Metabolism
Abstract
BACKGROUND While saturated fat intake leads to insulin resistance and nonalcoholic fatty liver, Mediterranean-like diets enriched in monounsaturated fatty acids (MUFA) may have beneficial effects. This study examined effects of MUFA on tissue-specific insulin sensitivity and energy metabolism.METHODS A randomized placebo-controlled cross-over study enrolled 16 glucose-tolerant volunteers to receive either oil (OIL, ~1.18 g/kg), rich in MUFA, or vehicle (VCL, water) on 2 occasions. Insulin sensitivity was assessed during preclamp and hyperinsulinemic-euglycemic clamp conditions. Ingestion of 2H2O/acetaminophen was combined with [6,6-2H2]glucose infusion and in vivo 13C/31P/1H/ex vivo 2H-magnet resonance spectroscopy to quantify hepatic glucose and energy fluxes.RESULTS OIL increased plasma triglycerides and oleic acid concentrations by 44% and 66% compared with VCL. Upon OIL intervention, preclamp hepatic and whole-body insulin sensitivity markedly decreased by 28% and 27%, respectively, along with 61% higher rates of hepatic gluconeogenesis and 32% lower rates of net glycogenolysis, while hepatic triglyceride and ATP concentrations did not differ from VCL. During insulin stimulation hepatic and whole-body insulin sensitivity were reduced by 21% and 25%, respectively, after OIL ingestion compared with that in controls.CONCLUSION A single MUFA-load suffices to induce insulin resistance but affects neither hepatic triglycerides nor energy-rich phosphates. These data indicate that amount of ingested fat, rather than its composition, primarily determines the development of acute insulin resistance.TRIAL REGISTRATION ClinicalTrials.gov NCT01736202.FUNDING German Diabetes Center, German Federal Ministry of Health, Ministry of Culture and Science of the state of North Rhine-Westphalia, German Federal Ministry of Education and Research, German Diabetes Association, German Center for Diabetes Research, Portugal Foundation for Science and Technology, European Regional Development Fund, and Rede Nacional de Ressonancia Magnética Nuclear.
Authors
Theresia Sarabhai, Sabine Kahl, Julia Szendroedi, Daniel F. Markgraf, Oana-Patricia Zaharia, Cristina Barosa, Christian Herder, Frithjof Wickrath, Pavel Bobrov, Jong-Hee Hwang, John Griffith Jones, Michael Roden
Abstract
EIF2AK4, which encodes the amino acid deficiency–sensing protein GCN2, has been implicated as a susceptibility gene for type 2 diabetes in the Japanese population. However, the mechanism by which GCN2 affects glucose homeostasis is unclear. Here, we show that insulin secretion is reduced in individuals harboring the risk allele of EIF2AK4 and that maintenance of GCN2-deficient mice on a high-fat diet results in a loss of pancreatic β cell mass. Our data suggest that GCN2 senses amino acid deficiency in β cells and limits signaling by mechanistic target of rapamycin complex 1 to prevent β cell failure during the consumption of a high-fat diet.
Authors
Ayumi Kanno, Shun-ichiro Asahara, Ayuko Furubayashi, Katsuhisa Masuda, Risa Yoshitomi, Emi Suzuki, Tomoko Takai, Maki Kimura-Koyanagi, Tomokazu Matsuda, Alberto Bartolome, Yushi Hirota, Norihide Yokoi, Yuka Inaba, Hiroshi Inoue, Michihiro Matsumoto, Kenichi Inoue, Takaya Abe, Fan-Yan Wei, Kazuhito Tomizawa, Wataru Ogawa, Susumu Seino, Masato Kasuga, Yoshiaki Kido
Abstract
There is limited understanding of the role of host metabolism in the pathophysiology of human tuberculosis (TB). Using high resolution metabolomics with an unbiased approach to metabolic pathway analysis, we discovered that the tryptophan pathway is highly regulated throughout the spectrum of TB infection and disease. This regulation is characterized by increased catabolism of tryptophan to kynurenine, which was evident not only in active TB disease, but also in latent TB infection (LTBI). Further, we found that tryptophan catabolism is reversed with effective treatment of both active TB disease and LTBI in a manner commensurate with bacterial clearance. Persons with active TB and LTBI also exhibit increased expression of indoleamine 2,3-dioxygenase-1 (IDO-1), suggesting IDO-1 mediates observed increases in tryptophan catabolism. Together, these data indicate IDO-1-mediated tryptophan catabolism is highly preserved in the human response to Mycobacterium tuberculosis and could be a target for biomarker development as well as host-directed therapies.
