Metabolic roles of PGC-1α and its implications for type 2 diabetes.

PGC-1α is a transcriptional coactivator expressed in brown adipose tissue, liver, pancreas, kidney, skeletal and cardiac muscles, and the brain. This review presents data illustrating how PGC-1α regulates metabolic adaptations and participates in the aetiology of type 2 diabetes (T2D). Studies in mice have shown that increased PGC-1α expression may be beneficial or deleterious, depending on the tissue: in adipose tissue, it promotes thermogenesis and thus protects against energy overload, such as seen in diabetes and obesity; in muscle, PGC-1α induces a change of phenotype towards oxidative metabolism. In contrast, its role is clearly deleterious in the liver and pancreas, where it induces hepatic glucose production and inhibits insulin secretion, changes that promote diabetes. Previous studies by our group have also demonstrated the role of PGC-1α in the fetal origins of T2D. Overexpression of PGC-1α in ß cells during fetal life in mice is sufficient to induce ß-cell dysfunction in adults, leading to glucose intolerance. PGC-1α also is associated with glucocorticoid receptors in repressing expression of Pdx1, a key ß-cell transcription factor. In conclusion, PGC-1α participates in the onset of diabetes through regulation of major metabolic tissues. Yet, it may not represent a useful target for therapeutic strategies against diabetes as it exerts both beneficial and deleterious actions on glucose homoeostasis, and because PGC-1α modulation is involved in neurodegenerative diseases. However, its role in cellular adaptation shows that greater comprehension of PGC-1α actions is needed.

Genetic evidence of the programming of beta cell mass and function by glucocorticoids in mice.

AIMS/HYPOTHESIS: Prenatal exposure to excess glucocorticoids associates with low birthweight in rodents, primates and humans and its involvement in programming glucose homeostasis is suspected. Our aim was to further dissect the role of glucocorticoids on beta cell development and function in mice. METHODS: Using the model of maternal general food restriction during the last week of pregnancy, we thoroughly studied in the CD1 mouse-mothers and fetal and adult offspring--the pancreatic, metabolic and molecular consequences of maternal undernutrition associated with excess glucocorticoids. The specific involvement of the glucocorticoid receptor (GR) was studied in mutant fetuses lacking GR in pancreatic precursors or mature beta cells. RESULTS: Maternal general food restriction in the mouse is associated with decreased maternal glucose and increased corticosterone levels. Fetuses from underfed dams had increased corticosterone levels, decreased pancreatic endocrine gene expression but increased exocrine gene expression and a lower beta cell mass. The offspring of these dams had a low birthweight, permanent postnatal growth retardation and, as adults, impaired glucose tolerance, decreased beta cell mass (-50%) and massively reduced islet expression (-80%) of most of the genes involved in beta cell function (e.g. Pdx1, Sur1 [also known as Abcc8], insulin). Moreover, using mutant fetuses lacking GR in pancreatic precursors or beta cells we show that the deleterious effect of undernutrition on fetal beta cell development requires the presence of the GR in pancreatic precursor cells. CONCLUSIONS/INTERPRETATION: These results demonstrate the crucial role of excess fetal glucocorticoids and the importance of GR signalling in progenitor cells to programme beta cell mass and dysfunction.

Different mechanisms operating during different critical time-windows reduce rat fetal beta cell mass due to a maternal low-protein or low-energy diet.

