title: Serum Amyloid A3 Secreted by Preosteoclasts Inhibits Parathyroid Hormone-stimulated cAMP Signaling in Murine Osteoblasts.
abstract: Continuous parathyroid hormone (PTH) blocks its own osteogenic actions in marrow stromal cell cultures by inducing Cox2 and receptor activator of nuclear factor κB ligand (RANKL) in the osteoblastic lineage cells, which then cause the hematopoietic lineage cells to secrete an inhibitor of PTH-stimulated osteoblast differentiation. To identify this inhibitor, we used bone marrow macrophages (BMMs) and primary osteoblasts (POBs) from WT and Cox2 knock-out (KO) mice. Conditioned medium (CM) from RANKL-treated WT, but not KO, BMMs blocked PTH-stimulated cAMP production in POBs. Inhibition was reversed by pertussis toxin (PTX), which blocks Gαi/o activation. Saa3 was the most highly differentially expressed gene in a microarray comparison of RANKL-treated WT versus Cox2 KO BMMs, and RANKL induced Saa3 protein secretion only from WT BMMs. CM from RANKL-stimulated BMMs with Saa3 knockdown did not inhibit PTH-stimulated responses in POBs. SAA added to POBs inhibited PTH-stimulated cAMP responses, which was reversed by PTX. Selective agonists and antagonists of formyl peptide receptor 2 (Fpr2) suggested that Fpr2 mediated the inhibitory actions of Saa3 on osteoblasts. In BMMs committed to become osteoclasts by RANKL treatment, Saa3 expression peaked prior to appearance of multinucleated cells. Flow sorting of WT marrow revealed that Saa3 was secreted only from the RANKL-stimulated B220(-) CD3(-)CD11b(-/low) CD115(+) preosteoclast population. We conclude that Saa3 secretion from preosteoclasts, induced by RANKL in a Cox2-dependent manner, inhibits PTH-stimulated cAMP signaling and osteoblast differentiation via Gαi/o signaling. The induction of Saa3 by PTH may explain the suppression of bone formation when PTH is applied continuously and may be a new therapeutic target for osteoporosis.
authors.affiliation: New England Musculoskeletal Institute, University of Connecticut Health, Farmington, Connecticut 06030 From the Departments of Medicine and.
authors.forename: Shilpa
authors.initials: S
authors.lastname: Choudhary
authors.affiliation: New England Musculoskeletal Institute, University of Connecticut Health, Farmington, Connecticut 06030.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Goetjen
authors.affiliation: New England Musculoskeletal Institute, University of Connecticut Health, Farmington, Connecticut 06030.
authors.forename: Thomas
authors.initials: T
authors.lastname: Estus
authors.affiliation: Immunology.
authors.forename: Christian E
authors.initials: CE
authors.lastname: Jacome-Galarza
authors.affiliation: Immunology.
authors.forename: Hector L
authors.initials: HL
authors.lastname: Aguila
authors.affiliation: New England Musculoskeletal Institute, University of Connecticut Health, Farmington, Connecticut 06030 From the Departments of Medicine and.
authors.forename: Joseph
authors.initials: J
authors.lastname: Lorenzo
authors.affiliation: New England Musculoskeletal Institute, University of Connecticut Health, Farmington, Connecticut 06030 From the Departments of Medicine and pilbeam@uchc.edu.
authors.forename: Carol
authors.initials: C
authors.lastname: Pilbeam
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D000242:Cyclic AMP / Q000235:genetics / Q000378:metabolism*; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis / Q000187:drug effects / Q000235:genetics; D010281:Parathyroid Hormone / Q000378:metabolism / Q000494:pharmacology*; D053245:RANK Ligand / Q000235:genetics / Q000378:metabolism; D044042:Receptors, Formyl Peptide / Q000235:genetics / Q000378:metabolism; D015290:Second Messenger Systems / Q000187:drug effects* / Q000235:genetics; D000685:Serum Amyloid A Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D010281:Parathyroid Hormone; D053245:RANK Ligand; D044042:Receptors, Formyl Peptide; C076498:Saa3 protein, mouse; D000685:Serum Amyloid A Protein; C505689:Tnfsf11 protein, mouse; C481578:formyl peptide receptor 2, mouse; D000242:Cyclic AMP; C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2
keywords: G protein-coupled receptor (GPCR); bone; cyclooxygenase (COX); formyl peptide receptor; macrophage; osteoporosis; prostaglandin; ptgs2 knockout; receptor activator of nuclear factor κB ligand (RANKL)