Expression of the kynurenine pathway enzymes in the pancreatic islet cells. Activation by cytokines and glucolipotoxicity.

The tryptophan/kynurenine pathway (TKP) is the main route of tryptophan degradation and generates several neuroactive and immunomodulatory metabolites. Experimental and clinical data have clearly established that besides fat, muscle and liver, pancreatic islet tissue itself is a site of inflammation during obesity and type 2 diabetes. Therefore it is conceivable that pancreatic islet exposure to increased levels of cytokines may induce upregulation of islet kynurenine metabolism in a way resembling that seen in the brain in many neurodegenerative disorders. Using normal rat islets and the INS-1 ß-cell line, we have demonstrated for the first time that: 1/only some TKP genes are constitutively expressed, both in ß-cells as well as non ß-cells; 2/ the regulatory enzyme indoleamine 2,3-dioxygenase (IDO1) is not constitutively expressed; 3/ IDO1 and kynurenine 3-monoxygenase (KMO) expression are potently activated by proinflammatory cytokines (IFN-γ, IL-1ß) and glucolipotoxicity respectively, rather in ß-cells than in non ß-cells; 4/ Islet kynurenine/kynurenic acid production ratio is enhanced following IFN-γ and glucolipotoxicity; 5/ acute exposure to KYN potentiates glucose-induced insulin secretion by normal islets; and 6/ oxidative stress or glucocorticoid modulates TKP genes only marginally. Pancreatic islets may represent a new target tissue for inflammation and glucolipotoxicity to activate the TKP. Since inflammation is now recognized as a crucial mechanism in the development of the metabolic syndrome and more specifically at the islet level, it is needed to evaluate the potential induction of the TKP in the endocrine pancreas during obesity and/or diabetes and its relationship to the islet cell functional alterations.

Maternal diabetes, programming of beta-cell disorders and intergenerational risk of type 2 diabetes.

A substantial body of evidence suggests that an abnormal intra-uterine milieu elicited by maternal metabolic disturbances as diverse as malnutrition, placental insufficiency, diabetes and obesity may be able to programme susceptibility of the foetus to later develop chronic degenerative diseases such as obesity, hypertension, cardiovascular diseases and type 2 diabetes (T2D). As insulin-producing cells have been placed centre stage in the development of T2D, this review examines developmental programming of the beta-cell mass (BCM) in various rodent models of maternal protein restriction, calorie restriction, overnutrition and diabetes. The main message is that whatever the initial maternal insult (F0 generation) and whether alone or in combination, it gives rise to the same programmed BCM outcome in the daughter generation (F1). The altered BCM phenotype in F1 females prohibits normal BCM adaptation during pregnancy and, thus, diabetes (gestational diabetes) ensues. This gestational diabetes is then passed from one generation (F1) to the next (F2, F3 and so on). This review highlights a number of studies that have identified epigenetic mechanisms that may contribute to altered BCM development and beta-cell failure, as observed in diabetes. In addition to their role in instilling the programmed defect, these non-genomic mechanisms may also be involved in its intergenerational transmission.

Early environmental factors, alteration of epigenetic marks and metabolic disease susceptibility.

The environmental conditions that are experienced in early life can profoundly influence human biology and long-term health. Early-life nutrition and stress are among the best documented examples of such conditions because they influence the adult risk of developing metabolic diseases, such as type 2 diabetes mellitus (T2D) and cardiovascular diseases. It is now becoming increasingly accepted that environmental compounds including nutrients can produce changes in the genome activity that in spite of not altering DNA sequence can produce important, stable and transgenerational alterations in the phenotype. Epigenetic changes, in particular DNA methylation and histone acetylation/methylation, provide a 'memory' of developmental plastic responses to early environment and are central to the generation of phenotypes and their stability throughout the life course. Their effects may only become manifest later in life, e.g. in terms of altered responses to environmental challenges.

