The orphan G-protein coupled receptor RDC1: evidence for a role in chondrocyte hypertrophy and articular cartilage matrix turnover.
OBJECTIVE
RDC1 is a class A orphan G-protein coupled receptor of unknown function. The purpose of this study was to identify compound RDC1 agonists and use these as tools to determine the effect of RDC1 activation in human chondrocytes and cartilage explant tissue.


METHODS
Computational chemistry was employed to build a homology model of the RDC1 receptor. A virtual screen of in-house compounds was then performed and positive hits screened for their ability to invoke a Ca2+ response in a recombinant RDC1 HEK293 cell line, as measured by FLIPR. The effect of RDC1 activation on human chondrocytes and cartilage explant gene expression was determined by quantitative real-time polymerase chain reaction (PCR), and these effects validated as being mediated by RDC1 using siRNA antisense.


RESULTS
Tissue expression profiling demonstrated that RDC1 expression was predominant in cartilage tissue. Treatment of human primary chondrocytes with RDC1 agonist induced a Ca2+ response, suggesting the receptor is active in this tissue type. Treatment for 24h with RDC1 agonist led to altered expression of a number of genes associated with chondrocyte hypertrophy and increased matrix degradation in human primary chondrocytes, and elevated total matrix metalloproteinase (MMP) activity in cartilage explant. Transfection with RDC1 siRNA caused a >90% reduction in human primary chondrocyte RDC1 expression and significantly reduced the impact of RDC1 agonist on the previously identified RDC1-regulated genes.


CONCLUSIONS
RDC1 activation in human chondrocytes and cartilage explant leads to changes in gene expression and activity associated with chondrocyte hypertrophy, angiogenesis and increased matrix degradation, suggesting signalling via the RDC1 receptor may play an important role in the early development of osteoarthritis (OA).
Jones
S W
SW
Respiratory and Inflammation Research Area, Alderley Park, AstraZeneca, Macclesfield SK10 4TG, United Kingdom. simon.w.jones@astrazeneca.com
Brockbank
S M V
SM
Mobbs
M L
ML
Le Good
N J
NJ
Soma-Haddrick
S
S
Heuze
A J
AJ
Langham
C J
CJ
Timms
D
D
Newham
P
P
Needham
M R C
MR
D002118:Calcium / Q000378:metabolism; D002358:Cartilage, Articular / Q000378:metabolism* / Q000473:pathology; D002460:Cell Line; D019902:Chondrocytes / Q000378:metabolism* / Q000473:pathology; D005109:Extracellular Matrix / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D006984:Hypertrophy; D007150:Immunohistochemistry / Q000379:methods; D020782:Matrix Metalloproteinases / Q000032:analysis; D009389:Neovascularization, Pathologic / Q000378:metabolism; D020370:Osteoarthritis, Knee / Q000378:metabolism*; D054387:Receptors, CXCR; D043562:Receptors, G-Protein-Coupled / Q000819:agonists / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014162:Transfection
C501896:ACKR3 protein, human; D054387:Receptors, CXCR; D043562:Receptors, G-Protein-Coupled; D011994:Recombinant Proteins; D020782:Matrix Metalloproteinases; D019204:GTP-Binding Proteins; D002118:Calcium