Cyclooxygenase-2 regulates mesenchymal cell differentiation into the osteoblast lineage and is critically involved in bone repair

Insulin receptor substrate-1 (IRS-1) is an essential molecule for intracellular signaling of insulin-like growth factor (IGF)-I and insulin, both of which are potent anabolic regulators of bone and cartilage metabolism. To investigate the role of IRS-1 in bone regeneration, fracture was introduced in the tibia, and its healing was compared between wild-type (WT) mice and mice lacking the IRS-1 gene (IRS-1 ؊/؊ mice). Among 15 IRS-1 ؊/؊ mice, 12 remained in a non-union state even at 10 weeks after the operation, whereas all 15 WT mice showed a rigid bone union at 3 weeks. This impairment was because of the suppression of callus formation with a decrease in chondrocyte proliferation and increases in hypertrophic differentiation and apoptosis. Reintroduction of IRS-1 to the IRS-1 ؊/؊ fractured site using an adenovirus vector significantly restored the callus formation. In the culture of chondrocytes isolated from the mouse growth plate, IRS-1 ؊/؊ chondrocytes showed less mitogenic ability and Akt phosphorylation than WT chondrocytes. An Akt inhibitor decreased the IGF-Istimulated DNA synthesis of chondrocytes more potently in the WT culture than in the IRS-1 ؊/؊ culture. We therefore conclude that IRS-1 deficiency impairs bone healing at least partly by inhibiting chondrocyte proliferation through the phosphatidylinositol 3-kinase/Akt pathway, and we propose that IRS-1 can be a target molecule for bone regenerative medicine.

Section: Discussionmentioning

confidence: 99%

Impairment of Bone Healing by Insulin Receptor Substrate-1 Deficiency

Shimoaka

Kamekura

Chikuda

et al. 2004

“…Although the functional significance of COX-2 overexpression in initiation or propagation of osteoarthritis or ankylosing spondylitis is currently not known, our findings that the aberrant COX-2 expression interferes with skeletal development suggest that COX-2 may play a pivotal role in pathogenesis of these diseases. In addition, COX-2 has been shown to be involved in bone repair (36), suggesting that COX-2 also plays an important role in the homeostasis of adult skeleton.…”

Section: Discussionmentioning

confidence: 99%

Embryonic Expression of Cyclooxygenase-2 Causes Malformations in Axial Skeleton

Shim

Foley

Anna

et al. 2010

Cyclooxygenases (COXs) have important functions in various physiological and pathological processes. COX-2 expression is highly induced by a variety of stimuli and is observed during certain periods of embryonic development. In this report, the direct effect of COX-2 expression on embryonic development is examined in a novel COX-2 transgenic mouse model that ubiquitously expresses human COX-2 from the early stages of embryonic development. COX-2 transgenic fetuses exhibit severe skeletal malformations and die shortly after birth. Skeletal malformations are localized along the entire vertebral column and rib cage and are linked to defective formation of cartilage anlagen. The cartilage anlagen of axial skeleton fail to properly develop in transgenic embryos because of impaired precartilaginous sclerotomal condensation, which results from the reduction of cell number in the sclerotome. Despite the ubiquitous expression of COX-2, the number of apoptotic cells is highly increased in the sclerotome of transgenic embryos but not in other tissues, suggesting that it is a tissue-specific response. Therefore, the loss of sclerotomal cells due to an increased apoptosis is probably responsible for axial skeletal malformations in transgenic fetuses. In addition, the sclerotomal accumulation of p53 protein is observed in transgenic embryos, suggesting that COX-2 may induce apoptosis via the up-regulation of p53. Our results demonstrate that the aberrant COX-2 signaling during embryonic development is teratogenic and suggest a possible association of COX-2 with fetal malformations of unknown etiology.

“…Cyclooxygenase 2 (COX-2) is an important inducer of osteoblastic differentiation in bone biology (28). To further confirm the pro-osteogenic effect of fMLP, we examined expression of osteoblast marker genes.…”

Section: H]inositol or [mentioning

confidence: 99%

N-Formyl-Methionyl-Leucyl-Phenylalanine (fMLP) Promotes Osteoblast Differentiation via the N-Formyl Peptide Receptor 1-mediated Signaling Pathway in Human Mesenchymal Stem Cells from Bone Marrow

Shin

Jang

Yoo

et al. 2011

Binding of N-formyl-methionyl-leucyl-phenylalanine (fMLP) to its specific cell surface receptor, N-formyl peptide receptor (FPR), triggers different cascades of biochemical events, eventually leading to cellular activation. However, the physiological role of fMLP and FPR during differentiation of mesenchymal stem cells is unknown. In this study, we attempted to determine whether fMLP regulates differentiation of mesenchymal stem cells derived from bone marrow. Analysis by quantitative-PCR and flow cytometry showed significantly increased expression of FPR1, but not FPR2 and FPR3, during osteoblastic differentiation. fMLP, a specific ligand of FPR1, promotes osteoblastic commitment and suppresses adipogenic commitment under differentiation conditions. Remarkably, fMLP-stimulated osteogenesis is associated with increased expression of osteogenic markers and mineralization, which were blocked by cyclosporine H, a selective FPR1 antagonist. In addition, fMLP inhibited expression of peroxisome proliferator-activated receptor-␥1, a major regulator of adipocytic differentiation. fMLP-stimulated osteogenic differentiation was mediated via FPR1-phospholipase C/phospholipase D-Ca 2؉ -calmodulin-dependent kinase II-ERK-CREB signaling pathways. Finally, fMLP promoted bone formation in zebrafish and rabbits, suggesting its physiological relevance in vivo. Collectively, our findings provide novel insight into the functional role of fMLP in bone biology, with important implications for its potential use as a therapeutic agent for treatment of bone-related disorders.