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

AIMS/HYPOTHESIS: We used the GK/Par rat, a spontaneous model of type 2 diabetes with early defective beta cell neogenesis, to determine whether the development of GK/Par offspring in a non-diabetic intrauterine/postnatal environment would prevent the alteration of fetal beta cell mass (BCM) and ultimately decrease the risk of diabetes later in adult life. METHODS: We used an embryo-transfer approach, with fertilised GK/Par ovocytes (oGK) being transferred into pregnant Wistar (W) or GK/Par females (pW and pGK). Offspring were phenotyped at fetal age E18.5 and at 10 weeks of age, for BCM, expression of genes of pancreatic progenitor cell regulators (Igf2, Igf1r, Sox9, Pdx1 and Ngn3), glucose tolerance and insulin secretion. RESULTS: (1) Alterations in neogenesis markers/regulators and BCM were as severe in the oGK/pW E18.5 fetuses as in the oGK/pGK group. (2) Adult offspring from oGK transfers into GK (oGK/pGK/sGK) had the expected diabetic phenotype compared with unmanipulated GK rats. (3) Adult offspring from oGK reared in pW mothers and milked by GK foster mothers had reduced BCM, basal hyperglycaemia, glucose intolerance and low insulin, to an extent similar to that of oGK/pGK/sGK offspring. (4) In adult offspring from oGK transferred into pW mothers and milked by their W mothers (oGK/pW/sW), the phenotype was similar to that in oGK/pGK/sGK or oGK/pW/sGK offspring. CONCLUSIONS/INTERPRETATION: These data support the conclusion that early BCM alteration and subsequent diabetes risk in the GK/Par model are not removed despite normalisation of the prenatal and postnatal environments, either isolated or combined.

IL-1 antagonism reduces hyperglycemia and tissue inflammation in the type 2 diabetic GK rat.

Recent studies suggest an inflammatory process, characterized by local cytokine/chemokine production and immune cell infiltration, regulates islet dysfunction and insulin resistance in type 2 diabetes. However, the factor initiating this inflammatory response is not known. Here, we characterized tissue inflammation in the type 2 diabetic GK rat with a focus on the pancreatic islet and investigated a role for IL-1. GK rat islets, previously characterized by increased macrophage infiltration, displayed increased expression of several inflammatory markers including IL-1beta. In the periphery, increased expression of IL-1beta was observed primarily in the liver. Specific blockade of IL-1 activity by the IL-1 receptor antagonist (IL-1Ra) reduced the release of inflammatory cytokines/chemokines from GK islets in vitro and from mouse islets exposed to metabolic stress. Islets from mice deficient in IL-1beta or MyD88 challenged with glucose and palmitate in vitro also produced significantly less IL-6 and chemokines. In vivo, treatment of GK rats with IL-1Ra decreased hyperglycemia, reduced the proinsulin/insulin ratio, and improved insulin sensitivity. In addition, islet-derived proinflammatory cytokines/chemokines (IL-1beta, IL-6, TNFalpha, KC, MCP-1, and MIP-1alpha) and islet CD68(+), MHC II(+), and CD53(+) immune cell infiltration were reduced by IL-1Ra treatment. Treated GK rats also exhibited fewer markers of inflammation in the liver. We conclude that elevated islet IL-1beta activity in the GK rat promotes cytokine and chemokine expression, leading to the recruitment of innate immune cells. Rather than being directly cytotoxic, IL-1beta may drive tissue inflammation that impacts on both beta cell functional mass and insulin sensitivity in type 2 diabetes.

The GK rat beta-cell: a prototype for the diseased human beta-cell in type 2 diabetes?

