Metabolism
Abstract
Patients with active acromegaly (ACRO) exhibit low hepatocellular lipids (HCL) despite pronounced insulin resistance (IR). This contrasts the strong association of IR with non-alcoholic fatty liver disease in the general population. Since low HCL in acromegaly might be caused by changes in oxidative substrate metabolism, we investigated mitochondrial activity and plasma metabolomics/lipidomics in active acromegaly. Fifteen ACRO and seventeen healthy controls (CON) matched for age, BMI, gender and body composition underwent 31P/1H-7T-MR-spectroscopy of the liver and skeletal muscle, as well as plasma metabolomic profiling and an oral glucose tolerance test. ACRO showed significant lower HCL but ATP-synthesis rate was significantly increased compared to CON. Furthermore, a decreased ratio of unsaturated to saturated intrahepatocellular fatty acids was found in ACRO. Within assessed plasma lipids, lipidomics, and metabolomics, decreased carnitine species also indicate increased mitochondrial activity. We therefore conclude that excess of growth hormone (GH) in humans counteracts hepatocellular lipid accumulation by increased hepatic ATP-synthesis. This is accompanied by a decreased ratio of unsaturated-to-saturated lipids in hepatocytes and by a metabolomic profile reflecting the increase in mitochondrial activity. Thus, these findings help to better understand GH-regulated antisteatotic pathways and provide a better insight into potential novel therapeutic targets for treating NAFLD.
Authors
Paul Fellinger, Peter Wolf, Lorenz Pfleger, Patrik Krumpolec, Martin Krssak, Kristaps Klavins, Stefan Wolfsberger, Alexander Micko, Patricia Carey, Bettina Gürtl, Greisa Vila, Wolfgang Raber, Clemens Fürnsinn, Thomas Scherer, Siegfried Trattnig, Alexandra Kautzky-Willer, Michael Krebs, Yvonne Winhofer
Abstract
Background Salt-sensitive hypertension is often accompanied by insulin resistance in obese individuals, but the underlying mechanisms are obscure. Microvascular function is known to affect both salt-sensitivity of blood pressure and metabolic insulin sensitivity. We hypothesized that excessive salt intake increases blood pressure and decreases insulin-mediated glucose disposal, at least in part by impairing insulin-mediated muscle microvascular recruitment (IMMR). Methods In 20 lean and 20 abdominally obese individuals, we assessed mean arterial pressure (MAP; 24h ABPM), insulin-mediated whole body glucose disposal (M/I-value; hyperinsulinemic, euglycemic clamp technique), IMMR (contrast enhanced ultrasound), osmolyte and water balance, and excretion of mineralocorticoids, glucocorticoids, and amino and organic acids after a low and high salt diet during seven days in a randomized double-blind cross-over design. Results On a low, as compared to a high salt intake, MAP was lower, M/I-value was lower and IMMR was greater in both lean and abdominally obese individuals. In addition, Ln IMMR was inversely associated with MAP in lean participants on a low salt diet only. On a high salt diet, free water clearance decreased, and excretion of glucocorticoids and of amino acids involved in the urea cycle increased. Conclusion Our findings imply that hemodynamic and metabolic changes resulting from alterations in salt intake are not necessarily associated. Moreover, they are consistent with the concept that a high salt intake increases muscle glucose uptake as a response to high-salt-induced, glucocorticoid-drive muscle catabolism to stimulate urea production and thereby renal water conservation. Clinical Trial Registration Number: NCT02068781
Authors
Monica T.J. Schütten, Yvo H.A.M. Kusters, Alfons J.H.M. Houben, Hanneke E. C. Niessen, Jos op 't Roodt, Jean L.J. M. Scheijen, Marjo P. van de Waarenburg, Casper G. Schalkwijk, Peter W. de Leeuw, Coen D.A. Stehouwer
Abstract
The blood hormone erythropoietin (EPO), upon binding to its receptor (EpoR), modulates high fat-diet (HFD)-induced obesity in mice, improves glucose tolerance, and prevents white adipose tissue inflammation. Transgenic mice with constitutive over-expression of human EPO solely in brain (Tg21) were used to assess the neuro-endocrine EPO effect without increasing the hematocrit. Male Tg21-mice resisted HFD-induced weight gain, showed lower serum ACTH, corticosterone and C-reactive protein levels, and prevented myeloid cell recruitment to hypothalamus compared with WT-males. HFD-induced hypothalamic inflammation (HI) and microglial activation were higher in male mice, and Tg21-males exhibited lower increase in HI than WT-males. Physiological EPO function in the brain also showed sexual dimorphism in regulating HFD response. Targeted deletion of EpoR gene expression in neuronal and glial cells worsened HFD-induced glucose intolerance in both male and female mice, but increased weight gain and HI in the hypothalamus in male mice only. Female estrogen production blocked reduced weight gain and HI. Both male and female Tg21-mice kept on normal-chow and HFD showed significantly improved glycemic control. Our data indicates that cerebral EPO regulates weight gain and HI in a sex-dependent response, distinct from EPO regulation of glycemic control, and independent of erythropoietic EPO response.
