51
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Jiang JX, Török NJ. MLK3 as a regulator of disease progression in Non-alcoholic steatohepatitis. Liver Int 2014; 34:1131-2. [PMID: 24690035 PMCID: PMC4392882 DOI: 10.1111/liv.12556] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Accepted: 03/26/2014] [Indexed: 12/16/2022]
Affiliation(s)
- Joy X Jiang
- Department of Internal Medicine, Division of Gastroenterology, Hepatology UC Davis Medical Center, Sacramento, CA, USA
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52
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Lu Y, Liu X, Jiao Y, Xiong X, Wang E, Wang X, Zhang Z, Zhang H, Pan L, Guan Y, Cai D, Ning G, Li X. Periostin promotes liver steatosis and hypertriglyceridemia through downregulation of PPARα. J Clin Invest 2014; 124:3501-13. [PMID: 25003192 DOI: 10.1172/jci74438] [Citation(s) in RCA: 105] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Accepted: 05/22/2014] [Indexed: 02/06/2023] Open
Abstract
Hepatosteatosis is characterized by an aberrant accumulation of triglycerides in the liver; however, the factors that drive obesity-induced fatty liver remain largely unknown. Here, we demonstrated that the secreted cell adhesion protein periostin is markedly upregulated in livers of obese rodents and humans. Notably, overexpression of periostin in the livers of WT mice promoted hepatic steatosis and hypertriglyceridemia. Conversely, both genetic ablation of periostin and administration of a periostin-neutralizing antibody dramatically improved hepatosteatosis and hypertriglyceridemia in obese mice. Overexpression of periostin resulted in reduced expression of peroxisome proliferator-activated receptor α (PPARα), a master regulator of fatty acid oxidation, and activation of the JNK signaling pathway. In mouse primary hepatocytes, inhibition of α6β4 integrin prevented activation of JNK and suppression of PPARα in response to periostin. Periostin-dependent activation of JNK resulted in activation of c-Jun, which prevented RORα binding and transactional activation at the Ppara promoter. Together, these results identify a periostin-dependent pathway that mediates obesity-induced hepatosteatosis.
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53
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Gadang V, Konaniah E, Hui DY, Jaeschke A. Mixed-lineage kinase 3 deficiency promotes neointima formation through increased activation of the RhoA pathway in vascular smooth muscle cells. Arterioscler Thromb Vasc Biol 2014; 34:1429-36. [PMID: 24790140 PMCID: PMC4084683 DOI: 10.1161/atvbaha.114.303439] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Mitogen-activated protein kinase pathways play an important role in neointima formation secondary to vascular injury, in part by promoting proliferation of vascular smooth muscle cells (VSMC). Mixed-lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase that activates multiple mitogen-activated protein kinase pathways and has been implicated in regulating proliferation in several cell types. However, the role of MLK3 in VSMC proliferation and neointima formation is unknown. The aim of this study was to determine the function of MLK3 in the development of neointimal hyperplasia and to elucidate the underlying mechanisms. APPROACH AND RESULTS Neointima formation was analyzed after endothelial denudation of carotid arteries from wild-type and MLK3-deficient mice. MLK3 deficiency promoted injury-induced neointima formation and increased proliferation of primary VSMC derived from aortas isolated from MLK3-deficient mice compared with wild-type mice. Furthermore, MLK3 deficiency increased the activation of p63Rho guanine nucleotide exchange factor, RhoA, and Rho kinase in VSMC, a pathway known to promote neointimal hyperplasia, and reconstitution of MLK3 expression attenuated Rho kinase activation. Furthermore, cJun NH2-terminal kinase activation was decreased in MLK3-deficient VSMC, and proliferation of wild-type but not MLK3 knockout cells treated with a cJun NH2-terminal kinase inhibitor was attenuated. CONCLUSIONS We demonstrate that MLK3 limits RhoA activation and injury-induced neointima formation by binding to and inhibiting the activation of p63Rho guanine nucleotide exchange factor, a RhoA activator. In MLK3-deficient cells, activation of p63Rho guanine nucleotide exchange factor proceeds in an unchecked manner, leading to a net increase in RhoA pathway activation. Reconstitution of MLK3 expression restores MLK3/p63Rho guanine nucleotide exchange factor interaction, which is attenuated by feedback from activated cJun NH2-terminal kinase.
