Issue published March 1, 2005 Previous issue | Next issue
- Volume 115, Issue 3
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Science in Medicine
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Abstract
Gestational diabetes mellitus (GDM) is defined as glucose intolerance of various degrees that is first detected during pregnancy. GDM is detected through the screening of pregnant women for clinical risk factors and, among at-risk women, testing for abnormal glucose tolerance that is usually, but not invariably, mild and asymptomatic. GDM appears to result from the same broad spectrum of physiological and genetic abnormalities that characterize diabetes outside of pregnancy. Indeed, women with GDM are at high risk for having or developing diabetes when they are not pregnant. Thus, GDM provides a unique opportunity to study the early pathogenesis of diabetes and to develop interventions to prevent the disease.
Authors
Thomas A. Buchanan, Anny H. Xiang
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Review Series
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Abstract
The prognosis of heart failure is worse than that of most cancers, but new therapeutic interventions using stem and other cell-based therapies are succeeding in the fight against it, and old drugs, with new twists, are making a comeback. Genetically engineered animal models are driving insights into the molecular mechanisms that cause hearts to fail, accelerating drug discoveries, and inspiring cell-based therapeutic interventions for both acquired and inheritable cardiac diseases.
Authors
Ivor J. Benjamin, Michael D. Schneider
×Abstract
A constant supply of oxygen is indispensable for cardiac viability and function. However, the role of oxygen and oxygen-associated processes in the heart is complex, and they and can be either beneficial or contribute to cardiac dysfunction and death. As oxygen is a major determinant of cardiac gene expression, and a critical participant in the formation of ROS and numerous other cellular processes, consideration of its role in the heart is essential in understanding the pathogenesis of cardiac dysfunction.
Authors
Frank J. Giordano
×Abstract
There is growing evidence that the altered production and/or spatiotemporal distribution of reactive oxygen and nitrogen species creates oxidative and/or nitrosative stresses in the failing heart and vascular tree, which contribute to the abnormal cardiac and vascular phenotypes that characterize the failing cardiovascular system. These derangements at the integrated system level can be interpreted at the cellular and molecular levels in terms of adverse effects on signaling elements in the heart, vasculature, and blood that subserve cardiac and vascular homeostasis.
Authors
Joshua M. Hare, Jonathan S. Stamler
×Abstract
Factors that render patients with cardiovascular disease at high risk for heart failure remain incompletely defined. Recent insights into molecular genetic causes of myocardial diseases have highlighted the importance of single-gene defects in the pathogenesis of heart failure. Through analyses of the mechanisms by which a mutation selectively perturbs one component of cardiac physiology and triggers cell and molecular responses, studies of human gene mutations provide a window into the complex processes of cardiac remodeling and heart failure. Knowledge gleaned from these studies shows promise for defining novel therapeutic targets for genetic and acquired causes of heart failure.
Authors
Hiroyuki Morita, Jonathan Seidman, Christine E. Seidman
×Abstract
In broad terms, there are 3 types of cardiac hypertrophy: normal growth, growth induced by physical conditioning (i.e., physiologic hypertrophy), and growth induced by pathologic stimuli. Recent evidence suggests that normal and exercise-induced cardiac growth are regulated in large part by the growth hormone/IGF axis via signaling through the PI3K/Akt pathway. In contrast, pathological or reactive cardiac growth is triggered by autocrine and paracrine neurohormonal factors released during biomechanical stress that signal through the Gq/phospholipase C pathway, leading to an increase in cytosolic calcium and activation of PKC. Here we review recent developments in the area of these cardiotrophic kinases, highlighting the utility of animal models that are helping to identify molecular targets in the human condition.
Authors
Gerald W. Dorn II, Thomas Force
×Abstract
In response to acute and chronic stresses, the heart frequently undergoes a remodeling process that is accompanied by myocyte hypertrophy, impaired contractility, and pump failure, often culminating in sudden death. The existence of redundant signaling pathways that trigger heart failure poses challenges for therapeutic intervention. Cardiac remodeling is associated with the activation of a pathological gene program that weakens cardiac performance. Thus, targeting the disease process at the level of gene expression represents a potentially powerful therapeutic approach. In this review, we describe strategies for normalizing gene expression in the failing heart with small molecules that control signal transduction pathways directed at transcription factors and associated chromatin-modifying enzymes.
Authors
Timothy A. McKinsey, Eric N. Olson
×Abstract
The mitochondrion serves a critical role as a platform for energy transduction, signaling, and cell death pathways relevant to common diseases of the myocardium such as heart failure. This review focuses on the molecular regulatory events and downstream effector pathways involved in mitochondrial energy metabolic derangements known to occur during the development of heart failure.
Authors
Janice M. Huss, Daniel P. Kelly
×Abstract
Structural and functional alterations in the Ca2+ regulatory proteins present in the sarcoplasmic reticulum have recently been shown to be strongly involved in the pathogenesis of heart failure. Chronic activation of the sympathetic nervous system or of the renin-angiotensin system induces abnormalities in both the function and structure of these proteins. We review here the considerable body of evidence that has accumulated to support the notion that such abnormalities contribute to a defectiveness of contractile performance and hence to the progression of heart failure.
Authors
Masafumi Yano, Yasuhiro Ikeda, Masunori Matsuzaki
×Abstract
Recently, low — but abnormal — rates of cardiomyocyte apoptosis have been observed in failing human hearts. Genetic and pharmacological studies suggest that this cell death is causally linked to heart failure in rodent models. Herein, we review these data and discuss potential therapeutic implications.
