Insulin is a key regulator of adipose tissue lipolysis, and impaired adipose tissue insulin action results in unrestrained lipolysis and lipotoxicity, which are hallmarks of the metabolic syndrome and diabetes. Insulin regulates adipose tissue metabolism through direct effects on adipocytes and through signaling in the central nervous system by dampening sympathetic outflow to the adipose tissue. Here we examined the role of insulin signaling in agouti-related protein (AgRP) and pro-opiomelanocortin (POMC) neurons in regulating hepatic and adipose tissue insulin action. Mice lacking the insulin receptor in AgRP neurons (AgRP IR KO) exhibited impaired hepatic insulin action because the ability of insulin to suppress hepatic glucose production (hGP) was reduced, but the ability of insulin to suppress lipolysis was unaltered. To the contrary, in POMC IR KO mice, insulin lowered hGP but failed to suppress adipose tissue lipolysis. High-fat diet equally worsened glucose tolerance in AgRP and POMC IR KO mice and their respective controls but increased hepatic triglyceride levels only in POMC IR KO mice, consistent with impaired lipolytic regulation resulting in fatty liver. These data suggest that although insulin signaling in AgRP neurons is important in regulating glucose metabolism, insulin signaling in POMC neurons controls adipose tissue lipolysis and prevents high-fat diet–induced hepatic steatosis.
Introduction Epidemiologic studies have demonstrated an association between diabetes and dementia. Insulin signaling within the brain, in particular within the hypothalamus regulates carbohydrate, lipid, and branched chain amino acid (BCAA) metabolism in peripheral organs such as the liver and adipose tissue. We hypothesized that cerebral amyloidosis impairs central nervous system control of metabolism through disruption of insulin signaling in the hypothalamus, which dysregulates glucose and BCAA homeostasis resulting in increased susceptibility to diabetes. Methods We examined whether APP/PS1 mice exhibit increased susceptibility to aging or high-fat diet (HFD)-induced metabolic impairment using metabolic phenotyping and insulin-signaling studies. Results APP/PS1 mice were more susceptible to high-fat feeding and aging-induced metabolic dysregulation including disrupted BCAA homeostasis and exhibited impaired hypothalamic insulin signaling. Discussion Our data suggest that AD pathology increases susceptibility to diabetes due to impaired hypothalamic insulin signaling, and that plasma BCAA levels could serve as a biomarker of hypothalamic insulin action in patients with AD.
Objective Obese women experience worse reproductive outcomes compared to normal weight women, specifically infertility, pregnancy loss, fetal malformations and developmental delay. The objective of this study was to use a genetic mouse model of obesity in order to recapitulate the human reproductive phenotype and further examine potential mechanisms and therapies. Methods New inbred, polygenic Type 2 diabetic TallyHO mice and age matched control C57BL/6 mice were superovulated to obtain morulae or blastocysts stage embryos which were cultured in human tubal fluid media. Deoxyglucose uptake was performed on insulin-stimulated individual blastocysts. Apoptosis was detected by confocal microscopy using TUNEL assay and Topro-3 nuclear dye. Embryos were scored for %TUNEL positive/total nuclei. AMPK activation, TNFα expression, and adiponectin expression were analyzed by western immunoblot and confocal immunofluorescent microscopy. Lipid accumulation was assayed by Bodipy. Finally all measured parameters were compared between TallyHO mice in morulaes cultured to blastocyst embryos in either human tubal fluid (HTF) media or HTF with 25ug/ml metformin added. Results TallyHo mice developed whole body abnormal insulin tolerance, decreased litter number and increased NEFA. Blastocysts demonstrated increased apoptosis, decreased insulin sensitivity, and decreased activation of AMP activated protein-kinase (AMPK). As a possible cause of the insulin resistance/abnormal P-AMPK, we found that Tumor necrosis Factor (TNFα) expression and lipid accumulation as detected by BODIPY were increased in TallyHO blastocysts and adiponectin was decreased. Culturing TallyHO morulae with the AMPK activator, metformin lead to a reversal of all abnormal findings, including increased p-AMPK, improved insulin-stimulated glucose uptake and normalization of lipid accumulation. Conclusions Women with obesity and insulin resistance experience poor pregnancy outcomes. Previously we have shown in mouse models of insulin resistance that AMPK activity is decreased and that activators of AMPK reverse the poor embryo outcomes. Here, we show for the first time using a genetically altered obese model, not a diet-induced model, that metformin reverses many of the adverse effects of obesity at the level of the blastocyst. Expanding on this we determine that activation of AMPK via metformin reduces lipid droplet accumulation, presumably by eliminating the inhibitory effects of TNFα, resulting in normalization of fatty acid oxidation and HADH2 activity. Metformin exposure in vitro was able to partially reversing these effects, at the level of the blastocyst and thus may be effective in preventing the adverse effects of obesity on pregnancy and reproductive outcomes.
Table of tables EVALUATION OF RESULTS…………………………………………………………23 vi Acknowledgments This thesis project would not have been possible without the support of many people. We would like to express our gratitude to our thesis adviser, Stacy Frauwirth who has been abundantly helpful and offered invaluable assistance, support and guidance. Deepest gratitude are also due to the members of Marin Autism Collaborative, Karen Kaplan and Meg Cadiz, without whose knowledge and assistance this study would not have been successful. We would also like to convey thanks to Rocio de Smith for providing assistance with translating the fotonovela and helping us overcome recruitment challenges.
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