Metabolism
Abstract
Glucagon-like peptide-1 (GLP-1) is an incretin hormone that potentiates glucose-stimulated insulin secretion. GLP-1 is classically produced by gut L cells; however, under certain circumstances α cells can express the prohormone convertase required for proglucagon processing to GLP-1, prohormone convertase 1/3 (PC1/3), and can produce GLP-1. However, the mechanisms through which this occurs are poorly defined. Understanding the mechanisms by which α cell PC1/3 expression can be activated may reveal new targets for diabetes treatment. Here, we demonstrate that the GLP-1 receptor (GLP-1R) agonist, liraglutide, increased α cell GLP-1 expression in a β cell GLP-1R–dependent manner. We demonstrate that this effect of liraglutide was translationally relevant in human islets through application of a new scRNA-seq technology, DART-Seq. We found that the effect of liraglutide to increase α cell PC1/3 mRNA expression occurred in a subcluster of α cells and was associated with increased expression of other β cell–like genes, which we confirmed by IHC. Finally, we found that the effect of liraglutide to increase bihormonal insulin+ glucagon+ cells was mediated by the β cell GLP-1R in mice. Together, our data validate a high-sensitivity method for scRNA-seq in human islets and identify a potentially novel GLP-1–mediated pathway regulating human α cell function.
Authors
Mridusmita Saikia, Marlena M. Holter, Leanne R. Donahue, Isaac S. Lee, Qiaonan C. Zheng, Journey L. Wise, Jenna E. Todero, Daryl J. Phuong, Darline Garibay, Reilly Coch, Kyle W. Sloop, Adolfo Garcia-Ocana, Charles G. Danko, Bethany P. Cummings
Abstract
Extracellular vesicles (EVs) are implicated in the crosstalk between adipocytes and other metabolic organs, and an altered biological cargo has been observed in EVs from human obese adipose tissue (AT). Yet, the role of adipocyte-derived EVs in pancreatic β-cells remains to be determined. Here, we explored the effects of EVs, released from both rodent and human isolated adipocytes and human AT explants, on survival and function of pancreatic β-cells and human pancreatic islets. EVs from healthy 3T3-L1 adipocytes increased survival and proliferation and promoted insulin secretion in INS-1E β-cells and human pancreatic islets, both untreated or exposed to cytokines or glucolipotoxicity, while EVs from inflamed adipocytes caused β-cell death and dysfunction. Human lean adipocyte-derived EVs produced similar beneficial effects, while EVs from obese AT explants were harmful for human EndoC-βH3 β-cells. We observed differential expression of microRNAs in EVs from healthy and inflamed adipocytes, as well as alteration in signaling pathways and expression of β-cell genes, adipokines and CKs in recipient β-cells. These in vitro results suggest that, depending on the physiopathological state of AT, adipocyte-derived EVs may influence β-cell fate and function.
Authors
Iacopo Gesmundo, Barbara Pardini, Eleonora Gargantini, Giacomo Gamba, Giovanni Birolo, Alessandro Fanciulli, Dana Banfi, Noemi Congiusta, Enrica Favaro, Maria Chiara Deregibus, Gabriele Togliatto, Gaia Zocaro, Maria Felice Brizzi, Raul M. Luque, Justo P. Castaño, Maria Alessandra Bocchiotti, Simone Arolfo, Stefania Bruno, Rita Nano, Mario Morino, Lorenzo Piemonti, Huy Ong, Giuseppe Matullo, Juan M. Falcón-Pérez, Ezio Ghigo, Giovanni Camussi, Riccarda Granata
Abstract
To extract energy from stored lipids, fatty acids must first be liberated from triglyceride before their β-oxidation in mitochondria in a coordinated and stepwise manner. To determine the independent and interdependent roles of hepatic triglyceride hydrolysis and fatty acid oxidation, mice were generated with a liver-specific defect in triglyceride hydrolysis (AtglL–/–), fatty acid oxidation (Cpt2L–/–), or both (double knockout). The loss of either gene resulted in the compensatory increase in the other, demonstrating their coordination. The loss of individual components of fatty acid catabolism (carnitine palmitoyl transferase 2 [Cpt2], adipose triglyceride lipase [Atgl], and Pparα) resulted in largely independent effects on hepatocyte morphology, intermediary metabolism, and gene expression in response to fasting. However, high-fat feeding revealed the interdependent role of Atgl and Cpt2, as the loss of only one of the genes resulted in steatosis (fatty liver) but the loss of both components resulted in significant steatohepatitis (inflammation and fibrosis). Lipolysis and β-oxidation are intimately linked within a continuous pathway, and disruption of their coordination leads to unique cellular and molecular phenotypes that ultimately result in liver disease.
