Endocrinology
Abstract
BACKGROUND. Accumulation of diacylglycerol (DAG) and sphingolipids is thought to promote skeletal muscle insulin resistance by altering cellular signaling specific to their location. However,the subcellular localization of bioactive lipids in human skeletal muscle is largely unknown. METHODS. We evaluated subcellular localization of skeletal muscle DAGs and sphingolipids in lean individuals (n = 15), endurance-trained athletes (n = 16), and obese men and women with (n = 12) and without type 2 diabetes (n = 15). Muscle biopsies were fractionated into sarcolemmal, cytosolic, mitochondrial/ER, and nuclear compartments. Lipids were measured using liquid chromatography tandem mass spectrometry, and insulin sensitivity was measured using hyperinsulinemic-euglycemic clamp. RESULTS. Sarcolemmal 1,2-DAGs were not significantly related to insulin sensitivity. Sarcolemmal ceramides were inversely related to insulin sensitivity, with a significant relationship found for the C18:0 species. Sarcolemmal sphingomyelins were also inversely related to insulin sensitivity, with the strongest relationships found for the C18:1, C18:0, and C18:2 species. In the mitochondrial/ER and nuclear fractions, 1,2-DAGs were positively related to, while ceramides were inversely related to, insulin sensitivity. Cytosolic lipids as well as 1,3-DAG, dihydroceramides, and glucosylceramides in any compartment were not related to insulin sensitivity. All sphingolipids but only specific DAGs administered to isolated mitochondria decreased mitochondrial state 3 respiration. CONCLUSION. These data reveal previously unknown differences in subcellular localization of skeletal muscle DAGs and sphingolipids that relate to whole-body insulin sensitivity and mitochondrial function in humans. These data suggest that whole-cell concentrations of lipids obscure meaningful differences in compartmentalization and suggest that subcellular localization of lipids should be considered when developing therapeutic interventions to treat insulin resistance. FUNDING. National Institutes of Health General Clinical Research Center (RR-00036), National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) (R01DK089170), NIDDK (T32 DK07658), and Colorado Nutrition Obesity Research Center (P30DK048520).
Authors
Leigh Perreault, Sean A. Newsom, Allison Strauss, Anna Kerege, Darcy E. Kahn, Kathleen A. Harrison, Janet K. Snell-Bergeon, Travis Nemkov, Angelo D’Alessandro, Matthew R. Jackman, Paul S. MacLean, Bryan C. Bergman
Abstract
The adrenal cortex undergoes remodeling during fetal and postnatal life. How zona reticularis emerges in the postnatal gland to support adrenarche, a process whereby higher primates increase prepubertal androgen secretion, is unknown. Using cell-fate mapping and gene deletion studies in mice, we show that activation of PKA has no effect on the fetal cortex, while it accelerates regeneration of the adult cortex, triggers zona fasciculata differentiation that is subsequently converted into a functional reticularis-like zone, and drives hypersecretion syndromes. Remarkably, PKA effects are influenced by sex. Indeed, testicular androgens increase WNT signaling that antagonizes PKA, leading to slower adrenocortical cell turnover and delayed phenotype whereas gonadectomy sensitizes males to hypercorticism and reticularis-like formation. Thus, reticularis results from ultimate centripetal conversion of adult cortex under the combined effects of PKA and cell turnover that dictate organ size. We show that PKA-induced progenitor recruitment is sexually dimorphic and may provide a paradigm for overrepresentation of women in adrenal diseases.
Authors
Typhanie Dumontet, Isabelle Sahut-Barnola, Amandine Septier, Nathanaëlle Montanier, Ingrid Plotton, Florence Roucher-Boulez, Véronique Ducros, Anne-Marie Lefrançois-Martinez, Jean-Christophe Pointud, Mohamad Zubair, Ken-Ichirou Morohashi, David T. Breault, Pierre Val, Antoine Martinez
Abstract
Hypoglycemia is commonly associated with insulin therapy, limiting both its safety and efficacy. The concept of modifying insulin to render its glucose-responsive release from an injection depot (of an insulin complexed exogenously with a recombinant lectin) was proposed approximately 4 decades ago but has been challenging to achieve. Data presented here demonstrate that mannosylated insulin analogs can undergo an additional route of clearance as result of their interaction with endogenous mannose receptor (MR), and this can occur in a glucose-dependent fashion, with increased binding to MR at low glucose. Yet, these analogs retain capacity for binding to the insulin receptor (IR). When the blood glucose level is elevated, as in individuals with diabetes mellitus, MR binding diminishes due to glucose competition, leading to reduced MR-mediated clearance and increased partitioning for IR binding and consequent glucose lowering. These studies demonstrate that a glucose-dependent locus of insulin clearance and, hence, insulin action can be achieved by targeting MR and IR concurrently.