Authors
Soumyadeep Dey, Zhenzhong Cui, Oksana Gavrilova, XiaoJie Zhang, Max Gassmann, Constance T. Noguchi
Abstract
Lung cancer (LC) is a leading cause of cancer-related deaths worldwide. Its rapid growth requires hyperactive catabolism of principal metabolic fuels. It is unclear whether fructose, an abundant sugar in current diets, is essential for LC. We demonstrated that, under the condition of coexistence of metabolic fuels in the body, fructose was readily used by LC cells in vivo as a glucose alternative via upregulating GLUT5, a major fructose transporter encoded by solute carrier family 2 member 5 (SLC2A5). Metabolomic profiling coupled with isotope tracing demonstrated that incorporated fructose was catabolized to fuel fatty acid synthesis and palmitoleic acid generation in particular to expedite LC growth in vivo. Both in vitro and in vivo supplement of palmitoleic acid could restore impaired LC propagation caused by SLC2A5 deletion. Furthermore, molecular mechanism investigation revealed that GLUT5-mediated fructose utilization was required to suppress AMPK and consequently activate mTORC1 activity to promote LC growth. As such, pharmacological blockade of in vivo fructose utilization using a GLUT5 inhibitor remarkably curtailed LC growth. Together, this study underscores the importance of in vivo fructose utilization mediated by GLUT5 in governing LC growth and highlights a promising strategy to treat LC by targeting GLUT5 to eliminate those fructose-addicted neoplastic cells.
Authors
Wen-Lian Chen, Xing Jin, Mingsong Wang, Dan Liu, Qin Luo, Hechuan Tian, Lili Cai, Lifei Meng, Rui Bi, Lei Wang, Xiao Xie, Guanzhen Yu, Lihui Li, Changsheng Dong, Qiliang Cai, Wei Jia, Wenyi Wei, Lijun Jia
Abstract
SNAP23 is the ubiquitous SNAP25 isoform that mediates secretion in non-neuronal cells, similar to SNAP25 in neurons. However, some secretory cells like pancreatic islet β cells contain an abundance of both SNAP25 and SNAP23, where SNAP23 is believed to play a redundant role to SNAP25. We show that SNAP23, when depleted in mouse β cells in vivo and human β cells (normal and type 2 diabetes [T2D] patients) in vitro, paradoxically increased biphasic glucose-stimulated insulin secretion corresponding to increased exocytosis of predocked and newcomer insulin granules. Such effects on T2D Goto-Kakizaki rats improved glucose homeostasis that was superior to conventional treatment with sulfonylurea glybenclamide. SNAP23, although fusion competent in slower secretory cells, in the context of β cells acts as a weak partial fusion agonist or inhibitory SNARE. Here, SNAP23 depletion promotes SNAP25 to bind calcium channels more quickly and longer where granule fusion occurs to increase exocytosis efficiency. β Cell SNAP23 antagonism is a strategy to treat diabetes.
