IU Indianapolis ScholarWorks :: Browsing by Author "Linnemann, Amelia K."

Browsing by Author "Linnemann, Amelia K."

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Aberrant gene expression induced by a high fat diet is linked to H3K9 acetylation in the promoter-proximal region
(Elsevier, 2021-03) Morral, Núria; Liu, Sheng; Conteh, Abass M.; Chu, Xiaona; Wang, Yue; Dong, X. Charlie; Liu, Yunlong; Linnemann, Amelia K.; Wan, Jun; Medical and Molecular Genetics, School of Medicine
Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, with an estimated global prevalence of 1 in 4 individuals. Aberrant transcriptional control of gene expression is central to the pathophysiology of metabolic diseases. However, the molecular mechanisms leading to gene dysregulation are not well understood. Histone modifications play important roles in the control of transcription. Acetylation of histone 3 at lysine 9 (H3K9ac) is associated with transcriptional activity and is implicated in transcript elongation by controlling RNA polymerase II (RNAPII) pause-release. Hence, changes in this histone modification may shed information on novel pathways linking transcription control and metabolic dysfunction. Here, we carried out genome-wide analysis of H3K9ac in the liver of mice fed a control or a high-fat diet (an animal model of NAFLD), and asked whether this histone mark associates with changes in gene expression. We found that over 70% of RNAPII peaks in promoter-proximal regions overlapped with H3K9ac, consistent with a role of H3K9ac in the regulation of transcription. When comparing high-fat with control diet, approximately 17% of the differentially expressed genes were associated with changes in H3K9ac in their promoters, showing a strong correlation between changes in H3K9ac signal and gene expression. Overall, our data indicate that in response to a high-fat diet, dysregulated gene expression of a subset of genes may be attributable to changes in transcription elongation driven by H3K9ac. Our results point at an added mechanism of gene regulation that may be important in the development of metabolic diseases.
Allergic airway recall responses require IL-9 from resident memory CD4+ T cells
(American Association for the Advancement of Science, 2022) Ulrich, Benjamin J.; Kharwadkar, Rakshin; Chu, Michelle; Pajulas, Abigail; Muralidharan, Charanya; Koh, Byunghee; Fu, Yongyao; Gao, Hongyu; Hayes, Tristan A.; Zhou, Hong-Ming; Goplen, Nick P.; Nelson, Andrew S.; Liu, Yunlong; Linnemann, Amelia K.; Turner, Matthew J.; Licona-Limón, Paula; Flavell, Richard A.; Sun, Jie; Kaplan, Mark H.; Microbiology and Immunology, School of Medicine
Asthma is a chronic inflammatory lung disease with intermittent flares predominately mediated through memory T cells. Yet, the identity of long-term memory cells that mediate allergic recall responses is not well defined. In this report, using a mouse model of chronic allergen exposure followed by an allergen-free rest period, we characterized a subpopulation of CD4+ T cells that secreted IL-9 as an obligate effector cytokine. IL-9-secreting cells had a resident memory T cell phenotype, and blocking IL-9 during a recall challenge or deleting IL-9 from T cells significantly diminished airway inflammation and airway hyperreactivity. T cells secreted IL-9 in an allergen recall-specific manner, and secretion was amplified by IL-33. Using scRNA-seq and scATAC-seq, we defined the cellular identity of a distinct population of T cells with a proallergic cytokine pattern. Thus, in a recall model of allergic airway inflammation, IL-9 secretion from a multicytokine-producing CD4+ T cell population was required for an allergen recall response.
