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Nonalcoholic Fatty liver disease: focus on lipoprotein and lipid deregulation. J Lipids 2011; 2011:783976. [PMID: 21773052 PMCID: PMC3136146 DOI: 10.1155/2011/783976] [Citation(s) in RCA: 141] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2011] [Revised: 04/26/2011] [Accepted: 04/27/2011] [Indexed: 12/12/2022] Open
Abstract
Obesity with associated comorbidities is currently a worldwide epidemic and among the most challenging health conditions in the 21st century. A major metabolic consequence of obesity is insulin resistance which underlies the pathogenesis of the metabolic syndrome. Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of obesity and metabolic syndrome. It comprises a disease spectrum ranging from simple steatosis (fatty liver), through nonalcoholic steatohepatitis (NASH) to fibrosis, and ultimately liver cirrhosis. Abnormality in lipid and lipoprotein metabolism accompanied by chronic inflammation is the central pathway for the development of metabolic syndrome-related diseases, such as atherosclerosis, cardiovascular disease (CVD), and NAFLD. This paper focuses on pathogenic aspect of lipid and lipoprotein metabolism in NAFLD and the relevant mouse models of this complex multifactorial disease.
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202
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Kwon S, Christian JL. Sortilin associates with transforming growth factor-beta family proteins to enhance lysosome-mediated degradation. J Biol Chem 2011; 286:21876-85. [PMID: 21521695 PMCID: PMC3122242 DOI: 10.1074/jbc.m111.228262] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Revised: 04/15/2011] [Indexed: 01/17/2023] Open
Abstract
Transforming growth factor (TGF)-β family proteins are synthesized as precursors that are cleaved to generate an active ligand. Previous studies suggest that TGF-β activity can be controlled by lysosomal degradation of both precursor proteins and ligands, but how these soluble proteins are trafficked to the lysosome is incompletely understood. The current studies show that sortilin selectively co-immunoprecipitates with the cleaved prodomain and/or precursor form of TGF-β family members. Furthermore, sortilin co-localizes with, and enhances accumulation of a nodal family member in the Golgi. Co-expression of sortilin with TGF-β family members leads to decreased accumulation of precursor proteins and cleavage products and this is attenuated by lysosomal, but not proteosomal inhibitors. In Xenopus embryos, overexpression of sortilin leads to a decrease in phospho-Smad2 levels and phenocopies loss of nodal signaling. Conversely, down-regulation of sortilin expression in HeLa cells leads to an up-regulation of endogenous bone morphogenic protein pathway activation, as indicated by an increase in phospho-Smad1/5/8 levels. Our results suggest that sortilin negatively regulates TGF-β signaling by diverting trafficking of precursor proteins to the lysosome during transit through the biosynthetic pathway.
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Affiliation(s)
- Sunjong Kwon
- From the Department of Cell and Developmental Biology, Oregon Health & Science University, Portland, Oregon 97239
| | - Jan L. Christian
- From the Department of Cell and Developmental Biology, Oregon Health & Science University, Portland, Oregon 97239
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203
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Abstract
DNA sequence variants are major components of the "causal field" for virtually all medical phenotypes, whether single gene familial disorders or complex traits without a clear familial aggregation. The causal variants in single gene disorders are necessary and sufficient to impart large effects. In contrast, complex traits are attributable to a much more complicated network of contributory components that in aggregate increase the probability of disease. The conventional approach to identification of the causal variants for single gene disorders is genetic linkage. However, it does not offer sufficient resolution to map the causal genes in small families or sporadic cases. The approach to genetic studies of complex traits entails candidate gene or genome-wide association studies. Genome-wide association studies provide an unbiased survey of the effects of common genetic variants (common disease-common variant hypothesis). Genome-wide association studies have led to identification of a large number of alleles for various cardiovascular diseases. However, common alleles account for a relatively small fraction of the total heritability of the traits. Accordingly, the focus has shifted toward identification of rare variants that might impart larger effect sizes (rare variant-common disease hypothesis). This shift is made feasible by recent advances in massively parallel DNA sequencing platforms, which afford the opportunity to identify virtually all common as well as rare alleles in individuals. In this review, we discuss various strategies that are used to delineate the genetic contribution to medically important cardiovascular phenotypes, emphasizing the utility of the new deep sequencing approaches.