Increasing evidence indicates that decreased functional beta-cell mass is the hallmark of type 2 diabetes (T2D) mellitus. Nowadays, the debate focuses on the possible mechanisms responsible for abnormal islet microenvironment, decreased beta-cell number, impaired beta-cell function, and their multifactorial aetiologies. This review is aimed to illustrate to what extend the Goto-Kakizaki rat, one of the best characterized animal models of spontaneous T2D, has proved be a valuable tool offering sufficient commonalities to study these aspects. We propose that the defective beta-cell mass and function in the GK model reflect the complex interactions of multiple pathogenic players: (i) several independent loci containing genes responsible for some diabetic traits (but not decreased beta-cell mass); (ii) gestational metabolic impairment inducing an epigenetic programming of the pancreas (decreased beta-cell neogenesis and/or proliferation) which is transmitted to the next generation; and (iii) loss of beta-cell differentiation due to chronic exposure to hyperglycemia/hyperlipidemia, inflammatory mediators, oxidative stress and to perturbed islet microarchitecture.

Type 2 diabetes - a matter of failing beta-cell neogenesis? Clues from the GK rat model.

Now that reduction in beta-cell mass has been clearly established in humans with type 2 diabetes mellitus (T2D), the debate focuses on the possible mechanisms responsible for decreased beta-cell number. Appropriate inbred rodent models are essential tools for this purpose. The information available from the Goto-Kakizaki (GK) rat, one of the best characterized animal models of spontaneous T2D, is reviewed in such a perspective. We propose that the defective beta-cell mass in the GK model reflects mostly a persistently decreased beta-cell neogenesis. The data discussed in this review are consistent with the notion that poor proliferation and/or survival of the endocrine precursor cells during GK foetal life will result in a decreased pool of endocrine precursors in the pancreas, and hence an impaired capacity of beta-cell neogenesis (either primary in the foetus or compensatory in the newborn and the adult). As we also demonstrated that beta-cell neogenesis can be pharmacologically reactivated in the GK model, our work supports, on a more prospective basis, the concept that facilitation of T2D treatment may be obtained through beta-cell mass expansion after stimulation of beta-cell regeneration/neogenesis in diabetic patients.

Defective IGF2 and IGF1R protein production in embryonic pancreas precedes beta cell mass anomaly in the Goto-Kakizaki rat model of type 2 diabetes.

AIMS/HYPOTHESIS: The Goto-Kakizaki (GK) rat is a spontaneous model of type 2 diabetes. Defective beta cell mass detectable in late fetal age precedes the onset of hyperglycaemia. Our hypothesis was that an embryonic IGF production deficiency might be involved in beta cell mass anomaly in the diabetic GK rat. To test this, we evaluated during pancreatic organogenesis: (1) the beta cell development in GK rats on embryonic day (E) 13.5 and E18.5; (2) IGF2 and IGF1 receptor (IGF1R) pancreatic protein production on E13.5 and E18.5; (3) the in vitro development of GK pancreatic rudiment on E13.5; and (4) the in vitro effect of IGF2 addition on beta cell mass. MATERIALS AND METHODS: Beta cell quantitative analyses were determined by immunohistochemistry and morphometry. IGF2 and IGF1R pancreatic protein production was evaluated using western blot analyses. Dorsal pancreatic rudiments were dissected on E13.5, separated from surrounding mesenchyme and cultured for 7 days without or with recombinant IGF2. RESULTS: While beta cell mass was already decreased on E18.5, the differentiation of the first beta cells was in fact normal in E13.5 GK pancreas. Moreover, defective IGF2 and IGF1R protein production was detected in GK pancreatic rudiment as early as E13.5. The isolated GK pancreatic rudiment as maintained in vitro mimics the GK beta cell deficiency observed in vivo. This last approach enabled us to show that GK beta cells were fully responsive to IGF2 as far as their net growth is concerned. CONCLUSIONS/INTERPRETATION: In diabetic GK rat, defective IGF2 and IGF1R protein production in embryonic pancreas precedes beta cell mass anomaly. IGF2 supplementation expands the pool of beta cells.

Undernutrition does not alter the activation of beta-cell neogenesis and replication in adult rats after partial pancreatectomy.