Authors
Roger S.-Y. Foo, Kartik Mani, Richard N. Kitsis
×Abstract
In humans, the biological limitations to cardiac regenerative growth create both a clinical imperative — to offset cell death in acute ischemic injury and chronic heart failure — and a clinical opportunity; that is, for using cells, genes, and proteins to rescue cardiac muscle cell number or in other ways promote more efficacious cardiac repair. Recent experimental studies and early-phase clinical trials lend credence to the visionary goal of enhancing cardiac repair as an achievable therapeutic target.
Authors
Stefanie Dimmeler, Andreas M. Zeiher, Michael D. Schneider
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Commentaries
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Abstract
The causative genes for essential tremor (ET), one of the most common genetic neurological disorders, have eluded scientists despite intensive search. Two gene loci linked to ET, one on chromosome 3q13 and another on chromosome 2p24.1, have been identified, and a missense mutation in the HS1-BP3 gene on the 2p has been suggested as the cause of the disorder in about 10% of American ET patients. Therefore, the genetic basis for the vast majority of familial ET is still unknown. In this issue of the JCI, the gene coding for the γ-aminobutyric acidA (GABAA) receptor α1 subunit is suggested as a potential candidate gene for ET, as mice lacking the gene express a phenotype that overlaps with some clinical characteristics of the human condition.
Authors
Joseph Jankovic, Jeffrey L. Noebels
×Abstract
Recently, type I interferons IFN-α and IFN-β (IFN-α/β) have been evaluated in pilot clinical trials for the treatment of active ulcerative colitis. However, the underlying mechanisms that may contribute to a potential therapeutic effect are incompletely understood. A new study in this issue demonstrates a protective role for IFN-α/β, induced by activation of a Toll-like receptor 9–dependent pathway, in a rodent model of experimental colitis.
Authors
Stefan Wirtz, Markus F. Neurath
×Abstract
Remodeling of the arterial wall occurs mainly as a consequence of increased wall stress caused by hypertension. In this issue of the JCI, Azizi et al. report that in humans with a kallikrein gene polymorphism that lowers kallikrein activity, the brachial artery undergoes eutrophic inward remodeling in the absence of hypertension or other hemodynamic changes. It has also been reported that alterations of the kallikrein-kinin system are associated with formation of aortic aneurysms. Conversely, after vascular injury, kinins mediate the beneficial effect of angiotensin-converting enzyme inhibitors that prevent neointima formation. These findings raise the intriguing possibility that decreased kallikrein-kinin system activity may play an important role in the pathogenesis of vascular remodeling and disease, while increased activity may have a beneficial effect.
Authors
Oscar A. Carretero
×Abstract
Numerous viruses cause latent infections in humans, and reactivation often results in pain and suffering. While vaccines for several of these viruses are available or currently being studied in clinical trials, and antiviral therapies have been successful in preventing or treating active infection, therapy to eradicate latent infection has lagged behind. A new study reported in this issue of the JCI shows that treatment of cells latently infected with Kaposi sarcoma–associated herpesvirus (KSHV) with glycyrrhizic acid, a component of licorice, reduces synthesis of a viral latency protein and induces apoptosis of infected cells. This finding suggests a novel way to interrupt latency.
Authors
Jeffrey I. Cohen
×Abstract
The DEAD-box RNA helicases are enzymes involved in many critical aspects of RNA metabolism within both eukaryotic and prokaryotic organisms. Several studies have shown that these proteins may have important functions in mediating microbial pathogenesis. A new study in this issue of the JCI identifies the first DEAD-box RNA helicase in the pathogenic fungus Cryptococcus neoformans and proposes novel roles for this family of proteins in the development and progression of cryptococcosis.
Authors
Lena J. Heung, Maurizio Del Poeta
×Abstract
Recent evidence has demonstrated that endothelial-specific growth factors affect the development of apparently unrelated organs and cells. Expanding this evidence further, new findings in this issue of the JCI show that neurotrophic factors can affect neovascularization. Neurotrophic factors achieve proangiogenic effects not only by directly affecting endothelial cells, but also by recruiting hematopoietic precursors. Further understanding of the biology of angiogenic factors, as well as of the function of hematopoietic cells in tissue neovascularization, will lead to improved therapeutic strategies for the treatment of diseases ranging from ischemia to cancer.
Authors
Dan G. Duda, Rakesh K. Jain
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Research Articles
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Abstract
MMPs are implicated in LV remodeling after acute myocardial infarction (MI). To analyze the role of MMP-2, we generated MI by ligating the left coronary artery of MMP-2–KO and WT mice, the latter of which were administered orally an MMP-2–selective inhibitor or vehicle (TISAM). The survival rate was significantly higher in MMP-2–KO and TISAM-treated mice than in control WT mice. The main cause of mortality in control WT mice was cardiac rupture, which was not observed in MMP-2–KO or TISAM-treated mice. Control WT mice, but not MMP-2–KO or TISAM-treated mice, showed activation of the zymogen of MMP-2, strong gelatinolytic activity, and degradation of ECM components, including laminin and fibronectin, in the infarcted myocardium. Although infarcted cardiomyocytes in control WT mice were rapidly removed by macrophages, the removal was suppressed in MMP-2–KO and TISAM-treated mice. Macrophage migration was induced by the infarcted myocardial tissue from control WT mice and was inhibited by treatment of macrophages with laminin or fibronectin peptides prior to migration assay. These data suggest that inhibition of MMP-2 activity improves the survival rate after acute MI by preventing cardiac rupture and delays post-MI remodeling through a reduction in macrophage infiltration.