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MESH Headings
- Animals
- Carotid Arteries/enzymology
- Carotid Arteries/pathology
- Carotid Artery Injuries/enzymology
- Carotid Artery Injuries/genetics
- Carotid Artery Injuries/pathology
- Cell Proliferation
- Cells, Cultured
- Disease Models, Animal
- Hyperplasia
- JNK Mitogen-Activated Protein Kinases/antagonists & inhibitors
- JNK Mitogen-Activated Protein Kinases/metabolism
- MAP Kinase Kinase Kinases/deficiency
- MAP Kinase Kinase Kinases/genetics
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/enzymology
- Muscle, Smooth, Vascular/pathology
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/enzymology
- Myocytes, Smooth Muscle/pathology
- Neointima
- Protein Kinase Inhibitors/pharmacology
- Rho Guanine Nucleotide Exchange Factors/metabolism
- Signal Transduction
- Time Factors
- rho GTP-Binding Proteins/metabolism
- rho-Associated Kinases/metabolism
- rhoA GTP-Binding Protein
- Mitogen-Activated Protein Kinase Kinase Kinase 11
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Affiliation(s)
- Vidya Gadang
- From the Department of Pathology, Metabolic Diseases Institute, University of Cincinnati, OH
| | - Eddy Konaniah
- From the Department of Pathology, Metabolic Diseases Institute, University of Cincinnati, OH
| | - David Y Hui
- From the Department of Pathology, Metabolic Diseases Institute, University of Cincinnati, OH
| | - Anja Jaeschke
- From the Department of Pathology, Metabolic Diseases Institute, University of Cincinnati, OH.
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54
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Endoplasmic reticulum stress does not contribute to steatohepatitis in obese and insulin-resistant high-fat-diet-fed foz/foz mice. Clin Sci (Lond) 2014; 127:507-18. [DOI: 10.1042/cs20140026] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Unlike in mice developing simple steatosis, endoplasmic reticulum stress does not contribute to the pathogenesis of insulin resistance and steatohepatitis in high-fat-diet-fed foz/foz mice, which develop progressive liver disease in the metabolic context seen in human non-alcoholic steatohepatitis.
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55
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Abstract
SIGNIFICANCE Understanding isoform- and context-specific subcellular Nox reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase compartmentalization allows relevant functional inferences. This review addresses the interplay between Nox NADPH oxidases and the endoplasmic reticulum (ER), an increasingly evident player in redox pathophysiology given its role in redox protein folding and stress responses. RECENT ADVANCES Catalytic/regulatory transmembrane subunits are synthesized in the ER and their processing includes folding, N-glycosylation, heme insertion, p22phox heterodimerization, as shown for phagocyte Nox2. Dual oxidase (Duox) maturation also involves the regulation by ER-resident Duoxa2. The ER is the activation site for some isoforms, typically Nox4, but potentially other isoforms. Such location influences redox/Nox-mediated calcium signaling regulation via ER targets, such as sarcoendoplasmic reticulum calcium ATPase (SERCA). Growing evidence suggests that Noxes are integral signaling elements of the unfolded protein response during ER stress, with Nox4 playing a dual prosurvival/proapoptotic role in this setting, whereas Nox2 enhances proapoptotic signaling. ER chaperones such as protein disulfide isomerase (PDI) closely interact with Noxes. PDI supports growth factor-dependent Nox1 activation and mRNA expression, as well as migration in smooth muscle cells, and PDI overexpression induces acute spontaneous Nox activation. CRITICAL ISSUES Mechanisms of PDI effects include possible support of complex formation and RhoGTPase activation. In phagocytes, PDI supports phagocytosis, Nox activation, and redox-dependent interactions with p47phox. Together, the results implicate PDI as possible Nox organizer. FUTURE DIRECTIONS We propose that convergence between Noxes and ER may have evolutive roots given ER-related functional contexts, which paved Nox evolution, namely calcium signaling and pathogen killing. Overall, the interplay between Noxes and the ER may provide relevant insights in Nox-related (patho)physiology.
