Metabolism
Abstract
Transient neonatal diabetes mellitus (TNDM) is a rare inherited diabetic syndrome apparent in the first weeks of life and again during early adulthood. The relative contributions of reduced islet β cell number and impaired β cell function to the observed hypoinsulinemia are unclear. The inheritance pattern of this imprinted disorder implicates overexpression of one or both genes within the TNDM locus: ZAC, which encodes a proapoptotic zinc finger protein, and HYMAI, which encodes an untranslated mRNA. To investigate the consequences for pancreatic function, we have developed a high-copy transgenic mouse line, TNDM29, carrying the human TNDM locus. TNDM29 neonates display hyperglycemia, and older adults, impaired glucose tolerance. Neonatal hyperglycemia occurs only on paternal transmission, analogous to paternal dependence of TNDM in humans. Embryonic pancreata of TNDM29 mice showed reductions in expression of endocrine differentiation factors and numbers of insulin-staining structures. By contrast, β cell mass was normal or elevated at all postnatal stages, whereas pancreatic insulin content in neonates and peak serum insulin levels after glucose infusion in adults were reduced. Expression of human ZAC and HYMAI in these transgenic mice thus recapitulates key features of TNDM and implicates impaired development of the endocrine pancreas and β cell function in disease pathogenesis.
Authors
Dan Ma, Julian P.H. Shield, Wendy Dean, Isabelle Leclerc, Claude Knauf, Rémy Burcelin, Guy A. Rutter, Gavin Kelsey
Abstract
Regulation of energy balance by leptin involves regulation of several neuropeptides, including thyrotropin-releasing hormone (TRH). Synthesized from a larger inactive precursor, its maturation requires proteolytic cleavage by prohormone convertases 1 and 2 (PC1 and PC2). Since this maturation in response to leptin requires prohormone processing, we hypothesized that leptin might regulate hypothalamic PC1 and PC2 expression, ultimately leading to coordinated processing of prohormones into mature peptides. Using hypothalamic neurons, we found that leptin stimulated PC1 and PC2 mRNA and protein expression and also increased PC1 and PC2 promoter activities in transfected 293T cells. Starvation of rats, leading to low serum leptin levels, decreased PC1 and PC2 gene and protein expression in the paraventricular nucleus (PVN) of the hypothalamus. Exogenous administration of leptin to fasted animals restored PC1 levels in the median eminence (ME) and the PVN to approximately the level found in fed control animals. Consistent with this regulation of PCs in the PVN, concentrations of TRH in the PVN and ME were substantially reduced in the fasted animals relative to the fed animals, and leptin reversed this decrease. Further analysis showed that proteolytic cleavage of pro–thyrotropin-releasing hormone (proTRH) at known PC cleavage sites was reduced by fasting and increased in animals given leptin. Combined, these findings suggest that leptin-dependent stimulation of hypothalamic TRH expression involves both activation of trh transcription and stimulation of PC1 and PC2 expression, which lead to enhanced processing of proTRH into mature TRH.
Authors
Vanesa C. Sanchez, Jorge Goldstein, Ronald C. Stuart, Virginia Hovanesian, Lihong Huo, Heike Munzberg, Theodore C. Friedman, Christian Bjorbaek, Eduardo A. Nillni
Abstract
The role of different tissues in insulin action and their contribution to the pathogenesis of diabetes remain unclear. To examine this question, we have used genetic reconstitution experiments in mice. Genetic ablation of insulin receptors causes early postnatal death from diabetic ketoacidosis. We show that combined restoration of insulin receptor function in brain, liver, and pancreatic β cells rescues insulin receptor knockout mice from neonatal death, prevents diabetes in a majority of animals, and normalizes adipose tissue content, lifespan, and reproductive function. In contrast, mice with insulin receptor expression limited to brain or liver and pancreatic β cells are rescued from neonatal death, but develop lipoatrophic diabetes and die prematurely. These data indicate, surprisingly, that insulin receptor signaling in noncanonical insulin target tissues is sufficient to maintain fuel homeostasis and prevent diabetes.
Authors
Haruka Okamoto, Jun Nakae, Tadahiro Kitamura, Byung-Chul Park, Ioannis Dragatsis, Domenico Accili
Abstract
We investigated the chronic in vivo effect of resistin on insulin sensitivity and glucose metabolism by overexpressing resistin protein in male Wistar rats using intravenous administration of an adenovirus encoding mouse resistin. After 7 days of elevated resistin levels at a supraphysiological concentration, the animals displayed glucose intolerance and hyperinsulinemia during glucose tolerance tests, and insulin tolerance tests demonstrated an impaired glucose-lowering effect of insulin. The glucose clamp studies were performed at submaximal (4 mU/kg/min) and maximal (25 mU/kg/min) insulin infusion rates and demonstrated the presence of insulin resistance induced by elevated resistin levels. Indeed, the insulin-stimulated glucose infusion rate was decreased by 12–31%; suppression of hepatic glucose output was attenuated by 28–55%; and insulin suppression of circulating FFA levels was inhibited by 7%. Insulin receptor substrate–1 and –2 phosphorylation and Akt activation were impaired in muscle and adipose tissue. Interestingly, activation of AMP-activated protein kinase in skeletal muscle, liver, and adipose tissue was also significantly downregulated. Together, these results indicate that chronic “hyper-resistinemia” leads to whole-body insulin resistance involving impaired insulin signaling in skeletal muscle, liver, and adipose tissue, resulting in glucose intolerance, hyperinsulinemia, and hypertriglyceridemia. Thus elevated resistin levels in normal rats fed a regular chow diet produce many of the features of human syndrome X.
Authors
Hiroaki Satoh, M.T. Audrey Nguyen, Philip D.G. Miles, Takeshi Imamura, Isao Usui, Jerrold M. Olefsky
Abstract
Resistin is an adipose-derived hormone postulated to link adiposity to insulin resistance. To determine whether resistin plays a causative role in the development of diet-induced insulin resistance, we lowered circulating resistin levels in mice by use of a specific antisense oligodeoxynucleotide (ASO) directed against resistin mRNA and assessed in vivo insulin action by the insulin-clamp technique. After 3 weeks on a high-fat (HF) diet, mice displayed severe insulin resistance associated with an approximately 80% increase in plasma resistin levels. In particular, the rate of endogenous glucose production (GP) increased more than twofold compared with that in mice fed a standard chow. Treatment with the resistin ASO for 1 week normalized the plasma resistin levels and completely reversed the hepatic insulin resistance. Importantly, in this group of mice, the acute infusion of purified recombinant mouse resistin, designed to acutely elevate the levels of circulating resistin up to those observed in the HF-fed mice, was sufficient to reconstitute hepatic insulin resistance. These results provide strong support for a physiological role of resistin in the development of hepatic insulin resistance in this model.
Authors
Evan D. Muse, Silvana Obici, Sanjay Bhanot, Brett P. Monia, Robert A. McKay, Michael W. Rajala, Philipp E. Scherer, Luciano Rossetti
Abstract
Glycerol, a product of adipose tissue lipolysis, is an important substrate for hepatic glucose synthesis. However, little is known about the regulation of hepatic glycerol metabolism. Here we show that several genes involved in the hepatic metabolism of glycerol, i.e., cytosolic and mitochondrial glycerol 3-phosphate dehydrogenase (GPDH), glycerol kinase, and glycerol transporters aquaporin 3 and 9, are upregulated by fasting in wild-type mice but not in mice lacking PPARα. Furthermore, expression of these genes was induced by the PPARα agonist Wy14643 in wild-type but not PPARα−null mice. In adipocytes, which express high levels of PPARγ, expression of cytosolic GPDH was enhanced by PPARγ and β/δ agonists, while expression was decreased in PPARγ+/– and PPARβ/δ–/– mice. Transactivation, gel shift, and chromatin immunoprecipitation experiments demonstrated that cytosolic GPDH is a direct PPAR target gene. In line with a stimulating role of PPARα in hepatic glycerol utilization, administration of synthetic PPARα agonists in mice and humans decreased plasma glycerol. Finally, hepatic glucose production was decreased in PPARα-null mice simultaneously fasted and exposed to Wy14643, suggesting that the stimulatory effect of PPARα on gluconeogenic gene expression was translated at the functional level. Overall, these data indicate that PPARα directly governs glycerol metabolism in liver, whereas PPARγ regulates glycerol metabolism in adipose tissue.
Authors
David Patsouris, Stéphane Mandard, Peter J. Voshol, Pascal Escher, Nguan Soon Tan, Louis M. Havekes, Wolfgang Koenig, Winfried März, Sherrie Tafuri, Walter Wahli, Michael Müller, Sander Kersten
Abstract
Uncontrolled hepatic glucose production contributes significantly to hyperglycemia in patients with type 2 diabetes. Hyperglucagonemia is implicated in the etiology of this condition; however, effective therapies to block glucagon signaling and thereby regulate glucose metabolism do not exist. To determine the extent to which blocking glucagon action would reverse hyperglycemia, we targeted the glucagon receptor (GCGR) in rodent models of type 2 diabetes using 2′-methoxyethyl–modified phosphorothioate-antisense oligonucleotide (ASO) inhibitors. Treatment with GCGR ASOs decreased GCGR expression, normalized blood glucose, improved glucose tolerance, and preserved insulin secretion. Importantly, in addition to decreasing expression of cAMP-regulated genes in liver and preventing glucagon-mediated hepatic glucose production, GCGR inhibition increased serum concentrations of active glucagon-like peptide-1 (GLP-1) and insulin levels in pancreatic islets. Together, these studies identify a novel mechanism whereby GCGR inhibitors reverse the diabetes phenotype by the dual action of decreasing hepatic glucose production and improving pancreatic β cell function.