In previous work, we demonstrated that a 65% protein calorie food restriction started during the third trimester of gestation in rats caused a reduced beta-cell mass at 4 days of life that persisted until adult age. In this study with adult undernourished (U) rats, we investigated 1) whether undernutrition affects the beta-cell growth potential and both beta-cell proliferation and differentiation and 2) the implication of the IGFs, highly responsive to nutritional status, in these processes. To this end, we used the 90% pancreatectomy (Px) procedure in U and control (C) adult rats. The results show that, on day 2 after Px, beta-cell replication was significantly higher in C rats, whereas the beta-cell neogenesis was markedly increased in U/Px rats. Both the serum levels of IGF-I and the liver IGF-I mRNA expression were reduced in adult U rats before and after Px compared with C rats. Pancreatic IGF-I mRNA expression was reduced in U animals on day 0. However, on day 2 after Px, the increase of pancreatic IGF-I mRNA expression was significantly higher in U rats than in C rats. These data suggest that beta-cells still have the capacity to regenerate in the adult U rats, with a higher efficiency than C rats on day 2, and that both beta-cell neogenesis and beta-cell replication are stimulated. The increased pancreatic IGF-I mRNA may be instrumental in these processes.

GLP-1 based therapy for type 2 diabetes.

Type 2 diabetes mellitus is a major and growing health problem throughout the world. Current treatment approaches include diet, exercise, and a variety of pharmacological agents including insulin, biguanides, sulfonylureas and thiazolidinediones. New therapies are still needed to control metabolic abnormalities, and also to preserve beta-cell mass and to prevent loss of beta-cell function. Glucagon-like peptide 1 (GLP-1) is a drug candidate which potentially fulfils these conditions. GLP-1 is an incretin hormone secreted by intestinal L-cells in response to meal ingestion is a novel pharmacological target with multiple antihyperglycemic actions. GLP-1 glucoregulatory actions include glucose-dependent enhancement of insulin secretion, inhibition of glucagon secretion, slowing of gastric emptying and reduction of food intake. GLP-1 is rapidly inactivated by amino peptidase, dipeptidyl peptidase IV (DPP-IV) and the utility of DPP-IV inhibitors are also under investigation. There is a recent upsurge in the development of GLP-1 mimetics and DPP-IV inhibitors as potential therapy for type 2 diabetes. However, both the strategies are having their own advantages and limitations. The present review summarizes the concepts of GLP-1 based therapy for type 2 diabetes and the current preclinical and clinical development in GLP-1 mimetics and DPP-IV inhibitors. Further, the potential advantages and the limitations of both the strategies are discussed.

Keratinocyte growth factor and beta-cell differentiation in human fetal pancreatic endocrine precursor cells.

AIMS AND HYPOTHESIS: Keratinocyte growth factor (KGF) is a member of the heparin-binding fibroblast growth factor family with a high degree of specificity for epithelial cells in vitro and in vivo. Our aim was to study the effect of KGF on beta-cell growth and differentiation on islet-like cell clusters derived from human fetal pancreas. METHODS: We investigated the effects of KGF, in vitro, on beta-cell differentiation from undifferentiated pancreatic precursor cells and in vivo after transplantating human fetal pancreatic cells into athymic rats treated with KGF. RESULTS: Treatment of islet-like cell clusters with KGF in vitro did not change the number of insulin producing cells, as measured by the measurement of insulin content or DNA. The in vivo treatment of recipient rats with KGF increased the number of beta cells within the grafts 8 weeks after transplantation. At this time, glucose-stimulated insulin secretion was evaluated by glucose stimulation tests in rats bearing the transplants. Measurements of human C-peptide concentrations after glucose challenge showed that the newly differentiated beta cells in the KGF-treated group were functionally competent as opposed to the control group, where the graft failed to release insulin appropriately. CONCLUSION/INTERPRETATION: These findings suggest that in vivo, KGF is capable of inducing human fetal beta-cell expansion. The growth promoting effect of KGF on beta cells occurred mainly through the activation of ductal cell proliferation and their subsequent differentiation into beta cells.

