Robb Flynn
Vanderbilt University, Surgery, Faculty Member
- Hiedit
To examine the effects of Roux-en-Y gastric bypass (RYGB) surgery with and without laparoscopic removal of omental fat (omentectomy) on the temporal gene expression profiles of skeletal muscle.
Research Interests: Genetics, Data Analysis, Anthropometry, Inflammation, Adolescent, and 15 moreGene expression, Multidisciplinary, Nuclear Receptor, Humans, Female, Male, Cluster Analysis, Middle Aged, Adult, Biological markers, Gastric Bypass, Gene Expression Regulation, Gene expression profiling, Differential expression, and Omentum
Nonalcoholic fatty liver disease (NAFLD) occurs frequently in a setting of obesity, dyslipidemia and insulin resistance, but the etiology of the disease, particularly the events favoring progression to nonalcoholic steatohepatitis (NASH)... more
Nonalcoholic fatty liver disease (NAFLD) occurs frequently in a setting of obesity, dyslipidemia and insulin resistance, but the etiology of the disease, particularly the events favoring progression to nonalcoholic steatohepatitis (NASH) as opposed to simple steatosis (SS), are not fully understood. Based on known zonation patterns in protein, glucose and lipid metabolism, coupled with evidence that phosphatidylcholine may play a role in NASH pathogenesis, we hypothesized that phospholipid zonation exists in liver and that specific phospholipid abundance and distribution may be associated with histologic disease. A survey of normal hepatic protein expression profiles in the Human Protein Atlas revealed pronounced zonation of enzymes involved in lipid utilization and storage, particularly those facilitating phosphatidylcholine (PC) metabolism. Immunohistochemistry of obese normal, SS and NASH liver specimens with anti-phosphatidylethanomine N-methyltransferase (PEMT) antibodies showe...
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Bile acids (BAs) are a family of hydroxylated steroids secreted by the liver that aid in the breakdown and absorption of dietary fats. BAs also function as nutrient and inflammatory signaling molecules, acting through cognate receptors,... more
Bile acids (BAs) are a family of hydroxylated steroids secreted by the liver that aid in the breakdown and absorption of dietary fats. BAs also function as nutrient and inflammatory signaling molecules, acting through cognate receptors, to coordinate host metabolism. Commensal bacteria in the gastrointestinal tract are functional modifiers of the BA pool, affecting composition and abundance. Deconjugation of host BAs creates a molecular network that inextricably links gut microtia with their host. In this review we highlight the roles of BAs in mediating this mutualistic relationship with a focus on those events that impact host physiology and metabolism.
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A challenge in advanced drug delivery is selectively traversing the plasma membrane, a barrier that prohibits the intracellular delivery of most peptide and nucleic acid-based therapeutics. A variety of short amino acid sequences termed... more
A challenge in advanced drug delivery is selectively traversing the plasma membrane, a barrier that prohibits the intracellular delivery of most peptide and nucleic acid-based therapeutics. A variety of short amino acid sequences termed protein transduction domains (PTDs) first identified in viral proteins have been utilized for over 20 years to deliver proteins nondestructively into cells, however, the mechanisms by which this occurs are varied and cell-specific. Here we describe the results of live cell imaging experiments with AZX100, a cell-permeable anti-fibrotic peptide bearing an "enhanced" PTD (PTD4). We monitored fluorescently labeled AZX100 upon cell surface binding and subsequent intracellular trafficking in the presence of cellular process inhibitors and various well-defined fluorescently labeled cargos. We conclude that AZX100 enters cells via caveolae rapidly, in a manner that is independent of glycoconjugates, actin/microtubule polymerization, dynamins, multiple GTPases, and clathrin, but is associated with lipid rafts as revealed by methyl-beta-cylodextrin. AZX100 treatment increases the expression of phospho-caveolin (Y14), a critical effector of focal adhesion dynamics, suggesting a mechanistic link between caveolin-1 phosphorylation and actin cytoskeleton dynamics. Our results reveal novel and interesting properties of PTD4 and offer new insight into the cellular mechanisms facilitating an advanced drug delivery tool.