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Affiliation(s)
- Francisco R M Laurindo
- Vascular Biology Laboratory, Heart Institute (InCor), University of São Paulo School of Medicine , São Paulo, Brazil
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56
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Degradation of Keap1 activates BH3-only proteins Bim and PUMA during hepatocyte lipoapoptosis. Cell Death Differ 2014; 21:1303-12. [PMID: 24769730 DOI: 10.1038/cdd.2014.49] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Revised: 02/24/2014] [Accepted: 03/13/2014] [Indexed: 12/25/2022] Open
Abstract
Non-alcoholic steatohepatitis is characterized by hepatic steatosis, elevated levels of circulating free fatty acids (FFA) and hepatocyte lipoapoptosis. This lipoapoptosis requires increased JNK phosphorylation and activation of the pro-apoptotic BH3-only proteins Bim and PUMA. Kelch-like ECH-associated protein (Keap)-1 is a BTB/Kelch protein that can regulate the expression of Bcl-2 protein and control apoptotic cell death. Yet, the role of Keap1 in hepatocyte lipotoxicity is unclear. Here we demonstrate that Keap1 protein was rapidly degraded in hepatocytes, through autophagy in a p62-dependent manner, in response to the toxic saturated FFA palmitate, but not following incubation with the non-toxic FFA oleic acid. Stable knockdown of Keap1 expression, using shRNA technology, in hepatocarcinoma cell lines induced spontaneous cell toxicity that was associated with JNK1-dependent upregulation of Bim and PUMA protein levels. Also, Keap1 knockdown further sensitized hepatocytes to lipoapoptosis by palmitate. Likewise, primary hepatocytes isolated from liver-specific Keap1(-/-) mice displayed higher Bim and PUMA protein levels and demonstrated increased sensitivity to palmitate-induced apoptosis than wild-type mouse hepatocytes. Finally, stable knockdown of Bim or PUMA expression prevented cell toxicity induced by loss of Keap1. These results implicate p62-dependent autophagic degradation of Keap1 by palmitate as a mechanism contributing to hepatocyte lipoapoptosis.
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57
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Ibrahim SH, Gores GJ, Hirsova P, Kirby M, Miles L, Jaeschke A, Kohli R. Mixed lineage kinase 3 deficient mice are protected against the high fat high carbohydrate diet-induced steatohepatitis. Liver Int 2014; 34:427-37. [PMID: 24256559 PMCID: PMC3977027 DOI: 10.1111/liv.12353] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2013] [Accepted: 09/25/2013] [Indexed: 12/14/2022]
Abstract
BACKGROUND & AIMS C-Jun N-terminal kinase (JNK) activation is pivotal in the development of nonalcoholic steatohepatitis (NASH). Mixed lineage kinase 3 (MLK) 3 is one of the mitogen activated protein kinase kinase kinase (MAP3K) that mediates JNK activation in the liver. Despite this concept, the role of MLK3 in modulating liver injury during nutrient excess has not been explored. Our aim was to determine if MLK3 deficient mice were protected against high fat high carbohydrate (HFHC) diet-induced NASH. METHODS We employed eight-week-old Mlk3(-/-) male C57BL/6J mice, and wild type (WT) mice C57BL/6J as controls. Mice were fed a HFHC or a chow diet adlib for 16 weeks. RESULTS Hepatic JNK activating phosphorylation was readily absent in the Mlk3(-/-) mice fed the HFHC diet, but not in WT mice. This inhibition of JNK activation was hepatoprotective. Despite a comparable increase in weight gain, hepatic steatosis by histological examination and hepatic triglyceride quantification was reduced in HFHC diet-fed Mlk3(-/-) mice compared with WT mice. In addition, compared with the WT mice, HFHC diet-fed Mlk3(-/-) mice had significantly attenuated liver injury as manifested by reduced ALT levels, hepatocyte apoptosis, markers of hepatic inflammation and indices of hepatic fibrogenesis. CONCLUSION Our results suggest that loss of MLK3 in mice is protective against HFHC diet-induced NASH, in a weight-independent fashion, through attenuation of JNK activation. MLK3 is a potential therapeutic target for the treatment of human NASH.