AIMS/HYPOTHESIS: Adverse events during intra-uterine life may programme organ growth and favour disease later in life. In animals, protein or energy restriction during gestation alters the development of the endocrine pancreas, even though the duration of malnutrition is different. Here, we evaluate the specific effects of both diets during different periods of gestation and the mechanisms underlying the decreased beta cell mass. METHODS: Pregnant Wistar rats were fed either a low-protein or a low-energy diet during the last week of gestation or throughout gestation. Fetuses and their pancreases were analysed at days 15 and 21 of gestation. RESULTS: The low-energy diet reduced the beta cell mass from 21-day-old fetuses by 33 or 56% when administered during the last week or throughout gestation, respectively. Fetal corticosterone levels were increased. At 15 days of fetal age, the number of cells producing neurogenin 3 (NEUROG3) or pancreatic and duodenal homeobox gene 1 (PDX-1) was reduced. Neither islet vascularisation nor beta cell proliferation was affected. The low-protein diet, in contrast, was more efficient in decreasing the fetal beta cell mass when given during the last week of gestation (-53%) rather than throughout gestation (-33%). Beta cell proliferation was decreased by 50% by the low-protein diet, independently of its duration, and islet vascularisation was reduced. This diet did not affect NEUROG3- or PDX-1-positive cell numbers. CONCLUSION/INTERPRETATION: Although both diets reduced the fetal beta cell mass, the cellular mechanisms and the sensitivity windows were different. Early alteration of neogenesis due to elevated corticosterone levels is likely to be responsible for the decreased beta cell mass in low-energy fetuses, whereas impaired beta cell proliferation and islet vascularisation at later stages are implicated in low-protein fetuses.

Glucocorticoid signalling affects pancreatic development through both direct and indirect effects.

AIMS/HYPOTHESIS: Beta cell development is sensitive to glucocorticoid levels. Although direct effects of glucocorticoids on pancreatic precursors have been shown to control beta cell mass expansion, indirect effects of these hormones on pancreatic development remain unexplored. This issue was addressed in mice lacking the glucocorticoid receptor (GR) in the whole organism. MATERIALS AND METHODS: The pancreatic phenotype of GR(null/null) mice was studied at fetal ages (embryonic day [E]) E15.5 and E18 by immunohistochemistry and beta cell fraction measurements. To distinguish between direct and indirect effects, mutant E15.5 fetal pancreata were grafted under the kidney capsule of immunodeficient mice and analysed after 1 week. RESULTS: E18 GR(null/null) fetuses had smaller digestive tracts and tiny pancreata. Massive pancreatic disorganisation and apoptosis were observed despite the presence of all cell types. E15.5 GR(null/null) mutants were indistinguishable from wild-type regarding pancreatic size, tissue structure and organisation, beta cell fraction and production of exocrine transcription factor Ptf1a, neurogenin 3 and Pdx-1. Grafting E15.5 GR(null/null) pancreata into a GR-expressing environment rescued the increased apoptosis and mature islets were observed, suggesting that GR(null/null) pancreatic cell death can be attributed to indirect effects of glucocorticoids on this tissue. Heterozygous GR(+/null) mutants with reduced GR numbers showed no apoptosis but increased beta cell fraction at E18 and the adult age, strengthening the importance of an accurate GR dosage on beta cell mass expansion. CONCLUSIONS/INTERPRETATION: Our results provide evidence for GR involvement in pancreatic tissue organisation and survival through indirect effects. GR does not appear necessary for early phases, but its accurate dosage is critical to modulate beta cell mass expansion at later fetal stages, presumably through direct effects.

Nutrition, glucocorticoids and pancreas development.

Low birth weight is strongly predictive of hypertension, cardiovascular diseases, obesity, insulin resistance and diabetes. The mechanisms by which fetal undernutrition and, hence, low birth weight increase the risk of developing these diseases are unclear. To investigate the hypothesis of a primary defect in beta-cell development, we designed a rat model of undernutrition, involving an overall reduction in maternal food intake. In this model, fetuses with intrauterine growth retardation have a decreased beta-cell mass, which persists into adulthood and ultimately causes glucose intolerance, thereby mimicking features of the metabolic syndrome. Maternal undernutrition causes elevations in glucocorticoid concentrations, which, in turn, cause a reduction in beta-cell mass in the fetus. Our data also suggest a key role of glucocorticoids when nutrient supply is normal. By combining in-vitro studies with in-vivo investigations in mice lacking the glucocorticoid receptor in the whole organism or in specific pancreatic cell populations, we have shown that the glucocorticoid receptor is critical for ensuring pancreatic architecture and survival, as well as for beta-cell mass expansion during a critical developmental window. Glucocorticoids act on precursor cells before the onset of hormone gene expression and are likely to programme beta-cell differentiation by modifying the balance of specific transcription factors, mostly Pdx-1. Glucocorticoids should therefore be considered as important hormones in pancreatic development, in situations of both normal nutrition and undernutrition. To investigate whether this is also the case in human pancreatic development, we studied the expression of the glucocorticoid receptor and that of the transcription factor Pdx-1 on pancreatic specimens from very early to late stages of development of the human embryo. In terms of beta-cell ontogeny, expression of the glucocorticoid receptor in the pancreas coincides with that of the transcription factor Pdx-1 in beta cells. These results are consistent with a possible role for glucocorticoids during human pancreatic development.

