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      Tumor necrosis factor-α stimulates fractalkine production by mesangial cells and regulates monocyte transmigration: Down-regulation by cAMP

      , , , ,   ,
      Kidney International
      Wiley-Blackwell

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          Abstract

          Fractalkine is a CX3C chemokine for mononuclear cells that has been implicated in the recruitment and accumulation of monocytes seen in glomerular diseases. We investigated the mechanisms by which tumor necrosis factor (TNF)-alpha stimulates mesangial cell (MC) fractalkine expression, and the effects of MC-derived fractalkine on monocyte transmigration.

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          Role for neuronally derived fractalkine in mediating interactions between neurons and CX3CR1-expressing microglia.

          A recently identified chemokine, fractalkine, is a member of the chemokine gene family, which consists principally of secreted, proinflammatory molecules. Fractalkine is distinguished structurally by the presence of a CX3C motif as well as transmembrane spanning and mucin-like domains and shows atypical constitutive expression in a number of nonhematopoietic tissues, including brain. We undertook an extensive characterization of this chemokine and its receptor CX3CR1 in the brain to gain insights into use of chemokine-dependent systems in the central nervous system. Expression of fractalkine in rat brain was found to be widespread and localized principally to neurons. Recombinant rat CX3CR1, as expressed in Chinese hamster ovary cells, specifically bound fractalkine and signaled in the presence of either membrane-anchored or soluble forms of fractalkine protein. Fractalkine stimulated chemotaxis and elevated intracellular calcium levels of microglia; these responses were blocked by anti-CX3CR1 antibodies. After facial motor nerve axotomy, dramatic changes in the levels of CX3CR1 and fractalkine in the facial nucleus were evident. These included increases in the number and perineuronal location of CX3CR1-expressing microglia, decreased levels of motor neuron-expressed fractalkine mRNA, and an alteration in the forms of fractalkine protein expressed. These data describe mechanisms of cellular communication between neurons and microglia, involving fractalkine and CX3CR1, which occur in both normal and pathological states of the central nervous system.
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            Fractalkine and CX3CR1 Mediate a Novel Mechanism of Leukocyte Capture, Firm Adhesion, and Activation under Physiologic Flow

            Leukocyte migration into sites of inflammation involves multiple molecular interactions between leukocytes and vascular endothelial cells, mediating sequential leukocyte capture, rolling, and firm adhesion. In this study, we tested the role of molecular interactions between fractalkine (FKN), a transmembrane mucin-chemokine hybrid molecule expressed on activated endothelium, and its receptor (CX3CR1) in leukocyte capture, firm adhesion, and activation under physiologic flow conditions. Immobilized FKN fusion proteins captured resting peripheral blood mononuclear cells at physiologic wall shear stresses and induced firm adhesion of resting monocytes, resting and interleukin (IL)-2–activated CD8+ T lymphocytes and IL-2–activated NK cells. FKN also induced cell shape change in firmly adherent monocytes and IL-2–activated lymphocytes. CX3CR1-transfected K562 cells, but not control K562 cells, firmly adhered to FKN-expressing ECV-304 cells (ECV-FKN) and tumor necrosis factor α–activated human umbilical vein endothelial cells. This firm adhesion was not inhibited by pertussis toxin, EDTA/EGTA, or antiintegrin antibodies, indicating that the firm adhesion was integrin independent. In summary, FKN mediated the rapid capture, integrin-independent firm adhesion, and activation of circulating leukocytes under flow. Thus, FKN and CX3CR1 mediate a novel pathway for leukocyte trafficking.
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              Transcription factor-kappa B (NF-kappa B) and renal disease.

              Transcription factor-kappa B (NF-kappa B) and renal disease. Nuclear factor-kappa B (NF-kappa B) comprises a family of dimeric transcription factors that regulate the expression of numerous genes involved in inflammation and cell proliferation. Although NF-kappa B was initially identified in lymphocytes, it has been found to be a transcription factor present in virtually all cell types. In resting cells, NF-kappa B dimers remain in the cytoplasm in an inactive form bound to the inhibitory subunit I kappa B. Upon stimulation, I kappa B is phosphorylated, ubiquitinylated, and ultimately degraded by proteolytic cleavage by the proteasome system. As a result, NF-kappa B dimers are translocated into the nucleus and activate the transcription of target genes. Increasing data suggest a pivotal role for NF-kappa B in a variety of pathophysiological conditions in which either inflammation or cell number control are critical events. NF-kappa B has been found to be activated in experimental renal disease. Importantly, both in vivo and in vitro, NF-kappa B activation can be modulated by pharmacological maneuvers. Indeed, it is now widely acknowledged that the anti-inflammatory action of steroids is basically obtained through the inhibition of the transactivation of NF-kappa B-dependent genes. In addition, some of the beneficial effects of angiotensin-converting enzyme inhibitors and statins may, at least in part, be mediated by an inhibition of NF-kappa B activation. A better understanding of the mechanisms involved in NF-kappa B regulation and its modulation may provide new tools to improve the treatment of renal diseases with a better sound pathophysiological approach.
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                Author and article information

                Journal
                Kidney International
                Kidney International
                Wiley-Blackwell
                00852538
                February 2003
                February 2003
                : 63
                : 2
                : 474-486
                Article
                10.1046/j.1523-1755.2003.00766.x
                b35689ef-a8e5-4e5e-a7a9-9e5cfea3e74e
                © 2003

                http://www.elsevier.com/tdm/userlicense/1.0/

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