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Dei Cas M, Montavoci L, Pasini C, Caretti A, Penati S, Martinelli C, Gianelli U, Casati S, Nardecchia F, Torella A, Brunetti-Pierri N, Trinchera M. Loss of function and reduced levels of sphingolipid desaturase DEGS1 variants are both relevant in disease mechanism. J Lipid Res 2024; 65:100517. [PMID: 38342436 PMCID: PMC10940770 DOI: 10.1016/j.jlr.2024.100517] [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: 08/02/2023] [Revised: 01/29/2024] [Accepted: 01/30/2024] [Indexed: 02/13/2024] Open
Abstract
The last step of ex novo ceramide biosynthesis consists of the conversion of dihydroceramide into ceramide catalyzed by sphingolipid Δ4-desaturase DEGS1. DEGS1 variants were found to be responsible for heterogeneous clinical pictures belonging to the family of hypomyelinating leukodystrophies. To investigate the mechanisms making such variants pathogenic, we designed a procedure for the efficient detection of desaturase activity in vitro using LC-MS/MS and prepared a suitable cell model knocking out DEGS1 in HEK-293T cells through CRISPR-Cas9 genome editing (KO-DES-HEK). Transfecting KO-DES-HEK cells with DEGS1 variants, we found that their transcripts were all overexpressed as much as the WT transcripts, while the levels of cognate protein were 40%-80% lower. In vitro desaturase activity was lost by many variants except L175Q and N255S, which maintain a catalytic efficiency close to 12% of the WT enzyme. Metabolic labeling of KO-DES-HEK with deuterated palmitate followed by LC-MS/MS analysis of the formed sphingolipids revealed that the ceramide/dihydroceramide and sphingomyelin/dihydrosphingomyelin ratios were low and could be reverted by the overexpression of WT DEGS1 as well as of L175Q and N255S variants, but not by the overexpression of all other variants. Similar analyses performed on fibroblasts from a patient heterozygous for the N255S variant showed very low variant DEGS1 levels and a low ratio between the same unsaturated and saturated sphingolipids formed upon metabolic labeling, notwithstanding the residual activity measured at high substrate and homogenate protein concentrations. We conclude that loss of function and reduced protein levels are both relevant in disease pathogenesis.
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Affiliation(s)
- Michele Dei Cas
- Department of Health Sciences, Università degli Studi di Milano, Milan, Italy
| | - Linda Montavoci
- Department of Health Sciences, Università degli Studi di Milano, Milan, Italy
| | - Claudia Pasini
- Department of Health Sciences, Università degli Studi di Milano, Milan, Italy
| | - Anna Caretti
- Department of Health Sciences, Università degli Studi di Milano, Milan, Italy
| | - Sara Penati
- Department of Health Sciences, Università degli Studi di Milano, Milan, Italy
| | - Carla Martinelli
- Department of Health Sciences, Università degli Studi di Milano, Milan, Italy
| | - Umberto Gianelli
- Department of Health Sciences, Università degli Studi di Milano, Milan, Italy; S.C. di Anatomia Patologica, ASST- Santi Paolo e Carlo, Milan, Italy
| | - Sara Casati
- Department of Biomedical, Surgical and Dental Sciences, Università degli Studi di Milano, Milan, Italy
| | - Francesca Nardecchia
- Department of Human Neuroscience, Unit of Child Neurology and Psychiatry, Sapienza University of Rome, Italy
| | - Annalaura Torella
- Department of Precision Medicine, University of Campania "Luigi Vanvitelli", Naples, Italy
| | - Nicola Brunetti-Pierri
- Telethon Institute of Genetics and Medicine, Pozzuoli, Italy; Department of Translational Medicine, Medical Genetics, University of Naples Federico II, Naples, Italy; Scuola Superiore Meridionale (SSM, School of Advanced Studies), Genomics and Experimental Medicine Program, University of Naples Federico II, Naples, Italy
| | - Marco Trinchera
- Department of Medicine and Surgery (DMC), University of Insubria, Varese, Italy.
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Osinuga A, Solis AG, Cahoon RE, Al-Siyabi A, Cahoon EB, Saha R. Quantitative Dynamic Analysis of de novo Sphingolipid Biosynthesis in Arabidopsis thaliana. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.08.570827. [PMID: 38105963 PMCID: PMC10723408 DOI: 10.1101/2023.12.08.570827] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Sphingolipids are pivotal for plant development and stress responses. Growing interest has been directed towards fully comprehending the regulatory mechanisms of the sphingolipid pathway. We explore its de novo biosynthesis and homeostasis in Arabidopsis thaliana cell cultures, shedding light on fundamental metabolic mechanisms. Employing 15N isotope labeling and quantitative dynamic modeling approach, we developed a regularized and constraint-based Dynamic Metabolic Flux Analysis (r-DMFA) framework to predict metabolic shifts due to enzymatic changes. Our analysis revealed key enzymes such as sphingoid-base hydroxylase (SBH) and long-chain-base kinase (LCBK) to be critical for maintaining sphingolipid homeostasis. Disruptions in these enzymes were found to affect cellular viability and increase the potential for programmed cell death (PCD). Thus, this work enhances our understanding of sphingolipid metabolism and demonstrates the utility of dynamic modeling in analyzing complex metabolic pathways.