Decreased beta-cell proliferation impairs the adaptation to pregnancy in rats malnourished during perinatal life.

We investigated the cellular mechanisms responsible for the inability of 8-month-old previously malnourished (PM) females to adapt their beta-cell mass during pregnancy. The evolution during pregnancy of beta-cell fraction, size and proliferation was studied. At day 21 of pregnancy beta-cell fraction increased less in PM than in control females, compared with their non-pregnant values. A slight beta-cell hypertrophy was observed during pregnancy in both groups. In control females, beta-cell 5-bromo-2'-deoxyuridine (BrdU) labelling index (LI) increased from 0.07+/-0.04% before pregnancy to 1.13+/-0.20% at day 12 and decreased thereafter to reach again basal levels at day 21. In PM females, beta-cell proliferation rate was decreased at day 12 (0.74+/-0.15%, P<0.05) but similar to controls at all other stages studied. Separate analysis of the head and tail parts of the pancreas in control animals revealed that the beta-cell fraction during pregnancy increased more in the head than in the tail; similarly, BrdU LI increased 20-fold in the head and 10-fold in the tail, compared with non-pregnant values. In PM females, no adaptation of beta-cell fraction could be observed in the head, where BrdU LI was decreased by half at day 12 of pregnancy. In PM females the lactogenic activity was twice that of controls at day 12 whereas all beta-cells expressed the prolactin receptor. In conclusion, perinatal malnutrition impairs subsequent adaptation to pregnancy by decreasing beta-cell proliferation in the head of the pancreas at a critical time during pregnancy.

Localization of alpha-endosulphine in pancreatic somatostatin delta cells and expression during rat pancreas development.

AIMS/HYPOTHESIS: alpha-Endosulphine, a protein that belongs to the cAMP-regulated-phosphoprotein family, has been reported to modulate insulin secretion in vitro through interaction with the pancreatic beta-cell ATP-sensitive potassium (K(ATP)) channel. In this study, we analysed the tissue distribution of alpha-endosulphine and determined its pancreatic cellular localization. METHODS: Quantitative tissue distribution of alpha-endosulphine was studied by RIA on tissue extracts and cellular/subcellular localization was done using immunocytochemistry, morphometry and western blot analysis. alpha-Endosulphine and somatostatin release from RINT-3 somatostatin-secreting cells was quantified by RIA. RESULTS: alpha-Endosulphine, concentrated particularly in the central nervous system, was also detected in a wide variety of tissues including the pancreas. Immunohistochemistry analysis of adult rat pancreatic sections showed that alpha-endosulphine localized in somatostatin delta cells, where its expression increased during post-natal development. Immunoreactive cells were detected from foetal age E19, and the number of somatostatin cells co-expressing alpha-endosulphine increased with developmental age from E19 until adult. alpha-Endosulphine, highly expressed in the cytoplasm of RINT3 somatostatin-secreting cell line, was recovered in the particulate fraction of RINT3 cell extracts but was not co-secreted with somatostatin. CONCLUSION/INTERPRETATION: alpha-Endosulphine is expressed in all tissues tested including pancreas and is also detected in plasma. Pancreatic alpha-endosulphine is specifically localized in somatostatin delta cells. This cytosolic protein is not co-secreted with somatostatin and could be physically associated with particulate components of the cells. These findings are not in favour of an endocrine/paracrine effect of alpha-endosulphine on the beta-cell K(ATP) channel.

