Glucocorticoids in T cell apoptosis and function.
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ABSTRACT:
SUBMITTER: Herold MJ
PROVIDER: S-EPMC2792342 | biostudies-other | 2006 Jan
REPOSITORIES: biostudies-other
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Project description:To identify microRNAs (miRNAs) in human T cells that can explain known antiinflammatory properties of steroids.Activated human CD4+ T cells from healthy donors were exposed to 1 ?M methylprednisolone (MP) in vitro and then subjected to miRNA and messenger RNA microarray analyses. Changes in expression profiles were recorded. Using quantitative polymerase chain reaction (qPCR), flow cytometry, and enzyme-linked immunosorbent assay (ELISA), we confirmed the suppression of predicted targets, and through miRNA transfection experiments, we could suggest mechanistic links.We identified numerous steroid-responsive genes and miRNAs-many known and some novel-including multiple previously unknown proinflammatory genes suppressed by MP. Further studies using qPCR, flow cytometry, and ELISA demonstrated that methylprednisolone increased the expression of miRNA-98 (miR-98) and suppressed the levels of predicted targets, including interleukin-13 and 3 tumor necrosis factor receptors (TNFRs): Fas, FasL, and TNFR superfamily member 1B. Forced expression of miR-98 in T cells resulted in suppression of the same targets.The findings of this study demonstrate a link between miR-98 expression and the effects of MP and provide evidence suggesting that MP acts through miR-98 to inhibit specific proinflammatory targets. Identification of this antiinflammatory mechanism of glucocorticoids is important, since it may pave the way toward the elusive goal of dissociating adverse effects from therapeutic effects.
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Project description:Glucocorticoids and their synthetic derivatives are known to alter cardiac function in vivo; however, the nature of these effects and whether glucocorticoids act directly on cardiomyocytes are poorly understood. To explore the role of glucocorticoid signaling in the heart, we used rat embryonic H9C2 cardiomyocytes and primary cardiomyocytes as model systems. Dexamethasone (100 nm) treatment of cardiomyocytes caused a significant increase in cell size and up-regulated the expression of cardiac hypertrophic markers, including atrial natriuretic factor, ?-myosin heavy chain, and skeletal muscle ?-actin. In contrast, serum deprivation and TNF? exposure triggered cardiomyocyte apoptosis, and these apoptotic effects were inhibited by dexamethasone. Both the hypertrophic and anti-apoptotic actions of glucocorticoids were abolished by the glucocorticoid receptor (GR) antagonist RU486 and by short hairpin RNA-mediated GR depletion. Blocking the activity of the mineralocorticoid receptor had no effect on these glucocorticoid-dependent cardiomyocyte responses. Aldosterone (1 ?m) activation of GR also promoted cardiomyocyte hypertrophy and cell survival. To elucidate the mechanism of the dual glucocorticoid actions, a genome-wide microarray was performed on H9C2 cardiomyocytes treated with vehicle or dexamethasone in the absence or presence of serum. Serum dramatically influenced the transcriptome regulated by GR, revealing potential glucocorticoid signaling mediators in both cardiomyocyte hypertrophy and apoptosis. These studies reveal a direct and dynamic role for glucocorticoids and GR signaling in the modulation of cardiomyocyte function.
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Project description:Glucocorticoids modulate immune development and function through the induction of lymphocyte apoptosis via mechanisms requiring alterations in gene expression. Recently, short, noncoding, microRNAs have been identified as key regulators of lymphocyte function; however, it is unknown whether glucocorticoids regulate noncoding microRNAs and whether this regulation contributes to lymphocyte apoptosis. We now show by both microarray and deep sequencing analysis that microRNAs are substantially repressed during glucocorticoid-induced apoptosis of primary rat thymocytes. Mechanistic studies revealed that primary microRNA transcripts were not repressed, whereas the expression of the key microRNA processing enzymes: Dicer, Drosha, and DGCR8/Pasha, were significantly reduced at both the mRNA and protein levels during glucocorticoid-induced apoptosis. To delineate the role of Dicer depletion and microRNA repression in apoptosis, we silenced Dicer expression in two human leukemic cell lines and demonstrated that Dicer depletion significantly enhanced glucocorticoid-induced apoptosis in both model systems. Finally, in vitro and in vivo overexpression of the conserved miR-17-92 polycistron, which was repressed significantly by dexamethasone treatment in both our microarray and deep sequencing studies, blunted glucocorticoid-induced apoptosis. These studies provide evidence of altered post-transcriptional microRNA expression and the repression of the microRNA bioprocessing pathway during glucocorticoid-induced apoptosis of lymphocytes, suggesting a role for microRNA processors and specific microRNAs in cell life/death decisions.
