ABSTRACT
Myasthenia gravis (MG) is an autoimmune disease of neuromuscular junctions where thymus plays a pathogenetic role. Thymectomy benefits patients, and thymic hyperplasia, a lymphoid infiltration of perivascular spaces becoming site of autoantibody production, is recurrently observed. Cytokines and chemokines, produced by thymic epithelium and supporting survival and migration of T and B cells, are likely to be of great relevance in pathogenesis of thymic hyperplasia. In thymic epithelial cell (TEC) cultures derived "in vitro" from normal or hyperplastic age-matched MG thymuses, we demonstrate by gene profiling analysis that MG-TEC basally overexpress genes coding for p38 and ERK1/2 MAPKs and for components of their signaling pathways. Immunoblotting experiments confirmed that p38 and ERK1/2 proteins were overexpressed in MG-TEC and, in addition, constitutively activated. Pharmacological blockage with specific inhibitors confirmed their role in the control of IL-6 and RANTES gene expression. According to our results, IL-6 and RANTES levels were abnormally augmented in MG-TEC, either basally or upon induction by adhesion-related stimuli. The finding that IL-6 and RANTES modulate, respectively, survival and migration of peripheral lymphocytes of myasthenic patients point to MAPK transcriptional and posttranscriptional abnormalities of MG-TEC as a key step in the pathological remodelling of myasthenic thymus.
Subject(s)
B-Lymphocytes/enzymology , B-Lymphocytes/immunology , Chemokine CCL5/biosynthesis , Extracellular Signal-Regulated MAP Kinases/metabolism , Interleukin-6/biosynthesis , Myasthenia Gravis/enzymology , Myasthenia Gravis/immunology , T-Lymphocytes/enzymology , T-Lymphocytes/immunology , Adolescent , Adult , B-Lymphocytes/pathology , Case-Control Studies , Cell Movement , Cell Survival , Child , Enzyme Activation , Epithelial Cells/enzymology , Epithelial Cells/immunology , Extracellular Signal-Regulated MAP Kinases/genetics , Female , Gene Expression , Humans , MAP Kinase Signaling System , Male , Middle Aged , Mitogen-Activated Protein Kinase 1/genetics , Mitogen-Activated Protein Kinase 1/metabolism , Mitogen-Activated Protein Kinase 3/genetics , Mitogen-Activated Protein Kinase 3/metabolism , Myasthenia Gravis/pathology , T-Lymphocytes/pathology , Thymus Gland/enzymology , Thymus Gland/immunology , Thymus Gland/pathology , p38 Mitogen-Activated Protein Kinases/genetics , p38 Mitogen-Activated Protein Kinases/metabolismABSTRACT
Cytokines and adhesion receptors are key mediators in the dialog occurring between thymic epithelial cells (TEC) and thymocytes and regulating T cell maturation and epithelial embryonic differentiation. Among cytokines, IL-6 can be critical in the thymus, fostering proliferation, differentiation and/or survival of both TEC and thymocytes. We have previously reported in human normal TEC that clustering of the laminin receptor alpha6beta4 integrin induced by thymocyte contact or monoclonal antibody-mediated cross-linking regulates IL-6 gene expression via activation of NF-kappaB and NF-IL6 transactivators. Here we show that alpha6beta4 integrin activates p38 mitogen-activated protein kinase (MAPK) and that p38 is essential for IL-6 gene expression. In fact, beta4 cross-linking activated p38 and extracellular signal-regulated kinase (ERK) MAPK, Rac1, p21-activated protein kinase 1 (PAK1) and MAPK kinases (MKK) 3/MKK6. However, pharmacological blockade of p38 or ERK demonstrated that p38 inhibition abrogated both basal and beta4 integrin-induced production of IL-6 preventing NF-kappaB and NF-IL6 activation, whereas ERK inhibition reduced IL-6 production, hampering only NF-kappaB activation. Overall, our results indicate that p38 MAPK and alpha6beta4 integrin, expressed by TEC throughout their life, are critical regulators of the intrathymic availability of a cytokine controlling fate and functions of cells governing development and maintenance of thymic architecture and immune responses.