12 results on '"Sparling, David"'
Search Results
2. Inhibition of γ-secretase in adipocytes leads to altered IL-6 secretion and adipose inflammation.
- Author
-
Sparling DP, McCullough N, Pajvani U, and Humphrey MB
- Subjects
- 3T3-L1 Cells, Adipose Tissue pathology, Amyloid Precursor Protein Secretases antagonists & inhibitors, Animals, Biomarkers, Cytokines metabolism, Inflammation Mediators metabolism, Lipopolysaccharides immunology, Macrophage Activation immunology, Macrophages immunology, Macrophages metabolism, Macrophages pathology, Mice, Panniculitis etiology, Panniculitis pathology, Protease Inhibitors pharmacology, Signal Transduction, Adipocytes metabolism, Adipose Tissue metabolism, Amyloid Precursor Protein Secretases metabolism, Interleukin-6 biosynthesis, Panniculitis metabolism
- Abstract
Adipocyte-mediated inflammatory signalling has been proposed to alter adipose physiology in obesity and Type 2 diabetes mellitus. Novel targets for alteration of inflammatory signalling are needed to improve obesity-related outcomes. The γ-secretase enzyme complex has been suggested to play a role both in adipocyte function as well as in immune regulation. We hypothesized that adipocyte-specific γ-secretase inhibition could alter the inflammatory makeup of adipose tissue. We found that genetic blockade of γ-secretase in adipocytes leads to a decrease in EMR1 (F4/80) expression, as a marker of macrophage presence, in adipose tissue without changes in expression of markers of other inflammatory cell types. To explore the mechanism by which adipocytes can alter macrophage function in vitro , fully differentiated 3T3-L1 adipocytes were treated with a γ-secretase inhibitor in the presence of lipopolysaccharide (LPS) and transcription of IL6 and ccl2 (MCP1) were quantified. IL-6 expression and secretion were significantly inhibited by γ-secretase blockade, with little effect on MCP1. Preconditioned media from 3T3-L1 adipocytes treated with a γ-secretase inhibitor also alters macrophage activation but did not affect macrophage translocation in vitro . Therefore, γ-secretase inhibition in fully differentiated adipocytes can alter IL-6 signalling to macrophages, consistent with our hypothesis that that γ-secretase is involved in adipocyte-initiated inflammatory signalling cascades.
- Published
- 2020
- Full Text
- View/download PDF
3. Weight Loss Results in Increased Expression of Anti-Inflammatory Protein CRISPLD2 in Mouse Adipose Tissue.
- Author
-
Jackson RM, Griesel BA, Short KR, Sparling D, Freeman WM, and Olson AL
- Subjects
- Animals, Male, Mice, Mice, Inbred C57BL, Adipose Tissue drug effects, Cell Adhesion Molecules metabolism, Interferon Regulatory Factors metabolism, Obesity drug therapy, Weight Loss drug effects
- Abstract
Objective: Obesity is a major risk factor for cardiovascular disease, metabolic syndrome, and type 2 diabetes mellitus, whereas weight loss is associated with improved health outcomes. It is therefore important to learn how adipose contraction during weight loss contributes to improved health. It was hypothesized that adipose tissue undergoing weight loss would have a unique transcriptomic profile, expressing specific genes that might improve health., Methods: This study conducted an RNA-sequencing analysis of the epididymal adipose tissue of mice fed either a high-fat diet (HFD) or a regular rodent chow diet (RD) ad libitum for 10 weeks versus a cohort of mice fed HFD for the first 5 weeks before being swapped to an RD for the remainder of the study (swapped diet [SWAP])., Results: The swapped diet resulted in weight loss, with a parallel improvement in insulin sensitivity. RNA sequencing revealed several transcriptomic signatures distinct to adipose tissue in SWAP mice, distinguished from both RD and HFD adipose tissue. The analysis found a unique upregulated mRNA that encodes a secreted lipopolysaccharide-binding glycoprotein (CRISPLD2) in adipose tissue. Whereas cellular CRISPLD2 protein levels were unchanged, plasma CRIPSLD2 levels increased in SWAP mice following weight loss and could correlate with insulin sensitivity., Conclusions: Taken together, these data demonstrate that CRISPLD2 is a circulating adipokine that may regulate adipocyte remodeling during weight loss., (© 2019 The Obesity Society.)
