Abstract
The fibrocartilage chondrocyte phenotype has been recognized to attribute to osteoarthritis (OA) development. These chondrocytes express genes related to unfavorable OA outcomes, emphasizing its importance in OA pathology. BMP7 is being explored as a potential disease-modifying molecule and attenuates the chondrocyte hypertrophic phenotype. On the other hand, BMP7 has been demonstrated to relieve organ fibrosis by counteracting the pro-fibrotic TGFβ-Smad3-PAI1 axis and increasing MMP2-mediated Collagen type I turnover. Whether BMP7 has anti-fibrotic properties in chondrocytes is unknown. Human OA articular chondrocytes (HACs) were isolated from end-stage OA femoral cartilage (total knee arthroplasty; n = 18 individual donors). SW1353 cells and OA HACs were exposed to 1 nM BMP7 for 24 h, after which gene expression of fibrosis-related genes and fibrosis-mediating factors was determined by RT-qPCR. In SW1353, Collagen type I protein levels were determined by immunocytochemistry and western blotting. PAI1 and MMP2 protein levels and activity were measured with an ELISA and activity assays, respectively. MMP2 activity was inhibited with the selective MMP-2 inhibitor OA-Hy. SMAD3 activity was determined by a (CAGA)12-reporter assay, and pSMAD2 levels by western blotting. Following BMP7 exposure, the expression of fibrosis-related genes was reduced in SW1353 cells and OA HACs. BMP7 reduced Collagen type I protein levels in SW1353 cells. Gene expression of MMP2 was increased in SW1353 cells following BMP7 treatment. BMP7 reduced PAI1 protein levels and -activity, while MMP2 protein levels and -activity were increased by BMP7. BMP7-dependent inhibition of Collagen type I protein levels in SW1353 cells was abrogated when MMP2 activity was inhibited. Finally, BMP7 reduced pSMAD2 levels determined by western blotting and reduced SMAD3 transcriptional activity as demonstrated by decreased (CAGA)12 luciferase reporter activity. Our data demonstrate that short-term exposure to BMP7 decreases the fibrocartilage chondrocyte phenotype. The BMP7-dependent reduction of Collagen type I protein expression seems MMP2-dependent and inhibition of Smad2/3-PAI1 activity was identified as a potential pathway via which BMP7 exerts its anti-fibrotic action. This indicates that in chondrocytes BMP7 may have a double mode-of-action by targeting both the hypertrophic as well as the fibrotic chondrocyte phenotype, potentially adding to the clinical relevance of using BMP7 as an OA disease-modifying molecule.
Highlights
The fibrocartilage chondrocyte phenotype has been recognized to attribute to osteoarthritis (OA) development
Bone morphogenetic protein 7 (BMP7) reduces the expression of markers associated with the fibrocartilage chondrocyte phenotype. (A) SW1353 cells were exposed to 1 nM BMP7 for 24 h after which fibrocartilage chondrocyte markers SERPINF1, transmembrane protein 119 (TMEM119), S100 calcium-binding protein A4 (S100A4), CEMIP, COL1A1 and P4HA3 were measured using real-time quantitative PCR (RT-qPCR)
To understand whether BMP7 has the capacity to counteract the fibrocartilage chondrocyte phenotype, SW1353 cells were exposed to BMP7 for 24 h and subsequently expression of a selection of genes positively associated with the fibrocartilage chondrocyte phenotype according to Ji et al.[5] and Chou et al.[6] was determined
Summary
The fibrocartilage chondrocyte phenotype has been recognized to attribute to osteoarthritis (OA) development. The BMP7-dependent reduction of Collagen type I protein expression seems MMP2-dependent and inhibition of Smad2/3-PAI1 activity was identified as a potential pathway via which BMP7 exerts its anti-fibrotic action This indicates that in chondrocytes BMP7 may have a double mode-of-action by targeting both the hypertrophic as well as the fibrotic chondrocyte phenotype, potentially adding to the clinical relevance of using BMP7 as an OA diseasemodifying molecule. The fibrocartilage chondrocyte phenotype is relatively rare and mainly found in late-stage OA c artilage[5,7] It is characterized by increased expression of collagen type I and III (COL1A1 and COL3A1), as well as alpha smooth muscle actin (α-SMA), S100A4 ( known as fibroblastspecific protein 1 (Fsp1)), TIMP1 (tissue inhibitor of metalloproteinase-1) and CEMIP (Cell Migration Inducing Hyaluronidase-1)[5,8,9,10,11]. The changes in the molecular microenvironment of the fibrocartilage chondrocyte fuels OA pathophysiology by disturbing the integrity of the cartilage E CM12 and enhances fibrosis[13,14]
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