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Manganese Detoxification by MntE Is Critical for Resistance to Oxidative Stress and Virulence of .
Grunenwald CM, Choby JE, Juttukonda LJ, Beavers WN, Weiss A, Torres VJ, Skaar EP
(2019) MBio 10:
MeSH Terms: Animals, Cation Transport Proteins, Disease Models, Animal, Gene Expression Regulation, Bacterial, Homeostasis, Iron, Manganese, Mice, Inbred BALB C, Microbial Viability, Oxidative Stress, Staphylococcal Infections, Staphylococcus aureus, Transcription Factors, Transcription, Genetic, Virulence
Show Abstract · Added April 2, 2019
Manganese (Mn) is an essential micronutrient critical for the pathogenesis of , a significant cause of human morbidity and mortality. Paradoxically, excess Mn is toxic; therefore, maintenance of intracellular Mn homeostasis is required for survival. Here we describe a Mn exporter in , MntE, which is a member of the cation diffusion facilitator (CDF) protein family and conserved among Gram-positive pathogens. Upregulation of transcription in response to excess Mn is dependent on the presence of MntR, a transcriptional repressor of the Mn uptake system. Inactivation of or leads to reduced growth in media supplemented with Mn, demonstrating MntE is required for detoxification of excess Mn. Inactivation of results in elevated levels of intracellular Mn, but reduced intracellular iron (Fe) levels, supporting the hypothesis that MntE functions as a Mn efflux pump and Mn efflux influences Fe homeostasis. Strains inactivated for are more sensitive to the oxidants NaOCl and paraquat, indicating Mn homeostasis is critical for resisting oxidative stress. Furthermore, and are required for full virulence of during infection, suggesting experiences Mn toxicity Combined, these data support a model in which MntR controls Mn homeostasis by balancing transcriptional repression of and induction of , both of which are critical for pathogenesis. Thus, Mn efflux contributes to bacterial survival and virulence during infection, establishing MntE as a potential antimicrobial target and expanding our understanding of Mn homeostasis. Manganese (Mn) is generally viewed as a critical nutrient that is beneficial to pathogenic bacteria due to its function as an enzymatic cofactor and its capability of acting as an antioxidant; yet paradoxically, high concentrations of this transition metal can be toxic. In this work, we demonstrate utilizes the cation diffusion facilitator (CDF) family protein MntE to alleviate Mn toxicity through efflux of excess Mn. Inactivation of leads to a significant reduction in resistance to oxidative stress and mediated mortality within a mouse model of systemic infection. These results highlight the importance of MntE-mediated Mn detoxification in intracellular Mn homeostasis, resistance to oxidative stress, and virulence. Therefore, this establishes MntE as a potential target for development of anti- therapeutics.
Copyright © 2019 Grunenwald et al.
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15 MeSH Terms
Water Homeostasis and Cell Volume Maintenance and Regulation.
Delpire E, Gagnon KB
(2018) Curr Top Membr 81: 3-52
MeSH Terms: Animals, Cell Size, Homeostasis, Humans, Signal Transduction
Show Abstract · Added April 2, 2019
From early unicellular organisms that formed in salty water environments to complex organisms that live on land away from water, cells have had to protect a homeostatic internal environment favorable to the biochemical reactions necessary for life. In this chapter, we will outline what steps were necessary to conserve the water within our cells and how mechanisms have evolved to maintain and regulate our cellular and organismal volume. We will first examine whole body water homeostasis and the relationship between kidney function, regulation of blood pressure, and blood filtration in the process of producing urine. We will then discuss how the composition of the lipid-rich bilayer affects its permeability to water and salts, and how the cell uses this differential to drive physiological and biochemical cellular functions. The capacity to maintain cell volume is vital to epithelial transport, neurotransmission, cell cycle, apoptosis, and cell migration. Finally, we will wrap up the chapter by discussing in some detail specific channels, cotransporters, and exchangers that have evolved to facilitate the movement of cations and anions otherwise unable to cross the lipid-rich bilayer and that are involved in maintaining or regulating cell volume.