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Project description:Glucocorticoids play an important biphasic role in modulating neural plasticity; low doses enhance neural plasticity and spatial memory behavior, whereas chronic, higher doses produce inhibition. We found that 3 independent measures of mitochondrial function-mitochondrial oxidation, membrane potential, and mitochondrial calcium holding capacity-were regulated by long-term corticosterone (CORT) treatment in an inverted "U"-shape. This regulation of mitochondrial function by CORT correlated with neuroprotection; that is, treatment with low doses of CORT had a neuroprotective effect, whereas treatment with high doses of CORT enhanced kainic acid (KA)-induced toxicity of cortical neurons. We then undertook experiments to elucidate the mechanisms underlying these biphasic effects and found that glucocorticoid receptors (GRs) formed a complex with the anti-apoptotic protein Bcl-2 in response to CORT treatment and translocated with Bcl-2 into mitochondria after acute treatment with low or high doses of CORT in primary cortical neurons. However, after 3 days of treatment, high, but not low, doses of CORT resulted in decreased GR and Bcl-2 levels in mitochondria. As with the in vitro studies, Bcl-2 levels in the mitochondria of the prefrontal cortex were significantly decreased, along with GR levels, after long-term treatment with high-dose CORT in vivo. These findings have the potential to contribute to a more complete understanding of the mechanisms by which glucocorticoids and chronic stress regulate cellular plasticity and resilience and to inform the future development of improved therapeutics.
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Project description:Glucocorticoids (GCs) are potent anti-inflammatory drugs whose mode of action is complex and still debatable. One likely cellular target of GCs are monocytes/macrophages. The role of GCs in monocyte survival is also debated. Although both granulocyte macrophage-colony stimulating factor (GM-CSF) and macrophage-CSF (M-CSF) are important regulators of macrophage lineage functions including their survival, the former is often associated with proinflammatory functions while the latter is important in lineage homeostasis. We report here that the GC, dexamethasone, induces apoptosis in GM-CSF-treated human monocytes while having no impact on M-CSF-induced monocyte survival. To understand how GCs, GM-CSF, and M-CSF are regulating monocyte survival and other functions during inflammation, we firstly examined the transcriptomic changes elicited by these three agents in human monocytes, either acting alone or in combination. Transcriptomic and Ingenuity pathway analyses found that dexamethasone differentially modulated dendritic cell maturation and TREM1 signaling pathways in GM-CSF-treated and M-CSF-treated monocytes, two pathways known to be regulated by ERK1/2 activity. These analyses led us to provide evidence that the GC inhibits ERK1/2 activity selectively in GM-CSF-treated monocytes to induce apoptosis. It is proposed that this inhibition of ERK1/2 activity leads to inactivation of p90 ribosomal-S6 kinase and Bad dephosphorylation leading in turn to enhanced caspase-3 activity and subsequent apoptosis. Furthermore, pharmacological inhibition of GC receptor activity restored the ERK1/2 signaling and prevented the GC-induced apoptosis in GM-CSF-treated monocytes. Increased tissue macrophage numbers, possibly from enhanced survival due to mediators such as GM-CSF, can correlate with inflammatory disease severity; also reduction in these numbers can correlate with the therapeutic benefit of a number of agents, including GCs. We propose that the ERK1/2 signaling pathway promotes survival of GM-CSF-treated proinflammatory monocytes, which can be selectively targeted by GCs as a novel mechanism to reduce local monocyte/macrophage numbers and hence inflammation.
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Project description:BackgroundThe microenvironment and stress factors like glucocorticoids have a strong influence on breast cancer progression but their role in the first stages of breast cancer and, particularly, in myoepithelial cell regulation remains unclear. Consequently, we investigated the role of glucocorticoids in ductal carcinoma in situ (DCIS) in breast cancer, focusing specially on myoepithelial cells.MethodsTo clarify the role of glucocorticoids at breast cancer onset, we evaluated the effects of cortisol and corticosterone on epithelial and myoepithelial cells using 2D and 3D in vitro and in vivo approaches and human samples.ResultsGlucocorticoids induce a reduction in laminin levels and favour the disruption of the basement membrane by promotion of myoepithelial cell apoptosis in vitro. In an in vivo stress murine model, increased corticosterone levels fostered the transition from DCIS to invasive ductal carcinoma (IDC) via myoepithelial cell apoptosis and disappearance of the basement membrane. RU486 is able to partially block the effects of cortisol in vitro and in vivo. We found that myoepithelial cell apoptosis is more frequent in patients with DCIS+IDC than in patients with DCIS.ConclusionsOur findings show that physiological stress, through increased glucocorticoid blood levels, promotes the transition from DCIS to IDC, particularly by inducing myoepithelial cell apoptosis. Since this would be a prerequisite for invasive features in patients with DCIS breast cancer, its clinical management could help to prevent breast cancer progression to IDC.
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