Author Correction: Super-resolution microscopy compatible fluorescent probes reveal endogenous glucagon-like peptide-1 receptor distribution and dynamics
(Nature Publishing Group, 2020-10-09) Ast, Julia; Arvaniti, Anastasia; Fine, Nicholas H. F.; Nasteska, Daniela; Ashford, Fiona B.; Stamataki, Zania; Koszegi, Zsombor; Bacon, Andrea; Jones, Ben J.; Lucey, Maria A.; Sasaki, Shugo; Brierley, Daniel I.; Hastoy, Benoit; Tomas, Alejandra; D’Agostino, Giuseppe; Reimann, Frank; Lynn, Francis C.; Reissaus, Christopher A.; Linnemann, Amelia K.; D’Este, Elisa; Calebiro, Davide; Trapp, Stefan; Johnsson, Kai; Podewin, Tom; Broichhagen, Johannes; Hodson, David J.; Pediatrics, School of Medicine
Editorial: Pancreas Imaging Across the Spectrum
(Frontiers Media, 2021-01-03) Linnemann, Amelia K.; Poitout, Vincent; Rutter, Guy A.; Pediatrics, School of Medicine
Expanded LUXendin Color Palette for GLP1R Detection and Visualization In Vitro and In Vivo
(American Chemical Society, 2022-04-04) Ast, Julia; Novak, Alissa N.; Podewin, Tom; Fine, Nicholas H.F.; Jones, Ben; Tomas, Alejandra; Birke, Ramona; Roßmann, Kilian; Eichhorst, Jenny; Lehmann, Martin; Linnemann, Amelia K.; Hodson, David J.; Broichhagen, Johannes; Pediatrics, School of Medicine
The glucagon-like peptide-1 receptor (GLP1R) is expressed in peripheral tissues and the brain, where it exerts pleiotropic actions on metabolic and inflammatory processes. Detection and visualization of GLP1R remains challenging, partly due to a lack of validated reagents. Previously, we generated LUXendins, antagonistic red and far-red fluorescent probes for specific labeling of GLP1R in live and fixed cells/tissues. We now extend this concept to the green and near-infrared color ranges by synthesizing and testing LUXendin492, LUXendin551, LUXendin615, and LUXendin762. All four probes brightly and specifically label GLP1R in cells and pancreatic islets. Further, LUXendin551 acts as a chemical beta cell reporter in preclinical rodent models, while LUXendin762 allows noninvasive imaging, highlighting differentially accessible GLP1R populations. We thus expand the color palette of LUXendins to seven different spectra, opening up a range of experiments using wide-field microscopy available in most labs through super-resolution imaging and whole animal imaging. With this, we expect that LUXendins will continue to generate novel and specific insights into GLP1R biology.
Factor VIII trafficking to CD4+ T cells shapes its immunogenicity and requires several types of antigen-presenting cells
(American Society of Hematology, 2023) Kaczmarek, Radoslaw; Piñeros, Annie R.; Patterson, Paige E.; Bertolini, Thais B.; Perrin, George Q.; Sherman, Alexandra; Born, Jameson; Arisa, Sreevani; Arvin, Matthew C.; Kamocka, Malgorzata M.; Martinez, Michelle M.; Dunn, Kenneth W.; Quinn, Sean M.; Morris, Johnathan J.; Wilhelm, Amelia R.; Kaisho, Tsuneyasu; Munoz-Melero, Maite; Biswas, Moanaro; Kaplan, Mark H.; Linnemann, Amelia K.; George, Lindsey A.; Camire, Rodney M.; Herzog, Roland W.; Pediatrics, School of Medicine
Despite >80 years of clinical experience with coagulation factor VIII (FVIII) inhibitors, surprisingly little is known about the in vivo mechanism of this most serious complication of replacement therapy for hemophilia A. These neutralizing antidrug alloantibodies arise in ∼30% of patients. Inhibitor formation is T-cell dependent, but events leading up to helper T-cell activation have been elusive because of, in part, the complex anatomy and cellular makeup of the spleen. Here, we show that FVIII antigen presentation to CD4+ T cells critically depends on a select set of several anatomically distinct antigen-presenting cells, whereby marginal zone B cells and marginal zone and marginal metallophilic macrophages but not red pulp macrophages (RPMFs) participate in shuttling FVIII to the white pulp in which conventional dendritic cells (DCs) prime helper T cells, which then differentiate into follicular helper T (Tfh) cells. Toll-like receptor 9 stimulation accelerated Tfh cell responses and germinal center and inhibitor formation, whereas systemic administration of FVIII alone in hemophilia A mice increased frequencies of monocyte-derived and plasmacytoid DCs. Moreover, FVIII enhanced T-cell proliferation to another protein antigen (ovalbumin), and inflammatory signaling-deficient mice were less likely to develop inhibitors, indicating that FVIII may have intrinsic immunostimulatory properties. Ovalbumin, which, unlike FVIII, is absorbed into the RPMF compartment, fails to elicit T-cell proliferative and antibody responses when administered at the same dose as FVIII. Altogether, we propose that an antigen trafficking pattern that results in efficient in vivo delivery to DCs and inflammatory signaling, shape the immunogenicity of FVIII.