Maternal undernutrition during late gestation-induced intrauterine growth restriction in the rat is associated with impaired placental GLUT3 expression, but does not correlate with endogenous corticosterone levels.

Fetal intrauterine growth restriction (IUGR) is a frequently occurring and serious complication of pregnancy. Infants exposed to IUGR are at risk for numerous perinatal morbidities, including hypoglycemia in the neonatal period, as well as increased risk of later physical and/or mental impairments, cardiovascular disease and non-insulin-dependent diabetes mellitus. Fetal growth restriction most often results from uteroplacental dysfunction during the later stage of pregnancy. As glucose, which is the most abundant nutrient crossing the placenta, fulfills a large portion of the fetal energy requirements during gestational development, and since impaired placental glucose transport is thought to result in growth restriction, we investigated the effects of maternal 50% food restriction (FR50) during the last week of gestation on rat placental expression of glucose transporters, GLUT1, GLUT3 and GLUT4, and on plasma glucose content in both maternal and fetal compartments. Moreover, as maternal FR50 induces fetal overexposure to glucocorticoids and since these hormones are potent regulators of placental glucose transporter expression, we investigated whether putative alterations in placental GLUT expression correlate with changes in maternal and/or fetal corticosterone levels. At term (day 21 of pregnancy), plasma glucose content was significantly reduced (P<0.05) in mothers subjected to FR50, but was not affected in fetuses. Food restriction reduced maternal body weight (P<0.001) but did not affect placental weight. Plasma corticosterone concentration, at term, was increased (P<0.05) in FR50 mothers. Fetuses from FR50 mothers showed reduced body weight (P<0.001) but higher plasma corticosterone levels (P<0.05). Adrenalectomy (ADX) followed by corticosterone supplementation of the mother prevented the FR50-induced rise in maternal plasma corticosterone at term. Food restriction performed on either sham-ADX or ADX mothers induced a similar reduction in the body weight of the pups at term (P<0.01). Moreover, plasma corticosterone levels were increased in pups from sham-ADX FR50 mothers (P<0.01) and in pups from ADX control mothers (P<0.01). Western blot analysis of placental GLUT proteins showed that maternal FR50 decreased placental GLUT3 protein levels in all experimental groups at term (P<0.05 and P<0.01), but did not affect either GLUT1 or GLUT4 protein levels. Northern blot analysis of placental GLUT expression showed that both GLUT1 and GLUT3 mRNA were not affected by the maternal feeding regimen or surgery. We concluded that prolonged maternal malnutrition during late gestation decreases maternal plasma glucose content and placental GLUT3 glucose transporter expression, but does not obviously affect fetal plasma glucose concentration. Moreover, the present results are not compatible with a role of maternal corticosterone in the development of growth-restricted rat fetuses.

Endocrine pancreas development is altered in foetuses from rats previously showing intra-uterine growth retardation in response to malnutrition.

AIMS/HYPOTHESIS: We have shown that perinatal malnutrition decreases beta-cell mass at birth and impairs the adaptation of the endocrine pancreas to a subsequent pregnancy. The aim of this study is to investigate the impact of this maternal inadaptation on the development of endocrine pancreas in foetuses. METHODS: Female rats malnourished during their perinatal life and showing intra-uterine growth retardation at birth were mated at 8 months of age. The development of the endocrine pancreas was studied at embryonic days 14, 17 and 20 in their foetuses by immunohistochemistry and morphometrical measurements on pancreatic sections. RESULTS: At embryonic day 20, both alpha and beta-cell fractions were decreased in foetuses from IUGR dams. Beta-cell mass was reduced (197 +/- 27 microg, vs 281 +/- 40 microg in control, p < 0.01) and so were insulin content and islet number per cm(2), as in the first generation foetuses. At embryonic day 14, the number of cells expressing only insulin was decreased by half in foetuses from intra-uterine growth retardation dams. At embryonic day 17, 50 % of the homeodomain protein Pdx-1 cell population expressed insulin but all the insulin cells expressed Pdx-1 in both groups; in foetuses from intra-uterine growth retardation dams the number of epithelial cells expressing Pdx-1 was decreased (415 +/- 40 cells/ mm(2) vs 481 +/- 28 cells/mm(2) in control foetuses, p < 0.05) and the mesenchymal fraction in the pancreas was increased by 36 % ( p < 0.05). CONCLUSION/INTERPRETATION: Early malnutrition decreases beta-cell mass in the first generation of offspring and impairs the subsequent beta-cell adaptation to pregnancy. The beta-cell alteration is also present in the next generation and involves a decreased expansion of the epithelial population expressing Pdx-1.

