title: Activation of WNT and BMP signaling in adult human articular cartilage following mechanical injury.
abstract: Acute full thickness joint surface defects can undergo repair, which involves tissue patterning and endochondral bone formation. Molecular signals regulating this process may contribute to the repair outcome, chronic evolution and, eventually, the onset of osteoarthritis. We tested the hypothesis that mechanical injury modulates morphogenetic pathways in adult human articular cartilage explants. Adjacent articular cartilage explants were obtained from preserved areas of the femoral condyles of patients undergoing arthroplasty for osteoarthritis, or from a normal joint of a patient undergoing lower limb amputation. Paired explants were individually maintained in explant culture. From each pair, one explant was mechanically injured and the other left uninjured as a control. Cultures were terminated at different time points for histochemistry, immunohistochemistry and gene expression analysis by reverse transcription real time PCR. Bone morphogenetic protein 2 (BMP-2) mRNA was upregulated in the injured explants. We detected phosphorylation of SMAD-1 and SMAD-5, consistent with activation of the bone morphogenetic protein (BMP) pathway. FRZB-1 mRNA was downregulated in the injured explants, suggesting de-repression of WNT signaling. Accordingly, expression of the canonical WNT target genes Axin-2 and c-JUN was upregulated in the injured explants. Activation of the canonical WNT signaling pathway by LiCl treatment induced upregulation of COL2A1 and Aggrecan mRNA, suggesting an anabolic effect. Phosphorylation of SMAD-1/-5 and downregulation of FRZB were confirmed in vivo in a mouse model of joint surface injury. Taken together, these data show modulation of the BMP and WNT pathways following mechanical injury in vitro and in vivo, which may play a role in the reparative response of the joint surface. These pathways may, therefore, represent potential targets in protocols of biological joint surface defect repair.
authors.affiliation: Department of Rheumatology, King's College London, London, UK. francesco.dellaccio@kcl.ac.uk
authors.forename: Francesco
authors.initials: F
authors.lastname: Dell'Accio
authors.forename: Cosimo
authors.initials: C
authors.lastname: De Bari
authors.forename: Noha M F
authors.initials: NM
authors.lastname: El Tawil
authors.forename: Francesca
authors.initials: F
authors.lastname: Barone
authors.forename: Thimios A
authors.initials: TA
authors.lastname: Mitsiadis
authors.forename: John
authors.initials: J
authors.lastname: O'Dowd
authors.forename: Costantino
authors.initials: C
authors.lastname: Pitzalis
mesh_terms: D000368:Aged; D053674:Aggrecans / Q000235:genetics; D000818:Animals; D060466:Axin Protein; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000235:genetics / Q000378:metabolism*; D002358:Cartilage, Articular / Q000293:injuries* / Q000378:metabolism / Q000503:physiopathology*; D024043:Collagen Type II / Q000235:genetics; D003598:Cytoskeletal Proteins / Q000235:genetics; D005260:Female; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008875:Middle Aged; D009924:Organ Culture Techniques; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051898:Smad1 Protein / Q000378:metabolism; D051902:Smad5 Protein / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D051153:Wnt Proteins / Q000378:metabolism*; D000099274:Frizzled-Related Proteins
chemical_list: D053674:Aggrecans; D060466:Axin Protein; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D024043:Collagen Type II; D003598:Cytoskeletal Proteins; D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D012333:RNA, Messenger; D051898:Smad1 Protein; D051902:Smad5 Protein; D016212:Transforming Growth Factor beta; D051153:Wnt Proteins; D000099274:Frizzled-Related Proteins; C491761:AXIN2 protein, human; C525718:BMP2 protein, human; C525719:Bmp2 protein, mouse; C499177:COL2A1 protein, human; C497399:SMAD1 protein, human; C497797:SMAD5 protein, human; C497401:Smad1 protein, mouse; C497798:Smad5 protein, mouse