The purpose of these studies was to investigate the impact of high-fat diet (HFD) exposure during pregnancy and the early post-natal period on fetal and post-natal development of the endocrine pancreas of the Japanese macaque. Specifically I hypothesized that the HFD would alter islet morphology and lead to disturbances in glucose homeostasis in these animals. Adult female Japanese macaques were placed on either a control (CTR) or HFD diet for 4 years. Fetuses were collected at gestational day 130 (G130), while other offspring from the CTR and HFD mothers were carried to term. After birth, infant animals were maintained with their mothers on the same diet then weaned onto either the CTR or HFD diet for five months. Animals were studied up to 13 months of age, yielding 4 postnatal groups: CTR/CTR, CTR/HFD, HFD/CTR and HFD/HFD. Pancreata were collected from these offspring for gene expression and immunohistochemical analysis. Physiological measurements, including body weight, body fat percentage, fasting glucose, insulin, glucagon and response to intravenous glucose tolerance tests (IVGTTs) and an intravenous insulin tolerance test (IVITT) were collected from the post-natal offspring. Total fetal islet mass and β cell mass were not changed, but α cell mass was significantly decreased in HFD fetuses, leading to a significant increase in the β cell to α cell ratio in HFD fetal offspring. The HFD offspring displayed a significant change from CTR offspring in expression of genes involved in glucose homeostasis and islet neogenesis, including PDX1, NeuroD, Glucokinase and Glut2. Postnatal HFD animals were significantly heavier than CTR offspring and had increased adiposity by 6-7 months of age. There was no significant effect on fasting or stimulated insulin secretion at this time point, but HFD offspring were significantly insulin resistant just prior to weaning. At 13 months of age, basal and glucose-stimulated insulin secretion were elevated in HFD/HFD animals and the CTR/HFD group displayed moderate insulin resistance. There was also a significant sex effect, with males from the HFD/CTR and HFD/HFD group having increased body weight and elevated fasting glucose. Although pancreata from both the HFD/HFD and CTR/HFD animals displayed significant changes in expression of genes involved in glucose homeostasis, the pattern was distinct for the two groups. Islet mass was also elevated in both of these groups; yet, HFD/HFD only displayed an increase in β cell area, while CTR/HFD had a concomitant increase in α cell area, which served to normalize the β cell to α cell ratio to control levels. In contrast, the HFD/HFD group exhibited a 40% increase in the β cell to α cell ratio. These studies demonstrate that in-utero exposure to a HFD leads to decreased α cell plasticity in response to chronic post-natal HFD consumption. Animals exposed to the HFD during pregnancy and the early post-natal period become insulin resistant, but remain normoglycemic. HFD consumption during the post-weaning period causes similar complications in glucose homeostasis and islet mass in both the CTR/HFD and HFD/HFD animals. However, there are distinct differences in the molecular and cellular adaptive response between these two groups.

Indiana University-Purdue University Indianapolis (IUPUI) / The islet beta cell is unique in its ability to synthesize and secrete insulin for use in the body. A number of factors including proinflammatory cytokines, free fatty acids, and islet amyloid are known to cause beta cell stress. These factors lead to lipotoxic, inflammatory, and ER stress in the beta cell, contributing to beta cell dysfunction and death, and diabetes. While transcriptional responses to beta cell stress are well appreciated, relatively little is known regarding translational responses in the stressed beta cell. To study translation, I established conditions in vitro with MIN6 cells and mouse islets that mimicked UPR conditions seen in diabetes. Cell extracts were then subjected to polyribosome profiling to monitor changes to mRNA occupancy by ribosomes. Chronic exposure of beta cells to proinflammatory cytokines (IL-1 beta, TNF-alpha, IFN-gamma), or to the saturated free fatty acid palmitate, led to changes in global beta cell translation consistent with attenuation of translation initiation, which is a hallmark of ER stress. In addition to changes in global translation, I observed transcript specific regulation of ribosomal occupancy in beta cells. Similar to other privileged mRNAs (Atf4, Chop), Pdx1 mRNA remained partitioned in actively translating polyribosomes during the UPR, whereas the mRNA encoding a proinsulin processing enzyme (Cpe) partitioned into inactively translating monoribosomes. Bicistronic luciferase reporter analyses revealed that the distal portion of the 5’ untranslated region of mouse Pdx1 (between bp –105 to –280) contained elements that promoted translation under both normal and UPR conditions. In contrast to regulation of translation initiation, deoxyhypusine synthase (DHS) and eukaryotic translation initiation factor 5A (eIF5A) are required for efficient translation elongation of specific stress relevant messages in the beta cell including Nos2. Further, p38 signaling appears to promote translational elongation via DHS in the islet beta cell. Together, these data represent new insights into stress induced translational regulation in the beta cell. Mechanisms of differential mRNA translation in response to beta cell stress may play a key role in maintenance of islet beta cell function in the setting of diabetes.