Authors
Tao Liang, Tairan Qin, Fei Kang, Youhou Kang, Li Xie, Dan Zhu, Subhankar Dolai, Dafna Greitzer-Antes, Robert K. Baker, Daorong Feng, Eva Tuduri, Claes-Goran Ostenson, Timothy J. Kieffer, Kate Banks, Jeffrey E. Pessin, Herbert Y. Gaisano
Abstract
Inducible nitric oxide synthase (iNOS) and arginase-2 (ARG2) share a common substrate, arginine. Higher expression of iNOS and exhaled NO are linked to airway inflammation in patients. iNOS deletion in animal models suggests that eosinophilic inflammation is regulated by arginine metabolism. Moreover, ARG2 is a regulator of Th2 response, as shown by the development of severe eosinophilic inflammation in ARG2–/– mice. However, potential synergistic roles of iNOS and ARG2 in asthma have not been explored. Here, we hypothesized that arginine metabolic fate via iNOS and ARG2 may govern airway inflammation. In an asthma cohort, ARG2 variant genotypes were associated with arginase activity. ARG2 variants with lower arginase activity, combined with levels of exhaled NO, identified a severe asthma phenotype. Airway inflammation was present in WT, ARG2–/–, iNOS–/–, and ARG2–/–/iNOS–/– mice but was greatest in ARG2–/–. Eosinophilic and neutrophilic infiltration in the ARG2–/– mice was abrogated in ARG2–/–/iNOS–/– animals. Similarly, angiogenic airway remodeling was greatest in ARG2–/– mice. Cytokines driving inflammation and remodeling were highest in lungs of asthmatic ARG2–/– mice and lowest in the iNOS–/–. ARG2 metabolism of arginine suppresses inflammation, while iNOS metabolism promotes airway inflammation, supporting a central role for arginine metabolic control of inflammation.
Authors
Kewal Asosingh, Chris D. Lauruschkat, Mario Alemagno, Matthew Frimel, Nicholas Wanner, Kelly Weiss, Sean Kessler, Deborah A. Meyers, Carole Bennett, Weiling Xu, Serpil Erzurum
Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency
Abstract
Background: Liver disease in urea cycle disorders (UCDs) ranges from hepatomegaly and chronic hepatocellular injury to cirrhosis and end-stage liver disease. However, the prevalence and underlying mechanisms are unclear. Methods: We estimated the prevalence of chronic hepatocellular injury in UCDs using data from a multicenter, longitudinal, natural history study. We also used ultrasound with shear wave elastography and FibroTestTM to evaluate liver stiffness and markers of fibrosis in individuals with argininosuccinate lyase deficiency (ASLD), a disorder with high prevalence of elevated serum alanine aminotransferase (ALT). To understand the human observations, we evaluated the hepatic phenotype of the AslNeo/Neo mouse model of ASLD. Results: We demonstrate a high prevalence of elevated ALT in ASLD (37%). Hyperammonemia and use of nitrogen-scavenging agents, two markers of disease severity, were significantly (p<0.001; p=0.001) associated with elevated ALT in ASLD. In addition, ultrasound with shear wave elastography and FibroTestTM revealed increased echogenicity and liver stiffness even in individuals with ASLD and normal aminotransferases. The AslNeo/Neo mice mimic the human disorder with hepatomegaly, elevated aminotransferases, and excessive hepatic glycogen noted prior to death (3-5 weeks of age). This excessive hepatic glycogen is associated with impaired hepatic glycogenolysis and decreased glycogen phosphorylase and is rescued with helper-dependent adenovirus expressing Asl using a liver specific (ApoE) promoter. Conclusions: Our results link urea cycle dysfunction and impaired hepatic glucose metabolism and identify a mouse model of liver disease in the setting of urea cycle dysfunction. Trial Registration: NCT03721367, NCT00237315 Funding: NIH, Burroughs Wellcome Fund, NUCDF, Genzyme/ACMG Foundation, CPRIT
Authors
Lindsay C. Burrage, Simran Madan, Xiaohui Li, Saima Ali, Mahmoud A. Mohammad, Bridget M. Stroup, Ming-Ming Jiang, Racel Cela, Terry Bertin, Jian Dai, Danielle Guffey, Milton Finegold, Sandesh Nagamani, Charles G. Minard, Juan Marini, Prakash Masand, Deborah Schady, Benjamin L. Shneider, Daniel H. Leung, Deeksha Bali, Brendan Lee
Abstract
Posttransplantation diabetes mellitus (PTDM) is a common and significant complication related to immunosuppressive agents required to prevent organ or cell transplant rejection. To elucidate the effects of 2 commonly used agents, the calcineurin inhibitor tacrolimus (TAC) and the mTOR inhibitor sirolimus (SIR), on islet function and test whether these effects could be reversed or prevented, we investigated human islets transplanted into immunodeficient mice treated with TAC or SIR at clinically relevant levels. Both TAC and SIR impaired insulin secretion in fasted and/or stimulated conditions. Treatment with TAC or SIR increased amyloid deposition and islet macrophages, disrupted insulin granule formation, and induced broad transcriptional dysregulation related to peptide processing, ion/calcium flux, and the extracellular matrix; however, it did not affect regulation of β cell mass. Interestingly, these β cell abnormalities reversed after withdrawal of drug treatment. Furthermore, cotreatment with a GLP-1 receptor agonist completely prevented TAC-induced β cell dysfunction and partially prevented SIR-induced β cell dysfunction. These results highlight the importance of both calcineurin and mTOR signaling in normal human β cell function in vivo and suggest that modulation of these pathways may prevent or ameliorate PTDM.