Fluorescently conjugated annular fibrin clot for multiplexed real-time digestion analysis
(Royal Society of Chemistry, 2021-12) Zeng, Ziqian; Nallan Chakravarthula, Tanmaye; Muralidharan, Charanya; Hall, Abigail; Linnemann, Amelia K.; Alves, Nathan J.; Emergency Medicine, School of Medicine
Impaired fibrinolysis has long been considered as a risk factor for venous thromboembolism. Fibrin clots formed at physiological concentrations are promising substrates for monitoring fibrinolytic performance as they offer clot microstructures resembling in vivo. Here we introduce a fluorescently labeled fibrin clot lysis assay which leverages a unique annular clot geometry assayed using a microplate reader. A physiologically relevant fibrin clotting formulation was explored to achieve high assay sensitivity while minimizing labeling impact as fluorescence isothiocyanate (FITC)-fibrin(ogen) conjugations significantly affect both fibrin polymerization and fibrinolysis. Clot characteristics were examined using thromboelastography (TEG), turbidity, scanning electron microscopy, and confocal microscopy. Sample fibrinolytic activities at varying plasmin, plasminogen, and tissue plasminogen activator (tPA) concentrations were assessed in the present study and results were compared to an S2251 chromogenic assay. The optimized physiologically relevant clot substrate showed minimal reporter-conjugation impact with nearly physiological clot properties. The assay demonstrated good reproducibility, wide working range, kinetic read ability, low limit of detection, and the capability to distinguish fibrin binding-related lytic performance. In combination with its ease for multiplexing, it also has applications as a convenient platform for assessing patient fibrinolytic potential and screening thrombolytic drug activities in personalized medical applications.
An In Vivo Zebrafish Model for Interrogating ROS-Mediated Pancreatic β-Cell Injury, Response, and Prevention
(Hindawi Publishing Corporation, 2018-03-28) Kulkarni, Abhishek A.; Conteh, Abass M.; Sorrell, Cody A.; Mirmira, Anjali; Tersey, Sarah A.; Mirmira, Raghavendra G.; Linnemann, Amelia K.; Anderson, Ryan M.; Biochemistry and Molecular Biology, School of Medicine
It is well known that a chronic state of elevated reactive oxygen species (ROS) in pancreatic β-cells impairs their ability to release insulin in response to elevated plasma glucose. Moreover, at its extreme, unmitigated ROS drives regulated cell death. This dysfunctional state of ROS buildup can result both from genetic predisposition and environmental factors such as obesity and overnutrition. Importantly, excessive ROS buildup may underlie metabolic pathologies such as type 2 diabetes mellitus. The ability to monitor ROS dynamics in β-cells in situ and to manipulate it via genetic, pharmacological, and environmental means would accelerate the development of novel therapeutics that could abate this pathology. Currently, there is a lack of models with these attributes that are available to the field. In this study, we use a zebrafish model to demonstrate that ROS can be generated in a β-cell-specific manner using a hybrid chemical genetic approach. Using a transgenic nitroreductase-expressing zebrafish line, Tg(ins:Flag-NTR)s950 , treated with the prodrug metronidazole (MTZ), we found that ROS is rapidly and explicitly generated in β-cells. Furthermore, the level of ROS generated was proportional to the dosage of prodrug added to the system. At high doses of MTZ, caspase 3 was rapidly cleaved, β-cells underwent regulated cell death, and macrophages were recruited to the islet to phagocytose the debris. Based on our findings, we propose a model for the mechanism of NTR/MTZ action in transgenic eukaryotic cells and demonstrate the robust utility of this system to model ROS-related disease pathology.