Authors
Shin-ichiro Matsumura, Shiro Iwanaga, Satsuki Mochizuki, Hiroyuki Okamoto, Satoshi Ogawa, Yasunori Okada
×Abstract
Neutrophil gelatinase–associated lipocalin (Ngal), also known as siderocalin, forms a complex with iron-binding siderophores (Ngal:siderophore:Fe). This complex converts renal progenitors into epithelial tubules. In this study, we tested the hypothesis that Ngal:siderophore:Fe protects adult kidney epithelial cells or accelerates their recovery from damage. Using a mouse model of severe renal failure, ischemia-reperfusion injury, we show that a single dose of Ngal (10 μg), introduced during the initial phase of the disease, dramatically protects the kidney and mitigates azotemia. Ngal activity depends on delivery of the protein and its siderophore to the proximal tubule. Iron must also be delivered, since blockade of the siderophore with gallium inhibits the rescue from ischemia. The Ngal:siderophore:Fe complex upregulates heme oxygenase-1, a protective enzyme, preserves proximal tubule N-cadherin, and inhibits cell death. Because mouse urine contains an Ngal-dependent siderophore-like activity, endogenous Ngal might also play a protective role. Indeed, Ngal is highly accumulated in the human kidney cortical tubules and in the blood and urine after nephrotoxic and ischemic injury. We reveal what we believe to be a novel pathway of iron traffic that is activated in human and mouse renal diseases, and it provides a unique method for their treatment.
Authors
Kiyoshi Mori, H. Thomas Lee, Dana Rapoport, Ian R. Drexler, Kirk Foster, Jun Yang, Kai M. Schmidt-Ott, Xia Chen, Jau Yi Li, Stacey Weiss, Jaya Mishra, Faisal H. Cheema, Glenn Markowitz, Takayoshi Suganami, Kazutomo Sawai, Masashi Mukoyama, Cheryl Kunis, Vivette D’Agati, Prasad Devarajan, Jonathan Barasch
×The secreted glycoprotein lubricin protects cartilage surfaces and inhibits synovial cell overgrowth
Abstract
The long-term integrity of an articulating joint is dependent upon the nourishment of its cartilage component and the protection of the cartilage surface from friction-induced wear. Loss-of-function mutations in lubricin (a secreted glycoprotein encoded by the gene PRG4) cause the human autosomal recessive disorder camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP). A major feature of CACP is precocious joint failure. In order to delineate the mechanism by which lubricin protects joints, we studied the expression of Prg4 mRNA during mouse joint development, and we created lubricin-mutant mice. Prg4 began to be expressed in surface chondrocytes and synoviocytes after joint cavitation had occurred and remained strongly expressed by these cells postnatally. Mice lacking lubricin were viable and fertile. In the newborn period, their joints appeared normal. As the mice aged, we observed abnormal protein deposits on the cartilage surface and disappearance of underlying superficial zone chondrocytes. In addition to cartilage surface changes and subsequent cartilage deterioration, intimal cells in the synovium surrounding the joint space became hyperplastic, which further contributed to joint failure. Purified or recombinant lubricin inhibited the growth of these synoviocytes in vitro. Tendon and tendon sheath involvement was present in the ankle joints, where morphologic changes and abnormal calcification of these structures were observed. We conclude that lubricin has multiple functions in articulating joints and tendons that include the protection of surfaces and the control of synovial cell growth.
Authors
David K. Rhee, Jose Marcelino, MacArthur Baker, Yaoqin Gong, Patrick Smits, Véronique Lefebvre, Gregory D. Jay, Matthew Stewart, Hongwei Wang, Matthew L. Warman, John D. Carpten
×Abstract
The study of fungal regulatory networks is essential to the understanding of how these pathogens respond to host environmental signals with effective virulence-associated traits. In this study, a virulence-associated DEAD-box RNA helicase–encoding gene (VAD1) was isolated from a mutant defective in the virulence factor laccase. A Δvad1 mutant exhibited a profound reduction in virulence in a mouse model that was restored after reconstitution with WT VAD1. Loss of VAD1 resulted in upregulation of NOT1, a gene encoding a global repressor of transcription. NOT1 was found to act as an intermediary transcriptional repressor of laccase. Vad1 was located within macromolecular complexes that formed cytoplasmic granular bodies in mature cells and during infection of mouse brain. In addition, VAD1 was shown by in situ hybridization to be expressed in the brain of an AIDS patient coinfected with C. neoformans. To understand the role of VAD1 in virulence, a functional genomics approach was used to identify 3 additional virulence determinants dependent on VAD1: PCK1, TUF1, and MPF3, involved in gluconeogenesis, mitochondrial protein synthesis, and cell wall integrity, respectively. These data show that fungal virulence-associated genes are coordinately regulated and that an analysis of such transcriptomes allows for the identification of important new genes involved in the normal growth and virulence of fungal pathogens.
