The leptin receptor has no role in delta-cell control of beta-cell function in the mouse
Introduction: Leptin inhibits insulin secretion from isolated islets from multiple species, but the cell type that mediates this process remains elusive. Several mouse models have been used to explore this question. Ablation of the leptin receptor (Lepr) throughout the pancreatic epithelium results in altered glucose homeostasis and ex vivo insulin secretion and Ca2+ dynamics. However, Lepr removal from neither alpha nor beta cells mimics this result. Moreover, scRNAseq data has revealed an enrichment of LEPR in human islet delta cells. Methods: We confirmed LEPR upregulation in human delta cells by performing RNAseq on fixed, sorted beta and delta cells. We then used a mouse model to test whether delta cells mediate the diminished glucose-stimulated insulin secretion in response to leptin. Results: Ablation of Lepr within mouse delta cells did not change glucose homeostasis or insulin secretion, whether mice were fed a chow or high-fat diet. We further show, using a publicly available scRNAseq dataset, that islet cells expressing Lepr lie within endothelial cell clusters. Conclusions: In mice, leptin does not influence beta-cell function through delta cells. Overall design: We aimed to understand the differences in expression between human beta and delta cells.  To complete this project, we obtained islet samples from five non-diabetic human donors. Current protocols for sorting live islets do not reliably distinguish beta and delta cells. Therefore, we used a procedure to sort cells using internal cell-specific markers. Islets were fixed and suspended into a single-cell suspension. The cell membranes were perforated, and cells were indirectly fluorescently immunolabeled using antibodies against insulin and somatostatin. We found that delta cells express the machinery that beta cells use to sense glucose and secrete insulin (except for insulin). Delta cells were also enriched for genes such as Somatostatin, HHex, Leptin Receptor, Erb-B2 Receptor Tyrosine Kinase 4 and Dopamine Receptor 2, Serpin Family A Member 1, Nuclear receptor coactivator 7, several GABA receptors, Growth Hormone Receptor, and several solute transporters. Characterization of differentially expressed cell-surface molecules could lead to better sorting of live human beta and delta cells.Islets from non-diabetic human donors were obtained from the IIDP, cultured in Prodo Complete Media, then fixed in 1% PFA, 01.% saponin, and 1:100 Rnasin before staining with Somatostatin and Insulin and FACS sorting