not fully manifest with low-dose therapy. Taken together, the present study indicates that peptidic GCGR antagonists can positively influence alpha-cell turnover and lineage in identity in multiple low-dose STZ mice, but that such effects are dose-related.

Background: Pancreatic islet β‐cell mass expands during pregnancy, but underlying mechanisms are not fully understood. This study examines the impact of pregnancy and cafeteria diet on islet morphology, associated cellular proliferation/apoptosis rates as well as β‐cell lineage.Methods: Non‐pregnant and pregnant Ins1^Cre/+;Rosa26‐eYFP transgenic mice were maintained on either normal or high‐fat cafeteria diet, with pancreatic tissue obtained at 18 days gestation. Immunohistochemical changes in islet morphology, β‐/α‐cell proliferation and apoptosis, as well as islet cell identity, neogenesis and ductal cell transdifferentiation were assessed.Results: Pregnant normal diet mice displayed an increase in body weight and glycaemia. Cafeteria feeding attenuated this weight gain while causing overt hyperglycaemia. Pregnant mice maintained on a normal diet exhibited typical expansion in islet and β‐cell area, owing to increased β‐cell proliferation and survival as well as ductal to β‐cell transdifferentiation and β‐cell neogenesis, alongside decreased β‐cell dedifferentiation. Such pregnancy‐induced islet adaptations were severely restricted by cafeteria diet. Accordingly, islets from these mice displayed high levels of β‐cell apoptosis and dedifferentiation, together with diminished β‐cell proliferation and lack of pregnancy‐induced β‐cell neogenesis and transdifferentiation, entirely opposing islet cell modifications observed in pregnant mice maintained on a normal diet.Conclusion: Augmentation of β‐cell mass during gestation arises through various mechanisms that include proliferation and survival of existing β‐cells, transdifferentiation of ductal cells as well as β‐cell neogenesis. Remarkably, cafeteria feeding almost entirely annuls pregnancy‐induced islet adaptations, which may contribute to the development of gestational diabetes in the setting of dietary provoked metabolic stress.

Background/Objective: Kisspeptin peptides are being increasingly recognised as regulators of metabolism, but whether these actions differ depending on peptide isoform remains unclear. Methods: The current study compared the enzymatic stability and biological effects of kisspeptin-14 (KP-14), kisspeptin-13 (KP-13) and kisspeptin-10 (KP-10) on beta-cell health and function, glucose homeostasis and appetite. Peptide stability was assessed in murine plasma and, following confirmation of KISS1R expression in BRIN-BD11 beta-cells, actions on insulin secretion, beta-cell proliferation and apoptosis were investigated, with additional secretory studies in isolated murine islets. Metabolic effects of KP-14, KP-13 and KP-10 were subsequently evaluated in healthy male and female mice. Results: KP-14 was resistant to plasma degradation, whereas KP-13 and KP-10 underwent N-terminal proteolysis, with KP-13 degradation generating KP-10 amongst other fragment peptides. The kisspeptin peptides exerted modest direct effects on insulin secretion from BRIN-BD11 cells, with KP-13 being the most efficacious, a bioactivity profile that was confirmed in islets. In addition, KP-13 significantly enhanced beta-cell proliferation and protected against cytokine-induced apoptosis, producing superior beta-cell proliferative effects compared to exenatide. Acute administration of all kisspeptin peptides elevated circulating glucose concentrations, and while KP-14 and KP-10 impaired glucose tolerance, KP-13 did not. Interestingly, KP-14 enhanced glucose-stimulated insulin secretion, with KP-13 and KP-10 being devoid of such actions. All kisspeptin isoforms suppressed food intake, although only KP-13, and especially KP-10 administration, led to an inhibition of feeding. Conclusions: Taken together, these data identify KP-13 as possessing the most favourable overall metabolic actions, based on a combination of beneficial actions on beta-cell health and function together with inhibition of feeding and lack of prominent glucose-elevating actions, suggesting possible therapeutic application for type 2 diabetes.