Authors
Jeffrey M. Collins, Amnah Siddiqa, Dean P. Jones, Ken Liu, Russell R. Kempker, Azhar Nizam, N. Sarita Shah, Nazir Ismail, Samuel G. Ouma, Nestani Tukvadze, Shuzhao Li, Cheryl L. Day, Jyothi Rengarajan, James C. M. Brust, Neel R. Gandhi, Joel D. Ernst, Henry M. Blumberg, Thomas R. Ziegler
Abstract
Insulin receptor signaling is crucial for white adipose tissue (WAT) function. Consequently, lack of insulin receptor (IR) in WAT results in a diabetes-like phenotype. Yet, causes for IR downregulation in WAT of diabetic patients are not well understood. By using multiple mouse models of obesity and insulin resistance, we identify a common downregulation of the IR with a reduction of mRNA expression of the selenoproteins Txnrd3, Sephs2, and Gpx3. Consistently, GPX3 is also decreased in adipose tissue of insulin resistant and obese patients. Inducing Gpx3 expression via selenite treatment enhances IR expression via activation of the transcription factor Sp1 in 3T3-L1 preadipocytes and improves adipocyte differentiation and function. Feeding mice a selenium-enriched high-fat diet alleviates diet-induced insulin resistance with increased insulin sensitivity, decreased tissue inflammation and elevated IR expression in WAT. Again, IR expression correlates positively with Gpx3 expression, a phenotype which is also conserved in humans. Consequently, decreasing GPx3 using siRNA technique reduces IR expression in 3T3-L1 preadipocytes and insulin sensitivity. Overall our data identify GPx3 as a novel regulator of IR expression and insulin sensitivity in adipose tissue.
Authors
Robert Hauffe, Vanessa Stein, Chantal Chudoba, Tanina Flore, Michaela Rath, Katrin Ritter, Mareike Schell, Kristina Wardelmann, Stefanie Deubel, Johannes F. Kopp, Maria Schwarz, Kai Kappert, Matthias Blüher, Tanja Schwerdtle, Anna P. Kipp, Andre Kleinridders
Abstract
Pancreatic islets secrete insulin from β cells and glucagon from α cells and dysregulated secretion of these hormones is a central component of diabetes. Thus, an improved understanding of the pathways governing coordinated β and α cell hormone secretion will provide insight into islet dysfunction in diabetes. However, the three-dimensional multicellular islet architecture, essential for coordinated islet function, presents experimental challenges for mechanistic studies of intracellular signaling pathways in primary islet cells. Here, we developed an integrated approach to study the function of primary human islet cells using genetically modified pseudoislets that resemble native islets across multiple parameters. Further, we developed a microperifusion system that allowed synchronous acquisition of GCaMP6f biosensor signal and hormone secretory profiles. We demonstrate the utility of this experimental approach by studying the effects of Gi and Gq GPCR pathways on insulin and glucagon secretion by expressing the designer receptors exclusively activated by designer drugs (DREADDs) hM4Di or hM3Dq. Activation of Gi signaling reduced insulin and glucagon secretion, while activation of Gq signaling stimulated glucagon secretion but had both stimulatory and inhibitory effects on insulin secretion which occur through changes in intracellular Ca2+. The experimental approach of combining pseudoislets with a microfluidic system, allowed the co-registration of intracellular signaling dynamics and hormone secretion and demonstrated differences in GPCR signaling pathways between human β and α cells.