Research Interests: Electron Microscopy, Fluorescence Microscopy, Biology, Medicine, Cell Culture, and 15 moreInternalization, In Vitro, Humans, Pharmaceutical Sciences, Membrane transport, Peptides, Skin, Dermis, Caveolae, Amino Acid Sequence, Internalisation, Protein Transport, Molecular Sequence Data, fibroblasts, and Pharmacology and pharmaceutical sciences
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N-acyl-phosphatidylethanolamine phospholipase D (NAPE-PLD) (EC 3.1.4.4) catalyzes the final step in the biosynthesis of N-acyl-ethanolamides (NAEs). Reduced NAPE-PLD expression and activity may contribute to obesity and inflammation, but... more
N-acyl-phosphatidylethanolamine phospholipase D (NAPE-PLD) (EC 3.1.4.4) catalyzes the final step in the biosynthesis of N-acyl-ethanolamides (NAEs). Reduced NAPE-PLD expression and activity may contribute to obesity and inflammation, but a major obstacle to elucidating the role of NAPE-PLD and NAE biosynthesis in various physiological processes has been the lack of effective NAPE-PLD inhibitors. The endogenous bile acid lithocholic acid (LCA) inhibits NAPE-PLD activity (IC50 68 μM) but LCA is also a highly potent ligand for TGR5 (EC50 0.52 μM). Recently, the first selective small molecule inhibitor of NAPE-PLD, ARN19874, was reported (IC50 34 μM). To identify more potent inhibitors of NAPE-PLD, we screened compounds using a quenched fluorescent NAPE analog, PED-A1, as a substrate for recombinant mouse NAPE-PLD. Screened compounds included a panel of bile acids as well as a library of experimental compounds (the Spectrum Collection). Muricholic acids and several other bile acids inhi...
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The gut-to-brain axis exhibits significant control over motivated behavior. However, mechanisms supporting this communication are poorly understood. We reveal that a gut-based bariatric surgery chronically elevates systemic bile acids and... more
The gut-to-brain axis exhibits significant control over motivated behavior. However, mechanisms supporting this communication are poorly understood. We reveal that a gut-based bariatric surgery chronically elevates systemic bile acids and attenuates cocaine-induced elevations in accumbal dopamine. Notably, this surgery reduces reward-related behavior and psychomotor sensitization to cocaine. Utilizing a knockout mouse model, we have determined that a main mediator of these post-operative effects is the Takeda G protein-coupled bile acid receptor (TGR5). Viral restoration of TGR5 in the nucleus accumbens of TGR5 knockout animals is sufficient to restore cocaine reward, centrally localizing this TGR5-mediated modulation. These findings define TGR5 and bile acid signaling as pharmacological targets for the treatment of cocaine abuse and reveal a novel mechanism of gut-to-brain communication.
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During reduced energy intake, skeletal muscle maintains homeostasis by rapidly suppressing insulin-stimulated glucose utilization. Loss of this adaptation is observed with deficiency of the fatty acid transporter CD36. A similar loss is... more
During reduced energy intake, skeletal muscle maintains homeostasis by rapidly suppressing insulin-stimulated glucose utilization. Loss of this adaptation is observed with deficiency of the fatty acid transporter CD36. A similar loss is also characteristic of the insulin resistant state where CD36 is dysfunctional. To elucidate what links CD36 to muscle glucose utilization we examined whether CD36 signaling might influence insulin action. First, we show that CD36 deletion specific to skeletal muscle reduces expression of insulin signaling and glucose metabolism genes. It decreases muscle ceramides but impairs glucose disposal during a meal. Second, in primary-derived human myotubes depletion of CD36 suppresses insulin signaling and the mechanism is shown to involve functional CD36 interaction with the insulin receptor (IR). CD36 promotes tyrosine phosphorylation of IR by the Fyn kinase, enhances IR recruitment of P85 and downstream signaling. Third, pretreatment for 15 minutes with ...
