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Mediated Mechanism (mediated + mechanism)
Selected AbstractsOestrogen receptor-alpha activation augments post-exercise myoblast proliferationACTA PHYSIOLOGICA, Issue 1 2010A. Thomas Abstract Aim:, Our laboratory has shown that oestrogen acts to augment myoblast (satellite cell) activation, proliferation and total number and that this may occur through an oestrogen receptor (OR)-mediated mechanism. The purpose of this study was to further investigate the mechanism of oestrogen influence on augmentation of post-exercise myoblast numbers through use of a specific OR-, agonist, propyl pyrazole triol (PPT). Methods:, Ovariectomized rats were used (n = 64) and separated into four groups: sham, oestrogen supplemented, agonist supplemented, and a combined oestrogen and agonist supplemented group. These groups were further subdivided into control (unexercised) and exercise groups. Surgical removal of white vastus and soleus muscles was performed 72 h post-exercise. Muscle samples were immunostained for the myoblast markers Pax7 and MyoD. Results:, A significant increase in total (Pax7-positive) and activated (MyoD-positive) myoblasts was found in all groups post-exercise. A further significant augmentation of total and activated myoblasts occurred in oestrogen supplemented, agonist supplemented and the combined oestrogen and agonist supplemented groups post-exercise in white vastus and soleus muscles relative to unsupplemented animals. Conclusion:, These results demonstrate that both oestrogen and the specific OR-, receptor agonist, PPT, can significantly and to similar degrees augment myoblast number and activation following exercise-induced muscle damage. This suggests that oestrogen acts through an OR-mediated mechanism to stimulate myoblast proliferation following exercise, with OR-, playing a primary role. [source] ,9 -Tetrahydrocannabivarin suppresses in vitro epileptiform and in vivo seizure activity in adult ratsEPILEPSIA, Issue 8 2010Andrew J. Hill Summary Purpose:, We assessed the anticonvulsant potential of the phytocannabinoid ,9 -tetrahydrocannabivarin (,9 -THCV) by investigating its effects in an in vitro piriform cortex (PC) brain slice model of epileptiform activity, on cannabinoid CB1 receptor radioligand-binding assays and in a generalized seizure model in rats. Methods:, ,9 -THCV was applied before (10 ,m,9 -THCV) or during (10,50 ,m,9 -THCV) epileptiform activity induced by Mg2+ -free extracellular media in adult rat PC slices and measured using multielectrode array (MEA) extracellular electrophysiologic techniques. The actions of ,9 -THCV on CB1 receptors were examined using [3H]SR141716A competition binding and [35S]GTP,S assays in rat cortical membranes. Effects of ,9 -THCV (0.025,2.5 mg/kg) on pentylenetetrazole (PTZ),induced seizures in adult rats were also assessed. Results:, After induction of stable spontaneous epileptiform activity, acute ,9 -THCV application (,20 ,m) significantly reduced burst complex incidence and the amplitude and frequency of paroxysmal depolarizing shifts (PDSs). Furthermore, slices pretreated with 10 ,m,9 -THCV prior to induction of epileptiform activity exhibited significantly reduced burst complex incidence and PDS peak amplitude. In radioligand-binding experiments, ,9 -THCV acted as a CB1 receptor ligand, displacing 0.5 nm [3H]SR141716A with a Ki,290 nm, but exerted no agonist stimulation of [35S]GTP,S binding. In PTZ-induced seizures in vivo, 0.25 mg/kg ,9 -THCV significantly reduced seizure incidence. Discussion:, These data demonstrate that ,9 -THCV exerts antiepileptiform and anticonvulsant properties, actions that are consistent with a CB1 receptor,mediated mechanism and suggest possible therapeutic application in the treatment of pathophysiologic hyperexcitability states. [source] Hepatocytes as cytotoxic effector cells can induce cell death by CD95 ligand-mediated pathway,HEPATOLOGY, Issue 6 2006Clifford S. Guy The liver plays an increasingly recognized role in the host's immune responses. The direct contribution of hepatocytes as effector cells to local immunity, pathogen containment, and liver disease is not determined. This in vitro study examined whether hepatocytes can eliminate other cells via a CD95 ligand (CD95L or FasL)/CD95 (Fas),mediated mechanism and whether this cytotoxic activity can be modulated by cytokines such as interferon gamma (IFN-,) or tumor necrosis factor alpha (TNF-,). We have found that normal woodchuck and human hepatocytes, both