Stimulation of BMP-2 expression by pro-inflammatory cytokines IL-1 and TNF-alpha in normal and osteoarthritic chondrocytes.
BACKGROUND
Destruction of cartilage in osteoarthritis is a direct effect of an imbalance between catabolic and anabolic activities in the tissue. While a great deal is known about catabolism, we sought to determine the biochemical basis of the anabolic activity.


METHODS
Cartilage was isolated from normal and osteoarthritic patients and subjected to both cell and explant culture. mRNA expression levels of the growth and differentiation factors bone morphogenetic protein-2 (BMP-2), BMP-4, BMP-6, cartilage-derived morphogenetic protein-1 (CDMP-1), connective tissue growth factor (CTGF), and activin were determined. BMP-2 was localized in osteoarthritic cartilage by immunohistochemistry. To determine the mechanism of BMP-2 stimulation, chondrocytes were cultured with TGF-beta (transforming growth factor-beta), insulin-like growth factor-1 (IGF-1), interleukin-1beta (IL-1beta), and tumor necrosis factor-alpha (TNF-alpha). The BMP-2 response was monitored by quantitative real-time polymerase chain reaction to ascertain mRNA levels and by Western blot analysis, BMP-2 protein quantitation, and immunohistochemistry to determine protein levels.


RESULTS
BMP-2 was found to be up-regulated in osteoarthritic chondrocytes and cartilage. In cell culture, IL-1beta and TNF-alpha increased BMP-2 mRNA and protein levels by eightfold and fifteenfold, respectively, whereas IGF-1 and TGF-beta1 had no effect. In cartilage explant cultures, IL-1beta and TNF-alpha increased BMP-2 levels both intracellularly and extracellularly. Functional relevance was suggested by co-localization of BMP-2 and newly synthesized type-II procollagen within the same cells.


CONCLUSIONS
BMP-2 acts as a stimulus of anabolic activities in normal and osteoarthritic chondrocytes. Furthermore, the pro-inflammatory cytokines IL-1beta and TNF-alpha, known to be present in synovium and cartilage of patients with osteoarthritis, stimulate the production of active BMP-2.
Fukui
Naoshi
N
Zhu
Yong
Y
Maloney
William J
WJ
Clohisy
John
J
Sandell
Linda J
LJ
D000368:Aged; D000369:Aged, 80 and over; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000235:genetics*; D002358:Cartilage, Articular / Q000166:cytology; D002454:Cell Differentiation / Q000235:genetics*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology*; D005260:Female; D005786:Gene Expression Regulation / Q000276:immunology*; D006801:Humans; D007375:Interleukin-1 / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000276:immunology*; D012333:RNA, Messenger / Q000235:genetics; D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D015854:Up-Regulation / Q000502:physiology
C525718:BMP2 protein, human; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D007375:Interleukin-1; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha