Jamileh Movassat

Early-Life Origins of Type 2 Diabetes: Fetal Programming of the Beta-Cell Mass

A substantial body of evidence suggests that an abnormal intrauterine milieu elicited by maternal metabolic disturbances as diverse as undernutrition, placental insufficiency, diabetes or obesity, may program susceptibility in the fetus to later develop chronic degenerative diseases, such as obesity, hypertension, cardiovascular diseases and diabetes. This paper examines the developmental programming of glucose intolerance/diabetes by disturbed intrauterine metabolic condition experimentally obtained in various rodent models of maternal protein restriction, caloric restriction, overnutrition or diabetes, with a focus on the alteration of the developing beta-cell mass. In most of the cases, whatever the type of initial maternal metabolic stress, the beta-cell adaptive growth which normally occurs during gestation, does not take place in the pregnant offspring and this results in the development of gestational diabetes. Therefore gestational diabetes turns to be the ultimate insult targeting the offspring beta-cell mass and propagates diabetes risk to the next generation again. The aetiology and the transmission of spontaneous diabetes as encountered in the GK/Par rat model of type 2 diabetes, are discussed in such a perspective. This review also discusses the non-genomic mechanisms involved in the installation of the programmed effect as well as in its intergenerational transmission.

Insulin administration enhances growth of the β-cell mass in streptozotocin-treated newborn rats

We have previously reported that the damage caused by streptozotocin (STZ) administration to the β-cells in newborn rats was followed by spontaneous recovery from neonatal diabetes. Our present data indicate that STZ administration on the day of birth (day 1) reduced the total β-cell mass on day 4 to only 10% of the normal value and that after sucb damage, 27% of the corresponding normal β-cell mass was spontaneously regained on day 7. During days 4–7, the contribution of the predicted β-cell growth (due to the replication of preexisting differentiated β-cells) to the total β-cell growth represented only 56%. Therefore, recruitment of new β-cells from a precursor pool indeed represents a significant mechanism for β-cell regeneration after STZ during this period of life. Here, we report for the first time that 1) insulin therapy from days 2 to 4 did not significantly influence the occurrence of β-cell damage after STZ administration (total β-cell mass on day 4 was reduced to 12% of the normal value) and 2) insulin therapy from days 2 to 6 did improve the otherwise spontaneous β-cell regeneration, since on day 7 total β-cell mass was 44% of the corresponding normal β-cell mass. During days 4-7, the contribution of the predicted β-cell growth to the total β-cell growth represented only 32% in the insulin-treated STZ group. Finally the insulin-favored regeneration of the β-cells reflects both an increased replication from differentiated β-cells and an increased neogenesis from precursor/stem cells, with this last pathway being preferentially activated.

Activation of the GLP-1 Receptor Signalling Pathway: A Relevant Strategy to Repair a Deficient Beta-Cell Mass

Recent preclinical studies in rodent models of diabetes suggest that exogenous GLP-1R agonists and DPP-4 inhibitors have the ability to increase islet mass and preserve beta-cell function, by immediate reactivation of beta-cell glucose competence, as well as enhanced beta-cell proliferation and neogenesis and promotion of beta-cell survival. These effects have tremendous implication in the treatment of T2D because they directly address one of the basic defects in T2D, that is, beta-cell failure. In human diabetes, however, evidence that the GLP-1-based drugs alter the course of beta-cell function remains to be found. Several questions surrounding the risks and benefits of GLP-1-based therapy for the diabetic beta-cell mass are discussed in this review and require further investigation.

Mechanisms of KGF Mediated Signaling in Pancreatic Duct Cell Proliferation and Differentiation

Background Keratinocyte growth factor (KGF; palifermin) is a growth factor with a high degree of specificity for epithelial cells. KGF is an important effector of epithelial growth and tissue homeostasis in various organs including the pancreas. Here we investigated the intracellular signaling pathways involved in the mediation of pancreatic ductal cell proliferation and differentiation induced by exogenous KGF during beta-cell regeneration in diabetic rat. Methodology and Results In vitro and in vivo duct cell proliferation was measured by BrdU incorporation assay. The implication of MAPK-ERK1/2 in the mediation of KGF-induced cell proliferation was determined by inactivation of this pathway, using the pharmacological inhibitor or antisense morpholino-oligonucleotides against MEK1. In vivo KGF-induced duct cell differentiation was assessed by the immunolocalization of PDX1 and Glut2 in ductal cells and the implication of PI3K/AKT in this process was investigated. We showed that KGF exerted a potent mitogenic effect on ductal cells. Both in vitro and in vivo, its effect on cell proliferation was mediated through the activation of ERK1/2 as evidenced by the abolition of duct cell proliferation in the context of MEK/ERK inactivation. In vivo, KGF treatment triggered ductal cell differentiation as revealed by the expression of PDX1 and Glut2 in a subpopulation of ductal cells via a PI3K-dependent mechanism. Conclusion Here we show that KGF promotes beta-cell regeneration by stimulating duct cell proliferation in vivo. Moreover, we demonstrated for the first time that KGF directly induces the expression of PDX1 in some ductal cells thus inducing beta-cell neogenesis. We further explored the molecular mechanisms involved in these processes and showed that the effects of KGF on duct cell proliferation are mediated by the MEK-ERK1/2 pathway, while the KGF-induced cell differentiation is mediated by the PI3K/AKT pathway. These findings might have important implications for the in vivo induction of duct-to-beta cell neogenesis in patients with beta-cell deficiency.