- Published
- 2019
- Full Text
- View/download PDF
4. Macrophage-Derived microRNA-155 Increases in Obesity and Influences Adipocyte Metabolism by Targeting Peroxisome Proliferator-Activated Receptor Gamma.
- Author
-
Tryggestad JB, Teague AM, Sparling DP, Jiang S, and Chernausek SD
- Subjects
- 3T3-L1 Cells, Adipocytes pathology, Adolescent, Adult, Animals, Cells, Cultured, Female, Gene Expression Regulation, Humans, Lipid Metabolism genetics, Macrophages pathology, Male, Mice, MicroRNAs metabolism, Obesity metabolism, Obesity pathology, PPAR gamma metabolism, RAW 264.7 Cells, Up-Regulation genetics, Young Adult, Adipocytes metabolism, Macrophages metabolism, MicroRNAs genetics, Obesity genetics, PPAR gamma genetics
- Abstract
Objective: This study aimed to investigate cellular sources of microRNAs (miRNA) within adipose tissue and the impact of obesity on miRNA expression, as well as to examine targets of miRNAs., Methods: miRNA expression by quantitative polymerase chain reaction was examined in adipocytes, adipose tissue macrophages (ATM), and peripheral blood mononuclear cells from and individuals with normal weight and with obesity. Differentiated 3T3-L1 adipocytes were cocultured with macrophages, and 3T3-L1 and differentiated human mesenchymal stem cells were transfected with miR-155, with peroxisome proliferator-activated receptor gamma (PPAR-γ) and solute carrier family 2 member 4 (GLUT4) abundance measured via Western blot analysis., Results: Abundance of miR-155 and miR-210 was increased in ATM of participants with obesity by 6.7-fold and 2.9-fold (P = 0.002 and P = 0.013, respectively). miR-130b expression was increased 1.8-fold in ATM and 4.3-fold in adipocytes from participants with obesity (P = 0.007 and P = 0.02, respectively). PPARG mRNA expression decreased 32% (P = 0.044) in adipocytes from individuals with obesity. In 3T3-L1 cells exposed to macrophages, PPARG expression decreased 99.4% (P = 0.02). PPAR-γ protein content declined 75% (P = 0.001) in 3T3-L1 cells transfected with miR-155. GLUT4 protein levels were reduced by 55% (P = 0.021) in differentiated human mesenchymal stem cells exposed to miR-155., Conclusions: Adipose tissue miRNAs are influenced in a cell type-specific fashion by obesity, with macrophage miR-155 potentially impacting neighboring adipocytes., (© 2019 The Obesity Society (TOS).)