Copyright © 2018 Elsevier Inc. All rights reserved.
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MeSH Terms
Metformin reduces liver glucose production by inhibition of fructose-1-6-bisphosphatase.
Hunter RW, Hughey CC, Lantier L, Sundelin EI, Peggie M, Zeqiraj E, Sicheri F, Jessen N, Wasserman DH, Sakamoto K
(2018) Nat Med 24: 1395-1406
MeSH Terms: Adenosine Monophosphate, Aminoimidazole Carboxamide, Animals, Base Sequence, Chickens, Disease Models, Animal, Fructose-Bisphosphatase, Glucose, Glucose Intolerance, Homeostasis, Humans, Hypoglycemia, Liver, Metformin, Mice, Inbred C57BL, Mutation, Obesity, Prodrugs, Ribonucleotides
Show Abstract · Added March 26, 2019
Metformin is a first-line drug for the treatment of individuals with type 2 diabetes, yet its precise mechanism of action remains unclear. Metformin exerts its antihyperglycemic action primarily through lowering hepatic glucose production (HGP). This suppression is thought to be mediated through inhibition of mitochondrial respiratory complex I, and thus elevation of 5'-adenosine monophosphate (AMP) levels and the activation of AMP-activated protein kinase (AMPK), though this proposition has been challenged given results in mice lacking hepatic AMPK. Here we report that the AMP-inhibited enzyme fructose-1,6-bisphosphatase-1 (FBP1), a rate-controlling enzyme in gluconeogenesis, functions as a major contributor to the therapeutic action of metformin. We identified a point mutation in FBP1 that renders it insensitive to AMP while sparing regulation by fructose-2,6-bisphosphate (F-2,6-P), and knock-in (KI) of this mutant in mice significantly reduces their response to metformin treatment. We observe this during a metformin tolerance test and in a metformin-euglycemic clamp that we have developed. The antihyperglycemic effect of metformin in high-fat diet-fed diabetic FBP1-KI mice was also significantly blunted compared to wild-type controls. Collectively, we show a new mechanism of action for metformin and provide further evidence that molecular targeting of FBP1 can have antihyperglycemic effects.
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19 MeSH Terms
Evidence for the Role of the Cecal Microbiome in Maintenance of Immune Regulation and Homeostasis.
Chhabra P, Spano AJ, Bowers D, Ren T, Moore DJ, Timko MP, Wu M, Brayman KL
(2018) Ann Surg 268: 541-549
MeSH Terms: Animals, Cecum, Diabetes Mellitus, Experimental, Diabetes Mellitus, Type 1, Female, Gastrointestinal Microbiome, Homeostasis, Humans, Immunoglobulin M, Mice, Mice, Inbred NOD
Show Abstract · Added July 12, 2018
OBJECTIVE (S) - Our objective was to investigate alterations in the cecal microbial composition during the development of type 1 diabetes (T1D) with or without IgM therapy, and correlate these alterations with the corresponding immune profile.
METHODS - (1) Female nonobese diabetic (NOD) mice treated with IgM or saline (n = 20/group) were divided into 5-week-old nondiabetic; 9 to 12-week-old prehyperglycemic stage-1; ≥13-week-old prehyperglycemic stage-2; and diabetic groups. 16S rRNA libraries were prepared from bacterial DNA and deep-sequenced. (2) New-onset diabetic mice were treated with IgM (200 μg on Days 1, 3, and 5) and their blood glucose monitored for 2 months.