Perinatal malnutrition programs sympathoadrenal and hypothalamic-pituitary-adrenal axis responsiveness to restraint stress in adult male rats.

In humans, an altered control of cortisol secretion was reported in adult men born with a low birth weight making the hypothalamic-pituitary-adrenal (HPA) axis a possible primary target of early life programming. In rats, we have recently shown that maternal food restriction during late pregnancy induces both an intrauterine growth retardation and an overexposure of fetuses to maternal corticosterone, which disturb the development of the HPA axis in offspring. The first aim of this work was to investigate, in adult male rats, whether perinatal malnutrition has long-lasting effects on the HPA axis activity during both basal and stressful conditions. Moreover, as the HPA axis and sympathetic nervous system are both activated by stress, the second aim of this work was to investigate, in these rats, the adrenomedullary catecholaminergic system under basal and stressful conditions. This study was conducted on 4-month-old male rats malnourished during their perinatal life and on age-matched control animals. Under basal conditions, perinatal malnutrition reduced body weight and plasma corticosteroid-binding globulin (CBG) level but increased mineralocorticoid receptor (MR) gene expression in CA1 hippocampal area. After 30 min of restraint, perinatally malnourished (PM) rats showed increased plasma noradrenaline, adrenocorticotropin hormone (ACTH) and corticosterone concentrations similarly as controls, but calculated plasma-free corticosterone concentration was significantly higher and adrenaline level lower than controls. During the phase of recovery, PM rats showed a rapid return of plasma ACTH and corticosterone concentrations to baseline levels in comparison with controls. These data suggest that in PM rats, an elevation of basal concentrations of corticosterone, in face of reduced CBG and probably increased hippocampal MR lead to a much larger impact of corticosterone on target cells that mediate the negative-feedback mechanism on the activities of both the HPA axis and sympathoadrenal one.

Glucocorticoids impair fetal beta-cell development in rats.

In rats, poor fetal growth due to maternal food restriction during pregnancy is associated with decreased beta-cell mass at birth and glucose intolerance in adulthood. Overexposure to glucocorticoids in utero can induce intrauterine growth retardation in humans and animals and subsequent glucose intolerance in rodents. The aims of this study were to investigate whether glucocorticoid overexposure mediates the effect of undernutrition on beta-cell mass and to study their potential role in normally nourished rats. Undernutrition significantly increased maternal and fetal corticosterone levels. Twenty-one-day-old fetuses with undernutrition showed growth retardation and decreased pancreatic insulin content; adrenalectomy and subcutaneous corticosterone implants in their dams prevented the maternal corticosterone increase and restored fetal beta-cell mass. In fetuses with normal nutrition, fetal corticosterone levels were negatively correlated to fetal weight and insulin content; fetal beta-cell mass increased from 355 +/- 48 microg in sham to 516 +/- 160 microg after maternal adrenalectomy; inhibition of steroid production by metyrapone induced a further increase to 757 +/- 125 microg. Our data support the new concept of a negative role of glucocorticoids in fetal beta-cell development.

Maternal undernutrition during late gestation induces fetal overexposure to glucocorticoids and intrauterine growth retardation, and disturbs the hypothalamo-pituitary adrenal axis in the newborn rat.