- Published
- 2019
- Full Text
- View/download PDF
5. Continuous Glucose Monitoring Profiles in Healthy Nondiabetic Participants: A Multicenter Prospective Study.
- Author
-
Shah VN, DuBose SN, Li Z, Beck RW, Peters AL, Weinstock RS, Kruger D, Tansey M, Sparling D, Woerner S, Vendrame F, Bergenstal R, Tamborlane WV, Watson SE, and Sherr J
- Subjects
- Adolescent, Adult, Age Factors, Aged, Benchmarking, Child, Circadian Rhythm, Female, Healthy Volunteers, Humans, Male, Middle Aged, Prospective Studies, Reference Values, Sex Factors, Young Adult, Blood Glucose analysis, Blood Glucose Self-Monitoring methods, Hyperglycemia diagnosis, Hypoglycemia diagnosis, Monitoring, Physiologic methods
- Abstract
Context: Use of continuous glucose monitoring (CGM) is increasing for insulin-requiring patients with diabetes. Although data on glycemic profiles of healthy, nondiabetic individuals exist for older sensors, assessment of glycemic metrics with new-generation CGM devices is lacking., Objective: To establish reference sensor glucose ranges in healthy, nondiabetic individuals across different age groups using a current generation CGM sensor., Design: Multicenter, prospective study., Setting: Twelve centers within the T1D Exchange Clinic Network., Patients or Participants: Nonpregnant, healthy, nondiabetic children and adults (age ≥6 years) with nonobese body mass index., Intervention: Each participant wore a blinded Dexcom G6 CGM, with once-daily calibration, for up to 10 days., Main Outcome Measures: CGM metrics of mean glucose, hyperglycemia, hypoglycemia, and glycemic variability., Results: A total of 153 participants (age 7 to 80 years) were included in the analyses. Mean average glucose was 98 to 99 mg/dL (5.4 to 5.5 mmol/L) for all age groups except those over 60 years, in whom mean average glucose was 104 mg/dL (5.8 mmol/L). The median time between 70 to 140 mg/dL (3.9 to 7.8 mmol/L) was 96% (interquartile range, 93 to 98). Mean within-individual coefficient of variation was 17 ± 3%. Median time spent with glucose levels >140 mg/dL was 2.1% (30 min/d), and median time spent with glucose levels <70 mg/dL (3.9 mmol/L) was 1.1% (15 min/d)., Conclusion: By assessing across age groups in a healthy, nondiabetic population, normative sensor glucose data have been derived and will be useful as a benchmark for future research studies., (Copyright © 2019 Endocrine Society.)
- Published
- 2019
- Full Text
- View/download PDF
6. Congenital hypothyroidism and thyroid dyshormonogenesis: a case report of siblings with a newly identified mutation in thyroperoxidase.
- Author
-
Sparling DP, Fabian K, Harik L, Jobanputra V, Anyane-Yeboa K, Oberfield SE, and Fennoy I
- Subjects
- Congenital Hypothyroidism pathology, Congenital Hypothyroidism surgery, Humans, Infant, Newborn, Male, Prognosis, Siblings, Thyroid Gland metabolism, Thyroidectomy, Autoantigens genetics, Congenital Hypothyroidism genetics, Iodide Peroxidase genetics, Iron-Binding Proteins genetics, Mutation genetics, Thyroid Gland abnormalities, Thyroid Hormones blood
- Abstract
Background: Thyroid dyshormonogenesis continues to be a significant cause of congenital hypothyroidism. Over time, forms of thyroid dyshormonogenesis can result in goiter, which can lead to difficult management decisions as the pathologic changes can both mimic or lead to thyroid cancer., Methods: Herein we describe the cases of two brothers diagnosed with congenital hypothyroidism, with initial findings consistent with thyroid dyshormonogenesis. One brother eventually developed multinodular goiter with complex pathology on biopsy, resulting in thyroidectomy., Results: Whole exome sequencing revealed the brothers carry a novel frameshift mutation in thyroperoxidase; the mutation, while not previously described, was likely both deleterious and pathogenic. Conlcusions: These cases highlight the complex pathology that can occur within thyroid dyshormonogenesis, with similar appearance to possible thyroid cancer, leading to complex management decisions. They also highlight the role that a genetic diagnosis can play in interpreting the impact of dyshormonogenesis on nodular thyroid development, and the need for long-term follow-up in these patients.
- Published
- 2016
- Full Text
- View/download PDF
7. mTORC1-independent Raptor prevents hepatic steatosis by stabilizing PHLPP2.
