Expression and function of visfatin (Nampt), an adipokine-enzyme involved in inflammatory pathways of osteoarthritis

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Laiguillon, Marie-Charlotte | Houard, Xavier | Bougault, Carole | Gosset, Marjolaine | Nourissat, Geoffroy | Sautet, Alain | Jacques, Claire | Sellam, Francis Berenbaum And Jérémie

Edité par CCSD ; BioMed Central -

International audience. Introduction:Visfatin is an adipokine that may be involved in intertissular joint communication in osteoarthritis(OA). With a homodimeric conformation, it exerts nicotinamide phosphoribosyltransferase (Nampt) enzymaticactivity, essential for nicotinamide adenine dinucleotide biosynthesis. We examined the tissular origin andconformation of visfatin/Nampt in human OA joints and investigated the role of visfatin/Nampt in chondrocytesand osteoblasts by studying Nampt enzymatic activity.Methods:Synovium, cartilage and subchondral bone from human OA joints were used for protein extraction orincubated for 24 hours in serum-free media (conditioned media), and synovial fluid was obtained from OA patients.Visfatin/Nampt expression in tissular extracts and conditioned media was evaluated by western blot and enzyme-linkedimmunosorbent assay (ELISA), respectively. Nampt activity was assessed in OA synovium by colorimetric assay. Primarycultures of murine chondrocytes and osteoblasts were stimulated with visfatin/Nampt and pretreated or not withAPO866, a pharmacologic inhibitor of Nampt activity. The effect on cytokines, chemokines, growth factors andhypertrophic markers expression was examined by quantitative reverse transcriptase polymerase chain reactionand/or ELISA.Results:In tissular explants, conditioned media and synovial fluid, visfatin/Nampt was found as a homodimer,corresponding to the enzymatically active conformation. All human OA joint tissues released visfatin/Nampt (synovium:628 ± 106 ng/g tissue; subchondral bone: 195 ± 26 ng/g tissue; cartilage: 152 ± 46 ng/g tissue), with significantly higherlevel for synovium (P<0.0005). Nampt activity was identified ex vivo in synovium. In vitro, visfatin/Nampt significantlyinduced the expression of interleukin 6, keratinocyte chemoattractant and monocyte chemoattractant protein 1 inchondrocytes and osteoblasts. APO866 decreased the mRNA and protein levels of these pro-inflammatory cytokines inthe two cell types (up to 94% and 63% inhibition, respectively). Levels of growth factors (vascular endothelial growthfactor, transforming growth factor β) and hypertrophic genes were unchanged with treatment.Conclusion:Visfatin/Nampt is released by all human OA tissues in a dimeric enzymatically active conformation andmostly by the synovium, which displays Nampt activity. The Nampt activity of visfatin is involved in chondrocyte andosteoblast activation, so targeting this enzymatic activity to disrupt joint tissue interactions may be novel in OAtherapy.

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