Authors
John Panepinto, Lide Liu, Jeanie Ramos, Xudong Zhu, Tibor Valyi-Nagy, Saliha Eksi, Jianmin Fu, H. Ari Jaffe, Brian Wickes, Peter R. Williamson
×Abstract
Kaposi sarcoma–associated herpesvirus (KSHV) is linked with all clinical forms of Kaposi sarcoma and several lymphoproliferative disorders. Like other herpesviruses, KSHV becomes latent in the infected cells, expressing only a few genes that are essential for the establishment and maintenance of its latency and for the survival of the infected cells. Inhibiting the expression of these latent genes should lead to eradication of herpesvirus infection. All currently available drugs are ineffective against latent infection. Here we show, for the first time to our knowledge, that latent infection with KSHV in B lymphocytes can be terminated by glycyrrhizic acid (GA), a triterpenoid compound earlier shown to inhibit the lytic replication of other herpesviruses. We demonstrate that GA disrupts latent KSHV infection by downregulating the expression of latency-associated nuclear antigen (LANA) and upregulating the expression of viral cyclin and selectively induces cell death of KSHV-infected cells. We show that reduced levels of LANA lead to p53 reactivation, an increase in ROS, and mitochondrial dysfunction, which result in G1 cell cycle arrest, DNA fragmentation, and oxidative stress–mediated apoptosis. Latent genes are involved in KSHV-induced oncogenesis, and strategies to interfere with their expression might prove useful for eradicating latent KSHV infection and have future therapeutic implications.
Authors
Francesca Curreli, Alvin E. Friedman-Kien, Ornella Flore
×Abstract
The neurotrophin brain-derived neurotrophic factor (BDNF) is required for the maintenance of cardiac vessel wall stability during embryonic development through direct angiogenic actions on endothelial cells expressing the tropomysin receptor kinase B (TrkB). However, the role of BDNF and a related neurotrophin ligand, neurotrophin-4 (NT-4), in the regulation of revascularization of the adult tissues is unknown. To study the potential angiogenic capacity of BDNF in mediating the neovascularization of ischemic and non-ischemic adult mouse tissues, we utilized a hindlimb ischemia and a subcutaneous Matrigel model. Recruitment of endothelial cells and promotion of channel formation within the Matrigel plug by BDNF and NT-4 was comparable to that induced by VEGF-A. The introduction of BDNF into non-ischemic ears or ischemic limbs induced neoangiogenesis, with a 2-fold increase in the capillary density. Remarkably, treatment with BDNF progressively increased blood flow in the ischemic limb over 21 days, similar to treatment with VEGF-A. The mechanism by which BDNF enhances capillary formation is mediated in part through local activation of the TrkB receptor and also by recruitment of Sca-1+CD11b+ pro-angiogenic hematopoietic cells. BDNF induces a potent direct chemokinetic action on subsets of marrow-derived Sca-1+ hematopoietic cells co-expressing TrkB. These studies suggest that local regional delivery of BDNF may provide a novel mechanism for inducing neoangiogenesis through both direct actions on local TrkB-expressing endothelial cells in skeletal muscle and recruitment of specific subsets of TrkB+ bone marrow–derived hematopoietic cells to provide peri-endothelial support for the newly formed vessels.
Authors
Pouneh Kermani, Dahlia Rafii, David K. Jin, Paul Whitlock, Wendy Schaffer, Anne Chiang, Loic Vincent, Matthias Friedrich, Koji Shido, Neil R. Hackett, Ronald G. Crystal, Shahin Rafii, Barbara L. Hempstead
×Abstract
Inactivation of the growth factor–regulated S6 kinase RSK2 causes Coffin-Lowry syndrome in humans, an X-linked mental retardation condition associated with progressive skeletal abnormalities. Here we show that mice lacking RSK2 develop a progressive skeletal disease, osteopenia due to impaired osteoblast function and normal osteoclast differentiation. The phenotype is associated with decreased expression of Phex, an endopeptidase regulating bone mineralization. This defect is probably not mediated by RSK2-dependent phosphorylation of c-Fos on serine 362 in the C-terminus. However, in the absence of RSK2, c-Fos–dependent osteosarcoma formation is impaired. The lack of c-Fos phosphorylation leads to reduced c-Fos protein levels, which are thought to be responsible for decreased proliferation and increased apoptosis of transformed osteoblasts. Therefore, RSK2-dependent stabilization of c-Fos is essential for osteosarcoma formation in mice and may also be important for human osteosarcomas.
Authors
Jean-Pierre David, Denis Mehic, Latifa Bakiri, Arndt F. Schilling, Vice Mandic, Matthias Priemel, Maria Helena Idarraga, Markus O. Reschke, Oskar Hoffmann, Michael Amling, Erwin F. Wagner
×Abstract
Blockade of prostaglandin (PG) production by COX inhibitors is the treatment of choice for inflammatory pain but is also prone to severe side effects. Identification of signaling elements downstream of COX inhibition, particularly of PG receptor subtypes responsible for pain sensitization (hyperalgesia), provides a strategy for better-tolerated analgesics. Here, we have identified PGE2 receptors of the EP2 receptor subtype as key signaling elements in spinal inflammatory hyperalgesia. Mice deficient in EP2 receptors (EP2–/– mice) completely lack spinal PGE2-evoked hyperalgesia. After a peripheral inflammatory stimulus, EP2–/– mice exhibit only short-lasting peripheral hyperalgesia but lack a second sustained hyperalgesic phase of spinal origin. Electrophysiological recordings identify diminished synaptic inhibition of excitatory dorsal horn neurons as the dominant source of EP2 receptor–dependent hyperalgesia. Our results thus demonstrate that inflammatory hyperalgesia can be treated by targeting of a single PG receptor subtype and provide a rational basis for new analgesic strategies going beyond COX inhibition.