Inhibition of 12/15-Lipoxygenase Protects Against β-Cell Oxidative Stress and Glycemic Deterioration in Mouse Models of Type 1 Diabetes
(American Diabetes Association, 2017-11) Hernandez-Perez, Marimar; Chopra, Gaurav; Fine, Jonathan; Conteh, Abass M.; Anderson, Ryan M.; Linnemann, Amelia K.; Benjamin, Chanelle; Nelson, Jennifer B.; Benninger, Kara S.; Nadler, Jerry L.; Maloney, David J.; Tersey, Sarah A.; Mirmira, Raghavendra G.; Pediatrics, School of Medicine
Islet β-cell dysfunction and aggressive macrophage activity are early features in the pathogenesis of type 1 diabetes (T1D). 12/15-Lipoxygenase (12/15-LOX) is induced in β-cells and macrophages during T1D and produces proinflammatory lipids and lipid peroxides that exacerbate β-cell dysfunction and macrophage activity. Inhibition of 12/15-LOX provides a potential therapeutic approach to prevent glycemic deterioration in T1D. Two inhibitors recently identified by our groups through screening efforts, ML127 and ML351, have been shown to selectively target 12/15-LOX with high potency. Only ML351 exhibited no apparent toxicity across a range of concentrations in mouse islets, and molecular modeling has suggested reduced promiscuity of ML351 compared with ML127. In mouse islets, incubation with ML351 improved glucose-stimulated insulin secretion in the presence of proinflammatory cytokines and triggered gene expression pathways responsive to oxidative stress and cell death. Consistent with a role for 12/15-LOX in promoting oxidative stress, its chemical inhibition reduced production of reactive oxygen species in both mouse and human islets in vitro. In a streptozotocin-induced model of T1D in mice, ML351 prevented the development of diabetes, with coincident enhancement of nuclear Nrf2 in islet cells, reduced β-cell oxidative stress, and preservation of β-cell mass. In the nonobese diabetic mouse model of T1D, administration of ML351 during the prediabetic phase prevented dysglycemia, reduced β-cell oxidative stress, and increased the proportion of anti-inflammatory macrophages in insulitis. The data provide the first evidence to date that small molecules that target 12/15-LOX can prevent progression of β-cell dysfunction and glycemic deterioration in models of T1D.
Interleukin 6 protects pancreatic β cells from apoptosis by stimulation of autophagy
(Federation of American Societies for Experimental Biology, 2017-09) Linnemann, Amelia K.; Blumer, Joseph; Marasco, Michelle R.; Battiola, Therese J.; Umhoefer, Heidi M.; Han, Jee Young; Lamming, Dudley W.; Davis, Dawn Belt; Pediatrics, School of Medicine
IL-6 is a pleiotropic cytokine with complex roles in inflammation and metabolic disease. The role of IL-6 as a pro- or anti-inflammatory cytokine is still unclear. Within the pancreatic islet, IL-6 stimulates secretion of the prosurvival incretin hormone glucagon-like peptide 1 (GLP-1) by α cells and acts directly on β cells to stimulate insulin secretion in vitro. Uncovering physiologic mechanisms promoting β-cell survival under conditions of inflammation and stress can identify important pathways for diabetes prevention and treatment. Given the established role of GLP-1 in promoting β-cell survival, we hypothesized that IL-6 may also directly protect β cells from apoptosis. Herein, we show that IL-6 robustly activates signal transducer and activator of transcription 3 (STAT3), a transcription factor that is involved in autophagy. IL-6 stimulates LC3 conversion and autophagosome formation in cultured β cells. In vivo IL-6 infusion stimulates a robust increase in lysosomes in the pancreas that is restricted to the islet. Autophagy is critical for β-cell homeostasis, particularly under conditions of stress and increased insulin demand. The stimulation of autophagy by IL-6 is regulated via multiple complementary mechanisms including inhibition of mammalian target of rapamycin complex 1 (mTORC1) and activation of Akt, ultimately leading to increases in autophagy enzyme production. Pretreatment with IL-6 renders β cells resistant to apoptosis induced by proinflammatory cytokines, and inhibition of autophagy with chloroquine prevents the ability of IL-6 to protect from apoptosis. Importantly, we find that IL-6 can activate STAT3 and the autophagy enzyme GABARAPL1 in human islets. We also see evidence of decreased IL-6 pathway signaling in islets from donors with type 2 diabetes. On the basis of our results, we propose direct stimulation of autophagy as a novel mechanism for IL-6-mediated protection of β cells from stress-induced apoptosis.—Linnemann, A. K., Blumer, J., Marasco, M. R., Battiola, T. J., Umhoefer, H. M., Han, J. Y., Lamming, D. W., Davis, D. B. Interleukin 6 protects pancreatic β cells from apoptosis by stimulation of autophagy.

Browsing by Author "Linnemann, Amelia K."

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