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Insulin Metabolism in Polycystic Ovary Syndrome: Secretion, Signaling, and Clearance. Int J Mol Sci 2023; 24:ijms24043140. [PMID: 36834549 PMCID: PMC9962893 DOI: 10.3390/ijms24043140] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Revised: 01/23/2023] [Accepted: 02/03/2023] [Indexed: 02/09/2023] Open
Abstract
Polycystic ovary syndrome (PCOS) is the most common endocrine and metabolic disorder in women of reproductive age. Its heterogeneous clinical presentation is characterized by hyperandrogenemia, reproductive changes, polycystic ovary morphology, and insulin resistance (IR). The primary pathophysiological process in its multifactorial etiology has not yet been identified. However, the two most proposed core etiologies are the disruption of insulin metabolism and hyperandrogenemia, both of which begin to intertwine and propagate each other in the later stages of the disease. Insulin metabolism can be viewed as the interconnectedness of beta cell function, IR or insulin sensitivity, and insulin clearance. Previous studies of insulin metabolism in PCOS patients have yielded conflicting results, and literature reviews have focused mainly on the molecular mechanisms and clinical implications of IR. In this narrative review, we comprehensively explored the role of insulin secretion, clearance, and decreased sensitivity in target cells as a potential primary insult in PCOS pathogenesis, along with the molecular mechanism behind IR in PCOS.
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Janez A, Herman R, Poredos P, Mikhailidis DP, Blinc A, Sabovic M, Studen KB, Jezovnik MK, Schernthaner GH, Anagnostis P, Antignani PL, Jensterle M. Cardiometabolic Risk, Peripheral Arterial Disease and Cardiovascular Events in Polycystic Ovary Syndrome: Time to Implement Systematic Screening and Update the Management. Curr Vasc Pharmacol 2023; 21:424-432. [PMID: 37779406 DOI: 10.2174/0115701611269146230920073301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2023] [Revised: 08/22/2023] [Accepted: 08/30/2023] [Indexed: 10/03/2023]
Abstract
Polycystic ovary syndrome (PCOS) is a highly prevalent endocrine disorder in women of reproductive age. It presents with gynaecologic, metabolic, and psychologic manifestations. The dominant drivers of pathophysiology are hyperandrogenism and insulin resistance. Both conditions are related to cardiometabolic risk factors, such as obesity, hypertension, dyslipidaemia, hyperglycaemia, type 2 and gestational diabetes, nonalcoholic fatty liver disease and obstructive sleep apnoea. Women with PCOS of reproductive age consistently demonstrated an elevated risk of subclinical atherosclerosis, as indicated by different measurement methods, while findings for menopausal age groups exhibited mixed results. Translation of subclinical atherosclerosis into the increased incidence of peripheral arterial disease and major cardiovascular (CV) events is less clear. Although several expert groups have advised screening, the CV risk assessment and prevention of CV events are frequently underdiagnosed and overlooked aspects of the management of PCOS. A combination of lifestyle management and pharmacotherapy, including the promising new era of anti-obesity medicine, can lead to improvements in cardiometabolic health.
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Affiliation(s)
- Andrej Janez
- Department of Endocrinology, Diabetes and Metabolic Diseases, University Medical Centre Ljubljana, Ljubljana, Slovenia
- Department of Internal Medicine, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
| | - Rok Herman
- Department of Endocrinology, Diabetes and Metabolic Diseases, University Medical Centre Ljubljana, Ljubljana, Slovenia
- Department of Internal Medicine, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
| | - Pavel Poredos
- Department of Vascular Diseases, University Medical Centre Ljubljana, Ljubljana, Slovenia
| | - Dimitri P Mikhailidis
- Division of Surgery and Interventional Science, Department of Surgical Biotechnology, University College London Medical School, University College London (UCL), UK
- Department of Clinical Biochemistry, Royal Free Hospital Campus (UCL), London, UK
| | - Ales Blinc
- Department of Internal Medicine, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
- Department of Vascular Diseases, University Medical Centre Ljubljana, Ljubljana, Slovenia
| | - Miso Sabovic
- Department of Internal Medicine, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
- Department of Vascular Diseases, University Medical Centre Ljubljana, Ljubljana, Slovenia
| | - Katica Bajuk Studen
- Department of Internal Medicine, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
- Department of Nuclear Medicine, University Medical Centre Ljubljana, Ljubljana, Slovenia
| | - Mateja Kaja Jezovnik
- Department of Advanced Cardiopulmonary Therapies and Transplantation, The University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Gerit-Holger Schernthaner
- Division of Angiology, Department of Medicine 2, Division of Angiology, Medical University of Vienna, Vienna, Austria
| | - Panagiotis Anagnostis
- Unit of Reproductive Endocrinology, 1st Department of Obstetrics and Gynaecology, Medical School, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | | | - Mojca Jensterle
- Department of Endocrinology, Diabetes and Metabolic Diseases, University Medical Centre Ljubljana, Ljubljana, Slovenia
- Department of Internal Medicine, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
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Abstract
The immune and endocrine systems collectively control homeostasis in the body. The endocrine system ensures that values of essential factors and nutrients such as glucose, electrolytes and vitamins are maintained within threshold values. The immune system resolves local disruptions in tissue homeostasis, caused by pathogens or malfunctioning cells. The immediate goals of these two systems do not always align. The immune system benefits from optimal access to nutrients for itself and restriction of nutrient availability to all other organs to limit pathogen replication. The endocrine system aims to ensure optimal nutrient access for all organs, limited only by the nutrients stores that the body has available. The actual state of homeostatic parameters such as blood glucose levels represents a careful balance based on regulatory signals from the immune and endocrine systems. This state is not static but continuously adjusted in response to changes in the current metabolic needs of the body, the amount of resources it has available and the level of threats it encounters. This balance is maintained by the ability of the immune and endocrine systems to interact and co-regulate systemic metabolism. In context of metabolic disease, this system is disrupted, which impairs functionality of both systems. The failure of the endocrine system to retain levels of nutrients such as glucose within threshold values impairs functionality of the immune system. In addition, metabolic stress of organs in context of obesity is perceived by the immune system as a disruption in local homeostasis, which it tries to resolve by the excretion of factors which further disrupt normal metabolic control. In this chapter, we will discuss how the immune and endocrine systems interact under homeostatic conditions and during infection with a focus on blood glucose regulation. In addition, we will discuss how this system fails in the context of metabolic disease.
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Lair B, Laurens C, Van Den Bosch B, Moro C. Novel Insights and Mechanisms of Lipotoxicity-Driven Insulin Resistance. Int J Mol Sci 2020; 21:E6358. [PMID: 32887221 PMCID: PMC7504171 DOI: 10.3390/ijms21176358] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Revised: 08/27/2020] [Accepted: 08/27/2020] [Indexed: 02/07/2023] Open
Abstract
A large number of studies reported an association between elevated circulating and tissue lipid content and metabolic disorders in obesity, type 2 diabetes (T2D) and aging. This state of uncontrolled tissue lipid accumulation has been called lipotoxicity. It was later shown that excess lipid flux is mainly neutralized within lipid droplets as triglycerides, while several bioactive lipid species such as diacylglycerols (DAGs), ceramides and their derivatives have been mechanistically linked to the pathogenesis of insulin resistance (IR) by antagonizing insulin signaling and action in metabolic organs such as the liver and skeletal muscle. Skeletal muscle and the liver are the main sites of glucose disposal in the body and IR in these tissues plays a pivotal role in the development of T2D. In this review, we critically examine recent literature supporting a causal role of DAGs and ceramides in the development of IR. A particular emphasis is placed on transgenic mouse models with modulation of total DAG and ceramide pools, as well as on modulation of specific subspecies, in relation to insulin sensitivity. Collectively, although a wide number of studies converge towards the conclusion that both DAGs and ceramides cause IR in metabolic organs, there are still some uncertainties on their mechanisms of action. Recent studies reveal that subcellular localization and acyl chain composition are determinants in the biological activity of these lipotoxic lipids and should be further examined.
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Affiliation(s)
- Benjamin Lair
- INSERM, UMR1048, Institute of Metabolic and Cardiovascular Diseases, 31432 Toulouse, France; (B.L.); (C.L.); (B.V.D.B.)
- University of Toulouse, Paul Sabatier University, 31330 Toulouse, France
| | - Claire Laurens
- INSERM, UMR1048, Institute of Metabolic and Cardiovascular Diseases, 31432 Toulouse, France; (B.L.); (C.L.); (B.V.D.B.)
- University of Toulouse, Paul Sabatier University, 31330 Toulouse, France
| | - Bram Van Den Bosch
- INSERM, UMR1048, Institute of Metabolic and Cardiovascular Diseases, 31432 Toulouse, France; (B.L.); (C.L.); (B.V.D.B.)
- University of Toulouse, Paul Sabatier University, 31330 Toulouse, France
| | - Cedric Moro
- INSERM, UMR1048, Institute of Metabolic and Cardiovascular Diseases, 31432 Toulouse, France; (B.L.); (C.L.); (B.V.D.B.)
- University of Toulouse, Paul Sabatier University, 31330 Toulouse, France
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Abstract
PURPOSE OF REVIEW Insulin resistance (IR) is recognized to play an important role in the pathogenesis of dyslipidemia. This review summarizes the complex interplay between IR and dyslipidemia in people with and without diabetes. RECENT FINDINGS IR impacts the metabolism of triglycerides, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and very low-density lipoprotein cholesterol (VLDL-C) by several mechanisms. Trials with insulin sensitizing therapies, including biguanides and thiazolidinediones, have provided inconsistent results on lipid lowering in people with and without diabetes. In this review, we focus on the pathophysiological interplay between IR and dyslipidemia and recapitulate lipid and lipoprotein data from insulin-sensitizing trials. Further research elucidating the reciprocal relationship between IR and dyslipidemia is needed to better target these important risk factors for cardiovascular disease.
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Affiliation(s)
- Petter Bjornstad
- Department of Pediatrics, Division of Endocrinology, University of Colorado School of Medicine, 13123 East 16th Ave, Box B26, Aurora, CO, 80045, USA.
- Department of Medicine, Division of Renal Diseases and Hypertension, University of Colorado School of Medicine, Aurora, CO, USA.
| | - Robert H Eckel
- Department of Medicine, Division of Endocrinology and Division of Cardiology, University of Colorado School of Medicine, Aurora, CO, USA.