Authors
Heiko Reinold, Seifollah Ahmadi, Ulrike B. Depner, Beate Layh, Cornelia Heindl, May Hamza, Andreas Pahl, Kay Brune, Shuh Narumiya, Ulrike Müller, Hanns Ulrich Zeilhofer
×Abstract
Rap1b, an abundant small GTPase in platelets, becomes rapidly activated upon stimulation with agonists. Though it has been implicated to act downstream from G protein–coupled receptors (GPCRs) and upstream of integrin αIIbβ3, the precise role of Rap1b in platelet function has been elusive. Here we report the generation of a murine rap1b knockout and show that Rap1b deficiency results in a bleeding defect due to defective platelet function. Aggregation of Rap1b-null platelets is reduced in response to stimulation with both GPCR-linked and GPCR-independent agonists. Underlying the defective Rap1b-null platelet function is decreased activation of integrin αIIbβ3 in response to stimulation with agonists and signaling downstream from the integrin αIIbβ3. In vivo, Rap1b-null mice are protected from arterial thrombosis. These data provide genetic evidence that Rap1b is involved in a common pathway of integrin activation, is required for normal hemostasis in vivo, and may be a clinically relevant antithrombotic therapy target.
Authors
Magdalena Chrzanowska-Wodnicka, Susan S. Smyth, Simone M. Schoenwaelder, Thomas H. Fischer, Gilbert C. White II
×Abstract
Coagulase-negative staphylococci, with the leading species Staphylococcus epidermidis, are the predominant cause of hospital-acquired infections. Treatment is especially difficult owing to biofilm formation and frequent antibiotic resistance. However, virulence mechanisms of these important opportunistic pathogens have remained poorly characterized. Here we demonstrate that S. epidermidis secretes poly-γ-DL-glutamic acid (PGA) to facilitate growth and survival in the human host. Importantly, PGA efficiently sheltered S. epidermidis from key components of innate host defense, namely antimicrobial peptides and neutrophil phagocytosis, and was indispensable for persistence during device-related infection. Furthermore, PGA protected S. epidermidis from high salt concentration, a key feature of its natural environment, the human skin. Notably, PGA was synthesized by all tested strains of S. epidermidis and a series of closely related coagulase-negative staphylococci, most of which are opportunistic pathogens. Our study presents important novel biological functions for PGA and indicates that PGA represents an excellent target for therapeutic maneuvers aimed at treating disease caused by S. epidermidis and related staphylococci.
Authors
Stanislava Kocianova, Cuong Vuong, Yufeng Yao, Jovanka M. Voyich, Elizabeth R. Fischer, Frank R. DeLeo, Michael Otto
×Abstract
Experimental colitis is mediated by inflammatory or dysregulated immune responses to microbial factors of the gastrointestinal tract. In this study we observed that administration of Toll-like receptor 9 (TLR9) agonists suppressed the severity of experimental colitis in RAG1–/– but not in SCID mice. This differential responsiveness between phenotypically similar but genetically distinct animals was related to a partial blockade in TLR9 signaling and defective production of type I IFN (i.e., IFN-α/β) in SCID mice upon TLR9 stimulation. The addition of neutralization antibodies against type I IFN abolished the antiinflammatory effects induced by TLR9 agonists, whereas the administration of recombinant IFN-β mimicked the antiinflammatory effects induced by TLR9 agonists in this model. Furthermore, mice deficient in the IFN-α/β receptor exhibited more severe colitis than wild-type mice did upon induction of experimental colitis. These results indicate that TLR9-triggered type I IFN has antiinflammatory functions in colitis. They also underscore the important protective role of type I IFN in intestinal homeostasis and suggest that strategies to modulate innate immunity may be of therapeutic value for the treatment of intestinal inflammatory conditions.
Authors
Kyoko Katakura, Jongdae Lee, Daniel Rachmilewitz, Gloria Li, Lars Eckmann, Eyal Raz
×Abstract
The capacity to adjust energy intake in response to changing energy requirements is a defining feature of energy homeostasis. Despite the identification of leptin as a key mediator of this process, the mechanism whereby changes of body adiposity are coupled to adaptive, short-term adjustments of energy intake remains poorly understood. To investigate the physiological role of leptin in the control of meal size and the response to satiety signals, and to identify brain areas mediating this effect, we studied Koletsky (fak/fak) rats, which develop severe obesity due to the genetic absence of leptin receptors. Our finding of markedly increased meal size and reduced satiety in response to the gut peptide cholecystokinin (CCK) in these leptin receptor–deficient animals suggests a critical role for leptin signaling in the response to endogenous signals that promote meal termination. To determine if the hypothalamic arcuate nucleus (ARC) (a key forebrain site of leptin action) mediates this leptin effect, we used adenoviral gene therapy to express either functional leptin receptors or a reporter gene in the area of the ARC of fak/fak rats. Restoration of leptin signaling to this brain area normalized the effect of CCK on the activation of neurons in the nucleus of the solitary tract and area postrema, key hindbrain areas for processing satiety-related inputs. This intervention also reduced meal size and enhanced CCK-induced satiety in fak/fak rats. These findings demonstrate that forebrain signaling by leptin, a long-term regulator of body adiposity, limits food intake on a meal-to-meal basis by regulating the hindbrain response to short-acting satiety signals.