cultured and primary freshly isolated, as well as human HepG2 cells, intrinsically transcribe not only CD95 but also CD95L when examined by reverse transcription-polymerase chain reaction (RT-PCR) assays. The functional competence of CD95L, which was detectable in hepatocytes and HepG2 cells by Western blotting, was confirmed in bioassays by induction of apoptosis of CD95-bearing P815 and LS102.9 cell targets and validated by inhibition of the cell killing with CD95 antagonistic antibody or with a general caspase inhibitor. Furthermore, exposure of cultured hepatocytes to IFN-, or their stable transfection with IFN-, cDNA or TNF-, cDNA increased hepatocyte CD95L/CD95,mediated cell killing. In conclusion, hepatocytes express both CD95L and CD95 and they can induce death of other cells by a CD95L-dependent mechanism. IFN-, and, to a lesser extent, TNF-, can enhance hepatocyte CD95L-mediated cytotoxicity. This suggests that the local cytokine environment may modulate the hepatocyte contribution to liver immunity. (HEPATOLOGY 2006;43:1231,1240.) [source] Direct Measurement of Hormone-Induced Acidification in Intact BoneJOURNAL OF BONE AND MINERAL RESEARCH, Issue 3 2000Glenn S. Belinsky Abstract Previous findings have shown that osteoblasts respond to parathyroid hormone (PTH) with an increase in extracellular acidification rate (ECAR) in addition to the known effect of PTH to increase local acidification by osteoclasts. We, therefore, investigated use of the Cytosensor to measure the ECAR response of whole intact bone to PTH employing microphysiometry. The Cytosensor measures a generic metabolic increase of cells to various agents. Using neonatal mouse calvaria, we found that the area surrounding the sagittal suture was particularly responsive to PTH. In this bone, the increase in ECAR was slower to develop (6 minutes) and more persistent than in cultured human osteoblast-like SaOS-2 cells and was preceded by a brief decrease in ECAR Salmon calcitonin also produced an increase in ECAR in this tissue but with a different pattern than that elicited by PTH. Because PTH stimulates osteoclastic bone resorption in mouse calvaria via a cyclic adenosine monophosphate (cAMP)-mediated mechanism, we showed that the adenylyl cyclase activator forskolin also stimulated ECAR in this tissue. When the protein kinase A (PKA) pathway was activated by maintaining a high intracellular concentration of cAMP using N6 -2,-0-dibutyryladenosine-cAMP (db-cAMP), there was a reduction of PTH-induced acidification, while isobutylmethylxanthine pretreatment potentiated the PTH-induced acidification, consistent with a PKA-mediated pathway. Thapsigargin and the protein kinase C (PKC) activator phorbol myristate acetate had no effect on the PTH-induced increase in ECAR in calvaria, indicating that PKC does not play a major role in the ECAR response in intact bone. These results indicate the utility of using microphysiometry to study ECAR responses in intact tissue and should enable elucidation of the relative importance of extracellular acidification by osteoblasts and osteoclasts to the anabolic and catabolic activities of PTH, respectively. [source] NAAG peptidase inhibitor increases dialysate NAAG and reduces glutamate, aspartate and GABA levels in the dorsal hippocampus following fluid percussion injury in the ratJOURNAL OF NEUROCHEMISTRY, Issue 4 2006Chunlong Zhong Abstract Traumatic brain injury (TBI) produces a rapid and excessive elevation in extracellular glutamate that induces excitotoxic brain cell death. The peptide neurotransmitter N -acetylaspartylglutamate (NAAG) is reported to suppress neurotransmitter release through selective activation of presynaptic group II metabotropic glutamate receptors. Therefore, strategies to elevate levels of NAAG following brain injury could reduce excessive glutamate release associated with TBI. We hypothesized that the NAAG peptidase inhibitor, ZJ-43 would elevate extracellular NAAG levels and reduce extracellular levels of amino acid neurotransmitters following TBI by a group II metabotropic glutamate receptor (mGluR)-mediated mechanism. Dialysate levels of NAAG, glutamate, aspartate and GABA from the dorsal hippocampus were elevated after TBI as measured by in vivo microdialysis. Dialysate levels of NAAG were higher and remained elevated in the ZJ-43 treated group (50 mg/kg, i.p.) compared with control. ZJ-43 treatment also reduced the rise of dialysate glutamate, aspartate, and GABA levels. Co-administration of the group II mGluR antagonist, LY341495 (1 