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Affiliation(s)
- Abraham Osinuga
- Department of Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
| | - Ariadna Gonzalez Solis
- Department of Biochemistry and Center for Plant Science Innovation, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
| | - Rebecca E Cahoon
- Department of Biochemistry and Center for Plant Science Innovation, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
| | - Adil Al-Siyabi
- Department of Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
| | - Edgar B Cahoon
- Department of Biochemistry and Center for Plant Science Innovation, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
| | - Rajib Saha
- Department of Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
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3
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Mucinski JM, McCaffrey JM, Rector RS, Kasumov T, Parks EJ. Relationship between hepatic and mitochondrial ceramides: A novel in vivo method to track ceramide synthesis. J Lipid Res 2023; 64:100366. [PMID: 37028768 DOI: 10.1016/j.jlr.2023.100366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 03/22/2023] [Accepted: 03/24/2023] [Indexed: 04/08/2023] Open
Abstract
Ceramides (CERs) are key intermediate sphingolipids implicated in contributing to mitochondrial dysfunction and the development of multiple metabolic conditions. Despite the growing evidence of CERs role in disease risk, kinetic methods to measure CER turnover are lacking, particularly using in vivo models. The utility of orally-administered 13C3, 15N L-serine, dissolved in drinking water, was tested to quantify CER 18:1/16:0 synthesis in 10 week-old male and female C57Bl/6 mice. To generate isotopic labeling curves, animals consumed either a control (CD) or high fat diet (HFD; n=24/diet) for two weeks and varied in the duration of the consumption of serine-labeled water (0, 1, 2, 4, 7, or 12 days; n=four animals/day/diet). Unlabeled and labeled hepatic and mitochondrial CERs were quantified using liquid chromatography tandem mass spectrometry. Total hepatic CER content did not differ between the two diet groups while total mitochondrial CERs increased with HFD feeding (60%, P<0.001). Within hepatic and mitochondrial pools, HFD induced greater saturated CER concentrations (P<0.05) and significantly elevated absolute turnover of 16:0 mitochondrial CER (mitochondria: 59%, P<0.001 versus liver: 15%, P=0.256). The data suggest cellular redistribution of CERs due to the HFD. These data demonstrate that a two-week HFD alters the turnover and content of mitochondrial CERs. Given the growing data on CERs contributing to hepatic mitochondrial dysfunction and the progression of multiple metabolic diseases, this method may now be used to investigate how CER turnover is altered in these conditions.
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4
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Wang D, Ho ES, Cotticelli MG, Xu P, Napierala JS, Hauser LA, Napierala M, Himes BE, Wilson RB, Lynch DR, Mesaros C. Skin fibroblast metabolomic profiling reveals that lipid dysfunction predicts the severity of Friedreich's ataxia. J Lipid Res 2022; 63:100255. [PMID: 35850241 PMCID: PMC9399481 DOI: 10.1016/j.jlr.2022.100255] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2021] [Revised: 07/07/2022] [Accepted: 07/08/2022] [Indexed: 12/26/2022] Open
Abstract
Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a triplet guanine-adenine-adenine (GAA) repeat expansion in intron 1 of the FXN gene, which leads to decreased levels of the frataxin protein. Frataxin is involved in the formation of iron-sulfur (Fe-S) cluster prosthetic groups for various metabolic enzymes. To provide a better understanding of the metabolic status of patients with FRDA, here we used patient-derived fibroblast cells as a surrogate tissue for metabolic and lipidomic profiling by liquid chromatography-high resolution mass spectrometry. We found elevated HMG-CoA and β-hydroxybutyrate-CoA levels, implying dysregulated fatty acid oxidation, which was further demonstrated by elevated acyl-carnitine levels. Lipidomic profiling identified dysregulated levels of several lipid classes in FRDA fibroblast cells when compared with non-FRDA fibroblast cells. For example, levels of several ceramides were significantly increased in FRDA fibroblast cells; these results positively correlated with the GAA repeat length and negatively correlated with the frataxin protein levels. Furthermore, stable isotope tracing experiments indicated increased ceramide synthesis, especially for long-chain fatty acid-ceramides, in FRDA fibroblast cells compared with ceramide synthesis in healthy control fibroblast cells. In addition, PUFA-containing triglycerides and phosphatidylglycerols were enriched in FRDA fibroblast cells and negatively correlated with frataxin levels, suggesting lipid remodeling as a result of FXN deficiency. Altogether, we demonstrate patient-derived fibroblast cells exhibited dysregulated metabolic capabilities, and their lipid dysfunction predicted the severity of FRDA, making them a useful surrogate to study the metabolic status in FRDA.