Authors
Gregory J. Morton, James E. Blevins, Diana L. Williams, Kevin D. Niswender, Richard W. Gelling, Christopher J. Rhodes, Denis G. Baskin, Michael W. Schwartz
×Abstract
Herpesvirus entry mediator (HVEM), a TNF receptor superfamily member, has been previously described as a T cell costimulatory receptor. Surprisingly, HVEM–/– T cells showed enhanced responses to in vitro concanavalin A (ConA) stimulation when compared with WT T cells. Consistent with these findings, HVEM–/– mice exhibited increased morbidity and mortality as compared with WT mice in a model of ConA-mediated T cell–dependent autoimmune hepatitis. HVEM–/– mice produced higher levels of multiple cytokines, which were dependent on the presence of CD4+ T cells. Furthermore, HVEM–/– mice were more susceptible to MOG peptide–induced experimental autoimmune encephalopathy, and they showed increased T cell proliferation and cytokine production in response to antigen-specific challenge. Taken together, our data revealed an unexpected regulatory role of HVEM in T cell–mediated immune responses and autoimmune diseases.
Authors
Yang Wang, Sumit K. Subudhi, Robert A. Anders, James Lo, Yonglian Sun, Sarah Blink, Yugang Wang, Jing Wang, Xiaojuan Liu, Karin Mink, Daniel Degrandi, Klaus Pfeffer, Yang-Xin Fu
×Abstract
Hepatic insulin resistance is a critical component in the development of type 2 diabetes mellitus. In many cases, insulin resistance in liver is associated with reduced expression of both major insulin receptor substrate (IRS) proteins, IRS-1 and IRS-2. To investigate the specific functions of IRS-1 and IRS-2 in regulating liver function in vivo, we developed an adenovirus-mediated RNA interference technique in which short hairpin RNAs (shRNAs) are used to knock down IRS-1, IRS-2, or both, by 70–80% in livers of WT mice. The knockdown of IRS-1 resulted in an upregulation of the gluconeogenic enzymes glucose-6 phosphatase and phosphoenolpyruvate carboxykinase, as well as a marked increase in hepatic nuclear factor–4 α. Decreased IRS-1 was also associated with a decrease in glucokinase expression and a trend toward increased blood glucose, whereas knockdown of IRS-2 resulted in the upregulation of lipogenic enzymes SREBP-1c and fatty acid synthase, as well as increased hepatic lipid accumulation. The concomitant injection of IRS-1 and IRS-2 adenoviral shRNAs resulted in systemic insulin resistance, glucose intolerance, and hepatic steatosis. The alterations in the dual-knockdown mice were associated with defective Akt activation and Foxo1 phosphorylation. Taken together, our results demonstrate that hepatic IRS-1 and IRS-2 have complementary roles in the control of hepatic metabolism, with IRS-1 more closely linked to glucose homeostasis and IRS-2 more closely linked to lipid metabolism.
Authors
Cullen M. Taniguchi, Kohjiro Ueki, C. Ronald Kahn
×Abstract
Omenn syndrome is a severe primary immunodeficiency with putative autoimmune manifestations of the skin and gastrointestinal tract. The disease is caused by hypomorphic mutations in recombination-activating genes that impair but do not abolish the process of VDJ recombination, leading to the generation of autoreactive T cells with a highly restricted receptor repertoire. Loss of central tolerance in genetically determined autoimmune diseases, e.g., autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy, is associated with defective expression by medullary thymic epithelial cells of AIRE, the transcription activator that induces thymic expression of tissue-specific antigens. Analysis of AIRE expression in the thymi of 2 Omenn syndrome patients and 1 SCID patient, by real-time RT-PCR and immunohistochemistry, demonstrated a profound reduction in the levels of AIRE mRNA and protein in patients as compared with a normal control subject. Lack of AIRE was associated with normal or even increased levels of keratin and lymphotoxin-β receptor mRNAs, while mRNAs of the self-antigens insulin, cytochrome P450 1a2, and fatty acid–binding protein were undetectable in thymi from immunodeficiency patients. These results demonstrate that deficiency of AIRE expression is observed in severe immunodeficiencies characterized by abnormal T cell development and suggest that in Omenn syndrome, the few residual T cell clones that develop may escape negative selection and thereafter expand in the periphery, causing massive autoimmune reactions.
Authors
Patrizia Cavadini, William Vermi, Fabio Facchetti, Stefania Fontana, Seiho Nagafuchi, Evelina Mazzolari, Anna Sediva, Veronica Marrella, Anna Villa, Alain Fischer, Luigi D. Notarangelo, Raffaele Badolato
×Abstract
Regions in the vasculature that are exposed to steady laminar blood flow are protected from atherosclerosis as compared with regions where flow is disturbed. We found that flow decreased TNF-mediated VCAM1 expression by inhibiting JNK and p38. JNK inhibition correlated with inhibition of apoptosis signal–regulating kinase 1 (ASK1), a JNK and p38 activator. Thioredoxin-interacting protein (TXNIP) is a stress-responsive protein that inhibits thioredoxin (TRX) activity. Since thioredoxin inhibits ASK1, we hypothesized that changes in TXNIP-TRX-ASK1 interactions mediate the antiinflammatory effects of flow. To explore this, we used perfused vessels and cultured ECs. Exposure of rabbit aortae or ECs to normal flow (12 dyn/cm2, 24 hours) was associated with decreased TXNIP expression and increased TRX activity compared with exposure to low flow (0.4 dyn/cm2). Normal flow inhibited TNF activation of JNK/p38 and VCAM1 expression. In cultured ECs, reduction of TXNIP expression by small interfering RNA increased TRX binding to ASK1 and inhibited TNF activation of JNK/p38 and VCAM1 expression. Conversely, overexpression of TXNIP stimulated JNK and p38. In aortae from TXNIP-deficient mice, TNF-induced VCAM1 expression was inhibited. The data suggest that TXNIP and TRX are key components of biomechanical signal transduction and establish them as potentially novel regulators of TNF signaling and inflammation in ECs.