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Petersen MC, Shulman GI. Mechanisms of Insulin Action and Insulin Resistance. Physiol Rev 2018; 98:2133-2223. [PMID: 30067154 PMCID: PMC6170977 DOI: 10.1152/physrev.00063.2017] [Citation(s) in RCA: 1324] [Impact Index Per Article: 220.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Revised: 03/22/2018] [Accepted: 03/24/2018] [Indexed: 12/15/2022] Open
Abstract
The 1921 discovery of insulin was a Big Bang from which a vast and expanding universe of research into insulin action and resistance has issued. In the intervening century, some discoveries have matured, coalescing into solid and fertile ground for clinical application; others remain incompletely investigated and scientifically controversial. Here, we attempt to synthesize this work to guide further mechanistic investigation and to inform the development of novel therapies for type 2 diabetes (T2D). The rational development of such therapies necessitates detailed knowledge of one of the key pathophysiological processes involved in T2D: insulin resistance. Understanding insulin resistance, in turn, requires knowledge of normal insulin action. In this review, both the physiology of insulin action and the pathophysiology of insulin resistance are described, focusing on three key insulin target tissues: skeletal muscle, liver, and white adipose tissue. We aim to develop an integrated physiological perspective, placing the intricate signaling effectors that carry out the cell-autonomous response to insulin in the context of the tissue-specific functions that generate the coordinated organismal response. First, in section II, the effectors and effects of direct, cell-autonomous insulin action in muscle, liver, and white adipose tissue are reviewed, beginning at the insulin receptor and working downstream. Section III considers the critical and underappreciated role of tissue crosstalk in whole body insulin action, especially the essential interaction between adipose lipolysis and hepatic gluconeogenesis. The pathophysiology of insulin resistance is then described in section IV. Special attention is given to which signaling pathways and functions become insulin resistant in the setting of chronic overnutrition, and an alternative explanation for the phenomenon of ‟selective hepatic insulin resistanceˮ is presented. Sections V, VI, and VII critically examine the evidence for and against several putative mediators of insulin resistance. Section V reviews work linking the bioactive lipids diacylglycerol, ceramide, and acylcarnitine to insulin resistance; section VI considers the impact of nutrient stresses in the endoplasmic reticulum and mitochondria on insulin resistance; and section VII discusses non-cell autonomous factors proposed to induce insulin resistance, including inflammatory mediators, branched-chain amino acids, adipokines, and hepatokines. Finally, in section VIII, we propose an integrated model of insulin resistance that links these mediators to final common pathways of metabolite-driven gluconeogenesis and ectopic lipid accumulation.
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Affiliation(s)
- Max C Petersen
- Departments of Internal Medicine and Cellular & Molecular Physiology, Howard Hughes Medical Institute, Yale University School of Medicine , New Haven, Connecticut
| | - Gerald I Shulman
- Departments of Internal Medicine and Cellular & Molecular Physiology, Howard Hughes Medical Institute, Yale University School of Medicine , New Haven, Connecticut
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Insulin Resistance, Obesity and Lipotoxicity. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 960:277-304. [PMID: 28585204 DOI: 10.1007/978-3-319-48382-5_12] [Citation(s) in RCA: 264] [Impact Index Per Article: 37.7] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Lipotoxicity , originally used to describe the destructive effects of excess fat accumulation on glucose metabolism, causes functional impairments in several metabolic pathways, both in adipose tissue and peripheral organs, like liver, heart, pancreas and muscle. Lipotoxicity has roles in insulin resistance and pancreatic beta cell dysfunction. Increased circulating levels of lipids and the metabolic alterations in fatty acid utilization and intracellular signaling, have been related to insulin resistance in muscle and liver. Different pathways, like novel protein kinase c pathways and the JNK-1 pathway are involved as the mechanisms of how lipotoxicity leads to insulin resistance in nonadipose tissue organs, such as liver and muscle. Mitochondrial dysfunction plays a role in the pathogenesis of insulin resistance. Endoplasmic reticulum stress, through mainly increased oxidative stress, also plays important role in the etiology of insulin resistance, especially seen in non-alcoholic fatty liver disease. Visceral adiposity and insulin resistance both increase the cardiometabolic risk and lipotoxicity seems to play a crucial role in the pathophysiology of these associations.
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Petersen MC, Shulman GI. Roles of Diacylglycerols and Ceramides in Hepatic Insulin Resistance. Trends Pharmacol Sci 2017; 38:649-665. [PMID: 28551355 DOI: 10.1016/j.tips.2017.04.004] [Citation(s) in RCA: 234] [Impact Index Per Article: 33.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Revised: 04/19/2017] [Accepted: 04/20/2017] [Indexed: 12/22/2022]
Abstract
Although ample evidence links hepatic lipid accumulation with hepatic insulin resistance, the mechanistic basis of this association is incompletely understood and controversial. Diacylglycerols (DAGs) and ceramides have emerged as the two best-studied putative mediators of lipid-induced hepatic insulin resistance. Both lipids were first associated with insulin resistance in skeletal muscle and were subsequently hypothesized to mediate insulin resistance in the liver. However, the putative roles for DAGs and ceramides in hepatic insulin resistance have proved more complex than originally imagined, with various genetic and pharmacologic manipulations yielding a vast and occasionally contradictory trove of data to sort. In this review we examine the state of this field, turning a critical eye toward both DAGs and ceramides as putative mediators of lipid-induced hepatic insulin resistance.
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Affiliation(s)
- Max C Petersen
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Gerald I Shulman
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520, USA; Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520, USA; Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06520, USA.
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Softic S, Cohen DE, Kahn CR. Role of Dietary Fructose and Hepatic De Novo Lipogenesis in Fatty Liver Disease. Dig Dis Sci 2016; 61:1282-93. [PMID: 26856717 PMCID: PMC4838515 DOI: 10.1007/s10620-016-4054-0] [Citation(s) in RCA: 394] [Impact Index Per Article: 49.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2016] [Accepted: 01/21/2016] [Indexed: 12/11/2022]
Abstract
Nonalcoholic fatty liver disease (NAFLD) is a liver manifestation of metabolic syndrome. Overconsumption of high-fat diet (HFD) and increased intake of sugar-sweetened beverages are major risk factors for development of NAFLD. Today the most commonly consumed sugar is high fructose corn syrup. Hepatic lipids may be derived from dietary intake, esterification of plasma free fatty acids (FFA) or hepatic de novo lipogenesis (DNL). A central abnormality in NAFLD is enhanced DNL. Hepatic DNL is increased in individuals with NAFLD, while the contribution of dietary fat and plasma FFA to hepatic lipids is not significantly altered. The importance of DNL in NAFLD is further established in mouse studies with knockout of genes involved in this process. Dietary fructose increases levels of enzymes involved in DNL even more strongly than HFD. Several properties of fructose metabolism make it particularly lipogenic. Fructose is absorbed via portal vein and delivered to the liver in much higher concentrations as compared to other tissues. Fructose increases protein levels of all DNL enzymes during its conversion into triglycerides. Additionally, fructose supports lipogenesis in the setting of insulin resistance as fructose does not require insulin for its metabolism, and it directly stimulates SREBP1c, a major transcriptional regulator of DNL. Fructose also leads to ATP depletion and suppression of mitochondrial fatty acid oxidation, resulting in increased production of reactive oxygen species. Furthermore, fructose promotes ER stress and uric acid formation, additional insulin independent pathways leading to DNL. In summary, fructose metabolism supports DNL more strongly than HFD and hepatic DNL is a central abnormality in NAFLD. Disrupting fructose metabolism in the liver may provide a new therapeutic option for the treatment of NAFLD.
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Affiliation(s)
- Samir Softic
- Section on Integrative Physiology and Metabolism, Joslin Diabetes Center, One Joslin Place, Boston, MA, 02215, USA
- Department of Gastroenterology, Hepatology and Nutrition, Boston Children's Hospital, Boston, MA, USA
| | - David E Cohen
- Division of Gastroenterology, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
| | - C Ronald Kahn
- Section on Integrative Physiology and Metabolism, Joslin Diabetes Center, One Joslin Place, Boston, MA, 02215, USA.
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Hsu C, Shih H, Chang Y, Huang Z, Tsai M, Chia Y, Chen C, Lai Y, Weng C. The beneficial effects of tetracosanol on insulin-resistance by insulin receptor kinase sensibilisation. J Funct Foods 2015. [DOI: 10.1016/j.jff.2015.01.033] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
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Gondoin A, Morzyglod L, Desbuquois B, Burnol AF. [Control of insulin signalisation and action by the Grb14 protein]. Biol Aujourdhui 2014; 208:119-36. [PMID: 25190572 DOI: 10.1051/jbio/2014013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Indexed: 11/15/2022]
Abstract
The action of insulin on metabolism and cell growth is mediated by a specific receptor tyrosine kinase, which, through phosphorylation of several substrates, triggers the activation of two major signaling pathways, the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway and the Ras/extracellular signal-regulated kinase (ERK) pathway. Insulin-induced activation of the receptor and downstream signaling is also subjected to a negative feedback control involving several mechanisms, among which the interaction of the insulin receptor and its substrates with inhibitory proteins. After summarizing the major mechanisms underlying the activation and attenuation of insulin signaling, this review focuses on its control by the Grb14 adaptor protein. Grb14 has been identif-ied as an inhibitor of insulin signaling and action, and is involved in insulin resistance associated with type 2 diabetes and obesity. Studies on the molecular mechanism of action of Grb14 have shown that, through interaction with the activated insulin receptor, Grb14 inhibits its catalytic activity and the activation of downstream signaling. However, the consequences of Grb14 gene invalidation are complex and tissue-specific, and some effects of Grb14 on insulin signaling appear to be linked to its interaction with effector proteins downstream the insulin receptor. Pharmacological inhibition of Grb14 should allow to enhance insulin sensitivity and improve energy homeostasis in insulin-resistant states.
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Affiliation(s)
- Anaïs Gondoin
- INSERM, U1016, Institut Cochin, 22 rue Méchain, 75014 Paris, France - CNRS, UMR 8104, Institut Cochin, 22 rue Méchain, 75014 Paris, France - Université Paris Descartes, Sorbonne Paris Cité, 24 rue du Faubourg Saint Jacques, 75014 Paris, France
| | - Lucie Morzyglod
- INSERM, U1016, Institut Cochin, 22 rue Méchain, 75014 Paris, France - CNRS, UMR 8104, Institut Cochin, 22 rue Méchain, 75014 Paris, France - Université Paris Descartes, Sorbonne Paris Cité, 24 rue du Faubourg Saint Jacques, 75014 Paris, France
| | - Bernard Desbuquois
- INSERM, U1016, Institut Cochin, 22 rue Méchain, 75014 Paris, France - CNRS, UMR 8104, Institut Cochin, 22 rue Méchain, 75014 Paris, France - Université Paris Descartes, Sorbonne Paris Cité, 24 rue du Faubourg Saint Jacques, 75014 Paris, France
| | - Anne-Françoise Burnol
- INSERM, U1016, Institut Cochin, 22 rue Méchain, 75014 Paris, France - CNRS, UMR 8104, Institut Cochin, 22 rue Méchain, 75014 Paris, France - Université Paris Descartes, Sorbonne Paris Cité, 24 rue du Faubourg Saint Jacques, 75014 Paris, France
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12
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Joseph D, Kimar C, Symington B, Milne R, Essop MF. The detrimental effects of acute hyperglycemia on myocardial glucose uptake. Life Sci 2014; 105:31-42. [PMID: 24747137 DOI: 10.1016/j.lfs.2014.04.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Revised: 03/20/2014] [Accepted: 04/07/2014] [Indexed: 01/14/2023]
Abstract
AIMS Although acute hyperglycemic (AHG) episodes are linked to lower glucose uptake, underlying mechanisms remain unclear. We hypothesized that AHG triggers reactive oxygen species (ROS) production and increases non-oxidative glucose pathway (NOGP) activation, i.e. stimulation of advanced glycation end products (AGE), polyol pathway (PP), hexosamine biosynthetic pathway (HBP), PKC; thereby decreasing cardiac glucose uptake. MAIN METHODS H9c2 cardiomyoblasts were exposed to 25 mM glucose for 24h vs. 5.5mM controls ± modulating agents during the last hour of glucose exposure: a) antioxidant #1 for mitochondrial ROS (250 μM 4-OHCA), b) antioxidant #2 for NADPH oxidase-generated ROS (100 μM DPI), c) NOGP inhibitors - 100 μM aminoguanidine (AGE), 5 μM chelerythrine (PKC); 40 μM DON (HBP); and 10 μM zopolrestat (PP). ROS levels (mitochondrial, intracellular) and glucose uptake were evaluated by flow cytometry. KEY FINDINGS AHG elevated ROS, activated NOGPs and blunted glucose uptake. Transketolase activity (pentose phosphate pathway [PPP] marker) did not change. Respective 4-OHCA and DPI treatment blunted ROS production, diminished NOGP activation and normalized glucose uptake. NOGP inhibitory studies identified PKCβII as a key downstream player in lowering insulin-mediated glucose uptake. When we employed an agent (benfotiamine) known to shunt flux away from NOGPs (into PPP), it decreased ROS generation and NOGP activation, and restored glucose uptake under AHG conditions. SIGNIFICANCE This study demonstrates that AHG elicits maladaptive events that function in tandem to reduce glucose uptake, and that antioxidant treatment and/or attenuation of NOGP activation (PKC, polyol pathway) may limit the onset of insulin resistance.
