title: Prostaglandin-mediated inhibition of PTH-stimulated β-catenin signaling in osteoblasts by bone marrow macrophages.
abstract: Bone marrow macrophages (BMMs), in the presence of cyclooxygenase-2 (Cox2) produced PGE2, secrete an inhibitory factor in response to Rankl that blocks PTH-stimulated osteoblastic differentiation. This study was to determine if the inhibitory factor also blocks PTH-stimulated Wnt signaling. Primary calvarial osteoblasts (POBs) were co-cultured with conditioned medium (CM) from Rankl-treated wild type (WT) BMMs, which make the inhibitory factor, and Cox2 knockout (KO) BMMs, which do not. PTH induced cAMP production was blocked by WT CM but not by KO CM. In the presence of KO CM, PTH induced phosphorylation at β-catenin serine sites, ser552 and ser675, previously shown to be phosphorylated by protein kinase A (PKA). Phosphorylation was blocked by WT CM and by H89, a PKA inhibitor. PTH did not increase total β-catenin. PTH-stimulated transcription factor/lymphoid enhancer-binding factor response element activity in POBs was blocked by WT CM and by serum amyloid A (SAA), the human recombinant analog of murine Saa3, which has recently been shown to be the inhibitory factor. In POBs cultured with Cox2 KO CM, PTH increased expression of multiple genes associated with the anabolic actions of PTH and decreased expression of Wnt antagonists. This differential regulation of gene expression was not seen in POBs cultured with WT CM. These data highlight the ability of PTH to phosphorylate β-catenin directly via PKA and demonstrate the ability of a Cox2-dependent inhibitory factor, secreted by Rankl-stimulated BMMs, to abrogate PTH stimulated β-catenin signaling. Our results suggest that PTH can stimulate a novel negative feedback of its anabolic actions by stimulating Rankl and Cox2 expression.
authors: Department of Biomedical Engineering, University of Connecticut, Storrs, 263 Farmington Ave, Farmington, CT 06030, CT, United States; New England Musculoskeletal Institute, UConn Health, 263 Farmington Ave, Farmington, CT 06030, CT, United States. Electronic address: estus@uchc.edu.
authors: Thomas L
authors: TL
authors: Estus
authors: New England Musculoskeletal Institute, UConn Health, 263 Farmington Ave, Farmington, CT 06030, CT, United States; Department of Medicine, UConn Health, 263 Farmington Ave, Farmington, CT 06030, CT, United States. Electronic address: schoudhary@uchc.edu.
authors: Shilpa
authors: S
authors: Choudhary
authors: Department of Biomedical Engineering, University of Connecticut, Storrs, 263 Farmington Ave, Farmington, CT 06030, CT, United States; New England Musculoskeletal Institute, UConn Health, 263 Farmington Ave, Farmington, CT 06030, CT, United States; Department of Medicine, UConn Health, 263 Farmington Ave, Farmington, CT 06030, CT, United States. Electronic address: pilbeam@uchc.edu.
authors: Carol C
authors: CC
authors: Pilbeam
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D002417:Cattle; D017077:Culture Media, Conditioned / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011453:Prostaglandins / Q000494:pharmacology*; D000685:Serum Amyloid A Protein / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D014158:Transcription, Genetic / Q000187:drug effects; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
chemical_list: D017077:Culture Media, Conditioned; D010281:Parathyroid Hormone; D011453:Prostaglandins; D000685:Serum Amyloid A Protein; D051176:beta Catenin; D000242:Cyclic AMP
keywords: Cyclooxygenase-2; Protein kinase A; Serine 552/675; Serum amyloid A; Wnt genes