Authors
John T. Walker, Rachana Haliyur, Heather A. Nelson, Matthew Ishahak, Gregory Poffenberger, Radhika Aramandla, Conrad Reihsmann, Joseph R. Luchsinger, Diane C. Saunders, Peng Wang, Adolfo Garcia-Ocana, Rita Bottino, Ashutosh Agarwal, Alvin C. Powers, Marcela Brissova
Abstract
Recent studies in distinct preclinical tumor models have established the nucleotide synthesis enzyme inosine-5′-monophosphate dehydrogenase (IMPDH) as a viable target for antitumor therapy. IMPDH inhibitors have been used clinically for decades as safe and effective immunosuppressants. However, the potential to repurpose these pharmacological agents for antitumor therapy requires further investigation, including direct comparisons of available compounds. Therefore, we tested structurally distinct IMPDH inhibitors in multiple cell and mouse tumor models of the genetic tumor syndrome tuberous sclerosis complex (TSC). TSC-associated tumors are driven by uncontrolled activation of the growth-promoting protein kinase complex mechanistic target of rapamycin (mTOR) complex 1 (mTORC1), which is also aberrantly activated in the majority of sporadic cancers. Despite eliciting similar immunosuppressive effects, the IMPDH inhibitor mizoribine, used clinically throughout Asia, demonstrated far superior antitumor activity compared with the FDA-approved IMPDH inhibitor mycophenolate mofetil (or CellCept, a prodrug of mycophenolic acid). When compared directly to the mTOR inhibitor rapamycin, mizoribine treatment provided a more durable antitumor response associated with tumor cell death. These results provide preclinical support for repurposing mizoribine, over other IMPDH inhibitors, as an alternative to mTOR inhibitors for the treatment of TSC-associated tumors and possibly other tumors featuring uncontrolled mTORC1 activity.
Authors
Alexander J. Valvezan, Molly C. McNamara, Spencer K. Miller, Margaret E. Torrence, John M. Asara, Elizabeth P. Henske, Brendan D. Manning
Abstract
The therapies available for management of obesity and associated conditions are limited, because they are often directed toward an individual component of metabolic syndrome and are associated with adverse effects. Here, we report the multifaceted therapeutic potential of histidine-tagged recombinant soluble (pro)renin receptor (sPRR), termed sPRR-His, in a mouse model of diet-induced obesity (DIO). In the DIO model, 2-week administration of sPRR-His lowered body weight and remarkably improved multiple metabolic parameters in the absence of fluid retention. Conversely, inhibition of endogenous sPRR production by PF429242 induced diabetes and insulin resistance, both of which were reversed by the sPRR-His supplement. At the cellular level, sPRR-His enhanced insulin-induced increases in glucose uptake via upregulation of phosphorylated AKT and protein abundance of glucose transporter 4. Promoter and gene expression analysis revealed PRR as a direct target gene of PPARγ. Adipocyte-specific PPARγ deletion induced severe diabetes and insulin resistance associated with reduced adipose PRR expression and circulating sPRR. The sPRR-His supplement in the null mice nearly normalized blood glucose and insulin levels. Additionally, sPRR-His treatment suppressed DIO-induced renal sodium-glucose cotransporter-2 (SGLT2) expression. Overall, sPRR-His exhibits a therapeutic potential in management of metabolic syndrome via interaction with PPARγ.
Authors
Fei Wang, Renfei Luo, Chang-Jiang Zou, Shiying Xie, Kexin Peng, Long Zhao, Kevin T. Yang, Chuanming Xu, Tianxin Yang
Abstract
The role of the renal organic anion transporters OAT1 (also known as SLC22A6, originally identified as NKT) and OAT3 (also known as SLC22A8) in chronic kidney disease (CKD) remains poorly understood. This is particularly so from the viewpoint of residual proximal tubular secretion, a key adaptive mechanism to deal with protein-bound uremic toxins in CKD. Using the subtotal nephrectomy (STN) model, plasma metabolites accumulating in STN rats treated with and without the OAT inhibitor, probenecid, were identified. Comparisons with metabolomics data from Oat1-KO and Oat3-KO mice support the centrality of the OATs in residual tubular secretion of uremic solutes, such as indoxyl sulfate, kynurenate, and anthranilate. Overlapping our data with those of published metabolomics data regarding gut microbiome–derived uremic solutes — which can have dual roles in signaling and toxicity — indicates that OATs play a critical role in determining their plasma levels in CKD. Thus, the OATs, along with other SLC and ABC drug transporters, are critical to the movement of uremic solutes across tissues and into various body fluids, consistent with the remote sensing and signaling theory. The data support a role for OATs in modulating remote interorganismal and interorgan communication (gut microbiota–blood-liver-kidney-urine). The results also have implications for understanding drug-metabolite interactions involving uremic toxins.
