The osteoprotegerin/receptor activator of nuclear factor kappaB/receptor activator of nuclear factor kappaB ligand system in cartilage.
OBJECTIVE
The receptor activator of nuclear factor kappaB (RANK) is a member of the tumor necrosis factor receptor family. It is activated by the secreted or cell surface-bound RANK ligand (RANKL). Osteoprotegerin (OPG) is a soluble nonsignaling receptor for RANKL and interferes with RANK activation. This receptor-ligand system regulates the differentiation of osteoclasts and dendritic cells. The present study examined human articular cartilage for the expression of these molecules and the role of RANKL in the regulation of chondrocyte function.


METHODS
Normal and osteoarthritic (OA) human articular cartilage was used for explant tissue culture or for isolation of chondrocytes and cell culture. Expression of RANK, RANKL, and OPG was analyzed by immunohistochemistry, Western blotting, or reverse transcription-polymerase chain reaction. Recombinant RANKL was added to cartilage or chondrocyte cultures, and gene expression, collagenase and nitric oxide production, and NF-kappaB activation were determined.


RESULTS
RANK, RANKL, and OPG messenger RNA (mRNA) were expressed in normal cartilage. By immunohistochemistry, RANK, RANKL, and OPG were detected in the superficial zone of normal cartilage. OA cartilage contained increased levels of OPG mRNA, and expression of the 3 proteins extended into the midzone of OA cartilage. OPG was detected by Western blotting, and was increased in response to interleukin-1beta stimulation. OPG, RANK, and RANKL protein were also detected in cultured chondrocytes. Addition of exogenous RANKL did not activate NF-kappaB, induce expression of genes encoding proinflammatory mediators in chondrocytes, or stimulate the production of collagenase and nitric oxide.


CONCLUSIONS
These results demonstrate the expression of OPG, RANK, and RANKL in cartilage. However, RANKL does not activate human articular chondrocytes.
Komuro
H
H
Division of Arthritis Research, The Scripps Research Institute, La Jolla, California 92037, USA.
Olee
T
T
Kühn
K
K
Quach
J
J
Brinson
D C
DC
Shikhman
A
A
Valbracht
J
J
Creighton-Achermann
L
L
Lotz
M
M
D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002358:Cartilage, Articular / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D002478:Cells, Cultured; D018946:Chemokine CCL5 / Q000235:genetics; D019902:Chondrocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D017364:Collagenases / Q000378:metabolism; D051546:Cyclooxygenase 2; D015870:Gene Expression / Q000276:immunology; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007375:Interleukin-1 / Q000235:genetics; D015850:Interleukin-6 / Q000235:genetics; D007527:Isoenzymes / Q000235:genetics; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism; D008565:Membrane Proteins; D016328:NF-kappa B / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D010003:Osteoarthritis / Q000276:immunology* / Q000378:metabolism; D053244:Osteoprotegerin; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics; D053245:RANK Ligand; D012333:RNA, Messenger / Q000032:analysis; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics* / Q000378:metabolism; D018124:Receptors, Tumor Necrosis Factor; D015398:Signal Transduction / Q000276:immunology; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics
D002352:Carrier Proteins; D018946:Chemokine CCL5; D006023:Glycoproteins; D007375:Interleukin-1; D015850:Interleukin-6; D007527:Isoenzymes; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D016328:NF-kappa B; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor; C505686:TNFRSF11A protein, human; C506030:TNFRSF11B protein, human; C505688:TNFSF11 protein, human; D014409:Tumor Necrosis Factor-alpha; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D017364:Collagenases