Authors
Ruojing Yang, Margaret Wu, Songnian Lin, Ravi P. Nargund, Xinghai Li, Theresa Kelly, Lin Yan, Ge Dai, Ying Qian, Qing Dallas-yang, Paul A. Fischer, Yan Cui, Xiaolan Shen, Pei Huo, Danqing Dennis Feng, Mark D. Erion, David E. Kelley, James Mu
Abstract
BACKGROUND. In type 1 diabetes (T1D), adjuvant treatment with inhibitors of the renin-angiotensin-aldosterone system (RAAS), which dilate the efferent arteriole, is associated with prevention of progressive albuminuria and renal dysfunction. Uncertainty still exists as to why some individuals with long-standing T1D develop diabetic kidney disease (DKD) while others do not (DKD resistors). We hypothesized that those with DKD would be distinguished from DKD resistors by the presence of RAAS activation. METHODS. Renal and systemic hemodynamic function was measured before and after exogenous RAAS stimulation by intravenous infusion of angiotensin II (ANGII) in 75 patients with prolonged T1D durations and in equal numbers of nondiabetic controls. The primary outcome was change in renal vascular resistance (RVR) in response to RAAS stimulation, a measure of endogenous RAAS activation. RESULTS. Those with DKD had less change in RVR following exogenous RAAS stimulation compared with DKD resistors or controls (19%, 29%, 31%, P = 0.008, DKD vs. DKD resistors), reflecting exaggerated endogenous renal RAAS activation. All T1D participants had similar changes in renal efferent arteroilar resistance (9% vs. 13%, P = 0.37) irrespective of DKD status, which reflected less change versus controls (20%, P = 0.03). In contrast, those with DKD exhibited comparatively less change in afferent arteriolar vascular resistance compared with DKD resistors or controls (33%, 48%, 48%, P = 0.031, DKD vs. DKD resistors), indicating higher endogenous RAAS activity. CONCLUSION. In long-standing T1D, the intrarenal RAAS is exaggerated in DKD, which unexpectedly predominates at the afferent rather than the efferent arteriole, stimulating vasoconstriction. FUNDING. JDRF operating grant 17-2013-312.
Authors
Julie A. Lovshin, Geneviève Boulet, Yuliya Lytvyn, Leif E. Lovblom, Petter Bjornstad, Mohammed A. Farooqi, Vesta Lai, Leslie Cham, Josephine Tse, Andrej Orszag, Daniel Scarr, Alanna Weisman, Hillary A. Keenan, Michael H. Brent, Narinder Paul, Vera Bril, Bruce A. Perkins, David Z.I. Cherney
Abstract
Compared with persons of European descent (ED), persons of African descent (AD) have lower aldosterone (ALDO) levels, with the assumption being that the increased cardiovascular disease (CVD) risk associated with AD is not related to ALDO. However, the appropriateness of the ALDO levels for the volume status in AD is unclear. We hypothesized that, even though ALDO levels are lower in AD, they are inappropriately increased, and therefore, ALDO could mediate the increased CVD in AD. To test this hypothesis, we analyzed data from HyperPATH — 1,788 individuals from the total cohort and 765 restricted to ED-to-AD in a 2:1 match and genotyped for the endothelin-1 gene (EDN1). Linear regression analyses with adjustments were performed. In the total and restricted cohorts, PRA, ALDO, and urinary potassium levels were significantly lower in AD. However, in the AD group, greater ALDO dysregulation was present as evidenced by higher ALDO/plasma renin activity (PRA) ratios (ARR) and sodium-modulated ALDO suppression-to-stimulation indices. Furthermore, EDN1 minor allele carriers had significantly greater ARRs than noncarriers but only in the AD group. ARR levels were modulated by a significant interaction between EDN1 and AD. Thus, EDN1 variants may identify particularly susceptible ADs who will be responsive to treatment targeting ALDO-dependent pathways (e.g., mineralocorticoid-receptor antagonists).
Authors
Jia W. Tan, Tina Gupta, Worapaka Manosroi, Tham M. Yao, Paul N. Hopkins, Jonathan S. Williams, Gail K. Adler, Jose R. Romero, Gordon H. Williams
Abstract
Primary and secondary hypertension are major risk factors for cardiovascular disease, the leading cause of death worldwide. Elevated secretion of aldosterone resulting from primary aldosteronism (PA) is a key driver of secondary hypertension. Here, we report an unexpected role for the ubiquitin ligase Siah1 in adrenal gland development and PA. Siah1a–/– mice exhibit altered adrenal gland morphology, as reflected by a diminished X-zone, enlarged medulla, and dysregulated zonation of the glomerulosa as well as increased aldosterone levels and aldosterone target gene expression and reduced plasma potassium levels. Genes involved in catecholamine biosynthesis and cAMP signaling are upregulated in the adrenal glands of Siah1a–/– mice, while genes related to retinoic acid signaling and cholesterol biosynthesis are downregulated. Loss of Siah1 leads to increased expression of the Siah1 substrate PIAS1, an E3 SUMO protein ligase implicated in the suppression of LXR, a key regulator of cholesterol levels in the adrenal gland. In addition, SIAH1 sequence variants were identified in patients with PA; such variants impaired SIAH1 ubiquitin ligase activity, resulting in elevated PIAS1 expression. These data identify a role for the Siah1-PIAS1 axis in adrenal gland organization and function and point to possible therapeutic targets for hyperaldosteronism.
Authors
Marzia Scortegagna, Annabel Berthon, Nikolaos Settas, Andreas Giannakou, Guillermina Garcia, Jian-Liang Li, Brian James, Robert C. Liddington, José G. Vilches-Moure, Constantine A. Stratakis, Ze’ev A. Ronai
Abstract
The secretion of insulin and glucagon from the pancreas and the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) from the gastrointestinal tract is essential for glucose homeostasis. Several novel treatment strategies for type 2 diabetes (T2D) mimic GLP-1 actions or inhibit incretin degradation (DPP4 inhibitors), but none is thus far aimed at increasing the secretion of endogenous incretins. In order to identify new potential therapeutic targets for treatment of T2D, we performed a meta-analysis of a GWAS and an exome-wide association study of circulating insulin, glucagon, GIP, and GLP-1 concentrations measured during an oral glucose tolerance test in up to 7,828 individuals. We identified 6 genome-wide significant functional loci associated with plasma incretin concentrations in or near the SLC5A1 (encoding SGLT1), GIPR, ABO, GLP2R, F13A1, and HOXD1 genes and studied the effect of these variants on mRNA expression in pancreatic islet and on metabolic phenotypes. Immunohistochemistry showed expression of GIPR, ABO, and HOXD1 in human enteroendocrine cells and expression of ABO in pancreatic islets, supporting a role in hormone secretion. This study thus provides candidate genes and insight into mechanisms by which secretion and breakdown of GIP and GLP-1 are regulated.
Authors
Peter Almgren, Andreas Lindqvist, Ulrika Krus, Liisa Hakaste, Emilia Ottosson-Laakso, Olof Asplund, Emily Sonestedt, Rashmi B. Prasad, Esa Laurila, Marju Orho-Melander, Olle Melander, Tiinamaija Tuomi, Jens Juul Holst, Peter M. Nilsson, Nils Wierup, Leif Groop, Emma Ahlqvist
Abstract
Loss-of-function mutations of GNA11, which encodes G-protein subunit α11 (Gα11), a signaling partner for the calcium-sensing receptor (CaSR), result in familial hypocalciuric hypercalcemia type 2 (FHH2). FHH2 is characterized by hypercalcemia, inappropriately normal or raised parathyroid hormone (PTH) concentrations, and normal or low urinary calcium excretion. A mouse model for FHH2 that would facilitate investigations of the in vivo role of Gα11 and the evaluation of calcimimetic drugs, which are CaSR allosteric activators, is not available. We therefore screened DNA from > 10,000 mice treated with the chemical mutagen N-ethyl-N-nitrosourea (ENU) for GNA11 mutations and identified a Gα11 variant, Asp195Gly (D195G), which downregulated CaSR-mediated intracellular calcium signaling in vitro, consistent with it being a loss-of-function mutation. Treatment with the calcimimetic cinacalcet rectified these signaling responses. In vivo studies showed mutant heterozygous (Gna11+/195G) and homozygous (Gna11195G/195G) mice to be hypercalcemic with normal or increased plasma PTH concentrations and normal urinary calcium excretion. Cinacalcet (30mg/kg orally) significantly reduced plasma albumin–adjusted calcium and PTH concentrations in Gna11+/195G and Gna11195G/195G mice. Thus, our studies have established a mouse model with a germline loss-of-function Gα11 mutation that is representative for FHH2 in humans and demonstrated that cinacalcet can correct the associated abnormalities of plasma calcium and PTH.
