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Abstract
The prevalence and diagnosis of nonalcoholic fatty liver disease (NAFLD) is on the rise worldwide and currently has no FDA-approved pharmacotherapy. The increase in disease burden of NAFLD and a more severe form of this progressive liver disease, nonalcoholic steatohepatitis (NASH), largely mirrors the increase in obesity and type 2 diabetes (T2D) and reflects the hepatic manifestation of an altered metabolic state. Indeed, metabolic syndrome, defined as a constellation of obesity, insulin resistance, hyperglycemia, dyslipidemia and hypertension, is the major risk factor predisposing the NAFLD and NASH. There are multiple potential pharmacologic strategies to rebalance aspects of disordered metabolism in NAFLD. These include therapies aimed at reducing hepatic steatosis by directly modulating lipid metabolism within the liver, inhibiting fructose metabolism, altering delivery of free fatty acids from the adipose to the liver by targeting insulin resistance and/or adipose metabolism, modulating glycemia, and altering pleiotropic metabolic pathways simultaneously. Emerging data from human genetics also supports a role for metabolic drivers in NAFLD and risk for progression to NASH. In this review, we highlight the prominent metabolic drivers of NAFLD pathogenesis and discuss the major metabolic targets of NASH pharmacotherapy.
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Key Words
- acc, acetyl-coa carboxylase
- alt, alanine aminotransferase
- aso, anti-sense oligonucleotide
- ast, aspartate aminotransferase
- chrebp, carbohydrate response element binding protein
- ci, confidence interval
- dgat, diacylglycerol o-acyltransferase
- dnl, de novo lipogenesis
- fas, fatty acid synthase
- ffa, free fatty acid
- fgf, fibroblast growth factor
- fxr, farnesoid x receptor
- glp-1, glucagon-like peptide-1
- hdl, high-density lipoprotein
- homa-ir, homeostatic model assessment of insulin resistance
- ldl, low-density lipoprotein
- nafld, nonalcoholic fatty liver disease
- nas, nonalcoholic fatty liver disease activity score
- nash, nonalcoholic steatohepatitis
- or, odds ratio
- pdff, proton density fat fraction
- ppar, peroxisome proliferator-activated receptor
- sglt2, sodium glucose co-transporter 2
- srebp-1c, sterol regulatory element binding protein-1c
- t2d, type 2 diabetes
- t2dm, type 2 diabetes mellitus
- tg, triglyceride
- th, thyroid hormone
- thr, thyroid hormone receptor
- treg, regulatory t cells
- tzd, thiazolidinedione
- vldl, very low-density lipoprotein
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Affiliation(s)
- William P Esler
- Internal Medicine Research Unit, Pfizer Worldwide Research, Development, and Medical, Cambridge, Massachusetts
| | - Kendra K Bence
- Internal Medicine Research Unit, Pfizer Worldwide Research, Development, and Medical, Cambridge, Massachusetts.
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Hawley S, Ross F, Gowans G, Tibarewal P, Leslie N, Hardie DG. Phosphorylation by Akt within the ST loop of AMPK-α1 down-regulates its activation in tumour cells. Biochem J 2014; 459:275-87. [PMID: 24467442 PMCID: PMC4052680 DOI: 10.1042/bj20131344] [Citation(s) in RCA: 160] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Revised: 01/16/2014] [Accepted: 01/27/2014] [Indexed: 12/18/2022]
Abstract
The insulin/IGF-1 (insulin-like growth factor 1)-activated protein kinase Akt (also known as protein kinase B) phosphorylates Ser487 in the 'ST loop' (serine/threonine-rich loop) within the C-terminal domain of AMPK-α1 (AMP-activated protein kinase-α1), leading to inhibition of phosphorylation by upstream kinases at the activating site, Thr172. Surprisingly, the equivalent site on AMPK-α2, Ser491, is not an Akt target and is modified instead by autophosphorylation. Stimulation of HEK (human embryonic kidney)-293 cells with IGF-1 caused reduced subsequent Thr172 phosphorylation and activation of AMPK-α1 in response to the activator A769662 and the Ca2+ ionophore A23187, effects we show to be dependent on Akt activation and Ser487 phosphorylation. Consistent with this, in three PTEN (phosphatase and tensin homologue deleted on chromosome 10)-null tumour cell lines (in which the lipid phosphatase PTEN that normally restrains the Akt pathway is absent and Akt is thus hyperactivated), AMPK was resistant to activation by A769662. However, full AMPK activation could be restored by pharmacological inhibition of Akt, or by re-expression of active PTEN. We also show that inhibition of Thr172 phosphorylation is due to interaction of the phosphorylated ST loop with basic side chains within the αC-helix of the kinase domain. Our findings reveal that a previously unrecognized effect of hyperactivation of Akt in tumour cells is to restrain activation of the LKB1 (liver kinase B1)-AMPK pathway, which would otherwise inhibit cell growth and proliferation.