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Affiliation(s)
- Danzil Joseph
- Cardio-Metabolic Research Group (CMRG), Department of Physiological Sciences, Stellenbosch University, Stellenbosch 7600, South Africa
| | - Charlene Kimar
- Cardio-Metabolic Research Group (CMRG), Department of Physiological Sciences, Stellenbosch University, Stellenbosch 7600, South Africa
| | - Burger Symington
- Cardio-Metabolic Research Group (CMRG), Department of Physiological Sciences, Stellenbosch University, Stellenbosch 7600, South Africa
| | - Robyn Milne
- Cardio-Metabolic Research Group (CMRG), Department of Physiological Sciences, Stellenbosch University, Stellenbosch 7600, South Africa
| | - M Faadiel Essop
- Cardio-Metabolic Research Group (CMRG), Department of Physiological Sciences, Stellenbosch University, Stellenbosch 7600, South Africa.
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Hsu CY, Shih HY, Chia YC, Lee CH, Ashida H, Lai YK, Weng CF. Rutin potentiates insulin receptor kinase to enhance insulin-dependent glucose transporter 4 translocation. Mol Nutr Food Res 2014; 58:1168-76. [DOI: 10.1002/mnfr.201300691] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Revised: 12/03/2013] [Accepted: 12/05/2013] [Indexed: 01/17/2023]
Affiliation(s)
- Chia-Yu Hsu
- Institute of Biotechnology; National Dong-Hwa University; Hualien 97401 Taiwan
- Institute of Biotechnology & Department of Life Science; National Tsing Hua University; Hsinchu 30013 Taiwan
| | - Hung-Yuan Shih
- Institute of Biotechnology; National Dong-Hwa University; Hualien 97401 Taiwan
| | - Yi-Chen Chia
- Department of Food Science & Technology; Tajen University; Ping Tung Hsien Taiwan
| | - Chia-Hung Lee
- Institute of Biotechnology; National Dong-Hwa University; Hualien 97401 Taiwan
| | - Hitoshi Ashida
- Department of Agrobioscience; Graduate School of Agricultural Science; Kobe University; Nada-ku Kobe 657-8501 Japan
| | - Yiu-Kay Lai
- Institute of Biotechnology & Department of Life Science; National Tsing Hua University; Hsinchu 30013 Taiwan
| | - Ching-Feng Weng
- Institute of Biotechnology; National Dong-Hwa University; Hualien 97401 Taiwan
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14
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The renin-angiotensin system in adipose tissue and its metabolic consequences during obesity. J Nutr Biochem 2013; 24:2003-15. [PMID: 24120291 DOI: 10.1016/j.jnutbio.2013.07.002] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Revised: 05/24/2013] [Accepted: 07/22/2013] [Indexed: 02/07/2023]
Abstract
Obesity is a worldwide disease that is accompanied by several metabolic abnormalities such as hypertension, hyperglycemia and dyslipidemia. The accelerated adipose tissue growth and fat cell hypertrophy during the onset of obesity precedes adipocyte dysfunction. One of the features of adipocyte dysfunction is dysregulated adipokine secretion, which leads to an imbalance of pro-inflammatory, pro-atherogenic versus anti-inflammatory, insulin-sensitizing adipokines. The production of renin-angiotensin system (RAS) components by adipocytes is exacerbated during obesity, contributing to the systemic RAS and its consequences. Increased adipose tissue RAS has been described in various models of diet-induced obesity (DIO) including fructose and high-fat feeding. Up-regulation of the adipose RAS by DIO promotes inflammation, lipogenesis and reactive oxygen species generation and impairs insulin signaling, all of which worsen the adipose environment. Consequently, the increase of circulating RAS, for which adipose tissue is partially responsible, represents a link between hypertension, insulin resistance in diabetes and inflammation during obesity. However, other nutrients and food components such as soy protein attenuate adipose RAS, decrease adiposity, and improve adipocyte functionality. Here, we review the molecular mechanisms by which adipose RAS modulates systemic RAS and how it is enhanced in obesity, which will explain the simultaneous development of metabolic syndrome alterations. Finally, dietary interventions that prevent obesity and adipocyte dysfunction will maintain normal RAS concentrations and effects, thus preventing metabolic diseases that are associated with RAS enhancement.
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15
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Tee MK, Miller WL. Phosphorylation of human cytochrome P450c17 by p38α selectively increases 17,20 lyase activity and androgen biosynthesis. J Biol Chem 2013; 288:23903-13. [PMID: 23836902 DOI: 10.1074/jbc.m113.460048] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Cytochrome P450c17, a steroidogenic enzyme encoded by the CYP17A1 gene, catalyzes the steroid 17α-hydroxylation needed for glucocorticoid synthesis, which may or may not be followed by 17,20 lyase activity needed for sex steroid synthesis. Whether or not P450c17 catalyzes 17,20 lyase activity is determined by three post-translational mechanisms influencing availability of reducing equivalents donated by P450 oxidoreductase (POR). These are increased amounts of POR, the allosteric action of cytochrome b5 to promote POR-P450c17 interaction, and Ser/Thr phosphorylation of P450c17, which also appears to promote POR-P450c17 interaction. The kinase(s) that phosphorylates P450c17 is unknown. In a series of kinase inhibition experiments, the pyridinyl imidazole drugs SB202190 and SB203580 inhibited 17,20 lyase but not 17α-hydroxylase activity in human adrenocortical HCI-H295A cells, suggesting an action on p38α or p38β. Co-transfection of non-steroidogenic COS-1 cells with P450c17 and p38 expression vectors showed that p38α, but not p38β, conferred 17,20 lyase activity on P450c17. Antiserum to P450c17 co-immunoprecipitated P450c17 and both p38 isoforms; however, knockdown of p38α, but not knockdown of p38β, inhibited 17,20 lyase activity in NCI-H295A cells. Bacterially expressed human P450c17 was phosphorylated by p38α in vitro at a non-canonical site, conferring increased 17,20 lyase activity. This phosphorylation increased the maximum velocity, but not the Michaelis constant, of the 17,20 lyase reaction. p38α phosphorylates P450c17 in a fashion that confers increased 17,20 lyase activity, implying that the production of adrenal androgens (adrenarche) is a regulated event.
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Affiliation(s)
- Meng Kian Tee
- Department of Pediatrics, University of California, San Francisco, California 94143, USA
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Diamanti-Kandarakis E, Dunaif A. Insulin resistance and the polycystic ovary syndrome revisited: an update on mechanisms and implications. Endocr Rev 2012; 33:981-1030. [PMID: 23065822 PMCID: PMC5393155 DOI: 10.1210/er.2011-1034] [Citation(s) in RCA: 1036] [Impact Index Per Article: 86.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Polycystic ovary syndrome (PCOS) is now recognized as an important metabolic as well as reproductive disorder conferring substantially increased risk for type 2 diabetes. Affected women have marked insulin resistance, independent of obesity. This article summarizes the state of the science since we last reviewed the field in the Endocrine Reviews in 1997. There is general agreement that obese women with PCOS are insulin resistant, but some groups of lean affected women may have normal insulin sensitivity. There is a post-binding defect in receptor signaling likely due to increased receptor and insulin receptor substrate-1 serine phosphorylation that selectively affects metabolic but not mitogenic pathways in classic insulin target tissues and in the ovary. Constitutive activation of serine kinases in the MAPK-ERK pathway may contribute to resistance to insulin's metabolic actions in skeletal muscle. Insulin functions as a co-gonadotropin through its cognate receptor to modulate ovarian steroidogenesis. Genetic disruption of insulin signaling in the brain has indicated that this pathway is important for ovulation and body weight regulation. These insights have been directly translated into a novel therapy for PCOS with insulin-sensitizing drugs. Furthermore, androgens contribute to insulin resistance in PCOS. PCOS may also have developmental origins due to androgen exposure at critical periods or to intrauterine growth restriction. PCOS is a complex genetic disease, and first-degree relatives have reproductive and metabolic phenotypes. Several PCOS genetic susceptibility loci have been mapped and replicated. Some of the same susceptibility genes contribute to disease risk in Chinese and European PCOS populations, suggesting that PCOS is an ancient trait.
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Abstract
Nonalcoholic fatty liver disease (NAFLD) is now the most frequent chronic liver disease in Western societies, affecting one in four adults in the USA, and is strongly associated with hepatic insulin resistance, a major risk factor in the pathogenesis of type 2 diabetes. Although the cellular mechanisms underlying this relationship are unknown, hepatic accumulation of diacylglycerol (DAG) in both animals and humans has been linked to hepatic insulin resistance. In this Perspective, we discuss the role of DAG activation of protein kinase Cε as the mechanism responsible for NAFLD-associated hepatic insulin resistance seen in obesity, type 2 diabetes, and lipodystrophy.
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Affiliation(s)
- François R Jornayvaz
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06510, USA
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18
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Samuel VT, Shulman GI. Mechanisms for insulin resistance: common threads and missing links. Cell 2012; 148:852-71. [PMID: 22385956 DOI: 10.1016/j.cell.2012.02.017] [Citation(s) in RCA: 1467] [Impact Index Per Article: 122.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Indexed: 02/07/2023]
Abstract
Insulin resistance is a complex metabolic disorder that defies explanation by a single etiological pathway. Accumulation of ectopic lipid metabolites, activation of the unfolded protein response (UPR) pathway, and innate immune pathways have all been implicated in the pathogenesis of insulin resistance. However, these pathways are also closely linked to changes in fatty acid uptake, lipogenesis, and energy expenditure that can impact ectopic lipid deposition. Ultimately, these cellular changes may converge to promote the accumulation of specific lipid metabolites (diacylglycerols and/or ceramides) in liver and skeletal muscle, a common final pathway leading to impaired insulin signaling and insulin resistance.
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Affiliation(s)
- Varman T Samuel
- Department of Medicine, Yale University School of Medicine, New Haven, CT 06510, USA.