Authors
Hideyuki Yamawaki, Shi Pan, Richard T. Lee, Bradford C. Berk
×Abstract
The induction of potent CD8+ T cell responses by vaccines to fight microbes or tumors remains a major challenge, as many candidates for human vaccines have proved to be poorly immunogenic. Deoxycytidyl-deoxyguanosin oligodeoxynucleotides (CpG ODNs) trigger Toll-like receptor 9, resulting in dendritic cell maturation that can enhance immunogenicity of peptide-based vaccines in mice. We tested whether a synthetic ODN, CpG 7909, could improve human tumor antigen–specific CD8+ T cell responses. Eight HLA-A2+ melanoma patients received 4 monthly vaccinations of low-dose CpG 7909 mixed with melanoma antigen A (Melan-A; identical to MART-1) analog peptide and incomplete Freund’s adjuvant. All patients exhibited rapid and strong antigen-specific T cell responses: the frequency of Melan-A–specific T cells reached over 3% of circulating CD8+ T cells. This was one order of magnitude higher than the frequency seen in 8 control patients treated similarly but without CpG and 1–3 orders of magnitude higher than that seen in previous studies with synthetic vaccines. The enhanced T cell populations consisted primarily of effector memory cells, which in part secreted IFN-γ and expressed granzyme B and perforin ex vivo. In vitro, T cell clones recognized and killed melanoma cells in an antigen-specific manner. Thus, CpG 7909 is an efficient vaccine adjuvant that promotes strong antigen-specific CD8+ T cell responses in humans.
Authors
Daniel E. Speiser, Danielle Liénard, Nathalie Rufer, Verena Rubio-Godoy, Donata Rimoldi, Ferdy Lejeune, Arthur M. Krieg, Jean-Charles Cerottini, Pedro Romero
×Abstract
Genetic factors are known to strongly influence susceptibility to allergic inflammation. The Th2 cytokine IL-13 is a central mediator of allergy and asthma, and common single-nucleotide polymorphisms in IL13 are associated with allergic phenotypes in several ethnically diverse populations. In particular, IL13+2044G→A is expected to result in the nonconservative replacement of arginine 130 (R130) with glutamine (Q). We examined the impact of IL13+2044G→A on the functional properties of IL-13 by directly comparing the activity of WT IL-13 and IL-13 R130Q on primary human cells involved in the effector mechanisms of allergic inflammation. Our results show that IL-13 R130Q was significantly more active than WT IL-13 in inducing STAT6 phosphorylation and CD23 expression in monocytes and hydrocortisone-dependent IgE switching in B cells. Notably, IL-13 R130Q was neutralized less effectively than WT IL-13 by an IL-13Rα2 decoy. Decreased neutralization of the minor variant could contribute to its enhanced in vivo activity. Neither IL-13 variant was able to engage T cells, which suggests that increased allergic inflammation in carriers of IL13+2044A depends on enhanced IL-13–mediated Th2 effector functions rather than increased Th2 differentiation. Collectively, our data indicate that natural variation in the coding region of IL13 may be an important genetic determinant of susceptibility to allergy.
Authors
Frank D. Vladich, Susan M. Brazille, Debra Stern, Michael L. Peck, Raffaella Ghittoni, Donata Vercelli
×Abstract
Due to its relatively slow clinical progression, B cell chronic lymphocytic leukemia (B-CLL) is classically described as a disease of accumulation rather than proliferation. However, evidence for various forms of clonal evolution suggests that B-CLL clones may be more dynamic than previously assumed. We used a nonradioactive, stable isotopic labeling method to measure B-CLL cell kinetics in vivo. Nineteen patients drank an aliquot of deuterated water (2H2O) daily for 84 days, and 2H incorporation into the deoxyribose moiety of DNA of newly divided B-CLL cells was measured by gas chromatography/mass spectrometry, during and after the labeling period. Birth rates were calculated from the kinetic profiles. Death rates were defined as the difference between calculated birth and growth rates. These analyses demonstrated that the leukemic cells of each patient had definable and often substantial birth rates, varying from 0.1% to greater than 1.0% of the entire clone per day. Those patients with birth rates greater than 0.35% per day were much more likely to exhibit active or to develop progressive disease than those with lower birth rates Thus, B-CLL is not a static disease that results simply from accumulation of long-lived lymphocytes. Rather, it is a dynamic process composed also of cells that proliferate and die, often at appreciable levels. The extent to which this turnover occurs has not been previously appreciated. A correlation between birth rates and disease activity and progression appears to exist, which may help identify patients at risk for worsening disease in advance of clinical deterioration.