RESULTS - Significant dysbiosis was observed in the cecal microbiome with the progression of T1D development. The alteration in microbiome composition was characterized by an increase in the bacteroidetes:firmicutes ratio. In contrast, IgM conserved normal bacteroidetes:firmicutes ratio and this effect was long-lasting. Furthermore, oral gavage using cecal content from IgM-treated mice significantly diminished the incidence of diabetes compared with controls, indicating that IgM specifically affected mucosa-associated microbes, and that the affect was causal and not an epiphenomenon. Also, regulatory immune cell populations (myeloid-derived suppressor cells and regulatory T cells) were expanded and insulin autoantibody production diminished in the IgM-treated mice. In addition, IgM therapy reversed hyperglycemia in 70% of new-onset diabetic mice (n = 10) and the mice remained normoglycemic for the entire post-treatment observation period.
CONCLUSIONS - The cecal microbiome appears to be important in maintaining immune homeostasis and normal immune responses.
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11 MeSH Terms
Fur regulation of Staphylococcus aureus heme oxygenases is required for heme homeostasis.
Lojek LJ, Farrand AJ, Weiss A, Skaar EP
(2018) Int J Med Microbiol 308: 582-589
MeSH Terms: Aerobiosis, Bacterial Proteins, Gene Expression Regulation, Bacterial, Heme, Heme Oxygenase (Decyclizing), Homeostasis, Iron, Mixed Function Oxygenases, Oxygenases, Repressor Proteins, Staphylococcus aureus
Show Abstract · Added March 15, 2018
Heme is a cofactor that is essential for cellular respiration and for the function of many enzymes. If heme levels become too low within the cell, S. aureus switches from producing energy via respiration to producing energy by fermentation. S. aureus encodes two heme oxygenases, IsdI and IsdG, which cleave the porphyrin heme ring releasing iron for use as a nutrient source. Both isdI and isdG are only expressed under low iron conditions and are regulated by the canonical Ferric Uptake Regulator (Fur). Here we demonstrate that unregulated expression of isdI and isdG within S. aureus leads to reduced growth under low iron conditions. Additionally, the constitutive expression of these enzymes leads to decreased heme abundance in S. aureus, an increase in the fermentation product lactate, and increased resistance to gentamicin. This work demonstrates that S. aureus has developed tuning mechanisms, such as Fur regulation, to ensure that the cell has sufficient quantities of heme for efficient ATP production through aerobic respiration.
Copyright © 2018 Elsevier GmbH. All rights reserved.
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11 MeSH Terms
TRAF6 Mediates Basal Activation of NF-κB Necessary for Hematopoietic Stem Cell Homeostasis.
Fang J, Muto T, Kleppe M, Bolanos LC, Hueneman KM, Walker CS, Sampson L, Wellendorf AM, Chetal K, Choi K, Salomonis N, Choi Y, Zheng Y, Cancelas JA, Levine RL, Starczynowski DT
(2018) Cell Rep 22: 1250-1262
MeSH Terms: Animals, Enzyme Activation, Hematopoiesis, Hematopoietic Stem Cells, Homeostasis, I-kappa B Kinase, Mice, Mice, Transgenic, NF-kappa B, Signal Transduction, TNF Receptor-Associated Factor 6
Show Abstract · Added February 26, 2018
Basal nuclear factor κB (NF-κB) activation is required for hematopoietic stem cell (HSC) homeostasis in the absence of inflammation; however, the upstream mediators of basal NF-κB signaling are less well understood. Here, we describe TRAF6 as an essential regulator of HSC homeostasis through basal activation of NF-κB. Hematopoietic-specific deletion of Traf6 resulted in impaired HSC self-renewal and fitness. Gene expression, RNA splicing, and molecular analyses of Traf6-deficient hematopoietic stem/progenitor cells (HSPCs) revealed changes in adaptive immune signaling, innate immune signaling, and NF-κB signaling, indicating that signaling via TRAF6 in the absence of cytokine stimulation and/or infection is required for HSC function. In addition, we established that loss of IκB kinase beta (IKKβ)-mediated NF-κB activation is responsible for the major hematopoietic defects observed in Traf6-deficient HSPC as deletion of IKKβ similarly resulted in impaired HSC self-renewal and fitness. Taken together, TRAF6 is required for HSC homeostasis by maintaining a minimal threshold level of IKKβ/NF-κB signaling.
Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.
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11 MeSH Terms
Hepatic Gi signaling regulates whole-body glucose homeostasis.
Rossi M, Zhu L, McMillin SM, Pydi SP, Jain S, Wang L, Cui Y, Lee RJ, Cohen AH, Kaneto H, Birnbaum MJ, Ma Y, Rotman Y, Liu J, Cyphert TJ, Finkel T, McGuinness OP, Wess J
(2018) J Clin Invest 128: 746-759
MeSH Terms: Animals, Blood Glucose, Extracellular Signal-Regulated MAP Kinases, Female, GTP-Binding Protein alpha Subunits, Gi-Go, Gene Expression Profiling, Glucagon, Gluconeogenesis, Glucose, Hepatocytes, Homeostasis, Humans, Liver, Male, Mice, Mice, Inbred C57BL, Mice, Knockout, Oxygen, Phosphatidylinositol 3-Kinases, Phosphorylation, Reactive Oxygen Species, Receptors, Glucagon, Signal Transduction
Show Abstract · Added March 14, 2018
An increase in hepatic glucose production (HGP) is a key feature of type 2 diabetes. Excessive signaling through hepatic Gs-linked glucagon receptors critically contributes to pathologically elevated HGP. Here, we tested the hypothesis that this metabolic impairment can be counteracted by enhancing hepatic Gi signaling. Specifically, we used a chemogenetic approach to selectively activate Gi-type G proteins in mouse hepatocytes in vivo. Unexpectedly, activation of hepatic Gi signaling triggered a pronounced increase in HGP and severely impaired glucose homeostasis. Moreover, increased Gi signaling stimulated glucose release in human hepatocytes. A lack of functional Gi-type G proteins in hepatocytes reduced blood glucose levels and protected mice against the metabolic deficits caused by the consumption of a high-fat diet. Additionally, we delineated a signaling cascade that links hepatic Gi signaling to ROS production, JNK activation, and a subsequent increase in HGP. Taken together, our data support the concept that drugs able to block hepatic Gi-coupled GPCRs may prove beneficial as antidiabetic drugs.
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23 MeSH Terms
The Role of Aquaporins in Ocular Lens Homeostasis.
Schey KL, Petrova RS, Gletten RB, Donaldson PJ
(2017) Int J Mol Sci 18:
MeSH Terms: Animals, Aquaporins, Biological Transport, Active, Eye Proteins, Homeostasis, Humans, Lens, Crystalline, Permeability, Protein Isoforms, Water
Show Abstract · Added April 3, 2018
Aquaporins (AQPs), by playing essential roles in the maintenance of ocular lens homeostasis, contribute to the establishment and maintenance of the overall optical properties of the lens over many decades of life. Three aquaporins, AQP0, AQP1 and AQP5, each with distinctly different functional properties, are abundantly and differentially expressed in the different regions of the ocular lens. Furthermore, the diversity of AQP functionality is increased in the absence of protein turnover by age-related modifications to lens AQPs that are proposed to alter AQP function in the different regions of the lens. These regional differences in AQP functionality are proposed to contribute to the generation and directionality of the lens internal microcirculation; a system of circulating ionic and fluid fluxes that delivers nutrients to and removes wastes from the lens faster than could be achieved by passive diffusion alone. In this review, we present how regional differences in lens AQP isoforms potentially contribute to this microcirculation system by highlighting current areas of investigation and emphasizing areas where future work is required.
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10 MeSH Terms
Systemic inflammation is associated with exaggerated skeletal muscle protein catabolism in maintenance hemodialysis patients.