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Affiliation(s)
- Dezhen Wang
- Center for Excellence in Environmental Toxicology, Department of Systems Pharmacology and Translational Therapeutics, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Elaine S. Ho
- Center for Excellence in Environmental Toxicology, Department of Systems Pharmacology and Translational Therapeutics, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - M. Grazia Cotticelli
- Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - Peining Xu
- Center for Excellence in Environmental Toxicology, Department of Systems Pharmacology and Translational Therapeutics, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Jill S. Napierala
- University of Alabama at Birmingham, Department of Biochemistry and Molecular Genetics, UAB Stem Cell Institute, Birmingham, Alabama, USA
| | - Lauren A. Hauser
- Department of Neurology and Pediatrics, Children’s Hospital of Philadelphia, Abramson Research, Philadelphia, Pennsylvania, USA
| | - Marek Napierala
- University of Alabama at Birmingham, Department of Biochemistry and Molecular Genetics, UAB Stem Cell Institute, Birmingham, Alabama, USA
| | - Blanca E. Himes
- Department of Biostatistics, Epidemiology and Informatics, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Robert B. Wilson
- Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - David R. Lynch
- Department of Neurology and Pediatrics, Children’s Hospital of Philadelphia, Abramson Research, Philadelphia, Pennsylvania, USA
| | - Clementina Mesaros
- Center for Excellence in Environmental Toxicology, Department of Systems Pharmacology and Translational Therapeutics, University of Pennsylvania, Philadelphia, Pennsylvania, USA,For correspondence: Clementina Mesaros
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5
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Satapati S, Downes DP, Metzger D, Shankaran H, Talukdar S, Zhou Y, Ren Z, Chen M, Lim YH, Hatcher NG, Wen X, Sheth PR, McLaren DG, Previs SF. Using measures of metabolic flux to align screening and clinical development: Avoiding pitfalls to enable translational studies. SLAS DISCOVERY : ADVANCING LIFE SCIENCES R & D 2022; 27:20-28. [PMID: 35058172 DOI: 10.1016/j.slasd.2021.10.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Screening campaigns, especially those aimed at modulating enzyme activity, often rely on measuring substrate→product conversions. Unfortunately, the presence of endogenous substrates and/or products can limit one's ability to measure conversions. As well, coupled detection systems, often used to facilitate optical readouts, are subject to interference. Stable isotope labeled substrates can overcome background contamination and yield a direct readout of enzyme activity. Not only can isotope kinetic assays enable early screening, but they can also be used to follow hit progression in translational (pre)clinical studies. Herein, we consider a case study surrounding lipid biology to exemplify how metabolic flux analyses can connect stages of drug development, caveats are highlighted to ensure reliable data interpretations. For example, when measuring enzyme activity in early biochemical screening it may be enough to quantify the formation of a labeled product. In contrast, cell-based and in vivo studies must account for variable exposure to a labeled substrate (or precursor) which occurs via tracer dilution and/or isotopic exchange. Strategies are discussed to correct for these complications. We believe that measures of metabolic flux can help connect structure-activity relationships with pharmacodynamic mechanisms of action and determine whether mechanistically differentiated biophysical interactions lead to physiologically relevant outcomes. Adoption of this logic may allow research programs to (i) build a critical bridge between primary screening and (pre)clinical development, (ii) elucidate biology in parallel with screening and (iii) suggest a strategy aimed at in vivo biomarker development.
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Affiliation(s)
- Santhosh Satapati
- Merck & Co., Inc, 213 E. Grand Ave, South San Francisco, CA, 94080, USA
| | - Daniel P Downes
- Merck & Co., Inc, 2000 Galloping Hill Rd, Kenilworth, NJ, 07033, USA
| | - Daniel Metzger
- Merck & Co., Inc, 213 E. Grand Ave, South San Francisco, CA, 94080, USA
| | - Harish Shankaran
- Merck & Co., Inc, 213 E. Grand Ave, South San Francisco, CA, 94080, USA
| | - Saswata Talukdar
- Merck & Co., Inc, 213 E. Grand Ave, South San Francisco, CA, 94080, USA
| | - Yingjiang Zhou
- Merck & Co., Inc, 213 E. Grand Ave, South San Francisco, CA, 94080, USA
| | - Zhao Ren
- Merck & Co., Inc, 213 E. Grand Ave, South San Francisco, CA, 94080, USA
| | - Michelle Chen
- Merck & Co., Inc, 213 E. Grand Ave, South San Francisco, CA, 94080, USA
| | - Yeon-Hee Lim
- Merck & Co., Inc, 213 E. Grand Ave, South San Francisco, CA, 94080, USA
| | - Nathan G Hatcher
- Merck & Co., Inc, 770 Sumneytown Pike, West Point, PA, 19486, USA
| | - Xiujuan Wen
- Merck & Co., Inc, 2000 Galloping Hill Rd, Kenilworth, NJ, 07033, USA
| | - Payal R Sheth
- Merck & Co., Inc, 2000 Galloping Hill Rd, Kenilworth, NJ, 07033, USA
| | - David G McLaren
- Merck & Co., Inc, 2000 Galloping Hill Rd, Kenilworth, NJ, 07033, USA
| | - Stephen F Previs
- Merck & Co., Inc, 2000 Galloping Hill Rd, Kenilworth, NJ, 07033, USA.