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Key Words
- akt
- amp-activated protein kinase (ampk)
- cancer
- cross-talk
- tumour suppressor
- acc, acetyl-coa carboxylase
- aicar, 5-amino-4-imidazolecarboxamide riboside
- ampk, amp-activated protein kinase
- brsk, brain-specific kinase
- camkk, calmodulin-dependent kinase kinase β
- dmem, dulbecco’s modified eagle’s medium
- gsk3, glycogen synthase kinase 3
- hek, human embryonic kidney
- igf-1, insulin-like growth factor 1
- lkb1, liver kinase b1
- mef, mouse embryonic fibroblast
- mo25α, mouse protein-25α
- mtorc1, mammalian (or mechanistic) target of rapamycin complex 1
- neaa, non-essential amino acid
- pi3k, phosphoinositide 3-kinase
- pka, protein kinase a (camp-dependent protein kinase)
- pten, phosphatase and tensin homologue deleted on chromosome 10
- s6k1, s6 kinase 1
- st loop, serine/threonine-rich loop
- stradα, ste20-related adapter protein-α
- wt, wild-type
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Affiliation(s)
- Simon A. Hawley
- *Division of Cell Signalling & Immunology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K
| | - Fiona A. Ross
- *Division of Cell Signalling & Immunology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K
| | - Graeme J. Gowans
- *Division of Cell Signalling & Immunology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K
| | - Priyanka Tibarewal
- *Division of Cell Signalling & Immunology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K
| | - Nicholas R. Leslie
- *Division of Cell Signalling & Immunology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K
| | - D. Grahame Hardie
- *Division of Cell Signalling & Immunology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K
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Abstract
Leptin is a versatile 16 kDa peptide hormone, with a tertiary structure resembling that of members of the long-chain helical cytokine family. It is mainly produced by adipocytes in proportion to fat size stores, and was originally thought to act only as a satiety factor. However, the ubiquitous distribution of OB-R leptin receptors in almost all tissues underlies the pleiotropism of leptin. OB-Rs belong to the class I cytokine receptor family, which is known to act through JAKs (Janus kinases) and STATs (signal transducers and activators of transcription). The OB-R gene is alternatively spliced to produce at least five isoforms. The full-length isoform, OB-Rb, contains intracellular motifs required for activation of the JAK/STAT signal transduction pathway, and is considered to be the functional receptor. Considerable evidence for systemic effects of leptin on body mass control, reproduction, angiogenesis, immunity, wound healing, bone remodelling and cardiovascular function, as well as on specific metabolic pathways, indicates that leptin operates both directly and indirectly to orchestrate complex pathophysiological processes. Consistent with leptin's pleiotropic role, its participation in and crosstalk with some of the main signalling pathways, including those involving insulin receptor substrates, phosphoinositide 3-kinase, protein kinase B, protein kinase C, extracellular-signal-regulated kinase, mitogen-activated protein kinases, phosphodiesterase, phospholipase C and nitric oxide, has been observed. The impact of leptin on several equally relevant signalling pathways extends also to Rho family GTPases in relation to the actin cytoskeleton, production of reactive oxygen species, stimulation of prostaglandins, binding to diacylglycerol kinase and catecholamine secretion, among others.
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Key Words
- adipocyte
- cytokine
- janus kinase/signal transducer and activator of transcription pathway (jak/stat pathway)
- leptin receptor
- obesity
- signalling cascade
- acc, acetyl-coa carboxylase
- ampk, 5′-amp-activated protein kinase
- cntf, ciliary neurotrophic factor
- ct-1, cardiotrophin-1
- erk, extracellular-signal-regulated kinase
- hif-1α, hypoxia-inducible factor 1α
- il, interleukin
- irs, insulin receptor substrate
- jak, janus kinase
- jnk, c-jun n-terminal kinase
- lif, leukaemia inhibitory factor
- mapk, mitogen-activated protein kinase
- nf-κb, nuclear factor κb
- npy, neuropeptide y
- osm, oncostatin-m
- pde, phosphodiesterase
- pi3k, phosphoinositide 3-kinase
- pka, protein kinase a
- pkc, protein kinase c
- ptp1b, protein tyrosine phosphatase 1b
- sh2, src-like homology 2
- shp-2, sh2 domain-containing protein tyrosine phosphatase
- socs, suppressor of cytokine signalling
- stat, signal transducer and activator of transcription
- tnfα, tumour necrosis factor α
- tyk2, tyrosine kinase 2
- vegf, vascular endothelial growth factor
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Affiliation(s)
- Gema Frühbeck
- Department of Endocrinology, Clínica Universitaria de Navarra and Metabolic Research Laboratory, University of Navarra, 36 Avda. Pío XII, 31008 Pamplona, Spain.