Impaired beta-cell regeneration after partial pancreatectomy in the adult Goto-Kakizaki rat, a spontaneous model of type II diabetes.

In the Goto-Kakizaki (GK) rat, a genetic model of type II diabetes, there is a restriction of the beta-cell mass as early as fetal age, which is maintained reduced in the adult animal. In order to investigate the beta-cell growth potential in the adult hyperglycemic GK rat, and to determine whether it differs from non-diabetic Wistar (W) rats, we have performed 90% pancreatectomy (Px) in 8- to 10-week-old male animals. Spontaneous beta-cell regeneration and involvement of beta-cell replication, beta-cell neodifferentiation from ductal precursor, and beta-cell apoptosis were evaluated by immunocytochemistry and morphometry at different time points: day 0 (D0), D2, D7, and D14 after Px. In GK rats, deterioration of the diabetic state with severe and chronic hyperglycemia was evident as soon as D2, while in W/Px, normoglycemia to moderate hyperglycemia was observed. In W/Px rats, the total beta-cell mass gradually increased on D2, D7, and D14, as compared to non-Px W rats. By contrast, in GK/Px rats, there was only a non-significant tendency to increased total beta-cell mass, as compared to related non-Px group. Adult GK rats displayed lower beta-cell proliferation rates compared to W. In response to Px, early increase of beta-cell proliferation was present in both W/Px and GK/Px rats on D2, but it returned to non-Px values in GK rats on D7 and D14, while in W/Px rats beta-cell proliferation was maintained increased as compared to non-Px W rats. The very low apoptotic beta-cell frequency on D0, D2, D7, and D14, in both W and GK, either non-Px or Px, did not allow us to conclude that any significant differences exist between the different groups. beta-cell neoformation from ducts, and more specifically from foci of regeneration, was found to be less activated in GK/Px rats as compared to W/Px. Together, these results suggest that in the adult hyperglycemic GK rat undergoing Px, beta-cells still have the capacity to regenerate, but with a lower efficiency as compared to non-diabetic W rats. This defect in the GK rat is the result of both genetic predisposition contributing to an altered beta-cell neogenesis potential already present in the neonatal period, and environmental factors (chronic hyperglycemia) leading to a reduced beta-cell proliferative capacity specific to the adult animals.

Impaired pancreatic duct-cell growth in focal areas of regeneration after partial pancreatectomy in the adult Goto-Kakizaki rat, a spontaneous model of non-insulin dependent diabetes mellitus.

The Paris colony of adult Goto-Kakizaki (GK/Par) rat, a genetic model of non-insulin dependent diabetes mellitus, is characterized by a restriction of the beta-cell mass and reduced beta-cell regeneration capacity. In order to have a better understanding of the impaired mechanism(s) leading to reduced beta-cell plasticity in the GK/Par rat, we have investigated duct-cell growth capacity following 90% pancreatectomy, a well-defined procedure leading in non-diabetic rats, to sequential duct proliferation and subsequent differentiation. To this aim, we have performed pancreatectomy in 8-10-week-old male normoglycaemic Wistar and diabetic GK rats. Duct-cell proliferation and apoptosis were evaluated at different time points: day 0 (D0), day 2 (D2), day 7 (D7) and day 14 (D14) after pancreatectomy. A transient wave of duct-cell proliferation was observed on D2 in both small and main ducts in the pancreatectomized Wistar rats. A similar increase occurred in the similarly treated GK rats, but to a higher extent as compared to the Wistar rats. Thereafter, duct-cell proliferation from main or small ducts returned to non-pancreatectomized values on D7 and remained at this level on D14 in both the Wistar and GK pancreatectomized groups. In the common pancreatic duct, the number of proliferative duct-cells was higher in GK rats compared to Wistar on D0. In both the operated Wistar and GK rats, duct-cell proliferation from the common pancreatic duct similarly decreased on D2. On D7 and D14, the same parameter returned to non-pancreatectomized values in the Wistar rats, while it was maintained lower in the GK rats as compared to the GK values on D0. In focal areas of regeneration, duct-cell proliferation was significantly lower in the pancreatectomized GK group compared to the age-related Wistar group on D7 (Wistar: 5.85+/-0.98%, GK: 3.02+/-0.69%; p < 0.01) and D14 (Wistar: 3.82+/-0.29%, GK: 2.62+/-0.27%; ns). Only a few apoptotic duct-cells were observed, with no difference between the Wistar and GK groups, and that whatever the time after pancreatectomy and the duct category. Together, these results suggest that in the adult hyperglycaemic GK/Par rat facing pancreatectomy, duct-cell proliferation and apoptosis from the common pancreatic duct, main ducts and small ducts were not impaired compared to the Wistar rat. However, reduced duct-cell proliferation capacity in focal areas of regeneration in the treated GK rats probably contributes to the lower beta-cell neogenesis potential previously observed in this model.

