Subchondral bone osteoblasts induce phenotypic changes in human osteoarthritic chondrocytes.
OBJECTIVE
To determine the influence of osteoarthritic (OA) phenotype of subchondral osteoblasts on the phenotype of human chondrocytes.


METHODS
Human chondrocytes were isolated from OA cartilage and cultured in alginate beads for 4 or 10 days in the absence or in the presence of osteoblasts in monolayer. The osteoblasts were either isolated from non-sclerotic (N) or sclerotic (SC) zones of human subchondral bone. Before co-culture, osteoblasts were incubated for 72 h with or without 1.7 ng/ml interleukin (IL)-1beta, 100 ng/ml IL-6 with its soluble receptor (50 ng/ml) or 10 ng/ml oncostatin M. SOX9, type I, II and X collagen (COL1, COL2, COL10), osteoblasts-stimulating factor (OSF)-1, bone alkaline phosphatase (ALP), parathyroid hormone related peptide (PTHrP) and its receptor (PTH-R) messenger RNA (mRNA) levels in chondrocytes were quantified by real-time polymerase chain reaction.


RESULTS
In comparison with chondrocytes cultured alone in alginate beads, chondrocytes after 4 days in co-culture with N or SC osteoblasts expressed significantly less SOX9 and COL2 mRNA. The decrease of SOX9 and COL2 gene expression was significantly more pronounced in the presence of SC than in the presence of N osteoblasts (P<0.001). OSF-1 mRNA level in chondrocyte was increased by both N and SC osteoblasts, but to a larger extent by SC osteoblasts (P<0.001). PTHrP expression in chondrocytes was 21-fold increased by N osteoblasts but four-fold inhibited by SC osteoblasts. PTHrP secretion was also increased by N but reduced by SC osteoblasts. SC, but not N osteoblasts, induced a significant decrease of PTH-R gene expression in chondrocyte. In our experimental conditions, chondrocytes did not express COL1, COL10 or ALP, even after 10 days of co-culture with osteoblasts.


CONCLUSIONS
In co-culture, SC subchondral osteoblasts decrease SOX9, COL2, PTHrP and PTH-R gene expression by chondrocytes but increase that of OSF-1. These findings suggest that SC osteoblasts could initiate chondrocyte phenotype shift towards hypertrophic differentiation and subsequently further matrix mineralization.
Sanchez
C
C
Bone and Cartilage Metabolism Research Unit, Institute of Pathology, University Hospital, CHU B23, Sart-Tilman, 4000 Liège, Belgium.
Deberg
M A
MA
Piccardi
N
N
Msika
P
P
Reginster
J-Y L
JY
Henrotin
Y E
YE
D000368:Aged; D002102:Cadaver; D019902:Chondrocytes / Q000276:immunology / Q000473:pathology*; D018920:Coculture Techniques; D024043:Collagen Type II / Q000235:genetics; D005269:Femur; D015870:Gene Expression; D006609:High Mobility Group Proteins / Q000235:genetics; D006801:Humans; D007375:Interleukin-1 / Q000276:immunology; D007719:Knee Joint / Q000276:immunology / Q000473:pathology; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000235:genetics / Q000276:immunology / Q000473:pathology*; D010006:Osteoblasts / Q000276:immunology / Q000473:pathology*; D044162:Parathyroid Hormone-Related Protein / Q000235:genetics; D010641:Phenotype; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000235:genetics; D055758:SOX9 Transcription Factor; D012598:Sclerosis / Q000473:pathology; D013977:Tibia; D014157:Transcription Factors / Q000235:genetics
D024043:Collagen Type II; D006609:High Mobility Group Proteins; D007375:Interleukin-1; D044162:Parathyroid Hormone-Related Protein; D044168:Receptor, Parathyroid Hormone, Type 1; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; D014157:Transcription Factors