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Affiliation(s)
- Samar H. Ibrahim
- Division of Pediatric Gastroenterology and Hepatology Mayo Clinic, College of Medicine, MN, USA
| | - Gregory J. Gores
- Division of Gastroenterology and Hepatology, Mayo Clinic, College of Medicine, Rochester, MN, USA
| | - Petra Hirsova
- Division of Gastroenterology and Hepatology, Mayo Clinic, College of Medicine, Rochester, MN, USA
| | - Michelle Kirby
- Division of Gastroenterology, Hepatology and Nutrition, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, USA
| | - Lili Miles
- Department of Pathology, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, USA
| | - Anja Jaeschke
- Department of Pathology and Laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
| | - Rohit Kohli
- Division of Gastroenterology, Hepatology and Nutrition, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, USA
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58
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Varela LM, Bermúdez B, Ortega-Gómez A, López S, Sánchez R, Villar J, Anguille C, Muriana FJG, Roux P, Abia R. Postprandial triglyceride-rich lipoproteins promote invasion of human coronary artery smooth muscle cells in a fatty-acid manner through PI3k-Rac1-JNK signaling. Mol Nutr Food Res 2014; 58:1349-64. [DOI: 10.1002/mnfr.201300749] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 01/03/2014] [Accepted: 01/22/2014] [Indexed: 01/09/2023]
Affiliation(s)
- Lourdes M. Varela
- Laboratory of Cellular and Molecular Nutrition; Instituto de la Grasa, Consejo Superior de Investigaciones Científicas (CSIC); Seville Spain
| | - Beatriz Bermúdez
- Laboratory of Cellular and Molecular Nutrition; Instituto de la Grasa, Consejo Superior de Investigaciones Científicas (CSIC); Seville Spain
| | - Almudena Ortega-Gómez
- Laboratory of Cellular and Molecular Nutrition; Instituto de la Grasa, Consejo Superior de Investigaciones Científicas (CSIC); Seville Spain
| | - Sergio López
- Laboratory of Cellular and Molecular Nutrition; Instituto de la Grasa, Consejo Superior de Investigaciones Científicas (CSIC); Seville Spain
| | - Rosario Sánchez
- Laboratory of Cellular and Molecular Nutrition; Instituto de la Grasa, Consejo Superior de Investigaciones Científicas (CSIC); Seville Spain
| | - Jose Villar
- Experimental Clinic Ward for Vascular Risk, IBIS; Virgen del Rocio University Hospital, CSIC, University of Seville; Seville Spain
| | - Christelle Anguille
- Center de Recherche en Biochimie Macromoléculaire; Centre National de la Recherche Scientifique (CNRS); Universite Mixte de Recherche 5237; Montpellier France
| | - Francisco J. G. Muriana
- Laboratory of Cellular and Molecular Nutrition; Instituto de la Grasa, Consejo Superior de Investigaciones Científicas (CSIC); Seville Spain
| | - Pierre Roux
- Center de Recherche en Biochimie Macromoléculaire; Centre National de la Recherche Scientifique (CNRS); Universite Mixte de Recherche 5237; Montpellier France
| | - Rocío Abia
- Laboratory of Cellular and Molecular Nutrition; Instituto de la Grasa, Consejo Superior de Investigaciones Científicas (CSIC); Seville Spain
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59
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Abstract
Non-alcoholic steatohepatitis (NASH) is a disorder marked by alterations in hepatic lipid homeostasis as well as liver injury in the form of cell death, inflammation and fibrosis. Research into the pathophysiology of NASH is dynamic. New concepts from the fields of cell biology, microbiology, immunology and genetics are being tested for their applicability to NASH; discoveries in each of these areas are enriching our understanding of this complex disease. This review summarizes how recent developments from the bench and bedside are merging with more traditional concepts to reshape our view of NASH pathogenesis. Highlights include human studies that emphasize the role of de novo lipogenesis in NASH and experimental work uncovering a role for the inflammasome in NASH. Genetic predispositions to NASH are being clarified, and intestinal microbiome is emerging as a determinant of fatty liver. These unique ideas are now taking their place within an integrated picture of NASH pathogenesis.