Glucagon-like peptide-1 and exendin-4 stimulate beta-cell neogenesis in streptozotocin-treated newborn rats resulting in persistently improved glucose homeostasis at adult age.

In neonatal Wistar rats injected with streptozotocin (STZ) at birth (n0-STZ model), a recognized model of beta-cell regeneration, we investigated the capacity of early treatment with glucagon-like peptide 1 (GLP-1) or exendin-4 to promote beta-cell regeneration and thereby improve islet function in the long term, when animals become adults. To this end, n0-STZ rats were submitted to GLP-1 or exendin-4 from postnatal day 2 to day 6 only, and their beta-cell mass and pancreatic functions were tested on day 7 and at 2 months. On day 7, both treatments increased body weight, decreased basal plasma glucose, decreased insulinemia, and increased pancreatic insulin content in n0-STZ rats. At the same age, the beta-cell mass, measured by immunocytochemistry and morphometry methods, was strongly increased in n0-STZ/GLP-1 and n0-STZ/Ex rats compared with n0-STZ rats, representing 51 and 71%, respectively, of the beta-cell mass in Wistar rats, whereas n0-STZ beta-cell mass represented only 21% of the Wistar control value. Despite such early improved beta-cell mass, which is maintained at adult age, the basal and glucose-stimulated insulin secretion (in vivo after intravenous glucose load or in vitro using perfused pancreas) were not improved in the 2-month-old n0-STZ rats previously treated with GLP-1 or exendin-4 compared with untreated n0-STZ rats. However, both treated groups significantly exhibited a decreased basal plasma glucose level and an increased plasma glucose clearance rate compared with the 2-month-old untreated n0-STZ group at adult age. These findings in the n0-STZ model indicate for the first time that GLP-1 or exendin-4 applied during the neonatal diabetic period exert both short- and long-term beneficial effects on beta-cell mass recovery and glucose homeostasis. However, the increase in beta-cell mass, which is still present in the adult n0-STZ rats previously treated, contrasts with the poor beta-cell responsiveness to glucose. Further studies are needed to understand the dissociation between beta-cell regeneration and the lack of improvement in beta-cell function.

Defective glucose-dependent cytosolic Ca2+ handling in islets of GK and nSTZ rat models of type 2 diabetes.