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19
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Unluturk U, Harmanci A, Kocaefe C, Yildiz BO. The Genetic Basis of the Polycystic Ovary Syndrome: A Literature Review Including Discussion of PPAR-gamma. PPAR Res 2011; 2007:49109. [PMID: 17389770 PMCID: PMC1820621 DOI: 10.1155/2007/49109] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2006] [Revised: 11/24/2006] [Accepted: 12/03/2006] [Indexed: 02/06/2023] Open
Abstract
Polycystic ovary syndrome (PCOS) is the most common endocrine disorder of the women of reproductive age. Familial clustering of PCOS has been consistently reported suggesting that genetic factors play a role in the development of the syndrome although PCOS cases do not exhibit a clear pattern of Mendelian inheritance. It is now well established that PCOS represents a complex trait similar to type-2 diabetes and obesity, and that both inherited and environmental factors contribute to the PCOS pathogenesis. A large number of functional candidate genes have been tested for association or linkage with PCOS phenotypes with more negative than positive findings. Lack of universally accepted diagnostic criteria, difficulties in the assignment of male phenotype, obscurity in the mode of inheritance, and particularly small sample size of the study populations appear to be major limitations for the genetic studies of PCOS. In the near future, utilizing the genome-wide scan approach and the HapMap project will provide a stronger potential for the genetic analysis of the syndrome.
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Affiliation(s)
- Ugur Unluturk
- Department of Internal Medicine, Faculty of Medicine, Hacettepe University, Hacettepe, 06100 Ankara, Turkey
| | - Ayla Harmanci
- Department of Internal Medicine, Faculty of Medicine, Hacettepe University, Hacettepe, 06100 Ankara, Turkey
- Endocrinology and Metabolism Unit, Faculty of Medicine, Hacettepe University, Hacettepe, 06100 Ankara, Turkey
| | - Cetin Kocaefe
- Department of Medical Biology, Faculty of Medicine, Hacettepe University, Hacettepe, 06100 Ankara, Turkey
| | - Bulent O. Yildiz
- Department of Internal Medicine, Faculty of Medicine, Hacettepe University, Hacettepe, 06100 Ankara, Turkey
- Endocrinology and Metabolism Unit, Faculty of Medicine, Hacettepe University, Hacettepe, 06100 Ankara, Turkey
- *Bulent O. Yildiz:
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Abstract
Premature pubarche, or the development of pubic hair before the age of 8 in girls or 9 in boys, is most commonly caused by premature adrenarche. Adrenarche is the maturation of the adrenal zona reticularis in both boys and girls, resulting in the development of pubic hair, axillary hair, and adult apocrine body odor. Although originally thought to be a benign variant of normal development, premature adrenarche has been associated with insulin resistance and the later development of metabolic syndrome and polycystic ovary syndrome. Although further studies are needed to confirm these relationships, the case presented herein argues for periodic assessment of children at risk. Indeed, recognition of these associations may allow for early preventive measures.
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Affiliation(s)
- Sharon E Oberfield
- Division of Pediatric Endocrinology, Diabetes, and Metabolism, Department of Pediatrics, Columbia University Medical Center, New York, New York 10032, USA.
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Stout MB, Liu LF, Belury MA. Hepatic steatosis by dietary-conjugated linoleic acid is accompanied by accumulation of diacylglycerol and increased membrane-associated protein kinase C ε in mice. Mol Nutr Food Res 2011; 55:1010-7. [DOI: 10.1002/mnfr.201000413] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Revised: 01/30/2011] [Accepted: 01/26/2011] [Indexed: 12/11/2022]
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Bremer AA. Polycystic ovary syndrome in the pediatric population. Metab Syndr Relat Disord 2011; 8:375-94. [PMID: 20939704 DOI: 10.1089/met.2010.0039] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Polycystic ovary syndrome (PCOS) is a common disorder characterized by hyperandrogenism and disordered gonadotropin secretion, often associated with insulin resistance. The syndrome, which modulates both hormonal and metabolic processes, is the most common endocrinopathy in reproductive-age women and increases a woman's risk of infertility, endometrial pathology, and cardiometabolic disease. As it is currently defined, PCOS most likely encompasses several distinct diseases with similar clinical phenotypes but different underlying pathophysiological processes. However, hyperandrogenism remains the syndrome's clinical hallmark. The clinical manifestations of PCOS often emerge during childhood or in the peripubertal years, suggesting that the syndrome is influenced by fetal programming and/or early postnatal events. However, given that the full clinical spectrum of PCOS does not typically appear until puberty, a "two-hit" hypothesis has been proposed: (1) a girl develops hyperandrogenism via one or more of many different potential mechanisms; (2) the preexisting hyperandrogenism subsequently disturbs the hypothalamic–pituitary–ovarian axis, resulting in ovulatory dysfunction and sustained hyperandrogenism. No consensus guidelines exist regarding the diagnosis and management of PCOS in the pediatric population; however, because the syndrome is a diagnosis of exclusion, the clinical evaluation of girls suspected of having PCOS is aimed at excluding other causes of androgen excess and menstrual dysfunction. For the syndrome's management, emphasis is placed on lifestyle and symptom-directed treatment.
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Affiliation(s)
- Andrew A Bremer
- Department of Pediatrics, Division of Endocrinology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-9170, USA.
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Abstract
Insulin resistance has long been associated with obesity. More than 40 years ago, Randle and colleagues postulated that lipids impaired insulin-stimulated glucose use by muscles through inhibition of glycolysis at key points. However, work over the past two decades has shown that lipid-induced insulin resistance in skeletal muscle stems from defects in insulin-stimulated glucose transport activity. The steatotic liver is also resistant to insulin in terms of inhibition of hepatic glucose production and stimulation of glycogen synthesis. In muscle and liver, the intracellular accumulation of lipids-namely, diacylglycerol-triggers activation of novel protein kinases C with subsequent impairments in insulin signalling. This unifying hypothesis accounts for the mechanism of insulin resistance in obesity, type 2 diabetes, lipodystrophy, and ageing; and the insulin-sensitising effects of thiazolidinediones.
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Affiliation(s)
- Varman T Samuel
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06536-8012, USA
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Kadoyama K, Funakoshi H, Ohya-Shimada W, Nakamura T, Matsumoto K, Matsuyama S, Nakamura T. Disease-dependent reciprocal phosphorylation of serine and tyrosine residues of c-Met/HGF receptor contributes disease retardation of a transgenic mouse model of ALS. Neurosci Res 2009; 65:194-200. [PMID: 19595710 DOI: 10.1016/j.neures.2009.06.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2009] [Revised: 06/30/2009] [Accepted: 06/30/2009] [Indexed: 11/19/2022]
Abstract
Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by progressive degeneration of motoneurons. We have demonstrated that hepatocyte growth factor (HGF) attenuates loss of both spinal and brainstem motoneurons of ALS model mice expressing mutated human SOD1(G93A) (G93A). This study was designed to assess disease-dependent regulatory mechanisms of c-Met/HGF receptor (c-Met) activation in the facial motoneurons of G93A mice. Using double transgenic mice expressing HGF and mutated SOD1(G93A) (G93A/HGF), we showed that phosphorylation of c-Met tyrosine residues at positions 1230, 1234 and 1235 (phospho-Tyr), and thereby its activation, was slightly evident in G93A and highly obvious in G93A/HGF mice (but absent in WT and HGF-Tg mice). Phosphorylation of the c-Met serine residue at position 985 (phospho-Ser), a residue involved in the negative regulation of its activation, was evident in WT and HGF-Tg mice. Protein phosphatase 2A (PP2A), which is capable of dephosphorylating c-Met phospho-serine, is upregulated in the facial motoneurons of G93A and G93A/HGF mice compared with WT and HGF-Tg mice. Thus, c-Met activation is reciprocally regulated by phosphorylation between c-Met serine and tyrosine residues through PP2A induction in the presence or absence of mutant SOD1 expression, and HGF functions more efficiently in ALS and ALS-related diseases.
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Affiliation(s)
- Keiichi Kadoyama
- Division of Molecular Regenerative Medicine, Department of Biochemistry and Molecular Biology, Osaka University Graduate School of Medicine, Osaka 565-0871, Japan
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Cai X, Wu JH, Exum ST, Oppermann M, Premont RT, Shenoy SK, Freedman NJ. Reciprocal regulation of the platelet-derived growth factor receptor-beta and G protein-coupled receptor kinase 5 by cross-phosphorylation: effects on catalysis. Mol Pharmacol 2008; 75:626-36. [PMID: 19092051 DOI: 10.1124/mol.108.050278] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Signaling by the platelet-derived growth factor receptor-beta (PDGFRbeta) is diminished when the PDGFRbeta is phosphorylated on seryl residues by G protein-coupled receptor kinase-5 (GRK5), but mechanisms for GRK5 activation by the PDGFRbeta remain obscure. We therefore tested whether the PDGFRbeta is able to tyrosine-phosphorylate and thereby activate GRK5. Purified GRK5 was tyrosine-phosphorylated by the wild-type PDGFRbeta to a stoichiometry of 0.8 mol phosphate/mol GRK5, an extent approximately 5 times greater than observed with a Y857F PDGFRbeta mutant that fails to phosphorylate exogenous substrates but autophosphorylates and activates Src normally. The degree of PDGFRbeta-mediated phosphorylation of GRK5 correlated with GRK5 activity, as assessed by seryl phosphorylation of the PDGFRbeta in purified protein preparations, in intact cells expressing a tyrosine-to-phenylalanine GRK5 mutant, and in GRK5 peptide phosphorylation assays. However, tyrosyl phosphorylation of GRK5 was not necessary for GRK5-mediated phosphorylation of the beta(2)-adrenergic receptor, even though beta(2)-adrenergic receptor activation promoted tyrosyl phosphorylation of GRK5 in smooth muscle cells. Phosphorylation of the PDGFRbeta by GRK5 in smooth muscle cells or in purified protein preparations reduced PDGFRbeta-mediated peptide phosphorylation. In contrast, phosphorylation of GRK5 by the PDGFRbeta enhanced the V(max) of GRK5-mediated peptide phosphorylation, by 3.4-fold, without altering the GRK5 K(M) for peptide. We conclude that GRK5 tyrosyl phosphorylation is required for the activation of GRK5 by the PDGFRbeta, but not by the beta(2)-adrenergic receptor, and that by activating GRK5, the PDGFRbeta triggers its own desensitization.
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Affiliation(s)
- Xinjiang Cai
- Departments of Medicine/Cardiology, Duke University Medical Center, Durham, North Carolina, USA
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26
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Saha S, Sarkar C, Biswas SC, Karim R. Correlation between serum lipid profile and carotid intima-media thickness in Polycystic Ovarian Syndrome. Indian J Clin Biochem 2008; 23:262-6. [PMID: 23105767 DOI: 10.1007/s12291-008-0059-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Abnormal lipid profile is often found in women with Polycystic Ovary Syndrome. To assess the impact of abnormal lipid profile on atherosclerosis in young Polycystic Ovary Syndrome women, carotid intima-media thickness as judged by B-mode ultrasonography were done in 30 young (18-35 yrs) Polycystic Ovary Syndrome women and in similarly age-matched 30 apparently healthy controls. Compared to controls, young Polycystic Ovary Syndrome women had significantly elevated serum total cholesterol, triglyceride and LDL-C levels and carotid intima-media thickness. HDL-C level did not differ significantly between two groups of women. In Polycystic Ovary Syndrome women carotid intima-media thickness was positively correlated with serum total cholesterol, triglyceride and LDL-C and negatively correlated with serum HDL-C. Our study suggests that even young Polycystic Ovary Syndrome women are prone to atherosclerosis from early age.