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6
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Snider JM, Luberto C, Hannun YA. Approaches for probing and evaluating mammalian sphingolipid metabolism. Anal Biochem 2019; 575:70-86. [PMID: 30917945 DOI: 10.1016/j.ab.2019.03.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Revised: 03/22/2019] [Accepted: 03/22/2019] [Indexed: 01/02/2023]
Abstract
Sphingolipid metabolism plays a critical role in regulating processes that control cellular fate. This dynamic pathway can generate and degrade the central players: ceramide, sphingosine and sphingosine-1-phosphate in almost any membrane in the cell, adding an unexpected level of complexity in deciphering signaling events. While in vitro assays have been developed for most enzymes in SL metabolism, these assays are setup for optimal activity conditions and can fail to take into account regulatory components such as compartmentalization, substrate limitations, and binding partners that can affect cellular enzymatic activity. Therefore, many in-cell assays have been developed to derive results that are authentic to the cellular situation which may give context to alteration in SL mass. This review will discuss approaches for utilizing probes for mammalian in-cell assays to interrogate most enzymatic steps central to SL metabolism. The use of inhibitors in conjunction with these probes can verify the specificity of cellular assays as well as provide valuable insight into flux in the SL network. The use of inhibitors specific to each of the central sphingolipid enzymes are also discussed to assist researchers in further interrogation of these pathways.
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Affiliation(s)
- Justin M Snider
- Department of Medicine, Stony Brook University, Stony Brook, NY, USA; The Stony Brook Cancer Center, Stony Brook University, Stony Brook, NY, USA
| | - Chiara Luberto
- The Stony Brook Cancer Center, Stony Brook University, Stony Brook, NY, USA; Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA
| | - Yusuf A Hannun
- Department of Medicine, Stony Brook University, Stony Brook, NY, USA; The Stony Brook Cancer Center, Stony Brook University, Stony Brook, NY, USA; Departments of Biochemistry, Pathology and Pharmacology, Stony Brook University, Stony Brook, NY, USA.
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7
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Chen Y, Berejnaia O, Liu J, Wang SP, Daurio NA, Yin W, Mayoral R, Petrov A, Kasumov T, Zhang GF, Previs SF, Kelley DE, McLaren DG. Quantifying ceramide kinetics in vivo using stable isotope tracers and LC-MS/MS. Am J Physiol Endocrinol Metab 2018; 315:E416-E424. [PMID: 29509438 DOI: 10.1152/ajpendo.00457.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Numerous studies have implicated dyslipidemia as a key factor in mediating insulin resistance. Ceramides have received special attention since their levels are inversely associated with normal insulin signaling and positively associated with factors that are involved in cardiometabolic disease. Despite the growing literature surrounding ceramide biology, there are limited data regarding the activity of ceramide synthesis and turnover in vivo. Herein, we demonstrate the ability to measure ceramide kinetics by coupling the administration of [2H]water with LC-MS/MS analyses. As a "proof-of-concept" we determined the effect of a diet-induced alteration on ceramide flux; studies also examined the effect of myriocin (a known inhibitor of serine palmitoyltransferase, the first step in sphingosine biosynthesis). Our data suggest that one can estimate ceramide synthesis and draw conclusions regarding the source of fatty acids; we discuss caveats in regards to method development in this area.
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Affiliation(s)
- Ying Chen
- MRL, Merck & Co., Inc., Kenilworth, New Jersey
| | | | - Jinqi Liu
- MRL, Merck & Co., Inc., Kenilworth, New Jersey
| | | | | | - Wu Yin
- MRL, Merck & Co., Inc., Kenilworth, New Jersey
| | | | | | - Takhar Kasumov
- Department of Pharmaceutical Sciences, Northeast Ohio Medical University, Rootstown, Ohio
| | - Guo-Fang Zhang
- Division of Endocrinology, Metabolism and Nutrition, Duke Molecular Physiology Institute, and Department of Medicine, Duke University , Durham, North Carolina
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8
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Hu T, Zhang JL. Mass-spectrometry-based lipidomics. J Sep Sci 2017; 41:351-372. [PMID: 28859259 DOI: 10.1002/jssc.201700709] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Revised: 08/17/2017] [Accepted: 08/18/2017] [Indexed: 01/09/2023]
Abstract
Lipids, which have a core function in energy storage, signalling and biofilm structures, play important roles in a variety of cellular processes because of the great diversity of their structural and physiochemical properties. Lipidomics is the large-scale profiling and quantification of biogenic lipid molecules, the comprehensive study of their pathways and the interpretation of their physiological significance based on analytical chemistry and statistical analysis. Lipidomics will not only provide insight into the physiological functions of lipid molecules but will also provide an approach to discovering important biomarkers for diagnosis or treatment of human diseases. Mass-spectrometry-based analytical techniques are currently the most widely used and most effective tools for lipid profiling and quantification. In this review, the field of mass-spectrometry-based lipidomics was discussed. Recent progress in all essential steps in lipidomics was carefully discussed in this review, including lipid extraction strategies, separation techniques and mass-spectrometry-based analytical and quantitative methods in lipidomics. We also focused on novel resolution strategies for difficult problems in determining C=C bond positions in lipidomics. Finally, new technologies that were developed in recent years including single-cell lipidomics, flux-based lipidomics and multiomics technologies were also reviewed.