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Affiliation(s)
- Caroline C Duwaerts
- Liver Center and Department of Medicine, University of California, San Francisco, San Francisco, CA
| | - Jacquelyn J Maher
- Liver Center and Department of Medicine, University of California, San Francisco, San Francisco, CA
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60
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Tsedensodnom O, Sadler KC. ROS: redux and paradox in fatty liver disease. Hepatology 2013; 58:1210-2. [PMID: 23703804 PMCID: PMC4072499 DOI: 10.1002/hep.26497] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Accepted: 04/23/2013] [Indexed: 12/16/2022]
Affiliation(s)
- Orkhontuya Tsedensodnom
- Department of Medicine, Division of Liver Diseases, Icahn School of Medicine at Mount Sinai, New York, NY,Department of Developmental and Regenerative, Biology, Icahn School of Medicine at Mount Sinai, New York, NY
| | - Kirsten C. Sadler
- Department of Medicine, Division of Liver Diseases, Icahn School of Medicine at Mount Sinai, New York, NY,Department of Developmental and Regenerative, Biology, Icahn School of Medicine at Mount Sinai, New York, NY,Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, NY
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61
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Kant S, Barrett T, Vertii A, Noh YH, Jung DY, Kim JK, Davis RJ. Role of the mixed-lineage protein kinase pathway in the metabolic stress response to obesity. Cell Rep 2013; 4:681-8. [PMID: 23954791 PMCID: PMC3769115 DOI: 10.1016/j.celrep.2013.07.019] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Revised: 06/10/2013] [Accepted: 07/16/2013] [Indexed: 01/18/2023] Open
Abstract
Saturated free fatty acid (FFA) is implicated in the metabolic response to obesity. In vitro studies indicate that FFA signaling may be mediated by the mixed-lineage protein kinase (MLK) pathway that activates cJun NH2-terminal kinase (JNK). Here, we examined the role of the MLK pathway in vivo using a mouse model of diet-induced obesity. The ubiquitously expressed MLK2 and MLK3 protein kinases have partially redundant functions. We therefore compared wild-type and compound mutant mice that lack expression of MLK2 and MLK3. MLK deficiency protected mice against high-fat-diet-induced insulin resistance and obesity. Reduced JNK activation and increased energy expenditure contribute to the metabolic effects of MLK deficiency. These data confirm that the MLK pathway plays a critical role in the metabolic response to obesity.
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Affiliation(s)
- Shashi Kant
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
| | - Tamera Barrett
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
| | - Anastassiia Vertii
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
| | - Yun Hee Noh
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
| | - Dae Young Jung
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
| | - Jason K. Kim
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
| | - Roger J. Davis
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
- Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
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62
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Gadang V, Kohli R, Myronovych A, Hui DY, Perez-Tilve D, Jaeschke A. MLK3 promotes metabolic dysfunction induced by saturated fatty acid-enriched diet. Am J Physiol Endocrinol Metab 2013; 305:E549-56. [PMID: 23860122 PMCID: PMC3891220 DOI: 10.1152/ajpendo.00197.2013] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2013] [Accepted: 07/08/2013] [Indexed: 01/22/2023]
Abstract
Saturated fatty acids activate the c-Jun NH₂-terminal kinase (JNK) pathway, resulting in chronic low-grade inflammation and the development of insulin resistance. Mixed-lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase (MAP3K) that mediates JNK activation in response to saturated fatty acids in vitro; however, the exact mechanism for diet-induced JNK activation in vivo is not known. Here, we have used MLK3-deficient mice to examine the role of MLK3 in a saturated-fat diet model of obesity. MLK3-KO mice fed a high-fat diet enriched in medium-chain saturated fatty acids for 16 wk had decreased body fat compared with wild-type (WT) mice due to increased energy expenditure independently of food consumption and physical activity. Moreover, MLK3 deficiency attenuated palmitate-induced JNK activation and M1 polarization in bone marrow-derived macrophages in vitro, and obesity induced JNK activation, macrophage infiltration into adipose tissue, and expression of proinflammatory cytokines in vivo. In addition, loss of MLK3 improved insulin resistance and decreased hepatic steatosis. Together, these data demonstrate that MLK3 promotes saturated fatty acid-induced JNK activation in vivo and diet-induced metabolic dysfunction.
