Adrenomedullin increases fibroblast-like synoviocyte adhesion to extracellular matrix proteins by upregulating integrin activation

FLSs were isolated from synovial tissues from RA and osteoarthritis (OA) patients. Plates were coated overnight with the ECM proteins vitronectin, fibronectin, and type I collagen (Coll.I). Adrenomedullin was used as a soluble FLS ligand before plating. We tested interactions with the adrenomedullin receptor antagonist (22-52)adrenomedullin and with the protein kinase A (PKA) inhibitor H-89, and inhibition of co-receptor RAMP-2 by siRNA. Cell adhesion was measured by using color densitometry. Activation of α2 and β1 integrins was evaluated by fluorescent microscopy; integrin inhibition, by RGD peptides; and the talin-integrin interaction, by immunoprecipitation (IP).Adrenomedullin specifically increased RA-FLS adhesion to vitronectin, fibronectin, and Coll.I; no such effect was found for OA-FLS adhesion. Basal or adrenomedullin-stimulated RA-FLS adhesion was inhibited by (22-52)adrenomedullin, H-89, and RAMP-2 siRNA. Adrenomedullin-stimulated adhesion was inhibited by RGD peptides, and associated with α2 and β1 integrin activation. This activation was shown with IP to be related to an integrin-talin interaction and was significantly decreased by (22-52)adrenomedullin.Adrenomedullin-stimulated RA-FLS adhesion was specific for ECM proteins and mediated by α2 and β1 integrins. This effect of adrenomedullin was dependent on adrenomedullin receptors. These results support a new role for adrenomedullin in rheumatoid synovial fibroblast pathobiology.Rheumatoid arthritis (RA) is a chronic inflammatory joint disease in which fibroblast-like synoviocytes (FLSs) invade the extracellular matrix (ECM) of cartilage and bone, causing destruction of both tissues. FLSs in patients with RA (RA-FLSs) differ from normal FLSs regarding both morphologic and biologic characteristics [1]. More specifically, RA-FLSs can adhere to ECM proteins [1,2] by a number of adhesion molecules.Among the adhesion molecules expressed by FLSs, integrins interact with several ECM proteins, including collag