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Affiliation(s)
- Sarama Saha
- Department of Biochemistry, Institute of Post Graduate Medical Education and Research, Kolkata, 700 020 W.B India
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Germani D, Puglianiello A, Cianfarani S. Uteroplacental insufficiency down regulates insulin receptor and affects expression of key enzymes of long-chain fatty acid (LCFA) metabolism in skeletal muscle at birth. Cardiovasc Diabetol 2008; 7:14. [PMID: 18485240 PMCID: PMC2396605 DOI: 10.1186/1475-2840-7-14] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2008] [Accepted: 05/18/2008] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND Epidemiological studies have revealed a relationship between early growth restriction and the subsequent development of insulin resistance and type 2 diabetes. Ligation of the uterine arteries in rats mimics uteroplacental insufficiency and serves as a model of intrauterine growth restriction (IUGR) and subsequent developmental programming of impaired glucose tolerance, hyperinsulinemia and adiposity in the offspring. The objective of this study was to investigate the effects of uterine artery ligation on the skeletal muscle expression of insulin receptor and key enzymes of LCFA metabolism. METHODS Bilateral uterine artery ligation was performed on day 19 of gestation in Sprague-Dawley pregnant rats. Muscle of the posterior limb was dissected at birth and processed by real-time RT-PCR to analyze the expression of insulin receptor, ACCalpha, ACCbeta (acetyl-CoA carboxylase alpha and beta subunits), ACS (acyl-CoA synthase), AMPK (AMP-activated protein kinase, alpha2 catalytic subunit), CPT1B (carnitine palmitoyltransferase-1 beta subunit), MCD (malonyl-CoA decarboxylase) in 14 sham and 8 IUGR pups. Muscle tissue was treated with lysis buffer and Western immunoblotting was performed to assay the protein content of insulin receptor and ACC. RESULTS A significant down regulation of insulin receptor protein (p < 0.05) and reduced expression of ACS and ACCalpha mRNA (p < 0.05) were observed in skeletal muscle of IUGR newborns. Immunoblotting showed no significant change in ACCalpha content. CONCLUSION Our data suggest that uteroplacental insufficiency may affect skeletal muscle metabolism down regulating insulin receptor and reducing the expression of key enzymes involved in LCFA formation and oxidation.
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Affiliation(s)
- Daniela Germani
- Department of Public Health and Cell Biology, Tor Vergata University, 00133 Rome, Italy.
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28
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Tee MK, Dong Q, Miller WL. Pathways leading to phosphorylation of p450c17 and to the posttranslational regulation of androgen biosynthesis. Endocrinology 2008; 149:2667-77. [PMID: 18187541 PMCID: PMC2329260 DOI: 10.1210/en.2007-1527] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Cytochrome P450c17 (P450c17) is the single enzyme that catalyzes steroid 17alpha-hydroxylase and 17,20 lyase activities and hence is the crucial decision-making step that determines the class of steroid made in a steroidogenic cell. Although both activities are catalyzed on a single active site, the ratio of these activities is regulated by posttranslational events. Serine phosphorylation of P450c17 increases 17,20 lyase activity by increasing the enzyme's affinity for its redox partner, P450 oxidoreductase. We searched for the relevant kinase(s) that phosphorylates P450c17 by microarray studies and by testing of kinase inhibitors. Microarrays show that 145 of the 278 known serine/threonine kinases are expressed in human adrenal NCI-H295A cells, only six of which were induced more than 2-fold by treatment with 8-Br-cAMP. Key components of the ERK1/2 and MAPK/ERK kinase (MEK)1/2 pathways, which have been implicated in the insulin resistance of PCOS, were not found in NCI-H295A cells, implying that these pathways do not participate in P450c17 phosphorylation. Treatment with various kinase inhibitors that probe the protein kinase A/phosphatidylinositol 3-kinase/Akt pathway and the calcium/calmodulin/MAPK kinase pathway had no effect on the ratio of 17,20 lyase activity to 17alpha-hydroxylase activity, appearing to eliminate these pathways as candidates leading to the phosphorylation of P450c17. Two inhibitors that target the Rho-associated, coiled-coil containing protein kinase (ROCK)/Rho pathway suppressed 17,20 lyase activity and P450c17 phosphorylation, both in NCI-H295A cells and in COS-1 cells transfected with a P450c17 expression vector. ROCK1 phosphorylated P450c17 in vitro, but that phosphorylation did not affect 17,20 lyase activity. We conclude that members of the ROCK/Rho pathway act upstream from the kinase that phosphorylates P450c17 in a fashion that augments 17,20 lyase activity, possibly acting to catalyze a priming phosphorylation.
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Affiliation(s)
- Meng Kian Tee
- Department of Pediatrics and the Metabolic Research Unit, University of California, San Francisco, San Francisco, California 94143-0978, USA
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29
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Bremer AA, Miller WL. The serine phosphorylation hypothesis of polycystic ovary syndrome: a unifying mechanism for hyperandrogenemia and insulin resistance. Fertil Steril 2008; 89:1039-1048. [PMID: 18433749 DOI: 10.1016/j.fertnstert.2008.02.091] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2007] [Revised: 12/20/2007] [Accepted: 02/07/2008] [Indexed: 11/19/2022]
Abstract
Polycystic ovary syndrome (PCOS) is a common endocrinopathy affecting 4%-8% of reproductive-aged women. The syndrome is characterized by hyperandrogenemia and disordered gonadotropin secretion and is often associated with insulin resistance. However, rather than being one disease entity caused by a single molecular defect, PCOS under its current diagnostic criteria most likely includes a number of distinct disease processes with similar clinical phenotypes but different pathophysiologic mechanisms. The serine phosphorylation hypothesis can potentially explain two major features of PCOS--hyperandrogenemia and insulin resistance. Further defining the molecular mechanisms regulating androgen biosynthesis and insulin action in PCOS patients will permit a better understanding of the syndrome and may lead to the generation of novel specific pharmacologic therapies.
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Affiliation(s)
- Andrew A Bremer
- Department of Pediatrics, Division of Endocrinology, University of California-Davis, Sacramento, California.
| | - Walter L Miller
- Department of Pediatrics, Division of Endocrinology, University of California-San Francisco, San Francisco, California
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Waraich RS, Weigert C, Kalbacher H, Hennige AM, Lutz SZ, Häring HU, Schleicher ED, Voelter W, Lehmann R. Phosphorylation of Ser357 of rat insulin receptor substrate-1 mediates adverse effects of protein kinase C-delta on insulin action in skeletal muscle cells. J Biol Chem 2008; 283:11226-33. [PMID: 18285345 DOI: 10.1074/jbc.m708588200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The activation of the protein kinase C (PKC) family of serine/threonine kinases contributes to the modulation of insulin signaling, and the PKC-dependent phosphorylation of insulin receptor substrate (IRS)-1 has been implicated in the development of insulin resistance. Here we demonstrate Ser(357) of rat IRS-1 as a novel PKC-delta-dependent phosphorylation site in skeletal muscle cells upon stimulation with insulin and phorbol ester using Ser(P)(357) antibodies and active and kinase dead mutants of PKC-delta. Phosphorylation of this site was simulated using IRS-1 Glu(357) and shown to reduce insulin-induced tyrosine phosphorylation of IRS-1, to decrease activation of Akt, and to subsequently diminish phosphorylation of glycogen synthase kinase-3. When the phosphorylation was prevented by mutation of Ser(357) to alanine, these effects of insulin were enhanced. When the adjacent Ser(358), present in mouse and rat IRS-1, was mutated to alanine, which is homologous to the human sequence, the insulin-induced phosphorylation of glycogen synthase kinase-3 or tyrosine phosphorylation of IRS-1 was not increased. Moreover, both active PKC-delta and phosphorylation of Ser(357) were shown to be necessary for the attenuation of insulin-stimulated Akt phosphorylation. The phosphorylation of Ser(357) could lead to increased association of PKC-delta to IRS-1 upon insulin stimulation, which was demonstrated with IRS-1 Glu(357). Together, these data suggest that phosphorylation of Ser(357) mediates at least in part the adverse effects of PKC-delta activation on insulin action.
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Mannack G, Graf D, Donner MM, Richter L, Gorg B, Vom Dahl S, Haussinger D, Schliess F. Taurolithocholic acid-3 sulfate impairs insulin signaling in cultured rat hepatocytes and perfused rat liver. Cell Physiol Biochem 2008; 21:137-50. [PMID: 18209481 DOI: 10.1159/000113756] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/04/2007] [Indexed: 12/23/2022] Open
Abstract
BACKGROUND/AIMS The role of bile acids for insulin resistance in cholestatic liver disease is unknown. METHODS The effect of taurolithocholic acid-3 sulfate (TLCS) on insulin signaling was studied in cultured rat hepatocytes and perfused rat liver. RESULTS TLCS induced insulin resistance at the level of insulin receptor (IR) beta Tyr(1158) phosphorylation, phosphoinositide (PI) 3-kinase activity and protein kinase (PK)B Ser(473) phosphorylation in cultured hepatocytes. Consistently, the insulin stimulation of the PI 3-kinase-dependent K(+) uptake, hepatocyte swelling and proteolysis inhibition was blunted by TLCS in perfused rat liver. The PKC inhibitor Go6850 and tauroursodeoxycholate (TUDC) counteracted the suppression of insulin-induced IRbeta and PKB phosphorylation by TLCS. Rapamycin and dibutyryl-cAMP, which inhibited basal signaling via mammalian target of rapamycin (mTOR), restored insulin-induced PKB- but not IRbeta phosphorylation. In livers from 7 day bile duct-ligated rats PKB Ser(473) phosphorylation was decreased by about 50%. CONCLUSION TLCS induces insulin resistance by a PKC-dependent suppression of insulin-induced IRbeta phosphorylation and the PI 3-kinase/PKB path. This can in part be compensated by a decrease of mTOR activity, which may release insulin-sensitive components downstream of the insulin receptor from tonic inhibition. The data suggest that retention of hydrophobic bile acids confers insulin resistance on the cholestatic liver.
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Affiliation(s)
- Gudrun Mannack
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University Dusseldorf, Dusseldorf, Germany
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32
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Jin UH, Kang YJ, Chang YC, Kim CH. Secretion of atherogenic risk factor apolipoprotein B-100 is increased by a potential mechanism of JNK/PKC-mediated insulin resistance in liver cells. J Cell Biochem 2008; 103:908-19. [PMID: 17647275 DOI: 10.1002/jcb.21462] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Apolipoprotein B-100 (ApoB) is the main protein of the atherogenic lipoproteins and plasma ApoB levels reflect the total numbers of atherogenic lipoproteins. Induction of insulin resistance was accompanied by a considerable rise in the production of hepatic very low density lipoprotein (VLDL) containing ApoB and triglyceride. Increased plasma levels of ApoB and triglyceride in VLDL are common characteristics of the dyslipidemia associated with insulin resistance and type 2 diabetes mellitus. Thus, we investigate whether phorbol 12-myristate-13-acetate (PMA)-induced insulin resistance affects the increase of ApoB secretion. PMA increased ApoB secretion and transcriptional level of microsomal triglyceride transfer protein (MTP). PMA treatment also resulted in increase of insulin receptor substrate 1 (IRS1) serine312 (Ser312) and serine1101 (Ser1101) phosphorylation and induction of IRS1 degradation. Additionally, PMA induced activation of c-jun N-terminal kinase (JNK) and protein kinase C (PKC) isoforms (alpha, betaI, delta, zeta, theta), and reduced AKT8 virus oncogene cellular homolog (AKT) activation in a time dependent manner. PMA-induced ApoB secretion, MTP promoter activities, and IRS1 degradation was significantly decreased by treatment of JNK and PKCs inhibitors. Orthovanadate, a potent tyrosine phosphatase inhibitor, increased tyrosine phosphorylation of IRS1 and decreased ApoB secretion of Chang liver cells although PMA was co-treated. From the results, it was concluded that PMA-induced insulin resistance, through induction of serine phosphorylation of IRS1 mediated by activated JNK and PKCs, increases ApoB secretion in Chang liver cells.
