Dissecting the Role of Glucocorticoids on Pancreas Development

Abstract

To determine whether glucocorticoids are involved in pancreas development, glucocorticoid treatment of rat pancreatic buds in vitro was combined with the analysis of transgenic mice lacking the glucocorticoid receptor (GR) in specific pancreatic cells. In vitro treatment of embryonic pancreata with dexamethasone, a glucocorticoid agonist, induced a decrease of insulin-expressing cell numbers and a doubling of acinar cell area, indicating that glucocorticoids favored acinar differentiation; in line with this, expression of Pdx-1, Pax-6, and Nkx6.1 was downregulated, whereas the mRNA levels of Ptf1-p48 and Hes-1 were increased. The selective inactivation of the GR gene in insulin-expressing ␤-cells in mice (using a RIP-Cre transgene) had no measurable consequences on ␤-or ␣-cell mass, whereas the absence of GR in the expression domain of Pdx-1 (Pdx-Cre transgene) led to a twofold increased ␤-cell mass, with increased islet numbers and size but normal ␣-cell mass in adults. These results demonstrate that glucocorticoids play an important role in pancreatic ␤-cell lineage, acting before hormone gene expression onset and possibly also modulating the balance between endocrine and exocrine cell differentiation. Diabetes 53:2322-2329, 2004 I ncreasing evidence from epidemiological studies led to the concept of the early-life origins of adult diseases, suggesting that late-onset disorders such as type 2 diabetes, glucose intolerance, or hypertension may be programmed by nutritional inadequacy in utero (1-5). Excess glucocorticoids also retard fetal growth, and overexposure to these hormones during intrauterine life has been shown to play a role in fetal programming in both humans (6) and rodents (7). The link between glucocorticoid overexposure in utero and the occurrence of metabolic diseases in adulthood has been well documented in rats. Maternal treatment with dexamethasone (DEX), a glucocorticoid agonist, induces in the offspring growth retardation at birth as well as hyperglycemia and increased systolic blood pressure at adult age (8 -10).Similarly, inhibition of the placental 11␤-hydroxysteroid dehydrogenase type 2, the enzyme that protects the fetus from maternal glucocorticoids, induces intrauterine growth retardation as well as glucose intolerance and hypertension in adults (11).We have previously shown that maternal general food restriction during late pregnancy decreased the ␤-cell mass of newborn rats (12). This reduction was irreversible and persisted in adults despite restoration of normal nutrition from weaning (13), ultimately leading to impaired glucose tolerance associated with aging (14) or pregnancy (15). These results sustain the notion that some of the late alterations observed in humans born with intrauterine growth retardation may result from altered ␤-cell development in utero, as initially suggested by Hales and Barker (2). Additionally, we have recently demonstrated that maternal general food restriction in the rat induced a rise in both maternal and fetal corticosterone levels, which in turn w...

Glucocorticoid signalling affects pancreatic development through both direct and indirect effects

“…From our previous work investigating the direct effects of glucocorticoids on pancreatic development, by inactivating the GR either in all pancreatic progenitors (GR Pdx-Cre mice) or specifically in insulin-producing cells (GR RIP-Cre mice), we concluded that the GR is not necessary for beta cell development but rather prevents it through a direct effect on pancreatic progenitors [29]. By studying mice deleted for GR in the whole organism (GR null/null mice), we show here that GR is not required for the early induction of pancreatic development and differentiation but is nevertheless necessary in the pancreatic environment, and thereby through indirect effects, for pancreatic morphogenesis during late fetal development.…”

“…Several studies have suggested that fetal overexposure to glucocorticoids can alter pancreatic development and thereby programme consequences for glucose homeostasis in the adult [28,29,34]. From our previous work investigating the direct effects of glucocorticoids on pancreatic development, by inactivating the GR either in all pancreatic progenitors (GR Pdx-Cre mice) or specifically in insulin-producing cells (GR RIP-Cre mice), we concluded that the GR is not necessary for beta cell development but rather prevents it through a direct effect on pancreatic progenitors [29].…”

“…The entire digestive blocks from E18 fetuses as well as pancreata from E15.5 fetuses and adult GR +/null and GR +/+ mice were fixed in 3.7% formalin solution, dehydrated and embedded in paraffin, as previously described [29]. Tissues were entirely cut into 6-μm-thick sections, transversally for the digestive blocks and sagittally for the pancreata.…”

“…Quantification of beta cell proliferation and islet number in the grafts Dual immunohistochemistry for BrdU and insulin was performed as previously described [29] and proliferation was expressed as the percentage of insulin-positive cells showing a BrdU-positive nucleus. The number of islets composed of at least two insulin-positive cells associated with one glucagon-positive cell was counted on every fifth section of the grafts throughout their length.…”

“…Beta cell development is thus sensitive to glucocorticoids. More precisely, the conditional inactivation of the GR in all pancreatic progenitors (GR Pdx-Cre mice) led to a doubling of beta cell mass [29].…”