Glucose Is Necessary for Embryonic Pancreatic Endocrine Cell Differentiation

Abstract

Mature pancreatic cells develop during embryonic life from endodermal progenitors, and this developmental process depends on activation of a hierarchy of transcription factors. While information is available on mesodermal signals controlling pancreas development, little is known about environmental factors, such as the levels of nutrients including glucose, that may control this process. Here, we studied the effects of glucose on pancreatic cells development. We used an in vitro model where both endocrine and acinar cells develop from early pancreatic and duodenal homeobox-1 (PDX1)-positive embryonic pancreatic progenitors. We first showed that glucose does not have a major effect on global pancreatic cell proliferation, survival, and acinar cell development. On the other hand, glucose controlled both alpha and beta cell development. Specifically, the surface occupied by insulin-positive cells was 20-fold higher in pancreases cultured in presence than in absence of glucose, and this effect was dose-dependent over the range 0.5-10 mM. Glucose did not appear to control beta cell development by activating the proliferation of early progenitors or beta cells themselves but instead tightly regulated cell differentiation. Thus, glucose did not modify the pattern of expression of Neurogenin3, the earliest marker of endocrine progenitor cells, but was necessary for the expression of the transcription factor NeuroD, a direct target of Neurogenin3 known to be important for proper pancreatic endocrine cell development. We conclude that glucose interferes with the pancreatic endocrine cells development by regulating the transition between Ngn3 and upstream NeuroD.The mature mammalian pancreas contains two types of tissues: endocrine islet cells that produce hormones such as insulin (beta cells) and glucagon (alpha cells) and exocrine tissue whose acinar cells produce enzymes (e.g. amylase) that are secreted via the pancreatic ducts into the intestine. The pancreas originates from the dorsal and ventral regions of the foregut endoderm directly posterior to the stomach (1). Research conducted in the last few years has shed light on the processes controlling pancreatic endocrine-cell development. Studies of genetically engineered mice have identified a hierarchy of transcription factors regulating pancreas organogenesis and islet-cell differentiation (2, 3). The endodermal region committed to a pancreatic fate expresses the transcription factor Pancreatic and duodenal homeobox-1 (Pdx-1) (4, 5). The basic helix-loop-helix factor Neurogenin3 (Ngn3) is then expressed in epithelial pancreatic progenitor cells prior to endocrine differentiation (6). Ngn3 is necessary for pancreatic endocrine cell development, and Ngn3-deficient mice lack pancreatic endocrine cells (7). Lineage tracing experiments have also provided direct evidence that NGN3-expressing cells are islet progenitors (8). Thus, Ngn3 is a valuable marker for monitoring pancreatic endocrine-cell differentiation. NGN3 controls the expression of another member of the basic ...

Maturation of Stem Cell-Derived Beta-cells Guided by the Expression of Urocortin 3

“…For example, fetal rat islets only demonstrate a mature biphasic pattern of GSIS when cultured under high glucose conditions [111]. In addition, while glucose did not alter the differentiation frequency of either PDX1-positive cells or NGN3-positive endocrine precursor cells, in cultured E13.5 rat pancreas, NeuroD expression as well as the insulin and glucagon cell masses were increased under high glucose conditions [112]. A postnatal increase in MAFA expression is a crucial aspect of beta-cell maturation [75], and MAFA expression in differentiating cultures could potentially be increased by glucose [113] to enhance the maturation process.…”

Regulation of beta cell replication

“…It has long been suggested that exposure to glucose (short-term and doses within physiological ranges) play a stimulatory role in the pancreatic islet growth in rodent model systems (Swenne, 1985;Bonner-Weir et al, 1989;Guillemain et al, 2007); whereas continual elevated glucose exposure and hyperglyceamia are deleterious to beta cell function including the beta cell differentiation process (Olson, et al, 1995, Jonas, et al 1999, Poitout and Robertson, 2002. In vitro studies have shown that glucose increases the number of beta cells entering the cell cycle rather than the cell cycle rate (Swenne 1985).…”

A euglycaemic/non-diabetic perinatal environment does not alleviate early beta cell maldevelopment and type 2 diabetes risk in the GK/Par rat model

“…Expression of these genes can be altered by mutations and/or epigenetic modifications orchestrated by the cell environment. For example, glucose is now recognised to be an important modulator of pancreatic endocrine cell differentiation through its control of production of the transcription factors, NGN3 and NeuroD [25], and hyperglycaemia correlates with DNA hypomethylation and aberrant gene expression in a diabetic zebrafish model [26]. Some of these genes (Igf2, Igf1r, Pdx1, Sox9, Neurog3) are not correctly expressed in fetal GK pancreatic tissue (this study).…”