Cyclooxygenase-2 Deficiency Causes Delayed Ossification Of Lumbar Vertebral Endplates Via Noggin/BMP-2 Pathway

Introduction:Based on the previous findings that cyclooxygenase-2 (COX-2) is a critical molecule in chondrocyte differentiation and skeletal repair, we hypothesized that COX-2 deficiency or inhibition affects the ossification of vertebral endplates (VEP) and degeneration of intervertebral discs (IVD) and thus is involved in the pathogenesis of low back pain (LBP). We aimed to delineate the COX-2 working mechanism and its interacting molecules, and explore the effect of NSAIDs and selective COX-2 inhibitor on degenerative spinal diseases.Methods:Lumbar spinal samples harvested from COX-2 mutant (COX-2-/-) and wild type (WT) mice were used for histological examinations. Nucleus pulposus (NP) cells isolated from rat were treated with PGE-2 followed by RT-PCR analysis of PGE-2 effect on the expression of TGF-β superfamily members, VEGFs, cytokines, cartilage matrix proteins and matrix degrading enzymes. Mouse endplate chondrocytes (mEC) isolated from mice were treated with a recombinant sonic hedgehog (Shh) protein. RT-PCR and western blotting were performed to assess the changes Shh effect. Human lumbar endplate chondrocytes were cultured and treated Celecoxib. A mouse IVD organ culture system was establish and treated COX-2 inhibitor Celecoxib. Immunohistochemical (IHC) studies were done in the human and mouse VEP samples.Results:Radiographic and histological examinations revealed delayed VEP ossification in COX-2-/-- mice compared to WT ones. PGE-2 upregulated Shh expression in rat NP cells and Shh enhanced noggin expression in mEC. IHC showed that noggin expression was increased while pSmadl expression decreased in the VEP of COX-2-/- mice. Human VEP samples from patients with severe IVD degeneration showed decreased expression of Shh and noggin and increased expression of COX-2 and pSmadl compared with milder cases. In human vertebral endplate chondrocytes and cultured mouse IVDs, Celecoxib enhanced expression of Shh and noggin and decreased Smadl phosphorylation.Conclusions:COX2/PGE-2 axis plays an important role in VEP ossification and IVD degeneration through crosstalk with Noggin/BMP signaling pathway. These findings may facilitate clinical use of COX-2 inhibitor to prevent LBP progression.