We examined to what extent the abnormal glucose-dependent insulin secretion observed in NIDDM (non-insulin-dependent diabetes mellitus) is related to alterations in the handling of cytosolic Ca2+ of islets of Langerhans. Using two recognized rat models of NIDDM, the GK (Goto-Kakizaki) spontaneous model and the nSTZ (neonatal streptozotocin) induced model, we could detect several common alterations in the glucose-induced [Ca2+]i cytosolic responses. First, the initial reduction of [Ca2+]i following high glucose (16.7 mM) observed routinely in islets obtained from non-diabetic Wistar rats could not be detected in GK and nSTZ islets. Second, a delayed response for glucose to induce a subsequent 3% increase of [Ca2+]i over basal level was observed in both GK (321+/-40 s, n=11) and nSTZ (326+/-38 s, n=13) islets as compared with Wistar islets (198+/-20 s, n=11), values representing means+/-s.e.m. Third, the rate of increase in [Ca2+]i in response to a high glucose challenge was 25% and 40% lower in GK and nSTZ respectively, as compared with Wistar islets. Fourth, the maximal [Ca2+](i) level reached after 10 min of perifusion with 16.7 mM glucose was lower with GK and nSTZ islets and represented respectively 60% and 90% of that of Wistar islets. Further, thapsigargin, a blocker of Ca2+/ATPases (SERCA), abolished the initial reduction in [Ca2+]i observed in response to high glucose and induced fast [Ca2+]i oscillations with high amplitude in Wistar islets. The latter effect was not seen in GK and nSTZ islets. In these two NIDDM models, several common alterations in glucose-induced Ca2+ handling were revealed which may contribute to their poor glucose-induced insulin secretion.

Early development of beta-cells is impaired in the GK rat model of type 2 diabetes.

The Goto-Kakisaki (GK) rat is a genetic model of type 2 diabetes obtained by selective inbreeding of mildly glucose-intolerant Wistar rats. Previous studies have shown that at birth, the beta-cell mass of the GK rat is severely reduced compared with that of the Wistar rat. Therefore, beta-cell deficit could be the primary defect leading to type 2 diabetes in this model. To identify the abnormality at the origin of the beta-cell mass deficit, we compared the fetal development of GK and Wistar rats. Our study reveals that during early development (embryonic day 12-14 [E12-14]), GK fetuses present a delayed global growth that progressively recovers: at birth, no size or weight difference persists. However, from E18 onward, the weight and DNA content of the pancreas and liver are reduced by 30% in the GK fetuses. Cell proliferation is reduced in the GK pancreas from E16 to E20. Whereas apoptotic cells are scarce in the Wistar fetal pancreas, a wave of apoptosis from E16 to E18 was detected in the GK pancreas. Analysis of pancreas differentiation revealed that from E12 to E14, there are no significant differences in the number of alpha- and beta-cells between the GK and Wistar pancreas. However, by E16, the average number of beta-cells in the GK pancreas represents only 50% that of the Wistar pancreas, and this difference persists until birth. The number of alpha-cells was reduced by 25% from E18 to E21. To determine whether the defect in GK pancreas development depends on intrinsic pancreatic factors or on endocrine extrapancreatic factors, we performed in vitro cultures of E12 pancreatic rudiments. The cultures show that in vitro, the growth and endocrine differentiation of the GK and Wistar pancreatic rudiments are identical. Thus, impaired development of the GK pancreas probably results from insufficiency of extrapancreatic factor(s) necessary for the growth and survival of fetal pancreatic cells.

beta-cell function and viability in the spontaneously diabetic GK rat: information from the GK/Par colony.

The GK rat model of type 2 diabetes is especially convenient to dissect the pathogenic mechanism necessary for the emergence of overt diabetes because all adult rats obtained in our department (GK/Par colony) to date have stable basal mild hyperglycemia and because overt diabetes is preceded by a period of normoglycemia, ranging from birth to weaning. The purpose of this article is to sum up the information so far available related to the biology of the beta-cell in the GK/Par rat. In terms of beta-cell function, there is no major intrinsic secretory defect in the prediabetic GK/Par beta-cell, and the lack of beta-cell reactivity to glucose (which reflects multiple intracellular abnormalities), as seen during the adult period when the GK/Par rats are overtly diabetic, represents an acquired defect (perhaps glucotoxicity). In terms of beta-cell population, the earliest alteration so far detected in the GK/Par rat targets the size of the beta-cell population. Several convergent data suggest that the permanently reduced beta-cell mass in the GK/Par rat reflects a limitation of beta-cell neogenesis during early fetal life, and it is conceivable that some genes among the set involved in GK diabetes belong to the subset of genes controlling early beta-cell development.

