Activation of WNT and BMP signaling in adult human articular cartilage following mechanical injury

Francesco Dell'Accio,Costantino Pitzalis,Noha Mf El Tawil,Thimios A Mitsiadis,Cosimo De Bari,John O'Dowd,Francesca Barone

doi:10.1186/ar2029

Francesco Dell'Accio, Costantino Pitzalis + Show 5 more

Open Access

https://doi.org/10.1186/ar2029

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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.

Highlights

Chronic symptomatic full thickness defects of the joint surface are commonly regarded to have a poor repair capacity
Scattered clinical and animal studies have suggested that acute full thickness joint surface defects (JSDs) exhibit potential for repair, which is dependent on age, the size of the lesion, and biomechanical factors
Under our experimental conditions, uninjured explants preserved metachromatic staining with safranin O (Figure 1b) and toluidine blue for at least 6 days. To validate this in vitro assay, we tested if we could detect in this injury model upregulation of metalloproteinase (MMP)-3 and MMP-13, as has been reported following mechanical cartilage injury in vitro and in vivo [26,27,28]

Summary

Introduction

Chronic symptomatic full thickness defects of the joint surface are commonly regarded to have a poor repair capacity. Age dependent spontaneous repair of relatively small experimental full thickness JSDs has been reported in rabbits [6,7] and dogs [8]. In rabbits, this repair process entails invasion of the fibrin clot, filling the defect by BMP = bone morphogenetic protein; glycogen synthase kinase 3 = GSK-3; DAPI = 49,6-diamidino-2-phenylindole; FBS = fetal bovine serum; JSD = joint surface defect; MMP = metalloproteinase; OA = osteoarthritis; Q-PCR = quantitative real time PCR; RT-PCR = reverse transcription PCR; TBST = tris buffered saline; TCF/LEF = T-cell factor/lymphoid enhancer factor

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