Deger SM, Hung AM, Gamboa JL, Siew ED, Ellis CD, Booker C, Sha F, Li H, Bian A, Stewart TG, Zent R, Mitch WE, Abumrad NN, Ikizler TA
(2017) JCI Insight 2:
MeSH Terms: Adult, Animals, Biomarkers, C-Reactive Protein, Cytokines, Disease Models, Animal, Female, Homeostasis, Humans, Inflammation, Integrin beta1, Kinetics, Male, Mice, Mice, Knockout, Middle Aged, Multivariate Analysis, Muscle Proteins, Muscle, Skeletal, Regression Analysis, Renal Dialysis, Renal Insufficiency, Chronic, SKP Cullin F-Box Protein Ligases, Tripartite Motif Proteins, Ubiquitin-Protein Ligases
Show Abstract · Added March 14, 2018
BACKGROUND - Systemic inflammation and muscle wasting are highly prevalent and coexist in patients on maintenance hemodialysis (MHD). We aimed to determine the effects of systemic inflammation on skeletal muscle protein metabolism in MHD patients.
METHODS - Whole body and skeletal muscle protein turnover were assessed by stable isotope kinetic studies. We incorporated expressions of E1, E214K, E3αI, E3αII, MuRF-1, and atrogin-1 in skeletal muscle tissue from integrin β1 gene KO CKD mice models.
RESULTS - Among 129 patients with mean (± SD) age 47 ± 12 years, 74% were African American, 73% were male, and 22% had diabetes mellitus. Median high-sensitivity C-reactive protein (hs-CRP) concentration was 13 (interquartile range 0.8, 33) mg/l. There were statistically significant associations between hs-CRP and forearm skeletal muscle protein synthesis, degradation, and net forearm skeletal muscle protein balance (P < 0.001 for all). The associations remained statistically significant after adjustment for clinical and demographic confounders, as well as in sensitivity analysis, excluding patients with diabetes mellitus. In attempting to identify potential mechanisms involved in this correlation, we show increased expressions of E1, E214K, E3αI, E3αII, MuRF-1, and atrogin-1 in skeletal muscle tissue obtained from an animal model of chronic kidney disease.
CONCLUSION - These data suggest that systemic inflammation is a strong and independent determinant of skeletal muscle protein homeostasis in MHD patients, providing rationale for further studies using anticytokine therapies in patients with underlying systemic inflammation.
FUNDING - This study was in part supported by NIH grants R01 DK45604 and 1K24 DK62849, the Clinical Translational Science Award UL1-TR000445 from the National Center for Advancing Translational Sciences, the Veterans Administration Merit Award I01 CX000414, the SatelliteHealth Normon Coplon Extramural Grant Program, and the FDA grant 000943.
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25 MeSH Terms
Müller glial microRNAs are required for the maintenance of glial homeostasis and retinal architecture.
Wohl SG, Jorstad NL, Levine EM, Reh TA
(2017) Nat Commun 8: 1603
MeSH Terms: 3T3 Cells, Animals, Cell Movement, Cells, Cultured, DEAD-box RNA Helicases, Ependymoglial Cells, Gene Expression Profiling, Homeostasis, Mice, Mice, Knockout, Mice, Transgenic, MicroRNAs, Microscopy, Confocal, Neuroglia, Retina, Ribonuclease III
Show Abstract · Added February 14, 2018
To better understand the roles of microRNAs in glial function, we used a conditional deletion of Dicer1 (Dicer-CKO) in retinal Müller glia (MG). Dicer1 deletion from the MG leads to an abnormal migration of the cells as early as 1 month after the deletion. By 6 months after Dicer1 deletion, the MG form large aggregations and severely disrupt normal retinal architecture and function. The most highly upregulated gene in the Dicer-CKO MG is the proteoglycan Brevican (Bcan) and overexpression of Bcan results in similar aggregations of the MG in wild-type retina. One potential microRNA that regulates Bcan is miR-9, and overexpression of miR-9 can partly rescue the effects of Dicer1 deletion on the MG phenotype. We also find that MG from retinitis pigmentosa patients display an increase in Brevican immunoreactivity at sites of MG aggregation, linking the retinal remodeling that occurs in chronic disease with microRNAs.
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16 MeSH Terms