mg/kg, i.p.) partially blocked the effects of ZJ-43 on dialysate glutamate and GABA, suggesting that NAAG effects are mediated through mGluR activation. The results are consistent with the hypothesis that inhibition of NAAG peptidase may reduce excitotoxic events associated with TBI. [source] Ephedrine in the cat lung vasculatureACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 8 2003A. M. Fields Background:, Ephedrine is one of the most commonly used non-catecholamine sympathomimetic agents. It is used in operating rooms and critical care settings worldwide. While it has many side effects, its ability to rapidly raise blood pressure makes it an ideal agent to maintain homeostasis as well as in emergency situations. While its effects are known to be mediated by an ,-mediated mechanism, the exact , subtype is unknown. In addition, no studies using ephedrine have been performed in the pulmonary vascular bed of the cat. Methods:, The effects of phentolamine, a non-selective ,-receptor blocker, and prazosin, an ,1 -selective antagonist, were investigated on pulmonary arterial responses to ephedrine, phenylepherine, norepinephrine, and U-46619. Lobar arterial perfusion pressure was continuously monitored, electronically averaged, and recorded with constant flow in the isolated left lower lobe vascular bed of the cat. Results:, Phentolamine and prazosin significantly reduced vasoconstrictor pulmonary perfusion pressure increases induced by ephedrine. Conclusion:, Ephedrine has significant vasopressor activity in the pulmonary vascular bed of the cat meditated predominantly by ,1 adrenergic receptor activation. [source] Functional specialization and differential regulation of short-chain carboxylic acid transporters in the pathogen Candida albicansMOLECULAR MICROBIOLOGY, Issue 6 2010Neide Vieira Summary The major fungal pathogen Candida albicans has the metabolic flexibility to assimilate a wide range of nutrients in its human host. Previous studies have suggested that C. albicans can encounter glucose-poor microenvironments during infection and that the ability to use alternative non-fermentable carbon sources contributes to its virulence. JEN1 encodes a monocarboxylate transporter in C. albicans and we show that its paralogue, JEN2, encodes a novel dicarboxylate plasma membrane transporter, subjected to glucose repression. A strain deleted in both genes lost the ability to transport lactic, malic and succinic acids by a mediated mechanism and it displayed a growth defect on these substrates. Although no significant morphogenetic or virulence defects were found in the double mutant strain, both JEN1 and JEN2 were strongly induced during infection. Jen1-GFP (green fluorescent protein) and Jen2-GFP were upregulated following the phagocytosis of C. albicans cells by neutrophils and macrophages, displaying similar behaviour to an Icl1-GFP fusion. In the murine model of systemic candidiasis approximately 20,25% of C. albicans cells infecting the kidney expressed Jen1-GFP and Jen2-GFP. Our data suggest that Jen1 and Jen2 are expressed in glucose-poor niches within the host, and that these short-chain carboxylic acid transporters may be important in the early stages of infection. [source] Diagnosis and therapy of food allergyMOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 5 2004Jesús F. Crespo Abstract According to the recently revised nomenclature for allergy [1] the term "Food Hypersensitivity" is proposed to define a reaction on food exposure causing objectively reproducible symptoms or signs at a dose tolerated by normal subjects. Those reactions to food in which immunologic mechanisms are demonstrated comprise the term "Food Allergy". Immunologic reactions to food in which an immunoglobulin E (IgE)-mediated mechanism is established are defined as IgE-mediated food allergy. This review focuses on IgE-mediated allergic reactions to foods. [source] Effect of angiotensin II and endothelin-1 receptor blockade on the haemodynamic and hormonal changes after acute blood loss and after retransfusion in conscious dogsACTA PHYSIOLOGICA, Issue 4 2004R. C. E. Francis Abstract Aim:, This study investigates angiotensin II and endothelin-1 mediated mechanisms involved in the haemodynamic, hormonal, and renal response towards acute hypotensive haemorrhage. Methods:, Conscious dogs were pre-treated with angiotensin II type 1 (AT1) and/or endothelin-A (ETA) receptor blockers or not. Protocol 1: After a 60-min baseline period, 25% of the dog's blood was rapidly withdrawn. The