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Bai X, Smith HE, Golden A. Identification of genetic suppressors for a BSCL2 lipodystrophy pathogenic variant in Caenorhabditis elegans. Dis Model Mech 2024; 17:dmm050524. [PMID: 38454882 PMCID: PMC11051982 DOI: 10.1242/dmm.050524] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Accepted: 03/04/2024] [Indexed: 03/09/2024] Open
Abstract
Seipin (BSCL2), a conserved endoplasmic reticulum protein, plays a critical role in lipid droplet (LD) biogenesis and in regulating LD morphology, pathogenic variants of which are associated with Berardinelli-Seip congenital generalized lipodystrophy type 2 (BSCL2). To model BSCL2 disease, we generated an orthologous BSCL2 variant, seip-1(A185P), in Caenorhabditis elegans. In this study, we conducted an unbiased chemical mutagenesis screen to identify genetic suppressors that restore embryonic viability in the seip-1(A185P) mutant background. A total of five suppressor lines were isolated and recovered from the screen. The defective phenotypes of seip-1(A185P), including embryonic lethality and impaired eggshell formation, were significantly suppressed in each suppressor line. Two of the five suppressor lines also alleviated the enlarged LDs in the oocytes. We then mapped a suppressor candidate gene, lmbr-1, which is an ortholog of human limb development membrane protein 1 (LMBR1). The CRISPR/Cas9 edited lmbr-1 suppressor alleles, lmbr-1(S647F) and lmbr-1(P314L), both significantly suppressed embryonic lethality and defective eggshell formation in the seip-1(A185P) background. The newly identified suppressor lines offer valuable insights into potential genetic interactors and pathways that may regulate seipin in the lipodystrophy model.
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Affiliation(s)
- Xiaofei Bai
- Department of Biology, University of Florida, Gainesville, FL 32610, USA
- Genetics Institute, University of Florida, Gainesville, FL 32610, USA
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Harold E. Smith
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Andy Golden
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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2
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Yang G, Li C, Wang S, Liang X, Yang B, Zhang Y, Zhang X, Chang X, Meng X. Molecular characterization of the grass carp bscl2 gene and its expression response to lipid accumulation, nutritional status, insulin and glucagon. Comp Biochem Physiol B Biochem Mol Biol 2024; 270:110931. [PMID: 38070669 DOI: 10.1016/j.cbpb.2023.110931] [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: 07/12/2023] [Revised: 12/03/2023] [Accepted: 12/03/2023] [Indexed: 01/10/2024]
Abstract
Bscl2 plays a role in lipid metabolism of mammals, however its role in teleost fish remains unclear. Using the grass carp (Ctenopharyngodon idella) as a model, the bscl2 gene was isolated from the brain and characterized. Thereafter, the tissue distribution of the gene was examined, before expression was analyzed as a function of fasting, refeeding, oral glucose administration and overfeeding. In addition, bscl2 mRNA levels were evaluated in grass carp primary hepatocytes treated with glucagon, insulin, oleic acid, and glucose. Results showed that the cloned bscl2 gene was 1341 bp, encoding 446 amino acids, and was highly expressed in the brain, heart, and gonad. Following oral glucose administration, bscl2 expression increased. Expression of bscl2 decreased in fasted fish but increased following refeeding. Overfeeding, which resulted in elevated lipid accumulation, also stimulated bscl2 expression. In primary hepatocytes, bscl2 levels were increased by glucose, oleic acid, and insulin treatments, and reduced by glucagon treatment. These data suggest that bscl2 may play an important role in nutrient metabolism in teleost fish.
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Affiliation(s)
- Guokun Yang
- College of Fisheries, Henan Normal University, Xinxiang 453007, PR China; Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang 453007, PR China
| | - Chengquan Li
- College of Fisheries, Henan Normal University, Xinxiang 453007, PR China
| | - Sunan Wang
- College of Fisheries, Henan Normal University, Xinxiang 453007, PR China
| | - Xiaomin Liang
- College of Fisheries, Henan Normal University, Xinxiang 453007, PR China
| | - Boya Yang
- College of Fisheries, Henan Normal University, Xinxiang 453007, PR China
| | - Yanmin Zhang
- College of Fisheries, Henan Normal University, Xinxiang 453007, PR China; Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang 453007, PR China
| | - Xindang Zhang
- College of Fisheries, Henan Normal University, Xinxiang 453007, PR China; Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang 453007, PR China
| | - Xulu Chang
- College of Fisheries, Henan Normal University, Xinxiang 453007, PR China; Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang 453007, PR China
| | - Xiaolin Meng
- College of Fisheries, Henan Normal University, Xinxiang 453007, PR China; Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang 453007, PR China.
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3
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Awuah WA, Tan JK, Shkodina AD, Ferreira T, Adebusoye FT, Mazzoleni A, Wellington J, David L, Chilcott E, Huang H, Abdul-Rahman T, Shet V, Atallah O, Kalmanovich J, Jiffry R, Madhu DE, Sikora K, Kmyta O, Delva MY. Hereditary spastic paraplegia: Novel insights into the pathogenesis and management. SAGE Open Med 2023; 12:20503121231221941. [PMID: 38162912 PMCID: PMC10757446 DOI: 10.1177/20503121231221941] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Accepted: 11/28/2023] [Indexed: 01/03/2024] Open
Abstract
Hereditary spastic paraplegia is a genetically heterogeneous neurodegenerative disorder characterised primarily by muscle stiffness in the lower limbs. Neurodegenerative disorders are conditions that result from cellular and metabolic abnormalities, many of which have strong genetic ties. While ageing is a known contributor to these changes, certain neurodegenerative disorders can manifest early in life, progressively affecting a person's quality of life. Hereditary spastic paraplegia is one such condition that can appear in individuals of any age. In hereditary spastic paraplegia, a distinctive feature is the degeneration of long nerve fibres in the corticospinal tract of the lower limbs. This degeneration is linked to various cellular and metabolic processes, including mitochondrial dysfunction, remodelling of the endoplasmic reticulum membrane, autophagy, abnormal myelination processes and alterations in lipid metabolism. Additionally, hereditary spastic paraplegia affects processes like endosome membrane trafficking, oxidative stress and mitochondrial DNA polymorphisms. Disease-causing genetic loci and associated genes influence the progression and severity of hereditary spastic paraplegia, potentially affecting various cellular and metabolic functions. Although hereditary spastic paraplegia does not reduce a person's lifespan, it significantly impairs their quality of life as they age, particularly with more severe symptoms. Regrettably, there are currently no treatments available to halt or reverse the pathological progression of hereditary spastic paraplegia. This review aims to explore the metabolic mechanisms underlying the pathophysiology of hereditary spastic paraplegia, emphasising the interactions of various genes identified in recent network studies. By comprehending these associations, targeted molecular therapies that address these biochemical processes can be developed to enhance treatment strategies for hereditary spastic paraplegia and guide clinical practice effectively.
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Affiliation(s)
| | | | - Anastasiia D Shkodina
- Department of Neurological Diseases, Poltava State Medical University, Poltava, Ukraine
| | - Tomas Ferreira
- Department of Clinical Neurosciences, School of Clinical Medicine, University of Cambridge, Cambridge, UK
| | | | - Adele Mazzoleni
- Barts and the London School of Medicine and Dentistry, London, UK
| | - Jack Wellington
- Cardiff University School of Medicine, Cardiff University, Wales, UK
| | - Lian David
- Norwich Medical School, University of East Anglia, Norwich, UK
| | - Ellie Chilcott
- Cardiff University School of Medicine, Cardiff University, Wales, UK
| | - Helen Huang
- Royal College of Surgeons in Ireland, University of Medicine and Health Sciences, Dublin, Ireland
| | | | - Vallabh Shet
- Faculty of Medicine, Bangalore Medical College and Research Institute, Karnataka, India
| | - Oday Atallah
- Department of Neurosurgery, Hannover Medical School, Hannover, Germany
| | | | - Riaz Jiffry
- Royal College of Surgeons in Ireland, University of Medicine and Health Sciences, Dublin, Ireland
| | | | | | | | - Mykhailo Yu Delva
- Department of Neurological Diseases, Poltava State Medical University, Poltava, Ukraine
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Bai X, Smith HE, Golden A. Identification of Genetic Suppressors for a Berardinelli-Seip Congenital Generalized Lipodystrophy Type 2 (BSCL2) Pathogenic Variant in C. elegans. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.22.559059. [PMID: 37790539 PMCID: PMC10542546 DOI: 10.1101/2023.09.22.559059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/05/2023]
Abstract
Maintaining the metabolic homeostasis of fatty acids is crucial for human health. Excess fatty acids are stored in lipid droplets (LDs), the primary energy reservoir that helps regulate fat and lipid homeostasis in nearly all cell types. Seipin (BSCL2), a conserved endoplasmic reticulum protein, plays a critical role in LD biogenesis and regulating LD morphology. Pathogenic variants of seipin are associated with multiple human genetic diseases, including Berardinelli-Seip Congenital Generalized Lipodystrophy Type 2 (BSCL2). However, the cellular and molecular mechanisms by which dysfunctional seipin leads to these diseases remain unclear. To model BSCL2 disease, we generated an orthologous BSCL2 pathogenic variant seip-1(A185P) using CRISPR/Cas9 genome editing in Caenorhabditis elegans . This variant led to severe developmental and cellular defects, including embryonic lethality, impaired eggshell formation, and abnormally enlarged LDs. We set out to identify genetic determinants that could suppress these defective phenotypes in the seip-1(A185P) mutant background. To this end, we conducted an unbiased chemical mutagenesis screen to identify genetic suppressors that restore embryonic viability in the seip-1(A185P) mutant background. A total of five suppressor lines were isolated and recovered from the screen. The defective phenotypes of seip-1(A185P) , including embryonic lethality and impaired eggshell formation, were significantly suppressed in each suppressor line. Two of the five suppressor lines also alleviated the enlarged LDs in the oocytes. We then mapped a suppressor candidate gene, R05D3.2 (renamed as lmbr-1 ), which is an ortholog of human LMBR1 (limb development membrane protein 1). The CRISPR/Cas9 edited lmbr-1 suppressor alleles, lmbr-1(Ser647Phe) and lmbr-1(Pro314Leu) , both significantly suppressed embryonic lethality and defective eggshell formation in the seip-1(A185P) background. The newly identified suppressor lines offer valuable insights into potential genetic interactors and pathways that may regulate seipin in the lipodystrophy model.