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Affiliation(s)
- Vidya Gadang
- Department of Pathology, Metabolic Diseases Institute, University of Cincinnati, Cincinnati, Ohio
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63
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Sharma M, Gadang V, Jaeschke A. Critical role for mixed-lineage kinase 3 in acetaminophen-induced hepatotoxicity. Mol Pharmacol 2012; 82:1001-7. [PMID: 22918968 PMCID: PMC3477232 DOI: 10.1124/mol.112.079863] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2012] [Accepted: 08/23/2012] [Indexed: 12/13/2022] Open
Abstract
c-Jun NH(2)-terminal kinase (JNK) activation plays a major role in acetaminophen (APAP)-induced hepatotoxicity. However, the exact mechanism of APAP-induced JNK activation is incompletely understood. It has been established that apoptosis signal-regulating kinase 1 (ASK1) regulates the late phase of APAP-induced JNK activation, but the mitogen-activated protein kinase kinase kinase that mediates the initial phase of APAP-induced JNK activation has not been identified. Oxidative stress produced during APAP metabolism causes JNK activation, which promotes mitochondrial dysfunction and results in the amplification of oxidative stress. Therefore, inhibition of the initial phase of JNK activation may be key to protection against APAP-induced liver injury. The goal of this study was to determine whether mixed-lineage kinase 3 (MLK3) mediates the initial, ASK1-independent phase of APAP-induced JNK activation and thus promotes drug-induced hepatotoxicity. We found that MLK3 was activated by oxidative stress and was required for JNK activation in response to oxidative stress. Loss of MLK3 attenuated APAP-induced JNK activation and hepatocyte death in vitro, independent of receptor-interacting protein 1. Moreover, JNK and glycogen synthase kinase 3β activation was significantly attenuated, and Mcl-1 degradation was inhibited in APAP-treated MLK3-knockout mice. Furthermore, we showed that loss of MLK3 increased expression of glutamate cysteine ligase, accelerated hepatic GSH recovery, and decreased production of reactive oxygen species after APAP treatment. MLK3-deficient mice were significantly protected from APAP-induced liver injury, compared with wild-type mice. Together, these studies establish a novel role for MLK3 in APAP-induced JNK activation and hepatotoxicity, and they suggest MLK3 as a possible target in the treatment of APAP-induced liver injury.