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Abnormal fatty acid (FA) metabolism contributes to diabetes and cardiovascular disease. The FA receptor CD36 has been linked to risk of metabolic syndrome. In rodents CD36 regulates various aspects of fat metabolism but whether it has... more
Abnormal fatty acid (FA) metabolism contributes to diabetes and cardiovascular disease. The FA receptor CD36 has been linked to risk of metabolic syndrome. In rodents CD36 regulates various aspects of fat metabolism but whether it has similar actions in humans is unknown. We examined impact of a coding single-nucleotide polymorphism in CD36 on post-prandial hormone and bile acid (BA) responses. To examine if the minor allele (G) of coding CD36 variant rs3211938 (G/T) which reduces CD36 level by approximately 50% influences hormonal responses to a high-fat meal (HFM). Obese African American (AA) women carriers of the G allele of rs3211938 (G/T) and weight-matched noncarriers (T/T) were studied before and after a HFM. Two-center study. Obese AA women. High-fat meal. Early preabsorptive responses (10 min) and extended excursions in plasma hormones (c-peptide, insulin, incretins, ghrelin, FGF19, FGF21), BAs and serum lipoproteins (chylomicrons, VLDL) were determined. At fasting, G allel...
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Standard harvest and preparation of human saphenous vein (HSV) for autologous coronary and peripheral arterial bypass procedures is associated with injury and increased oxidative stress that negatively affect graft performance. In this... more
Standard harvest and preparation of human saphenous vein (HSV) for autologous coronary and peripheral arterial bypass procedures is associated with injury and increased oxidative stress that negatively affect graft performance. In this study we investigated the global metabolomic profiles of HSV before (unprepared; UP) and after standard vein graft preparation (AP). AP-HSV showed impaired vasomotor function that was associated with increased oxidative stress, phospholipid hydrolysis and energy depletion that are characteristic of mechanical and chemical injury. A porcine model (PSV) was utilized to validate these metabolomic changes in HSV and to determine the efficacy of an improved preparation technique (OP) using pressure-regulated distension, a non-toxic vein marker, and graft storage in buffered PlasmaLyte solution in limiting metabolic decompensation due to graft preparation. Deficits in vasomotor function and metabolic signature observed in AP-PSV could be largely mitigated w...
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Molecular signaling events associated with the necroinflammatory changes in nonalcoholic steatohepatitis are not well understood. To understand the molecular basis of NASH, we evaluated reversible phosphorylation events in hepatic tissue... more
Molecular signaling events associated with the necroinflammatory changes in nonalcoholic steatohepatitis are not well understood. To understand the molecular basis of NASH, we evaluated reversible phosphorylation events in hepatic tissue derived from Class III obese subjects by phosphoproteomic means with the aim of highlighting key regulatory pathways that distinguish NASH from NAFLD. Class III obese subjects undergoing bariatric surgery underwent liver biopsy (8 NOR, 8 simple steatosis and 8 NASH). Our strategy was unbiased, comparing global differences in liver protein reversible phosphorylation events across the 24 subjects. Of the 3,078 phosphorylation sites assigned (2,465 phosphoserine, 445 phosphothreonine, 165 phosphotyrosine), 53 were altered by a factor of 2 among cohorts, and of those, 12 were significantly increased or decreased by ANOVA (P < 0.05). Statistical analyses of canonical signaling pathways identified carbohydrate metabolism and RNA post-transcriptional mo...