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Abstract
Cells store excess energy in the form of lipid droplets (LDs), a specialized sub-compartment of the endoplasmic reticulum (ER) network. The lipodystrophy protein seipin is a key player in LD biogenesis and ER-LD contact site maintenance. Recent structural and in silico studies have started to shed light on the molecular function of seipin as a LD nucleator in early LD biogenesis, whilst new cell biological work implies a role for seipin in ER-mitochondria contact sites and calcium metabolism. In this minireview, I discuss recent insights into the molecular function of seipin.
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Affiliation(s)
- Veijo T. Salo
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
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Generalized lipoatrophy syndromes. Presse Med 2021; 50:104075. [PMID: 34562560 DOI: 10.1016/j.lpm.2021.104075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2021] [Revised: 08/31/2021] [Accepted: 09/15/2021] [Indexed: 11/23/2022] Open
Abstract
Generalized lipodystrophy (GL) syndromes are a group of rare heterogenous disorders, characterized by total subcutaneous fat loss. The frequency of GL is currently assessed as approximately 0,23 cases per million of the population, in Europe - as 0,96 cases per million of the population. They can be congenital (CGL) or acquired (AGL) depending on the etiology and the time of the onset of fat loss. Both CGL and AGL are often associated with different metabolic complications, such as hypertriglyceridemia, insulin resistance and lipoatrophic diabetes mellitus, metabolically associated FLD, arterial hypertension, proteinuria, reproductive system disorders. In this review we aimed to summarize the information on all forms of generalized lipodystrophy, especially the ones of genetic etiology, their clinical manifestations and complications, the perspectives for diagnostics, treatment and further research.
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Spastin mutations impair coordination between lipid droplet dispersion and reticulum. PLoS Genet 2020; 16:e1008665. [PMID: 32315314 PMCID: PMC7173978 DOI: 10.1371/journal.pgen.1008665] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2019] [Accepted: 02/12/2020] [Indexed: 12/22/2022] Open
Abstract
Lipid droplets (LD) are affected in multiple human disorders. These highly dynamic organelles are involved in many cellular roles. While their intracellular dispersion is crucial to ensure their function and other organelles-contact, underlying mechanisms are still unclear. Here we show that Spastin, one of the major proteins involved in Hereditary Spastic Paraplegia (HSP), controls LD dispersion. Spastin depletion in zebrafish affects metabolic properties and organelle dynamics. These functions are ensured by a conserved complex set of splice variants. M1 isoforms determine LD dispersion in the cell by orchestrating endoplasmic reticulum (ER) shape along microtubules (MTs). To further impact LD fate, Spastin modulates transcripts levels and subcellular location of other HSP key players, notably Seipin and REEP1. In pathological conditions, mutations in human Spastin M1 disrupt this mechanism and impacts LD network. Spastin depletion influences not only other key proteins but also modulates specific neutral lipids and phospholipids, revealing an impact on membrane and organelle components. Altogether our results show that Spastin and its partners converge in a common machinery that coordinates LD dispersion and ER shape along MTs. Any alteration of this system results in HSP clinical features and impacts lipids profile, thus opening new avenues for novel biomarkers of HSP.
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Hoa Chung L, Qi Y. Lipodystrophy - A Rare Condition with Serious Metabolic Abnormalities. Rare Dis 2020. [DOI: 10.5772/intechopen.88667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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9
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Zhou H, Xu C, Lee H, Yoon Y, Chen W. Berardinelli-Seip congenital lipodystrophy 2/SEIPIN determines brown adipose tissue maintenance and thermogenic programing. Mol Metab 2020; 36:100971. [PMID: 32246911 PMCID: PMC7136632 DOI: 10.1016/j.molmet.2020.02.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/25/2019] [Revised: 02/18/2020] [Accepted: 02/25/2020] [Indexed: 01/12/2023] Open
Abstract
Objective Understanding the mechanisms that control brown adipose tissue (BAT) mass and functionality is crucial for our understanding of how the disruption of energy homeostasis leads to obesity. Bernerdinali Seip Congenital Lipodystrophy (BSCL) type 2 (BSCL2, a.k.a. SEIPIN), a lipodystrophy-associated protein, has been shown to not be required for brown adipogenesis, but it has been shown to be essential for perinatal BAT development. However, its role in mature BAT maintenance and thermogenic programing remains poorly understood. Methods We subjected Bscl2f/f and Bscl2UCP1-BKO (BKO) mice with a brown adipose-specific loss of BSCL2 through UCP1 promoter-driven Cre to environmental, pharmacological and diet interventions to challenge BAT functionality and reprogramming. We carried out physiological, molecular and transcriptomic analyses of BAT. Results The deletion of BSCL2 in mature brown adipocytes increased sympathetic nervous system-independent cAMP/protein kinase A (PKA) signaling in BAT. Such activation reduced BAT triglyceride content and mass and was sufficient to reduce plasma triglyceride, but not enough to combat thermoneutral and high fat diet-induced obesity. Surprisingly, BKO mice displayed an impaired response to acute and chronic cold challenges despite cAMP/PKA activation. When subjected to chronic cold exposure or the administration of a β3-adrenergic agonist, CL 316,243, BKO mice failed to induce BAT recruitment and underwent dramatic brown adipocyte loss. Transcriptomic analysis revealed pathological BAT remodeling with inflammation and fibrosis, which was further exacerbated by a chronic thermogenic challenge in BKO mice. Mechanistically, we found abnormal mitochondrial shapes and function in BAT of BKO mice housed at 21 °C; as well as mitochondrial DNA depletion and necroptotic-mediated brown adipocyte death after chronic thermogenic insult. Conclusion BSCL2-mediated lipid catabolism within BAT is crucial for mature brown adipocyte function and survival both during times of activation and quiescence. BSCL2 is an important regulator of mature brown adipocyte mitochondrial metabolism, necroptosis and thus adaptive thermogenesis. Mature BAT-specific loss of BSCL2 (Bscl2UCP1-BKO) activates SNS-independent cAMP/PKA signaling. Bscl2UCP1-BKO increases BAT mitochondrial fission and uncoupling. Bscl2UCP1-BKO reduces plasma triglyceride but not adiposity under thermoneutrality or high fat diet. Bscl2UCP1-BKO blunts BAT reprograming and causes cold intolerance. BSCL2 deletion exposes brown adipocyte to necroptosis under chronic thermogenic stress.
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Affiliation(s)
- Hongyi Zhou
- Department of Physiology, Medical College of Georgia at Augusta University, Augusta, GA 30912, USA
| | - Cheng Xu
- Department of Physiology, Medical College of Georgia at Augusta University, Augusta, GA 30912, USA
| | - Hakjoo Lee
- Department of Physiology, Medical College of Georgia at Augusta University, Augusta, GA 30912, USA
| | - Yisang Yoon
- Department of Physiology, Medical College of Georgia at Augusta University, Augusta, GA 30912, USA
| | - Weiqin Chen
- Department of Physiology, Medical College of Georgia at Augusta University, Augusta, GA 30912, USA.
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Fernández-Marmiesse A, Sánchez-Iglesias S, Darling A, O'Callaghan MM, Tonda R, Jou C, Araújo-Vilar D. A de novo heterozygous missense BSCL2 variant in 2 siblings with intractable developmental and epileptic encephalopathy. Seizure 2019; 71:161-165. [DOI: 10.1016/j.seizure.2019.07.019] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2019] [Revised: 07/17/2019] [Accepted: 07/24/2019] [Indexed: 12/11/2022] Open
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11
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Exploring Seipin: From Biochemistry to Bioinformatics Predictions. Int J Cell Biol 2018; 2018:5207608. [PMID: 30402103 PMCID: PMC6192094 DOI: 10.1155/2018/5207608] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Revised: 08/12/2018] [Accepted: 09/03/2018] [Indexed: 01/30/2023] Open
Abstract
Seipin is a nonenzymatic protein encoded by the BSCL2 gene. It is involved in lipodystrophy and seipinopathy diseases. Named in 2001, all seipin functions are still far from being understood. Therefore, we reviewed much of the research, trying to find a pattern that could explain commonly observed features of seipin expression disorders. Likewise, this review shows how this protein seems to have tissue-specific functions. In an integrative view, we conclude by proposing a theoretical model to explain how seipin might be involved in the triacylglycerol synthesis pathway.
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Eisenberg-Bord M, Mari M, Weill U, Rosenfeld-Gur E, Moldavski O, Castro IG, Soni KG, Harpaz N, Levine TP, Futerman AH, Reggiori F, Bankaitis VA, Schuldiner M, Bohnert M. Identification of seipin-linked factors that act as determinants of a lipid droplet subpopulation. J Cell Biol 2018; 217:269-282. [PMID: 29187527 PMCID: PMC5748981 DOI: 10.1083/jcb.201704122] [Citation(s) in RCA: 86] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Revised: 09/21/2017] [Accepted: 10/23/2017] [Indexed: 02/07/2023] Open
Abstract
Functional heterogeneity within the lipid droplet (LD) pool of a single cell has been observed, yet the underlying mechanisms remain enigmatic. Here, we report on identification of a specialized LD subpopulation characterized by a unique proteome and a defined geographical location at the nucleus-vacuole junction contact site. In search for factors determining identity of these LDs, we screened ∼6,000 yeast mutants for loss of targeting of the subpopulation marker Pdr16 and identified Ldo45 (LD organization protein of 45 kD) as a crucial targeting determinant. Ldo45 is the product of a splicing event connecting two adjacent genes (YMR147W and YMR148W/OSW5/LDO16). We show that Ldo proteins cooperate with the LD biogenesis component seipin and establish LD identity by defining positioning and surface-protein composition. Our studies suggest a mechanism to establish functional differentiation of organelles, opening the door to better understanding of metabolic decisions in cells.
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Affiliation(s)
| | - Muriel Mari
- Department of Cell Biology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
| | - Uri Weill
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Eden Rosenfeld-Gur
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Ofer Moldavski
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Inês G Castro
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Krishnakant G Soni
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, TX
| | - Nofar Harpaz
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Tim P Levine
- UCL Institute of Ophthalmology, London, England, UK
| | - Anthony H Futerman
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Fulvio Reggiori
- Department of Cell Biology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
| | - Vytas A Bankaitis
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, TX
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Maria Bohnert
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
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Lipid droplet growth and adipocyte development: mechanistically distinct processes connected by phospholipids. Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1862:1273-1283. [PMID: 28668300 DOI: 10.1016/j.bbalip.2017.06.016] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2017] [Revised: 06/20/2017] [Accepted: 06/23/2017] [Indexed: 12/19/2022]
Abstract
The differentiation of preadipocytes into mature adipocytes is accompanied by the growth and formation of a giant, unilocular lipid droplet (LD). Mechanistically however, LD growth and adipogenesis are two different processes. Recent studies have uncovered a number of proteins that are able to regulate both LD dynamics and adipogenesis, such as SEIPIN, LIPIN and CDP-Diacylglycerol Synthases. It appears that phospholipids, phosphatidic acid in particular, play a critical role in both LD budding/growth and adipocyte development. This review summarizes recent advances, and aims to provide a better understanding of LD growth as well as adipogenesis, two critical aspects in mammalian fat storage. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.