blood was retransfused 60 min later and data recorded for another hour. Protocol 2: Likewise, but preceded by AT1 blockade with i.v. Losartan. Protocol 3: Likewise, but preceded by ETA blockade with i.v. ABT-627. Protocol 4: Likewise, but with combined AT1plus ETAblockade. Results:, In controls, haemorrhage decreased mean arterial pressure (MAP) by approximately 25%, cardiac output by approximately 40%, and urine volume by approximately 60%, increased angiotensin II (3.1-fold), endothelin-1 (1.13-fold), vasopressin (116-fold), and adrenaline concentrations (3.2-fold). Glomerular filtration rate and noradrenaline concentrations remained unchanged. During AT1 blockade, the MAP decrease was exaggerated (,40%) and glomerular filtration rate fell. During ETA blockade, noradrenaline increased after haemorrhage instead of adrenaline, and the MAP recovery after retransfusion was blunted. The decrease in cardiac output was similar in all protocols. Conclusions:, Angiotensin II is more important than endothelin-1 for the short-term regulation of MAP and glomerular filtration rate after haemorrhage, whereas endothelin-1 seems necessary for complete MAP recovery after retransfusion. After haemorrhage, endothelin-1 seems to facilitate adrenaline release and to blunt noradrenaline release. Haemorrhage-induced compensatory mechanisms maintain blood flow more effectively than blood pressure, as the decrease in cardiac output , but not MAP , was similar in all protocols. [source] Effects of cevoglitazar, a dual PPAR,/, agonist, on ectopic fat deposition in fatty Zucker ratsDIABETES OBESITY & METABOLISM, Issue 6 2009D. Laurent Aim:, By acting as both insulin sensitizers and lipid-lowering agents, dual-acting peroxisome proliferator-activated receptors ,/, (PPAR,/,) agonists may be used to improve glucose tolerance in type 2 diabetic patients without inducing adiposity and body weight gain. Here, in an animal model of obesity and insulin resistance, the metabolic response to cevoglitazar, a dual PPAR,/,, was characterized using a combination of in vivo and ex vivo magnetic resonance methodologies and compared to treatment effects of fenofibrate, a PPAR, agonist, and pioglitazone, a PPAR, agonist. Methods:, Four groups of fatty Zucker rats: (i) Vehicle; (ii) fenofibrate 150 mg/kg; (iii) pioglitazone 30 mg/kg; and (iv) cevoglitazar 5 mg/kg were investigated before and after treatment. Animals were fed a fat-enriched (54% kcal fat) diet for 6 weeks, 2 weeks high of fat,exposure alone followed by a 4-week dosing period. Results and conclusions:, Cevoglitazar was as effective as pioglitazone at improving glucose tolerance. However, unlike pioglitazone, both fenofibrate and cevoglitazar reduced BW gain and adiposity, independent of food intake. All three treatment regimens normalized intramyocellular lipids. Metabolic profiling showed that in the muscle cevoglitazar improves the lipid profile via both PPAR,- and PPAR,-mediated mechanisms. Pioglitazone reduced hepatic lipid accumulation, while cevoglitazar and fenofibrate reduced hepatic lipid concentration below baseline levels (p < 0.05). Metabolic profiling showed that in the liver, cevoglitazar functions largely through PPAR, agonism resulting in increased ,-oxidation. Cevoglitazar only induced small changes to the lipid composition of visceral fat. In subcutaneous fat, however, cevoglitazar induced changes similar to those observed with fenofibrate suggesting export of fatty acids from this depot. [source] Reduction of intracellular pH inhibits constitutive expression of Cyclooxygenase-2 in human colon cancer cellsJOURNAL OF CELLULAR PHYSIOLOGY, Issue 2 2004Daniela Pirkebner Cyclooxygenase-2 (COX-2) over-expression is critically involved in tumor formation. Intracellular pH (pHi) has been shown to be alkaline in cancer cells, and to be an important trigger for cell proliferation. This study therefore analyzed the relationship between pHi and COX-2 expression. HRT-18 and Caco-2 cells cultured in medium with bicarbonate maintained a pHi of ,7.6, which is higher than that of non-neoplastic cells. Cells grown in bicarbonate-free medium with a pH at 6.8 showed a reduction in pHi to approximately 7.0. Importantly, reduction of pHi resulted in a complete inhibition of COX-2 mRNA and protein expression. When cells were grown in bicarbonate-supplemented medium at pH 6.8, pHi maintained at ,7.6 and COX-2 expression was not inhibited. Additionally, analysis utilizing protein synthesis inhibitor cycloheximide demonstrated that pHi mediated inhibition of COX-2 mRNA expression requires de novo protein synthesis of regulatory protein(s). These data strongly suggest that an alkaline pHi is an important trigger for constitutive COX-2 expression. Defining pHi -mediated mechanisms that govern the constitutive COX-2 expression may help in developing new strategies to block COX-2 over-expression in cancer cells. J. Cell. Physiol. 