Authors
Ebru S. Selen, Joseph Choi, Michael J. Wolfgang
Abstract
Reduced expression of the plasma membrane citrate transporter INDY (acronym I’m Not Dead, Yet) extends life span in lower organisms. Deletion of the mammalian Indy (mIndy) gene in rodents improves metabolism via mechanisms akin to caloric restriction, known to lower blood pressure (BP) by sympathoadrenal inhibition. We hypothesized that mIndy deletion attenuates sympathoadrenal support of BP. Continuous arterial BP and heart rate (HR) were reduced in mINDY-KO mice. Concomitantly, urinary catecholamine content was lower, and the decreases in BP and HR by mIndy deletion were attenuated after autonomic ganglionic blockade. Catecholamine biosynthesis pathways were reduced in mINDY-KO adrenals using unbiased microarray analysis. Citrate, the main mINDY substrate, increased catecholamine content in pheochromocytoma cells, while pharmacological inhibition of citrate uptake blunted the effect. Our data suggest that deletion of mIndy reduces sympathoadrenal support of BP and HR by attenuating catecholamine biosynthesis. Deletion of mIndy recapitulates beneficial cardiovascular and metabolic responses to caloric restriction, making it an attractive therapeutic target.
Authors
Diana M. Willmes, Martin Daniels, Anica Kurzbach, Stefanie Lieske, Nicole Bechmann, Tina Schumann, Christine Henke, Nermeen N. El-Agroudy, Andrey C. Da Costa Goncalves, Mirko Peitzsch, Anja Hofmann, Waldemar Kanczkowski, Kristin Kräker, Dominik N. Müller, Henning Morawietz, Andreas Deussen, Michael Wagner, Ali El-Armouche, Stephen L. Helfand, Stephan R. Bornstein, Rafael de Cabo, Michel Bernier, Graeme Eisenhofer, Jens Tank, Jens Jordan, Andreas L. Birkenfeld
Abstract
Somatostatin (SS) inhibits glucagon-like peptide-1 (GLP-1) secretion in a paracrine manner. We hypothesized that blocking somatostatin subtype receptor 2 (SSTR2) and 5 (SSTR5) would improve glycaemia by enhancing GLP-1 secretion. In the perfused mouse small intestine the selective SSTR5 antagonist (SSTR5a) stimulated glucose-induced GLP-1 secretion to a larger degree than the SSTR2 antagonist (SSTR2a). In parallel, mice lacking the SSTR5R showed increased glucose-induced GLP-1 secretion. Both antagonists improved glycaemia in vivo in a GLP-1 receptor (GLP-1R) dependent manner, as the glycaemic improvements were absent in mice with impaired GLP-1R signalling and in mice treated with a GLP-1R specific antagonist. SSTR5a had no direct effect on insulin secretion in the perfused pancreas whereas SSTR2a increased insulin secretion in a GLP-1R independent manner. Adding a dipeptidyl peptidase 4 inhibitor (DPP-4i) in vivo resulted in additive effects on glycaemia, however, when glucose was administered intraperitoneally the antagonists was incapable of lowering blood glucose. Oral administration of SSTR5a, but not SSTR2a lowered blood glucose in diet induced obese mice. In summary, we demonstrate that selective SSTR antagonists can improve glucose control primarily through the intestinal GLP-1 system in mice.