Authors
Bradley T. Messmer, Davorka Messmer, Steven L. Allen, Jonathan E. Kolitz, Prasad Kudalkar, Denise Cesar, Elizabeth J. Murphy, Prasad Koduru, Manlio Ferrarini, Simona Zupo, Giovanna Cutrona, Rajendra N. Damle, Tarun Wasil, Kanti R. Rai, Marc K. Hellerstein, Nicholas Chiorazzi
×Abstract
α-Defensins are abundant antimicrobial peptides in polymorphonuclear leukocytes and play an important role in innate immunity. We have previously shown that α-defensin-1 can inhibit HIV-1 replication following viral entry. Here we examined the molecular mechanism(s) of α-defensin-1–mediated HIV-1 inhibition. α-Defensin-1 had a direct effect on HIV-1 virions at a low MOI in the absence of serum. The direct effect on HIV-1 virions was abolished by the presence of serum or an increase in virus particles. Studying the kinetics of the HIV life cycle revealed that α-defensin-1 inhibited steps following reverse transcription and integration. Analysis of PKC phosphorylation in primary CD4+ T cells in response to α-defensin-1 indicated that α-defensin-1 inhibited PKC activity. Pretreatment of infected CD4+ T cells with a PKC activator, bryostatin 1, partially reversed α-defensin-1–mediated HIV inhibition. Like α-defensin-1, the PKC isoform–selective inhibitor Go6976 blocked HIV-1 infection in a dose-dependent manner. Furthermore, kinetic studies and analysis of HIV-1 products indicated that α-defensin-1 and Go6976 blocked HIV-1 infection at similar stages in its life cycle, including nuclear import and transcription. Taken together, our studies demonstrate that, in the absence of serum, α-defensin-1 may act directly on the virus, but, in the presence of serum, its effects are on the cell, where it inhibits HIV-1 replication. At least 1 of the cellular effects associated with HIV inhibition is interference with PKC signaling in primary CD4+ T cells. Studying the complex function of α-defensin-1 in innate immunity against HIV has implications for prevention as well as therapeutics.
Authors
Theresa L. Chang, Jesus Vargas Jr., Armando DelPortillo, Mary E. Klotman
×Abstract
Essential tremor is the most common movement disorder and has an unknown etiology. Here we report that γ-aminobutyric acidA (GABAA) receptor α1–/– mice exhibit postural and kinetic tremor and motor incoordination that is characteristic of essential tremor disease. We tested mice with essential-like tremor using current drug therapies that alleviate symptoms in essential tremor patients (primidone, propranolol, and gabapentin) and several candidates hypothesized to reduce tremor, including ethanol; the noncompetitive N-methyl-D-aspartate receptor antagonist MK-801; the adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA); the GABAA receptor modulators diazepam, allopregnanolone, and Ro15-4513; and the L-type Ca2+ channel antagonist nitrendipine. Primidone, propranolol, and gabapentin reduced the amplitude (power) of the pathologic tremor. Nonsedative doses of ethanol eliminated tremor in mice. Diazepam, allopregnanolone, Ro15-4513, and nitrendipine had no effect or enhanced tremor, whereas MK-801 and CCPA reduced tremor. To understand the etiology of tremor in these mice, we studied the electrophysiological properties of cerebellar Purkinje cells. Cerebellar Purkinje cells in GABAA receptor α1–/– mice exhibited a profound loss of all responses to synaptic or exogenous GABA, but no differences in abundance, gross morphology, or spontaneous synaptic activity were observed. This genetic animal model elucidates a mechanism of GABAergic dysfunction in the major motor pathway and potential targets for pharmacotherapy of essential tremor.
Authors
Jason E. Kralic, Hugh E. Criswell, Jessica L. Osterman, Todd K. O’Buckley, Mary E. Wilkie, Douglas B. Matthews, Kristin Hamre, George R. Breese, Gregg E. Homanics, A. Leslie Morrow
×Abstract
Tissue kallikrein (TK), the major kinin-forming enzyme, is synthesized in several organs, including the kidney and arteries. A loss-of-function polymorphism of the human TK gene (R53H) induces a substantial decrease in enzyme activity. As inactivation of the TK gene in the mouse induces endothelial dysfunction, we investigated the vascular, hormonal, and renal phenotypes of carriers of the 53H allele. In a crossover study, 30 R53R-homozygous and 10 R53H-heterozygous young normotensive white males were randomly assigned to receive both a low sodium–high potassium diet to stimulate TK synthesis and a high sodium–low potassium diet to suppress TK synthesis, each for 1 week. Urinary kallikrein activity was 50–60% lower in R53H subjects than in R53R subjects. Acute flow-dependent vasodilatation and endothelium-independent vasodilatation of the brachial artery were both unaffected in R53H subjects. In contrast, R53H subjects consistently exhibited an increase in wall shear stress and a paradoxical reduction in artery diameter and lumen compared with R53R subjects. Renal and hormonal adaptation to diets was unaffected in R53H subjects. The partial genetic deficiency in TK activity is associated with an inward remodeling of the brachial artery, which is not adapted to a chronic increase in wall shear stress, indicating a new form of arterial dysfunction affecting 5–7% of white people.
Authors
Michel Azizi, Pierre Boutouyrie, Alvine Bissery, Mohsen Agharazii, Francis Verbeke, Nora Stern, Alessandra Bura-Rivière, Stéphane Laurent, François Alhenc-Gelas, Xavier Jeunemaitre
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ISSN: 0021-9738 (print), 1558-8238 (online)