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Affiliation(s)
- Manju Sharma
- Department of Pathology, Metabolic Diseases Institute, University of Cincinnati, Cincinnati, Ohio 45237, USA
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64
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Seki E, Brenner DA, Karin M. A liver full of JNK: signaling in regulation of cell function and disease pathogenesis, and clinical approaches. Gastroenterology 2012; 143:307-20. [PMID: 22705006 PMCID: PMC3523093 DOI: 10.1053/j.gastro.2012.06.004] [Citation(s) in RCA: 379] [Impact Index Per Article: 31.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/06/2012] [Revised: 06/05/2012] [Accepted: 06/11/2012] [Indexed: 02/08/2023]
Abstract
c-Jun-N-terminal kinase (JNK) is a mitogen-activated protein kinase family member that is activated by diverse stimuli, including cytokines (such as tumor necrosis factor and interleukin-1), reactive oxygen species (ROS), pathogens, toxins, drugs, endoplasmic reticulum stress, free fatty acids, and metabolic changes. Upon activation, JNK induces multiple biologic events through the transcription factor activator protein-1 and transcription-independent control of effector molecules. JNK isozymes regulate cell death and survival, differentiation, proliferation, ROS accumulation, metabolism, insulin signaling, and carcinogenesis in the liver. The biologic functions of JNK are isoform, cell type, and context dependent. Recent studies using genetically engineered mice showed that loss or hyperactivation of the JNK pathway contributes to the development of inflammation, fibrosis, cancer growth, and metabolic diseases that include obesity, hepatic steatosis, and insulin resistance. We review the functions and pathways of JNK in liver physiology and pathology and discuss findings from preclinical studies with JNK inhibitors.
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Affiliation(s)
- Ekihiro Seki
- Department of Medicine, University of California, La Jolla, CA, USA.
| | - David A. Brenner
- Department of Medicine, Division of Gastroenterology, University of California, San Diego, School of Medicine, La Jolla, CA, USA
| | - Michael Karin
- Laboratory of Gene Regulation and Signal Transduction, Department of Pharmacology, University of California, San Diego, School of Medicine, La Jolla, CA, USA
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65
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Flamment M, Hajduch E, Ferré P, Foufelle F. New insights into ER stress-induced insulin resistance. Trends Endocrinol Metab 2012; 23:381-90. [PMID: 22770719 DOI: 10.1016/j.tem.2012.06.003] [Citation(s) in RCA: 233] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Revised: 06/01/2012] [Accepted: 06/02/2012] [Indexed: 12/12/2022]
Abstract
Insulin resistance is a major characteristic of obesity and type 2 diabetes (T2DM). During the last decade, endoplasmic reticulum (ER) stress has emerged as a new player in this field and a considerable number of recent studies have pointed out its role in the onset of insulin resistance (IR). ER stress appears to act directly as a negative modulator of the insulin signaling pathway but also indirectly by promoting lipid accumulation. This review aims to summarize and decipher the abundant new literature concerning the emerging and multifaceted involvement of ER stress in the development of metabolic dysfunctions in insulin target tissues.
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Affiliation(s)
- Mélissa Flamment
- Institut National de la Santé et de la Recherche Médicale (INSERM), Centre de Recherche des Cordeliers, Unité Mixte de Recherche en Santé (UMR-S) 872, Paris, F-75006 France
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66
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Adenosine A(2a) receptor stimulation prevents hepatocyte lipotoxicity and non-alcoholic steatohepatitis (NASH) in rats. Clin Sci (Lond) 2012; 123:323-32. [PMID: 22439844 DOI: 10.1042/cs20110504] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
NEFA (non-esterified 'free' fatty acid)-mediated lipotoxicity plays a critical role in the pathogenesis of NASH (non-alcoholic steatohepatitis). In the light of the growing need for new therapeutic options for NASH, we investigated the action of A2aR (adenosine A(2a) receptor) stimulation against lipotoxicity. The effects of the A(2a)R agonist CGS21680 [2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxyamidoadenosine] were evaluated 'in vitro' in liver cells exposed to SA (stearic acid) and 'in vivo' in rats with NASH induced by 8 weeks of feeding with an MCD diet (methionine/choline-deficient diet). In cultured hepatocytes, SA promoted apoptosis by inducing MKK4 (mitogen-activated protein kinase kinase 4)/SEK1 (stress-activated protein kinase/extracellular-signal-regulated kinase kinase-1) and JNK-1/2 (c-Jun N-terminal kinase-1/2) activation. CGS21680 addition prevented JNK-1/2 activation and reduced apoptosis without interfering with lipid accumulation. CGS21680 action required PI3K (phosphoinositide 3-kinase)/Akt-mediated block of MKK4/SEK1. Consistently, PI3K inhibition with wortmannin abolished the cytoprotective action of CGS21680 and reverted MKK4 inhibition. SA lipotoxicity was also prevented by transfecting HTC cells with a specific MKK4/SEK1 siRNA (small interfering RNA). In rats receiving the MCD diet, the development of NASH was associated with MKK4/SEK1 and JNK-1/2 activation. CGS21680 (0.5 mg/kg of body weight, intraperitoneal) administration to MCD-fed rats prevented JNK-1/2 activation by acting on MKK4/SEK1. CGS21680 also effectively reduced NASH-associated ALT (alanine aminotransferase) release, hepatocyte apoptosis, liver inflammation and fibrosis without affecting hepatic steatosis. Taken together, these results demonstrate that, by inhibiting JNK-1/2, A(2a)R stimulation reduces lipotoxicity and ameliorates NASH, giving a rationale to investigate A(2a)R agonists as possible new therapeutic agents in preventing fatty liver progression to NASH.