- Author
-
Kim K, Qiang L, Hayden MS, Sparling DP, Purcell NH, and Pajvani UB
- Subjects
- Animals, Blood Glucose metabolism, Blotting, Western, Chromatography, Gel, Diet, High-Fat, Fatty Liver genetics, Fatty Liver metabolism, Immunoprecipitation, Insulin metabolism, Mechanistic Target of Rapamycin Complex 1, Mice, Multiprotein Complexes, Non-alcoholic Fatty Liver Disease metabolism, Obesity metabolism, Phosphoprotein Phosphatases metabolism, Regulatory-Associated Protein of mTOR, Reverse Transcriptase Polymerase Chain Reaction, Signal Transduction, TOR Serine-Threonine Kinases, Triglycerides metabolism, beta-Transducin Repeat-Containing Proteins metabolism, Adaptor Proteins, Signal Transducing genetics, Hepatocytes metabolism, Lipogenesis genetics, Liver metabolism, Non-alcoholic Fatty Liver Disease genetics, Obesity genetics, Oncogene Protein v-akt metabolism
- Abstract
Mechanistic target of rapamycin complex 1 (mTORC1), defined by the presence of Raptor, is an evolutionarily conserved and nutrient-sensitive regulator of cellular growth and other metabolic processes. To date, all known functions of Raptor involve its scaffolding mTOR kinase with substrate. Here we report that mTORC1-independent ('free') Raptor negatively regulates hepatic Akt activity and lipogenesis. Free Raptor levels in liver decline with age and in obesity; restoration of free Raptor levels reduces liver triglyceride content, through reduced β-TrCP-mediated degradation of the Akt phosphatase, PHLPP2. Commensurately, forced PHLPP2 expression ameliorates hepatic steatosis in diet-induced obese mice. These data suggest that the balance of free and mTORC1-associated Raptor governs hepatic lipid accumulation, and uncover the potentially therapeutic role of PHLPP2 activators in non-alcoholic fatty liver disease.
- Published
- 2016
- Full Text
- View/download PDF
8. Adipocyte-specific blockade of gamma-secretase, but not inhibition of Notch activity, reduces adipose insulin sensitivity.
- Author
-
Sparling DP, Yu J, Kim K, Zhu C, Brachs S, Birkenfeld AL, and Pajvani UB
- Abstract
Objective: As the obesity pandemic continues to expand, novel molecular targets to reduce obesity-related insulin resistance and Type 2 Diabetes (T2D) continue to be needed. We have recently shown that obesity is associated with reactivated liver Notch signaling, which, in turn, increases hepatic insulin resistance, opening up therapeutic avenues for Notch inhibitors to be repurposed for T2D. Herein, we tested the systemic effects of γ-secretase inhibitors (GSIs), which prevent endogenous Notch activation, and confirmed these effects through creation and characterization of two different adipocyte-specific Notch loss-of-function mouse models through genetic ablation of the Notch transcriptional effector Rbp-Jk (A-Rbpj) and the obligate γ-secretase component Nicastrin (A-Nicastrin)., Methods: Glucose homeostasis and both local adipose and systemic insulin sensitivity were examined in GSI-treated, A-Rbpj and A-Nicastrin mice, as well as vehicle-treated or control littermates, with complementary in vitro studies in primary hepatocytes and 3T3-L1 adipocytes., Results: GSI-treatment increases hepatic insulin sensitivity in obese mice but leads to reciprocal lowering of adipose glucose disposal. While A-Rbpj mice show normal body weight, adipose development and mass and unchanged adipose insulin sensitivity as control littermates, A-Nicastrin mice are relatively insulin-resistant, mirroring the GSI effect on adipose insulin action., Conclusions: Notch signaling is dispensable for normal adipocyte function, but adipocyte-specific γ-secretase blockade reduces adipose insulin sensitivity, suggesting that specific Notch inhibitors would be preferable to GSIs for application in T2D.