Authors
Sara L. Jepsen, Nicolai J. Wewer Albrechtsen, Johanne Agerlin Windeløv, Katrine D. Galsgaard, Jenna Elizabeth Hunt, Thomas B. Farb, Hannelouise Kissow, Jens Pedersen, Carolyn F. Deacon, Rainer E. Martin, Jens J. Holst
Abstract
MC4R mutations represent the largest monogenic cause of obesity, resulting mainly from receptor misfolding and intracellular retention by the cellular quality control system. The present study aimed at determining whether pharmacological chaperones (PC) that restore folding and plasma membrane trafficking by stabilizing near native protein conformation, may represent valid therapeutic avenues for the treatment of melanocortin type 4 receptor (MC4R) linked obesity.To test the therapeutic PC potential, we engineered humanized MC4R mouse models expressing either the wild type (WT) human MC4R or a prevalent obesity-causing mutant (R165W). Administration of a PC able to rescue cell surface expression and functional activity of R165W-hMC4R in cells, restored the anorexigenic response of the R165W-hMC4R obese mice to melanocortin agonist, providing a proof-of-principle for the therapeutic potential of MC4R-targetting PC in vivo. Interestingly, the expression of the WT-hMC4R in mice revealed lower sensitivity of the human receptor to alpha-melanocyte-stimulating hormone (α-MSH) but not β-MSH or MTII, resulting in a lower penetrance obese phenotype in the WT-hMC4R versus R165W-hMC4R mice. In conclusion, we created two new obesity models, one hypomorph highlighting species differences, and one amorphic that provides a pre-clinical model to test the therapeutic potential of PC to treat MC4R-linked obesity.
Authors
Patricia René, Damien Lanfray, Denis Richard, Michel Bouvier
Abstract
Dedifferentiation has been implicated in β cell dysfunction and loss in rodent diabetes. However, the pathophysiological significance in humans remains unclear. To elucidate this, we analyzed surgically resected pancreatic tissues of 26 Japanese subjects with diabetes and 11 nondiabetic subjects, who had been overweight during adulthood but had no family history of diabetes. The diabetic subjects were subclassified into 3 disease stage categories, early, advanced, and intermediate. Despite no numerical changes in endocrine cells immunoreactive for chromogranin A (ChgA), diabetic islets showed profound β cell loss, with an increase in α cells without an increase in insulin and glucagon double-positive cells. The proportion of dedifferentiated cells that retain ChgA immunoreactivity without 4 major islet hormones was strikingly increased in diabetic islets and rose substantially during disease progression. The increased dedifferentiated cell ratio was inversely correlated with declining C-peptide index. Moreover, a subset of islet cells converted into exocrine-like cells during disease progression. These results indicate that islet remodeling with dedifferentiation is the underlying cause of β cell failure during the course of diabetes progression in humans.
Authors
Kikuko Amo-Shiinoki, Katsuya Tanabe, Yoshinobu Hoshii, Hiroto Matsui, Risa Harano, Tatsuya Fukuda, Takato Takeuchi, Ryotaro Bouchi, Tokiyo Takagi, Masayuki Hatanaka, Komei Takeda, Shigeru Okuya, Wataru Nishimura, Atsushi Kudo, Shinji Tanaka, Minoru Tanabe, Takumi Akashi, Tetsuya Yamada, Yoshihiro Ogawa, Eiji Ikeda, Hiroaki Nagano, Yukio Tanizawa
Abstract
Insulin-mediated suppression of white adipose tissue (WAT) lipolysis is an important anabolic function that is dysregulated in states of overnutrition. However, the mechanism of short-term high-fat diet (HFD)-induced WAT insulin resistance is poorly understood. Based on our recent studies we hypothesize that a short-term HFD causes WAT insulin resistance through increases in plasma membrane (PM) sn-1,2-diacylglycerols (DAG), which promotes protein kinase C-ε (PKCε) activation to impair insulin signaling by phosphorylating insulin receptor (Insr) Thr1160. To test this hypothesis, we assessed WAT insulin action in 7-day HFD-fed versus regular chow diet-fed rats during a hyperinsulinemic-euglycemic clamp. HFD feeding caused WAT insulin resistance, reflected by reductions in both insulin-mediated WAT glucose uptake and suppression of WAT lipolysis. These changes were specifically associated with increased PM sn-1,2-diacylglycerol (DAG) content, increased PKCε activation and impaired insulin-stimulated InsrY1162 phosphorylation. In order to examine the role of InsrT1160 phosphorylation in mediating lipid-induced WAT insulin resistance, we examined these same parameters in short-term HFD-fed InsrT1150A knockin mice (mouse homolog for human Thr1160). Similar to the rat study HFD feeding induced WAT insulin resistance in WT control mice but failed to induce WAT insulin resistance in InsrT1150A mice. Taken together these data demonstrate that the PM sn-1,2-DAG - PKCε - InsrT1160 phosphorylation pathway plays an important role in mediating lipid-induced WAT insulin resistance and represents a potential therapeutic target to improve insulin sensitivity in WAT.