198: 295,301, 2004© 2003 Wiley-Liss, Inc. [source] A novel subpopulation of B-1 cells is enriched with autoreactivity in normal and lupus-prone miceARTHRITIS & RHEUMATISM, Issue 12 2009Xuemei Zhong Objective B-1 cells have long been suggested to play an important role in lupus. However, reports to date have been controversial regarding their pathogenic or protective roles in different animal models. We undertook this study to investigate a novel subpopulation of B-1 cells and its roles in murine lupus. Methods Lymphocyte phenotypes were assessed by flow cytometry. Autoantibody secretion was analyzed by enzyme-linked immunosorbent assay, autoantigen proteome array, and antinuclear antibody assay. Cell proliferation was measured by thymidine incorporation and 5,6-carboxyfluorescein succinimidyl ester dilution. B cell Ig isotype switching was measured by enzyme-linked immunospot assay. Results Anti,double-stranded DNA (anti-dsDNA) autoantibodies were preferentially secreted by a subpopulation of CD5+ B-1 cells that expressed programmed death ligand 2 (termed L2pB1 cells). A substantial proportion of hybridoma clones generated from L2pB1 cells reacted to dsDNA. Moreover, these clones were highly cross-reactive with other lupus-related autoantigens. L2pB1 cells were potent antigen-presenting cells and promoted Th17 cell differentiation in vitro. A dramatic increase of circulating L2pB1 cells in lupus-prone BXSB mice was correlated with elevated serum titers of anti-dsDNA antibodies. A significant number of L2pB1 cells preferentially switched to IgG1 and IgG2b when stimulated with interleukin-21. Conclusion Our findings identify a novel subpopulation of B-1 cells that is enriched for autoreactive specificities, undergoes isotype switch, manifests enhanced antigen presentation, promotes Th17 cell differentiation, and is preferentially associated with the development of lupus in a murine model. Together, these findings suggest that L2pB1 cells have the potential to initiate autoimmunity through serologic and T cell,mediated mechanisms. [source] A novel tumor necrosis factor ,,responsive CCAAT/enhancer binding protein site regulates expression of the cartilage-derived retinoic acid,sensitive protein gene in cartilageARTHRITIS & RHEUMATISM, Issue 5 2008Toshihiro Imamura Objective Inflammatory processes in rheumatoid arthritis are primarily regulated by the cytokines tumor necrosis factor , (TNF,) and interleukin-1, (IL-1,). Previous studies in our laboratory have shown that IL-1, represses expression of the cartilage characteristic genes, cartilage-derived retinoic acid,sensitive protein (cd - rap) and type II collagen (COL2A1); this mechanism of repression involves activation of a CCAAT/enhancer binding protein (c/EBP) site within promoter regions. The aim of this study was to investigate novel TNF,-mediated mechanisms that regulate the expression of cd - rap. Methods Rat chondrosarcoma cells were transiently transfected with complementary DNA constructs encoding cd - rap, in the presence of TNF,. The expression of c/EBP,, SOX9, and p300 in rat chondrosarcoma cells and primary human articular chondrocytes after treatment with TNF, was examined by reverse transcription,polymerase chain reaction and Western blotting. The effect of TNF, on endogenous binding of c/EBP, or SOX9 to the cd - rap promoter was examined by chromatin immunoprecipitation assays. Results We identified a new c/EBP binding site in the cd - rap promoter (from position ,1059 bp to position ,1046 bp). Binding of c/EBP to this site was regulated by TNF, but not IL-1,, resulting in down-regulation of cd - rap expression. This effect was reversed by mutational inactivation of the c/EBP motif. In addition, the activation potential of SOX9 and CREB binding protein/p300 on the cd - rap promoter was enhanced after mutation of the new c/EBP binding site, indicating that blockage of this site would increase transcription. Conclusion TNF, regulates the expression and/or DNA-binding potential of key positive-acting and negative-acting transcription factors that control the expression of the cartilage matrix gene, cd - rap. [source] | |||||||||||||