- Published
- 2015
- Full Text
- View/download PDF
9. GLUT4 enhancer factor (GEF) interacts with MEF2A and HDAC5 to regulate the GLUT4 promoter in adipocytes.
- Author
-
Sparling DP, Griesel BA, Weems J, and Olson AL
- Subjects
- Adipocytes cytology, Animals, COS Cells, Chlorocebus aethiops, DNA-Binding Proteins genetics, Dimerization, Glucose Transporter Type 4 genetics, Histone Deacetylases genetics, MEF2 Transcription Factors, Mice, Mice, Transgenic, Myogenic Regulatory Factors genetics, Phosphorylation, Protein Binding physiology, Protein Isoforms genetics, Protein Isoforms metabolism, Transcription Factors genetics, Adipocytes metabolism, DNA-Binding Proteins metabolism, Glucose Transporter Type 4 metabolism, Histone Deacetylases metabolism, Myogenic Regulatory Factors metabolism, Promoter Regions, Genetic, Transcription Factors metabolism
- Abstract
The insulin-responsive glucose transporter, GLUT4, is regulated in various physiologic states at the transcriptional level. When expressed in transgenic mice, the human GLUT4 promoter is governed by two cis-acting sequences: an MEF2 binding domain and Domain I, that function both as positive and negative regulators depending on the physiologic state. MEF2 proteins and GLUT4 enhancer factor (GEF) are known ligands for these cis-acting elements, but their mechanism of action is unclear. To begin to understand this important process, we have characterized GEF structural domains and its interactions with the MEF2A isoform. We find that the C terminus of GEF comprises its DNA-binding domain, but does not contribute to GEF homo-oligomerization. We also have found that GEF dimerizes with increased affinity to a hypophosphorylated form of MEF2A. Furthermore, we demonstrated that MEF2A binding to its cognate binding site can increase the DNA binding activity of GEF to Domain I, suggesting a novel mechanism for MEF2A transcriptional activation. Finally, we have demonstrated that the transcriptional co-repressor HDAC5 can interact with GEF in the absence of MEF2 proteins and specifically inhibit GLUT4 promoter activity. These findings lead to the hypothesis that GEF and the MEF2 proteins form a complex on the GLUT4 promoter that allows for recruitment of transcriptional co-regulators (repressors and/or activators) to control GLUT4 promoter activity.
- Published
- 2008
- Full Text
- View/download PDF
10. Hyperphosphorylation of MEF2A in primary adipocytes correlates with downregulation of human GLUT4 gene promoter activity.
- Author
-
Sparling DP, Griesel BA, and Olson AL
- Subjects
- Adipose Tissue metabolism, Animals, Binding, Competitive, COS Cells, Cells, Cultured, Chlorocebus aethiops, Glucose Transporter Type 4 metabolism, Humans, MEF2 Transcription Factors, Mice, Mice, Transgenic, Phosphorylation, Transcription, Genetic, Adipocytes metabolism, Down-Regulation, Glucose Transporter Type 4 genetics, Myogenic Regulatory Factors metabolism, Promoter Regions, Genetic physiology
- Abstract
GLUT4 promoter activity is regulated by hormonal, metabolic, and tissue-specific controls. This complicates the study of GLUT4 gene transcription, as no cell culture model adequately recapitulates these extracellular regulators. While investigating cultured primary adipocytes as a model system for GLUT4 transcription, we observed that GLUT4 mRNA was specifically and rapidly downregulated upon tissue dispersal. Downregulation of GLUT4 mRNA was mediated in part by loss of regulatory control by the trans-acting factors that control GLUT4 transcriptional activity [the myocyte enhancer factor 2 (MEF2) transcription factor family and the GLUT4 enhancer factor] and their cognate DNA binding sites in transgenic mice. The differences in GLUT4 transcription when whole adipose tissue and cell culture model systems are compared can be correlated to a posttranslational phosphorylation of the transcription factor MEF2A. The difference in the MEF2A phosphorylation state in whole tissue vs. isolated cells may provide a further basis for the development of an in vitro system that could recapitulate fully regulated GLUT4 promoter activity. Development of an in vitro system to reconstitute GLUT4 transcriptional regulation will further efforts to discern the molecular mechanisms that underlie GLUT4 expression.