As fetal overexposure to glucocorticoids has been postulated to induce intrauterine growth retardation (IUGR) in humans, we investigated the effects of maternal 50% food restriction (FR50) in rats during the last week of gestation on the hypothalamo-pituitary adrenal (HPA) axis activity in both mothers and their fetuses. In mothers, FR50 increased both the plasma corticosterone (B) level from embryonic days 19-21 and the relative adrenal weight at term. FR50 decreased at term both the maternal plasma corticosteroid-binding globulin level and placental 11beta-hydroxysteroid dehydrogenase type 2 expression. In newborns, maternal FR50 reduced body and adrenal weights, glucocorticoid and mineralocorticoid receptor expressions in the hippocampus, corticoliberin expression in the hypothalamic paraventricular nucleus, and plasma ACTH. In FR50 newborns, the plasma B level was increased at birth and decreased 2 h later. When maternal circulating B was maintained at the basal level by adrenalectomy and B supply, FR50 induced IUGR in pups and decreased placental 11beta- hydroxysteroid dehydrogenase type 2 expression at term, but did not disturb the offspring's HPA axis. These results suggest that maternal undernutrition during late gestation induces both IUGR and an overexposure of fetuses to maternal B, which disturb the development of the HPA axis.

Impaired beta-cell regeneration in perinatally malnourished rats: a study with STZ.

We investigated the mechanisms implicated in beta-cell mass reduction observed during late fetal and early postnatal malnutrition in the rat. Beta-cell regeneration, including proliferation and neogenesis, was studied after neonatal beta-cell destruction by streptozotocin (STZ). STZ was injected at birth and maternal food restriction was continued until weaning. Beta-cell mass, proliferation, and islet number were quantified by morphometrical measurements on pancreatic sections in STZ-injected normal (C-STZ) and malnourished (R-STZ) rats, with noninjected C and R rats as controls. At day 4, only 20% of the beta cell-mass remained in C-STZ rats. It regenerated to 50% that of noninjected controls, mainly through active neogenesis, as shown by the entire recovery of islet number/cm(2), and also through moderately increased beta-cell proliferation. In contrast, beta-cell mass from R-STZ animals poorly regenerated, despite a dramatic increase of beta-cell proliferation, because islet number/cm(2) recovered insufficiently. In conclusion, perinatal malnutrition impairs neogenesis and the capacity of beta-cell regeneration by neogenesis but preserves beta-cell proliferation, which remains the elective choice to increase beta-cell mass. These results provide an explanation for the impaired capacity of malnourished animals to adapt their beta-cell mass during aging or pregnancy, which aggravate glucose tolerance.

Age-dependent inability of the endocrine pancreas to adapt to pregnancy: a long-term consequence of perinatal malnutrition in the rat.

We have recently shown that maternal food restriction during late pregnancy decreased beta-cell mass in the offspring at birth. Prolonged maternal malnutrition until weaning led to irreversible decrease of beta-cell mass in the adult male progeny. During pregnancy, the maternal endocrine pancreas demonstrates an acute and reversible increase in beta-cell mass. The aim of this work was to investigate whether perinatal malnutrition could have long-lasting effects on glucose homeostasis and the adaptation of the endocrine pancreas to a subsequent pregnancy. This study was conducted on 4- and 8-month-old female rats malnourished during their perinatal life and on age-matched control animals. Oral glucose tolerance tests (OGTT), pancreatic insulin content, and islet mass quantitation after dithizone staining were performed on the same animals. Four-month-old nonpregnant previously malnourished animals showed normal glucose tolerance but a significant decrease in insulin secretion during OGTT. These animals were, however, still able to adapt pancreatic insulin contents and doubled their islet mass in late gestation. At 8 months of age, insulin content before pregnancy was reduced to half that of controls. Moreover, it did not show the characteristic increase during gestation that could still be observed in pregnant control females. In those control animals, the islet mass increased regularly until late gestation (14.1+/-1.8 mg at day 20.5, vs. 9.8+/-1.2 mg, nonpregnant), whereas in previously malnourished animals the islet mass remained throughout pregnancy similar to the nonpregnant values (8.5+/-1.4 mg at day 20.5 vs. 8.9+/-3.6 mg, nonpregnant). In conclusion, early malnutrition has dramatic consequences on the capacity of the endocrine pancreas to meet the increased insulin demand during pregnancy and aging.