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Schuldiner M, Bohnert M. A different kind of love - lipid droplet contact sites. Biochim Biophys Acta Mol Cell Biol Lipids 2017. [PMID: 28627434 DOI: 10.1016/j.bbalip.2017.06.005] [Citation(s) in RCA: 128] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Lipid droplets (LDs) store lipids and hence serve as energy reservoir and as a source for building-blocks for the organelle membrane systems. LD biology therefore depends on tight communication with other organelles. The unique architecture of LDs, consisting of a neutral lipid core shielded by a phospholipid-monolayer, is however an obstacle to bulk-exchange of bilayer-bounded vesicles with other organelles. In recent years, it is emerging that contact sites, places where two organelles are positioned in close proximity allowing vesicle-independent communication, are an important way to integrate LDs into the organellar landscape. However, few LD contact sites have been studied in depth and our understanding of their structure, extent and function is only starting to emerge. Here, we highlight recent findings on the functions of LD contact sites and on the proteins involved in their formation and hypothesize about the unique characteristics of the contact sites formed by these intriguing organelles. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.
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Affiliation(s)
- Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Maria Bohnert
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel.
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15
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Hepatic BSCL2 (Seipin) Deficiency Disrupts Lipid Droplet Homeostasis and Increases Lipid Metabolism via SCD1 Activity. Lipids 2016; 52:129-150. [DOI: 10.1007/s11745-016-4210-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Accepted: 10/25/2016] [Indexed: 12/11/2022]
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16
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Wang H, Becuwe M, Housden BE, Chitraju C, Porras AJ, Graham MM, Liu XN, Thiam AR, Savage DB, Agarwal AK, Garg A, Olarte MJ, Lin Q, Fröhlich F, Hannibal-Bach HK, Upadhyayula S, Perrimon N, Kirchhausen T, Ejsing CS, Walther TC, Farese RV. Seipin is required for converting nascent to mature lipid droplets. eLife 2016; 5. [PMID: 27564575 PMCID: PMC5035145 DOI: 10.7554/elife.16582] [Citation(s) in RCA: 253] [Impact Index Per Article: 31.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 08/25/2016] [Indexed: 12/16/2022] Open
Abstract
How proteins control the biogenesis of cellular lipid droplets (LDs) is poorly understood. Using Drosophila and human cells, we show here that seipin, an ER protein implicated in LD biology, mediates a discrete step in LD formation-the conversion of small, nascent LDs to larger, mature LDs. Seipin forms discrete and dynamic foci in the ER that interact with nascent LDs to enable their growth. In the absence of seipin, numerous small, nascent LDs accumulate near the ER and most often fail to grow. Those that do grow prematurely acquire lipid synthesis enzymes and undergo expansion, eventually leading to the giant LDs characteristic of seipin deficiency. Our studies identify a discrete step of LD formation, namely the conversion of nascent LDs to mature LDs, and define a molecular role for seipin in this process, most likely by acting at ER-LD contact sites to enable lipid transfer to nascent LDs.
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Affiliation(s)
- Huajin Wang
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, United States.,Department of Genetics and Complex Diseases, Harvard T H Chan School of Public Health, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Michel Becuwe
- Department of Genetics and Complex Diseases, Harvard T H Chan School of Public Health, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States
| | | | - Chandramohan Chitraju
- Department of Genetics and Complex Diseases, Harvard T H Chan School of Public Health, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Ashley J Porras
- Department of Genetics and Complex Diseases, Harvard T H Chan School of Public Health, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Morven M Graham
- Center for Cellular and Molecular Imaging, Department of Cell Biology, Yale School of Medicine, New Haven, United States
| | - Xinran N Liu
- Center for Cellular and Molecular Imaging, Department of Cell Biology, Yale School of Medicine, New Haven, United States
| | - Abdou Rachid Thiam
- Laboratoire de Physique Statistique, École Normale Supérieure, PSL Research University, Université Paris Diderot Sorbonne Paris-Cité, Sorbonne Universités UPMC Univ Paris 06, CNRS UMR 8550, Paris, France
| | - David B Savage
- The University of Cambridge Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Cambridge, United Kingdom
| | - Anil K Agarwal
- Division of Nutrition and Metabolic Diseases, Department of Internal Medicine, UT Southwestern Medical Center, Dallas, United States
| | - Abhimanyu Garg
- Division of Nutrition and Metabolic Diseases, Department of Internal Medicine, UT Southwestern Medical Center, Dallas, United States
| | - Maria-Jesus Olarte
- Department of Genetics and Complex Diseases, Harvard T H Chan School of Public Health, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Qingqing Lin
- Department of Genetics and Complex Diseases, Harvard T H Chan School of Public Health, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Florian Fröhlich
- Department of Genetics and Complex Diseases, Harvard T H Chan School of Public Health, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States.,Molecular Membrane Biology Section, Department of Biology/Chemistry, University of Osnabrück, Osnabrück, Germany
| | - Hans Kristian Hannibal-Bach
- VILLUM Center for Bioanalytical Sciences, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Srigokul Upadhyayula
- Department of Cell Biology, Harvard Medical School, Boston, United States.,Department of Pediatrics, Harvard Medical School, Boston, United States.,Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, United States
| | - Norbert Perrimon
- Department of Genetics, Harvard Medical School, Boston, United States.,Howard Hughes Medical Institute, Boston, United States
| | - Tomas Kirchhausen
- Department of Cell Biology, Harvard Medical School, Boston, United States.,Department of Pediatrics, Harvard Medical School, Boston, United States.,Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, United States
| | - Christer S Ejsing
- VILLUM Center for Bioanalytical Sciences, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Tobias C Walther
- Department of Genetics and Complex Diseases, Harvard T H Chan School of Public Health, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States.,Howard Hughes Medical Institute, Boston, United States.,Broad Institute of Harvard and MIT, Cambridge, United States
| | - Robert V Farese
- Department of Genetics and Complex Diseases, Harvard T H Chan School of Public Health, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States.,Broad Institute of Harvard and MIT, Cambridge, United States
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17
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Chen Y, Wei L, Tian J, Wang YH, Liu G, Wang C. Seinpin knockout exacerbates cerebral ischemia/reperfusion damage in mice. Biochem Biophys Res Commun 2016; 474:377-383. [PMID: 27109482 DOI: 10.1016/j.bbrc.2016.04.116] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 04/20/2016] [Indexed: 01/17/2023]
Abstract
BACKGROUND AND PURPOSE Seipin, which regulates adipocyte differentiation and lipolysis, inducing severe lipodystrophy and metabolic syndromes, is also highly expressed in the nervous system and affects some neurological diseases. However, the impacts of seipin in stroke remain unclear. METHODS AND RESULTS In this study, we subjected seipin knockout mice to cerebral ischemia/reperfusion injury and found that seipin knockout mice exhibited exacerbated neurological disorder and enlarged infarct size, companied by blood-brain barrier (BBB) damages. Furthermore, we showed that seipin knockout aggravated endoplasmic reticulum (ER) stress and significantly increased glucose levels, decreased leptin and adiponectin levels in mouse plasma. CONCLUSIONS Our findings reveal that seipin knockout exacerbates cerebral I/R-induced damages by increasing BBB permeability, amplifying ER stress and increasing glucose levels, as well as decreasing leptin and adiponectin levels, indicating that seipin may be a potential therapeutic target for stroke.
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Affiliation(s)
- Yong Chen
- Department of Neurology, People's Hospital of Deyang City, Taishian North Road 173, Deyang City, 618000, China
| | - Lili Wei
- Institute of Cardiovascular Sciences, Peking University Health Science Center, 38 Xueyuan Rd, Hai Dian District, 100083, Beijing, China
| | - Jing Tian
- Department of Neurology, People's Hospital of Deyang City, Taishian North Road 173, Deyang City, 618000, China
| | - Yu-Hui Wang
- Institute of Cardiovascular Sciences, Peking University Health Science Center, 38 Xueyuan Rd, Hai Dian District, 100083, Beijing, China
| | - George Liu
- Institute of Cardiovascular Sciences, Peking University Health Science Center, 38 Xueyuan Rd, Hai Dian District, 100083, Beijing, China.
| | - Chun Wang
- Department of Neurology, People's Hospital of Deyang City, Taishian North Road 173, Deyang City, 618000, China.
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18
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Choudhary V, Ojha N, Golden A, Prinz WA. A conserved family of proteins facilitates nascent lipid droplet budding from the ER. J Cell Biol 2016; 211:261-71. [PMID: 26504167 PMCID: PMC4621845 DOI: 10.1083/jcb.201505067] [Citation(s) in RCA: 214] [Impact Index Per Article: 26.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Visualization of nascent lipid droplets reveals that they form lens-like structures inside the ER membrane bilayer and that FIT proteins are necessary for lipid droplet protrusion toward the cytoplasm. Lipid droplets (LDs) are found in all cells and play critical roles in lipid metabolism. De novo LD biogenesis occurs in the endoplasmic reticulum (ER) but is not well understood. We imaged early stages of LD biogenesis using electron microscopy and found that nascent LDs form lens-like structures that are in the ER membrane, raising the question of how these nascent LDs bud from the ER as they grow. We found that a conserved family of proteins, fat storage-inducing transmembrane (FIT) proteins, is required for proper budding of LDs from the ER. Elimination or reduction of FIT proteins in yeast and higher eukaryotes causes LDs to remain in the ER membrane. Deletion of the single FIT protein in Caenorhabditis elegans is lethal, suggesting that LD budding is an essential process in this organism. Our findings indicated that FIT proteins are necessary to promote budding of nascent LDs from the ER.