Neonatal growth and regeneration of β-cells are regulated by the Wnt/β-catenin signaling in normal and diabetic rats

Wnt/beta-catenin signaling is critical for a variety of fundamental cellular processes. Here, we investigated the implication of the Wnt/beta-catenin signaling in the in vivo regulation of beta-cell growth and regeneration in normal and diabetic rats. To this aim, TCF7L2, the distal effector of the canonical Wnt pathway, was knocked down in groups of normal and diabetic rats by the use of specific antisense morpholino-oligonucleotides. In other groups of diabetic rats, the Wnt/beta-catenin pathway was activated by the inhibition of its negative regulator GSK-3beta. GSK-3beta was inactivated by either LiCl or anti-GSK-3beta oligonucleotides. The beta-cell mass was evaluated by morphometry. beta-cell proliferation was assessed in vivo and in vitro by BrdU incorporation method. In vivo beta-cell neogenesis was estimated by the evaluation of PDX1-positive ductal cells and GLUT2-positive ductal cells and the number of beta cells budding from the ducts. We showed that the in vivo disruption of the canonical Wnt pathway resulted in the alteration of normal and compensatory growth of beta-cells mainly through the inhibition of beta-cell proliferation. Conversely, activation of the Wnt pathway through the inhibition of GSK-3beta had a significant stimulatory effect on beta-cell regeneration in diabetic rats. In vitro, GSK-3beta inactivation resulted in the stimulation of beta-cell proliferation. This was mediated by the stabilization of beta-catenin and the induction of cyclin D. Taken together, our results demonstrate the involvement of the canonical Wnt signaling in the neonatal regulation of normal and regenerative growth of pancreatic beta-cells. Moreover, we provide evidence that activation of this pathway by pharmacological maneuvers can efficiently improve beta-cell regeneration in diabetic rats. These findings might have potential clinical applications in the regenerative therapy of diabetes.

Interleukin-7 Regulates Adipose Tissue Mass and Insulin Sensitivity in High-Fat Diet-Fed Mice through Lymphocyte-Dependent and Independent Mechanisms

Although interleukin (IL)-7 is mostly known as a key regulator of lymphocyte homeostasis, we recently demonstrated that it also contributes to body weight regulation through a hypothalamic control. Previous studies have shown that IL-7 is produced by the human obese white adipose tissue (WAT) yet its potential role on WAT development and function in obesity remains unknown. Here, we first show that transgenic mice overexpressing IL-7 have reduced adipose tissue mass associated with glucose and insulin resistance. Moreover, in the high-fat diet (HFD)-induced obesity model, a single administration of IL-7 to C57BL/6 mice is sufficient to prevent HFD-induced WAT mass increase and glucose intolerance. This metabolic protective effect is accompanied by a significant decreased inflammation in WAT. In lymphocyte-deficient HFD-fed SCID mice, IL-7 injection still protects from WAT mass gain. However, IL-7-triggered resistance against WAT inflammation and glucose intolerance is lost in SCID mice. These results suggest that IL-7 regulates adipose tissue mass through a lymphocyte-independent mechanism while its protective role on glucose homeostasis would be relayed by immune cells that participate to WAT inflammation. Our observations establish a key role for IL-7 in the complex mechanisms by which immune mediators modulate metabolic functions.

Procyanidins modulate microRNA expression in pancreatic islets.