Authors
Kun Lyu, Dongyan Zhang, Joongyu D. Song, Xiruo Li, Rachel J. Perry, Varman T. Samuel, Gerald I. Shulman
Abstract
Glucagon regulates glucose and lipid metabolism and also promotes weight loss. Thus, therapeutics stimulating glucagon-receptor (GCGR) signaling are promising for obesity treatment; however, the underlying mechanism(s) have yet to be fully elucidated. We previously identified that hepatic GCGR signaling increases circulating Fibroblast Growth Factor 21 (FGF21), a potent regulator of energy balance. We reported that mice deficient for liver Fgf21 are partially resistant to GCGR-mediated weight loss, implicating FGF21 as a regulator of glucagon’s weight-loss effects. FGF21 signaling requires an obligate co-receptor (B-Klotho, KLB), with expression limited to adipose tissue, liver, pancreas, and brain. We hypothesized that the GCGR-FGF21 system mediates weight loss through a central mechanism. Mice deficient for neuronal Klb (Klb∆CNS) exhibit a partial reduction in body weight with chronic GCGR-agonism (via IUB288) compared to controls (p<0.0001), supporting a role for central FGF21 signaling in GCGR-mediated weight loss. Substantiating these results, mice with central KLB inhibition via a pharmacological KLB antagonist (1153) also display partial weight loss (p<0.0001). Central KLB, however, is dispensable for GCGR-mediated improvements in plasma cholesterol and liver triglycerides. Together, these data suggest GCGR-agonism mediates part of its weight loss properties through central KLB and has implications for future treatments against obesity and metabolic syndrome.
Authors
Shelly R. Nason, Jessica P. Antipenko, Natalie Presedo, Stephen E. Cunningham, Tanya H. Pierre, Teayoun Kim, Jodi R. Paul, Cassie L. Holleman, Martin E. Young, Karen L. Gamble, Brian Finan, Richard DiMarchi, Chad S. Hunter, Alexei Kharitonenkov, Kirk M. Habegger
Abstract
Computational models based on recent maps of the red blood cell proteome suggest that mature erythrocytes may harbor targets for common drugs. This prediction is relevant to red blood cell storage in the blood bank, in which the impact of small molecule drugs or other xenometabolites deriving from dietary, iatrogenic or environmental exposures (“exposome”) may alter erythrocyte energy and redox metabolism and, in so doing, affect red cell storage quality and post-transfusion efficacy. To test this prediction, here we provide a comprehensive characterization of the blood donor exposome, including the detection of common prescription and over-the-counter drugs in 250 units donated by healthy volunteers from the REDS-III RBC Omics study. Based on high-throughput drug screenings of 1,366 FDA-approved drugs, we report a significant impact of ~65% of the tested drugs on erythrocyte metabolism. Machine learning models built using metabolites as predictors were able to accurately predict drugs for several drug classes/targets (bisphosphonates, anticholinergics, calcium channel blockers, adrenergics, proton-pump inhibitors, antimetabolites, selective serotonin reuptake inhibitors, and mTOR) suggesting that these drugs have a direct, conserved, and significant impact on erythrocyte metabolism. As a proof of principle, here we show that the antiacid ranitidine – though rarely detected in the blood donor population – has a strong effect on RBC markers of storage quality in vitro. We thus show that ranitidine supplementation to blood units could improve erythrocyte metabolism and storage quality when supplemented to blood bags, through mechanisms involving sphingosine 1-phosphate-dependent modulation of erythrocyte glycolysis and/or direct binding to hemoglobin.
Authors
Travis Nemkov, Davide Stefanoni, Aarash Bordbar, Aaron Issaian, Bernhard O. Palsson, Larry J. Dumont, Ariel M. Hay, Anren Song, Yang Xia, Jasmina S. Redzic, Elan Z. Eisenmesser, James C. Zimring, Steve Kleinman, Kirk C. Hansen, Michael Busch, Angelo D’Alessandro
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