IL-4-induced macrophage-derived IGF-I protects myofibroblasts from apoptosis following growth factor withdrawal.
The development of idiopathic pulmonary fibrosis (IPF) is associated with myofibroblast accumulation and collagen deposition in the lung parenchyma. Recent studies have suggested that the fibroproliferative response is associated with immune deviation toward a T helper cell type 2 (Th2) cytokine profile. In addition, myofibroblast accumulation may be the result of resistance to physiologic apoptosis. If and how these events are linked remain largely unknown. Insulin-like growth factor-I (IGF-I) is a fibroblast growth and survival factor that has long been implicated in the pathogenesis of IPF. We have previously shown that interstitial macrophage-derived IGF-I correlates with disease severity in IPF, and the Th2 cytokines interleukin (IL)-4 and IL-13 stimulate the expression and secretion of IGF-I by macrophages. In the present study, we tested the hypothesis that IL-4-induced, macrophage-derived IGF-I protects myofibroblasts from apoptosis. Using a growth factor withdrawal model of apoptosis in the myofibroblast cell line, CCL39, we demonstrate that conditioned media from IL-4-stimulated macrophages protect myofibroblasts from apoptosis. The survival effect is lost when IGF-I is immunodepleted from macrophage-conditioned media with IGF-I-specific antibodies. We also show that the protection of myofibroblasts by macrophage-derived IGF-I correlates with and is dependent on the activation of the prosurvival kinases Akt and extracellular signal-regulated kinase. These findings support the view that IL-4-stimulated, macrophage-derived IGF-I may contribute to the persistence of myofibroblasts in pulmonary fibrosis in the Th2-deviated environment of the fibrotic lung.
Program of Cell Biology, Department of Pediatrics, National Jewish Medical and Research Center, Denver, CO 80206, USA.
Murry W
MW
Wynes
Stephen K
SK
Frankel
David W H
DW
Riches
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D002450:Cell Communication / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D006133:Growth Substances / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015847:Interleukin-4 / Q000276:immunology / Q000494:pharmacology*; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008809:Mice, Inbred C3H; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011658:Pulmonary Fibrosis / Q000378:metabolism; D018418:Th2 Cells / Q000276:immunology / Q000378:metabolism
D017077:Culture Media, Conditioned; D006133:Growth Substances; D011518:Proto-Oncogene Proteins; D015847:Interleukin-4; D007334:Insulin-Like Growth Factor I; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048052:Mitogen-Activated Protein Kinase 3