Procyanidins modulate glucose metabolism, partly due to its effects on pancreas. Given the role of microRNAs (miRNAs) in the regulation of diabetes and the fact that flavonoids modulate miRNAs in other tissues, we hypothesized that procyanidins might target miRNAs in the pancreas. We investigated the miRNA expression profile in pancreatic islets isolated from rats treated with a daily dose of grape seed procyanidin extract (GSPE) (25 mg/kg of body weight) for 45 days. The miRWalk database identified putative target genes of these miRNAs. We found that GSPE altered significantly the expression of miR-1249, miR-483, miR-30c-1*, and miR-3544. In silico prediction studies suggested that ion transport and response to glucose are among the regulated pathways. As a conclusion, this is the first study showing that procyanidins can also exert their bioactivity on pancreatic islets by modifying the miRNA expression pattern.

Diabetic GK/Par rat β-cells are spontaneously protected against H2O2-triggered apoptosis. A cAMP-dependent adaptive response

The alteration of the beta-cell population in the Goto-Kakizaki rat (GK/Par line), a model of spontaneous type 2 diabetes, has been ascribed to significantly decreased beta-cell replication and neogenesis, while beta-cell apoptosis is surprisingly not enhanced and remains in the normal range. To gain insight into the mechanisms by which those beta-cells are protected from death, we studied ex vivo the apoptotic activity and the expression of a large set of pro/antiapoptotic and pro/antioxidant genes in GK/Par islet cells. This was done in vitro in freshly isolated islets as well as in response to culture conditions and calibrated reactive oxygen species (ROS) exposure (i.e., H2O2). We also investigated the intracellular mechanisms of the diabetic beta-cell response to ROS, the role if any of the intracellular cAMP metabolism, and finally the kinetic of ROS response, taking advantage of the GK/Par rat normoglycemia until weaning. Our results show that the peculiar GK/Par beta-cell phenotype was correlated with an increased expression of a large panel of antioxidant genes as well as pro/antiapoptotic genes. We demonstrate that such combination confers resistance to cytotoxic H2O2 exposure in vitro, raising the possibility that at least some of the activated stress/defense genes have protective effects against H2O2-triggered beta-cell death. We also present some evidence that the GK/Par beta-cell resistance to H2O2 is at least partly cAMP dependent. Finally, we show that such a phenotype is not innate but is spontaneously acquired after diabetes onset as the result of an adaptive response to the diabetic environment.

Impact and Mechanisms of Pancreatic Beta-Cell Mass Programming by Maternal Diabetes - Insight from Animal Model Studies

The incidence of type 2 diabetes mellitus (T2D) is growing worldwide. It is now established that interactions between the individual genetic makeup and environment contribute to the development of T2D. In this review, we first discuss the evidence for beta-cell dysfunction in IUED (in utero exposure to maternal diabetes), IUEO (in utero exposure to maternal overnutrition) and IUGR (in utero growth restriction) humans. We then evaluate relevant animal models of IUED, IUEO and IUGR focusing on the strengths and limits of each, in order to define critical periods and types of alterations that can lead to impaired beta-cell function. Finally, we discuss several potential mechanisms dissected in relevant animal models that begin to explain these outcomes.

0061 : Exercice training impaired energy metabolism and function of the type 2 diabetic Goto-Kakizaki (GK) rat heart during ischaemiareperfusion injury

Background Informations about the effects of exercice training on diabetesinduced myocardial dysfunctions are lacking. Consequently, we investigated the effect of exercice training on the sensitivity of the type 2 diabetic Goto-Kakizaki (GK) rat heart to ischaemia-reperfusion injury by using a multiparametric approach combining 31P magnetic resonance spectroscopy (MRS) with simultaneous measurement of contractile function and biochemical assays. Materials and Methods 8-month-old male GK rat (n=11, trained GK) rats ran 60 min on a treadmill 5 days/week at a speed of 20 m/min for 7 weeks and compared with age-matched male Control (n=6) and untrained GK (n=11) rats. Then, isolated rat hearts were perfused with a physiological buffer containing 0.4 mM palmitate, for 24 min before switching to 1.2mM palmitate during 32min low-flow (0.5 ml/min-1.g wet wt-1) ischaemia. Next, flow was restored with 0.4 mM palmitate buffer for 32 minutes. High energy compounds and intracellular pH were followed using 31P MRS with simultaneous measurement of contractile function. Total adenine nucleotides (TAN) and energy charge (EC) were determined in freeze-clamped tissues by H.P.L.C. Results Heart to body weight ratios were significantly higher in both untrained and trained diabetic groups (p Conclusion The intensity of exercice training exacerbed the sensitivity of the type 2 diabetic 8-month-old Goto-Kakizaki rat to myocardial ischaemiareperfusion by impairing energy metabolism and myocardial performance. Other exercice protocols and/or therapeutic approaches need to be explored to limit myocardial ischaemia-reperfusion injury in type 2 diabetes.