The molecular mechanisms by which glomerular inflammation progresses to glomerular scar and fibrosis are unknown. Although interleukin-1 (IL-1) was originally described as an intercellular signal between leukocytes, production of IL-1 may represent a fundamental response to injury, and local synthesis of the cytokine may be a key mediator in the fibrogenesis that follows the initial insult to the glomerulus. A number of recent studies demonstrate that intrinsic glomerular cells in culture express characteristics that could be important in both the restorative and destructive processes that follow glomerular injury: The mesangial cell (MC) is a specialized pericyte that appears not only to control glomerular filtration but also can be induced to express a secretory phenotype. Cycling MC express the genes encoding IL-1 and translate the resulting transcripts. Many investigators have logically assumed that activated MC contribute to either IL-1 synthesis or IL-1 receptor expression within nephritic kidneys is limited. Equally important, little is understood about the molecular mechanisms by which the MC cell alters its phenotype from pericyte to secretory cell. We have hypothesized that activated MC in injured glomeruli synthesize IL-1 and are key participants in the pathogenesis of glomerulonephritis and glomerulosclerosis. To test this postulate, we propose experiments to detect IL-1 synthesis and IL-1 gene expression will be assessed in solution hybridization studies will anatomically localize the site of IL-1 gene expression and, when combined with immunohistochemical studies, will identify the cellular source. IL-1 receptor expression will be assessed using quantitative autoradiography. We will study the regulation of IL-1 synthesis and IL-1 receptor expression both by the use of depletion and blocker experiments in experimental glomerulonephritis as well as by short-term infusion of selected proinflammatory mediators. Since the pathways controlling IL-1 gene expression in the MC appear to be different form those in the macrophage, we propose to study molecular mechanisms of IL-1 gene expression both as a model of MC activation and as well as to better understand the pathways regulating this gene. Steady-state stimuli of MC IL-1 gene expressing will be identified and the kinetics of each response will be defined in interactions between stimuli characterized. Nuclear transcription assays will next be used to identify stimuli of transcriptional activation. Finally, chimeric expression vectors containing fragments of the proIL- 1Beta 5' flanking sequence in a reporter gene will be transfected into MC. After cis-acting elements are identified, we will use electrophoretic gel mobility shift assays in DNase I footprinting to determine if nuclear factors bind into the regulatory sequences.
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