- Published
- 2007
- Full Text
- View/download PDF
11. Exercise increases MEF2- and GEF DNA-binding activity in human skeletal muscle.
- Author
-
McGee SL, Sparling D, Olson AL, and Hargreaves M
- Subjects
- Adult, DNA-Binding Proteins genetics, Gene Expression Regulation, Glucose Transporter Type 4 genetics, Humans, MEF2 Transcription Factors, Male, Myogenic Regulatory Factors genetics, Promoter Regions, Genetic genetics, Transcription Factors genetics, DNA metabolism, DNA-Binding Proteins metabolism, Exercise physiology, Muscle, Skeletal metabolism, Myogenic Regulatory Factors metabolism, Transcription Factors metabolism
- Abstract
Overexpression of GLUT4 exclusively in skeletal muscle enhances insulin action and improves glucose homeostasis. Transgenic studies have discovered two regions on the GLUT4 promoter conserved across several species that are required for normal GLUT4 expression in skeletal muscle. These regions contain binding motifs for the myocyte enhancer factor 2 (MEF2) family and GLUT4 enhancer factor (GEF). A single bout of exercise increases both GLUT4 transcription and mRNA abundance; however, the molecular mechanisms mediating this response remain largely unexplored. Thus, the aim of this study was to determine whether a single, acute bout of exercise increased the DNA-binding activities of MEF2 and GEF in human skeletal muscle. Seven subjects performed 60 min of cycling at approximately 70% of VO2peak. After exercise, the DNA-binding activities of both the MEF2A/D heterodimer and GEF were increased (P<0.05). There was no change in nuclear MEF2D or GEF abundance after exercise, but nuclear MEF2A abundance was increased (P<0.05). These data demonstrate that exercise increases MEF2 and GEF DNA binding and imply that these transcription factors could be potential targets for modulating GLUT4 expression in human skeletal muscle.
- Published
- 2006
- Full Text
- View/download PDF
12. Regulation of muscle GLUT4 enhancer factor and myocyte enhancer factor 2 by AMP-activated protein kinase.
- Author
-
Holmes BF, Sparling DP, Olson AL, Winder WW, and Dohm GL
- Subjects
- AMP-Activated Protein Kinases, Aminoimidazole Carboxamide analogs & derivatives, Aminoimidazole Carboxamide pharmacology, Animals, Biological Transport drug effects, Cell Nucleus chemistry, Cell Nucleus metabolism, DNA metabolism, DNA-Binding Proteins analysis, DNA-Binding Proteins physiology, Enzyme Activation drug effects, Humans, MEF2 Transcription Factors, Muscle, Skeletal chemistry, Muscle, Skeletal ultrastructure, Myogenic Regulatory Factors analysis, Myogenic Regulatory Factors physiology, Phosphorylation, Promoter Regions, Genetic genetics, RNA, Messenger analysis, Rats, Recombinant Proteins metabolism, Ribonucleotides pharmacology, Transcription Factors analysis, Transcription Factors physiology, DNA-Binding Proteins genetics, Gene Expression Regulation drug effects, Gene Expression Regulation physiology, Glucose Transporter Type 4 genetics, Multienzyme Complexes metabolism, Myogenic Regulatory Factors genetics, Protein Serine-Threonine Kinases metabolism, Transcription Factors genetics
- Abstract
As the primary glucose transporter in skeletal muscle, GLUT4 is an important factor in the regulation of blood glucose. We previously reported that stimulation of AMP-activated protein kinase (AMPK) with 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) increased GLUT4 expression in muscle. GLUT4 enhancer factor (GEF) and myocyte enhancer factor 2 (MEF2) have been shown to be important for normal GLUT4 expression because deletion or truncation of the consensus sequences on the promoter causes depressed GLUT4 mRNA expression. This led to the current study to investigate possible roles for GEF and MEF2 in mediating the activation of GLUT4 gene transcription in response to AMPK. Here we show that, although AMPK does not appear to phosphorylate MEF2A, AMPK directly phosphorylates the GEF protein in vitro. MEF2 and GEF are activated in response to AMPK as we observed translocation of both to the nucleus after AICAR treatment. Nuclear MEF2 protein content was increased after 2 h, and GEF protein was increased in the nucleus 1 and 2 h post-AICAR treatment. Last, GEF and MEF2 increase in binding to the GLUT4 promoter within 2 h after AICAR treatment. Thus we conclude that GEF and MEF2 mediate the AMPK-induced increase in transcription of skeletal muscle GLUT4. AMPK can phosphorylate GEF and in response to AICAR, GEF, and MEF2 translocate to the nucleus and have increased binding to the GLUT4 promoter.
- Published
- 2005
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.