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Obesity and its associated medical conditions continue to increase and add significant burden to patients, as well as health-care systems, worldwide. Bariatric surgery is the most effective treatment for severe obesity and its... more
Obesity and its associated medical conditions continue to increase and add significant burden to patients, as well as health-care systems, worldwide. Bariatric surgery is the most effective treatment for severe obesity and its comorbidities, and resolution of diabetes is weight loss-independent in the case of some operations. Although these weight-independent effects are frequently described clinically, the mechanisms behind them are not well understood and remain an intense area of focus in the growing field of metabolic and bariatric surgery. Perceptions of the mechanisms responsible for the beneficial metabolic effects of metabolic/bariatric operations have shifted from being mostly restrictive and malabsorption over the last 10 to 15 years to being more neuro-hormonal in origin. In this review, we describe recent basic and clinical findings of the major clinical procedures (adjustable gastric banding, vertical sleeve gastrectomy, Roux-en-Y gastric bypass, and biliopancreatic div...
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Research Interests: Plant Biology, Tobacco, Membrane Proteins, Mitochondria, Cytoskeleton, and 15 moreAnchoring, Biomembrane, Endoplasmic Reticulum, Catalase, Ultrastructure, Peroxidases, Peroxisome, Peroxisomes, Membrane Protein, Fusion Protein, Planta, Transient Expression, Ascorbate Peroxidase, Cell Membrane, and Nicotiana tabacum L
The spectrum of nonalcoholic fatty liver disease (NAFLD) describes disease conditions deteriorating from nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH) to cirrhosis (CIR) to hepatocellular carcinoma (HCC). From a... more
The spectrum of nonalcoholic fatty liver disease (NAFLD) describes disease conditions deteriorating from nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH) to cirrhosis (CIR) to hepatocellular carcinoma (HCC). From a molecular and biochemical perspective, our understanding of the etiology of this disease is limited by the broad spectrum of disease presentations, the lack of a thorough understanding of the factors contributing to disease susceptibility, and ethical concerns related to repeat sampling of the liver. To better understand the factors associated with disease progression, we investigated by next-generation RNA sequencing the altered expression of microRNAs (miRNAs) in liver biopsies of class III obese subjects (body mass index ≥40 kg/m(2)) biopsied at the time of elective bariatric surgery. Clinical characteristics and unbiased RNA expression profiles for 233 miRs, 313 transfer RNAs (tRNAs), and 392 miscellaneous small RNAs (snoRNAs, snRNAs, rRNAs) were...
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Triglyceride content in the liver is regulated by the uptake, production and elimination of lipoproteins, and derangements in these processes contribute to nonalcoholic fatty liver disease (NAFLD). Previous studies show a direct... more
Triglyceride content in the liver is regulated by the uptake, production and elimination of lipoproteins, and derangements in these processes contribute to nonalcoholic fatty liver disease (NAFLD). Previous studies show a direct relationship between intrahepatic fat and production of apolipoprotein B100 (apoB100) containing particles, VLDL and LDL, but little consensus exists regarding changes in lipoprotein production in the development of simple steatosis (SS) versus nonalcoholic steatohepatitis (NASH). Further, ethnic variations in lipoproteins among SS and NASH are unknown as is how such variations might contribute to the differential prevalence of disease among Caucasians versus African Americans. In this study, we assessed plasma lipoprotein profiles by nuclear magnetic resonance (NMR) spectroscopy in 70 non-diabetic class III obese females recruited from the surgical weight loss clinic. Of these, 51 females were stratified by biopsy-staged NAFLD severity (histologically norma...
Research Interests: Obesity, Anthropometry, Biomarkers, Magnetic Resonance Spectroscopy, Multidisciplinary, and 15 moreInsulin Resistance, Prospective studies, Humans, Female, PLoS one, Apolipoprotein B, African Americans, Prevalence, Middle Aged, Adult, Lipoproteins, European Continental Ancestry Group, Disease Progression, Case Control Studies, and non alcoholic fatty liver disease
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Roux-en-Y gastric bypass (RYGB) is the most effective treatment for morbid obesity and resolution of diabetes. Over the last decade, it has become well accepted that this resolution of diabetes occurs before significant weight loss;... more
Roux-en-Y gastric bypass (RYGB) is the most effective treatment for morbid obesity and resolution of diabetes. Over the last decade, it has become well accepted that this resolution of diabetes occurs before significant weight loss; however, the mechanisms behind this effect remain unknown and could represent novel therapeutic targets for obesity and diabetes. Bile acids have been identified as putative mediators of these weight loss-independent effects. To identify the longitudinal changes in bile acids after RYGB, which may provide mechanistic insight into the weight loss-independent effects of RYGB. Observational study before/after intervention. Academic medical center. Samples were collected from morbidly obese patients (n = 21) before and after RYGB. RYGB. Seventeen individual bile acid species were measured preoperatively and at 1, 6, 12, and 24 months postoperatively. Anthropometric, hormonal, and hyperinsulinemic-euglycemic clamp data were also examined to identify physiolog...