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Affiliation(s)
- Vineet Choudhary
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
| | - Namrata Ojha
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
| | - Andy Golden
- Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
| | - William A Prinz
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
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19
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Abstract
Congenital generalized lipodystrophy (CGL) is a heterogeneous autosomal recessive disorder characterized by a near complete lack of adipose tissue from birth and, later in life, the development of metabolic complications, such as diabetes mellitus, hypertriglyceridaemia and hepatic steatosis. Four distinct subtypes of CGL exist: type 1 is associated with AGPAT2 mutations; type 2 is associated with BSCL2 mutations; type 3 is associated with CAV1 mutations; and type 4 is associated with PTRF mutations. The products of these genes have crucial roles in phospholipid and triglyceride synthesis, as well as in the formation of lipid droplets and caveolae within adipocytes. The predominant cause of metabolic complications in CGL is excess triglyceride accumulation in the liver and skeletal muscle owing to the inability to store triglycerides in adipose tissue. Profound hypoleptinaemia further exacerbates metabolic derangements by inducing a voracious appetite. Patients require psychological support, a low-fat diet, increased physical activity and cosmetic surgery. Aside from conventional therapy for hyperlipidaemia and diabetes mellitus, metreleptin replacement therapy can dramatically improve metabolic complications in patients with CGL. In this Review, we discuss the molecular genetic basis of CGL, the pathogenesis of the disease's metabolic complications and therapeutic options for patients with CGL.
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Affiliation(s)
- Nivedita Patni
- Division of Paediatric Endocrinology, Department of Paediatrics, Department of Internal Medicine, Centre for Human Nutrition, UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-8537, USA
| | - Abhimanyu Garg
- Division of Nutrition and Metabolic Diseases, Department of Internal Medicine, Center for Human Nutrition, UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-8537, USA
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20
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Seipin mutation at glycosylation sites activates autophagy in transfected cells via abnormal large lipid droplets generation. Acta Pharmacol Sin 2015; 36:497-506. [PMID: 25832430 DOI: 10.1038/aps.2014.164] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2014] [Accepted: 12/29/2014] [Indexed: 12/27/2022] Open
Abstract
AIM Seipin is a protein that resides in endoplasmic reticulum, and involved in both lipid metabolic disorders and motor neuropathy. The aim of this study was to investigate the effects of mutant seipin on autophagy system and the morphology of lipid droplets in vitro. METHODS HEK-293, H1299 and MES23.5 cells were transfected with the plasmids of mutated seipin at glycosylation sites (N88S or S90L) and GFP-LC3 plasmids. The cells were subjected to immunofluorescence and flow cytometry assays, and the cell lysates were subjected to immunoblot analysis. Nile Red was used to stain the lipid droplets in the cells. RESULTS Overexpression of the mutated seipin proteins N88S or S90L activated autophagy in the 3 cell lines, and substantially altered the sub-cellular distribution of the autophagosome marker GFP-LC3, leading to a number of large vacuoles appearing in the cytoplasm. The sub-cellular location of GFP-LC3 and mutated seipin proteins highly overlapped. Moreover, and the mutated seipin proteins caused diffuse small lipid droplets to fuse into larger lipid droplets. Treatment of mutated seipin-transfected cells with the autophagy inhibitor 3-MA (5 mmol/L) facilitated the fusion of mutated seipin-induced large vacuoles. The protein glycosylation inhibitor tunicamycin could mimic the mutated seipin-induced effects, and treatment of the wild-type seipin-transfected cells with tunicamycin (2.5 μg/mL) produced similar morphological and biochemical properties as in the mutated seipin-transfected cells. CONCLUSION The mutation of seipin at glycosylation sites disrupt its function in regulating lipid droplet metabolism, and the autophagy acts as an adaptive response to break down abnormal lipid droplets. The interruption of autophagy would accelerate the fusion of abnormal lipid droplets.
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21
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Tokunaga M, Shiheido H, Hayakawa I, Utsumi A, Takashima H, Doi N, Horisawa K, Sakuma-Yonemura Y, Tabata N, Yanagawa H. Hereditary spastic paraplegia protein spartin is an FK506-binding protein identified by mRNA display. ACTA ACUST UNITED AC 2014; 20:935-42. [PMID: 23890011 DOI: 10.1016/j.chembiol.2013.05.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Revised: 05/22/2013] [Accepted: 05/24/2013] [Indexed: 11/15/2022]
Abstract
Here, we used mRNA display to search for proteins that bind to FK506, a potent immunosuppressant drug, and identified spartin, a hereditary spastic paraplegia protein, from a human brain cDNA library. We demonstrated that FK506 binds to the C-terminal region of spartin and thereby inhibits the interaction of spartin with TIP47, one of the lipid droplet-associated proteins. We further confirmed that FK506 inhibits localization of spartin and its binder, an E3 ubiquitin ligase AIP4, in lipid droplets and increases the protein level of ADRP (adipose differentiation-related protein), which is a regulator of lipid homeostasis. These results strongly suggest that FK506 suppresses the proteasomal degradation of ADRP, a substrate of AIP4, by inhibiting the spartin-TIP47 interaction and thereby blocking the localization of spartin and AIP4 in lipid droplets.
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Affiliation(s)
- Mayuko Tokunaga
- Department of Biosciences and Informatics, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
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22
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Zhou L, Yin J, Wang C, Liao J, Liu G, Chen L. Lack of seipin in neurons results in anxiety- and depression-like behaviors via down regulation of PPARγ. Hum Mol Genet 2014; 23:4094-102. [PMID: 24651066 DOI: 10.1093/hmg/ddu126] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Affiliation(s)
- Libin Zhou
- State Key Laboratory of Reproductive Medicine and Department of Physiology, Nanjing Medical University, Nanjing 210029, China
| | - Jun Yin
- Department of Physiology, Nanjing Medical University, Nanjing 210029, China
| | - Conghui Wang
- Department of Physiology, Nanjing Medical University, Nanjing 210029, China
| | - Jiawei Liao
- Institute of Cardiovascular Sciences, Peking University and Key Laboratory of Cardiovascular Sciences, China Administration of Education, Beijing 100191, China
| | - George Liu
- Institute of Cardiovascular Sciences, Peking University and Key Laboratory of Cardiovascular Sciences, China Administration of Education, Beijing 100191, China
| | - Ling Chen
- State Key Laboratory of Reproductive Medicine and Department of Physiology, Nanjing Medical University, Nanjing 210029, China
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23
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Wei S, Soh SLY, Xia J, Ong WY, Pang ZP, Han W. Motor neuropathy-associated mutation impairs Seipin functions in neurotransmission. J Neurochem 2014; 129:328-38. [DOI: 10.1111/jnc.12638] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 11/18/2013] [Accepted: 12/12/2013] [Indexed: 12/11/2022]
Affiliation(s)
- Shunhui Wei
- Laboratory of Metabolic Medicine; Singapore Bioimaging Consortium, A*STAR; Singapore
| | - Stephanie Li-Ying Soh
- Laboratory of Metabolic Medicine; Singapore Bioimaging Consortium, A*STAR; Singapore
| | - Julia Xia
- Laboratory of Metabolic Medicine; Singapore Bioimaging Consortium, A*STAR; Singapore
- Child Health Institute of New Jersey; Department of Neuroscience and Cell Biology; Rutgers Robert Wood Johnson Medical School; New Brunswick New Jersey USA
| | - Wei-Yi Ong
- Department of Anatomy; Yong Loo Lin School of Medicine; National University of Singapore; Singapore
| | - Zhiping P. Pang
- Child Health Institute of New Jersey; Department of Neuroscience and Cell Biology; Rutgers Robert Wood Johnson Medical School; New Brunswick New Jersey USA
| | - Weiping Han
- Laboratory of Metabolic Medicine; Singapore Bioimaging Consortium, A*STAR; Singapore
- Institute of Molecular and Cell Biology; A*STAR; Singapore
- Department of Biochemistry; Yong Loo Lin School of Medicine; National University of Singapore; Singapore
- Cardiovascular and Metabolic Disorders Program; Duke-NUS Graduate Medical School; Singapore
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24
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Clément S, Fauvelle C, Branche E, Kaddai V, Conzelmann S, Boldanova T, Bartosch B, Minehira K, Negro F. Role of seipin in lipid droplet morphology and hepatitis C virus life cycle. J Gen Virol 2013; 94:2208-2214. [PMID: 23907395 DOI: 10.1099/vir.0.054593-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Infectious hepatitis C virus (HCV) particle assembly starts at the surface of lipid droplets, cytoplasmic organelles responsible for neutral fat storage. We analysed the relationship between HCV and seipin, a protein involved in lipid droplet maturation. Although seipin overexpression did not affect the total mean volume occupied by lipid droplets nor the total triglyceride and cholesterol ester levels per cell, it caused an increase in the mean diameter of lipid droplets by 60 %, while decreasing their total number per cell. The latter two effects combined resulted in a 34 % reduction of the total outer surface area of lipid droplets per cell, with a proportional decrease in infectious viral particle production, probably due to a defect in particle assembly. These results suggest that the available outer surface of lipid droplets is a critical factor for HCV release, independent of the neutral lipid content of the cell.
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Affiliation(s)
- Sophie Clément
- Division of Clinical Pathology, University Hospital, University of Geneva School of Medicine, Geneva, Switzerland
| | - Catherine Fauvelle
- Department of Immunology and Pathology, Faculty of Medicine, University of Geneva, Switzerland
| | - Emilie Branche
- Department of Immunology and Pathology, Faculty of Medicine, University of Geneva, Switzerland
| | - Vincent Kaddai
- Department of Immunology and Pathology, Faculty of Medicine, University of Geneva, Switzerland
| | - Stéphanie Conzelmann
- Department of Immunology and Pathology, Faculty of Medicine, University of Geneva, Switzerland
| | - Tujana Boldanova
- Department of Biomedicine, University Hospital Basel, Switzerland
| | - Birke Bartosch
- CRCL, INSERM U1052, CNRS 5286, University of Lyon, France
| | - Kaori Minehira
- Department of Physiology, University of Lausanne, Switzerland
| | - Francesco Negro
- Gastroenterology and Hepatology, University Hospital, University of Geneva School of Medicine, Geneva, Switzerland.,Division of Clinical Pathology, University Hospital, University of Geneva School of Medicine, Geneva, Switzerland
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25
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Yang W, Thein S, Guo X, Xu F, Venkatesh B, Sugii S, Radda G, Han W. Seipin differentially regulates lipogenesis and adipogenesis through a conserved core sequence and an evolutionarily acquired C-terminus. Biochem J 2013; 452:37-44. [PMID: 23458123 DOI: 10.1042/bj20121870] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/11/2024]
Abstract
Homozygous mutations in BSCL2 (Berardinelli–Seip congenital lipodystrophy)/seipin cause CGL2 (congenital generalized lipodystrophy type 2). Recent data suggest that seipin regulates LD (lipid droplet) dynamics and adipocyte differentiation, but whether these roles are mechanistically linked remains unclear. To understand how seipin regulates these processes, we investigated the evolutionary changes of seipin orthologues, and studied individual domains in regulating lipid accumulation in non-adipocytes and adipocytes. Mammalian seipins comprise at least two distinct functional domains, a conserved core sequence and an evolutionarily acquired C-terminus. Despite its requirement for adipocyte formation, seipin overexpression inhibited oleate-induced LD formation and accumulation in nonadipocytes, which was mediated by the core sequence. In contrast, seipin overexpression did not inhibit LD accumulation during adipocyte differentiation or the adipogenic process in 3T3-L1 cells. However, adipogenesis and LD accumulation were impaired in 3T3-L1 cells expressing a seipin mutant lacking the C-terminus. Furthermore, expression of the same mutant without the C-terminus failed to rescue the adipogenic defects in seipin-knockdown cells, demonstrating the importance of the C-terminus for seipin's function in adipocyte development. We propose that seipin is involved in lipid homoeostasis by restricting lipogenesis and LD accumulation in non-adipocytes, while promoting adipogenesis to accommodate excess energy storage.
