Conversion of α-Cells to ß-Cells in the Postpartum Mouse Pancreas Involves Lgr5 Progeny.

In contrast to the skin and the gut, where somatic stem cells and their niche are well characterized, a definitive pancreatic multipotent cell population in the adult pancreas has yet to be revealed. Of particular interest is whether such cells may be endogenous in patients with diabetes, and if so, can they be used for therapeutic purposes? In the current study, we used two separate reporter lines to target Cre-recombinase expression to the Lgr5- or glucagon-expressing cells in the pancreas. We provide evidence for the existence of a population of cells within and in the proximity of the ducts that transiently express the stem-cell marker Lgr5 during late gestational stages. Careful timing of tamoxifen treatment in Lgr5EGFP-IRES-CreERT2 ;R26 Tomato mice allowed us to show that these Lgr5-expressing progenitor cells can differentiate into α-cells during pregnancy. Furthermore, we report on a spontaneous lineage conversion of α- to ß-cells specifically after parturition. The contribution of Lgr5 progeny to the ß-cell compartment through an α-cell intermediate phase early after pregnancy appears to be part of a novel mechanism that would counterbalance against excessive ß-cell mass reduction during ß-cell involution.

In utero exposure to dexamethasone programs the development of the pancreatic ß- and α-cells during early postnatal life.

AIMS: The aim of the present study was to clarify if in utero exposure to DEX would affect the development of different types of pancreatic endocrine cells during postnatal life. MAIN METHODS: We investigated morphological and transcriptional features of both pancreatic ß- and α-cell populations within the pancreatic islets during the early postnatal life of rats born to mothers treated with DEX (0.1 mg/kg) from day 14 to 19 of pregnancy. Untreated pregnant Wistar rats of the same age (12-week-old) were used as control (CTL). Pups were euthanized on the 1st, 3rd and 21st (PND1, PND3 and PND21, respectively) days of life, regardless of sex. Serum insulin and glucagon levels were also evaluated. KEY FINDINGS: Rats born to DEX-treated mothers exhibited increased pancreatic α-cell mass, circulating glucagon levels and Gcg, Pax6, MafB and Nkx2.2 expression. Rats born to DEX-treated mothers also presented a rise in serum insulin levels on the PND3 that was paralleled by reduced ß-cell mass. Such increase in serum insulin levels, instead, was associated with increased expression of genes associated to insulin secretion such as Gck and Slc2a2. SIGNIFICANCE: Altogether, the present data reveals yet unknown changes in endocrine pancreas during early postnatal life of rats exposed to DEX in utero. Such data may contribute to the understanding of the metabolic features of rats born to DEX-treated mothers.

Maternal protein restriction during gestation impairs female offspring pancreas development in the rat.

A maternal low-protein (LP) diet programs fetal pancreatic islet ß-cell development and function and predisposes offspring to metabolic dysfunction later in life. We hypothesized that maternal protein restriction during pregnancy differentially alters ß- and α-cell populations in offspring by modifying islet ontogeny and function throughout life. We aimed to investigate the effect of an LP maternal diet on pancreatic islet morphology and cellular composition in female offspring on postnatal days (PNDs) 7, 14, 21, 36, and 110. Mothers were divided into 2 groups: during pregnancy, the control group (C) was fed a diet containing 20% casein, and the LP group was fed an isocaloric diet with 10% casein. Offspring pancreases were obtained at each PND and then processed. ß and α cells were detected by immunohistochemistry, and cellular area and islet size were quantified. Islet cytoarchitecture and total area were similar in C and LP offspring at all ages studied. At the early ages (PNDs 7-21), the proportion of ß cells was lower in LP than C offspring. The proportion of α cells was lower in LP than C offspring on PND 14 and higher on PND 21. The ß/α-cell ratio was lower in LP compared with C offspring on PNDs 7 and 21 and higher on PND 36 (being similar on PNDs 14 and 110). We concluded that maternal protein restriction during pregnancy modifies offspring islet cell ontogeny by altering the proportions of islet sizes and by reducing the number of ß cells postnatally, which may impact pancreatic function in adult life.

Single-Cell Transcriptomics of the Human Endocrine Pancreas.

Human pancreatic islets consist of multiple endocrine cell types. To facilitate the detection of rare cellular states and uncover population heterogeneity, we performed single-cell RNA sequencing (RNA-seq) on islets from multiple deceased organ donors, including children, healthy adults, and individuals with type 1 or type 2 diabetes. We developed a robust computational biology framework for cell type annotation. Using this framework, we show that α- and ß-cells from children exhibit less well-defined gene signatures than those in adults. Remarkably, α- and ß-cells from donors with type 2 diabetes have expression profiles with features seen in children, indicating a partial dedifferentiation process. We also examined a naturally proliferating α-cell from a healthy adult, for which pathway analysis indicated activation of the cell cycle and repression of checkpoint control pathways. Importantly, this replicating α-cell exhibited activated Sonic hedgehog signaling, a pathway not previously known to contribute to human α-cell proliferation. Our study highlights the power of single-cell RNA-seq and provides a stepping stone for future explorations of cellular heterogeneity in pancreatic endocrine cells.