Effect of ageing on beta-cell mass and function in rats malnourished during the perinatal period.

AIMS/HYPOTHESIS: In a recently developed rat model, maternal food restriction from day 15 of pregnancy until weaning induced low birth weight and a 70% reduction of beta-cell mass in the offspring at day 21 after birth. Subsequent renutrition from weaning was insufficient to fully restore beta-cell mass in young adult rats. The aim of this study is to investigate the long-term consequences of early malnutrition on beta-cell mass and function. METHODS: Oral glucose tolerance tests were done in 3- and 12-month-old animals and beta-cell mass and apoptosis were determined by morphometrical measurements on pancreatic sections. The specific impact of postnatal malnutrition was studied by comparing control animals (C group) with animals malnourished during their fetal life only (R/C group), and animals malnourished during fetal life and until weaning (R group). RESULTS: In 3-month-old R/C animals beta-cell mass reached 8.0 +/- 1.5 mg with no further increase until 12 months (8.1 +/- 1.5 mg), compared with 9.3 +/- 1.9 mg in control rats. Twelve-month-old R/C animals showed normal plasma insulin responses and borderline glucose tolerance. In R animals, apoptosis reached 1.9 +/- 0.4% of the beta cells at 3 months, compared with 0.7 +/- 0.5% in control rats, and beta-cell mass did not increase between 3 and 12 months (4.7 +/- 0.8 mg at 12 months). In aged control and R animals, apoptosis affected 8% of the beta cells. At 12 months only, R animals showed profound insulinopenia and marked glucose intolerance. CONCLUSION/INTERPRETATION: In conclusion, perinatal malnutrition profoundly impairs the programming of beta-cell development. In animals with decreased beta-cell mass the additional demand placed by ageing on the beta cells entails glucose intolerance since beta-cell mass does not expand and apoptosis is increased.

Beta-cell mass and proliferation following late fetal and early postnatal malnutrition in the rat.

We have recently shown that maternal food restriction during late pregnancy in rats decreased beta-cell mass in the offspring at birth, without altering beta-cell proliferation. The aim of the present work was to determine: 1) whether sustained maternal undernutrition until weaning (R group) more dramatically alters beta-cell mass in the offspring and if normal food supply from weaning until adulthood could reverse the deleterious effects and; 2) if altered beta-cell proliferation was responsible for the decreased beta-cell mass. Beta-cell fraction and proliferative capacity were determined during the suckling period and at adult age after ad libitum feeding from weaning in the R animals and in age-matched controls (C group). At day 21, the offspring born and nursed by food-restricted mothers (R animals) showed a 66% reduction in beta-cell mass and number, which did not increase from birth to weaning, although beta-cell proliferation remained normal. At 3 months of age, R animals had 35% decreased beta-cell fraction, with a 50% decrease in the head of the pancreas. In that area, beta-cell proliferation was similar to that of the controls. In the tail of the pancreas, beta-cell fraction was only slightly impaired but beta-cell proliferation was increased by 37%, as compared with the controls. This increase was associated with a shift in islet size distribution towards medium and large islets compared with the head of pancreas from these R animals. No regional variations of beta-cell fraction, proliferation or islet size distribution were observed in adult control animals. In conclusion, prolonged malnutrition until weaning impairs beta-cell development but not beta-cell proliferation. Subsequent re-nutrition is followed by increased beta-cell proliferation but this is insufficient to fully restore beta-cell mass.

Postnatal somatic growth and insulin contents in moderate or severe intrauterine growth retardation in the rat.