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Affiliation(s)
- Wulin Yang
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, 11 Biopolis Way, Singapore 138667
| | - Shermaine Thein
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, 11 Biopolis Way, Singapore 138667
| | - Xiangxiang Guo
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, 11 Biopolis Way, Singapore 138667
| | - Feng Xu
- Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), 30 Medical Drive, Singapore 117609
| | - Byrappa Venkatesh
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore 138673
| | - Shigeki Sugii
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, 11 Biopolis Way, Singapore 138667
- Duke-NUS Graduate Medical School, Singapore 169857
| | - George K. Radda
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, 11 Biopolis Way, Singapore 138667
| | - Weiping Han
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, 11 Biopolis Way, Singapore 138667
- Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), 30 Medical Drive, Singapore 117609
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore 138673
- Duke-NUS Graduate Medical School, Singapore 169857
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597
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26
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Guo J, Qiu W, Soh SLY, Wei S, Radda GK, Ong WY, Pang ZP, Han W. Motor neuron degeneration in a mouse model of seipinopathy. Cell Death Dis 2013; 4:e535. [PMID: 23470542 PMCID: PMC3613842 DOI: 10.1038/cddis.2013.64] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Heterozygosity for missense mutations (N88S/S90L) in BSCL2 (Berardinelli–Seip congenital lipodystrophy type 2)/Seipin is associated with a broad spectrum of motoneuron diseases. To understand the underlying mechanisms how the mutations lead to motor neuropathy, we generated transgenic mice with neuron-specific expression of wild-type (tgWT) or N88S/S90L mutant (tgMT) human Seipin. Transgenes led to the broad expression of WT or mutant Seipin in the brain and spinal cord. TgMT, but not tgWT, mice exhibited late-onset altered locomotor activities and gait abnormalities that recapitulate symptoms of seipinopathy patients. We found loss of alpha motor neurons in tgMT spinal cord. Mild endoreticular stress was present in both tgMT and tgWT neurons; however, only tgMT mice exhibited protein aggregates and disrupted Golgi apparatus. Furthermore, autophagosomes were significantly increased, along with elevated light chain 3 (LC3)-II level in tgMT spinal cord, consistent with the activation of autophagy pathway in response to mutant Seipin expression and protein aggregation. These results suggest that induction of autophagy pathway is involved in the cellular response to mutant Seipin in seipinopathy and that motoneuron loss is a key pathogenic process underlying the development of locomotor abnormalities.
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Affiliation(s)
- J Guo
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
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27
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Peng XG, Ju S, Fang F, Wang Y, Fang K, Cui X, Liu G, Li P, Mao H, Teng GJ. Comparison of brown and white adipose tissue fat fractions in ob, seipin, and Fsp27 gene knockout mice by chemical shift-selective imaging and (1)H-MR spectroscopy. Am J Physiol Endocrinol Metab 2013; 304:E160-7. [PMID: 23149622 DOI: 10.1152/ajpendo.00401.2012] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Brown adipose tissue (BAT) plays a key role in thermogenesis to protect the body from cold and obesity. White adipose tissue (WAT) stores excess energy in the form of triglycerides. To better understand the genetic effect on regulation of WAT and BAT, we investigated the fat fraction (FF) in two types of adipose tissues in ob/ob, human BSCL2/seipin gene knockout (SKO), Fsp27 gene knockout (Fsp27(-/-)), and wild-type (WT) mice in vivo using chemical shift selective imaging and (1)H-MR spectroscopy. We reported that the visceral fat volume in WAT was significantly larger in ob/ob mice, but visceral fat volumes were lower in SKO and Fsp27(-/-) mice compared with WT mice. BAT FF was significantly higher in ob/ob mice than the WT group and similar to that of WAT. In contrast, WAT FFs in SKO and Fsp27(-/-) mice were lower and similar to that of BAT. The adipocyte size of WAT in ob/ob mice and the BAT adipocyte size in ob/ob, SKO, and Fsp27 mice were significantly larger compared with WT mice. However, the WAT adipocyte size was significantly smaller in SKO mice than in WT mice. Positive correlations were observed between the adipocyte size and FFs of WAT and BAT. These results suggested that smaller adipocyte size correlates with lower FFs of WAT and BAT. In addition, the differences in FFs in WAT and BAT measured by MR methods in different mouse models were related to the different regulation effects of ob, seipin, or Fsp27 gene on developing WAT and BAT.
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Affiliation(s)
- Xin-Gui Peng
- Jiangsu Key Laboratory of Molecular and Functional Imaging, Department of Radiology, Zhongda Hospital, Medical School, Southeast University, Nanjing, China
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28
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Wei S, Soh SLY, Qiu W, Yang W, Seah CJY, Guo J, Ong WY, Pang ZP, Han W. Seipin regulates excitatory synaptic transmission in cortical neurons. J Neurochem 2012; 124:478-89. [PMID: 23173741 DOI: 10.1111/jnc.12099] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2012] [Revised: 11/20/2012] [Accepted: 11/20/2012] [Indexed: 12/20/2022]
Abstract
Heterozygosity for missense mutations in Seipin, namely N88S and S90L, leads to a broad spectrum of motor neuropathy, while a number of loss-of-function mutations in Seipin are associated with the Berardinelli-Seip congenital generalized lipodystrophy type 2 (CGL2, BSCL2), a condition that is characterized by severe lipoatrophy, insulin resistance, and intellectual impairment. The mechanisms by which Seipin mutations lead to motor neuropathy, lipodystrophy, and insulin resistance, and the role Seipin plays in central nervous system (CNS) remain unknown. The goal of this study is to understand the functions of Seipin in the CNS using a loss-of-function approach, i.e. by knockdown (KD) of Seipin gene expression. Excitatory post-synaptic currents (EPSCs) were impaired in Seipin-KD neurons, while the inhibitory post-synaptic currents (IPSCs) remained unaffected. Expression of a shRNA-resistant human Seipin rescued the impairment of EPSC produced by Seipin KD. Furthermore, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-induced whole-cell currents were significantly reduced in Seipin KD neurons, which could be rescued by expression of a shRNA-resistant human Seipin. Fluorescent imaging and biochemical studies revealed reduced level of surface AMPA receptors, while no obvious ultrastructural changes in the pre-synapse were found. These data suggest that Seipin regulates excitatory synaptic function through a post-synaptic mechanism.
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Affiliation(s)
- Shunhui Wei
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, A*STAR, Singapore
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29
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Renvoisé B, Stadler J, Singh R, Bakowska JC, Blackstone C. Spg20-/- mice reveal multimodal functions for Troyer syndrome protein spartin in lipid droplet maintenance, cytokinesis and BMP signaling. Hum Mol Genet 2012; 21:3604-18. [PMID: 22619377 DOI: 10.1093/hmg/dds191] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Hereditary spastic paraplegias (HSPs; SPG1-48) are inherited neurological disorders characterized by lower extremity spasticity and weakness. Loss-of-function mutations in the SPG20 gene encoding spartin cause autosomal recessive Troyer syndrome (SPG20), which has additional features of short stature, cognitive deficits and distal amyotrophy. To identify cellular impairments underlying Troyer syndrome, we generated Spg20-/- mice, which exhibit progressive gait defects. Although gross central nervous system pathology appeared largely normal, cerebral cortical neurons cultured from neonatal Spg20-/- mice exhibited increased axon branching, a phenotype suppressed by reintroducing spartin and which required its interaction with the endosomal sorting complex required for transport (ESCRT)-III protein IST1. Analysis of the bone morphogenetic protein (BMP) signaling pathway in Spg20-/- embryonic fibroblasts indicated that Smad1/5 phosphorylation is modestly elevated, possibly due to alterations in BMP receptor trafficking. Cytokinesis was impaired in embryonic fibroblasts cultured from Spg20-/- mice, and binucleated chondrocytes were prominent in epiphyseal growth plates of bones in Spg20-/- mice, perhaps explaining the short stature of patients. Finally, adipose tissue from Spg20-/- female mice exhibited increased lipid droplet (LD) numbers and alterations in perilipin levels, supporting a role for spartin in LD maintenance. Taken together, our results support multimodal functions for spartin that provide important insights into HSP pathogenesis.
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Affiliation(s)
- Benoît Renvoisé
- Cell Biology Section, Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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Yang L, Ding Y, Chen Y, Zhang S, Huo C, Wang Y, Yu J, Zhang P, Na H, Zhang H, Ma Y, Liu P. The proteomics of lipid droplets: structure, dynamics, and functions of the organelle conserved from bacteria to humans. J Lipid Res 2012; 53:1245-53. [PMID: 22534641 DOI: 10.1194/jlr.r024117] [Citation(s) in RCA: 165] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Lipid droplets are cellular organelles that consists of a neutral lipid core covered by a monolayer of phospholipids and many proteins. They are thought to function in the storage, transport, and metabolism of lipids, in signaling, and as a specialized microenvironment for metabolism in most types of cells from prokaryotic to eukaryotic organisms. Lipid droplets have received a lot of attention in the last 10 years as they are linked to the progression of many metabolic diseases and hold great potential for the development of neutral lipid-derived products, such as biofuels, food supplements, hormones, and medicines. Proteomic analysis of lipid droplets has yielded a comprehensive catalog of lipid droplet proteins, shedding light on the function of this organelle and providing evidence that its function is conserved from bacteria to man. This review summarizes many of the proteomic studies on lipid droplets from a wide range of organisms, providing an evolutionary perspective on this organelle.
