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A Critical Role for Adrenomedullin-Calcitonin Receptor-Like Receptor in Regulating Rheumatoid Fibroblast-Like Synoviocyte Apoptosis¹

Benjamin Uzan^*, Hang-Korng Ea^*, Jean-Marie Launay^,, Jean-Michel Garel^*, Romuald Champy^*, Michèle Cressent^* and Frédéric Lioté^2,*,

^* Institut National de la Santé et de la Recherche Médicale, Unité 606, IFR 139, Centre Viggo Petersen, Hôpital Lariboisière, Paris, France; Service de Biochimie, IFR 139, Hôpital Lariboisière, Paris, France; EA3621, Faculté de Pharmacie, Paris 5 University, Paris, France; and UFR Denis-Diderot Médecine, Paris 7 University, Paris, France

Rheumatoid arthritis (RA) is characterized by fibroblast-like synoviocyte (FLS) hyperplasia, which is partly ascribable to decreased apoptosis. In this study, we show that adrenomedullin (ADM), an antiapoptotic peptide, is constitutively secreted in larger amounts by FLS from joints with RA (RA-FLS) than with osteoarthritis (OA-FLS). ADM secretion was regulated by TNF-. Peptidylglycine -amidating monooxygenase, the ADM-processing enzyme, was expressed at the mRNA level by both RA-FLS and OA-FLS. Constituents of the ADM heterodimeric receptor calcitonin receptor-like receptor (CRLR)/receptor activity-modifying protein (RAMP)-2 were up-regulated at the mRNA and protein levels in cultured RA-FLS compared with OA-FLS. ADM induced rapid intracellular cAMP production in FLS and reduced caspase-3 activity, DNA fragmentation, and chromatin condensation in RA-FLS exposed to apoptotic conditions, indicating that CRLR/RAMP-2 was fully functional. ADM-induced cAMP production was less marked in OA-FLS than in RA-FLS, suggesting differences in receptor regulation and expression. ADM dose-dependently inhibited RA-FLS apoptosis, and this effect was reversed by the 22–52 ADM antagonist peptide. ADM inhibited RA-FLS apoptosis triggered by extrinsic and intrinsic pathways. Our data suggest that ADM may prevent or reduce RA-FLS apoptosis, via up-regulation of its functional receptor CRLR/RAMP-2. Regulation of ADM secretion and/or CRLR/RAMP-2 activation may constitute new treatment strategies for RA.