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Affiliation(s)
- Un-Ho Jin
- Molecular and Cellular Glycobiology Unit, Department of Biological Sciences, SungKyunKwan University, 300 Chunchun-Dong, Suwon, Kyunggi-Do 440-746, Korea
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Shahid G, Hussain T. GRK2 negatively regulates glycogen synthesis in mouse liver FL83B cells. J Biol Chem 2007; 282:20612-20. [PMID: 17517892 DOI: 10.1074/jbc.m700744200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
G-protein-coupled receptor (GPCR) kinases (GRKs) are serine/threonine kinases that desensitize agonist-occupied classical GPCRs. Although the insulin receptor (IR) is a tyrosine kinase receptor, the IR also couples to G-proteins and utilizes G-protein signaling components. The present study was designed to test the hypothesis that GRK2 negatively regulates IR signaling. FL83B cells, derived from mouse liver, were treated with insulin and membrane translocation of GRK2 was determined using immunofluoresecence and Western blotting. Insulin caused an increase in the translocation of GRK-2 from cytosol to the plasma membrane. To determine the role of GRK2 in IR signaling, GRK2 was selectively down-regulated ( approximately by 90%) in FL83B cells using a small interfering RNA technique. Basal as well as insulin-induced glycogen synthesis (measured by d-[U-(14)C]glucose incorporation) was increased in GRK2-deficient cells compared with control cells. Similarly, GRK2 deficiency increased the basal and insulin-stimulated phosphorylation of Ser(21) in glycogen synthase kinase-3alpha. Insulin-induced tyrosine phosphorylation of the IR was similar in control and GRK2-deficient cells. Basal and insulin-stimulated phosphorylation of Tyr(612) in insulin receptor subunit 1 was significantly increased while phosphorylation of Ser(307) was decreased in GRK2-deficient FL83B cells compared with control cells. Chronic insulin treatment (24 h) in control cells caused an increase in GRK2 (56%) and a decrease in IR (50%) expression associated with the absence of an increase in glycogen synthesis, suggesting impairment of IR function. However, chronic insulin treatment (24 h) did not decrease IR expression or impair IR effects on glycogen synthesis in GRK2-deficient cells. We conclude that (i) GRK2 negatively regulates basal and insulin-stimulated glycogen synthesis via a post-IR signaling mechanism, and (ii) GRK2 may contribute to reduced IR expression and function during chronic insulin exposure.
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Affiliation(s)
- Gulnar Shahid
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, 4800 Calhoun, Houston, TX 77204, USA
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Rondinone CM. Kinase-dependent pathways and the development of insulin resistance in hepatocytes. Expert Rev Endocrinol Metab 2007; 2:195-203. [PMID: 30754170 DOI: 10.1586/17446651.2.2.195] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Hepatic insulin resistance is considered to be a dominant component in the pathogenesis of fasting hyperglycemia in Type 2 diabetes. The role of nutrients, free fatty acids and secretory inflammatory factors released by visceral fat in the pathogenesis of liver insulin resistance requires clarification, but a number of signaling pathways and serine kinases have been implicated. These include the discovery of c-Jun N-terminal kinase, I κβ kinase, protein kinase C θ, δ and ε, and ribosomal protein S6 kinase 1 as critical regulators of insulin action and steatosis in liver. In this article, the causes and mechanisms involved in the development of hepatic insulin resistance, and the signaling pathways and kinases involved, will be discussed. Elucidation of the molecular mechanisms underlying regulation and specificity may prompt novel approaches to the pharmacological modulation of protein kinase activities involved in hepatic insulin resistance. This review will detail recent discoveries and highlight emerging kinase targets that hold potential to reduce hepatic insulin resistance and normalize blood glucose.
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Affiliation(s)
- Cristina M Rondinone
- a Hoffmann-La Roche, Department of Metabolic Diseases, 340 Kingsland Street Nutley, New Jersey 07110, USA.
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35
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Samuel VT, Liu ZX, Wang A, Beddow SA, Geisler JG, Kahn M, Zhang XM, Monia BP, Bhanot S, Shulman GI. Inhibition of protein kinase Cepsilon prevents hepatic insulin resistance in nonalcoholic fatty liver disease. J Clin Invest 2007; 117:739-45. [PMID: 17318260 PMCID: PMC1797607 DOI: 10.1172/jci30400] [Citation(s) in RCA: 371] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2006] [Accepted: 01/03/2007] [Indexed: 12/25/2022] Open
Abstract
Nonalcoholic fatty liver disease is strongly associated with hepatic insulin resistance and type 2 diabetes mellitus, but the molecular signals linking hepatic fat accumulation to hepatic insulin resistance are unknown. Three days of high-fat feeding in rats results specifically in hepatic steatosis and hepatic insulin resistance. In this setting, PKCepsilon, but not other isoforms of PKC, is activated. To determine whether PKCepsilon plays a causal role in the pathogenesis of hepatic insulin resistance, we treated rats with an antisense oligonucleotide against PKCepsilon and subjected them to 3 days of high-fat feeding. Knocking down PKCepsilon expression protects rats from fat-induced hepatic insulin resistance and reverses fat-induced defects in hepatic insulin signaling. Furthermore, we show that PKCepsilon associates with the insulin receptor in vivo and impairs insulin receptor kinase activity both in vivo and in vitro. These data support the hypothesis that PKCepsilon plays a critical role in mediating fat-induced hepatic insulin resistance and represents a novel therapeutic target for type 2 diabetes.
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Affiliation(s)
- Varman T. Samuel
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
Veterans Administration Medical Center, West Haven, Connecticut, USA.
Isis Pharmaceuticals Inc., Carlsbad, California, USA.
Department of Cellular and Molecular Physiology and
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Zhen-Xiang Liu
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
Veterans Administration Medical Center, West Haven, Connecticut, USA.
Isis Pharmaceuticals Inc., Carlsbad, California, USA.
Department of Cellular and Molecular Physiology and
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Amy Wang
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
Veterans Administration Medical Center, West Haven, Connecticut, USA.
Isis Pharmaceuticals Inc., Carlsbad, California, USA.
Department of Cellular and Molecular Physiology and
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Sara A. Beddow
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
Veterans Administration Medical Center, West Haven, Connecticut, USA.
Isis Pharmaceuticals Inc., Carlsbad, California, USA.
Department of Cellular and Molecular Physiology and
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - John G. Geisler
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
Veterans Administration Medical Center, West Haven, Connecticut, USA.
Isis Pharmaceuticals Inc., Carlsbad, California, USA.
Department of Cellular and Molecular Physiology and
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Mario Kahn
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
Veterans Administration Medical Center, West Haven, Connecticut, USA.
Isis Pharmaceuticals Inc., Carlsbad, California, USA.
Department of Cellular and Molecular Physiology and
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Xian-man Zhang
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
Veterans Administration Medical Center, West Haven, Connecticut, USA.
Isis Pharmaceuticals Inc., Carlsbad, California, USA.
Department of Cellular and Molecular Physiology and
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Brett P. Monia
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
Veterans Administration Medical Center, West Haven, Connecticut, USA.
Isis Pharmaceuticals Inc., Carlsbad, California, USA.
Department of Cellular and Molecular Physiology and
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Sanjay Bhanot
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
Veterans Administration Medical Center, West Haven, Connecticut, USA.
Isis Pharmaceuticals Inc., Carlsbad, California, USA.
Department of Cellular and Molecular Physiology and
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Gerald I. Shulman
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
Veterans Administration Medical Center, West Haven, Connecticut, USA.
Isis Pharmaceuticals Inc., Carlsbad, California, USA.
Department of Cellular and Molecular Physiology and
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
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Kang SG, Brown AL, Chung JH. Oxygen Tension Regulates the Stability of Insulin Receptor Substrate-1 (IRS-1) through Caspase-mediated Cleavage. J Biol Chem 2007; 282:6090-7. [PMID: 17179152 DOI: 10.1074/jbc.m610659200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The insulin and insulin-like growth factor-1 (IGF-1) receptors mediate signaling for energy uptake and growth through insulin receptor substrates (IRSs), which interact with these receptors as well as with downstream effectors. Oxygen is essential not only for ATP production through oxidative phosphorylation but also for many cellular processes, particularly those involved in energy homeostasis. The oxygen tension in vivo is significantly lower than that in the air and can vary widely depending on the tissue as well as on perfusion and oxygen consumption. How oxygen tension affects IRSs and their functions is poorly understood. Our findings indicate that transient hypoxia (1% oxygen) leads to caspase-mediated cleavage of IRS-1 without inducing cell death. The IRS-1 protein level rebounds rapidly upon return to normoxia. Protein tyrosine phosphatases (PTPs) appear to be important for the IRS-1 cleavage because tyrosine phosphorylation of the insulin receptor was decreased in hypoxia and IRS-1 cleavage could be blocked either with H(2)O(2) or with vanadate, each of which inhibits PTPs. Activity of Akt, a downstream effector of insulin and IGF-1 signaling that is known to suppress caspase activation, was suppressed in hypoxia. Overexpression of dominant-negative Akt led to IRS-1 cleavage even in normoxia, and overexpression of constitutively active Akt partially suppressed IRS-1 cleavage in hypoxia, suggesting that hypoxia-mediated suppression of Akt may induce caspase-mediated IRS-1 cleavage. In conclusion, our study elucidates a mechanism by which insulin and IGF-1 signaling can be matched to the oxygen level that is available to support growth and energy metabolism.
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Affiliation(s)
- Sung Gyun Kang
- Laboratory of Biochemical Genetics, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA
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Mazurkiewicz-Munoz AM, Argetsinger LS, Kouadio JLK, Stensballe A, Jensen ON, Cline JM, Carter-Su C. Phosphorylation of JAK2 at serine 523: a negative regulator of JAK2 that is stimulated by growth hormone and epidermal growth factor. Mol Cell Biol 2006; 26:4052-62. [PMID: 16705159 PMCID: PMC1489095 DOI: 10.1128/mcb.01591-05] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The tyrosine kinase JAK2 is a key signaling protein for at least 20 receptors in the cytokine/hematopoietin receptor superfamily and is a component of signaling for multiple receptor tyrosine kinases and several G-protein-coupled receptors. In this study, phosphopeptide affinity enrichment and mass spectrometry identified serine 523 (Ser523) in JAK2 as a site of phosphorylation. A phosphoserine 523 antibody revealed that Ser523 is rapidly but transiently phosphorylated in response to growth hormone (GH). MEK1 inhibitor UO126 suppresses GH-dependent phosphorylation of Ser523, suggesting that extracellular signal-regulated kinases (ERKs) 1 and/or 2 or another kinase downstream of MEK1 phosphorylate Ser523 in response to GH. Other ERK activators, phorbol 12-myristate 13-acetate and epidermal growth factor, also stimulate phosphorylation of Ser523. When Ser523 in JAK2 was mutated, JAK2 kinase activity as well as GH-dependent tyrosyl phosphorylation of JAK2 and Stat5 was enhanced, suggesting that phosphorylation of Ser523 inhibits JAK2 kinase activity. We hypothesize that phosphorylation of Ser523 in JAK2 by ERKs 1 and/or 2 or other as-yet-unidentified kinases acts in a negative feedback manner to dampen activation of JAK2 in response to GH and provides a mechanism by which prior exposure to environmental factors that regulate Ser523 phosphorylation might modulate the cell's response to GH.
