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.

Clinical, Biochemical, and Genetic Features of 41 Han Chinese Families With Primary Hypertrophic Osteoarthropathy, and Their Therapeutic Response to Etoricoxib: Results From a Six-Month Prospective Clinical Intervention

“…However, the interesting links detected between serum bone metabolism markers and urinary PGE 2 levels suggested the potential role of decreased PGE 2 in periostosis management. The roles of PGE 2 on skeletal metabolism were also indicated in previous studies, but its effect on either bone formation or resorption was complicated or even opposite in different test systems. Clarifying the mechanisms of bone changes in PHO patients would provide a better understanding of PGE 2 ‐related skeletal biological process.…”

Endoplasmic reticulum stress remodels alveolar bone formation after tooth extraction

“…Primary calvarial osteoblasts (POBs) were extracted from neonatal (2-to 3-day-old) C57B6L mice. 35 POBs were cultured at 37°C in a humidified atmosphere of 5% CO 2 in α-MEM with 10% FBS (Gibco, Thermo Fisher) and 1% penicillin-streptomycin. For cellular ALP staining, the POBs were quantified utilizing a cell imaging system after 7 days.…”

Molecular genetics and targeted therapy of WNT-related human diseases (Review)

“…By contrast, activation of BCR-ABL, FLT3, KIT, SRC or RET tyrosine kinases and GPCR-mediated PKA activation induce β-catenin phosphorylation at Y654 and S675, respectively, which also promotes nuclear translocation of β-catenin and β-catenin-dependent transcription. FSHR ( 275 ), GLP1R ( 276 ), MC1R ( 277 ), PTGER2/EP2 ( 278 , 279 ), PTGER4/EP4 ( 278 , 280 ) and PTH1R ( 281 ) are GPCRs that are reported to induce cAMP-dependent PKA activation and subsequent β-catenin activation. AXIN2 , CCND1 , DKK1 , FGF20 , FZD7 , JAG1 , MYC , NEUROD1 and NOTUM are representative targets of the WNT/β-catenin signaling cascade; however, β-catenin target genes are context-dependently upregulated owing to additional transcriptional regulation by the tyrosine kinase and PKA signaling cascades.…”