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Affiliation(s)
- Ting Hu
- State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Peking Union Medical College & Chinese Academy of Medical Sciences, Beijing, PR China
| | - Jin-Lan Zhang
- State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Peking Union Medical College & Chinese Academy of Medical Sciences, Beijing, PR China
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9
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Luo F, Feng Y, Ma H, Liu C, Chen G, Wei X, Mao X, Li X, Xu Y, Tang S, Wen H, Jin J, Zhu Q. Neutral ceramidase activity inhibition is involved in palmitate-induced apoptosis in INS-1 cells. Endocr J 2017; 64:767-776. [PMID: 28674283 DOI: 10.1507/endocrj.ej16-0512] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Neutral ceramidase (NCDase) is a class of ceramidases, a key enzyme in ceramide degradation. Recently, it was observed that NCDase activity was suppressed by saturated fatty acids to increase ceramide content in rat muscle. However, little is known about its changes in activity and roles in palmitate (Palm)-induced lipotoxicity in pancreatic β cells. Here, we demonstrated that Palm treatment significantly down-regulated NCDase activity, mRNA and protein levels in rat INS-1 cells. In addition, Palm caused a significant accumulation of ceramide, while SPH level remained unchanged, suggesting that inhibition of NCDase activity led to no change of SPH level after treatment with Palm for 24 h. Furthermore, NCDase overexpression significantly reduced Palm-induced apoptosis in INS-1 cells. Conversely, NCDase siRNA knockdown markedly exacerbated Palm-induced apoptosis. In conclusion, Palm treatment suppressed the activity of NCDase and down-regulated its mRNA and protein expression. Furthermore, NCDase inhibition was involved in Palm-induced apoptosis by blocking ceramide degradation in INS-1 cells.
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Affiliation(s)
- Fen Luo
- Department of Endocrinology, The Second Affiliated Hospital of Nanjing Medical University, Nanjing 210011, China
| | - Yamin Feng
- Department of Endocrinology, The Second Affiliated Hospital of Nanjing Medical University, Nanjing 210011, China
| | - Huimin Ma
- Department of Endocrinology, The Second Affiliated Hospital of Nanjing Medical University, Nanjing 210011, China
| | - Chao Liu
- Endocrine and Diabetes Center, Jiangsu Province Hospital on Integration of Chinese and Western Medicine, Nanjing University of Traditional Chinese Medicine, Branch of China Academy of Chinese Medical Science, Nanjing 210028, China
| | - Guofang Chen
- Endocrine and Diabetes Center, Jiangsu Province Hospital on Integration of Chinese and Western Medicine, Nanjing University of Traditional Chinese Medicine, Branch of China Academy of Chinese Medical Science, Nanjing 210028, China
| | - Xiao Wei
- Endocrine and Diabetes Center, Jiangsu Province Hospital on Integration of Chinese and Western Medicine, Nanjing University of Traditional Chinese Medicine, Branch of China Academy of Chinese Medical Science, Nanjing 210028, China
| | - Xiaodong Mao
- Endocrine and Diabetes Center, Jiangsu Province Hospital on Integration of Chinese and Western Medicine, Nanjing University of Traditional Chinese Medicine, Branch of China Academy of Chinese Medical Science, Nanjing 210028, China
| | - Xingjia Li
- Endocrine and Diabetes Center, Jiangsu Province Hospital on Integration of Chinese and Western Medicine, Nanjing University of Traditional Chinese Medicine, Branch of China Academy of Chinese Medical Science, Nanjing 210028, China
| | - Yijiao Xu
- Endocrine and Diabetes Center, Jiangsu Province Hospital on Integration of Chinese and Western Medicine, Nanjing University of Traditional Chinese Medicine, Branch of China Academy of Chinese Medical Science, Nanjing 210028, China
| | - Shan Tang
- Department of Endocrinology, The Second Affiliated Hospital of Nanjing Medical University, Nanjing 210011, China
| | - Honghua Wen
- Department of Endocrinology, The Second Affiliated Hospital of Nanjing Medical University, Nanjing 210011, China
| | - Junfei Jin
- China-USA Lipids in Health and Disease Research Center, Guilin Medical University, Gulin 541001, China
| | - Qun Zhu
- Department of Endocrinology, The Second Affiliated Hospital of Nanjing Medical University, Nanjing 210011, China
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10
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Brandsma J, Bailey AP, Koster G, Gould AP, Postle AD. Stable isotope analysis of dynamic lipidomics. Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1862:792-796. [PMID: 28302590 DOI: 10.1016/j.bbalip.2017.03.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 03/07/2017] [Accepted: 03/09/2017] [Indexed: 11/28/2022]
Abstract
Metabolic pathway flux is a fundamental element of biological activity, which can be quantified using a variety of mass spectrometric techniques to monitor incorporation of stable isotope-labelled substrates into metabolic products. This article contrasts developments in electrospray ionisation mass spectrometry (ESI-MS) for the measurement of lipid metabolism with more established gas chromatography mass spectrometry and isotope ratio mass spectrometry methodologies. ESI-MS combined with diagnostic tandem MS/MS scans permits the sensitive and specific analysis of stable isotope-labelled substrates into intact lipid molecular species without the requirement for lipid hydrolysis and derivatisation. Such dynamic lipidomic methodologies using non-toxic stable isotopes can be readily applied to quantify lipid metabolic fluxes in clinical and metabolic studies in vivo. However, a significant current limitation is the absence of appropriate software to generate kinetic models of substrate incorporation into multiple products in the time domain. Finally, we discuss the future potential of stable isotope-mass spectrometry imaging to quantify the location as well as the extent of lipid synthesis. This article is part of a Special Issue entitled: BBALIP_Lipidomics Opinion Articles edited by Sepp Kohlwein.