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Abstract
The protective effect of dietary saturated fatty acids against the development of alcoholic liver disease has long been known, but the underlying mechanism is not completely understood. We examined the involvement of the adipocyte hormone adiponectin. Circulating adiponectin levels were significantly elevated by chronic ethanol administration to mice consuming a diet high in saturated fat. The increase in circulating adiponectin was associated with the activation a set of hepatic signaling pathways mediated through AMP-activated protein kinase, PPAR-alpha, and PPAR-gamma coactivator alpha, which in turn led to markedly increased rates of fatty acid oxidation, prevention of hepatic steatosis, and alleviation of liver enzyme changes. Furthermore, treatment of rat 3T3-L1 adipocytes with saturated fatty acids (palmitic or stearic acids) in the presence of ethanol increased secretion of adiponectin and enhanced activity of a mouse adiponectin promoter. In conclusion, the protective action of saturated fat against the development of alcoholic fatty liver in mice is partially mediated through induction of adiponectin. The present findings suggest a novel paradigm for dietary fatty acids in the pathogenesis of alcoholic liver disease and provide a promising therapeutic strategy-nutritional modulation of adiponectin-in treating human alcoholic fatty liver disease.
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Key Words
- adipose tissue
- hormone
- signal transduction
- amp-activated kinase
- liver steatosis
- ampk, amp-activated protein kinase
- acc, acetyl-coa carboxylase
- cpt i, carnitine palmitoyltransferase i
- pparα, peroxisome proliferator-activated receptor α
- pparγ, peroxisome proliferator-activated receptor γ
- pgc-1α, peroxisome proliferator-activated receptor γ co-activator-alpha
- aox, acetyl-coa oxidase
- ppre, ppar response element
- β-ohb, β-hydroxybutyrate
- ffa, free fatty acids
- alt ,alanine aminotransferase
- rt-pcr, reverse transcription-polymerase chain reaction
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Affiliation(s)
- Min You
- Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
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Abstract
Malaria, a tropical disease caused by Plasmodium sp., has been haunting mankind for ages. Unsuccessful attempts to develop a vaccine, the emergence of resistance against the existing drugs and the increasing mortality rate all call for immediate strategies to treat it. Intense attempts are underway to develop potent analogues of the current antimalarials, as well as a search for novel drug targets in the parasite. The indispensability of apicoplast (plastid) to the survival of the parasite has attracted a lot of attention in the recent past. The present review describes the origin and the essentiality of this relict organelle to the parasite. We also show that among the apicoplast specific pathways, the fatty acid biosynthesis system is an attractive target, because its inhibition decimates the parasite swiftly unlike the 'delayed death' phenotype exhibited by the inhibition of the other apicoplast processes. As the enzymes of the fatty acid biosynthesis system are present as discrete entities, unlike those of the host, they are amenable to inhibition without impairing the operation of the host-specific pathway. The present review describes the role of these enzymes, the status of their molecular characterization and the current advancements in the area of developing inhibitors against each of the enzymes of the pathway.