Authors
Sarah A. Howles, Fadil M. Hannan, Caroline M. Gorvin, Sian E. Piret, Anju Paudyal, Michelle Stewart, Tertius A. Hough, M. Andrew Nesbit, Sara Wells, Stephen D.M. Brown, Roger D. Cox, Rajesh V. Thakker
Abstract
In rodent models, obesity and hyperglycemia alter cerebral glucose metabolism and glucose transport into the brain, resulting in disordered cerebral function as well as inappropriate responses to homeostatic and hedonic inputs. Whether similar findings are seen in the human brain remains unclear. In this study, 25 participants (9 healthy participants; 10 obese nondiabetic participants; and 6 poorly controlled, insulin- and metformin-treated type 2 diabetes mellitus (T2DM) participants) underwent 1H magnetic resonance spectroscopy scanning in the occipital lobe to measure the change in intracerebral glucose levels during a 2-hour hyperglycemic clamp (glucose ~220 mg/dl). The change in intracerebral glucose was significantly different across groups after controlling for age and sex, despite similar plasma glucose levels at baseline and during hyperglycemia. Compared with lean participants, brain glucose increments were lower in participants with obesity and T2DM. Furthermore, the change in brain glucose correlated inversely with plasma free fatty acid (FFA) levels during hyperglycemia. These data suggest that obesity and poorly controlled T2DM progressively diminish brain glucose responses to hyperglycemia, which has important implications for understanding not only the altered feeding behavior, but also the adverse neurocognitive consequences associated with obesity and T2DM.
Authors
Janice J. Hwang, Lihong Jiang, Muhammad Hamza, Elizabeth Sanchez Rangel, Feng Dai, Renata Belfort-DeAguiar, Lisa Parikh, Brian B. Koo, Douglas L. Rothman, Graeme Mason, Robert S. Sherwin
Abstract
GIP-dependent Cushing’s syndrome is caused by ectopic expression of glucose-dependent insulinotropic polypeptide receptor (GIPR) in cortisol-producing adrenal adenomas or in bilateral macronodular adrenal hyperplasias. Molecular mechanisms leading to ectopic GIPR expression in adrenal tissue are not known. Here we performed molecular analyses on adrenocortical adenomas and bilateral macronodular adrenal hyperplasias obtained from 14 patients with GIP-dependent adrenal Cushing’s syndrome and one patient with GIP-dependent aldosteronism. GIPR expression in all adenoma and hyperplasia samples occurred through transcriptional activation of a single allele of the GIPR gene. While no abnormality was detected in proximal GIPR promoter methylation, we identified somatic duplications in chromosome region 19q13.32 containing the GIPR locus in the adrenocortical lesions derived from 3 patients. In 2 adenoma samples, the duplicated 19q13.32 region was rearranged with other chromosome regions, whereas a single tissue sample with hyperplasia had a 19q duplication only. We demonstrated that juxtaposition with cis-acting regulatory sequences such as glucocorticoid response elements in the newly identified genomic environment drives abnormal expression of the translocated GIPR allele in adenoma cells. Altogether, our results provide insight into the molecular pathogenesis of GIP-dependent Cushing’s syndrome, occurring through monoallelic transcriptional activation of GIPR driven in some adrenal lesions by structural variations.
Authors
Anne-Lise Lecoq, Constantine A. Stratakis, Say Viengchareun, Ronan Chaligné, Lucie Tosca, Vianney Deméocq, Mirella Hage, Annabel Berthon, Fabio R. Faucz, Patrick Hanna, Hadrien-Gaël Boyer, Nicolas Servant, Sylvie Salenave, Gérard Tachdjian, Clovis Adam, Vanessa Benhamo, Eric Clauser, Anne Guiochon-Mantel, Jacques Young, Marc Lombès, Isabelle Bourdeau, Dominique Maiter, Antoine Tabarin, Jérôme Bertherat, Hervé Lefebvre, Wouter de Herder, Estelle Louiset, André Lacroix, Philippe Chanson, Jérôme Bouligand, Peter Kamenický
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