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O010 Increased GPR22 activation triggers osteoarthritis
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  1. L-A Guns1,
  2. S Monteagudo1,
  3. D Calebiro2,
  4. M Lohse3,
  5. F Cailotto4,
  6. R Lories1
  1. 1Skeletal Biology and Engineering Research Centre, KULeuven, Belgium
  2. 2Rudolf Virchow Centre, Würzburg
  3. 3Rudolf Virchow Centre, University of Würzburg, Germany
  4. 4CNRS – Université de Lorraine, UMR7365, Nancy, France

Abstract

Introduction G protein-coupled receptors (GPCRs) are considered interesting drug targets. GPR22, an orphan receptor, was previously associated to osteoarthritis (OA) in a genome wide association study.

Objectives To investigate GPR22 expression in human healthy and OA cartilage and asses the functional role of GPR22 with in vitro and in vivo models.

Methods GPR22 protein levels were examined by immunohistochemistry. Chondrogenic ATDC5 cells stably overexpressing Gpr22 (GPR22+) and embryonic limb bud cells from mutant Gpr22V385A/V385A mice were cultured as micromasses, and read-outs included gene expression and evaluation of the extracellular matrix. Downstream GPR22 signalling was determined with a PKA activity fluorescence-based assay. Cholecystokinin receptor antagonist AG-041R was tested as GPR22 antagonist. PKA concentrations and kinetics were measured by fluorescence resonance energy transfer (FRET) imaging by PKA sensors in ATDC5 cells. Destabilisation or removal of the medial meniscus (DMM or TMM), for 12 or 8 weeks respectively, was surgically induced in mutant 8 week-old Gpr22V385A/V385A and wild-type C57/Bl6 mice. Vehicle or AG-041R was injected in the knee joint every 5 days, starting 1 week post-DMM until the mice were sacrificed. Severity was analysed according to OARSI scoring and immunohistochemistry.

Results In healthy human articular cartilage, GPR22 protein was absent, while it is present in OA cartilage. GPR22 +cells showed increased mineralization and decreased proteoglycan content compared to controls after 21 days. Gene expression demonstrated a decrease in Aggrecan and Collagen 2. In contrast, levels of hypertrophic markers Col10 and Mmp13 were increased, suggesting a shift of the cells’ differentiation status. PKA activity was reduced in GPR22 +cells compared to controls. The effects on markers, proteoglycan content and mineralization were antagonised by AG-041R. FRET imaging confirmed the neutralising effect of AG-041R on intracellular PKA concentration in GPR22 +cells. In vivo, DMM- and TMM- operated knees of GPR22 V385A/V385A mice showed increased cartilage damage, and increased GPR22 and COL10 expression compared to controls. Intra-articular injections of AG-041R prevented cartilage damage in DMM-induced GPR22 V385A/V385A mice.

Conclusions GPR22 is present in human OA cartilage and not in healthy tissue. Overexpression of GPR22 accelerates chondrocyte hypertrophy. GPR22 can be antagonised by AG-041R. Our preliminary in vivo data show a therapeutic effect of AG-041R in the DMM model. Thus, GPR22 is genetically and functionally linked to OA and may be a potential therapeutic target.

Disclosure of interest None declared

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