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Roux-en-Y gastric bypass (RYGB) is highly effective in reversing obesity and associated diabetes. Recent observations in humans suggest a contributing role of increased circulating bile acids in mediating such effects. Here we use a... more
Roux-en-Y gastric bypass (RYGB) is highly effective in reversing obesity and associated diabetes. Recent observations in humans suggest a contributing role of increased circulating bile acids in mediating such effects. Here we use a diet-induced obesity (DIO) mouse model and compare metabolic remission when bile flow is diverted through a gallbladder anastomosis to jejunum, ileum or duodenum (sham control). We find that only bile diversion to the ileum results in physiologic changes similar to RYGB, including sustained improvements in weight, glucose tolerance and hepatic steatosis despite differential effects on hepatic gene expression. Circulating free fatty acids and triglycerides decrease while bile acids increase, particularly conjugated tauro-β-muricholic acid, an FXR antagonist. Activity of the hepatic FXR/FGF15 signalling axis is reduced and associated with altered gut microbiota. Thus bile diversion, independent of surgical rearrangement of the gastrointestinal tract, impar...
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Nonalcoholic fatty liver disease (NAFLD) occurs frequently in the setting of metabolic syndrome, but the factors leading to nonalcoholic steatohepatitis (NASH) are not fully understood. This study investigated toll-like receptor 4 (TLR4)... more
Nonalcoholic fatty liver disease (NAFLD) occurs frequently in the setting of metabolic syndrome, but the factors leading to nonalcoholic steatohepatitis (NASH) are not fully understood. This study investigated toll-like receptor 4 (TLR4) signaling in human liver with the goal of delineating whether activation of this pathway segregates those with nonalcoholic fatty liver (NAFL) from those with NASH. Experiments were performed using liver biopsy tissue obtained from Class III obese subjects undergoing bariatric surgery, and extended to an immortalized human hepatocyte HepaRG cell line and primary human hepatocytes. The bacterial endotoxin lipopolysaccharide (LPS) and total free fatty acid levels were significantly increased in plasma of NASH patients. TLR4 mRNA levels were significantly increased in subjects with NASH compared to NAFL as was IRF3 in the myeloid differentiation factor 88- (Myd88-) independent signaling pathway. In HepaRG cells, NF-ҡB nuclear translocation and function...
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Germplasm evaluation of ex situ collections is needed to document collection characteristics, enhance utilization, and to determine collection needs. The objectives of this study were to (1) provide oil and meal evaluation information for... more
Germplasm evaluation of ex situ collections is needed to document collection characteristics, enhance utilization, and to determine collection needs. The objectives of this study were to (1) provide oil and meal evaluation information for a major portion of the United States Department of Agriculture (USDA) safflower (Carthamus tinctorius L.) collection, (2) compare ranges, variances and means between 203 core and
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Recent data from studies of peroxisome assembly and the subcellular sorting of peroxisomal matrix and membrane proteins have led to an expansion of the &#39;growth and division&#39; and &#39;endoplasmic... more
Recent data from studies of peroxisome assembly and the subcellular sorting of peroxisomal matrix and membrane proteins have led to an expansion of the &#39;growth and division&#39; and &#39;endoplasmic reticulum-vesiculation&#39; models of peroxisome biogenesis into a more flexible, unified model. Within this context, we discuss the proposed role for the endoplasmic reticulum in the formation of preperoxisomes and the potential for 15 Arabidopsis peroxin homologs to function in the biogenesis of peroxisomes in plant cells.