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Affiliation(s)
- Li Yang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
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Cui X, Wang Y, Meng L, Fei W, Deng J, Xu G, Peng X, Ju S, Zhang L, Liu G, Zhao L, Yang H. Overexpression of a short human seipin/BSCL2 isoform in mouse adipose tissue results in mild lipodystrophy. Am J Physiol Endocrinol Metab 2012; 302:E705-13. [PMID: 22234369 DOI: 10.1152/ajpendo.00237.2011] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) is a recessive disorder characterized by an almost complete loss of adipose tissue, insulin resistance, and fatty liver. BSCL2 is caused by loss-of-function mutations in the BSCL2/seipin gene, which encodes seipin. The essential role for seipin in adipogenesis has recently been established both in vitro and in vivo. However, seipin is highly upregulated at later stages of adipocyte development, and its role in mature adipocytes remains to be elucidated. We therefore generated transgenic mice overexpressing a short isoform of human BSCL2 gene (encoding 398 amino acids) using the adipocyte-specific aP2 promoter. The transgenic mice produced ∼150% more seipin than littermate controls in white adipose tissue. Surprisingly, the increased expression of seipin markedly reduced the mass of white adipose tissue and the size of adipocytes and lipid droplets. This may be due in part to elevated lipolysis rates in the transgenic mice. Moreover, there was a nearly 50% increase in the triacylglycerol content of transgenic liver. These results suggest that seipin promotes the differentiation of preadipocytes but may inhibit lipid storage in mature adipocytes.
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Affiliation(s)
- Xin Cui
- School of Biotechnology and Biomolecular Sciences, Univ. of New South Wales, Sydney, Australia
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Chapman KD, Dyer JM, Mullen RT. Biogenesis and functions of lipid droplets in plants: Thematic Review Series: Lipid Droplet Synthesis and Metabolism: from Yeast to Man. J Lipid Res 2012; 53:215-26. [PMID: 22045929 PMCID: PMC3269164 DOI: 10.1194/jlr.r021436] [Citation(s) in RCA: 245] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2011] [Revised: 10/31/2011] [Indexed: 12/22/2022] Open
Abstract
The compartmentation of neutral lipids in plants is mostly associated with seed tissues, where triacylglycerols (TAGs) stored within lipid droplets (LDs) serve as an essential physiological energy and carbon reserve during postgerminative growth. However, some nonseed tissues, such as leaves, flowers and fruits, also synthesize and store TAGs, yet relatively little is known about the formation or function of LDs in these tissues. Characterization of LD-associated proteins, such as oleosins, caleosins, and sterol dehydrogenases (steroleosins), has revealed surprising features of LD function in plants, including stress responses, hormone signaling pathways, and various aspects of plant growth and development. Although oleosin and caleosin proteins are specific to plants, LD-associated sterol dehydrogenases also are present in mammals, and in both plants and mammals these enzymes have been shown to be important in (steroid) hormone metabolism and signaling. In addition, several other proteins known to be important in LD biogenesis in yeasts and mammals are conserved in plants, suggesting that at least some aspects of LD biogenesis and/or function are evolutionarily conserved.
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Affiliation(s)
- Kent D. Chapman
- Department of Biological Sciences, Center for Plant Lipid Research, University of North Texas, Denton, TX
| | - John M. Dyer
- USDA-ARS, US Arid-Land Agricultural Research Center, Maricopa, AZ
| | - Robert T. Mullen
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
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Wolinski H, Kolb D, Hermann S, Koning RI, Kohlwein SD. A role for seipin in lipid droplet dynamics and inheritance in yeast. J Cell Sci 2011; 124:3894-904. [PMID: 22100922 DOI: 10.1242/jcs.091454] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Malfunctions of processes involved in cellular lipid storage and mobilization induce the pathogenesis of prevalent human diseases such as obesity, type 2 diabetes and atherosclerosis. Lipid droplets are the main lipid storage depots for neutral lipids in eukaryotic cells, and as such fulfil an essential function to balance cellular lipid metabolism and energy homeostasis. Despite significant progress in identifying key metabolic enzymes involved in lipid storage and their regulation in various model organisms, some fundamental questions as to the biogenesis, subcellular distribution and inheritance of lipid droplets are as yet unsolved. In this study, we applied a set of imaging techniques such as high-resolution four-dimensional (4D) live-cell imaging, quantitative microscopy, transmission electron microscopy and electron tomography to gain insight into the spatio-temporal organization of lipid droplets during cellular growth in the yeast Saccharomyces cerevisiae. This analysis revealed a high level of organization of the subcellular positioning of lipid droplets in individual cells, their directed migration towards the cellular periphery and a coordinated transfer of a subpopulation of lipid droplets into daughter cells during cell division. Lipid droplets appear to remain associated with ER membranes during cellular growth independently of their size and subcellular localization. Deletion of FLD1, the functional orthologue of the human BSCL2 gene encoding seipin, leads to impaired dynamics of yeast lipid droplets and defective lipolysis, which might be due to aberrant ER structures in these mutants. Our data suggest a role for yeast seipin as a scaffolding protein that is required for the dynamics of a specific subdomain of the ER, and provide a new aspect for the interpretation of abnormal lipid droplets phenotypes in yeast mutants lacking seipin.
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Affiliation(s)
- Heimo Wolinski
- Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50/II, 8010 Graz, Austria
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Ito D, Yagi T, Ikawa M, Suzuki N. Characterization of inclusion bodies with cytoprotective properties formed by seipinopathy-linked mutant seipin. Hum Mol Genet 2011; 21:635-46. [DOI: 10.1093/hmg/ddr497] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
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Fei W, Li H, Shui G, Kapterian TS, Bielby C, Du X, Brown AJ, Li P, Wenk MR, Liu P, Yang H. Molecular characterization of seipin and its mutants: implications for seipin in triacylglycerol synthesis. J Lipid Res 2011; 52:2136-2147. [PMID: 21957196 DOI: 10.1194/jlr.m017566] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human lipodystrophy gene product Berardinelli-Seip congenital lipodystrophy 2/seipin has been implicated in adipocyte differentiation, lipid droplet (LD) formation, and motor neuron development. However, the molecular function of seipin and its disease-causing mutants remains to be elucidated. Here, we characterize seipin and its mis-sense mutants: N88S/S90L (both linked to motoneuron disorders) and A212P (linked to lipodystrophy) in cultured mammalian cells. Knocking down seipin significantly increases oleate incorporation into triacylglycerol (TAG) and the steady state level of TAG, and induces the proliferation and clustering of small LDs. By contrast, overexpression of seipin reduces TAG synthesis, leading to decreased formation of LDs. Expression of the A212P mutant, however, had little effect on LD biogenesis. Surprisingly, expression of N88S or S90L causes the formation of many small LDs reminiscent of seipin deficient cells. This dominant-negative effect may be due to the N88S/S90L-induced formation of inclusions where wild-type seipin can be trapped. Importantly, coexpression of wild-type seipin and the N88S or S90L mutant can significantly reduce the formation of inclusions. Finally, we demonstrate that seipin can interact with itself and its mutant forms. Our results provide important insights into the biochemical characteristics of seipin and its mis-sense mutants, and suggest that seipin may function to inhibit lipogenesis.
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Affiliation(s)
- Weihua Fei
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Hui Li
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Guanghou Shui
- Department of Biochemistry, National University of Singapore, Singapore, 117597 Republic of Singapore
| | - Tamar S Kapterian
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Christopher Bielby
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Ximing Du
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Andrew J Brown
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Peng Li
- School of Life Sciences, Tsing-Hua University, Beijing, People's Republic of China; and
| | - Markus R Wenk
- Department of Biochemistry, National University of Singapore, Singapore, 117597 Republic of Singapore; Department of Biological Sciences, National University of Singapore, Singapore, 117597 Republic of Singapore
| | - Pingsheng Liu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, People's Republic of China
| | - Hongyuan Yang
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia;.
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Peng XG, Ju S, Qin Y, Fang F, Cui X, Liu G, Ni Y, Teng GJ. Quantification of liver fat in mice: comparing dual-echo Dixon imaging, chemical shift imaging, and 1H-MR spectroscopy. J Lipid Res 2011; 52:1847-55. [PMID: 21737754 DOI: 10.1194/jlr.d016691] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
We evaluated dual-echo Dixon in-phase and out-of-phase (IP-OP), chemical shift imaging (CSI), and (1)H MRS (hydrogen MR spectroscopy) in estimating fat content (FC) in phantoms and in livers of mice. Phantoms were made according to the volume percentage of fat ranging from 0% to 100%. The three MR methods were performed to measure FC in phantoms and in livers of obese leptin-deficient (ob/ob), human BSCL2/seipin gene knockout (SKO), and wild-type (WT) mice. The results were compared with known FC in phantoms and to a reference standard from mice by histological semiautomatic vacuole segmentation (HIS-S) procedure and liver lipid (LL) chemical analysis. In phantoms, CSI underestimated FC from 50% to 100%, to a lesser extent than IP-OP. In vivo, liver FC in ob/ob and SKO mice measured by the three MR methods were all significantly higher than that in WT mice. Liver FC measured by IP-OP were significantly lower than that measured by CSI and MRS, with no significant difference between CSI and MRS. CSI and MRS showed a linear correlation with LL analysis and with each other. IP-OP underestimated FC, whereas CSI and MRS were more accurate for quantifying FC in both phantoms and liver. CSI and MRS have the potential to replace HIS-S and LL analysis in longitudinal studies.
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Affiliation(s)
- Xin-Gui Peng
- Laboratory of Molecular Imaging, Department of Radiology, Zhongda Hospital, Southeast University, Nanjing 210009, China
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Fei W, Du X, Yang H. Seipin, adipogenesis and lipid droplets. Trends Endocrinol Metab 2011; 22:204-10. [PMID: 21497513 DOI: 10.1016/j.tem.2011.02.004] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 02/05/2011] [Accepted: 02/13/2011] [Indexed: 11/18/2022]
Abstract
Seipin, the human Berardinelli-Seip congenital lipodystrophy 2 gene product, regulates adipocyte differentiation and lipid droplet (LD) formation. The molecular function of seipin, however, remains to be elucidated. Here we summarize recent advances in the investigation of congenital generalized lipodystrophies (CGLs) and the cellular dynamics of LDs. Increasing evidence suggests that phospholipids play a crucial role in some key forms of CGL and also in determining the size and distribution of LDs. We explore the hypothesis that seipin functions in the metabolism of phospholipids, and that seipin deficiency causes accumulation of lipid intermediates and/or alters membrane phospholipid profiles. These changes could lead to tissue-specific abnormalities upon seipin dysfunction, such as defective adipocyte development and clustered LDs in fibroblasts.