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Affiliation(s)
- Joost Brandsma
- Academic Unit of Clinical & Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton, United Kingdom
| | - Andrew P Bailey
- The Francis Crick Institute, 1 Midland Road, London, United Kingdom
| | - Grielof Koster
- Academic Unit of Clinical & Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton, United Kingdom; National Institute of Health Research Biomedical Research Unit in Respiratory Medicine, University Hospitals Southampton NHS Foundation Trust, United Kingdom
| | - Alex P Gould
- The Francis Crick Institute, 1 Midland Road, London, United Kingdom
| | - Anthony D Postle
- Academic Unit of Clinical & Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton, United Kingdom.
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11
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Cai L, Oyeniran C, Biswas DD, Allegood J, Milstien S, Kordula T, Maceyka M, Spiegel S. ORMDL proteins regulate ceramide levels during sterile inflammation. J Lipid Res 2016; 57:1412-22. [PMID: 27313060 DOI: 10.1194/jlr.m065920] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Indexed: 12/21/2022] Open
Abstract
The bioactive sphingolipid metabolite, ceramide, regulates physiological processes important for inflammation and elevated levels of ceramide have been implicated in IL-1-mediated events. Although much has been learned about ceramide generation by activation of sphingomyelinases in response to IL-1, the contribution of the de novo pathway is not completely understood. Because yeast ORM1 and ORM2 proteins negatively regulate ceramide levels through inhibition of serine palmitoyltransferase, the first committed step in ceramide biosynthesis, we examined the functions of individual mammalian ORM orthologs, ORM (yeast)-like (ORMDL)1-3, in regulation of ceramide levels. In HepG2 liver cells, downregulation of ORMDL3 markedly increased the ceramide precursors, dihydrosphingosine and dihydroceramide, primarily from de novo biosynthesis based on [U-(13)C]palmitate incorporation into base-labeled and dual-labeled dihydroceramides, whereas downregulation of each isoform increased dihydroceramides [(13)C]labeled in only the amide-linked fatty acid. IL-1 and the IL-6 family cytokine, oncostatin M, increased dihydroceramide and ceramide levels in HepG2 cells and concomitantly decreased ORMDL proteins. Moreover, during irritant-induced sterile inflammation in mice leading to induction of the acute-phase response, which is dependent on IL-1, expression of ORMDL proteins in the liver was strongly downregulated and accompanied by increased ceramide levels in the liver and accumulation in the blood. Together, our results suggest that ORMDLs may be involved in regulation of ceramides during IL-1-mediated sterile inflammation.
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Affiliation(s)
- Lin Cai
- School of Pharmacy, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298
| | - Clement Oyeniran
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298
| | - Debolina D Biswas
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298
| | - Jeremy Allegood
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298
| | - Sheldon Milstien
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298
| | - Tomasz Kordula
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298
| | - Michael Maceyka
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298
| | - Sarah Spiegel
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298
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12
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Martínez-Montañés F, Schneiter R. Tools for the analysis of metabolic flux through the sphingolipid pathway. Biochimie 2016; 130:76-80. [PMID: 27208414 DOI: 10.1016/j.biochi.2016.05.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 05/13/2016] [Indexed: 01/26/2023]
Abstract
Discerning the complex regulation of the enzymatic steps necessary for sphingolipid biosynthesis is facilitated by the utilization of tracers that allow a time-resolved analysis of the pathway dynamics without affecting the metabolic flux. Different strategies have been used and new tools are continuously being developed to probe the various enzymatic conversions that occur within this complex pathway. Here, we provide a short overview of the divergent fungal and mammalian sphingolipid biosynthetic routes, and of the tracers and methods that are frequently employed to follow the flux of intermediates throughout these pathways.
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Affiliation(s)
| | - Roger Schneiter
- University of Fribourg, Department of Biology, 1700 Fribourg, Switzerland.
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13
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Oyeniran C, Sturgill JL, Hait NC, Huang WC, Avni D, Maceyka M, Newton J, Allegood JC, Montpetit A, Conrad DH, Milstien S, Spiegel S. Aberrant ORM (yeast)-like protein isoform 3 (ORMDL3) expression dysregulates ceramide homeostasis in cells and ceramide exacerbates allergic asthma in mice. J Allergy Clin Immunol 2015; 136:1035-46.e6. [PMID: 25842287 PMCID: PMC4591101 DOI: 10.1016/j.jaci.2015.02.031] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Revised: 01/28/2015] [Accepted: 02/27/2015] [Indexed: 12/21/2022]
Abstract
BACKGROUND Asthma, a chronic inflammatory condition defined by episodic shortness of breath with expiratory wheezing and cough, is a serious health concern affecting more than 250 million persons. Genome-wide association studies have identified ORM (yeast)-like protein isoform 3 (ORMDL3) as a gene associated with susceptibility to asthma. Although its yeast ortholog is a negative regulator of de novo ceramide biosynthesis, how ORMDL3 contributes to asthma pathogenesis is not known. OBJECTIVES We sought to decipher the molecular mechanism for the pathologic functions of ORMDL3 in asthma and the relationship to its evolutionarily conserved role in regulation of ceramide homeostasis. METHODS We determined the relationship between expression of ORMDL3 and ceramide in epithelial and inflammatory cells and in asthma pathogenesis in mice. RESULTS Although small increases in ORMDL3 expression decrease ceramide levels, remarkably, higher expression in lung epithelial cells and macrophages in vitro and in vivo increased ceramide production, which promoted chronic inflammation, airway hyperresponsiveness, and mucus production during house dust mite-induced allergic asthma. Moreover, nasal administration of the immunosuppressant drug FTY720/fingolimod reduced ORMDL3 expression and ceramide levels and mitigated airway inflammation and hyperreactivity and mucus hypersecretion in house dust mite-challenged mice. CONCLUSIONS Our findings demonstrate that overexpression of ORMDL3 regulates ceramide homeostasis in cells in a complex manner and suggest that local FTY720 administration might be a useful therapeutic intervention for the control of allergic asthma.