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Research Interests: Dermatology, Humans, Keloid, Animals, Analog, and 15 morePhosphorylation, Fibrosis, Proteins, Actin Cytoskeleton, Clinical Sciences, Cyclic nucleotides, Heat Shock, Heat Shock Protein, INVESTIGATIVE, Lysophosphatidic Acid, Small Heat Shock Protein, Endothelins, Protein requirement, fibroblasts, and Cricetinae
Changes in protein abundance in skeletal muscle are central to a large number of metabolic and other disorders, including, and perhaps most commonly, insulin resistance. Proteomics analysis of human muscle is an important approach for... more
Changes in protein abundance in skeletal muscle are central to a large number of metabolic and other disorders, including, and perhaps most commonly, insulin resistance. Proteomics analysis of human muscle is an important approach for gaining insight into the biochemical basis for normal and pathophysiological conditions. However, to date, the number of proteins identified by this approach has been limited, with 107 different proteins being the maximum reported so far. Using a combination of one-dimensional gel electrophoresis and high performance liquid chromatography electrospray ionization tandem mass spectrometry, we identified 954 different proteins in human vastus lateralis muscle obtained from three healthy, nonobese subjects. In addition to a large number of isoforms of contractile proteins, we detected all proteins involved in the major pathways of glucose and lipid metabolism in skeletal muscle. Mitochondrial proteins accounted for 22% of all proteins identified, including...
Research Interests: Mass Spectrometry, Calcium, Multidisciplinary, Molecular and cellular biology, Humans, and 15 moreGlucose, Insulin, Lipid metabolism, Electron Transport, Enzyme, High Pressure Liquid Chromatography, Middle Aged, Homeostasis, Adult, Molecular weight, Gel electrophoresis, Contractile Proteins, Extracellular Matrix Proteins, Complex I, and Electrospray Ionization
Mitochondria can be isolated from skeletal muscle in a manner that preserves tightly coupled bioenergetic function in vitro. The purpose of this study was to characterize the composition of such preparations using a proteomics approach.... more
Mitochondria can be isolated from skeletal muscle in a manner that preserves tightly coupled bioenergetic function in vitro. The purpose of this study was to characterize the composition of such preparations using a proteomics approach. Mitochondria isolated from human vastus lateralis biopsies were functional as evidenced by their response to carbohydrate and fat-derived fuels. Using one-dimensional gel electrophoresis and HPLC-ESI-MS/MS, 823 unique proteins were detected, and 487 of these were assigned to the mitochondrion, including the newly characterized SIRT5, MitoNEET and RDH13. Proteins detected included 9 of the 13 mitochondrial DNA-encoded proteins and 86 of 104 electron transport chain (ETC) and ETC-related proteins. In addition, 59 of 78 proteins of the 55S mitoribosome, several TIM and TOM proteins and cell death proteins were present. This study presents an efficient method for future qualitative assessments of proteins from functional isolated mitochondria from small ...