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Key Words
- antimalarial
- apicoplast
- fatty acid biosynthesis pathway
- malaria
- plasmodium falciparum
- triclosan
- acat, acyl-coa:acp transacylase
- acc, acetyl-coa carboxylase
- acp, acyl carrier protein
- cer, cerulenin
- fas, fatty acid synthase
- inh, isoniazid
- inha, enoyl-acp reductase of mycobacterium tuberculosis
- kas, β-oxoacyl-acp synthase (β-ketoacyl-acp synthase)
- mcat, malonyl-coa:acp transacylase
- orf, open reading frame
- pdh, pyruvate dehydrogenase
- pep, phosphoenolpyruvate
- pf, plasmodium falciparum
- tlm, thiolactomycin
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Affiliation(s)
- Avadhesha Surolia
- *Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
| | - T. N. C. Ramya
- *Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
| | - V. Ramya
- *Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
| | - Namita Surolia
- †Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India
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Brown JM, Boysen MS, Jensen SS, Morrison RF, Storkson J, Lea-Currie R, Pariza M, Mandrup S, McIntosh MK. Isomer-specific regulation of metabolism and PPARgamma signaling by CLA in human preadipocytes. J Lipid Res 2003; 44:1287-300. [PMID: 12730300 PMCID: PMC1351019 DOI: 10.1194/jlr.m300001-jlr200] [Citation(s) in RCA: 181] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Trans-10,cis-12 conjugated linoleic acid (CLA) has previously been shown to be the CLA isomer responsible for CLA-induced reductions in body fat in animal models, and we have shown that this isomer, but not the cis-9,trans-11 CLA isomer, specifically decreased triglyceride (TG) accumulation in primary human adipocytes in vitro. Here we investigated the mechanism behind the isomer-specific, CLA-mediated reduction in TG accumulation in differentiating human preadipocytes. Trans-10,cis-12 CLA decreased insulin-stimulated glucose uptake and oxidation, and reduced insulin-dependent glucose transporter 4 gene expression. Furthermore, trans-10,cis-12 CLA reduced oleic acid uptake and oxidation when compared with all other treatments. In parallel to CLA's effects on metabolism, trans-10,cis-12 CLA decreased, whereas cis-9,trans-11 CLA increased, the expression of peroxisome proliferator-activated receptor gamma (PPARgamma) and several of its downstream target genes when compared with vehicle controls. Transient transfections demonstrated that both CLA isomers antagonized ligand-dependent activation of PPARgamma. Collectively, trans-10,cis-12, but not cis-9, trans-11, CLA decreased glucose and lipid uptake and oxidation and preadipocyte differentiation by altering preadipocyte gene transcription in a manner that appeared to be due, in part, to decreased PPARgamma expression.
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Key Words
- conjugated linoleic acid
- fatty acids
- lipid metabolism
- glucose metabolism
- triglycerides
- peroxisome proliferator-activated receptor gamma
- acbp, acyl-coa binding protein
- acc, acetyl-coa carboxylase
- ap2/fabp, adipocyte fatty acid binding protein
- bca, bicinchoninic acid
- bmi, body mass index
- bsa, bovine serum albumin
- cd-36, fatty acid translocase
- c/ebpα, caat/enhancer binding protein α
- cla, conjugated linoleic acid
- gc, gas chromatography
- glut4, insulin-dependent glucose transporter 4
- gpdh, glycerol-3-phosphate dehydrogenase
- hsl, hormone-sensitive lipase
- ibmx, isobutylmethylxanthine
- la, linoleic acid
- lpl, lipoprotein lipase
- mufa, monounsaturated fatty acid
- oro, oil red o
- ppar, peroxisome proliferator-activated receptor
- ppre, peroxisome proliferator response element
- scd-1, stearoyl-coa desaturase-1
- sfa, saturated fatty acid
- sv, stromal vascular
- tg, triglyceride
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Affiliation(s)
- J. Mark Brown
- Department of Nutrition, University of North Carolina at Greensboro, Greensboro, NC 27402-6170; Department of Biochemistry and Molecular Biology
| | - Maria Sandberg Boysen
- University of Southern Denmark, Odense, Denmark; Department of Food Microbiology and Toxicology
| | - Søren Skov Jensen
- University of Southern Denmark, Odense, Denmark; Department of Food Microbiology and Toxicology
| | - Ron F. Morrison
- Department of Nutrition, University of North Carolina at Greensboro, Greensboro, NC 27402-6170; Department of Biochemistry and Molecular Biology
| | - Jayne Storkson
- Food Research Institute, University of Wisconsin-Madison, Madison, WI 53706; and
| | - Renee Lea-Currie
- Zen Bio, Inc., 3200 Chapel Hill-Nelson Boulevard, Suite 104, Research Triangle Park, NC 27709
| | - Michael Pariza
- Food Research Institute, University of Wisconsin-Madison, Madison, WI 53706; and
| | - Susanne Mandrup
- University of Southern Denmark, Odense, Denmark; Department of Food Microbiology and Toxicology
| | - Michael K. McIntosh
- Department of Nutrition, University of North Carolina at Greensboro, Greensboro, NC 27402-6170; Department of Biochemistry and Molecular Biology
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