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Affiliation(s)
- Clement Oyeniran
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Va
| | - Jamie L Sturgill
- Department of Microbiology & Immunology, Virginia Commonwealth University School of Medicine, Richmond, Va; School of Nursing, Virginia Commonwealth University, Richmond, Va
| | - Nitai C Hait
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Va
| | - Wei-Ching Huang
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Va
| | - Dorit Avni
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Va
| | - Michael Maceyka
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Va
| | - Jason Newton
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Va
| | - Jeremy C Allegood
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Va
| | - Alison Montpetit
- School of Nursing, Virginia Commonwealth University, Richmond, Va
| | - Daniel H Conrad
- Department of Microbiology & Immunology, Virginia Commonwealth University School of Medicine, Richmond, Va
| | - Sheldon Milstien
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Va
| | - Sarah Spiegel
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Va.
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14
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Application of stable isotopes to investigate the metabolism of fatty acids, glycerophospholipid and sphingolipid species. Prog Lipid Res 2014; 54:14-31. [PMID: 24462586 DOI: 10.1016/j.plipres.2014.01.002] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Revised: 12/30/2013] [Accepted: 01/07/2014] [Indexed: 11/22/2022]
Abstract
Nature provides an enormous diversity of lipid molecules that originate from various pathways. To gain insight into the metabolism and dynamics of lipid species, the application of stable isotope-labeled tracers combined with mass spectrometric analysis represents a perfect tool. This review provides an overview of strategies to track fatty acid, glycerophospholipid, and sphingolipid metabolism. In particular, the selection of stable isotope-labeled precursors and their mass spectrometric analysis is discussed. Furthermore, examples of metabolic studies that were performed in cell culture, animal and clinical experiments are presented.
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15
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Li M, Yang L, Bai Y, Liu H. Analytical Methods in Lipidomics and Their Applications. Anal Chem 2013; 86:161-75. [DOI: 10.1021/ac403554h] [Citation(s) in RCA: 145] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Min Li
- Beijing National Laboratory for Molecular Sciences, Key
Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry
of Education, Institute of Analytical Chemistry, College of Chemistry
and Molecular Engineering, Peking University, Beijing 100871, China
| | - Li Yang
- Beijing National Laboratory for Molecular Sciences, Key
Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry
of Education, Institute of Analytical Chemistry, College of Chemistry
and Molecular Engineering, Peking University, Beijing 100871, China
| | - Yu Bai
- Beijing National Laboratory for Molecular Sciences, Key
Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry
of Education, Institute of Analytical Chemistry, College of Chemistry
and Molecular Engineering, Peking University, Beijing 100871, China
| | - Huwei Liu
- Beijing National Laboratory for Molecular Sciences, Key
Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry
of Education, Institute of Analytical Chemistry, College of Chemistry
and Molecular Engineering, Peking University, Beijing 100871, China
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16
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Li J, Hoene M, Zhao X, Chen S, Wei H, Häring HU, Lin X, Zeng Z, Weigert C, Lehmann R, Xu G. Stable isotope-assisted lipidomics combined with nontargeted isotopomer filtering, a tool to unravel the complex dynamics of lipid metabolism. Anal Chem 2013; 85:4651-7. [PMID: 23537127 DOI: 10.1021/ac400293y] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Investigations of complex metabolic mechanisms and networks have become a focus of research in the postgenomic area, thereby creating an increasing demand for sophisticated analytical approaches. One such tool is lipidomics analysis that provides, a detailed picture of the lipid composition of a system at a given time. Introducing stable isotopes into the studied system can additionally provide information on the synthesis, transformation and degradation of individual lipid species. However, capturing the entire dynamics of lipid networks is still a challenge. We developed and evaluated a novel strategy for the in-depth analysis of the dynamics of lipid metabolism with the capacity for high molecular specificity and network coverage. The general workflow consists of stable isotope-labeling experiments, ultrahigh-performance liquid chromatography (UHPLC)/high-resolution Orbitrap-mass spectrometry (MS) lipid profiling and data processing by a software tool for global isotopomer filtering and matching. As a proof of concept, this approach was applied to the network-wide mapping of dynamic lipid metabolism in primary human skeletal muscle cells cultured for 4, 12, and 24 h with [U-(13)C]-palmitate. In the myocellular lipid extracts, 692 isotopomers were detected that could be assigned to 203 labeled lipid species spanning 12 lipid (sub)classes. Interestingly, some lipid classes showed high turnover rates but stable total amounts while the amount of others increased in the course of palmitate treatment. The novel strategy presented here has the potential to open new detailed insights into the dynamics of lipid metabolism that may lead to a better understanding of physiological mechanisms and metabolic perturbations.