Research Interests: Proteomics, Oxidative Stress, Mitochondria, Mitochondrial DNA, Humans, and 15 moreFatty acids, Mice, Animals, Cell Death, Proteins, Electron Transport, High Pressure Liquid Chromatography, Amino Acids, MRP, Cell nucleus, Electrophoresis, Gel electrophoresis, Proteome, OXPHOS, and Biochemistry and cell biology
Protein phosphorylation plays an essential role in signal transduction pathways that regulate substrate and energy metabolism, contractile function, and muscle mass in human skeletal muscle. Abnormal phosphorylation of signaling enzymes... more
Protein phosphorylation plays an essential role in signal transduction pathways that regulate substrate and energy metabolism, contractile function, and muscle mass in human skeletal muscle. Abnormal phosphorylation of signaling enzymes has been identified in insulin-resistant muscle using phosphoepitope-specific antibodies, but its role in other skeletal muscle disorders remains largely unknown. This may be in part due to insufficient knowledge of relevant targets. Here, we therefore present the first large-scale in vivo phosphoproteomic study of human skeletal muscle from 3 lean, healthy volunteers. Trypsin digestion of 3-5 mg human skeletal muscle protein was followed by phosphopeptide enrichment using SCX and TiO(2). The resulting phosphopeptides were analyzed by HPLC-ESI-MS/MS. Using this unbiased approach, we identified 306 distinct in vivo phosphorylation sites in 127 proteins, including 240 phosphoserines, 53 phosphothreonines, and 13 phosphotyrosines in at least 2 out of 3 ...
Research Interests: Skeletal muscle biology, Computational Biology, Proteomics, Biological Sciences, Humans, and 13 moreMale, Tandem Mass Spectrometry, Phosphorylation, High Pressure Liquid Chromatography, CHEMICAL SCIENCES, Middle Aged, Liquid Chromatography / Electrospray Ionization Mass Spectrometry, Skeletal Muscle, Adult, Amino Acid Sequence, Proteome, Phosphopeptides, and Molecular Sequence Data
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Research Interests: Obesity, Skeletal muscle biology, Diabetes, Mass Spectrometry, Proteomics, and 14 moreBiopsy, Humans, Female, Male, Body Mass Index, Middle Aged, Skeletal Muscle, Adult, Proteome analysis, Type 2 Diabetes Mellitus, Reference Values, Gene expression profiling, Chaperonins, and Medical and Health Sciences
Research Interests: Skeletal muscle biology, Asthma, Signal Transduction, Humans, Smooth muscle, and 13 moreAnimals, Subarachnoid hemorrhage, Hyperplasia, Skeletal Muscle, Rats, Myocardium, Mechanism of action, Muscle Function, Amino Acid Sequence, Phosphopeptides, Biochemistry and cell biology, Small Heat Shock Protein, and Molecular Sequence Data
Peroxisomes are highly dynamic organelles with regard to their metabolic functions, shapes, distribution, movements, and biogenesis. They are also important as sites for the development of some viral pathogens. It has long been known that... more
Peroxisomes are highly dynamic organelles with regard to their metabolic functions, shapes, distribution, movements, and biogenesis. They are also important as sites for the development of some viral pathogens. It has long been known that certain members of the tombusvirus family recruit peroxisomes for viral RNA replication and that this process is accompanied by dramatic changes in peroxisome morphology, the most remarkable of which is the extensive inward vesiculation of the peroxisomal boundary membrane leading to the formation of a peroxisomal multivesicular body (pMVB). While it is unclear how the internal vesicles of a pMVB form, they appear to serve in effectively concentrating viral membrane-bound replication complexes and protecting nascent viral RNAs from host-cell defences. Here, we review briefly the biogenesis of peroxisomes and pMVBs and discuss recent studies that have begun to shed light on how components of the tombusvirus replicase exploit the molecular mechanisms...
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Adenosine triphosphate (ATP) synthase uses chemiosmotic energy across the inner mitochondrial membrane to convert adenosine diphosphate and orthophosphate into ATP, whereas genetic deletion of Sirt3 decreases mitochondrial ATP levels.... more
Adenosine triphosphate (ATP) synthase uses chemiosmotic energy across the inner mitochondrial membrane to convert adenosine diphosphate and orthophosphate into ATP, whereas genetic deletion of Sirt3 decreases mitochondrial ATP levels. Here, we investigate the mechanistic connection between SIRT3 and energy homeostasis. By using both in vitro and in vivo experiments, we demonstrate that ATP synthase F1 proteins alpha, beta, gamma, and Oligomycin sensitivity-conferring protein (OSCP) contain SIRT3-specific reversible acetyl-lysines that are evolutionarily conserved and bind to SIRT3. OSCP was further investigated and lysine 139 is a nutrient-sensitive SIRT3-dependent deacetylation target. Site directed mutants demonstrate that OSCP(K139) directs, at least in part, mitochondrial ATP production and mice lacking Sirt3 exhibit decreased ATP muscle levels, increased ATP synthase protein acetylation, and an exercise-induced stress-deficient phenotype. This work connects the aging and nutrient response, via SIRT3 direction of the mitochondrial acetylome, to the regulation of mitochondrial energy homeostasis under nutrient-stress conditions by deacetylating ATP synthase proteins. Our data suggest that acetylome signaling contributes to mitochondrial energy homeostasis by SIRT3-mediated deacetylation of ATP synthase proteins.