Authors
Chunhua Dai, John T. Walker, Alena Shostak, Ana Padgett, Erick Spears, Scott Wisniewski, Greg Poffenberger, Radhika Aramandla, E. Danielle Dean, Nripesh Prasad, Shawn E. Levy, Dale L. Greiner, Leonard D. Shultz, Rita Bottino, Alvin C. Powers
Abstract
The ciliopathies Bardet-Biedl Syndrome and Alström Syndrome are genetically inherited pleiotropic disorders with primary clinical features of hyperphagia and obesity. Methionine aminopeptidase 2 inhibitors (MetAP2i) have been shown in preclinical and clinical studies to reduce food intake, body weight, and adiposity. Here we investigated the effects of MetAP2i administration in a mouse model of ciliopathy produced by conditional deletion of the Thm1 gene in adulthood. Thm1 conditional knock-out (cko) mice show decreased hypothalamic pro-opiomelanocortin expression as well as hyperphagia, obesity, metabolic disease and hepatic steatosis. In obese Thm1 cko mice, two-week administration of MetAP2i reduced daily food intake and reduced body weight 17.1% from baseline (vs. 5% reduction for vehicle). This was accompanied with decreased levels of blood glucose, insulin and leptin. Further, MetAP2i reduced gonadal adipose depots and adipocyte size and improved liver morphology. This is the first report of MetAP2i reducing hyperphagia and body weight, and ameliorating metabolic indices in a mouse model of ciliopathy. These results support further investigation of MetAP2 inhibition as a potential therapeutic strategy for ciliary-mediated forms of obesity.
Authors
Tana S Pottorf, Micaella P. Fagan, Bryan F. Burkey, David J Cho, James E Vath, Pamela V. Tran
Abstract
In humans, chronic glucocorticoid use is associated with side effects like muscle wasting, obesity, and metabolic syndrome. Intermittent steroid dosing has been proposed in Duchenne Muscular Dystrophy patients to mitigate the side effects seen with daily steroid intake. We evaluated biomarkers from Duchenne Muscular Dystrophy patients, finding that, compared with chronic daily steroid use, weekend steroid use was associated with reduced serum insulin, free fatty acids, and branched chain amino acids, as well as reduction in fat mass despite having similar BMIs. We reasoned that intermittent prednisone administration in dystrophic mice would alter muscle epigenomic signatures, and we identified the coordinated action of the glucocorticoid receptor, KLF15 and MEF2C as mediators of a gene expression program driving metabolic reprogramming and enhanced nutrient utilization. Muscle lacking Klf15 failed to respond to intermittent steroids. Furthermore, coadministration of the histone acetyltransferase inhibitor anacardic acid with steroids in mdx mice eliminated steroid-specific epigenetic marks and abrogated the steroid response. Together, these findings indicate that intermittent, repeated exposure to glucocorticoids promotes performance in dystrophic muscle through an epigenetic program that enhances nutrient utilization.
Authors
Mattia Quattrocelli, Aaron S. Zelikovich, Zhen Jiang, Clara Bien Peek, Alexis R. Demonbreun, Nancy L. Kuntz, Grant D. Barish, Saptarsi M. Haldar, Joseph Bass, Elizabeth M. McNally
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