Effect of early dietary restriction on insulin action and secretion in the GK rat, a spontaneous model of NIDDM.

The availability of the Goto-Kakisaki (GK) rat model of non-insulin-dependent diabetes mellitus prompted us to test the effect of a limited period of undernutrition in previously diabetic young rats on their insulin secretion and insulin action during adult age. Four-week-old female GK rats were either food restricted (35% restriction, 15% protein diet) or protein and energy restricted (35% restriction, 5% protein diet) for 4 wk. Food restriction in the young GK rat lowered weight gain but did not aggravate basal hyperglycemia or glucose intolerance, despite a decrease in basal plasma insulin level. Furthermore, the insulin-mediated glucose uptake by peripheral tissues in the GK rat was clearly improved. We also found that food restriction, when it is coupled to overt protein deficiency in the young GK rat, altered weight gain more severely and slightly decreased basal hyperglycemia but conversely aggravated glucose tolerance. Improvement of basal hyperglycemia was related to repression of basal hepatic glucose hyperproduction, despite profound attenuation of basal plasma insulin level. Deterioration of tolerance to glucose was related to severe blunting of the residual glucose-induced insulin secretion. It is, however, likely that the important enhancement of the insulin-mediated glucose uptake helped to limit the deterioration of glucose tolerance.

Glucose-induced insulin mRNA accumulation is impaired in islets from neonatal streptozotocin-treated rats.

According to the glucose toxicity hypothesis, hyperglycemia contributes to defective beta-cell function in type 2, non-insulin-dependent diabetes mellitus. This concept is supported by substantial data in rodent models of diabetes. However, the ability of glucose to stimulate the accumulation of insulin mRNA, a critical feature of normal beta-cell physiology, has not been investigated in in vivo models of chronic hyperglycemia. The aim of this study was to determine whether glucose-induced insulin mRNA accumulation is impaired in the neonatal streptozotocin-treated rat (n0-STZ rat), a model of non-obese, non-insulin-dependent diabetes mellitus. Islets of Langerhans isolated from n0-STZ and control rats were cultured for 24 h in the presence of 2.8 or 16.7 mmol/L glucose, and insulin mRNA levels were measured by Northern analysis. Insulin mRNA levels were increased more than twofold by glucose in control islets. In contrast, no significant effect of glucose was found on insulin mRNA levels in n0-STZ islets. We conclude that insulin gene regulation by glucose is impaired in n0-STZ rat islets.

Glucose-induced insulin mRNA accumulation is impaired in islets from neonatal streptozotocin-treated rats.

According to the "glucose toxicity" hypothesis, hyperglycemia contributes to defective beta-cell function in type 2, non-insulin-dependent diabetes mellitus. This concept is supported by substantial data in rodent models of diabetes. However, the ability of glucose to stimulate the accumulation of insulin mRNA, a critical feature of normal beta-cell physiology, has not been investigated in in vivo models with chronic hyperglycemia. The aim of this study was to determine whether glucose-induced insulin mRNA accumulation is impaired in the neonatal streptozotocin-treated rat (n0-STZ rat), a model of non-obese, non-insulin-dependent diabetes mellitus. Islets of Langerhans isolated from n0-STZ and control rats were cultured for 24 h in the presence of 2.8 or 16.7 mmol/l glucose, and insulin mRNA levels were measured by Northern analysis. Insulin mRNA levels were increased more than twofold by glucose in control islets. In contrast, no significant effect of glucose was found on insulin mRNA levels in n0-STZ islets. We conclude that insulin gene regulation by glucose is impaired in n0-STZ rat islets.