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Affiliation(s)
- Anna M Mazurkiewicz-Munoz
- Graduate Program in Cellular and Molecular Biology, The University of Michigan Medical School, Ann Arbor, MI 48109-0622, USA
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38
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Ishida-Takahashi R, Rosario F, Gong Y, Kopp K, Stancheva Z, Chen X, Feener EP, Myers MG. Phosphorylation of Jak2 on Ser(523) inhibits Jak2-dependent leptin receptor signaling. Mol Cell Biol 2006; 26:4063-73. [PMID: 16705160 PMCID: PMC1489076 DOI: 10.1128/mcb.01589-05] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The leptin receptor, LRb, and other cytokine receptors are devoid of intrinsic enzymatic activity and rely upon the activity of constitutively associated Jak family tyrosine kinases to mediate intracellular signaling. In order to clarify mechanisms by which Jak2, the cognate LRb-associated Jak kinase, is regulated and mediates downstream signaling, we employed tandem mass spectroscopic analysis to identify phosphorylation sites on Jak2. We identified Ser523 as the first-described site of Jak2 serine phosphorylation and demonstrated that this site is phosphorylated on Jak2 from intact cells and mouse spleen. Ser523 was highly phosphorylated in HEK293 cells independently of LRb-Jak2 activation, suggesting a potential role for the phosphorylation of Ser523 in the regulation of LRb by other pathways. Indeed, mutation of Ser523 sensitized and prolonged signaling by Jak2 following activation by the intracellular domain of LRb. The effect of Ser523 on Jak2 function was independent of Tyr570-mediated inhibition. Thus, the phosphorylation of Jak2 on Ser523 inhibits Jak2 activity and represents a novel mechanism for the regulation of Jak2-dependent cytokine signaling.
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39
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Reiter CEN, Wu X, Sandirasegarane L, Nakamura M, Gilbert KA, Singh RSJ, Fort PE, Antonetti DA, Gardner TW. Diabetes reduces basal retinal insulin receptor signaling: reversal with systemic and local insulin. Diabetes 2006; 55:1148-56. [PMID: 16567541 DOI: 10.2337/diabetes.55.04.06.db05-0744] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Diabetic retinopathy is characterized by early onset of neuronal cell death. We previously showed that insulin mediates a prosurvival pathway in retinal neurons and that normal retina expresses a highly active basal insulin receptor/Akt signaling pathway that is stable throughout feeding and fasting. Using the streptozotocin-induced diabetic rat model, we tested the hypothesis that diabetes diminishes basal retinal insulin receptor signaling concomitantly with increased diabetes-induced retinal apoptosis. The expression, phosphorylation status, and/or kinase activity of the insulin receptor and downstream signaling proteins were investigated in retinas of age-matched control, diabetic, and insulin-treated diabetic rats. Four weeks of diabetes reduced basal insulin receptor kinase, insulin receptor substrate (IRS)-1/2-associated phosphatidylinositol 3-kinase, and Akt kinase activity without altering insulin receptor or IRS-1/2 expression or tyrosine phosphorylation. After 12 weeks of diabetes, constitutive insulin receptor autophosphorylation and IRS-2 expression were reduced, without changes in p42/p44 mitogen-activated protein kinase or IRS-1. Sustained systemic insulin treatment of diabetic rats prevented loss of insulin receptor and Akt kinase activity, and acute intravitreal insulin administration restored insulin receptor kinase activity. Insulin treatment restored insulin receptor-beta autophosphorylation in rat retinas maintained ex vivo, demonstrating functional receptors and suggesting loss of ligand as a cause for reduced retinal insulin receptor/Akt pathway activity. These results demonstrate that diabetes progressively impairs the constitutive retinal insulin receptor signaling pathway through Akt and suggests that loss of this survival pathway may contribute to the initial stages of diabetic retinopathy.
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Affiliation(s)
- Chad E N Reiter
- Dept. of Cellular and Molecular Physiology, Juvenile Diabetes Research Foundation Diabetic Retinopathy Center, Penn State College of Medicine, Hershey, PA 17033, USA
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40
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Abstract
Lipids as fuel for energy provision originate from different sources: albumin-bound long-chain fatty acids (LCFA) in the blood plasma, circulating very-low-density lipoproteins-triacylglycerols (VLDL-TG), fatty acids from triacylglycerol located in the muscle cell (IMTG), and possibly fatty acids liberated from adipose tissue adhering to the muscle cells. The regulation of utilization of the different lipid sources in skeletal muscle during exercise is reviewed, and the influence of diet, training, and gender is discussed. Major points deliberated are the methods utilized to measure uptake and oxidation of LCFA during exercise in humans. The role of the various lipid-binding proteins in transmembrane and cytosolic transport of lipids is considered as well as regulation of lipid entry into the mitochondria, focusing on the putative role of AMP-activated protein kinase (AMPK), acetyl CoA carboxylase (ACC), and carnitine during exercise. The possible contribution to fuel provision during exercise of circulating VLDL-TG as well as the role of IMTG is discussed from a methodological point of view. The contribution of IMTG for energy provision may not be large, covering ∼10% of total energy provision during fasting exercise in male subjects, whereas in females, IMTG may cover a larger proportion of energy delivery. Molecular mechanisms involved in breakdown of IMTG during exercise are also considered focusing on hormone-sensitive lipase (HSL). Finally, the role of lipids in development of insulin resistance in skeletal muscle, including possible molecular mechanisms involved, is discussed.
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Affiliation(s)
- Bente Kiens
- Copenhagen Muscle Research Centre, Dept. of Human Physiology, Institute of Exercise and Sports Sciences, University of Copenhagen, 13 Universitetsparken, DK-2100 Copenhagen, Denmark.
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41
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Johnson DR, O'Connor JC, Satpathy A, Freund GG. Cytokines in type 2 diabetes. VITAMINS AND HORMONES 2006; 74:405-41. [PMID: 17027525 DOI: 10.1016/s0083-6729(06)74017-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Daniel R Johnson
- Department of Animal Sciences, University of Illinois, Urbana, Illinois 61801, USA
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42
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Abstract
Insulin resistance is a hallmark of Type II diabetes. It is well documented that insulin sensitizers such as peroxisome-proliferator-activated receptor gamma agonists and aspirin improve insulin action in vivo. The detailed mechanisms by which the insulin sensitizers promote insulin signalling, however, are not completely understood and remain somewhat controversial. In the present review, we summarize our studies attempting to explore the molecular mechanisms underlying the effects of insulin sensitizers in cells and in animal models of insulin resistance. In 3T3-L1 adipocytes and/or in HEK-293 cells stably expressing recombinant IRS1 protein (insulin receptor substrate protein 1), the peroxisome-proliferator-activated receptor gamma agonist rosiglitazone and aspirin promote insulin signalling by decreasing inhibitory IRS1 serine phosphorylation. Increased IRS1 Ser-307 phosphorylation and concomitant decreased insulin signalling as measured by insulin-stimulated IRS1 tyrosine phosphorylation and Akt threonine phosphorylation were observed in adipose tissues of Zucker obese rats compared with lean control rats. Treatment with rosiglitazone for 24 and 48 h increased insulin signalling and decreased IRS1 Ser-307 phosphorylation concomitantly. Treatment of the Zucker obese rats with rosiglitazone for 24 h also reversed the high circulating levels of free fatty acids, which have been shown to correlate with increased IRS1 serine phosphorylation. Taken together, the results suggest that IRS1 inhibitory serine phosphorylation is a key component of insulin resistance and its reversal may be physiologically relevant to insulin sensitization in vivo.
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Affiliation(s)
- G Jiang
- Metabolic Disorders - Diabetes, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
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Abstract
Cytochrome P450 enzymes catalyze the degradation of drugs and xenobiotics, but also catalyze a wide variety of biosynthetic processes, including most steps in steroidogenesis. The catalytic rate of a P450 enzyme is determined in large part by the rate of electron transfer from its redox partners. Type I P450 enzymes, found in mitochondria, receive electrons from reduced nicotinamide adenine dinucleotide (NADPH) via the intermediacy of two proteins-ferredoxin reductase (a flavoprotein) and ferredoxin (an iron/sulfur protein). Type I P450 enzymes include the cholesterol side-chain cleavage enzyme (P450scc), the two isozymes of 11-hydroxylase (P450c11beta and P450c11AS), and several vitamin D-metabolizing enzymes. Disorders of these enzymes, but not of the two redox partners, have been described. Type II P450 enzymes, found in the endoplasmic reticulum, receive electrons from NADPH via P450 oxidoreductase (POR), which contains two flavin moieties. Steroidogenic Type II P450 enzymes include 17alpha-hydroxylase/17,20 lyase (P450c17), 21-hydroxylase (P450c21), and aromatase (P450aro). All P450 enzymes catalyze multiple reactions, but P450c17 appears to be unique in that the ratio of its activities is regulated at a posttranslational level. Three factors can increase the degree of 17,20 lyase activity relative to the 17alpha-hydroxylase activity by increasing electron flow from POR: a high molar ratio of POR to P450c17, serine phosphorylation of P450c17, and the presence of cytochrome b(5), acting as an allosteric factor to promote the interaction of POR with P450c17. POR is required for the activity of all 50 human Type II P450 enzymes, and ablation of the Por gene in mice causes embryonic lethality. Nevertheless, mutation of the human POR gene is compatible with life, causing multiple steroidogenic defects and a skeletal dysplasia called Antley-Bixler syndrome.
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Affiliation(s)
- Walter L Miller
- Department of Pediatrics, Building MR-4, Room 209, University of California, San Francisco, San Francisco, California 94143-0978, USA
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Puljak L, Pagliassotti MJ, Wei Y, Qadri I, Parameswara V, Esser V, Fitz JG, Kilic G. Inhibition of cellular responses to insulin in a rat liver cell line. A role for PKC in insulin resistance. J Physiol 2005; 563:471-82. [PMID: 15649984 PMCID: PMC1665596 DOI: 10.1113/jphysiol.2004.080333] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The initial response of liver cells to insulin is mediated through exocytosis of Cl- channel-containing vesicles and a subsequent opening of plasma membrane Cl- channels. Intracellular accumulation of fatty acids leads to profound defects in metabolism, and is closely associated with insulin resistance. It is not known whether the activity of Cl- channels is altered in insulin resistance and by which mechanisms. We studied the effects of fatty acid accumulation on Cl- channel opening in a model liver cell line. Overnight treatment with amiodarone increased the fat content by approximately 2-fold, and the rates of gluconeogenesis by approximately 5-fold. The ability of insulin to suppress gluconeogenesis was markedly reduced indicating that amiodarone treatment induces insulin resistance. Western blot analysis showed that these cells express the same number of insulin receptors as control cells. However, insulin failed to activate exocytosis and Cl- channel opening. These inhibitory effects were mimicked in control cells by exposures to arachidonic acid (15 microm). Further studies demonstrated that fatty acids stimulate the PKC activity, and inhibition of PKC partially restored exocytosis and Cl- channel opening in insulin-resistant cells. Accordingly, activation of PKC with PMA in control cells potently inhibited the insulin responses. These results suggest that stimulation of PKC activity in insulin resistance contributes to the inhibition of cellular responses to insulin in liver cells.