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Recent data from studies of peroxisome assembly and the subcellular sorting of peroxisomal matrix and membrane proteins have led to an expansion of the &#39;growth and division&#39; and &#39;endoplasmic... more
Recent data from studies of peroxisome assembly and the subcellular sorting of peroxisomal matrix and membrane proteins have led to an expansion of the &#39;growth and division&#39; and &#39;endoplasmic reticulum-vesiculation&#39; models of peroxisome biogenesis into a more flexible, unified model. Within this context, we discuss the proposed role for the endoplasmic reticulum in the formation of preperoxisomes and the potential for 15 Arabidopsis peroxin homologs to function in the biogenesis of peroxisomes in plant cells.
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Research Interests: Genetics, Data Analysis, Skeletal muscle biology, Anthropometry, Inflammation, and 23 moreAdolescent, Gene expression, Multidisciplinary, Signal Transduction, Nuclear Receptor, Humans, Protein Turnover, Female, Male, Cluster Analysis, Young Adult, Transcription Factor, PLoS one, Middle Aged, Skeletal Muscle, Adult, Reproducibility of Results, Biological markers, Gastric Bypass, Whole Body, Gene Expression Regulation, Gene expression profiling, and Differential expression
Peroxisomal ascorbate peroxidase (APX) (EC 1.11.1.11) was shown recently to sort through a subdomain of the ER (peroxisomal endoplasmic reticulum; pER), and in certain cases, alter the distribution and/or morphology of peroxisomes and pER... more
Peroxisomal ascorbate peroxidase (APX) (EC 1.11.1.11) was shown recently to sort through a subdomain of the ER (peroxisomal endoplasmic reticulum; pER), and in certain cases, alter the distribution and/or morphology of peroxisomes and pER when overexpressed transiently in Nicotiana tabacum L. cv. Bright Yellow 2 (BY-2) cells. Our goal was to gain insight into the dynamics of peroxisomal membrane protein sorting by characterizing the structure and formation of reorganized peroxisomes and pER. Specifically, we test directly the hypothesis that the observed phenomenon is due to the oligomerization of cytosol-facing, membrane-bound polypeptides, a process referred to as membrane "zippering". Results from differential detergent permeabilization experiments confirmed that peroxisomal APX is a C-terminal "tail-anchored" (Cmatrix-Ncytosol) membrane protein with a majority of the polypeptide facing the cytosol. Transient expression of several APX chimeras whose passenger polypeptides can form dimers or trimers resulted in the progressive formation of "globular" peroxisomes and circular pER membranes. Stable expression of the trimer-capable fusion protein yielded suspension cultures that reproducibly maintained a high degree of peroxisomal globules but relatively few detectable pER membranes. Electron micrographs revealed that the globules consisted of numerous individual peroxisomes, seemingly in direct contact with other peroxisomes and/or mitochondria. These peroxisomal clusters or aggregates were not observed in cells transiently expressing monomeric versions of APX. These findings indicate that the progressive, independent "zippering" of peroxisomes and pER is due to the post-sorting oligomerization of monomeric, cytosol-facing polypeptides that are integrally inserted into the membranes of "like" organelles. The dynamics of this process are discussed, especially with respect to the involvement of the microtubule cytoskeleton.