A rat model of perinatal malnutrition was designed to study the role of nutrition in postnatal somatic growth and insulin stores until adulthood. Maternal food restriction (50%) from day 15 of pregnancy resulted in intrauterine growth retardation (IUGR) in the offspring. The outcome of moderate or severe IUGR was investigated. Neonates with moderate IUGR normally nourished postnatally showed normal body and organ weights and normal insulin contents in adulthood. Offspring with severe IUGR normally nourished postnatally also rapidly recovered normal body and pancreatic weights, but liver and kidney weights were significantly reduced at adult age. Malnutrition until weaning in offspring with severe IUGR induced marked growth retardation (50%) in body and organ weights at weaning. Although pancreatic weight recovered at adult age, body, liver and kidney weights were irreversibly affected, despite several months of normal nutrition. Furthermore, severe IUGR at birth resulted in decreased insulin content at adult age, irrespective of postnatal nutrition. In conclusion, this animal model demonstrates that normalization of adult size can be dissociated from organ growth and also that altered insulin stores in adulthood are more dependent on the severity of IUGR at birth than on postnatal catch-up in organ growth.

In utero undernutrition impairs rat beta-cell development.

The role of nutrition on the development of the endocrine pancreas was studied in a rat model obtained by maternal food restriction. A 50% food restriction was applied to female rats from day 15 of pregnancy and resulted in intrauterine growth-retardation (IUGR) in the offspring. At day 1 postnatal, beta-cell mass was significantly decreased in IUGR pups as compared to controls (0.70 +/- 0.06 vs 1.07 +/- 0.06 mg, p < 0.0001), as well as insulin content. This change in beta-cell mass can be attributed to a reduced number of islets, since the density of insulin-positive aggregates in pancreatic sections of IUGR rats was 20% lower than in controls. Proliferative capacity of beta cells, as measured by 5-bromo-2-deoxyuridine (BrdU) labelling index, was not altered in growth-retarded animals. Body as well as pancreatic weight were fully recovered in IUGR pups after 21 days of normal feeding by control mothers. However, these animals retained a 25% decrease in insulin content, 40% decrease in beta-cell mass (1.58 +/- 0.18 vs 2.78 +/- 0.42 mg, p < 0.001) and a strong reduction in the density of insulin positive aggregates per cm2, as compared to controls, suggesting that the total islet number was likely to be reduced. Beta-cell proliferative capacity remained normal. In conclusion, in utero undernutrition in rats does not impede postnatal growth but durably impairs beta-cell development. Impairment of beta-cell differentiation might be suggested.

Glucagon acts through its own receptors in the presence of functional glucagon-like peptide-1 receptors on hamster insulinoma.

The observations that glucagon binds to glucagon-like peptide-1 (tGLP-1) receptors have raised the question of whether glucagon receptors mediate the insulinotropic effect of glucagon. We have investigated the presence and selective activation of glucagon and tGLP-1 receptors on tumor-derived cells. Northern blot analysis detected either glucagon or tGLP-1 receptor messenger RNA in hamster (HIT) and mouse (beta TC3) beta-cell lines, respectively, whereas both receptor messenger RNA were revealed in Syrian hamster insulinoma. Their expression in insulinoma plasma membranes was confirmed by specific covalent labeling with either [125I]glucagon or [125I]tGLP-1. Both glucagon and tGLP-1 receptors showed a single class of high affinity binding sites with respective Kd values of 1.11 +/- 0.11 and 0.82 +/- 0.11 nM. [125I]tGLP binding was dose dependently inhibited with a hierarchy of exendin-4 > tGLP-1 > exendin-(9-39) > oxyntomodulin > glucagon. [125I]Glucagon binding was only inhibited by glucagon and oxyntomodulin. Both glucagon and tGLP-1 increased cAMP formation in insulinoma plasma membranes in a dose-dependent manner, with ED50 values of 170.0 +/- 25.0 and 3.1 +/- 0.4 pM, respectively. Exendin-(9-39), a tGLP-1 receptor antagonist, inhibited tGLP-1-induced, but not glucagon-induced, cAMP formation. Our data demonstrate on hamster insulinoma the presence of high affinity glucagon and tGLP-1 receptors selectively coupled to adenylyl cyclase. The observed low affinity of tGLP-1 receptors for glucagon sustains the idea that each hormone has a direct insulinotropic effect.