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Affiliation(s)
- A J Marian
- Center for Cardiovascular Genetics, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Sciences Center, 6770 Bertner Street, Suite C900A, Houston, TX 77030, USA.
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204
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Current world literature. Curr Opin Cardiol 2011; 26:270-4. [PMID: 21490464 DOI: 10.1097/hco.0b013e328346ccf1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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205
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Dubé JB, Johansen CT, Hegele RA. Sortilin: An unusual suspect in cholesterol metabolism. Bioessays 2011; 33:430-7. [DOI: 10.1002/bies.201100003] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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206
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Bauer RC, Stylianou IM, Rader DJ. Functional validation of new pathways in lipoprotein metabolism identified by human genetics. Curr Opin Lipidol 2011; 22:123-8. [PMID: 21311327 DOI: 10.1097/mol.0b013e32834469b3] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
PURPOSE OF REVIEW Recent genome-wide association studies (GWAS) have identified approximately 100 genomic loci that are associated with plasma lipid traits, two-thirds of which had never been previously associated with lipoprotein metabolism. Identification of the causal genes and variants, functional validation of these genes and biological pathways, and elucidation of molecular mechanisms is required and poses a daunting task. RECENT FINDINGS Human genetics have been used to recently 'validate' genes, such as LIPG, SCARB1 and ANGPTL3, which were previously implicated in lipoprotein metabolism through classical wet bench approaches. Additionally, many novel genes have been identified as associated with plasma lipid traits by GWAS, though only relatively few have been functionally validated through targeted sequencing and genetic manipulation in cells and animals. These types of studies have defined new roles in lipid metabolism for the novel lipid genes SORT1 and TRIB1. These examples demonstrate the ways in which human genetics can validate candidate genes, as well as provide a novel discovery that requires functional validation at the bench, and point towards a more complete understanding of the molecular physiology of lipoprotein metabolism. SUMMARY This review summarizes recent developments in the use of human genetics to validate candidate genes in lipoprotein metabolism as well as in the functional validation of novel GWAS loci associated with plasma lipid traits.
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Affiliation(s)
- Robert C Bauer
- Institute for Translational Medicine and Therapeutics and Cardiovascular Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA
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207
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Abstract
PURPOSE OF REVIEW Comparative genomics allows researchers to combine genome-wide association data from humans with studies in animal models in order to assist in the identification of the genes and the genetic variants that modify susceptibility to dyslipidemia and atherosclerosis. RECENT FINDINGS Association and linkage studies in human and rodent species have been successful in identifying genetic loci associated with complex traits, but have been less robust in identifying and validating the responsible gene and/or genetic variants. Recent technological advancements have assisted in the development of comparative genomic approaches, which rely on the combination of human and rodent datasets and bioinformatics tools, followed by the narrowing of concordant loci and improved identification of candidate genes and genetic variants. Additionally, candidate genes and genetic variants identified by these methods have been further validated and functionally investigated in animal models, a process that is not feasible in humans. SUMMARY Comparative genomic approaches have led to the identification and validation of several new genes, including a few not previously implicated, as modifiers of plasma lipid levels and atherosclerosis, yielding new insights into the biological mechanisms of these complex traits.
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Affiliation(s)
- Stela Z Berisha
- Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, Ohio, USA
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208
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Abstract
PURPOSE OF REVIEW Sortilins are sorting receptors that direct proteins through secretory and endocytic pathways of the cell. Previously, these receptors have been shown to play important roles in regulating protein transport in neurons and to control neuronal viability and death in many diseases of the nervous system. Recent data, including genome-wide association studies, now suggest equally important functions for sortilins in control of systemic lipoprotein metabolism and risk of cardiovascular disease. This review discusses the evidence implicating two members of this gene family, sortilin and SORLA, in cardiovascular processes. RECENT FINDINGS SORLA is a multifunctional receptor expressed in macrophages and vascular smooth muscle cells. It may act proatherogenic by promoting intimal SMC migration and by regulating apolipoprotein A-V dependent activation of lipoprotein lipase to modulate systemic triglyceride levels. Sortilin, encoded by the cardiovascular risk locus 1p13.3, is a novel regulator of hepatic lipoprotein production. It interacts with apolipoprotein B-100 to control release of very low-density lipoproteins, thereby affecting plasma cholesterol concentrations. SUMMARY Recent data shed light on the importance of sorting receptors in control of cellular and systemic lipoprotein metabolism and how altered trafficking pathways may represent a major risk factor for dyslipidemia and atherosclerosis in the human population.