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Affiliation(s)
- Jia Li
- CAS Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China
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17
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Blachnio-Zabielska AU, Persson XMT, Koutsari C, Zabielski P, Jensen MD. A liquid chromatography/tandem mass spectrometry method for measuring the in vivo incorporation of plasma free fatty acids into intramyocellular ceramides in humans. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2012; 26:1134-40. [PMID: 22467464 PMCID: PMC3370409 DOI: 10.1002/rcm.6216] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
RATIONALE Sphingolipids are important components of cell membranes that serve as cell signaling molecules; ceramide plays a central role in sphingolipid metabolism. De novo ceramide biosynthesis depends on fatty acid availability, but whether muscle uses circulating free fatty acids or pre-existing intracellular stores is unknown. Our goal was to develop a method to detect the incorporation of intravenously infused [U-(13)C]palmitate into intramyocellular ceramides. METHODS We used liquid chromatography/tandem mass spectrometry (LC/MS/MS) to measure the concentrations of different sphingolipid species and (13)C-isotopic enrichment of 16:0-ceramide. Chromatographic separation was performed using ultra-performance liquid chromatography. The analysis was performed on a triple quadrupole mass spectrometer using a positive ion electrospray ionization source with selected reaction monitoring (SRM). RESULTS The sphingolipids ions, except enriched ceramide, were monitored as [M+2+H](+). The [(13)C(16)]16:0-ceramide was monitored as [M+16+H](+). By monitoring two different transitions of the [(13)C(16)]16:0-ceramide (554/536 and 554/264) we could indirectly measure enrichment of the palmitate that is not a part of the sphingoid base. Concentration and enrichment could be measured using 20 mg of muscle obtained from volunteers receiving a low dose [U-(13)C]palmitate infusion. CONCLUSIONS LC/MS/MS can be used to detect the incorporation of plasma palmitate into muscle ceramides in humans, in vivo.
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Affiliation(s)
| | | | | | | | - Michael D. Jensen
- Correspondence: Michael D. Jensen, MD, Endocrine Research Unit, 200 1st St SW, Rm 5-194 Joseph, Rochester, MN 55905, 507-255-6515 (tel), 507-255-4828 (fax),
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18
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Abstract
PURPOSE OF REVIEW Lipidomics characterizes the composition of intact lipid molecular species in biological systems and the field has been driven by some spectacular advances in mass spectrometry instrumentation and applications. This review will highlight these advances and outline their recent application to address clinical issues. RECENT FINDINGS This review first identifies recent advances in lipid detection and analysis by a variety of mass spectrometry techniques, then reviews specific application including stable isotope labelling of lipids, lipid mass spectrometry imaging, data analysis and bioinformatics, and finally presents examples of the application of lipidomics to selected disease states. SUMMARY Lipidomics so far has been principally concerned with identifying novel methodologies, but recent advances demonstrating applications in diabetes, neurodegenerative diseases, cystic fibrosis and other respiratory diseases clearly indicate the potential usefulness of lipidomics both to generate biomarkers of disease and to probe signalling and metabolic processes.
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Affiliation(s)
- Anthony D Postle
- Clinical and Experimental Sciences, University of Southampton, Hampshire, UK.
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19
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Subramaniam S, Fahy E, Gupta S, Sud M, Byrnes RW, Cotter D, Dinasarapu AR, Maurya MR. Bioinformatics and systems biology of the lipidome. Chem Rev 2011; 111:6452-90. [PMID: 21939287 PMCID: PMC3383319 DOI: 10.1021/cr200295k] [Citation(s) in RCA: 123] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Shankar Subramaniam
- Department of Bioengineering, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
- San Diego Supercomputer Center, 9500 Gilman Drive, La Jolla, California, 92093, USA
- Departments of Chemistry and Biochemistry, and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, California 92093, USA
| | - Eoin Fahy
- Department of Bioengineering, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
| | - Shakti Gupta
- Department of Bioengineering, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
| | - Manish Sud
- San Diego Supercomputer Center, 9500 Gilman Drive, La Jolla, California, 92093, USA
| | - Robert W. Byrnes
- San Diego Supercomputer Center, 9500 Gilman Drive, La Jolla, California, 92093, USA
| | - Dawn Cotter
- San Diego Supercomputer Center, 9500 Gilman Drive, La Jolla, California, 92093, USA
| | - Ashok Reddy Dinasarapu
- Department of Bioengineering, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
| | - Mano Ram Maurya
- Department of Bioengineering, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
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20
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Merrill AH. Sphingolipid and glycosphingolipid metabolic pathways in the era of sphingolipidomics. Chem Rev 2011; 111:6387-422. [PMID: 21942574 PMCID: PMC3191729 DOI: 10.1021/cr2002917] [Citation(s) in RCA: 527] [Impact Index Per Article: 40.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2011] [Indexed: 12/15/2022]
Affiliation(s)
- Alfred H Merrill
- School of Biology, and the Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, Georgia 30332-0230, USA.
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