ABSTRACT
Up- and downregulation of eosinopoiesis control pulmonary eosinophilia in human asthma. In mice, eosinopoiesis is suppressed in vitro by prostaglandin E2 (PGE2) and in vivo by diethylcarbamazine, through a proapoptotic mechanism sequentially requiring inducible NO synthase (iNOS) and the ligand for death receptor CD95 (CD95L). We examined the roles of iNOS, cAMP-mediated signaling, caspases, and CD95L/CD95 in suppression of eosinopoiesis by PGE2 and other agents signaling through cAMP. Bone-marrow collected from BALB/c mice, or from iNOS-, CD95-, or CD95L-deficient mutants (and wild-type controls), was cultured with interleukin-5 (IL-5), alone or associated with PGE2, cAMP-inducing/mimetic agents, caspase inhibitor zVAD-fmk, iNOS inhibitor aminoguanidine, or combinations thereof, and eosinopoiesis was evaluated at various times. PGE2, added up to 24 hours of culture, dose-dependently suppressed eosinopoiesis, by inducing apoptosis. This effect was (a) paralleled by induction of iNOS in eosinophils; (b) duplicated by sodium nitroprusside, isoproterenol, and cAMP-inducing/mimetic agents; (c) prevented by protein kinase A inhibition. NO was produced through iNOS by dibutyryl-cAMP-stimulated bone-marrow. Overall, PGE2 and isoproterenol shared a requirement for four effector elements (iNOS, CD95L, CD95, and terminal caspases), which together define a pathway targeted by several soluble up- and downmodulators of eosinopoiesis, including drugs, mediators of inflammation, and cytokines.
Subject(s)
Caspases/metabolism , Cyclic AMP-Dependent Protein Kinases/metabolism , Dinoprostone/pharmacology , Eosinophils/metabolism , Fas Ligand Protein/metabolism , Isoproterenol/pharmacology , Nitric Oxide Synthase Type II/metabolism , fas Receptor/metabolism , Adenylyl Cyclases/metabolism , Animals , Bone Marrow Cells/drug effects , Caspase Inhibitors/pharmacology , Cells, Cultured , Cyclic AMP/metabolism , Dexamethasone/pharmacology , Fas Ligand Protein/genetics , Interleukin-5/pharmacology , Mice , Mice, Inbred BALB C , Mice, Mutant Strains , Nitric Oxide Synthase Type II/antagonists & inhibitors , Nitric Oxide Synthase Type II/genetics , fas Receptor/geneticsABSTRACT
BACKGROUND: Platelet-derived growth factor (PDGF) is a mitogen and chemoattractant for cells of mesenchymal origin. Over-expression of PDGF-B can promote formation of inflammatory lesions in the lungs of transgenic mice. Moreover, continuous exposure to PDGF inhibits collagen production by osteoblastic cells. Thus, the expression of mitogenic factors in an inflammatory context may limit the differentiated function of cells, and thereby limit repair following periodontal attachment and bone loss. The goals of the present study were to test whether PDGF is present at increased levels in inflamed gingiva and to localize its expression in gingival biopsies from individuals with chronic periodontitis. METHODS: Tissues obtained during therapeutic procedures from inflamed and control sites of 9 patients were subjected to protein extraction, descriptive histology by hematoxylin and eosin, or immunohistochemistry assays. Quantification was calculated with an enzyme-linked immunosorbent assay (ELISA) kit specific for PDGF-AB. For the immunolocalization, anti-PDGF-A and -B antibodies were employed. RESULTS: PDGF concentration in the total protein extract was approximately 3 times higher in the inflamed sites (0.60 +/- 0.18 ng/mg versus 0.20 +/- 0.05 ng/mg; P = 0.03). Immunohistochemistry revealed prominent expression of PDGF in the pocket epithelial cells as well as the adjacent connective tissue. In contrast, little or no expression was detected in control biopsies devoid of the pocket epithelium and granulation tissue. CONCLUSIONS: PDGF is present in increased levels in the human inflamed gingiva and is mainly localized to the pocket epithelium. It is possible that chronic expression of PDGF contributes to the inflammatory changes that occur during periodontal diseases.