Authors
Kevin T. Bush, Prabhleen Singh, Sanjay K. Nigam
Abstract
Semaglutide, a glucagon-like peptide 1 (GLP-1) analog, induces weight loss, lowers glucose levels, and reduces cardiovascular risk in patients with diabetes. Mechanistic preclinical studies suggest weight loss is mediated through GLP-1 receptors (GLP-1Rs) in the brain. The findings presented here show that semaglutide modulated food preference, reduced food intake, and caused weight loss without decreasing energy expenditure. Semaglutide directly accessed the brainstem, septal nucleus, and hypothalamus but did not cross the blood-brain barrier; it interacted with the brain through the circumventricular organs and several select sites adjacent to the ventricles. Semaglutide induced central c-Fos activation in 10 brain areas, including hindbrain areas directly targeted by semaglutide, and secondary areas without direct GLP-1R interaction, such as the lateral parabrachial nucleus. Automated analysis of semaglutide access, c-Fos activity, GLP-1R distribution, and brain connectivity revealed that activation may involve meal termination controlled by neurons in the lateral parabrachial nucleus. Transcriptomic analysis of microdissected brain areas from semaglutide-treated rats showed upregulation of prolactin-releasing hormone and tyrosine hydroxylase in the area postrema. We suggest semaglutide lowers body weight by direct interaction with diverse GLP-1R populations and by directly and indirectly affecting the activity of neural pathways involved in food intake, reward, and energy expenditure.
Authors
Sanaz Gabery, Casper G. Salinas, Sarah J. Paulsen, Jonas Ahnfelt-Rønne, Tomas Alanentalo, Arian F. Baquero, Stephen T. Buckley, Erzsébet Farkas, Csaba Fekete, Klaus S. Frederiksen, Hans Christian C. Helms, Jacob F. Jeppesen, Linu M. John, Charles Pyke, Jane Nøhr, Tess T. Lu, Joseph Polex-Wolf, Vincent Prevot, Kirsten Raun, Lotte Simonsen, Gao Sun, Anett Szilvásy-Szabó, Hanni Willenbrock, Anna Secher, Lotte Bjerre Knudsen
Abstract
A GLP-2 analogue is used in individuals with intestinal failure at risk for liver disease, yet the hepatic actions of GLP-2 are not understood. Treatment of high fat diet (HFD)-fed mice with GLP-2 did not modify development of hepatosteatosis or hepatic inflammation. In contrast, Glp2r-/- mice exhibited increased hepatic lipid accumulation, deterioration in glucose tolerance, and upregulation of biomarkers of hepatic inflammation. Both mouse and human liver expressed the canonical GLP-2R, and hepatic Glp2r expression was upregulated in mice with hepatosteatosis. Cell fractionation localized the Glp2r to hepatic stellate cells (HSC), and markers of HSC activation and fibrosis were increased in livers from Glp2r-/- mice. Moreover, GLP-2 directly modulated gene expression in isolated HSCs ex vivo. Taken together, these findings define an essential role for the GLP-2R in hepatic adaptation to nutrient excess and unveil a gut hormone-HSC axis, linking GLP-2R signaling to control of hepatic stellate cell activation.
Authors
Shai Fuchs, Bernardo Yusta, Laurie L. Baggio, Elodie M. Varin, Dianne Matthews, Daniel J. Drucker
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