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Kakisaka K, Cazanave SC, Fingas CD, Guicciardi ME, Bronk SF, Werneburg NW, Mott JL, Gores GJ. Mechanisms of lysophosphatidylcholine-induced hepatocyte lipoapoptosis. Am J Physiol Gastrointest Liver Physiol 2012; 302:G77-84. [PMID: 21995961 PMCID: PMC3345964 DOI: 10.1152/ajpgi.00301.2011] [Citation(s) in RCA: 149] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Isolated hepatocytes undergo lipoapoptosis, a feature of hepatic lipotoxicity, on treatment with saturated free fatty acids (FFA) such as palmitate (PA). However, it is unknown if palmitate is directly toxic to hepatocytes or if its toxicity is indirect via the generation of lipid metabolites such as lysophosphatidylcholine (LPC). PA-mediated hepatocyte lipoapoptosis is associated with endoplasmic reticulum (ER) stress, c-Jun NH(2)-terminal kinase (JNK) activation, and a JNK-dependent upregulation of the potent proapoptotic BH3-only protein PUMA (p53 upregulated modulator of apoptosis). Our aim was to determine which of these mechanisms of lipotoxicity are activated by PA-derived LPC. We employed Huh-7 cells and isolated murine and human primary hepatocytes. Intracellular LPC concentrations increase linearly as a function of the exogenous, extracellular PA, stearate, or LPC concentration. Incubation of Huh-7 cells or primary hepatocytes with LPC induced cell death by apoptosis in a concentration-dependent manner. Substituting LPC for PA resulted in caspase-dependent cell death that was accompanied by activating phosphorylation of JNK with c-Jun phosphorylation and an increase in PUMA expression. LPC also induced ER stress as manifest by eIF2α phosphorylation and CAAT/enhancer binding homologous protein (CHOP) induction. LPC cytotoxicity was attenuated by pharmacological inhibition of JNK or glycogen synthase kinase-3 (GSK-3). Similarly, short-hairpin RNA (shRNA)-targeted knockdown of CHOP protected Huh-7 cells against LPC-induced toxicity. The LPC-induced PUMA upregulation was prevented by JNK inhibition or shRNA-targeted knockdown of CHOP. Finally, genetic deficiency of PUMA rendered murine hepatocytes resistant to LPC-induced apoptosis. We concluded that LPC-induced lipoapoptosis is dependent on mechanisms largely indistinguishable from PA. These data suggest that FFA-mediated cytotoxicity is indirect via the generation of the toxic metabolite, LPC.
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Affiliation(s)
- Keisuke Kakisaka
- Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Rochester, Minnesota
| | - Sophie C. Cazanave
- Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Rochester, Minnesota
| | - Christian D. Fingas
- Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Rochester, Minnesota
| | - Maria E. Guicciardi
- Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Rochester, Minnesota
| | - Steven F. Bronk
- Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Rochester, Minnesota
| | - Nathan W. Werneburg
- Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Rochester, Minnesota
| | - Justin L. Mott
- Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Rochester, Minnesota
| | - Gregory J. Gores
- Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Rochester, Minnesota
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