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Affiliation(s)
- Livia Puljak
- Department of Internal Medicine, University of Texas South-western Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8887, USA
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Andrade Ferreira I, Akkerman JWN. IRS-1 and Vascular Complications in Diabetes Mellitus. VITAMINS AND HORMONES 2005; 70:25-67. [PMID: 15727801 DOI: 10.1016/s0083-6729(05)70002-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/01/2023]
Abstract
The expected explosive increase in the number of patients with diabetes mellitus will increase the stress on health care. Treatment is focused on preventing vascular complications associated with the disorder. In order to develop better treatment regimens, the field of research has made a great effort in understanding this disorder. This chapter summarizes the current views on the insulin signaling pathway with emphasis on intracellular signaling events associated with insulin resistance, which lead to the prothrombotic condition in the vasculature of patience with diabetes mellitus.
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Affiliation(s)
- I Andrade Ferreira
- Thrombosis and Haemostasis Laboratory, Department of Hematology, University Medical Center Utrecht, 3584 CX Utrecht, The Netherlands
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46
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Miller WL. Disorders of androgen synthesis--from cholesterol to dehydroepiandrosterone. Med Princ Pract 2005; 14 Suppl 1:58-68. [PMID: 16103714 DOI: 10.1159/000086185] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2004] [Accepted: 08/14/2004] [Indexed: 01/29/2023] Open
Abstract
Androgens and estrogens are primarily made from dehydroepiandrosterone (DHEA), which is made from cholesterol via four steps. First, cholesterol enters the mitochondria with the assistance of the steroidogenic acute regulatory protein (StAR). Mutations in the StAR gene cause congenital lipoid adrenal hyperplasia (lipoid CAH), a potentially lethal disease in which virtually no steroids are made. Lipoid CAH is common among Palestinian Arabs and people from eastern Arabia, and among Korean and Japanese people. Second, within the mitochondria, cholesterol is converted to pregnenolone by the cholesterol side chain cleavage enzyme, P450scc; disorder of this enzyme is very rare, probably due to embryonic lethality. Third, pregnenolone undergoes 17alpha-hydroxylation by microsomal P450c17. 17alpha-Hydroxylase deficiency, manifesting as female sexual infantilism and hypertension, is rare except in Brazil. Finally, 17-OH pregnenolone is converted to DHEA by the 17,20 lyase activity of P450c17. The ratio of the 17,20 lyase to 17alpha-hydroxylase activity of P450c17 determines the ratio of C21 to C19 steroids produced. This ratio is regulated posttranslationally by at least three factors: the abundance of the electron-donating protein P450 oxidoreductase (POR), the presence of cytochrome b5 and the serine phosphorylation of P450c17. Mutations of POR are a new, recently described disorder manifesting as the Antley-Bixler skeletal dysplasia syndrome, and a form of polycystic ovary syndrome.
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Affiliation(s)
- Walter L Miller
- Department of Pediatrics, University of California, San Francisco, California 94142-0978, USA.
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47
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Kani S, Oishi I, Yamamoto H, Yoda A, Suzuki H, Nomachi A, Iozumi K, Nishita M, Kikuchi A, Takumi T, Minami Y. The receptor tyrosine kinase Ror2 associates with and is activated by casein kinase Iepsilon. J Biol Chem 2004; 279:50102-9. [PMID: 15375164 DOI: 10.1074/jbc.m409039200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Ror2, a member of the mammalian Ror family of receptor tyrosine kinases, plays important roles in developmental morphogenesis, although the mechanism underlying activation of Ror2 remains largely elusive. We show that when expressed in mammalian cells, Ror2 associates with casein kinase Iepsilon (CKIepsilon), a crucial regulator of Wnt signaling. This association occurs primarily via the cytoplasmic C-terminal proline-rich domain of Ror2. We also show that Ror2 is phosphorylated by CKIepsilon on serine/threonine residues, in its C-terminal serine/threonine-rich 2 domain, resulting in autophosphorylation of Ror2 on tyrosine residues. Furthermore, it was found that association of Ror2 with CKIepsilon is required for its serine/threonine phosphorylation by CKIepsilon. Site-directed mutagenesis of tyrosine residues in Ror2 reveals that the sites of phosphorylation are contained among the five tyrosine residues in the proline-rich domain but not among the four tyrosine residues in the tyrosine kinase domain. Moreover, we show that in mammalian cells, CKIepsilon-mediated phosphorylation of Ror2 on serine/threonine and tyrosine residues is followed by the tyrosine phosphorylation of G protein-coupled receptor kinase 2, a kinase with a developmental expression pattern that is remarkably similar to that of Ror2. Intriguingly, a mutant of Ror2 lacking five tyrosine residues, including the autophosphorylation sites, fails to tyrosine phosphorylate G protein-coupled receptor kinase 2. This indicates that autophosphorylation of Ror2 is required for full activation of its tyrosine kinase activity. These findings demonstrate a novel role for CKIepsilon in the regulation of Ror2 tyrosine kinase.
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Affiliation(s)
- Shuichi Kani
- Department of Genome Sciences, Faculty of Medical Sciences, Graduate School of Medicine, Kobe University, Kobe 650-0017, Japan.
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48
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Werner ED, Lee J, Hansen L, Yuan M, Shoelson SE. Insulin Resistance Due to Phosphorylation of Insulin Receptor Substrate-1 at Serine 302. J Biol Chem 2004; 279:35298-305. [PMID: 15199052 DOI: 10.1074/jbc.m405203200] [Citation(s) in RCA: 174] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Inhibitory serine phosphorylation is a potential molecular mechanism for insulin resistance. We have developed a new variant of the yeast two-hybrid method, referred to as disruptive yeast tri-hybrid (Y3H), to identify inhibitory kinases and sites of phosphorylation in insulin receptors (IR) and IR substrates, IRS-1. Using IR and IRS-1 as bait and prey, respectively, and c-Jun NH(2)-terminal kinase (JNK1) as the disruptor, we now show that phosphorylation of IRS-1 Ser-307, a previously identified site, is necessary but not sufficient for JNK1-mediated disruption of IR/IRS-1 binding. We further identify a new phosphorylation site, Ser-302, and show that this too is necessary for JNK1-mediated disruption. Seven additional kinases potentially linked to insulin resistance similarly block IR/IRS-1 binding in the disruptive Y3H, but through distinct Ser-302- and Ser-307-independent mechanisms. Phosphospecific antibodies that recognize sequences surrounding Ser(P)-302 or Ser(P)-307 were used to determine whether the sites were phosphorylated under relevant conditions. Phosphorylation was promoted at both sites in Fao hepatoma cells by reagents known to promote Ser/Thr phosphorylation, including the phorbol ester phorbol 12-myristate 13-acetate, anisomycin, calyculin A, and insulin. The antibodies further showed that Ser(P)-302 and Ser(P)-307 are increased in animal models of obesity and insulin resistance, including genetically obese ob/ob mice, diet-induced obesity, and upon induction of hyperinsulinemia. These findings demonstrate that phosphorylation at both Ser-302 and Ser-307 is necessary for JNK1-mediated inhibition of the IR/IRS-1 interaction and that Ser-302 and Ser-307 are phosphorylated in parallel in cultured cells and in vivo under conditions that lead to insulin resistance.
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Affiliation(s)
- Eric D Werner
- Joslin Diabetes Center and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA
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49
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Ranganathan S, Liu CX, Migliorini MM, Von Arnim CAF, Peltan ID, Mikhailenko I, Hyman BT, Strickland DK. Serine and threonine phosphorylation of the low density lipoprotein receptor-related protein by protein kinase Calpha regulates endocytosis and association with adaptor molecules. J Biol Chem 2004; 279:40536-44. [PMID: 15272003 DOI: 10.1074/jbc.m407592200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low density lipoprotein receptor-related protein (LRP) is a large receptor that participates in endocytosis, signaling pathways, and phagocytosis of necrotic cells. Mechanisms that direct LRP to function in these distinct pathways likely involve its association with distinct cytoplasmic adaptor proteins. We tested the hypothesis that the association of various adaptor proteins with the LRP cytoplasmic domain is modulated by its phosphorylation state. Phosphoamino acid analysis of metabolically labeled LRP revealed that this receptor is phosphorylated at serine, threonine, and tyrosine residues within its cytoplasmic domain, whereas inhibitor studies identified protein kinase Calpha (PKCalpha) as a kinase capable of phosphorylating LRP. Mutational analysis identified critical threonine and serine residues within the LRP cytoplasmic domain that are necessary for phosphorylation mediated by PKCalpha. Mutating these threonine and serine residues to alanines generated a receptor that was not phosphorylated and that was internalized more rapidly than wild-type LRP, revealing that phosphorylation reduces the association of LRP with adaptor molecules of the endocytic machinery. In contrast, serine and threonine phosphorylation was necessary for the interaction of LRP with Shc, an adaptor protein that participates in signaling events. Furthermore, serine and threonine phosphorylation increased the interaction of LRP with other adaptor proteins such as Dab-1 and CED-6/GULP. These results indicate that phosphorylation of LRP by PKCalpha modulates the endocytic and signaling function of LRP by modifying its association with adaptor proteins.
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Affiliation(s)
- Sripriya Ranganathan
- Department of Surgery, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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50
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Ueki K, Kondo T, Kahn CR. Suppressor of cytokine signaling 1 (SOCS-1) and SOCS-3 cause insulin resistance through inhibition of tyrosine phosphorylation of insulin receptor substrate proteins by discrete mechanisms. Mol Cell Biol 2004; 24:5434-46. [PMID: 15169905 PMCID: PMC419873 DOI: 10.1128/mcb.24.12.5434-5446.2004] [Citation(s) in RCA: 492] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Insulin resistance is a pathophysiological component of type 2 diabetes and obesity and also occurs in states of stress, infection, and inflammation associated with an upregulation of cytokines. Here we show that in both obesity and lipopolysaccharide (LPS)-induced endotoxemia there is an increase in suppressor of cytokine signaling (SOCS) proteins, SOCS-1 and SOCS-3, in liver, muscle, and, to a lesser extent, fat. In concordance with these increases by LPS, tyrosine phosphorylation of the insulin receptor (IR) is partially impaired and phosphorylation of the insulin receptor substrate (IRS) proteins is almost completely suppressed. Direct overexpression of SOCS-3 in liver by adenoviral-mediated gene transfer markedly decreases tyrosine phosphorylation of both IRS-1 and IRS-2, while SOCS-1 overexpression preferentially inhibits IRS-2 phosphorylation. Neither affects IR phosphorylation, although both SOCS-1 and SOCS-3 bind to the insulin receptor in vivo in an insulin-dependent fashion. Experiments with cultured cells expressing mutant insulin receptors reveal that SOCS-3 binds to Tyr960 of IR, a key residue for the recognition of IRS-1 and IRS-2, whereas SOCS-1 binds to the domain in the catalytic loop essential for IRS-2 recognition in vitro. Moreover, overexpression of either SOCS-1 or SOCS-3 attenuates insulin-induced glycogen synthesis in L6 myotubes and activation of glucose uptake in 3T3L1 adipocytes. By contrast, a reduction of SOCS-1 or SOCS-3 by antisense treatment partially restores tumor necrosis factor alpha-induced downregulation of tyrosine phosphorylation of IRS proteins in 3T3L1 adipocytes. These data indicate that SOCS-1 and SOCS-3 act as negative regulators in insulin signaling and serve as one of the missing links between insulin resistance and cytokine signaling.
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Affiliation(s)
- Kohjiro Ueki
- Research Division, Joslin Diabetes Center, and Departmentof Medicine, Harvard Medical School, Boston, MA 02215, USA
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