Authors
Kyle W. Sloop, Julia Xiao-Chun Cao, Angela M. Siesky, Hong Yan Zhang, Diane M. Bodenmiller, Amy L. Cox, Steven J. Jacobs, Julie S. Moyers, Rebecca A. Owens, Aaron D. Showalter, Martin B. Brenner, Achim Raap, Jesper Gromada, Brian R. Berridge, David K. B. Monteith, Niels Porksen, Robert A. McKay, Brett P. Monia, Sanjay Bhanot, Lynnetta M. Watts, M. Dodson Michael
Abstract
Elevated FFA concentrations have been shown to reproduce some of the metabolic abnormalities of obesity. It has been hypothesized that visceral adipose tissue lipolysis releases excess FFAs into the portal vein, exposing the liver to higher FFA concentrations. We used isotope dilution/hepatic vein catheterization techniques to examine whether intra-abdominal fat contributes a greater portion of hepatic FFA delivery in visceral obesity. Obese women (n = 24) and men (n = 20) with a range of obesity phenotypes, taken together with healthy, lean women (n = 12) and men (n = 12), were studied. Systemic, splanchnic, and leg FFA kinetics were measured. The results showed that plasma FFA concentrations were approximately 20% greater in obese men and obese women. The contribution of splanchnic lipolysis to hepatic FFA delivery ranged from less than 10% to almost 50% and increased as a function of visceral fat in women (r = 0.49, P = 0.002) and in men (r = 0.52, P = 0.002); the slope of the relationship was greater in women than in men (P < 0.05). Leg and splanchnic tissues contributed a greater portion of systemic FFA release in obese men and women than in lean men and women. We conclude that the contribution of visceral adipose tissue lipolysis to hepatic FFA delivery increases with increasing visceral fat in humans and that this effect is greater in women than in men.
Authors
Soren Nielsen, ZengKui Guo, C. Michael Johnson, Donald D. Hensrud, Michael D. Jensen
Abstract
E2F transcription factors are thought to be key regulators of cell growth control. Here we use mutant mouse strains to investigate the function of E2F1 and E2F2 in vivo. E2F1/E2F2 compound-mutant mice develop nonautoimmune insulin-deficient diabetes and exocrine pancreatic dysfunction characterized by endocrine and exocrine cell dysplasia, a reduction in the number and size of acini and islets, and their replacement by ductal structures and adipose tissue. Mutant pancreatic cells exhibit increased rates of DNA replication but also of apoptosis, resulting in severe pancreatic atrophy. The expression of genes involved in DNA replication and cell cycle control was upregulated in the E2F1/E2F2 compound-mutant pancreas, suggesting that their expression is repressed by E2F1/E2F2 activities and that the inappropriate cell cycle found in the mutant pancreas is likely the result of the deregulated expression of these genes. Interestingly, the expression of ductal cell and adipocyte differentiation marker genes was also upregulated, whereas expression of pancreatic cell marker genes were downregulated. These results suggest that E2F1/E2F2 activity negatively controls growth of mature pancreatic cells and is necessary for the maintenance of differentiated pancreatic phenotypes in the adult.
Authors
Ainhoa Iglesias, Matilde Murga, Usua Laresgoiti, Anouchka Skoudy, Irantzu Bernales, Asier Fullaondo, Bernardino Moreno, José Lloreta, Seth J. Field, Francisco X. Real, Ana M. Zubiaga
Abstract
We explored the effects of bile acids on triglyceride (TG) homeostasis using a combination of molecular, cellular, and animal models. Cholic acid (CA) prevents hepatic TG accumulation, VLDL secretion, and elevated serum TG in mouse models of hypertriglyceridemia. At the molecular level, CA decreases hepatic expression of SREBP-1c and its lipogenic target genes. Through the use of mouse mutants for the short heterodimer partner (SHP) and liver X receptor (LXR) α and β, we demonstrate the critical dependence of the reduction of SREBP-1c expression by either natural or synthetic farnesoid X receptor (FXR) agonists on both SHP and LXRα and LXRβ. These results suggest that strategies aimed at increasing FXR activity and the repressive effects of SHP should be explored to correct hypertriglyceridemia.
Authors
Mitsuhiro Watanabe, Sander M. Houten, Li Wang, Antonio Moschetta, David J. Mangelsdorf, Richard A. Heyman, David D. Moore, Johan Auwerx
Copyright © 2021 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)