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Affiliation(s)
- Weihua Fei
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW 2052, Australia
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38
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Cui X, Wang Y, Tang Y, Liu Y, Zhao L, Deng J, Xu G, Peng X, Ju S, Liu G, Yang H. Seipin ablation in mice results in severe generalized lipodystrophy. Hum Mol Genet 2011; 20:3022-30. [DOI: 10.1093/hmg/ddr205] [Citation(s) in RCA: 132] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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39
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Molecular mechanisms controlling human adipose tissue development: insights from monogenic lipodystrophies. Expert Rev Mol Med 2010; 12:e24. [DOI: 10.1017/s1462399410001547] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Appropriately functioning adipose tissue is essential for human health, a fact most clearly illustrated by individuals with lipodystrophy, who have impaired adipose development and often suffer severe metabolic disease as a result. Humans with obesity display a similar array of metabolic problems. This reflects failures in fat tissue function in obesity, which results in consequences similar to those seen when insufficient adipose tissue is present. Thus a better understanding of the molecules that regulate the development of fat tissue is likely to aid the generation of novel therapeutic strategies for the treatment of all disorders of altered fat mass. Single gene disruptions causing lipodystrophy can give unique insights into the importance of the proteins they encode in human adipose tissue development. Moreover, the mechanisms via which they cause lipodystrophy can reveal new molecules and pathways important for adipose tissue development and function as well as confirming the importance of molecules identified from studies of cellular and animal models.
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40
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Hooper C, Puttamadappa SS, Loring Z, Shekhtman A, Bakowska JC. Spartin activates atrophin-1-interacting protein 4 (AIP4) E3 ubiquitin ligase and promotes ubiquitination of adipophilin on lipid droplets. BMC Biol 2010; 8:72. [PMID: 20504295 PMCID: PMC2887783 DOI: 10.1186/1741-7007-8-72] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2010] [Accepted: 05/26/2010] [Indexed: 01/01/2023] Open
Abstract
Background Spartin protein is involved in degradation of epidermal growth factor receptor and turnover of lipid droplets and a lack of expression of this protein is responsible for hereditary spastic paraplegia type 20 (SPG20). Spartin is a multifunctional protein that associates with many cellular organelles, including lipid droplets. Recent studies showed that spartin interacts with E3 ubiquitin ligases that belong to the neural precursor cell-expressed developmentally downregulated gene (Nedd4) family, including atrophin-1-interacting protein 4 (AIP4/ITCH). However, the biological importance of the spartin-AIP4 interaction remains unknown. Results In this study, we show that spartin is not a substrate for AIP4 activity and that spartin's binding to AIP4 significantly increases self-ubiquitination of this E3 ligase, indicating that spartin disrupts the AIP4 autoinhibitory intramolecular interaction. Correspondingly, spartin has a seven times higher binding affinity to the WW region of AIP4 than the binding of the WW region has to the catalytic homologues of the E6-associated protein C-terminus (HECT) domain, as measured by enzyme-linked immunosorbent assay. We also show that spartin recruits AIP4 to lipid droplets and promotes ubiquitination of lipid droplet-associated protein, adipophilin, which regulates turnover of lipid droplets. Conclusions Our findings demonstrate that spartin acts as an adaptor protein that activates and recruits AIP4 E3 ubiquitin ligase to lipid droplets and by this means regulates the level of ubiquitination of adipophilin and potentially other lipid-associated proteins. We propose that this is one of the mechanisms by which spartin regulates lipid droplet turnover and might contribute to the pathology of SPG20.
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Affiliation(s)
- Christopher Hooper
- Department of Molecular Pharmacology and Therapeutics, Loyola Chicago University, Maywood, IL, USA
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41
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Kolb SJ, Sutton S, Schoenberg DR. RNA processing defects associated with diseases of the motor neuron. Muscle Nerve 2010; 41:5-17. [PMID: 19697368 DOI: 10.1002/mus.21428] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Rapid progress in the discovery of motor neuron disease genes in amyotrophic lateral sclerosis, the spinal muscular atrophies, hereditary motor neuropathies, and lethal congenital contracture syndromes is providing new perspectives and insights into the molecular pathogenesis of the motor neuron. Motor neuron disease genes are often expressed throughout the body with essential functions in all cells. A survey of these functions indicates that motor neurons are uniquely sensitive to perturbations in RNA processing pathways dependent on the interaction of specific RNAs with specific RNA-binding proteins, which presumably result in aberrant formation and function of ribonucleoprotein complexes. This review provides a summary of currently recognized RNA processing defects linked to human motor neuron diseases.
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Affiliation(s)
- Stephen J Kolb
- Department of Neurology, Ohio State University Medical Center, Hamilton Hall, Room 337B, 1645 Neil Avenue, Columbus, Ohio 43210-1228, USA
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Chen W, Yechoor VK, Chang BHJ, Li MV, March KL, Chan L. The human lipodystrophy gene product Berardinelli-Seip congenital lipodystrophy 2/seipin plays a key role in adipocyte differentiation. Endocrinology 2009; 150:4552-61. [PMID: 19574402 PMCID: PMC2754678 DOI: 10.1210/en.2009-0236] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Mutations in the Berardinelli-Seip congenital lipodystrophy 2 gene (BSCL2) are the underlying defect in patients with congenital generalized lipodystrophy type 2. BSCL2 encodes a protein called seipin, whose function is largely unknown. In this study, we investigated the role of Bscl2 in the regulation of adipocyte differentiation. Bscl2 mRNA is highly up-regulated during standard hormone-induced adipogenesis in 3T3-L1 cells in vitro. However, this up-regulation does not occur during mesenchymal stem cell (C3H10T1/2 cells) commitment to the preadipocyte lineage. Knockdown of Bscl2 by short hairpin RNA in C3H10T1/2 cells has no effect on bone morphogenetic protein-4-induced preadipocyte commitment. However, knockdown in 3T3-L1 cells prevents adipogenesis induced by a standard hormone cocktail, but adipogenesis can be rescued by the addition of peroxisome proliferator-activated receptor-gamma agonist pioglitazone at an early stage of differentiation. Interestingly, pioglitazone-induced differentiation in the absence of standard hormone is not associated with up-regulated Bscl2 expression. On the other hand, short hairpin RNA-knockdown of Bscl2 largely blocks pioglitazone-induced adipose differentiation. These experiments suggest that Bscl2 may be essential for normal adipogenesis; it works upstream or at the level of peroxisome proliferator-activated receptor-gamma, enabling the latter to exert its full activity during adipogenesis. Loss of Bscl2 function thus interferes with the normal transcriptional cascade of adipogenesis during fat cell differentiation, resulting in near total loss of fat or lipodystrophy.
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Affiliation(s)
- Weiqin Chen
- Division of Diabetes and Endocrinology, Department of Medicine, Baylor College of Medicine, Diabetes and Endocrinology Research Center, Houston, Texas 77030, USA
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Garg A, Agarwal AK. Lipodystrophies: disorders of adipose tissue biology. BIOCHIMICA ET BIOPHYSICA ACTA 2009; 1791:507-13. [PMID: 19162222 PMCID: PMC2693450 DOI: 10.1016/j.bbalip.2008.12.014] [Citation(s) in RCA: 126] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2008] [Revised: 11/26/2008] [Accepted: 12/23/2008] [Indexed: 11/15/2022]
Abstract
The adipocytes synthesize and store triglycerides as lipid droplets surrounded by various proteins and phospholipids at its surface. Recently, the molecular basis of some of the genetic syndromes of lipodystrophies has been elucidated and some of these genetic loci have been found to contribute to lipid droplet formation in adipocytes. The two main types of genetic lipodystrophies are congenital generalized lipodystrophy (CGL) and familial partial lipodystrophy (FPL). So far, three CGL loci: 1-acylglycerol-3-phosphate-O-acyltransferase 2 (AGPAT2), Berardinelli-Seip Congenital Lipodystrophy 2 (BSCL2) and caveolin 1 (CAV1) and four FPL loci: lamin A/C (LMNA), peroxisome proliferator-activated receptor gamma (PPARG), v-AKT murine thymoma oncogene homolog 2 (AKT2) and zinc metalloprotease (ZMPSTE24), have been identified. AGPAT2 plays a critical role in the synthesis of glycerophospholipids and triglycerides required for lipid droplet formation. Another protein, seipin (encoded by BSCL2 gene), has been found to induce lipid droplet fusion. CAV1 is an integral component of caveolae and might contribute towards lipid droplet formation. PPARgamma and AKT2 play important role in adipogenesis and lipid synthesis. In this review, we discuss and speculate about the contribution of various lipodystrophy genes and their products in the lipid droplet formation.
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Affiliation(s)
- Abhimanyu Garg
- Division of Nutrition and Metabolic Diseases, Department of Internal Medicine, Center for Human Nutrition, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, USA.
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Eastman SW, Yassaee M, Bieniasz PD. A role for ubiquitin ligases and Spartin/SPG20 in lipid droplet turnover. ACTA ACUST UNITED AC 2009; 184:881-94. [PMID: 19307600 PMCID: PMC2699154 DOI: 10.1083/jcb.200808041] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
HECT (homologous to the E6AP C terminus) ubiquitin ligases have diverse functions in eukaryotic cells. In screens for proteins that bind to the HECT ubiquitin ligase WWP1, we identified Spartin, which is also known as SPG20. This protein is truncated in a neurological disease, Troyer syndrome. In this study, we show that SPG20 associates with the surface of lipid droplets (LDs) and can regulate their size and number. SPG20 binds to another LD protein, TIP47, and both proteins compete with an additional LD protein, adipophilin/adipocyte differentiation-related protein, for occupancy of LDs. The mutant SPG20 present in Troyer syndrome does not possess these activities. Depletion of SPG20 using RNA interference increases the number and size of LDs when cells are fed with oleic acid. Binding of WWP1 to SPG20 and the consequent ubiquitin transfer remove SPG20 from LDs and reduce the levels of coexpressed SPG20. These experiments suggest functions for ubiquitin ligases and SPG20 in the regulation of LD turnover and potential pathological mechanisms in Troyer syndrome.