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209
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210
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Vaegter CB, Jansen P, Fjorback AW, Glerup S, Skeldal S, Richner M, Erdmann B, Nyengaard JR, Tessarollo L, Lewin GR, Willnow TE, Chao MV, Nykjaer A. Sortilin associates with Trk receptors to enhance anterograde transport and neurotrophin signaling. Nat Neurosci 2011; 14:54-61. [PMID: 21102451 PMCID: PMC3808973 DOI: 10.1038/nn.2689] [Citation(s) in RCA: 145] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2010] [Accepted: 10/12/2010] [Indexed: 02/05/2023]
Abstract
Binding of target-derived neurotrophins to Trk receptors at nerve terminals is required to stimulate neuronal survival, differentiation, innervation and synaptic plasticity. The distance between the soma and nerve terminal is great, making efficient anterograde Trk transport critical for Trk synaptic translocation and signaling. The mechanism responsible for this trafficking remains poorly understood. Here we show that the sorting receptor sortilin interacts with TrkA, TrkB and TrkC and enables their anterograde axonal transport, thereby enhancing neurotrophin signaling. Cultured DRG neurons lacking sortilin showed blunted MAP kinase signaling and reduced neurite outgrowth upon stimulation with NGF. Moreover, deficiency for sortilin markedly aggravated TrkA, TrkB and TrkC phenotypes present in p75(NTR) knockouts, and resulted in increased embryonic lethality and sympathetic neuropathy in mice heterozygous for TrkA. Our findings demonstrate a role for sortilin as an anterograde trafficking receptor for Trk and a positive modulator of neurotrophin-induced neuronal survival.
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MESH Headings
- Adaptor Proteins, Vesicular Transport/deficiency
- Adaptor Proteins, Vesicular Transport/genetics
- Adaptor Proteins, Vesicular Transport/metabolism
- Adaptor Proteins, Vesicular Transport/physiology
- Animals
- Axonal Transport/genetics
- Axonal Transport/physiology
- Cell Culture Techniques
- Cerebral Cortex/metabolism
- Embryo, Mammalian/pathology
- Ganglia, Spinal/cytology
- Ganglia, Spinal/metabolism
- HEK293 Cells
- Hippocampus/metabolism
- Humans
- Mice
- Mice, Knockout
- Nerve Growth Factor/pharmacology
- Nerve Growth Factors/physiology
- Neurites/drug effects
- Neurites/physiology
- Receptor Cross-Talk/physiology
- Receptor, Nerve Growth Factor/genetics
- Receptors, Nerve Growth Factor/genetics
- Receptors, Nerve Growth Factor/metabolism
- Receptors, Nerve Growth Factor/physiology
- Signal Transduction/physiology
- Superior Cervical Ganglion/metabolism
- Superior Cervical Ganglion/pathology
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Affiliation(s)
- Christian B. Vaegter
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Pernille Jansen
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Anja W. Fjorback
- MIND Center, Stereology and Electron Microscopy Laboratory, Aarhus University, 8000 Aarhus C, Denmark
| | - Simon Glerup
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Sune Skeldal
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Mette Richner
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Bettina Erdmann
- Max-Delbrück-Center for Molecular Medicine, 13125 Berlin, Germany
| | - Jens R. Nyengaard
- MIND Center, Stereology and Electron Microscopy Laboratory, Aarhus University, 8000 Aarhus C, Denmark
| | - Lino Tessarollo
- Center for Cancer Research, National Cancer Institute, Frederick, Maryland 21702, USA
| | - Gary R. Lewin
- Max-Delbrück-Center for Molecular Medicine, 13125 Berlin, Germany
| | | | - Moses V. Chao
- Kimmel Center at Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York 10016, USA
| | - Anders Nykjaer
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
- NeuronIcon, Gustav Wieds vej 10, DK-8000 Aarhus C, Denmark
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