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Affiliation(s)
- Scott W Eastman
- Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10065, USA
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45
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Ito D, Suzuki N. Seipinopathy: a novel endoplasmic reticulum stress-associated disease. ACTA ACUST UNITED AC 2008; 132:8-15. [PMID: 18790819 DOI: 10.1093/brain/awn216] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
The Seipin/BSCL2 gene was originally identified as a loss-of-function gene for congenital generalized lipodystrophy type 2 (CGL2), a condition characterized by severe lipoatrophy, insulin resistance, hypertriglyceridaemia and mental retardation. Recently, gain-of-toxic-function mutations (namely, mutations N88S and S90L) in the seipin gene have been identified in autosomal dominant motor neuron diseases such as Silver syndrome/spastic paraplegia 17 (SPG17) (OMIM #270685) and distal hereditary motor neuropathy type V (dHMN-V) (OMIM #182960). Detailed phenotypic analyses have revealed that upper motor neurons, lower motor neurons and peripheral motor axons are variously affected in patients with these mutations. The clinical spectrum for these mutations is broad, encompassing Silver syndrome, some variants of Charcot-Marie-Tooth disease type 2, dHMNV and spastic paraplegia, even within a common pedigree. Therefore, we propose that seipin-related motor neuron diseases can be collectively referred to as 'seipinopathies'. Expression of the seipin protein can be detected in motor neurons in the spinal cord and white matter in the frontal lobe. This is consistent with the distribution of seipinopathies in the upper and lower motor neurons. Recent studies have shown that seipin, an endoplasmic reticulum (ER)-resident membrane protein, is an N-glycosylated protein that is proteolytically cleaved into N- and C-terminal fragments and is polyubiquitinated. Interestingly, the N88S and S90L mutations are in the N-glycosylation motif, and these mutations enhance ubiquitination and degradation of seipin by the ubiquitin-proteasome system (UPS). Furthermore, both mutations appear to result in proteins that are improperly folded, which leads to accumulation of the mutant protein in the ER. We have shown that expression of mutant forms of seipin in cultured cells activates the unfolded protein response (UPR) pathway and induces ER stress-mediated cell death. These findings suggest that seipinopathies are novel conformational diseases and that neurodegeneration in these diseases is tightly associated with ER stress, which has recently been reported to be associated with other neurodegenerative diseases. Further study of the pathological mechanisms of the mutant forms of seipin may lead to important new insights into motor neuron diseases, including other spastic paraplegia diseases and amyotrophic lateral sclerosis.
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Affiliation(s)
- Daisuke Ito
- Department of Neurology, School of Medicine, Keio University, Tokyo, Japan.
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Payne VA, Grimsey N, Tuthill A, Virtue S, Gray SL, Dalla Nora E, Semple RK, O'Rahilly S, Rochford JJ. The human lipodystrophy gene BSCL2/seipin may be essential for normal adipocyte differentiation. Diabetes 2008; 57:2055-60. [PMID: 18458148 PMCID: PMC2494687 DOI: 10.2337/db08-0184] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2008] [Accepted: 04/28/2008] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) is a recessive disorder featuring near complete absence of adipose tissue. Remarkably, although the causative gene, BSCL2, has been known for several years, its molecular function and its role in adipose tissue development have not been elucidated. Therefore, we examined whether BSCL2 is involved in the regulation of adipocyte differentiation and the mechanism whereby pathogenic mutations in BSCL2 cause lipodystrophy. RESEARCH DESIGN AND METHODS Following the characterization of BSCL2 expression in developing adipocytes, C3H10T1/2 mesenchymal stem cells were generated in which BSCL2 expression was knocked down using short hairpin RNA (shRNA). These cells were used to investigate whether BSCL2 is required for adipogenesis. BSCL2 constructs harboring pathogenic mutations known to cause lipodystrophy were also generated and characterized. RESULTS BSCL2 expression was strongly induced during adipocyte differentiation, and the induction of BSCL2 expression was essential for adipogenesis to occur. The initial induction of key adipogenic transcription factors, including peroxisome proliferator-activated receptor (PPAR)gamma and CAAT/enhancer-binding protein-alpha, was preserved in cells lacking BSCL2. However, the expression of these critical factors was not sustained, suggesting that the activity of PPARgamma was impaired. Moreover, expression of key genes mediating triglyceride synthesis, including AGPAT2, lipin 1, and DGAT2, was persistently reduced and lipid accumulation was inhibited. Analysis of pathogenic missense mutants of BSCL2 revealed that the amino acid substitution A212P causes aberrant targeting of BSCL2 within the cell, suggesting that subcellular localization of BSCL2 may be critical to its function. CONCLUSIONS This study demonstrates that BSCL2 is an essential, cell-autonomous regulator of adipogenesis.
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Affiliation(s)
- Victoria A Payne
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, UK
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Ito D, Fujisawa T, Iida H, Suzuki N. Characterization of seipin/BSCL2, a protein associated with spastic paraplegia 17. Neurobiol Dis 2008; 31:266-77. [PMID: 18585921 DOI: 10.1016/j.nbd.2008.05.004] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2008] [Revised: 04/17/2008] [Accepted: 05/06/2008] [Indexed: 10/22/2022] Open
Abstract
Seipin, which is encoded by the BSCL2 gene, is a glycoprotein of unknown biochemical function that is associated with dominant hereditary motor neuron diseases. Mutations in the N-glycosylation site of seipin are associated with the disease states and result in accumulation of unfolded protein in the endoplasmic reticulum (ER), leading to the unfolded protein response (UPR) and cell death, suggesting that these diseases are tightly associated with ER stress. Here, we determined the subcellular localization, functional domains, and distribution of seipin in tissues. Our studies show that the transmembrane domains in seipin are critical for ER retention, ubiquitination, formation of inclusions, and activation of UPR. Using immunohistochemistry, seipin expression is detected in neurons in the spinal cord and in the frontal lobe cortex of the brain. The present study provides new insights into the biology of seipin protein that should help our understanding of the pathogenesis of seipin-related diseases.
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Affiliation(s)
- Daisuke Ito
- Department of Neurology, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan.
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Abstract
Lack of adipose tissue, either complete or partial, is the hallmark of disorders known as lipodystrophies. Patients with lipodystrophies suffer from metabolic complications similar to those associated with obesity, including insulin resistance, type 2 diabetes, hypertriglyceridemia, and hepatic steatosis. The loss of body fat in inherited lipodystrophies can be caused by defects in the development and/or differentiation of adipose tissue as a consequence of mutations in a number of genes, including PPARG (encoding a nuclear hormone receptor), AGPAT2 (encoding an enzyme involved in the biosynthesis of triglyceride and phospholipids), AKT2 (encoding a protein involved in insulin signal transduction), and BSCL2 (encoding seipin, whose role in the adipocyte biology remains unclear). The loss of body fat can also be caused by the premature death of adipocytes due to mutations in lamin A/C, nuclear lamina proteins, and ZMPSTE24, which modifies the prelamin A post-translationally. In this review, we focus on the molecular basis of inherited lipodystrophies as they relate to adipocyte biology and their associated phenotypic manifestations.
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Affiliation(s)
- Anil K Agarwal
- Division of Nutrition and Metabolic Diseases, Department of Internal Medicine and the Center for Human Nutrition, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9052, USA
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Fei W, Shui G, Gaeta B, Du X, Kuerschner L, Li P, Brown AJ, Wenk MR, Parton RG, Yang H. Fld1p, a functional homologue of human seipin, regulates the size of lipid droplets in yeast. ACTA ACUST UNITED AC 2008; 180:473-82. [PMID: 18250201 PMCID: PMC2234226 DOI: 10.1083/jcb.200711136] [Citation(s) in RCA: 372] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Lipid droplets (LDs) are emerging cellular organelles that are of crucial importance in cell biology and human diseases. In this study, we present our screen of approximately 4,700 Saccharomyces cerevisiae mutants for abnormalities in the number and morphology of LDs; we identify 17 fld (few LDs) and 116 mld (many LDs) mutants. One of the fld mutants (fld1) is caused by the deletion of YLR404W, a previously uncharacterized open reading frame. Cells lacking FLD1 contain strikingly enlarged (supersized) LDs, and LDs from fld1Delta cells demonstrate significantly enhanced fusion activities both in vivo and in vitro. Interestingly, the expression of human seipin, whose mutant forms are associated with Berardinelli-Seip congenital lipodystrophy and motoneuron disorders, rescues LD-associated defects in fld1Delta cells. Lipid profiling reveals alterations in acyl chain compositions of major phospholipids in fld1Delta cells. These results suggest that an evolutionally conserved function of seipin in phospholipid metabolism and LD formation may be functionally important in human adipogenesis.
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Affiliation(s)
- Weihua Fei
- Department of Biochemistry, National University of Singapore, Singapore 117597, Republic of Singapore
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The lipodystrophy protein seipin is found at endoplasmic reticulum lipid droplet junctions and is important for droplet morphology. Proc Natl Acad Sci U S A 2007; 104:20890-5. [PMID: 18093937 DOI: 10.1073/pnas.0704154104] [Citation(s) in RCA: 463] [Impact Index Per Article: 27.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Lipodystrophy is a disorder characterized by a loss of adipose tissue often accompanied by severe hypertriglyceridemia, insulin resistance, diabetes, and fatty liver. It can be inherited or acquired. The most severe inherited form is Berardinelli-Seip Congenital Lipodystrophy Type 2, associated with mutations in the BSCL2 gene. BSCL2 encodes seipin, the function of which has been entirely unknown. We now report the identification of yeast BSCL2/seipin through a screen to detect genes important for lipid droplet morphology. The absence of yeast seipin results in irregular lipid droplets often clustered alongside proliferated endoplasmic reticulum (ER); giant lipid droplets are also seen. Many small irregular lipid droplets are also apparent in fibroblasts from a BSCL2 patient. Human seipin can functionally replace yeast seipin, but a missense mutation in human seipin that causes lipodystrophy, or corresponding mutations in the yeast gene, render them unable to complement. Yeast seipin is localized in the ER, where it forms puncta. Almost all lipid droplets appear to be on the ER, and seipin is found at these junctions. Therefore, we hypothesize that seipin is important for droplet maintenance and perhaps assembly. In addition to detecting seipin, the screen identified 58 other genes whose deletions cause aberrant lipid droplets, including 2 genes encoding proteins known to activate lipin, a lipodystrophy locus in mice, and 16 other genes that are involved in endosomal-lysosomal trafficking. The genes identified in our screen should be of value in understanding the pathway of lipid droplet biogenesis and maintenance and the cause of some lipodystrophies.
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